Coal Chemical Looping Gasification Research Articles

Evaluation of Fe-Ni Composite Oxygen Carrier in Coal Chemical Looping Gasification

Although coal chemical looping gasification (CCLG) is a promising technology for the efficient utilization of coal, limited studies concerned about the industrial application of oxygen carrier in CCLG system owing to its performance requirements including high reactivity with solid fuel, high carbon conversion, and good mechanical property. To meet the requirements of oxygen carriers in CCLG system, novel Fe-Ni composite oxygen carrier (OC) samples were successfully prepared. The performances of these OCs were evaluated in a fixed bed reactor, where they were reduced by solid fuel and then fully oxidized by air. Both fixed bed tests and thermodynamic analysis showed that the prepare OCs exhibited high reactivity with coal and syngas selectivity, making them suitable for the CCLG process. Specifically, when the loading amount of NiO was 20 wt%, the Fe-Ni composite OCs achieved the highest carbon conversion (93.03%) and synthesis gas selectivity (73.29%). Additionally, the thermogravimetric data revealed that the Curie temperature of the OCs was higher than 550°C, making them suitable for magnetic separation of the OC particles and carbon residue in the CCLG system.

Dynamic optimal control of coal chemical looping gasification based on process modeling and complex risk computation

The safe and steady running of coal chemical looping gasification system (CCLGS) is directly related to the whole production benefit. CCLGS is composed of dryer, pyrolyzer, decomposer, fuel reactor (FR), and air reactor (AR), which reflects the complexity of the entire production process. In this paper, a novel dynamic safety control strategy based on process modeling and complex risk computation is put forward to ensure the stable operation of CCLGS. First, the process modeling of CCLGS is carried out by Aspen Plus, and the obtained simulation results are in agreement with experimental results. Then, the CCLGS complex network is formed by constructing the adjacency matrix and calculating comprehensive indicator (Ci) value to evaluate the importance of the variables and support risk computation. Subsequently, the risk values of five units are computed based on the unit maximum material coefficient (UMMC), unit general risk coefficient (UGRC), and unit special risk coefficient (USRC). The results prove that FR and AR have higher risk grades than other units. Finally, dynamic control study for FR and AR processes is conducted with the aim of evaluating pressure controllers by safety integrity level. The research will provide beneficial approaches for the safety control of actual plant.

Molecular dynamics and steady-state process simulation coupled research on CCLG system design for cleaner production of EG

BackgroundThe CO2 capture technologies such as chemical-looping gasification (CLG) and reformation (CLR) receive more and more attention under the globally warming environment. In this paper, the mechanism of coal chemical-looping gasification (CCLG) process with copper-based oxygen carrier is analyzed by molecular dynamics (MD) simulation and steady-state process simulation to produce high purity ethylene glycol (EG). MethodsFirstly, the effect of temperature and mass ratio of coal and CuO on CCLG process are investigated with gasification experiments. Secondly, the MD simulations in ReaxFF force field are performed in purpose of obtaining the micro-level information and cross-reference with experimental results. Finally, an innovative process to produce high purity EG is designed based on CCLG process from the above simulations and experiment results. Significant findingsThe results of gasification experiments show that the optimal reaction temperature is 850°C and the optimal mass ratio of coal to CuO is 1:1.5. The results obtained from the MD simulations are found accordant with the experimental results. The EG targeted CCLG process basically meets the mass ratio required by the production of EG, and the CO2 emissions of the whole process is only 0.018 kg-CO2/kg-EG.

Process optimization and thermodynamic analysis of autothermal coal chemical looping gasification industrial demonstration system

Chemical looping gasification (CLG) is an innovative clean coal conversion technology with industrial application prospects. The technical reliability of coal CLG (CCLG) in an autothermal state remains to be investigated. To clarify the process characteristics of an autothermal CCLG process, a CCLG autothermal operation system was established based on a CLG industrial demonstration unit. Process modeling of the CCLG reactor system and economizer, air preheater, and other heat exchange units was performed, to ensure autothermal operation of the global CCLG process. The optimal operating parameters of the system were established, the optimal heat exchange network was designed, and the source and distribution of thermodynamic irreversibility were clarified. The results showed that the optimal coal feed flow rate, air feed temperature and flue gas circulation temperature were 437.07 kg/h, 550 °C and 450 °C, respectively. The fuel reactor (FR) flue gas circulation was not conducive to system autothermal, resulting in weakened gasification performance. The optimal heat exchange plan allowed the system to operate without an external heat source. The thermodynamic irreversibility mainly originated from the redox process. The system heat efficiency was 81.63 %, the product exergy efficiency was 78.06 %, the total exergy efficiency was 41.10 %, and the total exergy destruction rate was 55.40 %. Additionally, the FR flue gas circulation caused high exergy loss, resulting in reduced system thermodynamic efficiency.

