delta marin report - study of hydraulic and electric driven deepwell cargo pump options 190407

8/13/2019 Delta Marin Report - Study of Hydraulic and Electric Driven Deepwell Cargo Pump Options 190407

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STUDY OF HYDRAULIC AND ELECTRICDRIVEN DEEPWELL CARGO PUMP

OPTIONS

Deltamarin Ltd19.4.2007

REPORT


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REPORT FOR PROJECT 1046

STUDY OF HYDRAULIC AND ELECTRIC DRIVEN DEEPWELL CARGO PUMP

OPTIONS

CLIENT: HAMWORTHY SVANEHJ

PREPARED BY: DELTAMARIN/ JM

DATE: 19.4.2007

DELTAMARIN LTD.

Date InitialsDESIGNED: 19.4.2007 JM

CHECKED: 19.4.2007 JN

APPROVED: 19.4.2007 JN

DELTAMARIN LTD

Purokatu 1

FIN-21200 RAISIO

Tel. +358-2-4336 300

Fax. +358-2-4380 378

Email: [email protected]

File: Study of cargo pump options.doc


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DELTAMARIN LTD. - 1- 19.4.2007

STUDY OF HYDRAULIC AND ELECTRIC DRIVEN DEEPWELL CARGO PUMP OPTIONS

0. INTRODUCTION

Purpose of this study is to compare two cargo handling arrangements on small

chemical and oil products carriers. Neither alternative arrangement contains a pumproom, but both arrangements contain individual pumps for each cargo tank. The

compared cargo pump arrangements are the following

Hydraulic submersible cargo pumps (one per cargo tank). The pumps arepowered by common electric motor driven power packs. This alternative is

referred to as the hydraulic system.

Electric deepwell cargo pumps (one per cargo tank). The pumps areindividually controlled by frequency converters, one converter per one pump.

This alternative is referred to as the electric system.

This study contains comparative analysis on three different reference vessels. These

reference vessels represent typical small chemical and oil products carriers in sizes of

approximately 6 000 ton, 13 000 ton and 45 000 ton in deadweight. Both systems

technical and economical aspects are taken into consideration and compared head to

head in all of the three reference vessels.

Economical and technical comparison data presented in this study is that of collected

by Deltamarin. Where applicable and possible, source of data is expressed. Some of

the information contained in this study is based on the experiences of owners that

operate both electric and hydraulic systems onboard their fleet of tankers.

Aim of this is to provide a transparent comparison with enough background

information given in order for the reader to objectively compare the two

arrangements.


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1. EXECUTIVE SUMMARY

In this study two alternative cargo handling solutions for small chemical and oil

products tankers have been examined. The first alternative is submerged hydraulicpumps with electric motor driven hydraulic powerpacks. The second alternative is

frequency converter controlled electric deepwell pumps. Neither alternative contains

a pump room.

Both of these systems are applied to three reference vessels and their technical and

economical aspects have been compared. The three reference vessels represent sizes

of approximately 6 000 ton (vessel A), 13 000 ton (vessel B) and 45 000 ton in

deadweight (vessel C).

Technical comparison of the two systems reveals the following differences:

The electric system uses energy more efficiently and therefore requires less fuel

to operate than the hydraulic system. In reference vessels the fuel savings for

cargo handling range from 11% to 17%.

The electric system requires less space outside the cargo area. In reference

vessels A and B approximately 20 m2 of machinery space is saved, in reference

vessel C approximately 60m2 of machinery space is saved.

There are some variations in weights of the systems. In vessel A the electrical

system weights 6 tons less, in vessel B it weights 13 tons less, and in vessel C itweights 3 tons less.

Electrical system has no noise problems, while hydraulic system is known for its

high-pitched noise.

Pumps of both systems have individual and independent stepless control. In both

systems the nominal torque is available in a wide enough pump speed range to

enable effective pumping of all relevant cargoes.

Due to electric drive, there are no limits onboard a diesel-electric ship to the

number of pumps being operated concurrently. Size of powerpacks limits thenumber of hydraulic pumps being operated concurrently.

Pumps in the hydraulic system have shorter shaftlines than in the electric system.

This has no effect in normal or abnormal operation of the cargo pumps. The only

drawback from long shaftline is its increased sensitivity to torsional vibrations,

but this issue can adequately be dealt with good design.

In both systems the cargo is protected in a similar manner against possible

contamination from hydraulic or lubricating oil.

Both systems have about the same amount of redundancy. If need be, the electricsystems redundancy can be more easily enhanced.


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Emergency pumping can be arranged as easily in both of the systems. There are

instances, however, when emergency pumping is not possible with the hydraulic

system.

Hydraulic system requires more maintenance than the electric system. However,this increased need of constant maintenance does not translate into a need of a

bigger crew.

