Efficient Sludge Drying with Tongli’s Rotary Sludge Dryer

Introduction:
- As human society and the economy develop and urbanization accelerates, managing sewage sludge has become a pressing issue. The “four modernizations” of sewage sludge management—reduction, stabilization, harmlessness, and resource utilization—are essential. A crucial step in this process is sludge drying and conveyor belt. Tongli Company has developed an advanced rotary sludge dryer that effectively dries materials with approximately 85% moisture content into finished products in a single operation.
Innovative Design for Enhanced Efficiency:
Recognizing the challenges of sludge drying and screening, particularly its tendency to agglomerate, Tongli has innovated beyond the typical single-channel dryer. Our dryer incorporates a combined self-cleaning device, significantly expanding its applicability. It is not only capable of drying various types of sludge but also handles high-viscosity materials with ease.
Rotary Sludge Dryer Data table for model selection:
Item | Specification |
---|---|
Drying materials: | sludge cake (after extrusion by plate and frame filter press) |
Initial moisture: | 70~75%(W1) |
Final moisture: | 28~32%(W2) |
Output per hour: | 5t/h |
Thermal efficiency of hot blast furnace: | 95% |
Inlet air temperature: | 850 Celcius(t1) |
Exhaust gas temperature: | 120 Celcius(t3) |
Specific heat of raw materials: | 1.05KJ/kg |
Discharge temperature: | 110 Celcius(t3) |
Innovative Design for Enhanced Efficiency
Rotary Dryer Selection Guide Selecting the right rotary dryer is crucial for efficient sludge cake drying. Here, we’ll guide you through the process, focusing on key considerations and calculations to ensure optimal performance. The initial moisture content of the sludge cake is 75%. To determine the hourly evaporation requirement, we use the formula:
Evaporation Requirement (W):
W=G×1000×(100−W1)(W1−W2)
Where:
- G = hourly output in tons (5 tons in this case)
- W1 = initial moisture content (75%)
- W2 = final moisture content (32%) Plugging in the values:
W=5×1000× (100−75) (75−32) =8600 kg/h of H2O
This calculation shows that the dryer needs to evaporate 8600 kg of water per hour.
Determining Dryer Capacity
To ensure the selected rotary dryer meets this requirement, the drying power must be sufficient. The formula used is:
G′=0.785×D2×L×A≥W
Where:
- D = drum diameter
- L = drum length
- A = evaporation rate (700-750 kg water/m³.h, we use an average value of 725 kg/m³.h)
First, solve for the required area:
D 2 ×L≥ 0.785×A W = 0.785×725 8600 =15.23 m 2
Selecting the Drum Dimensions
Assuming a drum diameter (D) of 2.0 meters:
L≥ 2.0 2 15.23 =3.81 meters
However, considering practical design and operational efficiency, a length (L) of greater than 20 meters is recommended. For effective drying of sludge cake with an initial moisture content of 75% and requiring an evaporation rate of 8600 kg/h, a rotary dryer with a drum diameter of 2.0 meters and a length of over 20 meters is suitable. Ensuring these specifications will help achieve optimal drying performance. By following these guidelines, you can select a rotary dryer that meets your drying needs efficiently and effectively.
Heat Balance Calculation for Drying Raw Materials
When drying raw materials, the hot air temperature entering the dryer (t1) is set at 750°C. The amount of flue gas required to evaporate each kilogram of water is denoted as n kg. The heat balance calculation is based on the evaporation of 1 kg of water.
Heat Income
- Heat from Hot Gas
When the hot gas is at 850°C, the average specific heat is C1 = 1.4 KJ/kg°C. The heat brought by the hot gas (Q1) can be calculated as: Q1=n×C1×t1=n×1.4×850=1190n(KJ/kg H2O)
Heat from Evaporated Water in Wet Material
- The specific heat of water (C2) is 4.19 KJ/kg°C, and the ambient temperature (t2) is 20°C. The heat brought by the evaporated water (Q2) is: Q2=C2×t2=4.19×20=83.8(KJ/kg H2O)
Heat Expenditure
Heat Consumed to Evaporate Water The total heat required to evaporate water (Qw) is given by:
Qw=(2490+1.8922)×(120−4.19)×20=4750271(KJ/kg H2O)
Heat Taken Away by Dryer Gas
The average exhaust gas temperature is 120°C, with an average specific heat (C3) of 1.3 KJ/kg°C. The heat taken away by the dryer gas (Q3) is:
Q3=n×C3×t3=n×1.3×120=156n(KJ/kg H2O)
Heat Consumed by Heating Materials
The specific heat of the raw materials (C’) is 1.05 KJ/kg°C. The heat consumed by heating the materials (Q4) is calculated as:
Q4=(W1−W2)(100−W1)×[C′×100(100−W2)+C2×100W2]×(t4−t2)
Given W1=75, W2=32 and t4 = 110:
Q4= (75−32) (100−75) ×[0.84× 100 (100−32) +4.19× 100 32 ]×(110−20)=9.188(KJ/kg H2O)
Surface Heat Dissipation
Q1+Q2=Qw+Q3+Q4+Q5
The heat dissipation (Q5) through the dryer surface can be determined using the formula: Q5=W1.15×π×D×L×K×Δt
D=2, 𝐿 = 20 L=20, 𝐾 = 58 K=58, and Δ 𝑡 = 50 Δt=50:
Q5= 8600 1.15×π×2×20×58×50 =48.7312(KJ/kg H2O)
Balance According to the principle of balance, the total heat income equals the total heat expenditure:
Q1+Q2=Qw+Q3+Q4+Q5
We get: n=C1×t1−C3×t3Qw+Q4+Q5−Q2
Substituting the values: n= 1190−156 4750201+9.188+48.7312−83.8 =4594(KJ/kg H2O)
By maintaining precise control over these parameters, efficient drying of raw materials can be achieved, ensuring optimal energy utilization.
Selecting the Drum Dimensions
- The core component of our sludge dryer is a rotating cylinder, slightly inclined from the horizontal. This design supports downstream drying. Materials are introduced at the upper end of the rotary drum via a feeding device. Within the drum, lifting plates rotate at a speed of 5 to 8 revolutions per minute, facilitating the flow of material. The incoming materials interact with hot air, flowing at a rate of 1.3 to 1.5 meters per second at a temperature of 850°C.
- To further enhance efficiency, the rotary drum features an internal rotating split mixing chain and self-turning weight. These elements rapidly break down larger, sticky materials, ensuring they are evenly distributed and come into full contact with the hot air. This process not only improves drying efficiency but also breaks down larger pieces into granules in a single step.
- After 35 to 60 minutes of processing, the dried sludge is discharged through the outlet, resulting in a product with the desired moisture content.
Benefits of Tongli’s Rotary Sludge Dryer
- High Efficiency: The dryer processes high-moisture content materials in one operation.
- Versatility: Suitable for various sludge types and high-viscosity materials.
- Innovative Design: The self-cleaning mechanism prevents clogging and ensures consistent operation.
- Quality Output: Produces uniformly dried sludge with optimal moisture levels.
Conclusion:
Tongli’s rotary sludge dryer represents a significant advancement in sludge management technology, addressing the critical needs of urban and industrial waste treatment processes. By enhancing drying efficiency and broadening the range of applicable materials, our solution supports sustainable and effective sludge reduction and resource utilization.