Efficient Utilization Of Coal Research Articles

Multi-scale modeling and control of chemical looping gasification coupled coal pyrolysis system for cleaner production of synthesis gas

The cleaner and efficient utilization of coal is of great significance to achieve energy conservation enhancement and CO2 emission reduction targets. Coal pyrolysis (CP) and chemical looping gasification (CLG) are both new coal utilization technologies. A cleaner system integrating CP and CLG processes is put forward in this paper to produce high purity synthesis gas with lower CO2 emission for the sustainable development of coal industry, with the aid of multi-scale modeling means including molecular dynamics (MD) simulation, computational fluid dynamics (CFD) simulation, and process simulation. First, MD simulation is executed for CP process with a coal model consisting of 3860 atoms to obtain the optimum operation parameters by mechanism analysis. The obtained coal density of 1.2 ± 0.11 g/cm3 is consistent with the experimental result of 1.28–1.33 g/cm3, ensuring the optimized coal geometry model below 1100 K. Second, the CLG process is simulated by CFD method. CuO is selected as oxygen carrier based on its better heat transfer performance before its residence time is determined based on the fuel reactor (FR) model. Then the CP-CLG system is simulated with Aspen Plus software on the basis of above MD and CFD results. The process simulation result indicates that the purity of synthesis gas produced by CP-CLG system is about 20% higher than single coal CLG system as the latter generates much more CO2. Finally, one control scheme is designed to keep the operational stability of CP-CLG based cleaner synthesis gas production system with the aid of Aspen Dynamics software.

Characterization of slag from anthracite gasification in moving bed slagging gasifier

Gasification has become an effective way to realize clean and efficient utilization of coal. Anthracite is characterized by low grindability index and low gasification reactivity, which is not suitable for fluidized gasifier and entrained-flow gasifiers for low carbon conversion and high crushing cost. However, due to its high thermal and mechanical strength, it is preferred to be gasified in moving bed slagging gasifier. In this work, three slag samples were collected from pilot plant of moving bed slagging gasifier using anthracite as feedstock, and residual char was found in slag. In order to reveal formation mechanism of slag and residual char in the slags, properties of mineral matter and residual char were analysed. Results showed that slag taken from stable operation condition had low contents of residual char and crystalline phases. However, a lot of residual char particles were found in other two slags. Comparing to coal char prepared at 850 °C, residual chars in slags had higher graphitization degree and surface areas. Besides, it presented a higher gasification activity, which mainly depends on its porous structure and surface areas. In addition, formation of metallic iron, interface of char-slag and invasion of char by slag were observed in slag with residual char. It was found that occurrence of residual char in slag from anthracite gasification in moving bed slagging gasifier was strongly influenced by low reactivity of anthracite, unreacted limestone, high molten slag level.

Clean and highly-efficient utilization of coal

Clean and highly efficient utilization of coal is an important scientific and technological issue.As the petroleum resource decreases but its consumption increases, all of the countries in the world have to face the big issue of sustainable development of energy and economy and protection of environment.Therefore, study on clean coal technology (CCT) has attracted much attention and become one of important themes of energy research.

Prospects for the Low Pollutant Emission Control of Circulating Fluidized Bed Combustion Technology

With the pollutant emission standards becoming increasingly stringent and considering the pressure of carbon neutral by 2060, the low pollutant emission potential of circulating fluidized bed (CFB) combustion technology needs to be further exploited, thus to promote the market competitiveness of CFB boilers; this is critical for the clean and efficient utilization of coal as well as for the energy transformation in China. In this article, we summarize the pollutant emission characteristics of CFB combustion, and review the development of major technologies for CFB boiler emission control. Based on the energy development strategies and corresponding policies in China, development suggestions are proposed for reducing pollutant emission of the CFB combustion technology. The most significant approach is to push the limits of original pollutant emission for CFB combustion by re-specifying the fluidization state and through in-furnace combustion adjustment, while the boiler thermal efficiency should be ensured. For the long-term development of coal energy, the new-generation CFB combustion technology with ultra-low emission should be researched and developed while combining with technologies such as supercritical/ultra-supercritical, intelligent operation, carbon capture, utilization, and storage, and energy storage technologies. The existing CFB boilers with small or medium capacity should also be upgraded. Considering the fuel flexibility of CFB combustion, biomass power generation should be promoted to realize low-cost and high-efficiency consumption of low-heat value fuels, urban refuse, industrial wastes, etc. The peak load regulation capacity and low pollutant emission property of the CFB boilers should be promoted to improve operation flexibility and renewable energy consumption. Moreover, the desulphurization ash produced in CFB combustion should be comprehensively utilized, and the N2O emission problem is also significant. The pollutant emission standards and related policies need to be formulated from an overall perspective to guide the healthy development of the energy industry.

