Imperial College London

DrNiallMac Dowell

Faculty of Natural SciencesCentre for Environmental Policy

Reader in Energy Systems
 
 
 
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Contact

 

+44 (0)20 7594 9298niall Website

 
 
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Location

 

16 Prince's GardensSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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121 results found

Bui M, Flø NE, de Cazenove T, Mac Dowell Net al., 2020, Demonstrating flexible operation of the Technology Centre Mongstad (TCM) CO<inf>2</inf> capture plant, International Journal of Greenhouse Gas Control, Vol: 93, ISSN: 1750-5836

© 2019 Elsevier Ltd This study demonstrates the feasibility of flexible operation of CO2 capture plants with dynamic modelling and experimental testing at the Technology Centre Mongstad (TCM) CO2 capture facility in Norway. This paper presents three flexible operation scenarios: (i) effect of steam flow rate, (ii) time-varying solvent regeneration, and (iii) variable ramp rate. The dynamic model of the TCM CO2 capture plant developed in gCCS provides further insights into the process dynamics. As the steam flow rate decreases, lean CO2 loading increases, thereby reducing CO2 capture rate and decreasing absorber temperature. The time-varying solvent regeneration scenario is demonstrated successfully. During “off-peak” mode (periods of low electricity price), solvent is regenerated, reducing lean CO2 loading to 0.16 molCO2/molMEA and increasing CO2 capture rate to 89–97%. The “peak” mode (period of high electricity price) stores CO2 within the solvent by reducing the reboiler heat supply and increasing solvent flow rate. During peak mode, lean CO2 loading increases to 0.48 molCO2/molMEA, reducing CO2 capture rate to 14.5%, which in turn decreases the absorber temperature profile. The variable ramp rate scenario demonstrates that different ramp rates can be applied successively to a CO2 capture plant. By maintaining constant liquid-to-gas (L/G) ratio during the changes, the CO2 capture performance will remain the same, i.e., constant lean CO2 loading (0.14–0.16 molCO2/molMEA) and CO2 capture rate (87–89%). We show that flexible operation in a demonstration scale absorption CO2 capture process is technically feasible. The deviation between the gCCS model and dynamic experimental data demonstrates further research is needed to improve existing dynamic modelling software. Continual development in our understanding of process dynamics during flexible operation of CO2 capture plants will be essential. This paper provides additi

Journal article

Heuberger CF, Bains PK, Mac Dowell N, 2020, The EV-olution of the power system: a spatio-temporal optimisation model to investigate the impact of electric vehicle deployment, Applied Energy, Vol: 257, Pages: 1-18, ISSN: 0306-2619

Power system models have become an essential part of strategic planning and decision-making in the energy transition. While techniques are becoming increasingly sophisticated and manifold, the ability to incorporate high resolution in space and time with long-term planning is limited. We introduce ESONE, the Spatially granular Electricity Systems Optimisation model. ESONE is a mixed-integer linear program, determining investment in power system generation and transmission infrastructure while simultaneously optimising operational schedule and optimal power flow on an hourly basis. Unique data clustering combined with model decomposition and an iterative solution procedure enable computational tractability. We showcase the capabilities of the ESONE model by applying it to the power system of Great Britain under CO2 emissions reduction targets. We investigate the effects of a spatially distributed large-scale roll-out of electric vehicles (EVs). We find EV demand profiles correlate well with offshore and onshore wind power production, reducing curtailment and boosting generation. Time-of-use-tariffs for EV charging can further reduce power supply and transmission infrastructure requirements. In general, Great Britain’s electricity system absorbs additional demand from ambitious deployment of EVs without substantial changes to system design.

Journal article

Bahzad H, Katayama K, Boot-Handford ME, Mac Dowell N, Shah N, Fennell PSet al., 2019, Iron-based chemical-looping technology for decarbonising iron and steel production, International Journal of Greenhouse Gas Control, Vol: 91, ISSN: 1750-5836

© 2019 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.

Journal article

Hepburn C, Adlen E, Beddington J, Carter EA, Fuss S, Mac Dowell N, Minx JC, Smith P, Williams CKet al., 2019, The technological and economic prospects for CO2 utilization and removal, Nature, Vol: 575, Pages: 87-97, ISSN: 0028-0836

The capture and use of carbon dioxide to create valuable products might lower the net costs of reducing emissions or removing carbon dioxide from the atmosphere. Here we review ten pathways for the utilization of carbon dioxide. Pathways that involve chemicals, fuels and microalgae might reduce emissions of carbon dioxide but have limited potential for its removal, whereas pathways that involve construction materials can both utilize and remove carbon dioxide. Land-based pathways can increase agricultural output and remove carbon dioxide. Our assessment suggests that each pathway could scale to over 0.5 gigatonnes of carbon dioxide utilization annually. However, barriers to implementation remain substantial and resource constraints prevent the simultaneous deployment of all pathways.

