Note: Descriptions are shown in the official language in which they were submitted.
~. C373177~
The present application is a divisional of
Application Serial No. 244479 filed Jan~ 29, 1976.
The present invention relates to a gas exhaust
device, which may be used as part of an apparatus for removing
ammonia-nitrogen from a wastewater by vacuum desorption of the
wastewater.
In recent years, substantial advances have been
made in the technology for treating wastewater, both domestic and
industrial, so that it may be introduced in-to receiving bodies of
water with a minimum of pollution. The requirements for treating
wastewater have steadily increased. One of the requirements which is
becoming more important is the elimination of nitrogen from wastewater
effluent after the effluent has been processed for removing other pol-
luting constituents. The desirability of eliminating nitrogen was
set forth in a recent United States Environmental Protection Agency
publication entitled "Nitrification and Denitrification
,,'~ ~
.
~0~3'77~:;
Facilitie~, Wastewater Treatment". In this article which
was published in 1973, the Techn~logy Transfer Seminar
publication stated in part "with regard to eutrophication of
surface water, nitrogen in the fixed form o ammonium and
S ni~rate ion~ is considered to be one of the major nutrient
supporting blooms of green and non-nitrogen fixing blue-green
alga~. Nitrogen removal fr~m wastewaters is being requested
in soma areas and considexed in many others. Where discharge i5
to lakes or reservoirs with significant detention times, seasonal
removal will not ~uff ice and performance 365 day~ per year
will be expected." This same article recommends biological
~ystem~ o~ nitrification followed by biological denitrification
to remove nitrogen from wastewater. The biological systems
are complicated by various factors, ~uch a~ the presence o~
fragile bacteria, temperature change, c~ll residence time,
carbonaceous B.O.D., p~, carbon source availability and po-
tent:Lal repollution by the sy~tem. AQ a follow-up to thi~
1973 article, a 1974 publ~cation by the United State3 En-
; vironmental Protection Agency entitled "Physical-Chemical
. Nitrogen Removal-Wastewater Treatm nt" concludes that all
20l processes now under study fGr removing nitrogen from waste-
water have certain disadvan~ages, and no single process is
considered superior and adapted for ge~eral use in removin~
nitrog~n from wastewater, Some c:f the system~ outlined in
thi5 1974 article include physical-chemical systems, such
a~ ~on exchange and breakp~int chlorinati~n, which systems
are of questionable value due to their exce~sive cost, cun~
trol diff iculties and poYsible recontamination by the re-
~ultiny substances. Another system described in the 1974
article is the ammonia stripping process. Ammonia strip-
ping o~ ammonia nitro~en ~rom wastewater, has at least
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'1~737~76
~ome th~oretial advantages sinee this syst~m can treat con-
ventional wastewater treatment equipment effluent. In an
ammonia stripping process, wastewater containing dissolved
ammonia is passed through a scrubbing tower having air
S circulating therethrough~ The circulated air removes a certain
portion of the ammonia which separates from the wastewate~
effluent. In such a system, the pH of the wastewater effluent
is increased to concentrate the am~unt ~f nitrogen in the
form of ammonia gas within the wastewater as compared to the
amount of nitrogen in the form of dissolved ammonium ions.
Amrnonia stripping does not remove all of the ammonia gas sinc~
thi~ gas is highly soluble in the wastewater. The ammonia
~trlpping proces~ has the disadvantage of poor efficiency in
cold weather and the potenti~l for scaling problems that may
reduce its efficiency and also raises concern over ammon~a
ga3 di~charge to the atmosphere.
The present inven~ion i5 adapted to operate in
many diff i~ult types of pr~cesses containing objec~ionable
quantities of ammonia-rlitrogen. Ammonia-ni rogen ls pre~ent
in wastewater as both ammonium ions and ammonia ~as~ ~he
ratio of the quantity of ammonia gas to ammonium ions i3
a functio~ of both the pH a~d temperature of the wa~tewater
or wa3tewater effluent. As an example, the ratio of amm~nia
to a!lunonium ions ~or a wa~tewater at approximately 25C may be
expres~ed ~y the foll~ing equation~
_ -
log 3 ~ pH~9.25
~l NH4
At higher temperatures, the percentage o ammonia
gas increases for any given p~. In a like manner, at lower
temperatures, the percentage of ammonia ga~ decreases for a
-3- .
~073776
give~ pH.
In some ammonia stripping processea, the incomi~g
wastewater effluent~ which may have been previously processed
to remove other pollutant~, is mixed witll a ~ubst~n~e, such
S as lime, to create a hig~ly basic liquid. The use o lime has
the ancillary advantage of removing phosphates by precipita-
tion~ The p~l of the liquid i~ increased to over a pEl of 1OJ
As was previously mentioned, the higher the pH, the higher
the ratio of ammonia ga~ t~ ammonium ions in the w~stewater
or wa~tewater e~fluent. By providing higher concen~ra~ions
of ammonla gas, th~ pre~ent invention, which will be defined
later, can remove ~ higher percentage of the amrnonia ga3 ln
order to sub~tantially reduce ~he total a~monia-nltrogen
content of ~he was~ewater.
~5 As ~urther ba~kground to the present ~nventlon, it
i~ known that ammonia ga~ may be driven from a li~uld con-
taminated wit~ ammonia if the liquid i-~ boiled by heating the
li~uid to th~ boiling temperature. Thi~ coneept i~ used in
. the KeI~dahl te~t for ammonia in a liquid. Such boillng may
al~o be ~ndu~ed by lcwering the absolute pressur~ over the
bcdy of liquid containing dis~olved ammonia gas to the vapor
pre~3ure proportional to the temperature of the contaminated
liquid.
Di3advantage~ of prior ~y~tems for removing ammon~a
ga~ fxom wastewater or wa~tewater effluent are overcome by
the present invention which relate~ to ~ met~od and apparatu~
for ~acuum de~orption o am~onia ga# from wa~tewat~r
effluent. ~hroughout thi~ ~pecification wa~tewat~r i8 u~ed
to mean any wastewatex 'Liquid irrc~peotive of prior treatment.
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1~:)73776
In accordance with the present invention, there i8
provid~d a method for removing ammonia nitrogen from waste-
water, which comprises increa~ing th~ pH of ~aid water to a
highly baqic condition and removing ~ree ammonia from said
wastewater, the removal being carried out by applying a
vacuum to said wa~tewater 50 a~ to create an absolute pre~- -
sure no greater than approximately ~he vapor pres~ure of
said wastewater whereby a~monia i~ de~orbed ~rom ~aid wa~te-
water effluent, and absorbing said de-Rorbed ammonia in a
body of liquid having a pH 3ub~tantially les~ ~han ~ha~ of
the waqtewater in said highly basic condi~lon.
