CO2 Capture from Industrial Sources by High-temperature Sorbents

Among the emerging CO2 capture technologies, systems based on high temperature (HT) regenerable sorbents had a significant development in recent years. In addition to power plants, HT sorbents technologies can be particularly promising for CO2 capture in carbon intensive industrial processes such as cement plants, steel mills and hydrogen plants. Calcium looping (CaL) is a combined post-combustion and oxyfuel combustion technology which uses calcium oxide (CaO) as CO2 sorbent. In this process, CO2 in combustion flue gases is absorbed in a carbonator reactor by forming calcium carbonate (CaCO3) through the exothermic carbonation reaction. Carbonated sorbent is then regenerated to CaO through the reverse calcination reaction in a calciner, where reaction heat is provided by oxyfuel combustion. A CO2 concentrated stream is therefore released from the calciner, which can be purified and compressed as in conventional oxyfuel product gas. Calcium looping is particularly promising for application in cement plants, because the raw materials used for the production of clinker (the energy intensive process in cement manufacturing) are rich of CaCO3, which is also the starting material of the CaL CaO sorbent. Therefore, no additional material needs to be imported or is released as waste when CaL is integrated in a cement plant. Two main configurations can be assumed to integrate the CaL process into a cement burning line: (i) the tail-end configuration, where the CaL process is used as a post-combustion, end-of-pipe capture process and (ii) a highly integrated configuration, where the CaL reactors are integrated into the raw meal preheating tower of the clinker production process and the CaL oxyfuel calciner coincides with the raw meal pre-calciner. Another class of processes where CaO is used as CO2 sorbent is sorption enhanced reforming (SER) technologies, where CO2 is absorbed within a steam methane reforming (SMR) reactor. The advantage of this class of processes is that the heat released by sorbent carbonation reaction matches very well with the steam methane reforming reaction. Moreover, the removal of the CO2 reaction product allows a greater advancement of the reforming and water gas shift (WGS) reactions. As a result, with a SER reactor, a H2 production and CO2 separation are performed in a single adiabatic reactor operating at moderate temperature (~650°C) instead of a sequence of reactors for steam reforming (~900°C), WGS (200-400°C) and CO2 separation (~30°C) operating in a wide temperature range as in conventional H2 production processes. In addition to material development, the main challenge in SER technologies is in the endothermic sorbent regeneration step. Several process schemes have been proposed for sorbent calcination, such as: (i) oxyfuel combustion, (ii) high temperature heat exchangers, (iii) direct contact heating with hot solids from a chemical looping combustion loop. Both fluidized bed and packed bed reactors are proposed for SER processes operating at different temperature and pressure range. If a CO2 sorbent is active at intermediate temperatures (~400°C), such as in the case of hydrotalcite-based sorbents, it can be adopted in sorption enhanced WGS (SEWGS) processes. As in the SER principle, the in-situ removal of CO2 form the gas phase allows a higher advancement of the WGS reaction. Therefore, H2-rich gas production and CO2 separation can be performed in a single pressurized reactor. While this concept can be adopted in hydrogen production plants, a promising application is in steel mills, where most of the CO2 emissions are associated to the combustion of the blast furnace gas (BFG) in the steel mill power plant. BFG is a byproduct of the pig iron production process and is a low calorific value fuel rich of CO, CO2 and N2. By processing BFG in a SEWGS reactor, a H2-N2 stream is produced, which can be burned at high efficiency in a low emission combined cycle. CaL, SER and SEWGS processes illustrated above for CO2 capture in industry, are being developed in the three ongoing EU FP7 and H2020 projects Cemcap (G.A. 641185), Ascent (G.A 608512) and Stepwise (G.A. 640769). In this work, the potential of these processes in terms of CO2 capture efficiency and energy efficiency will be discussed and compared with benchmark technologies, based on process integration and simulation studies

Improved flexibility and economics of Calcium Looping power plants by thermochemical energy storage

Abstract In this work, a Calcium looping (CaL) system including high temperature sorbent storage is presented, allowing to reduce the size of the calciner and the associated capital-intensive equipment (ASU and CPU). Reduction of the capital costs is particularly important for power plants with low capacity factors, which is becoming increasingly frequent for fossil fuel power plants in electric energy mixes with increasing share of intermittent renewables. The process assessment is performed by: (i) defining pulverized coal power plant (PCPP) with CaL capture system with and without sorbent storage and their mass and energy balances at nominal load; (ii) defining a simple method to predict the performance of the plant at part-load; (iii) defining the economic model, including functions for the estimation of the plant equipment cost; (iv) performing yearly simulations of the systems to calculate yearly electricity production, CO2 emissions and levelized cost of electricity for different sizes of the calcination line and the storage system and (v) performing sensitivity analysis with different power production plans and carbon taxes. With this process, optimal size of the calciner and of the storage system minimizing the cost of electricity have been found. The optimal plant design was found to correspond to a solids storage system sized to manage the weekly cycling and a calciner line sized on the average weekly load. However, to avoid excessively large solids storage system, sizing the calciner on the average daily load and the storage system to manage the daily cycling appears more feasible from the logistic viewpoint and leads to minor economic penalty compared with the optimal plant design. For the selected case sized on the daily cycling, reduction of the cost of CO2 avoided between 16% and 26% have been obtained compared to the reference CaL plant without solids storage, for representative medium and low capacity factor scenarios respectively

