MINIMUM LOAD/RAMP TEST PROCEDURE FOR COAL BASED … · 2020. 4. 27. · Thermal Power Plants (TPPs)...

MINIMUM LOAD/RAMP TEST PROCEDURE FOR COAL BASED THERMAL POWER PLANTS (TPPs)

DisclaimerThis document is made possible by the support of the American People through the United States Agency for International Development (USAID). The contents of this document are the sole responsibility of Deloitte Consulting LLP., and do not necessarily reflect the views of USAID or the United States Government or the Government of India. This document is prepared under Contract Number AID-386-TO-17-00001.

GREENING THE GRID (GTG) – RENEWABLE INTEGRATION AND SUSTAINABLE ENERGY (RISE) INITIATIVE A PARTNERSHIP BETWEEN USAID AND GOVERNMENT OF INDIA

DisclaimerThis document is made possible by the support of the American People through the United States Agency for International Development (USAID). The contents of this document are the sole responsibility of Deloitte Consulting LLP., and do not necessarily reflect the views of USAID or the United States Government or the Government of India. This document is prepared under Contract Number AID-386-TO-17-00001.

April 2020

MINIMUM LOAD/RAMP TEST PROCEDURE FOR COAL BASED THERMAL POWER PLANTS (TPPs)

GREENING THE GRID (GTG) – RENEWABLE INTEGRATION AND SUSTAINABLE ENERGY (RISE) INITIATIVE

A PARTNERSHIP BETWEEN USAID AND GOVERNMENT OF INDIA

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USAID’s GREENING THE GRID (GTG) – RENEWABLE INTEGRATION AND SUSTAINABLE ENERGY (RISE) INITIATIVE

Acknowledgements

The USAID India “Greening the Grid Program” is being funded by the United States Agency for International Development (USAID) and is an initiative of the U.S. Government.

The purpose of the minimum load/ramp test procedure is to support Coal BasedThermal Power Plants (TPPs) across the country in preparing and conducting low load and cyclic operations to facilitate integration of renewable energy (RE) into thegrid. This document has been prepared under the USAID’s Greening the Grid – Renewable Integration and Sustainable Energy (GTG-RISE) initiative, a bilateral program with the Ministry of Power, Government of India. As a part of USAID’s GTG-RISE initiative, a series of innovative pilots are being implemented to support Government of India’s efforts in managing the large-scale integration of RE into the grid. One of the key pilots focus on flexible operations of coal-based power plants. This report documents the procedures for low load test runs based on the successful demonstration conducted in the select units of NTPC Ltd and Gujarat State Electricity Corporation Limited (GSECL). The report will be handy for units willing to carry out low load test runs in their respective units.

The procedures and protocols in the report have been developed with in-house expertise of GTG-RISE team along with support from Central Electricity Authority (CEA), Bharat Heavy Electricals Limited (BHEL) and other individual experts. We would like to earnestly thank Mr. Prakash Tiwari, Director Operations, NTPC Ltd for his active leadership on GTG-RISE initiative, which informed the creation of this welltimed document. We thank Mr. Anjan Kumar Sinha, Senior Grid Integration Advisor(GTG-RISE) in developing these test procedures with key insights and support fromMr. Y. M. Babu, General Manager, BHEL and Mr. Sandeep Chittora from Siemens. Wealso acknowledge and thank Mr. B. C. Mallick, Chief Engineer - Thermal Renovation& Modernization, CEA and his team for their guidance and support in preparing this document.

We further would like to thank the core team from BHEL, NTPC (Dadri & MaudaStations), GSECL (Ukai & Wanakbori stations) who participated and supported the GTG-RISE team in conducting the test runs as part of pilots on flexible generation.

Minimum Load/Ramp Test Procedure

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Table of Contents

1. Introduction 72. Purpose of the test 73. General Testing Approach 84. Expected issues – Low Load/Ramping operation 95. Planning for Test Runs 116. Detailed Information of the target Unit 157. Test targets 198. Test Description 21Annexure 26

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USAID, under its GTG-RISE initiative, is implementing pilots on flexible operations of thermal power plants (TPPs), As a part of this pilot, GTG-RISE is enabling flexible operations of thermal power plants through guidance on technical, commercial, operational and regulatory aspects. To execute these pilots, USAID partnered with India’s largest power generation utility, NTPC Ltd, that generates approximately 25 per cent of the country’s total electricity generation, and with another state-level utility, GSECL. GTG-RISE has carried out the pilot studies to assess the technical feasibility and commercial implications of flexible operations at NTPC’s Ramagundam (210 MW) and Jhajjar (500 MW) and GSECL’s Ukai TPS (210 & 500 MW) units. The pilots have examined the preparedness of the selected coal based units and provided the business case for policy and regulatory changes for the enabling flexible operations. Over the past three years, GTG-RISE has carried

out a series of technical feasibility studies for 1410 MW of units for both the utilities followed by low-loadtest runs conducted at their select units, which provides the evidence and basis for the nationwide scale-up of flexible operations. These tests were conducted at NTPC’s Mauda Unit, based on the low-load (flexible) test run procedures developed and guided by GTG-RISE experts and BHEL. Similar to NTPC, GSECL has also successfully conducted low-load test runs at its Ukai and Wanakbori stations. The GTG-RISE team has developed these procedures based on successful demonstration of low load test runs conducted in the select units and have also carried out analysis of the data that has emerged from the tests. The low load test procedures shall act as a guidance tool for coal based stations across the country wanting to carry out low load test runs in their respective units.

1. Introduction

The purpose of the test is to identify the minimum load and ramp rates that can be achieved by the TPPs. This test procedure document covers the chronological steps involved in flexible operation like minimum load operation and ramp tests. Temporary solutions and manual interventions may be necessary

to achieve the flexible operation requirements. The test will not focus on solving all problems such that the plant can be operated at the minimum load outside the test regime. For this, additional automation may be necessary, which the test can also identify.

