Freezing Bed Research Articles

Velocity characterization of solids in binary fluidized beds

Owing to challenges in velocimetry techniques, flow hydrodynamics of binary fluidized beds have remained largely unexplored. Thus, the present study seeks to address unraveling the velocity distributions in the binary fluidized bed of glass beads (0.5 and 2 mm) in fluidized with 10, 30, and 40% of coarser fractions. In order to decipher the velocity distributions, RPT was implemented, which yielded velocity distributions of both the 0.5 and 2 mm fractions. Distinct features of solids flow were observed with varying bed compositions. The mean velocity of finer flotsam (0.5 mm particles) fractions were found to diminish upon increasing the jetsam fraction (2 mm) due to variation in bed voidage. On the contrary, an enhanced coarser fraction of 2 mm particles in the bed diminished solids’ fluctuation, which led to a corresponding reduction in the RMS velocities. Similar trends were also noted when solids’ diffusivity was estimated for various bed compositions. Finally, the efficacy of this technique was independently verified qualitatively through mixing patterns obtained from ‘bed freezing’.

Study on Cause Analysis and Treatment Measures of Lining Cracking and Ballast Bed Freezing at Tunnel Portal in Seasonally-Frozen Regions

The purpose of this study is taking the ZEST tunnel of Xilin hot-Ulanhot Railway in Inner Mongolia province of China as an example to investigate the cause and treatment measures of lining cracking and ballast bed freezing at tunnel portal in seasonally-frozen regions. Field investigation method was used to investigate the characteristics of lining cracking and ballast bed freezing in winter. The results show that the longitudinal cracks in the side wall are symmetrical and located in the middle of the wall. The longitudinal cracks have obvious seasonal characteristics, which mainly occur in winter, and the width of cracking was alternatively varied and broadened year by year, of which the process proved to be irreversible. The number of cracks and the width and length of the cracks all have the trend of further development in the last year. Numerical calculation method was used to study the internal force change law of the lining structure of the ZEST tunnel under seasonal frost heaving force. The results show that the lining cracking is mainly caused by the frost heaving force load. Based on the above analysis results, the treatment measures for the frost heave cracking, ballast bed freezing and the leakage of water leakage during the spring thawing period are proposed, the remediation measure proposed is quite effective and the problems such as cracking, ballast bed freezing and water leaking of tunnel lining are completely solved.

A viscoelastic flowline model applied to tidal forcing of Bindschadler Ice Stream, West Antarctica

The motion of Bindschadler Ice Stream, West Antarctica, is dominated by sliding over a nearly plastic bed, according to analysis of kinematic GPS data using a new viscoelastic flowline model. Inversions of time-averaged velocity data with viscous ice-flow models can be consistent with multiple sliding laws, but propagation of velocity perturbations in a viscoelastic model can distinguish between sliding laws with different exponents. We develop such a model and apply it to a time series of velocity for the tidally modulated flow of Bindschadler Ice Stream (formerly Ice Stream D). Observed velocity perturbations are found to be consistent with a flow-law exponent m≥8, which indicates basal motion with a relatively weak till bed; lower exponents consistent with motion dominated by deformation within the ice over a hard or frozen bed are found to be unlikely. This result suggests that Bindschadler Ice Stream would respond rapidly and significantly to any future loss of buttressing from the Ross Ice Shelf.

Freeze–thaw treatment of RBC sludge from a remote mining exploration facility in subarctic Canada

Freeze-thaw conditioning of RBC (Rotating Biological Contactor) sludge was tested using a pilot-scale freezing bed placed in a mobile freezer operated at -10°C. Sludge samples from a remote mining exploration facility were flown in every 2 weeks, and added to the freezing bed in 8 layers of 10 cm thick. Approximately 4 months after the first layer of sludge was added, the pilot unit was removed from the freezer and thawed at ambient temperatures. After one day of thawing, the solids concentration increased from 2.6% to 16.2%. The final cake solids concentration was 21%. Melt water had increasing turbidity, COD, TSS, VSS, nitrogen and phosphorus concentrations during the thawing period. Freeze-thaw conditioning also decreased the initial densities of fecal coliforms and Salmonella in sludge. The results of this study showed that freeze-thaw technology successfully dewatered RBC sludge without the need for mechanical equipment, and is a sustainable option for sludge dewatering in cold and remote regions.

