(Mehr Chand Polytechnic College, India) — The term ‘brick’ refers to a small unit of building material, often made from fired clay and secured with mortar, a bonding agent comprising of cement, sand, and water. A popular construction material, brick retains heat, withstands corrosion, and resists fire. Because each unit is small -usually four inches wide and twice as long, brick is an ideal material for structures in confined spaces, as well as for curved designs.
Moreover, with minimal upkeep, brick buildings generally last a long time. Brick making has undergone several improvements over a period of time like absolute uniformity in shape, decrease in weight and making the firing process speedier, fuel efficient and eco-friendly.
In olden days bricks were made in small batches, relying on relatively inefficient firing methods. One of the most widely-used methods was an open clamp, in which bricks were placed on fire beneath a layer of dirt and used bricks. Such a method gradually became obsolete and was replaced by the Hoffmann kiln, invented in Germany. Better suited to the manufacture of bricks in bulk, this kiln contained a series of compartments, through which stacked bricks were transferred for pre-heating, burning, and cooling.
Bricks are heated to anywhere between 600 to 1100oC to get the fired product (as per IS – 1077). Kilns can be classified into intermittent and continuous categories. In intermittent kilns, fire is allowed to die out and the bricks to cool after they have been fired. The kiln must be emptied, refilled and a new fire started for each load of bricks. In intermittent kilns most of the heat contained in the hot flue gases and the fired bricks is lost. In a continuous kiln, fire is always burning and bricks are being warmed, fired and cooled simultaneously in different parts of the kiln. Heat in the fuel gas is utilised for heating green (sun dried) bricks and the heat in fired bricks is used for heating air for combustion. As a result, continuous kilns are generally more efficient.
Clamp, Scove, Scotch and Down-Draught are among the different types of intermittent kilns. Those of the continuous type include moving fire annular kiln (Hoffmann, Bull’s trench, Zig-zag), and moving ware kilns (Tunnel, Vertical Shaft).
The Indian brick industry, with an estimated coal consumption of 15-20 million tonnes per year, is the third largest consumer of coal in the country after power plants and steel industry. Burning of coal results in the release of several air pollutants, such as carbon dioxide (CO2), carbon monoxide (CO), sulphur dioxide, nitrogen oxides and particulate matter. At local level (in the vicinity of a brick kiln) some of these pollutants cause injury to human health, animal and plant life. At global level, pollutants like CO2 contribute to the phenomena of global warming and climate change.
With growing environmental consciousness, the pollution caused by the brick industry is coming under close scrutiny. Pollution control and energy conservation are inter-related – the key to controlling combustion-related pollution in brick industry lies in increasing the efficiency of fuel use in brick kilns. Specific fuel consumption, in terms of tonnes of fuel consumed for firing one lakh bricks, is the popular way of expressing performance of brick kilns in India. The traditional method of brick making uses 18 to 20 tonnes of coal for producing one lakh bricks, which can go down by 20 per cent with usage of improved technology. Time has come to think of using alternative fuels, such as rice husk, coconut shell charcoal, biomass (rice straw, bagasse, wood waste, wild bushes), biogas etc. Of course the ultimate will be use of solar energy.
Brick making has undergone several changes, so as to make the process and output cost effective and efficient in usage.
Perforated hollow bricks (Resource-efficient bricks): With an aim to reduce carbon emissions, United Nations Development Program’s Global Environment Facility (UNDP-GEF) is supporting a project on manufacture of energy-efficient bricks. The Punjab State Council for Science and Technology (PSCST), which is the local resource Centre for North India, will provide technical guidance to about 5,000 kilns in Punjab and Haryana. The Union Ministry of Environment and Forests is the implementing agency and The Energy and Resource Institute (TERI) is a partner in the project. One of the important components in this project is enhancing public awareness through holding of workshops on promotion of Resource Efficient Bricks (REBs). In Europe and other developed countries, transition from conventional solid bricks to perforated hollow bricks has already taken place. REBs have several advantages like less consumption of top soil and coal (estimated to be about 20 per cent), reduced carbon dioxide emissions, more strength and reduced water absorption, resulting in reduced (estimated to be 7 per cent) cost of construction, besides reduced (estimated to be 5 per cent) power bill due to better insulating property. In India, with the entry of international brick manufacturers like Wienerberger, mechanisation of brick kilns and better products may soon see the light of the day.
