RU2179709C1 - Device for precision measurement of liquid level in reservoir - Google Patents

Abstract

FIELD: measurement of level of liquids, such as oil, gasoline, diesel fuel in reservoirs with fixed top. SUBSTANCE: device has measuring well mounted vertically and liquid level sensor mounted in top end portion of measuring well by means of flange join. One multi-point temperature sensor is mounted vertically inside reservoir with foundation. Intake branch pipe is designed for taking liquid from various levels in reservoir. Second multi-point temperature sensor is mounted vertically inside measuring well which is mounted on its own foundation together with sensor outside the reservoir. Measuring well is communicated with reservoir by connecting it to gas part reservoir with the aid of upper pipe. Lower portion of measuring well is communicated with lower portion of reservoir by means of lower branch pipe and adjustable gate; communication with buffer vessel is effected through pump by means of connecting branch pipes. Multi-point sensors, pump and adjustable gate are connected with computer unit. EFFECT: enhanced accuracy. 4 dwg

Description

 The invention relates to techniques for measuring the level of liquid products, and more specifically for measuring the level of oil, gasoline, diesel fuel in tanks with a fixed roof.

 As you know, measurement error has two main components: instrumental and methodological. Modern precision level sensors have a low intrinsic instrumental measurement error. For example / 1 /, modern radar level sensors have an absolute measurement error of less than 0.5 millimeters, which corresponds to a relative error of less than 0.005 percent with a tank height of more than 10 meters. At the moment, there are no instruments for directly measuring the mass and volume of petroleum products in tanks with a similar relative measurement error.

 Therefore, at present, in tank farms for commercial accounting of oil and oil products, both by weight and volume, as a rule, the liquid level is measured with subsequent recounting and adjustment to the required value.

 A device containing a float sensor / 1 / is widely used for level measurement. The float moves along the rod (see figure 1), fixed by means of a flange connection on the lid of the tank hatch. The position of the float corresponds to the height of the air gap. The filling height (bump) of the product is determined by subtracting from the base height of the tank, which is considered constant for a given tank, the value of the air gap.

 The disadvantage of this measurement method is the presence of a significant methodological error due to deformation of the tank roof. The actual height of the tank can vary significantly and the measurement error can reach 5 or more cm, which is unacceptable with commercial accounting of petroleum products.

 Another device is known, which includes an ultrasonic level sensor / 2 /, which is mounted on the lid of the roof of the tank by means of flanges (see figure 2). The distance (distance) from the sensor to the surface mirror is measured, followed by subtraction from the base value (height) of the tank. The resulting value corresponds to the height of the product. Obviously, as in the previous case, the measurement results contain a methodological component of the error of an unacceptable value.

 Closest to the proposed device is a device (see Fig. 3), made in accordance with the recommended standards of the American Petroleum Institute (API) / 3 / and including a measuring well, representing a vertically mounted steel pipe located in the tank, the lower end resting on the bottom reservoir, on the top - through a flange connection a precision liquid level sensor is installed (for example, a radar / 1 /), a multipoint thermometer mounted vertically in the reservoir, a computing unit / 1, 3 /. There are a number of holes in the measuring well, thanks to which the same liquid level is established in the tank and in the measuring well, as well as the same pressure in the gas spaces.

 The disadvantage of this device is that in the measurement results there is a significant methodological component of the error due to the uncertainty of the base, relative to which the liquid level is calculated. Indeed, studies show / 3 / a complex deformation of the bottom with a change in the liquid level in the tanks. In addition, the length of the measuring well on which the liquid level sensor is mounted also changes with temperature. Under the influence of these factors, the distance measured by a precision liquid level sensor changes with a constant actual volume of liquid in the tank.

 The technical result of the present invention is to increase the accuracy of measuring the liquid level in closed tanks, approximating the total measurement error to the instrumental error of a precision liquid level sensor.

 The technical result is achieved by the fact that in the known device for precision measurement of the liquid level in tanks, consisting of a measuring well mounted vertically, a computing unit, a precision liquid level sensor installed by means of a flange connection to the upper end part of the measuring well, a multi-point temperature sensor mounted vertically inside reservoir, a measuring well with a precision liquid level sensor is removed from the reservoir and installed on its own the basement into a heat-insulating shell, and the measuring well is in communication with the tank by attaching it at the top to the gas part of the tank by means of the upper pipe, and the lower part is connected to the buffer tank through the pump using connecting pipes, in addition, the lower part of the measuring well is connected to the lower part of the tank by means of the lower and intake pipes, a controlled valve, and a multi-point temperature sensor is vertically installed inside the measuring well, moreover, precision the first liquid level sensor, both multipoint temperature sensor, the pump, controlled by the valve are connected with a computing unit.

