Surrogate Reaction Mechanism for Waste Incineration and Pollutant Formation

Abstract

The incineration of municipal solid waste (MSW) is an attractive technology to generate thermal energy and reduce landfill waste volume. To optimize primary measures to ensure low emission formation during combustion, numerical models that account for varying waste streams and their impact on nitrogen oxide (NO x ) formation are needed. In this work, the representation of the fuel by surrogate species is adopted from liquid fuel and biomass combustion and applied to solid waste devolatilization and combustion. A surrogate formulation including biomass components, protein, inorganics, and plastic species is proposed, and a comprehensive description of the heterogeneous and homogeneous reactions is developed. The presented work combines and extends available schemes from the literature for woody and algae biomass, coal, and plastic pyrolysis. The focus is set on the prediction of fuel NO x and its precursors, including cyclic nitrogen-containing hydrocarbons. Additionally, the interaction of NO x with sulfur and chloride species is accounted for, which are typically released during the devolatilization of MSW. The model allows for predicting thermogravimetric analysis measurement of waste fractions and different waste mixtures. The proposed kinetic mechanism well reproduces NO x formation from ammonia and hydrogen cyanide and its reduction under selective non-catalytic reduction conditions. The chemical model is successfully applied to predict the released gas composition along a grate-fired fuel bed using a stochastic reactor network.

Chemical Model for Thermal Treatment of Sewage Sludge

“…It is selected since it is targeted to solve large detailed chemistry schemes and to resolve the devolatilization, heterogeneous reactions of solid and gas phase, and reactions in the gas phase. Depending on the provided chemistry and operating conditions, it allows us to model pyrolysis, gasification, and combustion applications [31,41,42].…”

“…The classical approach in biomass and waste research is to determine kinetic parameters for specific waste fractions and their mixtures [15,[21][22][23][24][25][26][27][28][29] or to determine pseudo representative species for an individual feedstock [30]. These methods are based on empirical material-specific apparent reaction rates and cannot directly be transferred to other feedstocks [31]. Contrary, the flexible representation of various solid fuels using reoccurring characteristic surrogate species offers the description of the needed dependencies of the solid fuel and the gas phase products (gas, tar, and emission precursors) [31][32][33].…”

“…These methods are based on empirical material-specific apparent reaction rates and cannot directly be transferred to other feedstocks [31]. Contrary, the flexible representation of various solid fuels using reoccurring characteristic surrogate species offers the description of the needed dependencies of the solid fuel and the gas phase products (gas, tar, and emission precursors) [31][32][33]. The surrogate concept is the state-of-the-art in liquid (e.g., Diesel and gasoline) and gaseous fuels modeling and has previously been used within the solid fuel conversion of coal and biomass [32][33][34][35][36][37][38].…”

“…For example, Debiagi et al [36] achieved the mathematical description of more than 500 biomass and waste fraction samples, such as woods, grass plants, algae and food industry wastes, with nine reference species, including moisture and ash. Recently, the concept was also applied to describe the heterogeneous feedstock of municipal solid waste (MSW) [31]. Žnidarčič et al [39] empathized the ability of a surrogate model to account for different sewage sludge properties and introduced a surrogate model for the description of the gas phase.…”

“…The presented work aims to formulate a mathematical description of sewage sludge to model thermal treatment units. The model is formulated by selecting existing surrogate components from the literature [31,32,38] and their devolatilization schemes and combing them with corresponding gas-phase chemistry [31]. The model development is described in Section 2.2, discussing the surrogate species selection (Section 2.2.1), their devolatilization scheme (Section 2.2.2), and their combination to a sewage sludge surrogate (Section 2.2.3).…”