Stock Thickening

April 20, 2004

The best Pulp & Paper application for Vincent presses has been to squeeze as much water as possible from reject fiber. Typically we are working with screen rejects, knots & shives, and clarifier underflow. If the waste solids are to be landfilled, they are squeezed to only 35% to 40% solids, minimizing abrasive wear within the press. If the waste is to be used as boiler fuel, then the discharge pressure of the same press is increased and cake with 50% solids is achieved.

A different application involves thickening a flow of fiber and water to a solids consistency of only 30% to 35%. This need exists where good fiber must be thickened (a) for temporary storage, (b) ahead a deinking kneader, or (c) between stages of a counterflow wash or bleaching operation. In these applications it is important not to squeeze too hard as fiber damage can result, and the cake produced will no longer be sufficiently fluid.

On three occasions we have sold Series VP presses for stock thickening, with good results.

Earlier this year excellent results were achieved using a Series KP press. This series of machines was introduced in 1996 for "soft squeeze" applications. The initial market, dewatering cannery and fresh-cut produce waste, required a light, low-torque machine. This changed almost immediately as we entered the farm market for producing cow bedding from manure. This application required the same economical press, but with three times the horsepower.

Until last year the market for Series KP presses was limited to 16" screws. However sales were made to corn canneries that needed machines that could handle up to 100 tons per hour of corn husk and cob. That led to the introduction of 24" and 30" Series KP machines. Converting this waste into silage by-product was once again a high torque application.

It was recognized that the Series KP press technology had evolved to where it could be suitable for stock thickening in paper mills. Tests were run, demonstrating that the press was easy to set to hold 33% to 36% output solids. Typical of operation with the interrupted flight screw design used by Vincent, this output consistency held over a wide range of feed consistencies. Capacity of the 20-hp KP-16 was 30 tons per day, air dry solids, so a Model KP-30 press was recommended for the 100 TPD load at the mill.

This testing was performed at the Linpac mill in Cowpens, South Carolina, where deinking capacity is limited by insufficient prethickening capacity ahead of the kneader. The testing demonstrated that a Series KP screw press could be placed in parallel with the existing prethickening press in order to relieve the bottleneck.

Issue 152