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Downdraft gasification of pellets made of wood, palm-oil residues respective bagasse: Experimental study
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
2011 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 3, 899-908 p.Article in journal (Refereed) Published
Abstract [en]

The downdraft gasification technology has an increased interest among researchers worldwide due to the possibility to produce mechanical and electrical power from biomass in small-scale to an affordable price. The research is generally focused on improvement of the performance and optimizing of a certain gasifier, on testing different fuels, on increasing the user-friendliness of the gasifier and on finding other uses for the product gas than in an IC-engine, for example liquid fuel production.

The main objective with the gasification tests presented here is to further contribute in the field by studying the impact of the char bed properties such as char bed porosity and pressure drop on the gasification performance as well as the impact of fuel particle size and composition on the gasification process in one and the same gasifier. In addition, there is very little gasification data available in literature of “before disregarded” fuels such as sugar cane bagasse from sugar/alcohol production and empty fruit bunch (EFB) from the palm-oil production. By pelletizing these residues, it is possible to introduce them into downdraft gasification technology which has been done in this study.

The results show that one and the same reactor can be used for a variety of fuels in pellet form, but at varying air–fuel ratios, temperature levels, gas compositions and lower heating values. Gasification of wood pellets results in a richer producer gas while EFB pellets give a poorer one with higher contents of non-combustible compounds. In this gasification study, there is almost linear relation between the air–fuel ratio and the cold-gas efficiency for the studied fuels: Higher air–fuel ratios result in better efficiency. The pressure drop in the char bed is higher for more reactive fuels, which in turn is caused by low porosity char beds.

Place, publisher, year, edition, pages
2011. Vol. 88, no 3, 899-908 p.
Keyword [en]
Downdraft gasification, Pellets, Agricultural residues, Palm-oil, Cane sugar, Bagasse
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-14071DOI: 10.1016/j.apenergy.2010.08.028ISI: 000285217400036Scopus ID: 2-s2.0-78149354852OAI: oai:DiVA.org:kth-14071DiVA: diva2:329557
Note
QC 20120323Available from: 2010-07-12 Created: 2010-07-12 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Comparative study of residue pellets from cane sugar and palm-oil industries with commercial wood pellets, applied in downdraft gasification
Open this publication in new window or tab >>Comparative study of residue pellets from cane sugar and palm-oil industries with commercial wood pellets, applied in downdraft gasification
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

While biomass utilization for energy conversion in the industrialized nations is being largely developed, highly efficient and environmentally friendly, many tropical countries still use biomass at low efficiencies and high emission levels. The main reasons for these gaps are both political and technological: the energy markets are different, the Gross National Product (GDP) differs widely, and the feedstock differs in form and conversion behaviour. By implementing newer technologies adapted for tropical biomass feedstock, there would be a large potential in these countries for increased energy services since access to modern energy still is an essential step for improving the GDP for a country. Two dominant and tropically placed industries available for energy improvements are the cane sugar and palm-oil industries, which both produce an abundant amount of biomass residues. One step towards enhanced utilization of the residues, which would not require large investment costs in the power plant section nor in the processes of these industries, would be to install a pelletizing unit in the industry area to make fuel out of the excess residues for sale to the nearby villages. The pellets could be used both for cooking/heating and for small-scale power generation in a gasification-IC engine plant.

The overall objective of this study is to experimentally evaluate the biomass residues in pellet form from the cane sugar and palm oil industries during conversion to useful energy in small-scale systems.

The thesis is built upon five publications which include experimental analysis on flaming pyrolysis and rapid heating of pellets (paper I), pyrolysis in oxygen-free atmosphere and slow heating with subsequent steam gasification (paper II), global pelletizing data such as relative energy consumption, temperature levels, particle size and moisture content for successful pelletizing process (paper III), downdraft gasification evaluation including reactor temperature distribution, gas composition, cold-gas efficiency and packed-bed mechanics (paper IV) and a numerical model including the overall system efficiency for residue-to-electric power based in a small-scale gasifier system (paper V).The single-pellet studies revealed that pyrolysis in reducing atmosphere is to prefer compared to flaming pyrolysis in oxidizing environment with regards to the char quality.

The studies also showed favourable thermochemical and mechanical behaviour for smaller size pellets (Ø6- Ø8mm) compared to larger size ones (Ø12 mm). Therefore, a downdraft gasifier of closed constricted type was designed for real gasification tests of the residue pellets of sizes Ø6- Ø8mm. These tests showed that all the studied pellet sorts could be used in one and the same gasifier, resulting in different reactor temperature distributions and gas compositions with lower heating values in the range of 4.1-5.4 MJ/m3n dry gas. The reactor bed dynamics showed to be dependent both on the fuel reactivity and the size, with less pressure drop for larger size pellets with lower reactivity. The pelletizing process itself revealed that the selected residues all needed higher moisture content and smaller particle size than recommended for wood for successful pelletizing. The relative electric energy consumption was lower when producing larger size pellets Ø8 mm than smaller ones (Ø6 mm) of same material. For untreated wet empty-fruit bunch (EFB) a stand-alone power plant with integrated EFB pre-treatment and gasification could generate 380 kWh of net electricity per ton of EFB at a “well-to-wheel” efficiency of 15%.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 54 p.
Series
Trita-KRV, ISSN 1100-7990 ; 2009:03
Keyword
energy engineering
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-11300 (URN)978-91-7415-455-9 (ISBN)
Public defence
2009-10-28, Sal M3, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100712Available from: 2009-10-15 Created: 2009-10-15 Last updated: 2010-07-15Bibliographically approved

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