Inventory control general considerations

SITE-SPECIFIC ANALYSES OF MAJOR SECONDARY WASTE ISSUES Overview of Secondary Waste Inventories, 36 General Waste Characterization Considerations, 37 Waste Control Limits and Vapor Screening Level, 37 Site-Specific Characterization According to Permit Requirements, 39 Analysis of Waste Categorization Situation Across Sites, 42 Spent Activated Carbon Waste, 45... 

Where custody transfer or assessment of taxes, duties, or royalties are involved, the gauging instruments and inventory control system are required to be officially approved and certified for this pmpose. In countries where such legal certification does not yet apply, verification of the measimements is often carried out by surveying companies. They generally use dip tapes, portable thermometers and sampling cans to measime level, temperature, and density prior to and after the product transfers. This is labor intensive and requires considerable time. 

Then, product quality control loops are closed on each of the individual units. These loops typically use fast PI controllers to hold product streams as close as possible to specification values. Since these loops are considerably faster than the slow inventory loops, interaction between the two is generally not a probleia Also, since the manipulated variables used to hold product qualities are often streams that are internal to each individual unit, changes in these manipulated variables have little effect on the downstream process. The manipulated variables frequently are utility streams that are provided by the plant utility system, i.e. cooling water, steam, refrigerant, etc. Thus, the boiler house will be disturbed, but the other process units in the plant will not see disturbances coming from upstream process units. Of course, this is only tme when the plant utilities systems have effective control systems that can respond quickly to the many disturbances that they see coming in from units all over the plant. 

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