A Case Study Report on Air Pollution in Cement Industry

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Bangladesh University of Engineering &
Technology
A case study on Air Pollution in Cement
Industry
Course Title: Industrial Pollution Control
Course No: CHE 485
Submitted To, Submitted By,
Nusrat Ara Irin
Dr. Md. Easir Arafat Khan
Jannatul Osman Arju
Assistant Professor,
Fahim Shahriar Sakib
Department of Chemical Engineering, BUET
Syed Alvi Sadat Ishmam
Arkabur Rahman Arnob
Date of Submission: 10.12.2020
Author’s email: fssakib98@gmail.com

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Table of contents
Chapter Page number
1. Introduction 4
2. Cement Industry 5
3. Major Pollutants of Cement Industry & Their Sources 8
4. Emission Monitoring 13
5. Emission Inventory 17
6. Air Pollution Modeling 21
7. Pollution Control Equipment 25
8. Conclusion 29
9. References 29

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Introduction
Bangladesh cement industry, one of the fastest growing cement markets in the world, grew at
approximately 11.5% CAGR over the last seven years as demand doubled from 14.6 million
MT per year to around 31.3 million MT per year. Per capita cement consumption in Bangladesh
almost doubled from 95 KG in 2011 to 187 KG in 2018. Despite huge growth of the industry
in last two decades, Bangladesh is still one of the lowest consumers of cement in the world.
Approximately 81% of the total market share is held by top ten manufacturers. By the end of
2018, local manufacturers had grabbed 86% of the market, a reversal in scenario from 15 years
earlier. Once a cement importer, Bangladesh is now a cement exporting nation. Bangladesh
exported cement worth US$13 million during FY17-18, compared to US$9.5 million earned in
the year before representing 16.68% growth in export earnings YoY with India being the main
destination for cement exports. On the back of massive infrastructure investment by the
government, rising remittance income, growing urban population and impressive GDP growth,
cement demand is expected to grow at even higher than the historical rate. Although self-
sufficient in cement production, Bangladesh needs to import almost all of the raw materials
used in cement manufacturing. Moreover, increased raw materials price and intense price war
have squeezed the profit margin for cement manufacturers. Recent changes in tax laws, higher
fuel & transportation cost and cost of fund have added more sufferings for the industry players.
Hence, although the outlook for cement demand growth is very robust; profitability still
remains a concern for all.

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Cement Industry
A cement is a binder, a substance used for construction that sets, hardens, and adheres to other
materials to bind them together. Cement is seldom used on its own, but rather to bind sand and
gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry,
or with sand and gravel, produces concrete. Concrete is the most widely used material in
existence and is only behind water as the planet's most-consumed resource.
Types of Portland Cements
In the construction industry, there are different types of cement. The differences between each
type of cement are its properties, uses and composition materials used during the manufacturing
process.
Various types of cement are produced in Bangladesh but Portland cement and blended cement
are by far the most common. Although they are primarily consisting of a kiln fired and fused
material known as clinker and addition of some materials make them applicable for different
purpose. Portland cement primarily consists of clinker that is ground and combined with small
amounts of gypsum or a similar material and is produced in several grades designed to provide
certain properties to concrete. The major ingredients of blended cement are clinker, gypsum,
fly ash, slag and limestone. Besides the Portland cement and blended cement, smaller amount
of specialty cements is produced in Bangladesh i.e., masonry, off-white Portland cements etc.
Manufacturing Process of Cement
The main stages in cement production can be discussed under the following sub-headings:
1. Raw Material Acquisition: Most of the raw materials used in cement production are
extracted from the earth through mining and quarrying and can be divided into the
following groups: lime, silica, alumina, and iron (Madsen et al., 2004). Quarry
operations consist of drilling, blasting, excavating, handling, loading, hauling, crushing,
screening, stockpiling, and storing. Naturally occurring calcareous deposits such as
limestone, marl or chalk provide the source for lime whether silica, iron oxide and
alumina are generally found in sand, iron ore, shale, and clay. Power station ash, blast
furnace slag, and other process residues collected from different industry can also be
used as partial replacements for the natural raw materials if they do not affect the cement
properties.

