FIELD OF THE INVENTION

The present invention relates to an apparatus and a method for the treatment of a waste anesthetic gas based on adsorption/desorption of one or more gaseous

anesthetic agents from a gas stream containing the waste anesthetic gas. Adsorption/ desorption of the anesthetic agent is in preferred variants combined with removal of nitrous oxide, preferably by catalytic decomposition, after the adsorption of the

anesthetic agents. The waste anesthetic gas typically derives from air exhaled by one, two or more patients to which an anesthetic gas containing the agent has been administered via inhalation.

Exhaled air, exhalation air, exhaled anesthetic gas etc will further on be used

synonymously. The same will also apply to inhaled air, inhalation air, inhaled

anesthetic gas etc. Waste gas or waste anesthetic gas will mean exhaled anesthetic gas possibly diluted with ambient atmosphere and intended to be wholly or partly

discarded. TECHNICAL BACKGROUND

A gaseous anesthetic agent is typically a volatile halo-containing organic compound, such as a halo-containing hydrocarbon or a halo-containing ether exhibiting an

anesthetic effect when inhaled, or other volatile organic compounds having this effect including for instance hydrocarbons not containing halo substituents. The anesthetic agent is typically administered in an anesthetic gas which is inhaled by a patient. The anesthetic gas contains the anesthetic agent often in admixture with nitrous oxide

(N ₂ 0) and/or oxygen and/or normal air and/or and/or some other physiologically active gaseous agent having the same function as nitrous oxide (e.g. having anesthetic and/or analgesic effects). In an inhaled anesthetic gas, the anesthetic agent in most cases constitutes < 10 % with typically levels being 0.25-3 %, such as 0.5-2 %, and nitrous oxide (if present) and the like > 10%, such as 20-70 % or less. In exhaled anesthetic gas, the levels of these agents are about the same as in inhaled anesthetic gas while the content of moisture and carbon dioxide typically are elevated. In larger hospitals and in many other health care units, the exhaled air is typically diluted at least 5-20 times with normal air by the internal gas handling system of the hospital/unit before the levels of anesthetic agent(s) and other added physiologically active gaseous agents in the anesthetic gas are reduced to acceptable levels before the exhaled anesthetic gas is to be delivered to ambient atmosphere.

The treatment of waste anesthetic gas by previously known methods typically comprises at least one or two main steps for the reduction of the levels of anesthetic agents, nitrous oxide and/or the like. One main step comprises reduction of the level of the anesthetic agent or agents (1 ^st main step). Another main step comprises reduction of the level of physiologically active gaseous agents, e.g. nitrous oxide, other than anesthetic agents, provided such other agents are present in the exhaled anesthetic gas (2 ^nd main step). Typically, anesthetic agents are removed before other physiologically active agents are removed. Normal air constituents such as oxygen gas (0 ₂ ), nitrogen gas (N ₂ ), carbon dioxide (C0 ₂ ) etc are not considered as physiologically active gaseous agents to be removed in this context.

There are various alternatives for these main steps. Anesthetic agents can be removed from anesthetic gases by a) absorption to a porous adsorbent from which the agents subsequently are desorbed and optionally collected, or b) condensation possibly together with nitrous oxide and/or other gaseous constituents of the inhaled anesthetic gas. Nitrous oxide can also be removed by being passed through a porous solid material containing a catalyst capable of degrading nitrous oxide to nitrogen gas (N ₂ ) and oxygen gas (0 ₂ ).

The adsorbent processes for removal of anesthetic agents can be cyclic in the sense that the adsorbent is regenerated by desorption and reused in the process. Different alternatives can be used for desorption. Prerequisites are that adsorption/desorption should be quick with a high efficiency and result in a regenerated adsorbent which is ready to be recycled in the process.

The condensation processes are typically disadvantageous because the volume of gas to be treated is significant and the levels of the particular anesthetic agents to be removed are relatively low. Compare that the waste anesthetic gas to be treated is normally diluted with respect to anesthetic agents and nitrous oxide by the internal gas handling system of many health care units..

