Hydrogen Purging/ CO2 Purging

PROCEDURE FOR PURGINGOUT GEN CASING H2 WITH CO2 :

Preconditions:

• Turbine generator should preferably be on barring gear. Incase if the machine is not on the barring gear then consumption of CO2 will be more.
• Seal oil system is in service, with one AC Seal Oil pump running, if stand by seal oil p/p takes start, and then there will be chance of seal oil ingression into LLDs. Stop second seal oil pump by taking FG SEAL OIL in MANUAL mode. However DC SOP will take start on protection, in case the running seal oil pump trips, thereby preventing any breaking of seal till hydrogen is completely purged out of generator casing.
• Keep H2 circulating fan in service, so long as H2 is there inside generator.
• Check that the CO2 Expansion tank is filled with the heat transfer fluid. Switch on CO2 Expansion tank heater & oil circulating pump power supply. Check for operation of its
• thermostat for maintaining set temperature. The evaporator should maintain oil temperature in a range of 120-1500C.
• For normal purging, take clearance from EMD, TMD and C&I before starting of purging operation.
• At least 60 CO2 filled & tested cylinders should be available in the Unit where purging is to be done. Resp: Sr Mgr(EMD),Generator Group
• Arrangement for pouring hot water on CO2 cylinder / lines (to avoid freezing/ice formation) must be ready. Tools for opening and connecting CO2 cylinders (28 mm size non-sparking spanners) should be available.
• Inform C&I maintenance to set range selector switch in CO2 / H2 purity transmitter to measure 0 to100 % CO2 in H2. Resp.: Sr Mgr ( C&I)
• Remove all the Hydrogen cylinders from H2 / CO2 gas room. Resp:SCE/Sr Mgr(Recommng).
• EMD to shift the cylinders to H2 plant. Resp:Sr Mgr (EMD-Gen group)
• EMD to deploy their maintenance group for attending leakage from any valve/line immediately. Resp: Sr Mgr(EMD)Gen Group

Activities:

• Close all the valves in the supply side of H2 from H2 rack & near valve station.
• Open the vent valve MKG 80 AA 001 and MKG44AA001 so that the H2 pr. in gen. casing will be dropped to 0.3 - 0.5 ksc. The pr. can be decreased at any rate, for this no limitation
• Now the scavenging of H2 is to be carried out with CO2 as per the following procedure.
• First check the line up of the system for CO2 filling at bottom of the gen. casing & (H2 + CO2) mixture displacing (venting) from top of the gen. casing.
• Check the following valve position in the gas rack.

1. Final isolating valve for CO2 connected to the pipe line at bottom of gen-Open
2. Isolating valve in the bottom of the   Generator casing-Close
3. Isolating valve in the top line- Open
4. Vent valve to vent line- Close
5. Control valve for removal of mist at the beginning-Close 
6. CO2 regulating valve before Expansion device- Close

• Start the CO2 expansion device oil circulating pump from control panel.
• Start the heater from control panel 5 minutes prior to the starting of CO2 purging.
• Observe the temp. of oil through indicator
• Then charge the CO2 bottle supply. Keep open the mist control valve MKG 61 AA 251 till all mists are removed.
• Then slowly open the CO2 flow control valve MKG 61 AA 001 & monitor the flow through flow indicator MKG 63 CF 001(100 M3/Hr). Also the pressure of filling through pressure indicator MKG 63 CP 001 , slowly raise the casing pr. To 1 KSC.
• As CO2 in cylinder expands, there will be ice formation in the cylinder and in the line which may cause choking of flow, For this, hot water should be continually poured over the cylinder and CO2 Line to keep them warm.
• Then slowly open the vent valve MKG 80 AA 001 & vent the casing to release the H2 which is occupied at top due to less density as compared to CO2. Once the pr. is dropped to 0.5 KSC again start filling.
• The CO2 gas purity in gen. casing can be monitored through purity indicator. For this the purity meter is to be properly line up. (Open valve on casing side & on vent line).
• This pressurisation & venting procedure will be carried out till the CO2 inside gen. casing attains 98 % purity.
• Continue the process until at least 2 consecutive samples of generator gas, have purity of 98 % (CO2 in H2) or more as per Orsat Analysis by chemist. Compare and ensure that the purity values checked by chemist match with the purity value shown by the Online Gas Analyzer.
• The CO2 / H2 purity system measures the purity of the vent gas.
• After attaining the purity , Generator casing pressure maintain at 0.5Ksc, close the Co2 isolating valve to Generator casing  Resp:SCE/ Sr Mgr(Recommng)/Sr Mgr(Chem).

