19" International Conference of the System Dynamics Society
MODELLING AND ANALYSIS OF ENVIRONMENTAL POLLUTION IN
AN INTEGRATED STEEL PLANT
K. Vizayakumar
Professor, Indian Institute of Technology, Kharagpur
K. R. Divakar Roy
Reader, Andhra University College of Emgineering, Visakhapatnam
Abstract
Gaseous, liquid, and solid pollutants that are released from the production processes in an
integrated steel plant are modeled here using system dynamics. This is a macro model.
This model is simulated and experimented with various pollution abating policies, mainly
in terms of the investment made for pollution control. The results provide a broad idea of
the extent of actions that are required to control pollution.
1. Introduction
The integrated iron and steel plant in large and complex. It had several operations that
produce huge amounts of gaseous, liquid and solid wastes. Impact of these pollutants, if
uncontrolled, commence from the factory or work place it self, and extend to the
surrounding areas. The important operations include preparation of raw materials, such
as coke making and sorting, iron ore beneficiation, production of sinter, processing of
lime stone etc., hot metal and pig iron production using blast furnace, steel making using
BF-BOF route and the rolled products like wire rods. Each of these processes produce
pollutants, either /or gaseous, liquid and solids. Therefore, steel industry faces a major
pollution problem as the pollution is not confined to a single processing stage. As the
industry is very large, pollution control also is costly and has to be applied at many points
(UNEP, 1986).
The gaseous emissions, namely, suspended particulate matter, sulphur dioxide, nitrogen
oxides, carbon monoxide and hydrocarbons, directly enter the atmosphere causing the
values of the said variables to increase. The residence times of these variables in
atmosphere depend on the atmospheric conditions, namely temperature, wind speed and
rail fall (Vizayakumar, 1990). It is observed that, during rainy season, the values of these
variables particularly, SPM, are very low as the particles get loaded by the rain. In
summer, its value is very high. It was reported that in favourable conditions, the SPM
and other gaseous emissions travel as far as 50kms from the source in the direction of the
wind.
Therefore, it is necessary to take into consideration the climatic factors of the location of
the plant and include them appropriately in the model equations.
2 Model description:
The model is mainly organized in three sections - gaseous, liquid and solid waste.
However, the sources of these pollutants are the same except some, where they may be
negligible. As is observed, the environmental model is completely related to the
production of hot metal, Sinter, steel, etc. However, the production variables are
aggregated taking the maximum and minimum of their values to test and analyze the
pollutants generation.
2.1: Gaseous emissions
As shown in Figure 6.1, gaseous emissions are taken as level variables as they
accumulate over a period of time depending on the generation and attrition of that
pollutant.
The suspended particulate matter, i.e., dust in the atmosphere is the main visual pollutant.
It is expressed as
SPM=SPM+DT*(SPMGR-SPMAR)
Where SPM =Suspended particulate matter
SPMGR= SPM generation rate
SPMARS=SPM attrition rate
SPMGR is taken as the sum of the dust released at various processes i.e.,
SPMGR=(A SINTR*DSINTN+A COLCO*(DCLCRN*SDCLCN)+A INPBF*(DINBFN+
SDINBN)+ASTEKO*(DSTELN+SDSTEN)+A BLOMO*DSTBLN)*DMDCA
Where ASINTR, ACOLCO, AINPBF, ASTELO, ABLOMO represent the average
production of sinter, coke, hot metal, steel and steel products respectively.
DSINTN is the normal fraction of the dust released due to sinter production.
DCLCRN, SDCLCN, DINBEN, SDINBN, DSTELN, SDSTEN, DSTBLN are the similar
fractions.
DMDCA is the Dust multiplier from dust control actions.
The values of these fractions are taken from UNEP (1986). The dust values vary from
the source of input materials. For example, the dust quantity of coal depends on its
quality and varies from source to source. It may also depend on the blend made at the
mine. Therefore, it is difficult even at the factory to monitor and determine exactly the
dust quantity. That is why the values provided in the UNEP report are taken as
acceptable approximations.
The equation of SPMGR gives the uncontrolled dust production rate. No company can
operate with out controlling the emissions not only due to the environmental legislation,
but also due to the increased awareness of the employees, who are the first sufferers.
However, the rate of control may depend on the investment made in pollution control.
Several reports indicate that an amount of 10% of the total investment in capital
equipment is required to control pollution to the desired limit. The investment is taken as
required for all gaseous, liquid and solid pollutants. It is assumed here that the company
invests in control of all the pollutants in an equitable manner. Therefore, the control of
pollutants is related to the ratio of investment made in pollution control to the total capital
investment. Therefore, control function is added to dust generation, SPMGR, by
multiplying it with DMDCA where DMDCA is Dust multiplier from dust control
activities. It is expressed as a fraction related to the ratio of total investment to desired
investment( RATINV).
RATINV =TINDRN/DINDRN
Where TINDRN=total investment in pollution control and
DINDRN=Desired investment in pollution control
TINDRN is expressed as level variable
TINDRN=TINDRN+DT*(RINDRN-DRINDR)
Where RINDRN= Rate of investment in pollution control and
DRINDR=depreciation rate of pollution control equipment
RINDRN is expressed as a policy variable, the discrepancy between the investment made
and desired investment
RINDRN=+(DINDRN-TINDRN)/AT
Where AT= Adjustment time, may be 1 year, 2 years, 3years depending on the
policy
Depreciation is assumed as the linear depreciation over 10 year period.
DRINDR=TINDRN*DRINDF
DRINDF=0.1
The desired investment in pollution control is expressed as
DINDRN=GROSBK*DINDRF
Where GROSBK is the Gross Block, taken from finance sector and DINDRF is the
fraction investment required in pollution control which value is taken as 5%.
DINDRF=0.1
For the purpose of this sect oral model, the Gross Block is taken as a level variable and is
expressed as
GROSBK=GROSBK+DT*NETGRR
Where NETGRR=Net Growth of gross block rate which is taken as a fixed growth value
of 5%
NETGRR=GROSBK*NETGRT
NETGRT=Net growth of gross block fraction=0.05
The attrition rate (SPMAR) of a gaseous pollutant depends upon the amount resident in
atmosphere as well as on the atmospheric conditions, namely, temperature, relative
humidity and wind speed. Therefore, SPMAR is expressed as
SPMAR=(SPM/DAT)*DMWC
Where DAT =dust attrition time. The average attrition time in normal conditions
of 27degrees Centigrade temperature, relative humidity of 90 and 11.5 m/sec
wind speed is given as 1 month =1/12year
DMWC=Dust multiplier from weather conditions which is taken as the average of
all three impacts.
DMWC=(DMT+DMRH+DMWS)/3
Where DMT=dust multiplier from temperature
DMRH-=dust multiplier from relative humidity
DMWS=dust multiplier from wind speed
They are the multiplier values depending on the temperature, relative humidity and wind
speed respectively. The relationships are expressed in terms of table values:
TEMP | 20 23 26 29 31 33 36 40
DMT /1.2 1.14 1.09 1.0 0.95 0.91 0.88 0.85
ws i 9 11 13 15 17 19 20
DMWS | 1.2 1.14 1.09 1.0 0.95 0.91 0.88 0.85
RH 60 70 80 90 100 110 120 130
DMRH | 0.5 0.75 0.9 1.0 11 1.25 1.35 1.4
Other emissions, i.e, S02, NOX, CO and HC are also modeled in the similar way but the
parameter values change.
SOX =SOX +DT*(SOX GR-SOXAR)
SOX GR=(A SINTR*SOSNTN+A COLCO*SOCLCN+A INPBF* SOINBN
+A STELO*SOSTEN+A BLOMO*SOTBLN)*SOMPC
SOSNTN, SOCLCN, SOINBN, SOSTEN, SOTBLN are the respective
parameters for Sulphur dioxide emission at various stages.
SOMPC = Sulphur dioxide multiplier from pollution control expressed as table
function depending on the investment to desired investment ratio.
SOXAR=(SOX/SAT)*SMWC
Where SAT=SOX _ attrition time=1/15year
SMWC=(SMT+SMRH+SMWS)/3
Where SMT, SMRH,SMWS are expressed in the following table:
TEMP 20.0 | 23.0 | 26.0 | 29.0 | 31.0 | 33.0 | 36.0 | 40.0
SMT/NMT/CMT/HMT | 1.4 1.24 | 1.19 | 1.0 0.95 | 0.9 0.85 | 0.8
Ws 7 9 11 13° 715 17 19 | 20
SMWS/NMWS/CMWS/HMWS | 1.0 | 1.12 | 1.21 | 1.26 | 1.31 | 1.35 | 1.38 | 1.4
RH 60 | 70 80 90 100 /110 | 120 | 130
SMRH/NMRH/CMRH/HMBH | 0.7 | 0.76 | 0.86 | 0.96 | 1.06 | 1.16 | 1.26 | 1.3
NOX =NOX +DT*(NOXGR-NOXAR)
Where NOX =Nitrogen oxides
NOX GR=Nitrogen oxides generation rate
NOXAR=Nitrogen oxides attrition rate
NOXAR=(A SINTR* NOSNTN+A COLCO*NOCLCN+A INPBF* NOINBN+
ASTELO*NOSTEN+A BLOMO*NOTBLN)*NOMPC
Where NOSNTN, NOCLCN, NOINBN, NOSTEN, NOTBLN are the
respective parameters for Nitrogen oxide emissions at various processes
NOXAR=(NOX/NAT)*NMWC
Where NAT= Nitrogen attrition time, 0.125 year
NMWC=nitrogen oxides emission multiplier from weather
conditions=(NMT +NMRH+NMWS)/3
CO=CO+DT*(COGR-COAR)
Where CO= Carbon monoxide
COGR= Carbon monoxide generation rate
COAR=Carbon monoxide attrition rate
COGR=(A SINTR*ACOLCO*COCLCN+AINPBF*COINBN+A STELO*COSTEN
+ABLOMO*COTBLN)*COMPC
COAR=(CO/CAT)*CMWC
CAT=0.08
CMWC=(DMT+CMRH+CMWB)/3.
HC=HC+DT*(HCGR-HCAR)
Where HC =hydrocarbons emitted
HCGR=Hydrocarbons emission rate
HCA R=Hydrocarbons attrition rate
HCGR=(A SINTR*HCSNTN+A COLCO*HCCLCN+A INPBF*HCINBN
+A STELO*HCSTEN+A BLOMO*HCTBLN)*HCMPC
The parameter values are:
HCSNTN=0.001, HCCLCN=0.0002, HCINBN=0.00005, HCSTEN=0.0005,
HCTBLN=0.002
HCAR=(HC/HAT)*HMWC
HAT=0.25 year
HMWC=(HMT+HMRH+HMWS)/3
SOMPC, NOMPC, COMPC and HOMPC are similar to DMDCA, and dependent
on the ratio of investment in pollution control to desired investment.
2.2: Water Effluents:
Integrated steel plant operations release the following pollutants into water effluents.
Water is used in an integrated plant in most of the operations for coal washeries, cooling
or granulation at iron, steel and ingot making as well as hot and cold rolling. The
pollutants released are: suspended solids, phenols, cyanides, chlorides and sulphates.
Therefore, the treatment of water is essential before releasing to the outside streams,
lakes, water bodies etc. However, in this plant, the water, after treatment, is reused in the
plant operations. The water has to be treated after every use. It is found that phenols,
cyanides, etc. are only trace elements constituting 2% of the total pollutants released
through effluents. Therefore, they are not considered in the model. As all these
pollutants accumulate over time, they are modeled as level variables.
SS=SS+DT*(SSGR-SSRR)
Where SS=Suspended solids
SSGRS5SS generation rate
SSRR&=SS removal rate
SSGR=(A SINT R* SSSNTN+A COLCO*SSCLCN+AINPBF*SSINBN
+A STELO*SSSTEN+A BLOMO*SSTBLN)
where SSSNTN=0.00028, SSCLCN=0.0003, SSINBN=0.00024, SSSTEN=0.00007,
SSTBLN=0.0002
SSRR=SS*WTFSS
CHLORD=CHLORD +DT*(CHLGR-CHLRR)
CHLORD=A mount of chlorides in effluent
CHLGR=Chlorides generation rate
CHLRR=Chlorides removal rate
CHLGR=AINPBF*CHINPBF+A STELO*CHSTEN+A BLOMO*CHTBLN
No Chlorides are released during sintering and coking processes. The values of the
parameters are:
CHINBN=0.00005, CHSTEN=0,.00005, CHTBLN=0.0002
CHLRR=CHLORD*CHMCA
The amount of sulphate is expressed as:
SULPHT=SULPHT+DT*(SULGR-SULRR)
SULPHT=A mount of sulphates in the effluent
SULGR=Sulphates generation rate
SULRR=Sulphates removal rate
SULGR=A SINTR*SUSNTR+A INPBF* SUINBN+A BLOMO*SUTBLN
No sulphates are released during coking and steel making process. The parameter values
are:
SUSNTN=0.000004, SUINBN=0.000003, SUTBLN=0.0004
SULRR=SULPHT*SUMCA
Control of these pollutants depends upon the effluent water treatment both quantity and
quality of treatment. It is directly related to investment made and operational
expenditure. It is presumed here that once acquired the company puts the plant in
operating condition. Therefore, investment is only considered here to determine the
amount of pollution control. The relationship between the investment and the extent of
pollution control in each case are given in the following table values:
RATINV 0.0 0.2 0.4 0.6 0.8 1.0
SSMCA 0.0 0.05 0.2 0.5 0.75 0.9
CHMCA/SUMCA 0.0 0.05 0.2 0.35 0.65 0.75
6.2.3 Solid Pollutants:
Solid pollutants or solid wastes generally include dust also. However, here, dust
emissions are considered in the gaseous emissions. Slag and sludge are only considered
here under solids. Though sludge is semi liquid slurry, it is taken as a solid waste as it is
not discharged through water. Mill scales and oily wastes are released in the rolling units
but are negligible in quantity compared to other solid wastes. Therefore, they are ignored
in this model.
