Yao Bin Yang

Investigation of biomass combustion systems using CFD techniques: a parametric study of packed-bed burning characteristics

In this paper, mathematical equations governing the fluid flow, heat and mass transfer and heterogeneous reactions in packed-bed combustion systems are described and sub-models for individual processes are presented. A model estimating the mixing rate between the under-grate air and the released volatile gases is described. Parametric study was carried out to assess the effects of fuel moisture content, kinetic rate of devolatilisation, primary air flow rate and particle mixing levels caused by grate movement. Useful conclusions were drawn in terms of flame temperature, reaction zone thickness, mass loss rate, combustion staging and residual carbon in ash.

Numerical simulation of Municipal Solid Waste incineration in a moving-grate furnace and the effect of waste moisture content

Mathematical equations governing the physical and chemical processes in grate combustion systems are described and a full-scale municipal solid waste incinerator was simulated. The effects of waste moisture content as well as preheated air temperature have been assessed. Combustion efficiency around 98% was obtained for moisture levels less than 30% while moisture over 35% resulted in poor combustion efficiency. Depending on the waste moisture content, the maximum gas temperature ranges from 1240C to 1510C and the maximum solid temperature inside the packed-bed from 980C to 1230C. The main reaction zone thickness ranges from 250 mm to 350 mm along the bed height.

Mathematical modelling of sewage sludge incineration in a bubbling fluidised bed with special consideration for thermally-thick fuel particles

Fluidised bed combustor (FBC) is one of the key technologies for sewage sludge incineration. In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed consisting of a fast-gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The model further improves over previous works by taking into account throughflow inside the bubbles as well as the floating and random movement of the fuel particles inside the bed. Validation against both previous lab-scale experiments and operational data of a large-scale industrial plant was made. Calculation results indicate that combustion split between the bed and the freeboard can range from 60/40 to 90/10 depending on the fuel particle distribution across the bed height under the specific conditions. The bed performance is heavily affected by the variation in sludge moisture level. The response time to variation in feeding rate is different for different parameters, from 6 min for outlet H2O, 10 min for O2, to 34 min for bed temperature.

Mathematical model of biomass gasification using high temperature air in fixed beds

A mathematical model has been formulated for predicting the main chemical and physical processes taking place during the fixed-bed gasification of biomass fuels using high temperature air (up to 10 ...

The effect of changing waste compositions on the incineration process of Municipal Solid Wastes in packed-bed systems: a CFD approach

With the recent changes in waste management policy across many EU countries, more and more efforts are now being made on wastes recycling and minimisation. In this paper, the effects of the changing compositions of wastes on the operation of incineration plants are addressed. CFD technique is used to simulate the incineration processes in grate systems and advanced mathematical models are employed. The incineration characteristics have been expressed as functions of the percentage of combustible materials in wastes taken away for recycling. To offset the deteriorated performance of incineration in some cases, alternative operation modes have been suggested and simulated.