Journal article

Yao JG, Bui M, Dowell NM, 2019, Grid-scale energy storage with net-zero emissions: comparing the options, Sustainable Energy and Fuels, Vol: 3, Pages: 3147-3162, ISSN: 2398-4902

The transition to a low-carbon economy is an enormous challenge. With increasing deployment of intermittent renewable energy, there is a recognised need for scalable options for grid-scale, long-term, high energy density, energy storage. Grid-scale energy storage combined with carbon capture and utilisation (CCU) potentially provides a high level of flexibility and reliability. However, previous power-to-gas (P2G) studies have only examined the use of synthetic natural gas (SNG) derived from electrolytic hydrogen and either biomass- or industrially-derived CO2 for this application; making the whole power-to-power (P2P) value chain low carbon at best. Instead, our work assesses the techno-economic feasibility of using direct air capture to develop truly carbon-neutral P2P pathways. After assessing nine net-zero emission configurations using existing technologies, we found that using SNG as an energy storage carrier may be the least expensive route despite being more complex than power-to-hydrogen (P2H). P2H is currently held back by the high cost of H2 storage and the low volumetric density of H2 relative to SNG. Thus, bringing down the cost of H2 storage and building more salt caverns will be imperative for P2H, whereas reducing the cost of carbon capture should be a key priority for accelerating the deployment of power-to-methane (P2M) technologies.

Journal article

Cumicheo C, Mac Dowell N, Shah N, 2019, Natural gas and BECCS: A comparative analysis of alternative configurations for negative emissions power generation, International Journal of Greenhouse Gas Control, Vol: 90, Pages: 1-11, ISSN: 1750-5836

There is a reliance on negative emissions technologies (NETs), primarily in the form of Bioenergy with Carbon Capture and Storage (BECCS) in most Integrated Assessment Model (IAM) scenarios which are capable of limiting the maximum global temperature rise to 1.5–2 °C. Two currently independent features of transition pathways are fuel switching from a coal to gas, and the deployment of BECCS. The former makes natural gas an important transition fuel which at the same time could be combined with biomass to further abate emissions. To date the majority of studies have considered BECCS in the context of a conversion from coal-fired base configuration. There is therefore a pressing need to identify routes for the effective utilization of biomass-derived fuels in the context of gas-fired power generation infrastructure. In this contribution, we study three distinct CCS-based processes which combine natural gas and biomass capable of producing low-, or carbon-negative power. Both fuel supply chains are considered in order to quantify the net overall CO2 emissions. An important insight is the configuration-specific impact of biomass co-combustion on the overall carbon intensity of power generated. We found that an external biomass combustion configuration was the most carbon negative, removing between 0.5–1 ton of CO2 per MWh of power generated. Results revealed a trade-off between carbon negativity and efficiency of the processes. The generation of net carbon negative power is observed to be highly sensitive to the carbon footprint of the biomass supply chain.

Journal article

Albanito F, Hastings A, Fitton N, Richards M, Martin M, Mac Dowell N, Bell D, Taylor SC, Butnar I, Li P-H, Slade R, Smith Pet al., 2019, Mitigation potential and environmental impact of centralized versus distributed BECCS with domestic biomass production in Great Britain, Global Change Biology Bioenergy, Vol: 11, Pages: 1234-1252, ISSN: 1757-1693

New contingency policy plans are expected to be published by the United Kingdom government to set out urgent actions, such as carbon capture and storage, greenhouse gas removal and the use of sustainable bioenergy to meet the greenhouse gas reduction targets of the 4th and 5th Carbon Budgets. In this study, we identify two plausible bioenergy production pathways for bioenergy with carbon capture and storage (BECCS) based on centralized and distributed energy systems to show what BECCS could look like if deployed by 2050 in Great Britain. The extent of agricultural land available to sustainably produce biomass feedstock in the centralized and distributed energy systems is about 0.39 and 0.5 Mha, providing approximately 5.7 and 7.3 MtDM/year of biomass respectively. If this land‐use change occurred, bioenergy crops would contribute to reduced agricultural soil GHG emission by 9 and 11 urn:x-wiley:17571693:media:gcbb12630:gcbb12630-math-0001/year in the centralized and distributed energy systems respectively. In addition, bioenergy crops can contribute to reduce agricultural soil ammonia emissions and water pollution from soil nitrate leaching, and to increase soil organic carbon stocks. The technical mitigation potentials from BECCS lead to projected CO2 reductions of approximately 18 and 23 urn:x-wiley:17571693:media:gcbb12630:gcbb12630-math-0002/year from the centralized and distributed energy systems respectively. This suggests that the domestic supply of sustainable biomass would not allow the emission reduction target of 50 urn:x-wiley:17571693:media:gcbb12630:gcbb12630-math-0003/year from BECCS to be met. To meet that target, it would be necessary to produce solid biomass from forest systems on 0.59 or 0.49 Mha, or alternatively to import 8 or 6.6 MtDM/year of biomass for the centralized and distributed energy system respectively. The spatially explicit results of this study can serve to identify the regional differences in the potential capture of CO2 from BECC

