GB2531490A

GB2531490A - Distillation unit

Info

Publication number: GB2531490A
Application number: GB1315655.9A
Authority: GB
Inventors: Abela Stephen; Ghirlando Robert; Refalo Paul
Original assignee: Solar Desalination Technik; Water Services Corp; Universita ta Malta UM
Current assignee: Solar Desalination Technik; Water Services Corp; Universita ta Malta UM
Priority date: 2013-09-03
Filing date: 2013-09-03
Publication date: 2016-04-27
Also published as: GB201315655D0

Abstract

A distillation unit 2 comprises an evaporation chamber 12, a condenser 22, and a cooler 25 adapted to externally cool the condenser. An air heater 6 in the form of a solar chimney may be provided between an inlet 14 of the evaporation chamber and condenser. The heater may serve to heat air passing through it in order to increase convection currents within the distillation unit. In use the heated air passes to the evaporation chamber where water is evaporated from sea water contained preferably in a basin 44 before entering the condenser for example an externally sea water cooled copper pipe. Condensate formed on the inside of the copper pipe is collected preferably in a tank 60 and cooled air is returned to the heater. Preferably the distillation unit is used to desalinate water in order to render the water drinkable. A further invention characterised by a solar chimney is also disclosed.

Description

DISTILLATION UNIT

This invention relates to a distillation unit.

Distillation is a useful process for purifying many liquids. Distillation can be particularly useful in order to purify water and may be used to remove impurities and/or salt from water in order to render the water drinkable.

io The use of solar energy in such distillation units is known and has particular application either in remote locations where power may not be readily available or following an emergency or disaster where power has been cut off from an area.

Water is one of the primary vital resources. The issue of availability of water to the population as a whole is therefore of great importance. More than 97% of the water found on earth is trapped as saline water in oceans and seas.

The continuous growth of the world population, worldwide economic development and contamination of current natural water resources are threatening the availability of fresh water. In addition, climate change is causing more countries to face a shortage of water and to experience droughts. There is therefore a growing need to be able to desalinate water efficiently and reliably.

According to a first aspect of the present invention there is provided a distillation unit comprising an evaporation chamber, a condenser, and a cooler adapted to externally cool the condenser.

The distillation unit according to a first aspect of the present invention may be used to distil any desirable liquid, but is particularly useful for distilling water. Still further, the distillation unit may be used to remove a range of impurities from water and in particular may be used to desalinate water.

In known water distillation units, it is known to cool the condenser internally. This results in condensation taking place externally to the condenser.

By means of the present invention condensation takes place internally using a coolant in contact with the condenser. This reduces the thermal thermal mass of the unit since the cooler does not form part of the condenser..

The evaporation chamber may comprise an inlet and an outlet, the inlet and the outlet both being operatively connected to the condenser..

The evaporation chamber may be directly or indirectly connected to the condenser.

In some embodiments of the invention the distillation unit may comprise a heater. In such embodiments of the invention the heater may be positioned between the inlet of the evaporation chamber and the condenser.

The heater may comprise any convenient heater and in particular may comprise an air heater. In other words, the heater may be adapted to heat up air within the distillation unit. However, the air is also likely to contain at least a small amount of vapour formed from the fluid being distilled in the unit. In embodiments of the invention where water is being distilled then the air is likely to contain at least some water vapour.

The heater forming part of the distillation unit according to the invention serves to heat the air passing through it in order to increase convection currents within the distillation unit.

The air may be heated by any convenient means, and in some embodiments of the invention, the heater comprises a solar heater.

In such embodiments, the condenser may have an inlet and an outlet, and the solar heater may comprise a solar chimney having an inlet operatively connected to the outlet of the condenser, and an outlet operatively connected to the inlet of the evaporation chamber.

In such embodiments, the solar chimney will provide the necessary ventilation inside the evaporation chamber and will also cause the latter to heat up when hot air from the solar chimney passes into the evaporation chamber.

