Ind. Eng. Chem. Res. 1991,30, 2143-2147 um. J. Chin. Chem. 1982,29 (2), 71-80. Jwo, J. J.; Chen, Y. H.; Chang, E. F. Isomerization of maleic-acidto fumaric-acid catalyzed by cerium(IV) and N-bromo compounds. J . Chin. Chem. 1983,30 (2), 103-115. Katunin, V. Kh.; Penkina, V. I. Isomerization of maleic-acid with thiourea. Zh.Prikl. Khim. 1963,36 (lo), 2261-2265. Marquardt, D. W. An algorithm for least squares estimation of nonlinear parameters. SAM J . Appl. Math. 1963,II, 431-441. Mathai, I. M. Kinetics of the olefin-bromine reaction. X Influence of producta on the kinetics of bromine addition to unsaturated acids. J. Sci. Znd. Res. (India) 1958, I7B,145149. Mezaki, R.;Kittrell, J. R.Parametric sensitivity in fitting nonlinear kinetic models. Znd. Eng. Chem. 1967,59 (3), 63-69. Nozaki, K.; Ogg, R. Cis-trans isomerizations. The mechanism of a catalyzed isomerization of maleic acid to fumaric acid. J. Am. 1941,63,2583-2586. Chem. SOC.
2143
P W ,L.; Segarra, R.Cingtica de la isomerizacidn maleico-fum6rico. Afinidad (E) 1973,30, 13-21. Reti, T.; Kovacs, T.; Bognar, J.; Kolonics, Z.; Tuba, G.; Halas, G.; Bassa, R.;Legradi, L.; Horvath, 1.; Meszaros, P. Preparation of pure fumaric acid from maleic acid-containing industrial wastee. Br. U.K. Pat. Appl. GB2,207,915, 1989. Russell, J. L.; Ridgewood, N. J.; Olenberg, H. Procedure to manufacture fumaric acid of good color from maleic acid. US. Pat. 3,389,173, 1968. Schliesser, W. Catalytic activity of thiourea and ita analogs in the isomerization of maleic-acid to fumaric-acid. Angew. Chem. 1962, 74, 429-430. Received for review May 22, 1990 Revised manuscript received December 26, 1990 Accepted May 21,1991
Reactivation of Fly Ash and Ca(OH)2Mixtures for SO2 Removal of Flue Gas Juan C. Martinez, Jose F. Izquierdo, Fidel Cunill,* Javier Tejero, a n d Javier Querol Chemical Engineering Department, University of Barcelona, Mart; i Franques 1, 08028 Barcelona, Spain
Mixtures of fly ash and Ca(OH)2 were hydrated, characterized, and tested in laboratory-scale experiments. Hydrated mixtures developed a high total surface area, greater than the arithmetical addition of surface areas of initial solids before hydration. The relative surface area increment increased with temperature, time of hydration, and fly a ~ h / c a ( O H ratio, ) ~ the temperature effect being the most important. Tetracalcium aluminate monosulfate and tetracalcium aluminate were assumed to be responsible for these area increments. Only 5 % SO2 removal was observed with untreated fly ash after 1h of contact and at high humidity. High SO2capture occurred with hydrated mixtures. SO2removal correlates well with the relative surface area increment. The amount of SO2 capture increases strongly with the increasing relative humidity of the gas. Introduction Severe limits on emissions of sulfur dioxide from coal combustion plants have risen drastically for large, new plants. These limits are not as strict for retrofitting existing power plants. These regulatory changes have resulted in the development of a variety of processes for removing SO2,removal of sulfur from flue gases being the most widely used process (Merrick and Vernon, 1989). Flue gas desulfurization processes can be grouped into three broad categories, dry adsorption, wet scrubbing, and dry/wet processes, based on the mechanism of removing SOz. In wet scrubbing processes, the removal of sulfur is by chemical absorption using a limestone or slaked lime slurry in spray towers. Dry adsorption systems used physical or chemical sorption on charcoal or other sorbent in a typical fixed bed to remove SO2, but these systems are expensive and hardly used. In the last few years, dry/wet processes (Yoon et al., 1986; Statnick et al., 1987; FECSA, 1986; Merrick and Veron, 1989), which are based on the injection of a solid sorbent and water into the flue gas duct work, are being developed by several companies because of their inherent low capital cost. Dry/wet systems can be categorized, based on the way in which sorbent and water are introduced in the duct, into two groups: those that inject sorbent as an slurry, namely, Bechtel CZD (Abrams et al., 1985; Bechtel Corp., 1987), General Electric IDS (Yoon et al., 1986; Statnick et al., 1987; Shilling, 1986; Martinelli et al., 19871, and EPA E-SOX (Yoon et al., 1986; Sparks et al., 1985; Ponder, 1985); and those that inject dry sorbent and water separately, namely, Dravo HALT (Yoon et al., 1986; Statnick
