Analysis of Valve Applications in the Coal Chemical Energy Industry (Part 1)

1 Overview of Coal Chemical Industry:
Coal chemical processes use coal as a raw material, converting it into gaseous, liquid, and solid fuels and chemicals through physical and chemical processing. This includes industrial processes such as coal coking, coal gasification, coal liquefaction, synthesis gas chemical engineering, and tar chemical engineering.
According to the maturity and development history of the industry, coal chemical industry can be divided into two categories: traditional coal chemical industry and modern new coal chemical industry. Traditional coal chemical industry mainly includes coal coking and synthesis ammonia. Modern new coal chemical industry mainly includes coal-to-oil, coal-to-methanol, coal-to-olefins, coal-to-dimethyl ether, coal-to-natural gas, coal-to-ethylene glycol, coal-to-aromatics and IGCC (Integrated Gasification Combined Cycle power generation system) power generation, etc. The overview process flow of coal chemical industry is shown in Figure 1.

2 Introduction to the Slag Locking Valve Process in Coal Chemical Industry Slag Discharge System
The slag discharge system of coal gasification equipment has very harsh conditions and very strict requirements for valves. The valves are required to have high wear resistance, erosion resistance, anti-scaling, anti-scarring, and quick shut-off functions. In particular, the slag locking valve operates under high pressure and high temperature, with a very high medium (coal slag) hardness, frequent opening and closing, fast opening and closing speed, good sealing performance, and high reliability.
The slag locking valve, also known as the lock hopper valve, generally uses a pneumatic two-position on-off ball valve. It is the most important valve in the water-coal slurry, multi-component slurry, and dry coal powder fluidized bed pressurized gasification equipment for liquid slag discharge. Each gasifier is equipped with three slag locking valves. Two slag locking valves are located on the pipeline connecting the gasifier quench chamber or slag breaker at the bottom to the lock hopper, which is the lock hopper inlet side. These are usually called upper lock gate valves. Valve 1 is controlled by a program and switches approximately every 30 minutes, while Valve 2 is normally open and online for standby, ready to be used at any time if Valve 1 leaks or malfunctions. When the gasifier quench chamber level is low, causing the gasifier safety system to interlock, Valve 1 also interlocks and closes to prevent process gas from entering the lock hopper system and causing adverse consequences. There is also one slag locking valve at the lock hopper discharge port, usually called the lower slag locking valve. The lower port of this valve communicates with the atmosphere. The slag locking valve participates in the gasifier slag discharge program control and is directly eroded by high-temperature, high-pressure ash slag. It switches frequently and is required to achieve bidirectional sealing under high pressure difference.
As shown in the slag discharge system process flow diagram of the water-coal slurry pressurized gasification process in Figure 2, the gasification pressure in the gasifier is usually 2.7 MPa to 8.5 MPa, while the slag pool communicates with the atmosphere. To discharge the ash slag from the furnace to the slag pool, the medium pressure must be reduced to atmospheric pressure. When Valve 2 is open and the lower slag locking valve is closed, the lock hopper and the gasifier are in the same system with equal pressure. At this time, the black water in the gasifier can be collected into the lock hopper. Conversely, when Valve 2 is closed and the lower slag locking valve is open, the lock hopper and the slag pool are in the same system with equal pressure. At this time, the black water in the lock hopper can be discharged into the slag pool.

Figure 2 Schematic diagram of the slag discharge system process flow of water-coal slurry pressurized gasification process
3 Introduction to Ball Valve Application Scenarios in Slag Locking Valve Process Section:
3.1 Typical Operating Conditions:
In a water-coal slurry gasification unit with an operating pressure of 6.5 MPa and a daily coal input of 705 tons, the slag locking valve passes approximately 270°C black water containing entrained ash slag: 1057 kg/h during normal slag discharge, and a maximum of 13700 kg/h. The slag and water are mixed, with ash slag accounting for 50%. The ash slag particles are generally 3 mm to 50 mm. The black water medium contains water, CI, H2S, Fe2O3, SiO2, Al22O3, etc. The process involves chemical corrosion and mechanical erosion. Therefore, the slag locking valve is mainly used in the working conditions of ash water, coal slurry, nitrogen, solid powder, and particles.
3.2 Selected Product Features:
① On-off ball valve is used, non-blocking flow switch design, capable of withstanding at least 100,000 pressure and temperature cycle operations.
② The valve is double-sealed, and the seal reaches ANSI B16.104 Class V under the maximum pressure difference when the downstream pressure is atmospheric pressure in both forward and reverse flow directions.
③ Consider the best availability of valve internals and flow path materials under medium impact, corrosion, and erosion. ④ The overpressure range of the valve design is greater than 150% of its maximum working pressure.
⑤ Requires fast action, with an action time of 3s to 8s from "fully open to fully closed" or "fully closed to fully open", ensuring the valve action is in place.
3.3 Introduction to BFA Series Metal Hard Seal Ball Valves
3.3.1 Product Structural Features
(1) Internal parts are made of 316 and special alloy materials, and the sealing surfaces are nitrided, Stellite alloy welded, or tungsten carbide sprayed for hardening treatment;
(2) The stem uses XM-19 or 630 precipitation-hardened stainless steel, and the stem is surface nitrided. The stem and ball are connected using a spline connection;
(3) Imported bearings are used to ensure bearing sealing effect and prevent coal powder from entering the bearings, causing wear and accelerating valve damage;
(4) The valve seat spring uses imported high-speed steel, and the spring performance is stable and reliable;
(5) Double-sealed, sealing grade can reach ANSI B16.104 Class VI;
3.3.2 BFA Series Metal Hard Seal Ball Valve Application Conditions (PDS High-Frequency Switching Conditions as an Example)
The PDS high-frequency switch-controlled ball valve is used in the PDS feeding unit of polypropylene and polyethylene plants. Due to the high-frequency switching of this ball valve (an average of over 100,000 operations per year, up to 500,000), and the presence of severe temperature fluctuations, ultra-fine powder, and three-phase flow media, the operating conditions are extremely harsh. Coupled with the interlocking and sequential control of the system, the stability and reliability of the product directly affect the stable operation of the plant. Once damaged, the entire plant must shut down, resulting in huge losses. To improve this situation, Ekmexun Company has researched and produced this type of valve, innovatively optimizing the structure of the high-frequency control ball valve, sealing pair materials, actuator and pneumatic accessories, manufacturing process, and quality inspection, solving the problem of easy damage to the ball seat sealing surface under high-frequency switching.