2. Purpose of the Test

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The key objective of the low load flexible operation is to reach the minimum load level the plant can achieve, and while achieving so there are possibility wherein technical and operation challenges might occur. The testing approach involves the load to be reduced until a challenge/obstacle occurs. Once the obstacle is identified, there will be need to define an approach to overcome any such obstacle/s. The general procedure is an iterative procedure (Figure 1). Some of the possible solutions to overcome any such obstacle may include:

• Manual intervention• Changing operation regime (e.g.

changing combination of mills, changing main steam pressure)

• Implementation of supplementary logic in the DCS

During the test, process data needs to be recorded and a detailed list for data requirement is shared further in this procedure document. The data requirement may vary from plant to plant and may need to be evolved for specific issues that may occur, which cannot be foreseen in advance.

There might be the cases where all problems or obstacles might not be solved immediately. For example, problems which requires implementation of supplementary logic may need the test to be interrupted, and again continue (hours or day/s) later.

3. General Testing Approach

Overcoming nextobstacle

Figure 1: Iterative Procedure

Load reduction, till next obsticle

occurs


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All the expected challenges or issues for the respective units of the TPPs considered for the low load and ramping operation needs to be identified based on the existing liabilities. This would involve evaluation of process data for the respective units.

i. Drum level control

It is reported from most of the utilities that the drum level control remains to be an issue during the changeover of steam supply to the turbine driven feed water pump, and/or switching of these pumps. However it can be done manually to gain stability by operating in a higher load range and making it possible to conduct the test run. For regular operation at minimum load this would need to be automated, but would necessitate more attention by the operators.

Boiler Feed pumps can pose problems

from steam source, and non-modulating recirculation valves.

ii. Hot reheat steam temperature

During the low load operations, reheat steam temperatures are not reached during minimum load. This results in lower fuel efficiency, which poses commercial problem and cannot be considered to be a technical problem. Efficiency at min load will be much worse anyway. It is then a commercial optimization on how the unit is dispatched - At lower load with less efficiency, or at higher load with better efficiency. During min load, some tests can be conducted to show the impact of several operating regimes on the reheat temperatures. Besides burner tilts (which are probably already in the uppermost position) the fire can be positioned higher in the furnace by using mills that

4. Expected issues – Low Load/Ramping operation

Figure 2: Expected Issues

G

APH

ESP FGD

DCS

V VVV V V

.

.

,

Drum Level Control

Ventilation, erosion, vibration

MS -Temp.RH-Temp.

FG Exit Temp

Feedwater- Temp.

Lower Heat Transfer toConvective Heating Surfaces

Combustion-Stability Temp. Distribution NOx-Emissions

Coal Pipes imbalance

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are firing the upper levels. It is therefore desirable to have upper mills in service.

iii. Main steam temperature

Main steam temperature is also identified to be concern during the low load test runs. There are several solutions how the test can be conducted anyway:

• Operation at a lower main steam temperature in order to have more margin before reaching material limits

• Implementation of a controller logic to give corrective signals to the existing DCS controller. This would be required to be implemented and tuned before the minimum load test.

iv. Flame scanners

In most of the cases it is observed that flame scanners at all loads does not work properly and sometimes not able to detect individual flames. This is a general safety issue which should be solved, but is not an issue specific to the min load test.

v. Primary Air Fan Stalling

In a typical case, where there are two primary air fans installed for a set of 6-7 mills, there can be issues at low loads when primary air flow is reduced. When the flow vs pressure is not maintained as per the design curve of the PA Fan, it can lead to a problem of stalling and even fan damage. It is therefore recommended to carry out the load reduction test very slowly and at very low load wherein one PA fan may be withdrawn from service. It is recommended that extra care should be taken to close all the dampers of the standby fan, to avoid tripping of the running fan or sudden reduction of primary air header pressure. Passing dampers may be rectified prior to the

test run.If necessary, oil guns may be taken into service for a short duration during the transient operation.

vi. Coal Pipes choking and improper balancing between different coal pipes

At low loads, it is important to maintain adequate PA flow with adequate mill outlet temperature through individual mills. Monitoring the temperature of coal pipes before burner would be helpful. Mill fineness would vary with change in mill loading. Before the test run, the classifier settings must be checked.

vii. FG Exit Temperature

The Flue Gas exit temperature must be monitored closely as lower FG temperatures can adversely affect the ESP and the exit gas path.

viii. Operational Threats

• Mill Performance

• Out of Service Burners

• Flame impingement of boiler components

• Air in-leakage upstream of the boiler O2 probes

• Biasing primary airflow

• Low Load O2 and NOX control

• Flame Scanner Performance

• Higher than optimal A/F ratios at low load (too many mills in-service)

• Boiler Heat Transfer

• Fireside-Steam Side Incompatibility

• Cycling to fast and hard

• Corrosion Control

• Water Chemistry Control


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To conduct the successful test run, it needs detailed planning including but not limited to identifying pre-requisites, internal & external coordination, defining boundaries within the plant, preparedness for manual and automation interventions, recording the data during the test run performance, etc. The details of the suggestive planning are outlined as below.

i. Test Pre-requisites

• All auto loops are to be made available and machine is to be put in CMC

• Fine tuning of CMC to be carried out to take care minimum deviation of important parameters like MS/HRH steam temp, throttle steam pressure, drum level, excess air or O2% at eco outlet and flue gas temp at boiler outlet during ramp tests.

• Attemperator system (isolating valves and control valves) and control valves are to be set tight and fast response to the changing demand system

• Dirty air flow test at regular interval to evaluate partially plugged coal pipes and burners

• Burner tilts are to be operational in full range in auto and SADC damper operation are to checked and correct feedback to be made available.

• WWSB and LRSB operation before pilot study.

• Air heater soot blowing at least once in a shift

• Air heater air leakages and tramp air is to be minimised.

• Replacement or repairing of

expansion joints if required and major duct revamping if any.

• Water chemistry instrumentation should be set right and linked with DCS.

• Boiler side high energy piping hanger indicator are to be marked and monitored.

• Low range FRS to be used to maintain required flow rate in economiser during cold or warm start up.

• D/A pegging steam from Aux steam and CRH to be made available for auto operation.

• Flame scanners to be maintained in perfect working condition all the time. If required it may be cleaned.

• Ensure proper coal of desired quality is fed into the boiler. For the test run coal can be prepared by blending before feeding into the bunkers.

ii. External & Internal Coordination

• Seek permission from RLDC/SLDC for ramp test and minimum load operation.

• Coordinate with NLDC to allow the generator to take trial. The generator should be exempt for SCED operation (For ISGS stations) during the trial period.

