Study On The Combustion Characteristics And Nitrogen Oxide Transformation During The Fluidized Bed Combustion Of Shale Char

Oil shales, which are kerogen-rich sediments, are one of the most important energy alternatives.1With the growing of the energy demand in today’s society, it has important significance to seek theeffective and economical ways to utilize oil shale. Unfortunately, there are still some vital problems inthe oil shale industry and one of them is the disposal of shale char.In order to utilize shale char effectively and solve some other problems in oil shale industry, someresearcher put forward the “New technology for the comprehensive utilization of Chinese oil shaleresources”. The key section of this system is the burning of shale char in circulating fluidized bedfurnaces to supply heat and generate electricity, which achieves high utilization-factors for both oilshale’s chemical and energy potentials, and avoiding serious environmental impacts.However, there are still some technical problems need to be overcome during the practicalindustrial application of burning shale char in circulating fluidized bed furnace. One of them is thelower ignition and combustion property of shale char due to its high ash content and low calorific value,which makes it difficult to be burned out in fluidized bed combustor. Another problem is the relativelyhigh N2O emission during the combustion due to the low-temperature combustion characteristics offluidized bed technical and the fuel characteristics of shale char.The research objects of this paper are just these two problems, it tries to reflect their essences andfind solutions to improve the combustion efficiency of shale char and reduce N2O emission. In thispaper, some basic properties of shale char were studied firstly. And then the combustion experiments ofshale char in fluidized bed apparatuses was carried out and the transformation of nitrogen oxide andfinal emission characteristics were obtained. After that the mathematical model of shale char burning influidized bed furnace was established and the numeraical simulation of combustion process andtransformation of nitrogen oxide were carried out. By comparing the experimental and simulationresults, the transformation discipline of nitrogen oxide in fluidized bed furnace was summarized. At last,thedemonstration experiment of shale char burning in industrial CFB boiler was carried out to verify thefeasibility of disposing shale char through fluidized bed technology.During the research of shale char basic properties, two main study aspects were the the catalysis effect of mineral matrix in shale char during its thermochemical conversion and the mass transfercharacteristics for oxygen in the ash layer of shale char. The research results indicate that minerals inshale char can accelerate the combustion rate of organic matter and the ash layer effective diffusivityalong the direction parallel to the bedding planes is almost an order of magnitude greater than that alongthe direction perpendicular to the bedding planes. And the calculated kinetic parameters of shale charcombustion and ash layer effective diffusivity can be used in the later numerical simulation work.During the research of combustion properties of shale char in fluidized bed furnace, firstly, theinfluences of particle size, Ca/S, circulation ratio and minerals on the pollutant emissions during thecombustion of shale char were investigated in a small-scale fluidized bed furnace, and theconcentrations of some gases at different height above distributor at standard condition were measured,thus the formation and abatement disciplines of nitrogen oxide during the FB combustion wereunderstood preliminarily. And then systematic experimental research of burning shale char in alarge-scale semi-industrial fluidized bed furnace was carried out, thus the formation and transformationproperties of nitrogen oxide at dfferent bed temperatures, secondary ratios and Ca/S conditions wereobtained preliminarily.During the research of numerical simulation of burning shale char in fluidized bed furnace, thepyrolysis experiment of shale char was carried out by using the small-scale fluidized bed furnace firstly,and the pyrolysis products model was established through the analysis and test to the pyrolysis residual,condensed liquid phase and non-condensable gas phase. Then the reactor model, multiphase flow model,kinetic model, crushing model etc were established according to the experimental results of burningshale char in small and large scale fluidized bed furnace. The numerical simulation of burning shalechar in fluidized bed furnace was carried out by integrating the above models. By comparing andanalyzing the simulation and experiment results, the key reactions for the conversion of nitrogen oxidewere summarized and the basic transformation mechanism of them was obtained, some effectiveemission reduction measures have been proposed.During the research of industrial demonstration experiment of burning shale char in CFB boiler,the industrial demonstration experiments at two conditions selected according to the preliminaryresearch results were carried out in an industrial CFB boiler. The experimental results certified that theCFB boiler burning shale char could operate stably, the basic parameters remained stable, thecombustion efficiency could reach more than95%, and the pollutan emissions meet the national standard.