A drying apparatus for drying a hollow object and a method of using the apparatus

The present invention relates to a drying apparatus for drying a hollow object. The apparatus is of the kind comprising a first means for transporting an intake airflow through the apparatus for drying of the hollow object, a refrigerating unit for initial removal of fluid from the intake airflow, thereby defining a first process airflow, and a dehumidifier for further removal of fluid from the first process airflow to produce a second process airflow having a reduced fluid content .

The present invention also relates to a method for drying a hollow object using the drying apparatus.

Known drying systems or apparatuses are conventionally adapted to a specific application, i.e. drying of a specific hollow object, which means that they are not capable of providing an effective drying within a wide range of applications.

Changing the application of a drying apparatus is equal to different demands on the performance of the drying apparatus. If a drying apparatus is to be used for a variety of different situations while still operating with high efficiency at all time it is necessary that the components of the drying apparatus are capable of operating with different performances depending on the specific situation.

European patent application no. EP 0 835 694 Al discloses a drying system used for drying a coated product in a spray booth. A blower motor and an associated frequency drive system controls the amount of dried air and a dehumidification unit, which is either heat-based or refrigeration-based, provides for the drying of the air. In this system the efficiency of the drying process is difficult to control under changing working

conditions and it is therefore not suited for purposes for prolonged drying tasks requiring high efficiency regarding the removal of fluid.

Hence there is a need within the art for improved apparatuses for producing dry air from an inexpensive air source such as atmospheric air.

As used in the present application the term "performance", e.g. of a mechanism, means the size of the output from the mechanism.

As used in the present application the term "regulate", e.g. of the performance, includes controlling and adjusting to a required or desired level or output.

In a first aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph capable of drying a wide variety of hollow objects with different dimensions, while still keeping the same effective drying.

In a second aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph capable of utilizing atmospheric air for effective drying of different hollow objects.

In a third aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph where the fluid content of the air processed by the drying apparatus is reduced.

In a fourth aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph where the refrigerating unit is better

prevented from blocking with ice when the performance of the drying apparatus is reduced than with known apparatuses.

In a fifth aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph where the efficiency of the dehumidifier is better prevented from decreasing when the performance of the drying apparatus is increased than with known apparatuses.

In a sixth aspect according to the present invention is provided a drying apparatus of the kind mentioned in the opening paragraph that is easy to use and transport.

The novel and unique way whereby this is achieved according to the present invention is the fact that the drying apparatus further comprises a first frequency transformer for regulating the amount of intake airflow, and a second frequency transformer for regulating the performance of the refrigerating unit .

Changing working conditions normally means that the amount of air transported through the drying apparatus must be changed. This change is expediently obtained by means of the first frequency transformer, which controls and adjusts the operation of the first means for transporting air to the current need and requirements .

The second frequency transformer serves for regulating the performance of the refrigerating unit to control the temperature of the first airflow of processed air leaving the refrigerating unit.

The advantage of controlling both the first means for transporting an intake airflow through the apparatus and the refrigerating unit is that when the working conditions of the drying apparatus changes over time during a specific drying

task or changes when the drying apparatus is to be used for different drying tasks, the drying apparatus still provides an effective drying at all time, because the performance of the refrigerating unit is continuously adapted to the performance of the first means for transporting an intake airflow through the apparatus .

Preferably the refrigerating unit can be a vapour compression refrigeration system of the kind comprising an evaporator, a compressor, an expansion valve, a refrigerating agent, and a condenser .

Advantageously the regulation by the first frequency transformer can be based on data selected from the group comprising the pressure of the output airflow from the drying apparatus, the temperature of the output airflow from the drying apparatus, the dew point of the second process airflow, and the amount of intake airflow. In another embodiment an operator can control the first frequency transformer manually.

In order to sustain an effective drying the second frequency transformer can regulate the pressure of the refrigerating agent in the evaporator by controlling the performance of the compressor. For example can the second frequency transformer regulate the rotational speed of the compressor, thereby regulating and controlling the evaporation pressure of the refrigerating agent in the evaporator to provide regulation of the surface temperature of the evaporator, which surface is the location where the actual cooling of the airflow takes place. If the load on the refrigerating unit decreases this regulation prevents the evaporator from blocking with ice by reducing the performance of the compressor and thereby substantially preventing the surface temperature of the evaporator from decreasing.

Blocking with ice is highly undesirable because it would inhibit an optimum airflow through the refrigerating unit since ice presents a physical obstacle to the airflow. Blocking with ice is also undesirable because removing the ice would require shutting the drying apparatus down or reducing the performance of the refrigerating unit with reduced efficiency of the drying apparatus as a result. Blocking with ice is even further undesirable because it could cause mechanical damage to the refrigerating unit.

In another situation where the load on the refrigerating unit increases, the regulation of the compressor prevents an increase in the temperature of the first process airflow by increasing the performance of the compressor and thereby preventing the surface temperature of the evaporator from increasing. An increase in the temperature of the first process airflow is highly undesirable because it would result in a decrease in the efficiency of the subsequent dehumidifier .

Advantageously the regulation by the second frequency transformer can be based on data selected from the group comprising the pressure of the refrigerating agent measured in the evaporator, the temperature of the first process airflow, and the surface temperature of the evaporator, hence the data is used as input and/or feed-back data for the drying process. This regulation could also be based on other kinds of data that is representative of the humidity and/or the temperature of the first process airflow. Preferably a pressure transmitter can be used for measuring said pressure.

Hence, these data is used as information relevant to the necessary performance of the refrigerating unit in order to provide a first process airflow that is effectively dried and with a constant temperature, which enables an efficient operation of the dehumidifier .

The pressure of the refrigerating agent measured in the evaporator can preferably be between -10 °C and 2 °C, and more preferably between -8 °C and 0 °C, and most preferably between -6 °C and -2 °C, in order to provide an optimum drying of the first process airflow.

The surface temperature of the evaporator can preferably be between -2 °C and 12 °C, and more preferably between -1 °C and 6 °C, and most preferably between 0 °C and 3 °C .

Preferably the refrigerating agent is R22 (chloro- difluoromethane) , but other agents can also be used.

The temperature of the first process airflow from the refrigerating unit can preferably be between 0 °C and 12 °C, more preferably between 1 °C and 8 °C, and most preferably between 2 °C and 4 °C .

Advantageously the drying apparatus can further comprise a second means for transporting air that removes heat from the refrigerating agent in the condenser, in order to increase the capacity of the refrigerating unit, which is especially desirable in situations where the load on the drying apparatus is especially high.

The performance of the second means for transporting air can advantageously be regulated by means of a third frequency transformer, in order to obtain a more efficient performance of the refrigerating unit.

The regulation by the third frequency transformer can advantageously be based on data representing the pressure of the refrigerating agent measured in the condenser. This regulation can also be based on other kinds of data

representing the performance of the compressor, such as the rotational speed of the compressor.

To facilitate the transport of air through the drying apparatus a third means for transporting air can be located between the refrigerating unit and the dehumidifier . Preferably this third means can provide a pressure sufficient to transport up to 6000 m ³ of air per hour through the refrigerating unit and the subsequent dehumidifier on its own.

In a preferred embodiment the drying apparatus can comprise pressure measuring means for measuring the pressure of the airflow before and after the third means for transporting air, so that, based on these measurement data, the first air transport means can be shut down in case the third air transport means malfunctions or its performance otherwise decreases .

Preferably the dehumidifier can comprise a dehumidification zone where fluid is removed from the first process airflow.

An effective drying of the hollow object is obtained when the dew point of the second process airflow is -30 °C or lower, as this means that the humidity of the second process airflow is very low.

If the dew point of the airflow entering the refrigerating unit decreases, then the load on the drying apparatus also decreases, resulting in a more economical performance of the drying apparatus. In extreme situations the drying apparatus can rely on the dehumidifier as the only means for removal of fluid while the refrigerating unit is turned off.

As the drying apparatus often is used in prolonged drying tasks the dehumidifier can advantageously be a sorption dehumidifier comprising a sorption rotor, where the rotation of the sorption

rotor can cause each part of the rotor to cycle past the dehumidification zone, a regeneration zone and a cooling zone in a continuously cycle. After sorbing of fluid in the dehumidification zone follows the regeneration zone where a fourth means for transporting air can provide a heated airflow to the rotor, and thereby remove fluid from the rotor. Then follows a cooling zone where the temperature of the rotor is lowered before entering the dehumidification zone and thereby starting the cycle all over.

