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The water-coal slurry gasification technology is one of the most advanced fluidized-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 co-production technologies in China’s coal chemical industry. It will **promote the advancement of coal chemical technologies in China and drive technological progress in related industries. In the process of production operation control, control valves play a very important role. Given the special operating conditions such as high temperature and pressure, flammability and explosiveness, intense reactions, and slag erosion, it is necessary to use appropriate, high-quality control valves for oxygen, coal slurry, and slag in order to ensure safe and stable control of temperature, pressure, and flow rates during production operations and interlock control processes. The combustion pressure in the gasification furnace ranges from 4.0 to 6.3 MPa, while the temperature is between 1100 and 1300°C. It is a high-temperature, high-pressure combustion chamber, and therefore a highly dangerous device; any accident could have catastrophic consequences. Hence, its safety and reliability are of utmost importance ； Secondly, to maintain a normal combustion state, it is necessary for the flow rate of the water-coal slurry injected and the flow rate of oxygen mixed in to be matched; otherwise, the coal powder may not burn completely or useless gases may be generated. An excess of oxygen can lead to explosions, which is why the control system requires high precision and good stability ； Third, a gasification furnace is a device that operates continuously and must have a relatively long service life. Due to the aforementioned characteristics of gasifier units, many technical requirements have been imposed on their auxiliary equipment and related control instruments. Control valves, which directly regulate the process media, must have a special structure suitable for gasification conditions. Several typical types of control valves are introduced below. 1. Oxygen shut-off valve and oxygen flow control valve: Inside the gasifier, combustion occurs at high pressure and high speed, with a large amount of oxygen being introduced. To maintain normal combustion conditions and ensure the safety of the gasifier, it is essential to precisely regulate and control the oxygen flow rate, as well as to quickly cut off the oxygen supply without any leakage. Given the high requirements for both regulation and shut-off functions, three control valves are typically used—namely, the oxygen flow control valve, the oxygen shut-off valve, and the oxygen vent valve. Collectively, these are referred to as oxygen valves. Compared to ordinary industrial process control valves, oxygen valves for gasifiers have several special requirements: high pressure difference. The shut-off pressure differential for oxygen shut-off valves is the highest, reaching 5.0–7.0 MPa. Under such high pressure differentials, these valves must also meet a leakage class of VI, which is difficult to achieve in ordinary control valve rooms; only O-ring shut-off valves can fulfill this requirement. Due to the high pressure difference, the lateral thrust exerted on the sphere **reduces the frictional torque between the sphere’s surface and the valve seat. The oxygen flow control valve is primarily used to precisely regulate the flow rate; therefore, it is required to have good flow characteristics ； Secondly, there is the shut-off performance; the leakage class is Class VI. Therefore, sleeve-type control valves are generally chosen. Materials. High-pressure oxygen flows at high speed through the valve, and this can cause friction with the components, generating heat; this is especially the case when the valve is made of carbon steel ； Nickel-based alloys (Inconel alloys) or ultra-low carbon austenitic stainless steels (such as 316L, 304L) are used; depending on the specific operating conditions, MONEL material is chosen for the valve body, while MONEL400/ALLY6 is used for the valve stem and seat. To prevent the valve stem from becoming clogged due to remaining in one position for an extended period, K500 material is utilized for the valve stem. Process requirements. All parts that come into contact with oxygen must be dehydrated and degreased to ensure they are clean. Since the flow velocity of high-pressure oxygen within the valve is 20–30 m/s, high-speed friction can occur if it comes into contact with burrs, grooves, shoulders, etc.; therefore, the geometric shapes of the inner walls of the flow channels and the valve components must have smooth transitions and smooth surfaces. As a result, strict manufacturing procedures are established at all stages such as design, processing, assembly, testing, and transportation to ensure that the desired technical requirements are met. Therefore, the special requirements for oxygen valves lie in the material and processing. Due to the explosive nature of high-pressure oxygen, the oxygen valve itself is an explosive and hazardous device ； To ensure safety, the nominal pressure of oxygen valves should be selected two pressure ratings higher than the actual operating pressure. For instance, if the pressure in a gasifier is 6.3 MPa, then the nominal pressure of the valve should be PN160 (ANSI Class 900). 2. Slurry cut-off valve and slurry ash-water control valve: Water-coal slurry is a two-phase mixture of a liquid phase and solid powder, which results in very high flow velocities at the annular throttle opening formed between the valve core and the valve seat. It faces three problems: 1. The coal slurry reaches a fairly high flow velocity at the throttle orifice of the valve; given that the coal slurry has a certain degree of hardness, its erosive power is quite significant ； Coal slurry can also accumulate and block the valve chamber; therefore, it is necessary that the flow channels within the valve be unobstructed with no dead corners ； The coal slurry is very fine and can penetrate into the guide clearance of the valve spool, which may cause the spool to get stuck. Coal slurry has a certain adhesive strength, which causes deposits to form on the sealing surfaces of the valve core and seat, affecting the leakage level when the valve is fully closed; therefore, it is necessary for control valves to be able to automatically remove these deposits. Therefore, there are also 3 special requirements for graywater valves: erosion resistance, anti-clogging, and self-cleaning. Gray water has little corrosive effect, so the valve body and valve cover can be made of carbon steel, while the core, seat, and other components can be made of ordinary austenitic stainless steel; a layer of wear-resistant cemented carbide applied to their surface is sufficient ； The scale formed by graywater has less adhesion than the coking layer, so there is no need for an actuator with high torque. Based on the above considerations, erosion-resistant eccentric rotary control valves are generally chosen for graywater control valves. The internal cavity of such valves is approximately cylindrical in shape, smooth with no dead corners, preventing coal ash from accumulating within it. Its valve core moves in a rotational manner, and within the gaps of the guide sleeves on both sides, ash and slag find it difficult to penetrate inward. Even if deposits do form, their weak adhesion means that they are easily crushed as the valve core rotates ； Furthermore, when the valve core is closed and comes into contact with the valve seat sealing surface, due to structural reasons, there is relative movement between the valve core and the valve seat, which allows the deposits on the sealing surface to be ground away; thus, it has a self-cleaning function. There is another important reason for choosing this control valve: it is small in size, light in weight, and easy to install ； Valves of the same diameter weigh only about one-third as much as angular control valves; moreover, components such as the valve body and valve cover can be made of carbon steel, which makes the price much lower. Since the combustion rate of the coal slurry in the gasifier is related to the reaction rates of other systems, as well as factors such as oxygen supply and cooling, it continuously adjusts the flow rate of the coal slurry in order to maintain a stable combustion state. This requires a high degree of precision in adjustment, and therefore a proportional flow characteristic is usually chosen. 3. Slag locking valve: The process medium for this valve is slagwater, with a slag content of 20%; it is corrosive and volatile ； The medium for the rinse water valve is graywater ； The operation frequency is 4 switches per hour. A ball valve is selected, with the valve body made of carbon steel to which Stellite alloy has been welded on the flow channels ； The valve stem should be designed with a blowout-proof rod structure, made of 1Cr13 forgings, plated with Ni, P ； The valve ball is of the fixed-ball type; the sealing surface and flow passages are surfaced with Stillite alloy, while the lip area of the valve ball is surfaced with Stillite alloy to a thickness of no less than 12 mm. The entire ball is coated or surfaced with cemented carbide ； The valve seat is made of 316 steel with a Stellite alloy surfacing; the thickness of this surfacing layer is at least 1 mm after processing. The spring located behind the valve seat is made of Inconel 750. A sand-proof structure must be present behind the valve seat to prevent ash and debris from entering the spring and causing it to fail. The valve chamber has an automatic pressure relief function: when the valve is closed and the pressure inside the chamber exceeds the closing pressure, the pressure is automatically relieved to the side where the pressure is lower. The filler is flexible graphite (lubricated). The hardness requirement is HRC 52-54 for the valve seat, and HRC 58-62 for the valve ball. Sufficient margin is provided in the selection of the actuator, allowing 1 million switching cycles without failure ； It uses a dual-cylinder, double-acting electro-hydraulic actuator, which provides high torque and high safety; it features torque protection to prevent the valve stem from being twisted or deformed. The slag locking valve is a two-way hard-sealed ball valve featuring hardened valve balls and seat surfaces, as well as a three-stage fixed-ball structure and a floating seat, which ensures timely slag discharge during gasification and safe interlocked operation. 