CO Capture from Flue gas using 2 Amino acid salt solutions Benedicte Mai Lerche Ph.D. Thesis August 2012 CO Capture from Flue gas using 2 Amino acid salt solutions (cid:19)(cid:138)(cid:484)(cid:7)(cid:484)(cid:3)(cid:23)(cid:138)(cid:135)(cid:149)(cid:139)(cid:149)(cid:3) (cid:5)(cid:155)(cid:3) (cid:5)(cid:135)(cid:144)(cid:135)(cid:134)(cid:139)(cid:133)(cid:150)(cid:135)(cid:3)(cid:16)(cid:131)(cid:139)(cid:3)(cid:15)(cid:135)(cid:148)(cid:133)(cid:138)(cid:135) (cid:884)(cid:882)(cid:883)(cid:884)(cid:3) (cid:6)(cid:8)(cid:21)(cid:8)(cid:3)(cid:486)(cid:3)(cid:6)(cid:135)(cid:144)(cid:150)(cid:135)(cid:148)(cid:3)(cid:136)(cid:145)(cid:148)(cid:3)(cid:8)(cid:144)(cid:135)(cid:148)(cid:137)(cid:155)(cid:3)(cid:21)(cid:135)(cid:149)(cid:145)(cid:151)(cid:148)(cid:133)(cid:135)(cid:149)(cid:3)(cid:8)(cid:144)(cid:137)(cid:139)(cid:144)(cid:135)(cid:135)(cid:148)(cid:139)(cid:144)(cid:137)(cid:3) (cid:7)(cid:135)(cid:146)(cid:131)(cid:148)(cid:150)(cid:143)(cid:135)(cid:144)(cid:150)(cid:3)(cid:145)(cid:136)(cid:3)(cid:6)(cid:138)(cid:135)(cid:143)(cid:139)(cid:133)(cid:131)(cid:142)(cid:3)(cid:131)(cid:144)(cid:134)(cid:3)(cid:5)(cid:139)(cid:145)(cid:133)(cid:138)(cid:135)(cid:143)(cid:139)(cid:133)(cid:131)(cid:142)(cid:3)(cid:8)(cid:144)(cid:137)(cid:139)(cid:144)(cid:135)(cid:135)(cid:148)(cid:139)(cid:144)(cid:137)(cid:3) (cid:23)(cid:135)(cid:133)(cid:138)(cid:144)(cid:139)(cid:133)(cid:131)(cid:142)(cid:3)(cid:24)(cid:144)(cid:139)(cid:152)(cid:135)(cid:148)(cid:149)(cid:139)(cid:150)(cid:155)(cid:3)(cid:145)(cid:136)(cid:3)(cid:7)(cid:135)(cid:144)(cid:143)(cid:131)(cid:148)(cid:141)(cid:3) (cid:7)(cid:14)(cid:486)(cid:884)(cid:890)(cid:882)(cid:882)(cid:3)(cid:14)(cid:137)(cid:149)(cid:484)(cid:3)(cid:15)(cid:155)(cid:144)(cid:137)(cid:132)(cid:155) 1 Copyright©: Benedicte Mai Lerche August 2012 Address: Center for Energy Resources Engineering Department of Chemical and Biochemical Engineering Technical University of Denmark Søltofts Plads, Building 229 DK-2800 Kgs. Lyngby Denmark Phone: +45 4525 2800 Fax: +45 4525 4588 Web: www.cere.dtu.dk Print: J&R Frydenberg A/S København October 2013 ISBN: 978-87-93054-09-7 2 (cid:3) (cid:3) (cid:498)(cid:4)(cid:149)(cid:3)(cid:150)(cid:138)(cid:135)(cid:3)(cid:150)(cid:148)(cid:151)(cid:135)(cid:3)(cid:143)(cid:135)(cid:150)(cid:138)(cid:145)(cid:134)(cid:3)(cid:145)(cid:136)(cid:3)(cid:141)(cid:144)(cid:145)(cid:153)(cid:142)(cid:135)(cid:134)(cid:137)(cid:135)(cid:3)(cid:139)(cid:149)(cid:3)(cid:135)(cid:154)(cid:146)(cid:135)(cid:148)(cid:139)(cid:143)(cid:135)(cid:144)(cid:150)(cid:481)(cid:3)(cid:150)(cid:138)(cid:135)(cid:3)(cid:150)(cid:148)(cid:151)(cid:135)(cid:3) (cid:136)(cid:131)(cid:133)(cid:151)(cid:142)(cid:150)(cid:155)(cid:3)(cid:145)(cid:136)(cid:3)(cid:141)(cid:144)(cid:145)(cid:153)(cid:139)(cid:144)(cid:137)(cid:3)(cid:143)(cid:151)(cid:149)(cid:150)(cid:3)(cid:132)(cid:135)(cid:3)(cid:150)(cid:138)(cid:135)(cid:3)(cid:136)(cid:131)(cid:133)(cid:151)(cid:142)(cid:150)(cid:155)(cid:3)(cid:153)(cid:138)(cid:139)(cid:133)(cid:138)(cid:3)(cid:135)(cid:154)(cid:146)(cid:135)(cid:148)(cid:139)(cid:135)(cid:144)(cid:133)(cid:135)(cid:149)(cid:484)(cid:3) (cid:23)(cid:138)(cid:139)(cid:149)(cid:3)(cid:136)(cid:131)(cid:133)(cid:151)(cid:142)(cid:150)(cid:155)(cid:3)(cid:12)(cid:3)(cid:150)(cid:148)(cid:135)(cid:131)(cid:150)(cid:3)(cid:145)(cid:136)(cid:499)(cid:484)(cid:3) (cid:514)William Blake(cid:481)(cid:3)All Religions