석탄회 함량이 활성탄 흡착능에 미치는 영향

김춘호,   진애국*,   서지미

한국에너지기술연구소, *안산열능연구소, 중국

The effect of coal ash content on activated carbon

performance

Choon-Ho Kim,  Ai-Guo Chen*, Jee-Mi Suh,

Korea Institute of Energy Research

* Anshan Research Institute of Thermo-Energy,  P. R. China

1 INTRODUCTION

For the coal-based activated carbon process, when increasing the strength of activation, the adsorption performance of activated carbon increases as the the yield decreases, but if the feed coal ash content is higher, when the yield decreases to a certain value, the adsorption performance of activated carbon decreases also.(1) In the process of manufacturing activated carbon, the ash doesn't take a profitable role and nearly all of the ash of feed coal transfers into activated carbon. So if the ash content of raw materials is very high we can't get high performance activated carbon by using it. Therefore, in order to get high quality activated carbon we seek to keep the ash content  of feed coal as low as possible. In this study, two kinds of Chinese coal and their clean coals ( obtained by a selective agglomeration process )  were taken as raw materials. Under various activation conditions the activated carbons were manufactured. The purpose was to determine effect of coal ash content on activated carbon adsorption performance.

2. EXPERIME.NTS

2.1 Feed coals

In this study, the feed coals used were Dandong coal(DDC) and Fushun coal(FSC) from Liaoning Province, China. The results of proximate analysis of the two coals are listed in Table 1. From this table we recognize that the Dadong coal is anthracite and Fushun is bituminous coal. For this study the agglomeration process was used to remove the ash of coal(2). The schema of the agglomeration experiment was that shown in Fig.1. First, the coal was crushed to <3 mm with crusher and ground in small ball mill for about 8 hrs, leting all coal pass through the sieves of 200 mesh. Some of them were made into coal slurry of 4 % concentration. A certain volume of coal slurry was put into the agglomeration unit and  premixed for 60 seconds,  after which the N-pentane was injected and agglomeration experiments were carried out. When this was completed,  the sieve was used to separate the clean coal ftom the refuse.  The clean coal was dried in an oven at 60 oC for 14 hrs. When agglomerant / coal = 0.5, agglomerating time was 45 sec. for FSC, agglomerant / coal = 0.75, agglomerating time was 30 sec. for DDC, The ash and yield of clean coal are listed in table 1.

Table 1  The Proximate Analysis and Ultimate Analysis of Coals

Sample Name	Proximate Analysis(wt%)				Ultimate Analysis (wt%)					Clean coal(wt%)
	Mois.	Ash	V.M.	F. B.	C	H	N	S	O	Ash	Yield
DDC	0.70	8.25	7.83	83.22	85.05	2.97	1.23	0.51	10.25	5.51	90.0
FSC	3.97	5.44	35.00	55.59	77.09	5.61	0.54	0.50	16.26	3.17	74.0

2.2 Manufacturing activated carbon

The above coals were made into pellets of □15×30 size. A rotary kiln-type furnance ( 7 cm in diameter and 160 cm in length ) heated by electricity  was adopted for carbonization and activation in this research. The rotary speed and slope of the rotary kiln was adjustable. For this experiment, two sample containers (□25×250mm) were put into the rotary kiln. Each container usually contained 20g sample. The rising rate of temperature of the rotary kiln was regulated at 4.5℃/min.. According to their TGA, carbonization temperature was selected as 650oC and 700℃ for FSC and DDC, respectively, and this temperature was kept  for 60 min. and N2 gas was then introduced at a certain flow rate into the rotary kiln until it reached the desired activation temperature. The activation tempetatures were varied from 850℃ to 950℃ and activation periods ranged from 1-5 hrs. The steam amount injected was 1.3g/hr.g·char and 1.5g/hr.g·char for FSC and DDC, respectively. When the steam injections were completed, the N2 gas was inserted again until the temperature was below 200℃ in order to prevent oxidation. The activated carbon yield (or 1-burn off), iodine number and B.E.T. specific surface area act. analysis were performed during these experiments..

