GB2273047A

GB2273047A - Low oxygen content gas for pest control in grain and bulk foodstuffs

Info

Publication number: GB2273047A
Application number: GB9224635A
Authority: GB
Inventors: Alan Peach; Baseer Sami
Original assignee: Aerogen Co Ltd
Current assignee: Aerogen Co Ltd
Priority date: 1992-11-24
Filing date: 1992-11-24
Publication date: 1994-06-08
Also published as: GB9224635D0

Abstract

In a method and apparatus for producing a low-oxygen content gas for pest control in foodstuffs, a fuel is burned in a burner (12) to produce a low oxygen content exhaust gas which contains water vapour. The exhaust gas is cooled to liquefy the water vapour content of the exhaust gas. This is achieved by passing the exhaust gas either over a cooling part (24) of a refrigerator system (20) or through a heat exchanges (38, 40; see figure 2) supplied with circulating fluid which has been cooled by the cooling part (24). The refrigeration system, which preferably comprises an absorption chiller 1 is driven by heat generated during formation of the combustion products, thereby improving the efficiency of the system. The low oxygen content gas renders pests inactive by oxygen starvation and/or asphyxiation. The reduction of the water content of the exhaust gas prevents subsequent condensation and damage to the foodstuff. <IMAGE>

Description

DESCRIPTION PEST CONTROL IN GRAIN AND BULK FOODSTUFFS The present invention relates to the production of a low oxygen content gas for use in pest control in grain and other bulk foodstuffs (hereinafter referred to as the "product".

It has been common practice in the past to protect grain and other bulk foodstuffs (product) by the use of pesticides. However, more recently, the immediate dangers and long-term damage that can arise from the use of some pesticides has resulted in the search for alternative methods of protection for such product. One method which is now used is to subject the product to a controlled atmosphere having relatively inert characteristics and a low oxygen content so that pests in the product, such as weevils, beetles and other living organisms, are killed or at least rendered inactive by oxygen starvation and/or asphyxiation.

The modified inert atmosphere that is used in the latter technique is usually produced by burning a gaseous hydrocarbon fuel, such as butane, propane,or natural gas, with air to produce a mixture of nitrogen, carbon dioxide, water vapour and a small amount of remanent oxygen ( < 2% by vol). It is necessary for these combustion products to be cooled before they can be used so as to eliminate as far as possible the entrained moisture. If this is not done, then when the temperature of the gas falls below the dew point of the water vapour, water liquefies from the gas and can damage the product. the known technique for removing moisture from the hot gas is to subject it to refrigeration prior to its application to the product.This has been achieved by the use of a conventional free-standing refrigerator plant disposed downstream of a dry air intercooler and a direct-contact water spray.

It is an object of the present invention to provide an improvement to the known apparatus wherein the performance and efficiency in the production of cooled inert gas is improved.

In accordance with the present invention in its broadest aspect, cooling of the combustion products is achieved by a refrigeration system whose driving energy is derived from heat generated during the formation of the combustion products.

In accordance with one aspect of the invention there is provided an apparatus for producing a lowoxygen content gas for use in pest control, comprising a burner for producing a low-oxygen content exhaust gas and a refrigeration system for cooling the exhaust gas, the refrigeration system being driven by heat generated at the burner.

The refrigeration system extracts the necessary heat from the exhaust gas to reduce the temperature of the water vapour content of the exhaust gas in order to liquefy the water vapour.

The invention also provides a method of producing a low-oxygen content gas for use in pest control, comprising burning a mixture of fuel and air to produce a low-oxygen content exhaust gas containing water vapour, using heat from the burner combustion products to drive a refrigeration apparatus, and passing the exhaust gas over a cooling part of the refrigeration apparatus to liquefy the water vapour content of the exhaust gas.

Preferably, the refrigeration system comprises an absorption chiller, for example an ammonia absorption chiller. Such a chiller comprises a boiler part, a condenser part, an absorber part and an evaporator part. In a preferred arrangement, the boiler part is heated by the burner combustion products and the evaporator part is disposed in a chamber through which the exhaust gas is passed, the evaporator part being arranged to extract heat from the combustion gas during its passage through the latter chamber sufficient to lower the temperature of the water vapour content of the exhaust gas below its dew point.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Fig.l illustrates diagrammatically a first embodiment of an apparatus in accordance with the invention; and Fig.2 illustrates diagrammatically a second embodiment of an apparatus in accordance with the invention.

Referring to Fig.l, box 10 represents a combustion generator in which a combustible gas mixture is established. The combustible mixture is preferably propane, butane or natural gas mixed with air in a venturi mixer. The combustible mixture is fed to a burner 12 disposed within a surrounding combustion chamber 14. Also disposed within the combustion chamber so as to be heated by the combustion products 16 is a boiler 18 forming the heater part of an absorption chiller system, indicated generally by the reference numeral 20. The top end of the boiler 18 is connected to the condenser of the absorption chiller system, indicated diagrammatically at 22 and the lower end is connected to an absorber of the system, indicated diagrammatically at 23.The condenser 22 and absorber 23 are in turn connected to the upper and lower ends of an evaporator coil 24 forming the fourth principal component of the absorption chiller system. The evaporator coil 24 is disposed within a chamber 26 which receives the combustion products from the combustion chamber 14 via pipework 28. The lower end of the evaporator coil 24 is connected back to the lower end of the boiler 18 by way of pipework 30 and absorber 23. The bottom of the evaporator chamber 26 contains an outlet duct 32 from which cooled products of combustion can be extracted by means of a supply blower 33 and led to the storage facility containing the product, such as grain or other bulk foodstuff, to be protected. The condensed water from the evaporator chamber 26 is expelled by means of a water drain trap 34.

