WO2017198684A1

WO2017198684A1 - Method of removing deposits from an inside surface of a conduit

Info

Publication number: WO2017198684A1
Application number: PCT/EP2017/061778
Authority: WO
Inventors: Richard RANDLE
Original assignee: Linde Aktiengesellschaft
Priority date: 2016-05-17
Filing date: 2017-05-16
Publication date: 2017-11-23
Also published as: GB201608651D0

Abstract

In order to overcome the limitations and problems that earlier methods have experienced a method of removing deposits from an inside surface of a conduit (5) is proposed, the method comprising: - forming a cleaning material, - introducing the cleaning material into the conduit (5) and forcing the cleaning material along within the conduit (5), wherein the cleaning material is formed by adding carbon dioxide into an ice-based slush (20).

Description

M E T H O D O F R E M O V I N G D E P O S I T S

F R O M A N I N S I D E S U R F A C E O F A C O N D U I T

Technical field of the present invention

The present invention relates to a method for removing deposits from an inside surface of a conduit involving so-called "ice pigging" and, in particular, to an improved method of ice pigging.

Technological background of the present invention

Ice pigging is a process in which an ice slurry is pumped into a pipe and forced along the inside in order to remove sediment and other unwanted deposits to leave the pipe clean. It has many applications in the water, sewage and food industries.

It is known to clean pipes with high velocity water to flush through the pipes. It is also known to force solid cleaning devices along pipes to clean them. Ice pigging provides benefits associated with both of these processes.

Typically an ice-water slurry comprising a significant ice fraction is introduced to and removed from pipes provided with suitable hydrants and valves. The large ice fraction lends several attributes which are particularly appealing for application in pigging. For example, it is able to hold itself together under continuous shear. If the ice becomes stuck then given enough time it will just melt and be carried away. It is fairly inexpensive to make since it is made from water. It leaves the pipe walls themselves generally undamaged and only removes waste residue. In a typical process, an ice pig is inserted into the pipe in a semi liquid form.

Ice pigging does not require expensive excavation or preliminary treatment because the ice pig can be inserted into a pipe through existing access points irrespective of their diameter and then expand to the size required. Likewise the ice will exit the pipe with ease through any valve. Ice pigging uses less water than traditional flushing pipe cleaning methods as it is more effective on the first pass.

Ice pigging is discussed in detail for example in WO 01/51224 A1 or in WO 2004/000475 A1.

Accordingly, it is desirable to provide an alternative method for conduit cleaning, and/or tackle at least some of the problems associated with the prior art or, at least, to provide a commercially useful alternative thereto. Disclosure of the present invention: object, solution, advantages

Starting from the disadvantages and shortcomings as described above as well as taking the prior art as discussed into account, an object of the present invention is to overcome the limitations and problems that earlier methods have experienced.

These objects are accomplished by a method comprising the features of claim 1. Advantageous embodiments and expedient improvements of the present invention are disclosed in the respective dependent claims.

The present invention basically provides for conduit cleaning.

According to a first aspect of the invention, the present disclosure provides a method of removing deposits from an inside surface of a conduit, the method comprising:

- forming a cleaning material,

- introducing the cleaning material into the conduit and forcing the cleaning material along within the conduit,

wherein the cleaning material is formed by adding carbon dioxide into an ice-based slush. The present invention will now be further described. In the following passages different aspects of the present invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

The present invention relates to a method of removing deposits from an inside surface of a conduit. By the term "conduit" is meant a channel suitable for conveying water or other fluids. The conduit is typically a tube having an inlet end and an outlet end and may be provided with suitable valves for isolating a portion of a larger conduit or conduit system to be treated.

The technique may be used for removing biofilm and sediments from water and wastewater pipes used in the chemical, water and sewerage industries.

In addition the method may be applied to surface preparation of conduits and treatment vessels prior to coating and painting, thereby removing the need for adding biocides to water-based paints. This could be used for oil refinery and petrochemical vessels and tanks.

The method may be used for the cleaning of process pipes in the food industry as a replacement for more conventional clean-in-place (CIP) applications that are chemical-intensive. For example, the technique might find application in plants involving the processing of dairy, jams and sauces, processed meats, drinks and beverages and the like.

Furthermore, the technique may be used as a replacement for corrosive chemicals, used by public house landlords in the preparation of "beer-slush" to clean pipes by natural, organic means and thereby minimise wastage.

In addition, because of the applicability of the technique to small ducts and orifices down to about 0.7 mm, it is possible to use the technique to sterilise medical products such as syringes or cannula by preparing the slush with chemical biocides.

The method comprises forming a cleaning material. The cleaning material is an ice-based slush comprising ice crystals suspended in water. By "ice-based" it is meant that at least fifty percent by weight of the slush is ice with the remainder water.

Preferably the ice crystals form from fifty weight percent to ninety weight percent of the slush, more preferably from sixty weight percent to eighty weight percent.

As will be appreciated, the inclusion of higher levels of ice leads to a more solid and viscous pig. Therefore the levels of ice in the slush may be fine-tuned to the specific application.

