COOLING TOWER UPGRADING: A TIMELY TOPIC
Do you need more air out of your cooling tower? Do you have increased process demands? Obsolete or inefficient fans? Strict noise specifications?
There are numerous reasons to consider cooling tower upgrading. With everyone feeling the pinch of reduced budgets along with increased production demand, and trying to do more with less, a short discussion of cooling tower performance may be in order.
Much can be done to upgrade an existing cooling tower by changing only the fan or the fan and drive system. Upgrading is generally simple, inexpensive and requires little downtime. Several options are:
1. Replace obsolete fans:
Many fans in service were originally produced by companies that are no longer in business, and many of these older fans suffer from low efficiency as well. Replacing such a fan with a higher efficiency power shaving Maya fan may be the only requirement. Several prominent INDIAN refineries have tried this approach and been pleased with the results. A fan can typically be installed in less than 3 hours, resulting in a minimum of down time.
2. Meet lower noise requirements:
Many fans in the field were designed and installed when occupational noise was not an issue. With today’s tougher noise standards, plant operators have shown a desire to switch to lower noise fans. Generally, it is required to change only the fan along with the drive ratio (increasing the number of blades and decreasing the RPM) to achieve this. Even greater savings are available with “MAYA” blades.
Before increasing airflow, it is advisable to contact the technical assistant to determine the effect of increased flow on motor and gearbox conditions. A larger motor may require changes in the shaft and wiring. In many cases, flow can be increased and noise reduced at the same time. For instance:
Consider a fan providing 120,000 ACFM (56.6 m3/sec) at 0.5" static pressure. A 12-ft 4-blade fan operating at a tip speed of 12,000 FPM (61.0 m/sec) can be replaced by a 9-blade fan operating with a tip speed of 8,290 FPM (42.1 m/sec). This would result in a 20% increase in flow to 144,000 ACFM (68.0 m3/sec) and a 40% increase in static pressure (to .72" static), while the noise level is reduced by 3 dBA.
3.Cooling tower cleaning is important, too:
Before rating a replacement fan for a cooling tower, we recommend checking for fin cleaning. Dirty, clogged fins decrease cooling capacity in several ways.
First, dirty fins increase the resistance to air flow and may increase the static pressure well above what the fan was designed to handle, resulting in fan stall and a marked decrease in flow and cooling capacity. Dirty fins also decrease the heat transfer coefficient, requiring more airflow to dissipate the required heat load.
Regular cleaning is good practice and is an integral part of a fan retrofit.
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