Guido Baum Dr. Peter Wilbring

Transcription

1 Determination of CO 2 and N 2 O emissions with CEM systems within the scope of greenhouse gas trading New regulation for the continuous measurement of CO 2 and N 2 O mass flow - requirements for the installed measuring systems with respect to the EU Monitoring Regulation No. 601/2012. Guido Baum Dr. Peter Wilbring TÜV Rheinland Energie und Umwelt GmbH Immissionsschutz / Environmental Protection Am Grauen Stein D Cologne (Germany) Guido.Baum@de.tuv.com wilbring@de.tuv.com / Since several years the determination, reporting and trading of greenhouse gases is an actual topic for plant operators from different kind of industries as well as the relevant authorities and verifying bodies. In the past for most of the applications the determination of CO 2 emissions has been performed by calculating the emission mass flow based on historic data of the fuel consumption or product flow of the plant and the relevant emission factors. This method is only suitable for plants which use homogenous and well known fuels. For several other industry plants and processes this method is not suitable. Since January 2013 the new monitoring regulation (European Commission regulation No. 601/2012) came into force. One topic of this monitoring regulation is the need for measurement of greenhouse gas emissions for plants at which the calculation based approach for greenhouse gas emissions is not possible. Article 42 of the new EU Monitoring Regulation describes the requirements for the quality assurance of measurement systems used for the greenhouse gas monitoring as well as the requirements for the measurement sections. In addition maximum uncertainties for the CEM systems are defined in relation to the emitted mass flow. This paper should give an overview of the requirements for measuring systems (combined concentration and flow measurement), the qualification procedures for CEMS used in the context of greenhouse gas monitoring (QAL1 and EN 15267) as well as the ongoing quality assurance for the field installations. Problems for the determination of the overall measurement uncertainty in relation to the required uncertainties from the European Monitoring Regulation will be discussed. 1. Requirements for continuous emission monitoring systems (CEMS) The requirements for CEM systems in the context of the measurement based approach for the determination of greenhouse gases is strongly adapted to the existing European regulations for the qualification of CEMS for the observation of emission limits a different kind of industrial plants. The EU Monitoring Regulation No. 601/2012 refers to the following standards:

2 EN ( Stationary source emissions Quality assurance of automated measuring systems ) for quality assurance of the CEMS EN ( Stationary source emissions Requirements for the measurement sections and sites and for the measurement objective, plan and report ): This standard describes how to achieve accurate and reliable results in emission testing, including in relation to sampling position In the EN the following quality assurance levels for the measuring equipment are defined: QAL 1: Type approval of the CEM system (Lab and field test in accordance to EN and regular audit in accordance to EN ) QAL 2: Calibration and validation of the CEM (parallel measurements with standard reference method); QAL 3: On-going quality assurance during operation (e.g. regular drift chekcs and other service work in the maintenance interval); AST: Annual surveillance test (functional test) The EN defines requirements for measurement sections and sites such as: Measurement / sampling strategy Requirements for measurement sections and measurement ports Requirements for working areas and working platforms Determination of homogeneity Altogether the requirements for CEMS for greenhouse gas applications are similar to the regulations for other CEMS. For plant operators it is important to install type approved measuring equipment in accordance of the QAL1 level of the EN The minimum requirements for the type approval of measuring equipment are defined in the EN part 3. In addition regular AST as well QAL2 tests have to be carried out by test institutes which are accredited in accordance to EN/ISO/IEC for this kind of service. The plant operator has to implement the on-going quality assurance level QAL3 which includes especially the regular drift checks for all measured components at zero and span point with suitable test equipment as well as other maintenance work required by the manufacturer of the CEM system or by the test house, which has conducted the type approval in accordance to the EN Following table gives an overview about the necessary actions and the involved parties to be done in the context of EN 14181: QAL1 QAL2 QAL3 AST When? Before Installation of the CEMS, certification has to be done once for a certain type of analyser Frequency? Once, valid for all analysers of the same model Who? Typically instructed by the manufacturer of the CEMS; plant operator has to take care to install QAL1 certified products First time after installation of the CEMS During operation, defined by maintenance interval Starting one year after QAL2 At least every five Continuously Annually years *) Accredited laboratory Plant operator *) more frequently if so required by legislation or by the competent authority Accredited laboratory

