Life cycle assessment of a district heating system that utilizes waste heat recovery from Alcoa aluminum production

Abstract

Approximately 30 - 45% of the total waste heat is accessible through the exhaust gas of the Alcoa Fjarðaál smelter. The hot water requirements of Reyðarfjörður can be met using both the waste heat generated by Fjarðaál. There are two different types of district heating systems introduced: a closed loop system that runs from the plant to Reyðarfjörður but can be open- or closed loop inside Reyðarfjörður. Cradle to gate application is the chosen concept for this life cycle analysis (LCA) study which is applied to the district heating system that utilize waste heat to usable heat. The objective is to compare the energy efficiency and the environmental impact of the two scenarios defining the functional unit as 1 mega joule (MJ) of usable heat. Each component was analyzed and life cycle impact assessments (LCIA) were conducted using GaBi software to model the two systems. Comparatively, the open loop scenario is more energy efficient and has fewer environmental impacts than the closed loop scenario. In both cases, emissions were less than the current system. The closed loop system reduces emissions by 64,17%, while the open loop system reduces them by 74%. However, the open loop scenario consumes significantly more potable water than the closed loop scenario and is more vulnerable for corrosion, resulting in shorter component lifetime. Using the results from this master thesis will provide a foundation for future work, to compare the current district heating system in Reyðarfjörðar and conduct a life cycle cost analysis (LCC).