Calculation of the pipe diameter for nitrogen sealing in internal floating roof storage tanks

For the design of the nitrogen sealing system in internal floating roof storage tanks, it is indeed necessary to take multiple factors into consideration. Even though HG 21502.2-1992 \"Steel Vertical Cylindrical Internal Floating Roof Storage Tanks\" states that internal floating roof storage tanks can significantly reduce evaporation losses compared to fixed-roof tanks, other technical requirements must also be taken into account when designing the nitrogen sealing system. 1. **Material balance criteria**: Material balance calculations usually need to be carried out based on the specific process flow and the properties of the substances involved, taking into account factors such as fluctuations in the material inside storage tanks, changes in temperature and pressure, as well as potential leakage amounts. 2. **Diameter calculation**: The diameter is determined primarily based on the flow rate requirement and the allowable flow velocity. Calculations can be performed using the Bernoulli equation or pipe flow formulas (such as the Darcy-Weisbach equation). Parameters to consider include the supply pressure of nitrogen, the required flow rate, as well as the length and elevation differences of the pipes. 3. **Self-acting control valve**: The choice of a self-acting control valve is usually based on the required precision of flow control, response speed, and operational stability. The specific models and specifications need to be determined based on actual requirements and the parameters of the nitrogen supply system. 4. **Breather valve**: The selection of a breather valve is based on the design pressure and vacuum of the storage tank, as well as environmental conditions. It is necessary to select appropriate pressure relief and vacuum resistance capabilities based on the operating pressure and design capacity of the storage tank. In general, when designing the nitrogen sealing system for internal floating roof storage tanks, detailed calculations are required, along with the selection of appropriate equipment, to ensure the safe, economical, and reliable operation of the system. It is recommended to refer to relevant professional standards and specifications, while designing in conjunction with specific engineering technical conditions and empirical data. If possible, it is more secure to work with engineers or consulting firms specialized in such design. .

Document No. Huanban 104 issued by the Office of the Ministry of Environmental Protection: “Notice on the Issuance of the ‘Guidelines for Identifying VOCs Pollution Sources in the Petrochemical Industry’ and the ‘Guidelines for Leak Detection and Repair in Petrochemical Enterprises’”. Attachment 2: Reference calculation tables for identifying VOCs pollution sources in the petrochemical industry. I performed some calculations; the leakage rate for two tanks with a capacity of 1,000 cubic meters is 30 kg/h for tanks with fixed roofs, and 2 kg/h for tanks with internal floating roofs. The conclusions are similar to those of HG 21502.2-1992.

Internal floating roof storage tanks have significant advantages over fixed roof storage tanks, performing better in reducing volatile organic compound (VOC) emissions. This is consistent with what is stated in \"HG 215022-1992 Steel Vertical Cylindrical Internal Floating Roof Storage Tanks Series\", which says that internal floating roof storage tanks can reduce evaporation losses by 85% to 90%. In an era with increasingly strict environmental regulations, using internal floating roof storage tanks for storage operations in the petrochemical industry not only helps to reduce environmental pollution but also enables companies to comply with relevant environmental laws and regulations, such as the guidelines for identifying and addressing VOCs pollution sources outlined in Document No. 104 issued by the Environmental Protection Agency. When selecting and designing equipment such as breather valves, pipe diameters, and self-acting control valves, it is extremely important to ensure that these devices can work effectively in conjunction with the structural characteristics and operational requirements of the storage tank, in order to maintain a low leakage rate. In addition, regular Leak Detection and Repair (LDAR) programs should also be considered to continuously control and reduce VOC emissions. Using internal floating roof tanks is a very effective method for reducing VOC emissions, and proper maintenance and supervision will further ensure their performance. .