The hot and humid air after the drying paper contains a lot of heat energy, although this heat energy will go through the heat recovery device to recover the waste heat, but even after this discharge to the external environment, the emission temperature will be very high. Although people are also trying to recover these waste heat, but because of the low economic efficiency of these energy recovery, it is not possible to find a place to recycle in the paper mill, so a large part of the waste heat of the paper mill is wasted.

1. Paper machine drying part closed air hood exhaust exhaust waste heat recovery

Generally, it is two-stage recovery, preheating the air inlet to the gas hood and heating the water to the paper mill.

2. Coater hot air/infrared dryer waste heat recovery

After the hot air dryer of the coating machine dries the paper, the exhaust temperature of the hot air dryer is about 325 ° C, and the humidity is about 300 ~ 350g/kg of dry air. After the air/gas heat exchanger preheats the air, the temperature is still as high as 200 ~ 250 ° C, containing a lot of heat energy.

3. Waste heat recovery of toilet paper machine Jonker dryer hot air dryer

Toilet paper machine Yanke cylinder hot air drying system exhaust air, through the heat exchanger to preheat the fresh air, exhaust temperature is often as high as 230℃ above, humidity of about 300 ~ 500g/kg dry air, heat taste medium. The recovered heat usually provides heat for the ventilation of the building, but only a small part of it can be used in this way, and most of the energy is directly drained.

The above schemes are the use of exhaust exhaust waste heat through the gas/gas heat exchanger, gas/water heat exchanger to process wind, process water preheating, in short, the use of exhaust exhaust waste heat as a heat source to heat the medium. Such as coater hot air dryer exhaust waste heat, toilet paper machine Yanke cylinder hot air dryer exhaust waste heat, although the number is large, but the taste is not too high, at present in the paper factory has not found the demand, had to distribute to the environment.

The cooling capacity is generally cooled by a compressor and converted from electrical energy. For the cold capacity, it can also be absorption refrigeration, which is converted by heat energy. From the efficiency of energy utilization, the conversion of heat energy is more efficient than the conversion of electric energy, and there happens to be a large number of low-quality waste heat in the paper mill, which has not yet found the right use, and this part of the waste heat can be used to convert into cold through lithium bromide refrigeration technology, so as to save high-grade electrical energy. There are two main types of places that need to be cooled in the paper mill: air conditioning systems, process low temperature water systems (mainly sizing or coating workstations and other equipment that needs to be cooled).

1. Air conditioning system

Almost all modern paper mills need to use air conditioning to ensure the safe operation of electrical equipment and to meet people's improvement of the working environment.

2. Low temperature water system

The use of low warm water in the paper mill is very small, in general, equipped with sizing or coating paper machines need to use low temperature chilled water. It mainly includes: the chilled water system of the coating preparation workshop, the working station feed tank, and the chilled water supply system of the coating head interlayer of the coating machine. Because the coating preparation system and the coating machine are two different systems, provided by different suppliers, the general paper mill has more than two sets of compression refrigeration systems, which not only consumes a lot of electricity but also a huge investment.

The method of recovery of waste heat in this scheme: first, the hot air is converted into hot water at a certain temperature (generally above 85℃) through the heat exchange equipment, such as heat pipes, and then the hot water is passed into the lithium bromide refrigeration equipment to recover the waste heat that can be used in the hot water, partially or completely replace the current compression refrigeration device, and produce low temperature water for air conditioning and process use, thus saving a lot of power.

1. Calculation of cooling capacity of exhaust air of hot air dryer of coated paper machine

Through calculation, it can be seen that in the exhaust heat of the hot air dryer of a coating machine, the heat can be recovered per hour is 7994836.9kJ/h, and the cooling capacity is 1776.6kW (6395869.5kJ/h) if these heat are used for refrigeration.

2. Calculation of cooling capacity of exhaust air and residual heat in hot air dryer of toilet paper machine

Through calculation, it can be seen that in the waste heat of Yanke air hood exhaust of this sanitary paper machine, the heat can be recovered per hour is 10734377.5kJ/h, and if these heat is used for refrigeration, the cooling capacity is 2385.4kW (8587502kJ/h).

This method of waste heat recovery can be combined with the existing refrigeration system for the paper mill, which greatly reduces the electricity consumption. For the new paper mill, it can also save the investment in electric refrigeration equipment, and at the same time, it can also provide cold source for factories with living facilities (such as canteens, dormitories, guest houses), saving the investment and operating costs of air conditioning systems. At the same time, in winter, when the demand for cold capacity is reduced, the hot water produced by this system can also be used as a heat source to heat pulp, process water, domestic water, etc., and can also be used to ventilate and heat the plant boiler and even to preheat the furnace air.