Waste oil recovery unit

Waste oil on board ship is disposed of usefully by burning in the ship's steam raising boiler. Apparatus for rendering the waste oil burnable comprises a tank with waste oil and fuel oil and fuel oil inlets, a tank heater, a drain pipe and filter for separated water, an agitator, an external pipe and pump and pump for recirculation of waste oil and fuel oil through the turn and a bleed off pipe from the external pipe to the ship's boiler fuel supply line. Other liquid or finely powdered organic waste (e.g. kitchen waste) may also be disposed of in the system.

This invention relates to an apparatus and method for treating waste oils 
on board ships, particularly oil tankers, to enable the waste oil to be 
disposed of by burning in the ships' boilers. 
Waste oil and oily sludges can be accumulated on board ship in considerable 
quantities, and with environmental standards prohibiting the discharge of 
oil into the sea there is a need for a simple method of an board disposal. 
The waste to be disposed of can be oily sludge from centrifugal 
separators, with its relatively high water content; it may be spent 
lubricating oil from main or auxiliary machinery; it may be oil drained 
from scavenge air belts or piston underside drains containing carbon or 
other particulate matter; or it might be the oil skimmed from oily water 
bilge separators. 
Up till now this waste oil has had to be retained on board ship and then 
discharged at a port with facilities for handling and disposing of it. 
Alternatively, relatively expensive incinerators have had to be installed 
on board. It has now been found that, if suitably treated and handled, all 
the above forms of waste oil can be disposed of by burning in the main 
furnaces of existing ships' boilers using only the standard oil burning 
equipment. Apparatus for treating and handling the waste oil to enable it 
to be so disposed of has also been designed. 
According to the present invention apparatus for treating waste oil on 
board ship to render it suitable for burning in ships' boilers comprises a 
tank having a waste oil inlet and a fuel oil inlet, a heater and an 
agitator within the tank, on outlet near the base connected to an oil 
absorbent filter, an external pipe from near the base to near the top of 
the tank with a circulating pump, and a branch from the pipe to the ships' 
boiler fuel supply line. 
The invention includes a method of treating waste oil on board ship to 
render it suitable for burning in ships' boilers using the apparatus 
described above comprising holding waste oil in the tank at above 
atmospheric temperature to allow water to separate, withdrawing the water 
through the outlet and oil absorbent filter, optionally adding fuel oil to 
the remaining waste oil, agitating the contents of the tank to suspend and 
disperse non-dissolved solids and liquids, stopping the agitation, 
recirculating the contents of the tank through the external pipe and 
bleeding off waste oil from the pipe to the ships' boiler fuel supply 
line. 
The apparatus and method may be used to any ship having a suitable boiler. 
Even motor driven ships are likely to have a boiler for driving auxiliary 
equipment and a preferred use of the apparatus and method is on motor 
ships driven by relatively heavy diesel engines. Centrifugal separators 
are normally used to treat the fuel for the engines, and they remove about 
1% of sludge, which can then be disposed of according to the present 
invention.