Journal article

Zhang D, Bui M, Fajardy M, Patrizio P, Kraxner F, Mac Dowell Net al., 2019, Unlocking the potential of BECCS with indigenous sources of biomass at a national scale, Sustainable Energy and Fuels, ISSN: 2398-4902

Bioenergy with carbon capture and storage (BECCS) could play a large role in meeting the 1.5C argets, but faces well-documented controversy in terms of land-use concerns, competition with food production, and cost. This study presents a bottom-up assessment of the scale at which BECCS plants – biomass pulverised combustion plants (“BECCS” in this study) and bioenergy combustion in combined heat and power plants (BE-CHP-CCS) – can be sustainably deployed to meet national carbon dioxide removal (CDR) targets, considering the use of both primary and secondary (waste-derived) biomass. This paper also presents a comprehensive, harmonised data set, which enables others to build upon this work. Land availability for biomass cultivation, processing, and conversion is quantified based on a land-use analysis, avoiding all competition with land used for food production, human habitation, and other protected areas. We find that secondary biomass sources provide a valuable supplement to primary biomass, augmenting indigenous biomass supplies. In initial phases of deployment, we observe that infrastructure is initially clustered near cities, and other sources of low cost, secondary biomass, but as CDR targets are increased and indigenous secondary biomass supplies are exhausted, infrastructure begins to move closer to potential biomass planting areas with higher yield. In minimising the cost of CDR on a cost per tonne CO2 removed basis, we find that the availability of secondary biomass, land availability, and yield are key factors that drive the cost of CDR. Importantly biomass conversion efficiency of a BECCS plant has an inverse effect on CDR costs, with less efficient plants resulting in lower costs compared to their more efficient counterparts. By consuming secondary biomass in BECCS and BE-CHP-CCS plants, the UK is able to be self-sufficient in biomass supply by utilising available indigenous biomass to remove up to 50 MtCO2 /yr, though for cost reas

Journal article

Danaci D, Bui M, Mac Dowell N, Petit Cet al., 2019, Exploring the limits of adsorption-based CO2 capture using MOFs with PVSA – from molecular design to process economics, Molecular Systems Design and Engineering, ISSN: 2058-9689

Metal-organic frameworks (MOFs) have taken the materials science world by storm, with potentials of near infinite possibilities and the panacea for adsorption-based carbon capture. Yet, no pilot-scale (or larger-scale) study exists on MOFs for carbon capture. Beyond material scalability issues, this clear gap between the scientific and engineering literature relates to the absence of suitable and accessible assessment of MOFs in an adsorption process. Here, we have developed a simple adsorbent screening tool with process economics to evaluate adsorbents for post-combustion capture, while also considering factors relevant to industry. Specifically, we have assessed the 25 adsorbents (22 MOFs, 2 zeolites, 1 activated carbon) against performance constraints – i.e. CO2 purity and recovery – and cost. We have considered four different CO2 capture scenarios to represent a range of CO2 inlet concentrations. The cost is compared to that of amine-based solvents for which a corresponding model was developed. Using the model developed, we have conceptually assessed the materials properties and process parameters influencing the purity, recovery and cost in order to design the ‘best’ adsorbent. We have also set-up a tool for readers to screen their own adsorbent. In this contribution, we show that minimal N2 adsorption and moderate enthalpies of adsorption are key in obtaining good process performance and reducing cost. This stands in contrast to the popular approaches of maximizing CO2 capacity or surface area. Of the 22 MOFs evaluated, UTSA-16 shows the best performance and lowest cost for post-combustion capture, having performance in-line with the benchmark, zeolite 13X. Mg-MOF-74 performs poorly. The cost of using the adsorbents remains overall higher than that of an amine-based absorption process. Ultimately, this study provides specific directions for material scientists to design adsorbents and assess their performance at the process scale. This

Journal article

Daggash HA, Mac Dowell N, 2019, Higher carbon prices on emissions alone will not deliver the Paris agreement, Joule, Vol: 3, Pages: 2120-2133, ISSN: 2542-4351

Limiting global warming to 2°C by 2100 requires anthropogenic CO2 emissions to reach zero by 2070 and become negative afterwards; therefore, large-scale carbon dioxide removal (CDR) from the atmosphere is critical. We investigate the effectiveness of carbon prices in achieving the deep decarbonization needed in the power system. We find that if only CO2 emitters are penalized, increasing prices to the social cost of carbon is sufficient to achieve a decarbonized system in the medium-term but not maintain it in the long-term. Unless carbon pricing mechanisms are adapted to remunerate CDR services, CDR technologies are not deployed. Incentivizing CDR could mean that lower levels of carbon taxation are needed to meet the Paris Agreement, which in turn lowers electricity costs.However, the deployment of CDR technologies could prolong the use of unabated fossil fuels in a carbon-constrained system, therefore, disincentives must be implemented to prevent this moral hazard from manifesting.

