High Coal Conversion Research Articles

Modelling of multiphase reactive flows in a full-loop coal-direct chemical looping combustor

The coal-direct chemical looping (CDCL) process is a promising clean coal combustion technology, yet the internal multiphase reactive flows in the full-loop system are not clear. In this paper, for the first time, a multi-fluid CFD model of gas–solid-powder reactive flow is developed to describe the gas-oxygen carrier-coal reactive flow in a full-loop CDCL unit, based on Eulerian-Eulerian-Lagrangian framework. The model is validated by comparing with experimental data in terms of flow and reaction behaviours. The model predicts the unique gas-oxygen carrier-coal flow in the full-loop moving-bed CDCL unit, including multiple fluidisations, mixing and separation between the oxygen carrier and coal. The mean residence time of coal particles is around 13 s ∼ 20 s through statistics of discrete particles at the reducer outlet. The high temperature in the CDCL system is observed in the AR riser, cyclone and the top section of the fuel reactor (FR); whereas the low temperature is observed at the bottom of the FR and the l-valve, as a collected result of endothermic and exothermic reactions. A less than 5 mol%, leaks of O2 from the combustor to the reducer can be captured, which is caused by the unbalanced pressure distribution. Overall, over 90 vol% CO2 concentration and 100 % coal carbon conversion are achieved at the FR outlet, which indicates a high CO2 separation efficiency and coal carbon conversion of this CDCL system. This work provides a useful tool for designing and optimising CLC processes.

Role of hydrogen donor and non-donor binary solvents in product distribution and hydrogen consumption during direct coal liquefaction

Direct liquefaction of Chinese Hami sub-bituminous coal was conducted with binary mixtures of hydrogen donor solvent tetralin (THN) and non-donor 1-methylnaphthalene (1-MN) or naphthalene (Nap.). Effects of solvent composition, temperature, atmosphere, and catalyst FeS2 on product distribution and hydrogen consumption were investigated at solvent/coal mass ratio of 2. The results show that oil yield increases from 47.70% to 59.95% with 1-MN/THN ratio changing from 2:1 to 1:2. Hydrogen donating ability of binary solvents increases with the rising ratio of THN. H2 contributes noticeably positive effect on coal conversion in the case of liquefaction with insufficient hydrogen donor solvent. Oil yield obtained during direct coal liquefaction (DCL) with Nap./THN is 58.32%, which is 10.62% higher than that with 1-MN/THN at same solvent ratio of 2:1. This is owing to demethylation effect of 1-MN under liquefaction condition. 1-MN demethylation is induced by active hydrogen and coal radicals, and could consume noticeable hydrogen during DCL. This indicates that the amount of alkylarenes included in liquefaction mixed solvents should be limited, or sufficient hydrogen donor solvent is required to achieve high coal conversion.

Production of Hydrogen through Photo-Electro-Catalytic Oxidation of Coal Using TiO2 Nanotube Arrays

Due to global warming concerns, major efforts have been devoted to reducing CO2 emission by switching from the use of coal to other clean fuels, such as natural gas. However, since coal is the most abundant hydrocarbon resource, it would be helpful to develop a non-traditional approach for the utilization of coal that substantially reduces its climate impacts, e.g., electro-oxidation of coal. Electro-oxidation of coal has been studied for many years. The basic concept provides for the production of gaseous pure hydrogen fuel (H2), along with a separate stream of CO2, and these products can be achieved at relatively mild reaction conditions as compared to conventional coal gasification. However, due to the formation of a diffusive barrier film at the coal surface during the oxidation reaction, sufficiently high kinetic rates leading to an acceptable level of conversion have not been achieved at atmospheric pressure. In addition, to obtain desired reaction rate and electrode stability, noble metal materials have to be used in this process, resulting in higher cost and a higher barrier for potential commercialization. To solve these problems, a modified electro-oxidation of coal concept has been developed, by combining pyrolysis and photo-electro-catalysis technology. As a widely used photo catalyst, black TiO2 nanotube arrays (bTNA) have been intensively studied as the anode material in the area of photo-assisted water electrolysis. However, in nontransparent systems, use of this process is still a challenge. In this modified process, coal can be oxidized by bTNA with the aid of sunlight, with iron cations serving as the shuttle catalyst. Along with the development of this concept, a series of parameters (e.g., the reaction conditions and methods for electrode preparation) were also examined to facilitate higher kinetic rates, higher coal conversions and overall higher energy efficiency.

