POWER May 2016 - 55

FUNDAMENTALS
2. A nozzle and lateral system above counter-flow fill packs. Courtesy:
Kevin Boudreaux, Nalco Co.
4. Foul. This circulating water pump's Inlet
screens are fouled with algae and solids.
Courtesy: Peter Ten Eyck, Nalco Co.
but it is one that is routinely seen throughout
the field.
Not only can cooling tower efficiency affect
condenser operation, but the ancillary
components of the cooling tower, in this case
recirculating water pump inlet screens (Figure
4), can also affect condenser performance.
In the following example, the subject unit
3. Read the signs. This photo shows both flooding (green circle) and starving (red circle)
of high-efficiency fill. The nozzle above the flooded area was broken off. Courtesy: Kevin Boudreaux,
Nalco Co.
uses a mechanical draft cooling tower with
Mississippi River water makeup. Although
the makeup water is normally clarified, total
suspended solids (TSS) do carry over during
clarifier upsets and accumulate in the bulk
water, further increasing the risk of fouling
equipment such as circulating water piping,
screens and filters, heat exchangers, and
cooling tower fill. To complicate the issue,
algae control in this particular system is very
difficult, increasing the potential for TSS adherence
to surfaces.
At this particular unit, the circulating
water pump inlet screens were becoming
obstructed with a TSS/algae agglomeration,
causing a reduction in circulating water flow.
That meant that each pound of water passing
through the condenser would then pick up
more heat than it was designed for. The result
was a rise in the outlet water temperature,
operating BP, and, subsequently, BP penalty
(the difference between the operating and expected
BP with design flow rates, Figure 5).
The increase in BP, 0.5 inHg in this exbiological
growth propagate. Conversely,
there are cases where nozzles have broken
off, or otherwise do not provide the proper
spray cone, which causes zones of flooding.
Whether starved or flooded, the L:G ratio is
adversely affected and cooling tower performance
degrades, directly affecting the plant's
overall heat rate.
Given the cooling tower's importance, inspecting
it online to identify poor water disMay
2016 | POWER
tribution is critical and a fairly simple task
(depending on the configuration, of course).
By walking the perimeter of the basin and
peering within the basin sections, it is easy
to determine if an area is flooded or starved.
Offline inspection is obviously easier, as long
as the inspector knows the signs of flooded/
starved sections (Figure 3).
Poor flow distribution is just one example
of how cooling towers affect plant operations,
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ample, means more Btus were being lost to
the cooling water instead of being transferred
to the steam turbine-the basis for the Carnot
principle. Assuming a derate condition,
the Btus lost equated to nearly 1.5 MW/hr
(Figure 6), or a decrease in revenue in excess
of $38,000 over a 30-day period. If considering
an efficiency loss and not a derate, the
degradation in heat rate was approximately
0.4% (Figure 6), or a monthly excess fuel expenditure
of over $30,000. Neither a derate
nor excess fuel cost is welcome, especially
for something so easy to monitor and fix.
It should be noted that the plant originally
determined the efficiency loss to be a condenser
issue, due to the increase in operating
55

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POWER May 2016

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