Slag and sludge also accumulate over a period of time and therefore, considered as level
variables.
SLAG=SLAG+DT*(SLAGGR-SLAGUR)
Where SLAG=A mount of slag accumulate
SLAGGR=Slag generation rate
SLAGURS=Slag utilization rate
SLAGGR=AINPBF*SGINBN+A STELO*SGSTEN
Slag is produced only during iron making process and steel making process and the
parameter values are:
SGINBN=0.3 and SGSTLN=0.1
SLAGUR=SLAG*(SLAGUF+SLAGDF)
SLAUGF=Slag utilization factor
SLAGDF=Slag dispatch factor
Similarly, sludge is expressed in the following equations:
SLUDGE=SLUDGE+DT*(SLDGGR-SLDGUR)
SLUDGE=A mount of sludge accumulated
SLDGGR=A mount generation rate
SLDUGR=Sludge utilization rate
SLDGGR=ACOLCO*SLCLCN+A INPBF*SLINBN+A STELO*SLSTEN
+ABLOMO*SLTBLN
Unlike slag, the sludge is also produced during coal processing and in rolling mills. The
parameter values are:
SLCLCN=0.002, SLINBN=0.012, SLSTEN=0.015 and SLTBLN=0.01
SLDGUR=SLUDGE*SLDGUF
SLDGUF=Sludge utilization factor
Generally, the solid wastes, slag and sludge, are reused and/or recycled either by the Steel
plant or by other industries such as cement plants. The solid waste that can not be reused
or recycled has to be dumped. It requires a large area of land for disposal. These
dumping sites create water pollution by leaching. They release effluents containing
hydrocarbon residues, soluble salts, sulphur compounds and toxic heavy metals.
6.3 Base Model Simulation and Results
The base model assumes no investment in pollution control. It means that the pollutants
are released unabatedly to atmosphere. It is assumed that the sorrounding environment
will get affected. In the case of air pollution, the impacts can be observed even as far as
50 kms. away in the favourable wind direction. However, the impact decreases with
distance. Here, an area of 125 sq. km. around the Steel Plant is considered as vulnerable
to a height of 100 m. It gives the impacted volume of 12.5 X 10° cu. m. Though the
impact decreases from the emission source point to the distant point in the area, the
impact is considered as uniform because the source points are too many making it almost
a non-point source situation. The level of pollutant in the atmosphere is determined by
the cumulative value of the pollutant in the atmosphere divided by the impacted volume.
The quality related to a pollutant is measured as a ratio of its permissible value to the
actual value.
The Steel Plant has an artificial water source made for the purpose, and the water is
reused. However, it is observed that some of the water is left to the municipal drain that
will ultimately lead to the sorrounding water bodies. For the purpose of modelling, water
used per 1 tonne of steel produced (i.e., 250,000 cu. m.) by the Steel Plant is taken as
water required. However, using more water reduces the level of pollutants in the water
source/effluent.
The solid waste (slag and sludge) is considered as unused and unrecycled in the basic
model. The model is simulated using DY MOSIM (Bora and Mohapatra, 1984). The
results are presented in Figs. 6.2 to 6.4. Fig. 6.2 depicts the behaviour of gaseous
pollutants in the atmosphere. Seasonal variations can be observed in the model. This is
due to the effect of the climatic factors, namely, temperature, wind speed, and relative
humidity. The behavior of the pollutants in liquid effluent is shown in Fig. 6.3. Here, we
observe that the quality of water due to suspended solids, sulphates, and chlorides is
decreasing though there is an initial increase observed in the case of sulphates and
chlorides. The quality of environment index (QEI) is having a decreasing trend though it
is varying seasonally as shown in Fig. 6. 3. As expected, the solid wastes, slag and
sludge, are increasing over the years as depicted in Fig. 6.4. This is the true picture of the
environment sorrounding any Steel Plant. In fact, huge hills of solid waste can be seen
near the plant site.
