Solids separation from the products of the solvent extraction of coal

In the first state of the NCB's coal liquefaction process, coal is extracted with a high-boiling process solvent. The removal of residual solids following extraction is an essential part of the process, which is achieved by filtration. In this study, the characteristics of the coal digest in relation to its filtration properties have been investigated. Filtration rates are discussed in relation to particle composition, fluid viscosity and the existing filtration theory as applied to coal digest. The filtration properties of the solids are principally dependent upon the size and nature of the particles and in particular the composition of the undissolved coal component, which is related to the maceral composition of the coal. A novel technique for characterising coal digest, which embodies the influence of particle size and nature upon filtration, is discussed.     

Filtration in coal liquefaction: 1. Influence of coal type

Commercial solvent extraction systems for coal must be able to process coals with various properties. In this study the influence of coal type upon the extraction yield of coal and the filtration of extraction products has been investigated. All the coals used gave high extraction yields in hydrogenated solvent but resultant products exhibited considerable differences in rates of filtration. This variation in filtration rates is dependent upon particle size, concentration and composition of the residual solids. No simple relation was found to relate coal type with filtration rate.     

Effect of process conditions on ash levels and trace elements in a coal liquefaction extract

The activity of hydrocracking catalysts used for the upgrading of coal extracts is reduced by mineral matter deposition. The influence of digestion and filtration conditions in a coal liquefaction process have been investigated to determine their effect on ash levels and trace elements in the extract solution. It has been shown that the digestion pressure has a significant effect on ash levels, while other conditions have little effect. Trace element proportions vary considerably from feed coal ash to extract solution ash with known deactivating species showing the largest increase.     

Filtration in coal liquefaction. Influence of filtration conditions in non-hydrogenated systems

A series of experiments has been carried out to study the effects of filtration conditions upon the rate of filtration of non-hydrogenated coal digests. The results show the dependence of cake resistivity on both the filtration temperature and pressure. Filter cakes were found to be compressible, resulting in smaller increases in rate with increasing pressure than with incompressible cakes. The filtration temperature determines the packing of residual solids in the cake which in turn affects the cake resistivity. An empirical relation has been derived between filtration temperature and resistivity. With increasing temperature there is an increase in filtration rate due to the reduced viscosity, but a reduction owing to a higher packing density of solids in the filter cake.     

Separation of Solids from Coal Liquefaction Products via Countercurrent Solvent Deasphalting

Abstract

Counter-current deasphalting is a key unit operation in the Dow Liquefaction Process. The Dow developed deasphalter removes typically 99.8–99.9% of the ash and 94–95% of the toluene insoluble hydrocarbons from the coal liquefaction product.

The deasphalted oil, after separation from solvent, contains less than 0.05% ash. Deasphalted coal liquefaction product, a low sulfur, low residue, premium synthetic oil, constitutes 40% of the net liquefaction products. The deasphalter residue typically contains 40% ash and up to 25% hydrocarbonaceous coal solids. It has a heating value of approximately 9000 BTU/1b and is produced as a viscous pumpable fluid. These properties are important in the Dow Process where deasphalter residue is gasified to generate the hydrogen for the liquefaction step. The solvent used in the deasphalter is a paraffinic 50–75° light oil cut from the liquefaction unit.

The counter-current deasphalting technology is based on the results from model and batch studies and results from the operation of two different 23 kg/hr continuous deasphalters. Operational parameters which have been studied include: extraction temperature and pressure, solvent to oil ratio, feedrate, coal oil composition and variations in column design.

The mass transfer which occurs during the deasphalting of coal liquefaction product is accompanied by interfacial tension gradients which develop naturally during the extraction process. The resulting interfacial convection (referred to as a Marangoni instability) profoundly enhances the rate of the extraction process and greatly simplifies the design of the extraction column.     

An overview of solid—liquid separation in coal liquefaction processes

A number of coal liquefaction processes are in various stages of development. Process slurries emanating from reactors generally contain 5 to 10 wt.% of solids. Solid—liquid separation processes must be used to separate the mineral residue and unconverted carbon from liquefied coal. Difficulties in removing those solid components represent a major obstacle to economic production of liquefied coal products. Various methods of solid—liquid separation (SLS) for coal liquefaction processes are reviewed. An overall perspective of the four stages of SLS is essential to solution of SLS problems. Filtration theory has been revised to explain filtration behaviour of liquefied coal.     

