L Xv M Tl

in which:


Figure 5 Schematic of a stage of a distillation column.

For the column bottom level it can then be written that:

where tl is the tray hydraulic time constant. Neighbouring trays will have similar parameter values, hence the term XSV is the same everywhere, and therefore initially all changes in liquid flows will remain the same. The mass balance on each tray will where KB is the gain of the bottom level in response to vapour flow changes.

From eqn [8] it can be seen that an inverse response can exist, as long as X is not equal to zero. The magnitude of the inverse response depends on the magnitude of X. For some columns negative values of X have been found; for others X is positive. It can be shown that bottom-level control on the steam (vapour flow) is strongly delayed by the effect of X when X > 0.5. The physical interpretation of the so-called X-effect is that with large tray loads, an increase in vapour flow will lead to stagnation of the liquid flow and consequently X will be larger than 1. With small tray loads an increase in vapour flow will push more liquid off the tray, thus a larger liquid flow to the lower bottom will result. Figure 6 summarizes all options for control.

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.

Get My Free Ebook

Post a comment