Modeling, prediction and multi-objective optimization of the coal gasification system

As global energy demand continues to increase, coal as basic energy still accounts for a significant proportion. Under the pressure of environmental protection, clean and efficient coal utilization technologies are in great demand. Coal gasification technology has the potential to realize near-zero-emissions for coal utilization. This paper establishes the coal gasification system model and analyzes the effect of oxygen/coal ratio and water/coal ratio on the system performance index of cold syngas efficiency, effective component ratio, carbon conversion ratio, and production ratio of hydrogen. The results show that when the oxygen/coal ratio increases, the efficiency of cold syngas and effective components ratio increase first and then decrease, carbon conversion ratio first increases and then remains unchanged, hydrogen production ratio gradually decreases; When the steam/coal ratio increases, the cold syngas efficiency, and carbon conversion ratio first increase and then decrease, effective component ratio ingredients gradually decreases, and the hydrogen production ratio increases. Using BP neural network to realize the prediction of the gasification system, and the mean square error reaches the magnitude of 10e-7. Multi-objective optimization results show that the oxygen/coal ratio and steam/coal ratio corresponding to the highest production ratio of hydrogen is 0.52 and 0.05. The highest carbon conversion ratio corresponds to the oxygen/coal ratio of 0.95 and the steam/coal ratio of 0.05.

Molecular structure characterization of low-medium rank coals via XRD, solid state 13C NMR and FTIR spectroscopy

In-depth understanding of coal molecular structures is crucial to the clean and efficient coal conversion, as they are the dominant factors determining the reactivity and reaction behaviors of coals in thermal conversions such as combustion, pyrolysis, gasification and liquefaction. However, the molecular structures of coals are still far from clear due to the intrinsic complexity and heterogeneity of coals. This work probes the molecular structures of eight coals of various metamorphic grades with combined spectral techniques of X-ray diffraction (XRD), solid state 13C NMR and FTIR spectra. The structural parameters were correlated with the coalification indicator Ro to investigate the structural evolutions during coal metamorphism. Consistent results concerning the structural evolution during coalification were obtained with different techniques. From the parameters of proximate and ultimate analysis, the increasing aromaticity and decreasing aliphatic fractions with rising coalification degree are observed. XRD patterns show the ubiquitous presence of amorphous carbon, the gradually condensing aromatic layers, and the size-growing but graphitizing crystallites during coalification. 13C NMR spectra reveal different types of carbons presented, the increasing aromatic and decreasing aliphatic components, the growing size and weight but reducing number of side-chains of the aromatic clusters. FTIR spectra indicate shortening and reducing of aliphatic chains, as well as enhancing aromaticity with the deepening metamorphism. These findings shed light on the structure features of coals and are potentially useful to the clean and efficient coal utilization.

Technical path analysis of clean and efficient utilization of coal in Shajingzi mining area

In Shajingzi mining area, the coal quality is very low, and many questions will be faced in the process of exploding the area. First, the author analyzed problems in resource development and utilization, and proposed the paths of clean and efficient utilization of coal, which are clean coal power generation technology (including SC, USC and near zero emission power generation technology), CHP energy saving and emission reduction technology, technical analysis of classification and quality utilization and coal transportation technology by pipeline. The author also analyzed the main characteristics in detail, which are high volatile content, high tar content, rich oil coal-high oil coal, and an ideal raw material for low temperature carbonization, tar hydro treating, semi coke gasification and CO combustion power generation. The author also summaries the advantages and disadvantages of coal transportation technology by pipeline, which is a new and efficient way of utilization. Finally, according to the development strategy of “clean, step-by-step, timely and comprehensive”, the author proposes the comprehensive industrial chain of coal, electricity and chemical industry will be the best path.

