In winter, as the temperature gradually decreases, when the measured medium is transmitted to the transmitter through the measurement pipeline, freezing, solidification, precipitation and crystallization often occur when the ambient temperature is too low, and the normal operating temperature range of the instrument used is exceeded due to the low ambient temperature, which directly affects the accuracy of the instrument measurement display. The measurement medium of various instrument points such as pressure, flow, liquid level, and temperature is mostly liquid, which is affected by low temperature, which is more likely to cause measurement errors, and in severe cases, it may cause safety accidents such as poisoning, fire, and explosion.
To sum up, the cold and frost protection of instruments is particularly important. Some large instrumentation users have taken measures early, such as power plants, water plants, petroleum, chemical industries, etc. have formulated cold and freeze protection work systems suitable for their own enterprises. Let's explore how winter meter users should carry out meter anti-freeze work.
For the antifreeze treatment of instruments and instrument measurement pipelines, the objects that need to be heat-traced and insulated mainly include transmitters installed in the instrument incubator, external float level transmitter or other forms of open-air installation liquid level transmission units, and detection and measurement pipelines of pressure, differential pressure, flow and other instruments. Avoid such accidents through selection or other means. The measures usually taken: selection, heat preservation and heat tracing, maintenance (point inspection, sewage discharge), etc.
1. Selection measures
(1) Optional instrument with thermal insulation device. According to the type and use of the instrument and the geographical location to be installed, put forward the thermal insulation and anti-freezing requirements of the instrument, and then submit it to the manufacturer for processing.
(2) The signal remote transmission instrument and display head should consider the ambient temperature resistance requirements, and the isolation liquid should consider the environmental temperature resistance requirements.
(3) Metal rotor flow meters, electric target flow meters, volumetric flow meters, mass flow meters, etc. generally do not need to be heated separately.
(4) When selecting a model, the first consideration is the practicality and economy of the instrument, which refers to convenient maintenance, accurate measurement, and economics are cheap to put it bluntly. The two should be combined with each other, not only for convenience and maintenance-free, but also to choose mass flow meters, metal rotors, electric targets, etc. Therefore, correct selection is also a measure of anti-freezing and anti-condensation. In addition, when installing the instrument, the anti-freezing and anti-condensation of the instrument should be fully considered, such as the pressure guide pipe should be as short as possible, frequent inspection and sewage discharge, and it should be convenient for heat tracing, etc., otherwise no matter how good the selection is, it will not work.
(5) In some places in the north, the temperature difference between day and night is too large, and it can reach more than -20 degrees at night. Choosing thermal insulation and heat tracing and maintenance (point inspection, sewage discharge) and other methods are the best solutions for anti-freezing.
2. Insulation measures
Insulation with insulation material, that is, use insulation material to wrap the parts of the instrument that are prone to freezing or afraid of freezing. When winter comes, it is necessary to inspect and discharge pollutants frequently to prevent damage to the insulation materials of the packaging.
3. Heat tracing measures
1. Steam heating measures
That is, use tube steam heating to keep warm. Before supplying steam in winter, check whether the steam insulation pipeline is unblocked or blocked. It is best to have steam 24 hours a day, not too hot, and sometimes adjust the amount of steam supplied to the insulation according to the temperature change of the weather, so as to prevent the temperature from being too high to vaporize the condensate in the transmitter pressure tube and affect the work of the transmitter or the condensate in the transmitter pressure tube is too low to affect the transmitter work smoothly.
2. Thermal insulation and protection box measures
a. The heating pipe heating incubator is composed of three parts: box, heater, instrument bracket, etc., its structural form is the same as the protective box, but the difference is that the box is equipped with an electrical heating device, the structural form is as shown in the figure, the electric heating device is composed of electric heating pipe, temperature controller, and the side of the box is equipped with a socket. Through repeated work, the temperature in the box can be maintained within a certain range. The main parameters of its thermostatic heater:
(1) Rated voltage 200V.50Hz
(2) Rated power 300~500W
(3) The control temperature can be customized by the user
(4) The constant temperature heater can also be made into an explosion-proof type
(5) There are three types of heating pipe materials: copper pipe, carbon steel pipe, and stainless steel pipe.
b. Steam pipe heat tracing incubator, the heat trace pipe is made of metal pipe into S-shaped structure. The upper and lower parts of the box are welded with welded plate joints and heat trace pipes, and the heat trace pipes are installed in the box for up and down, and the heating purpose is achieved through the circulation of steam in the tube cavity. Heat tracing pipe materials are generally divided into two types, namely copper pipes and seamless steel pipes (carbon steel).
c. Add another layer of insulation cotton to the key instrument box, and add glue and seal at the door of the incubator and the inlet and outlet pipeline to achieve a better thermal insulation and anti-freezing effect of the instrument system.
3. Electric heating belt measures
Electric heat tracing and insulation technology is a new type of heating technology that directly converts electrical energy into heat energy. Install insulation cables, wrap the heat trace around the instrument, or stick it inside the instrument cabinet (but pay attention to the length of the heat trace used, it should be economical and moderate).
It is suitable for heat tracing, anti-freezing and thermal insulation of pipelines, valves, pump bodies or maintaining the process temperature of instrument pipelines, the heat generation per unit length is constant, the output power is not changed by the change of ambient temperature, the length and power are directly proportional, and can be spliced arbitrarily during installation, but a heating node (i.e. at least 2.5m) must be retained, and the outer braid layer has the effect of heat transfer and heat dissipation, and can be used as a safe grounding for anti-static. It is mainly used for anti-freezing and thermal insulation of various pipelines and instruments, with a maximum maintenance temperature of 150°C. Note: Heat tracing and insulation of liquid lines that require strict temperature control (temperature controller must be used).
There is also a product on the market, which is a flexible packaging electric heat tracing protective cover, which is specially used for instrument heat tracing and explosion-proof in relatively small space, and is mainly installed in the pressure pipe section and valve of the instrument.
4. Maintenance measures
1. Installation measures
Reasonable selection of installation site: dry, no rain and snow dripping.
2. Inspection measures
If possible, a special person will conduct technical confirmation and technical disposal of whether the insulation material is damaged or whether the steam pipeline is blocked every day.
3. Alarm measures
If possible, a small sound and light alarm device in the state of steam leakage or power failure can be installed to facilitate the discovery and timely rectification of hidden dangers of thermal insulation and anti-freezing measures.
4. Inspection measures
The person in charge of regional instrument maintenance shall conduct regular inspections according to the predetermined inspection route. During the inspection, it is necessary to check whether the insulation pipeline valves are normal, whether the incubator is normal, whether the hydrophobic device is normal, whether the packaging of insulation materials is intact, and whether the electrical heat tracing power supply components are normal. Carry out key inspections on the instruments of freezing devices and make inspection records, carry out dry, complete and clean maintenance of the instruments and their insulation and anti-freezing measures, and solve the thermal insulation and heat tracing problems that occur on site in a timely manner.
