- Supply fan
- Air filters
- Air heater
- Air disperser
- Feed tank(s)
- Feed pump/supply pump
- Concentrate heater
- Filter
- Homogenizer/high pressure pump
- Feed line
- Rotary atomizer
- Pressure nozzle atomizer
- Two-fluid nozzle atomizer
- Cyclone
- Bag filter
- Wet scrubber
- Combinations of the above
- Pneumatic transport and cooling
- Fluid bed after dryer/cooler
- Lecithin treatment System
- Powder sieve

Drying chamber
The shape of the drying chamber, the location of the air disperser, atomizing device, exhaust air outlet, powder discharge and after treatment system determine the air flow pattern, product flow, product structure and quality. Various drying chamber types are applied for drying milk and have the following characteristics (Fig. 4.2.).
A) Chamber shape: |
a) wide body b) tall form c) horizontal box type |
B) Product flow: |
a) leaving the drying chamber with the exhaust air b) partially separated from the exhaust air in drying chamber |
C) Product discharge: |
a) by gravity (conical bottom) b) mechanically (flat bottom) |
D) Air flow pattern: |
a) rotary downward b) straight downward c) straight horizontal |
E) Air/spray mixing: |
a) concurrent b) counter-current |
F) Powder after-treatment: |
a) none b) pneumatic transport system c) external fluid bed d) integrated fluid bed e) integrated belt |

Hot air supply system
- Air Supply Fan
- Air Filters
- Air Heater
- Air Distribution.
Air supply fan
Air filters
- The air should be pre-filtered and supplied by a separate fan to the fan/filter/heater room. This room must be under pressure to avoid unfiltered air to enter.
- Filtration degree and filter position depend on the final temperature of the process air as follows:
Dairy-like products, equal to or better than 3A: | Test method: |
---|---|
Pre-filtration EU4 (or G4) Main air filtration EU7 (or F7 Secondary air filtration EU7 (or F7) |
35% Dust-spot efficiency 90% Dust-spot efficiency 90% Dust-spot efficiency |
Baby food products, equal to or better than IDF: | |
Pre-filtration EU6 (or F6) Main air filtration EU7 (or F7) Secondary air filtration EU9 (or F9) |
70% Dust-spot efficiency 90% Dust-spot efficiency >95% Dust-spot efficiency |
Air heater
The drying air can be heated in different ways:
- Indirect: Steam / Oil / Gas / Hot oil
- Direct: Gas / Electricity
Indirect: Gas / Electricity

Direct heater

The oxygen for the combustion originates from the atmospheric air with 21% O2 and 79% N2. All combustion yields small quantities of oxides of nitrogen as a result of the reaction of nitrogen and oxygen at elevated temperatures. Subsequent nitrogen oxide NO and nitrogen dioxide NO2 formation occurs and is referred to as the sum (NOx) of the two. It should be noted that high combustion temperatures, high heat transfer rates, high excess air, and low residence time in the combustion chamber are all factors increasing the formation of NOx.
For comparison the following approximate NOx concentration prevails:
Cigarette smoke: Exhaust gas from a car: Heavy traffic intersection: Natural gas boiler stack: WHO food limits for infants: Spray drying chamber: Normal fresh milk: Normal water supply: |
4000 ppm 2000 ppm 900 ppm 75 ppm 45 ppm 2-5 ppm <1 0.1 |
The level of NOx in the process air after the direct fired natural gas air heater will depend on many variable factors; however, with a well-adjusted air heater it should be limited to the above. Only about 2% of the NOx formed will be absorbed in the milk powder.
The level of NOx in milk powder depends not only on the method used for heating the process air, but also on the type of food used for the cows, as well as on the type of fertilizer and soil used for producing the food.
The NOx level in milk powder is:
- Indirect heating: Traces - 2 ppm
- Direct heating: 1 - 3.5 ppm
The level of nitrates (NO3) is in the order of 5-10 times the level of nitrites (NO2).
Electric air heaters are common on laboratory and pilot plant spray dryers. The heater has low investment costs, but is expensive in operation and therefore not used in industrial size plants.
Air dispersers
- Air disperser creating rotary air flow see Fig 4.5 a). and used in vertical wide body chambers. This type of air disperser operates usually with a rotary atomizer but is also suitable for pressure nozzles.

