To:
From:
Re:
B Motion:
Discussion:
City of Nashua, Public Works Division
Board of Public Works Meeting Date: October 27, 2016
Noelle Osborne, Plant Operations Supervisor
Wastewater Department
Digester Heat Exchanger
To approve the purchase in the amount of $37,600 from Alfa Laval Inc. of
Richmond, VA to supply one digester sludge heat exchanger (Asset ID:
PDSHX2) for the primary digester. Funding will be through Department: 169
Wastewater: Fund: Wastewater; Account Classification: 71 Equipment.
The heat exchanger located at the base of the primary anaerobic digester transfers
heat from the 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. The function of this digester reduces the volume of
solid waste to the City by approximately 60%. It additionally allows us to classify
our solids as “Class B” meaning we can land apply. Both of these are cost savings
to the City. Currently this heat exchanger has no redundancy. The one online,
which was purchased in 2011, developed a leak this year that was, fortunately,
repairable and was welded. If this were to fail, the lead time on this product is
close to five month and would have an astronomical financial impact to the City
of Nashua
For these reasons, the Wastewater Department is proposing to purchase a second
heat exchanger to have on hand in the event of failure. The new exchanger must
match the size and capacity of the existing heat exchanger. Hence Alfa Laval is
being sole sourced for this purchase.
