Electrostatic dedusting can be divided into four processes: gas ionization, dust charging, charged dust collection and cleaning. The basic principle is that after the electric field plus high voltage direct current, an anode plate and a cathode line in the electric field establish a Inhomogeneous high-voltage electrostatic fields, smoke passes between the cathode line in the electric field and the anode plate that is grounded, and is ionized by the strong electric field into positive ion negative electrons. Dust particles in the smoke encounter negative electrons and are charged and receive electric fields. The force moves to the anode and is adsorbed on the anode plate. Finally, the dust is removed through the cleaning system. For the electrostatic precipitator to achieve a good dust collection effect, a good matching power supply is also required. Power supply is mainly divided into industrial frequency SCR power supply and high frequency switching power supply.
This article will analyze and compare the technical indicators and economic benefits of traditional industrial frequency power supply and high-frequency switching power supply for electrostatic precipitators. It is recommended that high-frequency switching power supply be adopted for the electrostatic precipitator to meet the increasingly stringent environmental protection requirements in the new situation, and also for power generation enterprises. Create great economic benefits.
2. Electrostatic precipitator frequency SCR power supply
Electrostatic precipitator adopts power frequency SCR power supply. When the specific resistance of dust is relatively high and the anti-corona phenomenon easily occurs, the dust removal effect will be significantly reduced. Generally, the design criteria of the original electrostatic precipitator and the requirements of environmental protection emission standards are not met.
The power frequency power supply has the following disadvantages:
(1) The working frequency is low, and the efficiency conversion is low (generally less than 70%), so the energy consumption is high;
(2) The power input is a two-phase 380V AC power frequency power supply, which is also the power frequency phase adjustment, resulting in an input power factor as low as 0.7 or less, which easily leads to unbalanced distribution systems;
(3) The output ripple is large, the average voltage is about 25% lower than the pulsation peak voltage, resulting in a low corona voltage, and the waveform is a single power frequency wave. It is difficult to operate under high concentration dust, high specific resistance and other conditions. Up to the environmental emission requirements;
(4) The operating frequency is low, transformers and filters are bulky and heavy;
(5) The bulky power control cabinet and the power frequency transformer used for isolation and boosting are separated in two places, which consumes space, wastes cables, and increases infrastructure investment costs.
3. Electrostatic dust removal high-frequency power
The high-frequency power supply is a three-phase industrial frequency power supply to form a direct current through rectification, high-frequency alternating current through the inverter circuit, and then boost rectifier after the formation of high-frequency ripple current send dust collector, and its operating frequency is about 40kHz.
The high-frequency power supply current is composed of a series of narrow pulses. Its pulse amplitude, width and frequency can be adjusted. It can provide various voltage waveforms to the electrostatic precipitator, and the control method is flexible, so it can provide the most according to the operating conditions of the electrostatic precipitator. The appropriate voltage waveform improves the dust removal efficiency of the electrostatic precipitator, improves the power supply efficiency, and saves energy.
The three-phase AC input is rectified into a short-duration DC power supply, which is reversed to a high-frequency AC via a full-bridge, and a boosted DC-high voltage is output from the boosted rectifier. High frequency power supply operating frequency up to 40kHz, mainly includes three parts: inverter, transformer, controller. Among them, the full-bridge inverter realizes the conversion of DC to high-frequency AC, and the high-frequency transformer/high-frequency rectifier realizes the boosted rectifier output to provide power for the electrostatic precipitator.
The high frequency power supply adopts three-phase input, and it has no pollution to the power grid and no phase loss. It is a green power supply. The high-frequency power supply is multi-stage conversion and has good electromagnetic compatibility.
4. Comparison of technical specifications and application performance between high frequency power supply and commercial frequency power supply
According to the theoretical research and application of the high-frequency power of the electrostatic precipitator both at home and abroad, the high frequency power supply has unparalleled advantages over the conventional power frequency power supply.
The superiority of high-frequency power is mainly reflected in:
1) The conversion efficiency of high-frequency power can be as high as more than 90%, while the power-frequency power conversion efficiency is only 70%, and the conversion efficiency is different by 20%.
2) The power factor of high frequency power supply is above 0.9, and the power factor of power frequency power supply is generally lower than 0.7.
3) The high-frequency power source uses a balanced input of three-phase power supply. The harmonic components of the high-frequency power supply have little pollution to the power grid, and there will be no phase loss.
4) Compared with the power frequency power supply, the high frequency power supply can increase the corona power, thereby increasing the charge ability of the dust within the electric field. When the high-frequency power supply is in the pure DC power supply mode, the voltage fluctuation is small (generally about 1%, while the power frequency voltage fluctuation is >30%), the corona voltage is high (it can reach 130% of the secondary voltage of the power frequency power supply), corona The current is large (the peak current is 200% of the secondary current of the power frequency power supply).
