Gas station breathing process VOCs emission amount correction method based on oil gas recovery vacuum pump type

Abstract

The invention is suitable for the field of petrochemical engineering, and provides a gas station breathing process VOCs emission amount correction method based on the type of an oil gas recovery vacuum pump. Calculating the pressure increment caused by excessive oil gas recovery (the gas-liquid ratio is 1.1) and reverse air leakage of a vacuum pump in the oil tank in the secondary oil gas recovery process, and deducing a correction formula of VOCs emission factors; secondly, a discharge amount correction model is established by combining the use proportion and the leakage proportion of a gas station fixed-frequency pump, the installation proportion of a three-time oil gas recovery device and the annual gasoline sales volume; the accuracy of discharge amount calculation is verified by actually measuring the single discharge amount of VOCs at the P / V valve of the gas station and monitoring the opening and closing frequency of the P / V valve. According to the method, the problem that the influence of an existing method on reverse leakage of the fixed-frequency pump is ignored is solved, the precision of checking the VOCs emission amount of the gas station is remarkably improved, and a reliable basis is provided for precise pollution control and gas station VOCs emission supervision.

Description

Technical Field

[0001] The invention belongs to the field of petrochemical engineering, and in particular relates to a method for correcting VOCs emissions during a breathing process of a gas station based on an oil and gas recovery vacuum pump type. Background Art

[0002] The oil and gas in the refueling process at gas stations are recovered through secondary oil and gas recovery devices. Existing refueling guns are equipped with oil and gas recovery functions, and can recover oil and gas in equal or high proportions while refueling. There are two types of oil and gas recovery vacuum pumps at gas stations: fixed frequency pumps and variable frequency pumps. The design and start-stop method of fixed frequency pumps will accelerate the aging or wear of its seals, resulting in poor sealing of the vacuum pump. External air is easily reversely inhaled during operation, and excessive air enters the oil tank, causing increased pressure inside the oil tank and oil and gas emissions, causing environmental pollution and oil and gas loss. Using a variable frequency pump will prevent air from being inhaled into the oil tank.

[0003] The existing calculation method for respiration VOCs uses the emission factor method. Without considering the reverse leakage of the oil and gas processing device and the vacuum pump, the emission factor of VOCs in the respiration process is 120 mg / L. (0.164kg / t), but in fact, most of the gas stations operating on the market use fixed-frequency pumps for oil and gas recovery, and there is a problem of reverse leakage of fixed-frequency pumps, so the emission factor is underestimated in the actual operation of gas stations.

[0004] The existing technology tends to ignore the increase in VOCs emission factors and emissions in the breathing process caused by the reverse leakage of the fixed-frequency pump, resulting in a large deviation between the actual estimated VOCs emissions from major VOCs emission sources such as gas stations and the actual emissions, affecting precise pollution control and emission accounting. Summary of the invention

[0005] The purpose of the present invention is to provide a method for correcting VOCs emissions during the breathing process of a gas station based on an oil and gas recovery vacuum pump type, aiming to solve the technical problems existing in the prior art identified in the background technology.

[0006] The present invention is implemented as follows: a method for correcting VOCs emissions during the breathing process of a gas station based on an oil and gas recovery vacuum pump type, the method comprising: According to the ideal gas state equation, calculate the internal pressure of the oil tank; Calculate the pressure increment inside the tank caused by excess oil and gas when the gas-liquid ratio is set to 1.1; The air leakage generated by the unit refueling volume is measured through the flow meters at the outlet and inlet ends of the vacuum pump and the refueling volume data, and the air pressure increment caused by the reverse leakage of the vacuum pump is calculated; The VOCs emission factor is corrected by the ratio of the pressure increments under normal gas-liquid ratio conditions, when the vacuum pump has reverse leakage and when there is no reverse leakage; According to the usage ratio of fixed frequency pumps, the leakage ratio and the installation ratio of tertiary oil and gas recovery devices, the corrected VOCs emissions of gas stations are calculated; By measuring the single emission of VOCs at the P / V valve and monitoring the opening and closing frequency of the P / V valve.

