Liquid chemical looping gasification of biomass: Thermodynamic analysis on cellulose

Wei Guo, Bo Zhang, Jie Zhang, Zhiqiang Wu,2,*, Yaowu Li, Bolun Yang

1 Shaanxi Key Laboratory of Energy Chemical Process Intensification, School of Chemical Engineering and Technology, Xi’an Jiaotong University, Xi’an 710049, China

2 State Key Laboratory of High-Efficiency Utilization of Coal and Green Chemical Engineering, Ningxia University, Yinchuan 750021, China

3 Nuclear Power Institute of China, Chengdu 610213, China

Keywords:Liquid chemical looping conversion Biomass Thermodynamics Product distribution Oxygen carrier Simulation

ABSTRACT Liquid chemical looping technology is an innovation of chemical looping conversion technology.Using liquid metal oxide as the oxygen carrier during gasification process could prolong the service life of oxygen carrier and improve the process efficiency.In this paper, based on Gibbs minimum free energy method,the thermodynamic characteristics of biomass liquid chemical looping gasification were studied.Cellulose and lignin,the main components of biomass,were taken as the research objects.Bismuth oxide and antimony oxide were selected as liquid oxygen carriers.The results showed that when the temperature increased from 600 °C to 900 °C, the output of H2 and CO in the products of cellulose gasification increased from 0.5 and 0.3 kmol to 1.3 and 2.6 kmol respectively.Different ratios of oxygen carriers to gasification raw materials had the best molar ratio.The addition of steam in the system was beneficial to the increase of H2 content and the increase of H2/CO molar ratio.Bi2O3 and Sb2O3 with different mass ratios were used as mixed oxygen carriers.The simulation results showed that the gasification temperature of biomass with different mixed oxygen carriers had the same equilibrium trend products.It could be seen from the results of product distribution that the influence of the mixing ratio of Bi2O3 and Sb2O3 on gas product distribution could be neglected.These results could provide simulation reference and data basis for subsequent research on liquid chemical looping gasification.

1.Introduction

The use of renewable energy has attracted much attention.Biomass is the most abundant renewable resource on the earth, and plays an important role in the whole energy system[1-3].Besides,biomass is carbon neutral,and the carbon released during its use is equivalent to the carbon absorbed through photosynthesis during its life cycle.Therefore,the utilization of biomass energy is of vital positive significance for alleviating the energy crisis and environmental problems [4].The biomass chemical looping gasification(BCLG)can avoid the environmental problems caused by the traditional gasification with great development potential [5-9].

BCLG coupling strengthens the reaction separation process,and transforms the traditional chemical reaction into two or more reactions, thus realizing the effective utilization of resources and the low energy consumption of the separation process [10-13].The whole chemical reactions are carried out in two reactors, namely an air reactor and a fuel reactor.The circulation of the oxygen carrier in the reactor is the core of the whole process[14].The oxygen in the air reactor oxidizes the oxygen carrier,while fuel is partially oxidized by the oxygen carrier in the fuel reactor, thus producing syngas [10,15].

