Rising film evaporator technology is also referred to as Long Tube Vertical (LTV) technology. This technology has historically been used for kraft pulp mill multiple effect evaporation systems. The process utilizes the change in buoyancy of the liquor upon heating and evaporation to drive the liquor through the tubes. A typical body has a vertical tube bundle with a vapor head mounted on top of it with internal chevron type separators.

There are several advantages of LTV technology. First is the simplicity of the system; there are no recirculation pumps and the instrumentation is limited.

No recirculation pumps result faster system start up, lower operating costs and lower tendency to foam in the weak liquor effects. The simplicity of the system also results in low installed capital cost.

A disadvantage of the LTV technology is that in heavy liquor effects it is more prone to fouling than other technologies available. Also, an LTV requires a minimum temperature differential between the shell side vapor and the tube side liquor for the body to boil. As a result, there is a maximum number of effects that can be installed given a specified overall temperature difference from the first effect to the last effect. The minimum temperature differential required also leads to a loss in stability upon turndown.

The Lundberg Associates LTV technology incorporates several features to improve the performance of the body. Most larger bodies are supplied with external vapor bustles to efficiently distribute the vapor across the tube bundle. The tube bundle is longitudinally baffled to make two passes on the shell side and facilitate positive NCG flow. This baffle is open near the bottom tube sheet to permit gas to flow from one side to another. For condensate segregation an opposing dam is installed on the bottom tube sheet.

In the vapor head, we utilize chevron type separators either vertical or horizontal flow. The liquor deflector mounted above the upper tube sheet is two stage in the high vacuum effects. This increases the release area and minimizes the carry over of liquor into the vapor.