Gasification is a process that converts biomass into syngas (CO, H2, CO2) at high temperatures. This allows biomass to be more easily handled and converted into liquid fuels and chemicals through established processes. However, biomass gasification faces challenges like tar production and high oxygen content requiring more energy to remove. While some biomass gasification projects have begun, many have faced operating or funding difficulties. Gasification may be more economically viable when producing higher value chemicals rather than fuels alone.

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Gasification: the Flexible Answer to Biomass Conversion
By Dr. Terry Mazanec
Introduction
Biomass is a rich salad of chemicals that contains many highly valuable materials that are precursors to
fine chemicals, nutrients, and pharmaceuticals. But this strength is also a weakness of biomass. The
assortment of materials in biomass is bound together in a complex, stable structure in varying amounts.
Processing biomass to generate higher value products comprises disentangling and modifying the useful
fragments in a series of complex and costly steps. The challenge in biomass upgrading and utilization is
to balance the value of the chemicals produced against the cost of the feed and its transformation.
Figure 1. The value and yield of products from biomass conversion as a function of the extent of biomass
transformation.
Biomass conversion can be viewed in terms of the extent of transformation of its chemical structure
(Figure 1). Very little processing is required to use biomass as food, as a construction material, or as a
combustion fuel. With just a bit of transformation biomass can be a source of cellulose fibers and paper
on a grand scale. In some cases valuable finished products, like the nutritional supplemental omega-3
fatty acids EPA and DHA, may be extracted directly from biomass. Biochemical transformations under
mild conditions, such as fermentation, are capable of producing ethanol, butanols, etc
The most extreme transformations of biomass produce gases. Bio-gas forms slowly by simply allowing
biomass to sit under anaerobic conditions, as in a landfill. Bio-gas is roughly a 60/40 mix of methane and

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CO2, with small amounts of impurities, so it can be substituted for natural gas with only modest
separation.
A different sort of gas can be produced from biomass by gasification. In the gasification process biomass
is converted to syngas (CO, H2, CO2, and a few impurities) at high temperatures. Bio-syngas can be
converted to methanol, DME, or FT products via the same commercial processes practiced at massive
scale in the monetization of coal or natural gas.
Utilizing biomass as a gas allows one to sidestep many of the limitations of biomass. Gas mixtures are
easier to handle than solids, and have fewer corrosion, stability, or fouling problems compared to
complex liquid bio-oil mixtures. Established purification methods are available that can be adapted to
clean or adjust the composition of bio-derived syngas. A host of companies are developing technologies
to convert bio-derived gases to liquids, including Synthesis Energy Systems, Primus Green Energy,
Sundrop Fuels, Maverick Synfuels, Siluria, INFRA, Oberon, GTI, and Velocys.
Gasification
Like coal gasification, biomass gasification operates at high temperatures (> 700 ° C) with steam or air or
oxygen, and can be tuned to make “synthetic natural gas” (SNG), i.e. methane, or synthesis gas (CO, H2,
CO2).
Several processes occur in a gasification reactor, as shown in Figure 2 for a typical down-flow gasifier.
Solid biomass enters the upper part of the reactor and descends as a slowly moving mass. Air can be
introduced with the biomass or further down the reactor. Drying, pyrolysis, combustion, and reduction
take place in succession as the material descends. At the bottom of the reactor the ash is allowed to fall
to the reactor bottom and the produced gas is removed as a side stream. Other gasification reactor
designs include up-flow gasifiers, fluid bed gasifiers, and circulating fluid bed gasifiers.
In the drying zone of the gasifier, steam is evolved from the moisture in the biomass and by dehydration
reactions, and in the pyrolysis zone, volatile organic molecules vaporize from the solid char. The
volatiles and char move into the oxidation and reduction zones where they react with gasifying agents
to produce product gases. Air, steam, carbon dioxide, and/or pure oxygen are used depending on the
requirement of the downstream application. Using air in the gasifier generates a producer gas that is
diluted about 50% with nitrogen, so its energy content is only about 1/8th
that of natural gas. Processes
that use steam require a great deal of energy in order to drive the reactions, thus reducing thermal
efficiency, although increasing the H2 concentration. Carbon dioxide can act as a gasifying agent but the
reaction is slow.

