PQU Phase 2 CHP Plant Flow balance: Analysis for
PB do Brasil

The computational problem was formulated from the data provided (e.g. technical drawings and steam flow conditions). The HSRG pipeline connection (320 t/h of flow), named T1, was set at 1,100 mm from from the T2 connection. I have visualized the absolute pressure and the flow velocity. I have zoomed on to the three T connections (named T1, T2, T3).

Distances from the end points to the T-junctions are 5 diameters for T-junctions connecting INLETS, and 10 diameters for T-junctions connecting OUTLETS. (Details are shown below.) This choise was due to the assumption that the flow is clean in the inlet pipeline sections and “dirty” in the outlet sections. The results prove so.

The pressure is almost constant (equal to 114 bars), while there are enornous changes on the velocity field. This is of course due to the outflow conditions (set as specified.)

Problem Definition

  • Inlet temperature T = 510 Celsius
  • Inlet pressure p = 114.0 bar
  • Inlet density = 34.48 kg/m³ (linear interpolation from steam tables at 500 C)
  • Flow dynamic viscosity 3. 10^{-5} N m/s
  • Outlet: as specified in Flow Balance Drawing (Rev.1 /21.11.01)

Problem Approach

  • CFD solution (Navier-Stokes Equations)
  • 2D block-structured grid
  • Fully turbulent flow with k-eps model

Graphic Analysis (Juctions T1-T2 = 1,100 mm)

Graphic Analysis (Juctions T1-T2 = 1,500 mm)

Discussion of Results

The first calculation was performed with a distance T1-T2 of 1,500 mm. This turned out to be a different configuration than the actual installation, therefore the model was changed to take into accout the distance T1-T2 = 1,100 mm. All other parameters are the same.

The analysis is two-dimensional, e.g. the flow occurs in a plane. In the actual pipeline installation T1 and T2 come at 45 degs with respect to the horizontal. This effect is considered negligible, although the three-dimensional effect of the junction could be more important, especially if T1 and T2 are very close. A quantitative analysis will not be possible within the framework of this scope of work, but it is safe to assume that T1 and T2 should be placed as far as possible from each other, to avoid choking, unsteady loads, and vibrations.

The pressures change very little in the model, as they are around 114 bars everywhere (please check the scale in all the graphics). Therefore, no appreciable gradients have been found.

The case of the flow velocity is quite different. Both analyses show that there are major speed variations.

Comparison of Velocities at T1

T1-T2 = 1,100 mm: The flow is chocked in the direction of OUTFLOW to the PQU 8 MW turbine (this does not appear in the case T1-T2 = 1,500 mm).

Comparison of Velocities at T2

T1-T2 = 1,100 mm: The flow is chocked in the direction of OUTFLOW to the PHASE I 17 MW turbine (this does not appear in the case T1-T2 = 1,500 mm).

Comparison of Velocities at T3

No major differences were detected. The 50 t/h flow to the right is moderately slow.

It is believed that the installation with T1-T2 = 1,500 mm is better than the T1-T2 = 1,100 mm.

Filed on December 4, 2001

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Dr. A. Filippone
Dept of Mechanical and Aerospace Engineering
Thermo-Fluids Division, P.O. Box 88
Manchester M60 1QD
United Kingdom
phone (+44) 161 – 200 3702
telefax (+44) 161 – 200 3723