Termodinamica proyecto 1

7/28/2019 Termodinamica proyecto 1

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EVALUATION OF ENERGY RECOVERY IN AN EQUIPMENT

PLANT SUPPORT SERVICE

Flrez Cristian, Molina Mitchel, Muoz Johan, Nez Diana,Ramrez Daniel, Sanjuan Shirley

Cartagena University, Faculty of Engineering, Chemical Engineering ProgramThermodynamics II

Cartagena, Colombia

Abstract

This article presents the evaluation of energy use in a plant auxiliary services, usingthe exergy method by which it can be shown that it is misusing it. It was estimatedthat the plant exergetic efficiency is 44.27% and 97.65% of the exergy destruction is

concentrated in seven teams, which are three steam generators, two turbinegenerators, a deaereador and a hydraulic pump

Keywords: Energy, Exergy, Plant Auxiliary Services

Introduction

Most petrochemical plantsare currently

in operation were designed and built in

1970, when there was no concernabout the proper use of energy. This

situation currently makes most of these

plants are considered technologically

obsolete, are energy intensive and

contribute significantly to

environmental degradation, so it is

necessary to evaluate their use of

energy and the potential recovery of it.

In this study, is evaluating the potential

for energy recovery in the various plantequipment and ancillary services of a

petrochemical plant, whose function,

providing desmineralized water, steam,

cooling water, air service and

instruments and electrical energy,

which are necessary inputs for the

operation of different processes at

work in the plant.

The operations are carried on the soles

of Assistive use large amounts of

energy as heat and / or work, so it is ofinterest to evaluate energy

consumption and use of it, to have

technical features that allow proposals

aimed at optimizing energy

consumption in these services. This

assessment can be made using exergyanalysis based on the simultaneous

application of the first and second laws

of thermodynamics.

The exergy method has the feature of

using the same parameter for

evaluating the energy from the

definition given by Bejan exergy (Bejan,

1997): "The Exergy is the maximum

work that can develop when a system is

in thermal imbalance , kinetic, and

chemical potential with respect to theterms of reference state. "

Against this background, modern

analysis of energy use should be based

on exergy analysis, and in this work has

been applied to a plant auxiliary service

in order to evaluate the potential for

energy recovery in the same, and so

have the information needed to

subsequently propose actions for the

efficient use of energy.


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Nomenclature

Greek letters

Subndices

Process description

This section describes the plant andancillary services from its componentareas and sections that make up eacharea, it also describes the processes atwork in each area and lists the teamsthe same.In the Figure 1 shows the diagram ofthe areas and sections that make upthe plant and ancillary services. The

areas are two: the power and electricitygeneration.The force area is composed of sectionsof steam generation, waterdemineralization, water cooling and airservice and tools. The area of powergeneration is made up of the turbinesection.

Force area

This area comprises four sections: 1.

Water demineralization section 2.

Steam generation section 3. Cooling

water section and 4. Air Section Service

and instruments. The description of

these sections is below.


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Figure 1. Areas and sections that make up the plant and ancillary services

1. Water demineralization section

This section is shown in Figure 2 andconsists of 3 stages of demineralizationwith water treatment capacity of 31.5 l/ s each, through 3 anions (WIA-1, 2and 3) and 3 cations (WIC-1, 2 and 3) togive a total capacity of waterdemineralization of 94.5 l / s.Both cations (WIC-1, 2 and 3) andanions (WIA-1, 2 and 3) containselective resin inside. In that case theflow of circulating water flows first

through the cation and then the anion.This section is characterized by theformation of chemically pure water andideal for use in steam generationequipment.Demineralised water is placed in twostorage tanks and called TV-101 TV-103 to 1589.8 m3 capacity each.Condensate returns from plants isstored in the tank TV-102 and mixedwith demineralized water to feed theDeaerators ED-100 and supplied to the

steam generators, CB-1, CB-2, CB-3 andstew the ethylene plant.

2. Steam generation section

The steam required for thepetrochemical plant is generated bythree steam generators, two highpressure to 4.23 MPa with a generationcapacity of 125 ton / h each and onemedium pressure to 1.99 MPa, with ageneration capacity of 125 t / h. theoutline of this section as shown in

Figure 3. The high pressuresuperheated steam to 4.23 MPa and4000C is produced in the steamgenerators or CB-2 CB-3 and is supplieddirectly to the ethylene plant (highdensity, low density HDPE and LDPE) foruse in the turbines. In addition, the ED-100 requires deaereador vapor of 0.13MPa, which is supplied by the steamgenerator CB-1, after pressurereduction from 1.99 to 0.13 MPa.


