A Novel Approach for Solving the Problem of Bridging in Fixed Bed Gasifiers

The downward flow of the feedstock in the gasification process of fixed bed gasifiers is dictated by the force of gravity. However, in case of low density feedstock such as agricultural crop straws, softwood chips, etc., the flow is adversely affected by bridging and as a consequence the stability and result of the process can be hampered. In this paper a novel method is introduced for solving the problem of bridging in oil palm fronds gasification process. For the process of gasification single throat downdraft gasifier was used. In the experiment, after feeding the gasifier with 9 kg of oil palm fronds, 4 kg of 7 metal scraps were placed on top of the feedstock in order to increase the weight and enhance the downward flow. By applying metal scraps the problem of bridging was solved and stable gasification process was obtained. As a result of stable operation of the process, the percentage of combustible components of the syngas was improved. CO was increased from 15.4 to 22.8, CH4 from 1.7 to 1.9 and H2 from 8.4 to 9.6 in volume percentage. In addition, higher heating value was increased from 3.7 to 4.8 MJ/Nm3 and equivalent ratio was decreased from 0.29 to 0.27. The average oxidation temperature in the oxidation zone was also improved from 623 to 828°C.