Application of Sorption Enhanced Water Gas Shift for Carbon Capture in Integrated Steelworks

Abstract In integrated steelworks a large fraction of total CO2 is emitted from the power plant, where carbon- rich blast furnace gas (BFG) is burned to produce electricity by means of a steam cycle or a gas-steam combined cycle. The aim of the present paper is to assess the potential of Sorption Enhanced Water Gas Shift (SEWGS) process for CO2 capture from blast furnace gas. Firstly, a reference combined cycle applied to blast furnace steel plant is defined. Mass flow rate and composition of the steel plant off-gas used as fuel in the combined cycle have been derived from a large integrated steel plant. Then, the application of the SEWGS process is investigated and compared to a reference monoethanolamine (MEA)-based post-combustion absorption option. Two different SEWGS plant layouts are proposed together with two different sorbents. SEWGS achieves 85% of CO2 avoided with electric efficiency of 39% with the advanced sorbent

Gas permeation through carbon membranes:Model development and experimental validation

With a growing interest in carbon membranes for gas separation, understanding their performance and behaviour is essential for proper design of the membrane separation. Currently not many models exist that correctly describe transport through carbon membranes due to its complex nature. This work attempts to implement a general modelling approach which describes several key transport phenomena inside carbon membranes. The approach assumes a membrane wall to be a bundle of pores with parallel transport mechanisms using the pore size distribution as a weight factor to sum the different transport phenomena. This work adapts this approach specifically for carbon membranes, additionally accounting for molecular sieving and pore blocking effects. Imposing realistic boundary conditions, the model is solved using global optimization algorithms. For testing, four different CMSMs have been produced with hydroquinone and novolac precursors. Pure- and mixed gas permeation tests are done for these CMSMs with H2, N2, and CO2 and the model is fit to this permeation data. Fitting results with pure gas measurements show the model is able to predict the contributions of different mass transport mechanism for the different membranes. This is validated by comparing these results to gas-pair permselectivity data. The model is furthermore fit to mixed gas data. Existence of multi-component effects shows that the model could be further improved. Overall, the model presented in this work is shown to be able to describe complex mass transport behaviour for various different carbon membranes.</p

A novel time discretization method for solving complex multi-energy system design and operation problems with high penetration of renewable energy

Modelling and optimising modern energy systems is inherently complex and often requires methods to simplify the discretization of the temporal domain. However, most of them are either (i) not well suited for systems with a high penetration of non-dispatchable renewables or (ii) too complex to be broadly adopted. In this work, we present a novel method that fits well with high penetration of renewables and different spatial scales. Furthermore, it is framework-independent and simple to implement. We show that, compared to the full time discretization, the proposed method saves >90% computation time with <1% error in the objective function. Moreover, it outperforms commonly used methods of modelling through typical days. Its practical usefulness is demonstrated by applying it to a case study about the optimal hydrogen production from renewable energy. The increased modelling fidelity results in a significantly cheaper design and reveals operational details otherwise hidden by typical days

Reduced order modeling of the Shell-Prenflo entrained flow gasifier

Pre-combustion capture applied to an integrated gasification combined cycle is a promising solution for greenhouse gas emission’s mitigation. For optimal design and operation of this cycle, detailed simulation of entrained flow gasifiers and their integration in the flowsheet analysis is required. This paper describes the development of a reduced order model (ROM) for the Shell–Prenflo gasifier family, used for chemicals and power production because of its high efficiency and compatibility with a wide range of coal quality. Different from CFD analysis, ROM is computationally very efficient, taking around 1 min in a typical desktop or laptop computer, hence enabling the integration of the gasifier model and the overall power plant flowsheet simulation. Because of the gasifier complexity, which includes several gas recirculation loops and a membrane wall, particular attention is paid to: (i) the two-phase heat exchange process in the gasifier wall; and, (ii) the syngas quench process. Computed temperature, composition, velocity and reaction rate profiles inside the gasifier show good agreement with available data. The calculated cold gas efficiency is 82.5%, close to the given value of 82.8%. Results and several sensitivity analyses describe the implementation of the model to explore the potential for operating gasifiers beyond the design point.MIT-Italy ProgramProgetto Roberto Rocc

A Machine Learning-Aided Equilibrium Model of VTSA Processes for Sorbents Screening Applied to CO2 Capture from Diluted Sources

