The Study On Mechanism Of Chemical Looping Gasification Of Chlorella Vulgaris Based On Microwave Pretreatment

As a renewable green energy source, biomass has received more and more concern and attention with the increasingly serious envirionmental pollution and energy shortages problem. Microalgae, which is the third generation biofuel, has become the focus of the current research, owing to the short growth cycle, high biological yield, rich oil content, no occupation of agricultural land and the ability to fix CO2. Microalgae gasification is an important technology direction of microalgae energy utilization, wherein chemical looping gasification, as a novel gasification technology, has attracted the attention of researchers. At present, the foreign and domestic researches of chemical looping gasification biomass is still at the initial stage. Moreover, the research combining with microwave pretreatment has not been reported. In additon, there are many deficiencies in the study of mechanism and technogoly. Therefore, Chlorella vulgaris was the research object of this study. And then the study in-depth investigated the chemical looping gasification based on microwave pretreatment about the syngas characteristics, solid residue performance, TG properties, FTIR characteristics of gaseous products and the evolution behavior of solid residue structure, in order to understand and reveal the mechanism of chemical looping gasification based on microwave pretreatment. Moreover, this study has an improtant practical significance.Firstly, the reaction characteristics of chemical looping gasification Chlorella vulgaris were studied in the tubular fixed bed reactor in order to obtain the characteristics of syngas production, performance of solid residue and the optimal operation parameters. The results showed that CLG could significantly promoted the gasification reaction of Chlorella vulgaris. Compared with the conventional gasification, CLG increased significantly the gaseous products by 24.67 %. Moreover, there were obviously increase in H2, CO, CH4, CO2, gas yield, low heation value, carbon conversion and gasification efficiency of CLG. In addition, with the increase of oxygen carrier content, CLG improved gradually the gaseous production, CO2, gas yield, carbon conversion efficiency and Fe3+ content, but decreased H2,CH4 and low heation value, while CO and gasification efficiency increased first and then decreased continuously. With the increase of temperature, gaseous production, gas yield, carbon conversion efficiency and gasification efficiency increased firstly and then decreased, but CO2 and CH4 concentration decreased, while H2 and CO concentration increased. Therefore, 1.0 was the best proportion of oxygen carrier/Chlorella vulgaris. Moreover, 800℃ was the optimal temperature of CLG reaction and oxygen carrier oxidation.Secondly, the CLG experiments were studied in the tubular fixed bed reactor under different microwave pretreatment power and time, in order to obtain the influence of sygnas characteristics under microwave pretreatment conditions and the optimal microwave pretreatment condition. The results showed that CO, H2, LHV, gas yield, carbon conversion efficiency, gasification efficiency and Fe2+ content increased firstly and then decreased with the increase of microwave pretreatment power. On the contrary, CO2 concentration decreased firstly and then increased gradually, while CH4 concentration decreased continuously. With the increase of microwave pretreatment time, H2, CO, CH4, LHV, gas yield, carbon conversion efficiency, gasification efficiency and Fe2+ content increased firstly and then decreased, however, CO2 concentration decreased firstly and then increased gradually. In addition, the structure of solid residue became loose in appropriate microwave pretreatment power and time. Therefore, 750 W and 60 s were the optimal microwave pretreatment power and time respectively.Thirdly, the influence of CLG were studied in the thermalgravimetric analyzer under different heating rates and pretreatment conditions, in order to obtain the TG characteristics and kinetic parameters, and establish the reaction kinetic model of CLG. The results showed that the gasification process could be divided into four stages of drying, pyrolysis, char gasification, mineral decomposition and char gasification. Pyrolysis stage was the biggest weightlessness, followed by char gasification. The effect and reactivity of CLG were better than that of pyrolysis, specially, the effect and reactivity of microwave pretreatment were better. The solid conversion rate of CLG increased by 38.68 %, which continue to improve by 14.23 % after the microwave pretreatment. With the increase of heating rate, the weight loss rate, solid conversion rate, reactivity rate and reactivity of CLG enhanced, the reaction temperature raised, and the weight of solid residue increased. The fitting effects of Homogeneous Model were better than that of Shrinking Core Model in three main reaction stage. In addition, the suitable microwave pretreatment could reduce the activation energy and promote effectively CLG.Subsequently, the characteristics of CLG under different reaction conditons were analyzed by the TG-FTIR combined technique in order to obtain the characteristics of thermogravimetric and gaseous products, and the evolution path of gaseous products under CLG Chlorella vulgaris based on microwave pretreatment. The results showed that pyrolysis stage is the main precipitated interval of C-O(alcohols, phenols and ether), C=C(aromatic compounds), C=O(aldehyde, ketone, acid and ester), NH3 and HCN. NH3 and HCN emissions could be inhibited by CLG and microwave pretreatment, in particular, the emissions were lower after microwave pretreatment. In addition, the main precipitated interval of CO was pyrolysis and gasification stage. Moreover, CO emission increased in CLG, and CO emission was largest after microwave pretreatment. H2 O, CO2 and CH4 emissions of CLG were more than that of pyrolysis, however, after microwave pretreatment their emissions decreased but more than that of SiO2:Chlorella condition.Finally, the chemical structure of solid residue was analyzed by infrared pressing technology at a constant temperature, in order to obtain the variation of each chemical group and reveal the evolution behavior of the major functional groups and structures. The results showed that the first 1 min reaction was the main weight loss stage, followed by the 1 ~ 10 min reaction. Besides, the reaction performance of CLG was significantly higher than pyrolysis, in particular, the reaction performance was better after microwave pretreatment. After CLG, the functional groups of-OH、C-H、-CH2、-CH3 and C=O carried out fracture, condensation, restructuring and aromatization reactions, then precipitated H2 O, CH4, C2H4, C2H6, CO2 and other small molecule gaseous products. Therefore, these reactions reduced the absorption peak intensity of-OH, C-H,-CH2,-CH3 and C=O. with the increase of reaction time, the absorption peak intensity of aromatic nucleus C=C, ether bond and Fe2O3 increased first and then decreased gradually, in particular, the absorption peak intensity decreased obviously after microwave pretreatment. In addition, the absorption peak intensity of S=O reduced in CLG, but produced more H2 S and SO2, particularly, microwave pretreatment was beneficial to reduce the SOX pollutant emissions in the subsequent reaction.