Journal article

Bahzad H, Shah N, Dowell NM, Boot-Handford M, Soltani SM, Ho M, Fennell PSet 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.

Journal article

Cabral RP, Bui M, Dowell NM, 2019, A synergistic approach for the simultaneous decarbonisation of power and industry via bioenergy with carbon capture and storage (BECCS), International Journal of Greenhouse Gas Control, Vol: 87, Pages: 221-237, ISSN: 1750-5836

There is a need for a rapid and large scale decarbonisation to reduce CO2 emissions by 45% within 12 years. Thus, we propose a method that accelerates decarbonisation across multiple sectors via a synergistic approach with bioenergy with CCS (BECCS), which is able to remove 740 kgCO2 from air per MWh electricity generated. Industry is a hard-to-decarbonise sector which presents a unique set of challenges where, unlike the power sector, there are no obvious alternatives to CCS. One of these challenges is the significant variation of CO2 concentration, which directly influences CO2 capture costs, ranging from $10/tCO2 to over $170/tCO2 for high (95–99% CO2) and low CO2 concentration (4% CO2) applications, respectively. Re-purposing the existing coal-fired power plant fleet into BECCS displaces CO2 emissions from coal-use and enables a just transition, i.e., avoiding job loss, providing a supportive economic framework that does not rely on government subsidies. Negative emissions generated from capturing and storing atmospheric CO2 can be converted into negative emission credits (NECs) and auctioned to hard-to-decarbonise sectors, thus providing another revenue stream to the power plant. A levelised cost of electricity (LCOE) between $70 and $100 per MWh can be achieved through auctioning NECs at $90–$135 per tCO2. Offsetting the global industrial CO2 emissions of 9 GtCO2 would require 3000 BECCS plants under this framework. This approach could jumpstart industrial decarbonisation whilst giving this sector more time to develop new CCS technologies.

Journal article

Hankin A, Guillen Gosalbez G, Kelsall G, Mac Dowell N, Shah N, Weider S, Brophy Ket al., 2019, Assessing the economic and environmental value of carbon capture and utilisation in the UK, Briefing Note – summary of Briefing Paper No 3

• As a signatory to the 2015 Paris Climate Change Agreement, the UK has committed to an ambitious transformation of its economy.• Decarbonisation of the UK’s economy must be a priority, but carbon-based fuels and platform chemicals will remain important to the global economy; their production from captured carbon dioxide and renewable energy can support this industrial need.• In this Briefing Paper, we report on results of a systematic procedure developed to assess the viability of different carbon capture and utilisation (CCU) pathways.• Our findings on three CCU pathways show that proposed CCU projects should always be assessed on a case-by-case basis, using detailed, UK centric, cradle-to-grave life cycle analyses.• CCU cannot provide the emission mitigation rate of carbon capture and storage (CCS), but as the UK’s entire geological storage capacity is offshore, CCU could mitigate emissions from inland point sources.• Of the considered CCU pathways, presently the production of polyurethane is the most promising for the UK and could provide an immediate short-term mitigation solution for greenhouse gas (GHG) emissions. Currently, methanol production does not appear to be a viable solution.

Report

Hankin A, Guillen Gosalbez G, Kelsall G, Mac Dowell N, Shah N, Weider S, Brophy Ket al., 2019, Assessing the economic and environmental value of carbon capture and utilisation in the UK, Briefing paper, 3

• As a signatory to the 2015 Paris Climate Change Agreement, the UK has committed to an ambitious transformation of its economy.• Decarbonisation of the UK’s economy must be a priority, but carbon-based fuels and platform chemicals will remain important to the global economy; their production from captured carbon dioxide and renewable energy can support this industrial need.• In this Briefing Paper, we report on results of a systematic procedure developed to assess the viability of different carbon capture and utilisation (CCU) pathways.• Our findings on three CCU pathways show that proposed CCU projects should always be assessed on a case-by-case basis, using detailed, UK centric, cradle-to-grave life cycle analyses.• CCU cannot provide the emission mitigation rate of carbon capture and storage (CCS), but as the UK’s entire geological storage capacity is offshore, CCU could mitigate emissions from inland point sources.• Of the considered CCU pathways, presently the production of polyurethane is the most promising for the UK and could provide an immediate short-term mitigation solution for greenhouse gas (GHG) emissions. Currently, methanol production does not appear to be a viable solution.

