AUTOMATICAL IN SITU CONTROL OF THE CONFINED ENVIRONMENT OF METABOLICALLY ACTIVE PRODUCE

Abstract

A control system for controlling the storage of metabolically active produce in a defined confined environment. The control system comprises gas analyzing and pressure measurement means including a control unit for determining an adjusted gas medium composition of the confined environment for protecting the produce against metabolic degradation. An operating/actuating means for adapting the gas medium in the confined storage environment is based on the determined adjusted gas medium composition. The control unit is adapted for determining the adjusted gas medium composition based on a mathematical model of the system that determines a metabolic coefficient of the produce by combining measured changes of gas composition in the confined environment with dynamic pressure changes in the confined space. The value of the metabolic coefficient is used as input for a control algorithm to continuously adjust the gas composition in the confined space in response to the metabolic activity of the produce.

Claims

1.-47. (canceled)

48. A control system for controlling of respiratory produce in a confined environment, said control system comprising an operator/actuator, a gas analyser and an atmospheric pressure sensor, and a control unit adapted to receive the signals of the gas analyser and of the atmospheric pressure sensor and adapted to generate an output signal responsive to a change of gas composition and pressure in the confined environment, which output signal drives the operator/actuator to adjust the gas composition in the confined environment, characterized in that the control unit is programmed 1) to calculate a respiration coefficient as a function of the measured gas composition in the confined environment and as a function of the pressure in the in the confined environment, which respiration coefficient is determined by the control unit at least as a function of the gas composition and the pressure out of at least two consecutive times over a selective time period in the confined environment, 2) as a function of the calculated respiration coefficient to determine an adjusted gas medium composition, and 3) to generate an output signal that drives the operator/actuator to control the respiratory produce.

49. The system according to claim 48, wherein the control unit is programmed to determine the adjusted gas medium composition based on a mathematical model of the system that at least uses measured gas composition and pressure at least two consecutive times over a selective time period in the confined environment to calculate in real time a respiration coefficient; the adjusted gas medium composition being determined as a function of the calculated respiration coefficient in the confined environment, whereby the respiration coefficient is calculated in real time as the solution of the following system of equations: $\{\begin{array}{c}\frac{{\mathrm{dn}}_i}{\mathrm{dt}}=r_i.Math.m+\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\underset{j}{.Math.}.Math.\left(r_j\right).Math.m\right).Math.x_i^{}\\ n_i=x_i.Math.\frac{\mathrm{PV}}{\mathrm{RT}};.Math.n=\underset{i}{.Math.}.Math.n_i\\ x_i^{}=x_i.Math.H+x_{i,a}\left(1-H\right)\\ \mathrm{RQ}=f\left(r_i\right)\\ i=1,\mathrm{.Math.}.Math.,m\end{array}$ with $\frac{d}{\mathrm{dt}}$ the rate of change with time, x.sub.i the measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, m the mass of respiratory produce in the confined environment, r.sub.i is the rate of exchange of the gas with the metabolically active produce and f(r.sub.i) a defined mathematical function of r.sub.i values, the mole fraction x.sub.i* is defined by the function H that states that H=0 when P/t is larger than or equal to 0 and H=1 when P/t is smaller than 0.

50. The system according to claim 48, wherein the control unit is programmed to determine the adjusted gas medium composition based on a mathematical model of the system that at least uses measured gas composition and pressure at least two consecutive times over a selective time period in the confined environment to calculate in real time a respiration coefficient; the adjusted gas medium composition being determined as a function of the calculated respiration coefficient (RQ) in the confined environment, whereby the respiration coefficient (RQ) is the respiratory quotient of respiratory produce, and the gasses are O.sub.2, CO.sub.2 and N.sub.2; the respiration coefficient (RQ) is calculated in real time as the solution of the following system of equations: $\{\begin{array}{c}\frac{{\mathrm{dn}}_{O_2}}{\mathrm{dt}}=-r_{O_2}.Math.m+\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{O_2}^{}\\ \frac{{\mathrm{dn}}_{{\mathrm{CO}}_2}}{\mathrm{dt}}=r_{{\mathrm{CO}}_2}.Math.m+\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{{\mathrm{CO}}_2}^{}\\ \frac{{\mathrm{dn}}_{N_2}}{\mathrm{dt}}=\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{N_2}^{}\\ n_i=x_i.Math.\frac{\mathrm{PV}}{\mathrm{RT}};.Math.n=\underset{i}{.Math.}.Math.n_i\\ x_i^{}=x_i.Math.H+x_{i,a}\left(1-H\right)\\ \mathrm{RQ}=\frac{r_{{\mathrm{CO}}_2}}{r_{O_2}}\end{array}$ with $\frac{d}{\mathrm{dt}}$ the rate of change with time, x.sub.i the measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, m the mass of respiratory produce in the confined environment, r.sub.O.sub.2 is the oxygen consumption rate of the respiratory produce and r.sub.CO.sub.2 is the carbon dioxide production rate of the respiratory produce, the mole fraction x.sub.i* is defined by the function H that states that H=0 when P/t is larger than or equal to 0 and H=1 when P/t is smaller than 0.

51. The system according to claim 48 whereby the system comprises at least one gas analyser and at least one atmospheric pressure sensor connected to a control unit arranged to determine an adjusted gas medium composition of the confined storage environment for protecting the produce against fermentative degradation; and at least one operator/actuator arranged to adapt the gas medium in the confined storage environment based on said determined adjusted gas medium composition; wherein the control unit is programmed to determine the adjusted gas medium composition based on a mathematical model of the system that uses at least measured gas composition and pressure at two consecutive times over a selective time period in the defined confined storage environment to calculate in real time a respiration coefficient that is a function of the oxygen consumption rate and carbon dioxide production rate of the produce that characterize respiration and fermentation; the adjusted gas medium composition being determined as a function of the calculated respiration coefficient in the confined storage environment, whereby respiration coefficient is calculated in real time as the solution of the following system of equations: $\{\begin{array}{c}\frac{{\mathrm{dn}}_{O_2}}{\mathrm{dt}}=-r_{O_2}.Math.m+\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{O_2}^{}\\ \frac{{\mathrm{dn}}_{{\mathrm{CO}}_2}}{\mathrm{dt}}=r_{{\mathrm{CO}}_2}.Math.m+\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{{\mathrm{CO}}_2}^{}\\ \frac{{\mathrm{dn}}_{N_2}}{\mathrm{dt}}=\left(\frac{\mathrm{dn}}{\mathrm{dt}}-\left(r_{{\mathrm{CO}}_2}-r_{O_2}\right).Math.m\right).Math.x_{N_2}^{}\\ n_i=x_i.Math.\frac{\mathrm{PV}}{\mathrm{RT}};.Math.n=\underset{i}{.Math.}.Math.n_i\\ x_i^{}=x_i.Math.H+x_{i,a}\left(1-H\right)\\ \mathrm{RQ}=\frac{r_{{\mathrm{CO}}_2}}{r_{O_2}}\end{array}$ with $\frac{d}{\mathrm{dt}}$ the rate of change with time, x.sub.i the measured mole fraction of gas i in the confined environment, P the measured pressure in the confined environment, V the volume of the confined space, T the temperature in the confined environment, R the universal gas constant, m the mass of respiratory produce in the confined environment, r.sub.O.sub.2 is the oxygen consumption rate of the respiratory produce and r.sub.CO.sub.2 is the carbon dioxide production rate of the respiratory produce, the mole fraction x.sub.i* is defined by the function H that states that H=0 when P/t is larger than or equal to 0 and H=1 when P/t is smaller than 0.

52. The control system according to claim 48, whereby the gas analyser is indicative of a level or composition of the atmosphere in the confined environment or whereby the atmospheric pressure sensor is indicative of an atmosphere pressure in the confined environment, or whereby the control unit is configured to continuously receive the signals of the gas analyser and of the atmospheric pressure sensor.

53. The control system according to claim 48, whereby the respiration coefficient is calculated in real time or whereby the respiration coefficient, function of the oxygen consumption rate and carbon dioxide production rate of the produce, characterises respiration and fermentation of the produce.

54. The control system according to claim 48, whereby the control unit is designed to generate an output signal to control the respiratory produce or whereby the control unit is designed to generate an output signal to control the metabolic activity of the produce.

55. The control system according to claim 48, whereby the control unit is designed to generate an output signal to protect the produce against metabolic disturbance, or whereby the control unit is designed to generate an output signal to protect the produce against degradation or whereby the control unit is designed to generate an output signal to protect the produce against fermentative degradation.

56. The system according to claim 48, further comprising a temperature sensor and a control unit adapted to receive the signals of the temperature sensor and adapted to generate an output signal responsive to the temperature or further comprising a volumetric sensor and a control unit adapted to receive the signals of the volumetric sensor and adapted to generate an output signal responsive to volume.

57. The system according to claim 48, whereby the control unit is furthermore adapted to continuously receive the signals of the temperature sensor and adapted to generate an output signal responsive to the temperature or whereby the control unit is furthermore adapted to continuously receive the signals of the volumetric sensor and adapted to generate an output signal responsive to volume or whereby the atmospheric pressure sensor is a barometric pressure sensor or whereby the system controls gas composition with respect to at least one of the following gasses oxygen, carbon dioxide, nitrogen, ethanol, acetaldehyde, ethylene, ethane, acetone.

58. The system according to claim 48, where the function for the respiration coefficient is a linear or a nonlinear function of metabolic exchange rates of different relevant gasses with the produce or wherein the pressure and gas composition in the defined confined storage environment are measured continuously for a certain period of time or wherein the pressure and gas composition in the defined confined storage environment are measured periodically with a fixed or adaptive time interval for a certain period of time.

59. The system according to claim 48, wherein the total measurement time and time intervals between subsequent measurements of gas composition and pressure are optimized such that the measured gas composition and pressure signals contain the maximal amount of information of the metabolic rates of respiration and fermentation and the least possible measurement noise or wherein the measured gas composition and pressure signals are subjected to signal processing to filter out measured noise.

60. The system according to claim 48, wherein besides the metabolic rates of respiration and fermentation, also the error of the estimated metabolic rates and respiration coefficient are calculated, or wherein the calculated metabolic rates and/or respiration coefficient are subjected to evaluation based on validity criteria based on the calculated errors of the metabolic rates, respiration coefficient and pressure.

61. The system according to claim 48, wherein gas flows of oxygen gas, carbon dioxide gas and nitrogen gas, both from the environment of the confined space to the confined space itself as well as from the confined space to its environment due to leakage are taken into account to calculate the respiration coefficient or wherein carbon dioxide gas flow due to leakage from the environment to the confined space may neglected by the control algorithm when calculating the respiration coefficient.

62. The system according to claim 48, wherein control system is adapted to calculate the adjusted gas composition as a function of the determined metabolic rates or coefficient or wherein the control unit is adapted for comparing the calculated respiration coefficient to the set point value of the respiration coefficient, its integral or its differential and wherein the control unit is adapted for comparing the CO.sub.2 level to the maximum tolerable concentration of the produce, for instance fruit.

63. The system according to claim 48, wherein the control unit is also adapted for comparing the calculated respiration coefficient to the set point value of the respiration coefficient, its integral or its differential and wherein the control unit is adapted for comparing the O.sub.2 level to the minimal tolerable concentration of the produce, for instance fruit or wherein the control unit is also adapted for comparing the calculated respiration coefficient to the threshold value of the respiration coefficient and wherein the control unit is adapted for comparing the O.sub.2 level to the minimal tolerable concentration of the produce, for instance fruit, wherein the determined metabolic rates or respiration coefficient is used to calculate the adjusted gas composition, whereby the gas composition in the confined storage space are maintained a fixed composition.

64. The system according to claim 48, wherein the control unit comprises a PID controller for automatically calculating the future gas medium composition required to maintain the respiration coefficient at safe levels or wherein the control unit comprises a PID controller for automatically calculating the future gas medium composition required to maintain the respiration coefficient at a certain set point value, or wherein the control unit comprises a model predictive control for automatically calculating the future gas medium composition required to maintain the respiration coefficient at safe levels.

65. The system according to claim 48, whereby the operating or actuating means for adapting the gas composition in the confined storage environment comprises a means for flowing at least one gas into said the confined storage environment and a means for scrubbing at least one gas such as CO2 or Ethylene or wherein the confined space subject to control, may have a constant volume or wherein the confined space subject to control, may have a constant temperature or wherein the confined space are a reservoir inside another confined space such as a storage room.

66. The system according to claim 48 wherein the control system does not have to seal off the confined storage environment or part of the confined storage environment from gas flow in to or out of the confined storage environment from or to the external environment or wherein the control system does not have to estimate model parameters with uncertainty that may lead to introduction of errors in the estimates of the metabolic rates of respiration and fermentation and the respiration coefficient or wherein the control system does not have to estimate a leakage coefficient, equivalent leak hole diameter, pressure difference or pressure drop dynamics curve.

67. The system according to claim 48, whereby only the internal pressure is used for leakage flow calculation without a leakage parameter (k) estimation, or whereby due to the leakage disturbance correction mathematical model based on pressure driven leakage no equivalent leak hole diameter needs to be calculated or whereby dynamic control of relative gas composition in the confined environment is targeted instead of fixed relative gas composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0155] The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

[0156] FIG. 1 is a schematic view showing the details of the pressure-corrected control system based on a software assisted measurement system and control algorithm. The metabolically active produce (a) is contained in a confined environment (b). The pressure is measured with a pressure sensor (c) and the gas composition with a gas analyzer (d). The signals of the pressure sensor and gas analyzer are used by the control unit (e) to calculate a metabolic coefficient of the produce (a) that is used to calculate an output signal. The control unit output signal drives the operator/actuator (f) to adjust the gas composition in the confined environment using a gasses supplied from a gas control unit (g).

[0157] FIG. 2 is a schematic view of a confined space. The confined space contains metabolic active produce with mass M. The number of moles of the n different gasses present in the confined space is given by n.sub.1 to n.sub.n. The confined space has a free volume V, temperature T and internal pressure P. Due to its metabolic activity, gasses are consumed or produced with rate r.sub.1 to r.sub.n. The immediate environment of the confined space is at pressure P.sub.a. Given the confined space is not perfectly gastight, gas flows due to pressure driven leakage as occur, represented by q.sub.1 to q.sub.n.

[0158] FIG. 3 is a schematic view of a cooled storage room (cool room), indicated by a dashed line to stress the cool room is not perfectly gastight. The cool room contains respiratory produce with mass M. The number of moles of oxygen, carbon dioxide and nitrogen gas is given by n.sub.O2, n.sub.CO2 and n.sub.N2 respectively. The cool room has a free volume V, temperature T and internal pressure P. Due to its metabolic activity, the fruit is respiring and so consuming oxygen and producing carbon dioxide gas with rates r.sub.O2 and r.sub.CO2 respectively. The immediate environment of the cool room, in this case atmospheric air, has atmospheric pressure P.sub.a. Given the cool room is not perfectly gastight, gas flows due to pressure driven leakage of oxygen, carbon dioxide and nitrogen gas occur, represented by q.sub.O2, q.sub.CO2 and q.sub.N2 respectively.

[0159] FIGS. 4(a) and 4(b) depict the atmospheric (fullline) and internal pressure (dashed line) and measured (full line) and simulated (full line, o symbol) O.sub.2 partial pressures as well as measured (full line) and simulated (full line, o symbol) CO.sub.2 partial pressures during a time period of 120 minutes with increasing 4(a) and decreasing 4(b) internal pressure during the validation experiment in an empty storage container. The simulated gas using the pressure based leakage model fits the measured gas composition excellently, indicating the high accuracy of the pressure based leakage model.

[0160] FIGS. 5(a) to 5(c) show the results of the demonstration of the pressure based leak-corrected RQ measurement and resulting control of the gas compostion for apple storage where 5(a) shows the measured internal pressure, 5(b) measured and setpoint O.sub.2 partial pressures (dashed line and full lines respectively) and 5(c) corresponding RQ estimation with (upward pointing triangle) and without (downward pointing triangle) pressure based leak correction. It is shown that RQ estimates with leakage correction deliver reliable values of the RQ of the stored produce both during decreasing as well as increasing internal pressure, while RQ estimates without leak correction deliver reliable RQ values when internal pressure decreases and leak occurs from the storage space tot he environment, not significantly altering the internal gas composition.

[0161] FIGS. 6(a) to 6(d): Estimated values of the RQ of stored apple fruit as a function of pressure changes inside the room. Pressure based leakage correction represented by the green line and without pressure based leakage correction represented by the red line for different real RQ values of the stored fruit equal to 1.0 (a), 1.5 (b), 2 (c) and 2.5 (d).

[0162] FIG. 7 illustrates the calculated standard errors of the real-time RQ estimates in a storage space containing respiratory produce. The standard error of the RQ estimate is calculated every minute for a time period of 240 minutes, based on the standard error of the estimates of the approximations of the time derivatives in equation 26.