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Combustion of agricultural residues: Application for Stirling micro-combined heat and power
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0003-0042-0227
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Access to energy services is crucial for the development of countries. Therefore, in developing countries, the access to modern conversion technologies would contribute to reduce the poverty, improve health services and promote the economy especially in rural areas. Around 2.5 billion people in these countries use biomass for cooking. However, major concerns are due to the unsustainable use of biomass and the inefficient conversion technologies employed in rural areas. Therefore, the use of locally available biomass in modern biomass conversion technologies would significantly reduce emissions and improve the energy efficiency. These modern technologies may include residential pellet stoves and boilers which at the moment only are used for heating appliances in industrialized countries. Their combination with a prime mover like a Stirling engine could a very attractive solution to produce combined heat and power (CHP) though still in prototype stage. In this context, this study is mainly focused on the development of an energy system fuelled by locally available biomass to produce heat and electricity based on a Stirling engine. The main objective is to perform experiments to find relevant parameters that characterize the energy system proposed.

In the first stage of this work, the suitability of using agricultural residues in a pellet boiler was evaluated in comparison to commercial wood pellets. The agricultural residues used during the tests were: sugar cane bagasse, sunflower husks and Brazil nut shells. The first two residues were pelletized and the last one was reduced to a uniform size. Parameters and energy used during the pelletizing were found. Emission levels and boiler efficiency under steady-state and transient conditions were also presented for the different biomass sorts. In the second stage, the integration of the same pellet burner and the Stirling engine was characterized in terms of losses and efficiency calculations. Finally, the integration of the pelletizing, combustion, and heat and power generation was discussed based on experimental and predicted results.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xx, 85 p.
Series
TRITA-KRV, ISSN 1100-7990 ; 14:03
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-150350ISBN: 978-91-7595-241-3 (print)OAI: oai:DiVA.org:kth-150350DiVA: diva2:742495
Public defence
2014-09-22, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140903

Available from: 2014-09-03 Created: 2014-09-01 Last updated: 2014-09-03Bibliographically approved
List of papers
1. Pelletizing study of agricultural residues: Parameters and energy consumption
Open this publication in new window or tab >>Pelletizing study of agricultural residues: Parameters and energy consumption
2011 (English)Report (Other academic)
Alternative title[en]
Series
Internal report at Department of Energy Technology, Royal Institute of Technology, Stockholm, Sweden, EKV 05/11
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-107458 (URN)
Note

QC 20130618

Available from: 2012-12-11 Created: 2012-12-11 Last updated: 2014-09-03Bibliographically approved
2. Combustion of agricultural residues: An experimental study for small-scale applications
Open this publication in new window or tab >>Combustion of agricultural residues: An experimental study for small-scale applications
2014 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 115, 778-787 p.Article in journal (Refereed) Published
Abstract [en]

Energy services could be greatly improved by using of residues from local food industries in small-scale combustion units. Wood pellets are a reliant and proven fuel to be used in small-scale combustion units. However, these units should preferably be able to use different types of biomass depending what it is locally available. Therefore, studies have been focused on exploring the suitability of using agricultural residues for small-scale heat and power generation using direct combustion. This study targets to compare the combustion of different agricultural residues in a single unit designed for wood pellets. The different biomass fuels used are circle divide 6 mm and circle divide 8 mmwood pellets, circle divide 6 mmbagasse pellets, circle divide 6 mmsunflower husk (SFH) pellets and Brazil nut (BN) shells. The results reveal a decrease in the fuel power input, higher oxygen levels in the flue gases and shorter cycles for ash removal when using the agricultural residues. The excess air ratio was calculated based on a mass balance and compared with a standard equation showing a good agreement. CO and NO emission levels as well as the relative conversion of fuel-C to CO were higher for the BN shells and SFH pellets in comparison to the other biomass types. SO2 emission was estimated based on the analysis of unburned sulfur in ash and mass balances; the higher estimated levels corresponded to the BN shells and SFH pellets. All the biomass sorts presented over 95% relative conversion of fuel-C to CO2. Wood pellets and BN shells presented the highest amount of unburned carbon in ash relative to the fuel-C. The relative conversion of fuel-N to NO and fuel-S to SO2 were higher for wood pellets. Bagasse pellets showed similar emission levels and relative conversion efficiency to wood pellets.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Agricultural residues, Sugar cane bagasse, Sunflower husks, Brazil nut shells, Biomass combustion
National Category
Energy Systems
Identifiers
urn:nbn:se:kth:diva-128457 (URN)000325647000090 ()2-s2.0-84883138109 (Scopus ID)
Note

