AU764491B2 - Ripening gas delivery controller - Google Patents

Description

P/00/009 28/5/9 1 Regulation 3.2 Australia Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT RIPENING GAS DELIVERY CONTROLLER The following statement is a full description of this invention, including the best method of employing it known to me.

2 Invention Title: RIPENING GAS DELIVERY CONTROLLER

DESCRIPTION

The invention is described in the following statement: The present invention relates to the controlled delivery of applied ethylene or acetylene gas into fruit ripening or degreening rooms, both in refrigerated and non-refrigerated static land-based storage situations or in sea freight or road freight containers while in transit or any similar defined space employed for the purpose of such treatment of fruits or selected vegetables. The present invention includes means to achieve accurate control over and maintenance of the level of ripening gas within the space involved, irrespective of the natural leakage rate of that space, through a detection/feed-back mechanism to continuously control the release of the gas into that *Oo O S: space, including means to do so such that built-in safety checks will eliminate the risk of operator fault or equipment malfunction enabling the build up of these explosive gases to levels 15 at which an explosion could occur, means to actually measure the leakage rate of the space concerned, and also means to automatically control the accumulation of respired carbon dioxide from the produce within the same such rooms so that attainment of levels which retard the efficacy of the ripening gas do not occur.

Ripening is a term used to collectively describe the physiological changes which most fruit go through just prior to reaching a stage at which consumers regard them as ready to eat. During ripening the fruit often change their colour, starch is converted into sugar, the astringent flavours often characteristic of green fruit disappear, the pulp softens and both the flavour and texture of the fruit improve. Some fruits such as bananas and pears display all these characteristics when they ripen. A few, however, such as citrus, primarily show just a change in colour. Other small physiological and quality changes do occur with citrus but they are not readily obvious to the consumer. Effectively the skin or rind of this fruit changes colour but with virtually no change in sweetness or flavour. In these cases the process is more often called degreening rather than ripening, particularly by commercial traders.

On a plant, ripening of the fruit is initiated by ethylene gas which is a natural plant hormone produced by all fruit and vegetables. Treating harvested produce with ethylene also initiates the ripening process. This is often done commercially for a number of fruit. The aim of commercial ripening of fruit is to provide consumers with a product which has not only a good shelf-life but also excellent and consistent appearance and eating quality, and to have it available when and where required. People in many countries have come to use various methods to promote the ripening of fruit. Some of the methods used have included: a. mixing ripe and unripe product; b. exposing fruit to smoke; c. burning joss sticks in a room containing; d. packing fruit in holes underground either with or without other added plant material such as leaves; e. heating fruit in a room using kerosene heaters; f packing fruit with calcium carbide; g. exposing fruit to acetylene gas from cylinders; h. treating fruit with the chemical ethrel; and i. exposing fruit to coal gas *o In all of these methods, except and the causal agent is still ethylene. In the case of :i calcium carbide the causal agent is the chemically related gas acetylene, produced when the carbide reacts with water in the storage atmosphere and chemically breaks down, a gas which is also available in pure form compressed in cylinders from which it can be dispensed directly into a ripening space. Acetylene produces the same response in the fruit as ethylene however it is much less effective and it is necessary for much higher concentrations to be employed to obtain equivalent effects thus greatly increasing the risk of explosive levels accidentally being allowed to accumulate. In developed countries commercial ripening is usually initiated using ethylene with acetylene sometimes being employed in developing countries due to its availability and because of its lower cost.

To achieve maximum quality in ripened or degreened product, the process must be carried out under carefully controlled conditions of temperature, humidity, and ethylene and carbon dioxide levels. Commercial fruit ripening facilities are designed and operated to achieve as much control over these factors as possible in order to achieve predictable and reproducible product out-turns. Of these parameters, the three most critical in terms of the efficacy and consistency of commercial ripening results are the temperature (at which the ripening occurs), the concentration of ethylene (or acetylene) employed and the level of carbon dioxide (emitted by ripening fruit) allowed to accumulate within the room. For a long time, commercial ripeners have had appropriate means available to control the temperature at which ripening is carried out.

