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Exergy pp 5-53 | Cite as

Exergy, Exergy Costing, and Renewability Analysis of Energy Conversion Processes

Chapter
Part of the Green Energy and Technology book series (GREEN)

Abstract

This chapter introduces the foundations of the exergy, exergy production cost, and renewability analysis of energy conversion processes. Based on the concept of reversible work, the concept of exergy is derived and the exergy balance is presented as a combination of the energy and entropy balances. Some graphical representations are shown in which it is possible to determine or represent exergy and exergy balances. The exergy efficiency is introduced based on a general definition of efficiency, and the balance of cost is presented as an additional balance equation to be used in the performance analysis of energy systems. A brief discussion on cost partition criteria is presented to aid the analysis of the cost formation processes of the products of energy conversion processes. Finally, the renewability of energy conversion processes is analysed by means of a renewability exergy index that takes into account the type of inputs, renewable or fossil, the wastes, and the destroyed exergy of a given energy conversion process.

Keywords

Mass Flow Rate Steam Turbine Exergy Efficiency Exergy Destruction Cogeneration Plant 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Symbols

B

Exergy (kJ)

B

Exergy rate/flow rate (kW)

b

Specific exergy (kJ/kg)

Bemissions

Exergy rate of wastes that are not treated or deactivated (kW)

Bdestroyed

Destroyed exergy rate (kW)

Bdeactivation

Destroyed exergy rate of additional natural resources during waste de-activation (kW)

Bdisposal

Exergy rate or flow rate related to waste disposal of the process (kW)

Bfossil

Non-renewable exergy rate consumed on production processes chain (kW)

Bnat,res

Exergy rate of the natural resources consumed by the processes (kW)

Bprocessing

Exergy rate or flow rate required for extraction and preparation of the natural resources (kW)

Bproduct

Exergy rate or flow rate associated to the products and byproducts/useful effect (kW)

Breject

Exergy rate or flow rate of the rejects (kW)

Butilities

Exergy rate or flow rate required by the utilities of the process (kW)

C

Cost ($)

C

Cost rate ($/s)

c

Specific heat, J/(kg K), specific cost (kJ/kJ, $/kJ, $/kg)

cp

Specific heat at constant pressure, J/(kgK)

Ceq, Cr

Equipment cost of a given capacity ($); Equipment cost of a reference capacity ($)

E

Energy (kJ)

E

Energy rate/flow rate (kW)

fO&M

Annual operational and maintenance factor

fa

Capital recovery factor

g

Gravitational acceleration (9.8 m/s2); molar Gibbs free energy of formation (kJ/kmol)

Go

Gibbs free energy variation in the direction of a given chemical reaction (kJ/kmol)

H; h

Enthalpy flow rate (kW); specific enthalpy (kJ/kg)

HR

Enthalpy of reactants (kJ/kmol)

HP

Enthalpy of products (kJ/kmol)

Ie

Energy investment (kJ)

IVC

Investment rate of equipment inside control volume ($/h, $/s)

i

Interest rate (%)

LHV

Lower heating value (kJ/kg)

m

Mass flow rate (kg/s)

N

Capital recovery period, operating time (year)

Ni

Number of moles of species i

Q; q

Heat rate (kW); heat rate per unit of mass flow rate (kJ/kg)

P

Pressure (kPa)

R, \( \bar{R} \)

Ideal gas constant (kJ/kg K), universal gas constant (kJ/kmol K)

S; s

Entropy rate/flow rate (kW/K); specific entropy (kJ/kg K)

S, Sr

Component size, component reference size (see Table 2.8)

Sger; sger

Entropy generation rate (kW/K); entropy generation rate per unit of mass flow rate (kJ/kg K)

T

Temperature (°C, K)

U; u

Specific internal energy (kJ/kg), internal energy (kJ)

v

Specific volume (m3/kg); value scale

V

Volume (m3)

W; w

Power (kW); power per unit of mass flow rate (kJ/kg)

x

Mole or mass fraction

z

Elevation (m)

Greek symbols

α

Angle in Fig. 2.11, percent excess air, exponent of Eq. 2.84

γi

Activity coefficient of species i

Δcomb

Ratio between destroyed exergy and reactants exergy

η

Efficiency

θ

Carnot factor

λ

Renewability exergy index

µi

Chemical potential of species i (J/mol)

ν

Stoichiometric coefficient

υ

Velocity (m/s)

φ

Ratio between chemical exergy and lower heating value

Superscripts

Molar

*

Restricted reference state

s

System

Subscripts

0

Dead state; reference state

00

partial pressure

a

Input

ab

Absorber

air

Inlet air

B, b

Exergy, reboiler

btt

Heat transformer

carnot

Related to Carnot cycle

C, c, cd

Condenser

ch

Chemical

coreactants

Coereactants

de

Desorber

dest

Destroyed

e

Outlet, exit, electricity, energy

ef

Effective, effluents

env

Environmental

eq, equipment

Equipment

eqt

Equipment total

ev

Evaporator

f

Fossil

flue gases

Related to flue gases

fuel

Fuel

i

inlet, input, component

j, k

Component, species

kin

Kinetic

H

enthalpy

hp

High pressure

lp

Low pressure

m

Average, mass basis

max

Maximum

mix

Mixer

mr

Reversible engine

net

Net

o

Operational, outlet

P, p

Product, pump, perfection, process

ph

Physical

pot

Potential

process

Process

products; prod

Products

Q, q

Heat

r

Reference, renewable

reactants, react

Reactants

sep

Separator

sg

Steam generator

t

Thermal, during lifetime, turbine

tt

Heat transformer

u

Useful

VC

Control volume

w

Waste

W

Work

water

Water

wp

Production waste

wu

Utilization waste

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Copyright information

© Springer-Verlag London 2013

Authors and Affiliations

  1. 1.Mechanical Engineering DepartmentPolytechnic School of the University of São PauloSão PauloBrazil

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