3 The requirements of the EN are on one hand relevant for plant operators. It provides important information for the selection of a suitable installation point for the CEM system(s). It is essential to find a representative measuring section in the stack. Relevant are the length of the inlet and outlet sections as well as the homogeneity at the sampling point. The standard describes also the need of additional sampling ports and working platforms for the QAL2 tests. On the other hand the EN includes e.g. important information about the sampling strategy and the reporting for accredited test institutes which perform the AST and QAL2 test at the site. 2. Determination of the mass flow combination of concentration and flue gas flow measurement The determination of the greenhouse gas mass flow by a measurement based approach consist always of a measurement of the concentration (e.g. of CO 2 and N 2 O) and the measurement of the stack flow. For both elements type approved measurement equipment has to be used. According to Article 43 of the EU Monitoring Regulation No. 601/2012, the emissions have to be determined as hourly average concentration and the hourly average flow rate. In case of an existing data evaluation system which is based half hour averages; also the half hour averages can be used for the data evaluation. After that all hourly values of the reporting year are summed up for the total emissions of that emission point. If there are more than one emission source for one site (e.g. two separate stacks of a power plant), the total amount has to be calculated first for each source separately, before adding the emissions of all sources to result in the total emissions. Figure 1: Scheme of a combined CEMS for the determination for the Concentration and the stack flow with a data evaluation computer For different kind of plants it is also allowed to calculate the flue gas flow by using a mass balance model instead of a direct flow measurement. In certain cases this approach makes sense because the parameters which are needed for the mass balance calculation are often easier to measure (e.g. input air flow, oxygen concentration or input material flows). For the data acquisition systems there are at the moment in Europe no uniform minimum requirements. Actual there is an existing in a CEN TC 264 working group which is preparing on European test and a certification procedure for data acquisition systems. In the context of the greenhouse gas monitoring it exists at the moment only a general requirement that the operator has to ensure appropriate quality assurance by separate means, including in accordance with Articles 58(3) and 60 of the MRR.

4 Cureently there are several EN certified CEMS for the determination of CO 2 and N 2 O as well as stack flow available. Plant operators can get an overview of EN type approved analysers on the webpage 3. Continuous measurement of N 2 O emissions The requirements for the determination of the N 2 O mass flow by a measurement based approach are similar to the measurement of CO 2 emissions. The analysers have to fulfill the requirements of the EN Instead of a CO 2 analyser, a continuous N 2 O analyser has to be used. The stack flow measurement is similar to the determination of CO 2 mass flows. Typical applications for the measurement of N 2 O are nitric acid plants, adipic acid plants as well as glyoxal and glyoxylic acid plants. For the calculation of the CO 2 correlating to the measured N 2 O emissions, the following conversion has to be done: Formula: Em = Em(N 2 O) * GWP N2O Em emissions expressed as t CO 2(e) Em(N2O) emissions of N 2 O in tonnes GWP N2O Global warming potential of N 2 O as listed in MRR Annex VI section 3 Table Measurement uncertainty and tier requirements In the EU Monitoring Regulation No. 601/2012 for the continuous measurement of greenhouse gases, different tier levels are defined. For each tier level a maximum uncertainty has to be met by the installed measurement equipment for the determination of the greenhouse gas mass flow. The minimum tier level for a certain type of plant is defined in annex VIII of the EU Monitoring regulation. The tier level is depending on the category of the plant (category A to C). This category is defined by the annual CO 2 mass flow of an emission source / plant. The following table gives an overview about the maximum uncertainty for each tier level: Tier 1 Tier 2 Tier 3 Tier 4 CO 2 emission sources ± 10 % ± 7.5 % ± 5 % ± 2.5 % N 2 O emission sources ± 10 % ± 7.5 % ± 5 % n.a. CO 2 transfer ± 10 % ± 7.5 % ± 5 % ± 2.5 % (For the measurement of indirect CO 2 the highest tier (tier 4) has to be used, unless unreasonable costs or technical infeasibility are demonstrated.) For the QAL1 certification in accordance to the EN it is necessary to fulfill a total uncertainty budged for each measured component. This allowed uncertainty is expressed as percentage of the daily emission limit value (ELV). The allowed uncertainty results from the QAL1 test procedure for the concentration and the flow measurement are often much higher than the allowed uncertainty of tier 3 or tier 4. Typical allowed uncertainties for a QAL1 approved instrument are between 7.5 % and 15 % of the ELV or certification range. For CO 2 and stack flow daily emission limit values don t exist in the EU legislation. For the QAL1 uncertainty calculation of analysers for measuring components without existing ELV, at the moment the percentage deviation is compared with the certification range of the analyser. For greenhouse gas applications it is recommended to compare the uncertainty with annual average hourly concentration of the greenhouse gas at a certain plant.

