Comprehensive prevention and control measures for excessive loss of seal oil in dry gas cabinets

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Comprehensive preventive and control measures for excessive loss of sealing oil in dry gas tanks I. Introduction to the problem of excessive oil consumption The issue of excessive loss of sealing oil in dry gas tanks is an old one. The dry gas holder most widely used in China today is of the Oman Aran type. Its design was introduced from abroad around the early 1980s. As early as 1987, when such gas tanks were not yet widely used in China, the newly launched Zhengzhou natural gas project was the first to have two dry gas tanks, each with a storage capacity of 50,000 cubic meters, built. Overall, these two tanks have played a crucial role in maintaining the balance between supply and demand of natural gas in Zhengzhou. However, not long after the gas holders began to be in use, we found that the annual fuel consumption per holder was 4–5 tons. This raises our first question: With such high annual fuel consumption, is it due to quality issues in the design and construction of the gas holder, or is it an inevitable consequence of the production process? To address this, we invited experts from the original design and construction firm of the gas holder to conduct a review. During the on-site inspection, apart from some oil accumulation on the gas tank piston, no other severe oil leakage was detected. At that time, the gas holder had been in operation for just over a year; 6 tons of oil had been added to its sealing system, while only about 1 ton of oil had splashed onto the piston of the gas holder. Although this is one of the reasons for high fuel consumption, it is clearly not the only factor. The personnel from the original design and construction team of the gas holder explained that there were no issues with the design or construction quality of the gas holder. Several gas tanks of the same type that are in use in China currently face similar issues; some of these tanks consume dozens of tons of fuel per year, so the fuel consumption of the Zhengzhou gas tank is not excessive. As for the splashing of oil on the piston surface of gas cabinets, this phenomenon exists to varying degrees in such cabinets, and there are currently no effective measures to completely prevent it. Although others may say so, the consistently high fuel consumption and the cumbersome process of refueling each time are truly frustrating. Many problems plague us; it’s truly strange that no large amounts of oil leakage were detected, yet several tons of oil have disappeared without a trace. On the other hand, oil splashing above the gas tank piston is obvious, but it cannot be resolved immediately. II. Strive to explore comprehensive prevention and control measures; many issues require our answers. To this end, we conducted extensive technical research in hopes of finding answers through the technological transformation efforts of others, but we were not successful. We have reviewed a lot of materials, but the best solution isn’t in books. As users of gas cabinets, we have more time than the designers and cabinet builders to address these issues, and this is also our social responsibility. We often circle around the gas tank, observing the subtle changes that occur during its operation. When storing or supplying gas into the tank, we squat inside it and watch for a long time as the piston moves up and down, as well as the operation of the seal oil system, in an attempt to detect any signs of excessive oil consumption. We also collect information on the models and quality properties of the sealing oils, examine the operation records of the oil supply pumps, and conduct a comprehensive analysis of the internal relationships and mutual influences among all these elements. Finally, we decided to start by addressing the oil splashing on the piston surface. The seal oil in dry gas cabinets circulates. The seal oil is first pumped by a supply pump located on the ground outside the cabinet, and this oil is delivered to the static oil tank situated at the upper part of the gas tank. The oil in the tank settles, and then enters the gas holder through the oil drainage holes located at the top of the holder. Once the oil that passes through these holes enters the gas holder, it immediately flows down along the inner wall of the holder. The falling oil is captured by the oil cups surrounding the piston, and the oil in these cups then flows slowly through the gap between the piston and the inner wall of the holder, eventually reaching the oil sump located at the bottom of the holder. The oil accumulated in the oil sump at the bottom of the gas holder flows to the oil tank at the lower part outside the holder, where it is pumped under pressure by the fuel pump; thus, the oil completes one cycle. Standing on the piston inside the gas holder, one can see that the oil falling from the oil drainage holes at the top of the holder hangs on the high walls of the holder, resembling a waterfall descending from the sky. Due to the significant changes in cabinet volume, the height of the piston oil cup above the oil drain port also frequently varies within the range of 3 meters to 50 meters. Thus, it is unrealistic to expect a piston oil cup with a radius of only 0.46 meters to completely capture the falling oil. Oil splashing occurs right below the oil drain port. The severity of the problem lies in the fact that an annular walkway for inspections is located right next to the piston oil cup; the splashing of oil not only hinders proper inspections but also contaminates the pistons of the gas holder, which covers an area of over a thousand square meters, leading to waste. After several failures, we realized that a single measure to prevent oil splashing was hardly effective; therefore, we adopted a comprehensive approach that combines internal controls with external barriers. First, we installed a fuel supply throttling device between the inlet and outlet of the fuel pump. The purpose is to reduce the amount of oil supplied by the pump per unit of time, thereby decreasing the kinetic energy of the oil as it flows through the drain port. This allows the oil to flow as closely as possible against the inner wall of the gas tank, due to its viscosity, and thus reduces splashing. Practice has shown that this measure plays a certain role in controlling oil splashing. The principle of the oil pump throttle device is shown in Figure 1. Of course, this will increase the operating time of the oil pump per cycle, but the oil pump is designed to operate intermittently in the original design, and the interval between two starts of the oil pump is more than sufficient to meet the requirement of extending its operating time. Therefore, reducing the increase in the operating time of the oil pump caused by a lower unit fuel supply amount does not result in any negative effects. At the same time, we placed an oil splash collection tarp beneath each oil discharge port. The canvas traps the splashing oil and sends it back to the piston oil sump. It should be noted that in the original design of the gas holder, a steel oil splash collection plate was also installed below the oil drainage port. This steel plate measured 