For catalytic degradation the proper selection of catalysts is critical. In order for the removal process to be cost effective, the catalyst should be as cheap as possible, be stable for long periods of time, have a high efficiency in transforming low levels of nitrous oxide to nitrogen gas and oxygen gas, avoid formation of unacceptable levels of nitrogen oxides other than nitrous oxide (typically NO _x where x is 1 or 2) etc. It has normally been advantageous to remove particle material and moisture from the gas to be treated before environmentally harmful gaseous components are removed, i.e. prior to or between the main steps described above.

WO 2002026355 (US 7597858, US 7235222) Showa Denko K ; US 4259303 (GB 2059934) Kuraray Co Ltd; DE 4308940.2 Carl Heyer GmbH; and DE 4208752.1 Carl Heyer GmbH describe removal of anesthetic agents and nitrous oxide from a gas stream of waste anesthetic gas by adsorption/desorption of anesthetic agents prior to catalytic degradation of nitrous oxide.

EP 2165756 (Linde AG) describes a device for the removal of nitrous oxide from an anesthetic gas containing nitrous oxide

WO 2006124578 (US 20060254589, US 20060254590) Anesthetic Gas Reclamation describes fractionation of waste anesthetic gases by processes which comprise compression and condensation steps for reuse of the individual components.

EP 0284277 (Union Carbide) and US 5,231 ,980 (Praxair) describe an anesthesia machine which delivers air exhaled by the patient to an adsorbent selectively adsorbing the anesthetic agents in the exhaled air. The adsorbed anesthetic agent is desorbed at a separate location by the use of a purging gas such as nitrogen or air, worked up and reused. As part of background technology, both of the publications mention that steam has earlier been suggested as a purging gas for release of anesthetic agents from adsorbent material at a separate location.

EP 136840 (Siemens-Elema AB) illustrates that the principles of adsorption/desorption have earlier been applied to arrangements for recirculation of anesthetic agents/gases to the same patient.

WO 2010071538 and WO 2011075033 (both of Nordic Gas Cleaning AB) describes improvements relating to flow-through apparatuses for catalytic degradation of nitrous oxide. Preadsorption is indicated for removal of anesthetic agents.

US 20090101010 (Zensys GmbH) describes a filter cartridge in which anesthetic agents in an anesthetic gas can be adsorbed from a single patient and subsequently desorbed and regenerated by steam when the patient is disconnected. The carrier gas including nitrous oxide, if present, will passes through the cartridge into ambient atmosphere.

All US patents, US patent applications and international patent applications designated and entering the US are hereby incorporated by reference.

OBJECTS OF THE INVENTION

The main object of the invention is to provide improvements of methods which comprise an adsorption step for the removal of anesthetic agents from a gas stream containing anesthetic agents together with nitrous oxide, oxygen gas, normal air and/or the like at the levels discussed above. The main object also comprises to provide corresponding improvements relating to apparatuses and arrangements to be used in the methods of the invention. Typical improvements include more cost efficient apparatuses and methods for removal of anesthetic agents of the VOC type in anesthetic gases, preferably combined with the removal of nitrous oxide when present in this kind of gases. This includes in particular lowering the energy demand for the removal and providing compact apparatus that are service-friendly, cheap and easy to produce and install etc.

DRAWINGS

Figure 1 illustrates the flow-through adsorption unit of multi-adsorbent variants of the inventive apparatuses. All three main flow lines discussed below (main gas flow line, main steam flow line and main drying gas flow line) are present together with an adsorption unit comprising two chambers each of which comprises an adsorbent for anesthetic agents.

Figure 2 illustrates a preferred variant of the invention in which there is a unit for removal of nitrous oxide downstream of the flow-through adsorption unit.

THE INVENTION

The invention focuses on the removal of anesthetic agents by adsorption methods in which the adsorbed anesthetic agents are desorbed so that the adsorbent subsequently can be reused in the process.

The inventor has realized that cost efficient and improved processes of the kind defined above can be designed if anesthetic agents adsorbed by an adsorbent during the process are released from the adsorbent by allowing steam to pass through the adsorbent subsequent to the adsorption. The inventor has also realized that it can be advantageous to pass a stream of a drying gas through the adsorbent subsequent to the desorption but before reuse of the adsorbent.

