A CO2 CEM system consists of the following four subsystems:
Specifications for these subsystems are contained in sections 3.1 to 3.6, while Section 3.7 outlines the procedures for determining the value of the parameters, where applicable. The parameters and specifications for these subsystems are shown in Table 1.
Table 1 Design Specifications for CO2 CEM Systems
| Subsystem | Parameter | Specification | Text reference | |
|---|---|---|---|---|
| Specification | Test Procedures | |||
| Sample interface and conditioning | Location of calibration ports | See Table 2 | 3.1.1 | - |
| Gas analyzer | Operating range | Average monthly concentration between 40% and 75% of full scale (FS) | 3.2.1 | - |
| Interference | <4.0% FS for the sum of all interferences | 3.2.2 | 3.7.1 | |
| Temperature-response drifts | Zero drift <2.0% FS for 10°C change (5–35°C) | 3.2.3 | 3.7.2 | |
| Span drift <4.0% FS for 10°C change (5–35°C) | 3.2.3 | 3.7.2 | ||
| Stack gas flow monitor | Operating range | Maximum potential flow rate equal to 100% FS | 3.3.1 | - |
| Data acquisition | Averaging time | 1 hour | 3.5.1 | - |
| Missing data | ≤168 hours – backfill >168 hours – alternative CEM system |
3.5.2 | - | |
| Overall system | System cycle time* | ≤15 minutes for complete cycle (15/n minutes for any one stream in an n-stream system) | 3.6 | 3.7.3 |
* This design specification applies only to the time-shared systems.
This reference method does not specify measurement techniques. Components that meet the criteria specified in sections 3.1 to 3.6 and that allow the overall CEM system to achieve the certification specifications in Section 5 and the performance evaluations in Section 6 are acceptable.
The location of the system calibration gas injection port is the sole criterion for the sample interface/conditioning subsystem, with the location of this port being specific to the type of CEM system. The location of the ports for the various types of CEM systems is shown in Table 2.
Table 2 Location of System Calibration Gas Injection Ports for Specific CEM Systems
| System Type | Subsystem | Specification for location of system calibration gas injection port |
|---|---|---|
| Extractive | Direct measurement of gas concentrations | Calibration gas must be introduced no further than the probe exit. |
| Dilution (in-stack and external) | Calibration gas must be introduced prior to dilution. | |
| In situ | Point | Calibration gas must flood the measurement cavity of the analyzer. |
| Path | Calibration gas must provide a check on the internal optics and all electronic circuitry. System may also include an internal calibration device for simulating a zero and an upscale calibration value. |
The chosen range of the analyzer must encompass all anticipated concentrations for the gas stream being monitored. The average monthly concentration of each analyzed gas must fall between 40% and 75% of the chosen full-scale (FS) range. If the average monthly concentration of CO2 or oxygen (O2) falls outside these limits, the analyzer must be adjusted such that the average is brought back within these limits.
Note that numerous performance specifications are defined with reference to the full-scale (FS) setting of the CEM analyzers (see Table 1, Table 3 in Section 5 and Table 5 in Section 6). The gas analyzer of a CEM system may be capable of measuring levels higher than the defined FS level; however, this higher level cannot be applied to demonstrate conformance to the performance specifications, which are tailored to the characteristics of the EGU.
The highest range must include the maximum potential concentration anticipated for the EGU. Note that data that fall outside the range(s) of an analyzer are considered as missing and must be backfilled using the criteria shown in Section 3.5.2.
Each analyzer must exhibit a response of less than 4.0% of FS for the sum of all interferences due to other gas constituents, as measured by the procedures provided in Section 3.7.1.
Each gas analyzer used in the system must exhibit a zero drift less than 2.0% of the FS setting for any 10°C change over the temperature range of 5 to 35°C. Additionally, each analyzer must exhibit a span drift of less than 4.0% of the FS setting for any 10°C change over the temperature range of 5 to 35°C. Both the zero and span drift tests are to be carried out within the acceptable temperature operating range of the analyzer, as specified by the manufacturer. The procedures outlined in Section 3.7.2 must be followed to determine the temperature-response drift.
