*3.4.1.2 Two-stage horizontal spray dryer*

A horizontal spray dryer has been suggested as an alternative to the conventional vertical types [57, 58] for pharmaceutical materials and heat-sensitive food [59, 60]. The low temperatures of drying permit flavor reservation, controlled porosity and density, high solubility, as well as fine goodness agglomerated products. Essential energy provisions relative to the conventional vertical spray dryer with a lower electrical loading for a specific capacity.

A suggested design is described in **Figure 15**. The high-pressure pump is used for feed pushing to the spray nozzles. These nozzles are organized in several configurations. Then, the spray travels horizontally from the nozzles, and due to gravity, it goes down. After that, transporting of the dried powders using a conveying strap in the bottom and carried to bag filters or cyclones. A model for the horizontal spray dryer (6.0 m 3.0 m 3.0 m) has been presented by Cakaloz et al. [61].

In the single-stage horizontal spray dryer process (**Figure 16**), it has been shown that the dwell period might be overly short for allowing the droplets for drying completely. Therefore, to overcome this constraint, a new two-stage, two-dimensional horizontal spray dryer idea is suggested by Mujumdar [58] and shown in **Figure 15**,

#### **Figure 15.**

*Proposed layout of a two-stage horizontal spray dryer.*

#### **Figure 16.**

*Schematic layout of the horizontal spray dryer.*

which is prepared for permitting long drying periods. This is necessary for big droplet sizes and heat-sensitive products. The variance between single and two-stage horizontal spray driers is that in the single spray drier, there is a fluid-bed dryer, which is installed at the horizontal chamber bottom. Whereas, the two-stage horizontal spray drier is not commercialized yet. The CFD process could be utilized to emulate the horizontal spray dryer, which should be connected to a fluid-bed drying system. The droplet's surface moisture is taken away rapidly from the chamber of spraying. While the inner water occupies longer, which could be extracted in a thin layer, out of a deliberation dryer in the bottom of the room.

## *3.4.1.3 Low-humidity spray drying*

On occasion, it has to choose freeze dryers instead of spray dryers, particularly for pharmaceuticals and biochemicals drying. This is because spray drying utilizes hightemperature gas like the medium of drying and the sediments on the wall cannot be averted in feasible spray dryers. The products are subject to degradation by

*Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*

**Figure 17.**

*Schematic layout of the low-dew-point spray dryer.*

overheating [48]. Yet, the freeze dryer has high operating, and capital costs, as well as high energy consumption, compared with the spray dryer [62, 63].

To decrease the active compound degradation in the dried powders, a novel kind of spray dryer was proposed, such as low dew point (LDP) spray dryer. This type utilizes air at a nearby surrounding temperature of 80°C and quite minimum humidity (**Figure 17**). It comprises four units: the preprocessing system of drying air including heating and dehumidification; the preparation system of feed; the drying system and feed atomization including drying chamber, air disperser, and atomizer, etc., in addition to the system of product collection.

#### *3.4.1.4 Spray freeze drying*

The freeze drying (FD) is a significant drying machinery for pharmaceuticals, foods, and biochemicals, which could preserve the biological activity, aroma or flavor, etc. Freeze drying is a drying method, in which the solvent in the material is solidified at low temperatures, then sublimates directly from the solid into the vapor state under vacuum. The freeze-drying process of an aqueous solution contains three phases: product freezing, ice sublimation, and removal of solvent vapor. Nevertheless, compared with spray drying, the freeze drying is an order-of-magnitude costlier drying method because of its need for vacuum, refrigeration, and long operating times [64]. In a recent combination of both drying processes, called spray freeze drying (SFD), this process was carried out as a batch method as follows: The liquid nitrogen is atomized in a cryogenic medium to spray the droplets to freeze. Frozen droplets are scuttled in a cryogenic medium and processed out and dried in the freeze-dryer under a vacuum. A model flow slab is illustrated in **Figure 18**. This method is conducted in batches instead of continuously, because of the required long freeze-drying time. In addition, it is appropriate for high-significant products with low tonnages [65].

