EP-4736975-A1 - CLOSED LOOP HEAT PUMP ASSISTED DISTILLATION FOR LIQUID MIXTURE SEPARATION

EP4736975A1EP 4736975 A1EP4736975 A1EP 4736975A1EP-4736975-A1

Abstract

The disclosure pertains to distillation system comprising two columns operating at different pressure, a compressor, and a reboiler and a condenser that are heat integrated with each other.

Inventors

TYRASKIS, Ioannis
SARIC, Marija
ANSTIS, Olivia Kate
KISS, ANTON ALEXANDRU
CUI, Chengtian

Assignees

Nederlandse Organisatie voor toegepast- natuurwetenschappelijk onderzoek TNO
Technische Universiteit Delft

Dates

Publication Date: 20260506
Application Date: 20241101

Claims (11)

A heat pump assisted distillation system comprising: - a low pressure (LP) stripping column having an inlet for a feed mixture, a vapor outlet, a liquid outlet, and a vapor inlet; - a reboiler for boiling a part of the liquid from the LP stripping column having a vapor outlet connected to said vapor inlet of the LP stripping column; - a compressor connected to said vapor outlet of the LP stripping column, - a high pressure (HP) rectifying column connected to receive vapor from the LP stripping column through said compressor, and having a vapor inlet for said vapor, a bottom liquid outlet connected to an inlet of the LP stripping column, a vapor outlet and a liquid inlet; - a condenser for subjecting the vapor from the HP rectifying column to condensation at a pressure higher than the operating pressure of the LP stripping column, and having a liquid outlet for condensate, wherein a part of the condensate is re-introduced in an upper part of the HP rectifying column; wherein the condenser and the reboiler are in heat exchanging contact, preferably are provided as two heat exchanging compartments of a heat exchanger, and wherein the stages of the LP stripping column are not heat integrated with the stages of the HP rectifying column.
The system according to claim 1, wherein the compressor is a multistage compressor comprising two or more stages, with intercooling provided by heat exchange against a liquid from the LP stripping column, preferably wherein the liquid is withdrawn from an upper part of the LP stripping column.
The system according to claim 2, comprising a liquid flow line for a liquid from the intercooling heat exchanger to the LP stripping column.
The system according to any of the preceding claims, wherein the LP stripping column and the HP rectifying column are provided as two separate vessels that are not in direct heat exchanging contact.
The system according to any of the preceding claims, wherein the compressor is an electrical compressor.
A heat pump assisted distillation process carried out in the system according to claim 1, preferably having features of any of claims 2 to 5, the process comprising: - supplying a feed stream comprising a liquid mixture of a first liquid component and a second liquid component to the LP stripping column, - heating at least a part of the liquid from the LP stripping column in the reboiler, and purging a part of the liquid from the LP stripping column before or after heating in the reboiler, - compressing vapor from the LP stripping column in the compressor and supplying a compressed gas stream to the HP rectifying column, - condensing vapor from the HP rectifying column in the condenser to give a condensate, obtaining a part of the condensate as product, and supplying a part of the condensate to the liquid inlet of the HP rectifying column.
The process according to claim 6, wherein at least 90% of the condensate formed in the condenser is formed in heat exchange with the reboiler.
The process according to claim 6 or 7, wherein at least 30 wt.% of the liquid from the LP stripping column is vaporized in the reboiler, by the heat exchange with the condenser, to form a vapor that is supplied to the vapor inlet of the LP stripping column, preferably at least 40 wt.% of the liquid or at least 50 wt.% of the liquid is vaporized.
The process according to any of claims 6-8, wherein the mixture is a methanol and water mixture.
The process according to any of claims 6-9, wherein the rectifying section is operated at a pressure at least 3 bar higher than the stripping section.
The process according to any of claims 6-10, wherein the feed mixture is a methanol and water mixture, wherein the LP stripping column is operated at a pressure of 1.0 to 1.5 bar and the HP rectifying column is operated at a pressure of at least 5 bar.

Description

Field The invention pertains to a heat integrated distillation system, in particular to a heat integrated distillation system comprising a (closed loop) heat pump assisted distillation unit. The invention also pertains to a process of separating a mixture comprising two liquid components in the heat integrated distillation system, in particular to the separation of methanol and water. Introduction Distillation is one of the main separation technologies in chemical and petrochemical industries. However, the conventional distillation process has relatively low thermodynamic efficiency, typically below 20%, which makes the conventional distillation process energy intensive. According to Javed et al., Energies, 2022, 15, 6498, distillation accounts for 40-50% of the total plant operating cost in most refining and chemical processes. Accordingly, any improvement in thermodynamic efficiency of distillation process significantly increases overall process efficiency and decreases operational cost. As increasing overall process efficiency is beneficial also from a cost perspective and from an environmental perspective, there is a desire to provide a distillation system and process with an improved efficiency to offer a distillation process with a reduced carbon footprint and an overall reduced operational cost. Additionally, electrifying the distillation process is desired, to thereby eliminate the need for an external heat supply and be able to use only electricity as the energy source, and to thereby further reducing CO2 emissions and energy expenses Kiss et al., Energy, 2020, 203, 117788, reviews possible ways to reduce utilities consumption including the use of heat pumps, in particular in a heat integrated distillation column, cyclic distillation, reactive distillation, and dividingwall columns. US 2014/0008207 A relates to a heat integrated distillation column comprising a stripping part, a rectifying part, and a compressor between the stripping part and the rectifying part, and a heat exchange channel assembly for transferring heat from the rectifying part to the stripping part. Fig. 1 of US 2014/0008207 A schematically shows that the heat transfer from the rectifying part to the stripping part is achieved by a direct heat transfer between the rectifying part to the stripping part of the heat integrated distillation column. By employing the channel assembly as shown in Fig. 5 of US 2014/0008207 A, improved heat transfer characteristics can be achieved compared to a plate-fin heat exchange assembly. However, the heat integrated distillation columns of US 2014/0008207 A still have limited heat transfer and thermodynamic efficiency, despite the structure of the heat exchange assembly. EP 2644241 A relates to a heat integrated distillation apparatus comprising a stripping section, a rectifying section, a compressor, and a heat exchanger. The heat exchanger is provided in the stripping section, e.g. in a liquid sump unit, and has an inlet flow line for a compressed vapour stream from the stripping section and an outlet flow line for a condensed vapour stream, as shown in Fig. 7 of EP 2644241 A. The heat exchanger receives, e.g. in a tube bundle, the entire compressed vapour stream, which is supplied to the rectifying section via the heat exchanger. Thereby, the heat exchanger is a direct process-to-process heat exchanger heating a feed stream indirectly supplied to the liquid sump unit, in the stripping section and cooling the compressed vapour stream to yield a (partially or completely) condensed vapour stream supplied to the rectifying section. Thereby, such distillation apparatus allows for heat integration within the distillation process, a reduction of the amount of heat which needs to be supplied to a boiler in the stripper section and a reduction in the amount of heat which needs to be withdrawn in a condenser in the rectifying section. However, the distillation apparatus of EP 2644241 A requires a plurality of the heat exchangers as described above, which increases capital expenditure of building the distillation apparatus and requires a significant amount of maintenance, and is difficult in control. EP 2486965 A relates to a heat integrated distillation apparatus comprising a stripping column, a rectifying column, a compressor, a reboiler, a condenser, and a heat exchanger. Fig. 4 of EP 2486965 A teaches a heat exchanger provided in the rectifying column which is configured to receive a liquid stream withdrawn from the stripping column and to recycle it to the stripping column after a heat exchanging contact with a fluid stream in the rectifying column. Fig. 7 of EP 2486965 A teaches a heat exchanger provided in the stripping column which is configured to receive a fluid stream from the rectifying column and to recycle it to the rectifying column after a heat exchanging contact with a liquid in the stripping column. In both embodiments, the heat exchanger is configured as to act as a condenser and as a re