Furthermore, since the ice content will typically reduce during treatment as the ice melts, the above solids (ice) levels are with reference to the slush formed which is then introduced into the conduit at the start of the treatment.

In order to ensure a homogeneous slush mixture is formed, the slush will typically be produced in a large mixing tank. The slush is formed by the cooling of water to form ice within the remaining water and typically includes mixing and/or surface scraping. Control over the mixing speed and the rate of cooling allows control of the ice-crystal size and distribution.

The cleaning material is formed by adding carbon dioxide into an ice-based slush.

Preferably the carbon dioxide is added by being bubbled through an ice-based slush or through water during the formation of an ice slush. This aids in mixing of the slush and in distribution of the carbon dioxide such that it can be dissolved quickly. Under these conditions the addition is typically conducted in a pressurised vessel to prevent gas loss.

Alternatively, or in addition, dry ice (solid carbon dioxide) may be physically mixed through water or a partial slush to melt and dissolve while forming more ice.

Preferably the added carbon dioxide substantially dissolves in the ice-based slush. That is, preferably the carbon dioxide is used in an amount to ensure that none is lost to the atmosphere. The carbon dioxide can be added at levels such that the slush is substantially saturated with dissolved carbon dioxide.

Levels of carbon dioxide dissolved in water may be determined using measurement of the pH and the carbonate hardness (KH). The measurement of these two levels allows a determination of the amount of C0₂ in the slush for there to be any meaningful benefit as a cleaning material.

An exemplary chart is shown below with the amount of C0₂ provided in ppm. Methods for measuring pH and carbonate hardness are well known in the art.

The dissolution of carbon dioxide in water leads to the formation of carbonic acid. This is a weak acid which will reduce the pH of the cleaning material. Preferably the pH of the cleaning material is from 4.5 to 6.5, preferably from 5.5 to 6.5 and most preferably about 6.0.

The pH can be controlled by the amount of carbon dioxide dissolved in the slush. As will be appreciated, there is a balance between reducing the pH enough to be effective for cleaning, and reaching low levels of pH which require significant over-supply of C0₂.

According to one embodiment, the pH can be reduced to a desired level, such as about 6.0, by adding C0₂ gas to slush ice and then dry ice can be added. In this way, any C0₂ lost through neutralisations with salts/ debris during the pigging can be replaced by the dry ice as the slush melts and dry ice C0₂ subsequently dissolves in the water. The cleaning material is introduced into the conduit to be cleaned or cleared. The slush may be introduced through a valve and is typically pumped to be forced into the conduit. Apparatus for pumping the slush and for connecting to conduits for treatment are well known in the art.

Preferably the cleaning material forms a moveable plug within the conduit. That is, preferably the ice slush substantially fills the cross-section of the conduit such that every surface inside the conduit contacts the slush and is fully cleanable. The cleaning material is then forced along within the conduit. Preferably the cleaning material is forced along within the conduit by pressure applied to the cleaning material, preferably water pressure.

An ice/water slush has been proven to be an excellent means of mechanically scouring the internal pipework of sediments, biofilm and/or sewage sludge, the efficacy of the technology to removing certain other deposits is also given; in particular, foulants within pipework that convey fluids can vary in nature and constituents, ranging from corrosion products, scale, silt, biofilm or organic sludge.

By injecting carbon dioxide into the prepared ice-based slush for forming a slush pig, its affinity for acid soluble materials can be increased. Without wishing to be bound by theory, by depressing the pH of the slush, iron oxide and scale will partially dissolve in the first instance thereby loosening the less soluble deposits such as silt/muds and biofilm.

In so doing, the mechanical scouring effect described in the prior art is significantly enhanced. Furthermore, because carbonic acid is a weak acid and self-buffering, metallic surfaces will not be exposed to rapid corrosion that is otherwise associated with the more aggressive mineral acids, thereby minimising the risk of "red water" post-clean.

Carbonated ice-based slush has chemical as well as physical properties that are environmentally friendly and which enhance the cleaning in place (CIP) process.

The overall result is a more effective pigging process which leaves a cleaner surface.

The ice-based slush may be cryogenically cooled by releasing pressurised gas. Known methods of ice pigging are energy-intensive. Accordingly, it may be challenging to conduct the technique in more remote areas.

However, the ice-based slush can be prepared under such conditions by cryogenic cooling. That is, water may be chilled to form ice for the slush by the release of compressed gases from compressed gas tanks. Such cooling may rely on heat exchangers which are well known in the art. More preferably a dry ice slush may be prepared by the careful release of liquid carbon dioxide from a cryogenic tank controlled with pressure regulation and vaporisation. This is released into an already prepared slush, prepared using an alternative means of cooling, either through a traditional chilling process or cryogenically (liquefied gas, for example nitrogen).

