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Pollution Prevention and Control Technologies for Plating Operations
Section 3 - Chemical Recovery
3.3 VACUUM EVAPORATORS
3.3.2 Development and Commercialization
Evaporation has been used for centuries for food and beverage processing. Modern vacuum evaporator design for industrial use dates back to the early 1900's with the development of the rising film evaporator. Plating applications for vacuum evaporators began in approximately 1949, when systems were used to recover chromic acid (ref. 300). The early plating applications were purchased primarily to reduce operating costs through chemical conservation. Subsequently, evaporation was sporadically implemented as a pollution control method in response to local discharge standards. In some cases, this was a sufficient method of meeting the local standards for targeted pollutants such as cyanide and chromium. The early evaporators used for plating applications were the same types of units used by other industry segments (e.g., chemical processing, dairy, food and beverage industries). These units had large capacities, due in part because water conservation and pollution control were less important at the time, resulting in higher flow rates. Also, energy was much less expensive. In 1974, with the advent of rapidly rising energy costs, there began a movement to down-size recovery systems. Coupled with the Federal pollution control standards, first promulgated in 1979, plating shops turned to smaller and more energy efficient vacuum evaporators and the less expensive atmospheric evaporators for chemical recovery. Energy efficiency was achieved by the employment of multi-effect vacuum units and mechanical vapor compression. During the 1980's and early 1990's firms have sought methods of low or zero effluent discharge to reduce their regulatory requirements. As a result, the newer energy efficient vacuum evaporators were applied as end-of-pipe technologies (ref. 300, 375).
There are approximately 25 companies that manufacture and/or supply evaporative recovery equipment applicable to the plating industry. This includes vacuum and atmospheric evaporators for both chemical recovery and waste concentration (ref. 421). Of these companies, three firms have responded to the vendors survey (LICON, Inc., Calfran Int., and QPS Inc.).