GB2139121A

GB2139121A - Centrifugal cleaning of used mineral oils

Info

Publication number: GB2139121A
Application number: GB08409268A
Authority: GB
Inventors: Aloys Tenthoff
Original assignee: Westfalia Separator GmbH
Current assignee: GEA Mechanical Equipment GmbH
Priority date: 1983-04-23
Filing date: 1984-04-10
Publication date: 1984-11-07
Also published as: IT1178930B; BR8401846A; IT8467420A1; NL8401245A; DE3314859A1; BE899360A; ES531783A0; IT8467420A0; ES8502154A1; FR2544740A1

Abstract

In a process for centrifugal cleaning of used mineral oils, the solids - liquid mixture is fed to a centrifugal drum (1) by means of a central inlet (2). Solids and water are collected in the solids zone (5) of the drum and the cleaned oil is removed from the central area of the drum by means of a first discharge pipe (9) and a smaller partial oil flow is removed from the peripheral area of the drum by means of passages (7) and a second discharge pipe (10) and is returned to the inlet (2). As soon as the water level in the centrifugal drum reaches the start of the passages (7), water flows in the second discharge pipe (10). This is detected by a conductivity meter (12) located in the second discharge pipe and brings about the switching over of a changeover valve (11) also located in said pipe, so that the return to the inlet is interrupted. <IMAGE>

Description

SPECIFICATION Process and apparatus for the centrifugal cleaning of used mineral oils The invention relates to a process for the centrifugal cleaning of used mineral oils particularly heavy oils contaminated by dirt and water, whilst using an automatically discharging separator, whose centrifugal drum receives the solids - liquid mixture by means of a central inlet having a first discharge pipe for the liquid drawn from the central area of the centrifugal drum and a second discharge pipe for the liquid drawn off from the peripheral area of the centrifugal drum by means of passages.

Processes of the aforementioned type are generally known, the liquid levels of the liquids drawn from the central and peripheral areas being selected in such a way that there is a so-called separating zone within the centrifugal drum between the specifically heavier water and specifically lighter oil. This separation zone must be located in the vicinity of the feed zone for the centrifugal liquid into the disc stack, in order to achieve an optimum separation effect. If materials with different density differences are to be cleaned or purified, it is necessary to modify the setting of the outlet diameter for the two phases.

Before the start of separation and following each complete emptying, the centrifugal drum must initially be filled with water, in orderto seal offthe outlet from the peripheral area for the oil. This involves a corresponding fresh water consumption.

Another problem is the risk of the oil phase getting into the peripheral area of the drum, which not only leads to oil passing out of the outlet for the water phase and being lost, but also means that the waste water is contaminated. This risk of oil getting through is more particularly encountered when cleaning heavy oils, whose densities are in the range of water, so that it is in part necessary to add heavy water in the form of MgSO4, in order to ensure a completely satisfactory separation. Only oils having a maximum density of 0.991 g/cm3 can be centrifugally cleaned with the known processes without adding MgSO4. Since, for cost reasons, there is an increasing trend towards the use of heavy oils, the problem of the maximum permitted oil density for centrifugal cleaning has become particularly acute.

The problem of the invention is therefore to provide a process enabling oils with a higher density than 0.991 g/cm3 to be centrifugally cleaned in a reliable and loss-free manner. In addition, there is no need to supply water before the start of separation and after emptying processes have taken place, whilst there is no need for the setting of the separation zone.

According to the invention this problem is solved in that solids and water are collected in the solids area of the centrifugal drum and the liquid removed from the peripheral area is returned to the inlet for as long as oil flows out and the return is brought to an end as soon as water flows out.

Due to the fact that the drum is not filled with water before the start of separation, initially cleaned oil flows out of both liquid outlets. Dirt and water collect in the solids area or chamber of the centrifugal drum. As soon as the water reaches the channels for the outflow of liquid from the peripheral area, the way is blocked for the oil and only water passes out of the second discharge pipe. By measuring the conductivity of the outflowing liquid, this change can be established and a changeover valve can be switched over. The return of this liquid flow to the separator inlet is stopped for as long as water is flowing out. If the discharge channels coming from the peripheral area become clogged by collected solids, the liquid flow in the passages and in the second discharge pipe is interrupted.This interruption is detected by a suitable monitoring device and starts the emptying of the centrifugal drum. This cycle is continuously repeated. The process according to the invention consequently permits the optimization of the operation of the centrifugal drum, not only with respect to the cleaning of heavy oils, but simultaneously makes it possible to sense the volume of solids deposited in the centrifugal drum and to initiate an emptying or discharge in good time.

