FSO OKHA
1
P1231
HEATING SYSTEM FOR HAWSEPIPE
Heat Calculation
Hawse pipe
Hawse pipe particulars:
Affected Length
Inside Diameter
Wall Thickness
Outside Diameter
L
Di
Tp
Do
= 12000mm (12meters)
= 717.6 mm
= 22.2 mm
= 762 mm
Consider the inside wall of the pipe as a plate of dimension: L x W x Tp
: 12000 x π Di x 22.2
Area of This wall:
π Di L = 27.04 m2 → 290.95 ft2 ≈ 291 ft2
12000 mm
Tp = 22.2
T2
T1
+ 5° C
2253mm
-20° C
22.2
Heat flow across wall as:
T1
= -20° C or -4°F
T2
= +5 ° C or 41°F
∆T
= T2 - T1 = 25ºC or 45°F
Heat Transmission across Wall Section of Pipe:
Q
= U x A x ∆T
Q is Rate of heat transfer of Steel at 22.2 TBC
U = 33.75 Btu/hr/ft2/R in still Air
U is U value of wall(steel) = 33.75
A is Area = 27.04 m2 = 290.95 ft2
∆T is 25° C or 45°F
Q
= 33.75 x 290.95 x 45 → 441,880 Btu
Take 10% safety factor in above,
The heat load → 441,880 x 1.1
→ 486068 Btu/Hr
→ 142 KW heating
GB MARINE PTE LTD
SINGAPORE
FSO OKHA
2
P1231
Calculate heating Agent Flow from Calorifier through the I - tubes wrapped around:
As per ASHRAE:
Flow of heating agent
= total heat load / (500 x ∆T)
Where ∆T is temperature different between inlet and outlet of heating media via Tube &
Heaters.
We assume: inlet Temp → 200°F
Outlet Temp → 175°F
So ∆T → 25°F
But this is not the same as the Korean said, which is not practical at all >:
Flow of liquid / Agent
Heating agent flow rate
= Heat load / (500 x 25)
= 486068/ (500 x 25)
= 38.88 gpm
= 8.83 m3/Hr.
--- (ASHRAE)
Check Velocity at 8.83 m3/Hr → 12.20 m/sec → 2400 ft/ min→ Linear Flow
Tank Volume = 1.2 x 0.8 x 1.2H = 1.152 m3 = 1152 litres
Now we calculate the total surface area of heating coil required to transfer heat
of required amount through the 16 mm OD copper tube:
Surface Area
= Total Heating Load / Loading
Total Heating Load
= 486068
Loading (as per ASHRAE) = 550
As = 486068 / 550 = 883.76 ≈ 884 ft2
/
Pipe Diameter
= 16 mm = 0.0525 ft
Surface Area
= π D Lp
Where Lp → surface area(As) / π D = 884 / π D = 5362 ft = 1635 m
Add 10% safety factor on pipe → 1798 m → say 1800 m
GB MARINE PTE LTD
SINGAPORE
FSO OKHA
P1231
3
Check if this pipe can be wrapped around the Hose of 12m,
Figure
12000mm
12000 ÷ 16 mm pitch → 750 Turns → each turn at 2.5 m around hose pipe.
So, 750 x 2.5 → 1875 m of pipe is possible → OK
Observation
 Amount of Glycol remain over 1800m tube at all time
→ 350 ~ 360 litres heated at all time.
Observation/ Consideration
1)
2)
3)
4)
Temperature Gradient → 25°C or 45°F
Calorifier inlet/ outlet → 200°F / 175°F
∆T → 25°F
Not as suggested 70°C ???
Insulation must be improved to minimise loss due to any leak on tubes by rockwool of
Blanket type.
Exposed pipe/ tube from Calorifier to be insulated.
GB MARINE PTE LTD
SINGAPORE
FSO OKHA
4
P1231
Schematic of Piping
22.2 mm x 762 mm HOSE PIPE
Ckt 1
Ckt 2
Ckt 3
Ckt 4
Ckt 5
Supply
Header
Return
Header
200°F
From Calorifier
Total Tube length
175°F
To Calorifier
1800 meters on the body of the hose pipe
GB MARINE PTE LTD
SINGAPORE
FSO OKHA
P1231
5
COMMENTS
(1)
Glass wool thickness and density are not mentioned in the contractor quotation.
We recommend mineral glass wool blanket at about 4'' (100mm) thickness at
minimum 80 Kg/ m3 density.
(2)
All pipes, valves and fittings are to be suitably insulated.
(3)
It appears that there is a gap of 16mm between every turn of tubes. We do not agree to
this, as this will not be sufficient to cater for heat load. In other word, length of copper
tube as suggested by the contractor of 1,017m approximately to be substantially low.
We would recommend that there is no gap between the copper tube (length would be
approximately 1800m to 2000m).
(4)
In the calorifier specification, we note that temperature of Heating agent are
inlet: -20°C and outlet: + 50°C.
This seems to be not a reasonable figure as the temperature is extremely high to cause
any damage to calorifier internals.
It is only reasonable in calculation is to have ∆T about 20-25°F
Taking outlet → 200°F (93°C) of calorifier (inlet of supply Header) and
Inlet of calorifier as 175°F (79°C) which is outlet of return Header (See our
schematic).
(5)
Outlet from Calorifier to the hawsepipe should be installed from bottom to upwards.
(6)
Calorifier dimensions shown appear to be rectangular where as in description "type"
as vertical cylinder.
(7)
No comments are expressed on electrical heater and control parts for calorifier.
(8)
We assume that necessary pressure and temperature safety valve(s) will be arranged by
contractor.
(9)
We have not reviewed on overall pipes, fittings and valves etc., as we do not have any
layout, detailed drawings from vendor.
GB MARINE PTE LTD
SINGAPORE