Snaga Motora Termo

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MAN B&W Diesel A/S, Copenhagen, Denmark

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Contents:

Thermo Efficiency System (TES)for Reduction of Fuel Consumption and CO 2 Emission

Introduction ........................................................................... 3

Description of the Thermo Efficiency System ...................... 4

- Power concept and arrangement ...................................... 4

- Main engine performance data ......................................... 5

- Exhaust gas boiler and steam systems ............................ 6

Obtainable Electric Power Production ofthe Thermo Efficiency System ............................................. 8

- Exhaust gas turbine output.................................................. 8

- Exhaust gas and steam turbine generator output single pressure .................................................... 8

- Exhaust gas and steam turbine generator output dual pressure ....................................................... 10

- Payback time of the Thermo Efficiency System ............... 10

Summary ................................................................................ 13

References ............................................................................ 13


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3

Thermo Efficiency System (TES)for Reduction of Fuel Consumption and CO 2 Emission

Introduction

Following the trend of required higheroverall ship efficiency since the first oilcrisis in 1973, the efficiency of the mainengines has increased and, today, thefuel energy efficiency is about 50%.

This high efficiency has, among others,led to a correspondingly lower exhaustgas temperature after the turbochargers.

Even though a main engine fuel energyefficiency of 50% is relatively high, theprimary objective for the shipowner isstill to lower the total fuel consumptionof the ship and, thereby, to reduce theCO 2 emission of his ship.

Today an even lower CO 2 emission canbe achieved by installing a ThermoEfficiency System. However, the maindemand for installation of a Thermo

Efficiency System is that the reliabilityand safety of the main engine/ship op-eration must not be jeopardised.

As an example, the heat balance diagramfor the nominally rated 12K98ME/MCengine (18.2 bar) of the standard high-efficiency version is shown in Fig. 1a.Fig. 1b shows an example based onthe Thermo Efficiency System, valid fora single-pressure steam system, to-

gether with the corresponding figuresfor a dual-pressure steam systemshown in parenthesis.

The primary source of waste heat of amain engine is the exhaust gas heatdissipation, which accounts for abouthalf of the total waste heat, i.e. about

25% of the total fuel energy. In thestandard high-efficiency engine version,the exhaust gas temperature after theturbocharger is relatively low, and justhigh enough for production of the ne-cessary steam for a ships heating pur-poses by means of the exhaust gasfired boiler.

However, a main engine with changedtiming and exhaust gas bypass which

redistributes the exhaust gas heat fromhigh amount/low temperature to lowamount/high temperature increasesthe effect of utilising the exhaust gasheat, but at the same time may slightlyreduce the efficiency of the main engineitself. Such a system is called a ThermoEfficiency System (TES).

Shaft power output 49.3%

Lubricating oilcooler 2.9%

Jacket water cooler 5.2%

Exhaust gas25.5%

Air cooler 16.5%

Heat radiation0.6%

Fuel 100%

(171 g/kWh)

12K98ME/MC Standard engine version

SMCR : 68,640 kW at 94.0 r/min

ISO ambient reference conditions

Fig. 1a: Heat balance diagram of the nominally rated 12K98ME/MCengine of the standard engine version operating at ISO ambient

reference conditions and at 100% SMCR

Fig. 1b: Heat balance diagram of the nominally rated 12K98ME/MCengine in Thermo Efficiency System (TES) version operating atISO ambient reference conditions and at 100% SMCR

Fuel 100%(171 g/kWh)

Heat radiation0.6%

Air cooler 14.2%

Exhaust gas andcondenser 22.9% (22.3%)

Jacket water cooler 5.2%

Lubricating oilcooler 2.9%

El. power production of TES 4.9% (5.5%)

Gain = 9.9% (11.2%)

Shaft power output 49.3%

12K98ME/MC with TESSMCR : 68,640 kW at 94.0 r/minISO ambient reference conditionsTES : Single pressure (Dual pressure)

Total power output 54.2% (54.8%)


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4

Description of the ThermoEfficiency System

Power concept andarrangement

The Thermo Efficiency System (TES)consists of an exhaust gas fired boilersystem, a steam turbine (often called aturbo generator), an exhaust gas tur-

bine (often called a power turbine) anda common generator for electric powerproduction. The turbines and the gen-erator are placed on a common bed-plate. The system is shown schemati-cally in Fig. 2a, and the arrangement of the complete turbine generating set asproposed by Peter Brotherhood isshown in Fig. 2b.

