Infrastructure for CO 2 Capture from South African Power Generating Plant

Transcription

1 School of Chemical and Metallurgical Engineering University of the Witwatersrand Infrastructure for CO 2 Capture from South African Power Generating Plant Michael Daramola, PhD, C.Eng, MIChemE School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa michael.daramola@wits.ac.za 1

2 SA Power Generating Plant Coal-fired Steam Power Plant using pulverized coal 2

3 Advantages: SA has abundant coal reserves. SA Power Generation Coal-fired power stations are reliable. South Africa's infrastructure to generate electricity from coal is well established. Burning coal is the most cost-effective and energy efficient way of generating electricity. Disadvantages: Coal has the most waste problems of all energy sources. Waste includes sulphur and nitrogen oxides, organic compounds, heavy metals, radioactive elements, greenhouse gases and a lot of ash. Building a coal-fired power station is a long and expensive process. South Africa's coal fields are concentrated in Mpumalanga, which limits the location options for power stations. tricity.aspx 3

4 South Africa & CO 2 Emission Based on 2010 estimate: World s Emission = 33,508,901 thousands of CO 2 tonnes %CO 2 Emission/year (United States Department of Energy's Carbon Dioxide Information Analysis Center (CDIAC) for the United Nations 4

5 Key Questions Can Carbon Capture and Storage (CCS) reduce CO 2 emission and make the environment clean? If YES. How feasible is it in South Africa? What infrastructure do we need to make it feasible? 5

6 Stages & Infrastructure for CCS Storage Deep unmineable coal seams Geological formations (underground) Ocean/saline aquifers Depleted oil wells for enhanced oil recovery (EOR) CO 2 transportation Pipelines Ships Rails Road Carbon Capture Absorption system & absorbent Adsorption system & adsorbent Membrane system & long-life cheaper membranes Carbonate looping system 6

7 Current Situation of CCS in SA Storage (Deep unmineable coal seams) Estimated capacity of geological storage = 150 gigatonnes of CO 2 Almost 98% of the sites located offshore along the coast of South Africa Inadequate studies on CO 2 sorption behaviour of SA coals to produce enough CO 2 sequestration data have retarded the expected progress in this aspect Less effort geared towards CO 2 Capture & CO 2 transport in South Africa. ALTHOUGH NO STORAGE FACILITY, NO NEED TO CAPTURE & TRANSPORT. For holistic CCS technology in SA, CO 2 storage, CO 2 capture and CO 2 transport should be considered 7

8 CO 2 Capture in SA PGP o Ease to retrofit to an existing power plant with least difficult o Designing a system to handle enormous CO 2 produced is a great challenge o Very dilute CO 2 stream making application of membrane system impossible Post-combustion CO 2 Capture Spigarelli & Kawatra (2013) J. CO2 Utilization 1:

9 Infrastructure for Postcombustion CO 2 Capture 9

10 Absorption System & Absorbents Does not affect operation flexibility of the existing plant or new one built High cost (CAPEX and OPEX) Thermal efficiency of the power plant Could reduce by 10-15% due to solvent regeneration For every tonne of CO 2 captured, tonnes of MEA is emitted. A typical 2.4 GW power generating plant using pulverized black coal will emit 0.16 tonnes CO2 /min Spigarelli & Kawatra (2013) J. CO2 Utilization 1: MacDowell et al. (2010) Energy Environ Sci. 3:

11 Absorbent for CO 2 capture: Amine It is chemical absorption whereby CO 2 is weakly bonded to the solvent Monoethanolamine (MEA) is commonly used A blend of MEA with other amine such as 2-amino-2- methyl-1-propanol; diethanolamine, have been shown to outperform MEA absorption Problems: Losses of amine from the system due to volatility of the amine solution Corrosion of the equipment because O 2 in the flue gas reacts with the amine to form corrosive compounds Oxidative/thermal degradation of the solvent or reaction with sulphur. MacDowell et al. (2010) Energy Environ. Sci. 3:

12 Adsorption System & Adsorbents Adsorption is a process in which atoms, molecules, or ions accumulate on the surface of a (liquid or) solid material Physical adsorption, physisorption, which involves van der Waals forces (as in vapour condensation) Chemical adsorption or chemisorption, which involves chemical bonding (and often dissociation). Physical adsorption is a reversible process, while chemisorption is irreversible Spigarelli & Kawatra (2013) J. CO2 Utilization 1: Adsorption is always followed by regeneration of the adsorbent. 12

13 Adsorption System & Adsorbents Efficiency depends on: - selectivity of the solid material to CO 2 - specific surface areas of the solid (adsorbent) - Pore volume of the adsorbent - Chemical nature of the CO 2 and the solid - Temperature - Driving force Smaller size adsorbent results in higher utilization of internal surface area; but higher pressure drop for flow of bulk fluid through a mass of the adsorbent is a major problem 13

14 Chemical Adsorbents for CO 2 Capture Amine-based: - Amine-impregnated adsorbents - Amine-grafted adsorbents Basic organic group + inorganic metal oxide Interaction between CO 2 molecules and modified basic sites facilitates CO 2 adsorption via formation of covalent bonding Low heat of regeneration compared to amine because of low heat capacity of the support - Amine-impregnated adsorbents Polyethyleimine (PEI)-impregnated mesoporous silica PSI/amine PSI/CNT/amine Xu et al., 2002; Ma et al