The large design space of the sorbents' structure and the associated capability of tailoring properties to match process requirements make adsorption-based technologies suitable candidates for improved CO2 capture processes. This is particularly of interest in novel, diluted, and ultradiluted separations as direct CO2 removal from the atmosphere. Here, we present an equilibrium model of vacuum temperature swing adsorption cycles that is suitable for large throughput sorbent screening, e.g., for direct air capture applications. The accuracy and prediction capabilities of the equilibrium model are improved by incorporating feed-forward neural networks, which are trained with data from rate-based models. This allows one, for example, to include the process productivity, a key performance indicator typically obtained in rate-based models. We show that the equilibrium model reproduces well the results of a sophisticated rate-based model in terms of both temperature and composition profiles for a fixed cycle as well as in terms of process optimization and sorbent comparison. Moreover, we apply the proposed equilibrium model to screen and identify promising sorbents from the large NIST/ARPA-E database; we do this for three different (ultra)diluted separation processes: direct air capture, yCO2 = 0.1%, and yCO2 = 1.0%. In all cases, the tool allows for a quick identification of the most promising sorbents and the computation of the associated performance indicators. Also, in this case, outcomes are very well in line with the 1D model results. The equilibrium model is available in the GitHub repository https://github.com/UU-ER/SorbentsScreening0D

Integrating direct air capture with small modular nuclear reactors:understanding performance, cost, and potential

Direct air capture (DAC) is a key component in the transition to net-zero society. However, its giga-tonne deployment faces daunting challenges in terms of availability of both financial resources and, most of all, large quantities of low-carbon energy. Within this context, small modular nuclear reactors (SMRs) might potentially facilitate the deployment of DAC. In the present study, we present a detailed thermodynamic analysis of integrating an SMR with solid sorbent DAC. We propose different integration designs and find that coupling the SMR with DAC significantly increases the use of thermal energy produced in the nuclear reactor: from 32% in a stand-alone SMR to 76%-85% in the SMR-DAC system. Moreover, we find that a 50-MW SMR module equipped with DAC could remove around 0.3 MtCO2 every year, while still producing electricity at 24%-42% of the rated power output. Performing a techno-economic analysis of the system, we estimate a net removal cost of around 250 €/tCO2. When benchmarking it to other low-carbon energy supply solutions, we find that the SMR-DAC system is potentially more cost-effective than a DAC powered by high-temperature heat pumps or dedicated geothermal systems. Finally, we evaluate the potential of future deployment of SMR-DAC in China, Europe, India, South Africa and the USA, finding that it could enable up to around 96 MtCO2/year by 2035 if SMRs prove to be cost-competitive. The impact of regional differences on the removal cost is also assessed.</p

Optimization of Electric Ethylene Production:Exploring the Role of Cracker Flexibility, Batteries, and Renewable Energy Integration

The electrification of naphtha cracking for ethylene production could reduce the associated CO2 emissions but would require significantly larger electricity consumption. Within this context, the flexible operation of electric crackers opens opportunities for improved integration with the future electricity system. In this work, we developed a computationally efficient mixed-integer linear programming model to investigate flexibility in electric crackers, exploring the effect of operational parameters, such as operating envelope, ramping time, and start-up/shut-down time, on costs and emissions. We optimized three electric cracker systems: two with grid electricity consumption (with/without batteries) and one with electricity supply from dedicated renewable technologies. We find that the operating envelope of the cracker has the strongest impact on cost savings, enabling up to 5.5% reduction when using flexible electricity from the grid and 58% for systems with direct coupling to renewables. Moreover, the flexible operation of electric crackers relying on the electricity grid enhances the CO2 emission savings, achieving a 90.4% emission reduction against 54.6% of the constant operation case. Finally, we find that for direct coupling with renewables, electric crackers need to be flexible to avoid suboptimal oversizing of renewable technologies and especially unrealistic battery capacities.</p

Holistic development of a low-energy ammonia-based process for CO2 capture with solid formation