The evaporation chamber may comprise a basin containing the liquid to be distilled.

The basin may be dimensioned in order to hold an appropriate amount of water. The basin may further comprise an outlet through which liquid may exit the basin. The outlet is positioned to ensure that the basin is unlikely to be overfilled.

In such embodiments the evaporation chamber may have curved corners in order to facilitate flow and to decrease turbulence within the unit.

It is to be understood that the evaporation chamber could have any convenient shape and may for example be circular, oval or some other such shape in cross section.

The evaporation chamber may further comprise a first surface which may be positioned to be at a particular inclination relative to the horizontal, in use, and a plurality of sides positioned substantially vertically to define the evaporation chamber. The first surface may, be in use, an upper surface.

The sides of the evaporation chamber may be made from glass, particularly low iron glass.

In use, the liquid in the evaporation chamber will receive solar energy passing through the sides and top of the evaporation chamber, which solar energy will serve to heat up the liquid.

As the solar intensity increases, the temperature of the liquid in the basin increases and the rate of evaporation of the liquid also increases.

At the same time, as the temperature within the solar chimney increases, the density of air inside the chimney decreases, and warm air flows into the evaporation chamber situated above.

Further, as the air temperature inside the evaporation chamber increases, its capacity to carry water vapour increases. As air moves from the solar chimney to the evaporation chamber, the air is replaced with air from the condenser. Since the condenser is also connected to the evaporation chamber a convection cycle is created.

According to a second aspect of the present invention there is provided a distillation unit comprising an evaporation chamber having an inlet and an outlet, a heater, and a condenser having an inlet and an outlet, the heater comprising a solar chimney having an inlet operatively connected to the outlet of the condenser, and an outlet operatively connected to the inlet of the evaporation chamber.

A distillation unit according to the second aspect of the present invention may further comprise a cooler adapted to externally cool the condenser.

A solar distillation unit according to either the first aspect of the invention or the second aspect of the invention may comprise a cooler comprising a reservoir of coolant encompassing the condenser. In embodiments of the invention comprising a to desalination unit, the liquid may comprise sea water. Other coolants may also be used, and generally the coolant will comprise fluid, although gels may also be used.

The reservoir of coolant serves to cool the condenser externally. Because cooling takes place externally, condensation will occur internally, and smaller volumes of coolant will be necessary in order to effect the cooling. This increases the efficiency of the distillation unit.

During use of the distillation unit the temperature of the coolant in the reservoir will increase.

In embodiments in the invention comprising a desalination unit, the coolant may comprise liquid, the temperature of which liquid will increase throughout the day.

In order to use the latent heat of condensation, the heated liquid may be pumped into the base of the evaporation chamber in the morning of the following day. This further increases the efficiency of the distillation unit.

The distillation unit may comprise a pump. However it is not necessary to have a pump in order to transfer the heated liquid from the condenser into the evaporation chamber.

Instead, the liquid may be transferred manually, for example or may be gravity fed.

According to a further aspect of the present invention there is provided a distillation system comprising a plurality of distillation units according to either the first or the second aspect of the invention. In such a distillation system it may be possible to form a matrix of distillation units in which liquid from a first unit may be transferred to a second distillation unit and so on thus allowing the liquid to cascade through the system. In some embodiments the distillation system may be positioned on a slope and therefore liquid may be gravity fed from one distillation unit to the next.

In other embodiments of the invention, a flow of coolant is used to cool the condenser.

In embodiments of the invention comprising a water desalination unit, a flow of fresh sea water may be used. This flow may be either continuous or intermittent.

In such embodiments, it is not possible to recover the latent heat, by for example transferring the heated coolant into the basin of the evaporation chamber as described hereinabove. However, when a flow of coolant is used, the condensation capacity of the condenser is increased.

In such embodiments the heated coolant may be used in other ways for example to heat a swimming pool, for domestic water, or may be stored in a thermal storing gel, for 15 example.

