United States Environmental Protection Agency Hazardous Waste Engineering Research Laboratory Cincinnati OH 45268 Research and Development EPA/600/S2-87/016 June 1987 AEPA Project Summary Water Quality Characterization of an Eastern Coal Slurry C. David Cooper Current and projected uses of coal have resulted in several proposals for coal slurry pipelines in the eastern part of the United States. While several re- searchers have reported on the water quality aspects of western coal slurries, less work has been done with respect to eastern coals. An experimental study was conducted at the University of Cen- tral Florida from 1982 to 1983 with slur- ries of 50 percent eastern Kentucky coal and 50 percent water. Experiments were conducted with and without the addition of a corrosion inhibitor. Twenty-nine water quality parameters were measured as a function of pump- ing time in a 12-meter (40-ft) long, 2.54 cm (1 inch) diameter pipeline con- structed for this study. Also, the treatability of the 10-day slurry filtrate was assessed using both lime and alum addition. By about the fourth day in the pipeline, most parameters had reached equilibrium values. As expected for this high-ash, medium-sulfur coal, sulfates, TDS, and conductivity in the slurry fil- trate started high and increased with time. Dissolved oxygen quickly dropped to near zero. Concentrations of several heavy metals were substan- tial, but organics were generally very low, about 5-10 mg/L. Trihalomethane formation potential was quite low, never exceeding 35 ppb. Although the samples were consistent in any one run, samples from different runs on the "same'" coal were significantly differ- ent. Addition of the corrosion inhibitor increased the concentrations of sul- fates, TDS, and several other parame- ters. The characterization of this partic- ular coal slurry was compared with those of several western coal slurries reported in the literature. This Project Summary was devel- oped by ERA's Hazardous Waste Engi- neering Research Laboratory, Cincin- nati, OH, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). Introduction The United States is heavily depend- ent on coal for electricity generation. This reliance on coal is projected to in- crease even more in the future, as oil and gas decrease in supply and increase in price. The use of coal is expected to increase substantially in Florida and other southeastern and Gulf-coast states, based on their projected popula- tion growth and on their previously high percentage use of oil and gas for power generation. In recent years, the coal slurry pipeline has been promoted as a safe, reliable, and economical alternative to railroad transportation of coal. Basi- cally, coal slurry pipelining is a means of transporting coal that involves mix- ing pulverized coal with water and pumping it in a steel pipeline as shown schematically in Figure 1. First, the coal is pulverized to a powder consistency, then mixed with an equal weight of water to form a slurry. (A 50 percent coal slurry is a pumpable fluid that is somewhat more dense and substan- tially more viscous than water.) The slurry is then pumped through a pipeline, using a number of strategically placed pumping stations, from the coal source area to the receiving power ------- Slurry Preparation Export Figure 1. Power Plant Dewatering Plant Schematic diagram of a full scale coal slurry pipeline system. Source: A.D. Dorr is. 1981. Used by permission. plants. At the receiving sites, the slurry is dewatered and the coal is burned. The water is treated before re-use or dis- charge. One objection to coal slurry pipelines has been the possible pollution of waters at the receiving location by con- taminants leached from the coal while in the pipeline. Both inorganic and or- ganic chemicals are solubilized in con- centrations that depend on the physical and chemical nature of coal, the water source, and the time in the pipeline. Several researchers have studied vari- ous western coals, but less work has been done with respect to eastern coal slurries. Eastern coals typically contain more sulfur than western coals, and they typically have lower percentages of the alkaline metals (Na, K, Ca, Mg) in their ash. Thus, there could be substan- tial differences between the slurry water resulting from eastern coals and that from western coals. Purpose and Scope The primary objective of this work was to characterize the slurry