China built the first crude oil pipeline from Karamay Oilfield in Xinjiang to Dushanzi Refinery at 1958. The total length of the pipeline is 147km and the diameter is150 mm. The first natural gas pipeline was built in 1963. The pipeline runs from Jiulongpo, Baxian County, Chongqing to Banan District, with a total length of 84. 14km and a diameter of 400mm, which is called Bayu Line for short. 1976, China built the Golmud-Lhasa product oil pipeline. The pipeline starts in Golmud, Qinghai Province and ends in Lhasa, Tibet. It is located on the Qinghai-Tibet Plateau, the roof of the world. It is the highest oil product pipeline at present, with a total length of 1080km and a diameter of150 mm. Since then, with the development of oil and gas fields such as Daqing, Shengli, North China, Zhongyuan and Sichuan, natural gas pipelines and pipeline systems such as crude oil pipeline network, Sichuan-Chongqing natural gas ring network, Zhongwu, Shaanxi-Beijing and Senenglan have been built successively from west to east. By 20 13, the total length of oil and gas pipelines built in China has exceeded 10× 104km, initially forming an oil and gas pipeline network pattern that spans east and west, runs through north and south, covers the whole country and connects overseas.
I. Composition of oil and gas pipelines
There are many kinds of oil and gas pipelines, and their classification methods are different. According to the length and operation mode, oil and gas pipelines can be divided into internal pipelines and long-distance oil and gas pipelines. According to the different types of transmission media, oil and gas pipelines can be divided into crude oil pipelines, refined oil pipelines, natural gas pipelines and oil-gas mixed pipelines. According to the different locations of pipelines, oil and gas pipelines can be divided into onshore pipelines and submarine pipelines. The following mainly introduces the composition of long-distance oil pipeline and long-distance natural gas pipeline.
1. Composition of long-distance oil pipeline
Long-distance oil pipeline consists of oil transmission station, lines and auxiliary facilities, as shown in Figure 7-2 1.
Fig. 7-2 1 composition of long-distance pipeline
1-Well site; 2- Oil transfer station; 3- Oil pipeline from the well site; 4— Main facilities of the first station; 5- Dispatching Center; 6- pig distribution area; 7— Auxiliary facilities such as boiler room at the first station; 8— Microwave communication tower; 9— Pipeline valve chamber; 10- dormitory; 1 1- intermediate station; 12, 13, 14- railway and river crossing works; 15-the last stop; 16- refinery; 17- loading and unloading trestle; 18- loading and unloading port
The main function of oil transmission station is to pressurize and heat oil products. According to different locations, oil transmission stations can be divided into first station, intermediate station and last station. The oil transmission station at the beginning of the pipeline is called the first station, and its task is to receive the oil from the gathering and transportation joint station, the production workshop of the refinery or the port tanker, and then input it to the next station (for heating the pipeline) after being metered, pressurized and heated. The first station generally has more oil storage equipment, pressurized heating equipment and perfect metering facilities.
In the process of oil transportation along the pipeline, the pressure and temperature will continue to drop due to friction, heat dissipation, terrain changes and other reasons. When the pressure and temperature drop to a certain extent, in order to make the oil continue to be transported forward, it is necessary to set up an intermediate oil transmission station to pressurize and heat the oil. The independently pressurized oil transmission station is called the intermediate pumping station; The independently heated oil transmission station is called the intermediate heating station; The pressurized heating oil transmission station is called a heat pump station. According to different functions, intermediate stations are usually equipped with pressurized heating facilities, certain oil storage facilities, pig receiving and dispatching facilities, etc. The intermediate station shall provide the process of passing the station.
The terminal station is an oil transmission station (oil depot) located at the end of the pipeline, and its function is to receive the oil from the pipeline, store the oil or transport it to users. Terminal stations are generally equipped with more oil storage equipment, more accurate metering facilities, oil transportation facilities and pigging receiving and dispatching facilities.
