Chemical looping gasification of sewage sludge using copper slag modified by NiO as an oxygen carrier

Chemical looping gasification(CLG) provides a novel approach to dispose the sewage sludge.In order to improve the reactivity of the calcined copper slag,NiO modification is considered as one of the good solutions.The copper slag calcined at 1100℃ doped with 20 wt% NiO(Ni20-CS) was used as an oxygen carrier(OC) in sludge CLG in the work.The modification of NiO can evidently enhance the reactivity of copper slag to promote the sludge conversion,especially for sludge char conversion.The carbon conversion and valid gas yield(V_(g)) increase from 67.02% and 0.23 m^(3)·kg^(-1) using the original OC to 78.34% and 0.29 m^(3)·kg^(-1) using the Ni20-CS OC, respectively.The increase of equivalent coefficient(Ω) facilitates the sludge conversion and a suitable Ω value is determined at 0.47 to obtain the highest valid gas yield(0.29 m^(3)·kg^(-1)).A suitable steam content is assigned at 27.22% to obtain the maximum carbon conversion of 87.09%,where an acceptable LHV of 12.63 MJ·m^(-3) and Vg of 0.39 m^(3)·kg^(-1)are obtained.Although the reactivity of Ni20-CS OC gradually decreases with the increase in cycle numbers because of the generation of NiFe_(2) O_(4-δ) species,the deposition of sludge ash containing many metallic elements is beneficial to the sludge conversion.As a result,the carbon conversion shows a slight uptrend with the increase of cycle numbers in sludge CLG.It indicates that the Ni20-CS sample is a good OC for sludge CLG.

Experimental and numerical simulation of lignite chemical looping gasification with phosphogypsum as oxygen carrier in a fluidized bed

Phosphogypsum(PG)is a solid waste produced in the wet process of producing phosphoric acid.Lignite is a kind of promising chemical raw material.However,the high sulfur of lignite limits the utilization of lignite as a resource.Based on fluidized bed experiments,the optimal reaction conditions for the production syngas by lignite chemical looping gasification(CLG)with PG as oxygen carrier were studied.The study found that the optimal reaction temperature should not exceed 1123 K;the mole ratio of water vapor to lignite should be about 0.2;the mole ratio of PG oxygen carrier to lignite should be about 0.6.Meanwhile,commercial software Comsol was used to establish a fuel reaction kinetics model.Through computational fluid dynamics(CFD)numerical simulation,the process of reaction in fluidized bed were well captured.The model was based on a two-fluid model and coupled mass transfer,heat transfer and chemical reactions.This study showed that the fluidized bed presents a flow structure in which gas and solid coexist.There was a high temperature zone in the middle and lower parts of the fluidized bed.It could be seen from the results of the flow field simulated that the fluidized bed was beneficial to the progress of the gasification reaction.

Microscopic mechanism study and process optimization of dimethyl carbonate production coupled biomass chemical looping gasification system

Biomass chemical looping gasification technology is one of the essential ways to utilize abundant biomass resources.At the same time,dimethyl carbonate can replace phosgene as an environmentfriendly organic material for the synthesis of polycarbonate.In this paper,a novel system coupling biomass chemical looping gasification with dimethyl carbonate synthesis with methanol as an intermediate is designed through microscopic mechanism analysis and process optimization.Firstly,reactive force field molecular dynamics simulation is performed to explore the reaction mechanism of biomass chemical looping gasification to determine the optimal gasification temperature range.Secondly,steady-state simulations of the process based on molecular dynamics simulation results are carried out to investigate the effects of temperature,steam to biomass ratio,and oxygen carrier to biomass ratio on the syngas yield and compositions.In addition,the main energy indicators of biomass chemical looping gasification process including lower heating value and cold gas efficiency are analyzed based on the above optimum parameters.Then,two synthesis stages are simulated and optimized with the following results obtained:the optimal temperature and pressure of methanol synthesis stage are 150℃ and 4 MPa;the optimal temperature and pressure of dimethyl carbonate synthesis stage are 140℃ and 0.3 MPa.Finally,the pre-separation-extraction-decantation process separates the mixture of dimethyl carbonate and methanol generated in the synthesis stage with 99.11%purity of dimethyl carbonate.Above results verify the feasibility of producing dimethyl carbonate from the perspective of multi-scale simulation and realize the multi-level utilization of biomass resources.

Study on the mechanism and reaction characteristics of metal-supported phosphogypsum as oxygen carrier in a chemical looping gasification application

This study aimed to explore the chemical looping gasification(CLG)reaction characteristics of the metal-supported composite phosphogypsum(PG)oxygen carriers(OCs)and the thermodynamic mechanism.The FactSage 7.1 thermodynamic simulation was used to explore the oxygen release and H_(2)S removal mechanisms.The experimental results showed that the syngas yield of CLG with PG-CuFe_(2)O_(4)was more than that with PG-Fe_(2)O_(3)20/CuO40 or PG-Fe_(2)O_(3)30/CuO30 OC at 1023 K when the water vapor content was 0.3.Furthermore,the maximum syngas yield of the CO selectivity was 70.3% and of the CO_(2)selectivity was 23.8%.The H_(2)/CO value was 0.78,and the highest carbon conversion efficiency was 91.9% in PG-CuFe_(2)O_(4)at the gasification temperature of 1073 K.The metal-supported PG composite oxygen carrier was proved not only as an oxygen carrier to participate in the preparation of syngas but also as a catalyst to catalyze coal gasification reactions.Furthermore,both the experimental results and FactSage 7.1 thermodynamic analysis revealed that the trapping mechanism of H_(2)S by composite OCs was as follows:CuO first lost lattice oxygen as an oxygen carrier to generate Cu_(2)O,which,in turn,reacted with H_(2)S to generate Cu_(2)S.This study provided efficient guidance and reference for OC design in CLG.

