flammable gas alarmComposed of detector and alarm instrument, it is widely used in petroleum, gas, chemical, oil depot and other petrochemical industries with flammable gas, used to detect leaks in indoor and outdoor dangerous places, and is an important instrument to ensure production and personal safety. When flammable gas is present in the tested site, the detector converts the gas signal into a voltage signal or current signal and transmits it to the alarm instrument, and the instrument displays the percentage concentration value of the lower explosion limit of the flammable gas. When the flammable gas concentration exceeds the alarm set value, the sound and light alarm signal prompts, and the personnel on duty take safety measures in time to avoid explosion accidents.
The following is a brief introduction to the methods and precautions for the selection, installation, use and maintenance of flammable gas alarms as follows:
1. Precautions when applying
flammable gas alarmOnce the fixed-point installation is in place, its position is not easy to change. Based on the work experience accumulated over the years, the following points should be considered when applying it.
(1) Find out what possible leakage points are the devices to be monitored, analyze their leakage pressure, direction and other factors, and draw a probe position distribution map, which is divided into three grades: I., II., III. according to the severity of the leakage.
(2) According to specific factors such as the direction of airflow and wind direction of the site, the leakage direction of flammable gas is judged when a large amount of leakage occurs.
(3) According to the density of the leaking gas (greater or less than air), combined with the air flow trend, it is synthesized into a three-dimensional flow trend map of the leakage, and the initial point setting scheme is made at the downstream position of its flow.
(4) Study whether the leakage state of the leakage point is micro-leakage or jet-like. If it is a slight leak, the location of the point should be closer to the leakage point. If it is a jet leak, move slightly away from the leak point. Based on these conditions, the final plan for setting up the point was formulated. In this way, the quantity and variety that need to be purchased can be estimated.
(5) For places with large flammable gas leakage, a detection point should be set up every 10-20m apart according to relevant regulations. For small and discontinuous pumping rooms that are not on duty, the possibility of flammable gas leakage needs to be noted, and a detector should generally be installed at the downdraft.
(6) For places with hydrogen leakage, the detector should be installed on the plane above the leakage point.
(7) For mediums with a gas density greater than air, the detector should be installed on the lower plane below the leakage point, and pay attention to the characteristics of the surrounding environment. For places where flammable gas is easy to accumulate, special attention should be paid to the setting of safety monitoring points.
(8) For the open flammable gas diffusion and escape environment, if there is a lack of good ventilation conditions, it is easy to make the flammable gas content in the air in a certain part close to or reach the lower explosion limit concentration, which are safety monitoring points that cannot be ignored.
According to the analysis of the accidents on site, more than half of them were caused by incorrect installation and calibration. Therefore, it is necessary to introduce the considerations for proper installation and calibration to reduce failures.
2．flammable gas alarmInstallation precautions:
(1) There should be no strong electromagnetic field (such as high-power motors, transformers) around the alarm that affects the work of the instrument.
(2)AlarmIt is a safety instrument, with sound and light display functions, which should be installed in places that are easy for staff to see and hear, so as to eliminate hidden dangers in time.
(3) The installation height of the alarm should generally be 160-170cm to facilitate maintenance personnel to carry out daily maintenance.
(4) The alarm probe is mainly a detection element that contacts the combustion gas sensor, which is composed of a platinum wire coil covered with alumina and adhesive, and its outer surface is attached to platinum, palladium and other rare metals. Therefore, it is important to be careful when installing to avoid breaking 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 density of the measured gas is less than the air density, the probe should be installed 30cm away from the roof, in the direction downward; Conversely, the probe should be installed 30cm from the ground in an upward direction.
(6) The installation height of the open-air probe can be selected according to the density of the gas to be measured, and special attention should be paid to the probe should be installed on the downwind side.
(7) The connection cable of the alarm loop should be equipped with a protective sleeve, and it is best to add a metal hose at the wiring of the probe, and pay attention to the explosion protection of the factory.
(8) After installation and commissioning, be sure to install a breathable waterproof cover to prevent rainwater from entering and damaging the probe.
3．flammable gas alarmPrecautions for calibration
(1) In principle, the standard sample gas that has been certified by measurement and certification to match the gas to be tested should be used. The standard sample gas selected for the same tested medium is different, and the alarm points are also different.
(2) Before calibration, the surrounding environment of the probe should be free of flammable gas. If there is flammable gas, the rain cover should be removed first, filled with a certain amount of clean air, and then continuously injected into the sample gas to ensure the accuracy of the calibration.
(3) When the gas to be measured is a mixture of hydrocarbons, isobutane is the preferred sample gas, followed by propane.
(4) For non-hydrocarbon mixtures or hydrocarbon mixtures with a large difference in heat generated during the combustion of gases with lower explosion concentrations, butane, isobutane, propane and other easily available and stable one-component fuels can be used as sample gases as a last resort. In this case, the measuring range of the alarm must be adjusted according to a certain heartbeat conversion relationship.
4. Flammable gas alarm use and maintenance method
flammable gas alarmThere are many types and models, but the basic circuit principle is the same, so its use and maintenance methods are also similar. The methods of use and maintenance are described as follows:
(1) The service life of detection elements and compensation components is usually 3-5 years. Under reasonable conditions of use and proper maintenance, its service life can be extended.
(2) For alarms with test buttons, the test button should be pressed once a week to check whether the alarm system is normal. The zero point and measuring range of the alarm should be checked every 2 months.
(3) The detector should be checked frequently for accidental water intrusion. The detector ventilation cover should be removed and cleaned when the instrument is tested to prevent blockage.
(4) The detector is an explosion-proof explosion-proof equipment and shall not be used beyond the specified range. The detector must not be used in places containing sulfur. The detector should be used as much as possible when the concentration of flammable gas is lower than the lower explosion limit, otherwise, the component may be burned out.
(5) Hot wire semiconductor detectors should not be used under hypoxia conditions. Do not rush the probe with a large amount of flammable gas.