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Show 3.0 Intra-lean-Premixed Burner Development for Commercial Hot Water Boilers 3.1 Design Constraints The burner system designed for commercial boiler application has the following primary design constraints: 1. Performance: NOx and CO emission limits, flame stability, alternative fuel capability, efficiency, turndown, flame volume, flame shape; 2. Safety: No delayed ignition, no self ignition, and no danger if flashback occurs. Materials must be adequate for the application. 3. Cost: material, manufacturing process, blower pressure requirement and ancillary components. A challenge of this project was that ultra-lean premixed combustion system for the commercial market is a low pressure application. The maximum allowable pressure drop across the flameholder is only a few inches of water column. This challenge was overcome by unique designs of mixer and flameholder. 3.2 Mixer Design for Uniform Fuel/air Mixture Mixer design is probably the most important in the design and development of ultra-lean premixed combustion system. Since the size of the mixer is usually limited due to the design constraints, it is very difficult to achieve nearly perfect mixing. The objective of a mixer design is to achieve a satisfactory, spatially uniform fuel/air mixture with minimum mixing length and minimum pressure drop. Normally the pressure drop available is less than 2 to 3 inches of water column. A unique fuel/air mixer has been developed as a part of this technology. This mixer is capable of producing an extremely homogeneous fuel/air mixture at less than 2 inches of water column pressure drop. 3.3 Flameholder Design for Flame Stability The flameholder for ultra-lean premixed combustion for commercial boiler application requires a high flow capacity with minimum pressure drop. At the same time, it should be compact, capable of a wide operating range without flame lifting and deflagration, stable light-off and quiet extinction. Moreover, it should also be durable and made of low cost material. Swirl is used extensively in combustion systems as a means of increasing mixing rate, reducing flame size, shaping the flame, assisting complete combustion and changing the rate of formation and reduction of pollutants(3). At high degrees of swirl (Swirling Number> 0.6), vortex 6 |