Accurate accounting method for emission of VOCs in petrochemical circulating water

Abstract

The invention discloses an accurate accounting method for VOCs emission of petrochemical circulating water, and belongs to the field of VOCs emission accounting, sampling is carried out on a circulating water inlet and a circulating water outlet of a heat exchanger, the sum of a liquid sample and a flash vapor sample is determined as a total sample, and quantitative analysis is carried out by means of the total hydrocarbon concentration in the flash vapor sample. According to the method, the concentration of the circulating water VOCs is converted into the concentration of the circulating water VOCs, the concentration of the circulating water VOCs is added with the content of the organic carbon in the liquid sample, the total concentration of the VOCs in the sample is obtained, the accuracy of VOCs concentration data is guaranteed, and then the VOCs sample concentration CVOCs inlet at the water inlet and the VOCs sample concentration CVOCs outlet at the water outlet are calculated respectively. Finally, the weighted average value of the circulating water VOCs emission amount of all the heat exchanger circulating water devices is obtained, the total circulating water VOCs annual emission amount of all the heat exchanger circulating water devices is calculated, the accuracy of accounting data is guaranteed, and operability is high.

Description

Technical Field

[0001] The present invention relates to the field of VOCs emission accounting, and particularly to a precise accounting method for VOCs emissions from petrochemical circulating water. Background Art

[0002] Volatile organic compounds (VOCs) are important precursors for the formation of ozone and secondary organic aerosols, and are one of the key targets for current air pollution control. Due to problems such as heat exchanger leakage in petrochemical circulating water systems, abnormal VOCs emissions occur. The current accounting of VOCs emissions in circulating water in China mostly uses the VOCs emission coefficient of 7.19×10 -7 t·m -3 in the "Guidelines for the Investigation of VOCs Pollution Sources in the Petrochemical Industry" for circulating water cooling towers, ignoring the operating status of enterprises, equipment management levels, and flow differences, resulting in relatively large errors in emission accounting.

[0003] Due to the current single emission coefficient, it cannot well reflect the differences in the operating status of enterprise equipment, leakage conditions, and environmental management levels. Once the emissions are overestimated or underestimated, it will affect the evaluation of enterprise emission compliance and management work such as environmental protection taxes and over-standard determination. In addition, due to the long-term lack of actual measurement basis, dynamic correction cannot be carried out in combination with on-site monitoring data.

[0004] In view of the above problems, the present invention designs and manufactures a precise accounting method for VOCs emissions from petrochemical circulating water to overcome the above defects. Summary of the Invention

[0005] For the problems existing in the prior art, a precise accounting method for VOCs emissions from petrochemical circulating water provided by the present invention not only ensures the accuracy of accounting data, but also has strong operability.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A precise accounting method for VOCs emissions from petrochemical circulating water, the steps of which are as follows:

[0007] S1. Perform closed sampling at both the inlet and outlet of the heat exchanger circulating water.

[0008] S2. Calculate the concentration of the VOCs sample at the inlet and the concentration of the VOCs sample at the outlet respectively, and the sample is the sum of the liquid sample and the flash vapor sample;

[0009] S3. Use a TOC analyzer to measure the total organic carbon TOC of the liquid sample;

[0010] S4. Perform quantitative analysis on the total hydrocarbon concentration in the flash vapor sample using GC-FID;

[0011] S5. The total hydrocarbon concentration in the flash gas sample is converted to the VOCs concentration in the liquid sample;

[0012]

[0013] Where: C 折 ——Converted VOCs concentration in circulating water gas sample, mg·L -1 ;

[0014] C h ——Total hydrocarbon concentration in flash gas sample, mg·L -1 ;

[0015] V——Gas volume of flash gas phase in the sample, mL;

[0016] m——mass of water in the sample, g;

[0017] S6. Obtain the total VOCs concentration of the sample;

[0018] C VOCs =C 折 +TOC

[0019] Where: C VOCs ——Total VOCs concentration in the sample, mg·L -1 ;

[0020] TOC——Total organic carbon content in liquid samples, mg·L -1 ;

[0021] S7. Calculate the VOCs sample concentration at the inlet and outlet respectively And the VOCs sample concentration at the outlet

[0022] S8. Obtain the weighted average of circulating water VOCs emissions of all heat exchanger circulating water devices;

[0023]

[0024] Where:Flow 循环水 ——Weighted average concentration of VOCs emissions from circulating water, mg·L -1 ;

[0025] ——VOCs sample concentration at the outlet of the circulating water device of a heat exchanger at location i, mg·L -1 ;

[0026] ——VOCs sample concentration at the water inlet of the circulating water device of a heat exchanger at location i, mg·L -1 ;

[0027] —— Proportion of the circulating water flow rate of the heat exchanger circulating water device at location i in the total circulating water flow rate involved in the accounting, %;

[0028] S9. Calculate the annual emission of VOCs in the circulating water of the heat exchanger circulating water device at location i;

[0029] E 装置.i = Flow 循环水 ×Q×t×10 -6

[0030] In the formula: E 装置，i —— Annual emission of VOCs in the circulating water of the heat exchanger circulating water device at the i-th location, t·a -1 ;

[0031] Flow 循环水 —— Weighted average concentration of VOCs emissions in circulating water, mg·L -1 ;

[0032] Q—— Circulating water flow rate of the heat exchanger circulating water device at the i-th location, m3·h -1 ;

[0033] t—— Annual operating time of the device, h;

[0034] S10. Calculate the total annual emission of VOCs in the circulating water of all heat exchanger circulating water devices;

[0035]

[0036] In the formula: E 总 —— Total annual emission of VOCs from all heat exchanger circulating water devices in the enterprise, t·a -1 ;

[0037] E 装置，i —— Annual emission of VOCs in the circulating water of the heat exchanger circulating water device at the i-th location, t·a -1 .

[0038] Preferably, before sampling, confirm whether the heat exchanger circulating water device is in normal or abnormal working conditions, and obtain the total annual emission of VOCs in the circulating water under normal working conditions and the total annual emission of VOCs in the circulating water under abnormal working conditions respectively.

[0039] Preferably, the acquisition of the total hydrocarbon concentration C h in the flash vapor gaseous sample in S5 refers to HJ38—2017 "Determination of Total Hydrocarbons, Methane and Non-Methane Total Hydrocarbons in Exhaust Gas from Stationary Pollution Sources - Gas Chromatography Method", as shown in the following formula;

[0040]

[0041] In the formula: C h—— Total hydrocarbon concentration of the measured flash vapor sample, mg·L -1 ;

[0042] A h —— Total hydrocarbon peak area of the measured flash vapor sample, mV·s;

[0043] A da —— Peak area when injecting the hydrocarbon-free flash vapor sample, mV·s;

[0044] k h —— Slope of the total hydrocarbon calibration curve.

[0045] Preferably, sampling is carried out using a sampling bag, and the sampling bag is made of PTFE material.

[0046] Preferably, when sampling the VOCs samples at the total inlet and total outlet of all heat exchanger circulating water devices;

[0047] The annual VOCs emission of the device is given by the following formula

[0048]

[0049] In the formula, E 总 —— Annual VOCs emission of the device, t·a -1 ;

[0050] Q 循环 —— Circulating water flow rate, m 3 ·h -1 ;

[0051] —— VOCs concentration at the total outlet, mg·L -1 ;

[0052] —— VOCs concentration at the total inlet, mg·L -1 ;

[0053] t—— Annual operating time of the device, h·a-1, default is 8760 h·a -1 .

[0054] Preferably, set Alarm threshold, ΔC VOCs If it exceeds the alarm threshold, screen for suspected leakage devices.

[0055] Preferably, the GC-FID uses a GC9790Ⅱ type gas chromatograph.

[0056] Preferably, the TOC analyzer uses a German Jena N / C3100 type.

[0057] The advantages of this invention are as follows:

[0058] 1. The present invention can truly reflect the operating status and leakage status of enterprise equipment through the above method. By accurately calculating the VOCs emissions, the flexibility of environmental protection management can be improved more precisely.

[0059] 2. The sampling of the present invention adopts closed sampling, retains the flash vapor state sample, and then conducts quantitative analysis by means of the total hydrocarbon concentration in the flash vapor state sample. After converting it into the VOCs concentration of the circulating water and adding it to the content of organic carbon in the liquid sample, the total VOCs concentration in the sample is obtained, ensuring the accuracy of the VOCs concentration data. Moreover, the VOCs concentration in the flash vapor state is obtained through a new conversion method.

[0060] 3. The present invention divides the working conditions into two cases, and can respectively obtain the annual emissions of VOCs in the circulating water, which can more accurately reflect the impact of the actual operating status on VOCs emissions. Specific Embodiment

[0061] For the convenience of those skilled in the art to understand, the present invention is further described below.

[0062] A method for accurately calculating the VOCs emissions from petrochemical circulating water is as follows:

[0063] S1. Conduct closed sampling at both the inlet and outlet of the heat exchanger circulating water. The sampling uses a sampling bag made of PTFE material. The sampling bag can clearly observe the liquid phase flow state and color, and is resistant to temperature, pressure, corrosion, and organic solvents. This material has low friction and strong anti-adsorption ability, and is not easy to adsorb VOCs in the water sample. A 3L sampling bag is preferred;

[0064] S2. Calculate the VOCs sample concentration at the inlet and the VOCs sample concentration at the outlet respectively. The sample is the sum of the liquid sample and the flash vapor state sample;

[0065] S3. Use a TOC analyzer to measure the total organic carbon TOC of the liquid sample. The TOC analyzer uses the German Jena N / C3100 model;

[0066] S4. Use GC-FID to conduct quantitative analysis on the total hydrocarbon concentration in the flash vapor state sample. The GC-FID uses a GC9790Ⅱ type gas chromatograph. Specifically, it needs to be filled with hydrocarbon-free air and analyze the total hydrocarbon concentration;

[0067] S5. Convert the total hydrocarbon concentration in the flash vapor state sample into the VOCs concentration in the liquid sample;

[0068]

[0069] In the formula: C 折 —— The VOCs concentration in the converted circulating water gas sample, mg·L -1 ;

[0070] C h —— Total hydrocarbon concentration in the flash vapor sample, mg·L -1 ;

[0071] V —— Gas volume of the flash vapor phase in the sample, mL;

[0072] m —— Mass of the water sample in the sample, g;

[0073] Among them, 12 is the molar mass of carbon, g / mol; 16 is the molar mass of methane, g / mol.

[0074] Total hydrocarbon concentration C in the flash vapor sample h is obtained with reference to HJ38—2017 "Determination of Total Hydrocarbons, Methane and Non-Methane Total Hydrocarbons in Exhaust Gas from Stationary Pollution Sources - Gas Chromatography Method", as shown in the following formula;

[0075]

[0076] In the formula: C h —— Total hydrocarbon concentration of the measured flash vapor sample, mg·L -1 ;

[0077] A h —— Total hydrocarbon peak area of the measured flash vapor sample, mV·s;

[0078] A da —— Peak area when injecting the hydrocarbon-free flash vapor sample, mV·s;

[0079] k h —— Slope of the total hydrocarbon calibration curve.

[0080] S6. Obtain the total VOCs concentration of the sample;

[0081] C VOCs = C 折 + TOC

[0082] In the formula: C VOCs —— Total VOCs concentration in the sample, mg·L -1 ;

[0083] TOC —— Total content of organic carbon in the liquid sample, mg·L -1 ;

[0084] S7. Calculate the concentrations of the VOCs samples at the inlet and outlet respectively and the concentrations of the VOCs samples at the outlet Preferably set alarm threshold, ΔC VOCs If it exceeds the alarm threshold, screen for suspected leakage devices;

[0085] S8. Obtain the weighted average of the VOC emissions of the circulating water in all heat exchanger circulating water devices, which is the emission factor of the circulating water device;

[0086]

[0087] Where: Flow 循环水 —— The weighted average concentration of VOC emissions in the circulating water, mg·L -1 ;

[0088] —— The VOC sample concentration at the outlet of the circulating water device of a heat exchanger at a certain i, mg·L -1 ;

[0089] —— The VOC sample concentration at the inlet of the circulating water device of a heat exchanger at a certain i, mg·L -1 ;

[0090] —— The proportion of the circulating water flow of the circulating water device of the heat exchanger at this i in the total circulating water flow participating in the accounting, %;

[0091] S9. Calculate the annual VOC emissions of the circulating water in the circulating water device of this i-th heat exchanger;

[0092] E 装置.i = Flow 循环水 ×Q×t×10 -6

[0093] Where: E 装置，i —— The annual VOC emissions of the circulating water in the circulating water device of the i-th heat exchanger, t·a -1 ;

[0094] Flow 循环水 —— The weighted average concentration of VOC emissions in the circulating water, mg·L -1 ;

[0095] Q—— The circulating water flow of the i-th heat exchanger, m3·h -1 ;

[0096] t—— The annual operating time of the device, h;

[0097] S10. Calculate the total annual VOC emissions of the circulating water in all heat exchanger circulating water devices;

[0098]

[0099] Where: E 总 —— The total annual VOC emissions of all heat exchanger circulating water devices in the enterprise, t·a -1 ;

[0100] E 装置，i —— Annual emissions of circulating water VOCs from the circulating water device at the i-th location, t·a -1 。

[0101] Through the above method, the present invention can truly reflect the operating status and leakage status of enterprise equipment. By accurately calculating the VOCs emissions, the environmental protection management flexibility can be improved more precisely.

[0102] Before sampling, it is preferred to confirm whether the heat exchanger circulating water device is in normal or abnormal working conditions, and respectively obtain the annual total emissions of circulating water VOCs in normal working conditions and abnormal working conditions, so as to more accurately reflect the impact of the actual operating status on VOCs emissions.

[0103] Through measuring the actual situations of two enterprises, the present invention obtains the VOCs emission coefficients of the circulating water cooling device. The VOCs emission coefficient in normal working conditions is 6.45×10 -9 t·m -3 and the VOCs emission coefficient in abnormal working conditions is 3.07×10 -7 t·m -3 . The annual total volatile organic compounds (VOCs) emissions of the collected normal working condition devices and abnormal working condition devices are calculated respectively. In addition, according to the circulating water coefficient 7.19×10 -7 t·m -3 provided in the existing domestic reference material "Guide for the Investigation of VOCs Pollution Sources in the Petrochemical Industry" (hereinafter referred to as the "Guide") and the circulating water coefficient 1.24×10 -6 t·m -3 in "The Second National Pollution Source Census Emission Coefficient Manual - General Source Items of VOCs" (hereinafter referred to as the "Second Pollution Census"), the annual total VOCs emissions of the collected devices under normal and abnormal working conditions are calculated respectively. Table 1 summarizes the comparison results of VOCs emissions obtained based on different accounting coefficient methods.

[0104] Table 1 Comparison of VOCs emissions with different accounting coefficients

[0105]

[0106] According to the data in Table 1, there are significant differences in the VOCs emissions calculated by different accounting coefficients. The emission coefficient in normal working conditions is 6.45×10 -9 t·m -3 . For the corresponding normal working condition devices, the annual emissions of Factory A are 1.45t and those of Factory B are 0.455t, with a total of 1.90t; the emission coefficient in abnormal working conditions is 3.07×10 -7 t·m-3 For the corresponding non-normal operating conditions, the annual emissions of Plant A are 9.41 t and those of Plant B are 7.11 t, with a total of 16.52 t.

