Selection Of Tray Type
The three basic types of fractionation trays are the perforated (sieve), valve and bubble cap trays. In general, tray type selection is determined by evaluating various factors, such as process, cost, mechanical, installation and maintenance considerations. Some important areas of performance to be taken into account when selecting the type of tray are capacity, turndown, efficiency, pressure drop, tendencies toward fouling and scaling, corrosion and actual historical data from previous experience in the system.
A brief overview of the benefits or disadvantages of each of the three basic conventional tray types are mentioned below:
- Perforated trays are often used when a wide range of flexibility is not required and the lowest tray cost is desired. For very low liquid rate applications, perforated trays are not a good choice. Some instances that require extensive blanking of perforations could result in an ultimate cost greater than valve trays.
- Valve trays which usually have a cost comparable to perforated trays, afford the widest operating range and greatest capacity. Considering the additional operating range and capacity of valve rays over perforated trays, it can be concluded that valve trays are actually lower in cost. In many applications, vapor loading controls capacity. In many cases, valve trays may have as much as ten percent more capacity than perforated trays. Trays with valves comprised of three pieces (fixed caged, valve plate and orifice cover) have proven to be very efficient for glycol dehydrators and other services with low liquid rates. In many cases these valve trays can effectively be utilized to replace bubble cap trays (which are considerably more expensive) for these low liquid rate services.
- Bubble cap trays provide the lowest capacity and the highest cost of the conventional trays, but they are the best choice for use when leakage must be minimized. Bubble cap trays also require additional installation time due to the need to gasket all of the tray joints to prevent leakage.
Some less conventional trays such as dualflow, side-to-side and disc and donut trays are advantageous for special use where extremely high capacity, fouling and pressure drop are major considerations.
Mapesa has the technology and manufacturing capability to design and fabricate almost any type of conventional or specialty tray.