A Case Study of Chandrapura Thermal Power Station - Leaching Study of Trace Elements from Fly Ashes

Journal of Scientific & Industrial Research Vol. 59, September 2000, pp 852-855 A Case Study of Chandrapura Thermal Power Station - Leaching Study of Trace Elements from Fly Ashes Sanjay Kumar DVC, Training Institute Chandrapura, Bokaro 825 303 Received: 09 May 2000; accepted 09 June 2000 Electricity generation has been increasing at a rapid pace due to Industrialization and changing life styles. Coal is th e major source of energy, since India has vast reserves of thermal power grade coal. Nearly every naturally occurring element is likely to be present in coal and these get entrained in the resultant bottom ash. Indian coals contain high ash coupled with low calorific value, and consequently resulting huge amount of fly ash. This ash accumul ates in onsite piles and ponds, thereby resulting in serious environment problems, particularly trace elements contamination of ground and surface waters. This study envisages the environmental assessment of fly ash from Chandrapura Thermal Power Station. Leaching study of fly ash is made by the analysis of leaches from open percolation leaching column experiment s over a period of 274 d. Trace elements were observed within the regulatory limits. Many of the trace elements evaluated viz. Cr. Ni, Co, Se, AI, As, 8 , Ba, Sb and Hg were observed at below detection limits. Na, K, Ca, Mg, Fe, Pb, Cd and other dissolved ions leached at significant concentration levels, while Cu and Zn leached normally at lower concentration levels. The study suggests low-cost hi gh vo lume utilization of fly ash as fill material for reclaiming surrounding abandoned mined out areas which are environmentally acceptable. Introduction Fly ash is an alumino silicate glass consisting of the Electricity is an essenti al need of any industrial oxides of Si, AI , Fe and Ca with minor amounts of society and no nation can progress without adequate Mg, Na, K, Zn and S and various trace elements. The supply of power. Growth in its demand during the concentrati on associated with the ash may either be adsorbed on the surface of particle or incorporated past decades has been phenomenal and has into matrix. A mechanism that appears to be common outstripped all projections. India has vast reserves of for all ashes during their formation is the coal and it is expected th at thi s shall remain as prime condensation of metal and metalloid vapours on source of energy in the early part of 2 1st century. refractory core materials. As the particles and gas Presently, thermal power stations account for about steam exist from the combustion chamber and 70 per cent of installed generation capacity of 81000 2 proceed upto the gas , this results in locall y hi gher MW (ref. 1). In a pulverised coal fired thermal power concentrations of many trace elements at the surface plant, about 40-55 per cent ash is produced and about of ash particles and accounts for the generally higher 20 per cent is wasted due to gravity and is removed as concentration of these elements as particle size 3 bottom ash and the remaining as fly ash. This fly ash decreases . The association between trace elements is coll ected in the ash pond by hydrau li c and major elements, i.e., minerals may be an transportation process in the form of slurry. Thus the important factor m determining the leachate production of this waste is increasing continuously. composition of water in contact with ashes. It is The problem of disposal and utilization of fly ashes recognized that the health hazards and environmental has drawn considerable concern and attenti on of impacts from coal-fired thermal power stations result researchers of environmental groups, government and from the mobilization of toxic elements from ash. A regulators. large amount of ash that accumulates at thermal SANJAY KUMAR: CASE STUDY OF CHANDRAPURA THERM AL POWER STATIO 853 power pl ants, its possible reuse and the di spersion and permeability of the materi al. The open columns for mobilization of toxic elements from it , requires leaching experiments were made of PVC pipe 4 in in greater attention. Mobilization of various elements diam and 2 ft. in length. The top end of the column from the ash into the environment depends on climate, was exposed to the atmosphere and the fly end was 1 soil s, indigenous vegetation, and agri cultural connected to 11 in . tubing. The leachate was collected 4 through this tubing into 250 ml polypropylene practices . Environmental characteri zation studies beakers. with respect to analys is of trace elements of fly ash from Chandrapura Thermal Power Station are presented here. Elemental Analysis ofLeachates The leachate samples were