Application of Metal Sealed Ball Valve in Drain System of Thermal Power Plant

Introduction: In order to make the normal operation of hydrophobic systems, in addition to ensure the rational design of hydrophobic systems, select the appropriate hydrophobic device is also essential.

In thermal power plant systems, the hydrophobic system is the most complex, the most messy system. Although the importance of the system is not as large as the main steam system, but the normal operation of the system is not only related to the economic power plant, but also the safety of the entire plant will have a significant impact.

1, power plant hydrophobic system characteristics and the use of the status quo trap.

1.1 The mechanism of steam and hydrophobic damage.

Steam in the transmission of the inevitable loss of heat, when it tends to saturation temperature will precipitate condensed water that is hydrophobic, especially in the steam completely stop the flow of the region, although the steam super heat, but still produce hydrophobic. The formation of hydrophobic steam pipes on the unit's safety and economy will have an impact.

On the other hand, according to Dalton's law of partial pressure, on the other hand, according to Dalton's law of partial pressure, it is easy to make the heat transfer equipmen t, If the steam mixed with hydrophobic, it will make the steam rated pressure decreases, resulting in reduced steam work capacity, the system efficiency. Therefore, timely drainage of the steam system in the drainage, not only the safety requirements of steam pipelines and equipmen t, but also the need for energy efficiency of the steam system.

1.2 Thermal power plant hydrophobic system characteristics.

Thermal power plant hydrophobic can be divided into start-up hydrophobic and regular hydrophobic parts, according to the hydrophobic system can be divided into the factory pipeline hydrophobic, thermal equipmen t, hydrophobic, boiler auxiliary equipmen t hydrophobic, turbine body within the scope of hydrophobic and prevent Steam turbine water intake system and so on.

It is well known that the hydrophobic system of thermal power plant is very complicated. In order to ensure the normal operation of the hydrophobic system, it is very important to choose the proper hydrophobic device in addition to the rational design of the system and the arrangement of pipeline according to the characteristics of each hydrophobic part.

1.3 The use of steam trap status.

At present, the thermal power plant hydrophobic devices are more automatic trap, the device can be timely and automatic discharge of the steam system in the hydrophobic and non non condensing gases. According to the role of different principles can be roughly divided into thermal dynamic type, thermal static type, mechanical type and mixed type. These four types of traps have their own advantages and disadvantages, and the scope of application, selection of hydrophobic part of the actual need to be based on the hydrophobic temperature, pressure and hydrophobic to a comprehensive selection.

The start-up hydrophobic is hydrophobic in the ignition start-up stage of the unit, because the warm water condensate is large, and the steam-water two-phase flow scouring is also very serious, therefore, the domestic unit hydrophobic device generally use large diameter and washable Y Shaped shut-off valve.

Sub critical and above parameters of the main steam pipe unit, reheat steam pipe, shaft seal steam pipe, extraction steam pipe to prevent steam turbine inlet water system used in the hydrophobic valve, are high-end valves.

At present, due to technical, design and manufacturing, metal materials and other factors, the domestic valve manufacturers in energy saving, environmental protection, security, sustainable development strategy and the international advanced enterprises there are still gaps, can not meet the requirements of the trap. Therefore, in the more demanding conditions, the import valve still occupy the dominant position in the valve market.

With the further development of metal sealing ball valve technology, metal sealing ball valve in the field of start trap area, especially in the super critical and ultra-super critical unit, with the steam trap working parameters, metal seal ball valve superiority More obvious.

2 metal seal ball valve characteristics and application.

2.1 Ball valve characteristics.

Ball valve is widely used in industrial valves, it has a small fluid resistance, simple structure, reliable sealing, wide application and flexible operation and so on. However, due to the common ball valve commonly used soft seal, the use of temperature is limited (less than 200), which limits the ball valve in thermal power plants (especially high temperature, high pressure hydrophobic system) applications.

In recent years, with the ball valve technology, developed for higher temperature of the metal sealing ball valve, greatly expanding the ball valve in the thermal power plant applications.

2.2 The characteristics of metal sealing ball valve and its application.

2.2.1 Features of conventional metal-sealed ball valves.

For thermal power plant traps, metal seal ball valve gradually replace the traditional cut-off valve has become an inevitable trend, which is sealed by the metal ball valve compared to the advantages of traditional cut-off valve determined. The imported hydrophobic ball valve is made of Inconel as spheroidal material and sprayed with chrome carbide coating. It is characterized by high temperature resistance, corrosion resistance, erosion resistance, thermal shock and frequent operation. It is suitable for the drainage, Boiler exhaust, row row row, steam drum exhaust, super heater exhaust and hydrophobic, soot blower isolation, insulation and steam turbine insulation, hydrophobic main steam, exhaust hydrophobic, reheat hydrophobic, a steam isolation, two Sub-steam isolation and other conditions used. Metal sealing ball valve in the sealing performance, erosion resistance, noise and maintenance methods, and many other aspects of the cut-off valve has a greater advantage than the traditional.

To the requirements of the media, for example, cut-off valve requires the flow of pure media, can not contain impurities, which is put into operation many of the current power plant is not long on the main reason for leakage of imported hydrophobic cut-off valve. In the installation and maintenance of power plants will inevitably be retained in the steam pipe welding slag, iron oxide, metal particles and other debris, when these metal debris through the cut-off valve, the stop valve spool will bring greater impact and Wear, and then cause a leak, the valve will be serious and the valve seat on the Division too Li alloy washed out, this time the valve core can not be grinding maintenance, can only be replaced. The metal sealing ball valve has a self-cleaning function, allowing the valve to flow through the media containing impurities particles.

2.2.2 Characteristics and application of the new type metal seal ball valve.

With the development of science and technology, metal sealing ball valve technology is also innovative, early ball valve technology has been unable to meet the requirements of the current harsh conditions, and gradually be eliminated. In 2009, the US metal seal square hole ball valve into the Chinese valve market, the ball valve using the latest patent technology and metal surface hardening surface treatment technology (especially nano coating process), enhanced metal sealing ball valve in the higher demand and more Harsh conditions of application ability. Square-hole metal sealing ball valve is a major innovation of the existing round hole metal sealing ball valve, the hole of the crescent-shaped cross-section into a square square large cross-section.

At present, the new ball valve has been used in many domestic power plant hydrophobic system, for users to solve the high temperature, high pressure drainage conditions of leakage and leakage problems, reducing the maintenance workload, reduce costs, reduce heat loss, Improve the economic efficiency.

3 Conclusion.

Thermal power plant hydrophobic system is a very complex system, the entire power plant economic, safe operation has a great impact, it is necessary to ensure the normal operation of the system. In order to make the hydrophobic system run normally, besides the rational design of the system and arrangement of pipelines according to the characteristics of each hydrophobic part, the hydrophobic device should be selecte d rationally. Metal sealing ball valve than traditional valve in sealing performance, erosion resistance, noise and maintenance methods have advantages, especially the new metal seal side hole ball valve, metal seal ball valve will replace the traditional cut-off valve to become a trend.