EFFECTS OF TEMPERATURE CONDITIONS AND HEAT TREATMENT WITHIN A MULTIPLE EFFECT EVAPORATOR ON THIN STILLAGE FOULING CHARACTERISTICS

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1 EFFECTS OF TEMPERATURE CONDITIONS AND HEAT TREATMENT WITHIN A MULTIPLE EFFECT EVAPORATOR ON THIN STILLAGE FOULING CHARACTERISTICS B.Y. Zhng 1, D.B. Johnston 2, N.J. Engeseth 1, B.S. Dien 3, V. Singh 1, M.E. Tumleson 1 nd K.D. Rusch 1, * 1 Univeristy of Illinois t Urn-Chmpign, Urn, IL 2 Estern Regionl Reserch Center, ARS, USDA, Wyndmoor, PA 3 Ntionl Center for Agriculturl Utiliztion Reserch, ARS, USDA, Peori, IL *1304 W. Pennsylvni Ave., Urn, IL USA; krusch@illinois.edu ABSTRACT In the fuel ethnol industry, evportor fouling occurs when thin stillge is concentrted into coproduct clled condensed distillers solules. Fouling ffects the efficiency nd environmentl footprint of more thn 200 iorefineries in the US. This study investigted: 1) effects of ulk temperture nd initil proe temperture of the test pprtus on thin stillge fouling chrcteristics, 2) effects of exposure to evportor het tretment nd 3) effects of fcility shut down nd clening on fouling chrcteristics. Experiments were conducted using model thin stillge (1% strch solution) nd commercil thin stillge with vried temperture conditions. Incresed initil proe tempertures incresed fouling rtes nd mximum fouling resistnces for commercil thin stillge nd model thin stillge. At n initil proe temperture of 120 C, higher ulk temperture (80 C) incresed fouling rtes nd reduced induction periods. Effects of exposure to evportor het tretment were studied y exmining fouling ehvior mong smples from different loctions within n evportor. Effects of het tretment were not detected. Smples efore nd fter fcility clening were collected to study effects of fcility clening. Fouling tendencies were reduced fter fcility clening. INTRODUCTION The US Clen Air Act (1990) ws estlished for reformulted gsoline to reduce ir pollution. Ethnol nd methyl tertiry utyl ether (MTBE) were pproved s oxygentes nd fuel dditives. However, s the US Environmentl Protection Agency phsed out MTBE ecuse of environmentl nd humn helth issues, ethnol ecme the only suitle fuel dditive in the mrket. As result, ethnol demnd incresed nd ethnol production incresed more thn 10 times during the pst 10 yers, from 1.3 illion gl in 1994 to 14.3 illion gl in 2014 (RFA 2015). In 2015, there were more thn 200 ethnol fcilities in the US. Fuel ethnol is mde from corn y either dry grind or wet milling. In 2015, 90% of ethnol ws produced from the dry grind process (RFA 2015). In the dry grind process, nonfermentles (whole stillge) re centrifuged to seprte solule solids from insolule solids. Thin stillge, the overflow from the centrifuge, is concentrted using multiple effect evportors from 6 to 30% totl solids to form process strem known s syrup (condensed distillers solules) which is mixed with wet grins nd dried further to produce coproduct clled distillers dried grins with solules (DDGS). Het trnsfer fouling is the ccumultion nd formtion of unwnted mterils on het trnsfer surfces. This impedes het trnsfer nd increses resistnce to fluid flow. Fouling ffects energy consumption of industril processes nd lso results in frequent shut down nd clening. There re five types of fouling mechnisms (Bott 1995), which mkes fouling complicted phenomenon. Awd (2011) estimted het exchnger fouling costs consumed 5% of the US gross ntionl product (US$14.2 illion). Het trnsfer fouling increses cpitl investment to compenste for the reduced rte of het trnsfer s well s incresed operting costs to mintin desired tempertures nd fluid conditions. Mintennce costs re incresed to remedy effects of fouling (Bott 2007). Fouling of het exchngers my cuse environmentl hzrds nd emissions (Muller-Steinhgen et. l. 2009). In the corn dry grind process, fouling in evportors provides resistnce to het trnsfer nd restricts the flow of thin stillge. Fouling deposits