Study on air pollutant emission inventory of port operation machinery in container terminal

. In this paper, a calculation method system of air pollutant emission inventory of port operation machinery in container terminal is established. Through the special investigation of port machinery manufacturers and engine manufacturers, the average load rate data of main port machinery engines in domestic container terminals are obtained. Taking a domestic container terminal as an example, the dynamic method and fuel consumption method are used to calculate the air pollutant emission inventory of port operation machinery, and the calculation results of the two methods are compared and analyzed. The results show that the calculation method system of air pollutant emission inventory of port operation machinery established in this paper is highly practical, and the calculation results obtained by the two methods are very close.


Introduction
Compiling emission inventory of port is an important basis for port air pollution control. At present, research methods for port operation machinery emission inventory mainly include dynamic method and fuel consumption method. The research on the emission inventory of port operation machinery in China started relatively late, and the foreign basic emission factor data are often used in the localization application of the model, which leads to great uncertainty. The activity level data of dynamic method include the number of port operation machinery, rated power, average load rate of engine, working time and emission standard. According to the investigation of typical container terminals, the above data can be obtained from port statistical data except for the average load rate of engines. The activity level data of fuel consumption method include the quantity, rated power, emission standard of all kinds of port operation machinery and the fuel consumption of each machinery. The above data can be obtained through port statistical data. From the above analysis, it can be seen that the average load rate of the engine is the key parameter in the calculation of port operation machinery emission inventory by dynamic method.

Research status of emission inventory of port operation machinery
Dynamic method and fuel consumption method have been applied in China to compile emission inventory of port operation machinery. Dynamic method is based on the power and operation time of port machinery, combined with different machinery emission factors to calculate the emission inventory of air pollutants. Peng Yiqiang et al. from Hohai University corrected the emission factor by investigating and analyzing the holding quantity, activity level and equipment parameters of the operating machinery in container terminals, and established a "bottom-up" dynamic method based on the activity level of the mechanical engine in container port to establish a calculation model of the atmospheric pollutant emission inventory of container port [1] .Taking Nanjing Longtan Container Port (NPLC) as a case, the emission inventory is constructed. The results show that the total emissions of NPLC port operation machinery in 2014 are 4.25 tons of PM10, 3.91 tons of PM2.5, 82.98 tons of NOx, 1.06 tons of SO2, 23.84 tons of CO and 16.39 tons of HC. NOx is high-value emission pollutant; The port machinery is the largest source of PM and HC in comparison with other port area emitters. Compared with the 2013 NPLC-based study on fuel consumption, the activity-based emissions were lower.
The fuel consumption method is a method to calculate the emission inventory of air pollutants based on the survey data of fuel consumption of port operation machinery combined with different machinery emission factors. Based on the existing statistics of port machinery in China, the activity level data of the fuel consumption method is easier to obtain than that of the dynamic method. Therefore, this method is mostly used in the emission inventory research of the existing port machinery in China. On the basis of comprehensive analysis of domestic and foreign literature, Tan Hua et al. from Shanghai Environmental Monitoring Center combined with the investigation results of various types of port machinery in Shanghai port, corrected the calculation method of pollutant emission of port machinery, and obtained the statistical fuel volume of Shanghai port by using the method of field investigation, and established the air pollutants of Shanghai port operation machinery in 2010 Emission inventory [2] .The results show that the total emission of port machinery from the 106 enterprises surveyed is 2900 tons of NOx, 400 tons of VOCs, 800 tons of CO, 130 tons of PM2.5 and 5.8 tons of SO2. NOx is the most characteristic pollutant discharged by the port machinery, and SO2 is the least. Based on the on-site investigation of Nanjing Longtan container port, Jia Xu et al. analyzed the operation mode of container port and estimated the discharge of major air pollutants in the port area in 2013 by using the fuel consumption of port machinery obtained from the investigation [3] .The calculation results show that the total emission of various pollutants is 501.73 tons, among which NOx, CO and SOx are the main air pollutants, and their emissions are 229.9 tons, 190.5 tons and 17.4 tons respectively. Container loading and unloading bridge is the main source of air pollutants in the port area, accounting for 84% of the total emissions. Fan Xiaoli, from South China University of Technology, based on the field survey of pearl River Delta ports, proposed a refined estimation method of port machinery emission inventory based on unit operation mode and machine type, and finally established the Pearl River Delta port machinery emission inventory in 2014 by using this method [4] .The results show that the SO2, NOx, CO, PM10, PM2.5 and HC emitted by port machinery in the Pearl River Delta in 2014 are 633.6 tons, 4610.6 tons, 3391.2 tons, 226.9 tons, 216.0 tons and 728.8 tons respectively. Among them, container terminal is the most important port machinery use place, container special machinery and horizontal transport machinery is the main contribution type of machinery.
Based on the above literature research, it is found that both the dynamic method and the fuel consumption method have great differences in the selection and modification of emission factors and the selection of key factors such as load factors. The calculation process is quite complex and there is no unified standard. The results of the two methods are difficult to be compared directly, and the uncertainty is high. With the refinement of air pollution prevention and control management in China in recent years, the compilation of emission source inventory as a key basic work, it is urgent to deepen the research on the refinement of estimation methods.

