Method and apparatus for anesthetic gas reclamation with compression stage

A method and apparatus are disclosed for recovering and separating anesthetic gas components from waste anesthetic gases to be purged from a healthcare facility. Prior to a condensation step, a compressor is used to increase the waste anesthetic gas pressure in order to facilitate condensation of anesthetic gas components at higher temperatures and in greater amounts than through condensation at lower pressures. Condensing the anesthetic gas components from the compressed waste anesthetic gas stream is then achieved using conventional condensation systems, which remove anesthetic gases as either liquid condensates or solid frosts. A preferred embodiment of the invention may be used with existing high-flow scavenging or reclamation systems but is more preferably used with low-flow scavenging or reclamation systems, which employ intelligent waste anesthetic gas collection units to minimize the ingress of atmospheric gas when no waste anesthetic gas is to be purged from the healthcare facility.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns the treatment of waste anesthetic gases produced by one or more anesthesia delivery systems of a healthcare or other facility that use inhaled anesthetics for medical, dental, or veterinary purposes. In order to prevent atmospheric pollution, the invention pertains to the removal and reclamation of nitrous oxide, fluoro-ethers, and other halocarbons from a stream of waste anesthetic gases prior to its discharge to the atmosphere. In particular, this invention involves the removal and reclamation of anesthetic gases at elevated pressures, which allows the removal and reclamation process by condensation to be conducted at higher temperatures.

Anesthesia delivery systems in surgical facilities (medical, dental, and veterinary) produce significant quantities of waste anesthetic gases. Currently these gases are collected from the patients' exhalation by a dedicated or shared vacuum system. The healthcare facilities typically employ one or more centrally-located vacuum pumps to collect waste gases from individual anesthetizing locations. These vacuum pumps are usually oversized, because they are designed to collect exhaled anesthetics over a wide range of flow rates. Because these pumps operate continuously, the waste anesthetic gas suction system also entrains large amounts of surrounding room air from the anesthetizing locations, significantly diluting the waste anesthetic gases therein. At the central vacuum pump(s), the gas stream is often admixed with additional room air to further dilute it prior to its ejection from the facility. This dilute waste anesthetic gas/air mixture is typically pumped to a location outside of the surgical facility, where it is vented to the open atmosphere.

The waste anesthetic gases are generally collected at about 20-30° C. with a relative humidity ranging between 10 to 60 percent. The average composition of the waste gases is estimated to be (in volume percent): 25-32 percent oxygen, 60-65 percent nitrogen, 5-10 percent nitrous oxide, and 0.1-0.5 percent volatile halocarbons, including fluoro-ethers, such as isoflurane, desflurane and sevoflurane. The waste anesthetic gas may also contain trace amounts of lubricating oil vapor from the vacuum pumps.

An increasingly significant source of environmental concern, waste anesthetic gas halocarbons (similar in composition to Freon-12® and other refrigerants) have been linked to ozone depletion and to a lesser degree, global warming. The halocarbons used in anesthesia (primarily halogenated methyl ethyl ethers) now represent a significant emissions source, because other industrial and commercial halocarbon emissions have been greatly reduced by legislation and other initiatives in recent years. Although waste anesthetic gas emissions have so far escaped environmental regulation in the United States, legislative initiatives to strictly regulate waste anesthetic gas emissions will likely occur in the near future.

Several techniques have been proposed to treat waste anesthetic gases in an attempt to mitigate the growing problem of waste anesthetic gas emissions. For example, U.S. Pat. No. 4,259,303 describes the treatment of laughing gas with a catalyst, U.S. Pat. No. 5,044,363 describes the adsorption of anesthetic gases by charcoal granules, U.S. Pat. No. 5,759,504 details the destruction of anesthetic gases by heating in the presence of a catalyst, U.S. Pat. No. 5,928,411 discloses absorption of anesthetic gases by a molecular sieve, and U.S. Pat. No. 6,134,914 describes the separation of xenon from exhaled anesthetic gas. A cryogenic method for scrubbing volatile halocarbons from waste anesthetic gas is disclosed by Berry in U.S. Pat. No. 6,729,329, which is incorporated herein by reference.

Another cryogenic waste anesthetic gas condensation system has recently been disclosed by Berry, et al. in co-pending application Ser. No. 11/432,189, entitled “Anesthetic Gas Reclamation System and Method.” This system uses a batch-mode frost fractionation process whereby the temperatures of the individual anesthetic gases are lowered to a point such that they condense and collect as frost on the cooling surfaces of a cold trap/fractionator. This co-pending application, filed on May 11, 2006, is incorporated herein by reference.

