coal water slurry gasification unit:Multi-nozzle opposite type coal water slurry gasification plant

Valve design and selection of coal water slurry gasification unit (HY-industry technical centre)

coal water slurry gasification unit:Multi-nozzle opposite type coal water slurry gasification plantCoal water slurry gasification technology is one of the most advanced entrained bed coal gasification technologies in the world. It will provide key technologies for the development of coal liquefaction, integrated gasification combined cycle power generation (IGCC), and coal-based polygeneration technology in China’s coal chemical industry , Will greatly promote the development of China’s coal chemical technology and advance the technological progress of related industries. In the production and operation control process, the control valve plays a very important role. It is aimed at high temperature, high pressure, flammable and explosive, violent reaction, and slag gasification. For special conditions such as scouring, select appropriate, high-quality oxygen, coal slurry, and slag control valves for production operations and interlocking control processes to achieve safe and stable control of temperature, pressure, and flow rate process operating conditions.

Combustion pressure in the gasifier is 4.0~6.3MPa and the temperature is 1100~1300℃. It is a high-temperature and high-pressure combustion tank. It is a highly dangerous device. Once an accident occurs, the consequences are unimaginable, so its safety and reliability are the top priority; In order to maintain the normal combustion state, it is required that the injected coal water slurry flow rate and the mixed oxygen flow rate must match. Otherwise, the pulverized coal may be incompletely burned or useless gas may be generated, and an explosion may occur when the oxygen is excessive. Therefore, the automatic control system is required. The control accuracy is high and the stability is good; third, the gasifier is a continuous working device and must have a fairly long service period. Due to the above characteristics of the gasification furnace device, correspondingly many technical requirements have been put forward for its auxiliary equipment and related control instrument industry. The control valve directly controls the production medium and must have a special structure suitable for use in the gas chemical industry. For several typical controls The valve is introduced as follows.

1. Oxygen shut-off valve and oxygen flow control valve of Coal water slurry gasification unit

  • coal water slurry gasification unit:Inconel 625 CL1500 DN50 high temperature oxygen valveGasifier burns at high pressure and high speed, and a large amount of oxygen enters. In order to ensure the normal combustion state and ensure the safety of the gasifier, the flow of oxygen must be strictly regulated and controlled, and the oxygen can be cut off quickly and without leakage. The requirements for each function are very high, so three control valves are usually used to complete them, namely the oxygen flow control valve, the oxygen shut-off valve, and the oxygen vent valve, collectively called the oxygen valve. Compared with general industrial process control valves, there are several special requirements for oxygen valves for gasifiers:

  • High pressure difference: The closing pressure difference of the oxygen shut-off valve is relatively high, reaching 5.0~7.0MPa. Under such high pressure difference conditions, the leakage level is required to reach level VI. Generally, it is difficult to achieve the control valve chamber, and only the O-shaped shut-off valve is used. . Due to the high pressure difference, the lateral thrust that the ball bears greatly reduces the friction torque between the ball surface and the valve seat. The oxygen flow control valve mainly adjusts the flow accurately and requires it to have good flow characteristics; the second is the shut-off performance when it is closed. The leakage level is VI level, so the sleeve type control valve is generally used.

  • Material: High-pressure oxygen flows at high speed in the valve, which may cause friction with parts and generate heat. If carbon steel is required; alloy (Inconel nickel-based alloy) or ultra-low carbon austenitic stainless steel (such as 316L, 304L) should be used, Combining the difference of the working conditions on site, the valve body is made of Monel material, and the valve core and seat are made of Monel 400 or Stellite 6. In order to prevent the valve stem from being at a constant opening for a long time and fouling, the valve stem is made of Monel K500.

  • Process requirements: All parts exposed to oxygen must be dewatered and degreasing to ensure cleanliness. Because the flow rate of high-pressure oxygen in the valve is 20-30m/s, if it encounters burrs, grooves, shoulders, etc., high-speed friction occurs. Therefore, the geometrical shape of the inner wall of the flow channel and the valve inner parts should be smoothly transitioned, and the surface should be smooth, so in the design , Processing, assembling, testing, transportation and other links, all have formulated strict process regulations to ensure that the predetermined technical requirements are met. Therefore, the special requirements of the oxygen valve lie in materials and processing.

  • Due to the explosive characteristics of high-pressure oxygen, the oxygen valve itself is an explosive dangerous device; in order to ensure safety, the nominal pressure of the oxygen valve should be increased by 2 pressure levels. For example, the pressure of the gasifier is 6.3MPa, then the valve The nominal pressure requirement of PN160 (ANSIClass900) is selected.

2. Coal slurry shut-off valve and coal slurry ash water control valve of Coal water slurry gasification unit

  • Coal water slurry is a two-phase mixed medium of liquid and solid powder. The annular orifice formed between the valve core and the valve seat has a high flow rate. It faces three problems. The coal slurry reaches a very high flow rate at the throttle of the valve. Because the coal slurry has a certain degree of hardness, its erosion and destructive power is great;

  • Coal slurry will also accumulate and block the valve cavity, so the flow passage in the valve is required to be unobstructed without dead ends; the coal slurry is very fine and can penetrate into the guiding gap of the valve core, which may cause the valve core to jam.

  • Coal slurry has a certain degree of adhesion and cohesive force, which forms fouling on the sealing surface of the valve core and valve seat, which affects the leakage level of the valve when the valve is fully closed. Therefore, the control valve is required to automatically remove these fouling.

  • Therefore, there are 3 special requirements for the gray water valve: erosion resistance, anti-clogging, and self-cleaning. Gray water is almost non-corrosive, so the valve body and bonnet can be made of carbon steel, the valve core, valve seat and other basic materials can be made of general austenitic stainless steel, and a layer of erosion-resistant cemented carbide can be applied to the surface; The adhesion of the fouling formed by water is less than that of the coking layer, so it is not necessary to use a high-torque actuator.

  • According to the above situation, the gray water control valve generally chooses the erosion-resistant eccentric rotary control valve. The internal cavity of this valve is similar to a cylinder, which is unobstructed and has no dead angles, and coal ash cannot be stored in it. The valve core rotates. In the gap between the guide sleeves on the two sides, it is difficult for ash to penetrate into the interior. Even if fouling is formed, the valve core is easily crushed when it rotates due to weak adhesion. In addition, when the valve core is closed, When it touches the sealing surface of the valve seat, due to structural reasons, the valve core and the valve seat have a relative movement, which can grind off the deposits on the sealing surface, so it has a self-cleaning function.

  • There is another important reason for choosing this kind of control valve. It is small in size, light in weight and easy to install. The weight of the valve of the same caliber is only about one third of that of the angle control valve. In addition, the valve body, bonnet and other parts can be made of carbon. Steel is also much cheaper. Since the combustion rate of coal slurry in the gasifier is related to the reaction rate of other systems, it is also related to oxygen supply, cooling, etc., in order to maintain a stable combustion state, it constantly adjusts the flow of coal slurry, so it requires a very high adjustment accuracy. Usually use equal percentage flow characteristics.

3. Slag lock valve of Coal water slurry gasification unit

  • Process medium of the slag lock valve is slag water with a slag content of 20%, which is corrosive and volatile; the medium of the flushing water valve is gray water; the action frequency is switched on and off 4 times per hour.

  • coal water slurry gasification unit:Stainless steel slag locking valveSelect the ball valve, the valve body is made of carbon steel and flow channel surfacing Stellite alloy; the valve stem should be designed with a blowout rod structure, material 1Cr13 forgings, Ni, P plated; the valve ball adopts a fixed ball, sealing surface and flow Level crossing is welded with Stillite alloy, the thickness of the valve ball lip is not less than 12mm, and the ball is sprayed or surfacing hard alloy; the valve seat is stainless steel 316 surfacing Stellite alloy, and the surfacing layer is not less than 1mm after processing , The spring material behind the valve seat is Inconel X-750. There must be a sand control structure behind the valve seat to prevent ash and slag from entering the spring and causing spring failure. The valve cavity has an automatic pressure relief function. When the valve is closed, the pressure in the valve cavity is higher than closed. When pressure is applied, the pressure can be automatically relieved to the lower pressure side.

