Boiler is one of the most important machinery systems on the ship. An economic and efficient working of a marine boiler on a ship requires timely maintenance and special care in starting and stopping the boiler. Routine cleanup is extremely helpful in increasing the working life of a marine boiler.

In this article we have brought to you one such important procedure – boiler blow down, which has to be performed at a regular interval of times in order to increase the performance of the boiler.

Why Boiler blowdown?

The water which is circulated inside the boiler tubes and drum contains Total Dissolved Solids (TDS) along with other dissolved and undissolved solids. During the steam making process, i.e. when the boiler is in operation, the water is heated and converted into steam. However, these dissolved solids do not evaporate and get separated from water or steam, and they tend to settle at the bottom of the boiler shell due to their weight. This layer will prevent the transfer of heat amid the gases and the water, eventually overheating the boiler tubes or shell.

Related Read: The Science Behind Marine Boiler Water Circulation on Ships

Different dissolved and undissolved solids lead to scaling, corrosion, erosion etc. The solid impurities will also be carried over with the steam into the steam system, leading to deposits inside the heat exchanger surface where the steam is the primary heating medium. 

To minimise all these problems, boiler blowdown is done, which helps in removing the carbon deposits and other forms of impurities. 

Boiler Blow Down

Boiler blow down is done to remove carbon deposits and other impurities from the boiler.

Blow down of the boiler is done to remove two types of impurities – scum and bottom deposits. This means that blow down is done either for scum or for bottom blow down. Moreover, the reasons for boiler blow down are:

1.       To remove the precipitates formed as a result of chemical addition to the boiler water.

2.       To remove solid particles, dirt, foam or oil molecules from the boiler water. This is mainly done by scum valve and the procedure is known as “scumming.”

3.       To reduce the density of water by reducing the water level.

4.       To remove excess water in case of emergency.

Inside a marine boiler, the blowdown arrangement is provided at two levels; at a bottom level and the water surface level known as “scum blowdown”.  

Hence, when the bottom valve is used, the procedure is known as boiler blowdown, and when the Scum valve is used, the process is known as “scumming.”

Related Read: Video Tutorial: How Ship’s Boiler and Steam System Works?

The boiler water blowdown can be done in two ways depending upon the type, design, automation used, the capacity and the characteristics of the boiler feedwater system:

Intermittent or Manual blowdown: 

When blowdown is done manually by the boiler operator at regular intervals according to the established operating program, it is known as Manual blowdown. This type of blowdown is useful to remove sludge formation or suspended solids from the boiler. This type of blowdown comes handy when there is an oil ingress in the boiler water due to leakage in the heat exchanger. Using manual scumming, the oil present in the water surface can be taken out.

The major drawback of manual blowdown is the heat loss due to hot water going out of the water drum. The valve is opened slightly making a small quantity of water to go into the blowdown. Still, there is significant heat and pressure loss. 

Continuous blowdown: 

Many modern boilers are nowadays provided with blowdown automation. 

They allow the continuous blowdown of the boiler water, which helps in keeping the dissolved and suspended solids under boiler operating limits. This system is known as continuous blowdown. 

In this system, the automation monitors the blowdown continuously and in turn checks the quality of feed water and the quality of water inside a boiler shell for dissolved and undissolved impurities.  Accordingly, it will automatically open the blowdown valves if the boiler water TDS exceeds the permissible operating limit. 

As the blowdown valves are precisely controlled, the water discharged from the blowdown removes the maximum amount of dissolved impurities with minimum heat and water loss from the boiler water, maintaining the boiler efficiency.  

Most of the boiler with continuous blowdown automation are fitted with heat recovery systems, i.e. the hot water from the boiler blowdown is first sent to a heat exchanger unit which utilises the heat of the water (e.g. to preheat the feedwater by installing a heat exchanger or heat recovery equipment in the path) before it goes overboard.

The choice of blowdown system, i.e. either manual or continuous and automatic, will depend on various factors and the blowdown valves will be fitted with suitable accessories as per the system.

How to calculate the percentage of blowdown:

Quantity blowdown water/Quantity feedwater  X 100 = % blowdown

Related Read: Choosing A Marine Boiler While Designing A Ship

Procedure for Scumming and Bottom Blow Down

Below is the procedure for the boiler blow down using the blow down valve located at the bottom of the boiler. In order to do scumming, instead of bottom blow down, the scum valve is to be opened.

Steps for blow down procedure are as follows:

Kindly refer the diagram to understand the blow down procedure properly.

A modern boiler should never be blown down while the boiler is steaming at high rates. While performing the blowdown, the shipside valve should always be open first, then the blowdown valve. This will allow control to the operator in case a pipe burst.  

1.       Open the overboard or ship side valve(1) first.

2.       Open the blow down valve (2), this valve is a non-return valve.

3.       The blow down valve adjacent to the boiler (2) should be opened fully so as to prevent cutting of the valve seat or the “Wire drawing effect”.

4.       The rate of blow down is controlled by the valve (3).

5.       After blow down close the valve in reverse order.

6.       A hot drain pipe even when all valves are closed indicates a leaking blow down valve.

If the boiler is blown down for inspection, first the firing needs to be stopped and allow the boiler to cool off. Open the boiler vent plug which will allow natural cooling at atmospheric pressure. 

Ensure the overboard valve (non-return) is functioning properly so that no seawater can enter the boiler pipeline else it will create a vacuum due to sudden steam cooling leading to a pipe burst.

Once the boiler blowdown is completed, open the belly plug to remove the remaining content in the engine room bilges. 

*Make sure to do ‘Scum Blowdown’ before ‘Bottom Blowdown’ otherwise while doing bottom blowdown the scum settled on water surface or if any oil content it will get agitated, contaminating the boiler water. (Hat Tip – Gokul Nair)

Related Read: Boiler Mountings: A Comprehensive List

Advantages of boiler blowdown:

• Blowdown of boiler water at regular intervals keeps the total dissolved solid impurities under the rated limits
• The process helps in preventing corrosion as it removes the impurities which accelerate the corrosion process
• It helps in preventing scaling of boiler tubes and internal surface
• It prevents the carryover of impurities and contaminants with the steam, providing the pure steam
• It prevents scaling of internal parts of the heat exchanger where the pure steam goes as a heating medium

Disadvantages of boiler blowdown:

• If the procedure is not done correctly with the determined schedule, the blowdown of boiler water tends to increase the heat as well as pressure losses.
• The heat and pressure losses from the boiler water blowdown will reduce boiler efficiency.
• If the blowdown arrangement is manual, additional work hours needed to conduct the operation

Related Read: 6 Practical Tips On Improving Boiler Efficiency for Professional Marine Engineers

Requirements and Regulation:

• If there is oil sheen visible in the boiler gauge glass or hotwell inspection glass. As the oil will be on the water surface, ensure not to do scum blowdown else it will cause oil pollution
• The oil leakage inside the boiler water to be stopped and all efforts to be made to clear the oil from hotwell by filling freshwater and removing oil-water.
• Ensure the operator knows the Vessel General Permit areas and complies with chapter 12 of VGP and do not discharge any wastewater from the boiler blowdown in the restricted areas except for safety reasons.
• The vessel must ensure not to discharge any boiler water via boiler blowdown in port waters. This is because the water consists of different chemicals or other additives which are added to reduce impurities or prevent scale formations. 
• The boiler blowdown must be done as far from shore as possible.
• The Master and the duty officer on the bridge must be informed before commencing the blowdown operation.
• The boiler blowdown operation must be recorded in the Engine Room Logbook which must include the starting and the stopping time operation
• If the boiler blowdown or hot well water is transferred to the bilges, the same must be recorded in ORB and engine room logbook

Related Read: Safety of Life at Sea (SOLAS) & Convention for Prevention of Marine Pollution (MARPOL): A General Overview

The boiler blowdown can be done in territorial water or harbour only in the following conditions: 

• If the ship is entering the dry dock, it will need to blowdown boiler 
• For any safety reasons

How to minimise boiler blowdown?

Chemical Treatment:

The main aim of doing a boiler blowdown is to reduce the dissolved impurities in the boiler water, which leads to scale formation.

The scale formation will directly lead to heat transfer within the internal surface of the boiler leading to a reduction in boiler efficiency. 

If the boiler water can be tested regularly and accordingly treated effectively using various chemicals in the hot well, the feed water will have fewer impurities making it good for the use. 

