As the largest producer of titanium dioxide in the world with an annual production capacity of more than 3 million tons, the development of the titanium dioxide industry in China during the “13th Five-year Plan†period has attracted particular attention. “In the next long period of time, both the chlorination process and the sulfuric acid process will coexist, the industry will develop with more stringent environmental regulations, and mergers and acquisitions will increase in intensity and accelerate convergence with international standards.†In December From the 8th to the 9th China (Deyang) phosphorus-titanium chemical green development high-end forum held on the 8th to 9th, experts made judgments on the future pattern of the titanium dioxide industry.
Chlorination is the current mainstream of titanium dioxide production technology in the world and represents the direction of industrial development. However, due to the lack of titanium resources for the chlorination process in China, titanium raw materials must be imported at a high price. The chlorination process has not been able to break through the technical and economic ceiling. After years of research and development, the production line has not been completely opened up. Fu Yijiang, deputy general secretary of China National Coatings Industry Association Titanium Dioxide Industry Branch, stated that in this situation, the titanium dioxide industry must vigorously develop the chlorination process to make it mature as soon as possible; on the other hand, it must also continuously improve the sulfuric acid process. To regulate development with more stringent environmental regulations.
Bi Sheng, director of the Titanium Divider Center of the National Productivity Promotion Center of the Chemical Industry, also believes that, apart from the imperfect process of chlorination technology, investment of more than RMB 1 billion and several billion yuan is daunting. No matter whether it is the introduction of technology or independent research and development of technology, the chlorination process has not resolved the key core technical issues. It will take time to form industrialization and scale.
Despite many difficulties encountered, some experts are still optimistic about the development prospects of the domestic chlorination process. Xu Xingrong, deputy chief engineer of Donghua Engineering & Technology Co., Ltd., believes that the most stringent “pollutant emission standard for petrochemical industry†in history is to be implemented in existing enterprises from July 1, 2017. The standard is for existing titanium sulfate. White powder companies have more severe restrictions, and the chlorination process will usher in development opportunities. He also pointed out that at this stage, the development of chlorination process should be advanced, stable and reliable as the first choice, new installations must effectively reduce construction investment, but also pay more attention to "three wastes" governance.
The key to the development of sulfuric acid titanium dioxide is clean production and recycling economy. For example, Sichuan Longxi Group relied on the abundant iron and titanium resources in the Panzhihua region to speed up the development of recycled sulfuric acid process titanium dioxide technology, and the continuous improvement of resource utilization and energy consumption. Zhou Xiaokui, vice president of the group, stated that the sulfuric acid titanium dioxide powder has unique quality properties and will continue to be a mainstream species in China for a long time to come. Therefore, it is necessary to expedite the comprehensive utilization and clean production of sulfuric acid titanium dioxide waste by-products.
Industry experts believe that increasing mergers and acquisitions and accelerating the pace of international integration are major trends in the titanium dioxide industry. The decreasing number of manufacturers and the increasing size of individual manufacturers have become inevitable. Fu Yijiang said that in 2014, the total output of the top six manufacturers in the titanium dioxide industry accounted for 40.8% of the country's total output, and the industry concentration was significantly improved. During the “Thirteenth Five-Year Plan†period, the pace of reorganization and merger will accelerate, and it is necessary to build a number of key enterprises with great development potential and global influence. Bi Sheng believes that under the dual pressure of market and environmental protection, some small and medium-sized enterprises (SMEs) of 100,000 tons/year, especially 50,000 tons/year, will gradually fade out.
A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball Check Valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check Valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.
Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.
There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with Ball Valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.
A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.
A swing check valve or tilting disc check valve is check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.
A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.
A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.
An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process.
A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow.
A pneumatic non-return valve.
Multiple check valves can be connected in series. For example, a double check valve is often used as a backflow prevention device to keep potentially contaminated water from siphoning back into municipal water supply lines. There are also double ball check valves in which there are two ball/seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.
Check Valves
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