Effect of Ammonium Compounds as Additives on the Dissolution Rate of Limestone Samples Sourced From Tirunelveli District, Tamil Nadu, India

 

S. Vijaya Chitra

Department of Geology and Mining, Guindy, Chennai - 600 032 India

*Corresponding Author E-mail: vijchitra@yahoo.co.in

ABSTRACT:

Sulphur dioxide (SO₂) represents one of the most important air pollution generators. The rate of CaCO₃ dissolution in slurry scrubbers for flue gas desulphurization affects SO₂ absorption, CaSO₃ / CaSO₄ scaling and ultimate CaCO₃ utilization. Limestone is the low cost naturally occurring chemical which is the preferred reagent in many conventional WFGD systems. However, under normal system operating conditions, the limestone dissolves slowly. Therefore, in order to increase the alkalinity of the limestone slurry used in conventional WFGD systems and hence increase the system's SO₂ removal efficiency, the use of ammonium compounds as the possible additives has been examined in this study. Under normal operating conditions, once the slurry containing the dissolved limestone is sprayed into the SO₂ absorber, the dissolved limestone is quickly depleted making the slurry ineffective in removing more SO₂ and requiring a high rate of slurry recycle. As a result, high capital and operating costs are required when low cost limestone is employed as the reagent in WFGD systems. Increasing the limestone dissolution rate in WFGD systems allows courser limestone particles; lower limestone stoichiometry and lower slurry recycle rates to be employed, thereby saving capital and operating costs. Marginal grade limestone samples collected from Tirunelveli district, Tamil Nadu have been taken up for this particular study under conditions similar to those encountered in wet FGD processes.

 

 

 

INTRODUCTION:

The rocks occurring in southern district of Tamil Nadu comprises of Charnockite, Garnetiferous Biotite Gneiss of Archaean and coastal sedimentary rocks. Due to intense metamorphism coupled with intrusive activities, the formation seen as heterogeneous assemblages of metamorphic facies has developed. The arenaceous facies are represented by quartzite and garnetiferous gneiss¹. Argillaceous facies are represented by calcgneisses and calcareous facies are represented by crystalline limestone respectively. These rocks are generally termed as granulite group of rocks. There are some small pockets of shell limestone, Kankar and calcareous sandstone of tertiary age occurring in the coastal regions of Tuticorin, Kanyakumari and Tirunelveli districts

 

Although most of the limestones are similar in chemical and mineralogical composition, the complex organic and chemical origins of carbonate sediments lead to a wide range of textures and fabrics finding wide application in Industrial fields in the resulting limestones

 

Limestone is a low cost naturally occurring chemical which is the preferred reagent in many conventional WFGD systems. However, under normal system operating conditions, the limestone dissolves slowly. Therefore, in order to increase the alkalinities of the limestone slurry used in conventional WFGD systems, system's SO₂ removal efficiency is to be enhanced. Once the slurry containing the dissolved limestone is sprayed into the SO₂ absorber, the dissolved limestone is quickly depleted making the slurry ineffective in removing more SO₂ and requiring a high rate of slurry recycle. As a result, high capital and operating costs are required when low cost limestone is employed as the reagent in WFGD systems.Timckeener² et al have studied the limestone dissolution rate by changing the variables such as PH, Temperature, Particle size etc..

 

The rate of CaCO₃ dissolution in slurry scrubbers for flue gas desulphurization affects SO₂ absorption, CaSO₃/CaSO₄ scaling, and ultimate CaCO₃ utilization. The dissolution rates of limestone could become a critical limiting step for desulphurization. Increasing the limestone dissolution rate for limestone-containing slurries used in WFGD systems allows courser limestone particles; lower limestone stiochiometry and lower slurry recycle rates to be employed, thereby saving capital and operating costs. Robert S.Boynton³, has reported that most inorganic salts increase the Ca (OH)₂ solubility by 10-15 % in 0.1-0.2%  salt solutions.

