A dynamic thermal model for heating microalgae incubator ponds using off-gas

Many industrial processes, such as power stations and ore smelters discharge large outflows of “waste” heat in off-gasses rich in CO2. There is, however, rapidly growing interest in the mitigation of this CO2, including using it to enhance the growth of microalgae for producing biodiesel. The use of off-gas to support ponds that act as microalgae incubators could represent a significant benefit to an industry’s operational economics and the environment. However, many generators of off-gases, particularly those related to mining, are located in regions, such as in South America, Northern Europe and Canada that experience long periods of temperatures well below those optimal for microalgae growth. Under these conditions, utilization of the heat in the off-gas to maintain water temperatures in microalgae ponds represents a new approach to beneficially exploit this otherwise waste energy. A dynamic model for a distributed temperature profile of a microalgae incubator pond bubbled through with off-gas was, therefore, developed using energy conservation laws. Simulations were carried out to evaluate pond temperatures in response to changes in gas flow rate and temperature, as well as annual variations in air temperatures and solar radiation. The results demonstrate the feasibility of significantly extending the operation of a microalgae production facility through the year beyond what would be possible without the use of the off-gas.