- Air disperser creating straight air flow see Fig 4.5. b) and used exclusively with pressure nozzles for vertical downward air flow (for instance in the tall form dryer, multi stage dryer and the integrated filter dryer). Depending on the type of dryer one chamber can accommodate either just one or several air dispersers of this type (arranged symmetrically in the ceiling). The common goal is to have an air distribution and nozzle assembly that minimizes powder deposits in the drying chamber, and that the nozzles are interchangeable during the production to allow for continuous operation for weeks without stop. To secure a straight downward air flow, this type of air disperser is typically equipped with a number of perforated plates through which the long nozzle lances protrude. This results in a high pressure drop of the drying air (high energy consumption) and a difficult nozzle adjustment to obtain an optional agglomeration.
- Today a new type of air disperser has therefore been developed. See Fig. 4.6. It operates still with a straight downward airflow but without perforated plates i.e. the pressure loss is low. It is even possible to obtain a rotation of the drying air to utilize the drying air best possible. The nozzle lances are short and operator friendly, and it is easy to adjust the nozzle position - also during operation - to obtain the degree and type of agglomeration as wanted.

Feed supply system
Feed tank

Feed pump
Concentrate heater

Filter
Homogenizer/High-pressure pump

Feed line
Atomizing device
Droplet size | Number of droplets (x 106 ) | Total surface area m2 |
---|---|---|
1000 | 1.9 | 6 |
500 | 15.3 | 12 |
100 | 1909.8 | 60 |
50 | 15279.5 | 120 |
10 | 1909859.0 | 600 |
5 | 15278874.5 | 1200 |
Rotary wheel atomizer


Factor | Influence expressed in the power range of |
---|---|
Wheel speed | - 0.6 to - 0.8 |
Wheel diameter | - 0.2 (to - 0.85) |
Peripheral speed | - 0.54 to - 0.83 |
Feed rate | 0.17 to 0.24 |
Vane height | - 0.10 to - 0.12 |
Vane number | - 0.10 to - 0.12 |
Feed viscosity | 0. 10 to 0.20 |
Feed density | - 0.5 |
Feed surface tension | 0.1 |



Pressure nozzle atomizer

- Pressure nozzle with grooved core insert,
- Pressure nozzle with swirl chamber.

Two-fluid nozzle atomizer

Powder recovery system
- Cyclone separator
- Bag filter
- Wet scrubber
- Combinations of the above.
Cyclone separator



Bag filter

- The internal bag CIP cleans the bag from the inside towards the dirty side (outside). CIP liquid running on the inside of the bags is forced out through the filter material by the compressed air pulse by the reversed jet nozzle. Powder that has penetrated into the bag material is thus forced out towards the dirty side.
- The clean air plenum CIP cleans the clean air plenum of the bag filter above the whole plate. No recirculation of CIP liquid in this area.
- The hole plate CIP cleans the bottom side of the hole plate and the snap ring area of the bag using a specially designed nozzle. This nozzle is positioned on the bottom part of the hole plate between the bags, and it also cleans the outside of the filter bags. The nozzle has a dual purpose as well, as it during the drying process is purged with warm air to keep the hole plate free of deposits. Discolouring/denaturation are thereby minimized. The CIP liquid is recirculated.
- The shell CIP is performed by means of standard retractable CIP nozzles. The CIP water is recirculated.
- Low pressure loss across the bag filter and thus the entire exhaust system i.e. reduced energy consumption and noise emission
- Designed for optimum air-to-cloth ratio and powder load (due to one to four bag(s) being blown at the time)
- Better utilization of raw materials due to no second grade products
- Design with 4 or 6m bags to suit specific building requirements.
Wet scrubber

