The influence of liquid cargo properties on the discharge rate of submerged cargo pumps with hydraulic drive on modern product and chemical tankers

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T H E A R C H I V E O F M E C H A N I C A L E N G I N E E R I N G

VOL. LV 2008 Number 2

DOI: 10.24425/ame.2008.131620

Key words: product tankers, chemical tankers, hydraulics, flow control, drive, liquid cargo properties

_ANDRZEJ_ _BANASZEK_ ∗

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE

DISCHARGE RATE OF SUBMERGED CARGO PUMPS WITH

HYDRAULIC DRIVE ON MODERN PRODUCT

AND CHEMICAL TANKERS

The paper presents the influence of different liquid cargo properties on discharge
rate of hydraulic submerged cargo pumps on modern product and chemical tankers
is presented in the paper. Main parts of submerged cargo pumps and hydraulic drive
system are described. Some examples of technical solutions of the described systems
installed on board of the newly building constructed ship m/t ‘Helix’ are presented.
The formula of use application of flow and drive characteristics of cargo pumps is
given. These characteristics were made derived for a basic cargo (fresh water) for
the case of the service of a real cargo of different viscosity and density.

1. Introduction

In the 20 _th_ century, the majority of petroleum-based liquid cargoes and
chemicals are transported by sea. This is the result of large distances between
the locations of refineries, petroleum terminals, and the industrial centers in
the USA, Europe or in the Far East. Moreover, there are specialized ships,
called the product and chemical tankers, which are used for transporting these
liquid cargoes. The structure of the above mentioned vessels is characterized
by partition of the loading- part into many separate, smaller cargo tanks.
Additionally, each cargo tank is equipped with a separate submerged cargo
pump, designed for liquid cargo service. Such an idea of cargo system allows
for simultaneous transport of diverse liquid cargoes during one sea voyage.
The described cargo installation, with many different segregations on board,
is very flexible in operation. It permits better use of cargo tanks capacity and

∗ _Technical_ _University_ _of_ _Szczecin,_ _Faculty_ _of_ _Maritime_ _Technology;_ _Al._ _Piastów_ _41,_
_71-065_ _Szczecin,_ _Poland;_ _E-mail:_ _andrzej.banaszek@ps.pl_

174 ANDRZEJ BANASZEK

better adjustment to individual requirements of customers and brokers. It is
worth noticing that in a typical harbor, there are many different liquid cargoes
that are transported by the sea, however, the quantities of these products are
small. It results from growing diversification and strong competition on the
freight market of liquid cargoes transported by the sea. On the other hand,
transport of special cargoes (e.g. toxic, dangerous, aggressive ones) brings
high profits to the shipowner, although such cargoes usually appear in small
quantities in standard harbours. Therefore, the above-mentioned cargo system
solution enlarges the competitiveness of such a product and chemical cargoes,
and increases its profitability in exploitation. The example of such type tanker
is the product tanker of B578-I/1 class, m/t ‘Helix’, built in the Szczecinska
Shipyard S.A. (Szczecin, Poland) for the well-known ship-owner ‘SHELL’
from Australia (see Fig.1). The above mentioned tanker is equipped with 20
separate cargo tanks of various capacity (from 1534.4 - to 4719 [m3]) and

Fig. 1. View on the product tanker B578-class m/t “Helix” built in Szczecinska Shipyard /Poland

for the Owner SHELL                  - Australia

two slop tanks (with a capacity of 253 - 471.9 [m3]). Cargo tank system
is served by 20 separate FRAMO/Norway submerged cargo pumps. 16 of
them have nominal discharge flow of 500 [m3/h] with load of 135 [mlc] sp.g. 0.85 and kinematic viscosity of 1.0 [cSt], and 4 pumps - 300 [m3/h]
each. Additionally, two slop tanks are served by 2 cargo pumps of discharge
flow 200 [m3/h] each. However, the a/m cargo pumps are mounted inside the
cargo tanks in a dangerous environment due to the possibility of explosion

[3],[4],[5]. Therefore, a hydraulic drive system is commonly used there, as
it is safer than the alternative solution with electric motors. Because the
distance between cargo pumps and other hydraulic receivers mounted on the

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 175

deck is not too long, individual hydraulic feeding systems are, in this case,
too expensive [6] and are not applied in the shipbuilding practice. As a more
convenient one, the hydraulic central loading system is installed.