[0007] The beneficial effects of the present invention are: The present invention makes up for the shortcomings of existing methods in calculating VOCs emissions at gas stations, corrects the emission factor of VOCs in the breathing process, and thus makes the estimation of VOCs emissions at gas stations closer to the actual emissions. The data is more accurate and can better guide the implementation of VOCs pollution prevention and control policies at gas stations. DETAILED DESCRIPTION

[0008] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0009] A method for correcting VOCs emissions during the breathing process of a gas station based on an oil and gas recovery vacuum pump type is used to correct the VOCs emissions during the breathing process of a gas station, specifically: 1. Correction of the emission factor for the respiratory process:

[0010] When the normal gas-liquid ratio is 1, the oil tank outputs 1 volume of gasoline and recovers the same volume of oil and gas, and the internal temperature of the buried oil tank is generally fixed or changes very little (can be regarded as a constant temperature state), so the pressure in the buried oil tank can be considered to be in dynamic equilibrium. According to the ideal gas state equation, under constant temperature and constant volume conditions, the internal pressure of the oil tank has the following formula: ; If the gas-liquid ratio of a gas station is calculated as 1.1 on average, 1.1L of oil and gas will be recovered for every 1L of oil added. The extra 0.1L of oil and gas recovered will enter the underground oil tank, which will increase the pressure inside the tank. The volume of oil and gas is 0.1 times the amount of oil added. The formula for calculating the pressure generated by oil and gas inside the tank is as follows: ; Similarly, due to the reverse leakage of the vacuum pump, xL of air will enter the buried oil tank for every 1L of oil added. The pressure generated by the air inside the oil tank is calculated as follows: ; in, Indicates the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump; Therefore, the ratio of the pressure increment under normal gas-liquid ratio conditions, when the vacuum pump has reverse leakage and when there is no reverse leakage, is calculated as follows: ; In the formula, Indicates gas pressure, unit is pa; It indicates the increased gas pressure inside the oil tank caused by excessive oil and gas recovery during normal oil and gas recovery, in Pa; It indicates the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump, in Pa; Indicates the amount of gas molecules; Indicates the internal temperature of the oil tank, in K; It indicates the volume of non-liquid space above the oil tank, in L; represents the density of oil and gas vapor, taking 4.14 g·L -1 ; The molar mass of oil and gas is 68 g·L -1 ; Indicates the volume of recovered oil and gas, in L; Indicates the density of air, take 1.29g·L -1 , Indicates the molecular weight of air, taking 29 g·L -1 ; It indicates the volume of air inputted in reverse by the vacuum pump, in L; It is the amount of fuel added, in L.

[0011] for , calculated by the following method: Install a gas flow meter at the outlet end of the vacuum pump, lift the gun without adding oil, and hang up the gun after 1 minute.

[0012] Record the flow meter reading changes of the oil and gas recovery online monitoring connected to the flow meter and the refueling gun, and record the refueling amount: ; in It is the amount of air sucked in by the vacuum pump for every 1L of gasoline added, dimensionless; It is the reading of the gas flow meter at the outlet of the vacuum pump, in L; It is the flow meter reading of the oil and gas recovery online monitoring connected to the refueling gun, the unit is L, The refueling amount, in L.

[0013] Since the opening and closing of the P / V valve is completely determined by the internal pressure of the oil tank, and the opening and closing times of the P / V are proportional to the VOCs emission coefficient, therefore: ; in, is the corrected VOCs emission factor, For the emission factor before correction, take 0.164kg / t.

[0014] 2. Correction of VOCs emissions from gas stations: The VOCs emission increases due to reverse leakage of the vacuum pump, and the increase is calculated using the following formula: ; In the formula, Indicates the amount of VOCs emitted during the breathing process, in t; It represents the annual sales volume of gasoline at the gas station, in L; It indicates the proportion of gas stations using fixed frequency pumps. If variable frequency pumps are used, it is considered that there is no additional emission and the value is 0; Indicates the proportion of reverse leakage in fixed frequency pumps. Indicates the installed proportion of oil and gas processing equipment; Represents the corrected VOCs emission factor, in kg / t.

