Coal Gasification Reaction Research Articles

Thermodynamic Analysis of Blast Furnace Slag Waste Heat-Recovery System Integrated with Coal Gasification

The blast furnace (BF) slag waste heat was recovered by an integrated system stage by stage, which combined a physical and chemical method. The water and coal gasification reactions were used to recover the heat in the system. Based on the first and second law of thermodynamics, the thermodynamic analysis of the system was carried out by the enthalpy–exergy diagram. The results showed that the concept of the “recovery-temperature countercurrent, energy cascade utilization” was realized by this system to recover and use the high-quality BF slag waste heat. In this system, the high-temperature waste heat was recovered by coal gasification and the relatively low-temperature waste heat was used to produce steam. The system’s exergy and thermal recycling efficiency were 52.6% and 75.4%, respectively. The exergy loss of the integrated system was only 620.0 MJ/tslag. Compared with the traditional physical recycling method producing steam, the exergy and thermal efficiencies of the integrated system were improved significantly. Meanwhile, approximately 182.0 m3/tslag syngas was produced by coal gasification. The BF slag waste heat will be used integrally and efficiently by the integrated system. The results provide the theoretical reference for recycling and using the BF slag waste heat.

Pyrolysis and Gasification Reactivity of Several Typical Chinese Coals and Their Macerals

Coals with different reducibility and their macerals in China were chosen as the experimental samples. The pyrolysis and isotherm CO2-gasification reactivity and their influencing factors were investigated by thermogravimetric analysis method. The results show that the coal with stronger reducibility has higher pyrolysis reactivity and lower gasification extent than that of the coal with weaker reducibility. With the increase of holding temperature time and pyrolysis final temperature, coal pyrolysis extent increases, while the sample isotherm gasification reactivity presents different properties. Vitrinites show higher pyrolysis reactivity and lower gasification extent than that of raw coals and inertinites. In addition, maceral origin has a remarkable effect on the pyrolysis and isotherm gasification reactivity of coal samples.

Effects of fluxing agents on gasification reactivity and gas composition of high ash fusion temperature coal

A Na-based fluxing agent Na2O (NBFA) and a composite fluxing agent (mixture of CaO and Fe2O3 with mass ratio of 3:1, CFA for short) were used to decrease the ash fusion temperature of the Dongshan and Xishan coal from Shanxi of China and make these coal meet the requirements of the specific gasification process. The main constituents of the fluxing agents used in this study can play a catalyst role in coal gasification. So it is necessary to understand the effect of fluxing agents on coal gasification reactivity and gas composition. The results showed that the ash fusion temperature of the two coal used decreased to the lowest point due to the eutectic phenomenon when 5 wt% of CFA or NBFA was added. Simultaneously, the gas molar ratio of H2/CO changed when CFA was added. A key application was thus found where the gas molar ratio of H2/CO can be adjusted by controlling the fluxing agent amount to meet the synthetic requirements for different chemical products.

An investigation of steam production in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) for solid fuels

Chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) are being actively explored as solid fuel combustion technologies that have the potential to facilitate CO2 capture. While CLC and CLOU have similarities operationally, there are some key differences. In particular, the CLC process requires a coal gasification step where coal is first broken down into a syngas with the use of steam or CO2. The resulting syngas is then oxidized with the metal oxide to release energy. In the CLOU process the metal oxide releases oxygen that combusts the solid fuel, resulting in a lower residence time, as the coal gasification reactions are avoided. The CLC and CLOU systems were modeled with ASPEN Plus at a 10MWth scale, and the process streams were analyzed by ASPEN Energy Analyzer to determine the amount of industrial process steam that could be generated from CLC or CLOU. Both the air and fuel reactor were analyzed as two circulating fluidized beds, with metal oxide circulating between the two reactors. The air reactor, where metal oxide is oxidized, was fluidized with air. The fuel reactor, where the metal oxide is reduced, was fluidized with steam for CLC and recirculated CO2 for CLOU. It was identified that the CLOU process had the potential to produce more steam, approximately 7920kg/h, as compared to CLC (6910kg/h).

