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Retrofitting CHP Plant and Optimization of Regional Energy System
Mälardalen University, School of Sustainable Development of Society and Technology. (Bioenergy group)
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The use of biomass-based combined heat and power (CHP) plants is considered by the EU administration to be an effective way to increase the use of renewables in the energy system, to reduce greenhouse gas emissions and to alleviate the dependency on imported fossil fuels. At present in Sweden, most of the CHP plants are operated in part-load mode because of variations in heat demand. Further use of the potential heat capacity from CHP plants is an opportunity for integration with other heat-demanding processes. Retrofitting the conventional CHP plants by integration with bioethanol and pellet production processes is considered a feasible and efficient way to improve the plants’ performances.

 

Modeling and simulation of the CHP plant integrated with feedstock upgrading, bioethanol production and pellet production is performed to analyze the technical and economic feasibility. When integrating with bioethanol production, the exhaust flue gas from the CHP plant is used to dry the hydrolysis solid residues (HSR) instead of direct condensation in the flue gas condenser (FGC). This drying process not only increases the overall energy efficiency (OEE) of the CHP plant but also increases the power output relative to the system using only a FGC. Furthermore, if steam is extracted from the turbine of the CHP plant and if it is used to dry the HSR together with the exhaust flue gas, pellets can be produced and the bioethanol production costs can be reduced by 30% compared with ethanol cogeneration plants.

 

Three optional pellet production processes integrated with an existing biomass-based CHP plant using different raw materials are studied to determine their annual performance. The option of pellet production integrated with the existing CHP plant using exhaust flue gas and superheated steam for drying allows for a low specific pellet production cost, short payback time and significant CO2 reduction. A common advantage of the three options is a dramatic increase in the total annual power production and a significant CO2 reduction, in spite of a decrease in power efficiency.

 

The retrofitted biomass-based CHP plants play a crucial role in the present and future regional energy system. The total costs are minimized for the studied energy system by using wastes as energy sources. Analyses of scenarios for the coming decades are performed to describe how to achieve a regional fossil fuel-free energy system. It is possible to achieve the target by upgrading and retrofitting the present energy plants and constructing new ones. The conditions and obstacles have also been presented and discussed through optimizing the locations for proposed new energy plants and planting energy crops.

Place, publisher, year, edition, pages
Västerås: Mälardalen University , 2011.
Series
Mälardalen University Press Licentiate Theses, ISSN 1651-9256 ; 144
Keyword [en]
annual performance, combined heat and power, drying, ethanol, integration, part-load.
Keyword [sv]
årliga prestation, kraftvärme, torkning, etanol, integration, del-last.
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-13185ISBN: 978-91-7485-045-1 (print)OAI: oai:DiVA.org:mdh-13185DiVA: diva2:451867
Presentation
2011-11-28, Kappa, Mälardalen University, Västerås, 13:30 (English)
Opponent
Supervisors
Projects
REMOWE, CSC
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2011-11-09Bibliographically approved
List of papers
1. Influence of drying process on the biomass-based polygeneration system of bioethanol, power and heat
Open this publication in new window or tab >>Influence of drying process on the biomass-based polygeneration system of bioethanol, power and heat
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 90, no 1/SI, 32-37 p.Article in journal (Refereed) Published
Abstract [en]

One of the by-products from bioethanol production using woody materials is lignin solids, which can be utilized as feedstock for combined heat and power (CHP) production. In this paper, the influence of integrating a drying process into a biomass-based polygeneration system is studied, where the exhaust flue gas is used to dry the lignin solids instead of direct condensation in the flue gas condenser (FGC). The evaporated water vapor from the lignin solids is mixed with the drying medium for consequent condensation. Thus, the exhaust flue gas after the drying still has enough humidity to produce roughly the same amount of condensation heat as direct condensation in the existing configuration. The influence of a drying process and how it interacts with the FGC in CHP production as a part of the  polygeneration system is analyzed and evaluated. If a drying process is integrated with the polygeneration system, overall energyefficiency is only increased by 3.1% for CHP plant, though the power output can be increased by 5.5% compared with the simulated system using only FGC.

