Nicholas H. Florin

An overview of CO2 capture technologies

In this paper, three of the leading options for large scale CO2 capture are reviewed from a technical perspective. We consider solvent-based chemisorption techniques, carbonate looping technology, and the so-called oxyfuel process. For each technology option, we give an overview of the technology, listing advantages and disadvantages. Subsequently, a discussion of the level of technological maturity is presented, and we conclude by identifying current gaps in knowledge and suggest areas with significant scope for future work. We then discuss the suitability of using ionic liquids as novel, environmentally benign solvents with which to capture CO2. In addition, we consider alternatives to simply sequestering CO2—we present a discussion on the possibility of recycling captured CO2 and exploiting it as a C1 building block for the sustainable manufacture of polymers, fine chemicals, and liquid fuels. Finally, we present a discussion of relevant systems engineering methodologies in carbon capture system design.

Influence of High-Temperature Steam on the Reactivity of CaO Sorbent for CO2 Capture

Calcium looping is a high-temperature CO(2) capture technology applicable to the postcombustion capture of CO(2) from power station flue gas, or integrated with fuel conversion in precombustion CO(2) capture schemes. The capture technology uses solid CaO sorbent derived from natural limestone and takes advantage of the reversible reaction between CaO and CO(2) to form CaCO(3); that is, to achieve the separation of CO(2) from flue or fuel gas, and produce a pure stream of CO(2) suitable for geological storage. An important characteristic of the sorbent, affecting the cost-efficiency of this technology, is the decay in reactivity of the sorbent over multiple CO(2) capture-and-release cycles. This work reports on the influence of high-temperature steam, which will be present in flue (about 5-10%) and fuel (∼20%) gases, on the reactivity of CaO sorbent derived from four natural limestones. A significant increase in the reactivity of these sorbents was found for 30 cycles in the presence of steam (from 1-20%). Steam influences the sorbent reactivity in two ways. Steam present during calcination promotes sintering that produces a sorbent morphology with most of the pore volume associated with larger pores of ∼50 nm in diameter, and which appears to be relatively more stable than the pore structure that evolves when no steam is present. The presence of steam during carbonation reduces the diffusion resistance during carbonation. We observed a synergistic effect, i.e., the highest reactivity was observed when steam was present for both calcination and carbonation.

Life cycle greenhouse gas assessment of a coal-fired power station with calcium looping CO2 capture and offshore geological storage

Carbon Capture and Storage (CCS) is an essential technology for reducing global CO2 emissions in the context of continued fossil fuel use in the power sector. To evaluate the emission reduction potential of any low-carbon generation technology it is necessary to consider emissions over the entire lifetime of the plant. This work examines the lifecycle greenhouse gas emissions of a 500 MWe pulverised coal-fired power plant with post-combustion Calcium Looping (CaL) and off-shore geological storage. CaL uses solid CO2-sorbent derived from abundant and non-toxic limestone (CaCO3) and is currently being piloted at the 1–2 MWth scale in Europe (Spain and Germany). This technology promises to be very competitive with the more mature chemical absorption processes, with the potential to reduce the efficiency and cost penalties of CO2 capture. We demonstrate that the emission intensity of a coal-fired power plant with CaL is at least comparable with one using MEA-solvent technology (i.e., ∼ 229 gCO2e/kWh vs. 225 gCO2e/kWh). However, there is significant potential for additional emissions reduction when considering the recarbonation of exhausted sorbent in landfill. Furthermore, a coal-fired power plant with CaL could be carbon-neutral – or even achieve a net removal of CO2 from the atmosphere. That is, if the exhausted sorbent is used in the cement industry substituting the input of fresh-limestone; or if the exhausted sorbent is disposed in the ocean forming bicarbonate.

