Cleaning Plate and Liquor Draining Method for Internal Header of Pulp Digester
Publication Date: 2005-Apr-27
The IP.com Prior Art Database
An internal header in a cellulose pulp digester for collecting extracted liquor includes: a header chamber on an inside digester surface of the digester, wherein the header chamber is below a screen section of the digester; a header wall of the chamber opposite to the inside digester surface and a header bottom extending between the header wall and inside digester surface; a cover plate aperture in the header wall and having a bottom aperture edge adjacent the header bottom, and a cover plate attachable to the header wall and covering the aperture.
BACKground of the invention
 This invention relates to the field of digesters for the production of chemical cellulose pulp (e.g. kraft pulp) for both continuous and batch digesters. In particular, the invention relates to internal headers used in the digesters to collect liquor being removed from the kraft pulp in digester.
 Screen plates are used in digesters to extract liquor from the pulp flowing generally downward through the digester. Screen plates are filters that allow liquor to be extracted from a digester but prevent the extraction of the fibrous material of the pulp. The liquor passing through the screens flows into an annular screen chamber between the screen and an outer wall of the digester. The liquor from the screen chamber flows downward through a bottom annular plate of the screen chamber that has orifices to allow passage of the liquor. Below the bottom plate of the screen chamber is an internal header that collects the liquor flowing through the orifices in the bottom of the screen chamber.
 The internal header extends annularly around the inside surface of the digester and is immediately below the screen chamber. The header in an annular chamber that temporarily holds the liquor. Nozzles on the outside wall of the digester extract the liquor from the headers. The nozzles are typically mounted on the digester wall near the bottom of the header to ensure that the substantially all of the liquor can be drained form the header through the nozzles.
 The liquor in the header is typically drained when a digester is shut-down for service. In a typical shut down procedure, the pulp is removed from the digester through a bottom outlet. The liquor in the internal headers are drained through the nozzles on the outside of the vessel walls of the digester. With the header drained of liquor, the cover plates on the inside vertical walls of the headers are removed to provide access to the internal header chamber. The cover plates have conventionally been square plates, e.g., 12 inches by 12 inches, bolted over openings in the vertical inside wall of the internal header. The cover plates are conventionally positioned at the vertical center of the inside wall of the header. As these walls are typically 15 to 16 inches tall, there is approximately about one (1) to two (2) inches of header wall below the cover plates and above the bottom plate.
 A shallow pool of liquor typically remains at the bottom of the internal header after the header is drained by the nozzles. The nozzles are often about one (1) inch above the bottom of the header. Draining the header through the nozzle results in a one inch pool of liquor in the header. Removal of the cover plate does not drain the pool because the bottom edge of the plate is also above the pool. During maintenance work on the digester, liquor from the p...