The present invention relates to a compressor, and in particular an air compressor for use on a ship for compressing air at sea.

When installing heavy engineering structures to a seabed, such as the support structure for a wind turbine, it is often necessary to install piles into the seabed. The installation of piles into the seabed usually involves either drilling or driving the piles deep into the seabed, each of which can involve the use of heavy-duty percussive equipment, and thus percussive forces underwater, due to the presence of rocks and bedrock in the seabed.

In land-based applications, the sound from such percussive forces will dissipate in the air relatively easily, whereby the sound will only travel a relatively short distance, thus creating only localised sound pollution. However, such percussive forces are more troublesome underwater. This is due to the high and fast transmissivity of sound in water, as a result of which the sound from such percussive forces can travel very long distances in the water. That transmissivity of the sound in water can therefore create troublesome sound pollution in the water, which can create interference on sonar equipment, or cause confusion in creatures that use sonar, particularly whales and dolphins or other cetaceans.

This problem has been previously recognised and piling operators have established that using an air-bubble curtain around the underwater piling site can help to mitigate the problems that can arise from the sound transmission caused by piling operations underwater. Optimally, these air-bubble curtains need to be very large, and to provide a large enough air-bubble curtain, multiple air compressors need to be arranged on ships in the area around the piling site to pump air down to perforated pipes on the seabed around the piling site.

In some configurations, the perforated pipes form a ring around the piling site, the ring having a diameter of perhaps 400m or more. In some configurations, the ring is made from more than one pipe, each having a pipe diameter in excess of 1m. The compressors therefore need to pump very large volumes of air down to the ring to form a complete air-bubble curtain around the piling site, bearing in mind that the curtain needs to be large and intense enough to absorb or attenuate the sounds of the piling operation - at least to a sufficient degree to help mitigate the sound pollution problems that would otherwise arise from unfettered sound transmissions.

A further difficulty is that the deeper the water above the seabed, the more difficult it is to pump the air down to the ring of pipes, not least because a larger mass of air needs to be pumped to the seabed in a given time due to the air becoming more compressed at depth, and thus it reducing its effectiveness as a water curtain at depth. Typical industrial air compressors used for these air-bubble curtains can achieve depths of perhaps 20 to 50m, but it is anticipated that depths of 60 to 70m or more will be required in the near future as more and more wind farms are installed at sea.

Although we discuss the seabed above, and activities at sea below, it is also to be appreciated that the same principles apply in other bodies of water - i.e. in freshwater lakes and rivers.

The present invention generally concerns efforts to provide greater air compression capacity at sea, and thus either more powerful compressors or additional compressors, and the problems arising as a consequence of the use of the larger air compression capacity.

According to a first aspect of the present invention there is provided an air compressor comprising: an air compression unit with a low pressure air input and a high pressure air output; a heat exchanger system for cooling components and/or fluids of the air compressor, the heat exchanger system comprising at least one heat exchanger and at least one fan for driving airflow through the at least one heat exchanger; an exhaust for the airflow from the heat exchanger; an air intake for the one or more fan; and a housing for containing the air compression unit and the heat exchanger system; wherein: the housing comprises first, second and third sections, the sections separated from one another by internal walls of the housing, the first section housing the at least one heat exchanger and the at least one fan, the second section being a ventilation space and the third section being a compartment that houses the air compression unit; and the ventilation space has a lower opening in a bottom wall of the housing and an upper opening in a top wall of the housing for allowing air to be vented from the bottom to the top of the ventilation space.

As this first aspect of the present invention provides a ventilation space with a lower opening in a bottom wall of the housing and an upper opening in a top wall of the housing for allowing air to be vented from the bottom to the top of the ventilation space, two air compressors of the present invention can be stacked one above the other, with the lower opening in the upper air compressor aligned over the exhaust for the airflow from the heat exchanger in the lower air compressor such that airflow exiting through the exhaust of the lower air compressor can be vented through the upper air compressor through the ventilation space of the upper air compressor and out through the upper opening thereof.

The stack can be repeated to be three or more air compressors high if desired.

In some embodiments, the lower opening in the bottom wall of an upper air compressor’s housing has a perimeter that conforms to the shape of, or it is sized to encompass or surround, the exhaust for the airflow from the heat exchanger of the lower air compressor. In other words, the shapes of the lower and upper openings generally match, or sufficiently conform, or can stack, for inter-engagement therebetween between adjacent stacked air compressors. With this configuration, when two matching air compressors are stacked one above the other, the perimeter of the lower opening in the upper air compressor can be aligned to surround or encompass (or envelop) the exhaust for the airflow from the heat exchanger in the lower air compressor such that airflow exiting through the exhaust of the lower air compressor will be fully or mostly vented through the upper air compressor through the ventilation space of the upper air compressor. In some embodiments the two adjacent openings can seal against each other to provide a leak free connection. Either or each opening may be provided with a shutter or door for closing the opening in the event that the ventilation space is not being used, e.g. if the air compressor is not stacked on another air compressor.

In some embodiments, the third section provides a service space for the air compression unit. In some embodiments, the service space is in the compartment, the service space having a ventilation air intake and a ventilation air outlet.

In some embodiments, the three sections of the housing are linearly distributed along the length of the housing, preferably with the second section being between the first and third sections, in which case a vented exhaust from a lower compressor will pass through the ventilation space of an upper compressor between the first and third sections.

In some embodiments, the internal wall separating two or more of the three sections may be thermally insulated to reduce heat transfer between the ventilation space and the, or each, adjacent section. Preferably there is an insulated internal wall between the ventilation space any the service space in the third section.

In some embodiments the walls of the ventilation space are configured to minimise thermal pockets forming from the exhaust gas passing there-through. Such thermal pockets may form commonly where the ventilation space is throttled. Preferably, therefore, any angled wall that throttles the passageway there-through for the exhaust gas preferably has no folded wall angles sharper than 140 degrees. This then smooths out airflow velocities through the ventilation space, reducing high pressure performance losses, reducing the severity of any thermal pockets, and allowing lower flow resistance to the fan’s exhaust.

