Abstract: there are a large number of defects in the production and application of gate valve and diaphragm valve in chemical enterprises; The viewpoint of replacing butterfly valve is put forward. Through the practical application in circulating water system, brine, recovered brine, electrolyte system and other systems, it is proved that selecting the corresponding butterfly valve as the process control valve in the above systems has incomparable advantages of stop valve and gate valve in strengthening process control, reducing material leakage and reducing operation and maintenance intensity.

Key words: butterfly valve; Material system; Application;

A plant has always used stop valves, gate valves and diaphragm valves as process control valves in industrial water, brine, recovered brine, electrolyte, lye, hydrogen, sulfuric acid, chlorine, chlorine water and other systems. With the continuous expansion of production scale and the continuous improvement of process control level, a factory has higher and higher requirements for process control valves. The stop valves, gate valves and diaphragm valves used in the above systems for many years have a direct impact on their safety, reliability, economic rationality and operability due to their own structural and material defects, so they can not meet the needs of modern production. For example, the stop valve and gate valve have the defect that the valve core is easy to fall off; The diaphragm of diaphragm valve is easy to be damaged; The valve stems of stop valves and gate valves are generally sealed with packing. The packing directly rubs with the vertically moving valve stems. If the valve is often opened and closed, the packing is easy to wear, which not only causes material leakage, but also pollutes the environment; The transmission mechanism of stop valve and gate valve is exposed. If the valve is not opened and closed frequently or maintained improperly, the gap between the valve rod and the transmission nut is easy to cause difficulty in opening and closing the valve due to the accumulation of foreign matters such as rust or dust. In order to completely solve the above problems, the technicians of a factory began to gradually select butterfly valves with different sealing pairs to replace the original stop valve, gate valve and diaphragm valve according to the characteristics of each material system, and achieved certain results.

1 advantages of butterfly valve

Compared with stop valve, gate valve and diaphragm valve, butterfly valve has the following advantages: (1) reasonable structure, convenient replacement, smaller volume and lighter weight under the condition of the same diameter（ 2) When the valve is opened and closed, the valve stem is driven by the joystick or worm gear transmission device to make the valve disc rotate 90 °, and the valve will be opened or closed accordingly; Not only the valve opens and closes quickly, but also the operation is simple and labor-saving（ 3) It has large channel flow section ratio and excellent flow characteristics（ 4) The valve can be installed at any position and is not limited by the flow direction of medium（ 5) Rotate the joystick or hand wheel to adjust the medium flow of the pipeline, and have good cutting and adjustment performance（ 6) Compared with stop valve, gate valve and diaphragm valve, the static sealing point of each valve is reduced by two points to effectively reduce the probability of valve leakage（ 7) The valve seat fixed by bolts is fully adjustable. The valve seat can be adjusted on site or the valve seat and parts in the valve seat can be replaced without special tools or removing the valve, which is convenient for daily maintenance（ 8) The transmission device is sealed inside the valve seat, which completely avoids the erosion of external corrosive gas and moisture, requires no special maintenance, and reduces the labor intensity of operators.

2. Application and effect evaluation

2.1 circulating water system

The original use of gate valve, because the valve is not often opened and closed and placed in the open air, the gap between the valve rod and the transmission nut is easy to cause difficulty in opening and closing the valve due to rust or accumulation of dust and other foreign matters, especially Φ 300、 Φ Gate valves above 400 sometimes require the cooperation of 2 ~ 3 people to open and close the valve. In addition, the valve has large volume and mass, and the cooperation of hoisting machinery is required when replacing the valve. After the butterfly valve is changed into a butyl rubber ductile iron sealing auxiliary butterfly valve, not only the valve operation and adjustment are easy and convenient, which can be completed by only one person, but also the replacement of the valve no longer requires the cooperation of hoisting machinery.

2.2 brine, recovered brine and electrolyte system

Original use Φ 100 ~ 250 specification gate valve. Due to the strong corrosivity and permeability of the system materials, the valve packing is easy to leak and salt. Even if the daily inspection and maintenance are strengthened, it can not be fundamentally solved. In addition, valve manufacturers generally use carbon steel materials to make valve core cards, so that the valve core cards are easy to be corroded by materials, resulting in valve core falling off. The inlet and outlet valves of refined salt water pump, mixed salt water pump, electrolyte preheater and other equipment in a plant have been shut down and replaced locally for a short time due to valve core falling off several times, which has brought unstable factors to safety production. After that, according to the corrosion characteristics of the system materials, the technicians selected the butyl eye rubber ductile iron sealing auxiliary butterfly valve to replace the original gate valve, and gradually popularized it, eliminating the unstable factor that the valve core is easy to fall off, and the leakage problem is also solved.

