Characteristics Investigation On Biomass Chemical Looping Combustion And Gasification

Biomass chemical looping combustion and gasification technology have unique advantages in carbon emission reduction and biomass utilization, the technology changes the traditional extensive release way of chemical energy by disintegrating the combustion and gasification processes into independent two steps, realizing the cascade utilization of chemical energy in fuels; Recycling utilization of the oxygen carrier would save the cost, due to the similar reaction principles, chemical looping combustion and gasification can be controlled by regulating the reaction conditions, for different purposes of CO2 capture in combustion or obtain the syngas/hydrogen in gasification..This paper designed the thermal chemical looping experiments in fixed-bed reactor, specific to the typical biomass straw stalk, using Fe2O3 as oxygen carrier and aiming at investigating the influences of the temperature and oxygen carrier ratio had on syngas generation. The results showed that higher temperature meant to promote the decomposition of CH4 and the pyrolysis of coke or tar to form CO and H2; Under higher gasification temperature, the generation of CO and H2 during primary pyrolysis was suppressed while the Fe2O3 portion increased, CO yield in the secondary reaction also presented the effectiveness of rising first and falling later, but H2 generation was apparently promoted. Fe2O3 promoted the decomposition of tar and coke and enhanced the utilization rate of raw material, gas production rate and H2/CO2 yields, however, CO and other hydrocarbons yields were reduced and the same with the syngas heating value. Taken together, material: Fe2O3 = 1:1 was a proper ratio to produce H2 / CO syngas, when the ratio was below 1, CO2 rapidly increased to more than 50%.Combining with the TG experiments, it was observed that Fe2O3 devoted oxygen atom at high temperature as 780 oC, promoting the deep decomposition of primary pyrolysis products to form small-molecule gases. CO and CO2 released from the secondary reaction came out at 725 oC and 775 oC, and presented negative correlations with each other, indicating the existence of mutual transformation.TG- FTIR experiments indicated that biomass internal AAEMs could promote the pyrolysis of cellulose and form tar during regular gasification, anticipating the major weight-loss peak at the same time. Inorganic sodium and potassium lowered the precipitation temperature of initial volatile, inorganic magnesium and calcium enlarged the temperature range of cellulose pyrolysis and lowered the weight loss rate at the same time. Internal AAEMs lowered gasification temperature in higher temperature and promoted the coal gasification and chemical looping gasification to produce more CO2 in chemical looping gasification of straw. Inorganic sodium and potassium increased the intensity of weight loss peak at 800 oC, extended the gasification time of chemical looping gasification and improved the gasification efficiency. Inorganic magnesium had little impact on gasification period.Calcium ion attached to the biomass suppressed the oxygen-containing groups decomposition and absorbed CO2 in lower temperature. CaCO3 decomposed at 600 oC and released CO2, which increased the CO2 partial pressure of the system and inhibited the CO2 produced by decomposition of other oxygen-containing functional groups. All this resulted in the reactant amount increase in the chemical looping gasification at 700 ~ 1000 oC, giving a rise to syngas yield in this phase. Calcium ion promoted the decomposition of tar and suppressed the reaction of semicoke polycondensation for coke, thereby raising the gasification reaction degree, increasing the gas production rate and serving as an efficient catalyst for biomass chemical looping gasification.