must e removed periodiclly from the het trnsfer surfce. Periodicl clening nd mintennce results in incresed cpitl, opertion nd mintennce costs. Understnding fouling tendencies would result in reduced lor costs, downtime nd clening chemicl costs (Agisit et. l. 2003; Aror et. l. 2010; Wilkins et. l. 2006). Previous studies on thin stillge fouling included effects of Re, ph nd memrne filtrtion s well s corn oil, crohydrte nd totl solids contents (Agisit et. l. 2003; Aror et. l. 2010; Chll et. l. 2015; Rusch et. l. 2013; Singh et. l. 1999; Wilkins et. l. 2006; Wilkins et. l. 2006). Among these studies, ulk tempertures vried from ISBN: ; Pulished online 25

2 40 to 75 C nd initil proe tempertures vried from 100 to 120 C. Becuse of the complex composition nd vriility of commercil thin stillge, Rusch et. l. (2013) developed model fluids to study fouling. Use of model fluids llowed controlled mnipultion of thin stillge composition. Work y Chll nd coworkers (2015, 2017) exmined fouling chrcteristics of thin stillge nd concentrtes from different loctions of multiple effect evportor in dry grind fcility. Totl solids of smples vried from 7 to 11%. Fouling rtes incresed with incresed solids concentrtion. Ojectives were to: 1) determine effects of ulk temperture nd initil proe temperture of the test pprtus on fouling chrcteristics, 2) investigte effects of exposure to evportor het tretment nd 3) oserve effects of fcility shut down nd clening on fouling chrcteristics of smples from the thin stillge evportor. MATERIALS AND METHODS Test Apprtus nd Procedures The fouling test pprtus ws similr to tht used in previous reserch (Agisit et. l. 2003; Aror et. l. 2010; Chll et. l. 2015; Rusch et. l. 2013; Wilkins et. l. 2006; Wilkins et. l. 2006). The system consisted of n nnulr proe, 20 L tch tnk, centrifugl pump nd het exchnger (Fig. 1). The system ws used to detect fouling under ccelerted conditions, which were chieved y recycling test fluid under temperture conditions (ulk temperture, T, of 60 to 80 C) similr to the temperture (75 C) typicl of thin stillge from dry grind fcility; initil inner wll proe temperture, T i, ws 100 nd 120 C. To mplify potentil differences in fouling chrcteristics, surfce temperture conditions were more severe thn in multiple effect evportors in dry grind fcility. Test fluids were circulted from tch tnk using centrifugl pump (345 W, S-115 RZ, Iwki Wlchem, Iwki, Jpn). A wter th (20 L) nd cooling coil were used to mintin ulk temperture. The nnulr fouling proe (FIREROD 1025, Wtlow, St. Louis, MO) consisted of stinless steel (SS 316) outer tue contining resistnce heter (208 V, 2000 W). Fig. 1 Schemtic of fouling test pprtus with nnulr fouling proe. Fluid flow ws through the nnulr spce etween the rod nd outer housing tue. The rod contined n electricl resistnce heter nd five type K thermocouples emedded in the inner wll of the rod. Four thermocouples were used to mesure inner wll temperture (T w) t four loctions on the inner proe surfce. The fifth thermocouple ws used to shut off power supply to the heter rod when T w reched 200 C. The nnulr geometry test section, hs een used in severl fouling studies (Agisit et. l. 2003; Aror et. l. 2010; Chll et. l. 2015; Pnchl nd Wtkinson 1993; Rusch et. l. 2013; Wilkins et. l. 2006; Wilkins et. l. 2006; Wilson nd Wtkinson 1996). Ech fouling test ws operted t constnt het flux, velocity nd ulk temperture. Using tempertures mesured y the thermocouples, the overll het trnsfer coefficient (U) ws determined y: UU = qq/aa TT ss TT (1) Where q/a is the mount of het trnsferred (power input) per unit re (W/m 2 ); T s is proe surfce temperture nd T is fluid ulk temperture. T s is clculted from the inner wll temperture T w using Eq (2): TT ss = TT ww xx kk qq (2) AA Where x is the distnce from the thermocouple to the proe surfce nd k is therml conductivity of the proe metl. The x/k vlues were clculted for ech thermocouple on the proe using the method of Wilson (1915), where liner plot of 1/U vs V -n (V is fluid velocity) is drwn using experimentl dt. Fouling resistnce t time t (R f) cn e determined y het trnsfer coefficients using Eq (3): RR ff = 1 UU tt 1 UU 0 (3) Where U t (kw/m 2. K) is the overll het trnsfer coefficient t time t, U 0 is the initil (t = 0) overll het trnsfer coefficient for clen proe. By monitoring T nd T w, fouling resistnce R f t ech time point cn e clculted. During ech test, fouling dt (T, T w nd power input) were recorded every 1 min using dt logger. Fouling resistnce (R f) ws clculted s moving verge of three replictes for ech dt point nd R f vs time dt were plotted to demonstrte overll fouling tendencies. Fouling rtes for 1, 2 nd 5 hr, were defined s R f vs time liner regression lines for FR 1, FR 2 nd FR 5, respectively. Induction period (IP) ws defined s the period of time during which the 3 min moving verge of R f ws less thn 0.05 m 2 K/kW (Chll et. l. 2015). Mximum fouling resistnce (R mx) ws defined s the lrgest vlue of the 3 min moving verge of fouling resistnce during the 5 hr test period which lso ws used y Chll et. l. (2015, 2017). When deposits tht hve een formed rek free from the proe, resistnce to het flow is decresed nd R f will decrese suddenly, process clled sloughing. This cn e due to deposits hving low dhesion to the deposit lyers or proe surfce. A sloughing point (SP) ws defined s the point in time when R f decresed ruptly y more thn 30%. The fouling rte t the time of the first sloughing point (FR S) ISBN: ; Pulished online 26

3 ws defined s the slope of the regression line up to the first SP. After ech experiment, the fouling proe ws removed from the outer tue nd fouling deposits were removed prtilly using plstic sptul. The proe ws soked in 5% (w/v) NOH solution overnight to loosen residul deposits. Remining deposits were removed using wet sponge fter soking. Mens of fouling rtes (FR 1, FR 2, FR 5), mximum fouling resistnces (R mx) nd induction periods (IP) were clculted. One-wy nd two-wy ANOVA were used to compre mens. Sttisticl nlyses were performed using sttisticl softwre (RStudio , RStudio, Boston, MA) with significnce level of p < Experiment 1. Surfce nd ulk temperture effects on fouling chrcteristics Commercil thin stillge. Thin stillge smples were collected from commercil dry grind fcility. Thin stillge smples were stored for period of 1 to 2 week s in previous studies (Aror et. l. 2010; Singh et. l. 1999; Wilkins et. l. 2006; Wilkins et. l. 2006). Zheng (2013) stored commercil thin stillge smples t room temperture to nd found no differences in fouling chrcteristics up to 20 dys of storge. For this study, thin stillge smples were stored t room temperture (15 ± 5 C) nd tested within 7 dys. Five tches (50 L) were collected seprtely during 2 month period with four tests conducted per tch. A 10 L susmple ws used for ech fouling test. Totl solids were mesured using stndrd method (AACCI 2000). Ech fouling test ws strted fter the system ws clened. A commercil thin stillge (10 L) smple ws dded to the tnk nd ws mixed y circulting t mximum flow rte (14 to 19 L/min) for 5 min. Smple volume ws reduced to 7 L y drining. Wter th heted the smple to desired ulk temperture. Density nd viscosity were mesured fter fluid reched T for ech tretment. As Re ws found to ffect thin stillge fouling (Wilkins et. l. 2006), Re ws kept in rnge of 460 to 520 for ech tretment. Tp wter ws introduced in the het exchnge system to mintin T. Tretments were rrnged in rndomized complete lock design with three replictions for ech tretment. T ws djusted to the desired tretment conditions (60 ± 2 C nd 80 ± 2 C). After reching desired T, flow rte ws djusted nd proe power supply ws turned on. Test ws initited when T i reched desired conditions (100 ± 2 C nd 120 ± 2 C). Ech test lsted for period of 5 hr. T of 80 C nd T i of 120 C were similr to temperture conditions Chll et. l. (2015) used (T = 75 C, T i = 120 C). A stle T i ws difficult to