2.3 outlet valve of chlorine compressor

A factory originally used a stop valve. Although the sealing effect is good, the opening and closing time of the valve is long due to structural constraints. When the chlorine compressor was switched, the chlorine broke through the water seal due to the failure of opening and closing the outlet valve in time, resulting in a small amount of chlorine leakage. After that, the valve was changed to F4 stainless steel sealing auxiliary butterfly valve. After several years of use, the operator gave a high evaluation. It is agreed that the valve can be opened and closed easily and quickly, eliminating the chlorine leakage event that may be caused by the untimely opening and closing of the outlet valve during the switching of the chlorine compressor.

2.4 alkali liquor conveying system

When a factory delivers alkali liquor to the internal manufacturers of the company, it first uses the liquid lifter to measure, and then uses the compressed air to send the alkali hydraulically through the pipeline. The inlet and outlet valves of the liquid lifter originally used stop valves. Due to the compressed air pressure of 0.3 ~ 0.5MPa, the finished lye often leaks at the packing of the stop valve during the pressure feeding process. On the one hand, it causes the loss of finished lye, on the other hand, it also pollutes the environment. Therefore, the inlet and outlet valves of the liquid lifter were changed into nitrile ductile iron sealing auxiliary butterfly valve, and the problem of alkali liquor leakage was completely solved.

2.5 chlorine water system, sulfuric acid system and hydrogen system

Chlorine water system originally used Φ 200 polypropylene diaphragm valve. The disadvantage of the valve is that the diaphragm is easy to be damaged and the volume is huge. Change it to butterfly valve. Considering the environment of chlorine drying post and the strong corrosivity of chlorine water, f46-reinforced polypropylene sealing amplitude butterfly valve is selected, which has been in good use so far; Stainless steel core cast steel stop valve was originally used at the inlet and outlet of sulfuric acid pump. However, due to the large volume and mass of the valve, the labor intensity during operation and replacement is large. Later, a F4 stainless steel sealing auxiliary butterfly valve was tried, and the application effect was good; The inlet and outlet valves and return valves of the hydrogen pump were originally cut-off valves. The post operators reported that the operation of the original valves was time-consuming and laborious, especially in case of special events, the original valves could not meet the requirements of production control because of their slow opening and closing speed. Therefore, the technicians gradually changed the inlet and outlet valves to nitrile rubber ductile iron sealing auxiliary butterfly valves, so as to meet the needs of production control, Well received by operators.

3 benefits

Nearly 100 butterfly valves of different materials and specifications have been used in industrial water, brine, recovered brine, electrolyte, lye, hydrogen, sulfuric acid, chlorine water and other systems of a plant, which can directly or indirectly create the following benefits for a plant.

(1) Process control can be further strengthened. The butterfly valve has the advantages of rapid opening and closing, simple operation, labor saving, large channel overflow section rate and excellent flow characteristics, so it has good cutting and regulation performance. Especially for chlorine, hydrogen and other important systems, good cut-off, circulation and regulation performance ensure the long-term safe and stable operation of the main unit.

(2) Reduce material leakage and environmental pollution. After nearly 100 gate valves, globe valves and diaphragm valves were changed to butterfly valves, the static sealing points were reduced by nearly 200 points compared with those before the improvement. It not only reduces the probability of material leakage and leakage, but also provides hardware guarantee for the target cost management and on-site management of a factory to a new level. It also greatly reduces the occurrence of environmental pollution events that may be caused by material leakage, ensuring that a factory has won the honorary title of leak free factory.

(3) Reduce the labor intensity of operators and maintenance personnel. The opening and closing of butterfly valve drives the valve stem through the joystick or hand wheel, which is simple and labor-saving, and the transmission device is closed inside the valve seat without special maintenance, which greatly reduces the labor intensity of post operators compared with that before the improvement. In addition, compared with the gate valve, stop valve and diaphragm valve, the butterfly valve with the same nominal diameter is much smaller in both volume and quality, which can also reduce the labor intensity of maintenance personnel to repair and replace the valve.

In short, after several years of practical application, it has been proved that after the targeted and selective use of butterfly valves of different materials in the above systems, a factory has incomparable advantages of stop valve and gate valve in strengthening process system control, reducing material leakage, reducing environmental pollution, reducing operation and maintenance personnel labor.