High-temperature thermal destruction of poultry derived wastes for energy recovery in Australia

The high-temperature thermal destruction of poultry derived wastes (e.g., manure and bedding) for energy recovery is viable in Australia when considering resource availability and equivalent commercial-scale experience in the UK. In this work, we identified and examined the opportunities and risks associated with common thermal destruction techniques, including: volume of waste, costs, technological risks and environmental impacts. Typical poultry waste streams were characterised based on compositional analysis, thermodynamic equilibrium modelling and non-isothermal thermogravimetric analysis coupled with mass spectrometry (TG-MS). Poultry waste is highly variable but otherwise comparable with other biomass fuels. The major technical and operating challenges are associated with this variability in terms of: moisture content, presence of inorganic species and type of litter. This variability is subject to a range of parameters including: type and age of bird, and geographical and seasonal inconsistencies. There are environmental and health considerations associated with combustion and gasification due to the formation of: NO(X), SO(X), H(2)S and HCl gas. Mitigation of these emissions is achievable through correct plant design and operation, however, with significant economic penalty. Based on our analysis and literature data, we present cost estimates for generic poultry-waste-fired power plants with throughputs of 2 and 8 tonnes/h.

Hydrogen production from biomass

The ‘hydrogen economy’ has received considerable attention in academic, industrial and political contexts. There are opportunities for vast reductions in greenhouse gas emissions, increased energy security and greater overall efficiency. However, if hydrogen is to become a fundamental energy source for electrical power generation, as well as a transportation fuel, novel generation pathways will be necessary to meet the increase in demand. A promising means for generating hydrogen is the thermochemical conversion of biomass to a synthesis gas, composed of a mixture of hydrogen, carbon monoxide, carbon dioxide and methane. In order to manipulate the composition and maximise the hydrogen output, a calcium-based carbon dioxide sorbent can be utilised in situ. The removal of carbon dioxide alters the reaction chemistry to preferentially produce hydrogen. In this work we report on the characterisation of a likely Ca-based carbon dioxide sorbent and demonstrate the merits of hydrogen production from biomass, with in situ carbon dioxide capture, on the basis of a thermodynamic study. Using this model we show that hydrogen output from biomass gasification can be increased from 40%-vol to 80%-vol (dry basis) when a carbon dioxide sorbent is used.

Investigations into the Effects of Volatile Biomass Tar on the Performance of Fe-Based CLC Oxygen Carrier Materials

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.

Impact of Flue Gas Compounds on Microalgae and Mechanisms for Carbon Assimilation and Utilization

To shift the world to a more sustainable future, it is necessary to phase out the use of fossil fuels and focus on the development of low-carbon alternatives. However, this transition has been slow, so there is still a large dependence on fossil-derived power, and therefore, carbon dioxide is released continuously. Owing to the potential for assimilating and utilizing carbon dioxide to generate carbon-neutral products, such as biodiesel, the application of microalgae technology to capture CO2 from flue gases has gained significant attention over the past decade. Microalgae offer a more sustainable source of biomass, which can be converted into energy, over conventional fuel crops because they grow more quickly and do not adversely affect the food supply. This review focuses on the technical feasibility of combined carbon fixation and microalgae cultivation for carbon reuse. A range of different carbon metabolisms and the impact of flue gas compounds on microalgae are appraised. Fixation of flue gas carbon dioxide is dependent on the selected microalgae strain and on flue gas compounds/concentrations. Additionally, current pilot-scale demonstrations of microalgae technology for carbon dioxide capture are assessed and its future prospects are discussed. Practical implementation of this technology at an industrial scale still requires significant research, which necessitates multidisciplinary research and development to demonstrate its viability for carbon dioxide capture from flue gases at the commercial level.

Calcium looping technologies for gasification and reforming

Abstract This chapter demonstrates the broad potential of applying calcium looping for reforming and gasification applications. The highly integrated processes discussed herein offer potential step-change improvements in the thermal and cost efficiency of power production integrated with CO2 capture. While there has been a considerable amount of research focussed on elaborating the underlying science, there remains scope for further work to evaluate the reaction kinetics for sorption-enhanced water–gas shift and sorption-enhanced reforming, to measure the influence of impurities, and to overcome challenges associated with complex process integration.