GB2385544A

GB2385544A - An air scrubber for use in a mud scrubber.

Info

Publication number: GB2385544A
Application number: GB0130647A
Authority: GB
Inventors: Gordon Leslie Finnie
Original assignee: Integrated Engineering Services Ltd; Integrated Engineering Services
Current assignee: Integrated Engineering Services Ltd; Integrated Engineering Services
Priority date: 2001-12-21
Filing date: 2001-12-21
Publication date: 2003-08-27
Also published as: GB0130647D0

Abstract

An air scrubber unit 11 comprises an air cleaning unit which removes contaminants from an air stream has an air inlet 13, at least one water-spray device 14 which causes the contaminants to become entrained in water, an air outlet 18 and a separator 15 and collector 19 to remove water containing contaminants, the collector having a second separator which removes the contaminants from water accumulated in the collector. The mix of water and contaminants may have its water and/or oil components removed for separate treatment and/or decontamination. Scavenged water may be reintroduced to the spray device and thus reused. The device is especially suitable for use in cleaning the exhaust gas generated by shale shakers used to clean the drilling mud used when drilling an oil well.

Description

Mud Scrubber Unit The present invention relates to mud scrubber units, in particular those used to clean the exhaust from shale shakers.

During the drilling of an oil well drilling fluids of selected viscosity are pumped into the volume surrounding the drill bit to remove drill cuttings, lubricate the drilling process, and maintain the integrity of the drill hole. The cuttings become suspended in the drilling fluid and this mixture/suspension is pumped way from the drilling area for separation to allow the drilling mud to be re-used.

Shale shakers are commonly used in the oil industry to separate cuttings or shale from drilling mud which is returned from the oil well. Shale shakers consist essentially of vibrating horizontal screens over which the cutting laden drilling fluid passes. The solid waste passes over the screens and is collected and dumped as waste. The drilling fluid filters through the screen under gravity and can be recycled for further use as a drilling fluid. However, due to the nature of the drilling environment and the frictional heating which results from the drilling process, drilling fluids returned from oil wells are relatively hot. Thus, mechanical vibration of the returned drilling fluid suspension often causes the release of vapours, oil mist and airborne contaminants often into a confined area, usually some form of hood or enclosure, which is then mechanically vented.

Due to the hazardous nature of the exhausted air/discharge, health and safety legislation, and environmental legislation now dictate that the air be cleaned or"scrubbed"before it is exhausted into a public area. The health and safety issue is of particular concern on offshore drilling where space is at a premium and shale shaker units are often located close to manned areas of a drilling rig.

Mud scrubber units are often used to remove the hazardous contaminants from the air before it is exhausted. These generally comprise an arrangement in which the

contaminated air is passed through a series of water spray jets which form a water curtain and dissolve many of the contaminants into a liquid solution or slurry. The air then passes through a chevron separator which removes any remaining water from the air before the air is exhausted. The resulting slurry or solution contains a mixture of water, oil, and mud, amongst other things. This waste solution is in itself somewhat of an environmental problem and must be discharged or disposed of with care. However, in offshore applications the disposal of the water becomes more critical as the waste cannot be simply discharged into the sea and there is no space for the liquid to be stored for subsequent treatment or disposal. This often mitigates against the use of water scrubbers in offshore applications.

An object of the present invention is therefore to seek to overcome the drawbacks associated with mud scrubber units and their waste products.

According to an aspect of the present invention there is provided a air scrubber unit for removing contaminants from contaminated air, said air scrubber unit comprising: an air cleaning unit comprising an air inlet adapted to allow entry of contaminated air ; at least one water spray device arranged such that in use spray is directed at an incoming contaminated air stream coming from the air inlet to remove airborne contaminants from the air stream; a separator adapted to separate a mixture of water and contaminants formed by said water spray device from air in the incoming contaminated air stream, the mixture passing to a collection system; and an air outlet which exhausts air separated from the mixture of water and contaminants by the separator; the scrubber unit further comprising a water decontamination system adapted in use to separate the mixture of water and contaminants passed to the collection system.

Preferably, the mixture of water and contaminants passed to the collection system is transferred to a first separator in which oil and/or water components of said mixture are at least partially separated from other components of the mixture.

Conveniently, the at least partially separated oil and/or water components of said mixture are transferred to a second separator.

In preferred embodiments, the at least partially separated oil and/or water components of said mixture transferred to the second separator are at least partially separated by the second separator into an oil component and a water component.

Preferably, the at least partially separated oil component is transferred to an oil collection vessel. The oil component which is potentially harmful to humans and the environment can be safely stored for removal at convenient intervals.

Conveniently, the at least partially separated water component may be stored in the second separator.

In preferred embodiments, the at least partially separated water component is pumped out of the second separator to the one or more water sprays. This allows the relatively clean water to be recycled through the system and used more than once.

Additionally, this drastically reduces the amount of water which has to be passed out of the system reducing the risk of environment pollution.

