Note: Descriptions are shown in the official language in which they were submitted.
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Process and apparatus for cleaning of waste water.
The present invention relates to a process for improving plants for waste
water clean-
ing, in which evaporation by means of steam compression as a cleaning method
is a
part.
Waste water cleaning plants, which use evaporation by means of steam
compression,
are typically minor plants for cleaning of a special kind of waste water such
as e.g.
heavy metal containing waste water, used cooling lubricants, water-based
degrease
liquids and waste water from various washing processes. The cleaned water has
hith-
erto typically been reused or drained off for canalization. Types of waste
water con-
taming big amounts of compounds, which are mobile at the temperature and the
pH at
which the evaporation is taking place, are normally not suited for a cleaning-
up proc-
ess in a waste water cleaning plant, which uses evaporation by means of steam
com-
pression, because the cleaned water as a rule will be too unclean for re-use,
and fur-
thermore a draining off for canalization will be very problematic, because of
a too big
remaining content of mobile compound.
The process described in this invention makes waste water cleaning plants with
evapo-
ration by means of steam compression especially suited for cleaning of
biological
waste water containing mobile compounds in form of weak acids and weak bases.
As an example of a such kind of waste water, which often contains big amounts
of
mobile compounds, is waste water, which is produced in connection with one or
more
biological processes, such as e.g. manure from pigs, manure from cattles,
toilet water,
waste water from production of medicin, washing water from slaughteries and
cooling
lubricants, including said kinds of waste water, which have putrefied. A big
part of the
mobile compounds, which normally evolve by biological decomposition processes
will be present as weak acid/base couples.
The present invention relates to a process for cleaning of biological waste
water,
which contains more mobile compounds and less mobile compounds in relation to
the
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mobility of water, and which are present as weak acids and weak basis. The
proces
uses inter alia an evaporation of the waste water, where the waste water is
heated in a
boiler. The formed steam is cleaned by this approach for unwanted gaseous com-
pounds, and it is transferred from this boiling step via a compression step to
a heat
exchanging step, where the water is condensed and drained off in cleaned form
to the
recipient, and where the bigger part of the more mobile compounds is
concentrated
and drained off together with the remaining fraction of steam.
It appears that the described new process is advantageous in relation to prior
art inter
alia by the fact that the steam from the boiler is being led to a column,
where the
steam is tranferred in counterflow with a fraction of the condensed water. By
this
method the less mobile compounds are removed in a liquid form. Furthermore a
part
of the more mobile compounds and the less mobile compounds becomes a part of
the
related aqueous acid/base reactions.
Thus it appears that the less mobile compounds and a remaining part of the
more
mobile compounds are present in the steam from the heating of the waste water.
These
compounds are as mentioned led further from the column via the compression
step to
the heat exchanging step, where a concentration is taking place and draining
off of the
bigger part of the more mobile compounds together with a remaining fraction of
steam, and where eventually condensed and cleaned waste water is led out to
the re-
cipient.
The invention encompasses furthermore an apparatus for the embodiment of the
proc-
ess.
By evaporation of the biological waste water, which contains more mobile
compounds
and less mobile compounds relative to the mobility of the aqueous solvent it
is desir-
able that the amount of the more mobile compounds is as little as possible,
because a
presence hereof will require an increased supply of heat for a sufficient
evaporation.
The reason for this is that these more mobile compounds consist of compounds
which
are not condensable by the magnitudes of pressure and temperature which are
applied
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by the evaporation of the basic liquid of the solution, which normally is
water, and
therefore they will be inhibitory for the evaporation of water, because they
are present
as an insulating layer within the heat exchanger. Because such a layer will
act as an
inhibitor for the heat transmission to the condensable compounds within the
heat ex-
changer it will implicate an increase of the energy consumption.
By evaporation of liquid biological waste the more mobile dissolved compounds
pres-
ent will inter alia be carbon dioxide and ammonia and the less mobile
dissolved com-
pounds will inter alia be fatty acids, mineral acids and their salts. Included
are said
compounds in both neutral and charged form.
