Controlling operation of a centrifugal pump

A method for controlling the operation of a centrifugal pump pumping a cellulosic fiber suspension having a consistency of about 8-12 percent, and having gas entrained therein, comprising the steps of:

• (a) effecting rotation of the suspension so that a gas bubble is created in a central part of the pump;
• (b) effecing discharge of gas from the central part of the pump;
• (c) rotating the pump impeller at a speed sufficient to effect fluidization of the suspension, and effecting discharge of the fluidized suspension at a flow rate;
• (d) determining the differential pressure between the suspension just prior to fluidization thereof and the gas being discharged;
• (e) maintaining the rotational speed of the pump substantially constant and the discharge flow rate of the fluidized suspension substantially constant;
• and
• (f) significantly reducing the power consumption of the pump by controlling the pump head, which is accomplished by controlling the differential pressure determined in step (d).

A method for controlling the operation of a centrifugal pump pumping a suspension having a consistency of about 8-12 percent and containing gas, the pump having an inlet suspension pressure, a pressure head, a suspension discharge flow rate, and a suspension discharge pressure, comprising the steps of:

• (a) effecting rotation of the suspension within the pump so that a gas bubble is created in a central part of the pump;
• (b) discharging gas from the gas bubble in the pump central part, at a gas discharge pressure;
• (c) rotating the pump impeller at a speed sufficient to effect fluidization of the suspension, and effecting discharge of the fluidized suspension at a flow rate;
• (d) determining the differential pressure between the suspension inlet pressure and the suspension discharge pressure;
• (e) determining a differential pressure set value in response to the differential pressure measured in step (d);
• and
• (f) controlling the differential pressure between the suspension inlet pressure and the gas discharge pressure so that said differential pressure is approximately said differential pressure set value.

A method for controlling the operation of a centrifugal pump pumping a liquid or suspension containing gas, the pump having an inlet liquid or suspension pressure, a pressure head, and a liquid or suspension discharge flow rate, comprising the steps of:

• (a) effecting rotation of the liquid or suspension within the pump so that a gas bubble is created in a central part of the pump;
• (b) discharging gas from the gas bubble in the pump central part, at a gas discharge pressure, to an air vessel;
• (c) determining the differential pressure between the liquid or suspension inlet pressure and the gas discharge pressure, the gas discharge pressure measured in the air vessel;
• (d) controlling the head and/or discharge flow rate of the pump by controlling the differential pressure determined in step (c);
• and
• (e) at pump start up, or when a rapid differential pressure change is desired, feeding air at a controlled pressure and flow rate--from a source independent of the pump gas discharge--to the air vessel.

Apparatus for controlling the operation of a centrifugal pump pumping a suspension having gas entrained therein, comprising:

• a centrifugal pump having a suspension chamber with an impeller disposed therein, and a gas chamber in fluid communication with said suspension chamber and having rotating blades disposed therein;
• a suspension inlet to said suspension chamber, and a suspension outlet from said suspension chamber;
• a gas outlet from said gas chamber;
• means for measuring the flow in said suspension discharge line at a particular point;
• a valve in said suspension discharge line upstream of said particular point;
• means for determining the differential pressure between the suspension in said suspension chamber and the gas discharge in said discharge line;
• and
• means for controlling said valve in said suspension discharge line in response to the flow rate measurement by said flow measuring means, to maintain the suspension discharge rate substantially constant.

Apparatus for controlling the operation of a centrifugal pump pumping a suspension, comprising:

• said pump having a suspension chamber with an impeller, and a gas chamber in fluid communication with said suspension chamber, and rotatable blades in said gas chamber;
• an inlet to said suspension chamber, and an outlet from said suspension chamber;
• a gas discharge outlet from said gas chamber;
• an air vessel disposed in said gas discharge outlet;
• means for sensing the suspension inlet pressure;
• means for sensing the gas discharge pressure in said air vessel;
• means for determining the differential pressure between said sensed suspension inlet pressure and gas discharge pressure;
• and
• means for controlling the head and/or discharge flow rate of the pump by controlling the determined differential pressure.