Storage tanks for raw material and intermediates are often much larger than really necessary, usually because this makes it “easier” to operate the plant. The operating staff can pay less attention to ordering raw materials on time, or can accept downtime in a downstream processing unit, because upstream production can be kept in storage until the downstream unit is back on line. This convenience in operation can come at a significant cost in risk of loss of containment of the hazardous materials being stored. The process design engineers must question the need for all intermediate hazardous material storage, and minimize quantities where such storage is really needed. SimilarIy, hazardous raw material storage should also be minimized, with greater attention being given to “just in time” supply. Inventory reduction can also result in lower inventory costs, as well as increasing the inherent safety of the manufacturing facility.
The reduction in inventory resulting from greater attention to plant operations and design of unit interactions can be extremely large. Wade gives several excellent examples:
• An acrylonitrile plant eliminated 500,000 pounds (-277,000 kg) of inprocess storage of hydrogen cyanide by accepting a shutdown of the entire unit when the product purification area shut down. This applied pressure to the plant to solve the problems that caused shutdown of the purification area.
• Another acrylonitrile plant supplied by-product hydrogen cyanide to various other units. An inventory of 350,000 pounds (-159,000 kg) of hydrogen cyanide was eliminated by having the other units draw directly from the acrylonitrile plant. This required considerable work to resolve many issues related to acrylonitrile purity and unit scheduling.
• A central bulk chlorine system with large storage tanks and extensive piping was replaced with a number of small cylinder facilities local to the individual chlorine users. Total inventory of chlorine was reduced by over 100,000 pounds (~45,360 kg).