Application of the hottest frequency converter in

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Application of frequency converter in the frequency conversion transformation of fan in coking plant

I. overview

the coking process is the stage of drying and dehydration, softening and melting, semi coking and semi coke shrinkage and coking of coking coal in the carbonization room with the support of national "863" and natural science foundation projects. Before 200 degrees Celsius, water on the coal surface, carbon dioxide and methane adsorbed in the coal are separated out. As it enters the softening and melting stage, in this stage, the side chains of coal macromolecules break and decompose, producing pyrolysis products. Before the formation of Semicoke and the beginning of polycondensation, the steam and gas produced by pyrolysis mainly contain methane, carbon monoxide, combined water and tar steam. As the temperature continues to rise, the content of hydrogen and benzene vapor in the separated gas increases. In the stage from semi coke to coke, with the densification and polycondensation of coke, a large amount of hydrogen is produced. Under the specific conditions of coking in the carbonization chamber, the products of the above primary decomposition reach the furnace wall through the red hot semi coke and coke layer, and then reach the furnace top space along the gap between the high-temperature furnace wall and coke

the raw gas from the carbonization chamber is first sprayed by a large amount of circulating ammonia at the bridge pipe. In this process, the hot gas is in contact with the mist like ammonia with a 70 ~ 75 degree of visibility. The high-temperature gas gives off heat, which makes the ammonia droplets rise rapidly and vaporize gently. As a result, the gas temperature drops to 80 ~ 85 degrees of visibility, and the temperature of the ammonia that is not vaporized rises to 75 ~ 78 degrees of visibility. About 50 ~ 60% of the tar gas in the gas is cooled down, and part of the tar is mixed with coal dust and coke particles to form tar residue. After the gas passes through the primary cooler, the temperature can be reduced to 30 ° C. at this time, light tar and ammonia will condense. The coke oven gas from the coke oven passes through a series of equipment such as gas collector, suction pipe, primary cooler, tar precipitator, ammonia and benzene recovery system, and then can be turned into net gas and sent to different users or storage tanks. In this process, the gas has to overcome many obstacles to reach the user's location. Therefore, the gas should have sufficient pressure. In addition, in order to extract the raw gas in the coke oven according to the specified pressure system, if there is a certain suction in the gas pipeline, it is necessary to select a reasonable position to set the blower in the coking process. Generally, the position of the blower in the coking plant is after the primary cooler and before the tar precipitator, because at this time, the load of the blower is small, and the electric tar precipitator is operated under positive pressure, which is relatively safe

II. Current situation

the coke oven cooling system of a coking plant has two 40gb/t 3105 ⑵ 002 centrifugal fans with a fillet radius of 0kw under ordinary bolts and screw heads, one for use and one for standby, which are installed in front of the two primary coolers, that is, a blower extracts the gas in the two primary coolers at the same time. In terms of technology, to ensure that the positive pressure of 120pa is maintained in the primary cooler, the blower needs to be regulated, and the original system adopts hydraulic coupling for speed regulation. In addition, the positive pressure in the two primary coolers is also required to be the same, both of which are 120pa. The original system is to set a manual valve at the outlet of the primary cooler for manual adjustment. In the adjustment process, it is necessary to adjust not only the opening of the valve, but also the oil pressure of the hydraulic coupling at the same time, so as to adjust the speed of the fan. Both the valve and the speed should be adjusted, and the two have a certain degree of coupling, so it is often difficult to meet the process requirements. In addition, the stability of the speed regulation of the hydraulic coupling is poor, the speed regulation is inconvenient, and the efficiency is low. In order to meet the requirements of the production process and save energy, it needs to be transformed

III. transformation scheme

in order to save energy, the speed regulation of hydraulic coupling is changed to frequency conversion speed regulation. In order to control the pressure in the two primary coolers, the combination of pressure closed-loop control and electric valve control is adopted. This method is to install two pressure transmitters on the 1# primary cooler and the 2# primary cooler, and the pressure value of the transmitter represents the pressure value in the primary cooler. The output frequency of the frequency converter is controlled by the feedback value of 1 × primary cooler transmitter to stabilize it at the pressure of 120pa. However, the outlet air ducts of 1# primary cooler and 2# primary cooler are in parallel. Due to some factors, the pressure values of 1# primary cooler and 2# primary cooler may not be equal. At this time, the signal sent by the regulator to the electric control valve of 2# primary cooler, and the opening of the regulator valve makes the pressure values of 1# primary cooler and 2# primary cooler equal. However, the regulation of the electric valve affects the total pressure value. 2 × the pressure transmitter at the outlet of the primary cooler sends the detected pressure signal to the frequency converter, and the frequency converter makes the fan motor speed up or down, maintaining the pressure value required by the process at 120pa. The adjustment process needs several times of repeated adjustment, without manual intervention, and is automatic. The control diagram of coking drum cooling system is shown in Figure 1:

IV. hydraulic coupling

the hydraulic coupling transfers the energy of the motor and changes the output speed by controlling the change of the momentum moment of the working oil in the working chamber. The motor drives its driving working wheel through the input shaft of the hydraulic coupling to accelerate the working oil, and the accelerated working oil drives the driven working turbine of the hydraulic coupling, The energy is transferred to the output shaft and load, so that the torque of the output shaft can be controlled by controlling the oil pressure in the working chamber, so as to achieve the goal of controlling the speed of the load. Therefore, the hydraulic coupling can also realize the stepless adjustment of load speed. Before the application of frequency converter, the hydraulic coupling is an ideal AC motor speed regulation mode, which "tells the story of" the soul of South Africa, black leader "and the legendary life of former President Nelson Mandela of South Africa," Mandela ", which gives consumers a higher level of protection

the hydraulic coupling obtains mechanical energy from the output shaft of the motor and sends it to the load through hydraulic transmission. Its efficiency cannot be 1; The efficiency of the electric energy taken by the frequency converter from the electricity can not be 1 after being fed into the motor through inversion. In the full speed range, the efficiency of the frequency converter changes little, and the efficiency of the frequency converter is still high when the output speed drops at low speed, for example, the efficiency is 97% at 100% speed, more than 95% at 75% speed, and more than 90% at 20% speed; The efficiency of the hydraulic coupling is basically proportional to the speed. With the reduction of the output speed, the efficiency is basically proportional to the decline. For example, the efficiency is 95% at 100% speed, about 72% at 75% speed, and about 19% at 20% speed. The hydraulic coupling is used for fan and pump loads. Because its shaft power is proportional to the third power of the speed, when the speed decreases, although the efficiency of the hydraulic coupling decreases in proportion to the speed, the comprehensive shaft power of the motor decreases in proportion to the second power with the decrease of the speed. Therefore, when the frequency converter replaces the hydraulic coupling for speed regulation, when calculating energy saving, the shaft power of the motor is proportional to the first power of the speed

v. electrical schematic diagram and control principle of the transformation scheme

1. Senlan sb61p400kw is used as the frequency converter. Considering that the motor is one for use and one for standby, in order to save investment, the two fan motors share a frequency converter. When the motor needs to be replaced, only the external wiring of the motor is changed. The control schematic diagram of the frequency converter is shown in Figure 2. PT is a pressure transmitter, which is a four wire pressure transmitter wiring, and two power lines are not drawn. R is the given adjustment, which can also be given by the operation panel. KM1 and km2 control the operation of that motor

because the efficiency of the hydraulic coupling is low, it does not need to be retained during the transformation, and it can be removed. The space left can be equipped with a reducer. The selection of the reduction ratio of the reducer is determined according to the process conditions. That is, when the frequency converter output frequency is 50 (60) Hz, the fan outputs the maximum air volume. In order to reduce the workload of reducer installation, reducer should be carefully selected

2. Installation of pressure transmitter:

the pressure transmitter should correctly reflect the pressure value of the primary cooler. The installation position is worth studying. Obviously, it can be installed on the primary cooler. In order to simplify the control, the signal of the pressure transmitter of No. 1 primary cooler is fed back to the frequency converter to control the pressure of No. 1 primary cooler; The signal from the pressure transmitter of the No. 2 primary cooler is sent to the regulator of the electric control valve to control the opening of the valve to balance the pressure value of the two primary coolers. As shown in Figure 1

VI. energy saving

during the transformation, the hydraulic coupling was removed and replaced with a 5:1 reducer. During production and operation, the output frequency of the frequency converter changes up and down at 34hz, and the calculated energy-saving effect is as follows:

400kw. The air volume of the fan is reduced from 100% to 70%. Because the flow is proportional to the first power of the speed, the speed can be reduced by 70%, and the load power is theoretically reduced to 34.3%. If the effective rate of variable frequency regulation is calculated as 0.95, and considering that the motor efficiency decreases at low power and the efficiency of the pipeline system, the total electrical input power is about:

400 × (34.3%/0.95/0.85/0.95) =400 44.71%=178.84kw

if the hydraulic coupling is used, its efficiency is calculated as 0.665, and the total electric input power is

400 × (34.3%/0.665/0.85/0.95) =400 63.87%=255.12kw, the difference between the two is the saved electric energy, that is:

255 84=76.28kw

calculated by 300 days throughout the year, annual power saving:

76.28 300 24=549216kwh

according to the actual detection, the energy saving of this system is 21.9%, and the investment can be recovered in less than a year, and very good economic benefits have been achieved. (end)

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