Coal-based liquid fuels

The co-processing of coal with heavy crude oil or its heavier fractions is being developed to lower capital requirements for coal hquefaction and to integrate processing of the products of coal conversion into existing petroleum refineries. This development appears to represent the main route by which coal-based liquid fuels will supplement and perhaps someday displace petroleum-based fuels. 

Gasificationr-Based Liquid Fuels and Chemicals Liquid fuels and chemicals from gasification-based synthesis gas are described in the coal hquefaction section following this section. While the downstream areas of power system and indirect hquefaction plants will differ markedly, the gasification sections will be quite similar and are described in this section. 

Over the past few years, established analytical chemical methodology for crude oil and refined petroleum derivatives has been extended to the rapidly expanding field of coal liquefaction products and has assisted in the substantive reappraisal of such potential liquid fuel sources as oil shale, tar sands, and similar bitumenous deposits. While many of the analytical problems of separation, identification, and characterization are common to all of these fields, each area exhibits distinct requirements calling for specific development of appropriate methodology. Indeed, the added chemical complexity of the nonpetroleum-based liquid fuel sources presents many novel challenges to the chemical investigator. 

A recent paper by EIA (Energy Information Administration) within DOE (U.S. Department of Energy) indicates that CTL (coal-to-liquids) fuels, under the High Price B Case, could become a viable supplement to the petroleum liquids supply in U.S. by 2010 (1). CTL fuels made from the indirect liquefaction technology are free of sulfur and aromatics, and also have clean combustion properties. These fuels are compatible with the petroleum-based ultra-clean transportation fuels mandated by EPA (U.S. Environmental Protection Agency) for 2006 and beyond to help meet the new stringent specifications for vehicle emissions. The CTL fuels can be used either as a blending component or as neat fuel. 

BE vehicles. Results of one study found out that coal-to-liquid fuels and coal-to-hydrogen will most likely increase emissions, while coal-to-electricity combined with carbon capture and sequestration could cut emissions in half using short range (60 km) plug-in hybrid electric vehicles (PHEV) for some of the vehicle fleet demand. In reality, this study proves that coal for transportation could be argued for increased energy security (Jaramillo et al, 2009). However, coal-based electricity with carbon sequestration costs as much as, or more than, wind power does today. The cost of photovoltaic electricity is steadily falling, as well. 

Liquid fuels for use in internal-combustion engines are extracted and refined from crude oil, with diesel fuels being part of the middle distillate or kerosene fraction. Kerosene was initially derived from coal pyrolysis. The initial main use of this type of distillate was for the kerosene lamp, which had replaced lamps based on whale oil. 

Coal is the main energy reserve for many countries. In order to ensure energy security, many of these countries are looking at implementing large-scale coal-to-liquid (CTL) plants. Current CTL Fischer-Tropsch (FT)-based processes at best have a carbon efficiency near 45% that is, less than half the carbon that is fed to the process ends up as hydrocarbon fuels. This has large implications for the environment, in that more than half of the carbon in the feed to the CTL ends up... 

Gasification technologies offer the potential of clean and efficient energy. The technologies enable the production of synthetic gas from low or negative-value carbon-based feedstocks such as coal, petroleum coke, high sulfur fuel oil, materials that would otherwise be disposed as waste, and biomass. The gas can be used in place of natural gas to generate electricity, or as a basic raw material to produce chemicals and liquid fuels. 

Moving to the transport sector, Fig. 15.1 quantifies the continued oil stress of the transportation sector. Even when a rather aggressive development of biofuels is included, the transportation demand for oil does not go down. This underlines that in all likelihood the energy security issue is as much a long-term issue as the climate change issue. It induces a strong motivation around the world to develop non oil-based transportation fuels, even in the absence of CO2 emission concerns. Current investments in the area of Gas-to-Liquids (GTL) and plans for Coal-to-Liquids (CTL) attest to this [7]. 

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) ... 

Coal is our major source of fossil fuel, being about 87% of the total. Oil shale is 9%, petroleum is 2.5%, and natural gas is 1.5%. These estimates are based on the probable yield of liquid fuel. They are, at best, only very approximate (1, 9, 11). Thus, if all of the known oil-shale deposits in the United States were included, the probable yield of liquid fuel would be about 50% of the total since the 9% estimate excludes shale assaying less than 10 gallons per ton. Similarly, in estimating the probable yield of liquid fuel from coal, somewhat arbitrary assumptions must be made concerning the feasibility of mining thin seams. 

The principal method of indirect liquefaction is to react carbon monoxide and hydrogen produced by coal gasification in the presence of a catalyst to form hydrocarbon vapors, which are then condensed to liquid fuels. This procedure for synthesizing hydrocarbons is based on the work of Fischer and Tropsch in Germany in the 1920s. Just prior to and during World War II, Germany produced... 

---