Fighting against POLLUTION to Save Environment

Experience in implementation of environmental standards in lead industry. Proc. workshop Lead Pollution Control & Monitoring, ILZIC & CPCB, New Delhi, August, 1995:

Appeared in “Ecology in Practice” a collection of Articles for Prof. S.B. Chaphekar’s festschrift volume on his 60th birthday edited by C.S. Latto of Prof. S.B. Chaphekar Felicitation Committee,Bombay.

D. B. BORALKAR
Central Laboratory, Maharashtra Pollution Control Board
CIDCO Bhavan, CBD Belapur, New Bombay-400 614.

INTRODUCTION

An environment study was carried out in a large scale secondary lead smelting and refining plant which produces about 12000 tonnes per year of crude lead from the combination of lead concentrates and lead scrap. Since this is an air pollution potential industry and there is no significant discharge of trade effluent, the study was carried out with following objectives, in June 1994:

1. Air pollution control systems are adequate and in good order
2. Resources and materials are used efficiently
3. Waste management costs are minimised
4. Identification of further areas of improvement
5. Stack (point sources) emission and ambient air quality monitoring survey to find out quantity of lead emitted into the atmosphere.

1.1 Stack emission monitoring data of few lead smelting industries in small scale sector is also presented.

2. Raw materials used and products manufactured

2.1 With 5 numbers of rotary furnaces of 10 tonnes (t) capacity, 3 batch operations of 6 to 8 hours each for each furnace, about 12000 t per year of crude lead is produced. Refining operation is carried out in 5 kettles (2 kettles of 25 t capacity each and 3 kettles of 101 each) reactants in the kettles are heated with oil fired furnace, stirred and oxidized by air or oxygen. The reaction products are removed manually from the surface of the melts. Hot dressing, desilverising and dezincing are also done as required. The present study concentrated only on smelting process which has got maximum pollution potential.

3. Air pollution control measures

Each furnace was having control equipments such as settling chamber followed by cyclone and wet scrubber. Since this system was not adequate, the company decided to modify the same. Accordingly, the existing system of each furnace was modified by installing the following changes:

1. The burners were charged with new important Weishampt burners from Germany to increase the fuel efficiency at low pressure so as to minimize the emission through flue gases. Each burner is provided with an automatic control system based on temperature of furnace and flue gases. The cost of each furnace was Rs.5 lakhs.
2. The old pollution control system was totally scrapped and the new system now consists of:
   1. After burner chambers
   2. Cyclone
   3. 'U' tube coolers for cooling of the gases
   4. Cyclone
   5. Bag filter comprising of 180 bags of 3.5 m length each made out of Numax material which is imported from Germany
   6. 100 HP blower
   7. 2 stage water scrubber
   8. Stack

Table 1 : Results of stack (Point source) emission monitoring at a secondary lead smelting and refining plant.

Note : Emission limit: Particulate matter: 150 mg/Nm3 Lead: 10 mg/Nm3

Equivalent SO₂ A 400.0 kg/batch (=51.61 kg/hr)

Emission concentration = 6700 mg/m3

Assuming 60% scrubbing in venturi (as alkaline water is used)

Final emission to stack = 20.65 kg/hr