The outlet tube from the bubble jar carries the cooled and cleaned gas sample and is routed to a copper coil condenser kept in an ice bath (a bucket filled with chilled water). The condenser condenses the water vapor out of the gas sample. It has a coil for the gas to pass through along with a small container at the bottom to collect any condensed water. The collected water can be removed after completion of each test by disconnecting the condenser tubing.

The sample from the condenser is routed to a desiccant column to remove any water vapor that got through the condenser. The desiccant could be CaSO4 or silica gel or a similar regenerative type moisture absorbing anhydrous chemical. The purpose is to ensure that the gas sample is completely dry by the time it leaves the condenser. The column containing the desiccant is glass or plastic, transparent enough to observe the change in color of the desiccant on moisture absorption. Generally the desiccant is sent to labs for regeneration when a little over half the column has been exhausted.

The outlet of desiccant jar is connected to a vacuum pump, which pulls the sample out of the duct, and through the preceding stream. The pump discharge is routed to the gas analyzers through a flowmeter.

The temperatures are measured at the same locations where the flue gas sample is extracted, using K type thermocouples. The temperatures can be noted manually and averaged. When using data scanning software, all the thermocouple signals are brought together using networking cables and datascan boxes (used for analogue to digital conversion) and routed to a computer for data storage and analysis. A major advantage of using an a data acquisition and analysis software is that the test conditions and results can be monitored on line, while the test is actually in progress. Changes required if any or the manual inputs can be fed in and test runs recomputed at a later stage.

4.5.2Unburned in Flyash at Economizer Outlet

There are various methods that can be used for fly ash sampling namely isokinetic fly ash sampling, high volume fly ash sampling, and sampling from the air heater, economizer, or precipitator hoppers. Isokinetic sampling involves extracting flyash at the same rate at which the gas is flowing at measurement section and this requires special apparatus. On the

other hand, the sample obtained from a hopper shall not be representative of the duct as the carbon in fly ash is generally of a different weight than the other constituents of fly ash and is not evenly distributed.

A convenient method for flyash sampling involves removing fly ash from the gas stream using a High Volume sampling probe at economizer outlet on both sides of the boiler. The flue gas is sucked using a probe with an air aspirator and passed through a cylinder containing filter paper that catches the fly ash in collection canister. One probe each is traversed on either side simultaneously during the test and the sample collected at pre-determined points. Sampling bags or bottles are used to store the flyash sample till it is sent to the test laboratory where the % LOI is determined per ASTM D3174.

4.5.3Coal and Bottom Ash Sampling

Coal sampling is done manually from inlet chutes of all running feeders every 20 minutes during the test and a representative sample prepared from the gross sample collected by quartering and coning. A separate incremental sample is collected for determination of total moisture and kept in a sealed container. Bottom ash sample is collected after completion of the test from the Bottom ash hoppers’ disposal line at Ash Slurry discharge end. Incremental samples are collected every 5 minutes from each of the disposal line till the flushing is complete to form a gross sample. Bottom ash sample from scrapper system is collected during test period every twenty minutes.

4.6Prerequisites

4.6.1Traverse Specifications

4.6.2Test Ports in Flue Gas Duct for Boiler Performance Tests

Test ports at AH inlet and outlet in flue gas duct are made as per ASME PTC 19.10 to install a multi point flue gas monitoring system for sampling for the boiler performance test. The grid so installed provides a means of determining an oxygen and carbon monoxide profile for strategically placing the single point monitoring probes at the point that would provide the most representative sample of the weighted average of all the points. ASME PTC 19.10 Sections 3.02.4 and 3.02.5 discuss in detail, how to

determine how many sample locations are required and their locations. The following points need be noted while selecting the traverse locations.

a)The gas inlet traverse plane should be located as close as possible to the air heater inlet.

b)The air inlet traverse plane should be located after any air heating coils and as close as possible to the air heater inlet. Since the entering air temperature is typically uniform, it may be possible to reduce the numbers of traverse points. A trial traverse can be made to provide data to support this decision.

c)The gas outlet traverse plane should be located as far downstream from the air preheater as possible, to allow mixing of the flow to reduce

temperature and 02 stratification. However, it should not be located downstream of other equipment or access ways that might contribute to air ingress (e.g. Mechanical collectors, ESP’s, manholes, or ID fans).

d)The air outlet traverse plane should be located as far downstream from the air heater as possible to allow mixing of the flow to reduce the temperature stratification.

Sampling

Locations

APH

FG

Figure 4.

Location of sampling points and test ports.

It is recognized that many duct designs cannot conform completely to the guidelines in the code. In cases, where there are major differences between the existing port configuration and the code guidelines, testing must be performed to demonstrate the repeatability of the existing ductwork configuration.

For insertion of High Volume Sampler for fly ash sampling, 100-mm dia flanged openings are made at Economizer outlet on both sides. Approximate location is indicated in the sketch.

