Study On The Characteristics And Mechanism Of The Thermochemical Reaction Between Coking Wastewater And Gasification-coke

Coking wastewater treatment technology and coke gasification technology have always been the major concerns of clean coal utilization,and also an important basis for China to achieve"carbon emission peak"and"carbon neutrality".The process route proposed in this study utilizes coking wastewater and hot gasification coke for thermochemical reaction,which not only effectively utilizes the heat of hot coke to degrade pollutants in wastewater,but also produces syngas to prepare high value-added chemical products.Thereby,the resource utilization of coking wastewater can be realized.At present,the research on the thermochemical reaction between coking wastewater or organic matter in water and coke is not systematic and in-depth enough to guide the design,development and operation of the process route from a theoretical perspective.Therefore,it is particularly important to study the characteristics of the thermochemical reaction between coking wastewater and gasification coke and the thermochemical reaction mechanism.At the same time,this work also provides basic data and theoretical reference for the optimal design,practical application and stable operation of the process.In this study,a common industrial raw material for preparing gasification coke,Yuehua gas coal,and coking wastewater from a coking plant in Liaoning were selected as experimental raw materials.The thermochemical reaction characteristics of coking wastewater and gasification coke and the coking wastewater were systematically studied under the conditions of coke particle size ranging from 2 mm to 3 mm and water sample flow rate of 1.5 m L/min using a fixed bed thermochemical reactor at atmospheric pressure,revealing effect of the main organic pollutant（phenol）in coking wastewater on the thermochemical reaction of gasification coke.On this basis,the effects of phenol water concentration and reaction temperature on the thermochemical reaction of coke were further investigated,and the reaction kinetics were studied.Finally,through a series of characterization methods such as XRD,N₂ adsorption,SEM-EDS,Raman spectroscopy and multi-angle analysis methods,the evolution of the physicochemical structure of the gasification coke during the thermochemical reaction was deeply analyzed,revealing that phenol water can promote causes of coke thermochemical reactions.On the basis of the intermediate mechanism,a mechanism that can reasonably describe the thermochemical reaction between phenol water and coke-organic active intermediate mechanism is extended.The main contents and results of this thesis are as follows:（1）When the reaction temperature was 1000°C,the effects of pure water and coking wastewater on the thermochemical reaction of coke were comparatively studied.The thermochemical reaction characteristics of coking wastewater and gasification coke were analyzed by gas chromatography,gas chromatography-mass spectrometry,SEM,mercury intrusion instrument and other analytical methods,and some new discoveries and understandings were obtained.Compared with pure water,the thermochemical reaction of coking wastewater and gasification coke had a significant improvement and promotion effect on the volume,yield and calorific value of product gas（H₂,CO,CO₂ and CH₄）.Coking wastewater is more conducive to the thermochemical reaction of coke than pure water.In addition,the coke thermochemical reaction could significantly degrade the pollutants in the coking wastewater,with COD_Cr degraded by 87%and phenol,2-methylphenol and p-cresol by 75%,83%and 78%,respectively.（2）The previous experiments proved that phenol in coking wastewater plays a major role in promoting the thermochemical reaction of coke.On this basis,the effects of different concentrations of phenol water and different reaction temperatures on the thermochemical reaction of coke,as well as the thermochemical reaction kinetics,were further studied.The results showed that increasing the concentration of phenol water was beneficial to promote the generation of product gas and improved the thermochemical reactivity of coke.The degradation rates of phenol and COD_Cr in water were over 96%and 92%,respectively.Increasing the reaction temperature was more beneficial to the thermochemical reactivity of coke than increasing the concentration of phenol in water.Among the homogeneous model,unreacted shrinkage model and random pore model,the random pore model was the most suitable model to describe the thermochemical reaction;increasing the concentration of phenol water could effectively reduce the apparent activation energy of coke thermochemical reaction.The isoconversion method not only truly reflected the increasing trend of activation energy during the reaction,but also verified the reliability of the random pore model.（3）At the reaction temperature of 1000°C,coke samples at different reaction stages were prepared by a thermochemical reaction device.The thermochemical reaction mechanism between phenol water and coke was explored by various characterization and analysis methods such as XRD,Raman spectroscopy,and SEM-EDS.It was found that with the progress of the thermochemical reaction,the microcrystalline structure of coke carbon reacted with pure water and phenol water gradually developed towards the ordering direction.On the other hand,in the coke-carbon crystallite structure reacted with phenol water,the diameter of the carbon crystallite structure was significantly larger than that of the coke reacted with pure water,which was beneficial to increase the number of active sites and their contact area.In thermochemical reactions,phenol water preferentially consumed amorphous carbon structures or small aromatic ring systems.With the progress of thermochemical reactions,phenol water could promote the depolymerization of macrocyclic chemical structures in coke and gradually penetrate into the carbon matrix for reaction.In the coke reacted with phenol water,the number and types of organic functional groups of coke were more than pure water.Increasing the concentration of phenolic water was beneficial to the development of coke pore structure,increasing the proportion of coke micropores,thereby increasing the number of active sites.In the coke reacted with pure water,the ash phase had a scaly structure,and Al₂O₃,Si O₂ and Ca₂Al₂Si O₇ were found to be the main compounds on its surface,which would cause the sintering and agglomeration of ash phase as well as the prevention of the steam from further reacting with the coke.However,phenol water could effectively inhibit the sintering and agglomeration of the ash phase in the coke and improve its dispersibility on the carbon surface.Through systematic experiments and multi-angle analysis methods,the reason why phenol water can promote the thermochemical reaction of coke is revealed,and a mechanism that could reasonably describe the thermochemical reaction between phenol water and coke on the basis of the intermediate mechanism,i.e.,organic active intermediate mechanism,was proposed.