mintin when T ws lower thn 60 C. The lrgest temperture difference etween T nd T i for the system to e stle ws 60 C. Model thin stillge. Model fluids were used in previous work (Chll et. l. 2015; Rusch et. l. 2013) nd found to e repetle experimentl mteril. Model thin stillge using corn strch hd rpid fouling compred with other crohydrte mixtures. Regulr yellow dent mize strch (otined from Tte & Lyle, Dectur, IL, US) slurry (1% w/v) ws used s model thin stillge to study effects of T nd T i on fouling. Tp wter (7 L) ws circulted nd preheted to desired T (60 or 80 C) in the system. Strch (70 g) ws dded slowly into the tnk to form 1% strch slurry. Slurry ws circulted y the pump t mximum flow rte (15 L/min) for 30 min. Ech experiment ws strted when the proe power ws turned on nd reched the desired T i (100 or 120 C). Experiment 2. Evportor het tretment effects on fouling chrcteristics of thin stillge Smples from vrious loctions within multiple effect evportor from dry grind fcility were collected nd diluted to the sme solids content (7% ± 0.5) to reduce influence of solids content. Smples were collected from the fcility during period of 90 dys. Two tches of smples were collected efore scheduled complete fcility clening nd three tches were collected following the fcility clening. The evportion system hd two effects; ech effect contined four stges (Fig. 2). An oil skimming process took plce etween stges 7 nd 8. Fig. 2 Smple loctions (TS, E1, SK, E2) within multiple effect evportor in dry grind fcility. () First effect, () Second effect (dpted from Chll 2014). Smples (10 L) were collected t four loctions (Fig. 2): thin stillge (TS) prior to the evportor, concentrte from the end of effect 1 fter stge 4 (E1), concentrte fter skimming efore entering stge 8 (SK) nd concentrte from the end of effect 2 fter stge 8 (E2), lso known s condensed distillers solules or syrup. Totl solids contents were determined using stndrd oven method (AACCI 2000). Smples (20 ml) were dried in 49 C oven overnight (12 hr) nd further dried in 135 C oven for 2 hr. Three determintions were mde. Before ech fouling test, smples were diluted using tp wter to 7 ± 0.5% solids content, ISBN: ; Pulished online 27

4 similr to thin stillge smples, were stored t room temperture (15 ± 5 C) nd tested within 7 dys. Viscosity nd density of the smples fter diluting were tested when ulk temperture reched 75 C. Flow rtes were djusted (11 to 15 L/min) to mintin Re of 450 ± 50. Fouling tests were strted when T reched 80 C nd T i reched 120 C. Fouling tests lsted for 5 hr or when T w reched 200 C. T ws mintined constnt during tests (80 ± 2 C). Experiment 3. Comprison of fouling chrcteristics efore nd fter fcility shut down nd clening The entire fuel ethnol fcility ws shut down completely for 25 dys for extensive clening nd scheduled mintennce in ddition to the routine evportor clening which occurred every week. As descried ove, two tches were collected prior to clening nd mintennce nd three tches were collected following. Smples were collected from TS, E1, SK nd E2 from within the evportor (Fig. 2). Fouling chrcteristics efore nd fter fcility clening were compred. As method to ssess differences in fouling profiles (i.e., R f vs time plots), liner regression ws used to ssess linerity of the profiles using clculted R 2 vlue for ech 5 hr fouling test. Btches 3, 4 nd 5 were collected t 1, 2 nd 4 weeks, respectively, fter the fcility resumed opertion nd presumed to e operting under stedy conditions. RESULTS AND DISCUSSION Experiment 1. Surfce nd ulk temperture effects on fouling chrcteristics Effects on commercil thin stillge. At higher T i nd T, fouling chrcteristics tended to increse (Fig. 3). When T i = 120 C nd T = 80 C, fouling resistnce incresed rpidly during the first 2 hr. FR 1 nd FR 2 were higher for T i = 120 C nd T = 80 C thn for other tretments (Tle 1); R f did not increse fter reching n R mx of 7 m 2 K/kW. A sudden decrese of more thn 60% of