The need for the boiler blowdown will inturn reduce leading to saving of water and reduction in heat and pressure losses. 

Boiler Water Blowdown Reduction:

With an increase in boiler blowdown, the water and fuel consumption of the boiler water will increase. The best practice is to remove the manual blowdown system and to install an automatic boiler water measurement and blowdown system. 

This system will effectively monitor the impurities in the boiler and open the discharge blowdown valve accordingly, as explained in the continuous blowdown system above. 

You may also like to read: Procedure for Boiler gauge glass maintenance.

Blow-Down Procedure for Marine Boilers appeared first on Marine Insight - The Maritime Industry Guide

One of the important tasks of marine engineers on board ships is to ensure that all the machinery systems are running efficiently. Each machinery in the engine room is dependent on a variety of aspects, which decides its overall efficiency and performance.

Boiler is one such important machinery in the ship’s engine room that needs special attention, considering the fact that it supports several other operations and machinery, including the main engine. Maintaining and improving boiler efficiency requires taking note of a number of factors.

Mentioned below are 6 important points that must be considered in order to improve boiler efficiency.

1. Feed Water Temperature

To improve any system’s efficiency, it is important to maintain the standard of all the inputs of that system. In boiler system, it is the feed water which plays an important role in deciding the overall efficiency. For this, the feed water temperature must be maintained at approx. 80- 85 deg C to ensure boiler is operated at high efficiency. Any reduction in the water temperature will lead to more time for heating up the water to produce steam, more fuel consumption and decrease in the overall efficiency.

The hot well needs to be monitored for correct temperature and level. Any sudden fall in the level of hot well means more addition of cold water to maintain the level, which leads to reduction in the feed water temperature.

Pro-Tips:

• Maintain Feed Water temp- 80 to 85 deg. C
• Ensure hot well level controller is operating properly
• Monitor feed water temperature through hot well

2. Supply of Air/Steam to Burner

Air/steam is required to ensure adequate fire is generated inside the furnace through good combustion. It is therefore important to know the percentage of  air/steam for efficient combustion. For fuel oil fired marine boiler with register type burner, 15-20 % by weight of air is required for efficient combustion.

Controlling excess air within the required range will lead to decrease in the flue gas losses. Every 1% reduction in the excess air supplied to the furnace results in approx 0.6% increase in the boiler overall efficiency.

Pro-Tips:

• Excess Air/steam to be reduced or avoided
• Know the stoihiometric air fuel ratio for your boiler under its current rating
• Keep a check on the content of combustion gases using flue gas analyzer to adjust the air fuel ratio accordingly

3. Structural Importance

The boiler is a high pressure vessel generating high temperature steam for various purposes. The outer shell or structure is an important part which not only contains the pressure but keeps the temperature of the flue gas intact inside the boiler for better heat exchanging ability.

Things to Check:

• Leakage from the boiler shell must also be checked. This occurs mainly due to deformation or bulging of shell leading to cracks and leakage.
• The insulation of the boiler must be checked for any damage or leakage.
• The refractory should be checked at least once in a month for their condition. Any damage in the refractory will lead to localized heating of the shell and damage to the same.

 Pro-Tips:

• Check refractory and replace the damage refractory as soon as possible
• Check for any black spots in the outer plates of the boiler. This indicates the boiler shell has cracks and it is leaking
• Ensure insulation of the shell is properly maintained to minimise the heat loss and to maintain the boiler efficiency

4. Blow Down Control

It is normally observed that boiler blow down is not performed regularly by operators. Blow down is only performed when the water test results are high in chloride or when high conductivity alarm occurs. This leads to uncontrolled continuous blowdown which is actually waste of boiler heat and efficiency. This reduces prominent amount of high temperature water inside the boiler and addition of moderate temperature water from hot well.

The boiler burner will now fire for longer period to maintain the steam pressure hence fuel combustion will increase reducing the efficiency. It is recommended to perform regular blowdowns for short period which not only maintains the chloride level but also reduces the thermal stresses within the boiler.

Pro Tips:

• Avoid continuous long blowdown
• Regular short blowdown are recommended
• Keep a regular check on boiler water chloride content

5. Boiler Loading

Ships provided with more that one boiler or steam generators must ensure that the load of the boiler is neither too low nor too high. The best operating range to get the maximum boiler efficiency is 2/3rd of the boiler full load. If the boiler is operated below 50% load, more air is required to burn the fuel which increases the sensible heat loss. It is always better to run less number of boiler at high load than more number at low load.

Pro Tips:

• Highest efficiency of boiler can be achieved at 2/3rd of the full load
• Avoid running the boiler at below 25% load as the efficiency reduces significantly below this load

6. Soot deposits

 The oil fired boilers are prone to soot deposits in the tube and internal boiler surface which reduces the heat transfer rate. An elevated tube stack temperature is indication of increased soot deposits over the tube. An estimated 1 percent efficiency loss occurs with every 22 deg C increase in stack temperature and 3 mm of soot can cause an increase in fuel consumption by 2.5 percent due to increased flue gas temperatures. A regular cleaning of boiler and economiser tubes must therefore be performed. Record and observe the stack temperature for indication of soot deposits.

Pro tips:

• Recommended to install a dial type thermometer at the base of the stack to monitor the exhaust flue gas temperature
• When the flue gas temperature rises to about 20 oC above the temperature for a newly cleaned boiler, it is time to remove the soot deposits

Over to you…

Do you know any important points that can be added to this list for improving the efficiency of boilers on ships?

Let us know in the comments below.

6 Practical Tips On Improving Boiler Efficiency for Professional Marine Engineers appeared first on Marine Insight - The Maritime Industry Guide

Marine auxiliary boiler is only used in port and the exhaust boiler caters for all heating and steam needs while at sea. Generally if the burner routines are carried out religiously and the filters are cleaned, there is no major maintenance or routine that needs to be done

In this article the author is relating a problem faced on one ship and the troubleshooting done.

Scenario

One day the boiler shut down after flame failure alarm came.  After many futile attempts to restart the boiler on HFO, the boiler was changed over to diesel and manually fired. The auto firing mode was non operational and the FO pressure low alarm was coming and fuel pumps stopping.

The following checks were done that helped to restart the boiler:

• Correct pressure setting of the boiler: Generally the Fuel Oil pressure at the burner must be between 2 to 4 bars. In case the pressure is too high more fuel will be sent and the air fuel ratio disturbed. Less fuel pressure will give a lean mixture and flame will be unsteady and fail.

• The fuel pump might trip on overload. Check the pump for mechanical damage and jamming. It should be free to turn by hand.

• The over current relay may be at fault. Check the OCR setting and try increasing it if not correct. There is generally a test lever at back of OCR for testing.

• The fine filter also called as dirt trap on the burner may be dirty.

• The pressure transmitter may be giving wrong pressure feedback, check the wires.

• The pressure transmitter for DO is normally different from FO line, Check this pressure transmitter.

• The PLC will give command to stop due to pressure transmitter fault. Try calibrating the transmitter with the Master calibrator and check output. Output should be between 4 to 20 mA.

• The fuel oil line may be choked and blocked. This can be ascertained by high back pressure.

• The fuel oil temperature should be around 90 deg C. Check heater for correct functioning. High temperature can cause vapor lock that can lead to ignition failure.

• The PLC (Programmable Logic Controller) has a reset buttons and resetting it restores the default values, often solving the problem.

• Check any error code flashing on the display of the PLC or logic module and consult the manufacturer.

                   

• If a fuel oil (FO) low pressure alarm is generated it may be due to restriction in the line going to the pressure transmitter. There are also valves for isolation, they must be open.

• Local FO pressure gauge may be replaced with a new / calibrated one to get correct picture.

• If the boiler is firing on diesel oil (DO) then the burner should be generally ok, however if filters are partially dirty or the nozzle is partially choked, it may lead to this problem. Overhauling the burners may give correct picture. If the nozzle is choked it will create a back pressure.

• There are two fuel oil (FO) pumps, try starting the second pump.

• Check supply and return lines for correct functioning of valves.

• Check the megger reading of the pump motor.

• Check the suction line change over and return line change over valves.

• In case the system includes separate pressure control valves for HFO and MDO, change over the three way valve from MDO position to HFO position or close the stop valve before the MDO pressure control valve.

• Near the FO change over valves and near the burner assembly, there are pressure regulating valves on MDO and HFO line, try to adjust the pressure within 3 to 4 bars for HFO. Moreover there may be another pressure regulating valve near the pressure gauge of burner assembly. Use this for fine adjustment.

