Development and application of a microcomputer management system for piped liquefied gas

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This post was last edited by Wang Tianze on August 5, 2015, at 22:50. As a new method of gas supply, piped liquefied gas has seen rapid development since the 1990s. It has become one of the preferred directions for the development of urban gas supply in many medium- and small-sized cities as well as in newly developed areas surrounding large cities. As a supplementary gas source to conventional urban pipeline gas, piped liquefied gas holds great prospects for future development. With the development of pipeline liquefied gas and the widespread use of computers, developing a \"microcomputer management system for pipeline liquefied gas\" and utilizing microcomputer systems to address issues in the production, supply, and service management of pipeline liquefied gas is an important means of achieving scientific and intelligent management. I. Composition of the system The system is mainly composed of a high-pressure pressure transmitter, a low-pressure pressure transmitter, a concentration alarm probe, a gasification furnace monitor, an A/D and I/O acquisition board, a UPS, and a station computer. II. System Overview 1. Production Monitoring Subsystem: The system is primarily used to carry out 24/7 automatic monitoring and management of the equipment at various gasification sites, providing real-time alerts in case of any abnormal conditions. The main aspects of site monitoring include: 1. The operating status of the liquefied gas leak alarm; 2. The number of times the vaporization furnace starts up and its operating status; 3. The pressure conditions of the liquid phase and gas phase in the liquefied gas pipelines ； 4. Power supply status of the gasification station. 1.1 Monitoring of production operation status: The equipment currently used in the gasification station are all production devices with reliable signal output functions. Computer-based data acquisition devices are used to directly collect the output signals from these devices, which are then monitored in real time by the computer, thereby enabling the monitoring of the production operation status. The main conditions that need to be monitored at the gasification station are: ● Liquefied gas leaks between the cylinder banks and the gasification room. ●The on/off status and operating conditions of multiple groups of gasifiers. 1.2 Pressure signal monitoring The values of the liquid-phase pressure and gas-phase pressure within the pipelines of the gasification station are very important production parameters. The acquisition of pressure signals is carried out by pressure transmitters. The output of these transmitters is a standard 4–20mA current signal, which is converted into a 1–5V voltage signal using sampling resistors; this voltage signal is then captured in real time by the computer’s analog input card. After the computer captures the pressure signal, it monitors it in real time based on the pre-set upper and lower limits for the gas and liquid phase values. As soon as the gas and liquid phase values exceed the upper and lower limits, the computer immediately issues an alarm signal. 1.3 Power supply status monitoring: The vaporization station is equipped with modified, low-capacity uPs power supplies that supply power to the management system in the event of a failure in the municipal power grid. The management system sends a power outage signal to the control center, after which the system shuts down automatically until normal power supply is restored. 1.4 System Communication: In our design, we employ communication over the public telephone network by using an additional modem. This approach is one that developed countries have frequently adopted in recent years; by eliminating the need to develop and build complex data transmission networks, it offers advantages such as low costs, short development times, and no requirement for maintenance. 2 Intelligent meter reading subsystem: This system has the capability to perform automatic meter reading using a computer. Its working principle involves the relay communicators continuously checking each smart meter one by one. The computer at the site is responsible for monitoring all the relay communicators on the bus, obtaining information on the gas consumption and usage status of each meter, creating a database of users at that site, providing anomaly detection functions, and uploading the collected data to the central computer at the higher level, thereby completing the meter reading process. When the upper-level central computer receives the signal indicating the user’s prepaid payment from the billing system, it can transmit a signal to the lower-level station computers, and through relay communicators, this signal is sent to the smart meters for display, thereby completing the process of the user prepaying for gas. Its data transmission utilizes the highly reliable RS485 industrial fieldbus for communication. The relay communicator acts as a buffer between the station computer and smart meters, primarily to increase the load capacity of the RS485 communication bus. To ensure the accuracy of data transmission, a dual-CPU design is adopted in the structural setup: one CPU is responsible for communicating with the meters, while the other CPU is responsible for communicating with the station computers. The two CPUs exchange data through a dual-port RAM. As the constituent elements of a system, smart meters’ reliability and accuracy directly affect the viability of the entire system; they are the core of it. Therefore, in the process of developing our own smart meters, we placed great emphasis on the counting accuracy and reliability of the meters. Its main functions are as follows: 1) Accurately record the amount of gas used by the user and the amount purchased; 2) It has a pre-payment function ； 3) The display on the meter can show both the remaining gas volume and the total amount of gas used ； 4) An alarm for the remaining gas volume can be provided as required ； 5) The meter can keep counting correctly for over 48 hours in the event of a power outage ； 6) The meter features power-off data protection, allowing it to retain information on the user’s gas consumption and purchases for over 10 years even in the event of a complete power outage ； 3. Billing System: The main functions of the billing system include entering the gas consumption data read from meters, or receiving the data on gas usage from smart meters via data transmission; it also handles the calculation of costs for users, prints reports, and provides statistical analysis of gas usage patterns. The billing system connects the user’s gas consumption data management module to the central computer, enabling the transmission of the user’s gas purchase data to the computers at lower-level stations, and thus facilitating the functionality of determining the amount of gas that needs to be purchased as well as automatic meter reading and settlement. The billing system carries out billing by exchanging data with banks. 4 Data Communication and Wiring Methods The communication methods between smart gas meters, relay communicators, and site computers are as follows: 1) Wireless communication method ； 2) Communication method using a centralized meter reader ； 3) Power line carrier communication method ； 4) Wired transmission method ； In our engineering design, we use wired transmission for communication. Its advantages include direct data transmission via wires, strong resistance to interference, and reliable communication; one relay communicator can support up to 256 smart gas meters. However, its installation requires significant effort and involves high maintenance demands. The wiring method involves using shielded twisted-pair cables to enable communication via the RS485 industrial fieldbus. The maximum communication distance is 1200 meters, with a communication speed of up to 9600 bps. There are several ways for communication between the site computers and the central computer: 1) Using a centralized meter reading device for communication ； 2) Methods of wireless transmission and communication ； 3) Wired communication method ； 4) Communicating over landline phones by using an additional modem ； In our design, we adopt a method of using landline telephony for communication via an additional modem. This approach has been frequently used by developed countries in recent years; by eliminating the need to develop and build complex data transmission networks, it offers advantages such as low costs, short development times, and minimal maintenance requirements. III. Summary of System Application Since the deployment of this system, based on its current performance, it has achieved certain results in the following areas. 1. It helps to enhance safety capabilities. Safety first is a necessary prerequisite for the development of pipeline liquefied gas. The microcomputer management system for pipeline liquefied gas provides a means for 24/7 monitoring of leaks at gasification stations as well as the operating condition of equipment; any faults can be detected promptly, allowing for quick dispatch of personnel to resolve them. As the feedback time for information is **significantly reduced, the system’s security capabilities are enhanced. The gas supply conditions in the distribution network of Zone 2 are more stable. The traditional scheduling methods that relied on manual management made it difficult to control the operation of the distribution system. The microcomputer-based management system for liquefied gas enables full monitoring of the gas supply process in the network, allowing operators to easily regulate the distribution system in all aspects and thus ensuring that residents have a steady supply of gas. 3. It helps to improve the utilization rate of gasification equipment. The use of a microcomputer management system enables real-time collection of large amounts of data on actual operation. By analyzing and comparing this data, it is possible to understand the patterns in the equipment’s operation, develop optimized operation plans, and thereby increase the equipment’s utilization rate. 4 It helps to reduce staff while improving efficiency and economic benefits. With computer-based monitoring and management, only a certain number of inspection personnel are needed to manage each gasification station. The more gasification stations there are, the larger the supply scale, and the more significant the effect of reducing the workforce becomes. Since the opening of the first gasification station in a residential area by Nanjing Pipeline Liquefied Gas Company in 1996, the gasification equipment used there has had a high degree of automation. Together with the application of a microcomputer-based management system for pipeline liquefied gas, a approach of \"microcomputer monitoring combined with manual inspections\" is adopted, enabling the management of these gasification stations to move toward the concept of \"unmanned stations\". In the case of Nanjing Pipeline Liquefied Gas Branch, 10 stations have been set up. Previously, each station required at least 3 people, which meant a total of over 30 employees were needed. With the use of computer-based monitoring and management systems, only 2 people are required for inspections, 1 person for overall supervision, 5 maintenance workers, and 4 people for meter reading and billing. Clearly, this results in reduced labor costs. Moreover, as the number of gasification stations increases and the scale of supply grows, the impact of reducing the number of employees becomes even more significant. Furthermore, with a small workforce and high efficiency, management tasks become easier to handle, enabling the level of management for pipeline liquefied gas to reach a level comparable to that of developed countries.