Chemical Processing - September 2007 - (Page 39)

century, their adverse environmental impacts were recognized and many CFCs have since been phased out. While CFCs are still inherently safer than many alternatives with respect to flammability and acute toxicity hazards, society has decided that the previously unknown hazard of adverse environmental impact is unacceptable and is willing to apply passive, active and procedural strategies to manage the hazards associated with replacement refrigerants. Such switches aren’t necessarily easy or straightforward. For a home refrigerator, it may not be a good idea to simply replace the CFC with another refrigerant — say, a light hydrocarbon. The quantity of light hydrocarbon (perhaps several kilograms), if it leaked, would be sufficient to create an explosive atmosphere in a room the size of a kitchen. Many “green” refrigerators feature a complete redesign to significantly reduce the amount of refrigerant to as little as a couple of hundred grams to minimize the fire and explosion hazard in case of a leak. This illustrates the importance of considering the design of a complete system when implementing ISD to ensure that all known hazards are adequately managed. Different groups may perceive the inherent safety of technology options differently. A plant using chlorine has a choice between getting it in 1-ton cylinders or 90-ton railroad tank cars. Neighbors several miles away from the plant would consider the 1-ton cylinders to be inherently safer because a leak from one of these containers probably wouldn’t affect them. But plant operators would have to connect and disconnect 90 cylinders instead of one tank car, and each time they are at risk from chlorine exposure. So, the operators would consider the railroad car to be inherently safer because it requires less handling. Of course, procedures, personal protective equipment and other safety-management systems can control the risk to the operator, but these aren’t inherent. Both the neighbors and the operators are correct in their perceptions of the ISD characteristics of the chlorine supply options but they’re concerned about different kinds of incidents. To make an intelligent choice, the designer should not only understand these conflicting requirements but also the potential role of all risk-management systems (inherent, passive, active and procedural). It also is important to consider whether an ISD option just transfers risk somewhere else. For instance, a plant might reduce its risk by decreasing the size of a hazardous material storage tank on the site and thus its WYSSMONT ® ’s TURBO-DRYER® vs. Vacuum Dryer Thermal Processor for solvent recovery and/or low temperature drying: • • • • • • • • reliable, virtually unattended operation less dusty, more uniform product no vacuum equipment or seals to maintain no filters that plug very low maintenance no balled product scale-up advantages, more accurate, less space continuous (usually) or batchwise Actual comments from users where a Wyssmont TURBO-Dryer replaced a vacuum dryer: • “You’d have to break the operator’s arm to get it away from him.” - process engineer - rubber chemicals manufacturer • “It’s the best piece of equipment in our plant.” - plant engineer - antioxidant plant • “Why didn’t we buy this last time?” - production superintendent, optical brighteners plant. ® www.chemicalprocessing.com September 2007 • 39 http://www.wyssmont.com http://www.wyssmont.com http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - September 2007

Contents From the Editor Field Notes In Process Energy Saver Compliance Advisor Succeed at Simulation Rethink Your Approach to Process Safety Avoid Blending Blunders Get the Right Cartridge or Bag Filter Wireless Proponents Take HART Membrane Boasts Material Benefits Process Puzzler Plant InSites Chem Show Product Preview ISA Product Preview Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - September 2007

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