Thermochemical Conversion Of Coal Research Articles

A review on in-situ process analytical techniques for the thermochemical conversion of coal and biomass

Abstract Coal and biomass are important feedstocks for carbon energy from thermochemical conversion process. Fully understanding the analytical technology that characterizes the changes in physicochemical properties and structural characteristics of coal and biomass during the thermochemical reactions is a key prerequisite for the realization of appropriate utilization of energy fuels. Modern in-situ process analysis technology can accomplish the in-situ detection of the experimental process, and therefore reflect the experimental process more accurately. Moreover, it is developing towards automation, intelligentization, and comprehensive detection. Based on the characteristics of each detection technology, this paper summarizes the basic principles, application scope and performance characteristics of the three advanced in-situ process analysis technologies: hyphenated technology, synchrotron radiation, and online analysis. The practicability and accuracy of each detection technology in coal and biomass research are compared and analyzed, and its latest application and development trend are elucidated. These tools not only make up for the shortcomings of traditional detection techniques in characterizing the in-situ reaction, but also provide complementary information on molecular microscopic changes during fuel thermal conversion. This review paper can provide insights for relevant researchers in the selection of analytical techniques, and promote in-depth study on microcosmic mechanism of fuel conversion.

ReaxFF-MD simulation investigation of the degradation pathway of phenol for hydrogen production by supercritical water gasification

Wastewater from the thermochemical conversion of coal and biomass contains a significant amount of phenolic structures compounds. The degradation of these phenolic compounds to hydrogen-rich gasses can prevent environmental pollution and save energy. Supercritical water (SCW) gasification of phenol is experimentally studied and a reactive force field molecular dynamics (ReaxFF-MD) simulation is conducted to investigate the catalytic mechanism of Ni/Al2O3 in the phenol degradation. The experimental results indicate that Ni/Al2O3 facilitates the conversion of phenol to 1-ethoxy butane via ring opening, which is a crucial step for complete gasification. The ReaxFF-MD simulation demonstrated that Ni facilitates the formation of H3O free radicals and Ni-phenol intermediates. H3O free radicals can be decomposed into H2 and OH free radicals. Both the generated OH free radical and Ni-phenol intermediate promote the ring-opening reaction of phenol. Ni promotes the direct decomposition of phenol into C1, C2, and C3 fragments, which is beneficial for further complete gasification.

Thermochemical conversion of coal and biomass blends in a top-lit updraft fixed bed reactor: Experimental assessment of the ignition front propagation velocity

Co-thermochemical conversion of coal and biomass can potentially decrease the use of fossil carbon and pollutant emissions. This work presents experimental results for the so-called top-lit updraft fixed bed reactor, in which the ignition front starts at the top and propagates downward while the gas product flows upwards. The study focuses on the ignition front propagation velocity for the co-thermochemical conversion of palm kernel shell and high-volatile bituminous coal. Within the range of assessed air superficial velocities, the process occurred under gasification and near stoichiometric conditions. Under gasification conditions increasing coal particle size from 7.1 to 22 mm decreased ignition front velocity by around 26% regardless of the coal volume percentage. Furthermore, increasing coal volume percentage and decreasing coal particle size result in product gas with higher energy content. For the operation near stoichiometric conditions, increasing coal volume percentage from 10 to 30% negatively affected the ignition front velocity directly proportional to its particle size. Additional experiments confirmed a linear dependence of ignition front velocity on air superficial velocity. Further steps in the development of the top-lit updraft technology are implementing continuous solids feeding and variable cross-sectional area and optimizing coal particle size distribution.

In-situ investigation of coal particle fragmentation induced by thermal stress and numerical analysis of the main influencing factors

Particle fragmentation influences thermochemical coal conversion processes in different ways, which is of great significance for process design and control. Different mechanisms are proposed for fragmentation characterization, but direct and substantial optical evidence supporting these theories is rarely reported. In the present study, the fragmentation process of two anthracites with low volatiles is investigated in-situ with the aid of an optical system. The observed fragmentation phenomenon confirms that the thermal stress is the main driving force for the fragmentation of the investigated anthracite particles. Together with a model analysis, a fragmentation pattern different from previous reports is proposed. The tensile stress causes the particles to fragment from the center. Fine particles are produced by multiple tensile failure rather than by the spalling of particles’ outer shell caused by compressive stress. Based on the model, the impact of various process- and particle-related factors on the maximum thermal tensile stress and its appearance time are quantitatively evaluated, which significantly reduces the required time and effort in comparison to experimental analysis of the fragmentation. This study provides direct visual evidence and numerical validation of the fragmentation mechanism, which can be utilized to predict the coal particle behavior and the resulting particle size distribution.

Synthesis Gas Composition Prediction for Underground Coal Gasification Using a Thermochemical Equilibrium Modeling Approach

Underground coal gasification (UCG) is an in situ conversion technique that enables the production of high-calorific synthesis gas from resources that are economically not minable by conventional methods. A broad range of end-use options is available for the synthesis gas, including fuels and chemical feedstock production. Furthermore, UCG also offers a high potential for integration with Carbon Capture and Storage (CCS) to mitigate greenhouse gas emissions. In the present study, a stoichiometric equilibrium model, based on minimization of the Gibbs function has been used to estimate the equilibrium composition of the synthesis gas. Thereto, we further developed and applied a proven thermodynamic equilibrium model to simulate the relevant thermochemical coal conversion processes (pyrolysis and gasification). Our modeling approach has been validated against thermodynamic models, laboratory gasification experiments and UCG field trial data reported in the literature. The synthesis gas compositions have been found to be in good agreement under a wide range of different operating conditions. Consequently, the presented modeling approach enables an efficient quantification of synthesis gas quality resulting from UCG, considering varying coal and oxidizer compositions at deposit-specific pressures and temperatures.

Investigation on the thermal behavior characteristics and products composition of four pulverized coals: Its potential applications in coal cleaning

Although the thermochemical conversion of coal has dominated the research concerning the primary chemical production in the coal chemical industry utilization field, obtaining higher tar yield and lighter tar quality remain as challenges. The pyrolysis and its product distribution were studied using a thermogravimetric analyzer and a fixed bed reactor. A gas chromatograph (GC) and a gas chromatograph−mass spectrometer (GC-MS) were employed to test the properties and composition of the pyrolytic products. Here, we demonstrated that the tar yield only fluctuates when the carbon content is approximately 80%. The ratios of aliphatic hydrogen to all the functional groups (Ib1) are the largest in HM2 coal, while the change of the ratios of aromatic hydrogen to all of the functional groups (Ib2) is the same as that of the tar yield. With the increase of coalification, the ratio of CH2 to CH3 in the aliphatic structure (Ic1) decreases. The oxygen containing functional groups in YL coal were mostly converted into tar products, but the corresponding functional groups in ZC3 coal decompose to form more water. When the final pyrolysis temperature is below 550 °C, there was a higher yield of gaseous products containing carbon and oxygen than of gaseous products containing hydrogen. With the decrease of the H/C ratio, the relative content of the aliphatic hydrocarbon and phenolic compounds in tar increased, while the benzene series and polycyclic aromatic hydrocarbons decreased.

Thermochemical Conversion of Coal under Microwave Radiation

Thermochemical Conversion of Coal under Microwave Radiation

Toward Low-Temperature Coal Gasification: Experimental and Numerical Studies of Thermochemical Coal Conversion Considering the Interactions between Volatiles and Char Particles

Toward Low-Temperature Coal Gasification: Experimental and Numerical Studies of Thermochemical Coal Conversion Considering the Interactions between Volatiles and Char Particles

An approach for on-line analysis of multi-component volatiles from coal pyrolysis with Li+-attachment ionization mass spectrometry

Ion-attachment mass spectrometry (IAMS) is a technique used for measuring easily ionized organic compounds in a non-fragmenting mode by softly attaching a Li+ or another type of alkaline ion to the gaseous molecule. In this study, a prototype device for Li+ IAMS is developed for real-time quantitative monitoring of the vapor produced from thermochemical conversion of coal. Simulated tar vapor containing a suite of aromatics and the real vapor produced from the pyrolysis of coal are monitored by IAMS with a Li+ source. It is confirmed that both the simulated and real vapors are ionized without undergoing fragmentation and the sensitivities of these detected aromatic molecules are similar to one another. In addition, when the feeding rate of the coal sample is changed from 0.5 to 1.0g/min, the peak intensities increase nearly twice as much. These results show the possibility of applying IAMS to the quantitatively monitoring of coal-derived volatiles.

Flow pattern evaluation of the internal circulation gasifying principle

Gasification is a key process for the thermochemical conversion of coal for both energetic utilization and its application as a chemical feedstock. In this regard low grade coal with high-ash content gains in importance. Because of its high availability, production share is increasing. Therefore, adapted gasifiers of novel design are required to meet the demands associated with converting high-ash coals. The internal circulation (INCI) principle is a multi-stage gasification system with the ability to efficiently convert high-ash feedstock.The present paper introduces the test-scale COORVED reactor, which was designed according to the INCI principle. Particle image velocimetry (PIV) and computational fluid dynamics (CFD) simulations are conducted for ambient conditions in a cold-flow test facility to demonstrate the flow pattern according to the INCI principle. The evidence of a recirculation cell is provided by PIV experiments. CFD simulations show similar results in terms of overall flow pattern and size of the recirculation cell. After the intensive investigations of the flow pattern in the cold-flow test facility, first PIV results were obtained in the COORVED reactor. The complex accessibility of the reactor raised the necessity of the validation of the elaborate measurement setup. The reliability of the measurement results is proven by generating a laminar velocity profile at ambient conditions, whose results are comparable to analytical solutions.

Coal and Biomass to Liquid Transportation Fuels: Process Synthesis and Global Optimization Strategies

The thermochemical conversion of coal and biomass to liquid transportation fuels from a synthesis gas intermediate is investigated using an optimization-based process synthesis framework. Two distinct types of coal (LV bituminous and coal commonly found in the province of Anhui, China) and two types of biomass (hardwood and duckweed) are considered as feedstocks. The superstructure incorporates alternative conversion pathways of synthesis gas which include methanol formation and conversion into FischerTropsch hydrocarbons. Methanol may be converted to gasoline or olefins, and the olefins may be subsequently converted to gasoline and distillate. A rigorous deterministic global optimization branch-and-bound framework is utilized to determine the optimal process topology that produces liquid fuels at the lowest possible cost. Economies of scale are evident as the refinery capacity increases and it is observed that the fuel ratios of the final liquid products have a significant impact on the optimal topology of the plant. The results suggest that liquid fuels production from coal and biomass can be competitive with petroleum-based processes.

Mathematical modeling of thermal decomposition of coal

Pyrolysis, as a first step in all thermochemical coal conversion processes, has been investigated in detail over the years in order to evaluate the kinetic data and to establish reliable models for the complex reaction scheme. Since coal pyrolysis is not a single reaction but rather a multiplicity in different time intervals for isothermal pyrolysis, or in different time and temperature intervals for the case of heat-up, any set of parameters cannot be expected to represent data accurately over a wide range of conditions. In this study, different kinetic models were used to model the decomposition of coal in the variable and constant temperature regions of pyrolysis. In the variable temperature region, the selected mechanism takes into account the order of reaction as a variable and uses data obtained; in different types of equipment, using different types of coal and a range of heating rate values. In the constant temperature region, a fixed-bed reactor data was used. Various models have been examined and the model which takes into account the dependence of the apparent activation energy on time, total conversion and the volatile matter in coal; gave the best correlation. Various numerical and analytical techniques were utilized to find the kinetic constants of the equations.

Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

00/01996 Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

00/01996 Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

Reactive metal-oxide redox system for a two-step thermochemical conversion of coal and water to CO and H 2

A number of metal-oxide redox systems were examined for a two-step thermochemical conversion of coal and water to CO and H 2 for the purpose of utilizing solar high-temperature heat below 900°C: metal oxide+CH n (coal)→metal+CO+ n/2H 2, metal+H 2O→metal oxide+H 2. In 2O 3 and SnO 2 were found to be the most reactive oxidants for coal under an N 2 gas stream below 900°C. These reactive metal oxides were tested for the proposed two-step cyclic process in the pulse feeding mode of H 2O, with a temperature swing and under an N 2 gas stream. The two-step cyclic process using the In 2O 3/coal mixture could be repeated with high coal conversions of about 80% in the temperature range of 600–900°C by resupplying the consumed coal to the system. The repeated two-step process via the In 2O 3/In redox system resulted in efficient performance of the net reaction CH n (coal)+H 2O→CO+( n/2+1)H 2, while hydrogen was scarcely produced in the continuous feeding mode of H 2O/N 2 over the In 2O 3/coal mixture, at a constant temperature of 900°C. The separation of recovered In 2O 3 from the remaining coal ashes by In 2O evaporation was also proposed.

