Drying heat recovery - Industrial purification heat recovery

Corrosion-Resistant Air Heat Exchange Core and Dehumidification Heat Recovery Equipment for Heat Pump Drying Systems

In heat pump drying applications, especially for seafood processing, chemical sludge, and other salt-laden materials, the drying and baking environment places extremely high demands on air heat exchange equipment. Exhaust air often contains large amounts of water vapor, salt mist, and corrosive substances. Conventional aluminum heat exchangers are prone to corrosion, perforation, rapid efficiency loss, and frequent failures. For these harsh conditions, corrosion-resistant air heat exchange cores combined with dehumidification and exhaust heat recovery equipment are essential to ensure long-term stable operation of heat pump drying systems.

1. Typical Operating Conditions

Drying exhaust air from seafood processing and chemical sludge treatment usually has the following characteristics:

High humidity with large volumes of condensate
Presence of salt mist or chemical corrosive components
Continuous operation under medium to high temperatures
Long operating cycles with limited downtime for maintenance
High reliability requirements for heat pump systems

These conditions require heat exchange cores with excellent resistance to corrosion, condensation, and thermal stress.

2. Key Design Features of Corrosion-Resistant Air Heat Exchange Cores

1. Corrosion-Resistant Materials

The heat exchange core is manufactured using stainless-steel foil (304 / 316L) or other high-corrosion-resistant composite materials, effectively resisting salt mist, chloride ions, and chemical corrosion while significantly extending service life.

2. Air-to-Air Isolated Heat Exchange Structure

An air-to-air heat exchange design ensures complete separation between exhaust air and make-up air, preventing salt mist and corrosive components from entering the heat pump system.

3. Low-Resistance, Large-Channel Design

Wide airflow passages and low pressure drop support high-humidity, large-airflow drying chambers, minimizing fouling and blockage.

4. Efficient Condensate Drainage and Anti-Liquid Accumulation Design

Vertical airflow configuration combined with a bottom condensate collection tray enables rapid drainage, preventing liquid accumulation and corrosion.

3. Integrated Dehumidification, Exhaust Air Discharge, and Heat Recovery Principle

Within a heat pump drying system, the corrosion-resistant air heat exchange core works in coordination with the dehumidification and exhaust heat recovery module:

High-humidity hot air from the drying chamber enters the dehumidification heat exchange section.
Water vapor condenses on the surface of the heat exchange core and is discharged.
Latent and sensible heat released during condensation is recovered.
Recovered heat is used to preheat make-up air or recirculated air.
Reduced air humidity improves drying efficiency.
Heat pump load decreases, enhancing overall system energy efficiency.

This integrated process achieves both moisture removal and energy recovery simultaneously.

4. Application Areas

This type of corrosion-resistant air heat exchange core and heat recovery equipment is particularly suitable for:

Seafood drying and processing (fish, shrimp, seaweed)
Salt-containing agricultural and aquatic products
Chemical sludge and salt-bearing sludge drying
Heat pump drying systems for high-salinity waste materials
Drying chambers in coastal or high salt-mist environments

5. System Benefits

Applying corrosion-resistant air heat exchange cores under harsh operating conditions delivers:

Stable and reliable long-term operation
Effective dehumidification with shorter drying cycles
Recovery of exhaust heat to reduce heat pump energy consumption
Significantly reduced corrosion risk and maintenance costs
Extended service life and improved system reliability

6. Conclusion

In high-salinity, high-humidity, and corrosive drying environments such as seafood processing and chemical sludge treatment, conventional heat exchange equipment cannot ensure stable operation. The use of dedicated corrosion-resistant air heat exchange cores combined with dehumidification and exhaust heat recovery equipment provides a reliable, energy-efficient solution for heat pump drying systems. It represents a key enabling technology for safe, economical, and sustainable operation in complex drying conditions.

Exhaust Heat Recovery Retrofit for Textile Stenter Machines Using Full Stainless-Steel Air-to-Air Plate Heat Exchangers

Textile stenter machines generate high-temperature exhaust containing oil mist, fiber dust, additives, and high humidity, which often leads to corrosion, fouling, and unstable system operation. To address these challenges, a full stainless-steel air-to-air plate heat exchanger is used for exhaust heat recovery, integrating vertical exhaust channels, flat-plate passage structures, vertical spray washing, and a bottom condensate/ sludge settling tank. These optimized designs ensure reliable heat recovery specifically tailored for the textile printing and dyeing industry.

