Experimental Study On Enhanced Reforming Of Tar Based On Double-Effect Nickel-Based Catalyst

Tar is an inevitable by-product of coking industry.Its composition is complex and its output is large.It also has the hazards of blocking pipelines,corroding equipment and polluting environment.At present,the tar removal process has the problems such as:waste of water resources,waste of waste heat resources and cumbersome process.In recent years,researchers have carried out studies on tar removal by reforming method.Tar gas is mixed with water vapor and a series of reactions take place under the action of catalyst to obtain small molecular gases such as H2,CO,CO2 and CH4.However,most of the research objects are tar modulates and the catalytic properties of catalysts are not ideal.In order to solve the above problems,this study carried out an experimental study on removal of tar by adsorption enhanced steam reforming with Ni-CaO-(CaO)12(Al2O3)7 dualeffect catalyst.The purpose of this study is to use double-effect catalyst to catalyze tar water vapor to react and generate small molecular gas with high H2 concentration.The CO2 generated by the reforming reaction was adsorbed and fixed by the double-effect catalyst,which increased the concentration of H2,and promoted the reforming reaction to a deeper level.The specific work of this topic includes:(1).On the basis of component analysis and elemental analysis of tar samples,thermodynamic analysis is carried out on the process of adsorption enhanced steam reforming,and the reforming reaction results are predicted from the perspective of reaction equilibrium,so as to provide theoretical basis for subsequent experiments.(2).Based on Ni-CaO-(CaO)12(Al2O3)7 dual-effect catalyst,adsorption enhanced steam reforming experiment of tar was carried out to investigate the influence of temperature,water-carbon ratio and catalyst filling amount on reforming characteristics,and the optimal reaction conditions were obtained.(3).Ce,Fe and Mg doped double-effect catalysts were modified to analyze the role of Ce,Fe and Mg in the adsorption enhanced steam reforming of tar.The influences of different doping ratios on double-effect catalysts were investigated to optimize the performance of the catalysts.The conclusions are as follows:1.The components of tar samples are mostly cyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons,which are basically macromolecular organic compounds above C6.If tar is regarded as a compound,its chemical formula can be expressed as C10H7.21O0.98.2.Thermodynamic analysis showed that the main products of adsorption enhanced reforming reaction were H2,CO,CO2 and CH4.A rise in temperature will promote the reforming reaction,water gas shift reaction,and the optimal reaction temperature range is 500?700 ?.The improvement of water-carbon ratio can promote the progress of adsorption enhanced reforming reaction.However,with the increase of water-carbon ratio,the promotion effect gradually weakens.In addition,the improvement of water-carbon ratio can significantly reduce the carbon deposition rate of reforming reaction.Compared with ordinary steam reforming reaction without adsorption process,the hydrogen yield and H2 concentration of adsorption enhanced reforming reaction are higher,the optimal reaction temperature is significantly lower and the optimal reaction temperature range is wider.3.Adsorption enhanced reforming reaction of tar experimental results show that using NiCaO-(CaO)12(Al2O3)7 dual-effectc atalyst the largest hydrogen yield was 83.29%,under the condition of temperature 740?,water/carbon ratio of 15,and 30 g catalyst filling quantity.For tar adsorption enhanced reforming reaction,the rise of temperature will lead to an increase first and then decrease in hydrogen yield,and hydrogen yield can reach 80%in 700?800 ? temperature range;The increase of water-carbon ratio can also increase the hydrogen yield.The increase of catalyst filling amount can significantly reduce the CO2 concentration in the product,but the change range tends to be flat when the filling amount reaches 16g.In addition,the increase of catalyst filling amount also has a certain impact on the improvement of hydrogen yield and CO concentration.4.Ce doping can change the distribution of original active component Ni,promote the tar cracking reaction,water gas shift reaction,but excessive doping amount will cause the accumulation of the active material to reduce the catalytic effect,Ce modified catalyst with doping mass fraction of 6%showed the best catalytic activity,hydrogen yield could reach 86.84%.Fe doping can improve the adsorption performance of the original catalyst and promote the water gas shift reaction.In the reforming experiment,the modified catalyst with doping mass fraction of 9%and 12%showed higher activity,and the hydrogen yield was 85.54%and 85.80%,respectively.The doping of Mg can change the morphology of the active component from a small sphere to a prickly sphere,and increase the hydrogen production rate.Excessive doping can weaken the catalytic performance of the original catalyst but improve the stability of the catalyst.In the reforming experiment,when the mass fraction of Mg doped was 3%,the hydrogen yield was the highest,which was 85.22%.