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NOx Control Technologies

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What the Low NOx Burner Manufacturers do not want you to know!

ETEC LogoData obtained with Low NOx Burners (LNB) during the 1990s showed that NOx reduction up to 50% could be obtained from staged combustion. If staged combustion is limited to NOx reduction up to 50%, then how can the burner manufacturers claim to have achieved NOx emission levels of 20 ppmv? The answer is simple, Flue Gas Recirculation (FGR). To achieve higher levels of NOx reduction, several burner manufacturers have combined FGR with LNB. In the FGR NOx control process, a portion of the flue gas is recycled back to the burner. FGR can reduce uncontrolled NOx emissions by as much as 80%. For air pre-heated systems, FGR can reduce uncontrolled NOx emission by as much as 90%. Figure 1 summarizes some of the NOx reduction data obtained with FGR. Figure 1 indicates that most of the NOx reduction in newer burners comes from FGR, not from staged combustion. However, staged combustion is the more expensive part of the solution.

Most of the LNB manufacturers use the concept of internal flue gas recirculation to lower the flame temperature and reduce NOx formation. The LNB manufacturers sometimes refer to this hybrid technology as Ultra Low NOx Burners (ULNBs). ULNBs may be used only in bottom-fired, natural draft units. Unfortunately, ULNBs perform poorly on air pre-heated and wall-fired systems. Eliminating air pre-heat for ULNB applications not only increases the installation cost; it also increases operating costs due to the need for additional fuel to replace the air pre-heat. Field experience indicates that modifying the air pre-heater ductwork is challenging. It is extremely difficult to attain previous fuel efficiency and combustion performance with air pre-heater modifications. Most combustion experts agree that once the air pre-heater is removed, the combustion unit never returns to its original performance! Units modified in such a fashion have often required re-tubing, or even furnace replacement, to return to its previous performance.

To avoid the limitations of the newer burner designs, but still achieve NOx reduction, some burner vendors are offering external FGR along with LNB. However, the cost for these systems is equivalent to buying a Selective Catalytic Reduction (SCR) system. Since the total installed cost of burner systems is an order of magnitude higher than FGR; and since most of the NOx reduction in the newer burners is due to FGR (see Figure 1), the most cost-effective alternative is the proven stand-alone FGR technology.

Traditional FGR systems use a separate fan to move the flue gas and add to the cost of FGR. ETEC has developed a more cost-effective process referred to as Induced Flue Gas Recirculation (IFGR). ETEC's IFGR technology (patent pending) uses the existing forced-draft fan to induce flue gas into the combustion air at the fan inlet. Elimination of the fan requirement has made the IFGR system the most cost-effective NOx control technology on the market today! For solving NOx issues from air-preheated systems, IFGR is the most ideal solution. It is precisely for these reasons several speakers at the Symposium of Technology for Reducing Emissions in Texas (University of Houston, May 21, 2002) have claimed that IFGR is "the most cost-effective technology for NOx Control. Therefore, it is not surprising that a major burner manufacturer has recently abandoned burners and is now using FGR for NOx control in retrofit application!

IFGR Cost Comparison

ETEC has pioneered the establishment of IFGR as "the technology of choice" in the utility boiler market. ETEC has also been responsible for reducing the cost of NOx control in the utility sector by as much as 75%! ETEC is now bringing this “cost savings revolution” to the industrial boiler and process heater markets.

ETEC has demonstrated NOx reductions as high as 80% using IFGR, and even greater reductions may be possible for higher uncontrolled emitters. In several installations, ETEC has demonstrated IFGR NOx control levels that match those achieved with hybrid systems that combine LNB and FGR. Therefore, ETEC's experience indicates that, in many cases, burners are not required for NOx control. Eliminating the need for new burners can result in substantial cost savings. The installed cost of IFGR in retrofit applications is a fraction of the cost of LNB. This makes IFGR technology the most cost-effective technology available in the market today.

ETEC's IFGR technology has several advantages: minimum downtime for installation, only minor modifications needed for ductwork, little to no impact on system performance and operation, and elimination of existing flame impingement problems. Unlike other combustion control systems, ETEC's IFGR system improves fuel and air mixing and, in certain cases, improves energy use efficiency. In the utility retrofit market, ETEC's IFGR designs are now being used in over 80% of operating IFGR systems.

For operators of natural draft units who are planning on installing SCR technology, ETEC provides a modified IFGR technology called Slip Stream FGR technology (patent pending), where a slipstream downstream of the SCR fan is recirculated back into the flame zone to obtain high levels of NOx reduction. Combining ETEC's FGR-based systems with post-combustion SCR technology is more cost-effective than using SCR technology alone (Chemical Engineering, Feb 2001). This is because combining ETEC’s FGR technology with SCR reduces the capital and operating costs for the SCR. For example, the costs associated with the SCR catalyst requirements (equipment size, structural steel, etc.) and ammonia-handling systems are significantly reduced due to lower NOx concentrations at the inlet of the SCR system.

In certain situations, the reduction in ammonia usage alone has paid the cost for ETEC’s FGR system in less than six months!

In the Houston-Galveston ozone non-attainment area, several companies are retiring boilers and planning to import steam from third party-operated Cogen facilities. Depending on a third party for plant utilities not only limits operational flexibility; it also eliminates the energy-efficient option of burning waste gas streams in the boiler. The cost-effectiveness of ETEC's FGR systems makes it possible to continue operating these existing boilers while still achieving significant NOx reductions.

To determine if IFGR, Slip-Stream FGR, C-Mods, or other NOx reduction technologies are suitable for your needs, or if you need additional information please give is a call.