ENVIRONMENTAL POLLUTION FROM BRICK MAKING OPERATIONS AND THEIR EFFECT ON WORKERS
By Team Orion
Deepasree M Vijay
Poornima A Menon
IMK Senate House Campus
Emission of huge quantity of toxic elements from brick kilns is causing serious health hazards. The brick kilns emit toxic fumes containing suspended particulate matters rich in carbon particles and high concentration of carbon monoxides and oxides of sulphur (SOx) that are harmful to eye, lungs and throat.
These air pollutants stunt the mental and physical growth of children. According to the data, the primary source of SOx — the major pollutants in the air — is traffic vehicles (55.8%), followed by brick manufacturing industry (28.8%). And the primary source of NOx (nitrogen oxides) pollutants is also traffic vehicle (54.5%) and brick manufacturing industry (8.8%). Also, nearly 25 to 26 per cent of the country’s wood production are used for burning bricks every year, causing deforestation.
Indiscriminate burning of firewood in brick field kilns
According to the government rule the owners of brick fields are to pay lincence fee, VAT and land development tax at commercial rate, but the government is being deprived of such taxes due to unauthorised manufacturing of bricks.
The use of fire-woods in kilns of bricks fields is prohibited as per brick burning control ordinance of 1992 and the owners would be punished for violating the law. The brick field owners have been burning bricks with firewoods. As a result a large number of trees like keora, ‘chaila’, sundari, mehgini, bain etc are being felled indiscriminately. The dishonest brick field owners collect the fire woods from different forests with the help of their agents.
Spewing out eco time bomb Raising chimney heights of brick kilns fails to stop grave air pollution
Bricks are made for building. But the country’s brick kilns are churning out the basic ingredients for construction in a way that is doing more harm than good. The government recently ordered the brick kiln owners to raise their chimneys to a height of 120 feet in a move to limit the kilns destructive pollution emissions. It is not only crops that are being affected by the tons of smoke coming out of the chimneys. Experts now say that brick kilns are emitting harmful ‘particulate matters’ (pm) into the air, which are responsible for the alarming rise of respiratory ailments. According to available statistics, more than four thousand brick kilns are operating in and around the capital. The alarming figure suggests that city dwellers and inhabitants of surrounding areas are breathing more sulphur than oxygen. But the DoE seemed to be happy focusing their attention on bricks and mortars. Some even claimed a small success with the imposition of the height restrictions. There also seems to be a lack of proper monitoring of whether the brick kiln owners are obeying the Brick Kiln Control (amended) Act (2001), which prohibits the establishment of brick kilns within a three-kilometer radius of human inhabitation as well as fruit garden. The law remains only a piece of paper as brick kilns are even operating less than one kilometre of a densely populated area. Making matters worse, the brick kilns owners are flouting the existing laws of using only coal or gas to keep their furnaces burning, it is alleged, with some using worn tyres and plastic materials as a cheap form of fuel. Most shocking of all is the indiscriminate use of wood.
Fired clay brick is one of the most important building materials in the country. The current (2001) annual brick production in the country is estimated at 140 billion bricks. Brick making is a predominantly rural industry with brick making units belonging to small and informal sector. The number of brick producing units in the country is estimated to exceed 100,000. It consists of clay preparation, shaping, drying and firing operations. In India, good agriculture soil is preferred as the raw material for making bricks. It is estimated that the brick industry consumes around 400 million tons of good quality soil every year. The burning of fuel for firing bricks results in emissions of gaseous pollutants and ash into the environment. Brick firing being an energy intensive process, brick industry is one of the largest consumers of coal (around 24 million tons/year) in the country and hence is also an important air polluter. Air pollution and use of good quality agriculture soil are the major environmental concerns related with brick industry in the country.
The air pollution is defined as the presence in the atmosphere of substances in such amounts as to affect humans, vegetation, animals, or material adversely. Large scale burning of fuels — coal, oil, gas etc. to supply energy to industries, households and means of transportation is the main cause of air pollution. It is estimated that almost go% of the air pollution are related with the combustion of fuel. The major pollutants are particulate matters (smoke, dust),gases (Sulphur dioxide, Nitrogen oxides, carbon monoxide, carbon dioxide etc.), metals (e.g. lead) etc.