• If the fuel pumps are tripping in manual firing then there is pump problem or back pressure.

• In manual mode PLC should not be involved and as still pump is tripping there is some other fault.

• Check the input voltage to the pump and also the current by clamp meter.

• If both the pumps are tripping then it indicates Pressure switch or back pressure problem.

The information was related to Saacke boiler on board but may slightly differ with the make of the boiler and the piping system and automation on board.

What To Do During Marine Auxiliary Boiler’s Flame Failure or Fuel Pump Tripping? appeared first on Marine Insight - The Maritime Industry Guide

Failure in boiler starting is a common phenomenon on ship. There can be several reasons for the failure in staring of a boiler. In this article we will learn about the most common reasons for not starting of boiler.

1) Fuel inlet valve to the burner is in close position:

The fuel line for boiler’s burner consists of several valves located at fuel tank, pumps suction, discharge valve, or valve before the boiler burner. Any of these can be in closed position resulting in starvation of fuel.

2) Line filter at the inlet of the fuel line for burner is choked:

If the system runs in heavy oil then there are chances of filters in the line getting choke. To avoid this, boiler system are normally built for changeover from diesel to heavy oil during starting and heavy to diesel during stopping. This keeps the filter and the fuel line clean.

3) Boiler fuel supply pump is not running:

There are two main reasons for fuel pump not running. Normally when the pumps are in pairs, the change over auto system is kept in manual position, and if the operating pump trips, the stand by pump will not start automatically. Another reason is tripping of pump due to short circuit in the system etc.

4) Solenoid valve in the fuel supply line is malfunctioning

Nowadays most of the system adopts advance automation, but their can be a possibility wherein the solenoid in the fuel supply line is malfunctioning and not opening.

5) Flame eye is malfunctioning:

A Flame eye is a photocell operated flame sensor fitted directly on the refractory to detect weather the burner is firing or not. If the flame eye unit is malfunctioning, then it will give a trip signal even before the burner starts firing.

6) Air or Steam ratio setting is not proper

For proper and efficient combustion, air fuel ration is very important, if the supply of air is excess then there will be excess of smoke, and if it exceeds more than normal level the combustion will burn off causing flame failure.

7) Forced draft fan flaps malfunctioning

For removing excess gases trapped inside the combustion chamber forced draft fan (FDF) are used for pre purging and post purging operation and are connected with a timer to shut the fan flaps. If the flaps are malfunctioning then continuous forced air will go inside the chamber, preventing the burner to produce flame causing flame failure of the boiler.

8) Any contactor switch inside Control panel is malfunctioning

Boiler control panel consist of several contactors and PLC cards. Even one contactor malfunctioning may result in trouble for boiler starting.

9) Trip not reset

If any previous trips like low water level, flame failure, emergency stop etc. has not been reset than boiler will not start.

10) Main Burner atomiser is clogged

Main burners consist of atomizer for efficient burning of fuel. If the atomizer is clogged by sludge and fuel deposits then burner may not produce flame and trip the boiler..

11)   Pilot Burner nozzle is choked :

A Pilot burner nozzle is very small and can be blocked by carbon deposits and sludge resulting in flame failure. Some pilot burner consists of small filter which can be clogged after continuous operation resulting in flame failure because of carbon accumulation.

12)  Electrodes are not generating spark

Initial spark for generating a flame is produced by electrode which may be due to carbon deposits on them or fault in the circuit of electrodes etc.

If you liked this article, you may also like to read-Boiler cleaning, Boiler mountings & Boiler Gauge glass Maintenance

Boiler Starting Failure – Troubleshooting appeared first on Marine Insight - The Maritime Industry Guide

The quality of boiler water plays an important role in deciding the overall marine boiler efficiency. Contamination of boiler water leads to several types of problems, including the main ones – corrosion and scale formation. To eradicate the problem from the roots, it is important to understand the boiler water chemistry and how contaminants enter boiler feed water.

Inside the boiler system, the boiler feed water passes through a series of pipelines, tanks, and equipment. The feed water is always chemically treated to reduce the effects of harmful minerals and gases. However, the boiler feed water is not the only one responsible for problems related to boiler water contamination and boiler efficiency. The boiler feed water is always clean and chemically treated and is mainly affected by the corrosion of the boiler system, which is mostly harmless.

The main problem starts when a lot of this boiler feed water is lost through leakages and processes such as boiler blow down, soot blowing etc., and make-up water is needed to be introduced to compensate this loss. It is this make-up water that brings in a majority of the impurities into the boiler system.

How the make-up feed water is more contaminated?

The new feed water is taken into the boiler system by two ways

1. From fresh water tanks whose water is meant for drinking purpose
2. From sea water distillation plan or fresh water generator

Boiler feed water is mainly taken from the fresh water generator. The sea water contains a large amount of salts and other dissolved minerals and gasses. Moreover, the fresh water generated in the fresh water generator would often carry small droplets of salt water from the vapours. Salt droplets are also a result of salt water leaks in the distillate condenser. The feed water thus contains several dissolved minerals and salts.

Also, the dissolved gases in the seawater which are either absorbed from the air or are a result of decayed plant and animal bodies are also carried over with the vapour to the distilled water. Many of these gases and impurities are harmful, and which eventually lead to boiler problems.

Problems Due to Contaminated Boiler Feed Water

The problems arising due to contaminated boiler feed water can be classified into two main types:

1.  Corrosion

2. Scale formation

Technically, both the above mentioned problems are interlinked. Both of them results in loss in boiler efficiency and can cause boiler tube failures and inability to produce steam.

Corrosion

One of the most common reasons for boiler corrosion remains the action of dissolved oxygen in the make-up and feed water. Corrosion leads to failure of machinery from inside also reduces over all boiler efficiency.

Scale Formation

Scale formation or deposits in the boilers results from hardness contamination of feed water.

The primary minerals in the water that make the feed water “hard” are Calcium (Ca++) and Magnesium (Mg++).

These minerals form a scale over the surface of piping, water heaters, and on everything it comes in contact with. Hardness contamination of the feed water may also result from either deficient softener systems or raw water in leakage of the condensate.

This kind of scale/ deposits act as insulators and lower the heat transfer rate.

The insulating effect of deposits also causes the boiler metal temperature to rise and lead to tube-failure by overheating.

Large amounts of such deposits throughout the boiler would reduce the heat transfer enough to drop the overall boiler efficiency.

Additional read:

Important Points for Boiler Cleaning

Boiler Starting Failure – Trouble Shooting

Important Books on Marine Boilers

Understanding Boiler Feed Water Contamination appeared first on Marine Insight - The Maritime Industry Guide

The main purpose of refractory material that is used inside a marine boiler is to contain the heat generated by burning of the fuel in the furnace and to minimise heat losses from the furnace. It is therefore important that these materials have insulating properties and are able to withstand high temperatures. Also, the refractory to be used inside boiler furnace should not contaminate the material with which it is in contact.

Boiler refractory material should have sufficient mechanical strength and be able to withstand various forces like

• Weight of adjacent brickwork.
• Vibration action
• Cutting & abrasive action of frame
• Flue dust
• High temperature
• Sudden changes of temperature
• Load at service conditions
• Chemical and abrasive action of operational phases

The material  (pure compounds) which are used to make refractory (like MgO, SiC, Fireclay etc.) have high melting point in range of 1800° to 2800 ° C.

The material should be able to expand and contract uniformly with temperature change without cracking. Economically, it is not possible to use a single refractory in the boiler and thus different types are used to together after ascertaining that they are able to withstand the temperatures they are subjected to.

Important Terms defining the Boiler Refractory property:

Refractoriness: It is a property at which a refractory will deform under its own load and it is generally determined by the composition of material used to make a refractory.

Porosity: It is the property to resist against chemical attack ( usually by fuel and water). A low value of porosity means high strength and  good thermal conductivity.

Refractory Strength: It is the resistance of the refractory to compressive loads, tension and shear stresses.

Specific gravity: Mostly associated with brick type refractory, the specific gravity is associated with the weight of the brick. A higher specific gravity brink will have more strength.

Spalling: Spalling is a type of defect, also known as fracture of refractory, which is caused by excessive  thermal and/or mechanical load on the refractory.

Permanent Linear change (PLC) on reheating

Permanent change in the property of the refractory mostly caused by high temperature.

