Coal Chemical Industries
Coal Chemical Industries
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Coal Chemical Industries
The coal chemical industry is the industrial sector that uses coal as a raw material and converts it into solid, liquid and gaseous fuels, or other chemicals through chemical processing.
The control valve used in the coal chemical industry is subjected to a very difficult environment as multiphase flow composed of gas, liquid and solid usually flows into the control valve, in a high temperature, high pressure and high corrosion environment. Due to the particular steps that characterize the chemical process of coal, various control valves used in the production process are related to the stability and safety of production and play a fundamental role. S.
We now introduce specific analyzes on the application status of various types of key control valves, within different contexts and areas of coal chemical plants.
1. Uses and applications of valves in the coal chemical industry
Transportation of coal slurry (dust), including coal-water slurry (indirect liquefaction), coal-oil slurry (direct liquefaction), etc.
- Soot blowing system
- Waste water treatment system
- Slag discharge system
2. Characteristics of the valve control medium in the coal chemical industry
- The average temperature is high and the transport temperature can reach up to 350 ℃
- The working conditions of the gas-liquid-solid three-phase fluid are complex
- The working pressure is high and the pressure difference can reach more than 10 MPa, resulting in a high fluid flow rate
- The medium contains chloride ions, ammonia, strong corrosive media such as potassium salt, hydrogen sulfide or phosphoric acid.
3. Status quo of valves used in the coal chemical industry
The key valves of the coal chemical plant are basically based on imports. Due to the high price, short life of imported valves, the fact that the factory is far from China and the lack of timely after-sales service, the normal operation of coal chemical plants is complex. Fortunately, with the technical improvement of
domestic valve manufacturers and the increase of a large number of use performance, the location ratio of coal chemical control valves has also increased. The coal chemical plant must be shut down for maintenance every 3-6 months of operation. The key control valve is badly eroded and corroded and cannot work stably for a long period of time, thus limiting the normal operation of the device. The boiler feed water pressure of the coal chemical project is 16Mpa, and the steam produced by the boiler is basically 9.8Mpa and 540 ℃. Therefore, in the area of the boiler plant, the feed water control valve and the steam pressure reducing valve are very important and the cost is extremely high.
Boiler feed water valve
It is used to precisely control the liquid level of the steam drum. The water supply pressure is high (16Mpa) and the temperature is high (220 ℃). The coil structure can use the cage sleeve. The connection shape of the valve core and valve stem requires welding, and the shape of threads, pins and bolts is not used to prevent the valve stem and valve core from falling under high pressure erosion. The valve body material is usually WC6 or CF8M, the valve liner material is 304 or 316, and the valve stem material can be 304, 17-4PH (martensitic stainless steel, ultra high strength). If you select 304, then a force allowance of 1.5-2 times is required. The actuator can choose electric or pneumatic membrane actuator, considering the safety requirements of the control, it is necessary that the valve maintains the degree of opening in the event of an accident.
Minimum return valve of the boiler feed pump
Boiler feed pumps are often multistage pumps with degrees greater than 10, and the pressure difference between the inlet and outlet is extremely large. To ensure safe operation of the feed pump, the idle return valve is an important safety control accessory for the feed pump. Since the pressure difference is 16 MPa and the temperature is 220 ° C, the valve body and internal parts are greatly eroded, control is difficult and the price is high. In many places a pinch control valve with positioner is often used but, being difficult to control, it is often accompanied by vibration and erosion, and has a short life span. The true idle return valve is self-acting, and its core must be treated by spraying tungsten carbide. Furthermore, both the valve core and the body can be coated with the stellite alloy.
Steam pressure reducing valve
Now let’s especially consider the 9.8Mpa minus 1.0Mpa valve for which A, the CCI labyrinth sleeve pressure reducer is currently the first in the world. Although most manufacturers can also produce this type of valve and have certain performance, the key core technology is still up their sleeve. Structural and manufacturing industries. The labyrinth decompression sleeve used by CCI is still the best calculated and produced by CCI. However, the connection between the valve stem and the valve plug should also avoid pins and threads. Note that other imported brands often add grinding or noise reduction orifices to the inlet or outlet of the valve, which actually play a role in pressure reduction, but this design brings major problems. Typically, this type of valve is welded and, if the orifice plate is damaged, it will be fatal to the entire system. Also, under low load, the decompression and noise reduction effect of the orifice plate will decrease very quickly and will not play a normal role.
The area of the air separation unit consists of:
low temperature valve
oxygen valve
molecular sieve regeneration valve
Cryogenic valve
It can be produced both in China and abroad, such as Flowserve, Fisher, Yamatake, Koso, etc. The valve body and valve liner material is mainly 316.
Oxygen vent valve
Used as an emergency vent of the air separation unit after oxygen overpressure and is characterized by a large pressure difference, fast acting speed and large amount of vent (depending on the design load of the gasification). In principle, the line speed should not exceed 25 m / s (it is related to the purity and pressure of oxygen and a common value is taken here). Therefore, for the oxygen relief valve with a high pressure difference, the generally selected material is Inconel625 or Menel500, and since the valve body and internal parts are made of this type of special material, the cost of these valves is very high.
The types of valves can be:
globe
sleeve
sphere (little used due to the price)
Three rod valve for molecular sieve purification system
According to the characteristics of the molecular sieve regeneration process, the pipeline is generally thick with diameter greater than 900mm up to 1500mm), and the regeneration frequency is also high, the fluid is relatively clean, and the pressure and temperature are moderate.
The valve can be sealed individually. For such large diameter pipes, butterfly valves are usually used, possibly with triple eccentric.The three-stem valve is a butterfly valve with a special three-eccentric shape in which the rotating shaft is completely deviated from the center, similar to the structure of a robot arm.
During action, the valve plate first moves in the opposite direction to the fluid flow to separate the valve plate from its seat, then flips the plate over to overcome the friction between the plate and the valve seat. The gasification device is the most complex and is also the main device of the coal chemical industry. The valves used in this device are varied and have very strict requirements and, at the same time, it has an excellent relationship with the shape of the gasifier. Currently, gasifiers include Texaco, GSP, and four-nozzle coal and water slurry furnaces.
Coal sludge system and pulverized coal
Coal slurry is used as a control system for raw materials, coal slurry is used as transport equipment and flow regulation, and valves are used to control circulation and stoppage of coal slurry. According to the characteristics of the coal slurry, the first choice is the ball valve, the fixed two-way watertight ball, the internal parts can be selected from 316 and above, and can be hardened by nitriding and stellite alloy coating . The control system of pulverized coal as a raw material is relatively complicated and the wear effect caused by pulverized coal is more severe. Of course, based on the characteristics of the 9 types of valves, ball valves remain the first choice. We report 3 points of detail that we consider important to highlight and which also apply to the slag valve for gasification waste:
1) In the selection of the valve bearing, try to ensure the sealing effect of the bearing, so as to prevent carbon dust from entering the bearing, which will cause wear and accelerate the damage to the valve.
2) Choosing the material of the valve seat butterfly spring, it is recommended to choose high speed steel such as SKH-23.
3) When installing the valve, the actuator mounting bracket or hook should be installed to avoid the influence of too heavy implementation on the valve stem and bearing.
We recommend these 2 types of valves:
Orbital ball valve: also known as elastic ball valve. It should be noted that the orbital ball valve must consider the impact of the material on the bearing, valve stem and actuator, and the sealing must be addressed here;
Disc valve: has high performance in use but must be chosen with two way seal and it is also necessary to consider the seal of the valve stem and actuator.
Slag block valve
There are 3 slag block valves and 1 slag block valve on the drain port of the block bucket. The slag block valve adopts a sealed metal fixed ball structure, which directly participates in the program control of the block bucket system.
Synthesis valve and other devices
Valve selection of methanol synthesis and other subsequent devices basically follows the basic requirements of valve selection.
Depending on the characteristics of the process, attention should be paid to:
Use 304L or 316L for temperature and low temperature valve material selection.
For corrosive media such as hydrogen sulfide, in addition to 316L, 317L or two-phase steel can be selected.
For high toxicity or strong stimulation fluids The bellows seal type can be selected.
The production of polypropylene by the gas method requires high frequency valves and long switching times. At the moment, only a few products have good performance, so you need to pay attention to the selection.
Valves are currently basically divided into 9 categories:
1. Single seat valve
2. Double seat valve
3. Angle valve
4. Diaphragm valve
5. Ball valve
6. Throttle valve
7. Pinch valve
8. Eccentric rotary valve
9. Three-way valve
Based on the characteristics of the valve itself, the different requirements of the process and the
characteristics of the fluid, one of these valves is selected and optimized.
Of course, there are many other valves that are derived from the nine categories (such as plug valve and disc valve belong to the butterfly valve category). In addition to paying attention to the valve type and material, accessories such as actuators, positioners, air pressure relief components and valve position feedback components are also very important when selecting the valve.
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Coal Chemical Valve Guide
Which valves are coal chemical special valves?
In addition to some general valves that can be used in some coal chemical conditions, which valves are special valves for coal chemical industry? Let’s now look at the special valves for the coal chemical industry.
Wear resistant ball valve with rigid metal seal Including:
bucket lock valve
slag lock valve
ash lock valve
bleed valve
balancing valve
Black Water Control Valve
Gray Water Control Valve
High Differential Pressure Control Valve
Disc valve
Including
bucket lock valve
slag lock valve ash lock valve
bleed valve
balancing valve
Balancing valve
High temperature slag valve.
Pulverized coal control valve
Pulverized coal three-way reversal valve.
Pulverized coal switching valve
Coal water slurry shut-off valve
Oil-coal slurry shut-off valve
Gray water eccentric valve
Oxygen valve
Special ball valve for oxygen
Rigid seal pneumatic ball valve
Orbital ball valve
Gate valve
Vent control valve.
Pulse cleaning valve (reversing valve)
Special cleaning valve for ash filter.
Pneumatic eccentric ball control valve
In order to meet the energy facility adjustment needs in our country, large scale coal chemical equipment research and development has been listed as one of the top 16 technical equipment tasks we are developing in China.
The rapid development of the large-scale coal chemical industry requires the corresponding support of technical equipment, especially:
- coal-petroleum
- methanol
- synthetic ammonia
- coal-olefins
Localization of relevant technical equipment is important for reducing investment in the project, saving foreign currency and improving industrial competitiveness. Major R&D projects of large scale complete coal chemistry equipment include: large hydrogenation reactor, centrifugal pump and volumetric pump for coal liquefaction, special valve for coal liquefaction, heating furnace oil-coal slurry, large agitator for homogenizing coal slurry, large coal liquefaction, reciprocating thrust compressors and large centrifugal compressors, special boilers for waste heat, large coal preparation equipment, equipment for oil residue gasification, large natural gas hydrogen production equipment, etc.
Chemical ball valve for coal
The ball valve rotates 90 degrees and the body of the tap is a sphere with a circular through hole or a channel passing through its axis. It is mainly used to interrupt, distribute and change the flow direction of the fluid in the pipeline and it only needs to be rotated 90 degrees and a small torque can be closed tightly. Ball valves are best suited for shut-off and shut-off valves, but recent developments have also designed them to throttle and control flow.
Coal chemical gate valve
The gate valve moves in a straight line with the valve stem, which is called a lift rod gate, also called a riser rod gate. There is usually a trapezoidal thread on the lifting rod. Through the nut at the top of the valve and the guide groove on the valve body, the rotary motion is transformed into a linear motion, i.e. the operating torque is transformed into an operating thrust. When the valve is open, when the gate lift height is 1: 1 times the valve diameter, the fluid channel is completely free, but this position cannot be monitored during operation. In actual use, the apex of the valve stem is used as the sign, i.e. the position it cannot be opened, as the fully open position.
Carbon chemical butterfly valve
The opening and closing part of the butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so that the valve that can open, close or adjust is called a butterfly valve. The throttle valve is usually less than 90 degrees from fully open to fully closed. To position the butterfly plate it is necessary to install a worm gear reducer on the valve stem in which it not only makes the butterfly plate self-locking so that the butterfly plate can stop in any position, but also improves the operational performance of the valve .
Coal chemical shut-off valve
The opening and closing parts of the globe valve are plug-shaped discs, the sealing surface is flat or conical, and the disc moves linearly along the center line of the fluid. The shape of the valve stem movement includes a lifting rod type (the valve stem rises and lowers and the handwheel does not rise and fall) and there is also a type of lifting rotary rod (the handwheel rotates and rises together with the valve rod, and the nut is arranged on the valve body). The globe valve is only suitable for fully open and fully closed, no adjustments and throttling are allowed. The globe valve is a force-sealed valve, so when the valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak.
Coal chemical check valve
Depending on the structure, check valves can be divided into three types: lift check valves, swing check valves and butterfly check valves. Lift check valve can be divided into vertical and horizontal. The swing check valve is divided into three types: single-lobe, double-lobe and multi-lobe. The butterfly check valve is of the direct type. The above types of check valves can be divided into three types: threaded connection, flanged connection and welding. Large check valves must be independently supported so that they are not affected by the pressure generated by the piping system.
Coal chemical safety valve
When the pressure in the vessel exceeds a certain value, the valve opens automatically to quickly discharge a certain amount of fluid. When the pressure in the container drops to the allowable value the valve closes automatically, so that the pressure in the container is always below the upper limit of the allowable pressure and any accident or damage that may occur due to the overpressure is avoided. Therefore, the safety valve is also called the ultimate pressure vessel.
Coal chemical pressure reducing valve
The pressure reducing valve uses the opening degree of the opening and closing parts in the valve body to adjust the flow of the medium, reduces the pressure of the medium, and at the same time adjusts the opening degree of the opening and closing parts with the help of the pressure behind the valve to keep the pressure behind the valve within a certain range. Inside, and spray cooling water in the valve body or behind the valve to reduce the temperature of the medium, this kind of valve is called a pressure reducing and desuperheating valve.
The pressure reducing valve can be divided, according to the structure, into:
- film type
- spring film type
- piston type
- lever type
- bellows type
Coal chemical solenoid valve
Solenoid valve is the basic component of automation used to control fluid, it belongs to actuator; it is not limited to hydraulic and pneumatic. Solenoid valves are used to control the direction of hydraulic flow. The mechanical devices in the factory are generally controlled by hydraulic steel, so solenoid valves are used. There is a closed cavity in the solenoid valve. There are through holes in different positions. Each hole leads to a different oil pipe. There is a valve in the middle of the cavity, and two electromagnets on both sides. Which side is attracted to, by controlling the movement of the valve body to block or leak different oil discharge holes, and the oil inlet hole is normally open, the hydraulic oil will enter different oil discharge pipes, and then the oil will be pushed by the pressure of the oil. Just the piston, the piston drives the piston rod, and the piston rod drives the mechanical device to move. In this way, the mechanical movement is controlled by controlling the current of the electromagnet.
Coal chemical control valve
Control valves are used to adjust process parameters such as medium flow, pressure, temperature, and liquid level in the field of industrial automation process control. According to the control signal in the automation system, the opening of the valve is automatically adjusted, so as to realize the adjustment of the medium flow, pressure, temperature and liquid level. The regulating valve is usually composed of an electric actuator or a pneumatic actuator and a valve body. There are mainly two types of straight-through single-seat type and through-through two-seat type. The latter has the characteristics of large flow capacity, small unbalanced operation and stable operation, so it is usually especially suitable for occasions with large flow, high pressure drop and less leakage.
The main angular strokes are
- V-type electric regulating ball valve
- Electric butterfly valve
- Ventilation regulating valve
- Eccentric butterfly valve
technical requirements of the modern coal chemical industry for valve products
1. Valve material requirements
Due to the existence of oil-coal slurry in the direct coal liquefaction reaction, wear of the coal slurry on equipment materials such as valves and pipelines must be considered. It is therefore necessary that the materials used to manufacture the valves have complete properties that meet the requirements of use, namely:
1. Superior are the properties of compactness, purity and homogeneity, used to describe the intrinsic properties of materials, particularly important for thick steels (or large cross-sections).
2. To meet the requirements of chemical composition, ambient temperature and high temperature mechanical properties to meet the requirements of the design specification.
3. It should have environmental embrittlement resistance which can be used in harsh environments for a long time.
2. Valve process requirements
Direct liquefaction of coal not only has the characteristics of high temperature, high pressure and hydrogen in the hydrogenation unit, but also has the characteristics of coexisting corrosion and wear in the coal chemical industry. The foundry should strictly control the source of the raw materials, and the processed raw materials should not only be melted, but also further refined, especially the check before the kiln. Only in this way is it possible to guarantee the quality of the castings.
3. Valve Structure Requirements
The valve structure design should avoid coal slurry coking to make the valve ineffective and facilitate cleaning. Coal oil slurry has one feature: if the flow is not regular or stationary, that is, the flow conditions of the fluid are not good, it will settle and eventually polymerize, causing coke and blocking the valve.
Currently, the shut-off valves used in the direct liquefaction coal slurry pipeline are all ball valves. When the operation needs to cut the pipeline to close the ball valve, the oil-carbon slurry inside the valve ball cannot be discharged and deposited in the ball cavity, which could coke and block. The choice of ball valves, in fact, is not the most suitable choice in this working condition.
4. Valve wear requirements
The ball valve used in sewage conditions should be in the form of rigid metal seal and the material of the valve seat and the ball should be the same to ensure that the two have the same expansion coefficient and the “stuck” phenomenon of the ball will not occur in high temperature conditions. Since many valve operating conditions are difficult to open and close under high temperature conditions, the reason is asynchronous thermal expansion between the valve core and the valve body. Therefore, the manufacturer should perform a high temperature open and close test before leaving the factory because, in the actual use process, the valve heats up due to the high fluid temperature. At this point, the valve core heats up first and the outer surface of the valve slowly heats up. If the entire valve is inserted into the heat source, the valve body heats up first and the valve core heats slowly. After warming up, which is exactly the opposite of the actual working conditions, it is not possible to achieve the purpose of the test. The high temperature opening and closing test must establish a temperature gradient consistent with the actual working conditions.
The expansion rate of the coating and base material should be similar, otherwise, in the alternating process of high temperature and normal temperature or high temperature, cracks are likely to occur and the coating is more likely to peel off. For supersonic spraying (HVOF) or similar methods, the surface hardness of the coating is 64-68 HRC, and the adhesion force should not be less than 10 MPa, while for metallurgical casting or similar methods, the hardness of the coating surface it is 62-68 HRC and the adhesion strength is not less than 70 MPa. The actual thickness of the coating (excluding the transition layer) is between 0.2 and 0.5 mm.