Reactivation of Limestone-Derived Sorbents using Hydration: Preliminary Results From a Fluidised Bed

A simple method of CO~2~ capture is by using the calcium looping cycle. The calcium looping cycle uses CaCO~3~ as a CO~2~ carrier, via the reversible reaction CaO(s) + CO~2~(g) = CaCO~3~(s), to extract CO2 from the exhaust stream and provide a pure stream of CO~2~ suitable for sequestration. 
A problem associated with the technology is that the capacity of the sorbent to absorb CO~2~ reduces significantly with the number of cycles of carbonation and calcination. The energy penalty of the cycle is considerably increased by cycling unreacted sorbent: hydration of unreactive sorbent has emerged as a promising strategy of reducing this penalty by regenerating the reactivity of exhausted sorbent.
A small atmospheric pressure fluidised bed reactor has been built and tested, that allows repeated cycling between two temperatures up to 1000 °C. 
Work presented here focuses on the effects of variation of the calcination temperature before hydration. Hydration has been found to more than double the reactivity of a spent sorbent cycled under the mildest conditions studied (calcination temperature of 840 °C). However, as calcination temperature is increased the observed reactivation decreases until little reactivation is observed for the sorbent cycled at 950 °C. The primary reason for this appears to be a substantial increase in friability of particles, with reactivity normalised for mass losses appearing similar independent of cycling temperature

Balancing accuracy and computation burden - an evaluation of different sensitivity analysis methods for urban scale building energy models

Urban-scale building energy models capitalise on the increasing accessibility of large-scale urban data sets and allow the rapid evaluation of competing policy options, making them a vital tool for urban responses to the climate emergency. However, the vast number of different inputs required to model a complex urban environment makes it impossible to precisely quantify all inputs and the complex energy flows within models must be simplified to achieve tractable solutions, as a result, the outputs of these models inevitably have a significant range of variation. Without understanding these limits of inference resulting policy advice is inherently defective. Uncertainty Analysis (UA) and Sensitivity Analysis (SA) offer essential tools to determine the limits of inference of a model and explore the factors which have the most effect on the model outputs. Despite a wellestablished body of work applying UA and SA to models of individual buildings, very limited work has been done to apply these tools to urban scale models. This study presents a systematic comparison of three different sensitivity analysis methods for a high resolution, dynamic thermal simulation at the neighbourhood scale. Accuracy, processing time and complexity of application of each method is evaluated to provide guidance which can inform the application of these methods to other urban and large-scale building energy models. The results highlight the importance of considering both model form and input parameter scale when selecting an appropriate method. In this case, the elementary effects method (EER) offers good performance at relatively low simulation cost

A shrinking core model for steam hydration of CaO-based sorbents cycled for CO2 capture

Calcium looping is a developing CO2 capture technology. It is based on the reversible carbonation of CaO sorbent, which becomes less reactive upon cycling. One method of increasing the reactivity of unreactive sorbent is by hydration in the calcined (CaO) form. Here, sorbent has been subjected to repeated cycles of carbonation and calcination within a small fluidised bed reactor. Cycle numbers of 0 (i.e., one calcination), 2, 6 and 13 have been studied to generate sorbents that have been deactivated to different extents. Subsequently, the sorbent generated was subjected to steam hydration tests within a thermogravimetric analyser, using hydration temperatures of 473, 573 and 673 K. Sorbents that had been cycled less prior to hydration hydrated rapidly. However, the more cycled sorbents exhibited behaviour where the hydration conversion tended towards an asymptotic value, which is likely to be associated with pore blockage. This asymptotic value tended to be lower at higher hydration temperatures; however, the maximum rate of hydration was found to increase with increasing hydration temperature. A shrinking core model has been developed and applied to the data. It fits data from experiments that did not exhibit extensive pore blockage well, but fits data from experiments that exhibited pore blockage less well

