CO2 CAPTURE FROM EXHAUST GASES AND NATURAL GAS SWEETENING AT NTNU

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1 Proceedings of the 13 th International Conference of Environmental Science and Technology Athens, Greece, 5-7 September 2013 CO2 CAPTURE FROM EXHAUST GASES AND NATURAL GAS SWEETENING AT NTNU GEORGIOS K. FYTIANOS, HANNA KNUUTILA, HALLVARD F. SVENDSEN Norwegian University of Science and Technology. Department of Chemical Engineering. Environmental Engineering and Reactor Technology Group. Sem Sælands vei 4, 7491 Trondheim, Norway. EXTENDED ABSTRACT One of the most fundamental problems facing the earth today is global warming. The emissions of CO 2 contribute about 75% to the greenhouse gas effect and must be reduced, e.g. by CO 2 Capture and Storage (CCS). We have many research projects in this area funded by the Research Council of Norway, the industry, and the European Union. Our work is concentrated along two axes, one studying CO 2 capture from off gases from fossil fueled power plants and the other directed toward the removal of acid gases from natural gas. We were heavily involved in EU FP6 projects, e.g CASTOR and CAPRICE. We are also involved in many national projects. Chemical absorption using aqueous alkanolamines solutions is the most commonly used method for CO 2 capture and has already reached commercial stage. The work we do involves all steps from theoretical screening of new absorbents by use of computational chemistry, through experimental screening, testing of environmental properties, characterization of equilibrium, thermal properties, transport properties and kinetics, degradation rates and mechanisms up to testing in laboratory scale pilot plants. In parallel with the experimental work we develop models ranging from simple models for physical properties to rigorous kinetic and thermodynamic models, based on the electrolyte NRTL and extended UNIQUAC model frame-works. All these models are then implemented in our SINTEF/NTNU in-house simulator CO2SIM to simulate the whole absorption- /regeneration process. In this poster, our methods studying solvent degradation and corrosion are presented to give a good overview of the work we are doing. KEYWORDS: CO 2 capture, reactor technology 1. INTRODUCTION Environmental engineering and reactor technology is the largest research group in the department covering interests in the fields of chemical reactor research, process design, acid gas absorption, membrane research, and crystallization and particle design. The members of the environmental and reactor technology group are involved in topics like separation of CO 2 with polymer membranes, capture of CO 2 in systems with simultaneous crystallization of solids, dynamic modelling of absorption processes, and modelling and simulation of sorption enhanced steam methane reforming operated in fixed and circulating fluidized bed reactors. Our group is involved in research projects for the capture of CO 2. One example is the BIGCCS International CCS Research Centre which I s one of eight centres. Established by the Norwegian Research Council under the scheme of Environmentally Friendly Research Centres (CEER). The BIGCCS Centre focuses on sustainable power generation from fossil fuels based on cost-effective CO 2

2 capture, safe transport, and underground storage of CO 2. Our group has a close collaboration with SINTEF, the largest independent research organisation in Scandinavia. The work we do involves all steps from theoretical screening of new absorbents by use of computational chemistry, through experimental screening, testing of environmental properties, characterization of equilibrium, thermal properties, transport properties and kinetics, degradation rates and mechanisms up to testing in laboratory scale pilot plants. In parallel with the experimental work we develop models ranging from simple models for physical properties to rigorous kinetic and thermodynamic models, based on the electrolyte NRTL and extended UNIQUAC model frame-works. All these models are then implemented in our own SINTEF/NTNU in-house simulator CO2SIM to simulate the whole absorption- /regeneration process. Degradation of absorbents is of concern and we work on identification of degradation products and reaction mechanisms. We analyze trace level of amine, nitrosamines, organic acids, alkylamides and amide derivatives. Moreover, environmental effects are studied through eco-toxicity and bio-degradation tests. LC-MS, IC and GC-MS are used for the determination of the degradation products. 2. AMINE BASED CO 2 CAPTURE PLANTS Carbon dioxide (CO 2) is the primary greenhouse gas emitted through human activities mainly from the combustion of fossil fuels (coal, natural gas, and oil). 1 The development of innovative technologies for CO 2 emission reduction is of great importance. In this direction, CO 2 sequestration strategies can be used to minimize the emissions of carbon dioxide in fossil fuel power plants. From the various methods which have been proposed, CO 2 capture and separation processes are among the most promising. An effective capture technology is post-combustion CO 2 capture with chemical absorption. At this process, chemical absorption using aqueous alkanolamines solutions is the most commonly used method and has already reached commercial stage. Absorption using amines as solvents have been applied successfully for several decades in areas such as natural gas processing or coal gasification 2. Various alkanoamines can be used for CO 2 post-combustion capture. Monoethanolamine (HO-CH 2-CH 2-NH2) is nowadays the benchmark solvent due to its good properties towards CO 2 (fast absorption rate, cheap, non- volatile). 3 Furthermore, diethanolamine (DEA), N-Methyldiethanolamine (MDEA), piperazine (PZ) and 2-Amino-2-methylpropanol (AMP) are among the most commonly used amines in CO 2 capture. Recently, several new amines and blends of the common ones have gain interest. Although progress has been made in optimization of parameters CO 2 Capture Plants, further research, both theoretical and experimental, has to be done. Laboratory and pilotscale experiments together with modeling are used for studying different aspects regarding CO 2 capture plants with amine solvent. Additionally the corrosion rates and degradation mechanisms of different amines and the effect of process parameters on the plants are in focus. In this overview, the focus is on the methods used in our scientific group when studying solvent degradation and corrosion. Corrosion and degradation are considered to be one from the most severe operational problems in the CO 2 absorption process. 4 Corrosion can cause unscheduled downtime, production losses, reduced equipment life and even injury or death. A better understanding of parameters affecting corrosion, with amines present, improves process operations and allows a better amine selection. 5 Experience shows that amine degradation products often aggravate corrosion 4. In fact, corrosion and degradation are closely tied since the byproducts of monoethanolamine (MEA) have been shown to increase corrosion rates. 5, Degradation of amines can be oxidative or thermal and some

3 of the degradation products are corrosive agents and inevitably cause equipment corrosion in the absorption plant which leads to additional costs. What is more, amine degradation affects the system performance by decreasing the efficiency of CO 2 capture. Even though the degradation of the benchmark solvent MEA, is described in several literature sources, there are still several knowledge gaps in the degradation mechanisms of MEA and other commonly used amines. 3. MATERIALS AND METHODS The oxidative degradation setups are imitating the conditions in the absorber, where temperatures are typically between o C and oxygen is present. In the lab experiments the oxidative degradation can be enhanced by higher oxygen concentrations and/or temperatures. Thermal degradation setups are made to better understand the degradation happening in the desorber, where the degradation is mainly related to high temperatures and presence of CO 2. Corrosion experiments we can do in the absorber conditions or at desorberconditions. The thermal degradation experiments, performed in metal cylinders can also show good indication on how corrosive the solvents are Oxidative Degradation Setups In the open setup, 1 liter of absorption solutions is placed in the to a batch reactor. Gas is bubbled with a sparged into the solution. Most of the gas is recycled with a gas pump as shown in Figure 3.1. A gas blend of nitrogen and oxygen with 2% carbon dixide is constantly added through two mass flow controllers to control the gas composition in the reactor. To avoid water evaporation from the reactor, the gas is humidified prior the reactor andthe reactor temperature is maintained at a fixed temperature. The exit gas from the open reactor is cooled down to decrease loss of volatile solvent/decradation compounds. Samples are taken regularly from the liquid phase to monitor the degradation. More detailed information is available in Vevelstad et al., 2013a 8.. Figure 3.1: Flowsheet for open batch setup 8 In closed oxidative degradation setup, 1 liter of solvent si circulated through a miniabsorber over time period of 3-4 weeks. Similarly to the liquid, gas containing CO 2, O 2 and N 2 is circulated counter currently as shown in Figure 3.2. Gas/liquid mass transfer is enhanced by using a structured packing. The liquid is heated to around 50 C and kept at