In accordance with another aspect of the present
invention, there is provided an apparatus or removing
ammonia nitrogen from wastewater which comprises means for
increasing the pN of said wastewater, tank means for re-
aeiving ~aid highly basic wa~tewater, means for creating
a vacuum correRponding approximately to the vapor pre~sure
o ~aid wastewater, means for communicating said vacuum
creating means with ~aid tank means whereby armmonia i9 de-
7.0 sorbed from ~aid was~ewa~er, and means ~or holding a body
- of liquia having a pH les~ than said highly basic condition
.~ and for exposing said desorbed ammonia to ~aid liquid body
whereby said desorbed ammonia is reab80rbed by ~aid liquid
body.
In accordance with another aqpect og the present
: invention, means are provided for introducing bubbleæ of A
gas which is only slightly soluble in the wastèwater into
the deæorption tank. In thi~ manner, molecular agitation
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~0~3776
takes place in that ~he release of finc ga~ bubbles in the
wa~tewater reduOE~ surface tension. Since a vacuum correspond-
~ny to the vapor pressure of the wastewater is created over
the wastewater in the desorption tank, incoming gas intxDduced
S at approximately atmospheric pressure will expand drastically
in the tank and create a sub~tantial volume of bubble~ for
reducin~ the sur~ace tension and, thu3, incre~sing the rate
of removal of ammonia ga~ from the wastewa~er with very small
quantities of gas. ~his molecular agitation cauQed by 'che
introduction of a low solubility gas, such as nitrogen or
air, ~ubstantially enhanee~ the overall xemoval o~ ammonia
çla~, the percentage of which ha~ been incr~ased by tha changed
pH of the wa~tewa~er. These bubbles create ag1tation with
min~mum li~uid vapor carried from the body of wa~tewater
b~ing subjected to a high vacuum in the desorption tank.
In accordance with another aspect 0~ ~he pre~ent
invention, the liquid into which the de~orbed ammonia gas i5
~ub~equently abqorbed ha a reduced p~. In one embQdiment,
~h~ abssrblng liquid i8 a~idic . In addition, th ~ absorbing
2~ liquid ~ay have a reduced temperature crea~ed by ~efrigeratio~
or other cooling mean~ to further increase it~ abili~y to
absorb ammonia gas~
In ccordance w~h another aspect o$ the invention,
th~ wastewater in the desorption tank is heated to decrease
-~ 25 the surace ten~ion o~ t~e wa~tewater and decxea~e ~he ability
: o the wa3tewater to retain dissolved ammonia ga~. ~his
further enhance~ the removal o the amnonia ga~ from ~e
wastewater in the de~or~t~on tank.
The present invention lcwers t~e a~solute pre~ure
30 within the desorption tank or ves~el which containq was~ewater
.... . . . . .
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3L~73776
at a preselected p~ so that. the pres~ure over the wastewater
corresponds to the vapor pressure of the admixture for ~he
temperature of the wastewater. This causes a high release o~
ammonia gas even though the gas is highly soluble in the
S wastewater. secau5e of thiq high solubility of ammonia gas
in the wastewater~ an absolu~e pressure higher than the vapor
pres-~ure corresponding to the temperature of the wastewater
suffic.ient
will not result in7~emoval of ammonia gas by vacuum alone.
The pre~ent invention can exceed 90% removal which i~ highly
satis~actory. Vapors and desorbed gases are evacuated and
carried from the desorption ~ank or vessel into another
ve~sel wherein the gases and vapors are re-dissolved and/or
condensed ~or sub~equent disposal or reuse.
1~ accordance with the pr~ferred embodiment of the
lS present invention, the low pres~ures used in the desorption
tank are generated by a spaced vacuum generator includinq a
flr~t ves3el which is ~illed completely with a liquid and
~ealed rom atmosphere ingre~s of ga~. The liquid i5 then
removed from the filled ve~sel. In this manner, the absolute
; 20 pressure in the cavity of the fir t vessel created by the
removal of liquid therefrom will approach the vapor pressure
of the liquid in this first vessel. The vapor pressura of
the liquid in the evacuated vessel or tank is a function of
the temperature of the liquid~ For example, vapor pressure
~f water at 100C is equal to atmospheric pressure at sea
level, iOe- 760 mm. The vapor pressure of water at 20C
; i~ 17.S35 mm and at 0C the vapor pressure of water is only
4.5 mm. Thus, the vacuum created in the evacuated tank is
essentially the vapor pressure according to the temperature
of the liquid in the evacuated tanX. The above value~ assume
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1 ~ 7 3 77 ~
t~at the liquid in the evacuat~d tanX is water which can beu~ed for th~s purpose. ~h' s low pressure creat~d above ~he
liquid in the evacuated tanX and corresponding~ to the vapor
preSsure Of thiS liquid, in acco~dance with the preferred
embodiment of the invention, is then applied to the desorp-
tion tank t)r ves~el. In the preferred embodiment, thetemperature of the displaced liquid in the displacement kank~
or vassel~ is reduced to a temperature lesR than the was~2-
water temperature. Thus, the pre~sure of the vacuum w~thin
10 the desorpti~n tank will be redu~ed to a pressure approaching
the vapor pressure of the cooler li~uid in the displaced or
evacuated tank which i~ lower than the vapor p~essure of
the wastewater. The application o~ this lower pressure to
the desorption tank is continusd by the additional di~lacement
of the cooler liquid in the displacement ves~el until th~
displacement vessel i~ evacuated to a predetermined extent.
In th~ mannex, a relatively low pre~sure ~s applied to the
desorption ves~sl or tank which cause~ the desorptlon tank to
go to the vapor pres~ure of he wastewater hav~ng a temperature
above the displacem2nt liquid temperature. ~hu8, a high
percentage of dissolved ammonia gas is extra~ted ~rom the
wastewater being treated. The heat removed from the dis-
placemen~ ~iquid to reduce its temp~rature may be appliod to
~he wa~tewater.
In accordance with another aspect of the preferred
e~bodiment o~ the inventlon, the low pre~sure ~r va~um
applied to the desorption ~essel or tank is continued ~y
evacuation o~ a ~econd displacement tank that i~ filled
by the liquid being eva~uated or pumped ~rom the irst
mentioned displacement tank when it i5 being eYa~uated.
, .
~0~3776
By using two di.splacement tanks~ a substantially continuous
vacuum for use in the desorption tank is created by al
ter~ately evacuating the two tanks with liquid ~eing pumped
from one into the other and vice versa. After one of the
displacement ~anks has been evacuated, the cavity over the
liquid in this tank contains ammonia gas and other gases
which are partially soluble in water, such as air and nitro~en,
and vapor~J s~ch as water vapor, These gases and vapors have
been extracted in par~ from the liauid in the desorption tank
or ves~el containing the contaminated liquid and pulled by the
vacuum to the displacement tank. These gases and vapors
in the cavity above the liquid lev~l in the di~pla~ement
vessel will either be absorbed into the liquid o~ the displace-
ment ve~el or expelled into atmosphere when the vessel is
subsequently filled by liquid from the other displacement
tank. Since al~monia is highly soluble in low pH water and
similar li~uid~, the ammonia gas will be reabsorbed in the
water of the displacement tank unless an intercepting mech-
a~ism ~uch as an accumulator is used to reabsorb the ammonia
gas before it reaches the liquid in the displacement tank.
