Fluoropolymer Coated Condensing Heat Exchangers for Low-Grade Waste Heat Recovery

Low-grade waste heat from industrial processes usually has temperatures lower than ~232 °C, and thus has low thermal and economic values. However, low-grade waste heat is abundant and its total work potential is huge. To effectively recover low-temperature waste heat, i.e. recover both the sensible and latent heats, the exhaust streams usually need to be cooled to temperatures below the water and acid dew points, which causes severe corrosion problems in the heat exchangers. In this research, a fluoropolymer-based composite coating was applied to heat exchangers made of inexpensive metals (e.g. stainless steel, aluminum, carbon steel, etc.) to protect the surfaces contacting the waste streams. Corrosion tests were conducted in 80% sulphuric acid at ambient and elevated temperatures for more than 1500 h, and no corrosion was detected. The composite material has much higher thermal conductivity than virgin fluoropolymer, and can be applied to both bare and finned heat exchangers. The composite coating can be continuously utilized at temperatures up to ~260 °C. The coating also shows excellent adhesion strength to the substrate.