Apparatus for disposal of spent sterilant or biocidal gases

A method and control apparatus for the safe and effective ultimate disposal of spent biocidal gases such as alkylene oxides after their use in a reactor, including hopsital-type gaseous sterilizers, to reduce the concentration of viable organisms present as contaminants in articles treated in the reactor. The disposal is carried out in a manner to prevent air contaminating release of objectionable material into the atmosphere. The process includes the steps of pumping the biocidal gas from the reactor, delivering the gas to a combustion chamber fitted with a flue gas stack, and igniting and burning the gas in the combustion chamber in the presence of and aided by an added auxiliary combustible fuel augmented by a supply of air. Safety devices such as temperature controls and sensors, flame sensors, flash arrestors, and automatic shut off valves minimize potential hazards.

BACKGROUND OF THE INVENTION 
The present invention relates generally to gaseous sterilization and 
biocidal reduction processes of the type in which volatile gases such as 
alkylene oxides, are used as biocidal agents to reduce the concentration 
of viable organisms present as contaminants on and in articles in which 
such presence is objectionable. Gaseous sterilization and biocidal 
reduction with gaseous agents including ethylene oxide and propylene oxide 
are widely accepted techniques specially adapted to the treatment of 
perishable and fragile substances such as agricultural products, 
foodstuffs, pharmaceutical agents and medical and surgical instruments and 
apparatus, including ingredients instruments, devices and apparatus 
treated in hospital-type gaseous sterilizers. 
Alkylene oxides such as ethylene oxide or propylene oxide gases have been 
employed extensively in the sterilization and biocidal reduction of many 
types of materials because of the non-corrosive nature of the gases and 
because the gases are nondestructive with respect to most materials 
including plastics, adhesives, commestibles, drugs, and delicate equipment 
including delicate metallic devices. An additional attractive feature of 
these gases is that they are highly effective biocidal materials at 
ambient temperatures and that they act rapidly. 
However, the use of gases such as alkylene oxides as biocidal or 
sterilizing agents is subject to several objections, for example, a high 
degree of flammability. Additionally, mixtures of the lower alkylene 
oxides such as ethylene oxide and propylene oxide with air, in certain 
proportions, are explosive. In order to reduce or substantially to 
eliminate the hazards indicated, it has been a common practice to dilute 
alkylene oxides with inert gases such as halogenated hydrocarbons or with 
carbon dioxide. A commercially available mixture consists of about 12% by 
weight of ethylene oxide mixed with about 88% by weight of a halogenated 
hydrocarbon such as dichloro difluoro methane (Freon 12) to obviate 
flammability and to prevent formation of an explosive atmosphere. 
The conventional manner in which the biocidal gas system is used is to 
place articles or materials in a reactor tank or chamber and then to 
introduce a predetermined composition of biocidal gas at controlled 
conditions of temperature and pressure. Upon the elapse of a predetermined 
treatment period, the biocidal gas is pumped from the reactor and either 
discarded into the atmosphere; or diluted with water and discarded into 
the sewers or a dry well; or reclaimed for reconstitution and reuse. The 
discharge or release of the spent biocidal gas into the atmosphere, sewers 
or a dry well poses ecological problems. This is also true for biocidal 
gaseous systems which include the halogenated hydrocarbons as diluents. 
Moreover, the presence of such diluents has been found to have a deterent 
effect upon the activity of the biocidal gas itself, so that longer 
treatment periods have been required in order to ensure effective 
reduction in the concentration of viable organisms. 
The aim of the present invention is to obviate the shortcomings of prior 
art compositions and techniques and to provide a process and apparatus 
whereby the spent biocidal gases may be effectively and safely disposed of 
without hazard and without contaminating the ambient atmosphere with these 
gases. 
SUMMARY OF THE INVENTION 
The present invention provides a technique which enables one to dispose of 
the used biocidal gas, without inert diluent, so as to maintain the 
maximum biocidal effect of such sterilant gases. 
In accordance with the practice of the present invention, the practicality 
of using an undiluted biocidal gas such as alkylene oxide is achieved by 
providing an effective and safe method and apparatus whereby the spent 
biocidal gas may then be safely and effectively disposed of without any 
hazard of explosion and without contamination of the ambient atmosphere 
with the biocidal gas. 
