HAND TOOL SAFETY
Most office buildings utilize an outside WT contractor, and because of this, some Engineers assume the contractor is doing their job and follow up is not necessary. But, proper WT is one of the easiest ways of providing short-term and long-term value to an operation. It is also one of the easiest ways to show documented proof that the Engineering department is helping reduce the overall costs of an operation.
A WT program's major objective is controlling scale, corrosion and microbiologic deposits. This segment of Industry News will briefly address scale in cooling tower systems.
Scale is the result of the precipitation (dropping out) of dissolved solids from the re-circulated water. When evaporation occurs in a cooling tower, only pure water evaporates, leaving behind the dissolved solids. As a result, the dissolved solids content of the remaining water increases. If a tower were allowed to operate without makeup, the entire system would eventually dry out; but, a makeup valve opens and the water in the open loop system now holds the original dissolved solids plus all those brought in by the makeup water. After a few more hours of operation, the concentration will increase even further. If this were allowed to continue, the dissolved solids concentration would increase to a point at which the water could not hold any more solids in the solution. This condition is called "saturation". When saturation is reached, the dissolved salts and minerals drop out of solution, or precipitate, and deposit as scale on tower fill, louvers, heat exchangers, tubes, and piping.
To prevent scale precipitation and deposits, we limit the number of "cycles" by bringing in additional fresh water so that dissolved solids saturation is never reached. In addition, blow down of the hottest concentrated water also reduces the amount of dissolved solids in the system. Dissolved solids are measured as total dissolved solids or TDS. Make it a point to look over the next water treatment report from your WT contractor. Become familiar with the terms used on the report. This will familiarize you with the types of readings that are being taken, and the allowable limits for those readings.
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October 2008 |
