US 20070210007/A1
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0210007 A1
`Scheimann et al.
`(43) Pub. Date:
`Sep. 13, 2007
`
`(54)
`
`(76)
`
`METHOD OF DEVVATERING THIN
`STILLAGE PROCESSING STREAMS
`
`Inventors: David W’. Scheimann, Joliet, IL (US);
`Angela S. Kowalski, Shenzhen City
`(CN)
`
`Correspo11dence Address:
`NALCO COMPANY
`1601 VV. DIEHL ROAD
`NAPERVILLE, IL 60563-1198
`
`(21)
`
`App]. No.:
`
`11/611,599
`
`(22)
`
`Filed:
`
`Dec. 15, 2006
`
`Related U.S. Application Data
`
`(53)
`
`Contim1ation—in—part of application No. 10/888,327,
`filed on Jul. 9, 2004, now abandoned.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`B01D 21/01
`
`(2006.01)
`
`(52) U.S.Cl.
`
`............................................................ ..210/728
`
`(57)
`
`ABSTRACT
`
`A method dewatering thin stillage process streams generated
`in the processing of grain to ethanol comprising adding to
`the process streams an eifective flocculating amotmt of an
`anionic copolymer comprising acrylic acid sodium salt,
`methacrylic acid sodium salt or 2-acrylamido-2-methyl-l-
`propanesulfonic acid sodium salt to form a mixture of water
`and flocculated solids; and separating the water from the
`flocculated solids using, a dewatering device.
`
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`US 2007/0210007 Al
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`Sep. 13,2007
`
`METIIOD OF DEVVATERING THIN STILLAGE
`PROCESSING STREAIVIS
`
`CROSS R s F * RENCE TO RELATED
`APPLICATIONS
`
`[0001] This is a contim1ation—in—part of Ser. No. 10/888,
`327 filed Jul. 9, 2004.
`
`TECHNICAL FIELD
`
`[0002] This invention relates to a method and apparatus
`for dewatering dry grind ethanol process streams generated
`in the processing of germ containing grain, like corn, to
`ethanol. More particularly,
`this invention concerns using
`anionic flocculants alone or in combination with micropar—
`ticulate settling aids to enhance solid—liquid separation and
`increase the overall efficiency of the ethanol manufacturing
`process.
`
`BACKGROUND OF THE INVENTION
`
`In the dry milling process used for manufacturing
`[0003]
`both food and fuel grades of ethanol from com, a “beer
`mash” is made from which the ethanol is removed in a
`stripper column. The remaining mash is referred to as Whole
`stillage or thick stillage in the fuel ethanol industries and
`thick slop in the beverage industry. The stillage which is
`typically in the range of 11% to 15% solids contains all of
`the other no11—starch components of the com kernel that pass
`through the process (germ. protein. gluten, hull & fiber etc.).
`Horizontal dewatering centrifuges are then typically used for
`removing a portion of the suspended solids from the whole
`stillage stream.
`the process stream into two
`[0004] The centrifuges split
`fractions the first being a liquid stream called thin stillage
`and the second being the cake solids or distillers grains. The
`resulting solids or distillers grains, which typically contain
`about 65 to 85 percent Water, are sent to a drying operation
`Where the remaining water is removed by evaporation and
`the solids are dried to less than about 10 percent moisture.
`The dried solids, referred to as dry distiller grains (DDG’s)
`are used as a nutrient source in the manufacture of certain
`animal feeds. I11 certain applications the material from the
`centrifuges may be hauled off site and disposed of by land
`application techniques or discarded in a landfill.
`:0005] The liquid stream from the dewatering device is
`called centrate (thin stillage), which typically contains 6-10
`aercent solids by weight, with about 2 to 4% being sus-
`oended solids and about 4 to 6% being present as dissolved
`solids. The centrate or thin stillage from the centrifuge
`contains a number of valuable co—products some of which
`are soluble and some of which are suspended.
