Thread Content
Abstract: Based on parameters such as the pipeline transmission pressure of liquefied petroleum gas and natural gas, the rated pressure of burners, and gas consumption, the technical specifications of several imported brand pressure regulators were compared, and regulators suitable for both types of gas were recommended. 1 Overview: As the pilot site for China’s first liquefied natural gas project, the first phase of the project was completed by 2005, supplying the cities of Shenzhen, Dongguan, Guangzhou, and Foshan. The second phase is scheduled to come online in 2008, providing supply to five additional cities (Huizhou, Zhaoqing, Jiangmen, Zhongshan, and Zhuhai). Currently, aside from Guangzhou which uses oil-based gas, the other cities use liquefied petroleum gas and some natural gas substitutes. Gas combustion theory indicates that gases with different properties can be interchanged, and the conversion of natural gas poses a challenge for cities around the world. According to the preparations for transitioning to natural gas in Shenzhen, two plans have been developed for the gas supply process: one plan involves replacing all indoor pressure regulators. With 200,000 such regulators in Shenzhen, replacing them all would require an investment of 32 million yuan ； Another option is to install a building pressure regulator with a pressure range of 0.3MPa to 0.07MPa in each residential building; there are 3,000 such buildings, requiring an investment of 3 million yuan. As can be seen from the above plan, when switching to natural gas, the pressure regulator must also be replaced, which will require a significant amount of work and funding. Among the city gas users in the aforementioned cities of our province, those using pipeline gas account for only about 40% in cities where pipeline gas infrastructure is well developed. Before natural gas can be used, it is necessary to accelerate the development of pipeline gas systems, while also relying on liquefied petroleum gas as a transitional solution. Therefore, it is very meaningful to study at this stage how to select regulators that can meet the requirements of these two temperaments, in order to reduce future conversion workloads and save on investments. 2. Range of application for secondary pressure regulators: In the supply processes for liquefied petroleum gas and natural gas, pressure regulation can be divided into three types based on the method used: (1) Indoor pressure regulation process, also known as medium-pressure supply to households, which involves regulating the pressure after the medium-pressure gas reaches the household. (2) The building pressure regulation process involves centralized pressure regulation for each building or several residential buildings, followed by low-pressure supply to the households. (3) Regional pressure regulation refers to the process of reducing the pressure in municipal pipelines to low levels and then redistributing the water to users in a specific area. In the Pearl River Delta region, pipeline delivery of liquefied petroleum gas primarily relies on methods (1) and (2), while in the future, natural gas delivery can utilize all three of these methods. However, since method (3) covers a large area and requires the construction of dedicated pressure regulation stations, it is more suitable for areas that do not yet have pipeline users. This paper mainly discusses the selection of secondary voltage regulators for processes (1) and (2). 3 Criteria for selecting a secondary voltage regulator (1) Inlet and outlet pressures of the voltage regulator. As can be seen from the above process, if the minor pressure losses in the pipes are ignored, the inlet and outlet pressures for the two voltage regulation methods can be considered identical. The medium-pressure transmission pressure in municipal pipelines can be used as the inlet pressure for the pressure regulator, while the outlet pressure can be determined based on the rated pressure of the burner. Below are the comparisons in pressure regulation for the two temperaments. (2) Flow rate of the pressure regulator: Due to the differences in the number of users served by the two pressure regulation methods and in the calorific value of the two types of gas, the flow rate of the pressure regulator must be calculated separately for each case. ①Flow rate calculation for indoor pressure regulators: Indoor pressure regulators must meet the basic gas requirements of each household’s cooking appliances. It is standard to assume that each household has one stove and one water heater; taking Linai brand appliances as an example, the gas consumption amounts are shown in Table 2. ②Calculation of the flow rate for building pressure regulators: To determine the flow rate of a building pressure regulator, it is necessary to know the number of users served by that regulator. In the case of pressure regulation for a single building, the pressure regulator is usually placed in the meter box along with the gas meter. This approach takes into account the fact that since the low-pressure pipes and meter boxes are quite visible, in order to minimize the impact on the building’s appearance, one meter box cannot serve too many users; therefore, the number of households per floor should not exceed two ； Secondly, the longer the pipeline, the greater the pressure drop; based on the pressure drop per floor and the pressure regulation range, the number of floors that can be supplied with regulated pressure from a single building should not exceed 10 floors. For such a building, the number of households supplied by a pressure regulator can be determined to be 7–20. Based on the maximum gas consumption per household and the simultaneous operation factor, the results shown in Table 3 can be obtained. 