Cargo pumps are usually of centrifugal 1-stage type. They are designed
for direct installation inside the cargo tanks. The structure of a/m pumps with
hydraulic drive is shown in Fig.2. The main elements of the pumps are: the
head of pump, the concentric hydraulic lines with cargo discharge pipe and

Fig. 2. View of typical hydraulically-driven submerged cargo pump

the deck trunk with a hydraulic control block and connection ports to the
cargo deck installation, and other (e.g. hydraulic) service installations. In the
head, situated in the lower part of the pump, there is an impeller driven by
the hydraulic motor. As the rule, in this type of cargo pumps, a high speed
axial piston, hydraulic motors of constant displacement are mounted. Usually,
due to the required high service reliability and extremely difficult working
conditions inside the cargo tanks, there are used motors of A2FM type made
by Bosch Rexroth/Germany. The power of standard cargo pumps reaches the
level of approx. 200 [kW]. The hydraulic motor is powered by means of a
concentric pipe system, in which hydraulic oil flows from the control block

176 ANDRZEJ BANASZEK

mounted on the deck trunk. Such a construction, with the hydraulic drive
motor localized in the lower part of the cargo pump, makes it possible to
avoid an excessive noise and vibrations of the impeller drive shaft by reducing
its length to a minimum. Usually, a/m vibrations in classical long-shaft cargo
pumps with electric drive are caused by a bad state of the shaft bearings and
an unbalanced long-drive shaft. The liquid cargo, pumped by the impeller,
flows through the separate cargo pipe mounted in the pump structure to the
deck trunk connection port. At the end of the cargo installation, near the
pump, there is an installed cargo stop valve. It is used to cut the pump off
from the rest of the cargo system in the case of a pump damage. This valve
allows for executinge the stripping operation - removing the liquid cargo
remainders from the pump suction well and the pump interior cargo area.
The simultaneous drive of several cargo pumps requires the power reaching
up to 3000 [kW] and more. The hydraulic central loading system makes it
possible simultaneous and intependend feeding of many hydraulic receivers
with such a great total power. Therefore, the hydraulic central loading systems
mounted on board of modern product and chemical tankers, are counted
among the greatest hydraulic systems not only in the ocean technology, but
in the whole area of hydraulics, as well. A detailed description of this type
of hydraulic central loading systems was given in other papers by the author

[4],[5],[6].
There are many factors that influence the discharge flow of the cargo system.
The hydraulic drive and control adjustments are as important as the physical properties of the transported liquid cargoes, especially their density and
kinematic viscosity. This is the major problem for the designers of cargo
installations and their users, because the producers of cargo pumps give in
the catalogues only the flow performance characteristics pertaining to the
case of pumping a standard, basic liquid cargo, which, typically, is the fresh
or sea water. In the world literature there aren’t any mathematical algorithms
for calculation of drive and flow characteristics in the case of real liquid
cargoes. Referring to the influence of viscosity, many authors [7],[9] use the
results of Hydraulic Institute New York [10], which are published in the
nomogram form. Such an approach is impractical, because it requires that
the deck officers and fuel terminal staff supervising the unloading operations
of tankers should introduce manual corrections of drive and flow parameters,
and make necessary calculations. This situation can lead to errors in the staff
service, which could be extremely dangerous.

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 177

In this paper, the author presents a computing algorithm for determining
the influence of the liquid cargo density and kinematic viscosity on the change
of flow of cargo pumps and drive characteristics. The resulting change of flow
of the cargo system, in the case of shipment of some different liquid cargoes,
has also been shown. The presented computing algorithm can be also helpful
in more effective planning of works in harbour fuel terminals.