Advancements in biomass gasification research utilizing iron-based oxygen carriers in chemical looping:A review

Biomass,recognized as renewable green coal,is pivotal for energy conservation,emission reduction,and dualcarbon objectives.Chemical looping gasification,an innovative technology,aims to enhance biomass utilization efficiency.Using metal oxides as oxygen carriers regulates the oxygen-to-fuel ratio to optimize synthesis product yields.This review examines various oxygen carriers and their roles in chemical looping biomass gasification,including natural iron ore types,industrial by-products,cerium oxide-based carriers,and core-shell structures.The catalytic,kinetic,and phase transfer properties of iron-based oxygen carriers are analyzed,and their catalytic cracking capabilities are explored.Molecular interactions are elucidated and system performance is optimized by providing insights into chemical looping reaction mechanisms and strategies to improve carrier efficiency,along with discussing advanced techniques such as density functional theory(DFT)and reactive force field(ReaxFF)molecular dynamics(MD).This paper serves as a roadmap for advancing chemical looping gasification towards sustainable energy goals.

Chemical looping catalytic gasification of biomass over active LaNixFe1-xO_(3)perovskites as functional oxygen carriers

Oxygen carriers(OCs)with perovskite structure are attracting increasing interests due to their redox tunability by introducing various dopants in the structure.In this study,LaNixFe1-xO3(x=0,0.1,0.3,0.5,0.7,1.0)perovskite OCs have been prepared by a citric acid–nitrate sol–gel method,characterized by means of X-ray diffraction(XRD)analysis and tested for algae chemical looping gasification in a fixed bed reactor.The effects of perovskite types,OC/biomass mass ratio(O/B),gasification temperature and water injection rate on the gasification performance were investigated.Lower Ni-doped(0≤x≤0.5)perovskites crystalized in the rhombohedra system which was isostructural with LaNiO3,while those with composition 0.5≤x≤1 crystalized in the orthorhombic system.Despite the high reactivity for LaNiO_(3),LaNi_(0.5)Fe_(0.5)O_(3)(LN5F5)was found to be more stable at a high temperature and give almost as good results as LaNiO_(3)in the formation of syngas.The relatively higher syngas yield of 0.833 m^(3)·kg^(-1) biomass was obtained under the O/B of 0.4,water injection rate of 0.3 ml·min^(-1) and gasification temperature at 850C.Continuous high yield of syngas was achieved during the first 5 redox cycles,while a slight decrease in the reactivity for LN5F5 after 5 cycles was observed due to the adhesion of small grains occurring on the surface of OCs.However,an obvious improvement in the gasification performance was attained for LN5F5 compared to raw biomass direct gasification,indicating that LN5F5 is a promising functional OC for chemical looping catalytic gasification of biomass.

Biomass chemical looping gasification for syngas production using modified hematite as oxygen carriers

Syngas is a clean energy carrier and a major industrial feedstock. In this paper, syngas was produced via biomass chemical looping gasification(CLG) process. Hematite, the most common Fe-based oxygen carrier(OC), was modified with different metal oxides(CeO_(2), CaO and MgO) by the impregnation method. The hematite modified by CeO_(2), CaO and MgO was namely as CeO_(2)-hematite(CeO_(2)-H), CaO-hematite(CaO-H) and MgO-hematite(MgO-H), respectively. The introduction of CeO_(2), CaO and MgO enhanced the reactivity of lattice oxygen of hematite. The optimum condition for syngas production had been explored as the mass ratio of oxygen carrier to biomass(O/B) of 0.2, the mass ratio of steam to biomass(S/B) of0.75 and temperature of 800℃in the biomass CLG process. The CeO_(2)-H exhibited the most wonderful performance compared to that for CaO-H and MgO-H. The crystal composition of OC influenced greatly in the CLG process. CeFeO_(3)had a good oxygen mobility property and lattice oxygen releasing capacity due to the most oxygen vacancy distributed on the OC surface and the most active lattice oxygen, which is conducive to the biomass chemical looping gasification process for syngas production, leading to the highest gasification efficiency of 95.86% and gas yield of 1.20 m^(3)/kg of the three. Cyclic test proved that CeO_(2)-H had well sintering resistance and cyclic performance.