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Figure 2. Outline of water demineralization section

Figure 3. Schematic of the steam generation section


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3. Cooling water section

This consists of two cooling towers (DE-

1 and CT-8). The cooling tower-1 with a

capacity of 757 l / s, provides cooling

water to the PEBD plant and cooling

tower CT-8, with a capacity of 5047 l/s,

provides cooling water to the ethylene

plant the PEAD plant and ancillary

services. Figure 4 shows a schematic of

this section.

Figure 4. Scheme of the cooling water section

4. Area of power generation

In this section, the fuel gas is receivedin the gas metering station EMG-2, theground pressure of 4.31 MPa. Thissection reduces the pressure to 2.25

MPa, which subsequently passedthrough two gas separators to removecondensate. Upon exiting theseparator, the gas passes through apressure control valve to reducepressure up to 1.66 MPa, which is thepressure that is supplied to the twoturbine generators. Fuel gasconsumption is 220 m3/s are generated19 MW of electrical power per turbinegroup, to 13.80 kV and 60 Hz, andsubsequently raise its electrical

potential to 23 kV and under theseconditions the plants distributed the

process. This section is shown in Figure5.

Evaluation methodology

In this section the mathematical modelused for exergetic assessment of plantequipment and ancillary services,according to as proposed by Moran(Moran, 2004). The teams are discussedin the open systems model (volumecontrol), operating in steady state.The teams analyzed in this study arethose that make up the plant andancillary services described in Tables 1to 4.


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Figure 5. Outline the area of power generation.

The mathematical model used in thiswork is composed of the equations ofthe first and second law ofthermodynamics, the equation of

balance of the exergy and exergeticefficiency equation, which indicated asequations (1) to (4):

Equation of the first law of thermodynamics

Equation of the second law of thermodynamics (entropy balance)


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Balance equation of exergy

Equation of exergetic efficiency (second law efficiency)

Table 1. Components of the plant equipment and ancillary services

Service Nomenclature Process

Water

demineralization

unit

Bike pump

BA-10_A Water tank transfer to anions

BA-10_B Water tank transfer to anions

BA-10_C Water transfer UDA 100

BA-100_A Boiler feed water CB-2 and CB-3BA-100_B Boiler feed water CB-2 and CB-3

BA-101_A Boiler feedwater CB-1

BA-102_A Deaereada water to ethylene plant

BA-102_B Deaereada water to ethylene plant

BA-103_A Deaereador water to ED-100

BA-103_C Deaereador water to ED-100

BA-106_A Demineralized water or pre-treated plant(PEAD)

BA-106_B Water service PEAD and PEBD plants

BA-107_A Condensed section 07 PEAD plant

BA-107_B Water pre-treated PEAD plantTurbo pump

BA-100_C Bolier feed water CB-2 and CB-3

BA-100_D Bolier feed water CB-2 and CB-3

BA-101_A Bolier feed water to CB-1

Heat exchangers

ED-100 Deaereador

Moto Compresors

BC-100_A Instrument air

BC-100_B Air plant

BC-100_C Air service


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Steam generating

unit

Steam generators steam generation unitCB-1 Steam generation

CB-2 Steam generation

CB-3 Steam generation

Steam-stations of the steam generation section

EAVapor (AP) A steam or conditioning temperature 4,23 to4,23 Mpa sat (600 to 600 psi)

EAVapor (AMP) Pressure reduction and / or upgrading4,23 to 1,99 MPa (600 to 275 psi)

EAVapor (MBP) Pressure reduction and / or upgrading1,99 to 1,79 MPa (275 to 245 psi)

EAVapor (MBP) Pressure reduction and / or upgrading1,99 to 0,13 MPa (275 to 20 psi)



