How in a closed Rankine cycle, regeneration helps to increase efficiency?
Fundamentally is, using most of the heat transferred to the cycle. By doing that you can reduce two thing, by reducing the temperature at the inlet of the condenser you have to subtract less heat in the condensing process and also, in the heat exchange process you can increase the higher temperature target with less amount of heat injected.
When designing a pipeline system, what is the major concern regarding costs?
In a pipeline system, your major economic concern should be oriented to one goal, which is, delivering the desired fluid with the required flow and pressure. In order to properly calculate, we have to create a layout of the pipeline arrangement because the pressure drop is reduced with a bigger pipe diameter but a bigger pipe diameter implies a more expensive pipe. On top of that, you should consider the fluid being transported, the materials used, the purpose of the fluid and the pipe. And if you are designing for a specific industry, are there any codes involved in the design process that you should take into account.
What is the difference main between a steam turbine used in the geothermal industry and one used in a regular steam cycle?
The principles that apply to a steam turbine, in general, are the same. However, the main differences from these turbines come from the "type" of steam being used, in a conventional steam cycle (Rankine cycle) the steam is extremely clean and operates a very high pressure compared to that of a geothermal cycle, where the steam comes from the ground and carries a high amount of impurities (mostly non-condensable gases and dissolved solids). That being said, constructively the turbines will have different materials, those in geothermal being design for the corrosive conditions present and the lower pressures for geothermal cycles.