Cement, CCS and CO2 Uptake, Including an Update on the EU LEILAC Project

Portland cement manufacture is responsible for around 7% of anthropogenic CO2 emissions, a percentage which is rising. The majority of direct emissions come from the calcination of limestone to form calcium oxide and calcium silicates, the main constituent of Portland cement. However, after cement is hydrated to make concrete, it can react with carbon dioxide in the air to re-form calcium carbonate, completing a cycle. This carbonation mechanism can be measured and the rate at which the global inventory of concrete absorbs CO2 can be estimated – the results of such an exercise will be shown in this presentation. That said, concrete carbonation only counterbalances a small fraction of emissions from concrete production, the majority of which come from cement manufacture. Incremental improvements in composition and efficiency are not sufficient to reduce CO2 emissions by the extent necessary to hit a 1.5–2 °C temperature rise target – CCS is the only practical technology to achieve this ambition. The technological options for the cement-CCS will be presented. Three options – calcium looping, an oxy-fueled kiln, and direct capture – will be described and discussed in depth, including discussion of the effects of various highly integrated processes on the strength and other properties of the cement produced; for calcium looping and oxyfueled kilns, it will be shown that there are negligible effects on the quality of the cement produced. Direct Capture will be presented and discussed in detail, as part of a recently funded project in the process of producing results. This process is being developed as part of Leilac (Low Emissions Intensity Lime and Cement), a EU Horizon 2020 research and innovation project. This €21m project has received €12m from the EU (H2020 No 654465), with the balance provided by the consortium partners. It runs for five years from 2016 to 2020 and the project team includes industrial, technology and research & development partners. The objective is to pilot a breakthrough carbon capture technology that can capture the process emissions from the calcination of limestone, without imposing a significant energy or capital penalty. The pilot plant will be hosted by Heidelberg Cement at Lixhe in Belgium. Imperial College is carrying out research on the kinetics of calcination under the conditions of interest, suitability of product for destination industries, defining reference technologies for modelling and modelling of the radiative heat transfer in the reactor. Here, we shall present an overview of the project and the current status

Optimising Buildings Retrofits at the Stock Level: The Development of a Methodology

Optimisation has been widely applied to individual building energy models, however there exists a gap in the literature around stock-level optimisation approaches. This paper describes the early development of a novel methodology which aims to allow multi-objective optimisation to be performed over a stock of buildings. This would be valuable to parties such as local authorities who require decision support when mapping retrofit pathways for their stock. An early-stage workflow is described which is facilitated by a custom developed Python module and applied to an EnergyPlus stock model. An optimisation problem can be defined for the area, which influences how the module handles the parametric setup and optimisation. The setup involves specifying restrictions (e.g. listed buildings) and desires for the recommendations (e.g. if a standardised retrofit package should be applied to a certain dwelling type). According to this formulation, the module assists with parameter creation. The EnergyPlus file is automatically altered so that each parameter can be independent. Optimisation objectives and constraints can be derived from the model outputs. The module links EnergyPlus to the NSGA-II algorithm. Results are output in a format that allows easy segmentation, plotting and exporting. The workflow is demonstrated on an area of housing stock to showcase how the methods are informed by an example problem definition. The paper concludes with a discussion around advantages, challenges and future development. The intention is to build on this work and include stages which handle simplification of the stock model, sensitivity analysis and calibration

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

Towards a universal access to Urban Building Energy Modelling - The case of low-income, self-constructed houses in informal settlements in Lima, Peru

By 2050 urban population is estimated to grow from 4 billion to almost 7 billion, with over 90% expected in the Global South, where development often takes place as unplanned informal settlements, with essential shortage of critical infrastructure. In processing some of the associated rising challenges, Urban Building Energy Models can play a key role. However, such models have had limited presence in this context, highlighting the inequalities in the representation of such communities in this field. This paper works towards addressing this gap and presents the development of an Urban Building Energy Modelling workflow for analysing the thermal comfort in a self-constructed, low-income housing neighbourhood in Lima, Peru, using an innovative approach, based largely on open source software, such as EnergyPlus, QGIS and Python. The results highlight that the compact and dense built form of the building blocks, can cause higher heat retention, especially in lower thermal zones and therefore result in high indoor temperatures for longer. Additionally, the poor thermal performance of the buildings’ fabric, can cause hourly indoor temperatures to rise to critical levels, especially in higher thermal zones, which can have adverse impacts on the residents’ health. This first step in understanding some of the key issues these communities are facing, is critical in the early assessment of future building retrofit decisions

