WO2011075033A1

WO2011075033A1 - Decomposition unit for removal of an undesired gas component in a gas stream

Info

Publication number: WO2011075033A1
Application number: PCT/SE2010/000292
Authority: WO
Inventors: Szabó ISTVAN
Original assignee: Nordic Gas Cleaning Ab
Priority date: 2009-12-14
Filing date: 2010-12-08
Publication date: 2011-06-23
Also published as: EP2512624A1

Abstract

A decomposition unit which is suitable for the decomposition of a gaseous undesired component present in a gas stream comprising: i) a flow-through decomposition chamber in which the undesired component is decomposed and which has an outlet and an inlet, and ii) a heating arrangement, and iii) a flow line passing through the heat exchanger and the decomposition chamber via its inlet and outlet. The characteristic feature of the heating arrangement is that it comprises A) a regenerative heat exchanger which in the flow line downstream of the regenerative heat exchanger creates repetitive puffs containing the undesired component to be removed, and B) a puff filter connected to the flow line at a position downstream of the regenerative heat exchanger, said puff filter a) being capable of removing the undesired component in said puffs, and b) typically comprising a container in which the undesired component is removed from the puffs and has an inlet end and an outlet end.

Description

Decomposition unit for removal of an undesired gas component in a gas stream

TECHNICAL FIELD

The invention relates to a decomposition unit, apparatus containing the unit and a method for the catalytic removal of an undesired gaseous component in a gas stream by the use of the unit and/or apparatus.

The gas stream is typically air containing the undesired component, for instance air exhaled by a patient to whom a gaseous physiologically active agent has been administered via inhaled air. The administration is typically part of a treatment of the patient. The invention is also applicable to other gas streams containing a gaseous contaminant that is to be removed before the gas stream is further processed and/or delivered to ambient atmosphere. Nitrous oxide (N₂0) is a typical example of a gaseous physiologically active agent which is administered via inhaled air.

TECHNICAL BACKGROUND

The invention relates to problems encountered by applicant when designing compact decomposition apparatus and units for catalytic decomposition of nitrous oxide in air exhaled by patients undergoing treatment and care in hospitals, dentists and other health care units. For this kind of applications it is of utmost importance to have a compact apparatus providing a) an efficient removal process resulting in a minimum of residual levels of undesired components in the gas stream exiting the apparatus or unit (= waste gas stream or waste gas, effluent gas) together with b) an efficient energy balance to reduce costs. See WO

2010071538 (Nordic Gas Cleaning AB). At an early stage of our development process we recognized that the compactness and energy balance of could be significantly improved by combining a catalytic decomposition chamber with a regenerative heat exchanger. During the priority year it was recognized that this combination inherently meant that a puff of the untreated gas stream will appear downstream of this kind of heat exchanger every time the flow direction is reversed through the regenerative heat exchanger and the decomposition chamber. In this respect the design with a regenerative heat exchanger was not as good as conventional heat exchangers. Precautions were required in order to avoid repetitive puffs in order to comply with demands from customers and authorities.

The present invention deals with these precautions and their application to the decomposition of undesired components in gas streams in general. Apparatuses for the removal of an undesired component of the kinds discussed above from gas streams have been described before. See for instance technical background in WO 2010071538 (in particular figures 1-3) and publications given below. Based on WO

2010071538 (health care field) and figure 1 of the present specification previously known apparatuses (100) have as a rule comprised:

a) an inlet arrangement (104);

b) a flow-through decomposition unit (105) in which there is a flow- through decomposition chamber (106) in which the decomposition of the undesired component takes place, typically the use of a catalyst placed in the chamber,

c) an outlet arrangement (107),

d) a gas flow line (101) passing through a), b) and c) in the order given and having an inlet end (102) and an outlet end (103), and

The flow line in either one or both of the inlet and outlet arrangements may be a conduit with or without functionalities as discussed below and in WO 2010071538. The inlet end of the flow line is in the upstream direction in gas flow communication with one or more sources for the gas stream containing the component to be removed. The outlet end is in the downstream direction in gas flow communication with ambient atmosphere, an arrangement for further processing of remaining components in the gas stream including collecting the gas in a suitable container, etc.

The decomposition unit (105) typically comprises a heat exchanger for heating the gas stream which is about to enter the decomposition chamber (106) by the gas stream exiting the chamber. A heat exchanger is typically combined with an arrangement for separate heating (122) of the decomposition chamber and/or the catalyst material and/or the gas which is about to enter the chamber to secure sufficient temperature in the chamber and/or the catalyst material. As discussed in WO 2010071538 a conventional heat exchanger linked to the decomposition chamber can favourably be replaced with a regenerative heat exchanger (140) of the kind defined below.

The apparatuses typically also comprise a flow regulating arrangement and a control unit. Different parts of the flow regulating arrangement and the control unit may be placed within the inlet, outlet arrangement and/or decomposition unit. See e.g. WO 2010071538 and publications cited therein. Some earlier publications dealing with health care gases containing nitrous oxide are:

Gases containing an anaesthetic agent (anaesthetic sases): DE 42087521 (Carl Heyer GmbH), DE 4308940 (Carl Heyer GmbH), US 7,235,222 (Showa Denko KK), US 4,259,303 ( uraray Co., Ltd), WO 2006059606 (Showa Denko KK), WO 2002026355 (Showa Denko KK), JP publ No. 55-031463 (Kuraray Co Ltd), JP publ No. 56-01 1067 (Kuraray Co Ltd). Gases containing nitrous oxide without an anaesthetic agent 1 (maternity careafter delivery and the like): 7,235,222 (Showa Denko KK), WO 2006059606 (Showa Denko KK), WO 2002026355 (Showa Denko KK),

Undefined health care use of sases containing nitrous oxide: JP publ No. 2006230795 (Asahi Kasei Chemicals Corp).

Handling of waste anaesthetic gases are also discussed in WO 2002026355 (Showa Denko), GB 2059934 (Kuraray) and WO 2006124578 (Anaesthetic Gas Reclamation LLC).

Some publications dealing with purification of off-gases from process industries etc including for instance the use of regenerative heat exchangers are: WO 1986000389 (US 4,741 ,690, Heed), US 5,262,131(ABB Air preheater), WO 1998016300 (Katator AB), WO 1999047245 (US 7,399,451 Megtec System), WO 1993007954 (US 6,168,770, Heed), WO 2002092196 (Katator AB), WO 2006101366 (Enbion), US 4.542,782 (Berner). and US 5,178,101 (Radian Corp), US 6,328,941 (Watzenberg et al). The gases have contained volatile organic compounds and/or nitrogen oxides (NO, N0₂, N₂0 etc) etc.