[0015] The emission amount can also be determined by actually measuring the emission frequency, emission concentration and flow rate at the P / V valve. This method requires the installation of a valve opening and closing recorder and monitoring equipment for monitoring the oil and gas concentration and flow rate at the P / V valve outlet.

[0016] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0017] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

[0018] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for correcting VOCs emissions during the breathing process of a gas station based on an oil and gas recovery vacuum pump type, characterized in that: The method comprises: According to the ideal gas state equation, calculate the internal pressure of the oil tank : ； in, Indicates pressure, the unit is Pa; Indicates the amount of gas molecules, the unit is mol; Indicates the internal temperature of the oil tank, the unit is K; Indicates the volume of the non-liquid space above the tank, in m 3 , Indicates the density of the inhaled gas in g / L; Indicates the volume of the inhaled gas, in L; It represents the molar mass of the inhaled gas in g / mol; is a constant with the unit of J / (mol.K); Calculate the increase in oil and gas pressure in the tank caused by excessive oil and gas inhalation when the gas-liquid ratio is set to 1.1: ； in, It indicates the increased gas pressure inside the oil tank caused by recovering 0.1L of additional oil and gas in the secondary oil and gas recovery process, in Pa; Indicates the density of oil and gas vapor in g / L; It represents the molar mass of oil and gas in g / mol; Indicates the volume of recovered oil and gas, in L; is the amount of fuel added, in L; Indicates the internal temperature of the oil tank, the unit is K; Indicates the volume of the non-liquid space above the tank, in m 3 ; is a constant with the unit of J / (mol.K); Measure the air leakage corresponding to the unit refueling amount through the vacuum pump outlet and the oil and gas recovery flow meter (inlet end) , calculate the pressure increase in the oil tank caused by the entry of air during the reverse leakage process: ； in, Indicates the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump, in units of ; Indicates air density, unit is g / L; Indicates the volume of air, in L; It represents the molar mass of air in g / mol; Indicates the reverse suction volume of air per unit refueling volume, in L; Indicates the internal temperature of the oil tank, the unit is K; Indicates the volume of the non-liquid space above the tank, in m 3 ; is a constant with the unit of J / (mol.K); Corrected VOCs emission factors: ； in, is the corrected VOCs emission factor, is the emission factor before correction; According to the usage ratio of fixed frequency pumps, the leakage ratio and the installation ratio of tertiary oil and gas recovery devices, the corrected VOCs emissions of gas stations are calculated; By measuring the single emission of VOCs at the P / V valve and monitoring the opening and closing frequency of the P / V valve.

2. The method according to claim 1, characterized in that The method for measuring the reverse leakage of the vacuum pump air is as follows: Install a gas flow meter at the outlet of the vacuum pump, and hang the gun after one minute without refueling. Record the changes in the flow meter readings of the oil and gas recovery online monitoring connected to the refueling gun, and record the refueling amount at the same time: ； in It is the amount of air sucked in by the vacuum pump for every 1L of gasoline added, dimensionless; It is the reading of the gas flow meter at the outlet of the vacuum pump, in L; It is the flow meter reading of the oil and gas recovery online monitoring connected to the refueling gun, the unit is L, The refueling amount, in L.

3. The method according to claim 1, characterized in that In the emission factor correction: Oil and gas vapor density: =4.14 g / L; Oil and gas molar mass: =68 g / mol; Air Density: =1.29 g / L; Molar mass of air: =29 g / mol.

4. The method according to claim 1, characterized in that: The VOCs emission correction formula is: ； In the formula, Indicates the amount of VOCs emitted during the breathing process, in t; represents the annual gasoline sales volume of the gas station, in t; It indicates the proportion of gas stations using fixed frequency pumps. If variable frequency pumps are used, it is considered that there is no additional emission and the value is 0. Indicates the proportion of reverse leakage in fixed frequency pumps. Indicates the installation ratio of oil and gas processing equipment, Represents the corrected VOCs emission factor, in kg / t.

5. The method according to claim 1, characterized in that: It also includes installing opening and closing recorders, VOCs concentration and flow monitoring equipment at the P / V valve discharge port, and verifying the emission volume by measuring the emission frequency and single VOCs emission volume.

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