| OCR Text |
Show Construction cost must be included in this analysis. More importantly, the project team must evaluate the required shutdown time required to install the various technologies. For example, burner modifications are preferred over burner replacements, if the achievable N O x emissions are acceptable. S C R technologies that can be installed downstream of heat recovery sections (such as the Shell D e N O x System 4) would be preferred in some cases over conventional S C R units, due to the minimal shutdown time required for installation. Operating Cost Operating cost of a NOx reduction system is one of the most commonly neglected aspects of the cost effectiveness analysis. In almost all applications, the N O x reduction technology has an operating cost associated with it. Whether this cost is negative or positive, it is included in this analysis. ULNB typically have very little operating cost associated with them. However, one of the most commonly ignored cost or benefit is the efficiency change associated with the operating constraints of ULNB. In some cases, U L N B may require inert injection such as steam or low heating value gas. These types of inert gas injection will result in slight decreases in firebox efficiency, causing fuel cost increases. More importantly, the cost saving associated with the required low excess oxygen operation with U L N B must be considered. Since most fired units are not generally operated at these low excess oxygen levels, credit should be taken for the resulting demand to operate at these lower oxygen levels. SNCR will have operating costs associated with ammonia or urea usage and carrier air blower or compressor power. In addition, since the ammonia or urea with the carrier air is essentially an inert gas being injected into the fired unit, the lowering of firebox efficiency should be considered. SCR will have operating cost associated with ammonia usage and induced draft fan power (as necessary). In some cases, the addition of an induced draft fan will result in the elimination of a draft problem or limitation, resulting in an increase in capacity. In s o m e cases, relocation of an S CR has increased steam production4. In addition, the cost of catalyst must be factored into the equation. 4 Croce, Kinsfather, Ylstra, Hamilton, "Application of the Shell D e N O x System on GT-HRSG", Presented at the 1997 A S M E Turbo Expo Conference. KTI CORPORATION, CONCORD THE REAL COST OF NOx EMISSION REDUCTION 3 In many cases, the addition of NOx reduction technologies becomes an opportunity to remove a possible bottleneck in the fired unit. Examples would be the inclusion of an induced draft fan or possibly installing larger, higher capacity burners. With each of these examples, the cost associated with the increase in capacity must be considered in the cost effectiveness analysis since capacity increases represent a benefit for applying the N O x reduction technology to the given fired unit. Maintenance Cost Every NOx reduction technology will increase overall maintenance cost. The following are some of the most known maintenance items associated with the common N O x reduction technologies: Common to almost all NOx reduction technologies will be the need to install analyzers. NOx and oxygen analyzers are very time consuming to maintain, with daily maintenance not uncommon in the industry. ULNB will require three other types of maintenance; burner tip cleaning, fuel gas filter replacements, and furnace tuning. ULNB tips are generally smaller than those of conventional burners which will cause them to plug faster than the tips of existing burners. Gas filter replacement frequently is directly related to burner tip plugging. If filters are used and maintained, the frequency of burner tip cleaning can be greatly reduced. Furnace tuning is critical in achieving top performance from U L N B applications. State of art oxygen control systems should be used, however even with these, periodic furnace tuning and checking will be mandatory. SNCR technology will require periodic maintenance on items such as the carrier air blowers or compressors, ammonia or urea pumps, injector cleaning, system tuning. System tuning is mentioned here again, since most N O x reduction technologies will require some sort of control. These control schemes must be maintained and kept functioning in order for the technology to perform as warranted. SCR technology will have an ammonia injection system (air blowers, pumps, injection system, etc) that will require periodic maintenance in addition to the inducted draft fan (if needed). AFRC/JFRC 1998 SYMPOSIUM |