  • Packing is made of flexible graphite (with lubrication). The hardness requirements are HRC52-54 for valve seat and HRC58-62 for valve ball. The selection of the actuator has sufficient margin, the number of switching times is 1 million times without failure; the double-cylinder double-acting electro-hydraulic actuator is adopted, the torque is large, the safety is high, with the torque protection function, the valve stem will not be twisted Or deformed. The slag lock valve adopts two-way hard-sealed ball valve, hardened valve ball and valve seat, three-stage fixed ball structure, and floating valve seat to ensure the timing of gasification slag discharge and safe interlocking operation.

4. Syngas butterfly valve of Coal water slurry gasification unit

  • Synthesis gas at the outlet of the gasifier has a large flow rate, fast action, and high leakage level requirements. Therefore, the butterfly valve is used for flow control. The actuator adopts an electro-hydraulic actuator with a fault position. The torque is large, the vibration is small, and the normal service life can reach 1 million times. ; Concentric structure design of valve body, valve plate and valve shaft, 100% two-way gas VI-level seal; compact structure without bracket, light weight and small volume. The pinless connection is adopted, which is simple and easy to maintain; the backrestless design ensures that the torque is not increased after the valve is installed. The butterfly valve is an imported high-performance spraying plate, which is more wear-resistant than ordinary plates, has a longer life, and has excellent flow characteristics

  • Triple eccentric butterfly valve is selected based on the use experience. The structure of the triple eccentric butterfly valve is that the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body while the double eccentric valve stem axis position is eccentric. After the third eccentricity, the butterfly plate The sealing cross-section is no longer a circle, but an ellipse, the shape of the sealing surface is therefore asymmetrical, one side is inclined to the center line of the body, and the other side is parallel to the center line of the body. The major feature of the third eccentricity is that the sealing structure is fundamentally changed and is no longer a positional seal. It is torsion sealing, that is, it does not rely on the elastic deformation of the valve seat, but completely uses the contact surface pressure of the valve seat to achieve the sealing effect. Therefore, the problem of metal valve seat leakage is solved in one fell swoop, and because the contact surface pressure and the medium pressure are different Proportional, high-pressure and high-temperature resistance are also readily available.

5. Black water regulating valve of Coal water slurry gasification unit

  • coal water slurry gasification unit:Stainless steel slag locking ball valveRaw material gas and coal ash generated by the combustion of the gasifier are discharged separately from the lower part. After being cooled by spray water, most of the coal ash sinks into the lock hopper and is discharged; but the cooling water still contains a considerable amount of coal ash, so it is discharged from the gasification The cooling water discharged from the furnace is commonly called black water. It is adjusted by the control valve and then enters the next process. It is generally heated to about 250°C. At this time, many chemical components in the coal powder begin to decompose and chemically react with water to form a variety of corrosive extremes. Strong substance, therefore the valve body, bonnet and all parts in contact with hot coal slurry must be made of anti-corrosion materials, especially the valve body and bonnet, not ordinary austenitic stainless steel, but ferrite Body-austenite dual-phase crystalline stainless steel not only has strong corrosion resistance, but its mechanical strength is more than twice that of austenitic stainless steel.

  • According to the requirements of this technical characteristic, among the many structural types, the angle control valve meets the requirements. The single-seat structure of the angle control valve uses the top guide structure for the valve core, and there is a certain gap between the valve core handle and the guide sleeve. It is above the main stream, but black water will inevitably penetrate into the guiding gap. Once stopped, a coking film layer will be formed in the gap, which has strong adhesion; when restarting, the valve core is often stuck. . In order to prevent jamming, a scavenge structure is designed in the guide section of the valve core, and the coking powder shoveled can be discharged by itself through the escape groove, that is to say, this control valve also has the self-cleaning ability. Because the removal of coking requires a lot of thrust, it is often equipped with a large thrust electro-hydraulic actuator, whose thrust is far greater than ordinary pneumatic or electric actuators, and the thrust can be greater than 150kN.

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