A detailed design scheme for using a cross flow air-to-air heat exchanger for fresh air preheating in the waste heat recovery and utilization plan of a cat litter dryer. Drying cat litter (such as bentonite cat litter or tofu cat litter) usually involves high-temperature and high humidity exhaust gas, and cross flow heat exchangers are very suitable for such scenarios due to their efficient heat exchange performance and compact structure.
- Scheme principle
The cat litter dryer generates high-temperature and high humidity exhaust gas (usually at a temperature of 60 ℃ -150 ℃ and a humidity of 50% -90%) during the drying process, which contains a large amount of thermal energy. By using a cross flow air-to-air heat exchanger, the heat of the exhaust gas is transferred to the fresh cold air (fresh air) entering the dryer, achieving fresh air preheating, thereby reducing the energy consumption of the heating system and lowering the exhaust gas emission temperature.
The characteristic of a cross flow heat exchanger is that the exhaust gas and fresh air flow in a cross direction inside the heat exchanger, and the heat exchange efficiency is generally between 60% and 80%. It is suitable for the characteristics of high exhaust gas flow rate and high temperature in cat litter drying.
- System composition
Cross flow air-to-air heat exchanger: The core component, usually a plate structure, exchanges heat between exhaust gas and fresh air through staggered channels.
Exhaust gas pipeline: Guide the wet and hot exhaust gas discharged from the dryer to the hot side inlet of the heat exchanger.
Fresh air duct: Introduce external cold air into the cold side of the heat exchanger, preheat it, and send it to the dryer.
Fan: Installed separately in the exhaust gas and fresh air ducts to ensure stable airflow through the heat exchanger.
Drainage system: deals with the condensed water generated by the condensation of exhaust gas.
Filtering device: prevents cat litter dust from entering the heat exchanger and extends equipment life.
Temperature and humidity sensors: monitor exhaust gas and fresh air parameters to optimize operation. - Workflow
Waste gas input: The high-temperature and high humidity waste gas discharged from the cat litter dryer enters the hot side channel of the cross flow heat exchanger.
Heat exchange: The heat from the exhaust gas is transferred to the fresh air in the cold side channel through the metal plate of the heat exchanger, and the temperature of the fresh air increases.
Fresh air output: Preheated fresh air enters the heating system or drying chamber of the dryer, reducing heating energy consumption.
Exhaust gas emissions: The cooled exhaust gas is discharged from the heat exchanger and can be further treated (such as dust removal or dehumidification).
Condensed water discharge: The condensed water generated during the cooling of exhaust gas is removed through a drainage device. - Design parameter examples
Assuming the operating conditions of the cat litter dryer are as follows:
Exhaust gas temperature: 100 ℃
Exhaust gas flow rate: 3000 m ³/h
Exhaust gas humidity: 70%
Initial temperature of fresh air: 20 ℃
Heat exchanger efficiency: 70%
Calculation result:
The exhaust gas is cooled to about 44 ℃, releasing about 60-70 kW of heat.
Preheating the fresh air to about 76 ℃ can significantly reduce the subsequent heating demand.
- Implementation plan
Equipment selection:
Cross flow plate heat exchanger: made of stainless steel or aluminum alloy material, corrosion-resistant and capable of dealing with dust and humidity in cat litter exhaust gas.
The size is designed based on the exhaust gas and fresh air flow rate, for example, the heat exchange area is about 20-30 m ².
Installation layout:
The heat exchanger is placed near the exhaust port of the dryer to shorten the length of the exhaust pipe and reduce heat loss.
Install a filter screen at the fresh air inlet to prevent cat litter dust from blocking the heat exchanger.
System integration:
The temperature of the preheated fresh air should match the cat litter drying process (usually 80 ℃ -120 ℃), and if it is too high, a bypass valve can be added to adjust it.
Ensure a balance between exhaust gas and fresh air flow to avoid affecting the internal airflow of the dryer.
Control optimization:
Configure a temperature control system to dynamically adjust the fresh air flow rate based on the exhaust gas temperature and maintain drying efficiency. - Advantages
Efficient and energy-saving: Fresh air preheating can reduce heating energy consumption by 30% -50%, depending on the exhaust gas temperature and heat exchange efficiency.
Compact structure: The cross flow heat exchanger has a small volume and is suitable for cat litter production workshops with limited space.
Stable operation: The cross flow design has low airflow resistance and minimal impact on the original system of the dryer.
Cost effectiveness: Low equipment investment, simple maintenance, suitable for small and medium-sized cat litter processing enterprises. - Precautions
Dust management: The exhaust gas from cat litter drying may contain small particles, and an efficient filter (such as a bag filter) should be installed before the heat exchanger to prevent clogging.
Condensation water treatment: Due to the high humidity of the exhaust gas, condensation water is easily generated on the cold side of the heat exchanger. Therefore, it is necessary to design a drainage slope and conduct regular cleaning.
Corrosion resistance: The exhaust gas may contain trace amounts of acidic components, and the material of the heat exchanger needs to be corrosion-resistant to avoid performance degradation after long-term use.
Temperature control: The drying temperature of cat litter is sensitive (such as bentonite cat litter should not be too high), and preheating fresh air should avoid exceeding the upper limit of the process. - Benefit estimation
Taking a medium-sized cat litter dryer as an example:
Running for 10 hours a day, the heat recovery from exhaust gas is about 600-700 kWh.
Calculated by electric heating (0.8 yuan per kilowatt hour), the daily savings are about 480-560 yuan, and the annual income is about 150000 to 200000 yuan.
The cost of a cross flow heat exchanger is about 20000 to 30000 yuan, and the investment payback period is about 2-4 months. - Summary
The scheme of using a cross flow air-to-air heat exchanger for fresh air preheating is very suitable for the waste heat recovery needs of cat litter dryers. Its efficient heat exchange performance and compact design can significantly reduce energy consumption while maintaining the stability of the drying process. By selecting and managing dust, humidity, and other issues reasonably, this solution can bring considerable economic benefits and environmental value to cat litter production enterprises.