water re- sulting from an eastern coal. For charac- terization, 29 water quality parameters were measured on slurry filtrate sam- pled at various pumping times in a small pipe-loop system built for this study. The parameters included 11 gen- eral items (such as pH, dissolved solids, and sulfates); three organic tests (total organic carbon, trihalomethane forma- tion potential, and phenols); and 15 metals. The characteristics observed in this study were then compared with those of other coal slurries reported pre- viously in the literature. Another major objective was to as- sess the effects of the addition of a com- mercial corrosion inhibitor on water quality. Due to the potential for corro- sion of the pipeline by coal slurries, some consideration has been given to adding a chemical corrosion inhibitor. The effects of the addition of a nitrite- based inhibitor on slurry water quality were investigated in this research. A third objective was to address the question of treatability of the slurry water. Previous researchers have indi- cated that conventional technology is adequate to treat coal slurry waste- waters. Two of the more common treat- ment processes were used to treat the 10-day slurry water: high pH lime pre- cipitation and alum coagulation. After treatment, the wastewaters were ana- lyzed for the same parameters as above. In addition, the sludges from the treat- ment processes were subjected to the EP toxicity (leaching) test and tested for eight toxic metals. Experimental Procedures The coal used in this study was ob- tained with the help of personnel at the Mclntosh Power Plant in Lakeland, Flor- ida. Coal, shipped by unit train from an eastern Kentucky mine, was received al that power plant and processed through the usual sequence of processing steps. A portion of the feed stream of pulver- ized coal to one of the burners was di- verted into a custom designed barrel that caught the coal dust, but allowed the air to exhaust through an attached filter bag. Approximately two days were required to obtain a full drum (125 kg), thus allowing for some "time- averaging" of the coal sample. About 70 percent of the pulverized coal passed a 200 mesh screen. All slurries were processed in a pilot- scale system constructed specifically for this project. A 50-percent solids slurry was made by adding tap water from the University of Central Florida's potable water system to the pulverized coal in an open top 210-liter steel drum. The final volume of slurry was mixed in about one hour by hand-held steel rods and a small (12 volt, 15 amp) boat trolling motor. The slurry was transferred by hand into a closed top, nitrogen-inerted, 265- liter steel tank into which was mounted a Hazleton submersible slurry pump. The pump was belt driven with a 1.12 kw motor and had a speed controller. The pump worked very well; because it was submersible, seal leaks were not a problem. A second electric trolling motor installed in the tank kept the slurry well mixed during the run. The slurry was pumped through a 15 meter long, 2.54 cm diameter schedule 80 steel pipe loop that returned to the bot- tom of the tank. The pump speed was adjusted to achieve a slurry velocity of 1.2 to 1.8 m/s in the pipe. The tank was kept nitrogen-blanketed throughout the 10-day slurry runs. Cooling water flowed through an external concentric pipe to maintain the slurry temperature between 26°C and 32°C for all runs. A schematic diagram of the experimental system is presented in Figure 2. Samples of the slurry were taken sev- eral times throughout each 10-day run, more frequently in the first few days. The sample times were 3 hours, 7 hours, and 1, 2, 4, 7, and 10 days. Whole slurry samples were immedi- ately tested for pH, dissolved oxygen, and redox potential. The remaining samples were then vacuum filtered through a 24-cm diameter Whatman No. 1 filter paper, and then through a 0.45 micron glass filter. Some of the fil- trate was then acidified and refrigerated ------- N2 Supply Slurry Mixer ,->— i r Level Indicator i C ;H a /nrl t « 4* jj_ r (_r t i^ IT ,--• Slurry Pump - - f i ~i To Drain -Slurry Tank From Tap Water Cooling Pipe i . — 1X1 . | — — - (_ | l/a/ve ; Valve [ Valve Sampling Tee To Drain Figure 2. Schematic diagram of pilot-scale pipe loop used for coal slurry experiments. for later metals analysis; the rest of the filtrate was tested for a variety of water quality parameters. All analytical