The Preparation of Coal based Graphene and It’s Application in the Field of Thermal Conductivity

Graphene is a new material with good physical properties and high added value. Coal can be made into model compounds by different physical and chemical methods to realize the efficient utilization of coal, so that new coal based materials with high added value can be formed. Based on this, in the process of research and analysis, the preparation of coal based graphene and its application in the field of thermal conductivity were studied. Based on the lateral guiding excitation of graphene, its performance and application of thermal conductivity are analyzed comprehensively. On the basis of external force control, it has a positive effect on improving the thermal conductivity of graphene composites.

Enhanced liquid tar production as fuels/chemicals from Powder River Basin coal through CaO catalyzed stepwise degradation in eco-friendly supercritical CO2/ethanol

Developing eco-friendly thermal conversion technologies of coals into fuels/chemicals with minimal environmental impact is highly attractive and significant for efficient coal utilization. CaO catalyzed stepwise degradation at 350–400 °C in eco-friendly supercritical CO2/ethanol (scCO2/ethanol) was carried out to produce high-yield liquid tars as fuels/chemicals from Powder River Basin (PRB) coal. The total yield of the liquid tars increased from 53.9 wt% for non-catalytic stepwise degradation to 60.1 wt% for CaO catalyzed stepwise degradation, with an increase of 6.2 wt%. The resulting ash-free liquid tars are promising raw materials as clean liquid fuels for energy production due to their high H/C ratio (1.16–1.88) and heating values (32.84–35.84 MJ/kg). Compared with non-catalytic stepwise degradation, the energy recovery increases from 62.8% to 71.6% by CaO catalyzed stepwise degradation. More than 75% of the components in the liquid tars were volatilized and/or degraded at temperature <500 °C according to thermogravimetric analysis. The distributions of the functional groups and group components in the liquid tars are similar to each other. Phenols are the most abundant volatile group component in the liquid tars, accounting for about 43% of the volatile components released at 350 °C and 375 °C by CaO catalyzed stepwise degradation. The CaO promoted forming active H+ and CH3CH2O− from ethanol, which readily attacked and cleaved weak -C-O- bonds in the PRB coal, leading to producing more phenols and arenes. Thermal dissociation of the non-covalent interactions especially hydrogen bonds or the cleavage of weak -C-O- in PRB coal could interpret the generation of phenols.

Study on the pyrolysis kinetics of low-medium rank coals with distributed activation energy model

A deep understanding of coal pyrolysis behaviors is essential for the clean and efficient coal utilization. Detailed structural characterization and kinetic analysis could provide valuable information about coal pyrolysis. This work deals with structural analysis and pyrolysis kinetics of four low-medium rank coals with the distributed activation energy model (DAEM). The carbon structures, pyrolysis characteristic and kinetic parameters were correlated to gain some updated insights into coal pyrolysis. The results show that aliphatic carbons gradually convert into aromatic ones, and the aromatic clusters grow in both size and weight with the rise of coal rank. The side-chains of aromatic clusters are shortened and eliminated thus aromaticity is increased. Characteristic temperatures of pyrolysis are closely related to coal properties and carbon types. Both initial and peak temperatures increase with FCar and Cdaf while decrease with VMar and H/C. Meanwhile, the initial temperature is related to the aliphatic carbon (fal) and aliphatic carbon bonded oxygen (falo) due to their low bonding energies, while the peak temperature is linked to the aromatic carbon (fa) and aromatic bridgehead carbon (faB) because of their higher bonding energy. DAEM model is reliable for analyzing pyrolysis kinetics of bituminous coals. The range of activation energy gradually narrows down with the increase of coal rank, corresponding to the concentrating distribution of different carbon types. Moreover, DAEM could accurately predict the pyrolysis behavior of bituminous coals at very high heating rates, but the effectiveness of DAEM in modeling and predicting pyrolysis of lignite is less satisfying.

Modeling and Analysis of Coal-Based Lurgi Gasification for LNG and Methanol Coproduction Process

A coal-based coproduction process of liquefied natural gas (LNG) and methanol (CTLNG-M) is developed and key units are simulated in this paper. The goal is to find improvements of the low-earning coal to synthesis natural gas (CTSNG) process using the same raw material but producing a low-margin, single synthesis natural gas (SNG) product. In the CTLNG-M process, there are two innovative aspects. Firstly, the process can co-generate high value-added products of LNG and methanol, in which CH4 is separated from the syngas to obtain liquefied natural gas (LNG) through a cryogenic separation unit, while the remaining lean-methane syngas is then used for methanol synthesis. Secondly, CO2 separated from the acid gas removal unit is partially reused for methanol synthesis reaction, which consequently increases the carbon element utilization efficiency and reduces the CO2 emission. In this paper, the process is designed with the output products of 642,000 tons/a LNG and 1,367,800 tons/a methanol. The simulation results show that the CTLNG-M process can obtain a carbon utilization efficiency of 39.6%, bringing about a reduction of CO2 emission by 130,000 tons/a compared to the CTSNG process. However, the energy consumption of the new process is increased by 9.3% after detailed analysis of energy consumption. The results indicate that although electricity consumption is higher than that of the conventional CTSNG process, the new CTLNG-M process is still economically feasible. In terms of the economic benefits, the investment is remarkably decreased by 17.8% and an increase in internal rate of return (IRR) by 6% is also achieved, contrasting to the standalone CTSNG process. It is; therefore, considered as a feasible scheme for the efficient utilization of coal by Lurgi gasification technology and production planning for existing CTSNG plants.

Thermodynamic and environmental analysis of integrated supercritical water gasification of coal for power and hydrogen production

Coal combustion for thermal power generation causes serious environmental problems. Relatively efficient and clean coal utilization technologies need to be developed to alleviate the growing energy crisis and environmental pollution pressure. A novel integrated supercritical water gasification of coal system with 40 t/h throughput of coal and water was designed. A thermodynamic analysis and a life cycle environmental assessment under different conditions were performed using Aspen Plus 8.4 and SimaPro 9.0 based on the Ecoinvent 3 database, respectively. Results show that the maximum energy loss is induced by the waste heat of the effluent from the heat exchanger. By using organic Rankine cycle, the energy efficiency of the system could reach 53.3% when the temperature and coal concentration are 700 °C and 15 wt%, respectively. The global warming potential, acidification potential and nitrogen oxides are 0.058 kg carbon dioxide eq/(kW·h), 3.63 × 10−4 kg sulfur dioxide eq/(kW·h) and 7.04 × 10−5 nitrogen oxides eq/(kW·h), respectively, for the process combined with carbon dioxide capture and storage under the temperature of 700 °C and the coal concentration of 15 wt%. The comparison of the thermodynamic and environmental performance among different systems shows that the exergy and energy efficiencies of integrated supercritical water gasification of coal system combined with organic Rankine cycle are higher than those of integrated gasification combined cycle, and the environmental emissions of the integrated supercritical water gasification of coal system are less than those of integrated gasification combined cycle system. This study reveals that the integrated supercritical water gasification of coal is a relatively clean and efficient coal utilization technology with good industrialization prospects.

Experimental comparison and optimization on granular bed filters with three types of filling schemes

Coal pyrolysis is an important way to realize the clean and efficient utilization of coal in China. However, the problem of dust removal from coal pyrolysis gas has restricted its development. Granular bed filters (GBFs) are among the most promising dust removal technologies because of their convenient and efficient filter material. To meet different dust removal requirements, an optimum filling scheme of the GBF must be determined. In this study, the filtration performance of GBFs with three types of filling schemes, single-layer GBFs with uniform-sized particles, single-layer GBFs with mixed-sized particles and double-layer GBFs with two sizes of particles, was tested and compared. The results showed that among the single-layer GBFs, the GBFs with medium-sized particles (1–3 mm) and the GBFs with mixed-sized particles are recommended because of their high efficiency and a low pressure drop. Double-layer GBFs yielded better filtration performances than single-layer GBFs and were suitable in applications with high dust removal requirements. However, the filtration performance of double-layer GBFs was correlated with filter material collocation, which primarily depends on the lower-layer granules. To achieve optimum filtration performance, the lower layer of a double-layer GBF should be filled with particles with sizes less than 1 mm. The optimum ratio of the lower-layer height to the overall height should be approximately 0.2, and the value can rise slightly with increasing upper-layer granular size. These results can be used as a guide for optimally filling GBFs under different requirements to further promote the development of clean coal utilization.

