Design of Low Temperature Belt Sludge Drying Machine

Selection conditions for low-temperature belt dryer for sludge drying:

1. Only electricity serves as the heat source for drying sludge

2. No exhaust emissions are allowed

Working principle of low-temperature drying:

The sludge dehumidification and drying machine uses a dehumidification heat pump to condense, dehumidify, and dry sludge through hot air circulation;

Dehumidification drying is the process of recovering latent heat of water vapor and sensible heat of air from exhaust air. Traditional sludge thermal drying systems convert 90% of their heat supply into exhaust heat loss (latent heat of water vapor and sensible heat of hot air);

Dehumidification heat pump - is a device that uses a refrigeration system to cool and dehumidify humid air while recovering the latent heat of condensation of air moisture through the principle of heat pump to heat the air;

Dehumidification heat pump drying uses a refrigeration system to cool and dehumidify the humid air from the drying chamber, while recovering the latent heat of condensation of moisture through the principle of heat pump to heat the air to achieve the purpose of drying materials. Dehumidification heat pump is a combination of dehumidification (dehumidification and drying) and heating pump (energy recovery), which is used for energy recycling during the drying process.

The difference between dehumidification heat pump drying and traditional hot air drying lies in the different air circulation methods and the different ways in which the air in the drying room is dehumidified. When drying with a dehumidification heat pump, the air circulates in a closed manner between the drying chamber and the dehumidification dryer (without emitting any waste heat); Traditional hot air drying is an open system that uses a heat source to heat the air and discharge the moisture absorbed air (waste heat), resulting in low energy efficiency (20% -50%).

1. It can fully achieve the "reduction, stabilization, harmlessness, and resource utilization" treatment of sludge;

2. Sludge particles can be used for co firing fuel, incineration, building materials, biofuels, etc;

3. Suitable for domestic sludge, printing and dyeing, papermaking, electroplating, chemical, leather, and various types of sludge drying systems (including sludge with high sand content);

Stability:

1. Low temperature drying process below 80 ℃, fully suitable for sludge drying in municipal, printing and dyeing, and papermaking industries;

2. The system runs stably, without explosion hazards, and does not require nitrogen flushing operation;

3. The oxygen content during the sludge drying process is less than 12%; Dust concentration<60g/m3; Particle temperature<70 ℃;

4. Static spreading of sludge without mechanical static friction with the contact surface;

5. No "adhesive phase" stage in the drying process of urban sludge (about 60%)

6. The dry material is in granular form and poses no dust hazard;

7. Low discharge temperature (<50 ℃), no need for cooling, direct storage;

Energy saving:

1. Adopting heat pump heat recovery technology, the closed drying mode has no waste heat emissions;

2. Drying 80% wet mud to 10% per ton, with a comprehensive power consumption of 210kw. h;

3. Every 1 kWh of electricity can remove 3.7 kg of water (dehumidification performance ratio 1:3.7 kg. H2O/kw. h);

4. Drying 80% wet mud to 60% per ton, with a comprehensive electricity consumption of 128kw. h;

Environmental Protection:

1. Adopting a low-temperature (40-75 ℃) fully enclosed drying mode, there is no odor leakage and no need to install complex deodorization devices;

2. By adopting a low-temperature drying process, the precipitation of H2S and NH3 is greatly reduced;

3. Suitable for installation in urban sewage treatment plants

4. The disposal of condensate water (sludge moisture) is simple (or directly discharged), saving the cost of condensate water treatment during the drying process

High efficiency:

1. It can directly dry sludge with a moisture content of 83% to 10% without the need for segmented disposal (such as plate and frame pressure filtration+thermal drying, thin-layer drying+belt drying, etc.);

2. The drying process results in no loss of organic components and high calorific value of dry materials, making it suitable for later resource utilization;

3. Reduce capacity by 67% and weight by 80%, which can save a lot of transportation costs in the later stage;

4. Suitable for drying sludge with a moisture content of 83% -50%;

Stabilization

Adopting the Pasteur sterilization method - low-temperature heating sterilization, the drying temperature can reach above 70 ℃ for 90 minutes to 120 minutes, and can effectively kill over 96% of bacteria;

Save money

1. Small land area, with an average land area of about 4m2 per ton of mud;

2. Can be stacked up and down, occupying 2m2 per ton of mud;

3. No complex civil engineering structures or infrastructure construction, saving civil engineering costs

4. Equipment installation is simple, with short installation and debugging cycles;

5. Can be installed in the basement to save land area;

Intelligent

1. Fully automatic operation, saving a lot of labor costs

2. PLC+touch screen intelligent control, capable of remote transmission and centralized control

3. The moisture content of the discharged material can be adjusted arbitrarily (10% -50%)

Durable

1. Using corrosion-resistant materials such as stainless steel and electroplating anti-corrosion treatment for heat exchangers, with a long service life;

2. No mechanical wear during operation, with a service life of over 15 years;

3. No vulnerable or consumable parts, easy to use and manage;

　Strong applicability

1. The daily processing capacity of a single drying line can reach 50 tons (80% moisture content sludge cake), which can be suitable for sludge dispersion or centralized treatment mode, saving sludge transportation costs and reducing environmental pollution during transportation;

2. Suitable for urban life sludge dispersion drying+centralized disposal technology, which can effectively solve the problem of difficult urban sludge disposal;

3. Not affected by external environmental temperature (low temperature in winter) and humidity (humid in summer), suitable for use in various regions;

　Innovative Technology

1. Breaking through the bottleneck of high temperature technology in heat pump drying, with superior high temperature performance, solving the winter problems of air source heat pump drying machines (frosting and poor high temperature performance);

2. The intermediate heat exchange cooling dehumidification and temperature gradient utilization technology using the patented three effect dehumidification technology has a comprehensive dehumidification performance ratio (SMER) of over 3.3kg.H2o/kw. h.

