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The reliability of the Thousand-Yacht pumps is the same as that of the Dow Chemical Company. Dow Polyurethanes uses a deep vacuum at its Texas facility to remove water vapor and inert gas from its products. gas. In the past years, the company had been using rotary vane vacuum pumps to achieve the required degree of vacuum. Although rotary vane pumps have greatly improved performance compared to previous pumps, the reliability of such pumps remains a problem. Every pump has to be repaired several times a year due to problems such as normal pump wear and fluid ingress. The maintenance costs of these pumps total more than $180,000 per year. Dow realized that it should look for a new pump that would eliminate the invading oil from the pump and further improve the pump's operational reliability and flexibility.
Solution The steam jet pump was excluded from Dow because one of the limiting conditions for selecting the pump was not to increase the waste flow from the unit. Liquid ring pumps are also not considered as they will generate the fluid to be treated. Moreover, due to the warmer weather, the temperature of the sealing fluid of such pumps will increase and their operating efficiency will decrease. In addition, the liquid ring pump requires additional pressure boosters to achieve the required deep vacuum. CliffMoore, the company's polyurethane plant engineer, decided to look at the dry vacuum pump. Although the dry vacuum pump basically has no waste steam, he is still worried about the reliability of its design. Special attention should be paid to the fact that the pump must be able to solve the problem of liquid invading steam flow without causing harmful effects. After extensive investigations and investigations of other places where dry pumps were used, Dow decided to use Busch's COBRA dry thread vacuum pumps.
Compared with other similar pumps, Busch's COBRA dry screw vacuum pumps are more efficient and require lower maintenance costs because COBRA pumps have the following features. This chestnut adopts a single-stage structure, so it has fewer moving parts and no intercooler. Its oil-free work means that it does not produce waste and thus eliminates the cost of waste disposal. The small footprint of the COBRA pump saves space and its non-contact parts extend the pump's service life. The pump's flow path is straight and short, so that the pumped material does not accumulate in the pump or condense. In addition, this pump can also be used to inject liquids in special applications such as flushing or cooling. The working principle of the C0BR4 pump is also very simple. The gas entering the pump is trapped in each segment! Between the lines, and follows a short, straight path in the axial direction 11 to the exhaust port, and then discharged.
Results In 19S38, Dow installed three COBRAAC800 dry thread vacuum booster/pump systems. Since the installation of these pumps, Dow has tasted a lot of sweetness.
Thousand pumps do not create additional waste streams in the workflow.
The failure rate of equipment is reduced from once a month (running time) to once every three years. In fact, the only failure that Dow installed the Busch COBRA pump was due to a problem in the process, and it had nothing to do with the vacuum pump itself.
Vacuum pump maintenance costs are reduced by more than 80*.
* The COBRA vacuum pump/supercharger system can achieve a higher degree of vacuum, thereby shortening the required elution time and enhancing the working capability of the entire device. Several considerations for the thermal behavior of the bending force device include whether the austenitic stainless steel pressure vessel needs post-weld heat treatment. The post-weld heat treatment uses the reduction of the yield limit of the metal material at high temperatures, resulting in plastic rheology in places where the stress is high. To eliminate the welding residual stress. At the same time, the plasticity and toughness of the welded joints and heat-affected zone can be improved, and the ability to resist stress corrosion can be improved. This stress relieving method is widely used in carbon steel and low alloy steel pressure vessels having a body-centered cubic crystal structure. The crystal structure of the austenitic stainless steel is face centered cubic, and since the face-centered cubic crystal structure of the metal material has more slip planes than the body-centered cubic, it exhibits good properties and strain hardening properties. In addition, in the design of chemical equipment, stainless steel materials are often used for the purpose of preventing corrosion and meeting the special requirements of temperature. In addition, stainless steel is expensive compared with carbon steel and low alloy steel, so its wall thickness is not very thick. Therefore, from the standpoint of the safety of normal operation, there is no need to put forward requirements for post-weld heat treatment of austenitic stainless steel pressure vessels. As for the corrosion that occurs due to use, the instability of the material, such as fatigue, impact load, and other abnormal operating conditions, is a problem that is difficult to consider in conventional designs. If these conditions exist, relevant scientific and technical personnel (such as: design, use, research, and other relevant units) need to conduct in-depth studies, compare experiments, come up with practical heat treatment solutions and ensure that the comprehensive performance of pressure vessels is not affected. Otherwise, if you do not fully consider the need and possibility of heat treatment for austenitic stainless steel pressure vessels, simply comparing the conditions of carbon steel and low alloy steel to heat treatment requirements for austenitic stainless steel does not always work. .
The heat treatment of fixed tube-plate heat exchangers in which the shell medium is liquid ammonia fixes the tube-plate heat exchanger. The overall heat treatment cannot be performed due to its structural characteristics. If heat treatment is required due to the toxicity of the shell medium or stress corrosion characteristics, only secondary heat treatment is used to solve this problem. SP: First heat treatment of the heat exchanger shell, after the shell and tube sheet welding, local heat treatment of the two ring welds. However, due to the inconvenience of this method, some designers canceled the heat treatment requirements by referring to the phenomenon that the fixed tube-plate heat exchanger with liquid ammonia as the shell medium was not heat-treated. This practice is inappropriate.
Heat-jacketed jacketed vessels with jacketed vessels Because of the jacketed thermal insulation layer, hydrostatic tests are also required after the inner cylinder is heat-treated. Therefore, the jacket can only be non-destructively tested on the inner cylinder, heat treated, water The pressure test was passed before welding.
The pressure vessel always has a variety of interfaces for external connection, and the connectors or attachments welded to the housing should be heat treated together with the vessel. When the takeover must pass through the parts covered by the barrel jacket, the integral jacket cannot pass through the takeover, and only the method of splitting the welded sets can be used. S1): welding the pre-welding member in the welding position of the inner cylinder, the pre-welding member is heat-treated together with the inner cylinder body, and finally, the splitting jacket and the pre-welding member are welded and mutually welded.
Separating the pressure jackets of the pressure welding vessels will increase the difficulty of manufacture, which is the cost of pressure vessels for containing more severe media and is a measure that must be taken. If the jacket covered by the jacket is not on the same plane, the difficulty is even greater.
Conclusion Although the overall heat treatment of the pressure vessel after welding (including the heat-sinking process inside the furnace) is not energy-efficient and the cycle is long, and the actual operation is subject to various difficulties due to the pressure vessel structure and other factors, it is still the current pressure. The only method in the container industry that is acceptable by all parties to eliminate welding residual stress. Little 6 "Liao
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