Converting from electric to gas drying for energy savingsConverting from electric to gas drying for energy savings
September 22, 1998
Twinpak converted an existing electric dryer to use a Conair GasTrac process air heater. The molder of PET preforms saved by switching to the less expensive natural gas but also freed up electrical capacity for additional molding machines.
One of the big advantages of converting electric dryers to run on gas is the relative affordability of natural gas, especially in a city like Calgary. But a recent conversion to gas at Twinpak Inc.'s PET bottle plant also allowed the big molder to install additional molding capacity without upgrading the plant's electrical system.
Gary Kooistra, project engineer at Twinpak, reports, "We'll have to upgrade the electrical system eventually, but we didn't have to do it this year." That was thanks in the most part to the recent conversion of an existing dryer to a Conair GasTrac process air heater. Kooistra calculates he saved about $800 in the first month after converting to gas and another $1072 in the second month (all dollar figures are expressed in US$).
He calculated the savings by installing a separate gas meter on the GasTrac unit. With the help of the gas company, Kooistra calculated the number of gigajoules (gj) of heat produced by the gas consumed. Once you know the gj, that number can be converted readily to kilowatts for comparison.
Using an average electrical cost of $3.32/kW and a relatively conservative 80 percent efficiency factor for the gas burner, Kooistra's energy savings formula looks like this:
gj x (1000/3.6) x .8 = kW
then, kW x $3.32 - gas cost = savings
Based on early results, Kooistra is hoping to soon convert five other electric dryers to gas heating. "Our electrical rates, I think, are quite reasonable," he says, "but our natural gas prices are very low, and if we can still realize these kinds of savings, why not convert? When we retrofit more dryers, our gas consumption will increase, and we'll be eligible for an even better rate."
Money savings aside, Kooistra says the actual performance of the GasTrac system has been impressive. He notes electric heaters, because they use a heater bank that turns off and on to regulate temperature, have natural fluctuations that can vary significantly from the temperature setpoint. The gas-powered system uses a proportional blower that, he says, "fluctuates .1 to .2 deg C. But that is minute. It is nothing." Kooistra is currently testing a dryer from a competing manufacturer to compare the performance results of the two systems.
Installation of the GasTrac, which can be retrofit to any electric dryer regardless of manufacturer, is relatively simple. Kooistra says he simply disconnected the duct line from the blower on the electrical heaters, hooked up the GasTrac system in its place, and he was ready to dry. The gas heaters use the Pyrocore HT radiant heat burner and feature a ceramic/metal fiber matrix firing surface. Temperature is controlled with a variable-speed combustion blower. Conversion kits are available for use with drying systems ranging from 400 to 2000 cu ft/min. Cost to convert a typical dryer system, says Conair, is about $5000. The GasTrac systems themselves range from $15,600 to $19,600.
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