Steam Blowing Part -/I Abc Of Thermal Power Plant
Steam blowing of MS lines, CRH,HRH,SH,RH,HP & LP bypass pipe lines of turbine is carried out in order to remove welding slag, loose foreign materials, iron pieces, rust etc. from the system, generated during manufacturing, transportation & erection.
EFFECT OF BLOWING DEPENDS ON
1) Thermal shock
2) Removal force of steam
3) Cleaning force of steam
In earlier days steam blowing was done in puffing method . Boiler is being pressurized up to 40 kg/cm2 then blowing valve was opened and blowing starts . It gets completed when pressure drops down to 20 kg /cm2. Target plate was kept after some initial blows. Steam blowing operation starts in early morning to late evening. Night is being kept for cooling. In this operation fire was killed during blowing and lighted up after one cycle of blowing is over. Drum level has to be watched very minutely during blowing.
Around four year back before my retirement we conducted steam blowing on a 660MW boiler I will describe the same. Steam blowing procedure will be more or less same for an utility boiler. Now a days engineering software is available with the consultant to calculate disturbance factor etc of the blowing.
The Steam Generator is a once through supercritical plus Radiant Reheat Boiler. Major auxiliaries of the Boiler are Pulverisers, Feeders, Fans and miscellaneous valves. Boiler Recirculation Pump is provided to ensure proper circulation of water in the furnace wall circuits during initial subcritical mode operation.
The circuits which are subjected to steam blowing are Superheat sections of Boiler, Main steam lines up to HP Turbine inlet, Cold Reheat lines up to Reheater inlet, Reheater sections, Hot Reheat lines upto IP Turbine inlet, HP and LP bypass sections and all auxiliary steam lines.
Line Sizes
1. SH Outlet Pipes : ID 350 x 60
2. MSL : ID 460 x 85
3. CRH : 864 x 29
4. CRH to Reheater inlet : 660 x 23
5. RH to HRH : 711 x 42
6. HRH : 864 x 50
7. HP BP line : 323.9 x 48 / 508 X 27
8. LP BP line : 711 x 42
To remove scales, loose material, iron cuttings etc that might have remained entrapped in Super heaters , Reheater & Steam pipings during manufacture, storage and erection. Failure to remove the debris may result in damage to Turbine blades, valves etc.
Steam blowing shall be done in eight stages viz Stage 1a, 1b, 1c, 2a, 2b, 3a, 3b, 4.
Electrically Operated Temporary Valves (EOTVs) shall be located as shown in the scheme. Loop pipes from ESV and IV (if any) to Turbine shall not be steam blown. Hence proper care shall be taken for cleanliness of these pipes before erection.
All critical pipelines covered in stages 1a, 1b, 1c, 2a, 2b shall be steam blown using EOTVs.
Puffing method shall be adopted for carrying out Steam blowing of stages 1a, 1b, 1c, 2a, 2b in which Boiler Separator pressure shall be raised to 50 Kg/cm2 and released through a quick opening valve and steam blowing done till the Separator pressure drops from 50 Kg/cm2 to 25 Kg/cm2.
Steam blowing for stages 3a, 3b and 4 shall be carried out by continuous blowing method. Steam blowing by continuous method shall be done at 50% of normal operating pressure of the respective system. .Duration of each blow shall be 20 to 30 minutes. The time gap between two blows shall be 1 ½ to 2 hours.
The effects of steam blowing shall be evaluated and steam blowing concluded as per the completion criteria given .
Stage 1a -- Superheaters, Main Steam Lines upto ESVs, temporary lines from ESVs to EOTVs, temporary lines from EOTVs to CRH lines, CRH lines upto Reheater inlet and temporary lines upto exhaust. Tap off lines from CRH for Deaerator, TDBFPs, PRDS, HP Heaters 6A & 6B, Gland sealing etc., shall remain closed / isolated. Blowing of this stage shall be concluded by observing the indents on the target plates.
