Coal Conversion Rate Research Articles

Investigation of the co-processing technology of crude oil and coal and its deployment

Abstract The effect of process conditions on the co-processing technology of crude oil and coal was investigated. Crude oil/coal matching performance, swelling degree, crude oil/coal slurry viscosity-temperature characteristics and process parameters were obtained via the laboratory scale and pilot scale studies. The optimum reaction temperature of the co-processing was 445~450 oC, the pressure was 19 MPa, the catalyst addition was 3 wt.%, the reaction time was 2 h, and the ratio of hydrogen to crude oil was 1500 (V/V). Furthermore, the co-processing technology including catalyst and corresponding equipment based on the slurry bed hydrogenation were developed. By using this co-processing technology, the feed ratio of crude oil and coal can be 1:1, the coal conversion rate can be over 99%, the light oil (oil and aromatics) yield was over 70%, and the end products were gasoline, diesel, jet fuel, aromatics and LPG. The product quality meets the Euro V standard, whilst aromatics accounted for 48% of the light oil. So it was proved to be feasible to co-refine crude oil and coal at a ratio of 1:1. What’s more, the slurry bed hydrogenation plant and its equipment were tested for long-term operation, and it has been proved that this co-processing technology could be deployed as large-scale industrial application.

Co-hydrogenation behavior of Hami coal with Tahe residue

The hydrogenation and co-hydrogenation behaviors of Hami coal and Tahe residue were investigated in an autoclave, and the feasible technical route for co-hydrogenation was explored. The experimental results showed that Hami coal had good hydroliquefaction performance and the suitable reaction temperature was 445°C. At 445°C and 9 MPa, the coal conversion rate reached 98.74%, and the oil yield reached 68.54%. The hydrogenation tests of Tahe residue showed obvious coking tendency at the lower temperature, and it was difficult to achieve lightening. At 430°C, the conversion rate of Tahe residue was only 66.38%, the light oil yield was only 50.01%, and its coking rate was as high as 9.45%. The coking rate increased with the reaction temperature. When the mixtures of Hami coal and Tahe residue were co-hydrogenated directly, the conversion rate of the raw materials was lower, and the coke phenomenon was obvious. At the coal/oil ratio was 40/60, the conversion rate was 97.79%, and oil yield was 73.36%. Adding hydrogen solvents into the co-hydrogenation system could effectively inhibit coke formation, increase the conversion rate, and lighten co-hydrogenation products. When the amount of coal was 45% and Tahe residue was 20%, the conversion rate of raw materials was 98.38% and the oil yield was 74.82%.

Experimental Study on Coal Gasification in a Full-Scale Two-Stage Entrained-Flow Gasifier

In this paper, coal gasification characteristics in the reductor were investigated in a full-scale two-stage pressurized entrained-flow gasifier, which has been seldom conducted previously. The present study aimed at elucidating the effects of gasifying agent concentration, coal input rate, and operation period under full reductor load on the performance of a utility two-stage pressurized entrained-flow gasifier for the first time. When the steam input in the combustor was raised from 3318 kg/h to 5722 kg/h, the total outputs of H2, CO, and CO2 were increased by 1765 Nm3/h and 2063 Nm3/h, respectively, while the CH4 output was decreased by 49 Nm3/h. The coal conversion rate was minimal at low steam input. In addition, more coal gasified in the reductor could increase the output of CH4, while CH4 could reach 1.24% with the coal input in the range of 8000–10,000 kg/h. The present work can offer a further understanding of the gasification performance in the reductor of the full-scale two-stage pressurized entrained-flow gasifier, and motivates the potential for clean utilization of coal resource.

Comprehensive study of structure model, pyrolysis and liquefaction behaviour of Heidaigou lignite and its liquefied oil