The rate of displacement of liquid in the two displacement
tanks is proportional to a pumping rate determined by pumps
used to alternately fill and evacuate the two displacemen~
tank~ which act as a vacuum generator for creating the vacuum
used in the desorption tank or vessel.
The greater thé temperature differential betwe~n the
l~quid in the di.splacement tanks and the contaminated liquid
effluent ~n the desorption ve~sel, the greatex the vapor
pressure differential between these two tanks. ~he vapor
pressure differential control~ the desorption action and
.
_g_
-. " . - , . : ~
1~73776
the effectiveness of the desorption process is also a function
of the rate of displacement in the two vacuum generating dis-
placement tanks.
The absolute pressure applied in the desorption
tank may be further decreased by an auxiliary pumping mechanism,
such as a positive displacement pump or blower.
The gas exhaust device of the invention may be
used with the displacement tanks of the vacuum generator.
In accordance with the present invention there
is provided a gas exhaust device for a tank having a raising and
lowering liquid level, which comprises an outlet cavity having
an uppermost portion and positioned from said tank, a first valve
in said cavity and adjacent said tank having a first closed con-
dition and a second opened condition, a one way check valve means
allowing gas flow only from said cavityl said check valve means
being adjacent said uppermost portion of said cavity, a level sen-
sor for shifting said first valve to said first closed position
when said liquid level is in said cavity and above said first
valve means, and means for selectively shifting said first valve
means to said second opened condition when said level in said tank
is at a given level below said first valve means.
The invention will now be described with reference
to the accompanying drawings in which:
FIGURE 1 is a schematic flow diagram illustrating
an apparatus for removing ammonia-nitrogen from wastewater;
FIGURE 2 is a graph showing the ammonia gas
concentration in various pH solutions of wastewater;
FIGURE 3 is a graph illustrating removal of
ammonia gas from solution at various temperatures of the wastewater
and the effect which temperature has upon the rate of removal at
a pH of 10.5;
FIGURE 4, 4A and 4B are enlarged views showing
the gas exhaust device of the present invention;
--10--
.
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. . : . .
1073'77fi
~ FIGURE 5 is a partial cross-sectional view
: illustrating, somewhat schematically, the molecular agitation
concept employed in the preferred embodiment of the present
invention;
FIGURE 6 is a schematic, cross-sectional view
illustrating a two position quiescent valve which could be used
at the inlet of the displacement tanks employed in embodiments
of the present invention, as shown in FIGURES 1, 7 and 8;
FIGURE 7 is a schematic flow diagram illustrating
10 a simplification of the preferred embodiment of the present
,, - . - -- . :
~73~.J7~
invention;
FIGURES 7A, 7B, 7C, and 7D are views similar to
FIGURE 7 showing various operating characteristics of the
simplified structure illustrated in FIGURE 7, which description
applies to the embodiments shown in FIGURES 1 and 8;
FIGURE 8 is a flow diagram illus'trating, schematically,
a further simplified version of the preferred embodiment of the
invention shown in FIGURE l; and,
FIGURE 9 is a schema-tic flow diagram illustrating
certain concepts of the preferred embodiment of the present in-
vention.
I
Referring now to the drawings, wherein the showings
are for the purpose of illustrating a preferred embodiment of the
invention and not for the purpose of limiting same, FI5URE 1 shows
an apparatus A for removing ammonia gas from a wastewater, which
apparatus includes a vacuum generator 10, an ammonia desorption
tank or vessel 12, an inlet system 14, an accumulator 20, a first
vacuum connection system 22 and a second vacuum connection system
24. Each of these components will be described in detail, and
then the operation of the preferred embodiment illustrated in
FIGURE 1 will be apparent.
Referring now to vacuum generator 10, this generator
is used to develop a vacuum for application in tank 12 of a vacuum
which corresponds to the vapor pressure for the wastewater within
tank 12. When the vapor pressure of the effluent in tank 12 is
reached, the effluent boils to cause removal of ammonia even though
ammonia ishighly soluble in thewastewate,r and cannot beeasily removedin
-12-
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~L~73~7~i
appreciable quantity at higher pressures. various vacuum
generators could be used; however, in accordance wit~ the
preferred embodiment of the present invention, the vacuum
generator 10 includes an inlet line 30 for water or another
S appropriate pumping liquid. The inlet is controlled by a
selectively operated valve 32 for co~municating the inlet
with a vertically extending pipe 34. Upper branches 40,
dis~ement
42 of pipe 34 communicate with/tanks A, B, respectiv~ly,
through selectively actuated valves 44, 46, respectiYely.
These valves may be two position valves to create quiescent
conditions at the top of the filling cycles, as schematically
represented in PIGURE 6. Lower branches 50, 52 of vertical
pipe 34 include checX valves 54, 56, respectively, whiCh
~heck valves allow flow, as indicated by the arrows o~
lS FIGURE l.
For a purpose to be explained later, the preferred
embodiment of the invention includes a heat exchanger 60 to
cool the liquid flowing through vertically extending pipe
34. In accordance with the illustrated embodiment, heat
exchanger 60 includes an inlet 62 for cold liquid, such
as water, and a liquid outlet 6~. Liquid entering inlet 62
may be cooled by an appropriate refrigerating device, not
shown. Tanks A, B include lower pumps 70, 72, respectively,
for pumping li~uid between the two tanks, in a manner to be
25 described later. A drain 74 is controlled by a selectively
operated valve 76 for draining liquid from the vacuum gen-
erator lO when necessary. In the pre~erred embodiment shown
in FIGURE l, contamination of the liquid within tanks A and
B by ammonia ga5 frorn desorption tank 12 is somewhat eliminated
by the use of accumulator 20. ~he operation of the accumlator
-13-
~3~77~;
to remove ammonia gas from tank 12 will be described later.
When an absorbing component is used between vacuum generator
10 and tank 12, a substantial amount of time may elapse be-
ween successive rechargings of the liquid within tanks A, s.
In that situation, only vapor condensed in the liquid of tanks
A, B will cause the liquid volume to increase.
In the preferred embodiment, tanks A, B are provided
with appropriate device~ for sensing upper levels of liquid
within the tanks. This can be done by a variety of liquid
level sensing devices, which are schematically illustrated
as high level sensors 84, 86. The high level sensors, in
the pre~erred embodiment, do not discontinue the filling
cycle of the tanks. They are used in conjunction with
quiescent valves 44, 46, and shut off valves 104, 106 in a
manner to be described later.
