Experiments On Coal And Biomass Chemical Looping Gasification Based On CaO Sorbent

With the rapid development of human society,the consumption of energy is increasing every year.It is widely accepted that the coal plays an important role in CO₂ emission.The CO₂ Capture and Storage（CCS）technology is an effective way to reduce the CO₂ emission.Chemical looping technology is a new type of chemical conversion and energy utilization technology,which will not only avoid the disadvantages of traditional technology,but also realize the CO₂ capture with low cost.Thus,the chemical looping technology is considered as the most promising technology.The calcium-based chemical looping gasification received many attentions for reasonable price,wide resources,and the possibility to coupling with fluidized bed technology.The principle is:the lignite or biomass is introduced into the gasifier with steam,and the generated CO₂ is captured by the carbonation of CaO.Then CaCO3 is formed and be transferred into combustor.After the calcinations of CaCO3,the generated CaO will be transferred into gasifier again.Currently,the chemical looping gasification technology is still in its initial stage.In this paper,the effects of different parameters and feedstock on the components of gasification products will be studied.The calcium-based biomass/lignite chemical looping gasification experiments are performed on the dual fluidized bed facility.With the chosen parameters of gasification temperature（650-750℃）,H2O/C molar ratio（1.6-3.2）,Ca/C molar ratio（0-2）.The results obtained can be summarized as:with the increase of gasification temperature,H2O/C molar ratio and Ca/C molar ratio,the content of H2 in the product gas is rising.At the same time,the increase of gasification temperature and H20/C molar ratio led to the decrease of CO and CH4 and the rise of CO₂ for both feedstock.The addition of CaO has a great influence on product gas for both feedstock.With the increase of Ca/C molar ratio from 0 to 1,the concentration of H2 in product gas increased by more than 30%,and CO₂ decreased by about 20%.The CH4 showed different reactions when fed with different feedstock,when Ca/C ratio is rising.CH4 concentration increases with the increasing of Ca/C ratio when fed with biomass,but V decreases when fed with lignite.Moreover,when the Ca/C ratio continued increasing after it reaches 1.5,gas components changes inconspicuously.The persistent experiment of calcium-based chemical looping biomass/lignite gasification is also performed.The experimental results shows that,CO₂ capture capacity of CaO decreased within experiment for both feedstock,which led to the descend of H2 concentration in product gas through the experiment,and the rise of CO,CH4 and CO₂ concentration.Compared with biomass,when lignite is fed into reactor,the CO₂ capture capacity of CaO absorbent,descends more rapidly（30%to 10%）.Higher content of S in lignite,which has a great influence on CO₂ capture capacity of CaO,is the reason.When biomass or lignite is fed into reactor,the cold gas efficiency reached 71.54%,83.62%and the carbon content in product gas reached 39.12%,41.47%,respectively.Moreover,the cold gas efficiency and the carbon content in product gas of lignite are higher than that of biomass.If the question caused by S in lignite can be solved,or the S in lignite can be easily removed,lignite appeared to have more advantages as the feedstock of chemical looping gasification than biomass.