An integrated study involving structure model, pyrolysis and liquefaction behaviour of Heidaigou lignite (HL) and its liquefied oil was carried out to have an in-depth and comprehensive understanding of lignite and its direct liquefaction behaviour. Detailed information on HL was obtained using a molecular structural model constructed on the basis of ultimate analysis combined with solid-state 13C nuclear magnetic resonance (NMR), X-ray photoelectron spectrometer (XPS) and X-ray diffraction (XRD) studies. The HL model has few aromatic ring structures, which are composed of naphthalene, benzene, pyridine and pyrrole. The aromatic structures are linked by the aliphatic chains, and the carbon content in each chain is not less than three. Pyrolysis is the basis of liquefaction; as such, the pyrolysis behaviour of HL was investigated by TG/DTG. Results show that the maximum weight loss rate is about 425 °C. At below 500 °C, some Cal–Cal and Cal–Car broke, but Car–Car did not. The effects of time and temperature on the liquefaction behaviour of HL were investigated in a PARR-stirred high-pressure reactor. The liquefaction took a certain amount of time. With increasing temperature, the coal conversion rate and oil yield remained stable or increased slowly. The optimal time and temperature for liquefaction of HL are 40 min and 440 °C, and the maximum oil yield and HL conversion rate reach 56.68% and 89.79%, respectively. In addition, the optimal temperature of liquefaction (440 °C) is slightly higher than that of the maximum weight loss rate (425 °C). The composition of aromatics in the liquefied oil was determined using column chromatography and GC–MS. Most of the aromatics are tetraline, naphthalene and its derivatives and monocyclic benzenes. Agreements and consistency exist between the HL model, pyrolysis and aromatics in the liquefied oil.

Pyrolysis of a lignite briquette – Experimental investigation and 1-dimensional modelling approach

A laboratory-scale shaft furnace was used for the pyrolysis of the lignite briquette together with thermogravimetric analysis to study the intrinsic pyrolysis kinetics under two different heating rates, 10 °C/min and 100 °C/min. Apart from coal conversion rate, the tar yield, quality and radical concentration in char were also measured to explore the difference between lignite briquette and the respective pulverised powder. Additionally, a 1-D model coupled with the chemical percolation devolatilisation (CPD) code was developed to quantitatively understand heat transfer using temperature dependent parameters; product distribution and yields, and the pyrolysis mechanism. It was discovered that heat transfer was the limiting factor for pyrolysis of the lignite briquette, which subsequently lowered the heating rate and led to increased cross-linking and decreased tar production compared to a coal particle. Simultaneously, the primary tar also underwent internal cracking and even deoxygenation to decompose into light aromatics and gases inside the briquette char matrix. Providing a hot gas environment was found to facilitate the cracking of tar species compared to a slow heating rate where tar is released at a lower temperature. The changes in radical concentration in the solid material were linked to the structural changes predicted by the CPD model including bridge-breaking, tar release and cross-linking phenomena.

Energy and exergy analysis of alternating injection of oxygen and steam in the low emission underground gasification of deep thin coal

Recent studies have shown that by coupling the underground coal gasification (UCG) with the carbon capture and storage (CCS), the coal energy can be economically extracted with a low carbon footprint. To investigate the effect of UCG and CCS process parameters on the feasibility of the UCG-CCS process, we utilize a validated mathematical model, previously published by the same authors, that can predict the composition of the UCG product, temperature profile, and coal conversion rate for alternating injection of air and steam for unmineable deep thin coal layers. We use the results of the model to conduct an energy and exergy analysis of the UCG process. We study the effect of various process parameters on the efficiency of the UCG process, the zero-emission recovery factor of coal, and the total CO2 emission of the process. Moreover, we compare the alternating injection of air/steam with the injection of an air and steam mixture.Exergy analysis shows that the alternating injection of air/steam describes a practical process for UCG at low pressure. However, injecting a mixture of steam and oxygen results in a practical recovery factor of coal higher than the alternating injection process. Additionally, we show that the zero-emission conversion of unmineable deep thin coal resources in a coupled UCG-CCS process, that is not practical with the current state of technology, can be realized by increasing the energy efficiency of the carbon dioxide capture process.

Pyrolysis of pulverized coal to acetylene in magnetically rotating hydrogen plasma reactor

This paper presents a clean and one-step way to produce acetylene by plasma pyrolysis of coal. A self-designed MW-scale rotating plasma reactor is used to investigate the pyrolysis of pulverized coal, characterized by the upstream injection of coal particles into the rotating plasma. The rotating plasma arc has a stirring effect and the upstream injection facilitates particle transportation, allowing for a good mixing of coal with plasma and high heat-transfer efficiency. The effects of magnetic coil current, coal flow rate and synergetic parameters on the pyrolysis were studied, and the optimum operating conditions of pyrolysis process were screened by taking consideration of acetylene mole fraction, yield, specific energy requirement and coal conversion rate. The minimum specific energy requirement of 9.50kWh/kg-C2H2 was achieved with a magnetic coil current of 875A.

