Paul S. Fennell

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.

An overview of advances in biomass gasification

Biomass gasification is a widely used thermochemical process for obtaining products with more value and potential applications than the raw material itself. Cutting-edge, innovative and economical gasification techniques with high efficiencies are a prerequisite for the development of this technology. This paper delivers an assessment on the fundamentals such as feedstock types, the impact of different operating parameters, tar formation and cracking, and modelling approaches for biomass gasification. Furthermore, the authors comparatively discuss various conventional mechanisms for gasification as well as recent advances in biomass gasification. Unique gasifiers along with multi-generation strategies are discussed as a means to promote this technology into alternative applications, which require higher flexibility and greater efficiency. A strategy to improve the feasibility and sustainability of biomass gasification is via technological advancement and the minimization of socio-environmental effects. This paper sheds light on diverse areas of biomass gasification as a potentially sustainable and environmentally friendly technology.

Regeneration of sintered limestone sorbents for the sequestration of CO2 from combustion and other systems

Abstract The capacity of particles of CaO, produced by calcining limestone, to reactively absorb CO2, degrades with the number of cycles of carbonation and calcination. A novel method of reactivating the stone in humid, ambient air is described. Typically, a calcined limestone has a carrying capacity for CO2 which falls from ∼79% (on the basis of moles of CO2 per mole of CaO) to only about 20–30% after 30 cycles of regeneration and reuse. This new technique enables the carrying capacity to be restored to ∼55%, thereby improving the economics of sequestrating CO2 using a calcium-based sorbent.

Effect of wind direction and speed on the dispersion of nucleation and accumulation mode particles in an urban street canyon

There have been many studies concerning dispersion of gaseous pollutants from vehicles within street canyons; fewer address the dispersion of particulate matter, particularly particle number concentrations separated into the nucleation (10-30 nm or N10-30) or accumulation (30-300 nm or N30-300) modes either separately or together (N10-300). This study aimed to determine the effect of wind direction and speed on particle dispersion in the above size ranges. Particle number distributions (PNDs) and concentrations (PNCs) were measured in the 5-2738 nm range continuously (and in real-time) for 17 days between 7th and 23rd March 2007 in a regular (aspect ratio approximately unity) street canyon in Cambridge (UK), using a newly developed fast-response differential mobility spectrometer (sampling frequency 0.5 Hz), at 1.60 m above the road level. The PNCs in each size range, during all wind directions, were better described by a proposed two regime model (traffic-dependent and wind-dependent mixing) than by simply assuming that the PNC was inversely proportional to the wind speed or by fitting the data with a best-fit single power law. The critical cut-off wind speed (Ur,crit) for each size range of particles, distinguishing the boundary between these mixing regimes was also investigated. In the traffic-dependent PNC region (UrUr<<Ur,critUr,crit), concentrations in each size range were approximately constant and independent of wind speed and direction. In the wind speed dependent PNC region (UrUr>>Ur,critUr,crit), concentrations were inversely proportional to Ur irrespective of any particle size range and wind directions. The wind speed demarcating the two regimes (Ur,critUr,crit) was 1.23+/-0.55 m s(-1) for N10-300, (1.47+/-0.72 m s(-1)) for N10-30 but smaller (0.78+/-0.29 m s(-1)) for N30-300.

Investigation into potential synergy between power generation, cement manufacture and CO2 abatement using the calcium looping cycle

Here, we report the preliminary results of an investigation into the effects on cement chemistry of using as a feed calcium oxide (CaO) which is the spent sorbent from a promising CO2 capture process, the calcium looping cycle.

Comparison of the behaviour of manufactured and other airborne nanoparticles and the consequences for prioritising research and regulation activities

Currently, there are no air quality regulations in force in any part of the world to control number concentrations of airborne atmospheric nanoparticles (ANPs). This is partly due to a lack of reliable information on measurement methods, dispersion characteristics, modelling, health and other environmental impacts. Because of the special characteristics of manufactured (also termed engineered or synthesised) nanomaterials or nanoparticles (MNPs), a substantial increase is forecast for their manufacture and use, despite understanding of safe design and use, and health and environmental implications being in its early stage. This article discusses a number of underlining technical issues by comparing the properties and behaviour of MNPs with anthropogenically produced ANPs. Such a comparison is essential for the judicious treatment of the MNPs in any potential air quality regulatory framework for ANPs.

A novel calcium looping absorbent incorporated with polymorphic spacers for hydrogen production and CO2 capture

High temperature looping cycles can be used to produce hydrogen or capture CO2 from power stations, though sintering of absorbents is frequently a problem, reducing reactivity. In this work we develop materials, in which the crystal structure and volume of polymorphic materials change with temperature, as active spacers to reduce sintering.

Inhibiting the interaction between FeO and Al 2 O 3 during chemical looping production of hydrogen

Hydrogen of high purity can be produced by chemical looping using iron oxide as an oxygen carrier and making use of the reaction between steam and either iron or FeO. However, this process is viable only if the iron oxide can be cycled between the fully-oxidised and fully-reduced states many times. This can be achieved if the iron oxide is supported on refractory oxides such as alumina. Unfortunately, the interaction between alumina and oxides of iron to form FeAl2O4 hinders the kinetics of the reactions essential to the production of hydrogen, viz. the reduction of Fe(II) to metallic iron by a mixture of CO and CO2 prior to the oxidation by steam. Here, oxygen carriers containing Fe2O3 and Al2O3 were doped with Na2O and, or, MgO, in order to inhibit the formation of FeAl2O4 by forming NaAlO2 or MgAl2O4, respectively. The performance of the modified oxygen carriers for producing hydrogen, i.e. cyclic transitions between Fe2O3 (or Fe3O4) and metallic Fe at 1123 K were investigated. It was found that the interaction between FeO and Al2O3 was successfully mitigated in an oxygen carrier containing Mg, with an Al: Mg ratio of 2, resulting in consistently stable and high capacity for producing hydrogen by chemical looping, whether or not the material was oxidised fully in air in each cycle. However, the oxygen carrier without Mg only remained active when a step to oxidise the sample in air was included in each cycle. Otherwise it progressively deactivated with cycling, showing substantial interaction between Al2O3 and oxides of Fe.

An economically viable ionic liquid for the fractionation of lignocellulosic biomass

Cost-effective fractionation (pretreatment) of lignocellulosic biomass is necessary to enable its large-scale use as a source of liquid fuels, bio-based materials and bio-derived chemicals. While a number of ionic liquids (ILs) have proven capable of highly effective pretreatment, their high cost presents a barrier to commercial viability. In this study, we investigate in detail the application of the low-cost (ca.