CA1134282A - Filtering with pressure drop increasing stepwise - Google Patents
Filtering with pressure drop increasing stepwiseInfo
- Publication number
- CA1134282A CA1134282A CA302,462A CA302462A CA1134282A CA 1134282 A CA1134282 A CA 1134282A CA 302462 A CA302462 A CA 302462A CA 1134282 A CA1134282 A CA 1134282A
- Authority
- CA
- Canada
- Prior art keywords
- filter
- pressure drop
- process according
- continuous
- oil
- 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
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D37/00—Processes of filtration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/06—Filters with filtering elements which move during the filtering operation with rotary cylindrical filtering surfaces, e.g. hollow drums
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/44—Regenerating the filter material in the filter
- B01D33/46—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element
- B01D33/466—Regenerating the filter material in the filter by scrapers, brushes nozzles or the like acting on the cake-side of the filtering element scrapers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D33/00—Filters with filtering elements which move during the filtering operation
- B01D33/58—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element
- B01D33/60—Handling the filter cake in the filter for purposes other than for regenerating the filter cake remaining on the filtering element for washing
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
- Filtration Of Liquid (AREA)
- Fats And Perfumes (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT
A process for removing solid particles which form a compressible filter cake from a liquid stream by means of a continuous filter, for example of the rotary discs or drum type, comprising increasing the pressure drop across the filter from the minimum practicable value for an acceptable flow to the maximum permissable value across the filter in a few distinct steps.
A process for removing solid particles which form a compressible filter cake from a liquid stream by means of a continuous filter, for example of the rotary discs or drum type, comprising increasing the pressure drop across the filter from the minimum practicable value for an acceptable flow to the maximum permissable value across the filter in a few distinct steps.
Description
`:
~34Z~2 This invention relates to a process for the re-moval of solid particles which form a compressible filter cake from a liquid stream, the stream being conducted through a continuous filter, such as a rotary disc or drum filter.
It is known that in the removal of solid particles from a liquid by filtration the liquid is passed through a filter in which the solid particles are left behind.
With filtration in its most elementary form the problem is that when the filter has been in use for some time, a filter cake develops on it, which results in an increased resistance of the filter until finally com-plete blockage occurs. The yield of the filter in terms of filtered liquid will therefore gradually decrease.
A distinction can be made between two sorts of filter cake, viz. a compressible and a non-compressible type. It is known that with non-compressible filter cakes the yield of filtered liquid in principle increases according as the~pressure drop across the filter is increased. With compressible filter cakes, on the other hand, it is seen that once a threshold pres-sure drop is reached an increased pressure drop across the filter causes no perceptible increase in yield of filtered llquid.
S m ce the;~yield of filtered liquid rapidly decreases with compresslble filter cakes, ways have been sought to
~34Z~2 This invention relates to a process for the re-moval of solid particles which form a compressible filter cake from a liquid stream, the stream being conducted through a continuous filter, such as a rotary disc or drum filter.
It is known that in the removal of solid particles from a liquid by filtration the liquid is passed through a filter in which the solid particles are left behind.
With filtration in its most elementary form the problem is that when the filter has been in use for some time, a filter cake develops on it, which results in an increased resistance of the filter until finally com-plete blockage occurs. The yield of the filter in terms of filtered liquid will therefore gradually decrease.
A distinction can be made between two sorts of filter cake, viz. a compressible and a non-compressible type. It is known that with non-compressible filter cakes the yield of filtered liquid in principle increases according as the~pressure drop across the filter is increased. With compressible filter cakes, on the other hand, it is seen that once a threshold pres-sure drop is reached an increased pressure drop across the filter causes no perceptible increase in yield of filtered llquid.
S m ce the;~yield of filtered liquid rapidly decreases with compresslble filter cakes, ways have been sought to
- 2 - ;
3~Z~32 overcome this problem. This search has produced many variant.s of the continuou.s filter in which the filter cake is also removed continuously. Two important examples of this type of filter are the rotary disc filter and the rotary drum filter. With both types the pressure drop across the filter can be created by a positive pressure on the pressure side and/or reduced pressure on t'ne discharge side of the filter.