4. Syngas butterfly valve: The syngas flow rate at the outlet of the gasifier is high, the valve needs to operate quickly, and strict requirements are placed on leakage levels; therefore, a butterfly valve is used for flow control. An electro-hydraulic actuator with a function to indicate the fault position is selected, as it provides high torque, minimal vibration, and a normal service life of up to 1 million operations ； Concentric design of valve body, valve disc, and valve shaft; 100% double-direction air VI-grade sealing ； The bracketless design features a compact structure, light weight, and small size. Pinless connection is used, making maintenance simple and easy ； The backless design ensures that no additional torque is applied after the valve is installed. The butterfly valve features imported high-performance coating plates, which are more wear-resistant than ordinary plates, have a longer lifespan, and offer excellent flow characteristics. Based on practical experience, a triple-eccentric butterfly valve is chosen. The structural feature of this valve is that, in addition to the eccentricity of the valve stem axis, the conical axis of the butterfly valve’s sealing surface is also offset from the cylindrical axis of the valve body. As a result of this third level of eccentricity, the sealing surface of the butterfly valve is no longer circular but elliptical; consequently, its shape becomes asymmetric, with one side inclined relative to the center line of the valve body and the other side parallel to it. The most significant feature of the third type of eccentricity is that it fundamentally changes the sealing mechanism, no longer relying on positional sealing. It uses a torque seal; in other words, it relies not on the elastic deformation of the valve seat, but rather solely on the pressure exerted by the contact surface of the valve seat to achieve sealing. This approach solves the problem of leakage in metal valve seats once and for all, and since the contact surface pressure is proportional to the medium pressure, it also makes it easy to handle high pressures and temperatures. 5. Black water regulating valve: The raw gas and coal ash generated from the combustion in the gasifier are discharged separately from the bottom. After being cooled by spray water, most of the coal ash settles in the lock hopper and is then discharged ； However, the cooling water still contains a considerable amount of coal ash; therefore, the cooling water discharged from the gasification furnace is commonly referred to as \"black water\". After being regulated by control valves, it enters the next processing stage, where its temperature is usually raised to around 250°C. At this temperature, many chemical components in the coal powder begin to decompose and react with water, forming various highly corrosive substances. As a result, the valve bodies, valve covers, and all components that come into contact with the hot coal slurry must be made of corrosion-resistant materials. In particular, for the valve bodies and valve covers, ordinary austenitic stainless steel cannot be used; instead, ferritic-austenitic duplex stainless steel should be employed. This type of steel not only possesses excellent corrosion resistance but also has mechanical strength more than twice that of austenitic stainless steel. Given these technical requirements, among various structural types, angular control valves are a suitable choice. In angular control valves with a single-seat structure, the valve spool is guided from above; there is a certain gap between the spool shaft and the guide sleeve. Although it is located above the main flow path, black water inevitably seeps into this guiding gap. Once the system stops operating, a layer of caked material forms in this gap, which has strong adhesion properties ； When restarted, the valve core often gets stuck. To prevent jamming, a scooping structure is designed in the guiding section of the valve core, and the coked powder removed by this scooping action can be discharged automatically through escape grooves; in other words, this control valve also possesses self-cleaning capabilities. Since significant thrust is required to remove coking, high-thrust electro-hydraulic actuators are often used; their thrust is much greater than that of ordinary pneumatic or electric actuators, and can exceed 150 kN.