|
Packed And Bubble Cap Column
Packed Column
Designing a randomly packed column is a subtle blend of art and science. Packed columns are most frequently used to remove contaminants from a gas stream (absorption). However, packed columns can also be used to remove volatile components from a liquid stream by contacting it with an inert gas (stripping). They are also used in distillation applications where the separation is particularly difficult due to close boiling components. While we'll discuss all of these applications, we'll focus on absorption. However, the design methods are similar for any of the scenarios.
The first step in designing a packed tower is more science than art. The equilibrium data between the contaminant and the solvent (or the distillation components) is needed for the analysis. If tabulated data for your system is unavailable and the total amount of the contaminant is small (as it usually will be), Raoult's Law can be used to estimate the equilibrium data for absorption or stripping applications. For distillation, equilibrium data can be predicted by selecting the appropriate thermodynamic model. The operating line for the tower is constructed differently depending on whether you're dealing with distillation or absorption/stripping. Since we're focusing on absorption, we'll use it as an example. In absorption/stripping, the operating line is constructed differently depending on whether the contaminated stream can be considered "dilute" or if it must be treated as a concentrated stream. Usually, it is safe to treat the stream as dilute if the contaminant makes up less than 10 mole percent of the stream. For streams that cannot be considered dilute, the mass transfer coefficients must be evaluated in terms of the gas and liquid flows. Then, graphical evaluation of several integral relationships must be completed. This type of evaluation is outside the scope of this article and a text should be consulted for solving these types of problems. For this article, we will consider dilute streams which are more common for packed tower absorption and stripping.
Bubble-Cap Column
In a bubble-cap column for the distillation of high sediment or clogging liquids including a plurality of apertured plates arranged in spaced vertical relationship, each plate having a plurality of bubble-cap structures arranged in rows thereon and each comprising a bubble-cap overlying a neck portion extending through an aperture in said plate, the improvement wherein said bubble-cap structure are readily detachable from said plates and are removable through hatches provided in said column, the inner surfaces of said bubble-cap and said inner and outer surfaces of said neck portion being coated with an organic fluorine compound to which agglomerating sediments do not readily adhere.
A bubble-cap column according to claim 1 in which said bubble-caps in each row are mounted on an elongate carrier for cojoint removal of said bubble-caps from said column.
|
