초록 ▼

2. 개발내용 및 결과
- Pd계 분리막 개발 : 지지체 제조 표준화 및 분리막 제조조건 최적화에 의한 142ml/min/cm² 수소투과율(미국 DOE 2015년 목표치 150ml/min/cm²의 95%)
- 다층모듈 개발 : CO₂/H₂ 혼합가스 처리용량 0.5 Nm³/hr 다층모듈(분리막 4개)과 1 Nm³/hr의 다층 모듈 (분리막 10개)를 설계/제작/성능자료 확보함. 다층모듈의 고압운전을 위하여

2. 개발내용 및 결과
- Pd계 분리막 개발 : 지지체 제조 표준화 및 분리막 제조조건 최적화에 의한 142ml/min/cm² 수소투과율(미국 DOE 2015년 목표치 150ml/min/cm²의 95%)
- 다층모듈 개발 : CO₂/H₂ 혼합가스 처리용량 0.5 Nm³/hr 다층모듈(분리막 4개)과 1 Nm³/hr의 다층 모듈 (분리막 10개)를 설계/제작/성능자료 확보함. 다층모듈의 고압운전을 위하여 모듈 내/외부 압력의 상쇄를 유도하는 내압 챔버를 활용하였으며, 0.5 Nm³/hr 규모 다층모듈에 혼합가스(H₂:CO₂=6:4)를 이용한 이산화탄소 농축실험 결과, 20bar에서 92.3% 이상으로 이산화탄소를 농축함과 동시에 분리막 투과 수소는 99.5%를 얻음
- 탈 Pd계 신규 분리막 개발 : 수소, 이산화탄소/수소 분리특성 및 내구성 평가를 통한 선별
과정으로 바나듐 계열의 분리막 신조성을 5종 이상 개발하였음. V85Al10Co5, V99.8B0.2, V₉₉Y₁, V₉₀Al_9.75Y_0.25, V_89.8Cr₁₀Y_0.2 조성의 바나듐계 분리막은 Pd 대비 1000의 1 수준의 재료비로 Pd보다 높은 투과도를 얻을 수 있었으며, V99.8B0.2 분리막의 경우 65 ml/min․cm² (P=5 bar, t=500μm, 400℃)의 최대 투과량에 도달함
- 실험실규모 연소전 CO₂ 포집 공정 개발(2L/min) : 연소전 포집실험결과, 압력 15기압, 분리막단위 면적당 유량이 60cc/min.cm² 조건에서 CO₂ 포집가스(retentate) 조성은 CO:H₂:CO₂ = 2.0:7.6:90.4%로 CO₂를 90%이상 포집할 수 있음
- 벤치규모 연소전 CO₂ 포집 공정 개발(1Nm³/hr) : 실험실규모 공정실험 결과를 이용하여 벤치규모 공정 설계, 제작 및 시운전 함. WGS와 다층분리막을 연계한 벤치규모 연소전 공정으로, 최적조건에서 실험결과로 WGS 후단 조성은 CO:H₂:CO₂ = 0.76:59.45:39.79%, 분리막 공정 조건은 20기압, 400℃에서 CO₂ 포집가스 조성은 CO:H₂:CO₂ = 1.2:8.0:90.6%로 CO₂를 90%이상 포집할 수 있음

Abstract ▼

Although various technical portfolios are applied for the decrease of greenhouse gas, recently CCS (Carbon capture and storage) is emerged as a controllable high-capacity greenhouse gas treatment technique. Among the pre-combustion CO₂ recovery processes, the hydrogen membrane application

