Retrotec USACE - Manual (Page 174)

D44 ENERGY & PROCESS ASSESSMENT PROTOCOL
cooled below the dew point, water in the air condenses on the coil and runs
down the fi ns of the coil to the drain pan. This water can be collected from the
AHUs and used for plant irrigation, cooling tower makeup, and so forth.
D.4 Energy Generation and Distribution (Covers Central
Energy Plant and the Related Distribution Systems)
D.4.1 Boiler Systems
D.4.1.1 More Than 5% Boiler Water Blowdown (Waste)
Figure D69. Water blowdown from boiler is
discharged to nearby drain.
Steam heating systems require that some of the boiler water be discharged for
the removal of sludge and concentration of dissolved and suspended solids. As
steam is generated, the chemicals in the boiler water become more concen-
trated. If the concentration gets too high, the chemicals can begin to precipi-
tate out of the water and collect on the inside boiler tubes, which affects the
boiler effi ciency. To maintain the chemical solution at acceptable levels, boiler
water should be removed and replaced with fresh water. This removal is called
“boiler blowdown.” Often an excessive amount of boiler water is thrown away
so that the chemical concentrations are well within safe limits (Figure D69).
The removal of excessive boiler water wastes the heating energy required to
raise the temperature of this water to boiler temperature. The blowdown rate
depends on the system pressure, alkalinity, silica, and iron oxide limits and the
concentration of these chemicals in the makeup water.
D.4.1.2 Failure to Return Condensate (Waste)
The condensed steam is collected at a condensate receiver and pumped back
to the boiler plant in good steam distribution systems (Figure D70). Failure to
return the condensate wastes heating energy and requires additional chemicals
for water treatment. At times the condensate is not returned due to leaks in the
condensate return piping, due to malfunctioning condensate return pumps, or
by design. If a steam user is too far removed from the condensate return piping