A new method called a combined atmospheric spray and fluidized-bed freeze drying (ASFBFD) process was examined. The planned schematic flow graph is described in **Figure 19**. It mainly comprises internal fluidized bed, drying or freezing room, liquid nitrogen cooler, internal bag filter, fan, nozzles, valves, pipes, pump, etc. [65].

The process is briefly explained as follows: The feed is transported into the nozzle from the top through a pump, where it is atomized using a nozzle. The fine spray is

**Figure 18.** *A schematic flowchart of the conventional spray freeze drying.*

**Figure 19.** *Batch-type atmospheric pressure combined with spray and fluidized-bed dryer.*

connected with freeze nitrogen or air immediately. Upon the material of feed, the drying medium is frozen to about 90°C using liquid nitrogen and inflated by a fan within the fluidized-bed cribriform tray. The fluidized bed is placed at the bottom of the chamber. As the temperature of the cool air is lower enough for spray freezing, the frozen atoms conserve their main conditions and go to the bottom or to the fluidized bed through gravity. Nearly a few frozen atoms might be restricted by air or nitrogen; nonetheless, they are detached from the air using the interior bag filter. Throughout the phase, the spray freezing drying is investigated continuously until the exhaustion of feed in the batch procedure. After this phase is completed, suitable drying terms are chosen, such as liquid nitrogen, which is regulated to meet freeze-drying terms. Drying actual operation and its time terms should be specified. Many investigators have already investigated many studies on atmospheric freeze drying [66–72]. These reviews showed that the atmospheric spray and fluidized-bed freeze drying grouping is a viable new procedure that needs additional R&D. Lastly, a summary of the comparison between the four drying processes, such as SD, FD, SFD, and ASFBFD, is assumed in **Table 1**.

#### *3.4.1.5 Encapsulation*

Spray drying and fluid-bed drying lead to another common food application of these technologies, that is, microencapsulation. It is defined as a process by which one material or more is entrapped within alternative material [73]. This method is generally used to prevent the core material from degradation and to control releasing or separate reactive constituents in a formulation. Because the spray dryer is generally fast, available, economical and produces good-quality products [74], it enhances the

*Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*


#### **Table 1.**

*Drying method properties [65].*

most public means of encapsulation process. This procedure is simple and comparable with the one-phase spray drying technique. The coated substance is named active or core substance, and the coating substance is entitled a shell, while the wall substance is called a carrier or encapsulant [75]. The encapsulated active substance is scattered in the hydrocolloid transporter, such as maltodextrin, dextrin, Arabic gum, gelatin, and modified starch. Subsequently, the emulsifier is supplemented, and the mix should be homogenized to compose an oil-in-water emulsion, then it's consumed by the atomizer for the spray dry. In the drying room, the aqueous stage dries, and the active substance is captured as atoms through the protein film or hydrocolloid, discharging of the active substance from capsules under specific terms. The temperature, moisture, and pressure are the main controlling factors of its release [76].

#### *3.4.2 Energy efficiency enhancement*

Spray drying is an energy-intensive procedure. With the increased energy costs with overall production stage changes, spray dryer consumers have to look for techniques to enhance the spray dryer system's thermal efficiency. For typical single-stage drying, the best method to control energy practice is to raise the inlet temperature and keep the outlet temperature low, as well as take full benefit of the energy introduced. Nevertheless, the weakness of this procedure is the potential product degradation in food spray drying [52, 77, 78].

#### **3.5 Freeze drying**

Freeze drying is used for high-quality foodstuffs stabilization, certain biological materials, and pharmaceuticals such as proteins, vaccines, bacteria, and mammal cells. These substances are freeze-dried; thus, the quality of the dried product is retained [63, 79]. Freeze drying is a process in which the water or another solvent is sublimated by the direct transition of water from solid (ice) to vapor, thus omitting the liquid state, and then desorbing water from the "dry" layer [80–84].

