Basics of Piping Design
The basic concept of a geothermal piping design is to safely and economically transport steam, brine, or two- phase flow to the destination with acceptable pressure loss.
The piping associated with geothermal power plant can be divided in piping inside the power plant and the piping in the steam field.
Piping in the steam field consists of pipelines connecting the production wells to the separation station and those that run cross-country from the separation station to the power plant, and lastly to reinjection wells.
The cross-country pipelines run on top of ridges, up and down steep hill slopes, cross roads, areas threatened by earthquakes, wind, rain and landslides. The fundamentals flexible enough to allow thermal expansion but also stiff enough to withstand the seismic and operational load actions.
The steam field model used is a wet field as the piping encountered in this model covers most, if not all the possible types of fluids and piping that could be expected in any geothermal system.
The wet steam field system consists of:
1. Two-phase flow piping which collects the fluid from several wellhead and sends them to the separator;
2. The separator vessel;
3. The steam pipelines which take the steam from the separator to the power plant;
4. The brine pipelines which take the separated brine from the vessel to a wellpad where the fluid is re- injected into several wells;
5. Miscellaneous cross-country piping includes the instrumental air lines, the water- supply line and also the condensate line.
Two aspects of the design process of geothermal piping systems that must be considered are the process of preparing the design and the deliverables.
The scope of this paper will be in the piping for the steam field and the process of preparing the design divided in the following main categories: design criteria, produce process flow diagram, define control philosophy, separator location, route selection, dimension design, pressure design, load design, design codes and pipe stress analysis.