Continuous and batch processes

If a batch process manufactures only a single product, then the equipment can be designed and optimized for 

One of the major problems with batch processing is batch-to-batch conformity. Minor changes to the operation can mean slight changes in the product from batch to batch. Fine and specialty chemicals are usually manufactured in batch processes. Yet, these products often have very tight tolerances for impurities in the final product and demand batch-to-batch variation being minimized. 

Batch processes will be considered in more detail in Chapter 14. 

Continuous processes are designed to operate 24 hours a day, 7 days a week, throughout the year. Some down time will be allowed for maintenance and, for some processes, catalyst regeneration. The plant attainment that is, the percentage of the available hours in a year that the plant operates, will usually be 90 to 95%. 

Batch processes are designed to operate intermittently. Some, or all, the process units being frequently shut down and started up. 

Continuous processes will usually be more economical for large scale production. Batch processes are used where some flexibility is wanted in production rate or product specification. 

The choice between batch or continuous operation will not be clear cut, but the following rules can be used as a guide. 

The design work required in the engineering of a chemical manufacturing process can be divided into two broad phases. 

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Exhibit 6.2. Human Errors in Continuous and Batch Processes... 

Both continuous and batch process operations can be used. Batch processes are generally preferred for small-scale and specialty chemicals production. 

Cost reductions usually arise out of improvements to the process control for both continuous and batch processes. Process analyzers enable chemical composition to be monitored essentially in real time. This in turn allows control of the process to be improved by shortening start-up and transition times (for continuous processes) or batch cycle times (for batch processes). This is accomplished by improving the ability to respond to process disturbances, by enabling process oscillations to be detected and corrected, and by reducing product variability. Real-time monitoring of chemical composition in a process allows a manufacturing plant to ... 

For purposes of this chapter, model-predictive control can be discussed in the context of continuous and batch process applications. The former constitutes traditional applications the latter describes processes such as autoclave curing. We will discuss the former first, to put the latter into context. 

Taschler S J. Urban, Evaluation and Comparison of TNT Produced by Continuous and Batch Processes , PATR 4159 (1971) (Limited distrib) 8) E. Thomas, The ROF TNT Process , Joint US/UK Seminar on TNT Chemistry and Manufacture, Waltham Abbey, Engl (1971) (Limited distrib) 9) W.T. Bolleter, TNT Process Characterization Studies , Ibid (1971) 10) Anon, Rept ERDE-TR-106, Ibid (1972) (Limited distrib) 11) A. Lonnfors B. Jansson, ChemEngWorld VII (2), 33 (1972)... 

The use of ruthenium or ruthenium-based catalysts in the production of polyhydric alcohols by hydrogenation of aldoses or by simultaneous hydrolysis and hydrogenation of polysaccharides has been the subject of a considerable body of investigations.20,27 Ru-C was used in the hydrogenation of dextrose to sorbitol in both continuous and batch processing at elevated temperatures (100-180°C) and hydrogen... 

Nonsilicate peroxide bleach bath stabilizer. Effective in both continuous and batch processes, PEROWHITE TW allows bruise-free, full bleached fabric without characteristic silicate buildups. 

The same authors [6SbI also reported the difference between the quantity of bolli products MPDM and HNBB in continuous and batch processes of tiic niaitufaclure of TNT. 

Chemical and process engineering today is concerned with the understanding and development of systematic procedures for the design and optimal operation of chemical and process systems, ranging from micro-systems to industrial scale continuous and batch processes ( Mah, 1990 Thome, 1993 Savkovic-Stevanovic, 1995). 

Integrate tasks that is, combine operations into unit processes and decide between continuous and batch processing... 

Figure 12.1 Continuous and batch processes (a) continuous process (b) batch process (c) fed-batch process (d) batch-product removal process.

The analysis can be carried out for continuous and batch processes. It should address conceivably safety-relevant situations of the plant, in particular start-up... 

Chapter 11 deals with the application of these concq>ts to process calculations in large-scale vacuum and pressure filters used in continuous and batch processes, hi all the examples presented, the importance of the consideration of the fiill filter cycle is stressed. Along with the development of modem fitters capable of operating in thin-cake conditions, units are also included for the dewatering of cakes by gas displacement and squeezing. 

There are still many obstacles to overcome before the use of process modeling, simulation, and control reaches the potential that many think it holds. One of the most interesting possibilities is the development of systems capable of performing on-line optimization functions. Althou on-line plant optimization is still in the future, optimization of subprocesses is already a possibility. This is true for both continuous and batch processes, and there are now many examples of how process modeling and simulation have enabled process control strategy and design to move beyond strictly performance considerations. 

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