Study On Un-contacted Density And Level Measurement For The Flow System Of Viscous Slurry

With the development of electronic and measurement technology, there are many density and level measurement method with the characteristic of high precision, wide range, erosive enduring. In the field of the petroleum, chemical engineering, food industry and etc, a fluid with special characters, such as high temperature, high viscosity, high erosion, can not be measured by contact method, because the membrane of the sensor was adhered by the viscous material, leading to the isolation of the fluid and the sensor, even the sensitivity was influenced. Other methods working on the principle of optics, acoustic or radioactivity need complex equipments and can only be used to measure the uniform and separated fluid which can not guarantee the economical character as well as precision. So it is quite imperative to provide a new kind of un-contacted measurement method to measure density or level with low price and easy operation. There are some relative ideas with some limitation, for example using pure water as isolation material, can only be used to measure the fluid unsolved in water and lighter than water ,some method from air purge had been proposed by scholars domestic or abroad, steady gas source was needed, and the gas bubble can not be viewed by easily and steadily, so this method can not be used widely. Considering the requirements of the measurement site under specific working condition, a scheme of an un-contacted method was developed to measure the static pressure in flowing viscous slurry system by using a transducer filled with air proposed by this paper. In view of hydrostatic tank gauging method, the probe is optically powered, and then the information is transmitted through optical fiber to Micro-control unit far from the site. The membrane of the sensor and the viscous fluid was separated by the air, so the sticky and erosion problem can be solved, the system is safe in nature. Based on the thermodynamic law for ideal gas and mass transfer theory, the measurement equations were deduced, The predictions for the value of static pressure at the measuring position are well consistent with the experimental measurements with an error less than5%. Take air-water system as an example ,within the temperature range of 50~80℃and pressure range of 120~250 kPa, the volume change of working medium inside the transducer was less than 5% during a period of 90 days. It indicated that the method was fitted well with the engineering requirement for application in oil, mineral and some other process industry sectors. It indicated by the experiment and theoretical prediction that the saturated vapor pressure of liquid is the most important condition to determine the stability of the equipment, as to the slurry system of which saturated vapor pressure were much less than pure water, so the stability was much higher than air-water system. So the equipment can be used in other system with little limitation. The equipment had been installed on some plant pipeline with high temperature and viscous slurry flowing inside, the sensibility of the equipment agreed with that of semis PDS423H pressure sensor, the result was fairly accordant. In conclusion, the research of this thesis has proved that the laboratory slurry density measuring system proposed can absolutely meet the requirements for practical application because it's measuring precision can achieve 5percent and it has good working stability. All of the theoretical analysis and practical experiments have sufficiently verified that utilizing air as the isolation material to measure the slurry density is feasible.