NOx Emissions from Cement Mfg - US Environmental Protection ...

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higher than typical cement kiln flue gas temperatures especially in plants using heat recovery systems or baghouses for particulate collection. In general, the catalysts may be fouled or deactivated by the particulates present in the flue gas. In the case of cement plants, the presence of alkalies and lime as well as sulfur dioxide in the exhaust gases is also of concern. Because of fouling problems, the SCR system must be installed after the particulate collection. Recent developments have led to sulfur tolerant SCR catalysts which limit SO2 oxidation to less than 1 percent.25 Soot blowers may be used to prevent dust accumulation on SCR catalysts. Since the typical SCR operating temperatures are greater than the typical kiln exhaust flue gas temperatures, installation of an SCR unit would also need flue gas reheating to increase the flue gas temperatures to an appropriate level. Ammonia is typically injected to produce a NH3 : NOx mol ratio of 1.05-1.1 : 1 to achieve NOx conversion of 80 to 90 percent with a "slip" of about 10 ppm of unreacted ammonia in the gases leaving the reactor.26 The NOx destruction efficiency depends upon the temperature, NH3 : NOx mol ratio, and the flue gas residence time (or the space velocity) used in the catalyst bed. The SCR reactor system can be designed for a desired NOx reduction using appropriate reagent ratio, catalyst bed volume, and operating conditions. There are currently no installations of SCR units in any United States cement plants or elsewhere. In 1976, Hitachi Zosen, an SCR manufacturer, conducted three pilot test programs to evaluate SCR on cement kilns.2 During these tests, two suspension preheater kilns and a wet process kiln were tested for 5,400 hours each. Electrostatic precipitators were used to remove particulates before the flue gas entered the SCR unit. Also, a heat recovery system equipped with supplemental fuel firing was provided to raise the flue gas temperatures to the required reaction temperatures. Slipstreams of about 3,000 scfm 5-20
were treated with initial NOx removal efficiencies of 98 percent. However, after 5,400 hours of operation, NOx removal efficiencies dropped to about 75 percent due to catalyst coating. SCR is a possible technology for the NOx reduction in cement kiln emissions. Based on the experience in other industries, NOx reductions in the range of 80 to 90 percent are considered possible, regardless of kiln type.22 However, further developmental studies are needed to demonstrate the specific NOx reduction in the cement kiln exhaust gas environment. 5.2.2 Selective Noncatalytic Reduction (SNCR) This control technique relies on the reduction of NOx in exhaust gases by ammonia or urea in an appropriate temperature window of 870 to 1090 EC (1600 to 2000 EF) without using any catalyst. This process also involves the same reactions (5-3) and (5-4) as in the case of the SCR process. This approach avoids the problems related to catalyst fouling, as in SCR technology, but requires injection of the reagents in the kiln at an appropriate temperature between 870 to 1090 EC (1600 to 2000 EF). At these temperatures urea decomposes to produce ammonia which is responsible for NOx reduction. In principle, any of a number of nitrogen compounds may be used, e.g., cyanuric acid, pyridine, and ammonium acetate. However, for reasons of cost, safety, simplicity, and by-product formation, ammonia and urea have been used in most of the SNCR applications. Because no catalyst is used to increase the reaction rate, the temperature window is critical for conducting this reaction. At higher temperatures, the rate of a competing reaction for the direct oxidation of ammonia which actually forms NOx becomes significant. At lower temperatures, the rates of NOx reduction reactions become too slow resulting in too much unreacted ammonia slip. The effective temperature window range can be lowered to about 700 EC (1300 EF) by the addition of hydrogen along with the reducing agent.27 Several other reagents can also shift the temperature window to the 700 EC(1290oF) level.28 In a conventional long kiln the appropriate temperature 5-21
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EPA-453/R-94-004 ALTERNATIVE CONTRO
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ALTERNATIVE CONTROL TECHNOLOGY DOCU
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Chapter Page 4.1 MECHANISMS OF NO F
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TABLE OF CONTENTS (con.) Chapter Pa
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LIST OF TABLES Number Page 2-1 UNCO
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CHAPTER 1 INTRODUCTION Congress, in
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CHAPTER 2 SUMMARY This chapter pres
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2.2 NO EMISSION CONTROL TECHNOLOGIE
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TABLE 2-2. ACHIEVABLE NO REDUCTIONS
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TABLE 2-4. CAPITAL AND ANNUAL COSTS
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TABLE 2-5. COST EFFECTIVENESS OF NO
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eductions ranged from 470 tons/year