The exhaust gas turbine is driven by apart of the exhaust gas flow, which by-passes the turbochargers. The exhaust

gas turbine produces extra outputpower for electric power production,which depends on the bypassed ex-haust gas flow amount.

When a part of the exhaust gas flow isbypassed the turbocharger, the totalamount of air and gas will be reduced,and the exhaust gas temperature afterthe turbocharger and bypass will increase.

This will increase the obtainable steam

production from the exhaust gas firedboiler.

The exhaust gas bypass valve will beclosed for engine loads lower than about50% SMCR, which means that the ex-haust gas temperature will be reducedwhen operating below 50% SMCR.

The power output from the exhaust gasturbine is transmitted to the steam tur-bine via a reduction gear (see Figs. 2aand 2b) with an overspeed clutch, which

is needed in order to protect the exhaustgas turbine from overspeeding in casethe generator drops out.

The total electric power output of the TES which reduces the ships fuel costs is only a gain provided that it can re-place the power output of other electricpower producers on board the ship.Otherwise, a shaft power motor con-nected to the main engine shaft could

be an option, as also shown in Fig. 2a,but this extra system is rather expensive.

In general (without a shaft power motorinstalled), when producing too muchelectric power, the (high pressure) su-perheated steam to the steam turbineis controlled by a speed control governorthrough a single throttle valve, whichmeans that the surplus steam is dumpedvia a dumping condenser. When thegenerator is operating in parallel withthe auxiliary diesel generators, the gov-

Main engine

Exhaust gas receiver Shaft motor/generator

Diesel generators

Switchboard

Emergencygenerator

Superheatedsteam

Exh. gas boiler

Turbo-chargers

Generator, AC alternator

Reductiongearbox

Steamturbine

Reduction gear with overspeedclutch

LPHP

Exh. gasturbine

Steam for heatingservices HP

LP

Fig. 2a: Power concept for the Thermo Efficiency System


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ernor operates in the normal way togive correct load sharing.

Main engine performance data

The exhaust gas bypass and turbineare available with the following approx.effects, compared with a standardhigh-efficiency main engine versionwithout an exhaust gas bypass:

Open exhaust gas Parameters bypass for exhaust

gas turbine

Power output of exhaust gas turbine at 100% SMCR, up to +4.6% SMCR power

Reduction of total exhaust gas amount, approx. -13%

Total increase of mixed exhaust gas temperature after bypass, up to +50C

Increased fuel consumption from 0.0% to +1.8%

The mixed exhaust gas temperature be-fore the exhaust gas boiler, and valid forthe TES and based on ISO ambient ref-erence conditions, is shown as a functionof the engine load in Fig. 3. When oper-

ating under higher ambient air tempera-tures, the exhaust gas temperature will behigher (about +1.6C per +1C air), andvice versa for lower ambient air tempera-tures.

Fig. 2b: Arrangement of the complete turbine generating set as proposed by Peter Brotherhood Ltd

40

C

% SMCR50 60 70 80 90 100

250

Exhaust gas temperatureafter exh. gas bypass

Exh. gas bypass

closed open

Main engine shaft power

200

350

300

Tropical

ISO

Winter

ISOTropical

Winter 25 C air / 25 C c.w.45 C air / 36 C c.w.

15 C air / 36 C c.w.

Ambient reference conditions:

Fig. 3: Exhaust gas temperature after exhaust gas bypass for a main engine with TES

Generator, AC alternator

Reductiongearbox

Steam turbineReduction gear withoverspeed clutch

Exh. gasturbine

Approx. dimensionsreferring to a12K98ME/MC:

Length: 10 metres

Breadth: 3.5 metres

Weight: 58 tons withoutcondenser

Weight: 75 tons withcondenser


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The increased fuel consumption of themain engine depends on the actualmaximum firing pressure (P max ) used.

The P max used for TES will normally beincreased compared with a standardengine and thereby an increase of thespecific fuel oil consumption can beavoided when using TES.

