1 ALL PTWS Cancelled & Normalised Cancelled
2 IOM sent to CISF(Deployment of CISF person(IOM & information to CISF)(one person for Blr & Tur. Each)) Sent
3 Written Clearnce from Maintenance for BLU Done
4 Instrument Air & Service air Normalised Done
Following Manual valves to be opened:
5 CBD Manual valves Open
6 MS, FW, Drum , SS Sample Line Manual Opened Open
**Detecting Boiler Tube Leakage in a 210 MW BHEL Boiler at NTPC Dadri**
Boiler tube leakage is a critical issue in power plants like NTPC Dadri’s 210 MW units, which use subcritical BHEL-designed boilers (Combustion Engineering type, commissioned 1991-1994). Early detection minimizes downtime, prevents secondary damage (e.g., to turbine or other tubes), and maintains efficiency. Dadri has a strong record for minimizing tube failures, ranking among NTPC’s top plants, but leaks can still occur due to aging (30+ years), erosion, corrosion, or thermal stresses in high-pressure zones (drum pressure ~155 bar, superheater ~535°C). Below is a detailed guide to detecting boiler tube leaks, tailored to Dadri’s 210 MW BHEL boilers, combining practical methods, NTPC practices, and industry standards.
**Safety Valve Float Test in a Boiler (Specific to Power Plant Context like NTPC Dadri 210 MW Boiler)**
The safety valve float test, also known as the "popping test," is a critical procedure in a power plant boiler to verify that safety valves open at their designated set pressure to prevent overpressure conditions, ensuring boiler safety and compliance with regulations like the Indian Boiler Regulations (IBR) 1950. For a 210 MW boiler at NTPC Dadri, this involves testing drum and superheater safety valves (typically set at 155-160 bar for drum and 135-140 bar for superheater). Below is a concise, step-by-step guide to performing the safety valve float test, tailored to subcritical boilers like those at NTPC Dadri, with practical insights from thermal power plant operations.
### Understanding Heat Rate in a 210 MW Boiler at NTPC Dadri
The heat rate of a thermal power plant, including the 210 MW coal-fired units at NTPC Dadri (commissioned between 1991-1994), measures the amount of heat energy (in kcal/kWh) required to generate one kilowatt-hour of electricity. It is inversely proportional to the plant's thermal efficiency: a lower heat rate indicates higher efficiency, reduced fuel consumption (coal), lower emissions, and cost savings. For subcritical 210 MW units like those at Dadri, typical operating heat rates range from 2,300-2,500 kcal/kWh, with opportunities for optimization to below 2,300 kcal/kWh through targeted improvements.
### SOFA in Power Plants
In the context of power plants—particularly coal-fired thermal power plants—**SOFA** stands for **Separated Overfire Air** (also sometimes written as Separated Over Fire Air). This is a combustion technology used in boiler systems to reduce nitrogen oxide (NOx) emissions, which are harmful pollutants formed during high-temperature fuel combustion.
### Understanding Boiler Efficiency in 210 MW BHEL Units
A 210 MW BHEL boiler is typically a coal-fired, subcritical unit common in thermal power stations, where efficiency (often around 80-85% on a higher heating value basis) is influenced by combustion, heat transfer, and auxiliary losses. Improving it can reduce fuel consumption, emissions, and operational costs. Based on thermal audits and BHEL-specific practices, here are proven methods, categorized for clarity. These draw from operational optimizations, retrofits, and maintenance strategies.
CHECK LIST-VACUUM PULLING UNIT: DATE: SL NO ITEM DESCRIPTION STATUS
1. Fill Hot well up to normal level.
2. Vacuum pumps are ready for operation.
3. Turbine gland area is clean and loose debrises are removed.
4. One gland seal steam exhauster is kept in service.
5. One CEP is kept in service and condensate flow is established through GSC minimum recirculation.
6. Gland steam pressure control valve and Leak off control valves operation checking is complete. Oil level is OK in hydraulic actuators.
7. Charging of cooling water to condenser water boxes.
8. Control oil is charged.
ST-1 SHUTDOWN PROCEDURE
(Note-Tie CB means CB for tie between station buses as applicable)
1. Switch OFF SD bus I/C DC supply .
2. Ensure SB/SD/UB-3B tie already closed at SB end.
3. Tie CB to SB/UB-3B CB at SD end, take its selection in manual in CR-1 to check healthiness of “CB in manual “contact by EMD.
4. Remove tripping of SB end tie CB with help of EMD (otherwise on closing SD end breaker, SB end tie CB will open & fault appear in it in CR-1 . To avoid it, EMD will remove this tripping of SB end tie CB) 5. Close tie CB at SD end . Ensure SB end tie CB will not trip.
6. Open SB bus I/C from ST-1 .
Guidelines RELATED TO GENERATOR AIR TIGHTNESS TEST
CRITERIA FOR THE ACCEPTANCE OF TEST:
·
The test pressure drop in the system should be monitored
for a period of 24 hours. No break is allowed.
