Distillation plant with a heat pump

A distillation plant includes a heat pump whose working fluid is compressed by a vapor jet compressor. A collection location for a liquid is arranged in the stripper part of a distillation column of the plant. At least a portion of the collected liquid is provided in the vaporized form as strip vapor. Connections lead from the collection location to a first vaporizer and to a second vaporizer. The liquid can be vaporized in these vaporizers at an elevated and at a reduced pressure respectively. The vapor jet compressor is connected to the two vaporizers and to the column in such a manner that the vapor from the second vaporizer can be compressed under a driving jet action of the vapor from the first vaporizer and used in the column as strip vapor. A pump is arranged in the connection to the first vaporizer and at least one restrictor member is contained in the connection to the second vaporizer.

BACKGROUND OF THE INVENTION 
The invention relates to a distillation plant with a heat pump and to a 
distillation method with a plant of this kind. 
It is known that when carrying out distillation using a column the exhaust 
vapors can be utilized by means of a heat pump for the purpose of saving 
energy. A portion of the thermal energy arriving at the head of the column 
is brought to a higher temperature level by the heat pump and the 
so-transformed thermal energy is used for the heating of a sump vaporizer. 
In this arrangement a direct condensation of the exhaust vapors can, for 
example, be performed with radial compressors. 
It is known that a vapor jet compressor operated with water vapor can be 
used economically for condensing the exhaust vapors if the head product is 
water. The object of the invention is to provide an economical 
distillation plant with a vapor jet heat pump, in which the head product 
does not however consist of water. 
SUMMARY OF THE INVENTION 
The distillation plant comprises a heat pump whose working fluid is 
compressed by means of vapor jet compressor. A collection location for a 
liquid is arranged in the stripper part of the distillation column of the 
plant. At least a portion of the collected liquid is provided in vaporized 
form as strip vapor. Connections lead from the collection location to a 
first vaporizer and to a second vaporizer. In these vaporizers the liquid 
can be vaporized at an elevated pressure and at a reduced pressure 
respectively. The vapor jet compressor is connected to the two vaporizers 
and to the column in such a manner that the vapor from the second 
vaporizer can be compressed under the driving jet action of the vapor from 
the first vaporizer and used in the column as strip vapor. A pump is 
arranged in the connection to the first vaporizer and at least one 
restrictor member is contained in the connection to the second vaporizer. 
In a preferred special case the vapor jet compressor operates with a 
vaporized sump product as the propulsion jet and also as the working fluid 
(where working fluid is understood to mean the substance by means of which 
the heat pump performs the thermal transformation: taking up heat at a 
lower temperature/giving off heat at a higher temperature). The resultant 
vapor mixture is fed into the column and acts there as a stripping means. 
Instead of the sump product, liquid can be provided from a collection 
location which is arranged between two installation sections of the 
driving part. The low temperature heat is won through condensation of a 
portion of the vaporous head product or through condensation of vapor 
which is branched off between the installation sections of the upper part 
of the column. 
Instead of a single heat pump, a plurality of heat pumps with vapor jet 
compressors can also be provided, with, for example, the sump product 
being used as the working fluid of a first heat pump and with an 
intermediate product being used as the working fluid of a second heat 
pump. The temperatures of the low temperature heat sources can be the same 
or different. The driving jets of two or more heat pumps can be fed by a 
common vaporizer. A common low temperature source can also be associated 
with two or more heat pumps.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The distillation plant a with a heat pump shown in FIG. 1 comprises the 
following parts: a column 2 with a stripper part 20, a sump 24, a sump 
vaporizer 94, a head 25 and a condenser 95 for exhaust vapors from the 
column; a vapor jet compressor 10, a first vaporizer 7, a pump 70, a 
second vaporizer 8, a restrictor member 80; and furthermore, various 
connection lines. 
A raw solution F from a reservoir 3 is separated into fractions by the 
distillation, namely into a sump product B (reservoir 4) and a distillate 
D (reservoir 5). The raw solution F is for example a mixture of 
iso-propanol, water and acetone with the following composition in 
percentage by weight: 82.5, 16.5 and 1.0 respectively. The sump product 
which is produced is water which still contains acetone; the distillate 
consists of 85.6% iso-propanol, 13.4% water and 1.0% acetone. The 
following figures relate to this special example of the method. 
