PID application in gas station

　　At present, gasoline is the main source and destination oil of domestic gas stations. Due to the low boiling point (50~200e) of light oil products such as gasoline and its easy volatilization and other physical characteristics, the generation of hydrocarbon VOCs in gas stations is inevitable. Under normal circumstances, the VOC in the normal operation of the gas station is mainly produced in the loading, unloading and refueling operations. In the loading and unloading operation, the tanker truck dumps the oil into the storage tank through the oil pipeline, the liquid level in the tank rises, forming positive pressure, and the saturated oil vapor in the tank is discharged into the atmosphere by the vent pipe (this process is also called "big breathing"); During the refueling operation, due to the non-tight connection between the refueling gun and the tank port, a large amount of oil and gas is discharged from the tank port into the atmosphere. In addition, in the storage of oil products, due to the change of environmental temperature, the saturated oil and gas in the tank also has respiratory loss, but the emission of this part is relatively small.

　　Hazards of VOC gases

　　The harm of VOC is divided into two aspects：

　　Harm to human body

　　VOC gas has a great impact on human health. When human body is exposed to a certain concentration of VOC, it will cause damage to the nervous system and the destruction of hematopoietic function, and even lead to cancer and other serious diseases. When the VOC reached a certain concentration in the room, in a short time, people can feel headache, nausea, power and other conditions, serious convulsions, coma and other conditions.

　　Harm to the environment

　　VOC gas can also cause damage to the atmosphere. VOC is one of the important reasons for the increase of atmospheric ozone concentration and the formation of regional photochemical smog, acid rain, and smoke combined pollution. VOC is the precursor to the formation of PM2.5 and ozone, and VOC accounts for more than 25% of PM2.5 in the atmosphere. VOC will contribute to the greenhouse effect, resulting in global warming.

　　At present, photochemical pollution caused by volatile organic compounds (VOC) has become the important environmental problem faced by some cities in our country. The evaporation of oil products from urban gas stations is an important source of VOC emissions, and the chemical activity of VOC species contained in oil products steam is very high, so the contribution rate of VOC emissions from gas stations to ozone generation cannot be ignored.

　　Construction standard：

　　《Environmental information network construction standards》（HJ460-2009）

　　《Environmental protection application software development management technical specification》（HJ622-2011）

　　《Data transmission standard of on-line automatic monitoring and monitoring system for pollution sources》（HJ212-2005）

　　《Comprehensive discharge standards for air pollutants》（GB16297-1996）；

　　《Air pollutant discharge standard for oil storage》（GB20950-2007）；

　　《Emission standard for air pollutants in gasoline transportation》（GB20951-2007）；

　　《Emission standards of air pollutants for gas stations》（GB20952-2007）；

　　《Opinions of The State Council on Strengthening Key work of Environmental Protection》（State hair〔2011〕35号）；

　　《Policy on Volatile organic Compounds (VOCs) pollution Control Technology》Announcement of the Ministry of Environmental Protection【2013】31号；

　　《Notice on the issuance of Guidelines for the Control of Volatile Organic Matter Pollution in Key Industries of Jiangsu Province》（Suzhou International Environmental Affairs Office【2014】128号）；

　　《Issued by the Ministry of Environmental Protection〈Key points of national environmental emergency management in 2013〉Notice of》（Environmental affairs office〔2013〕10No.）

　　《Technical requirements of PID method for continuous automatic monitoring system of volatile organic compounds emission from fixed pollution sources》（DB44/T 1947-2016）

　　VOC online monitoring system for VOC gas in the air, combining wireless transmission technology, database technology, software technology and sensor detection technology, real-time monitoring gas station emissions of temperature, humidity, VOC concentration and other related parameters, through logical judgment and intelligent analysis, output VOC level and alarm signal. In order to improve and enhance the atmospheric environment remote monitoring and early warning capabilities, timely reminder of environmental deterioration.

　　The overall technical framework of VOC online monitoring system is as follows：

　　The sensor for detecting VOC gas in gas station VOC online monitoring system, two PID sensors for detecting VOC gas are recommended, namely PID-AH and PID-A1; PID-A1 is a large-range sensor, its detection range is 100ppb~6000ppm, while PID-AH is a product with a small range and high sensitivity, its detection range is 1ppb ~ 50ppm of VOC gas.

　　This section describes the principle of PID sensor

　　PID is a kind of photoionization detector, mainly used to detect low concentrations of volatile organic compounds and other toxic gases in the order of 1ppb-15000ppm. PID is a highly sensitive detector for a wide range of applications.

　　PID uses an ultraviolet lamp (UV) light source to ionize organic molecules into positive and negative ions (ionization) that can be detected by a detector. The detector captures the positive and negative charges of the ionized gas and converts them into current signals to measure the gas concentration. When the gas under test absorbs high energy ultraviolet light, the gas molecules are excited by ultraviolet light and temporarily lose electrons to become positively charged ions. When the gas ions are detected at the detector's electrodes, they quickly combine with electrons to reconstitute the original gas and vapor molecules. PID is a non-destructive detector that does not "burn" or change the gas molecules under test. The gas detected by PID can still be collected for further determination.

　　Theoretically, all chemicals can be ionized, but the amount of energy required to be ionized varies. The energy that can transfer an electron and ionize a compound is called ionization energy and is measured in electron volts (eV). The energy emitted by UV lamps can also be measured in electron volts. If the ionization energy of a gas is lower than the energy emitted by the lamp then the gas will be ionized. The main gases or volatiles that can be detected by PID are a large number of organic compounds containing carbon atoms (VOC).Include：

　　Aromatic：A series of compounds containing benzene rings, such as benzene, toluene, ethylbenzene, xylene, etc.

　　Ketones and aldehydes: Compounds containing the C=O bond. Such as: acetone, butyl ketone, formaldehyde, acetaldehyde, etc.

　　Amines and amino compounds: hydrocarbons containing N. Such as: diethylamine.

　　Halogenic hydrocarbons：Such as trichloroethylene (TCE), perchloroethylene (PCE), etc.

　　Sulfurous organic matter：Methyl mercaptan, sulfide, etc.

　　Unsaturated hydrocarbons：Butadiene, isobutene, etc；

　　Saturated hydrocarbons：Butane, octane, etc；

　　Alcohols：Isopropyl alcohol (IPA), ethanol, etc.

　　In addition to the above organic matter, PID can also measure some inorganic compound gases without carbon, such as: ammonia; Semiconductor gas: hydrogen arsenide (arsenane), phosphine (phosphoane), etc.; Hydrogen sulfide; Nitrogen oxide; Bromine and iodine；