In the coal-water slurry gasification process, the black water regulating valves in the gasifier and scrubber are indispensable components of the entire process. Due to extremely harsh working conditions, the service life of the black water regulating valves is very short, ranging from 1 month to 3 months. Therefore, it is crucial to design to extend their service life as much as possible.

Black water is a by-product produced during the scrubber and gasifier processes in the coal-water slurry gasification process. The process requires the recovery, purification, and secondary utilization of black water. This process involves various tests of solid, liquid, and gas phases.

In the solid phase, under high pressure difference and high flow rate conditions, solid particles become the primary difficulty in the design of the regulating valve, causing surface pits, scratches, and even cracks on the parts. At the same time, solid particles wear the fluid passage, causing scratches, scratches, and abnormal noises. Changes in direction also affect the local medium flow rate, generating vortices and turbulence, causing vibration and noise in the pipeline and valve cavity. Another hazard of solid particles is the sedimentation problem, which may cause the valve stem and guide to become stuck, affecting the stability of the valve stem. The wear and scratches on the valve stem surface also affect the sealing effect of the packing above the regulating valve and the valve stem, resulting in leakage of black water, escape of toxic gases, and other production accidents.

In the liquid phase, black water contains various strong corrosive ions. Long-term immersion at high temperature will cause erosion of the inner wall of the regulating valve and its components, weakening the metal oxide protective layer on the surface of the components. Under high pressure, the liquid first impacts the balanced area inside the regulating valve cavity, causing cracks, perforations, and other problems in the partition plate. The shape of the flow path in the valve cavity will affect the generation of blocked flow, local vortices and turbulence, affecting the flow capacity and regulating ability of the valve, as well as the vibration and noise of the valve body. The impact of black water liquid also directly affects the strength of the components inside the valve.

In the gas phase, the black water regulating valve is subjected to high pressure difference conditions, and flash evaporation and cavitation cannot be avoided, even causing surface fractures and pipe damage of the components. At the same time, the sudden change in fluid volume caused by flash evaporation will also cause vibration of the pipeline and the pipe openings of downstream process equipment, leading to unexpected problems in the downstream equipment, damaging the downstream equipment, and causing serious production accidents. 

In view of the above working conditions, the design of the black water regulating valve should pay attention to the following points:

First, the type of the regulating valve structure should be determined. The ideal regulating styles include straight-through or angle types. An angle-type regulating valve with smooth transition and less sedimentation should be selected. The flow direction should be side inlet and bottom outlet. The angle-type regulating valve can well guide the flow of the medium, allowing the medium to flow out of the regulating valve almost without any resistance when it is opened, and minimizing the impact of the medium on the regulating valve to the greatest extent.

Second, the impact of solid particles on the parts should be reduced. There are two solutions to reduce the direct impact on the components. One is to enhance the strength of the parts and increase the diameter of the valve stem. The simplest and most direct method is to spray hard alloys at the key impact points and use hard alloys throughout the parts to increase the lifespan of the components. The second is to guide the flow direction. By optimizing the flow direction of the components exposed in the fluid path or optimizing the flow structure of the components, the components will not directly bear the impact. By guiding the flow path, the fluid enters the valve core through a curved flow path, forming a certain angle with the valve core, which can significantly weaken the radial impact on the valve core and reduce vibrations. The protrusions, steps, and grooves of the components should be reduced, and the components should be optimized to have a certain angle and curvature to make the valve cavity as ideal as a bend. This helps to reduce solid particle deposition and improve the flow capacity of the valve cavity structure. The second solution is to design a diversion structure at the positions where solid particle deposition is likely to occur. The design of the valve cavity structure and the surface of the components should consider static diversion or discharge structures. Structures such as curved surfaces, inclinations, and depressions can be cast to guide solid particles to the discharge ports through gravity. The fluid can also be used to wash the deposition positions for auxiliary cleaning. The surface of the components can use grooves, ring grooves, etc. to scrape off the solid particles adhering to the surface of the components to prevent them from getting stuck. Solid particles adhering to the mating surface are inevitable. A design idea of spiral ring grooves + vertical grooves can be adopted to scrape off some solid particles adhering to the mating surface. The particles that have entered the mating surface can be discharged through liquid flushing and gravity along the ring grooves, reducing the probability of failure and jamming.

Third, the problem of solid particle sedimentation should be solved. There are two solutions. One is to reduce structural deposition. The structure of the valve cavity after deposition is the shape that the fluid ultimately flows through. The flow path can be optimized based on the deposition results. This is a very good model for studying and improving the fluid path. Solid particles are prone to deposit at low flow velocity corners, components' steps, etc. Active measures can be taken to reduce static dead corners in the valve cavity and components prone to deposition, allowing the fluid to spontaneously carry out solid particles out of the valve cavity and reducing structural deposition in the valve cavity. The valve cavity and components should be designed to be consistent with the fluid flow direction, and the straight edges and end faces of the components should be changed to certain angles and curvatures to form an overall streamline with the valve cavity path, which helps to reduce solid particle deposition and improve the flow capacity of the valve cavity structure. The diversion structure can be designed at the positions where solid particle deposition is likely to occur. Structures such as curved surfaces, inclinations, and depressions can be cast to guide solid particles to the discharge ports through gravity. The fluid can also be used to wash the deposition positions for auxiliary cleaning. The surface of the components can use grooves, ring grooves, etc. to scrape off the solid particles adhering to the surface of the components to prevent them from getting stuck. Solid particles adhering to the mating surface cannot be avoided. A design idea of spiral ring grooves + vertical grooves can be adopted to scrape off some solid particles adhering to the mating surface. The particles that have entered the mating surface can be discharged through liquid flushing and gravity along the ring grooves, reducing the probability of failure and jamming.

Fourth, the corrosion of the liquid should be reduced. For the basic pipeline, carbon steel or stainless steel with a lower carbon content that is resistant to corrosion can be considered. The key parts prone to erosion at the bends and reducers should be made of stainless steel. They can be welded or sprayed to enhance the erosion resistance and corrosion resistance of the pipeline. The black water regulating valve has a greater pressure-bearing function than the regulating function. Therefore, corrosion-resistant, high-strength austenitic stainless steel or duplex stainless steel can be used. Local thickness can be increased at the main erosion points such as fluid turning and sealing to ensure the pressure-bearing length and reliability.

Fifth, the problem of liquid impact should be solved. An unreasonable flow path design will cause unnecessary impact on the partitions in the inner wall part, resulting in vortex and turbulence in the valve cavity, impacting the valve core, valve cavity, causing vibrations and damaging the partitions in the valve cavity. The solution is to adopt a better streamlined structure for the valve body. The design of the solid particle deposition position can be referred to for improvement of the smoothness of the flow channel. The focus of the flow channel design is to ensure the stable outflow of liquid from the valve body. It is also advisable to appropriately enhance the reflux and diversion capabilities of the flow channel to evenly distribute the liquid pressure within the valve body cavity. The reflux and diversion can reduce the pressure on the valve core on one side, which is beneficial for stabilizing the valve core.

Sixth, address the issues of flash evaporation and cavitation. If a noise reduction plate is added at the valve outlet, the pressure at the valve outlet is increased, and the pressure difference at the valve seat outlet is reduced, which can control the saturated vapor pressure of the liquid at the current temperature and improve the conditions for liquid vaporization. However, the pressure behind the noise reduction plate is still very high, which will cause secondary impact on the downstream pipeline and valves. High flow velocity and large volume will cause severe vibration of the downstream pipeline, which may damage the inlet of the downstream equipment. A feasible solution is to install a Venturi expansion pipe at the internal valve seat outlet, and increase the length of the Venturi expansion pipe to control the vaporization phenomenon within the high-strength Venturi tube, protecting the downstream pipeline and equipment. At the same time, the strength of the valve seat, valve core, and Venturi tube can be increased by spraying hard alloys or using hard alloys throughout the body to enhance the local structural strength. Externally, a large-diameter buffer tank can be added after the Venturi tube, and the downstream pipeline can be thickened or welded, sprayed with hard alloys, etc. as wear-resistant materials.