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

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5.1.2.2 Kiln Fuel Changing the primary kiln fuel from natural gas to coal can reduce the flame temperatures significantly resulting in lower 5 thermal NO x emissions. Although nitrogen present in coal may provide greater fuel NO x contribution, switching the fuel burned in kilns from natural gas to coal has been shown to provide substantial reduction in the total NO x emissions in one 5 experimental study. In the dry process kilns tested in this study the average NO emissions decreased from 20.4 lb/ton of x clinker to 6.2 lb/ton of clinker when the fuel was changed from gas to coal. A number of cement kilns have already made the switch from gas to coal fuel and currently almost 80 percent of the primary fuel burned in cement kilns is coal. 6 Switching to a fuel with a higher heating valve and lower nitrogen content may reduce NO emissions in a cement kiln, e.g., x petroleum coke has a lower nitrogen content per million Btu than coal. The petroleum coke is also more uniform in terms of heat value, lower in volatile matter content and burns with a lower flame temperature. 5.1.2.3 Increasing Thermal Efficiency The thermal efficiency of the cement-making process may be increased by improving gas/solids heat transfer, e.g., using an efficient chain system, increasing heat recovery from clinker cooler, and by minimizing infiltration of cold ambient air leaking into the kiln. Heat recovery from a clinker cooler may be improved by increasing the proportion of secondary air. Recycling cement kiln dust from the dust collectors would reduce the energy requirement per ton of a clinker. By increasing the thermal efficiency, NO emissions are likely to be reduced per x ton of clinker produced. 5.1.3 Staging Combustion Air, Low NO Burner, and Flue Gas x Recirculation Staging of combustion air allows combustion of fuel to proceed in two distinct zones. In the first zone, the initial combustion is conducted in a primary, fuel-rich zone. This zone provides the high temperatures necessary for completion of the 5-4
clinkering reactions. However, in this zone, due to fuel-rich conditions and lack of available oxygen, formation of thermal and fuel NO is minimized. The lack of sufficient oxygen leads to x only partial combustion of the fuel. In the second, fuel-lean zone, additional (secondary) combustion air is added to complete the combustion process. The temperature in this second zone is, however, much lower than the first zone because of mixing with the cooler secondary air. The formation of NO is thus minimized x in spite of the excess available oxygen in the second zone. This approach can be used for combustion of all fossil fuels. The staged combustion is typically achieved by using only a part of the combustion air (primary air) for fuel injection in the flame zone with remaining secondary air being injected in a subsequent cooler zone. In a direct-fired cement kiln, air used for conveying pulverized coal from a coal mill, i.e., primary air, is typically 17 to 20 percent of the total combustion air. The amount of primary air may be reduced by separating the coal mill air from coal. A cement kiln using less than 10 percent of primary air is termed as an indirect-fired kiln. Conversion of a direct-fired kiln to an indirect-fired kiln involves adding particle separation equipment such as a cyclone or a baghouse and a compressor for additional power. Such conversion is, however, necessary for effective staging of combustion air to reduce NO x emissions. Cement kiln burners, specifically marketed as low-NOx 7,8 burners typically use 5 to 7 percent primary air and thus can be used only on indirect-fired kiln systems. An indirect-firing system increases overall energy efficiency by allowing a greater proportion of hot clinker cooler air as secondary combustion air. The reduction in NO emissions with reduced primary air was x demonstrated in an experimental study on a subscale coal-fired 9 kiln. The lowest proportion of primary air used in this study, however, was only 15 percent and the experimental results cannot be directly translated to a full-size kiln. In addition to changing the combustion air distribution, the 5-5
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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
Page 37 and 38: Figure 3-3. New technology in dry-p
Page 39 and 40: substantial levels of silica and al
Page 41 and 42: are achieved by clinker coolers of
Page 43 and 44: 126,000 to 963,000 tons/year with a
Page 45: such as crushing and grinding opera
Page 48 and 49: 4.1.1 Thermal NO Formation x Therma
Page 50 and 51: temperatures are on the order of 16
Page 52 and 53: 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 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 104 and 105: higher than typical cement kiln flu
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
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20 percent PEC cost for contingenci
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TABLE 6-7. ANNUALIZED COSTS FOR RET
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6-28
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PEC for model plant 300,000 ' Heat
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TABLE 6-9. ANNUALIZED COSTS FOR MID
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6-34
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TABLE 6-10. CAPITAL COSTS FOR A URE
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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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