03

Low

Low

aNot applicable. b Unknown.

c Recycle oil hydrogenation. d Small scale.

ePer train; three trains planned.

Source: Adapted from van Krevelen [1]; Miller [50]; HTI [51]; Elliot [2].

aNot applicable. b Unknown.

c Recycle oil hydrogenation. d Small scale.

ePer train; three trains planned.

Source: Adapted from van Krevelen [1]; Miller [50]; HTI [51]; Elliot [2].

ratio than petroleum: ~0.7 to >1.2. Direct liquefaction transforms coal into liquid hydrocarbons by directly adding hydrogen to the coal. Examples of some of the operating parameters of the primary processes are summarized in Table 5-11 [1,50].

Bergius/I.G. Farben Process

The Bergius process was put into commercial practice by I.G. Farben in Leuna, Germany, in 1927, and additional plants were erected in the 1930s. The process operated in two stages. Liquid-phase hydrogenation first transformed the coal into middle oils, with boiling points between 300 and 615°F, and subsequent vapor-phase hydrogenation then converted these oils to gasoline, diesel fuel, and other relatively light hydrocarbons [19]. The Bergius process converts 1 short ton of coal to 40 to 45 gallons of gasoline, 50 gallons of diesel fuel, and 35 gallons of fuel oil [22]. The gasoline fraction contains 75 to 80% paraffins and olefins and 20 to 25% aromatic compounds. Liquid-phase hydrogenation of low-rank coals was usually accomplished at 890 to 905°F under pressures of 250 to 300 atm using an iron-oxide hydrogenation catalyst. For liquid-phase hydrogenation of bituminous coals, temperatures were similar, but pressures were in the range of 350 to 700 atm.

Solvent Refining Processes

The solvent-refined coal (SRC) process is considered the least complex of the various process schemes. Hydrogenation of the coal in the SRC process occurs at elevated temperatures and pressures in the presence of hydrogen. Catalysts other than the minerals contained in the coal are not used [2].

SRC-I Process In the SRC-I process, ground and dried coal is fed to the reactor as a slurry. The transport liquid, or process solvent, is a distillate fraction recovered from the coal hydrogenation product and serves as the hydrogen donor. The coal slurry and hydrogen are introduced into a dissolver at 840°F and 1500 psig. The process produces a low-ash (~0.1%), low-sulfur (~0.3%), solid fuel with a heating value of ~ 16,000 Btu/lb. The SRC-I fuel was envisioned as a boiler fuel to replace natural gas and fuel oil. Testing of this process started with Gulf Oil in the 1960s. Much of the developmental work on this process was performed at Wilsonville, Alabama, in a 6 short ton/day plant with funding from the EEI, Southern Services, the DOE, and the EPRI. A 50 short ton/day plant was built at Fort Lewis, Washington, and testing was performed by Gulf Oil.

SRC-II Process The SRC-I process was modified to eliminate a number of processing steps and to produce an all-distillate, low-sulfur fuel oil from coal rather than a solid fuel. In the SRC-II process, pulverized and dried coal is mixed with recycled slurry solvent from the process. The slurry mixture is pumped to reaction pressure (~140 atm), preheated to about 700 to 750°F, and fed into the dissolver, which is operated at 820 to 870°F [2]. The dissolver effluent is separated into vapor- and liquid-phase fractions. The overhead vapor stream undergoes several stages of cooling and separations, and the condensed liquid is distilled to produce naphtha and a middle distillate oil, which are converted to gasoline and diesel fuel, respectively. The gaseous products are purified to remove hydrogen sulfide and carbon dioxide, and the hydrogen-rich gas is then recycled to the reactor with make-up hydrogen. The liquid-phase product acts as the solvent for the SRC-II process. SRC-II testing was performed at the Tacoma, Washington, pilot-plant by Gulf Oil. Funding for this work was provided by the DOE.

Costeam Process The costeam process, investigated at the Pittsburgh Energy Research Center (DOE) and the University of North Dakota/Grand Forks Energy Research Center was intended to produce low-sulfur liquid products from lignites and subbituminous coals. This process uses crude syngas containing about 50 to 60% carbon monoxide and 30 to 50% hydrogen, rather than pure hydrogen. The high moisture content of the low-rank coals provides the water that is converted to steam. Ground coal is slur-ried with recycled product oil from the process. The slurried coal is pumped to unit pressure (4000 psig), mixed with syngas, heated to 750 to 840°F, and maintained at conditions for periods of 1 to 2 hours to liquefy the coal. Severe operating conditions are required for the dissolution of the lignite. These operating conditions were a drawback for the process, as long residence times and high pressures are costly and present major engineering problems. This process, although a potential candidate for liquefying low-rank coals, was only tested in small-scale equipment. It is included in this discussion because it was considered a potential process for utilizing low-rank coals.

Catalytic Processes

The most important process of this group is the H-Coal process, developed by Hydrocarbon Research, Inc. (HRI) as an outgrowth of previous work on the hydrogenation of petroleum fractions. The development of this process was sponsored by the ERDA and a large group of oil companies [1].

H-Coal Process In the H-coal process, pulverized coal is slurried with recycled oil and, along with hydrogen, fed to an ebullated-bed reactor, a feature that distinguishes this process from others. Reactor conditions are normally in the range of 825 to 875°F and 2500 to 3500 psig. The reactor contains a bed of catalytic particles, cobalt molybdate on alumina oxide. The products from the reactor include hydrocarbon gases, light and heavy distillate oils, and bottoms slurry. Variations of the processing scheme can produce fuel oil, naphtha, synthetic crude, ammonia, and fuel gas. Further processing can produce gasoline and jet fuel. HRI operated several small-scale reactors in their Trenton, New Jersey, test facility, and a pilot plant producing 800 short tons coal per day was constructed in Cattletsburg, Kentucky.

In 1995, when it became an employee-owned company, HRI changed its name to Hydrocarbon Technologies, Inc. (HTI). HTI has modified its process, now known as HTI's direct coal liquefaction (DCL) process and shown schematically in Figure 5-36, and it has gone from a single- to double-stage reactor system [51]. In the HTI DCL process, pulverized coal is dissolved in recycled, coal-derived, heavy-process liquid at about 2500 psig and 800°F while hydrogen is added. Most of the coal structure is broken down in the first-stage reactor. Liquefaction is completed in the second-stage reactor, at a slightly higher temperature and lower pressure. A proprietary GelCat catalyst is dispersed in the slurry for both stages. The process produces diesel fuel and gasoline. HTI has entered into an agreement with Shenhua Group Corporation, Ltd., for a direct coal liquefaction plant to be constructed in the People's Republic of China [52]. The plant will be located approximately 80 miles south of Baotou, at Majata, Inner Mongolia in China. The plant will have an ultimate capacity of 50,000 barrels per day of ultra-clean, low-sulfur, diesel fuel and gasoline produced from Chinese coal. The plant is

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