An important object of the invention is to provide apparatus and a 
technique whereby spent biocidal gases such as ethylene oxide or propylene 
oxide may be safely and completely burned under carefully controlled 
conditions so as to preclude the hazard of explosion and to obviate 
atmosphere contamination. 
A functional feature of the invention is the provision of a combustion 
chamber in which the biocidal gas removed from the reactor, after use, is 
effectively burned. 
A related feature of the invention is the use of a flare stack which 
surmounts the combustion chamber further to ensure complete combustion of 
the spent biocidal gas. 
Yet another feature of the invention is the use of an auxiliary combustion 
gas as an aid to the effective and complete burning of the biocidal gas 
delivered to the combustion chamber. 
It is a feature of the invention that there is provided an auxiliary air 
input to the combustion chamber further to ensure the complete and 
effective combustion of the biocidal gas. 
An important object of the present invention is to provide a combustion 
system for the dissipation of biocidal gases, in which system any biocidal 
gases discharged into the ambient system are below concentrations 
permissible under anti-pollution legislation, and less than 0.1 kg/hr and 
20 mg/m.sup.3 for ethylene oxide. 
Yet another feature of the invention is the use of an evacuation pump in 
conjunction with a plurality of parallelly connected valves for 
controlling the rate of gas exhaust from the reactor or biocidal treatment 
chamber. 
A related feature of the invention is the use of a positive pump for 
introducing auxiliary air into the combustion chamber to enhance the 
burning of the biocidal gas. 
Still other features of the combustion system of the invention include 
flame sensors in the combustion chamber and flash arrestors in the gas 
input lead lines. 
General features of the invention include automatic controls which are 
keyed to the various sensing mechanisms and responsive to such mechanisms 
to shut off gas input to the combustion chamber in the event that the 
flame should become extinguished or if the internal temperature of the 
combustion chamber should exceed a predetermined critical value. 
A practical feature of the invention is that the entire combustion system 
may be incorporated in new installations or may, alternatively, be 
connected into existing gas sterilization or biocidal reduction systems, 
as a retrofit. 
Other and further objects, advantages, and features of the invention will 
become apparent from a consideration of the specification in conjunction 
with the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The objects and advantages of the invention are achieved by providing, for 
use with a gas sterilization or biocidal reduction system of the type 
utilizing a flammable sterilant gas, a combustion chamber fitted with a 
flue gas stack and sensing and control means for ensuring the proper rate 
of evacuation of biocidal gas from the reactor vessel. Auxiliary gas and 
air supply means are provided for controlling and for ensuring the 
complete combustion of the biocidal gas, even in the presence of 
substantial concentrations of water vapor contained in the biocidal gas. 
The schematic drawing illustrates a preferred embodiment of the invention 
in which the combustion system is connected to a reactor or biocidal 
reduction chamber which may be of conventional form including an access 
door, means for introducing sterilant or biocidal gas into and for removal 
of the sterilant or biocidal gas from the reactor, water vapor input 
lines, pressure gauges, heaters, thermometers and other control and 
sensing mechanisms. Such biocidal reduction systems or sterilizers are 
well known to those skilled in the relevant art and, accordingly, no 
detailed description is included herein. In the conventional, well-known 
procedure for utilizing a gaseous biocidal reduction material such as 
ethylene oxide, the articles to be treated are placed within the chamber 
and sterilization or biocidal reduction is effected by introducing the 
gaseous biocidal agent into the reactor through appropriate pipes and 
control valves. The process may be enhanced through the use of a heat 
exchanger and controls, all as known in the art. 
It has been the practice, heretofore, to discharge the biocidal gas to 
atmosphere or into the sewers after the gas has fulfilled its intended 
role. It is to the avoidance of this indiscriminate contaminating release 
of biocidal gas into the ambient system that the present invention is 
directed. 
Referring now to the drawing, there is shown, for illustrative purposes and 
not in any limiting sense, a sterilization or biocidal reduction chamber 
or reactor 10, a combustion chamber or vessel 20, and a control console 
30. A sterilant gas exhaust line 34 is connected to 10 and 20 for 
delivering gas from the sterilizer 10 to the combustion chamber 20 through 
a series of parallelly arranged control valves 33, 37, 38, 39, 40, and 42. 