Mathematical modeling of alternating injection of oxygen and steam in underground coal gasification

Recent successful low-pressure underground coal gasification pilot experiments that use alternating injection of air (oxygen) and steam have shown potential in large scale hydrogen production. This paper extends an existing steady state model to a transient model that can describe an alternating injection of air and steam for deep thin coal layers. The model includes transient heat conduction, where the produced heat during the air injection stage is stored in the coal and surrounding strata. The stored heat is used in the endothermic gasification reactions during the steam injection.The results show that product composition and temperature oscillation can be predicted with a reasonable accuracy. The stored heat can deliver additional energy that can maintain the gasification during the steam injection period for a limited time. During the steam injection cycle, at low pressure the volumetric flow and the hydrogen content of the product gas are both high, but at higher pressures while the hydrogen composition is still high the coal conversion decreases considerably. The results confirm that the alternating injection of air/steam describes a practical process for UCG at low pressure. However, at high pressure, injecting a mixture of steam and oxygen instead of alternating injection of oxygen/steam results in a higher coal conversion rate, with a final product that contains higher carbon content.

CO2 gasification of coal under concentrated thermal radiation: A numerical study

Solar coal gasification is a promising technology to convert coal into gaseous fuel. In this study, a steady-state one-dimensional (1D) two-phase model was developed to simulate CO2 gasification of coal in a quartz fluidized bed reactor directly exposed to concentrated thermal radiation as the heating source. Coupled with chemical kinetics, the present model encompasses energy equations for the gas phase, the solid phase, and the quartz reactor. The discretized energy equations were solved using the Levenberg–Marquardt algorithm. The initial carbon particle size was 140μm and the peak radiative heating flux was as high as 1270kWm−2. The CO2 flow velocity for fluidization was in the range of 0.10 to 4.0mmin-1 under standard conditions (25°C, 1bar). Simulated gas and coal particle temperature distributions, CO production rates, product gas compositions, and coal conversion rates were in good agreement with the experimental data reported in the literature. Furthermore, the present simulation provided insightful explanation on the optimum fluidization velocity for maximum CO production rate or maximum solar to chemical energy conversion. The present simulation also provided an energy balance analysis of the solar CO2 gasification process, which is challenging to conduct in experimental studies.

Enhanced Reaction Performance with Hematite/Ca2Al2SiO7 Oxygen Carrier in Chemical Looping Combustion of Coal

Chemical looping combustion (CLC) has been as a viable and efficient alternative for coal combustion with CO2 inherent separation. Iron ore is a promising candidate for CLC of coal due to its low cost. Due to a limitation of particle size of the iron ore used in the fluidized bed, the fines for the iron ore after sieving with a particle size of <0.075 mm were reused for reactivation in the present work. The calcium aluminate cement as a very cheap material was used to combine the fines to produce a cement-supported oxygen carrier. The CLC performance with the developed oxygen carriers was experimentally investigated using Chinese traditional anthracite as fuel. In this study, the components of Fe2O3 and cement were optimized to obtain a better reactivity in the coal CLC process. Further, two additives (Ni and K) were added as catalysts during the oxygen carrier preparation process in order to improve the coal conversion rate and gasification rate. The experimental results suggested that compared with the single iron-based oxygen carriers, the oxygen carriers in the presence of additives demonstrated a high carbon conversion rate, gasification rate, and greater oxygen usage. The effect of reducing temperature (850–950 °C) and reducing/oxidizing cycles (20 cycles) on the reaction performance of the oxygen carrier samples developed in this study were evaluated. Also, the attrition behavior during multiple cycles was investigated. The detailed catalytic mechanism under the effect of additives was further discussed.

Investigation of Chemical-Looping Combustion of Solid Fuels

The chemical-looping combustion process of solid fuels has been investigated using thermogravimetric analysis (TGA). Experimental results showed that CuO showed high reactivity during reduction process with coal. The coal conversion rate increased with the increase of reaction temperature, and the optimum reaction temperature was about 800 °C. When CuO was supported on TiO2, the temperature to initiate the reaction decreased and the coal conversion rate also increased. Candlenut wood ash, which contained high amount of alkali metal, displayed catalytic activity in mixtures with coal during the CLC process. A key issue is to find the ways for increasing the gasification rates during the CLC process in an industrial process.

