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1 Introduction
Pre-batching activities in some process industries like the fine chemicals-, pharmaceuticals-, food-, and beverages and juice industry may be responsible for frequent delays in production, because of late arrival of raw materials, or inability to handle the workload. Pre-batching involves preparing batches for various production areas by putting ingredients that are not stored at the production area per batch in the right quantities on a pallet. This staging process is important in above mentioned process industries. Efficient pre-batching results in increased consistency of product quality and reduced cost of production, because when the batch recipe is made, pours of ingredients and everything else needed is measured and precisely controlled prior to use in other production areas. This process is followed by picking and transporting the ingredients from the warehouse to the pre-batching production area (either manually or by forklift truck), and pouring the right quantities for each ingredient at the production area, followed by restoring the remaining quantities at the warehouse. Pre-batching also involves replenishment of stock levels of ingredients used on the production floor. Ingredients are typically stored in varying storage types with varying capacities.
The resulting business problem is to find out which ingredients have to be stored at the warehouse(s) and will be collected by the pre-batching department, and which ingredients have to be stored at the pre-batching production area. This area is comprised of storage areas, weighing areas, a mixing/blending (production) area, and a quality control area. Storage areas within pre-batching should be of sufficient capacity to allow orderly assignment of various categories of ingredients and materials, with proper separation and segregation due to the nature and packaging formats of materials. Increased demand variety, product improvements, change in raw material supplier, custom orders, and many other situations require frequent changes in the original storage space allocation and pre-batching activities. Yet, optimization solutions for the operation and improvement of storage allocation in this environment, with the aim to maximize total capacity utilization and increase responsiveness of pre-batching operations, are lacking.
In the last three decades, considerable developments in design and operations of different types of storage systems have taken place, and important models and review papers have appeared in the literature. [7] Hassini (2009), [11] Litvak and Vlasiou (2008) and...