Progress in biofuel production from gasification

Biofuels from biomass gasification are reviewed here, and demonstrated to be an attractive option. Recent progress in gasification techniques and key generation pathways for biofuels production, process design and integration and socio-environmental impacts of biofuel generation are discussed, with the goal of investigating gasification-to-biofuels’ credentials as a sustainable and eco-friendly technology. The synthesis of important biofuels such as bio-methanol, bio-ethanol and higher alcohols, bio-dimethyl ether, Fischer Tropsch fuels, bio-methane, bio-hydrogen and algae-based fuels is reviewed, together with recent technologies, catalysts and reactors. Significant thermodynamic studies for each biofuel are also examined. Syngas cleaning is demonstrated to be a critical issue for biofuel production, and innovative pathways such as those employed by Choren Industrietechnik, Germany, and BioMCN, the Netherlands, are shown to allow efficient methanol generation. The conversion of syngas to FT transportation fuels such as gasoline and diesel over Co or Fe catalysts is reviewed and demonstrated to be a promising option for the future of biofuels. Bio-methane has emerged as a lucrative alternative for conventional transportation fuel with all the advantages of natural gas including a dense distribution, trade and supply network. Routes to produce H2 are discussed, though critical issues such as storage, expensive production routes with low efficiencies remain. Algae-based fuels are in the research and development stage, but are shown to have immense potential to become commercially important because of their capability to fix large amounts of CO2, to rapidly grow in many environments and versatile end uses. However, suitable process configurations resulting in optimal plant designs are crucial, so detailed process integration is a powerful tool to optimize current and develop new processes. LCA and ethical issues are also discussed in brief. It is clear that the use of food crops, as opposed to food wastes represents an area fraught with challenges, which must be resolved on a case by case basis

Hydrogen production by sorption enhanced steam reforming (SESR) of biomass in a fluidised-bed reactor using combined multifunctional particles

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/gbiomass (122 g H2/kgbiomass) 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

Pilot testing of enhanced sorbents for calcium looping with cement production

One of the main challenges for commercialising calcium looping (CaL) as a CO2 capture technology is maintaining a high level of sorbent reactivity during long-term cycling. In order to mitigate the decay in carrying capacity, research has moved towards producing enhanced sorbents. However, this creates potential problems related to ease of scaling up production techniques and production costs, and raises the question as to whether such approaches can be used at large scale. On the other hand, a key advantage of CaL over other carbon capture technologies is synergy with the cement industry, i.e., use of spent sorbent as a feedstock for clinker production. In this work two enhanced materials: (i) limestone doped with HBr through a particle surface impregnation technique; and (ii) pellets prepared from limestone and calcium aluminate cement, were tested in a 25 kWth dual fluidised bed pilot-scale reactor in order to investigate their capture performance and mechanical stability under realistic CaL conditions. Moreover, the spent sorbent was then used as a raw material to make cement, which was characterised for phase and chemical composition as well as compressive strength. The HBr-doped limestone showed better performance in terms of both mechanical strength and stability of the CO2 uptake when compared to that of pellets. Furthermore, it was shown that the cement produced has similar characteristics and performance as those of commercial CEM 1 cement. This indicates the advantages of using the spent sorbent as feedstock for cement manufacture and shows the benefits of synthetic sorbents in CaL and suitability of end-use of spent sorbents for the cement industry, validating their synergy at pilot scale. Finally, this study demonstrates the possibility of using several practical techniques to improve the performance of CaL at the pilot scale, and more importantly demonstrates that commercial-grade cement can be made from the lime product from this technology