Heat Rate Improvement Guidelines

for

Indian Power Plants

Volume II

By:

Center for Power Efficiency and Environmental Protection, National Thermal Power Corporation Ltd.

In Association With

United States Tennessee Valley Authority

For:

United States Agency for International Development and

National Energy Technology Laboratory,

United States Department of Energy

Project Funded by:

USAID/India Greenhouse Gas Pollution Prevention Project (GEP)

Heat Rate Improvement Guidelines

for

Indian Power Plants

Volume II

Revision 1 June 2000

Principal Authors:

S.C. Deo Sharma, D.K. Agarwal, B.M. Singh, P. Bhartiya, L.M. Rastogi, A.K. Arora, M.K.S. Kutty, O.P. Agnihotri and R.J. Tramel

TVA’s Participation Under:

DOE Interagency Agreement No. DE-AI26-97FT97300

“TVA” is a registered trademark of the Tennessee Valley Authority

iv

CONTENTS

1.0Process Description

2.0Objective

3.0Evaluation Criteria

4.0References

5.0Test Procedure

1.0Process Description

This procedure provides a systematic method for conducting routine efficiency tests on steam turbine sections operating in the superheated steam region. The test results produce a statistic, which is an expression of the steam turbine section enthalpy drop efficiency.

2.0Objective

The objective of the efficiency test is to provide information to allow accounting for the contribution of steam turbine performance deficiencies on unit heat rate and capacity and to provide a check of accuracy of critical station instruments.

3.0Evaluation Criteria

ASME Performance Test Code 6S –1988 (reaffirmed 1995), Simplified Procedures for Routine Performance Tests of Steam Turbines.

4.0References

ASME Performance Test Code 6 – 1996, Steam Turbines.

ASME Performance Test Code 19.1 –1985, Measurement Uncertainty. ASME performance Test Code 19.2 – 1987, Pressure Measurement. ASME performance Test Code 19.3 – 1974, Temperature Measurement.

5.0Test Procedure

The test method outlined in this procedure is the enthalpy drop efficiency method. The procedure is performed prior to turbine overhaul to provide information to allow diagnosing the steam turbine condition; following overhaul to provide information to allow evaluation of the effects of the overhaul work on steam turbine performance; during normal operation to identify abnormal changes in performance of steam turbines and to provide information to allow identifying the cause of change.

This method determines the ratio of actual enthalpy drop across turbine section to the isentropic enthalpy drop. This efficiency method provides a good measure for monitoring purposes, provided certain qualifications are met in obtaining results.

Each section of the turbine must be considered a separate turbine. For example, a double flow high-pressure section consists of two turbines, the governor end section and the generator end section. Each section must be tested and the results of each trended separately. As well, it is necessary to operate the turbine with the same control valve setting from test to test for the test results to be comparable (preferably at valves wide open); it is also necessary that the feedwater heaters served by the turbine be in service and operated normally, otherwise stage pressure changes will be affected and mask any actual steam path problems.

To ensure accuracy, each independent variable must be controlled, such that all subsequent tests may be related to all previous tests.

5.1Test Instrumentation

The test instrumentation required to conduct the turbine efficiency test consists of temperature, pressure, flow and electric power measurement devices. The number and the type of instruments required depend on the size and configuration of the unit to be tested.

5.1.1Test Instrumentation & Measurements Required (Typical list for 200/210 MW Unit )

Note : 1.Extraction number as per station terminology.

2. *-- Instruments to be installed on tappings near turbine.

5.1.2Instrument Accuracy Requirements

The instruments must be accurate to specifications as listed.

5.1.3Instrument Calibration

Instrumentation required by this procedure will be calibrated once in two years. Typically the calibrations will be performed by an approved laboratory. Calibration records for these instruments will be maintained as permanent records and reference to the current calibration be made in the report.

All station instruments required by this procedure should have current calibrations. The calibration must be traceable to the NIST (National Institute for Standards and Technology). The calibrations may be performed by the plant staff, provided the plant has appropriate instrument standards available to them.

Calibration records for these instruments will be maintained as permanent records.

5.1.4Station Instrumentation Required

5.2Test Prerequisites

The test instruments required for the test must be assembled, installed and operability verified. If a problem is discovered with an individual instrument, the instrument will be repaired and calibrated before conducting the test.

5.2.1Instrument Installation

Instruments must be installed following good instrument practices. Reference the appropriate ASME Performance Test Code for each instrument type.

Pressure instruments which operate above atmospheric pressure require pressure-sensing lines to be blown down prior to installing the pressure instrument, and the instrument to be vented after pressurization.

5.2.2Pressure Measurement

Pressure sensing lines should be plumbed with a continuous downward slope from the pressure tap to the sensor to prevent pockets of steam or air.

The appropriate waterleg measurements for each pressure instrument should be made and entered as part of data for each instrument.

Instruments which operate below atmospheric pressure must be plumbed with a continuous upward slope from the pressure tap to the sensor to prevent the formation of pockets of condensate. A means to vent instruments which operate below atmospheric pressure prior to the start of each test run must be provided.

5.2.3Temperature Measurement

All thermowells should be cleaned and the bottoms polished prior to installing the temperature sensors. The RTDs should be installed in a manner to ensure good contact is made with the bottom well and secured

to ensure they are held firmly during use. Temperature sensor shafts which extend past the thermowells should be insulated.

5.3Test Instructions

Test runs must be conducted over the normal operating load range from Valves Wide Open (VWO) to Minimum Load.

5.3.1Units with Sequential Valve Control

Test runs must be conducted at the valve points.

5.3.2Units with Full Throttling Control

The operating range must be divided into equal increments based on the nominal load at

VWO (Valve Wide Open) and minimum.

5.3.3Exceptions to VWO (Valve Wide Open)

It may not be possible to achieve VWO with rated steam conditions on certain units. In this case, reducing the main steam pressure, and thereby increasing the steam specific volume, may allow VWO operation.

As an alternative, if VWO cannot be achieved with rated steam pressure, a lower valve point may be substituted for VWO on sequential valve controlled turbines. The travel of the control valve stem may be used on full throttling turbines.

5.3.4Operating Conditions for Each Test Run

5.3.4.1Unit Off Load Control and Steady

5.3.4.2Main Steam Pressure at Design Value

5.3.4.3Main Steam and Reheat Steam Temperatures at Current Expected Value

5.3.4.4Boiler Outlet O2 at Current Expected Value

5.3.4.5All Feedwater Heaters in Service, Normal Levels and Vent Settings, Normal Drain Routing