Combinations
Cyclone | Cyclone + Bag Filter | Cyclone + Wet Scrubber | SANICIP™ | |
---|---|---|---|---|
Emission | 20-400 mg/Nm3 | 5-20 mg/Nm3 | max. 20 mg/Nm3 | 5-20 mg/Nm3 |
Pressure loss Exhaust system (incl. ducts etc.) | 280 mm WG | 340 mm WG | 340 mm WG170 | mm WG |
Auxiliaries | none | compressed air | liquid circulating system | compressed air |
Cleaning | suitable for CIP | difficult | suitable for CI | suitable for CI |
Hygroscopic products | insensitive | sensitive | insensitive | insensitive*) |
Use of separated product | first grade | first and second grade | not recommended | first grade |
Maintenance | minimal | service of compressed air system and change of bags | minimal | service of compressed air system and change of bags |
Sanitary conditions | good | relatively good | less good | good |
Fines return system
- into the atomizing zone to form agglomerates,
- into the rear section of a vibrating fluid bed to produce non-agglomerated powders,
- into the end of vibrating fluid bed when emptying the system at the end of the production run.

For wheel atomizer

For pressure nozzles


Powder after-treatment system
Pneumatic conveying system
Fluid bed system




Lecithin treatment system

Powder sieve
Final product conveying, storage and bagging-off system

Instrumentation and automation


Índice
-
1.Introduction
-
2.Evaporation
- 2.1. Basic principles
- 2.2. Main components of the evaporator
- 2.2.1. Heat exchanger for preheating
- 2.2.1.1. Spiral-tube preheaters
- 2.2.1.2. Straight-tube preheaters
- 2.2.1.3. Preheaters to prevent growth of spore forming bacteria
- 2.2.1.3.1. Direct contact regenerative preheaters
- 2.2.1.3.2. Duplex preheating system
- 2.2.1.3.3. Preheating by direct steam injection
- 2.2.1.4. Other means to solve presence of spore forming bacteria
- 2.2.1.4.1. Mid-run cleaning
- 2.2.1.4.2. UHT treatment
- 2.2.2. Pasteurizing system including holding
- 2.2.2.1. Indirect pasteurization
- 2.2.2.2. Direct pasteurization
- 2.2.2.3. Holding tubes
- 2.2.3. Product distribution system
- 2.2.3.1. Dynamic distribution system
- 2.2.3.2. Static distribution system
- 2.2.4. Calandria(s) with boiling tubes
- 2.2.5. Separator
- 2.2.5.1. Separators with tangential vapour inlet
- 2.2.5.2. Wrap-around separator
- 2.2.6. Vapour recompression systems
- 2.2.6.1. Thermal Vapour Recompression – TVR
- 2.2.6.2. Mechanical Vapour Recompression - MVR
- 2.2.7. Condensation equipment
- 2.2.7.1. Mixing condenser
- 2.2.7.2. Surface condenser
- 2.2.8. Vacuum equipment
- 2.2.8.1. Vacuum pump
- 2.2.8.2. Steam jet vacuum unit
- 2.2.9. Flash coolers
- 2.2.10. Sealing water equipment
- 2.2.11. Cooling towers
- 2.3. Evaporator design parameters
- 2.3.1. Determination of heating surface
- 2.3.2. Heat transfer coefficient
- 2.3.3. Coverage coefficient
- 2.3.4. Boiling temperature
- 2.4. Evaporation parameters and its influrence on powder properties
- 2.4.1. Effect of pasteurization
- 2.4.1.1. Bacteriological requirements
- 2.4.1.2. Functional properties of dried products
