Application of frequency converter on centrifuge and analysis of effect

Ning Youlin, Ning Zhiwei, Yang Jianjun, Zheng Dejun, Li Yongsheng Abstract: This paper introduces the application of frequency conversion technology in the centrifuge of trona processing baking soda process and the effect analysis after transformation. Key words: frequency converter; centrifuge; application; effect analysis 1 Overview of working conditions Our company uses trona to process baking soda (NaHCO3). The WG - 1200 - 4B horizontal scraper is used for centrifugation. Machine, it is the key equipment for solid and liquid separation of baking soda crystallization liquid. During the operation, the working conditions of feeding, dehydrating, washing and unloading are changed repeatedly. Due to the simultaneous feeding and dehydration, the motor is intermittently overloaded, the motor temperature rises, the insulation aging is fast, and the motor is often burned. Moreover, according to the process requirements, at least 23 times of washing the net per shift (8 hours), when the net is washed, serious machine vibration is generated due to uneven material in the drum, in order to reduce the damage of the machine vibration to the equipment, the motor power is disconnected when washing the net. Relying on the centrifugal machine to rotate the inertia to wash the net, after the washing of the net, restart the motor, so that the motor starts and stops frequently, the centrifuge operation rate is low, the equipment damage rate is high, the maintenance and maintenance workload is large, the cost is high, and it directly restricts Product production capacity. According to the above situation, in order to solve the problems that existed, the installation of the frequency converter was installed in the centrifuge in April 2001. After one year of operation, the operation effect was very satisfactory. 2 analysis of transformation effects 2. 1 transformation plan Y250M -4 , 55 KW three-phase asynchronous motor with WG- 1200 - 4B centrifuge is started by Y - Δ starting mode. After starting, it runs at rated speed of 1200r/min regardless of the working condition. The vibration is very serious. Motor overload and overcurrent occur frequently during feeding. According to such operating conditions combined with the principle of frequency conversion speed regulation, the three-phase alternating current with fixed frequency (power frequency 50Hz) is converted into three-phase alternating current power with continuously adjustable frequency. By: N0 = 60 f / p Where: n0 ——— synchronous speed; f — the frequency of the current; p ———The number of magnetic pole pairs of the rotating magnetic field. It can be seen that when the frequency f is continuously adjustable, the synchronous speed n0 of the motor is also continuously adjustable. Also, because the asynchronous motor rotor speed nM is always slightly lower than the synchronous speed n0. Therefore, when n0 is continuously adjustable, nM is also continuously adjustable. The following principles were applied to the application of the principle of frequency conversion and the problems of the centrifuge. 1 Select Senlan BT40S75 KWTA type frequency converter to control the main motor of the centrifuge to form a set of AC variable frequency speed control system; 2 Y-Δ starter used in the original machine to run out, cold standby; 3 will be the original motor side The friction type centrifugal clutch type pulley is changed to a direct drive ordinary pulley. 2. 2 transformation effect The frequency converter is easy to operate and easy to control. It realizes the soft start of the motor, the starting current is small, the impact on the power grid is small, the equipment starts smoothly, and the starting fault is reduced. The starting equipment and transmission equipment are basically maintenance-free. The mechanical part of the maintenance work has dropped significantly. Using the frequency conversion speed regulation performance, combined with the process requirements, the centrifuge motor speed is set separately, namely: feeding, dewatering, washing and unloading at high speed (f = 40HZ, equipment speed n = 1200r/min) When the net is washed, it is completed at low speed (f = 20HZ, equipment speed n ≤ 600r/ min) or stepless speed regulation according to the process conditions. Meet the requirements of the process work, avoiding the machine vibration caused by washing the net. Operation data, function code and fault cause L ED Direct display, with over-current, short-circuit, grounding, overvoltage, undervoltage, overload, overheating, main device protection and other protection functions. The running current is set at Imax = 100A, which satisfies the mechanical drag power, and also effectively protects the motor and prolongs the service life of the motor. The pulley is changed to the ordinary pulley, which reduces the cost of the pulley and greatly reduces the maintenance cost. It completely eliminates the friction and smoke when the clutch starts, and eliminates the pollution of harmful gases to the environment. 3 Comprehensive economic analysis Due to the change of the starting mode, the friction centrifugal clutch is out of operation, all the accessories and materials are saved, such as: brake belt, cooling sleeve, pulley, cross iron, ferroniobium, etc., a single centrifuge can save 42452 yuan in the whole year. The centrifuges equipped with frequency converters and unmounted inverters were compared and saved. After one week of power consumption test, the average power saving per shift (8 hours) was 81kw/h, and the whole year was effectively produced in 11 months. Time calculation, annual electricity savings of 36085. 50 yuan. The service life of the motor is prolonged. On average, the motor burns down 3 units/time each year, and the repair cost is 10,800 yuan. The replacement of one motor affects the production for 3 hours and the non-invasive production value is 14,400 yuan. See the table above for details. In summary, it can be seen that the installation of the inverter is relatively large, but the cost of materials and electricity saving is 104,700 yuan/set. The increased investment can be recovered in less than six months. Appreciable, the site is practical and solves the problem of restricting production. Received a multiplier effect.

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