| Oil shale,a kind of potential and tremendous energy resource,is only next to coal in terms of the calorific value among the fossil fuels in the world.As spent shale,semi-coke is a low-grade fuel with low volatile,low calorific value,high ash content and is difficult to ignite and burnout.At same time,semi-coke has serious pollution to environment.Oil shale was retorted in a laboratory-scale fixed bed reactor to obtain semi-coke.After physicochemical properties and microstrnctures of oil shale and semi-coke were investigated,systematic theory and experimental investigations were conducted for the blends.Combustion experiments of the blends were conducted on thermo-gravimetric analyzer (TGA) with different heating rate,retorting temperature,particle size and blends ratio respectively.Theoretically,combustion kinetics has been determined by distributed activation energy model(DAEM) and activation energy profiles were analyzed.Based on compensation effect incorporation with TG curves,reactivity and prediction ability,co-combustion kinetics was studied in detail.The results indicated that some synergistic effects occured between oil shale and semi-coke during combustion and those effects improved combustion characteristics and reactivity.Logistic function was applied to simulate combustion process and the prediction ability of kinetic parameters was different at different stages.Combustion experiments of oil shale and semi-coke were conducted in bench-scale FBC reactor.Ash samples were obtained under different bed temperature and different resident time.Adsorption and desorption isotherms of samples were determined by Micromeritics Gemini 2380 specific area analyzer under nitrogen atmosphere.The specific surface area and pore size distribution were determined on the basis of BET and BJH theory respectively. While surface fractal dimensions were calculated with FHH model.The results indicated that the specific surface area and porous volume of oil shale ash increased first and then decreased whereas porous volume of semi-coke ash deceased all along with resident time increasing; Low combustion temperature favored the formation of porous structure.At early stage of combustion,the fractal dimension of ash samples increased sharply,and then decreased slightly.At the same time,the fractal dimension of all ash samples was significantly higher than that of original samples. Ignition and burnout characteristic of the blends were studied with different combustion modes.Changes of combustion technique related to different experimental conditions had strong effects on ignition mechanism.Oil shale fixed bed experiment and fluidized bed experiment for pulse feed indicated a homogeneous ignition mechanism.Oil shale ignition mechanism of fluidized bed experiment for once feed shifted from homogeneous to heterogeneous one.Ignition temperature was affected by different combustion technology to some extent.There was a lower ignition temperature for fixed bed experiment than others. Ignition temperature was high for once feed in fluidized bed experiments.CFBC pilot was set up for combustion of oil shale and semi-coke.Co-combustion of the blends was conducted in different conditions such as blends ratio,bed temperature and primary air ratio.Distributions of temperature,flue gas composition were obtained.The result of tests showed that semi-coke was suitable for combustion in CFB and the ash could be utilized as build material when the primary air ratio was not less than 66.7%.The combustion was even improved when 10～20 percent oil shale was added.The results may provide theoretical foundation for the design of large-scale CFB boiler fired with oil shale semi-coke.
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