- 2.4.1.2.1. Heat classified skim milk powders
- 2.4.1.2.2. High-Heat Heat-Stable milk powders
- 2.4.1.2.3. Keeping quality of whole milk powders
- 2.4.1.2.4. Coffee stability of whole milk powders
- 2.4.2. Concentrate properties
-
3.Fundamentals of spray drying
- 3.1. Principle and terms
- 3.1.1. Drying air characteristics
- 3.1.2. Terms and definitions
- 3.1.3. Psychrometric chart
- 3.2. Drying of milk droplets
- 3.2.1. Particle size distribution
- 3.2.2. Mean particle size
- 3.2.3. Droplet temperature and rate of drying
- 3.2.4. Particle volume and incorporation of air
- 3.3. Single-stage drying
- 3.4. Two-stage drying
- 3.5. Expansion of air bubbles during drying
- 3.6. Extended Two-stage drying
- 3.7. Fluid bed drying
-
4.Components of a spray drying installation
- 4.1. Drying chamber
- 4.2. Hot air supply system
- 4.2.1. Air supply fan
- 4.2.2. Air filters
- 4.2.3. Air heater
- 4.2.3.1. Indirect: Gas / Electricity
- 4.2.3.2. Direct heater
- 4.2.4. Air dispersers
- 4.3. Feed supply system
- 4.3.1. Feed tank
- 4.3.2. Feed pump
- 4.4. Concentrate heater
- 4.4.1. Filter
- 4.4.2. Homogenizer/High-pressure pump
- 4.4.3. Feed line
- 4.5. Atomizing device
- 4.5.1. Rotary wheel atomizer
- 4.5.2. Pressure nozzle atomizer
- 4.5.3. Two-fluid nozzle atomizer
- 4.6. Powder recovery system
- 4.6.1. Cyclone separator
- 4.6.2. Bag filter
- 4.6.3. Wet scrubber
- 4.6.4. Combinations
- 4.7. Fines return system
- 4.7.1. For wheel atomizer
- 4.7.2. For pressure nozzles
- 4.8. Powder after-treatment system
- 4.8.1. Pneumatic conveying system
- 4.8.2. Fluid bed system
- 4.8.3. Lecithin treatment system
- 4.8.4. Powder sieve
- 4.9. Final product conveying, storage and bagging-off system
- 4.10. Instrumentation and automation
-
5.Types of spray drying installations
- 5.1. Single stage systems
- 5.1.1. Spray dryers without any after-treatment system
- 5.1.2. Spray dryers with pneumatic conveying system
- 5.1.3. Spray dryers with cooling bed system
- 5.2. Two stage drying systems
- 5.2.1. Spray dryers with fluid bed after-drying systems
- 5.2.2. TALL FORM DRYER™
- 5.2.3. Spray dryers with Integrated Fluid Bed
- 5.3. Three stage drying systems
- 5.3.1. COMPACT DRYER™ type CDI (GEA Niro)
- 5.3.2. Multi Stage Dryer MSD™ type
- 5.3.3. Spray drying plant with Integrated Filters and Fluid Beds - IFD™
- 5.3.4. Multi Stage Dryer MSD™-PF
- 5.3.5. FILTERMAT™ (FMD) integrated belt dryer
- 5.4. Spray dryer with after-crystallization belt
- 5.5. TIXOTHERM™
- 5.6. Choosing a spray drying installation
- 6.Technical calculations
-
7.Principles of industrial production
- 7.1. Commissioning of a new plant
- 7.2. Causes for trouble-shooting
- 7.3. Production documentation
- 7.3.1. Production log sheets
- 7.3.2. General maintenance log book
- 7.3.3. Product quality specification
- 7.3.4. Operational parameter specification
- 7.4. Product quality control
- 7.4.1. Process quality control
- 7.4.2. Final quality control
-
8.Dried milk products
- 8.1. Regular milk powders
- 8.1.1. Regular skim milk powder
- 8.1.2. Regular whole milk powder
