Higher energy costs and a competitive economy have industrial facilities everywhere looking for ways to improve efficiency, cut costs and gain a competitive edge. Process heating equipment, critical to many manufacturing operations, is a significant energy user. Pulse firing control systems are used in a variety of processes to help reduce energy costs, improve quality and lower emissions.
How pulse firing systems work
Pulse firing is a proven technology used for heat-treating furnaces, commercial boilers, cement kilns, spray drying and other applications.
In pulse firing systems, the combustion process is controlled by varying the frequency of burner operation. Each burner in sequence — controlled independently — operates at a maximum firing rate for a controlled amount of time and then is cycled to low fire. This cycle is frequently repeated, and the process controller regulates the burner's rate of high fire (most efficient firing rate) and low fire. In a conventional proportional firing system, the burner setting can vary anywhere between low and high fire, and burners are controlled as a group.
Pulse firing systems use fast-operating air valves to switch from high to low fire. A small amount of air passes through the closed valve position to provide the low fire airflow, and a pulse regulator connected to the air valve controls fuel. A bypass controls the low fire gas flow. When the air valve opens, the burner switches to high fire. The process controller determines how much heat input is required, typically in response to a temperature sensor. Burners can be set at a predetermined frequency and rate, depending on the application.
Pulse firing control is most effective when used with high-velocity burners, which typically have an exhaust rate of 300 feet per second or more. Such an exhaust rate enhances circulation in the combustion chamber, increasing heat transfer and temperature uniformity. High-velocity burners work better at high fire, where the velocity and mass flow are the highest. Each time the pulse cycle switches from low to high fire operation, it uses the entrainment and stirring action of high-velocity burners to its best advantage.
Benefits of pulse firing
In the right application, a well-designed pulse firing control system provides a number of cost-saving and environmental benefits:
- Increased heat transfer rate
- Higher combustion efficiency with low excess air
- Improved thermal efficiency and temperature uniformity
- Reduced emissions of nitrogen oxides and carbon monoxide
- Shorter overall cycle times from faster heat-up
- Expanded temperature range of combustion equipment
The high capital outlay for pulse firing systems is a limiting factor in some instances. However, they can provide significant energy cost savings, resulting in a reasonable return on investment. These systems' high noise levels (up to 120 decibels) are reduced to acceptable sound levels with acoustic decouplers and insulation.
Success story: manufacturing plant goes outside the box for savings
In one manufacturing facility, pulse firing combustion was installed on a box style furnace, resulting in natural gas energy savings of 27%. An algorithm cycles the burners through a high fire/low fire sequence based on the required process temperatures, resulting in improved energy efficiency.