C hapter 10
This presentation is the property of its rightful owner.
Sponsored Links
1 / 43

C HAPTER 10 PowerPoint PPT Presentation


  • 126 Views
  • Uploaded on
  • Presentation posted in: General

C HAPTER 10. E NVIRONMENTAL IMPACT EVALUATION OF A CHEMICAL PROCESS FLOWSHEET – T IER 3. Goal.

Download Presentation

C HAPTER 10

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


C hapter 10

CHAPTER 10

ENVIRONMENTAL IMPACT EVALUATION OF A CHEMICAL PROCESS FLOWSHEET – TIER 3


C hapter 10

Goal

To perform a detailed environmental impact evaluation of a chemical process flowsheet in order to identify a set of environmental indexes (metrics) and evaluate the impact o risk of the entire process to the human health or to the environmental media


Order of topics

Order of topics :

  • Introduction

  • Estimation of environmental fates of emissions and wastes

  • Tier 3 metrics for environmental risk evaluation of process designs

  • Conceptual design of an environmental impact assessment of a chemical process flowsheet


Introduction

Introduction


What information is needed to perform a tier 3 environmental assessment

What Information is Needed to Perform a Tier 3 Environmental Assessment?

  • To establish a Process Flowsheet

  • To define the boundaries around the environmental assessment

  • To formulate environmental impact indicators (indexes or metrics)

  • To maximize the Mass Efficiency

  • To maximize the Energy Efficiency


Indexes or environmental metrics

Indexes or environmental metrics

Can be used for several important engineering applications related to process designs, including :

  • Ranking of technologies

  • Optimizing of in-process waste recycle/recovery processes

  • Evaluation of the modes of reactor operation


Emission assessment quantitative analyses

Emission assessment: Quantitative Analyses

EMISSIONS are the most important and basic information regarding process design flowsheets because :

Concentration and location are a (emissions, chemical properties and physical properties)

Transport and fate models can be used to transform emission values into their related environmental concentrations


Emission assessment quantitative analyses continued

Emission assessment: Quantitative Analyses ... continued

Toxicity and/or inherent impact information is required to convert concentration-dependent doses into probabilites of risk

Categories of environmental impact assessment steps :

  • Estimates of the rates of release for all chemicals in the process

  • Calculation of environmental fate and transport and environmental concentration

  • Accounting for multiple measures of risk using toxicology and inherent environmental impact information


Potential risk assessment

Potential Risk Assessment

...suitable for large scale applications where potential environmental and health risk assessment should be follow by quantitative analysis.

...better suited to compare the environmental risks of chemical process designs

...of chemical process and their design can be evaluated by impact benchmarking


Impact benchmarking

Impact Benchmarking

  • Is a dimensionless ratio of the environmental impact caused by a chemical’s release in comparison of the identical release of a well-studied (benchmark) compound

  • If the benchmark value is greater then 1, then the chemical has a greater potential for environmental impact then the benchmarked compound

  • Equivalent emission of the benchmark compound (in terms of environmental impact) = (Benchmarked enviromental impact potential) * (process emission rate)


Boundaries for impact assessment

Boundaries for impact assessment

From Allen (2004) Design for the Environment - http://www.utexas.edu/research/ceer/che341


Estimation of environmental fates and emission wastes

Estimation of Environmental Fates and Emission Wastes


C hapter 10

Goal

To determine the transport and reaction processes that affect the ultimate concentration of a chemical released to the environment (water, air and soil)

The evaluation is done by using environmental fate and transport models:

  • One compartment

  • Multimedia compartment


Choosing types of models

Choosing Types of Models

  • Accuracy :

    • This parameter varies according to the model’s method of incorporating environmental processes in it’s description of mass transfers and reactions

  • Ease of Use :

    • This parameter reflects the data and computational requirements which the model places on the environmental assessment


One compartment models

Advantages :

Little chemical and/or environmentally specific data required

Relatively accurate results using modest computer resources

Disadvantages :

Information is for only one media (severe limitation when multiple environmental impacts are being considered)

One Compartment Models

  • Examples :

    • Atmospheric dispersion models for predicting air concentrations from stationary sources

    • Groundwater dispersion models for predicting contaminant concentrations profiles in plumes


Multimedia compartment models mcms

Advantages :

Information on transport and fate in more than one media

Minimal data input required

Relatively simple and computationally efficient

Accounts for several intermediate transport mechanisms and degradations

Disadvantages :

Lack of experimental data can be used to verify the model’s accuracy

General belief that they only provide order-of-magnitude estimates of the environmental concentrations

Large computational requirements can result in difficult practical implementations for routine chemical process evaluations.