The routing part of long-distance oil pipeline includes the pipeline itself, the valve chamber along the pipeline and the structures crossing the obstacles such as rivers and valleys. Auxiliary facilities include communication, monitoring, cathodic protection, pig receiving and dispatching and living facilities for workers along the line.
2. Composition of long-distance gas pipeline
The composition of natural gas long-distance pipeline is similar to that of oil long-distance pipeline, including initial station, intermediate station, terminal station, trunk pipeline and auxiliary facilities, as shown in Figure 7-22.
The main function of the first gas pipeline station is to receive the incoming gas from the natural gas treatment plant, separate it (dry and remove dust), adjust the pressure and measure it, and then send it to the gas transmission trunk line. Different from oil transportation, due to the high pressure of gas production wells, all aspects of natural gas exploitation, treatment and transportation are closed. In order to make full use of gas well pressure, normally, the first station of long-distance natural gas pipeline is not equipped with pressurization equipment, and it can be transported to the next station by using the residual pressure of gas wells. For example, the first booster station of Shaanxi-Beijing line is located at the starting point of the pipeline 100km.
Figure 7-22 Composition of Long-distance Natural Gas Pipeline
According to different functions, intermediate stations of gas pipelines can be divided into receiving stations, off-take stations and compressor stations. The function of the receiving station is to receive the incoming gas from the branch line or the gas source along the line; The role of the off-take station is to supply gas to the users along the branch line or line; The function of the compressor station is to pressurize the gas.
The function of the gas transmission pipeline terminal station is to receive the gas from the pipeline, carry out separation, pressure regulation and metering, and then send it to the user gas distribution station. If the terminal station directly supplies gas to the city gas transmission and distribution network, it can also be called the city gate station. Conditional areas should build underground gas storage at the terminal station to adjust the gas supply imbalance.
Second, the characteristics and operation control of oil pipelines
(A) the characteristics of oil pipelines
1. Hydraulic characteristics
In the process of oil flowing in the pipeline, its pressure can gradually decrease, which is commonly called pressure drop. Pressure drop mainly includes pressure drop along the pipeline (traditionally called pipeline friction), local pressure drop and potential pressure difference.
(1) Pressure drop along the pipeline: mainly refers to the pressure energy consumed by friction between oil and pipe wall and between oil and oil when oil flows through the straight pipe section. Can be calculated by Darcy formula:
Where hL—— is the resistance loss along the pipeline, m;
λ-frictional resistance coefficient along the way, dimensionless, related to fluid flow pattern;
G—— acceleration of gravity, m/s2;
V—— the moving speed of oil, m/s;
D—— internal diameter of pipeline, m;
L—— calculated length of pipeline, m
(2) Local pressure drop: refers to the pressure energy consumed when oil products flow through various pipe fittings or valves. The pressure energy loss of long-distance oil pipeline is mainly caused by the resistance loss along the pipeline, and the local resistance loss is relatively small, so it is generally not calculated separately. Instead, according to the different topographic relief along the pipeline, 1% ~ 2% of the trunk line length is taken as the additional length of local friction loss along the pipeline, which is calculated together with the calculated length of friction loss along the pipeline. Generally, in flat terrain, the additional length of local pressure drop is 65438+ 0% of the calculated length of pressure drop along the line; Take 2% for areas with large topographic relief; The value of other lots can be between 1% and 2%.
(3) Potential pressure difference: refers to the increase or decrease of hydrodynamic pressure of oil transportation in the pipeline caused by topographic changes along the pipeline. The potential pressure difference of a pipe section is only related to the altitude of the end and start of the pipe section, and has nothing to do with the terrain change in the middle of the pipe section. The potential pressure difference of the pipe section is equal to the height difference between the end point and the starting point of the calculation section.
