Rectangular Square Cube heat recovery systems from DDI Heat Exchangers


Rectangular Square Cube heat recovery systems from DDI Heat Exchangers are designed to handle sludge with more than 26 percent solids without plugging.

Heat from sludge warmed for anaerobic digestion (95 degrees F Class B, 135 degrees F Class A) is recovered and used for direct heating of incoming cold raw material. By using direct sludge-to-sludge heat recovery, cold raw sludge can be heated to 75 degrees F before entering the digester, saving on boiler or electrical output, says Erwin Schwartz, company president.

To avoid plugging, the DDI system uses parallel 3-inch-high rectangular channels (3- to 6-inch sludge side gap and 1- to 6-inch channel water side gap). The channel width promotes fast flow and avoids the risk of baking. The funnel inlet allows passage of large, stringy, fibrous or viscous solids or debris.

Stacked layers of hot and cold sludge flow side by side for efficient heat transfer. As further insurance against fouling, high turbulence in the specially designed return bends and channels remove the stagnant internal film on the heat exchanger wall. Stacking also results in a compact footprint.

The unit is designed for high flows and very high viscosity. Two doors with removable Davit Arms, on opposite ends of the unit, swing open to provide access for cleaning if needed. Flushing connections are provided. A self-cleaning process using an external-mounted pig is available. The heat exchanger can be made from any weldable metal, including carbon steel, stainless steel, or duplex stainless steel.

The DDI unit requires minimal maintenance and can operate for seven years or more without cleaning, even at high percentage solids, although cleaning once every five years is recommended for most municipal applications. Standard and custom models are available, from small to very large. The system incorporates computerized data acquisition for system efficiency evaluation. 514/696-7961; www.ddi-heatexchangers.com.


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