Isomaltulose

Case Study: Centrifugal Spray Drying Project for 13,500 Tons of Oligoisomaltose Annual Production (Project Reference: Luzhou Food Group’s 13,000-Ton Oligosaccharide Project)

I. Factory Overview:

Our factory is affiliated with the Changzhou Light Industry Bureau. The original factory was established in 1958. Mingxing Drying Equipment Factory was established in 1993 as a spin-off of certain workshops from the original facility. We currently have 120 permanent employees, 30,000 square meters of factory space, and production equipment assets valued at 15 million yuan. We manufacture and market eight major series and over 50 varieties of drying equipment. With extensive production experience and strong technical capabilities, we have hired more than 10 domestic experts in the drying industry who are dedicated to long-term new product development. Following the completion of two sets of LPG3000-type spray drying equipment in Fujian in 1997, our factory subsequently completed three large-scale LPG2000–3500-type spray drying units in Yangshan, Guangdong; Haihua, Shandong; and Tonghua, Jilin. Among these, three units were equipped with KRH320 high-temperature heat-exchange hot air furnaces, while the remainder utilized oil-fired hot air furnaces. To date, only two specialized factories in China have actually manufactured the LPG3500-type spray drying equipment, and our factory is one of them. In 2002, our factory won the bid for the Beihai Project, undertaking the supply of one set each of LPG2000, LPG3000, and LPG4500 units, which are now in the installation phase. Because our factory has drawn on the best practices from various sources, the first LPG3000 spray drying unit was able to operate normally within a very short period of time (see the acceptance report for details), and subsequent units have achieved successful start-up on the first attempt; therefore, we possess substantial practical experience to undertake this project.

II. Brief Overview of the Spray Drying Mechanism

During the spray drying of the feed solution, massive heat and mass transfer occur within an extremely short period of time. Concentrated feed droplets exit the atomizer at a velocity of 100–200 m/s. Most of the moisture is removed during the deceleration phase of the droplets’ motion, during which the droplets lose their initial velocity and are carried by the drying air. Small droplets evaporate 90% of their moisture within 0.1 m of the atomizer; larger droplets require a distance of approximately 1 m.

Throughout the drying process, the temperature of the droplets lies between the ambient air temperature and the wet-bulb temperature; immediately after atomization, the droplets reach a temperature slightly higher than the wet-bulb temperature. Evaporation of moisture from the droplet surface begins during the constant-rate drying phase. During this phase, the droplets remain in a fluid state, and moisture easily migrates from the interior to the surface, keeping the surface wet.

In the subsequent drying stage, when the moisture content reaches a critical value, the droplets lose their fluid properties and become wet solids; a film forms on the surface and a crust develops. Under these conditions, when the heat absorbed exceeds the momentum of water migration, steam is generated, further increasing internal pressure and causing the crust to rupture. This stage is characterized by the sudden appearance of a moisture gradient in the radial direction of the droplets. As moisture diffuses outward through the interior of the particles, the drying rate begins to decline; this stage is known as the rate-decrease stage.

Due to its ability to remove moisture in an extremely short time, spray drying has become increasingly widely used in food drying in recent years, as it preserves the active ingredients, color, aroma, and flavor of the food. A fluidized bed is installed in the lower conical section of the drying tower to reduce the discharge temperature, allowing large particles of wet material to dry within the fluidized bed and effectively maintaining low-temperature drying of the material.

For the drying of oligosaccharide products, the Danish company NIRO recommends a two-stage drying process combining a high-speed centrifugal spray dryer with a fluidized bed, a method that has already been adopted by several companies in China.

III. Customer Requirements

1. Continuous daily production of 45 tons; the material must have good atomization properties and uniform particle size; the drying chamber must be spacious to prevent material from sticking to the walls; residence time must be short to keep material temperature low; the finished product must be cooled to below 30°C.

2. Drying of multiple product types: IMO500 isomaltulose, IMO900 isomaltulose, maltodextrin, maltose powder, and vegetable fat powder.

IV. Design Basis

This proposal is based on the following specifications for IMO500 isomaltulose with a daily production capacity of 45 tons: 50% solids content, moisture content ≤3%, amorphous powder form, 80-mesh sieve pass rate ≥97%, and no visible impurities. The following design is provided accordingly.