FIRST MAIN ASPECT (APPARATUS)

This aspect is an apparatus for the removal of a volatile anesthetic agent from a gas stream containing gaseous volatile anesthetic agents together with nitrous oxide. The apparatuses comprise a) a main gas flow line (101) for the gas containing anesthetic agents, and b) a main steam flow line (102), and c) preferably also a main drying gas flow line (103). MAIN GAS FLOW LINE FOR TRANSPORT OF A GAS STREAM CONTAINING AN ANESTHETIC AGENT

The main flow line (101) comprises in downstream direction:

a) an inlet part (104+104a+104b+109+110a+110b+113+115+ 118a),

b) an outlet part (105+105a+105b+lll+112a+112b),

c) an adsortion unit (106) placed between these to parts and containing i) at least one flow- through adsorbent (107a,b) capable of selectively adsorbing

(removing) the anesthetic agent from the gas stream, ii) an upstream end, and iii) a downstream end.

Each adsorbent is typically placed in a flow-through chamber (108a,b) having an upstream and a downstream end (= adsorption chamber). The downstream part

(104a,b) of the inlet part (104) of the main flow line is connected to the upstream end of the unit (106), chamber (108a,b) and adsorbent (107a,b). The upstream part

(105a,b) of the outlet part (105) of the main flow line is connected to the downstream end of the unit (106), chamber (108a,b) and adsorbent (107a,b). A flow of gas passing through a chamber is thus also passing through the adsorbent placed in the chamber.

Adsorption and desorption are carried out as separate steps in the adsorption unit/chambers.

The preferred adsorbents at the priority date of this specification are based on carbon with a particle size of 4 mm (EcoSorb, Jacobi Carbons AB, Kalmar Sweden). Other suitable adsorbents of potential use are described in the references given above.

The term "connected" with respect to how different parts of a flow line are interlinked means, if not otherwise indicated by the context, that the connection permits gas flow communication between connected parts. Normally the term refers to a direct connection but the term includes also that other parts of the flow line may be inserted between two parts that are said to be connected to each other (indirectly connected).

Preferred variants of the apparatus has an adsorption unit (106) which comprises two or more flow-through chambers (108a,b), each of which contains a flow-through adsorbent (107a,b) (= multi-adsorbent variants). In these variants the inlet part of the main gas line comprises

a) a branching arrangement (109),

b) a separate gas flow inlet subline (104a,b) for each chamber (108a,b) going from the branching arrangement (109) to the upstream end of the chamber, and c) a multi-way valve arrangement (HOa+b) associated with the branching

arrangement permitting entrance of the gas stream into at least one (but not all) of said two or more chambers while the other ones of the chambers are closed for entrance of gas.

The branching arrangement (109) typically comprises that the conduit of the incoming main steam flow line is divided into two or more branch conduits (primary branch conduits) at a first position, one or more of these branch conduits may be further divided into branch conduits (secondary branch conduits) at one or more positions etc finally ending in a number of unbranched branch conduits. Everyone of these unbranched branch conduits which end up at the adsorption unit is a gas inlet subline (104a,b) of the kind defined above.

The outlet part of the main gas flow line of multi-adsorbent variants preferably comprises

a) a merging arrangement (111),

b) a separate gas outlet subline (105a,b) for each chamber (108a,b) starting at the downstream end of the chamber and ending in said merging arrangement (111), and

c) preferably also a multi-way valve arrangement (112a+b) associated with the merging arrangement (111) permitting outlet of the gas stream from at least one (but not all) of said two or more chambers while the other ones of the chambers are closed for outlet of gas.

The number of chambers/adsorbents in the adsorption unit is preferably two meaning that the number of branching positions and merging positions in both the branching arrangement and in the merging arrangement, respectively, in this preferred variant typically is one with two gas sublines associated with each of the two arrangements (109 and 111, respectively),. See figure 1.

The multi-way valve arrangements of the main gas. flow line are designed such that both the inlet subline and the outlet subline connected to the same chamber are capable of being opened for flow-through by the valve arrangement(s) when the gas stream is to pass through the chamber. When the gas stream shall not pass through the chamber at least one, preferably both, of the inlet subline and the outlet subline are closed by the valve arrangement(s).