At the upper portion of tanks A, B there are provided
two gas discharge and liquid trapping mechanisms 90, 92 which
define respective gas outlet cavities for the tanks and
include check valves 94, 96, gas outlets 97, 98 positioned
at the top of stand pipes 100, 102 communicated with the
upper portion of tanks A, B, selectively operated valves
104, 106 and liquid level sensing devices 110, 112. The
valves 104, 106 are located in the outlet cavities. The
level sensing devices include downwardly extending probes
114, 116, respectively. These probes determine the maximum
upper level of liquid within tanks A, B during normal opera-
tion of vacuum generator 10. To complete the description of
the vacuum generator components, selectively operated valves
120, 122 communicate the stand pipes 100, 102, respectively,
with a vacuum line 130, which is communicated with tank 12
through vacuum connection systems 22, 24 and accumulator 20.
Referring now to FIGURES 7, 7A-D, the operation of
.. "~ .
-14-
~6~7377~
vacuum generator 10 is illustrated. In FIGURE 7, the apparatu~
A' i~ somewhat simplified. vacuum line 130 is communicated
directly to ammonia desorption tank 12 without going thr augh
'che two connecting systems 22, 24 and accumulator 20, This
is a simplified version of the preferred embodiment o~ the
invention and can be used to explain the operation of the
vacuum generator. As shown in FIGURE 7A, valve 32 is opened
t~ introduce li~uid, such as water, into vert;c~l line 34.
At thi~ time, valves 44, 46 are fully opened and valves 104,
106 are opened. Thus, tanks A, B, are filled t~ minimum
levels 80, 82 as ~chematically shown in FIGU~E 1. Any ga-
~entxapped within tanks A, B, is orced outward1y through
check valves 94, 96. After reaching the minimum ~vel a3
schematically 3h~wn in FIGURE 7As valve 46 i~ fully clo~0d
allowi~g all liquid from inlet line 30 to pas~ through pipe
34 into tank A. Check valves 54, S6 prevent ~low of liqu~d
downward throug~ pipe 34. A~ ~low of liquid i9 continued
into tanX Ao through upper branch 40 and valve 44, the liquid
level ri~es as indicated in FIGURE 7Bo ThiS compresses and
20 forces gas in ~he cavity above the rising liguid ~hrough
- ~pen valve 104 out gas outlet 97 through check val-ve 94.
T~.is filling action is continued until tank A i5 fully illed
which is determined by uppex level sensor 110, sh~wn in
F~URE 1. At that time, valves 32, 44, and 104 are clo~dO
2S Thi~ entraps liquid above valve 104 for a purpose to be
explained in connection with FIGU~E 4. As ~hown in FIGURE 7C~
pump 70 i~ then energized to evacuate liquid from tank A and
pump thi~ liquid th~ugh check valve 54, throu~h l~wer brarlch
50 and into vertically extending pipe 34. After a selected
time which purge~ any ~as within the vertical line 34, valve
~15~
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,~ . - . - j . . , . , ,: ,
., :. . . - ~ , . ,: , . .
.:, .,
~73776
46 of branch 42 is fully op~ned. This allows the liquid from
tank A to enter tank B. During this operation, valve 106
is opened so that as liquid enters tank B and fills this tank,
undissolved gas and any uncondensed vapor i~ f~rced through
S valve 106 and ~hecX valve 96 and out gas outlet 98. This
gas removal is continued until tank B is filled to a level
determined by probe 116 of level sensor 112, a~ shown in
FIGVRE 1. During this time, a vacuum is created above th~
decrea ing liquid level in tank A, which vacuu~ is communicated
by open valve 120 to the vacuum line 130 communicated with
ammonia de~orption tank 12.
The vacuum within tank A i9 determined by the vapor
:~ pre~sure of the li~uid within the tank, and this vapor pres~ure
decreases with temperature. For that reason, heat exchanger
60 shown in FIGURE 1 i~ used to reduce the temperature o~ th~
; liquid within tanks A and B. This increa~es the vacuum by
decreasing the vapor press~re obtainable above the liquid
level in the tank being evacuated.
. -After tank A has been evacuated and tank B ha~ been
; 20 filled, the reverse action takes place wherein tank B
i~ evacuated and tank A i8 illed. This is sh~w~ i~ FIGURE
7D. In thi~ situation, valve 44 is fully opened after pump
72 is energized to pump liquid from tank B ~o tank A. Valve
;: ' 104 is opened and valve 122 i5 opened. Thi~ communicates
:~ 25 vacuum line 130 with the low preRsure vacuum areated abov~the decreasing level of li~uid in tank B. To provide a
po~itive liquid seal above tank B, selectively operat2d
valve 106 i~ clo3ed during evacuation o~ tank B.
R~ferrl~g now to FIGURES 4, 4A and 4B, the li~uid
or tank ~ealina mean~
trapping m~ ~ and ~ is sch~matically
`~ 16-
.: .
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~3776
illustrated. D~ring a filling operation, compressed gas
first enters stand pipe 100 through open valve 104, as shown
in FIGURE 4. Ihis gas exits through check valve 94 and outlet
97 when its pressu.re exceeds atmospheric pressure. As ~he
tank continues to fill, liquid rises through stand pipe 100
and past open valve 104, as shown in FIGllR~ 4A. Compre3sed
gaq above the liquid is still forced through outlets 97 and ~
check valve 94. As the liquid reaches probe 114, which is oont~d in a
housing def~ng a cavity comm~cating wi~h the upper po~io~ of the di~
plac~nt tar~, liquid seIl~or 110 is ~nergized to cl~se the valve 104 and
start the re~r3e filling acl:ion. This stn~t~re traps liqu~d above llalve
104. In addition, level sensor llû al~o indicates
~hat the tank is filled and the opposite pumping action is to
take place, as previously described. Any appropriate c~ntrol
mechanism can be used for operating the various valves
and level sensors as described hexein and the structure of
the~e control mechanisms does not form a part of the present
invention. By entrapping liquid above closed valve 104, a
liquid gas seal is crea~ed to prevent inadvertent inqress of
atmospheric air while the tank under stand pipe 100 i~ being.
evacuated. As soon as the pump is energized to again fill
the tank under stand pipe 100~ valve 104 is opened. When
this happens, the liq~id above valve 104 i5 allowed to flow
by gravity into the tank for the next filling cycle~
As can be seen, vacuum is applied by vacuum generator
10 through line 130. This vacuum has a pressure determined by
the vapor pressure above the liquid in the evacuated tank~
which is temperature dependant~ By redu~ing the temperature
of the liquid in tanks ~, B lower vapor pressure i~ possible
and a higher vacuum is thereby created. Thi5 lower pressure
or higher vacuum is suf~icient to establish a low pressure
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~a373776
over the wastewater in tank 12 corresponding to the vapor
pressure of the wastawater. This causes a sufficiently
low pressure above this liquid to remo~e the dissolved
ammonia in the wastewater. The liquid in ~ank 12 is sub~
jected to a sufficiently low pressure equal to the vapor
pressure of the wastewater at its particular temperature.
