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PROCESS & TECHNOLOGY FOR METHANOL AND DME

2.1.2.3
GASIFICATION OF BLACK LIQUOR

Black liquor is a problematic by-product from paper mills; about 1.7 to 1.8 ton of black liquor
(dry basis) is produced for manufacture of one ton of pulp. Black liquor contains lignin,
hemicelluloses and about 30% inorganic chemicals. Many paper mills use this black liquor as
an energy source. Before use in a combustor, water is removed in multiple effect evaporators
and the concentrated liquor is burnt to recover the chemicals, which are recycled. In the
United States, most of the black liquor is converted into electricity. Although production of
energy from black liquor is an attractive option as an energy source with great reduction in
GHG emission, it is more attractive to produce syngas from black liquor by gasification. The
balance energy requirement of a paper mill could be met by burning low grade wood waste.
The additional investment for a paper mill for production of methanol/DME from black liquor
could be recovered in about 4 years as estimated in 2003 by ALTENER (Energy Framework
Program) of the European Union [9].The WTW energy for DME and synthetic diesel from black
liquor shows the lowest GHG emission [10].

2.1.2.4

SYNGAS FROM REFINERY OFF GASES
Petroleum refining is another process industry consuming a large amount of hydrocarbon source
as feedstock, for production of transportation fuels and energy. These refineries produce fuel
gas of different compositions. In fact, the diversity of composition, nature and the impurities of
these off gases make their handling rather complex. Secondly, the hydrogen demand of the
refineries is ever increasing. Most of the refineries produce hydrogen from naphtha or natural
gas (if available) by steam reforming. The available fuel gases are normally burnt but there is
interest in using these gases in the steam reformer, to save naphtha or natural gas.
Refinery off gases is a large source of low calorific value hydrocarbon gases. Therefore,
after recovering the specific hydrocarbons from these dilute gas streams, they use these
gases in their naphtha reformer to be converted to hydrogen. Refineries which manufacture
MTBE (Methyl Tertiary Butyl Ether) for gasoline octane boosting, may produce methanol. The
possibilities for utilization of off gases are shown in Fig 3.
Refineries primarily focus on the recovery of valuable chemicals from these dilute streams,
and production of hydrogen from the balance hydrocarbons.

2.1.2.5

SYNGAS FROM REFINERY RESIDUE AND PET COKE
To dispose of the heavier fractions of crude, many refineries also have a coking unit, which
produces coke as a solid saleable product. There is always a possibility to put up a residue
gasification plant using petroleum coke and other heavy residues for power and methanol
production through IGCC. Therefore, for a refinery, it is feasible to put up gasification plant
and produce methanol, but the economics may not be very favourable, particularly when the
conversion to hydrogen is possible within the available existing infrastructure.

With regard to refinery residue, tars and heavy oil or coke, the conventional disposal route is
to burn for generating power, if no other suitable outlet is available. However, with the recent
developments of gasification technology coupled with IGCC, co-production of hydrogen is
becoming popular. Since at present most of the refineries have a large hydrogen demand, IGCC

32 Methanol and DME Production: Survey and Roadmap | 2017