CN115031803A - A method for measuring the liquid level of mixed liquid interface in a liquid storage container - Google Patents

Abstract

The invention discloses a method for measuring the liquid level of a mixed liquid interface in a liquid storage container. The specific measurement method is as follows: the total height of the liquid level in the liquid storage container is obtained by measuring, which is defined as H; The static pressure of the total liquid level is defined as ΔP, and the interface liquid level height is defined as h. Using the formula h=ΔP-ρ _lower gH/(ρ _lower -ρ _upper )g, the interface liquid level height is calculated as h, where, ρ _{The lower} and _upper are the density values of the lower liquid and the upper liquid respectively, and g is the gravitational acceleration. The interface liquid level of the mixed liquid in the liquid storage container can be measured quickly and accurately, the real-time monitoring in the technological process can be realized, and the automatic control of the interface liquid level can be realized.

Description

A method for measuring the liquid level of mixed liquid interface in a liquid storage container

technical field

The invention relates to a method for measuring the liquid level, in particular to a method for measuring the liquid level of a mixed liquid interface in a liquid storage container.

Background technique

The measurement of liquid level is a routine operation in the chemical industry. The existing measurement methods mainly include differential pressure method and float method. But in many cases, it is often found that there are two immiscible liquids with different densities in a storage tank, and the phase interface formed by these two liquids is called interface. There are many equipments in chemical production that require the interface liquid level to be accurately controlled, such as phase separators, coalescers, extraction towers, etc. However, the measurement of the interface liquid level has always been a difficult problem. The differential pressure method is mainly used in situations where the total height of the liquid level is constant, while the float method is difficult to use in situations where there are hanging materials and material density changes.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a method for measuring the liquid level of the mixed liquid interface in the liquid storage container which can accurately measure the phase interface formed by two liquids with different densities.

The technical solution adopted by the present invention to solve the above technical problems is: a method for measuring the liquid level of the mixed liquid interface in a liquid storage container, the specific measurement method is as follows: the total height of the liquid level in the liquid storage container is obtained by measuring, which is defined as H , measure the static pressure of the total liquid level in the liquid storage container, define it as ΔP, define the interface liquid level height as h, and use the formula h=ΔP-ρ _under gH/(ρ _lower -ρ _upper )g to calculate the interface liquid The bit height is h, where ρ _lower and ρ _upper are the density values of the lower liquid and the upper liquid, respectively, and g is the acceleration of gravity.

Preferably, the total height H of the liquid level in the liquid storage container is measured by a float level gauge, and the static pressure ΔP of the total liquid level in the liquid storage container is measured by a differential pressure transmitter.

Further, the floating ball liquid level gauge is preferably a magnetostrictive floating ball liquid level gauge, which can improve the measurement accuracy, and the error is less than or equal to 1 mm. The preferred model of the differential pressure transmitter is: EJA-110E.

In order to ensure the measurement accuracy, the preferred local value of the gravitational acceleration g is g=9.7930.

Compared with the prior art, the present invention has the advantage of using dual sensors to measure the total height of the liquid level in the liquid storage container and the static pressure of the total liquid level respectively. The interface liquid level of the mixed liquid can realize real-time monitoring in the process, and provide the possibility to realize the automatic control of the interface liquid level.

Description of drawings

1 is a schematic diagram of a measuring device used in an embodiment of the present invention;

FIG. 2 is a schematic configuration diagram of a panel operation screen of a control system designed by using the method of the present invention in an embodiment of the present invention;

FIG. 3 is a schematic diagram of an algorithm configuration of a control system designed by using the method of the present invention in an embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments of the accompanying drawings.

Embodiment 1: A method for measuring the liquid level of a mixed liquid interface in a liquid storage container. For the liquid storage container 1 with two different liquids shown in FIG. 1, a conventional measurement and installation method is used to install a magnetic Due to the floating ball level gauge 2 and the differential pressure transmitter 3 of Yokogawa's model EJA-110E, the total height H of the liquid level in the liquid storage container 1 is measured by the float level gauge 2. The static pressure ΔP of the total liquid level in the liquid storage container 1 is measured by the transmitter 3, and the height of the interface liquid level is defined as h, _and the interface can be calculated by using the formula h=ΔP- _ρunder gH/(ρdown- _ρup )g The height of the liquid level is h. In the formula, ρ _lower and ρ _upper are the density values of the lower liquid and the upper liquid respectively, which are provided by the process, and g is the acceleration of gravity. In order to ensure the measurement accuracy, the local value is preferred.

The interface liquid level h measurement formula is derived as follows:

ΔP= _ΔPup + _ΔPdown

ΔP= _ρupg (Hh)+ _ρdowngh

h=ΔP-ρ _lower gH/(ρ _lower -ρ _upper ) g.

Using the method of the present invention, a set of control systems can be designed, as shown in FIG. 2 and FIG. 3 .

Figure 2 shows the interface of a control system, when the system is not started. Description in the figure: LIT-N03 is the interface liquid level calculated by DCS, LIT-N03A is the total differential pressure of the liquid level measured by the differential pressure transmitter, and LIT-N03B is the total liquid level height measured by the float level gauge.

In Figure 3, LIT-N03 is the interface liquid level calculated by DCS, LIT-N03A is the total differential pressure of the liquid level measured by the differential pressure transmitter, and LIT-N03B is the total liquid level height measured by the float level gauge. LV-N03 is a tower kettle discharge control valve, which is used to control the interface liquid level. LV-N03 and LIT-N03 form a PID control loop, which automatically controls the LIT-N03 interface liquid level to maintain the set interface liquid level.

In order to verify the correctness of the method of the present invention, we compare the calculation result with the on-site liquid level (glass of sight glass) after normal debugging. The densities of the two liquids in the liquid storage tank are respectively the density of the lower layer liquid ρ _down =1050kg/m ³ , and the density of the upper layer liquid ρ _up =850kg/m ³ .

Example 1: The measured total height of the floating ball is 1.6 meters, the total static pressure of the liquid level is 70kp, the calculated result is 6.518 meters, the site is 6.525 meters, and the absolute value of the height difference is 0.7cm.

Example 2: The measured total height of the floating ball is 1.5 meters, the total static pressure of the liquid level is 68kpa, the calculated result is 5.290 meters, and the field is 5.282 meters, and the absolute value of the height difference is 0.8cm.

It can be seen from the above examples that the absolute value of the height difference between the interface liquid level obtained by the method of the present invention and the observation of the sight glass on site is less than 1 cm, which fully meets the process control requirements.

Claims (5)

1. a measuring method of mixed liquid interface liquid level in the liquid storage container, it is characterized in that the concrete measuring method is as follows: measure the total height of the liquid level in the described liquid storage container, be defined as H, measure the described liquid storage container The static pressure of the internal total liquid level is defined as ΔP, and the interface liquid level height is defined as h, and the interface liquid level height is calculated by using the formula h=ΔP-ρ _lower gH/(ρ _lower - ρ _upper ) g, where, in the formula, ρdown _and ρup _are the density values of the lower liquid and the upper liquid, respectively, and g is the acceleration of gravity. 2. The method for measuring the liquid level of the mixed liquid interface in a liquid storage container as claimed in claim 1, wherein the total height H of the liquid level in the liquid storage container is measured by a float level gauge, so The static pressure ΔP of the total liquid level in the liquid storage container is measured by a differential pressure transmitter. 3. The method for measuring the liquid level of the mixed liquid interface in a liquid storage container as claimed in claim 2, characterized in that the described float level gauge selects a magnetostrictive float level gauge, and the described difference The selection model of the pressure transmitter is: EJA-110E. 4 . The method for measuring the liquid level of the mixed liquid interface in a liquid storage container according to claim 1 , wherein the gravitational acceleration g is selected from a local value. 5 . 5 . The method for measuring the liquid level of the mixed liquid interface in a liquid storage container according to claim 4 , wherein the local value of the gravitational acceleration g is g=9.7930. 6 .

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