FIG. 1illustrates a typical waste anesthetic gas reclamation system10of prior art for a healthcare facility. The system10includes a number of individual anesthetizing stations15A,15B,15C, each having an anesthetizing machine12A,12B,12C which delivers anesthesia to a patient via a mask14A,14B,14C or similar device. Excess anesthetic gases, patients' exhalation, and air are collected at the masks14A,14B,14C by the anesthetizing machines12A,12B,12C and discharged to a common collection manifold16. The waste anesthetic gas collection manifold16is typically hard plumbed into the healthcare facility, and the anesthetizing machines12A,12B,12C are removably connected to the collection manifold16at standard waste anesthetic gas connectors18A,18B,18C, e.g. 19 mm or 30 mm anesthetic connectors. The waste anesthetic gas reclamation system10operates at a vacuum pressure which is generated by one or more central vacuum pumps20. The collected waste gas stream is typically passed through a check valve35to a condenser unit22consisting of one or more heat exchangers. A source of liquid oxygen, or other suitable heat sink, extracts heat from the waste anesthetic stream, condensing the anesthetic gas components. The liquid anesthetic condensate is captured in collection vessel24, and any liquid water condensate is captured in collection vessel23. The remaining gas stream, stripped of waste anesthetic gas components, passes through a receiver26and the vacuum pump(s)20, and it is then exhausted to the atmosphere outside of the healthcare facility through vent46.

The current methods for scavenging waste anesthetic gases from anesthetizing locations15A,15B,15C in healthcare facilities generally involve drawing high flows of room air into the dedicated or shared vacuum collection manifold16to entrain waste anesthetic gases. The collection manifold16may also continuously draw in air through a number of idle anesthetizing machines12A,12B,12C. On average, the collection system manifold16extracts between 20-30 liters of waste anesthetic gas and/or room air per minute at each anesthetizing location15A,15B,15C. For a large hospital having between 20-30 operating rooms, it is estimated that waste anesthetic reclamation system10flow rate ranges between 500-1000 l/min. (14-35 scf/min.).

The advantages of a high-flow dilute waste gas system are that the system easily accommodates a wide range of anesthetic exhaust flows, the system is safer because little anesthetic can escape the system, and the system is more trouble-free because little maintenance is required. However, high-flow systems are energy-intensive, generally requiring large vacuum pumps20in order to maintain sufficient suction at a large number of anesthetizing stations15A,15B,15C. For example, in order to maintain a vacuum of about 200 mm Hg at a flow rate of 1-2cubic feet per minute (cfm) at each anesthetizing station15A,15B,15C, vacuum pumps of 100-200 cfm capacity are not uncommon.

Additionally, a diluted waste anesthetic gas stream is thermally inefficient. Removal of a waste gas component by condensation requires lowering the temperature of the entire flow stream to a point where the partial pressure of the gaseous waste component is equal to or greater than its saturated vapor pressure (at that temperature). Therefore, to cool the large volume of diluted waste anesthetic gas to a temperature below the saturated vapor pressure of its components, a sizeable cooling utility (i.e. a greater quantity of liquid oxygen, liquid nitrogen, etc.) is required. A method and system for increasing the efficacy and efficiency of condensation-type waste anesthetic gas scavenging and reclamation systems are thus desirable.

A low-flow scavenging system provides a more efficient means of waste anesthetic gas recovery through condensation, because a smaller volume of gas has to be cooled to the condensation temperatures of the individual gases. A low flow scavenging method, facilitated by a dynamic waste anesthetic gas collection apparatus, has recently been disclosed by Berry et al. in co-pending application Ser. No. 11/266,966, entitled “Method of Low Flow Anesthetic Gas Scavenging and Dynamic Collection Apparatus Therefor.” This co-pending application, filed on Nov. 4, 2005, is incorporated herein by reference.

Typically, anesthetic gases are highly volatile substances. For a given temperature, they have a higher vapor pressure than the vapor pressure of water and other lower volatile substances. Substances with higher vapor pressures generally require greater cooling to achieve the same or similar condensate recovery as substances with lower vapor pressures. Thus, anesthetic gases need to be cooled to extremely low temperatures, i.e. cryogenic temperatures, in order to recover appreciable amounts of anesthetic as condensate. However, these extremely low temperatures approach, and in many cases, fall below the freeze point of many anesthetics. In such situations, the waste anesthetic gas stream may still contain anesthetic concentrations that could be condensed except for the undesirable freezing of the system.

