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How to Approach 90+% NOx Control Cost-Effectively

PFD Download Theory of Cost Effective NOx Control

Now that TNRCC has adopted the new SIP, it is time to evaluate cost-effective strategies to comply with the rules. To help understand the cost impact of the new rules, EPA http://www.epa.gov/ttn/oarpg/t1/memoranda/) and TNRCC (http://www.tnrcc.state.tx.us/oprd/hgasip.html) have provided guidance documents. These documents conclude that the SCR alone achieves lower NOx reduction efficiencies and at a higher cost than that of a combination of SCR and combustion control. According to EPA, SCR only systems are an economically inferior option, and 90% reduction is the edge of the technology! Cost information from our recent article in Chemical Engineering, February 2001 issue, also indicates that a combination of combustion control and post-combustion control is the most reliable and cost-effective approach to reduce NOx emissions over 90%.

ETEC LogoAnother interesting aspect of the new SIP rule is that they allow NOx reduction beyond the state or federal limits to be banked as emission credits. The easiest way to generate emission credits is by installing cost-effective combustion control technology as soon as possible. A major advantage of early reductions is that the generated emission credits can be used to delay installations of the expensive SCR. Demand for emission credits will also be created by existing sources unable to meet reductions and by new sources. Although, actual value of emission credits will depend upon the market demand and availability, recent reports from California indicate that NOx has been traded as high as $100,000 per ton! This may not happen in Texas, however, the potential for the price to escalate cannot be ruled out. Thus, early installation of cost-effective combustion control technology to generate emission credits is an obvious option to profit from the new rules.

The Business Coalition for Clean Air has reported that the HGA NOx projects between 2002-2004 will exceed the available nationwide supply of engineers and suppliers to complete the first SIP requirements in 2004. The cost of retrofitting the existing chemical plants and refineries to comply with the new regulations in the HGA has been estimated to be as high as $ 8 billion. Using the approach outlined in our Chemical Engineering article, we believe that this figure can be significantly reduced. To understand the costs as a function of % NOx reduction, ETEC has developed a cost model and the results are shown in Figure 1. The relative cost in Figure 1 refers to the cost of control technology relative to the cost of LNB technology for 50% reduction. Conventional technology refers to use of LNB for NOx reductions up to 50%; and, for higher levels of NOx reduction, conventional technology refers to SCR. Hybrid technology refers to use of Induced Flue Gas Recirculation (IFGR) for NOx reductions up to 65%; and, for higher levels of NOx reduction, hybrid technology refers to a combination of IFGR with SCR. The results for conventional application indicates that as the amount of NOx reduction is increased to levels above 50%, there is an exponential increase in the control technology capital cost. Our analysis indicates that the cost can be reduced by as much as 60% using the “hybrid” approach. Similar results for cost effectiveness were obtained. The cost effectiveness at higher reduction levels of 90% is about 15 to 20 times that at levels of 65% reduction.

Based on cost information from our ChE article, our analysis indicates that for systems requiring NOx reductions of up to 70%, combustion control technologies are most cost-effective. The analyses also indicates that the capital cost for Low NOx Burners is about 2 to 3 times more expensive than IFGR, Water/Steam Injection (WSI) and Off-Stoichiometric (OS) combustion technologies. However, WSI technology is not attractive in terms of high operating costs resulting mainly from increased energy usage. OS technology is not widely used due to space constraints, high down time installation requirements, and in certain cases may also result in limiting the capacity of the unit. As such, for most systems with forced draft fans, IFGR is the most economical option.

Since IFGR technology works on a different principle than stoichiometry based combustion controls, it can be used very effectively with LNB or other stoichiometry based control technologies to control NOx emissions greater than 75%. For certain applications which require NOx reductions below 90%, a combination of IFGR with OS was found to be cost-effective. However, if the configuration of the combustion unit is not suitable for OS, a combination of IFGR with LNB is equally attractive, when compared to the alternative of IFGR and SCR.

For systems requiring NOx reductions greater than 90%, selecting the most cost-effective technology is not that straightforward and the economics should be determined on a case-by-case basis. The analysis indicates that a “hybrid” system consisting of a combination of combustion controls and post-combustion flue gas clean-up technologies is the most cost effective approach to obtain reductions in excess of 90%. The analysis published by EPA and TNRCC also indicates that such a “hybrid” system is the most cost-effective approach to meeting the new regulations. For gas and low sulfur oil fired combustion units with forced draft fan, our analysis indicates a combination of IFGR with SCR is more cost-effective compared to application of only SCR. This is because when SCR is used in combination with IFGR, the costs associated with catalyst and ammonia-handling systems are significantly reduced due to lower NOx concentration. Although in our example, the hybrid of IFGR and SCR was shown to be cost effective, this application may not be suitable for some situations. As such, other combinations of combustion control with post-combustion control technologies should be examined on a case-by-case basis for cost effective control.

One sure way to profit from the new TNRCC regulations is by installing combustion control technology early enough to generate emissions credits, either to cash them at a later date or to trade them at a higher value or to delay major capital expenses such as installation of SCR.

Entropy Technology & Environmental Consultants, Inc. (ETEC) offers a cost-effective technology- Induced Flue Gas Recirculation (IFGR) that eliminates the need for a separate FGR fan and wind box mixing devices. ETEC’s proprietary IFGR technology is based on utilizing the capacity of the existing forced draft fan to pull (induce) about 5 – 25 % of flue gas into the combustion air at the fan inlet. IFGR technology requires very minor modifications and has relatively little or no impact on performance and operation. IFGR systems cost about one third of low NOx burner systems and can be installed during a one-day turnaround! Unlike other combustion control systems, IFGR system improves fuel and air mixing inadequacies and improves the combustion efficiency. IFGR technology is best suited for gas and low sulfur oil fired units with forced draft fan. ETEC has been responsible for pioneering the installation of IFGR at the first electric utility boiler (see Reliant Energy Induced Flue Gas Recirculation Program: Final Report, June 2000, Electric Power Research Institute (EPRI), Palo Alto, CA). Since then, ETEC has successfully applied its proprietary IFGR technology on over 24 units ranging in size from 40 MM Btu/hr through 6,000 MMBtu/hr (600 MW) units.

To evaluate if IFGR technology is suitable for your needs, or if you need additional information on ETEC, IFGR and other NOx reduction technologies, please visit us at http://www.etecinc.net or contact us at (281) 807-7007 or by e-mail at: info@etecinc.net.