According to a further aspect of the present invention there is provided a method of removing contaminants from contaminated air, said method comprising: passing contaminated air into an air inlet of an air scrubbing unit; the air scrubbing unit having one or more water sprays directed at an incoming contaminated air stream coming from the air inlet to remove airborne contaminants from the air stream;

passing a mixture of water and contaminants formed by the one or more water sprays to a separator to separate said mixture of water and contaminants from air in the incoming contaminated air stream; passing the mixture to a collection system; exhausting the air separated from the mixture of water and contaminants by the separator; through an air outlet; and separating the mixture of water and contaminants passed to the collection system in a water decontamination system.

An embodiment of the present invention will now be described, by way of example only, with reference to the following drawing in which: Figure 1 illustrates a schematic of a mud scrubber unit according to the present invention.

The mud scrubber unit 10 as indicated in Figure 1 consists of an air cleaning or scrubber unit 11 and a related water recycling and re-circulation system 12. In use, extracted air from a shale shaker room (not shown) is drawn into an air inlet 13 of the scrubber unit 11, which is placed on the suction side of shale shaker extractor fans (not shown). The scrubber unit 11 incorporates specially designed water spray jets 14 arranged across the face of the incoming air stream. The water spray jets 14 form a water curtain which removes solid mud and oil contaminants from the air as it passes through the water curtain.

A critically designed air inlet duct (not shown) creates a specific air velocity (typically 14 m/s) for optimum contaminant removal by the water spray curtain. Following the water spray jets 14, two sets of chevron profile vane separators 15 are arranged to remove excess water from the air stream. This ensures clean, relatively dry air passes into a centrifugal fan suction inlet 17. The clean air is then exhausted through an air outlet 18.

The discharge water containing the washed out mud and oil particles from the air scrubber unit 11 is drained by gravity feed via a pipe or duct 16 to the water recycling or water recirculation system 12. The water recycling or water re-circulation system 12 consists of a pair of concentric, cylindrical tanks; an inner or mud tank 19 and an outer or oil/water tank

20. Initially, the discharge water containing the washed out mud and oil particles is fed into the mud tank 19. Any heavy mud residue settles to the bottom of the mud tank 19 and the water and oil component of the mixture gradually separates towards the top of the mud tank 19. Relatively clean water and oil from the mud tank 19 flows via an overflow sluice weir 21 into the oil/water tank 20.

The liquid in the oil/water tank 20 separates into an oil layer 22 and a water layer 23 due to the differences in density. The oil layer 22 floating on the top of the relatively clean water layer 23 is removed using an oil/water sensor (not shown) and a vacuum pump arrangement (not shown). The sensor determines the difference in the conductivity between the oil and water layers 22,23. When the oil layer 22 build up reaches a depth of around 25mm the sensor sends a signal to a control panel (not shown), which in turn energises a solenoid valve (not shown) in a compressed air line (not shown) to an open position. A vacuum is then drawn by the vacuum pump arrangement over an oil collection tank 24 creating a siphoning effect in a pipe 25 positioned level with the top of the oil/water tank 20. The oil layer 22 at the top of the oil/water tank 20 is then drawn through pipe 25 and discharged it into the oil collection tank 24 where it is then stored.

The oil collection tank 24 may be emptied periodically. The emptying cycle is controlled automatically by high and low level limit switches (not shown). When the oil collection tank 24 is full the high-level limit switch sends a signal to a control panel (not shown) which in turn relays a signal to a solenoid valve (not shown) in a vent line in the top of the oil collection tank 24 venting the air space in the tank. The high-level limit switch also sends a signal to a solenoid valve (not shown) in an oil tank discharge drain pipe 26. The opening of the vent breaks the vacuum in the oil collection tank allowing the collected oil to drain to a tundish drain 27 through pipe 26.

When the low level limit switch within the oil collection tank is triggered via the control panel, the solenoid valve in the drain line is energised to close. At the same time, the solenoid valve in the vent line in the top of the oil collection tank 24 is closed. This allows a vacuum to be drawn within the oil collection tank 24.

The relatively clean water collected in tank 20 can then be recycled for further use in the water spray jets 14. Water may be sucked out of the clean water tank 20 at a pump suction point 28 in the side of the tank and through a pipe 29 by means of two pumps 30,31. Two off regenerative type turbine pumps 30,31 with electric motors on automatic change over (run and standby) can supply 148 litres/min at 248 Pascal to the water spray jets 14 via 6.25 cm (2.5") inch stainless steel pipe work 32.

Auto changeover of the pumps is achieved by flow switches (not shown) located in the discharge pipe work 33 from each pump. Failure of the duty pump brings up an alarm at the control panel and initiates start up of the standby pump. Solenoid valves (not shown) will open and close depending on which pump has tripped and started. Water strainers 34 are located on the suction side of each pump to filter the water of any mud carryover. Non return valves (not shown) are located in the pump discharge line to prevent back flow through the pumps. To measure and regulate the correct supply flow rate from the pumps double regulation valves with measuring points (not shown) are also located in the discharge line from each pump.

For initial filling and monitoring of water level during operation there is a ballcock valve arrangement (not shown) located in the clean water tank. In the event of any malfunction of the ballcock, resulting in the water level exceeding the nominal operating height within the tank, any excess water may be piped away via an overflow pipe (not shown) to the tundish drain 27.

An electric immersion heater of around 5 kW may be fitted inside the clean water tank 20 so that if the temperature of the water within the tank falls below 4 C a thermostat (not shown) sends a signal to the control panel energising the immersion heater and preventing the tank water from freezing.

Certain types of mud when settled in the mud tank 19 may start to go solid, to counteract this a moving blade paddle 36, driven by electric motor (not shown) is arranged to stir the mud slurry collected in the bottom of the mud tank 19. The blade paddle 36 may be started manually from a control panel (not shown) at the discretion of the operators.

Manual emptying of the inner tank shall be via a 15 cm (6") butterfly valve 35. This operation is carried out at the operators discretion and depends on the type of mud in use at any one time. The frequency of the manual emptying will be determined during drilling operations. Once the emptying of the mud tank has been completed a manual flushing system comprising of two ring mains (one each for inner and outer tanks) and quick type connector points for pressurised water supply is turned on to flush out any residue left in the tank and the valve seat of valve 35 prior to closing the valve. The flushing system quick connect points are installed for introduction of pressurised water at 5 bar. This pressurised water may include detergent to improve the cleaning of the tank.

To reduce the footprint space required for the mud scrubber unit, the air cleaning unit 11 and water re-circulation system 12 are mounted on a common skid frame (not shown). The air cleaning unit 11 may be flange connected to the extract air duct of a shale shaker room and located on a platform above the mud, oil/water, and oil collection tanks 19,20, 24.

The air cleaning unit 11, supply pumps 30,31 and related valves may be located at high level on a service platform of the skid frame which is made of 4mm-durbar cheque plate.

Handrails and kick plates may surround the working maintenance area. Access to the upper service platform is via a fixed ladder with safety hoops. Local pump isolators of a pushbutton lockable type may be located on the skid frame on the upper service platform level.

The mud and oil/water tanks 19,20 may be cylindrical in shape and mounted within a support frame manufactured from 80 x 80 x 5mm thick 316-L stainless steel box section.

The oil collection tank 24 may be triangular shaped and mounted within a comer of the lower part of the skid frame. The oil collection tank 24 may be fitted with a door (not shown) to allow access to the interior of the tank for cleaning and inspection. The interface of the skid frame to a deck being four bolt down feet located at each comer of the skid frame.

Claims

Claims:

1. An air scrubber unit for removing contaminants from contaminated air, said air scrubber unit comprising: an air cleaning unit comprising an air inlet adapted to allow entry of contaminated air; at least one water spray device arranged such that in use spray is directed at an incoming contaminated air stream coming from the air inlet to remove airborne contaminants from the air stream; a separator adapted to separate a mixture of water and contaminants formed by said water spray device from air in the incoming contaminated air stream, the mixture passing to a collection system; and an air outlet which exhausts air separated from the mixture of water and contaminants by the separator; in which the air scrubber unit further comprises a water decontamination system adapted in use to separate the mixture of water and contaminants passed to the collection system.

2. An air scrubber unit according to claim 1 in which the mixture of water and contaminants passed to the collection system is transferred to a first separator in which oil and/or water components of said mixture are at least partially separated from other components of the mixture.

3. An air scrubber unit according to claim 2 in which the at least partially separated oil and/or water components of said mixture are transferred to a second separator.

4. An air scrubber unit according to claim 3 in which the at least partially separated oil and/or water components of said mixture transferred to the second separator are at least partially separated by the second separator into an oil component and a water component.

5. An air scrubber unit according to claim 4 in which the at least partially separated oil component is transferred to an oil collection vessel.

6. An air scrubber unit according to claims 4 or 5 in which the at least partially separated water component may be stored in the second separator.

7. An air scrubber unit according to any of claims 4 to 6 in which the at least partially separated water component is pumped out of the second separator to the one or more water sprays.

8. A method of removing contaminants from contaminated air, said method comprising: passing contaminated air into the air inlet of an air scrubbing unit; the air scrubbing unit having one or more water sprays which are directed at an incoming contaminated air stream coming from the air inlet to remove airborne contaminants from the air stream; passing a mixture of water and contaminants formed by the one or more water sprays to a separator to separate said mixture of water and contaminants from air in the incoming contaminated air stream; passing the mixture to a collection system; exhausting the air separated from the mixture of water and contaminants by the separator; through an air outlet; and separating the mixture of water and contaminants passed to the collection system in a water decontamination system.

9. An air scrubber unit as hereinbefore described with reference to the accompanying drawing.

10. A method of removing contaminants from contaminated air as hereinbefore described with reference to the accompanying drawing.