Pressure, in addition to temperature, can greatly influence condensation. Elevating the pressure of the condensation system is advantageous, because it allows condensation to occur at significantly higher temperatures than would otherwise occur at lower operating pressures. This also avoids the risk and problems associated with freezing of the condensate. For these types of vapor/liquid phase equilibrium systems, the most beneficial thermodynamic characteristic is that pressure has a much larger effect on the dew point of the vapor than the freezing point of the liquid. Thus, the dew point temperature of a typical anesthetic-laden vapor stream increases with increasing pressure while its freezing point temperature stays relatively constant for varying system pressures.

The increased temperature span between the dew point of the vapor and the freeze point of the condensate, due to increases in system pressure, provides greater operational flexibilities for condensation systems. For example, less cryogenic refrigerant is needed to effect the same amount of condensation, because condensation can occur at higher temperatures. Furthermore, if a more complete separation of the anesthetic from the waste gas stream is desired, the system temperature can be lowered while maintaining an elevated pressure. This permits additional anesthetic to be condensed from the vapor phase without the associated risk of condensate freezing. Thus, a strategy may be developed to achieve the optimum separation of anesthetic by simply adjusting the condensation system pressure relative to the condensation system temperature. Of course, the relative refrigeration versus compression costs should also be considered in any cost optimization strategy.

3. Identification of Objects of the Invention

A primary object of the invention is to provide an economical system and method for removing fluoro-ethers, nitrous oxide, and other volatile halocarbons from waste anesthetic gases from a surgical or other healthcare facility before such gases are vented to the atmosphere.

Another object of the invention is to provide an economical system and method for substantially preventing atmospheric venting of fluoro-ethers and other volatile halocarbons of waste anesthetic gas while eliminating the need of prior art catalysts, charcoal granules and heating techniques.

Another object of the invention is to provide a system and method which reclaims and allows re-distillation and/or reuse of a large percentage of the nitrous oxide and/or anesthetic halocarbons used in the facility.

Another object of the invention is to provide an economical system and method which utilizes and enhances existing waste anesthetic gas reclamation systems of healthcare facilities for minimal impact and cost.

Another object of the invention is to provide an economical system and method which utilizes existing liquid oxygen and/or liquid nitrogen storage and delivery systems of healthcare facilities for energy efficiency and minimal impact during the reclamation system installation.

Another object of the invention is to provide an economical system and method for separating various removed nitrous oxide, fluoro-ethers, and other volatile halocarbon components based on their characteristic bubble and dew points.

Another object of the invention is to provide an economical system and method for increasing the efficacy and efficiency of condensation-type waste anesthetic scavenging systems.

Another object of the invention is to provide a flexible system and method for increasing the efficacy and efficiency of condensation-type waste anesthetic scavenging system by operating the system under varying pressures and temperatures.

Other objects, features, and advantages of the invention will be apparent to one skilled in the art from the following specification and drawings.

SUMMARY OF THE INVENTION

The objects identified above, as well as other advantages and features, are preferably embodied in a system and method for the removal of nitrous oxide and volatile halocarbon gas components from waste anesthetic gases using one or more compression stages to elevate the pressure of the waste anesthetic gas stream prior to anesthetic reclamation by condensation. The waste anesthetic gas stream at elevated pressure is cooled in a condenser such that the temperature of the nitrous oxide and other anesthetic halocarbons are lowered to a point where the vapors condense as a removal liquid or collect as frost on the cooling surfaces of the condenser. In other words, to recover the anesthetic components from the effluent gas, the nitrous oxide and halocarbon components in the waste anesthetic gas are compressed and cooled to either condense them into a removable liquid condensate or solidify them onto the cooling coil surfaces of a heat exchanger/condenser. Whether the anesthetic gas components condense as a liquid or deposit as a solid depends on the operational temperature and pressure of the condenser/heat exchanger.

Compression of the waste anesthetic gas to a level above atmospheric pressure is advantageous, because the higher pressure essentially elevates the temperature at which saturation and condensation of the anesthetic gas can occur. Thus, compression of the gas above atmospheric pressure allows the same fraction of anesthetic to be removed by condensation at a higher temperature as would otherwise have occurred by condensation at atmospheric pressure and at a lower temperature. Moreover, a greater fraction of anesthetic may be condensed from the vapor phase as the temperature of the compressed waste anesthetic gas is lowered from this higher temperature. A strategy may be developed to achieve the optimum separation of anesthetic by simply manipulating the condensation system pressure relative to the condensation system temperature. Furthermore, energy and cost saving may be possible when the relative refrigeration versus compression costs are factored into the strategy.

In a preferred embodiment of the invention, a compressor unit consisting of one or more compression stages is located within the waste anesthetic gas scavenger system between the waste anesthetic gas collection unit and the condensation unit. The compressor unit is sized to compress the anesthetic waste gas from the collection unit to a pressure up to 50 psig for subsequent treatment in a condensation system using a refrigerant, i.e. liquid oxygen, liquid nitrogen, etc., supplied by a hospital or other medical, dental, or veterinary facility. In an alternative embodiment, the waste anesthetic gas stream is compressed to pressures well above 50 psig to take advantage of attendant increases in separation efficiency and fractional extraction. However, in this alternative embodiment, a separate refrigerant supply for the condenser is desirable in order to avoid the risk of contaminating the healthcare facility's gas supplies should an internal leak within the condenser occur.

In a preferred embodiment, the compressed waste anesthetic gas is passed through a multi-stage condenser/heat exchanger wherein heat from the waste anesthetic gas stream is exchanged with the liquid refrigerant. In the first condenser stage, any water vapor in the waste anesthetic gas stream is condensed and extracted. In subsequent condenser stages, the temperature of the compressed gas stream is reduced to a point where the partial pressure of each gaseous waste component is equal to or greater than its saturated vapor pressure (at that temperature and elevated pressure). At atmospheric pressure, the anesthetics are extracted from the waste gas into their purified components most efficiently at temperatures near their individual freezing points. However, separation of the anesthetic vapor mixture is achieved at temperatures higher than their individual freezing points when the waste anesthetic gas stream is condensed at elevated pressure. After condensation and extraction of the anesthetic gases into their purified components, the remainder of the anesthetic gas is vented to atmosphere. However, in a preferred embodiment, the waste gas stream is passed through an expansion valve to further cool the gas via the Joule-Thompson effect. This may also induce additional condensation of anesthetic components from the waste gas. More preferably, the waste gas stream is passed through a small turbine, which recovers the potential energy of compression and may induce additional condensation.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 2illustrates a high-flow waste anesthetic gas collection and reclamation system200according to a preferred embodiment of the invention for use in a hospital, surgical, dental, veterinary, or other healthcare facility. The reclamation system200is similar to the previously described prior art waste anesthetic gas reclamation system10ofFIG. 1except for the inclusion of an expansion valve43and one or more compression stages provided by a compressor42. Compressor42is preferably disposed between the waste anesthetic gas collection units15A,15B,15C and the condenser22. Expansion valve43is preferably disposed between the condenser22and the receiver45.

As shown inFIG. 2, excess anesthetic gases, patients' exhalation, and air are collected at masks14A,14B,14C by the anesthetizing machines12A,12B,12C and discharged to a common collection manifold16. The waste anesthetic gas collection manifold16is typically hard plumbed into the healthcare facility, and the anesthetizing machines12A,12B,12C are removably connected to the collection manifold16at standard waste anesthetic gas connectors18A,18B,18C, e.g. 19 mm or 30 mm anesthetic connectors. The waste anesthetic gas collection manifold16operates at a slight vacuum pressure, e.g. 5 cm, which is generated by compressor42. From the collection manifold16, the collected waste anesthetic gases are passed through a check valve35into the first stage of a single stage or multiple stage compressor42.

In a preferred embodiment, the compressor42is sized to compress the anesthetic waste gas from the collection units15A,15B,15C to a pressure up to 50 psig for subsequent treatment in a condensation unit22. Pressures above 50 psig are preferable in order to take advantage of attendant increases in separation efficiency and fractional extraction. Multistage compressors are used to avoid the problems associated with high compression ratios, such as high discharge temperatures and increased mechanical breakdowns. As a result, compressor manufacturers recommend a compression ratio of no more than 10:1, especially for low-temperature applications. Multistage compressors can also be more economical than single stage compressors because of the attendant power cost savings attributable to compression stages having smaller compression ratios. However, the compressor42of system200needs only a single compression stage, because a compression ratio of no more than 10:1 is anticipated.

