WELCOME TO TURBINE & ITS AUXILIARIES KNOWLEDGE GROUP PRESENTATION by madhukar srivastava, se (m), ktps, dvc

MOTOR DRIVEN BOILER FEED PUMP TROUBLE TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH INTRODUCTION: There are three Boiler Feed Pumps (3x 50%) in 2 X 500MW KTPS, DVC for supplying feed water to Boiler drum through HP heaters & economiser. Normally Turbine driven BFP is in operation and MDBFP  usually runs during start up, shutdown or during unavailability of any of the TDBFP’s .

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH Problem faced: On 01/02/2017, MDBFP of U# 1 was started for hydro test of boiler. After start-up, it was observed that main pump thrust bearing temperature was rising abnormally at higher rate with the increase in speed & thrust bearing vibration was also noticed to be high (around 7-8). The pump tripped at 4000 rpm on thrust bearing temp. high.

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH Observation: flow of Oil stream from mechanical seal housing drain line had been noticed which stopped soon after opening of breather of Hydro coupling.

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH Action taken: Boiler feed pump NDE side bearing cover was opened & clearance between working pad & thrust collar was checked and was found within design value (0.5mm). Thereafter thrust bearing pads was taken out for inspection in which rubbing marks (mostly at centre) was noticed. All pads were polished & blue matching was done. Thrust bearing pads alongwith their carrier were placed at its position & its clearance was checked which was found to be 0.55 mm.

Working side thrust pads with rub marks

Thrust pads blue matching before polishing

Trust pads after polishing

THRUST BEARING PADS BLUE MATCHING AFTER POLISHING

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH Pump was again run after box-up for hydrotest of boiler without breather & this time around, rpm was increased gradually upto 4300. At 4300 rpm of BFP & discharge pressure of 163 kg/cm2, Thrust bearing temperature (73 max) & BFP vibration (5-6) was observed to be normal under hydro test condition.

TRIPPING OF MDBFP ON THRUST BEARING TEMPERATURE HIGH Conclusion:- Probably an oil film had got developed in the strainer of breather which was obstructing flow of vapour through it. It may have pressurised the hydro coupling chamber. This could have resulted in the blockage of flow through the thrust bearing momentarily. Advice: It is advisable that the breather should be checked and if no oil vapour observed near surrounding area ,strainer should be cleaned if necessary.

INTERCEPTOR VALVE TROUBLE/PROBLEM Interceptor valve#2 of Main Turbine of Unit#1 was getting closed after opening up to 90%.

Possible areas of concern Test valve IV Servomotor Interceptor valve Brainstorming to find the actual cause of trouble. a)Test valve : Through this valve trip oil supplies to the Servomotor for its opening. It was dismantled to check any abnormality. However no problem was observed.

b)Servomotor: On operating the servomotor individually in decoupled condition, it was observed that it was opened to its maximum stroke (215mm)with out getting closed. c)Interceptor valve: In decoupled condition, valve lift was checked with the help of chain pulley block and it was found 200mm, which clearly indicates some obstruction , restricting full opening of the valve.

ACTION TAKEN Interceptor valve was dismantled. b) Findings: The Locking plate (Part no-26 drawing no. 1-11320-27000) provided for locking of Threaded ring(Part no. 16) got detached and had fallen in the cavity in between spindle and valve body, which was obstructing the full opening of the valve.

C) Locking Plate was welded to its place.

. D) Opening of valve was checked with the help of chain pulley block, in dismantled condition and valve travel was measured approx 215mm, same as that of drawing value. E) After box-up valve opening with servomotor was checked, and observed that valve was opening smoothly to its maximum stroke (215mm) without getting closed.

THANK YOU