This causes b~iling of the ~astewater and desorption of the
ammonia gas from the wastewatex.
Referring now to the vacuum ammonia desorption
tank 12, as shown in FIGURE 1, thi~ tank include3 an inlet
140 for wastewater which has been previGusly treated by
inlet system 14 with a substance to increase the p~ of the
incoming wastewater. In prac~ice, the pH of the incoming
wastewater is determined by the desired amount of ammonium
ions to be convsrt~d to ammonia gas and the temperature
of t~e wastewater taking into consideration the general
ammonia gas relationship of FIGURE 2. Since the ma~eria~s
us~d to increase the pH a~d cost to the total operation, the
pH is not increased beyond an optional balance between ~ost
and performance. At the upper portion of tank 12 there is
provided a ga3 and vapor outlet 142 which is used to communi~
cate the vacuum in line 130 of generator 10 to tank 12. A
vent valve 144 communicates with gas outlet 146 to vent tank
in order to drain tank 12 by gravity and vent the tank during
filling. A valve 148 in line 142 is used to ~ommunicate tank
- 12 with the vacuum created by generator 10. Valve 144 i9
opened when tank 12 is being filled with ammonia contaminated
wa~tewater~ Gas above tlae liquid level within the tank is
~ompressed and ~orced through valve 14~ and out outlet 146
to atmo~phere. By this arrangement, all the ga9 in tank 12
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1~73776
i~ not compressed and ~orced ~r drawn through connecting
systems 22, 24 into vacuum generator 10. A~ter tanX 12
has been fill~d, valve 148 can be opened to communicate
the vacuum of generator 10 to tank 12. In the preferred
embodiment, this connection is not a direct eonnection
as shown in FIGURE 7. The vacuum connection is throuqh
connecting systems 22, 24 and accumulator 20. Tank 12
may be partially evacuated by communication with the vacuum
by opening valve 148 and this can cause ~ucXing of liquid
into tank 12 from line 140 when control valve 188 i~ opened.
` In this filling operation, valve 188 is closed when tank 12 is
properly filled.
A recirculating system 150 i5 attached to tank 12.
Thi~ system includes line 152, pump 154, a diverter valve
156 and drain 158. A heat exchanger 160 is used ~o hea~
the waRtewater circulated through line 152 and includes
inlet 162 fox a heated liquid and liquid outlet 164. The
heat exchanger adds heat energy to the wastewater of tank 12
~o replace the heat lost by evaporation and to elevate the
2~ actual temperature o~ the wastewater. Since hea~ i~ added to
the wastewater in tank 12, in 'che preferred embodiment, heat
exchanger 160 can have a recuperator effect on the cooling
heat exchanger ~0 used in the vacuum generator 10. Heat
exchanger 160 is used to recapture and use the heat energy
extracted by heat exchanger 60 and other cooling heat exchangers
of apparatus A. Heating o~ the wastewater has various
advantageous effec~s on the operation of appàratus A. As
previously mentioned, the vapor pressure for a given liquid
i~ temperature ~enQitive~ Thu~, the higher the temperature
:. 30 o~ the wastewater in tank 12 the higher the boiling point
: pre~sure. ~he differential in temperature between the
.
--lg--
~1~737~76
liquid in genexator 10 and the wastewater in tank 12 allows
a pressure in generat~r 10 which is l~wer than the vapor
pressure of heated wastewater in ta~k 12. CQnsequently,
by heating the wastewater in ~anX 12 and cooling the liquid
in generator 10, a more effective vacuum system is obtained
and the vacuum applied to tank 12 tends to boil rapidly
the wa~tewater.
By increasing the temperature of the wastewater
in tank 12, a further advantage is obtained. ~his advantage
is apparent from the relationship shown in FIGURE 2. This
graph illustrates the curve for the percentage of the ammonium
ions converted to ammonia gas in the wastewater at different
pH values and at a given temperature, which is 25C in
FIGURE 2. It is noted that at 25C and at a pH of 12.0,
approximately 100% of the an~nonium ions have been converted
to ammonia ga~ within the wastewater and await desorption.
l~ the temperature of the wastewater decreases, the graph
of FIGURE 2 shifts to the right. Thu3, a lesser p~rcentage
of ammonium ions is converted to ammonia ga~ for a given
pH value. The reverse i~ true. If the temperature o~
the wa tewater i9 increased~ the graph shifts to the left.
Thus, for a given p~ value of the wastewater, a higher
per~entage of the ammonium ions is converted to ammonia
gas within the wa~tewater if the wastewater i~ heated.
Thus, by heating the wastewater in tank 12, the curve of
FIGURE 2 is shifted to the left and a greater percentage
of ammonia gas is present for a given pH. By shifting
the curve, a lesser basi.c solution could be used in tank 12.
Consequently, less material~ are required to obtain the needed
pH when the wastewater is heated. This reduces the overall
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. .
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1~7377G
cost of operating apparatus A. As i~ known, pH i5 a
logarithmic function and any redue~ion of required pH has
a substantial ~st savin~s effect on the pr~ess. This is
a further advantaye of heating the wastewater in tank 12
by available waste heat. Heat exchanger 160 may be heated
by using waste heat of Dther processes b~ing performed
adjacent the treatment facility ~sing apparatus A.
A ~urther advantage of incrPasing the temperature
of the wastewater in tanX 12 is illustr~ted by the graph of
FIGURE 3. This graph shows the removal of ammonia gas
from the wastewater at various temperatures for a given
vacuum, concentration and pH. The pH of ~his graph is
10.5. It is noted that as the temperature increaseq, a
higher percentage of ammonia gas is removed in a given
length o time. Thus, the x~sidence time of the wastewater
in tank 12 can oe reduced by increasing the temperature
of the wastewater to operate on a higher c~rve in FIGURE 3.
In addition, the rate of removal is increased to provlde
more cficient operation when the wastewater temperature is
increa~ed. This ~urve also relates to the effect of surface
tensionO Surface tension is decreased a~ the temperature Qf
the wastewater increases. Thus, by heating the wastewa~ex,
a lower surface ten~ion i~ obtained and an increased
rate o~ release for ammonia gas is realized in tank 12.
The curve of FIGURE 3 shows that by using the
preferred embodiment of the present i~vention, high percentages
of dissolved ammonia gas can be removed rom the WASteWater
at temperat-~res even as low as 5 C~ This is a substan~ial
improvement over other systems for removal of ammonia
gas which are temperature limiting and are basically in-
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1~7377~;
effective at temperatures below about 10-15C. The present
invention is temperature sensitive, but not temperature
limiting.
In the illustrat~d embodiment of the invention, a re-
ceptacle or tank 170 is com~unicated with drain 15B of tank 12.
By actuating diverter valve 156, liquid can flow through pump
154 and drain 158 into container or tank 170. Pump 154 can
be energized to increase the speed of discharge for the
processed wastewater of tank 12 after ~he desorption
process has been ~ontinued for the desired length of time.