tests were conducted according to Standard Methods for Ex- amination of Water and Wastewater, 14th edition (1975), or Methods for the Analysis of Water and Waste, EPA 6007 4-79-020 (1979). Metals were analyzed with a DC arc plasma emissions spec- trophotometer in lieu of an atomic ab- sorption unit. In all, the tests included 11 general water quality parameters, 3 measures of organic content including trihalomethane formation potential (THMFP), and 15 metals. All parameters were observed on each sample except for phenols and THMFP due to the lengthy test procedures for these two. On the tenth day, large volume sam- ples were drawn for treatability testing. A laboratory procedure was used to simulate conventional treatment proc- esses that might be anticipated in prac- tice: coal separation by sedimentation and decantation, chemical addition, co- agulation, flocculation, sedimentation, and filtration. The chemicals added were either lime or alum. The optimum dose was defined as that which maxi- mized turbidity removal on small aliquots of the untreated decantate. The remainder of the decantate was then treated at the optimum dose. The final treated effluent was analyzed for all the original parameters (except phenols) to determine removal efficiencies. Finally, the sludges produced by the treatments were later tested according to the EP toxicity test to assess their potential as a hazardous waste. Results and Discussion The coal used in this research project came by unit train from eastern Ken- tucky and can be characterized as a medium sulfur (1.9%), high ash (16%), eastern bituminous coal. Some test data for the coal used in the four exper- imental runs are presented in Tables 1 and 2. Also, a mineral analysis for the major components in the ignited ash showed approximately 50 percent sil- ica, 25 percent alumina, 17 percent fer- ric oxide, and about 6 percent basic metal oxides. The source water was University of Central Florida tap water. The water originated from an underground lime- stone aquifer and was aerated and chlo- rinated prior to distribution to the potable water system. Typical source water characteristics are shown along with the slurry filtrate analyses. Four valid experimental runs were completed. Runs 2 and 3 without a com- mercial corrosion inhibitor (nitrite based) and Runs 4 and 5 with the in- hibitor. (Run 1 was used for equipment and procedures shakedown.) The fact that there were significant variations in the coal quality was reflected in the re- sulting slurry qualities. In all runs, simi- lar trends in the time behavior of the slurry contaminants were observed. However, in Run 2 the concentrations of all pollutants were significantly higher than in Run 3. A similar situation existed for Runs 4 and 5. The slurry with the corrosion inhibitor had significantly higher concentrations of sulfates, TDS, conductivity, and alkalinity. Differences in the other parameters were not so pro- nounced or may have been masked by differences in the coal samples. Results of all the tests are tabulated in Tables 3 and 4, which present averaged data of the two runs without the corro- sion inhibitor and the two with the in- hibitor. Generally, most parameters reached equilibrium values in the first few days of the run. For the runs with- out inhibitor, the slurry pH dropped im- mediately on mixing but then rose to about 6 by the tenth day for all runs. The initial pH drop was suppressed by the corrosion inhibitor. Dissolved oxygen quickly dropped to near zero as it re- acted with the sulfur and other minerals in the coal. As expected for this coal, sulfates were high and reflected the sulfur con- tent of the coal. Equilibrium concentra- tions averaged about 1300 mg/L for the two runs without corrosion inhibitor, but surprisingly averaged about 3500 mg/L with the inhibitor. Apparently, the inhibitor enhanced some ion exchange process with the coal minerals because the inhibitor itself did not contain sulfur. This difference in the sulfates' behavior is shown graphically in Figure 3. Figure 4 presents the averaged data for pH, and highlights the differences observed with and without the corrosion in- hibitor. Furthermore, for the slurry with the inhibitor, it was observed that coal- water separation was more difficult. The concentrations of dissolved or- ganics were low for this coal slurry, as indicated by the tests for total organic carbon and phenols. TOC