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Gasification status
The US DOE 2015 Gasification Database lists 8
‘active’ biomass gasification projects, although
all appear to be in the planning/construction
phase or have run into operating or funding
difficulties. Sundrop Fuels began
commissioning and operation of an integrated
bioreforming demonstration facility in
Longmont, Colorado in December, 2015.
Sundrop’s technology includes biomass
preparation by ‘powderizing’ the feedstock
and a high temperature biomass reformer
system claimed to provide high syngas yields
and eliminate organic tars. Syngas upgrading
comprises conventional methanol synthesis
and methanol-to-gasoline processes.
Fulcrum Bioenergy is building a plant to gasify
municipal solid waste (MSW) to make
syncrude via FT conversion. The gasification
process is a variant of steam reforming that
will be installed at their $200 million 700 bpd
Sierra BioFuels Plant in Nevada, opening in
2017.
SNG can be produced directly or through a
syngas mixture that is catalytically converted
to methane in a second step. Göteberg Energi used the indirect process in their 20 MW GoBiGas plant,
opened in 2015. Operation was plagued by tar formation and benzene breakthrough, however, and low
oil prices sidelined the plant, written off for €90 million.
GreatPoint Energy, is developing its bluegas™ technology, a catalytic gasification process to convert coal,
petcoke, and biomass into a methane-rich SNG. In 2012 GreatPoint and China Wanxiang Holdings
signed an agreement to build a $1.25 billion coal to SNG plant, but to date construction has not started.
Synthesis Energy Systems (SES) uses a single-stage, bubbling fluidized-bed gasification system to
produce low-to-medium heating value syngas from coal, biomass, or wastes using oxygen or air in the
gasifier. The so-called U-GAS™ coal gasification process licensed from the Gas Technology Institute is
being marketed as “Growth With Blue Skies.” SES has operated a $250 million coal-to-methanol plant in
Henan Province in China since 2012 and has an $85 million hydrogen plant in the works. SES claims
success with biomass such as wood waste, straw, pelletized alfalfa stems, bagasse, rice straw, and
chicken litter.
Figure 2. A Downflow Biomass Gasifier (Ankur Scientific)

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Gasification challenges
Raw biomass gasification product gas includes particulate matter, ammonia, sulfur compounds,
hydrochloric acid, and alkali metal species as impurities. Different biomass feedstocks, gasifier designs,
gasifying agents, and gasification conditions produce different gas compositions and impurities. Tar and
particulate concentrations above the acceptable range are problematic for turbines, fuel cells, and
methanol or FT synthesis processes.
A major problem with biomass gasification is the production of tars that clog equipment and complicate
separation and recovery processes. Tars include complex polycyclic aromatics and oxygen containing
hydrocarbons. Upflow gasifiers and fluid bed gasifiers operating at lower temperatures (700-900 °C)
suffer more from tar formation than downflow gasifiers operating at higher temperatures (> 1000 °C).
Higher temperatures also favor the yield of H2 and CO, but suffer from ash melting to form slag that
coats or clogs equipment.
Two strategies for eliminating tars include gas cleanup and in-bed tar conversion. Gas cleanup is akin to
the cleanup of steam cracker products containing heavies. Cracker gas cleanup normally includes a
liquid quench or scrubber where tars are isolated for conversion, recycle, or disposal. ECN and Dahlman
have developed the OLGA cleanup system for recovering and recycling tars from their MILENA biomass
gasification reactor in an integrated gasification combined cycle (IGCC) process. It features both
condensation and scrubbing units that recover and recycle tar to the gasifier. Olefins and aromatics in
the products may provide more value as chemical intermediates than by combustion, provided they can
be recovered economically. In-bed tar conversion processes have focused on dolomite, Ni, olivine, and
FCC type catalysts, but catalyst cost and stability are concerns.
An even more significant hurdle for the competitive economics of biomass gasification is the high
oxygen content of biomass compared to natural gas or coal. For SNG or diesel fuel all of the oxygen
needs to be removed, and for syngas at least 40% needs to be rejected, requiring high temperatures and
energy, and reducing yield. Integrated gasification/methanol synthesis/hydrocarbon synthesis
processes are projected to achieve about 19% mass yield of gasoline and diesel range products.
Prospectus
Gasification of coal or petroleum coke has been successful where the products are chemicals rather than
fuels. CRV Refining annually produces 335,000 tonnes of ammonia and 574,300 tonnes of urea
ammonium nitrate solution from pet coke at its Coffeyville, KS refinery. Dakota Gasification is building a
plant in Beulah, ND to produce 1,100 tons of urea and 153 million cubic feet of SNG per day. By
contrast, Mississippi Power’s Kemper IGCC plant to convert coal to electricity via gasification was started
in 2010, is still not complete, and has ballooned from an original budget of $2.8 to $6.7 billion.
The experiences with coal gasification serve as both guide and warning for biomass gasification. With
lower heating value and higher oxygen content, the need to aim for higher value products than fuel is
vital.

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About the Author
Dr. Terry Mazanec has been involved in the renewable fuels and chemicals area for much of his 35 years
in R&D. Terry worked 21 years at BP in alternate energy R&D, and then as Chief Scientist at Velocys for
9 years where he led the team developing microchannel processes for natural gas upgrading and
chemicals production, including catalyst development, corrosion resistance, and metals coating. He has
been an independent consultant for the past 5 years serving clients in the USA, Europe, and Asia. He has
authored 20 refereed publications and has been granted more than 60 US Patents as well as numerous
international patents. He has experience in catalysis, biomass upgrading, chemicals process
development, natural gas conversion, solid oxide fuel cells, algae production, FMEA risk analysis,
technical due diligence, expert witness services, and intellectual property protection.