Starting & Stopping : ( Boiler -- Water Tube)

This article we will explain starting and stopping boiler during normal and emergency working conditions.

Precautions on Starting Boiler

Before start-up of the boiler plant, following general work and check procedures must be considered.

·         Check that the main steam valve, by-pass valve and circulation valves if provided scum valve, and blow-down valves are closed.

·         Open the feed water valves and the air valve. Fill the boiler with feed water to approximately 50 mm below normal water level. The water level rises due to expansion when the boiler is heated. If the temperature difference between the boiler and feed water exceeds approximately 50ºC, the boiler must be filled very slowly.

·         When filling a pressure less boiler, the shut-off valve after the feed water pump must be throttled. Otherwise the pump motor will be overloaded.

·         Check the water level in the water level gauges. Check frequently during the complete start-up. The water level gauges should be blown down several times to ensure a correct indication.

·         Check that the water level control system is connected and operational.

·         Check the oil system and start the fuel oil supply pump. Pre-heat the fuel oil if the burner should operate on heavy fuel oil.

·         Check the burner and the safety functions according to the manufacturer instruction.

Points to note while starting a boiler from cold condition :( with no super heater)

·         Check that the boiler is properly closed-up (especially after repairs).

·         Check (physically) that all appropriate valves are shut or open for safe starting of the boiler.

·         Boiler water filled to slightly below normal level.

·         Starting treatment chemicals may now be added to the boiler water.

·         Check and clear the furnace of any flammable materials.

·         Ensure that the boiler uptake passage is clear.

·         Pre-purging of furnace for a specified amount of time is necessary to clear the gas-side of flammable gases, to avoid a starting explosion!

·         On a cold boiler, the firing-up must not be speed up too much in order not to over strain the boiler material unnecessarily by quick, uneven temperature raises.

·         Keep the boiler vents open until a heavy steam jet is flowing out (until a boiler pressure of about 1 bar is reached).

·         Before the boiler is put on load, blow-through the gauge glasses, test the safety valves using easing gear and try out the safety cutouts.

Starting Boiler and Pressure Rise

1.      The following work procedures must be followed during start-up of the boiler.

2.      Check that the gauge board valve and pressure gauge valves are opened.

3.      Check that the air valve is open if the boiler pressure is below 1.0 bar.

4.      Check the water level & others parameters are normal.

5.      The forced draft fans should be started to purge the system to remove any trapped exhaust gases or oil vapors

6.      Start the burner on manual control and on low load. Check that the water level does not rise too high during the pressure rising period.

7.      If the air valve was opened close it when only steam blows out. A pressure reading should be indicated on the boiler pressure gauge before the air valve is closed.

8.      Tighten all covers such as manholes, hand holes, inspection doors, etc. during the pressure rising period. If required, check all flange joints on the plant.

9.      Change to automatic control of the burner when the boiler pressure is 0.5 bar lower than the working pressure of the boiler.

10.  Open the by-pass valve slowly to heat-up and pressurize the steam system. If the boiler is not provided with a by-pass valve, the main steam valve should be used to heat-up and pressurize the steam system.

11.  Open the main steam valve and close the by-pass valve.

12.  Open the valves to the steam consumers carefully in order to avoid water chocks.

13.  When the boiler is in normal operation, check that the water level control system and the gauge board functions are fully operational.

Stopping Boiler

Normal boiler shut down

If necessary, the boiler can be shut down at any load without special preparations.

When the boiler is stopped, sudden temperature and pressure drops should be avoided as they might expose mountings, pipe lines, and the boiler plant to inadmissible temperature gradients.

1.      When minimum load is obtained, stop the burner.

2.      Keeps the water level at normal level until the boiler stops producing steam.

3.      Stop the feed water pump and close the feed water valves.

4.      Close the main steam valve.

Emergency shut down

The boiler must be taken out of service immediately if parts of the heating surface have been glowing or the boiler shows recognizable deformations.

The supervising authorities must be informed, and the boiler must not be used until approval from these authorities is available a substantial loss of water is noted the feed water system is unable to provide the necessary amount of feed water, e.g. due to failure of parts the safety valve cannot function sudden cracks or damage are noted in the refractory, and if steam or moisture is coming out of the refractory oil in the feed water is detected too high salinity level is detected.

If an emergency shut down must be carried out, the fuel supply should be stopped. The main steam valve should be closed gradually, and the boiler must be cooled. The safety valves must not be operated. Parallel working boilers should be disconnected at once.

Stop for repair or inspection

The following describes the measures to be taken when the boiler is shut down for repair or inspection.

1.       Clean the boiler from soot with water.

2.       Operate the burner for at least 15 minutes after the soot removal to dry out the remaining water.

3.       Stop the boiler as mentioned previously.

4.       Check the furnace and the pin tubes with regard to cleanliness.

5.       Empty the boiler from water and clean it. Check if lime stone appears.

6.       Check and clean the outer fittings. Change gaskets where required.

7.       Clean the feed water tank and feed water pipes.

8.       Clean and grease the bearings of motor, pump, and fan.

9.       Check and align the burner, if necessary.

10.   If the boiler is shut down for a long period of time, the pin tubes must be thoroughly cleaned.

11.   Check that the necessary spare parts are available. Order complementary parts in time.

It is of extreme importance that the boiler is NOT operated without water when the oil burner is in operation, e.g. due to disconnection of the water level safety devices. This will immediately cause complete breakdown of the boiler.

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 Reference:

1. brighthubengineering.com

2. marineengineeringonline.com

3. Manual (AALBORG INDUSTRIES)

4.  Marine Engineers' World (Facebook)

5. Bangladesh Marine Academy