Learn how dropwise condensation using copper tubing can reduce freshwater use for power plant cooling, reduce condenser thermal resistance, improve heat exchanger performance and reduce turbine backpressure while saving hundreds of thousands of dollars.
By: Richard Bonner
What does it cost to create electricity? This simple question has a nuanced answer that is inextricably connected to freshwater availability and use. Over 40% of freshwater withdrawals are attributed to thermoelectric power generation in the United States [source: NETL]. These freshwater withdrawals are primarily used for cooling process steam in wet cooling towers and surface condensers. With many countries lacking fresh drinking water and water for daily industrial needs, water management and security have become a key focus of the Department of Energy.
At ACT, we worked with SUEZ – Water Technologies & Solutions [ref: Suez] for over three years to improve steam surface condenser performance in steam Rankine cycles. We have focused on applying SUEZ’s film-forming amine products applied to condenser surfaces to promote dropwise condensation. Conventionally, these products are used to resist flow accelerated corrosion in boiler systems on the magnetite phase of steel. Additionally, these coatings possess low surface energy and can create hydrophobic surfaces, as shown in Figure 1. Hydrophobic surface promoted dropwise condensation can yield thermal performance results 5-20x higher than filmwise condensation for convective heat transfer performance. Previous work in this area has focused on studying enhanced surfaces without regard to long lifetimes. In other words, most studies use coatings that oxidize quickly; whereas, film-forming amine products are self-healing or replenishable on the tubing surface. This is accomplished with an injection of the film-forming amine product.
Figure 1. Representation of film-forming amine products deposited on a metal surface for a steam surface condenser application.
An example of the experimental results is as follows. For a low carbon steel surface, the convective heat transfer was improved from 10,000 W/m2-K to 70,000 W/m2-K using self-healing film-forming amine products. This 7x improvement in the condensation heat transfer coefficient led to a:
- 38% reduction in the condenser thermal resistance (size)
- 59% improvement in the overall heat exchanger performance (U)
- 54 in Hg reduction in turbine back pressure
- 84% increase in power plant efficiency
- 24% reduction in net levelized cost
Economic analyses found that annual fuel cost savings for a power plant would be between $300K – $1.5M per year for a 500 MW power plant using market-priced fuel costs. An example of dropwise condensation performance observed on copper tubing is seen in the video.
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