Solvent-refined coal Liquefaction processing

Several processes have been developed for coal liquefaction. Large-scale pilot plants have been in operation for the solvent-refining coal (SRC) process, and a pilot plant is being constructed for the H-Coal process, which is a direct catalytic process. Construction of demonstration plants is under consideration. The coal liquids produced from the current processes contain large amounts of residual fuels. They probably will be used initially as boiler fuels for stationary power plants. However, the nitrogen content of coal liquids is much higher than the petroleum residual fuels. The sulfur contents of coal liquids can vary considerably they depend on the type of coal and the liquefaction process used. Current coal liquefaction processes are capable of produc-... 

Work has also continued on the solvent-refined coal + hydrocracking concept (the NT.SL, or non-integrat-ed, two-stage liquefaction process), and a pilot plant was operated by Amoco, DOE and the Electric Power Research Institute (EPRI) from 1974 to 1992. 

The development of three-phase reactor technologies in the 1970 s saw renewed interest in the synthetic fuel area due to the energy crisis of 1973. Several processes were developed for direct coal liquefaction using both slurry bubble column reactors (Exxon Donor Solvent process and Solvent Refined Coal process) and three-phase fluidized bed reactors (H-Coal process). These processes were again shelved in the early 1980 s due to the low price of petroleum crudes. 

The direct liquefaction technologies, which include Solvent Refined Coal, Exxon Donor Solvent and H-Coal processes have never been operated at a commercial scale. As discussed yesterday, these processes are not at advanced stages of development. The products from direct liquefaction processes are basically boiler fuels or synthetic crudes that could potentially be upgraded to... 

Proposed methods for predicting heats of formation and absolute entropies are tested on two fractions of synthetic crude oil obtained by the EDS process, one sample of H-Coal, one sample of Synthoil, two samples of Solvent Refined Coal, and five pure compounds found in coal liquefaction products. For these samples, the heats of combustion are calculated using predicted values of AHf° and compared in Table IV with observed values. Note that Equations 8 and 9 were used to predict AHf° and S° of the EDS heavy naphtha. Equations 6 and 7 are applied to other samples of coal-derived liquids, and Equations 3 and 4 to the pure compounds. 

Effect of Liquefaction Processing Conditions on Combustion Characteristics of Solvent-Refined Coal... 

The Solvent Refined Coal-I (SRC-I) process ( 1) provides a way in which coal, by way of direct hydrogenative liquefaction, can be transformed into an environmentally clean fuel for the electric utilities. Earlier tests (2, 3, 5) with pulverized SRC-I solid... 

Primary coal liquefaction products from three processes— solvent-refined coal, Synthoil, and H-Coal—were hydrotreated. Upgrading was measured in terms of the decrease in heptane and benzene insolubles, the decrease in sulfur, nitrogen, and oxygen, and the increase in hydrogen content. Hydrotreating substantially eliminated benzene insolubles and sulfur. An 85% conversion of heptane insolubles and an 80% conversion of nitrogen was obtained. Catalyst stability was affected by metals and particulates in the feedstocks. 

Tomlinson, G., Gray, D., and Neuworth, M., "Effect of Coal Rank on Direct Coal Liquefaction Processes Solvent Refined Coal (SRC-II) Process Experience," The MITRE Corp., 84W00308, July 1984. 

The first process was studied by Berthelot in 1867 and was further developed in Germany by Bergius in 1910. The early Bergius process involved the reaction of H2 under atmospheric pressure with pulverized coal suspended in an oil heated to about 450°C in the presence of a catalyst such as stannous formate or Mo. The liquid oil product is separated from the solid residue and processed as ordinary crude oil. Modem developments in this coal liquefaction approach include (1) Exxon Donner Solvent (EDS) process, (2) the HRI H-Coal process, and (3) the Gulf Solvent Refined Coal SRC-II process. The major improvement of these processes over the Bergius process is in the catalyst used, allowing for milder reaction conditions. 

Using microbore LC columns, a separation method was developed for a series of weakly basic cyclic and noncyclic secondary amines, which were identified as components of coal-derived solvents. As shown in another study, using normal HPLC on silica gel with Freon-113 elution, model mixtures of aliphatic and aromatic hydrocarbons and nonpolar constituents can be separated in coal-liquefaction process solvents. Encouraging results were obtained on both semipreparative (4.6 mm i.d.) and microbore (1 mm i.d.) columns. According to further reports, carbamate pesticides, polymer additives and solvent-refined coal were analysed, and the components of bergamot oil can be identified. GPC/FT-IR can be used to detect components of cold-rolling oil and to analyse polymers, whereas SEC/FT-IR can be applied to the analysis of coal liquids and to improve detection and identification of proteins. 

Figure 17.28 shows a schematic of the SRC-I process. The feed coal is crushed and mixed with a recycle solvent and hydrogen prior to entering the preheater. The preheater effluent, at 700 to 750°F (370-400°C), then is fed to the dissolver unit, or thermal liquefaction unit (TLU), which operates at 840 to 870°F (450-465°C). There is no upgrading step, as the desired product is a solid at room temperature and not a distillate. The solids removal from the liquid slurry is accomplished by critical solvent de-ashing (CSD). The solids-free resid from the CSD was separated by vacuum distillation into a recycle solvent (the light fraction) and a solvent refined coal product (the bottoms). 

Some coal liquefaction methods, such as the Synthoil (5) process and the CO-steam (6) process, are similar to solvent refining in their approach, but more severe conditions or a catalyst are used to give a fiuid product. In the Synthoil reaction, bituminous coal is pulverized, dispersed in a vehicle oil, and hydrogenated in a packed tubular reactor with or without added catalyst. The CO-steam process uses lignite coal and less expensive synthesis gas. The intended product is a heavy liquid fuel having ash, sulfur, and nitrogen contents suflBciently low to avoid stack-gas cleaning. Reactor temperature and pressure are normally 400°-450°C and 4000 psi, respectively. 

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