mama o; PEA 3m .swnmss m A "HORIZBNTIAL coacuaasm 3pm DRYER Thesis. #0: the Degree of M. 3. RQICHKEEAN STATE UNWERSHY 1M AflHfiz‘é PAW MAR 29%? THESIS N E L I B R A R Y P Elichigan State University 1 ROOM USE ONLY ABSTRACT DRYING OF PEA BEAN SLURRIES IN A HORIZONTAL CO—CURRENT SPRAY DRYER by Madhav Palnitkar Whole dry pea beans were soaked, cooked, pureed and dried in a horizontal co-current dryer to an instant pre— cooked bean powder. The variables examined were feed pump pressure, types of nozzles, outlet temperature, puree solids content and feed temperature. The test results were evalu— ated on the basis of dryer capacity, bean powder moisture content, average particle size, bulk density, flowability, solubility index, blue value index, color, viscosity of re— constituted bean powder, reconstitution properties and taste. In addition, the theoretical and experimental capacities and drying times required to dry bean slurry droplets under specific sets of conditions were obtained, Homogenizing bean puree prior to spray drying was found unacceptable because of excessive amount of cell break— age and free strach in the final product. Bean puree fed to the spray drier with a positive pump in conjunction with the high pressure pump of the spray drier gave satisfactory re— sults. Both high pressure and low pressure nozzles could be Madhav Palnitkar used. Outlet temperatures over ZOOOF were not satisfactory. The cooking methods did not influence the spray drying opera— tion. The characteristics of the bean powder were dependent on the average particle size and the amount of smaller size particles (44 and less). DRYING OF PEA BEAN SLURRIES IN A HORIZONTAL CO—CURRENT SPRAY DRYER by Madhav Palnitkar A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science 1967 ACKNOWLEDGMENT The author is appreciative of Professor Clifford L. Bedford for his guidance and ecouragement throughout the course of this work. The author is deeply indebted to Professor Fred W. Bakker—Arkema and Professor C. M. Stine for being on his guidance committee. The author especially wishes to express his gratitude to the Western Utilization Research and Development Division, Agriculture Research Service, United States Department of Agriculture, Albany, California for financial assistance of the project and to the co—ordinator Dr. H. K. Burr. Last but not the least, the author wishes to thank his parents Mr. and Mrs. Pandurang D. Palnitkar for their sacrifices and constant inspiration for a higher education. ii TABLE OF CONTENTS ACKNOWLEDGMENTS . . . . . . . . . . . . TABLE OF CONTENTS . . . . . . . . . . . LIST OF FIGURES . . . . . . . . . . . . LIST OF TABLES . . . . . . . . . . . . SYMBOLS . . . . . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . REVIEW OF LITERATURE . . . . . . . . . MATERIALS AND METHODS . . . . . . . . . Feed Systems . . . . . . . . . . . Spray Dryer . . . . . . . . . Spray Drying Variables . . . . . . . Moisture Content . . . . . . . . . . Bulk Density and Particle Size . . . Flowability . . . . . . . . . . . . Reconstitution . . . . . . . . . . . Solubility Index . . . . . . . . . Color . . . . . . . . . . . . . . Blue Value Index , . . . . . . . . Viscosity . . . . . . . . . . . . Sensory Evaluation . . . . . . . . . RESULTS AND DISCUSSION . . . . . . . . Spray Drying Variables . . . . . . . Capacity of the Spray Dryer . . . . Drying Time in the Spray Dryer . . . Pea Bean Powder Characteristics . CONCLUSIONS . . . . . . . . . . . . . . APPENDIX . . . . . . . . . . . . . . . BIBLIOGRAPHY . . . . . . . . . . . . . iii Page ii iii iv vi vii 11 ll 13 18 19 19 20 22 22 23 23 24 24 27 27 38 39 42 6O 62 66 Figure 10. ll. 12, LIST OF FIGURES Temperature Profile Twelve Feet From Front End of the Dryer . . . . . . . . . . . . . . . . Axial Velocity Profile at Ten Feet From Front End of the Dryer . . . . . . . . . . . . . . Co—current Horizontal Spray Dryer . . . . . . Apparatus Used for Measuring Flowability of Bean Powder (Adams Consistometer) . . . . . Percent Weight Distribution of the Dried Powder and the Average Particle Size at Various Points Over the Length of the Spray Dryer, Using a High Pressure Nozzle . . . . . . . . Percent Weight Distribution of the Dried Bean Powder and the Average Particle Size at Various Points Over the Length of Spray Dryer, Using a Low Pressure Nozzle . . . . . Spray Dryer Capacity of Water, Bean Slurry and Bean Powder as a Function of Orifice Diameter Capacity Versus Nozzle Pressure . . . . . . . Capacity Versus Slurry Solids Content . . . . The Effect of Outlet Temperature on Moisture Content . . . . . . . . . . . . . . . . . . The Effect of Maximum Bean Droplet Size on the Required Drying Time at Two Different Inlet and Outlet Temperature Differences . . . . . The Effect of Outlet Temperature, Nozzle Pressure, and Slurry Solids Content on the Average Particle Size of Bean Powder Dried With a High Pressure Nozzle . . . . . . . iv Page 16 16 17 21 30 31 33 33 36 36 39 47 Figure Page 13. The Effect of Average Particle Size on the Angle of Repose . . . . . . . . . . . . . . 47 14. The Effect of Pressure of a Low Pressure Nozzle on the Viscosity, Blue Value Index and Average Particle Size of Reconstituted Bean Powder . . . . . . . . . . . . . . . 55 Table LIST OF TABLES SOaking and Cooking Procedures for Dry Pea 393115.................... Capacity and Spray Angle of Pressure Nozzles Used for Atomizing Pea Bean Slurries . . . . Bean Powder Soup Mixture, List of Ingredients , Effect of Homogenizing Bean Puree on the Properities of the Resulting Bean Powder . . Effect of Spray Drying Variables on Moisture Content, Capacity, Bulk Density, the Average Particle Size and Flowability of Dried Bean Powder. . . . . . . . . . . . . . . . . . . . Effect of Spray Drying Variables on Solubility Index, Viscosity, Blue Value Index, Color and Reconstitution Properties of the Pea Powder . Relation of Particle Size to Bulk Density, Flowability, Color, Viscosity and Reconstitu- tion . . . . . . . . . . . . . . . . . . . . Sensory Evaluations (Preliminary) . . . . . . . Results of the Taste Panel of 47 Judges . . . . vi Page 12 15 26 28 43 45 51 58 59 ai ao wb SYMBOLS . . o SpelelC heat at constant pressure, BTU/lbm F. density of bone dried powder, lb/ft3. density of bean slurry, lb/ft3. density of outlet air, lb/ft3. particle diameter, ft. maximum drop diameter, ft. orifice diameter, ft. average convective heat transfer co—efficient, 2 BTU/hr ft OF. thermal conductivity of film, BTU/hr ft OF. moisture content of bean puree entering the dryer, lbs of water/lb of dry matter. moisture content of bean powder, lbs of water/lb of dry matter. rate of heat transfer, BTU/hr. time, hr. . . o inlet air temperature, F. outlet air temperature, 0F. 0 wet bulb temperature, F. velocity, ft/sec. volume of the dryer, ft drying rates, lbs of HZO/hr. vii (Auav TIT Pr = Re = temperature difference between outlet air and drop surface, oF. Logarithmic mean temperature difference, oF heat evaporation, BTU/lb. dynamic viscosity, units c.p. particle size, microns. Dimensionless Groups 2? (Nussult number) CE (Prandtle number) k DUE (Reynolds number) L1 viii IN TRODUCT I ON The annual farm value of dry beans in United States is about 125 million dollars. Michigan produces about 40 percent of the nation's total crop and 99.6 percent of the pea beans, about 800 million pounds. Pea beans are a highly nutrious, low cost food. They contain about 22 percent protein and cost approximately seven cents a pound at the farm. This makes dry beans an economical source of plant protein. Furthermore, they have a pleasant flavor and are well accepted where they are available. However, domestic per capita consumption has been declining in recent years possibly because of the long soaking and cooking time required to prepare beans for serving. Precooked bean powder was first made on a laboratory drum dryer at the Western Regional Research Laboratory, Albany, California (Morris, 1961). Being precooked, the powder is very convenient to use and show promise for use as instant soups, instant dips, meat extender and in a variety of other recipes in manufacturing formulations. This study was undertaken to determine if instant bean powder could be produced efficiently by spray drying and thus provide potential new uses for dry pea beans. 