Report

Daggash HA, Mac Dowell N, 2019, The implications of delivering the UK’s Paris Agreement commitments on the power sector, International Journal of Greenhouse Gas Control, Vol: 85, Pages: 174-181, ISSN: 1750-5836

Through the 2015 Paris Agreement, the UK committed to keeping average global temperature rise to “well below 2 °C”. Integrated Assessment Models show that this will require extensive greenhouse gas removal (GGR) from the atmosphere. For the EU, it is estimated that 20–70 GtCO2 of cumulative GGR by 2100 is required, all from bioenergy with carbon capture and storage (BECCS). Depending on how the burden of GGR is shared, the UK would need to remove 2–6 GtCO2 from the atmosphere. We apply a power systems planning model to determine how the electricity system would need to transition from 2015 to 2100 to meet the UK’s Paris Agreement commitments. We find that until 2050, increased penetration of renewables, interconnection capacity and energy storage, alongside 15–17 GW of CCGT−CCS, is sufficient to stay on the required emissions trajectory. Between 2050 and 2100, however, the deployment of 7–26 GW of BECCS and 2–5 GW of direct air capture and storage (DACS) is crucial to provide the GGR required. A Paris-compliant UK electricity system will require £620–700 billion of capital and operational expenditure by 2100, 3–16% greater than the cost of achieving a decarbonised system. For the upper-bound GGR target, local biomass supply is insufficient, so imports are necessary. By 2100, up to 26% of annual demand is met by imported biomass. Such heavy dependence on imports may raise energy security concerns. Also, should biomass imports not be available in the required quantities, alternative (and more expensive) GGR methods will be necessary thereby increasing the cost of delivering a Paris-compliant system.

Journal article

Algunaibet I, Pozo Fernandez C, Galan Martin A, Huijbregts M, Mac Dowell N, Guillen Gosalbez Get al., 2019, Powering sustainable development within planetary boundaries, Energy and Environmental Science, Vol: 12, Pages: 1890-1900, ISSN: 1754-5692

The concept of planetary boundaries identifies a safe space for humanity. Current energy systems are primarily designed with a focus on total cost minimization and bounds on greenhouse gas emissions. Omitting planetary boundaries in energy systems design can lead to energy mixes unable to power our sustainable development. To overcome this conceptual limitation, we here incorporate planetary boundaries into energy systems models, explicitly linking energy generation with the Earth’s ecological limits. Taking the United States as a testbed, we found that the least cost energy mix that would meet the Paris Agreement 2 degrees Celsius target, still transgresses five out of eight planetary boundaries. It is possible to meet seven out of eight planetary boundaries concurrently by incurring a doubling of the cost compared to the least cost energy mix solution (1.3% of the United States gross domestic product in 2017). Due to the stringent downscaled planetary boundary on biogeochemical nitrogen flow, there is no energy mix in the United States capable of satisfying all planetary boundaries concurrently. Our work highlights the importance of considering planetary boundaries in energy systems design and paves the way for further research on how to effectively accomplish such integration in energy related studies.

Journal article

Daggash HA, Mac Dowell N, 2019, Structural evolution of the UK electricity system in a below 2°C World, Joule, Vol: 3, Pages: 1239-1251, ISSN: 2542-4351

We employ an electricity system model to determine the least-cost transition necessary to meet a given carbon dioxide removal (CDR) burden in the UK. The results show that, while sufficient in the medium term, a system dominated by intermittent renewable energy technologies (IRES) cannot deliver CDR at the scale required in a cost-effective manner. The marginal value of IRES for climate change mitigation diminishes with time, especially in the context of the Paris Agreement. Deeper decarbonization precipitates a resurgence of thermal generation from bioenergy and gas (with carbon capture and storage) and nuclear. Such a system is inherently centralized and will require maintenance of existing transmission and distribution infrastructure. Current policy direction, however, encourages the proliferation of renewables and decentralization of energy services. To avoid locking the power system into a future where it cannot meet climate change mitigation ambitions, policy must recognize and adequately incentivize the new technologies (CCS) and services (CDR) necessary.

Journal article

Cabral RP, Heldebrant DJ, Mac Dowell N, 2019, A Techno-Economic Analysis of a Novel Solvent-Based Oxycombustion CO <inf>2</inf> Capture Process, Industrial and Engineering Chemistry Research, ISSN: 0888-5885

Copyright © 2019 American Chemical Society. The gas processing unit (GPU) has previously been identified as the least thermodynamically efficient element of an oxycombustion process. A marginal improvement of this unit operation can provide a greater decrease of the parasitic power to the oxycombustion process than an equivalent improvement in the air separation unit (ASU). Hence, capturing CO 2 from oxycombustion using an alternative method than the conventional cryogenic process has potential to reduce the parasitic power consumption of the GPU. In this work, the authors present an initial evaluation of a new process concept; a hybrid oxycombustion process that uses a solvent-based GPU to capture CO 2 from the flue gas. N-Ethyldiethanolamine (EDEA) is a tertiary alkanolamine that captures CO 2 by forming a zwitterionic ammonium alkylcarbonate ionic liquid in the absence of water as a cosolvent. The new solvent-based GPU proposed herein demonstrates a clear potential to improve the net power efficiency by 1%, a 9% CAPEX reduction, and up to 5% LCOE reduction of an oxycombustion process if the price of EDEA is below $270/kg. Both lower CAPEX and the potential of reduced LCOE demonstrates that alternative CO 2 capture methods for oxycombustion can be more economical.

