By : Kalpana Palkhiwala :India ranks as the second largest cement producing country in the world. There are about 130 large cement plants in India with an installed capacity of 160.24 million tonnes. The cement sector has been rapidly growing at a rate of 8% and is expected to grow further.
Cement industry is one of the major air polluting industries among the 17 identified by CPCB. The other are Aluminum, Cement, Chlor Alkali, Copper, Distillery, Dyes and dye intermediates, Fertilizers, Iron & steel, Oil Refineries, Petrochemicals, Pharmaceuticals, Pulp & Paper, Sugar, Tannery, Thermal Power Plants, Zinc and Pesticides.
The cement industry in its various processes emits Suspended Particulate Matter (SPM) and oxides of nitrogen besides carbondioxide, which is produced during calcinations process . The emission of carbondioxide depends on the type of production processes, their efficiency, fuel used etc. Particulate matter is the main pollutant emitted from cement industries. India produces different varieties of cement like Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), Portland Blast Furnace Slag Cement (PBFS), Oil Well Cement, Rapid Hardening Portland Cement, Sulphate Resisting Portland Cement, White Cement etc.
Cement manufacturing is an energy intensive process. Consuming energy from fossil fuels such as oil and coal creates carbon dioxide, the most important Greenhouse Gas causing climate change. In industrial sector, cement industry is the second largest emitter of carbondioxide and accounts for 5 per cent of global manmade carbondioxide emissions, of which 60 per cent is from the chemical process and 40 per cent from burning fuel.
Emission of carbon dioxide, which causes global warming, from Indian cement companies is significantly lower than European and American cement companies.
The steps taken to control pollution from the cement industry include notification of emission standards for cement industry, the adoption of Corporate Responsibility for Environment Protection (CREP) for 17 categories of industries including cement and regular monitoring for compliance of environmental standards.
Cement is a binder, a substance which sets and hardens independently and can bind other materials. Cements used in construction are characterized as hydraulic or non-hydraulic.
The cement industry holds immense promise in terms of utilizing wastes from other industries, fly ash (from the power sector), blast furnace slag (from the iron and steel industry) and phosphor-gypsum (from fertilizer plant) are used to manufacturer blended cement, without sacrificing the quality of cement. Today, about 12 per cent of total fly ash generated in India is used by the cement industry. Utilization of fly ash in cement sector is therefore very low.
As far as Clean Development Mechanism (CDM) projects in cement sector are concerned, the National CDM Authority has accorded approval to about 40 cement projects. 20 of these have since been registered. These 20 registered projects will help save 17.60 MT of carbondioxide till the year 2012.
Dust is another major pollutant emitted in the process of production of cement. Considering the contribution of air pollution by the cement industry, the Central Pollution Control Board in close consultation with the State Boards and the Association of cement industry had evolved emission standards for cement plants of different capacities.
The Emission Standards for Existing Cement Industry with plant capacity of 200 tonnes per day and less in all sections for protected area is 250 mg/Nm3 and in other area 400 mg/Nm3. Similarly the standard for plant capacity of greater than 200 tonnes per day in all sections for protected area is 150 mg/Nm3 and in other area 250 mg/Nm3
For New Cement Kilns including grinding units the particulate matter emission standards is 50 mg/Nm3 .
The main sources of fugitive emission in cement industry are open air handling and storage of raw materials and clinker; transfer; points; leaking joints; loading and unloading operation and vehicular movement on unpaved roads.
The methods employed for fugitive dust control in cement industry include exhaust ventilation system and water spray system. There are six types of Greenhouse Gases. They mainly include carbon dioxide, methane, nitrous oxides, hydroflurocarbons, perflurocarbons and sulphur hexafluoride.
In the process of calcinations, carbon dioxide emission in cement manufacturing originate from combustion of fossil fuels and from calcining the limestone in the raw mix. Calcium carbonate in limestone when calcined gets converted into lime and carbon dioxide.
About 60 percent of emission caused by making cement are from this chemical process alone. As a rough estimate, total carbon dioxide emissions range from 0.85 – 1.15 tonne of cement produce, assuming clinker to cement ratio as 0.95. The approximate contributions of each of the three main sources of carbon dioxide emissions are Calcinations – 50-55 percent ; Fuel combustion – 40-50 per cent and Electricity – 0-10% (assuming that electricity is generated from fossil fuels).
Various types of Air Pollution Control Devices (APCDs) in the form of dust collectors are used in cement plants to control the emission of dust to the atmosphere. The types of pollution control equipment used in cement industry to control particulate emission are cyclone and multicyclones, fabric filters/ bag filters, electronic precipitators and gravel bed filters.
Besides many other steps, the clean technologies adopted in cement industries. And the manufacture of clinker by Dry Process technology, manufacture of blended cements such as Portland Pozzolona Cement (PPC), Portland Blast Furnace Slag Cement (PBFS) and use of high calorific wastes as alternate fuels/source of energy.
