Integration of chemical looping combustion for cost-effective CO2 capture from state-of-the-art natural gas combined cycles

Chemical looping combustion (CLC) is a promising method for power production with integrated CO2 capture with almost no direct energy penalty. When integrated into a natural gas combined cycle (NGCC) plant, however, CLC imposes a large indirect energy penalty because the maximum achievable reactor temperature is far below the firing temperature of state-of-the-art gas turbines. This study presents a techno-economic assessment of a CLC plant that circumvents this limitation via an added combustor after the CLC reactors. Without the added combustor, the energy penalty amounts to 11.4%-points, causing a high CO2 avoidance cost of $117.3/ton, which is more expensive than a conventional NGCC plant with post-combustion capture ($93.8/ton) with an energy penalty of 8.1%-points. This conventional CLC plant would also require a custom gas turbine. With an added combustor fired by natural gas, a standard gas turbine can be deployed, and CO2 avoidance costs are reduced to $60.3/ton, mainly due to a reduction in the energy penalty to only 1.4$96.3/ton when a hydrogen cost of $15.5/GJ is assumed. Advanced heat integration could reduce the CO2 avoidance cost to$90.3/ton by lowering the energy penalty to only 0.6%-points. An attractive alternative is, therefore, to construct the plant for added firing with natural gas and retrofit the added combustor for hydrogen firing when CO2 prices reach very high levels

Enhanced sorbents for the calcium looping cycle and effects of high oxygen concentrations in the calciner

Increasing CO2 emissions from the energy and industrial sectors are a worldwide concern due to the effects that these emissions have on the global climate. Carbon capture and storage has been identified as one of a portfolio of technologies that would mitigate the effects of global warming in the upcoming decades. Calcium looping is a second generation carbon capture technology aimed at reducing the CO2 emissions from the power and industrial sectors. This thesis assesses the improvement of the calcium looping cycle for CO2 capture through enhanced sorbent production and testing at lab-, bench- and pilot-scale, and a new operational mode with high oxygen concentrations in the calciner through experimental campaigns in Cranfield’s 25 kWth pilot unit. Novel biomass-templated sorbents were produced using the pelletisation technique and tested at different conditions in a thermogravimetric analyser (TGA) and a bench-scale plant comprising a bubbling fluidised bed (BFB) reactor. Moreover, the effects of sorbent poisoning by SO2, and the influence of steam were studied in order to explore the effects of real flue gas on this type of material. In addition to the chemical performance, the mechanical strength, i.e. resistance to fragmentation of these materials was tested. In additon, two different kinds of enhanced materials were produced and tested at pilot-scale. Namely, calcium aluminate pellets and HBr-doped limestone were used in experimental campaigns in Cranfield’s 25 kWth pilot plant comprising a CFB carbonator and a BFB calciner. The suitability of these materials for Ca looping was assessed and operation challenges were identified in order to provide a basis for synthetic sorbent testing at a larger scale. Lastly, a new operational mode was tested, which is aimed at reducing the heat provided to the calciner through high oxygen concentration combustion of a hydrocarbon (in this case natural gas) in the calciner. This approach reduces or even eliminates the recirculated CO2 stream in the calciner. In consequence, this results in a lower capital (reduced size of the calciner) and operational cost (less oxygen and less fuel use). Several pilot plant campaigns were performed using limestone as solid sorbent in order to prove this concept, which was successfully verified for concentrations of up to 100% vol oxygen in the inlet to the calciner