Journal article

Lee R, Homan S, Mac Dowell N, Brown Set al., 2019, A closed-loop analysis of grid scale battery systems providing frequency response and reserve services in a variable inertia grid, APPLIED ENERGY, Vol: 236, Pages: 961-972, ISSN: 0306-2619

Journal article

Daggash H, Heuberger C, Mac Dowell N, 2019, The role and value of negative emissions technologies in decarbonising the UK energy system, International Journal of Greenhouse Gas Control, Vol: 81, Pages: 181-198, ISSN: 1750-5836

The UK is committed to the Paris Agreement and has a legally-binding target to reduce economy-wide greenhouse gas emissions by 80% relative to 1990 levels by 2050. Meeting these targets would require deep decarbonisation, including the deployment of negative emissions technologies. This study, via a power supply capacity expansion model, investigates the potential role of bio-energy with carbon capture and storage (BECCS) and direct air capture and storage (DACS) in meeting the UK's emissions reduction targets. We show that to achieve power sector decarbonisation, a system dominated by firm and dispatchable low-carbon generators with BECCS or DACS to compensate for their associated emissions is significantly cheaper than a system dominated by intermittent renewables and energy storage. By offsetting CO2 emissions from cheaper thermal plants, thereby allowing for their continued utilisation in a carbon-constrained electricity system, BECCS and DACS can reduce the cost of decarbonisation by 37–48%. Allowing some this value transferred to accrue to NETs offers a potential route for their commercial deployment.

Journal article

Harraz AA, Freeman J, Wang K, Mac Dowell N, Markides CNet al., 2019, Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-γ Mie, Energy Procedia, Vol: 158, Pages: 2360-2365, ISSN: 1876-6102

Diffusion-absorption refrigeration (DAR) is a clean thermally-powered refrigeration technology that can readily be activated by low- to medium-grade renewable heat. There is an ongoing interest in identifying or designing new working fluids for performance improvement, particularly in solar applications with non-concentrating solar collectors providing heat at temperatures < 150 °C. In this work, the state-of-the-art statistical associating fluid theory (SAFT) is adopted for predicting the thermodynamic properties of suitable DAR working fluids. A first-law thermodynamic analysis is performed in the software environment gPROMS for a DAR cycle using ammonia as the refrigerant, water as the absorbent and hydrogen as the auxiliary gas. The simulation results show good agreement with experimental data generated in a prototype DAR system with a nominal cooling capacity of 100 W. In particular, at a charge pressure of 17 bar and when delivering cooling at 5 °C, the model results agree with experimental COP data to within ± 7 % over a range of heat inputs from 150 to 500 W. The maximum coefficient of performance (COP) is estimated to be 0.24 at a heat input of 250 W. The group-contribution SAFT-γ Mie equation of state is of particular interest as it offers good agreement with experimental data and provides flexibility in extending the model to test different working fluids with a high degree of fidelity. A methodology is also presented that allows the DAR thermodynamic analysis and working-fluid modelling to be integrated into a more general technology optimisation framework.

Journal article

Patrizio P, Leduc S, Kraxner F, Fuss S, Kindermann G, Mesfun S, Spokas K, Mendoza A, Mac Dowell N, Wetterlund E, Lundgren J, Dotzauer E, Yowargana P, Obersteiner Met al., 2018, Reducing US Coal Emissions Can Boost Employment, JOULE, Vol: 2, Pages: 2633-2648, ISSN: 2542-4351

Journal article

Al-Saqlawi J, Madani K, Mac Dowell N, 2018, Techno-economic feasibility of grid-independent residential roof-top solar PV systems in Muscat, Oman, Energy Conversion and Management, Vol: 178, Pages: 322-334, ISSN: 0196-8904

Oman is a country characterised by high solar availability, yet very little electricity is produced using solar energy. As the residential sector is the largest consumer of electricity in Oman, we develop a novel approach, using houses in Muscat as a case study, to assess the potential of implementing roof-top solar PV/battery technologies, that operate without recourse to the electricity grid. Such systems target the complete decarbonisation of electricity demand per household and are defined in this study as grid-independent systems. The approach adopted starts with a technical assessment of grid-independent systems that evaluates the characteristics of the solar panel and the battery facility required to provide grid-independence. This is then compared to a similar grid-connected system and any techno-economic targets necessary to enhance the feasibility of residential roof-top PV systems in Muscat are identified. Such an analysis was achieved through developing a detailed techno-economic mathematical model describing four sub-systems; the solar panel DC source, the grid-independent sub-system, the grid-connected sub-system and the economic sub-system. The model was implemented in gPROMS and uses real hourly weather and climate conditions matched with real demand data, over a simulated period of 20 years. The results indicate that, in the context of the system studied, grid-independent PV systems are not feasible. However, combined with a sufficiently high electricity price, grid-independent systems can become economically feasible only with significant reductions in battery costs (>90% reductions).