Molten catalytic coal gasification with in situ carbon and sulphur capture

A molten catalytic process has been demonstrated for converting coal into a synthesis gas consisting of roughly 20% methane and 80% hydrogen using alkali hydroxides as both catalysts and in situ CO2 capture agents. Baselines studies were also conducted using no catalyst, weak capture agents (CaSiO3) and strong in situ capture agent for acid gases (CaO). While a similar gas composition can be achieved using CaO rather than alkali hydroxides, the rate of syngas production is greater when using molten alkali hydroxides than when using CaO as the in situ capture agent for acid gases, such as HCl, H2S and CO2. Parametric studies were conducted to understand the effects of temperature, pressure, catalyst composition, steam flow rate and the ratio of coal to alkali hydroxide on the performance of the molten catalytic gasifier in terms of kinetics and syngas composition. To measure the amount and the rate of coal conversion, we have developed a method for quantifying the coal conversion as the reduction charge remaining, which is related to the chemical oxygen demand remaining in the coal. At temperatures between 800 °C and 900 °C, we measured first-order steam-coal gasification rates using sub-bituminous coal of 2 h−1 in a fixed bed reactor while capturing significant quantities of both H2S and CO2, and while also generating 20% methane plus ethane in the syngas on a dry volume basis.

Use of ilmenite as an oxygen carrier in chemical looping combustion-batch and continuous dual fluidized bed investigation

Chemical looping combustion (CLC) is a novel way of burning carbonaceous fuel in which CO2 can be inherently separated. Though this technology is suitable for gaseous fuels, recently efforts have made to adopt this technology for solid fuels such as coal. Ilmenite as a suitable oxygen carrier for coal chemical looping combustion is investigated with respect to relevant chemical looping combustion properties. A parametric study conducted in a bubbling fluidized bed is presented in which the following are examined: ilmenite oxygen carrying capacity, ilmenite reactivity with gaseous and solid fuels with respect to redox cycle number, rate of coal conversion in the presence of ilmenite, and the influence of temperature on gas yield, conversion, and gas speciation during coal CLC. The conversion of syngas with ilmenite is best when ilmenite is fully oxidized; reactivity reduces as ilmenite is reduced. The reactivity of ilmenite with snygas increases with redox cycle number over the first cycles and close to 100% syngas conversion was measured. The carbon conversion was low at 900 °C but improved with increasing temperature. Likewise, the rate of gasification increased with increasing temperature approximately doubling when increasing the temperature from 900 to 950 °C. Furthermore, an equalmolar CO- H2 syngas was combusted at 900 °C in IFK’s CLC dual fluidized bed system using ilmenite as the oxygen carrier resulting in a steady-state conversion of circa 90%.

Metal-Oxide-Catalyzed CO2 Gasification of Coal Using a Solar Furnace Simulator

Metal-oxide-catalyzed CO2 gasification of coal was demonstrated in small packed-bed and fluidized-bed reactors using a solar furnace simulator, for the purpose of converting solar high-temperature heat to chemical fuels. The catalytic activities of In2O3 and ZnO were investigated because used In2O3 or ZnO catalyst may be separated from remaining coal ash by In2O or Zn evaporation at high temperatures and at a reducing atmosphere. Bituminous coal with or without the metal-oxide catalyst in the quartz-tube reactor was directly irradiated by the concentrated Xe-lamp beam and CO2 was fed to the reactor at pCO2 = 1.0. In the packed-bed reactor, In2O3 and ZnO much improved the chemical coal conversion by about 4−5 and 2−3 times at the catalyst loading of 17 wt %-In and 30 wt %-Zn in the coal−metal-oxide mixture, respectively, at temperatures around 1000−1400 K. In the fluidized-bed reactor at a small catalyst loading (8−10 wt %-metal in the coal−metal-oxide mixture) and at 1073−1163 K, In2O3 catalytically increased the coal-conversion rate by 3 times but ZnO scarcely showed the catalytic activity. This metal-catalyzed coal gasification process offers the efficient solar production of the syngas calorifically upgraded by solar energy.

Thermochemical CO2 Gasification of Coal Using a Reactive Coal-In2O3 System

A number of coal-metal oxide systems were examined for a thermochemical CO 2 gasification of coal in a two-step cyclic redox mode, as well as in a normal single-step mode for the purpose of utilizing solar high-temperature heat below 1173 K. In the two-step cyclic redox mode, metal oxide was reacted with coal powder as an oxidant in the absence of CO 2 at 1173 K to produce CO, H 2 , and the component metal which was reoxidized with CO 2 to generate CO at lower temperatures in a separate step. In 2 O 3 was found to be the most reactive metal oxide among the thermodynamically promising metal oxides. The two-step cyclic CO 2 gasification could be repeated using the In 2 O 3 /In redox system by resupplying the consumed coal to the system. About 80% of the coal supplied to the system was gasified at the temperature range of 1023--1173 K. The In 2 O 3 phase was completely regenerated without the formation of other solid phases after repeating the two-step gasification. In a normal single-step, continuous feeding mode of CO 2 at a constant temperature of 1173 K, the coal-In 2 O 3 system also showed the most reactivity for the Boudouard reaction of C + CO 2 → 2CO in the CO 2 gasification of coal at the metal content of 17 wt % in the coal and metal oxide mixture. Depending on the indium content in the mixture, the initial coal-conversion rates with the coal-In 2 O 3 system were 2.5-4 times as fast as that in the coal-CO 2 reaction without any catalysts. The separation of used In 2 O 3 from the remaining coal ash by In 2 O evaporation was also proposed.

Elucidation of Mechanism of Coal Liquefaction Using Tritium and 35S Tracer Methods

The reactivity of hydrogen in tetralin and in Taiheiyo coal in the presence of iron catalysts (pyrrhotite and iron pentacarbonyl (Fe(CO)5)) and sulfur were investigated using tritium and 35 S tracer methods under liquefaction conditions. Coal liquefaction was performed for 30 min at an initial pressure of 5.9 MPa and a temperature of 400 °C in the presence of tetralin solvent and tritiated hydrogen, with and without a catalyst and 35 S-labeled sulfur. The rate of coal conversion and the tritium distribution in coal were higher when Fe(CO)5 and sulfur were used than were obtained with conventional pyrrhotite. Further, the coal products obtained with the use of Fe(CO)5 and sulfur were lighter than those produced in the presence of added pyrrhotite. The results suggest that the catalyst derived from Fe(CO)5 and sulfur was successfully dispersed in the coal and directly acted on the coal to increase both the rate of coal conversion and the tritium transfer from the gas phase to the coal. The iron catalysts greatly promoted the hydrogen exchange between the gas phase and the tetralin solvent in the absence of coal. Part of the added sulfur participated in the sulfur exchange reaction with the pyrrhotite catalyst. The addition of sulfur increased the amount of hydrogen incorporated into the coal. This suggests that sulfur promoted the formation of tetralyl radicals during the hydrogen transfer from the solvent to the coal.

Oxygen elimination in the process of non-catalytic liquefaction of brown coal

The effects of process temperature, pressure and reaction time on brown coal conversion rate and accompanying degree and form of oxygen elimination were evaluated in a series of autoclave runs. The degree of total oxygen elimination depends mainly on the process temperature. Increase of temperature favours formation of H 2O.

Coal liquefaction in lignin-derived liquids under low severity conditions

It is found that lignin-derived liquids when reacted with coal under mild reaction conditions (375 °C and 2.17 × 10 6 − 3.55 × 10 6 N m −1) enhance the rate of coal depolymerization. Up to 30% enhancement in coal conversion rate is achieved using lignin-derived liquids. The influence of time of reaction and temperature on the degree of reaction was investigated. The lignin liquid-assisted coal depolymerization products (liquid) are observed to contain a significant amount of the desirable pentane-soluble fraction. Influence of the time of storage of lignin-derived liquids on coal conversion was also determined. Also reported are data on elemental analyses of the solid and liquid products. The liquid product analyses using n.m.r. and s.e.c. techniques are also presented. Based upon the experimental data collected, it is hypothesized that enhancement in coal depolymerization rate can be explained by a reaction pathway involving intermediates formed from lignin-derived lignin liquids. A mathematical model describing the reaction chemistry has been developed. Computed rate constants are also reported. The analysis indicates that the lignin-derived intermediates are short-lived as compared to the time needed for complete coal depolymerization.