posted on April 02, 2014 |
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Phenomena: Suspended Particle Impingement and Pipe Erosion
Potential Industry Applications:
- Waste Water
Oil & Gas
Food & Beverage
Main Software: STAR-CCM+
Secondary Software: Abaqus (structural analysis)
Analysis Type: CFD
- Erosion (Oka-correlation)
- Multiphase (gas, water, sand)
- Liquid Film
- Erosion exponentially related to gas velocity
- Water films located at erosion zones
- Increased water concentration can reduce erosion
- Simulation correctly predicted damage
When working with gas reservoirs located in Cenomanian deposits, you will often encounter gas with high solids in your productions. As a result, these production facilities will often experience high pipe erosion from the impingement of sand particles in flow, leading to both economic and production losses.
Choke valve model.
To combat this issue, Andrey Kudryavtsev Ph.D., Group Leader at Sarov Engineering Center in Russia, has been studying the phenomena using CFD analysis. In particular, Kudryavtsev focuses on the study of flow disrupting pipe formations, such as tee-junctions and choke valves.
“We examined the influence of the different factors of erosion rate. We investigated the dependence on particle diameters, silicate concentrations, and water/gas concentrations. We used about 200 variances of these parameters in our simulation. Therefore, the full automation ability of STAR-CCM+ was used thanks to a java macro used to set up each case,” said Kudryavtsev.
The parameter DOE:
- Particle size (diameter): 0.01, 0.1, 0.2 mm
- Concentration (sand): 0.5, 2, 10, 40 mm3/m3
- Concentration (water): 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 mm3/m3
The model methodology was created using multiphase Lagrangian flow models to simulate the gas, sand and water present in the flow. The simulation also used the Oka-correlation erosion model and liquid film models to represent the collection of water and impingement of sand at bends and obstructions.
The simulation is divided into four steps. The first step determines localized erosion zones and the effects of erosion on flow rate and particle concentration/size using a dry gas/sand simulation flow. Next, simulations of gas/water flows are used to determine where liquid films would form and how thick they will become. Additionally, a simulation of sand particle impingement into the liquid film is studied based upon film thickness. Finally, the simulation includes the alterations of the pipe shape using Abaqus structural analysis and a wall thinning rate (erosion rate). The new shape will naturally affect the fluids and particle flows resulting in an iteration process. The iteration time step was one year.
Liquid film forms where it is needed, at erosion zones.
The study found that the locations of highest concern in a choke valve are the needle, valve back side and the needle’s saddle. This is to be expected as they are the objects which impede the flow of the fluid from the inlet to the outlet.
“We see that the sand concentration and particle size produce a mostly linear dependence with erosion rate. This is due to the Oka correlation,” explains Kudryavtsev. “However, we see that the gas flow rate produces an exponential dependence. This is the first important conclusion for operators, they can reduce the flow rate to causing a large reduction to erosion at a small cost of production.”
“Water drops can form films in the pipes,” Kudryavtsev adds. “The films can reduce the particle speed and therefore reduce the damage caused by the impingement. Simulations of the impingement of sand particles through the film saw a dependence of water on the particle velocity. It also verified that water films form where it is needed, at erosion points. In fact, the film can even exclude smaller particles.”
Simulation predictions vs. Experimental results show a clear match.
In conclusion, Kudryavtsev’s simulation was able to accurately predict the locations of erosions from experimental tests, as seen in the image above. Similar results were also seen from the analysis of tee-junctions.
Thanks to this simulation, the areas of concern in the pipes can be addressed and scheduled for maintenance before leakage starts. Additionally, operators can perform tasks like reducing flow rates or adding water to further reduce pipe damage.
Source and Images courtesy of STAR-CCM+ Global Conference and Andrey Kudryavtsev Ph.D