Oil and gas production handbook An introduction to oil ... - ABB Group

after well completion and fracturing, the coal seam (layer of coal) must be
dewatered. A common solution is to extract water through the well tubing.
Generally, the water needs to be pumped out and therefore control is
needed to prevent the gas from entering the water in the tubing (the well
becomes gassy). This reduces the pressure and allows methane to desorb
from the matrix and be produced through the casing.
9.1.5 Coal, gas to liquids and synthetic fuel
Coal is similar in origin to oil shales, but typically formed from the anaerobic
decay of peat swamps and relatively free from non-organic sediment
deposits, reformed by heat and pressure. To form a 1-meter thick coal layer,
as much as 30 meters of peat was originally required. Coal can vary from
relatively pure carbon to carbon soaked with hydrocarbons, sulfur, etc.
(For synthesis gas, see also chapter 7.3.)
It has been known for decades that synthetic diesel could be created from
coal. This is done, first by creating water gas as synthesis gas by passing
steam over red-hot coke. The reaction is endothermic and requires heating:
C + H 2 O → H 2 + CO
More hydrogen is produced in the water gas shift reaction:
CO + H 2 O → H 2 + CO 2
Often two stages are used: a high temperature shift (HTS) at 350 °C with
catalyst iron oxide promoted with chromium oxide, and a low temperature
shift (LTS) at 190–210 °C with catalyst copper on a mixed support composed
of zinc oxide and aluminum oxide.
These synthesis gases are then used in the Fischer–Tropsch process:
(2n+1)H 2 + nCO → C n H (2n+2) + nH 2 O
This process runs at a pressure of 2-4 MPa. With iron catalyst a high
temperature process at 350 °C will yield a diesel fuel quite similar to normal
diesel with an average carbon number of 12, and a certain content of
unwanted aromatics. The low temperature process uses a cobalt catalyst
and a temperature of 200 °C and yields a pure synthetic diesel composed of
alkanes with a carbon number of 10-15 and an average carbon number of
12.
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