How to design a heat pump drying system for production drying with the most stable and reliable drying unit project? This is a typical example of a project with an energy-saving conversion project for a long-line gelatin skin drying production line. The process of the project is fresh air - medium efficiency filter - fresh air pre-treatment - return air from the production process - medium efficiency filter - lithium chloride desiccant - air supply cabinet - heating and drying in the drying chamber - exhaust fan - exhaust air (recycled air), with a total air circulation of 90,000 m³/h. The dry air at low temperature is humidified by lithium chloride solution, and the dehumidifier enters the long-line drying chamber and is heated by steam to meet the drying process requirements. A portion of the air with high temperature and high humidity has been dried and discharged directly to the outside through the ventilation fan, and part of it returns to the air conditioning cabinet and lithium chloride solution regenerator. This cycle will discharge a large amount of heat every day, leading to a significant energy impact. According to the production process requirements, this design includes the design content for the cold water production line, hot water drying room, and exhaust heat recovery system.
1: Initial production line configuration
The project is designed and used with two high-temperature water source heat pump units, connected in series with the return heat of the original system to the steam heating section. The return heat of the original system is pre-heated by adding the primary and secondary heating systems of the high-temperature water source heat pump unit. If the output water temperature of the heat pump does not reach the set 75℃ after heating, the steam heating system will automatically start. The primary high-temperature water source heat pump has a heating capacity of 818 kW and an input power of 235 kW; the two-stage high-temperature water source heat pump has a heating capacity of 806 kW and an input power of 265 kW.
2: Description of exhaust heat recovery conversion:
Add 10³m in the design, an insulated square water tank to transmit cold water at 15℃ to each ceiling air heat recovery unit via a circulation pump, and the hot water at 20℃ is heated by exhaust air back to the insulated water tank for heating by the high-temperature heat pump unit; reduce the enthalpy of the exhaust air and reduce the surrounding thermal pollution.
3: Description of the return air heat recovery conversion:
The return air contains a large amount of water vapor and high enthalpy. A ceiling-mounted heat recovery air cabinet is installed on the return air duct to reduce the water vapor content and enthalpy of the return air, reducing the energy consumption of the lithium chloride dehumidifier, and the recovered heat is supplied to the high-temperature heat pump unit.
4: Guide to recycle cold water heat pump in summer:
The original system is equipped with a 930 kW cooling unit to cool and dehumidify fresh air in summer and a lithium chloride dehumidifier. The water supply temperature is 12/7℃, while the heat pump can adjust the cold source water temperature to 12/7℃ when working in summer. The water supply and return at the cold source side can directly replace the original cooling unit's supply and return water, reducing the operating energy consumption of the original cooling unit system.