4 constant temperature during the experiment. The gas is analysed for CO 2 and O 2 and they are continuously logged.. Similarly as in the open setup, sample are withdrawn regurarly. More detailed information can be found in Vevelstad et al. 2013b 7.. a b c d e f g h i j Valve for loading solution Liquid pump Valve for taking sample Reactor Packing area Gas pump Cooler before gas analysers Flow meters for CO2,O2 analysers Valve used to empty the reactor Water lock to avoid pressure build up Figure 3.2: Simplified flow diagram for closed batch setup Thermal Degradation Setup Metal cylinders are constructed from 316 stainless steel tubes with an outer diameter of ½ inch and equipped with Swagelok end caps. The volume of cylinders is approximately 11ml and takes about 7ml of solution to completely surround metal coupons in the cylinder. In order to check for possible leakage, the cylinders including solutions will be weighed before and after incubation. 13 The cylinders will be held in an upright position and stored in a thermostat chamber at 135 o C. The total experimental time is 5 weeks. Every week, a sample is tested. It is analyzed to determine the amount of starting amine as well as the amount of metal ions in solution, while GC-MS is used to identify degradation products in the solution Corrosion Setup As mentioned earlier thermal degradation experiments presented above can give a good indication of corrosion in a real plant. When using the thermal degradation setup for corrosion, stainless steel A316 metal coupons of specific dimensions fitted with Teflon coverings can be placed inside the cylinders. Corrosion rates of 316 SS in the absorber conditions are studied in an open-batch apparatus at 50 ºC. Glass beakers are filled in with chosen solventcontaining 1 wt% degradation product and loaded with CO 2 (α=0.2). There beakers are introduced into an autoclave, whose environment is maintained constant by feeding a gas blend of CO 2, N 2, and O 2. This gas blend is conditioned through a MEA solution before entering the autoclave. Prior to the test, the metal specimens are prepared by degreasing with acetone, grinding with 500-grit silicon carbide paper, rinsing with 96 % ethanol, and drying with hot air. The clean, dry specimens are weighted and their dimensions are measured by a digital caliper. The prepared specimens are kept in a desiccator until used in the experiments. After the tests, the specimens are cleaned in 15 wt% diammonium citrate solution at 70 C during 10 min, rinsed with deionized water, dried with hot air and weighted. The cycle is repeated accordance with ASTM Standard G The average corrosion rate is calculated as follows:

5 where corrosion rate is in mm/yr; weight loss is in grams; area is in cm 2 ; time is in hours; and density is in g/cm RESULTS 4.1 Amine degradation Amines degrade in the process in presence of NOx, O 2 and CO 2 as well as due to high temperatures. The most common amine, 16 different degradation compounds has been identified in 30wt% MEA 12. Many of these compounds are formed in small amounts and good analytical methods are therefore important. IC is used to analyse for nitrate and nitrite as well as formic, oxalic, glycolic and acetic acids and some amines. Together with IC, we have a possibility to get LC-MS and GC-MS analyses for other possible degradation compounds like amides, amine derivatives and nitrosamines. An example of degradation compounds possibly found in degraded liquid 30wt% MEA solvent is presented in Figure 4.1 In the CO 2 capture research field new solvents are constantly suggested. These solvents need to have the right characteristics to be suitable. In the process point of view it is important that the solvent is stable in process conditions as well as that it does no foam and requires only a little energy for reversing the absorption reactions. Surplus to these it is important that the solvent and its degradation compounds are safe for the environment. Additionally as mentioned earlier corrosion is a possible issue. Corrosion happen due to the solvent is self or due to the degradation compounds that are formed during the operation. So to understand the degradation and to be able to analyze and identify degradation compounds is an important part of the research. An example of degradation compounds quantified during thermal degradation experiment is shown in figure 4.2. Figure 4.1: Examples of identified degradation products

6 Closed MEA Concentration (ppm) Concentration HEI (ppm) OZD HEA HEGly HEPO HEF BHEOX Formate Oxalate Nitrate Nitrite HEI Time (weeks) 0 Figure 4.2: Example of degradation compounds quantified in thermal degradation experiment. Data from ref [12] 4.2 Amine degradation An example of oxidative degradation experiment is shown in the figure 4.3 where the MEA concentration at temperatures of 55, 65 and 75 o C over the experiment (21 days) is shown 13. The figure indicates that MEA degrades faster with increasing temperature. In these experiments, performed in the open oxidative degradation setup air was used. Same trends are seen for other O 2 concentrations %O 2 Concentration (mol/l) C run1 55C run2 55C run3 65C run1 65C run2 75C Time (days) Figure 4.3: Loss of MEA in oxidative degradation experiment. Figure is from reference [11] The degration rate depends on the amine. An example of this is shown in Figure 4.4, where some results from thermal degradation experiments for four amines are shown. This figure illustrates why it is important to carefully test all promising solvents for thermal and oxidative degradation. The lab scale degradation experiments should be compared relatively to for example MEA since these experiments do not present the real situation in an absorption stripper system. However these give a good indication how stable the solvent is and it also allows relatively cheaply study the degradation mechanisms and identify possible degradation compounds that would likely be found in a real process.

