Liquid fuel from coal, production

Fan (1989) provided a detailed historical development of three-phase fluidization systems in reactor applications. Only a brief review of the significant accomplishments and the economic factors affecting the development of three-phase reactors will be provided here. Table 1 provides the important contributions in the application of three-phase fluidization systems for the past several decades. The direct liquefaction of coal to produce liquid fuels was the first commercial reactor application of three-phase fluidization systems, with development having occurred from the mid-1920 s throughout the 1940 s. A large effort was put forth at this time in Europe for the production of liquid fuels from coal as a direct... 

The first step toward making liquid fuels from coal involves the manufacture of synthesis gas (CO and H ) from coal. In 1925, Franz Fischer and Hans Tropsch developed a catalyst that converted CO and at 1 atm and 250 to 300°C into liquid hydrocarbons. By 1941, Fischer-Tropsch plants produced 740 000 tons of petroleum products per year in Germany (Dry, 1999). Fischer-Tropsch technology is based on a complex series of reactions that use to reduce CO to CH groups linked to form long-chain hydrocarbons (Schulz, 1999) ... 

We will examine three synthetic fuel scenarios and compare their implications regarding sulfur availability with the current and projected market for sulfur to the year 2000. The analysis will consider three production levels of synthetic fuels from coal and oil shale. A low sulfur Western coal will be utilized as a feedstock for indirect liquefaction producing both synthetic natural gas and refined liquid fuels. A high sulfur Eastern coal will be converted to naphtha and syncrude via the H-Coal direct liquefaction process. Standard retorting of a Colorado shale, followed by refining of the crude shale oil, will round out the analysis. Insights will be developed from the displacement of imported oil by synthetic liquid fuels from coal and shale. 

The extraction of coals with supercritical fluids is a promising route for the production of liquid fuels from coal. Generally, hydrocarbon solvents, notably toluene, have been used as the supercritical fluid. Supercritical water extraction has not received the same attention and only recently the first detailed study was reported. In that work, Holder et al. ( l) obtained high conversions for extraction of a German brown coal (70-75%) and a Bruceton bituminous coal (ca. 58%) with supercritical water at ca. 375°C and 23 MPa. These high yields, however, contrast with the much lower conversions briefly reported (.2—5) for other coals and there appears to be considerable variation in the extractive power of supercritical water with different coals, even allowing for the differences in the extraction procedure used. None of the above reports discussed in any detail the chemical nature of the products, nor how the products compare with those obtained from more conventional solvents. 

Early developments for producing liquid fuel from coal which can be found in many countries took place in the 1840s in Germany and England. They were the first steps of the petrochemical industry. These processes produced kerosene to fuel German airplanes during World War II and supplied up to 90% of the demand in liquid fuels at that time. Sasol s plants in the Republic of South Africa are the only industrial coal-to-liquid production capability that remains today with an annual production of 7.5 M tonnes of liquid fuels (gas oil, kerosene) and chemical products. 

As the production of natural gas and petroleum declines in the United States in the future, the possibility of producing substitute gaseous and liquid fuels from coal would seem to offer a solution to the shortage of convention fuels. 

One of the methods used in the production of liquid fuels from coal is to heat coal in the presence of solvents in order to dissolve and stabilize low molecular weight fragments. Many studies (1-6) have been devoted to elucidating the chemical mechanism of product formation in hydrogen donor and non-donor solvents. In most of these studies, the time dependence of the product yield was used as a measure of the rates of reaction, or the product yield was correlated with the solvent, the rank of the coal or other properties of the coal. In order to gain a better understanding of the nature of the coal-solvent interactions, we... 

Table IV summarizes the expected impact of the synfuel physical and chemical properties on the combustion process. In general, the properties of alternative and synthetic liquid fuels vary considerably as the fuel types range from unrefined to hydrogenated liquid fuels from coal, shale, and tar sands. Synthetic fuels of various levels of refinement will be used by the industrial, commercial, and utility sectors to produce thermal enegy for direct process heat, mechanical energy, steam, hot water, and the production of electricity. Consequently,...

The liquid-phase hydrogenation of coal has been a topic of interest since the early 1900s (for example, see Bergius, 1912, 1913, 1925), leading to one of the first commercial developments for the production of liquid fuels from coal. Of late, research efforts have been directed toward cheaper sources of hydrogen, better catalysts, less severe operating conditions, and simpleroperating procedures. There has even been some emphasis on the elimination of the carrier liquid and more facile separation of the products (Chapters 18 and 19). 

