Optimization of gas storage scale and device appli

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Discussion on Optimization of gas storage scale and device application in vehicle CNG filling station. The advantages of CNG gas replacing gasoline as automobile fuel have been recognized. 1m3 is equivalent to 1.14l gasoline. It is used to drive cars. The harmful compounds such as CO, CH and Cox in the exhaust emissions are reduced by more than 90%, 70% and 30% respectively compared with those produced by gasoline. A 15000m3/d standard CNG filling station can reduce the annual production of the above three harmful gases by 226400 m3, which can significantly reduce the steam pollution of urban atmospheric environment, and the environmental protection benefits are very significant; Secondly, the price of CNG gas is cheaper than that of gasoline, and the transportation cost can be reduced by 45%~50% when it is used to drive cars; Third, the octane number of CNG is equivalent to 130g gasoline. When used, the engine runs smoothly, has low noise, does not accumulate carbon, and the lubricant in the moving parts is less damaged and less worn, which can reduce the automobile maintenance cost by about 50%; Fourth, the annual production of a standard CNG station can replace 4300t gasoline. This is of great significance to alleviate the contradiction of energy demand in regions with different energy varieties and promote the economic development of the region. In terms of use safety, the natural gas has a low density, and once it leaks, it will quickly escape; And the ignition temperature is also higher than that of gasoline. Compared with gasoline, it is more complete to use. Therefore, CNG technology is applied by GAC to the automotive industry and other leaders

due to the good environmental protection and energy-saving benefits of CNG technology for vehicles, the state has vigorously promoted its application, and governments at all levels have taken the promotion and application of CNG technology as a friendly industry and a new economic growth point. At present, the industry is developing rapidly in China, and CNG filling stations for vehicles have been basically formed in Sichuan, Chongqing, Beijing and other cities

vehicle CNG technology is composed of vehicle CNG filling station and dual fuel vehicle technology. In terms of CNG filling station technology, in order to adapt to the development of CNG market, it is optimized according to the production process requirements and system engineering principles, and the most suitable economic scale is 13000m3/d~15000m3/d[1]. However, the economic scale of the gas station is determined by the CNG compressor pressurization and gas storage system. Therefore, it is inappropriate to determine the scale of the gas station according to the single CNG gas storage capacity. The reason is that the production scale is realized through large-scale exhaust compressor and small-scale gas storage or small-scale exhaust compressor and large-scale gas storage. Therefore, the determination and optimization of gas storage scale of gas station is a problem that must be solved by CNG filling station

2 proposal of gas storage scale

2.1 gas storage is the need of intermittent production in the filling station

automobile inflation is determined according to the operation law of transportation, which is manifested in more time and less gas or intermittent filling, thus forming the basic law of gas station production. CNG compressor is a continuous production equipment. In order to meet the needs of gap filling, it is necessary to set up a gas storage system to reduce the frequent startup times of the compressor, so as to reduce the wear and tear of the equipment, and provide a guarantee for the complete and reliable operation of the equipment in terms of production technology

2.2 dual fuel vehicle filling and peak shaving

the particularity of dual fuel vehicle filling gas is manifested in the "two high and one time" inflation law, that is, two peak and one sub peak filling gas, with the time distribution of 06:: 30 as the first peak area; The second peak is 11:: 30; The third peak area is 17:: 30. Peak inflation concentrates 80% of the daily production of Dacron, while the production time only accounts for about 1/2 of the daily production time. Therefore, to solve the peak inflation, the compressor shall not only produce at full capacity, but also rely on the CNG gas stored in the gas storage system for peak shaving. Therefore, peak shaving production is an important task of the gas station, and the setting of its gas storage system is very important

