Special workers must see! New "Attitude" of Slag Slurry Treatment in Acetylene Preparation

Chlor-alkali chemical industry is the most basic technology in chemical industry, which is widely used in chemical industry, light industry, textile, metallurgy, public utilities and other fields.

Chlor-alkali industry is mainly the industrial production of caustic soda, chlorine and hydrogen by dissolving electrolytic salt solution, and it is one of the important basic chemical industries in China at present. PVC is the core downstream product, and acetylene preparation section is the most basic part of its three core sections, and 70% of our country generally adopts calcium carbide method.

For the shut-off and adjustment of carbide slag slurry medium, ordinary metal materials or plastic-lined valves can no longer meet the site requirements, and long-term replacement and maintenance can not ensure the safe and stable operation of the process. Imported ceramic ball valves can solve this kind of problem well.

Brief introduction of acetylene section process

After the calcium carbide qualified by the calcium carbide crushing system is sent to the calcium carbide finished product storage tank, it is conveyed to the calcium carbide hopper through the inclined screw, and is continuously added to the generator through the electromagnetic vibration feeder, so that the calcium carbide reacts when it meets water. The solid content of calcium carbide slag slurry by-product of hydrolysis reaction is about 10%, and the temperature is about 75℃. Overflow to the slurry buffer tank through the closed pipeline, and the pressure is 1 ~ 3 k Pa.

The crude acetylene gas generated by hydrolysis reaction escapes from the top of the generator, enters the spray cooling tower after passing through the spray precooler and positive water seal, and then enters the gas holder through the packing cooling tower, or is compressed by the compressor for gas-liquid separation and acetylene purification.

The process is shown in figure 1:

Figure 1 Process Flow of Acetylene Workshop

Medium characteristic

The main component of calcium carbide slag slurry is calcium hydroxide, and the main components are shown in the table.

Its solubility in water is small, and with the decrease of temperature, solid calcium hydroxide particles gradually precipitate from the solution and become a dilute paste with poor fluidity. In addition, solid impurities (such as ferrosilicon, sand, coke, etc. ) What does not participate in the reaction in calcium carbide is also mixed in the slurry, which makes the slurry easy to generate hardened solid mixture and block valves or pipelines. The ferrosilicon, sand, coke and other substances contained in it have large particle size and high hardness.

Therefore, there are many problems in selecting valves according to the special conditions of the medium.

Main components of carbide slag slurry

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Application status of ball valve in carbide slag slurry level

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Technical problems 1 media factors

Due to the strong alkalinity of slag slurry, long-term use of carbide slag slurry causes corrosion to the valve core, which leads to valve core failure. In addition, the valve is frequently opened and closed, the corrosion and wear of the medium to the valve are very serious, and the valve often leaks or is not tightly closed, which seriously affects the stable operation of the working condition.

The valve has been corroded by calcium carbide slag slurry for a long time, which leads to the inflexible rotation of the valve core and the failure to close it in time in an emergency, which may cause the danger of emptying. In addition, carbide slag slurry contains a large number of incompletely reacted ferrosilicon and calcium carbide, which is easy to damage the valve core of ball valve, inconvenient to maintain and easy to cause internal leakage in subsequent maintenance work.

The operating frequency of the valve at the position of carbide slag slurry in acetylene section changes greatly. Some positions are possible? 1? It has been closed or opened for several months, or even longer without operation.

On the contrary, some locations have to be opened and closed several times per hour.

And some flow control valves, the switch position of the valve often changes, even every minute. Valves with frequent actions reduce the possibility of failure caused by dirt and deposits, but they are easy to wear.

The valves in this position are mostly made of surface spraying or special metal materials, but the regulating valve in the position of carbide slag slurry is in the process of adjustment? ,? The change of flow passage changes the fluid in the valve? ,? Is the velocity of the medium higher than that in the pipeline connected with it? ,? Is the valve core in a seriously worn working environment? ,? Coupled with the corrosiveness of mud, valves made of these materials usually cannot be used for a long time.

Economic issues 1

Maintenance cost In the production process of chlor-alkali industry, the consumption cost of valves accounts for a part of the product cost, and the funds occupied by valve reserves usually account for a large part of the total working capital of enterprises.

Due to the harsh working environment of carbide slag slurry in acetylene workshop, the valve replacement frequency is very high, which is extremely unfavorable to the safe operation and maintenance cost control of the whole set of equipment, and the potential emergency shutdown accident is extremely dangerous and costly.

Ceramic ball valve solution

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Ceramic ball valve can not only make the industrial pipeline system smoother and better in sealing performance, but also make the supporting equipment operation system safer and more stable, which will play a very positive role in promoting environmental protection, energy saving and emission reduction.

In the 2 1 century with rapid technological innovation, practitioners at home and abroad have gradually turned their attention to ceramic valves, and their application fields have gradually expanded.

Material characteristics of ceramic valves

With the development of science and technology, especially the development of energy and aerospace technology, materials need to be used in harsh environments, and the requirements for high temperature resistance, corrosion resistance and wear resistance of materials are becoming more and more strict.

Ceramic materials have excellent characteristics such as high strength, high hardness, high wear and corrosion resistance, low expansion coefficient, light weight and so on. They are widely used in various fields and play an increasingly important role.

The table shows the comparison of basic properties between ceramic materials and steel materials.

? Comparison of basic properties between ceramic materials and steel materials

1 hardness

Ceramic materials are brittle materials. When measuring hardness, pseudoplastic deformation caused by combined damage such as compression and shear will occur in the compression zone of the indenter, so the hardness of ceramic materials is difficult to directly correspond to the strength, but high hardness and good wear resistance are one of the main excellent characteristics of ceramic materials.

Mohs hardness is a scoring method, which is generally suitable for ceramics and mineral materials. Only the order of hardness from big to small can be expressed. The material with high order can cut the surface of the material with low order, but the specific hardness value cannot be given. The early standard classified Mohs hardness as 10, while the new standard classified it as 15, as shown in the table.

2 Fracture toughness

The fracture mode of ceramics is brittle fracture, so the crack sensitivity of ceramic materials is very strong Based on this characteristic of ceramics, fracture mechanical properties are an important index to evaluate the mechanical properties of ceramic materials, and fracture toughness (KIC) is the most commonly used parameter to evaluate the fracture mechanical properties of ceramic materials.

In order to give full play to the particularity of ceramics and expand its practical application, we must find ways to greatly improve and improve the toughness of ceramics. The table below shows the toughness values of ceramic materials.

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Structural characteristics of ceramic valves

The acetylene section of chlor-alkali industry needs a large number of valves. As long as we know the characteristics of the process, choose the valve type reasonably according to the characteristics of each system of the device, solve the problem of valve structure design and choose the appropriate material, we can improve its wear resistance and corrosion resistance, prolong the service life of the equipment and ensure the stable operation of the process.

O-type stop valve

V regulating valve

The regulating valve mostly adopts imported V-ball valve, which is composed of actuator and V-valve body.

The interior of the valve is made of special ceramics. There is a shear effect between the V-shaped open ball and the valve seat. When the medium contains fibers or solid particles, the sphere will not be stuck, and good sealing and adjustability can still be guaranteed.

The flow characteristics of V-ball valve are equal percentage flow characteristics, and the flow changes little when the opening is small, which can ensure the accuracy of adjustment and the stability of valve work.

Special ceramics have strong wear resistance, and the flow passage is also lined with special ceramics, which can prevent the direct erosion of fluid and prolong the service life of the valve.

At present, the commonly used brands of imported ceramic ball valves are: cera system under Samson, flowserve in the United States, masonielian under GE in the United States, metso in Finland and SSZ in the United States.

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Corrosion and wear

Imported structural ceramics have good chemical stability, hardly react with strong acid and alkali, high hardness, and can resist the wear of high-hardness granular media.

These excellent chemical and physical characteristics ensure that the imported ceramic ball valve can not only effectively resist strong corrosion, but also keep the internal structure of the valve from being damaged by wear, resulting in valve switch failure and internal leakage. ?

Short service life

The service life of imported ceramic valves can reach 6~8 times of that of metal valves, which reduces the number of on-site shutdowns and valve replacement, not only improves production efficiency, but also reduces the number and cost of manual maintenance, effectively prolonging the service life of valves.

High maintenance cost

Imported ceramic valves are made of imported structural ceramic materials, which improves the wear resistance, corrosion resistance and sealing performance of valve products and greatly prolongs the service life of valves.

The use of imported ceramic valves can greatly reduce the number of on-site maintenance and replacement, improve the safety and stability of supporting equipment operation system, and save equipment maintenance costs.