Claims of environmental friendliness over the other system cannot be

substantiated in the hydraulic systems case. More environmentally friendly

operational aspects clearly favour the electric system over the hydraulic system.

In economical comparison the initial cost is divided in two parts. Purchase cost is the

money paid to the supplier of the system and installation cost is the shipyards cost of

installing the system. In cost calculations labour costs and efficiency figures

applicable to South Korean shipyards have been used.

In this case vessels A and B, respectively 6.000 ton and 13.000 ton, are equipped

with one frequency converter per each cargo pump. The 45.000 ton vessel C is

equipped with one frequency converter per each two pumps. However, also in

vessels A and B it is possible to make a less expensive arrangement with two to four

cargo pumps being controlled by a single converter1. In this case the purchase price

will lower by 12 to 15% from the figures stated in this report. This also slightly

reduces the space requirements and weight of the electric system, but not to a very

significant degree.

1

Matrix Swichboard System, see http://www.hamworthy.com/docGallery/212.PDF


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Annual costs are also divided in two parts, in costs incurred by producing power for

the pump system and in costs directly incurred by the pumping system. Table 1

summarises all of these costs.

Table 1 Summary of costs (all figures in USD, rounded)

Initial costs can be regarded as annual capital costs during the vessels economic

lifetime. The total annual costs are calculated with assuming 20 years of economic

lifetime and interest rate of 8% for the capital costs.

!

!

!

!

" " # " $


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2. BASIS OF THE STUDY

2.1 Cargo handling system review

The two cargo handling systems compared in this study are electric deepwell pump

system and hydraulic submersible pumps system. Both of these systems comprises

cargo pumps that are located in cargo tanks (one cargo pump per tank)

The hydraulic submersible pumps are powered by electric motor driven hydraulic

powerpacks. The Powerpack Room is located away from the cargo area and in

machinery spaces. Hydraulic power for the pumps is provided via a pressure

pipeline, in which the hydraulic fluid is pressurised to over 250 bar. Hydraulic motor

itself is located down in the tank, some half to two meters above the tank bottom.

Hydraulic fluid is returned to the Powerpack Room by a return pipeline, in which a

pressure of around 10 bars is upheld.

Respectively, the deepwell pumps are powered by the frequency converter controlled

electric motors. Electric power is provided through the Converter Room, which is

located away from the cargo area and in machinery spaces. Electric power is led

from Converter Room to the pumps via cables and pumps electric motors speed is

controlled by frequency converter. Impeller inside the pump head at the bottom of a

tank is driven by the electric motor on main deck via a shaftline though the tank.

Figure 1. Electric deepwell pump system (left) and hydraulic submersible pump

system (right)


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Table 3 Dimensioning criteria of cargo handling arrangements

vessel A vessel B vessel C

capacity of each cargo pump 200 m3/h 230 m

3/h 500 m

3/h

total simultaneous capacity 1 400 m3/h 1 380 m

3/h 3 000 m

3/h

minimum unloading time 5,0 hours 10,8 hours 18,2 hours

The main items of cargo pump systems compared in this study are also presented in

the following table 4.

Table 4 The main items of cargo pump systems reviewed in this studyVessel A Vessel B Vessel CItem

el-pumps hyd-pumps

el-pumps hyd-pumps el-pumps hyd-pumps

Cargopumps

14 pcs

located

within cargo

tanks

14 pcs

located

within

cargo tanks

10 pcs

located within

cargo tanks

10 pcs

located

within

cargo tanks

18 pcs

located

within

cargo tanks

18 pcs

located within

cargo tanks

Cargo pumpe-motors /hyd-motors

14 pcs

located above

cargo tanks

14 pcs

located

within

cargo tanks

10 pcs

located above

cargo tanks

10 pcs

located

within

cargo tanks

18 pcs

located

above cargo

tanks

18 pcs

located within

cargo tanks

Powercontrolof cargopumps

14 converters

&

switchboard

Powerpacks 10 converters&

switchboard

Powerpacks 9 converters&

switchboard

Powerpacks

Powertransmissionof cargo

pumps

Cabling Hydraulic

piping

Cabling Hydraulic

piping

Cabling Hydraulic

piping


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Table 6 shows the operating profiles as cumulative annual hours in different

operating modes. Interested readers will find more detailed route information and

calculation into the presented figures in Appendix 1.

Table 6 Annual hours in different operating modesvessel A vessel B vessel C

at sea at full power 6 890 h 6 979 h 6 359 h

closing port,

manoeuvring

152 h 103 h 221 h

loading cargo 685 h 656 h 736 h

unloading cargo 913 h 902 h 1 324 h

off-hire 120 h 120 h 120 h

total annual hours 8 760 h 8 760 h 8 760 h


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3. TECHNICAL COMPARISONS

Technical implications of cargo pump selection can be divided into four main

categories. These are the selections impact on ship design, operational aspects,structural aspects and environmental aspects.

