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PROCESS & TECHNOLOGY FOR METHANOL AND DME

TABLE 9

Off Gases from Steel plant [12]
Steel Production
Gas Type Coke Gas Blast Furnace Gas Converted Gas
Source Coke Oven battery Blast Furnace Converter
Input Coal Coke and Iron ore Pig iron
Output Coke Pig iron Steel
Hydrogen % 50-70% 5% -
Methane % 25-30% - -
Carbon Monoxide % - 20% 60%+
Lower heating value kWh/Nm³ ~5.0 ~0.9 ~3

Since most steel plants use these low grade gases from different sections for power generation,
there is not much reported information about utilization of these gases for syngas production.
However, there may be some usage where such gases are mixed with natural gas, if available
locally, for use in the gasifier.
There are some reports from Sweden during 2013, where techno-commercial feasibility was
established when these gases are integrated with biomass gasification plant for production of
methanol. It was found that among several options considered biogas addition works out to be
most economical. [13]
For the Steel plants using air for combustion rather than oxygen, for any conversion to syngas
from these gases for methanol production, requires a nitrogen separation step. Therefore,
it may be difficult to use the, off gases directly for methanol production. However, it may be
possible to process at least the coke oven gas but for most of the steel plants the availability of
this gas will be uneconomical for a reasonable capacity methanol plant. With syngas available
from other sources, such as biomass or other fuels this is worth considering if surplus coke
oven gas is available [13]. In a theoretical study it has been shown that there is a possibility
of utilizing blast furnace off gases along with a combined cycle power generation unit [70, 71].
However, this strategy makes the operation more complicated and probably suited for grass
root plants only.
There are several options with coke oven gas and the simplest option is generation of power
or use as fuel in different sections of the plant or even exported. Methanol or hydrogen could
be produced after partial oxidation of both cooled and hot coke oven gas. It could also be
used for direct reduction. The choice depends upon the configuration of the complex and local
economics. [135]
Coke oven gas (COG) is rich in hydrogen and therefore has a relatively high heating value of
17.6 MJ/m3, compared with 3.5 MJ/m3 for blast furnace gas. About 40% of the coal and coke
energy input is converted into blast furnace gas. The carbon dioxide content of blast furnace
gas is high. About 70% of COG is used in iron and steel production processes 15% to heat
coke ovens and 15% for power generation. At most steel plants, COG is used to heat and to
fuel equipment such as boilers and reheat furnaces. The boilers supply steam for electricity
generation, turbine-driven equipment such as pumps and fans and for process heat. The
overall efficiency can be improved if the coke oven is fired with blast furnace gas and the COG
is put to a higher quality use, e.g. power generation. Combined cycle is preferred over steam
cycles. Some plants convert COG to chemicals. [136]

34 Methanol and DME Production: Survey and Roadmap | 2017