During the priority year the SE Patent Office have cited US 6,328,941 (Watzenberg et al), EP 1356840 (Siemens-Elema) and WO 2006101366 (Enbion) as documents defining the general state of the art.

All patents and patent applications cited in this specification are hereby incorporated in their entirety by reference.

OBJECTS OF THE INVENTION

The objects of the present invention comprise to provide solutions to the problems discussed above. This includes among others: " ^v " ' "·^■* ίυ ιυ ' υ u u «· 3 t-

4

a) Taking care of an undesired component in puffs which are originating from the use of a regenerative heat exchanger integrated with a decomposition chamber of the kind discussed above. In other words this object encompasses to reduce the overall level of the undesired component in the waste gas leaving the apparatus as well as the level of the component in the puffs. Target levels are within the same limits as given elsewhere in this specification for reduction of the level of the undesired component.

b) Providing compact apparatuses and decomposition units.

c) Providing increased cost-efficiency with respect to utilization of the catalyst, input of

energy etc.

Object (a) above is part of the more general object of providing a high reliability with respect to efficiency in decomposing the undesired component to harmless products. This includes accomplishing zero or only trace levels of any undesired components in the effluent gas, for instance unacceptable by-products from the decomposition. For gas streams containing nitrous oxide this means zero or trace levels of nitrous oxide and nitrogen oxides other than nitrous oxide (primarily NO_x (x = 1 or 2)).

See also international patent application WO 2010071538. DRAWINGS

Figure 1 illustrates a decomposition unit which has a regenerative heat exchanger without a puff filter.

Figure 2 illustrates a decomposition unit with a puff filter which is based on

adsorption/desorption of the undesired component.

Figure 3 illustrates a puff filter which is based on catalytic decomposition of the undesired

component.

Corresponding items in different figures have as a rule the same second and third digits.

Dashed lines represent data/signal communication between various functions along the flow line and those parts of the control unit which are present in the control block.

THE INVENTION

It has now been recognized that cost efficiency, energy balance and compactness can be improved for apparatuses and methods of the kind discussed herein if a conventional heat exchanger in which hot gas exiting the decomposition chamber is used to heat gas which is about to enter the decomposition chamber is replaced with a regenerative heat exchanger. It has also been realized that it is advantageous to combine this replacement with a puff filter placed along the flow line at a position downstream of the origin of the puffs, i.e. downstream of the heat absorbers of the regenerative heat exchanger with preference for downstream of the regenerative heat exchanger.

Accordingly the apparatus and the decomposition unit of the invention are of the kind generally defined under Technical Background above. The main characteristic feature is that the heat exchanger is a regenerative heat exchanger combined with a puff filter placed along the flow line at a position downstream of the origin of the puffs.

The flow-regulating arrangement, the control unit, the inlet arrangement and the outlet arrangement will be described with reference to figure 1. This figure represents a kind of apparatus which is specifically optimised for receiving a gas stream for which the flow velocity is changing as a function of time, e.g. a gas stream originating from a number of sources which are on/off independently from each other. For more details see WO

2010071438. This means that for other applications the various functions given for the flow- regulating arrangement and the control unit may be optional. . DECOMPOSITION UNIT

The decomposition unit (205,305) of the invention comprises as illustrated in figures 2-3 a) a temperature regulating arrangement containing a regenerative heat exchanger (240,340) preferably with a separate heating arrangement (222,322) for supporting correct process temperature of incoming gas in the decomposition chamber (206,306),

b) a puff filter (238,338),

c) a flow-through decomposition chamber (206,306) in which the factual decomposition of the component to be removed shall occur, and

d) preferably a temperature sensor arrangement for controlling the temperature in

decomposition chamber (corresponds to 128a-d,128a-d in figure 1), and

e) preferably a temperature sensor arrangement for controlling the temperature at the outlet end of the heat absorbers (temperature of treated gas exiting the heat absorbers)

(corresponds to 128e-f in figure 1)

Regenerative heat exchangers and puff filter Regenerative heat exchangers as applied to the present invention comprises that heat in the hot gas exiting the decomposition chamber is first transferred and stored in a heat absorber from which heat subsequently is transferred to incoming gas that is about to enter the decomposition chamber. This implies that for continuous processes and decomposition chambers of the type described in this specification (chamber with two alternating inlet/outlet openings) there is needed two heat absorbers connected to the decomposition chamber and a 4-way valve function (e.g. a 4-way rotor valve) with one way being connected to the downstream part of the flow l ine (outlet), one way to the upstream part (inlet), one way to one of the heat absorbers and one way to the other heat absorber. With this design it will be possible to cool gases exiting the decomposition chamber in one of the heat absorbers while simultaneously heat incoming gas in the other heat absorber and by switching the 4-way valve function reversing the flow through the heat absorbers and the decomposition chamber so that heat absorbed during cooling is used to heat incoming gas. This switching is done in a cyclic repetitive mode.

The term "regenerative heat exchanger" potential ly also includes so called rotary regenerative heat exchangers, e.g. comprising a rotor containing a heat adsorbing porous material placed in two physically separated longitudinal regions of the rotor body with an alternating inlet/outlet opening for gas at each end of a region. This kind of regenerative heat exchanger is illustrated in WO 2006101366 (Enbion) and US 4,542,782 (Berner).

A regenerative heat exchanger that is useful in the invention could have the design outlined for the apparatus/decomposition unit in figure 1 and comprise at least two separate heat exchangers (121a,b) each of which contains a heat absorber ( 123a,b). at least a multi-way valve function (124) and for instance also a heating arrangement (122). e.g. integrated with the decomposition chamber in one and the same block. The multi-way function shall permit reversal of flow through the decomposition chamber (106) and conduits (125a,b,c,d) linked together in a way enabling cycles comprising the steps of:

i) switching the valve function ( 124) to a first position so that hot gas will leave the

decomposition chamber ( 106) through a first transport conduit (125a) containing a first heat exchanger (121 a) with heat absorber ( 123a). whereafter the obtained cooled gas is transported in a common outlet conduit (125c) further downstream into the outlet arrangement (107), ii) switching the valve function (124). to a second position so that incoming gas from the inlet arrangement (104) via the common inlet conduit (125d) will pass through the first conduit ( 125a) containing the first heat exchanger (121a) with heat absorber (123a) thereby becoming heated before passing through and leaving the decomposition chamber (106) through a second conduit (125b) containing a second heat exchanger (121 b) with heat absorber (123b) whereafter the now cooled gas is transported in the common outlet conduit (125c) further downstream into the outlet arrangement.

iii) switching the valve function (124) to the first position thereby initiating repetition of the steps (i)-(iii) (= one cycle).

