Feedstocks and Feedstock. Characteristics
4.1 COALS AND COKE
Approximately 2250MMtoe/y of coal is consumed each year (BP 2002). Of this about 35 MMt/y is gasified to produce 150 million Nm3/d of synthesis gas (Simbeck and Johnson 2001). Roughly half of this gas is generated in the Sasol synfuels plants in South Africa where the synthesis gas is used for the production of liquid hydrocarbons and other chemicals. Most of the remainder of this gas is used for ammonia production and—in China—for the production of town gas.
The total proven reserves of coal amount to 984 x 109t worldwide. Coal consumption has been stable over the last ten years. Nonetheless it plays an important part in the thinking of many long-term energy strategies, despite its contentious role in the production of C02 as a greenhouse gas. The reason for this can be seen from the figures in Table 4-1. The ratio of reserves to current production (R/P ratio) is 216. In other words, at current consumption rates the world’s reserves would last 216 years.
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Table 4-1 World Coal Reserves by Region
Source: BP 2002 |
Compare this with 62 years for natural gas and 40 years for oil. Furthermore the reserves are more evenly distributed than oil (65% of reserves in the Middle East) or natural gas (72% in the Middle East and Russia).
The composition of coals is very complex, and the types of coal differ considerably. The detailed petrographic composition of the organic part of coals, often characterized by a so-called maceral analysis, has little influence on most gasification processes, and the interested reader is referred to the many treatises on this subject (e. g., Speight 1983; Smoot and Smith 1985; and Kural 1994). Important for gasification are the age of the coal, its caking properties, its water content, and its ash properties.