Apart from the described increase of the sufficient heat transmission as a
consequence
of a presence of the more mobile compounds during the evaporation another kind
of
disadvantages will be present at the evaporation of such liquid according to
prior art
and this involves inter alia the energy consumption in the subsequent
compression
step. A content of not condensable compounds, as for instance carbon dioxide,
will
firstly occupy space within that water steam which is withdrawn from the
boiler to the
heat exchanger, and this implies a loss of efficiency. Secondly, the presence
of the
more mobile compounds in the water steam from the column will cause to an
increase
of the energy consumption in the subsequent compression step.
Another main compound, which belongs to the group of the more compounds, is
fre-
quently as mentioned above ammonia, which it is likewise desirable to remove,
before
the vapours are led into the heat exchanger. An applicable method for this is
to con-
duct the ammonia vapours through a scrubber, as it is described in patent DK
171611.
This has proven to be efficient, but does, however, involve disadvantages, as
supply of
various chemicals are needed, which is in detail described in patent DK
171611. Such
a further proces step is both laborious and costly.
As mentioned compounds are present in the said liquid, which compounds are
less
mobile than the liquid in which they are dissolved, and the present invention
com-
prises furthermore a removal of these compounds. A method for this is
described in
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patent application DK 01288/96, according to which a concentration of the com-
pounds firstly takes place in the boiler used for the above described
evaporation. The
heated liquid is being led to a column, from which the more mobile compounds
in
gaseous form are led to the primary side of a first heat exchanger, so that
these more
S mobile compounds are condensed and led out from the primary side, and from
the
same column the less mobile compounds are led in liquid form to the secondary
side
of the above mentioned first heat exchanger, where they are heat exchanged
with the
condensed more mobile compounds. By this approach additional parts of the more
mobile compounds in the secondary side of the heat exchanger are evaporated
and led
to said column, from which they, in gaseous form, are led to the primary side
of said
first heat exchanger, and the heated liquid is led following a total or partly
separation
of the more mobile compounds back to the boiler. By more cycles of the column
and
the heat exchanger additional parts of the more mobile compounds are
evaporated and
carried to the column, from which they are circulated to the primary side,
where they
are condensed.
The present method is remarkable by a decreased enery consumption in relation
to
known methods and a consumption of chemicals which is totally eliminated. The
in-
vention will as an example in the following be described in more detail based
on
cleaning of manure, the method, however, is not to be limited to this.
Examples of
other liquids, which can be cleaned by an approach according to the present
invention
are - apart from the above mentioned biological waste liquids in general,
which as
already known inter alia comprise manure - emulgated liquids, as e.g.
cooling/oil lu-
bricants oil emulsions, degreasing liquids, oil containing waste water, waste
water
from laundries, solvents and waste water from food production and its like.
Based upon an example of manure as the liquid to be cleaned, the unwanted com-
pound will comprise C02, NH3, NH4+, fatty acids, including CH3COOH, and other
organic liquids. The unwanted compounds can be present in neutral and/or
charged
form and/or as salts.
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A method and an apparatus of the known type can as an example be formed
according
to the disclosure in patent DK 171611. Here manure is de-gassed and during
subse-
quent passage through a scrubber the present ammonia and acetic acid are
neutralized
by addition of calculated amount of acid and base.
5
In order to disclose the present invention in more details the technological
background
for this will be the until now known technology with reference to patent
application
DK 0868/94, patent DK 171611, and patent application DK 01288/96. The
disclosure
will be based on the below described figures 1-6, to which reference is made
to an
outline of the explanations for the used designations, which is placed at the
end of the
description.
Fig. 1 shows a plant for waste water cleaning with known technology by means
of
the scrubber 52 (comprising scrubber 53 and scrubber 54),
Fig. 2 shows a diagramme of an embodiment of a scrubber with known technology,
Fig. 3 shows a diagramme of an embodiment of the technology in a plant, which
uses the present invention with column and heat exchanger,
Fig. 4 shows especially that part of the plant with combination of a column
and a
heat exchanger in Fig. 3, which the present invention makes use of,
Fig. 5 shows in- and outlets from a column in an embodiment according to the
pre-
sent invention and the relevant chemical equilibriums, and
Fig. 6 shows a diagramme of an embodiment of a heat exchanger with its in- and
outlets according to the present invention.
