CSP World

The Mojave Solar plant being built by Abengoa in California has made a change in its design and will not use natural gas to avoid freezing of Heat Transfer Fluid, it will use instead a electric heating system.

The use of natural gas in Concentrated Solar Plants is very common. It's the easiest and sometimes cheapest way to keep HTF temperature above a minimum to avoid freezing or high viscosity. Therminol VP1, a widely used HTF has a crystallizing point of 54ºF. This new improvement in the design could be a significant advance for future designs to reduce the natural gas or other fossil fuels consumption in CSP plants.

In a document filed with the California Energy Commission (CEC) seen by CSP World, Mojave Solar LLC, a wholly owned subsidiary of Abengoa, makes a petition to amend the Commission's certification for the Mojave Solar plant. The company says this change will enhance the project design by removing two 21.5 MMBtu/hr natural gas fired, low-NOx burner auxiliary boilers. Furthermore, as no natural gas will be used in the plant, it "also completely avoids the need to construct a natural gas line, thus completely avoiding the potential impacts associated with gas line construction", the filling says.

Instead of using natural gas fired auxiliary boilers for equipment and HTF freeze protection, the plant will use HTF electric heaters. One HTF electric heater will be incorporated into the HTF piping system in each power block. The electric heater is a small vessel, and will not change the physical appearance of the power block when viewed from the outside. The electric heater will be used for freeze protection of the HTF.

The heater will take the full flow of the recirculation pump (20% of the total flow of the main circulation pumps) from the solar field return junction as the inlet. The heated fluid exiting the electric heater will be sent to the expansion vessel bottoms header. As additional protection, the HTF pumps can be circulated at high flow to add heat to the HTF, preventing freezing. The goal is to maintain the HTF above 120°F at all times to ensure that there are no cold spots in the solar field that might freeze. These are the same basic functions served by the natural gas fired units, but with the all-electric system.

This new design will avoid CO2 emissions and will avoid the construction of the gas pipeline, therefore improving the air quality and reducing other environmental impacts.