3. EXPERIMENTAL RESULTS AND DISCUSSION

The activated carbon adsorption performance normally increases with the increase of the activation temperature and results in a yield descrese, whose definition is Wa/Ws, where Ws is weight of sample and Wa is weight of activated  carbon. As  is  known, the basic reaction of  carbon with steam is

endothermic(3) and can be expressed as follows :

C + H2O  = CO + H2     △H = + 117 kJ / mol       (1)

CO + H2O  = CO2 + H2                               (2)

Similary, the reaction of carbon  with carbon dioxide  is

C + CO2  = 2CO          △H = + 159 kJ / mol       (3)

The reaction functions (1) and (2) show that elevation of the temperature is beneficial for the reaction of carbon with water steam and carbon dioxide. The results of this experiment also demonstrate this trend. When the activation time was 120 minutes, activation temperatures were 800oC, 850oC, 900oC and 950oC, the changing  of yields and the adsorption performance of activated carbon are listed in Table 2.  From this table  we see  that as the activation temperatures increase, the yields of all samples decrease. Under the condition  of  same  activating  times  and temperatures, however the steam

Table 2  Experimental data of manufacturing activated carbon

Temp. (oC)	DDC				FSC
	clean coal		raw coal		clean coal			raw coal
	I. D. (mg/g)	Yield (%)	I. D. (mg/g)	Yield (%)	I. D. (mg/g)	B.E.T (m2/g)	Yield (%)	I. D. (mg/g)	B.E.T (m2/g)	Yield (%)
800	685.8	58.3	650.9	59.4	889.0	675	49.0	793.8		48.9
850	750.5	52.4	704.9	55.0	994.4	742	41.2	914.4	641	43.6
900	813.8	48.5	758.7	51.1	1063.0	934	39.3	999.5	902	40.7
950	920.8	38.6	825.5	41.9	1111.3	1152	34.2	1051.6	950	34.2

amount injected was 1.5g/hr.g·char and 1.3g/hr.g·char  for  DDC and FSC respectively, the yields of FSC were lower than DDC and the iodine numbers of activated carbon were higher than the DDC. This indicated that the reactivity of FSC is higher than that of DDC and FSC is easier to activate than DDC. Comparing the clean coal and raw coal of FSC, when the activation temperature was from  800oC to 950oC, the iodine number of clean coal was 60 - 95 (mg/g) higher than raw coal. For DDC the  range was 35 - 95 (mg/g).

When the activation temperature was fixed at 900oC, the activation time was varied between  60 - 300 min., The experimental results are shown in Table 3. From table 3  we note  that  when extending the activation time the yield

Table 3  Experimental data of manufacturing activated carbon

Time (min.)	DDC				FSC
	clean coal		raw coal		clean coal		raw coal
	I. D. (mg/g)	Yield (%)	I. D. (mg/g)	Yield (%)	I. D. (mg/g)	Yield (%)	I. D. (mg/g)	Yield (%)
60	575.0	59.2	539.7	63.9	886.5	44.0	844.7	46.0
120	813.8	48.5	758.7	51.1	1063.0	41.2	999.0	43.6
180	889.0	44.4	831.8	45.9	1077.0	33.6	1038.9	36.5
240	1009.6	34.8	960.6	37.0	1140.0	28.0	1089.7	31.0
300	1176.0	23.5	1079.5	28.7

decreases rapidly and the iodine number of activated carbon increase substantially. It is demonstrated that adsorption performances of the activated carbon can be increased effectively by  extending the activating time. When the activation time was from 60 min. to 300 min., the iodine number of clean coal was 38 - 64 (mg/g) higher than that for raw coal for FSC. For DDC the tange was 35 - 96.5 (mg/g).

4. CONCLUSION

(1) For FSC,  when the ash content of coal was decreased 1%, the iodine number of activated carbon was increased by about 17 - 42 (mg/g),

(2) For DDC, as the  yield decreased, the difference of iodine number of clean coal and raw coal was increased substantially. When the ash content of coal was decreased by 1%, the iodine number of activated carbon was increased by 13-34 ( mg/g).

(3) DDC and FSC are suitable raw materials for manufacturing activated carbon. The activity of FSC is higher than that of DDC.

REFERENCES

1. B-S. Lee, S-C. Kim, A-G. Chen, I-S. Choi, J-K Kim, and C-H. Kim : "Coal Based Activated Carbon Manufacturing Process" 11th Korea-U.S.A. Joint Workshop on Coal Utilization Technology, October 2-3, 1995, Somerset, Pennsylvania U. S. A.

2. S-S. Kim : "Development of A Selective Agglomeration Process Using Light Hydrocarbons for Fine Coal Beneficiation" (Ph. D. Dissertation, University of  Pittsburgh, 1993)

3. T.Wigmans, "Industrial aspects of production and use of acrivated carbons", Carbon, Vol. 27, No. 1, 13-22(1989)