147 results found
Ghaedi H, Zhao M, Clough PT, et al., 2020, High CO2 absorption in new amine based-transition-temperature mixtures (deep eutectic analogues) and reporting thermal stability, viscosity and surface tension: Response surface methodology (RSM), JOURNAL OF MOLECULAR LIQUIDS, Vol: 316, ISSN: 0167-7322
González B, Kokot-Blamey J, Fennell P, 2020, Enhancement of CaO-based sorbent for CO<inf>2</inf> capture through doping with seawater, Greenhouse Gases: Science and Technology, Vol: 10, Pages: 878-883
© 2020 Society of Chemical Industry and John Wiley & Sons, Ltd. Limestone can be used to generate a sorbent suitable for CO2 capture via the reversible carbonation of CaO, in a process often referred to as calcium looping. This sorbent loses reactivity to CO2 upon cycles of carbonation and calcination (the reverse of carbonation). Several methods of improving sorbent performance have previously been investigated, including by generating synthetic sorbents or simple doping. Here, we demonstrate, for the first time, that sorbent performance can be enhanced by simple doping with seawater. This effect is consistent across five different limestones investigated and can be enhanced by steam addition. This would be a simple and inexpensive method for improving sorbent performance in calcium looping processes. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.
Gschwend FJ, Hennequin LM, Brandt-Talbot A, et al., 2020, Towards an environmentally and economically sustainable biorefinery: heavy metal contaminated waste wood as a low-cost feedstock in a low-cost ionic liquid process, Green Chemistry, Vol: 22, Pages: 5032-5041, ISSN: 1463-9262
In the present study, we used a low-cost protic ionic liquid, 1-methylimidazolium chloride, to simultaneously fractionate heavy metal contaminated wood and extract the metals from the wood at elevated temperature and short reaction time. This treatment selectively dissolves the lignin and hemicellulose in the biomass, leaving a solid cellulose-rich pulp, while coordinating and extracting 80–100% of the metal species present in the wood in a one-pot process. The lignin stream was recovered from the liquor and the cellulose was hydrolysed and then fermented into ethanol. The ionic liquid was recycled 6 times and the metals were recovered from the liquor via electrodeposition. This is the first time that highly contaminated waste wood has been integrated into a process which does not produce a contaminated waste stream, but instead valorises the wood as a feedstock for renewable chemicals, materials and fuels, while efficiently recovering the metals, converting a toxic environmental hazard into a rich source of biorenewables. We have therefore used an otherwise problematic waste as a low-cost lignocellulsoic feedstock for a circular bioeconomy concept.
Firth AEJ, Mac Dowell N, Fennell PS, et al., 2020, Assessing the economic viability of wetland remediation of wastewater, and the potential for parallel biomass valorisation, Environmental Science: Water Research & Technology, Vol: 6, Pages: 2103-2121, ISSN: 2053-1400
Constructed wetlands have been shown to consistently remove a wide range of pollutants from contaminated water. However, no wide-ranging studies exist on the economic viability of this technology. This paper performs a high-level economic comparison between wetland remediation and conventional water remediation technologies, for a wide range of contaminant inputs, outputs, and flow rates. The cases considered are nutrient removal from wastewater, and remediation of low-pH and circumneutral acid mine drainage (AMD). The first-order P-k-C* model is used for nutrient removal, while a zeroth-order model is used for AMD remediation, with removal rate data taken from the literature. The number of wetland cells employed was found to significantly affect the overall cost of nutrient removal, allowing savings of up to 86% and 42% for biochemical oxygen demand and phosphorus removal, particularly for low concentrations and flow rates. For integrated secondary and tertiary treatment, wetland remediation was economically competitive down to stringent effluent standards. A sensitivity analysis was performed on sizing and costing parameters of nutrient removal wetlands, with required wetland size found to be most strongly correlated with the assumed removal rate, and land costs found to have relatively little effect on overall costs. Wetland remediation of AMD was only found to be economically favourable for less severe conditions and lower flow rates when treating low-pH drainage, and was heavily influenced by the acidity removal rate. However, the majority of site data from literature was found to fall within this range of conditions. For circumneutral AMD, wetland remediation was found to be cheaper for all simulated cases. The feasibility of offsetting wetland remediation costs through biomass valorisation was investigated for a range of products, with area requirements for minimum economic production identified as the principal barrier.
