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Improving combustion control reduces energy costs for burners, furnaces and other heat-treating equipment.
Although manufacturers have made significant improvements in process heating efficiency, the U.S. industry’s total energy use for process heating is expected to increase. With overall thermal efficiency of process equipment varying from 15% to 80%, compared to the thermal efficiency of steam generation, which varies from 65% to 85%, there is clearly an opportunity to achieve significant energy savings, improve productivity and enhance competitiveness.
The U.S. Department of Energy’s Industrial Technologies Program (www.eere.energy.gov) has identified improved burner control systems as a significant opportunity for reducing energy operating costs, waste and environmental emissions.
Tuning burners to reduce excess air is a cost-effective technique for reducing heat lost in exhaust. Monitoring and adjusting air-to-fuel ratios to maintain optimum combustion
not only conserves fuel but also helps reduce emissions.
In many process-heating operations, such as drying, incineration and heat treating, excess air is often a process requirement. In these cases combustion air and excess air used to suppress emissions must be heated, which increases fuel consumption and may result in incomplete combustion.
One of the most effective techniques for improving efficiency and reducing emissions in these applications is a precise control strategy, based on mass flow measurement of fuel and airflow rates.
Sophisticated burner control systems optimize fuel-to-air ratio control to obtain peak thermal efficiency over the entire range of the burner, and to facilitate proactive emissions control. Mass flow control of air and fuel is used to automatically compensate for changes in temperature or pressure that affect combustion performance. Many systems also integrate fuel totalizing, air/fuel flow and valve position analog outputs for DCS interfacing, and remote system monitoring.
Accurate, repeatable measurement of air and gas, at low and varying flow rates, is a critical variable in advanced combustion control. Conventional flowmeters, such as orifice plates, venturis, differential pressure and turbine meters are volumetric measuring devices, and they require pressure and temperature transmitters to compensate for density changes.
The thermal mass flowmeter, however, measures gas mass flow directly, with no need for additional hardware. The thermal meter also provides better rangeability and a lower pressure drop than volumetric flowmeters.
The thermal flowmeter’s mass flow rate output may be used to execute flow control loops based on transmitted position information to the valve actuators, using measured flow versus flow requirement calculations. In addition to the primary benefits of direct measurement of mass flow rate, low-flow sensitivity, and fast response, the thermal meter’s no-moving parts design also reduces maintenance costs.
Fox thermal flowmeters are designed for use in fuel gas and air feed lines found in process heating and utility operations. Rugged construction, exceptional accuracy and ease of installation make them a cost-effective replacement for differential pressure, orifice plate, turbine and other volumetric flowmeters. Typical applications include:
- furnaces
- burners
- ovens
- heaters
- kilns
- smelters
- dryers
- heat-treating systems
- natural gas back-up power systems
- emission reduction systems
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