1 REVIEW OF LITERATURE Spray and drum drying are the two most economical dry— ing methods for the removal of excess moisture from low solid content foods (Anon, 1965). Bakker-Arkema et al., (1966) have described the technique of making instant precooked pea bean powder on a single and double drum dryer. Spray drying is a process for converting solutions or slurries almost instantly into a dry, free—flowing powder in one operation. It involves atomizing the slurry into small droplets within an enclosed chamber into which heated air is introduced. In the turbulent heated air environment most of the water from the slurry is evaporated instantly, resulting in a rapid drop of the drying gas temperature. The dried par— ticles fall by their own weight to the bottom of the dryer where they are removed by conventional recovery methods. The distinguishing characteristic of spray drying is the rapid rate of dehydration obtained by the exposure of large surface areas to the heated drying air. The principles of spray drying, with special emphasis on the theory of atom- ization has been discussed in detail by Marshall (1954). Spray driers are usually classified according to the 2 3 relative flow directions of the spray stream and drying air stream. Seltzer and Settlemeyer (1949) listed the following designations: 1) Horizontal co-current, 2) Simple vertical downward co-current, a) where air has a straight line flow, b) where air has a rotary motion, 3) Complex vertical downward co—current or mixed flow, 4) Vertical upward co—current, and 5) Vertical counter—current. Seltzer et al., (1949) stated that horizontal co—current driers are used for drying milk, eggs, coffee and other food materials. In addition to the above broad classification, many spray driers are designed or modified according to the requirements of a particular product. Several types of atomizers are used to spray the slurry into the drying chamber. The three most important types used in the food industry are: pressure spray heads, two fluid noz— zles and centrifugal atomizers. The atomization in pressure nozzles is effected by forcing the spray liquid under high pressure and with a high degree of spin through a small orifice. The spray pressure 4 may range from 100 to 10,000 pounds per square inch. The noz— zle orifice may vary from 0.013 to 0.15 inches in diameter. These variables are independent and will affect the capacity, the spray characteristics and the properties of the finished product. Pressure spray nozzles are extensively used in the dairy industry. The most important limitation of pressure spray nozzle is that the larger particles can easily obstruct the nozzle openings. Perry (1950) reported that two fluid nozzles do not operate effectively at high capacities and consequently are not used widely in plant size spray dryers. The chief advan— tage of this type nozzles is that they can operate under low pressures (liquid pressure 0—605xfig) while the atomization fluid is under a pressure between 10-100 psig. A two fluid nozzle has been developed especially for dispersion of thick paste and filter cake not previously capable of being handled in an ordinary pressure atomizer. In centrifugal atomizers the liquid slurry is atomized eas it is discharged from the periphery of a rapidly revolving \flheel. The number of revolutions may vary from 3,000 to 5CL,000 rpm depending upon the size of the dryer and particle size desired. The atomizer may be driven by electric motors, 5 steam turbines or compressed air (Van Arsdel et al., 1964). Particle size of any given spray product is determined by the peripheral speed of the disc. Centrifugal disc atomization is particularly advantageous for atomizing suspensions and pastes that erode and plug nozzles (Perry, 1950). Centrifugal atomizers are extensively used for drying of perfumes (Seltzer, 1949). Bower (1931) reported that potato slurries dried with centrifugal atomizers had less starch cell damage. Seltzer et al., (1949) reported that suspensions containing sugar crystals were dried without disintegrating sugar crys- tals and thick, pasty, malted cereal mixtures containing 60 percent or more solids have been spray dried using a centri- fugal atomizer where pressure nozzles would have been unsuit- able. Baran (1964) reported on a newly designed nozzle for drying heavy pastes sludges and slurries. The nozzle gave substantial increase in the capacity over conventional drying systems and offered better control of the product quality. The advantages of spray drying are: (Perry, 1950 and 'Van Arsdel, et al., 1964) continuous operation, low labor and Inaintenance cost, simplicity of operation, freedom from con— tamination, precise control of the final moisture content, elimination of dry particle size reduction or dry milling step, high production rates, favorable heat economies, rela— 6 tively high quality of product and brief retention time of the product in the dryer, minimum amount of moving or wearing part and production of uniform spherical particles leading to a uniform bulk density. The disadvantages of spray drying are: (Van Arsdel et al., 1964) low product densities especially at low nozzle pressures, relative inflexibility, high power requirement for pumping high viscosity slurries and high cost due to difficult product recovery and dust collection. The rate of drying of a liquid drop in a spray dryer is a function of the temperature, the humidity and the veloc- ity of the drying air; in addition, of the diameter of the particle, the dissolved or suspended material, the relative velocity between the drop and the airflow and finally, of the shape of the drying process. Frossling (1938) used boundary layer theory to develop a set of partial differential equations that describe the con- stant rate drying process (evaporation from a free water surface) in a spray dryer. The resulting equations, much like the Navier-Stokes equations for fluid flow, are very difficult to solve even for the most simple boundary conditions. By making a series of simplifying assumptions Gluckert (1962) developed an overall correlation of spray dryer per- formance. Gluckert's analysis is based on the premise that the capacity of a spray dryer is limited by the maximum amount of heat transferred between the largest droplets and the dry— ing air. The maximum heat transfer rate for a pressure nozzle according to Gluckert, is equal to: 2/3 10.98 k v AT D __g_ (1) D2 s s max 0.: Kirschbaum (1952) and Marshall (1954) reported that the size of spray dried particles is not substantially dif- ferent from the parent liquid droplets. If this is the case, a simpler expression than equation (1) for the maximum amount of heat transferred to a spherical droplet is: 2 q _ h n’Dmax (AT) av (2) and (ZXT) av = Tai - Tao (3) Tai T ln - W.b. Tao — Tw.b. The value of h has to be found from empirical relation— ships for the heat transfer from spheres. Dlouhy et al., (1960) reported that in spray drying it can be safely assumed that the simultaneous heat and mass transfer process takes place under stagnant conditions. In this case the Reynolds 8 number is equal to zero. From elementary heat transfer theory the following expression for the Nussult number can then be developed for spray droplets (Rohsenow et al., 1961): Nu = 2.0 (4) Bose et al., (1964), however, found that for droplet diameters between 40 and 12511 the relative motion between the particles and the air stream is of significant importance in the determination of heat and mass transfer in the spray dry- ing process. They recommended the use of a correlation developed by Ranz et al., (1952): Nu = 2.0 + 0.6 Re 0'5 Pr 0'33 (5) The drying rate of a liquid droplet containing a dis— solved material will exhibit two distinct phases: the constant rate period and the falling rate period. During the constant rate period the droplet surface will behave as a free water surface. The vapor pressure of the droplet during this period 'will be equal to the saturated vapor pressure at the prevail- ing wet bulb temperature in the dryer. When the internal diffusion in the droplet becomes less than the convective mass transfer, the constant rate drying period ends and the falling Inate drying period begins. During this period the vapor pres— sure at the droplet surface will be less than the saturated 9 vapor pressure. Ranz et al., (1952) develOped an empirical relationship for the falling rate drying time. Gluckert (1962), however, showed that no serious error was made by assuming that the full drying process in a spray dryer takes place at a constant rate. The same assumption was made in this study for calculating the evaporation rates and drying time of pea bean droplets. In calculating the drying time of the droplets pro- duced by an atomizing device in a spray dryer, the distribu— tion of the drop sizes should be considered. The smaller droplets will dry faster than the larger droplets. Uneven drying will thus result. Overdried particles may affect the flavor properties of a food product, while partially dried particles may cause deposition on the drying chamber wall. The drying time, therefore, should be no longer than the time required to dry the largest particle to a non-sticky condition and shorter than the time within which the smaller particles will burn. This last condition can be prevented by decreasing the inlet air temperature. Therefore, the first criterion will be used and the drying rates of the largest particles calculated as the required time to dry bean slurries with a particular nozzle. 10 The drying rate for drying a droplet can be calculated from equations (2), (3) and (5): 0.5 0.33 k(2.0 + 0.6 Re Pr )WDmaXflT)aV A The total time required to dry a bean droplet is then given by (6) W: the expression: ,Ad 3 d (M'C'in -M°C'out)7TDmax 6k(2.0 + 0.6 Re0'5 Pr 0'33) Dmax (am)av (7) MATERIALS AND METHODS Pea beans (variety Sanilac) were obtained from a local bean elevator and were stored at 35°F until used. Representa— tive samples of the beans were soaked and cooked as given in Table 1. Most of the studies on the spray drying variables were made on beans soaked 40 minutes at 210°F and retorted at 250°F for 90 minutes. After soaking and cooking the whole beans which now contained from 55 to 58 percent moisture, were pureed in a Langsenkamp pulper. The beans were put through the pulper twice, first with a 0.065 inch sieve and then with a 0.023 inch sieve. During the pureeing operation, water was added to aid in the pureeing and to adjust the moisture content to the desired level for spray drying. Two types of spray drying feed systems were investi- gated. In the first series of tests 15 percent solids content bean slurry was homogenized at 2,000 - 3,000 psig in a Manton Gaulin homogenizer and then fed to the high pressure pump of the spray dryer. In the second series of tests, the bean puree was adjusted to the desired percent solids content (be- tween 15 and 25 percent) and was fed by a positive pump to the ‘high pressure feed pump of the spray dryer. 11 12 Table l. Soaking and cooking procedures for dry pea beans. Soaking Time, Cooking Time, Cooking Method of Minutes at Temperature, Cooking 2100F Minutes OF 40 30 230 Retort 40 60 230 Retort 40 90 250 Retort - 90 210 Atmosphere — 120 210 Atmosphere 13 A horizontal co—current spray dryer manufactured by the C. E. Rogers Company of Detroit, Michigan, having an evap- oration rate of 300 pounds of water per hour at 325°F inlet temperature was used. The drying chamber is constructed in the form of an inverted 'tear drop.' The approximate dimen- sions are 7' 4" width at the widest point by 11' 5" height by 18' in length. A baffle plate is located at 13' 4" from the front (wet) to minimize product loss in the exit air stream. The spray dryer has three individual air inlets, (each inlet for one individual nozzle or bank of nozzles) but only one single nozzle placed in the center air inlet was used. The dryer is provided with a turboblower which delivered 300 cubic feet of air per minute at 3,420 rpm and 13.2 inches of water to the inlet end of the dryer and an exhaust fan operated at 1,790 rpm and 11.5 inch water column, exhausting 4,400 cubic feet of air per minute. The dryer operates under a partial suction draft. The spray dryer contains a screw conveyer for collect- ing the dried material. This device was not used due to the loss of powder in the powder collection system. Instead, the bottom of the spray dryer was lined with paper allowing for essentially complete collection of the powder at the bottom 14 of the drying chamber. The walls of the chamber were swept after each trial. The small amount of powder that did not settle in the drying chamber and accumulated in the two dryer cyclones was not recovered. The atomization of the bean slurry was accomplished with pressure type nozzles with a grooved- core insert. The nozzle produced a hollow cone spray pattern. All but one of the test series was performed with high pres— sure spray nozzles. Flat top cores (No. 20), having two grooves of nominal width and depth of 0.020 inches and 0.031 inches, were employed in the high pressure nozzles. A list of the nozzles used along with their measured water capacities and spray angles is given in Table 2. The maximum air velocity in the drying chamber was 240 feet per minute. Pal (1959) determined the temperature dis- tribution patterns (Figure l) at different distances from the spray nozzle during the spray drying of milk for the spray dryer used in this study. Also a typical velocity profile of ‘Ehe dryer as measured by Pal is shown in Figure 2. It should The noted that the direction of airflow in the upper half of 'the dryer was opposite to that in the lower half. The hori— zcnatal co-current spray dryer is shown in Figure 3. Pal con— cllnied: "Ninety percent of the drying process is accomplished 15 i mo oooa .om.¢m mmo.o mHNNoc whommmum zoqy mm 005 00.0N mmo.o mm com mm.hH mmo.o mm 0mm ma.ma ¥®N0.0 om ooom mm.mo m0¢o.o mm mm 00mm mo.mm mowo.o mm mm ooom mH.Nm movo.o mm mm oooa mm.hm mowo.o mm mm oom mm.hm mo¢o.o mm mm 000m «m.o¢ mmo.o mm mm oomm mm.bm mmo.o mm mm ooom m¢.mm mmo.o mm mm oooa oo.vm mmo.o mm mm oom em.ba mmo.o No on 000m mo.am mmmo.o mm on comm om.mm mmmo.o mm on ooom o¢.om mmmo.o mm on oooa mH.mH Nmmo.o mm on com sm.ma mmmo.o mm mm ooom hm.om mmo.o mm mm oomm mv.¢m mmo.o NS NS ooom Hm.am mmo.o NS NS oooa Hm.ma mmo.o mm mm oom mv.HH mmo.o Nb em ooom ma.ma omo.o or we comm HS.>H omo.o on do ooom om.mH omo.o on so OOOH vw.HH omo.o on so oom mm.m omo.o on mmumma mflmm u£\omm mcoHHmw mmSUGH wamcfi mmumm wmsmmwum mHNNoz muflommmv owuzmmmz scamawEHQ mOHMHHO uwQEDZ moamauo i} .moflunsHm smog 00m mGHNHEOum How Umm: mOHNNOG mHDmmmHm mo mamcm mmum m 6cm abdommmo . . N mHQmB 16 INLET AIR 300°? OUTLET Aid 2000? FIGURE 1: TEMPERATURE PROFILE TWELVE FEET FdOfi FRONT END OF TH4DRYEH. \ Hl—(u- \3 44% , n. . 