Impact on ship design can be further divided to include three aspects: difference in

energy consumption (already discussed in the preceding chapter), space requirements

and systems weights. Operational aspects studied in this report include noise,

control, emergency pumping, stripping, redundancy and maintenance requirements.

Structural aspects include structural evaluation of different components of the

pumping system as well as possibility of cargo being contaminated. Last, but not

least, are the environmental aspects of cargo handling system selection.

3.1 General arrangements

The selection of cargo handling arrangement has some impact on general

arrangements. There is no difference in positioning of the pumps in the cargo area,

but some variations in space requirements outside the cargo area. Both systems need

a Cargo Control Room to operate, but there are no significant differences in space

requirements between the two systems.

Besides the Cargo Control Room, the hydraulic version requires the following three

spaces outside cargo area:

Powerpack Room with sufficient space for the hydraulic powerpacks. From this

room hydraulic oil is pumped into the cargo pumps.

Hydraulic Oil Storage Tank with a volume equal to the total volume of hydraulic

oil inside the hydraulic system. This tank is installed for the sake of redundancy

of operation. In case the hydraulic oil is contaminated or leaking, oil can be

changed or added immediately where ever the vessel happens to be sailing

without extensive off-hire.

Hydraulic Oil Waste Tank with a volume of at least the total volume of hydraulic

oil inside the hydraulic system. This tank is required, so that contaminated and/or

removed hydraulic oil is not dumped overboard.

Besides the Cargo Control Room, the electric version requires the following space

outside cargo area:

Converter Room which houses the frequency converters.

When the required spaces have been identified, it is possible to compare the areasthey require. Table 7 shows space requirements for the above mentioned spaces


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assuming a deck height of 2 800 mm. For volume figures of the two hydraulic oil

tanks, please see Appendix 1.

Table 7 Space requirement

vessel A vessel B vessel Cpowerpack room 33,0 m

2 33,0 m

2 75,0 m

2

HO storage tank 1,6 m2 1,6 m

2 2,2 m

2

HO waste tank 1,7 m2 1,8 m

2 2,5 m

2

hydraulic version approx 36 m2 approx 36 m2 approx 80 m2

converter room 17 m2 13 m2 30 m2

In the two smaller reference vessels difference in the space required is around 20 m2.

Although not a big space saving, this nevertheless opens up some possibilities in

arranging the lay-out of machinery spaces.

As the cargo handling power requirements are bigger, as in reference vessel C, the

difference in space requirements becomes more obvious. A space saving of 50 m2in

a 45 000 ton ship is big enough space to be usefully utilised. How this extra space is

best utilised depends on the specific ship project, of course.

3.2 Weight

Difference in the two cargo handling systems weights can be evaluated by

calculating weights of all sub-parts of the two systems. Weights of majorcomponents are available, as well as specific weights of pipes, cables and cable trays.

Please note, that the hydraulic system requires some cabling, as electric power needs

to be transmitted from generators to the Powerpack Room. Similarly, electric system

needs some amount of hydraulic piping for the portable emergency pump.

Table 8 shows results of weight calculations. A more detailed break-down of weights

as well as used specific weights can be found from Appendix 2.

Table 8 Weight comparison (all weights in kg, rounded)vessel A vessel B vessel Chydr. electric hydr. electric hydr. electric

hydraulic piping 3 220 130 3 880 170 5 630 250

designated spaces 11 700 4 390 11 750 3 350 23 900 7 740

cabling 250 5 430 250 4 780 250 12 180

pumping 22 300 21 720 21 540 16 200 49 710 58 010

total 37 460 31 670 37 420 24 510 79 480 75 080


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3.3 Noise

Hydraulic cargo handling system is notorious for its loud noises. Especially the old

hydraulic systems generated a lot of most unpleasant noise when operated. Older

vessels with hydraulic cargo handling systems are therefore known to have beensubject to operating restrictions in some ports, especially in those where there are

settled areas near the port.

However, there has been a lot of progress made in combating the noise problem.

Noise levels of modern hydraulic systems are significantly lower than those of the

old ones. Unfortunately though, there is very little objective and quantitative

comparison data available on the noise levels of the two systems. This makes

quantitative comparison based on hard figures impossible.

On the other hand there are lots of qualitative and subjective data as well as a range

of opinions available on the hydraulic systems sound levels. This would suggest,

that a modern hydraulic system still makes a lot less pleasant noise when operated

than its electric counterpart. Even if a hydraulic systems noise would be at a sound

level comparable to that of an electric system, it is more high pitched and therefore

usually considered to be more annoying.

