Efforts In Air Pollution Control Engineering Essay

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Pollution prevention and control strategies continue to evolve in response to increased awareness and changing environmental regulations. The Pollution Prevention (P2) strategy is receiving significant attention in industries all over the world, over end-of-pipe pollution control and management strategy. The existing P2 frameworks are reviewed and compared to identify limitations of these frameworks. We have proposed a Pollution Prevention (P2) and Pollution Control (PC) framework to overcome the limitation of existing frameworks. Two important scenarios, design phase and retrofitting of existing plants are considered in proposed framework.

Efforts in air pollution control are focused on either development of advanced technologies to reduce the emissions or utilization of existing technologies in optimal manner. World Bank group report (1998) pointed out that pollution control shall consider both particulate as well as gaseous pollutants. Mcilvaine, B (2006) noted that techno-commercial evaluation of the technologies to face the future challenges of stringent norms is necessary. It is noted that efficiency of every air pollution control device depends on pollutant characteristics. The air pollutant characteristics not only influence the performance of control equipments but also influence health hazards. In this regard Government of India revised National Ambient Air Quality Standards prescribing upper limits for PM2.5 and PM10 (NAAQM Notification GOI 2009).

Quantification of environmental and social cost due to emissions is a major challenge. However, in the recent past some attention is paid to estimate the health cost and quantify the same. These estimation methods are broadly based on a) response functions and compounding factors b) affect of acute or chronic exposure to the pollutants and c) dose response studies. Akbar et al. (2003) proposed a method that assess and value the adverse health impacts due to exposure to air pollutants. Friedrich et al. (2001) presented a methodology of medical costing, it involve dispersion studies of the air pollutants right from the source till its final impact.

Selection of best possible P2 and PC strategy needs a fundamentally sound numerical/ analytical technique. Optimization is a major enabling area in this regard which evolved from a methodology of academic interest into a technology that has continues to make a significant impact. Shaban et al. (1997) proposed an optimization model for selection of suitable control option to minimize pollution load and maximize the profits. Multi Objective Optimization (MOO) has found extensive use in solving the P2 and PC problems in process industries (Mavrotas, 2006; Martinez et al. 2010). However, the optimization models reported in literature do not consider health cost of air pollutants exclusively in the objective functions for selection of optimal control strategy.

Objectives of the study:

With above preamble, the broad research objective of the present study is to formulate a mathematical model which minimizes the combined environmental and economical cost through optimal selection of air pollution prevention and control strategy within the frame work of statutory requirements. To achieve the broad objectives presented above the specific research objectives of the work identified are as follows:

To develop a generic mathematical model for optimal selection of air pollution prevention & control strategies after considering both economical and environmental cost.

To evaluate the efficacy of the proposed model for optimal selection of air pollution control strategies considering multiple sources, multiple air pollutants and multiple air pollution control devices simultaneously. Also to explore the benefits of resource recovery and reuse while identifying optimal strategy.

Incorporating the effect of pollutant's characteristics on the efficiency of control equipment while identifying the optimal air pollution control strategy using the proposed mathematical model.

Verification of proposed model for identification of environmental friendly raw material and techno-commercial evaluation of the same for reduction of air pollutants at source.

Application of the model to suggest necessary modifications in the existing air pollution control system to achieve norms prescribed by regulator in commercially operating process plants.

Development of mathematical model for optimal selection of air pollution prevention and control strategies

A mathematical/optimization model for selection of optimal air pollution prevention and control strategy is developed. The objective of the model is to minimize combined economic and environment cost. The model considers that multiple air pollutants (p) are emitting from multiple air emission sources (i) and multiple control options (j) are available for application.

The cost incurred during the operation of the air pollution preventive measures () and control () is considered. Such cost also includes power consumption, maintenance cost, labour cost, utility cost and others.

Operating cost = (1)

In the above equation net present value is calculated by taking combination of local interest rate and expected rate of inflation i.e. icom. In above equations (1) a binary variable is considered. If an option is not selected for application over any particular source then and becomes 1 when option is selected.

Similarly, the cost incurred during erection and commissioning of the air pollution prevention measure () and control () equipments is considered as installation cost. It is well known that cost of the equipment depends on the capacity, material of construction and availability of the equipment.

