A feasibility study of running a small-scale water purification unit with base station waste heat

Abstract

In this thesis, the potential of reutilizing waste heat from base stations to purify water is studied. Nokia’s recently developed liquid-cooled base station is used as heat source to drive a small-scale air gap membrane distillation unit (AGMD), a thermally driven water purification technology. The temperature difference over a hydrophobic membrane is the driving force inducing a part of the water to vaporize and transfer through the mem-brane. Then is a clean distillate produced, leaving the contaminants and other solutes in the hot stream.

The results from the experimental study show that 1.6 kW of heat can be transferred from a 3-kW base station, which results in a water distillate production of 1 l/h from the AGMD unit. This production is achieved since the hot water stream can be heated to 58°C, having the cooling water at 25°C. The dependency of the water production rate on the temperature difference over the membrane, was confirmed in the measurements - the larger the cross-membrane temperature difference, the higher the water production rate. The results of testing the base station-MD prototype also demonstrated a high sep-aration efficiency of the MD technology, decreasing the conductivity, of both tap water and seawater (0.32% -salinity), to the levels of highly purified water (HPW). Increasing the feedwater contamination level was found to slightly affect the performance of the prototype regarding the production rate.

The system of the base station driving a MD unit (BS-MD) was found to be a promising concept for future base station installations. It gives an opportunity to provide simulta-neously both connectivity as well as fresh water, and is thus a suitable concept for re-mote and arid locations where access to clean water is limited. Using waste heat in a secondary application saves both in energy costs of the secondary process, as well as reduces the carbon footprint of the base station. It can also reduce the production costs of clean water when compared to business cases where conventional energy sources are used.