 

The performance-enhancing additive that is incorporated in the limestone slurry in the WFGD system according to this study is a source of water soluble ammonium ions. The dissolution characteristics have been studied by using a pH-Stat method at 25°C, at pH value of 5, stirrer speed of 300 rpm and particle size of 150 microns 61 limestone Samples prepared in the sample size of 150 microns selected from Tirunelveli district of Tamil Nadu were taken up for the dissolution study

 

MATERIALS AND METHODS:

Apparatus:

A top loading stirrer motor driven with rpm indicator, a reaction vessel,   Solutions prepared using Analar standards, pH meter

 

Procedure:

0.75 gm of the sample was taken and 500ml of water added to it and kept for dissolution at 25*c with a disk rotation speed 300 rpm using a motor driven hanging stirrer. The ammonium ions incorporated into the solution through aqueous ammonia and water-soluble ammonium salts, such as ammonium sulfate, ammonium chloride, or ammonium carbonate. It was found that the dissolution rate was dependant on the disk rotating speed when the rotating speed was below 300 rpm when the rotating speed was greater than 300 rpm the lime dissolution become constant. After the suspension pH attained its equilibrium value close to 9 in around 5 min, a solution of pH5⁴which is a typical pH value in industrial slurry scrubbers, was added 25ml of   the aqueous ammonia 25%, and allowed for dissolution for 25 minutes and after checking the pH of the solution another increment of aqueous ammonia 25% has been added and the dissolution rate monitored. This time period choice is made with the consideration that initially the stirrer surface may have not been smooth and free of dust which can make the initial dissolution rate slightly greater and that with time elapse the solution may have a high ion concentration which may result in some deposition on the surface to make the dissolution rate decrease. The solution was allowed to settle and filtered through Whatmann40 filter paper with hot water washings, dried and ignited at 900*c. Percentage dissolution of the sample has been calculated.

 

Similar experiments carried out with water-soluble ammonium salts, such as Ammonium sulfate2%, Ammonium chloride 3%, Ammonium chloride 1.5% or Ammonium Nitrate 1.5% in increments of 50 ml at constant intervals twice with uniform stirring and with periodical checking of the pH values. The variations were observed with all the 61 samples taken up for the study. The pH was automatically controlled to ±0.1 units. The experiment   conducted for twenty five minutes, the period choice was made with the consideration that with time lapse the solution may have a high ion concentration which may result in some deposition on the surface to make the dissolution rate decrease. The consumption rate considered between 15 to 20 minutes. The solution was allowed to settle and filtered through whatmann40 filter paper with hot water washings, dried and ignited at 900*c. Percentage dissolution of the sample has been calculated. A set of 61 samples of present zone of interest have been taken up for the study.

 

RESULTS AND DISCUSSION

Ammonium chloride solution of 1.5% increased the dissolution rate by 20% at 25*c but addition of a solution of aqueous Ammonia 25 % decreased the dissolution rate considerably under similar conditions. Experiments done with Ammonium chloride solution of 3% increased the dissolution slightly. Addition of Ammonium sulphate solution of 2% has been found to enhance the dissolution by 2.5%. Addition of Ammonium nitrate solution of 1.5%% has been found to enhance the dissolution by about 25%. As could be seen from the results the dissolution rate is enhanced by the addition of ammonium ions (Table-1).

 

A series of experiments have been conducted with variations  in addition of water soluble ammonium compounds as additives to test the lime dissolution rate under similar conditions keeping the variables such as  pH, Temperature, and Particle size etc., constant (Table-1).

 

It could be seen from the results that Ammonium chloride has the ability to increase the dissolution rate This phenomenon was first considered a chemical reaction but the activation energy calculated from further tests on dissolution have that ammonium chloride in some way accelerates the mass transfer process indicated dissolution rate to a greater extent. The other Ammonium com pound, Ammonium sulphate 2% improved the limestone dissolution   slightly. Ammonium nitrate 1.5% has been found to enhance the dissolution by about 25%. A change in the concentration of Ammonium chloride improved the dissolution (Table-1).

 

Hillary Ruttol et al⁵ have reported that upon addition of 0.5 g of ammonium nitrate, the dissolution rate constants increased by 170%. A series of experiments have been conducted to test the lime dissolution rate. Except for the initial stages during which the suspension pH came down to the constant pH of dissolution (pH 5) from its natural pH 9, the conversion varied linearly with time This is probably due to the fact that the lime rotating stirrer is a surface source for dissolution while the limestone particles are well mixed in the solution and it is easier for the system to maintain a uniform pH value (Table-1).

