POWER June 2010 - 26

7. Maximum power as a function of humidity and inlet
air temperature. The DOE results map illustrates the power
predicted for an engine for a given set of site conditions as a function
of humidity and inlet air temperature in coded values. This prediction
is important to understand because the ambient conditions from site
to site, or even at a single site, can vary greatly. The figure shows that
the highest power output of the engine is achieved when the inlet temperature
and humidity are both low. Inlet air is denser under these cool
and dry conditions than when it is hot and damp, allowing the engine to
induct more air to burn with more fuel. The data are shown in terms of
percent variation from a design point for proprietary reasons. Source:
Dresser Waukesha and State-Ease
1.0
280 kW
140 kW
0.5
180
190
200
210
220
230
240
250
0.0
270
-0.5
250
240
230
-1.0
-1.0
-0.5
0.0
Ambient air temperature
9. Keep it clean. An oil skimmer separates oil from water before
discharging water back to the Arkansas River, keeping the North Little
Rock Electric Department in compliance with its environmental water
discharge permit. Courtesy: Abanaki Oil Skimmers
0.5
0.1
-0.50
-1.0
-0.5
0.0
Fuel lower heating value
(Figure 9) for over 10 years. The system has proven to be a dependable
and effective means of removing oil from the plant
water before it is discharged back into the Arkansas River. Before
Abanaki, a floating skimmer was used at the plant, although it
required significant maintenance. Now plant workers appreciate
the design of the Oil Grabber Model 8 for its high reliability and
its light maintenance schedule.
Another advantage of the Model 8 is its easy mounting in a
small footprint, making it ideal for cramped quarters. The Oil
Grabber Model 8 is situated in a retention sump that catches oil
leaks at a rate up to 40 gallons per hour from any hydraulics,
always a distinct risk in a hydroelectric facility.
The operation of the Model 8 is very simple. Oil skimmers make
use of the inherent surface tension and specific gravity differences
between oil and water. These physical characteristics allow
the skimming media to attract oil from the water's surface.
A belt, operating on a motor and pulley system, runs through
the water. After traveling over the head pulley, the belt passes
through tandem wiper blades, where oil is scraped off both sides
of the belt and collected in a container.
After the skimming stage, the water is pumped into holding
tanks and processed through a dedicated oil/water separator before
the water can be released back into the river. The staff noted
that this final filtering stage has not been used much since the
Model 8 was installed. Since the Oil Grabber was installed, the
skimmer removes the majority of the oil from the sump before it
is processed further. This means that the separator doesn't have
to run as long and doesn't need to be cleaned as often. ■
-Contributed by Abanaki Oil Skimmers.
26
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POWER | June 2010
0.5
0.1
260
-0.25
0.00
260
240
220
200
180
280 kW
140 kW
0.25
280
8. Maximum power as a function of fuel heating value
and air/fuel ratio. The DOE results map illustrates the predicted
power as a function of fuel heating value (LHV) and air/fuel ratio (O2
offset) in coded values. Since the engine can be applied in applications
that run on low-energy-content landfill or digester fuel gas in which the
fuel quality can fluctuate, it is also important to understand how the fuel
heating value and air/fuel ratio affect maximum power. For this engine,
the air/fuel ratio required to reach the maximum power output changes
with the lower heating value of the fuel. The lower the energy content
of the fuel, the richer the air/fuel ratio must be to reach the same power
output. Data are shown in terms of percent variation from a design point
for proprietary reasons. Source: Dresser Waukesha and State-Ease
0.50
220
240
260
Relative humidity
Oxygen offset
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POWER June 2010

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