A Method for Correcting VOCs Emission in the Breathing Process of Gas Stations Based on the Type of Oil and Gas Recovery Vacuum Pump

Abstract

The present invention is applicable to the field of petrochemical engineering, and provides a method for correcting the VOCs emissions during the breathing process of gas stations based on the type of oil and gas recovery vacuum pump. Specifically, based on the ideal gas state equation, the pressure increment in the oil tank during the secondary oil and gas recovery process due to excessive oil and gas recovery (gas-liquid ratio of 1.1) and reverse leakage of air by the vacuum pump is calculated, and the correction formula for the VOCs emission factor is derived. Secondly, combined with the usage ratio of fixed-frequency pumps, leakage ratio, installation ratio of the tertiary oil and gas recovery device, and annual gasoline sales volume of gas stations, an emissions correction model is established. By measuring the single emissions of VOCs at the P / V valve of gas stations and monitoring the opening and closing frequency of the P / V valve, the accuracy of emissions calculation is verified. The present invention solves the problem of ignoring the influence of reverse leakage of fixed-frequency pumps in the existing method, significantly improves the accuracy of VOCs emissions accounting for gas stations, and provides a reliable basis for precise pollution control and VOCs emission supervision of gas stations.

Description

Technical Field

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

[0002] During the refueling process of a gas station, the oil and gas are recovered through a secondary oil and gas recovery device. Existing fuel dispensers all have the function of oil and gas recovery, and can recover oil and gas in equal proportion or high proportion during refueling. There are two types of oil and gas recovery vacuum pumps for gas stations: fixed-frequency pumps and variable-frequency pumps. The design and start-stop mode of fixed-frequency pumps will accelerate the aging or wear of their seals, resulting in poor sealing of the vacuum pump. During operation, external air is likely to be reversely sucked in, and excessive air entering the oil tank causes an increase in the internal pressure of the oil tank and oil and gas emissions, resulting in environmental pollution and oil and gas loss. Using a variable-frequency pump will not cause air to be sucked into the oil tank.

[0003] The existing calculation method for VOCs during breathing uses the emission factor method. Under the condition of not considering the reverse leakage of the oil and gas treatment device and the vacuum pump, the emission coefficient of VOCs during the breathing process is 120 mg / L (0.164 kg / t), but in fact, most of the oil and gas recovery in gas stations on the market uses fixed-frequency pumps and there are problems with reverse leakage of fixed-frequency pumps. Therefore, the emission factor is underestimated during the actual operation of gas stations.

[0004] The existing technology easily ignores the increase in the VOCs emission factor and emission amount during the breathing process caused by the reverse leakage of fixed-frequency pumps, resulting in a large deviation between the estimated amount of VOCs emissions from this type of major VOCs emission source, gas stations, and the actual emissions, affecting precise pollution control and emissions accounting. Summary of the Invention

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

[0006] The present invention is implemented as follows. A method for correcting the VOCs emission amount during the breathing process of a gas station based on the type of oil and gas recovery vacuum pump, the method includes:

[0007] Calculate the internal pressure of the oil tank according to the ideal gas state equation;

[0008] Calculate the pressure increment in the oil tank caused by excessive oil and gas when the gas-liquid ratio is set to 1.1;

[0009] Measure the air leakage amount generated per unit refueling amount through the flow meters at the outlet and inlet ends of the vacuum pump and the refueling amount data, and calculate the air pressure increment caused by the reverse leakage of the vacuum pump;

[0010] The VOCs emission factor is corrected by the ratio of the pressure increments in two cases: reverse leakage of the vacuum pump under normal gas-liquid ratio conditions and no reverse leakage.

[0011] According to the usage ratio of fixed-frequency pumps, the leakage ratio, and the installation ratio of the three-stage oil and gas recovery device, the corrected VOCs emissions of gas stations are calculated.

[0012] By measuring the single emission amount of VOCs at the P / V valve and monitoring the opening and closing frequency of the P / V valve.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention makes up for the deficiencies of existing methods in calculating the VOCs emissions of gas stations, corrects the emission factor of VOCs in the breathing process, so that the estimated VOCs emissions of gas stations are closer to the actual emission situation, and the data is more accurate and can better guide the implementation of VOCs pollution prevention and control policies for gas stations. Specific embodiments

[0015] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to 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.

