Designing Materials and Processes for CO2 Capture with Solid Sorbents

Cyclic adsorption and regeneration of solid sorbents to remove CO2 from gas streams can be accomplished with a variety of different adsorbents and processes. Determining which adsorbents and which processes will be best suited for a given application requires simulations or experimental measurements of many different materials in many different processes. However, general principles can guide the development of carbon capture systems, based primarily on the performance and limitations of different adsorbents, types of gas-solid contactors used, heat exchange method, and managing pressure changes. The main types of adsorption processes are temperature swing, pressure swing, or a combined temperature and pressure swing. Temperature swing adsorption processes involve regenerating a sorbent saturated with CO2 through heating. In these processes heat transfer is generally the rate-limiting step and heating and cooling the sorbent is also the most energy intensive component of the process. To minimize the energy consumption of the process, the sorbent should have a moderate heat of adsorption to allow a large change in CO2 capacity through changing the temperature, the heat capacity of the heated and cooled material should be minimized, and heat transfer should be maximized. For pressure swing adsorption processes, on the other hand, the driving force for regenerating CO2 is provided by changing the partial pressure of CO2 between the adsorption and regeneration steps. Changing the pressure is the main component of the energy consumption and cycle time, and these are minimized by allowing complex process configurations with multiple pressure differentials and using an adsorbent with high capacity but low heat of adsorption. Combined temperature and pressure swing adsorption can be optimized through a combination of the factors above. Each of these cases yields a different optimal material, contacting strategy, and process configuration, but all can be approached using a common design methodology. This paper will present a design methodology for solid sorbent CCS systems. This will include design considerations for how to maximize the performance of a range of traditionally deployed and newly-discovered solid sorbents. Similarly, standard and novel process configurations will be discussed with descriptions of the possible benefits or drawbacks and the types of sorbent material that are best suited for each configuration. By comparing the performance of mature adsorbents and processes and the expected performance of adsorbents and processes currently under development, the state of the art and potential advances for CCS with solid adsorbents will be presented

Techno-Economic Analysis of a Secondary Air Stripper Process

We present results of an initial techno-economic assessment on a post-combustion CO2 capture process developed by the Center for Applied Energy Research (CAER) at the University of Kentucky using Mitsubishi Hitachi Power Systems’ H3-1 aqueous amine solvent. The analysis is based on data collected at a 0.7 MWe pilot unit combined with laboratory data and process simulations. The process adds a secondary air stripper to a conventional solvent process, which increases the cyclic loading of the solvent in two ways. First, air strips additional CO2 from the solvent downstream of the conventional steam-heated thermal stripper. This extra stripping of CO2 reduces the lean loading entering the absorber. Second, the CO2-enriched air is then sent to the boiler for use as secondary air. This recycling of CO2 results in a higher concentration of CO2 in the flue gas sent to the absorber, and hence a higher rich loading of the solvent exiting the absorber. A process model was incorporated into a full-scale supercritical pulverized coal power plant model to determine the plant performance and heat and mass balances. The performance and heat and mass balance data were used to size equipment and develop cost estimates for capital and operating costs. Lifecycle costs were considered through a levelized cost of electricity (LCOE) assessment based on the capital cost estimate and modeled performance. The results of the simulations show that the CAER process yields a regeneration energy of 3.12 GJ/t CO2, a $53.05/t CO2 capture cost, and LCOE of$174.59/MWh. This compares to the U.S. Department of Energy\u27s projected costs (Case 10) of regeneration energy of 3.58 GJ/t CO2, a $61.31/t CO2 capture cost, and LCOE of$189.59/MWh. For H3-1, the CAER process results in a regeneration energy of 2.62 GJ/tCO2 with a stripper pressure of 5.2 bar, a capture cost of $46.93/t CO2, and an LCOE of$164.33/MWh

In silico screening of carbon-capture materials

One of the main bottlenecks to deploying large-scale carbon dioxide capture and storage (CCS) in power plants is the energy required to separate the CO 2 from flue gas. For example, near-term CCS technology applied to coal-fired power plants is projected to reduce the net output of the plant by some 30% and to increase the cost of electricity by 60-80%. Developing capture materials and processes that reduce the parasitic energy imposed by CCS is therefore an important area of research. We have developed a computational approach to rank adsorbents for their performance in CCS. Using this analysis, we have screened hundreds of thousands of zeolite and zeolitic imidazolate framework structures and identified many different structures that have the potential to reduce the parasitic energy of CCS by 30-40% compared with near-term technologies. © 2012 Macmillan Publishers Limited. All rights reserved

Status and Analysis of Next Generation Post-combustion CO2 Capture Technologies

AbstractPost-combustion CO2 capture technologies tested above ∼20 MWe on flue gas slip streams from coal-fired power plants are thus far exclusively aqueous solutions of amines or ammonia. These near-term technologies, when combined with compression to pipeline pressures, impose a ∼25-30% load on a coal-fired power plant and nearly double the cost of electricity. Much of this increase is due to the relatively low CO2 concentration and ambient conditions of flue gas, which poses an inherently difficult separation. Nonetheless, this relatively high energy and monetary cost provides an incentive for the development of next generation lower-energy and lower-cost capture processes. Since 2006, the Electric Power Research Institute (EPRI) has had an active program to review and conduct due diligence on emerging post-combustion CO2 capture technologies. Using this knowledgebase, we critically review and analyze the status of the broad spectrum of next generation technologies, including solvents, adsorbents, membranes, and other capture processes. This effort spans some 125 post-combustion capture technologies and is part of EPRI's on-going effort to understand the landscape of CO2 capture technologies, to identify research gaps, and to accelerate relevant research fields. We use the taxonomy of technology readiness level (TRL) to rank and classify the landscape of CO2 capture technologies. We provide overview results of this ranking exercise and show how the findings will be used by EPRI and the utility industry to better identify opportunities to accelerate the development cycle and to anticipate the timing of major pilots and eventual commercial offerings. This analysis also leads us to several important insights, especially for capture technologies applied at power plant scales

Selection of Optimal Solid Sorbents for CO2 Capture Based on Gas Phase CO2 composition

AbstractOne method to reduce anthropogenic CO2 emissions is carbon capture via the separation of CO2 from gas streams that would otherwise be released to the atmosphere. In this work, we examine the applicability, performance, and desired material properties of solid sorbent materials to capture CO2 from gas streams with varying CO2 compositions. This paper focuses on optimizing material selection and process design for given applications and determines the effect on the calculated imposed load of performing carbon capture on various gas streams. For each gas stream for CO2 separation, an optimal separation material and operational process can be identified. Previous work on this topic has been focused on sorbent and process selection for CO2 separation from coal-derived flue gas[1,2]. In the current work, we expand the range of possible gas streams to include a wide range of CO2 concentrations from 1-99% CO2 with the balance N2. The purpose of this is not only to identify the sorbent materials that are energetically optimal for each application, but also to determine the effect of varying CO2 concentration on overall process performance. By quantifying the effect of increased CO2 concentration or partial pressure, trade-off curves can be calculated and the effect of combustion, pre-treatment, or recycle processes that can increase CO2 partial pressure can be analyzed. Further, this can provide a trade-off analysis between using process steps, such as recycling flue gas streams, to increase CO2 concentrations before carbon capture versus capturing CO2 directly from a lower concentration gas stream. Results include the range of materials that provide near-optimal energy performance for a given application and act as a guide for material developers