SYSTEM AND METHOD FOR CONCENTRATING SUBSTANCE-CONTAINING FLUIDS BY MEANS OF MULTI-STAGE EVAPORATION

Abstract

System and method for concentrating substance-containing fluids by multi-stage evaporation. System includes at least a first and a second evaporator, the first evaporator being connected to the second evaporator, whereby fluid concentrated in the first evaporator is conducted into the second evaporator to further concentrate fluid in the second evaporator, a first mechanically acting compressor unit, whereby vapor formed in the first evaporator is compressed downstream, and a second mechanically acting compressor unit, whereby vapor formed in the second evaporator is compressed downstream. System includes a first supply line supplying vapor compressed with the first mechanically acting compressor unit to the first evaporator. Vapor compressed by the second compressor unit is supplied to the first compressor unit. First and second compressor units include pluralities of compressors and vapor in the second compressor unit is compressed to a larger outlet temperature minus inlet temperature difference than in the first compressor unit.

Claims

1. A system for the concentration of substance-containing fluids by multi-stage evaporation, in particular of solutions such as N-methylmorpholine-N-oxide (NMMO), wherein the system is configured with at least a first evaporator and a second evaporator, wherein the first evaporator is connected to the second evaporator in a suitable manner such that fluid concentrated in the first evaporator can be conducted into the second evaporator in order to further concentrate concentrated fluid in the second evaporator, wherein a first mechanically acting compressor unit is provided, with which vapor formed in the first evaporator can be compressed downstream, and wherein the system comprises a first supply line for supplying vapor compressed with the first mechanically acting compressor unit to the first evaporator, wherein a second mechanically acting compressor unit is provided, with which vapor formed in the second evaporator can be compressed downstream, wherein vapor compressed by the second compressor unit can be supplied to the first compressor unit, wherein the first compressor unit comprises a plurality of compressors and the second compressor unit comprises a plurality of compressors, wherein vapor in the second compressor unit is compressed to a larger outlet temperature minus inlet temperature difference than in the first compressor unit.

2.-3. (canceled)

4. The system as claimed in claim 1, wherein the system comprises a second supply line for supplying vapor compressed with the first mechanically acting compressor unit to the second evaporator.

5. The system as claimed in claim 1, wherein a thermal compressor is not provided.

6. The system as claimed in claim 1, wherein the second evaporator is configured as a finisher, from which the concentrated fluid is withdrawn from the system.

7. A method for the concentration of substance-containing fluids by multi-stage evaporation, for example of solutions such as N-methylmorpholine-N-oxide (NMMO), in particular with a device as claimed in claim 1, wherein the fluid is concentrated in a first evaporator and the fluid concentrated in this manner is conducted into a second evaporator, in which the concentrated fluid is concentrated further, after which a concentrate is removed, wherein vapor formed in the first evaporator is compressed downstream with a first mechanically acting compressor unit and supplied at least in part to the first evaporator via a first supply line, wherein vapor formed in the second evaporator is compressed downstream with a second mechanically acting compressor unit and then supplied to the first compressor unit, wherein vapor in the second compressor unit is compressed to a higher outlet temperature minus inlet temperature difference than in the first compressor unit.

8. The method as claimed in claim 7, wherein the vapor compressed in the second evaporator is compressed in the first mechanically acting compressor unit together with the vapor formed in the first evaporator.

9. The method as claimed in claim 7, wherein vapor compressed in the first mechanically acting compressor unit is divided into partial streams, wherein one partial stream is supplied to the first evaporator and a further partial stream is supplied to the second evaporator.

10. The method as claimed in claim 7, wherein vapor formed in the second evaporator is compressed downstream with a plurality of compressors of the second mechanically acting compressor unit.

11. The method as claimed in claim 7, wherein vapor formed in the first evaporator is compressed downstream with a plurality of compressors of the first mechanically acting compressor unit.

12. The method as claimed in claim 7, wherein the first evaporator is operated at a higher pressure than the second evaporator.

13. (canceled)

Description

[0024] Further features, advantages and effects of the invention will become apparent from the exemplary embodiment described below. In the drawing, FIG. 1 shows a system design in accordance with the invention.

[0025] FIG. 1 shows a system 1 which is designed for concentrating NMMO. The system 1 comprises a first evaporator 2 and a second evaporator 3. An aqueous solution of NMMO is introduced into the evaporator circuit for the purposes of concentrating the solution. The NMMO solution is supplied to the first evaporator 2 for pre-concentration at a NMMO content of 20% by wt, for example. In the first evaporator 2, the temperature of the supplied NMMO solution is raised by supplying energy. The vapour which is generated thereby can be taken off overhead in the first evaporator 2. The pre-concentrated NMMO solution is taken from the bottom and supplied to the second evaporator 3 in which, in turn, the temperature of the supplied solution is raised so that in turn, vapour can be withdrawn overhead from the second evaporator 3 and so that in turn, an increase in concentration occurs and finally, a NMMO solution with 80% by wt NMMO can be taken off from the bottom of the second evaporator 3, which serves as a finisher.

[0026] The vapour emerging from the first evaporator 2 is reused in the further process. To this end, a first mechanically acting compressor unit 4 is provided. The first compressor unit 4 comprises a plurality of individual compressors 41. In the exemplary embodiment, the first compressor unit 4 comprises two compressors 41. The two compressors 41 of the first compressor unit 4, which are connected in series, are connected to the first evaporator 2 via a first take-off line 42. In similar manner, the second evaporator 3 is designed with a take-off line 52, which connects an overhead outlet from the second evaporator 3 to a second mechanically acting compressor unit 4. The second compressor unit 5 also comprises two individual compressors 51. The compressors 51 of the second compressor unit 5 are also connected in series.

[0027] As can be seen in FIG. 1, the compressors 51 of the second compressor unit 5 are equipped with a downstream line which discharges into the take-off line 42 of the first evaporator 2. Vapour compressed with the second compressor unit 5 is therefore combined with the vapour taken off from the first evaporator 2 before the vapour combined in this manner is compressed further in the first compressor unit 4. After this final compression, the compressed vapour is divided into two partial streams, namely a first partial stream for a first supply line 6 to the first evaporator 2, as well as a second supply line 7 to the second evaporator 3.

[0028] By means of the circuitry which is provided, it is possible for vapour from the second evaporator 3, which emerges at a relatively low temperature of approximately 30 C. lower than in the first evaporator 2, to initially be brought to a temperature which is approximately 30 C. to 40 C. higher with the compressors 51 of the second compressor unit 5 which are provided. This alone would not yet be a sufficient temperature for the operation of the second evaporator 3. By the additional compression with the first compressor unit 4, however, a further temperature rise of several C. is obtained, so that a temperature of the compressed vapour is sufficient to heat the second evaporator 3 sufficiently. Thus, a minimum number of mechanically acting compressors is sufficient to result in an energetically effective process. As can be seen in FIG. 1, in the first evaporator 3, the NMMO solution can be concentrated to approximately 40% by wt NMMO thereby and in the second, to a final 80% by wt NMMO.