Search

Coal resource is abundant in China, while the reserves of natural gas and petroleum are limited. Due to the rapid increase in the number of automobiles, a competitive way to produce liquid fuels from coal is urgently needed in China. A so-called “coal topping process” is under development at the Institute of Process Engineering, Chinese Academy of Sciences, from which liquid products can be obtained by flash pyrolysis in an integrated circulating fluidized bed system. In order to achieve a high yield of liquid products from high volatile coal, controlling the residence time of coal particles and produced gas may be of importance for minimizing the degree of the secondary reactions; i.e., polymerization and cracking of the liquid products. Experiments of the flash pyrolysis of coal have been conducted in an entrained bed reactor, which is especially designed to study the influence of the coal particle residence time on the product distribution. The results show that the gaseous, liquid, and solid product distribution, the gas compositions as well as the liquid compositions depend strongly on the gas and particle residence time.

The experiments on the flash pyrolysis of a. lignite were carried out in a fast-entrained bed reactor as a basic study on a so-called 'coal topping process'. The investigation focused on the effects of pyrolysis temperature and coal particle size on the product distribution and composition. The experimental results show that an increase in the pyrolysis temperature results in a higher yield of gaseous products while a larger particle size leads to a decrease of the liquid yield. An optimum temperature for the liquid yield was found to be 650 degrees C. A certain amount of phenol groups was found in the liquid products, which may be used to produce high-valued fine chemicals. The FTIR analyses of the coal and chars show that aliphatic structures in the chars are gradually replaced by aromatic structures with the increasing of pyrolysis temperature and coal particle size. The results of this study provide fundamental data and optimal conditions to maximize light oils yields for the coal topping process.

The flow structures in downers have been investigated by a micro-video and by analysis of local voidage signals in this work. The experiments of micro-video action shot were performed in a downer with an internal diameter of 0.09 m. The local voidage signals were collected in a downer with an internal diameter of 0.285 m. The micro-video action shot showed that there were particle-clustering phenomena in the downer and the clusters existed mainly in the form of floc and stick. Through wavelet analysis of local voidage signals, the cluster size and frequency were obtained. However, the probability density distributions of local voidage signals confirmed that the clusters in the downer were unstable and could not form a stable phase.

In larger combustion facilities, secondary reactions between char and chlorine and sulfur may be important. In this work, the interactions of chlorine and sulfur with biomass char during thermal conversion have been experimentally investigated. A laboratory-scale fixed-bed reactor was applied to study the capture of HCl and SO2 by biomass char in the temperature range of 400−950 °C. The observed reaction rate was sufficient for significant recapture of HCl and SO2 to occur under conditions typical for fixed-bed combustors. A maximum in the chlorine and sulfur retention existed at ∼600 °C. Relatively high amounts of chlorine and sulfur could be retained in the char samples over the entire temperature range, compared to the inherent chlorine and sulfur content in the biomass. Spectroscopic and chemical analyses revealed that HCl was mainly captured by the inherent metal species, whereas SO2 was mainly captured by the organic matrix. As a result, the maximum chlorine retention was dictated by the inherent me...

Experiments were carried out in a downer reactor integrated in a circulating fluidized bed combustor to examine the performance of the coal topping process. The effects of reaction temperature and coal particle size on the product distribution and their compositions were determined. The experimental results show that an increase in temperature will increase the yields of gas and liquid product, and the liquid yield decreases with the increase in coal particle size. The experiments exhibit an optimal condition for the liquid product. When the pyrolysis temperature is 660 °C and coal particle size is less than 0.28 mm, the yield of light tar (hexane-soluble fraction) reaches 7.5 wt % (dry coal basis). The light tar is composed of acid groups (57.1 wt %), crude gasoline (aliphatics) (12.9 wt %), aromatics (21.4 wt %), and polar and basic groups (8.6 wt %). The experiments indicate that the coal topping process is a promising technology for partially converting coal into liquid fuels and fine chemicals.

A mathematical model is developed to describe the hydrodynamics of the fully developed region in a downer reactor. The model is based on the energy-minimization and multi-scale (EMMS) principle. The influence of the friction coefficient, the solid flow rate and the superficial gas velocity on the flow pattern in the downer is simulated. The local solid concentration and gas/solid velocities are predicted. The model results show a good agreement with experimental data in literatures. In addition, cluster size and local slip velocity are discussed.

Based on the EMMS model, the local slip velocity between gas and solid is systematically analyzed and a theoretical correlation of local slip velocity with local voidage for a downer is derived as follows: u s ( r ) u t = D 8 / 7 ( 1 - ɛ mf ) - 2 / 7 [ 1 - ɛ ( r ) ɛ ( r ) ] 8 / 7 ɛ ( r ) 47 / 14 ɛ ( r ) - ɛ mf ɛ ( r ) . Using this correlation, the local gas-solid slip velocity in a downer is calculated. The calculated results are well consistent with experimental data. In addition, the variation of the local slip velocity with its corresponding solid holdup is also discussed.

Wavelet analysis has been used for studying dynamic behavior of fluidized beds, which proved effective in resolution of time series into different scales of components with distinct structure and in identification of transition from the dense phase to the dilute phase. By examining wavelet spectrum functions of various dynamic signals measured from fluidized beds, it is indicated that the signals can be decomposed into three scales of components: micro-scale (particle size), meso-scale (cluster size) and macro-scale (unit size). The principal component method was employed for phase separation from concentration signals measured by the optical probe. In this method, the maximum scale parameter s(0) of the wavelet spectrum function was chosen as the optimum scale parameter. The principal component method can reduce the computation time significantly and remain the benefit offered by the direct method described in our previous publication (Ren & Li, in: L. S. Fan, T. M. Knowlton (Eds.), Fluidization, Vol. IX, Engineering Foundation, New York, 1998, p. 629.). The method was also extended to detect the boundaries of clusters in 2-D digital images acquired from fluidized beds. (C) 2001 Elsevier Science Ltd. All rights reserved.

This paper presents the experimental results with radioactive tracer particles in an 80 MWth circulating fluidized-bed boiler. Batches of γ-ray emitting tracer particles were injected into the standpipe. The response curves of the impulse injection were measured by a set of successive scintillation detectors located at different parts of the boiler. The results show that there are significant differences of the response signals when boiler loading changes. A model has been developed to obtain information from the experimental data. The particle recirculating rate is obtained by fitting the model to the experimental data. In the same way, the average particle velocities in the furnace are estimated. The impact of loading on the particle recirculating rate and on the hydrodynamics of the boiler is discussed.

The gas-sensitive properties of nanostructured 94, 85, 71 and 7 mol% materials prepared by high-energy ball milling have been investigated in atmospheres containing alcohol, CO and gases. It has been found that the materials show a high sensitivity with a short response time to the alcohol gas and almost no sensitivity to the other two gases, CO and in the concentration ranges studied. Furthermore, the gas-sensitive behaviour of these materials in response to the alcohol gas has been discussed on the basis of the microstructure of the materials. It is found that the tin ion content in and tin ions on the surface of particles may play an important role in the enhancement of the gas sensitivity.

The flow pattern of a fluidized bed with non-fluidized zones is investigated both experimentally and theoretically. Experiments were carried out in such a way that air was introduced only through part of the distributor. The results show a significant amount of air flowing to the zone where no air is introduced. However, once the gas velocity exceeds the minimum fluidization velocity in the zone where the air is introduced, the cross-flow hardly changes upon further increase of the gas velocity. A continuity equation and Ergun's equation are used to describe the flow pattern and pressure distribution over the bed. Very good agreement between the experimental and calculated results is achieved without any fitting parameter. The results are relevant to the understanding of heat transfer behaviour of a fluidized bed combustor (FBC) that is only partly fluidized to control its load.

Background Succinic acid is one of the key platform chemicals which can be produced via biotechnology process instead of petrochemical process. Biomass derived bio-oil have been investigated intensively as an alternative of diesel and gasoline fuels. Bio-oil could be fractionized into organic phase and aqueous phase parts. The organic phase bio-oil can be easily upgraded to transport fuel. The aqueous phase bio-oil (AP-bio-oil) is of low value. There is no report for its usage or upgrading via biological methods. In this paper, the use of AP-bio-oil for the production of succinic acid was investigated. Results The transgenic E. coli strain could grow in modified M9 medium containing 20 v/v% AP-bio-oil with an increase in OD from 0.25 to 1.09. And 0.38 g/L succinic acid was produced. With the presence of 4 g/L glucose in the medium, succinic acid concentration increased from 1.4 to 2.4 g/L by addition of 20 v/v% AP-bio-oil. When enzymatic hydrolysate of corn stover was used as carbon source, 10.3 g/L succinic acid was produced. The obtained succinic acid concentration increased to 11.5 g/L when 12.5 v/v% AP-bio-oil was added. However, it decreased to 8 g/L when 50 v/v% AP-bio-oil was added. GC-MS analysis revealed that some low molecular carbon compounds in the AP-bio-oil were utilized by E. coli. Conclusions The results indicate that AP-bio-oil can be used by E. coli for cell growth and succinic acid production.

Biomass gasification and pyrolysis were studied in a laboratory-scale atmospheric pressure entrained flow reactor. Effects of operating parameters and biomass types on the syngas composition were investigated. In general, the carbon conversion during biomass gasification was higher than 90% at the optimal conditions of 1400 °C with steam addition. The biomass carbon that was not converted to gas in the gasification process only appeared as soot particles in the syngas in all of the experiments, except for the two experiments performed at 1000 °C, where a very small amount of char was also left. In comparison to pyrolysis, lower yields of soot, H2, and CO were produced during gasification. The yield of soot could be reduced by a longer residence time, larger feeder air flow, lower oxygen concentration, higher excess air ratio, higher steam/carbon ratio, and higher reactor temperature. Changes in residence time, feeder air flow, and oxygen concentration did not show a noticeable influence on H2 and CO yields. Increasing the excess air ratio decreased both the H2 and CO yields; increasing the steam/carbon ratio increased the H2 yield but decreased the CO yield; and increasing the reactor temperature increased both the H2 and CO yields. Wood, straw, and dried lignin had similar gasification behavior, except with regard to soot formation. The soot yield was lowest during straw gasification possibly because of its high potassium content.

Cement industry is one of the largest emitter of CO2 other than power generation plants, which includes the emissions from combustion of fuel and also from calcination of limestone for clinker production. In order to reduce CO2 emissions from the cement industry an effective an economically feasible technology is to be developed. The carbonate looping process is a promising technology, which is particularly suitable for the cement industry as limestone could be used for capture and release of CO2. Integration of carbonate looping process into cement pyroprocess has two advantages: 1) to capture emitted CO2 and 2) to generate power for internal use, because high quality energy can be recovered from carbonate looping which is operated at high temperature unlike amine process. A simple carbonate looping process model was developed based on average conversion of calcined limestone defined by Abanades et al. The model is used to investigate the influence of average conversion of limestone in the carbonator on the flow rates of different streams in the looping process and energy required in the calciner for re-activation. The model developed is used for studying the carbonate looping process integrated into cement pyro-process. The energy required for regeneration in the calciner increases with increase in average conversion of calcined limestone and energy that can be extracted from carbonator decreases with increasing average conversion. Further the influence of type of limestone on the calciner capacity is also investigated. The results from this simple model show the importance of cement industry to the carbon capture technology for its application to power plants.

The catalytic activity of calcined limestone and sulphated limestone on the oxidation for NH3 to NO were tested in a fixed bed, which simulates the interactions between SO2 and NOx emissions from a fluidized bed combustor caused by the CaO based sorbents. The calcined limestone is very active for oxidation of NH3 to NO, while the sulphated lime is almost an inert for this reaction. A model is proposed to describe the SO2 and NOx emissions and their interactions, in which the unsulphated CaO based sorbents capture the SO2 from coal and catalytically oxidize intermediate N compounds (NH3) to NOx. The sulphation of limestone is based on an approximate analytical solution of the general gas-solid reaction model with structure change of the particle. A simple scheme of NOx formation and destruction is used to describe the NOx emissions. The results of the model are compared with different sources of experimental data from fluidized bed combustion in literature. The comparisons show a good agreement.

Agglomeration of bed material is a major operational problem in fluidized bed combustion, especially when using biofuels. The main mechanism of agglomeration involves the formation of low melting point compounds, which results in increased particle stickiness and formation of agglomerates. The presence of alkali components from the biofuels leads to reactions with silica from the bed material, forming alkali silicates that have a melting point below the typical operating temperatures of about 850 °C. In addition, hydrodynamics and particle interaction mechanisms will play a role. If no counteraction is taken, severe agglomeration can eventually result in defluidization of the bed and subsequent shut-down of the installation. Therefore, an early warning system to reliably detect agglomeration is of high importance. Such a system typically consists of the measurement of operating variables such as pressure coupled with analysis of these data. Different methods proposed in the literature are reviewed in this chapter. As soon as agglomeration has been detected, appropriate counteractions should be taken, such as changing the operating conditions or using additives. Alternatively, different bed materials can be used or the fluidized bed design may be adapted to become less susceptible to agglomeration. Keywords: agglomeration; biofuels; fluidized bed; hydrodynamics; particle interaction; process monitoring

An approximate analytical solution, based on basic equations of gas-solid reactions, is proposed to describe the sulphur capture by calcium based sorbents, and their catalytic effects on NO X formation in FBC. The model is tested by experimental data obtained in both TGA and FBC units from literature. The model can well predict the optimal temperature for sulphur retention and the interactions between sulphur retention and NO X emissions from FBC.

The Coats-Redfern method was used to analyze the kinetic characteristics of biomass catalytic pyrolysis, indicating that it can be described by multi-step reactions, rather than as a simple first-order reaction. Friedman model-free calculations were used to describe the starting reaction types and the corresponding initial kinetic parameters. Finally, nonlinear regression of biomass catalytic pyrolysis showed that the reaction mechanism of the whole process could be kinetically characterized by three successive reactions: a one-dimensional diffusion reaction. followed by an apparent first-order reaction, and then by a two-dimensional diffusion reaction. The kinetic parameters and equations were also calculated. (C) 2009 Elsevier Inc. All rights reserved.

A simple model is presented to predict the sulfur retention and the NOx emission during fluidized bed combustion of coal by using basic coal and sorbent characterization parameters. The work is an extension of D.U.T. SURE model to NOx emission. Based on a simple kinetic model and on one phase ideally mixed hydrodynamics a set of analytical expressions is derived. The results from the model are in agreement with experimental observations.

This paper summarizes the major problems in firing and co-firing the annual biomass, such as straw, in both lab-scale and full-scale fluidized bed combustors. Two types of problems were studied: operational problems, such as agglomeration, deposition and corrosion; and emission problems, e.g. emissions of NO and SO2 . Measurements of deposition and corrosion rate on the heat transfer surfaces, as well as gas phase alkali metal concentrations, were performed in full scale CFB boilers (an 80 MWth and a 20 MWth plant), which have been co-firing coal with straw and other biomass. Severe corrosion and deposition were observed in the superheater located in the loop-seal of the 80 MWth boiler. The boiler load variation has impact on the operation parameters. When the fraction of biomass with a high K-content (>1 wt. %) was higher than 60% on a thermal basis, the boiler suffered from severe agglomeration problems. Lab-scale experiments were carried out for the fundamental understanding of phenomena found in full-scale boilers and for testing possible solutions to the problems. The results showed a strong tendency of agglomeration in fluidized beds during combustion of straw, which normally have a high content of potassium and chlorine. The results indicate that the operational problems may be minimized by a combination of additives, improved boiler design, split of combustion air and detection of agglomeration at an early stage.Copyright © 2003 by ASME

Heat transfer experiments were performed in a reactor, which was built to simulate the mixing between particles and particles in the entrance zone of a downer reactor being applied in the ‘coal topping process’ developed at Institute of Process Engineering, Chinese Academy of Sciences. Superficial heat transfer coefficients were measured with a ball probe. The experimental results show that the heat transfer coefficient increases with the bed temperature and the solid holdup, and decreases with the diameter of bed materials. A semi-empirical heat transfer coefficient correlation was obtained based on dimensionless analysis, taking into account the effect of the important operating parameters under simulated downer entrance conditions. The results calculated from the correlation show a fair agreement with the experimental data. The correlation was applied to estimate the heating rate of the coal particles used in a bench scale experimental apparatus for studying the coal topping process.Copyright © 2003 by ASME

The flash pyrolysis of Huolinhe coal was carried out in a fast-entrained bed reactor. The investigation focuses on the effects of pyrolysis temperature and particle size on pyrolysis product distributions and gas and liquid compositions. Increasing temperature results in an increase of the gaseous product. There is an optimum temperature on the maximum liquid yield, which is around 650°C. An increase in particle size leads to a decrease of liquid products. Some amount of phenol group was found in the liquid products, which may produce the chemicals with high value. The results provide fundamental data and optimal conditions to maximize light oils yields for the coal topping process.Copyright © 2003 by ASME

In order to solve the problems of high temperature chlorine induced corrosion and the emission of dioxins, a new type of double-dipleg circulating fluidized bed incinerator is under development at the Institute of Process Engineering, Chinese Academy of Sciences. Understanding the hydrodynamics of such new type of CFB incinerator are of crucial importance for successful design and operation of the system. Experiments have been carried out in a lab-scale double-dipleg circulating fluidized bed to study the hydrodynamics of such system. The investigation is focused on the pressure profile in the loop and residence time distribution of particles with different sizes and densities in the secondary dipleg. The results show that the pressure profile in such system is similar to that in the conventional CFB. The residence time distribution (RTD) function of particles in the second dipleg varies with particle recirculating rate, superficial gas velocity and the characteristics of the particles, such as density and size. The mean residence time of particles decreases sharply with an increase of the particle re-circulating rate and slightly decreases as the superficial gas velocity increases. It appears that the density of particle has a stronger influence on the residence time than the particle size. The lighter particles have a shorter residence time. The residence time distribution function of the particles is described by a tank-in-series model. The implication of the results to the design and operation of the double-dipleg circulating fluidized bed incinerator are discussed.Copyright © 2003 by ASME

Experiments have been carried out in a gas-solids co-current down-flow circulating fluidized beds. The radial profiles of particle velocity and solid concentrations were measured by a fiber optical probe. Local solid flux was calculated based on the measured local particle velocity and solid concentration. The influence of gas velocity and solid recirculation rate on the radial flow structure has been examined. The experimental results show that the radial flow structure at high gas velocity has its own prominent characteristics in comparison with that at low gas velocity.Copyright © 2003 by ASME

Acetol, as one of the components of biomass pyrolysis liquid, is a high value-added compound for medicine synthesis. If acetol can be extracted from the renewable pyrolysis liquid, much environmental and economic benefit may be obtained; but the instability of acetol makes its concentration difficult. To clarify what compounds are formed from acetol during the distillation process, the components in different distillation systems were analysed and the mechanisms of the conversions were speculated on. It was found that acetol may undergo aldol self-condensation reactions followed by a series of intramolecular dehydrations to form five-ring or six-ring compounds.

NH3 is an important volatile N-containing compound and a precursor for NOx formation in fluidized bed combustion (FBC). This work focuses on the influence of the sulfation process on the oxidation of NH3 to NO catalysed by different CaO based sorbents and other bed materials (sand, Al2O3). Experiments of simultaneous sorbent sulfation and oxidation of NH3 catalysed by the sorbents were performed in a laboratory fixed bed reactor in order to study changing catalytic activity. The influence of SO2 on the oxidation of NH3 to NO for different bed materials was investigated as well. The results show that desulfurization interferes with the catalytic conversion of NH3 to NO in two ways. First, CaO based sorbents are active catalysts for the oxidation of NH3 to NO; this catalytic activity decreases with an increase in the conversion of CaO to CaSO4. For the limestones, which are subject to pore plugging, the sorbents totally lose their activity for NO formation from NH3 when the maximum conversion of CaO to CaSO4 is reached. Second, the catalytic formation rate of NO decreases in the presence of SO2 for some bed materials. This means that the presence of SO2 inhibits oxidation of NH3 to NO. Moreover, it appears that SO2 inhibits the decomposition of N2O on the surface of the catalysts as well.

On the basis of laboratory experimental data on SO2 removal by sol-gel (SG) sorbents in a fixed bed within the temperature range 120–240 °C, both the reaction rate and the attainable conversion were found to depend strongly on three factors: quality of SG sorbent, water vapour concentration in the gas phase, and temperature. The ratio CaSO 3 CaSO 4 in spent SG sorbent is strongly related to its reactivity and the conditions of sorption. Regeneration of sulfated sorbents in a N2 + H2 gas mixture proved the feasibility of the process in the temperature range 750–850 °C with >90% conversion to CaO.

NOX emission from fluidized bed combustion is primarily determined by a series of competing formation and reduction reactions from fuel bound nitrogen. To provide an improved understanding of NOX emission from fluidized bed combustion of biomass, a systematic evaluation of the impact of fuel properties, including nitrogen content, mineral content, and co-combustion, on NOX emission was investigated.