1.5 meters in width and 4.1 meters in length, and it was mounted at a height of 3.7 meters above the piston oil cup. The area of the oil splatter collection plate is severely insufficient; there are empty areas in the three directions other than those along the cabinet walls, which results in a large amount of oil falling outside the oil collection cup. With such an oil splashing collection panel, even if it captures some of the oil falling from above, the oil will splash again upon coming into contact with the hard steel surface. On the other hand, as the oil flowing down along the cabinet walls enters the piston oil cup, it impacts the oil inside the cup, often causing the oil to splash over the rim of the cup and flow between the weight cement blocks on the piston, making cleanup extremely difficult. Compared to steel oil splash collection plates, oil splash collection canvas differs from them in terms of size, material properties, and installation location. The oil splash collection canvas is 3.5 meters wide and 5.8 meters long, providing sufficient area to capture oil splashes and send them back to the oil tank. For oil that falls from above, the excellent shock-absorbing properties of the canvas play a crucial role by preventing secondary splashing of the oil caused by steel materials. The oil splashing collection canvas is installed with its lower end pressed tightly against the mouth of the piston oil cup, and it extends radially into the oil cup by more than 0.2 meters; any oil droplets splashed up by oil flowing down from the cabinet walls are, without exception, caught by the canvas and sent into the oil cup. The oil splatter collection canvas is at a 60-degree angle to the horizontal plane. In this way, the directional flow of the oil is ensured without causing inconvenience to the inspectors walking in the passageway. For the installation of the splash guard canvas, refer to Figure 2. As is well known, large dry gas holders operate continuously. Comprehensive preventive and control measures for excessive loss of seal oil in dry gas tanks. Source: www.shu1000.com. Therefore, it is sometimes difficult to carry out thorough inspections on these massive structures that are dozens of meters tall. After completing the work on the upper part of the piston, we decided to take advantage of this rare opportunity when production was halted to inspect the gas tank below the piston. When examining the bottom of the cabinet, we found that a large amount of oil had accumulated in the central area of the bottom plate, outside the circular oil groove there. It turns out that the oil splashing below the piston is more severe. Since the middle area of the cabinet bottom plate is lower than the inner wall of the oil tank, the oil that splashes outside the tank remains there, resulting in a significant reduction in the amount of oil that should be involved in the circulation process. Here, when the oil accumulates to a certain level, it will flow through the gas tank’s piping into the trap installed on those pipes; in severe cases, this can block the inlet and outlet pipes, affecting the normal operation of the gas tank. However, the bottom of the cabinet is the operating area for the piston, and no splash suppression measures can be taken. Given the special circumstances here, an open-minded approach plays an important role. We carefully studied the structure at the bottom of the gas tank and analyzed it in relation to the normal operation of the sealing oil. Since during normal operation the elevation of the bottom of the cabinet is higher than that of the liquid level in the oil tank, we drill several holes in the inner wall of the oil tank at the bottom of the cabinet to connect the central area of the cabinet bottom with the oil tank, allowing the oil that splashes to that area to flow back automatically into the oil tank. It creates an internal small cycle of continuous oil splashing and reflux, thereby cleverly solving what seemed to be a very complicated problem. For details on the oil return process hole, see Figure 3. III. Current benefits of integrated control measures: After the comprehensive implementation of measures to address excessive loss of sealing oil in dry gas tanks, significant economic and social benefits have been achieved. Firstly, the dozens of tons of oil that were previously trapped in the middle area at the bottom of the tank re-enter the circulation system, and this alone allows the company to save nearly 100,000 yuan in costs. The oil recovered can be used to replenish the insufficient amount of oil in the circulation system, while the excess should be drawn out of the cabinet and stored for future use. Thanks to effective measures taken through a two-pronged approach, the oil contamination issue inside the cabinet was completely resolved. In recent years, the annual consumption of seal oil for gas tanks has decreased significantly, with each tank saving over 10,000 yuan in fuel costs per year. Looking at the comprehensive measures for preventing excessive loss of sealing oil: its application technology is reasonable, the construction process is safe and simple, the investment is low, and it offers significant economic and social benefits, making it worthy of wide-scale promotion. This technology plays a positive role in maintaining the safe operation of gas tanks, ensuring residents have regular access to gas, and increasing corporate revenue. The working principle of the oil throttle is to achieve throttling by installing a hydraulic throttle element between the inlet and outlet pipes of the existing GR36×4 oil pump, without replacing the pump itself. When the oil pump 8 is operating, the check valve 9 opens to supply oil to the oil tank in the gas holder. At the same time, check valve 5 is opened, and the hydraulic control valve 2 is pushed open via the hydraulic control tube 4; some oil returns to the oil tank through valve 2, thereby reducing the amount of oil supplied to the gas tank’s oil tank per unit of time. When the oil pump 8 stops operating, check valves 9 and 5 close simultaneously. There is still oil pressure in the hydraulic control tube 4, and this pressure is used to close the hydraulic control check valve through valve 3. In the diagram, there is a high-level oil pump and a low-level oil pump; the one marked with a dash is the high-level oil pump system. The high-level oil pump and low-level oil pump systems can operate independently or simultaneously. Comprehensive prevention and control measures for excessive loss of seal oil in dry gas cabinets. Source: www.shu1000.com. Gas cabinets are important facilities for gas storage as well as for ensuring safety and environmental protection. The 20,000 cubic meter dry gas holder has a total height of 33.9 meters and a diameter of 34.3 meters. It is equipped with facilities such as T-fences and pistons inside, and is sealed using a rubber membrane. Outside, it features devices such as leveling weights and vent pipes. It not only meets the requirements for safe operation under high loads in refineries but also offers good energy-saving and environmental protection benefits. Users who need technical information on dry gas tanks are requested to contact us. 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