Page 223 - Synthetic Fuels Handbook

FUELS FROM SYNTHESIS GAS 209

low-boiling hydrocarbons other than ethane. A variety of naphtha-types in the gasoline
boiling range may be employed, including feeds containing up to 35 percent aromatics.
Thus, following pretreatment to remove sulfur compounds, the feedstock is mixed with
steam and taken to the reforming furnace [675–815°C (1247–1499°F), 300 psi (2068 kPa)],
where hydrogen is produced.

Texaco Gasification (Partial Oxidation) Process. The Texaco gasification process is a
partial oxidation gasification process for generating synthetic gas, principally hydrogen
and carbon monoxide. The characteristic of Texaco gasification process is to inject feed-
stock together with carbon dioxide, steam, or water into the gasifier. Therefore, solvent
deasphalted residua, or petroleum coke rejected from any coking method can be used as
feedstock for this gasification process. The produced gas from this gasification process
can be used for the production of high-purity, high-pressurized hydrogen, ammonia, and
methanol. The heat recovered from the high-temperature gas is used for the generation of
steam in the waste heat boiler. Alternatively the less expensive quench type configuration is
preferred when high-pressure steam is not needed or when a high degree of shift is needed
in the downstream CO converter.
In the process, the feedstock, together with the feedstock carbon slurry recovered in the
carbon recovery section, is pressurized to a given pressure, mixed with high-pressure steam
and then blown into the gas generator through the burner together with oxygen.
The gasification reaction is a partial oxidation of hydrocarbons to carbon monoxide
and hydrogen:

C H + x/2O → xCO + yH
x 2y 2 2
C H + xH O → xCO + (x+y)H 2
x
2y
2
The gasification reaction is instantly completed, thus producing gas mainly consisting
of H and CO (H + CO = >90 percent). The high-temperature gas leaving the reaction
2
2
chamber of the gas generator enters the quenching chamber linked to the bottom of the gas
generator and is quenched to 200 to 260°C (392–500°F) with water.
7.3 STEAM-METHANE REFORMING

Steam reforming of natural gas, sometimes referred to as steam-methane reforming is the
most common method of producing commercial bulk hydrogen as well as synthesis gas.
Steam-methane reforming is a catalytic process that involves a reaction between natural
gas or other light hydrocarbons and steam (van Beurden, 2004). Steam-methane reform-
ing is the benchmark process that has been employed over a period of several decades for
hydrogen production. The process involves reforming natural gas in a continuous catalytic
process in which the major reaction is the formation of carbon monoxide and hydrogen
from methane and steam.
The steam reforming of methane consists of three reversible reactions: the strongly
endothermic reforming reactions [Eqs. (7.1) and (7.3)], and the moderately exothermic
water-gas shift reaction [Eq. 7.2]:
CH + H O → CO + 3H 2 ΔH 298 K =+97,400 Btu/lb (7.1)
4
2
In practice, it is necessary to terminate the reaction at the stage where the maximum
yields of carbon monoxide and hydrogen are produced.