Although various technical portfolios are applied for the decrease of greenhouse gas, recently CCS (Carbon capture and storage) is emerged as a controllable high-capacity greenhouse gas treatment technique. Among the pre-combustion CO₂ recovery processes, the hydrogen membrane application process is the best process of all with the highest energy efficiency. To succeed this process, the inexpensive CO₂/H₂ membrane with high permeability and high selectivity is required. In the present work, the Pd-based membranes with high permeability and high selectivity for H₂ and CO₂ separation have been investigated to apply for CCS. Thin-layer membrane coating over the surface of support is an essential factor to obtain the relatively higher membrane performance. In order to deposit the ultra thin Pd layer, 2~3 μm, on the surface of support, the preparation method of the porous nickel metal support was standardized to reduce its surface roughness and the membrane preparation condition was optimized. As a result, the hydrogen flux of prepared membrane was 142ml/min/cm², close to the goal for 2015, 150ml/min/cm² of US Department of Energy. Along with the membrane research, we performed the research of membrane module, able to operate in the relatively higher pressure. In the case of the unit-membrane module using metal double O-ring, it is possible to use in high pressure up to 21 bar. Also, in the case of the multi-membrane module using specially designed high-pressure chamber, it is possible to operate in a pressure higher than 30 bar. Applying the prepared unit-membrane module, we completed the CO₂ recovery experiment with the mixed gas (H₂:CO₂=6:4). More than 97% of CO₂ gas in the retentate side was concentrated in 20 bar and the hydrogen purity in the permeate side is 96.6%. In the case of the multi-module consisting of 4 plate-type membranes, able to treat the syngas of 0.5Nm3/h, we tested its performance with single-gas. The result showed that in 20 bar, the hydrogen flow rate in permeate side was approximately 15L/min and its selectivity(H₂/N2) was close to 750. For CO₂ recovery experiment with mixed gas (H₂:CO₂=6:4, feeding: 480 L/h), in 20 bar, more than 92.3% of CO₂ gas in the retentate side was concentrated and the hydrogen purity in the permeate side is 99.5%.
In the present research and experiments, membranes have been developed for the purpose of application in pre-combustion capture. Moreover, the membrane separation system development was also conducted for separation and enrichment of carbon dioxide of H₂/CO₂ mixture after coal gasification. The membrane separation system have advantages such as high thermal stability, hydrogen permeability and H₂/CO₂ selectivity in high pressure and temperature process. Highly thermal stable polymeric membrane was produced to develop membrane separation system for applying to pre-combustion CO₂ capture process under the high temperature and pressure conditions. In order to improve permeability, which was one of the weakness of previous membranes, production of membranes for high H₂ permeability was applied by highly thermal stable TR(thermally rearranged) membrane developed autonomously at Hanyang university. Thermally rearrangement is a rearrangement of polymer main chain by heating over the glass transition temperature of polymer. By this method, highly permeable material for a specific gas can be produced, increasing free volume and forming microcavities inside. New membrane suitable for hydrogen separation was produced by TR(thermal rearrangement) method. For new membrane, technology of tuned microcavity size, which was appropriate for hydrogen molecular size and shape, was researched by synthesis precursors of polymer in switching various monomers. Gas permeability test and the test under high temperature and high pressure were performed with this membrane. As a result, permeability of hydrogen was 2.0x10-8cm3(STP).cm/cm².s.cmHg and selectivity of H₂/CO₂ was 7. One step further, experiments for developing hollow fiber membrane having high flux and surfaces was performed, producing asymmetric membrane and testing gas permeability. It can be found for optimized values of concentration and flux under constant pressure by process valuables and its control, H₂/CO₂ gas mixture used in pre-combustion capture is suitable application of membrane separation technology because of these gases emission under high temperature and pressure, In addition, membrane technology is competitive in comparison of other technology by considering of high energy efficiency and economical energy costs.
Pre-combustion CO₂ capture technology is recently focused on one of reduction methods of carbon dioxide from power generation system in view of environmental (climate change) and sustainable point (Hydrogen economy). Separation of hydrogen from water-gas shift reactors through dense hydrogen transport membranes, while retaining CO₂ produces essentially pure hydrogen in the permeate and CO₂ at high pressure and high concentration, which is ideal for efficient sequestration of CO₂. To commercialize pre-combustion CO₂ capture process, the inexpensive CO₂/H₂ membrane with high permeability and high selectivity is required and also effective module design is necessary to investigate the performance and durability of membrane. In this work, novel composite membranes have been developed to separate hydrogen from mixed gases such as hydrogen, hydrogen/carbon dioxide, hydrogen/carbon dioxide with CO or/and H₂S which are model gases of water gas shift reaction. In addition various modules (screw type horizontal reactor and flange type vertical reactor) and sealing methods (glass melting, brazing, knife edge and O-ring) were designed and optimized for permeation test of membrane. In the case of the flange type membrane module with metal double O-ring, it is possible to obtain very low level leakage of 0.04 ml/min․cm² in high pressure (10 bar) and temperature (400℃).
The hydrogen flux of membrane with various compositions was investigated as a function of temperature, partial pressure of hydrogen and model gas mixtures.
