Like many of you, I have been in the chemical industry for many years.
It has been my experience that a gas became synthesis gas or syn-gas
after
various treatment processes to prepare it to synthesize a particular
chemical. Prior to preparing it for synthesizing it had other names.
Typically in the chemical/petrochemical industry it was prepared by
reforming natural gas. After reforming, it was called reformed gas.
Subsequently, the ratio of hydrogen to carbon monoxide was adjusted
(shifted) to the
proper value for the particular product that was being synthesized. That
gas was called shift gas. The next stage was to remove carbon dioxide.
At that stage the gas was called syngas, because it was then ready to be
synthesized into the final product.
In general terms, to synthesize methanol the ratio of hydrogen to carbon
monoxide was approximately 2:1. For synthetic natural gas it was 3:1 and
for ammonia, there was almost no carbon monoxide, but there was some
nitrogen,
in the ratio of 3 parts hydrogen to one part nitrogen.
Prior to the use of natural gas, coal gas (producer gas) was used after
suitable preparation and with the use of oxygen. Again it only became
synthesis gas prior to the final synthesis step. Gas that was used to
produce
hydrogen was never called synthesis gas
In my book, synthesis gas is a gas that has been made ready for the final
synthesis step into a particular chemical, regardless of what is was
before
i.e. the gas is used to directly synthesize another chemical product.
Wood gas is not synthesis gas, but it could become synthesis gas after
appropriate treatment. If a gas is cleaned and prepared for burning in
a kiln
or a boiler, it is fuel gas regardless of composition.
My preference is to call it wood gas (Tom's term) since it is made from
wood or, if you want to be more generic it is biomass gas but not
bio-gas.
As mentioned by others, the latter is usually used for gas that has been
produced by anaerobic digestion. If you want to be fancy call it
xylogas.
If the term syn-gas is used in any other way, it becomes too generic and
wood gas would loose its sense of identity. By some of the definitions
used in past correspondence, coal gas, biogas, SNG or even ethylene could
be
called syn-gas. Let's try to keep our identity by choosing a
descriptive
name rather than devolving into a generic descriptor.
There are some excellent descriptions of the various types of gases,
including synthesis gas, producer gas, blue gas, carbureted water gas in
the
"Gas Engineer's Handbook", if anyone is interested
More fuel for the fire.
John
Date: Wed, 29 Dec 2010 13:13:35 -0800
From: Bear Kaufmann <[email protected]>
To: [email protected]
Subject: [Gasification] A small literature review re: syngas
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
I looked through some of the papers I have on hand, and extracted the
interesting parts as they relate to the latest discussion, FWIW:
"Fuel gas can be used directly as fuel in gas burners or internal
combustion engines and gas turbines. Fuel gas, after purification and
possibly water gas shift to adjust the H2/CO ratio, can be described as
a syngas (a mixture of H2 and CO), which can be used to manufacture
methanol, ammonia, Fischer Tropsch liquids, or hydrogen for use in fuel
cells (4). The suitability for a particular usage, i.e. the fuel gas
quality, is determined by the gas composition and the level of
contamination by particulates, alkali compounds, nitrogen-containing
components, sulphur and tars (5)."
from Kalisz, S. et al. Energy Balance of High Temperature Air/Steam
Gasification of Biomass in Up-Draft, Fixed-Bed Type Gasifier. Int. Conf.
on Incineration and Thermal Treatment Technologies, Phoenix, Arizona
(2004).at
<http://gasunie.eldoc.ub.rug.nl/FILES/root/2004/3265200/3265200.pdf>
"Fast pyrolyzers rapidly (?1 s) heat dry biomass (10% H2O) to ?500?C and
thereby thermally transform biomass into bio-oil (?60% of mass), syngas
(?20% of mass), and charcoal (?20% of mass). The energy required to
operate a fast pyrolyzer is ?15% of the total energy that can be derived
from the dry biomass. Modern systems are designed to use the syngas
generated by the pyro- lyzer to provide all the energy needs of the
pyrolyzer."
from Laird, D.A. The Charcoal Vision: A Win Win Win Scenario for
Simultaneously Producing Bioenergy, Permanently Sequestering Carbon,
while Improving Soil and Water Quality. Agron J 100, 178-181(2008).
