Energy, exergy and cost analysis of flour production from wheat in Nigeria: Case study of Nigeria Eagle Flour mills, Ibadan

The significant increase in energy costs has generally contributed to an increase in the cost of production, flour production inclusive. In manufacturing industries, efforts are being made towards the reduction of the cost of energy consumed during production. This study was therefore designed to evaluate the energy requirements, operation costs, exergy losses, and propose methods for optimizing energy use in wheat flour production, using Nigeria Eagle Flour Mill, Ibadan as a case study. Analysis was carried out in three phases, pre-analysis, data collection and detailed analysis phases. A walk-through process analysis method was used for data collection and a model containing the mass, energy, and exergy balance equations were built in Microsoft Excel® 2010 to analyse data collected. Electrical energy was found to be the most used energy in both mills and the milling process was the most energy intensive in flour production, accounting for an average energy intensity of 187.49MJ/ton in Mill A and 280.37MJ/ton in Mill B. Lighting was observed to consume approximately 7% of the electrical energy supplied, prompting a lighting analysis to highlight potential energy savings. The energy cost per ton was found to be the lowest (4404naira/ton) when electrical energy from the gas plant accounted for 77 per-cent of energy input. The mill's overall irreversibility and exergetic efficiency were calculated to be 404.942KW and 15.74 percent, respectively. Only 16% of the total exergy input into the flour mill exited through product streams, 1% through waste streams, and 83% was destroyed due to irreversibilities. The B1/B2 rolling bench destroyed the most exergy, accounting for approximately 8.53 percent of the mill's irreversibility. It was established that the components with the highest waste streams had the highest irreversibilities. Minimizing waste streams would reduce the amount of exergy lost and increase the exergetic efficiency of components. To improve system efficiency, several process optimization and machine modifications were recommended.