Thermal conductivity: It indicates the general heat flow characteristics of the refractory

Thermal expansion: An important factor determining the ability of refractory product to expand during high temperature and contract during cooling

Bulk density: It is measured as weight of a given volume of the refractory and relates to apparent porosity of the material used. A refractory with higher bulk density is better in quality.

The materials from which the refractories are made are classified into three groups :

Acid materials which consists of clay, silica, quartz, sandstone, gamister.

Neutral material which consists of chromite, graphite, plumbago, alumina.

Alkaline or Base material which consists of lime, magnesia, zirconia.

Special care is to be taken while choosing the refractory material and it must be insured that the acid and alkaline material are kept apart as under high temperatures the two react with each other to form salt, which reduces the effectiveness of refractory.

For installation, the refractory material is available in two forms:-

1) Firebricks

The material is formed into bricks and these bricks are then fired at high temperature in special kilns.

Advantages:

• Hassle free performance
• High strength
• High temperature resistance
• Low maintenance costs

2) Monolithic Refractory

These refractory are supplied in unfired state and installed in the boiler. They are then fired in place or when the boiler is put into service. This type of refractory can be divided into :-

a) Moldable Refractory : This type is used when direct exposure to radiant heat takes place. It must be pounded in place during installation.

Advantages:

• High quality formulation
• High density
• Low maintenance costs
• Efficient performance

b) Castable Refractory: This type of refractory is placed where there is no direct exposure to radiant heat for e.g. behind water walls. It is installed in manner similar to building concrete.

Advantages:

• Efficient performance
• Long operational life
• High strength
• Low maintenance costs
• Dimensional accuracy

c) Plastic Chrome Core: This type is bonded with the clay and is used in construction of studded water walls. They can withstand very high temperature but have a very low mechanical strength. These are pounded onto the steel studs and welded to the tube. These studs provide addition strength and means of attachment for the refractory.

Advantages:

• high resistance to corrosion
• high in refractoriness
• High strength
• High temperature strength

Precautions to be taken during and after installation of boiler refractory:

1)  To prevent undue stresses in the refractory material ample space should be provided for expansion. It is made to ensure that the these spaces does not get blocked in any way and cause refractory to break off from attachment and bulge out, with danger of possible collapse.

2)  Refractory material determines the time required for raising steam. So greater amount of refractory slows down the steam raising process to prevent damage to refractory.

3)  Air dampers or checks should be closed as soon as boiler is shut down preventing cold air impingement on the hot refractory.  This impingement causes surface flaking which is commonly known as Spalling. Spalling causes reduction in wall thickness of the refractory.

4) Flame impingement should be avoided on the refractory as this causes build up of carbon deposit on the surface. The carbon penetrates into the refractory and damages the same.

5) Impurities in fuel like vanadium and sodium salts react with refractory material to form molten slag, which runs down to the furnace floor. This causes reduction of wall thickness and building up of this slag interferes with the shape of the flame. Thus impurities should be prevented from entering the boiler.

Different Causes for boiler refractory damage

1. Improper installation of the refractory
2. Installation of wrong shape ferrules
3. Improper refractory dry out post installation leading to thermal shock
4. Improper shut down operation leading to rapid cooling of the refractory
5. Ceramic cracking as a result of thermal, structural or mechanical stresses
6. High temperatures inside the furnace by improperly using a higher level of oxygen or loss of temperature control system
7. Failure due to corrosion resulting in cold spot, acid formation and undesired chemical reactions
8. Improper velocity of the flame
9. Erosion due to improper high loading under tension
10. Vibration as a result of improper design
11. Improper refractory selection

The refractory inside the boiler furnace is an important structure to safeguard the boiler structure and to increase the efficiency of it’s operation. The ship engineer responsible for the boiler maintenance must ensure regular visual inspection of refractory to be performed and boiler is correctly operated.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

Understanding Boiler Refractory And Its Types appeared first on Marine Insight - The Maritime Industry Guide

A gauge glass is used at many places on a ship. Gauge glass is a kind of a level indicator which shows the amount of fluid in a tank or any other storage place on a ship. In this article we will learn as to how the maintenance of a gauge glass is done on a ship. Gauge glass are mainly used in boiler of the ship.

Before learning about boiler gauge glass maintenance lets take a quick look at the working of a gauge glass.

Working of Boiler Gauge Glass

A gauge glass has two different compartments – top side and bottom side, connected to two different sections of a boiler. The top side of the gauge glass is connected to the steam side of the boiler and the bottom side is connected to the water side of the boiler. The pressure on both sides will equalize and the level of water can be seen in the gauge glass.

Maintenance During service check up

Refer the diagram for better understanding of boiler gauge glass.

• Check the nut (1) and tighten if necessary.
• Bolts on the boiler flanges are to be checked, if loose tighten them.
• Check if union nuts are loose.
• Bolt from screw 7 with cocks in open position.
• If the leak can not be stopped from water side on the gauge glass by tightening the screw 7 then the sealing surface of the cock plug 8 my be damaged or corroded.

Gauge glass blow down procedure

Gauge glass should be blown before lighting up of boiler, after stopping the boiler and regularly if the level in gauge glass is suspected to be wrong.

Cleaning the water side of gauge glass

• Close the valve S and W as shown in the figure.
• Now open the cock W and see if the water is coming out of the drain valve D indicating the drain line is clear.
• Now close the drain valve D and keep the cock W open and see if the water level rises in the gauge glass; this indicates the line to gauge glass is also clear.
• Repeat the steps two to three times to remove muds and deposits inside.

Cleaning the steam side of gauge glass

• Close both the cocks S and W.
• Now open the cock S and open the drain valve D and see the steam is coming out. The drain is opened only for 1-2 seconds only as steam may damage the sealing and service life decreases.

Putting the gauge glass in normal operating position

• Close all the valves S, W and the drain valve D.
• Now open the cock W and let the water fill inside the gauge glass.
• Now open the cock S and then the level can be seen as the pressure equalizes.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

Procedure for Boiler Gauge Glass Maintenance on a Ship appeared first on Marine Insight - The Maritime Industry Guide

Marine boilers used in ships today are mostly for auxiliary purposes in vessels that run on marine diesel engines or diesel-electric propulsion.

In the case of ships using steam turbines (mostly found in high-speed vessels used by navies), boilers are a part of the main propulsion system. However, in this article, we will focus on auxiliary boilers, i.e. boilers used for running auxiliary systems in a ship.

To look at this from a ship designer’s point of view, he/she should be able to choose the right kind of boiler for a particular ship depending on the requirement for that particular project.

The process is pretty much an application of first principles but in a somewhat different way.

To rate a boiler, one first needs to correctly estimate the steam output required from a boiler for the ship being designed. For this, the three main requirements are:

Requirement 1 – Steam consumption required to compensate heat losses in tanks.

Requirement 2 – Steam consumption required to raise the temperature of fuel oil in tanks.

Requirement 3 – Steam consumption required for other services.

We will discuss each of the requirements, and once done, we will see how the obtained data is used to estimate the capacity of the boiler.

Requirement 1- Steam consumption required to compensate heat losses in tanks:

Most ships run by diesel engines have fuel oil tanks that are used to store Heavy Fuel Oil (HFO). Since the viscosity of HFO is very high, stored HFO is almost as dense as tar, and its high viscosity makes it unable to flow.

But in order to transfer the stored HFO to the settling tanks and then the HFO service tank, the viscosity needs to be maintained at a level corresponding to which easy flow is possible. For this, HFO storage tanks are equipped with heating coils to maintain the fuel at a certain temperature.

The heating fluid in the heating coils is steam that is produced in the auxiliary boiler.

First, each HFO storage tank is located in the general arrangement drawing, and the surrounding space adjacent to each tank bulkhead is noted. Depending on the surrounding of each tank bulkhead (Engine Room, Void, Ballast Water Tank, Sludge Tank, etc.) the ambient temperature is fixed for heat transfer through each bulkhead of the tank in analysis.

