Drainage of internal floating roof tanks
Thread Content
We currently have two methanol tanks with a total capacity of 10,000 cubic meters, equipped with internal floating roofs. There are leaks at the drainage outlets, and these leaks cannot be fixed; therefore, it is necessary to transfer the liquid to another tank and replace the gaskets. However, since it’s an internal floating roof structure, there are floating plates inside, and these plates are surrounded by sealing strips. When the liquid level drops below those floating plates, they touch the bottom. When pumping liquid back up again, there is a risk that negative pressure could be created beneath the floating plates, potentially damaging them. I’m not sure if this will happen Is there any way to deal with it?
It won’t create negative pressure, right? Does your company’s storage tank have a oil level gauge? The gap between the floating disk and the storage tank should not be completely sealed
Check the storage tank design drawings! Typically, floating roof tanks are equipped with flame-arresting breather valves and rapid vent valves. When the floating deck descends to the height of the supports, the rapid vent valve opens automatically, allowing direct connection to the atmosphere; as a result, no negative pressure is created
Consider two questions: 1. Where are the leaks at the discharge outlet? Is it completely unmanageable? Is backflow necessary? (Do not reverse the flow unless it is absolutely necessary.) 2. When emptying the tank, the process can proceed as usual, but the flow rate should be reduced as the liquid level approaches the bottom (around 2 meters). In such a large tank, the floating disk should be equipped with a vent valve, a self-venting valve, and metering ducts, all of which allow air to enter beneath the floating disk, so there’s no need to worry about negative pressure. Given that the medium is methanol, the storage tank should be nitrogen-sealed throughout.