Page 125 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

When a campaign for a product is running, the rate of production is greater than the demand rate. When the
campaign has stopped, the demand rate is greater than the production rate of zero. Therefore, the
accumulation and depletion of product over the monthly period are similar to those shown in Figure 3.6.
The changing inventory of material is represented on this figure by the bottom diagram. The maximum
inventory, V , is the minimum storage capacity that is required for the product using this single-product
s
campaign strategy. The expression for calculating V is
s

(3.7)

Figure 3.6 Changing Inventory of Product during Single-Product Campaign Run within a Multiproduct
Process

where t camp is the campaign time. This assumes that the shipping rate of product from the plant is constant
during plant operating hours. Because shipping is usually itself a batch process, the actual minimum

storage capacity could be more or less than that calculated in Equation (3.7). The strategies for matching
shipping schedules to minimize cost (including storage costs and missed-delivery risks) are known as
logistics and are not covered here.

Determination of the minimum storage capacities for all products in Example 3.3 is given in Example 3.7.