Air pollution could have local as well as global impacts. All living beings inhaling or exposed to the polluted air gets affected by it. Particulate matters such as smaller dust and smoke particles penetrate deeply into the lungs and get deposited there. Sulphur dioxide causes irritation of the respiratory system. Carbon monoxide inhalation also causes dizziness, vomiting and in higher concentrations it can be fatal. Plant health is also adversely affected by air pollution. Pollutants like fluorine, lead and mercury cause damage to plants.
The harmful effects of air pollution are not only confined to the living beings directly exposed to the pollutants near its source, but are felt in a large area around the source of pollution. Acid rain is one such phenomenon, which is a cause of concern in heavily industrialized areas. Acid rain is caused because sulphur dioxide and oxides of nitrogen combines with water vapour in the atmosphere and forms mild acids. These acids then return to earth as rains, which have given, rise to the term acid rains. It causes extensive damage to plant life, to buildings and pollution of lakes and rivers. Fog is another phenomena whose effect can extend to nearby areas. Fog formation is accelerated due to air pollution. Normal life particularly transportation gets seriously hit due to fog and growth of crops is affected by reduction in sunlight.
Some of the effects of air pollution are not confined to local or regional environment but have the potential to affect all of the humanity. One such effect is global warming, which is resulting in a permanent change in the global climate. Scientists believe that increase in concentration of carbon dioxide mainly due to burning of fossil fuels (coal, petroleum products) is causing a global rise in temperature of the atmosphere and the earth’s surface. Even a few degrees rise in temperature can cause change in climate patterns world-wide, such as — melting of ice in polar regions resulting in rise in sea water levels which can submerge low lying coastal areas, change in rainfall pattern etc. Realising the threat from global warming, control of greenhouse gases (carbon dioxide, methane etc.) has now become an important issue in the global diplomacy and is expected to gain importance in near future.
Air Pollution from brick kilns
Being one of the largest consumers of coal in the country, it is one of the important sources of carbon dioxide emission in the country.
Other air pollutants from brick kilns are:
a) SPM in the flue gases which is generated mainly due to incomplete combustion of fuel (black smoke) or comes from fine coal dust, ash present in coal and burnt clay particles.
b) Hydrocarbons and carbon monoxide due to incomplete combustion of fuel.
c) Sulphur oxides, concentration of which mainly depends on the amount of sulphur present in the coal and is significant where high sulphur content coal is used
d) Dust pollution generated during removal and laying down of ash layer on the top of the kiln and also due to blowing of ash stacked on the top and sides of the kiln
While the local impact of pollution caused by small isolated brick kilns located in rural areas is not likely to be significant, it is the large brick kiln clusters, located in the vicinity of large brick demand centres (towns and cities) that are important cause of concern. Rapid urbanisation has resulted in expansion of these clusters. Air pollution in these clusters affects the workers, local nearby residents as well as crops in the vicinity.
Among the various categories of workers working on brick kilns, the firemen, unloaders and workers, which handle ash, has the maximum exposure to the pollutants. Inhaling of these pollutants causes irritation of skin and eyes and can cause pulmonary diseases such as pneumoconiosis and silicosis, which are caused by inhaling siliceous dust. Pollution also has an affect on agricultural crops and fruit plantations. The damage caused to mango and other fruit plantations due to pollutants from brick kilns is well known.
Measures to reduce air pollution from brick kilns
The measures to control air pollution can be classified into two categories:
a) Measures to reduce generation of pollutants at source or energy efficiency measures.
b) Measures to control or reduce the impacts of the emissions
To use an “add on” device to remove pollutants from the stack gases e.g. gravity settling chamber
Measures to reduce generation of pollutants by Improving combustion
As already mentioned, one of the important source of air pollution is incomplete combustion of fuel. Roughly about 10% of the fuel supplied to a BTK remains unburnt or partly burnt. Considerable scope exists for improving combustion in BTK and other traditional kilns. The main causes of incomplete combustion in a BTK are insufficient air supply and improper feeding of coal. By improving the kiln operation, particularly by increasing the draught, improving air control and improving fuel feeding practices, the unburnts can be reduced to a large extent.
Energy efficiency measures
Any measure that saves fuel also helps in emission reduction as the total amount of fuel burned is reduced. Apart from the improvement in combustion process, it is possible to reduce energy consumption by 10-15% in a BTK by making small improvements in kiln design, construction and operation. Better kiln insulation and increase in fire travel rate is the key to energy conservation in fixed chimney brick kilns.