5 For calculating (average hourly, kg/h) CO 2 emissions the MRR requires the use of equation 2 in Annex VIII of the Monitoring and Reporting Regulation: Values for the concentration and the flue gas flow shall be consistent and relate to the same conditions, e.g. to dry flue gas at standard conditions. The uncertainty associated with the determination of the concentration will have to be combined with the uncertainty associated with the determination of the flue gas flow: The resulting expanded uncertainty associated with the average hourly emissions is the value which needs to be compared to the uncertainty associated with the tier required by the MRR for the relevant emission source (see section 1 of Annex VIII of the MRR) In MRR Guidance document No. 7 it is described, that the result of the QAL1 can be an indicator for the suitability for greenhouse gas application. The wording is here: The quality assurance level 1 (QAL1) procedure is used to demonstrate the potential suitability of the CEMS before it is installed. This quality assurance level is not covered by EN but by EN ISO The CEMS has to meet the requirements in EN ISO Furthermore, EN provides the detailed procedures covering the QAL1 requirements of EN and the input data for QAL3. By using these standards it has to be proven that the total uncertainty of the results obtained from the CEMS meets the uncertainties required by the MRR. In QAL1 the total uncertainty is calculated by summing all the relevant uncertainty components arising from the individual performance characteristics. This includes taking account of all (major) sources of uncertainty (influence quantities) contributing to the uncertainty associated with the value of interest, i.e. the GHG concentration in this case. The total uncertainty of the measurement value is then determined by calculating the combined uncertainty by the means of error propagation. Information regarding the performance characteristics of the CEMS can be obtained e.g. from the specifications of its manufacturer or from other tests performed, e.g. certification systems under type approval schemes or other national schemes. An instrument-type that has been appropriately tested in accordance with EN can then be taken as automatically meeting QAL1 (as long as the scope of the EN tests confirms the instrument suitable for the type of process(s) at the destination installation). In those cases the QAL1 results accompanying the CEMS certification can be used without further calculations. It is recommended to compare the standard uncertainty from the QAL2 test with the allowed uncertainty of the tier level to show, that the deviations between CEMS and SRM method during the period of parallel sampling meet the allowed tier requirement. The MRR Guidance document No. 7 describes this as follows: However, the uncertainty associated with the determination of the concentration obtained by the QAL2 procedure) is the relevant input parameter for demonstrating compliance with the MRR. and

6 It is important that the GHG concentrations during calibration are as close as possible to the expected concentrations during normal operating conditions. Note that as described for QAL1, EN refers to ELVs. However, ELVs are not set in relation to EU ETS GHGs. The MRR accommodates this by stating that under such circumstances, the annual average hourly concentration of the GHG shall be used as a substitute for the ELV. There is added relevance in connection with measurement of N 2 O emissions since concentrations during periods without abatement differ significantly from those during normal operations. In this case, it may be necessary to operate more than one CEMS, if the range and calibration of a single instrument (CEMS) is not sufficient to cover both concentrations within the required uncertainty. The variability is then calculated as the standard deviation of the differences between each concentration value obtained by the CEMS and corresponding values obtained by the SRM measured in parallel (see sections 6.6. and 6.7 of EN for more details). However, this is not sufficient in the case of CEMS applied to GHGs in accordance with the MRR, where the uncertainty associated with the flue gas flow also needs to be taken into account. As a consequence, the standard deviation calculated above divided by the test value k V only has to be used as the u GHG concentration value in equation (3) in section 3.2. Therefore, the variability of the measured values obtained with the CEMS compared to the SRM, amended by the uncertainty associated with the determination of the flue gas flow, is the uncertainty to be compared with the uncertainty required by the MRR. It is still open how to deal with long term effects like partial uncertainty caused by drift effects during the reporting period of one year. 5. Possibilities for the improvement of the total uncertainty Like described above it is hard to fulfill the requirements of the total uncertainty for the tier levels of the monitoring regulation No. 601/2012. In general it is important to install type approved measuring equipment. With help of the QAL1 uncertainty calculation, which is part of the QAL1 certificate, it is possible to select measuring equipment with a low uncertainty budget. In addition it is possible to improve the accuracy of a CEM system with the following criteria: Some analysers are sensitive on variations of the ambient temperature. An installation in a temperature controlled rack or shelter can eliminate deviations in the ambient temperature and has a positive influence to the accuracy of the measured values. Other gases in the stack can have an interference effect to the analyser of the measured component. It is important to know which other substances are in the exhaust gas or process gas and to compare these with the interference test results of the EN test procedure. If an analyser has a critical interference against another gas in the stack, it makes sense to check if other CEMS have a better performance. The quality of the test gases which are used for the adjustment of the concentration measurement can be improved. A typical uncertainty for test gases is ± 2 % of the delivered concentration. It is possible to substitute these test gases with high quality test gases e.g. with an uncertainty of ± 1 % of the cylinder concentration

