顺序输送短管道的泵站一管道系统

在长距离油品输送过程中，由于成品油的品种多(如汽油、柴油、煤油等)，而每种成品油的运量不是很大，如果为每种油品单独敷设一条输油管道,不仅管道工程量大，使基建投资增加，而且由于输送每种油品的管道直径较小，使每吨公里的输油成本上升。因此，成品油长距离管道输送采用顺序输送工艺，即用同一条管道，按照一定顺序连续输送几种油品，从而把流向相同的几种油品沿一条管道输往消费地点获得较高的经济效益。
    由顺序输送工艺可以知道，在泵站一管道系统内可能同时存在两种或多种油品，如图1-50所示，以系统内同时存在两种油品(A一汽油,B-柴油)为例，分析油品顺序输送管道系统工作点的变化情况。
    A油为密度、黏度小的油品,B油为密度、黏度大的油品。由于两种油品密度不同，当油品切换时，仍用液柱高度表示泵站扬程和管道的摩阻损失不直观，因此,这里泵站及管路特性均以压力表示。

如图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，输送B油时的泵站特性(p-Q)g高于输送A油时的泵站特性(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,输送B油时的管道特性II较输送A油时的管道特性I陡。设输送A油时管道特性曲线为l，输送B油时的管道特性曲线为ll，则管道输送A油时的系统工作点为1,而输送油B时的系统工作点为3。
    当泵站和管道内均为A油品时,泵站特性(p-Q)A与管道特性1的交点1即为系统工作点;当A油品切换为B油品时，泵站内的离心泵机组很快就被B油品所充满，而管道内仍为A油品，此时泵站特性为(p- Q)B,管道特性仍为I,则泵站特性(p-Q)n与管道特性I的交点2为系统工作点;然后管道内的A油品逐渐被B油品所顶替，此时泵站特性仍为(p- Q)g,而管道特性逐渐从1向II转变，系统工作点也从2点沿泵站特性(p- Q)g向3点转换，当泵站和管道均为B油品时，泵站特性（p-Q）B与管道特性ll的交点3为系统工作点；当B油品切换为A油品时，泵站内的离心泵机组很快就被A油品所充满，而管道内仍为B油品，此时泵站特性为(p-Q)A，管道特性仍为ll，则泵站特性为(p-Q)A与管道特性ll的交点4为系统工作点，此后管道内的B油品逐渐被A油品所顶替，此时泵站特性仍为(p-Q)A，而管道特性逐渐从ll向l转变，系统工作点也从4点沿泵站特性(p-Q)A向1点转换，当渣浆泵厂家站和管道均为A油品时，系统工作点回到1点。

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.