Fluidized bed plants for heat and power production in future energy systems

Fluidized bed (FB) plants are used for heat and power production in several energy systems around the world, with particular importance in systems using large shares of renewable solid fuel, e.g., biomass. These FB plants are traditionally operated for base-load electricity production or for heat production, and thus characterized by relatively small and slow load changes. In parallel, as the transition towards energy systems with net-zero emissions increases the share of variable renewable energy (VRE) sources, the need for implementing variation management strategies at various timescales arises – giving heat and power plants the possibility to adapt their operations to accommodate the inherent variability of VRE sources. Following this, FB technology is envisioned for a wide range of novel applications expected to play significant roles in the decarbonization of energy systems, such as thermochemical energy storage and carbon capture and storage. In this context, research efforts are needed to investigate the technical and economic features of FB plants in energy systems with high levels of VRE.The aim of this thesis is to elucidate the capabilities of FB plants for heat and power production in net-zero emissions energy systems. For this purpose, two main pathways are explored: i) transient operation as fuel-fed plants, and ii) the potential conversion into decarbonized plants, i.e., into VRE-fed layouts providing dispatchable outputs.For fuel-fed FB plants, a dynamic model of biomass-fired FB plants has been developed, considering the two types of FB boilers (BFB and CFB) and including validation against steady-state and transient operational data collected from two commercial plants. As a novelty of this work the model describes both the gas (in-furnace) and water-steam sides such that the interactions between the two can be assessed. The results of the simulations show that i) the characteristic times for the gas side are shorter in BFB furnaces than in CFBs, albeit these times are for both furnace types not longer than those for the water-steam side; ii) the computed timescales for the dynamics of FB plants fall well within those required for offering complementing services to the grid; and iii) the use of control and operational strategies for the water-steam side can confer capabilities superior to fuel-feeding control in terms of avoiding undesirable unburnt emissions and providing temporary overload operation. The retrofit of fuel-fed FB plants into poly-generation facilities cogenerating a combustible biogenic gas is also assessed, revealing that partial combustion of this gas can be used to provide faster inherent dynamics than the original configuration.For VRE-fed FB layouts, techno-economic process modeling has been carried out for large-scale deployment of solar- and electricity-charging processes based on three different chemical systems: i) carbonation/calcination (calcium); ii) thermally reduced redox (cobalt oxides); and iii) chemically reduced redox (iron oxides). One attractive aspect of these layouts is the possibility to build part of them by retrofitting current fuel-fed FB plants. While the technical assessment for solar applications indicates that cobalt-based layouts offer the highest levels of efficiency and dispatchability, calcium-based processes present better economics owing to the use of inexpensive calcium material. The results also show that electricity-charged layouts such as iron looping can play an important role in the system providing variation management strategies to the grid while avoiding costly H2 storage. Further, the economic performances of VRE-fed FB layouts are benefitted by the generation of additional services and products (e.g., carbon capture and on-demand production of H2), and by scenarios with high volatility of the electricity prices

Efficient CO2 Capture from Lime Plants: Techno-economic Assessment of Integrated Concepts using Indirectly Heated Carbonate Looping Technology

The quest to decarbonize the lime and cement industry is challenging because of the amount and the nature of the CO2 emissions. The process emissions from calcination are unavoidable unless carbon capture is deployed. Nevertheless, the majority of the available carbon capture technologies are expensive and energy inefficient. The indirectly heated carbonate looping (IHCaL) process is a promising technology to capture CO2 from the lime and cement production, featuring low penalties in terms of economics and energy utilization. Previous works have highlighted the potential of the IHCaL, but the optimization of the process has not been discussed in enough detail and techno-economic implications are not yet fully understood. Within this work, ten scenarios using IHCaL technology to capture CO2 from a lime plant were simulated. Hereby, different process configurations, heat recovery strategies and fueling options were computed. The calculations for the capture facilities were performed with Aspen Plus® software and EBSILON®Professional was used to simulate the steam cycles. A techno-economic assessment was included as well, aided by the ECLIPSE software. The results demonstrate that the selection of the fuel for the combustor not only affects the CO2 balance and energy performance but is also an important cost driver —there were considerable economic advantages for the computed cases with middle-caloric solid recovered fuel (SRF). The analysis shows how the heat recovery strategy can be optimized to achieve tailored outcomes, such as reduced fuel requirement or increased power production. The specific primary energy consumption (from –0.3 to +2.5 MJLHV/tCO2,av) and cost for CO2 avoided (from –11 to +25 €/tCO2,av) using SRF are considerably low, compared with other technologies for the same application. The sensitivity study revealed that the main parameters that impact the economics are the discount rate and the project life. The capture plants are more sensitive to parameter changes than the reference plant, and the plants using SRF are more sensitive than the lignite-fueled plants. The conclusions from this work open a new pathway of experimental research to validate key assumptions and enable the industrial deployment of IHCaL technology before 2030

