NOx is a criteria pollutant regulated by the EPA and a key metric of burner performance. Recently, ClearSign demonstrated an 95% reduction in NOx emissions (from 100ppm down to less than 5ppm) using a prototype burner based on its novel Duplex™ burner architecture in a furnace operating at a temperature of ~1600F with O2 concentrations ranging from 2.5% to 3.2%.
Achieving NOx Results at or Below 5PPM
Strict new NOx control regulations are being implemented over the next two years in several regions of the country including Texas and California. California’s South Coast Air Quality Management District’s Rule 1146 requires that burners produce less than 9ppm of NOx no later than July, 2014. Industry groups anticipate that these limits will soon be further reduced to as low as 5ppm in some areas with the rest of the country to follow suit.
In our conversations with customers and partners, we hear both a sense of urgency and a great deal of uncertainty as the new regulations raise the specter of costly new challenges for combustion system owner operators.
To address this challenge, some burner and combustion system manufacturers have been able to develop systems that can achieve the NOx targets, but inherent design tradeoffs impose high costs to energy efficiency that become prohibitive at these very low emissions levels, even with natural gas at historically low prices.
The biggest cost associated with Low- and Ultra-Low NOx burners has been the significant loss in energy efficiency that results. This loss stems directly from the combined effect of recirculating flue gas and increasing excess air to cool the flame along with a loss of turn-down because of flame instability, and can result in increases in fuel consumption of as much as 20-30%.
The market has long preferred low NOx and Ultra-Low NOx burners to more costly post-combustion treatment alternatives such as Selective Catalytic Reduction (SCR) systems that are more costly to install, complex to operate and consume considerable quantities of hazardous materials such as anhydrous ammonia.
However, with the new regulations on the horizon and the inability of conventional burners to meet these criteria cost effectively, many operators are being forced to consider SCR.
By contrast, ClearSign’s Duplex™ Burner architecture achieves reductions in NOx to 5 ppm without costly FGR or SCR systems. In addition, flame length is reduced by up to 80%. And, unlike other low NOx systems, the Duplex Burner keeps oxygen at very low levels (around 3% or below), and can maintain a stable flame throughout a wide operating range. Because of these features, the Duplex burner architecture enables significant advantages in fuel efficiency and process throughput as compared to conventional Low- and Ultra-low-NOx burners.
Our ability to combine these features represents not only a technical breakthrough, but also a significant potential breakthrough for operating economics. Our goal is to reduce NOx to unprecedented levels without introducing the design compromises that drive cost of ownership to prohibitive levels.
In many instances, these improvements can translate to annual savings in the seven and eight figure range. Many traditional Low-NOx burners make use of increased flame length and reduced momentum to reduce NOx, but the resulting poor ‘flame pattern’ can cause flame impingement and coking. Refinery process heaters are particularly sensitive to this problem, due to the direct negative impact on product throughput and plant revenue as the firing rate must be throttled to avoid equipment damage. According to our analysis, a 3% to 7% loss in firing capacity due to poor flame pattern can cost millions of dollars annually in lost process throughput. Removing this bottleneck could improve plant profitability by between $12 and $28 million per plant, per year. This is of particularly high value because it leverages so much capital plant by increasing capacity.
The graphic above shows the essential elements of the ClearSign duplex burner comprising a lower story tile, an upper story tile, and fuel nozzles. When the fuel is directed to the lower story tile, the resulting hot gas recirculating there anchors the flame. This allows for start-up operation where furnace temperatures and NOx are low. Once the furnace reaches its operating temperature, the fuel is anchored to the upper-story tile. This dramatically reduces NOx by greatly increasing the amount of entrained flue gas to dilute NOx-forming species without any external fans or power. The greater entrainment also provides more thorough mixing and shorter flames. Since flame length is one parameter that limits the total heat release in a furnace, decreased flame length can allow for significantly greater process throughputs.
As the Duplex tile is activated, NOx drops precipitously to less than 10 ppm, and over several minutes to 5 ppm or lower. All the while operating parameters remain the same, and without elevating CO emissions. In fact, CO emissions are actually reduced.