In the description the known technique will be described based upon Fig. 1
with refer-
ence to Fig. 2, which especially discloses the function of the scrubber. By
explanation
of the approach in the present invention focus will be upon Fig. 3 with Fig. 1
as refer-
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ence. Figs. 4-6 serve especially the purpose of showing those processes which
in
combination replace and improve the until now known scrubbing, which is
included in
Fig. 1.
Fig. 1 shows a schematic illustration of an example of an embodiment for a
plant ac-
cording to known technology from Danish patent application DK 01288/96. The
plant
comprises a column l, a first heat exchanger 2, a compressor 3, a bottom
vessel 4 for
the column 1, a circulation pump 5 receiving liquid from outlet 36, a motor
valve 6, a
contravalve 7, a gas/liquid separator 8, a level sensor -9 for control of
liquid level in the
bottom vessel 4 for column l, a first section 10 of a second heat exchanger, a
second
section 11 of the second heat exchanger, a third heat exchanger 12, a first
motor valve
13, and a second motor valve 14. The column 1 is provided with nozzles 15 for
drain-
ing off of liquid biological waste in column 1.
The column 1 is provided with an inlet 16 for the liquid biological waste to
the col-
umn 1. As a non-limiting example of liquid biological waste will as mentioned
ma-
nure be applied in the following part of the description. The manure is led to
the col-
umn 1 in order to be separated in column 1 into more mobile compounds and less
mobile compounds. The more mobile compounds are led to a foam restrictor 17 in
an
upper part of the column 1. The less mobile compounds are led to the bottom
vessel 4
in the bottom of column 1. When the liquid biological waste is manure the more
mo-
bile compounds will inter alia comprise carbon dioxide (C02) and ammonia
(NH3),
and the less mobile compounds will inter alia comprise water (H20), fatty
acids and
mineral salts.
Before the manure is led to column 1 the manure is heated, because it is led
through a
secondary side of the first section 10 and a secondary side of the second
section 11 of
the second heat exchanger. The first section 10 of the second heat exchanger
is pro-
vided with an inlet 18 for the manure. The inlet 18 is provided with a motor
valve 14
for inlet of the manure to the first section 10. The first section 10 is
provided with an
outlet 19, which leads to an inlet 20 for the second section 11 of the second
heat ex-
changer. The second section 11 is provided with an outlet 21, which leads to
the inlet
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16 to the column 1. The manure is supposed to achieve a rise of temperature to
the
boiling point of the manure, before the manure is led to the nozzles 15 in
column 1.
Following the transference of the manure through the nozzles 15 in column 1
and as
mentioned separated into more mobile compounds and less mobile compounds the
more mobile compounds are led from an outlet 22 from the foam restrictor 17 to
the
compressor 3, where the more mobile compounds are compressed. After the more
mobile compounds are compressed the more mobile compounds are led to an inlet
23
of a primary side of the first heat exchanger 2. The more mobile compounds are
led
through the primary side of the first heat exchanger 2 to an outlet 24 from
the primary
side of the first heat exchanger 2. The more mobile compounds are thereafter
led to an
inlet 25 of a primary side of the second section 11 of the second heat
exchanger. The
more mobile compounds are led through the primary side of the second section
11
and to an outlet 26 of the second section 11 of a second heat exchanger.
After being led through the primary side of the first heat exchanger 2,
respectively the
second section 11 of th second heat exchanger the more mobile compounds are
partly
condensed and consist of a gas fraction and a liquid fraction. From the outlet
26 of the
primary side of the second section of the second heat exchanger the gas
fraction and
the liquid fraction of the more mobile compounds are led to an inlet 27 to the
gas/liquid separator 8.
The liquid fraction from an outlet 28 of the separator 8 is led to an inlet 29
of the liq-
uid fraction and to nozzles 30 in column 1 as reflux. The gas fraction from
the separa-
for 8 with the more mobile compounds are from an outlet 31 led to an inlet 32
to a
primary side of the third heat exchanger 12. In the third heat exchanger 12 a
total con-
densing of the gas fraction is taking place. By condensing of the gas fraction
the car-
bon dioxide (C02) diffuses into the liquid, where it together with water (H20)
and
ammonia (NH3) form ammonia hydrogen carbonate (NH4HC03). This ammonia hy-
drogen carbonate is led to an outlet 33 from the primary side of the third
heat ex-
changer and it can be stored in a normal closed container (not shown) and can
be
drained off from here.