fouling resistnce ws oserved nd ttriuted to deposit sloughing which lso ws oserved y Chll et. l. (2017). Rther thn reching mximum during n intermittent time point, R mx (0.36 m 2 K/kW) ws reched t the end of the 5 hr fouling tests for T i = 100 C nd T = 60 C. For most replictes tested under these conditions, sloughing did not occur during the 5 hr test period. IP rnged from 0.14 to 5 hr nd generlly incresed s T i or T were reduced. IP of 1.8 hr were oserved for tretments t T i = 120 C nd T = 60 C (Fig. 3, Tle 1). Test conditions for the lrgest FR 1, FR 2, FR 5, FR S nd R mx nd shortest IP occurred t T i = 120 C nd T = 80 C (Tle 1). Vrition of mens for FR, indicted y the coefficient of vrition (, Tle 2), were oserved generlly to increse s T nd T i conditions ecme less severe. This provided insight on temperture settings to use for future fouling tests; higher tempertures speeded dt collection protocols s well s reduced vriility in chrcteristics derived from the fouling dt. R f (m 2 K/kW) Ti = 120 C T = 80 C Ti = 120 C T = 60 C Ti = 100 C Time (hr) Fig. 3 Fouling resistnce of commercil smples of three replicte smples. T i = 100 or 120 C; T = 60 or 80 C. Tle 1. Men fouling rtes, induction periods nd mximum fouling resistnce of commercil thin stillge.* Ti/T 1 FR1 2 FR2 FR5 FRS 3 Rmx 4 IP 5 120/ / / c 100/ c *Mens of three replictes, vlue with the sme letter in the sme column were not different (p 0.05) 1 T i = initil proe nd T = ulk tempertures ( C) during tests 2 FR 1, FR 2 nd FR 5 = fouling rte during 1, 2 nd 5 hr testing, m 2 K/kW hr 3 FR S = fouling rte efore deposit sloughing, m 2 K/kW hr 4 R mx = mximum fouling resistnce, m 2 K/kW 5 IP = induction period, hr Tle 2. Coefficients of vrition (, %) for fouling rtes, induction periods nd mximum fouling resistnce of commercil thin stillge. Ti/T 1 FR1 2 FR2 FR5 FRS 3 Rmx 4 IP 5 120/ / / / T i = initil proe nd T = ulk tempertures ( C) during tests 2 FR 1, FR 2 nd FR 5 = fouling rte during 1, 2 nd 5 hr testing, m 2 K/kW hr 3 FR S = fouling rte efore deposit sloughing, m 2 K/kW hr 4 R mx = mximum fouling resistnce, m 2 K/kW 5 IP = induction period, hr Effects on model thin stillge. At T i = 120 C nd T = 80 C, fouling deposits ccumulted rpidly indicted y the fouling rte (FR 1 = 0.91 m 2 K/kW hr). IP were less thn 5 min (Fig. 4, Tle 3). R f decresed fter R mx reched 0.71 m 2 K/kW, indicting deposit removl from the proe surfce ws greter thn the rte of deposition. ISBN: ; Pulished online 28

5 At T i = 120 C nd T = 60 C, there were induction periods of pproximtely 1 hr (Tle 3). Increses in R f were smll fter reching R mx of 0.36 m 2 K/kW (Fig. 4). When T i ws 100 C, IP were longer thn 5 hr for ll tests. R mx ws lower thn 0.05 m 2 K/kW. No oservle deposits were found on the proe surfce fter the 5 hr tests. T i ws fctor in fouling chrcteristics in the spect of fouling rtes (1, 2 nd 5 hr), R mx nd IP. T ws significnt in FR 1 nd FR 2 fouling rtes ut not for FR 5. This corresponded with previous nlysis tht fouling rtes nd R mx incresed with the increse of initil proe temperture, while induction periods decresed. Decrese of T resulted in decrese of R mx nd incresed IP (Tle 3). R mx of 0.71 m 2 K/kW ws higher thn tht reported y Chll et. l. (2015) (1 m 2 K/kW) with the sme T i (120 C) nd slightly lower T (75 C). R f (m 2 K/kW) T i = 120 C T = 80 C T i = 120 C T = 60 C T i = 100 C T = 80/60 C Time (hr) Fig. 4 Fouling test temperture effects (T i nd T ) on fouling profiles of model thin stillge. Tle 3. Men fouling rtes nd mximum fouling resistnces of model thin stillge from vrious temperture conditions.