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順序輸送短管道的泵站一管道系統(tǒng)
在長距離油品輸送過程中，由于成品油的品種多(如汽油、柴油、煤油等)，而每種成品油的運(yùn)量不是很大，如果為每種油品單獨(dú)敷設(shè)一條輸油管道,不僅管道工程量大，使基建投資增加，而且由于輸送每種油品的管道直徑較小，使每噸公里的輸油成本上升。因此，成品油長距離管道輸送采用順序輸送工藝，即用同一條管道，按照一定順序連續(xù)輸送幾種油品，從而把流向相同的幾種油品沿一條管道輸往消費(fèi)地點獲得較高的經(jīng)濟(jì)效益。
由順序輸送工藝可以知道，在泵站一管道系統(tǒng)內(nèi)可能同時存在兩種或多種油品，如圖1-50所示，以系統(tǒng)內(nèi)同時存在兩種油品(A一汽油,B-柴油)為例，分析油品順序輸送管道系統(tǒng)工作點的變化情況。
A油為密度、黏度小的油品,B油為密度、黏度大的油品。由于兩種油品密度不同，當(dāng)油品切換時，仍用液柱高度表示泵站揚(yáng)程和管道的摩阻損失不直觀，因此,這里泵站及管路特性均以壓力表示。
如圖1-51所示，由于B油的密度大于A油的密度,因而在相同流量下，輸送B油時的泵站特性(p-Q)g高于輸送A油時的泵站特性(p-Q)A;而由于B油的黏度大于A油的黏度，因而在相同流量下,輸送B油時的管道特性II較輸送A油時的管道特性I陡。設(shè)輸送A油時管道特性曲線為l，輸送B油時的管道特性曲線為ll，則管道輸送A油時的系統(tǒng)工作點為1,而輸送油B時的系統(tǒng)工作點為3。
當(dāng)泵站和管道內(nèi)均為A油品時,泵站特性(p-Q)A與管道特性1的交點1即為系統(tǒng)工作點;當(dāng)A油品切換為B油品時，泵站內(nèi)的離心泵機(jī)組很快就被B油品所充滿，而管道內(nèi)仍為A油品，此時泵站特性為(p- Q)B,管道特性仍為I,則泵站特性(p-Q)n與管道特性I的交點2為系統(tǒng)工作點;然后管道內(nèi)的A油品逐漸被B油品所頂替，此時泵站特性仍為(p- Q)g,而管道特性逐漸從1向II轉(zhuǎn)變，系統(tǒng)工作點也從2點沿泵站特性(p- Q)g向3點轉(zhuǎn)換，當(dāng)泵站和管道均為B油品時，泵站特性（p-Q）B與管道特性ll的交點3為系統(tǒng)工作點；當(dāng)B油品切換為A油品時，泵站內(nèi)的離心泵機(jī)組很快就被A油品所充滿，而管道內(nèi)仍為B油品，此時泵站特性為(p-Q)A，管道特性仍為ll，則泵站特性為(p-Q)A與管道特性ll的交點4為系統(tǒng)工作點，此后管道內(nèi)的B油品逐漸被A油品所頂替，此時泵站特性仍為(p-Q)A，而管道特性逐漸從ll向l轉(zhuǎn)變，系統(tǒng)工作點也從4點沿泵站特性(p-Q)A向1點轉(zhuǎn)換，當(dāng)渣漿泵廠家站和管道均為A油品時，系統(tǒng)工作點回到1點。
Pump station pipeline system with short pipeline in sequence
In the long-distance oil transportation process, due to the variety of oil products (such as gasoline, diesel oil, kerosene, etc.), and the transportation volume of each oil product is not very large. If a separate oil pipeline is laid for each oil product, not only the pipeline engineering volume is large, the infrastructure investment is increased, but also the transportation cost per ton kilometer is increased due to the smaller diameter of each oil pipeline. Therefore, the long-distance pipeline transportation of product oil adopts the sequential transportation process, that is, the same pipeline is used to continuously transport several kinds of oil products in a certain sequence, so that several kinds of oil products with the same flow direction can be transported along a pipeline to the consumption place to obtain higher economic benefits.
From the sequential transportation process, it can be known that there may be two or more kinds of oil products in the pipeline system of the pump station, as shown in Figure 1-50. Taking two kinds of oil products (a-gasoline, b-diesel) in the system as an example, the change of the working points of the sequential transportation pipeline system of oil products is analyzed.
Oil a is the oil with low density and viscosity, oil B is the oil with high density and viscosity. Due to the different density of the two kinds of oil products, it is not intuitive to use the height of liquid column to express the head of pump station and the friction loss of pipeline when the oil products are switched. Therefore, the characteristics of pump station and pipeline are expressed by pressure.
As shown in figure 1-51, because the density of oil B is greater than that of oil a, the pump station characteristic (P-Q) g of oil B is higher than that of oil a at the same flow rate, while the viscosity of oil B is higher than that of oil a, so the pipeline characteristic II of oil B is steeper than that of oil a at the same flow rate. If the characteristic curve of pipeline is l when delivering oil a and ll when delivering oil B, the system working point of pipeline is 1 when delivering oil a and 3 when delivering oil B.
When the pump station and pipeline are all oil products a, the intersection point 1 of pump station characteristic (P-Q) a and pipeline characteristic 1 is the system working point; when oil product a is switched to oil product B, the centrifugal pump unit in the pump station is filled with oil product B very quickly, while the pipeline is still oil product a, at this time, the pump station characteristic is (P-Q) B, the pipeline characteristic is still I, the intersection point 2 of pump station characteristic (P-Q) n and pipeline characteristic I is the system working point; Then oil a in the pipeline is gradually replaced by oil B. at this time, the pump station is still (P-Q) g, The pipeline characteristics gradually changed from 1 to II, and the system working point also changed from 2 along the pump station characteristics (P- Q) When the pump station and pipeline are all oil products B, the intersection point 3 of pump station characteristic (P-Q) B and pipeline characteristic ll is the system working point; when oil product B is switched to oil product a, the centrifugal pump unit in the pump station will be filled with oil product a very quickly, while the pipeline is still oil product B, at this time, the pump station characteristic is (P-Q) a, the pipeline characteristic is still ll, then the pump station characteristic is the intersection point 4 of pump station characteristic (P-Q) a and pipeline characteristic LL It is the working point of the system. After that, oil B in the pipeline is gradually replaced by oil A. at this time, the characteristics of the pump station is still (P-Q) a, while the characteristics of the pipeline are gradually changing from l l to L. the working point of the system is also changing from 4 points along pump station characteristics (P-Q) a to 1 point. When both the station and pipeline of the slurry pump manufacturer are oil a, the working point of the system returns to 1 point.
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