I. How Tough are the Operating Conditions in Coal Chemical Plants?
The internal temperature of a coal gasification plant can reach over 1300°C, and the temperature of the medium in contact with the valves can reach 300 to 500°C. The system pressure is typically 2.0 to 8.0 MPa or even higher. Even more challenging is that the medium often contains high-hardness solid particles such as coal powder and ash, causing severe erosion; it also contains corrosive media such as hydrogen sulfide and chloride ions, posing a double challenge to the valve materials.
II. What are the Main Specialized Valves for Coal Chemical Plants?
1. Slag Locking Valve (Slag Hopper Valve) - The "Gatekeeper" of the Slag Discharge System The slag locking valve is installed at the inlet and outlet of the slag hopper at the bottom of the gasifier. It is responsible for intermittently cutting off the slag-water medium and is a key instrument valve for the gasifier to complete the slag removal operation and ensure long-term continuous operation.
2. Black... Water/Grey Water Valves: The "Special Forces" of Three-Phase Flow in Mining and Chemical Industries
Black water systems are among the harshest operating conditions in coal chemical industry. The black water medium not only contains corrosive substances such as hydrogen sulfide and chloride ions, but also a large number of solid particles. Valves must withstand severe erosion caused by the scouring of solid particles at high flow rates. The extreme pressure difference across the black water regulating valve can lead to severe flashing and cavitation, causing significant damage to the valve's internal components. Therefore, the industry typically uses duplex stainless steel as the valve body material, with chrome-plated hardened flow channels and solid sintered tungsten carbide and other hard alloys for internal components to ensure corrosion resistance and erosion resistance.
3. Oxygen Valves – The "Guardians" of Safety First
Oxygen regulating and shut-off valves are widely used in coal gasification processes and air separation units, playing a crucial role in precise regulation and rapid shut-off in oxygen transmission pipelines. Because oxygen is highly flammable... Combustion and explosion pose extremely high safety requirements for oxygen valves. They must undergo rigorous oil-free degreasing treatment and possess fire-resistant design, typically requiring SIL (Silicone Inertia) certification.
4. Pulverized Coal/Coal Slurry Valve – The "Grain Supply Officer" of the Feed System
In pulverized coal gasification processes, the conveying and regulation of pulverized coal directly affects the start-up and operation of the gasification unit. These valves must withstand the strong erosion of pulverized coal particles, commonly using high-strength, corrosion-resistant tempered steel and employing a special metal sealing structure. Disc valves are increasingly widely used in pulverized coal conveying.
5. Syngas Valve – The "Breathing Valve" of the Gasifier
Triple-eccentric metal-sealed butterfly valves are commonly used to control the flow rate of syngas in the scrubbing tower, affecting the normal delivery of process gas to the gasification unit and the stable production of subsequent conversion processes. Simultaneously, syngas contains corrosive components such as dust and H2S, posing a significant challenge to the valve's performance. High temperature resistance, abrasion resistance, and thermal shock resistance are equally stringent requirements.
III. Selection Points and Precautions
In selecting valves for coal chemical applications, the following points are particularly crucial:
* Material Selection: The valve body material should be selected appropriately based on the corrosive characteristics of the medium. For example, duplex stainless steel is used for black water applications. Internal valve components should be made of hard alloys or undergo hardening treatment, such as Stellite alloy overlay welding or integral sintered tungsten carbide.
* Structural Design: A design with no dead angles and a large radius arc should be adopted to avoid the accumulation and blockage of solid media. The valve stem should be thickened and the connection structure optimized to improve stability.
* Sealing and Anti-clogging: Bearings must ensure good sealing performance to prevent coal dust from entering and causing wear. High-speed steel is recommended for the valve seat spring material.
* Safety Certification: Valves for special operating conditions such as oxygen valves must undergo corresponding safety certifications (such as SIL level) and strict degreasing treatment.