Keyword
Bioethanol, lignin, drying, exhaust flue gas condenser, moisture content, polygeneration
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-13186 (URN)10.1016/j.apenergy.2011.02.019 (DOI)000297426100006 ()2-s2.0-80055041225 (Scopus ID)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2017-12-08Bibliographically approved
2. Techno-Economic Analysis of a Straw-Based Biorefinery System for Power, Heat, Pellet and Bioethanol Production
Open this publication in new window or tab >>Techno-Economic Analysis of a Straw-Based Biorefinery System for Power, Heat, Pellet and Bioethanol Production
(English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785Article in journal (Refereed) Submitted
Abstract [en]

Abstract: Bioethanol is considered an alternative to fossil fuels in the transportation sector. The use of pellets for heating is another efficient way to mitigate greenhouse gas emissions. This paper evaluates the techno-economic performance of a biorefinery system in which an existing combined heat and power plant integrates with the productions of bioethanol and pellets using straw as feedstock. A two-stage acid hydrolysis process for bioethanol production is used, and two different drying technologies are chosen for drying hydrolysis solid residues. A sensitivity analysis on critical parameters, such as the bioethanol selling price and feedstock price, is performed. The bioethanol production cost is also calculated for two cases at the conditions of ten-year and five-year payback time. The results show that the first case is a more feasible economic configuration at present, having an over 30% production cost reduction compared with the conventional cogeneration plants of bioethanol and solid fuel.

Keyword
combined heat and power, pellet, biorefinery, drying, bioethanol, straw.
National Category
Engineering and Technology
Research subject
Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-13187 (URN)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2017-12-08Bibliographically approved
3. Annual performance analysis and comparison of pellet production integrated with an existing combined heat and power plant
Open this publication in new window or tab >>Annual performance analysis and comparison of pellet production integrated with an existing combined heat and power plant
2011 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 102, no 10, 6317-6325 p.Article in journal (Refereed) Published
Abstract [en]

Three optional pellet production processes integrated with an existing biomass-based CHP plant using different raw materials (wood chips and solid hydrolysis residues) are studied. The year is divided into 12 periods, and the integrated biorefinery systems are modeled and simulated for each period. The annual economic performance of three integrated biorefinery systems is analyzed based on the simulation results. The option of pellet production integrated with the existing CHP plant with the exhaust flue gas and superheated steam as drying mediums has the lowest specific pellet production cost of 105 €/tpellet, the shortest payback time of less than 2 years and the greatest CO2 reduction of the three options. An advantage in common among the three options is a dramatic increase of the total annual power production and significant CO2 reduction in spite of a small decrease of power efficiency.

Keyword
Combined heat and power, pellet, integration, overall energy efficiency
National Category
Engineering and Technology
Research subject
Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-13189 (URN)10.1016/j.biortech.2011.02.042 (DOI)000291125800107 ()2-s2.0-79955021073 (Scopus ID)
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2017-12-08Bibliographically approved
4. Modeling and optimization of a regional waste-to-energy system: a case study in central Sweden
Open this publication in new window or tab >>Modeling and optimization of a regional waste-to-energy system: a case study in central Sweden
2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Conversion of wastes to energy by different technologies can contribute greatly to treating waste sustainably, reducing dependency on imported fossil fuels and protecting environment. A static model of energy balance for a certain region is constructed to simulate and optimize the energy system with the purpose to minimize the total costs, including collection, transportation and conversion or treatment of wastes, distribution of energy products as well as import and export of wastes and energy products. The objective is to find optimum positions for building new energy plants and planting energy crops for two scenarios. How to achieve a regional fossil-fuel-free energy system is also analyzed through a case study of the County of Västmanland in central Sweden. The boundary conditions are assumed to be the limit of local waste generation, capacity of energy plants, and the demands of energy products.

Keyword
waste, sustainable energy system, fossil-fuel-free, optimization
National Category
Engineering and Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-13190 (URN)
Conference
Proceedings Sardinia 2011, Thirteenth International Waste Management and Landfill Symposium. S. Margherita di Pula, Cagliari, Italy; 3 - 7 October 2011
Available from: 2011-10-27 Created: 2011-10-27 Last updated: 2012-11-15Bibliographically approved

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