The core of the chemical looping gasification technology is to use the lattice oxygen in the oxygen carrier to replace the conventional gasification medium to provide the fuel reactor with the oxygen required for the gasification reaction [16].The oxides of transition metals, such as copper, nickel, manganese, iron, etc.are often studied as carriers of metal oxygen.The most common metal-oxygen carriers are iron-based, copper-based and nickelbased [3,6,11,13,17].There are also many types of common nonmetal oxygen carriers,such as sulfates represented by calcium sulfate, barium sulfate, etc.Qin et al.[18]developed a mathematical model coupling chemical reactions, mass, and heat transfer inside a spherical particle composed of uniformly distributed CuO and CaCO3grains.Using the model, they simulated the dynamics of CuO and CaCO3conversion, the profiles of temperature and gas concentrations, and the porosity changes and the grain size inside the particle with time.In the related research on non-metal oxygen carriers, Liu et al.[19]studied the influence of gasification media on coal chemical cycle gasification with CaSO4as an oxygen carrier.The thermodynamic analysis showed that adding steam and CO2to the system can lower the reaction temperature, at which the concentration of syngas reached its maximum.Niu et al.[20]proposed the synthesis of Cu-Fe composite metal oxides by sol-gel combustion synthesis.This oxygen carrier was used on the chemical looping gasification of biomass.It was found that Cu5Fe5 (50% (mol)CuO+50%(mol)Fe2O3)oxygen carrier had the best comprehensive chemical looping gasification performance.Huang et al.[21]used the sol-gel method to prepare Fe-Ni bimetallic oxide (NiFe2O4)as the oxygen carrier for the chemical looping gasification of biomass.The thermodynamic analysis found that the maximum gasification efficiency could be obtained when the ratio of oxygen carriers to biomass was 0.30.Through non-isothermal experiments, a kinetic model of carbon reduction of oxygen carriers was obtained.The results showed that the activation energy of redox reaction gradually increased with the carbon conversion rate increase.

However, the use of solid oxygen carriers has many disadvantages.First,solid metal oxides were easy to coke and sinter at high temperature [22,23].Secondly, ash may be deposited on the surface of the oxygen carrier, thus affecting its service life [24].In recent years,Sarafraz et al.[24]from the Energy Technology Center of the School of Mechanical Engineering,Adelaide University,Australia, put forward the concept of liquid chemical looping gasification(LCLG).Fig.1 illustrates the flow diagram of LCLG.The molten metal oxide was used as the oxygen carrier for fuel gasification,and the system was composed of two interconnected bubble reactors.Sarafraz et al.[24]used liquid CuO as the oxygen carrier and studied the chemical looping characteristics of graphite via thermodynamic analysis.Results showed that the carbon conversion rate could reach up to 84.6%, and it could reach 100% in the combustion process.Besides, the mole fraction of gaseous CuO in the outlet gas stream of AR was estimated to be 10-11, which meant that no further process was required to separate the evaporated CuO from the synthesis gas.Sarafraz et al.[25]carried out the chemical looping gasification of carbon with molten bismuth oxide(Bi2O3) as the oxygen carrier.X-ray diffraction (XRD) was used to evaluate the possibility of liquid Bi2O3contamination and agglomeration of alumina containers.In the presence of Bi2O3,the conversion rate of partial carbon oxidation reaches 85%.Also,no liquid bismuth residue or corrosion was found in the alumina crucible at 900 °C.Therefore, the system avoids the occurrence of sintering and agglomeration and greatly improves the service life of the oxygen carrier compared with the chemical looping system using solid oxygen carriers[26].The LCLG provides a new direction for the gasification of fuel, and there are few studies on the technology.LCLG has many advantages compared with traditional chemical looping gasification [23-25].Due to the lack of research on LCLG,little analysis on the influence of composite oxygen carriers has been found [24].

Fig.1.Schematic diagram of the LCLG process.

This paper firstly analyzed the influence of several factors in the gasification of biomass(lignin,cellulose).However,the above simulations are based on a single metal-oxygen carrier.Then,the influence of liquid Bi-Sb mixed oxygen carriers (Bi2O3, Sb2O3) with different proportions on biomass gasification was studied.Taking cellulose as an example, the total feed mass was taken as 100 kg.The mass fraction of lignin was fixed at 70%,the total mass fraction of Bi2O3and Sb2O3is 30%.A series of Bi-Sb mixtures of different proportions were set oxygen carrier (the mass ratios of Bi2O3and Sb2O3are 2:8,4:6,6:4,and 8:2,respectively).According to the elemental analysis of lignin and related oxygen carriers’ ratio, the number of moles corresponding to different species can be calculated, which can simulate the influence of different ratios of Bi-Sb mixed oxygen carrier lignin gasification process.Similarly, the effect of temperature and steam addition on the equilibrium composition would also be studied in this case.In this study, thermodynamic characteristics of LCLG process were simulated and analyzed, and product distribution and quality of the gasification process were explored.

