Osamu Okuma

The advantages of vacuum-treatment in the thermal upgrading of low-rank coals on the improvement of dewatering and devolatilization

A new upgrading method for low-rank coals by a combined process of vacuum drying and tar coating has been developed, and some advantages have been observed. This upgrading technique is able to produce upgraded coals comparable to a bituminous coal; the surface of the coals can be effectively coated in order to suppress low-temperature oxidation and spontaneous combustion. The dewatering rate in the vacuum drying stage at 200 °C reached up to 93.81%, and degree of devolatilization significantly increased with elevation of upgrading temperature, from 15.7% at 200 °C to 35.9% at 300 °C. Furthermore, the specific surface area and susceptibility toward the low-temperature oxidation of coals were influenced by the upgrading treatment.

Chromatographic characterization of preasphaltenes in liquefied products from Victorian brown coal

Gel permeation chromatography was applied to the measurement of molecular weight distribution of the preasphaltenes in liquefied products from Victorian brown coal. When polar solvents such as N-methyl-2-pyrrolidone were used as elution solvents, two major peaks were separately observed at different retention times, reflecting the polarity of their components. By applying a new calibration method to the polar and non-polar components in the preasphaltenes, using a novolak phenol resin and polystyrenes respectively, the molecular weights of both components were estimated to be distributed around 103. According to the present evaluation, a high liquefaction temperature was found to be effective in reducing the polar components in the preasphaltenes.

Characterization of heavy organic products derived from brown coal in BCL process (1). Effects of liquefaction conditions on properties of CLB in primary hydrogenation

Abstract The properties of the heavy organic products (b.p. above 420°C, coal liquid bottom, CLB) derived from Victorian brown coal under various liquefaction conditions (temperature of 430–470°C, pressure of 9.8–24.5 MPa and solvent or bottom recycle modes) were investigated by using continuous process development units. The various CLBs and their solvent extraction fractions were characterized by ultimate analysis, 1 H-NMR, GPC and solvent extraction. With increase in severity of reaction conditions, the CLB yield and molecular weights of asphaltenes and preasphaltenes decreased. The changes in the structural parameters of the CLBs were explained by dealkylation and dehydrogenation reactions and elimination of oxygen from the heavier products. The elimination which is promoted by increase in the reaction temperature and pressure contributed to reduce the yield and molecular weight of the CLB.

High-temperature n.m.r. analysis of aromatic units in asphaltenes and preasphaltenes derived from Victorian brown coal

Average aromatic structures of asphaltenes and preasphaltenes in liquefied products of Victorian brown coal were investigated using high-temperature n.m.r. analysis. By applying gated decoupling and the DEPT pulse sequence, aromatic carbons in the samples were fractionated into protonated and quaternary carbons, the latter of which were further fractionated into outer and inner quaternary carbons. By comparing the numbers of fractionated aromatic carbons with those of model aromatic compounds, the differences in the aromatic structures of the asphaltenes and preasphaltenes are discussed.

Solvent de-ashing from heavy product of brown coal liquefaction using toluene 1. Solubility of heavy products and settling velocity of ash

The Brown Coal Liquefaction (BCL) process is a two-stage liquefaction (hydrogenation) process developed for Victorian brown coal in Australia. In the BCL process, the heavy product (vacuum residue) derived from the coal in the primary hydrogenation, which is named CLB (coal liquid bottom, boiling point > 420°C), is treated in a solvent (CLB/solvent ratio, 18–14, wt./wt.) under high temperature (200–290°C) and high pressure (4–5 MPa) to remove the ash and heavy preasphaltenes. This solvent de-ashing process uses toluene or coal-derived naphtha as a de-ashing solvent. After dissolving the CLB into the solvent, insoluble solid particles which consist of the ash and heavy preasphaltenes are settled in a settler by gravity and separated from the solution as an ash-concentrated slurry. The ash-concentrated slurry and the de-ashed solution are withdrawn from the settler as an underflow and overflow, respectively. The de-ashing solvent is recovered from both the overflow and underflow by distillation, and reused in the de-ashing process. The de-ashed heavy product recovered from the solution by eliminating the solvent is further hydrogenated in the secondary hydrogenation. This paper discusses the solubility of the CLB into toluene and settling velocity of the ash under the de-ashing conditions. The extraction experiments made clear that toluene dissolved ∼ 60 wt.% of preasphaltenes (benzene insoluble-pyridine solubles) in the CLB under the following conditions, temperature 100–300°C and CLB/toluene ratio (wt./wt.) of 13 or less. This solubility of CLB (ϵCLB) under the de-ashing conditions is expressed as ϵCLB = CBS + 0.6CBIorg, where CBS and CBIorg are the contents of benzene solubles and organic benzene insolubles, respectively, and organic CLB (ash-free CLB) = CBS + CBIorg. The de-ashing experiments confirmed that the insolubles including ash formed a boundary of concentration during the settling period, and the de-ashing efficiency was represented by the settling velocity of the boundary (V), V is expressed as V = ACLB(CSA/2.5)−0.91(T/573)9.5. Where, ACLB, CSAand T are parameters expressing the properties of organic CLB, ash content in the feed slurry (wt.%) and temperature (K), respectively. The ACLB is also expressed by using the analytical results of the organic insolubles in the CLB under the de-ashing conditions. The ash content of the de-ashed heavy product recovered from the upper zone of the boundary is less than 3000 ppm, which is low enough to feed as a mixture with two times of the middle distillate to the secondary hydrogenation over NiMo catalyst with fixed bed reactors.

Viscosity of brown coal-solvent slurry

Abstract The viscosities of coal-solvent slurries which consist of raw brown coal and coal-derived solvent from a two-stage liquefaction process were measured using a high temperature and high pressure viscometer, since viscosity strongly affects the transportation and heat transfer of the slurry. The dependence of slurry viscosity on temperature, coal concentration, and the properties of the recycling solvents was discussed, and equations to estimate and predict slurry viscosities were obtained based on the results of these measurements. The effects of the solvent properties on slurry viscosity were explained by the interaction between the coal and solvents. This interaction is closely related to the content of oxygen-containing compounds in the solvents, and correlates with the atomic ratio of oxygen to carbon of the solvent.

Effects of gas flow rate on brown coal liquefaction with a continuous reactor system. 1. Effects of gas flow rate and boiling point range of feed solvents

Abstract The effects of the gas flow rate in the reactors and the boiling point range of the feed solvent on conversion in brown coal liquefaction were investigated in the presence of iron-sulfur catalyst, using a continuous reactor system. An increase in the gas flow rate (GFR) markedly increased the distillate yield and the distillate/H 2 consumption ratio, converting effectively the heavier fraction derived from the coal. A light feed solvent provided a higher distillate yield than a heavy feed solvent at the same GFR. These results are explained by greater vaporization of lighter solvent fraction to concentrate the heavy fraction and hence to prolong the actual residence time of the latter fraction in the reactor. Analysis of the product and liquid sampled directly from the reactor proved that heavier components were left in the reactor at higher GFR.

Heat transfer characteristics of brown coal-solvent slurry in a dewatering process

Abstract A dewatering process for 60 wt.% moisture containing Victorian brown coal in a recylcing solvent with multi-tubular heat exchangers has been developed as a pretreatment of liquefaction. The heat transfer characteristics of the coal-solvent slurry pipe flow were measured under various conditions at preheating and evaporating stages. On the basis of these measurement results, the overall heat transfer coefficients between the slurry and a vertical pipe wall at both stages were determined, and the equations for estimating and predicting the coefficients were obtained. It was found that heat transfer was mainly affected by slurry viscosity and coal concentration at the preheating stage, and the flow rate of the evaporated steam from the coal was the most dominant factor at the evaporating stage.

Liquefaction of Tanito Harum coal with bottom recycle using FeNi and FeMoNi catalysts supported on carbon nanoparticles

Bottom recycling liquefaction of an Indonesian sub-bituminous Tanito Harum coal was performed to maximize the oil yield and catalyst utilization using FeNi and FeMoNi catalysts supported on carbon nanoparticles for single- and two-stage processes. Two procedures of bottom recycle were carried out: the first procedure (procedure 1) was to recycle crude liquid bottom without additional fresh catalyst, while the second procedure (procedure 2) was to make up recycling feed by purging a part of the bottom and adding fresh catalyst. At the same amount of the total catalyst, the second procedure was found to provide more oil yield than the first procedure, suggesting that the catalyst should be deactivated. High recycle ratio provided excellent oil yield over 74% with successful reduction of catalyst amount to 1 wt.% d.a.f. coal base. Two-stage liquefaction with bottom recycle gave oil yield as high as 82% with a half amount of the fresh catalyst required for the liquefaction without bottom recycle. Higher catalytic activity of FeMoNi/Ketjen Black (KB) provided the higher oil yield with less amount catalyst at smaller catalyst recycle ratio compared to FeNi/KB catalyst.

Solvent de-ashing from heavy product of brown coal liquefaction using toluene:: 2. concentration and separation of ash with a continuous de-ashing system

The brown coal liquefaction (BCL) process is a two-stage liquefaction (hydrogenation) process developed for Victorian brown coal in Australia. The BCL process has a solvent de-ashing step to remove the ash and heavy preasphaltenes from the heavy liquefaction product (vacuum residue) derived from the coal in primary hydrogenation and named CLB (coal liquid bottom). This solvent de-ashing step uses toluene or coal-derived naphtha as a de-ashing solvent (DAS). After dissolving the CLB into the solvent (CLB/solvent ratio, 1/8–1/4, w/w) under high temperature (200–290°C) and high pressure (4–5 MPa), insoluble solid particles which consist of ash and heavy preasphaltenes are settled by gravity and separated from the solution as an ash-concentrated slurry. The ash-concentrated slurry and the de-ashed solution are withdrawn from the settler as an underflow and overflow, respectively. The de-ashed heavy product is recovered from the solution by eliminating the solvent and is further hydrogenated in secondary hydrogenation. The authors have reported on the solubility of CLB in toluene and the settling velocity (V) of the boundary of ash content in the settler under de-ashing conditions. This paper discusses the effects of de-ashing conditions on ash concentration in the settler bottom and the operating conditions of a continuous de-ashing system. The ash content in underflow (CUF, kg/kg or wt.%) at the settler bottom was found to increase with temperature and to decrease with the rate (flux) of downward flow (underflow). The maximum CUF, Z, is expressed by the equation: Z=BCLB(FL/0.35)−0.32(T/523)4.26, where BCLB, FL and T are the characteristic parameters of organic CLB (kg/kg or wt.%), flux of underflow in the settler (kg/m2 s) and temperature (K), respectively. BCLB is also expressed by using the analytical results of organic insolubles in the CLB under de-ashing conditions. Finally, stable operating conditions of a continuous de-ashing system are confirmed to be determined as the following qualifications: |Vu| WSA/CUF and Z>CUF, where |Vu|, |V|, WSA and WUF are the upward velocity of the solution in the settler (mm/s), settling velocity of the ash boundary (mm/s) in the settler, flow rate of ash in the feed slurry (kg/h) and flow rate of underflow (kg/h), respectively. Under these qualified conditions, the 50 t/d pilot plant constructed in Australia was operated under stable conditions for 3700 h using toluene as a DAS.