Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1995-07-14
1998-05-05
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 3011, 162 31, D21C 1112
Patent
active
057468869
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a method for recovery of energy and chemicals from cellulose spent liquors having a high content of potassium, wherein the cellulose spent liquor is subjected to partial oxidation at 400.degree.-1200.degree. C. in a reactor, with evolution of a combustible gas and the potassium compounds formed under these conditions being separated and withdrawn from the combustible gas and dissolved in a liquid in order to prepare cooking liquor.
2. Background to the Invention
The closed effluent-free pulp mill has for a long time beckoned as being the final goal to satisfy all environmental demands. Naturally, such an installation is a physical impossibility and the aim should therefore be to seek to limit the effluents to as great an extent as possible and convert them into a manageable form in order eventually to be able to return the residues to their source as a constituent part of the natural cycle.
In recent years, the introduction of modified cooking and oxygen bleaching, in combination with the use of chlorine dioxide for final bleaching, has, in a very striking manner, decreased the pulp mills effluents of chlorinated pollutants to the recipient.
The novel technique of bleaching entirely without the addition of chlorine chemicals, so-called TCF bleaching, based on final bleaching with peroxides in combination with ozone, will completely eliminate the effluents of organic chlorine compounds, thereby eliminating of one of the most serious environmental problems.
Another area of importance, which has attracted increasing interest in recent years, not least because of the significant costs which are associated with the chemical and biological purification of water, is that of also closing the mill with regard to COD and BOD effluents.
The trend towards increasing closure of the mill in conjunction with the production of pulp will in the future entail increasing potassium and chloride concentrations in the liquor system of the mill, something which in turn can lead to operational problems when conventional recovery technology is used, principally due to the smelt and corrosion properties of the potassium compounds.
During the seventies, an extensive programme was carried out in order to evaluate the completely closed kraft pulp mill at Great Lakes Forest Products Co in Canada. The effluent from both the chlorine and extraction stages in the bleaching plant was returned to the chemical recovery, after which the white liquor was concentrated by evaporation. Chlorides were bled off in conjunction with the evaporation.
Such a process has many advantages per se, due to the fact that effluents of BOD, COD, suspended solid material and toxic substances, such as chlorinated organic compounds, holistically summarized as AOX, can also be minimized or completely eliminated.
However, recycle countercurrent of the effluents to the recovery in this manner makes it necessary to resolve several issues which are crucial to the whole production process.
In the first place, non process elements will be enriched in the system, which substances must be bled out in one way or another, and, in the second, the loading on the recovery system will increase. Another issue which has to be dealt with relates to the water balance in the mill.
The experimental runs at Great Lakes, involving the recycle of chloride-containing bleaching plant effluents, gave rise to significant operational problems, chiefly due to the increasing content of chloride in the liquors, and the corrosion, which was related to this, in the white liquor evaporator and boiler system.
The chloride problem in conjunction with the return of bleaching plant effluents obviously disappears with TCF bleaching, a bleaching method which is to be preferred from other points of view as well.
Another option for achieving a high degree of mill closure, while retaining the need for evaporation, is based on the principle of returning all liquid countercurrent through the bleaching plant and in this way transferring both chem
REFERENCES:
patent: 3020195 (1962-02-01), Casciani et al.
patent: 4692209 (1987-09-01), Santen et al.
patent: 4735683 (1988-04-01), Wong et al.
patent: 4738835 (1988-04-01), Kiiskila
patent: 4808264 (1989-02-01), Kignell
Backlund .ANG.ke
Stigsson Lars
Czaja Donald E.
Kvaerner Pulping AB
Melcher Jeff
Nguyen Dean T.
LandOfFree
Method for the recovery of energy and chemicals from cellulose s does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the recovery of energy and chemicals from cellulose s, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the recovery of energy and chemicals from cellulose s will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-50083