In some embodiments, the air compressor is configured such that the perimeter of the lower opening in the bottom wall of the housing is vertically aligned to a perimeter of the exhaust for the airflow from the heat exchanger. This is so that the perimeter of the exhaust for the airflow from the heat exchanger is positioned in vertical alignment above the lower opening in the bottom wall of the housing. With this configuration, two air compressors of the present invention can be stacked one above the other, with vertically aligned housings, and that alignment of the housing will position the exhaust of the lower compressor with the opening in the bottom of the upper compressor. With this arrangement, the airflow exiting through the exhaust of the lower air compressor can be vented through the upper air compressor through the ventilation space of the upper air compressor even when the housings are vertically aligned directly above one another. Such an alignment of the stacked housings provides a more stable stack configuration, allowing higher stacks to be provided, or more stable stacks on a moving body, such as on a ship.

In some embodiments, the housing has the general dimensions of an intermodal container (or a shipping container) for allowing the air compressor to be shipped to and from one location to another using conventional shipping techniques. Such containers go by many names, including simply a container, cargo or freight containers, ISO containers, shipping, sea or ocean containers, sea vans, sea boxes or Conex boxes, container vans, sea cans or c cans.

A preferred embodiment comprises a housing with a general configuration or compatibility with the general form of a 20ft (6.1m) intermodal (shipping) container - 8ft (2.44m) wide and 20ft (6.1m) long, with twistlock fittings in each of the eight corners for hoisting, stacking, and securing to other containers or the hull of a ship. By using such Standardised containerisation of the air compressors, this allows two stacked containers to be stacked and joined together in a stable and well known manner, for example using the twistlock fittings as commonly used for such intermodal (shipping) containers. This well-known form for the housing gives familiarity to the air container, both in singular and stacked arrangements, and confidence in the safety and floor fixedness (lack of likelihood of movement on the floor) of the air compressor or stack thereof at sea.

The present invention also provides a stack of air compressors, the stack comprising a first air compressor with a top vent for exhaust gas from a heat exchanger thereof, and a second air compressor stacked on the first air compressor, the second air compressor being as defined above and the lower opening of the second air compressor being aligned over the top vent of the first air compressor.

In some stacks, more than two air compressors are stacked upon one another.

Preferably the third or subsequent air compressors are also as defined above. In accordance with a second aspect of the present invention, therefore, there is provided a stack of at least two air compressors, one being a lower air compressor and the other being an upper air compressor, each air compressor comprising: an air compression unit with a low pressure air input and a high pressure air output; a heat exchanger system for cooling components and/or fluids of the air compression unit, the heat exchanger system comprising at least one heat exchanger and at least one fan for driving airflow through the at least one heat exchanger; a housing; an exhaust for the airflow from the heat exchanger in an upper wall of the housing; and an air intake for the one or more fan; wherein: the housing of the upper air compressor comprises first, second and third sections, the first section housing the at least one heat exchanger and the at least one fan of that air compressor, the second section being a ventilation space and the third section being a compartment that houses the air compression unit of that air compressor, and the ventilation space having a) a lower opening in a bottom wall of its housing that is aligned over the exhaust of the lower air compressor, and b) an upper opening in a top wall of its housing for allowing exhausted air from the lower air compressor to be vented from the exhaust of the lower air compressor through the ventilation space of the upper air compressor and out through the upper opening of the upper air compressor.

In some embodiments each air compressor is a containerised air compressor, the upper air compressor being for stacking on the lower air compressor in a secured or interconnected manner, the housing of each air compressor providing the containerisation, and being compatible for stacking with and interconnecting with each other. In some embodiments the housing is compatible for stacking with and interconnecting with intermodal containers of a similar size. For this purpose the containerisation of the air compressor is preferably such that the housing is sized to meet the requisite Standard for intermodal containers - ISO 6346.

Preferably the interlocking uses a standard a twistlock system. In some embodiments the stack is more than two high.

In some embodiments each air compressor is as defined above in respect of the first aspect of the invention.

In some embodiments, the air compressors are intended to operate substantially continuously to maintain an air-bubble curtain at sea. As a result they need to have minimal service downtime. In a maritime environment at sea, zero service time is not a realistic proposition as the saltwater environment is relatively hostile for mechanical machinery such as air compressors. As a consequence, multiple air compressors are usually provided in typically more than one stack - for example at least three stacks of two compressors. This provides suitable redundancy to thus then allow for downtime of at least one of the air compressors in the system. For such servicing, the service access space is preferably provided in the container/housing.

According to an aspect of the present invention, therefore, there is provided a platform having a plurality of air compressors arranged thereon, each air compressor having a service access space, the plurality of air compressors comprising at least one stack, the stack having an upper unit and a lower unit, the upper unit being an air compressor, and the lower unit being either an air compressor or an air filter unit.

In some embodiments, the plurality of air compressors comprises at least one air compressor as defined above,

In some embodiments the platform is on a ship. In a preferred embodiment the platform is the deck of a ship.

As these air compressors have service access spaces, the air compressors can be serviceable at sea, i.e. without removal from the platform.

A common issue on platforms in which multiple air compressors are laid out is that the environment surrounding air compressors, and thus any service space provided therefor, is heated by the exhausts from the air compressors, be that from the fan exhausts of the heat exchangers or the exhausts from generators for driving the air compression units, or even from the compressed air itself as compressing air generates heat. In prior art layouts, such as that shown in Figure 1, the intakes for the fans of the heat exchangers are arranged to face one another across a central aisle along the length of the ship, and with the exhausts from the fans/heat exchangers being to the sides of the housings of the air compressors. For example, Figure 1 shows containerised air compressors 10 with front doors 12 (for closing over the front end when the air compressor 10 is not being used) folded back into their open state, extending backwards at an angle to the sides of the housing of each air compressor 10, and with the air compressors’ front ends facing each other. This front ends are the air intakes (opened by opening the doors) and the doors, by angling backward, encourage the vented exhaust from the heat exchangers to flow backward down the space between adjacent air compressors towards the sides of the platform (here a ship). This arrangement thus sucks in air from the central aisle of the platform, passes that air through the fan and then the heat exchangers of the air compressor and then vents that heated air backwards towards the sides of the ship. At the rear of the air compressors will also be the engine exhausts for the air compression unit, which are also hot. The heat is thus passed away to the sides of the platform. However, as access into the service space for the air compression units is also through the side or rear of the housing, these air compressors - particularly the heat exchangers - need to be turned off to allow servicing as otherwise the environment would be too hot for service personnel. Some known air compressors try to alleviate this by using an exhaust from the heat exchangers that extends upwards, but that, prior to the present invention, made stacking of operating air compressors impossible.

