Development and Practical Tests of Insulating/cooling Capsule with Sensor for In-situ Measurements of CO Concentrations on Moving Grates in MSWI

The disposal of waste (particularly of municipal solid waste) that cannot be minimized, recycled or reused presents a huge international problem. The last 20 years is characterized by a gradual transition from landfilling of the municipal solid waste (MSW) to incineration. The incineration of MSW under existing legislation and operational boundary conditions is a very complex process with the application of two-stage combustion, minimization of emissions and production of energy (generally heat and electricity). In MSW incinerators, the first stage consists of combustion of heterogeneous waste on a moving grate that transports and mixes the waste during the combustion process. The grate combustion process involves drying, devolatilization, gasification/combustion and char burn-out. Thus, gasification and pyrolysis are subsets of the combustion problem. Mathematical modeling of combustion on the grate requires the solution of the flow field and concentrations of gaseous species in a reacting and moving bed, taking into account various heat transfer mechanisms. Development of an accurate mathematical model of the incineration process is limited by the lack of measured data for validation. Requirements for specific (in-situ) data essential for the development of an incinerator burning bed model and a better understanding of the grate combustion process prompted accurate measurement of concentrations of selected gases within a moving, burning bed of solid waste. For this purpose we have designed and developed a special cube-capsule with insulating refractory ceramic fibres and materials with cooling effects enabling measurements of CO and temperature by an electrochemical sensor, small gas pump and electronics placed inside. This unique self-contained and mechanically/thermally protected probe consisting of measuring and recording electronic components was able to withstand temperatures over 1000°C for a period longer than two hours. The measurement technique differs from all conventional methods of measurements in that the capsule (casket) can be introduced into the incinerator together with the waste and hence experiences the same conditions on the grate as the waste material. This novel device proved to be convenient for in-situ measurements in moving grate incineration. The capsule with sensor for CO measurement passed through three incinerator furnaces burning MSW and recorded CO concentration and two temperatures on opposing sides of the capsule, saving all data onto a computer memory chip. The cube-capsule was recovered from the incinerator ash pit and the recorded information was downloaded onto an Excel spreadsheet for subsequent analysis. A similar capsule/casket being designed with thermal insulation/cooling could be used for simultaneous measurement of CO, oxygen, CO2 (or pollutants as HCl) and temperatures to characterize the combustion process of waste. A vibration sensor, detection of casket position on the grate and measurement of temperatures and intake of gas samples from more surface positions will further improve the record of the trajectory/rolling of the capsule, to elucidate the effects of horizontal and vertical distance on the grate within the furnace and the overall history (residence time in various sections) experienced on the grate by waste.

MARTINEC Jiri;  SKÁLA Z;  SCHOSGER Jean-Pierre;  BAXTER David; 

SVOBODA Karel; 

2008-01-21

Czech Society of Chemical Engineers

JRC33553