·
The gas system can be considered sufficiently tight when
the pressure drop during a 24 hours test with compressed air does not exceed
0.15 bar or the loss of air is below 1.5m³/24 hrs (s.t.p).
·
If air loss is higher than 0.15 bar / 24 hrs, a search
for leakages must be made.
· The test pressure should correspond to the rated gas pressure of the generator (i.e. 3.5 bar) in normal cases, otherwise 4.0 Ksc if rotor is threaded out.
1)
Mill Operating Parameters and
Operation procedure: -
Ø
Maintain
Mill outlet temperature-> 55C
Ø
Mill
inlet temperature -> not more than 180 C
Ø
Observe
all 4 coal pipe temperature of Mills with biomass regularly. In case of any
deviation from rest of the pipes(any abrupt rise or fall), stop the mill and
give PTW for inspection.
Ø
Pre
start and post shutdown purging of mill is mandatory.
Ø Continuous monitoring of mill parameters most importantly mills inlet air temperature, mill outlet temperature, mill current and mill DP.
In stage 1 we have two station transformers
(ST1 and ST2). In case of planned outage or emergency tripping of one station
transformer the station bus of that station transformers can be charged via
available station transformer
Case 1 : Charging of station bus SC bus via station bus SA
a) Select Breaker CBE 216 ( SC incomer from ST#2) in SA-SC trip selector. (fig (i))
b) Turn the common synchronizer switch on common electrical vertical panel to check mode (fig (ii))
c) Put Synchroscope (on common electrical vertical panel ) in ON mode (fig (iii))
d) Select breaker CBE 217 (SC tie from SA) and check its permissive
e) After ensuring all the permissive are coming , close breaker CBE 217
f) After closing of CBE 217(SC tie from SA) breaker CBE 216 ( SC incomer from ST#2) will open in auto and SC bus will get charged by SA bus
S No | ACTIVITY | Responsibility | Status |
|---|---|---|---|
| 1. | Ensure MOT inspection & Pedestal closing clearance and Lub oil flushing Clearance from TMD and C&I. | Operation | |
| 2 | MOT Drain, Coolers drains and filters drain and vents are closed | Operation | |
| 3 | MOT level is >Low and <High | Operation | |
| 4 | All Instruments root valves are charged, & all instruments are healthy | C&I | |
| 5 | No insulation work is to be carried out on TG module and on its bearings during flushing & bearings pedestal area is to be maintained clean. | TMD | |
| 6 | Check one cooler, whose oil side as well as water side are lined up, in service | Operation | |
| 7 | MOT centrifuge is in service with purifier mode | TMD/Operation | |
| 8 | One VEF in service | Operation | |
| 9 | Provision of line filters in lub oil lines | TMD | |
| 10 | Clean baskets strainers are put in MOT. | TMD | |
| 11 | Availability of Lub oil pumps with P&I in service | Operation | |
| 12. | First DCEOP to be started for filling/venting of lines. Then DCEOP to be stopped & AOP to be srated. Check AOP discharge pr., current & MOT level. | Operation |
| 13. | MOT level will start dropping. Monitor the same and take necessary precautions. | Operation | |
|---|---|---|---|
| 14. | See oil flow through each bearing return oil pipe. | Operation | |
| 15. | Inspect all pedestals for oil leakages ( both external and from internal fittings, hoses , gauges,etc). | Operation | |
| 16. | Check for any oil leakage in MOT room, oil canal & pedestal area. | Operation | |
| 17. | Monitor choking of duplex filter. | Operation/TMD | |
| 19. | MOT coolers are filled and venting done. | Operation | |
| 20. | Stop AOP and clean the Oil line filters and MOT basket strainer after first four hours of oil flushing. | Operation/TMD | |
| 21. | Clean duplex filter when choked more than 50% | TMD | |
| 22 | Collection samples from MOT tank, Centrifuge inlet & outlet | Chemistry | |
| 23. | When frequency of cleaning of duplex filter reduces considerably and simultaneously clearance is received from chemistry department of mechanical impurities and moisture (both < 100 ppm) , oil flushing is stopped . | Operation/TMD/chemistry | |
| 24. | Basket strainer is removed, cleaned and put back in position. | TMD | |
| 25. | Remove oil line filters and replace with oil throttles. | TMD |
| Sr. No | ITEM DESCRIPTION | Responsibility | Status |
|---|---|---|---|
| 1 | Clearance from C&I, TMD, chemistry before putting on Barring | Operation | |
| 2 | Oil vapour extractor Normalised & ON | Operation | |
| 3 | Generator bearing chamber exhauster ON. | Operation | |
| 4 | Check for local line up of lube oil and jacking oil systems. | Operation | |
| 5 | All pipe connections are OK. | Operation/TMD | |
| 6 | Check lift of rotor journals at all bearing pedestals. | TMD | |
| 7 | Check hand barring is free prior to putting oil barring. | Operation/TMD |