Each of the heat absorber and the corresponding part of a transport conduit (125a,b) defines a heat exchanger (121a,b). Between each heat exchanger (121a,b) and the decomposition chamber (106) there preferably is a heating arrangement (122a,b). Each heating arrangement (122a,b) is "on" when gas heated in a heat exchanger (121) passes the arrangement in order to support the desired process temperature in the decomposition chamber/catalyst material and is "off when hot gas from the decomposition chamber (106) passes the arrangement. In preferred variants, the heat exchangers (121a and b), the heating arrangements (122a and b) (if present), and the decomposition chamber are preferably integrated into the same block as illustrated in figure 1. Typically each cycle will comprise a period of time in the interval of about 0.5 - 5 minutes with switching at each half and full time period, for instance a period of two minutes with switching the valve function (124) every minute.

Although not preferred the 4-way rotor valve mentioned above may be replaced by different x-way valve combinations resulting in a 4-way valve function at the junction of the four conduits (125a-d) (x = 2, 3 etc). During later development work it has been realized that combinations of stop-flow valves (x = 2) many times can be more reliable and simple and therefore preferred than 4-way valves.

A regenerative heat exchanger to be used in the present invention preferably comprises a separate heating arrangement (122) in addition to the heating arrangement which is implicit in the heat exchangers) (121). See WO 2010071538 (Nordic Gas Cleaning AB). This second heating arrangement shall be capable of raising the temperature of gas leaving a heat exchanger (121a,b) to the process temperature for the desired decomposition. In other words the heating arrangement (122) shall be capable of securing the process temperature by compensating for possibly temperature deficiencies for reaching a desired process temperature. A heating arrangement ( 122) typically comprises an electrical heater (122a,b), preferably integrated with the decomposition chamber (106,206,306), for instance

immediately upstream of the decomposition chamber (106,206,306) and/or preferably placed within the chamber (106,206,306), with heating elements distributed along the flow direction. The effect of a heating arrangement (122) in combination with a preceding heat exchanger ( 121a,b) should be sufficient for heating the chamber and incoming gases to a temperature within the process temperature interval. Typically the effect of a electrical heater (122a,b) of the heating arrangement (122) is adjustable within a certain range with a maximal effect being > 5 kW. such as > 10 kW or > 15 kW with typical upper limits being 100 kW, 50 kW, 40kW or 30 kW irrespective of lower limit.

A heat absorber (123a or 123b) as discussed above may be in the form of a porous bed of heat absorbing material through which the hot gas and the cold incoming gas alternately are passing. This bed may be a porous monolith or a bed of solid non-porous particles packed to a bed. The bed may or may not be catalytically active in decomposing the gaseous

physiologically active agent, e.g. nitrous oxide. Its adsorption capacity for the undesired component should be as low as possibly (= insignificant) since this would minimize the volume of the puffs (minimum volume is the void volume of the heat adsorbing bed). The term "regenerative heat exchanger" above includes variants containing two or more heat exchangers of the same kind as heat exchangers (121a and 121b) above and alternate use of them in cycles.

The same kind of regenerative heat exchanger is given in figures 2-3. Some reference numerals have been omitted for clarity reasons. The regenerative heat exchanger is designated (240,340).

We have realized that regenerative heat exchangers when used as described above will lead to an effluent gas stream containing repetitive small puffs containing the undesired component. The occurrence of repetitive puffs will decrease the overall efficiency of the decomposition unit. A function for neutralizing the puffs emanating from the use of a regenerative heat exchanger would be beneficial (= puff filter or puff-neutralizing function). Preferred puff filters are illustrated in figures 2 and 3 (variants 1 and 2, below). In addition to a puff filter (238,338), both figures shows a part of the flow line (201,301), a part of the inlet arrangement (204,304), the decomposition unit (205,305), the outlet arrangement (207,307) and parts of the control unit (the control block (215,315) and a nitrous oxide sensor arrangement (248,348). The decomposition unit comprises the regenerative heat exchanger (240,340), the decomposition chamber (206,306) and the puff filter (238,338). The inlet and the outlet arrangement (204,304 and 207,307, respectively) preferably also contain functions as outlined in figure 1. See also variants according to figures 1-3 of WO 2010071538. A puff filter typically has a 3 -way valve function permitting selective diversion of puffs into the puff filter. As illustrated in figures 2 and 3 this valve function (239,339) is placed downstream of the regenerative heat exchanger (240,340). When no puffs are passing the position of the puff filter (238,338), the 3 -way valve function (239,339) is in a by-pass position. Every time a puff is about to pass, the 3 -way valve function is switched to the puff diverting position and the puff diverted into the puff filter whereafter the valve is switched back to the by-pass position. The component to be degraded in the puff filter may then be neutralized in a number of different ways. Figures 2 and 3 represent two main approaches (adsorption/ desorption and catalytic degradation, respectively). The 3-way valve function may be composed of one 3-way valve or two 2- way valves (= stop-flow- valves) as discussed below.

The puff filter (238) in figure 2 comprises a container (241) with a porous adsorbent (242) which is capable of adsorbing the undesired component when the puff passes through the adsorbent (flow direction indicated with an arrow). The adsorbent is a carbon filter in the variant preferred at the filing of this specification. The adsorption for the undesired component should preferably be reversible thereby permitting regeneration of the adsorbent, e.g. by passing a gas not containing or being low, such as depleted, in nitrous oxide through the filter. The direction of flow during desorption is preferably reversed relative to the direction during adsorption. This puff filter (238) has

a) an inlet conduit (243) for diverting puffs from the main flow line (201) to the container (241), and

b) two outlet conduits (244a,b) for transporting gas out from the container (241). The inlet conduit (243) is at one end connected to the upstream end of the container (241) (= upstream end of the adsorbent) and at its opposite end to the flow line via a 3 -way valve function (239). The inlet conduit (243) is used for diverting puffs into the container via the 3- way valve function (239). This 3-way valve function may comprise two 2-way valves (239a and 239b, respectively (stop-flow valves) with one of the valves placed in the inlet conduit (243) and the other one in the flow line (201) upstream of the position where the inlet conduit (243) is connected to the flow line (201). Alternatively the valve function may be a 3-way valve (239) as illustrated in figure 3. One of the outlet conduits (244a) is at one end (1^st end) connected to the downstream end of the container (241) (= downstream end of the adsorbent) and at its other end (2^nd end) to the flow line (201) at a position downstream of the inlet conduit (243). The other outlet conduit (244b) is at one end connected to the upstream end of the container (241) (= upstream end of the adsorbent) and at its other end to the flow line (201) at a position close to and upstream of the function (208) for creating and changing flow (compare figure 1). The first outlet conduit (244a) has two main uses: a) returning puffs depleted in the undesired component to the flow line (201), and b) diverting a part of the flow in the flow line (201) to pass through the adsorbent (242) thereby desorbing the adsorbed undesired component and returning it back into the flow line via the second outlet conduit (244b). At this stage the flow direction through the adsorbent (242) is reversed relative to the flow direction used during the adsorption. The outlet conduit (244b) comprises a 2-way valve (245), preferably a stop-flow valve, and preferably also a function (246) (preferably a blower) for creating and/or changing the flow used for desorption of the undesired component from the adsorbent (242) and pass it back to the flow line (201) as discussed elsewhere in this specification.

