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Discussion on the Operation and Management Model of Large-scale Liquefied Petroleum Gas Vaporization Stations I. Overview Starting in 1982, Shenzhen adopted the approach of centralized liquefied petroleum gas supply through pipelines, a cost-effective and rapid method of urban gas supply that draws on the experience of community gasification in other regions. This approach was chosen to meet the needs of building a modern city. Guided by the principle of \"comprehensive planning, phased construction, gradual network expansion, and progressive establishment of gas supply pipelines,\" over the past decade or so, more than a dozen centralized vaporization stations have been built in areas such as Luohu, Binhe, Moutoulong, Baihua, Dongle, Lianhua, Jinhu, Luofang, and Nanyou. These stations provide high-quality gas supplies to over 300,000 residents and commercial users within the special economic zone. With the construction and development of Shenzhen’s gas pipeline network, the relatively independent community gasification stations were gradually connected to form a unified system. After the large-scale liquefied petroleum gas gasification station, the Luofang Gasification Station, came online in 1998, more than a dozen central gasification stations were shut down one after another, marking the beginning of a new era for Shenzhen’s pipeline gas industry – an era of centralized gas supply through a networked system. II. Introduction to the Luofang LPG Station The Luofang LPG station is currently the largest and most automated LPG vaporization station in China. Its design incorporates the new concept of a garden-style vaporization station. The original design of the Luofang station called for a supply capacity of 200,000 households; based on its current operational performance, we believe that its supply capacity can reach around 500,000 households. The station consists of the following seven components: 1. Tank area: The tank area of the Luofang station features six underground tanks with a capacity of 100 cubic meters each, resulting in a maximum storage capacity of 285 tons ； 2. Unloading platform: There are four unloading positions, allowing the gas to be unloaded from four gas tankers simultaneously ； 3. Compressor room: Equipped with two CORKEN--69l compressors of American manufacture ； 4. Gasification furnace area: Equipped with four American-made RANSoME ID–2500 open-flame water-bath gasification furnaces, with a gasification capacity of 4.8 tons per hour per unit ； 5. Power distribution area: It consists of both municipal power and backup power; the capacity of the backup generator is 90 kVA ； 6. Fire protection area: It consists of a fire water tank with a capacity of 600 cubic meters and two fire pumps with a flow rate of 100 cubic meters per hour ； 7. Control Center: This is the core part of the Luofang Gas Station. The station makes use of a modern computer monitoring system to control the operation of the entire facility. Each important process parameter within the station is transmitted to the control unit via secondary instruments; by sitting in front of this control unit, it is possible to monitor the operation of the gas station. The unit also allows for the control of valves, compressors, and vaporization furnaces located on the storage tanks. This system features a powerful early warning function – should any minor deviation occur during the operation of the station, the control unit will issue an alarm and switch to the corresponding alarm screen. The station’s staff can then take appropriate actions to address the issues indicated on the alarm screen. The Luofang gas station is highly automated; with the exception of the need for manual intervention to connect hoses and open the valves on the tank trucks during gas unloading, all other operational tasks are carried out by computers. During unloading, the computer automatically determines the liquid level in each storage tank, selects the tank with the lowest level, and automatically opens its inlet valve to start the unloading process. When the liquid level in that tank reaches 85%, the inlet valve closes automatically, after which the system selects the next tank with the lowest liquid level for unloading ； During gas supply, the computer will first select the tank with the highest liquid level to supply gas. When the liquid level in the tank being used for gas supply drops to 5%, the outlet valve closes automatically, after which the second tank with the highest liquid level is selected for gas supply. The computer monitoring system at the Luofang gas station is capable of controlling the gas supply operations at the station, as well as automatically recording historical data on the operational parameters, such as the liquid level and pressure in each storage tank on a hourly basis. It can even calculate the amount of gas supplied per hour, day, month, and year. Due to the high degree of automation at the Luofang gasification station, few workers are required; we have assigned only eight staff members to this station, which helps to **reduce operating costs**. All operational data from the Luofangqi gas station is transmitted to the company’s main server via the company’s internal network, allowing managers at all levels to access it from their computers in the office. III. Operation Management of Luofang Gas Station Although the Luofang Gas Station was designed optimally with top-quality equipment, we still encountered many difficulties in its early stages of operation. Through some trial and error, we took effective measures to overcome the problems that arose during its operation, and also developed some new management approaches. l. Uneven load on the gasification furnaces: The original design of the Luofang gas station called for a regulator to be installed at the outlet of each gasification furnace. This design cannot meet the operational requirements of any gas station, as it is difficult to adjust the outlet pressures of multiple regulators to be consistent; as a result, some regulators will deliver a larger volume of gas while others deliver less. This leads to some gasification furnaces receiving an excessive supply of gas and others having a lower supply volume, resulting in uneven gas supply across the furnaces. This uneven supply affects the efficiency of gasification and increases the risk of equipment damage. To address this issue, we used a balance pipe to connect the various regulators, thereby solving the problem of uneven gas supply to the gasification furnaces. Because no matter how the voltage regulators function, the load is evenly distributed to the gas supply vaporizers through balance pipes. 