However this has not been the case for carbon dioxide or for the ripening gas itself The level of carbon dioxide is generally arbitrarily and inaccurately controlled by periodically venting the room during the ripening process by opening a door and allowing the accumulated carbon dioxide to escape.

In most commercial ripening facility, ethylene is used as the ripening gas and is generally applied in one of two ways, one known as the "shot" method and the other as the "trickle" method. The "shot" method involves injecting a sufficient volume of ethylene into a ripening room to bring the room to the level or concentration of ethylene that may be desired. The 15 "trickle" method on the other hand, involves the continuous slow release of ethylene into a S"ripening room while at the same time maintaining a controlled rate of introduction of fresh air.

Both methods require careful mathematical calculations to establish how much ripening gas to apply for a particular room size to achieve the concentration desired. Both also require careful control of the delivery systems available to ensure the actual volume calculated as being required is actually delivered.

However all ripening rooms leak to some extent in that room air slowly exchanges with external air through small gaps in the room, usually around the door seals. This is not a major problem when the "trickle" ripening system is employed as the method is essentially one where a high controlled leakage rate of fresh air is deliberately employed. But it is a major problem for the "shot" method of application, the primary method employed in commercial practice, as leakage causes the level of ethylene applied to a room to fall relatively quickly. The "shot" method of application ensures a ripening room quickly comes to the level of ethylene intended (provided no calculation or delivery mistakes are made). However because of the natural leakage of the room, this level is not maintained, but falls gradually with time as fresh air exchange occurs through leaks within the room. Thus the stored product is subsequently being treated with a continuously changing level of the ripening gas being employed, with that rate of change, and hence the level actually being applied to fruit, being heavily dependent on the actual leakage rate of the room.

In the "shot" method, the level of natural leakage is usually insufficient to prevent an accumulation of carbon dioxide in the room as a result of product respiration. If the level of this gas reaches significant proportions, generally accepted as being about then it is recognized that such a level will interfere with the ripening process to a significant extent and also with the actual efficacy of the ethylene that is present. This is usually overcome in practice by ensuring a ripening room using this method is normally opened for 1-2 hours every 24 hours to allow fresh air exchange and the accumulated carbon dioxide to escape. It is also not uncommon for rooms using such a technique to be given another "shot" of ethylene after ventilation to return it again to the desired level of ripening gas. In the "trickle" method however, the controlled rate of introduction of fresh air is adjusted to ensure that the carbon dioxide level within the room never reaches above a predetermined desired level.

S" The shot" method is simple, but it does give this variable level of ethylene within the room Se 15 over time. Thus not only are there opportunities for error in calculating the amounts of ripening gas required and errors or variability in actually operating the available delivery systems thus enhancing the risks of explosions occurring, but also product out-turn quality is also variable and unpredictable due to the relatively variable leakage rates that occur from one room to another. In addition the method usually requires periodic ventilation of the room and the application of an additional dose of ethylene thus providing further opportunities for errors by the operator and variability in room ethylene levels and thus further increasing the difficulty of achieving consistent, predictable ripening results. The "trickle" method on the other hand, while it does accurately provide a constant level of ethylene and prevent carbon dioxide build up, it is more difficult to accurately calibrate such a room to the particular level of ethylene that may be required as the process is very dependent on the skill of the operator in measuring the "artificially high leakage rate" of the room, accurately completing the mathematical calculations that are then required and subsequently managing the operation of a delivery system to deliver the amount of ripening gas calculated as being necessary.

Since both ethylene and acetylene are explosive gases, a safety factor also comes into play particularly in employing the "shot" method. The Critical Explosive Concentrations for these ripening gases are: Ethylene 2.75% to 28.6% in air Acetylene 2.50% to 80.0% in air Atmospheres within these limits will explode, if ignited by sparking electrical equipment.

Hence the persons responsible for applying these gases need to be well trained and fully capable of operating the gas supply systems and predicting the levels of ethylene (or acetylene) needed.

Any significant error on their part can result in an explosion with potential loss of life.

It is not uncommon at present for the "shot" method of application to be automated using equipment designed to automatically inject a known, volumetrically measured amount of ethylene into a room at regular intervals. Such a system does remove some of the variability resulting from operator error and does also provide some compensation for leakage rate.

However the level in such a room will still regularly vary between an upper, set limit determined by the quantity actually injected into the room and the time delay between injections and a lower Slimit determined by the actual leakage rate of the particular room and again by the time delay S: between injections. Such automated systems do occasionally include regular, timed, operation 15 of ventilation ports as a means of maintaining some control over the accumulation of carbon S. dioxide thus removing the need to periodically open the room to allow fresh air exchange.

The present invention consists of a method for improving the efficacy of fruit ripening rooms by giving the room operator a simple procedure for selecting the level of gas required (thus 20 avoiding calculation errors), precise and repeatable control of the levels of ripening gas used, and elimination of any possibility of potentially dangerous explosive levels accidentally occurring through operator error or equipment malfunction. In addition it provides an accurate means for a ripening room operator to establish the actual leakage rate of a room being used and thus to take corrective measures to reduce unnecessary wastage of ripening gas. The invention also gives the room operator precise control of the level of carbon dioxide by automatically opening ventilating ports if the concentration rises above a predetermined level selectable by the room operator.

Essentially the invention is a method for achieving enhanced control over the commercial ripening and degreening of fruit and improved operational safety to operators through precise, direct and continuous control over gas concentrations within a ripening/degreening room, automatic control and management of the means for delivering the gas into the rooms, automatic monitoring and display of ripening gas levels within a room, direct and rapid detection of 15 o 2 excessively leaky rooms and rooms and continuous monitoring to detect failure of components within the control system or errors by ripening room operators combined with means for the initiation of failure alarms when necessary and involving: a. Direct monitoring of the concentration of the level of ripening gas within a room through the use of a calibrated sensor and use of the out-put of the calibrated sensor to establish when the room concentration is at or falls below the desired set point (due to room leakage) so as to cause the closure or opening of a gas dispensing solenoid thus stopping or starting the delivery of ripening gas into the room providing automatic and immediate adjustment of the level of the ripening gas within the room; b. Setting and storage of the desired gas room concentration set point for the ripening gas within a microprocessor operated control unit mounted external to the room; c. Use of the microprocessor to interpret sensor out-puts, automate the operation of the gas delivery system and alarms and to control an external visual display of actual gas concentration within the room; d. Controlling the delivery of gas to a room by the activation of one or more solenoid valves within an external gas delivery system and the rate at which that delivery system dispenses gas by the use of a restrictor within the ripening gas delivery line that has an orifice dimension such that, in combination with a regulated supply line pressure, over-shoot of the room set point does not occur or is minimized, irrespective of the room volume; e. Automatic calculation of room leakage rate from time data established while bringing the room to and maintaining it at a predefined set point and display of the room leakage rate on demand on a visual display array; f Automatically monitoring the carbon dioxide level within the room using a carbon dioxide specific sensor and automatic activation of air vents within the room, as a result of feedback from the sensor, to allow the infusion of fresh air as required so as to maintain the carbon dioxide level at a predefined set point; g. Automatic detection of any equipment malfunction or failures in the room control process which may result in safety being compromised followed by an immediate cessation of gas delivery until such time as the malfunction is corrected plus the simultaneous automatic display of appropriate alarms to indicate a malfunction has occurred; and h. Automatic regular monitoring and recording of sensor out-puts to facilitate correlation of product out-put quality with variations in the ripening room environment.

The method also includes means to prevent accidental delivery of ripening gas, through failure of control unit components or actions by the room operator, thus ensuring that critical explosive limits cannot be reached. It also includes means to alert room operators if safety over-ride action has been activated as well as means to provide a room operator with a direct and continuous readout of the concentration of ripening gas within a room thus further contributing to operational safety by enabling direct operator monitoring of the level of gas within a room.

The safety features incorporated into the ethylene controller are capable of detecting the S"following fault conditions and of automatically initiating cutoff of the gas supply to the ripening 15 room and the activation of a remote audible and/or visible alarm. They include tests to detect: 1. Loss of integrity in the communication signal between the remote sensor head and the controller; 2. Failure of the microprocessor in the sensor head; 3. Ethylene concentration in the ripening room reaching or exceeding 250 ppm; 4. No increase in the ethylene concentration in the ripening room after a programmable time interval of "solenoid on-time" has elapsed; No decrease in the ethylene concentration in the ripening room after a programmable time interval of "solenoid off- time" has elapsed; 6. A short-circuit or open-circuit condition occurring in the ethylene sensor itself.

These safety features thus come into play if the sensor itself malfunctions or if the system does not obtain an expected result once having initiated a specific response to the sensor readings.

Thus the operation of the system will be automatically shut down should the sensor itself fail or 9 should an expected response not occur due to a failure within electronics within the control system itself or due to ripening gas delivery not being accomplished through supply cylinders becoming exhausted, or a malfunction within the controlled delivery equipment itself or an accidental external disruption of the gas supply lines.

In its simplest form, the method employs a feed-back controlled gas solenoid valve to control the release of gas from a compressed cylinder through a needle valve or fixed dimension restrictor into the ripening space. However in addition to the above safety features, one version of the ripening gas delivery sub-system is designed to be constructed incorporating two gas solenoids which are connected in series with each other but with a volumetric loop between them. In this configuration, the programming of the controller is such that the two valves are never activated open) at the same time, thus eliminating any direct connection between the ethylene supply cylinder and the ripening room while injecting an amount of gas equivalent to Sgo the volume of the loop each time they operate. Another version of the gas delivery system 15 involves the use of an intermediate supply cylinder which is filled with ripening gas through the manual operation of a three way valve, which connects the intermediate cylinder to a main S supply cylinder, and which is then subsequently closed before the operation of the ripening controller is allowed to commence actual delivery from the intermediate cylinder into the ripening room. The intermediate supply cylinder is of a selected volume such that it is incapable of delivering sufficient gas into the room to cause an explosion should all the gas it contains be accidentally delivered through an equipment malfunction. Both these versions are variations to the preferred delivery system and have been designed in order to accommodate any out-dated Government safety regulations that may exist which were designed to limit operator error when using earlier more imprecise commercial practices.

By having the delivery of the gas under microprocessor control which in turn is responding directly to gas sensor out-puts means the microprocessor can also be used to establish the time necessary to initially attain the desired set point, the time that elapses before the room concentration falls below the desired set point and the time for which the dispensing system must again operate to return the room concentration to the desired set point. Using such data it is possible to calculate the room leakage rate without knowing the size of the room or the rate of delivery of the ripening gas into the room. This is done by employing the following mathematical relationship: Leakage Rate (Room vol/day) (t l x 60 x 24)/(to x t 2 where to is the time to initially reach the room set point, t 2 is the average time taken for the gas concentration to reduce through leakage to a point that the sensor detects a departure of the room concentration from the set point and t 1 is the average time the delivery system is in operation to restore the original set point.

The total system thus provides the means to accurately deliver and automatically control the level of ripening gas employed within a ripening room, automatically prevent the accumulation of carbon dioxide to levels that might interfere with the fruit ripening process and to automatically prevent the development of potentially explosive situations within fruit ripening rooms. The total system would be equally applicable to other enclosed storage environments in which ripening may need to be initiated such as shipping containers and road transportable containers.

o9 For commercial situations, the sensor employed can be a non-specific sensor such as a TGS 822 S 15 gas sensor. While such a sensor will respond to other volatiles within the ripening room environment, the levels of such interfering volatiles e.g. fruit volatiles, are very low so that the sensor response is primarily a reflection of the added ripening gas within the room. Such a sensor can provide sufficient accuracy for commercial purposes to enable the concentration of the ripening gas to be maintained within sufficiently small tolerances to ensure both out-put of consistent product quality out-put and operator safety.

9...i The method also includes the means to simultaneously deploy one or more additional detectors within the ripening facility and to detect which specific detectors have actually been deployed within a particular configuration of the invention. Thus it is possible, using in-built program control housed within a microprocessor, to allow out-puts from selected detectors to be ignored if any specific response these detectors would trigger is not required for the particular product with which or the circumstances in which the invention is to be employed.

The form of this invention in actual commercial practice will vary to some extent depending on the optional features actually required by the commercial user. It can be varied from a single detector and a single solenoid based delivery system suitable for an individual ripening room, which may have additional safety features in order to meet existing regulatory safety requirements, to a similar single detector system which has no direct control functions and simply exports the results of its detector out-puts to an external programmable logic control system; to a multiple detector system in which one or more detectors could be deployed in order to manage additional control options such as the delivery of gases other than ethylene for insect of disease control purposes or even to a multiple room system where separate individual control units and delivery sub-systems are deployed into each room with the out-puts of each unit being diverted to and recorded by a central control computer within the complex through which can be made direct changes to specific operating parameters within each individual control unit.

One preferred form of this invention as a ripening gas delivery controller, in which it is possible to achieve most of the capabilities defined above will be described as a means of further explaining the general mode of operation of the invention in all of its possible configurations.

As the benefits of the various aspects of the invention are largely maximized in a land-based ripening room, the preferred form of the methodology will be described in terms of its use in such a situation. However the invention can be also be employed in its simplest primary "i 15 functional role, the delivery and control of a ripening gas, in other enclosed storage spaces such as shipping containers or road transport containers.

0@ o• The preferred means necessary to apply the methodology described in a land-based ripening room comprise: 20 a. the use of an ethylene or acetylene sensitive sensor deployed within the ripening o0oo environment the out-put from which, converted to gas concentration units, is continuously presented on an LED display mounted within an external control unit.

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b. a gas delivery system, which in one form, is connected directly through a pressure regulator to a compressed source of the ripening gas with the pressure regulator output passing through one or more solenoid valves in series with a fixed orifice and then through a delivery tube into the room, with this combination thus forming a metering system, and with the total delivery system deployed external to the fruit ripening room.

c. a carbon dioxide infra red sensor also deployed within the ripening environment (c) linked to valves which respond (open or close) in response to out-put from this sensor via a control units; d. a humidity sensor and/or a temperature sensor also deployed within the ripening environment but operating passively in that their out-puts are simply recorded as required with that data being periodically recorded electronically within the system control unit; e. electro magnetically pulsed or electric motor operated valves designed to fit into existing air vents into the ripening environment, or vents specifically installed for the purpose, to control the ingress of fresh ambient air to the ripening environment and egress of room air from the environment; and f a programmed microprocessor, deployed within the external control/display unit which monitors the out-put of the sensors within the ripening environment; provides an LED display of individual sensor out-puts and regularly records the sensor outputs when required; activates a solenoid operated valve or valves within the external delivery system as required to deliver additional ripening gas activates as required the valves deployed within air vents to allow the exchange of room air with fresh external air until the carbon dioxide level within the ripening room environment returns to a predesignated set point; performs calculations as necessary to establish 15 the leakage rate of the room; displays the calculated leakage rate on the LED display when so selected; monitors the operation of the whole system to detect any component failures, operator errors, exhaustion of supply cylinders, leakage through solenoid control valves or a failure of the piped supply system to deliver gas to the room and, should any such failure within the total system be detected, closes down the delivery system while simultaneously activating alarms as necessary to make operators aware that some such failure has occurred and that shut down procedures have been implemented.

With the preferred form described, the invention can measure, record and display the ethylene or acetylene level within the ripening room environment and maintain it at any preset level required by activating the delivery system once the room level falls below a predetermined set point; measure, record and display the carbon dioxide level and prevent the accumulation of carbon dioxide within the room from increasing above a predefined limit; measure, record and display humidity and temperature within the ripening environment; detect and initiate alarms to indicate component failure, operator errors or disruption of gas supplies that might jeopardize the ripening operation or create a safety risk; and establish and display, when required, the leakage rate of the room within which it is deployed.

1 The preferred form is described diagrammatically in Figure 1 attached, which depicts a sealed storage environment e.g. land-based ripening room within which the level of ripening gas and/or other gases is to be controlled, containing a carbon dioxide sensor a ripening gas sensor a temperature sensor a humidity sensor an external display unit containing the microprocessor an external gas control delivery sub-system and the two electromagnetic or motor operated valves mounted within air vents in the room wall to allow the infusion of fresh air and egress of room air as necessary and, when required, to prevent the carbon dioxide level from exceeding a predefined set point. Other components shown in the drawing include:a an evaporator and fan which are an integral part of the room refrigeration system b a ripening gas delivery input tube within the room c the room door d an external compressed cylinder with associated regulator which contains the required ripening gas and e a power supply external to the room (12) to drive the invention.

The arrows shown in the figure depict a typical direction of air flow within the ripening room which may or may not employ forced air ventilation of the produce during the ripening operation. In the configuration shown, the fresh air input vent is shown located near a low pressure area to the rear of the fan and the room air exit vent in, if possible, a high pressure area also generated by the operation of the evaporator fan, thus maximizing fresh air exchange into the container whenever these vents are opened by the microprocessor housed within the control unit. Additional fans could also be employed, if required, at or adjacent to the vent openings with these being turned automatically directly by the micro controller at the same time the vent valves are opened or indirectly by being interlinked to the valves so that they are turned on as a result of the valves themselves being actuated.

The invention does not require specialized technical expertise for its installation or operation.

With minor software modification, the means defined above could also be used to control other gases delivered into fresh produce storage environments either for the purposes of disease control or insect disinfestations, provided the detector currently used for ripening gases is replaced by a more appropriate detector. Also with oxygen and/or carbon dioxide detectors fitted, the means described could also be used for the delivery of oxygen and/or carbon dioxide in order to create and control a room at very high levels, well above those in normal air, for relatively short periods of time as a supplement or support to other insect disinfestation treatments.

For the described situation, the method would operate as follows a. ripening room operator sets ripening gas equilibrium value and maximum carbon dioxide values into control unit; b. turning on the unit control unit checks current set point and current ripening gas sensor reading, if sensor reading is below the set point the unit initiates delivery of the ripening gas into the room by opening the ripening gas supply solenoid; c. the control microprocessor monitors sensor out-put and closes the ripening gas supply solenoid once the defined set point is reached; S. 15 d. the control unit continues to monitor the ripening gas sensor, the carbon dioxide sensor, the humidity sensor and the temperature sensor and record the readings obtained; e. the control unit again recommences delivery of gas at any time the ripening gas sensor shows that, through leakage, the room concentration has dropped below the defined set 0000 point; f. the control unit which regularly monitors the carbon dioxide sensor, opens the ventilation valves as soon as the carbon dioxide level in the room exceeds a defined set point and again closes the ventilation valves as soon as the carbon dioxide sensor out-put once more indicates the level in the room is below the defined set point.

g. the control unit establishes the time necessary initially to bring the room to the defined ripening gas set point, the time that elapses until it falls below the desired set point and the time necessary to bring the room back to the desired set point. From this data, if so requested, the control unit calculates and displays the room leakage rate.

h. The control unit continuously checks that it is receiving appropriate signals from the ripening gas sensor, that changes in the ripening gas level appropriately reflect the operation of the solenoid valve and the continued availability of ripening gas and closes down all gas delivery and displays an alarm should any errors be detected.

The present invention differs from all current systems being used in that the current commercial methods deliver a defined volume of ripening gas into a ripening room, the volume delivered being dependent on operator calculations of the amount of ripening gas required to attain a desired concentration in the room. The present unit actually measures the concentration within the room and automatically adjusts this concentration to a defined set point, chosen by the operator, by initiating the delivery of ripening gas into the room from a compressed gas supply source. In the most commonly used current method, "shot" ripening, while the desired concentration is achieved initially, at least approximately when it is dependent on the skills of the operator and even more so if an automatic volumetric dispensing system is employed, the concentration subsequently changes with time due to the natural leakage of the room. The present invention differs significantly in comparison to the "shot" method, in that having attained the desired concentration in the room it then maintains the room at the specified concentration required irrespective of the leakage rate of the room. While the "trickle" method will also maintain a constant concentration, the present invention will do the same with a much reduced usage of ripening gas and do so more accurately due to the manner in which the delivery of the gas is controlled. The invention is also unique in one other respect compared to other present techniques in that it can also easily run an automatic test on a room, using direct measurements of the level of the ripening gas, and determine and report the room leakage rate.

The invention, with an appropriate change of sensors, also enables the same procedure to be 20 applied to achieve accurate control over the level of other gases when used as an aid to insect disinfestation or to control disorder or disease development.