CA1105395A - Treatment of oily sludge - Google Patents
Treatment of oily sludgeInfo
- Publication number
- CA1105395A CA1105395A CA297,634A CA297634A CA1105395A CA 1105395 A CA1105395 A CA 1105395A CA 297634 A CA297634 A CA 297634A CA 1105395 A CA1105395 A CA 1105395A
- Authority
- CA
- Canada
- Prior art keywords
- filter
- filtration
- solvent
- sludge
- oily sludge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Filtration Of Liquid (AREA)
Abstract
ABSTRACT
Oily sludge is treated by filtering it through a precoated surface filter, treating the filtration residue with a hydro-carbon solvent and/or steam stripping the extracted residue.
The residual oil content of the treated sludge is very low and it can be used for land fill operations.
Oily sludge is treated by filtering it through a precoated surface filter, treating the filtration residue with a hydro-carbon solvent and/or steam stripping the extracted residue.
The residual oil content of the treated sludge is very low and it can be used for land fill operations.
Description
~l~S3~3!S
This invention relates to a method for treating oil contaminated solids, particularly the residues formed as a by-product from the treatment of oil contaminated water, such as refinery or other industrial plant effluent, or resulting from the long standing of crude petroleum or petroleum products in tanks or other forms of storage.
As a first step in the treatment of oil contaminated waters it is common practice to effect a rough separation in a gravity separator to remove the bulk of the oil and suspended solids. Suitable separators include parallel plate separators, settlement tanks and API Separators as described in the "Manual on Disposal of Refinery Wastes", published by the American Petroleum Institute in 1969.
Oil recovered from such devices can be used as a source of energy and the aqueous effluent is suitable for further treatment to reduce its oil content and ~OD to very low levels.
Such a further treatment is disclosed and claimed in our Canadian Patent No. 1026021 which claims a method for treating effluent water containing suspended oil which method comprises passing the effluent water firstly through a sand filter to remove the suspended oil and subsequently through a biological percolating filter.
Returning to the primary separation devices, there is a third product from them which builds up over a period of time and the disposal of which gives rise to problems. This is an oilysludge which can have a water content in the range ~' ```` 113!S3~S
20 - 95% by weight and an oil content in the range 5 - 70% by weight, the remainder being solid materials such as silt, rust, carbon, calcium carbonate, etc.
Other sources of oily sludge are sand filter backwash water from the effluent treatment process described in Canadian Patent No. 1026021 and the top oily sludge layer from gas/air flotation plants for the removal of dispersed oil and suspended solids from water.
Oily sludge is a difficult material to process since it tends to block filters and adhere to them.
The only environmentally accepted method of dealing with these sludges is by burning, but this requires the provision of special incinerators which are expensive to purchase, install, operate and maintain and which result in the wasteful destruction of oil.
A process has been disclosed in British Patent Specification 1340931 in which oily solid particles suspended in aqueous effluent are retained by a sand filter.
A sand filter operates by allowing the liquid to be filtered to percolate slowly downwards through a thick bed of filter sand. The sand is relatively coarse when compared with the solid particles to be retained and the particles, especially the finer ones, tend to pass through the upper reaches of the sand. Eventually, however, the packing results in tortuosities and restrictions which trap the particles, including the finer ones.
~.................................................................. .
3~3!5 Because of their effectiveness in dealing with materials which tend to block or pass through other filters, sand filters are widely used in oil refineries and similar installations The same factors which result in the efficiency of the sand bed when working as a filter give rise to problems when regeneration is necessary, however. In order to regenerate a filter, retained-solid particles must be removed. Because particles are trapped at all levels in the filter bed, regeneration, either by backward or forward flushing, means that some particles have again to traverse the bed and again are likely to meet with further restrictions which tend to retain them in the filter unless dislodged. In order to combat this, it is necessary to wash either frequently or for long periods and to use high flow rates and/or liquid under high pressure with the ever present risk, unless great care is exercised, of disturbing the structure of the filter bed and rendering it inefficient for subsequent filtration stages, unless restructured.
The residue resulting from the filtration of oily sludge adheres strongly to a sand filter and the difficulties of regeneration are such that sand filters have been rejected for such operations.
There exists a need, therefore, for a simple method of filtration which is capable of dealin( with concentrated oily sludge, a more difficult feedstock t}-an the dilute suspensions previously treated, and which uses a filter which is easily regenerable We have now discovered that a pre-coated surface 11~353~5 filter is capable of meeting this need. It is indeed surprising that a surface filter can be used since the teachings of the art would suggest that an even thicker depth filter would be necessary and that restructuring the filter bed after regeneration could not be avoided.
Thus according to the present invention there is provided a method for the treatment of an oily sludge which method comprises the steps of filtering the sludge undiluted with recovered oil in a pre-coated surface filter, treating the filtration residue with a light hydrocarbon solvent and/or steam stripping the extracted residue.