2.3 energy saving production requires gas storage scale

filling station equipment is a device for energy production and requires its own energy saving. From the perspective of CNG production cost composition, except for raw natural gas, power consumption is the main component of the cost. Therefore, power saving is the main way to reduce the production cost of the gas station. Most of China's power production is dominated by hydropower, and there is a large difference between the peak and trough electricity prices, usually about 3.5 times. Therefore, the gas is fully stored in the production at the power trough at night, and the peak filling can also be adjusted by less startup at the peak of power consumption during the day, so that the production of the gas station is in the energy-saving state. In this way, not only the production cost of CNG can be reduced, but also the gas station can adapt to the development needs of market economy as the infrastructure of urban construction. It also tends to be more reasonable in the use of energy, which is conducive to the coordinated development of economy. In short, energy-saving production requires reasonable gas storage scale and advanced gas storage devices

3 current situation of gas storage devices at home and abroad

gas storage devices at home and abroad can be divided into three types: underground steel tube well, gas cylinder group and large tank single chip microcomputer are the core control unit of the system for gas storage

3.1 underground steel pipe gas storage well

the underground steel pipe gas storage well is a gas storage device formed by using the imported N80 steel casing used in oil drilling to drill underground and fix the casing well according to its cementing process. The nozzle and bottom of the casing are closed with special structure. The commonly used casing diameters are 17.8cm and 22.9cm, made of 30mn4 or 28grmo6, and the length of a single well is l=80m/piece -20m/piece. The more mature process is to use a 17.8cm, l=100m/piece, V water volume =1.9 creep endurance tester 4m3/piece. The strength test pressure P is strong =1.25p (according to cjj84{technical scale of automobile gas filling station}), and the calculated fatigue strength times are 19000 times. The advantages of steel pipe gas storage well are that the gas storage device occupies less land and the underground gas storage is more complete than the surface gas storage, which is of great significance for the construction of CNG stations in urban areas. The disadvantage is that the steel pipe connection is weak and needs to be strengthened through effective cementing. At the same time, due to the difficulty of cementing, there is no complete method for routine maintenance and inspection of gas wells, which is currently in the stage of utilization and improvement. The unit construction investment is about 1.5 times that of gas storage of gas cylinder group

3.2 gas storage of cylinder group

the gas storage of cylinder group is composed of qualified CNG station steel cylinders. The commonly used gas cylinder in China is made of 35CrMo steel. The strength test pressure P is 1.5p, and it has passed the simulated explosion, fire, gunshot, fatigue and other tests. The fatigue strength was tested for 12000 times. The commonly used water volumes are 501 and 801, which are connected in parallel to form a gas storage. According to the needs of the process, the gas storage system of the gas station is composed of high, medium and low pressure small warehouses to meet the needs of the gas storage process. Total volume of gas storage V water =18m3. This kind of gas storage device is safe, reliable and flexible to use. It can be planned and implemented step by step during construction, which is conducive to reducing the construction cost of gas stations. It is widely used in gas stations at home and abroad. The disadvantage is that there are many joints in the cylinder group, resulting in many leakage points and large negative force of the system. Utilization coefficient of gas storage c=0.51~0.62 (utilization coefficient of other gas storage devices is also in this range)

the gas storage of cylinder group needs to build solid buildings or facilities to prevent the gas storage from reducing the hazard radius of accidents in case of emergencies

3.3 large tank gas storage

3.3.1 foreign large tank gas storage devices

the gas storage system composed of large tank gas storage units produced by American CPI company in accordance with ASME standards is better for foreign large tank gas storage devices. Each gas storage unit is of cylindrical type, which is closed by thermal processing to form a seamless container. The material is sa-372, which has high heat treatment (liquid quenching and tempering) quality. The strength test pressure P is strong =5/3p. The fatigue strength measured by the test can fully meet the process needs of CNG production. The service life is about 20 years. It is internationally recognized as an inspection free high-pressure vessel. The water volume of each gas storage unit is 2m3, 3m3, 4m3 and 6m3. The advantages of the gas storage device are that it is safe and reliable to use, the gas storage system has few leakage points, the negative force of the system is small during gas transmission and supply, and the unit weight ratio is reasonable. It is an ideal gas storage container for CNG station. However, the price of imported equipment is high, which is twice the construction cost of small bottle gas storage system