Multimedia Compartment Models (MCMs)


Multimedia models example level iii multimedia fugacity model

Multimedia Models Example: Level III Multimedia Fugacity Model

The model predicts steady-state concentrations of a chemical in four environmental compartments (1) air, (2) surface water, (3) soil, (4) sediment in response to a constant emission into an environmental region of defined volume

Allen, A.T., D.R. Shonnard (2002) Green engineering, Prentice Hall

MacKay, D.(2001) Multimedia environmental models: the fugacity approach, CRC Press


Fugacity and fugacity capacity

Fugacity and Fugacity Capacity

  • Air Phase

  • Water Phase

  • Soil Phase

  • Fugacity Capacity Factors


Fugacity air phase

Fugacity : Air Phase

  • Defined as :

    Where :

    • y is the mole fraction of the chemical in the air phase

    • Ф is the dimensionless fugacity coefficient which accounts for non-ideal behaviour

    • PT is the total pressure (Pa)

    • P is the partial pressure of the chemical in the air phase

  • Concentration and Fugacity :

    Where :

    • n is the number of moles of the chemical in a given volume V (mol)

    • V is the given volume (m3)

    • R is the gas constant (8.312 (Pa m3)/(mole K))

    • T is the absolute temperature (K)

    • Z1 is the fugacity capacity (=1/(RT))


Fugacity water phase

Fugacity : Water Phase

  • Defined as :

    Where :

    • x is the mole fraction

    • y is the activity coefficient in the Raoult’s law convention

    • PS is the saturation vapor pressure of pure liquid chemical at the system temperature (Pa)

  • Concentration and Fugacity :

  • Where :

    • vw is the molar volume of solution (water, 1.8x10-5m3/mole)

    • H is the Henry’s law constant for the chemical (Pa.*m3/mole)

    • Z2 is the water fugacity capacity for each chemical (=1/H)

    • C2 is the concentration in aqueous solution (moles/m3)


Fugacity soil phase

Fugacity : Soil Phase

  • Defined as :

  • Where :

    • Cs is the sorbed concentration (moles/kg soil or sediment)

    • C2 is the aqueous concentration (moles/L solution)

    • Kd is the equilibrium distribution coefficient (L solution/kg solids)

  • Distribution coefficient related to organic content:

  • Concentration and Fugacity :

  • Where :

    • р3 is the phase density (kg solid/m3 solid)

    • Ф3 is the mass fraction of organic carbon in teh soil phase (g organic carbon/g soil solids)

    • Koc is the organic carbon-based distribution coefficient (L/kg)

    • Z3 is the fugacity capacity


Fugacity capacities for compartments and phases in the environment

Fugacity Capacities for Compartments and Phases in the Environment

Note: For solid aerosols PSL=PSS/exp{6.79(1-TM/T)} where TM is the melting point (K). Adapted from Mackay et. Al. (1992).


Transport between interfaces

Transport between interfaces

Diffusive and Non-Diffusive Processes

  • Diffusive Processes

    • Can occur in more then one direction, depending on the fugacity signs of the different compartments

    • Rate of transfer : N = D(f)

    • Ex. Volatilization from water to air or soil to air

  • Non-Diffusive Processes

    • Is a one-way transport between compartments

    • Rate of transfer : N = GC = GZf = Df

    • Ex. Rain washout, wet/dry depositions to water and soil, sediment depositions and resuspensions


C hapter 10

Transport between interfaces... continued

Parameter Derivations : Air-Water Transports

  • A two film approach is used with mass transfer coefficients for air (u1 = 5m/h) and water (u2 = 0.05 m/h). The intermediate transport parameter for absorption is given as :

  • The D-value for rain washout can be given as :

  • The D-value for wet/dry deposition is given as :

  • The cumulative D-value for air to water tranfer :

  • The D-value for water to air transfer is :


C hapter 10

Transport between interfaces... continued

Parameter Derivations : Air-Soil Transports

  • After development, the d-value equation for air to soil diffusion is given as :

  • With :

  • The cumulative D-value for all air-to-soil processes is given by :

  • And the soil-to-air diffusion transport is :


Transport between interfaces continued

Transport between interfaces... continued

Parameter Derivations : Water-Sediment Transports

  • Water to sediment D-value can be estimated by :

    Where :

    • u8 is the mass transfer coefficient (m/h)

    • AW is the area (m2)

    • u9 is the sediment deposition velocity (m/h)

  • Sediment to water D-value can be estimated by :

  • Where :

    • u10 is the resuspension velocity (m/h)


Transport between interfaces continued1

Transport between interfaces... continued

Parameter Derivations : Soil-Water Transports

  • The D-value for soil to water transfer is :

