Heat integated distillation column (HIDiC)

The Heat Integrated Distillation Column (HIDiC) integrates heat transfer and separation. The vapor leaving the stripping section is compressed before it enters the rectifier. The rectifier thus operates at a higher pressure/temperature which allows heat integration between rectifier and stripper. Therefore, the reversibility of the distillation process  can be increased by upgrading the heat rejected in the rectification section and transferring it to the stripping section.

Two concepts of this advanced distillation technology are being developed in a consortium lead by ECN. Where the first concept is based on modification of conventional distillation columns, the second represents a more radical approach where distillation takes place within the channels of a modified heat exchanger. Several business cases have confirmed the cost and energy savings. For example for propane/propylene splitting a 25-30% reduction in energy use is shown compared to state-of-the-art vapour recompression columns (VRC) against lower investment costs.

Status of research

The HIDiC technology has been investigated in the past years in a cooperation of  TU Delft and ECN together with  industrial partners. The two alternative implementations of the HIDiC which have been studied are the concentric tray HIDiC concept based on a conventional column and the structured HIDiC (S-HIDiC). In a S-HIDiC the internals have an analogy with conventional structured distillation columns regarding purification and mass transfer inside the stripper and the rectifier as well as with compact heat exchangers for the heat transfer between both sections.

Milestones which have been achieved thus far in the development of the heat integrated distillation column include:

• Verification of high heat transfer performance and enhanced mass transfer performance in a pilot scale (0,8 m diameter) test unit at TU Delft
•  Design and testing of  S-HIDiC in rectifier and in stripper mode 
•  Validation of energy savings and investment cost reduction in various business cases including retrofitting options.

Current research focuses on several topics, largely related to scale-up of the system. Characterization of the performance on larger scale, liquid/gas distribution and control strategies are some of the issues addressed.

Industrial relevance

Distillation is by far the most important separation technique in the chemical and refinery industries, and is also the largest user of energy. Distillation accounts for about 40 % of the energy use in this sector, i.e. about 180 PJ/y in the Netherlands. Investment in distillation equipment in the Dutch petrochemical industry continues at about 700 M€ per year. Although emerging technologies such as membranes may partially replace distillation in the long term, there remains nevertheless a huge incentive to develop improved distillation techniques. It is well known that conventional distillation has a very low energy efficiency (exergetic efficiency < 10 %), so the scope for improvement is evident.

Several case studies have been carried out on newly developed tools for simulation, optimisation, and rapid screening of potential applications. Most extensive work has been done on the propane-propene splitter. Energy savings were calculated to be 25-35 % compared to a vapour-recompression column (VRC), or 75-90 % compared to a conventional distillation column. The total annual cost was estimated to be 10-20 % lower compared to a VRC, or 60 % lower compared to a conventional column.  Retrofitting a heat integrated distillation column can offer specific advantages as in many conventional distillation columns, the number of rectifier stages exceeds the number of stripping stages. A HIDiC could be implemented as a retrofit of an existing column, with the existing column providing the conventional rectifier stages and the heat-integrated stages being installed as a separate unit to increase capacity and reduce energy use. For the propane-propene splitter,  the techno-economic evaluations and comparisons showed the retrofit option (for increasing capacity) appears to be much more attractive than an additional VRC both in terms of cost and energy.

More information?

For more information on structured separations , please contact Dolf Bruinsma (bruinsma@remove-this-part-ecn.nl ) 

Publications

Bruinsma, D. and Spoelstra, S., (2010). Heat pumps in distillation, Proc. Distillation and Absorption 2010, 12-15 September 2010, Eindhoven (NL): 21-28.

Hugill.J.A. and van Dorst, E.M., The use of compact heat exchangers in heat-integrated distillation columns, 5th Int. Conf. on Enhanced, Compact and Ultra-Compact Heat Exchangers, September 2005, Hoboken, USA, 310-317 (2005)

Hugill.J.A., System for stripping and rectifying a fluid mixture, patent WO03011418 (A1) (2003)

Hugill.J.A., van Dorst, E.M. and de Jong, G., Design of a commercial-scale heat-integrated distillation column based on plate-fin heat exchangers, 6th Int. Conf. on Enhanced, Compact and Ultra-Compact Heat Exchangers, 16-21 September 2007, Potsdam, Germany, 475-482 (2007)