Predesign for Pollution Prevention and Control

CEP June 2007 www.aiche.org/cep 53 During the past few decades, pollution prevention and control has assumed a prominent role in the chemical engineering profession. Its study has become part of chemical engineering curricula throughout the world, and a new section on waste treatment has been added to “Perry’s Chemical Engineers’ Handbook.” The major responsibility for an operating plant’s cleanliness falls on its operators, final designers, contractors and maintenance personnel, but its inherent cleanliness is defined before construction. Preliminary designers don’t have the time or budget to fully scope a waste system and secure permits, but they can radically improve process cleanliness by devising ways to recycle or reuse streams and minimize or eliminate end-of-pipe remedies. The three types of emissions are fugitive, native and engineered emissions. Fugitive emissions (1) are the difficult-to-find, -control or -capture leaks from pipe joints, storage tank vents, and static or rotating seals. They include leaking gases, dripping lubricants and evaporating solvents. Final designers and contractors are charged with preventing their escape. Operators and maintenance people are responsible for finding and eliminating them. Preliminary designers can do little to prevent fugitive emissions other than to specify materials and equipment that will contain process streams responsibly. Native emissions are discharges from equipment such as furnaces, cooling towers and other devices that burn fuels or generate a utility stream. Process designers must usually accept whatever emissions are defined by available fuels and prevailing technology. A predesigner’s major concern is engineered emissions — that is, those from process vessels, reactors and separators, where engineering can influence the nature and quantity of effluent streams. The aim of this article is to help budding process analysts reduce or eliminate engineered emissions in projects that they influence.