Solutions
Oil and oil products pipeline simulation
The model of the oil products pipeline section is assembled in accordance with the process flow diagram.
Fig.1. Oil product pipeline model
The “Properties of isothermal fluid” block is used to set the rheological properties of the product - in particular, density and kinematic viscosity. This block does not have ports to connect to other blocks in the model, but shall be connected to "parent" block (tank [3] in this example) through the corresponding property.
Fig.2. “Tank” and “Fluid properties” blocks
The "Tank" block is installed at the beginning and end (or several ends) of the process section. The user-specified pressure in the tank determines the level of discharge - for example, 5 meters of liquid column correspond to 42 KPa of hydrostatic pressure, taking into account the density of the liquid equal to 840 kg/m3 when simulating the pumping of diesel fuel.
Blocks of “Centrifugal pump” type can be connected to the pumping station in series and in parallel: by setting different parameters of the units, both the booster (BCP) and the main pumping station (MPS) can be simulated. In our example, PS consists of two units connected in parallel - this circuit assumes the addition of flows and the total head of the station equal to the head of each pump.
Fig. 3. Using “Centrifugal pump” blocks to simulate PS
The Q-H characteristic of the pump unit can be set in the form of two corresponding vectors, or by specifying the extreme points of the characteristic between which a curve will be drawn for interpolation.
Fig. 4. Setting the pump unit characteristics
A “check valve” block, which prevents undesired flow of liquid in the reverse direction, is installed after each pump unit and, if necessary, at the pump station bypass. For this block, the user can set the actuation threshold and full opening pressure.
Fig.5. Properties of “Check valve” block
Pipe section” block is used to simulate the linear portion of a pipeline where pressure losses are distributed along its length. The user can specify all of the basic properties of the pipe-length, geodetic elevation difference, inside diameter, wall thickness, and surface finish. If it is necessary to simulate a complex pipe profile, it can be divided into sections.
Fig.6. Properties of “Pipeline section” block
The “Local resistance” block simulates local (not distributed along the length) losses in the pipeline section - for example, on a strainer at the end of the section in front of the tank battery. The user can set a loss factor for this block, which determines the actual loss at a given product flow rate.
Fig. 7. Setting of losses at local resistance at level of 2 kgf/cm2 (202.6 KPa)
The “Flow rate sensor” and “Pressure sensor” blocks provide operation of measuring instruments in the model. If there is no branching of the flux in the pipeline section, then in stationary processes it is enough to measure the fluid flow in the section in one place, since it is the same at any point of the pipeline.
Fig. 7. Setting of losses at local resistance at level of 2 kgf/cm2 (202.6 KPa)
Fig. 8. Comparison of liquid flow rate in DN200 and DN300 pipelines with the same length and the same pressure drop in the area
The pressure sensor in REPEAT measures the differential pressure between two points - this is convenient when it is necessary to determine the loss in the pipe or local resistance, as well as pump head.
Fig. 9. Connect sensor to measure head of pump station
Fig.10. Connect a sensor to measure pressure drop
The sensor reading in Figure 9 will be negative because, according to the definition, the drop itself is negative in this case. The drop will be positive in Figure 10 - the pressure measured upstream the resistance is greater than downstream it.
Fig.11 Connect the sensor to measure the overpressure
If it is required to measure overpressure at a point, connect the second output of the sensor to “Atmospheric pressure” block- in this case, the difference between the connection points is numerically equal to the desired value.
Simulation Results
Calculation results (pressure losses in various elements of the hydraulic scheme) at a mass flow rate of 100 kg/s compared to another software are provided in Table 1.
Table 1 - Pressure losses in various elements of the hydraulic scheme
