Influence Of Potassium Salts On Hydrogen Production From The Enhanced Steam Gasification Of Biomass

Hydrogen is one kind of the promising clean energ, and biomass is considered as the ideal primary energy source for replacing the fossil fuels to produce hydrogen. With the advantage of CO2 low emission, Ca-based biomass enhanced steam gasification for hydrogen production gets much attention in the recent years. Combination of CO2 capture enhanced hydrogen production from biomass steam gasification and catalysis of potassium salts in the low temperature, driving the existing hydrogen production process from high temperature to low temperature, the high efficient catalytic gasification technology for hydrogen production is achieved. With the favor of national sicence foundation of China “Mechanism study on the CO2 capture enhanced hydrogen production from low-temperature catalytic gasification of straw”, the effect of alkali metal K on hydrogen production in the enhanced biomass steam catalytic gasification was investigated.Firstly, a fixed bed gasification system, combining with gas chromatography, was used to study the effect of the K₂CO₃, KCl, CH3 COOK and K2SO4 on hydrogen-rich gas production in the steam gasification of biomass. The results showed that the K₂CO₃ dominantly catalyzed the pyrolysis of wheat straw in the low temperature and the low steam mass. The catalysis effect of the steam gasification of wheat straw char gradually increased with the rise of the temperature and S/B and achieved optimum catalytic effect in the temperature of 700℃ and the S/B of 4 which could get the maximum concentration and yield of H2. The catalytic effect of different K salts on hydrogen production in the steam gasification of biomass was researched. There were different effects with different salts. K2SO4 and KCl would restrain the hydrogen production and promote the char generation. On the contrary, K₂CO₃ and CH3 COOK would significantly promote the hydrogen production in the steam gasification of wheat straw and the catalytic effect of K₂CO₃ was superior to CH3 COOK.Secondly, the effect of KCl, K₂CO₃ and K2SO4 on Ca O catalytic absorbents in biomass volatile steam reforming was investigated via a two-stage gasification system. The results showed that a small amount（0.25 wt.%） of KCl was more beneficial to the Ca O carbonation performance and the excess amount（5wt.%） of KCl was more beneficial to the Ca O catalytic performance. For 0.25 wt.%KCl/Ca O catalytic absorbents, the optimum reaction temperature is 650 oC, the steam injection rate is 0.1-0.15 g/min, where the absorbent has the best carbonation performance. The carbonation performance would be seriously inhibited with the reaction temperature continued rise. There were different effects with different salts on Ca O: Be different with KCl, a small amount of K₂CO₃ would slightly suppress Ca O carbonation performance, but it cound also effectively inhibit the generation of CO2 from reforming reaction; Although K2SO4 cound improve Ca O carbonation performance, it would significantly inhibit volatile steam reforming.Finally the influence of KCl and K₂CO₃ with 5wt.% and 0.25 wt.% concentrations on the Ca O cyclic catalytic property in five times was in-depth studied. The pure Ca O was unstable and the catalytic activity rapidly decreased overall with the number of the cycles. Both of the potassium salts cound improve the cyclic reaction activity of Ca O-based catalysts, inhibit catalytic activity decay, keep the catalytic stability and increase catalytic cycle life. The improved effect of the four potassium salts showed: 5wt.%KCl>0.25 wt.%KCl>0.25 wt.%K₂CO₃>5wt.%K₂CO₃.