(215c) Equipment Design for Reboilers and Evaporators

Reboilers and evaporators represent a very relevant group of equipment in almost all fluid separation processes such as distillation, absorption, rectification etc.. In process as well as equipment design they deserve special attention as their proper design affects investment as well as operating costs of the process. For thermally and/or mechanically sensitive products they may also be a source for potential product damage. This is enforced by the aim to reduce the ?Time to market? for a new product significantly so that design decisions have to be made at very early process development phases.

This contribution presents a methodology for evaporator and reboiler design in the context of Conceptual Process Design. Equipment design is considered as a three stage process: the choice of the type of evaporation mechanisms guides the selection of the respective type of evaporator or reboiler. This is followed by the configuration of the apparatus with respect to all relevant functional elements. Finally the equipment is sized for the process conditions, desired capacity and capacity range. Equipment design builds on consistent mass and energy balances as obtained from a flowsheet simulation, e.g., plus the quantification of the process functionality. For reboilers this is typically quantified in terms of a heat flux while for evaporators the residual concentration of a light boiling component in an effluent stream might be the design-relevant criterion. We will choose the apparatus that provides the most economic solution to the process task under the given conditions.

The presentation will cover the most frequent types of reboiler and evaporators, i. e. thermosiphon reboiler, short-tube Robert-type reboiler, forced circulation reboiler, forced circulation flash reboiler, falling film evaporator, wiped film evaporators as well as short path evaporators. All equipment types with a sufficient match of equipment-related property profile with the process-related requirements profile will be considered suitable. All dimensions for this match are related to the process, such as temperature, pressure, capacity, capacity range, corrosivity etc., or to the treated product, e.g. viscosity, solid content, thermal and/or mechanical sensitivity.

In a first step all feasible equipment types are identified. These are configurated in a second step. This comprises the selection of the type of heat transfer surface, tubes vs. plates, or the type of liquid distributor system for falling film evaporators. This is followed by a shortcut sizing of the equipment as basis for a first estimation of investment as well as operating costs. As this procedure should be integrated into a modular process design and engineering concept, design boundaries include the column sump of a rectification column as well as the flash drum of an evaporation section. The concept is elaborated for selected cases.

A systemized and simulation-supported process for equipment design may contribute significantly to an acceleration as well as quality-assured process development and optimization. The definition of functional elements, their rapid identification and integration into an overall process concept are elementary preconditions. Additionally, a full view of typical process requirements and equipment properties will give hints for future research and development activities to broaden operating ranges, for increased energy efficiency or a higher economic competitiveness of specific reboiler types as well as the process as a whole.