Are One(cid:481)(cid:3)(cid:498)(cid:23)(cid:138)(cid:135)(cid:3)(cid:4)(cid:148)(cid:137)(cid:151)(cid:143)(cid:135)(cid:144)(cid:150)(cid:499)(cid:3)(cid:523)(cid:883)(cid:889)(cid:890)(cid:890)(cid:524)(cid:484)(cid:3) i 3 ii 4 Summary By implementing carbon dioxide (CO ) capture, it is possible to clean the flue gas 2 from coal-fired power plants, so that it is almost completely free of this greenhouse gas. The most advanced techniques towards practical application are based on chemical absorption, where CO in the flue gas is chemically bond by a 2 solvent, usually an aqueous solution of amines, resulting in a cleaned gas being released to the atmosphere. Heating of the solution, desorbs the CO and 2 regenerates the solvent, which is then ready for a new round of absorption. The captured CO can then be compressed and sent to storage. 2 Typical solvents for the process are based on aqueous solutions of alkanolamines, such as mono-ethanolamine (MEA), but their use implies economic disadvantages and environmental complications. Amino acid salt solutions have emerged as an alternative to the alkanolamines, partly because they are naturally occurring substances, and partly because they have desirable properties, such as lower vapor pressures and higher stability against oxidative degradation. One important feature of these new solvents is the formation of solids upon CO absorption, which 2 happens especially at higher CO loadings and/or amino acid salt concentrations. 2 The formation of solids poses challenges, but it also holds the promise for improving the efficiency of the capture process. This project focuses on phase equilibrium experiments of five CO + amino acid 2 salt + H O systems, at conditions relevant for the CO capture process. Also, 2 2 iii 5 attention is given to the chemical compositions of the precipitations, which forms as a result of CO absorption into the five amino acid salt solutions. 2 Phase equilibrium data are needed to develop safe and economically viable capture processes. Two different experimental apparatuses were used. One was developed specifically for this project and is based on an analytical semi-flow method. The other has recently been developed in another project, and is based on a synthetic method. The semi-flow method was used for measurements at 10 kPa CO partial pressure, total pressure equal to the atmospheric pressure and 2 temperatures of 298 K, 313 K and 323 K; these conditions cover the absorber part of the capture process. The apparatus based on the synthetic method was used to obtain data at different pressures and temperatures up to 353 K (80 ºC), which is the maximum operation temperature of some of the components in the apparatus. Ideally, measurements in the full temperature range for desorption, which usually needs approximately 393 K (120 ºC), would be desirable. Using the two apparatuses, CO solubility in aqueous solutions of MEA and the 2 potassium salts of taurine, glycine, L-alanine, L-proline and L-lysine were examined. It was found that all of the tested amino acid salt solutions have the potential to replace MEA. Nevertheless, solutions of the potassium salt of L-lysine showed the best properties. iv 6 The chapters of this thesis are organized as follows: Chapter 1 is a brief introduction to the central issues of this work, setting the subject of the project in perspective to the issues of global warming and CO 2 capture and