We were discussing “Cements and
its types” and “Clinker grinding process in cement
manufacturing unit” in our previous posts. We have also seen the “Clinker storage system” in our recent
post.
Today we are going to start here one very important
topic i.e. Cement industry pollution control measures.
We will understand the
various terminologies and engineering concepts used in cement technology with
the help of this category, but first read this article “Clinker cooling technology” and “Cement kiln refractory lining”.
Further we will go for discussion of clinker grinding,
cement packing and dispatch, pollution control and much more facts about cement
technology in our next post in this category of cement technology.
Sources of pollution and control technology
Water pollution
Cement industry is not a water polluting industry.
Only the cooling tower blowdown associated with the GCT is a source of waste
water generation, which does not have much significance as a water pollutant. The
waste water is treated in septic tanks or sewage treatment plants and is used
for gardening, irrigation and other purposes.
Air pollution
Cement industry is one of the major air polluting
industries. The source of dust emission may be categorized into following parts
Point Emission Source: - from raw mill, kiln,
clinker cooler, cement mill, coal mill.
Fugitive Emission Source: - The dust generated from
the transfer of raw materials,
intermediates and final products and during loading / unloading.
Kiln is the main source of dust emission.
Quantum of dust generated and recommended air pollution control equipment
SOURCE
|
NORMAL DUST
GENERATION RANGE ( g / N m 3 )
|
DUST COLLECTOR
|
Crusher
|
5 - 15
|
Bag Filter
|
Raw mill :
Gravity discharge
Air swept
|
20 - 80
300 - 500
|
Bag Filter / ESP
|
Coal Mill :
Gravity discharge
Drying / grinding
|
20 - 80
100 - 120
|
Bag Filter / ESP
|
Kiln : Dry
Semi - dry
Wet
|
50 - 75
10 - 20
30 - 50
|
Bag Filter / ESP
|
Clinker Cooler
|
5 - 10
|
ESP / Bag Filter with H.E
|
Cement Mill
|
60 - 150
|
Bag Filter / ESP
|
Packing Plant
|
20 - 40
|
Bag Filter
|
The dust emission can be controlled by providing
adequate pollution control equipment such as cyclone, ESP, bag - filters etc.
Their selection depends upon various factors, such as mentioned here
1.
Size of dust particles
2.
Flue gas characteristics
3.
Collection efficiency
4.
Emission limits prescribed by
authorities
5.
Techno - economic feasibility
Gaseous pollutants from the kiln are oxides of N (NOx)
and SO2. Ammonia is injected into the flue gas in the high temperature zone at
exit of the kiln where NOx is reduced to N2 in the presence of O2.
NO + 4 NH3 + O2 = 4 N2
+ 6 H2O
NO2 + 4NH3 + O2 = 3
N2 + 6 H2O
Hydrated lime Ca (OH) 2 is injected into
the flue gas to arrest SO2.
Ca (OH) 2 + SO2 + ½ O2
= CaSO4 + H2O
Plant Capacity
|
Emission Standards
for Particulate Emission ( mg / N m 3 )
|
200 tpd or less
Greater than 200 tpd
|
Protected
area Other areas
250 400
150 250
|
Noise Pollution
Noise is generated from operation of heavy duty
machines - crushers, tube mills, ball mills, fans, coolers etc. Noise level
depends upon nature, size and capacity of machines, running speed, feed
material etc. The noise level generally varies from 70 - 118 dB.
Following methods may be employed to control noise
pollution in cement industry
1.
Using vibration damping pads, isolating
vibrating parts etc. to reduce noise pollution in cement industry
2.
By enclosing the source and making them
sound insulated
3.
Using personal noise protectors like,
ear plugs, ear muffs etc
De-dusting and Pollution Control
Various types of pollution control equipment are
intensively used in the cement industry to minimise dust nuisance in the plant
area so as to maintain dust free atmosphere as far as practicable as well as to
maintain the dust emission level within acceptable limits.
Cement plant machinery work under negative pressure
to prevent dust from escaping into the atmosphere.
The different types of dust are
1.
Raw material and Raw mix dust
2.
Coal dust
3.
Exit dust from raw material dryers
4.
Exit dust from kilns
5.
Clinker dust
6.
Raw gypsum dust
7.
Cement dust
The Pollution - control equipment used are
1.
Electrostatic precipitator ( ESP )
2.
Dust - bag Filter
3.
Gravel - bed Filter
4.
Glass bag - house.
Do you have any suggestions? Please write in comment
box.
I am very thankful to Mr. Subrata Bhaumik,
Independent cement consultant, for providing such beautiful information and
contents about cement technology.
Mr. Subrata Bhaumik has more than 50 (Fifty) Years
(1965 - 2016) of Experience in Cement and other related Industry covering more
than 100 assignments in cement plants with capacities ranging from 100 tpd to
10,000 tpd in India and abroad involving visit to 25 countries overseas in
connection with work.
For more detailed information about the original
Author of this content, please click the Author profile link below.
Author Profile
Image courtesy: Google
No comments:
Post a Comment