Energy and Exergy Energy and Exergy Analysis of Diesel Engine Analysis of Diesel Engine Powered Cogeneration Powered Cogeneration

SystemsSystems

Dr. Aysegul AbusogluDr. Aysegul Abusoglu

Mechanical Engineering Mechanical Engineering DepartmentDepartment

University of GaziantepUniversity of Gaziantep

What is Cogeneration?What is Cogeneration? CogenerationCogeneration is the simultaneous generation of is the simultaneous generation of

heat and powerheat and power.. The principle behind cogeneration is simple: The principle behind cogeneration is simple: Conventional power generationConventional power generation, on average, is , on average, is

only 35% efficient – up to 65% of the energy only 35% efficient – up to 65% of the energy potential is released as waste heat. potential is released as waste heat.

CCombined cycle generation ombined cycle generation can improve this to can improve this to 55%55%..

Cogeneration reduces this loss by using the heat Cogeneration reduces this loss by using the heat for for industryindustry, , commercecommerce and and home home heating/coolingheating/cooling..

The Benefits of The Benefits of CogenerationCogeneration

Increased efficiency Increased efficiency of energy conversion and useof energy conversion and use Lower emissions to the environmentLower emissions to the environment CCost-effectiveness and reducing the need for waste disposalost-effectiveness and reducing the need for waste disposal::

Biomass fuels, some waste materials such as refinery gases, Biomass fuels, some waste materials such as refinery gases, process or agricultural waste can be used as fuelsprocess or agricultural waste can be used as fuels..

Large cost savingsLarge cost savings, providing additional competitiveness for , providing additional competitiveness for industrial and commercial users, and offering affordable heat industrial and commercial users, and offering affordable heat for domestic usersfor domestic users,,

An opportunity to move towards An opportunity to move towards more decentralised forms of more decentralised forms of electricity generationelectricity generation,,

An opportunity to increase the An opportunity to increase the diversity of generation plantdiversity of generation plant, , and provide and provide competition in generationcompetition in generation,,

Increased employmentIncreased employment: Development of cogeneration : Development of cogeneration systems is a generator of jobssystems is a generator of jobs..

Cogeneration TechnologiesCogeneration Technologies Cogeneration plant consists of Cogeneration plant consists of four basic elementsfour basic elements::

• A prime mover (engine)A prime mover (engine)• An electricity generatorAn electricity generator• A heat recovery systemA heat recovery system• A control systemA control system

Currently available Currently available drive systems drive systems for cogeneration units for cogeneration units include:include:• Steam turbinesSteam turbines• Reciprocating enginesReciprocating engines• Gas turbinesGas turbines• Combined cycleCombined cycle• Fuel cellsFuel cells• Stirling engineStirling engine• Micro – turbinesMicro – turbines

Reciprocating EnginesReciprocating Engines The reciprocating engines used in cogeneration are internal

combustion engines operating on the same familiar principles as their petrol and diesel engine automotive counterparts,

Reciprocating engines give a higher electrical efficiency, but it is more difficult to use the thermal energy they produce, since it is generally at lower temperatures and is dispersed between exhaust gases and engine cooling systems,

There are two types of reciprocating engines, classified by their method of ignition:

• Spark Ignition (SI) Engine• Compression Ignition (CI) Engine (DIESEL Engine).

Diesel Engine Powered Diesel Engine Powered CogenerationCogeneration

Diesel engines Diesel engines for large scale cogeneration are predominantly for large scale cogeneration are predominantly four-stroke direct injection four-stroke direct injection engines fitted with engines fitted with turbochargersturbochargers and and intercoolersintercoolers,,

Diesel engines will accept gas oil, heavy fuel oil and natural gas Diesel engines will accept gas oil, heavy fuel oil and natural gas ((latter in duel fuel mode with a small quantity of gas oillatter in duel fuel mode with a small quantity of gas oil),),

Shaft efficiencies are Shaft efficiencies are 35-45%35-45%, and output range is up to , and output range is up to 15 MW15 MW

Diesel engines up to 2 MWDiesel engines up to 2 MWee are derivated from original are derivated from original automative diesel operating on gas oil, and from 2 MWautomative diesel operating on gas oil, and from 2 MWee to 20 to 20 MWMWee evolved from marine diesels operating on dual fuel or evolved from marine diesels operating on dual fuel or residual fuels running at medium to low speed. residual fuels running at medium to low speed.

SANKO Diesel Engine Powered SANKO Diesel Engine Powered Cogeneration (DEPC)Cogeneration (DEPC)

The Diesel Engine Cogeneration Plant (SANKO Energy) The Diesel Engine Cogeneration Plant (SANKO Energy) has a total installed electricity and steam generation has a total installed electricity and steam generation capacities of capacities of 25.32 MW 25.32 MW and and 8.1 tons/hr 8.1 tons/hr respectively.respectively.

The electricity is generated by The electricity is generated by three, diesel engine three, diesel engine actuated generator sets each having actuated generator sets each having two two turbochargersturbochargers..

The engine is four stroke compression ignition engine The engine is four stroke compression ignition engine with with 18 cylinders in a V configuration18 cylinders in a V configuration..

Heavy fuel oil Heavy fuel oil is used as fuel for engines. is used as fuel for engines. The permissible annual electricity production is 217 The permissible annual electricity production is 217

GWh and the annual fuel consumption is nearly 45000 GWh and the annual fuel consumption is nearly 45000 tons at designed operating conditionstons at designed operating conditions. .

The Schematic of The Schematic of TheThe Actual Diesel Actual Diesel Engine Powered CogenerationEngine Powered Cogeneration

Plant data, thermodynamic properties, Plant data, thermodynamic properties, and exergies in the DEPC plant wrt and exergies in the DEPC plant wrt

state points in the schematic state points in the schematic

The Governing Laws The Governing Laws forfor Energy Energy and Exergyand Exergy

Steady flow conditions can be closely Steady flow conditions can be closely approximated byapproximated by devices that are intended for devices that are intended for continuous operation such as turbines, pumps, continuous operation such as turbines, pumps, boilers, condensers and heat exchangers of diesel boilers, condensers and heat exchangers of diesel power plants.power plants.

The governing equations below can be used for The governing equations below can be used for these and similar devices once the transient these and similar devices once the transient start-up period is completed and a steady start-up period is completed and a steady operation is establishedoperation is established..

Mass, energy, and exergy balances for any control volume Mass, energy, and exergy balances for any control volume at steady state with negligible kinetic and potential energy at steady state with negligible kinetic and potential energy changes can be expressed respectively by the equations;changes can be expressed respectively by the equations;

iiee hmhmWQ

ei mm

Diieeheat EememWE

TThe net exergy transfer by heat at temperature he net exergy transfer by heat at temperature TT, which, which is is given bygiven by

The specific flow exergy and the rate of total exergy are The specific flow exergy and the rate of total exergy are given bygiven by

Q)TT(Eheat

01

)()( 000 ssThhe

ie eemE i

The isentropic efficiencies of turbine generally The isentropic efficiencies of turbine generally range from 80 to 90% where as the isentropic range from 80 to 90% where as the isentropic efficiencies of compressor range from 70 to 85%efficiencies of compressor range from 70 to 85%..

The second-law (exergy) efficiency of a turbine The second-law (exergy) efficiency of a turbine can be defined as a measure of how well the can be defined as a measure of how well the stream availability of the fluid is converted into stream availability of the fluid is converted into shaft-work output asshaft-work output as

rev

aet, W

W

The second law efficiency of the compressor is defined The second law efficiency of the compressor is defined similarly assimilarly as

The second law-efficiency of the heat exchangers in the power plant is measured by the increase in the exergy of the cold stream divided by the decrease in the exergy of the hot stream,,

hieh

ciecehe, eem

eem

a

revec, W

W

The exergy destruction in a component is calculated from The exergy destruction in a component is calculated from the exergy balance the exergy balance asas

The rate of exergy destruction in a system for the kth The rate of exergy destruction in a system for the kth component can be compared to the exergy rate of the fuel component can be compared to the exergy rate of the fuel provided to the overall systemprovided to the overall system

TOTouti,

TOTini,D EEE

totF,

kD,kD, E

Ey

Alternatively, the component exergy destruction rate can Alternatively, the component exergy destruction rate can be compared to the total exergy destruction rate within the be compared to the total exergy destruction rate within the systemsystem

The exergy loss ratio is defined similarly by comparing the The exergy loss ratio is defined similarly by comparing the exergy loss to the exergy of the fuel provided to the overall exergy loss to the exergy of the fuel provided to the overall systemsystem

totD,

kD,*kD, E

Ey

totF,

kL,kL, E

Ey

The First Law Efficiency of The First Law Efficiency of DEPC DEPC

The first law thermal efficiency of the overall The first law thermal efficiency of the overall DEPC DEPC plant is plant is obtained from the ratio of the sum of the net electrical obtained from the ratio of the sum of the net electrical power and steam outputs to the heat input of the sum of power and steam outputs to the heat input of the sum of heavy fuel oil and fresh treated water at corresponding heavy fuel oil and fresh treated water at corresponding statesstates

water01212ff

water01313electricalnetDECGS hhmLHVm

hhmW

The Second Law Efficiency of The Second Law Efficiency of DEPCDEPC

The exergetic efficiency of the DECGS, based on the The exergetic efficiency of the DECGS, based on the chemical exergy input of the fuel oil and total exergy chemical exergy input of the fuel oil and total exergy destructions of the components in the plantdestructions of the components in the plant

cheETTQW

f

0steamelectricalnet

eDECGS,

1

The Second Law Efficiency of The Second Law Efficiency of Diesel Engine (1Diesel Engine (1stst Approach) Approach)

Exergetic efficiency of diesel engine may be obtained by Exergetic efficiency of diesel engine may be obtained by using two different approaches. The first approach is given using two different approaches. The first approach is given such assuch as

262153f

degen0eDE, 1

EEEEEST

che

The Second Law Efficiency of The Second Law Efficiency of Diesel Engine (2Diesel Engine (2nd nd Approach)Approach)

The second approach in the definition of the exergetic The second approach in the definition of the exergetic efficiency is that: the main purpose of the diesel engine is efficiency is that: the main purpose of the diesel engine is the production of electricity and the main exergy supplied the production of electricity and the main exergy supplied comes from fuel. Thus the alternative definition may be comes from fuel. Thus the alternative definition may be written aswritten as

cheEW

f

electricalneteDE,

Exergy of Fuels (F) and Exergy of Exergy of Fuels (F) and Exergy of Products (P) for DEPCProducts (P) for DEPC

RESULTSRESULTS

Energetic and Exergetic Analyses Energetic and Exergetic Analyses Results for the Sub-systems in the Results for the Sub-systems in the

DEPC PlantDEPC Plant

Exergy Flow Diagram of DEPC Exergy Flow Diagram of DEPC PlantPlant

The Rate of Exergy Destructions of the The Rate of Exergy Destructions of the Components in the DEPC PlantComponents in the DEPC Plant

Variation of Fuel Utilization Efficiency Variation of Fuel Utilization Efficiency (FUE) and Power to Heat Ratio (PHR) as (FUE) and Power to Heat Ratio (PHR) as a Function of Process Steam Output for a Function of Process Steam Output for DEPCDEPC

Concluding RemarksConcluding Remarks The total exergy input of fuel by considering three

diesel engine systems to DEPC plant is 62,757 kW.

40.4% of exergy entering the plant is converted to electrical power and 5% of this power is used for parasitic load in the plant to drive auxiliary components in the plant.

The net steam production of the plant represents only 0.3% of the total exergy input. The remaining 59.3% of the exergy input is destroyed.This corresponds to 37,246 kW, which is the total exergy destruction in the plant.

The exergetic efficiency of the plant is determined to be 40.6%.

The exergy destruction in the diesel engines of the cogeneration plant accounts about 46.0% of the total exergy input and 81.4% of the total exergy destruction in the plant.

The exergy destruction in the engine is mostly due to the highly irreversible combustion process, heat losses from the engine and friction.

The exergetic efficiencies of the compressor and turbine of the turbocharger are 82.6% and 88.1%, respectively. These values indicate sufficient exergetic performance from the turbocharger.

The exergetic efficiencies of the waste heat boiler and condenser are calculated as 11.4% and 16.6%, respectively making them the least efficient components of the plant.

The intercooler has an exergetic efficiency of 26.3%. Exergy destructions in these heat exchange units in the plant are mainly due to the high average temperature difference between the two unmixed fluid streams.

The percent of exergy loss associated with lubrication oil cooler is low. This is due to the cooling of lubrication oil by using low-temperature water.

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