Gasification
• Definition: conversion of carbonaceous materials
into carbon monoxide (CO) and and hydrogen (H2)
by reaction at high temperatures with oxygen and/or
steam.
• Desired products: CO and H2 (synthesis gas)
• Co-products:
- CO2 and water vapor
- methane (CH4) and other light hydrocarbons
- tar
- inorganic vapors and ash
• Energy conversion efficiency: 65-70%
Utilization of Products
• Fuel gas
- Combustion for heat
and power
- Fuel for fuel cells
• Synthesis of fuels
and chemicals
1938 Adler Diplomat with biomass gasifier
Key Aspects of Gasification
• Gasification is endothermic (needs heat to
drive it)
• Easy to accomplish with air or oxygen
• Requires external heat source with steam
• Some carbon residue with steam
• Tar residue at gasification temperatures below
1300oC
• Sulfur, alkali metals, ammonia, and chloride
are problematic for downstream processing
Syngas Requirements
• Fuel gas
- Transportable without condensation of tar
components
- Clean burning
• Fuel cells or chemical synthesis
- Free of tar
- Free of catalyst poisons: sulfur gases, halides,
NH3, NOX, HCN, alkali and other metals
- Shifted to product-specific H2/CO ratio
Characteristics of Biomass
for Gasification
SourceHHV, MJ/kg
(daf)Ash, % Sulfur Alkali metals Silica
Alfalfa stems 19.7 5.3 1.9 29.2 5.8
Wheat straw 19.2 7.0 4.4 27.3 55.3
Rice straw 18.6 18.7 1.2 13.3 74.7
Switchgrass 19.9 9.0 0.4 12.2 65.2
Bagasse 19.5 2.4 2.1 0.9 46.6
Corn stover 19.8 5.2
Fir 20.5 0.4 2.9 30.5 15.2
Hybrid poplar 19.5 2.7 2.0 9.8 5.9
Willow 19.9 1.7 1.8 16.0 2.4Source: Jenkins et al., Fuel Processing Technology,
1998
Biomass
gasifiers are
available
commercially
At least five
commercial
installations in
US and Europe
Commercially available
and under development:
•tar capture/destruction
•acid gas capture
•metals capture
•chloride capture
Water gas shift
technology is proven
and commercially
availableAvailable technology:
•F-T hydrocarbons
•Methanol
•Methanol-to-gasoline
Under development
•ethanol synthesis
Separations
technology
is proven
and
commerciall
y available
Status of Technology Components
Recycle
Gasificatio
n
Product
Synthesis
Gas
Conditioning
Gas
CleaningSeparation
Products
Biomass
Biomass
Gasifying agent
Cyclone
Return
leg
Gasifier
Raw
syngas
Ash
Stationary bed
gasifier
Recirculating
twin bed
gasifier
Externally heated
steam reformerBlack liquor
Circulating
bed gasifier
Oxygen
Biomass
Raw
Syngas
Slag
Biomass
Steam
Exhaust
gas
Raw
syngas
Entrained
flow
gasifier
Typical Component
Concentrations in Syngas
Heat provision Autothermal Allothermal
Gasifying agent Air O2/steam Steam
H2, vol-% 11-16 23-28% 35-40
CO, vol-% 13-18 45-55% 22-25
CO2, vol-% 12-16 10-15% 20-25
CH4, vol-% 2-6 <1 9-11
N2, vol-% 45-60 <5 <1%
LHV, MJ/Nm3 4-6 10-12 12-14
Bacovsky, D., et al.. IEA Bioenergy Task 39, Report T39-P1b (July 2010).
Syngas Cleaning
• Cleaning requirements: - tar & light organic <300 ppmv absorption,
reforming
- sulfur gases <0.1 ppmv adsorption,
absorption
- halides <10 ppbv adsorption
- NH3 <10 ppmv absorption
- CO2 <100 ppmv absorption
• Industrial syngas cleaning systems are
available
• Areas for improvement- tar reforming catalysts
-
Biomass gasifiers - U.S. and Europe
ProviderOperating plants Under construction Planned
Synthesis Power Synthesis Power Synthesis Power
Andritz/Carbona comm. comm.
Chemrec AB pilot demo
Conzepte Technik
Umweltdemo (2008)
Cutec pilot (1990)
ECN pilot demo
Enerkem pilot (2003) demo comm.
Foster Wheeler demo (2009)comm (6),
pilot (2)comm. comm.
Karlsruhe Inst. Tech. pilot
Nexterra comm. (3) comm. (4)
Rentech/Clear Fuels comm. (3)
Repotec comm. demo
Thermochem Recovery comm. demo (2)
Uhde GmbHcomm.
pilot