A gold-mining operation in South Africa required cooling water for its equipment and refrigerated air throughout the mine. Due to the mine's depth, rock-wall temperature reached 120oF (49oC). If refrigeration was lost, all 6,500 miners had to be evacuated immediately.

Wichita Falls, Texas-based Tranter developed a shallow pass-plate banked in a 35-plate cooling module to satisfy the mine's specific requirements. Dies were built to press the plates, and fatigue-testing verified that the unit could withstand pressure variations inherent in the operating cycle. A sample coil was exposed to more than 1.2 million cycles from 30 to 75 psig, and it did not leak.

The 48 x 150" Tranter Platecoil plates, constructed of 16/16 gauge 304L stainless steel, have a passivated finish. Liquid ammonia refrigerant enters the coils at the bottom at approximately 18oF (-7.78oC). The coil floods with liquid refrigerant while water cascades over the outside surface of the plate. The water causes the ammonia to evaporate, which exits as a gas at the top of the coil. Ice builds up on the outside surface to approximately 0.3125" thick in about 15 min.

Ice is harvested from the plate by stopping the flow of liquid refrigerant and introducing hot ammonia gas into the top of the coil. The hot gas allows the ice to release from the coil unit in sheet form. According to Tranter, the concept applied in the gold mine system also can be used as a falling-film cooler for low temperature liquid chilling.

For more information, call (940) 723-7125 or visit www.tranterphe.com.