443/ / w-IP .7 -_ v : 41+- if ::+': --—+—+::: J ' 3 J 1 v) 9 . "‘1‘”. FIGURE 2: AXIAL VELOCITY PROFILE AT TEN FEET FROM FRONT END OF THE DRYER. mm%ma demw Q spam 30H> 6cm l7 QESm. made .m.m 0 so LOSUOME mHOpDCOU 4 4 I lTll. nomj< H WOHNNOZ mOHNNOZ I «V, 1.1L 1 /. /// I 4} 1 I gobsumaom \\\\Hfl\\\\ a I h swumo: CH MH< 18 within the first five feet of the drying chamber, and the effec— tive utilization of the dryer chamber was limited to the first ten feet of the chamber length." The percent weight distribution and average particle size distribution of bean powder in the dryer was determined by placing twelve metallic dishes of 9" diameter 6" apart from each other over the cat walk (length) of the dryer. Twenty percent bean slurry was fed through the high pressure nozzle (orifice insert diameter 0.0465") and low pressure nozzle (orifice insert diameter 0.026”) at 2,500 and 500 psig, respec- tively. After completion of the trial the bean powder in each dish was weighed accurately and further analysed for the aver— age particle size. The following spray drying variables were studied: 1) Type of nozzle a) high pressure; b) low pressure 2) Exit air temperature a) 1600F; b) 1800F; c) ZOOOF; a) 220°F 3) Percent solids in the pea beans slurry a) 15; b) 20; C) 25 4) Feed temperature a) 86°F; b) 1220F; c) 158OF l9 5) Spray pump pressure a) homogenized slurry (1) 500 (2) 1,000 (3) 2,000 (4) 3, 000 (5) 4,000 psig b) unhomogenized slurry (1) 500 (2) 1,000 (3) 2,000 (4) 3,000 psig 6) Effect of feed pump pressure on outlet temperature keeping inlet air temperature constant a) 500; b) 1,000; c) 2,000 psig The following bean powder characteristics were studied: 1) Moisture content 7 The moisture content was deter- mined by using a calibrated Cenco Infra red moisture meter. 2) Bulk density — A calibrated 250 m1 graduated cylin— der was slowly filled with 100 g of bean powder and the loose volume was determined. The packed volume was determined by dropping the cylinder from a height of approximately 1 inch fifty times, turning it 15 degrees after each drop. The volume xyas estimated toI: 0.2 ml and the weights to :_0.1 g. The bulk moam mam mme one owe am .p.m umecmnmum In comm 0mm» coon comm omsv .m.0 camaoxooum Am muHmOUmfl> m.mn «.mm w.vm >.mm >.Hv maawo :mxonn usmuuwm .COHumCHmem Ufimoomouoflz m.om m.mm m.mm m.mm ms as .xmeaa muasanzsom m.¢~ o.mm H.mm m.m~ mm 1000mmev mmommu mo mamam .SUHHHnmson ogom H.3m 0.08 H.mo m.o~H \«.0uflm mauaunmm wmmum>a o.me m.mv «.me o.ov Ho.mm mum\nH .suflmame xasm s.am m.Hm c.0m s.mm m.om up\mna.moasom emaue mach Suflommmo H.m H.m o.m o.m m.¢ .m.3 ucmoumm .ucwusoo endumfloz oooa ooom ooom oooH oom mama Guzmmmum QESm Ummm wuaumfiumuomumno HmwBOm :mmm mcfluasmmu wo mmHuHonHm on» no woman smog mom mcfluflchOEoz mo uummmm *.Hw©30m cmwn .e magma 29 Feeding the bean slurry directly into the spray dryer was found to be satisfactory procedure providing a positive pump was used to maintain a constant supply of puree in order to prevent air from entering the high pressure pump. The positive pump did not affect the bean slurrying capacities of the dryer. In general this procedure was found to be satis— factory in producing the bean powder having less cell damage and free starch. Powder distribution in_the spray dryer — The dry bean powder fell over the length of the dryer. The present weight distribution depended on the nozzle used. With a high pres- sure nozzle (orifice insert diameter 0.0465", 2500 psig feed pressure, 20 percent bean slurry, and exist air temperature 18OOF) there was slight decrease in weight of powder unit length from the wet end to the dry end of the drying chamber (Figure 5). The low pressure nozzle (orifice insert diameter 0.026", 500 psig, 20 percent bean slurry exist air temperature 200°F) exhibited the opposite distribution (Figure 6). The average particle size ranged from 140;)to 1801/ for the low pressure nozzle and from 901/to 12011for the high pressure nozzle used. With the high pressure nozzle, the coarse particles were confined to the front and end zones of the dryer while the finer particles were found in a zone of 6 130 125 1. 120 :\ £21 53 115 U) 5‘3 0 110 B 32 :3 105 LL] :3 E 100 cf. 95 90 85 Wet End FIGURE 5: 30 ‘0 % weight Conditions 712 / '53 " 3 V “ dl‘LLJ}ULlO“ 20 percent slurry o \‘ Exit air temperature—1.80 F ‘11 Inlet air temperature—3IOOF Feed pump pressure—2500 psiq .-10 High pressure nozzle No. 56 is '59 38 J7 (I +6 ‘9 G 45 Average P.S. 34 (a) I J l l L J 1 I 1 1 2 4 6 8 10 12 14 16 18 20 Dry End Length feet PERCENT WEIGHT DISTRIBUTION OF THE DRIED POWDER AND THE AVERAGE PARTICLE SIZE AT VARIOUS POINTS OVER THE ‘LENGTH OF THE SPRAY DRYER USING A HIGH PRESSURE NOZZLE. D [STR I BUT ION ‘i‘E RCENT WEIGHT 31 I ON DI Z TRI BUT WE IGH’I’ PERCENT 185» 412 Q 180. 111 3: 170_ 310 m E u) 165 )- .19 ., /' . ' _ g Average P.S. 0“) Percent weight 3 160- distribution 48 L“ 155,. 0 .7 m 2 Conditions m ‘0 g 150' C ’o‘ 3’ 20 percent slurry '16 4 Exit air temperature ZOOOF 145. Feed temperature 86oF ‘5 Low pressure nozzle Spray pump pressure 500 93g 140, 14 l l k l l 1 l 1 4 L Wet 0 2 4 6 8 10 12 l4 16 18 20 Dry E d E d n Length feet n FIGURE 6: PERCENT WEIGHT DISTRIBUTION OF THE DRIED BEAN POWDER AND THE AVERAGE PARTICLE SIZE AI VARIOUS POINTS OVER ’3”IFFC",JZTTLIF THE LENGTH OF THE SPRAY DRYER, :‘j""‘.“ 9‘1 : 32 to 13 feet from the wet end (Figure 5). The coarser particles fell within 8 to 17 feet from the wet end and finer particles 0 to 8 feet from the dry end in the case of the low pressure nozzle (Figure 6). Orifice diameter - The larger the orifice diameter of the high pressure nozzles the greater was the capacity of the spray dryer. The capacity in pounds of dry solids per hour and in gallons of bean puree per hour is plotted versus the orifice diameter in Figure 7. In the same figure the rated or measured capacities in gallons of slurry per hour are also included. The data show that the conversion factor for con— verting the gallons of water per hour (measured capacity) to gallons of 15, 20 and 25 percent bean puree are 0.65, 0.85 and 0.90, respectively. These data are in agreement with those reported by McIrvine (1952) and Hayashi (1962) who found that the capacity of grooved core nozzles increases with viscosity as long as atomization occurs. Generally, for most of the substances, as the orifice diameter increased the average particle size increased with a constant nozzle pressure. Low pressure nozzles were reported by their manufacturer to be capable of producing a narrower particle size range, when used at low pressures (100 to 500. psig). Furthermore, it was indicated that the low pressure 33 \ -_‘~ l‘.’ h a _.I _' r‘: 2 '5 0‘.) PS ! 1' 30 901.1 113 i 1 v -< . v ‘1,"J‘Uj‘l luf-IE" :. RA 31-: it i, V b .. ‘ ‘ qp ."\ . ' “r“ 'r' I ,1. 1:191 .L L. 1'1 )8 I 300-1 b (11‘) NA 1 Hz , m wrc‘l HR. 200 .1. l. '3 :7 LR i. u.\ ‘W I" P13113135 q l 1". 111.5131, i .161 K: n .) ’" mo. .4. 2 () 2 0 3 0 L. O . 1’) 0.121101 .sI;-..:~ri";'t:v,1.«"07< ‘10 7181,":3}- 7: 9911.3“ 7171.3 III (1,3 PM 1'2"? ~11" NANCE . 35111; 5'} (32":“Y ASL: £73.31“; 2’2“)" \ \ \I w » "-3: ._ 1 -.. - ---- r‘rw v.5 it.) n ”111.11."? ”34111“? 131911-111 1*. W \ HUN} PER I ~ \ ' )“2 "' , . ,. , 1..., 3“ 1 0:03“ .qcnmi 1,,‘11317'11412R 1w 5.11.1..ij 1.00"? {’(fl'L‘x’l) Q ) \L 200 ‘1' S I. LI'RR ‘7 .1" A \ v ( : .. 1_)£..t\;.1‘n /.' ,- 1} .i‘\ POA'UL'R S I ,. ‘1'! i R ‘1’ OR l-JA'I.‘ HI «z 101.3 "" "'30 1L 1 '1 O 1000 2000 3mm .iv‘CZ'J. I?1-1EISS’.‘R1: pg: 9 ‘ ' :‘r'1\-/ 1‘. MW.“ ) \ 17' .1: POWDER . POUNDS t r i i“: ;} 4.’ (:1 HR Y 34 nozzle eliminated fines, because this type nozzle projects a hollow cone spray with a uniform distribution. The results of this study confirmed that the low pressure nozzle produced a narrower particle size range (Table 6). The coarse parti— cles of pea bean powder, obtained by using low pressure nozzle were agglomerated clusters of small particles when observed under microscope. A coarser slurry could be fed to the spray dryer when a low pressure nozzle was used. Nozzle pressure — The spray pump pressure of nozzle pressure affected the capacity of the spray dryer more than any other variable. For high pressure nozzles (Figure 8) and for the low pressure nozzle (Table 5) the capacity increased with the nozzle pressure. In Figure 8 the capacity of the spray dryer with nozzle No. 69 (orifice insert diameter 0.0292") and 15 percent bean puree is shown. The measured capacity in gallons of water per hour is included for comparison. The data showed that the capacity in terms of dry solids per hour increased by about a factor of two by increasing the nozzle pressure from 1,000 to 3,000 psig. From a commercial stand- point the higher the spray pressures are, therefore, to be preferred as far as the capacity is concerned. Solids content 9£_the bean puree — The solids content of the bean puree also affected the capacity of the spray dryer 35 in terms of pounds of dry powder per hour. Increasing the solids content from 15 to 25 percent increased the production of dry powder about 35 percent, from 60 pounds to 82 pounds per hour (Figure 9). This trend could have been predicted since it requires more BTU's to remove the excess water in low solids puree. Although a puree containing more than 25 percent solids would increase the dryer capacity, such concen— tration could not be used because the nozzles clogged rapidly. Also, excessive amounts of mechanical energy are required for pureeing to higher solids content. Feed temperature 9£_bean puree - To investigate the effect of this variable bean puree containing 20 percent solids was heated to 86°F, 1220F and 1580F prior to feeding to the spray dryer at 2,500 psig through the high pressure nozzle No. 56 (orifice insert diameter 0.0465”) and 1800F outlet air temperature. The moisture content of the bean powder decreased from 4.9 to 4.2 percent, and the average particle size de- creased from 1021/to 82A/as the feed temperature was increased (Table 6). Van Arsdel et al., (1964) reported that preheating prior to spray drying resulted in more uniform and smaller size particles as well as increasing the thermal efficiency of the dryer. Sensory evaluations of the powder indicated that feed W) q 36 23 )0 P81 .0’ 65" (”‘R'II’ICE DlAi-‘J’ “1’11 F Ul'flfi'l‘ I‘E'IPFRAKI" F1”. 180' 30 T I _T 13 90 25 "737‘ )‘7 1‘ r " -'\l. ‘3 1‘:\\-v\ ); ' . 51,111»; 3.} I11.‘ (\‘.~‘....- [i ,1} FIL'EF 9:(lAPA'.TI'i“.’ YER. US SLURRY SOTTT‘S ‘1“1‘7-‘11‘71. f) 1. in . ‘ P i\ 7 .111 . ,Pmmi TNT PEI L . 2500 PSI _, .0465" ORIFICE DIA‘T'VER 20" SOLIDS C ‘ 17R 1‘. L\ ~10] S? T T I 160 180 200 (‘4 "H.171” TETEPFPA'I'W-‘F . F1(fi‘-1"x<1§10:'i‘iit' ICE-‘FECT 0F OUTLET 'I‘E?~TI’1iRA'I 1.71317. «1‘71 1 K.) NJ 37 temperature above 86oF gave the powder an unacceptable flavor apparently due to the excessive heat treatment received by the product. Air temperatures — The Outlet temperature is usually the critical temperature variable in the spray drying of foods. It may be controlled either by varying the nozzle size or nozzle pressure or by increasing the air temperature. When the inlet air temperature was kept constant at 3000F and the feed pump pressure changed from 500 to 1,000 and 2,000 psig keeping the other conditions constant, the resulting outlet temperatures were 2400F, 2050F and 1900F, respectively (Table 5). Increasing the exit air temperature from 1600F to 220°F and using a high pressure nozzle No. 56 reduced the moisture content of the dried powder from 5.8 to 4.4 percent and in— creased the efficiency of the spray dryer. The sensory evalu— ation of the product, however, indicated that the powders made with outlet temperatures above 2000F were slightly less accept— able. The bean powder made using the low pressure nozzle (orifice insert diameter 0.026") in conjunction with an outlet temperature of ZOOOF, resulted in an acceptable product. It was necessary to use ZOOOF outlet temperature for the low pres— sure nozzle in order to get the final product with less than 5 percent moisture content. Thus, outlet temperatures of 1800F 38 to 1850F for high pressure nozzle and 2200F for low pressure nozzle gave an acceptable product Capacity g£_the Spraijryer The capacity of the spray dryer was calculated using the Gluckert (1962) equation for the rate of heat transfer. Two terms in the equation k, the thermal conductivity of air and water vapor mixture surrounding the droplet and Dmax' the diameter of the largest particle were difficult to determine with accuracy. In calculating k, it was assumed that the air — water vapor mixture acted as an ideal gas and the average relative humidity in the boundry layer was 90 percent. On this basis the absolute humidity and the weighted value for k of the moisture at the prevailing wet bulb temperature could be cal- culated. The same procedure was used to calculate the thermal diffusivity and kinematic viscosity for the Reynolds and Prandtle number. Dmax was calculated on the basis that the largest droplet in a spray population is three times the surface per unit volume average size. The spray dryer capacities measured from actual runs with bean puree were 30 to 60 percent lower than the theoret- ically calculated values. An example of the calculations can REQUIRED mum TIME, 39 50.03 [40.0 d TNT—TIA; \:.(1.‘9b 80“., ' ‘1," \1 j -7 30.0': tINxL "“wb 3 ‘ 30.0 4 10.0 J AT=165°F 4 O '1 LT=126 °F 0‘1 —r— I jfi I T rrIUI j —‘ 10 SD 100 200 300 WKXINIM DROPLET $1213.11 FIGURE 11: THE EFFECT OF MAXIMUM BEAN DROPLET SIZE ON THE REQUIRED DRUM? TIME AT TWO DIFFERENT INLET AND OUTLET TEPE’ERATURE DIFFERENCES. 40 be found in Appendix. One of the main reasons for the devia- tion between the theoretical and experimental values is the fact that Gluckert's equation is based on a constant rate of drying and does not take into consideration the falling rate period which may be significant with drying of bean puree. Drying Time ig_the Spray Dryer The required drying time of a bean droplet being dried from an initial moisture content of 30 percent to a final moisture content of 5 percent using equation (7) was calculated and plotted on a log scale as a function of Dmax and the difference between the inlet and outlet air temper— ature (Figure 10). The drying time is approximately propor— tional to the square root of the maximum bean droplet diameter. For example, at 126OF the required drying time decreased from 13.3 to 3.4 seconds with the decrease in the maximum size of the droplet from 100 u to 5011 . These re— sults agreed with those of Marshall (1954). Sample calcula— tions are shown in the Appendix. The importance of equations (1) and (7) is not the fact that exact data can be obtained for the required drying time. The equations allow the researcher or dryer operator to get an idea of what the approximate effect on the capacity and the drying time will be from changing one of the variables 41 such as moisture content, drOplet diameter, airflow or drying air temperature. Pea Bean Powder Characteristics The properties of the pea bean powder can be divided into three basic catagories: 1) Engineering or mechanical properties such as bulk density, average particle size and flowability. 2) Physicochemical properties such as recon— stitution, solubility index, viscosity, blue value index and color. 3) Sensory properties. Bulk density and average particle size - the bulk density and average particle size of powder are closely re— lated. The bulk density generally increased as the particle size decreased. Both were influenced by spray drying condi— tions (Table 5). The bulk density of bean powder increased from 44.6 to 47.6 pounds per cubic foot and the average particle size decreased from 102.5L1to 82.4LLwith an increase of feed tem— perature from 86 to 1580F. Marshall (1954) reported that the bulk density may either increase or decrease as the feed tem— perature was increased. With soap powders and chemicals the bulk density decreases. 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I : 00000I000 quumuooEwu 000 00x0 .00mo 0000 00300000 QESQ 0000 .:0000.0 uOuOEC0U 00NNOC .>Hus0m :000 0000000 >ucw3e I O .0000 muzumummeou 0000 .00000 I000 00300000E00 000 00x0 .CHmD 0000 ouuwmmuo QESQ 0000 .:0000.0 uwumemap 00NN0: .00000 um 0000:06 00 pwmem 0003 m000E0m m I 0 .0000 mudumuwofiwu 0000 .00000 mucumumoemu 00m 00x0 .z000.0 00006000 00NNOC 003mm000 300 .0uus0m cmwn ucoouom 00:03& I m 0.0 0.0 0.0 0.00 0.0 00 0.00 00.0 0000 000 00 00000I000 0000 0000 00 0.0 0.0 0.00 0.0 0.00 0.00 000.0 000m 000 0.00 00000-00N 00:0 0000 : m.00 0 ~.m ~.0~ 0.0 0.00 0.N0 0.0 0000 00 n0 moovm 0000 000 00 000 00x0 000 QEDQ 0000 00301000800 000 00x0 CO Opswwogm manm.0000 00 0.0 0 0.00 0.5 0.05 0.00 50.0 0000 000 00 00000 00 0.0 0 0.00 0.0 0.00 m.00 000.0 0000 000 0.00 0o-0 0 00 0.5 0.0 5.00 0.0 0.05 0.50 000.0 0000 000 00 0000 muzutuomeu 0000 0.00 0.00 0.0 0.00 5.0 0.05 0.00 050.0 0050 00 0.00 ««< 50E 000 00000 5.00 5.00 0.0 0.00 0.0 0.05 0.00 000.0 0000 00 0.00 ¢0< :0E 00 00000 0.00 0.5 0.0 5.00 0.0 0.05 0.00 00 0 0000 000 00 «0 00E 00 00000 0.0 0.0 0.m 0.50 0.0 0.55 0.00 000.0 0000 00 50 *0 C05 00 00000 0 0.0 N 0 h.m m.00 0.~ 0.00 0.00 000.0 0050 00 0.00 .0 :02 00 moomm 000xooo «o 00:00: 0.0 u 0 5.0 5.00 0.0 0.55 0.00 000.0 0000 000 00 00m0 0000 N.~0 0.0 0 0.00 0.0 0.00 0.00 000.0 0000 000 00 00mm 000 00 00 0.5 0.00 5.0 5.00 0 00 00.0 0000 000 0.00 00n0 000 m 00 00 0 0.00 0.0 0.mn 0.00 000.0 0000 010 0.00 00mm oomuomm 00NNOC wuzwwmum 300 00 00 00 005000 umm00 0E 00 00 0 £00004 00cm000m0< 0m00000000 mu0cD 0E m00nm0um> mcofluflpcou m005£0z .0EOB Aumcpumuv xmch 030m> .0 .U .D .m x0000 0:0000 c00usu0umcoowm 00000 0500 0000000000 prcmnmum 0000095000 xmuam Aposcflucoov .0 0000B 00 46 bean powder with increasing feed temperature may be due to the deaeration of the slurry by heating and the decrease in average particle size resulted from a change in viscosity of the slurry, Hayashi (1962) reported-similar results for non fat dried milk powder. As the outlet drying temperature was increased from 160 to ZZOOF the bulk density of the powder decreased 47.3 to 45.9 pounds per cubic foot and the average particle size from 93.0[1to 73.3LL(Figure 12). Marshall (1954) reported that the decrease in bulk density may be caused by decrease in cell wall thickness of the particles. Van Arsdel et al., (1964) indicated that the residence time in the dryer had more influence on the moisture content than the outlet tem- perature. Increasing the solids content of the pea bean slurry from 15 to 25 percent resulted in a slight increase in the bulk density and average particle size (Figure 12) of the dried powder. The effect of feed concentration on bulk den— sity is complicated by the fact that the drop size may be varied due to change in viscosity, As the feed pump pressure of the high pressure nozzle No. 69 (orifice insert diameter 0.0292") was increased there was a slight increase in the bulk density of the dried unho— w:xssrur,ps; KHZZIF '3 000- h) (.3 O L) 101:0 )‘.’(l .3 (ES?) N PI SCREEN 9 200 FRA'J'L'R {j , C' F 180 11mm) HU'J' L ET 1 u n 0 L771". . if'l‘ T I: DTP ERAT UR Li \\ 5 Lina. R ‘\ Y 301.3 US I J pw 1‘ , PIT} ,_ 3 0 500 q 30!.) 4 '. . “p 0 .\': A- .37! ix’l'i‘H A -.‘vr 1 \L .‘Y. Lu ||~ l‘)'!‘ ."Y i_' 'er r ‘ lo‘u!‘ 1‘ y. 5: I .‘oJ "L- ' 2‘7"“ " .‘ ','.\"‘II' “ " _; .lénnxu.mg:t,0~;0“0 .. v'] g‘f,"). 0“ ,V7\(v-v.' -‘ q. [H :‘ix !."\;".(’.l. 1).:\"\'.[(,L . 0‘. l‘. I"0'._‘ , 'r‘ f. ' —,' ”f ;;\.r ‘0L‘\I .\L\/ 1.1:! . I I ()l) l 1 '31") AW)“ ‘ . ‘.\ .0,ix ,, J. .00 __ [I “11.10 (IIN' 1.. L- S LIWIH Y -0~.-‘ \il’w‘i‘. AK!) SLU‘ I'VE" ilf‘Af‘J T’I‘sz FchTTTl3KTHL 1.‘ i T 1'} .TTEt \T‘." l .‘ Q) r q A:~JGI.!7 ‘V’i‘ L h 1 7‘9. 4 30 M? RFMHE' ,aZ-z'" RAG 37 PART { CH5. S I 7.73: ,) Wm 47 48 mogenized powder (43.7 to 45.9 lbs/ft3) but a marked increase in that of the homogenized powder (39.0 to 48.0 lbs/ft3). the average particle size decreased as the feed pump pressure was increased from 500 to 3,000 psig (122.4L1to 54.yu) and (120.9flito 50.@fl) for both unhomogenized and homogenized pow- ders, respectively. At a constant feed pump pressure the size of nozzle used (0.02 to 0.0465 inches) had no effect on the bulk density but the average particle size decreased as the nozzle size decreased (82.4U_to 66.#1). As the pressure of a low pressure nozzle increased from 250 psig to 1,000 psig, the bulk density increased (39.0 to 46.9 lb/ft3) and the average particle size decreased from 179.4L1to lOBLL The change in bulk density using the low pressure nozzle was similar to that obtained for homogenized bean slurry with the high pressure nozzle. Tracy et al., (1951) reported that increasing the nozzle size at constant feed pressure decreased the bulk den— sity of whole milk powder. Seltzer et al., (1949) indicated that with high pressure nozzles the particle size range was so wide that the bulk density could not be adjusted. Marshall (1954) reported that particle size was more dependent on the atomizing pressure than on the nozzle size. The bulk density and average particle size was similar 49 for both atmosphere and report cooked beans. The average particle size tended to decrease with increase cooking time but there was no difference in bulk density. The packaging and shipping costs of any dry powder are to a large extent determined by its bulk density. A few percent saving in packing and shipping costs may mean the difference between a loss or a profit of the spray drying operation. The results indicated that the bulk density changed from 31.1 to 48 pounds per cubic foot and the average parti—- cle from 179.7L1to 50.6LLunder the different spray drying conditions investigated in this study. Bakker Arkema et al., (1966) reported that the bulk density of drum dried bean pow- der can be readily changed. The dry milling of drum dried bean flakes makes this flexibility in bulk density possible. Flowability — the flowability of the dried product is an important mechanical property because it determines the ease with which the powder can be handled. Tripp et al., (1965) have reported that the angle of repose constitutes a good yardstick for measuring the flowability of dry powder. The smaller the angle of repose (Figure 4) the better the flow characteristics of the powder. The results indicated that the flowability could be decreased by increasing the exit air temperature, the feed 50 pump pressure, the solids content of the bean puree or the nozzle size. The flowability was not affected significantly by the feed temperature of the bean puree or the method of cooling (Table 5). The flowability of bean powder is related to the part— icle size. Size grading of one lot of bean powder showed that as the particle size decreased from 210 to 44 microns, the angle of repose increased from 15.3Oto 31.30 (Table 7). The relationships between flowability and screen size are also plotted in Figure 13. It is suspected that the flowability will also depend on the moisture content of the powder. Some workers have recommended the use of free flowing indgredients to improve the flowability of a powder (Cippola et al., 1961, Sjollema et al., 1963 and Linton Smith, 1961). Tripp et al., (1965) indicated that the flowability of milk powder was im— proved by 6 to 12 degrees when it was cooled from 74°F to 36°F. Reconstitution — Quick solubility and good suspensi— bility are the first requirements of satisfactory instant precooled bean powder. The results obtained with the spray dried bean powder indicate that their reconstitution properties are related to particle size (Table 7). Generally powders with larger particle sizes suspended more rapidly in water but had a rather short period of suspendibility while powders .MHSumuwmfiou 000m boom new @fima OOmN musmmmum Dean comm .mooma muzumumafimu umauso .:movo.o uwumfimfio maunoc .xuusam coon ucmuuma >ucm3a I wAmEmm m>wumasESU« ~w¢.mm .m.m .