In embodiments of the invention according to either the first or the second aspect of the invention, the condenser may comprise a hollow pipe extending from the evaporation chamber to the heater. The condenser may extend directly or indirectly from the evaporation chamber and may also be connected either directly or indirectly to the heater. In some embodiments of the invention the condenser is connected to both the evaporation chamber and the heater by connecting portions which may for example be in the form of connecting pipes.

In some embodiments of the invention the condenser comprises a plurality of hollow pipes.

The efficiency of the distillation unit is increased by using a plurality of pipes to increase the heat transfer surface area.

The pipes may be made from any convenient material. Since an exchange of heat occurs across the walls of the pipe, in many embodiments of the invention the pipes will be made from a material that conducts heat well, such as copper.

The pipes may include devices to enhance the rate of heat transfer such as extended surfaces, fins, and honeycomb structures welded to the pipe wall.

In use, the air temperature and pressure in the evaporation chamber will become higher than in the condenser. This means that liquid vapour will flow from the evaporation chamber into the condenser. As the liquid vapour flows through the condenser, its temperature will be reduced by means of the cooler, and it will condense against inner surfaces of the condenser, reducing the specific humidity of the air. The condensate may then be collected.

The distillation unit may comprise a distillate collector to collect the condensate.

In embodiments of the invention comprising a plurality of pipes, a distillate collector may be connected to each pipe. The distillate collector may direct the condensed liquid into a tank.

In some embodiments of the invention, the inlet of the condenser is, in use, higher than the outlet of the condenser. This means that in use, condensate formed in the condenser may be collected by gravity. This also helps to create the required convection currents as the cooler air sinks into a lower section of the condenser towards the heater to be further dried and heated.

In embodiments of the invention according to the first or second aspects of the invention, the distillation unit may further comprise a plenum chamber positioned between the evaporation chamber and the condenser. In such embodiments, during use of the distillation unit, the water vapour will flow from the evaporation chamber into the plenum chamber and then into the condenser either directly or via one or more connecting portions.

According to a third aspect of the present invention there is provided a method of distilling a liquid comprising the steps of: a. pouring a liquid to be distilled into an evaporation chamber; b. heating air using solar energy to produce vapour; c. heating the liquid using the heated air to produce vapour; d. passing the vapour through a condenser; e. externally cooling the condenser to produce condensate within the condenser; f. collecting the condensate.

The method according to the third aspect of the present invention may be carried out using a distillation unit according to the first aspect of the present invention.

According to a fourth aspect of the present invention there is provided a method of distilling a liquid comprising the steps of: a. pouring liquid to be distilled into an evaporation chamber; b. heating air using a solar chimney operatively connected to the evaporation chamber at a first end, and to a condenser at an opposite end; c. heating the liquid using solar energy to produce vapour; d. passing the vapour through the condenser, which condenser is operatively connected to the evaporation chamber at a second end thereof; and e. collecting the condensate.

The method according to the fourth aspect of the present invention may be carried out using the distillation unit according to the second aspect of the present invention.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic sectional representation of a distillation unit according to an embodiment of the invention; Figure 2 is a schematic perspective representation of the distillation unit in Figure 1; Figure 3 is a schematic representation of the distillation unit in Figure 1 showing a rear portion of the unit; Figure 4 is a schematic representation of the distillation unit of Figure 1 showing a top portion of the unit; and Figure 5 is a schematic representation of the distillation unit of Figure 1 showing flow of fluids around the distillation unit.