The amount of steam flow rate required to maintain the temperature of the fuel in each such tank is calculated using the following steps:

Heat loss from tank bulkhead

                                                Q1 = U A (T2 – T1)

Where

Qb = heat loss from bulkhead (W)

U = overall heat transfer co-efficient (W/m^{2 0}C)

A = Area of tank bulkhead under consideration (m²)

T2 = Temperature of the tank to be maintained (⁰C)

T1 = Temperature of the adjacent medium of the bulkhead considered (⁰C)

Heat loss from tank Qt = Sum of heat loss from all the six bulkheads of the tank

Q1 = sum of heat loss from all the tanks

As we know the heat transfer rate, the mass flow rate of steam can be calculated using the following formula :

m_s = Q1 / ∆h        

Where,

m_s = mass flow rate of steam (kg/s)

Q1 = calculated heat transfer (kW)

∆h = enthalpy drop of the steam (kJ/kg)

Requirement 2- Steam consumption required to raise the temperature of fuel oil in tanks:

Not only is steam required to compensate for the heat losses from fuel oil tanks, but steam is also used to heat the fuel oil to the required temperature before being used in the engine.

For this, the time (t) in hours, required to heat up the oil in each type of tank is generally considered as follows:

                                                                                    ∆T/t

• For Storage Tank – 0.2 DEG C/HR RISE IN TEMP.
• Service and Settling tank – 4 DEG C/HR RISE IN TEMP.
• All other Tanks – 1 DEG C/HR RISE IN TEMP.

This calculation includes two steps:

• Calculation of heat (Q in watts) required to heat contents of each tank, and summation of all the individual heat requirements to obtain total heat transfer required to raise the temperature of fuel oil in tanks (Q2)
• Utilising the above-obtained heat requirement to find the required mass flow rate of steam for this purpose.

A sample of this calculation is shown below:

The amount of heat required to raise the temperature of fuel oil tanks can be expressed as:

Q2 = m C_p dT / t  

Where Q2 = mean heat transfer rate (kW)

m = mass of fuel oil in the tank (kg)

C_p = specific heat capacity of the fuel oil (kJ/kg ^oC)

dT = Change in temperature of the fuel oil (^oC)

t = total time over which the heating process occurs (hours)

As we know the heat transfer rate, the mass flow rate of steam can be calculated using the following formula :

m_s = Q2 / ∆h    

Where m_s = mass flow rate of steam (kg/hr)

Q2 = calculated heat required to raise the temperature (kW)

∆h = enthalpy drop of the steam (kJ/kg)

Requirement 3- Steam consumption required for other services:

Steam is also used in ships to cater to other heating requirements, some of which are listed below:

• Used as a heat exchange medium in Heavy Fuel Oil purifiers, Light Diesel Oil purifiers, and Lube Oil purifiers.
• Steam is used as a heating medium in booster modules.
• To pre-heat the main engine jacket cooling water.
• Used as a heating medium in calorifiers (calorifiers are high-pressure storage units of heated water, which is used in gantry and toilet utilities).

Heat requirements by all such services are calculated individually and added. The obtained heat requirement is termed Q3 (for the purpose of this article only).

Once the heat requirements for the three purposes (mentioned above) are obtained, they are added to obtain the Total Heat Rate and Total Steam Mass Flow Rate Required for the boiler:

Total Heat Rate Required (Q) = Q1 + Q2 + Q3 (kW)

Total Mass Flow Rate Required is calculated from the relation: m_S = Q / ∆h (kg/hr)

Where ∆h = enthalpy drop of the steam (kJ/kg)

Now, there are two rating systems to obtain a suitable boiler:

From and At Rating:

In the above graph, the vertical axis corresponds to the steam output as a percentage of the from and at the rating, at different pressures. That is, for example:

At 15 bar,

If feed water temperature is 68 degrees Celsius,

Then the percentage from and at rating from the graph is 90%

So if a boiler has a rated steam output of 2000 kg/hr, the actual steam output of the boiler will be 90% of the rated output, which is 1800 kg/hr.

Now, when a designer chooses a boiler, he/she needs to specify the rated steam output to the boiler manufacturer. The boiler manufacturer, along with the boiler, provides the boiler from and at rating graph for the proposed boiler, and the above calculation is carried out for various boiler pressures and feed water temperatures, to check that the actual steam output is more than the steam flow rate (m_S) obtained in the initial design calculations that we have previously discussed.

Kilowatt Rating:

While some boiler manufacturers prefer from and at ratings, some others prefer another system called the Kilowatt rating system, which is however just a different way of expressing the same data.

In order to obtain the Actual Steam Flowrate from the kW rating of a boiler, the following relation is used:

In the above expression, the energy to be added refers to the amount of energy added to the boiler by the feed water (which in turn depends on the feedwater temperature).

The designer should make sure that the steam output obtained above is more than the steam flow rate (m_S) obtained in the initial design calculations that we have previously discussed.

The above checks are to be carried out at various working pressures of the boiler, and different ranges of feed water temperature, depending on the steam requirement at various sailing conditions. It is to be ensured that the chosen boiler meets the requirements in all such conditions, at different load combinations.

The type of boiler to be used in the ship is also to be chosen by the designer based on the following criteria:

• The functionality of the boiler.
• Space Constraints.

For most auxiliary boilers, shell and tube boilers are used, where the boiler drum holds the water reserve, and fire tubes run along the length of the drum.

The hot gases produced by the burner are carried in the fire tubes that provide more surface area for heat transfer to the water. In most cases, the auxiliary boilers are horizontally oriented in case there are no space constraints, as they prevent pressure fluctuations which is more in the case of vertically oriented boilers.

However, for exhaust gas economisers or exhaust gas boilers (These are boilers that do not have a furnace. They have also fired tube boilers, where exhaust gases from the engine are passed through the fire tubes to heat the water in the boiler drum.) vertical configurations are preferable, as it provides less back pressure on the exhaust gas system. Exhaust gas boilers are used when the vessel is on the voyage, and when in port, the auxiliary boiler is used.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendations on any course of action to be followed by the reader.

Choosing A Marine Boiler While Designing A Ship appeared first on Marine Insight - The Maritime Industry Guide

The boiler is one of the oldest machinery systems to be used in a ship’s engine room. In early days, the vessel’s propulsion system was powered by the steam produced by the boiler. With technical advancements and increasing emphasis on safety of ship and crew, various boiler mountings and boiler safety devices have been introduced.

Just installing a boiler on a ship doesn’t guarantee efficient working of a boiler. When a boiler installation is done on board a ship, it can only be considered as complete, when different types of boiler mountings, including boiler controls, are fitted to ensure safe and efficient operation of a gas boiler.

Related Reading: Choosing a marine boiler while designing a ship

The article describes a comprehensive list of boiler mountings, without which, a boiler cannot operate safely and efficiently on a ship.

1)     Main steam Stop Valve:

The steam generated in the boiler is supplied to ship’s system through this valve. It usually is non-return type of valve directly mounted on the steam space of the boiler shell. The body is made of cast iron, and the valve seat is of gunmetal.

Related Reading: How to identify metals in engine room – Observation and Spark Test

2)     Auxiliary steam Stop Valve:

In most of the steam system on ships, a separate steam line provided from the boiler for the small auxiliary system is supplied through this valve. The valve is smaller in size and usually of a non-return type.

3)     Boiler Safety valve:

This is one of the most critical boiler fitting used in the event of unsafe excessive pressure inside the boiler. The boiler safety valve is designed to come into action to release the overpressure. The lifting pressure of the valve is set prior to its installation and locked in the presence of a surveyor so that it cannot be changed later on.

Related Reading: 10 Boiler Operating Mistakes That Can Cost Big Time

Boiler safety valves are installed in pairs with one valve set at a little higher pressure to ensure boiler does not explode of overpressure in the event of failure of any one boiler safety valve.

4)     Boiler level gauge glass: Boiler gauge glasses are fitted in pairs for manually checking the water level inside the boiler drum. It is on the basis of the boiler pressure that the construction of the gauge glass is decided. The boiler water level indicator is an important boiler fitting as it tells the status of water level inside the steam drum of the boiler.

Related Reading: Procedure for boiler gauge glass maintenance on a ship

5)     Air release valve or boiler vent:

This valve is fitted in the headers, boiler drum etc., to avoid imploding of the boiler when it is depressurized or when initially raising the steam pressure. The term implosion is just opposite of an explosion. In this scenario, the pressure inside the boiler will reduce sufficiently below atmospheric pressure to cause the shell to buckle inwards.

6)     Feed check and control v/v:

This valve controls the supply of steam supply as per the demand and is fitted in both main and auxiliary steam line after the stop valve. They are non-return valves with a visible indication of open and closed position.

7)     Pressure gauge connection:

The pressure gauge can be fitted in the superheater, boiler drum and wherever it is necessary to read the real-time pressure reading from the local station.