Exhaust gas boiler and steamsystems

The exhaust gas boiler and steam tur-bine systems analysed in this paper arebased on the two types below:

1. Single-pressure steam system The simple single-pressure steam system is only utilising the exhaust gas heat. See the process diagram in Fig. 4 and the corresponding temperature/heat transmission diagram in Fig. 5. The steam drum from the

oil fired boiler can also be used in- stead of a separate steam drum.

Fig. 5: Temperature/heat transmission diagram of an exhaust gas boiler with single-pressuresteam system valid for a main engine with TES and operating at 85% SMCR/ISO

Fig. 4: Process diagram for the Thermo Efficiency System single-pressureexhaust gas boiler system with a single-pressure steam turbine

0 40

C

60 80 1000

50

100

Temperature

Heat transmission20

150

200

250

300

Feed-water

Ambient air

Steam/water

7 bar abs/165 CSaturatedsteam

%

Superheatedsteam

min 20 C

A B C

Exh. gas boiler sections:. Superheater. Evaporator. Preheater

A

CB

Exh. gas

Exh. gas

Sat. steamfor heating

services

Condenser

Steamturbine

Feedwaterpump

Circ. pump

Preheater

Evaporator

Superheater

Exhaust gas

Exh. gas boilersections:

Surplusvalve

Steamdrum

Hot well


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Fig. 6: Process diagram for the Thermo Efficiency System dual-pressureexhaust gas boiler system with a dual-pressure steam turbine

Fig. 7: Temperature/heat transmission diagram of an exhaust gas boiler with dual-pressure steam system valid for a main engine with TES and operating at 85% SMCR/ISO

0 40

C

60 80 100

0

50

100

Temperature

Heat transmission20

150

200

250

300

Feedwater preheatedby alternativeWHR sources

Ambient air

Steam/water 10 bar abs/180 C

SaturatedHP steam

%

Superheated

HP steam

min 20 C

A B C

Exh. gas boiler sections:. HP-superheater . HP-evaporator . HP-preheater . Possible LP-superheater . LP-evaporator

ABCDEExh. gas

ED

4 bar abs/144 C

min 15 C

Superheated LP steam

Exh. gas

HP-steamfor heating

services

Condenser

Steamturbine

Feedwaterpump

HP

LP

Alternative WHRsources for feedwaterpreheating

LP-steam drum

HP-steam drum

HP-circ. pump

LP-circ. pump

LP-Evaporator

HP-Preheater

LP-Superheater

HP-Evaporator

HP-Superheater

Exhaustgas

HP LP

Exh. gas boilersections:

Surplusvalve

Hot well

2. Dual-pressure steam systemWhen using the dual-pressure steamsystem, it is not possible to install anexhaust gas low-pressure preheatersection in the exhaust gas boiler, be-cause the exhaust gas boiler outlettemperature otherwise would be toolow and increase the risk of wet (oily)soot deposits on the boiler tubes.

The more complex dual-pressure

steam system, therefore, needssupplementary waste heat recovery(WHR) sources (jacket water andscavenge air heat) for preheating of the feedwater which, of course, willincrease the obtainable steam andelectric power production of TES.See the process diagram in Fig. 6and the corresponding temperature/ heat transmission diagram in Fig. 7.

If no alternative waste heat recoverysources are used to preheat thefeedwater, the low pressure (LP)steam may be used to preheat thefeedwater, involving an about 16% re-duction of the total steam production.

The available superheated steam usedfor the steam turbine is equal to thesurplus steam after deduction of thesaturated steam needed for heatingservices.

The exhaust gas boiler has to be desig-ned in such a way that the risk of sootdeposits and fires is minimised, Ref. [1].


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Obtainable Electric PowerProduction of the ThermoEfficiency System

Exhaust gas turbine output

The exhaust gas bypass for the exhaustgas turbine has a bypass gas amountof approx. 12% of the total exhaust gasamount at 100% SMCR. This bypass-gas

amount led through the exhaust gasturbine will typically produce an availablepower output of max. 4.6% of the SMCRpower when running at 100% SMCR.The corresponding electric power out-put will be somewhat lower because of generator and gear losses.

At part load running of the main engine,the power output will be reduced byapproximately the square root of theengine load.

As an example, the maximum availablepower output of the exhaust gas turbinevalid for a nominally rated 12K98ME/MC(18.2 bar) engine is shown in Fig. 8, asa function of the engine load.

