1.0 'Industrial Ecology'
- The Concept :
Most of the economic activity that
took place subsequent to the Industrial Revolution followed
an 'open-ended' approach as regards flow of materials
and energy in all production processes. The approach
involved transformation of natural resources into useful
products and returning the worn-out products and wastes
/ by-products of the production process back to the
Mother Nature. It had no concern whatsoever for conservation
of natural resources and environmental quality and hence,
led us to a situation where 'sustainable waste management'
has become our highest priority today.
Although the high consuming societies
of the developed world need to take lion's share of
the blame and responsibility for the environmental damage,
we in India cannot remain to be silent observers to
the worsening ecology around. To resolve this apparent
conflict between development and environment, hereafter,
all governments, businesses and individuals will be
required to move towards a framework where development
(or growth) becomes environmentally sustainable. This
is the basis of the 'industrial ecology' concept. It
aims to transform the 'open' system of production into
one where material and energy flows are 'closed', i.e.
all wastes and by-products get reused within the 'system'
as a result of transfers among 'symbiotic' participating
Utilization of waste materials in brickmaking
is one good example of industrial ecology at work.
2.0 'Sustainable Waste Management'
and Brickmaking :
Sustainable waste management is often
based on waste hierarchy - Reduce, Reuse, Recovery and
(safe) Riddance - in the descending order of priority.
Utilization of industrial, urban and agricultural wastes
in brickmaking achieves all these objectives simultaneously.
Not only does it solve the disposal problem of the generating
agencies and minimizes the requirements of primarily
extracted clays and fossil fuels, but it also has many
positive effects on the brickmaking process and the
brick quality. Therefore, all wastes have been categorized
below under 4 groups, depending upon their principal
effect on the manufacturing process / product quality.
1. Fuel containing wastes
2. Plasticity reducing / enhancing wastes
3. Fluxing wastes and
Of the above, although flyash can be
included under category '1' or '2' - and in some instances,
under category '3' - considering the volume of its production
/ availability and severity of its environmental impact,
flyash has been classified separately.
3.0 Non-Flyash Wastes :
3.1 Fuel containing wastes are 'Potential
Heat Carriers', in the sense they contain high percentage
of organic and / or carbonaceous matter. They are therefore
extensively used in the production of fired clay bricks.
This category includes residues from urban waste treatment
plants and wastes of coal processing, textile, tanning,
sugar, liquor, petroleum, paper, wood-processing and
host of other agro / food processing industries. The
calorific value of these wastes ranges from 1,200 to
33,000 KJ/kg . The addition of these wastes to brick
bodies is almost never more than 10 % by mass and their
main effects include energy saving during firing, increase
in porosity of fired goods (making them more lightweight,
thereby improving their heat / acoustic insulating properties)
and reduction in shrinkage and mechanical strength.
3.2 Plasticity reducing wastes (i.e.
'opening' or 'filler' materials) and plasticity enhancing
wastes (i.e. 'binders') play an important role in the
production of both fired as well as cured bricks. They
chiefly include wastes from mining, metallurgical and
chemical industries viz. blast furnace slag, red mud,
stone dust, burnt foundry sand, drilling muds, phosphogypsum
/ gypsum, coal washery sludges, ore processing wastes,
Coarse-grained wastes generally reduce
plasticity and their content in brick bodies varies
between 10 and 60 % by mass. They effect slight reduction
in shrinkage and mechanical strength and in some instances,
increase in efflorescence. Fine-grained wastes generally
enhance plasticity and they are added in quantities
ranging from 5 to 15 % by mass. Chemically reactive
substances such as pozzolanic materials, cement wastes,
lime sludges, red mud, phosphogypsum / gypsum, etc.
are ideally used in the production of 'cured' bricks.
3.3 Fluxing means 'glass formation'
and therefore it essentially involves firing. Fluxing
reduces the firing temperature (consequently saving
energy) and porosity (consequently increasing fired
strength). Fluxing wastes originate from glazing lines
of ceramic tile manufacturing units, plating plants
and a number of metallurgical / engineering industries.
They chiefly contain alumino-silicates
(> 50 % by mass) and variable contents of alkalies
/ alkaline-earth elements - which contribute to fluxing
- and heavy metals. Glazing sludge can be added upto
20 % by mass, and other wastes upto 5 % by mass to the
brick body to improve the brickmaking process / product.
3.4 Manufacturing technologies and Indian experiences
So far, hand-moulding and soft extrusion
technologies have been predominently employed in India
for manufacture of fired bricks from non-flyash wastes.
In case of cured / autoclaved bricks, semi-dry pressing
technology - incorporating either small vibro-compaction
/ toggle-type machines - has been utilized. Indian experience
with small capacity plants (3 to 10,000 bricks / day
/ shift) is much better as compared to large capacity
4.0 Flyash :
With a present share of about 40 %,
coal happens to be the world's most extensively used
fossil fuel for generating power. Its worldwide 'reserves
to production ratio' is 4 times that for the oil and
gas taken together. At the 1994 production level, economically
accessible global coal reserves are expected to last
at least another 230 years. This clearly shows the eminent
position coal is expected to enjoy during the foreseeable
future as a power-generation fuel.
