MEASUREMENT OF A MASS FLOW RATE

Abstract

Method and system for determining a specific mass flow rate of a highly viscous food product (1) having a viscosity of greater than 100 cP, which during processing in a continuous delivery flow is supplied to or removed from a buffer container (2) by means of a delivery pump (4), wherein a weighing device (7) is used to determine the change in the mass of the food product (1) in the buffer container (2) over a defined time period, which is in particular in the range of one or several minutes (m/t), wherein, in the same time period a pump parameter of the delivery pump (4) that is proportional to the expected delivery rate is registered, changes in the pump parameter over the time period are averaged to form an average pump parameter, wherein the current specific mass flow rate is calculated as a quotient from the change over time of the mass m/t and the averaged pump parameter and is output.

Claims

1. A method for determining a specific mass flow rate of a highly viscous food product (1) having a viscosity of greater than 100 cP, which during processing in a continuous delivery flow is supplied to or removed from a buffer container (2) by means of a delivery pump (4), wherein a weighing device (7) is used to determine the change in the mass of the food product (1) in the buffer container (2) over a defined time period, which is in particular in the range of one or several minutes (m/t), in that, in the same time period a pump parameter of the delivery pump (4) that is proportional to the expected delivery rate is registered, changes in the pump parameter over the time period being averaged to form an average pump parameter, in that the current specific mass flow rate is calculated as a quotient from the change over time of the mass m/t and the averaged pump parameter and is output.

2. The method according to claim 1, wherein a highly viscous to pasty processed cheese raw mixture (1) having a viscosity of greater than 1000 cP, in particular greater than 5000 cP, is processed as the food product.

3. The method according to claim 1, wherein the food product (1) is removed from the buffer container (2) by means of the delivery pump (4) and the decrease in mass is determined accordingly.

4. The method according to claim 3, wherein the speed of the delivery pump (4) per unit time is registered as a pump parameter and/or a parameter proportional to the speed, in particular the frequency of the frequency converter used to actuate the delivery pump (4) in the unit [Hz], is used.

5. The method according to claim 4, wherein current specific mass flow rate is calculated in the unit kilograms per hour and per revolutions of delivery pump or kilograms per hour and per Hz of frequency inverter.

6. The method according to claim 4, wherein the specific mass flow rate is assigned to one of a plurality of operating states of the delivery pump (4), the operating states correlating with different physical states of the food product, in particular with different viscosities and/or porosities and/or densities and/or friction coefficients of the food product.

7. The method according to claim 6, wherein the linear behavior of the operating states is used for the regulation of the delivery pump (4) for setting a specific delivery flow, in particular the delivery flow of a filling line.

8. The method according to claim 1, wherein from the value for the specific mass flow rate of the pump, the mass flow rate to be conveyed by the pump (4) is set by a variable being specified for the pump parameter, in particular by specifying the frequency at the frequency converter.

9. A system for determining a specific mass flow rate of a highly viscous food product (1) having a viscosity greater than 100 cP, in particular greater than 1000 cP, comprising a buffer container (2) and a delivery pump (4) for supplying or removing the food product (1) to or from the buffer container (2) in a continuous delivery flow, comprising: a weighing device (7) for determining the change over time of the mass (m/t) of the food product (1) in the buffer container (2) over a defined time period, a device for determining an average pump parameter of the delivery pump (4) that is proportional to the expected delivery rate in the same time period and a device for calculating and outputting the current specific mass flow rate as a quotient from the change over time of the mass m/t and the average pump parameter.

Description

[0021] In the following, the invention will be explained in greater detail on the basis of an embodiment shown in the drawings:

[0022] The FIGURE shows a diagram of a system for determining the claimed specific mass flow rate of a highly viscous food product which has a viscosity of greater than 1000 cP. The system shown here is integrated into a processing process in which, in the present case, various types of natural cheese are mixed to form a processed cheese raw mixture 1 and supplied to a buffer container 2 via a pipeline 3. In subsequent processing steps, this processed cheese raw mixture is melted in order to be supplied to the end of a machine that forms and packages the product. Appropriately designed delivery pumps 4 are used for transporting the product through the pipelines.

[0023] In the embodiment shown, the processed cheese raw mixture 1 is removed from the buffer container 2 via a pipeline 5 by the delivery pump 4. The delivery pump 4 is associated with a control unit 6, which adjusts the speed and thus the current delivery rate by means of a frequency converter via the bidirectional data line 11. The buffer container 2 stands on a weighing device 7, by means of which the weight of the buffer container 2, which decreases by a delivery flow that is as continuous as possible, is measured as a change over time in the mass (m/t) and is averaged over a predetermined defined time period. The value of the

[00001]$\frac{.Math..Math.m}{.Math..Math.t}=\stackrel{.}{\stackrel{\_}{m}}.Math.\left[\mathrm{kg}.Math.\text{/}.Math.h\right]$

average change over time in the mass is output via a data line 8 to a means 9 for calculating the specific mass flow rate. The means is implemented by a computer 9.

[0024] At the same time, a pump parameter proportional to the expected delivery rate, in the present case in particular the average of the frequency in Hz used for actuation, which is proportional to the pump speed, is determined via a corresponding means, in this case by means of the control unit 6. This value

f[Hz]

is also output via a data line 10 to the computer 9. From the average change in mass measured within the defined period of time and the average pump parameter determined approximately in the same period, the computer 9 calculates the current specific mass flow rate as the quotient of the two input variables in the present case to

[00002]${\stackrel{.}{m}}_{\mathrm{spez}}=\frac{\stackrel{.}{\stackrel{\_}{m}}}{\stackrel{\_}{f}}.Math.\left[\frac{\mathrm{kg}}{h.Math..Math.\mathrm{Hz}}\right]$

[0025] This specific mass flow rate can be understood as the incline of a straight line in a diagram 12 in which the mass flow rate in [kg/h] is plotted against the frequency of the converter in [kg/h]. In this case, the specific mass flow rate depends on the operating state 13 of the product. A product such as the processed cheese raw mass in question has few (in the present case only three, for example) defined (natural) operating states 13, which differ in terms of their flowability. During processing, the current operating state 13 of the product and thus the value for the specific mass flow rate is known at all times.

[0026] Using the value for the specific mass flow rate, the mass flow rate to be conveyed by the delivery pump can be set by specifying a certain frequency at the frequency converter:

[00003]$\stackrel{.}{m}={\stackrel{.}{m}}_{\mathrm{spez}}.Math.f.Math.\left[\frac{\mathrm{kg}}{h}\right]$

[0027] By way of the mass flow rate which can be predetermined in this way, the entire production process, in particular the delivery flow in a filling line, can be controlled.

[0028] A particularly advantageous use of the approach according to the invention in the production of processed cheese products lies in the option of setting or regulating the consistency of the raw mass to be processed:

[0029] It is known that protein breakdown progresses to different degrees depending on the degree of maturity of the cheese raw materials used in the processed cheese. As the cheese matures, it loses the ability to form a structure, and therefore a higher dry matter content must be set to ensure the desired consistency. On the other hand, when using particularly young raw material, dry matter can be saved, with the specified dry masses needing to be adhered to as the lower limit. Since the fluctuations in the degree of maturity of the matured cheese raw material used usually only become apparent during the melting process, it is advantageous to increase the dry masses in the raw mixture in a targeted manner and to adjust them via accurate metering of water such that the final consistency of the processed cheese meets the specifications. However, in order to be able to ensure accurate metering of water with fluctuating production quantities, the flow rate of the cheese raw mixture must be known.

[0030] Using the method of quantity measurement according to the invention, this value can be reliably set such that such consistency control or regulation is made possible. The water volume can be accurately supplied by means of a diaphragm pump which is automatically regulated to a viscosity setpoint which can be measured using an inline viscometer. Alternatively, the water supply can also be regulated by hand. In this case, the deviation from the target consistency is visually displayed to the plant operator.

[0031] Another use of the approach according to the invention is particularly advantageous system regulation in a continuous heating process. The aim of this system regulation is to heat a defined product quantity in [kg/h] to a defined temperature, the product quantity usually being regulated by indirect variables, such as pump speed or frequency of the frequency converter, and not by the effectively supplied product quantity in [kg/h]. Setting using indirect variables is only permissible, however, provided that a homogeneous product having uniform density and initial temperature is processed. Only then do specific pump speeds and frequencies of the frequency inverter correlate with specific system throughputs.

[0032] As stated above, processed cheese raw mixtures have different behavior. Depending on the recipe, fat content and temperature, this results in different porosities and conveying properties. In practice, for example, this may cause a pump to convey between 80 and 110 kg/h/Hz at the same setting on the frequency converter.

[0033] According to the invention, this problem can be counteracted by using the effective flow rate (kg/h) measured according to the invention for the regulation instead of just the pump speed or the frequency converter frequency. This stands up against the fluctuating conveying behavior of the pump and the lack of inhomogeneity in the product composition.