Journal article

Bui M, Tait P, Lucquiaud M, Mac Dowell Net al., 2018, Dynamic operation and modelling of amine-based CO2 capture at pilot scale, International Journal of Greenhouse Gas Control, Vol: 79, Pages: 134-153, ISSN: 1750-5836

This study combines pilot plant experiments and dynamic modelling to gain insight into the interaction between key process parameters in producing the dynamic response of an amine-based CO2 capture process. Three dynamic scenarios from the UKCCSRC PACT pilot plant are presented: (i) partial load stripping, (ii) capture plant ramping, and (iii) reboiler decoupling. These scenarios are representative of realistic flexible operation of non-baseload CCS power stations. Experimental plant data was used to validate a dynamic model developed in gCCS. In the capture plant ramping scenario, increased liquid-to-gas (L/G) ratio resulted in higher CO2 capture rate. The partial load stripping scenario demonstrated that the hot water flow directly affects reboiler temperature, which in turn, has an impact on the solvent lean loading and CO2 capture rate. The reboiler decoupling scenario demonstrates a similar relationship. Turning off the heat supply to the reboiler leads to a gradual decline in reboiler temperature, which increases solvent lean loading and reduces CO2 capture rate. The absorber column temperature profile is influenced by the degree of CO2 capture. For scenarios that result in lower solvent lean loading, the absorber temperature profile shifts to higher temperature (due to the higher CO2 capture rate).

Journal article

Budinis S, Krevor S, Mac Dowell N, Brandon N, Hawkes Aet al., 2018, An assessment of CCS costs, barriers and potential, Energy Strategy Reviews, Vol: 22, Pages: 61-81, ISSN: 2211-467X

© 2018 Elsevier Ltd Global decarbonisation scenarios include Carbon Capture and Storage (CCS) as a key technology to reduce carbon dioxide (CO2) emissions from the power and industrial sectors. However, few large scale CCS plants are operating worldwide. This mismatch between expectations and reality is caused by a series of barriers which are preventing this technology from being adopted more widely. The goal of this paper is to identify and review the barriers to CCS development, with a focus on recent cost estimates, and to assess the potential of CCS to enable access to fossil fuels without causing dangerous levels of climate change. The result of the review shows that no CCS barriers are exclusively technical, with CCS cost being the most significant hurdle in the short to medium term. In the long term, CCS is found to be very cost effective when compared with other mitigation options. Cost estimates exhibit a high range, which depends on process type, separation technology, CO2transport technique and storage site. CCS potential has been quantified by comparing the amount of fossil fuels that could be used globally with and without CCS. In modelled energy system transition pathways that limit global warming to less than 2 °C, scenarios without CCS result in 26% of fossil fuel reserves being consumed by 2050, against 37% being consumed when CCS is available. However, by 2100, the scenarios without CCS have only consumed slightly more fossil fuel reserves (33%), whereas scenarios with CCS available end up consuming 65% of reserves. It was also shown that the residual emissions from CCS facilities is the key factor limiting long term uptake, rather than cost. Overall, the results show that worldwide CCS adoption will be critical if fossil fuel reserves are to continue to be substantively accessed whilst still meeting climate targets.

Journal article

Fajardy M, Chiquier S, Mac Dowell N, 2018, Investigating the BECCS resource nexus: delivering sustainable negative emissions, Energy and Environmental Science, Vol: 11, Pages: 3408-3430, ISSN: 1754-5692

Bioenergy with carbon capture and storage (BECCS), and other negative emissions technologies (NETs), are integral to all scenarios consistent with meeting global climate ambitions. BECCS's ability to promptly remove CO2 from the atmosphere in a resource efficient manner, whilst being a net energy generator to the global economy, remains controversial. Given the large range of potential outcomes, it is crucial to understand how, if at all, this technology can be deployed in a way which minimises its impact on natural resources and ecosystems, while maximising both carbon removal and power generation. In this study, we present a series of thought experiments, using the Modelling and Optimisation of Negative Emissions Technologies (MONET) framework, to provide insight into the combinations of biomass feedstock, origin, land type, and transport route, to meet a given CO2 removal target. The optimal structure of an international BECCS supply chain was found to vary both quantitatively and qualitatively as the focus shifted from conserving water, land or biomass, to maximising energy generated, with the water use in particular increasing threefold in the land and biomass use minimisation scenario, as compared to the water minimisation scenario. In meeting regional targets, imported biomass was consistently chosen over indigenous biomass in the land and water minimisation scenarios, confirming the dominance of factors such as yield, electricity grid carbon intensity, and precipitation, over transport distance. A pareto-front analysis was performed and, in addition to highlighting the strong trade-offs between BECCS resource efficiency objectives, indicated the potential for tipping points. An analysis of the sensitivity to the availability of marginal land and agricultural residues showed that (1) the availability of agricultural residues had a great impact on BECCS land, and that (2) water use and land use change, two critical sustainability indicators for BECCS, were neg

