Combustion Catalog | Fives North American

Control | 4211 EcoFornax ™ LE

CONTROL Input and air/fuel ratio control for the LE utilizes fully metered oxidant and fuel flows (minimum one air and three fuel streams) as inputs to an electronic ratio control system. An oxygen sensor in the exhaust stream is commonly used to provide O2 trim. An O2 sensor may also be used to determine the vitiation level when FGR is mixed with the combustion air. Combustion air flow is measured with a North American 8631 Venturi Air Meter or other air flow determining device. Air flow control can be by control valve, blower IVD or VFD, as dictated by the air system design. A separate radial air blower is typically required when a VFD is used on the primary air blower or the primary air is preheated or vitiated. The critical primary air/ fuel ratio is maintained by the electronic ratio controller which also adjusts the secondary gas flow control valve as needed to maintain the overall excess oxygen at the exhaust O2 sensor. As input demand changes, the desired primary air/fuel ratio is maintained by cross-limiting the air and primary gas valves. To meet the lowest emissions requirements, fully modulated radial air and gas control valves are required, also allowing for thermal turndown as high as 20:1. When high turndown or ultimate ultra-low NOx operation is not a system requirement, the radial gas may be controlled via a bypass solenoid valve which allows for a two position "high/low" setting. Large capacity burners require modulated radial air regardless of emissions requirement.

PILOT and FLAME SUPERVISION Dual UV flame detectors are used. The pilot UV detector monitors the adequate establishment of the pilot and radial flames at startup. The main UV detector monitors the establishment of the primary flame and allows opening of the secondary fuel supply safety shutoff valves. Loss of the main UV signal will cause the secondary gas valves to close and re-establishes the pilot UV detector to monitor the operation of the unit on primary and radial gas only. Loss of the pilot UV signal will result in the unit shutting down completely, and require a re-start of the safety sequence following the appropriate code requirements. Contact North American for the specific requirements for configuration of flame supervision equipment and fuel safety shut off valves for each application.


Combustion Air






Main Gas Safety Fuel Train

Gas Supply




Figure 2. Typical Piping Schematic for LE Cold Air System. Preheat or vitiated combustion air systems require a second blower for radial and pilot air. Fuel train components omitted for clarity.

Bulletin 4211 Page 4

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