Pressurized CO2-enhanced gasification of coal

Carbon dioxide was considered as a co-gasifying agent in a coal gasification reactor. The work presented herein describes the simulation results for the process and the experimental data on coal char gasification with CO2 addition as the rate-controlling step for the entire process. To study the potentially beneficial effect of the introduction of CO2 into the gasification system, several simulations were conducted using the commercial process simulation software ChemCAD 6.3®. The results of a Gibbs equilibrium reactor were evaluated. The Boudouard reaction is a critical path for the development of this process, and the kinetics were studied experimentally. Four chars derived from the pyrolysis of Polish coals of different origins were selected for the experiments. The kinetic characteristics of this system were examined using a custom-designed pressurized fixed-bed reactor. To determine the effect of pressure on the gasification rate, several preliminary studies on the gasification of coal chars were performed isothermally at the temperature of 950 °C and pressures of 1, 10, and 20 bars. In contrast to the thermodynamic calculations, the experimental data revealed that increasing the CO2 pressure leads to a higher reaction rate for medium-rank coal chars and low-rank lignite coal char, resulting in higher efficiency for carbon monoxide production. The pressure influences the reactivity more strongly when varied from 1 to 10 bars; a further increase in pressure affects the rate almost insignificantly. The observed behavior representing the changes in carbon conversion degree during gasification is satisfactorily described by the grain model.

An Empirical Correlation between Char Gasification Reactivity and Its Parent Coal

AbstractThe reactivity of 16 coal chars of varying rank with CO2 and H2O was determined to examine the effects of fixed carbon, ash, and volatile matters of raw coal on the gasification reactivity of coal chars. An empirical correlation between the gasification reactivity of coal particles and coal types was presented. A general index, Rc, which was used to indicate the gasification reactivity of coals with CO2 and H2O, is presented. Rc only depends on the proximate analysis and ash composition of coal and reflects the gasification behavior in a combined way, so Rc is called the gasification characteristic index of coal. It is a very useful parameter for engineers and operators to use in predicting the reactivity of different types of coals. The difference between the reactivity indexes (R) of CO2 and H2O in gasification can be reflected by Rc. The lower the value of Rc, the greater the difference between the R and R gasification reactivity.

A comparative process study of chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) for solid fuels

A solid-fuel combustion system based on chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) has the potential to assist in the capture of CO2 from coal-fired power plants. In both processes an air separation unit is not required, and the flue gas streams from CLC and CLOU contain primarily carbon dioxide and water, which facilitates CO2 capture. CLOU offers a potential advantage for solid fuels as it uses combustion reactions. The O2 for the combustion reactions in CLOU is supplied from the reduction of a metal oxide (e.g. CuO). Iron-based materials are being considered for oxygen carriers in CLC, wherein the coal is gasified, and subsequently the product gas is oxidized to CO2 and H2O by reaction with the circulating oxygen carrier. CLOU affords faster coal char oxidation reaction rates, as compared to CLC coal gasification reactions, but CuO-based materials for CLOU will necessarily be more expensive. Furthermore, the stability of CuO-based oxygen carrier materials is also an important concern. In this paper, ASPEN PLUS process engineering models were developed for combustion of a Wyoming Powder River Basin coal using an iron-based oxygen carrier for CLC and a copper-based oxygen carrier for CLOU. The objective of these process models was to evaluate the material and energy requirements for a process development unit by incorporating insights from previously reported kinetic studies on laboratory scale units. A relative economic analysis has also been performed to address key technical challenges which will subsequently help in addressing the development of CLC and CLOU for solid fuels. Due to slower char gasification reaction times, CLC requires a larger reactor, which results in a relatively higher capital cost. It also manifests in a higher pressure drop and consequently higher energy costs for fluidizing the oxygen carrier.

Development of High-efficiency Oxy-fuel IGCC System

CO2 emission control is a significant issue as a countermeasure for a global warming problem. Carbon dioxide capture and storage technology is regarded as one of the methods of reducing CO2 emission, but it leads to a drop in a thermal efficiency. It is important to maintain thermal efficiency as high as possible for an efficient use of limited fossil fuel resources. CRIEPI started a joint project with Kyushu university to develop “High-efficiency oxy-fuel IGCC”, a high thermal efficiency integrated coal gasification combined cycle power generating system with CO2 capture, which can keep its efficiency more than 40% (HHV). This system gasifies coal with mixed gas of O2 and recirculated exhaust gas mainly composed by CO2, just as oxy-fuel combustion boiler. This paper is to introduce latest achievements done by CRIEPI on this project by quoting latest papers. In order to clarify the effect of CO2 enrichment on coal gasification reaction, coal gasification experiments were executed using pressurized entrained flow coal gasifier whose fuel capacity is 3TPD. And in order to evaluate characteristics of O2- CO2 gasifier by numerical simulation, pressurized drop tube experiments were performed to obtain reaction data necessary for constructing high precision reaction model for numerical simulation code. The data clarified difference between O2 gasification and CO2 gasification on soot behaviour. When we start this project, this system had a problem to be solved. That is carbon deposition on the surface of hot gas clean-up sorbent, installed to improve thermal efficiency. As CO concentration of syngas is so high that carbon particles are supposed to deposit on desulfurization sorbent. But fundamental experiments showed an appropriate countermeasure for carbon deposition, whose impact on thermal efficiency is quite small. Now it is time for us to summarize achievements and propose the next steps toward realization of this system.

Laboratory Study on Gasification Reactivity of Coals and Petcokes in CO2/Steam at High Temperatures

The gasification reactivity of 13 carbonaceous materials in CO2 or in steam was studied in the temperature range 1000–1600 °C. The gasification reaction was carried out in a drop-in-fixed-bed react...

Study of Effect of Ternary-Component Blended Coal on Coal Gasification Reaction at High Temperature

Three typical Chinese individual coals which existed remarkable difference on coal ash chemical composition and ash fusion temperature were selected to carry out coal blending experiments to study the coal gasification reaction at high temperature by means of using ternary-component blended coal technique and TGA-DTA method. According to ternary-component blended coal with a certain proportion, ash chemical composition and coal-char/CO2 gasification reactivity were analyzed by X-ray fluorescence (XRF) and thermogravimetric analysis-derivative thermogravimetric analysis (TGA-DTG), respectively. The results show that the ash chemical components change because ternary-component blended coals change the mineral composition, and hence, the gasification reactivity can be affected as well. Moreover, in accordance with reactivity index R, it indicates that the order of gasification reactivity of three individual coals and four blended coal options is coal x > option B > option A > option D > option C > coal z >coal y. Meanwhile, a new mathematical model called per unit ash alkali index B* was established by using the ash chemical component dates, which has a good corresponding relationship with R for four blending coal options. Utilizing ternary-component blended coal technique could improve the high-temperature coal ash gasification reaction.

Coupled Hydro-thermal Analysis of Underground Coal Gasification Reactor Cool Down for Subsequent CO2 Storage

The present study investigates the time dependency of a UCG (Underground Coal Gasification) reactor cool down process by comparing natural cool down with forced cooling driven by water flushing. The convective heat transport out of the UCG reactor was calculated using an analytical approach coupled to a numerical heat flow model of the geology surrounding the UCG reactor. Our results show that forced cooling by water flushing at flow velocities of 1 m/s can decrease the required time to retain initial in-situ temperature conditions by a factor of more than 300.

Laboratory Studies on Evaluation of Gasification Effect for Conversion of Coal Resources in Underground Coal Gasification (UCG) Reactors

Underground coal gasification (UCG) as a clean energy technology and efficient way for the conversion of the coal resources into energy in-situ has attracted wide public attention in recent years. Laboratory-scale experiments on coal blocks can provide significant insight into UCG process. The main goal of this study was evaluation of the gasification effect applying L-shape linking-hole and Coaxial-hole UCG models. Experimental results show the gas composition, AE activity and the temperature distribution inside the combustion reactors under similar operating parameters. Positive correlation was found between the temperature and cumulative AE events. The results shown that the gasification of L-shape linking-hole model obtained the average calorific value, as high as 11.3 MJ/m3, whereas in the Coaxial-hole model, the average calorific value of gas produced was only 5.79 MJ/m3under the experimental conditions. Even so, the results of conducted Coaxial-hole UCG experiment provide the original and sorely lacking data base for future new-style UCG research.

