控制阀的流量自感知及其在外泄漏自感知中应用

控制阀的外泄漏会造成物料损失，污染环境，甚至还会造成严重事故。利用控制阀外部的传感器来测外泄漏的传统方法低效，属于事后检测，使外泄漏事故得不到及时处理。为了实现控制阀外泄漏的快速自动检测，本文提出一种便于在工业现场实施的基于控制阀流量自感知的外泄漏检测方法。根据被控流体压力、控制阀开度等数据，建立控制阀的流量自感知模型，使控制阀具有流量自感知的能力。如果没有外泄漏，则由控制阀入口流进的流体质量和由出口流出的流体质量相等。如果控制阀发生外泄漏，则由控制阀入口流进的流体质量和由控制阀出口流出的流体质量不等，同时由于控制阀出口的流体质量减小，导致控制阀出口的压力等参数发生变化。为了恢复刚才泄漏前的稳态，闭环控制器向控制阀驱动器发出调节指令，增大阀门的开度，增加控制阀入口流量，以抵消外泄漏造成的影响。在相同的开度增量条件下，外泄漏引起的流量增量与正常操作所引起的不同。在实施控制阀的泄漏自感之前，根据平时正常的工况，预先确定各开度条件下的质量流量的名义最大值。根据流量自感知模型的质量流变化率和名义最大值，阀门控制器内嵌的泄漏诊断程序可实现外泄漏的自诊断，并发出外泄漏故障信号。此外，带流量自感知模型的控制阀，能当流量计用，可省掉管路中的流量测量设备。研究结果证明了所提出的外泄漏自感知方法的有效性。

External Leakage Self-sensing Based on Flow Rate Self-sensing of a Control Valve

External leakage is a common fault of a control valve, which can cause loss of energy resources, the pollution to our living environment, and even serious accidents. It is relatively inefficient to use chemical sensors arranged outside the valve to detect the leakage, which causes that leakage accidents cannot be prevented in time. In order to help the control valve to automatically perceive the external leakage, a novel method based on flow rate self-sensing of the control valve was presented. The proposed method used specific data such as the fluid pressure and the degree of corresponding opening of the valve to establish a self-sensing model of the flow rate, which could be easily implemented in industrial fields. During steady state operation, there was a nominal mass flow rate through the control valve. The mass flow rate of the inlet of the control valve was equal to that of the valve outlet. When an external leakage developed, the level of the mass flow rate of the outlet dropped, and some other operating parameters of the control loop would change. Feedback regarding the operating parameters such as the controlled fluid pressure and the degree of corresponding opening of the control valve was provided to the valve controller, and the controller altered the drive signal to the actuator of the control valve to change the flow rate to offset the external leakage. Consequently, mass flow rate to the control valve increased. By estimating mass flow rate of the controlled fluid over time, a diagnostics unit could be programmed to detect increases of the mass flow rate of the controlled fluid. The diagnostics unit could further be programmed with a nominal maximum flow rate above which the diagnostics routine would generate an external leakage signal. Additionally, the valve with the self-sensing model could be considered as a flowmeter, which helped the plants to eliminate the flow rate measurement devices in the pipeline system. The results showed that the control valve with the self-sensing model could automatically identify the external leakage in time, which validated the proposed method.