was in the 5-10 mg/L range and phenols were around 1 ppb. Also, for this particular coal slurry, THMFP was quite low, never exceeding 35 ppb. As shown in Tables 3 and 4, the concentrations of several metals increased one to three orders of magnitude over the levels in the mix water, the largest percentage gainers being iron and manganese. Some heavy metals exhibited little or no in- crease. Treatability results are not tabulated in this Summary. However, it was shown that both lime and alum addi- tions were effective in removing certain contaminants. Lime treatment removed metals better than alum, but alum re- moved organics better than lime. It should be obvious that the treatment processing sequence specified at a coal slurry receiving site depends on the characteristics of the particular coal slurry and the degree of treatment de- ------- Table 1. Coal Proximate Analysis (Dry Basis)* Parameter %Ash % Volatiles % Fixed Carbon Heating Value (Btu/lb) % Sulfur % Passing 200 mesh Run 2 15.28 32.85 51.87 11,632 2.26 80 Run 3 14.39 36.79 48.82 12,830 1.69 — Run 4 15.37 36.49 47.63 11,922 1.93 68 Run 5 18.50 35.13 46.37 11,500 1.70 72 Avg. 15.89 35.32 48.67 11,971 1.90 73 Composite as received, 2 unit trains (May and June, 1983)** 14.43 36.10 49.48 12,688 2.13 — 'SOURCE: Mclntosh Power Plant Chem. Lab., Department ofElec. and Water Utilities, Lake- land, Florida **SOURCE: Mclntosh Power Plant files Table 2. Trace Metals Analysis of Coal ppm in ignited ash, as the element Component Hg Se Cd Zn As Mn Cu Pb Ni Cr Ba Mg Ag Run 2 56 92 3.5 106 156 163 221 122 90 231 585 8,490 4.0 Run 3 47 83 4.3 311 238 541 139 101 136 133 837 15,900 2.0 Run 4 63 72 4.2 228 379 408 154 109 133 150 797 8,190 7.0 Run 5 59 63 4.2 219 421 505 110 104 135 123 720 9,610 2.5 Average 56 78 4.1 216 298 404 156 109 124 159 735 10,550 3.9 sired. However, this and previous stud- ies reported in the literature, indicate that conventional treatment with exist- ing technology should be sufficient. Conclusions and Recommendations Eastern coals typically have higher sulfur content and less alkaline ash than western coals. As expected, the slurry filtrate obtained in this study of an east- ern coal exhibited higher sulfate con- centrations and lower pH values than would be expected from a typical west- ern coal. For the particular coal used in this study, very few organics were leached into the water. TOC averaged 5-10 mg/L, phenols averaged about 1 ppb and THMFP never exceeded 35 ppb. Also, for this particular coal, very significant concentrations of iron (100-500 mg/L) and manganese (5-25 mg/L) leached into the water. Concentrations of lead, nickel, and aluminum also increased significantly, but each remained in the 0.1 to 1 mg/L range. It was shown that oxygen reacts readily with sulfur and other minerals in coal slurries, and thus care should be taken to exclude oxygen as much as possible when forming, pumping, or loading coal slurries com- mercially. Coal-water interactions require some time to reach equilibrium. For several parameters, at least four or five days must elapse before equilibrium is ap- proached. A corrosion inhibitor signifi- cantly increased the concentrations of sulfates, TDS, conductivity, and alkalin- ity. In addition, coal-water separation became more difficult. Even though the coal samples used in this study were from the same source and were obtained in a "time- averaged" manner, the properties of the coal samples were apparently differ- ent enough to result in significant differ- ences in the slurry filtrate observed in "replicate" runs. While the time-behav- ior trends for most parameters were similar, absolute levels in the filtrate were different. Thus, it is recommended that several replications be conducted to be able to characterize the slurry of any particular coal with confidence. In order to reach valid conclusions about the behavior of eastern coal slurries, at least 10 more eastern coals should be studied. Coal slurry wastewaters likely will re- quire treatment before reuse or dis- charge. Studies thus far indicate that present treatment technology can pro- vide adequate treatment, but the specific processing scheme will depend on the particular coal slurry characteris- tics and site specific regulations. The treatment sludges produced in this study did not fail the EP toxicity test. ------- 4OOO 3000 I 2000 10OO Runs4 &5(average) 0 Runs2 &3(average) o Mix 01234 