Air dryer for electrical enclosures

An air dryer having an internal orifice designed into an outlet end cap that eliminates the need for external valves or regulators to control the flow of air through the dryer. The internal orifice, which can be press-fit or threaded into the end cap, provides a consistent and stable outlet flow and dew point and eliminates the need for instruments to measure outlet flow and dew point. The orifice size can be easily changed for changing outlet flow and dew point. A protective tubular shroud is provided for shielding a membrane module of the dryer, and for routing sweep gas to a bottom vent.

FIELD OF THE INVENTION

The present invention relates generally to membrane gas dryers for drying a stream of gas and, more particularly, to membrane air dryers for drying compressed air.

BACKGROUND OF THE INVENTION

Food processing plants typically must be cleaned at regular intervals to comply with various governmental regulations intended to ensure food safety. In many food processing plants, this entails shutting down at least a portion of the plant and manually cleaning the plant using various detergents. In many cases, the detergents are applied by cleaning personnel via a hose or the like. In other cases, a fixed cleaning system including an array of nozzles may automatically wash down the plant.

In either case, during cleaning the potential exists for water and/or detergent solutions to enter electrical boxes within the plant associated with the food processing equipment. Since electrical components typically do not fare well when exposed to moisture, it is common to provide such electrical boxes with gaskets and other sealing elements in an attempt to make them waterproof. Regardless of such efforts, however, the opportunity remains for moisture to enter the boxes.

To address this issue, some food processing plants supply a stream of dry compressed air to each electrical box. Since compressed air is generally moisture-laden, membrane air dryers have been employed to dry the air after it is compressed. The dry air is then circulated through the boxes to absorb and remove any moisture therein.

Such dryers are known in the art of compressed gas systems and are devices that remove water from a compressed air system, specifically the water that exists in the vapor phase. The performance of such air driers, which typically contain a membrane module, is generally measured by the dewpoint suppression achieved as air passes through the module. The dewpoint is the temperature at which moisture will start to condense out of the moist air. Dewpoint suppression is the number of degrees the dew point is lowered as the air passes through the drier.

The dewpoint suppression is a function of the membrane area, feed flow rate, operating pressure and temperature, and sweep fraction. Membrane air dryers typically function by contacting one side of a semi-permeable membrane with a pressurized wet feed stream. The membrane preferentially allows water vapor to permeate therethrough resulting in a drying of the compressed air stream. A portion of the dried gas, commonly referred to as the “sweep”, is fed back to contact the other side of the membrane and acts to sweep away the water moisture that has permeated the membrane. The sweep is often controlled by an externally mounted valve or an internal orifice. Such dryers typically employ an external valve or pressure regulator for controlling the flow of compressed air through the dryer.

SUMMARY OF THE INVENTION

An air dryer having an internal orifice designed into an outlet end cap that eliminates the need for external valves or regulators to control the flow of air through the dryer. The internal orifice, which can be press-fit or threaded into the end cap, provides a consistent and stable outlet flow and dew point. Preset outlet flow and dew point is more user friendly and eliminates the uncertainty associated with having to determine the outlet flow and dew point. This feature is especially advantageous in applications that lack the instruments to measure outlet flow and dew point, such as food processing plants. Another benefit is that the orifice size can be easily changed with a wrench thereby changing outlet flow and dew point, if so desired.

In addition, since known air dryers are generally not suitable for use in air drying systems of food processing plants where they can be exposed to harsh cleaning chemicals and/or can harbor food particles that can encourage bacteria growth and unsanitary conditions, the air dryer includes a protective sleeve in the form of a tubular shroud. The tubular shroud shields the membrane module from exposure to cleaning chemicals and provides an exterior surface that is easy to clean and is generally free of cavities for food to accumulate. The air dryer also includes an exhaust port for venting the sweep gas at a lower side thereof such that, when mounted, the sweep gas exhaust port can be shielded from infiltration by food particles and/or cleaning chemicals.

Accordingly, a membrane air dryer, comprises a tubular hollow fiber membrane module, a tubular shroud enclosing the hollow fiber membrane module, and an outlet end cap including an outlet end cap body connected to an outlet end of the hollow fiber membrane module, the outlet end cap body having a central aperture fluidly connected with an outlet end of the membrane module, and at least one flow path externally spaced from the aperture and fluidly connected with an external sweep air region formed between the tubular membrane module and the tubular shroud. The at least one flow path can be formed by a channel along the exterior surface of the outlet end cap body, and the flow path is defined between the outlet end cap body and shroud. The outlet end cap can include an orifice for regulating flow through the aperture from the outlet end of the hollow fiber membrane module. The outlet end cap can further include an orifice body fixed within the central aperture of the end cap body, and defining the orifice. The orifice body can be press-fit or threadably received within the central aperture. The outlet end cap can be removably connected to the membrane module.