et al., 1987; Babu et ai., 1986; Forsythe and Kaiser, 1985), EPRI (Yoon et al., 1986; McElroy, 1985; Hooper et al., 1985),and Consol Coolside (Yoon et al., 1986; Statnick et al., 1987; Yoon et al., 1985a,b; Conoco, 1985; Stouffer et al., 1989). Nearly all of these employ hydrated lime as the sorbent, and SO2removal, drying of sorbent particles, and gas humidification occur simultaneously. SO2is removed not only by wet sorbent particles in the duct but also when they have been dried and the gas humidified, which can take place in the last part of the duct and in the particulate collection system. The advantages of dry/wet processes over conventional wet methods are that a dry solid waste is produced and that the equipment is easier to set up in existing power plant. High SO2 removal is well-known to be carried out by hydrated sorbents in the presence of humidity. The amount of SO2captured at a given temperature increases as the adiabatic saturation temperature is approached (Yoon et al., 1985a,b; Stouffer et al., 1989). In an attempt to explain these findings, puzzolanic reaction between fly ash, Ca(OH)2,and water was hypothesized to be the main factor for SO2 capture (Jozewicz and Rochelle, 1986; Jozewicz and Chang, 1987). So, in the range of temperatures from 20 to 100 "C, hydrated calcium silicate (CaO*Si02H20), dicalcium silicate hydrate (2Ca0*SiO2-H2O), and tetracalcium aluminate hydrate (4Ca0.A1203.13H20)can be formed. The presence of sulfates in the fly ash can lead to the formation of gehlenite (2Ca0.Al2O3.SiO2-8HTO), ettringite (3Ca0-A1203-3CaS04.32H20), and tetracalcium aluminate monosulfate (3Ca0A1203.CaS04-12H20).These highly hydrated products are probably responsible for SO2 removal.
0888-588519112630-2143$02.50/0 0 1991 American Chemical Society
2144 Ind. Eng. Chem. Res., Vol. 30,No. 9, 1991 Table I. Characterization of Fly Ash from the Power Plant of Cercs (Barcelona) density: 2.56 g/cmS mean particle size: 0.048 mm specific area: 0.42 m2/g chemical compositiona MgO: 1.57% SO2: 37.05% CaO: 34.21% K20 1.21% TiOp: 0.68% A1203: 13.45% N a 2 0 0.35% Fe203: 7.12% SO$ 4.7% P205: 0.14% aPercentage based on weight. Figure 1. Apparatus for the desulfurization test 1, reactor; 2, vaporizer; 3, thermostatic bath; 4, syringe pump; 5, ice trap; 6, SO2 analyzer.
It appears that the mechanism of fly ash activationstarts with the digestion of vitreous-phase silica and/or alumina by alkaline water (Jozewicz and Rochelle, 1986). This first stage is considered to be the rate-limiting step. Next, calcium aluminate silicate is formed and precipitated on the surface of the fly ash. The surface area of solids obtained increases with increasing temperature, time, and alkalinity. Previous studies (Reed et al., 1984)have shown that the reactivity of hydrated fly ash depends mainly on two factors: the surface area and the accessible alkalinity. The greater the surface area and alkalinity, the greater the amount of SO2 removal expected. The aim of this work is to report the laboratory evaluation of the potential for reactivation of fly ash and Ca(OH), mixtures in order to raise the amount of SO2capture in retrofitted control applications. Firstly, several solids were prepared by mixing fly ash and commercial Ca(OH)2 in different ratios. Secondly, the mixtures were hydrated under different conditions of time and temperature in a batch process. Finally, the resulting dry samples were tested for SO2removal at differents levels of humidity and temperature in a fixed bed. Experimental Section Apparatus and Procedures. The experiments were carried out in the apparatus depicted schematically in Figure 1. The jacketed glass reactor (12mm in diameter, 450 mm in height) was packed with 2 g of powdered fly ash and Ca(OH), mixed with stainless steel coils (2 mm in diameter) to prevent both plugging and a high pressure drop. Thermic fluid was pumped from a thermostatic bath to the reactor jacket to keep the catalyst bed isothermal within 0.1 "C. A stream of N2with SO2was fed to the reactor at a flow rate of 1.62 L/min measured at the conditions of the reactor. The nominal concentration of SO2 was 500 ppm, and the exposure time of the fly ash to the sulfurized gas was 1 h. Gas flow was monitored by using a flow control valve and an orifice meter. Water was metered by a syringe pump to the vaporizer. In the electrically heated vaporizer, packed with metallic Raschig rings, water was evaporated at about 180 "C and homogenized with the gas stream in order to control the humidity. The tubing upstream of the reactor and from the reactor to the ice bath was heated to prevent the condensation of water vapor. The ice bath cooled the gas and condensed the water vapor before it entered the SO2analyzer. Prior to each experiment, the bed was humidified by nitrogen at the relative humidity at which the run was to be performed for 10 min. The amount of condensed water vapor was determined to calculate the SO2concentration in the reactor from the
Figure 2. SEM microphotographof untreated fly ash sample.