The multi-way valve arrangement of a branching arrangement (109) typically comprises the branching positions and one stop-flow valve function (110a,b) associated with each of the inlet sublines (104a,b) of the arrangement. In the same manner the multi-way valve arrangement of a merging arrangement (111) typically comprises the merging positions and one stop-flow valve function (112a,b) associated with each of the outlet sublines. See figure 1. An alternative is that a multi-way valve is placed at every branching position and/or in every merging position, e.g. a two-way valve if two branch conduits are formed or merged. Combinations of stop-flow valves for certain sublines and multi-way valves for other sublines of the same valve arrangement are also possible.

The inlet part of the main gas flow line (101) typically also comprises a cooling arrangement (113) upstream of the adsorption unit (106) or encompassing the adsorption unit (106). The preferred position is upstream of the branching

arrangement. In the case it is placed downstream of the branching arrangement a separate cooler may be required for each inlet subline (104a,b) or flow-through chamber (108a,b). A temperature sensor (114a,b) is preferably placed in each flow-through

adsorbent/chamber (107a,b/108a,b).

The main gas flow line comprises a flow function (115) for creating or changing (increasing and/or decreasing) the flow of gas through the flow line (101). This function is typically a blower and is preferably adjustable with respect to changing the flow rate downstream of the flow function (115). The term "changing" in this context includes to maintain a preset flow velocity value when there are variations in incoming flow of waste anesthetic gas, e.g. incoming gas typically has a basic flow rate that may change with time and number of patients connected to the apparatuses. Therefore the flow function (115), e.g. speed of the blower, is often controlled by the flow rate of incoming gas and or the sub pressure at the inlet of the flow line. This flow creating/changing function may be placed upstream or downstream of the adsorption unit with preference for upstream. For multi-adsorbent variants the position is preferably upstream of the branching arrangement (109) and/or downstream of the merging arrangement (111).

A sensing arrangement (116,117a,b) may be associated with the adsorbing/desorbing unit (106) permitting real time measurement of the degree of saturation of an adsorbent with respect to uptake of anesthetic agent. This arrangement may comprise one sensing unit (sensor) (117a,b) per adsorbent/chamber or a sensing unit (sensor) (116) common for two or more chambers/adsorbents. The sensing arrangement may be for measuring content of anesthetic agent in

a) the gas stream/main gas flow line downstream of the adsorbent, with preference for downstream of the merging arrangement of the gas main flow line if two or more adsorbing/desorbing chambers are present (116), and/or

b) the adsorbent, for instance by weighing (increase in weight) (a weighing cell for each chamber or adsorbent) (117a,b). The main gas flow line preferably also comprises a 2-way valve arrangement

(118a+b,119a+b) in the upstream part of its inlet part (104) and/or in the downstream part of its outlet part (105), i.e. upstream and/or downstream of the adsorption unit (106). This kind of valve arrangement may be used for diverting flow from or into the main flow line, e.g. as by pass valves and/or as inlet valves for ambient atmosphere. If a cooling arrangement (113) and/or flow creating/changing function (115) are present in the inlet part of the main gas flow line, this kind of valves are typically placed upstream of the cooler and/or the flow creating/changing function. For multi- adsorbent variants the positions are upstream of the branching arrangement and/or downstream of the merging arrangement, respectively. By-passing, for instance, may be from a position upstream of a cooler (113), a flow function (115) and/or the adsorption unit (106) to a position downstream of any of these positions including also a catalytic chamber (see figure 2). The term "2-way valve" includes also other at least 2-way valve arrangements (i.e. other multi-way valve arrangements). An alternative to a cooler (113) is a compressor placed upstream of the adsorption unit and preferably upstream of the branching arrangement (109) (if present).

As illustrated in figure 2 the downstream part (206) of the main gas flow line (201) (figure 1 : 105 and 101, respectively) may be part of or comprise a decomposition arrangement (203) for the catalytic decomposition of nitrous oxide to N ₂ and 0 ₂ . The arrangement (203) contains a decomposition unit in which there is placed a catalyst suitable for this purpose as described in figure 1. The arrangement/unit (203) is placed in the main flow line at a position which is

a) downstream of an arrangement (202) which comprises as illustrated in figure 1 the adsorption unit (106), the inlet sublines (104a,b), the outlet sublines

(105a,b), the possible branching arrangement (109), the possible merging arrangement (111) etc of the main gas flow line (101), and

b) upstream of an outlet arrangement (204) which comprises the most downstream part of the main gas flow line (201).

Each of the main gas flow line (201), the main steam flow line (207) and the optional main drying gas flow line (210) comprises an inlet part (205,208,211, respectively) and an outlet part (206,209,212, respectively) in the same manner as in figure 1. The outlet part (212) of the main drying gas flow line (210) by-passes the decomposition arrangement/unit (203). Further details about the main steam flow line and the main drying gas flow line is give below.

The decomposition arrangement/unit (203) for decomposition of nitrous oxide may be as described in international patent applications WO 2010071538, WO 201 1075033, US SN 61/460,381 (all of Nordic Gas Cleaning AB), EP 2165756, WO 2010010642, WO 201010643 (all of Linde AG) and references cited in these publications and above under back-ground technology.

The arrangement (202), the arrangement (203) and the outlet arrangement (204) in figure 2 of this specification correspond to the inlet arrangement (104,204,304), adsorption unit (105,205,305) and the outlet arrangement (107,207,307), respectively, in figure 1-3 of WO 2010071538 (Nordic Gas Cleaning AB) which is hereby incorporated by refernce in its entirety. MAIN STEAM FLOW LINE

A main characteristic feature of the apparatus is the presence of a main steam flow line (102) which comprises

a) an inlet part (120+120a+120b+123+124a+124b) which in its downstream end is connected to one of the ends of everyone of the at least one adsorbent (107a,b) and chamber (108a,b), and

b) an outlet part (121+121a+121b+125+127a+127b+126+128) which in its upstream end is connected to the other one of the ends of everyone of the at least one adsorbent (107a,b) and chamber (108a,b).

The adsorption unit (106), adsorbent(s) (107a,b) and chamber(s) (108a,b) correspond to a flow line part which is common to both the main gas flow line (101) and the main steam flow line (102).

In preferred variants the downstream end (120a,b) of the inlet part (120) and the upstream end (121a,b) of the outlet part (121) of the steam flow line (102) are preferably connected to the downstream end and upstream end, respectively, of the adsorption unit (106), adsorbent(s) (107a,b) and chamber(s) (108a,b) (where upstream end and downstream end of the adsorption unit, chamber and adsorbent refer to the flow direction of the main gas flow line (101)). In other words the direction of the steam stream through the adsorbent is preferably opposite to the flow direction of the main gas stream (anaesthetic gas). In less preferred variants it is the other way round

The upstream end of the inlet part (120) of the main steam flow line (102) comprises or is connectable to a steam source (122), typically in the form of a steam generator, which is capable of delivering a stream of steam to the main steam flow line. The pressure of steam leaving the steam source has to be sufficient for the steam to pass through the main steam flow line including in particular through the adsorbent(s). In other words the pressure of the steam should be elevated compared to the pressure downstream of the adsorbent(s). This typically means that the pressure of steam leaving the steam source should be at an overpressure relative to ambient atmosphere, e.g. an overpressure > 0.1 bar, such as > 0.25 bar or more preferably > 0.5 bar. The upper limit is typically < 10 bar, such as < 8 bar or < 5 bar or < 3 bar. The steam is preferably water steam. The temperature of the steam when leaving the steam source is typically close to the boiling point of the liquid from which the steam is generated. For water this typically means a temperature of > +95 °C, such as > +100°C or > +120°C with increasing temperature for increasing overpressure, such as up to 160-200°C.

The downstream end of the outlet part (121) of the main steam flow line comprises or is connectable to a condenser arrangement (126) for condensing steam and the anesthetic agents desorbed by steam passing through the adsorbent(s). The condensation in the arrangement typically takes place below a temperature at which the anesthetic agents desorbed and the steam condense. For water steam this typically means that the condenser arrangement provide cooling of the steam to a temperature < +20°C, preferably < +10°C, such as < +5°C. The condenser arrangement may comprise one, two or more condensers, e.g. one condenser per outlet subline or subset of outlet sublines. Each condenser may have a cooling arrangement typically comprising conduits (134) for circulating cooling fluid and a valve arrangement (133) for regulating the flow of cooling fluid. See below.

In multi-adsorbent variants, the steam inlet part (120) of the main steam flow line comprises

a) a branching arrangement (123),

b) a separate steam inlet subline (120a,b) for each of the chambers (108a,b) going from the branching arrangement to the chamber, i.e. two or more steam inlet sublines, and

c) a multi-way valve arrangement (124a+b) of the same kind as for the main gas flow line but adapted to steam (see above).

In less preferred multi-adsorbent variants everyone of the individual steam inlet sublines start at the steam source and end at a separate chamber. The branching arrangement then is integrated with the steam source. The steam source can comprise a separate steam generator for a subset of steam inlet sublines/chambers and another steam generator for another subset of steam sublines/chambers. Typical variants are one separate steam generator for each inlet subline and chamber, or more preferably a common steam generator for all of the sublines and chambers.

The steam outlet part (121) of multi-adsorbent variants typically comprises a) a merging arrangement (125),

b) a separate steam outlet subline (121a,b) for each chamber starting at the chamber and ending at the merging arrangement and being in downstream gas flow communication with the condenser arrangement (126), and

c) preferably also a multi-way valve arrangement (127a+b) of the same kind

(112a+b) as in the outlet part (105) of the main gas flow line (101) (see above).

In a preferred merging arrangement, the conduits of the steam outlet sublines (121a,b) merge to a common conduit for transporting the main steam flow into the condenser arrangement. Alternatives comprise that the merging arrangement is integrated with the condenser arrangement, e.g. the individual outlet sublines are directly connected to a common condenser or to separate condensers, e.g. one for each steam outlet subline.

The steam branching arrangement (123) and the steam merging arrangement (125) of multi-adsorbent variants typically are of the same kind as the branching/merging arrangements described for the main gas flow line (101). See above and figure 1.

The multi-way valve arrangements (127a+b;124a+b) of the steam sublines (120a, b 121a,b) in multi-adsorbent variants typically comprise valve functions as described for the main gas flow line (101) , e.g. one stop-flow valve function

(127a,127b;124a,124) in every subline. See above and figure 1.

In the main steam flow line (102) the number of branching positions and sublines (120a,b) in the inlet part (120) and the number of merging positions and sublines (121a,b) in the outlet part (121) are typically the same as in the main gas flow line (101). This also applies to preferred numbers, i.e. one branching position and two sublines in each part.

The multi-way valve arrangement of the inlet part and the multi-way valve arrangement of the outlet part are controlled such that an inlet steam subline and an outlet steam subline connected to the same adsorbent/chamber are simultaneously opened or closed for allowing steam to pass trough or not to pass through the adsorbent/chamber. This is similar to valve arrangements of the inlet and outlet parts of the main gas flow line.

The multi-way valve arrangements in the inlet and outlet parts of the main gas flow line and of the main steam flow line are functionally interlinked to permit opening and closing of sublines to perform repetitive sequences as outlined for the second aspect of the invention (method).

A phase separating arrangement (128) can be placed in the steam outlet part at a position downstream of the condenser arrangement (126) and permit selective collection of either one or both of liquefied steam, typically a water phase, and the anesthetic agent (in a separate liquid phase). MAIN DRYING GAS FLOW LINE

In preferred variants of the apparatus there is a main flow line for a drying gas (103), e.g. air, to be passed through the at least one adsorbent/chamber after desorption by 5 steam. This main flow line comprises similar to the other main flow lines: a) an inlet part (129+129a+129b+135+136a+136b), b) an outlet part (130a,b) and c) the adsorption unit (106).

The inlet part (129) is in its downstream end connected to one of the ends of the0 adsorption unit (106) and the at least one adsorbent (107a,b) and chamber (108a,b), and the outlet part (130a,b) is in its upstream end connected to the other one of the ends of the adsorption unit (106) and the at least one adsorbent (107a,b) and chamber (108a,b). The adsorption unit, adsorbent(s) and chamber(s) are thus also part of this main flow line (103).

5

In preferred variants the downstream end of the inlet part and the upstream end of the outlet part of this main flow line are preferably connected to the upstream end and downstream end, respectively, of the adsorption unit. In other words the direction of the flow of drying gas through the adsorbent is in this preferred variant the same as the0 direction of the main gas stream and opposite to the flow direction of the steam.

The inlet part of this main flow line (103) comprises in its upstream part (129) a source for drying gas (131) or is connectable to such a source. The source may be ambient atmosphere, a storage tank for compressed gas, e.g. air etc. When ambient air is the5 drying gas the inlet part typically comprises some kind of pump or blower (132) to • initiate a stream of air to pass through this main flow line (103). The source as such or the connection of an external source of drying gas is placed at the upstream end of the inlet part. 0 The outlet part comprises in its downstream end an opening for delivering drying gas having passed through the adsorption unit to ambient atmosphere. This may be via a part which partially coincides with the outlet part of another main flow line, e.g. the main gas flow line. This is illustrated in figure 1 where the outlet part of the drying gas flow line and the part of the outlet part of the gas main flow line which are next to the adsorbent are coinciding.

As discussed above the outlet part (105) of the main gas flow line (101) of the inventive apparatuses may comprise a catalytic chamber for the degradation of nitrous oxide. If the main drying gas flow line and the main gas flow line coincide next downstream to the adsorbent in these variants, there, preferably should be functionality for diverting selectively the drying gas from the gas main flow line to prevent it from passing through the catalytic chamber. For this purpose the outlet part (105a,b/130a,b) of the main gas flow line/main drying gas flow line (101/129) may comprise a branching (137) combined with at least one two-way valve arrangements (138a+139a and 138b+139b) allowing

a) diversion of drying gas into the outlet part (130a,b) of the drying gas main flow line (103) preventing it from passing through the catalytic chamber, and

b) diversion of gas containing nitrous oxide into the main gas flow line for passage through the catalytic chamber. See figure 1.

In multi-adsorbent variants, the inlet part (129) of the main drying gas flow line (103) comprises

a) a branching arrangement (135),

b) a separate drying gas inlet subline (129a,b) for each of the chambers going from the branching arrangement to the chamber, i.e. two or more drying gas inlet sublines, and

c) a multi-way valve arrangement (136a+110a,136b+110b) associated with the branching arrangement and being of the same kind as for the other man flow lines (but adapted to drying gas). See above and figure 1.

The drying gas source (131) can comprise a separate source for a subset of drying gas inlet sublines and another source for another subset of drying gas inlet sublines, e.g. one separate steam generator for each of the drying gas inlet sublines, or more preferably a common source for all of the drying gas inlet sublines. In other multi- adsorbent variants every one of the individual inlet sublines for drying gas start at the drying gas source and end at a separate chamber. The branching arrangement then is integrated with the drying gas source.

The drying gas outlet part of multi-adsorbent variants has been discussed above. See also figures 1 and 2.

The drying gas branching arrangement of multi-adsorbent variants typically are of the same kind as described for the branching arrangement of the main gas flow line and the main steam flow line, i.e. the same preferred branching positions and number of sublines formed at each position, i.e. one branching position with branching into two sublines at this position. See above and figure 1.

The multi-way valve arrangements of the drying gas sublines in multi-adsorbent variants typically comprise valve functions as discussed above for the other main gas flow lines. The preferences typically are the same, i.e. a stop-flow valve in each subline. Se also figure 1.

The multi-way valve arrangement of the main drying gas flow line is functionally interlinked with the multi- way arrangements of the other main flow lines to allow for drying gas to pass through the chambers between a desorption step and an adsorption step as outlined for the second aspect of the invention (method).

The apparatus preferably comprises a control unit for automatic opening and closing of valves and adjusting flow velocities such that a process according to the second aspect of the invention can be carried automatically. The control unit comprises appropriate pressure sensors and sensors for nitrous oxide and unesthetic agents at the appropriate positions along the flow lines. Compare for instance our previous international patent application WO 2010071538 (Nordic Gas Cleaning AB).

Appropriate soft ware for following and controlling process parameters are typically located in a a control block (143).

SECOND MAIN ASPECT (METHOD AND USE OF THE APPARATUS )

This aspect of the invention comprises a method in which an anesthetic agent is adsorbed from a gas stream of an anesthetic gas containing the agent and preferably also nitrous oxide when present in the anesthetic gas. The method comprises the steps of:

i) providing an adsorption unit which comprises a flow-through chamber containing a) an adsorbent capable of adsorbing an anesthetic agent from the gas stream, b) an inlet for the gas stream, and c) an outlet for the gas stream, , ii) passing the gas stream containing the agent through the flow-through chamber under conditions supporting adsorption,

iii) passing a desorbing gas through the flow-through chamber under conditions

supporting desorption to obtain a mixed gas stream containing the desorbing gas and the desorbed anesthetic agent.

iv) optionally condensing the anesthetic agent in the mixture obtained in step (iii). Step (iii) is a regeneration step and comprises also conditioning of the adsorbent for reuse in a subsequent adsorption step (step ii).

The method is characterized in that the desorbing gas is steam, in particular water steam, and that the desorption is carried out within an apparatus as discussed for the first aspect of the invention. In preferred variants of the method the adsorption unit comprises two flow through chambers (1 ^st and 2 ^nd chamber) each of which contains an adsorbent which is capable adsorbing the anesthetic agent. Each of the chambers is then used alternatingly, i.e. one of the chambers is used in step (ii) while the other one is used in step (iii).

Applied to the sequence (i)-(iv) above this means that adsorption/desorption steps (ii) and (iii) are carried out in a repetitive mode, e.g.

a) passing the gas stream containing the anesthetic agent through the first flow- through chamber under adsorption conditions,

b) passing the desorbing gas through the second flow-through chamber under

desorption conditions for releasing the anesthetic agent from the adsorbent, c) repetitively carrying out

A) step (a) on the adsorbent having undergone desorption in the preceding step (b) and

B) step (b) on the adsorbent having undergone adsorption in the preceding step (a). In the case the adsorption unit comprises further chambers and adsorbents, the method can be generalised as outlined for inventive apparatuses containing two or more adsorbents or chambers. Steps (a) and (b) may be carried out in sequence, or preferably essentially simultaneously, i.e. in parallel. This also applies to steps (A) and (B). "Essentially simultaneously" and "in parallel" include that step (b) is allowed to comprise conditioning steps necessary for proper regeneration of the adsorbent and make it ready for reuse in the process, e.g. treatment with drying gas. See further below.

In other preferred variants, the desorption step (iii) and (b) above comprise that a stream of drying gas is passed through the adsorbent subsequent to the desorption of the anesthetic agent from the adsorbent (regeneration step). For preferred multi- adsorbent variants (methods, apparatuses and units), this means that the drying gas is passed through the chamber before a repetitive step (b) or (c) is carried out. Nitrous oxide will remain in the gas stream leaving the adsorption unit. Nitrous oxide is decomposed in the decomposition unit which may be present in the apparatus provided in step (i). Thus the method will comprise a fifth step:

v) decomposing nitrous oxide in the decomposition unit during step (ii) after having passed through the adsorption unit in step (ii).

Step (v) is kept ongoing during at least step (ii) and more preferably also during step (iii), if the adsorption unit is a multi-adsorbent variant as discussed above for the first aspect of the invention. Step (v) is preferably also ongoing while step (iv) is on-going.

The method aspect of the invention also comprises the use of the apparatus of the invention for removing an anaesthetic agent by adsorption and nitrous oxide by catalytical decomposition from a gas stream comprising an anesthetic gas containing both an anaesthetic agent and nitrous oxide. The use in preferred variants means a method comprising the steps (i)-(v) as indicated above. The best mode at the filing date is considered to the variant as described with reference to figures 1 and 2.

EXPERIMENTAL PART

Experiment 1

An air flow: 20 m /h at +8°C with a concentration of anesthetic agent of 5810 ppm and containing nitrous oxide is allowed to pass 10 kg of Ecosorb 4 mm from Jacobo (carbon based) placed in a cylindrical flow-through chamber (cross-sectional area and height of 0.5 m) until break-through. Un uptake of anesthetic agent of up 1580 g are likely to be accomplished which will correspond to a reduction level of 99.5% for the anesthetic agent in the air flow.

Subsequently a flow of 3 kg of water steam at an over pressure of 1 bar is allowed to flow through the adsorbent and desorbs essentially all the adsorbed anesthetic agent via a main steam flow line having an inlet part and an outlet part. After drying the adsorbent by passing air from ambient atmosphere through it, the adsorbent becomes regenerated and ready to be reused in the process.

Experiment 2

Essentially the same as experiment 1 but with a concentration of anesthetic agent of 6000 ppm. The achievable calculated reduction level is up to 99.1% corresponding to an uptake of up to 1700 g.

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.