* T i/t 1 2 FR 1 FR 2 FR 5 3 R mx IP 4 120/ / / c c 5.0c 100/ c c 5.0c *Mens of three replictes, vlues with the sme letter in the sme column were not different (p 0.05) 1 T i = initil proe nd T = ulk tempertures ( C) during tests 2 FR 1, FR 2 nd FR 5 = fouling rte during 1, 2 nd 5 hr testing, m 2 K/kW hr 3 FR S = fouling rte efore deposit sloughing, m 2 K/kW hr 4 R mx = mximum fouling resistnce, m 2 K/kW 5 IP = induction period, hr Experiment 2. Evportor het tretment effects on fouling chrcteristics of commercil thin stillge (efore nd fter fcility shut down) Before fcility shut down nd clening. For smples collected efore clening, deposits egn to ccumulte rpidly during fouling tests, indicted y rpid increse of fouling resistnce nd with lrge fouling rtes (efore deposit sloughing) of 3 to 0.86 m 2. K/kW (Tle 4, Fig. 5). IP were less thn hr (5 min). Due to high vriility in replicte tests, no differences were detected mong smple loctions (TS, E1, SK, E2). The cuse of the tch-to-tch vriility is not known. Among fouling rtes clculted (FR 1, FR 2, FR 5 nd FR S), FR S would e the est to illustrte fouling ehvior prior to deposit sloughing. When sloughing occurred, there ws decrese of fouling resistnce (more thn 30%), resulting in decresed fouling rtes. After reching mximum fouling resistnce, deposits often would slough off the proe surfce s indicted y sudden decrese of R f in the fouling curve (Fig. 5). Deposit sloughing took plce out 1 hr fter tests strted. A higher fouling rte ws oserved efore the sloughing took plce for SK nd E2 smples compred with TS nd E1 smples. Those smples (SK nd E2) tended to hve more complete sloughing, indicted y fouling resistnce vlues tht decresed to less thn 0.05 m 2. K/kW. Tle 4. Fouling prmeters for smples with the evportor efore fcility clening (see Fig. 2 for loctions).** R f (m 2. K/kW) Loction FR1 1 FR2 FR5 FRS 3 FSP 4 Rmx 5 IP 6 TS E SK E **Men vlue of two tests. 1 T i = initil proe nd T = ulk tempertures ( C) during tests 2 FR 1, FR 2 nd FR 5 = fouling rte during 1, 2 nd 5 hr testing, m 2 K/kW hr 3 FR S = fouling rte efore deposit sloughing, m 2 K/kW hr 4 FSP = time of first sloughing point, hr 5 R mx = mximum fouling resistnce, m 2 K/kW 6 IP = induction period, hr TS-1 E1-1 SK-1 E2-1 TS-2 E1-2 SK-2 E Time (hr) Fig. 5 Fouling resistnce of thin stillge nd evportor concentrtes efore fcility clening. TS, E1, E2, SK descried in Fig or 2 denote seprte tch results. T i = 120 C nd T = 80 C during ech test. ISBN: ; Pulished online 29

6 After fcility shut down nd clening. There were no differences mong fouling prmeters (FR 1, FR 2, FR 5 nd FR S) due to high vriility mong replicte tches. Although not conclusive from these dt, FR 5 would e useful prmeter to chrcterize fouling. From the men fouling curve (Fig. 6), we oserved thin stillge hd slower ccumultion of fouling deposits compred with concentrtes (E1, SK nd E2). TS men fouling rte ws (m 2 K/kW hr) nd E2 hd men fouling rte of m 2 K/kW hr (Tle 5). Induction periods of TS were 0.65 hr (40 min), while induction periods of concentrtes were 0.10 to 0.31 hr (15 to 17 min) (Tle 5). Mximum fouling resistnce ws 0.19 m 2 K/kW which ws lower thn R mx efore clening (0.52 m 2 K/kW) (Tle 4). Fouling ehvior of the smples collected t sme loctions vried from tch to tch. An verge coefficient of vrition () of more thn 50% ws oserved mong tches. E1 smples hd the lrgest level of vrition (more thn 90% for fouling rte nd mximum fouling resistnce). E2 smples hd the smllest level of vrition (30%) mong three tches. R f (m 2. K/kW) TS E1 SK E Time (hr) Fig. 6 Men fouling resistnce vs time for smples fter clening. Mens re from three oservtions. Smple loctions descried in Fig. 2. T i = 120 C nd T = 80 C during ech test. Tle 5. Fouling prmeters of thin stillge nd concentrtes fter clening. ** Loction FR1 1 FR2 FR5 FRS FSP 2 Rmx 3 IP 4 TS > E > SK > E > **Men vlue of three tests. T i = 120 C nd T = 80 C during ech test. No differences were detected mong ll tretment mens (p 0.05) 1 FR 1, FR 2, FR 5 = fouling rtes fter 1, 2, nd 5 hr of testing, respectively, FR S = fouling rte efore first sloughing time point, m 2 K/kW hr 2 FSP = first sloughing point, hr 3 R mx = mximum fouling resistnce, m 2 K/kW hr 4 IP = induction period, hr Experiment 3. Comprison of fouling chrcteristics efore nd fter fcility shut down