concentration value measured in the SO2analyzer (infrared photometer UNOR 6N). The SO2 concentration was measured continuously during the test, which gave us a ppm SO2versus time curve. Each run was exactly repeated in all conditions, but fly ash was substituted for inert silica. The amount of SO2removal was calculated from the area enclosed by these two curves. Sample Preparation and Characterization. A sample of fly ash, produced in the power plant of Cercs (Barcelona) firing a high sulfur lignite (4%), was received from the electrical company FECSA. The characterization of the fly ash is given in Table I. The presence of available CaO, silica, and alumina can be noted. Thus, the necessary ingredients for a puzzolanic reaction to take place are present, and high surface area compounds could be formed. Figure 2 shows a scanning electron microscopy (SEM) microphotograph of the fly ash sample. Fly ash spheres with smooth surfaces can be seen. Different sorbents were prepared by slurrying and drying mixtures of reagent-grade Ca(OH)2 (18m2/g BET area) with fly ash (0.4 m2/g BET area). The water-tosolids ratio was 151. The slurrying variables were temperature, time, and a ~ h / c a ( O Hratio. ) ~ After the slurrying time, the samples were vacuum filtered and microwave dried for about 7 min. The morphologies of some of them were characterized on an scanning electron microscope. The composition of the crystalline phases was detected with a X-ray diffractometer. The nitrogen BET surface of all samples was determined on an Accusorb 2100 from Micromeritics Co.
Results and Discussion of the Hydration Runs The hydration experiments were performed following a 23 factorial design. Table II shows the ranges of variables of the experimental design and the relative surface area increments of the solids obtained by the procedure de-
Ind. Eng. Chem. h.Vol. , 30,No. 9,1991 2145 Table 11. Variable Level8 of the Factorial Design and Relative Surface Area Increments Obtained at Long Timsample temp, OC time, h fly ash/Ca(OHI2 AS, 1 55 2 6 1.2 2 3 4 5 6 7 8 9 10 11
85 55 85 55 85 55 85 70 70 70
2 7 7 2 2 7 7 4.5 4.5 4.5
6 6 6 18 18 18 18 12 12 12
1.4 1.3 5.4 1.5 2.7 2.7 14.3 2.8 3.5 2.7
Table 111. Application of Yat"8 Algorithm to Solids Hydrated at Long Times sample as, estimated variable 1.2 av 3.8 1.4 1.3 5.4 1.5 2.7 2.7 14.3
Table IV. Spacinge and Intensity of Tetracalcium Aluminate and Tetracalcium Aluminate Monosulfate Peak8 in X-rav Analveis samde d, A counta/s 1 2 3 4 5 6 7 8 9 10 11
8.22 8.2 9.13 8.14 8.95
42.2 67 24.2 42 93.8
8.97 8.98 9.04 8.19 8.18 8.22
46.6 36.2 74.6 62.8 68.4 43.7
T
4.3 4.2 3.6 2.9 2.1 2.2 1.6
t
Tt
R TR tR TtR
scribed earlier. The relative surface area increment calculated from the relationship
was used as the objective function because fly ash/Ca(OW2
mixtures did not have the same initial surface area. The results of applying Yates's algorithm to the hydration data are given in Table 111. As can be seen, the overall hydration treatment has a positive effect on the relative surface area increment. The individual effect of each variable is positive as well. Therefore, we can conclude that the relative surface area increament increases with increasing temperature and/or hydration time and/or ash/Ca(OH), ratio. To evaluate quantitatively the effect of each variable, an empirical linear model without interaction terms was fitted to the following coded data by linear regression: t - 4.5 R - 12 T-70 3e1 = , x2=- 2.5 (2) '3 = 25 6 The model inadequately fit the data since the experimental F statistic was greater than the tabulated F