Boiler Special OperationsHydro TestSafety valve FloatingForced CoolingWet Preservation

Hydro TestDrum metal temp should be less than 80C.Ensure SH coils metal temperatures are

Isolate the power supply for MSV and its bypass MOV.IDs and FD Fans should be in stopped condition.Ensure locking of the spring supports in MST line &SH-III o/l header.Ensure the Gag on the SVs and tight close the HOV before the ERV.Keep open the manholes at 44ML and at 15 ML and some manholes in coil areas.Provide focus lights at 44ML & at 15ML for furnace inspection.Making through the dummy on the filling line.

Using fill pump fill the WW, Eco, Drum, and SHs contour.Ensure opening of the vent valves at the headers [5 nos of WW+4 nos of SH 2&3] and at the vent station [2for SH3; 2for SH2; 2for eco & 1for WW].In case the water temp is higher [say 60~70C] continue venting at that section alone.Make simulations in the logic for opening & closing of SH spray valves [both block & any one line] that will be used for pressure raising.

Pressurize up to 5 bar using fill pump and close all the HOV & MOV vent valves including SH 3 startup vent.Close the HOV &put back the dummy on filling line and before starting the BFP.Start BFP and using SH Attemperation line or low load line-Eco by pass line pressurize the contour using feed pump scoop.Advantage of using SH spray line is that we can get the measure of water flow during Pr raising but simulation is to be done for opening the valve.

During contour filling and pressurizing, check the MSV after valve drains for any water flow; and ensure that there is No Flow of water to turbine side.Rate of Pr rise is 2bar/min up to 50bar.Inspect the boiler contour for any leaks.Continue Pr raising up to 100bar at the same rate and inspect again.Start second BFP.Thereafter Pr rise is 1bar/min up to 170 bar in drum.

Offer the boiler for DCIB inspection.In case of delay in the arraival of DCIB; keep the drum pr at 120 bar and use the feed pumps alternately to maintain the pr in the system.Hold the pressure for hour using both BFPs.Depressurize the boiler by using BFP scoop at the same rate of pr raise.At 50 bar inspect ABGs and coils & Record the leaks.At 50 bar C&I will do flushing of impulse lines of SWAS.

Close all valves in the feed manifold and also in the spray station.Stop the BFPs.Open CBD line and release the pressure @ 2bar/min upto 0 bar.Open SH & Drum start up vents, drains before MSV.Drain the MS line, SHs and partly the Drum [up to working level]Remove all simulations & the gags in SVsUnlocking of the spring supports in MST line &SH-III o/l header.Avail supply for MSV and its bypass MOV.

In case of puncture note down the location of puncture and drain that particular section only.

Safety valve Floating

SV floating is done preferably before unit synchronization. SV floating is done after every SV servicing or after attending to valve passing.SV floating if done actually will subject all the system parts to high Pr.

REQUIREMENT OF SAFETY VALVE Proper functioning - Opening at correct set pressure - Correct blow down- Proper mechanical operation & Clean closure without leakage.

The set pr of the four SVs are as follows.Keep in hand the previous values and details like make no, seat area etcDrum Valve 101 located at left front side opens at 178 Ksc [measurement not in bar].Drum Valve 102 located at left rear side opens at 179 Ksc [measurement not in bar].Drum Valve 103 located at right side opens at 180 Ksc [measurement not in bar].SH Valve 104 located at SH-III outlet header on the left- front side opens at 168 Ksc [measurement not in bar].

CHATTERING- Rapid opening and closing of the valve is known as chattering.CAUSES - Insufficient blow down - More back pressure due to under size discharge piping - Insufficient steam flow to the valve - lifting with water

SIMMERINGThe valve is just about to open and has indefinite contact.It is an audible sound caused by the vibration of air molecules around the seat.

BLOWDOWN:Opening pre Closing pre----------------------------X 100Opening pressure

Valve should be set with in 1% of set pressure Valve should be hand popped at 75 to 80% of set pressureGAGGINGArresting the stem mechanically from lifting. - Do not gag in cold condition - Gag at 80% of low set value pressure.

