One way of biomass and/or waste recycling is its thermochemical conversion into combustible gas. Mainly composed of CO,H 2 and CH 4 , the gas may also contain varying amounts of impurities (dust, polluting products, tar or soot). Specifically, there is a tar problem: their high condensation temperature is incompatible with an industrial utilization. They can cause rapid fouling, corrosion and abrasion into turbines or engines. Proposed by EUROPLASMA, the CHO-Power process aims to generate electricity from a mixture of municipal waste and biomass using a fixed bed gasifier with conventional gas treatment. Its specificity consists of an unit called Turboplasma. This stage allows to reach very high temperature in order to obtain temperature around 1600K, and so to degrade all tars present, even heavier. Indeed, EUROPLASMA built a gasification pilot unit based on fluidized bed technology, (called KIWI) to qualify the synthesis gas produced. TURBOPLASMA pilot scale will be installed there. The objective of this work is the design of this high temperature stage thanks to numerical modeling. Reaction scheme used previously [4] to modelize tar degradation in the Turboplasma of CHO-Power, has been improved: a discrete phase modeling has been added providing a better view of the TURBOPLASMA internal behavior. Indeed, char particles from syngas can significantly change the reactor performance. This study shows that char particles react primarily with the H 2 O and CO 2 . Char gasification takes place in areas of high velocity and temperature gradient. Increased understanding of aerodynamics inside the reactor allows a better estimate of the overall performance of the reactor. Performance evaluation of the reactor is based on a set of parameters such as levels of heat loss, velocity gradient, mixing quality, residence time.

This investigation has been undertaken to better understand pollutant formation in Waste-to-Energy (WTE) systems by using Computation Fluid Dynamics (CFD). An above-grate gas phase only model was built and calculated in FLUENT™ with the intent of specifically studying the factors that influence the formation of NO x . Results are shown for a typical reciprocating-grate WTE boiler operating on municipal solid waste (MSW). Contours of velocity, temperature, CO 2 , CO, H 2 O, and O 2 agree well with previous modeling and data resulting in a high fidelity model that can be implemented in the next phase of this research. Preliminary data is shown for thermal NO x and the results are promising. The next phase of this research will include the development and implementation of detailed kinetic mechanisms (DKM) to model NO x formation with the current boiler presented as well as others with varying fuels.

The size reduction of municipal solid waste (MSW) particles on the reverse acting traveling grate of a waste-to-energy (WTE) combustion chamber was estimated by means of a numerical model combining the particle size distributions (PSD) of MSW and combustion residues and the Shrinking Core Model (SCM). This new integrated model was used to simulate the particle behavior on the grate. During their travel on the moving grate, the sizes of the particles are reduced by combustion, breakage, and compaction. This study shows the calculation of the particle size change using this model and comparison of the numerically derived PSDs of MSW and ash particles with experimental data. There is good agreement between calculated and measured values.

Covanta is using a multifaceted approach to problem solving in Waste-to-Energy systems which combines several types of computer modeling with physical cold flow models, field testing, and engineering experience. This problem-solving approach is applied to boiler corrosion, gas and particulate flow patterns, reagent injection, and APC system issues. Our goals are to bring the most appropriate tools to each issue and incorporate results back into the engineering approach in order to continually improve our technical capabilities. Several types of computer modeling are used. A commercially available energy balance program is used for steam cycle evaluations and boiler energy balance and heat transfer calculations. Computational Fluid Dynamics (CFD) models are developed to investigate temperature and flow patterns where local conditions must be understood in detail. We have made extensive use of cold flow models to improve performance of APC systems, and to evaluate overfire air mixing in furnaces, and flow distribution through tube banks in boilers. Field testing is used to investigate temperature fluctuations and distributions, flow stratification, corrosion rates, and to validate modeling or analytical results. Each of these approaches has its own set of advantages, disadvantages, and limitations, and must always be combined with a healthy dose of operating and engineering experience. Analytical work is done by, or in close cooperation with, our operations and engineering staff with many years of experience operating, designing, and modifying boilers, APC systems, and related equipment. This integrated approach has yielded significant improvements in many cases and is being used in increasingly complex applications.