L. P. Turbine

CONTENTS

1.0Introduction

2.0Objective and Scope

3.0Reference

4.0Design Data

5.0Test Instrumentation

6.0Instrument Installation

7.0Test Instructions

8.0Test Frequency and Duration

9.0Personnel Needed

10.0Test Setup

11.0Duration of Test Run and Frequency of Readings

12.0Calculation and Analysis

13.0Fault Analysis

14.0Report

1.0Introduction

A feedwater heater is a component designed to heat a given quantity of feedwater through a specified temperature range with steam at a specified enthalpy and pressure and with a limited pressure loss on the feedwater passing through the unit. The usual arrangement of this type of heater is a shell and tube unit with the feedwater passing through the tubes which are surrounded by the heating medium. The heating surface within the unit may be subdivided into zones as outlined below:

a)Condensing zone

b)Desuperheating zone and

c)Drain cooling zone

The performance of feedwater heaters can be analyzed by monitoring the terminal temperature difference (TTD), drain cooler approach temperature (DCA), the pressure drop on the feedwater side and the temperature rise across the heater. To monitor these it is desirable to carry out a simplified routine performance test on feed water heaters at a specified frequency. This will help in identifying the level of deviations and trending of performance. The purpose of this document is to layout a standard test procedure for all units.

2.0Objective And Scope

The scope is limited to HP heaters. The objectives of the routine high pressure feedwater heater test are:

2.1Prior to an outage, provide information to determine whether corrective action is required to maintain optimum feedwater heater performance and provide guidance in determining materials, tools and equipment, workers, cost estimates, and scheduling.

2.2Following an outage, provide information to allow evaluation of the effect of work on the feedwater heater.

2.3During normal operation, provide information to allow identification of abnormal changes in heater performance and provide information to assist in identifying the source of the change.

2.4During normal operation, provide information to assist in optimizing the operation of the heater.

2.5During normal operation, provide information to allow accounting for the contribution of heater performance deficiencies on unit heat rate and capacity.

3.0 Reference

Based on ASME performance test code PTC 12.1, 1978 on Closed Feed Water Heaters and HEI standards for Closed Feed Water Heaters.

4.0Design Data

HP heater design data as per Annexure – I

5.0Test Instrumentation

The parameters required to be monitored to conduct the HPH performance test consist of temperature, pressure/differential pressure instruments.

5.1Test Instruments & Measurement Required

The No. of instruments required per heater is as follows:

*Preferably individual heater or differential pressure across the heater train

5.2Instrument Accuracy Requirement

The instrumentation selected for the test shall be capable of achieving the following measurement accuracies:

5.3Instrument Calibration

The instruments used for the test will be calibrated once in two years. The calibration records of these instruments will be maintained as permanent records and reference to current calibration will be made in the report.

5.4The performance test data from test instruments will be recorded using sample format as given in Annexure - II.

5.5Measurement required from station instruments are given in Annexure - III This format will be used for collecting station measurement during the performance test.

6.0Instrument Installation

6.1Pressure Measurement

Pressure instruments which operate above atmospheric pressure require all pressure sensing lines to be blown down prior to installing the instrument, and the instrument vented after it is pressurized, if possible. The 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 the data for each instrument.

6.2Temperature Measurement

All thermowells should be cleaned and the bottoms polished prior to installing the temperature sensors. All temperature sensors should be installed in a manner to ensure they make good contact with the bottom of

the well and secured to ensure they are held firmly against the bottom during use. All temperature sensors whose shafts extend past the thermowells should be insulated.

6.3Data Acquisition System (DAS) and Processor & Analyzer System

It is preferable to use a portable DAS and processor and analyzer for performance testing. This will ease the testing process and provide on line monitoring of test data and results. It will also help in tracking the process stability and thereby reduce the uncertainty level of results.

6.3.1Portable Data Collection Unit

One/two portable units may be used to cover the inputs at the test location. Each DAS unit should have a minimum of 16 universal inputs as given below:

a)PT 100, 4 Wire RTD

b)4-20 mA, 2 Wire Transmitter output with a built-in facility to power the Transmitter.

6.3.2Portable Processor and Analyzer Unit

• IBM compatible portable machine with a Pentium processor

• Graphic display compatibility

• 32 megabytes of RAM

• Windows 95 with Microsoft Excel version 7.0

• IDAAS and DALITE Software as analyzer

6.3.3Installation

The following precautions should be taken during installation of the data collection unit with the portable processor.

•Identify the location of power supply.

