Characterization of a bubbling fluidized bed biomass gasifier
| dc.contributor.author | Lim, Mook Tzeng | |
| dc.date.accessioned | 2014-11-18T07:49:21Z | |
| dc.date.available | 2014-11-18T07:49:21Z | |
| dc.date.issued | 2007 | |
| dc.description | Master | en_US |
| dc.description.abstract | The recent increase in fossil fuel prices and worsening effects of global warming has prompted the use of biomass as a source of energy. A bubbling fluidized bed gasifier biomass gasifier (BFBG) was thus selected for energy conversion due to its high thermal output and ability to accept wide variety of fuels. It was designed with an internal diameter of 400mm and has a thermal output of 640kW. It is attached to a gas cleaning and cooling (GCC) that removes particulates and condensates from the system. The BFBG used silica river sand with a mean particle size, of 425 to 600μm and has a density of 1520kg/m3, which belongs to Geldart group B particles. The biomass used was rubber wood chips, obtained from a saw mill. Bubbling fluidization began once the superficial gas velocity reached 0.24m/s. The gas composition, lower calorific value of producer gas, LCVPG and cold gas efficiency, ηcold were then determined for different static bed heights with varying equivalence ratio. It was found that ηcold increases with increasing equivalence ratio until an optimum value before decreasing. LCVPG was found to decrease with increasing equivalence ratio. Between equivalence ratios of 0.177 to 0.452, LCVPG was highest at low 0.177, and was lowest at 0.452. Char had a LCV of 23.69MJ/kg, while wood chips had a LCV of 17.40MJ/kg from bomb calorimeter tests. Char had a particle size of 100μm from sieve analysis. The minimum fluidization velocity for char would be six to eight times of sand, thus elutriation of char from BFBG would be unavoidable. This caused the carbon conversion efficiency to be low at 95.40%, with average char collected to be 2.9kg. The average condensates flow rate was found to be of 9.15% of the biomass fed with low biomass feed rate. Analysis of the condensates showed that phenol was the main constituent, which is highly soluble with water and causes pollution. Incorporation of a wastewater treatment plant would be required to reduce contamination. Energy analysis of the system showed that heat loss was 21.42%. Most of the energy lost was contained in the condensates. To reduce condensate flow rates the maximum biomass feed rate was limited to 155kg/hr, thus the thermal output would be 530kW. From the internal combustion engines the electricity generated would be 172.5kWe. Thus the actual turndown ratio was found to be 1.98, compared to the design case of 2.67. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/596 | |
| dc.language.iso | en | en_US |
| dc.subject | Science Physic | en_US |
| dc.subject | bubbling fluidized | en_US |
| dc.subject | Bed Biomass Gasifier | en_US |
| dc.title | Characterization of a bubbling fluidized bed biomass gasifier | en_US |
| dc.type | Thesis | en_US |
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