The present invention relates to a method of pest con­trolling foods, such as f.e. beans and dried mushrooms and a system for carrying out said method.

The method of pest controlling foods according to the invention comprises the steps of providing an inert O₂ lacking atmosphere with O₂ between 0 and 5%, CO₂ bet­ween 1 and 20% and the balance N₂, exposing the food to said atmosphere in a gas tight food storage room and maintaining said atmosphere in the food storage room until the full mortality of the food pest.

It has been noted that by exposing the food pest to said atmosphere a 100% mortality is obtained within 3-35 days depending on the temperature and relative hu­midity of the food storage room.

According to a feature of the present invention the inert atmosphere is heated to a temperature higher than the ambient temperature to reduce the mortality time of the pest and is maintained at that temperature.

At a temperature f.e. of 27°C the mortality time is 10 days, which time lengthens in the case the tempera­ture lowers.

The mortality is total for eggs, larvas, pupas and adults, i.e. for all the different stages of develop­ment of the pest.

The invention includes also a system for carrying out the method.

The system according to the invention is characterized in that it comprises an inert atmosphere generator having two inputs, the one connected to an air intake and the other to a combustion gas intake and a cool­ing tower also provided with two inputs, the one con­nected to the output of the inert atmosphere generator and the other to a cooling water intake, and further provided with two outputs, the one connected to a gas tight food storage room and the other to a cooling water discharge.

The invention will be better understood from the fol­lowing detailed description, given merely as an ex­ample and therefore in no limiting sense, of two em­bodiments thereof, referring to the accompanying drawings, in which:

• Fig. 1 is a diagram of a system for carrying out the method according to the invention; and
• Fig. 2 is a diagram of an alternative embodiment of the system according to the invention.

The difference between the two systems is that in the first one the desired atmosphere is obtained in an open circuit., whereas in the second one it is ob­tained in a closed circuit.

Referring first to Fig. 1, an isothermic generator comprises a combustion chamber 1 provided with two burners, a main burner 8 and a secondary burner 9 connected by means of conduits and valves on the one side to a combustion gas input referred to as A and on the other side, through a fan 10, to an atmospheric air input referred to as B. The output of the combu­stion chamber 1 is connected to the input of a cataly­tic chamber 2 whose output is connected to the input of a cooling tower 3. An output of the cooling tower is connected, through an evaporator 5 and a condenser 6 being part of a refrigeration system 4, as well as through a heat exchanger 7, to the food storage room, not shown, the conduit leading to the storage room be­ing referred to as F.

The cooling tower is also in connection with a cooling water input C, which water is then discharged at E. The combustion chamber 1 and the catalytic chamber 2 are provided with a closed cooling circuit. The water heated in the combustion chamber 1 and the catalytic chamber 2, is supplied, through the pump 15, to the heat exchanger 7 and the heat exchanger 13 to exchange the heat previously absorbed in the combustion chamber 1 and the catalytic chamber 2. This circuit remains at a constant operation pressure in the case of lack of water or coolant supplied through the input C. In the case of overpressures the liquid is discharged in the discharge E through a safety device. D indicates the delivery outwards in the starting stage.

The system comprises finally two modulating valves 11, 12 inserted between the air intake B and an input of the cooling tower 3 controlled by a check or analysis system not shown.

The operation of the described system is as follows:

The combustion gas, propane or methane, or other combu­stible, f.e. gas oil, is taken from bottles or the sup­ly line and caused to flow from A to the burners 8 and 9 at a predetermined pressure. Simultaneously, a pre­determined air quantity is supplied continuously, by an electric fan 10, to the burners 8 and 9 of a special type in which the combustible gas or other combustible is mixed with air and then burnt in the combustion cham­ber 1 without leaving residual combustion products. In this operation air oxygen is lowered from 21% to 0,2 -­0,3%. The combustion products are thereafter cooled, f.e. to 500°C by the cooling jacket of the combustion chamber 1. The inert gas thus obtained is caused to flow through the catalyst 2 where possible unburnt parts are converted to CO₂ and H₂O without pro­ducing residual combustion products.