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Those parts of the manure, which are led to the second heat exchanger, are as
a start
led to a secondary side of the third heat exchanger 12. The manure is led to
an inlet 34
to the secondary side of the third heat exchanger 12 by means of the first
motor valve
13 and through the secondary side of the third heat exchanger 12 to an outlet
35 from
the secondary side. From the outlet 35 of the secondary side of the third heat
ex-
changer 12 the manure is led through the inlet 20 of the secondary side of the
second
section 11 of the second heat exchanger.
The less mobile compounds are as mentioned led to the bottom vessel 4 of the
column
1. From an outlet 36 from the bottom vessel 4 the less mobile compounds in
liquid
form are by means of a circulation pump 5 (receiving liquid from outlet 36)
led to an
inlet 37 for a secondary side of the first heat exchanger 2. The level sensor
9 in the
bottom vessel 4 of the column 1 assures that the less mobile compounds are not
led
from the bottom vessel 4, before a sufficient amount of the less mobile
compounds are
present in the bottom vessel 4 of the column 4. The less mobile compounds are
led
through the secondary side of the first heat exchanger 2 for evaporation of
possible
additional more mobile compounds and back to the bottom vessel 4 of the column
1.
Intermittently parts of the liquid containing the less mobile compounds are
drained off
during the circulation of the less mobile compounds from the bottom vessel 4
for the
column 1 and through the secondary side of the first heat exchanger 2. The
draining
off from the secondary side of first heat exchanger 2 is taking place through
outlet 38,
through the contra valve 7 and the motor valve 6. The part of the liquid
containing the
less mobile compounds can be described as de-gassed, this is to say free of
the more
mobile compounds, and it can be led further on to a possible additional
treatment such
as an evaporation.
The more mobile compounds will by compression in the compressor 3 achieve a
tem
perature which is higher than the temperature of the manure being led to the
nozzles
15 of the column 1.
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The less mobile compounds are led following passage of the motor valve 6 to a
vessel
41 for the processing, which is connected with the scrubber 52 (comprising
scrubber
53 and scrubber 54), and the functional correlation can be formed as described
in pat-
ent application DK 0868/94, and reference is made to the following Fig. 2.
According
to the known technique the polluted liquid is heated in the vessel 41 for the
processing
linked to the scrubber 52 (comprising the scrubber 53 and the scrubber 54),
whereafter
a circulation pump 43 (connected with outlet from the processing vessel) is
conducting
the liquid to the top of the evaporator. At the bottom an outlet is provided,
which can
drain off the concentrated and polluted part of from the processing vessel 41,
which is
linked to the scrubber 52 (comprising the scrubber 53 and the scrubber 54. At
the top
of this a steam tapping 47 is provided, which is linked to a compressor 49,
which fur-
thermore via said scrubber 52 is connected with a downdraught evaporation heat
ex-
changer 50, which is placed above the container for the processing vessel 41
(linked to
the scrubber 52) within the evaporator. In the bottom of said heat exchanger
50 an
outlet pipe S 1 is placed for the clean condensate.
Fig. 2 shows a plant of known type from Danish patent application DK 0868/94
com-
prising inter alia an evaporator 39 and the scrubber 52. At the top of the
evaporator a
liquid distribution system 40 is provided, and at the bottom the vessel for
the process-
ing 41 is present (linked with the scrubber 52), which contains the
concentrated proc-
essing liquid 42 (abbreviated C~). The vessel for the processing 41 is
connected with a
circulation pump 43 and a circulation pipe 44, which pumps the heated and
polluted
processing liquid 42 to the distribution system 40 at the top of the
evaporator. The
vessel 41 for the processing, which as mentioned is connected to the scrubber
52, has
an inlet pipe 45 for supply of polluted processing liquid 42 and an outlet
pipe 46,
which is used for emptying of the concentrated and polluting concentrate
(abbreviated
C~) from the vessel 41 for the processing, which is connected to the scrubber
52
(comprising the scrubber 53 and the scrubber 54).
