GB2023646A - Method of Processing Sludge from Used Cold Rolling Mill Oil to Prepare it for Combustion, and a Fuel so Produced - Google Patents

Abstract

In order usefully to recover the organic liquid component (i.e. grease/oil) of the sludge produced in the separation of water from used cold rolling mill oil, the sludge is thoroughly mixed with water water oil and/or fuel oil, the ratio of the organic liquid component to the waste and/or fuel oil being at most 1:2. After settling of this mixture, the phase containing the oil and the organic liquid component is mixed with fuel oil and used for combustion. Sludge is pumped from the heated and stirred buffer tank 32 into the also heated and stirred mixing tank 33, to which fuel or waste oil (e.g. oil from engine sumps and transmission systems) is fed. Stirring in the tank 33 is for 1 DIVIDED 2 to 1 hour. At least 3 hours after the stirring stops, the phases have separated sufficiently to be drawn off separately. <IMAGE>

Description

SPECIFICATION Method of Processing Sludge from Used Cold Rolling Mill Oil to Prepare it for Combustion, and a Fuel so Produced This invention relates to a method of processing sludge derived from used cold rolling mill oil to prepare it for combustion, and to a fuel prepared by the method.

Cold rolling mill oil is used as the lubricant in a cold rolling mill. Palm oil or animal oil to which emulsifiers have been added, are mostly used as the main component. They solidify in their pure form at about 300C, which means that they must be stored and transported warm. The lubricant is applied to the steel strip and to the rolls during cold rolling as an oil-in-water emulsion. In order to maintain the optimum rolling temperature large quantities of re-circulated water are sprayed on to the back-up rolls, working rolls and the strip.

Emulsion and cooling water are discharged after use, together with metal particles and dirt particles produced during rolling.

Economic and environmental considerations require that the spent cold rolling mill oil component of this mixture is recovered and reused. The first separator of the oil, from the greater part of the water, is effected by gravity in a settling tank, from which the floating layer still containing water and solid dirt is separated and treated in centrifuges in order to achieve the best possible separation into the three phases of oil, water and a sludge with the solid dirt component.

This sludge may in a typical case contain 70% water, 27% of the lubricant stated and 3% solid dirt, the solid dirt including all those substances which do not dissolve either in water or in organic solvents. According to a chemical analysis this solid dirt may consist of 67 weight % Fe (on an elemental basis).

So far the only known method of processing the sludge is to burn it. However, this is expensive and gives rise to problems of a technical nature, because the normal domestic refuse disposal plants with grate furnaces are not suitable for the purpose, and the burning can only take place in rotating drum furnaces designed for the incineration of chemical waste matter.

The object of the invention is to provide an inexpensive method of processing the sludge of used cold rolling mill oil, so as to produce a readily combustible product, thereby making it possible to use the full calorific value of the organic liquid component of the sludge.

Another object of the invention is thus to provide a fuel incorporating the organic liquid component of the sludge.

The invention is based on the realization that the sludge, even when it contains a considerable proportion of water, can without difficulty be mixed with fuel oil or waste oil, and the mixture can subsequently be processed to provide a combustible mixture of the solvent oil (fuel oil and/or waste oil) and the organic liquid component of the sludge.

The method of the invention is characterized in that the solid dirt and water components of the sludge are separated from the organic liquid component, and the organic liquid component is mixed with waste and/or fuel oil in a ratio of at least 2 parts of waste and/or fuel oil to 1 part of organic liquid component, the mixture thus formed being for use as a fuel oil to be subjected to combustion subsequently.

While it is possible for the separation of the solid dirt and water components to take place prior to the mixing with the waste or fuel oil, it is greatly preferred in the practice of the invention that said waste and/or fuel oil is mixed thoroughly with the sludge prior to the separation of the solid dirt and water components.

By organic liquid component, there is meant the organic compounds, e.g. vegetable or animal oils or greases, which form a liquid component, generally immiscible with water, at the temperature of the process, and which therefore generally dissolve in the solvent oil component.

The solvent oil is generally a mineral oil which is heavier than the lighter hydrocarbons, such as petrol. It may typically be conventional fuel oil as is burnt in furnaces for heating purposes. Waste oil can be used instead of, or in admixture with, fuel oil and maybe derived from many sources, but particularly preferred are oils drained from the sumps of combustion engines and transmission systems, and oil from separation of oil/water emulsions.

The invention provides the advantage that the combustible part of the sludge removed from circulation in this way can be stored, transported and ultimately burnt in admixture with the fuel or waste oil, so that separate and expensive facilities for storage, transhipment and transport of the sludge at elevated temperature, and special burners for it need not be provided.

Since solidified grease cannot be pumped, cannot be mixed with oil, cannot be freed of dirt, and on account of its low heat conductivity cannot be melted except with difficulty, the processing of the sludge should take p;ace above solidification point until a homogeneous mixture with the fuel or waste oil has been obtained. No solidification has been observed in this homogeneous mixture, not even at temperatures down to just above the freezing point of water. In practice the mixture is, however, preferably kept at about 500C or higher.

The mixing ratio of grease (i.e. organic liquid in the sludge): oil of 1:2 or more has been determined in view of the desirability of avoiding separation of the oil phase after mixing. Lower mixing ratios do not provide the certainty that separation will not occur. Waste oil is preferably used as the oil mixed with the sludge because separation of the water and dirt components has been found more effective. Typically, the grease of the sludge has a specific weight of 0.96 while the admixed oil has the specific weight of 0.88.

After being stored in a tank following thorough mixing, the bottom layer which contains the water and dirt components is tapped off. The top layer consisting of the grease/oil mixture is still homogeneous after three days of standing completely still. This mixture for example may then be added, for instance by injection or pumping to hot fuel oil, particularly to fuel intended for soaking pits, blast furnaces etc. The fuel oil used in this case is a viscous mineral oil (dynamic viscosity 3500 s), which is stored at 70 to 900C in supply tanks and can be kept moving continuously in them.

Alternatively the organic component/oil mixture phase is removed from the settling vessel before the water and dirt layer.

Dutch published patent application No. 72 00621 describes a process of removal of oil and water from sludge, particularly the sediment at the bottom of tanks etc. in a refinery. The sludge is mixed with very light hydrocarbons (C4 and C5 are mentioned) and water is separated off; the hydrocarbons are then re-separated from the oil from the sludge. In the present invention, light hydrocarbons are not used, and this final separation is not performed.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which~ Fig. 1 is a block diagram of the supply discharge flows to and from a processing plant adapted for the performance of the method according to the invention; Fig. 2 is a block diagram showing the flows in one general embodiment of such a plant; and Fig. 3 is a diagrammatic view of a particular embodiment of plant adapted to carry out the invention.

The diagram of Fig. 1 indicates by the box Z a plant for performing the method of the invention which has the following input and output flows: I Supply flow of waste oil (e.g. 55% oil, 45% water or in another case 71% oil 29% water) derived from any suitable source or sources, II Supply flow of sludge (e.g. 70% water, 27% grease or oil, 3% solid dirt) originating (as described above) from the separating centrifuges for used cold rolling mill oil, Ill Discharge flow of oil/grease mixture, also called regenerate, which is to be mixed elsewhere with fuel oil for subsequent combustion, IV Discharge flow of water, V Discharge flow of solid dirt, to a sintering plant for iron ore.

Further details of one form of the plant generally described by Fig. 1 are shown in Fig. 2 in which the broken-line rectangle indicates the plant Z and the arrows I-V indicate the same flows as in Fig. 1. This plant has a sludge processing plant DV and a sludge tank DB. Sludge (Flow II) is conveyed to the sludge processing plant DV. As flow I, waste oil enters DV in amount to provide a weight ratio of oil: sludge of 2:1. The solid dirt which settles is separate from DV with the water via a pipe 4 and enters the sludge tank DB. Here sedimentaion of the dirt takes place; the solid dirt leaves the system as discharge flow V to a sintering plant for iron ore.The water separated in DB is conveyed via pipe 3 as flow IV to a plant for the treatment of oil/water emulsions, for instance of the type described in Dutch patent application 75.05875.

The oil/grease mixture from which solid dirt and water have thus to a large extent been removed is discharged from the plant Z via a pipe 8 as flow Ill and pumped together with fuel oil (flow S) into a fuel oil tank ST. In the tank ST and major part (over 90%) of the water introduced with the flow II separates; this water is also conveyed to the already mentioned oil/water separating plant (arrow EC) via a pipe 9. The water content in the fuel oil discharged for combustion (flow H) appears to be no more than a few tenths of a percent.

The mixing ratio of oil: organic liquid component (grease) of the sludge should as already stated amount to at least 2:1. Desirably, stirring to mix the oil and the sludge takes place for at least 0.5 h and preferably for 1 h or more, in order to obtain a sufficiently homogeneous mixture of oil and the organic component. After three hours of standing of the mixture in the tank DV, a reasonable separation between solid dirt, water and oil/grease mixture is obtained.

In the particular and preferred embodiment of Fig. 3, there is a buffer tank 32 having with a steam jacket and a stirring device driven by a motor M2. The contents of the tank 32 are sent via a pump P1 to a mixing tank 33 which has a conical bottom wall and also has a steam jacket and a stirring device driven by motor M3. Fuel or waste oil is pumped from an oil tank 36 by a pump P2 into the tank 33 where it is mixed with the sludge of cold rolling mill oil delivered from the buffer tank 32. After thorough stirring and standing, the top layer of the mixture is returned by a pump P3 into the tank 36. A deposition tank 34 is used for an after-separation of the dirt and tapped off from the bottom of the tank 33.A pump P4 in this case designed as a steam jet ejector, pumps the water layer in the tank 34 to the oil/water separating plant (EC) for further treatment.

The plant of Fig. 3 is designed so that everywhere the sludge is kept hotter than 500C.

The buffer tank 32 as well us the mixing tank 33 are equipped for this purpose with steam heating and also have level indication. Preferably the stirring device in the buffer tank 32 rotates continuously.

Detailed operation is as follows: oil is pumped by the pump P2 from the tank 36 into the mixing tank 33. As soon as a certain level is reached, the stirring device therein starts rotating. The oil is heated by steam to about 700 C. When this temperature is reached sludge is pumped by pump P 1 from the buffer tank 32 into the mixing tank 33 up to the level corresponding to the desired mixing ratio. Then the stirring period of 0.5 to 1 h starts. Not until 3 hours have elapsed after the stirring device stops is the mixing tank 33 allowed to be emptied, because by that time dirt and water are sufficiently separated. First the top phase is pumped by the pump P3 to the tank 36 and after this has been accomplished (as shown by level indication), the dirt and water can be discharged to the tank 34 via a shut-off valve 37 and a pipe 38. The process is thus a batch one.

A number of advantages result from the method according to the invention: first and foremost external costs of transport and processing are saved. The organic portion of the sludge is fully utilized as a source of energy by introducing it into a fuel oil system together with waste oil or fuel oil. Finally the iron-bearing solid dirt released can be used in a sintering plant.

Claims (12)

Claims

1. A method of processing sludge derived from used cold rolling mill oil, which sludge comprises solid dirt, water and water-immiscible organic liquid components, the method comprising the steps of (a) thoroughly mixing said sludge with an oil component which is selected from waste oils, fuel oils and mixtures of waste and fuel oils, the amount of said oil component being (by volume) at least twice the amount of said organic liquid component, the mixing being carried out so that on settling the organic liquid component and the oil component form a single Dhase.

(b) allowing the mixture formed in step (a) to settle so that the said phase composed of the oil and organic liquid components separates from the solid dirt and water components, (c) removing said separated phase from the solid dirt and water components and (d) burning the said separated and removed phase.

2. A method according to claim 1 wherein during steps (a), (b) and (c), the temperature of the organic component is at least 5000.

3. A method of processing sludge derived from used cold rolling mill oil to prepare it for combustion, comprising the steps of: (a) separating the solid dirt and water components of the sludge from the organic liquid component, and before or after step (a), (b) mixing the organic liquid component with a solvent oil therefor selected from waste oil, fuel oil and mixtures of waste and fuel oil, in a ratio of at least 2 parts of the solvent oil to 1 part of said organic liquid component, the mixture thús formed being adapted for use as a fuel oil to be subjected to combustion subsequently.

4. Method according to claim 3 wherein the said solvent oil is mixed thoroughly with the sludge prior to the said separation of the solid dirt and water components.

5. Method according to claim 4 wherein stirring of the mixture of sludge and solvent oil takes place for a period of at least half an hour.

6. Method according to claim 5 wherein said stirring takes place for at least 1 hour.

7. Method according to any one of claims 3 to 6 wherein during the mixing the separation the mixture is maintained at a temperature of at least 50 C.

8. Method according to any one of claims 3 to 7 wherein after the mixing, the mixture is allowed to stand for at least 3 hours before said separation.

9. Method according to any one of claims 3 to 8 wherein the phase comprising the organic liquid component of the sludge and the solvent oil is removed from a vessel in which separation takes place before removal of the solid dirt and water components.

10. A method according to any one of claims 3 to 9 wherein the mixture of solvent oil and organic liquid component of the sludge is mixed with fuel oil prior to combustion.

11. A fuel comprising the said mixture of the organic liquid component of sludge derived from used cold rolling mill oil and said solvent oil, as produced by the method of any one of claims 3 to 10.

12. A method of processing sledge derived from used cold rolling mill oil, substantially as herein described with reference to the accompanying drawings.