Optimizing Process Vacuum Condensers
Vacuum condensers play a critical role in supporting vacuum processing operations. Although they may appear similar to atmospheric units, vacuum condensers have their own special designs, considerations and installation needs. By adding vacuum condensers, precondensers and intercondensers (Figure l), system cost efficiency can be optimized. Vacuum condensing systems permit reclamation of high value product by use of a precondenser, or reduce operating costs with intercondensers.
A precondenser placed between the vacuum vessel and ejector system will recover valuable process vapors and reduce vapor load to an ejector system minimizing the system’s capital and operating costs. Similarly, an intercondenser positioned between ejector stages can condense motive steam and process vapors and reduce vapor load to downstream ejectors as well as lower capital and operating costs.
Vacuum condensers cannot be designed or considered as typical process heat exchangers. Doing so will result in less than optimal performance with increased utility and condensate treatment costs. For instance, internal geometry may not be modeled well by standard heat transfer software because condenser design is proprietary and varies from one manufacturer to another. Also, tubefield layout and baffling are often
unconventional and not suited for standard software. It is also vital to incorporate ejector operation into vacuum condenser design.
A number of primary CPI processes (ranging from glycerin manufacture to urea prilling) use vacuum condensers each requiring a special design that depends on the type of vacuum condenser needed. For example, in urea plants, the main vacuum condensers are outfitted with spray nozzles above the tube field for removal of solidified product buildup.
Vacuum condenser systems
The prevalent type of vacuum condensers are shell-and-tube. These look similar externally to conventional shell-and-tube heat exchangers; however, their internal geometry is notably different. The major components of a vacuum condenser (Figure 2) include:
·Tubes
·Tubesheet( s)
·Shell
·Support plates
·Baffles
·Channels or bonnets
The design and optimum operation of a vacuum condenser is application specific, and determined by its tube-field layout and flow baffling. These geometries strongly affect condensation efficiency and pressure drop minimization. Under sub-atmospheric conditions, the need to minimize pressure drop is the key design consideration. Pressure drop across a vacuum condenser reduces condensation efficiency or product recovery and, therefore, increases the operating cost of a vacuum system....