Abstract
Gasification of municipal solid waste (MSW) with subsequent utilization of syngas in gas engines/turbines and solid oxide fuel cells can substantially increase the power generation of waste-to-energy facilities and optimize the utilization of wastes as a sustainable energy resources. However, purification of syngas to remove multiple impurities such as particulates, tar, HCl, alkali chlorides and sulfur species is required. This study investigates the feasibility of high temperature purification of syngas from MSW gasification with the focus on catalytic tar reforming and desulfurization. Syngas produced from a downdraft fixed-bed gasifier is purified by a multi-stage system. The system comprises of a fluidized-bed catalytic tar reformer, a filter for particulates and a fixed-bed reactor for dechlorination and then desulfurization with overall downward cascading of the operating temperatures throughout the system. Novel nano-structured nickel catalyst supported on alumina and regenerable Ni-Zn desulfurization sorbent loaded on honeycomb are synthesized. Complementary sampling and analysis methods are applied to quantify the impurities and determine their distribution at different stages. Experimental and thermodynamic modeling results are compared to determine the kinetic constraints in the integrated system. The hot purification system demonstrates up to 90% of tar and sulfur removal efficiency, increased total syngas yield (14%) and improved cold gas efficiency (12%). The treated syngas is potentially applicable in gas engines/turbines and solid oxide fuel cells based on the dew points and concentration limits of the remaining tar compounds. Reforming of raw syngas by nickel catalyst for over 20 h on stream shows strong resistance to deactivation. Desulfurization of syngas from MSW gasification containing significantly higher proportion of carbonyl sulfide than hydrogen sulfide, traces of tar and hydrogen chloride demonstrates high performance of Ni-Zn sorbents.
Highlights
Global municipal solid waste (MSW) generation rate is estimated at 1.3 billion tonnes per year in 2012, and it is expected to increase to 2.2 billion tonnes annually by 2025 [1]
A hot syngas purification system with downward cascading of syngas temperature was developed with satisfactory performance to treat raw syngas generated from downdraft gasification of real MSW and to produce clean syngas potentially applicable in more efficient downstream applications such as gas engines, cycle gas turbines (CCGTs), solid oxide fuel cells (SOFCs) and hybrid energy recovery systems
Operational stability was demonstrated for the fluidized-bed catalytic tar reformer with nano-structured F-Cat treating dirty raw syngas directly from gasifier without any preliminary treatment
Summary
Global municipal solid waste (MSW) generation rate is estimated at 1.3 billion tonnes per year in 2012, and it is expected to increase to 2.2 billion tonnes annually by 2025 [1]. Gasification is an advanced thermochemical conversion process which converts MSW into gaseous fuel (syngas) that can be utilized in gas engines, combined cycle gas turbines (CCGTs) [6], solid oxide fuel cells (SOFCs) [7], or hybrid systems [8] with higher electrical efficiency and better environmental performance [9] and optimize the utilization of wastes as a sustainable energy resources. Combustion of treated syngas as a homogenous gaseous fuel in gas engines/turbines instead of the direct combustion of highly heterogeneous MSW reduce the formation of dioxins and furans. This is because the well-controlled complete combustion eliminates the residual carbon in the flue gas that acts as a precursor for the formation of dioxins and furans [11]
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