Tuthill Process Pumps Successfully Pump Black Liquor Soap Skimmings From Kraft Process

Black liquor soap, a by-product of digestion in a kraft mill, tends to display characteristics such as abrasiveness, air entrainment, and a wide range of viscosities, dependent upon the temperature of the product. These characteristics require the use of a positive displacement pump, and the difficulties presented by the air entrainment and abrasives require the use of the Tuthill HD circumferential position design pump. Below is a short summary of how Major Southern Pulp Mill solved their black liquor soap issues with a Tuthill 330 process pump.

Major Southern Pulp Mill

The customer couldn’t find suitable pumps to pump black liquor soap skimmings resulting from the sulfate “Kraft” pulping process. Progressive cavity pumps had been tried and found unsuitable. Some models of internal gear pumps and external gear pumps would operate but required continual adjustment and excessive maintenance.

One part of the difficulty in pumping this black liquor soap, sometimes called tall oil soap, is its wide range of viscosities. Viscosities vary widely, according to temperature and other variables. Centipoise readings can range from 1800 to 8000 cps. The low lubricity of the soap skimmings also presents problems. And, it is almost unavoidable that the pump occasionally will have to run dry.

After examination, one Tuthill Model 330 process pump rated for 135 GPM at 120′ total dynamic head (TDH) was recommended and installed.

The original pump is still operating providing excellent service. The only maintenance required in the 1-1/2 years of operation has been to adjust shaft packing.

Based on the excellent performance of the first pump, five additional units are now in use at this plant all handling black liquor soap skimmings. The new pumps are matching the excellent performance record established by the initial pump in every way.

One additional saving is possible. It was previously necessary to have expensive level control instruments on each tank and to monitor tank levels closely so that the pumps would not be running dry. Since the Tuthill process pump can run dry without damage, it would be possible to eliminate these tank level controls on future construction.

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