Rissman J, Bataille C, Masanet E, et al., 2020, Technologies and policies to decarbonize global industry: Review and assessment of mitigation drivers through 2070, APPLIED ENERGY, Vol: 266, ISSN: 0306-2619
Yao JG, Boot-Handford ME, Zhang Z, et al., 2020, Pressurized In Situ CO2 Capture from Biomass Combustion via the Calcium Looping Process in a Spout-Fluidized-Bed Reactor, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 59, Pages: 8571-8580, ISSN: 0888-5885
Katayama K, Bahzad H, Boot-Handford M, et al., 2020, Process Integration of Chemical Looping Water Splitting with a Sintering Plant for Iron Making, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 59, Pages: 7021-7032, ISSN: 0888-5885
Chambon CL, Fitriyanti V, Verdía P, et al., 2020, Fractionation by sequential antisolvent precipitation of grass, softwood, and hardwood lignins isolated using low-cost ionic liquids and water, ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 3751-3761, ISSN: 2168-0485
In this study, fractionation by sequential antisolvent precipitation was applied to ionoSolv lignins for the first time. Pretreatment with the aqueous low-cost protic ionic liquid N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4], 80 wt % in water) was applied to Miscanthus (herbaceous), willow (hardwood), and pine (softwood) to extract lignin. Then, lignin was sequentially precipitated by the addition of water as an antisolvent. Fractionation appeared to be controlled by the molecular weight of lignin polymers. Fractions isolated with minimal water volumes were shown to have high molecular weight, polydispersity, thermal stability, and Tg (178 °C). Later precipitates were more monodisperse and had high phenolic and total hydroxyl content and lower thermal stability and Tg (136 °C). Addition of 1 g of water per gram of dry IL was able to precipitate up to 90 wt % of lignin. Fractional precipitation represents a novel lignin isolation technique that can be performed as part of the lignin recovery procedure enabling a high degree of control of lignin properties. The effect of the fractionation on lignin structural, chemical, and thermal properties was thoroughly examined by two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance, gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry and compared to the unfractionated lignin precipitate obtained by addition of an excess of water.
Yao JG, Fennell PS, Hallett JP, 2020, Chapter 4: Ionic liquids, RSC Energy and Environment Series, Pages: 69-105, ISBN: 9781788014700
© The Royal Society of Chemistry 2020. The use of ionic liquids (ILs) is a relatively new and promising technology for CO2 capture and storage (CCS). Ionic liquids, which are essentially organic salts with melting points below 100 °C, are particularly attractive owing to their negligible volatility, chemical and thermal stability, and most importantly, their designability. Their low reaction enthalpy with CO2 allows regeneration under less energy intensive conditions relative to conventional amine solvents, and choosing their anion/cation pairing can allow their properties to be controlled. Although conventional ILs are able to physically absorb CO2, greater capture capacities can be achieved by tethering functional groups which can chemically bind to CO2 on either or both of the cation and anion. In addition to liquid-gas capture, ILs have also demonstrated success when incorporated into gas separation membranes. To date, most studies have been focused at the laboratory scale and under ideal conditions (i.e., capture under high CO2 partial pressures, and regeneration in N2); however, in order to progress with this technology, it is imperative to explore the behaviour of ILs under industrially-relevant environments. In addition, further process simulation and economic studies should be carried out to help scale up the technology.
Hills TP, Sceats MG, Fennell PS, 2020, Chapter 10: Applications of CCS in the cement industry, RSC Energy and Environment Series, Pages: 315-352, ISBN: 9781788014700
© The Royal Society of Chemistry 2020. Cement manufacture is responsible for around 7% of global anthropogenic CO2 emissions. The process is unique in that around two-Thirds of the direct CO2 emissions are unavoidable as they come from the process chemistry rather than from fuel combustion. This makes reducing them particularly difficult, and carbon capture and storage is currently the only option that can reduce emissions by the extent required to allow cement manufacture to continue beyond the transition to low CO2-emission economies. Post-combustion capture options, which are similar to those described in Chapter 4, are available. Equally, oxy-fuel combustion is possible. Pre-combustion capture can only deal with one-Third of emissions from combustion, and so is generally not considered. Other cement-specific options exist, such as direct separation, and the synergies between calcium looping and cement manufacture are noteworthy. High CO2 intensity coupled with the relatively low price of cement means that CCS is expensive per unit of cement manufactured. The lack of large-scale capture facilities means that the costs are rather uncertain, although several estimates are given in this chapter. A summary of existing pilot plants is provided, the challenges of rolling out carbon capture in the cement sector are discussed, and a way forward is suggested.
