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PROCESS & TECHNOLOGY FOR METHANOL AND DME

of at least one type of biomass is assured.
6. In addition to the lignocellulosic materials the plant is designed with the capability
to process MSW from local source.
Although the combustion equipment of biomass is similar to that used for power generation or
syngas production, gasification is more complex to control.
Due to these inherent constraints there are some limitations for building Mega methanol/DME
plants based on biomass. The disadvantages of having smaller capacity are compensated
with positive gains through utilization of waste, much lower penalty for GHG emission and
availability of fuels at the user end without transportation over long distances. Putting these
together, particularly if cost tag is attached with the WTW carbon emission, methanol/DME is
a winner even if produced in moderate scale from waste biomass.
While pretreatment of coal or coke for gasifiers is simpler, due the wide variation in characteristics
of available biomass, the preparation of biomass for the gasification reactor requires attention.
Generally there are several pretreatment steps before the biomass is fed to the gasifier, such
as sizing, drying, torrefaction (especially suited for wood), pyrolysis etc. The typical operating
conditions are shown below in fig. 5.

FIG. 5
Typical Operating Conditions

2 4 6

Power
1 Drying 3 Pyrolysis 5 Generation and/or
200 to 300 C 400 to 600 C Chemical
o
o
Production
Gasification
Torrefaction 1000 C
o
Sizing
300 to 400 C Pressure amb.
o
to 5 Bar

Sizing includes chipping, cutting, pulverizing, milling, screening etc. to produce suitable
uniform sized product.
Drying is carried out either by heating with available gas or preferably with sunlight, if possible,
to reduce the moisture content to an acceptable level for transportation.
Torrefaction is particularly suitable for wood where wood chips are heated for a short time in
absence of oxygen to make them dry and brittle. This step removes the balance moisture and
makes the wood easier to handle in subsequent stages.

Pyrolysis is also carried out in absence of oxygen with the objective to extract valuable volatile
components from the biomass. This step helps in avoidance of tar formation in the gasifier.
There are several types of gasifier designs depending upon the type of biomass and size of
the gasifier as shown in Table10.
To summarize, biomass gasification is more complex compared to fossil fuel based gasifiers.
Before selection of suitable gasifier design, and the process scheme, the objective and

36 Methanol and DME Production: Survey and Roadmap | 2017