2. Density and viscosity range of the standard liquid cargoes in sea
transportation

The cargo pumps, destined for the service of liquid cargoes on modern
product and chemical tankers are, as it was mentioned above, of submerged,
centrifugal type, designed to direct montage inside cargo tanks. Physical
properties of the transported liquid cargoes have an influence on discharge
flow and drive loading value reached during the unloading operation. The
most important technical parameters characterizing the pumped liquid cargo
are its density, and the coefficient of kinematic viscosity. A cargo installation on board of product and chemical tankers must be appropriate for
serving a dozen of different cargoes during one sea voyage. The values
of density and kinematic viscosity of standard liquid cargoes in the sea
transportation market are presented in Table 1. It is important to remember
that the value of kinematic viscosity coefficient depends on temperature of
the liquid. Therefore, in Table 1 there are the values of cargo viscosity in
specific, standard temperatures. As it is shown in Table 1, standard liquid
cargoes in sea transport are characterized by a large variability of density
and the value of kinematic viscosity coefficient. Most of petroleum-based
liquid cargoes have a density smaller than fresh water, commonly treated
as the basic cargo in maritime area comparisons. However, the majority of
chemical liquid cargoes, especially acids, are characterized by much higher
density. An example: the density of sulphuric acid (98% liquid at temperature
20 [ ◦ C]) reaches 1830 [kg/m3]. The values of kinematic viscosity coefficient
of standard liquid cargoes are also quite diverse.

178 ANDRZEJ BANASZEK

Table 1.
Density and kinematic viscosity coefficient of standard liquid cargoes on sea transport market

[8],[12],[13]

Density
Name of liquid cargo [kg/m3] / 15[ ◦ _C_ ]

Temperature

Viscosity [ _cSt_ ]

[ ◦ _C_ ]

Crude Oil, Arabian Heavy,
887 37.8 8.5
Ras Tannura, Saudi Arabia

Crude Oil, Wilmington,
933 37.8 72.2
Long Beach, California USA

Crude Oil, Quiri,
959 37.8 164.0
Carpito, Wenezuela

SOR Heavy Fuel Oil (HFO) 940 15 40.0-70.0
SOR Light Fuel Oil (LFO) 830 15 1.0-2.0
Gasoline, Vehicle 710 15.6 0.7
Vegetable Oil (Oliva) 910 25 89.0
Hydraulic Oil Mobil VI = 146 859 40 15.0
DTE11M 100 3.7
MobilVI=141 879 40 46.0
DTE15M 100 7.9
Gear Oil, Mobil VI=140 859 40 120.0
Delvac 1MX2T 75W90 100 15.9
Mobil VI=139 870 40 310.0
80W140 100 31.2
Engine Oil, Vehicle 860 40 62.0
Mobil 1 10W-30 VI = 147 100 10.0
Glicerine 1136 0 10.6
20 5.4
Residual Fuel Oil 970 40 120.0
Sorbo 110 100 12.0
Methanol 790 0 1.1
60 0.4
Toluene 870 20 0.67
70 0.41
Benzen 900 20 0.72
50 0.49
Hydrochloric Acid 1161 0 2.7
(Liquid) 30 % 20 1.8
Sulphuric Acid (Liquid) 98% 1830 0 26.6
20 13.9

Generally, liquid cargoes transported by sea usually have higher viscosity
than fresh water ( 1.0 [cSt]). Particular cargoes, like gear oils, mazut or
bitumens, reach so great values of kinematic viscosity that it is necessary to
use intensive heating for their transport and shipment in [12]. In the case of
bitumen transport, the required minimum temperature reaches 135 degree of
Celsius. The deck officer, supervising the shipment operation in a harbour,
or ship cargo installation designers must take into account the value of liquid

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 179

cargo density and kinematic viscosity. Technical parameters of cargoes may
have an important influence on the shipment operation strategy. The value
of viscosity value of the transported cargo may decide about the start of
additional cargo heating, which is extremely expensive.

3. Flow and drive characteristics of typical submerged cargo pumps
with hydraulic drive

As it was mentioned in the introduction, the popular way of drive in cargo
pumps working in an area threatened with explosion, is the use of hydraulic
drive. Considering economical conditions, one realizes power supply of the
hydraulic equipment in the from of hydraulic central loading system [2][3].
The important technical parameters of the supply process in cargo pump
discharge flow control are:

