Research On Measuring Method Of Vertical Metal Tank Capacity

Vertical metal tank is the main measuring instrument in trade settlement of international petrochemical product, and is also the important measuring instrument and storage equipment for sending and receiving, trade settlement of domestic oil and liquid petroleum product. Its measuring accuracy not only affects the cost accounting and economic efficiency of enterprises, but also has a direct bearing on the economic interests of the country in domestic and foreign trade and national measurement reputation. Therefore, achieving accurate vertical metal tank capacity measurement is actually significant.Misalignment of vertical metal tank capacity measurement is a difficult problem that has not been solved so far. In the actual process, as a storage device and measurement instrument, vertical metal tank misalignment is occurred. The reason for that is bottom capacity increment and floating roof weight changing constantly, radial deviation can’t be measured totally, and there is no corresponding standard device used in level measurement internationally, the accuracy of liquid level measurement and related indexes can’t be evaluated.To this Situation, such work was completed as following:a. Traditional measurement of artificial climbing wall with a radial gauge has the problems of high danger and measuring accuracy is affected by higher tank and inaccurate measuring point positioning. To solved the problems, radial deviation measurement method with optical reference based on a kind of wall-climbing robot (WCR) is put forward.As the wall-climbing robot is the core of the method, this article focuses on designing and researching wall-climbing robot. Overall structure of the wall-climbing robot is designed, non-contact permanent magnet absorption way of WCR is analyzed and determined. A kind of four-wheel drive way is determined through analyzing the WCR’s movement way. Established the robot dynamics and kinematics model. Analyzed and determined mechanics balance conditions which provides reference for anti-overthrow design. Designed hardware of sport module, tilt angle module, the power module and of the WCR control system and realized control to the WCR’s motion attitude. The WCR’s main performances such as motion ability, obstacle crossing ability, and load capacity were tested. The test results show that its performance meets the site and the radial deviation measurement requirements.b. Put forward the on-line measurement method for floating roof weight and bottom capacity of vertical metal tank, to solve the problem of existing larger difference between the measurement of off-line state and loading state on the capacity and its changing value of vertical metal tank, which is caused by deformation of floating roof plate and bottom plate, it makes lower measurement precision.Based on analyzing disadvantages of existing off-line measurement method for bottom capacity and floating roof weight, presented online and real time measurement method of making use input level gauge to measure bottom increment and making use pressure transmitter to measure floating roof weight of vertical metal tank. Verified the feasibility of the measuring method by establish a set of experimental device to measure floating roof weight real time. The real-time measuring system of tank bottom capacity and floating roof weight was built with the input level gauge, pressure transmitter and analog acquisition module. Developed a software system which is compatible with original database of vertical metal tank measuring system of NITCC. The original tank capacity table is corrected, and the vertical metal tank capacity test system is completed.c. Proposed the plan of level measurement based on the principle of dual-frequency Laser interference. The standard devices for level gauge and flowmeter calibration are developed, then, the problems that level standard device for level gauge calibration has not been established and its measurement conflict can’t be judged are solved.The development of double-floats and double-rails structure measuring device is used to solve the problem of losing counts during measurement. Automatic calibration device was designed to solve the problem of high precision zero calibration of the standard device. Determined the scheme of two-way level control with the large and small pumps. Calculated and analyzed the standard tank body load, and put forward the standard tank manufacture scheme for that the tank height changes less than20um when tank top load changes500N. Presented air refractive index correction method with the variables of relative humidity based on Edlen formula.Developed level standard testing device, tested its steady-state characteristics. Steady-state range changes less than50μm of the device, meets the design requirement of level stability. The experiment device for oil and gas refractive index of oil tank is built. Determined multiple linear regression equation with the method of regression orthogonal test. Measured oil and gas refractive index of standard tank in the field by analyzing the multiple linear regression equation to compensate and correct the results.The principle and process of flow standard device based on the level standard device was established.