`:0006] The thin stillage stream can be processed or used in
`a number of different operations within the plant. The
`decision as to how the stillage stream will be split and
`orocessed in a particular plant is based upon the economics
`of each available option. Typically a fraction of the centrate
`or thin stillage is sent back to the head of the plant as
`make-up water for the fermentation process, this stream is
`ypically referred to as backset and may be as much as 50%
`of the thin stillage stream. The balance of the thin stillage
`stream is sent to an evaporation process Where the water is
`removed and the dissolved and suspended solids are con-
`
`centrated to a syrup with a solids content of 20 to 50 percent
`solids by weight. This material may then be blended with the
`distillers grains from the centrifuges or the dry distiller
`grains from the feed dryers to produce an animal feed at
`>88"/6 solids commonly referred to as dry distillers grains
`with solubles (DDGS). The material can also bypass the
`drying operation and be supplied as a material referred to as
`wet feed at 30 to 40% solids.
`
`[0007] The current standard in the dry grind ethanol
`industry is the use of high speed horizontal decanter type
`centrifuges for removing the suspended solids from the
`Whole stillage or thick slop. The centrifuges are only efi"ec-
`ive in capturing a portion of the suspended solids iii the
`whole stillage stream. Due to the high shear imparted in the
`unit a considerable portion of the smaller particles (fines) or
`he larger particles which are sheared can pass through the
`unit and are discharged in the centrate (thin stillage). A
`raction of solids present iii the thin stillage have a density
`very close to that of Water and are extremely sensitive to
`shear making their removal ir1 a centrifiige extremely diffi—
`cult. We have observed that the fine suspended solids in the
`hin stillage (centrate) do not settle even when allowed to
`stand undisturbed for extended periods of time (24 to 48
`rours or ir1 some cases more). Another component of the
`whole stillage stream that is of some concem is the oil,
`which is carried through the process, The oil fraction is
`oresent in the whole stillage as the germ of the cor11 kernel
`is not removed or recovered in corn dry milling operations.
`The centrifuges used for processing stillage have been
`optimized for solids capture efiiciency and as a result they
`only remove a portion of the oil present in the whole stillage
`stream.
`
`[0008] The use of the processing aids described in this
`invention and the mechanical component as described in this
`invention have resulted in significant improvements in sus-
`pended solids capture efiiciencies and the capture and
`removal of oils from the thin stillage, the backset and the
`syrup streams.
`
`[0009] Various processing aids (flocculants, coagulants,
`agglomeration aids) have been evaluated in centrifuges in
`order to improve the discharged cake solids and reduce the
`solids in the centrate. Due to the physical characteristics of
`the centrifuges the improvements in cake solids or centrate
`quality as a result of the addition of anionic flocculants to the
`centrifuges was negligible.
`[0010] Therefore, there is an ongoing need for improved
`solids/liquids separation technologies, dewatering and pro-
`cessing aids and the development of methods which improve
`the efficiency of solid—liquid separation in the whole stillage,
`thin stillage, backset and syrup streams, with concomitant
`reduction in the energy required to pre oare the dry distiller
`grains and produce ethanol.
`
`SUMMARY OF lH A INVWNTION
`
`[0011] We have discovered that the use of certain anionic
`polymers flocculants can significantly improve the agglom-
`eration of the solids in the centrate (thin stillage) from the
`centrifuges. The improvement is observed in both the rate at
`which the solids agglomerate and settle and also in their
`ability to Withstand mechanical shear as they are decanted.
`When the anionic polymer and any process aids are used in
`combination with a low shear mechanical solids liquids
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`US 2007/0210007 Al
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`Sep. 13,2007
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`separation device optimized for this application the resulting
`eflluent contains little to no suspended solids. The oil
`content of the effluent
`is also significantly reduced. The
`solids generated are also more concentrated and as a result
`the energy required for further processing is significantly
`reduced.
`
`[0012] Accordingly, this invention is a method of remov-
`ing suspended solids, fats, oils and 25 grease from thin a
`stillage of a dry grind ethanol process stream comprising
`
`(i) adding to the thin stillage process stream an
`[0013]
`effective flocculating amount of one or more anionic
`polymers, the anionic polymers comprising one or more
`anionic monomers selected from acrylic acid sodium salt.