3.4 Control

Old electric systems with two speed electric motors had problems in control of flow

and pressure. As there were only two speeds the motor and the pump could be

operated on, flow control was not optimal or sufficient. From technical point of view

the electric motor itself had to be over-dimensioned in normal use, to be able to

pump the cargoes with high specific gravity or the speed had to be reduced to a

dramatically low speed.

Nowadays those problems have been solved, as the modern electric system uses a

frequency converter to control the motor, in a stepless control of the pumps

rotational speed. Because of the variable speed it is possible to optimize motor and

pump in a cargo system, that is able to handle cargoes within the range of specific

gravity at maximum load without having an over-dimensioned motor.

Due to the frequency converter, the 50 Hz or 60 Hz networks do not limit the speed.

The pump speed can alter between 0 RPM and the pump maximum rotational speed

up to 3600 RPM.

With respect to control, one additional benefit of having frequency converters to

control the motor is that it can be programmed to be a smooth starter. This means,

that electric motor and pump can be started from zero speed and gradually increased.

This reduces wear and tear of all systems component as well as reduces generator

ratings onboard diesel-mechanical ships.


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The cargo system is designed to handle different specific gravity, typically ranging

from 0,5 to 2,5 ton/m3. This means that the pump can handle equally efficiently all

cargoes. The limitations in the discharge situation are the nominal motor power, the

rated pressure of the pipe system, and the maximum pressure for the land

installations.

One issue related to control is the number of pumps, which can be operated

concurrently. In a diesel-electric ship there is enough power available to operate all

pumps, while the number of hydraulic pumps being operated concurrently is limited

by size of the power pack. However, the number of simultaneously operated pumps

is also dependent on piping and segregation arrangements onboard.

As a conclusion it can be said, that the individual stepless control of each pump is

possible in both systems. Nominal torque is available in a range sufficient to

effectively pump all cargoes.

3.5 Emergency pumping

In case there is a failure of a single pump leading to inability to empty a tank, there

really are no differences in operation in between the two systems. If one pump fails,

it does not effect operation of other pumps. As a part of both systems there needs to

be a hydraulic operated submersible portable pump, which can be lowered down to

the cargo and used to empty the tank.

In a hydraulic system the hydraulic power is provided by the pressure pipeline andthe portable pump is connected to the pipeline by hoses. In the electric systems case

there needs to be a small emergency hydraulic powerpack onboard with a fixed

emergency pressure pipeline to provide the hydraulic power to any of the tanks. The

emergency pumping operation itself does not differ from one system to the other.

The emergency hydraulic power pack as well as the portable pump are parts of a

standard scope of supply of an electric system.

In case the entire pumping system fails, due to damage of powerpack or converter

room or due to damage of power providing network (pressure pipeline or electric

cabling), there are differences between the two systems. In hydraulic systems case

emergency pumping is not possible, as the emergency pump requires both thepowerpack and the pressure pipeline to be operational. Emergency pumping in

electric system is not dependant on the main pumping system, as it is a complete

stand-alone pumping system. Both the converter room and electric cabling can be

completely destroyed and emergency pumping can still be done.

3.6 Stripping

Stripping procedure of cargo pumps is important especially in chemical carriers.

However, it really is not a feature related to hydraulic or electric drive, but to the

overall pump and impeller design. If stripping procedures of typical hydraulic andelectric pumps are evaluated, significant differences are not found. It can be quite


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shortly concluded, that there are no relevant differences in stripping between the two

technologies.

3.7 Redundancy

It is possible to assess redundancy of a system by highlighting critical components

and spaces in which a damage would cause reduced operating capability or inability

to operate. Other part of reliability and redundancy assessment, likelihood of a given

inability causing incident taking place, is not discussed here.

First critical space is the room, from which power is delivered to the pumping

system. In hydraulic systems case this is the Powerpack Room and in electric

systems case it is the Converter Room. These spaces do not differ in the sense, that

if the space itself is damaged, the pumping system cannot be operated.

In bigger ships, like in reference vessel C, it could be useful to divide the converter

room into two separate spaces. In such a case typically port and starboard side pumps

are operated by separated converter rooms. This of course adds to the redundancy of

operation in case of one converter room being damaged. However, if one converter

room is damaged, pumps connected to this room cannot be operated from the other

side, unless this has been prepared for at the building phase. But if seen necessary,

very redundant arrangements can quite easily be built with the electric system.

It should also be possible to divide hydraulic systems Powerpack Room, when

nesessary. This requires extra piping and valve arrangements, so that both PowerpackRooms still provide power to the same pressure pipeline. In case one Powerpack

Room is damaged, there needs to be valve and piping arrangements so that the room

can be isolated from the common pressure piping. Usually hydraulic ships are

equipped with one Powerpack Room and one powerpack in it, so dividing the

powerpack into two separate units will most likely add to the cost of installation.

