According to the characteristics of power supply and consumption in iron and steel enterprises, combined with energy-saving technology, this paper analyzes and discusses how to save energy in enterprises, and puts forward energy-saving measures from the aspects of power supply layer and power consumption layer, improving power factor and harmonic processing of power system, power monitoring and management saving.
Keywords: iron and steel enterprises; Power saving measures; Power layer; Electricity consumption layer
Energy is the material basis of human existence and activities, which is directly related to the national economy and people's livelihood. With the global spread of the current world financial crisis, the economic benefits of some industries have fallen sharply or even lost money. Therefore, actively promoting scientific development and doing a good job in energy conservation and emission reduction are the most effective ways for enterprises to make profits.
1 energy saving in steel industry
In the process of integration and optimization, the level of technical assembly and automation in China iron and steel enterprises has reached the same level. But at present, iron and steel enterprises are still large energy consumers in the production chain, and they are process production line enterprises from cold to hot, and then from hot to cold. How to use the change of intermediate heat energy and reuse energy is a long-term plan for the sustainable development of an enterprise. CDQ power generation project, sintering waste heat power generation, gas waste heat recovery, boiler steam refrigeration and other energy-saving technologies. Is gradually widely used in various steel enterprises.
However, the application of energy-saving technology in large-scale projects is only the first level to achieve energy-saving goals. Taking overall energy-saving measures for the existing distribution network and its equipment is the second level to realize the energy-saving goal. Therefore, at present, there is still great potential for iron and steel enterprises to save electricity and increase efficiency. Combining with the actual situation and consulting relevant materials, this paper summarizes some thoughts on energy saving in iron and steel enterprises for analysis and discussion, so as to contribute to energy saving and efficiency improvement of enterprises.
2. Several measures to save electricity in iron and steel enterprises
The principle of electrical equipment is to meet the production process, and the self-energy saving of new equipment and process is the major premise. As an electrical equipment, it does work in the form of voltage and current, converting electric energy into mechanical energy and light energy needed for production. To reduce unnecessary power consumption, one is to improve the efficiency of electrical equipment and save electricity, the other is to improve the power factor of electrical system and save electricity through harmonic processing, the third is to save electricity through management and monitoring, and the fourth is to use green energy.
2. 1 Improve the efficiency of electrical equipment
To improve the efficiency of electrical equipment, it is mainly to reduce no-load loss, load loss and heat loss. It can be considered separately from the power supply layer and the power consumption layer.
2. 1. 1 power saving measures for power supply equipment layer
Distribution network reconfiguration technology, adjust the distribution network structure. The technology of changing distribution network topology to improve reliability, reduce line loss, balance load and improve power supply voltage quality is called distribution network reconfiguration technology. Distribution network reconfiguration technology is an important way to reduce the line loss of distribution network, an important means to optimize the technology of distribution system and improve the safety and economy of distribution system, with low investment and high efficiency. Distribution network reconfiguration includes network reconfiguration in normal operation and network reconfiguration in fault state, as shown in table 1.
Table 1 distribution network transformation
In the process of reconfiguration, the reconfiguration target constraint condition reconfiguration calculation of running state reduces line loss, balances load and improves power supply quality under normal circumstances. Mathematical optimization algorithm, optimal power flow mode algorithm, branch exchange method and artificial intelligence algorithm isolate fault sources, restore regional power flow equation of non-fault sources, branch current and power saving voltage, network topology (radial), switching operation times and relay protection reliability. The fault diagnosis algorithm takes the minimum line loss as the objective function, and balances load and improves power supply quality in the process of distribution network reconfiguration. By dimensionality reduction, the multi-objective nonlinear hybrid optimization problem is simplified to a single-objective nonlinear hybrid optimization problem. The following measures can be taken: (1) Adjust the contact mode of distribution lines reasonably. Distribution lines should adopt the best operation mode to minimize their losses, such as standby lines, handover lines, ring network lines, parallel lines, double-circuit lines, etc.
(2) Ring network power supply, selecting the disconnection point of the network according to the economic power distribution. For ring power network, it is normal to disconnect Line 67 in the fourth phase of electromechanical technology (20 10). According to the principle that the voltage drop on both sides is basically equal, an economical power disconnection point should be found to minimize the power loss of the line.
(3) Popularize live working and reduce the power outage time of lines. For double-circuit power supply network, double-circuit parallel connection is the most economical. If one of the lines is cut off due to maintenance work, the line loss will be greatly increased because the load current passes through the other running line. Therefore, live working should be used as much as possible to reduce the frequency and time of power failure of double-circuit lines.
(4) Adjust the operating voltage of the power grid. According to the different load characteristics of each process line, the working voltage of power supply network is adjusted. When the static characteristic parameters and U/U0 of main electrical equipment in iron and steel industry are reduced from 1.05 to 1.0, the changes of P/P0 and Q/Q0 are shown in the following table 2.
Table 2 Static characteristic parameters of main electrical equipment in iron and steel industry: industrial motors, pumps, fans, etc. Electric arc furnace, central air-conditioning room, air-conditioning smelting blower, industrial TV fluorescent lamp PV 0.05 0.08 2.01.0 QV0.61.64.62.51.65.23.0u/ U0 = 1.05 65448 For the average load of iron and steel industry, when the power supply voltage is higher than the rated voltage, the voltage will be reduced by 5%, and the reactive power will be reduced by about 8%. The active power of the equipment will be reduced very little, which will not affect the production, but the line loss caused by reactive current will be reduced, and the input of reactive power compensation equipment will also be reduced.
Transformer transformation, through reasonable distribution of transformer load, makes the improvement of transformer operation efficiency bring energy-saving benefits. It can fundamentally improve the economic operation of the current enterprise distribution network, reduce the capacity of power agreement, and improve the electromagnetic compatibility level and power supply quality of the distribution network.
(1) Reasonable selection of transformer capacity and number. When selecting the capacity and number of transformers, the load should be reasonably distributed according to the load situation, and the transformer with capacity suitable for the power load should be selected to work in the high efficiency area considering the investment and annual operation cost. When the load rate is lower than 30%, it should be adjusted or replaced. When the load rate exceeds 80% and the calculation is not conducive to economic operation, the primary capacity selection transformer can be enlarged. For the load that cannot be cut off after the workshop stops production, a special transformer should be set up. Large factory buildings and non-three-shift workshops should be equipped with special lighting transformers.
(2) Choose energy-saving transformers and replace or transform high-energy-consuming transformers. Energy-saving transformers such as SL7, SLZ7 and S9 should be selected for new construction or expansion projects. Compared with the old products, the no-load loss and short-circuit loss of SL7, SLZ7 non-excitation voltage regulating transformers and 10kV series are reduced by 4 1.5% and 13.93% respectively. 35kV series decreased by 38.33%, 16.22%. Compared with SL7 series, the no-load loss and short-circuit loss of S9 series are reduced by 5.9% and 23.33% respectively, and SL7 series saves 9 kW·h per kilovolt on average every year. In order to save investment, enterprises can also carry out technical transformation on the original SJ 1 and SL 1 high-energy transformers, but after transformation, they should meet the requirements of the national energy consumption standards for distribution transformers, that is, the no-load loss is reduced by 45% ~ 65%, the no-load current is reduced by 70%, the short-circuit loss reaches SL7 standard, and the impedance voltage is 4% ~ 4.9%.
(3) Strengthen the operation management to realize the economic operation of the transformer. In the case of enterprise load change, if the number and capacity of transformers put into operation remain unchanged, their load rate and operation efficiency will change, which will be beyond the scope of economic operation. Therefore, some transformers should be put into operation or removed in time to prevent light load and no-load operation of transformers. For transformers with long-term light load (load rate below 30%), small-capacity transformers can be selected according to actual load when necessary.
2. 1.2 power saving measures for electrical equipment layer
The main purpose of power saving measures in electrical equipment layer is to improve the efficiency of electric energy conversion. The efficiency of converting electrical energy into mechanical energy involves four links: (1) motor efficiency; (2) the efficiency of production equipment;
(3) transmission efficiency; (4) Opening of valves or baffles. The following four aspects put forward some specific energy-saving measures.
2. 1.2. 1 Power saving measures for motors
The economic operation of the motor includes the following aspects: (1) Try to make the motor run in the economic operation area. Generally, the economic operation area of motor is that the load factor β is within the range of 70%≤β≤ 100%, and the electromechanical research, design and manufacture 68 in the fourth phase of Electromechanical Technology of motor has the highest comprehensive operation efficiency and the most energy saving. When β < 40%, the efficiency will be greatly reduced (η < 60%) and the power factor will be less than 0.5.
(2) The motor adopts Y-Delta to automatically switch between light and heavy loads. In order to improve the power factor and reduce the loss, when the motor runs under intermittent light load (such as the load is less than 40% of the rated power), the stator winding connection can be changed from △ type to Y type. At this time, the voltage on the winding drops to 1/3 rated voltage. In this way, although the power of the motor is only 1/3 of the rated power, the motor can run under light load. At this time, the load rate of the motor is increased, the iron loss is reduced by 2/3, its power factor and stator current are obviously improved, and the power saving effect is remarkable.
(3) Improve the connection efficiency between the motor and the dragged machine. Using the correct traction (transmission) machinery to reduce friction and transmission resistance is also a measure to save electricity.
(4) Improve environmental conditions, strengthen ventilation and reduce the operating temperature of the motor. The resistance of motor winding increases with the increase of temperature. The higher the working temperature of the motor, the greater the active power loss.
2. 1.2.2 Power saving measures for pumps and fans
The effective adjustment of pumps and fans, choosing efficient equipment is not equal to energy saving, but also depends on whether the actual working condition is near the highest efficiency point of the equipment performance curve, which mainly depends on the following factors: (1) the variation law of working flow. When the working flow changes more than 90% of the rated flow, variable speed regulation is generally not adopted; When the working flow changes more than 85% of the rated flow, it is necessary to adopt efficient variable speed regulation, such as frequency conversion or cascade speed regulation; When the minimum working flow is 50% ~ 70% of the rated flow, a more economical and reliable high-frequency chopper cascade speed regulation device can be adopted. Considering the initial investment, the method of "delaying more" can be adopted, as shown in figure 1.
Figure 1 "one-to-many" electrical schematic diagram
When the motor starts and stops, the frequency converter will be put into operation one by one. After completion, the frequency converter will be cut off and run at power frequency. In the process of speed regulation, the input and output of the motor can be selected according to the working conditions.
(2) The ratio of static rise (static pressure) to total rise (total pressure) of pipeline performance curve. When the static head accounts for a large proportion, even if the working flow of the pump system changes greatly, the energy saving effect is not great because the speed change range of the speed change device is not large.
(3) the capacity of the pump or fan (shaft power). High-power pumps and fans are suitable for high-efficiency speed regulating devices with high initial investment because they save a lot of electricity every year.
2.2 Improve the power factor and harmonic processing of the electrical system (1). In the motor and its control, actively promote energy-saving new products such as frequency converter and soft start switch. Vigorously promote the application of various perfect sine wave high-capacity high-voltage converters represented by three stages. High-voltage motor adopts frequency conversion speed regulation technology, which not only solves the problems of motor soft start and stepless speed regulation, but also meets the needs of production technology, and can greatly save energy and reduce production costs.
(2) Among all kinds of AC low-voltage motor speed regulation systems, frequency conversion speed regulation system has better performance and higher efficiency, which is difficult to achieve by some mechanical speed regulation methods at present. A frequency converter can drive multiple motors to run at the same time. The inductive reactive current of the motor will not be transmitted to the power grid due to the isolation function of the front-stage rectification filter of the "AC -DC- AC" general frequency converter, which indirectly plays the role of reactive power compensation and improves the power factor, but the harmonics generated by its own rectifier and inverter can not be ignored.
(3) Because the inductive load produces reactive power, reactive power compensation and harmonic filtering devices are adopted. For old motor equipment, popularize the local compensator of motor reactive power terminal. After compensation, the current can be reduced by 10% ~ 20%, the reactive power can be reduced by 40% ~ 80%, the power factor can be increased to 92% ~ 97%, and the average power saving is about 20%. This method has the advantages of less investment, quick effect and good comprehensive benefit.
2.3 power monitoring and management of power saving
2.3. 1 establish a distribution network dispatching center, which can be configured online on a unified support platform. According to the actual needs of users, it can flexibly realize various application functions such as dispatching automation, feeder automation, electric energy billing, power grid analysis software, dispatching management function, geographic information system, distribution network management function and so on. It has good expansibility of system application software and hardware, and can well meet the dispatching requirements of power system and large industrial and mining enterprises.
2.3.2 Energy-saving evaluation management
(1) Take the lowest power consumption index of enterprises of the same industry, scale and type at home and abroad as the reference system.
(2) Based on the detailed decomposition of energy consumption assessment indicators, corresponding safeguard measures are formulated for each detailed indicator, and the progress of each measure is dynamically tracked and assessed.
(3) Realize the line loss investigation in the whole process, and find out the problems and potential loopholes, so as to grasp the line loss situation in the whole process more accurately and carefully.
(4) In view of the outstanding problems, a series of rectification measures were put forward, which were implemented in all units in the form of project contracting, and the responsibility and time limit for rectification were clarified, and these projects were included in the scope of efficiency supervision, which increased the implementation.
2.4 the use of green energy
The application of photovoltaic technology can give priority to landscape lighting and other places in the factory, and it will be widely used in the development.
3 Conclusion
China is a developing country. Compared with developed countries, technology and professional management are still relatively backward. As far as energy utilization is concerned, there is still great potential for energy conservation. For the survival and development of enterprises, iron and steel enterprises must put energy conservation in the first place and make contributions to the establishment of a resource-saving and environment-friendly society.
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Gu shenggu. Fundamentals of electric drive [M]. Beijing: Machinery Press, 2004.
Su Zhen. Analysis of energy-saving ways in iron and steel enterprises [J]. Henan Metallurgy, 2009, 17 (2): 22-24.
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