2.Experimental

2.1.Materials

In this paper,Bi2O3and Sb2O3were used as liquid oxygen carriers.The effects of temperature, mixing ratio of liquid oxygen carrier and steam addition on gasification were investigated.So the best gasification conditions can be found.Bi2O3and Sb2O3have good properties and can be used as selective carriers of liquid oxygen.Some of the properties were shown in Table 1.The raw materials for gasification were cellulose(CE) and lignin(LG), and the proximate analysis and ultimate analysis of them were shown in Table 2.According to elemental analysis, it can be obtained that the chemical formula of cellulose in this experiment is similar to CH0.669O0.64.The chemical formula of lignin is similar to CH0.998O0.389.Because the content of N and S elements is little,the influence of the two elements was not considered for the time being.The liquid oxygen carriers were bismuth oxide (Bi2O3) and antimony oxide (Sb2O3), and the metal oxide was reduced to Bi and Sb, respectively, when the reaction was complete.It was assumed that the reaction was carried out in an ideal state, so in the calculation process, the influence of the ash composition in the raw material on the simulation result of the equilibrium product could be ignored.In the input material, only the oxygen carriers Bi2O3and Bi, Sb2O3and Sb and the possible substances CO and H2of the reaction could be considered CO2,CH4,H2O and C,etc.

Table 1 Some properties of oxygen carriers

Table 2 Proximate analysis and ultimate analysis of CE and LG

Table 3 The main reactions between the liquid oxygen carriers and each component

2.2.Research methods

In the process of biomass liquid chemical looping gasification,there are many factors that may affect the gasification perfor-mance, including reaction temperature, pressure, oxygen carrier activity,and steam,etc.[23].The efficiency of biomass gasification in the fuel reactor is determined by the reaction with the liquid oxygen carrier, so selecting appropriate operating parameters is essential.When bismuth oxide was used as the oxygen carrier,the oxygen carrier was oxidized in the air reactor.In the fuel reactor, there are fuel pyrolysis, biomass pyrolysis products, biomass gasification reactions,etc.For such a complex system with multiple reactions, the final gasification product must result from comprehensive competition among various reactions.

One of the commonly used methods of thermodynamic calculations is the Gibbs free energy minimization method [27].In a system where the type of substance and the number of independent reactions is determined under given conditions.The Gibbs free energy is only related to the amount of constituent substances ni,and find the value of nicorresponding to the minimum Gibbs free energy method.Besides, when solving, the amount of component material niis also restricted by the material(element)conservation equation.The reactions that are mainly considered during the LCLG of biomass are shown in Table 3.And suppose that during the simulation, Bi2O3is all reduced to Bi, and Sb2O3is all reduced to Sb.

3.Results and Discussion

3.1.Influence of temperature

3.1.1.Cellulose

Temperature is an important factor affecting the gasification of biomass liquid chemical looping[3,28].The key to the gasification of LCLG is the liquid metal oxide, so the temperature could not be lower than the melting point of the metal-oxygen carrier.Too high temperatures may cause side reactions between the oxygen carrier and the container.When studying the influence of temperature on LCLG of cellulose,the total feed mass was taken as 100 kg,and the mass fractions of liquid oxygen carriers (bismuth oxide and antimony oxide) were 10%, 30%, and 50%, respectively.According to the elemental analysis of cellulose, the corresponding number of moles at different blending ratios can be calculated.The remaining gasification simulation calculations of cellulose with the two oxygen carriers were as the same.Fig.2 shows the effect of temperature on the chemical looping gasification process of CE/Bi2O3with different mass fractions of Bi2O3,and Fig.3 shows the effect of temperature on CE/Sb2O3with varying mass ratio of Sb2O3.

Fig.2.The effect of temperature on the chemical looping gasification process of CE/Bi2O3 with different mass fractions of Bi2O3.(a)The mass fraction of Bi2O3 is 10%,(b)The mass fraction of Bi2O3 is 30%, (c) The mass fraction of Bi2O3 is 50%.

From the simulation results of cellulose and bismuth oxide balance in Fig.2, it could be seen that the ratios of bismuth oxide to cellulose is different, the temperature gradually rises from 500 °C to 1200°C,and the trend of equilibrium composition was basically the same.The main components of gasification were H2and CO,which were similar to Sarafraz’s results, and the content of H2and CO increased gradually with the increase of temperature[20,29-31].Take Fig.2(a)as an example.As the increase of temperature, the centent of H2increased at first and then stabilized at about 1.25 kmol.At 900-950 °C, the maximum centent of carbon monoxide is about 2.5 kmol,and then the concentration remained unchanged with the increase of temperature.Therefore, the best gasification temperature of production could be selected at 950°C.For carbon, the residual fixed carbon content was 2.0 kmol at 500°C.When the temperature reaches 900°C,the remaining fixed carbon content was basically reduced to a minimum of about 0.9 kmol.It could be seen from Fig.2 that the carbon had reached the maximum conversion rate of the entire reaction process at this time.Therefore,the increase in temperature was beneficial to promote the conversion of carbon [29,32].Fig.3 shows the effect of temperature on the gasification process of CE/Sb2O3with different mass fractions of Sb2O3.Similar to CE/Bi2O3,the equilibrium products had basically the same trend with temperature.The gasification products were mainly H2(1.3 kmol, 1.0 kmol, and 0.8 kmol)and CO(2.6 kmol,2.2 kmol,and 1.6 kmol).Also,the maximum output could be basically reached at 900 °C, so the best gasification temperature for H2production could be selected as 900 °C.

Fig.3.The effect of temperature on the chemical looping gasification process of CE/Sb2O3 with different mass fractions of Sb2O3.(a)The mass fraction of Sb2O3 is 10%,(b)The mass fraction of Sb2O3 is 30%, (c) The mass fraction of Sb2O3 is 50%.

In order to study the effect of temperature on the gasification equilibrium composition of biomass and mixed oxygen carriers,cellulose was used as the gasification raw material.The total gasification raw material feed mass was taken as 100 kg, where the mass of cellulose was fixed at 70%, while the total mass fraction of Bi2O3and Sb2O3was 30%.Set a series of Bi-Sb mixed oxygen carriers in different proportions.The temperature was gradually increased from 500°C to 1500°C.Fig.4 shows the effect of temperature on the LCLG of cellulose with different Bi2O3/Sb2O3mass ratios.

It could be seen from the simulation results in Fig.4.With the temperature increasing,the trend of cellulose gasification products was the same.And it was similar to the gasification results of cellulose and Bi2O3alone.The optimal gasification temperature could also choose 950 °C.To further illustrate the influence of different mass ratios of Bi2O3and Sb2O3on the distribution of cellulose gasification products, Fig.5 was drawn based on experimental data.It could be seen from Fig.5 that when the mass proportion of Bi2O3increased from 0.2 to 0.8, the proportions of H2, CH4, CO, and CO2in the products remained almost unchanged.The low calorific value curve had almost maintained the level.Mixing Bi2O3and Sb2O3in different proportions had little effect on the distribution of products.

Fig.4.The effect of temperature on the chemical looping gasification process of CE with different Bi2O3/Sb2O3 mass ratios.(a) The mass ratio of Bi2O3/Sb2O3 is 2:8, (b) The mass ratio of Bi2O3/Sb2O3 is 4:6, (c) The mass ratio of Bi2O3/Sb2O3 is 6:4, (d) The mass ratio of Bi2O3/Sb2O3 is 8:2.

Fig.5.The gasification products distribution and low calorific value of CE with different Bi2O3/Sb2O3 mass ratios.

3.1.2.Lignin

When studying the influence of temperature on the lignin LCLG process,the same as cellulose,the total lignin feed mass was taken as 100 kg, and the mass fractions of liquid oxygen carriers (bismuth oxide and antimony oxide) were 10%, 30%, and 50%, respectively.Fig.6 shows the effect of temperature on the chemical looping gasification process of CE/Bi2O3and CE/Sb2O3with 10%mass fractions of Bi2O3and Sb2O3.From the simulation results shown in Fig.6, it could be found that the result was similar to CE/Bi2O3and CE/Sb2O3gasification process.It could be seen the gasification products of lignin were mainly H2and CO [30].With the temperature increased, the content of H2and CO gradually increased, while the CO2content was very small.

Fig.6.The effect of temperature on the chemical looping gasification process of LG/Bi2O3 and LG/Sb2O3 with 10%mass fractions of Bi2O3 and Sb2O3.(a)The mass fraction of Bi2O3 is 10%, (b) The mass fraction of Sb2O3 is 10%.

To study the effect of temperature on the gasification equilibrium composition of lignin and mixed oxygen carrier, the total gasification raw material feed mass was taken as 100 kg, where the mass of lignin was fixed at 70%, and the total mass fraction of Bi2O3and Sb2O3was 30%.Set a series of Bi-Sb mixed oxygen carriers in different proportions, and the temperature was gradually increased from 500 °C to 1500 °C.Fig.7 shows the effect of temperature on LCLG of lignin with different Bi2O3/Sb2O3mass ratios.It could be seen from the simulation results that the changing trend of lignin gasification products with different proportions of mixed oxygen carriers with temperature was the same and was similar to the gasification results of lignin and Bi2O3alone, and the optimal gasification temperature could also choose 900 °C.

To further illustrate the influence of different mass ratios of Bi2O3and Sb2O3on the distribution of lignin gasification products,Fig.8 was drawn based on experimental data.It could be seen from Fig.8 that when the mass proportion of Bi2O3gradually increased from 0.2 to 0.8,the proportions of H2,CH4,CO and CO2in the gasification products remained almost unchanged.The low calorific value curve was similar to a horizontal line with a changing trend.

Fig.7.The effect of temperature on the chemical looping gasification process of LG with different Bi2O3/Sb2O3 mass ratios.(a) The mass ratio of Bi2O3/Sb2O3 is 2:8, (b) The mass ratio of Bi2O3/Sb2O3 is 4:6, (c) The mass ratio of Bi2O3/Sb2O3 is 6:4, (d) The mass ratio of Bi2O3/Sb2O3 is 8:2.

Fig.8.The gasification product distribution and low calorific value of lignin with different Bi2O3/Sb2O3 mass ratios.

3.2.The influence of oxygen carrier mixing ratio

3.2.1.Cellulose

Obviously,the content of oxygen carriers has a more significant impact on the equilibrium composition of gasification [29,30,33].In exploring the influence of the mixing ratio of liquid oxygen carrier and cellulose on the equilibrium composition, cellulose and Bi2O3/Sb2O3were used as raw materials.Set the reaction temperature to 950°C and the pressure to atmospheric pressure.The molar amount of 1 kmol cellulose was given as the reference amount.Change the feed molar amount of Bi2O3and Sb2O3to change the mixing molar ratio of the two.By increasing the mixing amount of Bi2O3from 0.001 kmol to 0.8 kmol, and increasing the mixing amount of Sb2O3from 0.001 kmol to 2.0 kmol, the relationship between the equilibrium composition at 950°C and the molar ratio of Bi2O3/CE and Sb2O3/CE was obtained as shown in Fig.9.

It could be seen from the simulation results from Fig.9(a) that when the Bi2O3/CE molar ratio was 0.15,the mass ratio of the two was about 3.60.And the CO concentration reached the highest value.When the Bi2O3/CE molar ratio was lower than 0.15, the main products were H2and CO.When the Bi2O3/CE molar ratio was higher than 0.15, the content of H2and CO gradually decreased.The Bi2O3/CE molar ratio during the gasification of cellulose and Bi2O3liquid chemical looping could be taken as 0.15,and the Bi2O3/CE molar ratio in the actual system should be greater than 0.15.Similarly, it could be seen from Fig.9(b) that when the molar ratio of Sb2O3/CE was 0.40, the mass ratio of the two was 5.10, and the concentration of CO reached the highest value.In the actual system, the molar ratio of Sb2O3/CE should be slightly larger than this value.

Fig.9.The equilibrium composition at 950 °C varies with the molar ratio of Bi2O3/CE (a) and Sb2O3/CE (b).

3.2.2.Lignin

In exploring the mixing ratio of liquid oxygen carrier and lignin on the equilibrium composition, lignin was used as raw materials.Bi2O3and Sb2O3were used as oxygen carriers.Set the reaction temperature to 900 °C and the pressure to atmospheric pressure.The molar amount of 1 kmol lignin was given as the reference amount.Change the feed molar amount of Bi2O3and Sb2O3to change the mixing molar ratio of the two.By increasing the mixing amount of Bi2O3from 0.001 kmol to 0.8 kmol and increasing the mixing amount of Sb2O3from 0.001 kmol to 2.5 kmol,the relationship between the equilibrium composition at 900°C and the molar ratio of Bi2O3/LG and Sb2O3/LG was obtained as shown in Fig.10.

Fig.10.The equilibrium composition at 900 °C varies with the molar ratio of Bi2O3/LG (a) and Sb2O3/LG (b).

It could be seen from the simulation results from Fig.10(a)that when the Bi2O3/LG molar ratio was 0.20-0.25,the mass ratio of the two was about 5.00-6.00, the CO concentration reached the highest value.When the Bi2O3/LG molar ratio was lower than 0.20,the main products are H2and CO.When the Bi2O3/LG molar ratio was higher than 0.25, the content of H2and CO gradually decreased.The Bi2O3/LG molar ratio during the gasification of lignin and Bi2O3liquid chemical looping could be taken as 0.25, and the Bi2O3/LG molar ratio in the actual system should be greater than 0.25.Similarly,it could be seen from Fig.10(b)that when the molar ratio of Sb2O3/LG was 0.70, the mass ratio of the two was 10.60,and the concentration of CO reached the highest value.In the actual system,the molar ratio of Sb2O3/LG should be slightly larger than this value.

3.3.The effect of adding steam

3.3.1.Cellulose

The steam/biomass ratio is an essential parameter for biomass gasification to generate H2.The addition of steam is beneficial to increase the hydrogen content[23,29,34].In other words,the addition of steam provides more hydrogen to the system,which is conducive to the forward progress of the H2reactions (reactions (7),(8), and (9)).

Controlling the amount of steam added is particularly important for the gasification equilibrium composition of the system.When there is too little steam, there is insufficient hydrogen in the system, which affects the H2concentration at equilibrium.When steam is excessive, the system needs more heat, which will lower the reaction temperature and affect the gasification efficiency.

To study the effect of steam addition on the gasification of liquid chemical looping, cellulose and Bi2O3as raw materials, the reaction temperature was set to 950 °C.The pressure was atmospheric pressure, and the Bi2O3/CE molar ratio was set to 0.15,and then the feed molar amount of steam and cellulose was changed.The ratio gradually increased from 0.001 to 2.00.The simulation result was shown in Fig.11.Fig.11(a) shows the change of equilibrium composition with the molar ratio of H2O/CE.It could be seen from the simulation results that as the steam content gradually increased, the H2content gradually increased, and the CO2content also showed an increasing trend.However, the content of CO gradually decreased [4,29,30].This is because with the addition of steam, the oxygen content in the system increases accordingly,and part of the CO reacts with H2O to form CO2.However,if there is too much steam,it will increase the humidity of the generated gas, which was not conducive to the efficiency of entire gasification system.Fig.11(b) shows the trend that the H2/CO molar ratio of the main component of syngas gradually increased with the increase of the H2O/CE molar ratio.When the H2O/CE molar ratio reached about 2.0, the H2/CO molar ratio could reach about 2.0.In the actual liquid chemical looping gasification reaction system, it was necessary to reasonably control the amount of steam added to ensure that the cellulose gasification could be carried out effectively [29,30].

Fig.11.The effect of steam addition on the chemical looping gasification process of CE/Bi2O3 at 950 °C.(a) The trend of equilibrium composition, (b) The trend of H2/CO.

The following Fig.12 shows the equilibrium composition of CE/Sb2O3gasification at 950°C with the H2O/CE molar ratio.The simulation conditions were similar to CE/Bi2O3chemical looping gasification.Fig.12(a) shows the change of equilibrium composition with the molar ratio of H2O/CE.Similar to Fig.11,as the steam content gradually increased, the H2content gradually increased, and the CO2content also showed an increasing trend while the CO content gradually decreased.

Fig.12.The effect of steam addition on the chemical looping gasification process of CE/Sb2O3 at 950 °C.(a) The trend of equilibrium composition, (b) The trend of H2/CO.

3.3.2.Lignin

To study the effect of steam addition on the gasification process,lignin and bismuth oxide were used as raw materials.Set the reaction temperature to 900 °C and the pressure to be atmospheric pressure.Given the Bi2O3/LG molar ratio of 0.20, then changed the feed molar ratio of steam to lignin, gradually increasing from 0.001 to 3.00.The simulation results are shown in Fig.13.Fig.13(a) shows the change of equilibrium composition with the H2O/LG molar ratio.From the simulation results, it could be seen that as the steam content gradually increased,the H2content gradually increased and the CO2content also showed an increasing trend.However, the content of CO gradually decreased [30].Same as cellulose, this is because with the addition of steam, the oxygen content in the system increased accordingly, and part of the CO reacts with H2O to form CO2[29].Fig.13(b) shows the trend that the H2/CO molar ratio of the main component of syngas gradually increased with the increase of the H2O/LG molar ratio.When the H2O/LG molar ratio reached about 2.5,the hydrogen to carbon ratio could reach more than 2.0.In the actual liquid chemical looping gasification reaction system,it was necessary to reasonably control the amount of steam added to ensure that the lignin gasification could be carried out effectively.

Fig.13.The effect of steam addition on the chemical looping gasification process of LG/Bi2O3 at 900 °C.(a) The trend of equilibrium composition, (b) The trend of H2/CO.

4.Conclusions

Biomass liquid chemical looping technology has many advantages compared with traditional gasification technology.This article used simulation calculations for cellulose and lignin LCLG technology, and the main conclusions were obtained.As the temperature of fuel reactor increased, the efficiency of the biomass chemical looping gasification increased.The increase in temperature was conducive to the production of more CO and H2.When the Bi2O3blending ratio was 10%, 30%, and 50% of CE,the maximum content of H2was 1.3 kmol,1.0 kmol,and 0.8 kmol,respectively.And the maximum content of CO was 2.6 kmol, 2.2 kmol,and 1.6 kmol,respectively.When the oxygen carrier content gradually increased, the gasification system first underwent incomplete oxidation and then gradually underwent complete oxidation.The matching of different oxygen carriers and gasification raw materials had the best molar ratio.For example, the best blending mass ratio of CE/Bi2O3was 3.60.The addition of steam was conducive to the increase of H2content.As the steam content increased, the H2/CO molar ratio in system could reach more than 2.0.In the actual gasification reaction system,reasonable control of the amount of steam added could ensure the high efficiency of biomass chemical loop gasification.According to the product distribution results,the mixing ratio of Bi2O3and Sb2O3had little effect on the distribution of gas products and the effect of mixing ratio of Bi2O3and Sb2O3could be ignored.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors gratefully acknowledge the support of the National Natural Science Foundation of China(22038011,51976168),the K.C.Wong Education Foundation, China Postdoctoral Science Foundation (2019M653626), Foundation of State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering(2020-KF-06), the Promotion Plan for Young People of Shaanxi Association for Science and Technology(20180402),and the Technology Foundation for Selected Overseas Chinese Scholar in Shaanxi Province (2018015).