A further problem has also been identified with stacking prior art air compressors, even those with side vents for the heat exchanger exhaust. That is that if an attempt is made to stack the heat exchangers, the vented exhaust will tend to rise (as hot air rises) making the environment around the upper air compressor even hotter than that of the lower air compressor. As a result, in the prior art, stacking of air compressors of this nature has largely been avoided as it makes servicing too difficult or costly (due to needing to turn off multiple air compressors).

It is also to be observed that commonly the service area in the housing for the air compression unit will also be vented - with an air intake and an air outlet. These likewise need to be in the sides of the housing, and as such can also suffer from recirculation of the hot air of the exhaust from the heat exchanger - either from its own heat exchanger or that of a neighbouring air compressor. For this reason it is possible that multiple air compressors need to be disabled during servicing. Where the air compressors feed air to an air curtain for surrounding a subsea piling site, this can disable the air curtain, thus also necessitating a shutdown of the piling process.

The present invention therefore also helps to optimise the layout and configuration of air compressors on a platform for minimising hot air circulation from the exhaust of the heat exchanger and from the exhaust of the generator for the air compression unit, through the service space ventilation system After all, if the air compressors are not correctly laid out on the platform, the heat can become trapped or recycled between adjacent compressors, and thus ineffectively dissipates that heat, making the surrounding environment and the service space in and around the air compressors unsuitable for service personnel.

In a preferred configuration, a plurality of spaced but adjacent air compressors will operate such that they can provide a surrounding environment for the serviceable components that is operator-compatible - i.e. safe for service personnel - to ensure that the service personnel can safely service the equipment. Ideally this surrounding environment - including any service space inside the housings, should not exceed 35 degrees centigrade. With side-venting air compressors, this usually would rule out stacking the units as the heat from exhaust of the lower units (coming from the heat exchangers) would dissipate at least part of their heat upwards, overheating the upper container’s surrounding environment.

It is also to be noted that service access into the upper air compressors will be via a walkway between adjacent air compressors, which will physically block any attempt to vertically direct the exhaust from the side vents. Thus the heat from the heat exchangers that exits the exhaust for the fan(s) in the lower container cannot easily dissipate in any direction other than rearwardly along the sides of the air compressors (and to feed the exhaust forwards would recirculate it into the air intakes at the front of the air compressors, which also is not appropriate.

With the present invention, however, the exhaust can be located at the top of the lower container, even though an upper container may be stacked thereon, as the upper container provides its ventilation space through it for allowing the exhaust from the lower container to be passed upwards there-through. This is thus a first step in optimising the configuration of the air compressors as the heat from the heat exchangers of the lower container can be vented upwards, whereby it provides less of a negative impact on the working environment surrounding itself as well as the working environment of the air compressor above it.

The present inventors have also realised that larger air compression capacity can be beneficial as it can reduce the number of situations where the air curtain needs to be deactivated through shutdown of one or more air compressor. However, for a given size of platform, there is a limited amount of space for air compressors. For the prior art air compressors where stacking was an unsuitable solution, this typically necessitated either increasing the size of the platform (i.e. the ship) or having more than one ship. However, keeping a ship at sea costs a significant amount of money, and keeping two ships at sea costs double that sum, so the impact of increasing the number of air compressors, or the size of the compressors (an alternative approach for increasing air compression capacity - but likewise requiring additional space) can have more than a proportional effect on the cost of the operation of the air bubble curtain. For example, adding 10% more air compression capacity will require larger compressors, or additional compressors, and the increased size or number of compressors may not fit onto the deck of that ship (particularly as stacking is typically not a suitable option with prior art compressors), and thus either a larger ship deck is needed or a second ship is needed. Adding a second ship doubles the ship-hire costs despite only a 10% capacity gain. Likewise a larger ship can be significantly more costly than a smaller one - thus again increasing the cost disproportionately. With the present invention, however, stacking of air compressors becomes a viable option, thus allowing a significant increase in air compression capacity (potentially a 100% increase by stacking two high, or tripling if stacking three high, etc.) without increasing the base cost of the ship rental.

Thus, the platform of the present invention as defined above, with the stacked air compressor, provides a significant advantage over the prior art - with the non- stackable air compressors. In some embodiments, the platform is on a compressed air supply ship comprising a plurality of stacks of air compressors, upper air compressors in each stack being as defined above in respect of the first aspect of the present invention.

In some embodiments, the stacks are arranged in a regular array on the deck of the ship. The array is preferably two or three wide across the width of the ship. The array is preferably two or more long along the length of the ship.

In some embodiments the housings of the air compressors have a length and a width aligned respectively with the length and width of the ship. In the prior art they were usually arranged two wide on the ship, and unstacked, with their lengths arranged width wise on the deck of the ship (perpendicular to the length of the ship). By arranging them instead with their lengths and widths aligned respectively with the length and width of the ship, for a 60ft wide ship there will be room to accommodate three 8ft wide and 20ft long containerised air compressors across the width of the deck, with suitable walkway spaces to the sides thereof, all between the sidewalls of the 60ft wide ship.

In some embodiments the air compressors are provided as 20ft by 8ft containerised air compressors.

The provision of one or more air filter arrangement is a commonly specified requirement for a compressed air supply ship used for providing an air bubble curtain. The air filter arrangement can be to ensure that the air pumped into the sea is filtered air. This is to reduce or prevent pollutants being pumped into the water.

In some embodiments the air compressors are provided in a plurality of stacks, the majority of the stacks being stacks of two or more air compressors in accordance with the first aspect of the present invention, and at least one of the stacks comprising an air filter arrangement with an air compressor in accordance with the first aspect of the present invention stacked thereon. Preferably the air filter arrangement is provided within an intermodal frame to allow interconnection with its above-stacked air compressor, the above-stacked air compressor being a containerised air compressor - i.e. one meeting a similar intermodal container standard as the frame of the air filter arrangement. Typically there is a single air compressor stacked on the air filter arrangement, and each stack consists of two stacked air compressors.

As the air filter arrangement produces less heat than an air compressor and is usually best operated in the absence of any excessive external heat source, it is best located under the air compressor, rather than above it. If it was to be located above it, it would then need to vent the hot exhaust of the air compressor below it in a manner that avoids interference to the filtering process, which would require an unnecessary design specification.

