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8.4 Maintenance and Emergency Procedures
Proper equipment maintenance is vital for ensuring that unforeseen stoppages in production are minimized. The process simulation assumes that the plant is operational at full
capacity for 330 days a year to account for routine maintenance. Should any equipment fail unexpectedly, the profitability of the plant will be dramatically affected by halting revenues
while expensive equipment and labor remain idle. Avoiding this requires a mixture of corrective and preventative maintenance, as well as careful condition-based maintenance procedures, as
outlined by WIPRO Technologies.
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The reactor walls should be periodically inspected for signs of corrosion or heat damage. The catalyst packing must also be inspected regularly, and may
need to be regenerated if the active surface area decreases. It is estimated that the catalyst life will be approximately 2 years. Pumps and compressors should be closely monitored for signs of
performance losses and physical damage. The cost of back-ups for all liquid pumps used in this process are included in the economic analysis should any of the pumps fail unexpectedly. The
distillation columns, along with all associated reboilers, condensers, pumps, and trays, should be monitored for signs of wear and reduced performance. Operators must check the integrity of all
piping to avoid leaks and blockages, and the piping systems may need to be flushed with inert periodically to prevent build-up.
In the event of an emergency, the process contains control valves that can be closed to prevent the flow of feed to the reactor, product to various stages of the separation process, or
recycle gases to the feed mixture. In addition, the power can be cut to all of the compressors and pumps to halt the process. Should the reactor near the auto-ignition temperatures discussed in
Safety and Health Considerations , operators should seek refuge outside and away from the
concrete reactor containment unit. Proper fire extinguishers, flame retardant materials, and safety procedures should be implemented according to all building and industrial codes.
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Padmanabhan, H. Condition Based Maintenance Of Rotating Equipments on OSI PI Platform - RefineriesPetrochem Plants: Wipro Council for Industry Research.
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8.5 Process Safety and Health Concerns
This process involves the selective oxidation of a gaseous hydrocarbon, meaning that the primary safety concern is the possibility for explosion. As a result, great care has been taken to
ensure that all streams in the process are safely outside the flammability limits of propane. The process is controlled primarily by running under an excess of propane, making oxygen the
limiting reagent. The stream feeding the reactor contains the most oxygen in the process aside from the pure oxygen feed, and is 21.8 propane and only 4.6 oxygen, with the majority of
the stream being inert nitrogen at 61.6. The Upper Flammability Limit UFL of propane is 10.1 in air and 55 in pure oxygen. All streams are thus too oxygen-poor to allow combustion
to occur. It should be noted that all three mixers in the process M-101, M-102, and M-103 should be carefully monitored and isolated from all flames and sparks, as their contents may pass
through the flammable regime as they mix recycled propane with air and pure oxygen feeds. Another safety concern is the presence of high temperatures during the process. The
optimal reaction temperature is 750°F, and the reactor outlet temperature could rise as high as 780°F even with cooling with molten salts. This is still well under the auto-ignition temperature
of propane and propylene 878°F and 858°F, respectively. In the unlikely event that the reactor temperature begins to approach these values, a control valve upstream from the reactor V-101
could be closed to stop the flow of feed so that the reactor may cool. Still, it is recommended that a concrete shell be erected over the reactor in order to keep operators safe in the event of a fire or
explosion. Care must be taken to ensure propane does not leak from the reactor into this shell, where it may form a combustible mixture. The Occupational Safety and Health Administration
recommends using Detector Tubes manufactured by AUERMSA or Drager in order to detect concentrations greater than 200 ppm of propane in the air.
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The process also involves storage of liquefied propane and acrylic acid to account for changes in supply of propane from the pipeline and demand for acrylic acid. It is recommended
that the propane storage tank be stored in a pressure vessel so as to prevent explosive vapor from forming. In addition, the propane storage tank must be isolated from all sparks and flames, and
operators must be careful to check for leaks using the methods described above. The acrylic acid storage tank can be designed as a fixed cone roof because acrylic acid will have a relatively low
vapor pressure at storage conditions.
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U.S. Department of Labor. Propane. http:www.osha.govdtschemicalsamplingdataCH_264000.html
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