Analysis campaign for measurement of oxycombustion flue gas from Coal Fired Plants -

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1 Analysis campaign for measurement of oxycombustion flue gas from Coal Fired Plants - Morgane Riviere *, Daniel Missault, Patrick Mauvais, Samuel Daeden, Grégoire Béasse, Claire Bourhy-Weber, Jean-Marc Rabillier, Martine Carré. Air Liquide, Centre de Recherche Claude-Delorme, 1 Chemin de la Porte des Loges-Les Loges-en Josas, BP Jouy-en-Josas Cedex France * morgane.riviere@airliquide.com Abstract Oxycombustion is one of the competitive solutions for CO 2 capture for several industrial processes and could, in the medium term, have an impact on greenhouse gas abatement generated from fossil fuel combustion (especially coal) which is the main energy source. Air Liquide is a key contributor to the evolution of this technology with the development and improvement of the CO 2 CPU (Compression Purification Unit) through different collaboration projects. However, the reliable analysis of the impurities in the process stream(s) through the whole process plays a key role to demonstrate the capabilities of oxycombustion. A mobile laboratory featuring analyzers for all major flue gas components and key impurities has been designed and installed at the Callide Oxyfuel demonstration site and connected to more than twenty different sampling points on the CPU. Specific attention was paid to material selection and the design of the equipment used in the sampling line systems to achieve reliable measurements. Different types of analyzers such as multi-component analyzers based on NDIR or chemiluminescence were used to determine the effluent compositions at different steps of the process. Those analyzers were first tested in our research facilities to check the potential interferences and their effect on measurements. This document will illustrate the complexity of impurity measurements in CO 2 rich streams with some results from the test campaign carried out in 2013 at the Callide Coal-fired power station (Queensland, Australia). Introduction The greenhouse effect is a natural effect and is essentially due to greenhouse gases (carbon dioxide, methane, etc). Without this effect, the average planetary surface temperature should be around -19 C 1. However, since the industrial revolution, human activities have contributed to the emissions of these gases; especially carbon dioxide. CO 2 emissions in atmosphere have continuously risen in the last 150 years which has an impact on the Earth and leads to global warming. The growing awareness of this phenomenon has led the international community to take some measures to reduce GHG emissions, such as the development of less polluting technologies. In the medium term, one potential solution which could have an impact on GHG abatement is the capture and geological storage of the CO 2 generated from fossil fuel combustion, especially from coal-fired power plants which is a major contributor with 9 Gt of CO 2 emitted in Until the development of alternative energy sources, coal will remain the source of 1 Le Treut & al, 2007: Historical Overview of Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA 2 Global CCS Institute 2012, The Global Status of CCS: 2012, Canberra, Australia

2 primary energy for electricity production. Thus, Carbon Capture and Storage (CCS) technologies can be a solution to reduce CO 2 emissions while using fossil fuel combustion. Oxycombustion has been identified as a competitive option for CO 2 capture and Air Liquide is improving this technology by developing specific technologies such as the CPU and by participating in several demonstration projects, such as the Callide Oxyfuel project 3 in Australia. The main goal of this project was to evaluate oxyfuel combustion with the adaptation of an existing coal-fired power plant. This technology combusts the coal (typically based on boiler operation) using O 2 mixed with recycled flue gases as the oxidizer instead of air (Figure 1). This leads to a flue gas containing primarily CO 2. The CO 2 rich gas will then be purified downstream to achieve the targeted CO 2 specifications for geological storage. Figure 1: Oxycombustion principle 4 The downstream purification, the CO 2 Compression and Purification Unit (CPU), is designed to purify the oxycombustion flue gas to produce a CO 2 -rich gas stream with low levels of impurities which is suitable for both transportation and storage (Figure 2). In order to characterize the flue gas composition at each step of the CPU and determine the mass balance of each process step, analytical tools were required. These tools included appropriate sampling systems as well as suitable analyzers. The first stage of the CPU is composed of pre-purification, a scrubber and filters to remove the main acid impurities (SOx, HCl, HF ) and ash. The flue gas is subsequently compressed to about 20 bar. In order to complete acid impurity removal, a high pressure exchanger and scrubber is used. Moisture removal was achieved with adsorption. This step is critical to avoid ice formation during a subsequent cryogenic purification. Cryogenic purification is used to remove NOx and inert gases, such as N 2, O 2 and Ar, prior to CO 2 liquefaction. 3 C. Spero & al: Callide Oxyfuel Project CO 2 Storage Demonstration, Lessons Learned, Global CCS Institute, March N. Perrin & al: Oxycombustion for carbon capture on coal power plants and industrial processes: advantages, innovative solutions and key projects, Energy Procedia, 2013