>< HA m m m h «.0 m.v m.N ONA e.o> m.hv ma mw.ov mh.o mamfimm m>qum~5250a m N N o o 0 com m.m> «.mm 0m.am m.mv mn.o o.VN naoo.ov vvv mNm/ OH m m m e H OVN Nb m.@¢ 0N.om m.m¢ wn.o m.ma naoo.o vv mNm 0H m m.@ m m.o v ONH o.Hh m.mv om.mN o.m¢ hm.o m.NN aNoo.o mm CNN Na m.HH HA 0 n v oNH H.Hh H.mv 0N.mN N.hv oh.o m.w mNoo.o mo OmN AH AH m.o~ m m.n m om m.0n «.5v oN.¢N ¢.mv «v.0 m.~m oNoo.o vb ooN ma ma HA 0 m m ONH «.mo o.¢¢ oo.NN m.Nm Nm.o m. mmoo.o med ood ha ma ma CA N m 00H m.ho o.v¢ 0m.ma n.oN mv.o o.~ mmoo.o oHN mo 0m mN ON ma 0H m A flanged woman as muHcD umcnumw couuom wmommm um :0\QA OU\Em mOSUCH mousse: .wfifia noncmnmum mo wamcd nonwmumm :ofiusufiumcoumm xufimooma> uoHou huaawntOam hudmcmn xazm unwouwm mcwcoao sound: zmmz .coHuSufluwcoowu cum xuflmooma> .uoHou .>uflaflnm3on .muflmcwo Mada Ou muam mHUwuumm mo :ONumaoM .h manmfi Hm 52 with smaller particle sizes did not suspend as easily but once in suspension had greater suspendibility. The failure of pow— ders with small particle sizes to resuspend rapidly appeared to be due to a decrease in the ease of wettability. Solubility index — The solubility index of spray dried pea bean powder made from the unhomogenized slurries ranged from 15 to 18 m1 while those made of the homogenized slurry varied between 23 to 31 ml. The solubility index did not change significantly with increased exit air temperature, nozzle size, percent solids, method of cooking or feed temperature but increased with feed pump pressure especially in the case of homogenized slurries. Townley (1950) reported that the solubility index in— creased logarithmically with an increase in exit air tempera— ture above a certain temperature. Hunziker (1949) reported that the solubility index for non—fat dried milk powder lies usually between 0.05 to 1 m1; however, properly processed pow- der should be less than 0.2 m1. For condensed milk products the solubility index depends upon the preheating conditions prior to spray drying and on the amount of heat received in the later stages of drying (Van Arsdel et al., 1964). The solubility index for pea bean powder was poor prob— ably because of the high starch content of the product. 53 99193 — The color of the pea bean powder was similar for all methods of spray drying (Table 6). Retort cooking of the beans gave a browner powder than did atmosphere cooking due to carmelization of the sugar present at the higher tem— perature. The color is also influenced by the particle size (Table 7). The larger the particle size the browner the pow— der appeared as indicated by lower Agtron values or Gradner color difference meter L values. Also, increasing the outlet temperature from 180 to 2200F resulted in a slightly browner powder (Table 6). Blue value index - Blue value index measurements of the various pea bean powders produced indicated that the value is increased with increase of exit air temperature, increase of nozzle size and feed pump pressure using the low pressure nozzle and homogenizing the pea bean slurry (Table 6). It decreased with increased solids content of the puree and was not affected by the feed pump pressure when unhomogenized slurry was used. Increased time of cooking in the retort de— creased the blue value index while increased time of atmos- phere cooking increased the value. The blue value index is an indication of the amount of free soluble starch and, therefore, indicated the amount of cell breakage during the preparation and drying of the 54 powder (Table 4). The index ranged from 0.09 to 0.27 for un- homogenized pea bean powders and was in infinity for homogenized powders spray dried at feed pump pressures over 3,000 psig. Viscosity — The viscosity of rehydrated pea bean powder increased by increasing the percent solids in the slurry, the feed temperature, the length of cooking time and the outlet temperature (Table 6). As the feed pump pressure increased the viscosity increased for both high pressure nozzle and low pressure nozzle. For unhomogenized bean powder the viscosity ranged between 45 to 350 B.U. and 1650 to 4800 c.p. (Brook- field). Bean powder obtained from homogenized bean puree had viscosities ranging from 97 to 515 B.U. and 4150 to 8200 c.p. Increasing the feed pump pressure increased the viscosity of the rehydrated bean power (Figure 14). The viscosity was not significantly different for the particle sizes between 53 to 21011but increased markedly for smaller particle sizes (Table 7). The viscosity increases paralled the blue value index changes (Figure 14). Thus, the increase in viscosity is related to the amount of free starch in the powder. Sensory evaluations - The results of the preliminary evaluations indicated that the flavor of the powder at a feed temperature of 86oF was preferred over that of 1500F. No 55 5A- \\ \‘ ..._.\ _ r. -~.'v/N_C ._\%< ,J E I; 1:. “S “if; _ z -u o: :3“; IT. 0 .1; 56 significance was obtained between the two feed temperatures on the basis of texture. The sensory evaluation of the 1220F feed temperature was not made because of sample contamination. No significant difference was found between flavor or texture at the various outlet temperatures. However, there was a tendency to prefer the powder obtained when an outlet temperature below 1800F was used. Flavor evaluation showed no significant difference between nozzle numbers 56, 62 and 69, indicating that the lower nozzle sizes were preferable. Similar results were obtained for texture. The results of the flavor panel tests were not consistent for nozzle pressure variation but indicated that lower pressures were desirable. Pressures above 2,000 psig were undesirable when nozzle No. 69 was used. The judges found no significant difference in flavor or texture between the nozzle pressures 500, 700 and 1,000 psig when the low pressure nozzle (orifice diameter 0.026") was used. At 250 psig the flavor was significantly better than either 700 or 1,000 psig. 0n the basis of preliminary sensory evaluations the judges showed a preference for the powders dried under the following conditions: 57 1) High pressure nozzle Nozzle pressure 2,500 psig Outlet temperature 1800F Solids content 20 percent Feed temperature 86oF Nozzle diameter 2) Low pressure nozzle 0.0465 inches Nozzle pressure 250 psig Outlet temperature 2000F Solids content 20 percent 0 Feed temperature 86 F Nozzle diameter 0.026 inches When the bean powder sample made by using the high pressure nozzle was evaluated by 47 judges, the results indicated (Table 9) 6.6 average rating on 9 point hedonic scale. Eighty—two point nine percent people accepted the sample if rating 6 (like slightly) was considered as limit and 61.7 people preferred the sample if rating 7 (like moderately) was considered the consumer preference limit. 