Method And Apparatus For Cooling A Flow Of Gas

The present invention relates to a method and apparatus for cooling a flow of gas.

Known systems for cooling gas flows, such as air conditioners and industrial chillers, typically employ standard refrigeration cycles to provide the requisite cooling.

In a typical refrigeration cycle a refrigerant, such as Freon (RTM) , passes through a closed cycle in which it is sequentially compressed, condensed, expanded and evaporated. The evaporation and condensation phases are typically carried out by passing the refrigerant through respective sets of coils which facilitate heat transfer between the coils and their surroundings. Heat is absorbed from the surroundings during the evaporation phase and dissipated into the surroundings during the condensation phase. The evaporator coils are generally situated in a separate location to the condenser coils so that heat may be removed from one location (in the vicinity of the evaporator coils) and dissipated to a second location (in the vicinity of the condenser coils) .

A disadvantage of standard refrigeration equipment is that it requires an external power supply, such as electricity, to operate. In large scale operations this power requirement can be significant. A further disadvantage is that refrigerants in common use are damaging to the environment, in particular, to the Earth's ozone layer.

The method and apparatus of the present invention provides an alternative to standard refrigeration cycles for cooling a flow of air. The present invention may be used in many applications which require cooling of a flow of gas, for example, in portable air conditioning units or in chiller/condensers for scrubbing contaminants from a gas stream.

In a first aspect, the present invention provides an apparatus for cooling a gas stream comprising a plurality of thermally conductive baffles which are arranged, in use, to be in thermally conductive communication with a liquefied gas so that, in use, when a gas stream passes over the surface of the baffles, heat from the gas stream is conducted away from the surface of the baffles to the liquefied gas.

An advantage of the present invention is that it does not require an external power supply to operate.

The liquefied gas may be any suitable gas capable of existing in liquid form, for example, liquefied air, liquefied oxygen or liquefied helium (or other noble gas) .

However, the liquefied gas is preferably liquid nitrogen as liquid nitrogen is stable, inert, inexpensive and readily available .

In one embodiment the plurality of baffles are located within a housing. The housing may advantageously comprise an integral container for the liquefied gas. This is beneficial as the distance over which thermally conductive communication must be maintained can be minimised.

In a further embodiment the housing may comprise a drain for collecting contaminants which separate out from the gas stream as it passes over the plurality of baffles. This is particularly advantageous in gas scrubbing applications. In one application, the apparatus may be used to recover clean water from humid air.

The apparatus may suitably comprise means for driving the gas stream over the plurality of baffles such as a fan or a blower or any other appropriate means.

In one embodiment the plurality of baffles comprise a plurality of baffle plates and/or wires and/or rods. Preferably, the plurality of baffles are made of copper to exploit the good thermal conductivity properties of copper.

In a preferred embodiment, the apparatus may comprise a means for pre-cooling the gas stream upstream of the plurality of baffles to increase the degree of cooling achieved.

The means for pre-cooling the gas stream may comprise means for introducing a second gas stream into the gas stream. Preferably, the second gas stream comprises gas vented from a container containing the liquefied gas. This is beneficial as gas vented from a container containing the liquefied gas will be at a low temperature. Alternatively, the second gas stream may be passed through a heat exchanger over which the gas stream to be cooled passes.

In a second aspect, the present invention provides a method for cooling a gas stream comprising passing the gas stream

over the surface of a plurality of thermally conductive baffles which are in thermally conductive communication with a liquefied gas. The liquefied gas is preferably liquid nitrogen.

The method preferably further comprises pre-cooling the gas stream upstream of the plurality of baffles. Preferably, pre-cooling the gas stream comprises introducing a second gas stream into the gas stream. The second gas stream preferably comprises gas vented from a container containing the liquefied gas. Alternatively, the gas stream may be cooled by passing it over a heat exchanger through which the second gas stream flows.

In a preferred embodiment, the gas stream comprises entrained contaminants and the method further comprises separating at least a portion of the entrained contaminants from the gas stream as it passes over the plurality of baffles by condensation and/or collection of the entrained contaminants on the plurality of baffles. This is beneficial as contaminants may be retrieved from the gas stream as it is cooled.

The entrained contaminants may comprise gaseous and/or liquid droplet contaminants. The contaminants may typically comprise hydrocarbon contaminants. Additionally or alternatively, the gas stream may comprise water vapour which is recovered as the gas stream passes over the plurality of baffles.