A further advantage provided by the invention is that it is possible to operate with separating temperatures above 1 00 C, because there can be virtually no water evaporation and evaporation cannot influence the separation zone within the centrifugal drum required in the hitherto known processes. As the water content of heavy oils is generally below 1%, following each emptying or discharge, the centrifugal drum initially functions as a clarifying separator, no water being able to evaporate due to the high pressure in the centrifugal drum.

The apparatus for performing the process is characterized in that the second discharge pipe for the liquid coming from the peripheral area of the centrifugal drum is connected to the inlet for the supplied solids - liquid mixture. A changeover valve is provided in the second discharge pipe, which makes it possible to lead the outflowing liquid to some other random point in the installation, instead of to the inlet. The second discharge pipe is provided with a constriction, in order to set the discharge pressure and quantity. The pressure is monitored by a pressure switch located in the discharge pipe. A conductivity meter provided in the second discharge pipe makes it possible to establish the type of liquid flowing in the said pipe.

The invention is described in greater detail hereinafter relative to the drawing, which shows an embodiment according to the invention.

Centrifugal drum 1 is provided with a central inlet 2, through which the solids - liquid mixture is supplied to the centrifugal area or chamber 3, which comprises the separation zone 4 and the solids zone 5, the clarified liquid is removed on the one hand from the central area of the centrifugal drum by means of a paring disk 6 and on the other hand from the peripheral area thereof by means of passages 7 and a paring disk 8. Paring disk 6 is connected to a first discharge pipe 9, through which the cleaned oil is returned to the installation for further use. A second discharge pipe 10 associated with paring disk 8 is connected to inlet 2 in such a way that the liquid flow drawn off from the peripheral area of centrifugal drum 1 is returned to the latter. A changeover valve 11 in the second discharge pipe 10 also makes it possible to drain off the liquid flow to another random point.The second discharge pipe 10 is also equipped with a conductivity meter 12, a pressure switch 13 and a constriction 14. Solids zone 5 is peripherally provided with discharge openings 15, which can be opened or closed by an axially movable sliding piston 16.

Cleaned oil flows out of the two discharge pipes 9 and 10 at the start of separation, because the solids and water initially collect in solds zone 5. Changeover valve 11 is switched in such a way that the oil is returned to inlet 2. The outflowing liquid quantity is set to a relatively low value by means of constriction 14. When sufficient water has collected in solids zone 5 for the water level to reach passages 7, water flows out of the second discharge pipe 10 instead of oil. This is detected by the conductivity meter 12, and this information is supplied to a not shown control unit, which brings about the switching over of changeover valve 11 and consequently interrupts the return to inlet 2. If the solids level also reaches the inlet point to channel 7 the liquid flow in the second discharge pipe 10 is interrupted. The resulting pressure reduction in the second discharge pipe is indicated to the control unit by means of pressure switch 13 and the emptying of the centrifugal drum is started. The possible short pressure drop on changing from oil to water discharge in the second discharge pipe 10 is suppressed in known manner by a time lag provided in the control unit.

Claims

1. A process for the centrifugal cleaning of used mineral oils, particularly heavy oils contaminated by dirt and water, whilst using an automatically discharging separator, whose centrifugal drum receives the solids - liquids mixture by means of a central inlet having a first discharge pipe for the liquid drawn from the central area of the centrifugal drum and a second discharge pipe for the liquid drawn off from the peripheral area of the centrifugal drum by means of passages, wherein solids and water are collected in the solids area of the centrifugal drum and the liquid removed from the peripheral area is returned to the inlet for as long as oil flows out and the return is brought to an end as soon as water flows out.

2. A process according to claim 1, wherein when the passages leading out of the peripheral area are closed by the solids in the drum and the liquid flow flowing out of the second discharge pipe is inter rupted as a result thereof, a pulse is emitted, which initiates the automatic discharge of the centrifugal drum.

3. An apparatus for performing the process according to claims 1 and 2, wherein the second discharge pipe is connected to the inlet.

4. An apparatus according to claim 3, wherein a changeover valve is provided in the second dis charge pipe.

5. An apparatus according to claims 3 and 4, wherein a conductivity meter is provided in the second discharge pipe.

6. An apparatus according to one of the claims 3 to 5, wherein a pressure switch is provided in the second discharge pipe.

7. An apparatus according to one of the claims 3 to 6, wherein the second discharge pipe is provided with a constriction.

List of reference numerals 1 Centrifugal drum 2 Inlet 3 Centrifugal area or chamber 4 Separation zone 5 Solids zone 6 Paring disk 7 Passage 8 Paring disk 9 First discharge pipe 10 Second discharge pipe 11 Changeover valve 12 Conductivity meter 13 Pressure switch 14 Constriction 15 Discharge opening 16 Sleeve valve