Field test of sodium bicarbonate and liquid C[O.sub.2] use for accelerating char bed cooling.

Application: Short, high-volume bursts of coolant are apparently more effective than slow, steady application. Bicarbonate and liquid carbon dioxide appear to be worth the costs and the efforts involved in cooling a hot char bad after an ESP.

Both bicarbonate (NaHC[O.sub.3]) and liquid C[O.sub.2] work effectively to quickly cool a char bed, based on results from a simulated emergency shutdown procedure (ESP) was carried out in the No. 4 recovery boiler at Willamette Industries mill in Albany, Oregon, USA.

The results of the full-scale truial revealed no significant problems in applying either coolant to a hot, porous, actively burning bed and no indication that the bed reheated and re-ignited after we stopped the coolant application. These results suggest advantages to begin applying coolants as early as possible, consistent with safety considerations about possible smelt-water contact in an actual ESP.

Although early application of coolants to the hot burning bed is likely to require more coolant, the economics of accelerated bed cooling are such that the cost of using more chemical is usually overshadowed by the savings brought about by shortening the cooling time. The test results showed that short bursts of coolant at higher rates appeared to be more effective than slow, steady application. Proper technique is important. This includes identification and assessment of furnace access points, lance construction to allow easier handling and manipulation, capability to maneuver lances to the desired locations on the bed, and means for using the lances and coolant discharge to penetrate the bed surface.

Grace is adjunct professor, Tran and Kawaji are professors, Pulp & Paper Centre and Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada; email Tran at [e-mail].