The gas flowing out from the catalyst is supplied to the cooling tower 3 where it takes the desired tempe­rature. It is then caused to flow in the condition­ing system comprising the evaporator 5 and the conden­ser 6 to control the relative humidity of the produced atmosphere before introducing it in the food storage room. Finally, the gas flows in the heat exchanger 7 where it is moderately heated to shorten the morta­lity time of the pest.

The storage room is suitably provided with an over-­pressure valve to balance the pressures developed upon introduction of the desired atmosphere.

The generator can have a variable flow rate so that once the desired concentrations of O₂, CO₂ and N₂ are achieved, they can be maintained with a reduced flow of the generated atmosphere so as to maintain the food storage room at a pressure f.e. of 1-5 mm column of water and to prevent entry of air from outside with a reduced operating cost.

To this end, once the desired concentration is achie­ved, the main burner 8 is blown out and only the secondary burner 9 is left operative which burns only the quantity of air - combustion gas mixture strictly necessary for maintaining a minimum desired pressure in the storage room.

The modulating valves 11 and 12 have the function to control the supply of combustible gas in dependence on the changes in the oxygen concentration in the inert atmosphere so as to maintain this oxygen con­centration constant.

The generator has a combustion heat recovery device which is used for heating the air of the food storage room undergoing the pest control. This device compri­ses the heat exchanger 13 in which there is caused to flow in closed circuit by the pump 15 the cooling wa­ter of the jackets of the catalytic chamber 2 and the combustion chamber 1 which yealds heat substracted to the two chambers, in the pipe coil of the heat exchan­ger 7, to the inert atmosphere generated by the iso­thermic generator and, in the pipe coil of the heat exchanger 13 directly to the atmosphere of the food storage room.

In Fig. 2 there is shown the diagram of a system ac­cording to the invention operating in a closed cir­cuit.

The system comprises an oxygen converter 20 including a catalytic chamber 21 and a cooling tower 22. The catalytic chamber 21 has an input connected by means of a conduit 23 to a combustion gas source through a fan 24, upstream which a conduit 25 connected to the gas tight food storage room, not shown, is connected to the conduit 23. The cooling tower 22 has a first input connected by means of a conduit 26 to the out­put of the heated catalytic chamber 21 and a second input connected by means of a conduit 27 to a water refrigeration plant.

The cooling tower has a first output connected by means of a conduit 31, through an evaporator 28 and a condenser 29 being part of a refrigeration plant 20, to the food storage room. A discharge conduit 32 col­lects water both from the condenser 29 and the cooling tower 22.

The system of Fig. 2 operates as follows:

Air drawn from the gas tight food storage room enters the catalytic chamber 21, where by means of the in­troduction of a suitable quantity of combustible gas, a reduction of the oxygen at a temperature of 350°C takes place. Assuming that the combustible gas is pro­pane, the following reaction will take place:

C₃ H₈ + 50₂ = 300₂ + 4H₂O

As is seen, from the reaction no CO or unburnt residues result.

The so generated inert atmosphere is supplied to the cooling tower 22 where it is cooled and flows there­after in the evaporator 28 and the condenser 29 where their humidity is controlled and is supplied finally through the conduit 31 to the food storage room.

By this system the CO₂ quantity in each flow through the converter is reduced until the desired asphyctic atmosphere is achieved.

The converter, once the atmosphere of the storage room has been brought to the desired rate, maintains the O₂ at the desired levels, by entering automatically in operation each time the O₂ level exceeds the predeter­mined level. More particularly, an analizer (not shown) analizes the atmosphere of the food storage room and when the oxygen percentage exceeds a predetermined va­lue renders automatically again operative the oxygen converter 20 which, as is seen, operates intermittent­ly.