Kinetic study of polish hard coal and its char gasification using carbon dioxide

The kinetics of polish hard coal and its char gasification using carbon dioxide as gasifying agent was studied at atmospheric pressure between 293 and 1223K at different linear heating rates. Calculations using isoconversional method showed that coal gasification has two separate steps: pyrolysis in the range from 600 to 850K and gasification in the range from 1000 to 1273K. This proves the additivity of pyrolysis and gasification steps. The apparent activation energy calculated using the F1 model for coal char gasification is equal to 245kJ/mol, and logA is equal to 7.41/s, which is similar to the value obtained by the isoconversional method. Coal gasification reaction with carbon dioxide is faster and takes place in a lower temperature range than the gasification process of the char obtained in a separate process. The stabilized and chemically deactivated char is harder to gasify, and the same conversion is achieved at the higher temperature. The estimated shift may be as high as 150K.

Hydrogen Production from a Victorian Brown Coal with in Situ CO2 Capture in a 1 kWth Dual Fluidized-Bed Gasification Reactor

The removal of CO2 during coal gasification will improve H2 yield by promoting coal gasification reactions toward the production of H2. In this work, coal gasification with in situ CO2 capture has been investigated in a 1 kWth dual fluidized-bed gasification reactor. A Victorian brown coal was used as the feed stock. Coal gasification tests at 700 °C were performed with silica sands as the heat carrier and synthetic CaO sorbent for comparison. It was found that the addition of the sorbent improved H2 concentration in the outlet of the fuel reactor by nearly 53%. Carbon conversion rate was also increased and a maximum of ∼33% was reported. Calcium aluminate cement was used as a binder for the fabrication of the synthetic CaO sorbent, in an attempt to enhance its mechanical strength and improve its chemical properties.

S082023 CO_2回収型高効率IGCCの開発 : 再生熱交換器のコンパクト化検討

CCS technology is expected to reduce CO_2 emission, but its net efficiency is supposed 29 to 33% (HHV) because capture unit requires large m-house power. Proposed "oxy-fuel IGCC system" can keep high thermal efficiency more than 40% even after capturing CO_2. This system gasifies coal with mixed gas of recycled CO_2 flue gas and necessary amount of O_2, just as oxy-fuel combustion. Therefore, CO_2 concentration in exhaust gas is so high that CO_2 capture unit is not required. Moreover, CO_2 gas accelerates coal gasification reaction as gasifying agent CRIEPI and Kyusyu university are running various programs to develop fundamental technologies for this system. This paper is to report the newest findings by CRIEPI. It was concerned with difficulties to design large-scale regenerative heat exchanger, one of key components of this system. But finally we succeeded to design compact large-scale regenerative heat exchanger.

Effects of operating factors in the coal gasification reaction

The effects of operating factors on a gasification system were reviewed by comparing a computational simulation and real operation results. Notable operation conditions include a conveying gas/coal ratio of 0.44, an oxygen/coal ratio of 0.715, a reaction temperature of 1,000 °C, and reaction pressure of 5bar in the case of Adaro coal; based on this, the cold gas efficiency was estimated as 82.19%. At the point of the reaction temperature effect, because the cold gas efficiencies are more than 80% when the reaction temperatures are higher than 900 °C, the gasifier inner temperature must remain over 900 °C. At high reaction temperature such as 1,400 °C, the reaction pressure shows little effect on the cold gas efficiency. The addition of steam into the gasifier causes an endothermic reaction, and then lowers the gasifier outlet temperature. This is regarded as a positive effect that can reduce the capacity of the syngas cooler located immediately after the gasifier. The most significant factor influencing the cold gas efficiency and the gasifier outlet temperature is the O2/coal ratio. As the O2/coal ratio is lower, the cold gas efficiency is improved, as long as the gasifier inner temperature remains over 1,000 °C. With respect to the calorific value (based on the lower heating value, LHV) of produced gas per unit volume, as the N2/coal ratio is increased, the calorific value per syngas unit volume is lowered. Decreasing the amount of nitrogen for transporting coal is thus a useful route to obtain higher calorific syngas. This phenomenon was also confirmed by the operation results.