• Permission for machine to withdraw RGMO operation.

• Important parameters log sheet is to be configured for time to time logging and parameters retrieval during and after the tests are conducted.

5. Planning for Test Runs

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• Create a cross functional team, drawing members from operation, mechanical maintenance, electrical, C&I, efficiency, planning and chemistry with specific responsibilities.

iii. Precautions for safe Test Run

• Determination of which mills to be used in the test: This depends on actual coal quality and experience with former tests. Assuming at least four mills will be in operation, the tests will be conducted without supporting fuel (fuel oil).

• Inform dispatcher that there is an increased risk to trip during the tests.

• Put the unit in low, but stable load (exact load to be decided)

• Reduce main steam temperature set point in order to get a higher margin

before reaching material limits

• Lower the load slowly and in steps.

• Switch over to one boiler feed pump as early as possible.

• Load changes should be around 30 MW for a 500 MW unit (or equalling 5%). After each load reduction, wait about 30 minutes for stabilization and identify process instabilities. If no instabilities, reduce the load further.

• If there are instabilities, try to solve them by manual intervention. It might be necessary to temporarily increase load a little bit if instabilities are becoming too dangerous for operation.

• When instabilities cannot be eliminated, go back to last safe load.

• Depending on which instabilities occur, determine whether to change mills, main steam pressure, burner tilts etc., and repeat to lower load.


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Required process data

• For each mill: On/Off signal

• Burner tilt positions

• Oxygen in flue gas before air preheater

• Total air flow

• Speed of all boiler feed pumps

• Feedwater flow

• Position of steam valves (e.g. form extraction and cold reheat) which are feeding the turbine-driven boiler feed pumps

• Unit Load

• Throttle Pressure Set Point

• Throttle Press TRX SEL

• Main steam temperatures

• Main steam temperature setpoint

• Hot reheat steam temperatures

• Hot reheat steam temperature setpoint

• Total coal flow

• Turbine HPCV position

• Main steam flow

• Reheat pressure• Drum level• Drum level setpoint• SH spray flows• SH injection control valve positions• RH spray flows• RH injection control valve positions

The list may be expanded if specific problems need to be assessed. A complete list is given in Annexure-3

• Go as low as you feel comfortable with, even if this means going below 40%.

iv. Operational intervention

• In case there are control related issues, e.g. instabilities, oscillations, etc., the same must be attended.

v. Final automation

Before proceeding with the minimum load operation for the entire day, additional automation will be required, e.g. - automatization and optimization of steam supply to boiler feed pumps. This would include the following:• Switchover of boiler feed pump

• Stunning and/or additional logic of controls for lower load operation

• Load-dependant set points

• Automatic start and stop of fans, pumps, mills etc.

vi. Data acquisition

To establish the as-is functional performance details of the respective units of the TPPS considered for the test run, one can rely on the existing system for data acquisition. However, it can also rely on the archive files from the existing DCS (or PI or any other system). The data acquisition will allow to understand and record the performance deviations happen during the test runs.

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The preparedness for conducting test runs essentially would involve capturing inputs from plant operating history. This would include but not limited to the following information

i. General Description of the Plant:

The methodology proposed below is considered for a typical Unit having coal firing boiler of 500 MW capacity. The proposed methodology can vary from plant to plant and has to be customized or modified slightly as per the design, make, vintage, fuel characteristics of the unit. However, the broad principles will remain the same.

Plant description:Station: Unit No: Capacity –

Basic Design: Boiler: Controlled circulation with single drum, Directly fired by pulverized coal, Dry-Bottom, Radiant Reheat, Single Drum, Top Supported, Dry bottom, Manufactured by BHEL (CE Design), Tilting tangential firing Fuel Indian coal from different sources

Coal Mills

• Number of mills in operation:• Air flow per mill. t/h• Air temperature inlet

Mill outlet temperature

• Fineness % (through 70 200 mesh)• Burner tilt, deg

ii. Coal mill combinations for flame stability:

For base load operation of typical 500 MW design, the operation of six burner levels is usually sufficient. As per experience in some of the units, in part load the mills of burner levels B to F are used for a more stable operation. This was discovered by trial and error with different mill combinations. Two adjoining mills per burner level have to be in operation. Due to possible coal mixture inconsistency, flame stability problems may be observed.

iii. Drum Level controls:

The drum level control might cause problems. Auxiliary steam source is to be used while “ramping up” and while ramping down, the control is to be done manually.

iv. Fans:

With respect to part load, the ID fan causes no problems, No problems foreseen for FD fans. Typically, the primary air fans (2 x 50 percent) are not equipped with frequency control, but with blade pitch control. The switch from two fans to one fan in part load causes problems when one fan needs to be shut down. There can be problem of fan stalling

v. Boiler Feed Pumps:

A typical 500 MW (BHEL) units is equipped with one motor-driven und

6. Detailed Information of the target Unit

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two steam-driven Boiler Feed Pumps (BFP). The plant can be operated with one steam-driven BFP up to a load of approximately 300 MW. During normal operation of the power plant units, the 2 x 50 percent steam-driven BFPs are used. Usually the steam-driven BFPs are supplied by steam from an extraction line. The valves in the steam pipe to the BFPs are controlled by turbine speed (RPM). The valves open further when the speed decreases. At a certain value (when the valve is almost wide open) the steam supply is switched to a different steam source. A valve opens the auxiliary steam supply, which can be fed by the Cold Reheat line (or the auxiliary steam header, in which all other units deliver steam). The change usually occurs for unit loads below 70 percent. Especially during start-up procedure, problems can be observed regarding the stability of pressure and temperature in the supply steam.

For a load below 70 percent two BFP have to be used in parallel. The changeover in the steam supply for the steam-driven BFPs has to be improved with respect to reliability (typically problems with stability of flow and pressure decrease).

vi. Main Turbine:

Typical Turbine Specifications-Nominal rating 500 MW, Load 524.2 MW (VWO – valves wide open), Single-flow HP turbine, double-flow IP- and LP turbine, Manufactured by BHEL – KWU design

vii. Cooling Water System:

In a typical 500 MW unit, the cooling is maintained in a closed cycle with natural draft cooling tower. The following parameters have an influence (and limitation on part load operation):

viii. Others:

• Evaporator stability, ECO Stability/steaming, drum behaviour

• Combustion behaviour (stability of flame, effectivity, aerodynamic, permissible emissions, burner supported fuel: e.g. oil)

• Coal specification (mill operation)

• Boiler outlet parameters (HP/HRH temperatures, control systems, flue gas dampers, active burning levels in operation, attemperators etc.)