In the drawing, the system comprises a tank 1 with a valved waste oil inlet 
2, a valved fuel oil inlet 3, and a vent pipe 4 to atmosphere. A heating 
coil 5 is supplied with steam through pipes 6. Valved outlet 7 near the 
base leads to filter 8 containing an oil absorbent filter material. The 
tank has an agitator 9 driven by a motor 10. Pipe 11 leads from near the 
base of the tank through a recirculating pump 12 and spring-loaded valve 
13 to the top of the tank and a branch 14 from pipe 11 leads to the main 
fuel oil supply line 15 of the ships' boilers, the line having, according 
to normal practice, a filter 16 and pumps 17. 
In operation, the waste oil is pumped through inlet 2 into the tank and is 
allowed to settle under the influence of heat supplied by coil 5. The 
temperature should obviously not exceed 100.degree. C. and may 
conveniently be from 50.degree. to 80.degree. C. The heating is desirable 
to increase the fluidity of the waste oil and encourage the separation of 
water which collects at the base of the tank. After a period of heating 
and settling, typically between 2 and 6 hours, free water is drained from 
the bottom of the tank through filter 8 containing oil absorbent material. 
Only free water is drained off; at the first appearance of oil droplets, 
draining is stopped. Water leaving the filter is relatively free of oil 
and may be run back to bilge for eventual transfer overboard via a 
conventional oily bilge water separator. Any oil accumulating in the 
filter can be recovered and returned into the tank. 
After the free water has been drained off, fuel oil may be added through 
inlet 3 to the waste oil remaining in the tank. The quantity of fuel added 
will depend upon the nature of the waste being treated and also upon the 
viscosity and calorific value of the fuel oil added. Heating may be 
maintained during the fuel oil addition and the subsequent agitation and 
recirculation periods. 
In general the amount of fuel oil added may be from one to two volumes of 
fuel oil/volume of waste oil. At any stage additives may also be 
introduced into the tank, if necessary, to break down difficult sludges or 
to promote good combustion. The type of additives that could be used 
include flow improvers, emulsifiers, smoke suppressants, deposit 
modifiers, and corrosion inhibitors. 
The combined waste oil and fuel oil contents of the tank, are then 
homogenised and emulsified by the agitator 9 possessing high shear 
qualities. An auxiliary propeller 18 may also be fitted to the agitator 
shaft in order to help promote good circulation in the tank. Simple tests 
carried out at intervals during the agitating process for viscosity, free 
water content and unacceptable particle size may be used to determine when 
the mixture is suitable for burning in the standard combustion equipment 
fitted to the boiler. With the usual types of waste oil, the period of 
agitation may be from one to three hours. 
When an acceptable quality has been reached, the agitator 9 is stopped and 
the recirculating pump 12 started. This pump, which is of a type having 
emulsifying and mixing properties, draws from the bottom of the tank 
through line 11 and discharges through spring loaded valve 13 to the top 
of the tank. The spring loaded valve imposes a back pressure of sufficient 
magnitude on the recirculating pump, to enable oil tapped off through line 
14 to overcome the pressure head prevailing at inlet 15 to the ships' 
boiler oil pressure pump system. Treated waste oil can then be blended 
into the normal supply of fuel from the ship's service tanks to the 
boilers or can even be used by itself as fuel for the boiler. The rate of 
recirculation through line 11 may vary considerably depending on the ship, 
the type of waste oil, and the size of tank 1. By way of illustration 
only, the rate may be from 80 liters to 200 liters/min. The rate of draw 
off through line 14 will depend on the consumption rate of the boiler and 
may also vary widely from ship to ship and time to time. 
A connection 19 may be provided for admitting sewage and finely ground 
organic kitchen wastes from the ship's sewage and kitchen waste disposal 
systems. These wastes can be treated, when required, with the waste oil 
for blending into the normal supply of fuel, from the ship's service 
tanks, for the boiler. 
In a specific example, tank 1 had a capacity of 1000 liters. Waste oil and 
water from the fuel and lubricating oil centrifugal separators was pumped 
into the tank and allowed to settle for four hours at 60.degree. C. before 
draining off separated water. An equal volume of 1800 seconds fuel 
oil/vol. of waste oil was then added and the mixture was agitated for 
three hours. The agitator incorporated a special cutting/disintegrating 
head supplied by Peter Silver Ltd., rotating at 3600 rpm and driven by a 
7.5 h.p. electric motor. When the viscosity had reached approximately 600 
seconds Redwood 1 (at 60.degree. C.) the agitator was stopped and the 
mixture was recirculated at a rate of 160 l/m against a back pressure in 
value 13 of 3 atmospheres. The recirculating pump was of hypocycloidal 
design, being Mono type SH60R6, supplied by F. A. Hughes & Co. Ltd. The 
mixture was fed to the ship's boiler system at rates varying between 2.6 
and 17 liters/min. and the mixture formed between 15-100% volume of the 
fuel oil fed to the boilers. Firing of the boilers on fuel containing 
waste oil continued for 33/4 hours without any malfunctioning or 
accumulation of deposits in the boilers or burners. 
In a long term trial, a unit as described in FIG. 1 was use on an 
operational oil tanker for 11 months. The tanker was of 25,000 dead weight 
tons and the main propulsion engine was a slow speed diesel engine built 
by Societe Anonyme Cockerill of Belgium and running on high viscosity fuel 
(3,500 seconds Redwood No. 1, maximum at 100.degree. F.). All the waste 
oil generated in the engine room, amounting to between 0.5 and 1.0% of 
fuel consumed, was passed through a unit as described in FIG. 1 and burnt 
in the main steam-raising boiler. This main boiler was of the dual 
pressure, water-tube type, burning high viscosity fuel (3500 seconds 
Redwood No. 1 maximum at 100.degree. F.) in the furnace of the primary 
section. The burners were steam assisted pressure jet burners working at 
fuel pressures of up to 30 bars, and the boiler had two main and one pilot 
burner to give a maximum steam output of 27.5 tonnes per hour while 
burning 2360 kilograms of fuel per hour. 
During the 11 months of operation, no additional maintenance was incurred 
as a result of burning the waste oil; boiler tube, burner and register 
fouling were no worse than normal, while burner tip wear and fuel filter 
blockage did not increase to any noticable extent. Neither did the limited 
amount of brickwork and refractory in the boiler deteriorate during the 
period. 
The above description is purely illustrative and the unit of the present 
invention is considered suitable for use with any type of boiler and any 
type of burner (including spinning cup burners) burning medium to high 
viscosity fuel.