1. Application Background

Typical characteristics of stenter machine exhaust:
• Temperature 120–180°C
• Contains oil mist, fiber particles, chemical additives
• High moisture content; risk of condensation and corrosion
• Tendency to cause fouling and blockage in conventional heat exchangers

Aluminum exchangers cannot handle these harsh conditions. A full stainless-steel design with specialized structures is required to ensure long-term stable performance.

2. Key Structural Features

1. Full Stainless-Steel Heat Transfer Plates (304 / 316L)

• Excellent resistance to acidic condensate and dyeing chemicals
• High thermal and mechanical stability at elevated temperatures
• Supports high-frequency washing without deformation
• Considerably longer service life than aluminum plates

2. Flat Exhaust Passage Design

• Smooth, wide flow channels prevent fiber and oil mist accumulation
• Extended maintenance intervals
• Lower pressure drop, ideal for the large airflow of stenter machines

3. Vertical Exhaust Flow (L-Shaped Flow Path)

• Exhaust flows vertically downward or from top-side down
• Gravity assists removal of oil droplets and particles
• Reduces fouling on plate surfaces and prolongs cleaning cycles
• Enhances drainage efficiency during spray washing

4. Vertical Spray Cleaning System

• Periodic spray washing removes oil, fiber dust, and chemical residue
• Prevents fouling and restores heat transfer performance
• Allows online cleaning without dismantling the heat exchanger

5. Bottom Wastewater and Sludge Settling Tank

• Collects oil-contaminated water and fiber particles washed from plates
• Facilitates proper drainage and disposal
• Prevents recontamination of the heat exchanger
• Easy-to-clean structure, independent from the upper heat exchange area

3. Working Principle

High-temperature exhaust enters the vertical flat channels.
Heat is transferred through stainless-steel plates to the fresh-air side.
Moisture condenses and carries oil/dirt downward into the settling tank.
Fresh air absorbs waste heat and is preheated for reuse in the stenter machine or workshop ventilation.
Cooled exhaust is then discharged to downstream treatment (RTO, carbon adsorption, fans) with reduced thermal load.
The spray system periodically washes the exhaust channels to maintain stable efficiency.

Airflows remain completely separated to avoid cross-contamination.

4. Technical Advantages

1. Engineered Specifically for Textile Stenter Exhaust

Resistant to high temperature, corrosion, oil fumes, and fiber dust—solving long-standing issues in the dyeing and finishing industry.

2. Significant Energy Savings

Recovering exhaust heat to preheat fresh air can reduce gas, steam, or electric heating consumption by 20–35%.

3. Anti-Fouling, Stable Operation

Flat channels + vertical airflow + spray washing prevent blockages common in stenter exhaust systems.

4. Protects Downstream Equipment

Lower exhaust temperature reduces load on RTO, ducts, and fans, improving service life and reliability.

5. Low Maintenance

Routine spray cleaning and simple sludge removal are sufficient; no frequent disassembly required.

5. Typical Applications

• Textile heat-setting stenter machines
• Stretching, drying, and heat-setting production lines
• High-temperature exhaust with oil mist and fiber dust
• Pre-cooling and energy recovery before VOC treatment systems

BXB Energy-Saving Heat Exchanger for Flower and Herb Drying

High-Efficiency Waste Heat Recovery · Lower Drying Energy Consumption · Improve Product Quality

During the drying process of flowers, petals, herbs, and aromatic plants, a large volume of hot and humid air is discharged. This exhaust contains substantial reusable heat. The BXB energy-saving heat exchanger captures the sensible heat and part of the latent heat from the exhaust air and uses it to preheat fresh air or return air, significantly reducing energy waste.

Working Principle

Hot exhaust enters the heat exchanger after leaving the dryer.
Heat is transferred to fresh air, raising the fresh air temperature quickly.
Exhaust air temperature and humidity drop after heat exchange, improving discharge conditions.
Preheated fresh air returns to the dryer, reducing heater load and energy consumption.