The membrane air dryer can also include an inlet end cap including an inlet end cap body connected to an inlet end of the hollow fiber membrane module. A watertight seal can be provided between the inlet end cap and the tubular shroud. The tubular shroud can be captured between the inlet end cap and the outlet end cap.

In accordance with another aspect, a membrane air dryer comprises a tubular hollow fiber membrane module having an inlet, an outlet and a bundle of hollow fibers supported therein, at least one of the hollow fibers having an interior passageway for the flow of air through the module from an upstream end near the inlet to a downstream end near the outlet, the hollow fibers having interstitial spaces therebetween for the flow of a sweep gas, and an outlet end cap. The outlet end cap includes an end cap body connected to the outlet end of the membrane module, the end cap body having a central aperture fluidly connected with the outlet of the membrane module and having an orifice for regulating flow through the aperture from the outlet end of the membrane module. The orifice can be included in an orifice body fixed within the central aperture of the end cap body. The orifice body can be press-fit or threadedly received within the central aperture. The outlet end cap can be removably connected to the membrane module.

The membrane air dryer can further include a passageway for supplying a sweep gas to interstitial spaces between the hollow fibers, the passageway fluidly connecting the outlet of the membrane module to the interstitial spaces such that a portion of the air flowing through the hollow fibers can be utilized as sweep gas to remove moisture from the interstitial spaces. A sweep gas inlet orifice can be provided for controlling the flow of sweep gas through the passageway to the interstitial spaces.

An inlet end cap can also be provided including an end cap body attached to the inlet end of the membrane module, the inlet end cap and outlet end cap being secured to respective ends of the membrane module and in fluid communication with the interior passageways of the hollow fibers. A tubular shroud can surround the membrane module and extend between the inlet and outlet end caps, the tubular shroud and membrane module defining a longitudinally extending passageway for the flow of sweep gas. The membrane module can have at least one exhaust port for exhausting sweep gas from the within the membrane module into the longitudinally extending passageway, and the outlet end cap can have at least one exhaust channel through which the sweep gas can vent from the longitudinally extending passageway. The at least one exhaust channel can extend axially on an outer circumference of the outlet end cap body, the tubular shroud and outlet end cap being axially coextensive along a portion of the exhaust channel.

In accordance with another aspect, a method of assembling a membrane air dryer comprises the steps of connecting a first end cap to a first end of a tubular hollow membrane module, telescoping a tubular shroud over the membrane module, and attaching a second end cap to a second end of the tubular hollow membrane module while capturing the tubular shroud between the first and second end caps.

Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

DETAILED DESCRIPTION

InFIG. 1, an exemplary air drying system10for drying an electrical cabinet12is illustrated. The system10generally includes a compressed air supply14, an air dryer16, and electrical cabinet12. Compressed air is delivered to an inlet18of the air dryer16from the supply14. The air is dried as it passes through the air dryer16to outlet20. The dry air is then fed to the electrical cabinet12where it absorbs and removes any moisture from within the cabinet. The air dryer16includes a sweep gas exhaust port22on its bottom side near the outlet20for exhausting the sweep gas from the air dryer16. Although the air dryer16is shown and described in the context of a food processing plant air drying system, it will be appreciated that the air dryer16can be used in a wide variety of applications and can dry gasses other than air.

Turning toFIGS. 2 and 3, and initially toFIG. 2, the air dryer16is illustrated in partial cut-away cross-section. The air dryer16includes a membrane module24, inlet end cap28including inlet port18, outlet end cap30including outlet port20, and tubular shroud32. As best seen inFIG. 3, the inlet end cap28and outlet end cap30are threadedly engaged with threads on respective ends of the membrane module24. The tubular shroud32extends between the inlet and outlet end caps28and30and surrounds the membrane module24. In the illustrated embodiment, the tubular shroud32is captured between respective radially outwardly extending shoulders34and36on the inlet and outlet end caps28and30. A watertight seal can be provided between the inlet end cap28and the tubular shroud32. This can be accomplished with seal members such as o-rings, or by provided a raised bead37on the inlet end cap28that fits within the tubular shroud32immediately adjacent its end, for example as shown inFIG. 8.

With additional reference toFIGS. 4 and 5, the membrane module24generally includes a cylindrical membrane core40and a plurality of hollow fibers42supported therein. The hollow fibers42have passageways for the flow of the gas (e.g., air) to be dried. Interstitial spaces44between the plurality of hollow fibers42provide a flowpath for sweep gas to drive away moisture that permeates the hollow fibers42. As will be appreciated, the hollow fibers42can be made from a variety of materials including, but not limited to Polysulfone, Polyethersulfone, Polyimide, Polyamide, Polyvinylpyrrolidone, Polyphenylene Oxide, Polyphenylsulfone, & Polyvinylidene Fluoride, for example.