In tank 170, an acid inlet 172 ha~ing a selectively operat~d
valve 174 introduc~s acid into the tank to neutralize the
basic wastewater coming from tank 12. The neutralized
liquid i9 dlscharged from outle~ 176 for subsequent processing
or introduction into a qtream or repository which requires a
very low ammonium-nitrogen input load.
P~eferring now to the inlet system 14, a variety of
arrangement-~ ~ould be provided for increasing the pH of the
wastewater to be processed. In accordance with the illustrated
embodimen~, a holding and mixing tank 180 include~ a first
inlet 182 fox an ammonium-ammonia contaminated wastewater.
Lime or other substance to make the wastewater ~asic, is
added from a receptacle 184. As is well known, lime i~
u~eful in precipitating phosphates from wastewater, This
is an additional advantag~ of the system shown in FIGURE l.
An outlet 186 for the holding and m xing tan~ 180 is directed
to a selectively operated valve 188 for introducing a waste-
water having the desired high pH into tank 12. Of eourse
other arrangements could be used for obtaining a high pH
3Q for the wa~tewater and direoting the contaminated wa~tewater
. -22- '
.
,
~37'76
into inlet 140 of tank 12.
Re~erring now to the accumulator 20, this ~ccumulator
is used to intercept and absorb a major portic~n c~f the amm~nia
gas from tank 12 which all~ws vacuum generator 10 to function
primarily as a vacuum generator withou~ performing the added
function of absorbing the ammonia ~as desorbed in tank 12.
In the illustrated embodiment, accumulator 20 i8 in communica-
tion with the two vacuum connecting systems 22, 24 and include~
a tank 200 for holding a li~uid or liquid ~ody 202 having an
upper level 204. An outlet 206 is connected to a pump 210 for
forcing liquid 202 from tank 200 through a pump outlet 212,
through diverter valve 220 and to an inlet line 22~. A drain
224 allow3 di~charge of the li~uid ~rom tank 200 into a con-
tain~r 226 when the absorbed ammonia content of liquid 202 is
a~ a ~ufficiently hi~h concentration. Inlet line 222 of tanX
200 is communicated with an appropriately arra~ged ~pray head
230 for ~praying ~irculated liquid 202 ~nto the upper portion
of tar~c 200 and thu~ creating a m~st of Liql3id 202 ~n tank 200. Heat e~:hanger
240 having inlet 242 and outlet 244 is used to coDl Liquid 202 for increasing
its ability bo ab~orb ~n~a gas and for decreasi~ its vapor pressure,
fc~r reasons previou~ly described. The pH in accumulator 20,
in th~ pre~erred en~odiment, is quite low ~o that liqu~d 202
i8 acidic or nearly acidic. At least, the p~l should be
~ubstantially below the pH ~f the wastewater ef~luent in
tank 12. To produce thé acidic condition, ah acidie cGntrol
250 i~ provided which include~ an acid inlet 252 and a liquad
inlet 254. The liquid i~ generally water. A metering valve
256 metexs appropriate amounts of acid and liquid $nto line
: 212 through inlet line 258. At the charging cycleO dlv~rter
valve 220 i~ actuated to di~charge liquid 202 rom tan~ 200
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:.
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~3~776
through drain 224~ Thereafter, diverter valve 220 is close~
and an acid liquid mixture i5 forced into line 212. After a
sufficient amount t3f :Liquid has hPen intr~duced into the
accumulator, metering valve 256 is deactivated. Thereafter,
accumulator 20 is used to a~bs~ a~anania gas desorbed in
tan)c 12. Since the alTrnoni.a gas will change the pH of l.iquid
202, periodically it may be nece~sary to introduce more acid
c~r more acid and liquid through the acidic control 250. ~t~r
the liquid has beeome heavily laden with absorbed ammo~'a ga~,
th~ ac~umulator is again recharged as previou~ y diseus~ed.
To connect vacuum line 130 from vacuum generator 10
to gas outlet 142 of tank 12, two vacuum connec~ing ~ystems
22, 24 are provided. These ~ystem~ not only provide c~ anica~
tion of the vacuum from generator 10~ but al~o increas~ el~e
vacuum in accordance with the following die cussion. Referring
now to sy~tem 22, this ~3tem includes a positiv~ displ cement
ga~ pump 2~0 having a bypas3 valve 262. As i~ known, the
capa~ity of a ptssitive displacement gas pump or blow~r i~
a function of the differential in pres.qure acros~ ~he pump
from inlet to discharge. The lower the discharge pre.~ure
and the lower the dif~erential, the higher the vo~ume c~pac~ty
of the pump. Thus, when the vacuum of line 130 i3 fir~t intro-
duced to system 22, valve 262 is opened. qhis provide~ ~ high
vacuum on both sides of po~itive displacement pump 260
that a relatively lo~ differential will exist from inlet
to discharge. I~ereafter, the positive displacement pump
is actuated and valve 262 ls closed so that vacuum is d~wn
through po~itive displa-:ement pump 260 which acts upon the
cavity above the llquid in tanX 12 to further decrease the
. 30 pressure and assure that the vapor pressure of the wastewater
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.
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11017377~
is ~htained in desorpkion tank 12,
The ~econd vacuum connecting system 24 includes a
positi~e displacement pump 270, a bypass.v~ive 272, an inlet
274 and an outlet 276. After a v~cuum has been cxeated by
vacuum generator 10 through accumula~or 20 and sys~em 22,
valve 272 can be closed to all~w operation of positive
displacement pump 270. When this happens, ~he positive
displacement pumps 260, 270 further increase the differential
in pressure between vacuum generator 10 and tanX 12. Thi~
further decreases the pressure above the effluent within
tank 12 arld increases the withdrawal of ammonia ga fr~m the
wastewater i~ tank 12.
When vacuum generator 10 is operating and maintaining
a high vacuum in line 1~0, positive idiRplacement pumps 260,
270 further increase the vacuum applied ~rough line 142 to
tank 12. I~ a~ure~ that a ~ufficiently low pressure is
created in tank 12 to cause t~e heated wastewater to boil and
de~orb the ammonia gas. A3 previou~ly mentioned, to ~reate
proper l~w pressure in l:anX 12, the liquid of vacuwn generator
10 i3 at a temperature below the temperature of the wastewater
in tank 12. Thi~ can be accomplished by cooling the liquld
in the vacuum generator and/or heating the: wastewater. It
i~ pos~ible by using the positlve displacement pumps to
obtain the vapc~r pressure for th~ wastewater wi~hout the
llquid temperature differentiaI eon~ept of the preferred
en~od iment . . ` .
~e ammonia gas together with air, nitr9gen, and
water vapor of tank 12 are pumped by positive displacement
pump 270 to outle'c 276 which i9 directed into a~cumulator 20
directly above the spray head 230. 5he highly _oluble amrnonia
.