  • Where :

    • u11 is the run-off water velocity (m/h)

    • u12 is the run-off solid’s velocity (m/h)

  • The non-diffusive transport mechanism’s D-value used to describe the removal of chemical from the sediment via burial is :

  • Where :

    • uB is the sediment burial rate (m/h)


Transport between interfaces continued2

Transport between interfaces... continued

Parameter Derivations : Advective Transports

  • The total rate of inputs for each media is :

  • Where :

    • Ei is the emission rate (moles/h)

    • GAi is the advective flow rate (m3/h)

    • CBi is the background concentration external to compartment i (moles/m3)

  • The total rate of bulk flow outputs for each media is :

  • Where :

    • ZCi is the compartment i fugacity capacity


Reaction loss processes

Reaction Loss Processes

Reaction loss processes occuring in the environment include :

  • Biodegradation

  • Photolysis

  • Hydrolysis

  • Oxidation


Balance equations

Balance Equations

Mole Balance Equations for the Mackay Level III Fugacity Model.


Metrics for environmental risk evaluation of process design

Metrics for environmental risk evaluation of process design


C hapter 10

Tier 3 Metrics for Environmental Risk Evaluation of Process Designs

  • This tier will discuss how to combine data concerning emission estimation, environmental fate and transport information and environmental impact data in order to develop an assessment of the potential risks caused by the releases of substances from chemical process designs

  • Indices will be used and the multimedia compartment model example will be source of environmental concentrations that will be used in INDEXES


Tier 3 metrics for environmental risk evaluation of process designs

Tier 3 Metrics for Environmental Risk Evaluation of Process Designs

  • Environmental Indexes

  • Global Warming

  • Ozone Depletion

  • Acid Rain

  • Smog Formation

  • Toxicity and Carcinogenity


C hapter 10

Environmental indexes


Dimensionless risk index

Dimensionless Risk Index

  • Global Implications

    • Global Warming

    • Stratospheric Ozone Depletion

  • Regional Implications

    • Smog Formation

    • Acid Deposition

  • Local Implications

    • Toxicity

    • Carcinogenicity

  • Abiotic Impacts :

    • Global Warming

    • Stratospheric Ozone Depletion

    • Acidification

    • Eutrofiaction

    • Smog formation

B stands for the benchmark compound and i is the chemical of interest.


Global warming

Global Warming

  • GWP is a common index and is the cumulative infrared energy captured from the release of 1 kg of greenhouse gas relative to that from 1 kg of carbon dioxide

  • Index for GW can be estimated using the GWP with :

  • Using organic compound effects ...


Ozone depletion

Ozone Depletion

The Ozone Depletion Potential (ODP) is an integrated change of the stratospheric ozone caused by a specific quantity of a chemical.

It is a comparison between the damage caused by a specific quantity of given chemical and the damage caused by the same quantity of a benchmark compound.


Acid rain

Acid Rain

The relation between the number of moles of H+ created per number of moles emitted is called potential of acidification. The following equation (balance) provides this relationship.


Smog formation

Smog Formation

The following equations represent the most important process for ozone formation in the lower atmosphere (photo-dissociation of NO2)

VOC's do not destroy O3 but they form radicals which convert NO to NO2.

Smog Formation Potential

Process equivalent emission of ROG


Toxicity

Toxicity

Non-Carcinogenic Toxicity

Non carcinogenic toxicity is controlled by established exposure thresholds. Above this values a toxic response is manifested. The key parameters for these chemicals are the reference dose (RfD [mg/kg/d]) or reference concentration (RfC [mg/m3]).

Toxicity potential for ingestion route exposure

Toxicity potential for inhalation exposure

Non-carcinogenic toxicity index for the entire process (ingestion)

Non-carcinogenic toxicity index for the entire process (inhalation)


Toxicity1

Toxicity

Carcinogenicity

A method similar to the non-carcinogenicity toxicity is used for measuring cancer related risk; it is based on predicted concentrations of chemicals in the air and water from a release of 1000 kg/h.

Carcinogenic potential of a chemical determinated by the ratio of the chemicals risk to that for the benchmark compound.

Ingestion

Inhalation

Carcinogenic toxicity index for the entire process (ingestion)

Carcinogenic toxicity index for the entire process (inhalation)


C hapter 10

Conceptual design of an environmental impact evaluation of a chemical process flowsheet


Conceptual design of an environmental impact evaluation of a process

Conceptual design of an environmental impact evaluation of a process

Proposed by Allen (2004) Design for the Environment - http://www.utexas.edu/research/ceer/che341


  • Login