Related Reading: Different types of mechanical measuring tools and gauges used on ships

8)     Boiler blowdown valve:

A bottom blowdown valve is used to empty the boiler either completely for maintenance purpose or partially for water treatment of boiler when the chloride level in the boiler water is on a higher side.

9)     Scum blow down valve:

It’s a shallow dish type arrangement fitted at the normal water level which allows the blowdown of floating impurities, oil foaming etc. from the water surface.

Related Reading: Blow Down Procedure For Marine Boiler

10)  Sampling connection:

Generally, a sampling water cock arrangement is also fitted with the cooler, in series, so that water sample can be collected at any time for feed water analysis.

Related Reading: Understanding Boiler Feed Water Contamination 

11)  Whistle valve:

If there is a provision for the steam whistle in the ship, then steam is supplied directly from the boiler through a small bore type non-return valve known as whistle valve.

12)  Low-Level alarm:

This is a device used to initiate audible warning at low water level condition. Another shut down alarm (burner cut off) is fitted below this level (Low-Low Level alarm) to prevent overheat of boiler drum.

Related Reading: Troubleshooting boiler starting failure

13)  Soot blowers:

Required to blow the soot and the combustion products from the tube surfaces. It is operated by steam or compressed air.

14)  Automatic feed water regulator:

This device is essential to ensure appropriate water level in all load conditions and is fitted in the feed line. Multiple element feedwater control system is used in boilers with high evaporation rate.

15) Manhole:

The boiler is provided with multiple manhole doors, allowing inside access to the crew for inspection, cleaning and maintenance of boiler tubes and internal parts. Usually, one door is provided in the steam drum and one in the water drum.

16) Mud box:

The mud box in the boiler is provided at the bottom of the water drum to collect the mud (muddy impurities) of the water drum

Related Read: Do’s and Don’t For Efficient Boiler Operations On Ship 

17) TDS Sensor and Probe:

Nowadays, most of the modern boilers are provided with this arrangement to monitor the total dissolved solids within the boiler water continuously. The sensor compares the true value with the set point, and if the value is on the higher side, an audio-visual alarm is given. A manual blowdown can be done to introduce fresh feedwater to the system to lower the total dissolved solids.

Over to you..

Do you know any other important boiler mounting that should be added to the list?

Let’s know in the comments below.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

Boiler Mountings: A Comprehensive List appeared first on Marine Insight - The Maritime Industry Guide

A boiler is one of those machinery that gets the ship going. A boiler is something, though not required continuously in operating a ship, cannot be done away with.

Moreover, it’s dangerous equipment that generates steam at extremely high pressure, and it is for this reason that proper care should be taken while operating it.

In this article, we have brought to you a step-by-step procedure for starting and stopping a boiler on a ship. With this procedure, you can never go wrong, as far as boilers are concerned. Starting and stopping a boiler was never so easy.

Starting a Boiler

It is to note that the following steps may not apply to all types of boilers and each boiler requires some additional steps to be followed as per its system design. However, the basic steps remain the same:

1. Ÿ  Ensure that the vent valve on the boiler is open and check there is no pressure in the boiler.
2. Ÿ  Check that the steam stop valve is closed.
3. Ÿ  Check that all the valves for fuel are open, and let the fuel circulate through the system until it comes to the temperature required by the manufacturer recommendation.
4. Ÿ  Check and open the feed water valves to the boiler and fill the water inside the boiler drum to just above the low water level. This is done because it is not possible to start the boiler below the low water level due to safety features that prevent the boiler from starting. Also, the level is not filled much because if filled too much, the water inside the boiler might expand and over pressurize the boiler.
5. Ÿ  Start the boiler in automatic mode. The burner fan will start the purging cycle which will remove any gases present in the furnace by forcing it out through the funnel.
6. Ÿ  After the pre-set purge time the pilot burner will ignite. The pilot burner consists of two electrodes, through which a large current is passed, via the transformer, producing the spark between the electrodes. The pilot burner is supplied with diesel oil and when the oil passes over, the former ignites.
7. Ÿ  The main burner which is supplied by heavy oil catches fire with the help of the pilot burner.
8. Ÿ  Check the combustion chamber from the sight glass to ensure the burner has lit and the flame is satisfactory.
9. Ÿ  Keep a close eye on the water level as the pressure increases and open the feed water when the level of water inside the gauge glass is stable.
10. Ÿ  Close the vent valve after the steam starts coming outside.
11. Ÿ  Open the steam stop valve.
12. Ÿ  Once the working steam pressure is reached, blow down the gauge glass and float chambers to check for the alarms.

Stopping a boiler

1. Ÿ  If the boiler is needed to be stopped for a longer duration for maintenance or opened up for the survey, change the fuel to distillate fuel.
2. Ÿ  If a separate heating arrangement for heavy oil is present then there’s is no need to change over to distillate fuel and the oil is kept on circulation mode.
3. Ÿ  Stop the boiler automatic cycle.
4. Ÿ  Close the steam stop valves.
5. Ÿ  Close the boiler feedwater valves.
6. Ÿ  When the boiler pressure is just reduced to over atmospheric pressure the vent valve is kept open to prevent vacuum formation inside the boiler.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendations on any course of action to be followed by the reader.

Boiler Operation Made Easy : Procedure for Starting and Stopping a Boiler appeared first on Marine Insight - The Maritime Industry Guide

In the last article in this series on the energy audit of the ships boiler, we discussed the instruments required for ship’s audit, pre audit precautions and the energy conservation and optimization opportunities. In this article we discuss the other opportunities for energy conservation and also layout of the final audit report.

Read the first two parts of the series here:

1. Energy Audit on Ships

2. Audit of Marine Boilers

Energy Conservation and Optimization Opportunities

The other areas where energy conservation and optimization opportunities exist are as follows:

 Performance of Heat Transfer Areas: The heat transfer areas of the boiler must be monitored. The soot blowing of the boiler must be done religiously as build up of soot acts like an insulator and reduces the heat transfer rate. That means for generating the same amount of steam more fuel will be needed. The same goes for the buildup of scale in the tubes. The stack temperature must be monitored regularly and any increase in it means that heat recovery is not optimum. If the funnel temperature increases about 40 deg C after last cleaning it indicates that boiler cleaning must be done.

Read important points on boiler cleaning here.

Heat Loss Due to Inadequate Insulation: The boiler and steam lines along with condensate return to the hot well must be well insulated. Over a period of time insulation is damaged or worn out. Any analysis by an infra red camera or infra red thermometer can identify the hot spots and optimize fuel consumption.

 Optimum Hot Well temperature: The hot well temperature must be maintained at temperature specified by manufacturers which is generally about 80 to 85 deg C. A lower temperature will cause colder feed water to enter the boiler thus increasing the fuel cost due to loss of sensible heat. An overheated hot well will cause vapor lock in the feed pump and loss of suction.

Learn how to troubleshoot marine boiler starting failure here.

Steam Trap Losses: Steam traps are used to discharge condensate once it is formed, to prevent live steam from escaping and to remove air and non condensable gases from the line. However it is a largely neglected part of the steam piping. Steam traps that are stuck open allow live steam to escape thus resulting in loss of heat and also increasing the load of the condenser. Steam trap that is stuck shut results in reduced capacity of the equipment it is being supplied to.

 Radiation and Convection Losses: The boiler body loses lots of heat from the exposed surfaces to the surroundings. In cold climate the loss is greater. Effective insulation can reduce these losses.

Optimize Boiler Steam pressure: Running a boiler at lower pressure after optimizing steam usage will lower the fuel consumption.

Installation of variable speed drives: The air dampers use throttling to obtain capacity control. These old methods of capacity control lack accuracy and have poor control characteristics at the top and bottom of the operating range. In case the steam demand of the boiler is variable and changes from time to time, then replacing the damper type air register with the new electronically controlled variable speed drive forced draught fan should be considered.

Understand marine boiler water circulation here.
Reducing Steam Leakage: Though this is a simply understood principle that steam leakage leads to energy and fuel loss, it is common to see many leakages of steam unattended due to either fear or apathy. Just by controlling the leakages many of the boiler operational problems can be avoided.

Audit Report on Energy Saving Measures

The audit report of the boiler must indicate the energy opportunities that can be availed, the investment required, the fuel saving and returns. The owner must be provided with the economic viability and feasibility of the project. The energy measures recommended are of three types.