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2. Raw Materials Preparation: Raw milling involves mixing the extracted raw materials to
obtain the correct chemical configuration, and grinding them to achieve the proper
particle-size to ensure optimal fuel efficiency in the cement kiln and strength in the final
concrete product (Karstensen, 2006). Three types of processes- the dry process, the wet
process, or the semidry process may be obtained during raw milling. In the wet process,
water is added to the raw materials during grinding where in dry process, the raw
materials are ground in dry condition. The water used in the wet process is about 45%
of the raw material (Aziz, 1995). In the semidry process the materials are formed into
pellets with the addition of water in a pelletizing device.
3. Clinker Burning: In pyro-processing, the mix after raw milling is heated into a rotary
kiln to produce cement clinkers. A rotary kiln is a long steel cylinder used for pyro
processing, inclined about half to one foot, and is about 8 to 12 ft in diameter and 200
to 400 ft in length. The raw mix is supplied to the system as a slurry (wet process), a
powder (dry process), or as moist pellets (semidry process). The pyro-processing
system involves three steps: preheating, calcining (a heating process in which calcium
oxide is formed), and burning. The obtained cement clinkers after pyro-processing are
hard, grey, spherical nodules with diameters ranging from 0.32 - 5.0 cm created from
the chemical reactions between the raw materials. The fuel to be used for this purpose
is coal, oil or natural gas (Aziz, 1995). However, the use of supplemental fuels such as
waste solvents, scrap rubber, and petroleum coke has expanded in recent years to
promote the environmental sustainability.
4. Clinker Grinding: In this stage; the clinker is ground with other materials to form a fine
powder which is actually the “cement”. The hot clinker obtained from rotary kiln need
to be cooled before grinding. Gypsum is added to regulate the setting time of the
cement. Other chemicals or mineral additives or air entrainment or Cementous materials
may also be added to the ground clinker to achieve the particular properties.

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5. Cement Packaging & Dispatch: The finished product is transferred using bucket
elevators and conveyors to storage silos and then to packaging unit. After that cement
can be delivered to customers in bags (normally having 50kg weight) or sometimes in
loose amount by bulk conveyor.
Basic steps involve in cement manufacturing process are shown as flow chart in Fig 1
Figure 01: Overall cement manufacturing process

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Major Pollutants of Cement Industry & Their Sources
The entire process of cement manufacturing involves emission of enormous pollutants which
can affect the human health as well as the whole environment. Emissions from CMF include
particulate matter and combustion gases from cement kiln and other production process;
wastewater from the cooling of process equipment; slurries and sediments from wastewater;
plant maintenance waste; and research and laboratory wastes.
However, the air pollution from CMF has significant environmental impact and thus this
industry has been enlisted as the third largest industrial source of air pollution (USEPA, 2016).
Emission to air from CMF can be categorized into two groups:
(i) Gaseous Pollutants
(ii) Particulate Matter (PM)
Traditionally, compliance efforts have focused on pollutants including-
 Dust and other particulate matter (PM)
 Nitrogen oxides (NOx)
 Sulphur dioxide (SO2)
 Carbon monoxide (CO)
 Ammonia (NH3)
 THC (or TOC)
 Mercury and other heavy metals
 HCl
 Dioxins/furans
 Hydrogen fluoride (HF)

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Gaseous Pollutants
Oxides of nitrogen (NOx), sulfur dioxide (SO2), and carbon oxides (CO2 and CO) are the most
likely listed substances emitted during the production of cement as gaseous pollutants. Trace
quantities of volatile organic compounds (VOC) including benzene and phenol, ammonia,
chlorine, some listed metals, and hydrochloric acid may also be emitted (EETs Manual, NPI,
Australia, 1998). Gaseous pollutants emit generally during clinker production in rotary kiln and
also from preheater and clinker cooler.
NOx Emission
NOx releases from combustion of fuel at high temperature in the cement kiln. Three types of
NOx form in the cement kiln- thermal, fuel, and feed NOX. In kiln exhaust gases, more than
90% of NOx is NO; with NO2 generally makes up the remainder (Nielsen and Jepsen, 1990).
Thermal NOx is formed by oxidation of atmospheric nitrogen at high temperatures. The
literature cites threshold temperatures for the formation of thermal NOx ranging from about
1200–1600°C (2200–2900°F) (Nielsen and Jepsen, 1990). Since the flame temperature in a kiln
is significantly above these temperatures, considerable amounts of thermal NO are generated
in the burning zone. NOx emissions also result from the oxidation of nitrogen compounds in
the raw material feed to the kiln (feed NOx). It can also result from oxidation of nitrogen
compounds in fuel (fuel NOx).
SO2 Emission
In process of cement manufacturing SO2 are generated both from the sulfur compounds in the
raw materials and from sulfur in fuels used to fire a preheater/precalciner kiln system. The SO2
reacts with water vapor and other chemicals high in the atmosphere in the presence of sunlight
to form sulfuric acids. The acids formed usually dissolve in the suspended water droplets, which
can be washed from the air on to the soil by rain or snow. This is known as acid rain which is
responsible for acidification of soils, lake and stream, corrosion of buildings and monuments
and deforestation. Also, SO2 can form secondary particles like sulfates that cause haze and
reduce visibility.

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Figure 02: SO2 Reaction Process in Cement Production
Particulate Matter Emission
Particulate matters emit almost throughout total process flow of cement manufacturing
including quarrying, crushing, grinding (only in dry process), blending (only in dry process),
and transportation of raw materials, kilns operation, clinker cooling, stock piles and packaging.
Also, some of the gaseous pollutants and particulate matter may release due to the vehicular
movement at CMF for the transportation of raw materials or to delivery final finished cement
product. Although this vehicular emission may not be included in the emission from the core
cement manufacturing process.

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Figure 03: Particulate matter emitting sources
CO2 and CO Emission
CO2 as a by-product is released during the production of clinker (occur in the upper, cooler end
of the kiln, or a precalciner) in which CaCO3 is heated at temperatures of 600-900°C in a rotary
kiln and results in the conversion of carbonates to oxides. The simplified reaction is:
CaCO3+ heat CaO + CO2 (Gibbs et al., 2015)
In cement production about 60% of CO2 is released in unavoidable chemical reactions of
limestone (calcination process). The indirect emissions of CO2 and CO happen by burning the
fossil fuel (natural gas, oil or coal) to heat the kiln and electricity consumption during cement
production. Additional emission of CO2 and CO depends on the presence of organic matter in
raw material of cement. CO2 is a green-house gas and it is estimated that 5-6% of all CO2
greenhouse gases generated by human activities originates from cement production (Rodrigues
and Joekes, 2010). The estimated average carbon footprint is 0.83t CO2/t of traditional Portland
cement clinker (ranging from 0.7 to 1.4t). CO is weak greenhouse gas but its presence
influences the concentrations of other greenhouse gases like methane, tropospheric ozone and
CO2 (carbon monoxide: its environmental impact, n.d., para 3).

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VOC, Organic Matters and Heavy Metals Emission
Other cement related emissions in trace quantity include VOCs, dioxins, furans, methane,
heavy metals etc. The main source of VOC emission from cement kiln is organic matter present
in raw material. Occurrence of VOCs is also associated with incomplete combustion. VOCs
are precursor to ozone formation, which can also contaminate soil and ground water. It has
been identified that VOCs can cause retardation of plant growth, chlorosis and necrosis in broad
leaves plants. In cement manufacturing dioxins are also formed in the combustion system when
chlorine and organic compounds are present and it contaminates soil and ground water. Some
contents of fuel and raw material, which is naturally present in low concentration is liable for
heavy metal emission i.e. lead, cadmium, nickel, titanium, molybdenum. Heavy metals
contaminate soil and water and can adversely affect plant functions and cell structure.
Bioaccumulation of heavy metal can cause poising in aquatic and terrestrial life through
biomagnifications.

