CN101986108A - Differential pressure type liquid level measurement device for pressure container - Google Patents

Abstract

The utility model relates to a differential pressure type liquid level measuring device for a pressure vessel, which relates to a liquid level measuring technology of a pressure vessel. The device includes a steam outlet pipe, a saturated water outlet pipe, a positive pressure pipe and a differential pressure transmitter. The steam outlet pipe is directly connected with the positive pressure pipe, and an isolation valve is installed on the steam outlet pipe; the positive pressure pipe is arranged in a thermostatic outer casing filled with a constant temperature fluid, and a water injection valve is installed on the top of the positive pressure pipe. The saturated water outlet pipe and the negative pressure pipe are combined into one, installed at the zero point of the horizontal elevation of the high pressure vessel, and arranged horizontally. The differential pressure transmitter is installed on the saturated water outlet pipe, and the saturated water outlet pipe is connected to the positive pressure pipe through the differential pressure transmitter. The present invention effectively overcomes the uncertain density and liquid level caused by bubbles and vaporization of the water in the positive pressure tube in the single-chamber balanced container method and the dual-chamber balanced container method, as well as measurement errors caused by the installation position of the differential pressure transmitter. , has obvious characteristics in measurement accuracy, ease of use and manufacturing cost.

Description

A differential pressure liquid level measuring device for pressure vessels

technical field

The invention relates to a differential pressure liquid level measurement device, in particular to a differential pressure liquid level measurement technology for pressure vessels such as steam drums.

Background technique

At present, there are two most commonly used methods for water level measurement of pressure vessels such as steam drums, one is the single-chamber balance vessel method, and the other is the double-chamber balance vessel method.

Figure 1 is a schematic diagram of the principle of the single-chamber balance container steam drum water level measurement method. The upper part of the steam drum 1 is a steam space filled with saturated steam with a density of ρ _s ; the lower part is a space of saturated water with a density of ρ _w , and the water level of the steam drum is H. There is a steam outlet pipe 2 connected to the balance container 3 in the steam space on the upper part of the steam drum. There are two pressure measuring tubes in the lower part of the balance container, one is the positive pressure tube 4, connected to the positive pressure side of the differential pressure transmitter 6; the other is the negative pressure tube 5, connected to the negative pressure side of the differential pressure transmitter, The negative pressure pipe is also connected with the steam drum saturated water outlet pipe 7, and the horizontal elevation of the saturated water outlet pipe is also the zero point of the steam drum water level. The steam in the steam drum passes through the balance container and condenses into water with a density of ρ _c in the positive pressure tube. The pressure generated by the water in the positive pressure tube acts on the differential pressure transmitter as a positive pressure reference for the differential pressure transmitter. end. The upper part in the negative pressure tube is steam, the lower part is water, and the pressure in the negative pressure tube is used as the negative pressure reference end of the differential pressure transmitter. There is a certain functional relationship between the pressure difference Δp of the positive pressure reference end and the negative pressure reference end of the differential pressure transmitter and the drum water level height H, and the differential pressure transmitter converts the pressure difference Δp into a 4-20mA electrical signal The output is sent to the computer, and the computer calculates the H value of the steam drum water level height according to a certain functional relationship. According to the principle of physics, it can be concluded that the differential pressure value Δp output by the differential pressure transmitter is calculated as:

Δp=p+-p-=L(ρ _c -ρ _s )gH(ρ _w -ρ _s )g

or rewritten as:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; g</span>}}$

L in the formula is the height difference between the horizontal positions of the steam outlet pipe 2 and the saturated water outlet pipe 7, and is also the range of water level measurement. It can be seen from this that there is a linear correspondence between the drum water level H and the differential pressure value Δp output by the differential pressure transmitter, and this relationship is affected by ρ _w , ρ _s and ρ _c . ρ _w and ρ _s are determined by the pressure of the steam drum. Once the pressure is fixed, the values of ρ _w and ρ _s are fixed values. In the actual boiler computer control system DCS system, the calculation function of the computer is used to automatically correct the influence of the pressure on the relationship between the drum water level H and the differential pressure value Δp, but _ρc is a factor affected by the ambient temperature, steam temperature and pipe wall insulation, etc. The value affected by multiple factors, the single-chamber balance vessel drum water level measurement method does not consider the influence of ρ _c changes.

In order to overcome the shortcomings of the single-chamber balance container method, a double-chamber balance container method has emerged. The principle of the drum water level measurement method is shown in Figure 2. The inner chamber 8 of the balance container is connected to the positive pressure pipe 4, and the pipe contains saturated water condensed by steam. The outer chamber 9 of the balance container passes through the steam outlet pipe in the upper steam space of the steam drum and the steam outlet at the lower part of the outer chamber, so that the steam is filled with the outer chamber and continuously flows out. , whose purpose is to heat the inner chamber and the positive pressure pipe connected to it to keep the water in it saturated. Also according to the physical principle, the corresponding relationship between the drum water level H and the differential pressure value Δp output by the differential pressure transmitter can be obtained:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; g</span>}}$

It can be seen from this formula that the correspondence between H——Δp is only affected by ρ _w and ρ _s , while ρ _w and ρ _s are determined by the pressure of the drum, and the DCS system can automatically correct the pressure on H—— Δp relationship, so the double-chamber balance vessel method solves the defects in the single-chamber balance vessel drum water level measurement method.

However, the double-chamber balance container method also has many shortcomings: ① When the boiler is started, the reference water column cannot be condensed into the balance container of the differential pressure water level gauge, and water needs to be manually injected into the inner and outer chambers of the balance container, and the water injection method is complicated. ②Vapor bubbles often appear in the positive pressure tube, and even the upper water level of the inner chamber cannot be filled. Error in water level measurement. ③In order to ensure that the water in the inner chamber and the positive pressure pipe connected to it remains in a saturated state, the outer chamber must have enough space for the steam to heat the inner chamber, and the larger the size of the outer chamber, the higher its manufacturing cost. Because the outer chamber is connected with the steam drum, the outer chamber is a pressure vessel. ④ The position of the differential pressure transmitter is installed below the zero point of the level of the steam drum. The advantage is that the installation position has a large degree of freedom and is convenient, but the problems are also very prominent: The characteristics such as the density of water must be the same, otherwise measurement errors will occur. In actual engineering, since the operating conditions and the insulation conditions of the two pipes cannot be completely consistent, measurement errors cannot be avoided.

Contents of the invention

In view of the deficiencies and defects of the single-chamber balance container measurement method and the double-chamber balance container measurement method used in the prior art, the purpose of the present invention is to provide a differential pressure liquid level measurement device for pressure vessels, so that it can The invention is superior to the prior art in measurement accuracy, convenient use and manufacturing cost.

The purpose of the present invention is achieved through the following technical solutions:

A differential pressure liquid level measuring device for a pressure vessel, the device includes a steam outlet pipe, a saturated water outlet pipe, a positive pressure pipe, a negative pressure pipe and a differential pressure transmitter, characterized in that: the steam outlet pipe The positive pressure pipe is directly connected with the positive pressure pipe, and an isolation valve is installed on the steam outlet pipe; the positive pressure pipe is arranged in a constant temperature outer casing with a constant temperature fluid, and a water injection valve is installed on the top of the positive pressure pipe; the saturated water The outlet pipe and the negative pressure pipe are combined into one, installed at the zero point of the horizontal elevation of the high-pressure vessel, and arranged horizontally; the differential pressure transmitter is installed on the saturated water outlet pipe, and the saturated water outlet pipe transmits The device is connected to the positive pressure tube.

In the above technical solution, the constant temperature fluid is constant temperature water.

Compared with the technology, the present invention has the following advantages and outstanding effects: ① No need to consider whether the boiler is running or not, it can conveniently inject water into the positive pressure pipe to ensure the liquid level in the positive pressure pipe. ② It overcomes the defects in the prior art that the density and liquid level are uncertain due to the bubbles and vaporization of the water in the positive pressure tube due to pressure changes, thereby causing measurement errors. ③ The balance vessel in the prior art is a pressure-bearing part with a large volume, which requires thick-walled materials to withstand high temperature and high pressure, and the manufacturing cost is high. The invention cancels the balance container, and the constant temperature fluid in the outer sleeve is normal temperature and low pressure, and the outer sleeve does not need to bear high temperature and high pressure, and the manufacturing cost is much lower than that of the prior art. ④ The measurement error caused by the installation position of the differential pressure transmitter is avoided.

In a word, the present invention effectively overcomes the problems existing in the existing single-chamber balancing container method and double-chamber balancing container method, and has obvious technical progress in measurement accuracy, convenient use and manufacturing cost.

Description of drawings

Figure 1 is a schematic diagram of the principle structure of a single-chamber balance container steam drum water level measuring device.

Fig. 2 is a schematic diagram of the principle structure of the double-chamber balance container steam drum water level measuring device.

Fig. 3 is a schematic structural diagram of a differential pressure liquid level measuring device of the present invention.

In the figure: 1-steam drum; 2-steam outlet pipe; 3-balance container; 4-positive pressure pipe; 5-negative pressure pipe; 6-differential pressure transmitter; 7-saturated water outlet pipe; 8-balance container Inner chamber; 9-outer chamber of the balance container; 10-isolating valve; 11-water injection valve; 12-thermostatic outer casing.

Detailed ways

The specific structure, principle and working process of the present invention will be further described below in conjunction with the accompanying drawings.

Figure 3 is a schematic diagram of the principle of the differential pressure liquid level measuring device provided by the present invention, the device includes a steam outlet pipe 2, a saturated water outlet pipe 7, a positive pressure pipe 4 and a differential pressure transmitter 6, characterized in that: The steam outlet pipe is directly connected to the positive pressure pipe 4, and an isolation valve 10 is installed on the steam outlet pipe; the positive pressure pipe is arranged in a thermostatic outer casing 12 containing a constant temperature fluid, and a water injection valve is installed on the top of the positive pressure pipe 11. The saturated water outlet pipe and the negative pressure pipe are combined into one, installed at the zero point of the horizontal elevation of the high-pressure vessel, and arranged horizontally; the above-mentioned differential pressure transmitter is installed on the saturated water outlet pipe, and the saturated water The outlet pipe is connected with the positive pressure pipe through a differential pressure transmitter.

The working principle of the present invention is as follows: no matter whether the pressure vessel is working or not, closing the isolation valve 10 disconnects the connection between the positive pressure pipe and the pressure vessel, opening the water injection valve 11 can inject water into the positive pressure pipe 4, and when the water injection is too much, open the isolation After the valve 10, the excess water can flow back to the pressure vessel, so the liquid level in the positive pressure pipe can be well maintained. In addition, the water injection valve can also be used as an air release valve, and the bubbles in the positive pressure pipe can be released through the water injection valve, which can be easily It is best to ensure that the pressure of the water column in the positive pressure tube is accurate. The thermostatic outer casing 12 is equipped with a constant temperature fluid, which can be constant temperature water or other constant temperature liquids. The constant temperature fluid entering and exiting the thermostatic outer casing 12 is to ensure that the temperature of the liquid in the positive pressure tube is constant. The constant temperature should be lower than the pressure corresponding to the pressure vessel. A certain value of the saturation temperature prevents bubbles and vaporization in the positive pressure tube when the pressure of the pressure vessel changes. In winter in northern my country, the positive pressure tube in the single-chamber balanced container method sometimes freezes, and the positive pressure tube with external electric heating will vaporize the water in the positive pressure tube when the pressure of the pressure vessel is low. The water level and density of the water will cause measurement errors. The constant temperature water of the thermostatic outer casing 12 is equivalent to heating the liquid in the positive pressure tube in winter, and is equivalent to cooling the liquid in the positive pressure tube in summer. The differential pressure transmitter is installed at the zero point elevation of the water level of the pressure vessel, that is, the corresponding negative pressure pipe and the saturated water outlet pipe of the pressure vessel are combined into one and arranged horizontally, so the physical parameters such as the density of the water in the negative pressure pipe do not affect the differential pressure. The negative pressure reference junction value of the transmitter. The density ρ _c inside the positive pressure tube that affects the value of the positive pressure reference junction of the differential pressure transmitter is almost a constant value within the length L due to the constant temperature and lower than the saturation temperature, so the measurement error of the positive pressure reference junction value is very small, and L is The height difference between the horizontal position of the steam outlet pipe and the saturated water outlet pipe is also the range of water level measurement.

Parameters According to physical principles, the corresponding relationship between the water level H of the pressure vessel and the differential pressure value Δp output by the differential pressure transmitter:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;p</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; g</span>}}$

Among them, ρ _c is the density of the liquid in the positive pressure tube. ρ _c is affected by the temperature of the constant temperature water entering and exiting. According to the temperature of the constant temperature water entering and exiting, it can be conveniently corrected for its influence on the relationship between H——Δp. The same formula for ρ _w and ρ _s Can be corrected by pressure, so the measurement accuracy is more reliable than the existing technology.

In addition, the thermostatic outer sleeve 12 is used for cooling or heating the liquid in the positive pressure tube, without considering high temperature and high pressure, and the manufacturing cost is much lower than the balance container of the pressure-bearing parts in the prior art.

Compared with the prior art, the present invention overcomes the problems existing in the existing single-chamber balancing container method and the double-chamber balancing container method, and is superior to the prior art in terms of measurement accuracy, convenient use and manufacturing cost.

Claims (2)

1. A differential pressure liquid level measuring device for a pressure vessel, the device comprises a steam outlet pipe (2), a saturated water outlet pipe (7), a positive pressure pipe (4), a negative pressure pipe and a differential pressure transmitter device (6), characterized in that: the steam outlet pipe is directly connected to the positive pressure pipe (4), and an isolation valve (10) is installed on the steam outlet pipe; In the thermostatic outer casing (12), a water injection valve (11) is installed on the top of the positive pressure pipe; the saturated water outlet pipe and the negative pressure pipe are combined into one, and the pipe is installed at the zero point elevation of the water level of the high-pressure vessel. and arranged horizontally; the differential pressure transmitter is installed on the saturated water outlet pipe, and the saturated water outlet pipe is connected to the positive pressure pipe through the differential pressure transmitter. 2. The differential pressure liquid level measuring device according to claim 1, wherein said constant temperature fluid is constant temperature water.

Images