Steam and Hot Liquor Distribution for Batch Digester
Publication Date: 2003-Dec-19
The IP.com Prior Art Database
A batch digester for cooking fibrous cellulose material having: a cooking vessel with a vertical axis, an upper inlet to receive a slurry of cellulose chips and cooking liquor and a lower slurry discharge outlet; a center conduit aligned with the vertical axis and having a coupling external to the vessel attachable to a hot fluid source; at least one vertical screen arranged around an interior wall of the cooking vessel, and a chamber between the at least one vertical screen and the interior wall and said chamber having a liquor outlet connectable to a recirculation conduit. The center conduit may include a first center pipe having a first discharge output aligned with the vertical axis and having a first discharge port below the vertical screen; a second center pipe having a second discharge output vertically aligned with the vertical screen, and a third center pipe having a third discharge output above the vertical screen.
Steam and hot LIQUOR distribution for batch digester
background of the invention
 [lsp1] In the art of chemical pulping of comminuted cellulosic fibrous material, for example wood chips, the cellulose materials typically treated with cooking chemicals under pressure and temperature in one or more cylindrical vessels, known as digesters. The cooking chemicals are conventionally referred to as cooking liquor. The cooking liquor impregnates the fibrous materials. The cooking liquor, breaks down the bonds between the individual fibers of the cellulose material. The treatment can be performed continuously or in a batch mode. In the batch method, one or more batch digesters are filled with chips and cooking chemical, hot fluids are added, the vessel is capped and then cooking treatment commences. Once the treatment is finished, the contents of the batch digester are discharged. In either batch or continuous digesters, a slurry of comminuted cellulosic fibrous material and cooking chemical is treated in one or more a cylindrical vessels.
 Heat can be supplied to batch digesters directly or indirectly. Direct heating may be performed by injecting steam directly into the slurry of cooking liquor and wood chips in the digester. Steam may be injected into the vessel through one or more steam inlet ports arranged in the wall of a lower part of the vessel. Indirect heating may be performed by adding a hot liquor, e.g., hot water, into the digester to heat the cellulose material. When indirect heating is used, some steam may be added to the digester in combination with the hot liquor. During indirect heating, the hot liquor displaces the impregnation liquor around the cellulose material. Heat from the hot liquor and stem is transferred into the cellulose material. In both direct and indirect heating, the heat applied to the chips promotes a chemical reaction that results in the cooking chemicals impregnated in the chips breaking the chemical bonds between fibers in the chips.
 The addition of steam and hot liquor to heat a batch digester has, in the past, been done by injecting the steam and liquor into the digester vessel through ports. The ports are essentially flush with the side wall of the digester vessel. The ports do not extend in towards the center of the vessel. Steam or hot liquor enter through the ports and are discharged at the perimeter wall into the vessel. If the steam and hot liquor inlet ports are below the surface level of chips and cooking liquor in the vessel, the steam and hot liquor tend to collect at the perimeter of the vessel and heat the chips and cooking liquor near the perimeter of the vessel. If the steam and hot liquor inlet ports are above the surface level of chips and cooking liquor in the vessel, then the steam and hot liquor tend to shoot as a stream across the width of the vessel and hit the opposite side wall of the vessel. The steam and hot liquor collects at the perimeter of the vessel and heat the c...