statistic for a probability level of 95%. However, the model terms were significant, which accounted for the addition of the interaction terms in the first step to improve the model. So, the following interactive first-order terms were added: z4 = xIx2, x5 = ~1x3, = x g 3 , and x7 = 3tlxg3. The F test showed that the expanded model (Fd = 7.5 and Fbb = 18.5) adequately fit data and that all terms were significant for a probability level of 95%. In this way, the following first-order polynomial fits the coded data in a statistically significant fashion: S, = 3.59 + 2.14X1 + 2.11~2+ 1.46~3+ 1.79X4 + 9
1 . 0 5 ~+~1 . 0 8 ~ +~0 . 8 ~(3)~
It should be noted that the effects of temperature and time of hydration are more important than the effect of fly a ~ h / c a ( O Hratio ) ~ on the relative surface area increment. The relative surface area increment increases slightly as this ratio increased. It looks as if, for a given calcium content, further addition of Ca(OH)2does not affect to the specific area increment.
Figure 3. SEM microphotographof sample 8 after 7 h of hydration at 85 "C.
In order to explain the relative surface area increments, the hydrated solids were analyzed by X-ray and compared with the sample spectra before hydration. Peaks a t high spacing were found which had been no detected before (see Table IV). Peaks of tetracalcium aluminate hydrate (d = 8.2 A) and tetracalcium aluminate monosulfate (d = 9 A) were present in the hydrated samples (Joint Committee on Powder Diffractometer Standards, 1986). It can also be seen in Table IV that samples 4,6, and 8, hydrated a t 85 "C, have quite a strong peak for tetracalcium aluminate monosulfate as long as samples 3 and 7, hydrated for 7 h a t 55 "C,are present; also, this peak intensity is much lower. So it can be concluded that this compound is favorably formed a t higher temperatures and times of hydration, the effect of temperature probably being the most important. The presence of tetracalcium aluminate was detected in samples 1-3 and 9-11; all of these were hydrated a t shorter times and at lower temperatures than samples 4,6, and 8. The formation of these aluminates in the crystalline phase rather than silicates is not surprising if we take into account what is mentioned in the Introduction and that the fly ash used had a significant amount of alumina w h m dissolution apparently ( J m w i n and Chang, 1987) is faster than that of silica. On the other hand, it must be noted that the intensity (amount of product) of the peaks of these hydrates corresponds fairly well to the increase in relative surface area increment, which agrees with literature data (Jozewicz and Chang, 1987). The morphology of the hydrated samples was characterized by SEM. Figure 3, a SEM microphotograph of sample 8, shows the development of the surface area produced by the formed hydrates.
2146 Ind. Eng. Chem. Res., Vol. 30, No. 9, 1991 Table V. Variable Levels and the Relative Surface Area Increments Obtained at Zero Time fly ash/Ca(OH)* As, sample temp, "C A 85 6 0.6 B 85 18 1.7 6 0.1 C 55 18 D 55 0.6 Table VI. Desulfurization Tests. Conditions and Results mgS02/ % SO2 sample temp, O C re1 humid, % g solid removal fly ash 60 60 0.7 5.1 0.8 fly ash 60 80 1 60 60 9.4 46 1 80 20 3.9 17 12.6 1 80 60 66 12.9 11 60 65 60 9 80 20 4.1 19 11 70 13.2 80 60 94 18.9 8 60 60 8 80 20 7.4 33 8 80 60 100 18.8 18.2 60 60 93 Ca(OH)z 17.6 80 60 93 Ca(OH)z 51 9.4 B 80 60 32 5.9 D 80 60
i
I
-T:U\\P
80°Cc; HR= 20%
P 7 7 : T -
BO%.
sample HR- 60%
Figure 5. Effect of relative humidity on SO2removal for samples 1,8,and 9 at 80 O C .