As a rule, freeze drying produces the highest-quality food product obtainable by any drying method. This is due to the fact that freezing water in the material prior to lyophilization inhibits chemical and biochemical such as non-enzymatic browning, protein denaturation,, microbiological, and enzymatic reactions processes. Consequently, the content of various nutrients, smell, and taste do not change. Raw materials comprise water, ranging from 80% to 95%. The water is removed by sublimation resulting in extremely porous structure creation of the freeze-dried products, and the finalized rehydration or lyophilizing happens immediately when water is added to the substance at a later time [85, 86]. However, the water in foodstuffs could be free or bound to the solution using different powers. The free water is freezed, but the bound does not. In the freeze-drying method, the iced and some bound water should be detached. Consequently, lyophilization is an extremely complex and multistep procedure that comprises (a) freezing under atmospheric pressure phase, (b) main drying; appropriate freeze drying; ice sublimation, at decreased pressure. For example, iced water is managed, then sublimation at 0°C and absolute pressure of 4.58 mmHg could happen. Nevertheless, subsequently the water usually exists in a solution or a joint state, the substance should be cooled below 0°C to preserve water in a frozen phase. So, during the main drying step, the frozen layer temperature as showed in **Figure 20** is at 10°C or lower at absolute pressures of about 2 mmHg or less. As the ice sublimes, the sublimation interface, which began at the external surface (**Figure 20**), dried material retreats and porous shell residues. The latent heat (2840 kJ/kg ice) could be operated using the dried substance and frozen layers, as illustrated in **Figure 20**. The vaporized water is conveyed within the dried substance porous sheet. Through the main drying step, in the dried layer, a large amount of nonfrozen water might be desorbed. The desorption method might affect the amount of heat that reaches the sublimation interface, and subsequently, it might affect the velocity of the sublimation front moving. The period when there are no frozen sheets is possessed to perform the end of the primary drying phase. (c) Secondary drying phase; desorption drying; drying the product to the required final humidity, this stage starts at the end of the primary drying stage, and the desorbed water vapor is transported through the pores of the material that is dried [63, 80, 87]. During the above three phases, six main physical phenomena could be distinct, which have a significant impact on the process path, the quality of the obtained substance, and

#### **Figure 20.**

*Diagram of a material on a tray during freeze drying. The variable X denotes the position of the sublimation interface (front) between the freeze-dried layer (layer I) and the frozen material (layer II).*

#### *Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*

its overall costs [88]. Those phenomena are as follows: the water is transitioned into ice, then the ice to a vapor phase, the water particles are desorpted from substance structures, the obtainment of sufficiently low pressure, the resublimation of water vapor removed from the substance on the condenser surface, and the removal of a layer of ice from the capacitor surface.

In this context, the conditions of the freeze-drying process should be selected in a way that does not melt the water. The presence of water during freeze drying may result in many changes in the composition, morphology, and physical properties of foods (e.g., shrinkage), then reducing product quality during storage [89]. The effect of freeze-drying conditions on the nutritional properties, antioxidant activities, and glass transition characteristics of different food materials can be found in the literature [90–95]. Despite the long processing time and high cost, it is preferred for extreme-quality products. Though some damages in bio compounds could be set after freeze drying, this method is preferable to maintain nutritional qualities, particularly when operated under a vacuum. Moreover, the quality parameters such as freeze-dried products' rehydration and porosity are favorable for manufacturing foods. Newly, the freeze-drying process condensation with innovative technologies or pretreatments permit overcoming some of these drying processing challenges [96].

