Abstract
Applying Rankine cycles to smelter off-gas could increase the required off-gas fan power in an order of magnitude equivalent to the power production. Predicting the fan power is not straightforward since it is affected in two contradictory ways: 1) the heat recovery heat exchanger creates additional off-gas pressure loss, increasing fan power; 2) off-gas cooling reduces pressure loss in the off-gas handling system downstream of the cycle, reducing fan power. The purpose of our study is to analyze the effect of fan power on optimum system performance. While additional fan power can be calculated based on heat exchanger pressure loss, the reduction in fan power depends on the total pressure loss downstream of the cycle, which is unknown. As an alternative to calculating fan power reduction, we account for the off-gas cooling effect by including only parts of the fan power caused by heat exchanger pressure loss. Results from three cases show that both heat exchanger and cycle performance strongly depend on the potential for downstream pressure loss reduction. Thus, the total pressure loss in the downstream off-gas handling system has a significant impact on the optimum heat exchanger and cycle performance, and should be accounted for during system design.
Highlights
The aluminum industry is one of the most energy intensive industries in the world [1], and accounts for around 3.5% of global electricity consumption and 1% of global CO2 emissions [2,3]
We evaluate different downstream conditions, and different potential for fan power reduction, by including only parts of the fan power caused by heat exchanger pressure loss
To evaluate different boundary conditions, we investigate three cases that include different parts of the fan power caused by heat exchanger pressure loss: Case 1. : his hin hin À hout À hðpout; sinÞ
Summary
The aluminum industry is one of the most energy intensive industries in the world [1], and accounts for around 3.5% of global electricity consumption and 1% of global CO2 emissions [2,3]. Around half of the energy input to aluminum smelters is lost to the surroundings as surplus heat [5e7]. Recovering this surplus heat could significantly improve energy efficiency and reduce emissions in the aluminum industry. The two most efficient ways of utilizing surplus heat are direct re-use at the same temperature level and upgrading to a higher temperature level using a heat pump. Such reutilization is limited in the aluminum industry owing to the low quality of rejected heat and a lack of nearby demand for heat [5]. Further research is necessary to pave the way for cost-efficient and large-scale surplus heat utilization in the aluminum industry
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