Combustible gas alarms consist of detectors and alarms. They are widely used in petrochemical industries such as petroleum, gas, chemical, and oil depots where combustible gases are present. They are used to detect leaks in hazardous locations indoors and outdoors and are important for production and personal safety. instrument. When there is a flammable gas in the measured location, the detector converts the gas signal into a voltage signal or a current signal and transmits it to the alarm instrument. The instrument displays the percentage concentration of the lower explosive limit of the flammable gas. When the concentration of flammable gas exceeds the alarm setting value, an audible and visual alarm signal is generated. The on-duty personnel take safety measures in time to avoid the occurrence of a flaring accident.
1. Application considerations
Once the flammable gas alarm is installed in place, its location is not easily changed. According to the work experience accumulated over the years, the following points should be taken into consideration when it is applied.
(1) Find out which possible leakage points of the devices to be monitored, analyze their leakage pressure, direction and other factors, and draw the distribution map of the probes, and classify them into three grades I, II and III according to the severity of the leakage.
(2) According to specific factors such as airflow direction and wind direction at the site, determine the direction of leakage of flammable gas when a large amount of leakage occurs.
(3) According to the density of leaked gas (greater than or smaller than air), combined with the trend of air flow, integrate the three-dimensional flow chart of leakage and make an initial set-point scheme at the downstream position of the flow.
(4) The leakage status of the leaking point was studied as microleakage or jetting. If it is a microleakage, set the position of the point to be near the leak. If it is a spray-like leak, keep it slightly away from the leak. Combine these conditions and draw up a final plan. In this way, the number and type of purchases needed can be estimated.
(5) For locations where there is a large leakage of flammable gas, a test point should be set at a distance of 10-20 m in accordance with relevant regulations. For unattended, small, non-continuous pumping stations, attention should be given to the possibility of flammable gas leaking. A detector should normally be installed at the downtake.
(6) For locations with hydrogen leaks, the detector should be installed on the plane above the leak.
(7) For media with a gas density greater than air, the detector should be installed on the lower surface below the leak point and pay attention to the surrounding environment. Sites that are liable to accumulate flammable gas should pay special attention to the setting of safety monitoring points.
(8) For an open flammable gas diffusion escape environment, if there is no good ventilation, it is easy to make the flammable gas content in a certain part of the air close to or reach the lower explosion concentration. These are all non-negligible safety monitoring points. .
According to the results of field accident analysis, more than half of them were caused by incorrect installation and calibration. Therefore, it is necessary to introduce the correct installation and calibration precautions to reduce the failure.
2. Combustible gas alarm installation precautions
(1) There must be no strong electromagnetic fields (such as high-power motors and transformers) that affect the operation of the instrument around the alarm.
(2) The alarm is a safety instrument, sound and light display function, and it should be installed in the place where the staff can easily see and hear, so as to eliminate the hidden trouble in time.
(3) The installation height of the alarm should generally be 160-170cm so that the maintenance personnel can carry out routine maintenance.
(4) The alarm probe is mainly a detection element that contacts the combustion gas sensor. The platinum wire coil is coated with alumina and a binder to form a sphere. On the outer surface, platinum, palladium, and other rare metals are attached. Therefore, be careful when installing to avoid damaging the probe.
(5) The density of the gas to be measured is different, and the installation position of the indoor probe should also be different. When the measured gas density is less than the air density, the probe should be installed 30cm away from the roof, down direction; otherwise, the probe should be installed 30cm away from the ground, upward direction.
(6) Installation of open-air probes The installation height can be selected based on the density of the gas to be measured. It is especially important to note that the probes should be installed on the downwind side.
(7) The connection cable of the alarm circuit should be protected by a protective tube. It is best to add a metal hose at the connection of the probe, and pay attention to the explosion-proof grade of the factory.
(8) After installation and commissioning, be sure to install a breathable waterproof cover to prevent rain from entering the damaged probe.
3. Combustible gas alarm check notes
(1) In principle, the standard sample gas that matches the measured gas with the certified gas shall be used. The standard sample gas selected for the same measured medium is different, and the alarm point is also different.
(2) Before calibration, the surrounding environment of the probe should be free of flammable gas. If there is flammable gas, remove the rain cover, fill in a certain amount of clean air, and then continuously introduce sample gas to ensure the accuracy of the calibration.
(3) When the measured gas is a hydrocarbon mixture, isobutane is the preferred sample gas, followed by propane.
(4) For non-hydrocarbon mixtures or mixtures of gases with a lower explosive concentration and a greater difference in the amount of heat generated, a mixture of butane, isobutane, propane and other readily available and stable single components may be used. Fuel as a sample gas. At this time, the range of the alarm must be adjusted according to a certain detection signal conversion relationship.
4. Combustible gas alarm use and maintenance methods
The types and types of flammable gas alarms are numerous, but the basic circuit principles are the same, so their methods of use and maintenance are similar. The methods to be used and maintained are described below:
(1) The lifetime of the detection element and the compensation element is usually 3-5 years. Under the conditions of reasonable use and proper maintenance, its service life can be extended.
(2) For alarms with test buttons, press the test button once a week to check if the alarm system is normal. Check the zero and span of the alarm once every 2 months.
(3) The detector should always be checked for accidental flooding. When the detector breather cover is inspected by the instrument, it should be removed and cleaned to prevent clogging.