At the top of the processing vessel 41 a steam tapping 47 is provided, which
via a
pipeline 48 and a compressor 49 is connected with a downdraught evaporation
heat
exchanger 50, which is placed inside the evaporator 39. At the bottom of the
heat ex-
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~
changer 50 an outlet 51 is provided for clean condensate. The scrubber 52
(comprising
the scrubber 53 and the scrubber 54) is placed in the steam pipe 48, in which
also the
compressor 49 is mounted. In the shown situation the scrubber 52 is placed
upstream
to the compressor 49. This is preferred, but it is also without difficulty
possible to
5 place the scrubber 52 downstream to the compressor 49.
It appears that the electrical managing of the plant is not shown in the
drawing. How-
ever, such a managing system will be wellknown to a person skilled in the art
and
needs therefore no further explanation.
The polluted and concentrated process liquid 42 is transferred batchwise at
the pipe 45
and drained off after an concentration has taken place via the outlet pipe 46.
The clean
condensate is drained off via the outlet pipe 51.
1 S The scrubber 52 according to the known design comprises a first and a
second scrub
bing step 53, 54. The scrubber 53 contains an acid 55, and the scrubber 54
contains a
base 56. Each of the scrubbers 53, 54 is provided with a pipe for acid 57 and
a pipe for
base 58. By this approach it is possible to exchange as a consequence of the
measure
ments the liquid 55 and 56, so that the pH can be maintained constant during
the
evaporation.
The whole system is contained in a closed and insulated cabinet 59. An energy
neutral
process is thus achieved, because there is no needed exchange with the
surroundings.
This implies the advantage that condensation of the steam in an unwanted way
is
avoided at a step which has a lower temperature. If there were to be "cold
steps" the
process would stop, because the steam would condense in such a cold step
instead of
the wanted condensation in the downdraught evaporation heat exchanger 50.
When the polluted liquid is transferred into the processing vessel 41, which
is con-
nected to the scrubber 52, the shown level 60 for the processing liquid is
achieved at a
certain point of time, after which a float switch for regulation of the inlet
of the pol-
luted liquid 61 is activated, whereby a heating element (not shown) and a
circulation
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pump 43 are switched on. The temperature is hereby increased to a temperature
and
pressure, which is closely below the boiling point of the liquid, which is to
be cleaned
(the condensate). If the liquid is water the temperature is increased to
approximately
100°C.
S
The circulation pump 43 is started up in the plant to ensure that all
components have
the same temperature. When the temperature has achieved about 100°C the
compres-
sor 49 is started. The compressur 49 creates a vacuum in the processing vessel
41
linked to the scrubber 52 and thereby forces the steam placed over the
polluted and
concentrated processing liquid 42 through the scrubber 42, after which the
steam via
the pipeline 48 is transferred to the heat exchanger 50, where heat exchange
is taking
place of the steam at the one side of the heat exchanger and the heated,
polluted and
concentrated processing liquid 42 on the second side of the heat exchanger. By
this the
steam, which has been compressed in the compressor 49, will loose its energy,
which
is transferred to the circulated polluted liquid 42 on the second side of the
heat ex-
changer. This has the consequence of an evaporation of the liquid which is to
be
cleaned. This steam penetrates along the one side down to the downdraught
evapora-
tion heat exchanger 50 and is streaming down into the top of the process
vessel 41,
which is connected to the scrubber 52, and will thus pass via the steam outlet
47 and
through the scrubber 52, the pipeline 48 and the compressor 49 into the heat
ex-
changer 50. The steam is condensed during energy loss and can then be drained
off as
cleaned condensate via the outlet pipe S 1.