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CHAPTER 3 INDUSTRY DESCRIPTION 3.1
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Type II. Moderate-heat-of-hardening
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3 a TABLE 3-2. UNITED STATES CEMENT
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Figure 3-1. U.S. Portland cement pl
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Table 3-3. (con.) Rank Clinker 3 (1
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5 cement processes: wet process and
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Figure 3-3. New technology in dry-p
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substantial levels of silica and al
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are achieved by clinker coolers of
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126,000 to 963,000 tons/year with a
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such as crushing and grinding opera
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4.1.1 Thermal NO Formation x Therma
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temperatures are on the order of 16
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4-6
Page 54 and 55: expected to produce more fuel NO th
Page 56 and 57: introduce a large proportion of com
Page 58 and 59: will also mean a somewhat lower sec
Page 60 and 61: ILC systems: In these systems, the
Page 62 and 63: which indicates an average and the
Page 64 and 65: 4-18
Page 66 and 67: Uncontrolled NO x emissions Plant c
Page 68 and 69: from 2 to 9 lb/ton of clinker, and
Page 70 and 71: Capacity Heat in NO x emissions Met
Page 72 and 73: TABLE 4-3. (con.) Capacity Heat in
Page 78 and 79: in estimating uncontrolled and cont
Page 80 and 81: 13. Letter from Sheridan, S.E., to
Page 82 and 83: 44. Chemecology Corporation Source.
Page 84 and 85: 73. Letter and attachments from Smi
Page 86 and 87: NO control approaches applicable to
Page 88 and 89: 5.1.2.2 Kiln Fuel Changing the prim
Page 90 and 91: oxygen content of the primary air m
Page 92 and 93: tend to recirculate hot combustion
Page 94 and 95: e about 15 to 38 percent depending
Page 96 and 97: combustion system shown in Figure 5
Page 98 and 99: 5-14
Page 100 and 101: Figure 5-3. Schematic of hazardous
Page 102 and 103: 5-18
Page 106 and 107: window is in the middle of a kiln.
Page 108 and 109: Figure 5-4. Application of the sele
Page 110 and 111: in Section 5.1.2 is usually difficu
Page 112 and 113: 5.4 REFERENCES 1. Helmuth, R.A., F.
Page 114 and 115: 25. Letter from Wax, J., Institute
Page 116 and 117: TABLE 6-1. CEMENT KILN MODEL PLANTS
Page 118 and 119: 6-4
Page 120 and 121: 6-6
Page 122 and 123: The total capital cost is the sum o
Page 124 and 125: TABLE 6-3. ANNUALIZED COST ELEMENTS
Page 126 and 127: 6-12
Page 128 and 129: 6.1.3.7 Administrative Charges. The
Page 130 and 131: At this time only three installatio
Page 132 and 133: 6-18
Page 134 and 135: The annualized costs for low NOx bu
Page 136 and 137: No additional costs for utilities o
Page 138 and 139: 20 percent PEC cost for contingenci
Page 140 and 141: TABLE 6-7. ANNUALIZED COSTS FOR RET
Page 142 and 143: 6-28
Page 144 and 145: PEC for model plant 300,000 ' Heat
Page 146 and 147: TABLE 6-9. ANNUALIZED COSTS FOR MID
Page 148 and 149: 6-34
Page 150 and 151: TABLE 6-10. CAPITAL COSTS FOR A URE
Page 152 and 153: TABLE 6-11. ANNUAL OPERATING COSTS
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6-40
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TABLE 6-12. CAPITAL COSTS FOR AN AM
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TABLE 6-13. ANNUAL OPERATING COSTS
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6-46
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costs range from $9.9 million for t
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The estimated annualized costs for
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6.3 COST EFFECTIVENESS OF NOx CONTR
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emoved. Cost effectiveness were det
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TABLE 6-17. COST EFFECTIVENESS OF R
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6-58
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TABLE 6-18. COST EFFECTIVENESS OF M
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TABLE 6-19. COST EFFECTIVENESS OF U
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6.3.4 Selective Catalytic Reduction
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6-66
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TABLE 6-21. COST EFFECTIVENESS OF S
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6-70
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11. Letter and attachments from Nov
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Tables 7-1 7-2
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TABLE 7-2. REDUCTION IN NO x EMISSI
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model plants described in Section 6
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temperature and excess air may be u
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NOxemissions will form. The heater
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equirement for the flue gas reheati
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