Referring to the figures, a distillation unit according to an embodiment of the invention is designated generally by the reference numeral 2. In this embodiment the distillation unit comprises a solar desalination unit 4 powered by solar energy. The solar desalination unit 4 comprises a glazed solar air heater 6 having an inlet 8 and an outlet 10. The outlet is operatively connected to an evaporation chamber 12 at an inlet 14 to the chamber 12. The evaporation chamber comprises an outlet 16 that connects to a plenum chamber 18. The plenum chamber 18 may be made from any convenient material such as fibreglass and is in turn connected to pipes 20 which in this embodiment are made of glass reinforced plastic (fibreglass). The pipes 20 are connected to a condenser 22 which in this embodiment comprises four hollow copper pipes 24. The condenser is thus operatively connected to the evaporation chamber 12.

The copper pipes 24 pass through a cooler 25 comprising a reservoir 26 containing sea io water which acts as a coolant to the copper pipe condensers 24.

Each of the copper pipes 24 is then in turn connected to second pipes 28, which in this embodiment are made of glass reinforced plastic (fibreglass), which in turn are connected to an inlet 30 of the solar heater 6. The condenser is therefore also operatively connected to the solar heater 6.

The distillation unit 2 further comprises distillate collectors 34, 36 for collecting distillate as will be described in more detail hereinbelow.

The solar heater 6, in this embodiment comprises a solar chimney 40 having a glazed upper surface 42, and a black absorber 50.

In this embodiment, the solar chimney 40 is positioned at an angle of substantially 60 ° to the horizontal. However, this angle can vary from unit to unit depending on where the unit is to be positioned. In addition, in some embodiments of the invention, the angle of the solar chimney 40 may be adjusted to suit the prevailing conditions which may vary depending on the time of year, the country in which the unit is installed etc. The evaporation chamber has sides 51 and an upper surface 52 which are formed from a transparent material such as low iron glass in order to receive solar energy. Low iron glass may be used due to its high solar transmissivity. The evaporation chamber further comprises a basin 44 in which the liquid to be distilled, such as seawater, is contained.

In use, the reservoir 26 and the basin 44 are filled with sea water in the morning, preferably prior to sunrise. The reservoir is completely filled, whereas the basin 44 is filled up to a height of 15 to 20mm in this embodiment. This level was chosen so as to minimise the thermal capacity of the water stored in the basin and to reduce the likelihood that salts will crystallise once the water starts to evaporate. The higher the level of water, the longer it takes to heat the water, but if a small amount of water is poured, the salts will crystallise when water evaporates.

The base of the basin further comprises a protruding pipe 48 shown particularly in Figure 4. This is used as an overflow to ensure that an appropriate amount of sea water is contained within the basin 44.

As the solar intensity increases, the temperature of the water in the basin 44 increases and starts to evaporate. Simultaneously, as the temperature of the absorber 50 in the solar chimney increases, the density of air inside the chimney decreases. This means that as the temperature of the air increases, it flows into the evaporation chamber 12. The glazed surface 42 of the solar chimney is covered with low iron glass, and as mentioned above is installed at an angle of inclination of approximately 60° to the horizontal. The insolation at this angle varies throughout the year in many countries. In some embodiments therefore the angle of the solar chimney can be varied.

As the air temperature inside the solar chimney increases, the capacity of that air to carry water vapour increases. As air moves from the solar chimney to the evaporation chamber, it is replaced by air from the pipes 28 connected to the condenser pipes 24.

This creates a convection cycle flowing in a clockwise direction as shown in Figure 5.

At this point, the air temperature and pressure in the evaporation chamber are higher than that inside the condenser pipes. This results in water vapour from a top section of the evaporation chamber flows through an outlet of the chamber and into the plenum chamber 18.

As described hereinabove, in this embodiment the plenum chamber 18 is connected to four fibreglass pipes 20, which in turn are connected to four copper pipes 24. In other embodiments there could be a different number of pipes, including a single pipe. In this embodiment, each copper pipe has a diameter of about 108 mm and a wall thickness of about 1.5 mm. The copper pipes are fully immersed in the sea water of the reservoir 26.

In this embodiment the reservoir 26 is insulated with expanded polystyrene and painted white to reduce the heat gain from solar radiation.