The desorbing gas may also be transported to the outlet end of the container (241) by a conduit (not shown) that at one end is connected at the outlet end of the container and at its other end is in communication with a source for desorbing gas (not shown). The puff filter (238) works in the following way:

Step 1 (adsorption): The undesired component in a puff is bound to the adsorbent when the puff is passing through the container (241) whereafter the puff without the undesired component is returned back to the main flow line (201) via outlet conduit (244a). 3-way valve function (239): inlet conduit (243) is open (valve 239a open), flow line (201) closed for by-pass of flow (valve 239b closed).

2- way valve (245) closed.

Step 2 (desorption): The undesired component in the adsorbent (242) is released from the adsorbent by flow diverted by sucking part of the flow in the main flow line (201) into the outlet conduit (244a), through the adsorbent (242) and through the outlet conduit (244b) to the flow line (201) upstream of function (208). Sucking is caused by subpressure created by function (208) and function (246).

3- way valve function (239): inlet conduit (243) is closed (valve 239a closed), flow line (201) opened for by-pass of flow (valve 239b open).

2- way: valve (245): open.

Step 3 (disconnection of the puff filter, not imperative): Flow is by-passing the puff filter (238). No diversion of flow.

3- way valve function (239): inlet conduit (243) is closed (valve 239a closed), flow line (201) opened for by-pass of flow (valve 239b is open).

2-way valve: closed

Step 4 and onwards: Repetitive cycles, each of which comprises in sequence steps 1, 2 and 3 (optional). The puff filter (338) in figure 3 comprises a container (341) with a porous bed containing a catalyst material (342) which is capable of degrading the undesired component when the puff passes through the bed (flow direction indicated with an arrow). The catalyst material is typically selected according to the same principles as outlined for the catalyst material in the decomposition chamber (306). The puff filter (338) has a) an inlet conduit (343) for diverting puffs from the main flow line (301) to the container (341), b) an outlet conduit (344) for transporting gas out from the container (341), and c) a heater (347) for heating the incoming puff and the catalyst material to a temperature selected as outlined for the working temperature as discussed for decomposition chambers in general elsewhere in this specification. The inlet conduit (343) and the outlet conduit (344) are connected to the container (341) and to the flow line (301) as in figure 3.

The puff filter (338) works in the following way:

Step 1 (decomposition, flow in flow line is diverted through the puff filter): The undesired component is decomposed by the catalytic material in the bed (342). The puff is flowed through the inlet conduit (343) and the container/bed and returned back to the main flow line (301) via outlet conduit (344). Flow entering the puff filter and the catalyst material is heated by heating function (347)

3-way valve function (339): inlet conduit (343) is opened, flow line (301) closed for by- pass of flow.

Step 2 (flow by-passing the puff filter, optional but preferred): Gas flow containing no puff of the undesired component is by-passing the puff filter.

3-way valve function (339) : inlet conduit (343) is closed, flow line (301) is open for bypass.

Step 3 and onwards: Repetitive cycles each of which comprises in sequence steps 1 and 2.

In every cycle of a puff filter, step 1 should last for > 0.5 sec, such as > 1 sec and/or < 12 sec, such as < 10 sec and typically be within the interval of 1.5-5 sec, such as within 2-3 sec, and step 2 for 1-8 minutes, typically 1-5 minutes. Independent of the individual steps the total time for a cycle corresponds to the time a heat exchanger (321a or 321b) is used in a cycle. See elsewhere in this specification.

If and when the undesired component in a puff entering the puff filter is returned back to merge with the main flow (e.g. as in the variant of figure 2, i.e. after adsorption/desorption), it is important to balance the system such that no puffs of the undesired component is leaking out at positions that are open to ambient atmosphere, for instance at the inlet valve function (109, fig 1). Subpressure at inlet valve function (109, fig 1) shall be maintained meaning that the return flow should be sufficiently low for not disturbing the balance, typically < 25%, such as < 15%, with preference for < 10% or < 5% of the main flow at the merging position. The balancing is under the control of the control unit which will cause function (108,208,308) (e.g. a blower) to increase the main flow in flow line (101) if the subpressure at the merging point and/or at an inlet valve function (109, fig 1 , if present) is disappearing. The merging position should be upstream of the regenerative heat exchanger (240,340) with the preference for upstream of function (208,308) (e.g. a blower) for creating and changing flow. In the case an inlet valve function (109, fig 1) is present the merging position is preferably downstream such a function. Compare figure 2.

Returning of puffs depleted in the undesired component in the puff filter to the flow line

(201,301) may take place at in principle any position along the flow line provided the system is balanced as discussed above. The preference is for positions downstream of the

regenerative heat exchanger (240,340) with the highest preference for downstream of the puff filter (238,338). Alternatively, gas in puffs depleted in the puff filter with respect to the undesired component may also be guided directly in downstream direction in an outlet conduit (flow line)(not shown) which is separate from the main flow line (201, 301).

The opening/closing of conduits by the valve functions (239,339 and 245,345) during process conditions is typically controlled via the control unit by the opening/closing of conduits by multi-valve function (224,324).

A third possibility for a puff filter is to collect one or more puffs in an expandable container linked to the main flow line downstream of the regenerative heat exchanger whereafter the gas in the container is returned back to the flow line at a position upstream of the regenerative heat exchanger, with preference for the positions given for the variant discussed for fig 2. Further possibilities are likely to exist.

Temperature sensor arrangement

The decomposition unit preferably comprises a first temperature sensor arrangement (128 a,b,c,d..., fig 1) which is assisting in controlling the temperature of the decomposition chamber. The arrangement is typically in the form of a thermo element, at one, two, three, four, five or more positions along the flow line within the decomposition unit (105,205,305) for measuring the temperature at these positions. Suitable positions in the apparatus of figure 1 are i) at a position (128a) before/after the gas stream exits/enters the heat absorbers

(123a,b), within (128b,e) the heat absorbers (123a,b), at each end (128c,d) of the

decomposition chamber (106). Temperature sensors (128 a,b,c,d...) are also part of the control unit. In the variant preferred at the filing date, the number of temperature sensors are six with four placed within the catalyst material/chamber (106) and one in each of the heat absorbers (123a,b). The heating is then primarily controlled by one or more sensors (128c,d) in the chamber (106). Corresponding positions are applicable for the temperature sensors in figure 2 and 3 as indicated.

