Regeneration of a scrubbing agent

For regeneration of a loaded scrubbing agent, e.g. a polyethylene glycol ether containing H.sub.2 O and sour gases, the regeneration is conducted in a regeneration column equipped with a bottom heater and an overhead condenser, by stripping with vapor, e.g. stream provided by the heater vaporizing an aqueous condensate. After condensation of the vapor in the condenser, the stripped components are removed and the remaining condensate is recycled to the bottom part of regeneration column to avoid mixing the aqueous condensate with the loaded solvent. The condensate is fed directly into the bottom of the column or is fed into the line between the column and the bottom heater.

BACKGROUND OF THE INVENTION 
This invention relates to an improved process for regeneration of a loaded 
scrubbing agent in a regeneration column equipped with a bottom heater and 
an overhead condenser, and in particular to a process comprising utilizing 
a vapor other than the pure scrubbing agent for stripping purposes. In 
such processes, stripping vapor is condensed in the condenser, the 
stripped components are removed and the remaining condensate is recycled 
to the regeneration column. 
In many chemical and physical gaseous absorption processes regeneration is 
conducted by stripping with a vapor, which, for example, is produced by 
vaporization of a component contained in the scrubbing agent. In practice, 
for this purpose water contained in the loaded scrubbing agent is mostly 
used, but other fluids, such as, for example, methanol or hydrocarbons are 
also possible. In this case, the regeneration usually is performed in a 
regeneration column made up of two sections. The lower section is the 
actual regeneration section, while the upper section is used for 
rescrubbing of entrained scrubbing agent carried along by the stripping 
vapor. The loaded scrubbing agent is fed between the two sections, with 
the vapor necessary for the stripping being produced by heat at the bottom 
of the column. After condensation of the vapor in the head condenser, the 
components stripped from the scrubbing agent are removed in the gaseous 
form. The remaining condensate is fed as reflux to the upper part of the 
regeneration column and, after passing through this section, is mixed with 
the loaded scrubbing agent. 
A partial stream of the condensate is often removed and used for 
rescrubbing of the scrubbing agent at the top of the scrubbing column. 
After passing through this upper section, the condensate also is mixed 
with the scrubbing agent. 
Mixing of the condensate with the scrubbing agent is unsatisfactory 
inasmuch as the mixture has a higher boiling point than the pure 
condensate and boils at variable temperatures. It is also disadvantageous 
that by ad mixing of the condensate, the temperature in the actual 
regeneration section becomes substantially lower than without the mixing, 
and as a result the regeneration of the scrubbing agent is made 
unnecessarily difficult. 
SUMMARY OF THE INVENTION 
An object of one aspect of this invention is to provide an improved process 
of the type initially mentioned. According to this aspect of the 
invention, the condensate is fed into the lower part of the regeneration 
column, i.e., the bottom zone of the regeneration column and preferably 
below the actual regeneration section. 
Thus, according to the invention, the condensate is conducted around the 
regeneration section of the regeneration column to avoid the disadvantages 
of mixing of the condensate with the scrubbing agent, this passage of the 
condensate being accomplished in a particular manner as described below. 
In U.S. Pat. No. 4,670,027, issued June 2, 1987, a process is disclosed in 
which the condensate is likewise not fed back through the regeneration 
section, but in that proposed process it is absolutely necessary for a 
substantial part of the condensate, e.g., more than 30%, to be 
reevaporated in a separate external heat exchanger before being fed into 
the regeneration column. Conversely, according to the present invention, 
such evaporation in a separate heat exchanger is not absolutely necessary, 
as a result of which equipment savings are possible, or the evaporation of 
a very minor part, e.g., less than 30%, especially less than 20% is 
sufficient. 
According to the basic embodiment of said aspect of the invention, the 
condensate can be fed in liquid form directly into the bottom zone of the 
actual regeneration column. 
In another more preferable embodiment, it can be done indirectly by adding 
the condensate to the partial stream removed from the bottom of the 
regeneration column, a stream which is used for heating the bottom of the 
column. Preferably the condensate is added upstream of the heat exchanger. 
In both embodiments the process includes only a single external heat 
exchanger for heating a fluid comprising condensate before said fluid is 
returned to the bottom of the actual regeneration section of the column. 
In a third embodiment, a small portion, e.g. less than 30%, especially less 
than 20% of the condensate is vaporized in a separate heat exchanger thus 
enjoying the advantage of the low boiling temperature of the pure 
condensate but putting up with the disadvantage of a separate heat 
exchanger. 
Upon further study of the specification and appended claims, further 
objects and advantages of this invention will become apparent to those 
skilled in the art. 
It has proved to be especially favorable if at least a part of the 
condensate, e.g., 20 to 80%, before being fed into the lower area of the 
regeneration column, is fed as reflux to a section of the regeneration 
column above the feedpoint of the loaded scrubbing agent and is removed 
from the column also at a point still above the feedpoint of the loaded 
scrubbing agent. Thus, in this zone of the regeneration column, entrained 
scrubbing agent in the gas which leaves the regeneration part of the 
column, is recovered by the condensate. 
Often, a partial stream of the condensate in a similar way is fed to the 
top of a scrubbing column, to recover entrained scrubbing agent. In this 
case this partial stream is fed as reflux to a section of the scrubbing 
column located above the point of entry of the regenerated scrubbing agent 
and advantageously is again removed above the point of entry of the 
regenerated scrubbing agent and then fed into the lower area of the 
regeneration column. 
The process according to the invention can be used for regeneration of all 
appropriate scrubbing agents, for example, in chemical scrubbing 
processes, using hot potash, monoethanolamine or diethanolamine, or also 
in physical scrubbing processes with polyethylene glycol ethers or 
methanol, as well as in hybrid scrubbing processes, as with mixture of 
alkanolamine and methanol.

