Operation upset

Membrane Replacement Membrane replacement is a significant cost facdor, but membrane hfe and rehability are now reasonable. Membranes are more susceptible to operating upsets than more traditional equipment, but their field-reliability record in properly engineered, properly maintained installations is good to excellent. In N9 separations, membrane hfe is veiy long. 

In a fertilizer plant, the main source of potential air pollution is dusts and fiunes from spills, operating upsets, and dust emissions. It is essential that tight operating procedures be in place and that close attention be paid to constant cleanup of spills and to other housecleaning measures. 

A relief device must be installed on a vessel to protect against an operational upset. The relief must discharge 53,500 lb/hr of hydrocarbon vapor. The relief temperature is 167°F, and the set pressure is 75 psig. Assume an overpressure of 10% and a backpressure of 0 psig. The hydrocarbon vapor has a molecular weight of 65, a compressibility of 0.84, and a heat capacity ratio of 1.09. Determine the diameter of the relief. 

The advantage to this approach is that it provides a more complete identification of the hazards, including information on how hazards can develop as a result of operating procedures and operational upsets in the process. Companies that perform detailed HAZOPs studies find that their processes operate better and have less down time, that their product quality is improved, that less waste is produced, and that their employees are more confident in the safety of the process. The disadvantages are that the HAZOP approach is tedious to apply, requires considerable staff time, and can potentially identify hazards independent of the risk. 

Cryogenic temperatures can cause embrittlement of some materials of construction (eg., carbon steel) and must be considered in the design of inert gas delivery systems. Controls should be provided to ensure that operational upsets do not allow the migration of cryogenic liquids to piping or equipment not designed to withstand such low temperatures. 

Recommendation 3-6. A modified baseline process at Pueblo should include a four-zone (rather than three-zone) metal parts furnace with design provisions to ensure safe shutdown and restarting in the event of operational upsets, such as a loss of electrical power, combustion air supply, or exhaust gas capability. 

Minimizing material losses before, during and after an operational upset which caused the overpressure... 

Some of the more sophisticated techniques offer detailed information or levels of accuracy that are not required in day-to-day operations. However, when operational upsets cannot be handled by normal methods, details of the emulsion properties have to be understood. For example, subtle changes in the size distribution of the dispersed phase (while total oil, water, and solids remain constant) can be important in determining process performance. An oil-in-water or water-in-oil emulsion can invert during processing as one or the other phase is removed, and the point in the process when this inversion occurs can have implications for the efficiency of the operation. The addition of diluent to reduce oil-phase viscosity, for instance, is much more efficient if oil is the continuous phase. 

The detailed emulsion characterization methods discussed herein can be used to help resolve operational upsets only if a base line of data exists for normal operation. In fact, without a thorough characterization of the normal emulsion properties such as size distribution and mineral and organic composition, the techniques for detailed characterization may actually hinder the understanding and ultimate solution of a particular processing problem by introducing extraneous information. When a base line of data exists, detailed information on the size distribution and the relationship between the dispersed, continuous, and solid phases is invaluable. 

Eight of the Bahco scrubbers are located on oil-fired boilers in pulp mills. The boilers range in size from 50,000 to 375,000 Ibs/hr of steam and produce 10,000-145,000 ACFM of oflF-gas at about 340°-360°F. Each of these units operates with caustic soda as the scrubbing reagent. The units operate at a controlled pH of 6.5 which maximizes the production of sodium bisulfite and limits unwanted sulfate oxidation. The soluble bisulfite product is utilized in the pulping operation. Particulate and mist concentrations are held to about 0.02 grain/SCFW and SO levels are reduced by 97-99% from about 1500 to about 30 ppm. These units have operated continuously without any operational upsets. 

Mol sieves are routinely used for drying a number of reaction feeds to very low water levels. This is particularly important where expensive catalysts are susceptible to wet feed. Pervaporation has the advantage of continuous, steady operation, minimizing operational upsets, which can result from sieve regeneration. Simpler systems are especially attractive where toxic materials are involved. 

Most environmental problems stem from operational upsets. Indeed, if a facility is designed to meet the pertinent air and water quality standards then virtually aU environmental problems will result from improperly managed changes that lead to upset operating conditions. 

Most accidents and operating upsets involve some sort of human error. For example, Geyer et al. (1990) state that operator error is a direct cause of nearly a third of all pipework failures. (These errors consisted mostly of inadequately cleaning lines and incorrectly setting valves.)... 

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