Principle of energy saving and steam saving in drying section of paper machine

Whether the steam supply system of the drying section of the paper machine is reasonable has a great influence on the paper quality, steam consumption and operation management of the drying section.

This part of the paper machine is mainly designed according to the following principles:

1) It can ensure that the temperature of each part can be adjusted flexibly in order to obtain an appropriate drying temperature curve;

2) Effective use of steam to save energy;

3) It is convenient to discharge the non-condensable gas in the system in order to improve the heat transfer efficiency.

In order to meet these requirements, the method of multi-stage steam venting is generally adopted, while the method of single-stage steam venting is only reserved for some low-speed paper machines. The characteristic of the multi-stage steam ventilation system is to divide the drying cylinders of the multi-drying cylinder drying section into several groups (usually 3 to 5 groups, the number of drying cylinders is less than 20, and some are only divided into two groups), and the new steam from the boiler Generally, only the first group of drying cylinders is passed through, and the second group uses the secondary steam generated by the decompression and reboiling of the condensed water of the first group of drying cylinders, so the temperature of the second group of drying cylinders is lower than that of the first group. Likewise, the third group uses the secondary steam from the second group of dryers, and so on. Generally, the number of times the steam passes is called "segment", so it is called multi-stage steam. And because the steam is continuously flowing in the cylinder, it is also called the steam venting method with steam circulation.

The fresh steam from the boiler enters the first-stage drying cylinder before the calender, and the condensed water and uncondensed steam discharged from the drying cylinder enter the first-stage steam-water separator, and the re-boiling secondary steam and the first-stage steam The uncondensed steam enters the second stage as the heating steam of the second stage. Similarly, the uncondensed steam of the second stage and the secondary steam generated by the steam-water separator are used as the heating steam of the third stage.

The dry cloth cylinder is heated by new steam, and the secondary steam discharged from the condensed water through the steam-water separator can be mixed with the secondary steam of the first-stage steam-water separator and sent to the second-stage. If the temperature of the second stage is not enough, the inlet steam volume of the first stage can be increased, thereby increasing the amount of uncondensed steam in the first stage. You can also open the valve on the new steam line to directly add new steam. Similarly, when the temperature of the third stage is insufficient, new steam can also be directly added.

In the paper machine, in order to increase the pressure difference between each section, facilitate the circulation of steam and discharge non-condensable gas, the steam from the reboiler in the last section often enters the condenser connected with the vacuum pump, and the condensed water and the condensed water of each section are Return to the boiler together to recover its heat. The non-condensable gas is discharged by the vacuum pump.

The multi-stage steam ventilation in the paper machine can ensure that non-condensable gas does not accumulate in each drying cylinder, which is conducive to improving the heat transfer efficiency of the drying cylinder; since the temperature of each stage is different and can be adjusted, it can be determined according to the production process requirements. drying temperature curve.