The decomposition unit also comprises a second temperature sensor arrangement for measuring the temperature of the gas stream being treated in the chamber (106) after having been cooled in an heat absorber (123a or b). This sensor arrangement preferably has a temperature sensor (128e,f), e.g. of the same kind as described above, next to a heat absorber (123a or b) within each of the conduits (125a and b, respectively). This sensor arrangement (128e,f) is preferably used to control the opening and closing of conduits (125a-d) by the valve function (124) when decomposition is taking place within the unit. Thus when the control unit receive a signal from a sensor (128e or f) that the temperature is approaching a preset target temperature which indicates that the absorber is becoming saturated with heat, the control unit will direct valve function (124) to reverse the flow direction through the chamber. Simultaneously the control of the valve function is taken over by the other one of the temperature sensors (128e,f) until the target temperature is reached at this sensor.

Decomposition chamber

The description of the decomposition chamber will focus on its use for decomposing undesired components in the form of physiologically active agents administered to individuals to be treated and/or cared for within the health care sector.

The preferred component to be removed is physiologically active when administered in inhaled air and typically has anaesthetic and/or analgesic effects. It is primarily nitrous oxide (N₂0), which is known to have both of these effects, but may also include or be one or more other gaseous physiologically active agents, for instance having a pronounced anaesthetic effect (anaesthetic agents). Typically components of the latter kind are found amongst volatile organic compounds (VOCs), such as amongst halo-containing hydrocarbons and halo- containing ethers. When an anaesthetic agent, in particular in the form of a VOC, is included, the inhaled air/gas is called an anaesthetic gas. The agent may also be selected amongst other gaseous compounds, e.g. other VOCs, having a desired physiological effect on patients.

Normal air constituents are not included amongst physiologically active gaseous agents to be removed.

Within health care units nitrous oxide is used within surgery, dental care, maternity care, during delivery etc. The typical patient is allowed to inhale a gas mixture in which the main components are nitrous oxide (about 20-70 % v/v) and oxygen (= inhalation air). When an enhanced anaesthetic effect is desired, the mixture also contains a gaseous anaesthetic agent (as a rule < 2 % v/v). The composition of air exhaled by a patient receiving these kinds of gases is essentially the same as in inhaled air except that there typically is an increase in moisture (water) and carbon dioxide. Exhaled air from a patient inhaling a gas containing nitrous oxide is typically diluted with normal air before being further treated, e.g. in a nitrous oxide decomposition apparatus and/or passed further downstream, typically into ambient atmosphere. In addition to the health-care field discussed above there are numerous occasions when one wants to remove an undesired component from a gas stream, for instance off-gasses from the process industry, from vehicles etc. For this other fields the component to be removed may be found in the group consisting of:

A) volatile inorganic components containing one or more compounds containing

a) nitrogen in a positive or negative oxidation stage, e.g. ammonia, nitrous oxide, nitrogen oxides other than nitrous oxide (e.g. NO_x (x is 1 or 2)), hydrogen cyanide etc, b) sulphur in a positive or negative oxidation stage (e.g. hydrogen sulfide, sulphur oxides

(SO_x (x is 2 or 3)),

c) phosphorous in a positive or negative oxidation stage (phosphines and various

phosphorous oxides,

d) carbon monoxide, etc. and

B) volatile organic components containing one or more organic compounds selected amongst hydrocarbons such as methane, ethane, ethene, acetyhylene etc, halogenated

hydrocarbons, esters, alcohols , ethers, ketones, aldehydes, amines, etc.

Additional undesired components may be removed by including additional catalysts in the same or different decomposition chamber. Alternatively such components may be removed by adsorption, catalysis, scrubbers etc upstream or downstream of the inventive unit or apparatuses.

In preferred variants of the invention, a catalyst capable of decomposing the component to be removed preferably is in the form of a porous bed filling up the volume of the decomposition chamber (206,306). This bed is porous in the sense that its porosity is sufficient for the gas to pass through. The bed may be in the form of a porous monolith or in the form of porous or non-porous particles packed to a bed. The bed may be comprise parts that are separated from each other leaving a zone (part) devoid of catalyst material between two parts containing catalyst material (interrupted bed =discontinuous bed). If a heating arrangement (122) wholly or partly is placed within the decomposition chamber or bed as discussed above, it may be placed in a zone/part which is devoid of or in a zone/part which contains catalyst material. Dimensions and volumes of the bed/chamber (206,306) follow the same rules as those that are given for the decomposition chamber in WO 2010071538. The flow direction through the chamber is typical along its length/height, in particular for cylindrical chambers.

The decomposition chamber including the catalyst, capacity of flow creating functions etc should be designed as outlined in WO 2010071538.

In variants of the invention utilizing a catalyst, the decomposition chamber is defined as the portion of the flow line located between the upstream end and the downstream end of the catalyst. Suitable catalysts have characteristics as outlined in WO 201071538 . When the component to be decomposed is nitrous oxide the harmless products are N₂ and 0₂ with the undesired byproducts being primarily nitrogen oxides other than nitrous oxide.

Suitable catalysts may be found amongst those that are effective for decomposing the undesired component to harmless products or to acceptable levels or other products at temperature interval that typically should be within the interval of 200-900°C, such as 200- 750°C. Typically temperatures for nitrous oxide can be found within 350-900°C, such as 350-750°C or 350-550°C or 400-500°C and for VOCs within 250-500°C. Trace levels of the undesired component, such as nitrous oxide, refer to its level in gas exiting the decomposition unit and/or chamber and as a rule are < 4000 ppm, such as < 1000 ppm or < 500 ppm and may be higher or lower for components other than nitrous oxide. The trace level of the undesired component, e.g.nitrous oxide, may alternatively and preferably refer to its level in gas leaving the decomposition unit/chamber relative to its level in gas entering the unit/chamber and then typically is > 50 %, preferably > 60 % or > 70 % or > 80 %, such > 90 % or > 95 % > 99 % (reduction level). These intervals also apply to the gas stream

entering/exiting the apparatus via the outlet (102) of the apparatus. For nitrogen oxides other than nitrous oxide, such as NO_x, the term "trace levels" primarily refers to levels < 2 ppm, such as < 1 ppm or < 0.5 ppm or < 0.1 ppm or < 0.05 ppm

downstream of the decomposition unit/apparatus. Depending on the composition of the gas to be treated, it may be appropriate to include an adsorption column for other undesired components, such as anaesthetic gaseous agents, at a position upstream of the decomposition unit (205,305) or even upstream of the inlet end of the flow line (201,301), etc. See further in publications cited above and inparticular in WO 2010071538 and references cited therein.