The swing adsorption reactor cluster for post-combustion CO2 capture from cement plants

The swing adsorption reactor cluster is a promising new method for post-combustion CO2 capture using a synergistic combination of temperature and pressure swings. The pressure swing is carried out by a vacuum pump and allows for 90% CO2 capture using only a small temperature swing, which is carried out by a heat pump. The small temperature swing allows the heat pump to transfer heat from carbonation to regeneration at a very high efficiency, minimizing the energy penalty. When applied to a cement plant, the energy penalty reduces further relative to a coal power plant that has a lower CO2 content in the flue gas. Higher CO2 concentrations allow a given CO2 capture ratio to be achieved with a smaller temperature swing, thus further improving the heat pump efficiency. As a result of the high heat pump efficiency and of the limited amount of waste heat available, heat integration with the cement plant yielded negligible efficiency gains. A swing adsorption reactor cluster post-combustion CO2 capture facility can therefore be constructed independently from the cement plant, making it attractive for retrofits. The specific energy consumption for CO2 avoidance of the process was determined as 2.04 MJLHV/kgCO2 when using electricity from the average European power mix, which is lower than all competing technologies recently assessed in the literature aside from oxyfuel CO2 capture. Primary energy consumption will continue to decline as the electricity sector decarbonizes, increasing the attractiveness of the swing adsorption reactor cluster over coming decades.publishedVersio

Economic assessment of the swing adsorption reactor cluster for CO2 capture from cement production

Cement production is responsible for about 8% of global CO2 emissions. Most of these emissions originate from the process itself and thus cannot be avoided via clean energy, leaving CO2 capture as the only viable solution. This study investigates the prospects of decarbonizing the cement industry via the swing adsorption reactor cluster (SARC) – a new post-combustion CO2 capture technology that requires no integration with the host process, consumes only electrical energy and shows a competitive energy penalty. SARC operates by synergistically combining a temperature swing using a heat pump and a vacuum swing using a vacuum pump. In the present study, the SARC concept is evaluated economically and compared to several benchmarks. SARC achieves CO2 avoidance costs of €52/ton in the base case, which is higher than oxyfuel combustion, similar to calcium looping and lower than four other technology options. SARC can approach the cost of oxyfuel combustion with more optimistic assumptions regarding economies of scale, particularly for the vacuum pump. The local electricity mix is another important factor because SARC, as an electricity consumer, becomes more attractive when the price and CO2 intensity of electricity is low. Furthermore, the simplicity of retrofitting existing cement plants with the SARC process becomes increasingly valuable when rapid CO2 emissions reductions are targeted. SARC is therefore well positioned for a global decarbonization effort aiming to limit global warming well below 2 °C.publishedVersio

Application of the Sorption Enhanced-Steam Reforming process in combined cycle-based power plants

Abstract Sorption Enhanced-Steam Methane Reforming (SE-SMR) is a promising process which allows producing in a single reactor a hydrogen-rich syngas from natural gas, while capturing the CO 2 by reaction with a solid sorbent. Scope of this paper is to investigate the potentiality of the SE-SMR process coupled to a combined cycle, by estimating the plant performance and by discussing the main issues related to plant layout and reactors characteristics. The calculated net efficiency and carbon capture ratio are comparable with that obtained for a competitive technology based on Auto-thermal Reforming (ATR), but advantages could result from the higher plant simplicity and lower plant cost

Application of Molten Carbonate Fuel Cells in Cement Plants for CO2 Capture and Clean Power Generation

Abstract Cement production process features intrinsically large CO 2 emission due to the decomposition of limestone by calcination reaction and to fuel combustion, necessary for sustaining the endothermic calcination process and the formation of clinker. Conventional approaches to CO 2 emission reduction in cement plants are based on post-combustion capture with chemical solvents, requiring a substantial energy consumption for regeneration, or oxycombustion in the cement kiln, involving a deep redesign of the plant. The aim of this work is investigating the application of Molten Carbonate Fuel Cells in cement plants for CO 2 capture from the plant exhaust gases, using the fuel cells as active CO 2 concentrators of combustion flue gases and eventually obtaining a purified CO 2 stream through a cryogenic process. A novel configuration with MCFCs added along the exhaust line has been assessed by means of process simulations. The results show a remarkable potential in terms of equivalent avoided CO 2 emissions (exceeding 1000 g/kWh), high share of CO 2 avoided (up to about 70%) and low energy penalties