The combination of the regeneration and the cooling of the sorption rotor provide a very efficient removal of fluid from the first process airflow.

Advantageously the sorption rotor can comprise a humidity sorbing material that enables a highly efficient sorbing and retention of moisture, so that the second process airflow has a very low dew point. In one preferred embodiment this material can be silica gel, but other highly humidity sorbing materials could also be used.

In one preferred embodiment of the present invention the dehumidifier can be a dessicant dehumidifier MX5200 or MX6200 obtainable from Munters, Ryttermarken 4, 3520 Farum, Denmark with a rotational speed of the sorption rotor of about 6 to 10 rotations per hour during use.

Preferably the performance of the first means for transporting air can be between 800 m ³ per hour and 10000 m ³ per hour, more preferably between 1500 m ³ per hour and 8000 m ³ per hour, and most preferably between 2000 m ³ per hour and 6000 m ³ per hour, and the first means for transporting air can preferably provide a maximum differential pressure of 0,01 bar to 7 bar, more preferably 0,02 bar to 3 bar, and most preferably 0,03 bar to 1,3 bar between an outlet and an inlet of the first means for transporting air.

With this kind of capacity the drying apparatus is capable of drying large hollow objects, such as e.g. oil pipelines with lengths of e.g. 200 kilometres or even more and diameters of several meters, within an acceptable time. Within the scope of the present invention the apparatus can however quite as well be used for not hollow objects.

An extreme example of drying an object for which the apparatus according to the present invention is especially suited, is the drying of an oil pipeline with a length of 100 km, a diameter of 1,4 meters, containing 22 tons of water, and primarily located in the ground which has a temperature of 20 °C . The present invention can solve this drying task within about 200 hours, provided that a predryer initially has removed the major part of easy accessible water.

Preferably one or more of the first, second, third, and fourth means for transporting air can be at least one fan.

In a preferred embodiment of the present invention the first means for transporting air can be a positive displacement blower that is capable of providing a constant volumetric air displacement at a given rotational speed and independently of changes in the differential pressure between the outlet and the inlet of the first means for transporting air.

Advantageously the drying apparatus can further comprise a generator providing any or all of the compressor, the dehumidifier, and the first, second, third, and fourth means for transporting air with electrical energy. The generator is preferably a diesel generator with a fuel tank.

Preferably the drying apparatus can be integrated in a single compartment, more preferably a mobile single compartment, and most preferably a standard freight container. In this way the drying apparatus can easily be transported from location to

location. In case the apparatus is integrated in a standard freight container it is preferred that the freight container is of the kind that can be approved for transport by container ships, so that quick and economical transport of the drying apparatus over long distances is possible.

In a situation where the drying apparatus is integrated in a single compartment, it is preferred that the drying apparatus has unlimited access to air from the surrounding during use. This can e.g. be obtained when the single compartment is provided with one or more doors in proximity to the evaporator and when these doors are kept open during use.

A method for drying a hollow or otherwise configured objects, such as flat, wavy or the like objects, may advantageously make use of the above discussed drying apparatus.

Such a method comprises the steps of establishing a fluid communication between the drying apparatus and the hollow object for providing dried air to the hollow object, continuous regulation of the performance of the first means for transporting air by means of the first frequency transformer, and continuous regulation of the performance of the refrigerating unit by means of the second frequency transformer, and optionally the step of a continuous regulation of the operating performance of the second means for transporting air by means of the third frequency transformer.

In case of tasks including removal of large amounts of fluid from the hollow object the method may also comprise a pretreament step of predrying the hollow object prior to or in conjunction with using the apparatus described above.

The invention will be explained in greater detail below where further advantageous properties and example embodiments are described with reference to the drawings, in which

Fig. 1 illustrates a first embodiment of the apparatus according to the present invention,

Fig. 2 is another schematic view of the first embodiment, but with a more detailed indication of the various airflows,

Fig 3 is a schematic view similar to fig. 2 but illustrating a second embodiment, and

Fig. 4 schematically shows the structure of the dehumidifier .

The drying apparatus is in the figures designated in general by the reference numeral 1.

Fig. 1 and 2 show a preferred first embodiment of the drying apparatus 1 and will be described in conjunction in the following.

The drying apparatus 1 is indicated as integrated in a single compartment 2. The arrows A, B, C, and D indicate the flow direction of the various airflows through the drying apparatus 1. A first motor Ml, as seen only in fig. 1, drives a fan 3, representing the first means 3 for transporting air, and draws or otherwise transports the intake airflow A through the apparatus 1. First, the fan draws the intake air A through the refrigerating unit, generally designated by the reference numeral 4. The cooled first process airflow B exits the refrigeration unit 4 and is by means of the fan 5, representing the third air transport means 5, transported to the dehumidifier 6. A dehumidified second process airflow C exits the dehumidifier 6, passes the fan 3 and exits the apparatus 1 as dried air, as indicated by the arrow D.

In the preferred embodiment shown in fig. 1 the first means 3 is positioned after the dehumidifier 6, but in another

embodiment (not shown) it could e.g. be positioned before the refrigerating unit 4.

The refrigerating unit 4 has an evaporator 7 for providing an initial removal of fluid from the intake airflow A, thereby producing a first process airflow B. A refrigerating agent 8 cycles from the evaporator 7 to the compressor unit 9, which includes a motor M2 (as seen only in fig. 1) for driving the compressor, to the condenser 10, to the expansion valve 11, and back to the evaporator 7 to complete a refrigerating cycle.

The drying apparatus 1 has a first frequency transformer 12 for regulating the performance of the fan 3, and a second frequency transformer 13 for regulating the performance of the compressor 9.

The drying apparatus 1 further has a second means 14 for transporting air, which second means 14 provides removal of heat from the refrigerating agent 8 in the condenser 10 by removing air from the condenser 10.

In the preferred embodiments shown in fig. 1 and 2 the drying apparatus 1 also has a generator 15 that provides electrical energy to the compressor 9, the dehumidifier 6, the fan 3, the second means 14, and the fan 5 as indicated by the arrowed connection lines 16a, 16b, and 16c.

Fig. 3 shows a second preferred embodiment of the drying apparatus 1 corresponding to the first embodiment shown in figs. 1 and 2, except that it also has a third frequency transformer 17 for regulating the performance of the second means 14.

Fig. 4 shows the structure of a preferred embodiment of a dehumidifier 6 for use in the apparatus 1 according to the present invention, and especially the sorption rotor 18 and the

fourth means 19 for transporting air. The sorption rotor 18 has a dehumidification zone 20, a regeneration zone 21, and a cooling zone 22. The first process airflow B enters the dehumidification zone 20 and the second process airflow C exits the dehumidification zone 20. The rotation of the sorption rotor 18 is indicated by the arrow G, which shows that each part of the sorption rotor 18 is rotated in a cycle from the dehumidification zone 20 into the regeneration zone 21 followed by the cooling zone 22, and back to the dehumidification zone 20 to complete the cycle.

The fourth means 19 provides a heated airflow E that enters the regeneration zone 21 and exits the regeneration zone 21 as a humid containing airflow F.

The apparatus according to the present invention is primarily used for drying pipelines, oil pipes, fuel tanks, and reservoirs, but is not limited to these applications as it could also be used for drying other kinds of objects, including flat object.

The apparatus according to the present invention utilises in particular the fact that humidity in a hollow object can be removed by providing an airflow through the hollow object, where the humidity of the air in the provided airflow is lower than the humidity of the air original present in the hollow object. The initial removal of fluid in the refrigerating unit is based on the principle that fluid, such as humidity, condenses when the temperature is decreased.

In addition to the amount of intake air passing through the drying apparatus, an effective drying is also dependent on a sufficient low and stabile temperature of the first process airflow, which subsequent enters the dehumidifier . This is advantageously obtained by means of the second frequency transformer, which regulates the performance of the

refrigerating unit depending on data representing e.g. the humidity of the first process airflow, so that the performance of the refrigerating unit at all time is adjusted to the present situation.