ETI designs and fabricates convective heaters for use in gas, adsorptive regeneration, process heating, and heat transfer industries. ETI’s Model HTE (High Thermal Efficiency) is unique in that it has no radiant section. Instead, the heater is all economizer. In order to understand the design principle, one must keep in mind that the efficiency of any fired heater is only a function of the stack gas temperature and the amount of excess air used (assuming complete combustion). The excess air can be best controlled with a power burner and is usually set at 15% to 20% with gaseous fuels. A good burner doesn’t require the excess air for complete combustion, rather the excess is set to compensate for barometric and ambient temperature changes so that the air injected will never drop below the stoichiometric quantity required for complete combustion.
The ETI HTE heater introduces cool ambient air or re-circulated flue gas into the combustion chamber in order to reduce the combustion gas temperature to the desired level. Typically, the temperature is reduced from a flame temperature of 2500°F to 1100°F, although it may be reduced to a much lower value if sensitive or heat reactive materials are being processed. The high temperature energy is traded for a lower temperature gas with greater volume. Quench air is introduced to the combustion chamber with a control valve on the air or flue gas recirculating (FGR) fan.
ETI’s HTE heater has fast response and very little stored heat. If fluid flow stops, the burner is shut off by a low flow detector, or a high process or tube wall temperature controller and the process coil bundle is not damaged. Because a higher volume of convection gas is circulated, the outside transfer rate may be increased on the stack side of the exchanger, resulting in higher efficiency with fewer tubes.
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