Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1987-01-28
1989-02-28
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 3011, 162 31, 162 47, 423DIG3, D21C 1112
Patent
active
048082643
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for recovering cooking chemicals and energy from cellulose waste liquors obtained in the pulp and paper industry.
The object of the present invention is to recover chemicals and energy from waste liquors preferably black kraft liquors obtained in the pulp and paper industry, and in particular the pulp and paper industry producing according to the sulphate method, whereby a more specific object is to eliminate prior art known problems in the use of huge and technically and operationally complicated combustion furnaces in the recovery of chemicals and energy, and polluting the air with primarily sulfur containing exhaust gases, i e to recover substantially all chemicals and energy present in waste liquors in an efficient and environmentally attractive way.
The term waste liquors used herein means preferably black kraft liquor but includes waste liquors obtained from the sodium bisulfite and sodium carbonate processes as well. In the following the term waste liquors and black kraft liquor are used synonymously.
BACKGROUND OF THE INVENTION
When producing paper pulp a digestion liquor called black kraft liquor is obtained, which liquor besides numerous solubilized organic materials also contains the chemicals used for digesting the wooden raw material, i e sodium hydroxide and sodium sulphide, now mainly in the form of sodium carbonate and sodium sulphate. The black kraft liquor is generally concentrated before combustion for recovery of the energy content of the organic matter and for recovery of the cooking chemicals as so called green liquor.
Different processes have been proposed for recovering the energy and cooking chemicals, whereby the Tomlinson process is one, using a huge combustion furnace with steam raising heat recovery. Another proposed process is the so called cyclone combustion process, in which pyrolysis and combustion of the organic material takes place in a cyclone chamber. This latter process has, however, not gained any commercial success so far, and has only been tested in pilot plant.
DESCRIPTION OF THE PRESENT INVENTION
It has now by this invention been found possible to eliminate prior art known drawbacks, and to be able to recover essentially all of the chemicals and energy present in the black kraft liquor, i e to minimize losses, by a novel and elegant process, which is characterized as follows.
(i) introduction of the black kraft liquor into a pressurized gasification reactor, while being atomized and being subjected to a flash-pyrolysis, while mainly forming CO, CO.sub.2, H.sub.2, H.sub.2 S, Na.sub.2 CO.sub.3 and Na.sub.2 S.
(ii) introduction of oxygen or oxygen containing gas, preferably at some distance from the point of introducing black kraft liquor into said reactor, in order to support the endothermal pyrolysis reactions by combustion of a part of the gas formed by the pyrolysis of the organic matter present in the black kraft liquor. Optionally introducing a support fuel such as oil or gas to said reactor, if needed, for maintaining the heat balance around said reactor.
(iii) maintaining in said reactor a temperature of 700.degree. to 1300.degree. C., preferably 800.degree. to 1000.degree. C. to achieve complete gasification of the organic content of the black liquor and to form droplets of melted inorganic chemicals, mainly comprising Na.sub.2 CO.sub.3 and Na.sub.2 S.
(iv) transporting said melt of chemicals out of said reactor by means of the rapid gas flow obtained during said gasification and cooling said gas and melt of chemicals, mainly in the form of droplets, in an aqueous quench solution.
(v) washing said gas with regard to its contents of solubilizable inorganid chemicals using an alkaline solution such as sodium carbonate/sodium sulphide solution (green liquor), sodium hydroxide (or carbonate) solution, and water in adequate order for dissolving said inorganic chemicals and as complete absorption as possible of the sulfur bearing compounds in the pyrolysis gas.
(vi) removing remaining gas and using
REFERENCES:
patent: 3043655 (1962-09-01), Green et al.
patent: 3816239 (1974-06-01), Marks
patent: 3867251 (1975-02-01), Holme
patent: 4048286 (1977-09-01), Rossmaier
patent: 4431617 (1984-02-01), Farin
patent: 4601786 (1986-07-01), Santen et al.
patent: 4668341 (1987-05-01), Nilsson
Thomas; TAPPI, Feb. 1979, vol. 62, No. 2, pp. 51-57; "Process Simulation Program".
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