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Show Maintenance = Maintenance cost of system with new equipment ($/yr) NOx Reduced = Tons of NOx removed (tons/yr) In order to correctly apply the concept of cost effectiveness the project team must carefully analyzer the cost impact of each element of the equation. NOx Reduced It is important to discuss the NOx reduction element of cost effectiveness first as this information relates significantly to the various aspects of cost. Development of NOx reduction technologies has been extremely progressive over the last two to three decades. It has been found that in order to achieve consistent N O x reduction day in and day out, three main technologies have been common in the refining and petrochemical industry: • Ultra Low NOx Burners (ULNB) • Selective Non-Catalytic Reduction (SNCR) • Selective Catalytic Reduction (SCR) For a given application, the total installed cost and actual NOx reduction obtained from these technologies can vary significantly. Realistic reductions in N O x possible for several typical applications are presented in Table 1. In addition, listed are the factors that lead to how well a technology will perform. Note that all N O x emission values in this paper are based on refinery operation burning "refinery fuel gas", mixtures of several hydrocarbons. Reduction efficiencies of ULNB will vary greatly, depending on the inlet N O x concentration or "starting basis". It is generally expected that implementation of U L N B will result in outlet N O x emission levels between 20-75 ppmvd (0.024-0.089 lbs N O x per MMBtu), due to the variety of different types of fired equipment. Typical fired heater emissions can be reduced to less than 30 ppmvd (0.036 lbs N O x per MMBtu), while higher firebox temperature fired heaters (boilers, hydrogen reformers, etc) could be in excess of 40-50 ppmvd (0.047-0.059 lbs N O x per MMBtu). SNCR technology has generally been able to achieve reduction efficiencies of up to 60 %, depending on inlet N O x (this technology is better able to reduce N O x above 100 ppmvd versus N O x below 100 ppmvd). In addition, S N C R requires good ammonia or urea distribution and residence time, which is generally not found in fired heate Boilers are normally good candidates. SCR technology generally reduces NOx by 90-93 %, depending on how well the ammonia distribution can be designed. Limits of this technology could be applications where the existing N O x is so high that even with 90-93% reduction, the resulting N O x is above that which is acceptable. Regardless of which technology is used, the two primary factors that affect the denominator of the cost effectiveness equation (beside reduction efficiency) are inlet N O x concentration and fluegas flowrate. For a given cost, what ever can be done to maximize the tons of N O x removed will directly reduce the cost effectiveness. Capital Cost Capital cost (also known as total installed cost) should include all cost associated with implementing a given technology. One problem that most N O x projects have encountered is project growth or "scope creep". Scope creep results from the fact that most of these types of projects are being carried out on fired units that are old and general'1 not well maintained. It will be very important decide up-front whether upcoming shutdown maintenance will be included in the capital cost of these retrofits projects. Also note that some maintenance or upgrades are necessary for the technology to function as intended by the supplier3. Some of the more obvious and not so obvious costs associated with N O x reduction technologies are presented in Table 2. These are just some of the equipment costs associated with the capital cost portion of cost effectiveness analysis. In addition to equipment, engineering and construction costs must be included. In a modern refinery/petrochemical plant there is no such thing as a simple retrofit project. Each project, large or small will require a multi-discipline project approach. Most companies in our industry will require a multi-level approach which will generally include the following phases; feasibility analysis, options analysis, front-end engineering, detailed engineering, start-up, commissioning, and feedback analysis. This, in conjunction with the heightened safety awareness in our industry, is making project durations longer with resultant increased costs. 3 Croce, Fearon: "Operation and Control of N O x Reduction Systems", Presented at the A F RC International Symposium, October 19-21, 1992 K77 CORPORATION, CONCORD THE REAL COST OF NOx EMISSION REDUCTION AFRC/JFRC 1998 SYMPOSIUM |
