NWaste2H2- H2 Production by Reforming Bio-methane with Nitrogen Rich Waste Streams

Lead Research Organisation: University of Leeds
Department Name: Chemical and Process Engineering

Abstract

The NWaste2H2 project aims to demonstrate that reducing the energy requirements and the associated greenhouse gas (CO2, N2O) emissions of biogas production at anaerobic digestion at AD plants and wastewater treatment plants (WWTP) whilst producing the clean energy vector hydrogen from reforming of the renewable biogas can be effected economically in the UK.
This project brings together for 2 years a team of expert researchers in AD from wastes (Camargo-Valero), H2 production (Dupont) and energy systems (Cockerill) across three Engineering schools at Leeds, as well as industrial and external collaborators in the WWTP, AD research, H2 production industry, UK City and County Councils, with academic partners in India, China, Thailand and Malaysia who are members of the Scientific Advisory Board for the project. The combined efforts will deliver detailed process model, UK-wide technology deployment model considering the different uses of the H2 produced downstream of the process, economic evaluation and LCA of integrated H2 production from biogas and Nitrogen-rich waste streams from anaerobic digestion at Anaerobic Digestion and Wastewater Treatment plants.
Funding for the project will provide for the costs of employment of a postdoctoral assistant for 18 months, as well as the laboratory expenses for a PhD student funded through the Centre for Doctoral Training on Bioenergy at The University of Leeds, and the dissemination and travel costs associated with presenting the work at world conferences on bioenergy and hydrogen.
The premise behind the proposed technology is to exploit the ability of reforming nitrogen rich organic co-feeds to hydrogen and nitrogen gas, with carbon dioxide as co-product, which allows diverting a large waste stream from the denitrification stage at AD/wastewater treatment plants. Both catalytic processes of steam reforming and autothermal reforming will be investigated as potential H2 production routes. Denitrification of digestate liquor at WWT currently represents a very significant capital and energy burden which results in significant nitrous oxide (N2O) gas emissions, when N2O has a global warming potential roughly 300 times that of CO2 over a 100 years horizon. The NWaste2H2 process will have to show high conversions not just to hydrogen gas but also to nitrogen gas in order to significantly divert N-rich waste streams from the denitrification step.

Planned Impact

Denitrification (DN) is a necessary energy intensive and capital expensive process retrofit at wastewater treatment plants (WTTP), as nitrogen in their effluent can cause toxicity to fish and eutriphication of waterways. During DN, up to 14.6% of the total nitrogen load of wastewater treatment plants could be emitted to the atmosphere as nitrous oxide (N2O), a greenhouse gas with a global warming potential 298 times higher than CO2 and responsible for 8% of climate forcing. WTTP operate with two streams rich in N: the raw feedstock urine in the form of urea (upstream) and the digestate liquor (DL) in the form of mainly ammonia (downstream). In many AD processes, digestate liquor is not recycled as fertiliser. We have shown that using a catalyst, urea can successfully undergo steam reforming following: CO(NH2)2 +H2O = CO2 + 3H2 + N2, and that ammonia can also successfully undergo catalytically cracking with the same catalyst via reaction 2NH2= N2+2H2. Both urine and DL are highly aqueous and are proposed to be used as 'water' feedstock in the steam methane reforming reaction, their C, H, and N content yielding additional H2 product with direct conversion of the N content to harmless N2. This avoids significant N2O emissions as well as the energy costs (CO2 equivalent) of a subsequently much reduced denitrification burden at the WTTP or AD plant. This project explores the feasibility of reforming biogas with diverted urine and digestate liquor. Preliminary techno-economical assessment using AspenTech's Aspen Plus process modelling and economic evaluator of the proposed integrated processes have shown that significant synergies between a new H2 production plant and a WTTP at scale such as Yorkshire Water's at Esholt, , using input data collected via a current PhD project. Calculated impacts for Esholt's plant which treats 105,000 m3 of sewage/day, would be the production of 2,534 kg of hydrogen a day from the plant's biogas and digestate liquor, and would potentially save 1.8 tonne of CO2 equivalent per day in the form of avoided N2O emissions, with energy savings of 4,200 kWh/day in the integrated WWT/AD/H2/power process compared to the current WWT/AD/CHP configuration, due to reduced flows to the denitrification stage. The H2 production itself would be augmented by 6% compared to a H2 plant running on conventional steam reforming AD-generated biomethane.
The UK now processes more than 16 billion litres of wastewater a day (150 times Esholt's) and close to 2 Mt of food waste at its many AD plants (100 Nm3/ton of bio-CH4), significant avoidance of GHG emissions whilst producing renewable Hydrogen is strong.
The project will be able to make more detailed forecasts of what the deployment of the NWaste2H2 technology could mean for the UK and will also, through in depth Life Cycle Analysis, process evaluation, and rigorous techno-economic assessment planned in the project, define the wider range of impacts of a well-defined UK scenario for NWaste2H2 technology. This will be facilitated by the inputs from our external collaborators from industry (Northern Gas Networks, Leeds City Council and Lincolnshire County Council, TST Ltd, Defiant Renewables) who are members of our management board which will meet quarterly.
Although the feasibility study will focus on deployment in the UK, further impacts can be expected from the intake of this technology by countries where anaerobic digestion is fast growing as a means for producing renewable energy and waste management such as India, China, Malaysia, and Thailand, where our academic collaborators are based. This will be done firstly via academic impact, i.e. through joint publications and co-supervision of Masters and PhD projects, but in the future, we hope, leading to commercialisation and resulting creation of graduates, wealth and jobs in countries of low and middle income who will have to address soaring GHG emissions in the near future

Publications

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Description yet unpublished because part of thesis chapters currently being finalised by PhD student Oliver Grasham, we currently have the following key findings:
-sensitivity analysis of economic viability of integrating solid oxide fuel cell fuelled on site at wastewater treatment plant with its anaerobic digestion unit's biogas and recovered ammonia for combined heat and power (H & P) generation and complete H&P autonomy of the WWTP. Results show a viable economic integrated process with significant annual greenhouse gas emissions savings and low sensitivity to capital expenditure costs. Integrated plant is only viable if no other recent H&P is already present on site.
-sensitivity analysis of economic viability of integrated hydrogen production from co-steam reforming anaerobic digestion (AD) unit's biogas and catalytic cracking of recovered ammonia from AD unit's digestate at wastewater treatment plant. Results also show potential economic viability of integrated process but highly sensitive to selling price of green hydrogen and to compression pressure at which the H2 needs to be stored on site. For a price of 4.5£/kg H2 and compression of 500 bar (suitable for car/vehicle refueling), the plant can generate benefit beyond recouping investors' capital return within 14 years. With 20 bar compression (suitable for grid injection) and same price, plant turns a profit under 8 years. with 15% decrease in H2 selling price and 500 bar storage compression, H2 plant is no longer viable within 20 years.
Exploitation Route data obtained by Oliver Grasha with cost calculations and NPV will be made available via open access publications and open access DOI.
Sectors Chemicals,Energy,Environment,Manufacturing, including Industrial Biotechology