Machine-moulded bricks: Most of the brick kilns produce hand-moulded bricks. Installation of machines at kiln site demands extra capital and heavier power connection. However, machine-moulded bricks are certainly better in size and strength and are preferred for use in face-work.
Fly-ash based bricks: The use of fly ash, produced in large quantity, has assumed importance and is in use for manufacture of cement, bricks and embankments. The Ministry of Environment and Forests has made it mandatory for all brick kilns located within 50 kms radius of thermal plants to use fly ash in the production of bricks. Bricks produced in a conventional kiln by mixing fly ash with clay are certainly better in strength, size and have least water absorption property. The IS code for these bricks is IS – 13757. Fly ash lime bricks don’t use clay but lime, sand and fly ash. These are not burnt. These are also called FAL G bricks. The lime used in these bricks should be only C class, hydrated lime as per IS 712. The IS Code for these bricks is IS – 12894. When used, these are generally prescribed for buildings having less than two storeys. Clay-fly ash bricks, when tested for various physical requirements laid in IS 13757-1993, give satisfactory results. These bricks need to be tested for compressive strength, water absorption and efflorescence.
The rich, clayey soil on the banks of rivers is raw material for a whopping 140 billion bricks a year. Produced in over 1,00,000 brick kilns in India, these are part of a large but unorganised brick sector in the country.
It is generally perceived that the Indian brick industry has missed the bus of technological development and the environmental consciousness that follows it. One such innovation is the development of Vertical Shaft Brick Kiln (VSBK) in China. VSBK technology is very popular in rural China for small-scale production of bricks. It is estimated that around 50,000 VSBKs are operating in China.
Since 1990 the kiln has been demonstrated in Pakistan, Nepal, India and some countries of Africa. It is energy efficient and environmentally friendly. It consumes 40 per cent less energy and emits 90 per cent less pollution (TSP) compared to traditional brick kilns. It is estimated that each individual in Asia consumes about 250 bricks. If all brick kilns in Asia can be shifted into VSBK technology, it could save almost 72 million tonnes of CO2 annually in addition to the cleaner environment it provides.
In 1995, the Swiss Agency for Development and Cooperation (SDC) launched an A
ction Research Project aimed at improving efficiency of brick kilns in India. As a part of this project it was decided to field test the techno-economic feasibility of VSBK technology under Indian conditions. For this purpose, four VSBK pilot plants were constructed. The first VSBK pilot plant became operational in May 1996. The design and construction work of the VSBK pilot plants was carried out under the guidance of experts from Energy Research Institute of China.
The VSBK technology brought with it two major advantages – less fuel consumption and lower SPM (suspended particulate matter) emissions. Moreover, the VSBK could be operated perennially, as the kiln’s roof protected it from the vagaries of weather. With minimal land usage, development of multiple-shaft production units actually enhanced the ratio of land used to production output, and even better quality.
THINGS TO COME
Brick making is not going to be the traditional labour-intensive, energy guzzling sector for long. It is transitioning to more efficient, mechanised, fuel-efficient and environmental friendly with the onset of improved technology, alternate fuels and efficient kiln designs. Already many manufacturers are participating in total quality management and statistical control programmes. The latter involves establishing control limits for a certain process (such as temperature during drying or firing) and tracking the parameter to make sure the relevant processes are kept within the limits. Therefore, the process can be controlled as it happens, preventing defects and improving yields. Such and many other changes are underway.
By: Rajeev Bhatia is lecturer, Department of Civil Engineering, Mehr Chand Polytechnic College, Jalandhar, India