Analyzers installed and operated in a temperature-controlled environment are exempt from this specification.
The CEM system stack gas flow monitor must have the capability of carrying out checks at low and high flow rates as part of the system calibration procedures. Electronic simulation of low and high flow is acceptable provided that daily zero and span drift can be calculated. The sensor must cover the full range of gas velocities anticipated in the flue or duct. Flows exceeding the range of the sensor are deemed to be missing and must be backfilled, as described in Section 3.5.2 of this report.
The flow monitor must be designed and equipped in such a way to ensure that the moisture expected to occur at the monitoring location does not interfere with the proper functioning of the flow monitoring system.
If the flow monitor is based on the principle of differential pressure, the monitor must be designed and equipped in such a way to provide an automatic, periodic back purging (simultaneously on both sides of the probe) or equivalent method of sufficient force and frequency on a daily basis, at a minimum, to ensure that the probe and lines remain sufficiently free of obstructions to meet the calibration drift criteria set out in Section 5.1.2. The monitor must also be designed and equipped in such a way to provide a means for detecting leaks in the system on a quarterly basis, at a minimum.
If the flow monitor is based on the principle of thermal dissipation, the monitor must be designed and equipped in such a way to ensure on a daily basis, at a minimum, that the probe remains sufficiently clean to meet the calibration drift criteria set out in Section 5.1.2. This type of monitor shall not be used for stack gases containing water droplets.
If the flow monitor is based on the ultrasonic principle, the monitor must be designed and equipped in such a way to ensure on a daily basis, at a minimum, that the transceiver remains sufficiently free of dirt (e.g. through a back purging system) to meet the calibration drift criteria set out in Section 5.1.2.
The full-scale (FS) setting must be approximately 100% of the maximum potential flow rate.
Note that various performance specifications are defined with reference to the FS setting of the CEM flow monitor (see Table 1 above, Table 3 in Section 5 and Table 5 in Section 6). The flow monitor of a CEM system may be able to measure levels exceeding the defined FS level; however, this higher level cannot be applied to demonstrate conformance to the performance specifications, which are tailored to the characteristics of the EGU.
If flow varies widely, as in the case of stacks that serve several EGUs, then the use of multi-range flow monitors is acceptable. The highest range must take account of the maximum potential flow anticipated for the stack. Note that data that fall outside the range(s) of a flow monitor are considered as missing and must be backfilled using the criteria provided in Section 3.5.2.
If the CEM system includes a stack gas flow monitor and analyzers that measure on a dry basis, then the CEM system must include a moisture subsystem capable of estimating the hourly stack gas moisture levels all year round. The moisture estimate must be used to adjust the measured CO2 or O2 levels to a wet basis according to Section 7.
Tables 3 and 5 contain specifications for a moisture monitoring subsystem based on a single O2 analyzer. Alternative stack gas moisture monitoring subsystems may be used if it is demonstrated that the system is able to calculate the hourly factor (100 - Bws) with an error ≤2.0% all year-round.
The CEM system must include a microprocessor-based data acquisition subsystem that accepts the outputs of the gas analyzers and other associated equipment and converts these into a CO2 emission rate according to Section 7. The system must maintain a record of all parameters as indicated Section 8. The system must also record and compute daily zero and calibration drifts, provide for backfilling of missing data, and record any other relevant data that the operator may wish to include.
Data must be reduced to 1-hour averages for all measured parameters. The 1-hour averages must be used to compute CO2 mass emission rates, expressed as kg/hr as per Section 7.
For time-shared systems, 1-hour averages must be computed from four or more values, equally spaced over each 1-hour period, with the exception of periods during which calibrations, QA activities, maintenance, or repairs are being carried out. During these specific activities, a valid hour must consist of a minimum of two data points for a time-shared system or 30 minutes of data for a CEM system using dedicated analyzers. The calibrations must be conducted in a manner that avoids the loss of a valid hour of emissions data every time that a daily calibration is conducted. This may be achieved by using mixtures of several gases; by scheduling the calibration periods so that the emissions data loss is shared by two consecutive hours; or by scheduling the calibration of different analyzers at different hours of the day.
