Mixing multipurpose plants

There are three basic types of plants for the manufacture of fine chemicals dedicated plants, multiproduct and multipurpose plants, and mixed plants. 

A problem associated especially with multipurpose plants is the possible entry into an operating system of emical materials that are extraneous to the process in operation. For example, a solvent or raw material may be awaiting transfer to later use in another process in the same equipment. If incompatible with any of the materials used or produced in the process on line, the reserved solvent/raw material is a potential hazard unless positive steps are taken to exclude it from the ongoing process. Accidental intermingling is a two-way hazard. It is equally possible that a substance can leak from the process into the extraneous solvent/raw material. Inadvertent mixing can also cause difficulties in maintaining product quality and can present extra hazards to customers. 

Mixed plants are plants which are individually covered under more than one Part of the Verification Annex related to Article VI. The term covers, for example, a multipurpose plant that manufactures, in the same process line but at different points in time or parallel in several process lines. Schedule 2 and Schedule 3 chemicals (and/or DOCs). However, the term does not relate either to a case where a plant produces a Schedule 3 chemical in a multiple-step reaction involving the production of a DOC in the initial steps, or to a case when, during the production of a Schedule 3 chemical, a low concentration of a Schedule 2 chemical is simultaneously produced (this would be classified as either a Schedule 3 or a Schedule 2 plant depending on the applicable rules for low concentrations). 

A non-periodic plant operating mode defined over a given time horizon is considered. Mixed storage policies, shared intermediated states, material recycles and multipurpose batch plant equipment units with continuous sizes, are allowed. 

One of the greatest threats to peat bogs is gardening, as most bagged multipurpose potting mix is peat-based. Peat has become a mainstay of these soils because it is consistent, sterile and low in nutrients. But when peat becomes waterlogged it forms a solid mass that plant roots find hard to penetrate, and it has no benefit as a soil conditioner or a mulch. In recent years, non-peat soils, based on coir, composted wood, bark and green waste and other natural materials, have become widely available. 

Independent of the nature of the plant, either multiproduct or multipurpose, the most-used mathematical approaches are MILP (Mixed-Integer Linear Programming) or MINLP (Mixed-Integer Non-Linear Programming). The predominant objective function is based on an economic criterion. 

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