In a third aspect, the present invention provides an apparatus for use in the treatment of contaminated

particulate matter comprising: a rotatable inclined drum having a main axis, an inlet end and an outlet end, wherein the inlet end is located at a vertically lower position than the outlet end, the drum further comprising at least one internal vane located on the inner surface of the drum which is arranged to convey contaminated particulate matter from the inlet end to the outlet end when the drum is rotated about its main axis, a means for creating a flow of air through the drum, and a condenser which is arranged to condense entrained contaminants from the flow of air exiting the drum.

An advantage of this apparatus is that the contaminated particulate matter is agitated to a greater extent by being conveyed upwardly within the drum than it would be if it were conveyed downwardly within the drum. This is because the vane tends to pick up and drop the particulate matter as the drum rotates. Increased agitation of the contaminated particulate matter is beneficial as it increases the interaction between the contaminated particulate matter and the flow of air.

In one embodiment of the third aspect of the present invention the apparatus is arranged so that at least a portion of the air exiting the condenser is re-circulated through the drum. The condenser preferably comprises an apparatus according to the first aspect of the present invention.

In a fourth aspect, the present invention provides a method of treating contaminated particulate matter comprising: conveying the particulate matter from an inlet end to an

outlet end of an inclined rotatable drum having a main access, wherein the drum comprises at least one internal vane located on the inner surface of the drum and wherein the inlet end is at a vertically lower position than the outlet end, rotating the drum about its main access so that the particulate matter is conveyed by the at least one vane from the inlet end to the outlet end as the drum rotates, and passing a flow of air through the drum such that contaminates from the particulate matter become entrained in the flow of air.

The flow of air in the above recited method is preferably from the outlet end to the inlet end of the drum to improve the interaction between the flow of air and the particulate matter.

In a preferred embodiment of the forth aspect of the present invention the method further comprises retrieving the entrained contaminants from the flow of air by passing the flow of air through a condenser which preferably comprises an apparatus according to the first aspect of the present invention. At least a portion of the air exiting the condenser is preferably re-circulated through the drum.

An example of the invention will now be described with reference to the following figures in which:

Figure 1 is a schematic cross sectional elevational view of an apparatus for cooling a flow of gas,-

Figure 2 is a schematic cross sectional plan view of the apparatus of Figure 1 ; and

Figure 3 is a schematic cross sectional elevational view of an inclined rotatable drum from use in treating contaminated particulate matter.

Figure 1 shows an apparatus 10 for cooling a flow of air. The apparatus 10 comprises a housing 30 which has an inlet 32 and an outlet 34 via which a flow of air to be cooled enters and exits the apparatus. The direction of the flow of air is indicated by arrows 15.

A container 20 for containing liquid and gaseous nitrogen is located in an upper portion 31 of the housing 30. The container 20 is surrounded by insulation 22 over substantially its entire periphery in order to prevent heat being conducted to the interior of the container 20 from the surrounding environment. The container 20 has a one way pressure activated valve 26 which, in use, allows nitrogen gas to vent from the container 20 when a certain pre-defined pressure difference exists across the valve 26.

A plurality of baffle plates 40 are located within a lower portion of the housing 38. As shown in Figure 2, the baffle plates are arranged so that, in use, the flow of air passes through the apparatus 10 in a slalom like fashion. The baffle plates 40 are maintained in thermally conductive communication with the interior of the container 20 via thermally conductive members 42 so that, in use, heat from the flow of air may be conducted to the interior of the container 20.

As shown in Figure 1, the thermally conductive members 42 are a continuation of the baffle plates 40. A layer of

insulation 36 is located between the exterior of the container 20 and the lower portion of the housing 38. The thermally conductive members 42 pass through, and are insulated by, the layer of insulation 36 so that, in use, substantially only heat from the flow of air may be conducted to the interior of the container 20. The layer of insulation 36 may be integral with the insulation 22 surrounding the container 20.

The housing 30 further comprises a drain 50 located below the lower portion 38. The drain 50 is arranged to collect any liquid which condenses and/or collects on the baffle plates 40 as the flow or air passes over and is cooled by the baffle plates. Liquid collected by the drain 50 may be drained away for disposal or recycling.

As foreshadowed above, in use, a flow of air at a first temperature Tl enters the apparatus 10 via the inlet 32. The flow of air flows past the baffle plates 40 in a slalom like fashion (Figure 2) before emerging from the outlet 34 at a second lower temperature T2. Since the baffle plates 40 are maintained in thermally conductive communication with the interior of the container 20, which in use contains liquid nitrogen, heat from the flow of air is conducted away from the surface of the baffle plates 40 to the liquid nitrogen which is at a temperature of approximately -186 ¹ C.

In order to regulate the temperature of the baffles and the rate of cooling, the liquid nitrogen is supplied to the container 20 via an adjustable drip feed valve (not shown) . As the liquid nitrogen drips into the container 20 it absorbs heat from the flow of air and subsequently returns

to its gaseous state. The gaseous nitrogen is then vented from the container 20 via the one way pressure activated valve 26.

In one embodiment the outlet of the valve 26 may be directed via a conduit (not shown) to enter the flow of air at a position upstream of the baffle plates 40. The vented liquid nitrogen exiting through the valve 26 will be at a very low temperature. Therefore, introducing the vented liquid nitrogen into the upstream flow of air will help to pre-cool the flow of air before it reaches the baffle plates 40. Alternatively, the upstream flow of air may be cooled by passing it over a conduit, such as a copper pipe, through which the vented nitrogen gas, or another cold fluid, is passed.

The flow of air to be cooled may be supplied from an upstream process (an example of which is given below) or may supply a downstream process. The flow of air may be driven by the upstream or downstream process. Alternatively or additionally, the apparatus 10 may further comprise a blower (not shown) or a fan (not shown) to drive the flow of air past the baffle plates 40. Of course, the apparatus 10 may also be used to cool flows of gas other than air for example, gasses forming part of industrial processes.

In Figure 1 the thermally conductive members are depicted as continuations of the baffle plates 40. However, in an alternative embodiment, the baffle plates 40 may be in indirect thermally conductive communication with the interior of the container 20 via intermediate thermally conductive wires (not shown) which are in contact with both

the baffle plates 40 and the interior of the container 20. Because of its superior thermally conductive properties, the intermediate connecting wires preferably comprise copper.

In an alternative embodiment the baffle plates 40 may be substituted for a thicket of wires and/or rods. Alternatively, a combination of baffle plates 40, wires and/or rods may be used. At least a portion of the baffle plates, wires and/or rods preferably comprise copper.

The baffle plates 40, wires and/or rods may be arranged to cause the flow of air to decelerate as it passes through the apparatus 10 by preventing the flow of air from flowing along a direct path. An example of this is the slalom configuration of the baffle plates 40 shown in Figure 2. A greater or lesser extent of deceleration may be achieved by varying the spacing between the baffle plates 40, wires and/or rods. The apparatus 10 may be arranged to decelerate the flow of air further by being provided with a larger cross-sectional area than a conduit (not shown) through which the flow of air is conveyed to the apparatus 10.

As an alternative to the apparatus 10 described above, the liquid nitrogen may be fed to a separate intermediate tank (not shown) rather than to an integral container 20. In this embodiment thermally conductive communication between the baffle plates 40 and the interior of the separate intermediate tank is maintained via well insulated intermediate thermally conductive wires (not shown) .

In order to ensure a robust construction the container 30 may also function as a crash frame. Alternatively, the

container 30 may be located within a separate crash frame (not shown) . In a further alternative embodiment the baffle plates 40 (or thicket of wires and/or rods) may be installed in a suitably adapted chamber or room. For example as part of an industrial process. The apparatus therefore need not comprise a housing 30 in all embodiments.

Any suitable gas which can exist in the liquid phase may be used in place of the liquid nitrogen, for example, liquefied air, helium (or other noble gas) or oxygen.

An example of an upstream process which may supply the flow of air to be cooled will now be described with reference to Figure 3.

Figure 3 shows an apparatus 100 for use in the cleaning of drilling cuttings produced during the drilling of an oil wellbore or the like.

Drilling fluid, known as mud, is a vital component in the process of drilling oil wells. This mud is a combination of products formulated to optimise the cleaning and stabilisation of the wellbore during drilling. While this fluid is normally water based, there are numerous occasions when the use of a non-aqueous fluid (NAF) is technically desirable. These NAF normally consist of an emulsion where the continuous phase is an oil and the internal phase is water containing soluble salts. NAF are used for improved lubricity and greatly enhanced wellbore stability in difficult or reactive geological formations.

The increase in environmental awareness has led government regulators all over the world to place increasingly

stringent limits on the discharge of drilling cuttings contaminated with NAF into the sea. Drilling cuttings from NAF oil wells must therefore be cleaned before disposal. The apparatus 100 shown in Figure 3 may be used to at least partially clean the drilling cuttings from NAF oil wells.

