Carbon capture and storage update Boot-Handford, Matthew E; Abanades, Juan C; Anthony, Edward J ...
Energy & environmental science,
01/2014, Letnik:
7, Številka:
1
Journal Article
Recenzirano
In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO
...2
from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO
2
capture technologies, available in the short and long term, and their technological maturity, before discussing CO
2
transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO
2
from the air and CO
2
reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.
A comprehensive discussion of CCS technologies, deployment and prospects across the world.
The performance of combined CO₂-sorbent/catalyst particles for sorption enhanced steam reforming (SESR), prepared via a simple mechanical mixing protocol, was studied using a spout-fluidised bed ...reactor capable of continuous solid fuel (biomass) feeding. The influence of particle size (300⁻500 and 710⁻1000 µm), CaO loading (60⁻100 wt %), Ni-loading (10⁻40 wt %) and presence of dicalcium silicate support (22.6 wt %) on SESR process performance were investigated. The combined particles were characterised by their density, porosity and CO₂ carrying capacity with the analysis by thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH) and mercury intrusion porosimetry (MIP). All experiments were conducted with continuous oak biomass feeding at a rate of 0.9 g/min ± 10%, and the reactor was operated at 660 ± 5 °C, 1 atm and 20 ± 2 vol % steam which corresponds to a steam-to-carbon ratio of 1.2:1. Unsupported combined particles containing 21.0 wt % Ni and 79 wt % CaO were the best performing sorbent/catalyst particle screened in this study, when accounting for the cost of Ni and the improvement in H₂ produced by high Ni content particles. SESR tests with these combined particles produced 61 mmol H₂/g
(122 g H₂/kg
) at a purity of 61 vol %. Significant coke formation within the feeding tube and on the surfaces of the particles was observed which was attributed to the low steam to carbon ratio utilised.
In this study we present findings from investigations into interactions between biomass tar and two iron based oxygen carrier materials (OCMs) designed for chemical-looping applications: a 100% Fe2O3 ...(100Fe) OCM and a 60 wt% Fe2O3/40 wt% Al2O3 (60Fe40Al) OCM. A novel 6 kWe two-stage, fixed-bed reactor was designed and constructed to simulate a chemical-looping combustion (CLC) process with ex situ gasification of biomass. Beech wood was pyrolysed in the first stage of the reactor at 773 K to produce a tar-containing fuel gas that was used to reduce the OCM loaded into the 2nd stage at 973 K. The presence of either OCM was found to significantly reduce the amount of biomass tars exiting the reactor by up to 71 wt% compared with analogous experiments in which the biomass tar compounds were exposed to an inert bed of sand. The tar cracking effect of the 60Fe40Al OCM was slightly greater than the 100Fe OCM although the reduction in the tar yield was roughly equivalent to the increase in carbon deposition observed for the 60Fe40Al OCM compared with the 100Fe OCM. In both cases, the tar cracking effect of the OCMs appeared to be independent of the oxidation state in which the OCM was exposed to the volatile biomass pyrolysis products (i.e. Fe2O3 or Fe3O4). Exposing the pyrolysis vapours to the OCMs in their oxidised (Fe2O3) form favoured the production of CO2. The production of CO was favoured when the OCMs were in their reduced (Fe3O4) form. Carbon deposition was removed in the subsequent oxidation phase with no obvious deleterious effects on the reactivity in subsequent CLC cycles with reduction by 3 mol% CO.
The hydration reaction between calcium oxide (CaO) and steam has applications as (i) a means to increase the reactivity of CaO-based sorbents for calcium-looping (CaL) CO2 capture processes and (ii) ...a process for thermochemical energy storage. However, the hydration kinetics of CaO have not been widely investigated in the literature, with previous investigations generally performed under diffusion-controlled conditions in a thermogravimetric analyzer. This work uses three particle models including (i) a developed form of the shrinking core model (D-SCM), (ii) the random pore model (RPM), and (iii) a developed form of the grain catalyst model (D-GCM) to evaluate the behavior of the reaction between CaO and steam in an atmospheric fluidized bed reactor under typical CaL conditions while minimizing diffusional resistances. The D-SCM was developed to account for particle expansion and changing bulk concentrations while the D-GCM was developed to improve its handling of changing steam concentrations. The suitability of each of the three models is assessed under kinetic-controlled conditions by varying particle size (200–710 μm), steam concentration (10–20 mol %), particle calcination temperature (850–950 °C), and reaction temperature (300–400 °C). The D-SCM showed the greatest versatility and demonstrated greater accuracy over the SCM, providing a good fit for experimental data across all experimental conditions tested including data from literature. The RPM consistently bounded the data between a kinetics-controlled and diffusion-controlled prediction, and the D-GCM also showed greater accuracy over the GCM and produced consistent fits across steam concentrations at 300 °C but deteriorated at higher reaction temperatures. Further, a quantitative comparison of the modeling results was carried out by χ2 goodness-of-fit (χ2-GOF) statistical testing.
