Experimental Study On Cotton Stalk Microwave Pyrolysis Of Gas-Carbon Cogeneration

With the depletion of primary energy sources such as fossil energy,and the increasing amount of agricultural straw waste,the necessity and urgency of developing and using biomass energy is increasing.There are many ways and methods of using biomass resources,but there are few studies on the use of the microwave as a heating source for pyrolysis of crop stalks,especially one of China’s important economic crops which has huge yields:cotton stalk.In recent years,more and more scholars use microwave as heating source for pyrolysis research.How to use microwave as a heating source to pyrolysis cotton stalks and transform them into products with higher economic value is a great research direction which must be developed.Microwave pyrolysis biomass to produce high utilization value and high added value products is a relatively advanced waste straw treatment method.In this paper,"Zhongmian 60" cotton stalks were used as the research object,and the pyrolysis characteristics,products distribution characteristics,and gas phase products characteristics of cotton stalks under different process parameters were explored using thermal gravimetric analysis and gas phase analysis,and optimized the process parameters for producing products with the highest calorific value of combustible gas.In this paper,the main conclusions obtained from the experimental research of microwave pyrolysis gas-carbon combined production on cotton straw represented by "Zhongmian 60" are as follows:1.Pyrolysis characteristics analysis and thermodynamic analysis were performed on"Zhongmian 60" cotton stalk under different process parameters,and two thermodynamic parameters of cotton stalk pyrolysis,the apparent activation energy E and pre-factor K0,were obtained.The heating rate was one of the most important factors affecting the pyrolysis of cotton stalks.At a heating rate of 25K/min,the apparent activation energy of cotton stalk pyrolysis was 44.25kJ/mol.For impact of the additives,different additives had different degrees of improvement on the pyrolysis rate of cotton stalk.Among them,the maximum weight loss rate of cotton stalk decreased when NaOH and Na2CO3 were used as additives,and the maximum weight loss rate was increased when NaCl as an additive.2.By studied the effects of several factors on the pyrolysis characteristics and products distribution of cotton stalk,the following conclusions were obtained:moisture content,microwave power,and additive all had certain effects on the heating rate of cotton stalk microwave pyrolysis,and the effect of material size on it was scarcely.For moisture content,higher moisture content improved the heating efficiency of pyrolysis in the high temperature section,but higher moisture content caused the overall heating efficiency of the material to decrease.When the moisture content of the material was 24%,the overall heating efficiency was higher.For microwave power,increased the microwave power in a certain range can improve heating efficiency and final reaction temperature.For the effect of the additive on the heating rate of cotton stalk microwave pyrolysis,in addition to the fact that NaCl plays a reverse role in the pyrolysis rate,ZnCl2,NaOH,Na2CO3,and BioChar had significantly improved the reaction rate.Changes in cotton stalk size did not significantly change the heating rate of microwave stalk.Microwave power and moisture content had a greater impact on the distribution of three-phase products of cotton stalk microwave pyrolysis,while changes in material size had little effect on it.With the increased of microwave power,the proportion of gas phase products gradually increased,while the solid phase and liquid phase products gradually decreased.With the increased of moisture content,the proportion of solid-phase products decreased,the proportion of gasphase products increased first and then decreased,and the proportion of liquid-phase products increased.When the moisture content was 40%,the yield of gas phase products reached the highest value of 65.18%;when the moisture content was 48%,the yield of liquid products reached the highest value of 24.54%.The effect of additives on the distribution of three-phase products of microwave stalk pyrolysis of cotton stalks was vague,but the addition of all additives except Bio-Char reduced the proportion of gas-phase products to a certain extent.3.The single-factor tests were used to analyze the gas phase products of cotton stalk microwave pyrolysis,and the microwave power and moisture content were considered to be the more obvious factors affecting the high calorific value of flammable phase products of cotton stalk microwave pyrolysis:With the raised of microwave power,the calorific value of gas-phase products had a certain upward trend.Appropriate moisture content improved the microwave absorption efficiency of cotton stalks,as the moisture content increased,the high calorific value of the combustible gas increased first and then decreased,and when the moisture content was 32%,maximum high calorific value(HCV)reached 23737.1kJ Material size had less effect on pyrolysis.The ratio of the additive to the liquid products had a positive effect,but it had a negative effect on the high calorific value of the gas products.By using the central composite design method and using the high calorific value of the gas products as an indicator,the relationship between the high calorific value of the gas product and the microwave power(A),moisture content(B),and material size(C)was as follows:HCV=165.319-9.049A+8.714B-5.591C+2.751 ACAccording to analysis,when the microwave power was 2.8kW,the material size was 3.39mm,and the moisture content was 33.51%,the high calorific value of the gas products generated from 1kg of raw material could reach 24043.1kJ.It is verified through experiments that the high calorific value of gas products produced by pyrolysis 1kg of raw materials under these conditions reached 23681.7kJ,with an error of 1.5%.