|Title||Jade Ultra-Low NOx Tail Gas Thermal Oxidizer Burner|
|Contributor||Bietto, Stefano, and Martin, Matt|
|Spatial Coverage||Kauai, Hawaii|
|Subject||AFRC 2013 Industrial Combustion Symposium|
|Description||Paper from the AFRC 2013 conference titled Jade Ultra-Low NOx Tail Gas Thermal Oxidizer Burner by Kurt Kraus|
|Rights||No copyright issues|
The Jade burner from Callidus Technologies by Honeywell is the first purpose-designed and built Ultra-Low NOx Tail Gas Thermal Oxidizer Burner that delivers ultra-low NOx emissions with no special physical or operational provisions. Incorporating the Jade burner into a thermal oxidizer delivers the lowest nitrous oxides (NOx) - in certain cases, essentially no NOx - and carbon monoxide (CO) while requiring no special operating practices. Callidus uses patent pending Balanced Staging technology to deliver the proper proportions of both waste gas and fuel (assist) gas to the proper locations in the flame zones of the combustion chamber. Application of Balanced Staging simultaneously optimizes the counter-acting constraints of minimum NOx emissions, carbon monoxide emissions, operating temperature, assist gas consumption and residence time. The term "thermal oxidizer" spans a broad range of equipment sometimes variously termed combustors, incinerators or thermal reactors. The purpose of the thermal oxidizer is to combust (oxidize) or destroy by heat various organic or inorganic compounds entering the thermal oxidizer from other processing units. Waste streams may be composed of combinations of gaseous, liquid and solid materials. These waste streams may contain high or low calorific content. The Jade burner's Balanced Staging technology is best suited for waste gas streams that have relatively low calorific content such as tail gas from sulfur recovery units or CO gas from Fluidized Catalytic Cracking (FCC) units. Tail gases and similar low calorific content waste gas streams are usually comprised of large proportions of essentially inert constituents, principally molecular nitrogen and often varying amounts of carbon dioxide and water vapor. The stream of a low calorific value gas is regularly used to lower a burner's flame temperature by mixing the waste gas stream with a portion of the fuel gas (staged gas) prior to combustion. Lowering the burner's flame temperature and "inerting" the fuel stream retards the chemical mechanisms prevalent in the formation of thermal, prompt and fuel NOx thereby reducing the overall NOx emissions produced by the thermal oxidizer. BALANCED STAGING The first and most apparent characteristic of the Jade burner is that it splits the waste gas stream into two portions delivering the gas both in an annular gap at the periphery of the burner tile and through the center of the burner. In many thermal oxidizer applications, the waste gas is injected into the combustion chamber downstream of the burner. When the waste gas is injected downstream of the burner, the stream may have little effect on burner NOx production as the NOx has already been produced in the burner flame before mixing with the waste gas. Many other thermal oxidizer burners inject the waste gas in an annular gap surrounding the burner with or without staged fuel mixing with the waste stream before mixing with the combustion air and any remaining assist gas. Burners of this configuration can produce significantly lower NOx emissions when compared to burners without waste gas injection disposed such that it mixes with the assist gas. By injecting a portion of the waste gas into the throat of the burner and premixing it with the combustion air, the Jade burner effectively reduces the partial pressure of oxygen in the resulting flame. Lower oxygen partial pressure serves to reduce the oxidation of nitrogen (NOx formation) in all of the principal NOx forming mechanisms (thermal, prompt and fuel). This proportioning of waste gas, both around an annular gap and through the burner center, constitutes tail gas staging that is largely unique to the Jade. Also within the Jade burner, the assist fuel is staged to create primary and secondary flame zones. This considered combination of fuel staging and waste gas staging constitutes a portion of the Jade's patent pending Balanced Staging approach. BUT THERE IS MORE TO BALANCED STAGING Many equipment suppliers have found out the hard way (in the field) that too much staging of fuel gas, and too much mixing of low calorific value waste gas and staged fuel gas in thermal oxidizers, can result in incomplete combustion of waste gas constituents and the assist gas. The result is elevated CO, unburned hydrocarbons (UBHC) and volatile organic hydrocarbon (VOC) emissions. The Jade remediates this issue using the patent pending feature of design-adjustable Jade Ultra-Low Nox Tail Gas Thermal Oxidizer Burner Written by Kurt Kraus, P.E.; Stefano Bietto, Ph.D.; Matt Martin, Honeywell Engineering Fellow positioning of the staged fuel gas tips relative to the central air stream and the outer waste gas stream. The staged tips may be placed on a continuum from residing outside the burner, wholly within the oncoming externally staged waste gas stream, to inside the burner, residing wholly within the internal combustion air stream. This variable positioning is factory-set by Callidus and is not required to be field-adjusted. Instead, the design is tuned to a customer's specific requirements, minimizing the emissions of NOx without causing increased emissions of CO, UBHC and VOC. In some cases, a high level of mixing of staged assist gas and waste gas is desired prior to the main flame mixing zone which contains the balance of combustion air, waste gas, and assist gas. In other cases, in order to control CO, UBHC and VOC emissions, a lower level of mixing of waste gas and staged fuel gas is desired - potentially to the point of requiring air and assist gas to be mixed prior to mixing the staged assist gas with the staged waste gas. In still other cases, it is preferable to mix a portion of the staged waste gas, staged assist gas and combustion air simultaneously prior to mixing with remaining waste gas, assist gas and combustion air in the flame zone. The Jade burner allows for great flexibility in the design process. AND STILL THERE IS MORE The portion of the waste gas that is directed into the throat of the burner into the combustion air stream is adjusted to either mix quickly and thoroughly with the combustion air or to mix more slowly. When rapid mixing is required, a patent pending lobed mixer waste gas injection nozzle is used. The lobed mixer injection nozzle has a round inlet fitted to the upstream pipe, and an undulating or lobed outlet. The cross-sectional flow area of the inlet and outlet are roughly equivalent; but, due to the lobes, the perimeter of the outlet can be much greater than the inlet. The result is that the waste gas comes into fluid contact with a much greater portion of the combustion air in a shorter distance, thereby inducing rapid mixing of waste gas and air. Mixing of two fluid streams is often accomplished by inducing some pressure drop at or immediately downstream of the junction of the two streams. However, the allowable back pressure on waste gas streams is often very low. With the lobed mixer, effective mixing is achieved with little or no pressure loss on the system. In certain applications, it may be preferable to delay or retard mixing of the waste gas injected into the combustion air stream. Like mixing of the staged fuel and staged waste gas, too great or too rapid mixing of the primary waste gas and combustion air may, in certain situations, result in excessive CO, UBHC, and VOC emissions. When it is better to delay mixing, a simple blunt ended round pipe is effective and no lobed mixer is required. Variations of the optimized lobed mixer and a simple round pipe are considered when optimizing a design for particular cases. The exact position of the waste injection in the combustion air stream can be adjusted to affect mixing prior to or while entering the combustion zone. Again, like Balanced Staging, mixing rates and means of achieving those rates are custom design considerations that are critical to proper performance. While burners not tuned by this strict design criteria may function, they are likely not optimal for a given waste gas composition, flow rate and temperature. SO HOW DO WE DO IT? Callidus optimizes design variables using advanced design methodologies. These methods advance the art of thermal oxidizer design by identifying and ranking those variables which are most critical to successful field operations. These methods can also give a level of calculated confidence in the predicted outcomes, the emissions and performance guarantees. Key to the design optimization is process simulation in a virtual experimental format. This virtual experiment is simply a set of process design calculations and simulations produced in a coordinated and planned manner where multiple design parameters can be considered and optimized simultaneously. Fixed input design variables include the flow rate, temperature and composition of the waste stream(s), combustion air and assist fuel gas. Adjustable input design variables include the burner geometry and arrangement of staged and primary waste and fuel injectors and the burner throat. Optimized output variables include the resulting pressure loss of each flow stream, combustion chamber size and the resulting residence time, combustion chamber mix temperature and predicted output flow streams including guaranteed emission levels. Assist fuel consumption; flow stream pressure loss; combustion chamber temperature; NOx, CO, UBHC and VOC emissions; combustion chamber size; excess air; residence time and destruction efficiency are all simultaneously optimized. The physical basis for virtual simulation techniques is grounded in extensive development testing of the Jade burner. In the recently completed physical testing regime, the Jade was put through an extensive designed experiment matrix. This matrix was mimicked in the simulation tools in order to predict the eventual outcomes. With the completion of the physical testing, the simulation models were tuned and optimized to reflect physical test results providing the basis for optimal design. THE JADE ADVANTAGES By being purpose-designed for thermal oxidizer service, the Jade avoids the potential pitfalls of using burner designs intended for other services or applications such as ultra-low NOx burners for process heaters. Among the potential difficulties is that while waste gas is generally low in calorific value, it is not flue gas. Burners that rely solely on high levels of flue gas recirculation may deliver very low NOx when waste gas, such as tail gas, is substituted for flue gas. However, the same burners may produce excess CO, UBHC or VOC emissions unless the residence time (size of the combustor) is greatly increased - an outcome predicted by simulation and confirmed by the rigorous Jade testing program. In order to control the CO, UBHC and VOC emissions from misapplied burners in thermal oxidizer service, it may be necessary to modify the burner in ways that diminish the burner's low NOx performance. The Jade design addresses these limitations through the technical innovations of Balanced Staging and lobed mixing. Some other ultra-low NOx thermal oxidizer burners, such as those that use extreme deep staging or "flameless combustion" require "bootstrapping" to start the operation. "Bootstrapping" means starting the burner on conventional burner gas lances then switching to deeply staged operations. At start-up, the burner operates as a conventional burner and NOx emissions are not controlled. Then at some predetermined temperature, usually well over 1400°F (760 °C), the burner is transitioned to deep staging wherein low NOx emissions may be achieved. While the deep staging technology may produce very low NOx emissions, it also requires operational oversight and robust control systems. Changes or fluctuations in operating conditions such as changes in flow rates, temperature or composition require complex control schemes to maintain optimal performance. Typically, deep staging requires higher vessel bulk mix operating temperatures to achieve adequate destruction rates. The higher vessel temperature is achieved through excessive assist gas consumption. Deep staging technology may also require operating at elevated oxygen levels to achieve the lowest NOx levels thereby requiring increased assist gas consumption and residence time to achieve complete combustion. A purpose-designed Jade burner performs in a stable and robust manner, just as a conventional burner, over the broadest range of operating conditions at efficient low excess air levels. TAKING IT TO THE NEXT LEVEL The Jade burner from Callidus Technologies by Honeywell delivers ultra-low NOx emissions in thermal oxidizers with no need for special operational requirements. Rigorous design methodologies, patent pending technology, and reliable, repeatable performance are the hallmarks of the Jade burner.