Interposed in series in the reactor discharge line 34 are flame arrestors 
46 and 50 for preventing flashback of ignited gas from the combustion 
chamber 20. A pump 56 serves to exhaust the biocidal gas from the reactor 
10 through the exhaust line 34 and its associated valves, flame arrestors, 
and related elements. As indicated, the reactor 10 is provided with a 
sensor 60 responsive to the pressure of the sterilant gas contained in the 
reactor 10. The pressure sensors 48, 60, the control valves 33, 37, 38, 
39, 40, and 42, the flame arrestors 46 and 50, and the vacuum pump 56 are 
each connected by respective leads 48a, 60a, 33a, 38a, 39a, 40a, 42a, 46a, 
50a, and 56a to the console 30. 
Auxiliary combustible gas, from a conventional supply (not shown) is fed 
into the combustion chamber 20 through a gas conduit 70. The rate of 
auxiliary gas introduction is controlled by means of an inline valve 74 
and a pressure sensor 80, each being connected by corresponding lead lines 
74a and 80a to the control console 30. 
In the preferred embodiment of the combustion system illustrated, auxiliary 
combustion-supporting air is introduced into the combustion chamber 20 
through an air supply line 90 connected into the combustion chamber 20 
through a chamber-encircling air ring or channel 92. The air line 90 is 
fitted with a filter 96, a fan 100, and a control valve 104. The fan 100 
and the valve 104 are connected by corresponding lead lines 100a and 104a 
to the control console 30. 
At its upper portion, the flare burner combustion chamber 20 is surmounted 
by a frusto-conical section 110 from which there projects an elongated 
pipe or flue 114. 
Referring now briefly to the interior of the combustion chamber 20, the 
biocidal gas input from the reactor 10 is distributed through a 
manifold-like series of pipes 120 which constitute part of the biocidal 
gas burner 124 of the combustion system. The auxiliary gas is delivered 
into the combustion chamber 20 by means of a series of pipes 130 connected 
to the gas lead line 70. 
The combustion chamber 20 is provided with a pair of flame detectors 140 
and 142 connected to corresponding sensors 146 and 148, the latter being, 
in turn, connected by means of a lead line 150 to the control console 30. 
The operation of the sterilant or biocidal reduction gas combustion system 
will be readily understood with reference to the previous description 
considered in conjunction with the following additional explanatory 
material. In the preferred embodiment of the assembly illustrated, the 
burner 124 is designed for the effective combustion of essentially 100% 
ethylene oxide. In the contemplated use, the biocidal gas is supplied to 
the burner 124 at spaced time intervals of from about 4 to 16 hours by 
evacuation of the retort or reactor 10. Relevant parameters in the design 
criteria for the system shown provide for a maximum gas flow rate of about 
50 cubic meters per hour at a gas temperature of 20.degree. centigrade, a 
pressure of 1043 mbar for a gas having a molecular weight of about 44.1; 
that is, ethylene oxide. 
Biocidal gas, evacuated from the reactor 10 by means of the vacuum pump 56, 
passes through the flame arrestors 46 and 50 and is delivered to the 
burner 124. The sterilent or biocidal reduction gas supply system is 
pressure-dependent. That is, upon starting of the vacuum pump, only the 
control valve 33 is opened and gas is evacuated through control valve 37 
which is manually preset. When pressure sensor 48 senses the reaching of 
80 mbar it operates through lead line 48a and control console 30 to open 
the gas flow control valve 38. Immediately after opening of gas flow 
control valve 38 pressure at the input of the vacuum pump will rise aboue 
80 mbar and the output signal of sensor 48 is reset. 
After a certain time, the pressure at the input of the vacuum pump again 
will reach 80 mbar and pressure sensor 48 will operate through lead line 
48a and control console 30 to open the gas flow control valve 39. 
Immediately after opening of gas flow control valve 39, both 38 and 39 are 
open now, the pressure at the input of the vacuum pump will rise above 80 
mbar and the output signal of sensor 48 is reset. 
In a similar manner as described above, gas flow control valves 40 and 42 
will be opened subsequently. 
The substantive effect of the structure and controls describe is that the 
vacuum pump 56 supplies relatively constant mass flow of biocidal gas to 
the combustion chamber. 
Combustion air input to the combustion chamber 20 is regulated by a fan 100 
and valve 104 to deliver air through a ring channel 92 at the flame front 
of the burner 124. Auxiliary combustible gas input to the combustion 
chamber 20 is controlled and maintained by a pressure control 80, a valve 
74 and pilot burners 130. 