Purging the drier # 1 with CO2

• Open the inlet valves to gas drier # 1 & common inlet valve from CO2 side.
• Open the vent valve to the atmosphere.
• Purge the gas drier # 1 for five (5) minutes
• Close the inlet valves to gas drier # 1& common inlet valve from CO2 side & control the pressure in between 0.4 - 0.5 bar by Observing pressure gauge.
• Open the valves & and control the pressure to 0.4 -0.5 bar by observing pressure gauge .
• Purge for 5 min. & then close the valves  &
• Open the valve  & 
• Purge for 5 min & then close 
• Close the valve to the exhaust pipe Resp:SCE/ Sr Mgr(Recommng)

PROCEDURE FOR CO2 PURGING WITH INSTRUMENT AIR :

• Prior to commencing air filling in generator casing, the instrument air connection provided for this purpose is to be kept open for about half hour to drain off any moisture or oil in the line. Chemist should check, ensure that the air is sufficiently free of moisture before giving clearance for air filling.
• CO2 is displaced from gen. casing by using compressed air passing through a filter.
• For this please check the following valve positions

1. Main valve connected to the top of  the casing -Close
2. Valve in H2 line used for expelling CO2 -Open
3. Main valve in the bottom to casing -Open
4. Valve in CO2 line connected to main bottom line -Close
5. Vent valve to atmosphere Open
6. Valve before the air line is connected in H2 line  Close
7. Main isolation valve in air line Open

• Slowly air starts filling in the gen. casing. Open the vent line. So that CO2 from the bottom of gen. casing gets vented out maintain gen. pr. at 0.5 ksc.
• Continue this process till the CO2 residue in air has come down to 0.1 % Resp : DGM (Chem.)
• Purging of Drier # 1 & 2, generator Core Monitor, H2 Circulation Fan ,Generator leakage pipes & purity measuring device with Air

1. Follow the same procedure as explained for purging H2 with CO2
2. Open the valve to balance the top & bottom to atmospheric pressure.

• Values of purity of % Co2 in air is to be recorded in the prescribed format Resp:SCE/ Sr Mgr(Recommng)

PROCEDURE FOR CO2 FILLING( PURGING AIR WITH CO2):

Responsibility:

• If the CO2 / H2 filling is being carried out after Unit Overhaul, the overall responsibility of the activity is with the Recommissioning team leader.
• If the H2 has been purged out during any Unit Emergency or for some maintenance work, other than Unit Overhaul, then the overall responsibility of the activity will be with Shift Charge Engineer.

Preconditions:

• If the filling is being done after overhauling, then generator air leak test has been completed and air loss observed is within limit. In other cases filling is to be done after getting clearance from EMD.
• Generator is filled with air at a pressure of 4.0 ksc, after checking air leakage.
• Clearance obtained from EMD, TMD, C&I for filling of CO2 and subsequent filling of H2 in generator casing. All hot work should have been completed in the vicinity of generator, associated piping connections, filling area etc.
• Hose for filling compressed air, has been disconnected and removed.
• Seal oil system is in service, with one AC seal oil pump, one seal oil vac pump and VEFis running.
• At least 60 CO2 cylinders (tested) and 160 H2 cylinders (filled and tested) should be available, near the Unit where filling is to be done. Resp:Sr Mgr(EMD)Gen Group / Sr Mgr(Recommg) / SCE.
• Spanners for CO2 cylinder connection (28mm size), H2 cylinder connection (28mm size), cylinder key for opening H2 cylinder etc. are available. Only Non sparking tools are to be used.
• Arrangement for bringing and using hot water to keep the CO2 cylinder and filling lines warm should be ready.
• Check that CO2 flash evaporator is filled with heat transfer liquid. Switch on the supply of CO2 flash evaporator. The evaporator should maintain oil temperature in a range of 120-150 Deg C.