煤炭直接液化油收率极限理论及其应用

首次建立了煤炭直接液化油收率极限理论,在指定的液化试验装置上,当催化剂、助催化剂和试验条件一定时,可以确定煤种的低限油收率和高限油收率,从而阐明了煤种进行直接液化主反应的限度,掌握煤种的低限油收率和高限油收率可以识别煤炭直接液化催化剂性能,最大限度地降低前沥青烯和沥青烯等液化反应中间产物的产率,就可以获得接近高限油收率的液化油收率。     

Studies in magnetochemical engineering. 1. A pilot-scale study of high-gradient magnetic desulphurization of solvent-refined coal (SRC)

A pilot-scale high-gradient magnetic separation (HGMS) system for the magnetic filtration of mineral residue from liquefied coal has been designed and constructed. The system is equipped with a specially designed on-line product-sampling device for obtaining time-cut samples of the magnetically cleaned product at elevated temperatures and pressures. Filter feed slurries of Illinois No. 6 and Kentucky No. 9/14 coals obtained from SRC pilot plants at Wilsonville, Alabama and Tacoma, Washington have been magnetically filtered under a wide range of separation conditions. The effects of major separation variables on the removal of inorganic sulphur and extracted solids from SRC filter-feed slurries have been quantitatively investigated. Under optimum separation conditions observed in this study, HGMS effectively removes up to 93 wt % of the inorganic sulphur. A quantitative correlation between the magnetic desulphurization performance and separator capacity applicable over a wide range of separation conditions has been found experimentally. A comparison of the present work and reported exploratory bench-scale studies is given, and a new SRC processing scheme incorporating HGMS capable of achieving over 90 wt % total sulphur removal from pulverized feed coal is also suggested.     

An investigation of the design variables for producing activated carbons from victorian brown coals by reaction with steam

Activation of Latrobe Valley brown coal by reaction with steam was investigated in a continuous indirectly heated shaft activator. The variables studied were the degree of coal gasification achieved, the ratio of steam feed rate to coal feed rate and temperature of activation. The most important of these variables is the degree of gasification of the coal. The ratio of steam feed rate to solids feed rate is unimportant when the value of this variable is greater than 0.036 g/g, and temperature is unimportant in the range 720–930°C. Process limitations which can be caused by channelling of both gas and solids and by heat transfer limitations have been discussed briefly.     

煤炭直接液化高分散度固体酸催化剂的研制

煤炭直接液化反应的速率控制步骤一般是沥青烯生成液化油的中间化学反应．根据煤炭直接液化油收率极限理论,新型催化剂研制的方向和目标就是加快沥青烯生成液化油的反应速率,显著降低沥青烯的产率,获得接近高限油收率的试验油收率．首次确定了Fe2O3催化剂研制的重点必须放在表面酸性上．应用沉淀法制备Fe2O3超微颗粒催化剂,晶粒尺寸在72nm～81．3nm．通过化学计算,首次证明了液相沉淀反应体系的pH值与Fe^3 浓度对数lg[Fe^3 ]成线性关系,应用程序升温脱附法(TPD)测定了催化剂酸性。     

Multiplicity patterns in atmospheric fluidized bed coal combustors

A new mathematical model has been developed for the analysis of the steady state characteristics of Atmospheric Fluidized Bed Coal Combustors. A physical understanding of the different processes occuring within the bed is incorporated in the development of detailed mass and energy balances for the different reactor phases (bubble and emulsion phase, sorbent and coal particles). Care is placed on the modelling of the homogeneous and heterogeneous oxidation reactions, the growth of bubbles within the bed by coalescence and the heat transfer between the solids and the immersed steam generating tubes. Furthermore a population balance for the coal particles which accounts for variable size feed, fines elutriation and solids overflow enables the calculation of two very crucial bed operating variables: the carbon loading and the combustion efficiency. The model also predicts the temperature and the O₂ and CO concentrations within the combustor.The numerical solution of the dimensionless model equations is based on their reduction to a system of three nonlinear algebraic equations. Three steady states are obtained in the industrially important region of design and operational characteristics. They correspond to a high, intermediate and low reactor temperature and combustion efficiency. At the same time the respective values of carbon loading and O₂ concentrations are low, intermediate and very high. The results indicate that there exists a critical value of the coal feed rate, or of the superficial gas velocity, below which the bed is extinguished.     

Effect of coal liquefaction conditions on the trace element content of the soluble non-volatile product

Analysis of 18 trace elements via inductively coupled plasma atomic emission spectrometry has been performed on ‘in-house’ coal-derived non-volatile products. Analyses were conducted in a pyridine matrix to determine the effect of various conversion parameters on metal content. Four subbituminous coals (Wyodak 1–4) and one bituminous coal (Indiana V) were employed in conjunction with both non-basic (tetralin) and basic (1,2,3,4-tetrahydroquinoline) model process solvents. Trace metal data on solvent-refined coals as a function of feed coal, process solvent, reaction time, reaction temperature and extraction solvent are reported. Few trends in metal concentration are apparent on changing various liquefaction parameters. Metal concentrations are, however, approximately one to two orders of magnitude higher in pyridine soluble SRC relative to toluene soluble SRC. The majority of soluble metals, it is therefore suggested, are in the form of coordination complexes rather than true organometallics in SRC. Information regarding the effective molecular size of metal-containing species has been obtained via size exclusion chromatography with specific metal detection. Subtle changes are observed in the effective molecular size of metal-containing materials using different liquefaction parameters. For example, a greater fraction of each metal appears to be bonded to larger ‘sized’ molecules in pyridine soluble fractions than in toluene soluble fractions.     