The pyrolysis behaviour of beech wood, two rice husk variants from Brazil (BRH) and Thailand (TRH) and a solid waste water treatment residue from textile manufacture (TIR) were investigated using a ...lab-scale, 2-stage fixed-bed reactor at 773 K. Char yields increased and volatile yields decreased with increasing ash content. The TRH released 40% less tar than the BRH which was attributed to the substantially higher potassium content of the Thai species. The combustion reactivity of the TRH char in air at 773 K was similar to the BW char and almost double the reactivity of the BRH and TIR chars. The BW and TRH chars had a greater volume of macropores indicating that char combustion occurs predominantly through the growth and extension of the macroporous pore network. A different trend was observed for the char gasification reactivity with CO2 at 1173 K. The Ca and Mg content of the chars were found to have a more important catalytic role in the char gasification reactions with CO2.
The effect of exposing volatile products from beech wood pyrolysis to elevated temperatures (973–1173 K) and sand beds containing calcined limestone or dolomite in a simulated downdraft gasification environment was also investigated. Tar yields decreased after exposure to elevated temperature and calcined limestone or dolomite. Tar cracking favoured the production of CO. CO yields were between 22 and 23 wt% at 1173 K. Calcined dolomite was slightly more effective at cracking tar than calcined limestone, eliminating 98 wt% of the tar at 1173 K.
•Analysis of the biomass ash content can be used to predict the pyrolysis product distribution and char gasification and combustion behaviour.•A high potassium content favoured gaseous pyrolysis products over solid char products.•Ca and Mg ash content play important catalytic roles in high temperature char gasification reactions with CO2.•Calcined limestone and dolomite were effective tar cracking catalysts suitable for downdraft gasifier utilisation.
Biomass combustion with in situ CO2 capture via the calcium looping cycle is a novel process for the production of low- (or even negative-) carbon heat and power. Both processes can take place in the ...same unit vessel because of their compatible operating temperatures (600–700 °C). Combining the two process steps is beneficial in terms of reduced number of unit operations and process complexity. However, biomass combustion at this lower temperature range can result in the production of tar. In addition to reduced combustion efficiency, the presence of tar can lead to the blockages and fouling of downstream process equipment and loss of sorbent reactivity because of coking. Higher temperatures are known to increase tar conversion; however, this is detrimental to the rate of carbonation. Pressurizing the process allows higher CO2 partial pressures to be achieved and therefore alleviates the thermodynamic limitations on the process. Our work employed a novel high-temperature, pressurized fluidized-bed reactor to investigate the influence of temperature, pressure, and the presence of CaO on biomass combustion and tar yield. Higher operating pressures and temperatures or the addition of CaO were found to significantly reduce the gravimetric tar yield. However, the extent of CO2 capture appeared to have been limited by rapid combustion kinetics at the higher end of the investigated temperature and O2 partial pressure ranges. Size exclusion chromatography and ultraviolet fluorescence analysis of the product tars helped to provide insights into tar production and destruction pathways under different conditions.
Calcium looping is a Carbon Capture and Storage (CCS) technology which has the potential to be applied to both power generation plants and some industrial emission sources. The main problem with the ...use of calcium oxide-based sorbents is their characteristic decay in carrying capacity. This is caused by sintering and is made worse during multiple cycles of CO2 absorption (carbonation) and release (calcination). This paper provides an investigation into the degradation of a novel type of sorbent that is able to regenerate porosity during the temperature cycling of calcium looping. The porosity regeneration of this sorbent is a result of a dicalcium silicate additive undergoing a reliable phase change (α′↔β), which consequently has a useful volume change associated with it. The sorbent here, has been tested for the first time under reasonably realistic conditions within a TGA for multiple cycles. The results demonstrated that the sorbent displays the characteristic decline in carrying capacity when calcined in the presence of CO2, but not when calcined in the absence of CO2 in the fluidising gas. This paper also presents an improved method to conduct TGA carrying capacity measurements of CO2 sorbents which minimises the over carbonation between cycles.
•A novel chemical-looping concept for decarbonising iron and steel is presented.•The process involves the co-production of decarbonised H2 and a reduced iron product.•The H2 can be used to produce ...decarbonised direct reduced iron (DRI).•The heat integrated process is 12% more efficient than a conventional SMR process.•A techno-economic analysis of the process indicated the cost of H2 to be 1.16 $/kg-H2.