Within the pipe from the compressor 49 to the downdraught evaporation heat ex-
changer 50 a scrubber 52 has been placed, which as mentioned above is
separated into
two parts. The upper part 54 contains a base (NaOH) and the lower part 53 an
acid
(HN03), which are supplied through a pipe for each liquid. This permits a
regulation
of the added amounts of acid and base, respectively, as a consequence of the
results of
the current measurements, so that the pH can be maintained constant during the
entire
evaporation. The upperstream part in the scrubber 52 (comprising the scrubber
53 and
the scrubber 54) must always be supplied with acid in relation to the
downstream al-
kaline part, because the acids are more mobile than the bases.
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12 -
Both parts in the scrubber 52 are provided with devices for inhibition of
bubbles, rip-
ples and its like, which promotes splash and thereby risk of bringing droplets
out into
the steam pipe from the scrubber 52 to the heat exchanger 50.
S
The present approach, which is disclosed by this invention, is new and is
remarkable
in a surprising way which is advantageous in relation to the prior art and
knowledge,
including especially DK patent application 01288/96. The process according to
the
invention makes use of a mechanic and a process technical construction, which
is
more simple than the hitherto known technique within this field, which gives a
lower
level of expenditures. Apart from this the embodiment of this process renders
advan-
tages. It is thus a remarkable feature that the process is carried without
supply and use
of chemicals, which is a new and an obvious advantage with regard to the time
period
within which the process is taking place, as well as outside this time period.
Concern-
ing the time period in which the process is taking place, the hitherto known
technol-
ogy required thus a handling of the supply of the chemicals needed for the
process.
This handling is in all cases more or less laborious and therefore unwanted,
which
with the process according to the present invention can be avoided totally.
Addition-
ally, within that time period where the process is not working the needed
chemicals to
the process should - according to the hitherto known technique - be stored in
a storage
room, which of course is laborious and therefore desirable to avoid, and also
the plant
for both storage and handling should be approved by the authorities, which
thus makes
both the use and run of such a plant laborious. Those compounds, which are to
be used
here (see for instance DK patent application 01288/96), are favoured by a
special at-
tention by the authorities, because the use of the compounds are restricted
environ-
mentally, for what reason special measures are normally an inevitable
requirement to
an approval from the authorities. Finally it can be mentioned that the process
accord
ing to the invention also has that economic advantage that the expenditures
for pur
chase of chemicals are avoided, which makes the embodiment of the process
cheaper
in relation to the closest known technique.
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13 K
The disadvantages by the known technology, which is here shown by an example
of a
plant, is thus clearly that the operation is connected with the relatively
high consump-
tion of energy and a high use of chemicals.
The present invention will in the following be detailed with basis in Fig. 3,
which
shows an example of a flowsheet for a plant, which uses this invention.
The apparatus, which is shown in Fig. 3, consists of a downdraught evaporation
heat
exchanger 50, through which the liquid, that is under evaporation and is to be
cleaned,
is circulated by means of the circulation pump 43, connected with the outlet
from the
processing vessel. The boiler liquid 42 is heat exchanging on its way down
through
the heat exchanger 50 with the condensing water steam from a absorption column
62,
which constitutes an essential part of the present invention. Within the
column 62
acid/base reactions are taking place as something very essential for the
invention. Said
acid/base reactions are taking place between the present weak acids and weak
bases,
which as mentioned are more mobile compounds and less mobile compounds as
judged relatively to the mobility of water. By the heat exchanging 50 the
liquid is
brought to the boiling point.
The downdraught evaporation heat exchanger 50 is placed above the boiler 42 in
which a reservoir of liquid being under evaporation is present. The liquid is
circulated
by means of the pump 43. The pressure in the boiler 42 is kept constant during
the
evaporation by means of a pressor state 63 (for regulation of the heating
element 64)
which is activated when the pressure is below 5 mmbar overpressure compared to
the
surroundings. The steam which arises by the boiling of the liquid in the heat
ex-
changer 50 is streaming together with the liquid down into the boiler 42.
In the boiler 42 a liquid/steam separator 65 is placed which separates liquid
and steam
from each other, whereby the liquid is kept within the boiler 42, which the
steam
leaves through the separator 65. The steam flows from the liquid/steam
separator 65 to
the absorption column 62, in which the main part of impurities in the steam is
re-
moved. From the absorption column 62 the steam is flowing to the compressor
49,
09'~J4-20~J1 CA 02360349 2001-07-06 "~" -" ------'-
14 9 ~.. ~ _ . DK 000000013
which gives the steam an increase pressure, whereby the condensation
temperature of
the steam increases to such a degree that the steam is able to condense, when
it flows
over tv the heat exchanger 50.
