Energy-Exergy Analysis and Carbon (IV) Oxide Emission of an Aluminium Extrusion Plant in Nigeria

Abstract

Energy security, cost of production and environmental constraints have necessitated the need for proper energy utilisation in the manufacturing industries. This work analysed energy and production data from an aluminium extrusion plant in Lagos, Nigeria for energy efficiency, exergy efficiency (or process efficiency), energy cost per unit of production, CO 2 emission and pollution rate index. The input-output energy analysis method was used to estimate the embodied energy intensity. The pollution rate, energetic and exergetic efficiencies were estimated from the exergy analysis. The CO 2 emission was estimated from IPCC guideline on greenhouse inventories and the energy cost of unit produce was estimated from energy cost accounting method. The five-year average thermal and electrical utilisation ratio was 45/55, which deviated from the 70:30 of the global best practices. The embodied energy intensity for the five years’ ranges between 2.31 - 162.3 GJ/t which is in excess of the recommended range of (2.9 - 3.2 GJ/t). The mean energy efficiency for the five year was 79.4% and the mean exergetic efficiency was 57.8% indicating that production was well managed (>50%) with energy wastages very high in boiler energy conversion. The total energy used was 16 MJ and CO 2 emitted is 1.01 × 10 11 g during the study period. The average pollution rate index for the plant was 0.8695 indicating that the plant is negatively impacting the environment due to technological limitation of the energy conversion process employed in the manufacturing plant. The study reveals a distortion of the recommended best practice in energy balance ratio which accounted for the high average cost of production ( N 4418.3/t); process efficiency was generally low thereby negatively affecting industrial output for the company.