4 Recommendations for selecting voltage regulators (1) There are a large number of domestic and foreign secondary voltage regulators available on the market. In the Pearl River Delta region, the following types of imported voltage regulators are commonly used; their technical specifications are shown in Table 4. Firstly, the medium-pressure transmission pressure for natural gas is 0.2 or 0.3 MPa, which is much higher than the maximum allowable inlet pressure range of the aforementioned regulators ； Secondly, the rated pressure of natural gas appliances sold on the market is 2 KPa, which is lower than the output pressure range of the regulators currently in use. Therefore, the above-mentioned pressure regulator cannot meet the pressure regulation requirements when converting liquefied petroleum gas to natural gas. (2) Recommended products: This article recommends the Italian FIORENTINIC3, as well as the American FISHERR522 and S402 secondary voltage regulators. The technical specifications of the three voltage regulators are shown in Table 5. C3 can be used as an indoor pressure regulator; it has safety venting and emergency shut-off functions, which makes it more expensive than RC4N, but these two functions effectively prevent overpressure and severe leaks in indoor pipelines. If you find the price of C3 to be high, you can choose alternative products with more reasonable prices available in China. As building voltage regulators, R522 and S402 are cheaper than LV4403B4 and LV5503B6 when compared in terms of the cost per unit of heat regulated; especially for S402, the price advantage becomes even more significant if a valve port diameter of 6.4 mm is chosen. Based on the flow rates calculated using the previous two pressure regulation methods, it can be seen that the flow rates provided by the above three pressure regulators are more than sufficient to meet the gas usage requirements of these two gas types. Regarding pressure issues, the maximum pressure range allowed by the three pressure regulators is much higher than the medium-pressure transmission pressure of natural gas, thus meeting the operational requirements. The output pressure range can be adjusted to meet the required specifications by replacing the main spring of the pressure regulator. When the gas is liquefied petroleum gas, a spring with a pressure of 2.37–3.25 KPa should be used ； When the gas is natural gas, a spring with a pressure of 1.87 ± 0.37 K should be used. Using this method, it is very easy to solve the conversion problem. This method of replacement is widely used by industrial and commercial customers. Practice has shown that replacing the spring is a safe, cost-effective, and practical solution; for specific procedures, consult the supplier. 5 Issue of burner rated pressure: This is addressed by installing an additional pressure regulator in the building, which is used to adjust the medium-pressure delivery pressure of natural gas (0.2 MPa or 0.3 MPa) to 0.7 MPa, the medium-pressure delivery pressure for liquefied petroleum gas. This meets the pressure requirements at the input of the secondary regulator; as a result, the output pressure range of the secondary regulator remains unchanged, with the pressure at the stove being 2.4–3.3 KPa. According to Article 7.2.2 of the Urban Gas Design Code, the rated pressure for low-pressure natural gas appliances is 2.0 OKPa. Therefore, a pressure of 2.4–3.3 KPa at the stove cannot meet the requirements for the proper operation of such appliances. This article suggests that for already ventilated residential areas, before planning to adopt a solution involving the addition of pressure regulators on buildings, it is necessary to first discuss with the manufacturers the issue of the rated pressure of cooking appliances ； For residential areas that have not yet been pressurized, regulators capable of meeting both types of requirements should be used. 6 Conclusion: Although it is still some time before natural gas becomes available, the number of users is increasing. If preparations are not made in advance, it will inevitably lead to higher financial costs and more workloads. In summary, during engineering design, it is recommended to select a secondary pressure regulator suitable for both types of temperaments based on the actual conditions.