A thermodynamic analysis of a solar hybrid coal-based direct-fired supercritical carbon dioxide power cycle

Efficient utilization of coal for power generation with carbon capture as well as development of solar hybrid system are being aggressively researched currently. To advance the utilization of solar energy and achieve zero emission for coal-based power generation more efficiently, a novel direct-fired, oxy-combustion supercritical carbon dioxide power cycle integrated with the solar-driven coal gasification was proposed. In the proposed system, the concentrated solar energy is utilized for coal gasification, and then the produced syngas is combusted with high-purity oxygen to drive a semi-closed supercritical carbon dioxide power cycle with intensive heat recuperation and near-zero carbon emission. Detailed analytical models based on energy and material balance were developed and the overall system thermodynamic performance were determined by the process simulation. Results showed that, at the designate point, the proposed system can save 29.9% of coal consumption and the net system energy efficiency and exergy efficiency soar to 43.4% and 44.6%, respectively; and the annualized coal saving can reach 10.46 kilo tonnes with the annual solar-to-electricity efficiency at 16.9%. The proposed concept may provide a new approach to advancing solar-coal hybridization power generation with near-zero emission.

Evaluation of pulverized coal utilization in a blast furnace by numerical simulation and grey relational analysis

Pulverized coal injection is the key technology in energy saving and CO2 mitigation for an iron-making blast furnace. To obtain a high utilization efficiency of the pulverized coal, operating parameters are optimized frequently due to their operating flexibility. In this study, the effects of key operating parameters on coal utilization efficiency were evaluated based on computational fluid dynamics and grey relational analysis (CFD-GRA). The CFD simulation of pulverized coal combustion process was coupled with that of formation process of the major combustion zone (i.e., raceway). Then, the characteristics of coal utilization were analysed, two local indicators of coal utilization were proposed from the viewpoint of coal plume. The correlation degrees between the indicators and the operating parameters were obtained through employing GRA method, aiming to determine the primary operating parameter to coal utilization efficiency. Results of CFD-GRA evaluation indicate that the primary determinant of the raceway depth is the blast rate. Besides, the blast rate has stronger impacts on the overall burnout rate and intensive combustion zone in the coal plume. However, increasing the oxygen enrichment rate was observed to be more effective than the blast rate for improving medium particle utilization. Particle size distribution has the least impact on the local and overall coal utilization efficiency. Results yield an optimization strategy for operating parameters for achieving a high utilization efficiency.

Effect of volatile reactions on the yield and quality of tar from pyrolysis of Shenhua bituminous coal

Pyrolysis was an important route for coal conversion and also the fundamental for clean and efficient utilization of coal. As an important product of pyrolysis, coal tar can be used as the raw material for producing premium liquid fuels and high value-added chemicals (benzene-toluene-xylene, naphthalene, phenols, etc.). The products’ distribution and quality were significantly affected by the secondary reaction of volatiles. In this work, Shenhua bituminous coal was pyrolyzed with a two-stage reactor at a relatively low temperature, and the released volatiles underwent secondary reactions at various temperatures and residence time. The yields and quality of coal tar were characterized by gas chromatography–mass spectroscopy (GC–MS) and Fourier transformed infrared spectroscopy (FTIR). The results showed that secondary volatile reactions decrease tar yield but increase gas and coke yield. The volatile reaction results in a decrease in the content of aliphatics and phenols, and an increase in the content of arenes and polar compounds. The volatile reaction includes the following reactions: dehydroxylation, deoxygenation, cleavage of long chain aliphatic structures into short ones, and condensation of aromatic clusters, etc. The higher heating rate of pyrolysis reduces the content of aliphatic and polar compounds while increases that of arenes and phenols in the light tar (HS).

