steam blowing

Presented by Siddhartha Sankar Bharali Assistant Engineer Emp Code : M6B194

1Siddhartha Sankar Bharali, M6B194

REQUIREMENT OF STEAM BLOWING• For the new installed boiler, there will be sand, dirty, rusty plates, welding

slag and so on impurities left inside the pipes during the transportation, storage and erection process. If these impurities not be cleaned especially in the main steam and reheat steam systems, they would enter the high speed turbine blades, which would cause spots on the blades and affect the unit efficient, or even worse, they would cause the blade break and galloping and so on serious accident.


BOILER PARAMETERS Superheated steam flow (t/h) : 440 Superheated steam outlet Pressure (Mpa) :14.29 Superheated steam outlet Temperature ( ) : 540℃ Reheat steam flow (t/h) : 355.6 Reheat steam inlet Pressure (MPa) : 2.604 Reheat steam inlet Temperature ( ) :318 ℃ Reheat steam outlet Pressure (MPa) :2.407 Reheat steam outlet Temperature ( ) : 540℃ Feed water Temperature ( ) : 247℃


CIRCUIT OF STEAM BLOWING

Super heater Circuit. Main Steam pipes up to CRH NRV’s. CRH line to RH inlet with temporary

exhaust pipes (with provision of target plate at the boiler end).

Stage I + CRH inlet header to boiler. Reheater , its outlet header, HRH lines. HRH steam valves with temporary

blowing device & piping to atmosphere (with provision of target plate.)

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STAGE I STAGE II

Superheater system :•Divisional SH•LTSH•Platen SH•SH Finish

Reheater System:•RH inlet & outlet header•Platen RH•RH Finish

Siddhartha Sankar Bharali, M6B194

Contd.

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Main Steam, RH and HP bypass system of 9X135MW CPP, Jharsuguda


PREPARATORY WORK REQUIRED FOR STEAM BLOWING

The erection and insulation work of the boiler proper and its auxiliary equipmentsErection of supporting frames and gauges are completed. Equipments and valves

have been numbered and named. Boiler hydro test and chemical cleaning should be completed successfully.System check or system trial-run of each equipment is done.The steam lines should be completely insulated prior to steam blowing. Pressure gauges and temperature indicators should be calibrated and functional.Drum water level gauge is complete and clear with adequate illumination. The drum, heating surface, flue gas duct and furnace should be clean with no

impurities, no temporary supporting or temporary welding parts.

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Following activities should be completed prior to the commencement of Steam Blowing


Contd.Fire-fighting system . Turbine ,condenser system, feed water, deareator systems. All the local meters and gauges, control panels, panel gauges and

operation devices have been calibrated and are ready for operation. The oil guns and ignition gun of burner are in correct position with flexible

motions. Ignition device has been commissioned; the program control test and ignition test of the oil guns are successful.

All the valves, wind baffles have been commissioned.

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Trial run of the following equipments should be done : Induced draft fan, forced draft fan, primary air fan. Fuel oil feed equipments Electric feed pump, condensate pump, demineralized water pumpInstrument air compressor.


INSTALLATION OF TEMPORARY PIPING

Temporary piping should be fabricated with flanged joints so that installation time could be minimized.

HP bypass governor valve do not participate in the purging, It should be replace with short pipe. LP bypass valve and pipes are not for purging, which should be cleaned after the erection. Install temporary baffle at the pipe opening to the LP bypass.

To avoid being damaged during the purging, the desuperheating water system and main steam pipes flow rate measuring devices should not be erected in advance.

Temporary control gate is installed at the turbine side.

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Referring to the diagram

The main system uses two temporary purging control gates, with 350mm nominal diameter and pressure be 10MPa, temperature 450 , full open ℃and full close time≤60s.


STEAM BLOWING PROCEDURE

Preparation before Ignition: Operation, erection and commissioning personnel should check the boiler proper,

auxiliary systems, turbine systems, and make sure all the equipments and systems meet the demand of the ignition.

Testing of all the steam water valves are done. Calibration of gauges are checked. Fuel oil system and the oil circulation is checked. Each blow down and drainage system is checked.

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Boiler Light Up


Induced draft fan and forced draft fan is started and the flow rate is controlled keeping the furnace negative pressure to -50~100 Pa. (purging is continued 5 minutes).

After the ignition conditions are ready, first opposite 2 oil guns at AA level are put into operation. Ignition is observed.

For the boiler first ignition, saturated temperature rising rate should not be more than 50 /hr. ℃

For boiler first ignition, the leakage and expansion of the system is checked regularly. Boosting is stopped if any abnormity is found. Recover the boosting after the causes be found out and eliminated.

When the pressure reached to 0.2MPa,air valves are closed and purge the water level gauge.

Furnace outlet gas temperature is controlled below 540 .℃ When the drum pressure reached 0.8-1.0MPa,continuous blow down is put in to

operation.

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Start Up of Boiler


When the drum pressure reached 1.5MPa,bypass valve of the temporary control gate is opened to warm the pipes. During the pipe warming,the pipe expansion is observed .

Relevant drain valves should be opened to avoid inside water hammer.


KEY OPERATION DURING PURGING

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Operations


PURGING METHODEvery step down purging would last about 3minuts. The step down value

should be able to keep the drum saturated temperature decrease not over 42 . Every one hour, purging is done for 2 or 3 times. ℃

Boiler purging has two steps: The first step, purging is done for 20 times, then it is stopped and the boiler

is cooled down for 12 hours and clean the grain collector. Then the second step purging is continued. HP bypass part and main system is purged in alternation. Purge for 4 or 5

times and each time lasts for 4-5minutes. Purge the desuperheating water system before the pipe purging.


*Datas are referring to 9x135 MW CPP , Vedanta , Jharsuguda

SOME STATISTICSFirst stage:

opened at:

Pressure 5.5-6.0MPa closed at: 3.5-4.0Mpa

Main steam T 380 ～ 420℃ Makeup water volume: 300-400T/H

Second stage:

open at: 5.5-6.0MPa close at: 3.5-4.0Mpa

Main steam T 380 ～ 420℃ Reheat steam T 500℃ Makeup water volume: 300-400T/H

HP bypass: Open at 5.0MPa close at: 3.5MPa

Siddhartha Sankar Bharali, M6B194 14


Valves are opened from lower pressure to high pressure at first few purging, to check the fastness of the temporary pipes and the makeup method.

First: open at 3.5MPa close at 2.5MPa

Second: open at 4.5MPa close at 3.0MPa.

TARGET ACCEPTANCE CRITERIA The target to be exposed should be made from aluminium polished on its exposed

surface to a blemish free # 8 finish with a 1 inch by 9.875 inch exposed surface area.

The target should be exposed to twenty (20) minutes of a steady flow of steam at the rate, temperature and pressures as per agreed procedure. Steam blow sequence and acceptance at conditions should be such that the cleaning force ratio (CFR) is greater than 1 throughout the system being cleaned.

The top and bottom ½ inch of the target surface should be disregarded due to the effects of its attachment on the target inserter ram.

No impacts larger than 0.4 mm diameter and fewer than 3 impacts with an area of 1 Sq. inch on the central zone of the target plates and there shall not be any deformation of edges.


steam blowing

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