India is the 3rd largest producer of
coal in the world after China and U.S.A. However, Indian
coals have high ash content ( 35 to 48 % as compared
to 8 to 10 % in developed countries like U.S.A., Japan,
Germany, France, etc. ) and low calorific value (3,500
to 4,000 KCal/kg as compared to 6,000 to 7,000 Kcal
/kg in the developed countries). About 72 % of India's
present power generation capacity is coal-based. This
situation is expected to continue at least during the
early part of 21st century. Use of coal as fuel brings
in its wake its own share of problems, the most important
being that of flyash generation. When pulverized coal
(70 % passing through 200 mesh) is burned in a boiler
furnace within 900-1500 0C temperature range, non-combustible
part of the coal gets converted into ash. Nearly 80
% of this ash 'flies off' or gets carried away from
the furnace by flue gases, which is then separated out
by use of one or more Electro Static Precipitators (ESP's)
and is called 'flyash'. The balance 20 % ash 'agglomerates'
to larger particle sizes, ranging from 0.02 to 75 mm,
and falls down to the bottom of the furnace through
its grate as 'bottom-ash'. Both these ashes are mixed
with water and sent to ash pond for storage and further
About 1,000 million tonnes of flyash
has already accumulated in Indian ash ponds, which are
increasing at the alarming rate of about 80 million
tonnes every year. It is estimated that about 140,000
MW of additional power generation capacity would be
required by the end of the 10th Five Year Plan, i.e.
the year 2007, to meet the growing indigenous demand
arising out of rapid industrialization, farm mechanization
and changing individual lifestyles. This will then lead
to a staggering figure of 175 million tonnes of flyash
generated per year, which in turn would engage about
40,000 hectares of land for construction of ash ponds.
Storage of flyash in ash ponds requires
very large quantities of water ( average ash : water
ratio is 1 : 12 ) and it involves huge capital and operating
costs in setting up and running the mixing, pumping
and transport facilities, respectively. It not only
blocks large tracts of land permanently but also results
into serious groundwater contamination and deterioration
of the surrounding eco-system. This brings to the fore
the dire need of the hour to utilize as much quantity
of flyash as possible and to solve its critical disposal
4.1 Characterisation of Indian Flyashes
The chemical and physical properties
of flyash depend upon many parameters such as coal quality,
type of coal pulverization and combustion process followed,
nature of ash collection and disposal technique adopted,
etc. Flyash is generally 'pozzolanic' in nature while
bottom-flyash is generally not. Pozzolanicity of a material
is its capacity to react with CaO or Ca(OH)2 in presence
of water at room temperature to form solid and water-isoluble
cementitious compounds. The pozzolanicity of flyash
mainly stems from the presence of various silicates
and aluminates in amorphous form.
Chemical Composition :
Except Neyveli flyash, which is high in CaO (5.0 - 16.0
%) and MgO (1.5 - 5.0 %) contents and low in SiO2 (45.0
- 59.0 %) content, the range of chemical composition
of Indian flyashes is given in the following Table.
Corresponding data for American and German flyashes
is also given for comparative purpose.
Composition ( % by w/w ) :
Component Indianflyash American flyash Germanflyash
SiO2Al2O3Fe2O3CaOMgONa2OK2OSO3LOI 50.0 - 65.016.0 -
25.05.5 - 15.2 1.5 - 2.50.8 - 1.00.5 - 0.90.6 - 1.00.5
- 0.82.0 - 15.0 40.0 - 51.0 17.0 - 28.0 8.5 - 19.0 1.2
- 7.0 0.8 - 1.1 0.4 - 1.8 1.8 - 3.0 0.3 - 2.8 1.2 -
18.0 42.0 - 56.024.0 - 33.0 5.4 - 13.0 0.6 - 8.3 0.6
- 4.3 0.2 - 1.3 1.1 - 5.6 0.1 - 1.9 0.8 - 5.8
From the above data it can be seen
that Indian flyashes are more silicious and contain
higher percentage of unburnt carbon as compared to American
/ German flyashes.
Physical Properties :
Flyash is generally grey in colour, abrasive, acidic
and refractory in nature. Its specific surface area
varies between 4,000 and 10,000 cm2/g , which is lesser
than cement which has a specific surface area of about
3,000 to 3,500 cm2/g. Morphologically, flyash consists
of 3 types of particles - irregularly shaped particles,
solid spheres and cenospheres.
