lecture 1 - intro to envi engg (printed)

8/10/2019 Lecture 1 - Intro to Envi Engg (Printed)

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Units of measurement

In the study of environmental engineering, it isquite common to encounter both extremely large

quantities or extremely small ones, such as toxic

substancemaybe expressed in parts per billion

(ppb), or the rate of energy use maybemeasured in thousands of billions of watts

(terawatts)

Quite often, it is the concentration of somesubstance/sin air or water that is of interest.

In either medium, concentration maybe based on

mass, volume or a combination of both.


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Materials Balance Diagram


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Law of Conservation of Mass

When chemical reactions take place,matter is either created nor destroyed(though in nuclear reactions, mass is converted to

energy).

What this concept allows us to do is track

materials (pollutants) from one place to

another with mass balance equation.

Input

Rate

Output

Rate

Decay

Rate

Accumulation

Rate


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First Step in a Mass balance Analysis

Define a particular region in space that isto be analyzed.

A region maybe a simple mixing tank to

entire coal-fired power plant, a lake, airbasin, or the globe itself.

By picturing an imaginary around and

Identify the flow of materials across theboundary as well as the accumulation of

the materials within the region.


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Conservative Substances

Under steady-state conservative systems, there isno radioactive decay, bacterial decomposition, orchemical reaction occurring, thus, the decay rate iszero. Pollutants enter and leave the region at thesame rate.

Conservative substances areDissolved solid in a body ofwater. Heavy metals in soils.

Carbon dioxide in air.

Input

Rate

Output

Rate


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Sample of Nonconservative Pollutant


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First Law of Thermodynamics

The use of the First Law ofThermodynamicsto write energybalance equations that will help us analyze energy flows.

Energy can be neither created nor destroyed.

Energy can change forms in any given process.

To apply the first law, it is necessary to define the systembeing studied, much as was done in the analysis of massflows.

Systemsin which both energy and matter can flow across theboundary are referred to as open systems, while, those in whichenergy is allowed to flow but not of the matter, are called closedsystems.


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Energy Balance Equation System


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Second Law of Thermodynamics

Waste heat (Qc) is in any kinds of reaction.

When work is done, there is always be

some inefficiency; that is, some portion ofthe energy put into the process will end up

as waste heat.

Note: It is impossible to device a machine that

can convert heat to work with 100% efficiency

(page 23).


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Conductive heat transfer is usually associatedwith solids, the rate of heat transfer in a solid is

proportion to the thermal conductivity of the

material.

Convective heat transfer occurs when a fluid atone temperature comes in contact with a

substance at another temperature.

Radiation is transported by electromagneticwaves and does not require a medium to carry

the energy.

Example, radio waves, X-rays and gamma rays.


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Environmental Chemistry

Every pollution problem has a chemicalbasis. such as, greenhouse effect, ozone

depletion, toxic wastes, groundwater

contamination, air pollution, and acid rainrequires at least a rudimentary

understanding of some basic chemical

concepts.


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Basic Requirements for an Environment Engineer

An environmental engineer who mustdesign an emission control system or a

waste treatment plant must be grounded in

chemical principles and the techniques ofchemical engineering.

An essential chemical principles required

to understand the nature of the pollution

problems and the engineering approaches

to their solutions.


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StoichiometryStoichiometryis the branch of chemistry and chemical

engineering that deals with the quantities of substances thatenter into, and are produced by, chemical reactions.

Stoichiometryprovides the quantitative relationshipbetween reactants and products in a chemical reaction.

example, when methane unites with oxygen in completecombustion..

Such as 16g of methane require 64g of oxygen. At thesame time 44g of carbon dioxide and 36g of water areformed as reaction productions.


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Enthalpy in Chemical Systems

The use of conservation of mass to balancechemical equations, we can use conservation of

energy to learn about heat absorbed or released

during chemical reactions.

Since energy must be conserved, we should beable to track it from the beginning to end.

The change of enthalpyduring a constant

pressure reactionis equal to the heat absorbedby the system.


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The first law of thermodynamic, the energy in thereactants on the left side of the equation, plus

any heat added to the system, should be equal

to the energy contained in the reaction products

on the right side plus any work done during thereaction.

U1+ Q = U2+ W

where: U1 = internal energy of the chemical system at the beginning

U2= internal energy at the end

Q = heat absorbed during the reaction

W = work done by the system during the reaction


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Chemical Equilibriumreaction where, the ratesof reaction are the same (that is, products are

being formed on the right at the same rate as

they are being formed on the left).

Example: aA + bB cC + dD

H2O H+ + OH

Endothermic reactionheat is absorbed

Exothermic reactionheat is liberated

lecture 1 - intro to envi engg (printed)

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