Fresh water accounts for about 3% of the earth's water resources. Obtaining new fresh water resources through seawater desalination is a major trend in the world's water use in the future. At present, desalination has become the main way to obtain water sources in areas like water resources in the Middle East. 2 Titanium application in seawater desalination equipment Cnc Steel Plate Drilling Machine is one kind of CNC Plate Drillng Machine, mainly used for construction, bridge, tower and other steel structure in the connection plate drilling, it can also be used for boiler, petrochemical, refrigeration and other industries tube sheet, baffle and flange drilling and multi-holes drilling in the flat plate, parts drilling. This Plate Drilling Machine is the preferred equipment for flat steel in the construction steel structure connecting plates and other mechanical applications. CNC Steel Plate Drilling Machine Cnc Drilling Machine,Cnc Plate Drilling Machine,Cnc Steel Drilling Machine,Cnc Steel Plate Drilling Machine Jinan XingTian Sunshine CNC Machine Co.,Ltd , https://www.cncplate.de
1. World desalination status <br> By 1993, there were 9,014 desalination equipment in 5,738 regions around the world, with a total capacity of 1.624×107 m 3 /d, and the total capacity in the Middle East alone was 8.91*10 6 m. 3 / d, accounting for 55%, the United States is 2.37 * 10 6 m 3 / d, accounting for 5%.
As early as the 1950s, seawater desalination was used to produce fresh water. The main methods of seawater desalination are:
1 evaporation method: multi-stage flashing method, single-stage flashing method, vertical multi-effect method, horizontal multi-effect method, dip tube method, vapor compression method;
2 membrane method: electrodialysis method, reverse osmosis method;
3 compound method.
Among them, the evaporation method accounts for 60%, the reverse osmosis method accounts for 33%, and the electrodialysis method accounts for 5.5%. Table 1 shows the seawater desalination method mainly used in Japan and its practical ratio.
Table 1 Main seawater desalination method in Japan and its practical proportion of drinking water industry reverse water infiltration method 42% 56%
Electrodialysis 37% 18%
Evaporation method 21% 26%
2.1 desalination equipment in original heat pipe heat transfer tube desalination equipment mainly copper alloy tube, because many deficiencies copper alloy tube, has been high reliability and freedom from maintenance titanium tube replaced.
(1) Thickness of the thickness of the titanium tube The thickness of the heat-conducting tube is determined by the conditions of use, the material of the tube sheet, the construction ability of the tube expansion operation, and the welding technology of the tube end. Since the diameter of the heat-conducting tube is small, the strength is not high, so the actual use In the case of a pipe having a thin wall thickness, a wall thickness of a copper alloy pipe is generally 0.9 mm to 1.2 mm; instead of a titanium pipe, a thin-walled pipe having a wall thickness of 0.3 mm can be used in a place having low corrosivity.
2) The thermal conductivity of the titanium tube is different depending on the material of the heat transfer tube, such as 17W/(m•k) for titanium, lOOW/(m•k) for aluminum brass, and 47W for 90/10 white copper. m•k), 70/30 white copper is 29W/(m•k), so the heat conduction of the heat pipe can be controlled by the change of the wall thickness. Among the above materials, titanium has the lowest thermal conductivity. If a thin-walled titanium welded pipe is used, the thermal conductivity is worse than aluminum brass, but it is equivalent to 90/10 white copper, which is better than 70/30 white copper.
(3) Economical cost of titanium tube The unit mass price of titanium tube is 2.6 times higher than that of copper alloy. However, considering the cost performance, the price of titanium tube can compete with copper alloy tube. Because of the low density of titanium and the same wall thickness, the equivalent The length of the titanium tube is only 50% of the copper alloy tube. When the wall thickness of the titanium tube is 50% of the copper alloy tube, the mass of the titanium tube of the same heat transfer area is only 1/4 of that of the copper alloy tube. At the current price level, the overall price of thin-walled titanium welded pipes is the same as that of aluminum-copper pipes, which is cheaper than white copper pipes. It can be seen that the titanium tube is competitive in terms of price.
2.2 Development and application of thin-walled titanium welded pipes in Japan The development of titanium strip rolling technology has become the basis for mass production of titanium welded pipes. 60 years, in an aqueous caustic electrolytic production of silver, titanium wire used in Japan; the early 1990s, to prevent contamination, the production process of caustic soda was improved with the introduction of the diaphragm, with more than 700 tons of titanium is applied, Taking this as an opportunity, Japan has researched and developed the technology of continuously producing hot-rolled and cold-rolled titanium coils, established a mass production system for seawater desalination and coil thin-wall welded pipes for power station condensers, and developed thin-walled welded pipes accordingly. Production technology.
The power station condensers produced by Hitachi, Mitsubishi and Toshiba use titanium welded pipes with a thickness of 0.5 mm, and desalination devices produced by Mitsubishi, Kawasaki, Hitachi, Mitsui and Kobe Steel, using thicknesses of 0.5 mm to 0.7 mm. Titanium welded pipe. [next]
In application-based power plants, water desalination as a pipe titanium, iron smelting, ships, oil refining, chemical and other fields has been widely used in the heat transfer tube. By 1983, in 16 years, Japan had produced thin-walled titanium welded pipes 4038t for desalination equipment around the world, and there has been no damage due to seawater corrosion.
(1) Ventilation Condenser and Jet Compressor Japan's real seawater desalination equipment is a 2650t/d seawater desalination plant built by Songdo Carbon Mine Co., Ltd. in 1967. The ventilation condenser of the device and the heat transfer tubes and tube sheets of the injection compressor cannot be made of copper alloy due to corrosion of Br- in seawater. After replacing the titanium, there is no failure due to corrosion.
(2) The heat discharge condenser is a multi-stage flash condenser that uses seawater as cooling water to cool the water vapor generated by the flash chambers of various stages. Since seawater is often mixed with sediment and sea creatures, they are inside the heat transfer tubes and tubes. The end is attached and erodes the copper alloy tube. Therefore, titanium tubes are now used on the heat transfer condensers of almost all MSF type desalination plants. In particular, in order to kill bacteria in seawater, when it is necessary to inject oxygen, it is more necessary to use a titanium tube having good corrosion resistance.
(3) Heat recovery part condenser heat recovery part condenser heat transfer area is large, due to economic reasons, copper alloy tube is usually used, only in special occasions using titanium tube, such as medium containing ammonia or hydrogen sulfide and other pollutants The corrosion of copper alloy is severe. In 1977, the 3600t/d MSF type desalination device exported to Germany, because it is an auxiliary equipment of ammonia, can not use copper alloy, but uses titanium; due to corrosion of sulfurized oxygen, Peru's 3120t/dMSP type desalination equipment, use After 1 year, the aluminum brass tube was corroded, and finally all the heat transfer tubes were replaced with titanium tubes.
According to reports, the daily production of 100 tons of seawater desalination equipment with titanium pipes reached 60,000. From 1967 to 1994, in the past 30 years, a total of 52 sets of condensers for the original energy level thermal power generation and 7 sets of seawater desalination equipment were produced, using a total of 11,000 tons of titanium welded pipes.
3, should pay attention to the problem when using
(1) Galvanic corrosion Titanium has a positive potential in seawater and promotes corrosion of other metals when it is in contact with other metals. Preventive measures include the use of titanium for heat transfer tubes and tube sheets, or the use of sacrificial anodes. Above 80 ° C, in order to prevent hydrogen absorption, Fe-90%Ni alloy is used as a sacrificial anode; below 80 ° C, a coating or a rubber-lined steel sheet is used.
(2) Gap corrosion Titanium tube is installed on the titanium tube plate by pipe expansion method, and crevice corrosion can occur in seawater with pH 8 at 100 °C. However, a copper alloy is used in the actual water chamber, and even if the seawater temperature reaches 120 ° C, crevice corrosion does not occur. In reality, in order to improve the reliability of the equipment, pipe end welding is often used to prevent crevice corrosion when used above 100 °C.
(3) Hydrogen absorption in seawater above 80 °C; titanium may absorb hydrogen; when cathodic protection is applied, hydrogen absorption is caused by overprotection. If Fe-9% Nq alloy is used as the sacrificial anode plate, titanium hydrogen absorption does not occur.
(4) Vibration Due to the thin wall of the titanium tube, when replacing the copper alloy tube, attention should also be paid to the damage caused by the tube vibration. This problem can be solved by a method in which the spacing of the tube support plates of the copper alloy tubes is smaller.