This process is especially suitable for flower and herb drying, where stable temperature control is crucial for preserving color, fragrance, and quality.

Key Advantages

Energy Saving
The BXB structure provides large heat exchange surface and low air resistance, recovering a substantial portion of waste heat. Energy consumption can typically be reduced by twenty to forty percent.

Stable Drying Quality
Preheated air provides a more stable inlet temperature, reducing fluctuations and helping maintain natural color, aroma, and shape of dried flowers and herbs.

Improved Exhaust Conditions
After cooling, the exhaust becomes less humid and easier to discharge, reducing heat stress and moisture impact on the equipment.

Optimized for Low-Temperature Drying
Flower and herb drying requires gentle and precise temperature control. The BXB exchanger improves overall stability and enhances process controllability.

Flexible Installation
Suitable for both new drying lines and retrofit projects without altering the original drying process.

Application Fields

Flower drying
Rose petals, chamomile, lavender, jasmine, honeysuckle, and other delicate floral materials.

Herbal drying
Leaf-type or flower-type medicinal herbs requiring low-temperature drying to preserve active components.

Aromatic plant drying
Materials that need controlled temperature to retain fragrance.

Applicable to agricultural bases, herb processing factories, flower drying workshops, and food processing plants.

Industrial heat recovery applications: Utilization of residual heat from seafood drying

1. Sources and Characteristics of Waste Heat from Seafood and Aquatic Products Drying

Seafood and aquatic products (such as shrimp, fish, shellfish, etc.) are typically dried using hot air drying equipment, with heat sources primarily consisting of coal-fired, gas-fired boilers, or electric heating systems. The drying process generates a large amount of high-temperature, high-humidity exhaust gas (flue gas), with temperatures typically ranging from 50-100°C, containing significant sensible heat and latent heat:

Sensible Heat: The heat inherent in the high-temperature flue gas itself.

Latent heat: The heat released by the condensation of water vapor in the flue gas. Due to the high moisture content of seafood, the proportion of latent heat is particularly significant.

Exhaust gas characteristics: High humidity (containing a large amount of water vapor), may contain salts or organic matter, which can cause equipment corrosion or scale buildup on heat exchanger surfaces.

If these exhaust gases are directly emitted, not only will thermal energy be wasted, but thermal pollution and wet pollution will also increase, affecting the environment.

2. Features of the BXB Plate Heat Exchanger

The BXB plate heat exchanger is a highly efficient, compact heat exchange device widely used in industrial waste heat recovery, particularly suitable for handling high-temperature, high-humidity exhaust gases. Its main features include:

High-efficiency heat exchange: The plate structure provides a large heat exchange area, resulting in high heat transfer efficiency with recovery rates of up to 60-80%.

Compact design: Compared to shell-and-tube heat exchangers, it has a smaller footprint, making it suitable for space-constrained drying equipment.

Corrosion resistance: Stainless steel or titanium alloy plates can be selected to withstand corrosion from salts and organic compounds in seafood drying exhaust gases.

Easy maintenance: The removable design facilitates cleaning to address scaling or deposits in exhaust gases.

Low pressure drop: Minimal fluid resistance reduces system energy consumption.

3. Application of BXB Plate Heat Exchangers in Seafood and Aquatic Product Drying

(1) System Design

Process Flow:

Exhaust Gas Collection: High-temperature, high-humidity exhaust gas (50-100°C) emitted from drying equipment is conveyed through pipes into the hot-side inlet of the BXB plate heat exchanger.

Heat Transfer: The sensible and latent heat in the exhaust gas is transferred through the heat exchanger plates to the cold-side medium (typically cold air or cooling water).

Heat Utilization:

Preheating of Incoming Air: The recovered heat is used to preheat the incoming air to the drying chamber, reducing the energy consumption of the heater.

Hot water production: Heat is transferred to water to produce hot water for equipment cleaning or facility heating.

Dehumidification optimization: After cooling, the exhaust gas's humidity decreases, improving the efficiency of the dehumidification system.

