Typical Pre-Krete applications are in Kraft Mills, which produce Kraft Paper. Kraft paper is produced from wood pulp. It is strong and relatively coarse. Kraft paper is usually a brown color but can be bleached to produce white paper. It is used for paper grocery bags, multi wall sacks, envelopes and other packaging.
Wood chips are fed into vessels called digesters. The wood chips are combined with white liquor, a mixture of sodium hydroxide and sodium sulfide. The digester cooks the chips for several hours at 265 to 355 °F (130 to 180 °C). Under these conditions lignin is removed and the hemicellulose degrades to give fragments that are soluble in the strong basic liquid. The solid is collected and washed and fed into a paper machine to make paper. At this point the pulp is brown and known as “brown stock”. The combined liquids are known as black liquor. Kraft pulp is dark but it can be bleached to make very white pulp. Fully bleached kraft pulp is used to make high-quality paper where strength, whiteness and resistance to yellowing are important.
In order to minimize waste there is a recovery process to return white liquor back to the digester. The black liquor is concentrated in multiple effect evaporators, transferred to a Black Liquor Tank, and fed into the recovery boiler to recover the inorganic chemicals for re-use in the pulping process. From the recovery boiler the solution goes to a Smelt Tank also known as a Dissolving Tank. The molten salts (“smelt”) are dissolved in a process water known as weak wash.
At this point other chemical processes are induced. The process proceeds from the Smelt (Dissolving) Tank to a Green Liquor Clarifier, to a Causticizer, to a White Liquor Clarifier and finally to a White Liquor Storage Tank to be transferred into the digester as required.
The Causticizer also incorporates a cyclical process where “Mud Wash” from the White Liquor Clarifier is thickened and fed into a Lime Kiln that converts Calcium Carbonate to Calcium Oxide. This is fed into a Slaker Tank which supplies the Cautisizer with lime (calcium oxide).
The vessels referenced above that are bolded in Capital letters would utilize Pre-Krete C-17 to protect the substrate from the damaging effects of corrosion and abrasion.
This information is a broad and simplified overview of the operations of a Kraft Mill. Each mill has a unique process and process requirements.
In this process there are numerous other typs of vessles/structures that require protection from corrosion and/or abrasion. Dependent on the application, Pocono Fabricators’ Pre-Krete systems may be able to help. The equipment we have experience with is as follows:
Absorption Towers – Acid Tanks – Brown Stock Tanks – Seal Tanks – Spent Acid Tanks – Stock Chests – Sulphur Feed Tanks – Tall Oil Storage/Reactor Vessels – Washer Feed Tanks – Washer Vats
Typical application is for the Pre-Krete to be applied at a nominal 2” thickness over a 14 gage 2” x 4” welded wire fabric anchored to the substrate on 12” centers. Causticizers and some liquor tanks have agitators that cause severe abrasion to the floor area of the vessels. The floors will typically deteriorate twice as fast as the walls. In this case the Pre-Krete is applied at 2” to the walls and 4” on the floors.
Additionally, some Pulp & Paper plants have their own power/steam generation plants. See Power Generation for additional information.