A further problem in the filtration of particles which form compressible filter cakes from a liquid with the aid of a continuous filter is that in spite of the continuous remo~al of the filter cake the yield of filtered liquid drops relatively rapidly. For instance, when crystallized~wax particles are removed from a hydrocarbon oil with a rotary drum filter, it is found that although the filter cake is scraped off and the `
filter washed in counterflow the drum filter beco~es blocked within a period of only a few hours to such an extent that the yield of filtered oil drops below an acceptable minimum. The filter then has to be taken out of service and cleaned, which results in a loss of production. ,-The present invention aims to provide a method by which the yield of flltered llquid is lncreased for continuous filters over the period of time until ef-fective blocking occurs and/or by which this period is :
' ' .
~34Z~
extended. To this end, the pressure drop across the filter is increased stepwise in the process according to the invention.
Surprisingly, it has been found that - although the yield of filtered liquid as a function of time is almost independent of the pressure drop across the filter - a stepwise increase effects an increase in yield each time. Naturally, the yield gradually falls again after each increase, but the observed difference in yield before and aftèr the stepwise increase is found to persist.
Thus, according to the present invention, there is provided a process for the removal of wax particles, which form a compressible filter cake, from a hydrocarbon oil, the oil being conducted to a continuous filter, in which the pressure drop across the filter is increased stepwise by at least 0.1 bar at each step.
In this specification the term stepwise increase refers to an increase which takes place in a jump, i.e. which has the character of a distinct increase in pressure drop effected within a short time - hence clearly some time before a new increase.
According to a preferred embodiment of the invention, the pressure drop across the filter is created by reducing the pressure on the side of the filter through which the liquid leaves the filter. The liquid usually flows through continuous filters from the outside to the inside, so that in the case of the above-mentioned so-called reduced pressure filter the space round it can remain at atmospheric pressure and therefore does not require an exceptionally ~.~L3~
strong construction, whilst inside the filter a reduced pressure is maintained. In implementing this feature of the invention, it is advantageous that a relatively small volume is rapidly brought to the new reduced pressure.
In order to benefit most from the effect of the invention, i.e. an increase in yield, it is preferred to pass the liquid stream through the filter in a filtering zone and remove the particles left behind on the filter ;
in a cleaning zone by countercurrent washing, scraping off and/or blowing off with an inert gas in the reverse direction to that of the flow. In this way the filter resistance is continuously kept as low as possible. In addition, the effect of the invention then proves to be substantial. ;`
The removal of wax from mineral oil products, the so-called dewaxing, leads to the formation of compres-sible filter cakes and even with the continuous removal of the filter cake from a continuous filter, the total period during which the filter can be kept in operation is limited to a few hours. Tn view of the quantities of liquid to be filtered that are usually handled, the provision accordlng to the invention can result in a `
considerable saving.
In this dewaxing the stepwise increase in the , pressure drop across the filter is preferably carried :"
:
,~
.
~3~28,(3 out in such a way that the pressure drop is increased each time by at least 0.1 bar. This means a considerable restriction indeed in the total number of pressure drop increases possible (the reduced pressure being further reduced each time) in particular with the continuous filters whicll already have a reduced pressure inside the filter such as those which are usually employed for dewaxing. But it has been found that a few large pres-sure drop increases have a greater effect than a larger number of smaller pressure drop increases. It is even preferred to increase the pressure drop only once every thirty minutes.
In case the invention is applied to a process in ~-which the filter is taken out of service as soon as the quantity of liquid passed through per unit tlme has dropped below an unacceptable minimum, it is preferred according to the invention to increase the pressure drop across the filter stepwise at most three times over the period between putting the filter into service and withdrawing it from service. ~
Although differences are~found in individual cases, `
the best result will generally be achieved when the pressure drop is increased each time at a rate of at least 1 bar per hour. At too low a rate the result will be small, at too high a rate the cost of the equipment that is required for increaslng the pressure drop may become excessive or the filter may even be damaged. ~;-`;
~3~ 2 The invention will be further elucidated herein-after with reference to an example. The accompanying figure is a graph showing the yield of filtered liquid as a function of time for three experiments.