Redundant two-room arrangement is thus more complicated to arrange than in

electric systems case, but still a possible alternative.

It is also possible, that one single power providing component, a powerpack or a

converter, fails. In hydraulic systems case, if one of a typically two to four hydraulic

pumps fails, it leads to reduced pumping capacity. All the pumps can be operated,even simultaneously, but as the nominal flow is not available, at a reduced capacity.

If a converter fails, the pump connected to the converter cannot be operated. It can be

operated by another converter, typically the converter next to the failed one. When a

converter dimensioned for one pump is operating more than just a one pump,

reduced capacity is available. In this respect the situation does not differ from the

hydraulic systems case.

The next critical component is the means of transmitting power to the pumps. In

hydraulic system this is by a common pressure pipeline, in electric system this isachieved by cabling on a common cable tray. In case the pipeline or the cabling is


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damaged, the system can not be used. It is of course possible to enhance redundancy

by building alternative pressure pipeline or cabling, but there are no differences in

the two systems in this respect.

3.8 Maintenance

As the basic concepts in the two systems are different, there obviously are great

differences in the maintenance requirements. It can easily be argued, that the

hydraulic system is more mechanical in nature. Power distribution is by means of

distributing mechanical power in form of pressurised fluid. The structure required to

pressurise and distribute the hydraulic oil is comprised of mechanical components

including pressure pumps, pipelines and valves.

Electric system on the other hand can easily be considered as less mechanical. Power

is distributed by means of electric cabling and all in all there are very few mechanicalparts in the system. The only mechanical part of the system is the power transmission

from electric motor to impeller via a shaftline.

As a result of a more complicated basic concept, hydraulic system requires more

maintenance than electric system. There is a difference in the amount of continuous

maintenance required, but this difference is really not relevant from the shipowners

perspective. Differences in the need for continuous maintenance are not big enough

to require a bigger crew, so the theoretical difference does not come with any actual

extra labour costs.

What is important from a shipowners perspective, is both the amount of

unscheduled off-hire days due to failure of cargo system and required spare part

costs. These are the two maintenance-related factors which are relevant and which

directly contribute to the bottom line as reduced revenues and added costs. These

items are analysed, estimated and discussed in chapter 4.2.

It can also be argued, that reduced continuous maintenance requirement of the

electric system enables more preventive maintenance to be done. Hard economical

figures of such a benefit are difficult to present, but the fact is nevertheless worth

taking into account.

3.9 Structure

Structural solutions in the two pump concepts differ somewhat. In hydraulic system

the pump head and the motor running it are both submerged at the bottom of the

tank. In electric system the electric motor is located on main deck and the pump head

is driven by a long shaft.

Hydraulic pumps only structural benefit is, that its motor is located very near the

pump head. The shaft driving the pump head is only a half to two meters long and

therefore not subject to excessive alignment requirements for example. The hydraulic

motor is driven by high pressure hydraulic oil in 250+ bar, and lubricated by the


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return hydraulic oil. All parts of a hydraulic pump needing lubricating are actually

lubricated by the hydraulic oil.

Electric pumps motor on the other hand rests on the main deck and the pump head,

at the bottom of the tank, is driven by a shaft. Shafts bearings are lubricated bypumps own oil reservoir. The oil used to lubricate the bearings is actually the same

kind of oil as the one used in the hydraulic system as the hydraulic oil. So just as in

the hydraulic system, all lubricating needing parts of the system are lubricated by a

designated lubricating oil.

Electric systems structural drawback when compared to the hydraulic system is in

its long shaft. In reference vessels the shafts are 8 100, 9 100 and 15 300 mm in

length. They are all supported by one intermediate support to the ships structures,

while the longest of the three shaftlines has two such supports. The only drawback in

having a long shaft is increased possibility of torsional vibrations. However, withgood design this can be avoided.

The long shaft will not make any problems during normal or abnormal operation. In

the event that the pump head is being damaged, the long shaftline behaves in an

identical manner to the short one. The long shaft is supported by bearings at the top

of pump head and connected to a short shaft driving the impeller. In case the impeller

inside the pump head becomes damaged and unevenly balanced, resulting is a

vibrating mass at the end of a short shaft in both cases. In such a case the hot spots

would be the top of the pump head and the connection of pump and main deck. Also

in this case the only difference between the two systems lies in torsional vibrations.

On the other hand, damaged pump motor is more easily repaired in the electric

systems case. As the hydraulic motor is located down in the tank, the electric

systems pump motor is conveniently on main deck, where it is more easily

accessible.

3.10 Contamination of cargo

Protection against contamination of cargo has been taken care of identically in both

of the systems. In hydraulic system the high pressure hydraulic oil pipe is surrounded

in the tank by the lower pressure return pipeline up to the main deck. In electricsystem the shaftline is surrounded by lubricating oil. The only difference is, that

electric systems oil is not pressurised, where hydraulic systems oil is under about

10 bar pressure.