3.3.2 domestic substitute gas storage device

domestic large tank gas storage device, also known as substitute CNG station gas storage device at present. This type of vessel is a Class 3 pressure vessel produced in accordance with the bg150{steel pressure vessel} standard in China. The village quality is 19Mn6, the strength test pressure P is =1.25p, and the measured fatigue strength is 9000 times. The commonly used water volumes are 2m3, 3m3 and 4m3. Geometric shapes are spherical and circular. The advantages of large tank gas storage are less joints, less leakage points of the gas storage system and small system resistance during gas transmission and supply. The shortage is that the steel consumption is large, which is mainly reflected in the small volume weight of the container and the low fatigue strength. The adaptability to the alternating characteristics of CNG production pressure is specific to the production inspection, so it is called an alternative gas storage device. The unit construction investment is about ak/f=ak, and its unit is Joule/cm2 (j/cm2), which is 1.6 times that of small gas cylinder gas storage

the comparison of several domestic gas storage devices is shown in table 1

from table 1, it can be seen that the underground steel pipe gas storage well device is in the trial stage, and there are many problems that need to be solved in practice: the gas storage cylinder group has mature and reliable technology, but the system has large negative force, so the resistance of the gas storage system of the gas cylinder should be reduced during use; China is starting to destroy gas storage. It should actively research, develop and use new materials and new process technologies to improve the volume weight ratio of storage tanks and the fatigue strength of storage tanks, so as to meet the production process and technical requirements of gas stations. Table 1 technical and economic comparison of gas storage devices in domestic vehicle CNG filling stations

serial number name specification and quantity total investment (10000 yuan) technical performance

safety and economy remarks 1 N80 steel casing for imported drilling of underground steel pipe gas storage well, made of 30mn4 or 28crmo6; D= Φ 17.8cm (d> inner =15.71cm), l=100m/well, vshui = 1.94m3/well, n=7 well 98.5p strength =1.25p working =32mpa; Calculate the number of cycle fatigue 19000 times; H2S corrosion resistance after anti-corrosion in the pipe; High pressure vessels not suitable for gas storage in gas stations; Long pipeline for gas transmission; It is difficult to well cementing, and the safety factor at the weak part of the tube well that needs instrument detection for well cementing quality is only 2.5, which needs to be strengthened; Gas storage construction cost: 218 yuan/m3; reference price: 140000 yuan/well; 5000 yuan for auxiliary facilities; Covering an area of 10m2; There is no standard gas storage cylinder znpb (Beijing Tianhai) made of 35CrMo for gas storage station of 2 cylinder group for daily inspection and maintenance; D=26.7cm, l=181cm/piece, δ= 0.81cm, V water =801 PCs, n=230 PCs, 62.2p strength =1.5p working =375mpa; 12000 cycles of cyclic fatigue test; Generally resistant to H2S corrosion; The material is suitable for high-pressure gas storage of CNG station cylinders; The relative system resistance is large when transporting gas, and the production experiment proves that it is safe and reliable; The construction cost of gas storage is 58 yuan/m3, and the annual inspection cost; 1.25 million yuan/year, 1400 yuan/piece for reference; 120000 yuan for installation materials; The building covers an area of 30m2 and the construction cost is 100000 yuan; Installation cost: 80000 yuan; Bottle inspection fee of 1.67 million yuan/year 3 large gas storage spherical tanks (Dongfang Boiler Works) cnc/q-3, material 19Mn6, φ= 198cm × 9cm × 244.5cm, V water =3m3/piece, w=985t/piece, n=694.0p strength =125p working =32mpa; The number of cyclic fatigue test is 9000; H2S corrosion resistance after anti-corrosion in the tank; The material is not suitable for the high-pressure vessel used for gas storage in the gas station, and the transmission gas resistance is small; Comply with GB150 standard, and its CNG service performance is to be verified by production inspection; According to the construction cost of gas storage; 209 yuan/m3, annual inspection cost c2=7500 yuan/year gas storage device; The reference price is 150000 yuan/piece; 60m2; 40000 yuan for auxiliary facilities; Bottle inspection fee is 0.75 million yuan/year

Description: (1) each gas storage equipment is calculated according to the water volume of 18m3; (2) The total investment includes equipment, supporting equipment

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