56 7 8 9 10 Water Time, days Figure 3. Effect of corrosion inhibitor (Cl) on sulfates (Runs 2 and 3 without Cl and Runs 4 and 5 with Cl). ------- 7.0 6.0 \ 5.0 4.0 3.0 I—t Mix 0 1 2 3 4 5 6 7 8 9 10 Water Time, days Figure 4. Effect of corrosion inhibitor (Cl) on pH (Runs 2 and 3 without Cl and Runs 4 and 5 with Cl). Table 3. Data Summary Table—Average of Runs 2 and 3 Parameter, Units Typical Mix Water Average Concentrations in Slurry Filtrate by Time after Start of Run 3-hours 7-hours 1-day 2-days 4-days 7-days 10-day General Sulfates, mg/L 2 942 1016 1075 1070 1340 1306 1342 Chlorides, mg/L 19 36 43 58 72 86 108 116 TDS,mg/L 207 1612 1596 1740 1966 2400 2636 2695 Conductivity, mho/cm 366 1483 1468 1590 1713 1974 2120 2452 Dissolved Oxygen, mg/L 7.9 2.5 0.3 0.2 0.15 0.05 0.05 O.C Redox Potential, mv 526 211 158 62 -32 -84 -152 -196 pH 7.0 4.2 4.8 5.2 5.8 5.9 6.2 6.2 Acidity, mg/L as CaCO3 -96 470 423 480 530 778 878 852 Alkalinity, mg/L as CaCO3 120 12.4 14.3 12.4 22.2 15.2 22.4 13.2 Color, CPU 6 8 7.5 20.5* 94.5* 69* 132* 280* Turbidity, JTU 5.3 3.8 10.9 18.2* 52.2* 67.2* 65.2* 53.5 Organics TOC, ppm 6 7.4 5.1 3.6 5.0 6.1 6.2 5.6 THMFP.ppb 60 — — — — — — 23 Phenols, ppb — — 1.0 — 1.0 — 1.2 1.4 ------- Table 3. (continued) Parameter, Units Metals (mg/L) Hg Se** Cd Zn As** Mn Cu Al Fe Pb Ni Cr Ba Mg Ag Typical Mix Water 0.076 0.242 0.006 0.071 0.045 0.009 0.016 0.033 1.28 0.029 0.002 0.004 0.015 11.0 0.002 Average Concentrations in 3-hours 0.21 0.20 0.03 1.29 0.35 4.06 0.21 10.7 58.1 0.30 1.02 0.03 0.16 67 0.02 7-hours 0.18 0.22 0.03 0.96 0.38 4.36 0.01 2.89 92.4 0.30 0.76 0.03 0.12 67 0.02 1-day 0.24 0.21 0.02 0.46 0.36 4.98 0.02 0.78 168 0.30 0.30 0.03 0.09 68 0.01 Slurry Filtrate 2-days 0.26 0.23 0.02 0.20 0.50 6.44 0.02 0.30 214 0.28 0.09 0.02 0.12 67 0.02 by Time after Start of Run 4-days 0.40 0.33 0.03 0.17 0.58 10.2 0.03 0.52 313 0.34 0.10 0.03 0.12 74 0.02 7-days 0.42 0.38 0.04 0.17 0.68 10.5 0.02 0.38 344 0.36 0.08 0.03 0.12 76 0.02 10-days 0.45 0.37 0.04 0.15 0.63 10.9 0.03 0.47 358 0.40 0.14 0.04 0.10 78 0.02 NOTE: *=Precipitate formed, data not meaningful. **=Data suspect—instrument problems, see quality assurance section. Table 4. Data Summary Table—Average of Runs 4 and 5 Parameter, Units General Sulfates, mg/L Chlorides, mg/L TDS, mg/L Conductivity, mho/cm Dissolved Oxygen, mg/L Redox Potential, mv pH Acidity, mg/L as CaCOj Alkalinity, mg/L as CaCO3 Color, CPU Turbidity, JTU Organics TOC, ppm THMFP, ppb Phenols, ppb Metals (mg/L) Hg Se** Cd Zn As"* Mn Cu Al Fe Pb Ni Cr Ba Mg Ag Typical Mix Water 2 19 207 366 7.9 526 7.0 -96 120 6 5.3 6 60 — 0.076 0.242 0.006 0.071 0.045 0.009 0.016 0.033 1.28 0.029 0.002 0.004 0.015 11.0 0.002 Average Concentrations in 3-hours 1865 66 4398 4630 0.55 141 6.1 402 258 8 3 2.0 — — 0.05 0.24 0.007 0.09 0.23 7.55 0.07 0.28 0.52 0.36 0.36 0.79 0.06 775 0.008 7-hours 1920 80 4277 4480 0.35 62 6.6 416 208 9 4 3.8 — — 0.05 0.23 0.006 0.09 0.24 4.80 0.03 0.29 0.45 0.34 0.08 0.03 0.09 108 0.002 1-day 1955 112 4192 4455 0.10 -118 6.8 323 158 8 32* 12.6 — — 0.054 0.26 0.007 0.07 0.23 3.11 0.03 0.32 11.3 0.32 0.06 0.03 0.08 104 0.007 Slurry Filtrate by Time after Start of Run 2-days 2860 134 4364 4962 0.05 -102 6.3 568 78 7 50* 5.2 — — 0.09 0.37 0.07 0.76 0.36 8.80 0.03 0.29 737 0.39 0.72 0.04 0.78 728 0.07 4-days 3425 147 5624 5445 0.05 -744 6.2 920 40 8 774* 7.3 — 7.0 0.74 0.37 0.008 0.75 0.36 77.9 0.02 0.34 259 0.39 0.77 0.03 0.75 758 0.075 7-days 3430 160 5920 5410 0.05 -137 6.2 1010 54 8 94* 7.6 — 7.5 0.75 0.33 0.07 0.76 0.40 74.7 0.07 0.46 270 0.40 0.22 0.03 0.09 762 0.078 10-days 3680 178 5712 5362 0.05 -136 6.3 855 58 6 96* 18.6 8 1.0 0.75 0.37 0.07 0.75 0.38 76.6 0.02 0.45 270 0.42 0.32 0.03 0.03 763 0.076 NOTE: *=Precipitate formed, data not meaningful. **=Data suspect—instrument problems, see quality assurance section. ------- C. D. Cooper, J. D. Dietz, M. J. Flint, and M. R. Todd are with College of Engineering, University of Central florrda, Orlando, Florida 32816. Eugene F. Harris is the EPA Project Officer (see below). The complete report, entitled "Water Quality Characterization of an Eastern Coal Slurry," (Order No. PB 87-169 9757AS; Cost: $18.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Hazardous Waste Engineering Research Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 BULK RATE POSTAGE & FEES P/> EPA PERMIT No G-35 Official Business Penalty for Private Use $300 EPA/600/S2-87/016 0000329 ------- |