Preferably the cleaning material is devoid of any mineral acids or other additives. Brief description of the drawing For a more complete understanding of the present inventive embodiment disclosures and as already discussed above, there are several options to embody as well as to improve the teaching of the present invention in an advantageous manner. To this aim, reference may be made to the claims dependent on claim 1 ; further improvements, features and advantages of the present invention are explained below in more detail with reference to the following description of a preferred embodiment by way of non-limiting example and to the appended drawing figure taken in conjunction with the description of the embodiment, of which:

FIG. 1 shows a configuration of the apparatus useable for the method of the present invention. Detailed description of the drawings;

best way of embodying the present invention

Before explaining the present inventive embodiment in detail, it is to be understood that the embodiment is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the present invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In the following description, terms such a horizontal, upright, vertical, above, below, beneath and the like, are used solely for the purpose of clarity illustrating the invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the invention and are not intended to be to scale.

Turning to FIG. 1 , an ice pigging system 1 useable to clean a length of conduit 5 is shown. The conduit 5 includes a series of valves 6, 7, 8, 9 by which a section of the conduit 5 may be isolated and cleaned.

In particular, the system 1 may be connected through inlet valve 7 such that when inlet valve 7 and outlet valve 8 are open and conduit valves 6 and 9 are closed, the conduit between valves 7 and 8 may be cleaned. After treatment the inlet valve 7and the outlet valve 8 can be closed and the conduit valves 6, 9 can be opened to allow the conduit to resume its intended purpose.

The ice pigging system 1 comprises a high pressure storage vessel 10 containing liquid carbon dioxide. This vessel 10 is in fluid connection with a slush preparation tank 15 for holding slush 20, via a pressure let-down device 25 to meter and control the addition of carbon dioxide to the slush 20.

The slush 20 is prepared by cooling and partially freezing water in the slush preparation tank 15 with mixing. At the same time as the slush 20 is prepared, carbon dioxide gas is metered into the slush preparation tank 15 to dissolve therein.

The slush preparation tank 15 is in two-way fluid communication with a cooling device 30 which may be an electrically driven heat exchanger or may be cryogenically cooled by the release of trapped liquid nitrogen (LIN) from high-pressure tanks.

The slush preparation chamber 15 is connectable to the conduit 5 to be treated by a connection pipe 35. This allows slush 20 to be pumped to the conduit 5 to form an ice-pig (not shown).

Advantageously the slush 20 may be pumped from the slush preparation chamber 15 by an overpressure of added carbon dioxide in the slush preparation chamber 15.

The connection pipe 35 is also connected to a water source 40 for the provision of fluid pressure to drive the slush 20 along the conduit 5. That is, the water may be used to drive an already-formed ice- pig along within the conduit 5 to effect cleaning.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.

List of reference signs

1 ice pigging system

5 conduit

6 first conduit valve

7 inlet valve

8 outlet valve second conduit valve

storage vessel, in particular high pressure storage vessel

slush preparation chamber or slush preparation tank

slush

pressure let-down device

cooling device, in particular heat exchanger, for example electrically driven heat exchanger connection pipe

water source

Claims

1. A method of removing deposits from an inside surface of a conduit (5), the method comprising: forming a cleaning material,

introducing the cleaning material into the conduit (5) and forcing the cleaning material along within the conduit (5),

wherein the cleaning material is formed by adding carbon dioxide into an ice-based slush (20).

2. The method according to claim 1 , wherein the conduit (50) is a sewage pipe, a water pipe, a conduit for food or beverages, or a reusable medical treatment conduit.

3. The method according to claim 1 or 2, wherein the ice-based slush (20) comprises ice crystals suspended in water, wherein the ice crystals form from fifty weight percent to ninety weight percent of the slush (20).

4. The method according to claim 3, wherein the ice crystals form from sixty weight percent to eighty weight percent of the slush (20).

5. The method according to at least one of claims 1 to 4, wherein the carbon dioxide is added by being bubbled through the ice-based slush (20).

6. The method according to at least one of claims 1 to 5, wherein the ice-based slush (20) is cooled with a cooling device (30).

7. The method according to claim 6, wherein the cooling device (30) is a heat exchanger, in particular an electrically driven heat exchanger, for cryogenically cooling the ice-based slush (20) by releasing pressurised gas.

8. The method according to at least one of claims 1 to 7, wherein the added carbon dioxide substantially dissolves in the ice-based slush (20).

9. The method according to at least one of claims 1 to 8, wherein the pH of the cleaning material is from 4.5 to 6.5.

10. The method according to claim 9, wherein the pH of the cleaning material is from 5.5 to 6.5.

1 1. The method according to claim 9 or 10, wherein the pH of the cleaning material is about 6.0.

12. The method according to claim 8 and to at least one of claims 9 to 1 1 , wherein the pH of the cleaning material is controlled by the amount of carbon dioxide dissolved in the ice-based slush (20).

13. The method according to at least one of claims 1 to 12, wherein the cleaning material is forced along within the conduit (5) by applying pressure to the cleaning material.

14. The method according to claim 13, wherein the pressure is water pressure.

15. The method according to at least one of claims 1 to 14, wherein the cleaning material forms a moveable plug within the conduit (5).