90 BO
70 i
4
60
LT
50
8
500
N
p
40
30 20
10
: TS (0
Qc
HR-
(0%
m;
TI 8OQC, HR= 60%
Figure 6. Effect of temperature on SO2 removal for samples 1,8, and 11, fly ash, and Ca(OH)*at 60% relative humidity. 0 0
1
2 T ~ U I ~10-3 .
3
4
1.1
Figure 4. Effect of exposure time on the SO2 capture at 80 OC and 20% relative humidity: (+) concentration of SOz versus time for sample 8; ( 0 )concentration of SO2 versus time for inert solid.
Four experiments were performed at zero time, when water at a desired temperature was poured over solids and mixed for about 1 min before vacuum filtering and microwave drying. These experiments tried to approach the existing conditions in the duct of the dry/wet processes. The conditions of these hydrations and the relative surface area incrementa obtained are given in Table V. It can be seen that area increments are lower than those of samples hydrated at longer times. X-ray powder diffraction analysis of these four samples did not detected any s i g nificant amount of hydrated products in the vitreous phase, which correlates with the poor relative surface area determined. Perhaps the main cause is that there is not enough time for hydrates to crystallize. However, this does not mean that the solids prepared at short times were not able to capture SO2.
Desulfurization Results and Discussion The reagents used in the experiments of SO2 capture were untreated fly ash, Ca(OH)2,hydrated samples 1, 8, 9, and 11 (replication of 91, which are located in the diagonal of the cube of the factorial design, and samples B and D hydrated at zero time. Figure 4 shows, as an example, the effect of exposure time on the SO2capture by sample 8 at 80 "C and 20% relative humidity. In fact,
these SO2 capture measures are the values registered by the SO2analyzer and have to be corrected to the reactor conditions. The SO2capture data in Table VI are defined as the number of milligrams of SO2 captured by 1 g of sorbent after 1h of exposure to SO2in the f i e d bed. Table VI also shows the temperature and relative humidity at which each run was performed and the removal of SO2 expressed as the percentage of SO2 circulated during the experiment. As can be seen, the data show that only a small SO2 removd ( 5 % ) occurred with untreated fly ash even though the temperature and relative humidity were high. On the contrary, Ca(OH), showed a high SO2capture, more than 90%, at the same temperature and humidity levels. The SO2 removal for Ca(OHI2did not change when the temperature increased from 60 to 80 "C at constant relative humidity. SO2 capture for samples 1, 8, 9, and 11 was important depending on the temperature and humidity levels. The removal increases with increasing temperature and relative humidity, the effect of humidity being the most important. Figure 5 shows the effect of relative humidity on SO2capture by samples 1,9, and 8 at 80 "C. The increase of relative humidity from 20% to 60% tripled, at least, the SO2 capture for all the samples. The effect of temperature at 60% relative humidity is shown in Figure 6. The increase of 20 "C (from 60 "C to 80 "C) led to a less important increases except for untreated fly ash which increased fivefold. It should be noted that sample 8 is the most reactive sorbent and sample 1the most unreactive. This correlates well with the relative surface area increment of these samples. So the greater the surface area increment, the
Ind. Eng. Chem. Res., Vol. 30, No. 9,1991 2147 Table VII. Surface Areas before and after Desulfurization Tests SamDle S, (initial) S, (final)I
1 11 8
Ca(OHh B D
.