 

 

Table-1

EFFECT OF ADDITIVES
Particle size				150 MICRONS												Duration of mixing				2 HOURS
pH				5.00												Temperature				25*C
Effect of ammonium compounds
Sl no	%Ca	TCO3	PH5			Ammonia aq 25%				Ammo. chloride 1.5%			Ammo.chloride3%				Ammo. sulphate 2%		Ammonium nitrate 1.5%
			Residue wt		% dissolution	Residue wt		% dissolution		Residue wt		% dissolution	Residue wt		% dissolution		Residue wt	% dissolution	Residue wt	% dissolution
1	47.81	81.59	0.3324		55.68	0.5393		28.09		0.2020		73.07	0.2011		73.19		0.3144	58.08	0.1810	75.87
2	46.86	82.76	0.3331		55.59	0.5400		28.00		0.2027		72.97	0.2018		73.09		0.3151	57.99	0.1817	75.77
3	50.39	92.63	0.3071		59.05	0.5140		31.47		0.1767		76.44	0.1758		76.56		0.2891	61.45	0.1557	79.24
4	46.01	84.08	0.3789		49.48	0.5858		21.89		0.2485		66.87	0.2476		66.99		0.3609	51.88	0.2275	69.67
5	46.54	81.03	0.3792		49.44	0.5861		21.85		0.2488		66.83	0.2479		66.95		0.3612	51.84	0.2278	69.63
6	49.82	74.03	0.3302		55.97	0.5371		28.39		0.1998		73.36	0.1989		73.48		0.3122	58.37	0.1788	76.16
7	53.81	88.72	0.2924		61.01	0.4993		33.43		0.1620		78.40	0.1611		78.52		0.2744	63.41	0.1410	81.20
8	51.91	93.92	0.2444		67.41	0.4513		39.83		0.1140		84.80	0.1131		84.92		0.2264	69.81	0.0930	87.60
9	52.11	87.42	0.2912		61.17	0.4981		33.59		0.1608		78.56	0.1599		78.68		0.2732	63.57	0.1398	81.36
10	52.22	86.33	0.2907		61.24	0.4976		33.65		0.1603		78.63	0.1594		78.75		0.2727	63.64	0.1393	81.43
11	52.72	88.43	0.2899		61.35	0.4968		33.76		0.1595		78.73	0.1586		78.85		0.2719	63.75	0.1385	81.53
12	52.05	85.83	0.2843		62.09	0.4912		34.51		0.1539		79.48	0.153		79.60		0.2663	64.49	0.1329	82.28
13	48.82	93.96	0.3501		53.32	0.5570		25.73		0.2197		70.71	0.2188		70.83		0.3321	55.72	0.1987	73.51
14	45.59	87.37	0.3723		50.36	0.5792		22.77		0.2419		67.75	0.241		67.87		0.3543	52.76	0.2209	70.55
15	48.56	84.05	0.3304		55.95	0.5373		28.36		0.2000		73.33	0.1991		73.45		0.3124	58.35	0.1790	76.13
16	46.49	80.98	0.3707		50.57	0.5776		22.99		0.2403		67.96	0.2394		68.08		0.3527	52.97	0.2193	70.76
17	48.84	85.21	0.3498		53.36	0.5567		25.77		0.2194		70.75	0.2185		70.87		0.3318	55.76	0.1984	73.55
18	47.06	71.74	0.3572		52.37	0.5641		24.79		0.2268		69.76	0.2259		69.88		0.3392	54.77	0.2058	72.56
19	47.45	90.81	0.3314		55.81	0.5383		28.23		0.2010		73.20	0.2001		73.32		0.3134	58.21	0.1800	76.00
20	46.83	88.21	0.3361		55.19	0.5430		27.60		0.2057		72.57	0.2048		72.69		0.3181	57.59	0.1847	75.37
21	41.29	84.10	0.2912		61.17	0.4981		33.59		0.1608		78.56	0.1599		78.68		0.2732	63.57	0.1398	81.36
22	39.15	83.90	0.2903		61.29	0.4972		33.71		0.1599		78.68	0.159		78.80		0.2723	63.69	0.1389	81.48
23	48.83	83.70	0.2102		71.97	0.5958		20.56		0.0798		89.36	0.0789		89.48		0.1922	74.37	0.0588	92.16
24	44.20	81.28	0.3615		51.80	0.5684		24.21		0.2311		69.19	0.2302		69.31		0.3435	54.20	0.2101	71.99
25	48.84	78.82	0.3098		58.69	0.5167		31.11		0.1794		76.08	0.1785		76.20		0.2918	61.09	0.1584	78.88
26	50.91	93.03	0.3002		59.97	0.5071		32.39		0.1698		77.36	0.1689		77.48		0.2822	62.37	0.1488	80.16
27	50.17	90.98	0.3015		59.80	0.5084		32.21		0.1711		77.19	0.1702		77.31		0.2835	62.20	0.1501	79.99
28	49.00	87.85	0.3114		58.48	0.5183		30.89		0.1810		75.87	0.1801		75.99		0.2934	60.88	0.1600	78.67