Installation cost = (2)

Quantification of health impact for air pollutants is considered using the impact pathway analysis methodology (Friedrich et al. 2001). Friedrich et al. (2001) has calculated the value of a 'year of life lost' (YOLL) due to air pollution by considering value of statistical life' (VSL). It is then calculated for net present value of a series of discounted annual values. The ratio of VSL and value of a YOLL thus obtained depends on the discount rate. Also Nonfatal and fatal cancers (depending on the YOLL for each cancer type) has been considered. The health cost associated with emission of classical pollutant p is .The pollutants are emitted into the atmosphere through source i with outlet concentration and flow rate Qi. The terms indicate the total length of the operation.

Health cost = (3)

Some of the pollution control equipment recovers useful resources. The benefit associated with such recovery is also considered while selecting the optimal strategy. In the present study, a generic function RMC is proposed which relates benefits of recovery. Here, RMC can be visualized as a constant that gives cost in US dollars per unit quantity of material recovered

Cost of material recovered= (4)

Objective function Z is to minimize the total cost which includes operating, installation and health cost.

(5)

The model is generic enough for application to suggest optimal P2 and PC strategies. It can be extended further by incorporating the cultural and social cost, provided these costs can be estimated in due course. The effect of pollutant characteristic on efficiencies of the control equipment and their optimal selection are also possible using presented model. The benefits associated with recovery of resources are considered while selecting optimal air pollution control strategy.

Selection of optimal air pollution control strategy

The efficacy of the proposed optimization model is demonstrated for selection of optimal air pollution control strategy. The selection of optimal air pollution control strategy is illustrated by considering simulation case studies of a typical cement plant and a thermal power plant. The actual data is collected from four commercially operated cement plants located in state of Gujarat for three seasons in a year for four years. Three pollution control devices namely bag filter, electrostatic precipitator and cyclone separator were considered. The MINLP problem is solved using commercial software GAMS. The effect of regulatory norms on the optimal selection of the air pollution control devices are summarized in Table No. 1.

Table No. 1: Effect of outlet emission norms on optimal selection of air pollution control equipment for cement plant.

Sources

Outlet pollutant norms in mg/m3

Control Devices

PM

SO2

NOX

Bag filter

ESP

Cyclone

Crusher

65

40

40

1

1

1

Raw mill

65

40

40

1

1

1

Coal mill

65

40

40

1

1

1

Cooler

65

40

40

1

1

1

Cement Mill

65

40

40

1

1

1

Crusher

110

49

49

1

1

X

Raw mill

110

49

49

1

1

X

Coal mill

110

49

49

1

1

X

Cooler

110

49

49

1

1

X

Cement Mill

110

49

49

1

1

1

Crusher

250

74

74

1

1

X

Raw mill

250

74

74

1

1

X

Coal mill

250

74

74

X

1

1

Cooler

250

74

74

X

1

1

Cement Mill

250

74

74

1

1

X

Crusher

275

77

77

1

1

X

Raw mill

275

77

77

X

1

1

Coal mill

275

77

77

X

1

1

Cooler

275

77

77

X

1

1

Cement Mill

275

77

77

X

1

X

Crusher

300

80

80

X

1

1

Raw mill

300

80

80

X

1

1

Coal mill

300

80

80

X

1

1

Cooler

300

80

80

X

1

1

Cement Mill

300

80

80

X

1

X

It can be noted from Table 1 that as outlet emission norms become stringent all the control equipments are used to reduce emissions to required levels. During stringent norms health cost is least as illustrated in Fig.1 (a). However, installation and operating cost are higher during stringent norms and decreases as outlet norms relaxed, this can be observed from Fig 1(a) & Fig.1 (b). The benefit of recovering resources and total cost is illustrated Fig. 1(b). The profit obtained by recovering material is approximately 40 times more than cumulative cost incurred by installation, operation of air pollution control equipments and health cost for the case under consideration. Similarly, a typical power plant is taken into consideration for application of proposed model. Actual data of two commercially operated thermal power plants is collected thrice a year for two years. Electrostatic precipitator, bag filter and cyclone separator are considered for this case. The effect of outlet emission norms on economic as well as health cost for power plant is illustrated in Figure 2 (a, b). From the study it can be noted that 400 mg/m3 of PM is found to be optimal emission norms for power plant. Hence, the efficacy of the proposed model has been satisfactorily evaluated by considering simulation case studies of a typically operated cement plant and a thermal power plant.

Variation in the installation and health cost.

Variation in the operating cost

Figure 2: Effect of outlet emission norms on economic and environmental cost for cement plant

a. Effect of outlet emission norms on Operating, installation and health cost for thermal power plant.

b. Effect of outlet emission norms on Total cost for thermal power plant.

Figure 2: Effect of outlet emission norms on economic and environmental cost for power plant

.Selection of Optimal Air Pollution Control Strategies and effect of particle size distribution

The commercial process softwares Aspen plus® and CAMCAD® are used for simulation of air pollution control devices. The simulations are carried out to evaluate dependency of collection efficiencies of control devices on particle characteristics. Particle removal efficiency of control equipment when operated alone as well as when they are operated in combination with other control equipments are presented in Fig. 3(a) & Fig. 3(b) respectively.

Collection Efficiency single pollution control devices

Collection Efficiency of control devices in series.

Figure 3: Collection efficiencies of air pollution control devices with respect to particle size.

These simulation results along with economic and environmental cost are considered for optimal selection of air pollution control strategy. The proposed optimization model is used to minimize total cost consisting of economic cost & health cost due to emission of particulate matter including ultrafine particulate matter (PM2.5 & PM10). The simulation results are depicted in Table 2.

Table No.2: Effect of outlet emission norms considering ultrafine on optimal selection of air pollution control devices.

Pollutants

Selection of Air pollution control devices

PM2.5

PM10

SPM

SO2

NOx

 Sources

Cyc.

ESP1

ESP2

ESP3

ESP4

Scrb.

10

15

25

30

30

Incinerator

1

1

1

1

1

1

Drier

1

1

1

1

1

1

Boiler

1

1

1

1

1

1

15

20

30

35

35

Incinerator

1

1

1

1

1

1

Drier

1

X

1

1

1

1

Boiler

1

1

1

1

1

1

20

25

35

40

40

Incinerator

1

1

1

1

X

1

Drier

1

1

1

1

X

1

Boiler

X

1

1

1

1

1

30

35

45

50

50

Incinerator

1

1

1

1

X

1

Drier

1

1

1

1

X

1

Boiler

1

1

1

1

X

1

35

40

50

55

55

Incinerator

1

1

1

X

X

1

Drier

1

1

1

X

X

1

Boiler

1

1

1

1

X

1

45

50

60

70

70

Incinerator

1

1

1

X

X

1

Drier

1

X

1

X

X

1

Boiler

1

1

1

X

X

1

50

55

65

80

80

Incinerator

1

1

X

X

X

1

Drier

1

1

X

X

X

1

Boiler

1

1

1

X

X

1

It is noted from Fig. 4(a) & Fig. 4(b) that economic cost and health cost are relatively higher for respirable particulate matter. Similarly total cost is also relatively higher when respirable particulate matter is present as illustrated in Fig.4(c). This is due to selection of costlier air pollution control devices to capture fine particles to prescribed level as depicted in Table 2. From the Fig.4(c) it can be noted that 150 mg/m3 is found to be optimal emission norms.

Effect of outlet emission on economic cost.

Effect of outlet norms on environmental cost.

Effect of outlet norms on Total cost

Figure 4. Effect of outlet emission norms on economic cost and health cost of particulate matter

.

Air Pollution Prevention and Control Framework

Emission norms are expected to become stringent as time progresses. The existing P2 frameworks are reviewed and compared to identify their drawbacks. We have proposed a P2 and PC framework by incorporating the limitations of existing frameworks. Application of the proposed mathematical model is explained for optimal selection of P2 and PC alternatives within the proposed framework. The model can be used to evaluate the techno-commercial feasibility of selecting the alternative raw material. The case study of the typical utility section or commercially operated process plants are studied for selection of optimal fuels. The cost of steam generation using various fuel as well as cost of air pollution control strategy along with health cost is considered. The actual data from industrial boilers operated with variety of fuels is collected from manufacturer/suppliers of commercial boilers. The non availability of the natural gas at remote locations is also considered while evaluating the alternatives. The simulation results are tabulated in Table 3 &4.

Table 3: Optimal selection of P2 and PC strategy for fixed operating years.