Exhaust gas and steamturbine generator output single pressure

The single-pressure steam system is asystem where all heat recovered comesfrom the exhaust gas heat only, whichmakes it relatively simple, see Figs. 4and 5.

As low gas temperatures (risk of conden-

sed sulphuric acid) and low gas veloci-ties (risk of soot deposits) through theexhaust gas boiler may have a deterio-rating effect on the boiler, Ref. [1], wehave, in our studies, selected an exhaustgas boiler designed for a single-pressuresteam system of minimum 7 bar abs(6 bar g) steam pressure (165C), andminimum 20C pinch point. The super-heated steam temperature is about270C. The steam turbine is a multi-stage single-pressure condensing type.

The alternator/generator is driven bothby the steam turbine and the exhaustgas turbine.

As an example valid for the nominallyrated 12K98ME/MC (18.2 bar) engineoperating at ISO ambient referenceconditions, we have calculated the steamproduction and the electric power pro-duction of TES, see Figs. 10 and 11.

The total electric power production in %of the main engine shaft power outputis also shown as a function of the engineload, see Fig. 9.

The results for operation at 85% SMCRare shown in Fig. 14, together with thecalculated ISO ambient temperature basedresults for three other main engine types.

The corresponding results based ontropical ambient temperature conditionsare shown in Fig. 15. However, it shouldbe emphasised that it is probably morerealistic to use the ISO ambient tem-peratures as the average ambient tem-peratures in worldwide operation. InFig. 16, the ISO based total electricpower production at 85% SMCR is alsoshown as a function of the main enginesize measured in SMCR power.

Fig. 8: Expected available power output of exhaust gas turbine for a12K98ME/MC with SMCR = 68,640 kW x 94 r/min

Fig. 9: Expected electric power production in % of the main engine shaft power output valid for a 12K98ME/MC with Thermo Efficiency System (TES) and based on ISO ambient reference conditions

30 40

kW

% SMCR50 60 70 80 90 1000

500

1,000

1,500

2,000

2,500

3,000

3,500

Available power output of exhaust gas turbine

Exh. gas bypassclosed open

Main engine shaft power % SMCR50 60 70 80 90 1000

Main engine shaft power

1

2

3

4

5

6

7

89

10

11

Steam turbine

Exhaustgas turbine

Main engine 12K98ME/MCSMCR = 68,640 kW at 94 r/min

ISO amb. cond.

Single press.

Dual press.

%

12

13

Electric power production of TESrelative to the main engine power output


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Fig. 10: Expected steam production of an exhaust gas boiler with

single-pressure steam system valid for main engine 12K98ME/MCwith TES and based on ISO ambient reference conditions

Fig. 11: Expected electric power production of the Thermo Efficiency

System (TES) with a single-pressure steam system valid for mainengine 12K98ME/MC and based on ISO ambient reference conditions

Fig. 13: Expected electric power production of the Thermo Efficiency System (TES) with a dual-pressure steam system valid for main engine12K98ME/MC and based on ISO ambient reference conditions

kg/h

90 1000

5,000

10,000

Obtainable steam production

Main engine shaft power 40

15,000

20,000

25,000

30,000

% SMCR

35,000

50 60 70 80


Superheated steamfor steam turbine

12K98ME/MC with TES (single press.)SMCR = 68,640 kW at 94 r/minISO amb. cond. Total steamproduction

90 1000

1,000

2,000

Main engine shaft power40

3,000

4,000

5,000

6,000

% SMCR

7,000

50 60 70 80Exh. gas bypassclosed open

Exhaust

gas turbine

12K98ME/MC with TES (single press.)SMCR = 68,640 kW at 94 r/minISO amb. cond.

Steam turbine

Total el.production

kWElectric power production

8,000

90 1000

1,000

2,000

Main engine shaft power 40

3,000

4,000

5,000

6,000

% SMCR

7,000

50 60 70 80Exh. gas bypass

closed open

Exhaustgas turbine

12K98ME/MC with TES (dual press.)SMCR = 68,640 kW at 94 r/minISO amb. cond.

Steam turbine

Total el.production

kWElectric power production

8,000

Fig. 12: Expected steam production of an exhaust gas boiler with adual-pressure steam system valid for main engine 12K98ME/MCwith TES and based on ISO ambient reference conditions

90 1000

5,000

10,000

Main engine shaft power40

15,000

20,000

25,000

30,000

% SMCR

35,000

50 60 70 80


12K98ME/MC with TES (dual press.)SMCR = 68,640 kW at 94 r/minISO amb. cond. Total steam

production

kg/hObtainable steam production

40,000

SuperheatedHP steamfor steam turbine

SuperheatedLP steam forsteam turbine


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Exhaust gas and steamturbine generator output dual pressure

Besides the single-pressure steam system,a more complex and more expensivedual-pressure steam system is alsoavailabl e, see Figs. 6 and 7. The highand low steam pressures used areabout 10-11 and 4-5 bar abs (9-10 and3-4 bar g), respectively.

The steam turbine is a multi-stage dual-pressure condensing type. The alternator/ generator is driven both by the steamturbine and the exhaust gas turbine.

Because of the low steam pressure andcorresponding low saturated steam tem-perature (144C/4.0 bar abs), there is noroom for an LP-preheater section in theexhaust gas boiler for feedwater preheat-ing, because the exhaust gas boileroutlet temperature has to be higher thanabout 160-165C in order to avoid sulphu-ric acid corrosion of the boiler outlet.

The feedwater, therefore, has to bepreheated by means of alternative heatsources such as the jacket water andscavenge air cooler heat.

Furthermore, the pinch point should notbe too low (giving low gas velocitiesthrough the boiler) in order to protectthe exhaust gas boiler against sootdeposits and fires.

As an example valid for the nominallyrated 12K98ME/MC (18.2 bar) engineoperating at ISO ambient referenceconditions, we have calculated thesteam production and the electricpower production of the TES, seeFigs. 12 and 13.

The total electric power production in% of the main engine shaft power out-put is also shown as a function of theengine load, see Fig. 9.

The results for operation at 85% SMCRare shown in Fig. 14, together with thecalculated ISO ambient temperaturebased results for three other main en-gine types. The corresponding resultsbased on tropical ambient temperatureconditions are shown in Fig. 15. How-ever, it should be emphasised that it isprobably more realistic to use the ISOambient temperatures as the averageambient temperatures in worldwide op-

eration. In Fig. 16, the ISO based totalelectric power production at 85%SMCR is also shown as a function of the main engine size measured inSMCR power.

Payback time of the ThermoEfficiency System

The payback time of TES depends verymuch on the size of the main engineand the trade pattern (main engine loadand ambient temperatures) of the ship.

Fig. 14: Steam and electric power production and payback time of the Thermo Efficiency System (TES)when operating at 85% SMCR and ISO ambient reference conditions


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When for example operating at tropicalambient conditions, the electric poweroutput of the TES is higher than for ISOambient conditions, which again has ahigher TES output compared with win-ter ambient conditions.

Furthermore, the investment costs perinstalled kW e output of a TES plant arerelatively cheaper the bigger the plant is.

A simple estimation of the average savedfuel costs in service at ISO ambient tem-perature conditions for a 12K98ME/MCwith TES (for single or dual pressure)compared to a standard 12K98ME/MCengine can be found by means of thealready estimated relative TES1/TES2gain of 8.6%/9.8% of the main engineoutput, see Fig. 14.

Based on the average operation in ser-vice at 85% SMCR = 58,344 kW in 280

days a year, SFOC = 0.00017 t/kWhand a fuel price of 160 USD/t the annualmain engine fuel costs of the standard12K98ME/MC engine are as follows:

Fig. 15: Steam and electric power production of the Thermo Efficiency System (TES)when operating at 85% SMCR and tropical ambient conditions

Fig. 16: Expected total electric power production and possible annual fuel cost savings of the Thermo Efficiency System (TES) based on ISO ambient reference conditions and 85%SMCR, shown as a function of the main engine size, SMCR power

80,0000

Size of main engine, SMCR power

20,000 kW40,000 60,000


Normal service : 85% SMCR in 280 days/yearFuel consumption : 0.17 kg/kWhFuel price : 160 USD/t

kW Electric power production

1,000

2,000

3,000

4,000

5,000

6,000

7,000

Steam turbine

Exhaust gas turbine

Dual press.

Single press.

0

0.2

0.4

0.6

0.8

1.0

1.2

mill. USD/yearPossible annual savings of fuel costs


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Fuel costs = 280 days/y x 24 h/day x 0.00017 t/kWh

x 58,344 kW x 160 USD/t = 10,664,000 USD/year

For the single and dual-pressure sys-tems, respectively, the TES gain insaved fuel consumptions will then be asfollows:

TES1 savings = 0.086 x 10,664,000= 917,000 USD/year TES2 savings = 0.098 x 10,664,000

= 1,045,000 USD/year

as shown in Fig. 14.

The similar fuel cost savings valid for theother three cases with smaller main en-gines are also stated in Fig. 14, and incurve form in Fig. 16 as a function of the main engine size, SMCR power.

Based on the extra investment costs of the TES plant (without installation of ashaft power motor on the main engineshaft and minus the investment cost of a normal exhaust gas boiler system) forthe four main engine cases comparedto a standard main engine installation,the estimated payback time found is asstated in Fig. 14, i.e. in principle thesame for the single and dual-pressuresystems. For the 12K98ME/MC engine,the calculated payback time is about

five years.

In Fig. 17, the estimated payback timeof the TES plant is shown as a functionof the main engine size. The payback time is only valid provided all electricpower production savings are used onboard the ship.

It has been assumed that the increasedspecific fuel consumption of the TESmain engine has been avoided by usingan increased firing pressure, P max.

Fig. 17: Estimated payback time of the Thermo Efficiency System (TES) valid for both a single and a dual-pressure steam system

80,0000

Size of main engine, SMCR power20,000 kW40,000 60,000

Normal service : 85% SMCRIn service per year : 280 days/yearFuel consumption : 0.17 kg/kWhFuel price : 160 USD/t


YearPayback time of TES

1

2

3

4

5

6

78

9

10

11

12

13


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Summary

Our calculations indicate that for ISOambient reference conditions, a reduc-tion of the fuel consumption of 8-10%for a single-pressure system is possiblein the normal service range of the mainengine. The larger the engine load, thegreater the possible reduction.

For the more complex dual-pressuresystem, the corresponding reduction isabout 9-11%.

All calculations presume unchangedMTBOs (maintenance time betweenoverhauls) compared to todays expec-tations.

However, if the ship sails frequently incold weather conditions, the electricpower production of the steam turbinewill be reduced, and the above-stated

reduction of fuel consumption and cor-responding reduction of CO 2 emissionmight not be met.

The extra investment costs of the ThermoEfficiency System and the payback of the investment can be obtained bymeans of lower fuel/lube oil costs and,not to forget, the possibility of obtainingadditional freight charters and higherfreight rates, thanks to the green shipimage!

The payback time calculations basedon a large container vessel with a12K98ME/MC as main engine and asaverage operating at 85% SMCR andat ISO ambient reference conditions innormal service during 280 days/yearindicate a payback time of about 5 yearsfor the TES. The payback time is validfor both the single-pressure and thedual-pressure systems, because theincreased electric power productiongain of the dual-pressure system mightcorrespond to about the same relativeincrease of the investment costs com-pared to the single-pressure system.

When selecting the type of Thermo Effi-ciency System, the correspondingly in-volved higher risks for soot deposits andfires of the exhaust gas boiler has to beconsidered, see Ref. [1].

Because of this, but also because of themore simple single-pressure steam boilersystem, MAN B&W Diesel recommendsusing the single-pressure steam system,when installing TES.

Of course, the more complex and moreexpensive dual-pressure steam system,which gives a somewhat higher electricpower output, may also be used inconnection with MAN B&W Dieselstwo-stroke main engine types.

The TES is rather expensive, and relativelymore expensive the smaller the main

engine and the TES are, giving a rela-tively higher payback time. Therefore,the installation of the TES is normallyonly relevant for the large merchant ships,such as the large container vessels.

The TES may be delivered as a packageby Peter Brotherhood (turbines) in co-operation with Aalborg Industries (boiler)and Siemens (generator) or by othermakers.

References

[1] Soot Deposits and Fires in Exhaust Gas Boilers, MAN B&W Diesel A/S, Copenhagen, Denmark, p. 280, March 2004.

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