In both systems there is a contaminating preventing cofferdam surrounding the

lubricating/hydraulic oil and separating it from the cargo tank. Operating manuals of

both systems require purging of the cofferdam once during each trip, for that possible

leakage is detected.

It is of course also possible, that lubricating or hydraulic oil is contaminated bycargo. In electric systems case only one pumps bearings and shaftline would be


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amount of emissions per energy consumed is equal. The more energy consuming

system thus also causes more indirect emissions.

Additionally, during abnormal operation the hydraulic system may emit hydraulic

oil. Hydraulic pipelines are located on main deck, where they regularly come intocontact with the salty seawater. As time passes they will slowly rust and start to leak.

Obviously, in a particular ship it is possible to construct the entire pipeline with

stainless steel and to maintain it well enough to prevent it from leaking. But since on

the average the hydraulic systems leak oil into the worlds oceans, from LCAs point

of view these are emissions caused by operating the hydraulic system.

Emissions of hydraulic oil are very inconvenient, especially if they take place in

harbour or near the coast line. Such incidents are never good for business and always

bad publicity. National procedures in case of an oil spill differ somewhat, but as a

ground rule it can be said, that an oil spill in a developed country will irrevocably getthe attention of authorities.

Manufacturing of the two systems does not seem to contain any significant

differences. Both systems include quite similar electric motors and steel and stainless

steel parts. Possible differences lie in frequency converters and in hydraulic

powerpacks and pipes. Without more in-depth knowledge of differences in the

manufacturing processes and transportation needs it is impossible to conclude

anything more definite.

Based on the information available, nothing very definite can be said about disposing

of the systems either. Like in manufacturing, similarities lie in the electric motors

and in steel and stainless steel parts. Differences lie in disposing of frequency

converters, hydraulic powerpacks, pipes and the hydraulic oil.

As a conclusion it can be said, that environmental aspects connected in operating the

system clearly favour the electric system. It can also be concluded, that there are no

environmental aspects favouring the hydraulic system. A claim of hydraulic systems

higher environmental friendliness can thus not be substantiated. On the other hand,

claim of electric systems higher environmental friendliness does have merit.

3.12 Summary

Table 9 summarises and presents results of technical comparison between the two

systems.


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Table 9 Summary of technical comparison

hydraulic system electric system

energy consumption requires more energy tooperate

requires less energy to

operate

space requirementoutside cargo area(excluding cargo control)

36 m2

in vessel A36 m

2in vessel B

80 m2in vessel C

17 m2

in vessel A13 m

2in vessel B

18 m2in vessel C

weight of system 37 ton in vessel A37 ton in vessel B

79 ton in vessel C

32 ton in vessel A

25 ton in vessel B

75 ton in vessel C

noise makes high pitched noise no noise problems

control individual stepless control,nominal torque available

for all cargoes,

number of concurrently

operated pumps limited bysize of powerpack

individual stepless control,

nominal torque available

for all cargoes,

in a diesel-electric ship all

pumps can be concurrentlyoperated

emergency pumping easily possible in case thepressure pipeline or

powerpack is not damaged

always easily possible,

even if the entire main

pumping system is

destroyed

redundancy fair redundancy,can be increased with a

moderate effort

good redundancy,

can be increased with an

easy effort

maintenance requires more

maintenance

requires less maintenance

structure impeller driven by a shortshaftline

pump motor more difficult

to access

long shaft more sensitive

to torsional vibrations

pump motor easily

accessible

contamination of cargo cargo well protected cargo well protected

environmental aspects environmental friendlinesscan not be substantiated

more environmentally

friendly due to operational

aspects


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4. ECONOMICAL COMPARISONS

This chapter presents the cost calculations. The text itself contains all basis and

initial assumptions used in calculations as well as the final results. An interestedreader will find more detailed calculations and all relevant intermediate results in

Appendix 1.

4.1 Initial costs

Initial costs are best divided in two parts, in purchase costs and in installation costs.

Purchase cost is the amount of money a shipyard or owner has to pay to the system

supplier for a typical scope of supply. Purchase cost includes all required equipment,

but not the installation.

This part of initial cost is of course very much dependant on the market situation and

competition. The estimates of purchase price can therefore somewhat differ from

quotes shipyards and owners receive. On the other hand, this part of cost estimation

is the easiest one to replace in yards/owners own calculations, as the actual purchase

price will be clearly expressed in offers they receive.

Purchase prices of electric systems are the actual offers Hamworthy Svanehj

made for the reference vessels. Purchase prices of hydraulic systems are calculated

based on Deltamarins price data. Table 10 at the end of this subchapter presents all

initial costs in one table.