(4) The detector is explosion-proof explosion-proof equipment and shall not be used beyond the specified range. The detector must not be used in the presence of sulfur. The detector should be used as far as possible under the condition that the flammable gas concentration is lower than the lower explosion limit; otherwise, the device may be burned out.
(5) The hot wire semiconductor detector must not be used in the absence of oxygen. Do not use a large number of combustible gas probes.
1. Application considerations
Once the flammable gas alarm is installed in place, its location is not easily changed. According to the work experience accumulated over the years, the following points should be taken into consideration when it is applied.
(1) Find out which possible leakage points of the devices to be monitored, analyze their leakage pressure, direction and other factors, and draw the distribution map of the probes, and classify them into three grades I, II and III according to the severity of the leakage.
(2) According to specific factors such as airflow direction and wind direction at the site, determine the direction of leakage of flammable gas when a large amount of leakage occurs.
(3) According to the density of leaked gas (greater than or smaller than air), combined with the trend of air flow, integrate the three-dimensional flow chart of leakage and make an initial set-point scheme at the downstream position of the flow.
(4) The leakage status of the leaking point was studied as microleakage or jetting. If it is a microleakage, set the position of the point to be near the leak. If it is a spray-like leak, keep it slightly away from the leak. Combine these conditions and draw up a final plan. In this way, the number and type of purchases needed can be estimated.
(5) For locations where there is a large leakage of flammable gas, a test point should be set at a distance of 10-20 m in accordance with relevant regulations. For unattended, small, non-continuous pumping stations, attention should be given to the possibility of flammable gas leaking. A detector should normally be installed at the downtake.
(6) For locations with hydrogen leaks, the detector should be installed on the plane above the leak.
(7) For media with a gas density greater than air, the detector should be installed on the lower surface below the leak point and pay attention to the surrounding environment. Sites that are liable to accumulate flammable gas should pay special attention to the setting of safety monitoring points.
(8) For an open flammable gas diffusion escape environment, if there is no good ventilation, it is easy to make the flammable gas content in a certain part of the air close to or reach the lower explosion concentration. These are all non-negligible safety monitoring points. .
According to the results of field accident analysis, more than half of them were caused by incorrect installation and calibration. Therefore, it is necessary to introduce the correct installation and calibration precautions to reduce the failure.
2. Combustible gas alarm installation precautions
(1) There must be no strong electromagnetic fields (such as high-power motors and transformers) that affect the operation of the instrument around the alarm.
(2) The alarm is a safety instrument, sound and light display function, and it should be installed in the place where the staff can easily see and hear, so as to eliminate the hidden trouble in time.
(3) The installation height of the alarm should generally be 160-170cm so that the maintenance personnel can carry out routine maintenance.
(4) The alarm probe is mainly a detection element that contacts the combustion gas sensor. The platinum wire coil is coated with alumina and a binder to form a sphere. On the outer surface, platinum, palladium, and other rare metals are attached. Therefore, be careful when installing to avoid damaging the probe.
(5) The density of the gas to be measured is different, and the installation position of the indoor probe should also be different. When the measured gas density is less than the air density, the probe should be installed 30cm away from the roof, down direction; otherwise, the probe should be installed 30cm away from the ground, upward direction.
(6) Installation of open-air probes The installation height can be selected based on the density of the gas to be measured. It is especially important to note that the probes should be installed on the downwind side.
(7) The connection cable of the alarm circuit should be protected by a protective tube. It is best to add a metal hose at the connection of the probe, and pay attention to the explosion-proof grade of the factory.
(8) After installation and commissioning, be sure to install a breathable waterproof cover to prevent rain from entering the damaged probe.
3. Combustible gas alarm check notes
(1) In principle, the standard sample gas that matches the measured gas with the certified gas shall be used. The standard sample gas selected for the same measured medium is different, and the alarm point is also different.
(2) Before calibration, the surrounding environment of the probe should be free of flammable gas. If there is flammable gas, remove the rain cover, fill in a certain amount of clean air, and then continuously introduce sample gas to ensure the accuracy of the calibration.
(3) When the measured gas is a hydrocarbon mixture, isobutane is the preferred sample gas, followed by propane.
(4) For non-hydrocarbon mixtures or mixtures of gases with a lower explosive concentration and a greater difference in the amount of heat generated, a mixture of butane, isobutane, propane and other readily available and stable single components may be used. Fuel as a sample gas. At this time, the range of the alarm must be adjusted according to a certain detection signal conversion relationship.
4. Combustible gas alarm use and maintenance methods
The types and types of flammable gas alarms are numerous, but the basic circuit principles are the same, so their methods of use and maintenance are similar. The methods to be used and maintained are described below:
(1) The lifetime of the detection element and the compensation element is usually 3-5 years. Under the conditions of reasonable use and proper maintenance, its service life can be extended.
(2) For alarms with test buttons, press the test button once a week to check if the alarm system is normal. Check the zero and span of the alarm once every 2 months.
(3) The detector should always be checked for accidental flooding. When the detector breather cover is inspected by the instrument, it should be removed and cleaned to prevent clogging.
(4) The detector is explosion-proof explosion-proof equipment and shall not be used beyond the specified range. The detector must not be used in the presence of sulfur. The detector should be used as far as possible under the condition that the flammable gas concentration is lower than the lower explosion limit; otherwise, the device may be burned out.
(5) The hot wire semiconductor detector must not be used in the absence of oxygen. Do not use a large number of combustible gas probes.