At present, most of the oil sent and received by domestic gas stations is gasoline, which is determined by the physical characteristics of light oil such as gasoline with low boiling point (50 ~ 200e) and easy volatilization,Gas Station Hydrocarbon VOCsThe creation is inevitable. Under normal circumstances, VOC in normal operation of gas stations mainly comes from two links: loading and unloading and refueling operations: in loading and unloading operations, the tanker unloads oil into the storage tank through the oil pipeline, the liquid level in the tank rises to form positive pressure, and the saturated oil vapor in the tank is discharged into the atmosphere through the vent pipe (this process is also called "big breathing"); In the refueling operation, due to the non-tight connection between the refueling gun and the tank mouth, it makes a large amount of oil and gas discharged into the atmosphere from the tank mouth. In addition, during the storage of oil, due to the change of ambient temperature, the saturated oil and gas in the tank also has respiratory loss, but the emission of this part is relatively small.

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4. Hazards of VOC Gas

The hazards of VOC are divided into two aspects:

• Harm to the human body

VOC gas has a huge impact on human health. Human exposure to a certain concentration of VOC environment, will cause damage to the nervous system and hematopoietic function, and even lead to cancer and other serious diseases. When the indoor VOC reaches a certain concentration, in a short period of time, people can feel headache, nausea, force and other conditions, serious when there will be convulsions, coma and other conditions.

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• harm to the environment

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

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

Construction standard:

Code for Construction of Environmental Information Network (HJ460-2009)

Technical Specification for Development and Management of Environmental Protection Application Software (HJ622-2011)

Data Transmission Standard for Online Automatic Monitoring and Monitoring System of Pollution Sources (HJ212-2005)

Integrated Emission Standard of Air Pollutants (GB16297-1996);

Emission Standard of Air Pollutants for Oil Depots (GB20950-2007);

Emission Standard of Air Pollutants for Gasoline Transportation (GB20951-2007);

Emission Standard of Air Pollutants for Gas Stations (GB20952-2007);

Opinions of the State Council on Strengthening the Key Work of Environmental Protection (No. 35 [2011], State Council);

"Volatile Organic Compounds (VOCs) Pollution Control Technical Policy" Ministry of Environmental Protection Announcement [2013] No. 31;

Notice on Printing and Distributing Guidelines for Pollution Control of Volatile Organic Compounds in Key Industries of Jiangsu Province (Su Huan Ban [2014] No. 128);

Notice of the Ministry of Environmental Protection on Issuing the Key Points of National Environmental Emergency Management in 2013 (HB [2013] No. 10)

Technical Requirements for Photoionization Detector (PID) Method for Continuous Automatic Monitoring System of Volatile Organic Compounds Emissions from Stationary Sources (DB44/T 1947-2016)

VOC online monitoring system for the presence of VOC gas in the air, wireless transmission technology, database technology, software technology and sensor detection technology, real-time monitoring of gas station emissions inTemperature, humidity, VOC concentrationThrough logical judgment and intelligent analysis, VOC level and alarm signal are output, so as to improve and enhance the remote monitoring and early warning capability of atmospheric environment, and timely remind and deal with environmental deterioration.

The overall technical architecture of VOC online monitoring system for gas stations is as follows:

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

Introduction of PID sensor principle

PID is a photoionization detector, which is mainly used to detect low concentrations of volatile organic compounds and other toxic gases in the order of magnitude of 1ppb-15000ppm. PID is a highly sensitive detector with 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 charge of the ionized gas and converts it into a current signal to enable measurement of the gas concentration. When the gas to be measured absorbs high-energy ultraviolet light, the gas molecules are excited by the ultraviolet light and temporarily lose electrons to become positively charged ions. After the gas ions are detected on the electrodes of the detector, they are quickly combined with electrons to reconstitute the original gas and vapor molecules. PID is a non-destructive detector, it does not "burn" or permanently change the gas molecules to be measured, the gas detected by PID can still be collected for further measurement.

In theory, all chemicals can be ionized, but the energy required to ionize them is different. 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 a UV lamp can also be measured in electron volts. A gas will be ionized if its ionization energy is lower than the energy emitted by the lamp. The main gases or volatiles that can be detected by PID are the large number of organic compounds containing carbon atoms (VOCs). Includes:

• Aromatic: a series of compounds containing benzene rings, such as benzene, toluene, ethylbenzene, xylene, etc;
• Ketones and aldehydes: Compounds containing a C = O bond. For example: acetone, butanone, formaldehyde, acetaldehyde, etc;
• Amines and amino compounds: N-containing hydrocarbons. For example: diethylamine, etc;
• Halogenated hydrocarbons: such as trichloroethylene (TCE), perchloroethylene (PCE), etc;
• Sulfur-containing organic compounds: 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 compounds, PID can also measure some inorganic compounds without carbon gas,Such:

• Ammonia;
• Semiconductor gases: arsine (arsine), phosphine (phosphine), etc;
• Hydrogen sulfide;
• Nitrogen oxides;
• Bromine and iodine;