When estimating installation costs it has been assumed, that the reference vessels

would be built in the Far East. For this reason average labour cost and productivity

figures applicable to South Korea have been used. In the following basis for used

figures are explained, while the figures used can be found in Appendix 1.

Specific price of labour has been calculated by dividing the average monthly

wage in the South Korean manufacturing industry2by average monthly working

hours3 and by adding social costs of 15%

4. Average South Korean shipyards

overhead cost of 20%, based on Deltamarins own experience, has also been

added to the average hourly wage.

Required length of hydraulic piping is easily calculated when vessels main

dimensions and typical lay-out drawings are known. However, choice of pipe

material is up to the owner. While some owners require all pipes to be made of

2 Principal Economic Indicators, 10. Employment & Wages, National Accounts. Bank ofKorea. Republic of Korea 2005.

3

South Korea, Foreign Labor Trends. California Trade and Commerce Agency. USA 1997.4Embassy of Republic of Korea to Finland.


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stainless steel, some are satisfied with all pipes being made of steel. To represent

somewhat typical solution the pressure pipes are calculated as steel pipes and the

return pipes as stainless steel pipes.

Pipe installation efficiency is based on Deltamarins own experience. The statedefficiency for the given average pipe size includes all working phases required,

like installation, connecting, flushing, cleaning and testing. Installation efficiency

of stainless steel pipes is clearly smaller than that of steel pipes.

Required area of Powerpack Rooms is calculated by fitting the required number

of hydraulic power packs into the rooms.

Required area of Converter Rooms is calculated from lay-out drawings of the

converters, supplied by Hamworthy Svanehj.

Required volume of Hydraulic Oil Storage Tank is calculated from volume of the

hydraulic oil system. The Hydraulic Oil Waste Tank is assumed to be 10% bigger

than the storage tank.

Steelwork efficiency is based on Deltamarins own experience for typical steel

structures required to form boundaries for Powerpack and Converter Rooms and

Hydraulic Oil Tanks. Yards specialised in building cargo ships typically achieve

efficiencies as high as 20 to 30 h/ton, but these figures are applicable to only hull

structures with high plate thickness.

Lubricating oil of electric pumps is the same oil as is used as hydraulic oil in the

hydraulic system. Amount of lubricating oil is calculated from Hamworthy

Svanehj service manual and amount of hydraulic oil is calculated from the

volume of the hydraulic system (twice, as the storage tanks needs to be filled as

well). Price of lubricating/hydraulic oil is that of Shell Tellus 46 in March 2007.

Pumping system supplier provides its part of commissioning in a standard scope

of supply. It has been assessed, that there are no differences between the two

systems with respect to yards labour requirements in installing the pumps.

Need for cables and cable trays can be calculated as easily as the need for

hydraulic piping from the vessels lay-out drawings.

Cable installation efficiency is based on Deltamarins own experience and is

expressed as labour required per cable tray length. Approximately a third of the

cost of cable installation comes from installing of cable trays and mechanical

shielding, a third from making connections and a third from cable installation and

packing.

Specific prices of hydraulic piping, shipbuilding steel, cables and cable trays are

those of suppliers of these products.


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Table 10 shows the results, when all of the above data is applied to the reference

vessels. All figures are presented in USD and rounded. More detailed figures can be

found from Appendix 1.

Table 10 Initial costs (all figures in USD, rounded)

4.2 Operating costs

Operating costs are best examined, when they are divided into two main parts. The

first part includes running costs associated with power production for the cargo

handling system. These costs can further be divided into fuel oil, lubricating oil and

maintenance costs.

Calculating these costs is quite straight forward, as the annual power consumption is

a direct result of energy consumption and operating profile. Specific fuel and

lubricating oil consumption per power produced are both commonly available and

known figures. The specific maintenance cost of power plant is a figure based on

Deltamarins own experience and includes both spare parts and labour required to

maintain the power plant on an average.

The second part of operating costs consists of costs incurred by the cargo handling

system itself. As already discussed in chapter 3.8, differences in the need of

continuous maintenance are not included in this calculation. Because there are no

differences in crew requirements, neither system comes with any actual extra direct

maintenance related labour costs.

However, from shipowners perspective the amount of unscheduled off-hire days due

to failure of cargo system is very important. Similarly, required spare part costs are

very relevant as well. Both of these directly contribute to the bottom line as reduced

revenues and/or added costs.

Hydraulic systems average spare part costs can be reliably estimated based on

shipowners experience. Dividing annual fleetwide hydraulic systems spare part

costs by theoretical maximum pumping hours (annual pumping hours times number

of pumps) a reliable specific cost figure is obtained. Such a calculation yields

hydraulic systems specific spare part cost, which is presented in Appendix 1. When

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this figure is applied to theoretical maximum pumping hours of reference vessels,

estimated annual spare part cost per vessel is achieved.

Electric systems spare part costs can be estimated by analysing servicing intervals of

different parts of the system. In an electric system there are very few servicing orreplacing needing parts. The only regularly replacing needing parts are the shaft seals

of the pumps, which needs to be changed at certain intervals depending on the actual

cargo operating condition of the vessel. In addition to this the shaft lubricating oil

will need to be drained and refilled at the same time. For the purpose of this study, it

is assumed that the shaft sealings will need replacing a total of three times in the

vessels 20 years economical lifetime. No other mechanical parts in the pump system

need replacing. The other wearing mechanical parts are the shaft and electrical motor

bearings and converter cabinet cooling fans. During a normal vessels lifetime none

of these parts is forecasted replacement.

However, it is unrealistic to assume, that electric system would be this trouble free.

In any case there are problematic individual products and unforeseeable events,

which cause spare part costs. Although there have been only few problems with

modern electric motors and although field failure rate of frequency converters is

below 1%, for the sake of a realistic evaluation, unexpected spare part costs have to

be considered.

To be on a safe side, the unexpected spare part costs are best over-estimated. For the

purpose of this study it is assumed, that in all three reference vessels a major failure

of electric system occurs after 20 000 theoretical maximum pumping hours. Lets

further assume, that this major failure is in the magnitude of one frequency converteror electric motor being completely destroyed and in need of replacing. By assuming

this very high failure rate it is possible to compare electric systems spare part costs

with the actual spare part costs of hydraulic system.

When operated, the pumps consume some lubricating and hydraulic oil. According to

service manual the electric systems pumps shafts lubricating oil needs to be

replaced after 2 000 hours of operation. This oil changing interval has been used to

calculate the pumping systems oil costs.

There is no fixed hydraulic oil changing interval in the hydraulic system. On regularbasis oil samples need to be taken to monitor the oil quality. However, 2 000 hours

of operating is a good average estimate for the hydraulic oil changing interval. Table

11 presents all the relevant annual operating costs.


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(' ! * ! +,- .

Difference in the amount of unscheduled off-hire days due to failure of cargo

handling system is also an important operating related cost. Off-hire is expensive, as

through lost revenues it can directly be seen in the bottom line. Unfortunately

though, reliable and objective data on the average off-hire days is not available.

Average spare part costs, for example, could be used to estimate the difference, but

no such estimations are included in these calculations.

4.3 Total economy

Total economy of the two different cargo handling systems can be calculated, as both

initial and annual operating costs are known. For the purpose of estimating the one-

time initial payment and recurring annual payments, some method needs to be used

to consider both of these costs equally and to account for the time factor and price of

money.

The method used considers the initial one-time payment as a loan. The loan is paid

back in partial payments of similar sizes during the economic lifetime of the vessel.

This partial payment can directly be added to annual operating costs as capital costs

and thus total annual costs are obtained. Table shows results of such a calculation

with assumptions of 8% as the applied interest rate and 20 years as the economic

lifetime of the vessel.

Table 12 Total economy as annual costs (all figures in USD, rounded)

If in a given case the initial cost of one system is higher and operating costs lower

than it rivals, it is possible to calculate a payback time or break-even point. In none

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29/36



of the reference vessels this is the case, as the hydraulic system is more expensive in

light of both initial and operating costs.

4.4 Sensitivity analysis

These calculations are of course dependant on the initial assumptions made. By

altering the initial assumptions, or boundary conditions, different results are

obtained. In the following some initial assumptions and significance of altering them

are discussed.

Heavy fuel oil price has an effect on the annual operating costs. Because hydraulic

system needs more fuel, lower fuel price would favour it. Applied fuel price is quite

high historically, but altering it has very little effect on total economy. Even if HFO-

price would be halved, the basic results would not differ.

Alterations in operating profile have impact on all operating costs. As all operating

costs are higher in hydraulic system, the system would benefit from not using it.

However, significance of altering the profiles is quite small. Even if all the pumping

hours would be halved, basic results would not differ.

Price of labour has also influence on the final results. It does not affect the operating

costs, only the installation costs. As installing of hydraulic system requires more

labour, lower price of labour would favour it. But mere labour price change is

unrealistic, since the price of labour is dependant on the ships building country. As

there are great differences is prices of labour among the Far Eastern countries, alsothe efficiency of labour is different. As known, low price of labour usually correlates

with low efficiency.

However, to test the influence of change in price of labour, in calculations the price

can be changed without changes in efficiency. By lowering the price of labour even

by 70% from the South Korean actual value, there will be no differences in the final

results.

Interest rate applied in the total economy calculation has no effect on the final

results, even if the rate used would be 0.


30/36


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delta marin report - study of hydraulic and electric driven deepwell cargo pump options 190407

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