Column Sequencing

The sequencing and arrangement of columns to obtain multiple products has a major impact on energy and capital costs. In order to separate X amount of products, a minimum of X — 1 simple, conventional columns are required. If the products are removed as distillates, the arrangement is called a direct sequence. The direct sequence is favoured when the distillations are at high pressure and require refrigeration, such as olefin production. An indirect sequence is used if the products are withdrawn as bottoms. Indirect sequencing favours lower heat consumption. In many petrochemical plant configurations, both sequences are used or mixed as dictated by the many product requirements. An illustration of the direct and indirect sequence arrangement is given in Figures 9 and 10.

A number of heuristics have evolved from experience of sequencing columns. A few of the more common guidelines are listed below:

1. Leave the most difficult separations to the end. The binary separation of high purity products requires larger towers and higher energy consumption when non-key components are present.

2. Direct sequences are favoured when heating costs are less than cooling costs.

3. Less energy is expended when the top and bottom product flows are about equal.

The column sequencing depends upon numerous factors that make each case different. Refining, ethy-lene, aromatic and specialty chemical plants all have unique properties and idiosyncrasies that make generalizations difficult. The column arrangements

Figure 10 Indirect column sequence.

are commonly integrated with the total plant optimization to minimize overall capital costs, energy consumption and pollution reduction. Techniques such as pinch technology and exergy analysis are used to evaluate the global effect of equipment changes to arrive at the best plant design, which may not coincide with the best column design.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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