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Emission Monitoring
"Monitoring" means the collection and use of measurement data or other information to control
the operation of a process or pollution control device or to verify a work practice standard
relative to assuring compliance with applicable requirements. Emissions measurement,
monitoring and reporting contributes to understanding, documenting and improving the
industry’s environmental performance. Lack of emissions information can lead to local
concerns about plant operations. With regards to EPA's air quality regulatory requirements,
there are two basic types of monitoring with two different functions:
• Ambient air quality monitoring collects and measures samples of ambient air pollutants
to evaluate the status of the atmosphere as compared to clean air standards and historical
information; and
• Stationary source emissions monitoring collects and uses measurement data (or other
information) at individual stationary sources of emissions (i.e., facilities, manufacturing
plants, processes, emissions control device performance, or to verify work practices).
Air quality monitoring is useful in better understanding the sources, levels of different air
pollutants, effects of air pollution control policy, and exposure of various substances in the air.
The Environmental Protection Agency has established ambient air monitoring methods for the
criteria pollutants as well as for toxic organic compounds and inorganic compounds. The
methods specify precise procedures that must be followed for any monitoring activity related
to the compliance provision of the clean air act. These procedures regulate sampling, analysis,
calibration of instrument and calculations of emissions level i.e. concentration.
The number of monitoring stations should be minimum three. The location of station is
dependent upon the area of coverage and the wind rose diagram which gives the predominant
wind direction and speed. One station must be upstream of predominant wind direction and
other two must in downstream of predominant wind direction. Gaseous pollutants should be
monitored continuously while PM should be once every three days.

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Monitoring of particulate matter:
Isokinetic manual gravimetric method is applicable for the determination of particulate matter
emitted from stationary sources. A representative sample in the gas stream of a stack or duct is
withdrawn iso-kinetically through a nozzle and collected on a pre-weighed filter. The mass of
the particulate matter is then determined gravimetrically after removal of uncombined water
and its concentration calculated by relating to sample gas volume. Except where approval is
given by the EPA, Department of Environment and Natural Resources, the collection of the
particulate matter must be carried out from within the stack. Iso-kinetic sampling is sampling
at a rate such that the velocity and direction of the gas entering the sampling nozzle is the same
as that of the gas in the sampled gas stream at the sampling point.
In most stack, the velocity and concentration in the stack vary from point to point and from
time to time .The differences in velocity and particle concentration from place to place are
substantial . Higher nonuniformity is found near the bend or disturbance.It is required to take
measurement at multiple position in a cross section to get the average velocity and
concentration.
Figure 04: Particulate matter sampling method

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Sampling must be representative. There should be no leak in the sampling lines. Touching stack
walls with the probe when inserting the probe in the duct or when taking it out should be
avoided otherwise more particles will be deposited on the filter. Temperature of the nozzle
(opening), the probe and the filter must be controlled in order to avoid condensation. The
sampling must be isokinetic. Gas sample needs to be properly dried before it is taken to the gas
meter
Gaseous pollutant monitoring can be quantified and analysed by Spectrophotometry,
Chemiluminescence, Gas Chromatography-Flame Ionization Detector (GC-FID), Gas
Chromatography-Mass spectrometry (GC-MS), and Fourier Transform Infrared spectroscopy
(FTIR).
Chemiluminescence Analyzer:
NOx concentration is measured with this principle of chemiluminescence analyzer. Figure
presented below shows the working principle of chemiluminescence analyzer. By introducing
ozone (O3) to the sample gas, part of the nitrogen monoxide (NO) contained in the sample gas
will react with ozone, and oxidized to nitrogen dioxide (NO2). Part of the generated NO2 will
be in an excited state (NO2 * ), and when it returns to the normal state, it will radiate light. The
phenomenon is called chemiluminescence. The reaction is extremely fast and only the present
NO participates while being essentially unaffected by other existing species.
Figure 05: Working principle of a NOx analyzer

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Non-Dispersive Infra Red (NDIR):
An NDIR gas analyzer measures the concentration of CO, CO2 and NOx by determining the
absorption of an emitted infrared light source through a certain gas sample. The analyzer has
four major components: i) an infrared light source, ii) a sample chamber, iii) a wavelength filter
and iv)an infrared detector. Figure below shows the working principle of a NDIR analyzer. In
the figure it can be seen that there are two parallel sensors. One is sample cell, where sample
gases are introduced and other is the reference cell. The infrared light rays are directed through
the sample cell and reference cell. Infrared rays are absorbed by the sample containing of those
gas samples. Thus signal of each gas concentrations is obtained by calculating the difference
between the signal of reference cell and the sample cell. The quantity of the infrared radiation
absorbed by each component is proportional to the concentration.
Figure 06 : Working principle of NDIR gas analyzer
Analysis of sulphur dioxide :
Sulphur dioxide from air is absorbed in a solution of potassium tetrachloromercurate (TCM).
A dichlorosulphitomercurate complex, which resists oxidation by the oxygen in the air, is
formed. Once formed, this complex is stable to strong oxidants such as ozone and oxides of
nitrogen and therefore, the absorber solution may be stored for some time prior to analysis. The
complex is made to react with pararosaniline and formaldehyde to form the intensely colored
pararosaniline methylsulphonic acid. The absorbance of the solution is measured by means of
a suitable spectrophotometer.

