The application of Steam Trap Ball Valves in the Steam trap System of Thermal Power plants

To ensure the normal operation of the drainage system, in addition to guaranteeing a reasonable design of the drainage system, choosing the appropriate drainage device is also of vital importance.

Among the various systems in a thermal power plant, the drainage system is a complex and disordered one. Although the importance of this system is not as great as that of large systems such as the main steam, whether this system operates normally or not not only relates to the economy of the entire power plant, but also has a significant impact on the safety of the entire power plant.

Characteristics of the steam trap system in power plants and the current usage status of steam traps

The generation mechanism and hazards of steam hydrophobic

Steam inevitably loses heat during transmission. When it approaches the saturation temperature, condensate water, also known as hydrophobic water, will precipitate. Especially in areas where steam completely stops flowing, even though steam has superheat, hydrophobic water will still be produced. The condensate formed in the steam pipeline will have an impact on both the safety and economy of the unit.

On the one hand, the steam trap in the pipeline is the root cause of water shock and water hammer, posing a safety hazard to the equipment. The steam trap conveys impurities in the steam pipeline, which can easily lead to scaling of heat exchange equipment. On the other hand, according to Dalton's partial pressure law, if the steam is mixed with hydrophobic water, the rated pressure of the steam will decrease, resulting in a decline in the steam's working capacity and a decrease in the system's efficiency. Therefore, promptly draining the condensate from the steam system is not only a safety requirement for steam pipelines and equipment, but also a need for energy conservation and efficiency improvement in the steam system.

2. Characteristics of the drainage system in thermal power plants

Drainage in thermal power plants can be divided into two parts: start-up drainage and regular drainage. According to the system where the drainage is located, it can be further classified into drainage of internal pipelines, drainage of thermal equipment, drainage of boiler auxiliary equipment, drainage within the scope of the turbine body, and drainage systems to prevent water from entering the turbine, etc.

It is well known that the drainage system of thermal power plants is very complex. To ensure the normal operation of the drainage system, in addition to rationally designing the system and arranging pipelines according to the characteristics of each drainage part, choosing the appropriate drainage device is also of vital importance.

3. The current usage status of steam traps

At present, automatic steam traps are widely used in the steam drainage devices of thermal power plants. These devices can promptly and automatically discharge the condensate and non-condensable gases from the steam system. Steam traps can be roughly classified into thermodynamic type, thermostatic type, mechanical type and mixed type according to their different working principles. These four types of steam traps all have their own advantages, disadvantages and applicable scopes. When selecting, a comprehensive choice should be made based on the actual steam trap temperature, pressure and water volume of the actual steam trap part.

Start-up drainage is carried out during the ignition and start-up stage of the unit. Due to the large amount of condensate in the warm pipe and the severe scouring of the steam-water two-phase flow, the drainage devices of domestic units currently generally adopt large-diameter and erosion-resistant Y-shaped stop valves.

The steam trap valves used in the main steam pipeline, reheat steam pipeline, shaft seal steam pipeline, extraction pipeline and other systems to prevent water intake and drainage of the steam turbine for subcritical and above-parameter units all belong to high-end valves.

At present, due to the constraints of factors such as technology, design and manufacturing, and metal materials, domestic valve manufacturing enterprises in China still lag behind international advanced enterprises in terms of energy conservation, environmental protection, safety and sustainable development strategies, and are unable to produce steam traps that meet the requirements. Therefore, under more demanding working conditions, imported valves still dominate the valve market.

With the further development of metal-sealed ball valve technology, metal-sealed ball valves have begun to gain a foothold in the field of start-up steam traps, especially in supercritical and ultra-supercritical units. As the working parameters of steam traps increase, the advantages of metal-sealed ball valves become increasingly prominent.