Patzschke CF, Boot-Handford ME, Song Q, et al., 2020, Co-precipitated Cu-Mn mixed metal oxides as oxygen carriers for chemical looping processes, Chemical Engineering Journal, ISSN: 1385-8947
© 2020 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).
Bahzad H, Katayama K, Boot-Handford ME, et al., 2019, Iron-based chemical-looping technology for decarbonising iron and steel production, INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL, Vol: 91, ISSN: 1750-5836
Bahzad H, Shah N, Dowell NM, et al., 2019, Development and techno-economic analyses of a novel hydrogen production process via chemical looping, International Journal of Hydrogen Energy, Vol: 44, Pages: 21251-21263, ISSN: 0360-3199
In this work, a novel hydrogen production process (Integrated Chemical Looping Water Splitting “ICLWS”) has been developed. The modelled process has been optimised via heat integration between the main process units. The effects of the key process variables (i.e. the oxygen carrier-to-fuel ratio, steam flow rate and discharged gas temperature) on the behaviour of the reducer and oxidiser reactors were investigated. The thermal and exergy efficiencies of the process were studied and compared against a conventional steam-methane reforming (SMR) process. Finally, the economic feasibility of the process was evaluated based on the corresponding CAPEX, OPEX and first-year plant cost per kg of the hydrogen produced. The thermal efficiency of the ICLWS process was improved by 31.1% compared to the baseline (Chemical Looping Water Splitting without heat integration) process. The hydrogen efficiency and the effective efficiencies were also higher by 11.7% and 11.9%, respectively compared to the SMR process. The sensitivity analysis showed that the oxygen carrier–to-methane and -steam ratios enhanced the discharged gas and solid conversions from both the reducer and oxidiser. Unlike for the oxidiser, the temperature of the discharged gas and solids from the reducer had an impact on the gas and solid conversion. The economic evaluation of the process indicated hydrogen production costs of $1.41 and $1.62 per kilogram of hydrogen produced for Fe-based oxygen carriers supported by ZrO2 and MgAl2O4, respectively - 14% and 1.2% lower for the SMR process H2 production costs respectively.
Patzschke CF, Bahzad H, Boot-Handford ME, et al., 2019, Simulation of a 100-MW solar-powered thermo-chemical air separation system combined with an oxy-fuel power plant for bio-energy with carbon capture and storage (BECCS), Mitigation and Adaptation Strategies for Global Change, ISSN: 1381-2386
Ghosh S, Kokot-Blamey J, Boot-Handford ME, et al., 2019, Kinetics Modeling, Development, and Comparison for the Reaction of Calcium Oxide with Steam, ENERGY & FUELS, Vol: 33, Pages: 5505-5517, ISSN: 0887-0624
Fennell PS, 2019, Comparative Energy Analysis of Renewable Electricity and Carbon Capture and Storage, JOULE, Vol: 3, Pages: 1406-1408, ISSN: 2542-4351
Chambon CL, Chen M, Fennell PS, et al., 2019, Efficient fractionation of lignin- and ash-rich agricultural residues following treatment with a low-cost protic ionic liquid, Frontiers in Chemistry, Vol: 7, ISSN: 2296-2646
Agricultural residues from rice, wheat and sugarcane production are annually available at the gigaton-scale worldwide, particularly in Asia. Due to their high sugar content and ash compositions, their conversion to bioethanol is an attractive alternative to their present disposal by open-field burning and landfilling. In this work, we demonstrate application of the low-cost protic ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) for pretreatment of rice straw, rice husk, wheat straw and sugarcane bagasse. The feedstocks had high ash (up to 13 wt%) and lignin content (up to 28 wt%). Pretreatment effectiveness was examined at 150 and 170°C and an optimal pretreatment time was identified and characterized by glucose release following enzymatic saccharification (i.e., hydrolysis), biomass delignification observed by compositional analysis, and lignin recovery. The isolated lignin fractions were analyzed by 2D HSQC NMR to obtain insights into the structural changes occurring following ionic liquid pretreatment. After treatment at 170°C for 30–45 min, enzymatic hydrolysis of three agroresidues gave near-quantitative glucose yields approaching 90% while rice husk gave 73% yield. Glucose release from the pulps was enhanced by saccharifying wet pulps without an air-drying step to reduce hornification. According to pulp compositional analysis, up to 82% of lignin was removed from biomass during pretreatment, producing highly digestible cellulose-rich pulps. HSQC NMR of the extracted lignins showed that delignification proceeded via extensive cleavage of β-O-4′ aryl ether linkages which was accompanied by condensation reactions in the isolated lignins. The high saccharification yields obtained indicate excellent potential for valorization of low-cost agroresidues in large volumes, which is promising for commercialization of biofuels production using the ionoSolv pretreatment technology.