7 Amine loss (%) Time (week) KSAR KSAR* AB AB* KGlycine Figrue 4.4: Example of amine loss during thermal degradation experiment. Data from ref. [12] 4.3 Corrosion Test As mentioned above corrosion can be caused either by the solvent itself or due to the formation of corrosive degradation compound. In Figure 4.5 one can see some results from effect of acids on corrosivity of 30wt% MEA at 50 o C. It can be seen that the different acids have different effect on the corrosion. However corrosion rate at 50 o C would most likely vary from the corrosion rate in a real plant, since in reality the solvent is also exposed to high temperatrues. Figure 4.5: Corrosion rates at 50 C (in-house data) 5. CONCLUSIONS The paper gives an overview of our activities on solvent degradation and corrosion in post combustion CO 2 capture plants. It presents the main equipment and shows some results from the laboratory. Understanding degradation and corrosion is vital for the development of new solvents and degradation experiments should be done early in the qualification process of new solvents. At the same time degradation and corrosion work requires a good understanding of chemistry and access to good analytical equipment that allows identification and quantification of degradation compounds. REFERENCES 1. EPA 2. Bo Zhao, Yuekun Sun, Yang Yuan, Jubao Gao, Shujuan Wang, Yuqun Zhuo,Changhe Chen. Study on Corrosion in CO2 Chemical Absorption Process Using Amine Solution. Tsinghua university, Beijing , China. Energy Procedia 4 (2011) Eirik F. da Silva, Hélène Lepaumier, Aslak Einbu, Andreas Grimstvedt, Kai Vernstad, Solrun Johanne Vevelstad, Hallvard F. Svendsenb and Kolbjørn Zahlsena. Understanding MEA degradation in post-combustion CO2 capture SINTEF and NTNU.

8 4. Kohl, A., Nielsen, R. Gas Purification, Gulf Publishing Company, DuPart, M.S., Bacon, T.R., Edwards, D.J, Understanding corrosion in alkanolamine gas treating plants. Part 1&2. Hydrocarbon Processing, April 1993 issue, pages 75-80, and May 1993 issue, pages NTNU: Annual Report Department of Chemical Engineering. 7. Vevelstad, S.J., Grimstvedt, A., Einbu, A., Knuutila, H., da Silva, E.F., Svendsen, H.F., 2013a. Oxidative degradation of amines using a closed batch system. Submitted to the Journal of Greenhouse Gas Control. 8. Vevelstad, S.J., Grimstvedt, A., Elnan, J., da Silva, E.F., Svendsen, H.F., 2013b. Oxidative degradation of 2-ethanolamine; the effect of oxygen concentration and temperature on product formation. Submitted to The Journal of Greenhouse Gas Control. 9. Andreas Grimstvedt, Eirik Falck da Silva and Karl Anders Hoff Thermal degradation of MEA, effect of temperature and CO2 loading. TCCS 7, June da Silva, E.F., Lepaumier, H., Grimstvedt, A., Vevelstad, S.J., Einbu, A., Vernstad, K., Svendsen, H.F., Zahlsen, K., Understanding 2-Ethanolamine Degradation in Postcombustion CO2 Capture. Industrial & Engineering Chemistry Research 51, Vevelstad, SJ., Grimstvedt, A., Usman, M., Johansen, MT., da Silva, EF., Knuutila, H. and Svendsen, HF. Oxidative degradation of MEA; the effect of oxygen concentrations and temperature on product formation. The Trondheim CCS Conference, TCCS-7. June Vevelstad, S.J., Grimstvedt, A., Knuutila, H. and Svendsen, H.F. Thermal degradation on already oxidatively degraded solutions. 11 th International Conference on Greenhouse Gas Technologies, GHGT11, Kyoto, Japan, Ingvild Eide-Haugmo: Environmental impacts and aspects of absorbents used for CO2 capture. Doctoral thesis. NTNU Trondheim, 2011