Tobacco barn heat exchangers working Test results are coming in and the results are very good. Of the 21 commercial and home made bulk curing barn heat exchangers tested so far, all are greatly reducing nitrous oxide levels in the barns and all are allowing growers to cure tobacco with very low levels of tobacco specific nitrosamines. But, efficiency, quality and initial costs vary greatly.
"Every heat exchanger we've tested works," says Mike Boyette, Extension agricultural engineer, North Carolina State University. "The data are conclusive. There is a very small difference in the nitrosamine levels in tobacco tested from all the barns that are fitted with heat exchangers. So, it makes sense for those farmers who have not yet converted their barns from direct-fired units to shop around for the least expensive alternative, provided that less expensive unit is well made. Some units are twice as expensive as others."
Boyette says that better than 90 percent of the tobacco samples taken from converted barns are running below 0.5 parts per million TSNA, with the average running in the 0.2 ppm range. Most barns with TSNA levels running higher than 0.5 show signs of barn rot or tobacco mosaic virus or some other problem. Direct-fired barns are producing tobacco with TSNA levels averaging about 3.3 ppm. Indirect-fired barns are reducing TSNA levels about 94 percent.
To help tobacco growers make wise selections, Boyette is compiling a list of heat exchangers produced by all known manufacturers. He is asking each manufacturer to list which barns the units will fit as well as the price for each unit, including installation costs. He is also encouraging tobacco growers to go ahead and retrofit their barns as soon as possible to get ready for the 2001curing season.
"Whether a grower is going to contract directly with a tobacco company or sell his tobacco some other way, he's going to have to cure his tobacco in barns equipped with heat exchangers in 2001," Boyette notes. "One thing for sure, if you're going to contract you're going to have to get your barns retrofitted or buy barns with heat exchangers installed. I don't believe there will be a market for tobacco cured in direct-fired barns next year."
The engineer also says he believes the days of tobacco companies paying to retrofit barns are over.
"Quit waiting for a sugar daddy to come along," he cautions. "Get busy and go about converting your barns. There have been persistent rumors that retrofit funding is running out. That is not true. Growers who convert their barns can still get a portion of the cost of retrofitting their barns.
"The average reimbursement per barn through the end of September was $2,574. The average cost per conversion was $4,063. I don't think the money is going to run out. But, growers who wait too long might have a hard time getting the heat exchangers they want or getting them installed in time for the curing season. There are still thousands of barns that have not yet been converted."
How should growers decide which heat exchangers to purchase? First, Boyette suggests, contact the company that makes your barn and ask if they also produce retrofit units. Second, contact the Extension Service to get information on all available heat exchangers, including costs, installation costs, and which barns each unit will fit.
Not universal "I don't know of any unit that will fit every barn," Boyette says. "At some point we will have information about the energy efficiency of each unit. Growers can get that information, as soon as it is available, from their county Extension agents.
"We have seen efficiencies as low as 60 percent and as high as 87 percent. Many of the units are in the 70 to 80 percent efficiency range when they are installed. With a little tweaking we can get most of them into the 80s. We are checking both burner efficiency and heat exchanger efficiency. Growers need to install units that burn the fuel as efficiently as possible. Then they need to extract the heat with a heat exchanger as efficiently as possible. Some are more efficient than others."
There are also problems with the quality of some units. Boyette notes that some manufacturers have had problems with cracked welds, particularly in stainless steel units. As exchangers heat and cool, the metal flexes. In some cases the flexing is enough to put too much stress on the welds, resulting in cracks. If these cracks allow products of combustion to leak into the curing barn, TSNA levels may increase to unacceptable levels.
Boyette is working with Extension tobacco specialists in all the flue-cured states to gather information on all commercially available heat exchangers. He will compile that information and make it available to all interested growers.