_pG_   - working pressure value in hydraulic supply system
∆ _pS_  - drop pressure in cargo pump hydraulic motor.
The first parameter- working pressure in hydraulic system is defined as
the output pressure of the hydraulic main power pack unit. Its value can be
adjusted by means of p=const common main pump controller, installed directly on the power pack in the power pack room [2]. The value of _pG_ should
not be lower than the total pressure drop in hydraulic motor (most loaded
hydraulic receiver in the hydraulic system) ∆ _pS_ and hydraulic installation
with control valves on way of hydraulic oil flow. The next parameter ∆ _pS_
can be adjusted by means of the constant torque controller, located on the top
of each cargo pump. The values of both parameters, can be remotely adjusted
by deck officer using the control panel mounted in Cargo Office Room, or
by the managing computer. The flow and drive characteristics of a typical
submerged cargo pump, powered from hydraulic central loading system, are
presented in Fig.3. They were determined for cargo pump of FRAMO SD125
type, at fresh water as basic liquid cargo with a density of 1000 [kg/m3] and
kinematic viscosity coefficient ν = 1 [cSt]. The presented characteristics are
very important in practice, because the deck officer on board, who is responsible for unloading operation, has at his disposal in ship’s office only flow
and drive characteristics determined for basic liquid cargo (i.e. fresh water).
The real cargo transported at sea by tanker has usually different density and
viscosity than those of basic cargo. As it was mentioned in the previous
papers by the author [1][2], the density and the viscosity have an essential

180 ANDRZEJ BANASZEK

Fig. 3. Flow and drive characteristics of submerged cargo pump FRAMO SD125 type with

hydraulic drive for basic cargo      - fresh water sp.g=1.0, viscosity ν = 1 [cSt].

influence on the value of the load torque on the cargo pump impeller. This
is the result of the occurrence of viscosity friction between the liquid cargo
layers and the impeller blades and the pump body.
The weight and inertia of cargo has also some influence on the shaft drive
torque. This influences has a strongly non-linear character. Therefore, drive
and flow characteristics presented in Fig.3, prepared for basic cargo, are
not valid in the case of pumping other liquid cargoes. In shipping practice,
deck officer relays on nomograms nomographs established according to the
requirements of the Hydraulic Institute New York (HINY). The officer prepares suitable proof-corrections for flow characteristics determined for basic
cargo. All the corrections are introduced manually by deck officer based on
traditional nomographs from the literature (Troskolanski, Łazarkiewicz [7],
Jędral [9]). This is an important disadvantage of this approach.

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 181

4. Calculation of pump flow and drive characteristics in the case of real
liquid cargo pumping with different density and kinematic viscosity

4.1. Mathematical model

The analyzed cargo system contains submerged cargo pumps with hydraulic drive, mounted directly in the cargo tanks. The hydraulic drive is
powered from the hydraulic central loading system. This supply system is of
constant pressure type with main power pack unit equipped with the controller of p=const. [3][5]. Each pump is connected in parallel to the main
line of supply system. To control the operation of pumps, the constant torque
controller is mounted on the inlet of hydraulic oil flow to the cargo pump.
The hydraulic diagram of the analyzed hydraulic system is presented in Fig.4.
It illustrates the pressure losses at the hydraulic oil flow from the main power
pack unit to the hydraulic motor of the cargo pump.

Fig. 4. Hydraulic oil pressure drops in supply process of cargo pumps hydraulic motor

The value of pressure drop in the hydraulic motor ∆ _pS_ is defined as :

∆ _pS_ = _p_ 1 − _p_ 2 [bar] (1)

where : _p_ 1 - inlet pressure to the hydraulic motor,

_p_ 1 = _pG_        - ∆ _pRP_        - ∆ _pZO_        - ∆[ _REG_ [bar] (2)

_pG_ [bar] - working pressure of main hydraulic power pack unit
∆ _pZO_ [bar] - pressure drop in ball valve (we can neglect this value as

small in comparison to other components ∆ _pZO_ ≈ [13])

182 ANDRZEJ BANASZEK

∆ _pREG_ [bar] - adjusted value of pressure drop in constant-torque

controller
∆ _pRP_ - pressure drop in hydraulic main pressure line- we can

calculate this value, according to [15], from the following
equation:

- _m_

_j_ =1

_i_, _j_

_i_

- ρ _h_ - ν2
2 +

∆ _pRP_ =

- _n_

_i_ =1

λ _i_ - _li_

_di_

ζ _j_ - ρ _h_

ν 2

_j_

ν 2

_j_
; ν _i_, _j_ = 4 _Qi_ , _j_
2 π · _d_ 2

_i_,

π · _d_ 2

_i_,

(3)

where:

i - number of hydraulic resistance element of linear type in

hydraulic pressure line,
j - number of hydraulic resistance element of local type in

hydraulic pressure line,
n - total number of hydraulic resistance elements of linear type in

hydraulic pressure line,
m - total number of hydraulic resistance elements of linear type in

hydraulic pressure line,
λ _i_ [–] - coefficient of pressure losses in i _th_ resistance element of linear

type in pressure line
_li_, _di_ [m] - length and diameter of i _th_ - resistance element of linear type

(hydraulic pipe) in pressure line
ρ _h_ [ _kg_ / _m_ 3 ] - density of hydraulic oil
ν _i_, _j_ [m/s] - hydraulic oil velocity in

i _th_ - or j _th_ - resistant element in pressure line
_Qi_, _j_ [ _m_ 3 / _s_ ] - hydraulic oil flow in i _th_ - or j _th_ - resistant element in pressure

line
ζ _j_ [–] - coefficient of pressure losses in jth- resistance element of local

type in pressure line

We can determinate the outlet pressure in the hydraulic motor from the
following formula:

_p_ 2 = _pZP_ + ∆ _pZZ_ + ∆ _pRR_ [bar] (4)

where:

- ∆ _pRR_ [bar] - pressure drop in hydraulic main return line

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 183

- _m_ 1

_j_ 1=1

_i_ 1, _j_ 1

_i_ 1

- ρ · ν2
2 +

∆ _pRR_ =

where:

- _n_ 1

_i_ 1=1

λ _i_ 1 · _li_ 1

_di_ 1

ζ _j_ 1 · ρ ·

ν 2

_j_

2

_j_ 1
; ν _i_ 1, _j_ 1 = 4 _Qi_ 1, _j_ 1
2 π · _d_ 2

π · _d_ 2

_i_

(5)

il - number of hydraulic resistance element of linear type in

hydraulic return line,
jl - number of hydraulic resistance element of local type in

hydraulic return line,
n1 - total number of hydraulic resistance elements of linear

type in hydraulic return line,
m1 - total number of hydraulic resistance elements of linear

type in hydraulic return line,
λ _i_ [–] - coefficient of pressure losses in i _th_ resistance element of

linear type in return line
_lil_, _dIL_ [m] - length and diameter of il- resistance element of linear type

(hydraulic pipe) in return line
ν _il_, _jl_ [m/s] - hydraulic oil velocity in il- or jl- resistant element in return

line
_Qil_, _jl_ [m/s] - hydraulic oil flow in il- or jl- resistant element in return line
ζ _i j_ [–] - coefficient of pressure losses in jl- resistance element of local

type in return line
-∆ _pZZ_ [bar] - pressure drop in non-return valve

(practice proves that [14],[15],[16] we can assume the pressure drop value
on standard spring valve of this type as:

∆ _pZZ_ ≈ _const_ . = 0.5 [bar]

- _pZP_ [bar] - pressure value in support relief valve in filling -up system

of main hydraulic power pack unit

In the case of the above described product tanker m/t ‘Helix’, the value of
support valve pressure amounted to:

_pZP_ = 4 [bar]

Constant-torque controller establishing hydraulic oil flow to hydraulic motor
of cargo pump works in 2 ranges:.
In the first range, the pressure drop value in hydraulic motor is as follows:

184 ANDRZEJ BANASZEK

_p_ 1 − _p_ 2 < ∆ _pSN_ [bar] (6)

where:

∆ _pSN_ [bar] - adjustment pressure in the constant-torque controller of

a the nominal hydraulic oil pressure drop in the motor

then the controller acts as the flow regulator maintaining the constant flow
of hydraulic flowing to the hydraulic energy receivers. In this case, ignoring
volumetric losses in hydraulic motor, we can assume that the rotation speed
of cargo pump impeller is constant, independent of the load of drive.
In the next performance range of the constant-torque controller, the following
formula is valid:

_p_ 1 − _p_ 2 = ∆ _pSN_ (7)