FIGURE 18.18 Simplified representation of the production of refined liquid fuels from coal liquids. 

The Bergius process was one of the early processes for the production of liquid fuels from coal. In the process, lignite or subbituminous coal is finely ground and mixed with heavy oil recycled from the process. Catalyst is typically added to the mixture and the mixture is pumped into a reactor. The reaction occurs between 400°C and 500°C under a pressure of hydrogen and produces heavy oil, middle oil, gasoline, and gas ... 

The products of the Fischer-Tropsch reactions are a mixture of hydrocarbons, because a wide range of values for n can be used as coefficients in this reaction. As previously mentioned, Fischer-Tropsch has primarily been used for converting coal to liquid fuels, but the principle could be used for conversion of biomass as well. SASOL, a company in South Africa, has been producing liquid fuels from coal for over 30 years. 

Figure6.11.8 Development of production capacity of liquid fuels from coal in Germany by the Bergius-Pier and Fischer-Tropsch processes, [data from Haul (1985) Stranges, (2003)].

In order to produce methanol the catalyst should only dissociate the hydrogen but leave the carbon monoxide intact. Metals such as copper (in practice promoted with ZnO) and palladium as well as several alloys based on noble group VIII metals fulfill these requirements. Iron, cobalt, nickel, and ruthenium, on the other hand, are active for the production of hydrocarbons, because in contrast to copper, these metals easily dissociate CO. Nickel is a selective catalyst for methane formation. Carbidic carbon formed on the surface of the catalyst is hydrogenated to methane. The oxygen atoms from dissociated CO react with CO to CO2 or with H-atoms to water. The conversion of CO and H2 to higher hydrocarbons (on Fe, Co, and Ru) is called the Fischer-Tropsch reaction. The Fischer-Tropsch process provides a way to produce liquid fuels from coal or natural gas. 

Table VI gives an example of the reaction pathways proposed by different investigators for the production of liquid fuel from coal It is apparent that as the mechanism becomes more and more complicated, so do the mathematical models of the reaction.

The priorities in terms of liquid fuel production in Canada should be exploration for crude oil, further development of the oil sands, and, perhaps, liquefaction of coal. Liquefaction of wood should be pursued at a lower priority. Nevertheless, the attraction of security of supply of liquid fuel from a renewable resource does justify some research, development and demonstration on wood production and wood liquefaction. 

Typically, liquids derived from coal are lower in hydrogen content and contain more impurities than do petroleum products. These impurities consist of atoms other than hydrogen and carbon, that is, nitrogen, sulfur, oxygen, and inorganic materials. Upgrading of coal liquids to make specification fuels typically involves both hydrogen addition and removal of impurities. 

What, then, does the future hold This author believes that the catalytic hydrocarbonization/gasification concept will ultimately achieve commercial success for the production of liquid and gaseous fuels from coal. In selected applications, the mild hydrocarbonization of western coal to produce liquid and gaseous fuels with power generation from the low-sulfur char may also be commercially attractive. Finally, further development of the flash hydropyrolysis technology, as exemplified by the Rocketdyne project, may eventually lead to a technically and economically attractive liquefaction process. But the most important questions still remain unanswered. Does private industry have sufficient interest to pursue the possibilities Where is the interest focused Will a private consortium build a hydrocarbonization/ cogeneration complex using western coal Will the phoenix arise from the ashes ... 

A modem direct coal liquefaction plant can produce about 0.5-0.6t of liquid fuel from every ton of dry coal. In the cases where the hydrogen supply is also produced from coal, the overall system can produce about 11 of liquid fuel from every 3—4t of coal. China Shenhua Coal Liquefaction Co. Ltd is currently building a 20,000 bbl/day direct coal liquefaction plant in Inner Mongolia, China. The economic viability of this large-scale direct coal liquefaction remains to be revealed. Economic analysis performed in 19903 showed that the process of the two-stage conversion of CTL has a product cost of 38 per barrel. Several areas, such as improved pretreatment and cleaning methods, novel catalysts, and improved hydrocarbon recovery, were identified as ways to lower the cost further.1... 

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