"To improve the thermal efficiency and predict the composition of
syngas, several numeric models have been developed for biomass
conversion systems."
from Rogel, A. & Aguill?n, J. The 2D Eulerian Approach of Entrained Flow
and Temperature in a Biomass Stratified Downdraft Gasifier. American
Journal of Applied Sciences 3, 2068-2075(2006).
Comments: Shows a stratified downdraft model with inputs of air and
biomass, outputs of syngas and ashes
"The term ?pyrolysis? is typically used either for ...[analytical
purposes]... or for bioenergy systems that capture the off-gases emitted
during charring and used to produce hydrogen, syngas, bio-oils, heat or
electricity (Bridgwater et al, 1999)."
from Lehmann, J. & Joseph, S. Biochar for environmental management:
science and technology. (Earthscan/James & James: 2009).
"High purity syngas (i.e. low quantities of inerts such as N2) is
extremely beneficial for fuels and chemicals synthesis since it
substantially reduces the size and cost of downstream equipment.
However, the guidelines provided in Table 5 should not be interpreted as
stringent requirements. "
"There is more latitude with regard to syngas composition for engine
combustion than for turbine combustion."
"To be considered interchangeable with conventional fossil fuels
(natural gas or distillate oils) and to ensure maximum flexibility for
industrial or utility applications, syngas heating value needs to be
above 11 MJ/m3"
"At temperatures greater than 1200-1300oC, little or no methane, higher
hydrocarbons or tar is formed, and H2 and CO production is maximized
without requiring a further conversion step."
"Biomass gasification is the conversion of an organic...carbonaceous
feedstock by partial oxidation into a gaseous product, synthesis gas or
?syngas,? consisting primarily of [H2 and CO] with lesser amounts of
[CO2, CH4], higher hydrocarbons (C2+), and nitrogen (N2). The reactions
are carried out at elevated temperatures, 500-1400oC, and atmospheric or
elevated pressures up to 33 bar (480 psia). The oxidant used can be air,
pure oxygen, steam or a mixture of these gases. Air-based gasifiers
typically produce a product gas containing a relatively high
concentration of nitrogen with a low heating value between 4 and 6 MJ/m3
(107-161 Btu/ft3). Oxygen and steam-based gasifiers produce a product
gas containing a relatively high concentration of hydrogen and CO with a
heating value between 10 and 20 MJ/m3 (268-537 Btu/ft3)."
"Table 8. Compositions of Biomass-Derived Syngas" - includes N2 from
0-56%, H2 from 5-43.3%, CO from 9-67%, CO2 from 4-40%
...
from Ciferno, J.P. & Marano, J.J. Benchmarking biomass gasification
technologies for fuels, chemicals and hydrogen production. US Dep of
Energy NETL (2002).at
<http://seca.doe.gov/technologies/coalpower/gasification/pubs/pdf/BMassGasFi
nal.pdf>
"The resulting fuel is a producer gas (a synthesis gas or syngas) that
consists primarily of varying ratios of hydrogen and carbon monoxide
(CO)."
from Mukhtar, S. Manure to Energy: Understanding Processes, Principles
and Jargon. (2006).at
<http://repository.tamu.edu/bitstream/handle/1969.1/87462/pdf_2425.pdf?seque
nce=1>
In short, the usage from the above doesn't appear entirely clear.
But in general, syngas is often suggested to have been upgraded, or of a
higher CO/H2/energy content. Syngas is often used to refer to gas
intended to be used for synthesis of products. Syngas does also seem to
be used as general term in some cases.
My preferred usage has been to call the gas the air-blown GEK makes
"producer gas". Wood gas notes that the carbon source was biomass,
though I don't prefer the term. "Syngas" being made with O2 or steam.
The problem with the above is it doesn't leave a general catch-all term.
Cheers,
Bear Kaufmann
All Power Labs
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