I
7.5 7.1 21.5 18.3 3.8 2.2
1.1 1.1 7.9 9.1 1.1 0.7
higher SO2 removal was. X-ray analysis of samples 1, 11, and 8 after being exposed to SO2for 1h a t 80 O C and 60% relative humidity showed that tetracalcium aluminate hydrate had practically disappeared, and an important lowering of tetracalcium aluminate monosulfate had resulted in sample 8. considering that this sample presents 100%removal after 1h of exposition, we can conclude that it is not saturated by SOz. On the other hand, relative surface area increments of theae samples after contact with SOz are substantially lower (see Table VII). These findings suggest that calcium aluminate and/or aluminate sulfate highly hydrated could be responsible for SO2removal. Also, it is important to note the strong effect of humidity on SO2 removal. The amount of water adsorbed on the solid increases significantly with increasing relative humidity. However, the intrinsic mechanism of this effect is not completely understood. Additional efforts, particularly on the kinetics of the reaction, are needed in order to improve SO2removal by wetfdry process on the basis of the mechanism itself. What we can say in the light of the present paper and of literature is that moisture is essential and that the greater the better. Conclusions Atmospheric hydration of mixtures of fly ash and Ca(OH)2produced solids with a high surface area increment. The surface area increment increases with temperature and time of hydration and with fly a ~ h / c a ( O Hratio. ) ~ The most important effect is the temperature of hydration and the least important is ash/Ca(OH)z ratio. Crystals of 4Ca0*A1203aH20and 3Ca0.Al20&aSO4. xH20 ( x > 13) are present in hydrated samples. The amount of these hydrated compounds correlates well with the relative surface area increment. Tetracalcium aluminate monosulfate is formed favorably at higher temperatures and at longer times, and tetracalcium aluminate is formed at lower temperatures and at shorter times. Hydrated solids have significant reactivity and can provide substantial SO2removal, which correlates well with the relative surface area increment, increasing with increasing surface area increments. The observed SO2 removal increased strongly with the increasing relative humidity of gas. Ca(OH)2also has a high reactivity for SO2 capture. Thus, the reactivated fly ashes developed and studied in laboratory-scale experiments can make wet/dry process an attractive low-cost SO2control option. However, further work is needed to evaluate the reactivated fly ashes at the pilot and demonstration scales. Acknowledgment We are thankful for financial support of this investigation from the electrical company FECSA of Catalonia, and we thank the Jaume Almera Institute for analytical support. Nomenclature R = fly ash/calcium hydroxide weight ratio Sur= final surface area, m2.g-l
S~ = initial surface area, m2.g-' t = hydration time, h T = hydration temperature, K AS, = relative surface area increment
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Jozewicz, W.; Rochelle, G. T. Fly Ash Recycle in Dry Scrubbing. Environ. Prog. 1986,5 (4), 219-224. Martinelli, R.; Murphy, K.; Pennline, H. In-Duct Scrubbing Moderate SO2 Removal for Existing Power Plants. Pacific Coaet Electrical Association Annual Engineering and Operating Conference, Irvine, CA, March 1987. McElroy, M. EPRI'S Research Program on Furnace Sorbent Injection. Joint Symposium on Stationary Combustion NO, Control, Boston, MA, May 1985. Merrick, D.; Vernon, J. Review of Flue Gas Desulfurization Systems. Chem. Ind. 1989,6 Feb, 55-58. Ponder, W. H. Technologies for Controlling Pollutants from Coal Combustion. Chem. Coal Technology Conference, Arlington, Oct 1985.
Reed, G. D.; Davis, W. T.; Pudelek, R. E. Analysis of Coal Fly Ash Properties of Importance to Sulfur Dioxide Reactivity Potential. Environ. Sci. Technol. 1984, 18, 548-552. Shilling, N. Z.In-Duct Application of Dry Flue Gas Desulfurization of Sulfur Emissions. Proceedings of the Second Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1985. Sparks, L. E.; Plaks, N.; Ramsey, G. H.; Valentine, R. E. Investigation of Combined Particulate and SO2using ESOX. Ninth Symposium on Flue Gas Desulfurization, Cincinnati, OH, June 1985. Statnick, R. M.; Burke, F. P.; Koch, B. J.; McCoy, D. C.; Yoon, H. Status of Flue Gas Sorbent Injection Technologies. Proceedings of the Fourth Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1987. Stouffer, M. R.; Yoon, H.;Burke, F. P. An Investigation of the Mechanism of Flue Gas Desulfurization by In-Duct Dry Sorbent Injection. Ind. Eng. Chem. Res. 1989,28, 20-27. Yoon, H.; Stouffer, M. R.; Rosenhoover, W. A.; Statnick, R. M. Laboratory and Field Development of Coolside SOz Abatement Technology. Proceedings of the Second Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1985a. Yoon, H.; Ring, P. A.; Burke, F. P. Coolside SO, Abatement Technology: 1 MW Field Test. Proceedings of the Coal Technology '85 Conference, Pittsburgh, PA, Nov 1985b. Yoon, H.; Theodore, F. W.; Burke, F. P.; Koch, B. J.; Corder, W. C. Low Capital Cost, Retrofit SOz Control Technologies for High Sulfur Coal Applications. Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, June 1986. Received for review February 22,1990 Revised manuscript received July 5, 1990 Accepted July 23, 1990