The Calcium-Looping technology for CO2 capture: On the important roles of energy integration and sorbent behavior

The Calcium Looping (CaL) technology, based on the multicyclic carbonation/calcination of CaO in gas-solid fluidized bed reactors at high temperature, has emerged in the last years as a potentially low cost technology for CO2 capture. In this manuscript a critical review is made on the important roles of energy integration and sorbent behavior in the process efficiency. Firstly, the strategies proposed to reduce the energy demand by internal integration are discussed as well as process modifications aimed at optimizing the overall efficiency by means of external integration. The most important benefit of the high temperature CaL cycles is the possibility of using high temperature streams that could reduce significantly the energy penalty associated to CO2 capture. The application of the CaL technology in precombustion capture systems and energy integration, and the coupling of the CaL technology with other industrial processes are also described. In particular, the CaL technology has a significant potential to be a feasible CO2 capture system for cement plants. A precise knowledge of the multicyclic CO2 capture behavior of the sorbent at the CaL conditions to be expected in practice is of great relevance in order to predict a realistic capture efficiency and energy penalty from process simulations. The second part of this manuscript will be devoted to this issue. Particular emphasis is put on the behavior of natural limestone and dolomite, which would be the only practical choices for the technology to meet its main goal of reducing CO2 capture costs. Under CaL calcination conditions for CO2 capture (necessarily implying high CO2 concentration in the calciner), dolomite seems to be a better alternative to limestone as CaO precursor. The proposed techniques of recarbonation and thermal/mechanical pretreatments to reactivate the sorbent and accelerate calcination will be the final subjects of this review

Exploiting the potential of chemical looping processes for industrial decarbonization and waste to energy conversion. Process design and experimental evaluations

The impact of anthropogenic activities on the environment is leading to climate changes and exceptional meteorological phenomena all over the world. To address this negative trend, the scientific community agrees that the environmental impact from fossil fuels-based power production must be mitigated by the integration with alternative and sustainable technologies, such as renewable energy. However, the time required for the complete development and diffusion of such technology poses the urgency of finding a midterm solution to significantly reduce CO2 emissions. Carbon capture, utilization, and storage (CCUS) technologies represent an interesting option to mitigate CO2 emissions. CCUS involves (among other possible applications) the separation of the CO2 content from industrial off-gases, its transport and storage or its reconversion to a chemical/fuel. Chemical looping can be considered as an oxyfuel combustion where the oxygen supply comes from the lattice oxygen atoms of a solid. It is based on gas-solid reactions where a solid also known as oxygen carrier, generally a metal oxide, undergoes successive reduction and oxidation steps. In the reduction step, normally occurring at high temperatures (700-1000 °C), the oxygen carrier interacts with a reducing agent, such as coal, natural gas, syngas etc. and loses part of its oxygen atoms. By controlling the degree of reduction of the oxygen carrier is thus possible to achieve a complete oxidation of the reducing agent (the fuel) to CO2 and H2O (chemical looping combustion) or a partial oxidation to a syngas (chemical looping reforming and gasification). In these latter case, the introduction of external CO2 and H2O can be of help to support the reforming or gasification processes. The oxygen carrier in the reduced phase is then sent to an air reactor, where it reacquires the oxygen atoms by an exothermic reaction with air. This process presents several advantages according to the specific application. In chemical looping combustion, intrinsic separation of N2 and CO2 is achieved, because the two streams are involved in two different reaction steps. This largely simplifies the CO2 separation effort for storage or utilization purposes. On the other hand, in chemical looping reforming it is possible to achieve autothermal operation thanks to the exothermicity of the oxidation step in the air reactor, as well as high reforming efficiencies. Similarly, in chemical looping gasification the resulting syngas is characterized by no N2 dilution, lower tar release and possibility of autothermal operation. These benefits enhance the energy efficiency of the process, leading to a better energy utilisation. In this work, strategies for the decarbonisation and circularity of the industrial and power sector are proposed based on the synthesis of hydrogen and hydrogen-derived fuels. In particular, the potential of chemical looping technology is deeply studied aiming at exploiting its ability to reconvert or valorise CO2 or waste streams to a syngas and then to a liquid fuel/chemical, such as methanol or ammonia. This task is carried out through modelling and experimental evaluations. The modelling activities mainly concern design of process schemes involving the chemical looping section for waste or CO2 reconversion and the liquid fuel synthesis section. The experimental evaluations are focused on two crucial that have been limitedly discussed in the literature: the thermochemical syngas production step by oxidation with CO2 and H2O streams, the effect of high-pressure operation on the redox abilities of a typical iron and nickel-based oxygen carrier. In Chapter 1, a general overview on the main research developments on chemical looping technology is provided. A section is reserved for each chemical looping variant, i.e. combustion, reforming and gasification, and a general description of each process is provided along with the summary of the main research achievements. Subsequently, the technology is divided by application in power production and chemicals production. Main findings from techno-economic assessment and process designs are discussed in comparison with benchmark technologies and other clean pathways. In Chapter 2 steel mills are taken as an example of the hard-to-abate industry. A H2-based decarbonization strategy is proposed and assessed by Aspen Plus simulation. The strategy starts from an initial configuration that is characterized by a typical blast furnace-basic oxygen furnace steel mill and consider the introduction of direct reduction – electric arc furnace lines, that are more efficient and involve natural gas as reducing agent rather than coke. Sensitivity analyses are carried out to assess the effect of the introduction of H2/CH4 blendings in the direct reduction plant and of the utilization of scrap material in the electric arc furnace. The impact of each configuration on the CO2 emissions and the energy flows of the plant is assessed by mass and energy balances. The results indicate a promising decarbonization potential of the introduced technologies but require large investments to increase the renewable sources penetration in the energy mix and large availability of H2. Therefore, alternative pathways for an earlier decarbonization of hard-to-abate industries and for large scale syngas/H2 production need to be considered. In Chapter 3, a novel process scheme is proposed involving chemical looping for syngas production. The CO2 content in blast furnace gases is separated with a calcium looping cycle and subsequently injected with H2O into the oxidation reactor of a chemical looping cycle. Assuming an inlet stream of pure CO2, mass balances on the chemical looping plant are carried out to compare the performance of nickel ferrites and iron oxides in terms of required oxygen carrier flow rate to process 1 t/h of CO2. Computational fluid dynamics simulations with integrated reaction kinetics are then carried out to validate the assumptions on the oxygen carrier conversion and syngas compositions. In Chapter 4 and 5, experimental evaluations are carried out on two crucial aspects for the successful operation of a chemical looping plant aiming at syngas production. In Chapter 4, the syngas productivity by CO2 and H2O splitting over a Fe bed is investigated. This is a very important step, and the effect of various parameters was considered. Firstly, the CO2 splitting is analysed for different temperatures with an inlet flow rate of 1 NL/min to ensure a substantial dissociation of the CO2. Subsequently, combined streams of CO2 and H2O are evolved in the reactor. The effect of the total flow rate, reactants molar ratio and bed height is investigated and from the results, the optimal syngas composition is identified. SEM and XRD are used to assess the morphological evolution and the phase changes of the material during the test. On the contrary, in Chapter 5 the effect of high-pressure operation on the redox abilities of two NiFe aluminates is assessed. The aluminates present similar Fe loadings, but different Ni loadings. High pressure operation is crucial for the development of this technology because it facilitates downstream processing of the syngas to liquid fuels. For a comparative analysis, preliminary tests at low pressure are carried out at three temperatures. Subsequently, the effect of reactants flow rate, temperature, total pressure, gas composition is analysed at high pressure conditions. Finally, long term tests are performed both at ambient and high-pressure conditions. Material characterization by SEM, XRD and H2-TPR is used to support the comparative analysis. In Chapter 6, a techno-economic analysis on a process scheme encompassing methanol and ammonia production from chemical looping gases is carried out. Chemical looping hydrogen production is a very versatile technology and allows for the combined production of power and H2 or syngas. With proper calibration of the flow rates, a stream of high purity N2 can also be obtained at the air reactor outlet and used for ammonia synthesis. Back up with an alkaline electrolyser is considered for the supply of the required amount of hydrogen. Sensitivity analyses are carried out on the chemical looping plant to evaluate the effect of fuel flow rate, steam flow rate, and oxygen carrier inlet temperature to the fuel reactor. Subsequently, a techno-economic analysis is carried out evaluating several parameters among which: the specific CO2 emissions, the energy intensity, and the levelized cost of methanol and ammonia. Finally, a comparison with benchmark technologies and other clean alternatives is presented. In this way, the benefits as well as the drawbacks of chemical looping in terms of environmental and economic parameters are assessed and the missing elements to reach industrial competitivity are clarified