15 Carbonate Looping (CL) System Use of mature fluidised bed technology (CFB) that provides: Very good gas-solid contacting Uniform temp distribution Loss in capacity to capture CO 2 due to sintering, attrition, chemical deactivation MacDowell et al. (2010) Energy Environ Sci. 3:

16 Carbonate Looping (CL) System Cheap, abundant non-toxic sorbent derived from limestone Use of mature fluidised bed technology Potential to minimize energy requirement Shimizu et al.,

17 Carbonate Looping System Potential synergy with cement industry (spent sorbent has the potential to be sold to the cement industry, potentially de-carbonising both industries) Dean et al. (2011) Energy Environ Sci. 4:

18 Hydrate & Low Temperature Media Hydrate Medium Low Temperature Medium 18

19 Membrane-Absorption System CO 2 selective membrane for Separating CO 2 /N 2 + Solvent for absorption Post-combustion CO 2 capture contactor-type membrane reactor CO 2 -lean gas stream CO 2 /N 2 Solvent CO 2 Solvent +CO 2 19

20 Membrane-Absorption System Solvent: Amine (monoethanolamine (MEA), or blend of MEA with other amine),ionic liquid Promising membrane candidates: MFI (zeolite), ZIF-8 Problems: - High CO 2 -selective membranes and reproducibility - Regeneration of the solvent for re-use - Environmental issues with disposal of spent solvent (e.g. AMINE) - Corrosion issues (O 2 from flue gas reacts with MEA to form corrosive substance) Blend of MEA and other amine could out-perform only MEA 20

21 Research Activities at Wits Development of composite adsorbents for post-combustion CO 2 capture o Polymer-based adsorbents for CO 2 capture o Zeolite/MOFs composite adsorbent for CO 2 capture o Chitosan-based composite adsorbent for CO 2 capture Synthesis, evaluation and optimization of composite adsorbent materials Chitsiga, T., Daramola, M.O., Wagner, N., Ngoy, J. (2015) Effect of the presence of water-soluble amines on the carbon dioxide (CO 2 ) adsorption capacity of amine-grafted poly-succinimide (PSI) adsorbent during CO 2 capture, Energy Procedia (accepted) 21

22 Research Activities at Wits Development of membrane materials/systems for CO 2 capture onanocomposite silicalite-1 /ceramic membranes for CO 2 /N 2 separation o Nanocomposite SAPO-34/ceramic membranes for CO 2 /N 2 separation o Nanocomposite sodalite/ceramic membranes for CO 2 /H 2 separation o Mixed matrix membranes (with MOFs, zeolite as fillers) for CO 2 /CH 4 /N 2 separation Daramola et al. (2015) Synthesis and characterization of nanoccomposite ceramic/sodalite membrane via pore-plugging technique, Journal of Membrane and Separation Technology, 4(1):

23 Research Activities at Wits Optimization of CO 2 sorption capacity of SA coal for CO 2 storage oeffect of impurities on the sorption behaviour olong term storage and effect on coal morphology/structure In collaboration with TUT Dr Kasturie Premlall PhD student 23

24 Research Activities at Wits Modelling and techno-economic evaluation of membrane system and adsorption systems for CO 2 capture in power plants omodelling to provide information on synthesis and process optimization o Techno-economic studies to provide information on the technical and economic feasibility of integrating the systems to existing power plants In collaboration with Software - General Algebraic Modelling System (GAMS) - Aspen plus Prof. Thoko Majozi & Dr Jean WITS 24

25 CCS & Power Generating Station In principle, CCS could capture CO 2 from power stations (35% of total) (not from cars, domestic ) Capture and storage - would add ~ ZAR 0.30/kWh to cost for gas; more for coal - in both cases much more initially Storage- could (when location appropriate) be in depleted gas fields, depleted oil fields, deep saline aquifers Issues are safety and cost (capture typically reduces efficiency by 10 percentage points, e.g. 46% 37%, 41% 32%,..), and how to count for Carbon credits. 25

26 CCS & Power Generating Station With current technology: capture, transmission and storage would ~ double generation cost for coal-fired power plants Time Now Expected situations with CCS About 25% less electricity for the same amount of coal burned 20 years 14-15% less electricity than equivalent without CCS 40 years Penalty eliminated 26

27 Think about IGCC Power Plants In IGCC power plants, the coal is not burnt in a conventional steam power plant, but is initially dried and supplied to a gasifier, in which high temperatures prevail. More cleaner production/generation than the conventional steam power plants. Less NOx, SOx and CO 2 emission IGCC: Integrated Gasification Combined Cycle 27

28 Think about CO 2 Utilization Conversion of CO 2 to value-added products MacDowell et al. (2010) Energy Environ. Sci. 3:

29 PhD Students on CCS Acknowledgements Postdoc MSc Students on CCS 29

30 Acknowledgements A/Prof. Nikki Wagner (University of Johannesburg) Prof. Olav Bolland (NTNU) (EnPe-NORAD Agreement) A/Prof Salam Titinchi (University of the Western Cape) Dr Kasturie Premlall (TUT) 30