The column 2 contains sections 230, 240 and 250 with installed inserts, 
which are, for example, ordered packings. The installed inserts can also 
be bulk collections of filling bodies or bases. The raw solution F arrives 
via a distributor 203 at the installation section 230 with an installed 
insert. A liquid collector 6 (lamella 201, trough 202) is arranged under 
this section 230 and is constructed in such a manner that the flow of 
vapor streaming upwards is largely unrestricted. The liquid of the 
collection location 6 passes partly into a distributor 204 of the lower 
installation section 240 and is partly transported into the vaporizers 7 
and 8 via a line 26 and connections 27 and 28 respectively. The distillate 
D is conducted back into the head 25 of the column and is distributed 
there over the upper installation section 230 by means of the distributor 
205. 
The vapor jet compressor 10 is fed via the line 71 with driving vapor from 
the first vaporizer 7 (absolute pressure for the particular example of the 
method: 19 bar; temperature: 182.degree. C.). Vapor (1 bar; 83.degree. C.) 
is sucked in via the line 81 from the second vaporizer 8, whose heat 
source is formed by condensing exhaust vapors. The condensed exhaust 
vapors pass into the reservoir 5. A strip vapor (2.3 bar, 148.degree. C.) 
is produced by the vapor jet compressor and is fed into the column 2 via 
the line 11 at the collection location 6. Liquid from this collection 
location 6 is partly (67%) forwarded by the pump 70 into the first 
vaporizer 7 (pressure increase: 16.7 bar) and partly (33%) conducted via 
the restrictor member 80 into the second vaporizer 8 (pressure reduction: 
1.3 bar). In an embodiment, the vapor from the second vaporizer 8 is 
compressed by the vapor jet compressor 10 to a pressure which has about 
twice the value of the vaporizer pressure of the second vaporizer. 
The second exemplary embodiment, illustrated in FIG. 2, is distinguished 
from the first in two respects: 
a) The sump 24 of the column 2 is the collection location 6 for the liquid 
which is used for the production, in accordance with the invention, of 
strip vapor by the vapor jet compressor 10. 
b) Vapor, which is branched off in a space 265 between two installation 
sections 250 and 260 of the upper part of the column 2, forms the heat 
source for the second vaporizer 8. 
In the present example the vapor condensed out in the second vaporizer 8 is 
fed onto the middle installation section 260 by a distributor 206. Since 
the strip vapor is produced from the sump product B, a sump vaporizer 94 
is superfluous. The pump 70 is arranged in the line 26 upstream of the 
branch position where the two lines 27 and 28 branch off. This special 
arrangement is not necessary. The branch position could also lie upstream 
of the pump 70 so that the pump 70 would be located only in the connection 
27; and--if necessary at all--a second pump could be provided in the 
connection 28 if required to overcome a difference in the static liquid 
pressure between the sump 24 and the second vaporizer 8. 
Naturally other combinations of the two exemplary embodiments described are 
also possible: 
a) Arrangement of the vapor jet compressor 10 and of the first vaporizer 7 
as in the example of FIG. 2, arrangement of the second vaporizer 8 in 
accordance with FIG. 1; 
b) Arrangement of the vapor jet compressor of the first vaporizer 7 in 
accordance with FIG. 1, arrangement of the second vaporizer 8 in 
accordance with FIG. 2. 
An example of a method for the first combination in accordance with item a 
follows. 
Raw solution F, formed by a mixture of 1-butene, n-butane, c/t-2-butene, 
with a composition (% by weight): 99.0%, 0.2% and 0.8% 
respectively.--Resultant fractions with a corresponding composition in 
each case: distillate D with 99.8%, 0.0% and 0.2% respectively and sump 
product B with 55.6%, 7.8% and 36.6% respectively.--Vapor of the first 
vaporizer 7: 24.4 bar, 120.degree. C.--Vapor of the second vaporizer 8: 
2.8 bar, 27.degree. C.--Strip vapor produced by the vapor jet compressor 
10: 5.6 bar, 69.degree. C. 
In practice the methods described have to compete with distillation methods 
without heat pumps in which the strip vapor is produced by means of a sump 
vaporizer 94 and the exhaust vapors are liquefied without heat retrieval 
in a condenser 95. Substantial savings in costs in the expenditure for 
energy can be achieved with the plant in accordance with the invention, 
with the additional costs for the vapor jet compressor (including the 
equipment for the production of the drive jet) turning out to be 
relatively low. The savings in costs for the energy are 34% in the first 
example of the method (FIG. 1) and 36% in the second example of the method 
(combination in accordance with item a). 
As already mentioned, the invention also relates to plants in which a 
plurality of vapor jet heat pumps are in use simultaneously.