Natural Circulation Drum Boiler: Adjust the circulation loop design to cope with the circulation ratio requirements under different operating conditions

1. The basic principle of natural circulation drum boiler
The working principle of Natural Circulation Drum Boiler is based on the natural circulation formed by the difference in density between steam and water. In the boiler, the feed water enters the water-cooled wall tubes at the bottom of the furnace through the downcomer, absorbs the heat in the furnace and becomes a steam-water mixture, and then rises to the drum. In the drum, the steam-water mixture is separated from the steam and water, and the steam is sent to the superheater for further heating, while the separated water returns to the downcomer to form a cycle. This circulation method does not require external power, so it is called natural circulation.

2. Challenges and adjustments in circulation loop design
The circulation loop design of Natural Circulation Drum Boiler is the key to ensuring the stable operation of the boiler. The design of the circulation loop not only affects the thermal efficiency of the boiler, but is also directly related to the circulation ratio requirements of the boiler under different operating conditions. The circulation ratio refers to the proportion of steam in the circulating water, which directly reflects the steam-water circulation state of the boiler.

1. Challenges in circulation loop design
In Natural Circulation Drum Boiler, the design of the circulation loop faces many challenges. On the one hand, the change of boiler load will cause the change of steam-water circulation state, thus affecting the circulation ratio. On the other hand, the working pressure and temperature of the boiler will also affect the density difference of steam and water, which in turn affects the driving force of natural circulation. Therefore, how to design a reasonable circulation loop to adapt to the changing operating conditions has become a difficult problem in boiler design.

2. Adjust the circulation loop design to meet the challenges
In order to meet the above challenges, the circulation loop design of Natural Circulation Drum Boiler needs to be adjusted accordingly. The flow characteristics of the circulation loop can be improved by optimizing the diameter, length and layout of the downcomer and the riser. For example, increasing the diameter of the downcomer can reduce the flow resistance and increase the flow rate of the circulating water; while optimizing the layout of the riser can increase the rising speed of the steam-water mixture and enhance the circulation driving force.

The circulation ratio can be further adjusted by setting a steam-water separation and recirculation device in the circulation loop. The steam-water separation device can effectively separate steam and water to avoid excessive water in the steam, which affects the thermal efficiency of the boiler. The recirculation device can return part of the steam-water mixture to the downcomer to increase the flow rate and flow rate of the circulating water, thereby adjusting the circulation ratio.

3. How does the natural circulation drum boiler cope with the circulation ratio requirements under different operating conditions
During the operation of the Natural Circulation Drum Boiler, the requirements for the circulation ratio under different operating conditions are different. Therefore, the boiler needs to take corresponding measures to cope with these changes.

1. Countermeasures when the load changes
When the boiler load increases, the flow rate and flow rate of the steam-water circulation will increase accordingly. In order to maintain the stability of the circulation ratio, it can be dealt with by increasing the feed water and increasing the flow rate of the circulating water. At the same time, the working state of the steam-water separation device can also be adjusted to ensure that the dryness of the steam meets the requirements.

When the boiler load decreases, the flow rate and flow rate of the steam-water circulation will decrease accordingly. At this time, the circulation ratio can be kept stable by reducing the feed water and reducing the flow rate of the circulating water. At the same time, it is also necessary to prevent the steam-water mixture from stagnating or backflowing in the downcomer to avoid affecting the safe operation of the boiler.

2. Countermeasures when pressure and temperature change
The working pressure and temperature of the boiler will also affect the density difference between steam and water and the circulation driving force. When the boiler pressure increases, the density difference between steam and water decreases, and the circulation driving force decreases. At this time, the circulation ratio can be kept stable by adjusting the working state of the steam-water separation device and the recirculation device. At the same time, the circulation driving force can also be improved by optimizing the design of the circulation loop.

When the boiler temperature increases, the physical properties of the steam-water mixture will change, thus affecting the circulation ratio. At this time, it is necessary to pay close attention to the flow state and separation effect of the steam-water mixture, and timely adjust the operating parameters of the boiler and the working state of the steam-water separation device to keep the circulation ratio stable.