DURGAP UR SANDIP MONDAL SOURJA SAMADDAR NTPCSAIL POWER

DURGAP UR SANDIP MONDAL & SOURJA SAMADDAR NTPC-SAIL POWER COMPANY LTD DURGAPUR WE WELCOME ALL

TOPIC DURGAP UR RELIABILITY ENHANCEMENT IN DRUM LEVEL CONTROL BY MODIFICATION IN BFP SCOOP CONTROL & CONSEQUENT APC REDUCTION

SYNOPSIS DURGAP UR v PLANT OVERVIEW v EARLIER SCENARIO v IDENTIFICATION OF THE PROBLEM v MEASURES TAKEN v IMPLEMENTATION & SOLUTION TO THE PROBLEM v PAYBACK v CONCLUSION

DURGAP 2 X 60 MW

EARLIER SYSTEM SCENARIO • In NSPCL Durgapur, drum level control was done by 3 element control of FCV (using drum level controller) & FW header pressure control by BFP scoop (BFP scoop controller). • High DP across FRS means high energy loss and subsequent auxiliary power consumption due to high discharge pressure. • When drum pressure starts increasing beyond certain value leading to very low DP, drum level will start falling due to lesser flow.

BFP Scoop control in FW Header Pressure Mode

IDENTIFICATION OF PROBLEMS There had been such instance of unit tripping in drum level very low once in NSPCL Durgapur though drum level control was in auto mode. So to enhance the reliability of the total drum level control by removing this deficiency alternative control was the need of the hour.

PHILPSOPHY BEHIND FRS DP CONTROL BY BFP SCOOP There had been such instance of unit tripping in drum level very low once in NSPCL Durgapur though drum level control was in auto mode. FRS DP= Pb-Pc = (Pa-P line drop 1)-(Pd+ P line drop 2) = Pa-Pd- P line drop 1 - P line drop 2 = Pa-Pd-Total line Drop I. e. FRS DP ∞ (BFP Discharge pr- Economizer i/l pr) when line drop neglected.

BFP Scoop control in FRS DP Mode

FRS DP TAPPINGS TAPPING FOR DP TRANSMITTER FRS VALVE

DP TRANSMITTER MOUNTED

MEASURES TAKEN a) For measurement of FRS DP, Electronic DP transmitters procured, installed and commissioned. b) The necessary tapping with isolation valves from FW lines across both 100% FRS CV connected to the transmitter’s impulse lines. c) Spare pair identified in the existing cable to UCR and connection done to bring the FRS DP value as Process value for control in the controller and to the recorder for display, trend and data logging for future analysis purpose. d) The spare second loop (first loop using the FW Pr control) of the dual loop BFP Scoop controller is used for DP control.

IMPLEMENTATION Logic modification in Controller: a) Inclusion of FRS DP as PV value in the second loop as per with or without DP transmitter. b)Inclusion of control mode selection logic. Since, for both the loops, final control element is the same i. e. BFP scoop, so selection of loop is enabled by a new selector switch on the UCR desk.

IMPLEMENTATION Logic modification in Controller: c) Incorporation of the auto tracking of command output by both loops so that, in case emergency, if operator wants to transfer the mode of control from PR to DP or vice versa, there will be bump less transfer only by switching the selector switch. d) Incorporation of forced manual logic with alarm in case very high deviation (10 Ksc/sec) in FRS DP to alert the desk operator in case of any malfunction of the control system leading to sharp deviation in DP value as mentioned above.

IMPLEMENTATION Programming and Tuning: a)All the 4 nos BFP scoop controllers programmed with the modified logic and put into service. b)Online tuning was done keeping the loop control in auto and the PID parameters were fixed.

Controller trend in scoop control

Control Desk DRUM LVL DP/ FW PR PR DP SELECTOR SWITCH

Comparison of Power consumption in both modes of control Parameter Unit Feed Water eco inlet pressure Feed Water pressure before FCS Scoop % (Command) Kg/cm 2 FW Hdr. Pressure Control 109 Kg/cm 2 139 125 % 67 60 Scoop % (Actual) % 70 60 Control Valve opening position Differential Pressure across FCS BFP Current % 30 45 Kg/cm 2 30 16 AMP 180 162 44444. 5 40000 BFP Power Consumption KWH (Per day) -Theoretical FRS DP Control 109

COST BENEFITS & PAYBACK Actual Net Energy Savings: Cost Benefits BFP Current reduction = 18 amps = √ 3 VI Cos Ø=1. 732 x 6600 x 18 x 0. 90 x 24/1000 KWH /day = 4444. 5 KWH/day (in terms of units per day) = 4444. 5 x 365 KWH/annum for each BFP = 4444. 5 x 365 x 5 (cost per KWH unit) x 2 Annual Cost Saving = Rs. 1, 62, 22, 425 per year (for 2 Unit) Investment = Nil (with calculated DP logic), Cost of one DP Tx Rs 30000/- Payback Period = Immediate BFP Power Consumption (Per day) Annual Energy Saving Potential

TANGIBLE BENEFITS The success of this implementation is the reduction in auxiliary power consumption (0. 3%) & in turn cost benefit. It is very robust control and can be used during varying loads without any major drum level fluctuation resulting in reliability enhancement.

CONCLUSION In this era of tremendous competitiveness cost saving is achieved after implementation of the DP control logic. Above all reliability of the system has improved which is of utmost importance for a captive power plant.