Procedure:

• First check the line up of the system for CO2  filling at bottom of the gen. casing & (air + CO2) mixture displacing (venting) from top of the gen. casing.
• Check the following valve position in the gas rack.
• Final isolating valve for CO2 connected  to the pipe line at bottom of gen.Open
• Isolating valve connected to the bottom of  Gnerator casing Close
• Isolating valve in the top line Open
• Vent valve to vent line Close
• Control valve for removal of mist at the beginning.Close
• regulating valve bef. Expansion device.Close
• Start the CO2 expansion device oil circulating pump from local control panel.
• Start the heater from local control panel five(5) min before the starting of CO2 purging.
• Observe the temp. of oil through temp indicator MKG 62 CT 001.
• Then charge the CO2 bottle supply. Keep open the mist control valve MKG 61 AA 251 till all mists are removed.
• Then slowly open the CO2 flow control valve MKG 61 AA 001 & monitor the flow through flow indicator MKG 63 CF 001 (around 100 M3/Hr.). Also the pressure of filling through pressure indicator MKG 63 CP 001.
• Since the casing vent valve is in closed position at 1 ksc pressure stop filling of CO2.
• Then slowly open the vent valve MKG 80 AA 001 & vent the casing to release the air which is occupied at top due to less density as compared to CO2. Once the pr. is dropped to 0.5 KSC again start filling.
• The CO2 gas purity in generator casing can be monitored through purity indicator.For this the purity meter is to be properly lined up. (Open valve on casing side & on vent line).
• This pressurisation & venting procedure will be carried out till the CO2 inside gen.casing attains 98 % 
• Ask the chemist to collect one sample & test through Orsat apparatus. If it is more or equal to 98%, the venting can be stopped.Resp:Sr Mgr(Recommg) / SCE / SrMgr(Chem)
• Purging the drier # 1, drier # 2 , Core monitor with CO2, H2 Circulating Fan , Generator leakage pipes and purity measuring device with CO2 Resp:Sr Mgr(Recommg) / SCE

Caution

• After CO2 percentage is more than 98%, preparation should start for filling the system with H2 gas without delay. (Gen. casing should not be kept filled with CO2) Resp:Sr Mgr(Recommg) / SCE
• Now isolate the CO2 filling system by closing all the valves in the system.
• Isolate the CO2 bottle rack.
• Switch off the heater & stop the circulating oil pump from Gen. Auxillary panel
• Values of purity of CO2 measured by Orsat Analysis and Online Gas Purity Analyser are tobe recorded in the format. Resp:SCE/ Sr Mgr(Recommng)

PROCEDURE FOR CO2 PURGING WITH H2 PRESSURISATION :

Now for filling H2 the system to be lined up. Check the position of the following

valves.

1. H2 supply valve Open
2. H2 supply line valve near the top line Open
3. Air supply line isolating valve Close
4. H2 supply during operation Close
5. H2 supply during operation Close
6. H2 for purging of H2 driers Close
7. Isolating valve on the top line Close
8.  Isolating valve on the bottom line Open
9. CO2 filling isolation valve Close
10. H2 vent valve Close

• Now start gas filling to the system by opening H2 bottles at H2 rack. The flow can be monitored through flow indicator MKG 41 CF 001.
• Since the vent valve is closed the casing pressure will be increasing. At 1ksc pr. stop filling & start venting slowly through the vent valve MKG 80 AA 001 until at 0.5ksc
• Continue this operation filling & venting till the purity indicator indicates 98 % H2 in gen casing.
• Now the chemist can be asked to check one sample for gen casing H2 in CO2 .
• If it exceeds 98 % then stop venting & close the vent valve properly.

