Current Activities
Modeling of CO2 Capture in a Packed Absorber for CO2 Sequestration
Yannick Heintz
Due to human induced activities, atmospheric concentrations of carbon dioxide (CO2) and other greenhouse gases such as methane (CH4) and nitrogen oxides (NOx) are increasing. As a matter of fact the atmospheric concentration of CO2 increased from 280 ppmv during the pre-industrial era to 365 ppmv in 1998. Currently, CO2 is responsible for about 64% of the anthropogenic greenhouse effect. The potential impact of rising concentrations of greenhouse gases in the atmosphere is continuing as a global concern into the 21st century. To stabilize the atmospheric concentration of greenhouse gases (GHG), a huge reduction of CO2 emissions, which is mainly produced by burning fossil fuels, is required. The 1997 Kyoto Protocol calls upon industrialized nations to reduce their CO2 emissions to 95% of the 1990 levels by 2012. The CO2 emission into the atmosphere can be controlled either by reducing its production and release into the atmosphere (increase the efficiency of energy from production to its end-use, use less carbon-intensive energy and natural energy sources, nuclear, solar, wind, etc…) or by capturing and sequestration of the produced CO2. Various CO2 sequestration options have been proposed, including storage into deep oceans (hydrate form); disposal into geologic formations (deep saline aquifers, depleted oil and gas reservoirs, and unmineable coal beds) and consumption via advanced chemical and biological processes. In order to effectively sequester CO2, it has to be selectively captured and separated from the flue gas streams, which commonly contain O2, N2, H2O, NOx, and SOx.
The first objective of this research is to design and construct an absorber (jacketed column containing structured packing at different column heights) at NETL-DOE to capture CO2 from various gas streams employing aqueous monoethanol amine (MEA) solutions under different temperatures and reactant concentrations. The second objective is to develop a comprehensive mathematical model, encompassing CO2-MEA reaction kinetics, fluid hydrodynamics, and physico-chemical properties of all the components involved to simulate the performance of the absorber. The model first optimizes for the gas-liquid the interfacial area and the heat transfer coefficients by solving a set of partial differential equations (mass balance and energy balance), in the axial and radial directions. The model is then used to predict the effect of the operating variables on the overall process performance. The ultimate goal of the project is to build a computer code for CO2 capture in large-scale packed absorbers with various chemical sorbents.
Testing and Development of Fluorinated Physical Solvents for Selective CO2 Capture from Post WGS Reactor Streams under Elevated Pressures and Temperatures
Yannick Heintz
Currently, the main processes of choice for acid gas removal (AGR), including CO2 in commercial IGCC facilities are: a chemical solvent process using methyl-diethanolamine (MDEA); a physical process using chilled methanol (Rectisol) or a physical process using mixtures of dimethylethers of polyethelene glycol (Selexol). The MDEA process suffers from high heat requirements for solvent regeneration. The Rectisol process is complex and refrigeration makes it the most expensive AGR Process. The Selexol process is more expensive than the MDEA process and chilling option could increase the process costs. All these physical and chemical for AGR removal processes, however, require cooling of the gas stream and decreasing its pressure below their typical values at the exit of the gasifier or the water-gas-shift reactor, thus increasing the overall cost of the process.
The main objective of this research project is to select a number of fluorinated solvents, such as perfluoropolyethylene, perfluoropolypropylene, and perfluoroalkylpolysiloxanes for their capacity to selectively separate CO2 from different gaseous streams, containing CO2, CO, H2S, CH4, H2O, and H2 in concentrations typical to those produced from water-gas-shift reactors. The selected fluorinated solvents will selectively capture CO2 under gasifier and shift reactor conditions with minimum loss and without cooling or reducing the pressure of the gaseous streams, minimizing the overall process costs. The ultimate goals of the project are: (1) to study the economic feasibility of using these fluorinated physical solvents for CO2 capture from synthesis gas produced through IGCC and Shift reactor; and (2) to draw a comparison between the ability of these solvents to selectively capture CO2 and those of two the benchmark physical processes, specifically Selexol, and Rectisol.