Absorption-based gas treatment processes allow removing CO2 from flue gas streams of large CO2-point sources, e.g. coal and natural gas fired power plants, cement plants, and steelworks, and make CO2 available at conditions suitable for geological storage. Therefore, it represents a key option in the portfolio of measures required to mitigate climate change and a valuable bridging technology that can support the shift towards a renewable-based supply of energy and chemicals. Among existing options, the chilled ammonia process (CAP) is a promising solution on the verge of commercialization. In the CAP, a cold ammonia solution absorbs CO2 from the flue gas in an absorption tower. The resulting CO2-rich solution releases CO2 upon moderate heating, while the (partially) regenerated ammonia solution can be recycled to the absorption section. At several points in the process flow-scheme, the liquid composition may exceed the solubility of the intermediate compounds at the relevant temperature. Solid formation can lead to clogging of process units. On the other hand, the formation of solids can increase the CO2 uptake capacity of the solvent with beneficial effects on the specific energy demand per unit of mass of CO2 captured. We have developed a so-called controlled solid formation-CAP (CSF-CAP), which successfully reduces the energy demand by exploiting solid formation. The new process controls the formation, separation, and subsequent dissolution of solids in a dedicated process section, whereas the absorption and stripping columns are kept free of solids. Our holistic process development strategy comprises (i) thermodynamics and (ii) kinetics, (iii) process synthesis, (iv) process integration, and (v) process optimization. The work on thermodynamics makes use of phase diagrams of the CO2-NH3-H2O system to map the process streams and analyze criticalities with respect to solid formation and opportunities for optimization. The analysis showed that the energetic optimization pushes the solvent composition towards the solubility limit. In the CSF-CAP, the CO2-rich solution is cooled down in a crystallizer to form solid ammonium bicarbonate (BC). The generated suspension is separated in a hydro-cyclone into (i) a rich slurry, which is sent to the regeneration unit, and (ii) a clear solution, which is sent to the top of the absorber. Due to the solid formation and separation, the latter stream can be introduced at lower temperature enabling a more effective control of the NH3 slip to the gas. The investigation of the kinetics considers both mass transfer and solid formation. On the one hand, pilot plant tests of the CO2 absorber have been carried out in order to study the reactive absorption process. On the other hand, the crystallization kinetics of BC in aqueous solution has been measured. The experimental investigation of this system is complicated by the evaporation of CO2 and NH3 from the solution as well as by the decomposition of the salts. Therefore, a temperature-controlled batch reactor, in which the volume of the vapor phase is minimized to limit the influence of the VLE on the liquid composition, has been developed. Metastable zone width data have been obtained, and BC growth kinetics has been modelled from the concentration profile during batch cooling seeded crystallization experiments with the help of a population balance model. The synthesis of the solid handling section has been developed combining mass, energy and population balances for the crystallization and dissolution into a rigorous rated-based model. Several process configurations, where mixed suspension mixed product removal (MSMPR) are coupled with scraped surface heat exchangers (SSHE) crystallizers, have been compared by optimizing the process productivity and energy needs. As a result, different optimal crystallization trajectories have been identified. Our optimization approach relies on a performance assessment based on the irreversibilities of the process as objective function. Equilibrium-based process simulations under the assumptions reported by Sutter et al. [1] led to an efficiency improvement of 17% in the CSF-CAP with respect to the conventional CAP. In our presentation, we will show our latest results on absorption kinetics, BC growth rate modelling, optimized flow scheme for the solid handling section, and optimal operating conditions of the process found for different flue gas compositions and CAP configurations. [1] D. Sutter, M. Gazzani and M. Mazzotti, Faraday Discuss., 2016, 192, 59-8

Modeling hydrogen applications in combined cycle heat and power plants

Combined cycle heat and power (CHP) plants are expected to play an important role in balancing generation of heat and electricity from non-dispatchable renewable energy. Retrofitting a CHP plant for hydrogen combustion is a prominent option to decarbonize (part of) its electricity and heat generation. In this work, we study and optimize different options for using hydrogen in CHP plants, namely: direct combustion in the gas turbine, supplementary firing in the heat recovery boiler (duct burner), and oxy-fuel combustion of hydrogen for direct steam production

Net-zero emissions chemical industry in a world of limited resources

The chemical industry is responsible for about 5% of global CO2 emissions and is key to achieving net-zero targets. Decarbonizing this industry, nevertheless, faces particular challenges given the widespread use of carbon-rich raw materials, the need for high-temperature heat, and the complex global value chains. Multiple technology routes are now available for producing chemicals with net-zero CO2 emissions based on biomass, recycling, and carbon capture, utilization, and storage. However, the extent to which these routes are viable with respect to local availability of energy and natural resources remains unclear. In this review, we compare net-zero routes by quantifying their energy, land, and water requirements and the corresponding induced resource scarcity at the country level and further discuss the technical and environmental viability of a net-zero chemical industry. We find that a net-zero chemical industry will require location-specific integrated solutions that combine net-zero routes with circular approaches and demand-side measures and might result in a reshaping of the global chemicals trade.</p