Birmingham, United Kingdom, July 11, 2010 --(PR.com
)-- The hyperbolic cooling tower water at a major coal power-fired power station had traditionally been treated with gaseous chlorine prior to recirculation. When the time came for this system to be updated it was decided to move to a safer, gasless system which would instead dose liquid sodium hypochlorite. This was known to be far more cost effective than upgrading the current chlorine gas system, far safer due to the nature of the chemicals involved and much, much quicker to achieve.
Immediately, however, a number of challenges presented themselves.
Firstly, due to the lack of available space within the chemical house for the installation of a new dosing system it soon became apparent that the only place it could conceivably go would be in the chlorine house next to the existing gas dosing system. This meant that part of the gas system would have to be stripped out to create sufficient room.
This in turn created the second problem. During this ‘changeover’ period from the old gaseous chlorine dosing system to the new liquid hypochlorite dosing neither system could be online, meaning that the cooling tower water could not be treated.
If the water could not be treated prior to recirculation there could have been significant implications. Water exposed to the atmosphere can frequently contain the Legionella bacterium which in its own right can cause health problems.
The principle problem for an industrial site like this, though, would be the greatly reduced efficiency of the systems caused by biofouling – an unwanted build-up of biological contaminants such as microorganisms and algae. The interior of a hyperbolic cooling tower contains a series of wooden inserts designed to allow the water to cascade down, mixing it more freely with the air and thus cooling it more efficiently. Biofouling can reduce the heat exchange efficiency of the system. If this biofouling was allowed to spread to the heat exchange surface it may result in fouling. This in turn can lead to hot-spots, under-deposit corrosion and then, potentially, catastrophic failure.
The station’s operators were determined to proceed with the changeover, however, due to safety issues with continued chlorine dosing, but to install a traditional system – including transporting the storage tanks to the site, pouring concrete for the bund and waiting for it to cure and arranging the cabling between the tanks, the dosing pumps and the control system – the preparatory site work alone could have taken around 6-8 weeks and would have been heavily dependant upon the weather. That would be over a month when they wouldn’t have been able to treat the cooling tower water at all.
This was not acceptable. All parties agreed they needed a far swifter turnaround.
Gee's novel solution was to build a skid mounted Package Plant dosing unit that carried the two PVC GRP sodium hypochlorite storage tanks and the dosing skids, all carried above a mild-steel GRP-lined bund. A system like this could be manufactured at their Holborn Hill site, could be fully factory tested prior to despatch, and then Gee staff themselves could deliver the completed system to a holding area immediately outside the chemical house. Once the existing drum store was taken out the new Package Plant dosing system could be slid into its place, the power and telemetry could be connected and the system brought online.
This proposal was approved and put into action. By building the system off-site and fully factory testing it Gee were able to use the power station’s control logics so, in effect, the SCADA linkage was connecting to their existing control room from where they got the control logic to run it. As Gee were upgrading the control system for the power station concurrently it presented no problem to link into this.
The new system was installed, tested and then brought online which allowed all normal operations at the power station to continue without interruption. The significant cost saving were delivered as promised and the new, safer chemical dosing system met all of the criteria that had been set by the station’s owners.