Energy saving and steam saving in drying section of paper machine

Paper machine Whether the steam supply system of the dryer section is reasonable or not has a great influence on the paper quality, steam consumption and operation management of the dryer section.

This part is mainly designed according to the following principles:

1) It can ensure that the temperature of each part can be adjusted flexibly so as 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, and the method of single-stage steam venting is only reserved for some low-speed paper machines.

The feature of the multi-stage steam venting system is that the drying cylinders of the multi-drying cylinder drying section are divided 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.

Similarly, the third group uses the secondary steam from the second group of dryers, and so on.

Generally, the number of times the steam passes through is called "segment", so it is called multi-stage steam.

And because the steam flows continuously in the cylinder, it is also called the steam circulation method with steam circulation.

For multi-stage steam-vented drying cylinders, the number of drying cylinders in each section can be arranged in the following proportions: three sections, 1:2:4, or 1:3:6. Four paragraphs, 1:2:4:6. The one with the most number is the first paragraph, and it goes down in order.

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 in the second stage and the secondary steam produced by the steam-water separator are used as the heating steam in 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. The new steam pressure of the three-stage steam opening is 0.3~0.8MPa (3~8kg/cm2), while the exhaust gas pressure after the third stage is 0.02~0.8MPa (0.2~0.8kg/cm2).

Paper machine 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 pipeline to directly replenish the new steam. Similarly, when the temperature of the third stage is insufficient, new steam can also be directly added.

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 often enters the condenser connected with the vacuum pump, and the condensed water and the condensed water of each section are returned to the boiler together, to recover its heat. The non-condensable gas is discharged by the vacuum pump.

Paper machine Multi-stage steam ventilation 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 section is different and can be adjusted, a reasonable drying temperature can be determined according to the production process requirements. curve;