nd clening R f were generlly lower following the plnt shut down nd clening period (Fig. 6). Prior to clening, R mx rnged from 0.38 to 0.52 m 2 K/kW hr (Tle 4), wheres following clening, R mx mens for the four loctions rnged from to 0.19 m 2 K/kW hr (Tle 5). Fouling rtes nd mximum fouling resistnces of ll four smples decresed fter the fcility shut down nd clening (Fig. 7). Fouling rtes efore deposit sloughing for ech smple t the sme loction were different efore nd fter fcility shut down nd clening. R mx of TS, SK nd E2 smples were different efore nd fter fcility shut down nd clening; for E1, R mx mens were not different. Both fouling rtes nd mximum fouling resistnces decresed fter fcility clening. FR S decresed y more thn 90% fter fcility shut down nd clening. R mx decresed y more thn 50%. FR 1, FR 2 nd FR 5 decresed fter fcility clening t ech smple loction, while IP incresed (Tle 4 nd 5). R mx (m 2 K/kW) FR S (m 2 K/kW hr) efore fter TS E1 SK E2 Evportor Smple Loction () efore fter 0.0 TS E1 SK E2 Evportor Smple Loction () Fig. 7 () R mx nd () FR S for smples from vrious loctions within n evportor efore nd fter fcility clening. Letters distinguish mens (efore nd fter) within the sme loction (p < 0.05). Smple loctions descried in Fig. 2. ISBN: ; Pulished online 30

7 Fouling curves of smples tested fter clening were liner (R 2 = 0.98) while the fouling curves of smples tested efore clening were less liner (R 2 = 0.73). Fouling curves of smples were more liner (0.96 R ) fter clening thn efore clening (0.71 R ). Sloughing rrely ws oserved during these experiments. Only one sloughing point ws seen during the fouling tests fter clening. There were less sloughing points fter fcility clening (1 points) thn efore fcility clening (10 points). This my indicte tht deposits were thicker, or hd lower dhesion to the proe surfce or were softer in generl, llowing more sloughing for fluids tested prior to fcility clening. Even though smples were collected 1 to 4 week fter fcility strt up (nd thought to e collected during stedy conditions), shut down nd clening were fctors influencing fouling chrcteristics. It is theorized tht some s yet unmesured components tke time, on the order of severl weeks, to ccumulte within the process nd ffect fouling of the evportor surfces. CONCLUSIONS 1. T i nd T hd effects on commercil nd model thin stillge fouling chrcteristics. Fouling rtes nd R mx incresed with the increse of T i for commercil nd model thin stillge. 2. For model thin stillge, incresing T incresed R mx. T did not ffect R mx for commercil thin stillge. Lower T incresed IP in commercil nd model thin stillge fouling. 3. For T i = 120 C nd T = 80 C, rpid fouling ws oserved for commercil nd model thin stillge smples. For T i = 100 C nd T = 80 nd 60 C, little or no fouling occurred for oth test smples. 4. For commercil thin stillge, T i = 120 C nd T = 80 C were recommended temperture conditions for future fouling test protocols ecuse of rpid fouling nd less vrition in fouling prmeters. For future fouling tests of model thin stillge, T i = 120 C nd T = 60 C would e recommended temperture conditions ecuse of the rpid fouling nd repetle induction periods. 5. Lrge vritions of fouling prmeters mong tches were oserved for smples collected oth efore nd fter fcility clening. No differences mong the different het tretment smples were detected. 6. Fcility shut down nd clening hd effects on fouling chrcteristics of thin stillge nd concentrtes weeks following strtup. Fouling rtes nd R mx decresed nd induction period incresed for smples collected fter fcility clening. Fcility shut down nd clening reduced fouling in generl. 