Answer EKG Question 3

Q3. You were asked to join a ship as second engineer. During briefing you were informed about frequent boiler uptake fires happening onboard. prepare a plan for to reduce boiler uptake fires. How will you monitor the progress of your plan and what instructions you will issue to the watch keepers?

Answer: The uptake fire if occurring frequently in an auxiliary boiler, the problem is not so easy to eliminate immediately. The cause of uptake fire which is caused mainly due to accumulation of soot and unburnt carbon particles which are sticking to surfaces in the up take, due to incomplete combustion. In an auxiliary boiler, the flue gases normally pass through economizer or air pre heater or feed water heaters. All these types of heat exchangers are fin types. Hence large amounts of soot deposit on the fins. Along with the flue gases some un burnt carbon particles also get deposited on the fins of heat exchangers.

Normally dry soot deposits have a very high ignition temperature, but when soot gets wet with some hydrocarbon vapours, their ignition temperature may come down to as low as 150 deg cel. This may result in boiler uptake fire, by cleaning and washing the deposited soot may reduce the up take fire temporary but for permanent or long lasting solution other factors for accumulation of soot to be checked and necessary preventive action to be taken, this is little time consuming and tedious job but can reduce the occurrence to a great extent. For long lasting solution a plan to be drawn and implementation must be carefully monitored. As the main cause for soot fire is the unburnt carbon particles which generates due to incomplete or erratic combustion, to eliminate this the following steps to be adopted, (1) Regular inspection of boiler flame to ensure correct air fuel ratio is maintained. This will help proper and efficient combustion. (2) Oil may drip without atomizing due to defective or clogged burner tips and swirl plates, the cleaning and inspection to carry out at regular intervals as per PMS. (3) If the grade of fuel oil is not suitable, difficulties in proper combustion can be faced. To ensure proper grade and treatment is being maintained. (4) The line filters strainers should be clean, fuel oil heater temperature should be maintained not too low or high. (5) Furnace to be kept clean. (6) Regular soot blow (either by steam or air) will drive away the adhered soot components, the soot blowing equipment and line valves should be checked and to be ensure they are in working condition. (7) In spite of regular soot blow operation the heat exchangers inside the uptakes (if fitted) to be water washed periodically at convenient place and time, with proper protection and safety. (8) Prolong low load operation can cause improper combustion leading to formation of soot, such operation if not necessary to be avoided. (9) The boiler should be operated at full load periodically, which will help to drive away the accumulated soot. 10) Periodic use of soot remover chemicals like soot sticks or equivalent during combustion. 11) The up-take and the flame screen on top of the tunnel to be checked and if necessary to be cleaned. Considering all above facts a maintenance plan to make and the engine room watch keepers to be allotted for particular jobs as repair/ cleaning and to be recorded in regular basis. The engine room personnel to be allotted for various work considering their experience and capacity for example in every watch the flame to be checked and if any deviation noticed to be corrected by the senior watch keeper and action for correction to be recorded and signed. The second engineer will personally check and counter signed periodically (weekly) to make sure every thing according to plan is being carried out. Immediate action to reduce the occurrence temporary, to stop the boiler with the permission from office at suitable time, place as convenient en-route for couple of hours, and sweeping out the soot and then wash down the fins of the heat exchangers, in mean time furnace inspection and boiler burner cleaning to be carried out. For prolong solution the routine to follow regularly.

Theory of boiler uptake fire:-

A fire in the exhaust gas boiler on a motor ship may develop in two or three stages. They are;

(i) Ignition of soot:

(ii) Small soot fires;

(iii) High temperature fires.

(i) Ignition of soot:- -Ignition of soot may arise in the presence of sufficient oxygen when the deposits of combustible material have a sufficiently high temperature (higher than the flash point) at which they will liberate sufficient oil vapour, which will be ignited by a spark or a flame. The main constituent of soot deposits is particulates present in the exhaust gases, but in addition some un-burnt residues of fuel and lubricating oil may be deposited in the boiler due to faulty combustion equipment (like leaky fuel valve, improper lubrication etc.) Or especially in connected with starting and low speed running of the engine. The potential ignition temperature of the dry soot is laid in the region of 300 to 400°C, but the presence of un-burnt oil will lower the Ignition temperature to approximately 150°C. This means that ignition may also take place after shut down of the main engine - Even with an ignition temperature of the layer above the boiler tube wall temperature, glowing particles (sparks) in the exhaust gas may start a soot fire.

(ii) Small soot fire -Small soot fires in the exhaust gas boilers are most likely to occur during manoeuvring with the main engine running on low speed operation. During low speed operation the combustion process in the engine cylinder is not efficient causing carryover of un-burnt fuel which gets deposited it its exhaust path like in EGB - Due to the presence of oxygen in the gas the deposited soot on the EGB tubes may attain high temperature and reaching ignition temperature they become glowing particles and leads the generation of a soot fire. Small soot fires do not cause damage to the exhaust gas boiler on the damage is limited, but the Fires should be carefully monitored and appropriate action should be carefully monitored and appropriate action should be taken. -Continued circulation of boiler water, cause the major part of the heat to be conducted away causing the fire to cease. Combustion gases are also responsible to some extent for carrying away the heat -The probability in a small soot fire is very low that the tube wall temperature will rise sufficiently to start an iron. On hydrogen fire, provided water circulation is maintained steam on water leakages are not present (iii) High temperature fires: Under certain conditions a soot fire may develop into high temperature fire. Hydrogen fire - this occurs due to the fact that water dissociates into hydrogen and oxygen, in connection with carbon monoxide and hydrogen may occur certain conditions. Hydrogen fire will start if the temperature is above 1000°C. -Iron fire- an iron fire means that the oxidation of iron of high temperature occurs at a rate sufficiently high to make the amount of heat release from the reaction sustains the process. These reactions may take place at a temperature In excess of 1100 C. In this connection, it is important to realize that, water may also go in chemical reaction with iron i.e. the use of steam based soot blower may also feed the fire. -A small soot fire may develop into a high soot fire involving the following reactions. Hydrogen fire, temperature above 1000°C Dissociation of water into hydrogen and oxygen Iron fire-This may cause burning of tubes

Plan to reduce boiler uptake fires:- For the objective of prevention and reduction of boiler uptake fire we require to follow a proper practice of engine operation and timely maintenance. for which manufacturers recommendations must also be considered. The areas of avoidance to be pointed out and rectified. Following are steps for Prevention of Fire. (a) Check the bunker lab report before it is put into use. The quality must meet the standards required by manufacturers recommendations. (b) Maintain the main engine properly to acheive proper combustion of the fuel. (c) Maintain the boiler burner to achieve the proper combustion of the fuel. (d) regular washing of turbocharger to be carried out. (e) Avoid slow steaming of main engine (f) Ensure good fuel combustion in the main engine (g) Ensure fuel is treated and is of good quality while supplying to the engine. (h) Do regular soot blow of boiler tubes. (i) Do water washing in ports at regular interval. (j) Ensure design of exhaust trunk to be such to provide uniform heat to complete tube stack. (k) Pre-heated circulating water to be supplied to boiler mainly at the time of start-up. (l) Circulating pump should not be turn off at any time while main engine is running. (m) Do not stop circulating pump for at least two hours after the main engine is stopped. (n) Start circulating pump prior to 2 hours before starting the main engine

Monitoring the progress of plan Monitoring of progress of a plan towards a goal is equally important as the implementation of the same. The monitoring of the progress involve the following areas which required to be inspected/checked. (a) check and compare the log book reading and compare the parameters to ensure the implementation of plan is progressive. (b) frequently inspect the uptake for the deposition of the soot. (c) frequently check the exhaust gas color to analyze the combustion quality. (d) check the quality of washed out water from turbocharger and economizers to know the improvement in condition. (e) compare the slow steaming hours and discuss the results with chief engineer and captain. (f) keep record of all the circulation pump stating and stopping times to know that they were in operation for how long after engine stopped.

standing instructions you will issue to the watch keepers Standing Instructions: (a) In case a soot fire develops in the exhaust gas boiler it will be indicated by high uptake temp. (b) Sparks emission from funnel (c) High flue gas temperature alarm (d) Steam pressure increases abnormally and safety valve on the are boiler lifts In such a situation the following actions should be followed depending on the level of fire 1. Raise engineer's alarm 2. Inform Bridge and stop the engine, this will stop the feed of oxygen to the fire 3. Continue operating the boiler water circulating pump keeping an eye on the auxiliary boiler water level gauge to confirm that there is as tube failure 4. Never use soot blowers for lighting the fire as it may involve the risk developing into an iron fire 5. Stop air circulation through the engine by covering the turbocharger fitters and operating the air for closing the exhaust valve 6. Never open any inspection doors of the economizer until the economizer has cooled down sufficiently. 7. Once the economizer is cooled, Inspection door should be opened, and thorough water washing should be carried out, keeping the boiler water circulating pump running. An inspection should also be carried out to check for any damages. In a well-run plant, any fire that starts, will be small, if the above emergency actions are taken immediately, the fire will be damped down quickly, and water circulation will help to cool the tubes and reduce heat damage caused by fire. If the soot fire has not damped out and is increasing followed by a loss of water (like Indicated by too low boiler water level on gauge on excessive feed water consumption) then there is a possibility that the soot fire has turned into an iron fire on hydrogen fire. 1. In such situations the following actions should be taken 2. Stop the main engine, if it has not been stopped already 3. Stop the boiler water circulating pumps immediately 4. Close the valves on the circulating line 5. Do not use soot blowers 6. Drain out the water from the exhaust gas boiler 7. Do not open any inspection door of the EGB 8. Carry out boundary cooling of the EGB 9. If fire fighting gas is available, and is possible to slightly open the Inspection door, then inject the fire fighting gas through the inspection door. 10. Once the fire has reduced, cool down by plenty of splash water on the heart of the fire. Care should be taken when using water, otherwise it may turn into hydrogen fire, and thus a large amount of water should be applied directly on the heart of the fire. 11. Once it is Confirm that the fire has died down, carry out thorough water washing, and then check the Inside of the economizer to assess the extent of damage. If now the engine has to be started (like during maneuvering) and the economizer is damaged then dry operating of the economizer should be carried out as follows. 1. After cleaning and draining of the economizer, open the air vent valve. Do not start the boiler water circulating pump 2. Start the engine, and avoid low speed operation an as much as you can 3. Carry out frequent soot blowing 4. Once the maneuvering is complete, repair the damaged parts as soon as possible.