V. Performance Calculations

1. Output G = 1,875 kg/h

2. Absolute dry material G1 = 1,818 kg/h

3. Feed liquid F = 3,637 kg/h

4. Evaporation rate W = F – G = 1,762 kg/h (calculated as 1,800 kg/h)

5. Assume the inlet and outlet temperatures of the drying tower are 200°C and 95°C (adjustable)

6. Drying air flow rate L = 35,300 kg/h

7. Drying heat requirement: 1.8 million kcal/h

VI. Process Design

1. For the drying of maltodextrin (DE 20–40) by NIRO of Denmark, when the feed temperature is 50°C, the solids content is 50%, the inlet air temperature is 200°C, the outlet air temperature is 95°C, and the final moisture content is 4%, a two-stage drying process combining high-speed centrifugal spray drying and fluidized bed drying is recommended. This proposal adopts the process recommended by NIRO.

2. Refer to the attached diagram for the process flow.

3. Process Description

A: Heating is provided by a heat-exchange type coal-fired hot-air furnace, with an adjustable temperature up to 300°C. The hot air enters the tower through the hot-air distributor at the top of the tower, where it comes into contact with the material mist sprayed by the high-speed centrifuge. The material rapidly dehydrates and moves toward the bottom of the tower with the drying airflow. Coarse material falls to the fluidized bed at the tower base for further drying, while fine material is carried by the dry gas stream into the large centrifugal fan unit. After gas-solid separation, the material is discharged via a shut-off fan into the pneumatic conveying pipeline, and the exhaust gas is discharged to the atmosphere after dust removal in the scrubbing tower. After drying in the fluidized bed at the tower base, the material is conveyed via a shut-off fan into the pneumatic conveying pipeline. The pneumatic conveying system operates under negative pressure, simultaneously conveying the material and cooling it, thereby maintaining the material temperature below 30°C. The pneumatic conveying system consists of a small cyclone fan, an exhaust fan, a material silo, a shut-off fan, and filters. After being separated by the small cyclone fan, the material falls into the silo, while the air is drawn by the exhaust fan into the main exhaust fan unit, where it undergoes further dust removal before being discharged into the atmosphere.

B: The material tends to stick to the walls. Tower wall cooling air is used to cool the inner surface of the tower; an internal cyclone is installed within the tower to extract the material; and vibrators are installed on the tower walls, cyclone, and hopper.

C: According to NIRO, the two-stage drying system (spray and fluidized bed) can increase the inlet air temperature from 200°C to 225°C and reduce the exhaust air temperature from 95°C to 80°C. The moisture content of coarse material entering the fluidized bed can be as low as 8%, while fine powder is further dried within the large cyclone along with the exhaust gas to meet standard requirements. The fluidized bed inlet air temperature is 90°C, the fluidization velocity is 0.4 m/s, the residence time is 4 minutes, and the moisture content of the discharged material meets standards. The fluidized bed perforated plates are stamped tongue-shaped plates arranged in a spiral pattern, with their rotation direction aligned with the gas flow direction within the tower. The perforation rate is 1%, and the perforation velocity is 20 m/s. This design is manufactured according to NIRO’s drawings.

D: The average temperature of the material discharged from the fluidized bed and the large cyclone into the paddle cooler system is 55°C. After cooling in the paddle cooler, the material temperature drops below 30°C.

VII. Equipment Selection

1. Hot Air Furnace: Consists of a chain grate furnace and a heat exchanger, with a heat output of 2.5 million kcal/h, a supply temperature of 300°C (adjustable), and a coal consumption of 560 kg per hour.

2. Drying Tower: Diameter φ7 m, cylindrical height 11 m, cone angle 20°, effective drying volume 450 m³. The design spray rate is 4 tons per hour. The spray distance from the material to the tower wall incorporates a substantial safety margin to ensure the material does not adhere to the walls. The drying intensity is 4, providing a significant margin relative to relevant standards and empirical data. An air-cooled inner wall system is installed within the tower; the inner wall is made of 304B material, 3 mm thick; the outer wall is made of Q235 material, 5 mm thick; and a reinforcing frame and air deflectors are installed in the middle.

3. Fluidized Bed: Bed area 6.7 m².

4. Atomizer: Uses Mingxing’s in-house MRW4000 model, with a maximum spray rate of 4,000 kg/h and a power rating of 22 kW.