Outlet norms mg/m3

Control Options

Fuels

PM

SO2

NOX

ESP

BH

HEC

CS

Coal

NG

FO

Diesel

25

25

25

1

X

X

1

X

1

X

X

40

28

28

1

X

X

1

X

1

X

X

160

54

54

X

1

X

1

X

1

X

X

175

58

58

X

1

X

1

X

1

X

X

190

62

62

X

X

1

1

X

1

X

X

205

65

65

X

X

1

1

X

1

X

X

220

68

68

X

X

1

1

X

1

X

X

235

72

72

X

X

1

1

X

1

X

X

250

75

75

X

X

1

1

X

1

X

X

Table 4: Optimal Selection of P2 and PC strategy for change in operating years.

Operating years

Control Options

Fuels

ESP

BH

HEC

CS

Coal

NG

FO

Diesel

3

X

X

1

1

1

X

X

X

4

X

X

1

1

1

X

X

X

5

X

X

1

1

X

1

X

X

6

X

X

1

1

X

1

X

X

7

X

X

1

1

X

1

X

X

8

X

X

1

1

X

1

X

X

9

X

X

1

1

X

1

X

X

10

X

X

1

1

X

1

X

X

BH=bag house, HEC= high efficiency cyclone, CS=caustic scrubber

Hence, the efficacy of the model to select optimal preventive measures along with control strategy is demonstrated. Natural gas has been selected as a best environmental friendly fuel for the long term operations. However, for the short term operations coal has been selected.

The application of model to verify the adequacy of APMS in commercially operated process plants:

The state of Gujarat is a major hub/contributor for the production of dye and dye-intermediate industries. The industrial estate of Ahemdabad district region is having more than 500 small, medium and large scales of dye and dye intermediate industries. Most of these are in operation since last three decades. Scope of the study is limited to evaluation of APMS and to suggest suitable additional mitigation measures required to make the APMS adequate. The model proposed in this study is used to select the optimal air pollution control strategy to meet the particulate emission norms of 150 mg/m3. More than 75 dye units which utilize spray driers responsible for particulate matter emissions are monitored. The detailed design specifications of APCM are collected for such units. Actual sampling/monitoring and analysis of the process plant is carried out using standard methods. Industrial units with inadequate APMS are identified.. The commercial cost for modification of existing control devices as well as for additional control measure are obtained from the manufacturers/suppliers of these equipments. The proposed optimization model is applied to suggest an optimal air pollution control strategy for each industry. The simulation results are presented in Table 5. From the Table 5 it can be noted that it is possible to achieve the outlet emission norms by retrofitting existing APMS. The modifications of venturi are suggested for all the units considered. However, cyclone modifications are suggested to five out of seven units.

Table 5: An optimal Selection of air pollution control strategy for standard outlet emission norms for particulate matter (150 mg/Nm3).

SN

Name of company

Cost in millons USD per Annum

Control Device

O.C

I.C.

H.C.

T.C

Existing cyclone

Existing venturi

Modified cyclone

Modified venturi

1.

Nichem industries

8.8

1.1

1.3294

11.229

X

X

1

1

2.

Multi colourchem

8.8

1.1

2.1714

21.971

X

X

1

1

3.

Appollo

8.8

1.1

1.7726

11.672

X

X

1

1

4.

Shivanand polymer

8.8

0.6

1.1522

10.552

1

X

X

1

5.

Dynamic Dyes ltd.

8.8

1.1

1.5954

11.495

X

X

1

1

6.

Alfa

8.8

1.1

1.5954

11.495

X

X

1

1

7.

MAC

8.8

0.6

0.9306

10.330

1

X

X

1

Main Contributions of the Study

An optimization model is developed for optimal selection of air pollution prevention & control strategies after considering both economical and environmental cost. The environmental cost in terms of health effect due to emission of various air pollutants into atmosphere is exclusively considered while optimizing total cost

The efficacy of the model is demonstrated for multiple air pollutants, multiple sources and multiple control equipment. Benefits due to resource recovery is also been explored using same model.

The air pollution control equipments are simulated by commercial simulators to evaluate the effect of PSD on their collection efficiencies. The efficacy of proposed mathematical model is demonstrated with the help of a typical pharmaceutical plant.

A new P2 and PC framework is proposed which overcome the limitations/drawbacks of the existing frameworks reported in open literature. Two important scenarios, design phase and retrofitting of existing plants are considered in proposed framework. Utilization of the proposed mathematical model is explained for optimal selection of P2 and PC alternatives within the proposed framework. A case study is presented for utility section considering variety of fuel and control techniques.

The model has been used to suggest necessary modifications for adequate APMS in the commercial process industries to achieve the regulatory norms.

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