• Feed water parameters

• Air Preheater, dew point

• Flue gas cleaning system (effectivity)


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Plant level technical capabilities and liabilities• Availability of design/operation

documents/information• Boiler pre-assessment report• Investigation of the current

situation of the boiler/steam turbine. Investigations of problem/restrictions for static and dynamic operation and damage of boiler elements (tubes, header, pipes, valves, burners, vessels etc.):

• Operating experiences full/part load for several ambient conditions,

• Boiler inspections report if available. • Records of Technical problem

descriptions and interventions:• Warning and/or trips of boiler

(water/steam side, flue gas side) in the past

• Stability and steam temperature in evaporator,

• Drum level stability (water swell) during normal operation, load change, start-up

• Steaming of HP economizer• Boiler vibration (flue gas side)• HP Drum “carry-over” curves• HP/RH steam temperature

control (desuperheater) during start-up and operation

• Steam side corrosion• Flue gas corrosion (high/low

temperature)

• Mechanical design of HP/RH Superheater and Drum

• Safety and control valves etc.• Problems with specific components?

Components changed, improved or re-designed?

• Experience with slagging, fouling or corrosion on the flue gas side

• Experience with less power performance of the boiler/steam turbine?

• Life time loss of the main components (Steam pressure part Lines, Headers) if available

• Evaluation of the aging of the equipment

• Checking records of protections and interlocks, control system,

• Determination, which mills to use in the test. This depends on actual coal quality and operation experience with former tests as well based on mill operation diagrams. Since probably at least two mills will be in operation, the tests will be conducted without supporting fuel (fuel oil).

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7. Test targets

i. The test procedure includes 3 main parts:

• Reduce Min stable load (First current Target: Minimum technical limit of 55% without hardware invest) and then to 40%.

• Faster load Ramp up/Ramp down between new/old min load and base load (1,2 &3 % / min).

• Check of sliding pressure curves based on influence for steam generator

ii. The test target includes:

• Boiler pre-assessment. Investigation of current situation with boiler/steam turbine. Possible evaluation of aging of equipment. Check of control system, measurement, staff skill

• Identifying of the process limitations/restrictions (thermal, mechanical, aerodynamically, operation) during the new/old min load

• Collecting measurement data for calibration of thermal models for

boiler/steam turbine/BOP for further boiler thermodynamic analyze

• Boiler and steam turbine curves (water/steam cycle, coal, air, flue gas) for actual new/old load Ramp up/Ramp down for life time consumption investigations and for release the new boiler/steam turbine margins. Collecting measurement data

• Identifying of the process limitations/restrictions (thermal, mechanical) during the new/old Ramp up/Ramp down

• First impression about feasibility of flex retrofit for this plant “Go/No-Go”

• Definition of first measures which are needed to be implemented for this upgrade

• Determination of the operating range of one coal mill (what is the minimum flow rate per mill with a stable flame) by trial operation of minimum loading of coal mills. Test the minimum load of an individual mill: During the test special attention will be paid to control the behavior of the primary air temperature and

Figure 3: Test Target

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flow to fine tune the control loop of the mill (especially the primary air curve). These tests are to be performed step by step to reduce coal loading with minimum level of primary air. Simultaneously dirty pitot tests are to be conducted to monitor coal air mixture velocity within a reasonable limit around 25m/sec to avoid settle down of coal mixture in PC pipe and to avoid the condition of lean air mixture entry inside the furnace. At the same time mill outlet temp between 75-80 deg C to be maintained for low VM Indian coal.

• Review of

• Primary Air Flow Curve • Fuel air mix (to determine the

safe limits of “too lean and too rich mixture” as per combustion engineering.

• Coal pipe balancing at different mill loading- any balancing intervention required?

• Mill out temperature and control (within limits).

• Changes observed in flame intensity

• Matching mill loading with changes in furnace temperature profiles.

• Which mill /mill combination gives the most stable regime?

• Establish the mill cut out points v/s Load (Figure 4)

Figure 4: Establish the mill cut out points v/s Load


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8. Test Description

Test of new stable part load case

i. The test sequence:

• The boiler should operate in baseload with 2h w/o any operation change. Then the measurements (s list below) should be recorded.

• The boiler should operate in actual min load with 2h w/o any operation

change. Then the measurements (s list below) should be recorded.

• Stepwise decrease of actual min load at 55% to min achievable load (e.g.: 40%) every 1-2%-point, then 1,5 - 2 h stabilization of parameters and collecting of necessary data/information. If no instabilities, load can be reduced further. The control system may be operated manually if necessary.

Important Note on Necessary Precautions:The boiler should be operated based on existing manual/design handbook and safety rules.• The boiler main operation settings

(e.g. air excess ratio) should remain close to design value for actual min load. The change of values should be done if necessary, after risk and benefit analysis. The OEM may be consulted for any such change.

• If necessary, the test should be interrupted if the safety of boiler system is at risk.

• Preferred operation procedures shall include all expected operating modes of the boiler as operation with available coal with and w/o sliding pressure.

• The control setting of boiler systems (burner/combustion, coal milling and drying, APH, temperature and pressure control, drum level control etc.) may be out of operation/control range. If necessary, the control systems should be switched on manual mode (e.g. attemperator / steam temperature control).

• If necessary, after each part load step the combustion should be tuned

(stability, emissivity, equal steam temperature distribution – platen SH). The coal preparation system, APH etc. should also be tuned if necessary.

• No modifications, which can have the influence to safety of boiler, are allowed during, in-between, or after Test. All of boiler / plant protection should be activated.

• If necessary (instable operation behavior, danger of activation of boiler protection) the test should be interrupted.

• Preferred operation procedures shall include all expected automatic operating modes of the boiler as operation with available coal.

• Soot blower cleaning system should be operated in normal mode.

It might be necessary to temporarily increase the load slightly high, if instabilities are becoming too dangerous for operation. When instabilities cannot be eliminated, go back to last safe load. Depending on which instabilities occur, determine whether to adjust burner tilt, change mills, adjust pressure set point, adjust set point burner tilts, air to mills, air to burner etc., and repeat to lower load.