Freeze-Thaw Treatment of RBC Sludge: A Sustainable Option for Sludge Dewatering in Cold Regions

Freeze-Thaw Treatment of RBC Sludge: A Sustainable Option for Sludge Dewatering in Cold RegionsFreeze-thaw conditioning of RBC sludge was tested using a pilot-scale freezing bed placed in a mobile freezer unit operated at −10°C. Sludge samples from a remote mining exploration facility were flown in every 2 weeks, and added to the freezing bed in layers approximately 10 cm thick. A total of 8 layers of sludge were added to the pilot unit over 3 months. The total volume of sludge...Author(s)James DiakCorinne ProuxBanu ÖrmeciSourceProceedings of the Water Environment FederationSubjectSession 4: DewateringDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:4L.204;1-DOI10.2175/193864710802766903Volume / Issue2010 / 4Content sourceResiduals and Biosolids ConferenceFirst / last page(s)204 - 212Copyright2010Word count255

Freeze concentration of milk and saline solutions in a liquid–solid fluidized bed: Part I. Experimental

Fluidized bed freeze concentration is a novel technique that uses a fluidized bed heat exchanger (FBHE) to concentrate liquids through the process of freeze concentration. Ice formed on the cooled surface of the vertical heat exchanger is removed by particles fluidized inside the FBHE. In this paper, the operating conditions are reported for freeze concentration of saline solutions and milk in FBHE. The operation was tested with equilateral 4 mm and then 5 mm particles at different bed porosities, cooling rates and NaCl and milk concentrations. Experiments with NaCl solutions showed that the 5 mm particles were more aggressive than 4 mm in removing ice from the heat exchanger wall. Whilst particle size was considered responsible for this, the particle shape could have played a major role. A theoretical analysis on effect of FBHE parameters showed the size of particles to exert influence on FBHE performance. The result from experiments with skim milk and whole milk maintained the conclusions formed previously with NaCl experiments with regard to the effect of tested parameters on operational stability. However, the ice formed from milk was more difficult to remove than the ice formed from NaCl solutions. Whole milk showed even more resistance to ice removal. Skim milk was freeze concentrated from 13% to 27% TS content in these experiments. Installing a wash screen further improved the purity of separated ice.

The Freeze of Sludge

This technical note briefly discussed the current understanding to the freeze/thaw treatment on sludge, and proposed a simplified analysis to the horizontal freezing bed that could be used in full-scale treatment.

Basal ice temperatures during late Weichselian deglaciation: comparison of landform assemblages in west-central Sweden

AbstractThe mountainous area of west-central Sweden has a varied glacial morphology and three unique landform assemblages appear to mark areas of different basal thermal conditions during the decay of late Weichselian ice. A glacial geomorphological map was constructed through interpretation of aerial photographs at a scale 1:60 000. The relative abundance of landforms interpreted to indicate a frozen bed, a thawed bed, and late-frozen to thawed-bed conditions were used for a first-order reconstruction of the basal temperature pattern of the decaying ice sheet. The features used to outline areas with different temperature regimes during deglaciation are glacial scouring, flutings, eskers, meltwater channels, boulder blankets, Rogen moraines, relict surfaces and thermoerosion features.In the northern part of the area, as well as along most of the water divide to the Atlantic Ocean, the ice was warm-based during deglaciation. Glacially scoured bedrock, fluting/ drumlinization, subglacial eskers and extensive glacial lake sediments characterize the area. In the high mountain area, lateral meltwater channels are short and curve downslope to form chutes or eskers. The basal ice conditions changed from frozen- to thawedbed in a late stage of the late Weichselian cycle in most of the southern part of the area, shown by the Rogen moraines on both sides of the ice divide. However, substantial areas in the eastern and southern low mountains had frozen-bed conditions during the complete late Weichselian. In the high mountains in the north, only the summits were frozen.

Conditionnement et déshydratation de boues d'étangs aérés facultatifs à l'aide du gel – dégel naturel: résultats d'essais

This article presents the results of tests investigating the conditioning and dewatering of biological and chemical sludge (alum dephosphatation sludge) from facultative aerated lagoons using natural freeze–thaw. The results presented here highlight the excellent efficiency of this conditioning method used with drying beds. Following freeze–thaw, immediately after drainage, sludge presents little odor and has lost its liquid state since dry solid contents of more than 30% can be obtained with ease. Freeze–thaw also eliminates the gelatinous consistency of chemical sludge. The filtrates are clear and contain low levels of suspended solids but may have relatively high chemical oxygen demand. To maximize the depth of sludge that can be frozen, it is necessary to freeze the sludge in thin layers. This requires the pumping of sludge from a separate storage basin to a freezing bed for the duration of winter (separate basin–bed method). The storage basin may however be combined with the freezing bed provided the depth of the sole sludge layer does not exceed the maximum depth of sludge that can be frozen during the winter season (combined basin–bed method). Freeze–thaw is not affected by the initial dry solid content of the sludge. The grain size of the sludge can however have some influence, although quite marginal, and freeze–thaw is efficient for all types of aqueous sludge. Key words: conditioning, dewatering, sludge, facultative aerated lagoons, natural freeze–thaw, trials.

Interaction of Kinetic and Quality Aspects during Freeze Drying in an Adsorbent Medium

A kinetic analysis of freeze drying by immersion in an adsorbent fluidized bed process has been carried out and will be discussed in this paper. The process is described based on a uniformly retreating ice front model in spherical geometry. The model needs to know both temperature and pressure driving forces, correlated as a function of water content. The influence exerted by operational conditions on the heat and mass coefficients has been studied. Transport coefficients are correlated as a function of the operating conditions to obtain equations that can be used for predicting purposes in fluid bed freeze drying. Kinetic aspects are related to quality indicators determined through shrinkage of product to select the most adequate operating conditions.