 Figure 4 presents a drawing of the proposed device.

 The composition of the proposed device includes (see Fig. 4): 1 - measuring well, 1A - heat-insulating sheath, 2 - own foundation, 3 - upper pipe, 4 - lower pipe, 4A - controlled valve, 4B - intake pipe, 5 - precision liquid level sensor, 6, 11 - multi-point temperature sensors, 7 - computing unit, 8 - connecting pipes, 8A-pump, 9 - buffer capacity.

 In addition, the drawing shows: 10 - tank, 12, 12A - liquid, 13 - the foundation of the tank.

 The device operates in the following two modes: in the mode of direct measurement of the length of the measuring well and in the mode of measuring the liquid level in the tank.

 Consider the mode of measuring the length of the measuring well. The accuracy of measuring the liquid level is affected by temperature changes in the length of the measuring well 1. For periodic monitoring of the length of the measuring well 1, the proposed device implements a direct measurement of its length with a precision liquid level sensor. In this mode, the controlled valve 4A is closed. The oil product 12A is pumped out from the measuring well 1 to the buffer tank 9 by the pump 8A. Because the pumping time is short compared with the time the temperature of the walls of the measuring well 1 changes (the measuring well 1 is in the heat-insulating shell 1A), then the measured length of the empty measuring well is equal to the length of the filled measuring well. After the process of measuring the length of the empty measuring well is completed, the pump turns off, the controlled valve 4A opens, the oil 12 flows freely again through the nozzles 4, 4B and the controlled valve 4A from the tank 10 into the measuring well 1, and the level is established in the measuring well. Note that a turned off pump does not allow fluid to pass through it.

 Consider the mode of measuring the liquid level in the tank. In this mode, the pump 8A is turned off and the controlled valve 4A is open. Because the tank 10 and the measuring well 1 removed from the tank due to the pipe 3, the lower pipe 4 and the open controlled gate valve 4A represent a system of communicating vessels, then with the same profile of the liquid density in height in the tank 10 and the measuring well 1, the level in the tank and the measuring well will be the same. The level in the measuring well 1 is measured with a precision liquid level sensor 5 relative to the "absolute" base (level of its own foundation 2) as follows: the distance (distance) from the flange of the level sensor 5 to the surface of the oil product 12A in the measuring well 1 is measured, the obtained measurement result is subtracted from the length measuring well 1. The resulting difference corresponds to the liquid level relative to the level of its own foundation 2.

 The intake pipe is a pipe with slots of a certain size in height and is intended for the intake of fluid 12 from its various levels.

 The difference between the proposed device and the known ones is the fundamental possibility of reducing the total error of measuring the liquid level in the tank, including the methodological one, to the instrumental one, as well as the presence of an "absolute" reference base (level of the foundation of the device), independent of deformations of the bottom and roof of the tank.

Sources of information
1. Catalog "Combit", "Saab Tank Control".

 2. General Specifications Catalog III ", Endress + Hauser.

 3. Berto F.J. Review of tank measurement errors reveals techniques for greater accuracy. Pt. Oil and Gas J. -1997. -vol. 95, -P. 68-70, 72, 73.

Claims (1)

 A device for precision measurement of liquid level in tanks, consisting of a measuring well mounted vertically, a computing unit, a precision liquid level sensor installed by means of a flange connection to the upper end part of the measuring well, a multi-point temperature sensor mounted vertically inside the tank, characterized in that the measuring well with a precision liquid level sensor removed from the tank and installed on its own foundation in thermal insulation a shell, the measuring well being in communication with the tank by attaching it at the top to the gas part of the tank by means of an upper pipe, and the lower part being connected to the buffer tank through a pump by means of connecting pipes, in addition, the lower part of the measuring well is in communication with the lower part of the tank intake nozzles, controlled valves, and a multi-point temperature sensor is installed vertically inside the measuring well, with a precision liquid level sensor, both gotochechnyh temperature sensor, the pump, controlled by the valve are connected with a computing unit.

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