Air Removal for Pressure Diffuser
Publication Date: 2003-Dec-18
The IP.com Prior Art Database
John Weston: INVENTOR [+2]
A pressure diffuser is disclosed having a pressurized vessel having an inlet adapted to receive a slurry of cellulosic fibrous material and cooking liquor; an outer chamber having an assembly of screens, wherein the slurry flows through the outer chamber and a portion of the cooking liquor is extracted through the screens; a center chamber to receive cooking liquor extracted through the screens; an inner head capping the center chamber, wherein the inner head is impervious to gases escaping from the cooking liquor and collecting underneath the inner head, and a gas exhaust conduit extending from the inner head to an outlet external of the pressure diffuser, wherein the conduit has an inlet below the inner head.
title of the invention
PRESSURE DIFFUSER HAVING GAS VENT FOR COOKING LIQUOR
 Priority is claimed to U.S. Provisional Patent Application 60/382,604, filed May 24, 2002, the entirety of which is incorporated by reference.
 The present invention relates to pressure diffusers for pulp processing systems.
background of the invention
 Conventional pressure diffusers for use in pulp processing systems generally include a center column chamber for liquor extracted from the pulp processed in the outer annular region of the diffuser vessel. The extracted liquor contains gases, usually in the form of air bubbles, which gradually drift upward in the center chamber where the gases separate from the liquor and form a gas pocket at the top of the chamber. The top of the chamber is capped with a conical inner head that separates the chamber from the outlet head above the chamber. Conventionally, the inner head is perforated, e.g., with screen slots, to allow gases to pass through the inner head and enter the pulp slurry flowing through the outlet head. Other types of inner heads are not perforated, but the center chamber is entirely filled with cooking liquor so that gases remained entrained in the liquor.
 A difficulty with the conventional methods of allowing gases from the center chamber to be reintroduced into the pulp slurry or entrained in the cooking liquor is that the gases are not removed from the diffuser separately of the pulp and liquor. It is preferable to remove gases from the pulp and cooking liquor. If the gases are not removed in the pressure diffuser, then they must be removed from the pulp and liquor streams downstream of the pressure vessel. Filtrate tanks and other devices are traditionally used to separate gases from the pulp and liquor downstream of the pressure diffuser.
 Traditionally, cooking liquor flows from the pressurized center chamber of the pressure diffuser into an unpressurized filtrate tank. The pressure diffuser is pressurized, for example, in a range of 75 psi (pounds per square inch) to 150 psi. Due this pressurization, gases in the cooking liquor and center chamber are compressed and have a reduced gas volume. As the cooking liquor flows from the pressure diffuser to the filtrate tank, which may be at atmospheric pressure, the gases in the cooking liquor increase in volume as they enter the filtrate tank. Typically, a large filtrate tank is provided to allow for the entrained gas bubbles in the cooking liquor to rise to the surface of the cooking liquor and fill the upper regions of the filtration tank. The liquor is held in the tank for a certain retention time to allow for the bubbles to rise out of the liquid and into the upper gas section of the tank.
 There is a desire to eliminate the filtrate tank or at least reduce the size of the filtrate tank. If there is to be no filtrate tank or only a small filtrate tank, then there is a need for th...