4.2 Manufacturing Technologies and
Indian Experiences :
a) Flyash-Sand-Lime Bricks : Flyash-sand-lime
bricks are manufactured by mixing flyash sand and lime
in 70-80 %, 0-10 % and 8-20 %, respectively, proportions
which may be followed by addition of 0.2-0.3 % chemical
accelerator during wet mixing. This mixture is moulded
under 80-240 kg/cm2 pressure. The green bricks can be
air cured for 24-48 hours and then hot water / steam
cured or autoclaved at 1-14 kg/cm2 pressure and 100-1800
C temperature for 3-12 hours. Some of the organizations
which offer this know-how are NCB, CBRI, CFRI, ACC,
b) Flyash-Lime-Gypsum Bricks : 55-75
% flyash is mixed with 15-30 % lime and 10-15 % gypsum.
Chemical accelerator may or may not be added. This mix
is moulded under pressure. Air / sun drying may be done.
Green bricks are then water cured. Some of the organizations
which offer this know-how are AEC, Ahmedabad; ITC, Bhadrachalam;
NLC, Neyveli; INSWAREB, CBRI, CFRI, CPRI, RRL Bhopal,
c) Flyash-Clay Bricks : Flyash-Clay
bricks can be manufactured by mixing 20-60 % of flyash
with clay and hand-moulding or extruding the mix. Firing
can be done in fixed chimney / high-draught or any other
continuous kiln. Some of the organizations which offer
this know-how are CBRI, NML, CPRI, RRL Bhopal, Walter
Craven Ceramic Projects India Ltd.,Calcutta, etc.
d) Flyash-Stonedust-Cement / Lime Bricks
: 20-50 % flyash, 25-75 % stonedust, 5-25 % cement /
lime and upto 10 % chemical binder are wet mixed and
pressed between 200-300 kg/cm2. The bricks are either
water cured for 28 days or autoclaved. This know-how
is being offered by CPRI and Damle Clay Structurals
(P) Ltd., Pune.
Indian experience with large capacity
plants manufacturing fired flyash-clay or cured flyash
bricks is far from being satisfactory. In this light,
development of high capacity indigenous presses ( instead
of imported ones ) and thorough techno-economic evaluation
of projects need major attention. Small plants (of 10,000
bricks /day / shift capacity) employing hand-moulding,
egg-laying / toggle-type machines or mechanical / hydraulic
presses have been performing far better in comparison.
5.0 Future Scenario :
As mentioned earlier, the industrial
ecology concept - involving reuse and recycling of wastes
- holds much promise for the Indian Brick Industry.
It not only provides a way to reconcile our developmental
and environmental imperatives, but also throws open
a host of opportunities to develop, implement and market
environmentally sustainable technologies.
Perhaps a concrete example shall explain
this point better. At Kalundborg Industrial Complex,
Denmark - a small coastal industrial zone 75 miles west
of Copenhagen - a web of energy and material exchanges
among companies has emerged over the last 20 years.
The Kalundborg system consists of five core partners:
Asnaes Power Station (a 1,500 MW coal-fired power plant),
Statoil Refinery (of 3.2 million tonnes/year capacity),
Gyproc (a plasterboard factory making 14 million sq.
metres of gypsum wallboard a year), Novo Nordisk (an
international biotechnology company with annual sales
in excess of $2 billion, whose Kalundborg plant manufacturers
pharmaceuticals and industrial enzymes), and the City
of Kalundborg which supplies residential heat and water
to its 20,000 residents.
The power plant pipes residual steam
to the refinery, and in exchange, receives refinery
gas, which substitutes some of the coal. Excess steam
is also supplied to Novo Nordisk and the City (for heating).
This replaces almost 3,500 individual oil furnaces (a
major air pollution source). The power plant's desulphurisation
process also yields gypsum, which meets about 2/3rd
of Gyproc's needs. Sludge from Novo Nordisk's processes
is used as a fertilizer on nearby farms, and surplus
yeast from its insulin production is sold to farmers
as pig food.
Industrial Clusters, in the form of
industrial estates or industry belts, are quite common
in India. Therefore, planning and implementation of
'industrial recycling networks' at locations which are
either near to the source(s) of wastes (e.g. Coal-based
Thermal Power Plants) or markets, appears very much
feasible. However, to ensure the success of these industrial
eco-systems, 2 pre-requisites assume significance in
the Indian context. First, the economic benefits of
the exercise must be spelt out very clearly to the participating
industries and second, our policy and regulatory approaches
need drastic changes. Rather than being mere law-making,
enforcing and monitoring agencies, the Ministry of Environment
and Forests (MoEF) and Central / State Pollution Control
Boards need to achieve positive environmental outcomes
through co-operation with the industry and by adopting
incentive-based approaches. The recent MoEF Regulation,
which makes it compulsory for all brick manufacturers
within 50 kilometre radius of Coal-based Thermal Power
Plants to use at least 25 % flyash in their raw-mix
by mass and which makes all Thermal Power Plants accountable
for their actions, shall also need similar soft-landing
in order to be effective.