Energy-saving and steam-saving in the dryer section of the paper machine-Jinling Paper Machine
Whether the steam supply system of the drying section is reasonable has a great impact on the quality of the paper, steam consumption and operation management of the drying section.
This part is designed based on 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 and energy saving;
3) It is convenient to discharge the non-condensable gas in the system to improve the heat transfer efficiency.
In order to meet these requirements, the multi-stage steaming method is generally adopted, while the single-stage steaming method is only reserved for some low-speed paper machines.
The characteristic of the multi-stage ventilation system is to divide the drying cylinders of the drying section of the multi-drying cylinder into several groups (generally 3 to 5 groups, and some with less than 20 drying cylinders, 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. Therefore, 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 is called "stage", so it is called multi-stage steam.
Because the steam flows continuously in the cylinder, it is also called the steaming method with steam circulation.
Multi-stage steam dryer, the number of drying cylinders in each section can be arranged according to the following ratio: three stages, 1:2:4, or 1:3:6. Four paragraphs, 1:2:4:6. The more one is the first paragraph, and the lower one is in turn.
The fresh steam from the boiler enters the first dryer section before the calender. The condensed water and uncondensed steam discharged from the dryer section enters a steam-water separator, where the reboiled secondary steam and the first section The uncondensed steam enters the second stage as the heating steam of the second stage.
Similarly, the second-stage uncondensed steam and the secondary steam produced by the steam-water separator are used as the third-stage heating steam.
The dry cloth cylinder is heated by fresh steam, and the secondary steam discharged from the condensed water through the steam-water separator can be mixed with the second steam from the first-stage steam-water separator and sent to the second stage. The new vapor pressure of the three-stage steam is 0.3~0.8MPa (3~8kg/cm2), and the exhaust gas pressure after the third stage is 0.02~0.8MPa (0.2~0.8kg/cm2).
If the temperature of the second stage is not enough, the steam intake 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 add new steam. Similarly, when the temperature in the third stage is insufficient, fresh steam can also be directly added.
In order to increase the pressure difference between the sections, facilitate the circulation of steam and discharge the non-condensable gas, the steam from the reboiler often enters the condenser connected to the vacuum pump, and the condensed water and the condensed water in each section are returned to the boiler together. Recover its heat. The non-condensable gas is discharged by the vacuum pump.
Multi-stage steaming can ensure that no non-condensable gas accumulates in each drying cylinder, which is beneficial to improve the heat transfer efficiency of the drying cylinder; because the temperature of each section is different and can be adjusted, a reasonable drying temperature can be determined according to the requirements of the production process curve;