Page 329 - Sustainable On-Site CHP Systems Design, Construction, and Operations

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wind storm blew through the area, cardboard debris from nearby trash containers must
have blown up against the cooling tower and become lodged. To compensate for reduced
flow area, the cooling tower controller began running additional fans, increasing the
electric power consumption of the cooling tower and causing the observed substantial
decrease in cooling tower electric efficiency, η , but with little effect on cooling of the
CT, elec
cooling water. As a result, the cooling tower performance decreased significantly. The
technicians remove the cardboard and dispose of it properly. They return to the control
room. The entire inspection and repair took about 15 minutes.
Fifteen minutes later at 14:30, the effect of removing the cardboard is clearly apparent
in the monitored data. The fuel utilization efficiency has increased back to 59 percent.
The heat recovery effectiveness is nearly up to its preincident level at 62 percent, and the
cooling tower efficiency and electric utilization efficiency have both nearly fully recov-
ered to preevent levels, now being 68 percent and 6.5, respectively. The chiller output is
also close to fully recovered at 1185 kW . The cooling tower inlet water and outlet
cooling
water also have nearly returned to preevent temperatures. By 15:00, all parameters indi-
cate full recovery, concluding our performance monitoring scenario.
Without the level of monitoring indicated in this scenario, the cooling tower prob-
lem would likely have persisted for some time, possibly a day, a week, or even longer.
Fuel use and costs would have increased, cooling-output would have remained low,
and equipment would have run longer and harder. Detection of many different opera-
tion faults and causes of degradation are possible with close monitoring. The key is to
provide information in real-time or short-time intervals to enable plant operators to
continually know the state of the CHP plant, its major systems and components.
To illustrate application of the capabilities provided by the CxV algorithms, we pro-
vide the scenario that entails using hot water to fire an absorption chiller for commercial
cooling. In this case, the scenario focuses on the performance of the prime mover, a small
turbine, and the electric generator to produce electricity and waste heat in the exhaust
gases as a by-product.
The system manufacturer has rated the turbine at 1 MW at which it will produce
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1.7 MW of heat captured in hot water at 257°F (125°C). The hot water is produced by
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a matched heat recovery unit. When fired at 80 percent of capacity, the manufacturer’s
specification indicates that at an outdoor air temperature of 60°F (~15.6°C), the turbine
generator will produce 800 kW and 1.36 MW of heat in hot water at 257°F (125°C).
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Upon initial start-up of the system, after allowing time for the system to reach steady
operation at 80 percent of full firing rate, the CxV system reports the following:
• Electrical output, W , is 800 kW , which is within the expected range for the
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current outdoor temperature and fuel firing rate.
• Thermal output is 1100 kW , which is below the expected range.
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Using its diagnostic capabilities, the CxV system also reports that
• Turbine exhaust-gas temperature, T , is 670°F (354°C), higher than
Turbine,ex
expected (which is 620°F or 327°C)
• Hot water temperature leaving the HRU, T , is 302°F (150°C), higher than
HRU,w,o
expected (which is 257°F or 125°C)
and recommends checking control of the variable-speed water circulation pump, which
appears to be pumping at a lower rate than necessary.