A Study of the Limitations to Spray Dryer Outlet Performance

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h^-1, 1.6 kg h^-1, 1.8 kg h^-1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s^-1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.     

Characterization of a Spray Drying System for Soymilk

Soymilk slurries were spray dried at various combinations of inlet air temperature (1255. 265, and 275°C), feed rate (0.38 and 0.57 Lpm), and atomizer speed (119,300 and 26,800 rpm). Monitored dryer parameters included dry and wet bulb temperaturea of ambient and exhaust air, drying chamber's inlet and outlet air temperatures, product and feed temperatures, velocity pressure at exhaust pipe, atomizer speed, and feed rate. Weather data was included in the analysis.

Collected data was used to estimate the state of the outlet air using psychrometrics and assuming adiabatic saturation. Equations to predict outlet and product temperatures were developed. Average thermal and eveporative efficiencies were 65.9 and 78.4%. respectively.     

Spray Drying and Agglomeration of Instant Bayberry Powder

Optimum technology of spray-dried bayberry powder was studied using D-optimal experimental design. The operating conditions were varied within the following ranges: inlet air temperature 140-160°C, outlet air temperature 65-85°C, maltodextrin DE values 12 and 19, and feed concentrations of 7-17°B. The spray-dried bayberry powder was analyzed for moisture content and color. Moisture content of spray-dried powder was determined mainly by the inlet and outlet air temperatures, DE value, and the feed concentration. The inlet and outlet temperature had important effects on powder color. Finally, instant bayberry powder for beverages was produced by agglomeration of the spray-dried product.     

An Experimental Investigation of the Wall Deposition of Milk Powder in a Pilot-Scale Spray Dryer

A pilot-scale, co-current spray dryer has been used to investigate the effect of varying the swirl vane angle for the inlet air, inlet air temperature and liquid feed flowrate on the wall deposition flux of skim milk powder. The spray dryer was a cylinder-on-cone unit with a diameter of 0.8 m and a height of 2 m. It was fitted with adjustable swirl vanes surrounding a Delavan GA1 two-fluid atomizer. Swirl vane angles of 0, 25, and 30°, inlet air temperatures of 170, 200, and 230°C and feed flowrates of 1.4, 1.6 and 1.8 kg h^-1 were used. Inlet air swirl was found to significantly influence the wall deposition flux, with the highest swirl vane angle of 30° giving rise to the largest wall deposition flux. The difference between the particle and sticky-point temperatures of the skim milk powder was also found to be important in influencing the wall deposition flux. The wall deposition flux was the highest, at 16 g m^-2 h^-1, when the outlet particle temperature was furthest above the sticky-point temperature, and this occurred at the lowest value of the inlet air temperature (170°C) and highest product moisture content. No significant effect on the wall deposition flux was evident when using a nonstick food grade material (nylon), adhesive tape or stainless steel as the surface materials for the wall deposition tests. Therefore, it is likely that cohesion occurs at a similar rate to adhesion in the wall deposition of milk powder. Grounding the spray dryer also did not have a significant effect on the wall deposition flux. Relating the wall deposition flux to the sticky-point curve in this way suggests that the same trends (increased wall deposition fluxes above the sticky-point curve) may apply for other materials as well.     

STABILITY AND SENSORY QUALITY OF SPRAY DRIED AVOCADO PASTE

Avocado (Persea americand) paste was spray dried at inlet air temperature of 180°C, 80°C outlet air temperature, air velocity of 27 m/s and a feed flow rate of 0.642 l/min. Lipids in the paste were emulsified using 10 % Monoacylglyceride (MAG). Treatments were applied according to the following antioxidants mixtures: 1) BHA (butylated hydroxyanisole) + BHT (butylated hydroxytoluene) (0.05 % each); 2) TBHQ (Tertiary butylated hydroxyquinone) + Citric Acid (0.05 + 0.1 %); 3) BHA + BHT + Citric Acid (0.05 + 0.05 + 0.1 %); 4) BHA + Propyl gallate (0.05 + 0.05 %); or 5) BHA + Propyl gallate + Citric acid (0.05 + 0.05 + 0.1 %). Samples were stored at 6, 12, 25, 28 and 40 °C. Peroxide values were determined periodically. Development of rancidity was detected by sensory evaluation of the samples. For samples kept at 6 and 12 °C, an antioxidant mixture containing BHA and propyl gallate at 0.05% gave the least protection to the stored avocado powder. The mixture containing TBHQ and citric acid yielded the lowest rancidity development.     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

Abstract

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

Spray Drying Performance of a Laboratory Spray Dryer for Tomato Powder Preparation