The passageways in the hollow fiber42and the interstitial spaces44between the hollow fibers42are generally fluidicly isolated. In this sense, air flowing through the passageways of the fibers42enters the upstream end and exits the downstream end, while moisture in the air permeates the hollow fibers42to the interstitial spaces44. The ends of the membrane module24are sealed such that air from the inlet18may generally only flow into the passageways in the hollow fibers42and not to the interstitial spaces44between the hollow fibers42. As will be described in more detail below, the membrane core40has one or more sweep gas exhaust ports49for exhausting sweep gas from within the core40of the membrane module24.

Returning toFIG. 3, it will be appreciated that the inlet and outlet end caps28and30are threaded onto the membrane module24, with respective o-rings46and48forming a seal therebetween. As noted, this provides a generally isolated flow path for the compressed air from the inlet port18, through the membrane module24via the passageways in the hollow fibers42, to an outlet chamber50formed between the outlet end cap30and the membrane module24, to the outlet port20. In order to provide sweep gas to the interstitial spaces between the hollow fibers42, a sweep gas orifice51is located within the outlet chamber50for routing a portion of the dried gas flowing therethrough to the sweep gas circuit.

To regulate the flow of air through the dryer16, an orifice52is provided in the outlet end cap30. In the illustrated embodiment, the orifice52is threaded into a central bore54or aperture of the outlet end cap30. Thus, the orifice52is provided as part of a set screw body that can be installed and readily removed from the outlet end cap30, for example through the outlet port20. This permits various size orifices to be installed to generate different flow rates and/or dewpoint suppression for different applications. Alternatively, several different outlet end caps could be provided with different orifice sizes, and the entire outlet end cap could be change out as desired. In some cases, it may be desirable to press fit the orifice52into the bore54. The orifice52generally controls the flow from the outlet of the membrane module24through the central bore54.

Turning toFIGS. 6 and 7, the outlet end cap30is illustrated in detail. The outlet end cap30has a generally cylindrical body60including the axially extending central bore54. The opening of the bore54visible inFIG. 6is adapted for receiving an outlet end of the membrane module24. As such, internal threads can be provided on the interior of the bore54adjacent such opening for threadedly engaging corresponding threads on the membrane module24. The opposite opening of the bore62(not visible inFIG. 6) is adapted for receiving the outlet port20. A pair of axially extending sweep gas exhaust channels66in the outer circumferential surface of the body60cooperate with the tubular shroud32to form sweep gas exhaust passageways for exhausting the sweep gas from the air dryer10.

With reference toFIG. 9, the air dryer16is illustrated in an exploded state that shows the manner in which the various components are arranged when assembled. As will be appreciated, during assembly the inlet end cap28is connected to the membrane module24, the tubular shroud32is then telescoped over the membrane module24, and the outlet end cap30is then connected to the end of the membrane module24thereby trapping the tubular shroud between the shoulders34and36of the end caps.

Referring back toFIGS. 2 and 3, in operation compressed air is fed to the inlet port18from a compressed air supply, such as a compressor or accumulator tank. The compressed air then passes through the inlet end cap28and into the passageways of the hollow fibers42. As the air passes through the hollow fibers42, moisture in the air permeates the fibers42thereby drying the air. The dried air then exits the hollow fibers42into the chamber50formed by the outlet end cap30and the membrane module24. A majority of the dried air then flows through the orifice52to the outlet port20for supply to an electrical cabinet or other device. A portion of the dried air is routed back to the interstitial spaces44between the hollow tubes via sweep orifice51. This sweep gas serves to absorb the moisture that has permeated the hollow tubes42and to carry such moisture out of the membrane module24via cartridge exhaust ports49(SeeFIG. 5) in the membrane core40. The sweep gas then flows in the annular space between the tubular shroud32and the membrane module24, generally defining a longitudinally extending passageway, to the exhaust channels66of the outlet end cap30. The sweep gas then exits the air dryer16through the passageways formed between the tubular shroud32and the channels66in the outlet end cap30.

As will now be appreciated, the internal orifice52of the air dryer16provides a consistent and more stable outlet flow and dew point. By using the internal orifice52to preset the outlet flow and dew point, the air dryer16is more user friendly and eliminates the uncertainty associated with having to measure and set the outlet flow and dew point. This feature is especially advantageous in applications, such as a food plant setting, that may lack the instruments to measure outlet flow and dew point.

Further, the tubular shroud32of the air dryer16provides a more uniform surface that is free of catch points where food and/or other debris may catch and allow bacteria to grow. The tubular shroud also protects the membrane module24from harsh cleaning chemicals and provides a longitudinal passageway for the sweep gas enabling a bottom vent arrangement that is less prone to contamination or clogging from cleaning solutions and/or food particles.