Simulation analysis of ammonia distribution in methanol production from coal water slurry gasification

Aspen plus software was employed to simulate process. The system concludes gasification scrubbing system the opposed multi-burner gasifier （OMB） methanol production and purification shift system. The distributions of ammonia con- centration in streams were obtained. The study demonstrates that ammonium crystallization problem caused by ammonia ac- cumulation, and if the process has ammonia exports its concentration will greatly reduced and the ammonia salt problem will effectively alleviate. Aspen plus simulation is a useful tool strengthening the ammonia recycling use and reducing pollutant for improving water quality, maintaining stable production, emissions.

Comparison of steam-gasification characteristics of coal char and petroleum coke char in drop tube furnace

The steam-gasification reaction characteristics of coal and petroleum coke （PC） were studied in the drop tube furnace （DTF）. The effects of various factors such as types of carbonaceous material, gasification temperature （1100- 1400 ℃） and mass ratio of steam to char （0.4：1, 0.6：1 and 1：1 separately） on gasification gas or solid products were investigated. The results showed that for all carbonaceous materials studied, H2 content exhibited the largest part of gasification gaseous products and CH4 had the smallest part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon con- version of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of all char samples increased with increasing steam/char ratio. For all the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic effects when the gasification reaction of char was held in DTF, The calculating method for the equilibrium shift in this study will be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer （L002/d002） numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.

Assessment of coal gasification in a pressurized fixed bed gasifier using an ASPEN plus and Euler–Euler model

With the help of Aspen Plus,a two-dimensional unsteady CFD model is developed to simulate the coal gasification process in a fixed bed gasifier.A developed and validated two dimensional CFD model for coal gasification has been used to predict and assess the viability of the syngas generation from coal gasification employing the updraft fixed bed gasifier.The process rate model and the sub-model of gas generation are determined.The particle size variation and char burning during gasification are also taken into account.In order to verify the model and increase the understanding of gasification characteristics,a set of experiments and numerical comparisons have been carried out.The simulated results in the bed are used to predict the composition of syngas and the conversion of carbon.The model proposed in this paper is a promising tool for simulating the coal gasification process in a fixed bed gasifier.

Effect of heat treatment on structure and gasification reactivity of petroleum coke

Petroleum coke was thermally treated on a fixed bed reactor in a temperature range of 1173-1673 K. The changes of the elemental composition and crystalline structure of petroleum coke, with heat treatments as well as the gasification reactivity of the heat-treated petroleum cokes were investigated. The results showed that the petroleum coke was carbonized and grapbitized to a higher degree with increasing heating temperature, while the gasification reactivity decreased. The treatment at temperatures of 1173 and 1473 K significantly enlarged the specific surface area and the pore volume of petroleum coke. Both the specific surface area and the pore volume decreased at 1673 K. An empirical normal distribution function model （NDFM） was found to fit the gasification rates of petroleum coke well. The correlation coefficient of petroleum coke by normal distribution function model at different heat treatment temperatures is between 0.93 and 0.95.

Characteristics of single petcoke particle during the gasification process at high temperatures

Particle concentration significantly affected the gasification of petcoke particles according to our previous studies.In this work,gasification characteristics and morphological evolution of single petcoke particle were investigated using a high temperature stage microscope experimental setup.The results showed that the reaction temperature significantly affected the reactivity of petcoke in the temperature range of 1200–1300°C.While the promoting effect on gasification reactivity decreased with further increasing the reaction temperature,the SEM analysis demonstrated the pore development during the gasification process,which attributed to the increase of reaction rate with conversion.The Raman analysis,HRTEM and SEM–EDX analysis showed that the heterogeneous graphitization of petcoke and non-uniform distribution of catalytic elements in petcoke attributed to the development of surface pores with limited depth.The gasification mechanism of petcoke particle can be briefly described as the reaction rate mainly contributed from the fast-reaction area.Besides,the pore development in fast-reaction area also enlarged the surface area of petcoke particle.

Study on Absorption and Regeneration Performance of Novel Hybrid Solutions for CO_2 Capture

Recently, a kind of hybrid solution MEA-methanol shows a better CO_2 capture performance over aqueous MEA solution. However, the vaporization of methanol is the biggest disadvantage that hinders its application, so it is necessary to minimize the vaporization of methanol during both the absorption and regeneration processes. In this work, two kinds of hybrid solutions were studied and compared with aqueous MEA solution and MEA-methanol solution, including MEA/TEA/methanol solution and MEA/glycerol/methanol solution. The absorption property of MEA/glycerol/methanol solution is better than aqueous MEA solution within a certain period of time and the absorption property of MEA/TEA/methanol solution is too poor to be used in CO_2 capture. By increasing the concentration of TEA and decreasing the concentration of MEA, the absorption rate, CO_2 capture efficiency and absorption capacity all decreased. Upon adding glycerol, the cyclic capacity decreased and the generation temperature increased, and moreover, the density and viscosity also increased considerably. So after adding TEA and glycerol, the CO_2 capture performance of MEAmethanol solvent cannot be improved.

Experimental Study of the Absorption and Regeneration Performance of Several Candidate Solvents for PostCombustion CO_2 Capture

At present monoethanolamine(MEA) remains as the standard industrial solvent for CO_2 capture processes. But due to the degradation and high energy consumption problems of MEA, new efficient solvents should be found. In the present work, the absorption and regeneration performance of a hybrid solvent MEA-methanol was studied and compared to the aqueous solutions of monoethanolamine(MEA), diethanolamine(DEA) and triethanolamine(TEA) in a bubbling reactor. Also the performance of MEA-methanol solutions(including the absorption performance, regeneration performance,cyclic absorption performance, density and viscosity) was studied with different MEA concentrations. A pilot-plant CO_2 capture test bed was used to study the potential of MEA-methanol to replace aqueous MEA in industrial use. The results showed that the initial absorption rate of MEA-methanol solvent is the fastest compared with other solvents. The 30% MEA-methanol had a faster mass transfer coefficient, a higher CO_2 absorption efficiency and a lower regeneration energy consumption than aqueous MEA. And through the study of the reaction heat of CO_2 into MEA-methanol and aqueous MEA,it can be concluded that the desorption heat of rich MEA-methanol is only about 30% of rich aqueous MEA solvent in the regeneration process which showed that 30% MEA-methanol solvent is a promising candidate for CO_2 capture.

Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles under pressurized and fluidized conditions

Catalytic steam gasification of fine coal char particles was carried out using a self-made laboratory reactor to determine the intrinsic kinetics and external diffusion under varying pressures (0.1-0.5 MPa) and superficial gas flow velocities (GF Vs) of 13.8- 68.8 cm· s^-1. In order to estimate the in-situ gas release rate at a low GFV, the transported effect of effluent gas on the temporal gasification rate pattern was simulated by the Fluent computation and verified experimentally. The external mass transfer coefficients(kmam) and the effectiveness factors were determined at lower GF Vs, based on the intrinsic gasification rate obtained at a high GFV of 55.0 cm·s^-1. The kmamwas found to be almost invariable in a wider carbon conversion of 0.2-0.7. The variations of kmam at a median carbon conversion with GFV, temperature and pressure were found to follow a modified Chilton-Colburn correlation:Sh=0.311Re^2.83Sc1/3(P/P0)^-2.07 (0.04<Re<0.19), where P is total pressure and Po is atmospheric pressure. An intrinsic kinetics/extemal diffusion integrating model could well describe the gasification rate as a function of GFV, temperature and pressure over a whole gasification process.

Promoting Xylene Production in Benzene Methylation using Hierarchically Porous ZSM-5 Derived from a Modified Dry-gel Route

Methylation of benzene is an alternative low-cost route to produce xylenes, but selectivity to xylene remains low over conventional zeolitic catalysts. In this work, a combined dry-gel-conversion and steam-assisted- crystallization method is used to synthesize hierarchically porous zeolite ZSM-5 with varied Si/AI malar ratios. X-ray diffraction （XRD）, N2 physisorption, NH3-temperature programmed desorption （TPD）, scanning electronic microscopic （SEM） measurement and Fourier transform infrared （FT-IR） are employed to characterize the struc- ture and acidity of both hierarchically porous zeolites and their conventional counterparts. The method is found to be applicable to ZSM-5 with molar ratios of Si/A1 from 20 to 180. The ZSM-5 zeolites are used as catalysts for benzene methylation at 460 ℃ to investigate the effect of additional porosity and Si/A1 ratios. At low Si/AI ratios, the benzene conversions over conventional and hierarchical ZSM-5 are close, and selectivity to toluene is high over hierarchical ZSM-5. It is found that hierarchical porosity markedly enhances the utility of zeolite and the se- lectivity towards xylenes via improved mass transport at higher Si/Al ratios. Under an optimized hierarchical ZSM-5 catalvst, xvlene selectivity reaches 34.9% at a Si/AI ratio of 180.

Mechanisms of aliphatic hydrocarbon formation during co-pyrolysis of coal and cotton stalk

Pyrolysis experiments were carried out in a tubular furnace. The characteristics of pyrolysis tar were analyzed by GC/MS. The results indicated that the aliphatic hydrocarbon yield derived from co-pyrolysis tar of cotton stalk and Shenmu coal was obviously higher than that of Shenmu coal pyrolysis under optimum condition. Moreover, microcrystalline cellulose was selected as a model compound and the co- pyrolysis tar of microcrystalline cellulose and Shenmu coal was analyzed for comparison. Base on the experimental results, it was indicated that the alkyl radicals generated from pyrolysis were converted to aliphatic hydrocarbons by radical reactions. Furthermore, the mechanisms of aliphatic hydrocarbon formation were discussed during co-pyrolysis of cotton stalk and Shenmu coal.

Study on CO_2 Absorption by Aqueous Benzylamine and Its Formulations with Monoethanolamine as a Component for Post-Combustion Capture Process

Benzylamine(BZA) has been identified as a promising candidate for CO_2 capture process; however the evaluation of BZA in the packed column was very few. Thus, in this work, the absorption and regeneration performance of unblended BZA solvent as well as a series of amine concentrations and ratios in the formulations were studied using a semibatch bubbling reactor. And due to the formation of ivory-white precipitates in solvents containing higher BZA ratios, a 4:1 molar ratio of MEA/BZA mixed solvent was used to study its performance in a pilot-scale test bed. The results showed that a higher BZA ratio in the MEA/BZA mixed solvent resulted in a faster absorption rate, a higher mass transfer and heat transfer rate and a better cyclic performance, but the mass transfer rate of BZA decreased more quickly than MEA with the increase of CO_2 loading of the solvents. In addition, at high CO_2 loading in the MEA/ BZA mixed solvent with a molar ratio of 4:1, the ivory-white precipitates were generated which could cause blockage of the packing in the absorber, the stripper and the liquid pipelines.

Residence time distribution and modeling of the liquid phase in an impinging stream reactor

Based on some experimental investigations of liquid phase residence time distribution(RTD)in an impinging stream reactor,a two-dimensional plug-flow dispersion model for predicting the liquid phase RTD in the reactor was proposed.The calculation results of the model can be in good agreement with the experimental RTD under different operating conditions.The axial liquid dispersion coefficient increases monotonously with the increasing liquid flux,but is almost independent of gas flux.As the liquid flux and the gas flux increase,the liquid dispersion coefficient of center-to-wall decreases.The axial liquid dispersion coefficient is much larger than that of center-to-wall,which indicates that the liquid RTD is dominated mainly by axial liquid dispersion in the impinging stream reactor.

Experimental study on capturing CO_(2) greenhouse gas by mixture of ammonia and soil

This paper presents our study on removal of carbon dioxide(CO_(2)) greenhouse gas emissions by using the mixture of ammonia and soil.CO_(2) capture capacity using this method is 15%higher than the sum of ammonia chemical absorption capacity and soil physical adsorption capacity.Scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR)are utilized to study this synergism.The removal effect is not only reflected in ammonia chemical reaction with CO_(2).CO_(2) can also be absorbed by ammonium bicarbonate(NH_(4)HCO_(3)) crystal,which is the main component of the product,or wrapped in the pore of the crystal or packed in the gap between the crystal and the soil.CO_(2) can be permanently deposited as carbonated minerals in the subsoil earth layers.

Bulk flow properties of fly ashes at ambient and high temperature

The bulk flow properties of four different fly ashes were assessed at ambient temperature and at 500 ~C, using a high temperature annular shear cell. These powders all resulted from industrial processes and had similar chemical compositions but different particle size distributions. Applying a high temperature was found to increase the powder cohesion, with this effect being more significant in the case of the sample with the highest proportion of fines. To better understand the effect of temperature on the bulk flow properties of these materials, a model previously proposed by some of the authors was used to correlate the powder isostatic tensile strength with the interparticle forces and microscale particle contact struc- ture. This model combines the continuum approach with description of particle-to-particle interactions. A comparison with experimental data indicated that the effects of consolidation and temperature on the tensile strength of the fly ashes were correctly described by the model. This theoretical approach also elucidates the mechanism by which the temperature affects the bulk flow properties of fly ashes through modifications of the microscale intemarticle contacts.

Characterization of the flowability dynamics of granular material flowing down a narrow channel

The flowability of granular material is commonly determined from shear cell tests,but in the real world,the granular flow is quite different in many cases.For this paper,the flowabilities in a narrow channel of five different granular materials were investigated.The flow parameters of the granular flows were determined to classify the flowabil让ies.Granular flow surface velocities and flow heights and thicknesses were measured,and it was found that the mean shear rates in the linear portions of the velocity profiles in crease with both flow rates and incli nation.A universal parameter,the ratio of the sine of the inclin ation to the shear rate in the linear part of the velocity profile,is proposed as a constant.This constant is independent of particle properties.In addition,a flowability parameter,the ratio of the mean shear rate to the cosine of the inclination,is proposed to characterize the friction between the particles in the flowing granular material.

Flow properties and inter-particle forces in fuel powders

This work studied the mechanical properties of a series of industrial fuel powders： bituminite, lignite, and petroleum coke. Sieved cuts of these powders were assessed and the flow properties of each sample were used to calculate tensile strengths as functions of consolidation stress. In addition, BET surface areas and dispersive surface energies were estimated from surface energy analysis. To analyze the bulk flow properties of these fuel powders in terms of micro-contact mechanics, the fundamentals of fuel powder adhesion and consolidation were reconsidered based on the ＂stiff particles with soft contacts＂ model proposed by Tomas. In the present work, a multi-contact concept was introduced to account for the irregular shapes of actual particles. This modified model was based on elastic-plastic contact deformation theory and was employed to describe the contact between rough particles and to estimate the associated inter-particle forces. The results were used in conjunction with the Rumpf approach to relate the isostatic tensile strength to the degree of consolidation, Applying average values for the powder compressibility parameters allowed the model to be used for predictive purposes, and an acceptable level of agreement was found between predicted and measured tensile strengths.