Gschwend F, Chambon C, Biedka M, et al., 2019, Quantitative glucose release from softwood after pretreatment with low-cost ionic liquids, Green Chemistry, Vol: 21, Pages: 692-703, ISSN: 1463-9262
Softwood is an abundantly available feedstock for the bio-based industry, however, achieving cost-effective sugar release is particularly challenging owing to its guaiacyl-only lignin. Here, we report the highly effective pretreatment of the softwood pine (Pinus sylvestris) using ionoSolv pretreatment, a novel ionic liquid-based lignocellulose fractionation technology. Three protic, low-cost ionic liquids, 1-butylimidazolium hydrogen sulfate, triethylammonium hydrogen sulfate and N,N-dimethylbutylammonium hydrogen sulfate, were used to fractionate the biomass into a carbohydrate-rich pulp and a lignin. The carbohydrate-rich pulp was hydrolysed into fermentable sugars by enzymatic saccharification. Under the most successful pretreatment conditions, quantitative glucose release from the pulp was achieved, which equates to a projected glucose release of 464 mg per gram of pine wood entering the process. We further intensified the process by increasing the solid to solvent ratio up to 1:2 g/g while maintaining saccharification yields of 75% of the theoretical maximum. We also demonstrate for the first time that N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO4] is an excellent low-cost pretreatment solvent, surpassing the pretreatment effectiveness of its symmetrically substituted analogue triethylammonium hydrogen sulfate. This shows that ionoSolv pretreatment with protic hydrogen sulfate ionic liquids is a truly feedstock-independent pretreatment option, further increasing the commercial potential of this pretreatment technology.
Ji G, Yao JG, Clough PT, et al., 2018, Enhanced hydrogen production from thermochemical processes, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 2647-2672, ISSN: 1754-5692
Chambon C, Mkhize T, Reddy P, et al., 2018, Pretreatment of South African sugarcane bagasse using a low-cost protic ionic liquid: a comparison of whole, depithed, fibrous and pith bagasse fractions, Biotechnology for Biofuels, Vol: 11, ISSN: 1754-6834
BackgroundSugarcane bagasse is an abundant and geographically widespread agro-industrial residue with high carbohydrate content, making it a strong candidate feedstock for the bio-based economy. This study examines the use of the low-cost protic ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) to fractionate a range of South African sugarcane bagasse preparations into a cellulose-rich pulp and lignin. The study seeks to optimize pretreatment conditions and examine the necessity of applying a depithing step on bagasse prior to pretreatment.ResultsPretreatment of five bagasse preparations, namely whole, industrially depithed, laboratory depithed (short and long fiber) and pith bagasse with [TEA][HSO4]:[H2O] (4:1 w/w) solutions produced highly digestible cellulose-rich pulps, as assessed by residual lignin analysis and enzymatic hydrolysis. Pretreatment under the optimized condition of 120 °C for 4 h produced a pretreated cellulose pulp with up to 90% of the lignin removed and enabled the release of up to 69% glucose contained in the bagasse via enzymatic hydrolysis. Glucose yields from whole and depithed bagasse preparations were very similar. Significant differences in lignin recovery were obtained for laboratory depithed bagasse compared with whole and industrially depithed bagasse. The silica-rich ash components of bagasse were seen to partition mainly with the pulp, from where they could be easily recovered in the post-hydrolysis solids.ConclusionsThe five bagasse preparations were compared but did not show substantial differences in composition or cellulose digestibility after pretreatment. Evidence was presented that a depithing step appears to be unnecessary prior to ionoSolv fractionation, potentially affording significant cost and energy savings. Instead, lignin re-deposition onto the pulp surface (and, in turn, particle size and shape) appeared to be major factors affecting the conditioning of bagasse with the applied IL. We show that pith ba
Erans M, Jeremias M, Zheng L, et al., 2018, Pilot testing of enhanced sorbents for calcium looping with cement production, APPLIED ENERGY, Vol: 225, Pages: 392-401, ISSN: 0306-2619
