Steady state model and automatic control algorithm of a municipal solid waste (MSW) batch gasification system
Abstract
Americans generate almost 5 lbs of trash per person per day. Although large fractions of discarded paper, plastics, and organic waste can be economically separated and then recycled or composted, 55\% of the MSW in the US still ends up in American landfills. Many existing landfills collect methane produced during the decomposition of MSW to produce electricity and prevent methane from polluting the atmosphere. Additionally, many waste to energy (WTE) techniques and technologies have been developed to divert MSW from landfills by converting MSW into energy in the form of heat, electricity and valuable chemicals. The WTE technique of incineration produces electricity and steam at a large scale and requires human operators to monitor the process around the clock. MSW Gasification plus Oxidation (GPOX) is a promising WTE alternative to incineration because the lower air flow rates of the GPOX process lead to higher flame temperatures and smaller pollution control equipment. Smaller pollution control equipment in GPOX systems has the advantages of producing lower emissions from a smaller, portable system which can move to process waste at its source. GPOX is a thermal treatment technology which converts un-differentiated (un-sorted) and non-comminuted (un-shredded) MSW into a flammable gas called syngas via a carefully controlled, oxygen-starved, partial-combustion reaction. The syngas is then quickly oxidized to create a high temperature flame which destroys toxins and can generate usable process heat and electricity through a steam turbine. Because of the heterogeneous nature of MSW, the control of the GPOX process is particularly challenging. This thesis presents a mathematical model which can be used to predict the oxidation temperature and processing rates of a GPOX system as a function of MSW composition, valve positions, and process air flows. Additionally, this thesis presents a control algorithm for the GPOX process suitable for implementation on a PLC. The algorithm is designed to provide automated start-up, steady-state processing, and safe shut down of a batch MSW GPOX system for the purpose of converting waste into useful thermal energy. The process knowledge and control algorithm presented in this thesis has the ability to make smaller scale GPOX systems more economically feasible and reliable by eliminating constant human monitoring as is currently required.
Degree
M.S.E.C.E.
Advisors
Schubert, Purdue University.
Subject Area
Electrical engineering
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