storage (CCS). Chapter 2 explains the principle behind the chemical absorption of CO from flue 2 gas, emphasizing on the issues involving the solvent. Chapter 3 is dedicated to the concept of using amino acids salt solutions as solvents in CO capture, it includes a description of general amino acids chemistry 2 and an outline of the chemical reactions involved in CO absorption into amino 2 acids salt solutions. Chapter 4 deals with building and validation of the new apparatus for measuring of CO solubility based on the semi-flow method. A validation study of CO 2 2 solubility in aqueous solutions of MEA is presented. Chapter 5 focuses on determination of the chemical compositions of the precipitations, which arise in the five amino acid salt solutions upon CO 2 absorption. The solutions were saturated with CO at 298 K, using the apparatus 2 based on the semi-flow method. The precipitates were isolated and analyzed with XRD. v 7 Chapter 6 concerns a CO solubility study using the apparatus based on the semi- 2 flow method; CO solubility were examined in aqueous solutions of MEA and the 2 five amino acid salts, with concentrations between 2 and 8 molal and temperatures around 298 K, 333 K and 323 K. Chapter 7 describes a CO solubility study using the apparatus based on the 2 synthetic method. CO solubility in aqueous solutions of the potassium salts of L- 2 lysine and L-proline, with concentrations of 3.5 molal and 7 molal respectively, were studied at CO partial pressures up to about 760 kPa, and temperatures 2 around 313 K, 333 K and 353 K. Similar data were obtained with solutions of 7 molal MEA, at the same temperatures and at CO partial pressures up to around 2 2.3 MPa Chapter 8, concludes on the accomplishments of the project, and finally addresses considerations concerning future work. vi 8 Resumé (Dansk) Ved at implementere kuldioxid (CO ) fangst eller såkaldt ”CO capture” er det 2 2 muligt at rense røggassen fra kulfyrede kraftværker, således at den næsten er helt fri for denne drivhusgas. De teknikker, som er længst udviklede frem mod praktisk anvendelse, bygger på kemisk absorption, hvor CO i røggassen bindes 2 kemisk af en opløsning kaldet et solvent, sædvanligvis en vandig opløsning af aminer, hvilket resulterer i, at en renset gas frigives til atmosfæren. Opvarmning af opløsningen desorberer CO gassen igen og regenerer solventet, som så er klar 2 til en ny runde absorption. Den indfangede CO kan derefter komprimeres og 2 deponeres. Typiske solventer til denne proces er baseret på vandige opløsninger af alkanolaminer såsom mono-ethanolamin (MEA), men deres anvendelse indebærer økonomiske ulemper og miljømæssige komplikationer. Aminosyre salt opløsninger har vundet interesse, som alternativ til alkanolaminerne, dels fordi de er naturligt forekomne, og dels fordi de har ønskværdige egenskaber; såsom lavere damptryk og højre stabilitet over for oxidativ nedbrydning. Et vigtigt træk ved disse nye solventer er dannelsen af udfældninger, som følge af CO 2 absorptionen, hvilket sker især ved høj CO optagelse og/eller høje aminosyre salt 2 koncentrationer. Dannelsen af udfældning er en udfordring, men kan muligvis også forbedre effektiviteten af ”CO capture” processen. 2 Arbejdet i dette projekt vedrører faseligevægts eksperimenter for fem CO + 2 aminosyre salt + H O systemer, ved forhold som er relevante for ”CO capture” 2 2 vii 9
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