Immediate Returns: Those energy saving measures that give immediate returns and require no investment. For example overhauling the burner, calibrating the air register, cleaning the tubes of soot, repairing steam traps etc.

Medium Term return:  Those energy saving measures that require moderate investment and give returns in a medium time frame.  For example these can be equipment modification like change of burner and air register, change of insulation, retrofitting the furnace with a new burner etc.

Long term return: These require considerable investment and will benefit in long term only. For example if the boiler is old and unusable, under or over sized. Replacing an old boiler with an energy efficient new boiler may be a good strategy. It is only recommended if the company has plans for keeping the ship for a long time.

Financial analysis of the energy saving measures is the most important part of a boiler energy audit. Annual cost savings from the upgrades, retrofits and replacements must be provided to enable the owner make correct decision.

References:

Boiler Operations  By M P Murgai and Ram Chandra

Training Manual for Energy Efficiency By Asian Productivity Organization, 2010

Presentation on Energy Audit in Thermal Power Stations by H.S.Bedi

Hand Book on Energy Audit and Environment Management by Y.P.Abbi and Shashank Jain

Working manual on Energy Auditing in Industries By Asian Productivity Organization

Energy Conservation in Boilers and Making an Audit Report appeared first on Marine Insight - The Maritime Industry Guide

Every engine room machinery system requires a specific procedure for starting and stopping it. Boiler being one of the most important systems on board ships, requires special care and attention during operation and maintenance. Inability to do so leads to major failures and accidents, which can not only be life-threatening but also cause huge damage to the ship’s properly.

Mentioned below are 10 boiler operating mistakes that can lead to heavy loss of life and properly on board ships:

1. Starting a Boiler Without Pre-purging the Furnace: Almost all boilers come with an automation system of starting and stopping comprising of programmed pre-purging and post-purging of furnace before the burner is fired. Never ignore or isolate this safety feature. If the boiler has to run manually, it must be pre-purged by means of FD fan for at least 2 minutes. Avoiding this step can lead to blowback and even explosion.

2. Ignoring Furnace Blowback: Several accidents in the past involving furnace blowback have lead to fatal situations on board ships. Still marine engineers often overlook this danger and fire furnace even when the first attempt ends with flame failure and blowback. One of the reasons for this is stated above i.e. no pre-purging of furnace.

3. Bypassing Safety and Alarm: This is a common practice among seafarers, who bypass some of the safety or automation sequences to shorten operating procedure of boilers. Such systems are installed to ensure safety of ship personnel and thus should never be missed.

4. No checks on Boiler Refractory:  Boiler refractory provides better heat-exchanging efficiency and closes/seals gaps to restrict fire, heat, ashes etc. inside the boiler . Regular inspection of boiler refractory is important as damaged refractory would expose the boiler shell to flame and heat, leading to bulging or even cracking of the boiler shell.

5. Dirty Gauge Glasses: Gauge glasses installed on the boiler are the only physical means to check the water level of the boiler. Every engineer knows the procedure to blow the gauge glass for avoiding any kind of blockage. Neglecting this can lead to wrong water level indication and heavy damage to boiler tubes.

6. Pilot Burner Check: Many engineers remove the pilot burner to check the electrode spark. Such practice can lead to electrical shock and even fire if the surrounding are not properly cleaned or the pilot burner is kept on oily floor plate with rags. The best way to check the pilot burner operation is to fit it in place and watch the firing from boiler inspection manhole located opposite of the burner.

7. No Clean-up After Burner Maintenance: When any maintenance work is done on the burner assembly (pilot or main burner) and the surrounding area is not cleaned before trying out the boiler, there are high chances of fire and explosion as blowbacks are normal during starting-up after maintenance. Oil spilled inside the furnace and over the burner assembly can add more to this blowback, converting it into an explosion.

8. Cold Condition – Thermal Shock: Never fire a boiler continuously when starting from cold condition to avoid thermal shock. Thus in cold condition, boiler should be started by following an intermediate firing pattern, for e.g.  2 minutes of firing followed by 10 minutes of break. Also, once the boiler starts to warm up the “break” time gradually decreases and the “firing” period increases simultaneously

9. Wrong Operation of EGB Circulating Pump: Exhaust gas boiler (EGB) normally comes with water circulating pump. It is important to start this pump well ahead, at least 2 hours, of starting the main engine and to be stopped 12 hours (the time may reduce depending upon the capacity of the boiler and the geographical condition) after stopping the main engine to avoid thermal shock and EGB fire.

10. Cleaning of EGB tubes:  The exhaust gas boiler (EGB) tubes are arranged in the passage of exhaust gases, which heats the water in the tubes. If these smoke tubes are not cleaned regularly, it can lead to soot deposits over the tubes and during low load operation or improper combustion oil can mix up with the soot. When ignited, the soot can lead to major soot fire followed by hydrogen or iron fire.

Are you aware of any other boiler operating mistakes that can be extremely dangerous to ship’s crew and property?

Let us know in the comments below.

10 Boiler Operating Mistakes On Ships That Can Cost Big Time appeared first on Marine Insight - The Maritime Industry Guide

Marine boiler is one of the most easy-to-operate systems on board ships. Though most of the mariners will agree to this, they also know that it’s a complex machinery which requires highest standards of safety precautions and correct operating procedures.

Read 10 boiler operating mistakes on ships here.

Accidents on board ships involving marine boiler has caused severe damage to the property and even claimed human lives in the past. Mariners know the dangers of high temperature steam and therefore do not take any chances when it comes to operation and maintenance of boilers.

According to an analysis, one of the main reasons behind accidents are improper operating procedures and overriding safety precautions while operating boilers. The main concern of any ship engineer is to operate  all engine room machinery and systems to achieve maximum efficiency without hampering it’s operating life and safety measure.

Read 6 practical tips to improve boiler efficiency.

When it comes to marine boilers, the steam demand is the main criteria of operating a boiler at a given load. It is therefore important not to over-stress the boiler to achieve the desired output. Also it is necessary to ensure that the boiler is operated within all safety limits.

Below are some of the important Do’s and Don’ts which a marine engineers must consider while operating a marine boiler in a safe and efficient manner:

Do’s:

1. Operating Procedure: Follow the correct operating procedure when lighting up the boiler from the cold condition. Ensure to pre and post purge every firing and also make sure that the air vent is kept open while initially firing and shutting down the boiler.

Operating procedures for Boiler. 

2. Blow Down: A regular gauge glass blow down (once every watch) is a must. Boiler blow down is to be performed once a day to keep the chloride level to minimum. If floating impurities are suspected (oil, foaming etc.) scum blow down is to be carried out.

Read blowdown procedure here.

3. Soot Blow: Perform a soot blow for the boiler tube to continue the heat exchanging ability of the boiler tubes.

Do Soot Blowing to prevent fires.

4. Smoke: Check the smoke from the boiler trunk coming out of the ship’s funnel on every watch to gauge the combustion quality.

5. Lubricate: All the boiler mechanical parts and links to be lubricated and greased at regular interval of time.

6. Emergency Shut Down: Ensure to check emergency shut down of the boiler, which is located in the ECR, is working. This is to be tested as per the safety routine described in the company Safety management System (SMS).

7. Valves and Dampers: Ensure all the fuel line valves, steam valves and safety valves are working fine. Check the quick closing valves and safety valves for their correct operation.

8. Attend Leakage: Steam system is prone to leakages because of their fluctuating steam pressure. Attend all the leakages at the earliest to maintain the efficiency of the boiler at all times.

9. Check Furnace: Keep a check on the furnace for refractory deterioration and fuel dripping near the burner assembly. Any defect to be attended at the earliest.

10. FFA for Boiler: Boiler is a high pressure machinery with its own set of prescribed fire fighting equipment. Check the functioning of local fire extinguisher (foam type) and High pressure jet fog system. Drill to be carried out regularly to train the crew for fighting the boiler fire.

Don’ts:

1. Untrained Operator: Never leave a boiler operation at the hand of an assistant engineer or untrained operator, especially when lighting up the boiler from the cold condition.

2. Blow Down: Never do excess blow down as the feed water system will add cold water in the boiler drum to compensate which will lead to decrease in the thermal efficiency and stresses in the boiler.

3. Soot blow: Never Operate a soot blow system when the boiler is operating at high load.

4. Unusual Observation: Don’t avoid any unusual observation in the boiler whether it’s sound, smoke, flame quality or other boiler parameters. Always rectify abnormalities related to boiler at the earliest.