The application of iron-based chemical-looping processes offers an efficient and convenient strategy for decarbonising iron and steel production. Here we present a novel chemical-looping with water splitting process for the co-generation of hydrogen and a saleable, reduced iron product (CLWSFe). The high-purity H2 stream provides a decarbonised fuel source for producing direct reduced iron (DRI), and the spent oxygen carrier, OC (if removed in reduced form) is a source of iron that could be blended with the DRI for casting or further processing to steel.
A fully heat integrated model of the CLWSFe process developed in ASPEN-PLUS is presented. The thermal and exergy efficiencies of the optimised process were studied and compared with a conventional steam-methane reforming (SMR) process. An assessment of the economic feasibility based on CAPEX, OPEX and the production cost of hydrogen was carried out. The added value associated with the reduced iron (spent OC) product and its effect on the process CAPEX and OPEX was considered. The effective efficiency of the CLWSFe process was 20.8% higher than a conventional SMR process with the advantage of producing a saleable Fe product. The hydrogen production cost was 1.16 $/ kg-H2.
The multicycle performance of different iron ores and steel production residues supplied by Nippon Steel Corporation were also studied in a thermogravimetric analyser at conditions relevant to both conventional chemical-looping combustion and CLWS processes. Kinetic and cyclic performance data provided useful inputs for the model assisting with reactor sizing and the estimation of oxygen carrier replenishment rates.
The combination of concentrated solar power–chemical looping air separation (CSP-CLAS) with an oxy-fuel combustion process for carbon dioxide (CO
2
) capture is a novel system to generate electricity ...from solar power and biomass while being able to store solar power efficiently. In this study, the computer program Advanced System for Process Engineering Plus (ASPEN Plus) was used to develop models to assess the process performance of such a process with manganese (Mn)-based oxygen carriers on alumina (Al
2
O
3
) support for a location in the region of Seville in Spain, using real solar beam irradiance and electricity demand data. It was shown that the utilisation of olive tree prunings (
Olea europaea
) as the fuel—an agricultural residue produced locally—results in negative CO
2
emissions (a net removal of CO
2
from the atmosphere). Furthermore, it was found that the process with an annual average electricity output of 18 MW would utilise 2.43% of Andalusia’s olive tree prunings, thereby capturing 260.5 k-tonnes of CO
2
, annually. Drawbacks of the system are its relatively high complexity, a significant energy penalty in the CLAS process associated with the steam requirements for the loop-seal fluidisation, and the gas storage requirements. Nevertheless, the utilisation of agricultural residues is highly promising, and given the large quantities produced globally (~ 4 billion tonnes/year), it is suggested that other novel processes tailored to these fuels should be investigated, under consideration of a future price on CO
2
emissions, integration potential with a likely electricity grid system, and based on the local conditions and real data.
•Co-precipitated Cu-Mn oxides were tested as oxygen carriers for CLOU and CLAS.•The oxygen carrier properties were optimised by tuning the synthesis conditions.•A rate-based method to determine the ...O2 equilibria was presented and applied.•Differences in reaction pathways and particle evolution with CLC mode were elucidated.
Chemical looping with oxygen uncoupling (CLOU) and chemical looping air separation (CLAS) are novel and potentially promising processes for the combustion of solid fuels (e.g. biomass) for power generation with inherent CO2 capture. Redox-experiments at 850–950 °C confirmed that copper manganese spinel oxides are promising oxygen carriers for these processes, as they combine a relatively high O2 release capacity and fast O2 release kinetics. Furthermore, this work presents a novel method to calculate the O2 partial pressure equilibrium and the heat of O2 release from observed rates of reaction. To demonstrate this method, oxygen carriers were prepared via mechanical mixing and co-precipitation with varying molar Cu:Mn ratios and synthesis conditions, thereby tuning material properties and the pore structure. The precursors and calcined materials were characterised, and the crystalline phases were determined using X-ray diffraction. The insights from the post cycling analysis of the oxygen carriers and the experimentally obtained O2 release capacities were combined to elucidate the redox-reactions relevant for the two processes. It was found that the presence of a higher partial pressure of O2 during the O2 release results in the formation of different (perovskite-like) phases than those occurring during the decomposition in an O2-free environment. The oxygen carriers demonstrated excellent stability at CLOU and CLAS process conditions during extended redox cycling (100 cycles in a thermo-gravimetric analyser and 50 cycles in a fluidised bed reactor), showing no significant loss of reactivity or O2 release capacity and a high resistance towards attrition and agglomeration. The degree of degradation after 100 cycles was in the order: temperature swing (CLAS) < O2 partial pressure swing (CLOU) < reduction with CH4 (chemical looping combustion).
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