Cooling water

section

Byke pump

DE-P1 Cooling water DE-1

DE-P1-A Cooling water DE-1

DE-P2 Cooling water DE-1

DE-P2-A Cooling water DE-1

BA-1-A Cooling water C1-8

BA-1-B Cooling water C1-8

BA-1-C Cooling water C1-8

BA-1-D Recirculating water cooling CT-8

BA-1-F Recirculating water cooling CT-8

Turbo pump

BA-1-E Cooling water C1-8

Table 4. components of the plant equipment and ancillary services


Section of turbo

generators

Turbo generators

TG-1 Electric power generation (19 MW)

TG-2 Electric power generation (19 MW)

The exergy analysis was applied to eachof the teams considered in the AuxiliaryServices Plant shown in previous tables,for each case simplifying the

mathematical model equationsaccording to the situation analyzed. InFigures 6 to 12 show diagrams of thecomputers as well as in the Table 5


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equations applicable to each of theseteams.

Figure 6. Diagram of a jet pump

Figure 7. Diagram of a turbo pump

Figura 8. Diagram of a steam-station

Figura 9. Diagram of a heat exchanger

separate streams

Figura 10. Diagram of a compressor motor


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Figura 11. Diagrama de un generador de vapor


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Results

From the equations in Table 5 for eachof the computers was raised exergybalance and calculated the energysupplied, the recovered exergy, the

exergy destroyed and exergeticefficiency.

For the first stage of Figure 2(demineralization of water), calculationsand results were:

Conditions of water entering the systemafter pretreatment

P = 1 atm

T = 25C

Velocity = 3m/s

Velocity of water leaving the pump:

6,3 m/s

Flow: 95,5 l/s

To determine the balance exegeticalpumps A, B and C, we have:

Where W = exergy supplied

= exergy

recovered

I = irreversibility

To calculate which is the exergy

supplied to the pump, proceed to

calculate each of the terms of the

proposed equation:

We calculate the density at T = 25 C.

According to the density tables in the

text of Fluid Mechanics by Potter and

interpolation:

Therefore:

Now, according to the F1 table of text

introduction to the thermodynamics of

Vann Ness, the enthalpy at 25 C is:

As is equal to:

The entropy at T = 25 C according to

the F1 table Vann Ness text is

You know the value of , we can

estmate , if we perform an

interpolation to the values of enthalpy

gives us Table F1:


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In consequence:

Now we calculate the irreversibility

described as:

Therefore, the exergy supplied for each

pump (BA-10 A/B/C) system is:

The efficiency of each of the pumps(BA-10 A/B/C) is given by:

Following a similar approach for therest of the plant equipment, we

obtained the following results shown in

Table 6:


Equipment Exergy suppliedKW

Exergyrecovered

KW

Exergydestroyed

KW

Exergetycefficiency

%

BA-10_A 30 10 20 33,33

BA-10_B 30 10 20 33,33

BA-10_C 30 10 20 33,33

BA-100_A 447 174 273 38,92

BA-100_B 447 174 273 38,92

BA-101_A 261 158 103 60,53

BA-102_A 112 53 59 47,32

BA-102_B 112 53 59 48,21

BA-103_A 56 27 29 48,21

BA-103_C 56 27 29 50,00


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BA-106_A 30 15 15 50,00

BA-106_B 30 15 15 78,95

BA-107_A 19 15 4 68,42

BA-107_B 19 13 6 68,50

BA-1-A 746 511 235 68,50

BA-1-B 746 511 235 68,50BA-1-C 746 511 235 68,50

BA-1-D 746 511 235 68,50

BA-1-F 746 511 235 68,50

DE-P1A 447 296 151 66,21

DE-P1 447 296 151 66,21

DE-P2 186 97 89 52,15

BA-1-E 1714 521 1193 30,39

BA-100-C 625 296 329 47,36

BA-100-D 625 296 329 47,36

BA-101-B 625 158 467 25,28

BA-103-B 174 25 149 14,37

EAC-1 2954 2826 128 95,66

EAC-2 8914 8729 185 97,92

ED-100 4203 2084 2119 48,58

BC-100-A 597 250 347 41,88

BC-100-B 447 201 246 44,97

BC-100-C 447 201 246 44,97

C-752 521 128 393 24,57

CB-1 100899 36917 63982 36,59

CB-2 109011 62652 46359 57,47

CB-3 109011 62652 46359 57,47TG-1 74747 19000 55747 25,42

TG-2 74747 19000 55747 25,42

If we add the values in each column, we

get:

Total exergy supplied: 496750 KW

Total exergy recovered: 219934 KW

Total exergy destroyed: 276816 KW

Consequently, the total exergetic

efficiency is:

For a better analysis, we classified theirreversibility rates in four categoriesaccording to their magnitudes, asshown in Table 7.