`2—acrylamido—2—methyl—1—propanesulfonic acid sodium
`salt and methacrylic acid sodium salt and optionally one
`or more acrylamide monomers to form a mixture of water
`and coagulated and flocculated solids; and
`
`(ii) separating the water from the flocculated solids
`[0014]
`using a solids/liquids separation device.
`
`[0015] The dewatering process of this invention sigr1ifi—
`cantly improves the agglomeration of the solids, the fines
`capture and the settling rate of the solids such that they can
`be settled and removed in a low shear mechanical dewater—
`i11g device. As a result ofthe improvements in agglomeration
`and settling the supemate containing very few solids can be
`sent back to the head of the process. The solids from the
`bottom of the settling apparatus can be concentrated and
`then sent to syrup evaporation or possibly to the feed dryer.
`The anionic polymer or cationic coagulant/anionic polymer
`combinations of this invention is mo st preferred in low shear
`dewatering apparatus, but has shown activity in high shear
`applications. The improvement
`in particle agglomeration
`and solids capture also significantly reduces the time
`required to process the stillage a11d thereby improves the
`plant throughput.
`DETAIL 4 D D A SCRIP I ION OF THE
`INVENTION
`
`[0016] The method of this invention is suitable for enhanc-
`ing solid—liquid separation i11 thin stillage process streams
`generated in processes for preparing ethanol from the fer-
`mentation of grains including com and other germ contain-
`ing grain and the like. The method is particularly suitable for
`thin stillage process streams generated ir1 processing of corn
`to ethanol.
`
`[0017] As used herein “thin stillage process stream”
`means any process strea1n(s) generated in the ethanol plant
`subsequent to dewatering of the whole stillage, including the
`thin stillage, the backset and the syrup streams,
`[0018] The anionic polymers suitable for use in the
`method of this invention are prepared by polymerizing
`acrylic acid sodium salt, r11etl1acrylic acid sodium salt or
`2-acrylamido-2-methyl-l-propanesulfonic acid sodium salt
`or a combination thereof and optionally one or more acry-
`lamide monomers under free radical forming conditions
`using methods known in the art of polymer synthesis. Many
`anionic polymers are commercially available, for example
`from Nalco Company, Naperville, Ill.
`[0019]
`“Acrylamide monomer” means an electrically neu-
`tral monomer derived from acrylamide. Representative acry-
`
`la1r1ide monomers include acrylamide, methacrylamide,
`N —methylacrylamide,
`N ,N —di1nethyl(meth)acrylamide,
`N—isopropyl(meth)acrylamide,
`N—(2—hydroxypropyl—
`)methacrylamide, N-methylolacrylamide, and the like. Pre-
`ferred acrylamide monomers include acrylamide and meth-
`acrylamide. Acrylamide is r11ore preferred.
`
`[0020] The anionic polymer may be cross—linked with
`about 0.005 to about 10 ppm of one or more cross linking
`agents. “Cross-linking agent” means a multifunctional
`monomer that when added to polymerizing monomer or
`monomers results ir1 “cross—linked” polymers in Wl1icl1 a
`branch or branches from one polymer molecule become
`attached to other polymer molecules. Representative cross-
`linking agents include N,N—methylenebisacrylamide, N,N—
`methylenebismethacrylamide, triallylarnine, triallyl ammo-
`nium salts, ethylene glycol dimethacrylate, diethylene
`glycol dimethacrylate, polyethylene glycol diacrylate, tri-
`ethylene glycol dirnethylacrylate, polyethylene glycol
`dimethacrylate, N-vinylacrylamide, N-methylallylacryla-
`mide, glycidyl acrylate, acrolein, glyoxal, vinyltrialkoxysi—
`la11es and the like. Preferred cross-linking agents are selected
`from N,N-methylenebisacrylamide. polydiethyleneglycold-
`imethacrylate, trimethylolpropane ethoxylate (X l-7.0/y OI-I)
`tri(meth)acrylate, where x=l-20 a11d y=1-5, trimethylolpro-
`pane propoxylate (x EU/y OH) triacrylate, where x=1—3 and
`y= 1 -3, and 2—hydroxyethylmethacrylate.
