Note: Descriptions are shown in the official language in which they were submitted.
~39~6;~
1 In general, treatment of organic sludge i5 the
combina-tion of independent processes such as diges-tion
process, concentration process, dehydrating process,
combustion process and the like. ~1hese processes, however,
entail various problems centering around environmen-tal
pollution by combustion or digestion gas as the result of
chemical pretreatment applied on the sludge-to--treat for
enhancing its dewaterbility. ~uch a pretreatment is
required for precluding incompleteness in the decomposing
state of organic substances usual in the foregolng processes.
~ he wet oxidiza-tion method for -the treatment of sludge
enables to conduct substantially the same processes from
digestion to incineration by means of single equipment
with a comparatively easy operation, wherein not only
decomposition of the organic matter is adjustable mainly
by adjusting the temperature, but also production of
isolated solid matter may be minimized and obtained in
a stabilized state.
~ his invention relates to improvement of the conven-
tional wet oxidization method, for example, improvementof dewatering of not only sewag0 but also petrochemical
waste water, foods-processing waste water and the like 7
prevention of malodor generation from the treating system,
and further effectivel~ removing sands out of the sludge
thereb~ obtaining the elongation of life of the apparatus
for treating the organic sludge.
According to the Zimmerman method, sludge is heated
to over 200C by its own calorific power within a reactor,
admixed with irreducibly minimized necessary air under
pressure of 100 ~g/cm2, thence being decomposed b~ o~idiza-
tion in a pressure resistable vessel. In this method,
however, organic material incorporated in the sludge is
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~39863
1 partly rendered soluble by the hi~h temperature to r~sul-t
in an increase of BOD value of the isolated liquid after
treatment. Consequently, when the isolated liquid is
returned for treatment -to the biochemical treatment system,
BOD value in said system increases thereby not only losing
the treating efficiency thereof but also resulting in the
development of scales at -the heat exchanging portion due
to processing of the preheating oxidization u~der high
temperature with the resul-t of increased loss of heat.
In this invention, the reaction temperature is set
below 150C, the amount of air directly fed into the
reactor being over a theoretical amount required for
reducing the COD (chemical ox~gen demand) of the sludge
by 2 - 4% and within the realm of 10 - 30 ti~es -the amount ~-
of the sludge to be treated, and further the amount of
steam for heating the sludge being varied in correspondence
to reaction temperature detected b~ thermocouple and the
like provided within the reactor, thereby enabling to
maintain the reaction -temperature substantially a-t a
predetermined level ~elow 150Co ~his invention provides
a method for treating organic sludge under conditions as
mentio~ed above and an apparatus for putting into force
said method so that this inventio~ may give a drastic
solution to the defects of conventional methods in this
field as referred to alread~ hereinbefore.
A first object of this i~vention is to provide a i-
method for effectively treating orga~ic sludge at com~arative-
ly low temperature so as to reduce the adhesion of scales
of baked sludge to the heat exchanger and also lessen the
~0 generation of sludge caused by isolated liquid.
~ second object of this in~e~tion is to provide a
method for -treating organic sludge in which sand within
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1 the sludge-to--treat is preliminarily removed -therefrom
thereby preven-ting pipes ~rom stuffing, abrasion and the
like and valves from damaging.
A -third object of this invention is to provide a
method for trea-ting organic sludge in which the sludge-
incorporated gas is deodorized thereby precluding the
ejection of malodorous gas to the atmosphere.
A fourth object of this invention is to provide a
method for treating organic sludge in which heat of trea-ted
sludge is available as the source of heat for preheating
the sludge to be treated at the heat exchanger thereby
economizing the consumption of calories for -the required
treatment.
A fifth object of this invention is -to provide an ;-
appara-tus for putting into force -the above-mentioned methods
simpl~ and precisely.
A sixth obaect of this invention is to provide an
apparatus enabling to function the sludge oxidization and
heat concentration withou-t fail so that an effective sludge
treatment ma~ be obtained.
In order that this invention ma-g be readily understood,
reference is made hereinunder t-o the annexed drawing which
illustrates7 by way of examples, preferred embodiments of
this invention.
~ig. 1 is a flow sheet of a sludge treating plant ~or
p~tting into force the treating method of this invention
in the first embodiment.
Fig. 2 is a magnified section of a reactor in the
above.
Fig. 3 is a magnlfied section of a reactor in the
second embodiment.
~ig~ 4 is a magnified longitudinal section of a sand
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~L~39~3
1 removing device ln this invention.
In ~ig. 1, s1udge taken out of an orgc~nic sewage
treating system is stored in a reservoir (no-t sho~Jn) after
get-ting incorpora-ted me-tal pieces and -the like removed
there~rom, other forei~n materials within said sludge
inside said reservoir being crushed -to ~rag~ents by a
crushing device 1. ~hence the sludge is pressure-fed to
a heat exchanger 3 by a high pressure pump 2 whereby it
is preheated to around 120C by way of indirec-tl~ absorbing
hea-t from already-oxidized high temperature sludge.
r~he preheated sludge, as shown in Fig. 4, flows into
a sand removing device proper 42 through a flowing pipe
40 of a cyclone-system sand removing device 4. ~he ;~
flowed-in sludge i~ high temperature is little viscostic
thereby making it easier for -the sand to separate therefrom
under the effect of the specific gravity di~ference between
the sand and the sludge, the heavier sand naturally
precipitating to lie on a sand reservoir ~ formed at the
bottom of said device 4. ~he sand removing device proper
42 has a bypass pipe 45 to use for its cleaning.
~ he sludge after ge-t-ting said sand isolated therefrom
passes through a sludge supply pipe 10 and enters in a
reactor 5 after admixing with steam from a boiler 6 and
compressed air from a compressor 7 adjacent the inlet of
said reactor 5 at the lower por-tion thereof.
~ Fig. 2 showing the first embodiment of the reactor
5, a condensed-sludge supply pipe 10 connecting afore-
mentio~ed sa~d removing device 4 to the inlet of said
reactor 5 at its lower portion further connects with a
steam pipe 11 from the boiler 6 and an airpipe 7 from the
compressor 7 thereby enabling to admix the air a~d steam
with the sludge by an ejector 13. Wi-thin the reactor 5
863
1 are disposed numerous bubble plates 28 in tiers keeping
a suitable spac~ between each other, at the upper portion
of said reactor 5 being provided a partitioning plate 23
for dividing -the space -therein into a sludge oxidizing
chamber 22 and a heat concentrating chamber 29, at the lower
portion of said reac-tor 5 being provided a space 21 wherein
to admix untreated sludge with compressed air and s-team.
In said heat concentrating chamber 29, there are a liquid
level controller 26 and an automa-tic sludge exhaustion valve
18 under the control of said controller 26 thereby enabling
to keep the liquid at a predetermined level. Also, a
pressure indicating-recording co~troller 25 is disposed
within said reactor 5 to keep pressure therein as predeter-
mined.
In this embodiment, the sludge, air and steam flowed -~
into said reactor 5 through lower portion thereof combi~e
to pass through every hole of the bubble plate 28 in
turbulence thereby resulting in the liquid-steam contact
to a satisfactory state. ~nd accordingly the oxidizing
chamber 2~ is free from the generation of dead space and
also short-path of organic sludge therein.
The reactor 5 in the second embodiment is shown in
~ig. 3 in which, similar -to the first embodiment, a sludge
suppl~ pipe 10 connecting to the inlet of said reactor 5
at its lower portion ~urther connects to a steam pipe 11
and an airpipe 12 thereby enabling to admix said sludge
wi-th said air and steam by an ejector 13 before being sent
into sai~ reactor 5. In this embodiment~ however, the
reactor 5 differs in internal organization from that in
the first embodiment, i.e., the reac-tor in the second
embodiment is divided into two compartmen-ts by a partitioning
plate 32 erected from the botto~ thereof to a suitable
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1 height, one compartment being an oxidizing chamber 30 on
the sludge influx side and the o-ther a heat concentrating
chamber 33 on the sludge outflow side.
Within said oxidizing chamber 30 are disposed a plural
number of inclined plates 31 in tiers alternately on the
peripheral wall of the reactor 5 and -the afore-mentioned
parti-tioning plate 32 in order -to enhance the steam-liquid
contacting effect. ~nd withir. the heat concentratin~
chamber 33 are provided a liquid level controller 36, an
automatic sludge ejecting valve 18 u~der the control of
said controller 36, so as to maintain the liquid at a pre-
determined level.
In any of the foregoing embodiments, when the liquid
reaches a level higher than proper wi-thin said reactor 5, ~;
the automatic sludge exhaustion valve 18 opens in response
to signals from the liquid level controller 26 and 36
thereby discharging the sludge and as a result maintaining
the liquid level as predetermined. Also, when reaction
pressure inside the reactor 5 drops below the predetermined ~ ,
pressure around 10 kg/cm2 due to the exhaustion of -the
sludge therefr~m resulting in the fall of the liquid level,
air may be pressure-fed therein from the compressor 7 in
response to signals from the afore-mentioned pressure
indicating controller 25 and 34. On -the contrary, when
the reactio~ pressure rises above the predetermined level
due to generation of decomposed gas from the sludge, a
safety valve 17 as will be referred to later may work to
set back said pressure to the predetermined one in the
reactor 5.
~he slud~e flowed into the reactox 5 as described
above may be oxidized through consump-tion of oxygen in the
air. And the sludge makes a contact with the air fed from
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98~;3
1 the compressor 7 ln the oxidizing chambers 22 and 30 with
the application of temperature and pressure additionally
thereto, whereas -the fed air has a capaci-ty of oxygen
supply by only 2 - 4% o~ -the amount required for the perfect
oxidization of said sludge. Accordingly the sludge comple-tes
its oxidizing reaction as predetermined through the lapse
of time as it travels through said oxidizing chambers 22
and 30. ~he sludge which overflowed over the partitioning
plates 23 and 32 brings the heat concentration to a
completion at the heat concentrating chambers 29 and ~3
under the influence of temperature and pressure as mentioned
hereinafter.
As described hereinbefore, the sludge heat-treated
in the reactor 5 has a temperature at the neighborhood of
145C. Said sludge, lowering said temperature to 50 - 60C
as it travels through -the heat exchanger ~, enters a
condensing tub 19 after being controlled for its outward
flowing amount by the automatic sludge exhaustion valve 18.
~he heat-treated sludge having a favorable precipitating
property comes to a condensed state by way of a thermal
sedimentation, isolated liquid being returned to the sewage ~ -
treating system, said condensed sludge being filtered through
a filter 20 such as a belt filter, filter press and the
like thereby becoming cake state containing about 40% of
water.
An exhaustion pipe 24 communicating with the reactor
5 at its upper portion also communicates with a deodorizing ;
device 25 thereby providing a rou-te for the escape of
malodorous gas from within said reactor 5 in a deodorized
state to the atmosphere. ~everal deodorizing methods such
as combustion method, alkali fumigation method, water
washing method and the like can be employed for this
1~398~3
1 deodorizing device 25, but the combustion me-thod may be
the best suitable from a view poin~ that organic chemical
compounds takes -the grea-ter portion of the source of
malodor in this invention method.
The safety valve 17 as shown in Fig. 1 is operated
irrespective of operation of said compressor 7 so as to
maintain the gas pressure within said reactor 5 as predeter-
mined (10 kg/cm2), said malodorous gas passing through said
valve 17 being exhausted into the atmosphere after being
deodorized by the deodorizing device 25. The air to be `
blo~n in the reactor 5 needs to be sufficient in amount
so that an oxidizing rate necessary for the sludge to improve
its dewaterbility may be obtained and also the generated
malodorous ingredients may be stripped from said sludge,
said air amount in concrete terms being required -to be
around 10 - 30 -times the amount of the sludge to be treated.
Also the reaction speed varies in accordance to the kind
and density of the sludge to be treated, and the steam-liquid
contacting hours i.5 subject to the above but a duration
longer than 30 minutes is required anyway for this process.
Furthermore, the relation between the ratio of oxygen (oxygen
supply percentage) in the supplied air as against the oxygen
~mount required for the complete oxidization of the sludge
and the proportional resistance designating dewaterbility
of the sludge is as below: when the reac-tion temperature
is 145C and the reaction duration is 30 minutes with the
pressure in the reactor being 10 kg/cm2, the proportional
resistance may be the lowest, that is, about 107 sec.2/g
with the oxygen supply ratio at 2 - ~%, thus the sludge
of substantially stabilized properties being obtainable.
As described hereinbefore, this invention enables to
treat sludge at comparatively low reaction temperatures
863
1 ranging from 130 to 150C by adjusting the influx of ~-team
in-to the reactor, consequently adhesion of scales wi-thin
the heat exchan~er being less -than in case of the conven-
tional method in which the sludge is treated at high
temperatures. ~his invention there~ore enables to minimize
the heat loss resulting from the gro~th of scales within
the heat exchanger.
~his invention has further advantages in that:
solubility of the sludge is reduced with the result that
BOD of the isolated liquid is reduced by about one-half
and the generation of sludge from the isolated liquid i~s
reduced by 20 - 3~/0 as compared with the case of the conven-
tional method; since the reaction is effected at comparatively
low temperatures, calories re~uired for heating may be
economized by 30 - 40%; and since the increase of the BOD
in the biological treatment system resulting from the
return of the isolated liquid is only about 10%~ the waste
water treatment system is practically free from the effect
of said increase.
Moreover, high temperature above 200C re~uired for
the reaction in the conventional method results in an ;~
increase in the growth of what is known as the source of
malodor within the reactor, such as amines, mercaptans,
sulfides, and the like. In this invention, however, the
low reaction temperature helps reduce the generation of ~-
amines, mercaptans, and suhfides. Also, the gases generated
in the reactor are isolated from the oxidized sludge and
discharged directly from said vessel, whereby oxidized
sludgR free from gases is led into the heat exchanger and
utilized to preheat the sludge to be treated. ~hus, the
malodorous ingredients are prevented from being trans~erred
into gases, reconcentrated and admixed with the oxidized
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~39863
1 sludge in the reactor as in case of the conventional method.
~herefore, malodorous gases are scarcely exhausted into
the atmosphere in the subsequent processes.
~ urther in this invention, sands are removed by a sand
removing device from sludge which has reduced viscosit~
through preheating treatment in a heat exchanger, this
sludge condition enabling to obtain a perfect sand removal
with ease. ~his invention therefore has an advantage in
that it enables to preclude the risk of clogging and abrasion ~ -
of the piping and wear of the valves caused by such sands
in the oxidization-treating plant.
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