This work investigates the performance of a spray dryer for tomato powder preparation by spray drying of tomato pulp. Samples of tomato pulp with a 14% constant total solids concentration were used, and a pilot scale spray dryer (Buchi, B-191) with cocurrent operation and a two-fluid nozzle atomizer was employed for the spray drying process. Twenty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying rate, and the air inlet temperature. In each experiment the air outlet temperature was recorded. Data for the residue remaining in the chamber and cyclone walls was gathered and two types of efficiencies were calculated as an indication of the spray dryer performance. Analysis of experimental data yielded correlations between residue accumulation and the variable operating conditions. The same operating parameters had a great influence on the air outlet temperature whereas temperature deviations were observed comparing measured air outlet temperatures with corresponding outlet adiabatic saturation temperatures.     

Supercritical CO2 extraction of biological active compounds from loquat seed

Amygdalin and β-sitosterol from roasted powder and ground unroasted loquat seed were extracted using supercritical CO₂. Loquat seed is the waste of loquat fruit (Eribotrya japonica), that called biwa in Japan. Loquat seed contains some active compounds, such as amygdalin, sterol and β-sitosterol. Amygdalin is used for medical purposes, mainly as drug in cancer. β-Sitosterol is found in health supplement for various physical ailments. In this work, extraction was conducted at pressure of 20, 30 and 45 MPa, temperature of 40, 60 and 80 °C, and CO₂ flow rate of 3 ml/min for 180 min. Roasted powder and ground unroasted loquat seeds were used as materials. Component in extract was analyzed by HPLC carried out on 5C18-MS column at 27 °C for amygdalin, and 35 °C for β-sitosterol using acetonitrile:water (85:15 v/v) as mobile phase. Based on results, a change in temperature and pressure affected the yield of total extract, amygdalin and β-sitosterol recovery. For comparison between extract from roasted powder and ground unroasted loquat seed, total extract and β-sitosterol recovery from roasted powder loquat seed were higher than that from unroasted one. On the other hand, amygdalin recovery from ground unroasted seed was much higher than that from roasted powder. The optimum condition of extract from roasted powder and ground unroasted loquat seed and amygdalin recovery were obtained at 80 °C and 20 MPa.     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10-20% of solids was dried at different inlet air temperatures (120-160°C), air flow rate of 0.19 kg dry air s^-1 and different feed rates (1.4 - 4.2 × 10^-4 kg dry solids s^-1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

Spray Drying of Yogurt: Optimization of Process Conditions for Improving Viability and Other Quality Attributes

Plain yogurt was subjected to spray drying to determine the optimum processing conditions that yield maximum survival ratio of lactic acid bacteria, maximum overall sensory attributes, minimum color change, and acceptable moisture content. The inlet (150–180°C) and outlet air temperatures (60–90°C) and the feed temperature (4–30°C) were the independent factors. A pilot-scale spray dryer was used to conduct a set of drying experiments where the process conditions were selected according to central composite rotatable design (CCRD). The resulting yogurt powder at each condition was also subjected to the measurement of some physical properties (water activity, titratable acidity [lactic acid, %] and pH) to determine the effects of spray-drying conditions. The morphological structure of the powder was inspected by scanning electron microscopy (SEM) analysis. Optimization by the application of the desirability function method resulted in air inlet temperature of 171°C, air outlet temperature of 60.5°C, and feed temperature of 15°C as the optimum processing condition. The mathematical optimum condition was experimentally verified.     

Drying Kinetics and Color Retention of Dehydrated Rosehips

Freshly harvested rosehips (Rosa canina L.) were dehydrated in a parallel flow type air dryer at six air temperatures (30, 40, 50, 60, and 70°C) at air velocities of 0.5, 1.0, and 1.5 m/s. Drying air temperature and velocity significantly influenced drying time and energy requirement. Minimum and maximum energy requirement for drying of rosehips were determined as 6.69 kWh/kg for 70°C at 0.5 m/s, and 42.46 kWh/kg for 50°C, 1.5 m/s. In order to reduce drying energy consumption, it is recommended that the drying air velocity must not be more than 0.5 m/s and drying air temperature should be 70°C. In addition, the influence of drying air temperature and air velocity on the color of dried rosehip has been studied. Hunter L, a, b values were used to evaluate changes in the total color difference (ΔE) on dried rosehips. 70°C drying air temperature and 1 m/s air velocity were found to yield better quality product.     