At local it is preferable to mount precision gauges. If one valve is to be floated all the other valves are to be gagged. By actual float we can know the Opening, Closing Pr and we can compute the Blow down. It is always advisable to use oil burners for actual float test. Drum level surges will take place and hence level simulations have to be done to avoid boiler trip.

ATTENTION!! - Do not stand near Discharge pipe of the Safety Valve

- Test and achieve within minimum number of pops.

- Bring Blow down between 3 and 5 %

In TREVI test SV floating shall be done after synchronization preferably in full opr Pr.Instead if TREVI test is done the system pr is the steady opr pr but the external force is given to the valve spindle for opening the valve.

The applied hydraulic cylinder pr will pull the valve stem upwards against the spring force. We can know only the Opening pr but not the Closing Pr and so we cannot compute the Blow down.

No need of oil burners. No need for gagging the SVs. Drum level surges will not take place. Some agencies give valve lift plotting graph.

Forced CoolingAFTER BOILER IS TRIPPED DO NOT CLOSE STOP VALVE.

HP BY PASS & LP BY PASS WILL COME INTO SERVICE ON AUTO.

CARRY OUT BOILER PURGE.

FEED THE BOILER USING BFP UPTO +400MM.

MAINTAIN 400T/HR AIR FLOW INITIALLY.

STOP BOTH CGR FANS.

USING PR SET POINT OF THE BY PASS VALVE GRADUALLY REDUCE BOILER DRUM PRESSURE.

DRUM INNER TOP/BOTTOM TEMP SHOULD NOT EXCEED 25C.

IN CASE OF INCREASING TREND REDUCE AIR FLOW.

STOPPING FD FAN IS TO BE CONSIDERED IF MANY POINTS HAVE DELTA T AND RESTARTING AFTER NORMALISATION.

CHECKING THE CLINKER FALLING AT LOCAL, GRADUALLY STEP UP AIR FLOWTO UPTO 700T/HR.

4 HRS AFTER BOILER TRIP, START BOTH GR FANS.

FEED THE BOILER USING BOILER FEED PUMP WHENEVER - LEVEL GOES OUT OF RANGE.

ONCE THE BY PASS IS CLOSED SHUT THE BOILER STOP VALVE.

OPEN SH VENTS AT 6 BAR DRUM PR.OPEN DRUM VENTS AT 3 BAR PR.

HOT DRAIN THE DRUM, ECO, WW AT 140C.

FANS TO BE KEPT IN SERVICE TILL RH, SH TUBE TEMP IS AROUND 60C

SLAG BATH CAN BE DRAINED AFTER 24 HOURS

FURNACE MANHOLE DOORS CAN BE OPENED AFTER 24 HOURS

ONE FD FAN CAN BE STOPPED WHEN SLAG BATHWATER IS DRAINED

SECOND FD FAN, ONE ID FAN CAN BE STOPPED AFTER 36 HOURS AFTER BOILER TRIP

SECOND ID FAN TO BE STOPPED /KEPT IN SERVICE IN CONSULTATION WITH BOILER MTCE DIVISION.

WET PRESERVATIONBoiler water drained fully @ room temp.

One CST was isolated. i.e DM Water line valve from WCTP was closed.

CST inter connection valve was closed.

Liquid hydrazine [N2H4] was added from the top of the tank

200 PPM hydrazine solution prepared in the CST by starting fill pump and recirculating water.

Some amount of liquid Ammonia was added to improve PH value in this solution.

All boiler drains were closed tightly.

Using down comer drain lines fill pump was started and chemical filled upto Drum working level i.e +300 mm

All vents were closed to box-up the SH coils in lieu of N2 capping.

Nothing was done to preserve the RH coils.

Periodically, say once a week, check solution concentration in water.

If the solution concentration decreses, chemical dept will add more chemical solution after draining some water.