KILN CONNECTION: Gas Pains? Join the Club
Don’t count on prices declining to solve your energy problem. According to Alan Greenspan, Federal Reserve chairman, “Today’s tight natural gas markets have been a long time in coming, and futures prices suggest that we are not apt to return to earlier periods of relative abundance and low prices anytime soon.”1
Why are prices so high? Well, for starters, natural gas supplies are 29% below their five-year average. In the last year alone, supplies have been 39% lower than average. At the same time, demand is at an all-time high, even with the recession. When industrial output increases, prices will likely be even higher.
What can you do, aside from rearranging the deck chairs on the Titanic? Every kiln that I evaluate has the potential for significant energy savings—evaluate your firing systems to save real money now. The fastest results will be obtained through precise adjustment, and additional gains can be achieved through informed investment. This month, we’ll look at adjustment possibilities.
Obtain Critical DataStart by figuring out how much fuel you are using. If you followed my advice last year, all of your kilns have metering systems so you can determine fuel consumption on a kiln-by-kiln basis. Next, figure out what load you are processing, including kiln furniture and the ware to be fired. Calculate the specific fuel consumption, in Kg/kilocalorie or BTU/pound, based on fired weight. Compare these values with industry benchmarks for your products to get an idea of where your kilns stand. (This information can often be obtained by talking to other manufacturers in your field. Ceramic Industry’s website also features helpful information in the Reference section.)
Take a look at your process in detail. Make an energy balance by computing the exhaust flow/BTU loss, heat losses from the kiln structure, and the theoretical heat input into your load (ware and kiln furniture). This will provide the data that shows where the expensive fuel is going.
Measure the oxygen levels. In the case of tunnel kilns, make a survey at 500-degree increments to develop the oxygen profile of the kiln, including early cooling. In a periodic kiln, measure the oxygen (again, at 500-degree increments) through the entire firing cycle.
Interpret the DataFor tunnel kilns, you can sometimes save 10% or more by readjusting the air flow exchange between cooling and heating, followed by adjustment of the hot zone burners. The goal is to take advantage of the hot air coming from the cooling zone by using it as a portion of combustion air. Setting up the hot zone burners at increasingly rich values will accomplish this task.
If the TK preheating zone employs burners, supplemental BTUs can be added to the preheating area by increasing the flow of gases from cooling to the hot zone. This will allow a reduction of fuel input into the preheating burners, for additional savings.
Evaluate the oxygen profile to figure out where the oxygen is coming from. Possibilities include burner excess air, as well as leaks between kiln car seals and around sand seals, or around burners, sight holes, etc. Take the appropriate action based on your findings, keeping in mind that the changes you make must take into account possible harm to temperature uniformity.
In the case of periodic kilns, there are simple possibilities for savings. Many kilns operate with excessive excess air, but it doesn’t all come from the burners. Frequently, kiln pressures are too low, allowing for significant airflow into the kiln by leakage. In a typical kiln, the leakage area can amount to several square feet around car, door and sand seals, as well as sight holes. A mere 13 cu ft of air weighs 1 lb; a large kiln can have inflow leakage of thousands of cubic feet of air during a cycle! Evaluate the operation of your burners, compare their settings to the oxygen profile obtained through sampling, and then calculate the leakage. You may save some serious money here.
In the next “Kiln Connection” column (December issue), we’ll review the viability of informed investments in many areas, including pulse firing upgrades, kiln furniture and refractories, preheated air systems, utilization of exhaust gases in other processes, and cycle acceleration.