The condenser22preferably uses a liquid oxygen, liquid nitrogen, or similar refrigerant obtained from the common supply of these liquefied gases normally available at a hospital or other medical, dental, or veterinary facility. If the waste anesthetic gas is compressed above the facility's gas supply pressure (e.g. 50 psig), then contamination of the common refrigerant supply with waste anesthetic is possible should an internal leak occur within the condenser unit22. In an alternative preferred embodiment, the waste anesthetic gas stream is compressed to pressures well above 50 psig to take advantage of the attendant increases in separation efficiency and fractional extraction. For compression above 50 psig, however, a separate supply of liquid oxygen, liquid nitrogen, or similar refrigerant, is recommended in order to avoid the risk of contaminating the common gas supplies of the healthcare facility with waste anesthetic should an internal leak occur within the condenser unit22.

After compression, the waste anesthetic gas flows through a collection vessel or receiver26which allows any liquid condensed due to compression to be removed and separated from the compressed waste anesthetic gas stream. Prior to condensation recovery of the anesthetic components, any water vapor in the gas stream should be removed to prevent freezing of the liquid water condensate in the condenser22. A preferred method to remove water vapor from the waste anesthetic gas stream is to use a first condenser stage222A (FIG. 3), however, alternative water removal processes (not shown) may be employed, such as desiccation, adsorption, filtration, semi-permeable or hydrophobic membranes, etc. These various gas drying methods may be used at any point prior to the condensation of the anesthetic gases, including before the compression stage.

The compressed waste anesthetic gas stream is then cooled in a single or multiple stage condenser22such that the temperature of the nitrous oxide and other anesthetic halocarbons are lowered to a point where the vapors either condense as a removal liquid on the condenser coils236B (FIG. 3) or collect as frost on the condenser coils136(FIG. 4). The temperature and pressure at which the condensation process is conducted controls whether the anesthetic gas components are condensed as a removable liquid or deposited as a frost.

After the anesthetic components are removed through condensation, the remaining waste gas (mainly composed of entrained air) may be vented to the atmosphere46. Preferably, the compressed waste gas is first passed through an expansion valve43and a receiver45prior to atmospheric venting46. The expansion valve43reduces the compressed waste gas to atmospheric pressure and further cools the compressed waste gas via the Joule-Thompson effect. Any additional anesthetic components in the waste gas may be condensed through Joule-Thompson adiabatic expansion. These anesthetic condensates are collected in the receiver45prior to the atmospheric discharge46of the waste gas. More preferably, however, the compressed waste gas is first throttled through a small turbine44(FIG. 5) or similar device and a receiver45prior to atmospheric release46(FIG. 5) in order to capture the potential energy of the compressed waste gas. The captured energy may then be used to power the compressor42or supply other energy requirements of the method and system. Any anesthetic components condensed by expansion of the waste gas in turbine44are likewise collected in the receiver45prior to the atmospheric discharge46of the waste gas.

Moreover, prior to atmospheric discharge, heat integration of the cooled waste gas with streams to be cooled may reduce the overall cooling utility of the method and system. For example, compression of the waste anesthetic gas stream causes the temperature of the gas stream to increase. The cooled waste gas stream to be vented46could be used to cool this compressed waste anesthetic gas stream prior to condensation in order to reduce the overall refrigerant requirement of the heat exchanger/condenser22.

Berry discloses two cryogenic methods for recovering volatile halocarbons from waste anesthetic gas. First, U.S. Pat. No. 6,729,329 discloses the use of liquid oxygen to condense anesthetic gas components into recoverable liquid condensates.FIG. 3generally illustrates the system and method of the '329 patent, which has been modified for an entering compressed waste anesthetic gas stream. Because the dew point temperature of a typical anesthetic-laden vapor stream increases with increasing pressure, this first recovery method is significantly and advantageously affected by the increased pressure of the waste anesthetic gas stream.

A condenser unit22is provided which includes first and second condensers222A and222B. The outlet line221for liquid oxygen from supply tank220is fluidly connected to the condensing coils236B of the second vessel222B. The outlet of condensing coils236B is fluidly connected via flow line225to the inlet of coils236A of first vessel222A. The outlet of coils236A is fluidly connected via flow line227to valve214and flow lines connected thereto (not shown) of the healthcare facility.