Drying rate and shrinkage effect interaction during freeze drying in an adsorbent medium.

A Kinetic analysis of freeze drying by immersion in an adsorbent fluidised bed process has been carried out in this paper. The process is described based on a uniformly retreating ice front model in spherical geometry. The model needs to know both temperature and pressure driving forces, correlated as a function of water content.The influence exerted by operational conditions on the heat and mass coefficients has been studied. Transport coefficients are correlated as a function of the operating conditions to obtain equations that can be used for predicting purposes in fluid bed freeze drying. Kinetic aspects are related to quality indicators determined through shrinkage of product to select the most adequate operating conditions.

Fundamentals of Sludge Dewatering in Freezing Beds

After several years of research, the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) has developed a new unit operation for sludge dewatering called a freezing bed. The freezing bed uses natural freeze-thaw to dewater sludge. Essentially, it is the cold regions counterpart to the drying bed. Pilot and full-scale studies conducted in the United States have demonstrated that freezing beds can dewater both water and wastewater treatment sludges to greater than 20% total solids content. The best results were obtained with alum sludge, which was dewatered to 82% solids. The design of freezing beds will depend on the depth of sludge that can be frozen and thawed at the proposed site. Mathematical models capable of calculating the design depth are presented.

A Pilot‐Scale Study of Alum Sludge Dewatering in a Freezing Bed

The purpose of this study was to demonstrate the capability of a sludge‐freezing bed for dewatering alum sludge. Alum sludge containing average total solids of 0.5 percent was applied to the pilot‐scale bed and frozen in layers 2–10 cm thick over the winter of 1989–90. By the end of the winter, 99 cm of sludge had been frozen. After thawing and draining of meltwater, the depth of sludge remaining in the bed was reduced to 3–5 cm, a 96 percent reduction in volume. The remaining solids had a granular consistency similar to medium‐sized sand. The meltwater drained through the granular solids as easily as through the underlying sand. Column tests show that these granular solids could accumulate in the bed for several years before removal would be necessary.

Optimization of fixed and fluidized bed freezing processes

Fixed and fluidized bed freezing phenomena were studied with the aid of a computer model to determine the optimum operating conditions for freezers. Experimental procedures were developed to determine the convective heat transfer coefficient, h, and its relationship to the superficial air velocity, u, during freezing. Dimensionless correlations show h to be dependent on u in the fized bed phase. In the fluidized bed phase, h was constant and independent of u. Using green peas, cherries and radishes (of diameters 7, 19 and 25 mm, respectively), it was found that the optimum bed height which resulted in the minimum energy use per unit weight of product frozen was smaller for the smaller sized particles.

Development and Design of Sludge Freezing Beds

A new unit operation called a sludge freezing bed is proposed for dewatering sludges produced by treatment facilities in cold regions. This unit operation uses natural freezethaw to condition the s...

USE OF TIME‐TEMPERATURE DATA DURING FLUIDIZED BED FREEZING TO DETERMINE FROZEN FOOD PROPERTIES

ABSTRACTMost of the methods proposed in literature for freezing time calculation require the previous knowledge of the enthalpy change and thermal conductivity of frozen materials. Ordinarily these properties are not easy to obtain, and often need a special approach depending on the process under consideration.This paper deals with a new and simple method that affords an estimation for Fluidized Bed Freezing of small food pieces (20‐40 mm) immersed in a cold fluidized bed of fine inert particles. Based upon Plank equation and temperature‐time recordings, the method more particularly yields the latent heat to be removed for bringing the product below the freezing poatt and the thermal conductivity of the matter in this final state. The associated percentage of water actually frozen during operation may be also determined.With the help of this technique properties have been determined for various fruits and vegetables (banana, carrot, potato, turnip and cucumber). The values that have been found agree well with literature data: latent heats correspond to the latent heat required to freeze 80% of the water in the products, and thermal conductivities lie between 1 and 2 W/m °C. Helpful correlations for Fluidized Bed Freezing time calculation are proposed that simply relate these properties to the total water content of materials.

GAS PARTICLE HEAT TRANSFER COEFFICIENT IN FLUIDIZED PEA BEDS

ABSTRACT Individually Quick Frozen food production has led to the development of fluidized bed freezing equipment, where the previously cooled fluidizing air freezes the food by direct heat transfer. The operating conditions of these beds, as well as their design characteristics, are consequently related to the gas‐particle heat exchange including the fluid dynamic complexity of aggregative fluidization. The purpose of this paper is the experimental determination of gasparticle heat transfer coefficients for fluidized pea beds and their extension to conditions prevailing in industrial processing. Heat transfer coefficients were determined for both, peas and porous alumina pellets, in a system where particles were dryed by the fluidizing air. Transfer coefficients were evaluated for various gas velocities and bed depths. The results obtained for alumina pellets and those for peas can be satisfactorily correlated by using the Archimides number, and show good agreement with correlations obtained by other authors.