(97d) Efficiency Comparison of Distillation Schemes: Heat Integrated Distillation Column (HIDiC) and Heat Pump Systems

Authors: 
Shenvi, A. A., Purdue University
Agrawal, R., Purdue University
Herron, D. M., Air Products and Chemicals, Inc.


Distillation is the most important separation unit operation in process industries. Conventionally, heat is supplied at a higher temperature in the reboiler and is rejected at a lower temperature in the condenser. If the heat rejected in the condenser is not utilized, then it generally leads to inefficiency. Increased emphasis on energy efficient processes has led to a renewed interest in intensifying this unit operation.

Intensification can be achieved by upgrading the heat rejected in the rectifying section and transferring it to the stripping section. There are various options available to achieve this objective. Heat integrated distillation column (HIDiC) scheme performs this transfer of heat from the rectifying section to the stripping section throughout the length of each section by operating the rectifying section at a higher pressure than the stripping section. Whereas, in a heat pump (direct vapor recompression) scheme, a one point heat transfer operation can be used wherein heat only from the top of the rectifying section is upgraded and is transferred to the bottom of the stripping section. Also, by using a heat pump system incorporated with one intermediate reboiler and/or one intermediate condenser, heat integration at a second point can be achieved. The advantage of these latter arrangements is that one does not need HIDiC hardware to continuously transfer heat from the rectifying section to the stripping section. This simplifies the design of the distillation column and associated equipment.

In the literature, HIDiC system has been compared against conventional distillation columns and been shown to provide considerable energy savings. However, there is a need to compare the HIDiC system against alternative heat pump schemes. Thus, the purpose of this work is to systematically compare the performance of the HIDiC scheme with alternative heat pump systems and recognize its merits/demerits. Initial results show that under reasonable operating conditions, a majority, if not all, power benefits of HIDiC can be achieved by use of simple one or two stage heat pumps between the rectifying and the stripping sections.