Thai Biogas Generator : Biomass Gasification

Operational Mechanism

After the raw biomass material was put into the gasifier, chemical processes like pyrolysis reaction and deoxidization were taken place with the burning, part of raw material was burned with the oxygen, provide heat for the pyrolysis, but more biomass materials were pyrolyzed in high temperature, and separate out volatile and char. The volatile reacted for the second time within the high temperature region and the tar was pyrolyzed further into gas. At the same time, reduction reactions were happened between the char and gas, and between the gases themselves. In the end, gas phase tar and gas went to the separator, accompanying with some small char particles and ash particles and gas phase been separated, part of the char re-circulate to the gasifier to react again, gas phase tar was cleaned by water after scrubber. And the clean gas meets with the requirement of the gas engine to generate power.

Operational Parameters

This system is used air as gasification medium, and the operating temperature should between 650-850 C? The components of fuel gas include: N₂ (nitrogen), O₂ (oxygen), H₂ (hydrogen), CO2 (carbon dioxide), CO (carbon monoxide), CH₄ (methane) and C_nH_m, etc. and the heat value of the gas in between 4600-6300kJ/Nm³.

Take an example of 1 MW rice hull gasification and power generation system. After the successful ignition of the gasifier, the power generating system begins to operate. Comparing with other kinds of biomass materials, rice hull has a high ash content, as much as 20%,When the temperature is more than 850 C? silica and potassium oxide in the ash will slag on the surface of the rice husk particles, forming a glass-like barrier, which prevents the further reaction of the remaining char and jams in exit of the ash; When the temperature is less than 700 C? part of carbon in the fuel remains un-burnt and accumulates in the reactor, resulting in lower efficiencies. Due to such characteristics of the ash, the CFB gasifier is supposed to be a promising choice for rice husk, since the bed temperature can be kept below the ash slagging temperature by controlling its operating parameters properly. At general condition, the reacting temperature inside the gasifier should be steadily kept around 750-850 C?

Credit to : web: china-power-contractor.cn