•List out the inputs with respect to Channel No.

•Review the status of fuses.

•Tag input leads at both ends by masking tape, etc.

•Connect the inputs as per channel listing. Cascade the output from one data collection unit to other using the network cables, connect RS 232 cable from data collection to the interface unit/portable processor unit.

•The network cable should be laid away from movement areas, without obstructing the plant equipment and 2-3 meters above the floor level.

•Ensure the tightness of all connections.

•Charge the power supply and check for the channels healthiness.

•Verify the system is networking.

•Carry out a test run to scan and ensure proper system functioning.

7.0Test Instructions

7.1Unit should be in operation at normal full feedwater flow steady state condition.

7.2Ensure the heater drains are cascading as per the specified cycle conditions.

7.3Ensure venting of steam side and water side to remove non-condensable gases.

7.4Operation of the feedwater heater shall be brought to the steady state condition prior to initiating the test run. It shall be kept at this condition throughout the test run.

7.5Every effort shall be made to conduct the test runs under design conditions. Allowable variations from design conditions in feedwater flow and extraction steam pressure shall not exceed +/- 10%.

7.6First test run is conducted at heater water level at normal design valve. Subsequently, other test runs are conducted by varying the heater levels above and below the normal level.

8.0Test Frequency And Duration

8.1Routine testing every 6 months

8.2Special requests for various reasons.

8.3Each run shall continue for a period sufficiently long to ensure accurate and consistent results. With the online computational software described in Section 6.3, each run duration should be 20 minutes long after attaining steady state condition.

9.0Personnel Needed

The test requires two/three persons, for test set-up and for taking data at site and at control room.

10.0Test Setup

10.1First notify the Shift Incharge and Unit Controller about the programmer for conducting the test and inform about test equipment/instrument being installed.

10.2Install the pressure transmitters and RTDs (as per Section 6.1 & 6.2) at the locations described as per clause 5.1

10.3The output of transmitters and RTDs to be connected to data collection unit and this in turn to be connected to data processing unit as indicated in Clause No.6.3

11.0Duration of Test Run and Frequency of Readings

11.1 CASE I - Testing by Using DAS and Processor and Analyzer System

11.1.1Test duration: Each test run may be conducted for a period of 15-20 min, after achieving minimum uncertainty.

11.1.2Frequency of test data: After achieving the point of minimum uncertainty as shown by the data processor, the test may be commenced and the readings taken at the frequency given below:

•test instrument readings by data processor as per normal scan rate.

•manual readings from control room at an interval of 5 min.

11.2CASE II - Testing by manual data collection

11.2.1Test Duration: Each test run should be conducted for a period of 30-45 minutes after achieving stable parameters.

11.2.2Frequency of Test Data: All readings should be taken at 5-minute intervals.

11.3Data Verification

During the course of testing compare the historical performance data showing expected value of the critical measurements as appropriate. This will help in assessing the error, if any, in data being collected.

12.0Calculation and Analysis

12.1Calculate the Terminal Temperature Difference (TTD) for each Feedwater Heater Tested as per Annexure - IV.

12.2Calculate the Drain Cooler Approach Temperature (DCA) for each Feedwater Heater Tested as per Annexure - IV.

12.3Calculate the Temperature Rise across each Feedwater Heater Tested as per Annexure - IV.

12.4Analyze Calculated Values. Plot TTD, DCA, and Temperature Rise on separate control charts or a time line graph’s showing the historical and expected data. Look for adverse trends, sudden changes, etc. Identify areas for possible improvement.

13.0Fault Analysis

An increase in either the TTD or DCA, and/or a decrease in the temperature rise indicates a problem with the heater. This deterioration in performance could be the result of any or all of the following causes:

1.Fouled heater tubes (either steam or water side).

2.Internal leakage (leakage through the waterbox partition plate resulting in a partial internal bypassing of the heater, or, tube-to-tube sheet leakage resulting in feedwater leaking to the steam side).

3.External leakage (through the bypass valve)

4.Plugged tubes (reducing the heat transfer area, while increasing tube velocity

The detailed Fault Tree is given in Annexure – V.

14.0Report

The report should include a narrative describing any unusual findings as well as the following:

14.1Executive Summary

14.2Objective

14.3Scope

14.4Background

14.5Test Methodology

14.6Results

14.7Discussions

14.8Conclusions

14.9Recommendations

14.10Acknowledgment

14.11References

14.12Complete set of Appendices

14.12.1Analysis and Results

14.12.2Test Data

14.12.3Test Equipment and Instrumentation