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I. Overview: The Storage and Transportation Plant of Qilu Petrochemical currently has 29 internal floating roof storage tanks for chemical products, which utilize floating tube-type internal floating roofs. In several of these tanks, such as those with numbers 112, 125, and 144, the floating floors often experience issues such as tilting, damage, and breakdowns during operation, which has a significant impact on the stable functioning of the equipment and normal production processes. Additionally, due to the reduced sealing efficiency, the toxic gases emitted pose a threat to the environment surrounding the tank area as well as to the health of the workers. The reason for this is, firstly, that it is difficult to control the flow rate of the medium as it enters the tank, which results in significant shock forces and thus causes damage to the floating disk. Under the current processing conditions, it is hard to control the medium’s flow rate in the short term ； Secondly, traditional floating tube type floating pads have inherent shortcomings in terms of structural strength and sealing performance, and even partial structural improvements find it difficult to adapt to existing manufacturing conditions. Given the above circumstances, we believe it is necessary to utilize new technologies and introduce floating pads with entirely new structural designs in order to adapt to the existing conditions and ensure the stable operation of the storage tanks. II. Structural Features and Comparisons of Common Internal Floating Disk Types 1. Structural Features of the Float Tube Type Floating Disk The main components of the float tube type floating disk are the float tubes, frame, decking, and supports, with buoyancy being provided by the float tubes. The diameter of the floating tube is 200 mm, and its length is generally 2 to 4 meters. An alloy aluminum plate with a thickness of 0.6 mm and a width of 1.2 to 1.4 meters is usually placed above the frame and the floating tube. In the early installations carried out by our factory, the floating discs were mostly connected to the pillars. Based on usage and maintenance experience, the main disadvantages of the floating tube type internal float are poor sealing performance, insufficient structural strength, and weak resistance to oil and gas impacts. 2. Structural features of box-type internal floating roofs: Common box-type internal floating roofs are typically single-pan assembled types, consisting of sealed hollow boxes made of aluminum plates; each box acts as an independent structural unit, and the entire internal floating roof is formed by connecting multiple such floating boxes together. Its main feature is that the floating tank covers the oil surface directly, eliminating any space for oil vapor to escape; this helps to effectively suppress oil evaporation. The annual oil evaporation loss is 0.2% to 0.5% of that in tanks with fixed roofs ； Secondly, it has a strong overall structure, with large and uniform buoyancy, allowing multiple people to walk around on the floating deck freely ； Thirdly, it can withstand the normal shocks that occur when oil enters or leaves the tank, ensuring smooth and steady movement of the floating disk up and down. Through comparative investigation, we believe that the box-type floating pad technology is advanced and has a rational structure, fundamentally overcoming the inherent defects of the floating tube-type floating pad, such as large oil and gas volumes, poor overall structural strength, and uneven buoyancy distribution. To address practical issues, we first discussed the technical details in detail with specialized companies, continually putting forward our ideas and requirements, such as using fluororubber for the sealing of the benzene tank’s floating disk and installing anti-rotation steel cables for positioning the floating disk. We also decided to conduct a feasibility study on applying a box-type internal floating disk to one storage tank first. III. Structural Application Analysis of Benzene Storage Tanks We first select a 2000 m3 144 benzene storage tank for analysis. The use of box-type floating trays on benzene tanks is significant in terms of environmental protection, storage safety, and reducing material loss. The float tube-type inner floating disk of this tank was installed in May 1997. After more than 8 years of operation, the floating disk became damaged and severely tilted; there were multiple instances of leakage of feed material due to the float tubes. The bag seals wore out, resulting in poor sealing performance, and these bag seals tended to carry material with them. The disk was repaired on several occasions during tank cleaning, which posed certain difficulties for further maintenance work. Based on the actual conditions of the storage tank and relevant operational experience, several technical improvements were proposed for this aluminum inner floating disk structure during the design of the technical plan: 1. The height of the supports is adjustable; under normal use, their operating height is set at 0.9m to enhance stability ； The maintenance height is 1.8m, facilitating workers to enter the tank for maintenance tasks. 