Progress and Development Trend of Clean and Efficient Coal Utilization Technology

Progress and Development Trend of Clean and Efficient Coal Utilization Technology

Slag mobility in entrained flow gasifiers optimized using a new reliable viscosity model of iron oxide-containing multicomponent melts

Entrained flow gasification is a promising approach in clean and efficient utilization of coal as well as biomass. Knowledge of slag mobility is of fundamental as well as practical importance to maintain high performance in entrained flow coal or biomass gasification applications. Due to the complex behavior of slag mobility, especially in iron oxide-containing fuel slags, slag tap blockage remains a challenge. Slag mobility is directly related to the structure-dependent property viscosity. In this paper, a reliable, general viscosity model is therefore developed by taking into account the structure determined by temperature and composition and, for the first time, by oxygen partial pressure. The structure is described by means of a non-ideal associate solution used to describe the Gibbs energy of the liquid phase. This is a novel approach to bridge chemical and physical properties. In order to obtain a reasonable set of the model parameters, the viscosity behavior with respect to temperature, composition, and oxygen partial pressure is critically assessed in conjunction with the melt structure. The model calculations are further extended to evaluate systems with more than three components and the similarity in the predicted viscosity behavior in comparison to the experimental results in turn implies the validation of model parameters. The viscosities of several real coal and biomass slags are used to validate the model. The results show that the model gives a good performance in describing the viscosity over the whole range of compositions and a wide range of temperatures, as well as predicting the influence of oxygen partial pressures. This is achieved using only one set of model parameters, which have a clear physico-chemical meaning. The model is a self-consistent, reliable, predictive tool for use in the regions where no experimental data are available. In combination with the phase relation this reliable model is applied to determine an optimum liquid slag system according to a target viscosity value under given conditions through a proper blending proportion of several fuel slags, which prevents a potential complex slag mobility of liquid-solid mixtures. The limitations of the current model applied to describe the slag mobility in real entrained flow gasifiers are also specified.

Stair-like Multivariable Generalized Predictive Control of Pulverizing System in Thermal Power Plants

Pulverizing system is an important part in the clean and efficient utilization of coal in thermal power plant, and the optimal control of the system is an important way to achieve this goal. This paper presents a stair-like multivariable generalized predictive control scheme for a pulverizing system. This control scheme focuses on the problem of predictive control algorithm in practical application, and integrates the feedforward experience in traditional control schemes of pulverizing system. Simulation results showed that the scheme are able to realize the decoupling control of the pulverizing system, avoid the problem of matrix inversion, reduce the amount of calculation, and has certain engineering application value.

Investigation of fluctuation behavior in viscosity of coal slags used in entrained-flow gasifiers

Entrained-flow gasification has attracted extensive attention because of its clean and efficient utilization of coal as well as flexible application in industry for power generation and chemical production. Numerous theoretical and experimental investigations on slag flow in entrained-flow gasifiers have been performed to ensure a smooth operation, but an unscheduled shutdown due to slag tap blockage remains an ongoing challenge. A fluctuation phenomenon of slag viscosity gives a rise in the risk of slag tap blockage. In this work, three Chinese coal slags with low silicon content and high iron content were used to investigate the viscosity fluctuation phenomenon. It was found that the crystalline phases and suspended bubbles can cause the fluctuation phenomenon. The fluctuation degree is related to the volume fraction of crystalline phases and the crystallization rate. In the search for the mechanism of the viscosity fluctuation, an in-situ observation using a high temperature stage microscope system (HTSM) in combination with XRD and SEM analyses was carried out. In addition, the viscosity of investigated slags with the suppression of solid phases as well as the phase distribution at high temperatures was calculated. Based on a comprehensive analysis of the results, a possible mechanism has been proposed that the viscosity fluctuation is attributed to an instant local change in the macrostructure such as the deformation of suspended bubbles, the change of the orientation of acicular crystals and the interaction of the acicular crystals and suspended bubbles.