Because the copper pipes are immersed in relatively cool sea water, as the water vapour flows through the pipes, its temperature is reduced and water condenses against the internal surface of the pipes. This reduces the specific humidity of the air in the pipes. The condensate formed in the pipes trickles down the inclined pipes which are positioned so that a top end is higher than a bottom end. This means that the condensate may trickle down under the force of gravity.

A distillate collector connected to each of the pipes 28 directs the distillate into a product tank 60 shown in Figure 1. The air then flows back into the solar chimney to be io reheated.

The distillate produced against the inclined upper surface 52 and vertical sides 50 of the evaporation chamber is collected from a separate distillate collector 34 as shown in Figure 1.

When water vapour flowing through the copper pipes 26 condenses, the latent heat of condensation is conducted through the copper pipe walls and dissipates to the sea water mass stored in the reservoir. The volume of the sea water in the reservoir in this embodiment is about 120 litres and is capable of absorbing a latent heat of condensation of around 4 kilograms of condensate with a temperature rise of around 20°C. As the temperature of the water in the reservoir increases with time, the condensation drive decreases. Similarly as the difference between the pressures of the air inside the evaporation chamber and of the air in the copper pipes decreases, the air flow rate decreases. This slow downs the condensation process taking place inside the condenser and so more water vapour condenses against the inner surface of the main covering glass of the evaporation chamber.

As more of the water vapour generated in the evaporation chamber condenses in the condensers and not against inner surfaces of the evaporation chamber, the temperature of the inner surface of the glass in the evaporation chamber is maintained low and its solar transmissivity is not impaired by the condensate formed. Moreover, as the temperature of the covering glass forming the upper surface 52 is low, the heat lost by convention from it is decreased.

The temperature of the sea water in the reservoir will increase throughout the day. In order to use the latent heat of condensation, the heated sea water can be pumped into the basin of the evaporation chamber in the morning of the following day.

In an alternative embodiment of the invention, a continuous flow of fresh sea water could be used in order to keep the temperature of the copper pipe low. This would mean that it would not be possible to recover any latent heat but on the other hand the condensation capacity of the condensers would be increased.

Turning now to Figure 5, operation of the distillation unit 12 is illustrated.

Typically, the following steps will be carried out in order to desalinate water in to accordance with embodiments of the invention.

Initially, the basin 44 is filled with 15 to 20 mm of sea water as represented by the arrow 100. The water can be either manually poured into the basin or can be pumped into the basin.

In some embodiments of the invention, sea water contained in the reservoir 26 which has been heated from the previous day's use may be pumped or otherwise transferred into the reservoir. In such embodiments it may not be necessary to add any further water into the basin. This is indicated by the arrow 200.

The basin 44 comprises an overflow pipe 48 which ensures that any excess water pours away down the overflow pipe to ensure that the water is filled to a depth of 15 to 20 mm. The overflow is shown by the arrow 300.

During use of the distillation unit 2 water will evaporate from the sea water contained in the basin 44 as depicted by arrows 400.

Air will then flow from the condenser pipes 24 to the solar heater which comprises a solar chimney 40 as shown by arrows 500.

Warm air from the solar chimney 40 will then flow into the evaporation chamber 12 as illustrated by arrows 600.

Next, air will flow from the evaporation chamber 12 to plenum chamber 18 as shown by arrows 700.

Condensate will form against inner walls of the copper condensers 28 as depicted by arrows 800. This condensate will then trickle down through pipes 28 and will be collected in a tank 60 as illustrated by arrows 900.

Condensate will also form against the inner surfaces of the evaporation chamber as represented by arrows 1000. This condensate will trickle along the inclined upper surface of the evaporation chamber and will be collected from a trough 1110 in the upper chamber as represented by arrows 1100.

1 o Finally, any brine that is not to be recycled into the basin 44 the following day may be discharged from the sea water reservoir.