Enhancing the Steam Gasification Reactivity of Coal by Boosting the Factors Affecting the Gasification Reactions in the Stepwise Coal Conversion

Factors affecting the steam gasification reactivity of coal have been reviewed. Studies have been performed on investigating the effects of organo-refining (solvent extraction) using coal-derived solvents, such as anthracene oil and liquid paraffin. The residual coals obtained from the organo-refining of coal were subjected to steam pyrolysis at 650°C to generate active chars. The steam gasification reactivity of original coal, anthracene oil extracted residual coals, anthracene oil–liquid paraffin (successively) extracted residual coals, and their chars were studied first in a laboratory gasifier and then by using thermogravimetric analysis apparatus in steam atmosphere. Nonisothermal kinetic studies revealed that organo-refining and steam pyrolysis are beneficial pretreatments for the steam gasification of coals/chars. These pretreatments leave sufficient residual volatile matter in coals/chars, increase the active surface area, and expose and make available the finely dispersed mineral matter of coal (which acts as catalysts). These observations were also supported by the DTG studies. Present studies led to the development of a stepwise coal conversion process, a clean coal technology to generate H2 or for use of the integrated gasification combined cycle power generation or of fuel cells.

Dual-Bed Gasification of Petcoke: Model Development and Validation

In this work, the problem of modeling a previously proposed dual-bed gasification scheme [Sudiro et al., Energy Fuels 2008, 22, 3894−3901] is addressed. The process consists of a combustor and a gasifier, which are thermally coupled by the circulation of an inert solid, to use air instead of pure oxygen in the combustor. The coal gasification reactor is modeled, taking into account both chemical kinetics and mass transfer between gas phase and char particles. First, the model is developed and validated with reference literature and experimental data for conventional coal gasification using oxygen in both entrained-flow and fluid-bed gasifiers. A series of sensitivity analyses is performed with regard to a conventional gasifier fed by petcoke, and the effects of residence time and oxygen/carbon mass ratio in the feed are investigated over three process variables: char conversion at the gasifier exit, temperature at the gasifier exit, and amount of useful syngas (H2 and CO) produced, in terms of N m3 per ton of petcoke. Finally, the model is extended for application to the dual-bed process. Results from this simulation are compared to those obtained under equilibrium conditions, with an energetically equivalent syngas throughput.

The resource utilization of algae—Preparing coal slurry with algae

Nowadays, the occurrence of harmful algal blooms is increasing rapidly all over the world. However, the methods of resource utilization of algae are very few. In this study, we propose a new way to dispose algae, which is gasification of coal–algae slurry. Coal slurries prepared with algae were investigated, and gasification reactivity of coal–algae slurry was compared with that of coal–water slurry (CWS). The results showed that, anaerobic fermentation, chemical treatment, high-speed shearing and heating are effective pre-treatment methods on reducing the viscosity of algae, which could obviously increase the maximum solids concentration of coal–algae slurry. When the de-ionized water/algae ratio is 1:1, the maximum solids concentration could get to 62.5 wt.%, which is almost the same as that of CWS. All the coal–algae slurries exhibit pseudo-plastic behavior, and this type of fluid is shear-thinning. Compared with CWS, the stability of coal–algae slurry is much better, which could be no solids deposition after 70 h. The coal–algae slurry displays better gasification reactivity than CWS.

Partial gasification of coal in a fluidized bed reactor: Comparison of a laboratory and pilot scale reactors

A 0.1 MWth lab-scale and 2 MWth pilot-scale experimental rigs were constructed to demonstrate the technical feasibility of a new process. The aim of the lab-scale study is to optimize coal partial gasification reactions operating conditions, which were applied in the pilot-scale tests. A comparison between the laboratory and pilot scale experimental results is presented in this paper in order to provide valuable information for scaling-up of the PFB coal partial reactor to industrial applications. The results show that trends and phenomena obtained in the laboratory reactor are confirmed in a pilot plant operating at similar conditions. However, many differences are observed in the two reactors. The higher heat loss in the lab-scale reactor is responsible for higher equivalence ratio (ER) and lower gas heating value at the similar reactor temperature. With respect to the pilot-scale reactor, mass transfer limitation between bubbles and emulsion phase may become important. Hence, longer contact time is required to achieve the same conversions as in the lab-scale reactor. This difference is explained by a significant change of the hydrodynamic conditions due to the formation of larger bubbles.