7. Future work is needed to study chnges of thin stillge composition fter fcility clening tht ffect fouling. NOMENCLATURE A heted re of proe, m 2 E1 smple loction, concentrte from end of evportor effect 1 fter stge 4 E2 smple loction, concentrte from end of evportor effect 2 fter stge 8, lso known s condensed distillers solules FR fouling rte, m 2 K/kW hr FSP time of first sloughing point, hr IP induction period, hr k therml conductivity of proe metl q power input, W q/a het flux to proe, W/m 2 R f fouling resistnce, m 2. K/kW R mx mximum fouling resistnce, m 2. K/kW Re Reynolds numer SK smple loction, concentrte fter skimming efore entering stte 8 of evportor SP time of sloughing, when deposits ruptly detch from proe surfce, hr T temperture, C TS initil thin stillge from dry grind process T s proe surfce temperture, C T fluid ulk temperture, C T w inner wll temperture of proe, C U overll het trnsfer coefficient, kw/m 2 K U t het trnsfer coefficient t time t, kw/m 2 K U 0 het trnsfer coefficient of clen proe, kw/m 2 K x distnce from the thermocouple to the proe surfce x/k rtio determined experimentlly y method of Wilson (1915) Suscript 1, 2, 5, S rte t 1, 2 nd 5 hr nd time of sloughing, respectively ulk i initil s surfce w inner wll REFERENCES AACCI, 2000, Approved Methods of the Americn Assocition of Cerel Chemists. 10th edition. Methods 44-15A, 44-19, Section, Approved Methods of the Americn Assocition of Cerel Chemists. 10th edition. Methods 44-15A, 44-19, AACC Interntionl: St. Pul, MN, Agisit, R. M., Singh, V., Vlenti, J. J., Kkles, M., Tumleson, M. E. nd Rusch, K. D., 2003, Technique to mesure surfce-fouling tendencies of steepwter from corn wet milling, Cerel Chemistry, Vol. 80, pp Aror, A., Dien, B. S., Belye, R. L., Singh, V., Tumleson, M. E. nd Rusch, K. D., 2010, Het trnsfer fouling chrcteristics of microfiltered thin stillge from the dry grind process, Bioresour Technol, Vol. 101, pp Awd, M. M Fouling of Het Trnsfer Surfces, Het Trnsfer - Theoreticl Anlysis, Experimentl Investigtions nd Industril Systems. InTech. Bott, T. R., 1995, Fouling of Het Exchngers, Elsevier, N. Y. Bott, T. R., 2007, Fouling control nd energy conservtion, IEEE, New York. Chll, R., Johnston, D., Singh, V., Tumleson, M. nd Rusch, K., 2015, Fouling chrcteristics of model ISBN: ; Pulished online 31

8 crohydrte mixtures nd their interction effects, Food Bioprod. Process., Vol. 93, pp Chll, R., Zhng, Y. B., Johnston, D., Singh, V., Engeseth, N., Tumleson, M. E. nd Rusch, K. D., 2017, Evportor Fouling Tendencies of Thin Stillge nd Concentrtes from the Dry Grind Process, Het Trnsfer Engineering, Vol. 38, pp. Muller-Steinhgen, H., Mlyeri, M. R. nd Wtkinson, A. P., 2009, Het Exchnger Fouling: Environmentl Impcts, Het Trnsfer Engineering, Vol. 30, pp Pnchl, C. B. nd Wtkinson, A. P., 1993, Chemicl rection fouling model for single-phse het trnsfer, ACS Symp. Ser., Vol. 295, pp Rusch, K. D., Chll, R., Zhng, Y. A., Johnston, D., Dien, B. S., Singh, V. nd Tumleson, M. E., 2013, Fouling of evportors in mize processing: developing fundmentl understnding., Proceedings of Interntionl Conference on Het Exchnger Fouling nd Clening. M. R. Mlyeri, H. Muller-Steinhgen nd A. P. Wtkinson, eds, Budpest, Hungry. pp RFA, 2015, Ethnol industry outlook. Going glol. Rep: Wshington, DC. Singh, V., Pnchl, C. B. nd Eckhoff, S. R., 1999, Effect of corn oil on thin stillge evportors, Cerel Chem., Vol. 76, pp Wilkins, M. R., Belye, R. L., Singh, V., Burik, P., Wllig, M. A., Tumleson, M. E. nd Rusch, K. D., 2006, Anlysis of het trnsfer fouling y dry-grind mize thin stillge using n nnulr fouling pprtus, Cerel Chem., Vol. 83, pp Wilkins, M. R., Singh, V., Belye, R. L., Burik, P., Wllig, M. A., Tumleson, M. E. nd Rusch, K. D., 2006, Effect of ph on fouling chrcteristics nd deposit compositions in dry-grind thin stillge, Cerel Chem., Vol. 83, pp Wilson, D. I. nd Wtkinson, A. P., 1996, A study of utoxidtion rection fouling in het exchngers, Cn. J. Chem. Eng., Vol. 74, pp Wilson, E. E., 1915, A sis for rtionl design of het trnsfer pprtus, Trns. ASME, Vol. 37, pp Zheng, Y., 2013, Effects of compositionl vriles on fouling ehvior of thin stillge, M.S. thesis. Agriculturl & Biologicl Engr, University of Illinois t Urn-Chmpign. ISBN: ; Pulished online 32