Anaerobic Digester Expansion

A municipal wastewater treatment plant, handling sludge from area wastewater treatment plants, had a project to increase its anaerobic digester capabilities. Plans involved expanding by 50%, implementing a "two-phase" digestion process.

The design criteria required a range of operating conditions, including heating a stream of 6% mixed sludge from ambient to approximately 100°F. Conventional style heat exchangers are prone to clogging. The characteristics of sludge at that concentration are such that non-laminar flow could not be guaranteed.

In two-phase digestion an acid phase is followed by a methane phase. The advantage over conventional single phase digestion is a more efficient process resulting in an overall reduction in solids retention time. The retention time in the acid phase is relatively low compared to the methane phase. Consequently the entire flow stream is channeled through one acid phase digester prior to feeding the multiple methane phase digesters. This process requires the entire flow stream to be heated from ambient to about 100°F as it enters one digester, rather than heated at multiple digesters as would be the case in single stage digestion. Direct steam injection offered an efficient means of achieving that "instant" heating.

Start-up of the Pick Heaters went smooth and have performed reliably. Also, there have been no problems from plugging or erosion. The systems took up a fraction of the floor space required by conventional heat exchangers allowing for a compact and simple installation. Pick provided ongoing on-sight support during the start-up phase. The Pick Heaters provided more efficiency at lower capital cost.

 

The Solution:

Four (4) Pick 6X100-3BX Fabricated Constant Flow Direct Steam Injection Heaters

Features and Benefits:

• Instantaneous Heat Transfer
• Non-Clogging Design
• Low Capital Cost
• Less Floor Space Required
• Lower Maintenance Costs