Screw Feeders Meter Lime at Containerboard Plant

General Description

Lime is used extensively by the pulp and paper industry to dissolve wood chips, bleach pulp, and neutralize various byproducts created during the papermaking process. As such, lime must always be available to ensure continuous operation. While lime is recovered and recycled with great efficiency, many paper mills also bring in lime from outside sources to prevent unplanned downtime.

A major containerboard mill stores lime in silos, and it is metered into the process by screw feeders. Outsourced lime is kept at ambient temperatures, but lime recovered from within the mill can be extremely hot, remaining at temperatures up to 1,500-degrees F. Conveying equipment must be designed to handle the extreme conditions, as well as be both accessible and replaceable for maintenance purposes. KWS designed and provided screw feeders, pin gates and slide gates for the difficult application to keep the mill operating at peak efficiency.

Design Parameters

1. Product Type: Lime
2. Material Density: 40 to 60 Lbs. per Cubic Foot
3. Design Temperature: Ambient to 1,500-Degrees F
4. Capacity: 2,200 Cubic Feet per Hour
5. Designed Duty: 24 Hours per Day, 7 Days per Week

KWS Advantages

With over 50 years of experience in the bulk material handling industry, KWS has provided engineered solutions for hundreds of pulp and paper applications. Metering hot lime at up to 1,500-degrees F is extremely difficult, but KWS has the knowledge and expertise to solve the problem.

Lime is stored in silos and then metered by screw feeders into the process. KWS provided pin gates located on the bottom of each silo. Heavy-duty pins are driven through the head load of lime, restricting flow, and supporting the material above it. Below the pin gates are slide gates that are engaged to fully seal off the opening without the need to close through a column of lime.

The unique cantilevered screw feeder design accurately meters lime into the process while keeping bearings out of the material flow and elevated temperature.

KWS Special Features

KWS designed and manufactured the screw feeders and gates from 304 stainless steel to withstand high material temperatures and potential corrosion. Each pin gate utilizes seven 2-inch diameter rods machined from round bar to restrict the opening. The rods are hammered or hydraulically driven through the headload of lime to close the gate. Slide gates operate on bushed rollers to minimize friction.

Cantilevered screw feeders are mounted below each gate assembly. Supporting the screws only on the drive end precludes the need for a tail bearing, removing a potential leak and maintenance point. The heavy-duty screw flights are mounted on 6-inch heavy-wall pipe with a shrink-fit drive shaft. The single-piece screw/shaft assembly provides a rigid assembly and removes any clearance issues when compared to a bolted screw/shaft connection. Dual pillow block bearings ensure proper alignment and support of the screw assembly.