QC 20131114

Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2017-04-28Bibliographically approved
3. Thermal power analysis of flue gases during the combustion of agricultural residues in a residential pellet boiler
Open this publication in new window or tab >>Thermal power analysis of flue gases during the combustion of agricultural residues in a residential pellet boiler
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-150348 (URN)
Note

QS 2014

Available from: 2014-09-01 Created: 2014-09-01 Last updated: 2014-09-03Bibliographically approved
4. Integration of a wood pellet burner and a Stirling engine to produce residential heat and power
Open this publication in new window or tab >>Integration of a wood pellet burner and a Stirling engine to produce residential heat and power
2014 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 73, no 1, 669-678 p.Article in journal (Refereed) Published
Abstract [en]

The integration a Stirling engine with a pellet burner is a promising alternative to produce heat and power for residential use. In this context, this study is focused on the experimental evaluation of the integration of a 20 kWth wood pellet burner and a 1 kWe Stirling engine. The thermal power not absorbed by the engine is used to produce hot water. The evaluation highlights the effects of pellet type, combustion chamber length and cycling operation on the Stirling engine temperatures and thermal power absorbed. The results show that the position of the Stirling engine is highly relevant in order to utilize as much as possible of the radiative heat from the burner. Within this study, only a 5 cm distance change between the Stirling engine and the pellet burner could result in an increase of almost 100 °C in the hot side of the engine. However, at a larger distance, the temperature of the hot side is almost unchanged suggesting dominating convective heat transfer from the hot flue gas. Ash accumulation decreases the temperature of the hot side of the engine after some cycles of operation when a commercial pellet burner is integrated. The temperature ratio, which is the relation between the minimum and maximum temperatures of the engine, decreases when using Ø8 mm wood pellets in comparison to Ø6 mm pellets due to higher measured temperatures on the hot side of the engine. Therefore, the amount of heat supplied to the engine is increased for Ø8 mm wood pellets. The effectiveness of the engine regenerator is increased at higher pressures. The relation between temperature of the hot side end and thermal power absorbed by the Stirling engine is nearly linear between 500 °C and 660 °C. Higher pressure inside the Stirling engine has a positive effect on the thermal power output. Both the chemical and thermal losses increase somewhat when integrating a Stirling engine in comparison to a stand-alone boiler for only heat production. The overall efficiency of the pellets fired Stirling engine system reached 72%.

Keyword
Biomass, Wood pellets, Stirling engine, Micro-CHP, Polygeneration
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-150347 (URN)10.1016/j.applthermaleng.2014.08.024 (DOI)000346543400068 ()2-s2.0-84906831303 (Scopus ID)
Funder
Sida - Swedish International Development Cooperation Agency
Note

QC 20140903

Available from: 2014-09-01 Created: 2014-09-01 Last updated: 2017-12-05Bibliographically approved
5. An experimental study of a Stirling engine micro-CHP system fuelled on wood and sugarcane bagasse pellets
Open this publication in new window or tab >>An experimental study of a Stirling engine micro-CHP system fuelled on wood and sugarcane bagasse pellets
(English)Manuscript (preprint) (Other academic)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-150349 (URN)
Note

QS 2014

Available from: 2014-09-01 Created: 2014-09-01 Last updated: 2014-09-03Bibliographically approved

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