Evaporation enhancement from evaporation ponds using collector plate units

摘要

Water is vital for human activity. In the past abundant fresh water supplies were believed to be limitless. In the last two decades dwindling reserves of freely accessible water at the surface and subsurface environment have raised community awareness about the need to ensure that industrial production operates in a sustainable way that won’t constrain the development and sustainability of regional cities and towns that draw on downstream ground waters for their potable and non potable water requirements. In this paper, a method of augmenting the widely practiced evaporation pond approach is investigated for disposing of brine wastewaters to improve the sustainability of industrial operators employing this practice. The approach involves the adoption of solar plate collector technology. The solar technology referred to as unglazed transpired collectors (UTCs). It may be considered a hybrid concept as it’s a UTC except inclined like a typical solar collector plate. A pilot scale collector plate unit was designed and constructed to evaluate the enhanced evaporation capabilities of a collector plate unit (UTCs). The experimental program covered a 14 month study period from June 2005 to August, 2006. This research investigated the ability to enhance evaporation using three different brine concentrations (3.5% NaCl, 7.0% NaCl and 12.5% NaCl), and three film heights (0.15 mm, 0.2mm and 0.3 mm) over a 14 month experimental period between June 2005 and August 2006. The research investigated the relationship between key weather parameters, solar irradiation (MJ/m2/d), wind speed (m/s), ambient air temperature (°C), and relative humidity (%), and enhanced evaporation and collector plate evaporation from the collector plate unit. Data analysis found weather conditions low in relative humidity (less than 40%), high in total incident solar radiation (greater than 20 MJ/m2/d), steady, constant wind speeds (between 1.1 and 1.3m/s), and high daily average air temperatures (greater than 25°C) would generally produce evaporation enhancement ratio (EER) results between 2.0 and 3.0 for brine solutions with concentrations up to 7.0% NaCl. The peak EER result of 3.01 (achieved during summer) equated to the collector plate unit achieving a rate of evaporation 301% higher than an equivalent surface area of evaporation pond containing similar brine wastewater and subject to similar weather conditions. The mean EER result over the 14 month sampling period was 1.52. The research found in the scenario where 100 nr collector plate 1 m2 units were connected to an evaporation pond covering 20,000m2 and 1 m in depth, subject to typical Melbourne CBD weather conditions, and a testing period of 100 days. The collector plate unit had the potential to reduce the surface area by 0.44% representing an 88m2 reduction in surface area for the 1 m deep evaporation pond. An energy balance was developed for the collector plate unit that considered energy in and out of the unit, by way of solar radiation, convection and evaporation. It was found the collector plate lost over 49% of its energy to evaporation as compared with 76% by the evaporation pond due to evaporation under the same weather conditions. The research found collector plate technology had the potential for augmenting existing and future evaporation ponds located in regions and countries where the meteorological conditions are favourable to evaporation.