'The condensate from the steam runs down to the bottom of the heat exchanger
50, in
which it is collected until a ccztain level is achieved, which is determined
by the float
switch 66, which by activation opens valve 67 which permits the condensate to
flow to
the vessel 68. The level of liquid in boiler 42 is kept constant by means of
valve 7D;
which opens by activation through the float switch G9 which permits that the
liquid
which is to evaporate flows through said valve 7D, a first heat exchanger 71
(in which
the polluted liquid heat exchanges with the condensate), a second preheat
exchanger
72 {in which the polluted liquid is heat exchanging with the steam) and is
nxixed i~rith
the liquid from the boiler 42, which is under evaporation and thereafter
introduced into
the downdraught cvapvradon heat exchanger 50.
In the condensate vessel 68 a reservoiar of condetssate is collected until the
level which
is dcterrniacd by the level sensor 'I3 is achieved, which permits that the
valve ?4 opens
and 75~95% of the condensate (abbreviated C~ leaves the apparatus through the
fixst
preheat exchanger 71, which is the heat exchanger which receives the incoming
ague;
ous liquid W.
A part o~ the condensate (5%-25%) is pumped by meatns of pump 75 to the top of
the
absorption column b2, in which it is disfiributed to the column elements
witlziri. the
column. On its wey down to the absorption calumv b2 the condensate absorbs the
im-
parities from the steam, which rises up from the boiler 42 and acid/base
reactions are r
taking place. In the legend to Fig. 4 these:reactions are further explained.
The condcnsate containing the impurities is led fronn the bottom of the
absvrption,col-
umn 62 to the process vessel 41, in which it is riiixed with the liquid which
is under
evaporation and ele~wing. '1"he part of the steam containing the more mobile
cotn-
pounds is led froth the column 62 via the compressor 49 to the heat exchainger
30. The
part hereof, which by passing through the heat ex-
AMENDED SHEET
b0~ 9~ ~N . - ._. _ _ . .~dS E S/d 3QtidltJd 0~ : SI ZA0Zi~0/60
CA 02360349 2001-07-06
WO 00/41462 PCT/DK00/00013
changer 50, is not condensing, will in concentrated form together with the
remaining
amount of steam, flow over into the second preheat exchanger 72, in which it
is cooled
and condensed by heat exchanging with the incoming liquid W, to which is
hereby
added a further temperature rise. When the gas/liquid mixture temperature in
the sec-
5 and heat exchanger 72 has fallen down to a certain level the termostate 76
is activated,
whereby valve 77 opens, and the gas/liquid mixture flows to the vessel 78, in
which
the gas phase is separated from the liquid phase in the gas/liquid mixture in
the second
preheat exchanger 72.
10 The gas is drained off and in vessel 78 a reservoir of liquid is built up
until a certain
level determined by level sensor 79, after which valve 80 opens and the liquid
flows to
the process vessel 41, in which it is mixed with the liquid under evaporation
and
cleaning.
15 Fig. 4 shows that part of the plant in Fig. 3 that in concentrated form
visualizes the
invention, which thus combines an absorption column with a heat exchanger in
which
the condensate runs in counterstream with the steam which is to be condensated
with
an evaporation system.
Fig. 5 shows an example of an absorption column according to the invention,
where a
part of the condensate flows in countercurrent with the steam flowing from
below. In
the column the surface of the column elements is giving place for a number of
acid/base reactions. Some relevant reactions in this connection are the
equilibrium
reaction ( 1 )-(4)
(1) CH3COOH (gas) <____> CH3COOH (aq),
(2) CH3COOH (aq) <----> CH3C00~ + H+,
(3) NH3 (gas) <_____> NH3 (aq),
(4) NH3 (aq) <_____> NH4+ + OH-,
CA 02360349 2001-07-06
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16
which in addition are shown in the circle of the figure. In the left side of
the circle are
shown the compounds from the below coming steam and what is mentioned in the
right side are relevant equilibria for what is flowing down to the bottom
vessel.