`
`[0021] Preferred anionic polymers for use in the method of
`this invention include dry polymers, emulsion polymers and
`dispersion polymers. Dry polymers and emulsion polymers
`are more preferred.
`
`“Emulsion polymer” and “latex polymer” mean an
`[0022]
`invertible water-in-oil polymer emulsion comprising an
`anionic polymer according to this invention in the aqueous
`phase, a hydrocarbon oil for the oil phase, a water-in-oil
`emulsifying agent and. potentially. an inverting surfactant.
`Inverse emulsion polymers are hydrocarbon continuous with
`the water-soluble polymers dispersed as micron sized par-
`ticles within the hydrocarbon matrix. The advantages of
`polymerizing water— soluble monomers as inverse emulsions
`include 1) low fluid viscosity can be maintained throughout
`the polymerization, permitting efiective mixing and heat
`removal, 2) the products can be pumped, stored, and used
`easily since the products remain liquids, and 3) the polymer
`“actives” or “solids“ level can be increased dramatically
`over simple solution polymers, which, for the high n1olecu—
`lar weight flocculants, are limited to lower actives because
`of viscosity considerations. The inverse emulsion polymers
`are then “inverted” or activated for use by releasing the
`polymer from the particles using shear, dilution, and, gen-
`erally, another surfactant, which may or may not be a
`component of the inverse emulsion.
`
`Inverse emulsion polymers are prepared by dis-
`[0023]
`solving the desired monomers in the aqueous phase, dis-
`solving the emulsifying agent(s) i11 the oil phase, emulsif§ -
`ing the water phase in the oil phase to prepare a water-in-oil
`emulsion,
`ir1 some cases, homogenizing the water-in-oil
`emulsion, polymerizing the monomers dissolved in the
`water phase of the water-in-oil emulsion to obtain the
`polymer as a water-in-oil emulsion. If so desired, a self-
`inverting surfactant ca11 be added after the polymerization is
`complete in order to obtain the water-in-oil self-inverting
`emulsion.
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`US 2007/0210007 Al
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`L3.)
`
`Sep. 13,2007
`
`Z0024] The oil phase comprises any inert hydrophobic
`liquid. Preferred hydrophobic liquids include aliphatic and
`aromatic hydrocarbon liquids including benzene, xylene,
`toluene, paraffin oil, mineral spirits, kerosene, naphtha, and
`he like. A parafiinic oil is preferred.
`
`Z0025] Free radical yielding initiators such as benzoyl
`weroxide,
`lauroyl peroxide, 2,2'—azobis
`(isobutyronitrile)
`AIBN),
`2,2’-azobis(2,4-dimethylvaleronitrile)
`(AIVN),
`ootassium persulfate and the like are useful i11 polymerizing
`vinyl and acrylic monomers. 2,2‘—azobis(isobutyronitrile)
`AIBN) and 2,2‘-azobis(2,4-dimethylvaleronitrile) (AIVN)
`are preferred. The initiator is utilized in amounts ranging
`etween about 0.002 and about 0.2 percent by weight of the
`monomers, depending upon the solubility of the initiator.
`
`Z0026] Water-in-oil emulsifying agents useful for prepar-
`ing the e1nulsio11 polymers of this invention include sorbitan
`esters of fatty acids, ethoxylated sorbitan esters of fatty
`acids, and the like or mixtures thereof. Preferred emulsifying
`agents include sorbitan monooleate, polyoxyethylene sorbi-
`tan monostearate, and the like. Additional details on these
`agents may be found in McCutcl1eon’s Detergents and
`Enmlszfiers, North American Edition, 1980. Any inverting
`surfactant or inverting surfactant mixture described in the
`prior art may be used.
