Study On Hydrogen Production By Synergistic Electrolysis Of Coal Slurry And Wastewater

As an important secondary energy source,hydrogen energy is critical to China’s energy security,regional environmental pollution control,and the response to global climate change.Water electrolysis,one of the significant means of hydrogen production,has many considerable advantages.However,its application and development are limited due to the high electricity consumption.Coal slurry electrolysis for hydrogen production reduces the electricity consumption as oxygen evolution is replaced by coal oxidation at the anode,but its disadvantage is the low electrolysis rate.At the same time,China is rich in coal resources,and the wastewater of coal chemical industry needs to be utilized as resources.Based on these factors,this paper puts forward hydrogen production by synergistic electrolysis of coal slurry and wastewater,and that the wastewater of coal chemical industry can be used to improve the effect of coal slurry electrolysis for the first time.In this paper,the characteristics of hydrogen production from various wastewater coal slurry electrolysis are studied.Meanwhile,the influencing factors and the influencing mechanism of wastewater on coal slurry electrolysis are explored.The main research contents and conclusions of this paper are as follows:In the experiment,sulfur wastewater,gasification wastewater,slag discharge wastewater,external wastewater,carbonized wastewater,coking wastewater and Lurgi gasifier wastewater are used to prepare wastewater coal slurry.It is found that sulfur wastewater,gasification wastewater and slag discharge wastewater are beneficial to hydrogen production by coal slurry electrolysis.Then,taking the gasification water as the representative of the wastewater,it is found that compared with the electrolysis of water and coal slurry,the electrolysis of gasification wastewater coal slurry（GWCS）has significant advantages in reaction rate and energy consumption.Hydrogen production from electrolysis of GWCS is feasible from the angle of hydrogen current efficiency and hydrogen purity.The hydrogen current efficiency is 99% and the hydrogen purity is 98%.The gas produced from the anode is mainly CO₂,containing a small amount of CO.In the electrolysis process,the anode electrolyte shows "carbon reduction and oxygen increase",and COD decreases.For a long time,with the consumption of high reducing organics in the gasification wastewater,the current density gradually decreases but is higher than that of coal slurry electrolysis.In order to explore the influencing factors of electrolysis process,the experimental parameters were changed.It is found that with the increase of stirring rate,the current density curve first rises sharply and then slows down.The concentration and type of coal powder,the presence or absence of catalyst and the concentration of catalyst mainly affect the oxidation of coal particles,whose corresponding voltage range is 0.7-1V,but there is no effect in the voltage range of 1-1.3V.In the voltage range of 0.7-1V,the electrolysis rate will increase with the addition of Fe³⁺ and when coal with low metamorphic degree and small particle size is used.With the increase of coal concentration,the current density will increase,but with the excessive coal,the agglomeration and precipitation of coal particles will be caused,which will weaken the promotion effect of coal concentration on the current density and even reduce the current density.With the increase of the concentration of Fe³⁺,the current density curve shows a trend of sharp rise first,and then gradually slows down.The change of the temperature and the concentration of the gasification wastewater has an effect on each voltage range.The influence rule of gasification wastewater concentration is that with the increase of gasification wastewater concentration,the current density first rises sharply,then slows down or even decreases.The influence of temperature is in accordance with Arrhenius equation,and the apparent activation energy of the electrolysis of GWCS on 1.1V is 45.75 k J/mol.The influence mechanism of gasification wastewater on coal slurry electrolysis was studied through numerical simulation and single component control.It is found that the addition of gasification wastewater can improve the conductivity of electrolyte,but has little effect on the electrolysis process.Cl^-in gasification wastewater affects the electrolysis at the stage of coal particles oxidation and chlorine evolution.Then the mechanism of the influence of gasification wastewater on coal slurry electrolysis in different voltage range is put forward.In the range of 0.7-1V,the main reaction is the oxidation of coal particles,which includes both direct oxidation and Fe³⁺ catalytic oxidation,and generates intermediate oxidation products and CO₂ gas.Cl^-in gasification wastewater is adsorbed on the surface of coal particles,which makes the coal particles move more easily to the electrode,accelerates the oxidation of coal particles and improves the electrolysis rate.In this voltage range,the secondary reaction is the catalytic oxidation of some organics in gasification wastewater by Fe³⁺.In the range of 1-1.3V,the main reaction is the oxidation of high reducing organic compounds in gasification wastewater,which is not catalyzed by Fe³⁺,and generates intermediate oxidation products and CO₂ gas.In the early stage of constant voltage electrolysis,the main reaction is the oxidation of high reducing organic compounds in gasification wastewater.In the later stage,the oxidation of coal particles occurs,which is similar to that in the voltage range of 0.7-1V.Above 1.3V,the main reaction is chlorine evolution.In addition,the synergistic oxidation of Cl^-,Fe³⁺,and coal particles takes place.The high valence chlorine participates in the oxidation process of coal particles.