Usually, the known type absorption units are placed along the air feeding duct towards a metal-air battery in order to reduce the carbon dioxide rate of the air, or, given their characteristics, said absorption units can be used to treat the air in closed environments.

The European Patent Application no. EP 0 677 883 discloses an absorption unit comprising a container placed through the duct, one or more drawer-like permeable elements arranged in series, in a removable way, inside the container, each of said drawer-like elements contains a material which absorbs the carbon dioxide.

Each drawer-like element can be periodically removed to regenerate the material therein contained, and said element is preferably formed by hydroxide or hydrate beads of a metal of the Ia group, or by beads

of a porous alkaliproof material impregnated with an aqueous solution of a hydroxide of a metal of the Ia group.

The absorption unit described in the above mentioned patent application has some disadvantages due to the material used to absorb the carbon dioxide, since said material is rather expensive, and to the regeneration methods required by said material. In fact, these methods, besides being rather complex and expensive as well, require not only the lifting of the drawer-like elements, but also the lifting of said material from the drawer- like element.

The purpose of the present invention is to realise a carbon dioxide absorption unit, which can be easily regenerated, has a high absorption power with respect to the carbon dioxide, and which does not require the lifting of the active material from the absorption bed during the regeneration phase.

According to the present invention, a carbon dioxide absorption unit is realised which comprises a container device having an entry and an exit, both of which are connected to a feeding duct of a forced air flow, and absorption means placed, in a removable way, inside the container device, said absorption

means are made of a material which can absorb the carbon dioxide present in said air flow; the unit is characterised in that said absorption means comprise a cartridge of absorption material made of a ion exchange base resin which can be regenerated and which has a carbon dioxide absorption power from the gaseous phase.

Further, the present invention refers to a method to regenerate a carbon dioxide absorption unit.

According to the present invention, a method to regenerate a carbon dioxide absorption unit is disclosed, said method is characterised by comprising the hydration phase of an absorption material made of a renewable ion exchange resin contained inside a cartridge and previously saturated through the absorption of carbon dioxide; a regeneration phase of said material by removing the carbon dioxide and by restoring the initial basicity; and a phase of injection of inert gas or of carbon dioxide free air through said cartridge in order to remove liquid residues which might be present in said material.

The invention will now be described with reference to the attached drawing which shows, through section views and by removing certain parts

for clarity sake, a preferred embodiment disclosed as a non limiting example of an embodiment of an absorption unit of the removal of the carbon dioxide.

With reference to the attached figure, numeral 1 indicates a whole carbon dioxide absorption unit.

The unit 1 is placed along a duct 2 which feeds air to a user device 3 formed by a battery or by an environment for the use of the treated air, and said unit is suitable to eliminate the carbon dioxide from the air fed to said user device 3.

The unit 1 comprises a container 4, an absorption cartridge 5 placed inside a housing 6 of said container 4, and a blower 7 to feed the air to the user device 3.

The container 4 has just one section, and is provided with an entry 8 and with an exit 9 both of which are connected to the duct 2. Further, the container 4 comprises a distribution device 10 connected to the entry 8 in order to guarantee a homogeneous distribution of the incoming air flow over the entire surface of the cartridge 5, a manifold 20 to collect the outgoing flow, and a fixed perforated upper cover 11 placed close to the distribution device 10.

The container 4 further comprises a removable

perforated cover 12 suitable to lay on the cartridge 5, and four elastic elements 13 (just two of said elastic elements are shown) defined by the respective springs, said elements are compressed between the two covers 11 and 12 in order to press the cover 12 against the cartridge 5.

According to another embodiment (not shown), the springs which define the above mentioned elements 13 can be substituted by pressing means preferably, but not necessarily, made of rubber or of other materials having defined elastic characteristics.

Finally, the container 4 comprises a lower cover 14, a screen net 15 placed over said cover 14, and a series of annular tabs 16 placed inside the housing 6, and suitable to improve the air flow circulation through the cartridge 5 by preventing the formation of preferred paths.

The cartridge 5 is permeable and is realised with a renewable material which can absorb the carbon dioxide and is formed by a strongly basic ion exchange resin, and, as it will be better explained hereinafter, the regeneration of said cartridge is realised through water steam stripping with a humid air or inert gas flow, which do not require any further treatment.

Alternatively, the material of the cartridge 5 is made of an oxide of an element of the IIa Group, in particular of magnesium, in order to realise a system suitable to absorb the carbon dioxide and which can be easily regenerated by heating.

The dimensions of the cartridge 5 are selected, during the design phase, as a function of the concentration of incoming carbon dioxide and of the desired concentration at the exit 9, and as a function of the air flow to be treated and of the desired lifetime of the cartridge 5.

Alternatively, in order to improve the purification characteristics of the unit 1, or in order to better suit said unit 1 to the specific situations, it is possible to place several cartridges 5 in series, or, further, to place them in two blocks.

The previously described unit 1 has some advantages, as, for instance, the achievement of a low carbon dioxide concentration in the air which exits from said unit 1, the complete absence of residues to be disposed of inside the cartridge 5, and a low hydrostatic load loss along said unit 1, with the possibility to have blowers 7 or similar devices with reduced dimensions and costs.

During use, the air flow to be sent to the user device 3 is directed through the cartridge 5 thus causing the carbonation of the absorption material.

In the case that the absorption material of the cartridge 5 is made of ion exchange resins, it is possible to see, during use, a decrease of the volume of the absorption material following dehydration of said absorption material.

The presence of the elastic materials 13, during the volume decrease of the resins, causes the movable cover 12 to stay continuously in contact with the upper surface of said cartridge 5, thus preventing the change of the mechanical characteristics of said cartridge 5.

Once that, at the exit 9 from the unit 1, the air flow does not meet the characteristics required by the user device 3, i. e. the filtering characteristics of the material of the cartridge 5 have decreased, the cartridge 5 is extracted from the container 4 and is introduced into a regeneration unit (not shown) wherein the material therein contained is, through subsequent steps, hydrated; regenerated; and subjected to a carbon free flow of air in order to move away the liquid residues still present in the material.

The regeneration is alternatively realised using an aqueous solution of sodium or ammonium hydroxide, followed by washing with water until the achievement of neutral conditions, while the hydration is realised using a flow of carbonate free air or of humid inert gas through the cartridge 5, or, alternatively, by placing said cartridge 5 in carbonate free water, or, else, by using a flow of inert gas or of carbonate free air at growing values of humidity and temperature through the cartridge 5.

By percolating the cartridge 5 with an aqueous solution of sodium or ammonium hydroxide, after having hydrated the material inside said cartridge 5, there is the advantage of saving sodium or ammonium hydroxide.

Alternatively to the above, the regeneration of the material of the cartridge 5 can be realised by using a gaseous flow at a temperature comprised between 50°C and 70°C. The just described gaseous flow is formed by inert gas or by carbonate free air which are both saturated with water steam.

Alternatively, when the material contained in the absorption cartridge is formed by an oxide of the IIa group with a pellet shape, the regeneration is simply realised by heating at temperatures higher

than 500°C in a flow of carbonate free air or inert gas.

The heating and the cooling of the absorption material is realised through a gradual ramp up of the temperatures in order to minimise the inner stresses between the single particles due to the thermal expansion.

The regeneration of the cartridge 5, as it has been above described in the different embodiments, has the advantage of not producing or of reducing to the minimum terms the residues to be disposed of or toxic and harmful substances.