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Gossman Consulting, Inc.

GCI TECH NOTES©


Volume 1, Number 07                  A Gossman Consulting, Inc. Publication                             July, 1995
Appropriate Sampling Frequency for Cement Plant Process Samples During Stack Testing

David Gossman

Introduction

In order to better understand the effects of process variables on emissions at cement plants it is necessary to obtain representative samples of process inputs and outputs during emissions testing. Representative process sampling is also required for BIF Compliance Tests and Trial Burns. EPA guidance on Trial Burns suggests (but does not require) sampling each process stream every fifteen minutes. This sampling frequency is clearly based on EPA's experience with hazardous waste incinerators. EPA has never demonstrated that a fifteen minute sampling frequency can improve the accuracy of process sample determinations for a cement plant. Process streams at cement plants are substantially more uniform based on the cement production requirements and methods. A simple grab sample is frequently considered representative of an entire day's worth of feed or production. Somewhere between those two extremes would seem to be a conservative and technically defensible sampling frequency.

Process Sample Types

Process inputs include kiln feed and fuels. Kiln feed is ground and stored in large batches prior to feeding to the kiln. It is stored as either a fine dry powder or wet slurry. Dry powder kiln feeds are stored in blend silos. Slurries are stored in slurry tanks which maintain a continuous agitation system. With either of these systems, batch sizes are frequently twenty-four hours worth of feed or larger. However, some dry feed systems have storage for as little as ten hours worth of raw material. Fuel is fed in a variety of forms into cement kilns. Coal and coke is ground to a fine powder prior to being blown into the kiln. The large quantities of these fuels purchased and stockpiled at a cement plant result in a very uniform feed. Waste fuels include solvents, containerized solids/sludges, ground solids, tires, (both whole and chipped), as well as other miscellaneous materials. Liquids are accumulated in large batch tanks which are continuously agitated. Depending on feed rates and tank sizes, batches will last ten hours or more. Other fuels are accumulated and fed in large enough quantities to maintain uniform feedstream characteristics just as with the coal and coke.

Process outputs other than emissions include cement clinker and cement kiln dust. Cement clinker by virtue of its product quality requirements is a uniform process output. Cement kiln dust is similarly uniform. Changes in process outputs that may occur as a result of sudden input changes, metal spiking as an example, typically take four to ten hours to have full effect. The large residence time for materials in the kiln combined with internal recirculating loads will necessarily result in any changes occurring over a number of hours.

Data From 1992 COC Tests

During the 1992 COC Tests performed to comply with the BIF regulations, two plants (Holnam - Clarksville, MO and Holly Hill, SC) with three kilns analyzed both run by run and daily composites of most process inputs and outputs. All samples were taken on an hourly basis. Both run composites (three to four hourly samples) and daily composites (ten to fourteen hourly samples) were made and analyzed. The remarkable consistency in the data demonstrates the uniformity of cement plant feed streams. Bear in mind that the typical analysis of duplicate samples can vary 10 to 25% for these types of determinations. Results close to the detection limit can vary even more. The data is consistent enough that problems with sample digestion, such as the

coal/coke kiln 2 run 2 results, and other analytical problems are easily spotted. Tables 1 and 2 demonstrate the consistency of the slurry (kiln feed) and coal/coke. Table 3 provides similar information for the liquid hazardous waste fuel at both plants. Tables 4 and 5 demonstrate the consistency of the kiln outputs - clinker and cement kiln dust. Clearly, had there been significant variation in these process streams that would require more frequent sampling, such as every 15 minutes, these results could not be as consistent.

Table 1 - Slurry



Kiln 1


Kiln 2


Kiln 3



Units Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily
Arsenic ppm ND ND ND ND 5.2 5.4 6.3 4.8 3.0 3.2 2.9 2.9
Barium ppm 48 45 49 49 88 87 82 86 61 62 57 58
Beryllium ppm 0.50 0.47 0.52 0.52 1.4 1.4 1.3 1.4 1.3 1.3 1.2 1.3
Chromium ppm 9.9 10.5 12.9 12.8 37 37 35 37 36 34 32 33
Nickel ppm NA NA NA NA 19 23 22 20 21 10 16 20
Lead ppm 3.4 3.4 3.3 2.9 6.6 6.9 6.6 6.4 7.5 7.8 7.2 7.2
Antimony ppm ND ND ND ND 0.9 1.3 <0.6 1.0 1.4 1.2 0.9 1.1
Chlorine ppm 130 109 129 134 ND ND ND ND ND ND ND ND
Sulfate ppm 350 324 326 345 616 613 598 512 1350 1380 1450 1390