In some embodiments there are seven stacks, five of the stacks being stacks of air compressors in accordance with the second aspect of the present invention, and two of the stacks comprising an air filter arrangement with an air compressor in accordance with the first aspect of the present invention stacked thereon.

In some embodiments, the or each stack comprising an air filter arrangement under an air compressor is arranged in a central, internal or middle row of stacks, the rows of stacks extending along the length of the ship. The or each stack comprising an air filter arrangement under an air compressor produces less heat than the stacks of two air compressors due to there being fewer air compressors in the air filter stacks. It is thus a “lower-thermal-output stack” compared to the stacks with two air compressors. Therefore, by positioning those lower-thermal-output stacks in a central, internal or middle row, rather than in one of the side-most rows, and positioning stacks with two or more compressors and no air filter unit to the side-most rows (rows extending along the length of the platform), the array of stacks formed by those lower-thermal-output stacks and those stacks with two or more compressors and no air filter unit, will suffer a lower overall recirculation or cross-contamination of heated air between adjacent stacks compared to an arrangement in which the lower-thermal-output stacks are instead located in one of the side-most rows relative to the width of the ship.

As recirculation of hot air through the service space can result in a heating cycle for that air, one aspect of the present invention is to reduce that recirculation, and the above repositioning of the lower-thermal-output stacks certainly provides such an advantage. However, it is also possible to reduce recirculation if outlet vents from the service spaces in the air compressors can be modified or correctly positioned relative to neighbouring inlet vents for service spaces in the air compressors. One approach for helping with this is to provide, in place of louvres or grills in the sidewalls at the outlets for the service space, chimneys extending from the vents and extending vertically upwards to a point at or above the top of the respective stack. Where the upper air compressor is located above an air filter unit, a short chimney can be provided to place the top thereof above the stack. It can extend from the outlet vent to just above the top of the stack. By positioning the outlet vent in a sidewall, but up towards a top region of the housing (preferably in a top third of the sidewall), the height of the chimney can be less than half the height of the vent, albeit with its top above the top of the vent. It then can redirect a traditional sidewards outflow of the heated air of the service space (heated by the equipment in the engine room, such as the engine and the compression unit) into an upwards flow direction - up to and above, and then away from, the top of the stack. This can then help to avoid or reduce recirculation of that outflow into neighbouring air inlets, as otherwise readily occurs from a sidewards outflow - which instead relies on the “hot-air-rises” principle for upward dissipation.

In some embodiments the chimney’s cross section largely matches that of the outlet vent (i.e. the “window” in the side wall (or rear wall) of the housing).

A chimney may be provided for each outlet vent, or a combined chimney may encompass both or all outlet vents if more than one is provided.

In some embodiments, the chimney’s top is chamfered, for example at a 50 degree angle from horizontals. Chamfering it can offer a larger top opening size which ensures less throttling of the outflow by the chimney, and thus less load on the fan for the airflow through the outlet vent, where that vent is powered by a fan - as is typically the case to force airflow through the service space. In some embodiments the inlet vent might be powered by a fan instead, or as well.

In some embodiments, louvres are provided at the top of the chimney, which can serve to prevent or reduce the incidence of rainfall or other water (e.g. sea spray) entering the top of the chimney. The louvres may be spring to revert to a closed state when there is insufficient airflow through the chimney, as known for bathroom vent covers. In some embodiments, for example for a lower air compressor in a stack of two or more air compressors, the chimney is extended from the blower air compressor’s outlet vent up to and past the outlet vent of the upper air compressor, both outlet vents using the chimney as a common chimney. In some embodiments a singular chimney is provided for two outlets in two sidewalls, one of a lower air compressor and the other of an upper air compressor, and a second chimney is provided for two outlets in two rear walls, one of a lower air compressor and the other of an upper air compressor. These two chimneys thus each provide a common chimney for the two air compressors. In some embodiments, the two chimneys are combined into a singular chimney that wraps across all four outlet vents.

In some embodiments these extended chimneys are at least 1.3x the height of the housing of the upper air compressor.

In some embodiments the tops of these extended chimneys are chamfered, much like those of the previously described shorter chimneys for a singular air compressor.

In some embodiments, a plurality of stacks are arranged in a regular array that is at least two stack rows long and three stack columns wide, these air compressors having air intakes for heat exchangers at their short ends that face away from each other in the rows, with at least one of the two stacks in the central column being a stack with an air compressor at the top and an air filter unit at the bottom, wherein an additional stack of air compressors is provided to form a further row, the compressors in the further row being turned 90 degrees relative to the other stacks to direct side and outward venting of air in a service space within that stack’s air compressors away from the regular array. That seventh stack is thus rotated relative to the other six stacks to extend its longest axis perpendicular to the centreline of the ship, rather than longitudinally along the length of the ship.

In some embodiments each air compressor has an air intake for a service space within it and an air outlet as well for that service space, the air inlet and the air outlet being positioned on different sides of the air compressors.

In some embodiments the intake for the heat exchangers in the seventh stack is arranged inbound on the ship, rather than facing the adjacent sidewall of the ship. In some embodiments the front most stacks in the array of stacks is positioned with its front end at least a full air compressor length from the forward wall of the deck, and preferably with nothing loaded on the subsequent space of the deck in front of that front end having a height higher than the lower unit of those stacks. More preferably the front most stacks in the array of stacks is positioned with its front end at least 1 ,5x or 2x a full air compressor length from the forward wall of the deck, again preferably with nothing loaded on the subsequent space of the deck in front of that front end having a height higher than the lower unit of those stacks. The free space at the second unit height reduces incidences of eddies from the front wall or tall structure at the front of the ship causing recirculation of hot air exiting the air compressor’s exhausts or outlets. In particular, by moving the stacks rearwardly on the deck in this manner, they overall become further spaced from the front wall or tall structure at the front of the ship. This can effectively neutralise any recirculation effect caused by eddying of airflow behind the front wall or tall structure of the ship.

In some embodiments the air compressors have one or more walkway to either or both sides of the housing and/or to a rear and/or front of the housing. These walkways may be to allow access into the service spaces inside the third sections of the housings, or for accessing other serviceable areas of the air compressors, as doors are provided in one or each side of the housings for accessing the internal service space, and hatches or doors can be provided to accesses other equipment of the air compressors, e.g. from external of the housing. These walkways can be accessed using ladders or stairs (not shown) as is well known on ships or other platforms.