2. Issues with the gas supply for the burner in the gasification furnace: The gas source used to heat the burner in an open-water bath type gasification furnace usually comes from the gas phase outlet of the furnace. In theory, liquefied petroleum gas should be fully vaporized after absorbing heat through the heat exchange mechanism in the gasification furnace. However, liquefied petroleum gas contains, to some extent, components that are difficult to vaporize. These unvaporized components reach the burner in the gasification furnace via the combustion tube, causing blockages in the burn control valves and preventing them from functioning properly, which in turn affects the normal supply of gas. To ensure the proper operation of the gasifier, it is necessary to shut down the furnace and clean the combustion control valve every two weeks. To achieve this, we connect a pipe from the vapor line of the storage tank to the gasifier; natural gas from the storage tank is used to supply heat for combustion within the gasifier. Since the naturally vaporized petroleum gas is relatively pure, the combustion control valve in the gasifier does not get clogged. 3. Improvement of the lightning protection system: Since the Luofang gas station is operated with computer-based monitoring, many secondary instruments have been installed on-site. The originally designed lightning protection system was too simple, featuring only two lightning rods 12 meters tall in the tank area, which was far from sufficient to protect the station from lightning strikes. As a result, during the first thunderstorm season after the station began operation, five pressure transmitters, four level transmitters, and two flowmeters were damaged, resulting in losses of over 200,000 yuan. Later, we asked the Guangdong Lightning Protection Center to assist in redesigning and installing the lightning protection system. After on-site inspections and calculations, three lightning rods 32 meters high were installed, and lightning protection units were placed throughout the system, from the power supply to the wiring terminals at the site. Since then, the electronic equipment at the Luofang gas station has not been damaged by lightning strikes again. 4. Control of pressure in underground storage tanks The Luofang gas station uses underground storage tanks to store liquefied petroleum gas. Since sunlight cannot reach these underground tanks directly, the surface temperature of the tanks remains around 20 degrees Celsius. The saturated vapor pressure of the petroleum gas inside the tanks is below 0.5 MPa. In large-scale liquefied petroleum gas vaporization stations, it is easy to control the pressure in the underground storage tanks, and controlling this pressure is crucial for the safe operation of the station as well as for handling emergency situations. We control the pressure in the underground tanks using the following methods: (1) Controlling the tank pressure through natural vaporization. At the Luofang gas station, since gasification is carried out using open-flame water bath reactors, each reactor requires more than 30 kilograms of gas per hour for heating and combustion; this gas comes from the natural vaporization within the storage tanks. As a result, the operating pressure of these tanks can be adjusted. We generally keep the tank pressure below 0.5 MPa. When the liquid level in the tanks drops to 5%, we reduce the pressure to below 0.2 MPa. When liquefied gas trucks arrive at the station to unload their cargo, it is not necessary to use the compressors or pumps located at the station. By taking advantage of the pressure difference between the full-loaded gas tanks (whose pressure is usually above 0.5 MPa) and the underground tanks, it is possible to unload 10 tons of gas within one hour. This alone saves around 100,000 yuan in operating costs per year. By controlling the pressure in the underground tanks, the pressure of all gas supply systems within the station was also under control; as a result, leaks at all moving and stationary sealing points were less likely to occur. For this reason, the Luofang Gas Station was established as a \"leak-free station\". (2) Emergency pressure relief through underground pipelines: When there is a severe leak at the first valve of an underground storage tank, it is very helpful to quickly reduce the pressure inside that tank to around 0.1 MPa, which is crucial for dealing with the incident. The major gas explosion in Xi’an was caused by the failure to address this issue properly. As for how to deal with leaks in the first valve of an underground tank, our approach is to first close the inlet and outlet valves of the gasifier and all tanks, then open the vapor valve of the tank in question. Next, we adjust the outlet pressure of the natural gas vaporizer regulator to twice the operating pressure of the pipeline network, so as to quickly discharge the vapor from that tank into the underground pipeline network. We conducted several emergency relief tests, and the results showed that it was possible to reduce the pressure in the underground tank from 0.5 Mpa to 0.15 Mpa within 20 minutes using the aforementioned method. Since the released underground tank rapidly vaporizes naturally within a short period of time, and no sufficient heat can be absorbed from the outside to sustain this vaporization process, ice (or frost) forms on the exterior of the tank during emergency release. Once the tank pressure drops to 0.15 Mpa and the release stops, the low pressure remains due to freezing effects for 2–3 hours; we can take advantage of these valuable few hours to control the leak by injecting water or sealing it off, while simultaneously addressing the source of the leak. 5. Selection of the gasification furnace: The gasification furnace used at the Luofang gas station is a RANSOME ID–2500 open-flame water-bath type gasification furnace manufactured in the United States. This furnace features a compact design, requires little space, and has a thermal efficiency of up to 75%. The cost of gasifying one ton of liquefied petroleum gas is only 8 kilograms of LPG, making it the burner with the lowest operating costs among those we have used. In addition, this gasification furnace boasts a high degree of automatic control and strong warning functions that help prevent various accidents. It can also automatically record the operation history of the furnace, making it the ideal choice for large-scale gasification stations. IV. Conclusion Since its commissioning in 1998, the Luofangqi gas station has operated stably thanks to our continuous efforts and careful maintenance. The above are merely some of our practical experiences and insights regarding the operation and management of large-scale liquefied petroleum gas vaporization stations; they are provided for reference only by colleagues in the same field. We welcome corrections from experts where there may be any inaccuracies. “Discussion on the Operation and Management Models of Large-scale Liquefied Petroleum Gas Vaporization Stations” – This post was last edited by zhangyong6404 on 2009-3-10 09:51