5. Large Centrifugal Fan Units: φ1,200 × 4.

6. Main Induction Fan: 9-26, 110 kW

7. Internal Circulating Fan: φ3000/φ2200 mm

8. Dust Collector Fan: φ1300, airflow 45,000 m³/h.

9. Paddle-type Cooler: Cooling area 17 m², internal dimensions: 3400 × 1200 × 950 mm

10. Screw Feeder: φ219 mm

11. Cooling Air Blower: 4-72-4.5A, 7.5 kW, Airflow 9,000 m³/h, 2,000 Pa.

12. Fluidized Bed Blower: 9-19-9D-18.5 kW, Airflow 4,500 m³/h, 4,500 Pa.

13. Electrical Control: Touchscreen DCS control with manual and automatic operation modes, process display, centralized monitoring, measurement, display, and alarm functions.

14. Screw Pump: GF30-2, 7.5 kW, flow rate 7 m³.

VIII. Materials Used in Equipment Construction

1. Parts in contact with the material are manufactured from 3 mm thick stainless steel; reinforced with a carbon steel frame.

2. Welding rods are selected to match the base material; stainless steel components are welded using TIG welding.

3. The touch screen, PLC, and frequency converters for the atomizer and screw pump are imported products; all other components are domestically produced and sourced from major state-designated manufacturers.

X. Quality Assurance

1. Technical Specifications of the LPG1800 Spray Dryer

①. Inlet air temperature: 200°C; exhaust air temperature: 95°C (adjustable)

②. Furnace heat output: 2.5 million kcal/h

③. Annual production capacity: 13,500 tons (based on 300 days, 24 hours per day)

④. Water evaporation capacity: 1,800 kg/h

⑤. Product moisture content: 3%

⑥. Coal consumption per ton of product: 280 kg; electricity consumption per ton of product: 138 kWh.

⑦. Equipment rated power: 301 kW; actual power consumption: 248 kW.

⑧ Dust emissions: 114.8 mg/m³; total material recovery rate >98%; product yield ≥99%

⑨ Material particle size: 97% at 80 mesh; no visible impurities; no amorphous powder.

⑩ Solid content of slurry provided by the user: ≥50%

3. The equipment warranty period is one year. Within this period, any defects resulting from manufacturing quality will be repaired free of charge by our factory, and we will honor the “three guarantees” policy. If the user requires our personnel to resolve issues on-site, we will arrive within 48 hours. Minor issues will be repaired within 24 hours, and major issues within 48 hours.

4. Equipment acceptance shall be conducted in accordance with relevant national, ministerial, and enterprise standards; the requirements listed in the tender documents; the indicators agreed upon by both parties; and the drawings and documents mutually recognized by both parties.

XI. Equipment Spare Parts

1. Screw pumps, slurry filters, and atomizers are supplied on a one-active-one-spare basis.

2. For the atomizer, spare parts include 2 atomizing discs, 1 high-speed shaft, 4 bearings, 4 shaft sleeves, and 6 sealing rings.

3. A set of specialized tools for the atomizer will be supplied by our factory.

4. Consumables are to be purchased by the user.

5. After the warranty period expires, all products manufactured by our factory and machinable spare parts will be supplied to the user at a discounted rate.

XII. Technical Services

1. We will provide one week of free training to the user using specialized training materials. We will assist the user in expanding production capacity and developing new products, offering discounted rates or free services depending on the circumstances.

2. We will visit the user once every six months to resolve practical production issues free of charge.

3. We will provide free training for operators until the equipment is operating normally.

XIII. Equipment Manufacturing and Installation Schedule

1. Manufacturing Schedule

The manufacturing cycle begins on the first day the advance payment for the equipment is received by our factory and ends on the first day the complete set of equipment is shipped to the user, totaling 75 days.

2. Installation and Commissioning Schedule

The installation and commissioning period begins on the first day the equipment is hoisted onto the installation foundation and ends upon completion of commissioning for the entire set of equipment, totaling 20 days. Personnel training and other tasks will be conducted concurrently.

XIV. Transportation Method

The complete set of equipment will be transported to the customer by truck. Our factory is responsible for packaging and loading. Freight costs shall be borne by the supplier.

XV. Requirements for Customer Cooperation

1. The customer must assist with unloading the equipment upon its arrival.

2. The customer must assist with lifting operations during equipment installation; costs shall be borne by the supplier.

3. The customer must assist with certain large tools required on-site; costs shall be borne by the supplier.