5) The spark control characteristics of the high-frequency power supply are good. It takes only a short time (<25us, and the power frequency power supply needs 10000us) to detect the spark and immediately turn off the power supply pulse, so the spark energy is very small and the electric field recovers quickly (only It requires 20% of the power-frequency power recovery time, which greatly reduces the invalid air ionization.
6) The high frequency power supply is smaller, lighter, and highly integrated. The distribution system, control system, high-frequency rectifier transformers, and rapping and heating control systems of high-frequency power supplies can be designed and integrated into a single box as required, and the volume and total mass can be greatly reduced. The installation of high-frequency power supplies is also more convenient. There are fewer auxiliary devices and they are installed directly on the top of the electrostatic precipitator. This not only saves space in the distribution room, but also saves most of the signal cables and control cables and reduces installation costs.
5. Comparison of engineering operation parameters of high-frequency power supply and commercial power supply
In recent years, the dust removal and high frequency power supply has been greatly promoted in many power plant transformation projects. From the perspective of the actual commercial operation of the product, the high frequency power supply operates stably and reliably, fully achieving the purpose of energy conservation and emission reduction. Take some domestic coal-fired power plant units as an example, compare the dust removal efficiency and operating energy consumption before and after the high-frequency power is used in the electrostatic precipitator.
The No. 2 boiler of a 2×300MW unit in the middle of the power plant was originally a dual-chamber, three-electric-field horizontal electrostatic precipitator, which was later converted into a double-row, double-chamber, and four-field electric field. (Dust removal efficiency is guaranteed by 99.86%). After the transformation of the project, the efficiency test was carried out and two comparative tests were performed on the electric field of the right chamber of the B dust collector using a high frequency power supply (0.8A/72kV) and a power frequency power supply (0.8A/72kV) to illustrate the electrostatic precipitator. The use of high-frequency power can increase the electric field strength, reduce the load of the rear electric field, and help improve the efficiency of the electrostatic precipitator.
Single high-frequency power energy efficiency calculation:
High-frequency power input power S = U1 × I1 × √ 3 = 385 × 85 × 1.732 = 56.68kVA
High-frequency power output power P = U2 × I2 = 66 × 750 = 49.50kW
Power input power S=U1×I1=385×185=71.23kVA
Power frequency output power P=U2×I2=56×750=42.00kW
High-frequency power energy = 71.23-56.68=14.55kVA
Energy Saving Ratio=14.55/71.23=20.4%
Taking the high-frequency output power 49.50kW as a benchmark, the industrial frequency output power is 42.00kW. If the power frequency power supply is consistent with the output power of the high-frequency power source, it is also 49.50kW. It is considered that the power factor and efficiency are 42.00kW and 49.5kW when the power frequency output is output. Without change, the output power of the power frequency power supply can be calculated to increase 49.50/42.00 times, and the input power of the power frequency power supply can be calculated as 49.50/42.00×71.23=83.95kVA.
Energy savings after conversion=83.95-56.68=27.27kVA
Energy Saving Ratio after Conversion=27.27/83.93=32.5%
6. Investment Estimation and Economic Analysis
6.1 Investment Estimation
The high-frequency power supply is higher in price than the power-frequency power supply. After the high-frequency power supply is used, the project cost will increase. However, after using high-frequency power, other parts of equipment and materials can be reduced accordingly.
Because the high-frequency power supply is an integrated structure, it is directly installed on the top of the electrostatic precipitator. Only the power cable and the communication cable are connected to the power distribution room of the electrostatic precipitator. Many cables will no longer be needed or the length and specifications will be reduced. investment. Taking an electric field in the middle of the country as an example, the comprehensive engineering cost of each unit increased by 1.32 million yuan.
6.2 Energy Savings Estimation
Electrostatic precipitator energy-saving and power-saving benefits The entire unit's precipitator is optimized for energy saving. All high-voltage parts are replaced with high-frequency power. The annual energy-saving benefit is 2.34 million yuan, while the investment in equipment is increased compared to the power-frequency power supply. Ten thousand yuan can recover the increased investment in half a year, and the economic benefits are obvious. Moreover, it can effectively increase the dust removal efficiency of the dust collector and meet the increasing environmental protection emission requirements.
7. Conclusion
In summary, the high-frequency power of the electrostatic precipitator has experienced many years of development and field application, and its high-efficiency reliability has been verified. Although the initial investment has increased, the energy-saving and consumption-reducing index is remarkable, and it has a high cost performance and is in line with the country. Energy conservation and emission reduction. Therefore, high-frequency power technology is recommended.
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