As it is desirable for any hot air surrounding the air compressors to rise up and away from the stacks to minimise hot air recirculation, and since hot air tends to rise unless influenced otherwise, it is desirable that these walkways be made with perforated decks to minimise any resistance they may present to that rising hot air. For example, they may be made with decks of expanded metal mesh, or otherwise perforated sheeting, or perforated fibreglass sheets.

These and other features and aspects of the present invention will now be described in further detail, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a prior art configuration for a plurality of air compressors on the deck of a ship;

Figure 2 shows a perspective view of a first configuration for a plurality of air compressors, and two air filter units, in accordance with an aspect of the present invention;

Figure 3 shows a schematic cut-through view of an air compressor in accordance with an aspect of the present invention stacked on an air filter unit;

Figure 4 shows a stack of two air compressors in accordance with an aspect of the present invention;

Figure 5 shows a top plan view of the configuration in figure 2;

Figure 6 shows airflow pattern information derived from a computational fluid dynamics (CFD) simulation of the heat exchangers and air flow there-through for the stack of figure 4;

Figure 7 shows a possible modification for a ventilation space through one of the air compressors for helping to smooth out air flow velocities through the ventilation space;

Figure 8 shows temperature pattern information derived from a computational fluid dynamics (CFD) simulation of the heat exchangers in the stack of figure 4;

Figures 9 and 10 show temperature pattern information for horizontal cut planes through, respectively, the bottom and top containers’ engine room ventilation inlets, as provided for ventilating a service space in the housing, as derived from a CFD simulation in a zero wind speed scenario surrounding the air compressors in the stack of figure 4;

Figures 11 and 12 show temperature pattern information for horizontal cut planes through, respectively, the bottom and top containers’ engine room ventilation outlets, as also provided for ventilating a service space in the housing, as derived from a CFD simulation in a zero wind speed scenario surrounding the air compressors in the stack of figure 4;

Figure 13 shows streamlines showing the route of air through and around the bottom containers numbered one, two and four in figure 5, and the calculated temperatures of that air, in each case as approximated or calculated using CFD simulation, until it enters the bottom container numbered five in figure 5;

Figure 14 shows temperature and flow direction on a vertical cut plane in the longitudinal axis of the ship, and thus through containers one and two as numbered in figure 5, as approximated or calculated using CFD simulation in the situation of a bow wind load, showing the influence of the tall structures at the forward area of the ship on recirculation of the air around the air compressors;

Figures 15 and 16 are similar to figures 9 and 10, but instead for the situation of a bow wind load as in figure 14;

Figures 17 and 18 show modified versions of the stacks of figures 3 and 4 in which chimneys instead of louvered vents vent the ventilation outflow from the service space area of the air compressors;

Figures 19 and 20 show, respectively, a perspective and a plan view of a modified configuration for the air compressors on the ship of figure 2 and figure 5 to further reduce heat recirculation through the service spaces of the air compressors by repositioning the air filter units into different ones of the stacks and by moving all of the stacks further rearward on the ship - further away from the tall structures at the forward area of the ship;

Figures 21 and 22 show the improved temperature profiles surrounding the air compressors when using the modified configuration of figures 19 and 20, these figures showing temperatures on a horizontal cut plane at bottom and top container engine room ventilation inlets for zero wind situations, as approximated or calculated using CFD simulation, and can be compared with figures 9 and 10, respectively; Figures 23 and 24 show the improved temperature profiles surrounding the air compressors when using the modified configuration of figures 19 and 20, instead in a bow wind load, these figures showing temperatures on a horizontal cut plane at bottom and top container engine room ventilation inlets, as approximated or calculated using CFD simulation, and can be compared with figures 15 and 16, respectively;

Figure 25 shows a further possible configuration of the present invention in which nine stacks are provided, and thus a similar number of air compressors as shown in figure 1 , albeit with each air compressor being of a larger air compressing capacity than those shown in figure 1 , schematically illustrated by the size of the housing thereof; and

Figures 26 to 33 show, respectively, top plan, side elevation, front elevation, rear elevation, opposing side elevation, front top perspective, bottom plan and bottom rear perspective views of a containerised air compressor implementing the first aspect of the present invention.

Referring first to Figure 1 , a known arrangement for air compressors 10 on a ship is shown. As can be seen, the air compressors are arranged in an array, the array comprising 16 air compressors, arranged in two lines of 8, with a central access passageway or aisle. Each compressor 10 is of a containerised design, with a housing having a rectangular footprint. The long sides of the footprint are arranged to align with neighbouring containers in the array along the length of the array, with front doors 12 for covering over air intakes at the front ends of the housings being folded back to their open states in which they adopt an angled back position between adjacent air compressors 10. Each air compressor’s air intake is for one or more heat exchanger of the air compressor 10, and those air intakes face the central aisle to draw fresh air into the heat exchangers.

The array extends two by two along the length of the ship with the containers’ long sides being perpendicular to the aisle. With this arrangement, the array of 16 compressors occupy approximately 50% of the length of the ship, and the majority of the deck space (more than 50%). All the remaining available deck space is then occupied by miscellaneous other equipment 18. It is also to be observed that this ship features tall structures 16 at the forward area of the ship, which house the crew quarters and the bridge, and other non-outdoor spaces, and sidewalls 14 around the deck.

Referring next to figures 2 and 5, a modified configuration for the ship is shown in which air compressors of the present invention are provided. In this modified configuration, the air compressors 10 are presented in stacks. As will become apparent in later figures, there are seven stacks in this embodiment, five of which comprise pairs of air compressors 10 and two of which comprise an air compressor 10 stacked on an air filter unit 20. There are thus 12 air compressors. These are compressors are of a longer length to those of Figure 1 and each one offers a higher air compression capacity than those of Figure 1, schematically represented by the overall longer length of each air compressor, and as such this modified configuration can overall offer a similar or larger air compression capacity to that of the configuration of Figure 1 , yet it occupies a smaller overall footprint on the ship - perhaps a third of the length of the ship. This reconfiguration - particularly the stacking - this permits even more stacks to be provided on the ship - see, for example, Figure 25, which fits 9 stacks (18 containerised units) in an overall smaller space than that occupied by the 16 containerised units (air compressors) of Figure 1, observing that in Figure 25, a larger area for additional miscellaneous other equipment 21 can be fitted into the additional deck space freed up by this stacked configuration versus that of Figure 1.

