The theoretical absolute limit of evaporation is dictated by the amount of water that the air can hold until saturated. For an average size unit, this is typically 3 kg/s per machine, averaged over a year. Practically this limit is never reached for the following reasons:
- Any atomisation process results in a size distribution of droplets. A certain amount of water that is atomized into large droplets will therefore always fall out.
- In any process of exposing droplets to the environment (cannon, fracturing fan, nozzles), the exposure is decreased by wind speed. Therefore, at high wind speeds more water can be evaporated, but not directly proportional to the wind speed.
- Depending on the sensitivity of the site, an evaporation plant might not be allowed to evaporate in high wind speeds due to drift and overspray. This could lower the effective operating time of a plant.
- Some technologies (such as the cannon type) cannot evaporate into the wind. The wind direction could therefore also limit the effective operating time.
The simple claims in the evaporation industry that a certain percentage of the pumped water is evaporated can be very misleading.
The Enervap proprietary prediction software takes all the factors into account. This includes the following:
- Atomisation and droplet distribution, for any technology.
- Influenceof the wind on droplet exposure.
- Influenceof drift sensitivity on the available operating time.
- Influence of the type of technology on the operating time (land based vs. pond based, cannon vs. fracturing).
- Daily and monthly variation in the wind speed, relative humidity and temperature.
Enervap evaporation prediction software has been validated through numerous tests, both locally and internationally.
DRIFT PREDICTION & ENVIRONMENTAL SENSITIVITY
Since forced evaporation is an open process, droplets cannot be indefinitely small or be blown indefinitely high, as this could result in overspray and environmental contamination. This is especially true on environmentally sensitive sites, where all water needs to be contained within the dam for which water use licenses have been issued. In situations where the release of water is not an option, evaporation can be a cost effective solution. In such cases overspray is, however, not an option.
The use of validated prediction models, site layout planning and technology selection ensure that the required plant capacity is obtained while remaining within the environmental limits.