A flow line239connects the waste anesthetic gas flow lines from receiver26(FIGS. 2 and 5) of the healthcare facility to an inlet of heat exchanger/condenser222A. The temperature of oxygen flowing at the inlet of the coils236A is controlled thermostatically by valve233such that the temperature of the oxygen supply at valve214is approximately room temperature, i.e. about 25° C. The waste anesthetic gas enters heat exchanger/condenser222A via flow line239at an elevated temperature due to compression. The compressed waste anesthetic gas enters at the top or entrance of heat exchanger/condenser222A and passes downward over coils236A wherein it exchanges heat with the liquid oxygen flowing countercurrently through the coils236A. Water vapor in the compressed waste anesthetic gas condenses to liquid water at a specific temperature (above 0° C.), which is dependent upon the pressure of the compressed waste anesthetic gas stream. The liquid water then falls by gravity to tank23for storage and removal.

The cooled compressed gas near the bottom of vessel222A is conducted via flow line241to the top or entrance of heat exchanger/condenser222B where it is applied at a temperature greater than 0° C. The cooled compressed gas applied to the top of heat exchanger/condenser222B passes over coils236B wherein it exchanges heat with the liquid oxygen flowing countercurrently through the coils236B. The oxygen from flow line221enters the coils236B at a temperature of approximately −150° C. and leaves the coils236B via flow line225at an increased temperature. If necessary, an intermediate bypass valve235may be provided in line221to bring the temperature in line225at the inlet of coils236A to approximately 0° C. The temperature of the compressed waste anesthetic gas from flow line241is lowered while passing over the coils236B such that the halocarbons of the waste gas are liquefied and discharged into a collection tank24. The remainder of the compressed waste gas, i.e., those components which are not harmful to the atmosphere, are vented to the atmosphere via flow line46, throttled through an expansion valve43(FIG. 2) to induce additional anesthetic condensation, throttled through a small turbine44(FIG. 5) to capture the potential energy of the compressed gas, or subjected to further processing by existing catalytic techniques (not shown).

Second, co-pending application Ser. No. 11/432,189, entitled “Anesthetic Gas Reclamation System and Method,” discloses the use of a batch-mode frost fractionation process whereby the temperatures of the individual anesthetic gases are lowered to a point such that they collect as frost on the cooling surfaces of a cold trap/fractionator. The cold trap/fractionator is periodically cycled through a thawing stage, during which the cooling surfaces, caked with frost gas components deposited from the waste anesthetic gas passing thereby, are gently warmed to sequentially separate and collect the trapped components.FIG. 4generally illustrates the system and method of the this co-pending patent application, which has been modified for an entering compressed waste anesthetic gas stream. However, because the freezing point temperature of a typical anesthetic-laden vapor stream remains relatively constant for varying system pressures, this second system and method of waste anesthetic reclamation is not as significantly affected by increases in the pressure of the waste anesthetic gas stream.

As shown inFIG. 4, a condenser unit22consisting of a cold trap/fractionator125is provided with cooling coils136therein. The outlet line121for liquid oxygen from supply tank120is fluidly connected to the condensing coils136of cold trap/fractionator125. The flow of oxygen at the inlet of the coils136is controlled thermostatically by valve133. The existing heat exchanger122, used to warm the liquid oxygen, preferably remains in place fluidly connected in parallel with cold trap/fractionator125between liquid oxygen tank120and oxygen flow line127to warm the oxygen when the cold trap/fractionator125does not keep pace with facility oxygen demand, is operating in its thaw cycle as described below, or is out of service, for maintenance or repair, for example. Valve129normally remains closed when heat exchanger122is not in use. The oxygen from flow line121enters the coils136at a temperature of approximately −150° C. and leaves the coils136at approximately 0° C. Oxygen intended for use by the healthcare facility may be further warmed by a subsequent process or mixed with warmer oxygen effluent from heat exchanger122to reach room temperature or an appropriate temperature. The outlet of coils136is fluidly connected via flow line127to valve114and flow lines connected thereto (not shown) of the healthcare facility.

A flow line139connects the waste anesthetic gas flow lines from receiver26(FIGS. 2 and 5) of the healthcare facility to an inlet131of heat exchanger/condenser125. The temperature of the waste anesthetic gas enters heat exchanger/condenser125via flow line139at an elevated temperature due to compression. The compressed waste anesthetic gas enters at the top or entrance131of heat exchanger/condenser125and passes downward over coils136wherein it exchanges heat with the liquid oxygen flowing countercurrently through the coils136. The waste anesthetic gas leaves the heat exchanger/condenser125through fitting137and is purged to the atmosphere via flow line46.

This countercurrent heat exchanger arrangement results in a temperature gradient where the top of the cold trap/fractionator125is the warmest and where the bottom of the cold trap/fractionator125is the coldest. The upper region160of the cooling coils136of the cold trap/fractionator125cools the compressed waste anesthetic gas to a temperature of approximately −5° C. to extract water vapor as frost on the coils136. The upper middle region162of the cooling coils136next cools the compressed waste anesthetic gas to a temperature of approximately −60° C. which allows sevoflurane to condense and solidify onto the coils136. Next, the lower middle region163extracts nitrous oxide by condensation and solidification at a temperature of approximately −90° C., and finally the lower region164of the cooling coils136extracts isoflurane and desflurane by condensation and solidification onto the coils136at the lowest temperature (between approximately −100° C. and −110° C.). Alternatively, if heat exchanger/condenser125is operated under low pressure (i.e. vacuum pressure), then the anesthetic components may be desublimated/deposited directly onto coils136without first entering a liquid phase. The remainder of the compressed waste anesthetic gas, i.e., those components which are not harmful to the atmosphere, are vented to the atmosphere via flow line46, throttled through an expansion valve43(FIG. 2) to induce additional anesthetic condensation, throttled through a small turbine44(FIG. 5) to capture the potential energy of the compressed gas, or subjected to further processing by existing catalytic techniques.

The cold trap/fractionator125is periodically cycled through a thaw process in order to defrost the cooling coils136. Thawing of coils136is effectuated by reducing or prohibiting the flow of liquid oxygen therethrough by thermostatic control valve133. This allows the cold trap/fractionator125to warm to room temperature through heat transfer with its ambient surroundings. In an alternate embodiment, warmed oxygen from heat exchanger122may be partially or completely directed through the cooling coils136by simultaneously opening valve159and closing valves133,154. In yet a third embodiment, another fluid (not shown) may be directed through cooling coils136to achieve a controlled thaw.

A funnel-shaped hopper157forms the lowest point of heat exchanger/condenser125and preferably drains into a 4-way selector valve158, which in turn is fluidly coupled to anesthetic collection tanks24A,24B and a water collection tank23. As the temperature of the coils136increases above approximately −100° C. during the thawing stage, desflurane (melting point of approximately −108° C. at atmospheric pressure) and isoflurane (melting point of approximately −103° C. at atmospheric pressure) melt from the lower region164of cold trap/fractionator125and collect in the hopper157. Selector valve158is concurrently aligned to allow the liquid desflurane and isoflurane to gravity feed into one of the collection tanks24A,24B. As the cold trap/fractionator continues to warm above −90° C., the trapped nitrous oxide melts from the lower middle region163of cold trap/fractionator125and collects in the hopper157. Selector valve158is concurrently aligned to allow the liquid nitrous oxide to gravity feed into one of the collection tanks24A,24B. As the temperature warms further still above −65° C., sevoflurane (melting point of approximately −67° C. at atmospheric pressure) melts from the upper middle region162of the cooling coils136and collects in the hopper157. Selector valve158is concurrently aligned to allow the liquid sevoflurane to gravity feed into one of the collection tanks24A,24B. Likewise, as the cold trap/fractionator125continues to warm, the water vapor frost will melt above 0° C. from the upper region160and be channeled by selector valve158into the water collection tank23. By this method, the fluoro-ethers are fractionated as they are removed from the waste anesthetic gas.

FIG. 5illustrates a low-flow waste anesthetic gas collection and reclamation system500according to an alternative preferred embodiment of the invention for use in a hospital, surgical, dental, veterinary, or other healthcare facility. The reclamation system500is the same as the previously described reclamation system200ofFIG. 2except for the replacement of expansion valve43with turbine44and the inclusion of intelligent waste anesthetic gas collection units30A,30B,30C located at or near each anesthetizing station15A,15B,15C in the healthcare facility. As disclosed in co-pending application Ser. No. 11/266,966 by Berry, the intelligent waste anesthetic gas collection units30A,30B,30C are preferably fluidly coupled within the individual legs of the collection manifold16near the standard waste anesthetic gas connectors18A,18B,18C. Each intelligent gas collection unit30A,30B,30C includes a collection chamber32A,32B,32C, an exhaust valve34A,34B,34C to selectively isolate the suction of the collection manifold16at the respective anesthetizing station when waste anesthetic gas is not being produced, and associated pressure sensors40A,40B,40C, circuitry, controls, or mechanisms to operate the exhaust valve34A,34B,34C. The collection chambers32A,32B,32C may be rigid, flexible (such as an elastic bag), or a combination of both.

Referring toFIG. 5, waste anesthetic gas enters from the anesthetizing machine12A,12B,12C exhaust into chamber32A,32B,32C through a 19 mm, 30 mm, or similar standard anesthetic waste-gas connector18A,18B,18C. Within the chamber32A,32B,32C is a sensitive pressure sensor40A,40B,40C electrically coupled to a solenoid-operated exhaust valve34A,34B,34C located at the exhaust side of the chamber32A,32B,32C. The pressure measured by pressure sensor40A,40B,40C is the difference between the pressure of chamber32A,32B,32C and the outside (ambient) air pressure. If the pressure within the chamber32A,32B,32C rises to slightly above ambient, the increased pressure is detected by the pressure sensor40A,40B,40C which by control circuitry causes the exhaust valve34A,34B,34C to open. Opening valve34A,34B,34C fluidly connects the chamber32A,32B,32C to the vacuum source in collection manifold16, resulting in a rapid decrease in pressure in chamber32A,32B,32C. As the chamber pressure approaches ambient, the sensor40A,40B,40C detects the pressure drop and causes the exhaust valve34A,34B,34C to close.

The waste anesthetic gas collection manifold16operates at a slight vacuum pressure, e.g. 5 cm, which is generated by compressor42. Therefore, isolating the collection manifold16from entraining room air when no waste anesthetic gas is being produced reduces the average anesthetic scavenging flow by approximately 90 percent and subsequently reduces the necessary capacity of the compressor42, heat exchanger/condenser22, piping, and associated other hardware. For a large hospital having between 20-30 operating rooms, it is estimated that waste anesthetic gas flow rate of 500-1000 l/min with the prior art reclamation system10ofFIG. 1is reduced to 50-100 l/min with the reclamation system500ofFIG. 5. Furthermore, a low-flow scavenging system provides a more efficient means of waste anesthetic gas recovery through condensation, because a smaller volume of gas has to be cooled to the condensation temperatures of the individual anesthetic gases.

From vacuum manifold16, the collected waste gas stream is passed through a check valve35to compressor42. Compressor42has a single compression stage sized to elevate the pressure of the anesthetic waste gas from collection units30A,30B,30C to a pressure above atmospheric pressure for subsequent treatment in a condensation unit22. After compression, the waste anesthetic gas flows through a collection vessel or receiver26which allows any liquid condensed due to compression to be removed and separated from the compressed waste anesthetic gas stream. The compressed waste anesthetic gas stream is then cooled in a multi-stage condenser22such that the temperature of the nitrous oxide and other anesthetic halocarbons are lowered to a point where the vapors condense on the condenser coils236B as a removal liquid (see disclosure with respect toFIG. 3). Alternatively, a single stage cold trap/fractionator125(FIG. 4) could be used to condense and collect the vapors as a frost on condenser coils136(FIG. 4) (see disclosure with respect toFIG. 4). The temperature and pressure at which the condensation process is conducted controls whether the anesthetic gas components are condensed as a removable liquid or deposited as a frost. The liquid anesthetic condensate is captured in a collection container24A,24B and the liquid water condensate is captured in a collection container23.

As previously disclosed, the compressed waste gas is preferably first throttled through a small turbine44or similar device prior to atmospheric release46in order to capture the potential energy of the compressed waste gas. The captured energy may then be used to power the compressor42or supply other energy requirements of the method and system. Reducing the pressure of the compressed work anesthetic gas stream through turbine44may induce additional condensation of anesthetic components. Therefore, receiver45is provided to collect these anesthetic condensate prior to atmospheric discharge46of the remaining waste gas.

The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a means by which to determine quickly from a cursory inspection the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.

While some embodiments of the invention have been illustrated in detail, the invention is not limited to the embodiments shown; modifications and adaptations of the above embodiment may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth herein: