Seeking advice on the design of atmospheric pressure tanks and low pressure tanks
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We encountered a problem during the project: one of the solvent tanks on site was designed by the design firm as a tank at atmospheric pressure, with a capacity of around 500 cubic meters. However, in order to meet the exhaust emission requirements, we asked the design firm to increase the pressure slightly; the firm stated that such a tank would still be considered a low-pressure vessel. I would like to know how much the cost will increase for such a container, when the pressure is changed from normal pressure to low pressure, meaning it can now withstand only 0.5 kilograms of pressure If it’s a low-pressure tank, what is the maximum pressure it can withstand? Will adding an internal floating roof to the tank reduce exhaust emissions? Thank you. This post was last edited by chinazwr on 2008-12-12 20:22.]
The key is that pressure vessels need to be inspected regularly, and they are also subject to supervision by the technical oversight agency, which introduces many complications; normal-pressure vessels, on the other hand, don’t have such issues.
Steel containers are not a concern during regular inspections, as pressure vessels are commonly used in chemical plants. We can make overall arrangements.
The design of pressure vessels is different from that of atmospheric storage tanks, with many different requirements. Even low-pressure tanks need to be designed from scratch.
According to standards, the diameter of a 500m3 fixed-roof tank is 8920 mm. If the design pressure is 0.5 kgf/cm2, the load on the foundation slab (without considering hydrostatic pressure) is approximately 3480 kN. One can imagine how much higher the construction costs will be in such a case. The investment required for the tank itself will also increase; the exact amount can be determined through calculations. The API standards specify designs for slightly positive pressure tanks (I believe the maximum pressure allowed is around 40 kPa). In such cases, the foundation needs to be anchored with bolts, reinforced with beams, and equipped with rebar, which results in very high construction costs. In China, the maximum pressure allowed for so-called slightly positive pressure tanks is 6 kPa {just an impression though}. My personal suggestion is that you use an internal floating roof tank. Although its investment is slightly higher than that of a fixed-roof tank, the breathing losses associated with internal floating roof tanks can be reduced by 95% compared to fixed-roof tanks. This not only helps save resources but also meets environmental requirements to a large extent. If those requirements still cannot be met, you can opt for a nitrogen seal or add an activated carbon adsorption system (using a nitrogen seal requires less investment).
Thank you for the detailed response from above. We currently plan to use a design similar to that of the micro-positive pressure tank you mentioned, which would allow us to increase the pressure of the exhaust gas to 5 KPa. But will the use of an internal floating roof reduce the amount of exhaust gas emitted? I am referring to the designed emission amount determined after considering various design conditions, as the design of emissions takes into account primarily the release of sealed nitrogen gas that occurs when material is fed into the tank.