Enso-gutzeit Oy

Ahlstrom Machinery Oy

Andritz Oy

Ahlstrom Machinery, Inc.

Enso-gutzeit Osakeythio

Enso-gutzeit Osakeyhito

Holger Engdahl

Pekka Tormikoski

Matti Lankinen

Martti Tolvanen

Jaakko Savolainen

Yrjo Luukkainen

Raimo O Kohonen

Jorma Surakka

Simo Suutari

Martti Pokkinen

Jouni Jantti

Juha Lumikko

Antti Mattelmäki

Jukka Niskanen

Markku Kosonen

Jouni Jäntti

Mika Kottila

Markku Lankinen

The present invention relates to a method of treating lime mud slurry being generated in a causticizing process in a pulp mill in a disc filter, in which method the lime mud is fed in the filter, thickened on the filter discs and removed from the filter discs. The lime mud is treated in at least two stages in one and the same disc filter in such a way that the lime mud slurry entering the filter is fed onto only a part of the filter discs, on which lime mud is thickened and removed from the discs, and the removed lime mud is re-slurried in liquid, and the lime mud slurry thus obtained is fed onto a second part of the filter discs, on which lime mud is thickened and removed from the filter and led into a subsequent process stage. The invention also relates to an apparatus.

Method and apparatus for thickening lime mud in a disc filter

Clarifying and/or filtering of green liquor and an apparatus therefore

A method of regulating the temperature in a chemical melt dissolving tank, where chemical melt produced in combustion of spent liquor of a cellulose pulp mill is dissolved in liquid, producing green liquor, provides excellent heat economy, while minimizing the amount of liquid needed to dissolve the melt to produce green liquor at a temperature below boiling. Green liquor produced in the dissolving tank is expanded (and thereby cooled) in a vacuum tank, and a least a significant part of the cooled liquor is returned to the dissolving tank, for regulating the temperature in the tank. The heat energy contained in the generated expansion steam may be used in many different ways, for example, for indirectly heating (e.g. in a heat exchanger acting as a condenser) water or other liquid to a sufficiently high temperature so that the liquid is useful elsewhere in the pulp mill. The vacuum tank may be positioned above dissolving the tank to receive liquor directly from it, and the condenser may be positioned in it to return condensate directly to the dissolving tank. Alternatively the vacuum tank and condenser may be remote from the dissolving tank and connected to the dissolving tank by conduits.

Method and apparatus for regulating the temperature in a chemical melt

Falling film cross filtration apparatus

A filtering method and apparatus pass the suspension (e.g. green liquor) to be filtered in a falling film down a first side of a filtering surface of a filter element at a different (higher) pressure than a second side, so that due to the pressure difference prevailing across the filtering surface the filtrate flows through the filtering surface and separated solids substantially remain in the suspension, without forming an undesirable solids layer on the filtering surface. A uniform liquid film falling on the filtering surface is generated by recirculating suspension from the bottom of the filter housing to an upper portion of the filter element. Nozzles may direct flow toward the filtering surface in localized areas. The method may be practiced continuously or in batches.

Clarification of green liquor by falling film cross-flow filtration

The invention concerns a causticizing procedure by which from soda liquor derived from a sulphate cellulose digesting process and from unslaked lime is produced white liquor for reuse in the digesting process, over lime slaking and a subsequent causticizing reaction proper. It is essential in the invention that the lime slaking is carried out using white liquor, whereafter the causticizing reaction proper is allowed to take place between the slaked lime and soda liquor combined therewith. The requisite white liquor is obtained by recirculating part of the white liquor produced by the causticizing process, to the slaking step, where it either completely or partially replaces the soda liquor employed in prior art. By using white liquor, one avoids the foaming, interfering with the process, which is encountered in the slaking step.

Causticizing process

In a procedure for filtering lime sludge meant to be regenerated to lime. Lime sludge is produced in the causticizing process in a sulphate cellulose mill, where it can be reused after regeneration to lime. In the procedure, lime sludge suspension is filtered on a filter drum in continuous rotation by depositing lime sludge on the drum and detaching part of the superficial layer of the lime sludge on the drum with a scraper so that the deeper lime sludge layer on the drum, which by-passes the scraper, serves as filtering medium for the superficial layer that is detached (as a so-called pre-coat). The purpose is to arrange the control of the filtering process so that the dry matter content of the lime sludge detached from the drum is substantially constant, and its essential feature is that the dry matter content of the lime sludge detached from the drum is followed so that when the dry matter content tends to decrease, the speed of rotation of the drum is first raised within a given control range and, after the control range has been used up, the scraper is moved closer to the surface of the drum so that at least part of the deeper lime sludge layer on the drum, serving as filtering medium, is detached and, if the scraper is returned to its earlier position, is replaced with a new lime sludge layer, whereupon the control is again continued with the aid of the drum's speed of rotation.

Procedure for filtering lime sludge meant to be regenerated to lime

The present invention seeks to provide a method in which the soda lye obtained as a result of cellulose cooking process and unslaked lime are used for producing white liquor which can be re-used in the cooking process. In this method, the heat released by the slaking of lime with soda lye is recovered by a high pressure slaking process wherein the heat is transferred, either to the steam separating from the lye, which steam is then led to the desired application, or to some other medium to be heated. The present invention is characterized in that the soda lye to be causticized is divided into two parts, one of which is used for the slaking of lime by adding to it all the unslaked lime needed for the causticizing process, and that, following slaking, the two volumes are brought together for the actual causticizing reaction involving the total amount of lye needed. The present invention provides the advantage that the amount of lye needed is smaller, and so the temperature can be increased.

Causticizing method

An intermittently operating pressurized filter for concentrating a solid matter suspension, comprising a filtering tank with an inlet conduit provided with a feed pump for introducing under pressure the suspension to be filtered, and a draining conduit provided with valve for removal of the concentrated sludge, and a plurality of filtering elements suspended from the roof, through which the filtrate flows and of which the interior communicates with a filtrate collecting tank located above and which thereby collect on their external surface sludge, which has been arranged to be periodically removed by voiding the pressure within the filtering tank by opening for the suspension therein an exit flow path through a draining conduit. The filtrate in the collecting tank will pass in countercurrent fashion through the filtering elements. In the pressurized filter the filtrate has been arranged to be removed during the filtering step by a filtrate draining conduit departing from the collecting tank, by effect of the pressure produced by the feed pump in the suspension inlet conduit. The collecting tank is of enclosed construction. The sludge has been arranged to be removed from the surface of the filtering elements by the aid of the hydrostatic pressure of the filtrate in the collecting tank, by placing th draining conduit of the collecting tank under atmospheric pressure.

Pressurized filter

Periodically operating pressure filter for the concentration of a solid matter suspension, comprising a filtering tank with an input conduit for introducing the suspension to be filtered under pressure, and a drain conduit for removal of the concentrated sludge, and a number of filtering elements suspended from the ceiling, through which the filtrate flows and which are internally in communication with a filtrate collecting tank located above and which thereby collect sludge on their outer surface. The sludge has been arranged to be periodically detached by making the pressure inside the filtering element higher than on its outside. The filtrate is under atmospheric pressure in the collecting tank. For detaching the sludge periodically from the outer surfaces on the filtering elements the pressure has been arranged to be removable from the filtering tank by opening for the suspension residing there, an exit flow, whereby the filtrate in the collecting tank will pass under hydrostatic pressure effect in counter-current fashion through the filtering elements.

Filters with filtrate chamber overflow partitions having plural outlets

Growing community of inventors

Savonlinna, Finland

Holger Engdahl