Daggash HA, Patzschke CF, Heuberger CF, et al., 2018, Closing the carbon cycle to maximise climate change mitigation: Power-to-Methanol vs Power-to-Direct Air Capture, Sustainable Energy and Fuels, Vol: 2, Pages: 1153-1169, ISSN: 2398-4902
It is broadly recognised that CO2 capture and storage (CCS) and associated negative emissions technologies (NETs) are vital to meeting the Paris agreement target. The hitherto failure to deploy CCS on the required scale has led to the search for options to improve its economic return. CO2 capture and utilisation (CCU) has been proposed as an opportunity to generate value from waste CO2 emissions and improve the economic viability of CCS, with the suggestion of using curtailed renewable energy as a core component of this strategy. This study sets out to quantify (a) the amount of curtailed renewable energy that is likely to be available in the coming decades, (b) the amount of fossil CO2 emissions which can be avoided by using this curtailed energy to convert CO2 to methanol for use as a transport fuel – power-to-fuel, with the counterfactual of using that curtailed energy to directly remove CO2 from the atmosphere via direct air capture (DAC) and subsequent underground storage, power-to-DAC. In 2015, the UK curtailed 1277 GWh of renewable power, or 1.5% of total renewable power generated. Our analysis shows that the level of curtailed energy is unlikely to increase beyond 2.5% until renewable power accounts for more than 50% of total installed capacity. This is unlikely to be the case in the UK before 2035. It was found that: (1) power-to-DAC could achieve 0.23–0.67 tCO2 avoided MWh−1 of curtailed power, and (2) power-to-Fuel could achieve 0.13 tCO2 avoided MWh−1. The power-to-fuel concept was estimated to cost $209 tCO2 avoided−1 in addition to requiring an additional $430–660 tCO2 avoided−1 to finally close the carbon cycle by air capture. The power-to-DAC concept was found to cost only the $430–660 tCO2 avoided−1 for air capture. For power-to-fuel to become profitable, hydrogen prices would need to be less than or equal to $1635 tH2−1 or methanol prices must increase to $960 tMeOH−1. Absent this ch
Clough P, Boot-Handford M, Zheng L, et al., 2018, Hydrogen production by sorption enhanced steam reforming (SESR) of biomass in a fluidised-bed reactor using combined multifunctional particles, Materials, Vol: 11, ISSN: 1996-1944
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.
Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.
Vuppaladadiyam AK, Yao JG, Florin N, et al., 2018, Impact of Flue Gas Compounds on Microalgae and Mechanisms for Carbon Assimilation and Utilization, CHEMSUSCHEM, Vol: 11, Pages: 334-355, ISSN: 1864-5631
Bond T, Tse Q, Chambon C, et al., 2018, The feasibility of char and bio-oil production from pyrolysis of pit latrine sludge, Environmental Science: Water Research and Technology, Vol: 4, Pages: 253-264, ISSN: 2053-1400
Sustainable methods are required in developing regions to treat and recover value from pit latrine sludge. One strategy is to pyrolyse pit latrine contents and generate char and bio-oil, which can then be used as a soil enhancer and fuel, respectively. Despite the many benefits associated with the process, there is very limited relevant literature available. This study examines its feasibility. Initially, the energy balance for the pyrolysis of sewage sludge was calculated using data from 14 literature studies. The average net energy recovery from pyrolysis of dewatered and dried sewage sludge followed by use of bio-oil as fuel was calculated as 4.95 ± 0.61 MJ kg−1. For dewatered sewage sludge, an average net energy input of 2.23 ± 0.31 MJ kg−1 was required. Parallel calculations were undertaken where pit latrine sludge with 0–100% water content was the hypothetical feedstock. On average, net energy recovery from produced bio-oil was achievable when pit latrine sludge with a water content of ≤∼55% was the feedstock. When both bio-oil and char were utilised, net energy recovery was feasible at a water content value of ≤∼65%. Char production is more favourable from stabilised pit latrine sludge with lower moisture and volatile solids content. Barriers to the pyrolysis of pit latrine sludge include its heterogeneous composition and the difficulty of collecting high-viscosity sludge. Overall, this study demonstrates the potential of pyrolysis as a disposal and value addition method for pit latrine sludge. Innovative methods for sludge drying and pit emptying will expedite the process becoming a reality.
