Study On The Charicteristic And Kinetic Of Biomass And Coal Co-pyrolysis

Biomass and coal co-pyrolysis is a great potential technology and a relative new researchfield in the world. Its core problem is the synergistic effect of co-pyrolysis. Under ourlaboratory conditions, the co-pyrolysis synergistic effect of6kinds of biomasses and coalswere studied and investigated in this thesis. Distribution activation energy method （DAEM）was introduced into this thesis to study the co-pyrolysis kinetics of biomass and coal, and to getthe co-pyrolysis related kinetics parameters. The aim of this thesis is to find more effectiveways to achieve the synergistic effect in biomass and coal co-pyrolysis. This main researchcontents and results are summarized as follows:1. Slow co-pyrolysis behavior of biomass and coalMono-pyrolysis and co-pyrolysis of biomass and coal were studied by using the TG-FTIRtechnology. It is found that the actual co-pyrolysis degrees are deeper than the theoretical ones.The effect of biomass and lignite co-pyrolysis is the best with actual results deviatingtheoretical value greatly. The synergistic effects are expressed as the biomass catalytic effect oncoal at high temperature region. According to results of the TG-FTIR, it can be concluded thatthe oxides of Fe, Ca, Mg, Si, and other trace elements in biomass inhibit the formation of coalcolloid, and make the initial gas product of coal pyrolysis be able to escape. Synergistic effectaccelerates coal pyrolysis to produce gas and decrease liquid products. The bimetallic dolomitebased catalyst further promotes the co-pyrolysis reaction, and improves the carbon conversionrates and utilization of raw materials in the co-pyrolysis process.2. Fast co-pyrolysis behavior of biomass and coalFast co-pyrolysis process of biomass and coal were studied in a small fixed-bed reactor. Itis found that the pyrolysis temperature impact on fast co-pyrolysis of biomass and coalsignificantly. The synergistic effect is more obvious in the higher temperature. With theincrease of temperature, the H₂content and gas product yields increase, and the solid productyields greatly decrease. The deviation of theoretical value and actual value of co-pyrolysis gas and solid yields fully prove that the synergistic effect in fast co-pyrolysis process. Gasproductions increase with incremental biomass ratio in blending raw material. Biomass andcoal fast co-pyrolysis reaction can obtain hydrogen-rich gaseous products. Especially, when theratio of sawdust to bituminous is2to8, fast co-pyrolysis reactions get highest H2content of42.53%. The CO production decreases in higher biomass mixing ratio. The CO₂actual yield islower than the theoretical value. The CH₄yield decrease with the coal rank and biomass to coalratio increase. However, co-pyrolysis process effectively improves the production of otherhydrocarbons.3. Fast co-gasification behavior of biomass and coalSteam fast co-gasification and mixing water fast co-gasification processes were studied ina small fixed-bed reactor by fast heating-up mode. Steam fast co-gasification of biomass andcoal can produce hydrogen-rich gaseous products, and promote the H₂/CO to3-4, butsignificantly reduces the yield of CO and hydrocarbon. CO₂production change of this processis not very remarkable. Mixing water fast co-gasification process of biomass and coal canpromote the synergistic effect occur. The gaseous product yield of biomass and coal mixingwater fast co-gasification significantly increases. With the co-gasification reaction temperaturerise, the H2content increases significantly, while a slight decrease for the CO content occurs.Comparing the two methods of co-gasification, it can be concluded that steam fastco-gasification get the hydrogen-rich gas which is suitable for synthesizing liquid fuels,especially as the raw gas of methanol synthesis, while mixing water fast co-gasification getmuch higher heat value combustible gas which can be used for burning, power generation andgas supply.4. Co-pyrolysis behavior of torrefaction biomass and coalThe process and product of slow and fast co-pyrolysis of torrefied biomass and coal werestudied by TG analysis technique and a small fixed-bed reactor respectively. In the slowco-pyrolysis research, it can be concluded that250℃and30min is a suitable torrefactioncondition for biomass. The torrefaction of biomass is better for biomass and lignite fast co-pyrolysis to get more gaseous product. Fast co-pyrolysis reactions of torrefaction biomassand coal have the effect of reducing H2content significantly, increasing CO content a bit andaccruing CO2and CmHncontent vastly. However, the heat values of gaseous product arechanged slightly. Fast co-pyrolysis of torrefied biomass and coal has a positive effect onlowering tar yield.5. Kinetic analysis of biomass and coal co-pyrolysis and tar catalytic crackingIn this part, Coats-Redfern and DAEM methods were used to analyze the dynamiccharacteristics of biomass and coal co-pyrolysis. In Coats-Redfern method, heating rates haveless effect on the activation energy, but have some influences on pre-exponential factor. Theco-pyrolysis process is divided into some single reactions, and lower activation energy which isan average value of whole pyrolysis process is obtained. Average activation energy is difficultto describe the whole co-pyrolysis process. So Coats-Redfern is not the most effective methodto simulate co-pyrolysis kinetics. An activation energy function that change with theconversion rate is obtained by DAEM mode. The activation energy fuction shows an increased-smooth-increased trend. When using DAEM method to simulate the whole co-pyrolysisprocess, pre-exponential factors go up with the increase of activation energy and showcompensation effect. The Gaussian fitting for co-pyrolysis process has good correlations whichprove the excellent applicability of the DAEM for co-pyrolysis process. The test co-pyrolysisactivation energy values are lower than the calculated ones which further verify the existenceof synergistic effect in the co-pyrolysis process.The catalytic characterizations were tested with tar simulated by naphthalene.93%naphthalene is decomposed at950℃. Activation energy of63.96kJ/mol and pre-exponentialfactor of396.2/s are calculated, which shows the lowest apparent activation energy in allreferrences. A first order apparent kinetic model is developed.r_A=396.2×exp（-925.34×1/T）C_A...