Physical and chemical properties of powder produced from spray drying of inulin component extracted from Jerusalem artichoke tuber powder

In this study, inulin was extracted from Jerusalem artichoke tuber (JAT) powder and then concentrated before spray drying. The aims of this study were to (1) determine the drying condition that provided high powder yield together with superior qualities of JAT inulin powder and (2) investigate the chemical and physical properties of inulin powder. The inulin extracts at different concentrations of 10, 20, and 30 °Brix were spray-dried and then compared. The spray drying experiments were conducted at the inlet/outlet air temperatures of 150/90, 170/90, and 190/90?°C for the chosen concentration of inulin extract. It appeared that spray drying of the 30 °Brix extract at the inlet/outlet drying air temperatures of 190/90?°C resulted in the highest value of powder recovery, bulk density, water solubility and the lowest moisture content and hygroscopicity in comparison with its counterparts. SEM micrographs showed that the powder produced by this condition was more stable and less sticky than others. The sugars, total fructo-oligosaccharides (1-kestose, nystose, and 1^F-β-fructofuranosyl nystose) and inulin-type fructans contents of powder were 12.88, 11.12, and 64.36?g/100?g of powder, respectively. The moisture sorption data and models developed in this work could be used for determining the suitable condition of surrounding air for inulin powder storage.     

Development of a catalytically assisted combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. This combustor is composed of a burner section and a premixed combustion section behind the burner section. The burner system consists of six catalytic combustor segments and six premixing nozzles, which are arranged alternately and in parallel. Fuel flow rate for the catalysts and the premixing nozzles are controlled independently. The catalytic combustion temperature is maintained under 1000°C, additional premixed gas is injected from the premixing nozzles into the catalytic combustion gas, and lean premixed combustion at 1300°C is carried out in the premixed combustion section. This system was designed to avoid catalytic deactivation at high temperature and thermal or mechanical shock fracture of the honeycomb monolith. In order to maintain the catalyst temperature under 1000°C, the combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected for the combustor test. A combustor for a 20 MW class multi-can type gas turbine was designed and tested under high pressure conditions using LNG fuel. Measurements of NO_x, CO and unburned hydrocarbon were made and other measurements were made to evaluate combustor performance under various combustion temperatures and pressures. As a result of the tests, it was proved that NO_x emission was lower than 10 ppm converted at 16% O₂, combustion efficiency was almost 100% at 1300°C of combustor outlet temperature and 13.5 ata of combustor inlet pressure.     

Test results of a catalytic combustor for a gas turbine

A catalytically assisted low NO_x combustor has been developed which has the advantage of catalyst durability. Combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected. A combustor for multi-can type gas turbine of 10 MW class was designed and tested at high-pressure conditions using liquefied natural gas (LNG) fuel. This combustor is composed of a burner system and a premixed combustion zone in a ceramic type liner. The burner system consists of catalytic combustor segments and premixing nozzles. Catalyst bed temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to catalytic combustion gas and lean premixed combustion is carried out in the premixed combustion zone. As a result of the combustion tests, NO_x emission was lower than 5 ppm converted at 16% O₂ at a combustor outlet temperature of 1350°C and a combustor inlet pressure of 1.33 MPa.     

Spray Drying of Chicken Meat Protein Hydrolysate: Influence of Process Conditions on Powder Property and Dryer Performance

The influence of operational conditions of a spray dryer on powder properties and equipment performance during spray drying of chicken meat hydrolysate was evaluated by a central composite rotatable design. The independent variables were inlet air temperature (120 to 200°C) and feed flow (0.1 to 0.38 kg/h). Spray dryer performance was assessed through estimation of product recovery, outlet air temperature, thermal efficiency, and energy on the dryer, obtained by mass and heat balance in the dryer system. Powder property was characterized in respect to antioxidant activity. The stable free radical diphenylpicrylhydrazyl (DPPH) was used to estimate the antioxidant activity of protein hydrolysate powder. This response varied from 38.7 to 59.4% and was only affected by inlet air temperature. Moreover, the results demonstrate a significant effect of the processing conditions on dryer performance. The increase of feed flow results in higher thermal efficiency and lower energy on dryer. Higher product recovery values were obtained at lower inlet air temperature and feed flow.     