- 8.1.3. Whole milk powder with high free fat content
- 8.1.4. Butter milk powder
- 8.1.4.1. Sweet butter milk powder
- 8.1.4.2. Acid butter milk powder
- 8.1.5. Fat filled milk powder
- 8.2. Agglomerated milk powders
- 8.2.1. Agglomerated skim milk powder
- 8.2.2. Agglomerated whole milk powder
- 8.2.3. Instant whole milk powder
- 8.2.4. Agglomerated fat filled milk powder
- 8.2.5. Instant fat filled milk powder
- 8.3. Whey and whey related products
- 8.3.1. Ordinary sweet whey powder
- 8.3.2. Ordinary acid whey powder
- 8.3.3. Non-caking sweet whey powder
- 8.3.4. Non-caking acid whey powder
- 8.3.5. Fat filled whey powder
- 8.3.6. Hydrolysed whey powder
- 8.3.7. Whey protein powder
- 8.3.8. Permeate powders
- 8.3.9. Mother liquor
- 8.4. Other Dried Milk Products
- 8.5. Baby food
- 8.6. Caseinate powder
- 8.6.1. Coffee whitener
- 8.6.2. Cocoa-milk-sugar powder
- 8.6.3. Cheese powder
- 8.6.4. Butter powder
-
9.The composition and properties of milk
- 9.1. Raw milk quality
- 9.2. Milk composition
- 9.3. Components of milk solids
- 9.3.1. Milk proteins
- 9.3.2. Milk fat
- 9.3.3. Milk sugar
- 9.3.4. Minerals of milk
- 9.4. Physical properties of milk
- 9.4.1. Viscosity
- 9.4.2. Density
- 9.4.3. Boiling point
- 9.4.4. Acidity
- 9.4.5. Redox potential
- 9.4.6. Crystallization of lactose
- 9.4.7. Water activity
- 9.4.8. Stickiness and glass transition
-
10.Achieving product properties
- 10.1. Moisture content
- 10.2. Insolubility index
- 10.3. Bulk density, particle density, occluded air
- 10.4. Agglomeration
- 10.5. Flowability
- 10.6. Free fat content
- 10.7. Instant properties
- 10.7.1. Wettability
- 10.7.2. Dispersibility
- 10.7.3. Sludge
- 10.7.4. Heat stability
- 10.7.5. Slowly dispersible particles
- 10.7.6. Hot water test and coffee test
- 10.7.7. White Flecks Number (WFN)
- 10.8. Hygroscopicity, sticking and caking properties
- 10.9. Whey Protein Nitrogen Index (WPNI)
- 10.10. Shelf life
-
11.Analytical methods
- 11.1. Moisture content
- 11.1.1. Standard oven drying method (IDF Standard No.26-1964 [32])
- 11.1.2. Free moisture
- 11.1.3. Total moisture
- 11.1.4. Water of crystallization
- 11.2. Insolubility index
- 11.3. Bulk density
- 11.4. Particle density
- 11.5. Scorched particles
- 11.6. Wettability
- 11.7. Dispersibility
- 11.8. Other methods for determination of instant properties
- 11.8.1. Sludge
- 11.8.2. Slowly dispersible particles
- 11.8.3. Hot water sediment
- 11.8.4. Coffee test
- 11.8.5. White flecks number
- 11.9. Total fat content
- 11.10. Free fat content
- 11.11. Particle size distribution
- 11.12. Mechanical stability
- 11.13. Hygroscopicity
- 11.14. Degree of caking
- 11.15. Total lactose and α-lactose content
- 11.16. Titratable acidity
- 11.17. Whey Protein Nitrogen Index (WPNI)
- 11.18. Flowability (GEA Niro [31])
- 11.19. Lecithin content
- 11.20. Analytical methods for milk concentrates
- 11.20.1. Total solids
- 11.20.2. Insolubility index
- 11.20.3. Viscosity
- 11.20.4. Degree of crystallization
- 12.Troubleshooting operations
-
References