Referring next to figure 3, a first form of stack is shown. In this stack, and air compressor 10 of the present invention is stacked on an air filter unit 20. Air filter units are well known the art and serve to filter the air either entering or exiting the air compression units within the air compressors 10. The air filter unit is only shown schematically in this figure, although a containerisation frame 22 is shown surrounding the air filters 24 of the filter unit 22 allow the air filter unit 20 to be readily stacked and connected to the air compressor above it, and likewise to the ground (the platform/deck of the ship). Being only schematic, pipework between the air filters and the air compression unit are not shown, as they can be conventional in form, and are already known in respect of configurations as shown in figure 1 , albeit without being stacked. For example, in figure 1 , two or more of the illustrated air compressors 10 might be air filter units. It will also be understood that the stacks might comprise no separate air filter units, for example if the compressors are all oil free compressors, as also known in the art for reducing downstream oil contamination.

Referring next to figure 4, a second form of stack is shown. In this stack, to air compressors of the present invention are stacked one above the other. There is thus a lower air compressor 26 and an upper compressor 28 in the stack.

In figures 3 and 4, the air compressors 10 are shown with part of the sidewall of the housing cut away, and with simplified internal components for clarity. For example, each air compressor 10 can be seen to have a housing 30 that comprises first, second and third sections 32, 34, 36 linearly spaced along a length of the housing 30, with internal walls 38, 40 separating the three sections 32, 34, 36.

The first section 32 houses at least one heat exchanger 42. In this embodiment there are three heat exchangers 42, each for cooling different fluids of the air compressor 10. The first section also houses at least one fan 44 (see figure 4) which sucks air through the heat exchangers 42 and blows the subsequently hotter air out through an exhaust 46 at the top of the first section 32. Air can thus be sucked through a front opening or inlet of the housing through the heat exchangers and out through the exhaust 46.

The second section 34 instead provides a ventilation space that extends substantially vertically through the air compressor 10 from a lower opening 50 in a bottom wall of the housing to an upper opening 52 in a top wall of the housing. The motor 54 for the fan 44 may extend into this ventilation space, depending upon the configurations thereof. However, the ventilation space would simply circulate around that motor 54. Likewise, pipework 56 can extend across the ventilation space 48 between the first section 32 and the third section 36 for feeding fluids from the third section to the first section and from first section to the third section-e.g. to connect the heat exchangers 42 to the equipment for which they provide fluidic cooling.

The third section 36 then houses the engine room of the air compressor 10 which engine room will have an air compression unit and an engine for driving it. The engine room also provides a service space for at least part of the engine and the air compression unit 58 provided therein, as these components will need regular servicing. Details of the air compression unit can be conventional thus are only indicated herein in schematic form, with an integrated engine. Likewise the connection to pipework for piping the output compressed air to the seabed (for providing an air curtain around a piling site) is not shown as it also can be conventional.

As the third section 36 provides a service space for personnel, and since the air compression unit 58 will generate significant amounts of heat in the engine room as both the engine will get hot and will have a hot exhaust pipe and the air compression unit itself will generate significant amounts of heat, ventilation for the service space is needed. For that purpose, a ventilation air intake and a ventilation air outlet is provided for the service space. The air intake will pull air from the surrounding environment of the housing, taken through a sidewall of the housing, and the air outlet will vent the air again through that sidewall of the housing. Between the air inlet and the air outlet, however, the air will be heated by the heat generated by both the engine and the air compression unit. To schematically represent this air flow through the service space, figure 6 provides an L-shaped pipe having two air inlets 60 for each air compressor 10 and two air outlets 62 for each air compressor 10 (see Figures 11 and 12, for an example of two air outlets - one in a back wall and one in a side wall opposite the sidewall with the two air inlets 60). This figure additionally shows exhaust flues 64 for the engine, which will also heat the environment at the rear of the housing, external of the service space. These exhaust flues 64 extend upwards above the stack to better distribute the exhaust heat upwards from the stack, although the sidewalls of these exhaust these will still be very hot.

Still referring to figure 6, its shading illustrates air flow velocities within the stack of two air compressors 10, as calculated using CFD simulation, both through the first and second sections 32, 34 and through the representative L-shaped pipe representing the service space (simplified in this manner to facilitate CFD simulation as the actual layout internal of the engine room would be very complicated to simulate precisely, and yet only general airspeeds are realistically needed for confirming suitability for personnel access - in particular as the ventilation airflow is always likely to be lower than that through the heat exchangers. From this it can be seen that there are stagnant areas around the outside of the housing, and in the service space, which airflow is effectively zero or non-significant and there are variable air flows within and around the heat exchangers, the fan, the exhaust in the first section 32, the ventilation space in the second section 34. Vortexes, however, form in various parts of the second section 34 which are illustrated by the darker areas 72 on corners at the bottom of the upper housing where the exhaust from the lower housing enters the upper housing, and around the bend just below the motor 54 of the fan in the upper housing. There is also a high-speed area 64 as the air exits the fan for both fans, which is to be expected.

The vortexes shown by the darker areas 72 represent flow efficiency losses in the ventilation space for the exhaust exiting the lower air compressor 10. Because of them, the lower fan will need to work harder - additionally so as the ventilation space already throttles that exhaust at least to a certain degree. One aspect of the present invention is to reduce that additional loading on that fan. For that purpose, referring next to figure 7, a modified shape 66 for the forward wall is shown. As can be seen, the corner sitting below the motor 54 of the upper fan is chamfered to make the throttle point for the exhaust flow less severe. As a result, a smoother or more uniform airflow can pass through the ventilation space.

Ideally the walls of the ventilation space would be smooth and curved to mostly eliminate sharp throttling. However, chamfering back that corner to the heavy black line 68, to provide a less sharp angle - for example an angle not exceeding 140° or more preferably not exceeding 120°, can be enough to offer a worthwhile benefit.

It is to be noted that this ventilation space is deliberately arranged overall to angle or extend rearwardly from the bottom towards the top, rather than perpendicular to the bottom wall (i.e. directly vertically). In this example that involves angling it rearwardly at the input end of the ventilation space (the bottom end), with the outlet end (top end) then being vertical. This “angled” configuration is to put the inlet therefor into a more forward position than its outlet. In this example it is to put the inlet specifically into vertical alignment with the fan exhaust of the first section 32. This is to allow vertical stacking of two such air compressors to align the ventilation space’s inlet (i.e. of the upper air compressor 28) over the fan exhaust of the lower air compressor 26, as shown in Figure 4. The exhaust of the lower air compressor 26 thus directly exhausts from its fan into the ventilation space of the upper air compressor 28.

