DRYING OF SOY PULP (OKARA) IN A BED OF INERT PARTICLES

ABSTRACT

Drying of okara, an insoluble pulp residue waste byproduct of tofu production, was investigated in a continuously moving bed of inert particles subjected to vortex-like motion. The experimental variables in their respective ranges included the mass of Teflon pellets used as inert particles (0.4–1.2 kg), feed rate (0.5–1.4 kg/h), inlet air temperature (100–145°C) and airflow rate (195–271 m³/h). The dryer showed good performance in general and produced dry okara with moisture content ranging from 5 to 33% wb depending upon the operating conditions. The product recovery ranged from 80 to 90% on dry basis in most experiments. The specific water evaporation rate in okara drying increased with increasing of the feed rate and mass of Teflon pellets. However, the specific heat consumption decreased with an increase in the okara feed rate. Results showed that specific heat consumption for okara drying in a bed of inert particles was about 3 to 4 times higher in comparison with that of free water.     

Drying of Slurries in Fluidized Bed of Inert Particles

A fluid bed dryer with inert particles was used for drying of slurries. Experiments were performed in a cylindrical column 215 mm in diameter and 1200 mm in height with glass spheres as inert particles. Slurries of Zineb fungicide, copper hydroxide, calcium carbonate, and pure water were used as the feed material. The effects of operating conditions on dryer throughput and product quality were investigated. Main performance criteria, i.e., specific water evaporation rate, specific heat consumption, and specific air consumption, were quantified. Temperature profile along the bed was mapped, and nearly isothermal conditions were found due to thorough mixing of the particles. The material hold-up and residence time were determined. Simple heat and mass balances predict the dryer performance quite well.     

SIMULATION OF FLUIDIZED-BED DRYING OF CARROT WITH MICROWAVE HEATING

A mathematical model of coupled heat and mass transfer was applied to batch fluidized-bed drying with microwave heating of a heat sensitive material—carrot. Four kinds of microwave heating with intermittent variation were examined. The numerical results show that different microwave heating patterns can affect the fluidized bed drying significantly. Changing the microwave input pattern from uniform to intermittent mode can prevent material from overheating under the same power density. Supplying more microwave energy at the beginning of drying can increase the utilization of microwave energy while keeping temperature low within the particle. For a particle diameter of 4 mm, fluidization velocity of 2 m/s, inlet airflow temperature of 70°C and the bed area factor of 80, the drying time are 750 and 1000 s, respectively, for the two good operating conditions with on/off periods of 125/375 s and 375/375 s. The cumulative microwave energy absorbed by particles at the end of drying is 1415 and 2300 kJ/kg (dry basis), respectively.     

Drying Kinetics and Quality of Soy Residue (Okara) Dried in a Jet Spouted-Bed Dryer

The objective of this study was to investigate experimentally the effects of various drying parameters, i.e., inlet air velocity, inlet air temperature, initial bed height and heating duration, on both the drying kinetics and various quality attributes of dried okara viz. percentage changes of the total protein content, color, urease index, as well as the specific energy consumption during drying in a jet spouted-bed dryer. It was observed that all drying conditions tested could reduce the amount of urease to an acceptable level and increasing the heating duration, air velocity, and hot air temperature led to a significantly higher rate of reduction of urease activity. The percentage change of the total protein content of okara undergoing different drying conditions was not significantly different, however. After drying, the redness of okara was the highest changing color index, but its absolute value was still much lower than those observed for the lightness and yellowness. Hence, dried okara appeared light-brown. The specific energy consumption of the process was found to be in the range of 3.69 to 5.89 MJ/kg evaporated water.     

洗衣粉悬浮液在惰性粒子流化床中干燥的研究

针对气体分布板开直孔的惰性粒子流化床,开展了洗衣粉悬浮液在床内的干燥性能研究。测定了流化床的床层压降曲线,考察了进料量、进风温度、进风速度及惰性粒子直径对于流化床传热性能的影响,且与气体分布板开斜孔的传热性能进行了初步比较。结果表明,流化床的床层压降主要是由惰性粒子的流化阻力所致;适当增加进料量和进风速度,或减小惰性粒子直径,以及将气体分布板的孔道由直孔改为斜孔,均可提高流化床的传热性能,但过高的进风温度则可能导致传热性能的下降。     

内热式惰性粒子流化床中膏状物料干燥模型

通过对惰性粒子流化床中膏状物料干燥机理的分析,得到了干燥时间及单位面积床层水分汽化量的数学计算式,可对干燥器的性能进行预测。采用带浸没加热管的惰性粒子流化床对膏状钛白物料进行干燥中试研究,采用气流式喷嘴将膏状物料分散成200～400μm的小液滴喷洒在惰性粒子表面进行干燥,探索了适宜的干燥条件,测定和确定了最佳的干燥工艺参数、操作参数和设备参数。结果表明:该干燥工艺能强化床内传热传质,促进高黏性膏糊状物料很好地分散,床层温度分布均匀,干燥器的操作弹性大,热量消耗低,干燥强度高,传热系数可达300W·m-2·K-1以上。     

ANALOGY BETWEEN HEAT AND MASS TRANSFER IN THREE SPOUTED BED ZONES DURING THE DRYING OF LIQUID MATERIALS

This work, presents an experimental study of simultaneous heat and mass transfer in spouted bed zones during the drying of liquid materials. Distilled water was used as the liquid material and glass beads as inert material. The effect of the inlet gas temperature (100 to 140 °C), the feed air flow rate relative to air flow at minimum spouting (1.1 to 1.3), and liquid feed flow rate to the bed were investigated. The similarity between heat and mass transfer was analyzed using the Lewis and Chitton-Colburn analogies. Results showed that the ratio between the heat and mass transfer Chilton-Colbum factors lay between 1,31 and 1.74.     

A Small-Scale Pneumatic Conveying Dryer of Rough Rice

This article studies the possibility of reducing the high initial moisture content of wet rough rice using a small-scale low-cost pneumatic conveying dryer as a first stage dryer. The parameters investigated are final moisture content, surface temperature of rough rice, head rice yield, drying rate, power consumption per unit mass of evaporated water, and physical characteristics of rice. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, initial moisture content from 22 to 26% (wet basis), and drying air temperature from 35 to 70°C. From the experimental results, it is found that this drying method can be used for fresh rough rice with an initial moisture content of over 24% (wet basis). The drying process is able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. The moisture content can be reduced to approximately 18% (wet basis) or about 5-6% of the initial moisture content within 3-4 s. The optimal drying air temperature is in the range of 50 to 60°C. A comparison of pneumatic conveying drying data obtained from the present study with fluidized bed drying data reported in the open literature is also discussed.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D_e) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X_o). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

SORPTION DRYING OF SOYBEAN SEEDS WITH SILICA GEL. I. HYDRODYNAMICS OF A FLUIDIZED BED DRYER

Fluidization technology has been employed to mix soybean seeds and silica gel particles in aim of sorption drying of particulate agricultural products. The characteristic fluidization velocities, mixing mechanisms and fluidization quality have been studied in a 180 mm I.D. fluidized bed. Two sizes of silica gel particles (SG2 and SG3) were selected, with the mass fractions in the range of 0.33-0.75 to form a static bed with height from 100 to 280 mm (H/D = 0.56-1.56). The results show that the dispersion rate of soybean seeds is increased with addition of either SG2 or SG3, and that the frequency and the span of pressure fluctuations within the bed are increased. It is inferred that the gas-solids contacting is improved with addition of small particles in the bed of large particles. In addition, for practical design and operation of such a fluidized bed of binary mixtures, empirical correlations for characteristic fluidization velocities were developed with a wide application.     

MOBILE FLUIDIZED BED PADDY DRYER

The objectives of this research are to design, construct and test a mobile fluidized bed paddy dryer with a drying capacity of 2.5-4.0 t/h. Suitable drying conditions are recommended as follows : drying capacity 3.8 t/h, bed velocity 2.8 m/s, average drying air temperature 144 °C, bed height 13.5 cm, fraction of air recycled 0.8. Residence time of paddy was approximately 1.3 minutes. Test results showed that moisture content of paddy was reduced from 32.6 % dry-basis to 25.8 % dry-basis. Consumption of electrical power and diesel fuel was 12.9 kW and 21.71 1/h respectively. Primary energy consumption was 910.9 MJ/h. The dryer could evaporate water 218.8 kg/h. Specific primary energy consumption was 4.2 MJ/kg-water evaporated. Cost of paddy drying was 1.48 baht/kg-water evaporated of which 0.53 was fixed cost and 0.95 was energy cost (US$1 =34baht).     

惰性粒子流化床中的悬浮液干燥

用惰性粒子流化床干燥器对混凝土外加剂等5种物料进行了干燥实验研究，提出了计算体积传热系数的关联式．实验结果表明，由于惰性粒子的存在，强化了传热传质，体积传热系数可达3000W·m~(-3)·K~(-1)，但是，床层压力降较高．干燥强度（以蒸出水计）可达50～60kg·m~(-3)·h~(-1)，热效率30％～43％，若提高热风进口温度，后两项指标还可提高.     

HEAT AND MASS TRANSFER DURING DRYING OF A LIQUID FILM FROM THE SURFACE OF A SINGLE INERT PARTICLE

ABSTRACT

This paper presents the results of theoretical and experimental studies on drying of aqueous suspensions of finely dispersed solids sprayed over the surface of an inert ceramic sphere. The effects of temperature and air velocity on kinetics of heat and mass transfer as well as peeling off the layer of a dry material from the sphere surface are described. The mathematical model of a drying process based on simplified ?gradientless? approach to transfer phenomena is proposed. The adequacy of the model developed for drying of the wet coat from a single sphere to the real drying process taking place in a bed of particulate carrier is confirmed by results of drying of several organic dyestuffs in an industrial spouted bed dryer with inert particles.     

Drying Kinetics and Quality of Soy Residue (Okara) Dried in a Jet Spouted-Bed Dryer

ABSTRACT

The objective of this study was to investigate experimentally the effects of various drying parameters, i.e., inlet air velocity, inlet air temperature, initial bed height and heating duration, on both the drying kinetics and various quality attributes of dried okara viz. percentage changes of the total protein content, color, urease index, as well as the specific energy consumption during drying in a jet spouted-bed dryer. It was observed that all drying conditions tested could reduce the amount of urease to an acceptable level and increasing the heating duration, air velocity, and hot air temperature led to a significantly higher rate of reduction of urease activity. The percentage change of the total protein content of okara undergoing different drying conditions was not significantly different, however. After drying, the redness of okara was the highest changing color index, but its absolute value was still much lower than those observed for the lightness and yellowness. Hence, dried okara appeared light-brown. The specific energy consumption of the process was found to be in the range of 3.69 to 5.89 MJ/kg evaporated water.     

Comparison of Drying Kinetics of Paddy Using a Pneumatic Conveying Dryer with and without a Cyclone

The objective of the present work is to find the possibility of reducing the high initial moisture content of wet paddy using a small-scale, low-cost pneumatic conveying dryer that can be provided for each farming household. The dryer without a cyclone equipped at the exit of the dryer is studied and the data obtained from this system is compared with those obtained previously from the dryer with a cyclone. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, and drying air temperature from 35 to 70°C. From the experimental results it is found that the drying process with and without a cyclone are able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. For the same experimental conditions, the cyclone-equipped dryer gives around 1% higher decrease of moisture content, 2°C higher average surface temperature of paddy, 3-4% higher average percentage of head rice yield, and 2 kg/h higher average evaporation rate. However, the energy consumption per evaporated mass of water is 20-30% lower than the non-cyclone-equipped dryer.     

FILTERS AND FILTRATION HANDBOOK 4th Edition (1997) By T. Christopher Dickenson Publisher: Elsevier Advanced Technology The Boulevard,Langford Lane,Kidlington, Oxford OX5 1GB,U.K.

Abstract

Revolving air flow was generated by oblique holes on air distribution board in a fluidized bed dryer. Such a revolving air flow shows a large scale velocity fluctuation in radial as well as tangential directions. This turbulent flow of air can fluidize the inert particles with superior performance than vibrated fluidized bed. The revolving fluidized bed is simpler in fabrication and easier in operation. For two types of inert particles tested, 4 mm glass beads and 4 mm × 5 mm Teflon cylindrical extrudates, the volumetric heat transfer coefficients were found to increase with the liquid feed flowrate and air flow velocity but decrease with the air inlet temperature, height of static bed, and liquid concentration. The revolving fluidized bed gives an increase of volumetric heat transfer coefficient by 1 kW/m³ K, and represents a 15–25% enhancement from ordinary fluidized bed operated at a bed height of 60 mm, bed diameter of 140 mm, superficial air flow velocity of 3.5 m/s, liquid feed (Soya milk) flowrate of 20 mL/min at a concentration of 6.7%, and a temperature ranges of 80–140°C using Teflon extrudates as inert particles.     

ANALOGY BETWEEN HEAT AND MASS TRANSFER IN THREE SPOUTED BED ZONES DURING THE DRYING OF LIQUID MATERIALS

ABSTRACT

This work, presents an experimental study of simultaneous heat and mass transfer in spouted bed zones during the drying of liquid materials. Distilled water was used as the liquid material and glass beads as inert material. The effect of the inlet gas temperature (100 to 140 °C), the feed air flow rate relative to air flow at minimum spouting (1.1 to 1.3), and liquid feed flow rate to the bed were investigated. The similarity between heat and mass transfer was analyzed using the Lewis and Chitton-Colburn analogies. Results showed that the ratio between the heat and mass transfer Chilton-Colbum factors lay between 1,31 and 1.74.     

Kinetics Study of Green Peas Drying in a Spouted Bed in the Presence of a Heat Carrier

In this study, a drying kinetics model for predicting the drying of green pea particles using a bench-scale spouted bed with heat carriers is investigated. The experiments were carried out under different operating conditions. The effect of inert particle diameter, inert particle type, and the mass ratio of inert particles to green peas was examined based on the performance of the dryer and the rate of drying. As expected, the rate of drying increased with increased mass ratio of inert particles to green peas and thermal diffusivity of inert particles.     

An Experimental Study of the Thermal Performance of a Screw Conveyor Dryer

In the present study drying of fine crystalline solid was carried out in a non-insulated jacketed screw conveyor dryer SCD of 3 m length and 0.072 m screw diameter. It is nitrogen-swept to carry off the evaporated moisture. Dryer performance was evaluated in terms of the final moisture content, heat-transfer coefficient, thermal efficiency and power consumption. From the experimental results it was observed that drying under low pressure gives 92% moisture removal compared to 30-40% using low flow rates of nitrogen. The initial moisture content was in the range of 5 to 6%. Over the parameter range studied, the overall heat transfer coefficient was found to be in the range of 46-102 W/m²K. The average rise in the temperature of the product was 40 to 50°C. Thermal efficiency (based on sensible and latent heat) of the dryer obtained was found to be in the range of 25-62%, typical values obtained in falling rate drying period. Power consumption per metric ton of dried material was found to be a strong function of screw speed and material feed rate, material properties, and drive efficiency.     

Improvement in the Efficiency and Capacity of Chopped Spring Onion Drying

ABSTRACT

Appropriate strategy for drying chopped spring onion with a batchwise flat bed was investigated. Both experimental and simulated results such as product quality, drying capacity and energy consumption were taken into consideration. For simulation work, equations of drying parameters such as specific heat, equilibrium moisture content and thin layer drying were first developed from the lab-scale experimental results. Then a mathematical model including shrinkage for a batchwix flat bed drying was developed. The model was lested with the results obtained from a food processing plant with an acceptable accuracy. Appropriate drying strategy war then investigated. The approximate conclusion was that the drying should be devided into 3 stages. In the 1^st stage, drying air temperature was 80°C, specific air flow rate was 33.9 m³/min -kg dry matter and drying time was 0.5 h. In the 2nd stage, drying air temperature and drying time were kept unchanged but specific air flow rate was decreased to 13.5 m³/min - kg dry matter. In the final stage, drying air temperature was decreased to 67°C, specific air flow rate was also decreased to 6.8 m³/min - kg dry matter and drying time was approximately 1.7 h. Following the suggested strategy, specific primary energy cornsumption was 6.2 MJ/kg H₂O, drying time was 2.7 h and product quality was maintained. It was proven that energy consumption was approximalcly 70% of that of the present practice in the plant.