After the paper is dried, there will be hot and humid air, producing a lot of heat.Although it is said that the waste heat is recovered by the heat recovery device and then discharged to the external environment, it still can not solve the discharge of high temperature. Therefore, many people are trying to recover the waste heat from waste water and waste paper. because they can not find a suitable place for application, a large part of the waste heat of the paper mill is wasted.
Typical waste heat recovery methods in paper mills at present.
1. Waste heat recovery from exhaust air of airtight cover in drying part of paper machine.
Generally, it is a two-stage recovery, the air intake of the air cover is preheated by the gas heat exchanger, and the clear water of the paper mill is heated by the steam-water heat exchanger.
two. Waste heat recovery of hot air / infrared dryer of coating machine.
After the paper is dried by the hot air dryer of the coating machine, the exhaust air temperature of the hot air dryer is about 325 ℃, and the humidity is about 300--350g/kg dry air. After the air is preheated by the gas / gas heat exchanger, the temperature is still as high as 200ml 250 ℃, which contains a lot of heat energy.
3. Recovery of waste heat from Yanke hood of toilet paper machine.
After the fresh air is preheated by the heat exchanger, the exhaust air temperature is often as high as 230C, the humidity is about 300--500g/kg dry air, and the hot taste is medium. The recovered heat usually provides heat for the ventilation of the plant, but only a small part of the heat can be used, and most of the energy can be emptied directly.
Analysis of existing hot air recovery.
The above schemes use exhaust air waste heat to preheat process air and process water through gas / gas heat exchanger and gas / water heat exchanger. In short, exhaust air waste heat is used as a heat source to heat the medium.
Such as coating machine hot air dryer exhaust air waste heat, toilet paper machine Yang Ke cylinder hot air dryer exhaust air waste heat and so on, although the quantity is large, but the taste is not too high, at present, the demand has not been found in the paper mill, so it has to be distributed to the environment.
The technology of optimizing the scheme.
The cooling capacity is generally cooled by the compressor and converted by electric energy. As far as cooling capacity is concerned, it can also be cooled by absorption, which is converted by heat energy. In terms of energy utilization efficiency, the efficiency of heat conversion is higher than that of electric energy conversion, and there happens to be a large number of medium and low quality waste heat in the paper factory that has not yet found a suitable use. this part of the waste heat can be used to convert into cold energy through lithium bromide refrigeration technology, thus saving high-grade electric energy.
There are two main types of cold places in the paper mill: air conditioning system, process low temperature water system (mainly sizing or coating workstations and other cold equipment).
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 the improvement of people's working environment.
two. Cryogenic water system.
In paper mills, the use of low-temperature water is very small, generally speaking, paper machines equipped with sizing or coating need to use low-temperature frozen water. It mainly includes: paint preparation workshop frozen water system, paint workstation bucket slot interlayer frozen water supply system (working station feed tank), coating machine coating head sandwich frozen water supply system, because the coating preparation system and coating machine are two different systems, provided by different suppliers, the general paper factory has more than two sets of compression refrigeration system, which not only consumes a lot of electricity but also invests heavily.
The method of recovering waste heat in this scheme is as follows: first, the hot air is converted into hot water at a certain temperature (generally above 85 ℃) through heat exchange equipment, such as heat pipe, and then the hot water is put into the lithium bromide refrigeration equipment to recover the waste heat that can be used in the hot water. partially or completely replace the currently used compression refrigeration equipment to produce low-temperature water for air conditioning and process use, so as to save a lot of electricity.
Economic benefit analysis.
1. Calculation of cooling capacity of exhaust air waste heat in hot air dryer of coating paper machine.
Through the calculation, it is known that in the exhaust heat of the hot air dryer of a coating machine, the heat that can be recovered per hour is 7994836.9kJ / h. If these heat are used for refrigeration, the cooling capacity is 1776.6kW (6395869.5kJ/h).
two. Calculation of exhaust waste heat cooling capacity of hot air dryer of toilet paper machine.
Through the calculation, it is known that in the exhaust heat of the hot air cover of the Yangke cylinder of this toilet paper machine, the heat that can be recovered per hour is 10734377.5 kJ / h. if these heat are used for cooling, the cooling capacity is 2385.4kW (8587502kJ/h).
Like this waste heat recovery method, for the currently operating paper mills, it can be used in conjunction with the refrigeration system, so that electricity consumption can be greatly reduced. For the new type of paper mill, it can also save a lot of investment costs. Not only that, in winter, it can also be used as a heat source to bring more benefits to the paper mill.