Purging of Drier # 1 & 2, generator Core Monitor, H2 Circulation Fan,Generator leakage pipes & purity measuring device with H2

• Follow the same procedure as explained above for purging CO2 with H2 . (In stead of valve , open valve ).
• Now the gen casing is to be pressurised to the rated pr. of 4.0 ksc.
• Number of H2 cylinders to be consumed for attaining 98 % purity will be 90 & for pressurisation to 4.0 ksc will be 60 nos.
• After pressurisation completely isolate the H2 system.
• Isolate gas purity meter MKG 90 CQ 003 & line up MKG 90 CQ 1/2 for gen. operation.
• For normal gas filling during gen. in operation  are to be kept open – Presently this system not inservice, to be kept closed always.

Points of concern :

• Do not pressurise above 0.5 ksc, otherwise it will consume more cylinders.
• Maintain proper flow in CO2 system (100M^3/hr) while filling otherwise ice formation may take place.

Purity Measurement during Purging CO2 with H2

• Open the valve before purity measuring device 
• Adjust pressure to 0.3 bar approx. 
• Adjust flow rate to 100 ml/min.
• If the H2 gas purity is > 98% purging of H2 dryers should be done. Resp:SrMgr(Recommg)/SCE/Sr Mgr(Chem).
• Values of purity of H2 measured by Orsat Analysis and Online Analyser are to be recorded in the format Resp:SCE/ Sr Mgr(Recommng)
• H2 purity must be monitored and maintained above 98.4% by purging with additional cylinders, if required during rolling & after synchronisation. Resp:Sr Mgr(Recommg) / SCE
• Ensure that sufficient Nos of filled CO2 cylinders( i.e. 45 Nos) are available near Gas Filling Room of the Unit for next complete purge out of the Generator                      Resp:Sr Mgr(Recommg)/SCE/Sr mgr (EMD)

ACTION TO BE TAKEN IN CASE OF TOTAL SEAL OIL SYSTEM FAILURE( In any Unit of Stage-I):

• In case of total Seal Oil System failure in any UNIT of Stage-I due to any reason resulting in non-availability of all Seal Oil Pumps including DC SOP of the UNIT, following actions are to be taken:

1. Turbo Generator will trip on protection (Seal oil DP H2 LOW-LOW), otherwise Unload& shutdown the Unit.
2. Open the vent valve in the H2/CO2 valve rack ( ‘0’ mt) to vent out hydrogen from Generator casing .Immediately, start purging H2 gas with CO2 as per procedure detailed above..
3. Restore Generator Seal Oil System at the earliest. Barring operation without Seal Oil System in service may cause damage to generator seal rings.Resp: UCE / SCE /AGM(O)

ACTION TO BE TAKEN IN CASE OF CONTINUOUS, ABNORMAL /UNCONTROLLABLE DROP IN GENERATOR CASING H2 PRESSURE WITH SEAL OIL SYSTEM IN SERVICE ( In any Unit of Stage-I):

• In case of continuous, abnormal / uncontrollable drop in generator casing H2 pressure with Seal Oil System in service ( which may be due to leakage in generator, H2 gas system piping/ valves, Gas Drier or failure of DP Controller etc.) following actions are to be taken:

1. Reduce Unit load when generator casing pressure drops uncontrolled. Unload & shutdown generator if casing pressure continues to drop.
2. Open the vent valve in the H2/CO2 valve rack ( ‘0’ mt) to vent out hydrogen from Generator casing. Immediately, start purging H2 gas with CO2 as per proceduredetailed above. Resp:UCE / SCE