In the US, fossil energy is important for security, with coal producing nearly 30% of the nation’s electricity. To help ensure the continued success of this energy resource, NETL is funding research to modernise the grid and improve the efficiency of the existing coal-fired power plant fleet with the goal of strengthening the reliability of electricity generation.
In coal and other fossil fuel-based power plants, high pressure, high temperature steam drives turbines that spin electricity-producing generators. After exiting the turbine, steam moves through the condenser where it is converted back into liquid so it can be re-heated and re-pressurised to be used again. Condenser performance is largely dependent on how efficiently cold tubes cool the steam and condense it back to liquid.
When steam contacts the metal tubes, a film or condensation can form. This layer acts as an insulator between the cold metal and steam, limiting heat transfer and lowering efficiency.
John Rockey, Technology Manager for Transformative Power Generation at NETL, said: “Condensers can also have issues with fouling, which is the buildup of scale (deposits of hard minerals, corrosion and organisms) on interior and exterior cooling tubes, which further inhibits heat transfer.”
The company is working closely with industry partners to address these issues. One technology moving forward has been developed by Oceanit Laboratories Inc. and tested extensively at the Hawaiian Electric Company’s Kahe generating station (USA).
Oceanit’s solution to improve efficiency is a coating called HeatX™, which is applied to the surfaces of condenser components. The ultrathin, non-toxic coating forces the condensing water to form into droplets that quickly roll off, rather than adhere to, condenser surfaces.
The company’s officials presented results from field tests at the 2019 International Pittsburgh Coal Conference. They concluded that the product reduced fouling on condenser units, increased heat transfer rates and helped extend the amount of time a unit can remain in service before it must be taken down for maintenance.
Kahe burns diesel fuel (which, like coal, is a fossil fuel) to produce electricity. Oceanit anticipates testing the coating at coal-fired power plants in 2020, according to Matthew Nakatsuka, the company’s technical lead for the project.
The project is one example of efforts taken by NETL to lower emissions of carbon dioxide and ensure a reliable supply of affordable electricity for US consumers.
Rockey explained: “Fossil fuels such as coal are abundant and inexpensive compared to other energy sources. But energy extraction from fossil fuels is only about 40%. Much of the potential energy is lost in the condenser.
“By improving the efficiency of the condenser, less fuel needs to be burned to achieve the same levels of energy output, lowering both consumption costs and emissions.”