[0016] A method for correcting the VOCs emissions in the breathing process of gas stations based on the type of oil and gas recovery vacuum pump, which is used to correct the VOCs emissions in the breathing process of gas stations, specifically as follows:

[0017] 1. Correction of the emission factor in the breathing process:

[0018] When the normal gas-liquid ratio is 1, for every 1 volume of gasoline output from the oil tank and the same volume of oil and gas is recovered, and the internal temperature of the underground oil tank generally remains fixed or changes very little (can be regarded as a constant temperature state). Therefore, it can be considered that the pressure in the buried oil tank is in dynamic equilibrium. According to the ideal gas state equation, under the conditions of constant temperature and constant volume, the following formula exists for the pressure inside the oil tank:

[0019] ;

[0020] If the gas-liquid ratio of the gas station is calculated as an average of 1.1, for every 1 L of gasoline added, 1.1 L of oil and gas will be recovered. The additional 0.1 L of oil and gas entering the underground oil tank will cause the pressure inside the oil tank to increase. The volume of the oil and gas is 0.1 times the refueling volume. The formula for calculating the pressure generated by the oil and gas inside the oil tank is as follows:

[0021] ;

[0022] Similarly, due to the reverse leakage of the vacuum pump, for every 1 L of oil added, x L of air will enter the buried oil tank. The calculation formula for the pressure generated by the air inside the oil tank is as follows:

[0023] ;

[0024] Among them, represents the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump;

[0025] Therefore, the ratio of the pressure increments in the two cases of reverse leakage and no reverse leakage of the vacuum pump under normal gas-liquid ratio conditions is calculated as follows:

[0026] ;

[0027] In the formula, represents the gas pressure, with the unit of Pa; represents the increased gas pressure inside the oil tank caused by excessive oil and gas recovery during normal oil and gas recovery, with the unit of Pa; represents the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump, with the unit of Pa; represents the amount of substance of gas molecules; represents the temperature inside the oil tank, with the unit of K; represents the volume of the non-liquid space above the oil tank, with the unit of L; represents the density of oil and gas vapor, taking 4.14 g·L -1 ; represents the molar mass of oil and gas as 68 g·L -1 ; represents the volume of the recovered oil and gas, with the unit of L; represents the density of air, taking 1.29 g·L -1 , represents the molecular weight of air, taking 29 g·L -1 ; represents the volume of air input reversely through the vacuum pump, with the unit of L; is the refueling volume, with the unit of L.

[0028] For , it is measured by the following method:

[0029] Install a gas flowmeter at the outlet end of the vacuum pump. Do not refuel with the nozzle, and hang up the nozzle after 1 minute.

[0030] Record the change in the reading of the flowmeter connected to this flowmeter and the on-line monitoring flowmeter of the oil and gas recovery of this refueling nozzle, and record the refueling volume at the same time:

[0031] ;

[0032] Among them is the amount of air inhaled by the vacuum pump for every 1 L of gasoline added, dimensionless; is the reading of the gas flow meter at the gas outlet end of the vacuum pump, with the unit of L; is the reading of the flow meter for on-line monitoring of oil and gas recovery connected to the fuel nozzle, with the unit of L, is the refueling volume, with the unit of L.

[0033] Since the opening and closing of the P / V valve are completely determined by the internal pressure of the oil tank, and the number of opening and closing times of the P / V is proportional to the VOCs emission coefficient, therefore:

[0034] ;

[0035] Among them, is the corrected VOCs emission factor, is the emission factor before correction, taking 0.164 kg / t.

[0036] II. Correction of VOCs emissions from gas stations:

[0037] Due to the reverse leakage of the vacuum pump, the VOCs emissions increase, and the increased amount is calculated by the following formula:

[0038] ;

[0039] In the formula, represents the amount of VOCs emitted during the breathing process, with the unit of t; represents the annual gasoline sales volume of the gas station, with the unit of L; represents the proportion of gas stations using fixed-frequency pumps. If variable-frequency pumps are used, it is considered that there is no additional emission, taking 0; represents the proportion of reverse leakage of fixed-frequency pumps, represents the installation proportion of oil and gas treatment devices; represents the corrected VOCs emission factor, with the unit of kg / t.