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Emission Inventory
An emissions inventory is a database that lists, by source, the amount of air pollutants
discharged into the atmosphere during a year or other time period. The emissions inventory, is
the primary task to identify the various sources of pollution from the particular plant. It provides
the physical and geographical conditions of the source of pollutant.
Emissions may come from different points in cement production processes, depending on the
raw materials and fuels, preparation procedures and kiln systems, and emissions control
systems used. The largest volume substances emitted during the production of cement are
particulate matter (dust), oxides of nitrogen, sulfur dioxide, carbon dioxide and carbon
monoxide. Trace quantities of volatile organic compounds, acid gases, some trace metals, and
organic micro pollutants may also be emitted. The range of emissions of the main pollutants
are shown below:
Reported emissions from European cement kilns
Pollutant Average
concentration
Concentration range
from/to
Average specific
emission
Dust 20.3 mg/Nm3
0.3/227 mg/Nm3
46.7 g/t ck
NOx as NO2 785 mg/Nm3
145/2040 mg/Nm3
1.805 kg/t ck
SO2 219 mg/Nm3
Up to 4837 mg/Nm3
0.504 kg/t ck
CO Up to 2000 mg/Nm3
VOC/THC as C 22.8 mg/Nm3
1/60 mg/Nm3
52.4 g/t ck
• Concentrations are reference concentrations, i.e. 273°k, 101.3 kPa, 10% O2 and dry gases
• Specific emissions are based on kiln exhaust gas volumes of 2300 m3
/ton clinker
Source: BREF on cement, lime and magnesium oxide manufacturing industries, May 2010
Quantum of dust generated in different process of cement industry is shown below:
SOURCE NORMAL DUST GENERATION RANGE
( g / N m 3 )
Crusher 5 - 15
Raw mill :
Gravity discharge
Air swept
20 - 80
300 - 500

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Coal Mill :
Gravity discharge
Drying / grinding
20 - 80
100 - 120
Kiln : Dry
Semi - dry
Wet
50 - 75
10 - 20
30 - 50
Clinker Cooler 5 - 10
Cement Mill 60 - 150
Packing Plant 20 - 40
For the Emission inventory development source identification is essential. Systematic
procedure of emission inventory involves the source identification which includes:
• Release Type
• Location
• Emission of criteria air pollutants
There are a number of methods for the estimation of the emission rate and emission
concentration from each source .Such as:
• Manufacturer’s design specifications,
• Direct measurement
• Emission factors
An emission factor is a quantity derived to calculate the emission of a pollutant throughout the
process. These factors narrate an average value of available data of acceptable quality, and is
generally represented the long-term averages of the source type. The emission factors are used
when other information is not available.
The emissions from cement uses the general equation:

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Epollutant  ARproductionEFpollutant where
Epollutant is the emission of a pollutant
ARproduction is the annual production of cement
EFpollutant is the emission factor of the relevant pollutant
This equation is applied at the national level, using annual national total cement production
data. This method assume an ‘averaged’ or typical technology and abatement implementation
in the country and integrate all different sub-processes in the cement production between
feeding the raw material into the process and the final shipment off the facilities.
Figure 07: Emission factors of major pollutants in different country from cement industry

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The uncontrolled emission factor for cement manufacturing in different stages are shown in
tabulated from below:
Table 01: UNCONTROLLED EMISSION FACTORS FOR CEMENT
HANUFACTURING--COAL COMBUSTION
Process Particulate Sulfur dioxide Nitrogen oxide
kg/Mg lb/ton kg/Mg lb/ton kg/Mg lb/ton
Dry process kiln
dryer
128 256 3.5 7.0 2.9 5.7
Wet process kiln
dryer
120 240 3.0 6.0 4.1 8.2
Clunker cooler 4.6 9.2 - - - -
Preheater kiln - - 0.4 0.8 2.8 5.5
Precalciner kiln - - 0.5 1.0 2.4 4.8

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Air Pollution Modeling
Air pollution modeling is nothing but a numerical way to demonstrate the relationship between
emissions, deposition, atmospheric concentration, meteorology and other factors.
Mathematical modeling helps to give quantitative information about concentrations and
deposition but only for a specific time and location (Daly 2003, p 15-28). As a nature of
mathematical modeling, we assume some data for doing this like assuming the atmosphere in a
predictable format. For numerical modeling, meteorology data and terrain data are needed.
Emission rate is calculated from the volume and composition of a pollution source
(https://www.aeroqual.com/air-pollution-modelling, accessed at 10 december 2020, 11:55 am).
Pollution source is mainly two types and each has also two types.
• Static
Point source
Area source
• Dynamic
Point source
Area source
Air pollution modeling has some advantages. It forecasts a hypothetical situation which helps
to implement a new project. Modeling helps to determine the concentration and deposition of
pollutants of new upcoming industry in an area. Regulatory board can get an idea of the
pollution of that industry from modeling. It also helps them to compare with another alternative.
The disadvantage is the model relies on the input parameters like meteorology data, terrain
data, source particle data etc. So, they do not always reflect reality with accuracy.
The concentrations of the pollutants in the atmosphere are determined by:
• Diffusion
• Transportation
• Chemical transformation
• Ground deposition

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There are several types of air quality models, all used for different purposes. Most common
models are known as Atmospheric Dispersion Models (ADM). Here they are,
1. AERMOD: Aermod is a form of Gaussian plume model (GPM) and it is steady state.
GPM is developed early due to overcome the challenge of understanding the diffusion
properties of plumes which was very hard (Sutton 1932, Bosanquet 1936). It develops
meteorological data from surface, onsite station, upper air and geophysical terrain data.
It uses a single wind to transport pollutants. Here is a sample of aermod modeling
simulation.
Surface station: Bergman field, Alamosa, Colorado (USAF 724620 WBAN 23061
ICAO KALS)
Upper air station: Grand junction airport, Alamosa, Colorado (WBAN 23066)
Terrain location: Alamosa, Colorado (UTM 13S, NAD83 Datum)
Pollutant: (SO2, emission rate 0.8 g/s, release height 40 m, stack inside diameter 10 m,
gas exit velocity 5 m/s)
Figure 08: Wind velocity and direction vector (blowing to)

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Figure 09: Wind class frequency distribution
Figure 10: Aermod modeling pollutant concentration

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Figure 11: Aermod modeling of total deposition
2. CALPUFF: Calpuff is a form of Langrangian puff dispersion model and it is non steady
state. It is used for long range simulation and rough weather. CALMET is a
meteorological diagnostic model that uses data from surface, upper-air, over-water
stations, precipitation stations and geophysical data to produce a fully 3-dimensional
gridded wind field for the CALPUFF simulation.
There is some photochemical modeling like CMAQ, CMAX, UAM, CALGRID. Some models
are plume rise models, particle models, odor modeling statistical models which are not
described here. For cement industry, Aermod and Calpuff is used worldwide.

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Pollution Control Equipment
Cement industries are a major source of air pollution. Air pollution occurs mainly through dust.
A few other pollutants include oxides of N (NOx) and SO2, which are produced during burning
of raw materials. Since most of the cement industries in Bangladesh import clinker, emphasis
has been given on dust pollution controlling equipment in this section. But some controlling
measures for gaseous pollutants will be discussed at the end of this section.
Pollution control in cement industries is done mostly using the following equipment
1) Bag filters
2) Electrostatic precipitators (ESP)
1)Bag Filter
A bag filter (also known as Baghouse, Baghouse filter or fabric filter) is a popular choice of
dust pollution control device in Power plants, steel mills, pharmaceutical producers, food
manufacturers, chemical producers and other industrial companies. It is also used in cement
production during transport and packaging. Bag filters came into widespread use in the 1970s
Figure 12: Bag Filter
following the invention of fabrics with temperature tolerance of up to 350 ℉. The main appeal
of bag filters is the fact that using simplified mechanisms, bag filters can achieve an efficiency
of about 99 percent.

