KILN CONNECTION: Conservation is Key
I recently spent a couple of days at Tecnargilla 2004 in Rimini, Italy, and saw that energy conservation was a prominent element in most of the kiln exhibition stands. Fuel prices in Italy (and the rest of Europe, too) are significantly higher than our prices in the U.S. With crude oil prices increasing, more pressure will be put on liquified petroleum gas (LPG) and natural gas pricing worldwide. While natural gas prices are fairly steady right now at $5-$6 per MMbtu, the U.S. Department of Energy (DOE) projects continually increasing prices for natural gas over the next several years. Worldwide demand is increasing, and a smart energy plan is imperative to avoid running out of energy.
Historical TechniquesDuring the fuel pinch in the '70s, conservation was a key element in reducing the cost of energy. We Americans were far more diligent, both personally and commercially, in avoiding waste. Turning off lights, setting thermostats lower in the winter, and carefully monitoring fuel consumption in our industrial processes were standard operating procedures.
Many companies developed an energy program and energy reduction strategies for their process heating. Additionally, many heating systems were retrofitted with dual fuel systems-typically gas and #2 fuel oil-to offset supply shortages and curtailments, and also to use the lowest-cost fuel option when both were available. LPG tanks were often used as standby systems, with the advantage that aerating the propane fuel properly (achieving the same Wobbe index for gas and aerated propane) allowed for seamless switching back and forth as needed.
Modern ApproachesWhat to do today? In many facilities I've visited, fuel savings of 5 to 10% are achievable through conservation and combustion adjustment alone. These relatively simple techniques include thorough analysis of the firing cycles and excess air schedules, and fine tuning the burner systems. Kiln loading optimization (i.e., increasing the density of ware setting) results in nearly free energy costs for the extra load.
Modification of combustion equipment provides another possibility. I've recently participated in several retrofits of periodic kilns where energy reductions of 30 to 40% have been achieved by conversion to pulse firing. These conversions have been accompanied by a total renewal of the instrumentation system to programmable logic control (PLC) with supervisory control/data acquisition (SCADA) overview, resulting in "like new" performance-higher yields, faster firing cycles and nearly perfect cycle-to-cycle duplication of performance. Normally, oxygen sensors are used to monitor the combustion process, and dedicated metering systems are applied to each burner for the low- and high-fire air and fuel flows. Use of real-time fuel flow data for the entire cycle allows operators to carefully monitor fuel input during every phase of firing.
These systems are also capable of enabling minimal energy use for the cooling phase of products that must be cooled very slowly-large abrasive grinding wheels, for example. Burners can be used during the slow cooling part of the cycle with minimal input to achieve significant energy savings. Overall, these designs, complete with instrumentation upgrades, new wiring, burners and controls, have a payback of about one year for a large shuttle kiln. As fuel prices continue to climb, the return of capital will be even shorter.
Another option to consider is the use of preheated air, particularly for high-temperature (2500°F and higher) cycles. The bulk of the energy used during most periodic cycles occurs during the highest temperature heating portion of the cycle. Using preheated air (800°F) in these kilns often saves 20 to 30% of the normal energy required-a substantial savings. Using 800§F as the upper limit of hot air normally means that black iron piping can be used in lieu of stainless steel, although it is normally necessary to increase the air piping size, and sometimes the combustion air source, to achieve proper flows. Electronic or mechanical ratio control mechanisms will also be necessary to maintain the correct fuel-to-air ratios with varying air temperatures. These modifications must often be accompanied by a burner change to allow for hot air, but returns on invested capital are again on the order of a year or two, depending on the exact application.
The best thing to do is to start now. Analyze your fuel consumption in standard units-kcal/kg of product or BTU/lb of product-and compare your values to industry standards. Make inquiries to reputable companies to determine what you might achieve with modern systems, and if the investments look favorable, buy now. Energy pricing has nowhere to go but up.
Ralph Ruark is a registered professional engineer with degrees in ceramic engineering and business, and 29 years of experience in the ceramic industry. He formed Ruark Engineering Inc. several years ago and serves as a technical consultant to a number of ceramic manufacturers and kiln companies. He is dedicated to assisting ceramic companies with a variety of kiln and firing needs, leading kiln analysis efforts, providing training expertise, and improving operations. Ruark can be reached at (941) 360-3111, fax (941) 360-3211, e-mail firstname.lastname@example.org or online at http://www.ruarkengineering.com .