Exhaust gas emission: The cooled exhaust gas (temperature reduced to 40–50°C) is further treated through the dehumidification system before emission, reducing thermal pollution.

Equipment Configuration:

Heat Exchanger Type: BXB plate heat exchangers are selected, with stainless steel 316L or titanium alloy plates recommended to prevent salt corrosion.

Plate Design: Corrugated plates are used to enhance turbulence, improve heat transfer efficiency, and reduce scaling.

Auxiliary Systems: Equipped with exhaust gas filtration devices (to remove dust and organic compounds) and an automatic cleaning system to extend the heat exchanger's lifespan.

(2) Working Principle

Heat from the exhaust gas is transferred to the cold-side medium through the metal plates of the plate heat exchanger. The narrow channels between the plates enhance heat transfer efficiency.

During the heat exchange process, part of the water vapor in the high-temperature, high-humidity exhaust gas condenses, releasing latent heat and further improving heat recovery efficiency.

The cold-side medium (such as air or water) absorbs the heat, increasing its temperature, and can be directly used for drying preheating or other process requirements.

(3) Application Scenarios

Preheating of Incoming Air: Recovering exhaust gas heat to heat fresh incoming air for drying rooms reduces heat source consumption.

Hot Water Supply: Utilizing recovered heat to produce 40-60°C hot water for cleaning seafood processing equipment or providing hot water for industrial use.

Dehumidification Optimization: Reducing exhaust gas humidity through cooling and condensation improves dehumidification efficiency and enhances drying performance.

4. Benefit Analysis

Energy Conservation and Emission Reduction: The BXB plate heat exchanger can recover 50-80% of exhaust gas heat, reducing drying energy consumption by 20-40%, and decreasing fuel consumption and CO2 emissions. For example, recovering 60% of residual heat can significantly reduce energy costs per ton of seafood processing.

Economic Benefits: By reducing fuel and electricity consumption, equipment investment typically recovers costs within 1-2 years.

Environmental Benefits: Lowering exhaust gas temperature and humidity reduces thermal and moisture pollution, meeting environmental protection requirements.

Product Quality: Maintaining stable drying temperatures prevents overheating or excessive humidity, enhancing the quality of seafood drying.

Translated with DeepL.com (free version)

What is a Gas-Gas Plate Heat Exchanger?

Gas-Gas Plate Heat Exchanger

A gas-gas plate heat exchanger is a highly efficient heat transfer device designed to recover heat from high-temperature exhaust gases and transfer it to incoming cold air or other gas streams. Unlike traditional heat exchangers, its compact plate structure maximizes the heat transfer surface area, achieving thermal efficiencies of 60% to 80%. The exchanger consists of thin, corrugated metal plates (typically stainless steel) that create separate channels for hot and cold gases, allowing heat to pass through the plates without mixing the gas streams.

This technology is particularly suited for industrial processes that generate significant waste heat, such as drying systems in ultrasonic cleaning machines used for hardware components. By capturing and reusing this heat, the gas-gas plate heat exchanger reduces the energy required for heating processes, lowering operational costs and carbon emissions.

Waste Heat Recovery Systems for Industrial Dryers

Waste heat recovery systems for industrial dryers capture and reuse thermal energy from hot exhaust gases or air streams to improve energy efficiency, reduce operating costs, and lower emissions. These systems are valuable for energy-intensive drying processes in industries like chemical, food, ceramics, and textiles. Below, I outline key technologies, benefits, and U.S.-based suppliers with contact information.

Key Technologies for Waste Heat Recovery in Industrial Dryers
Industrial dryers produce hot, moist exhaust air containing sensible and latent heat. Recovery systems extract this heat for reuse. Common technologies include:

Air-to-Air Heat Exchangers:
Transfer heat from hot exhaust air to incoming fresh air via plate or rotary heat exchangers. Polymer air preheaters resist corrosion and fouling.
Applications: Preheating dryer inlet air, reducing fuel consumption by up to 20%.
Advantages: Simple, cost-effective, low maintenance.
Air-to-Liquid Heat Exchangers:
Capture heat from exhaust to warm liquids for process heating or facility HVAC.
Applications: Heating process water in food processing plants.
Advantages: Versatile heat reuse.
Heat Pumps:
Upgrade low-temperature waste heat to higher temperatures for reuse.
Applications: Lifting heat for dryer air preheating in chemical or dairy industries.
Advantages: High efficiency for low-temperature sources.
Direct Contact Heat Exchangers:
Hot exhaust gases directly contact a liquid to transfer heat, often cleaning flue gas contaminants.
Applications: Recovering heat from kilns, ovens, or dryers.
Advantages: Cleans exhaust while recovering heat.
Waste Heat Boilers:
Convert high-temperature exhaust into steam for process use or power generation.
Applications: High-temperature dryers in ceramics or minerals processing.
Advantages: Generates steam or electricity.
Benefits of Waste Heat Recovery for Dryers
Energy Savings: Efficiency improvements of up to 20%.
CO2 Reduction: Every 1% efficiency gain cuts CO2 emissions by 1%.
Cost Reduction: Payback periods from months to 3 years.
Environmental Compliance: Reduces emissions and waste heat release.
Process Optimization: Stable temperatures enhance product quality.
Challenges and Solutions
Fouling and Corrosion: Polymer heat exchangers or in-line cleaning systems mitigate issues.
Heat Sink Availability: Requires nearby heat use for economical integration.
System Design: Custom engineering ensures compatibility.

how does air to air heat exchanger work in Spray drying heat recovery

In spray drying heat recovery, an air-to-air heat exchanger is used to recover waste heat from the hot, moist exhaust air leaving the drying chamber and transfer it to the incoming fresh (but cooler) air. This reduces the energy demand of the drying process significantly.

How It Works:

Exhaust Air Collection:
- After spray drying, hot exhaust air (often 80–120°C) contains both heat and water vapor.
- This air is pulled out of the chamber and sent to the heat exchanger.
Heat Exchange Process:
- The hot exhaust air flows through one side of the heat exchanger (often made of corrosion-resistant materials due to possible stickiness or mild acidity).
- At the same time, cool ambient air flows through the other side, in a separate channel (counter-flow or cross-flow setup).
- Heat is transferred through the exchanger walls from the hot side to the cool side, without mixing the air streams.
Preheating Incoming Air:
- The incoming fresh air gets preheated before entering the spray dryer’s main heater (gas burner or steam coil).
- This lowers the fuel or energy required to reach the desired drying temperature (typically 150–250°C at the inlet).
Exhaust Air Post-Treatment (optional):
- After heat extraction, the cooler exhaust air can be filtered or treated for dust and moisture before being released or further used.

Benefits:

Energy Savings: Cuts down fuel or steam consumption by 10–30% depending on setup.
Lower Operating Costs: Less energy input reduces utility expenses.
Environmental Impact: Reduces CO₂ emissions by improving energy efficiency.
Temperature Stability: Helps maintain consistent drying performance.

how does air to air heat exchanger work in nmp heat recovery

An air-to-air heat exchanger in NMP heat recovery transfers thermal energy between a hot, NMP-laden exhaust air stream from an industrial process and a cooler incoming fresh air stream, improving energy efficiency in industries like battery manufacturing.

The hot exhaust air (e.g., 80–160°C) and cooler fresh air pass through separate channels or over a heat-conductive surface (e.g., plates, tubes, or a rotary wheel) without mixing. Heat transfers from the hot exhaust to the cooler fresh air via sensible heat transfer. Common types include plate heat exchangers, rotary heat exchangers, and heat pipe heat exchangers.

NMP-specific designs use corrosion-resistant materials like stainless steel or glass fiber-reinforced plastic to withstand NMP’s aggressive nature. Larger fin spacing or clean-in-place systems prevent fouling from dust or residues. Condensation is managed to avoid blockages or corrosion.

The hot exhaust air transfers heat to the fresh air, preheating it (e.g., from 20°C to 60–80°C) and reducing energy needs for subsequent processes. The cooled exhaust air (e.g., 30–50°C) is sent to an NMP recovery system (e.g., condensation or adsorption) to capture and recycle the solvent. Heat recovery efficiency is 60–95%, depending on the design.