4.6.3Special Test Instruments

The special test instruments required for this test should be assembled and their operability verified before the test. The instrument calibrations

should be reviewed to verify that the calibrations are current. Any instrument whose calibration record is not available or has expired should be recalibrated.

4.6.4Station Instruments

The calibration records of the following station instruments should be reviewed and a reference to the permanent record of their calibration included in the test report. Any instrument whose calibration has expired should be recalibrated.

4.6.5Mills’ Performance Test

Pulverizer performance tests should be conducted in the two weeks prior to testing using Dirty Pitot performance kit to establish mill performance data vis. Capacity, PA flow, Mill Outlet temperature and PF fineness levels. Any deviations observed should be corrected and logged prior to Boiler tests.

4.6.6Miscellaneous

Gross efficiency of the boiler is calculated by heat loss method. The heat credits to be measured or assigned if not measured, the heat losses to be measured or assigned where not measured as well as permissible deviation in efficiency between duplicate test runs are defined in advance. The test personnel are identified and responsibilities allocated. Test conditions, no. of tests, duration of tests, basis of rejection of test runs, instruments to be used, methods of data collection whether manual or using a data acquisition software, corrections to be made for deviations from specified operating conditions – all these factors are decided prior to the tests.

4.7Test Instructions

Quality control will be accomplished by meeting the requirements of this procedure in the following areas:

a)Instrument calibration

b)Instrument operation

c)Unit operation (allowable fluctuations of critical measurements, defined operating constraints etc.)

d)Data taker qualifications and training

Quality assurance will be accomplished by meeting the documentation and evaluation requirements of this procedure and by independent review of test methods and results analysis. The following records will be maintained and referenced as part of the test report:

a)Calibration records; traceability

b)Station charts; unit stability

c)Original data sheets

d)Test log

4.7.1Unit OperationOperating Conditions of Test Runs

Test runs should be conducted at an easily repeatable level so that a test runs over a period of time are comparable. The operating conditions for each test run are as follows:

1.Prior to conducting the efficiency test, furnace wall blowers and the air heater sootblowers should be operated. However, the sootblowing cycle should be complete at least two hour before testing begins. This is to ensure roughly the same level of furnace cleanliness in all the tests.

2.Unit should be operating at steady test regime for last 2hours..

3.Main Steam pressure and temperature and Reheat Steam temperature should be set at design values.

4.Boiler O2 should be maintained at an optimum value based on the past database.

5.Ensure that steam coil air heaters’ steam supply is isolated and gas recirculation dampers if any, are tightly shut.

6.No sootblowing or mill change over should be done during the test.

7.Economizer hopper deashing or bottom hopper deashing should not be done during the test.

4.7.2Method of Verifying steady State Operation

The test director shall be responsible for ensuring that the unit has reached steady state condition before beginning a test run. It is important that the airflow, gas flow and boiler excess air remain constant throughout the test. In some cases it may be necessary to terminate a run prematurely because of inability to maintain one or more of the operating conditions at the desired value. Generally, the steam generator output should remain constant for about 60 minutes prior to beginning the test.

4.7.3Data Collection

No of test personnel required would vary with the number of measurement locations and the type of test set up. Use of a scanning software with networking amongst different locations increases the accuracy of the test results besides reducing the manpower requirement. The frequency of scanning of parameters collected through portable DAS installed for the test is generally 20 seconds.

4.7.4Test Duration and Frequency of Observations

Each test run should be conducted for a minimum of one hour, but as long as required for each test group to complete the required duct traverses. The frequency of control room data collection shall be 15 minutes. The control room data can also be collected through the existing DAS system on a specific log prepared for the tests. Two separate test crews should be working at the gas inlet and gas outlet ducts simultaneously to obtain the gas analysis data for the test period. The actual duration of test runs from which the final test data are derived must be stated clearly in the test report. Typical log sheets for various locations are attached as Annexures

4.7.5Data Verification

The test director should prepare and have available a set of design and historical test values. Comparison of the test values with the design and historical values should allow the detection of any gross measurement errors.

4.8Results

The losses listed in Section 4.1 are generally computed using a spreadsheet on a computer. A typical calculation of the losses is enclosed as Annexure. In this computation the losses / boiler efficiency has been recalculated using the design values of coal and design ambient conditions.

4.9Report

A formal report with a short executive summary that includes results, recommendations and any unusual findings must be prepared for every test. The test objectives should be listed, and test setup outlined with a brief on the test equipment used, their locations, measurement range etc. Also, its important to include a list of measured inputs, computations and the constants used or assumptions if any (such as the fuel cost or the reference air temperature, etc.)

The report should in addition to reporting results, also analyze the data to determine the causes and recommend possible corrective actions. Major deviations, if any, should be expressed in monetary terms as well apart from the absolute values.