Densification of nanocrystalline MgO ceramics by hot-pressing

Densification of pure nanocrystalline MgO powder with 10 nm particle size by hot-pressing was investigated in the temperature range 700–800 °C, applied pressure range 100–200 MPa, and for durations of up to 240 min. It was shown that significant densification under the pressure begins above 440 °C. Densities higher than 99.5% with grain size of 73 nm were achieved at 790 °C and 150 MPa for a 30 min duration. Remarkable densification from 90 to 99.5% was observed by temperature change from 700 to 790 °C, for which the grain size was doubled only. The final grain size decreased with increasing the applied pressure. Higher shrinkage rates and cumulative shrinkages were recorded by the application of pressure at 550 °C rather than from room temperature. The temperature at which the pressure was applied is crucial in determining the maximum shrinkage rate in the nanocrystalline compacts. This effect was related to the morphological changes of the particles caused by plastic deformation at lower temperatures. Analysis of the densification rate and its comparison to the literature data was in agreement with Coble creep, where self-diffusion of Mg²⁺ cations along the grain boundaries acts as a main densification mechanism.     

Effects of initial cell concentration,growth phase,and process parameters on the viability of Lactobacillus rhamnosus GG after spray drying

Abstract

During spray drying, probiotics encounter several stresses which can reduce their viability. To obtain powder with a sufficient amount of viable probiotics, we evaluated the effects of different process parameters, such as initial cell concentration and the bacterial growth phase, on the viability of the model probiotic Lactobacillus rhamnosus GG. Increasing the initial biomass did not positively impact bacterial viability after spray drying. For growth, we found that stationary grown bacterial cells were more resistant to the spray-drying process than mid-log grown cells, probably owing to an initiated stress response. Furthermore, a full factorial 3³ design was used to assess the influence of three different conditions of inlet temperature, feed rate, and atomizing air flow on the outlet temperature and bacterial viability after spray drying. As expected, inlet temperature had the largest influence on both outlet temperature and log-reduction in bacterial viability. An interaction effect was also observed between feed rate and inlet temperature. Considering the viability of L. rhamnosus GG, the optimal outlet temperature ranged between 50 and 60?°C for obtaining powders with the lowest log-reductions in viability.     

Spray Drying of Raisin Juice Concentrate

Raisin juice concentrate is a natural sweetener in syrup or paste form and it is produced from second-grade dry raisins by leaching them with water. Dried raisin juice, although is easier to handle and has more potential applications than the syrup, is not available in the market. In the present study, raisin juice powder was produced with a lab-scale spray dryer. The problem of stickiness in the drying chamber was overcome through the use of 21 DE, 12 DE, and 6 DE maltodextrins as drying aid agents. For each type of maltodextrin, the dryer operating conditions and the minimum concentration of maltodextrin in the feed, necessary for successful powder production, were determined. The maximum ratio of (raisin juice solids)/(maltodextrin solids) achieved was 67/33 and was made possible with the use of 6 DE maltodextrin. The inlet and outlet drying air temperatures were 110 and 77°C respectively, while the feed contained 40% w/w total solids. The physical and sensory properties of all powders produced were determined and found to be satisfactory, the only exception being their high hygroscopicity.     

LEAFLASH SPRAY DRYER: INVESTIGATION OF THE ATOMIZATION PROCESS

The atomization process of the LEAFLASH spray dryer has been investigated by laser diffractometry and video imaging. The LEAFLASH atomizer is a particular pneumatic nozzle where the pressurized gas is the hot drying air. The drying and the atomization processes are interrelated in the spray dryer. Consequently the mixing of the liquid droplets and the drying medium is very efficient, permitting to work with short drying duration and reduced chamber volume. The mean diameter and the drop size distribution are measured at the outlet of the nozzle by laser diffraction. We studied the coupling effects of the air temperature (150 to 300° C) and pressure (1.20 to 1.50 bars abs) and of the dry matter content of the liquid feed (aqueous maltodextrin solution, 20 to 55% w/ w) on the droplets/ size distribution and on the general pattern of the spray. Analyses of video images of the generated spray give the general pattern of the spray and an estimation of the liquid velocity     

DRYING CHARACTERISTICS OF THE HAZELNUT

Equilibrium moisture content isotherms for Spanish hazelnut (Corylus avellana L.) at different temperatures (30°C-80°C) were determined using static gravimetric method. Thin layer drying experiments were done with forced air circulation and were conducted with different operating conditions to determine the drying characteristics of hazelnuts. The effect of air temperature (30°C-70°C), air velocity (0.5 m/s - 2 m/s) and drying bed loading density (50 kg/m² - 150 kg/m²) on drying of unshelled and shelled hazelnuts was studied. Six mathematical models were used to fit the experimental equilibrium moisture content data, from which the G.A.B. model was found to give the best fit. Diffusion coefficients were determined by fitting experimental thin-layer drying curves to the Fick's diffusion model. Variation of the effective diffusion coefficient with temperature was of the Arrhenius type. The Page equation was found to describe adequately the thin layer drying of hazelnut. Page equation drying parameters k and n were correlated with air temperature and relative humidity.