This reduces energy consumption by 15–30%, lowers greenhouse gas emissions, and improves NMP recovery by cooling the exhaust air for easier solvent capture. Challenges like fouling are addressed with wider gaps, extractable elements, or cleaning systems, while robust sealing prevents cross-contamination.

In a battery manufacturing plant, a plate heat exchanger preheats fresh air from 20°C to 90°C using 120°C exhaust air, reducing oven energy demand by ~70%. The cooled exhaust air is processed to recover 95% of NMP.

how does air to air heat exchanger work in wood drying

An air-to-air heat exchanger in wood drying transfers heat between two air streams without mixing them, optimizing energy efficiency and controlling drying conditions. Here's how it works:

Purpose in Wood Drying: Wood drying (kiln drying) requires precise temperature and humidity control to remove moisture from wood without causing defects like cracking or warping. The heat exchanger recovers heat from exhaust air (leaving the kiln) and transfers it to incoming fresh air, reducing energy costs and maintaining consistent drying conditions.
Components:
- A heat exchanger unit, typically with a series of metal plates, tubes, or fins.
- Two separate air pathways: one for hot, humid exhaust air from the kiln and one for cooler, fresh incoming air.
- Fans or blowers to move air through the system.
Working Mechanism:
- Exhaust Air: Hot, moisture-laden air from the kiln (e.g., 50–80°C) passes through one side of the heat exchanger. This air carries heat energy from the drying process.
- Heat Transfer: The heat from the exhaust air is conducted through the exchanger’s thin metal walls to the cooler incoming fresh air (e.g., 20–30°C) on the other side. The metal ensures efficient heat transfer without mixing the two air streams.
- Fresh Air Heating: The incoming air absorbs the heat, raising its temperature before it enters the kiln. This preheated air reduces the energy needed to heat the kiln to the desired drying temperature.
- Moisture Separation: The exhaust air, now cooler, may condense some of its moisture, which can be drained away, helping to control humidity in the kiln.
Types of Heat Exchangers:
- Plate Heat Exchangers: Use flat plates to separate air streams, offering high efficiency.
- Tube Heat Exchangers: Use tubes for air flow, durable for high-temperature applications.
- Heat Pipe Exchangers: Use sealed pipes with a working fluid to transfer heat, effective for large kilns.
Benefits in Wood Drying:
- Energy Efficiency: Recovers 50–80% of heat from exhaust air, lowering fuel or electricity costs.
- Consistent Drying: Preheated air maintains stable kiln temperatures, improving wood quality.
- Environmental Impact: Reduces energy consumption and emissions.
Challenges:
- Maintenance: Dust or resin from wood can accumulate on exchanger surfaces, requiring regular cleaning.
- Initial Cost: Installation can be expensive, though offset by long-term energy savings.
- Humidity Control: The system must balance heat recovery with proper moisture removal to avoid overly humid conditions.

In summary, an air-to-air heat exchanger in wood drying captures heat from exhaust air to preheat incoming air, improving energy efficiency and maintaining optimal drying conditions. It’s a critical component in modern kiln systems for sustainable, high-quality wood processing.

how does a heat exchanger work in a boiler

A heat exchanger in a boiler transfers heat from the combustion gases to the water circulating in the system. Here's how it works step by step:

Combustion occurs: The boiler burns a fuel source (like natural gas, oil, or electricity), creating hot combustion gases.
Heat transfer to the heat exchanger: These hot gases flow through a heat exchanger—typically a coiled or finned metal tube or series of plates made of steel, copper, or aluminum.
Water circulation: Cold water from the central heating system is pumped through the heat exchanger.
Heat absorption: As the hot gases pass over the surfaces of the heat exchanger, heat is conducted through the metal into the water inside.
Hot water delivery: The now-heated water is circulated through radiators or to hot water taps, depending on the boiler type (combi or system boiler).
Gas expulsion: The cooled combustion gases are vented out through a flue.

In condensing boilers, there's an extra stage:

After the initial heat transfer, the remaining heat in the exhaust gases is used to preheat incoming cold water, extracting even more energy and improving efficiency. This process often creates condensate (water), which is drained from the boiler.

Category Archive Drying heat recovery