The Valve Design And Selection Of Coal Water Slurry Gasification Unit

- Sep 27, 2019-

Coal water slurry gasification technology is one of the world;s most advanced gas flow bed coal gasification technologies, and 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. It will greatly promote the development of China;s coal chemical technology and promote the technological progress of related industries. In the process of production operation control, the control valve plays an important role, aiming at gasification high temperature, high pressure, flammable and explosive, severe reaction, slag Special working conditions such as scouring, select the appropriate, high-quality oxygen, coal slurry, slag control valve for production operation, interlock control process, to achieve safe, stable control of temperature, pressure, flow process operating conditions.





Material selection:

GS-C251.0619,WCB.WCC,LCB,LCC,LC3,4C,4D,WC6,C5,C12, C12A,CA15CF3,CF8(-196’C),CF3M,CF8M,CF8C,CD4MCu,CK3MC   uN,ZG200-400,ZG230-450,ZG270-500,2G40Cr1,ZG20CrM0.2G15C   r1Mo1V,ZG35Cr1MO.ZG16CrMOG(1Cr5Mo),ZG1Cr13,ZGOCr18Ni9 Ti.5A.KmTB   Cr26.4A




Resin sand casting, etc.

The combustion pressure in the gasifier is 4.0~6.3MPa, and the temperature is 1100~1300°C. 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 based on the front position; In order to maintain the normal combustion state, the flow rate of the injected coal water slurry and the mixed oxygen flow rate must be matched. Otherwise, the pulverized coal combustion may be incomplete or useless gas. If the oxygen is excessive, the explosion may occur. Therefore, the automatic control system is required. The control precision is high and the stability is good. Thirdly, the gasifier is a continuous working device and must have a relatively long service life. Due to the above characteristics of the gasifier, corresponding technical requirements have been put forward for its ancillary equipment and related control instrument industry. The control valve directly controls the production medium, and must have a special structure suitable for gas chemical use, for several typical controls. The valve is described below.

stainless steel Check valve

1. Oxygen shut-off valve and oxygen flow control valve

The high pressure in the gasifier burns at 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 controlled, and the oxygen should be cut off quickly and without leakage. The requirements of each function are very high, so it is usually completed with three control valves, namely oxygen flow control valve, oxygen shut-off valve, oxygen vent valve, collectively called oxygen valve. Compared to 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 differential pressure conditions, the leakage level is required to reach the level VI. It is difficult to achieve the general control valve chamber. Only the O-shaped cutting valve is used. . Due to the high pressure difference, the lateral thrust of the ball greatly reduces the frictional moment between the surface of the ball and the valve seat. The oxygen flow control valve mainly adjusts the flow rate accurately, and requires it to have good flow characteristics. Secondly, it is the shut-off performance when it is closed. The leakage level is VI, so the sleeve type control valve is generally used.

Material: High-pressure oxygen flows at high speed in the valve, may rub against parts, generate heat, such as carbon steel; apply nickel-based alloy (Inconel alloy) or ultra-low carbon austenitic stainless steel (such as 316L, 304L), In combination with the difference of on-site working conditions, the valve body material is made of MONEL material, and the valve core and valve seat material are made of MONEL400/ALLY6 material. In order to avoid the valve stem from being in a constant opening for a long time, the valve stem is made of K500 material.

Process requirements: All parts that come into contact with oxygen must be degreased and degreased to ensure clean and clean. Because the high-pressure oxygen flow rate in the valve is 20~30m/s, if high-speed friction occurs in the burr, groove, shoulder, etc., the geometry of the inner wall of the flow channel and the inner part of the valve should be smooth and smooth, so the surface is smooth, so the design, processing, assembly, testing, transportation and other aspects, have developed strict technical procedures to ensure that the predetermined technical requirements are met. Therefore, the special requirements for oxygen valves are in materials and processing.

Due to the explosive nature of high pressure oxygen, the oxygen valve itself is an explosive and dangerous device; to ensure safety, two pressure levels should be increased when the nominal pressure of the oxygen valve is selected. For example, if the pressure of the gasifier is 6.3 MPa, then the valve The nominal pressure requirement is PN160 (ANSI Class 900).

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

The coal water slurry is a mixed medium of two phases of liquid phase and solid powder, and the annular throttle shape formed between the valve core and the valve seat has a high flow velocity. It faces three problems. The coal slurry reaches a fairly high flow rate at the orifice of the valve. Because the coal slurry has a certain hardness, the erosion of the coal slurry is very large;

Coal slurry will also accumulate and block the valve cavity, so it is required that the flow passage in the valve is smooth and free of dead angles; the coal slurry is very fine and can penetrate into the valve core guiding gap, which may cause the valve core to be stuck.

Coal slurry has a certain adhesion and adhesion, and fouling is formed on the sealing surface of the valve seat, which affects the leakage level when the valve is fully closed. Therefore, the control valve is required to automatically remove the scale.

Therefore, there are three 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 material, and the basic materials such as valve core and valve seat are made of general austenitic stainless steel, and the surface is hot-coated with an erosion-resistant hard alloy; The scale formed by water has less adhesion than the coke layer, so it is not necessary to use a large torque actuator.

According to the above situation, the gray water control valve generally adopts an erosion-resistant eccentric rotary control valve. The valve body cavity of the valve is approximately a cylinder, and there is no dead angle, and the coal ash cannot be accumulated therein. The spool is rotated. In the gap between the guide sleeves on the two sides, the ash is difficult to penetrate into the interior. Even if fouling is formed, the adhesion is not strong, and the spool is easily crushed when rotated. In addition, when the spool is closed, when it touches the sealing surface of the valve seat, due to the structural reason, the valve core and the valve seat have a relative movement, which can grind the scale on the sealing surface, so there is 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 valve of the same diameter has only one-third of the quality of the angle control valve, and the carbon of the valve body and valve cover can be used. Steel, the price is also much cheaper. Since the burning 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 rate of the coal slurry, thus requiring a relatively high adjustment precision. Equal percentage flow characteristics are usually chosen.

Butterfly valve

3, lock slag valve

The process medium of the lock slag valve is slag water, the slag content is 20%, corrosive and volatile; the flushing water valve medium is gray water; the operating frequency is switched 4 times per hour. Ball valve is selected, the valve body is made of carbon steel and runner welding Stellite alloy; the valve stem should be designed with anti-spray rod structure, material 1Cr13 forging, Ni, P; ball is fixed ball, sealing surface and flow The Stillite alloy is welded at the crossing, the thickness of the valve ball lip weld is not less than 12mm, the ball is sprayed or surfacing hard alloy; the valve seat is 316 surfacing Stellite alloy, and the surfacing layer is not less than 1mm after processing. The spring of the valve seat is made of Inconel 750. The valve seat must have a sand control structure to prevent the spring from failing when the ash enters the spring. The valve chamber has an automatic pressure relief function. When the valve is closed, the pressure inside the valve chamber is higher than the closing pressure. Automatic pressure relief to the side with low pressure. The filler is made of flexible graphite (with lubrication). The hardness requirements are valve seat HRC52-54, valve ball HRC58-62. The choice of actuator has sufficient margin, the number of switching is 1 million times without failure; the double-cylinder double-acting electro-hydraulic actuator has large torque, high safety, with torque protection function, and the valve stem will not be broken or deformation. The lock slag valve adopts two-way hard seal ball valve, ball and seat hardening treatment, three-stage fixed ball structure and floating valve seat to ensure gasification timing slagging and safety interlock operation.

4, syngas butterfly valve

The gasification of the synthesis gas at the outlet of the gasifier is large, the action is fast, and the leakage level is high. Therefore, the butterfly valve is used for flow control. The actuator selects the electro-hydraulic actuator with the fault position. The torque is large, the vibration is small, and the normal service life can reach 1 million times. The valve body, valve plate and valve shaft are concentric structure design, 100% two-way gas VI-level sealing; the structure without bracket is compact, light in weight and small in size. With no pin connection, the maintenance is simple and easy; the no-back design ensures that the torque is not increased after the valve is installed. The butterfly valve is an imported high-performance spraying board, which is more wear-resistant than the ordinary board, has a longer service life and excellent flow characteristics.

The triple eccentric butterfly valve is used in combination with the experience. The structure of the triple eccentric butterfly valve is that the conical axis of the disc sealing surface is deflected to the main cylinder axis while the double eccentric stem axial position is eccentric, after the third eccentric rear disc The sealing section is no longer a circle, but an ellipse, and its sealing surface shape is also asymmetrical, with one side inclined to the center line of the body and the other side parallel to the center line of the body. The larger feature of the third eccentricity is that it fundamentally changes the sealing structure and is no longer a positional seal. Instead of relying on the torsion seal, that is, not relying on the elastic deformation of the valve seat, but completely using the contact surface pressure of the valve seat to achieve the sealing effect, the metal seat leakage problem is solved in one fell swoop, and the contact surface pressure and the medium pressure are It is directly proportional to the high pressure and high temperature.

5, black water regulating valve

The raw material gas and coal ash generated by the combustion of the gasification furnace are respectively discharged from the lower part. After being cooled by the spray water, most of the coal ash is discharged into the lock bucket and discharged; however, the cooling water still contains a considerable amount of coal ash, so the gasification is performed. 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 poles. Strong material, so the valve body, bonnet and all parts in contact with the hot coal slurry must be made of corrosion-resistant materials, especially the valve body and bonnet. Instead of ordinary austenitic stainless steel, use ferrite. The body-austenitic two-phase crystalline stainless steel not only has strong corrosion resistance, but also has more than twice the mechanical strength of austenitic stainless steel. According to the technical characteristics, in many structural types, the angular control valve is more in line with the requirements. The angle control valve of the single seat structure has a top guide structure for the valve core, and a certain gap between the valve core handle and the guide sleeve, although It is above the main beam, but the black water inevitably penetrates into the guiding gap. Once stopped, it forms a coke film layer in the gap and has strong adhesion. When restarting, the valve core is often stuck. . In order to prevent the jam, the scooping structure is designed in the guiding section of the valve core, and the coking powder under the scooping can be discharged by the escape trough, that is to say, the control valve also has self-cleaning capability. Because it requires a lot of thrust to remove the coking, it is often equipped with a large thrust electro-hydraulic actuator, the thrust is much larger than the ordinary pneumatic or electric actuator, the thrust can be greater than 150kN.