Energy Monitoring in Gins - 2011

Authors: Hardin Iv, Robert; Funk, Paul

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2012
Publication Date: 5/1/2012
Citation: Hardin IV, R.G., Funk, P.A. 2012. Energy Monitoring in Gins - 2011. In: 2012 Beltwide Cotton Conference, January 3-6, 2012, Orlando, Florida. p. 641-650.

Interpretive Summary: Energy costs are the second largest source of variable costs for cotton gins, with electricity and dryer fuel accounting for 27% of variable costs. Energy use has typically not been a major consideration in gin design; consequently, a significant opportunity exists to improve gin profitability by reducing energy use. Studies of gin energy use have been conducted previously; however, this research only used data from utility bills or a single measurement during the ginning season. More comprehensive research is needed to understand causes of variation in electricity use at gins and identify specific opportunities in gins for energy conservation. In this study, electricity use was monitored throughout the 2010 and 2011 season for several gins across the cotton belt. Motor loads were recorded for the large motors in gins: gin stands, fans, cleaning machinery, module feeders, and bale presses. Total power consumed by the gins was also monitored. Fuel consumption was estimated at two gins during the 2011 season by measuring temperatures and air flow rates. In 2010, the gins averaged 35.8 kWh/bale, slightly less than the average electricity use, 40-56 kWh/bale, reported in past surveys. Differences in electricity use between monitored gins were likely due to differences in layout and installed equipment. The breakeven idling time, the maximum length of time that gin equipment should be allowed to run idle instead of being shut down, averaged 12 minutes. Both gins monitored in 2011 used slightly less electricity than in 2010. Plant modifications had been made that increased processing rate or reduced power demand. Average propane (LPG) use by the first stage drying system was 0.41 gal/bale. Only one of the gins operated the second stage drying system, using 0.09 gal/bale. Processing rate was the primary factor affecting electricity use per bale and also significantly affected dryer fuel use. Managers should operate gins at full capacity as frequently as possible and avoid idling equipment for long periods. Material handling uses over one-half of the electricity in gins because pneumatic conveying is inherently energy intensive. Replacing fans used for pneumatic conveying with mechanical conveying systems can significantly reduce energy use. While some cleaning of seed cotton and lint is required to produce acceptable grades, bypassing unnecessary cleaners can also reduce energy use. To maximize processing rate and minimize fuel use, seed cotton must be properly stored so that cotton enters the gin at a suitable moisture content.

Technical Abstract: Energy costs are the second largest source of variable costs for gins, accounting for 27% of variable costs. Energy use has typically not been a major consideration in gin design and previous studies of energy use have utilized instantaneous readings or aggregated season-long values. Electricity use was monitored throughout the season for several gins across the cotton belt in 2010 and 2011, while fuel consumption was measured at two gins during the 2011 season. Motor loads were recorded for gin stands, fans, cleaning machinery, module feeders, and bale presses. Power consumption and power factor were recorded at motor control center disconnects. Temperatures and air flow rates in drying systems were measured to estimate fuel use. In 2010, the monitored gins averaged 35.8 kWh bale-1, slightly less than the annual average values reported in past surveys. The breakeven idling time varied from 7.6 to 16.6 min. Gins monitored in 2011 used slightly less electricity than in 2010, likely due to plant modifications. Differences in electricity use between monitored gins were due to differences in layout and installed equipment. Average LPG consumption by the first stage drying system was 1.54 L bale-1 (0.41 gal bale-1). Only one gin operated the burner for the second stage drying system, using 0.35 L bale-1 (0.09 gal bale-1). Processing rate was the primary factor affecting electricity use per bale at a specific gin and also affected dryer fuel use. For maximum energy efficiency, cotton ginners should operate at full capacity as much as possible and avoid idling equipment during significant downtime.