Example An oil containing 2~.7 %w wax in the form of small crystals which produced a compressible filter cake was filtered with the aid of a rotary drum filter in which a reduced pressure was maintained inside the cylindrical filter. The filter was continuously scraped.
As it had been found that the rotational speed of the drum filter has an influence on the oil content of the filter cake and consequently on the yield of fil-tered oil, the three experiments were carried out at the same rotational speed, i.e. 36 revolutions per hour.
The first experiment was performed at a pressure drop across the filter of 0.8 bar; i.e. the pressure outside the filter was 1.0 bar and inside the fil~er 0.2 bar. The experiment was started with a clean filter. The yield of filtered oil was continuously determined with continuous scraping off and blowing off of wax from the filter for four hours, after which the experiment was stopped. The result has been shown in the graph (curve A), in which the yield of filtered oil in tonnes per day has been plotted against filtration time in minutes.
The experiment was then repeated with a clean filter and with a pressure drop across the filter of ;~
only 0.2 bar (see curve B).
~3~
Then, a third experiment was carried out ~see curve C), which was started with a clean filter again and with an initial pressure drop across the filter of 0.2 bar.
During this third filtration the pressure drop was increased stepwise three times according to the inven-tion, viz. after 70 minutes from 0.2 bar to 0.4 bar, after 130 minutes from 0.4 bar to 0.6 bar and after 190 minutes from 0.6 to 0.8 bar. These stepwise increases of the pressure drop were effected each time within lO `
minutes.
The graph shows that at a pressure drop of 0.8 bar the yield is almost equal to the yield at a pressure -drop of 0.2 bar (curves A and B); the pressure drop of 0.8 bar initially caused a somewhat higher and subse-quently (after about 80 minutes) a somewhat lower yield than the pressure drop of 0.2 bar. ~ `~
From curve C it is seen that the stepwise pressure drop increases raise the yield to a level that is higher than that of curves A and B and that the yield is in-creased in particular during the pressure drop increase ;~
proper, whilst the relative increase persists, at least ~
partly, after each pressure drop increase. -It will be clear that the surface area under the curve is a measure of the total yield of filtered liquid and that this totaI yield is highest for curve C.
'.
A further problem in the filtration of particles which form compressible filter cakes from a liquid with the aid of a continuous filter is that in spite of the continuous remo~al of the filter cake the yield of filtered liquid drops relatively rapidly. For instance, when crystallized~wax particles are removed from a hydrocarbon oil with a rotary drum filter, it is found that although the filter cake is scraped off and the `
filter washed in counterflow the drum filter beco~es blocked within a period of only a few hours to such an extent that the yield of filtered oil drops below an acceptable minimum. The filter then has to be taken out of service and cleaned, which results in a loss of production. ,-The present invention aims to provide a method by which the yield of flltered llquid is lncreased for continuous filters over the period of time until ef-fective blocking occurs and/or by which this period is :
' ' .
~34Z~
extended. To this end, the pressure drop across the filter is increased stepwise in the process according to the invention.
Surprisingly, it has been found that - although the yield of filtered liquid as a function of time is almost independent of the pressure drop across the filter - a stepwise increase effects an increase in yield each time. Naturally, the yield gradually falls again after each increase, but the observed difference in yield before and aftèr the stepwise increase is found to persist.
Thus, according to the present invention, there is provided a process for the removal of wax particles, which form a compressible filter cake, from a hydrocarbon oil, the oil being conducted to a continuous filter, in which the pressure drop across the filter is increased stepwise by at least 0.1 bar at each step.
In this specification the term stepwise increase refers to an increase which takes place in a jump, i.e. which has the character of a distinct increase in pressure drop effected within a short time - hence clearly some time before a new increase.
According to a preferred embodiment of the invention, the pressure drop across the filter is created by reducing the pressure on the side of the filter through which the liquid leaves the filter. The liquid usually flows through continuous filters from the outside to the inside, so that in the case of the above-mentioned so-called reduced pressure filter the space round it can remain at atmospheric pressure and therefore does not require an exceptionally ~.~L3~
strong construction, whilst inside the filter a reduced pressure is maintained. In implementing this feature of the invention, it is advantageous that a relatively small volume is rapidly brought to the new reduced pressure.