-~5-
. .
~073776
yas passing into accumulator 20 from outlet 276 is rapidly
absorbed by th~ ].ow pH liq~id 202 spraying fr~m spray head
230. In addition, the surface contact o~ the soluble anunonia
gas with the low pH liquid eauses rapid absorption of the
anunonia yas into the body of liquid in accumulator 20. Thi9
absorption is enhanced by c~oling liquid 202 with heat ex-
changer 240. Since the pH of li~uid 2û2 i9 low, a large
percentage of the absorbed ammonia gas i9 converted 'co
ammonium ions which rema in within the liquid. This is shown
by the relationship illustrated in ~he graph of FIGURE 2
wherein approxima~ely all of the ammonia gas is converted to
ammonium ions at the neu'cral 7.0 pH value and a~ any pH less
than neutral. Ihe curve of FIGURE 2 is shifted to the right
fox decreases in temperature. qhus, the tendency to convert
~5 the ammonia gas into ammonium ions is enhanced in the co~led
body of liquid 202 of accumulator 20.
A cGndenser 280 having an inlet 282 communicated
with the upper portion o~ accumulator 20 and an outlet 2~4
communicated with vacuum connecting qystem 22 further
precludes undesirable gases fxom being directed to the vacuum
generator 10 and reducing the effectiveness o~ the generator
The cooling coil3 286 receive cooled liquid from inlet 290
and expel the liquid through outlet 292. ~y using the
condens~r, any conden~able ga e~, sueh as water vapor9 ~an
~5 be conden~ed and drained back into accumulator 20. Since
a vast majority of the highly ~oluble ammonia ga~ is
removed by the l~w p~ liquid 202 ln accumulator 20, the
majority o~ gases passin~ into condenser inlet 282 are th~
~lightly soluble ga~es, ~uch as air and nitrogen, and
condensable vapor~, such as water vapor. The condensable
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, . ..
~73776
vapors will be removed by condenser 280. Thu3, line 13
essentially receives only the slightly soluble gases,
such as oxygen and nitrogen from tank 12. Only a slight
amount of ammonia gas and water vapor is passed through
5 line 130 to the vacuum generator. Since the vacuum generator
received primarily sli~htly soluble gases, there is very
little tendency to absorb thes~ ~ases in the ~urnp~ng liquid
of tanks A and B. For that reason, the gases of tanks Ao B
are generally expelled through outlets 97, 98, in~tead of
being absorbed by the liquid of vacuum generator 10. In
this embodiment, there is very little ammonia concentxation
in the l~ quid of tanks A and B. It is neces~ary ~o drain
the liquid from vacuum generator lO only after prolonged
operation, if at all. If accumulator 20 were not used to
absorb the desorbed ammonia gas, as shown in the ~mplified
: structures of FIGURES 7 and 8, then periodic di~charge of the
pumping liquid from generator 10 may be necessary. The
pumpinq liquid discharged ~rom the generator ha~ a high
amount of ammonia gas dissolved therein when using the
~chema~ic embodiments shown in FI~URES 7 and 8. In a like
mann~r~ the liquid discharged from accumulator 20 has a
high concentration of ammonium ion~. These discharged llquid~
are use~ul by-products of apparatus Ao This by-product may
be u~ed by itself or combined with an acid to produce a
desirable salt for subséquent commercial use.
.
As previsusly mentioned, the ~urfacè~tensi~n of th~
wa~tewater in tank 12 affects the rate at whlch thQ d~olved
ammonia gas is desorbed from the wastewater . ~y increa sing
the temperatuxe o the wastewater, the surface ten~ion of the
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. . .
~7377~i
wastewater is decreased and the rate of desorption is
increased. I~ accorda~ce with another aspect of the
present invention, a further mechanism is used for
increasing ~he rate of, desorption in tank 12. Thi~ aspect
include~ a molecular agitator mec~anism 310 shown in FXGURES
1 and 5. This mechanism introduces gas bubbl~s into the
wastewater at a pressure greater than the pressura over th~
wa~tewaterO q~he gas is orle which is not highly ~olubl~ in
tne wastewater, such as nitrogen. A variety of mechanism~
could be used for this purpose; however, in accordanca with
the illustrated embodiment, the molecular agita'cor mechanism
includes an inlet 312, a control valve 314 and a tube 316
extending into tank 12 adjacent the lowar portic)n thereof.
A plurality of apextures or openings 318 ~re provided in
tube 316. The low or ~lightly soluble gas is lntrodùced
into tube .~16 and small gas bubbles are created within the
liguid wa~tewater of tank 12 ~y openings 318. These ga~
bubbles expand rapidly because of 'che low pre~ure a~ve
the wastewater in tank 12. Ihus, there i~ a rapid increase
in ~olume of the ga~ entering into tank 12. Thi~ increase i3
proportional to the ratio of the incoming ga~ pre~sure and the
pressure over the wastewaterO The gas bubbles create a certa~n
amount or agitation which reduces the surface tension of the
w~tewater and increa~es the rate at which absorbed ammonia
gas is desorbed f~om thé wastewater. Other arrangement~
could be used to pro~ride thi~ molecular agi~ation by
incoming ~lightly ~oluble ga~. Becau~e of its low ~olubilit:y
the ga~ does not tend to be ab~orbed hy the wastewater
in t~nk 12. 'I~e bubble~ expand or explode and continue to
flow upwardly thrt ugh the liquid towaxd the va~uum above
.
-~8-
~173~7~;
the wastewater in tank 12. Thi~ system mechani~ally forces
~as molecules into the vacuum sp~ce in tank 12.
Referring again t~ the vacuum generator 10, the
upper sensors 84, 86 are used to provide a quiescent condition
as liquid approaches the filled position in both tanks A and
B. As is well known, agitation of liquid causes entrapment
of gases. Thus, to f~rce a maximum am~unt of gas from tanks
A and B it is advantageous to provide a quiescent condition,
especially at the latter part ~f the filling cy~le, Thi
can ~e done by a variety of mechanisms. One of these is to
provide.valves 44, 46 with three separate position~. One
position i~ closed, the next position is partially opened
and the third position is fully opened. Thus, when fully
opened, liquid from vertical pipe 34 flow~ rapidly into one
o~ the tank~ A, B. By shifting the open valve 44 or 46 to
a part~ally closed position, a relatively low flow is then
created to ~omplete the filling of the ~anks. Referring now
to FIGURE 6, a schematically represented quie~cent valve 44
illu3trates this concept~ Although only valve 44 is illus-
trated, this descriptio~ will apply equally to the other
quiescent valve 46 and other valves could be used. Valve 44
includeq an inlet chambe~ 330 and an outlet chamber 332a A
three positio~ valve element 334 includes a first valve ele
2S ment 336 and a second valve element 338. In the position
~ chown in FIGURE 6, valve 44 i8 fully opened and liquid i~
:~ ~lowing through branch 40 into tank A at a rapid rate.