The apparatus 100 comprises a drum 110 which is supported on bearings 120 at an angle of approximately 30° to the horizontal. The drum 110 has an inlet 112 and an outlet 114 through which, in use, drilling cuttings 140 enter and exit the drum. Although not illustrated in Figure 3, the angle of the drum 110 to the horizontal is adjustable between about 10° to about 60° to the horizontal by a jacking means such as, for example, a screw jack (not shown) .

The bearings 120 allow the drum 110 to be rotated about its main axis by, for example, a chain belt drive (not shown) . The drum 110 may have any suitable dimensions selected by a designer but may typically be approximately 10m in length and Im in diameter.

The drum 110 has an internal spiral vane 130 located on its internal surface. The vane 130 may be orientated at any suitable angle to the main axis of the drum 110 but will typically define an angle of approximately 60° to the main axis of the drum 110. As shown in Figure 3, the vane 130 is orientated within the drum 110 to point towards the outlet end 114 of the drum 110.

In use, cuttings 140 contaminated with NAF are introduced into drum 110 via the inlet 112. As the drum 110 rotates about its main axis the cuttings are transported upwardly by

the vane 130 to exit the drum 110 via the outlet 114. On exiting the drum 110 the cuttings may be discharged directly into a hopper or may be fed in to another process or apparatus .

A flow of air is directed through the drum 110 from the uppermost end 118 to the lowermost end 116 as indicated by arrow 15. As the drum rotates, the cuttings are lifted and dropped by the vane 130. In this way interaction between the flow of air travelling in one direction and the contaminated cuttings 140 travelling in the other is maximised. As the flow of air passes over the cuttings 140 it picks up oil from the NAF coating the chippings in the form of evaporated hydrocarbons or liquid droplets.

On exiting the drum 110 the flow of air is cleaned by separating out the entrained contaminants from the flow of air. This cleaning process may be by way of filtration but is more preferably carried out by passing the flow of air through a chiller/condenser. The chiller/condenser may be a known chiller/condenser cooled by a standard refrigeration cycle as discussed above. However, the chiller/condenser is preferably an apparatus 10 as described above with reference to Figures 1 and 2.

The flow of air will typically contain water vapour which may form a layer of ice on the cooling elements within the chiller/condenser. The baffle plates 40 of the apparatus 10 described above are maintained at a very low temperature by the liquid nitrogen. Water vapour in the flow of air will therefore form a layer of ice on the baffle plates 40. Since the entrained hydrocarbon contaminants in the flow of

air will have a lower freezing point than water, they will condense on top of the ice and run down it in into the drain 50. Alternatively or additionally, the baffles 40 may be coated with a non-stick/low-friction coating such as Teflon (RTM) .

In order to improve the efficiency of the cleaning process the flow of air is preferably heated before it enters the uppermost end 118 of the drum 110. In this way, a greater proportion of the oil from the NAF may be made to evaporate into the flow of air. The air may be heated, for example, by being passed through a conduit (not shown) which is heated by a jacket through which circulates radiator cooling fluid from the drilling rig's engines.

Alternatively or additionally, the cuttings 140 may be preheated to facilitate the stripping of the liquids from the drilled cuttings. Typically the cuttings 140 will be transported from conventional Solids Removal Equipment (not shown) by means of a screw conveyor or auger (not shown) . The screw conveyor or auger may be fitted with infra red heaters to raise the temperature of the cuttings 140 being conveyed to the rotating drum inlet 112.

The residence time of the cuttings 140 within the drum 110 may be varied by altering the inclination and /or speed of rotation of the drum 110. The residence time of the cuttings 140 within the drum 110 may also be varied by altering the velocity of the flow of air as the air will tend to blow the cuttings backwards (towards the inlet 112) when they are airborne.

In certain circumstances it may be desirable to reverse the direction of travel of the cuttings 140 within the drum 110. For example, to reduce the residence time of the cuttings within the drum 110. For this purpose, the drum 110 may be pivoted at its central point to permit the angle of the drum to be altered through a much greater range than that mentioned above. Thus, the drum may be arranged to pivot such that the cuttings 140 travel "downhill" within the drum instead of "uphill".

The vanes 130 may be perforated to allow liquid contaminants to flow back down the inner surface of the inclined drum 110.

Once the flow of air has been cleaned it may be re- circulated through the heating jackets and drum 110. The flow of air may be driven by a fan (not shown) , blower (not shown) or other suitable means.