640
The Chemistry and Technology of Petroleum
The gas from the carbon scrubber is further cooled by the fuel gas and boiler feed water and
led into the sulfur compound removal section, where hydrogen sulfide (H 2 S) and carbonyl sulfide
(COS) are removed from the gas to obtain clean fuel gas. This clean fuel gas is heated with the hot
gas generated in the gasifier and finally supplied to the gas turbine at a temperature of 250°C–300°C
(480°F–570°F).
The exhaust gas from the gas turbine having a temperature of about 550°C–600°C (1020°F–
1110°F) flows into the heat recovery steam generator consisting of five heat exchange elements. The
first element is a superheater in which the combined stream of the high pressure saturated steam
generated in the waste heat boiler and in the second element (high pressure steam evaporator)
is superheated. The third element is an economizer, the fourth element is a low-pressure steam
evaporator, and the final or the fifth element is a de-aerator heater. The off-gas from heat recovery
steam generator having a temperature of about 130°C is emitted into the air via stack.
In order to decrease the nitrogen oxide (NO x ) content in the flue gas, two methods can be applied.
The first method is the injection of water into the gas turbine combustor. The second method is to
selectively reduce the nitrogen oxide content by injecting ammonia gas in the presence of de-NO x
catalyst that is packed in a proper position of the heat recovery steam generator. The latter is more
effective than the former to lower the nitrogen oxide emissions to the air.
23.5.2 HyBrId gAsIFICAtIon ProCess
In the hybrid gasification process, a slurry of coal and residual oil is injected into the gasifier where
it is pyrolyzed in the upper part of the reactor to produce gas and chars. The chars produced are then
partially oxidized to ash. The ash is removed continuously from the bottom of the reactor.
In this process, coal and vacuum residue are mixed together into slurry to produce clean fuel gas.
The slurry fed into the pressurized gasifier is thermally cracked at a temperature of 850°C–950°C
(1560°F–1740°F) and is converted into gas, tar, and char. The mixture oxygen and steam in the
lower zone of the gasifier gasify the char. The gas leaving the gasifier is quenched to a temperature
of 450°C (840°F) in the fluidized-bed heat exchanger and is then scrubbed to remove tar, dust, and
steam at around 200°C (390°F).
The coal and residual oil slurry is gasified in the fluidized-bed gasifier. The charged slurry is
converted to gas and char by thermal cracking reactions in the upper zone of the fluidized bed. The
produced char is further gasified with steam and oxygen that enter the gasifier just below the fluidizing gas distributor. Ash is discharged from the gasifier and indirectly cooled with steam and then
discharged into the ash hopper. It is burned with an incinerator to produce process steam. Coke
deposited on the silica sand is removed in the incinerator.
23.5.3 HydroCArBon gAsIFICAtIon
The gasification of hydrocarbons to produce hydrogen is a continuous, non-catalytic process that
involves partial oxidation of the hydrocarbon. Air or oxygen (with steam or carbon dioxide) is used
as the oxidant at 1095°C–1480°C (2000°F–2700°F). Any carbon produced (2%–3% by weight of
the feedstock) during the process is removed as a slurry in a carbon separator and pelletized for use
either as a fuel or as raw material for carbon-based products.
23.5.4 HyPro ProCess
The hypro process is a continuous catalytic method for hydrogen manufacture from natural gas or
from refinery effluent gases. The process is designed to convert natural gas:
CH
C H
4
2
2
Æ +
The Chemistry and Technology of Petroleum
The gas from the carbon scrubber is further cooled by the fuel gas and boiler feed water and
led into the sulfur compound removal section, where hydrogen sulfide (H 2 S) and carbonyl sulfide
(COS) are removed from the gas to obtain clean fuel gas. This clean fuel gas is heated with the hot
gas generated in the gasifier and finally supplied to the gas turbine at a temperature of 250°C–300°C
(480°F–570°F).
The exhaust gas from the gas turbine having a temperature of about 550°C–600°C (1020°F–
1110°F) flows into the heat recovery steam generator consisting of five heat exchange elements. The
first element is a superheater in which the combined stream of the high pressure saturated steam
generated in the waste heat boiler and in the second element (high pressure steam evaporator)
is superheated. The third element is an economizer, the fourth element is a low-pressure steam
evaporator, and the final or the fifth element is a de-aerator heater. The off-gas from heat recovery
steam generator having a temperature of about 130°C is emitted into the air via stack.
In order to decrease the nitrogen oxide (NO x ) content in the flue gas, two methods can be applied.
The first method is the injection of water into the gas turbine combustor. The second method is to
selectively reduce the nitrogen oxide content by injecting ammonia gas in the presence of de-NO x
catalyst that is packed in a proper position of the heat recovery steam generator. The latter is more
effective than the former to lower the nitrogen oxide emissions to the air.
23.5.2 HyBrId gAsIFICAtIon ProCess
In the hybrid gasification process, a slurry of coal and residual oil is injected into the gasifier where
it is pyrolyzed in the upper part of the reactor to produce gas and chars. The chars produced are then
partially oxidized to ash. The ash is removed continuously from the bottom of the reactor.
In this process, coal and vacuum residue are mixed together into slurry to produce clean fuel gas.
The slurry fed into the pressurized gasifier is thermally cracked at a temperature of 850°C–950°C
(1560°F–1740°F) and is converted into gas, tar, and char. The mixture oxygen and steam in the
lower zone of the gasifier gasify the char. The gas leaving the gasifier is quenched to a temperature
of 450°C (840°F) in the fluidized-bed heat exchanger and is then scrubbed to remove tar, dust, and
steam at around 200°C (390°F).
The coal and residual oil slurry is gasified in the fluidized-bed gasifier. The charged slurry is
converted to gas and char by thermal cracking reactions in the upper zone of the fluidized bed. The
produced char is further gasified with steam and oxygen that enter the gasifier just below the fluidizing gas distributor. Ash is discharged from the gasifier and indirectly cooled with steam and then
discharged into the ash hopper. It is burned with an incinerator to produce process steam. Coke
deposited on the silica sand is removed in the incinerator.
23.5.3 HydroCArBon gAsIFICAtIon
The gasification of hydrocarbons to produce hydrogen is a continuous, non-catalytic process that
involves partial oxidation of the hydrocarbon. Air or oxygen (with steam or carbon dioxide) is used
as the oxidant at 1095°C–1480°C (2000°F–2700°F). Any carbon produced (2%–3% by weight of
the feedstock) during the process is removed as a slurry in a carbon separator and pelletized for use
either as a fuel or as raw material for carbon-based products.
23.5.4 HyPro ProCess
The hypro process is a continuous catalytic method for hydrogen manufacture from natural gas or
from refinery effluent gases. The process is designed to convert natural gas:
CH
C H
4
2
2
Æ +