Modeling of fouling layer deposition in cross-flow microfiltration during tomato juice clarification

The effect of parameters, such as transmembrane pressure and axial flow rate, on membrane fouling during tomato juice clarification were studied by cross-flow microfiltration using flat sheet polyvinylidenefluoride membranes. The effect of fouling on permeate flux was modeled using a classical constant pressure dead-end filtration equation and its modified form for cross-flow filtration. The main physico-chemical properties of tomato juice were evaluated. The clarified juice was very similar to the feed except for insoluble solids and lycopene, which were concentrated in the retentate. Cake formation was identified as the main reason for flux decline. At different axial flow rates, the fouling mechanism evolves from cake filtration to an intermediate pore blocking mechanism with increasing pressure.     

Effect of media size in stirred ball mill grinding of coal

As a prerequisite to producing super-clean coal with any physical coal-cleaning process, such as microbubble flotation, the feed coal must be micronized to liberate finely disseminated mineral matter. The stirred ball mill is regarded as one of the most efficient devices for micronizing coal. Using a 13.4 cm batch mill, the optimum operating conditions have been determined in terms of media size, feed size and media type. The rate of breakage determined with monosized feeds are compared on the basis of specific energy consumption. It has been found that a 20:1 ball size/particle size ratio gives optimum grinding conditions.     

Effect of Wyodak coal properties on hydroliquefaction reactivity

The effect of Wyodak coal properties on liquefaction reactivity as measured by distillate yield and cyclohexane conversion has been investigated. Spot samples of four Wyodak subbituminous coals from the Anderson and Canyon coal seams in the Powder River Basin of NE Wyoming were liquefied in microautoclave and batch reactor experiments. Runs were made using two different Wyodak coal-derived solvents. Emphasis in this work was directed toward correlation of C₄-700 K distillate yield and cyclohexane conversion as functions of measurable physical, chemical and petrographic properties of the feed coal. Reactivity rankings were found to be the same using either measure of coal reactivity. However, the data indicated that distillate yields were a function of both solvent quality and feed coal properties. For each solvent studied, selected coal properties, including carbon content, total and organic sulphur content, vitrinite content and total reactive maceral (vitrinite plus exinite) content, were found to give statistically significant correlations with distillate production and cyclohexane conversion. Pyritic and sulphate sulphur contents did not appear to enhance liquefaction yield or conversion at the reaction conditions studied. However, any catalytic effects due to pyrite or sulphate sulphur may have been masked by the use of two high quality liquefaction solvents.     

煤炭直接液化过程的元素平衡分析

对煤直接液化过程的原料和产物进行了元素平衡研究，并对C，H，N，S，O各元素在产品中的分布进行了分析。对煤直接液化反应的深入解析和过程优化具有一定的指导作用。     

Coal liquefaction using a hydrogenated creosote oil solvent: H-atom transfer from hydrogen donor components in the solvent

The presence of hydroaromatic, hydrogen donor components in a coal-derived solvent is one of the more important factors in the successful operation of a non-catalytic coal liquefaction process. Various hydrogen donor species present in a hydrogenated creosote oil have been identified. Their rate of disappearance under conditions that are consistent with a short residence time coal liquefaction process has been used to rank the reactivities of the various hydrogen donors. 1,2,3,10b-Tetrahydrofluoranthene was found to be an exceptional donor while 4,5-dihydropyrene, the hexahydropyrenes and 9,10-dihydrophenanthrene were found to be quite active. Sym.-octahydrophenanthrene and 2a,3,4,5-tetrahydroacenaphthene exhibited moderate activity. Tetralin and the four methyltetralin isomers were found to be unreactive under the coal liquefaction conditions employed.     

溶胀对神华煤结构及液化性能的影响

采用甲苯和吡啶对中国神华煤进行直接液化前的溶胀处理,通过对溶胀度及抽提率的测定、IR光谱分析、热重分析以及溶胀煤的直接液化实验,探讨了溶胀预处理对神华煤结构及液化性能的影响.结果表明:经溶胀预处理,煤的溶胀度、抽提率获得了显著提高,煤结构中的弱共价键断裂,进而改善了其液化性能并提高了煤的直接液化转化率和油气产率.     

A NEW METHOD FOR MEASURING SOLID CIRCULATION RATE IN AN COMPARTMENTED FLUIDISED BED GASIFIER

A mini pilot coal gasification plant (4-10 kg/h coal feed), incorporating a novel Compartmented Fluidised Bed Gasifier (CFBG) for gasification and combustion has been used for hot experiments. An important operating requirement for steady operation is maintaining the correct solids circulation rate (SCR) between the two compartments. A new technique has been developed for measuring the SCR and can be applied equally easily to hot and cold operation. The method has been applied in a 2⁴ factorial experiment with 2 replicates to obtain a statistical model for SCR as a function of the operating variables over the whole practical operating range. The model derived from the factorial experiment has been further tested against a vareity of operating conditions, including hot experiments at typical operating conditions.