58 Table 8. Sensory Evaluations (Preliminary) a) Feed temperature 86oF 1580F Flavor 5.6 4.7 Texture 5.3 5.0 b) Outlet temperature 1400F 1600F 180°F 200°F 220°F Flavor 4.6 4.5 5.6 4.5 Texture 4.9 4.4 5.4 4.7 c) Nozzle variation Nozzle number 56 62 69 72 76 Flavor 5.6 5.0 5.1 4.2 4.2 Texture 5.8 5.1 4.7 d) Pressure variation Feed pump pressure psig 500 1000 2000 3000 Flavor 5.8 . Texture 5.3 4.0 4.7 3.8 e) Low pressure nozzle (0.026") pressure variation Nozzle pressure psig 250 500 700 1000 Flavor 5.8 4.7 4.8 4.4 Texture 5.3 4.0 59 Table 9. Results of the taste panel of 47 judges No. of People Rating Giving Their Percent Rating 9 1 2.13 8 15 31.91 7 13 27.66 6 10 21.28 5 2 4.25 4 2 4.25 3 4 8.50 Average rating 6.6. Note: Twenty percent solids bean slurry, nozzle diameter 0.0465", feed pump pressure 2500 psig, exit air temperature 1800F, feed temperature 86°F. C ONC LUS I ONS Homogenizing the bean puree prior spray drying is an unsatisfactory procedure because the powder when recon— stituted had excessive pastiness. Both high and low pressure nozzles can be used to produce bean powder which is acceptable. The average particle size and the amount of smaller size particles (44))and less) mainly determine the character- istics of bean powder such as solubility index, blue value index, reconstitution properties and viscosity of the re- hydrated powder. Outlet air temperatures over 2000F were unsuitable. The theoretical spray dryer capacities were between 30 and 60 percent above the measured capacities for bean slurry. Different powder distribution patterns were obtained when a low pressure nozzle and high pressure nozzle was used. The drying time for 10011diameter bean droplets was 13.3 seconds and for 50}1diameter bean droplets 3.4 seconds for a logarithmic mean temperature difference of 126OF. Sensory evaluations of the reconstituted powder indicated that either low or high pressure nozzle may be used. Pow— 60 61 ders produced with 20 percent solids bean slurry fed at 80°F through high pressure nozzle at 2500 psig and through low pressure nozzle at 250 psig with drying temperatures of 1800 to 2000F tended to be preferred. APPENDIX Calculation of Spray Dryer Capacity Drying conditions of typical spray drying operation: 0 Bean puree initial temperature 86 F Solids content of the slurry 20 percent Final moisture content 5 percent Nozzle No. 56 orifice insert diameter, 0.0465 inches Inlet air temperature 3100F Exit air temperature 1800F Atmospheric temperature 70°F Wet bulb temperature of surround— 0 ing air 59 F Measured product flow rate 390 lbs of bean puree/hr Theoretical capacity was calculated using Gluckert's equation 10.98 k v2/3 AT , D d (1) q = 2 S t D d maX S where, k, thermal conductivity of film 0.0157 BTU/hr. ft. oF (Holman, 1963). v, volume of the dryer, ft Assuming the dryer to be circular in cross section and diameter of the dryer 7.0 ft. and length 17 ft. 62 63 TTrzl Total volume 3.1416. 49 . 17 u) bl 653. 9 ft So W 1,150,000 2000 575 lbs of H20/hr The actual rate of drying was 390 lbs of HZO/hr. Hence, percentage difference = 575-390 = 185 = 31.8% 575 575 Calculation 9£_Drying Time The total time required to dry a bean droplet was calculated using equation 7. led (M.c.in — M. Wont)7T'Dm t: 0.5 0.33 + 6 k . (2.0 0.6 Re . Pr )7TDmaX(AT)av 3 dd, density of bone dried powder was assumed to be 100 1b/ft M.C.. , moisture content of bean puree (20 percent solids) entering the dryer on dry basis. - -—§9- = 4 lbs of H 0/1b of dr matter 7 100-80 2 y and M'C°out’ moisture content of bean powder on dry basis 5 - 100—5 — 0.05 lbs of H20/lb of dry matter Atav = Tai — Tao = 310 _ 180 = 126OF. T T 1n 310 - 108 1n ai - ao 180 — 108 T _ 64 0.5 0.33. . . . The value of Re . Pr is negligible Since the Reynolds number contains the term diameter of the droplet which is very small (100 LL). Z:t, temperature difference between outlet air and drop sur— fgggFis equivalent to Tout - wa ; Tout outlet temperature is wa the wet bulb temperature of drop surface was found out fromP%ychrometric chart to be 1080F. 0 Hence, At — Tout — wa — 180 — 108 — 72 F De, orifice diameter of nozzle No. 56 is 0.0465 ft. ” 12 Dmax’ maximum drop diameter was assumed to be 100 microns or —4 D _ 100 x 10 ft max 30.5 dt' the density of outlet air was found from psychrometric data to be 0.071 lb/cu.ft. ds, the density of 20 percent bean puree is 62 lb/ft3. Substituting the values in equation No. l: = 10.98 . 0.015 . 653.92/3 . 72 . 0.0465 0.071 (100 x 164) 2 12 62 30.5 1,150,000 BTU/hr. The drying rate, W = q/A_ ,1, was assumed to be 2,000 BTU/1b. [Hall (1957) in Figure 2.6 page 40 showed that the latent heat of wheat (10 percent moisture) is approximately 1400 BTU/lb. In the case spray drying of bean slurry much energy is lost due to conduction and radiation, hence a higher value was assumed.] 65 Substituting the values in equation No. 7: 4 t = 2000 . 1000 . (44_o.5) . 3.14(1oo x 10‘ ) . 3600 30.5 6 . 0.015 . 2.. 3.14 (100 x 10’4) 126 30.5 13.5 seconds BIBLIOGRAPHY Anon. (1965) Higher quality drying at lower cost. Food Proc. 26, 92. Bakker-Arkema, F. W., Patterson, R. J., and Bedford, C. L. (1966) Drying characteristics of pea beans on single and double drum dryers. A.S.A.E. Paper No. 66-316 presented at Annual A.S.A.E. meeting, Amherst, Massa— chusetts. Baran, S. J. (1964) Heavy paste dispersion drying system. Ind. Eng. Chem. 56, 10. Bose, A. K. Pei D.C.T. (1964) Evaporation rates in spray drying. Can. J. Chem. Eng., 42, 6, 259. Bower, W. S. (1931) Spray drying of Idaho's surplus potatoes. Food Inds. 3, 380. » Cippola, R. H., Davis, D. W. and Vander Linder C. R. (1961) Free flowing dried dairy products. U.S. Patent 2, 995, 447. Cording, J., Jr., Sullivan, J. F., and Eskew, R. K. (1959) Potato Flakes - a new form of dehydrated mashed potatoes. IV. Effects of cooling after precooking. U.S. Dept. Agr., Agr. Res. Serv. Ars. 73-25. Dlouhy, J. and Gauvin, W. H. (1960) Heat and mass transfer in spray drying. A. I. Ch. E. J., 6, l, 29. Frossling, N. (1938) Zerstaubungstrocknen Gerlands Beitr. Geophys 52, 170. Gluckert, F. A. (1962) A theoretical correlation of spray dryer performance. A. I. Ch. E. J., 3, 4, 461. Hall, C. W. (1957) Drying farm crops. 4th Edition, Agr. Consulting Associates Inc. Hayashi, H. (1962) Studies on spray drying mechanism of milk powders. Rept. Res. Lab. Snow Brand Milk Prod. Co. Ltd., Japan No. 66. 66 67 Holman, J. P. (1963) Heat Transfer, McGraw Hill Book Co., New York. Hunziker, O. F. (1949) Condensed milk and milk powder. 7th Edition, published by the author, LaGrange, Ill. Kirschbaum, E. (1952) Grundsatzliches and Neues Uber die Zerstaubungstrocknung. Chem Eng. Tech., 24, l, 4. Linton-Smith, L. (1961) Free flowing milk powder. Aust. J. Dairy Technol, 16, 22.- Marshall, W. R. (1954) Atomization and spray drying. Chem. Eng. Progr. Monograph series, 2, 50. McIrvine, J. D. (1952) Atomization of viscous liquids with centrifugal pressure nozzle. M. S. thesis, Dept. of Chem. Eng. Univ. of Wisconsin. Morris, H. J. (1961) Instant bean powders. Proc.Fifth Ann. Dry Bean Research Conf., Denver, Colorado, U.S. Dept. Agr. Research Serv., West. Utiliz. Research and Development Div., Albany, Calif. Pal, J. P. (1959) Temperature and air flow analysis in a spray dryer. M. S. thesis, Dept. of Agr. Eng., Mich. State Univ. Ranz, W. E., and Marshall, W. R., Jr. (1952) Evaporation from drops. Chem. Eng. Progr. 48, 141. Perry, J. H. (1950) Chemical Engineer's Handbook. 3rd Edition. McGraw Hill Book Co., New York. Rohsenow, W. M., and Choi, H. Y. (1961) Heat, Mass and Momentum Transfer. Prentice-Hall, Inc. Englewood cliffs, New Jersey. Seltzer, E., and Settlemeyer, J. T. (1949) Spray drying of foods. Advances in Food Research 6, 399., Ed. by Mark, E. M., and Stewart, G. F., Academic Press, New York. Sjollema, A. (1963) Free flowing properties and porosity of milk powder. Neth. Milk Dairy J. 17, 245. 68 Townley, V. M. (1950) The operation of a spray dryer at high temperatures and under pressure. M. S thesis, Dept. of Dairy Industries, Univ. of Minnesota. Tracy, P. H., Hetrick, J. H., Krienke., W. A. (1951) Effect of spraying pressure and orifice size on the physical characteristics and keeping quality of.spray.dried whole milk. J. of Dairy Sc. 34, 6, 583. Tripp, R. C., Anderson and Richardson, R. (1965) Flowability of high fat dried dairy products. Paper M-7O pre— sented at 60th Annual A.D.S.A. meeting, Lexington, Kentucky. Van Arsdel, W. B., and Copeley, M. J. (1964) Food Dehydra— tion. Vol II AVI Publishing Co., Westport, Conn. 4 9 6 2 4 4| 3 O 3 9 l 'I II I I l l I l III II. I II I l I II l l l l I l I' I II III I | l I III. I ll |l3 I II III I l