Recent energy cost increases and the introduction of anaerobic thermophilic processes as part of wasted industrial process and municipal-sludge digestion has prompted the use of heat recovery exchangers. Attempts to modify existing spiral and tube-and-tube heat exchangers to prevent exchanger plugging or baking in heat recovery applications for wasted industrial process and municipal-sludge digestion have largely failed. This has led to the development of large-gap, rectangular-channeled heat exchangers. They are designed to provide non-plugging operation in the presence of stringy and sticky materials found in some industrial processes as well as municipal sludge.
Large-gap, rectangular-channeled exchangers are finding use in industrial pasteurization applications such as dairy, beer or other liquids. They also are being employed in wastewater treatment plants (WWTPs) as well as in dairy cow manure farms. They can be used to heat sludge in a mesophilic digester (95°F [35°C]) or a thermophilic digester (134°F [55°C]). They can help processors conform to the current Class A solids-disposal law via heating the waste to about 160°F (71°C) for pasteurization.