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Opportunities and limitations for existing CHP plants to integrate polygeneration of drop-in biofuels with onsite hydrogen production
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-4932-7368
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-3485-5440
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0003-0300-0762
2020 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 221, article id 113109Article in journal (Refereed) Published
Abstract [en]

Over the past few years, there has been increasing research interest in retrofitting existing combined heat and power (CHP) plants with new technologies to co-produce other products. The focus has been on the design of fixed-sized processes for integration into CHP plants without affecting their performance. The primary objective of this study was to test the limits of a CHP plant with respect to retrofitting flexible thermochemical conversion of waste to drop-in biofuels with properties similar to petroleum fuels. Waste conversion to drop-in biofuels also requires significant amount of hydrogen for drop-in biofuels synthesis — Required hydrogen was also produced onsite in thermochemical processes integrated with CHP plant. The secondary objective was to determine the maximum number of days a flexible retrofitted waste-thermochemical process can run annually using only excess heat from a CHP plant, and whether such processes are profitable when operating flexibly. The results show that the selection of heat extraction points for the utilization of excess heat from the CHP plant for energy-intensive processes is critical for maintaining the flexibility of the integrated thermochemical processes. Thermochemical processes integrated with CHP plants were able to operate on approximately 180 days of the year by utilizing only excess heat from the CHP plant. Integration of pyrolysis showed more flexibility than integration of gasification. Onsite hydrogen production was the main limiting factor for the integration of thermochemical process with the existing CHP plant to produce drop-in biofuels. Hydrogen produced with a solid oxide electrolysis cell (SOEC) decreased the overall system efficiency and limited the capacity of the overall process. However, hydrogen production from a water gas shift (WGS) reactor was more expensive. The results also indicated that small changes in the financial parameters have a large impact on the economic performance of the integrated process. 

Place, publisher, year, edition, pages
Elsevier Ltd , 2020. Vol. 221, article id 113109
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:mdh:diva-49400DOI: 10.1016/j.enconman.2020.113109ISI: 000572863500001Scopus ID: 2-s2.0-85087309116OAI: oai:DiVA.org:mdh-49400DiVA, id: diva2:1453266
Available from: 2020-07-09 Created: 2020-07-09 Last updated: 2020-10-14Bibliographically approved
In thesis
1. Waste-integrated biorefineries: A path towards efficient utilization of waste
Open this publication in new window or tab >>Waste-integrated biorefineries: A path towards efficient utilization of waste
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Waste-management systems have progressed from landfilling and dumping to waste prevention, recycling and resource recovery. In state-of-the-art waste-management industries, waste is separated into various fractions and treated with suitable processes. The non-recyclable organic fraction of waste can be incinerated for combined heat and power (CHP) production, while biodegradable waste can be converted to biomethane through the anaerobic digestion (AD) process. Thermochemical processes such as gasification and pyrolysis provide alternative methods for treating various fractions of waste. This thesis aims to design energy-efficient and cost-effective waste-integrated biorefineries by integrating thermochemical processing of waste with existing WtE technologies.

A system analysis of five process-integration case studies have been performed. The first case assesses the limitations and operational limits of thermochemical processes retrofitted in an existing waste-based CHP plant. The second and third case studies evaluate the feasibility of the current waste-based CHP plant to shift from cogeneration to polygeneration of biofuels, heat and power. In the fourth case study, a new process configuration is presented that couples AD of biodegradable waste with pyrolysis of lignocellulosic waste. The last case deals with the handling of digested sludge from WWTPs by the integration of thermochemical processes.

The findings suggest that waste-integrated biorefineries can utilize infrastructure and products from existing waste industries through process integration and improve the overall process efficiencies and economics. Existing waste-based CHP plants can provide excess heat for integrated thermochemical processes; however, the modifications required are different for different gasifiers and pyrolyzers. Similarly, refuse-derived fuel (RDF) — processed from municipal solid waste (MSW) — can be utilized for production of various biofuels alongside heat and power without disturbing the operation of the CHP. But biomethane and dimethyl ether (DME) showed higher process feasibility than methanol and drop-in biofuels.

The integration of pyrolysis with the AD process can almost double biomethane production compared with a standalone AD process, increasing efficiency to 67% from 52%. The integration is an attractive investment when off-site — rather than on-site — integration of pyrolysis and AD is considered.

Drying of sludge digestate from wastewater treatment plants (WWTPs) is a bottleneck for its post-processing by thermochemical processes. However, waste heat from the existing CHP plant can be utilized for drying of sludge, which can also replace some of the boiler feed through co-incineration with waste biomass.

The economic performance of waste-integrated biorefineries will depend on the volatility of market conditions. Finally, assessment of the effects of uncertainty of input data and process parameters on metrics of technical and economic performance is vital for evaluation of overall system performance.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2020
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 322
Keywords
Gasification; Pyrolysis; Anaerobic digestion; Process integration; Aspen Plus; Ebsilon; Techno-economic analysis
National Category
Energy Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-49878 (URN)978-91-7485-476-3 (ISBN)
Public defence
2020-10-23, Beta + (Online, Zoom), Mälardalens högskola, Västerås, 09:00 (English)
Opponent
Supervisors
Available from: 2020-09-04 Created: 2020-09-03 Last updated: 2020-09-23Bibliographically approved

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Salman, Chaudhary AwaisThorin, EvaYan, Jinyue

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