Any CO2 emissions data that are missing due to a malfunction of the CEM system must be substituted for a period of up to 168 hours for any single episode using data derived from the most recent CO2 emission versus load or heat input correlations determined by a certified and quality assured CEM system, provided that the correlations are based on a minimum of 168 hours. The method used to develop this correlation must be described in the CEM system’s Quality Assurance/Quality Control (QA/QC) manual.
If the malfunction occurs before the certified CEM system could accumulate a minimum of 168 quality-assured hours of CO2 emission data, then the missing data shall be backfilled on the basis of design heat rate or load during the malfunction period. Calculation procedures for this potential backfilling period must be tailored to the specific conditions of the EGU. This must be described in the CEM system’s Quality Assurance/Quality Control (QA/QC) manual.
When a CEM system malfunction extends beyond 168 hours for any single episode, data must be generated by means of another CEM system or replacement CEM system components that meets all design and performance specifications presented in this RM. When using another CEM system, the stack gas sample must be extracted from the sample port(s) used for the RM during certification of the CEM system.
All emissions data must be quality-assessed by the operator to identify suspected data using procedures to be described in the QA/QC manual (Section 6.1). The procedures must include automatic flagging of a) out-of-range concentrations and flows, b) abnormal system calibration response times, c) abnormal flow-to-input or flow-to-output levels, and d) abnormal concentrations during periods when the EGU burned no fuel.
The flagged data must be investigated and either accepted or backfilled using the criteria provided in Section 3.5.2. The quarterly report must identify such flagged data and provide a summary of reasons for their acceptance or backfilling.
The specification for cycle time applies to time-shared systems measuring emissions from a number of EGUs using a single set of gas analyzers. One complete measurement cycle of all streams must be completed in 15 minutes or less, generating a minimum of four sets of concentration and emissions data for each hour of operation. For a CEM system measuring the emissions from "n" stacks, the maximum time available for each EGU being monitored would be 15/n minutes, including switching, stabilization and analyzer output integration times.
It is acceptable to carry out this test after the analyzers have been installed in the CEM system or in a laboratory or other suitable location before the analyzers are installed. The analyzer being tested must be allowed to warm up to manufacturer’s specifications and then calibrated by introducing appropriate low- and high-level gases directly to the analyzer sample inlet. After the initial calibration, test gases must be introduced sequentially, each consisting of a single interfering gas at a concentration representative of that species in the gas flow to be monitored. The magnitude of the interference of each potential interfering species on the target gas must then be determined.
The analyzer is acceptable if the combined response of all interfering gases is less than 4.0% of the FS setting.
The analyzer must be placed in a climate-controlled chamber in which the temperature can be varied from 5 to 35°C. The analyzer must be allowed to warm up to manufacturer’s specifications, and then the analyzer must be calibrated at 25°C using appropriate zero and span gases. The temperature of the chamber must be adjusted to 35, 15 and 5°C. It must be ensured that the analyzer temperature has stabilized and that the analyzer’s power source remains on for the duration of this test.
When the analyzer has stabilized at each climate chamber temperature, each of the calibration gases must be introduced at the same flow or pressure conditions, and the response of the analyzer must be noted.
The temperature-response zero drift is calculated from the difference between the indicated zero reading and the reading at the next higher or lower temperature. The analyzer is acceptable if the difference between all adjacent (i.e., 5/15, 15/25, and 25/35°C) zero responses is less than 2.0% of the FS setting.
The temperature-response span drift is calculated from the differences between adjacent span responses. The analyzer is acceptable if the difference between all adjacent span responses is less than 4.0% of the FS setting.
The system cycle time is set by the manufacturer during design and must meet the specifications shown in Section 3.6.
Specifications for both interference and temperature-response drifts have been met if the analyzer manufacturer certifies that an identical, randomly selected analyzer, manufactured in the same quarter as the delivered unit, was tested according to the procedures found in sections 3.7.1 and 3.7.2, and the parameters were found to respect the specifications.