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City of Nashua, Public Works Division
Board of Public Works Meeting Date: December 16, 2021
David L. Boucher, Superintendent
Wastewater Department
Digester Heat Exchanger
To approve the purchase of one digester sludge heat exchanger (Asset ID:
PDSHX) in the amount of $57,000 from Alfa Laval Inc. of Richmond, VA for the
primary digester. Funding will be through Department: 169 Wastewater: Fund:
WERF; Account Classification: 81 Capital Equipment.
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The heat exchanger located at the base of the primary anaerobic digester transfers
heat from the energy recovery generators and boiler to the solids in the digester.
This maintains the temperature of the digester to an optimal 99 degrees, which is
best for decomposition of the solids and for gas production. This heat exchanger,
which was purchased in 2011, developed a leak in 2016 which was able to be
welded and has lasted us to this year. Recently another leak has developed, which
is not able to be welded in place. We have used a temporary epoxy while we line
up the replacement.
The Wastewater Department is proposing to purchase a new heat exchanger to
replace the one that has reached the end of its useful life. The new exchanger must
match the size and capacity of the existing heat exchanger and is an in kind
replacement. Alfa Laval is the sole source for this purchase, at a cost of $57,000.
