The design of 50 kWth multistage downdraft wood gasification system

Abstract

Gasification, an incomplete combustion process with a controllable oxygen amount, can increase the value of non-commercial feedstock into marketable fuel. It converts the feedstock using thermo- chemical conversion from carbonaceous material into producer gas consisting of CO and H2 as the major contents. Instead of coal gasification, biomass gasification recently becomes more popular respecting to the green house gases effects, the resource supply and economic issues. Due to the fact that tar problem occurs on biomass gasification process, there have been many reactor designs developed to analyze the gasifier performance. Yet, the fixed model to settle the problem has not been found in the literature. This study was performed on gasification system design of wood biomass in a fixed bed downdraft type gasifier. The gasification system consists of a multistage downdraft gasifier, equipped with a series of purification system such as a cyclone, a heat exchanger, a bag filter, a blower, and a flare tower. The design was calculated on the gasification process power output of 50 kWth, air equivalence ratio (ER), and gasification temperature of 700°C. The dimension of gasifier was determined based on the measurements of essential parameters as well as the theoretical and experimental data from literatures. As a result, a design of gasifier was achieved which has 0.15 m of internal diameter, 0.1 m of internal ceramic coating and castable refractory material wrapped by a paper tape. The height of gasifier is 2. 1 m, with three parts inside: hopper, gasifier zone, and ash chamber. It has three stages of air injection with uniform elevation (30cm per stage) and nine air nozzles installed around the gasifier at constant range and angle. The cyclone diameter was 0.127 m with inlet height and width of 0.064 m and 0.031 m respectively. A 1,2 shell and tube heat exchanger with 0.46 m outside diameter, 0.36 m inside diameter, 2 m length, and 86 tubes. The bag house has four fiberglass filters. The induced draft type of blower was used to absorb the synthetic gas from gasification process. The gasifier also equipped with a two m length of flare tower to burn the gas. The design was used for the experimental testing and calculation of multistage wood gasification.