29	43.84	74.10	0.3712		50.51	0.5781		22.92		0.2408		67.89	0.2399		68.01		0.3532	52.91	0.2198	70.69
30	52.39	85.26	0.2912		61.17	0.4981		33.59		0.1608		78.56	0.1599		78.68		0.2732	63.57	0.1398	81.36
31	50.73	82.05	0.3016		59.79	0.5085		32.20		0.1712		77.17	0.1703		77.29		0.2836	62.19	0.1502	79.97
32	49.36	85.61	0.3022		59.71	0.5091		32.12		0.1718		77.09	0.1709		77.21		0.2842	62.11	0.1508	79.89
33	50.84	87.33	0.3021		59.72	0.5090		32.13		0.1717		77.11	0.1708		77.23		0.2841	62.12	0.1507	79.91
34	49.07	86.04	0.3102		58.64	0.5171		31.05		0.1798		76.03	0.1789		76.15		0.2922	61.04	0.1588	78.83
35	52.33	93.33	0.3006		59.92	0.5075		32.33		0.1702		77.31	0.1693		77.43		0.2826	62.32	0.1492	80.11
36	49.59	89.23	0.3112		58.51	0.5181		30.92		0.1808		75.89	0.1799		76.01		0.2932	60.91	0.1598	78.69
37	48.22	90.18	0.3204		57.28	0.5273		29.69		0.1900		74.67	0.1891		74.79		0.3024	59.68	0.1690	77.47
38	51.78	88.50	0.3010		59.87	0.5079		32.28		0.1706		77.25	0.1697		77.37		0.2830	62.27	0.1496	80.05
39	45.72	85.32	0.3612		51.84	0.5681		24.25		0.2308		69.23	0.2299		69.35		0.3432	54.24	0.2098	72.03
40	50.52	87.45	0.2021		73.05	0.4090		45.47		0.0717		90.44	0.0708		90.56		0.1841	75.45	0.0507	93.24
41	54.58	91.10	0.2101		71.99	0.4170		44.40		0.0797		89.37	0.0788		89.49		0.1921	74.39	0.0587	92.17
42	49.43	90.66	0.3021		59.72	0.5090		32.13		0.1717		77.11	0.1708		77.23		0.2841	62.12	0.1507	79.91
43	47.56	88.02	0.3372		55.04	0.5441		27.45		0.2068		72.43	0.2059		72.55		0.3192	57.44	0.1858	75.23
44	48.49	89.13	0.3659		51.21	0.5728		23.63		0.2355		68.60	0.2346		68.72		0.3479	53.61	0.2145	71.40
45	53.16	91.15	0.2144		71.41	0.4213		43.83		0.0840		88.80	0.0831		88.92		0.1964	73.81	0.0630	91.60
46	42.91	81.25	0.3748		50.03	0.5817		22.44		0.2444		67.41	0.2435		67.53		0.3568	52.43	0.2234	70.21
47	38.86	81.35	0.5517		26.44	0.6175		17.67		0.4213		43.83	0.4204		43.95		0.5337	28.84	0.4003	46.63
48	45.48	82.79	0.2235		70.20	0.4304		42.61		0.0931		87.59	0.0922		87.71		0.2055	72.60	0.0721	90.39
49	44.61	82.53	0.3007		59.91	0.5076		32.32		0.1703		77.29	0.1694		77.41		0.2827	62.31	0.1493	80.09
50	47.69	83.03	0.3010		59.87	0.5079		32.28		0.1706		77.25	0.1697		77.37		0.2830	62.27	0.1496	80.05
51	51.76	86.27	0.2491		66.79	0.4560		39.20		0.1187		84.17	0.1178		84.29		0.2311	69.19	0.0977	86.97
52	39.74	81.30	0.5317		29.11	0.6386		14.85		0.4013		46.49	0.4004		46.61		0.5137	31.51	0.3803	49.29
53	49.66	87.36	0.2512		66.51	0.4581		38.92		0.1208		83.89	0.1199		84.01		0.2332	68.91	0.0998	86.69
54	49.20	80.56	0.2499		66.68	0.4568		39.09		0.1195		84.07	0.1186		84.19		0.2319	69.08	0.0985	86.87
55	49.73	80.65	0.2412		67.84	0.4481		40.25		0.1108		85.23	0.1099		85.35		0.2232	70.24	0.0898	88.03
56	51.85	89.96	0.2136		71.52	0.4205		43.93		0.0832		88.91	0.0823		89.03		0.1956	73.92	0.0622	91.71
57	52.77	92.99	0.2009		73.21	0.4200		44.00		0.0705		90.60	0.0696		90.72		0.1829	75.61	0.0495	93.40
58	44.99	81.20	0.3012		59.84	0.5081		32.25		0.1708		77.23	0.1699		77.35		0.2832	62.24	0.1498	80.03
59	48.18	82.10	0.3201		57.32	0.5270		29.73		0.1897		74.71	0.1888		74.83		0.3021	59.72	0.1687	77.51
60	47.23	83.10	0.3211		57.19	0.5280		29.60		0.1907		74.57	0.1898		74.69		0.3031	59.59	0.1697	77.37
61	47.30	80.77	0.3204		57.28	0.5273		29.69		0.1900		74.67	0.1891		74.79		0.3024	59.68	0.1690	77.47