[0107] In contrast, the VOCs emission factor provided by the working guidelines is 7.19×10 -7 t·m -3 , and the corresponding annual emissions for the normal operating conditions of the plant are 212.28 t, and 38.69 t for the non-normal operating conditions; the VOCs emission factor for the secondary pollution census is 1.24×10 -6 t·m -3 , and the corresponding annual emissions for the normal operating conditions of the plant are 366.11 t, and 66.72 t for the non-normal operating conditions. However, both the guidelines and the secondary pollution census use fixed emission factors and do not distinguish between normal and non-normal operating conditions, so they cannot accurately reflect the impact of the actual operating status on VOCs emissions. Based on on-site monitoring data, this study calculated the emission factors under normal and non-normal operating conditions and carried out accounting in combination with the corresponding flow rates. Since the VOCs emissions in the circulating water under normal operating conditions are usually low, and the fixed coefficients in the guidelines and the secondary pollution census do not reflect this difference, directly applying these coefficients may lead to an overestimation of emissions.

[0108] The annual emissions of the plant corresponding to the normal operating condition emission factor calculated in this study are only 1.90 t, far lower than the 212.28 t calculated by the working guideline factor and the 366.11 t calculated by the census factor, 111 times and 192 times lower respectively; similarly, the annual emissions of the non-normal operating condition plant calculated by the non-normal operating condition emission factor are 16.52 t, also lower than the 38.69 t calculated by the working guideline factor and the 66.72 t calculated by the census factor, 2.3 times and 4 times lower respectively. This difference indicates that directly applying the fixed emission factors in the guidelines or the secondary pollution census may lead to an overestimation of emissions, while the emission factors calculated in combination with on-site monitoring data can better reflect the actual situation of the enterprise and help improve the accuracy of emission accounting.

[0109] In addition, when sampling the VOCs samples at the total inlet and the total outlet of all heat exchanger circulating water devices in the present invention;

[0110] The annual VOCs emissions of the device are shown in the following formula:

[0111]

[0112] In the formula, E 总 —— Annual VOCs emissions of the device, t·a -1 ;

[0113] Q 循环 —— Circulating water flow rate, m 3 ·h-1 ;

[0114] —— Total VOCs concentration at the total water outlet, mg·L -1 ;

[0115] —— Total VOCs concentration at the total water inlet, mg·L -1 ;

[0116] t —— Annual operating time of the device, h·a-1, default is 8760 h·a -1 .

[0117] It should be understood that the use of these embodiments is only for illustrating the present invention rather than intending to limit the protection scope of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art can make various changes, modifications and / or variations to the present invention, and all these equivalent forms also fall within the protection scope defined by the appended claims of this application.