Chemical looping gasification characteristics and kinetic analysis of Chlorella and its organic components

Chemical looping gasification(CLG)characteristics and kinetic analysis of Chlorella(CHL),simulated Chlorella(V-CHL)and medium-chain triglycerides(MCT)were investigated using a thermogravimetric analyzer coupled with an online mass spectrometer.The apparent activation energy was obtained via Kissinger-Akahira-Sunose(KAS)method.In the result of the weightless behavior,the addition of oxygen carrier inhibited the decomposition of V-CHL at lower temperatures but promoted its decomposition at high temperatures.The values of chemical looping process characteristic parameters showed that a 10 wt%oxygen carrier would maximize the release of volatile products in the CLG of MCT,with 5.12×10^(-6)%⋅min^(-1)⋅℃^(-3).Oxygen carriers also affected gaseous products.The LHV of gaseous products of CHL reached the largest when the oxygen carrier was 10 wt%,which was 8.13 MJ/m^(3).And the gaseous product of MCT had the largest LHV with 30 wt%oxygen carrier,which was 8.83 MJ/m^(3).According to the kinetic analysis,the minimum value of apparent activation energy of MCT chemical looping gasification was 89.54 kJ⋅mol^(-1) with the oxygen carrier of 30 wt%,which was 50%less than that of MCT pyrolysis.And the minimum value for V-CHL was obtained when the mass fraction of Fe2O3 was 50 wt%.This paper could provide a reference for the choice of algae,the design of reactors,and the targeted regulation of the gaseous product for the algae CLG process.

Retention mechanism of calcium ferrite and compositions of ash on selenium during chemical looping gasification

Selenium pollution by coal utilization is of increasing concern.Calcium-iron(Ca-Fe)oxygen carriers(OCs)and alkali metal ions have strong inhibitory effects on selenium,which can reduce the emissions of selenium vapor.The retention mechanisms of selenium by Fe_(2)O_(3),CaFe_(2)O_(4),Ca_(2)Fe_(2)O_(5) and bottom ash are investigated during chemical looping gasification(CLG).Iron-based OC can oxidize H_(2)Se(g)to SeO_(2)(g);furthermore,lattice oxygen is released by Fe_(2)O_(3),contributing to the formation of an Fe-O-Se structure to retain selenium and form selenite.Because calcium ferrite is poorly oxidizing,it cannot oxidize H_(2)Se(g),but the CaO produced when OCs are reduced can react with H_(2)Se(g)to form CaSe(s),and this process can be promoted by H_(2)S(g).The best retention rates reached 32.301%when Ca_(2)Fe_(2)O_(5) was used.In the cyclic experiment,the selenium retention of the bottom ash gradually increases.Alkali metal ions in bottom ash are the main factor in retaining selenium.Ca^(2+) and Mg^(2+) do not easily vaporize due to their high melting points;therefore,their selenium retention is significantly better than that of K^(+) and Na^(+).This research provided a new idea for the removal of selenium by using OCs and bottom ash par-ticles during CLG.

A novel hybrid digestion-gasification process integrated with membranes for efficient conversion of biomass to bio-alcohols

There is an urgent need to develop technologies which enable the conversion of biomass into liquid biofuels to fill the gap between limited fossil fuel supplies and increasing worldwide demand.In order to achieve the EU 2030 vision of at least 15%of the fuels used in the road transportation sector will be biofuels derived from non-food biomass feedstocks,the R&D of clean,inexpensive,highly end-user compatible biofuels from a virtually inexhaustible source of biomass should be pursued to make breakthroughs in cost-effective biomass to liquid biofuels(BTL)technologies.Thus,an innovative,consolidated,and sustainable technology using a hybrid digestion-gasification process integrated with membranes to produce next generation bio-alcohols from different biomass feedstocks was designed.The proposed concept was theoretically estimated to achieve an overall BTL efficiency of 44%and a cost reduction for bioalcohol production of 18.6%.Moreover,this technology can potentially achieve an overall CO2 emission reduction of>75%for road transport based on the preliminary analysis.

Simulation study on the gasification process of Ningdong coal with iron-based oxygen carrier

Chemical looping gasification(CLG) of Ningdong coal by using Fe_(2) O_(3) as the oxygen carriers(OCs) was studied,and the gasification characteristics were obtained.A computation fluid dynamics(CFD) model based on Eulerian--Lagrangian multiphase framework was established,and a numerical simulation the coal chemical looping gasification processes in fuel reactor(FR) was investigated.In addition,the heterogeneous reactions,homogeneous reactions and Fe_(2) O_(3) oxygen carriers' reduction reactions were considered in the gasification process.The characteristics of gas flow and gasification in the FR were analyzed and it was found that the experiment results were consistent with the simulation values.The results show that when the O/C mole rate was 0.5:1,the gasification temperature was 900℃ and the water vapor volume flow rate was 2.2 ml·min^(-1),the mole fraction of syngas reached a maximum value of the experimental result and simulation value were 71.5% and 70.2%,respectively.When the O/C mole rate was 0.5:1,the gasification temperature was 900℃,and the water vapor volume flow was 1.8 ml·min^(-1);the gasification efficiency reached the maximum value was 62.2%,and the maximum carbon conversion rate was 84.0%.