An important feature of the invention is the regulating circuit which 
controls the dosage of the combustion air. At full biocidal gas pressure 
in the retort or reactor 10, as measured by pressure sensor 60 the 
regulating valve 104 in the air supply line 90 is fully open. With 
increased vacuum (drop in the pressure within the reactor 10) the 
regulating valve 104 tends to close until, upon reaching a pressure of 
about 20 mbar, the air valve 104 locks at about 15% open. 
The sterilant or biocidal reduction gas combustion system is provided with 
automatic safety and control mechanisms pertaining both to the ignition 
system and to the evacuation of the reactor 10. 
After predetermined biocidal treatment time is over, the control console 30 
sends a signal along lead line 164 to open valves 160 and 162. Nitrogen 
from nitrogen supply line 166 is supplied to the conduits at input and 
output side of the vacuum pump during a preset time of about 100 seconds. 
The substantial effect of this operation is to purge the biocidal gas 
carrying conduits with nitrogen to ensure that only a non-explosive 
mixture is present in these conduits at the start of the combustion 
system. 
After the nitrogen purge time is over, the ignition system is started 
automatically. Successful ignition of pilot gas will be detected by the 
two flame sensors 140 and 142. Sensing of the flame at the sensors 140 and 
142 terminates the ignition cycle and closes a contact in control console 
30 enabling the starting of the vacuum pump 56, air fan 100 and opening of 
control valve 33, appropriate signals being received through respective 
electrical lead lines 56a, 100a and 33a. Other inert gases, e.g. CO.sub.2 
may be used. 
When the vacuum pump 56 and air fan 100 are operational, the biocidal gas 
is evacuated from the reactor 10 and supplied to combustion chamber 20. 
Upon reaching 80 mbar at the input of the vacuum pump the secondary valves 
38, 39, 40 and 42 are opened subsequently in the manner previously 
described. Upon reaching 20 mbar in the reactor vessel 10, sensed by 
pressure sensor 60, the control console 30 sends signals through the 
appropriate lead lines 33a, 38a, 39a, 40a, 42a, 56a, 74a, 100a to close 
all valves in the vacuum line, to stop the vacuum pump, to close the valve 
in the auxiliary gas line and to shut off the fan 100. 
Several additional safety features are provided in the apparatus described. 
For example, the burner assembly 124 includes a pilot gas pressure control 
80 so that if the pilot gas pressure falls below a predetermined value, an 
alarm horn sounds. Additionally, if the pressure drops below 35 mbar, the 
pressure control 80 feeds a signal to the control console 30 whereupon a 
responsive signal is fed along the line 74a to close the gas valve 74. An 
emergency shutdown procedure is simultaneously activated under which the 
control console 30 sends signals along the lines 33a, 38a, 39a, 40a and 
42a to close the valves 33, 38, 39, 40 and 42 in the vacuum line. 
Additional signals along the lines 56a and 100a turn off the vacuum pump 
56 and the fan 100. 
The flame arrestors 46 and 50 are each provided with temperature sensors. 
If the measured temperature at the flame arrestors rises aabove a 
predetermined maximum level, signals are fed to the control console 30 
along lines 46a and 56a to activate a temperature alarm. Concurrently, the 
emergency shutdown system is activated, completely shutting off the 
combustion furnace and the control valves 33, 38, 39, 40 and 42 regulating 
the gas input to the combustion furnace 20. 
As directed, the apparatus involved in the combustion system utilizes 
control instrumentation, audible and visual alarms, and all necessary 
switches and controls. Such control instrumentation and its proper use are 
well known in the relevant art. Accordingly, no exhaustive treatment is 
provided herein. All circuitry wiring and control elements are designed 
with due regard to safety and simplicity requirements. Again, since the 
controls and related circuitry are well-known to those in the art, no 
detailed description is included herein, or necessary. 
While the present invention has been described with reference to a specific 
arrangement of pumps, valves, sensors, an air supply system and an 
auxiliary gas supply system, and while a particular form of the combustion 
vessel of the invention has been shown and described, it is to be 
understood that the disclosure is directed to a preferred embodiment. 
Various changes and modifications will occur to those skilled in the art, 
and such changes and modifications will occur to those skilled in the art, 
and such changes and modifications may be resorted to without departing 
from the concept of the invention or from the ambit of the following 
claims. All such modifications and variations are deemed to fall within 
the scope of the subject invention.