Table 2 - Coal/Coke



Kiln 1


Kiln 2


Kiln 3



Units

Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily
Arsenic ppm ND ND ND ND 7.6 <0.8 5.7 5.7 4.4 4.9 10.5 4.5
Barium ppm 12 20 14 15 107 26 76 84 42 58 79 64
Beryllium ppm 5.6 4.8 4.8 5.4 4.4 0.6 5.2 7.7 6.2 6.3 6.0 6.9
Chromium ppm 9.2 9.2 8.0 13.1 22 1 14 15 7.2 10.0 11.9 10.7
Nickel ppm NA NA NA NA 124 16 164 188 231 178 150 194
Lead ppm 2.8 1.9 2.8 2.2 15 2 16 12 4.1 5.2 6.7 5.1
Antimony ppm ND ND ND ND <0.8 <0.8 0.8 1.3 1.1 1.2 0.8 0.9
Chlorine ppm 800 606 822 642 1070 924 1080 1400 1730 1050 785 635
Sulfur ppm 33200 30200 38300 36400 20800 23100 15900 18900 20600 25200 15200 21400
Heat Content BTUs/lb 12800 11900 12500 13000 12700 12300 12100 12300 11600 13400 11900 12700

Table 3 - Liquid Hazardous Waste Fuel



Kiln 1


Kiln 2


Kiln 3



Units Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily
Barium ppm 757 1040 764 662 509 579 554 573 675 527 663 628
Beryllium ppm 0.7 0.9 0.6 0.6 0.6 0.6 0.8 0.8 0.5 0.3 0.4 0.4
Cadmium ppm 4.4 6.3 4.6 3.7 7.8 8.0 7.1 7.3 11.2 9.5 11.4 10.5
Chromium ppm 134 225 160 120 106 114 104 101 94 74 92 90
Nickel ppm NA NA NA NA 23 25 21 23 43 37 42 40
Lead ppm 361 500 369 314 319 400 341 329 325 257 321 304
Antimony ppm 11 16 14 9 26 31 23 33 27 25 26 34
Chlorine ppm 49000 53000 51000 50600 18500 19300 20500 20100 24400 23000 19800 17900
Sulfur ppm 1970 2440 2380 1900 4180 4390 4830 4210 2710 3690 2560 2080
Heat Content BTUs/lb 15800 16300 14600 16300 11300 11300 11100 11500 11300 11000 10300 11000
Viscosity cp 45 39 41 84 30 41 41 41 50 46 53 43
SpecificGravity
0.88 0.85 0.87 0.87 0.90 0.90 0.91 0.90 0.93 0.92 0.92 0.89

Table 4 - Clinker



Kiln 1


Kiln 2


Kiln 3



Units Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily
Arsenic ppm 23 22 19 22 24 46 56 33 23 23 34 23
Barium ppm 135 177 134 131 216 195 216 224 225 202 291 221
Beryllium ppm 9.1 14.5 8.9 8.8 13.6 11.8 13.0 13.7 13.5 11.5 16.3 11.7
Chromium ppm 295 258 277 251 405 368 439 436 551 395 469 403
Nickel ppm NA NA NA NA 40 37 38 40 84 54 60 57
Lead ppm 7.5 5.9 5.7 6.7 3.3 3.0 2.2 6.3 4.2 7.2 6.3 5.9
Antimony ppm 1.6 1.4 <0.8 <0.8 152 162 165 152 94 93 126 94

Table 5 - Cement Kiln Dust



Kiln 1


Kiln 2


Kiln 3



Units Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily Run 1 Run 2 Run 3 Daily
Arsenic ppm NA NA NA NA 22 47 48 35 36 32 49 26
Barium ppm NA NA NA NA 259 281 264 274 214 214 212 213
Beryllium ppm NA NA NA NA 12.1 12.3 11.7 12.4 12.1 12.5 12.5 12.2
Cadmium ppm NA NA NA NA 171 151 149 168 136 130 135 134
Chromium ppm NA NA NA NA 324 374 382 364 325 332 341 336
Nickel ppm NA NA NA NA 35 35 34 35 31 39 32 35
Lead ppm NA NA NA NA 1420 1610 1650 1610 1400 1420 1490 1420
Antimony ppm NA NA NA NA 148 157 175 161 135 26 151 109
Selenium ppm NA NA NA NA 9.1 8.2 7.6 9.1 6.6 6.3 8.3 7.1
Thallium ppm NA NA NA NA 1.6 1.5 1.7 1.4 1.1 1.0 0.9 0.7
Chlorine ppm NA NA NA NA 11000 10900 12000 11400 22400 11100 10400 12500
Sulfate ppm NA NA NA NA 4240 4840 3260 4620 11900 11800 10700 11600

Conclusion and Recommendations

For the majority of cement plant process streams, hourly sampling is a conservative sampling strategy. More frequent sampling is unnecessary during normal/stable operations. Samples can be composited on a run by run or daily basis depending on the data quality objectives and how the data is to be utilized.