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Show Performance of Low and Ultra-Low NOx Burners Firing HydrogenEnriched Syngas in a Refractory Lined Furnace H. Christopher Ballance and Bradley A. Ochs Georgia Institute of Technology, Atlanta, GA 30332, USA Abstract The following paper documents the design, construction and operation of a test furnace facility built to serve the time critical need of an industrial sponsor. The facility was designed, built and operational in less than 4 months. The new facility was used to research the relationships between flame stability, furnace operating temperature, and emissions for a hydrogen-enriched gas fired in traditional, dry low NOx and ultra-dry low NOx burners in refractory lined, direct fired refinery heaters. Introduction In response to ever tightening NOx regulations, industry has funded considerable research in dry low and ultra-dry low NOx natural gas burners. Emissions controls technology for natural gas fired burners has approached maturity in the last ten years, and now efforts are under way to limit NOx emissions of burners firing hydrogen rich refinery gases and other syngases. The following paper documents the design, construction, and operation of a test furnace facility built to research the relationships between flame stability, furnace operating temperature, and emissions for a hydrogen-enriched gas fired in traditional, dry low NOx and ultra-dry low NOx burners for typical refractory lined industrial heater. Facility Design The industrial sponsor that awarded Georgia Tech the project to build the test furnace facility had a time critical need address a pressing emissions compliance issue. The project was awarded on the condition that new facility would be designed, built, and operational in less than 4 months. To work within the tight schedule established by the sponsor and provide quality performance and emissions data a number of design compromises had to be made and creative solutions found, one which included locating the facility in the open lab space of the existing Ben T. Zinn Combustion Lab. The schematics in Figures 1 & 2 show the following critical facility systems: gas fuel, combustion, exhaust, and cooling water. The gas fuel system shown in Figure 1 is a dual fuel system capable of providing methane-hydrogen mixes containing up to 50% by mass hydrogen. Hydrogen is supplied by packs of gas bottles, and methane is provided by the lab's high pressure natural gas system. Both gas fuel trains are provide with double block and bleed valves and gas is metered by temperature corrected subcritical orifices. Flow in each train is controlled by regulators using downstream pressure. After each train the mixed gas pressure supplied to the burner. The sponsor did not require fuel gas preheating and natural gas was burner pilot fuel. Data acquisition from all facility instruments is through a National Instruments CompactRIO, and hydrogen and 1 natural gas pressures, temperatures, and mass flow rates are captured and stored in the facility's LabVIEW based control system. Figure 1. Gas Fuel System The combustion system consists of the burner and furnace. The sponsor provided four different premix and partially premixed burner designs to evaluate in front wall firing configuration. Combustion air for each burner is provided unheated, and to simplify the system no forced draft fan was installed. The burner wind boxes providing primary and secondary air splits were integral to the burners. The 324 ft3 (9.2 m3) refractory lined furnace was modeled after the direct fired heaters common in the refinery and petrochemical industry. Georgia Tech designed the furnace based on experience from previous lab projects, field visits to other research facilities, and well known literature [1], [2], [3]. The furnace is designed for a maximum continuous heat input of 1.5 MMBtu/hr (450 kW) heat input with a design firebox temperature of 2281°F (1523 K). The furnace has the following inside dimensions: 9 ft x 6 ft x 6ft (2.74 m x 1.83 m x 1.83 m). The inside walls of the furnace was lined with 4.5 inches of insulating firebrick backed up by 4 inches of Kaowool backer board. Structural support and furnace sealing was provided by welded plate steel casing and structural steel. A single furnace access door was provided in the side of the furnace. The following Figure 3 shows annotated CAD model of the test furnace beside front outside view of the furnace. 2 Figure 2. Combustion, Exhaust & Cooling Water Systems Figure 3. Test Furnace Model with Instruments and key items called out and front view photo of furnace Furnace side and rear wall quartz windows provide optical access to the furnace, and optical diagnostic methods based raw and CH filtered flame images enable study of flame shape and location. During operation, furnace temperature, static pressure and differential pressure is captured by the control system. The control system calculates the burner heat input based on the fuel gas flow mass flow rates. 3 The test furnace facility's exhaust system is tied into the Zinn Lab's induced draft exhaust system. The lab's exhaust system has a 25 MMBtu/hr capacity and combined with the variable stack draft inductor, the test furnace is able operate at a vacuum of 0.8 inH2O (200 Pa). Compressed air from the building low pressure air system is used by the inductor. Low pressure compressed air is also used for furnace purge. Stack temperature at the outlet of the furnace and O2, CO2, NOx, and CO emissions are continuously measured by a water-cooled sample probe and multi-gas analyzer. The water cooled sample probe was designed and fabricated by Georgia Tech based pervious work and references [4], [5], [6]. Tunable process simulation is provided by the test facility's retractable cooling water system. The water cooled pendant type tube coil on the rear wall of the furnace enables the study of the effect of burner design and fuel mixtures on flame radiant heat flux. Cooling water flow rate and the temperatures leaving and entering and leaving the tube coil are recorded by the control system and heat absorption calculated. Experimental Results To demonstrate the capabilities of the facility, combustion test results are presented for four different burner technologies firing a hydrogen-enriched gas. The following table provides baseline NOx emissions the various burners while operating the facility 2% O2 (volume, dry) with an average of 30% H2 - 70% CH4 by mass fuel mix. Baseline Emissions for Tested Burners Burner Type NOx emissions (Corrected 3% O2) Ultra-low Nox 10 ppm Low NOx 22 ppm Standard Premix with Fuel Augmentation 32 ppm Standard Premix with out Fuel Augmentation 38 ppm Conclusions After less than four months of work, the industrial sponsor that funded the development of the new furnace test facility was able emissions data that enable the sponsor to answer a time critical emissions compliance question. The project provide Georgia Tech with a new research facility and valuable experience. References [1] P. Mullinger and B. Jenkins, Industrial and Process Furnaces, Principles, Design and Operation, 2008. [2] C.E. Baukal, The John Zink Combustion Handbook, 2001 [3] S.R. Turns, An Introduction to Combustion Concepts and Applications, 3rd Edition, 2011. [4] R. Bilger, "Probe measurements in turbulent combustion," in Combustion measurements: Modern techniques and instrumentation, 1976, pp. 333-348. 4 [5] J. Ballester and T. Garcia-Armingol, "Diagnostic techniques for the monitoring and control of practical flames," Progress in Energy and Combustion Science, vol. 36, no. 4, pp. 375-411, 2010. [6] M. Heitor and A. Moreira, "Thermocouples and sample probes for combustion studies," Progress in Energy and Combustion Science, vol. 19, no. 3, pp. 259-278, 1993. 5 |