6.4 Policy Analysis
The policy analysis, here, is very complex. Because there are several pollutants, several
source points and differing alternatives from one type to another type of pollutant. This
macro model is therefore used to experiment with broad policies that are expected to
affect on all types of emissions. As explained in section 6.2.1, differing investments are
taken as different policies that affect the gaseous emissions and the liquid effluents.
Where as, the utilization factors are considered as policy altematives for slag and sludge.
The investment alternatives considered to abate the gaseous and liquid pollutants are
40%, 50%, 65%, and 80% of the desired amount. Figs. 6.5 to 6.9 shows the
environmental quality due to SPM, SOX, NOX, CO, and HC respectively. It is observed
that a minimum of 80% investment is required to achieve good quality of environment.
Similarly, Figs. 6.10 to 6.12 show the quality of water due to suspended solids, chlorides,
and sulphates respectively. The quality of environment index has reached the maximum
value of 1 (one) in Policy 4 only as observed in Fig. 6.13. Figs. 6.14 and 6.15 show the
results of varying utilization factors of slag and sludge. Even after 50% utilization, the
accumulation is around 100,000 tons. The model can be used to experiment to know the
value of the utilization factor to limit the quantity of solid waste to a desired value.
Further analysis is required for micro level policy analysis, i.e., to determine the number
of Electro Static Precipitators, Dust Arresters, type and number of effluent treatment
plants required, etc., to control pollution. However, such micro level analysis is outside
the scope of this study. The results, depicted here, only show what level of actions are
required to be taken to contain pollution with in the threshold limits.
References
Bora, M. C., and P. K.J. Mohapatra, DY MOSIM, IIT, Kharagpur, India.
UNEP, 1986, Guidelines for Environmental Management of Iron and Steel Works,
United Nations Environmental Programme, Industry and Environment office, Nairobi,
Kenya.
Vizayakumar, K., 1990, A Study on some Aspects of Environmental Impact Analysis,
Unpublished Ph. D. Thesis, IIT, Kharagpur, India.
FIG 6.2 BASE MODEL - AIR POLLUTION
oy
-e-soxo
+ Ie-noxo
i on ae
“Tha Maa
1994 1996 1998 2000 2002 2008 2006 2008
FIG. 6.4 SOLID WASTE
2500000
2000000
1500000
—e— SLAG
1000000 —# SLUDGE
500000 +
0
1994 1999 2004
YEAR
IG. 6.5 AIR QUALITY DUE TO SPM.
[Base MODEL
|-=-Pouicy 1
| = rouicy 2
|—rouicy 3
|epouicy 4
YEAR
FIG. 6.6 AIR QUALITY DUE TO SOX
[-+-ease wODEL
|-=-ouicy 2
} = Puicy 2
|-=-powicy 3
eouicy +
YEAR
FIG. 6.7 AIR QUALITY DUE TO NOX
[ease MODEL
|-2-Pouicy 1
| Pouicy2
|-—pouicy 3
Lsrouicy 4
FIG. 68 AIR QUALITY DUE TO CO
[= BASE MODEL]
|-=-pouicy 1
| pouicy 3
|--pouicy 4
|e-poucys
FIG. 69 AIR QUALITY DUE TO HC
FIG. 6.10 WATER QUALITY DUE TO SS
[> BASE MODEL]
|-=-PoLicy 1
| = poucy 2
| Poucy 3
Le POUcy 4
[-o-BASE MODEL
|-=-Poucy 1
| »-poucy 2
|-poucy 3
Lepouicy 4
FIG. 6.11 WATER QUALITY DUE TO SULPHATES
FIG. 6.12 WATER QUALITY DUE TO CHLQ
[-=-BASE MODEL
|-e-roucy 1
| Poucy 2
|-Poucy 3
eroucy 4
[BASE MODEL
|-s-rouicy 1
| = Poucy 2
|-—Pourcy 3
|x-Poucy 4
FIG. 6.13 QEI- POLICY RESULTS
FIG. 614 SOLID WASTE POLLUTANT
[= aASE WODEL
|-=-Poucy
| --Poucy 2
|--poucy 3
Le-poucy &
[BASE MODEL
|-e-POLIcy 5
| Poucy 6
L-Poucy 7
SLUDGE
FIG.615 SLUDGE PRODUCTION
[+ BASE MODEL]
|-=-POUcy 5
| =-Poucy 6
[pou 7