Classification of port operation machinery
Referring to the second, third and fourth classification in The Technical Guide for The Compilation of Emission Inventory of Air Pollutants from Non-road Mobile Sources (Trial) [5] , the three-level classification of port operation machinery in container terminals is carried out. The first level classification is divided into quayside container crane, rail type container gantry crane, rubber-tyred container gantry crane, container front lifting crane, empty container stacker, container straddle carrier, container transfer gantry crane, container forklift, etc. the second level classification is divided into ＜ 37KW, 37-75kw, 75-130kw, ≥ 130kW according to the rated power; the third level is divided into three categories According to the emission standards, the emission standards can be divided into five stages, namely, the first stage, the second stage, the third stage and the fourth stage.  [6] .

Dynamic method
The formula for calculating the air pollutant emission inventory of port operation machinery by dynamic method is shown in the following formula.
where: -total discharge amount of pollutant i of port operation machinery, T; -the quantity of some port operation machinery, vehicle; -rated power of certain port operation machinery, kW; -the average load rate of a certain port operation machinery engine, dimensionless; -emission factor of certain port operation machinery, g/kW h; -working time of certain port operation machinery, h; -pollutant types, including CO, HC, NOx and PM; -power section of engine of some port operation machinery; -emission standard of certain port operation machinery.

Fuel consumption method
The formula for calculating air pollutant emission inventory of port operation machinery by fuel consumption method is shown in the following formula.
Where: -total discharge amount of pollutant i of port operation machinery, T; -the quantity of some port operation machinery, vehicle; -emission factor based on fuel consumption of certain port operation machinery, g/kg fuel; -fuel consumption of certain port operation machinery, L; -fuel density, kg/L; density of No.0 diesel oil can be taken as 0.83kg/L; -pollutant types, including CO, HC, NOx and PM; -power section of engine of some port operation machinery; -emission standard of certain port operation machinery.

Calculation of SO2 emission inventory
SO2 emission is only related to sulfur content of fuel oil, and its calculation method is relatively simple. The calculation method of SO2 emission is shown in the following formula. where: -total emission of SO2, T; -fuel consumption, kg; -sulfur content of fuel, mg/kg. According to Vehicle Diesel Oil (GB 19147-2016) [7] , since January 1, 2019, sulfur content of diesel oil is not more than 10 mg/kg, so the sulfur content of fuel oil is taken as 10 mg/kg.

Emission factor for dynamic method
The emission factor for dynamic method is shown in Table

Emission factor for fuel consumption method
The emission factor for fuel consumption method is shown in

Statistics of Port Enterprise
A special investigation on a domestic container terminal was carried out, and the types and parameters of its basic operation machinery in 2019 were mastered. The statistical analysis was carried out according to the three-level classification of container terminal port operation machinery, as shown in Table 5.

Average load rate of engine for port operation machinery
A special investigation has been conducted on port machinery manufacturers and engine manufacturers, and the average load rate data of main port operating machinery engines in domestic container terminals are obtained. The results are shown in Table 6.

Calculation results for dynamic method
The formula (1) was used to calculate the emission of pollutants other than SO2 of port operation machinery, and the formula (3) was used to calculate SO2 emission. The emission factors in Table 3 and the average engine load rate in Table 6 were selected. The calculation results are shown in Table 7.

Calculation results for fuel consumption method
The formula (2) was used to calculate the emission of pollutants other than SO2 of port operation machinery, and the formula (3) was used to calculate SO2 emission. The emission factors in Table 4 were selected.
The calculation results are shown in Table 8.

Comparison of calculation results
The calculation results of dynamic method and fuel consumption method are compared and analyzed. The results are shown in Table 9. It can be seen from the table that in general, the calculation results of the emission inventory of air pollutants from port operation machinery of container terminals calculated by the power method and the fuel consumption method are very close. The calculation deviations of the overall emission inventory of CO, HC, NOx and PM are -2.3%, -3.8%, -4.0% and -3.1%, respectively.
According to the type of machinery, the deviation between the calculation results of RTG and frontal crane is small. The calculation deviations of CO, HC, NOx and PM emission inventory of RTG are 5.7%, 3.6%, 1.9% and 3.8% respectively, while those of frontal crane are 3.7%, 0.0%, 2.1% and 0.0%, respectively. The deviation between the calculation results of Empty Container Stacker and forklift truck is relatively large, but both are less than 50%, which is also within the acceptable range. The calculation deviations of CO, HC, NOx and PM emission inventory of Empty Container Stacker are -39.4%, -40.0%, -40.5%, -38.5%, respectively, while those of forklift truck are -14.3%, -25.0%, -21.1% and 0.0%, respectively.

Conclusion
In this paper, the classification of port operation machinery, the calculation method of dynamic method and fuel consumption method, emission factor, activity level and other aspects of port operation machinery air pollutant emission inventory are comprehensively sorted out, and the calculation method system of port operation machinery air pollutant emission list is established. Through the special investigation of port machinery manufacturers and engine manufacturers, the average load rate data of main port machinery engines in domestic container terminals are obtained.
The actual emissions of a domestic container port are calculated and compared by using dynamic method and fuel consumption method respectively. The results show that the calculation method system of air pollutant emission inventory of port operation machinery established in this paper is highly practical, and the calculation results obtained by the two methods are very close.