The FGI FD5000S Medium Voltage Drive helps improve energy efficiency in the overseas sugar industry
A certain sugar factory in Pakistan is located in Pakistan. Punjab Province The company's current output value has reached a pressing capacity of 38,000 tons per day. It is the largest sugar factory in Asia, and the company's main products are raw materials for sugar and alcohol.
The sugar production from sugarcane is roughly divided into four steps: The first is the pretreatment of sugarcane; The second is exploitation; The third is clarification evaporation; The fourth is to boil sugar.
The sugarcane is first leveled by the belt conveyor through the flattening machine, then chopped by the sugarcane tearing machine, and immediately sent to the press. The sugarcane undergoes six squeezings, and the liquid squeezed out is directly transported to the juice tank by the water pump. The remaining residue is sent to the boiler for drying by the conveyor belt and then undergoes waste utilization treatment. The liquid in the juice box undergoes clarification, evaporation and sugar boiling processes, and finally white granulated sugar is produced.
The sugarcane sugar factory press is an important equipment for extracting sugarcane juice by the pressing method. The main equipment for juice extraction by pressing includes tearing machines, pressing machines and their driving devices, as well as corresponding conveying equipment. The tearing machine is composed of sugarcane knives and a driving device. The press is composed of three rollers and a frame. The three rollers of the press are assembled into a triangle and are respectively called the top roller, the front roller and the rear roller according to their positions. There is a certain gap between the top roller and the front and rear rollers, and the pressing roller has a ring groove. The shaft ends of the three rollers are connected by transmission gears or chains. The top roller is driven by an electric motor, steam turbine or steam engine through a reduction device, so that the three pressing rollers rotate at the same speed.
The principle of extracting juice from sugarcane by pressing mainly involves tearing the sugarcane into fine filaments and sending them into a press. Under the pressure of the press, the cell walls of the sugarcane filled with juice break, and at the same time, the juice is discharged. With the aid of the infiltration system, the bagasse that has begun to expand and is discharged from the press is impregnated with hot water or diluted juice to dilute the sugar content within the cells, and then sent to the next press for pressing. Through multiple stages of pressing, more sugarcane juice is extracted.
3.Reasons for equipment renovation
It is well known that the extraction rate of the press is one of the main factors affecting sugar absorption. If the extraction rate of the press increases by 1%, the total recovery rate will increase by 0.88% to 0.92%.
The main factors influencing the extraction rate are as follows:
The fibers in sucrose expand again when they leave the outlet of the press after being compressed. At this time, the fibers that have been pressed will absorb part of the already extracted sucrose juice at the outlet. Also, due to the efficiency of the press, not all the sugar in the sugarcane can be extracted. This leads to the loss of sugar in the sugarcane residue.
The degree of crushing and the shape of the sugarcane material are the prerequisites for the first press to extract. Good crushing of sugarcane makes it easier to extract the sucrose juice, and the permeation effect improves.
Reducing the moisture content of the sugarcane residue is the guarantee for improving the extraction rate.
Ensuring the uniform thickness of the sugarcane layer transported from the shredding machine is very important for improving the extraction rate. If the sugarcane layer is too thick, the pressing is not thorough, causing waste of sugarcane residue; if the sugarcane layer is too thin, the sugarcane residue cannot be dried thoroughly, and the moisture content is too high, affecting the extraction rate.
In the later stage of the sugarcane pressing season, due to the increasingly severe wear of the press rollers, the gap between the rollers expands, resulting in a decrease in the extraction rate.
The original on-site press was started by a back-pressure steam turbine. A set of press was composed of a steam turbine, a reducer and gears. Firstly, steam drove the steam turbine to operate the reducer. The bearings of the reducer were connected to the gears, which then drove the press to work. The on-site pictures of the steam turbine are as follows:
Since other equipment at the site requires a large amount of steam, and small back-pressure steam turbines have:
(1) Low efficiency: Since small back-pressure steam turbines do not have equipment such as condensers, the exhaust temperature is higher and the efficiency is lower.
(2) High pollutant emissions: They are suitable for fuels with pollutants such as crushed coal, and they emit a large amount of pollutants.
Furthermore, the speed of the press machine is not adjustable. From the shredding machine, about 10% of the time the thickness of the sugarcane layer does not meet the requirements, which will cause the average extraction rate of the sugarcane juice to be lower than 95.4%. The lower the extraction rate, the greater the loss of sugarcane juice, and thus the output will decrease. If the speed of the press machine can be adjusted, when the thickness of the sugarcane layer is insufficient, the speed of the press machine motor can be reduced to make the sugarcane layer reach the normal thickness before pressing, so that the pressing will be more thorough, and the average extraction rate can be increased by more than 0.2%. At the same time, due to the reduction in speed, the current decreases, thereby achieving the purpose of energy saving and electricity conservation. Therefore, the user proposed to carry out skillful modification of the press machine equipment.
4.Modification scheme
According to the on-site requirements, a medium voltage inverter and an electric motor were adopted to replace the original steam turbine driving the press. An electric motor was used instead of the original steam turbine, and a high-voltage frequency converter was adopted as the starting device for the electric motor. This not only enables the motor to start smoothly but also reduces the impact of direct starting on the power grid and the overheating of the motor windings caused by the large current at the moment of starting, thereby accelerating insulation aging. It has a significant impact on the service life of the motor. The second is that it is easy to operate and maintain. Thirdly, it is convenient for speed regulation and meets the process requirements of the press.
According to the production process requirements, each production line has 5 presses. The first press adopts a high-voltage frequency converter one-to-one high-voltage motor method. The high-voltage motor is a variable-frequency three-phase asynchronous motor improved and produced by Shanxi Motor Manufacturing.
Since it is an export product, the FGI frequency converter adopts an all-English design. Its interface diagrams and parameter settings are all explained in English, making it convenient for users to translate and read.
The control system consists of a controller, optical fibers, PLC boards, human-machine interface and upper computer.
The controller is composed of three optical fiber boards, one signal board, one main control board and one power supply board.
The optical fiber board transmits data signals through optical fibers to the power unit, and each optical fiber board controls all the units of one phase. The optical fiber board periodically sends pulse width modulation (PWM) signals or working modes to the power unit. The power unit receives its trigger instructions and status signals through the optical fibers, and sends fault code signals to the optical fiber board in case of a fault.
The main control board uses a high-speed DSP single-chip microcomputer to complete all the functions of motor control. It generates three-phase voltage commands with pulse width modulation by using the sine wave carrier phase-shifting method. Data exchange is carried out with the human-machine interface main control board through the RS232 communication port. The status parameters of the frequency converter are provided to the human-machine interface, and the parameters set by the human-machine interface main control board are accepted.
The human-machine interface provides users with a friendly full-English operation interface, responsible for information processing and communication with the outside world. An upper-level monitoring option can be selected to achieve networked control of the frequency converter. Data collected by the main control board and PLC board is used to calculate operating parameters such as current, voltage, power, and operating frequency, providing a recording function, and implementing alarms and protection for motor overload and overcurrent. It is connected to the main control board via the RS232 communication port and to the PLC board via the RS485 communication port, enabling real-time monitoring of the status of the frequency converter system. The main interface of the FGI frequency conversion control system is shown in the figure below.
The PLC board is used for the logical processing of switch signals inside the frequency converter, as well as on-site operation signals and status signals, enhancing the flexibility of the frequency converter's on-site application. The PLC board has the capability to handle 4 analog input channels and 2 analog output channels. The analog input is used to process analog signals such as flow and pressure from the site or setting signals during analog Settings. The analog output quantity is a frequency-given signal.
The upper computer communicates with the PLC board via the RS485 interface to facilitate users' operation of the frequency converter and to monitor the operating parameters of the frequency converter in real time. If it is connected to a printer, work records can also be printed at any time. As long as the various operating parameters of the frequency converter are set properly, the operator can perform various operations in the monitoring room without entering the high-voltage electrical control room. This is both convenient and safe, thereby reducing the labor intensity of workers and improving work efficiency.
This system is composed of high-voltage switch cabinets and high-voltage frequency converters. Each cabinet is equipped with 5 sets of high-voltage frequency converters and high-voltage switch cabinets, as shown in the figure.
(4) Technical features of the FGI FD5000S series medium voltage drive
The FGI FD5000S series of medium voltage drive are equipped with a high-speed DSP as the control core. They adopt the speed vector control technology and the power unit series multi-level technology. They are high-high voltage source type frequency converters. Their harmonic indicators are much lower than the harmonic national standard of IEEE519-1992. They have a high input power factor and good output waveform quality. No input harmonic filter, power factor compensation device or output filter is required. There are no problems such as additional motor heating caused by harmonics, torque pulsation, noise, high output dv/dt, and large common mode voltage. Ordinary asynchronous motors can be used. The FGI high-voltage frequency converter has been rated as a Chinese famous brand product. Specifically, in addition to having the performance of ordinary frequency converters, the FGI high-voltage frequency converter also has the following outstanding features:
Adopting high-speed DSP as the central processing unit, the computing speed is faster and the control is more precise. Coasters start function. It can identify the speed of the motor and start it directly without stopping the motor. In the rotating restart function. During operation, if there is a sudden power failure of high voltage, it will be restored within 3 seconds. The high-voltage frequency converter will not stop. After the high voltage is restored, the frequency converter will automatically run back to the frequency before the power failure.
The effect after the transformation
After the transformation of the press, it has been recognized by users. Firstly, it is easy to operate and maintain, reducing the input of labor. Second, it reduces the emission of steam and optimizes the working environment.
5.After the renovation and commissioning, the following advantages are achieved:
(1) It can achieve soft start, and the start-up time and start-up method can be adjusted according to the on-site conditions.
(2) The power factor is high, reaching above 0.95, and no additional power factor compensation device is required, avoiding fines caused by reactive power.
(3) It does not generate harmonic pollution to the motor, effectively reducing the heat generation of the motor.
(4) The torque pulse is very low, which will not cause resonance in the motor and other mechanical equipment, and also reduces the wear of the transmission mechanism.
(5) The output waveform is perfect, with a distortion degree of less than 4%.
(6) It reduces the phenomenon of the pressing machine stopping due to the thick sugar layer and the pressing machine getting stuck.
