HOW TO DO BOILER ALKALI BOIL OUT DURING BOILER COMMISSIONING
Today we introduced about a very important topic all of you regarding power plant commissioning activity that’s is ALKALI BOILOUT.Alkali boil out process is carried out of the boiler as apart of pre-commissioning operations in order to remove oil, grease and other impurities adhering to the interior pressure parts of the boiler.This cleaning is carried out after the total completion of the boiler erection.
2. SCOPE :
Generating surfaces, drum and economizer are covered under the chemical cleaning scope.
3. TECHNIQUE :
For starting the process of alkali BOILOUT we are taking 1000 ppm of Trisodium Phosphate and 500 ppm of Disodium Phosphate are used as chemical agents.Alkali boil out is carried out at drum pressure of 40 Kg/cm2.
Ensure the following :-
-Boiler erection to be completed in all respects with required control and instrumentation.
-Ensure boiler auxiliaries such as fans,feed pumps , stoker with it s associated systems and other connected machineries are trial run and their operation fully proved in all respects.
-Dearator and the feed tank are ready in all respects.
-Boiler instrumentation control panel made ready for regular operation.
-Ensure refractory and insulation work of the boiler is completed. All scaffolding, temporary supports and any supports preventing boiler expansion is removed.
-Arrangements are made for permanent lighting facilities at all operating floor levels.
-Trained operating personnel for taking care of boiler operation.
-Ensure fire fighting equipments provided at all vantage points in the boiler house and persons working in the unit be conversant with the usage of the fire fighting equipments.
-Drum internals remain in position during boil out.
-Chemical quantities required for the boil out to be ensured.
-Before starting the alkali boil out ensure hydraulic test of the boiler is completed to the required parameter before the commencement of alkali boil out.
-Pre –boiler system should be flushed with alkali solution
-HP/LP dozing system should be made ready for dozing of chemicals during boil out activity.
-Chemical lab facilities for testing of samples.
-First aid box and safety appliances should be made available.
5. PROCESS :-
-Boiler is filled with D M water & drained as fast as possible to remove suspended matter to the extent possible .This operation is repeated one or two times till the draining water appears clear.
-Once the above operation is completed, fill up the boiler with DM water until the water is seen little above the bottom of the steam drum. Keep the manhole cover open.
-Prepare a solution of tri-sodium phosphate and di-sodium phosphate as per dosage mentioned in DM water and charge the chemicals in to the boiler drum through the manhole by several increments. The entire quantity of the chemicals is dosed in to the boiler.
-Close the manhole cover and light up the boiler as per O&M instructions. Raise the steam pressure slowly to 40 kg/cm2 . Boiler expansion readings should be recorded at 10, 20, 30 and 40 kg/cm2 & uniformity must be ensured. Maintain the pressure for 12 hrs.
-Maintain the boiler pressure at 35 to 40 kg/cm2. Give blow down through the bottom header drain valves in order to ensure removal of muck and other impurities collected at the bottom.The opening and closing of the drain valves should be done very quickly and not exceeding one minute operation per valve. It is equally important, during the entire operation to maintain the drum level.
-The low point blow downs are to be operated once in two hours and six such blow downs are given during the 12 hours operatio0n of boil out.
-Boiler water sample is collected after every blow down and analyzed for pH and alkalinity.
-After the completion of 12 hours of boil out operation, the boiler is boxed up and allowed to cool naturally, so that the pressure is dropped to 1 kg/cm2. At 1 kg/cm2 . pressure, the boiler is drained through low point drains.The super heaters are back flushed thoroughly. The boiler is filled and drained 2 or 3 times using DM water till the pH of the flushing water approaches to that of DM water according to above give process.The drums are inspected and any debris collected at the bottom drum removed manually.
During alkali boil out operation ,important parameters like pressure, feeding rate ,temperature and water analysis etc. are systematically logged. The boiler is then prepared for steam blowing operations.
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