Patent ID: 8480854

Claim:
A method for crystallizing calcium carbonate, in a short circulation of a fiber web machine, the method comprising: (a) obtaining filtrate from the fiber web machine, (b) preparing paper making stock from at least said filtrate and various fiber components, (c) pumping said paper making stock from its preparation towards the fiber web machine, and (d) providing the paper making stock with calcium carbonate crystals by feeding carbon dioxide and milk of lime into the short circulation of the fiber web machine and letting the carbon dioxide and milk of lime to react with one another, wherein the step of providing the paper making stock with calcium carbonate crystals comprises mixing at least either carbon dioxide or milk of lime into a liquid flow comprising at least one of at least one fiber component, filler component and paper making stock by (i) injecting the at least either carbon dioxide or milk of lime from one or several nozzles into the liquid flow by using as a feed or injection liquid at least one of the following: a filtrate obtained from a fiber web machine, a clear or turbid filtrate obtained from a fiber web machine, a fiber suspension used for producing a fiber web, a fiber or other component of a fiber suspension used in the fiber web production, an accept flow, a reject flow, an overflow or a bypass flow of a short-circulation, and clean water, (ii) performing the injecting in a direction substantially transverse to a direction of liquid flow, and substantially at a feed velocity that is higher than a flow velocity of the liquid; wherein (iii) the injecting taking place as sufficiently small-sized particles or bubbles such that the at least either carbon dioxide or milk of lime is spread substantially evenly into the liquid flow independently of the flow conditions of the liquid flow, and such that the crystallization reaction on the surfaces of fibres substantially completes in less than fifteen seconds, thereby achieving an applicable size distribution of the homogenous calcium carbonate crystals, preventing the formation of oversized PCC crystals, PCC agglomerations and PCC precipitations, and thus enabling improved runnability of a fiber web machine.