`
`include
`surfactants
`inverting
`[0027] Representative
`ethoxylated nonylphenol, ethoxylated linear alcohols, and
`tl1e like. Preferred inverting surfactants are ethoxylated
`linear alcohols.
`
`[0028] The polymer is prepared by polymerizing the
`appropriate monomers at from about 30° C. to about 85° C.
`over about 1 to about 24 hours, preferably at a temperature
`of from about 40° C. to about 70° C. over about 3 to about
`6 hours.
`
`“Dispersion” polymers mean a water-soluble poly-
`[0029]
`mer dispersed in an aqueous continuous phase containing
`one or more inorganic salts. Representative examples of
`dispersion polymerization of Water-soluble anionic and non-
`ionic monomers in an aqueous continuous phase can be
`found in US. Pat. Nos. 5,605,970, 5,837,776, 5,985,992 and
`6,265,477.
`
`[0030] Dispersion polymers are prepared by combining
`water, one or more inorganic salts, one or more water-
`soluble monomers, any polymerization additives such as
`chelants, pH buffers or chain transfer agents, and a Water-
`soluble stabilizer polymer. This mixture is charged to a
`reactor equipped with a mixer, a thermocouple, a nitrogen
`purging tube, and a water condenser. The monomer solution
`is mixed vigorously, heated to the desired temperature, and
`then a water-soluble initiator is added. The solution is
`purged with nitrogen while maintaining temperature and
`mixing for several hours. During the course of the reaction,
`a discontinuous phase containing the water-soluble polymer
`is formed. After this time, the products are cooled to room
`temperature, and any post-polymerization additives are
`charged to the reactor. VVater—continuous dispersions of
`Water- soluble polymers are free flowing liquids with product
`viscosities generally 100-10,000 cP, as measured at low
`shear. The advantages of preparing water-soluble polymers
`as Water co11tinuous dispersions are similar to those already
`mentioned in association with the inverse emulsion poly-
`mers. The water continuous dispersion polymers have the
`
`further advantages that they contain no hydrocarbon oil or
`surlactants, and require no surfactant for “inversion” or
`activation.
`
`“Dry polymer” means a polymer prepared by gel
`[0031]
`polymerization. “Gel” polymerization is defined as a process
`for producing polymers as dry powders. The preparation of
`high molecular weight water-soluble polymers as dry pow-
`ders using a gel polymerization is generally performed as
`follows: an aqueous solution of water-soluble monomers,
`generally 20-60 percent concentration by weight, along with
`any polymerization or process additives such as chain trans-
`fer agents, chelants, pH bufiers, or surfactants, is placed in
`an insulated reaction vessel equipped with a nitrogen purg-
`ing tube. A polymerization initiator is added, the solution is
`purged with nitrogen, and the temperature of the reaction is
`allowed to rise uncontrolled. When the polymerized mass is
`cooled, the resultant gel is removed from the reactor, shred-
`ded, dried, and ground to the desired particle size.
`[0032] Anionic polymers suitable for use in the method of
`this invention preferably have an anionic charge of about 10
`to about 100 mole percent, more preferably about 30 to
`about 70 mole percent.
`[0033]
`In a preferred aspect of this invention, the anionic
`polymer is selected from the group consisting ofacrylamide-
`acrylic acid sodium salt copolymer and acrylamide—2—acry—
`lamido-2-methyl-1-propanesulfonic
`acid
`sodium salt
`copolymer.
`[0034]
`T11 another preferred aspect, acrylamide—acrylic
`acid sodium salt copolymer and acryla1nide-2-acrylan1ido-
`2—methyl—1—propanesulfonic acid sodium salt copolymer
`have an 25 anionic charge of about 10 to about 90 mole
`percent.
`
`In another preferred aspect, acrylamide—acrylic
`[0035]
`acid sodium salt copolymer and acrylamide-2-acrylan1ido-
`2-methyl-1-propanesulfonic acid sodium salt copolymer
`have 2111 anionic charge ofabout 30 to about 70 mole percent.