In the process of pipeline transportation, the consumed pressure energy is provided by the pump unit. Therefore, a certain oil pump station should be set along the pipeline to meet the pressure energy consumed by oil flow. When arranging the pumping station, the hydraulic gradient line is usually drawn on the longitudinal section of the pipeline according to the working parameters of the pipeline, and the possible arrangement position of the pumping station is initially determined, and then the site is appropriately adjusted by comprehensively considering the humanities, geology, environment, traffic and life of the pipeline.
2. Thermal characteristics
The common method of transporting "three high" oil products is heating transportation, which aims to increase the oil temperature and prevent the oil flow from freezing in the pipeline. Reduce the precipitation of paraffin and colloid in oil products and the condensation on the pipe wall; Reduce crude oil viscosity and pipeline pressure drop.
The temperature drop of oil flow in pipeline is related to many factors, such as throughput, ambient temperature, heat dissipation conditions, oil temperature and so on. The variation law of oil flow temperature along the hot oil pipeline can be calculated by Shukhov temperature drop formula, namely:
Where g is the mass throughput of the pipeline, kg/s;
K refers to the heat transfer coefficient of oil flow through the pipe wall to the surrounding environment where the pipe is located, w/(m2℃);
L—— the distance from the temperature calculation point to the outlet of the thermal power station, m;
T0—— temperature of medium around the pipeline,℃;
Tc-outlet oil temperature of heating station,℃;
Tl—— oil temperature at outlet L,℃.
C refers to the specific heat capacity of oil at the average transportation temperature, j/(kg℃).
D—— the calculated diameter of the pipeline (for the pipeline without thermal insulation, the diameter of the steel pipe is taken; For pipes with insulation layer, take the average value of internal and external diameters of insulation layer), m.
In fact, the supply and demand of heat energy and pressure energy for heating oil pipelines are interrelated and influence each other. With the increase of heat energy supply, the transportation temperature increases, the viscosity of oil decreases and the friction of pipeline decreases. Increasing pressure energy supply, on the one hand, the throughput increases and the temperature drop slows down; On the other hand, under higher pressure, the fluid with lower temperature can be transported. Among these two interrelated and interacting energy sources, thermal energy plays a leading role. Therefore, we should comprehensively consider the thermal and hydraulic characteristics of heating oil pipeline, calculate the number of heating stations needed for the whole pipeline according to the thermal characteristics, and determine the number of pumping stations needed for the whole pipeline according to the hydraulic characteristics. Then, the heating station and pumping station should be arranged on the longitudinal section of the pipeline and checked and adjusted.
(2) Operation control of oil pipeline
Adjustment and control of operating parameters
During the operation of oil pipeline, due to the influence of many factors, its operating conditions will change to some extent. Therefore, it is sometimes necessary to adjust and control the parameters during the actual operation of the pipeline.
Generally, the adjustment is based on the delivery volume, and the control is based on the inlet and outlet pressure of the pumping station.
There are many methods to adjust the displacement, such as changing the pump speed, rotating the pump impeller, disassembling the impeller stage of multi-stage centrifugal pump, matching the large and small pumps, and throttling the inlet and outlet.
The purpose of pressure regulation is to ensure the stability of the pipeline during operation, and the object of pressure regulation is the inlet and outlet pressure of the oil transmission station. The common measures of pressure regulation are to change the speed, throttling and reflux of oil pump unit.
2. Water hammer in oil pipeline and its control
During the normal operation of the oil pipeline system, its flow pattern is stable. However, in the actual production process, it is necessary to start and stop the pump, switch the valve and switch the process. All these operations will cause a sudden change in the flow velocity of the fluid in the pipeline, thus causing a sudden change in the pressure in the pipeline. This is the so-called water hammer.
The harm of water hammer is mainly reflected in two aspects: one is the harm of overpressure, which may make the pressure of pipeline system exceed the bearing capacity of pipeline and cause pipeline damage; Second, decompression damage may make the pressure of pipeline system lower than the normal working pressure, leading to pipeline instability and deformation. Of course, the pressure wave generated by water hammer may also spread upstream or downstream, which will have a certain impact on the characteristics of upstream or downstream pumping stations. Therefore, effective measures should be taken to control the harm of water hammer. Commonly used methods mainly include pressure relief protection, automatic adjustment of regulating valve and automatic stop of pump group.
