| Title |
NOx Control with Lime-Urea Hydrate on Coal-Fired Boilers |
| Creator |
Himes, Richard M.; Muzio, Lawrence J.; Thompson, Richard E. |
| Publisher |
Digitized by J. Willard Marriott Library, University of Utah |
| Date |
1990 |
| Spatial Coverage |
presented at San Francisco, California |
| Abstract |
Coal-fired boilers have generally relied upon combustion modifications and/or lowNOx burners to achieve initial NOx reductions on the order of 15%-50%. Selective noncatalytic reduction (SNCR) technologies (e.g. Thermal DeNOx and urea injection) can potentially produce higher levels of NOx removal, however, with the SNCR processes it is necessary to address the reactions between ammonia (NH~ emissions from the process and sulfur trioxide (SO~. The NH3 can react with S03 forming ammonium sulfates, which in turn, can lead to air heater fouling. NOx reductions of 80%-90% will thus likely require the use of selective catalytic reduction (SCR) unless some of the other technologies are used in combination. Recently, however, a cost effective dry S02/NOx control technology has been developed utilizing lime-urea hydrate injection in the upper furnace or convective pass regions of coal-fired boilers. Although primarily intended for simultaneous reductions of S02 and NOx, the proportion of urea to lime in the hydrate may be adjusted so as to focus the emissions reduction potential on NOx. The presence of the lime in the hydrate serves to react with, and remove any S03 prior to the flue gas reaching temperature conditions favorable for reaction with ammonia emissions. In this manner, air heater fouling attributable to ammonium sulfates formation is potentially alleviated. Pilot-scale test results have demonstrated simultaneous removals of S02 and NOx on the order of 65% at a Ca/S ratio of 3 and N/NOx ratio of 1.5. The current paper focuses on the use of the lime-urea hydrate principally for NOx control. By being able to optimize the temperature window for NOx control, removals of approximately 60% can be achieved at N/NOx ratios of 1. Further emissions reduction potential for NOx are possible by implementing the technology in combination with combustion modifications and/or low NOx burners. An economic assessment of the lime-urea hydrate technology for NOx control has indicated capital costs of less than 40 S/kW for a 100 MW unit. Levellzed busbar costs for a plant with a 65% capacity factor and 20 years remaining plant life were calculated to be on the order of 3.6 mills/kWh. Cost comparisons with alternative NOx reduction technologies demonstrated the lime-urea hydrate, in combination with low NOx burners, to be a cost effective alternative to SCR while achieving similar overall NOx emissions reductions. |
| Type |
Text |
| Format |
application/pdf |
| Language |
eng |
| Rights |
This material may be protected by copyright. Permission required for use in any form. For further information please contact the American Flame Research Committee. |
| Conversion Specifications |
Original scanned with Canon EOS-1Ds Mark II, 16.7 megapixel digital camera and saved as 400 ppi uncompressed TIFF, 16 bit depth. |
| Scanning Technician |
Cliodhna Davis |
| ARK |
ark:/87278/s6j968x8 |
| Setname |
uu_afrc |
| ID |
6019 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s6j968x8 |
| Title |
Page 18 |
| Format |
application/pdf |
| OCR Text |
Two principle observations can be made from these figures regarding the lime-urea economics. First, the technology represents a cost effective approach for achieving a broad range of pollutant emissions reductions. As shown in Figure 6, the capital cost associated with 60% emissions reductions is almost one-third that associated with SCR, and is directly comparable with coal-reburning on a cyclone boiler. Second, the levellzed costs of the lime-urea technology are competitive with all other technologies examined for a given level of emissions reductions. The principle difference In levelized costs between coal reburnlng and lime-urea hydrate is a direct reflection of the sorbent cost with all other costs being roughly the same. Overall, the lime-urea hydrate technology provides a means for minimizing up front capital expenditures. When combined with low NOx burners, the lime-urea hydrate technology can also provide emissions reductions on the order of SCR. SUMMARY Based on the foregoing economic assessment, the lime-urea hydrate technology has been found to be a cost effective approach for the reduction of NOx emissions. By virtue of the relative low capital cost associated with the lime-urea hydrate technology, as well as its inherent flexibility with respect to achievable emissions reductions, the technology can meet a broad range of applications which include: 1) a primary pollutant control technology for substantial reductions of NOx' 2) a trimming technology for maintaining compliance with NOx during peak usage periods of a unit, or 3) a backup pollutant control system for maintaining compliance during breakdowns of primary pollution control equipment. No significant cost impacts, beyond the added cost of the urea itself, were found to be associated with the production of the lime-urea hydrate. The current price level of urea was also evaluated and found to not be sensitive to any increased demand from the utility industry. It should be noted that equivalent transportation costs of 100 miles by truck and 400 miles by rail were incorporated in the lime-urea hydrate cost. Although off-site hydration was assumed for the economic assessment, levelized costs could be reduced significantly should on-site hydration prove to be a viable alternative for a given site, or if 30-day storage requirements could be reduced. A comparison of the economics with alternative technologies demonstrated that the lime-urea hydrate approach is cost effective. Due to its variable cost orientation, the lime-urea hydrate exhibits low capital costs relative to selective catalytic reduction. Also, by combining the lime-urea hydrate technology with low NOx burners, comparable NOx emission reductions to SCR can be achieved. -18- |
| Setname |
uu_afrc |
| ID |
6016 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s6j968x8/6016 |