Referring next to Figure 8, approximated temperatures of the airflow flowing through the first and second sections 32, 34 and the service space are shown. These are provided through CFD simulation. As can be seen, cold air is drawn in by the two fans 44 from the environment at the front of the stack of two air compressors 10. That air passes through the heat exchangers 42 and heats up before being vented by the fans through the respective exhausts 46. The exhaust 46 of the upper air compressor 28 vents the heated air upwards and above the stack. The exhaust 46 of the lower air compressor 26 instead vents into the ventilation space 48 of the upper air compressor 28. That airflow thus likewise will vent upwards and above the stack through the ventilation space 48 of the upper compressor 28. The heat from the heat exchangers is thus substantially all vented upwards, although there can be some heat transfer between the internal walls between the various sections of the housing.

Separately, airflow is vented through the service space represented by the L-shaped pipe 70. In this example, the two air inlets 60 are shown to be drawing in air at two different temperatures. This is because the more forward-positioned air intake 60 will be further away from the air outlets 62 than the more rearwardly positioned air intake 60, and thus the air at the more forward-positioned air intake will be cooler than that of the more rearwardly positioned air intake.

As that airflow passes through the service space 70, it will be heated by the engine and air compression unit, as represented by a heat source 74 in figure 8, and thus there will be hotter air venting out through the air outlets 62.

Additionally as shown in figure 8, the exhaust flues 64 will create localised hot points 76, and a generally hot area around them.

So long as the air being pulled in at the air intakes is adequately cool, the overall temperature in the service space will remain suitable for personnel access. Only immediately around the heat source, i.e. the engine and the air compression unit, does the temperature become unmanageable, but this equates to the personnel not touching the equipment.

Referring next to figures 9 and 10, the environmental temperature surrounding the various stacks is shown to demonstrate whether the air intakes will be able to source adequately cool air for maintaining a suitable service space for personnel access. These two figures both show temperature pattern information for horizontal Planes through, respectively, the bottom and top containers’ air inlets 60. For reference, the air outlet 62 are also shown, although in practice these may be raised relative to the air inlets to allow hot air to rise and be vented from the air outlets in the service space, as these air inlets and outlets will typically be fan driven vents in or on the walls of the housing, with the air inlets sucking and the air outlets blowing the air in and out of the service space.

Referring now to figure 9 specifically, which represents the lower tier of the stacks, we can refer to the individual stacks using the stack numbering shown in figure 5, where, as shown in figure 5, from left to right, top row to bottom row, the stacks are numbered as stack 7, stack 6 and stack 5 for the top row, stack 1 and stack 2 for the middle row, and stack 3 and stack 4 for the bottom row, there herein being seven stacks. The air surrounding those stacks is such that stack number 7 has generally cool air surrounding it. However, the lower unit in that stack is an air filter unit 20. It thus does not have significant heat sources therein, if any. Likewise, the lower unit in stack number 6 is an air filter unit 20. Thereafter the air compressors on this lower level are oriented such that the three air intakes for the heat exchangers of the front-most air compressors all face forwards and the air intakes for the two rearmost heat exchangers face rearwards. This ensures that the heat exchangers draw air from cooler air supplies and condenses the exhaust flues and the air outlets from the service spaces together.

The lower unit in stack number 6, although having a cool environment around the end closest to stack number 7, has a warmer environment around its end closest to stack number 5. That is because stack number 5 will vent heated air from its service space, and the air outlet 62 of the lower air compressor 26 of stack number 5 at least partially faces stack number 6. Furthermore, the exhaust flues 64 of stack number 5 will heat that surrounding area.

Likewise, the air surrounding stack numbers 1 and 3 will be similar to that of stack number 6, with cold air at the rear ends thereof (relative to the ship) and hotter air at the front ends thereof. This again is due to the proximity of the front ends thereof to the air outlets and the condensing of the exhaust flues of stacks 2 and 4.

As for the air surrounding stacks 5, 2 and 4, that is generally warmer than that of the other stacks due to the greater density of exhaust flues and air outlets, and since the sidewalls 14 of the platform/ship reduce sideward ventilation. As a consequence, air being drawn into the air inlets of these air compressors is typically higher than that of say stack number 1 , although as stack number 1 vents its air outlet towards the air inlet of stack number 3, stack number 3 can also draw in hot air through its air inlet. Nevertheless, for the most part the drawn in air is not of an excessively high temperature for the lower level air compressors 26.

Referring next to figure 10, the upper level is shown. Here all 7 stacks now show air compressors. As before the air surrounding stacks 7 and 6 is generally cool. Further, the air above the sidewalls and at the front of the ship is all cool. Therefore, each of stacks 7, 6, 1 , 3 and 4 can draw in cool air for their service areas. Indeed, the upper air compressor 28 in stack 4 can draw in cooler are than that of the lower air compressor in stack 4 as the sidewalls of the ship only extend high enough to block circulation to the lower air intakes. However, the air intakes for the upper air compressors of stacks 5 and 2 still may draw in hotter air. This is due to the concentration of heat from the exhaust flues of six of the air compressors on that level and all 5 from the level below, and also the outlets 62 from the service spaces of the air compressors of stacks 1 , 2, 4 and 6, which will circulate towards the air inlets for the service spaces of stacks 2 and 5, as shown by the airflow lines in Figure 13.

Therefore, in each of stacks 2 and 5, for both the upper and lower air compressors, there is a possibility of a raised temperature in the service space, as shown in Figures 11 and 12, which show the outflow temperatures - note in particular the hot air venting from the outflow from the outlets 62 of stacks 2 and 5 - particularly stack 5 which suffers the most in this simulation.

Figures 9 to 13 relate to a situation where there is no wind surrounding the air compressors 10. However, adding in wind can change the airflow characteristics over and around the stacks on the deck. With this illustrated arrangement of stacks, a side wind makes little practical difference to the temperatures of the service spaces, and likewise a tail wind makes little difference to the temperatures of the service spaces. However, a bow wind can create new difficulties due to the tall structure 16 in front of the stacks. That tall structure 16 can create a partial eddy behind the tall structure in the situation of a bow wind (blowing from the front to the back of the ship). That partial eddy can cause the exhaust from the heat exchangers to start to recirculate into the space between the front of the stacks and the tall structure, which can lead to increase temperatures throughout the air compressor. The partial eddy might even cause the exhaust from the exhaust flues of the engines for the air compression units to start to recirculate to the front, although from the CFD analysis provided in Figure 14, the main recirculation seems to be from the heat exchanger’s exhaust.