`
`In another preferred embodiment, the anionic poly-
`[0036]
`mer is acrylamide-sodium aerylate-sodiurn methacrylatc ter-
`polymer.
`
`In another preferred embodiment, the acrylamide-
`[0037]
`sodium acrylate—sodium methacrylate terpolymer has an
`anionic charge of about 1 to about 50 mole percent.
`[0038] The anionic polymers preferably have a reduced
`specific viscosity of about 10 to about 60 dl/g, more pref-
`erably about l5 to about 40 dl/g.
`
`“Reduced specific viscosity” (RSV) is an indica-
`[0039]
`tion of polymer chain length and average molecular weight.
`The RSV is measured at a given polymer concentration and
`temperature and calculated as follows:
`
`[0040] wherein 1]=viscosity of polymer solution;
`
`[0041]
`and
`
`r|0=viscosity of solvent at the same temperature;
`
`[0042]
`
`c=co11centration of polymer in solution.
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`US 2007/0210007 A]
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`Sep. 13,2007
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`As used herein, the units of concentration “c” are (grams/
`100 ml or g/deciliter). Therefore,
`the units of RSV are
`dl/g. The RSV is measured at 30“ C. The viscosities 1] and
`no are measured using a Cannon-Ubbelohde semimicro
`dilution viscometer, size 75. The viscometer is mounted in
`a perfectly vertical position in a constant temperature bath
`adjusted to 30:0.02° C. The error inherent in the calcu-
`lation of RSV is about 2 dl/g. Similar RSVS measured for
`two li11ear polymers of identical or very similar con1po—
`sition is one indication that the polymers have similar
`molecular weights, provided that the polymer samples are
`treated identically and that the RSVs are measured under
`identical conditions.
`
`[0043] The elfective dosage, addition point(s) and mode of
`addition of anionic polymer to the thin stillage process
`stream car1 be empirically determined to obtair1 the proper
`polymer/particle interaction and optimize the chemical treat-
`n1ent program performance. For higher RSV product
`samples more mixing is typically required. For lower RSV
`polymers less mixing is required.
`[0044] The anionic polymer dosage required for optimum
`dewatering is based upon a number of factors including
`i11verted polymer concentration, thin stillage process stream
`solids, available polymer/particle mixing energy and the
`type of dewatering device used. A preferred polymer dosage
`is about 50 to about 500 ppm of anionic polymer is added to
`the thin stillage process strtmm.
`[0045] Emulsion polymers are typically inverted as a 0.1
`to 5.0 percent by weight solution in clean water according to
`standard practices
`for
`inverting latex flocculants
`as
`described herein. The polymer is applied to the thin stillage
`or thin slop process stream. Dry anionic polymer llocculants
`are used iii a similar fashion with the product being made up
`at concentrations of 0.1 to 1.5 percent polymer product
`according to the standard practices ar1d recommended poly-
`mer aging times for preparing dry flocculants.
`[0046]
`In addition the invention may also include a water-
`soluble cationic coagulant added to the dry grind ethanol
`process.
`In another preferred aspect of this invention, one or
`[0047]
`more microparticulate settling aids are added to the thin
`stillage process stream.
`[0048]
`“Microparticulate settling aids” refers to certain
`insoluble materials which are added to the process stream
`which physically interact with the suspended solids, fats,
`oils and greases in the process stream a11d facilitate the
`separation and removal of these components by physical
`interaction. VVithout being limited by theory, we believe that
`addition of these materials provides a surface area and sites
`Where polymers can interact and bridge the suspended
`particles forming a11 agglomerated particle or a lloc. The use
`of a microparticle results in a floc or agglomerated particle
`that is more resistant to mechanical shear and as a result uses
`a physical sweep Iloc mechanism to capture and remove
`suspended solids, fats, oils and greases from the water phase.
`Once the desired polymer particle interaction is achieved the
`microparticulate settling aid is designed to facilitate the
`separation process by increasing the rate of solids settling.
`Representative microparticulate settling aids include bento-
`nite clay, montmorillonite clay, particularly montmorillonite
`clay available from CETCO, Arlington Heights, Ill. under
`the tradename AltaFloc, microsand (80 mesh silica sand),
`colloidal silica, and the like,
`
`silica” and “colloidal borosilicate”
`“Colloidal
`[0049]
`mean a stable aqueous dispersion of tunorphous silica par-
`ticles or amorphous borosilicate particles, respectively, usu-
`ally having a particle size less than about 100 nm. Colloidal
`silica and colloidal borosilicate can be manufactured from
`materials such as sodium silicate or borosilicate and are
`commercially available, for example from Nalco Company,
`Napervillc, Ill.
`
`include
`[0050] Preferred microparticulate settling aids
`bentonite, montmorillonite, microsand, colloidal silica and
`colloidal borosilicate.
`
`[0051] The microparticulate settling aid is preferably
`added to the thin stillage process stream prior to addition of
`the anionic polymer and any coagulant(s) at a dosage of
`about 10 to about 1,000 ppm.
`
`[0052] Separation of the Water from the coagulated and
`flocculated thin stillage solids may be accomplished using
`any means commonly used for solid-liquid separation.
`
`the separation is accon1—
`In a preferred aspect,
`[0053]
`plished in a low-shear separation device such as a settling
`tank or dissolved air flotation GDAF) unit. A settling tank is
`r11ore preferred.
`
`[0054] A cut—away view of a preferred settling tank is
`shown in FIG. 2. The tank 1 ca11 be, cylindrical, rectangular
`or square and contains a center chamber 2. A cylindrical
`settling tank with a conical bottom is preferred. The center
`chamber can be either cylindrical or rectangular Witl1 the
`preferred design being cylindrical.
`
`[0055] The overall sizing of the settling tank depends upon
`the characteristics of the suspended solids, oil and grease
`concentrations in the influent process stream and the desired
`efiluent rate and quality.
`In general
`there will be one
`combined inlluent stream into the Lmit and two discharge or
`effluent streams. The primary eftluent stream is the treated
`process stream, which contains little to no suspended solids,
`fats, oils or greases. The second efiluent stream is the
`underfiow stream Where solids, fats, oils and greases are
`concentrated and discharged for further processing.
`
`[0056] The settling tank is preferably equipped with
`means for adjusting the depth of the center chamber for
`optimum settling and control of the solids and the liquid
`layer interface. There are a number of ditferent methods
`available for controlling or adjusting the height of the center
`section of the clarifier. For example, the adjustment can be
`made manually by adjusting a supporting structure which
`suspends the center chamber. In n1ore complicated designs
`the adjustment may be made automatically using settled
`solids monitoring devices like a bed depth detector or a
`solids/liquid interface monitoring system. The optimum
`setting of the center chamber height is dependent upon a
`number of factors present in the process such as influent
`flow, solids loading and mass balance. microparticulate
`settling aid dosage, polymer dosage,
`floc size,
`influent
`stream characteristics and oil a11d grease concentration, etc.
`
`[0057] Thin stillage of a dry grind ethanol process stream
`treated with anionic polymer and any process aids according
`to this invention is transferred in to the center well of the
`solids settling unit by gravity flow i11 order to prevent
`shearing ofthe agglomerated solids. The solids then settle to
`the bottom of the unit, The settled material is removed from
`
`(cid:0)H(cid:0)Y(cid:0)D(cid:0)R(cid:0)I(cid:0)T(cid:0)E(cid:0) (cid:0)E(cid:0)X(cid:0)H(cid:0)I(cid:0)B(cid:0)I(cid:0)T(cid:0) (cid:0)1(cid:0)0(cid:0)1(cid:0)4
`

`
`US 2007/0210007 Al
`
`U‘:
`
`Sep. 13,2007
`
`the bottom of the unit with a pump and transferred to another
`tank or process prior to addition to the distillers grains.
`
`[0058] Typical thin stillage process influent flow may be
`as low as about 100 gpm or as high as about 2000 gpin. In
`applications where the flow is above about 200 gpm it is
`possible to treat the system and run the units in either
`parallel or series in order to optimize the performance of the
`unit and achieve the desired eflluent quality.
`
`[0059] The center chamber ofthe settling unit should have
`a retention time or volume sufficient to provide about 1 to
`about 15 minutes, preferably about 3 to about 7 minutes of
`retention. Total retention time in the settling Lmit is prefer-
`ably froin about 20 to about 100 minutes depending upon the
`composition and characteristics of the thin stillage stream
`being treated and the final eJTluent quality desired.
`
`[0060] The total volume of the settling unit should he 15
`to 100 times the flow into the unit. The height to diameter
`ratio of the solids liquids separation unit described in this
`preferred 5 embodiment should be in the range of 1.4: I to as
`much as 3.521
`
`[0061] Control of the level of the settled solids bed in the
`unit is critical as in some process streams it’s advantageous
`to draw the influent stream through the bed or just across the
`surface of the settled solids While in other process streams
`it’s advantageous to have a gap between the solids and the
`influent stream.
`
`111 a preferred aspect of this invention, the solids
`[0062]
`mass balance of the settling chamber is controlled by
`adjusting the influent flowrate.
`
`111 another preferred aspect, the solids mass balance
`[0063]
`of the settling chamber is controlled by adjusting the rate at
`which the solids are removed from the bottom of the settling
`chamber.
`
`111 another preferred aspect, the thin stillage process
`[0064]
`stream is treated with the anionic polymer and any coagu-
`lants and microparticulate settling aids and then mixed in a
`slow mix tank prior to introduction to the settling tank. The
`treatment can occur in line prior to the mix tank or in the mix
`tank itself. The preferred method is to treat the process
`stream in-line just before the mix tank. The process stream
`enters the mix tank through or near the bottom of the tank
`Where it is subjected to gentle mixing designed to enhance
`agglomeration of the particles. The mixing can be accom-
`plished by any means suitable for the desired gentle mixing.
`The sizing ofthis tank can vary depending upon the physical
`characteristics of the process stream being treated. The slow
`mix tank is preferably equipped with a variable speed mixer
`a11d a flat paddle prop in order to obtain the desired mixing
`energy and particle agglomeration.
`
`[0065] The slow mix tank should have a holding or
`retention time for polymer particle 25 interaction of about 1
`to about 15 minutes. The sizing ofthis chamber is dependent
`upon the composition and characteristics of the thin stillage
`stream being treated and the mixing energy available. Typi-
`cal retention times of 3 to 5 minutes are preferred.
`
`[0066] As noted above, the mixture of Water and agglom-
`erated solids is then transferred to the settling tank.
`
`[0067] The method of this invention is preferably prac-
`ticed as a continuous process where a stillage stream is
`
`continuously treated with the anionic polymer(s) and any
`process aids and transferred from the process to the mix
`tank. hi
`this scenario a continuous effluent stream and
`concentrated solids stream are generated.
`[0068] However, in certain instances it may be advanta-
`geous to operate the method as a batch treatment process
`Where the material is treated with the processing aid and
`transferred to a settling tank. The tank would be allowed to
`stand undisturbed for some period of time after which the
`solids are drawn ofi” and the clean Water decanted. ln this
`embodiment the settling unit could consist of either a single
`settling unit or a series of settling units.
`[0069] The foregoing may be better understood by refer-
`ence to the following examples, which are presented for
`purposes of illustration and are not intended to limit the
`scope of this invention.
`
`EXAMPLE 1
`
`[0070] A sample of thin stillage is obtained from the
`discharge side of a centrifuge in an ethanol plant. The
`physical properties of the stream are analyzed and the
`sample consists of 5.25% total solids with 3.50% being
`dissolved solids and 1.75% being suspended solids. Labo-
`ratory bench testing using a Phipps and Bird jar testing unit
`is conducted in orde