Process hazards High Pressure

Examine all process parameters. Parameters (e.g., pressure, temperature, flow rate, level, pH) that are controlled or measured in a process are good indicators of possible process hazards. Process parameters should be examined for all modes of operation, independent of process chemicals, because some hazards exist that do not involve the chemicals. For example, if a process uses high-pressure steam, then both thermal energy and pressure-volume energy hazards exist even though steam is non-toxic, non-flammable, and non-reactive with most materials. 

Close proximity of hazardous process. High pressure vessels which may fail explosively. 

As discussed in Chapter 2, The Toller Selection Process, evaluating the site s safe work practice procedures should have been a part of the review during the toller selection process. Still, new materials may indicate a need to revise or develop special procedures to address unique chemical and physical hazards. New hazards such as vacuum, ciyogenics, ultra-high pressure, or new rotating equipment could be introduced. Medical monitoring requirements or special handling and spill response procedures for the toll s raw materials and products may indicate a need to write or revise safe work practices. 

Polymerization Exothermic reaction which, unless carefully controlled, can run-away and create a thermal explosion or vessel overpressurization Refer to Table 7.20 for common monomers Certain processes require polymerization of feedstock at high pressure, with associated hazards Many vinyl monomers (e.g. vinyl chloride, acrylonitrile) pose a chronic toxicity hazard Refer to Table 7.19 for basic precautions... 

Unfortunately, many times it is not clear which of several process alternatives is inherently safer. Because nearly all chemical processes have a number of hazards associated with them, an alternative which reduces one hazard may increase a different hazard. For example, process A uses flammable materials of low toxicity process B uses noncombustible materials, which are volatile and moderately toxic, and process C uses noncombustible and nontoxic materials but operates at high pressure. Which process is inherently safer The answer to this question will depend on the specific details of the... 

Certain processes require polymerization of feedstock at high pressure, with associated hazards... 

METLCAP is a chemical cement that encapsulates, stabilizes, and solidifies hazardous heavy metals in solid form, in slurry form, or in solution. The cement is composed of magnesium oxychloride, which forms when magnesium chloride and magnesium oxide, with water, are mixed together with the metals. The hardened cement product is insoluble and itself becomes a usable resource as cement or as fill material. The METLCAP technology is applicable as an in sitn or ex situ treatment or for high-pressure injection grouting and construction of slnrry walls. Currently, the process is patented and commercially available from Stark Encapsulation, Inc. 

The Texaco gasification process (TGP) is a patented ex situ commercial technology for the treatment of hazardous and nonhazardous liquid or solid waste. The high-temperature, high-pressure. 

Under laboratory conditions, carbon dioxide in its supercritical state allows the separation of unstable compounds from the matrix. It is also used in industrial processes to extract certain food products (for example, decaffeination, recovery of aromas and spices, elimination of fats). Carbon dioxide has the advantage that it can be eliminated at rather low temperatures without leaving any toxic residue. However, the use of relatively high pressures creates potential hazards in industrial installations. 

The major hazard that can occur in the high-pressure polyethylene process is a runaway of the reactor and decomposition of ethylene as well as fires, explosion, and disintegration of high-pressure parts. Although the last incidents are well understood, the reasons for runaway and ethylene decomposition have been evaluated only recently. Experience over twenty years has shown that decomposition mostly takes place in the reactor and in the high-pressure separator, but decompositions have also been reported from ethylene-feed and product lines. 

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