Abstract: The sugar press adopts AC frequency conversion and comprehensively considers the extraction rate and the pressing amount to set the appropriate rotation speed. Then the automatic control system automatically adjusts the rotation speed of the press according to the requirements of the pressure equalization, maximally increases the sugar production and saves the electric energy. . Key words: press frequency control, increase the extraction rate of sucrose, save energy Second, the press process analysis 1, SB70 vector control inverter user manual hope Senlan Technology Co., Ltd.
I. Overview
Sugar is one of the main living materials of people. Sugar and protein, fat and inorganic salts are the main nutrients for human health. Each gram of sugar can produce 16748J of heat in the human body to maintain the body's activities. Therefore, sugar is an important food for humans, especially athletes and babies, and sugar is one of the important condiments in people's daily lives. In addition to being directly consumed, sugar is an important industrial raw material. The food industry, the pharmaceutical industry, and the chemical industry all have a close relationship with sugar. China is one of the earliest countries in the world to use sugar cane to make sugar. It has a history of more than 2,000 years. The sugar cane sugar production process is roughly divided into the following processes:
Sugar cane must be crushed before it enters the press or exudate - called pretreatment. The purpose of the pretreatment is to break the strip of sugar cane into flakes or filamentous cane, tear the fibrous tissue of the sugar cane, and fully break the sugar cells. The pretreated cane is pressed with a press to press out the cane juice. The pressed cane juice also contains a lot of impurities, and it is necessary to carry out the processing of the cane juice through multiple processes to ensure the smooth progress of the next process. These processes include: sulphurous acid cleansing (or other methods of cleansing), pre-ashing and heating processes, sulfuric acid neutralization of cane juice, sedimentation of cane juice, and cane juice. After the cane juice is cleaned, the thin juice containing a large amount of water passes through the evaporation section to remove a large amount of water, and is concentrated into a syrup of about 60 degrees Bx, and crystallized to produce commercial white sugar.
The press is the main equipment for sugar cane juice. The complete set of equipment consists of an electric motor, a reducer, a drive mainframe (ie press) and a hydraulic system. As an important production equipment of the sugar factory, the total capacity of the 5- or 6-stage press motor accounts for more than half of the installed capacity of the sugar plant, but the traditional control method has been used for a long time: fixed speed operation, DC speed regulation or hydraulic transmission system. .
There are many factors affecting the sugar extraction rate. If the extraction rate of the press is increased by 1%, the total recovery rate will increase by 0.88% to 0.92%. The factors affecting the extraction rate are mainly due to the following reasons:
1. The pressing efficiency is generally measured by the two indexes of the processing volume and the extraction rate of the press. Generally speaking, under certain conditions of the press equipment, the extraction rate is increased, and the extraction rate is often decreased. Conversely, if the extraction rate is increased, the crushing amount will be affected, so the treatment volume and the extraction rate are contradictory and mutually restrictive. In general, setting a suitable pressing speed requires a certain amount of pressing without causing the extraction rate to be too low.
2. The fiber in the sugar cane expands when it leaves the press exit after being pressed. At this time, the pressed fiber absorbs a part of the squeezed cane juice at the exit with its own expansion, and is affected by the machine efficiency. It is impossible to extract all the sugar in the middle. The technical principle of “reducing the load of the front roller to reduce the load of the whole machine to improve the pressing efficiency†is to change and reduce the opening and opening ratio of the roller before and after the press, and improve the juice yield of the front roller. The pressure of the roller draining juice reduces the re-absorption and reduces the water content of the bagasse, thereby achieving the ultimate goal of increasing the extraction rate of the single machine and the whole machine while reducing the energy consumption of the electromechanical.
3. The degree of fragmentation and shape of the cane material is the prerequisite for ensuring the extraction of the first-stage press. The sugar cane has good breakage, the cane juice is easy to be pressed out, and the extraction rate is increased.
4. The uniform thickness of the cane layer conveyed from the sugarcane machine is very important to improve the extraction rate. If the cane layer is too thick, the pressing is not complete; if the cane layer is too thin, the cane layer is not dried, and both affect the extraction rate.
5. In the late stage of the pressing season, as the wear of the press rolls becomes more and more serious, the gap of the press rolls is enlarged, and the extraction rate is lowered.
When running at constant speed, after the motor is decelerated by the reducer, the speed of the press roll satisfies the requirement of a certain amount of pressing without causing the extraction rate to be too low. Since the speed of the press is not adjustable, when the raw sugar cane is changed, the speed of the press roll should be changed accordingly to ensure that the extraction rate of sucrose is within the control range. In addition, depending on the site, the speed of each level may be adjusted. As for the change of the thickness of the cane layer conveyed by the sugarcane machine, the sugarcane machine is generally controlled automatically. When the thickness of the cane layer changes, the rotation speed of the sugarcane machine is automatically changed to ensure a balanced press, but the sugarcane machine is purely Speed ​​regulation does not necessarily fully meet the requirements of balanced press.
The early press press adopts more DC speed control system, which can meet the speed regulation requirements of the press, and solves the problems existing in the fixed speed operation. The operation is also relatively stable and reliable, and is currently the control method still used by sugar factories. But there are also many problems:
1. The efficiency of the DC motor is 2%-3% lower than that of the AC asynchronous motor, and the energy consumption is large.
2, the sugar workshop environment is poor, DC motor failure rate is high, affecting production; maintenance, maintenance troubles, cost. In the sugar-making workshop, dust containing sugar is deposited on the commutator of the DC motor, causing the commutator to ablate, and the ablation is more serious in the late season, often having to stop to repair the commutator.
Third, press machine frequency control system control plan
In summary, because the speed of the press is not adjustable, the thickness of the cane layer conveyed from the sugar cane machine will not reach the requirement of about 10% of the time, so that the average extraction rate of the cane juice is less than 95.4%. The first press maintains a certain fixed speed according to the pressing requirement. The 2-5-seat press relies on its own instantaneous speed regulation to stabilize the respective material level, thus ensuring uniform thickness of the cane layer through each press and achieving high press. High extraction and low load. The average extraction rate can be increased by more than 0.2%. At the same time, the speed is reduced, the load is reduced, and the current is reduced to achieve energy saving.
The original system of a sugar factory in Zhanjiang is DC speed regulation. In order to improve the extraction rate and energy saving, the DC electric drive of the sugarcane machine is changed into AC electric drive. The press unit is a series of 5 Ф 670×1200 presses with a motor power of 200 kW. The modified system consists of inverter cabinet, switch cabinet and remote control console. Each press is logically interlocked with 1#, 2# cane belt, high speed belt and 1~4# gearing machine. Motor fan fault alarm, power main circuit fault alarm, inverter fault alarm, high temperature alarm of press motor, and “emergency stop†and “interlock/manual†switching functions. All equipment interlock protection, equipment failure alarm, equipment start-stop, etc. are completed by PLC control in the remote control console. The functions are complete, the quality is stable and reliable, and the baghole blocking phenomenon is effectively solved. The current and speed of the press motor adopt digital indicator, which is beautiful, accurate and intuitive. The temperature of the press motor is indicated by an 8-point digital inspection instrument, which saves the space of the console, is beautiful, accurate and intuitive. The schematic diagram of the control main circuit is as follows:
The main functions of the system are:
1. After the reform of the press, the system is equipped with: original system operation, adjustment, new system power frequency start, new system frequency conversion start, new system automatic control.
2. Manual control: Install one inverter cabinet and one inverter conversion cabinet for each motor. When the inverter cabinet is faulty or abnormal, the system can be switched to the original starter cabinet through the frequency conversion cabinet, so that the press can be continuously produced continuously. The frequency conversion converter is also equipped with an AC reactor, which can effectively suppress the influence of harmonics on the power grid, and protect the frequency converter from the surge voltage of the power grid.
3. When the thickness of the cane layer of the sugarcane machine changes, the electronic belt scale feeds the signal of the cane layer to the inverter of the sugarcane machine, so that the inverter of the sugarcane machine adjusts the rotation speed of the press according to the amount of the cane, the electronic belt scale The signal is large, indicating that the thickness of the cane layer is thick, the inverter will increase the speed of the motor; the signal of the electronic belt scale is small, indicating that the cane layer is thin, and the inverter will reduce the rotation speed of the motor, thereby ensuring uniform thickness of the cane layer and helping to extract the extraction. rate.
4. In order to improve the extraction rate and ensure the thickness of the cane layer is the premise of balanced injection, the speed adjustment of the simple cane conveyor machine may not fully meet the requirements of balanced injection. In each press, the Hall sensor is added to detect the actual current of the motor. As the feedback signal of the inverter, the inverter controls the motor speed according to the feedback signal. If the cane layer is too thick and the current of the motor becomes larger, the inverter will increase the speed of the motor, so that the cane layer is pressed as soon as possible; if the cane layer is too thin, the motor current becomes smaller, the inverter will reduce the motor speed, so that Stack the cane as thoroughly as possible. This allows the motor current to always fluctuate within a small range, thereby ensuring uniform thickness of the cane layer and helping to increase the extraction rate.
V. Benefit analysis after transformation
1. Increased extraction rate: According to calculations, the average extraction rate can be increased by more than 0.2%. Now it is conservatively estimated that the extraction rate is increased by 0.1%, and the annual sugar extraction is 550,000 tons of sugar cane, sugar is 13.5%, and cooking is 86%. The season produces more than 550,000 tons of sugar *13.5% * 0.1% * 86% = 63.85 tons, according to 2700 yuan / ton of sugar: 63.85 tons * 2700 yuan / ton = 172,000 yuan, so that the company will generate more than 172,000 per crop season yuan.
2. The power saving effect is remarkable: the total capacity of the five juicers installed is 2000kW. According to the calculation, the power consumption of the tons of sugar cane has decreased from 33.02 degrees to 31.22 degrees after the transformation, which has reached the normal level of sugar plants of this size. Reasonable energy consumption level. The electricity consumption per ton of sugar cane is reduced by 1.8 degrees, and the annual output of 550,000 tons of sugar cane is calculated: annual energy saving: 550,000 tons * 1.8 degrees / ton = 990,000 degrees according to 0.5 yuan / kWh: 800,000 degrees * 0.5 yuan / Degree = 400,000 yuan.
3. Reduced maintenance and shutdown losses and saved a lot of maintenance costs.
Conclusion
The AC variable frequency speed regulation of the sugar cane sugar press can increase the extraction rate of sucrose and has significant energy saving effect. In the modern society where energy supply is becoming more and more tense, the energy-saving and consumption-reducing work of sugar-making enterprises has a long way to go. How to maximize production, reduce coal and electricity consumption, and save energy are powerful measures for enterprises to improve their competitiveness. First, it is also the main means to improve economic efficiency.
references:
2, Peng Haiyu Du Junming calculation method of variable frequency speed regulation energy saving "Automation Expo" 2008.5