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ii. Conducting the Test RunA typical example for 500 MW BHEL tangential fired boiler (For other units the procedure may be customized accordingly)

a) Ramp down test @1% from full load to tech min load:

With 1 % ramp up rate in 15 min time( 5MW/MIN) load may be reduced to 425 MW with 6 mills in service from full load and then one mill ( top one) is to be cut out and is to be stabilized in next 15 min for further ramp down to 350MW . Then 5th mill is to be cut out for further lowering to 275 MW. Thus, the time required for ramp down is 75 min mainly due to milling system intervention. During these ramp test important parameters like MS/HRH temp, SH/RH metal temp, drum level, furnace draft and load achieved during each ramp are to be noted.

The ramp rate will be 1% and on sliding pressure mode operation Stabilize the unit load at full load with 6 mills. • Give the load set point of 425 MW. • Start reducing the mill loading of

bottom most mill gradually to meet firing demand with 5 mills and cut out the mill.

• Stabilize the unit around 425 MW. • Give the next load set point of 350

MW. • Start reducing the mill loading of

top mill preferably till the mill is completely unloaded. Trip the mill.

• Stabilize the unit around 350 MW with 4 mills

• Give the load set point of 275 MW and stabilize with 4 mills in service.

The parameters and load achieved are to be logged for further fine tuning the auto loops.

b) Ramp up test @1% from tech min to full load:

As mentioned above from 275MW to full load ramp up test @1% ( 5MW/MIN) is to be carried out with manual intervention of cutting in mill at 350 MW and 425 MW load respectively. c) Ramp test @3% from full load to tech min load (55%):

The same ramp down test @3% can be undertaken with sliding pressure mode operation with manual intervention and stabilization followed by milling cut out. The time and desired MW target can be logged and time to complete the test run may be evaluated at the end.

d) Slow ramp down to min load operation:

• Gradually mill loading may be reduced and 3 mills operation may be resorted at 230 MW of load finally all 3 mills are to be continuous ( C,D,E or D,E,F ).

• Observe flame intensity, its performance likely to be improved with 3 mills operation with respect to 4 mills.

• One TDBFP recirculation valve may be kept open and both pump should deliver running at around 3500 RPM.

• With 3 mills in service almost in full load (150 TPH in 3 mills) with around 110 TPH of PA flow in each mill.

• PA header pr of around 800 mm wc is to be maintained with around 350 TPH of air flow to prevent any incidence of stalling of fans.

After stabilisation at 200 MW load, continue operation at same load for more than 1 hr to take parameters for determining heat rate and Aux power of the units at such low load.


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Simultaneously in all coal pipe air coal mixture velocity may be measured with ISO kinetic sampling and coal sampling may be carried out for mill fineness and for proximate analysis.

e) Slow ramp up to 275 MW and upto full load @3%:

After successful minimum load operation slow ramp up to the mandated tech min load (55%) with one mill cut in through manual intervention and stabilise operation at 275 MW load with 4 mills in service. The unit should be run with both TDBFP in service with Recirculation valves closed condition. The machine should be ready for 3% ramp up upto 500 MW in similar sequence as it was done with ramp down operation like ramp up in staircase of 75 MW (In 5 MIN) with manual intervention of cutting in mill at 350 MW and 425 MW load.

During the entire period the important parameters logging is to be prepared as per sequence of different types of operation and same will be analysed subsequently for finding root cause of deviation if any and for further recommendation.

For stepwise procedure refer to Annexure-2

iii. Test of Last Ramp up/Ramp down between new and old min load with new and old last ramp transient

The test sequence:

a) The boiler should operate in new achievable min load with 2h w/o any operation change. Then the measurements (s list below) should be recorded.

b) Load Ramp up/Ramp down between new and old min load with old load transient (5 MW/min) with 1% ramp. The wall temperature margins of boiler for superheater HP/RH and HP Drum steam turbine may be deactivated only for the test, and then activated again. The ramps may be repeated. Collecting of necessary data/information based on list.

c) Repeat test sequence 2 with 10 MW /Min (2% Ramp)

d) Repeat test sequence 3 with 15 MW/Min (3% Ramp)

e) Load Ramp up/Ramp down between new min load and baseload with old load transient (5 MW/min) and new sliding pressure curve (e.g. 40 to 70% rel. load). The wall temperature margins of boiler for superheater HP/RH and HP Drum and steam turbine may be deactivated only for the test, and then activated again. Sliding pressure curve should be implemented. The ramps may be repeated. Collecting of necessary data/information based on list

f) Load Ramp up/Ramp down between new min load and baseload with new load transient (10/15 MW/min) and new sliding pressure curve (e.g. 40 to 70% rel. load). The wall temperature margins of boiler for superheater HP/RH and HP Drum steam turbine may be deactivated only for the test, and then activated again. Sliding pressure curve should be implemented. The ramps may be repeated. Collecting of necessary data/information based on list

At new min load according to with new sliding pressure curve the “Approach Point” should be checked (in order to prevent steaming in the Economizer). If at this point of operation there still is a sufficient margin, the IP valves at the

24


turbine could be throttled (which would increase the reheat pressure and thus the final feed water temperature) until there

is no margin left and steaming in the Economizer starts

System Risk description and evaluation

HP Economizer system

The partial steaming of Economiser and hammering may occur. These events are allowed for short time. If intensity increases, the test should be interrupted. The risk with damage of pipe and tubes is very low. The increase of cycle life time fatigue consumption due to increase of load transient is marginal.

HP Evaporator system

The risk with damage of pipe and tubes is very low. The hammering may occur. These events are allowed for short time. If intenseness of that will increase the test should be interrupted. The drum water level may achieve high and low levels and may be instable and fluctuated. The control setting of drum level control system may be out of operation/control range. Manual operation of drum level control system and tuning are necessary. The temperature/pressure margins of boiler should be deactivated. The increase of cycle life time fatigue consumption due to increase of load transient is marginal

For the test in sliding pressure operation the carry-over may occur. The long-term effect is very small. Further investigations will be necessary.

HP/RH superheater system

Material/steam temperature and temperature difference between parallel outlet pipes can increase. The risk with damage of pipe and tubes are very low. If steam temperature (as well as temperature difference) will achieve the design limit the test should be interrupted. Because the operation pressure will remain or will decrease based on sliding pressure curve the risk with creep life time consumption with temperature will not change. The attemperator control system may be instable and fluctu-ated. The overspray/overheating can occur. The control setting of tem-perature control system may be out of operation/control range. Manual operation of attemperators control valves and tuning are necessary.

The temperature/pressure margins of boiler should be deactivat-ed. The increase of cycle life time fatigue consumption due to increase of load transient is marginal.

Combustion(Burner)

The minimum burner level may switch out (preferred bottom burner level). The operation of burner can achieve. If necessary the vibration/combustion instability, demolition of flame, increase of emission (CO, dust) may occur. These events are allowed for short time. If intenseness of that will increase the test should be interrupted.

The control setting of burner control system may be out of operation/control range. Manuel operation of combustion control system and tuning are necessary.The risk with damage of burner systems is very low.

iv. Risk Identification


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System Risk description and evaluation

Coal preparation (Coal milling/drying)

The mils operation restrictions (vibration/instability in milling and coal/air stream, mechanical restrictions, operation behaviour for part load) may occur. These events are allowed for short time. If intenseness of that will increase the test should be interrupted. Manual operation of coal preparation control system and tuning are necessary.

The control setting of mill control system may be out of operation/control range. Manual operation of mill / coal feed control system and tuning are necessary. The min operation of mill can achieve. The stream behaviour of coal/air mixture to burner may be changed and out of operation range. The aerodynamic disturbances and negative impact to combustion may occur

The risk with damage of equipment is very low.

APH (Air part)

The air preheating operation restrictions (vibration/instability, mechanical restrictions of fans primary, secondary, temperature operation behav-iour for part load) may occur. These events are allowed for short time. If intenseness of that will increase the test should be interrupted. The control setting of air control system may be out of operation/control range. Manual operation of air preheating control system and tuning are necessary.

The risk with damage is very low.

Flue gas system

The flue gas operation restrictions (vibration/instability, mechan-ical restrictions of fan, dew point, temperature operation behaviour for part load) may occur. These events are allowed for short time. If intense-ness of that will increase the test should be interrupted. The control setting of flue gas/filter control system may be out of operation/control range. Manual operation and tuning are necessary.

The risk with damage is very low.

HP turbine HP inlet: margins for shaft and casing margins might be exceeded ; low risk for small number of eventsHP exhaust temperature may increase depending on IP-valve position low risk if HP exhaust < 400°C

IP-turbine No additional risk identified

LP-turbine No additional risk identified

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Annexure-1List of tests:

1.1. Load ramp down tests at 1% per minute from full load to 60% load

1.2. Unit operation at 60% load

1.3. Load ramp down tests at 1% per minute from 60% load to 40% load


1.5. Load ramp up tests at 1% per minute from 40% load to 60% load


1.7. Load ramp up tests at 1% per minute from 60% load to full load

1.8. Load ramp down tests at 3% per minute from full load to 60% load


1.10. Load ramp down tests at 3% per minute from 60% load to 40% load


1.12. Load ramp up tests at 3% per minute from 40% load to 60% load


1.14. Load ramp up tests at 3% per minute from 60% load to full load

Annexure-2A. Step-wise Test procedure for load ramp down tests from full load to 60% load at 1% per minute (Target Time: 40 minutes) and 3% per minute (Target Time: 13 minutes):

2A.1. Stabilize the unit load at full load with 6 mills.

2A.2. Give the load set point of 450 MW.

2A.3. Start reducing the mill loading of bottom most mill gradually to meet firing demand.

2A.4. Stabilize the unit around 450 MW.


2A.6. Start reducing the mill loading of bottom most mill gradually till the mill is completely unloaded. Trip the bottom most mill.


Annexure


27


2A.9. Start reducing the mill loading of bottom most mill gradually to meet firing demand.



2A.12. Start reducing the mill loading of bottom most mill gradually till the mill is completely unloaded. Trip the bottom most mill.


B. Step-wise Test procedure for load ramp down tests from 60% load to 40% load at 1% per minute (Target Time: 10 minute) and 3% per minute (Target Time: 3 minutes):

2B.1. Stabilize the unit load at 60% load with 4 mills.

2B.2. Give the load set point of 250 MW.

2B.3. Start reducing the mill loading of all mills gradually with higher unloading of bottom most mill to meet firing demand.

2B.4. Manually switchover to single BFP operation as further load ramp down is taken up.

2B.5. Maintain both PA Fans in service, if fans are operating near to their stall zone then manually switchover to single PA Fan operation as further load ramp down is taken up.

2B.6. Stabilize the unit around 250 MW.

2B.7. Give the load set point of 200 MW.

2B.8. Start reducing the mill loading of all mills gradually with higher unloading of bottom most mill to meet firing demand.

2B.9. Stabilize the unit around 200 MW.

C. Step-wise Test procedure for load ramp up tests from 40% load to 60% load at 1% per minute (Target Time: 10 minutes) and 3% per minute (Target Time: 3 minutes):

2C.1. Stabilize the unit load at 40% load with 4 mills and lesser loading in bottom most mill.

2C.2. Give the load set point of 250 MW.

2C.3. Start increasing the mill loading of all mills gradually with higher loading of bottom most mill to meet firing demand.

2C.4. Stabilize the unit around 250 MW.

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2C.5. Give the load set point of 300 MW.

2C.6. Start increasing the mill loading of all mills gradually with higher loading of bottom most mill to meet firing demand.

2C.7. Manually take second BFP also in service, if not taken earlier, and balance both BFP.

2C.8. Manually take second PA Fan in service, if not taken earlier, and balance both fans.

2C.9. Equalize loading of all mills.

2C.10. Stabilize the unit around 300 MW.

D. Step-wise test procedure for load ramp up tests from 60% load to full load at 1% per minute (Target Time: 40 minutes) and 3% per minute (Target Time: 13 minutes):

2D.1. Stabilize the unit load at 60% load with 4 mills.

2D.2. Take the fifth mill in service (preferably adjacent to mills already in service and topmost amongst the standby mills) with minimum loading and allow the mill to stabilize.

2D.3. Give the load set point of 350 MW.

2D.4. Increase the mill loading of fifth mill gradually to meet firing demand. Simultaneously adjust the mill loading of other four mills to meet firing demand and till the time fifth mill is sufficiently loaded and stabilized.

2D.5. Stabilize the unit around 350 MW.


2D.7. Increase the mill loading of fifth mill gradually to meet firing demand. Simultaneously adjust the mill loading of other four mills to meet firing demand and till the time fifth mill is sufficiently loaded and stabilized.

2D.8. Stabilize the unit around 400 MW and equalize the mill loading.

2D.9. Take the sixth mill in service (preferably adjacent to mills already in service and topmost amongst the standby mills) with minimum loading and allow the mill to stabilize.


2D.11. Increase the mill loading of sixth mill gradually to meet firing demand. Simultaneously adjust the mill loading of other five mills to meet firing demand and till the time sixth mill is sufficiently loaded and stabilized.

2D.12. Stabilize the unit around 450 MW.


2D.14. Increase the mill load of sixth mill gradually to meet firing demand. Simultaneously adjust the mill loading of other five mills to meet firing demand and till the time sixth mill is sufficiently loaded and stabilized

2D.15. Stabilize the unit at full load and equalize the mill loading.


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Plant Name /XXXX TPP - XXX MW

Plant Type Sub critical

Notes:

1. All data required for every 15 seconds for the following conditions:• Load ramp-down from 100% load to 40 % load (with ramp rate of 1

% per min.)• Load ramp-up from 40% load to 100 % load (with ramp rate of 1 %

per min.)• Load ramp-up from 40% load to 100 % load (with ramp rate of 3 %

per min.)• Load ramp-down from 100% load to 40 % load (with ramp rate of 3

% per min.)2. Mills cut in/off time is required during the load ramp up/down.

Sl.No Parameter Unit

1 Unit Load MW

2 Target Load MW

3 Ramp Rate for Load Variation %

4 No. of Mills Nos.

5 Mill combination

6 Oil Firing - Elevations

7 MS Flow TPH

8 Economiser I/L Flow TPH

9 SH Spray Flow (L&R) TPH

10 RH Spray Flow (L&R) TPH

11 Burner Tilt demand & feedback %

12 O2 at Economiser Outlet (L&R) %

13 Hot Secondary Air Flow (L&R) TPH

14 Total Air Flow TPH

15 Total Coal Flow TPH

16 SHO Pressure kg/cm2(g)

17 Drum Pressure kg/cm2(g)

18 Drum Level mm

19 CRH Pressure kg/cm2(g)

20 HRH Pressure kg/cm2(g)

21 FW Pressure at Economiser Inlet kg/cm2(g)

22 FW Temp at Economiser Inlet DEG C

23 FW Temp at Economiser Outlet DEG C

Annexure 3: List of Parameters for load change & ramps.

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24 Drum O/L Temp DEG C

25 LTSH I/L Header Temp (L&R) DEG C

26 LTSH O/L Header Temp (L&R) DEG C

27 SH PANEL I/L Header Temp (L&R) DEG C

28 SH PANEL O/L Header Temp (L&R) DEG C

29 SH PLATEN I/L Header Temp (L&R) DEG C

30 SH PLATEN O/L Header Temp (L&R) DEG C

31 FINAL SH I/L Header Temp (L&R) DEG C

32 FINAL SH O/L Header Temp (L&R) DEG C

33 Economiser O/L Flue Gas Temp (L&R) DEG C

34 PAPH I/L Flue Gas Temp (L&R) DEG C

35 PAPH O/L Flue Gas Temp (L&R) DEG C

36 SAPH I/L Flue Gas Temp (L&R) DEG C

37 SAPH O/L Flue Gas Temp (L&R) DEG C

38 Secondary Air APH O/L TEMP DEG C

39 Primary Air APH O/L TEMP DEG C

40 Furnace Pressure mmwc

41 Windbox to Furnace DP (L&R) mmwc

42 Hot Primary Air Header Pressure mmwc

43 Individual Mill Air Flow TPH

44 Individual Mill Outlet Temperature DEG C

45 Individual mill HAD opening %

46 Individual mill CAD opening %

47 Individual Mill fineness % thru 200 mesh

48 Individual Mill fineness % thru 50 mesh

49 MTM Thermocouples reading

a Drum DEG C

b Final SH DEG C

c Final RH DEG C

50 Proximate Analysis of Coal - As fired basis

a Fixed Carbon % by Weight

b Volatile Matter % by Weight

c Moisture % by Weight

d Ash % by Weight


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e HHV kcal/kg

51 Flame intensity for all elevations %

52 SADC deamd & feedback for all elevations %

53 Main Steam Pressure at Turbine Inlet (L&R) kg/cm2(g)

54 Main Steam Temperature at Turbine Inlet (L&R) DEG C

55 First stage Pressure kg/cm2(g)

56 HPT Exhaust Pressure kg/cm2(g)

57 HPT Exhaust Temperature DEG C

58 Hot Reheat Pressure at IPT inlet (L&R) kg/cm2(g)

59 Hot Reheat Temperature at IPT inlet (L&R) DEG C

60 Extraction-5 pressure at turbine end kg/cm2(g)

61 Extraction-5 temperature at turbine end DEG C

62 IPT Exhaust / LPT inlet Pressure kg/cm2(g)

63 IPT Exhaust Temperature DEG C

64 Extraction-3 pressure at Turbine end kg/cm2(g)





69 Extraction-1 temperature at Turbine end DEG C

70 Condenser vacuum kg/cm2(g)

71 Speed RPM

72 LPH-1 Inlet Temperature DEG C

73 LPH-2 inlet Temperature DEG C

74 LPH-3 Inlet Temperature DEG C

75 LPH-3 outlet/ Deaerator Inlet Temperature DEG C

76 Condensate Pressure at Deaerator Inlet kg/cm2(g)

77 Deaerator shell pressure kg/cm2(g)

78 Deaerator shell temperature DEG C

79 BFP suction Temperature DEG C

80 BFP Suction Pressure kg/cm2(g)

81 HPH-5 inlet Temperature DEG C

82 HPH-5 inlet Pressure kg/cm2(g)

83 HPH-5 outlet Temperature DEG C

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84 HPH-5 outlet Pressure kg/cm2(g)

85 HPH-6 outlet Temperature DEG C

86 HPH-6 outlet Pressure kg/cm2(g)

87 Final Feed water Inlet Pressure kg/cm2(g)

88 Final Feed water Temperature DEG C

89 HPT Casing Temperature DEG C

90 HPT shaft/Rotor Temperature DEG C

91 Main Steam Valve casing Temperature DEG C

92 IPT Casing Temperature DEG C

93 IPT Shaft / Rotor Temperature DEG C

94 IP Valve casing Temperature DEG C

95 X-Criteria satisfied (Yes/ No) – X1, X2 , X3, X4, X5, X6 and X7

96 TSE Parameter

97 Bearing Vibrations (At all bearings including generator) mm/sec

98 Shaft Vibrations mm/sec

99 Lube oil Temperature at Bearing DEG C

100 Axial shift value mm

101 Differential expansion value mm

102 Position of HP and LP Bypass valve- (valve opening) %

103 Position of HPCV and IPCV-(valve opening) %

104 Generator Parameters

a Voltage V

b Current A

c Power Factor

d H2 pressure kg/cm2(g)

105 No. of TDBFP in service

106 No. of CEP in service

107 Deaerator Level mm

108 Hotwell level mm

109 Back Pressure kg/cm2(g)

110 CW Inlet Temperature DEG C

111 CW Outlet Temperature DEG C

112 CEP Discharge Pressure kg/cm2(g)

113 CEP Discharge Temperature DEG C


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114 CEP Discharge Flow TPH

115 BFP Discharge Pressure kg/cm2(g)

116 BFP Discharge Temperature DEG C

117 BFP Discharge Flow TPH

118 BFP Suction Flow TPH

119 Status of BFP recirculation valve

120 Condensate flow to D/A TPH

121 Throttle Pressure Set point kg/cm2(g)

120 Water Chemistry parameters at following locations:

a Hotwell

b CEP Discharge

c CPU Outlet

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a Feedwater

b Drum

c Saturated Steam

a Main Steam

123 SH Spray Valve demand & feedback %

124 RH Spray Valve demand & feedback %

125 PAPH I/L Flue Gas Pressure (L&R) mmwc

126 PAPH O/L Flue Gas Pressure (L&R) mmwc

127 SAPH I/L Flue Gas Pressure (L&R) mmwc

128 SAPH O/L Flue Gas Pressure (L&R) mmwc

129 SAPH I/L Pressure mmwc

130 SAPH O/L Pressure mmwc

131 PAPH I/L Pressure mmwc

132 PAPH O/L Pressure mmwc

133 PA Fan Discharge Pressure (L&R) mmwc

134 PA Fan Suction Pressure (L&R) mmwc

135 ID Fan Discharge Pressure (L&R) mmwc

136 ID Fan Suction Pressure (L&R) mmwc

137 FD Fan Discharge Pressure (L&R) mmwc

138 FD Fan Suction Pressure (L&R) mmwc

139 PA Fan Blade Pitch Demand & Feedback (L&R) %

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140 FD Fan Blade Pitch Demand & Feedback (L&R) %

141 ID Fan VFD Demand & Feedback (L&R) %

142 PA Fan Discharge Temp (L&R) DEG C

143 PA Fan Suction Temp (L&R) DEG C

144 ID Fan Discharge Temp (L&R) DEG C

145 ID Fan Suction Temp (L&R) DEG C

146 FD Fan Discharge Temp (L&R) DEG C

147 FD Fan Suction Temp (L&R) DEG C

148 Ambient Conditions (RH, Temperature) DEG C

149 O2 at APH Outlet (L&R) %


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Annexure 4: FAQs

These FAQs are based on the previous information available from the utilities:

Question: Is there any SH & RH side temperature difference observed?

Answer: During normal running of the Units there is not much difference between SH & RH Steam Temperature. However, during abrupt change of load due to imposing or lifting of back down or Coal interruption to the furnace, due shear pin failure or overload tripping of RC Feeder.

Question: Does the Boiler operate in pure sliding pressure operation or Constant Pressure operation? Can the boiler operate purely on sliding pressure mode?

Answer: Boilers at Thermal Plant mainly operation in sliding pressure mode as Pressure master control in all the Units is non-functional

Question: What are the common limiting factors?

Answer: The following aspects were given as the most limiting factors preventing the minimum load being reduced further:

• Flame intensity/combustion at low load if specific coal is less than 0.6

• Less PA flow resulting in PA fan operation near stalling zone

• Low extraction pressure resulting in BFPs changeover to ACV mode (ACV means cold re-heat as steam source for auxiliary steam). Drum level control is not smooth when BFPs are in ACV mode

• Low feed water flow resulting in BFPs recirculation valves being open

• High MS HP temperature, high spray and low HRH temperature

To ensure the maximum possible reheater outlet temperature during the planned low load operation in future, the upper burner levels should be investigated, namely mill H, J and K . At low load, the deviation between actual behavior and design of HRH needs to be investigated. In particular, the interaction of the tilting burners in conjunction with the spray type (water) attemperators, especially between the re-heater heating bundles, should be thoroughly investigated and modified, if applicable.

About Greening the Grid ProgramUSAID’s Greening the Grid (GTG) is a five-year program implemented in partnership with India’s Ministry of Power (MOP) under the USAID’s ASIA EDGE (Enhancing Development and Growth through Energy) Initiative. The program aims to support the Government of India’s (GOI) efforts to manage the large-scale integration of RE into the grid and combines the following three components which interact with each othe.

USAID/India Renewable Integration and Sustainable Energy (RISE) InitiativeDeloitte Consulting LLP503-504, Fifth Floor, DLF Place Mall Office Block, Saket, New Delhi - 110017Tel: +91-11-4045-0737/38www.gtg-india.com

ADDRESS

CONTACTMonali Zeya HazraSenior Clean Energy SpecialistUSAID/IndiaEmail: [email protected]

Tushar SudChief of PartyUSAID GTG-RISE InitiativeEmail: [email protected]

MINIMUM LOAD/RAMP TEST PROCEDURE FOR COAL BASED … · 2020. 4. 27. · Thermal Power Plants (TPPs)...

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Transcript of MINIMUM LOAD/RAMP TEST PROCEDURE FOR COAL BASED … · 2020. 4. 27. · Thermal Power Plants (TPPs)...