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

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Figure 5-4. Application of the selective noncatalytic reduction technique (SNCR) in preheater kilns. 29 SNCR system is the addition of methanol injection downstream of the urea injection point to improve overall NOx removal. Nalco also recently introduced an improved NOxOUT PLUS, which is said to broaden the operating temperature window and to reduce ammonia slip and CO and NO2 formation. The NOx reduction efficiency of SNCR depends upon the temperature, residence time, as well as ammonia and NOx concentrations in the flue gas. Injection of ammonia at a NH3: 3NOx proportion of 1 to 1.5 will reduce NOx emissions between 60 5-24
to 80 percent. Using a mol ratio of 0.5 will give NOx reductions of approximately 40 percent.23 The reagent consumptions can be significantly higher with greater ammonia slip in SNCR systems as compared to SCR systems. Operating experience has identified several concerns with both ammonia and urea-based SNCR processes. The most frequently reported is the buildup of ammonium bisulfite scale which is significant for sulfur-containing fuels. SNCR processes also appear to convert some NO to N2O.33 The rate of N2O formation is a weak function of both the reactant and the NO concentration. However, N2O formation seems to be inherently more prevalent in systems using urea than those using ammonia.34 The NOx destruction efficiency also depends upon the flue gas residence time in the appropriate temperature window. Unlike an SCR system where the reaction temperature is controlled in a dedicated reactor, an SNCR system relies on the existing gas temperature profile to provide an adequate residence time for a desired NOx destruction. Maximum achievable NOx reduction in a cement kiln may thus depend upon the gas temperature profile. 5.3 SUMMARY OF APPLICABLE NOx CONTROL TECHNOLOGIES Combustion zone control approaches discussed in Section 5.1.1 are based upon providing optimum kiln operating conditions which will increase the energy efficiency and productivity of the cement-making process while minimizing NOx emissions. Such measures will provide a baseline of NOx emissions in cement kilns without any specific NOx control equipment. Although these simple process control approaches will reduce NOx emissions in poorly operated kilns; for the purposes of this ACT document, such approaches are considered to be needed for proper kiln operation and not specifically considered as NOx control tech- niques. Information obtained during this study indicated that some plants indeed relied on process monitoring and control and process modifications as a means to maintain NOx emissions within their respective permit limits. The NOx reduction effect of process modifications discussed 5-25
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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
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expected to produce more fuel NO th
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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
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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
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Page 100 and 101: Figure 5-3. Schematic of hazardous
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Page 104 and 105: higher than typical cement kiln flu
Page 106 and 107: window is in the middle of a kiln.
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
Page 154 and 155: 6-40
Page 156 and 157: 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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