Heat Balance Analysis of Annealing Furnaces and Zinc Pot in Continuous Hot Dip Galvanizing Lines

Hot dip galvanizing facilities have energy intensive operations with electrical and gaseous or oil fuel energy representing a significant share of total energy usage. Benchmarking galvanizing energy consumption and understanding the specific energy consumption is important. The enhanced galvanizing energy profiler decision support system (E-GEPDSS) was developed to identify specific energy consumption through comprehensive heat balance analysis. The results presented in this article will assist users make energy efficient decisions for product, process and system level parameters. This research on the analysis of galvanizing operations focused on the annealing furnaces and zinc coating pot (hereafter referred to simply as the "pot") for energy consumption. The heat balance model was developed and applied using data collected from various manufacturing plants. Sensitivity analysis was performed to study the impact on heat loss from the hot dip galvanizing system of changing the product, process and system level parameters. Based on the results produced by E-GEPDSS for the manufacturing plants, it was found that less than 50% of heat supplied to the furnace is absorbed by the product; the remainder of the input heat energy dissipates as losses. Heat loss from the wall surfaces and flue gas stack was found to be significant, while heat lost due to opening and phase changes were minimal. In the case of zinc pot analysis, when there is no pre-melt pot, the largest heat loss was associated with the ingot melting process and the energy system required to maintain constant pot temperature. When there is a pre-melt pot in the process, the largest heat loss in the main pot is from zinc coating. Using the heat balance model, galvanizing manufacturers will be able to identify opportunities to reduce these losses for energy savings and optimize energy system performance. Emissivity, di mensions of the furnace, pot temperatures, furnace zone temperatures, thermal conductivity of insulation materials and steel strip temperature at the entry and exit at each zone have significant impact on the total heat loss.