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Patent Issued for Method of Producing Cellulose Pulp

July 8, 2014

By a News Reporter-Staff News Editor at Journal of Technology -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Turunen, Esko (Aanekoski, FI); Kovasin, Kari (Rauma, FI), filed on June 22, 2012, was published online on June 24, 2014.

The patent's assignee for patent number 8758555 is Metsa Fibre Oy (Metsa, FI).

News editors obtained the following quote from the background information supplied by the inventors: "According to such a method, a lignocellulose-based raw material is cooked in an alkaline cooking liquor which comprises, besides conventional cooking chemicals of sulphate cooking, also polysulphide and antraquinone.

"An alkaline cooking liquor which comprises polysulphide is often called orange liquor. Hereinafter, when associated with the present invention, this term is used as a synonym of alkaline cooking liquor which comprises polysulphide.

"Use of polysulphide (PS) in combination with antraquinone (AQ) in sulphate pulp cooking, i.e. 'PSAQ cooking', is a method which is known and applied industrially. PSAQ cooking is used in about ten factories in the world. PSAQ cooking is particularly suitable to be used together with traditional batch cooking and continuous cooking, because in traditional cooking all the white liquor is dosed at the beginning of the cooking process. In this case, it is possible to fully exploit particularly the effect of increasing the hemicellulose yield of PS at a low temperature in the absorption stage of the cooking.

"In the case of modified cooking, the white liquor is dosed in several steps into the cooking process. As in traditional cooking, the first dosing point is at the beginning of the cooking, under low temperature conditions (

"Methods which aim at utilising the PS as efficiently as possible and in a way which suits the process in question in an optimal way have been developed for use in combination with modified cooking.

"For example, Metso has filed a patent application for a method by which PSAQ cooking is carried out in a Super Batch batch cooking process (EP 1702101). The same company also has a method of using polysulphide in modified continuous cooking (PCT-patent application WO 2003/057979).

"In neither of the Metso methods is it possible to fully exploit the PS effect because several tens of per cents of the alkaline cooking liquor batch are consumed in the actual cooking stage.

"Patent application US 2009/0126883, in International Paper (hereinafter 'IP'), describes different ways of applying PSAQ cooking in modified continuous cooking. The solution which is described in the IP patent application differs from previous methods associated with PS cooking in that it is possible to dose the entire white liquor dose, which comprises PS, at the beginning of the cooking thereby maximising the improvement in yield. This is enabled by arranging the cooking liquors in such a way that liquors are replaced one by another and the removed liquors are used in later stages of the process.

"One liquor is taken out of the boiler but a totally different liquor is brought back. In other words, the liquor which is taken out is directed to a different part of the boiler or removed from the cooking process and, correspondingly, the liquor which is brought back is sourced from a different part of the total process. Consequently, the liquor circulations become in practice very complicated when executed according to the solution in IP."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "The purpose of the present invention is to eliminate at least some of the problems associated with the known technology and to generate a completely new solution for producing cellulose pulp by polysulphide and antraquinone cooking.

"In particular, the purpose of the present invention is to generate a method of producing cellulose pulp by using polysulphide/antraquinone cooking in a continuously operating cooking apparatus which is comprised of at least one absorption unit and at least one continuously operating cooking unit, connected in series.

"The present invention is based on the principle that the alkaline cooking liquor used is orange liquor (i.e. white liquor which comprises polysulphide) which is produced in a standard way by applying commercially available methods for producing PS liquor. This alkaline cooking liquor is dosed, together with the raw material and AQ, into the input of the absorption unit at a temperature which is elevated but always below C. The absorption process is continued for a period of time, typically at least half an hour, generally at least an hour, in a such a way that it achieves an efficient absorption of orange liquor and effects a stabilising of the hemicellulose of the PS at such temperatures where decomposition of the hemicellulose matrix of the raw material does not essentially take place.

"After that, alkaline cooking liquor is separated from the raw material, the temperature of which liquor is increased in a heat exchanger to the cooking temperature, which is, depending on the raw material and the target kappa number, within the range of C.

"The heated alkaline cooking liquor is recirculated back and directed to the beginning of the actual cooking stage of the raw material, in which case it is possible to rapidly increase the temperature of the wood chips to the temperature required for the cooking stage.

"Thus, in the cooking stage, the same alkaline cooking liquor is used which originally was dosed into the input of the absorber, but the temperature of which is increased. The liquor used for absorption is not removed and there is no need to use any new (fresh) liquor for the cooking stage.

"More specifically, the method according to the present invention is mainly characterised in that the cooking liquor is mixed before the cooking into the raw material which is to be defibred, the cooking liquor is allowed to absorb into the raw material at a temperature which is at maximum approximately C., after that, cooking liquor used in the absorption is separated from the raw material treated, the separated cooking liquor is heated to a temperature of approximately C., after which, the generated hot cooking liquor is, as such, fed back to the treated raw material, the alkaline cooking liquor used in the cooking stage thus being the one which originally was dosed into the absorption process and the temperature of which has been increased, and the raw material is defibred with a hot cooking liquor in order to produce pulp which has a desired kappa number.

"Considerable advantages are achieved with the present invention. Thus, in PSAQ cooking, the entire white liquor dosage of the liquor, which comprises PS, can be used at the beginning of the cooking in conditions which are very advantageous and which remove the need for liquor draw-off and circulation into later stages of the process, which actions are used in known solutions. Liquor used for the absorption step is not removed and there is no need to use any new kind of liquor (makeup) for the cooking stage. This enables maximal use of polysulphide in advantageous conditions and the whole arrangement is simple because there is no need to use circulation measures described in generally known techniques. Also, the improvement in yield is substantial, as described in the example below.

"The present invention is especially suitable for a process of continuous cooking which has a separate absorption vessel. The adaptations required in the cooking process are only minor, in which case it is easy to carry out cost-efficiently the required implementation in existing cooking areas. If the cooking areas are newly built, the arrangements will not increase the investment costs of the cooking departments compared to a non PSAQ case.

"In a preferred embodiment of the present invention, the first part of a continuous cooker (continuous digester), i.e. the first cooking zone, is utilised for prolongation of the absorption process, in which case it is possible to substantially increase the efficiency of the absorption and the capacity of the part of the apparatus used for the absorption. In the case of a traditional vertical continuous digester, the first cooking zone means that part of the cooker which is located above the first screen zone.

"In the present invention, only one liquor is circulated in order to reach the cooking temperature quickly. Consequently, there is no need to adjust the alkali profile and it is easier to carry out the cooking process than in the known technology. The cooking process is simple but, at the same time, the whole PS dose is fed in at the beginning of the cooking and undergoes a long absorption."

For additional information on this patent, see: Turunen, Esko; Kovasin, Kari. Method of Producing Cellulose Pulp. U.S. Patent Number 8758555, filed June 22, 2012, and published online on June 24, 2014. Patent URL:

Keywords for this news article include: Technology, Metsa Fibre Oy.

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Source: Journal of Technology

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