Fig. 6 shows a heat exchanger according to the invention. On the figure is
shown a
downdraught evaporation heat exchanger, in which the condensing steam flows
coun-
tercurrent to its own condensate.
The more mobile compounds in the steam, compared to the mobility of water,
will be
collected and drained off from the top of the heat exchanger. If the waste
liquid which
is to be cleaned is manure then a ammonia will be a big part of the above
mentioned
drained off material. At the bottom the condensate which is the cleaned liquid
will be
drained off.
Explanation for designations in Figs. 1-6:
l: column
2: first heat exchanger
3: compressor
4: bottom vessel for the column 1
5: circulation pump receiving liquid from outlet 36
6: motor valve
7: contra valve
8: gas/liquid separator
9: level sensor
10: first section of heat exchanger
11: second secton of heat exchanger
12: third heat exchanger
13: first motor valve
14: second motor valve
15: nozzles for draining off of liquid biological waste from column 1
16: inlet for liquid biological waste to column 1
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17
17: foam restrictor for upper part of column 1
18: inlet for manure
19: outlet from first section 10 of second heat exchanger
20: inlet for second section 11 of second heat exchanger
21: outlet from second section 11 of second heat exchanger
22: outlet from foam inhibitor 17
23: inlet for the primary side of the first heat exchanger 2
24: outlet from the primary side of the first heat exchanger 2
25: inlet from the primary side of the second section 11 of the second heat
exchanger
26: outlet from second section 11 of second heat exchanger
27: inlet to gas/liquid separator 8
28: outlet from separator 8
29: inlet containing liquid for the nozzles 30
30: nozzles 30 in column 1
31: outlet containing gas fraction from the separator 8
32: inlet containing the gas fraction to the primary side of the third heat
exchanger
33: outlet from primary side of the third heat exchanger
34: inlet containing manure to the secondary side of the third heat exchanger
12
35: outlet from the secondary side of the third heat exchanger 12
36: outlet from the bottom vessel 4
37: inlet from the secondary side of the first heat exchanger 2
38: outlet from the secondary side of the first heat exchanger 2
39: evaporator
40: a liquid distribution system
41: process vessel connected with scrubber 52
42: concentrated process liquid (concentrate Cc)
43: circulation pump connected with the outlet from the process vessel
44: circulation pipe
45: inlet pipe
46: outlet pipe with outlet of concentrate (Cc)
47: steam tapping
48: pipe for steam
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18
49: compressor
50: downdraught evaporation heat exchanger
51: outlet pipe for clean condensate
52: scrubber comprising scrubber 53 and 54
53: scrubber containing acid
54: scrubber containing base
55: acid
56: base
57: pipe for acid
58: pipe for base
59: isolated cabinet
60: level hight for process liquid
61: level sensor for regulation of supply of polluted liquid
62: absorption column
63: pressostate for regulation of heating element 64
64: heating element
65: separator for separation of steam and liquid
66: float switch, which by activation opens valve 67
67: valve, which by opening permits condensate to flow to vessel 68
68: vessel for condensate
69: float switch, which by activation opens valve 70
70: valve, which by opening permits the polluted liquid to pass through to a
first pre-
heat exchanger 71
71: first preheat exchanger, through which the polluted liquid heat exchanges
with
condensate
72: second heat exchanger, in which the polluted liquid heat exchanges with
steam
73: level sensor (in vessel 68), which by activation opens valve 74
74: valve which by opening permits the condensate (Cd) to pass through the
first pre-
heat exchanger 71
75: pump, which takes a part of the condensate to the top of 62
76: termostate which by activation opens valve 77
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19
77: valve which opening permits the gas/liquid mixture from 72 to pass further
on to
vessel 78
78: vessel, in which gas phase is separated from liquid phase in the
gas/liquid mixture
in 72
S 79: level sensor, which by activation opens valve 80
80: valve which by opening permits the liquid to flow further to the process
vessel 41
C~: See 42 and 46 above
C~: See 74 above
W: Incoming polluted liquid, which is desired to be cleaned.
