Note: Technical notes are aimed at promoting discussion.

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Technical Note necessarily those of the editors or the Australian Acoustical Society. Contributions are not
formally peer-reviewed.

LOW NOISE FANS FOR UK COOLING TOWERS

Martin Huis in ‘t Veld
Sales Manager Retrofit, Howden Netherlands b.v.

Connah’s Quay is a 4x345MW combined-cycle power plant fan speed at all time leading to unnecessary low water
situated on the River Dee estuary in Wales, United Kingdom. The temperatures, power consumption and noise emission.
plant has been operational since 1996. It has hybrid cooling towers The major goal was to improve the power plant’s efficiency and
to reduce visible plume and special routines for cooling water reduce the visible plume of the cooling tower, without increasing
makeup withdrawal. Each generating unit is supported by two the existing noise emission. To achieve this goal, the following
adjacent cooling towers comprised of five cells above a common actions were recently taken:
pond, making 10 cells per unit. Figure 1 shows a schematic • The fan outlet attenuation baffles were removed, increasing
diagram of the hybrid cooling tower and the cooling cycle of the the air flow through the cooling tower pack and reducing
Connah’s Quay power plant. the mechanical stresses during start-up.
• The existing fans were replaced by Howden ultra low noise
SX-Series fans in order to operate within the constraints set by
the Environment Agency without the attenuation equipment.
• With the Howden SX fans in place, the existing gearboxes
became the dominant noise source at the fan outlet. To operate
within the constraints set by the Environment Agency, they
were refurbished to a new low noise specification.
• The lower sound power level of both the fan and the
gearbox allow adaptation of the dry section attenuation,
increasing the warm air flow to the mixing plenum. This
increases the outlet air temperature while reducing the
outlet air humidity and subsequently reducing the visible
plume generation.
Since the fan noise is primarily related to operating speed, it was
decided that the original fan drive and gear box ratio would be
maintained. Although the air supply increased with the installation
Figure 1.Schematic diagram of the hybrid cooling tower and cooling cycle. of the SX fans, the aerodynamic performance remained almost
unchanged as the static pressure loss was reduced due to
the removal of the noise attenuation baffles. Figures 2 and 3
The cooling tower air flow was severely restricted by noise
respectively show the previously existing noise attenuation baffles
attenuation, due to the environmental constraints imposed during
at the fan outlet, and with the installation of the low noise SX fan
the construction of the plant because of the close proximity of local
instead of the attenuation baffles. Table 1 illustrates the improved
residents. The noise attenuation equipment adds static pressure
airflow and noise reduction achieved through the use of Howden’s
loss to the system and reduces the thermal efficiency of the tower,
ultra low noise SX fans. The total sound power was improved
leading to the generation of low level plume and contributing to
even with the removal of the noise attenuation baffles.
major failures in the fan drive trains. The detrimental effects on
plant and performance due to the restriction of the airflow can be
summarized as follows:
• The water/air ratio required to achieve optimum
performance is not being achieved.
• At times the tower operates very close to the point where
low level plume will be generated.
• The restriction to air flow in the fan outlet stack induces
mechanical stress in the fan drive train, contributing to a
high level of failures especially during start-up of the fan.
The repairs often require the removal of the attenuation, the
fan and the gearbox. This leads to major production losses.
The engineers are therefore reluctant to shut down the fans
as a way of controlling the cooling tower during hours of
Figure 2. Noise attenuation baffles at fan outlet.
reduced ambient temperatures. Instead, they maintain 100%

Acoustics Australia Vol. 39 August (2011) No. 2 - 75

 • Production losses because of repairs will be reduced to a
minimum. As a consequence, the reliability of the plant
will rise significantly.
In summary, the benefit of the installation of the super low noise
fans is twofold. The SX impeller performs a similar duty with a
significantly lower sound power output. Improved airflow and
noise reduction was achieved without any need for changing the
fan speed or gear box ratio. It is expected that the entire cost of the
modification will be recovered in seven years through efficiency
gains alone. In addition, there will be additional savings arising
from other factors. The fans can now be shut down whenever
required without the risk of stress failure when they are restarted,
avoiding unnecessary power consumption. The modification also
eliminates the cost of major repairs and production losses.

ACKNOWLEDGEMENTS
This case study is a publication of Howden Netherlands.
Special thanks are due to the Plant Manager, Mr Pacey, and to the
Project Engineers, Mr Stevens and Mr Barrow of Connah’s Quay
Power Station for making this publication possible.

For further details on Howden fans, please contact

Peter Yallamas, Howden Australia
Email: p.yallamas@howden.com.au

Figure 3. SX fan instead of the attenuation baffles.

Table 1. Fan data before and after installation of the SX fans.

Fan Type Original Fan SX Fan

RPM 89.9 89.9
Volume flow (m3/s) 465 500
Static pressure (Pa) 163 147
Sound power level fan (dB(A)) 101.3 93.7
Attenuation baffles (dB(A)) -7 Baffles removed
Total sound power level (dB(A)) 94.3 93.7

With the introduction of the new cooling fans, the temperature

of the cooling water system was improved by 1.4˚C. This improved
efficiency by 0.13%, which equates to a combined cycle output
improvement of 0.8MW. The efficiency figures may appear
low, but in reality they represent a significant improvement. The
projected results are as follows:
• The steam-turbine will be more efficient, and consequently
the gas-turbine consumes less gas.
• The reduction in gas consumption will reduce CO2
production by 7,500 tonnes per year.
• The incidence of low level plumes will drop from ± 142
days to ± 23 days due to the improved water distribution
alone. The fan exchange will further reduce this to ± 6 days.
• Maintenance costs are expected to drop dramatically.
Savings will also be made by preventing unnecessary
power consumption.

76 - Vol. 39 August (2011) No. 2 Acoustics Australia