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

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(150 to 750 ft) long] equipped with an electrical drive to rotate at 1 to 3 rpm. It is a countercurrent heating device slightly inclined to the horizontal so that material fed into the upper end travels slowly by gravity to be discharged onto the clinker cooler at the lower discharge end. The burners at the firing end, i.e., the lower or discharge end, produce a current of hot gases that heats the clinker and the calcined and raw materials in succession as it passes upward toward the feed end. Refractory bricks of magnesia, alumina, or chrome-magnesite combinations line the firing end. In the less heat-intensive midsection of the kiln, bricks of lower thermal conductivity are often used. Abrasion-resistant bricks or monolithic castable linings are used at the feed end. The cement formation process in the kiln may be divided into four stages, correlated with temperature of the materials in the rotary kiln : 6 ! Uncombined water evaporates from raw materials as material temperature increases to 100 EC (212 EF). ! As the material temperature increases from 100 EC (212 EF) to approximately 900 EC (1650 EF), dehydration and material heating occur. ! At 900 EC (1650 EF), calcination occurs in which CO is 2 liberated from carbonates. ! Following calcination, a chemical reaction of the dehydrated and decarbonated raw materials occurs in the burning zone of the rotary kiln at temperatures of about 1510 EC (2750 EF), producing clinker. About 20 to 25 percent of the material is molten. ! The cement clinker continues to change in character as it passes the zone of maximum temperature. The duration and location of these stages in an actual kiln depend upon the type of process used, e.g., wet or dry, and the use of preheaters and precalciners as discussed in the following section. It is desirable to cool the clinker rapidly as it leaves the burning zone. This is best achieved by using a short, intense flame as close to the discharge as possible. Heat recovery, preheating of combustion air, and fast clinker cooling 3-16
are achieved by clinker coolers of the reciprocating-grate, planetary, rotary, or shaft type. Most commonly used are grate coolers where the clinker is conveyed along the grate and subjected to cooling by ambient air, which passes through the clinker bed in cross-current heat exchange. The air is moved by a series of undergrate fans and becomes preheated to 370 to 800 EC (700 to 1500 EF) at the hot end of cooler. A portion of the heated air serves as secondary combustion air in the kiln. Primary air is that portion of the combustion air needed to carry the fuel into the kiln and disperse the fuel. 3.3.4.1 Wet Process Kilns. In a long wet-process kiln, the slurry introduced into the feed end first undergoes simultaneous heating and drying. The refractory lining is alternately heated by the gases when exposed and cooled by the slurry when immersed; thus, the lining serves to transfer heat as do the gases themselves. Because large quantities of water must be evaporated, most wet kilns are equipped with chains to maximize heat transfer from the gases to the slurry. The chains also serve to break up the slurry into nodules that can flow readily down the kiln without forming mud rings. After most of the moisture has been evaporated, the nodules, which still contain combined water, move down the kiln and are gradually heated to about 900 EC (1650 EF) where the calcination reactions commence. The calcined material further undergoes clinkering reactions. As the charge leaves the burning zone and begins to cool, clinker minerals crystallize from the melt, and the liquid phase solidifies. The granular clinker material drops into the clinker cooler for further cooling by air. 4 Long process kilns typically represent an older cement technology with smaller capacity kilns. In the United States wet cement kiln capacities range from 90,000 to 1,312,000 tons/year with an average of 325,000 tons/year (41 tons/hour). 3 3.3.4.2 Dry Process Kilns. The dry process utilizes a dry kiln feed rather than a slurry. Early dry process kilns were short, and the substantial quantities of waste heat in the exit 3-17
Page 1 and 2: EPA-453/R-94-004 ALTERNATIVE CONTRO
Page 3 and 4: ALTERNATIVE CONTROL TECHNOLOGY DOCU
Page 5 and 6: Chapter Page 4.1 MECHANISMS OF NO F
Page 7 and 8: TABLE OF CONTENTS (con.) Chapter Pa
Page 9 and 10: LIST OF TABLES Number Page 2-1 UNCO
Page 11 and 12: CHAPTER 1 INTRODUCTION Congress, in
Page 13 and 14: CHAPTER 2 SUMMARY This chapter pres
Page 15 and 16: 2.2 NO EMISSION CONTROL TECHNOLOGIE
Page 17 and 18: TABLE 2-2. ACHIEVABLE NO REDUCTIONS
Page 19 and 20: TABLE 2-4. CAPITAL AND ANNUAL COSTS
Page 21 and 22: TABLE 2-5. COST EFFECTIVENESS OF NO
Page 23 and 24: eductions ranged from 470 tons/year
Page 25 and 26: CHAPTER 3 INDUSTRY DESCRIPTION 3.1
Page 27 and 28: Type II. Moderate-heat-of-hardening
Page 29 and 30: 3 a TABLE 3-2. UNITED STATES CEMENT
Page 31 and 32: Figure 3-1. U.S. Portland cement pl
Page 33 and 34: Table 3-3. (con.) Rank Clinker 3 (1
Page 35 and 36: 5 cement processes: wet process and
Page 37 and 38: Figure 3-3. New technology in dry-p
Page 39: substantial levels of silica and al
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 88 and 89: 5.1.2.2 Kiln Fuel Changing the prim
Page 90 and 91:
oxygen content of the primary air m
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tend to recirculate hot combustion
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e about 15 to 38 percent depending
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combustion system shown in Figure 5
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5-14
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Figure 5-3. Schematic of hazardous
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5-18
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higher than typical cement kiln flu
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window is in the middle of a kiln.
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Figure 5-4. Application of the sele
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in Section 5.1.2 is usually difficu
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5.4 REFERENCES 1. Helmuth, R.A., F.
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25. Letter from Wax, J., Institute
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TABLE 6-1. CEMENT KILN MODEL PLANTS
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6-4
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6-6
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The total capital cost is the sum o
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TABLE 6-3. ANNUALIZED COST ELEMENTS
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6-12
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6.1.3.7 Administrative Charges. The
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At this time only three installatio
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6-18
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The annualized costs for low NOx bu
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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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