#### *3.5.1 Microwave freeze drying*

The limitations on heat transfer amounts in conventionally managed freeze-drying operations have led to providing internal heat generation with the use of microwave energy [97, 98]. Hypothetically, the use of microwaves must result in an instant drying rate, because the transferring of heat does not need internal temperature slopes and the temperature of ice could be preserved near to the maximum allowable temperature for the frozen layer exclusive of the need for extreme surface temperatures. For example, if it is allowable to keep the iced layer at 12°C, after that it has been assessed that the drying time for an ideal process using microwaves for a hypothetical 1-in. slab would be 1.37 h [99]. It should be notable that this drying time compares very approvingly with 8.75 h needed for the heat input within the dry layer, while 13.5 h for heat input within the iced layer without the removal of dry layer, and even with relatively short time of 4 h of drying for continuous removal of dry layer. Examining the freeze drying of a 1-in.-thick slab beef, the actual drying time of slightly over was 2 h, compared with 15 h for traditionally dried slabs [100]. Despite these benefits, the microwave application has not been successful [99, 101–105]. Because of the following reasons: (A) Supplied energy in the microwave form is too expensive [101]. (B) The tendency to glow discharge, which could cause gases ionization in the room and food deleterious changes, and losses of useful energy. The tendency to glow discharge is larger in the pressure ranged from 0.1 to 5 mmHg and could be decreased by operating the freeze dryers at pressures under 50 mm. The operation at low pressures has a double drawback: (1) it is much expensive, because of the demand for condensers operating at a very low temperature and (2) At these low pressures, the drying rate is much slower. (C) The process control is very difficult. Meanwhile, water has an inherently greater dielectric loss factor than ice, any localized melting produces a rapid chain reaction, which results in runaway overheating. (D) The economical equipment suitable for a large continuous scale is not yet available. In spite of these constraints, microwave freeze drying is considered a potential development [101].

#### *3.5.2 Industrial freeze dryers*

The main types of industrial freeze dryers include the following:

### *3.5.2.1 Tray and pharmaceutical freeze dryers*

The hugest amount of industrial freeze dryers in process are of the vacuum batch style with freeze drying of the food stuff in trays. There are two main styles, depending on the type of condenser used. The first style showed the condenser plates in the same chamber and near the tray-heater assembly. The second style is representing the condenser in a separate chamber linked to the first by a wide, in over-all, butterfly valve. This latter type of the factory is permanently used in pharmacological industries, but it can also be used for freeze-drying foods. To reduce product contamination risk, especially in the pharmaceutical industries, a new freeze-dryer plant concept has been developed. The system, as illustrated in **Figure 21,** has two doors: a little one is for charging the stuff before drying, when the full door, which is opposed to the little door, is for discharging the stuff after drying. The condenser is positioned on the floor, which is under the first floor, where the drying chamber is placed. The freeze dryer shelves are lowered to the drying chamber bottom and then lifted one by one to a location in line with the filling machine. The charging of foodstuff is prepared under a laminar flow of sterilized air; the little door is unlocked only for each plate filling and then is directly closed [87].

#### **Figure 21.**

*Industrial freeze dryer design with stoppering device (Criofarma model C300-7): 1, drying chamber; 2, inspection window; 3, automatic small door opening; 4, full door; 5, hydraulic press for stoppering the bottles after drying; 6, PTFE elbows for double sterile condition inside the stoppering plug; 7, reenforcing member and cooling coils after steam sterilization; 8, isolation butterfly valve; 9, ice condenser chamber; 10, loading device; 11, discharging device; 12, unloaded shelves.*

*Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*

#### *3.5.2.2 Multi-batch freeze dryers*

The freeze-drying system in a batch factory is usually programmed and organized to minimalize the drying time and enlarge the factory production. With a single-batch factory, the load on the several systems will be very variable during the drying rotation. The product flow and handling operations will be alternating because of the batch process specifically. This means that optimum use of supplies will not be probable in a sole-cabinet batch system. To extent this weakness, an industrial freezedrying factory is built with numerous batch cabinets instructed to operate with staggered and overlying drying rotations. Each cabinet can be filled with materials from the same system, and they are assisted by the similar central system for vacuum pumping, tray heating, and condenser refrigeration. Although, the procedure is individually organized in each cabinet from a unattached control panel. This builds probably the simultaneous different foodstuffs production, which rises the operation flexibility of the factory. With only two cabinets in operation, an important part of the batch weakness may be excluded; for example, with four cabinets, an excellent leveling of loads will be accomplished. A huge amount of industrial freeze-drying factories operate today in this style as multi-cabinet batch factories [81, 99, 106].