 

 

Fig 1.

 

 

Berner, A.R. and J.W. Morse⁶ have studied the dissolution Kinetics of Calcium Carbonate in Sea Water. Gao xiang et al⁷ have studied the dissolution rate of limestone for flue wet gas desulphurization in the presence of sulphite. Ukawa, N., et al⁸ have reported effects of Salts on limestone dissolution Rate in wet Limestone .Flue Gas Desulfurization". Optimisation of a wet FGD pilot plant using fine limestone and organic acids has been studied by Jan B.W. Frandsen,Søren Kiil and Jan Erik Johnson⁹. Dissolution of Limestone in Simulated slurries for removal of Sulfur Dioxide from Stack Gases¹⁰ has been taken up for studies by Kim, K.Y., M.E. Deming et al Samples collected from certain areas of Pillaiyanatham village in Sankarankoil taluk, Tirunelveli district showed to be of more industrial utility and the dissolution rate in the presence of additives has been found to be 55-67% Samples collected from certain Karanthaneri, Venkatrangapuram, Kilasadaiyamankulam, Gangainadankulam showed calcium content ranging from the dissolution percentage has been found to be 65-75% suitable for FGD purpose. In the Samples of Nanguneri Taluks Tirunelveli district the dissolution rate has been found to be 65-85% suitable for FGD purpose. Samples from Venkatrangapuram, Karisalapatti, Pillaikulam, Ganganarkulam and Pattankadu villages of Ambasamudram taluk, Tirunelveli district the dissolution has been found to be 51-73 % .The samples collected from these areas could be useful for FGD systems with addition of ammonium compounds in suitable concentrations.

Under normal system operating conditions, the limestone dissolves slowly. Under similar operating conditions SO₂ removal efficiency is higher when additives are added to the system along with lime stones. These additives are relatively inexpensive, tend not to oxidize and could be recovered from waste water. Such additives have been reported to improve system performance by buffering the slurry pH and improving its effectiveness. The performance enhancement that is achieved in many cases is of a sufficient magnitude. The limestone dissolution rate for limestone-containing slurries used in wet flue gas desulfurization (WFGD) systems is enhanced by the addition of ammonium ions.

 

Patent of Gal, Eli¹¹ states that the performance-enhancing additive that had been incorporated in the limestone slurry in the WFGD system according to their invention was a source of ammonium ions. The impact of dissolved ammonium ions on the limestone dissolution rate has been indicated by the dissolution rate curves., With no chlorides present, the dissolution rate has been reported to increase from 14.6 mmole/h/g to 127 mmole/h/g when 1000 ppm ammonium ions (as ammonium sulfate) are added to the slurry. The rate increases to 197 and 286 mmole/h/g when 3090 ppm and 6440 ppm ammonium ions are used, respectively. With 50,000 ppm chlorides, the dissolution rate is only 8.8 mmole/h/g, but increases five-fold to 42.4 mmole /h/g with 6440 ppm ammonium ions in the solution.

The limestone dissolution rate for limestone-containing slurries used in wet flue gas desulfurization (WFGD) systems is enhanced by the addition of ammonium ions¹¹

 

Increasing the limestone dissolution rate (Fig.1) for limestone-containing slurries used in WFGD systems allows courser limestone particles; lower limestone stoichiometry and lower slurry recycle rates to be employed, thereby saving capital and operating costs. The ammonium ions may be recovered and reused in the process. It is imperative that much research and development programme should be undertaken for the proper utilization of existing marginal grade   limestone deposits. Since many of the applications have either not developed or only established to a small extent, there is a tremendous scope. To mitigate this adverse effect of reduced availability, focused efforts are required for proper utilization of marginal grade limestone for different industrial purposes.

 

A careful search for the new deposits adopting modern methods of prospecting and exploration is essential. After fixing the new finds, they may be sorted according to their suitability for the different industries; the recent technological innovations the world over have also provided ways and means of utilizing relatively impure varieties of limestone to lead to a better method of predicting and optimizing the performance for FGD. It would especially be desirable if the capital and operating costs of limestone-based WFGD systems could be reduced by the use of a low cost recoverable additive while at the same time, achieving significantly increased limestone dissolution rates and hence increased SO₂ removal efficiency. It is towards providing such performance-enhanced limestone-based WFGD systems that the present study is focused.

 

It has been proposed to  do further study on the effect of  other additives on the dissolution rate of the limestone samples from Tjrunelveli district. Tamil Nadu, India with the intention of increasing the utility level of  the marginal grade limestones available in the present zone of study for FGD purposes.

 

ACKNOWLEDGEMENT:

The author expresses her sincere thanks to the Commissioner of Geology and Mining, Guindy, Chennai.600 032 for the encouragement throughout this work.

 

REFERENCES:

1.       M. SubbaRao, Carbonate rocks of TamilNadu, Journal of Sedimentary Research, 1958 .V.28 (3), 274-285,

2.       Tim C. Keener, S.J. Khang, J. Wang, The effect of additives on lime dissolution rates: February 1995Project report, University of Cincinnati, Cincinnati:.

3.       Robert S. Boynton., Chemistry and technology of lime and limestone, John Wiley & Sons, Inc., 2nd ed., New York. :118-125

4.       Robert C. Weist, CRC Handbook of Physics and Chemistry, Critical Reviews, July 1971,

5.       Hillary Ruttol^a, Zachariah Siagi^a and M. Mbarawa^a  Effect of Ammonium compounds on dissolution rate of South African Calcium-based material, Journal of Hazardous Materials,  2009; 168 ; 2-3 : 1532-1536

6.       Berner, A.R. and J.W. Morse, Dissolution Kinetics of Calcium Carbonate in Sea Water- Theory of Calcite Dissolution, American Journal of Science 1974;274(2); 108-34.

7.       Gao xiang. guo Rui-tang, Ding Hong- lei, Luo Zhong-yang, and Cen Ke fa, Dissolution rate of limestone for flue wet gas desulphurization in the presence of sulphite, Journal of Hazardous materials, 2009:168;  2-3::15: 1059-1064.

8.       Ukawa, N., S. Okino, M. Oshima, and T. Oishi. Effects of Salts on Limestone Dissolution Rate in Wet Limestone Flue Gas desulfurization: J.of Chem. Eng. of Japan, 1993. 26: No. 1, pp. 112-113,

9.       Jan B.W. Frandsen, Søren Kiil and Jan Erik Johnson. Optimisation of a wet  FGD pilot plant using fine limestone and organic acids, Chemical Engineering Science: May 2001: 56(!0): 3275-3287

10.     Kim, K.Y., M.E. Deming, and J.D. Hatfield, Dissolution of Limestone in Simulated Slurries for Removal of Sulfur Dioxide from Stack Gases: Env. Sci. Tech. 1975: 9(10), 949-52.

11.    Gal, Eli Wet flue gas desulphurisation process using limestone. Abstract of corresponding document: US5630991. European Patent EP0777519 Kind Code: B1 .

 

 

Received on 21.05.2010        Modified on 12.06.2010

Accepted on 24.06.2010        © AJRC All right reserved