5. Overload: Never operate the boiler at higher load as a regular practice. Boiler can be overloaded sometimes due to load demand but regular overloading will lead to high stresses and tube failure.

6. Feed water: Never include sea water in any circumstances. If the hot well is filled with sea water (due to heavy leakage in the condenser), shut down the plant and rectify the problem.

7. Leaking Tubes: Don’t Operate the boiler when any water tube is leaking. Rectify the leakage at the earliest.

8. Water Level: Don’t trust the water level indicator located at remote position i.e. in the control room. Keep a check through local gauge glass to get the clear picture. Read Science behind boiler water circulation.

9. Furnace Door: Don’t keep the boiler furnace door open unnecessarily. If it is opened for burner cleaning or furnace inspection, close the door if the equipment is unattended or once the job is over.

10. Periodic maintenance: Don’t skip the periodic maintenance of boiler and boiler auxiliaries as it will decrease the efficiency of the boiler over a period of time.

The above mentioned Do’s and Don’ts provide a general overview to ensure that boiler efficiency is maintained while the safety aspect is kept intact.

Over to you..

Do you know any important point that can be added to this list of do’s and don’ts of marine boiler?

Do’s and Don’ts for Efficient Boiler Operations On Ships appeared first on Marine Insight - The Maritime Industry Guide

In continuation with the last article on energy audit on ships, we discuss the energy audit of the ship’s boiler. One of the major and important machinery on the ship, a marine boiler comes under special emphasis in an energy audit due to many well marked and potential energy saving areas.

A well maintained boiler is not only safe but is also fuel efficient.

Basic Steps of Boiler Audit

As discussed earlier, the steps involved in an energy audit are data collection, data analysis and making report.

• Data Collection: Finding how the ship uses steam, costs of fuel consumed per day and issues by reducing steam consumption for utilities. For example reduction of domestic hot water temperature or reduction of accommodation heating etc.
• Data Analysis: Identifying measures that would lead to energy conservation. These include measures with no investment, with medium investment and with large investment.
• Audit Report: The report has to be presented to the owners with the economic viability to enable making decision.

Instruments Required for Boiler Audit

In any energy audit the use of proper calibrated instruments is essential. The instruments that are required to carry out an in depth boiler energy audits are as follows:

• Portable Oscilloscope: It’s an all in one tool. It is used for visual display and interpretation of data, trend analysis, data logger, spectrum analyzer and measuring capacitance, resistance, continuity, AC and DC voltage, power measurement for single phase and three phase, total power, apparent power, reactive power, power factor, frequency and current etc.
• Infrared Remote Thermometer: It is used for temperature measurement and for finding hot spots.
• Tachometer: For speed measurement of motors and shafts as slippage of belts and lowering of speeds can cause improper air fuel ratio.
• Master Pressure and Temperature Calibrator: For calibrating the online instruments and sensors in the boiler control panel.
• Infrared Camera: This camera can take infrared photographs thus indicating trouble areas and hot spots.
• Flue Gas Analyzer: For analyzing flue gas and measuring concentration of O₂, CO₂, CO, NO_x, and SOx etc.
• Ultra Sonic Leak Detector: It is used for checking steam traps that are leaking and pin-hole leakages of steam.
• Other Instruments: The other instruments that are used are digital manometers, calibrated pressure gauges, Multi meter, Clamp ammeter, Contact thermometer, Non contact water flow meter, power analyzer etc.

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Pre-audit Precautions

Before carrying out energy audit on the boiler some precautions must be taken to ensure accuracy and reliability of measurement.

• The boiler load should be kept constant during the audit.
• No soot blowing should be done during the audit.
• No blow down should be done during the audit.

Energy Conservation and Optimization opportunities

Depending on the layout of the ship, make of the boiler, the quality of maintenance and the condition of the boiler there may be some ship specific problems and recommendations; but in addition to these there are some common areas where generally loss of heat occurs and there is scope of energy conservation

• Excess air in combustion: Specified quantity of air is required as per stoichiometric air fuel ratio for combustion. However as metering in inadequate some extra air is always supplied to avoid incomplete combustion. Excess air lowers efficiency because it does not take part in the combustion and takes away the heat of the furnace.
• Less air in combustion: If the air is less than the recommended stoichiometric air fuel ratio, incomplete combustion will result. Carbon will not fully burn to carbon-di-oxide but will partially burn to form carbon monoxide. This will cause loss of energy.

• Maximum Waste Heat Recovery: The funnel stack temperature must be as low as possible but with sufficient margin to be above the dew point to avoid sulphur corrosion. Generally a funnel temperature of 165 to 195 deg C when using Fuel Oil is considered optimum. In any case when the funnel (Exhaust Stack) temperature is higher than 200 deg C, a more stringent waste heat recovery program should be required.
• Feed Water Preheating: If the funnel temperature is higher than 200 deg C it can be utilized for feed water preheating, thus increasing the waste heat recovery. It will increase the overall efficiency of the plant
• Combustion Air Preheating: In case there is still a margin in funnel temperature combustion air preheating may be considered.
• Blow- Down Optimization: The blow down of the boiler is required for controlling the amount of TDS in the boiler. Blow down must be calculated and done after measuring the TDS amount. Some engineers merrily blow down the boiler excessively without need even when the parameters are in control and it results in loss of precious water and heat. Blow down must be done in response to the conductivity and the pH.

In the next article we will look into the areas of energy conservation and optimization opportunities and audit report.

References

• Boiler Operations  By M P Murgai and Ram Chandra
• Training Manual for Energy Efficiency By Asian Productivity Organization, 2010
• Presentation on Energy Audit in Thermal Power Stations by H.S.Bedi
• Hand Book on Energy Audit and Environment Management by Y.P.Abbi and Shashank Jain
• Working manual on Energy Auditing in Industries By Asian Productivity Organization

Energy Audit on Ships: Audit of Marine Boiler appeared first on Marine Insight - The Maritime Industry Guide

The most important aspect of any marine boiler is maintaining the correct water level. As the boiler fires, steam liberates from the surface of the water and thus as the steam gets consumed, there is subsequent drop in water level inside the boiler.

Steam gets produced only when there is an effective circulation of water within the boiler. For tank type boilers, circulation is not distinct and the water circulates within the tank of the boiler itself. For water tube boilers, circulation is necessary within each and every tube and headers.

This happens naturally if both the steam and water drums are connected with tubes. But there is some basic design reason which has to be emphasized on.

Natural Circulation within a Water Tube Boiler

The steam drum and water drum may or may not be separated depending upon the boiler design. To understand the boiler water circulation principle, we will assume the following components to be separate. A steam drum at the top is connected to the water drum at the bottom through down comers outside the boiler shell and risers inside the boiler shell.

Cold water is fed to the top drum/steam drum, by water feed pump through a screw down non-return valve and a check valve. As we all know, hot water stays on top and relatively cold water (being denser) travels to the bottom of the drum.

The steam/water drum has down comers connecting to the water ring at the bottom of the boiler. The down comers are located outside the boiler shell and are large in diameter when compared to the water tubes.

As the cold water from the down comers reach the water ring in the bottom, the circulation starts within the tubes and drums. As the water particles enter the water tubes, which are inside the boiler furnace, they start to heat up and become wet steam with some bubbles. As they are less dense, they immediately rise up to the steam drum and thus are continuously being replaced by relatively cold water from down comers. Thus boiler water circulation happens naturally inside a water tube boiler.

Design Aspect

If the circulation has to happen in a natural way, then there are some design considerations to be observed. Ratio between the amount of steam leaving the risers & the amount of water entering the down comers is of the order 4:1.

It is important to have more water than steam on the risers. If the riser at some point becomes completely full of steam, the tube would over heat and “BURN OUT”.

“BURN OUT” is where the tube metal over heats can no longer resist the pressure forces within the tube and thus ruptures.

Reasons for having External Downcomers

It is known that as the pressure and temperature increases, the density of water decreases. Thus the density difference between water and the steam reduces & thus at higher pressures, the natural circulation of water-steam is impaired.

Thus to maintain the natural circulation, external, unheated down comers are fitted. These external down comers are large bore tubes connecting the steam drum with the water drum.

You may also like to read-Boiler Mountings: A Comprehensive List

The Science Behind Marine Boiler Water Circulation on Ships appeared first on Marine Insight - The Maritime Industry Guide