One of the causes of SPM generation is the high ash content in coal. Some of the ash is carried by flue gases. It is possible to mix a part of the fuel in the powdered form with the clay during clay preparation. This fuel is referred as internal fuel as it is present inside the brick. As the brick is heated in the kiln, combustion of internal fuel takes place. However, in this case as the fuel particles are entrapped in the brick, the ash associated with them remains inside the brick and does not come out. This helps in reducing the pollution.
Measures to control/reduce impact of pollutants
Reduction in pollution generation at source by better utilization of fuel is the best way to control pollution. However, it is not always possible to reduce the emissions to a level below the acceptable limit just by improvement in combustion and energy conservation measures. In these circumstances techniques to arrest pollutants before they are released in the atmosphere are employed. These techniques involve use of filters, scrubbers, gravity settling chambers etc. In case of fixed chimney kilns gravity-settling chamber, the most basic technique for arresting SPM is employed. It should be kept in mind that all the techniques for arresting pollutants result in pressure loss and hence require additional energy. Low flue gas velocities and draught in fixed chimney kilns make it virtually impossible to use any other add-on device other than gravity settling chamber.
The harmful effect of pollutants locally can be reduced by reduction in concentration of pollutants through dispersion of pollutants in a large area. That is why recommendations for taller chimneys are given. Tall chimneys ensure release of pollutants at a higher height, which gives more time to pollutants to disperse in the atmosphere before reaching the ground.
Achieve high combustion efficiency:
The two stages in the combustion of coal are:
· Devolatisation and combustion of volatiles.
· Char combustion
When coal is heated to a temperature of 350 o C, volatiles (gases such as methane, hydrogen, carbon monoxide etc.) are released from the coal. The process of devolatisation extends till a temperature of about 600 o C. The volatiles mix with hot air, and once this mixture has attained the ignition temperature, some time is required (ignition delay) before the mixture can ignite. The combustion reactions are faster at higher temperatures i.e. ignition delay is lower at higher temperatures. The burning volatiles are observed as flames in the kiln. The char (solid part) that remains after the release of volatiles can burn only at temperatures in excess of 600 o C . Smaller coal particles burn faster compared to bigger coal particles. Therefore, the conditions for achieving high combustion efficiency in the kiln are:
a) Feed coal only when the temperature in the firing zone is above 600 o C.
b) Keep sufficiently long firing zone (coal feeding zone of atleast 3-4 lines) so that the volatiles get sufficient space (high temperature zone) to mix and burn.
c) Use coal with particle size smaller than 3/4 inch.
The combustion efficiency can be judged by observing the colour of the smoke during the coal-feeding period (dark black smoke signifying poor combustion efficiency) as well as by the amount of char accumulated at the bottom of the kiln setting.
d) Optimum utilisation of the kiln production capacity
In general in a BTK, increasing the throughput (daily production) helps in lowering the specific fuel consumption and the fuel cost per brick. For a given kiln, the surface and structure heat loss per day is almost constant and it is almost independent of the fire travel rate or production rate of the kiln. It means that by increasing the fire travel rate the specific energy consumption of the kiln can be decreased.
Reducing the wastage of good quality agriculture soil in brick making
Use of good quality agriculture soil in large quantities for brick making is also a grave area of concern. In geographical regions having thin topsoil, this result in reduction in the productivity of land and in extreme cases the land does not remain fit for agriculture use. To reduce this wastage following steps can be taken:
a) Promoting deep mining of clay for brick making instead of surface mining.
At present only top surface (3 ft to i0 ft) is utilized for brick making, resulting in large surface area being affected due to excavation of soil for brick making. Deep mining of clay can reduce the area affected due to excavation of soil for brick making.
b) Promoting use of waste materials like fly ash in brick making.
Use of waste materials such as fly ash, boiler ash, stone dust etc. can reduce to use of good quality agriculture soil in brick making.
c) Promoting use of perforated and hollow bricks.
A reduction of up to 40% in the material use is possible by going for perforated/hollow bricks instead of solid bricks. Perforated/hollow products require less energy for firing and produce less pollution per unit.Perforated and hollow bricks also has better insulating properties resulting in reduction in air conditioning and heating loads inside buildings made from perforated and hollow bricks.
All the above mentioned measures would require mechanization of some of the processes in brick making. Development of appropriate low cost machinery for making perforated/hollow products as well as support for popularising these products on large scale are essential for reducing wastage of agriculture soil in brick making.