With that partial recirculation, it can be seen by comparing Figure 9 (no wind) with Figure 15 (bow wind and partial recirculation at the front) that the recirculation causes an overall higher temperature around all of the stacks, and particularly between stacks 1 and 2 and in front of stacks 5, 2 and 4. As a consequence it is clear that the air intakes for the service spaces will tend to draw in hotter air, and the working environment in the service spaces in stacks 1 and 2 may be unsuitable for service personnel. This is particularly pronounced for the lower air compressors as shown in figure 15, although the space in front of stacks 5, 2 and 4 are also clearly hotter in the top layer, versus that shown in Figure 10.

As recirculation of hot air through the service space can result in a heating cycle for that air, one aspect of the present invention is to reduce that recirculation, and if the outlets 62 from the service space can be modified to reduce their recirculation, that would be beneficial. Referring to Figures 17 and 18 one approach for helping with this is shown. As can be seen, in place of louvres or grills in the sidewalls at the outlets for the service space, chimneys are provided. As shown in Figure 17, for the stacks where the upper air compressor 28 is located above an air filter unit 20, a short chimney can be provided. It can extend from the outlet to just above the top of the stack. IT then can redirect sidewards outflow into an upwards flow direction - up and away from the top of the stack. This can then avoid or reduce recirculation of that outflow into neighbouring air inlets, as otherwise occurs as shown in Figure 13. Ideally the chimney’s cross section largely matches that of the outlet “window” in the side or rear of the housing (a chimney may be provided for each outlet, or a combined chimney may encompass both outlets 62. In this example, the chimney’s top is also chamfered - in this example at 50 degrees - which can offer a larger top opening size which ensures less throttling of the outflow by chimney, and thus less load on the fan for the airflow through the outlet 62. Louvres can again be provided at the top of the chimney if desired, which can serve to prevent or reduce the incidence of rainfall or other water entering the top of the chimney. Referring then instead to Figure 18, a stack with two air compressors 10 is shown. This time the chimney is extended from the bottom air compressor’s outlet 62 up to and past the outlet 62 of the upper air compressor 28. In this example, it is a singular chimney for both outlets in the two sidewalls, and a second chimney for the two outlets 62 in the two rear walls of the two air compressors. Similar to that of Figure 17, the tops are again chamfered for the same benefits, and again have louvres.

Referring next to Figures 19 and 20, a modified configuration for the seven stacks is shown. In this modified arrangement, the two stacks that have an air filter unit under an air compressor are moved to position them along the centreline of the ship, rather than to a side of the ship. Further, the seventh stack formerly in position 7 of Figure 5, is relocated and rotated relative to the other 6 stacks to extend perpendicular to the centreline of the ship, rather than longitudinally. It is thus now adjacent and behind (relative to the forwards direction of the ship) the stacks previously numbered 1 and 3, rather than behind stack position 6. It is also oriented to position the intake for the heat exchangers inbound on the ship so that the outlets from the service space is not directed towards stack position 1 , and instead it vents away from the stacks. The other stack positions are also all moved to shift the whole set of stacks rearwardly on the deck (including the moved and rotated seventh stack). However, all but the seventh stack remain longitudinally arranged along the length of the ship.

By moving the stacks rearwardly on the deck, they overall become further spaced from the tall structure 16 at the front of the ship. This allows the eddy effect discussed above to be substantially neutralised. Instead miscellaneous other equipment 21 can be located in the space in front of the air compressors, similar to that shown in Figure 25, perhaps relocated from behind the air compressors. Further, by reorienting the seventh stack, it neither vents its heated service space air towards other air compressors, nor has its exhaust flues from the engine (as it is now a double air compressor stack) adjacent the air intakes of the heat exchangers in stacks 1 and 3.

With this modified arrangement, as shown in Figures 20 and 21, there is an improved temperature profile surrounding the air compressors 10. Figures 20 and 21 respectfully show temperatures on a horizontal cut plane at bottom and top container engine room ventilation inlets for zero wind situations, as approximated or calculated using CFD simulation, and can be compared with figures 9 and 10, respectively. From that comparison, whereas in Figure 9 there is a clear elevated temperature on the bottom level around the service space outlet ends of each of the lower air compressors 26 in stack positions 6, 5, 1, 2, 3 and 4, in Figure 21 there is no evidence of elevated temperatures at the intakes for the service space. This is for a zero wind scenario. Furthermore, whereas in Figure 10 there is likewise clear elevated temperature on the upper level around the service space outlet ends of each of the upper air compressors 28 in stack positions 6, 5, 1, 2, 3 and 4, in Figure 22 there is hardly any evidence of elevated temperatures at the intakes for the service spaces for those upper air compressors 28. Only near the exhaust flues of stack number 7 (see figure 20)3 and 5 are a slight elevation of temperature evident, and these are all spaced from the air inlets 60 for the service spaces. These adjustments to the configuration have thus effectively eliminated recirculation of heated air through the service space.

Referring next to Figures 23, a similar benefit can be seen even for a bow wind. Comparing Figure 23 with Figure 15, there is again now no evidence of hot air recirculation for the air intakes of the lower air compressors, whereas before there was a considerable amount. As for the upper air compressors 28, as shown in Figure 24, the recirculation into the heat exchangers in stacks 5, 2 and 4 is eliminated and overall the amount occurring in stacks 1, 3, 6 and 7 overall is greatly reduced.

Finally, referring to each of Figures 5 and 20, between the stacks can be seen walkways 78. These walkways 78 are to allow access into the service spaces as doors are provided in one or each side of the housings. These walkways can be accessed using ladders or stairs (not shown) as is well known. As it is desirable for any hot air surrounding the air compressors 10 to rise, and since hot air tends to rise unless influenced otherwise, it is desirable that these walkways be made with perforated decks to minimise any resistance they may present to that rising hot air. For example, they may be made with decks of expanded metal mesh, or perforated fibreglass sheets.

The present invention and the advantages provided thereby, have been described above purely by way of example. Modifications in detail may be made within the scope of the invention as defined in the claims appended hereto.