Application of mass flow meter in barreled liquid filling line

1. Introduction

In the chemical and food industries, the filling of barreled liquids is very common. For medium and above filling volumes (above 10Kg), the filling methods generally adopt electronic weighing and flow meter. Among them, the electronic weighing method has been widely used in China. Due to the development of flow meter technology, especially our successful experience in using mass flow meters in recent years, we believe that it is more reasonable to use mass flow meters for high-precision filling of medium and above volumes. Now we introduce an automatic production line independently developed by us that uses mass flow meters to measure highly corrosive and viscous liquids with high precision. This line covers almost all aspects of the functions of barreled liquid filling lines and has typical significance.

2. Overview of filling production line

2.1 Material characteristics and process conditions

1) Filling material temperature: 5~35℃
2) Material density: organic acid about 1.2g/cm3, organic acid salt about 1.3g/cm3
3) Material viscosity: organic acid about 50CP, organic acid salt about 150CP
4) Feed pipeline inlet pressure: ≥0.2Mpa, fluctuation range ±10%
5) The whole set of equipment meets GMP hygiene requirements

Filling capacity: 25L (square barrel); 200L (round barrel); 1000L (IBC barrel)
Filling accuracy: (mass accuracy): 0.1%, filling accuracy meets the European "OIML R61-1 1996 issue" standard
Filling speed: 25L barrel (30Kg): 6 barrels/minute; 200L barrel (250 Kg): 1 barrel/minute; 1000L barrel (1200 Kg): 1 barrel/4 minutes

2.2 Process flow

: empty barrels sorting - empty barrels entering the filling station - detection and positioning - filling head descending - filling valve opening - filling starting - mass measurement - reaching 90% × (set value - compensation value) - regulating valve throttling becomes smaller - reaching 100% × (set value - compensation value) - filling valve closing - vacuum adsorption - full barrels leaving the filling station - turning - hanging caps - screwing caps - labeling - palletizing - winding - finished product output

2.3 Overview of filling system

The entire filling system consists of mass flowmeter, control valve, filling head, bracket, guide rail, pneumatic actuator, control system, etc. (see schematic diagram)

(1) Filling system accuracy

The filling system accuracy mainly depends on the accuracy of the mass flowmeter, filling speed and system stability.

(2)

During flow control filling, the actual filling volume must be greater than the set flow of the mass flowmeter. It must be set through the PLC program to require the flowmeter to send a signal in advance to control the closing of the filling valve, so as to ensure that the actual filling volume is consistent with the set volume of the mass flowmeter.

(3) Flow control (filling speed control)

In order to ensure the accuracy of the filling system, the filling speed of the filling system is designed to be fast and slow. The flow control valve automatically controls the filling speed by controlling the flow rate. Since the opening precision of the control valve will not affect the filling accuracy, the use of the automatic regulating valve on the market is expensive, bulky, inconvenient to install, and requires increased control requirements. Therefore, the flow control valve adopts a self-designed three-position butterfly valve, namely, maximum opening (fully open), 1/3 opening (manually set and adjustable), and fully closed. It has outstanding advantages and stable performance.

(4) Anti-drip

filling After the viscous material remaining on the surface of the filling head takes a certain amount of time to flow out, so the material will drip onto the surface of the container and cause pollution. The filling system is designed with a vacuum generator back-suction system to ensure no dripping. The vacuum generator has a large suction flow, simple structure, low cost, fast vacuum generation and release, and easy installation and maintenance.

(5) Filling head

The filling valve of the filling head adopts a self-designed pneumatic stop valve with simple structure, fast opening and closing, easy cleaning and good sealing. The fluororubber seal is food grade.

2.4 Flowmeter Selection

There are many types of flowmeters. The selection of flowmeters is mainly determined by material properties and on-site process conditions. For filling with high precision requirements, only mass flowmeters can be selected. [page]

The metering system of a mass flowmeter includes a sensor and a transmitter for signal processing. The mass flowmeter is based on Newton's second law: force = mass × acceleration (F = ma).

As shown in Figure 2, when a particle with a mass of m moves at a speed V in a pipe rotating at an angular velocity ω about the P axis, the particle is subject to two components of acceleration and its force:

(1) Normal acceleration, that is, centripetal acceleration αr, its magnitude is equal to 2ωr, toward the P axis;

(2) Tangential angular velocity αt, that is, Coriolis acceleration, its value is equal to 2ωV, and its direction is perpendicular to αr. Due to the compound motion, a Coriolis force Fc = 2ωVm acts on the particle in the αt direction, and the pipeline acts on the particle with a reverse force -Fc = -2ωVm.
When a fluid with a density of ρ flows at a constant velocity V in a rotating pipe, any length Δx of the pipe will be subjected to a tangential Coriolis force ΔFc:

ΔFc=2ωVρAΔx (1)

Where A is the cross-sectional area of ​​the pipe.

Since there is a relationship: mq=ρVA

, ΔFc =2ωqmΔx (2)

Therefore, the mass flow rate can be measured by directly or indirectly measuring the Coriolis force of the fluid flowing in the rotating pipe.

Figure 2

The mass flowmeters with relatively good comprehensive performance include EMERSON, E+H, KROHNE, etc. For the design flow of the existing filling system, the metering error of the flowmeter itself consists of two parts: nominal measurement error and zero-point stability error, that is, maximum measurement error = nominal measurement error ± zero-point stability error.

The accuracy of the flowmeter is the most critical factor in the filling accuracy of the entire filling system. Considering the entire filling system, it is very important to select a mass flowmeter with high accuracy, good repeatability and stable performance to ensure that the system meets the design requirements.

2.5 Control system composition and control scheme

2.5.1 Control system composition, see Figure 3

Figure 3 Composition of automatic control system

2.5.2 Control scheme description

In order to reduce on-site wiring as much as possible, make the system more reasonable, more complete in function and more convenient to operate, an MB+ master station is set up at PLC1, and several MB+ substations are set up in places where input and output devices are concentrated on the production line, as shown in the figure above.

Since the filling accuracy requirements of the system are extremely high, if general flow meters and analog data acquisition and calculation are used, it will not meet the use requirements. Therefore, in addition to selecting mass flow meters of internationally renowned brands as measuring instruments, we also use the most advanced Schneider QUANTUM series products as the main controller in the data acquisition and control terminal in the scheme design; in order to quickly collect the frequency output pulses of 12 mass flow meters, three high-speed counting modules (5 channels/module, 100kHz) are configured, which have fast acquisition speed and simple and convenient hardware configuration.

3 Features of the entire production line

(1) The main body material of the entire line is 316L, and the fluid seal is EPDM, which meets the requirements of strong corrosion resistance and food grade.
(2) High degree of automation and advanced control technology.
(3) The filling speed of mass flow meter is nearly twice that of electronic weighing;
(4) The filling accuracy of mass flow meter is higher than that of electronic weighing, up to 0.1%, and the positive and negative deviations can be set manually;
(5) The equipment is simple, occupies a small area, works reliably, and requires little maintenance.

4 Conclusion

For high-precision filling of large-volume liquids, mass flow meter measurement is a reliable and simple technical solution. Compared with electronic weighing, it has higher filling accuracy and filling speed, and requires less investment. It is a filling technology worth promoting (end)