The Problem

Weyerhaeuser operates a 1,000 ton per day bleached pulp mill at one of their facilities. As part of the process, reburned lime exits a kiln, is crushed, then conveyed to a hot lime storage bin. Hot, reburned lime is then metered with fresh lime from a separate bin to a slaker to begin recausticizing.

Problems were encountered maintaining reliable feed from the hot lime bin. Pluggages were experienced many times every shift, exposing operating personnel to potential safety incidents, and creating an environmental concern due to the discharge of fine lime dust to the surrounding area. The pluggages also caused swings in slaker operation, which carried through to the causticizers, resulting in inconsistent liquor quality.

Jenike & Johanson's Solution

To solve the pluggage problems, Jenike & Johanson suggested conversion of at least a portion of the hopper to mass flow, with a larger and more robust outlet size and shape. It was not practical, nor required, to redesign the bin for complete mass flow, as flow properties tests (conducted using our unique furnace tester) showed ratholing was not a concern for larger diameter outlets. It was also necessary to replace the existing feeder with a properly designed mass flow screw feeder so that the entire outlet would remain active.

The Result

The modified bin and original screws are still in operation, without any pluggages occurring with the hot lime. A video camera that was required to monitor the old arrangement, to ensure that hot lime flow was maintained, was gladly retired.

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