3 Driers Compressor LP scrubber HP scrubber Cold box (connected to field gas analyzers) CPU Figure 2: Gas and liquid analysis points at the different process steps in the CPU The analyzers were selected to determine the oxycombustion flue gas composition at each step of the CPU (see Figure 2) with sampling points at the inlet and outlet of each process step within the CPU. In order to accomplish this, the analyzers need to be able to analyze multi-component mixtures containing high levels of impurities (NOx, SOx, H 2 O, HCl, etc.) in CO 2. The flue gas composition changes as it progresses through the CPU (Table 1), therefore the analyzers needed to detect variations with a high degree of accuracy as the flue gas composition changed. Table 1: Typical Composition of the oxycombustion flue gas at different steps within the CPU T ( o C) P (bar) Particulate content (mg.nm -3 ) Moisture content (%) CO 2 (%)* N 2 (%)* Ar (%)* CO (ppm)* SO 2 (ppm)* NO (ppm)* NO 2 (ppm)* Inlet Outlet *molar composition (dry) O 2 (%)* Analytical laboratory: Design and cross interferences validation For the determination of the effluent composition in the gas phase prior to cryogenic purification, a multi-component analyzer based on NDIR (Non-Dispersive Infra-Red) and a total mercury analyzer based on cold vapor atomic fluorescence were utilized. The NDIR analyzer is an analysis system for continuous flue gas monitoring and all IR active species (H 2 O, NO, NO 2, CO, CO 2, SO 2, HCl, CO 2 ) in the flue gas can be analyzed (single-beam transmission infrared photometer, applying the single-beam dual-wavelength method and the gas filter correlation method depending on components to be analyzed, cell path length = 6m). In order to measure the oxygen concentration, a ZrO 2 probe was utilized and was implemented directly in the multi-component analyzer. The mercury device includes a gold coated adsorption / desorption system to determine trace levels of mercury in gases and a specific probe heated at 700 C containing a catalyst to convert oxidized mercury to elemental mercury. To measure NO/NOx after cryogenic purification, an analyzer based on chemiluminescence equipped with a catalyst to convert NOx to NO for NOx determination was utilized in addition to the IR analyzer. The utilization of the additional NOx analyzer was necessary to reach lower detection limits anticipated after the cryogenic step. Air gases were analyzed using a Gas Chromatograph with a Thermo-Conductibility Detector (GC/TCD) equipped with two different channels. Each channel was independent and consisted of an injector, a column and a detector (carrier gas: helium). The first channel was for CO 2 analysis

4 using 10m Pora Plot Q (PPQ) column and the second channel was for Ar, O 2, CO and N 2 analysis using 20m Molsieve 5A column with a backflush system (pre-column PPQ 3m). Two analyzers per analytical technique (except for the mercury determination) were purchased and integrated in the analytical laboratory in order to simultaneously analyze the inlet and the outlet of the different process steps. The different analytical techniques were first tested within Air Liquide to validate analyzer performances, check cross interferences and if necessary implement corrections. Cross interferences were evaluated using a multi-component mixer designed to produce synthetic gas with different levels of NO, NO 2, SO 2, HCl, O 2, N 2, H 2 O, CO 2 and Hg (Hg 0 and Hg 2+ ) which would be representative of the oxycombustion flue gas at each step of the CPU. Some corrections and modifications were implemented depending on the results obtained 5. The measurement uncertainty (see Table 2) was also evaluated and was between 2 and 30% depending on components and the measuring ranges. Table 2: Measurement uncertainty depending on analyzer technology Analyzer Highest uncertainty* Lowest uncertainty* NDIR multi component analyzer 30% for ppm NO 2 range with high moisture content 2% for % CO 2 range Chemiluminescence-based 3% for ppm 8% for ppm NO/NOx range analyzer NO/NOx range GC/TCD 15% for 0-1,5% Ar/O 2 range 2% for % CO 2 range * 95% confidence level Therefore, this analyzer evaluation was a very important step to assure reliable results when analyzing real samples on site. Callide analysis campaign - Sampling system & results Sampling system The sampling system specification was as important as the analytical technique selection to provide results from representative streams. More than twenty gas sample points with a wide range of conditions in terms of temperature, pressure and composition, were connected to the analytical laboratory (see Figure 3). For some analysis points, the distance between the process and the analyzers was more than 50m and therefore a fast sample loop was implemented to reduce the sample transfer time from the unit to the laboratory. The sampling system was heated prior the cryogenic purification step to avoid gas composition changes (water condensation, corrosion ) especially for the streams with high moisture content. Teflon heated transfer lines were installed to prevent Hg losses. Silcosteel lines were installed to connect the process to a heated pre-sample panel (filter, pressure reducer and safety valves) because of pressure rating limitations with Teflon lines. Stainless steel tubing transfer lines as well as heated pre-sample panels (for pressure reduction of high CO 2 content samples) were installed in the cryogenic section. 5 T. Jacksier & al, Analytical Validation of Near-Zero Emissions from Coal-Fired Plants, CEM Prague, 2011

5 Figure 3: Analytical laboratory installed on Callide site Analysis campaign The main goal of the analysis campaign at Callide undertaken in 2013 was to optimize impurities removal, to understand and validate the component mass balance (CO 2, SOx, NOx, Hg ) throughout the entire process and to provide feedback from operations. All the real-time data from analyzers as well as from the process were collected by the pilot system implemented in the laboratory to simplify the data treatment. Gas and liquid analysis from the CPU inlet to the Cold box inlet The flue gas composition from the inlet to the cold box was determined using the multicomponent system based on Infra-Red (IR). Liquid analysis of condensates and scrubbing solutions were also done externally in AL R&D facilities. A dedicated analytical method by Ionic Chromatography (IC) with a conductivity detector (KOH eluant, separation column IonPac AS18 (4x250 mm), pre-column IonPac AG18 (4x50 mm) & guard column IonPac CP1 Na+Form -cation polisher (6x16 mm)) was developed for analyzing aqueous samples from the oxycombustion process. The concentrations of the following anions were determined with this method: chloride, fluoride, sulfate, sulfite, total dissolved carbons (carbonate, bicarbonate and CO 2 ), nitrate, nitrite and phosphate (see Figure 4). Figure 4: Typical Chromatogram for the analytical method

6 These measurements, as well as sulfuric acid measurements, helped to determine the CPU performances for the main acid impurities removal. The analytical results obtained for HCl and HF impurities are given in Table 3. Table 3: HCl and HF removal results Gas analysis Liquid analysis CPU inlet Scrubber outlet CPU inlet Scrubber outlet HCl/ Chloride ~10 ppm < DL ~ 30 mg/l* < DL HF/ Fluoride Not analyzed Not analyzed ~25 mg/l < DL DL : Detection Limit *Chloride from process + chloride from scrubbing solution Gas and liquid analysis showed that these impurities were removed in the washing section of the CPU as expected. Regarding SOx removal, the same behavior was found and showed that sulfuric acid and sulfur dioxide are removed efficiently (<< 10 ppm). However, analytical problems were encountered with an analyzer based also on NDIR which was continuously monitoring the SO 2 content at the outlet of the washing section. High SO 2 concentrations (between 10 & 20 ppm) were measured with this analyzer whereas the multi-component system and another analyzer based on UV fluorescence gave results below 1 ppm for the same flue gas. After some investigations with CO 2 calibration gases (see Table 4), it was found that the correction model underestimated CO 2 interference on the SO 2 analysis (SO 2 readings on the analyzer with a gas containing only CO 2 and/or N 2 ). Table 4: Analysis of CO 2 calibration gas cylinders with the SO 2 analyzer from process Gas cylinder composition SO 2 reading (ppmv) CO 2 reading (% vol) 55% CO 2 balance N % CO 2 balance N % N These results showed the importance of the pre-work at Air Liquide facilities and how these measurements can have a significant impact on the process conditions. The pre-work carried out to check cross-interferences on the analyzers was very useful to get reliable results. The IR analyzer behaved as expected during the whole analytical campaign. During data processing, some correlations were found between NO, CO and O 2 concentrations (see No. 1 in the Figure 5) for the analysis points at the CPU inlet. Indeed, the CO concentration (in green), the O 2 concentration (in yellow) and to the NO concentration (in light blue) of the flue gas seem to be linked.

7 1 2 Time Figure 5: IR-based analyzer measurements, CO concentration in green, O 2 concentration in yellow, NO concentration in white, dark blue and red depending on ranges Some investigations were carried out to evaluate if it was an analyzer interference problem. As shown in No. 2 and 3 in the Figures 5 & 6, it was possible to find examples with only CO fluctuations or only CO and O 2 fluctuations. The response of the different ranges for NO concentration, low range (in white), mid range (in dark blue) and high range NO (in red but mixed with the light blue curve in No. 1) were checked to prove that it was not a problem related to the analytical range changes and indeed the same fluctuations for NO measures were observed for each range. Concentration Concentration 3 Time Figure 6: IR-based analyzer measurements CO concentration in green, O 2 concentration in yellow, NO concentration light blue

8 These observations show that it was not an analytical problem (interferences) but it comes from process fluctuations. Measurements were also carried out on additional sample points with the IR-based analyzer and significant interferences were identified on SO 2 and NO 2 channels. The analyzer response was quite difficult to analyze and one or more unknown interfering component might have been present in the gas which would have disturbed the measurements. Figure 7 represents the analyzer response for NO 2 in the different ranges. High range NO 2 NO 2 concentration Middle range NO 2 Lowrange NO 2 Time Figure 7: IR-based analyzer measurements, low range NO 2 in green, middle range NO 2 in purple, high range NO 2 in red The response of the high NO 2 range channel was quite different from the response of the low (in green) & middle (in purple) NO 2 range channels which had similar responses. The concentration measured by the high range (in red) started to decrease to reach 0 ppm whereas the other ranges were still detecting NO 2. Concentrations up to 1000 ppm SO 2 were also found in this stream which was considered quite unlikely. Investigations are ongoing to identify the interfering component(s) and a Fourier Transform Infra Red (FTIR) analyzer will be used during the next campaign on this specific analysis point. Total mercury analysis Total mercury measurements were carried out on the analysis points prior the cryogenic purification in order to check the mercury removal through the warm part of this process and to validate that the level of mercury entering the cold box was lower than the accepted limit value to avoid corrosion (Liquid Metal Embrittlement) problems inside the cold box. Only gas analysis was performed (see Figure 8) with different collection times of the mercury on the gold coated adsorption/desorption system depending on mercury concentration in the flue gas (higher collection time to achieve lower detection limit). Only 30 second collection was achieved at the CPU inlet to avoid gold trap saturation due to the high mercury content and 10 min collection time at the cold box inlet to be sure that the mercury level was below the detection limit of the analytical method (0.1 µg/nm 3 ).

9 Figure 8: Total mercury removal through the CPU process Results illustrating that mercury were mainly removed in the washing section via the liquid phase and the Hg tot concentration at the cold box inlet was lower than 0.1 µg/nm 3. Gas analysis for the cryogenic step A gas chromatograph equipped with Thermo-Conductibility Detector (TCD) for CO 2, N 2, O 2, Ar and CO determination as well as a chemiluminescence-based analyzer for NO/NOx analysis was used to evaluate the performances of the cold box. The challenge was to measure oxygen levels at % levels as well as ppm levels, which was close to the detection limit of the TCD. Two methods were developed: one for low ppm levels and one for % levels O 2. As it was not possible to switch methods during the automatic campaigns, chromatogram reprocessing was required to ensure reliable results. It was then possible to evaluate the purity of the CO 2 product at the CPU outlet. Table 5: CO 2 product purity (external laboratory results) Component Concentration CO 2 > 99,9% vol SO 2 < 1 ppmv NOx < 20 ppmv H 2 O < 20 ppmv < 30 ppmv O 2 CO 2 product analysis was compared with an external laboratory and the results match the results obtained directly on site (see Table 5). Moreover, very high CO 2 purity has been achieved at the CPU outlet with a CO 2 content higher than 99,9%.

10 Conclusion The data collected during this analytical campaign have been used in data reconciliation models and helped to better understand the CPU. Mass balances of key impurities have been done and performances of this unit have been evaluated. Reliable results have been obtained thanks to the prior evaluation of the analytical techniques and the detailed sampling system selection. These first results will enable cost reduction (equipment sizing) and performance improvements (equipment efficiency) for large scale units, especially for the FutureGen plant design in the USA. This project aims at demonstrating the CPU technology for industrial scale with an objective of 1 Mt CO 2 captured per year. Another analytical campaign on the Callide site is planned in 2014 to collect additional data, identify interfering component on certain streams and check the previous results. Additionally testing of other operating parameters will also be evaluated. Acknowledgment The authors would like to thanks Callide Oxyfuel Services Pty Ltd (COSPL) and CS Energy Ltd for their support and assistance during this analysis campaign. 6 N. Perrin & al: Oxycombustion for carbon capture on coal power plants and industrial processes: advantages, innovative solutions and key projects, Energy Procedia, 2013