Claims

1. A precise accounting method for VOCs emissions in petrochemical circulating water, characterized in that, The steps are as follows: S1. Conduct closed sampling at both the inlet and outlet of the heat exchanger circulating water. S2. Calculate the VOCs sample concentration at the inlet and the VOCs sample concentration at the outlet respectively. The sample is the sum of the liquid sample and the flash vapor sample. S3. Use a TOC analyzer to measure the total organic carbon TOC of the liquid sample. S4. Use GC-FID to quantitatively analyze the total hydrocarbon concentration in the flash vapor sample. S5. Convert the total hydrocarbon concentration in the flash vapor sample to the VOCs concentration in the liquid sample. Where: C 折 —— Concentration of VOCs in the converted circulating water vapor sample, mg·L -1 ; C h —— Total hydrocarbon concentration in the flash vaporized gaseous sample, mg·L -1 ; V—the gas volume of the flash vapor phase in the sample, mL; m—the mass of the water sample in the sample, g; S6. Obtain the total VOCs concentration of the sample. C VOCs = C 折 + TOC Where: C VOCs —— Total VOCs concentration in the sample, mg·L -1 ; TOC - Total content of organic carbon in liquid sample, mg·L -1 ; S7. Calculate the concentrations C of the VOCs samples at the inlet and outlet respectively VOCs入口 and the concentrations C of the VOCs samples at the outlet VOCs出口 ; S8. Obtain the weighted average of the VOCs emissions of the circulating water of all heat exchanger circulating water devices. Where: Flow 循环水 —— Weighted average concentration of VOCs emissions in circulating water, mg·L -1 ; —— Concentration of VOCs sample at the outlet of the circulating water device of the heat exchanger at a certain point i, mg·L -1 ; —— The concentration of VOCs sample at the water inlet of the circulating water device at a certain point i, mg·L -1 ; —— Proportion of the circulating water flow rate of the heat exchanger circulating water device at the i-th location in the total circulating water flow rate involved in the calculation, %; S9. Calculate the annual VOCs emissions of the circulating water of the heat exchanger circulating water device at the i-th location. E 装置.i = Flow 循环水 ×Q×t×10 -6 where: E 装置，i —— Annual emissions of VOCs in the circulating water of the heat exchanger at the i-th location, t·a -1 ; Flow 循环水 —— Weighted average concentration of VOCs emissions in circulating water, mg·L -1 ; Q —— The circulating water flow rate of the i-th heat exchanger, m3·h -1 ; t—the annual operating time of the device, h; S10. Calculate the total annual VOCs emissions of the circulating water of all heat exchanger circulating water devices. Where: E 总 —— Total annual emissions of VOCs from the circulating water devices of all heat exchangers in the enterprise, t·a -1 ; E 装置，i —— Annual VOCs emissions of the circulating water in the i-th heat exchanger circulating water device, t·a -1 。 2. The precise accounting method for VOCs emissions from petrochemical circulating water according to claim 1, wherein Before sampling, confirm whether the heat exchanger circulating water device is in normal or abnormal conditions, and obtain the total annual VOCs emissions of the circulating water in normal conditions and the total annual VOCs emissions of the circulating water in abnormal conditions respectively.

3. A precise accounting method for VOCs emissions in petrochemical circulating water according to claim 1, characterized in that, Total hydrocarbon concentration C in the flash vapor gaseous sample in S5 h is obtained with reference to HJ 38—2017 Determination of Total Hydrocarbons, Methane and Non-Methane Total Hydrocarbons in Exhaust Gas from Stationary Pollution Sources - Gas Chromatography Method, as shown in the following formula; Where: C h —— Total hydrocarbon concentration of the measured flash vapor state sample, mg·L -1 ; A h —— Total hydrocarbon peak area of the measured flash vapor gaseous sample, mV·s; A da —— Peak area during injection of hydrocarbon-removed flash vapor gaseous sample, mV·s; k h —— Slope of the calibration curve for total hydrocarbons.

4. A precise accounting method for VOCs emissions in petrochemical circulating water according to claim 1, characterized in that, The sampling uses a sampling bag, and the sampling bag is made of PTFE material.

5. A precise accounting method for VOCs emissions in petrochemical circulating water according to claim 1, characterized in that, When sampling the total inlet VOCs sample and the total outlet VOCs sample of all heat exchanger circulating water devices; The annual VOCs emissions of the device are shown in the following formula: where E 总 —— annual VOCs emissions of the device, t·a -1 ; Q 循环 —— Recirculating water flow rate, m 3 ·h -1 ; —— Total VOCs concentration at the main outlet, mg·L -1 ; —— Total inlet VOCs concentration, mg·L -1 ; t — annual operating time of the device, h·a-1, default value is 8760 h·a -1 。 6. The accurate accounting method for VOCs emissions in petrochemical circulating water according to claim 1, wherein, Settings Alarm threshold, ΔC VOCs When the alarm threshold is exceeded, screen for suspected leakage devices.

7. A precise accounting method for VOCs emissions in petrochemical circulating water according to claim 1, characterized in that, GC-FID uses a GC9790Ⅱ type gas chromatograph.

8. A precise accounting method for VOCs emissions in petrochemical circulating water according to claim 1, characterized in that, The TOC analyzer uses a German Jena N / C3100 type.

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