Carbon-negative hydrogen from biomass using gas switching integrated gasification: Techno-economic assessment

Ambitious decarbonization pathways to limit the global temperature rise to well below 2 °C will require large-scale CO2 removal from the atmosphere. One promising avenue for achieving this goal is hydrogen production from biomass with CO2 capture. The present study investigates the techno-economic prospects of a novel biomass-to-hydrogen process configuration based on the gas switching integrated gasification (GSIG) concept. GSIG applies the gas switching combustion principle to indirectly combust off-gas fuel from the pressure swing adsorption unit in tubular reactors integrated into the gasifier to improve efficiency and CO2 capture. In this study, these efficiency gains facilitated a 5% reduction in the levelized cost of hydrogen (LCOH) relative to conventional O2-blown fluidized bed gasification with pre-combustion CO2 capture, even though the larger and more complex gasifier cancelled out the capital cost savings from avoiding the air separation and CO2 capture units. The economic assessment also demonstrated that advanced gas treatment using a tar cracker instead of a direct water wash can further reduce the LCOH by 12% and that the CO2 prices in excess of 100 €/ton, consistent with ambitious decarbonization pathways, will make this negative-emission technology economically highly attractive. Based on these results, further research into the GSIG concept to facilitate more efficient utilization of limited biomass resources can be recommended.publishedVersio

Technologies for Coal based Hydrogen and Electricity Co-production Power Plants with CO2 Capture

Integrated Gasification Combined Cycle (IGCC) plants allow the combination of the production of hydrogen and electricity because coal gasification process produces a syngas that can be used for the production of both commodities. A hydrogen and electricity power plant has been denominated as HYPOGEN. This report starts by reviewing the basics of the coal gasification process and continues by trying to map all the technological options currently available in the market as well as possible future trends that can be included in a HYPOGEN system . Besides, it offers an overview of the operating conditions and outputs of each process in order to provide the modeller with a useful information tool enabling an easier analysis of compatibilities and implementation of the model.JRC.F.7-Energy systems evaluatio

The Oxy-CaL process: A novel CO2 capture system by integrating partial oxy-combustion with the Calcium-Looping process

This paper proposes a novel CO2 capture technology from the integration of partial oxy-combustion and the Calcium-Looping capture process based on the multicycle carbonation/calcination of limestone derived CaO. The concentration of CO2 in the carbonator reactor is increased by means of partial oxy-combustion, which enhances the multicycle CaO conversion according to thermogravimetric analysis results carried out in our work, thus improving the CO2 capture efficiency. On the other hand, energy consumption for partial oxy-combustion is substantially reduced as compared to total oxy-combustion. All in all, process simulations indicate that the integration of both processes has potential advantages mainly regarding power plant flexibility whereas the overall energy penalty is not increased. Thus, the resulting energy consumption per kilogram of CO2 avoided is kept smaller than 4 MJ/kg CO2, which remains below the typical values reported for total oxy-combustion and amine based CO2 capture systems whereas CO2 capture efficiency is enhanced in comparison with the Calcium-Looping process.Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-R, CTQ2014-52763-C2-1-R, MAT2013-41233-