Planning now is essential--it is time to consider your company energy strategy. Since kilns consume the highest amount of energy used in most factories, we will concentrate on energy management over my next few columns.
This month's column will cover alternative fuel sources. Down the road, we will examine fuel consumption of various periodic and continuous firing systems, and look at potential efficiency improvements.
Propane. The simplest way to weather short interruptions in natural gas supply is to use propane as a backup. Propane backup systems are relatively low in first cost, but the best characteristic of correctly designed propane backup systems is that they allow for almost seamless switching during times of natural gas curtailment. This system also uses the same fuel distribution system--piping, valves, burners, etc.--and tends to produce slightly lower NOx emissions.
To meet these requirements, propane is mixed with air-aerated propane--with carefully controlled aeration rates, so that the Wobbe index of the mixture matches that of the natural gas it is replacing. No burner adjustments are required under the above circumstances. The air to propane mix is, of course, below the explosive limit.
On the minus side, however, propane availability varies. During an energy crunch, some clients report that propane is difficult to obtain, and prices can fluctuate considerably. Large tanks are required for storage, and regulations vary for security and protection of the system, proximity to buildings, etc. Since propane is heavier than air (specific gravity is 1.55), care must be taken to eliminate leaks, and pit ventilation for burners located below floor elevation is imperative. For all but the smallest systems, a burner--heated vaporizer is required. Last, but not least, the propane to air mixture must be maintained at the correct value as predicated by the Wobbe index, otherwise the kilns and other devices connected to the system will not perform identically to the natural gas firings, sometimes resulting in an inability to maintain temperature.
Oil Firing (#2 oil). Purchasing dual fuel burners that are suitable for oil and gas firing is another way to achieve independence from natural gas, but extra care in design is essential. The capital cost can be significant, as new burners must be purchased in most cases. In addition, an atomizing air fan, oil pumps and the associated piping must be installed. Oil storage tanks must also meet environmental codes.
In many ways, fuel oil systems are more difficult to manage than natural gas systems. Fuel cleanliness is critical, as oil flow ports are small and easily clogged. Most oil burners do not have the same range of operation (turndown) nor the same excess air capabilities as their natural gas counterparts. While these limitations are not a significant liability for continuous kilns, they can have a serious impact in periodic kiln performance.
On the plus side, fuel oil is likely to be more abundant, at costs that are more stable than propane. With correct kiln management, oil firing is a sound way to proceed, as long as it is handled correctly. Planning how to manage the use of oil and the modifications to the firing program--especially in periodic kilns--is critical.