Multiproduct equipment

Where multiproduct plants are produced using the same processing equipment. 

The typical factors to consider when pondering B2C will include size and scale of operation, use of existing equipment, flexibility for multiproduct operation, start-up and shutdown, cleaning frequency, inventory, validation, traceability of product with respect to raw materials, equipment design, and availability as well as operational experience [50]. 

Plants for the manufacture of fine chemicals are discussed in Chapter 7 with emphasis put on multiproduct plants. Types of production plants and typical equipment for multiproduct plants with cost considerations are presented in more detail. Problems of designing and scheduling multiproduct and multipurpose plants with particular emphasis given on process data needed to realise this task are discussed. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

Combining equations (7.4-24)-(7.4-26) gives a system of non-linear equations that can be solved using iterative techniques. Savings in equipment costs as compared to initial guesses are approximately 30 %. The real savings will be lower because the optimal choices for equipment units are usually not available on the chemical equipment market. The standard sizes greater but nearest to the optimal sizes will be selected. The total cost for the standard equipment is very close to the minimum found. Robinson and Loonkar (1972) extended their procedure for multiproduct batch plants. 

A major problem to be solved for multiproduct plants is the occurrence of disparities in the cycle times and size requirements for the different stages. In the following it will be assumed that the size factors as well as the cycle times of all units are independent on equipment size. This assumption is usually relaxed in further stages of the design. In case of batch heating and cooling, or reactors operated in semi-continuous mode, this is necessary in order to adopt the cycle times to the capacity of equipment, which is related to batch size. 

Figure 7.4-10. Equipment. sizing (multiproduct plant, non-overlapping campaigns). 

So far plants have been considered involving a single product. However, batch processes often produce multiple products in the same equipment. Here two broad types of process can be distinguished. In flowshop or multiproduct plants, all products produced require all steps in the process and follow the same sequence of operations. In jobshop or multipurpose processes, not all products require all steps and/or might follow a different sequence of steps9. 

Production schedules for batch processes can be sequential, overlapping, parallel, use intermediate storage, or use a combination of these. Such schedules can be analyzed using Gantt charts. Batch processes often produce multiple products in the same equipment and can be distinguished as flowshop or multiproduct plants. Equipment cleaning and material transfer policy have a significant effect on the production schedule. 

When a multiproduct plant is constructed, the amount of each product to be made each year must be included in the scope. This is called the product mix. It is important because the product mix determines the size of much of the equipment. One resin may require a reaction cycle of three hours, while another takes six hours. If the majority of the product is the former resin, a smaller reactor is required than if the majority were the latter. 

Digital computers, however, can do some things the analog equipment cannot. They offer the opportunity of using more advanced control concepts. These are not necessary for 90% of the processes, but they can increase production and reduce waste for some hard-to-manage processes. For multiproduct plants, direct digital... 

Most multiproduct batch plants have more than one piece of equipment of each type. Routing refers to determining the specific pieces of equipment that will be used to manufacture each run on the long-term... 

The interaction between the batch and the continuous parts of the plant is a major concern of plant design and operating procedures. When the production volume reaches certain levels, continuous operation may be more economical. More often, batch chemical plants are built to produce more than one product. The objective is the use of existing equipment, which becomes idle when market demands are fulfilled. These plants can be classed in one of two broad categories multiproduct and multipurpose. The difference between the two types is illustrated in Fig. 1. 

In a multiproduct plant, all products follow nearly the same path through the process. Only one product, or in a complex case a few products, is produced at one time. Although it is feasible to alternate batches of different products to reduce idle time of equipment, this is rarely, if ever, done to minimize operational error and cross-contamination. Product changeovers are not frequent, especially if extensive cleanout between changeovers is required. 

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