In this case, the controller adjusts the pressure drop ∆ _pREG_ so that the pressure drop in a hydraulic motor is maintained on the same level:

∆ _pS_ = ∆ _pSN_ (8)

In the classical approach, the deck officer should use the pump flow
and drive characteristics, determined for basic cargo, and the kinematic viscosity coefficient of current liquid cargo for manual calculations to set the
value of the following correction factors from nomographs given by the Hydraulic Institute New York [10] (see Troskolanski-Łazarkiewicz [6], Jędral

[8], Kutyrkin-Postnikow [17]):

_fQ_ - cargo pump flow correction coefficient [-]

_fQ_ = _Q_

_Q_ 0

[−−] (9)

where:

_Q_ [ _m_ 3 / _h_ ] - cargo pump flow at current liquid pumping
_Q_ 0 [ _jm_ 3 / _h_ ] - cargo pump flow at fresh water (basic cargo) pumping

_fH_ - pumping pressure (lifting height) correction coefficient of cargo pump

_fH_ = _H_

_H_ 0

[−−] (10)

where:

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 185

_H_ [mlc] - pumping pressure (lifting height) of cargo pump at viscous

liquid pumping
_H_ 0 [mlc] - pumping pressure (lifting height) of cargo pump at fresh

water (basic cargo) pumping
( mlc - meters of liquid cargo - unit of pumping pressure, popular in

liquid cargoes sea transport technology)

_f_ η - efficiency correction coefficient of cargo pump

_f_ η = η [−−] (11)

η0

where:

η [–] - total efficiency of cargo pump at current liquid cargo pumping
η0 [–] - total efficiency of cargo pump at fresh water (basic cargo) pumping

The driving power correction coefficient of cargo pump _fP_ can be determined, based on the dependencies (9),(10) and (11), in the following form:

- ρ
ρ0

_fP_ = _P_

_P_ 0

= _fQ fH_

_f_ η

[−−] (12)

where:

_P_ [kW] - driving power of cargo pump at current liquid pumping
_P_ 0 [kW] - driving power of cargo pump at fresh water (basic cargo)

pumping
ρ [ _kg_ / _m_ 3 ] - current liquid cargo density
ρ0 [ _kg_ / _m_ 3 ] - basic cargo (fresh water) density

In classical approach, the deck officer is forced to manually execute the
necessary calculations for every performance point of cargo pump separately.
It is troublesome. Additionally, this can result in many mistakes, which is
dangerous. Therefore, in order to automatize and accelerate calculations in
managing computer system in the deck office, it is better to use the algorithm
presented below.
In a modificated way, we can, according to vector record rules [11], define
correction coefficients vector f :

_fQ_ ( _Q_ 0, _H_ 0, ν)
_fH_ ( _Q_ 0, _H_ 0, ν)
_f_ η( _Q_ 0, _H_ 0, ν)

_fQ_
_fH_
_f_ η





(13)

f =



186 ANDRZEJ BANASZEK

The value of vector components can be calculated from the following
formula:

1
_ai_
for
1 + _bi_ - _e_ − _c_ _j_ · _xk_

_xk_ ≥ _xki_
_xk_ - _xki_

_fi_ =



where:
i = Q, H, η
_ai_, _bi_, _ci_ - proportional coefficients of characteristics for the

given cargo pump type
_xk_ = _xk_ (ν, _Q_ 0, _H_ 0) - influence function
_xki_ - critical value of influence function

The basic state vector in logarithmic co-ordinates S is :

(14)

(15)

ln(ν)

ln( _Q_ 0)
lm( _H_ 0)

_l_



S =



wherein:
ν [cSt] - liquid cargo kinematic viscosity coefficient
_Q_ 0 [ _m_ 3 / _h_ ] - cargo pump flow at fresh water (basic cargo) pumping
_H_ 0 [mlc] - pumping pressure (lifting height) of cargo pump at fresh

water (basic cargo) pumping

In the result, the basic state vector S can be use for calculation of particular values of influence function from the equation:

_xk_ = _xk_ (ν, _Q_ 0, _H_ 0) = K ∗ S (16)

where:
K - constant values vector.
One can determine the values of particular constants and vector components
on the basis of experimental flow characteristics and their simplified forms
of regression graphs (complying with basic state vector S ), for a given type
of cargo pump.
For example, for the cargo pump FRAMO SD type, assuming that the basic
cargo is fresh water with density equal ρ = 1000[kg/ _m_ 3 ] and kinematic
viscosity ν = 1.0 [cSt], one can evaluate these values as:

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 187

1.040 1.232 · 10 −3 - 5.233
1.023 1.214 · 10 −3 - 4.343
1.000 2.775 · 10 −3 - 5.551

_aQ_ _bQ_ _cQ_
_aH_ _bH_ _cH_
_aeta_ _b_ η _c_ η



(17)





{ _ai_ _bi_ _ci_ } =



K = {0.158     - 0.040     - 0.076 0.541}
(18)
{ _xkQ_ _xkH_ _xk_ η} = {0.652 0.652 0.295}

On the basis of the cargo parameters presented above (17)(18), the corrected drive characteristics of cargo pump can be determined from the following dependence:

∆ _pS_ = ∆ _pS_ 0 · _fQ_ · _fH_

_f_ η

- ρ
ρ0

(19)

where:

∆ _pS_ [bar] - pressure drop in hydraulic motor of cargo pump at current

liquid cargo pumping;
∆ _pS_ 0 [bar] - pressure drop in hydraulic motor of cargo pump at basic

cargo (fresh water) pumping.

When the value ∆ _pS_ exceeds the adjustment range of constant-torque
controller, the system will limit hydraulic the magnitude of oil flow affecting
the hydraulic motor of cargo pump in such a way that the dependence (8) i.e.
∆ _pS_ = ∆ _pSN_ will be fulfilled. The minimum value of performance pressure of
main power pack unit controller, i.e. adjustment of p=const. regulator should
be not less than :

_pG_ min ≥ ∆ _ps_ + ∆ _pRP_ + ∆ _pZO_ + ∆ _REG_ + _pZP_ + ∆ _pZZ_ + ∆ _pRR_ (20)

In order to avoiding the problems with stability of the controller, in
shipping practice, the value of regulator adjustment _pG_ is fixed on the level
of:

_pG_ = ∆ _ps_ + ∆ _pRP_ + ∆ _pZO_ + ∆ _REG_ + _pZP_ + ∆ _pZZ_ + ∆ _pRR_ + 10[ _bar_ ] (21)

4.2. Numerical calculations of corrected pump flow and drive
characteristics

For numerical calculations, we used the set of 5 different liquid cargoes,
among those three petroleum based cargoes and two acids as liquid chemicals

188 ANDRZEJ BANASZEK

(see table 2.). All cargoes are often met in maritime transportation. These
liquids are transported with the use of the described product and chemical
tankers. Special attention must be paid to the fact that petroleum-based cargoes (cargo No 1,2,3 ) are characterized by density lower than fresh water,
at the same time having much higher values of kinematic viscosity. The
properties of the chemicals are just quite opposite. In the analyzed case,
acids (cargo No 4 and 5) have kinematic viscosity almost the same, relative
to the basic value 1.0 [cSt], but with much higher density. The appreciation
of such a difference in technical properties- of liquid cargoes makes it possible to properly evaluate the influence the density and viscosity have on the
performance characteristics of the analyzed cargo pumps. As basic flow and
drive characteristic, we accepted the results of research on the cargo pump
FRAMO 125-5, performed for the basic cargo - fresh water with density
ρ _w_ = 1000[ _kg_ / _m_ 3 ] and kinematic viscosity coefficient value ν _w_ = 1.0[ _cSt_ ].

Table 2.
Technical properties of liquid cargoes used in the analysis

No of Densitykg/m3¿kg/m3 ViscositycSt¿cSt
Name of liquid cargo
Cargo

1 SOR Heavy Fuel Oil (HFO) 940 70.0
2 Crude Oil, Quiri, 959 164.0
Carpito, Wenezuela
3 Gear Oil, 870 310.0
Delvac 1MX2T
Mobil 80W140 VI = 139
4 Nitric Acid 1513 0.8
(Liquid)
5 Sulphuric Acid (Liquid) 98% 1830 13.9
6 Basic cargo    - fresh water 1000 1.0

THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 189

Fig. 5. Corrected flow and drive characteristics of cargo pump FRAMO SD 125 the in case of

pumping the following liquid cargoes:
Cargo No 1- Heavy fuel oil HFO ρ = 940−[ _kg_ / _m_ 3 ], ν = 70.0[ _cSt_ ]
Cargo No 2- Crude oil Quiri/Wenezuela ρ = 959−[ _kg_ / _m_ 3 ], ν = 164.0[ _cSt_ ]

Cargo No 3- Gear oil 80W140 ρ = 870−[ _kg_ / _m_ 3 ], ν = 310.0[ _cSt_ ]

Cargo No 4- Nitric acid ρ = 1513−[ _kg_ / _m_ 3 ], ν = 0.8[ _cSt_ ]
Cargo No 5- Sulphuric acid ρ = 1830−[ _kg_ / _m_ 3 ], ν = 13.9[ _cSt_ ]

We assumed the hydraulic controller adjustment value of nominal drop
pressure on hydraulic motor on the level of ∆ _pSN_ = 240[ _bar_ ] and a nominal
speed of cargo pump _n_ 0 = 2480 [rpm]. The results of calculations are shown
in Fig. 5.

5. Summary

The cargo system, designed for servicing liquid cargoes on modern product and chemical tankers, is based on submerged cargo pumps. These are of
centrifugal type with hydraulic drive. As they are installed in a dangerous
areas, threatened with explosion, the pumps are often powered from hydraulic
central loading system. This powering system is most effective and popular in
shipbuilding practice. Cargo pumps drive - and its flow characteristics with

190 ANDRZEJ BANASZEK

technical parameters, are provided by the producers only for basic liquid
cargo. Usually, it is fresh water with density equal to 1000 [kg/m 3 ] and kinematic viscosity coefficient of 1 [cSt]. Performance characteristics determined
in such a way are not applicable in the case of pumping liquid cargoes with
density and viscosity different than those of basic cargo. Therefore, the deck
officer or terminal operator supervising unloading operation should estimate
the corrected discharge rate value of cargo pump and cargo system. In order
to do it, is important to take into account liquid cargo properties especially including its density and viscosity. The algorithm for calculation of the
corrected flow and drive characteristics has been presented in the paper. The
most important conclusions from the presented analysis are as follows:

- The properties of pumped liquid cargoes, including density and kinematic viscosity, must be into account in calculations of the corrected cargo
pump flow and drive characteristics,

- The increased value of density of the pumped liquid cargo has an
essential influence on the load of the cargo pump in hydraulic drive, with
almost invariable cargo pump flow,

- The increased value of the pumped liquid cargo viscosity has a lower
influence on the cargo pump drive load than that of liquid density, and
deteriorates the performance flow characteristics of the pumps.

Manuscript received by Editorial Board, May 15, 2008

REFERENCES

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[3] Banaszek A.: _The_ _concept_ _of_ _capacity_ _control_ _of_ _hydraulic_ _submerged_ _cargo_ _pumps_ _in_ _liquid_

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[4] Banaszek A.: _Central loading systems on product and chemical tankers_ (in Polish). Hydraulika

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THE INFLUENCE OF LIQUID CARGO PROPERTIES ON THE DISCHARGE RATE OF... 191

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Wpływ własności ładunku płynnego na wydajność zanurzeniowych pomp ładunkowych

z napędem hydraulicznym na współczesnych produktowcach i chemikaliowcach

S t r e s z c z e n i e

W referacie przedstawiono wpływ własności różnych ładunków płynnych na wielkość wynikowej raty wyładowczej zanurzeniowych pomp ładunkowych z napędem hydraulicznym stosowanych na współczesnych produktowcach i chemikaliowcach. Opisano budowę głównych elementów
zanurzeniowych pomp ładunkowych oraz strukturę napędowego układu hydraulicznego. Zaprezentowano przykładowe rozwiązania omawianych systemów na nowo wybudowanym statku m/t ‘Helix’.
Podano formułę wykorzystania charakterystyk przepływowych i napędowych pomp, sporządzonych
dla ładunku wzorcowego (wody słodkiej), dla przypadku obsługi rzeczywistego ładunku - różnej
lepkości oraz gęstości.

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