Suitable pre-coat materials include diatomaceous earth, fly ash and powdered polymers, e.g., polyurethanes.
Before filtering sludges with a high solids content, water is preferably added as a diluent. Alternatively a light hydrocarbon solvent maybeemployed.
The filtration may be carried out at ambient or elevated temperature. If elevated temperature is used, the oily sludqe may be directly heated by conventional means, e.g., steam coils.
Suitable surface filters include plate, leaf and tube or candle filters. The filters are preferably operated under pressure as opposed to vacuum.
In such filters, the pre-coat is effectively the filter medium and the function of the plate, leaf and tube or candle, etc., is to act as a support.
The preferred hydrocarbon washing solvent is kerosine, but other solvents such asnaphtha are also suitable.
Treatment may be at ambient temperature but higher 5.
~1~5395 temperatures may be advantageous in certain cases.
Solvent washing may be carried out in two stages, with the relatively clean solvent from the second stage of one cycle being used in the first stage of the next cycle to wash heavily contaminated solids.
Filter aids similar to or identical with the pre-coat medium may be added to the sludge before filtration to ensure longer and improved filtration by increasing the porosity of the filter cake, reducing the differential pressure per unit cake thickness and preventing the cake from blinding, For a low concentration of up to 1% by weight solids in the feed sludge, the amount of filter aid used is preferably in the range 2 - 4 times the weight of solids.
For a medium concentration of 1 - 4% solids, the amount of filter aid used is preferably in the range 1 - 2 times the weight of solids. For a high concentration, e.g., 4% or higher solids, the amount of filter aid used is preferably in the weight range 0.5 - 1.5 times the weight of solids. In general, the finer the particle si~e of the solids, the more filter aid is required.
It is advantageous to use the minimum quantity of filter aid consistent with satisfactory filtration, since the less filter aid employed, the slower the build up of filter cake and the longer the filtration run.
As an additional feature, it may be advantageous to interpose a drying stage after the filtration and before the solvent extraction. Drying may be achieved by treatment with hot or cold air The filtration flowrate is suitably in the range ~s~
1 - 2Q0 gallons per square foot of filtration area per hour (0.Q5 - 10 m3/m /hr), preferably in the range 10 to 50 gal/ft /
hr (Q.5 - 2.5 m3/m2/hr).
Solvent consumption and flowrate are dependent on the ; oil content of the filtered solids.
Steam consump~on and flowr-ate are dependent on-tlle boiling point of the solvent.
The filtered solids are easily removed from the filter, e.g., by scraping or centrifugal action, thus leaving the filter clean to resume the next cycle.
It is believed that the solid particles present in the ~-sludge stabilise emulsification of the oil and water also present and that, with their removal, the oil and water can subsequently separate more easily. Some oil, however, is retained by the solids a~d is removed by the solvent extraction and/or steam stripping.
By the method of the present invention it is possible to convert an oily sludge to a dry solid containing less than 1~ by weight oil. Such material is suitable for land fill operations.
The invention is illustrated by the following example.
Example Sludge used : Refinery API Separator Bottom Sludge Analysis : Oil 40%
Water 52.5 Solid 7.5~
Filter : Stainless Steel Candle Filter.
The filter tube (100 micron aperture) was pre-coated with diatomaceous earth to a thickness of 3mm. rrne....................... .;
~1~53~5 sludge was slurried with 9 parts water to 1 part sludge and 0.4% w/w diatomaceous earth was added to the slurry as a filter aid. The slurry was then filtered at ambient temperature at an average flowrate of 24 gallons/hr/ft of filtration area (1,25 m3/m2/hr). The filtration was terminated at a maximum differential pressure of 4 bar when 3.4 gallons/ft2 of filtration area (150 mitre/m2) had been filtered. The filter body was drained and filled with kerosine at ambient temperature. The , filtered solids were then washed in situ with 3 gallons kerosine/ft2 of filtration area. The filtration body was drained and the filtered solids steam stripped in situ for 15 minutes. The steam pressure was 25 psig (1,7 bar (ga)), Analysis of filter cake : Oil 0.8%
Water 0.6%
Solid 98,6%
This invention relates to a method for treating oil contaminated solids, particularly the residues formed as a by-product from the treatment of oil contaminated water, such as refinery or other industrial plant effluent, or resulting from the long standing of crude petroleum or petroleum products in tanks or other forms of storage.
As a first step in the treatment of oil contaminated waters it is common practice to effect a rough separation in a gravity separator to remove the bulk of the oil and suspended solids. Suitable separators include parallel plate separators, settlement tanks and API Separators as described in the "Manual on Disposal of Refinery Wastes", published by the American Petroleum Institute in 1969.
Oil recovered from such devices can be used as a source of energy and the aqueous effluent is suitable for further treatment to reduce its oil content and ~OD to very low levels.
Such a further treatment is disclosed and claimed in our Canadian Patent No. 1026021 which claims a method for treating effluent water containing suspended oil which method comprises passing the effluent water firstly through a sand filter to remove the suspended oil and subsequently through a biological percolating filter.
Returning to the primary separation devices, there is a third product from them which builds up over a period of time and the disposal of which gives rise to problems. This is an oilysludge which can have a water content in the range ~' ```` 113!S3~S
20 - 95% by weight and an oil content in the range 5 - 70% by weight, the remainder being solid materials such as silt, rust, carbon, calcium carbonate, etc.
Other sources of oily sludge are sand filter backwash water from the effluent treatment process described in Canadian Patent No. 1026021 and the top oily sludge layer from gas/air flotation plants for the removal of dispersed oil and suspended solids from water.
Oily sludge is a difficult material to process since it tends to block filters and adhere to them.
The only environmentally accepted method of dealing with these sludges is by burning, but this requires the provision of special incinerators which are expensive to purchase, install, operate and maintain and which result in the wasteful destruction of oil.
A process has been disclosed in British Patent Specification 1340931 in which oily solid particles suspended in aqueous effluent are retained by a sand filter.
A sand filter operates by allowing the liquid to be filtered to percolate slowly downwards through a thick bed of filter sand. The sand is relatively coarse when compared with the solid particles to be retained and the particles, especially the finer ones, tend to pass through the upper reaches of the sand. Eventually, however, the packing results in tortuosities and restrictions which trap the particles, including the finer ones.
~.................................................................. .
3~3!5 Because of their effectiveness in dealing with materials which tend to block or pass through other filters, sand filters are widely used in oil refineries and similar installations The same factors which result in the efficiency of the sand bed when working as a filter give rise to problems when regeneration is necessary, however. In order to regenerate a filter, retained-solid particles must be removed. Because particles are trapped at all levels in the filter bed, regeneration, either by backward or forward flushing, means that some particles have again to traverse the bed and again are likely to meet with further restrictions which tend to retain them in the filter unless dislodged. In order to combat this, it is necessary to wash either frequently or for long periods and to use high flow rates and/or liquid under high pressure with the ever present risk, unless great care is exercised, of disturbing the structure of the filter bed and rendering it inefficient for subsequent filtration stages, unless restructured.
The residue resulting from the filtration of oily sludge adheres strongly to a sand filter and the difficulties of regeneration are such that sand filters have been rejected for such operations.
There exists a need, therefore, for a simple method of filtration which is capable of dealin( with concentrated oily sludge, a more difficult feedstock t}-an the dilute suspensions previously treated, and which uses a filter which is easily regenerable We have now discovered that a pre-coated surface 11~353~5 filter is capable of meeting this need. It is indeed surprising that a surface filter can be used since the teachings of the art would suggest that an even thicker depth filter would be necessary and that restructuring the filter bed after regeneration could not be avoided.
Thus according to the present invention there is provided a method for the treatment of an oily sludge which method comprises the steps of filtering the sludge undiluted with recovered oil in a pre-coated surface filter, treating the filtration residue with a light hydrocarbon solvent and/or steam stripping the extracted residue.
Suitable pre-coat materials include diatomaceous earth, fly ash and powdered polymers, e.g., polyurethanes.
Before filtering sludges with a high solids content, water is preferably added as a diluent. Alternatively a light hydrocarbon solvent maybeemployed.
The filtration may be carried out at ambient or elevated temperature. If elevated temperature is used, the oily sludqe may be directly heated by conventional means, e.g., steam coils.
Suitable surface filters include plate, leaf and tube or candle filters. The filters are preferably operated under pressure as opposed to vacuum.
In such filters, the pre-coat is effectively the filter medium and the function of the plate, leaf and tube or candle, etc., is to act as a support.
The preferred hydrocarbon washing solvent is kerosine, but other solvents such asnaphtha are also suitable.
Treatment may be at ambient temperature but higher 5.
~1~5395 temperatures may be advantageous in certain cases.
Solvent washing may be carried out in two stages, with the relatively clean solvent from the second stage of one cycle being used in the first stage of the next cycle to wash heavily contaminated solids.
Filter aids similar to or identical with the pre-coat medium may be added to the sludge before filtration to ensure longer and improved filtration by increasing the porosity of the filter cake, reducing the differential pressure per unit cake thickness and preventing the cake from blinding, For a low concentration of up to 1% by weight solids in the feed sludge, the amount of filter aid used is preferably in the range 2 - 4 times the weight of solids.
For a medium concentration of 1 - 4% solids, the amount of filter aid used is preferably in the range 1 - 2 times the weight of solids. For a high concentration, e.g., 4% or higher solids, the amount of filter aid used is preferably in the weight range 0.5 - 1.5 times the weight of solids. In general, the finer the particle si~e of the solids, the more filter aid is required.
It is advantageous to use the minimum quantity of filter aid consistent with satisfactory filtration, since the less filter aid employed, the slower the build up of filter cake and the longer the filtration run.
As an additional feature, it may be advantageous to interpose a drying stage after the filtration and before the solvent extraction. Drying may be achieved by treatment with hot or cold air The filtration flowrate is suitably in the range ~s~
1 - 2Q0 gallons per square foot of filtration area per hour (0.Q5 - 10 m3/m /hr), preferably in the range 10 to 50 gal/ft /
hr (Q.5 - 2.5 m3/m2/hr).
Solvent consumption and flowrate are dependent on the ; oil content of the filtered solids.
Steam consump~on and flowr-ate are dependent on-tlle boiling point of the solvent.
The filtered solids are easily removed from the filter, e.g., by scraping or centrifugal action, thus leaving the filter clean to resume the next cycle.
It is believed that the solid particles present in the ~-sludge stabilise emulsification of the oil and water also present and that, with their removal, the oil and water can subsequently separate more easily. Some oil, however, is retained by the solids a~d is removed by the solvent extraction and/or steam stripping.
By the method of the present invention it is possible to convert an oily sludge to a dry solid containing less than 1~ by weight oil. Such material is suitable for land fill operations.
The invention is illustrated by the following example.
Example Sludge used : Refinery API Separator Bottom Sludge Analysis : Oil 40%
Water 52.5 Solid 7.5~
Filter : Stainless Steel Candle Filter.
The filter tube (100 micron aperture) was pre-coated with diatomaceous earth to a thickness of 3mm. rrne....................... .;
~1~53~5 sludge was slurried with 9 parts water to 1 part sludge and 0.4% w/w diatomaceous earth was added to the slurry as a filter aid. The slurry was then filtered at ambient temperature at an average flowrate of 24 gallons/hr/ft of filtration area (1,25 m3/m2/hr). The filtration was terminated at a maximum differential pressure of 4 bar when 3.4 gallons/ft2 of filtration area (150 mitre/m2) had been filtered. The filter body was drained and filled with kerosine at ambient temperature. The , filtered solids were then washed in situ with 3 gallons kerosine/ft2 of filtration area. The filtration body was drained and the filtered solids steam stripped in situ for 15 minutes. The steam pressure was 25 psig (1,7 bar (ga)), Analysis of filter cake : Oil 0.8%
Water 0.6%
Solid 98,6%
Claims (14)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE
DEFINED AS FOLLOWS:
1. A method for the treatment of oily sludge which method comprises the steps of filtering the sludge in a pre-coated surface filter, treating the filtration residue with a hydro-carbon solvent and steam stripping the extracted residue.
2. A method according to claim 1 wherein the pre-coat material is diatomaceous earth.
3. A method according to claim 1 wherein the sludge is diluted with water before filtration.
4. A method according to claim 1, 2 or 3 wherein the surface filter is a plate or candle filter.
5. A method according to claim 1, 2 or 3 wherein the filter is operated under pressure.
6. A method according to claim 1, 2 or 3 wherein the solvent is kerosine.
7. A method according to claim 1, 2 or 3 wherein the solvent is heated.
8. A method according to claim 1, 2 or 3 wherein solvent washing is carried out in two stages with solvent from the second stage of one cycle being used in the first stage of the next cycle.
9. A method according to claim 1, 2 or 3 wherein a filter aid is added to the oily sludge before filtration.
10. A method according to claim 1, 2 or 3 wherein diatomaceous earth is added as a filter aid to the oily sludge before filtration.
11. A method according to claim 1, 2 or 3 wherein a drying stage is interposed after filtration and before solvent extraction.
12. A method according to claim 1, 2 or 3 wherein the filtration flowrate is in the range 0.05 - 10 m3/m2/hr.
13. A method according to claim 1, 2 or 3 wherein the filtration flowrate is in the range 0.5 - 2.5 m3/m2/hr.
14. A method according to claim 1, 2 or 3 wherein the filtered solids are removed from the filter by scraping or centrifugal action.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA297,634A CA1105395A (en) | 1978-02-23 | 1978-02-23 | Treatment of oily sludge |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA297,634A CA1105395A (en) | 1978-02-23 | 1978-02-23 | Treatment of oily sludge |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105395A true CA1105395A (en) | 1981-07-21 |
Family
ID=4110852
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,634A Expired CA1105395A (en) | 1978-02-23 | 1978-02-23 | Treatment of oily sludge |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1105395A (en) |
-
1978
- 1978-02-23 CA CA297,634A patent/CA1105395A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |