Power plants – Combustion products used as motive fluid
Patent
1994-11-29
1996-04-16
Casaregola, Louis J.
Power plants
Combustion products used as motive fluid
60 3912, 162 3011, F02C 328, F02C 330
Patent
active
055071414
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an improved process for recovering energy from a combustible gas generated during gasification of cellulose waste liquors, the improvement comprising a cooling zone, wherein the combustible gas is cooled to a temperature below 150.degree. C., simultaneously recovering sensible and latent heat in one or more heat exchangers, discharging the cooled combustible gas for use as fuel in a water and/or steam injected recuperative gas turbine cycle.
BACKGROUND OF THE INVENTION
The kraft process is currently the dominant chemical pulping process. During pulping large quantities of recoverable energy in the form of black liquor is generated. Worldwide some 2.8 billion GJ (780 TWh) of black liquor was produced in 1990 at kraft pulp mills.
The kraft recovery system has two principal functions: and electrical power.
The chemical recovery process contributes significantly to the capital intensity of the kraft process. About 35% of the capital cost of a modern pulp mill is attributable to the recovery process.
The predominant method today for recovery of chemicals and energy from black liquor is the Tomlinson recovery boiler, a technology which was introduced well over fifty years ago. Although an established technology, there are some wellknown disadvantages with conventional recovery technology.
Most often the recovery boiler with its inherent in flexibility constitutes the main production bottleneck in the pulp mill. Economics of scale dictate large capacity units.
Other disadvantages include the low thermal efficiency and risk of smelt water explosions which in turn con stitute a safety problem.
These and other areas of concern have been the driving force for development of new methods and principles for recovering chemicals and energy from black liquor. One of the more promising routes is gasification of the liquor in entrained or fluidized beds. In some cases these alternative processes can be installed as incremental capacity boosters, providing an opportunity to eliminate the recovery boiler bottleneck.
One of the major driving forces for development of new recovery technology has been to improve thermal efficiency accompanied with higher power to steam output ratios. The present invention relates to a major improvement in this area, using technology based on gasification and energy recovery in a recuperated gas turbine cycle.
Gasification of black liquor can be performed at various temperatures and pressures, resulting in different forms of the recovered inorganic constituents and different calorific values of the combustible process gas.
The inorganics, mainly sodium compounds, are solubilized to form an aqueous alkaline liquid called green liquor, which liquor is used for cooking liquor preparation.
Kraft pulp mills are significant producers of biomass energy and today most mills are designed to use the biomass fuel available at the kraft mill to meet on site steam and electricity needs via back pressure steam turbine cogeneration system. Electricity demand is often higher than internally generated, in particular for integrated mills and often electricity is imported from the grit.
Process steam requirements for a modern kraft pulp mill is in the order of 10 GJ per ton of air dried pulp. The internal electricity demand is around 600 kWh/ton of air dried pulp.
The biomass gasification gas turbine cogeneration system of the present invention will meet mill steam demand and has the potential to produce excess electricity for export.
The present invention can be practised using various types of gas generators and gasification principles exemplified in prior art documents.
In U.S. Pat. No. 4,917,763 and U.S. Pat. No. 4,692,209, gasification of spent cellulose liquor, such as black liquor, is described. The gasification temperature is in the range of 1000.degree.-1300.degree. C., resulting in the evolvement of molten inorganics and a combustible gas. The molten alkaline chemicals are withdrawn from the gas stream in a cooling and quenching stage where an aq
REFERENCES:
patent: 4682985 (1987-07-01), Kohl
patent: 4733528 (1988-03-01), Pinto
patent: 4753068 (1988-06-01), El-Masri
Casaregola Louis J.
Kvaerner Pulping Technologies AB
Marcou George T.
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