Nitrous oxide decomposing catalysts giving none or only trace levels of nitrogen oxides other than nitrous oxide are well known in the literature. See for instance US 7,235,222 (Showa Denko K.K), WO 2006/059506 (Showa Denko K.K), US 4,259,303 (Kuraray Co, Ltd), US 6,347,627 (Pioneer Inventions, Inc) etc. Thus suitable catalyst material can be found amongst a) a support carrying at least one type of metal selected from the group consisting of magnesium, zinc, iron and manganese, possibly together with aluminum and/or rhodium, b) alumina support carrying oxides of at least one type of metal selected from the group consisting of magnesium, zinc, iron and manganese possibly together with rhodium, or c) rhodium carried on a support formed of a spinel-type crystalline compound oxide with at least a portion thereof comprising aluminum together with at least one metal selected from the group consisting of magnesium, zinc, iron and manganese.

Preferred catalyst materials are particulate materials that comprise a catalytically active metal oxide, with preference for comprising either one or both of copper and manganese and/or a support material based on alumina with the content of metal oxide as discussed in the next paragraph. This in particular apply if the component to be decomposed is nitrous oxide.

For the decomposition of nitrous oxide we have found particular useful catalyst material among those that are suitable for removing/decomposing volatile organic compounds (VOCs) in industrial off-gases. Thus the preferred catalysts are capable of decomposing both VOCs and nitrous oxide. Particular preferred catalyst materials for the decomposition of nitrous oxide are typically based on a support material, e.g. an alumina support in the form of particles, and comprises a catalytically active combination of metal oxides, with preference for oxides of copper and/or manganese, typically in the range of 5 -30 % with preference for 1 1 -17 % (by weight).

FLOW REGULATING ARRANGEMENT

The flow regulating arrangement of figure 1 comprises i) a function (108) for creating and changing (increasing and decreasing) the flow velocity and/or ii) a valve function (109) to ambient atmosphere (by-pass valve). Valve function (ii) (109) is upstream of function (i) (108) when both of them are present simultaneously. This flow regulating arrangement is in particular adapted to situations at which the influx of gas containing the undesired component fluctuates in an irregular manner, e.g. gases containing nitrous oxide in hospitals.

The function (108) and/or valve function (109) are preferably gradually adjustable in the sense that they allow for adjustment of the flow velocity by function (108) and of inlet and outlet flow of gas from/to ambient atmosphere by valve function (109), respectively. Valve function (109) thus typically comprises a valve (109a) providing an adjustable opening to ambient atmosphere (110). The opening can be preset to desired values each of which will support a range of different target/desired values for inlet flow from ambient atmosphere and/or subpressure values in the flow line at valve (109a). Function (108) is preferably a blower. It is typically placed upstream or downstream of the decomposition chamber (106) or the decomposition unit (105). Preferred positions are within the inlet arrangement, and/or downstream of one or more valve functions (e.g. 109), if present. The pressure differential that creates flow through the flow line (101) may wholly or partly also be created at the inlet or at the outlet end (102,103) of the flow line (101) and/or even upstream or downstream of these ends.

The flow-regulating functions (108) may be defined by a combination of two or more separate functions creating and/or changing the flow.

The flow line may also comprise other kinds of valves and valve functions not directly involved in securing a proper and stabile flow through the decomposition chamber. Thus there may be a 3-way valve function (111) for disconnecting in a stop-flow wise manner incoming flow. This valve function may contain a branching (113) with a separate stop-flow valve

(l l la,b) in one or both of the branches (113a,b).

See further in WO 2010071538.

CONTROL UNIT

The control unit comprises various kinds of sensors located along the flow line for measuring different process parameters, e.g. flow through the inlet arrangement, flow through the decomposition chamber etc, and/or subpressure in the flow line of the inlet arrangement etc. In preferred variants the control unit also comprises soft-ware for comparing/checking and adjusting process parameters, and one or more computers loaded with such soft-ware. The latter parts of the control unit is called the control block (115,215,315).

The control unit is capable of a) measuring flow of gas entering the decomposition chamber, and, if so desired, also the subpressure in the inlet arrangement, optionally combined with b) comparing/checking obtained values with desired preset values, respectively, and/or c) adjusting flow and/or subpressure to be above a threshold value for flow and/or within a preset subpressure interval around a preset desired subpressure value. A desired level for flow is typically above a corresponding threshold value.

A flow sensor (116,216,316) for measuring flow may be placed in the flow line (101,201,301) downstream or preferably upstream of the decomposition chamber (106,206,306), and/or upstream or downstream of the flow regulating function (108,208,308). In the case this flow- regulating function is combined with a valve function (109), the flow sensor (116) is typically placed downstream of such a valve.

An extra flow sensor (117) may be placed downstream of the above-mentioned valve function (109) for measuring exclusively the incoming flow without including influx from ambient atmosphere via valve function (109).

The two flow sensors (1 1 6) and (1 17) of figure 1 provide one way to control the process flow. This way includes utilizing a preset target value for the flow difference measured by the tw^ro flow sensors as outlined in WO 201071538. A pressure sensor (118) for measuring pressure may be used for regulating flow through the decomposition chamber (106) is typically placed upstream of flow-regulating function (108) with preference when the inlet valve (109a) is present. Illustrative threshold values for flow are suitably > 0.5 m³/h or > 1 m³/h > 5 m³/h >10 m³/h.

The pressure in the flow line of the inlet arrangement (104) at the valve (109a) is typically below the pressure of ambient atmosphere in gas flow communication with this part of the flow line. Preferred subpressure values at this position to be used as preset desired/target values are found in the interval of- 1 Pascal to - 500 Pascal, such as -1 Pascal to -100 Pascal or - 1 Pascal to - 50 Pascal. See further the experimental part.

An important part of the control unit is the two temperature sensor arrangements (128a-d and 128e-f) of the decomposition unit. These sensor arrangements are typically used by the control systems for achieving the correct process temperature and optimal times for reversing flow through the decomposition chamber during process conditions (control of the multi- valve function (124,224,324)).

See further WO 201071538.

INLET ARRANGEMENT

The inlet arrangement (104) primarily comprises the upstream part of the flow-line (101) and various flow and pressure regulating functions as described for the gas regulating arrangement together with various sensors and metering/measuring functionalities as described for the control unit.

In a preferred variant there may thus be a particle filter (119). The particle filter (119) is in preferred variants associated with the presence of a upstream valve (111b) for closing the flow line (101) at the inlet end (102) and downstream valve function (109) to ambient atmosphere. A sensor (120) for measuring changes in pressure drop and/or flow resistance across the particle filter (119) is preferably associated with the particle filter.

See further in WO 2010071538. OUTLET ARRANGEMENT

The outlet arrangement (207,307) comprises the downstream part of the flow line (201,301).

The outlet arrangement may also comprise a sampling function (134) for a sensor

arrangement ( 134-137,248,348) for measuring the levels of products formed in the

decomposition chamber and/or of residual levels of the undesired component. The position for the sampling is typically downstream of the decomposition chamber (106,206,306) with preference for downstream of both the puff filter (238,338) and the regenerative heat exchanger (121-125,240,340).

A sensor arrangement (134-137,248,348) for the undesired component preferably also comprises a sampling function (134a) connected to the flow line at a position upstream of the decomposition chamber (106,206,306) and/or regenerative heat exchanger ( 121-125,240,340). The gas sampled upstream (134a) of the decomposition chamber is typically diluted with air in separate dilutor (137) before the undesired component is measured. The dilution is to a concentration comparable with the concentration at the downstream sampling position.

METHOD ASPECTS OF THE INVENTION

This aspect comprises the use of the apparatus and/or the decomposition unit of the invention for removing an undesired component as defined above in a gas stream flowing in a main flow line through the apparatus/unit. In its most general variant the inventive method is characterized by comprsing the steps of:

i) providing the gas stream,

ii) providing an apparatus of the present invention comprising a decomposition unit which is capable of decomposing the undesired component,

iii) lowering the total level of the undesired component in the gas stream by transforming the gas stream within the decomposition unit to a gas stream containing a) repetitive puffs of gas containing the undesired component at essentially the same level as in the incoming gas stream, and b) between the puffs is substantially depleted with respect to the same undesired component,

iv) removing the undesired components in the puffs by guiding them one by one into a side stream and through the puff filter of the decomposition unit thereby removing the undesired components in the puffs, and v) guiding the side stream to further processing or to ambient atmosphere a) by merging the side stream downstream of the puff filter with the main gas stream, or b) as a separate gas stream.

The apparatus, decomposition unit, process variables etc used in the method aspects of the invention are preferably as described above for the apparatus and unit of the invention.

EXPERIMENTAL PART EXAMPLE 1. REGENERATIVE HEAT EXCHANG ER LINKED TO A PUFF FILTER

The apparatus is the same as described in figure 1 except that a puff filter of the type illustrated in figure 2 is used (nitrous oxide adsorbent).

Controlling the process flow.

The process flow rate through the decomposition unit is controlled relative to the incoming flow by the aid of a) a subpressure sensor ( 118). which measures the subpressure at the inlet valve (109a), b) the opening to ambient atmosphere of inlet valve (109a), and c) the speed of blower (108). The blower (108) and the opening of inlet valve (109a) are initially set to give a desired subpressure at sensor ( 118) for a normal rate of the incoming gas flo containing nitrous oxide. Typical subpressure values are found in the interval of - 1 Pa to -150 Pa, e.g. - 5Pa. - l OPa, -50Pa eller - l OOPa.

The flow sensor (116 ) located upstream of the flow-regulating function (108 ) is used to control that a minimum flow is maintained through the decomposition chamber ( 106). See above. This flow sensor may also be placed downstream of function (108). The design with an inlet valve (109a) in free communication with ambient atmosphere (110) and subpressure at the subpressure sensor (118) will secure that nitrous oxide will pass into the flow line (101 ) of the apparatus and prevent it from exit the system via the inlet valve (109a). The design will also secure that the process flow in the apparatus will remain undisturbed even if there are quick and uncontrolled changes in the incoming flow that the blower (108) cannot manage.

During operation at a fixed incoming gas flow the blower ( 108) is set to give the preset target subpressure at subpressure sensor (118). • When incoming flow is increasing, the subpressure at subpressure sensor ( 1 18) will decrease. The control unit will speed up the blower which means that the flow within the flow line will increase and the subpressure will restore to the preset target subpressure. This situation is applicable to cases in which the number of patients connected to the apparatus is increasing.

• When incoming flow is decreasing, the subpressure at the subpressure sensor (118) will increase. The control unit will slow down the blower which means that the flo within the flow line will decrease and the subpressure will restore to the preset target subpressure. This situation is applicable to the situation when the number of patients connected to the apparatus is decreasing.

Starling up: The blower (108) must be on and give a predetermined flow through the apparatus in order to start the heaters (122a,b).

1. The blower (108) and valves along the flow line are set in positions to allow for the gas stream not containing the undesired component to pass through the apparatus, e.g. 100 m³/h or to a suitable flow minimizing the required heating time for reaching the process temperature, e.g. > 50 m³/h or > 100 mVh or >150 m³/h but less than 200 m³/h. The appropriate optimal value for starting up flow depends on the size/capacity of the apparatus but a typical mean flow for the apparatus used is 100 m³/h.

2. Changes in in opening of valves (124) are locked to fixed times which for the starting up typically means cycle times of two minutes.

3. The heaters (122a,b) are turned on and controlled by temperature sensors (128b,c) within the catalyst bed (106). A target value in the interval of 500-550°C is selected. When the target value is reached the apparatus is switched to run position.

4. Run position means that a gas stream containing the undesired component (nitrous oxide) is allowed to pass the decomposition chamber at the process temperature. The heaters (122a,b) is controlled as described elsewhere in this specification, i.e. according to a temperature target value for the catalyst bed which is in the interval of 500-650°C.

Changes in valve (124) openings are controlled by the exit temperature from the chamber (106). More particular the temperature is measured at a position downstream of one of the heat absorbers (123a,b) by the use of the appropriate temperature sensor (128e or 128f). When the exit temperature at this sensor reaches a preset value, e.g. in the interval 40- 60°C, such as 40°C, valve (124) will reverse the flow direction through the chamber (106) and the exit temperature of the other heat absorber will be measured at the other one of the heat absorbers (123a,b).

Normal working without change of the number of sources: The gas flow is adjusted by the use of the blower (108) via the pressure sensor (1 18) in the inlet arrangement (103) to be above a certain threshold flow which is controlled by the flow sensor (1 16) while

simultaneously keeping a certain preset subpressure in the flow channel at subpressure sensor (118). Disturbances in incoming flow are taking care of by the control functions as discussed above.

Nitrous oxide adsorbent (242): 10 L particles of extruded coal based on activated carbon (Exosorb® BXB (diameter 3 mm), Jacobi Carbon AB, Varvsholmen, Kalmar, Sweden). Heat absorbers (123a och 123b): Each contains 50 L of Duranit® Inerta kulor ¼" (Christian Berner AB, P.O. Box 88, SE 435 22 Molnlycke, Sweden/Vereignete Fullkorper Fabriken GmbH, Postfach 552, D-56225 Ransbach-Baumbach, Germany).

Decompositon chamber: The catalyst is a VOC catalyst (Metox 3) from Stonemill, Hasslarp, Sweden, and has a process temperature interval of 500-650°C (480-500°C) for decomposition of nitrous oxide.

Time per step of a regenerative cycle in the heat exchanger: 120 sec between two consecutive switches of valve (224) (= maximal time for adsorption plus desorption in puff filter).

Flow in main flow (201): 60 m /h through regenerative heat exchanger (240) (= 17 L/sec) Adsorption step: Forward flow through puff filter (238) is 17 L/sec during about 3 sec (= 51 L). Valve (239a) is open and valves (245 and 239b) are closed.

Desorption step: Reversed flow 2 L/sec not containing nitrous oxide during 120 sec minus 3 sec - 1 17 sec. Valve (239a) is closed and valves (245 and 239b) are open. Based on experiments at 2 L/sec, there is required 120 L gas depleted in nitrous oxide (depleted in the experiments meant reduction of the level of to 5% in the decomposition chamber (206) to desorb the nitrous oxide adsorbed during the previous adsorption step. It follows that desorption is completed after about 60 sec which is more than sufficient compared to 1 17 sec available. The expression "depleted in the puff filter" means reduction to a level which preferably is < 5% of the starting level. The function (208) for creating and changing flow in the flow line (201) can be balanced to secure a predetermined target subpressure value at the inlet valve (109, fig 1) by the use of the control unit. The desorption flow 2 L/sec is sufficiently low compared to the flow in the main flow line (201) (17 L/sec) for maintaining this balancing. Leakage of nitrous oxide to ambient atmosphere via inlet valve function (109, fig 1) is not possible as long as the target subpressure at the inlet valve is maintained.

By the use of a puff filter it is typical to lower the overall level of an undesired component in gas exiting the unit/apparatus with additional 1 -10 percentage units, i.e. reduction of 80-90 % could be increased to 90 to 99.5 or even higher.

Addendum: In preferred variants, the apparatus of the invention comprises modules that are possible to link together in order to facilitate construction of apparatus with different capacities. Such preferred apparatuses comprise mainly two different kinds of modules. One kind (1^st) of module comprises a reaction chamber (106), two heat absorbers (123a,b), and two heaters (122a,b) and preferably the appropriate sensors as described above and in WO 201071538. This kind of modules may be produced with different capacities, i.e. the volume of the decomposition chamber and/or the volume of the heat absorbers differ between modules of different capacities. The other kind of module (2^nd) comprises the multi-way valve function (124), the puff filter (238,338) and typically also other functions, such as flow regulating function (108), particle filter, inlet valve function (109) etc. The module concept comprises that modules of type 1 can replace each other with one or more of them being linked to a common module of type 2. While the invention has been described and pointed out with reference to operative embodiments thereof, it will be understood by those skilled in the art that various changes, modifications, substitutions and omissions can be made without departing from the spirit of the invention. It is intended therefore that the invention embraces those equivalents within the scope of the claims which follow.

Claims

C L A I M S

1. A decomposition unit suitable for the decomposition of a gaseous undesired component present in a gas stream, said unit comprising a i) a flow-through decomposition chamber in which the undesired component is decomposed and which has an outlet and an inlet, and ii) a heating arrangement, and iii) a flow line passing through the heat exchanger and the decomposition chamber via the inlet and outlet of the chamber,

characterized in that said heating arrangement comprises

A) a regenerative heat exchanger which in the flow line downstream of the regenerative heat exchanger creates repetitive puffs containing the undesired component to be removed, and

B) a puff filter connected to the flow line at a position downstream of the regenerative heat exchanger, said puff filter being capable of removing the undesired component in said puffs. 2. The unit of claim 1, characterized in that the regenerative heat exchanger comprises a) a heat absorber around the flow line at each of the inlet and outlet of the decomposition chamber, and

b) valvings and tubings permitting reversal of the flow direction through the

decomposition chamber and heat absorbers in a cyclic (repetitive mode) giving rise to said repetitive puffs, and

c) a container in which the undesired component is removed from the puffs and has an inlet end and an outlet end.

The unit of claims 2, characterized in that said puff filter comprises conduits and valves permitting

a) selective diversion of said puffs from the flow line into said container via an inlet conduit which at one end is connected to the main flow line at a position downstream of the regenerative heat exchanger and at its other end to the inlet end of the container, and

b) outlet of the puffs from the container after removal of the undesired component via an outlet conduit, said conduit at one end being connected to the outlet end of the container and at its other end possibly to the main flow line at a position downstream of the position at which the inlet conduit is connected.

4. The unit of any of claims 2-3, characterized in that said container comprises an adsorbent removing the undesired component when the puffs are passing through the adsorbent.

5. The unit of any of claims 2-4, characterized in that said puff filter comprises conduits and valves permitting passing a desorbing gas through the adsorbent, said conduits comprising:

a) a first conduit for inlet of the desorbing gas to the adsorbent, which conduit is

connected

i) at one of its end to the outlet end of the adsorbent/container, and

ii) at its other end to a source of desorbing gas which source may be the main flow line at a position downstream of the position of the inlet conduit for puffs, and b) a second conduit for outlet of the desorbing gas from the container which conduit is connected

i) at one of its end to the inlet end of the adsorbent/container, and

ii) at its other end to the main flow line at a position upstream of the regenerative heat exchanger, with preference for upstream of a function for creating and/or changing flow in the main flow line, such as a blower.

6. The unit of any of claims 2-5, characterized in that said undesired component is a

physiologically active gaseous agent, such as nitrous oxide, and said container comprises a) an adsorbent capable of adsorbing said agent, or b) a catalyst capable of decomposing said agent.

7. The unit of any of claims 1-6, characterized in that said gas stream derives from air

exhaled by one or more individuals inhaling said undesired component.

8. The unit of any of any of claims 1-7, characterized in that the unit is part of an apparatus comprising an inlet arrangement and an outlet arrangement which

A) are placed upstream and downstream, respectively, of the decomposition unit, and B) contain flow regulating functions and control functions, and said flow line of the decomposition unit extending through these two arrangement and the outlet end of the flow line typically being in downstream gas flow communication with ambient air.