The detailed operation of absorption chiller systems is well known in principle and will not be described in detail herein. A refrigerant liquid, preferably an "environmentally friendly" type such as ammonia, is contained in liquid form in the boiler 18.

Waste heat from the combustion of the gases supplied by the combustion generator 10 and burnt in the burner 12 is used to heat the ammonia in the boiler so that it vapourises and passes out of the top of the boiler to the condenser 22 where it cools and liquefies. The resulting refrigerant passes on to the evaporator where it extracts heat from the combustion products flowing over the coil 24 and then returns via the pipework 30 and absorber 23 to the boiler. The heat extracted from the combustion products by this process is sufficient to lower the temperature of the water vapour content of the combustion products below the dew point so that the water vapour liquefies and collects in the lower part of the evaporator chamber 26, from where it can be drained via a suitable outlet such as a water drain trap 34.

The principal feature to note is that the energy to effect cooling of the combustion products in the evaporator 26 is generated by the waste heat from the combustion of the gases in the burner 12. This results in a particularly efficient process since no extra energy has to be provided to achieve the necessary cooling of the water vapour component of the combustion gases to a temperature below its dew point.

The second embodiment, illustrated in Fig.2, is generally similar to the first embodiment, and similar items have been given the same reference numerals.

The main difference is that in the first embodiment the combustion products pass directly over an evaporating coil 24 and are thereby cooled, whereas in the second embodiment the evaporator coil 24 is used to cool a fluid which is in turn passed through further cooling coils over which the combustion products pass.

More specifically, the evaporating coil 24 within the cooling chamber 26 is surrounded by water which is circulated through the chamber by means of a pump 36.

The cooled water is pumped through a two-stage heat exchanger 38,40 and the combustion products are passed over the heat exchanging coils 42 in the heat exchanger, thereby cooling the combustion products and reducing the temperature of any water vapour to below its dew point so that the water vapour liquefies. The water collects in the lower part of each of the heat exchanger stages 38,40, from where it can be drained by means of suitable articles, such as water drain traps 44.

The apparatus also optionally includes a second burner 12' which is fed with a fuel/air mixture via an inlet 46 from a combustion generator. The provision of a second burner helps to produce a thermal balance relative to changing ambient temperatures, increases the capacity of the apparatus and allows the cooling system to operate at its rated capacity.

Claims

1. An apparatus for producing a low-oxygen content gas for use in pest control, comprising a burner for producing a low-oxygen content exhaust gas and a refrigeration system for cooling the exhaust gas, the refrigeration system being driven by heat generated at the burner.

2. An apparatus as claimed in claim 1, wherein the refrigeration system comprises an absorption chiller.

3. An apparatus as claimed in claim 2, wherein a boiler part of the absorption chiller is heated by the burner combustion products.

4. An apparatus as claimed in claim 2 or claim 3, wherein the exhaust gas is passed over an evaporator part of the absorption chiller.

5. An apparatus as claimed in any of claims 1 to 3, wherein the refrigeration system comprises a heat exchanger through which the exhaust gas is passed, the heat exchanger being supplied with circulating fluid which is cooled by means of heat generated at the burner.

6. An apparatus as claimed in claim 5, wherein the circulating fluid is cooled by an evaporator part of an absorption chiller which is driven by heat generated at the burner.

7. A method of producing a low-oxygen content gas for use in pest control, comprising burning a mixture of fuel and air to produce a low-oxygen content gas containing water vapour, using heat from the burner combustion products to drive a refrigeration apparatus and passing the exhaust gas over a cooling part of the refrigeration apparatus to liquefy the water vapour content of the exhaust gas.

8. A method as claimed in claim 7, wherein the refrigeration apparatus comprises an absorption chiller.

9. A method as claimed in claim 8, wherein a boiler part of the absorption chiller is heated by the burner combustion products.

10. A method as claimed in claim 8 or claim 9, wherein the burner combustion products are passed over an evaporator part of the absorption chiller.

11. A method as claimed in any of claims 7 to 9, wherein the burner combustion products are passed through a heat exchanger which is supplied with circulating fluid which has been cooled by means of heat generated during burning.

12. A method as claimed in claim 11, wherein the circulating fluid is cooled by an evaporator part of an absorption chiller which is driven by heat generated at the burner.

13. An apparatus for producing a low-oxygen content gas for use in pest control, substantially as herein described, with reference to and as illustrated in Fig.l or Fig.2 of the accompanying drawings.

14. A method for producing a low-oxygen content gas for use in pest control, substantially as herein described, with reference to and as illustrated in Fig.1 or Fig.2 of the accompanying drawings.