Gas: heating and illuminating – Processes – Manufacture from methane
Patent
1996-05-17
1999-02-09
Yoon, Tae
Gas: heating and illuminating
Processes
Manufacture from methane
48197R, 48DIG3, 159 173, C01B 322, B01D 126, B01D 5300
Patent
active
058688056
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/SE94/01,046, filed Nov. 8, 1994.
TECHNICAL FIELD
The present invention relates to a process for integrated evaporation and gasification of spent liquor from the production of cellulose., the evaporation and gasification being integrated in the same system while utilizing the thermal energy in the combustion gases after the gasification.
STATE OF THE ART
A number of systems are already known for evaporating and gasifying spent liquors from cellulose cooking. The spent liquor or the black liquor, as it is usually termed, contains both organic substances and inorganic chemicals, principally alkali, in aqueous solution. The chemical energy which is present in the black liquor is utilized by the organic material being burnt at the same time as the inorganic chemicals are extracted so that they can be re-used in the process. For it to be possible to burn the organic material partially and to recover the chemicals, the major part of the water in the black liquor must be evaporated in advance so that a concentrated spent liquor can be supplied either to a recovery boiler or a gasification reactor.
Evaporation of black liquor is normally effected in several stages, for example in five evaporators coupled in series. For example, evaporation is carried out using three evaporation apparatus coupled in series and the intermediate liquor produced in these apparatus is then supplied to a pair of evaporation apparatus coupled in series for final evaporation, with thick liquor being obtained from these latter apparatus. Heat for the evaporation is supplied by means of admission steam, which expediently has a temperature of 140.degree. C. and which leaves the system at a temperature of 60.degree. C., for example. To make this possible, use is made of vacuum pumps.
Other systems for concentrating black liquor involve pressurizing the liquor after preliminary evaporation, with the liquor then being allowed to expand in an expansion vessel, whereupon steam vaporizes. Such a system is described, for example, in the U.S. Pat. No. 4,909,899.
A further system, which utilizes venturi scrubbers and separators, is described in the Swedish patent 318 469. In this system, use is made of vacuum fans, and exhaust gases are employed at a low temperature which is initially approximately 280.degree. C. and which falls to 74.degree. C. at the outlet for the exhaust gases.
TECHNICAL PROBLEM
The problem with the known solutions is that use must either be made of a supply of admission steam or else the process must be carried out using large installations at relatively low temperature.
There is often a shortage of capacity, both for the spent-liquor evaporation and the recovery stage, the latter being either in the form of a recovery boiler or a gasifier. If a gasifier is used, there is thus usually the need for an equivalent capacity-increasing effect, as regards spent-liquor evaporation, to be achieved in a manner which is cost-effective, energy-saving and environmentally acceptable. There is also the need for the spent liquor to be subjected to an additional concentration-increasing stage prior to the gasifier, at the same time as gasified alkali metal compounds are separated out of the combustion gases as rapidly as possible and returned to the reactor.
SOLUTION
In accordance with the present invention, a process has therefore been developed for evaporating and gasifying spent liquor from the production of cellulose, which process integrates these two process steps, the gasification taking place in a reactor at a pressure of from atmospheric pressure up to about 150 bar and at a temperature of about 500.degree.-1600.degree. C., by means of partial combustion of the spent liquor, a gas phase and a phase of solid and/or smelted material being formed in the reactor and being removed from this reactor, which process is characterized in that the combustion gases from the reactor are brought together, in direct contact, with the spent liquor in a first stage in a venturi
REFERENCES:
patent: 3439724 (1969-04-01), Mason
Kvaerner Pulping AB
Taltavull W. Warren
Yoon Tae
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