This causes the level of liquid to in~rease toward level
~ensor 84. A~ the level in tank A reaches Yensor 84,
operator 40 of valve 44 pushes valve element 334 downward
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1~73776
by an arm 342 t~ a fir~t position clo~:ing thi~ val-Je element
336 and leaving element 338 open. I'his substantially
decreases the flow of liquid through branch 40 qo that tho
level of liquid in tank A gradually increa~es at a 910w rate
which allows escape of any entrapped gas. After a quiet,
gradual increase of the liquid level, the level reaches
.~ level sensor 110. At this time operator 340 fully clo8e~
. valve 44 by closing the second valve element 3~8. Ot~.er
arrangement~ ~ould be provided for cr~ating thl~ qui~ce~t
flow at the end of the liquid filling cycl~ of tank~ A, B.
. Thi~ further enhance~ the ef~iciency of vacuum generator 10~
Referring now to FIGURE 8, a -~implif~d v~r~l~n Of
appara~us A i8 illustrated. In this ver~ibn, l~ko comp~nent~
of the preferred embodiment have liXe numbers. IC i9 noted
that a ~ingle po~itive d$splacement pump 270 ~ 8 eonnected
between vacu~m line 130 and ga~ ~utlet 142 of tank 12. Thi~
increase~ the vacuum on tank 12, as previously described7
wi~hout requiring two positive displacement pumpg. In thi8
illustxated Qystem, the ammonium gas desorbed in tank 12
.~
will be ab~orbed by the liquid in tanks A and B. ~ox that
reason, these tanks mu~t be periodically recharged with a
new body of liquid. TXe di~oharged liSluid will eontain a
~5 h$gh amount of nitrogen in the form of diss~lved amm~nia ga~
and ammonium ions. The pH of the liquid in tanks A and B i~
le~s than the pH of the wastewater coming into~tank 12. Re-
~erring now to FIGURE 9, this fiyure contains a ~ematic
drawing illu~trating certain a~pect~ of the pxefèrred em-
bodiment ~hown in FIGURE 1~
'
. --30- ~
~C~7377~
The ab~olute preqsure in the cavity above the
evacuated tanXq A, B approaches the saturation vapor pres~ure
c~rresp~nding t~ th~ liquid temperature of that particular
tanX. Thi~ absolute pressure will be limited by gases trapp~d
in the veq~el, by any leakage of the vessel and by th~
absorbed gases in the li~uid being evacuated. In other words,
duxing evacuation certain gases in the tank ~ tgelf may appear
above the lowering level of liquid in the evacuated v~ssel.
As gases are drawn into the ~ank A, B being evacuated~ ~ome
of them will be absorbed by the liquid and the gaQes not
. abss)rbed will be forced out when the tank i9 ~ubsequently
filled. The absorption o~ ammonia gas in the lit;luid of the
vacuum generator is a function of the temperature and pH
of the llquid in this generator. Ammonia gas will change
fzom the ammonia ~orm to an i~n as a function o~ ~h~ pH
a8 i~ illustra ted in the graph ~hown ir FIGURE 2 ~
true also ~ the liquid in accumulator 20 shown ln FIGURE 1.
In that instance. the ab~orption of ~mmonia takes plac~ in
2,0 the accumulator and very little ammonia actually pas e~ ~o ~he
vacuum ~enerator~ .
After a length of time proportional to the differential
pre~sure be~ween the absolu~e pressure in the space over
the liquid ln tank 12 and the vacuum generator pres~ure, the
~5 proces~ed wa~tewater in tank 12 can b~ removed either by
~, ~ - draining, venting or pumping. Thereafter, new ammonia
.~ contaminated liquid is ~ntroduced into tank 12. The p~
- o the proces8ed, deammoniated li~Uid may be modlfied ~urther
by adding acid in the neutra1ization ~ank 170. The sy~tem
and method as described herein is somewhat dependent upon the
, .
, . . .
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107377G
temperature differ2nce between the liquid in generator 10
and the wastewater or ammonia contaminated liquid in tank 12.
The flow o~ gases from the desorbing tank 12 to the accumulator
20 or vacuum generator 10 is due to the difference in absolute
pressures corresponding to the vapor pressure for the tempera-
ture in each of the respective components. The absolute
pressure in the displacement tanks will approach the ideal
vapox pressure as a function of the dissolved gases and
efficient purging of non-condensable gases and slightly
soluble gases, such as air and nitrogen.
When the level of liquid reaches the level sensors
110, 112, the respective valves 104, 106 are first closed.
Thereafter, the opened one of valves 44, 46 is closed and
the particular pump 70, 72 which is energized is de-energized.
By providing cooling for the liquid in vacuum~generator 10
in FIGURES 1 and 8, and for both the vaouum generator and
accumulator 20 in FIGURE 1, a freezing point depressant
substance can be used for ~hese cooled liquids to reduce
; the temperature thereof to a temperature bel~w the normal
freezing point ~or water or other liquid in generator 10 or
accumulator 20. This provides a correspondingly low vapor
pressu~e in the vacuum generator and in the accumulator.
Thi3 iS primarily important in the vacuum generator.
The positive displacement pump or blower capacity
ln CFM is a function of the ra~io of the absolute intake
pressure to the absolute exhaust pressure for a given blower~
- or pump speed. Thus, the éf~e~tivénes~ of t~e po~itive
di-~pLacement pumps is ircreased with a decrease in the
temperature o the li~uid within tank~ A, B. By using one
or more positive displacement booster pumps, an increase vacuum
,
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. ~ . . .. . . ..
- . , . , , ., . . . , . : . . :
~(973776
force is created in the desorption tank 12 which asQures
a rapid rate of gas removal and permits the desorption
of gas at liquid temperatures previously unobtainable in
any biological system and/or in any ammon~ a s~ripping
process now in use. By using the positive displacement
pumps, it is possible to desorb ammonia gas from liquid
in tank 12 at temperatures equal to or even lower than the
temperature of the liquid in the vaeuum generator. By
providing a low vacuum for the discharge pressures from
tank 12, low energy requirements are experienced ~y
apparatu~ A, a~ shown in ~IGURE 1. By providing the by-pass
arrangement for the po~itive displacement pUYTlpS or blowers,
there is very low energy required t~ operate the3e pumps
to reduce, ~till fuxth~r, the ab~olute prcsqure above the
liquid in tank 12. ~ ~
q!he accumulat~r 20 i ~ useful in reduoinq the amount
of ga~ and vapor carried by the va~uum line 130 into the
vacuum generator~ Addition o~ acid to tha accumulator liquid
:: will counter ~alance any vapor and/or ammonia ga~ carried
from tank 12 to the accumulator. T~e heat removed by heat
exchanger~ 60, 240 and condenser 280 can be used ~or the
h~at ~xchanger 160 to con~erve energy in the ltotal sy3tem.
- ' I
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.,
-33-
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