Pressure relief protection is to install a special pressure relief valve at the position where overpressure may occur in the pipeline. When overpressure occurs due to water hammer, open the pressure relief valve to release a certain amount of liquid from the pipeline to reduce the pressure in the pipeline and avoid the harm of water hammer.
Automatic adjustment protection of regulating valve is to automatically adjust the opening of valve according to the change of pipeline working pressure to meet the requirements of protecting pipeline system. The automatic regulation protection of regulating valve is often used in conjunction with other protection measures.
Automatic shutdown of the pump unit means that when the suction pressure of the pump station is too low and the outlet pressure is too high, one or more oil pumps are shut down through the automatic control system, thus reducing the energy output of the pump station, reducing the transportation capacity of the pump station, reducing the outlet pressure and increasing the inlet pressure. This method is mainly used to protect the pumping station of series pump unit.
Third, the sequential transportation of petroleum products.
Sequential transportation of refined oil refers to the continuous transportation of different types of refined oil in pipelines according to a certain batch and sequence. Due to the frequent changes of oil transportation varieties, when the two oils alternate, a mixed oil will be produced at the contact interface. There are two main factors that cause oil mixing: first, because the liquid velocity is unevenly distributed in the radial direction on the cross section of the pipeline, the oil behind enters the oil in front in a wedge shape; The second is due to the turbulent diffusion of liquid in the pipeline.
(A) the detection of mixed oil
In order to guide the operation and management of sequential transportation pipelines, it is necessary to detect the mixing of two oils in the alternating process. At present, the commonly used detection methods of mixed oil concentration are density method, ultrasonic method and marking method.
The principle of density method is that there is a linear superposition relationship between the density of mixed oil and the density and concentration of each component oil. This method is to install a detection instrument that can automatically and continuously measure the density of oil products along the pipeline, and detect the change of mixed oil concentration by continuously detecting the change of mixed oil density.
Ultrasonic wave method is based on the characteristics that sound waves travel at different speeds in oil products with different densities. At room temperature, the greater the density of oil, the faster the sound wave propagates in oil. According to this principle, the ultrasonic method of mixed oil concentration is to install ultrasonic detection instruments along the pipeline, and determine the density of oil flow in the pipeline by continuously measuring the time of sound wave passing through the pipeline, so as to detect the concentration of mixed oil.
Marking method is to dissolve substances with marking function, such as fluorescent substances and chemical inert gases, in organic solvents with similar properties to transport oil products to make marking solutions. When in use, a small amount of marking solution is added to the initial contact area of two oil products at the beginning of the pipeline, and the marking solution flows with the oil flow and diffuses along the axial direction, and the concentration distribution of marking substances in the oil flow is detected along the pipeline, so as to determine the oil mixing section and the oil mixing interface.
(b) Measures to reduce the amount of mixed oil
In the sequential transportation of oil products, we always want to reduce the amount of mixed oil as much as possible, and there are many measures to control the amount of mixed oil. First, advanced and reasonable technical measures can be taken to reduce the amount of mixed oil (for example, simplifying the process, increasing the throughput of alternate oil products, adopting closed transportation process, etc.). ); Secondly, take some special measures to reduce the amount of mixed oil, such as mechanical isolation method and liquid isolation method.
Mechanical isolation method is to place certain mechanical facilities between the two oils to isolate the two oils, so as to reduce the mixing of the oils. Commonly used isolation facilities are rubber isolation balls and cup isolators.
Liquid isolation method is to inject isolation liquid between two alternating oils to reduce the mixing amount of oil. The substances commonly used as isolation fluid are: the third oil product with similar properties to the two oils, the mixed oil of the two oils, the gel of water or oil, the gel of other compounds, etc. Among them, gel spacer has good application characteristics.
