Abstract: Heat pumps can save energy. The heat generated by the heat pump condenser is used for printing, coating and drying, and the cooling is used for the refrigeration of workshops and office buildings. Using heat pump to achieve energy saving and emission reduction of coating machine.
First, the working principle and advantages of heat pump
Heat pump technology is an energy technology in the 21st century. Through the form of heat pumps, energy efficiency can be improved. Energy efficiency has two meanings. From an environmental perspective, it can reduce greenhouse gas emissions and reduce harmful factors to the environment. From another aspect, it is a technology that solves the high power load.
Just as water flows from high to low, heat always flows from high to low temperatures. Just like using a water pump to lift water from low to high, we can also use a heat pump to draw heat from low to high temperatures. Therefore, the heat pump is essentially a heat lifting device. The function of the heat pump is to absorb heat from the surrounding environment and transfer it to the heated object.
The heat pump works according to the principle of reverse Carnot cycle. When it works, it consumes a part of the energy, excavates the energy stored in the environmental medium, and uses the heat transfer cycle system to increase the temperature. The work consumed by the entire heat pump device is only output. A small part of the work, so using heat pump technology can save a lot of high-level energy. In operation, the evaporator absorbs heat from the surrounding environment to evaporate the heat transfer working medium. After the steam is compressed by the compressor, the temperature and pressure rise. When the high-temperature steam is condensed into a liquid by the condenser, the released heat is transferred to the water storage tank. Heat medium such as water or air. The condensed heat transfer working medium is returned to the evaporator through the expansion valve, and then is evaporated again, and so on.
The compressor uses 1 part of electricity and can handle several parts of heat, which is better understood. Heat pumps also follow the laws of energy conversion and conservation of physics. The electrical energy consumed by the compressor is converted into heat by the negative energy of friction through mechanical energy, which is emitted in the condenser. Some people who are not familiar with the heat pump often confuse the two different concepts of the power consumed by the compressor and the energy transferred by the entire heat pump system, thinking that only as much heat as there is electricity can be. Air conditioners (a type of heat pump) are marked with an energy efficiency rating (generally 3 to 4), which means that one degree of electricity can handle several times the energy.
The heat pump has four advantages. The first is energy saving, which is conducive to the comprehensive utilization of energy. The second is beneficial to environmental protection. The third is the combination of heat and heat, which has a high equipment application rate and saves investment. The fourth is the electric drive, which is more convenient to regulate. Therefore, the heat pump has attracted everyone's attention and has developed rapidly in the United States and other countries in recent decades.
Application of heat pump technology in the field of printing and packaging
Printing and packaging workshops often require constant temperature and humidity. In summer, office buildings and other places also need air conditioning and refrigeration, while printing coaters need to be dried and hot air is used. If heat pump cooling is used for workshops and office buildings, and the heat generated by the other end of the heat pump is used for printing, coating and drying systems, coupled with the heat pump cooling and heating, it has several times the thermal efficiency, so that one degree of electricity is consumed on the heat pump, then Achieving the effect of carrying several times the amount of heat can greatly save electricity costs. It is a good solution for environmental protection and energy saving, and it is worth promoting vigorously.
The printing industry uses more air heat pump water heaters. The air energy heat pump system obtains a low-temperature heat source through natural energy (air heat storage). After cooling, the air is used for cooling in workshops, office buildings, and film blowing machines; the condenser emits heat to heat water for heating (supply) or supply The hot water goes to the heat exchanger of the drying system of the printing and coating machine and heats the air intake of the oven. The heat collection efficiency of the entire system is very high.
The following is a comparison of the annual operating costs and costs of heating methods commonly used in printing and packaging factories.
The lowest operating cost is the solar energy + heat pump method, which heats hot water through a solar device. The hot water flows through the heat exchanger of the printing machine, coating machine, compound machine, and aging room. The amount of hot water is used to control the drying. Dry temperature; in the absence of sunlight, the system uses hot air to provide hot water through an air heat pump. Domestic companies like Nanjing Zhaokai have many successful cases in the application of solar energy + heat pump.
Application of heat pump technology in coating machine
The heat pump technology can also be applied to the coating machine to achieve closed VOC-free and energy-saving clean production.
In the figure, 1 is the first stage of the oven, 2 is the second stage of the oven, 3 is the heat exchanger of the oven hot air and the gas condensed by the evaporator, 4 is the heat pump evaporator, 5 is the heat pump compressor, and 6 is the heat pump throttle valve. , 7 is an air pipe, and 8 is a heat pump condenser.
The solvent concentration in the front oven of the coating machine is relatively high, and a closed-type drying system is formed by filling with inert gas (such as nitrogen and carbon dioxide). The heat pump evaporator of the exhaust gas of oven 1 is cooled to precipitate the solvent (recyclable), and then heated by the compression condenser. After that, the hot air is recycled to the oven; the traditional hot air drying method is used at the rear to ensure that the residual solvent of the product does not exceed the standard. After the evaporator has cooled, the gas is exchanged with the hot air coming out of the oven in the opposite cross-flow (as shown in Figure 3). After the hot air is discharged from the oven, it is preheated and then sent to the condenser through the air pipe 7 for heating, and then returned to the coating. The last drying box n of the compound machine. The exhaust gas from the rear oven is reused in the front oven to reduce the total external exhaust volume. Using heat pump technology, the exhaust gas is cooled and condensed by the heat pump evaporator 6 to recover the solvent. The exhaust air is heated by the heat pump condenser 8 The heated higher temperature gas is sent back to the oven for recycling. This can achieve solvent-free emissions, which is both environmentally friendly and energy efficient.
Because organic solvents such as benzene, esters, and ketones are flammable and explosive, in order to increase the gas concentration before condensation, reduce energy consumption, improve the condensation effect, and ensure the safety of the production process, the oven cycle The use gas is preferably free of oxygen (or low oxygen concentration), and non-toxic and economical inert gas such as nitrogen, carbon dioxide or mixed gas can be used instead of the original air.