In order to benefit most from the effect of the invention, i.e. an increase in yield, it is preferred to pass the liquid stream through the filter in a filtering zone and remove the particles left behind on the filter ;
in a cleaning zone by countercurrent washing, scraping off and/or blowing off with an inert gas in the reverse direction to that of the flow. In this way the filter resistance is continuously kept as low as possible. In addition, the effect of the invention then proves to be substantial. ;`
The removal of wax from mineral oil products, the so-called dewaxing, leads to the formation of compres-sible filter cakes and even with the continuous removal of the filter cake from a continuous filter, the total period during which the filter can be kept in operation is limited to a few hours. Tn view of the quantities of liquid to be filtered that are usually handled, the provision accordlng to the invention can result in a `
considerable saving.
In this dewaxing the stepwise increase in the , pressure drop across the filter is preferably carried :"
:
,~
.
~3~28,(3 out in such a way that the pressure drop is increased each time by at least 0.1 bar. This means a considerable restriction indeed in the total number of pressure drop increases possible (the reduced pressure being further reduced each time) in particular with the continuous filters whicll already have a reduced pressure inside the filter such as those which are usually employed for dewaxing. But it has been found that a few large pres-sure drop increases have a greater effect than a larger number of smaller pressure drop increases. It is even preferred to increase the pressure drop only once every thirty minutes.
In case the invention is applied to a process in ~-which the filter is taken out of service as soon as the quantity of liquid passed through per unit tlme has dropped below an unacceptable minimum, it is preferred according to the invention to increase the pressure drop across the filter stepwise at most three times over the period between putting the filter into service and withdrawing it from service. ~
Although differences are~found in individual cases, `
the best result will generally be achieved when the pressure drop is increased each time at a rate of at least 1 bar per hour. At too low a rate the result will be small, at too high a rate the cost of the equipment that is required for increaslng the pressure drop may become excessive or the filter may even be damaged. ~;-`;
~3~ 2 The invention will be further elucidated herein-after with reference to an example. The accompanying figure is a graph showing the yield of filtered liquid as a function of time for three experiments.
Example An oil containing 2~.7 %w wax in the form of small crystals which produced a compressible filter cake was filtered with the aid of a rotary drum filter in which a reduced pressure was maintained inside the cylindrical filter. The filter was continuously scraped.
As it had been found that the rotational speed of the drum filter has an influence on the oil content of the filter cake and consequently on the yield of fil-tered oil, the three experiments were carried out at the same rotational speed, i.e. 36 revolutions per hour.
The first experiment was performed at a pressure drop across the filter of 0.8 bar; i.e. the pressure outside the filter was 1.0 bar and inside the fil~er 0.2 bar. The experiment was started with a clean filter. The yield of filtered oil was continuously determined with continuous scraping off and blowing off of wax from the filter for four hours, after which the experiment was stopped. The result has been shown in the graph (curve A), in which the yield of filtered oil in tonnes per day has been plotted against filtration time in minutes.
The experiment was then repeated with a clean filter and with a pressure drop across the filter of ;~
only 0.2 bar (see curve B).
~3~
Then, a third experiment was carried out ~see curve C), which was started with a clean filter again and with an initial pressure drop across the filter of 0.2 bar.
During this third filtration the pressure drop was increased stepwise three times according to the inven-tion, viz. after 70 minutes from 0.2 bar to 0.4 bar, after 130 minutes from 0.4 bar to 0.6 bar and after 190 minutes from 0.6 to 0.8 bar. These stepwise increases of the pressure drop were effected each time within lO `
minutes.
The graph shows that at a pressure drop of 0.8 bar the yield is almost equal to the yield at a pressure -drop of 0.2 bar (curves A and B); the pressure drop of 0.8 bar initially caused a somewhat higher and subse-quently (after about 80 minutes) a somewhat lower yield than the pressure drop of 0.2 bar. ~ `~
From curve C it is seen that the stepwise pressure drop increases raise the yield to a level that is higher than that of curves A and B and that the yield is in-creased in particular during the pressure drop increase ;~
proper, whilst the relative increase persists, at least ~
partly, after each pressure drop increase. -It will be clear that the surface area under the curve is a measure of the total yield of filtered liquid and that this totaI yield is highest for curve C.