Thermochemical conversion of coal and water to CO and H 2 by a two-step redox cycle of ferrite

Redox systems of iron-based oxides (ferrites) mixed with coal powder have been studied to determine the most reactive and selective working materials for thermochemical conversion of coal and water to CO and H 2. Reactions were performed in a two-step redox cycle in which the ferrites were reacted with coal powder at 900°C to produce CO, H 2, and reduced ferrites (coal-gasification step); these were then reoxidized with water vapor to generate H 2 at 700°C in a separate step (water-decomposition step). Magnetite and Mg(II)-, Mn(II)-, Ni(II)-, Zn(II)-, and In(III)-ferrites have been screened for reactivity and selectivity in the coal-gasification step. The In(III)-ferrite showed the greatest reactivity and selectivity for CO formation from coal at 900°C. The CO-production rate in the coal-In(III)-ferrite reaction was 3.5 times as fast as that in the single-step direct coal-H 2O reaction. The metallic phase of α-Fe and In, produced by the coal-In(III)-ferrite reaction, was reoxidized to the ferrite phase to generate H 2 in the water-decomposition step at 700°C. The amount of H 2 evolved using In(III)-ferrite was 5 times larger than that using magnetite. The processes were repeated in the temperature range 700–900°C, with the highly efficient net reaction CH τ(coal) + H 2O→CO + ( τ 2 + 1)H 2 .

Theoretical analysis of schemes for complex coal processing

The chemical technological processes (CTP) of coal conversion to methanol, coke, energy and heat have been studied. High-temperature gasification serves for a thermochemical conversion of coal to gaseous products and coke. The imitation models of such processes are created, and the mathematical modelling, thermodynamic analysis, optimization and calculations of the exergy efficiency of CTP are performed. Relationship between the main operation parameters of the coal gasification, their properties and the target products yield was studied.

Biological bleaching of water-soluble coal macromolecules by a basidiomycete strain

There is need for new effective technologies to convert coal into environmentally acceptable liquid fuels. Thermochemical coal-conversion processes occur under extreme conditions. Thus there is a potential to use the biotransformation of coal as a cheap alternative method. A basidiomycete strain, which decomposes coal macromolecules, was isolated from humic-acid-rich soil of a lignite surface-mining region. The isolate showed the ability to decolorize liquid dark-brown media containing water-soluble coal-derived substances (humic acids). The presence of an easily available substrate is necessary for the biodegradation. The influence of different culture conditions on the bleaching effect was studied. Evidence for decomposition of water-soluble coal substances was provided by measuring the decrease of absorbance and the modification in the distribution of molecular masses. The degradation process resulted in a complete decolorization of the coal-derived humic acids and was also combined with massive alterations in their molecular structure. Solid-state #13C-NMR spectroscopy showed an increase of carboxylic groups as well as hydroxylated and methoxylated aliphatic groups, which indicates an oxidative attack. Enzymatic analysis showed the presence of a Mn peroxidase in the culture supernatant. Extracellular lignin peroxidase and laccase activities were not detectable. The production of the peroxidase was induced by addition of humic acids. But, in vitro, this enzyme did not cause a decolorization or reduction in molecular mass of the coal-derived humic acids.

95/04995 Enhancement of thermochemical conversion of coal

95/04995 Enhancement of thermochemical conversion of coal

Coal bioprocessing research at the institute of gas technology

Coal bioprocessing research at the Institute of Gas Technology (IGT) has included solubilization, gasification, desulfurization, denitrogenation, production of specialty chemicals, and the remediation of organic and inorganic wastes associated with coal utilization. Currently, research is focused on desulfurization and remediation. Desulfurization research concerns the development of processes to remove organic sulfur or to convert a portion of pyritic sulfur to sulfuric acid rapidly, thereby serving as a pretreatment to aid the thermochemical conversion of coal to coke and liquid products. The removal of as much as 91% organic sulfur from coal has been achieved, and biodesulfurization of coal has been confirmed by seven analytical techniques performed in six different laboratories. Recent studies have involved the use of molecular genetics to develop strains of bacteria with higher levels of desulfurization activity, and the development of methods for the preparation, storage, and utilization of biodesulfurization catalysts. Remediation studies include the development ofin situ and on-site technologies to treat soil contaminated with coal tar, the leaching of metals from fly ash, and the treatment of waste water resulting from fly ash leaching or from acidic mine drainage (AMD). IGT currently has two projects in EPA’s SITE program concerned with the remediation of coal tar-contaminated soil, and other related technologies are being developed. Efficient laboratory-scale processes for the removal of metals from fly ash and from soil so that the solids pass EPA’s TCLP test, and the subsequent treatment of the leachates or AMD to meet all regulatory requirements have been developed. Data obtained in these projects are presented in particular, and a general discussion of the application of biotechnology to coal is offered.