Boot-Handford M, Virmond E, Florin N, et al., 2017, Simple pyrolysis experiments for the preliminary assessment of biomass feedstocks and low-cost tar cracking catalysts for downdraft gasification applications, Biomass and Bioenergy, Vol: 108, Pages: 398-414, ISSN: 0961-9534
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.
Zhang Z, Yao JG, Boot-Handford M, et al., 2017, Pressurised chemical-looping combustion of an iron-based oxygen carrier: reduction kinetic measurements and modelling, Fuel Processing Technology, Vol: 171, Pages: 205-214, ISSN: 0378-3820
Chemical-looping combustion (CLC) is a novel combustion techology offering the potential to provide uninterrupted and reliable heat and power production from fossil or bio-derived fuels with integrated, intrinsic CO2 capture and minimal energy penalty. Operation of CLC at elevated pressures provides the potential for integration with a combined cycle, which makes the use of solid fuels significantly more feasible. To date, only a few experimental studies investigating CLC processes and oxygen carrier performance under pressurised conditions have been reported in the open literature. This article reports findings from investigations into the effect of pressure, temperature and CO concentration on the intrinsic reaction kinetics of an Al2O3-supported Fe-based oxygen carrier. Our study employed an innovative pressurised fluidised-bed reactor, designed for operation at temperatures up to 1273 K and pressures up to 20 bara, to simulate ex-situ gasification of solid fuels at elevated pressures. An intrinsic reaction model was developed and pseudo-intrinsic rate constants were derived. Differences in the activation energies and pre-exponential factors of the Al2O3-supported Fe2O3 and a pure Fe2O3 oxygen carriers were observed, indicating a change in reaction mechanism when Al2O3 was present. Subsequently, an adapted random pore model was developed to describe the variation of reaction rate with solid conversion. The good agreement between the adapted random pore model and empirical measurements indicated that the change in mechanism was due to a significantly higher product layer diffusivity for the Al2O3-supported Fe2O3 oxygen carrier compared with the pure Fe2O3 material. When pressurised, the observed reaction order with respect to CO was slightly lower than 1. The model developed using atmospheric pressure measurements was successfully applied to predict reaction kinetics at elevated pressures up to 5 bara providing further validation of the model.
Fennell PS, yao JG, maitland GC, et al., 2017, Pressurized Calcium Looping in the Presence of Steam in a Spout-Fluidized-Bed Reactor with DFT Analysis, Fuel Processing Technology, Vol: 169, Pages: 24-41, ISSN: 0378-3820
Calcium looping is a high-temperature solid-looping process for CO2 capture, exploiting cyclical carbonation of CaO. Previous work investigating the effects of steam on the carbonation reaction has produced conflicting results, with the majority of work conducted using thermogravimetric analyzers (TGA). Here, pressurized carbonation kinetics in the presence of steam in a 3 kWe pressurized spout-fluidized bed reactor, gives a rigorous insight into the effects of steam. Pseudo-intrinsic kinetics were determined using an effectiveness factor model along with activation energies and kinetic expressions. The mechanism in which steam promotes CO2 adsorption on the surface of CaO was investigated using density functional theory (DFT). The molecular-scale changes on the CaO surface owing to the presence of steam compared to the base case of CO2 adsorption on a ‘clean’ (without steam) surface were simulated with the Cambridge Serial Total Energy Package (CASTEP) software. The results suggest that steam promotes CO2 adsorption via the formation of surface OH groups on the CaO surface.
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