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A traditional bag filter usually employs cylindrical bags made of woven or felted fabrics as
filtering medium. Pleated non – woven cartridges are used for cases with low dust loading and
temperature below 250 ℉.
Bag filters are usually classified by the methods used to clean them. There are mechanical
shakers, reverse air and pulse jet baghouse. Air along with dust particles enters the filters, and
the air passes through the fabric leaving all the dust particles. The dust accumulation is
accompanied by a pressure drop. Cleaning process is initiated after a sufficient p-0ressure drop
occurs.
2)Electrostatic precipitators
Electrostatic precipitators are another form of air pollution control device that removes
particulate matters from the air by using static electricity. Compared to wet scrubbing process,
the energy is applied to the particulates being removed. Hence energy consumption is
minimized.
Figure 13: Plate type Electrostatic Precipitator
Electrostatic precipitators have a fairly simple operational procedure. The Precipitator employs
two electrodes for removing particulates. The shapes of the electrodes vary based on the type
of precipitator used. One of the electrodes is charged with a high negative charge. This
electrode imparts negative charges to the particulates of the passing gas. The second electrode,

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charged with a high positive charge is placed right after the first electrode. The negatively
charged particulates are hence pulled towards this electrode.
ESP are highly efficient, and their efficiency can reach up to 99 percent. But the efficiency of
the precipitators varies based on two particulate properties –
1. Electrical resistivity
2. Particle size distribution
A list of pollutant source along with dust accumulation and preventive equipment is given
below-
SOURCE DUST COLLECTOR
Crusher Bag Filter
Raw mill:
Gravity discharge
Air swept
Bag Filter / ESP
Coal Mill:
Gravity discharge
Drying / grinding
Bag Filter / ESP
Kiln:
Dry
Semi - dry
Wet
Bag Filter / ESP
Clinker Cooler ESP / Bag Filter with H.E
Cement Mill Bag Filter / ESP
Packing Plant Bag Filter
Pollution control measurement for gaseous pollutant
Main gaseous pollutants are NOx and SO2 produced during burning of the raw materials in the
kiln.

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NOx emission control
NOx emission from the kiln can be reduced in three ways –
1. Using process modification: Reduction of excess air from 10% - 5%, NOx emissions
can be reduced up to 15%. Addition of a small amount of steel slag can reduce NOx
emissions up to 30%. Since NOx emission is directly proportional to the amount of
energy consumed, use of low nitrogen alternative fuels are also recommended as it also
reduces the amount of energy required.
2. Combustion control: Technical literature and industrial reports indicate that up to
2347% reduction in NOx emission can be achieved using low-NOx burners. Usage of
alternative fuel can also contribute to reduced NOx emission
3. NOx emission: Ammonia is injected at the high temperature zone near the kiln exit.
This ammonia reduces NOx to NO2 in the presence of O2.
NO + 4 NH3 + O2 = 4 N2 + 6 H2O
NO2 + 4NH3 + O2 = 3 N2 + 6 H2O
SO2 emission control
Using gas-based fuel instead of coal-based fuel reduces the SO2 content of the flue gas greatly.
The produced SO2 is removed from the flue gas by injecting hydrated lime. This reacts with
the sulfur dioxide to produce calcium sulfate salt.
Ca (OH) 2 + SO2 + ½ O2 = CaSO4 + H2O
This process can reduce SO2 emission to about 50-70%.

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Conclusion
In this report we have discussed the overall pollution scenario and methods used to prevent
them from a global perspective. But in Bangladesh such laws and regulations are not followed
as much. Especially most local companies do not collect any excess data regarding the
emission, and in some cases, emission was found out to be around thrice the acceptable value.
The government policy should be reinforced, and sufficient measurements should be taken by
both the appropriate authority. Government backing and encouragement should help speed up
this process
References
1. Daugherty, K. E. & Wist, A. O. Air pollution control in the cement industry.
Amer.Inst.Chem.Engns Symp.Ser. 70, 50–55 (1974).
2. EMEP EEA. EMEP/EEA air pollutant emission inventory guidebook 2019: Cement
production. 1–18 (2019).
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