3. Breaking through the technological bottleneck of traditional dehumidifiers and ordinary heat pump dehumidifiers and dryers: solving the technical problem of poor dehumidification performance or even idling (compressor operation not removing water) of traditional dehumidification equipment under high temperature and low humidity conditions;

4. Different molding techniques can be used for mud cakes with different moisture contents to reduce drying time and provide comprehensive energy efficiency for the drying system.

Design and selection of low-temperature belt sludge dryer

1. Drying temperature

The hot drying process can be divided into low-temperature drying (below 150 ℃) and high-temperature drying (above 150 ℃) according to the different drying temperatures. According to the different forms of heat transfer, it can be divided into direct heat drying and indirect heat drying.

2. Low temperature drying

Low temperature drying is divided into two types: direct low-temperature drying and indirect low-temperature drying. Indirect low-temperature thermal drying has a low utilization rate of heat and occupies a large area of equipment, so it is less commonly used in the field of sludge treatment. Direct low-temperature thermal drying has a high thermal efficiency due to the direct action of hot air on the sludge. However, the low temperature does not cause the organic matter in the sludge to decompose and evaporate, and the circulating hot air only takes away water from the sludge;

3. High-temperature drying

High temperature drying is divided into direct high-temperature drying and indirect high-temperature drying.

Direct high-temperature drying has excellent drying efficiency due to the high temperature and direct contact between the heat medium and sludge. However, direct high-temperature heating can easily decompose the organic matter in the sludge, increase the difficulty of tail gas treatment and heat recovery, and result in higher energy consumption and other costs.

Indirect high-temperature drying is a process in which a heat source is transferred to the heater wall through media such as steam and hot oil, causing the sludge on the other side of the wall to be heated and the water to evaporate, resulting in lower thermal efficiency compared to direct drying. However, the heat energy from indirect drying is relatively easy to reuse and has lower energy consumption. However, the thermal efficiency is lower compared to direct drying, and it is easier to crack the organic matter in the sludge, increasing the difficulty of tail gas treatment without causing the organic matter in the sludge to crack and evaporate. The circulating hot air only takes away water from the sludge;

During the high-temperature thermal drying process, some volatile substances in the sludge are decomposed by heat, forming a foul odor. The odor generated during this process is polluting and needs to be treated to meet the standards before being discharged. In general engineering, biological filters are used for deodorization or directly burned as combustion air. The water vapor formed by evaporation is generally captured by condensation, which generates a certain amount of wastewater (about 20-25kg/kg. evap.). The concentration of COD in wastewater increases by about 200-4000mg/L, and the concentration of SS increases by about 20-400mg/L. The wastewater needs to be further treated before meeting the discharge standards. The use of fossil fuel sludge drying facilities will generate a certain amount of flue gas emissions, and the different mud, fuel, and incinerator types will cause significant differences in the composition of the generated flue gas. Selection of drying temperature:

Select direct low-temperature drying, with a drying temperature of 45-50 ℃ (inlet temperature of the dehumidification pump); Supply air temperature 60-75 ℃; (Lower layer) 4. Drying model

The plan adopts a closed dehumidification and drying mode, which does not require the introduction of external energy sources (steam, thermal oil, hot air) and does not require exhaust gas treatment systems;

The sludge dehumidification and drying machine uses a dehumidification heat pump to condense, dehumidify, and dry sludge through hot air circulation; The latent heat of vaporization of sludge moisture is equal to the latent heat of condensation of water vapor in a dehumidification heat pump (energy conservation). The drying process does not require external heat, and the energy consumption is the input power consumption of the compressor.

Dehumidification dryer is equivalent to dehumidification heat pump and belt conveyor (belt drying);

Dehumidification heat pump - is a device that uses a refrigeration system to cool and dehumidify humid air while recovering the latent heat of condensation of air moisture through the principle of heat pump to heat the air. Dehumidification heat pump=a combination of dehumidification (dehumidification and drying) and heat pump (energy recovery). Dehumidification heat pumps can recover all latent and sensible heat during the exhaust process, without emitting waste heat to the outside world.

Mesh belt drying has good breathability and can increase the contact area between hot air and materials, resulting in high heat transfer efficiency; Static placement of sludge to reduce dust and extend the service life of the mesh belt;

3 cooling methods

To prevent exhaust gas leakage, a closed drying mode is adopted, and the waste heat generated by the conversion of electrical energy such as compressors and fans needs to be dissipated to the outside through a heat dissipation device; The scheme design adopts centralized water cooling;

4. Control of moisture content in dry materials

The mesh belt reducer adopts variable frequency speed control and stepless speed regulation, which is conducive to adjusting the moisture content of the discharged material;

The dehumidification heat pump adopts a modular design, which can automatically adjust the number of operating modules and save operating electricity costs