Through the screening test, we have developed 5 different novel membranes with high hydrogen flux and stability; V85Al10Co5, V99.8B0.2, V99Y1, V90Al9.75Y0.25, V89.8Cr10Y0.2. The price of these vanadium base metal alloy membranes were 1000 times lower than that of Pd membrane and in the case of V99.8B0.2 membrane with 500 μm thickness, the maximum flux of 65 ml/min․cm² and selectivity of 4000 were obtained in the condition 5 bar and 400 ℃. On the other hand, the oxide barrier layer was developed to prevent the inter-diffusion between membrane metal and top side catalyst layer using anodizing method. After long term operation it was known that this method was effective to inhibit the inter-diffusion.
Coal gasification is the essential technology that can meet the interim hydrogen demand of large quantity before entering the hydrogen economy. Membrane processes for gas separation have many advantages of energy saving, compact size, and easy scale-up. Solid oxide components such as protonic separation membranes for the hydrogen purification require thermo-chemical stability and high conductance. The perovoskite Y:BaCeO₃ exhibits good proton conduction at high temperatures, but shows poor thermo-chemical stability. Substituting Zr for Ce in Y:BaCeO₃ improves the thermo-chemical stability but reduces proton conduction. In this work, Y:BaZrO₃ and Y:BaCeO₃ were systematically investigated for chemical stability. In addition, SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-β and SrCe_0.95Yd_0.05O_3-α-Ce_0.9Y_0.1O_2-β composites in CO₂ and H₂ gases were investigated. Thermogravimetric analysis (TGA) was performed in gaseous CO₂ and electrical conductivity of the protonic conductors were also measured between 500 and 900℃ in air and H₂ atmosphere. Y:BaZrO₃ and SrCe0.95Gd0.05O_3-α-Ce0.9Gd0.1O2-β showed good chemical stability of in CO₂ and boiled water atmosphere, and high conductivity at hydrogen condition. For high efficiency of hydrogen separation, ultimate thin and dense Pd-BaZr^0.85Y^0.15O₃ membrane has to be coated on porous substrate using Dual sputter and Aerosol deposition processes. Ultimate thin and dense Pd-BaZr_0.85Y_0.15O₃ membrane was successfully synthesized on a YSZ porous substrate with disk and cylinder type. The structural and chemical features of the Pd-BaZr_0.85Y_0.15O₃ membrane were investigated by X-ray diffraction and showed that well-crystallized membrane, Pm-3m space group of BaZrO₃, was synthesized. The structural morphologies of deposited membrane were assessed by scanning electron microscopy and transmision electron microscopy of surface and cross section. The cross section of Pd-BaZr_0.85Y_0.15O₃ membrane shows that the coating is quite dense with columnar structure. Pd-BaZr_0.85Y_0.15O₃ membrane with cylindrical type was evaluated under the condition of H₂(60%)-CO₂(40%) mixed gas ranging from 1 to 25 bar pressures at 500-800oC, and their H₂ flux and selectivity shows 31.2 ml/min-cm² and 1,100, respectively. Also, the durability of Pd-BaZr_0.85Y_0.15O₃ membrane maintained over 95% after 240 h.
The importance of developing CO₂ capture and storage(CCS) technologies is increasing rapidly as it is closely related with preventing climate change by global warming. Among various CCS technologies, pre-combustion CO₂ capture process using membranes are regarded as a next-generation capture process due to its effectiveness and economic feasibility, and R&D for pre-combustion CO₂ capture with membrane is lively on the way in many advanced countries.
In this study, a core process for pre-combustion CO₂ capture has been developed using water-gas shift reactors and dense hydrogen transport membranes. For the past three years of this project, tests for membranes, developing lab-scale and bench-scale process, and design for upgrading system have been performed, and test for reaction/separation process is also proceeded. An efficiency analysis of developed membranes which is used for pre-combustion CO₂ capture is performed, and its results are used for the background data of design of overall CO₂ capture process. In addition, to set up the development direction, compared evaluation of Pd-Cu membrane and commercial membranes from A company(A membrane) is carried out.
Water-gas shift(WGS) unit process for converting syngas to CO₂ and H₂ is developed, and it is composed of HTS and LTS. Gas compositions of the rear site of LTS were given by H₂=57-60%, CO₂=36-42%, and CO=under 1% at operation conditions of pressure=1-20bar, S/C ratio=2.5-5, temperature of HTS=350-400℃, and temperature of LTS=180-230℃. To develop the lab-scale pre-combustion CO₂ capture process(2L/min), WGS and membrane process-combined system for integrating coal gasification process was designed, manufactured using ASPEN and Fluent and operated using Pd-Cu membrane module and A membrane module. Pre-combustion CO₂ capture test results showed that the composition of CO₂ captured gas(retentate) was CO:H₂:CO₂ = 2.0:7.6:90.4vol% at conditions of pressure=15bar and flow rate per unit membrane area=60cc/min·cm², and it achieved over 90% of CO₂ concentration.
In case of A membrane, it showed the retentate gas composition as CO:H₂:CO₂ = 1.0:35.7:63.3vol% at condtions of pressure=10bar and flow rate per unit membrane area=26cc/min·cm². For the purpose of developing bench scale pre-combustion CO₂ capture process(1Nm3/hr), lab-scale experimental results were used for designing, manufacturing and operating of bench-scale process. The optimum results of bench-scale pre-combustion process composed of WGS and multi-layer membrane module showed that the composition of CO₂ captured gas(retentate) was CO:H₂:CO₂ = 1.2:8.8:90.6vol% at operation conditions of pressure=20bar, temperature=200℃, composition of gas stream from WGS as CO:H₂:CO₂ = 0.8:59.5:39.7vol%. This experimental result also obtained over 90% of CO₂ concentration. As using experimental results from bench-scale process and process interpretation tools, fundamental design data of advanced CO₂ capture process which is integrated with 1ton-coal/day scale coal gasification is attained. In addition, after development of consecutive reaction/separation process-based technology that performs WGS reaction through catalysts and CO₂ capture using membranes at the same time, over 130% of CO conversion rate is achieved. In conclusion, in this project, bench-scale pre-combustion CO₂ capture process(1Nm3/hr) has been developed, and its performance proved to show over 90% of CO₂ recovery at the conditions of temperature=400℃ and pressure=20bar. In the next step of this project, coal gasification system integrated pre-combustion CO₂ capture process will be developed.