Fuel Characterization Study and Simulation of Dewatered Domestic Wastewater Sludge Gasification Using ASPEN Plus

Abstract

Dewatered domestic wastewater sludge (DDWS) is one of the largest contributors of waste material in the world, and it immediately elevates local environmental problems, especially in the urban area. The conversion of this material into a usable form of green energy, such as syngas through gasification, can be a vital solution. Hence, this method not only solves the environmental issues related to DDWS disposal but also participates as an energy source. To achieve this goal, the essential fuel characterization, which includes initial moisture content, high heating value, ultimate analysis, and proximate analysis, were carried out to assess the potential energy in DDWS. Due to the high expenses of the successful design of the gasifier reactor, and there are no efficient methods to predict the gasification performance, the model of the DDWS gasification process using ASPEN Plus software was developed. As ASPEN Plus software does not contain a built-in gasifier reactor model, a combination of various reactors is used to simulate the gasification processes. These processes were divided out into two stages. In the first stage, DDWS was decomposed into its element by specifying yield distribution. By using Gibbs free energy minimization approach, the gasification reactions were modeled. The current model was validated with the previously published work. From the characterization findings, DDWS showed high initial moisture content 84.64% and potential energy with 16.84 MJ/kg high heating value. The proximate analysis based on the dry base of DDWS exhibited that more than 55.42 % of their mass is composed of volatile materials, and ash content is found to be less than 25.79%. The elemental of carbon, hydrogen, nitrogen, sulfur, and oxygen component in the DDWS sample was 34.29%, 5.20%, 5.80%, 3.12%, and 25.80%, respectively. By applying operating parameters, which include reaction temperature, reaction pressure, airflow rate, and moisture content, it's found that the increase in reaction temperature (673-1673K) enhanced the production of CO and H2 while increasing reaction pressure adversely affected the generation of H2 and CO. The increase in the airflow rate increases CO2 mole fraction in syngas and shift the gasification process to combustion. The heating value of syngas sharply decreased with the increase in the DDWS moisture content. From the simulation results, ASPEN Plus simulator software is presented with the high capability to be used as a predictive tool for optimization of the gasifier performance.