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 Cause analysis and improvement measures for unstable liquid level of glass tube level gauge

Cause analysis and improvement measures for unstable liquid level of glass tube level gauge

  • Abstract: the liquid level of glass tube level gauge is the main basis for normal operation, fault analysis and judgment of refrigeration system operation managers. According to the working principle of glass tube liquid level gauge, aiming at the mistakes in engineering design and field construction, this paper analyzes the causes of liquid level instability, points out the type of glass tube liquid level gauge that should be selected and the steps and methods of transformation, so as to ensure the normal operation of the refrigeration system.
Product details
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Abstract: the liquid level of glass tube level gauge is the main basis for normal operation, fault analysis and judgment of refrigeration system operation managers. According to the working principle of glass tube liquid level gauge, aiming at the mistakes in engineering design and field construction, this paper analyzes the causes of liquid level instability, points out the type of glass tube liquid level gauge that should be selected and the steps and methods of transformation, so as to ensure the normal operation of the refrigeration system.
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Background
A chemical industry Co., Ltd. of Guangxi has purchased four glass tube level meters with heat exchange area of 26.3 m3 produced by Jingjiang Container Manufacturing Co., Ltd. the structural diagram provided by the manufacturer is shown in Fig. 1, which is mainly used for cooling ethylene ketone gas. The temperature of acetophenone gas at the outlet of four glass tube level gauges is required to be - 5 ℃, 10 ℃, 15 ℃ and - 5 ℃, respectively 20 ℃ to separate water and acetic acid from ketene gas and prevent freezing.
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Guangxi chemical industry Co., Ltd. entrusts a refrigeration engineering Co., Ltd. in Guangzhou to design and install the project. Based on the equipment provided by the manufacturer and in combination with the equipment data and drawings provided by the equipment manufacturer, the plate type liquid level gauge is directly installed on the liquid level control ports 4 and 8.
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During the commissioning and operation of the refrigeration system, it was found that ammonia bubbles began to form at the bottom of the plate type liquid level gauge, which rose slowly until the liquid level disappeared, and the liquid level floated up and down with a large amplitude, which could not be stabilized in a certain position. With the operation of the system, the lower part of the liquid level gauge begins to condense and frost, and the frosting height gradually increases, and the frost turns into ice, so the liquid level cannot be observed, see 2. At the same time, the screw type refrigeration compressor appears "tide car" phenomenon.
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Because the operator can not judge the accurate position of the liquid level, in order to prevent the accident, he was forced to stop the machine, which seriously affected the production of materials.
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2. Cause analysis
? ? Glass tube level gauge The plate level gauge is directly installed on the liquid level control port of the evaporator, and the plate level gauge is filled with the liquid level equal to that of the evaporator. After the refrigeration system is running, due to the suction effect of the refrigeration compressor, the pressure inside the evaporator gradually decreases. When the pressure drops to the corresponding gasification temperature of the refrigerant, the refrigerant liquid in the shell tube absorbs the heat of the materials in the heat transfer tube, and the air bubbles formed by the refrigerant below the liquid level slowly rise to the liquid level and disappear. With the increase of material load, the boiling of refrigerant is intensified and the liquid level fluctuates greatly. As the evaporator is connected with the liquid level meter, the bubble will rise and the liquid level will be unstable. When the refrigerant in the liquid level gauge vaporizes, it absorbs the heat of the external environment, and the water vapor in the air is cooled, and the phenomenon of condensation, frosting and freezing occurs. When the liquid level inside the evaporator is too high or boiling violently, the refrigerant gas carries the refrigerant droplets into the screw refrigeration compressor, resulting in "wet car" phenomenon. ?
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3 solutions
Through the cause analysis, the instability of the liquid level in the plate type liquid level gauge and the external frosting are caused by the low boiling point of the liquid inside the plate level gauge. If the plate type liquid level gauge is replaced by the oil bag type liquid level gauge, the refrigerant inside the liquid level gauge will be changed into lubricating oil, and the liquid level of the level gauge will be unstable and the external frosting will not occur. Replace the oil level gauge according to the following steps. ?
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1. On site processing and manufacturing of oil package. The oil level gauge consists of oil package and plate type liquid level gauge, which is connected by pipeline and valve. The oil ladle is the key component of the oil level gauge. If the volume is too small or the connection with the plate level gauge does not meet the requirements, the liquid level may rise and fall slowly, the liquid level response is not sensitive, or the oil package frosts. Figure 3 is the dimension drawing of oil package processing, and the field processing is made according to the drawing requirements.
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2. Collect the refrigerant in the evaporator and charge nitrogen to remove the residual ammonia. Close the liquid supply valve of the glass tube level gauge, start the refrigeration compressor, and vacuumize the evaporator repeatedly and repeatedly. When the gas outlet valve of the glass tube level gauge is closed, the internal pressure of the evaporator does not change within 1 h, and the air extraction is stopped. Open the flange at the control port of the liquid level gauge on the upper part of the evaporator, and then open the flange of the drain outlet of the evaporator, and fill nitrogen from the control port of the liquid level gauge until the gas at the drain outlet has no peculiar smell. 3. Install the oil level gauge. According to the actual situation of the glass tube level gauge on site, the installation diagram of the oil package level gauge (Fig. 4) is drawn. The welding and installation are carried out under the condition that the drain outlet is open to the atmosphere and the safety officer supervises on site.
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4. Nitrogen pressure maintaining and ammonia leak test. Connect the horizontal shell and tube type
After the flange of the control port of the liquid level gauge on the upper part of the evaporator, 1.2 MPa nitrogen is filled into the evaporator through the drain outlet of the evaporator, and the pressure is maintained for 24 h. There is no pressure change caused by leakage, and nitrogen is eliminated. Slightly open the outlet valve of the evaporator, fill 0.2 MPa ammonia into the evaporator by using the system pressure, and check that there is no leakage with phenolphthalein test paper. ?
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5. Add lubricating oil to the oil package. When the oil level of a and B is closed through the screw plug of the oil level gauge a and B, close the oil filling valve at the upper part of the oil level gauge a and B, and then close the oil filling valve at the oil level gauge a and D. ?
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6. Adjust the glass tube level gauge to the working state. Check that the drain valve, liquid supply valve, drain valve and vent valve B of the glass tube level gauge are closed, and the outlet valve, safety stop valve, oil drain valve, interface valve of liquid level gauge and valves a, C and D of the oil level gauge of the glass tube level gauge are in the open state. ?
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4 implementation effect
After the glass tube level gauge is modified, the material (ethylene ketone gas) is input The internal oil level of the oil level gauge is clear and stable, and there is no frost on the level gauge. The operator timely adjusts the opening of the liquid supply valve of the evaporator according to the liquid level. There is no "wet car" phenomenon in the refrigeration compressor, which ensures the safe operation of the system and the normal cooling of materials.
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 Cause analysis and improvement measures for unstable liquid level of glass tube level gauge

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