'.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the removal of wax particles, which form a com-pressible filter cake, from a hydrocarbon oil, the oil being conducted to a continuous filter, in which the pressure drop across the filter is in-creased stepwise by at least 0.1 bar at each step.
2. A process according to claim 1, characterized in that the pres-sure drop across the filter is created by reduced pressure on the side of the filter whence the liquid leaves the filter.
3. A process according to claim 1, characterized in that the oil conducted to the continuous filter is passed through the filter in a filter-ing zone and in that the particles left behind on the filter are removed in a cleaning zone, by a technique selected from at least one of the following, countercurrent washing, scraping and blowing off with an inert gas in re-verse direction to that of the oil conducted to the continuous filter.
4. A process according to claim 1, characterized in that the pres-sure drop is increased only once every thirty minutes.
A process according to claim 3, in which the filter is taken out of service as soon as the quantity of liquid discharged per unit time has dropped below an unacceptable minimum, characterized in that the pressure drop across the filter is increased stepwise at most three times over the period between putting the filter into service and withdrawing it from service.
6. A process according to claim 1, characterized in that the pressure drop is increased each time at a rate of at least 1 bar per hour.
7. A process according to claim 1, wherein the continuous filter is a rotary disc or a drum filter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7705928A NL7705928A (en) | 1977-05-31 | 1977-05-31 | PROCESS FOR THE REMOVAL OF SOLID PARTICLES FROM A FLOW LIQUID. |
| NL7705928 | 1977-05-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134282A true CA1134282A (en) | 1982-10-26 |
Family
ID=19828641
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,462A Expired CA1134282A (en) | 1977-05-31 | 1978-05-02 | Filtering with pressure drop increasing stepwise |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS53148769A (en) |
| AU (1) | AU528474B2 (en) |
| BE (1) | BE867398A (en) |
| CA (1) | CA1134282A (en) |
| DE (1) | DE2823380A1 (en) |
| FR (1) | FR2392704A1 (en) |
| GB (1) | GB1589004A (en) |
| IN (1) | IN148504B (en) |
| NL (1) | NL7705928A (en) |
| ZA (1) | ZA783052B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU2002368091A1 (en) * | 2002-07-22 | 2004-02-09 | Heinkel Ag | Method for increasing the volume flow of a filtrate in separation processes with filter cake formation, and device for carrying out said method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR867532A (en) * | 1939-02-11 | 1941-11-10 | Texaco Development Corp | Mineral Oil Dewaxing Improvements |
| GB1278629A (en) * | 1968-08-30 | 1972-06-21 | Mta | Continuous filtration process with recirculation |
-
1977
- 1977-05-31 NL NL7705928A patent/NL7705928A/en not_active Application Discontinuation
-
1978
- 1978-05-02 CA CA302,462A patent/CA1134282A/en not_active Expired
- 1978-05-03 IN IN324/DEL/78A patent/IN148504B/en unknown
- 1978-05-24 BE BE1008895A patent/BE867398A/en not_active IP Right Cessation
- 1978-05-29 ZA ZA00783052A patent/ZA783052B/en unknown
- 1978-05-29 JP JP6343678A patent/JPS53148769A/en active Pending
- 1978-05-29 DE DE19782823380 patent/DE2823380A1/en not_active Withdrawn
- 1978-05-29 AU AU36585/78A patent/AU528474B2/en not_active Expired
- 1978-05-29 FR FR7815895A patent/FR2392704A1/en active Granted
- 1978-05-30 GB GB23733/78A patent/GB1589004A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1589004A (en) | 1981-05-07 |
| BE867398A (en) | 1978-11-24 |
| AU528474B2 (en) | 1983-04-28 |
| IN148504B (en) | 1981-03-14 |
| NL7705928A (en) | 1978-12-04 |
| JPS53148769A (en) | 1978-12-25 |
| FR2392704B1 (en) | 1983-01-28 |
| ZA783052B (en) | 1979-07-25 |
| AU3658578A (en) | 1979-12-06 |
| DE2823380A1 (en) | 1978-12-07 |
| FR2392704A1 (en) | 1978-12-29 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |