COMMISSIONING BOILER ALKALI BOIL OUT ,ACID CLEANING PART -III-ABC OF THERMAL POWER PLANT

During the acid cleaning process, all the permanent boiler instruments are isolated except

providing a temporary pressure gauge of        0 to 5 kg/ cm2 in the drum for monitoring

nitrogen pressure in the drum during nitrogen capping. 

For alkali boil out, neutralizing and passivation processes, essential control and instruments

viz. Protections, interlock, alarms, measurement, annunciation etc. required for  light up

of boiler are made available.  

Boiler is flushed thoroughly including the temporary pipe lines and system. Pre boiler

flushing to be completed for the availability of Boiler Feed Pump ( same will be discussed

during turbine commissioning). 

For chemical cleaning process, the internals of the non-return valve provided in the

economiser recirculation line is removed in order to facilitate fast filling and draining of the

boiler. 

All the boiler auxiliaries are made ready and available for boiler light up. This includes

Auxiliary steam, chemical dozing pumps, tanks, boiler circulating pumps, fans, oil pumps

etc. 

Drum vent lines, Nitrogen capping lines are properly tagged and taken to suitable location

for easy operation. 

Drum internals including primary and secondary separators, orifices at the bottom drum are

to be installed after the chemical cleaning process. The baffle plates inside the bottom

drums are to be installed before the alkali boil out. 

In addition to drum metal temperature 04 number metal temperature to be provided at

the corners of ring header and wired up to control room.  

Instruments are installed as per schemes. 

Various drains from the system at different operations during the process are to

be connected to a common drain leading to neutralizing pit. 

Boiler tube coupons placed at two ends inside the drum and bottom ring header to see the

effectiveness of the cleaning. 

Proper neutralising arrangement is available at site to neutralize and dispose off the effluent

in line with statutory authority of the state.

Chemical dosing system is ready in all respect.

 

MD-BFP is available for regular operation.

ALKALI BOIL OUT

The boiler (steam generating surfaces and economiser) is filled with an alkaline solution

containing 500 ppm of disodium phosphate  and 1000 ppm of Tri sodium phosphate  then

fired to raise the pressure to 40 kg/ cm2, following the specified operational procedures.

During the process, rotation of boiler circulating water pumps should be done as per

operating instructions. 

Procedure

Prepare the boil out chemical solution in hot demineralised water in the chemical mixing

tank. The solution is formulated by dissolving the following proportionate quantities of

chemicals, depending on the volume of the system to be cleaned. 

1.       0.05% Na2  HPO4       12 H2O

2.       0.1  % Na3 PO4         12 H2O 

Hold the solution prepared as above in the tank and homogenise the same by recirculating

the solution by operating chemical injecting pumps. 

Start filling the boiler with demineralised water, with simultaneous blend filling of already

prepared boil out chemical solution. 

Light up the boiler as per O & M instructions and gradually raise the pressure to 40 kg/

cm2 .  Hold the pressure for four hours. Obtain boiler water sample from CBD sampling point

and analyse for alkalinity, phosphate content, dissolved silica and oil content. Prescribe

blow down every 2 Hrs. once, after killing the fire; Duration the blow down shall be for one

minute  Ensure that the drum level does not go out of gauge glass vision. Repeat the

operation of raising the pressure to 40 kg/ cm2

 .

The boil out is declared completed when the oil value is no longer detected or minimum

eight blow downs are completed whichever is later.

Drain the boiler, when it is cooled, as per O & M instructions. Once the draining is

completed, fill the boiler with demineralised water, heated to 80 deg C, through boiler fill

pump. Back flush the super heaters with DM water containing 200 ppm hydrazine and pH

10.0 with NH3  till it overflows into the drum. Drain the boiler to the waste disposal system.

Inspect the lower and upper drum. Manually clean them.

Usual procedure of light up and shut down as described in O&M manual should be followed.

Temporary Piping arrangements and other arrangements at the boiler.

Continued to Part-IV for acid cleaning /edta cleaning procedure.

 P.S If  you are looking to earn few legitimate extra money from the comfort of your home then please click on the link given below

LINK 1 - PLEASE CLICK HERE 

LINK 2 - PLEASE CLICK HERE