Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Reexamination Certificate
2000-11-03
2003-02-04
Nguyen, Dean T. (Department: 3629)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
C162S041000, C162S189000, C210S928000
Reexamination Certificate
active
06514379
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a procedure for arranging water circulations in an integrated paper mill, including a pulp mill based on refiner mechanized pulp and/or groundwood pulp and/or waste paper and/or chemical pulp, and paper and/or board manufacturing lines.
BACKGROUND OF THE INVENTION
Various impurities enter the water circulations in a paper mill in different phases of the pulp and paper production process. Fouling of water is mainly caused by organic ingredients accumulating from fiber raw material and, on the other hand, mainly by inorganic chemicals added therein in different phases. As unwanted chemical agents, such impurities, in high proportions, are detrimental to the operation of the process and the quality of the paper produced.
A paper making process can be divided into two or three main phases being partly separate in water circulations, the first phase thereof including pretreatment, defibering and cleaning of fibre raw material and preferably also pulp thickening and pressing. The second phase includes improving of pulp quality, and paper manufacture. Currently, also the water circulation of the paper manufacture has been separated, whenever needed, from the water circulation of the quality improvement phase into a third water circulation by arranging pulp thickening and/or pressing between the process phases. The second quality improvement phase includes, depending on the need, pulp processing phases such as dispersing, bleaching and sorting.
The pretreatment may include various operations, such as barking, washing of chip, thermal and chemical treatment, waste paper pulping and pulp cleaning.
In pretreating raw material, namely in the defibering, pulping and cleaning phases, addition of chemicals can be employed, or the phases can be carried out without any chemicals. When producing mechanical pulp, about 2 to 5 per cent of the wood material is dissolved or dispersed as colloid particles in the process water. Most of the process water fouling takes place in connection with chip treatment and defibering, whereby, for instance, the water coming from the mass suspension of a TMP grinder contains dissolved and colloid organic matter in great quantities. Moreover, when using waste paper, paper fillers and additive agents from the raw material end up into the circulation water in the defibering and cleaning phases, in addition to organic agents, additive agents used in converting paper, and completely foreign agents accumulated in the use or recycling of paper. Particularly difficult foreign agents are sticky agents which are adhesive in nature and originated from various adhesives and plastics.
Inorganic chemicals enter the water circulation in the pulp quality improvement phase, in bleaching and in the wet end of the paper machine, in which phases also organic matter is dissolved. In addition, in different phases of producing recycled mass, chemicals are used in great quantities e.g. for chalking print dye pigments, as auxiliary foaming agents, in pulp bleaching, and in end acidification.
In different phases of a paper making process, great quantities of water are needed for various purposes, such as for dilution of pulp and chemicals, transport and cleaning. In addition, water is needed e.g. for cooling and sealing. By circulating the process waters of the paper mill, endeavors are made to recover and to reuse the useful ingredients originated from the process and contained in the circulation water, such as fibers, fines, filling agents and paper making chemicals, as well as heat. Some of the water needed by the paper mill is generally provided from outside the mill as raw water which has to be cleaned prior to introduction to use and heated if need be to appropriate temperature. Clean water is needed e.g. for certain washing jets in the paper machine and for dilution of chemicals.
In order to maintain the contents of unwanted agents below the risk limits, fresh water is usually brought into the process at the same time as part of the circulation water is removed from the system as effluent. When the paper mill process waters are generally circulated counter-current from the paper machine towards the pulp mill, the organic and inorganic agents entered in the circulation water in different phases of the process are usually concentrated most in the circulation and effluent waters of the defibering phase of the pulp. On the other hand, the organic and inorganic matter released in different process phases travels to some extent downstream together with the pulp to the paper machine, which travelling is attempted to be reduced by the thickening, dilution and pressing apparatus positioned between the pretreatment, defibering and cleaning phases and the pulp quality improvement phase, which systems have currently been positioned, whenever needed, also between the pulp quality improvement phase and the paper making phase. With the aid of presses, the pulp can be thickened, depending on the apparatus, to about 25 to 35% thickening, whereas the thickening achieved with the aid of thickening apparatus is only about half thereof.
In Finnish patent applications Nos. 962176, 962177, 062178, an arrangement is described in which some of the fresh water amount usually needed by the paper mill is replaced by jet waters selectively recovered from the waters fouled in the paper mill and by waters to be cleaned locally, and the concentrates thus obtained from the water cleaning phases are utilized whenever appropriate by making them flow counter-current relative to the raw material flow for reuse in the paper mill, by means of which measures the level of the quantities of unwanted agents circulating in the paper mill is controlled. By said arrangement, unwanted agents are transferred counter-current from the water circulation of the paper machine into the water circulation of the pulp mill, wherefrom they can be conducted to an effluent evaporation plant and concentrated for combustion at the same time as the cooling water circulation of the evaporation plant is advantageously connected to the cooling and jet water system of the paper mill and the clean condensate is conducted as jet water for substitution of fresh water.
The organic and inorganic matter circulates in due time in the water circulations of the mill and is finally discharged from the process mainly among the effluents and to a lesser extent with the paper and into the atmospheric air. The main fractions of the effluents are formed by the controlled overflow of the filtrate of the circulation water system of the pretreatment /defibering /cleaning phases and by the reject waters of the cleanings of the pulp and the water circulations in different phases, in addition to which sporadic emissions occur to some extent.
Pressure towards reducing the consumption of fresh water by closing water circulations are on one hand caused by the costs of raw water and the effluent, and on the other hand, by the availability of raw water and by the emission restrictions concerning effluents. A complete shut-off of a paper mill is not possible because emissions of effluents are needed for removal of unwanted agents from the process. When reducing the consumption of the fresh water entering into the water circulation of the paper machine mainly through jets and dilution targets, an excessive temperature rise and concentration of colloid and dissolved organic and inorganic unwanted agents, particularly salts, in the water circulations of the paper machine and of the pulp mill may become a problem to the extent which is detrimental to the quality and production of pulp and paper. If e.g. the content of unwanted agents in the circulation water of the paper machine is increased too much, the action of the retention chemicals will be weakened, the formation of interfiber bonds will be impaired and the strength of paper being manufactured will suffer. A first drawback lies therein, that for instance with the increased content of the agents dissolved in the circulation water used for pulp bleaching, the degree o
Gartz Rainer
Kaijaluoto Sakari
Kokkonen Kari
Metso Paper Inc.
Nguyen Dean T.
Steinberg & Raskin, P.C.
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