69
Steam Gasification and Reforming Technologies
literature has shown that as temperature increases, the nature of tar undergoes the
following transformation [99–103]:
Mixed oxygenates (400°C) ( primary) →
Phenolic ethers (500°C) (sec condary) →
Alkyl phenolics (600°C) (tertiary-alkyl) →
(4.55)
Heterocyclic ethe
l
rs (700°C) (tertiary-PNA) →
PAH * (800°C) → Larger PAH (900 0 °C)
In the above reaction, PAH* is high-molecular-weight polynuclear aromatic
h ydrocarbons. Along with the temperature, tar concentration depends on the reaction time, the amount of oxygen, and the presence of a suitable catalyst during
steam gasification. Higher oxygen concentration generally reduces tar concentration
through the processes of cracking and oxidation among others. The conventional
steam gasification operated at 700°C–800°C produces tar with naphthalenes, acenaphthylenes, fluorenes, phenanthrenes, benzaldehydes, phenols, naphthofurans,
and benzanthracenes. While high-temperature steam gasification operating between
900°C and 1000°C produces tar that contains naphthalenes, acenaphthylenes, phenanthrenes, fluranthenes, pyrenes, acephenanthrylenes, benzanthracenes, benzopyrenes, 226 MW (molecular weight) polycyclic aromatic hydrocarbons (PAHs), and
276 MW PAHs. Milne et al. [100] further characterized tar in terms of primary, secondary, and tertiary products based on molecular beam mass spectroscopy. Some of
the details of the constituents of primary, secondary, and tertiary products and their
behavior with temperature are described by Milne et al. [100].
4.5.1.5 Black liquor
Huang and Ramaswamy [104] examined steam gasification of black liquor coming
out of the paper and pulp industry at temperatures as high as 1500°C. Their results
were in agreement with other reports. The carbon conversion was nearly complete at
temperatures higher than about 750°C. Hydrogen concentration first increased with
temperature but showed a maximum at high temperatures because of the dominance
of reverse water–gas shift reaction. Higher steam gave higher hydrogen concentration in the product gas. Operating with a 0.3 < SBR < 0.6 in combination with high
pressure of 30 atm, high temperature of 1000°C appears to be the most beneficial
for obtaining smelt with no C(s) and maximizing Na and S capture in the melt. Here
SBR is steam-to-dry black liquor ratio.
Black liquor gasification can be used to substitute the existing combustion process for potential higher energy efficiency, lower greenhouse gas emissions, and
more safety. The steam gasification of black liquor technology can help the current
paper and pulp mills technology to be extended into future biorefineries. In general,
the equilibrium model examined by Huang and Ramaswamy [104] indicates that
the hydrogen concentration in the product increased with a decrease in pressure
and an increase in SBR, and it showed a maximum with an increase in temperature.
Li and Heiningen [38] also illustrated the conversion data for a black liquor via
Steam Gasification and Reforming Technologies
literature has shown that as temperature increases, the nature of tar undergoes the
following transformation [99–103]:
Mixed oxygenates (400°C) ( primary) →
Phenolic ethers (500°C) (sec condary) →
Alkyl phenolics (600°C) (tertiary-alkyl) →
(4.55)
Heterocyclic ethe
l
rs (700°C) (tertiary-PNA) →
PAH * (800°C) → Larger PAH (900 0 °C)
In the above reaction, PAH* is high-molecular-weight polynuclear aromatic
h ydrocarbons. Along with the temperature, tar concentration depends on the reaction time, the amount of oxygen, and the presence of a suitable catalyst during
steam gasification. Higher oxygen concentration generally reduces tar concentration
through the processes of cracking and oxidation among others. The conventional
steam gasification operated at 700°C–800°C produces tar with naphthalenes, acenaphthylenes, fluorenes, phenanthrenes, benzaldehydes, phenols, naphthofurans,
and benzanthracenes. While high-temperature steam gasification operating between
900°C and 1000°C produces tar that contains naphthalenes, acenaphthylenes, phenanthrenes, fluranthenes, pyrenes, acephenanthrylenes, benzanthracenes, benzopyrenes, 226 MW (molecular weight) polycyclic aromatic hydrocarbons (PAHs), and
276 MW PAHs. Milne et al. [100] further characterized tar in terms of primary, secondary, and tertiary products based on molecular beam mass spectroscopy. Some of
the details of the constituents of primary, secondary, and tertiary products and their
behavior with temperature are described by Milne et al. [100].
4.5.1.5 Black liquor
Huang and Ramaswamy [104] examined steam gasification of black liquor coming
out of the paper and pulp industry at temperatures as high as 1500°C. Their results
were in agreement with other reports. The carbon conversion was nearly complete at
temperatures higher than about 750°C. Hydrogen concentration first increased with
temperature but showed a maximum at high temperatures because of the dominance
of reverse water–gas shift reaction. Higher steam gave higher hydrogen concentration in the product gas. Operating with a 0.3 < SBR < 0.6 in combination with high
pressure of 30 atm, high temperature of 1000°C appears to be the most beneficial
for obtaining smelt with no C(s) and maximizing Na and S capture in the melt. Here
SBR is steam-to-dry black liquor ratio.
Black liquor gasification can be used to substitute the existing combustion process for potential higher energy efficiency, lower greenhouse gas emissions, and
more safety. The steam gasification of black liquor technology can help the current
paper and pulp mills technology to be extended into future biorefineries. In general,
the equilibrium model examined by Huang and Ramaswamy [104] indicates that
the hydrogen concentration in the product increased with a decrease in pressure
and an increase in SBR, and it showed a maximum with an increase in temperature.
Li and Heiningen [38] also illustrated the conversion data for a black liquor via