Regarding the design conditions of storage tanks
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For example, methanol is the medium – is the design pressure of its storage tank based on the saturated vapor pressure of methanol at the design temperature? How is its design temperature calculated? I originally wanted to use a fixed-roof storage tank, but after checking the design manual, I found that the designed pressure for such tanks is 2 kPa, while the saturated vapor pressure of methanol at 40 degrees is over 35 kPa. Does this mean that fixed-roof tanks are not suitable for storing methanol?
Methanol tanks generally use a fixed roof combined with a vent valve. Additionally, due to the high temperatures in summer, external spraying for cooling is usually required. Although the saturated vapor pressure is in the range of several dozen kPa, a vent valve is still necessary. . The common practice abroad is insulation, especially in areas with high sunlight intensity; insulation is widely used there. In China, the spraying method is often adopted simply by the design institutes, but it proves to be troublesome and unsightly when used in factories, haha.
For storage tanks with fixed roofs, according to HG25012-1993, the design pressure is -0.5 to 2 kPa, and the design temperature ranges from -18 to 150 degrees Celsius. This design pressure is not sufficient to meet the saturated vapor pressure of methanol at normal temperatures.
If the design pressure is 2 kPa, then the operating pressure of the breather valve must be less than 2 kPa; in that case, a large amount of methanol would evaporate. In such a situation, it would be more cost-effective to use a floating roof instead
Float roof tanks aren’t necessarily unsuitable; it depends on the volume of your storage tank. Float roof tanks are generally used for tanks with very large capacities, such as oil tanks with a capacity of 50,000 m3 or gas holders with capacities of several hundred thousand m3. Your methanol tank doesn’t fall into that category. Is it this big? And floating roof tanks are quite expensive. . Besides, as I said earlier, during the hot summer months, spraying is used to cool down and maintain low temperatures for methanol; foreigners generally opt for insulation instead. . . It’s something truly terrifying to think that a methanol tank, along with all the methanol contained within it, can reach a temperature of 40°C. . . You don’t go to the site very often, do you? Floating roof tanks are generally not used for methanol storage, both domestically and internationally. . You can look up information online about the breathing loss of methanol storage tanks and do the calculations yourself. . Of course, if your client really has plenty of money to spare, you can go ahead and install a floating roof tank for him. . Hehe. .
We want to replace the previous fixed-roof storage tank with a capacity of 2,000 cubic meters by an internal floating-roof tank; internal floating-roof tanks come in capacities of several hundred cubic meters as well. You are referring to external floating roofs, right, like those used in gas tanks and similar structures
Methanol belongs to Category A substances; according to the regulations, storage tanks for Category A B and Category B A should be floating roof tanks (including internal floating roofs), as the use of fixed-roof tanks is not acceptable. Generally, methanol systems are equipped with a nitrogen sealing system.
Furthermore, the methanol vapor pressure mentioned by the poster refers to absolute pressure, while the design pressure of 2 kPa for the storage tank refers to gauge pressure; clearly, 2 kPaG is greater than 35 Kpaa.
Where was this seen in a standard? I really didn’t notice such a requirement
Code for Fire Protection Design of Petrochemical Enterprises ____GB50160-2008
The \"Code for Fire Protection Design of Petrochemical Enterprises\" ____GB50160-2008 specifies that for storing Class A/B liquids with a boiling point below 45°C, pressure vessels or low-pressure storage tanks should be used. The boiling point of methanol is 64.8°C, so a dome tank with nitrogen blanketing can be used.