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Table 7. Classification irreversibility

High Regular Lower middle low

Equipment KW % Equipment KW % Equipment KW % Equipment KW %CB-1 63982 23,45 BA-101-B 467 0,17 E-AC-2 185 0,07 DE-P2 89 0,032

TG-1 55747 19,77 C-752 393 0,14 BC-100-B 246 0,09 BA-102-B 59 0,021

TG-2 55747 19,77 BC-100-A 347 0,13 BC-100-C 246 0,09 BA-102-A 59 0,021

CB-2 46359 16,75 BA-100-C 329 0,12 DE-P1-A 151 0,05 BA-10-C 20 0,007

CB-3 46359 16,75 BA-100-D 329 0,12 DE-P1 151 0,05 BA-10-B 20 0,007

ED-100 2119 00,75 BA-100-A 273 0,10 E-AC-1 128 0,05 BA-10-A 20 0,007

BA-100-B 273 0,10 BA-101-A 103 0,04 BA-106-B 15 0,005

BA-1-A 235 0,08 BA-106-A 15 0,005

BA-1-B 235 0,08 BA-107-B 6 0,002

BA-1-C 235 0,08 BA-103-C 4 0,001

BA-1-D 235 0,08 BA-103-A 4 0,001

BA-1-F 235 0,08 BA-107-A 4 0,001

BA-1-E 4 0,001

BA-103-B 4 0,001

In this table we see that the teams

ranked in the category of irreversibility

high (> 1000), seven and correspond to

the steam generators, the turbine, the

Deaerators and a hydraulic pump.

Together, these teams produce 97.65%of the exergy destruction, but if we

remove from this group Deaerators and

hydraulic pump, the steam generators

and turbine generators produce 96.88%

of the irreversibility generated in the

plant and ancillary services.

The teams ranked in the category ofregular irreversibility produce 1.3% ofthem, the computer group consideredas irreversibility medium-low,

contributing 0.44% and the last group,under teams irreversibility low,contributing only 0.12% of the total.

Conclusion

This paper raised the foundations ofexergy analysis and applied to a plantof Assistive of a petrochemical plant.This made it possible to assess theirreversibility delivered, retrieved and

destroyed in each of the teams thatmake up the plant and its exergeticefficiencies associated with this

information shows that the use ofenergy in the plant is deficient, becausein form global exergetic efficiency is44.27%, indicating that only thisfraction of the available energy is beingused and the rest is destroyed.

An important aspect of exergy analysisis to identify computers that havehigher exergy destruction, which in thiscase were the steam generators,turbine generators, the deaereador anda hydraulic pump (97.65%). Thisinformation is necessary to maketechnical proposals aimed at improvingenergy use, paying special attention tothese teams and significantly optimizethe use of energy in the entire plant.

A proposal to optimize the operation of

this plant is to use the exergy flow of

content in the flue gas of turbo-

generators to power a heat recovery

boiler. This will decrease the fuel they

consume one of steam generators,

saving fuel and reducing pollutant

emissions to the atmosphere, thus

contributing to environmental

protection. Proposals such as these

highlight the importance of evaluation


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of energy losses through the

application of exergy method.

The Continuous application of exergyanalysis to Plant Auxiliary Services willidentify the equipment or processes inwhich there is a greater destruction of

exergy while proposing actions andprograms to achieve more efficient useof energy in the plant.

References

Bejan, A, Advances EngineeringThermodynamics, 2nd edition, Jhon

Wiley and Sons, 1997.

Moran, M.J., and Shapiro, H.N.,Fundamentals of EngineeringThermodynamics", 5a. edicin, JohnWiley and Sons, 2004.

Merle Potter, David Wiggert. FluidMechanics, 3rd edition, Thomson,2002.

Pedro Quinto. Evaluation of energyrecovery in a petrochemical plantassistant, Mechanical Engineering andDevelopment Review, 2008.

Smith, Vann Ness., Introduction toChemical Engineering Thermodynamics,5th Edition, McGraw-Hill, 1996

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