[0040] The emissions can also be determined by actually measuring the emission frequency, emission concentration and flow rate at the P / V valve. This method requires installing 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.

[0041] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as these technical feature combinations do not conflict, they should all be considered as the scope described in this specification.

[0042] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several variations and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

[0043] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for correcting the VOCs emission amount during the breathing process of a gas station based on the type of oil and gas recovery vacuum pump, characterized in that, The method includes: Calculate the internal pressure of the oil tank according to the ideal gas state equation : ； Among them, represents the pressure, with the unit of Pa; represents the amount of substance of gas molecules, with the unit of mol; represents the internal temperature of the oil tank, with the unit of K; represents the volume of the non-liquid space above the oil tank, with the unit of m 3 , represents the density of the inhaled gas, with the unit of g / L; represents the volume of the inhaled gas, with the unit of L; represents the molar mass of the inhaled gas, with the unit of g / mol; is a constant, with the unit of J / (mol·K); Calculating the increment of the oil and gas pressure in the tank caused by excessive oil and gas inhalation when the gas-liquid ratio is set to 1.1: ； Among them, represents the increased gas pressure inside the oil tank caused by the additional 0.1 L of oil and gas recovered during the secondary oil and gas recovery process, with the unit of Pa; represents the density of oil and gas vapor, with the unit of g / L; represents the molar mass of oil and gas, with the unit of g / mol; represents the volume of the recovered oil and gas, with the unit of L; is the refueling volume, with the unit of L; represents the temperature inside the oil tank, with the unit of K; represents the volume of the non-liquid space above the oil tank, with the unit of m 3 ; is a constant, with the unit of J / (mol·K); Measure the air leakage volume corresponding to the unit refueling volume through the air outlet end of the vacuum pump and the oil and gas recovery flowmeter , and calculate the pressure increment in the oil tank caused by the entry of air during the reverse leakage process: ； Among them, represents the increased gas pressure inside the oil tank caused by the reverse leakage of air from the vacuum pump, with the unit of Pa; represents the air density, with the unit of g / L; represents the air volume, with the unit of L; represents the molar mass of air, with the unit of g / mol; represents the reverse inhalation volume of air per unit refueling volume, with the unit of L; represents the internal temperature of the oil tank, with the unit of K; represents the volume of the non-liquid space above the oil tank, with the unit of m 3 ; is a constant, with the unit of J / (mol·K); Correcting the VOCs emission factor: ； Among them, is the corrected VOCs emission factor, is the emission factor before correction; Calculating the corrected VOCs emissions of the gas station according to the usage ratio of fixed-frequency pumps, the leakage ratio, and the installation ratio of the three-stage oil and gas recovery device; Measuring the single VOCs emissions at the P / V valve through actual measurement and monitoring the opening and closing frequency of the P / V valve.

2. The method according to claim 1, characterized in that, The measurement method of the air reverse leakage amount of the vacuum pump is: Installing a gas flowmeter at the outlet end of the vacuum pump, hanging up the gun one minute after the gun is lifted without refueling, recording the change in the readings of this flowmeter and the flowmeter of the on-line oil and gas recovery connected to the refueling gun, and simultaneously recording the refueling volume: ； is the reading of the gas flow meter at the outlet end of the vacuum pump, with the unit of L; is the reading of the flow meter for on-line monitoring of oil and gas recovery connected to the fuel dispenser, with the unit of L, is the fuel filling volume, with the unit of L.

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

4. The method according to claim 1, wherein The correction formula for the VOCs emissions is: ； In the formula, represents the amount of VOCs emitted during the breathing process, with the unit of t; represents the annual gasoline sales volume of the gas station, with the unit of t; represents 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 0 is taken. represents the proportion of reverse leakage in the fixed-frequency pump; represents the installation proportion of the oil and gas treatment device; represents the corrected VOCs emission factor, with the unit of kg / t.

5. The method according to claim 1, wherein It also includes installing an opening and closing recorder, a VOCs concentration and flow monitoring device at the P / V valve discharge port, and verifying the emissions by actual measurement of the emission frequency and the single VOCs emissions.

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