#### *3.5.2.3 Tunnel freeze dryers*

The process in the tunnel freeze dryer (**Figure 22**) takes place in a large vacuum cabinet into which the tray-carrying trolleys are loaded at intervals through a large vacuum lock at one end of the tunnel and discharged similarly at the other end. The drying conditions are carefully controlled in a number of sections of the tunnel by temperature-pneumatic controllers [81]. The plates of vapor constriction fit closely inside the channel walls yet permitting the trolleys to passage through two locations in the tunnel main unit, and gate valves turn off the locks from the main unit. Thus, the tunnel is divided into five autonomous process zones. When trolley is not moving during the period, a tray-lifting scheme causes all trays to sit in each trolley on heaters below the top. The heaters consume flat-top surfaces and ribs under which vacuum

**Figure 22.** *Typical tunnel freeze dryer schematic diagram.*

steam passes. They are cantilevered in couples from both sides of the tunnel. Vacuum steam heating has numerous benefits, including high latent heat of condensation and temperature control operating pressure. The cooling system comprises a great aqua ammonia absorption freezer instead of a compression factory. Because of easiness with the refrigeration, load can be diverse by controlling the feed of oil to the boiler that heats the absorber.

The whole capacity of the tunnel freeze dryer can be boosted as it increases volume of business. Large business factories for cottage cheese and coffee processing have been set up in this way. The tunnel freeze dryers have the same benefits of factory capacity operation that can be attained as in multi-batch factories. On the other hand, the flexibility for simultaneous production of materials or in swapping between products is missing.

#### *3.5.2.4 Vacuum spray freeze dryers*

The vacuum spray freeze dryer system is illustrated in **Figure 23**. It has been industrialized for tea infusion, coffee extract, or milk. The product is applied by spraying from a sole jet upward or downward in a cylindrical tower of about 3.7-m diameter by about 5.5-m high [81, 107]. The solutions are solidified into little particles by evaporative freezing. In the tower, a frozen helical condenser is coiled between the internal wall and central hopper, the latter accumulating the partially dry powder as it drops freely to the tower bottommost. This is in turn associated with a tunnel where the drying technique is accomplished on a stainless-steel belt migrant among radiant heaters. The dried material passes into a hopper that feeds a vacuum padlock, allowing alternating product removal for packing. The whole system operates under a vacuum of about 67 Pa. In the initial evaporation, the diameter of frozen particles obtained by spraying into a vacuum is about 150 mm and loses about 15% moisture, and there is no sticking of these particles.

**Figure 23.** *Vacuum spray freeze dryer layout.*

*Drying Technology Evolution and Global Concerns Related to Food Security… DOI: http://dx.doi.org/10.5772/intechopen.109196*

#### *3.5.2.5 Continuous freeze dryers*

Continuous freeze dryers are used for products drying in trays and for agitating bulk material drying. When the product is handled in trays, then the most delicate treatment of the product is attained. The food material is placed in the tray. Hence, it is not exposed to scratch, and it falls in contact with surfaces only that completely meet required hygiene values. While agitating a crushed product, more efficient heat transfer to sole product particles can be realized. Thus, a significant decrease in the heating surface is achievable. Although, scratch of the product by agitation increased the production of water vapor per unit, the heating surface tends to bring little product particles with vapor stream away from the bulk bed of product and cause product loss. Any system problems for water vapor elimination to retrieve the product loss may more than counterbalance the advantage of the higher heater surface load [108]. The heat transfer to the product and the trays is by radiation, which is the easiest mode to safeguard a correct as well as consistently distributed heat transfer to the material during the practice. The radiant heat is formed by horizontal heater saucers that are gathered within temperature zones. Each tray remains for a fixed time in each temperature zone for drying time minimized [108].
