Can steam be used for the replacement of spherical tanks? What are the potential hazards?
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After the pressure was released from the spherical tank at the start-up of the unit, it was planned to use steam for displacement. Can it be completely replaced? What harm does it cause to the spherical tank?
Liquefied hydrocarbon spheres are generally purged with nitrogen. Replacing it directly with steam may present several issues: 1. Can the material of the tank withstand the temperature of steam? 2. Will the internal materials react after being heated, such as through crystallization or excessive pressure? 3. How is the condensed water formed during cooling discharged? What to do after adding materials?
The steam volume is too high; the storage tanks cannot withstand such temperatures, and it can also cause burns to people. A low-wattage system will produce a large amount of condensate (if replaced with a low-wattage version)； The steam volume is too low; in a tank of this size, the steam quickly condenses into water, and it’s not possible to use it for displacing fresh fruit.
Under normal circumstances, steam can be used for steaming and displacement. Below are the steps for maintaining spherical tanks: Method 1: Fill the spherical tank with fire water or another water source; water is injected from the bottom, and once water appears at the top, it indicates that the tank has been properly displaced. Then, close the valves, install blind flanges, and either drain the water or transfer it to another spherical tank for maintenance. Advantage: One replacement, convenient. Disadvantages: It requires a large amount of water, and operational errors by personnel can lead to leakage accidents, just like the incident that occurred at Shandong Shida Technology. Evaluation: It’s best not to use it; it’s quite dangerous. Method 2: Use a pump to evacuate the material and then close the valve; fill the spherical tank with nitrogen, and burn the released gas in a flare. Once the concentration of flammable gases at the top of the tank is below 0.5%, open the manhole for natural ventilation. If necessary, steam can be introduced through the bottom manhole for steaming. Advantages: Safe and reliable. Disadvantages: Longer processing time, high consumption of nitrogen, and frequent use of flares, which is a waste of resources. Evaluation: It is currently used quite widely; if steam cooking is required, it is necessary to determine the design temperature of the spherical tank, and the cooking temperature must not exceed this design temperature.
The opinions from above are quite professional, but it’s difficult to keep the steaming and cooking temperature below the designed level. After all, the design temperature for domestic liquefied hydrocarbon spheres is generally set at 50°C.
Steam can be introduced slowly using DN25 hoses; by controlling the amount of steam, low-temperature steaming can be achieved. Spherical tanks hold media that are highly volatile and evaporate quickly
I’ve learned it; coincidentally, we need to inspect the liquid ammonia tank this year. Last year, when testing the ethylene and propylene tanks, we carried out a complete nitrogen displacement process.