Research of coal-direct chemical looping hydrogen generation with iron-based oxygen carrier modified by potassium

Coal-direct chemical looping hydrogen generation (CLHG) is a promising process for hydrogen production with high coal conversion efficiency and low carbon footprint. In this work, experiments on coal-direct CLHG process were carried out using K2CO3 modified Fe2O3/ZrO2 as oxygen carrier (OC) and Shenmu (SM) char as fuel in a fixed-bed reactor. The effect of char/OC mass ratio on CO2/CO volume ratio, H2 production and phase transformation was investigated. Multicycle tests with SM char and deashed SM char were conducted to investigate the activity stability of OC and the reason for the deactivation of OC. The results confirm the feasibility of coal-direct CLHG process. Higher char/OC mass ratio could enhance the H2 production and decrease the CO2/CO volume ratio and oxidation state of iron oxides in OC. In the multicycle tests with SM char, carbon conversion and H2 production remained almost constant during the first 2 redox cycles and then decreased abruptly in the 3rd cycle. During the 3 cycles, the phases of OC residues remained unchanged and no detectable surface sintering was observed. Furthermore, the K contents of residues decreased slightly. In the multicycle tests with deashed SM char, the carbon conversion and accumulation H2 production were stable during the first 10 cycles and then decreased slowly. Some morphology features changes appeared during the 11 cycles, but no obvious surface sintering was observed. The K contents of residues declined by 2/3 after the 10th cycle.

41.架橋抑制-水素化促進を目指した石炭の迅速熱分解反応設計

41.架橋抑制-水素化促進を目指した石炭の迅速熱分解反応設計

Transformation Characteristics of Sodium of Zhundong Coal Combustion/Gasification in Circulating Fluidized Bed

In this study, the transformation characteristics of sodium in Zhundong coal were investigated, following its combustion (oxidizing atmosphere) and gasification (reducing atmosphere) in a circulating fluidized bed (CFB) experimental system of 0.25 t/d high alkali coal thermochemical conversion. The equilibrium distribution of Na is predicted under the oxidizing and reducing atmospheres by the thermodynamic equilibrium calculation. Na in bottom ash and fly ash evidently decreases as the temperature increases in both the combustion and gasification processes. More Na is retained in the ash during the gasification process. Na exists as sodium aluminosilicate in both combustion bottom ash and gasification bottom ash, and mainly as sodium sulfate (Na2SO4) in combustion fly ash and sodium chloride (NaCl) in gasification fly ash. Na undergoes different transformation processes through combustion and gasification. Gaseous metallic sodium, Na2O and NaCl are released from the coal and condense directly on the cold ...

Parametric and dynamic studies of an iron-based 25-kWth coal direct chemical looping unit using sub-bituminous coal

The iron-based Coal-Direct Chemical Looping (CDCL) combustion process is an alternative to conventional oxy-combustion technologies, where the oxygen used for fuel conversion in the CDCL process is provided by an iron-oxide based oxygen carrier instead of an air separation unit. The iron oxide is reduced using coal in the reducer reactor, producing highly-pure CO2 in the flue gas, and the reduced iron oxide is regenerated in a separate combustor reactor using air. The CDCL process at Ohio State has been developed and demonstrated in a 25 kWth sub-pilot unit, and it is the first chemical looping demonstration unit with a circulating moving bed reactor for solid fuel conversion. To date, the CDCL sub-pilot unit at OSU has been operated for more than 680 h, with a 200-h continuous operation, providing important data on long term operability as well as parametric optimization. This paper discusses recent parametric operational experience with sub-bituminous coal as the fuel, where dynamic changes in variables were performed to observe the effects on the unit itself. Measurements included temperature, pressure, and gas concentrations from the reducer and combustor. Furthermore, effects of different variables, such as flue gas recycle ratios (enhancer gas flow rates), feed port injection, and temperature, were observed. Tests confirmed high coal conversions with high purity of CO2 achieved in the flue gas. Overall, the moving bed design of the reducer results in nearly full coal conversion with a high purity of CO2, eliminating the need for additional down-stream fuel polishing and/or separation units. The combustor gas contained lean oxygen concentrations with minute amounts of carbonaceous gases detected, indicating proper regeneration of the oxygen carrier as well as good gas sealing between the reducer and combustor.

Direct liquefaction on low rank Batu Arang coals of Malaysia: Influence of petrographic composition

2 Novosibirsk city, Krolev street 21, Russia Abstract: A direct liquefaction study was performed on a set of low-rank Malaysian coals from Batu Arang, Selangor in Peninsular Malaysia. The analysis was carried out in a 1000 mL high temperature and high-pressure reactor batch- wise system using tetralin as hydrogen donor solvent, at temperature of 420°С and at pressure of 4МРа. The influence of maceral composition was investigated based on comparison made on the percentage of coal conversion and product yield for the three coals that were analysed. These analysed samples contain reactive macerals (vitrinite + exinite) in the range of 76% - 92%. The high coal conversion and oil+gas yields are attributed predominantly to the high content of reactive macerals of vitrinite and exinite maceral groups, with some contribution from the inertinite maceral group. This suggests the analysed Batu Arang coals possess good potential to act as an alternative liquid fuel in the future through direct liquefaction process.

Investigation of Coal Slags and Related Oxide Systems by KEMS

Alkali release and behaviour of coal slags are among the main problems in the high temperature coal conversion processes. Therefore, the thermodynamic properties of slags and the related synthetic oxide systems are important. This article gives several examples of vaporisation investigations on coal slags and synthetic oxide systems by KEMS performed in our lab in the recent years.

Thermodynamic Assessment of a Novel Concept for Integrated Gasification Chemical Looping Combustion of Solid Fuels

A novel integrated gasification chemical looping combustion (IGCLC) process is proposed here for combustion of solid fuels, particularly coal. The proposed process incorporates an ex situ step for gasification of the solid fuel, but unlike conventional ex situ methods, the gasification process is fully integrated with the combustion process. This is achieved using a three-step chemical loop for the production of hydrogen, combustion of gaseous fuels, and regeneration of metal oxides. A detailed thermodynamic chemical equilibrium assessment of the IGCLC process was carried out to evaluate its technical viability. The relevant analyses were performed using Aspen Plus process simulation software. The IGCLC process was found to be thermodynamically feasible. More specifically, it was uncovered that the gasification process can operate at an adequate temperature (above 1023 K) at thermoneutral conditions with high coal conversion (95%). It was also found that, to achieve the highest hydrogen production, the steam/hydrogen to carbon ratio (SHTCR) had to be set to 2, at which the gasification temperature was around 1070 K, coal conversion was 95%, gaseous fuel reactor (i.e., combustor) temperature was 1140 K, and H2 productivity was 0.85 mol/mol carbon. Mass and energy balance calculations were also performed. It demonstrated that the proposed IGCLC system can achieve an electricity efficiency of 49.5% at SHTCR ∼ 2 and feed temperature of 1100 K with some appropriate assumptions, which is 80% higher than a conventional coal-fired power station with carbon capture and storage (CCS) measures.

A Comparison of FeS, FeS + S and solid superacid catalytic properties for coal hydro-liquefaction

Catalyst plays an important role in direct coal liquefaction. This paper focuses on the catalytic behavior of a novel SO 4 2 - / ZrO 2 superacid catalyst in coal hydro-liquefaction. A series of hydro-liquefaction experiments were conducted under mild conditions – 400 °C, 30 min and H 2 initial pressure 4 MPa in a batch autoclave with a volume of 100 ml. The catalytic property of SO 4 2 - / ZrO 2 was compared with FeS and FeS + S by Shenhua coal. The liquefaction products catalyzed by different catalysts were analyzed by FTIR spectrum, 1H NMR spectrum and element analysis. In addition, the SO 4 2 - / ZrO 2 solid superacid was characterized. The results indicated that the SO 4 2 - / ZrO 2 solid superacid shows outstanding catalytic property for direct liquefaction of coal and gives the highest coal conversion and gas + oil yield compared to other two catalysts. The THF conversion and the extraction yield of CS 2/NMP mixed solvent of liquefied coal catalyzed with SO 4 2 - / ZrO 2 are 76.3%, daf and 81.2%, daf respectively, and the yield of gas + oil is 62.5%, daf under the condition used in this study. The pyrolysis of coal macromolecular clusters can be promoted by catalysts such as FeS, FeS + S and SO 4 2 - / ZrO 2 . There may be only the pyrolysis of volatile matter and the relaxation of the structure of coal macromolecular clusters in non-catalytic liquefaction at 400 °C. Added sulfur in FeS can improve the catalytic activity of hydrogenation. SO 4 2 - / ZrO 2 is a notable catalyst in the study of coal direct liquefaction because it shows excellent catalytic activities for the pyrolysis and the hydrogenation. In addition, it has been found that the C–O bond is the most stable group in coal liquefaction reaction except for the covalent bond between carbon and carbon.

Liquefaction Studies of Low-Rank Malaysian Coal Using High-Pressure High-Temperature Batch-Wise Reactor

ABSTRACT Direct liquefaction of low-rank Malaysian coal from the Mukah Balingian (MB) area was successfully carried out in a 1000 ml high-temperature (360–450°C) high-pressure (4–13 MPa) batch-wise reactor system using tetralin as hydrogen donor solvent. The results indicated that the percent coal conversion obtained were in the range of 31–90%. At optimum conditions of 450°C and 4 MPa, the oil + gas, asphaltene and preasphaltene of the coal extract were 80%, 7%, and 2%, respectively. It was observed that heat plays an important role in comparison to pressure in contributing to high coal conversion, oil yield, and organic properties of the residues. The high coal conversion and oil yield correlate well with the high content of reactive macerals, i.e., vitrinite and exinite, in the coal. Other parameters that were also investigated include the effect of reaction time (0–120 min) and coal-to-solvent ratio. A high yield of asphaltene and preasphaltene was obtained at the longest reaction time (i.e., 120 min). Coal conversion and oil yield increase with increasing in coal-to-solvent ratio, with the optimal ratio being 1:5.

04/00679 Study on quick liquefaction reaction of coal: Lin, K. et al. Ranliao Huaxue Xuebao, 2003, 31, (1), 49–52. (In Chinese)

The reaction process of quickly liquefying Chinese Yangcun bituminous coal was studied under pressure of hydrogen 70?MPa(cold) by using resonance agitation reactor The results show that a high coal conversion has been obtained at short reaction time (coal quick liquefaction) by raising reaction temperature appropriately and enhancing active hydrogen concentration and improving its transfer speed and path in the reaction system The best reaction temperature of coal quick liquefaction (CQL) is the upper limit of the coal pyrolysis temperature range in TGA Compared coal conversion and benzene soluble (BS) yield of CQL with those of common liquefaction,CQL greatly enhances efficiency of coal liquefaction and it is favorable for further utilizing coal liquefaction product

AN ENZYMATIC METHOD FOR REMOVAL OF PHENOL FROM INDUSTRIAL EFFLUENT

ABSTRACT Phenols in an aqueous solution were removed after treatment with peroxidase in the presence of hydrogen peroxide. Phenols occur in wastewater of a number of industries, such as high temperature coal conversion, petroleum refining, resin and plastic, wood and dye industries, etc. It can be toxic when present at elevated levels and is known to be carcinogeneous. Thus, removal of such compound from these industrial effluents is of great importance. An enzymatic method for removal of phenols from industrial wastewater, using turnip peroxidase, has been developed. Phenol-containing industrial wastewater was treated with immobilized turnip peroxidase in the presence of hydrogen peroxide. In the reaction, a number of phenols are oxidized to form the corresponding free radicals in the presence of hydrogen peroxide as an oxidant. Free radicals polymerize to form substances that are less soluble in water than the original substances. The precipitates were removed by conventional methods and residual phenol was estimated. The present report describes the immobilization of turnip peroxidase on silica via covalent coupling, and its utility in phenol removal. A comparative study was also carried out with other immobilization techniques, viz., calcium alginate entrapment, polyacrylamide gel entrapment, etc. Peroxidase, covalently bound to silica, showed 95% removal of phenol, whereas naphthol was removed up to 99%.

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.

Effect of coal pre-treatment with swelling solvents on coal liquefaction

Pre-treatment of coal with swelling solvents may enhance coal porosity and thus facilitate catalyst action. The yields of products obtained by coal liquefaction were very much dependent on the type of swelling solvent used. Those studied included ethanol, tetrahydrofurane (THF) and tetrabutylammonium hydroxide (TBAH). After this treatment coal was liquefied using ZnCl 2 as catalyst, both alone and mixed with Fe 2O 3 or ICI 41-6 (Co–Mo). When ethanol was used, the highest coal conversion was obtained, although this solvent had the lowest swelling ratio, probably because a better catalyst impregnation was achieved. On the other hand, although the swelling ratio of TBAH was the greatest, lower overall coal conversions and higher oils yields were observed. In an attempt to interpret these results, coal structure before and after swelling pre-treatment was also studied using SEM.

The use of coal liquefaction catalysts for coal/oil coprocessing and heavy oil upgrading

The catalytic hydrogenation of heavy oil and mixed coal-heavy oil (coprocessing) systems has been the focus of a recent study at the Federal Energy Technology Center (FETC). The intent of this effort was to extend the use of coal liquefaction technologies to heavy oil upgrading and coprocessing systems. Specifically, new dispersed molybdenum-based catalysts developed at FETC and a novel silica-doped hydrous titanium oxide (HTO : Si)-supported NiMo catalyst developed at Sandia National Laboratories (SNL) were tested in these systems. The results indicate the potential of coal liquefaction catalysts for use in coprocessing and heavy oil upgrading. High conversions of coal–oil mixtures were observed with dispersed catalyst loadings as low as 100 ppm Mo. Similar results were observed in heavy oil systems. Also, the novel NiMo/HTO : Si catalyst was at least as effective as commercially-available supported catalysts (e.g. Amocat 1C) for conversion of high boiling point material to distillable products and aromatics removal.

Iron sulfate/sulfur-catalyzed liquefaction of Wandoan coal using syngas–water as a hydrogen source

Water-soluble iron sulfate/sulfur-catalyzed coal liquefaction using three kinds of hydrogen sources including syngas–water has been investigated. The liquefaction of Wandoan coal, an Australian subbituminous, with iron sulfate/sulfur as a catalyst precursor using syngas–water or carbon monoxide–water afforded higher coal conversions and oil yields than those using pressurized hydrogen gas. The pretreatment at relatively low temperature (200°C) was indispensable to achieve the high coal conversion. In the two-staged liquefaction (400°C, 60 min+425°C, 60 min), the use of syngas–water as a hydrogen source afforded higher coal conversion of 90.1% together with a high oil yield of 46.2% than those using pure hydrogen, and almost comparable to those using carbon monoxide–water, indicating the presence of synergistic effects of two hydrogen sources. At the early stage of the reaction, the contribution of carbon monoxide–water was predominant, whereas hydrogen gas significantly took effect at the latter stage. The XRD and XPS study revealed the formation of pyrrhotite, a possible active species, covered with a small amount of sulfate species.

Efficient Thermochemical Cycle for CO2 Gasification of Coal Using a Redox System of Reactive Iron-Based Oxide

A two-step thermochemical process using a redox system of metal oxides for converting coal and CO2 to CO was studied on a number of iron-based oxides (ferrites) for the purpose of utilizing solar high-temperature heat below 1173 K. In the first step, ferrite was reacted with coal powder as an oxidant to produce CO, CO2, and the component metals. Pure magnetite (Fe3O4) was readily reduced to FeO but the reduction from FeO to α-Fe scarcely proceeded in 30 min of the reaction with coal at 1173 K. It was found that Ni(II)- or In(III)-substitution for Fe(II) or Fe(III) in magnetite strongly enhances the phase transition from FeO to metallic phase to improve the efficiency for coal conversion. The reactive Ni(II)- and In(III)-ferrites were almost reduced to the metallic phases of Ni−Fe alloy and the mixture of α-Fe and In, respectively. The Ni(II)- and In(III)-ferrite reactions yielded high coal conversion of 60−70% which was about 3 times as large as that by a conventional single-step CO2 gasification of coal. In the second step, the reduced reactive ferrites were reoxidized with CO2 to generate CO at 1073 K. The metallic phase of α-Fe and In was completely converted to oxidized phases with CO2 while the Ni−Fe alloy could not be completely oxidized. The two-step process using In(III)-ferrite could be repeated with high coal conversions of 60−90% by resupplying the consumed coal to the system, although the conversion gradually decreased by the accumulation of ashes. Our findings suggest that the highly efficient net reaction CHn(coal) + CO2 → 2CO + n/2H2 may be conducted using concentrated solar radiation as the energy source for high-temperature process heat below 1173 K.

Pressurized fluidized bed combustion and gasification of coal using flue gas recirculation and oxygen injection

A combined cycle incorporating pressurized fluidized bed combustion of coal with pure oxygen and recycled flue gas followed by pressurized combustion of the fuel gas using pure oxygen, is a process which produces electricity and heat with a high efficiency and a flue gas with a high CO2 concentration. CO2 recovery from this process can be done more easily than from conventional coal conversion processes. In this way a high efficiency coal conversion process can be realized with low CO2 emissions. The specific aim of the project is to assess the technical feasibility of this process. For this purpose a 1.6 MWth pressurized fluidized bed combustion test rig has been modified to study experimentally the gasification process and the pressurized combustion of the resulting low calorific value fuel gas. The objectives of the project, the modified test rig and the experimental results obtained from combustion experiments with coal, recirculated flue gas and pure oxygen are described. The conversion efficiencies and the emission of harmfull components measured during these experiments are analyzed and compared with values obtained during combustion and gasification using air.