2. A fully automatic pressure relief valve is added; it is easy to install, and the pressure discharge level can be adjusted according to specific process requirements. In emergency situations, it allows for rapid discharge of oil and gas, thereby reducing the impact force ； Under normal conditions, it can provide good sealing. 3. The floating disk manhole is equipped with an automatic opening and closing device; it has a simple structure. In addition to meeting the basic requirements for maintenance and routine operations, it can also serve partially as a pressure relief valve. 4. The aluminum material used for the floating boxes has been changed from 0.6mm to 0.8mm in order to enhance their structural strength. 5. Perform corresponding modifications to the inlet diffuser tube of the benzene tank by increasing its length; holes are made in all four directions of the diffuser tube – top, bottom, left, and right – to distribute the impact force caused by the injection of liquid product and thereby reduce the risk of damage due to such impact. 6. To improve its resistance to oil and gas impact, in addition to using two anti-rotation steel ropes, it is also proposed to reduce its operating height to 0.9 m, so as to ensure close contact between the floating disc and the oil surface at as low a liquid level as possible, thereby reducing the space occupied by oil and gas. 7. The sealing mechanism has been changed from a pouch-type seal to a tongue-type seal; the sealing tape used is high-plasticity fluororubber tongue tape. In addition to being fastened with screws at the junction of the floating box on the lower surface of the floating disc, welding points have also been added. A fluororubber seal is further installed on the upper surface of the floating disc, with glue used for comprehensive bonding, thereby maximizing the sealing performance and reducing the risks associated with maintenance. By examining its performance in the two tanks at Zhenhai Refining & Chemical, it has been proven that this internal floating disk moves up and down smoothly during use, has relatively high structural strength, and provides a better sealing effect than previous floating disks. Since the floating disc is in close contact with the liquid surface, there is no air or oil space during normal operation, resulting in more accurate oil measurement compared to before. The typical service life of float tube type floating pads is 5 years, while box-type floating pads can have a significantly longer lifespan due to their optimized design. IV. Benefit Analysis 1. Economic Benefit Analysis The calculation of investment benefits is carried out by comparing the floating tube method and the floating box method, with the calculation period being one cycle of tank maintenance, that is, 6 years. Based on the current market prices for float-type floating pads and drawing on past installation examples of such pads, the investment required to install float-type floating pads for 144 tanks is approximately 2/3 of that for box-type floating pads, amounting to around 120,000 yuan. The 144 floating tube type floating pads have been repaired and modified 3 times; their average service life is 3 years, while the box-type floating pad manufacturers provide a 10-year warranty. Thus, direct investment can be saved over one cycle: 12×2-18=60,000 yuan. Over 6 years, tank cleaning and maintenance are carried out twice. Assuming that the cost of each such operation, the oil loss incurred, and the impact on the operation of production and storage systems all amount to 80,000 yuan, an indirect savings in investment can be achieved: 8×2=160,000 yuan. Furthermore, based on the formula established by the U.S. Environmental Protection Agency, for a tank with a volume of 2000 m3 and a diameter of 15.696 m, the oil loss rate for a floating roof tank with a floating tube is 4699 kg/year, while the oil loss rate for a box-type floating roof tank is 581.3 kg/year. At a price of 5 yuan per kg for oil, over 6 years, using a floating box type float will result in less loss compared to a floating tube type float: (4699 – 581.3) × 5 × 6 = 123,531 yuan. Total economic benefit: 6+16+123531=343,531 yuan ； Annual economic benefit: 343531/6 = 57255 yuan, with an annual return on investment of over 31%. 2. Social benefit analysis: The social benefits of the new floating box-type inner floating platform are primarily reflected in terms of safety, environmental protection, and the physical and mental health of employees; it aligns with the principles and requirements promoted by the company’s HSE policy. Since the box-type internal floating roof sits directly on the surface of the oil, there is almost no space for oil vapor to accumulate, which effectively prevents the evaporation of oil vapor and can **increase the safety factor of oil tank operation. Applying it to 144 cans can maximize pollution control and protect human health. In summary, the use of a box-type internal floating disk for benzene tanks is highly feasible.