DETAILED DESCRIPTION OF THE DRAWINGS 
According to FIG. 1 loaded scrubbing agent is carried by pipe 1 from a 
scrubbing process (not shown) and is fed into a middle zone of a 
regeneration column 2. Column 2 is equipped with a bottom heater 3 and an 
overhead condenser 7. After regeneration of the scrubbing agent by 
stripping with vapor rising from the bottom, the scrubbing agent is 
removed by pipe 4 and partially recycled through the heater 3 to the 
bottom of the column while the major amount of the regenerated scrubbing 
agent is removed by pipe 5 and returned to the scrubbing process. 
The stripping vapor, which contains the stripped components, leaves column 
2 as overhead via conduit 6, is partially condensed in condenser 7 and is 
fed to phase separator 8. The stripped gas is removed from the separator 
by conduit 15 and the condensate is removed from the separator by conduit 
9 and is fed as reflux to the upper column section. 
To avoid mixing of the condensate with scrubbing agent according to the 
invention, in the upper column section above the point of entry of the 
loaded scrubbing agent, a tray 10 is installed so that the condensate can 
be removed by conduit 11 above the tray. It is conducted around the 
regeneration section of column 2 and fed directly into the lower area of 
column 2. 
As indicated in broken lines, a part of the condensate can be fed from 
conduit 9 by conduit 13 to the adsorber column for recovery of withdrawn 
scrubbing agent from the purified gas. This partial stream returned by 
pipe 14 after recovery of the scrubbing agent, is mixed in conduit 11 with 
the condensate removed from column 2. 
A partial stream of the bottoms 4 of the regeneration column is fed to the 
reboiler 3 and partially vaporized thus producing the stripping vapor. As 
only a small portion of the stream has to be vaporized, the liquid/vapor 
ratio at the exit of the reboiler can easily be adjusted to the 
requirements of the specific reboiler type. 
In the embodiment represented in FIG. 2 the condensate, removed by pipe 11, 
is not fed directly into the lower area of regeneration column 2, but is 
fed into the partial stream branched from the bottom product, and the 
resultant mixture is fed to heat exchanger 3 for bottom heating. 
Thus the concentration of the condensate in this stream is higher and 
consequently the boiling temperature is lower. 
Without further elaboration, it is believed that one skilled in the art 
can, using the preceding description, utilize the present invention to its 
fullest extent. The following preferred specific embodiments are, 
therefore, to be construed as merely illustrative, and not limitative of 
the remainder of the disclosure in any way whatsoever. 
In the foregoing and in the following examples, all temperatures are set 
forth uncorrected in degrees Celsius and unless otherwise indicated, all 
parts and percentages are by weight. 
The entire text of all applications, patents and publications, if any, 
cited above and below are hereby incorporated by reference. 
EXAMPLE 
In a specific embodiment, 1000 m.sup.3 /h of tetraethylene glycol dimethyl 
ether, loaded with SO.sub.2 and containing water, are withdrawn from a 
flue gas scrubbing column and introduced by conduit 1 into the middle of 
regeneration column 2. The impurities are stripped from the loaded 
scrubbing agent with about 120 kmol/h of steam. The regenerated scrubbing 
agent is removed from the bottom by conduits 4 and 5 and returned to the 
flue gas scrubbing column. 
About 145 kmol/h of steam with 25 kmol/h of stripped gases, especially 
SO.sub.2 and CO.sub.2, with a temperature of 72.degree. C. and a pressure 
of 0.45 bar are removed by conduit 6. Most of the steam is condensed in 
heat exchanger 7 at about 30.degree. C. and fed to separator 8. From the 
separator the condensed water is removed by pipe 9 and fed as reflux to 
column 2. At the top of separator 8 about 30 kmol/h of stripped-out gases 
are removed by conduit 15. About 115 kmol/h of condensate at a temperature 
of about 76.degree. C. is removed from column 2 above tray 10 and fed by 
pipe 11 to the lower zone of column 2. 
A partial stream of condensate, for example 50 kmol/h, can be removed by 
conduit 13, fed as reflux to the scrubbing column and returned by conduit 
14 where it is again mixed with the condensate in conduit 11 at a 
temperature of about 25.degree. C. 
The preceding example can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages and 
conditions.