Full-loop CFD simulation of lignite Chemical Looping Gasification with phosphogypsum as oxygen carrier using a circulating fluidized bed

The excellent gas-solid mixing efficiency of the Circulating Fluidized Bed (CFB) makes it the recommended choice for coal Chemical Looping Gasification (CLG). In this paper, a 3D Computational Fluid Dynamics (CFD) full-loop model with multiphase distribution was developed to investigate the fluidization behavior and the CLG performance in CFB. Cold flow simulations show that particle size, static particle stock and inlet gas velocity were critical to the CFB stable operation. The optimal conditions for this system were: a static particle stock of 0.300 m, a particle size of 150 μm, and an inlet gas velocity lower than 0.2 m s−1 was recommended. Thermal flow simulations show that increasing the temperature increased the syngas yield. However, extremely high temperatures inhibit the H2 production. The contribution of CO production to syngas production was particularly obvious. To ensure sufficient H2 production, the molar content of water vapor and the PG/lignite molar ratio should be controlled at approximately 0.3 and 0.2, respectively. Cold flow model was extended to thermal simulation. This would lead to an undesirable phenomena, which should be corrected according to the kinetic model. The simulation results were in a well agreement with the experimental results, which verified the validity of the simulation model.

Comprehensive optimization of coal chemical looping gasification process for low CO2 emission based on multi-scale simulation coupled experiment

Carbon dioxide (CO2) emission reduction has become an urgent topic to be studied and solved with the in-depth understanding of global warming and frequent occurrence of extreme climate. At present, the application of chemical looping technology in coal gasification to produce high purity synthesis gas is an important way to achieve CO2 emission reduction, ensure energy security, and promote ecological civilization. In this paper, a new fusion research method combining multi-scale modeling and experimental testing is adopted to comprehensively optimize the coal chemical looping gasification (CCLG) process, aiming at ruducing CO2 emissions in the synthesis gas production of CCLG. In order to investigate the effect of main reaction conditions on CCLG process, the pyrolysis and gasification experiments of Meihuajing coal are carried out in a tubular furnace reactor with Fe2O3 and CuO as oxygen carriers respectively. Subsequently, the multi-scale simulation of CCLG process including molecular dynamics (MD) and computational fluid dynamics (CFD) simulations is performed to validate the experimental results and supplement important reaction kinetics data. Both of multi-scale modeling and experimental testing suggest that the optimum pyrolysis temperature range, gasification temperature range, char/oxygen carrier mass ratio (C/O), and steam flow are below 900 ℃, 900–950 ℃, 1:1.5, and 0.15 g/min respectively, providing an effective guidance for the optimal design of practical CCLG pilot plant.

Behavior of Selenium during Chemical-Looping Gasification of Coal Using Copper-Based Oxygen Carrier

The migration and transformation behavior of selenium during coal chemical looping gasification (CLG) under the impact of a CuO/Bentonite (Ben) oxygen carrier (OC) were studied in a batch fluidized bed reactor. In the CLG process, the total percentage of selenium released in gaseous phase was 73.06%. In the conventional gasification process, 91.71% of the total selenium was released in a gaseous state. The addition of CuO/Ben OC apparently promoted the transformation from gaseous selenium to particulate selenium. The oxygen–carbon ratio (O/C) played an important role in affecting the fraction of gaseous selenium released in the gasification process, with results showing that the amount of selenium adsorbed by CuO/Ben OC was added along with the increase in OC. By means of X-ray photoelectron spectroscopy (XPS) characterization, we found that the reduced CuO/Ben OC contained a small amount of Cu2Se due to the oxidation and adsorption of selenium onto their porous surface. The regeneration performance of the CuO/Ben OC was favorable after 10 regeneration cycles of the CLG process. The increase in the pore volumes and specific surface areas contributed to the enhanced capacity of retaining selenium for CuO/Ben OC.

Long-term coal chemical looping gasification using a bimetallic oxygen carrier of natural hematite and copper ore

Coal chemical looping gasification (CCLG) is a promising gasification technology for coal utilization with high resource utilization rate, energy saving and environmental protection properties. Development of suitable oxygen carriers and optimization of operating conditions for CCLG are the key for the coal conversion and H2&CO production (H2, CO). In this study, Cu-Fe bi-ore oxygen carrier prepared by spray drying granulation method using hematite and copper ore as raw materials was tested for CCLG. The effects of the reaction temperature, oxygen carrier to coal (O/L) ratio and steam addition amounts were systematically evaluated by reaction tests combing with various analytical methods. Most importantly, over 100 redox chemical looping cycles were performed to demonstrate the excellent stability of Cu-Fe bi-ore oxygen carrier during the redox reactions. Results showed that the optimal gasification condition is 950 °C with oxygen carrier-to-coal mass ratio of 3:1 and steam rate of 0.08 ml/min. Syngas yield of 58 mmol/g, as well as 75.2% syngas selectivity and 85.3% carbon conversion were achieved. After 100 redox cycles, the synthesis gas yield can still reach 46 mmol/g despite a decline, and the carbon conversion kept above 72%, without obvious sintering in the long-term test. The characterization results showed that the synergistic effect between Cu and Fe metals contributed to its good oxygen release ability and reducibility. The Cu-Fe bi-ore oxygen carrier undergoes a gradual reduction Fe3+→Fe8/3+→Fe2+→Fe and Cu2+→Cu process during the gasification reaction, accompanying with the lattice oxygen migration from bulk to the particle surface. This work demonstrated the economical method for the industrial application of CCLG process using spray-drying-derived oxygen carriers.

Reactivity of iron-based oxygen carriers with coal ash in pressurized chemical looping gasification

Coal ash is one of the significant factors for the operating efficiency of pressurized coal chemical looping gasification (CLG). To explore the influence mechanism of physical deposition and chemical combination of coal ash on iron-based oxygen carrier (OC) under pressurized conditions, the effects of coal ash content, coal ash components and pressure on the reduction performance of Fe2O3/Al2O3 OC are investigated. The micro-structure and phase transformation of OC particles under pressurized conditions are characterized by SEM, BET and XRD. It shows that coal ash deposition only has a significant inhibition on the reduction process of Fe2O3 to Fe3O4. The deposition inhibition is the resistance of internal diffusion, which is generated by coal ash coating the surface of OC particles and blocking pores. Then a modified kinetic model is developed to analyze inhibitory mechanism of coal ash deposition at different pressure. There is a fairly strong coating ability of new composite metal compounds ((MgAl0.74Fe1.26)O4, Ca2Fe2O5 and CaAl2SiO6) on OC particles. However, when pressure is greater than 7 bar, (MgAl0.74Fe1.26)O4 is reduced to (MgO)0.239(FeO)0.761, which can weaken coating effect. Additionally, when pressure is greater than 10 bar, Fe3O4 is largely reduced and converted into CaFe5O7, which can inhibit formation of Ca2Fe2O5.

Mechanism analysis and simulation of methyl methacrylate production coupled chemical looping gasification system

Nowadays, the efficient and cleaner utilization of coal have attracted wide attention due to the rich coal and rare oil/gas resources structure in China. Coal chemical looping gasification (CCLG) is a promising coal utilization technology to achieve energy conservation and emission reduction targets for highly pure synthesis gas. As a downstream product of synthesis gas, methyl methacrylate (MMA), is widely used as raw material for synthesizing polymethyl methacrylate and resin products with excellent properties. So this paper proposes a novel system integrating MMA production and CCLG (CCLG-MMA) processes aiming at “energy saving and low emission”, in which the synthesis gas produced by CCLG and purified by dry methane reforming (DMR) reaction and Rectisol process reacts with ethylene for synthesizing MMA. Firstly, the reaction mechanism of CCLG is investigated by using Reactive force field (ReaxFF) MD simulation based on atomic models of char and oxygen carrier (Fe2O3) for obtaining optimum reaction temperature of fuel reactor (FR). Secondly, the steady-state simulation of CCLG-MMA system is carried out to verify the feasibility of MMA production. The amount of CO2 emitted by CCLG process and DMR reaction is 0.0028 (kg CO2)−1·(kg MMA)−1. The total energy consumption of the CCLG-MMA system is 45521 kJ·(kg MMA)−1, among which the consumption of MMA production part is 25293 kJ·(kg MMA)−1. The results show that the CCLG-MMA system meets CO2 emission standard and has lower energy consumption compared to conventional MMA production process. Finally, one control scheme is designed to verify the stability of CCLG-MMA system. The CCLG-MMA integration strategy aims to obtain highly pure MMA from multi-scale simulation perspectives, so this is an optimal design regarding all factors influencing cleaner MMA production.

A novel coal chemical looping gasification scheme for synthetic natural gas with low energy consumption for CO2 capture: Modelling, parameters optimization, and performance analysis

Natural gas is regarded as a clean energy source, but its global supply is seriously insufficient. An alternative route to synthetic natural gas production from other energy sources is thus urgently needed. There is the conventional coal gasification to synthetic natural gas process, but it suffers from high energy consumption because of air separation and CO2 capture. Coal chemical looping gasification is regarded as a state-of-the-art technology that avoids conventional air separation and reduces energy consumption. A new process of coal chemical looping gasification that creates synthetic natural gas is therefore proposed, where low energy consumption for CO2 capture is achieved simultaneously by increasing the CO2 concentration. The results show that the exergy efficiency of the new process is increased by 21%; the internal rate of return is increased by 9%; the fixed capital investment and production costs are reduced by 36% and 29%; and the CO2 emissions are reduced by 15% in comparison with the conventional coal to synthetic natural gas process. This study provides a promising method for the energy-saving, profitable, and sustainable development of coal into synthetic natural gas.

Characteristic Evaluation and Process Simulation of CuFe2O4 as Oxygen Carriers in Coal Chemical Looping Gasification.

Chemical looping gasification (CLG) has been described as an innovative and low-cost gasification technology to convert carbonaceous fuels into synthesis gases. Oxygen carrier (OC) is the key to resolve the contradiction between rapid carbon conversion and appropriate partial oxidation of coal. At present, the solid fuel conversion in the CLG process is limited by an iron-based OC, and a copper-based carrier has difficulty in maintaining the reduction atmosphere. Hence, CuFe2O4 has been proposed as a high-performance OC because of its synergistic effect. The present study first conducted a characteristic evaluation on CuFe2O4, including the reducibility and oxygen release capacity. The results showed that the addition of copper made a great contribution to the reduction process, and the presence of ferrite better relieved the deep oxygen loss of CuFe2O4. The thermodynamic limitation and evolution behavior of CuFe2O4 in the reduction process were discussed for the simulation. An Aspen model of the CLG process with coal as the fuel and CuFe2O4 as the OC was then established and validated by the experimental data. By consideration of the high carbon conversion and high syngas productivity in the operation, an OC/fuel mass ratio of approximately 1.25–2.25 and a gasification temperature range of 800–900 °C were thought to be optimal in the coal CLG process.

Chemical looping gasification of maceral from low-rank coal: Products distribution and kinetic analysis on vitrinite

The product distribution and kinetic analysis of low-rank coal vitrinite were investigated during the chemical looping gasification (CLG) process. The acid washing method was used to treat low-rank coal, and the density gradient centrifugation method was adopted to obtain the coal macerals. By combining thermogravimetric analysis and online mass spectrometry, the influence of the heating rate and oxygen carrier (Fe2O3) blending ratio on product distribution was discussed. The macroscopic kinetic parameters were solved by the Kissinger-Akahira-Sunose (KAS) method, and the main gaseous product formation kinetic parameters were solved by the iso-conversion method. The results of vitrinite during slow heating chemical looping gasification showed that the main weight loss interval was 400–600 °C, and the solid yield of sample vitrinite-Fe-10 at different heating rates was 64.30%–69.67%. When β = 20 °C·min−1, the maximum decomposition rate of vitrinite-Fe-10 was −0.312%·min−1. The addition of Fe2O3 reduced the maximum decomposition rate, but by comparing the chemical looping conversion characteristic index, it could be inferred that the chemical looping gasification of vitrinite might produce volatile substances higher than the pyrolysis process of vitrinite alone. The average activation energy of the reaction was significantly reduced during chemical looping gasification of vitrinite, which was lower than the average activation energy of 448.69 kJ·mol−1 during the pyrolysis process of vitrinite alone. The gaseous products were mainly CO and CO2. When the heating rate was 10 °C·min−1, the highest activation energy for CH4 formation was 21.353 kJ·mol−1, and the lowest activation energy for CO formation was 9.7333 kJ·mol−1. This study provides basic data for exploring coal chemical looping gasification mechanism and reactor design by studying the chemical looping gasification process of coal macerals.

Reactivity and Structure Evaluation of Coal Chemical Looping Gasification Based on Cu-Fe Oxygen Carrier

Reactivity and Structure Evaluation of Coal Chemical Looping Gasification Based on Cu-Fe Oxygen Carrier

A Novel Design of Methyl Methacrylate Synthesis Process with Low CO2 Emission

Methyl methacrylate (MMA) is an important raw material for synthesising polymethyl methacrylate, plastic modifier, and surface coating. In this paper, an optimum “energy saving and low emission” process is proposed for MMA production. MMA is synthesised from ethylene and synthetic gas generated from coal chemical looping gasification (CLG), which can largely reduce CO2 emission. Firstly, the reaction mechanism of coal CLG is investigated using molecular dynamics simulation. Secondly, to verify the feasibility of the process, the steady-state simulation of MMA production process is carried out by Aspen Plus. Finally, based on the steady-state simulation results, one control scheme is verified with Aspen Dynamics to strictly control the purity of MMA.

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

Abstract Chemical looping gasification (CLG) of Ningdong coal by using Fe2O3 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 Fe2O3 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 °C 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 °C 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 %.

Chemical Looping Co-Gasification Characteristics of Cyanobacterial/Coal Blends

The frequent outbreak of cyanobacteria bloom results in an urgent need for the resource utilization of cyanobacteria. However, the development of routine thermal treatment (i.e., gasification and pyrolysis) is hindered by the issue of high moisture content. In order to minimize the dewatering requirement, this study investigated the chemical looping co-gasification of the cyanobacteria/coal mixture. The results showed that the residual moisture of cyanobacteria not only could serve as the gasifying agent of coal, but also presented a better gasification effect than the injecting steam. Meanwhile, blending cyanobacteria also improved the performance of coal chemical looping gasification in terms of the syngas quality, gasification rate, and carbon conversion efficiency. Cyanobacteria pyrolysis supplied abundant hydrocarbons and hydrogen-rich gases. The highest syngas yield of 1.26 Nm3/kg was obtained in the mixture fuel of 46 wt.% cyanobacteria and 54 wt.% coal under a 0.3 oxygen carrier-to-fuel ratio. A slight interaction effect was observed in the pyrolysis process, in which the reactivity of coal pyrolysis was enhanced by the oxygenated groups of cyanobacteria volatile. The dominant motive of the interaction effect was the catalytic effect of alkali metals of cyanobacteria ash on the coal gasification. However, the formation of aluminosilicates deactivated alkali metals and further inhibited the char gasification. The intensity of interaction effect was demonstrated to be highly relevant with the (Na + K)/Al molar ratio of ash. The most prominent interaction effect occurred for the sample with 82 wt.% cyanobacteria, but a negative interaction was observed in the sample with 10 wt.% cyanobacteria. Both homogeneous reaction and shrinking core models showed the excellent fitting performance in the char gasification process. However, these two models could not be applied to the initial pyrolysis process because of the intricate mechanisms.

Kinetics of Coal Char Gasification with Fe-Based Oxygen Carriers under Pressured Conditions

Under high-pressure conditions, coal chemical looping gasification (CLG) is a potential technology for industrial applications based on its ability to provide clean and efficient conversion of coal...

Novel design and dynamic control of coal pyrolysis wastewater treatment process

The wastewater discharged by coal pyrolysis process contains ammonium, phenol and other organic compounds, which are harmful to the environment if not disposed properly. Phenol should be particularly removed because it accounts for 60–80% of organics in coal pyrolysis wastewater (CPW) and thus brings severe threaten to the human health. This paper proposes a novel “generation and treatment integration” system to dispose of such CPW. First, the source of CPW is simulated followed by its effect analysis on the quality of synthesis gas in coal chemical looping gasification (CLG) process with Aspen Plus software to verify the importance of CPW treatment. The simulation results show that the flow rate of phenol in CPW stream is 833 kg/h with a significant influence on the quality of synthesis gas. Second, the stable configuration and interaction energy between three extraction solvents including methyl propyl ketone (MPK), methanol, and synergistic extraction solvent of MPK and methanol with phenol molecule are studied by quantum mechanics. The interaction energy between the synergistic extraction solvent and phenol molecule is found equal to 67.7 kJ·mol−1, higher than both 40.99 kJ·mol−1 of MPK and 33.58 kJ·mol−1 of methanol. Then the treatment process of CPW is comparatively simulated using the three extraction solvents. Results demonstrate that the synergistic extraction solvent behaves best for extracting organics of CPW, consistent with quantum mechanics results. Finally, one control scheme of CPW treatment is proposed and its anti-disturbance ability is verified with Aspen Dynamics software. Dynamic simulation results show that the control structure can promptly make the process back to steady state in the face of disturbance.

Transformation and Migration of Mercury during Chemical-Looping Gasification of Coal

Transformation and migration of mercury during coal chemical-looping gasification (CLG) of lignite were studied in a batch-fluidized bed with magnetic CuFe2O4 as the oxygen carrier. The results sho...