Cement Energy and Environment

Sources of C0 1 Generation In cement manufacture, carbon dioxide (C0 2 ) is generated basically from two sources i.e. Calcination of limestone Use of coal as fuel in cement manufacture proper besides for captive power generation. The pyroprocessing of limestone (CaC0 3 ) inside the rotary kiln liberates an equimolar proportion of C0 2 _ Coal , predominantly used as fuel in the pyroprocessing, also liberates C0 2 Add to this C0 2 produced from burning of coal for captive power generation, where installed. While the various measures of energy management mentioned earlier contribute in their own way to reduce C0 2 generation, manufacture of blended cements needs special mention in view of the substantial reduction it effects in this regard through replacement of clinker by pozzolanic materials by 20 to 65 per cent as the case may be. Global C0 1 Profile and Sequestration Carbon monoxide (CO) as well as carbon dioxide (C0 2 ) are very important atmospheric contaminants. Human activities are responsible for the release of increasing quantities of these gases to the atmosphere. CO is particularly important because of its potent mammalian toxicity, while C0 2 is most significant because of its ability to regulate global temperature. Neither gas is thought to cause direct damage to vegetation at the current ambient concentrations as monitored. CO has not been shown to produce acute effects on plants at concentrations below I 00 ppm for exposures from I to 3 weeks. The threshold of C0 2 toxicity to plants is in such excess of the ambient conditions as to be completely unimportant. C0 2 concentration of the global atmosphe re is estimated to have been approximately 290 ppm in the middle of the 19'h century. Today, it is approximately 335 ppm. One-fourth of this increase is estimated to have occurred between 1967 and 1977. Some atmospheric scientists have warned that the earth's mean temperature is likely to increase by several degrees in the new century and that such a significant warming would result in far reaching changes. The changes envisaged include shifts in the zonation of vegetation and alteration in the quantity and distribution of rainfall , melting of polar ice caps, expansion of ocean water. rise of sea levels and inundation of low coastal areas. This alarming increase 12 in C0 2 and the resultant GHG has prompted the international community to sit up and take note of the situation, and introduce measures to arrest the trend. At another plane, it has been suggested that increased atmospheric C0 2 may stimulate vegetative growth through enhancement of photosynthesis and that the biota may seNe as sink for the C0 2 Currently the 700 billion tonnes of carbon in the atmosphere in the form of C0 2 is supplemented by 2.3 billion tor.nes more annually, representing a 3 per cent increase every decade. Anthropogenic combustion of fossil fuels contributes 5 billion tonnes of carbon to the atmosphere annually. A comparable or even greater amount of carbon may be released to the atmosphere via forest clearance and soil losses. Approximately 75 per cent of the carbon introduced to the atmosphere from all sources is removed by effective sink mechanism. The guesstimated annual global sink strength due to photosynthesis in forest eco system is 70 X 10 12 kg. Photosynthesis is the most important metabolic process of forest ecosystems and primarily responsible for forest productivity. In simple terms, it is the reduction of C0 2 to CH 2 0 and the oxidation of water to molecular oxygen ; plants derive approximately 95 per cent of their dr1 weight by this process. The few published reports en rates of net photosynthesis (gross C0 2 fixation less losses due to respiration in light and dark) of intact leaves of mature trees suggest that such rates are in general greater than I 0 mg and less than 200 mg C0 2 uptake per gram dry weight per day. Reported daily rates are generally greater for deciduous trees than for conifers on a leaf weight basis. Rates of net photosynthesis for any tree are a function of time as well as location. Under tropical conditions as obtain in many Indian States, there is abundant solar radiation and where good ground coverage is managed, the increase in biomass is estimated to be I kg. Wt increase in biomass/sq ft of surface/year= 100 tonnes/hectare/ year. Kyoto Protocol and After In December 1997, parties to the UN Framework Convention on Climate Change agreed upon the Kyoto Protocol - which commits industrialised countries to an average 5.3 per cent reduction of GHG from the 1990 levels by the year 20 I 0. The steps proposed to -