Journal article

Iruretagoyena Ferrer D, Sunny N, Chadwick D, Mac Dowell N, Shah Net al., Towards a low carbon economy via sorption enhanced water gas shift and alcohol reforming

Book chapter

Najjaran Kheirabadi A, Harraz AA, Freeman J, Mac Dowell N, Markides CNet al., 2018, Numerical and experimental investigations of diffusion absorption refrigeration systems for use with low temperature heat sources, ECOS 2018 - 31st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS

he diffusion absorption refrigeration (DAR) cycle is a technology of increasing interest thanks to its suitabilityfor providing cooling from a thermal energyinputin a range of applications. Itcan bedistinguished from other absorption refrigeration cycles by its employment of a thermally-driven bubble pump to circulate the working fluid, which gives it anability to operate entirely off-gridwithout an electricity input. In this work,we present results from an experimentalcampaign aimed atcharacterisingthe performance of aprototypeammonia-water-hydrogen DAR system with a nominal cooling capacity of 100 W,over a range of operating conditions, specifically with a view ofadaptingthe system for use in low-temperature applications. In the experiments, the heat input to the DAR generator is provided over a range of temperatures from175to215°Cby using electrical cartridge heaters. The system is charged to 22 bar, and the ammonia mass concentration of the working fluid mixture is 30%. The resulting coefficient of performance (COP) of the system is measured in the range 0.12to 0.26. A new methodology for the selection of optimal working-fluid mixtures using the state-of-the-art, statistical associating fluid theory (SAFT) approach implemented within the process modelling software gPROMS®is also presented. The experimental results will be used for futurevalidation of a thermodynamic model of the cycle. Finally,the performance of the system in a solar application is investigated, with a thermal inputprovided by an array of evacuated tube heat pipe solar collectors. The system pressure and condensation temperature are found to be key factors in determining the performance of solar-DAR systems.

Conference paper

Heuberger CF, Rubin ES, Staffell L, Shah N, Mac Dowell Net al., 2018, Power capacity expansion planning considering endogenous technology cost learning (vol 204, pg 831, 2017), APPLIED ENERGY, Vol: 220, Pages: 974-974, ISSN: 0306-2619

Journal article

Fajardy M, Mac Dowell N, 2018, The energy return on investment of BECCS: is BECCS a threat to energy security?, Energy and Environmental Science, Vol: 11, Pages: 1581-1594, ISSN: 1754-5692

Compliance with long term climate targets whilst maintaining energy security is understood to relyheavily on the large-scale deployment of negative emissions technologies (NETs). One option,Bioenergy with Carbon Capture and Storage (BECCS) is prominent in Integrated AssessmentModels (IAMs), with projected annual contributions of 8 – 16.5 GtCO2/yr of atmospheric carbondioxide removal whilst contributing 150 – 300 EJ/yr, or 14 to 20% of global primary energy supply,in 2100. Implicit in these scenarios is the assumption that BECCS is a net producer of energy.However, relatively energy intensive biomass supply chains and low power generation efficiencycould challenge this ubiquitous assumption. Deploying an energy negative technology at thisscale could thus represent a threat to energy security. In this contribution, we evaluate the energyreturn on investment (EROI) of an archetypal BECCS facility. In order to highlight the importanceof biomass sourcing, two feedstock scenarios are considered: use of domestic biomass pellets(UK) and import of biomass pellets from Louisiana, USA. We use the Modelling and Optimisationof Negative Emissions Technologies (MONET) framework to explicitly account for growing, pre-treating, transporting and converting the feedstock in a 500 MW BECCS facility. As an example,we illustrate how the net electricity balance (NElB) of a UK-based BECCS facility can be eitherpositive or negative, as a function of supply chain decisions. Power plant efficiency, fuel efficiencyfor transport, transport distance, moisture content, drying method, as well as yield were identifiedas key factors that need to be carefully managed to maximise BECCS net electricity balance. Akey insight of this contribution is that, given an annual carbon removal target, increasing BECCS’power generation efficiency by using a more advanced biomass conversion and CO2capturetechnology could improve BECCS net electricity balance, but at the cos

Journal article

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