(3) Treatment method of mixed oil
There are two main methods to treat mixed oil: one is to mix mixed oil into pure oil in batches for sale or degradation on the premise of ensuring the requirements of oil quality standards. For example, when gasoline and diesel are transported sequentially, the mixed oil storage tank of gasoline can receive the mixed oil section with high gasoline concentration, and the mixed oil storage tank of diesel can receive the mixed oil section with high diesel concentration, and the two mixed oils can be mixed into pure oil of gasoline and diesel in small batches for sale. This method is suitable for the case of light oil mixing and large sales of products at both ends. The second is to transport the mixed oil to the nearest refinery for processing. This method is suitable for situations where the degree of oil mixing is heavy, or the net sales volume of mixed oil at the end point is small.
Four, gas pipelines and urban gas transmission and distribution
Natural gas pipeline is the only means to transport a large amount of natural gas on land. One of the ways to transport natural gas by sea is to reduce the temperature of natural gas to-160℃ to become liquefied natural gas, and then ship it for transportation. After being transported to the destination, it changes from liquid to gas after being heated, and the performance of natural gas is restored. Another way of offshore natural gas transportation is still laying submarine gas pipelines. The natural gas produced by Beihai Oilfield in the Atlantic Ocean is transported to Britain and continental Europe through the 1000km submarine pipeline.
The main components of natural gas are hydrocarbons such as methane, ethane, propane and butane, as well as a small amount of hydrogen sulfide, carbon dioxide and water vapor, and sometimes there are liquids such as condensate oil and water in gas wells. Hydrogen sulfide and carbon dioxide must be removed in the treatment plant before entering the pipeline.
Natural gas pipeline has the following characteristics: first, the gas pipeline is a continuous closed transportation system with pressure from beginning to end, unlike the oil transportation system, sometimes oil will enter the atmospheric oil tank; Second, natural gas pipelines directly serve users and directly supply families or factories; Third, the density of natural gas is small, and the influence of static head is less than that of oil pipeline. The static head with height difference less than 200m can be ignored in design, and the gas pipeline is hardly affected by slope. Fourth, natural gas is compressible, so there is no water hammer problem caused by sudden stop of transportation; Fifth, natural gas pipelines should pay more attention to safety than oil pipelines; Sixth, natural gas pipelines are different from urban gas pipelines. The natural gas pressure of gas wells is higher than that of city gas. After the natural gas pipeline enters the city terminal, it should be decompressed to the pressure of the city pipe network to supply gas to the city.
A complete urban gas distribution system is mainly composed of the following parts:
(1) gas distribution station. The gas distribution station is the starting point and general hub of the urban gas distribution system, and its task is to receive the incoming gas from the trunk gas pipeline, and then carry out necessary dust removal, deodorization and other treatments. According to the user's needs, after metering and adjustment, it is input into the gas distribution network for users to use.
(2) Gas storage station. The task of gas storage station is to store natural gas to balance the imbalance of urban gas consumption. The main equipment in the station is various gas tanks. In practice, gas distribution stations and gas storage stations are usually built together, which are collectively referred to as storage and distribution stations.
(3) Pressure regulating station. The pressure regulating station is located between pipelines with different pressure grades in the urban gas distribution network system, or between some special users, and is divided into two types: above-ground and underground. The main equipment in the station is pressure regulator, whose task is to adjust the pressure of natural gas in the pipe network according to the requirements of users to meet the needs of users.
(4) Gas distribution network. Gas distribution network is a pipeline system that transports and distributes natural gas to users. According to the shape, it can be divided into dendritic gas distribution network and annular gas distribution network. The former is suitable for gas supply in small cities or enterprises, and its characteristic is that the gas at each gas point can only come from one direction; The annular gas distribution network can supply gas from many directions, and when local faults occur, it will not cause all gas supply interruption, with high reliability, but large investment.