filtered and acidified with 2 ml of nitric acid and then preserved in Study Area polypropylene sampling bottles. The samples were The Chandrapura Thermal power Stati on (C kept in a refri gerator until further analys is. Sodium TPS) of Damodar Vall ey Corporati on (DVC) is and potassium were determined usin g Systroni cs situated in Bokaro di strict of Bihar State covering an fl ame photometer. Concentrati on levels of trace area of 750 ha of land. It is bounded by the Damodar elements were evaluated using Atomi c Absorpti on ri ver on the south, Pokhari a Nullah on the east and Spectrophotometer (AAS) GBC-902. Working/ hills on th e north and west. standards solutions were prepared, according to instructions given in the operati on manual of the GBC-902 AAS. Experimental Procedure The ashes coll ected/sampled were analyzed fo r their leaching characteri sti cs, using open column Results and Discussion technique. The columns of the fl y ashes were packed Anylys is of twentytwo e lements were carried on April 1996 and leachates were collected sixty fi ve out each time and the observati ons are summari sed in times in a time peri od of about 274 d. up to February Tabl e I. It is observed that the concentrati on of 1997. Everytime the leachates were analyzed for trace thirteen elements namely chromium, nickel, cobalt, elements . Standard leaching analysis methods were cadmium, selenium, aluminum, sil ver, arseni c, boron, fo ll owed in this leaching study of fl y ash. These are barium, vanadium, antimony and mo lybdenum were briefl y described below. below the detecti on limit (.001 mg/1 ) during the study. Among other nine elements, onl y calcium and Sampling magnesium were observed in the leachates trhoghout the study, while the concentrati on of other elements Fly ash samples from Chandrapura Thermal showed a decreasing trend to BDL. A compari son of Power Stati on were coll ected on different days and a the concentrati on of the nine elements in the leachates final homogeni sed sample was prepared while with the permissible limits, as per IS: 2490 and appropritely mi xin g vari ous porti ons. IS : 10500, given in Table 2, indicates that the concentrati on of all the elements during the entire Leaching Chemistry study was below the permissible limits. The toxicity Open column percolation leaching experiments of bottom ash with respect to elements, as observed, were carried out on the fl y ash sample to ascertain its was within manageabl e limits. It can be inferred that leachate chemi stry, as described subsequentl y. no significant leaching occurs and toxicity is manageabl e with respecr to trace elements in the leachates. Open column leaching experiments may be Open Percolation Column Experiment used for predicting the long-term leaching behaviour In this experiment, deioni zed water was that can be observed in the fi eld . Fly ash leachates, as percolated through a packed column in the presence generated from open percolati on column leaching of oxygen at a rate depending on the natural experiments, do not pose any signi ficant 854 J SCI IND RES VOL 59 OCTOBER 2000 Table I - Summary of leachate analysis of fly ashes Open column lechate experiments Elements FA# I FA#2 Range Average Range Average Iron BDL-2.92 2.88 BDL-3. 12 3.4 Lead BDL-.089 0.072 BDL-0.08 0.07 Calcium 10 -25 24 28-40 38 Magnesium II - 24 22 20 -32 30 Copper BDL-0.094 0.09 BDL-0.088 0.08 Zinc BDL-1.082 1.074 BDL-1.10 1.09 Manganese BDL-0.099 0.085 BDL-0.092 0.086 Sodium BDL-10 9 BDL-16 14 Potassium BDL-20 18 BDL-36 34 Chromium BDL BDL BDL BDL Nickel Cobalt Cadmium Selenium Aluminum Silver Arsenic Boron Barium Vanadium Antimony Molybdenum BDL-Below Detecti ve Limits, BDL-0.00 I mg/1, Concentration in PPM environmental impacts in the disposal system. (ii) Out of lhe nme elements found in the Overall, fly ash will not pose any environmental leachates, only calcium and magnesium were problem during its utilization and/or di sposal. found to be leaching in the entire period. The other seven elements namely iron, lead, Conclusions copper, zinc, manganese, sodium and Based on the study of the leaching of trace potassiu m leaching was sometimes elements of the ashes of CTPS, following conclu sions intermittent. The leachi ng of sodium and are drawn: potassium practically stopped after 35 and 40 (i) In the study period of about 274 d, there was d respectively. practically no leaching of thirteen elements (iii) The concentration of the elements in the namely chromium, selenium, aluminum, leachates was invariably well below the silver, arsenic, boron, barium, vanadium, permissible limits for di scharge of effluents antimony and molybdenum from a ll the fl y as per IS:2490 and also fo r drinking water as ash samples.

Load more