The combustion system is a key element in efficient thermal processing of ores, minerals, and similar bulk solids in a rotary kiln.
The process requirements are stringent in a variety of thermal processing systems such as in cement-making, limestone calcining, recovery of lime in pulp mills, and the combustion of wastes to name a few.
The burner system is an important and an integral component of a rotary kiln system to optimize the combustion of fuels to release heat in the kiln.
Safety considerations, ease and flexibility of operation, product quality, energy efficiency, maintenance costs, and the environmental impact of the products of combustion are some of the most critical areas that a kiln operator must evaluate in selecting a kiln burner.
Metso has built and designed complete firing systems with safety panels. Firing systems are used to apply heat to the process. In most rotary kiln application fuel is injected directly in the end of the kiln. Firing systems could use any kind of fuel and be of any size. The firing systems can be over 100 MBTU.
The burner is where the fuel is injected, atomized and ignited. The fuel is mixed with air before or in the burner. The burner positions a flame in such a manner that continuous ignition is accomplished. The f lame temperature is a factor of fuel type, fuel/air ratio, and other burning conditions.
Burner flame geometry (or flame shape) is also important because of the fact that it can change the temperature profile or where the heat is focused. To achieve the optimum flame shape and the most efficient combustion possible, the rate of mixing of both the fuel and combustion air through the burner is required. Many factors can go into burner design. This can include velocities and how much air is needed. Each different fuel offers its own challenges. Each burner is designed for the given fuel and application. It is not a one fits all. Additional concerns, in the burner design, have been made over the product ion of NOx, Sox and other emissions. It is important to balance all factors.
Less costly fuels often require more energy to prepare and burn. These parameters must be fully understood when selecting the fuel type, preparing costs or calculating efficiencies. For example, coal and coal derivatives may require the use of a heated milling operation for which the cost of the fuel used in the preheat, the mill drive and the fuel transportation pumps and fans must be included in the total energy analysis. The impact that the fuel has on the quality of the lime directly affects the value and size of the market for the product, and should be included in the fuel cost analysis.
In comparison, natural gas requires no ancillary equipment and therefore the burner cost can be considered to be the total cost. This is not to imply that natural gas is a less expensive fuel to use, but it does require less energy to prepare and burn it. Furthermore, the fuel cost may be affected by its efficiency in the kiln. The lower radiant capabilities of natural gas decrease the efficiency in the kiln relative to coke or coal.
Metso can design a firing system for your application. We have been experimenting with alternate fuels. See how different fuels can be used to fuel your kiln.