Sludge Heater for Thermophilic Anaerobic Digestion

Municipal Wastewater facilities facing growing processing demands and limits in their current facilities, are considering thermophilic digestion as a solution. Thermophilic digestion differs from mesophilic digestion in that it operates at approximately 132°F. The advantage that thermophilic has over mesophilic is a faster solids destruction rate which is stimulated by higher temperatures. Operating at a higher process temperature puts sludge closer to the point at which it burns. To address this problem, heating strategies which employ multiple heat exchangers (2-3) in series are used to spread out the temperature rise. This approach presents the following challenges when heating sludge: * Spreading the temperature rise across 2-3 heat exchangers still exposes the sludge to scorch problems which can lead to plugging and fouling. Heat exchangers must be operated above the desired set-point in order to achieve the temperature transfer. * Multiple heat exchangers significantly add to the pressure drop across the heating system. This increased pressure drop places a higher demand on the sludge pumps, which leads to increased energy consumption. * Heat exchangers, by design, operate in a temperature add/lag response mode. Monitoring and managing the temperature control system becomes complex and makes temperature control difficult to achieve.