7 The span gas concentration for the QAL3 check should be as close as possible to the typical concentration level of the plant. The concentration in the test gas cylinder should be similar to the concentration level in the stack. The use of higher concentrated test gas and a dilution system system does not make sense, because the additional uncertainty of the dilution system has an negative influence to the total measurement uncertainty of the CEMS. For some type of plants the right selection of the measuring principle for the flow measurement has an influence to the measurement uncertainty. For example at stacks with temperatures below the dew point it is possible that water drops bock the bore holes of the pitot tube. In such cases an automatic bow back or better another measuring principle (e.g. ultrasound measurement) can improve the measurement results. If the homogeneity in the stack is insufficient and it is not possible to find another installation sections for the flow measurement (especially a problem of older plants) it is possible to use two flow analysers which can measure e.g. in an angle of 90 to each other. From both analysers the average flow value can be calculated and has to be taken into account for the greenhouse gas mass flow calculation. The simultaneous measurement on two axes across the stack delivers a more representative result for the stack flow. The period between the drift checks in the frame of QAL3, which has to be done by the plant operator, is defined by the maintenance interval of the analyser. The determination of the maintenance interval is a test criterion of the type approval procedure (QAL1) in accordance to the EN The quality of the measurement results can be improved by executing the QAL3 procedure (zero and span check of the analysers) more often than required by the maintenance interval. Possible drift effects can be identified earlier by this higher frequency. In some cases it makes sense to define lower drift limits as criteria for an adjustment of the CEMS. 6. Summary Like described above, the reader can see that the regulations and the requirements for the measurement of greenhouse gases are adapted to the existing European requirements for other CEM systems. It is still critical to fulfill the uncertainties of the different tier levels. The allowed uncertainty results from the QAL1 test procedure for the concentration and the flow measurement are often much higher than the allowed uncertainty of tier 3 or tier 4. One approach is to take the standard deviation from the QAL2 tests (variability test) between the installed CEMS and the SRM method into account and to compare this with the relevant tier level. For other CEM application the percentage of the deviation are always compared with the daily emission limit value (ELV). For CO 2 and stack flow emission limit values don t exist in the EU legislation. For the QAL1 uncertainty calculation of analysers for measuring components without existing ELV, at the moment the percentage deviation is compared with the certification range of the analyser. Instead of this, for greenhouse gas applications it is recommended to compare the uncertainty with annual average hourly concentration of the greenhouse gas at a certain plant. The comparison of the standard uncertainty from the QAL2 test with the allowed uncertainty of the tier level is a possible way to show, that the deviations between CEMS and SRM method during the period of parallel sampling met the allowed tier requirement. Still open is how to deal with long term effects like partial uncertainty caused by drift effects during the reporting period of one year. The general recommendation is to minimize the total uncertainty by a faithful selection of the right measurement equipment depending of the kind of process, the improvement / stabilization of the ambient conditions at the installation area of the CEMS and an increase of the number of QAL3 checks to be able to recognize drift effect as soon as possible and to be able to correct these.

8 Literature EU ETS Directive: Directive 2003/87/EC of the European Parliament and of the Council of 13 October 2003 establishing a scheme for greenhouse gas emission allowance trading within the Community and amending Council Directive 96/61/EC, most recently amended by Directive 2009/29/EC. MRG 2007: Commission Decision 2007/589/EC of 18 July 2007 establishing guidelines for the monitoring and reporting of greenhouse gas emissions pursuant to Directive 2003/87/EC of the European Parliament and of the Council. A&V Regulation: Commission Regulation (EU) No. 600/2012 of 21 June 2012 on the verification of greenhouse gas emission reports and tonne-kilometre reports and the accreditation of verifiers pursuant to Directive 2003/87/EC of the European Parliament and of the Council. M&R Regulation: Commission Regulation (EU) No. 601/2012 of 21 June 2012 on the monitoring and reporting of greenhouse gas emissions pursuant to Directive 2003/87/EC of the European Parliament and of the Council. MRR Guidance Document No. 4 of the European commission of 05 October 2012 on the monitoring and reporting Regulation guidance on uncertainty assessment. MRR Guidance Document No. 7 of the European commission of 13 November 2013 on the monitoring and reporting Regulation continuous emission monitoring systems (CEMS).