Temperature high, equipment safety

Accidents. In an industry that has massive equipment, high temperature operations, and many moving objects, the potential for accidents is always present. Safety is taken seriously and is the direct responsibiUty of the plant superintendent. Accidents do occur, although in the United States the rate in the steel industry compares favorably with heavy industry as a whole. 

At the low-pressure side of the reducing valve it is usually essential to fit a relief or safety valve. If any of the steam-using equipment connected to the low-pressure range is designed to withstand a pressure below that of the upstream steam supply, then a safety valve is mandatory. Further, it may be called for when it is sought to protect material in process from over-high temperatures (Figure 22.9). 

A safety trip can be incorporated in a control loop as shown in Figure 5.24a. In this system the high-temperature alarm operates a solenoid valve, releasing the air on the pneumatic activator, closing the valve on high temperature. However, the safe operation of such a system will be dependent on the reliability of the control equipment, and for potentially hazardous situations it is better practice to specify a separate trip system such as that shown in Figure 5.24b. Provision must be made for the periodic checking of the trip system to ensure that the system operates when needed. 

As mentioned in a CCPS Safety Alert (CCPS 2001a), chemical reactivity is a highly desirable trait that permits numerous useful materials to be synthesized. It also allows products to be made under relatively moderate conditions of pressure and temperature, saving energy and reducing the physical risks of high-temperature or high-pressure equipment. However, the same properties that make chemical reactivity so useful also pose hazards... 

Normal safety precautions for laboratory work and for the use of electrical equipment, especially variable temperature accessories, must be observed. The thermal analysis experiment involves high temperatures and there is a danger of being burned. Consult instrument operating manual for specific cautions regarding operation. 

Unattended operations must be planned with automatic safety switches that prevent serious damage (fire, flooding, explosion) in case of accidental equipment failure or interruption of utility services such as electricity, water, or gas supplies. Of special concern are the constant flow of cooling water and the operation of high-temperature baths. In the case of water flow, a device should be installed in the water line to (1) automatically regulate the water pressure (so as to avoid surges that might disconnect or rupture a water hose), and (2) automatically turn off electrical connections and water-supply valves in case of a total loss of water supply. In the case of hot thermostat baths or ovens, a sensor/control device should be installed that automatically turns off the electrical power to all heaters if the temperature exceeds some preset upper limit. 

Solvent Fractionation. This process is the most expensive because of solvent loss, solvent recovery equipment, much lower temperature requirement, and stringent safety features. The process involves the use of solvents such as hexane or acetone. The oil is first dissolved in the solvent followed by cooling to the desired temperatures to obtain the desired crystals. Cooling is effected by brine if very low temperature is required. The miscella containing the partially crystallized oil and solvent is then filtered under vacuum suction in an enclosed drum filter. The olein miscella and stearin miscella are then separately distilled to remove the solvent and recover the fractions. Yield of olein is about 80%. The solvent process nowadays is only viable in the production of high value products such as cocoa butter equivalent or other specialty fats. 

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