GB2275210A

GB2275210A - Regenerating of degreasing liquid

Info

Publication number: GB2275210A
Application number: GB9403051A
Authority: GB
Inventors: Herbert Weiss
Original assignee: OEKOLOGIA BETEILIGUNGS HANDELS
Current assignee: OEKOLOGIA BETEILIGUNGS HANDELS
Priority date: 1993-02-17
Filing date: 1994-02-17
Publication date: 1994-08-24
Also published as: ATA30093A; ITMI940282A1; ITMI940282A0; DE9401272U1; GB9403051D0; DE4402185A1; AT399515B; IT1273881B

Description

2275210 CLEANSING DEGREASING LIQUIDS The invention relates to a process

for the continuous cleaning of degreasing liquids. Alkaline or acid degreasing liquids from one or more degreasing baths, particularly for the pickling or finishing of workpieces or stock material, preferably steel, are removed from-the bath(s). The removed liquid is subjected to solid separation, to oil and grease separation stage, and 10 thereafter the purified liquid is returned to the degreasing bath(s). The invention also relates to a circulating system cleaning plant for carrying out the process.

In surface treatment by zinc powder coating and galvanization, the workpieces or stock material must be pre-treated.

This pre-treatment is divided into one or more degreasing steps, one or more hydrochloric or sulphuric acid picklings, one or more rinsings and, in the case of zincing plants, a flux bath. In electroplating works, the electroplating baths follow. The volume of these treatment baths lies between 5 and 80 m3 per bath, and generally between 10 to 30 m3. With optimum bath management. these operational plants can be driven partly without a waste water plant. The rinsing water is, in this connection, used to make up water losses, and is replaced by clean water. The used pickling solutions can be processed to valuable materials, such as precipitation agents for clarifying plant. Only the degreasing baths have to be renewed at intervals of six months to 1 year.

Alkaline degreasing liquids customarily include caustic sodar phosphates, borates and surface-active agents. while acid degreasing liquids contain acid phosphates, surface-active agents and inhibitors.

is In degreasing baths, the workpieces are immersed prior to pickling or further treatment. The baths remove grease, oils, swarf and scale. The degreasing agents are adulterated after a short period with hydrocarbons, predominantly oils and grease, and phosphate mud.

However, this gives rise to substantial disadvantages. The operation of the entire pre-treatment plant, and in any case that of the degreasing baths, must often be interrupted in order to undertake an exchange of the degreasing liquid. The contaminated degreasing liquid must then be concentrated and disposed of properly. Added to this is the problem that the quantities to be disposed of are very large, and the corresponding environmental requirements for waste disposal become ever more stringent. This is wasteful of not only time and labour, but it adds significantly to the cost of waste disposal.

WO-Al-89/01056 discloses a process and apparatus for cleaning used degreasing solutions, consisting of a degreasing plant for emulsified oil and grease, wherein continuously, or on the achievement of a given predetermined degree of contamination of the degreasing bath, degreasing solution is drawn from this and fed back into the degreasing bath after treatment. The treatment of the degreasing solution takes place, in this connection, in such a fashion that the degreasing solution is first heated and then cooled, whereafter the cooled degreasing solution is passed through a coarse filter for removal of coarse contamination, and thereafter the separation of oil and grease takes place by means of an oil separator and fine filter. Before the treated degreasing solution can be fed back into the is degreasing bath, fresh emulsifier to replace that which was destroyed during the treatment must be added thereto, and the degreasing solution adjusted to the desired composition.

The disadvantages of this known process are that, above all, as a result of the necessary heating and cooling steps, the continuous addition of emulsifier, and the additional requirements of the waste disposal of filter paper and active carbon, the process is labour- and costintensive, both constructionally and in terms of process management.

The object of the present invention is to avoid or reduce these disadvantages. It does this by prolonging the service life of the degreasing baths, wherein the degreasing agent, by removal of the constituents which arise during use and which are damaging, without the use of other means for disposing of this waste. such as filter paper, active carbon and the like. should be continuously purified, and the waste water arising should be kept very low. Furthermore, the damaging constituents should be treated equally in suich a way that their disposal or further processing is possible in a simple environmentally appropriate and cost-effective fashion.

Accordingly, the process in accordance with the invention consists in that in a first process step, the solid materials, consisting of suspended matter or sludge such as lime, phosphates, scale, swarf, dirt and rust by sedimentation, and continuously separated from the stream of degreasing liquid, and then, in a second process step, the degreasing liquid freed from solids is passed through a coalescence phase for oil and grease separation, is whereafter the oil and grease floating on the surface of the degreasing liquid are removed. In addition, the separated oil and grease may be subjected to a residual water separation step.

The above combination of steps enables a smooth continuous running of the cleaning process without likelihood of interruption. The cleaning process in accordance with this invention can be used both during production operation and also at other times. In each case. using the process in accordance with the invention, a substantial improvement in quality of degreasing as well as raising of the quality standards of the zinccoated or galvanised workpieces or stock material, is obtained. Additionally, an increase in the lifetime of the treatment baths by up to double their previous lifetimes, that is up to 1 to 2 years, is achieved. The cleaning process in accordance with the invention can be carried out with the avoidance of temperature changes, that is without heating and subsequent cooling at an even temperature in the region of from 20 to WC, and the destruction and disposal of the emulsifier. Thus this process is suited for cleaning alkaline or acid degreasing liquids. 5 The separated solids from a concentrate which can be fed to waste disposal or further processing. This gives rise to a particularly effective enriching of the oil and grease on the surface of the degreasing agent, and thereby removal of the oil and grease from the degreasing agent.

The invention also relates to a circulating cleaning plant for carrying out the above process. The plant comprises a container with a solids separation chamber with a feed for the degreasing agent diverted from the degreasing bath, and an oil and grease separation chamber connected to the solids separation chamber, with an outlet for the cleaned degreasing agent.

Accordingly, the degreasing agent can be cleaned simply with feedback of the cleaned degreasing agent into the degreasing bath, wherein the suspended solids or sludge separation, and the oil and grease separation, can take place in a common container. Such a cleaning plant is capable of being installed at any desired position in space-saving fashion and can have its inlet and outlet connected to the degreasing bath.

An advantageous embodiment of the cleaning plant in accordance with the invention is characterised in that the solids separation chamber, and the oil and grease separation chamber are arranged horizontally adjacent one another in a common container, wherein between the chambers there is a weir in contact with the floor of the container, and a further wall is arranged on the side of the oil and grease separation chamber running parallel to the weir extending above the weir and spaced from the floor of the container. Thereby it is guaranteed that only the degreasing agent which flows through the solids separation chamber can attain its further purification in the oil and grease separation chamber. The weir is preferably provided with an overflow comb.

In an alternative embodiment, the solids separation chamber and the oil and grease separation chamber are arranged vertically, with the oil and grease separating chamber being above the solids separation chamber without an intermediate separation wall. This mode of construction is particularly advantageous if limited space is available.

In one form of invention there are arranged in the solids separation chamber plate lamellae set parallel to one another above settling funnels arranged on the floor in the container. The inlet for the degreasing agent to be cleaned is arranged in the container wall at the level of the upper region of the plate lamellae, which are preferably inclined away from the container wall carrying the feed inlet within an angular range between 20 and 40. Thereby a particularly good separation of the solids can be achieved in that the degreasing agent fed in through the inlet flows downwardly past the settling funnels and then flows upwardly through the plate lamellae. In this connection, the solids components are lowered by the inclined arranged plate lamellae without flow turbulence, and collect themselves together as a sludge in the precipitation funnels.

According to a further feature of the invention, in the container wall, in each case, debouching at the outlet of each precipitation funnel are draw-off ports attached to which are filter devices such as bag filters, filter presses or belt filters. In continuous cleaning circulation of the decreasing agent, the sludge sediment collected in the sedimentation funnels can be drawn off at intervals and then dewatered by means of the filter units in simple fashion in order to obtain compact sludge concentrate which can be easily further processed or disposed of.

In the oil and grease separating chamber there are arranged spaced coalescence plates forming a stack. On the outlet side, adjacent the coalescence plates stack there is provided an underflow weir and optionally an overflow weir, wherein the outlet for the cleaned degreasing agent is arranged in the container wall at a height above the top of coalescence stack.

Because the degreasing agent flows into the oil and grease separating chamber freed from solids, a problem the coalescence of the finest oil droplets contained in the degreasing agent is possible on flowing the degreasing agent through the coalescence plate stack. These larger oil droplets and pools are very easy to remove from the surface of the treated degreasing agent.

Above the coalescence plate stack there may be arranged a suction or stripping device for the oil and grease floating on the surface in the oil and grease separation chamber, such as a skimmer or an overflow channel, whereby in particularly simple and effective fashion, the oil and grease floating on the surface can be drawn off 8 from the degreasing agent. These skimmers, which can also be installed with a vertical construction of the cleaning plant, can be tube skimmers, disc skimmers or hose skimmers.

On this suction or stripping unit, in accordance with a further feature of the invention, a run-out channel may be connected which debouches into an oil separator, particularly a light oil or gravity separator. By this means, residual water in the drawn-off oil can be removed. The oil with only a small proportion of water can accordingly be fed to combustion or waste disposal.

The subject matter of the invention will be illustrated is in more detail in what follows by way of example with reference to the accompanying drawings, wherein:

Figure 1 shows a schematic illustration of pre-treatment plant including a degreasing liquid treatment plant in accordance with the invention; Figure 2 is a schematic illustration of the liquid cleaning plant in accordance with the invention; Figure 3 is a diagrammatic isometric view of the plant shown in Figure 2; Figure 4 is a view similar to Figure 3 of a second embodiment of a cleaning plant in accordance with the invention; Figure 5 is an isometric view of a third embodiment of the invention; Figure 6 is an isometric view of a fourth embodiment of the invention. and Figure 7 is an isometric view of a vertically-disposed circulating cleaning plant in accordance with the invention.

Figure 1 shows the arrangement of several different treatment baths such as degreasing bath E, and rinsing and pickling baths of an entire plant for the pretreatment of workpieces and stock material of steel. Connected to the first bath of this pre- treatment plant is a circulating cleaning plant 1 connected via a feed line 2 for contaminated degreasing agent, and a is return feed 3 for cleansed degreasing agent. The degreasing agent to be cleaned flows via pumps or gravity into the plant 1, and the cleaned degreasing agent is in turn returned along the return flow line 3. by means of gravity pumps back into the degreasing bath E. The circulating plant 1 comprises a solids separation chamber A and an oil and grease separation chamber B. The solids components sedimented in the solids chamber as sludge are drawn off via ports 4 and dewatered in an attached filter unit 5. The oil separated in the oil and grease separating chamber B is collected in an oil container 6.

Figure 2 shows a vertical cross-section of the cleaning plant in accordance with the invention. Contaminated degreasing agent drawn off from the degreasing bath E is introduced via an inlet 7 into the solids separation chamber A, which is arranged with the oil and grease separation chamber B in a common container 8. In chamber A the contaminated degreasing agent flows in the direction of arrow 9 downwardly towards sludge collection funnels 10 past them as indicated by arrows 11, and upwardly through plate stack 12. The solids sedimented into the funnels 10 as sludge 13 is drawn off at intervals via withdrawal ports 14 and can then, with filter units such as bag filters, filter presses or belt filters, be dewatered for disposal or processing.

The degreasing agent, cleaned of suspended materials, floats over a weir Al, as indicated by arrows 15, into the oil and grease separation chamber B. In this chamber, the degreasing agent has to flow through a packing formed from coalescence plates 16. In this, the finest oil and grease droplets combine to form larger ones and subsequently float in the direction of arrows 17 is upwards to the surface. The oil and grease floating on the surface is drawn off by means of a suction or stripping unit B2. The cleaned degreasing agent flows under a barrier Bl and through an outlet 18 in the container 8 and the return lead connected thereto. not illustrated here, under gravity or by means of a feed pump into the degreasing bath. The degreasing liquid is not changed chemically and no replacement additives have to be added to it.

Figures 3 to 7 show various embodiments of the circulating cleaning plant in accordance with the invention, wherein the feed for contaminated degreasing agent from the degreasing bath, and the return feed for the cleaned degreasing agent into the degreasing bath, are not illustrated.

According to Figure 3 to 6, in the container 8 the solids separation chamber A and the oil and grease separation chamber B are installed horizontally adjacent one another, wherein between both chambers A and B is a weir 20 in contact with the floor 19 of the container 8. Spaced from the weir is a wall 21 projecting above the weir 20 and spaced from the floor 19 of the container 8.

The weir 20, which is provided with an overflow comb 22, forms with the wall 21 the weir A1 over which the degreasing agent freed of solids flows into the oil and grease separation chamber B. The container 8, of volume between 1 and 10 m3, generally between 2 and 5 m3 is made of acid- and alkali-resistant plastics, preferably of polypropylene, and is generally, as illustrated in Figure 3 to 7. a rectangular containerr the floor and side walls of which are, as well as its upper end. reinforced with strengthening ribs. in the solids separation chamber A, the lamellae plates 12, which are arranged parallel to one another, are arranged above the sedimenting funnels 10 provided at the floor in container 8. In the long side end wall 23 of container 8 is the feed 7 for the degreasing agent which is first to be cleaned in the solids separating chamber A arranged at the height of the upper region of the lamellae plates 12, wherein the first lamellae plate lying opposite the inlet 7 serves as an impact or deflector plate which deflects the incoming degreasing liquid. The lamellae 12 are inclined to the vertical at an angle within the range between 20 and 40.

In the long side walls 24, in each case debouching at the apex of a settlement funnel 10. there are arranged withdrawal ports 14 via which the sedimented sludge 13 can be drawn off.

In the oil and grease separation chamber B, installed in accordance with Figures 3 to 6 in the horizontal direction directly adjacent the solids separation chamber A in the container 8 there are starting from the floor 19 of container 8, vertically spaced coalescence plates 16 forming a stack. When the degreasing agent freed of solids flows through the stack a coalescence of the oil droplets takes place to form larger ones which then can float to the surface, as indicated with arrows 17. In the other face wall 25 of container 8 there is arranged the outflow 18 for the cleaned degreasing agent arranged at a height lying above the coalescence plate stack, wherein the (not illustrated) return lead to the degreasing bath is connected to the outlet 18. On the outlet side, adjacent the coalescence plate packing, a is further outflow weir 26 is provided.

As illustrated in Figure 3 above the coalescence plate packing, preferably touching the upper edge of the container 8, there is arranged a tube skimmer 27 as a suction or stripping unit by which the oil and grease floating on the surface can be drawn off. The tube skimmer is additionally equipped with a stripper rubber 28 and an oil gutter 29. Via a tube 30 connected to the oil gutter 29, the separated oil and grease are fed into an oil separator 31 likewise installed in the container 8. in which any residual water is separated from the oil and grease. The oil separator 31 preferably constructed as a heavy or light oil separator, gravity or flotation, is provided with a water take-off 32 and an oil overflow port 33, which leads into an oil waste barrel. The container 8 is also further equipped with an emptying outlet 34.

According to Figure 4. the suction or stripping device for the oil and grease floating on the surface in the oil and grease separating chamber B is provided by a disc skimmer 127 which is provided with a stripping rubber 128. The stripped-off oil and grease flow into an oil gutter 129 from which they flow via a pipe 130 into the oil separator 31 for removal of residual water.

As shown in Figure 5, the suction or stripping unit is a tube skimmer 227. Via an oil gutter 229 and through a pipe 230 connected thereon, the separated oil is further fed for residual water separation into the oil separator 31.

According to the embodiment shown in Figure 6, the suction or stripping unit in the oil and grease separating chamber B for the oil and grease floating on the surface is constructed as an overflow gutter 327 from which the oil and grease drawn off are again fed to residual water separation in the oil separator 31 via a tube connection 330. Otherwise, the circulating cleaning units illustrated in Figures 4, 5 and 6 correspond to those in accordance with Figure 3.

In accordance with Figure 7, the solids separation chamber A and the oil and grease separating chamber B are arranged vertically in the container 108. wherein the oil and grease separation chamber B is constructed directly above the solids separation chamber A without the interposition of a separating wall. In the solids separation chamber A there are arranged lamellae 112 which are arranged aligned parallel to one another above the settling funnels 110 provided on the floor in the container 108. The container 108 built of plastics, preferably polypropylene, is square shapedr the floor and walls of which are reinforced with strengthening ribs.

In the right hand (as viewed) side wall 123 of the container 108 is arranged the inlet 107 for the degreasing agent to be cleaned. In the solids separation chamber A at the height of the upper region of the lamellae 112, wherein the first lamellae plate lying opposite the inlet 107 serves as an impact or diverter plate which deflects downwardly the flow of the degreasing agent entering into the solids separation chamber. The lamellae 112 are inclined to the vertical at an angle within the range between 20 and 40.

In the front and rear side container walls 124. there are arranged, debouching in each case at the apex of a settling funnel 110, outlet ports 114 via which the sedimented sludge 113 can be drawn off.

Connected directly above the lamellae 112 is the oil and grease separation chamber B in which are arranged coalescence plates 116 as a stack through which the degreasing agent freed of solids is to flow vertically.

In the left hand side wall 125 of container 108 is arranged the outlet 118 for the cleaned degreasing agent at a height lying above the stack of coalescence plates, wherein also connected to the outlet 118 is the (not illustrated) return lead to the degreasing bath. On the outlet side, adjacent the coalescence plate stack, are provided further an overflow weir 126 and a barrier 226 projecting past the overflow weir 126 as well as the outlet 118.

Also with this vertical construction, the circulating cleaning unit can be equipped with a suction or stripping unit, such as a skimmer or overflow gutter for drawing off the oil and grease floating on the surface of the degreasing agent in the oil and grease separation chamber B. - 16

Claims

1. A process for continually cleaning liquid degreasing agents wherein the degreasing liquid is drawn off from at least one degreasing bath and subjected successively to a solids separation step and thereafter to an oil and grease separation step, after which the cleaned degreasing liquid is returned to a degreasing bath, in which in the first step the solids are continuously separated from the degreasing liquid by sedimentation and in which, in the second step. the degreasing liquid freed of solids is caused to undergo a coalescence step to coalesce the oil and grease with the oil and grease floating on the surface of the degreasing agent being drawn off.

2. Plant for continually cleaning liquid degreasing agents, comprising a container housing both a solids separation chamber, the container having an inlet for the degreasing liquid to be cleaned, and an oil and grease separation chamber connected in cascade with the solids separation chamber, the container having an outlet for the cleaned degreasing agent leaving the oil and grease separation chamber.

3. Plant as claimed in Claim 2, in which the solids separation chamber and the oil and grease separation chamber are arranged horizontally adjacent one another in the container, in which between both chambers is arranged a weir separating the two chambers and in which an internal wall is positioned downstream of the weir and upstream of the oil and grease separation chamber, the internal wall being spaced from the floor of the container.

4. Plant as claimed in Claim 3. in which the weir is surmounted by an overflow comb.

5. Plant as claimed in Claim 2, in which the solids separation chamber is positioned below the oil and grease separation chamber without the interposition of a separating wall.

6. Plant as claimed in any one of Claims 2 to 5, in which in the solids separation chamber is arranged a series of parallel lamellae above sediment collectors on the floor of the container.

7. Plant as claimed in Claim 6, in which the inlet for the degreasing liquid to be cleaned is arranged in the container wall at the height of the upper region of the lamellae which are inclined to the vertical at an angle between 20 and 40.

8. Plant as claimed in Claim 7 in which connected to the suction or stripping unit is an outlet gutter which debouches into an oil separator. 20

9. A plant for cleaning degreasing liquid substantially as hereinbefore described with reference to any one of Figures 3 to 6 of the accompanying drawings.

8. Plant as claimed in Claim 6 or 7, in which in the container wall. debouching in each case at the outlet of a sediment collector, are arranged draw-off ports to which filter units may be connected.

9. Plant as claimed in any of Claims 2 to 8 in which the oil and grease separation chamber houses a stack of spaced-apart oil-coalescence plates in which, on the downstream side of the stack, there is provided an underflow barrier and in which the outlet for the cleaned degreasing agent is arranged in the container wall at a height above the said stack.

10. Plant as claimed in any of Claims 2 to 9 in which above the stack of oil-coalescence plates is arranged a suction or stripping unit for the oil and grease floating to the surface of the liquid in the oil and grease separation chamber. 5 11. Plant as claimed in Claim 10 in which connected to the suction or stripping unit is an outlet gutter which debouches into an oil separator.

12. A plant for cleaning degreasing liquid substantially as hereinbefore described with reference to any one of Figures 3 to 7 of the accompanying drawings.

- ig - Amendments to the claims have been filed as follows 1. Plant for continually cleaning liquid degreasing agentst comprising a container having an inlet for the degreasing liquid to be cleaned, and an outlet for the cleaned degreasing agent, the container housing both a solids separation chamber, and an oil and grease separation chamber connected in cascade with the solids separation chamber wherein, the solids separation chamber and the oil and grease separation chamber are arranged horizontally adjacent one another in the container, in which between both chambers is arranged a weir separating the two chambers and in which an internal wall is positioned downstream of the weir and upstream of the oil and grease separation chamber, the internal wall being spaced from the floor of the container.

2. Plant as claimed in Claim 1, in which the weir is surmounted by an overflow comb.

3. Plant as claimed in Claim 1 or 2, in which in the solids separation chamber is arranged a series of parallel lamellae above sediment collectors on the floor of the container.

4. Plant as claimed in Claim 3, in which the inlet for the degreasing liquid to be cleaned is arranged in the container wall at the height of the upper region of. the lamellae which are inclined to the vertical at an angle between 20 and 400.

5. Plant as claimed in Claim 3 or 4, in which in the container wall, debouching in each case at the outlet of a sediment collector. are arranged draw-off ports to 1 - o - which filter units may be connected.

6. Plant as claimed in any of Claims 1 to 5 in which the oil and grease separation chamber houses a stack of spaced-apart oil-coalescence plates in which, on the downstream side of the stack, there is provided an underflow barrier and in which the outlet for the cleaned degreasing agent is arranged in the container wall at a height above the said stack-. 10 7. Plant as claimed in any of Claims 1 to 6 in which above the stack of oil-coalescence plates is arranged a suction or stripping unit for the oil and grease floating to the surface of the liquid in the oil and grease 15 separation chamber.