How to save energy scientifically?

If you intend to save energy, you must rely on science and technology, and brute force is useless. Whether it is energy utilization or energy-saving behavior, the first and second laws of thermodynamics are basic principles that must be observed. Although everyone is already familiar with these two laws, they seem to be taken for granted, but they are often forgotten by people. Many people want to invent a "perpetual motion machine" but fail to realize it, just violating scientific principles and using their efforts in vain. Nowadays, many people ignore the high-quality energy and waste it casually, hoping that the waste heat can be used to make up for it. The result is more than the loss. The first law of thermodynamics is called the law of conservation of energy, which states that the total energy is equal before and after the energy is converted (used). However, energy is converted into effective energy and ineffective energy during use. For example, the coal in the boiler is converted into steam and waste heat existing in flue gas, slag, etc. after being burned. The former is effective energy and the latter is ineffective energy. There are more effective energy parts, and the thermal efficiency is high, on the contrary, the thermal efficiency is low. The technical level of the boiler equipment plays a decisive role. At this time, it is necessary to research and adopt advanced boilers to improve thermal efficiency, so that the same amount of coal can produce more steam, or the same amount of steam uses less coal, thereby saving Energy. The second law of thermodynamics is called the principle of energy devaluation, which refers to energy not only in quantity but also in quality; in the process of energy conversion (use), high-quality energy is always spontaneously converted to low-quality energy. For example, heat is always transferred spontaneously from a high temperature to a low temperature. Relatively speaking, effective energy is high-quality energy, and ineffective energy is low-quality energy, or it is called "waste heat." To save energy, we must do everything possible to increase the rate of exergy and cherish the use of it, and then recycle the ineffective energy that has become "waste heat".

In China, industry consumes the most energy, accounting for half of the country's total energy consumption. Of course, it is also the focus of energy conservation, with huge potential for savings. Industrial boilers, electric boilers, industrial kilns, and metallurgical furnaces are all energy-consuming "big holes", and all kinds of process equipment consume energy. The level of their efficiency is directly related to the intensity of the energy consumption of the product, and there is a lot of knowledge about energy saving. Let us take them as examples to show that there is a lot of potential to directly request energy from science and technology.

Industrial boilers are the power equipment of general factories and are called the heart of factories. Generally, the evaporation capacity of industrial boilers is less than 65 tons/hour, and the boiler parameters are pressure less than 4 MPa (about 40 atmospheres) and temperature less than 450°C. This type of boiler is widely used in factories to provide power, and is also used for heating and domestic hot water supply. There are about 600,000 industrial boilers nationwide, and the annual consumption of standard coal is about 350 million tons. Due to various reasons, including rough coal processing, numerous small boilers, and backward combustion technology, boiler efficiency is generally low, with an average thermal efficiency of only 60% to 65%.

That is, only about 60% of the calorific value of the fuel is converted into steam, and the rest of the heat is lost. The thermal efficiency is 20% lower than the international level. If the efficiency of the thermal boiler can be increased by 15% to about 80%, the country can save 0.7 per year. 100 million tons of standard coal. To improve the thermal efficiency of the boiler, it is necessary to make improvements in coal processing, boiler structure and combustion technology, especially the use of large boilers. Large-scale boilers have high thermal efficiency. The construction of centralized boiler rooms for steam supply in industrial areas where many factories are concentrated is an important way to save energy to replace the scattered situation of one factory and one small furnace. After deducting the loss of the pipe network, this method of steam supply generally saves 20% of fuel and greatly reduces environmental pollution.

A similar situation exists in the fuel boilers of thermal power plants. Thermal power plants are also large coal consumers. China has developed rapidly in recent years. The annual coal consumption for thermal power generation has reached 600 million tons of standard coal. But at present, China's thermal power generation units are still relatively backward, and coal consumption is still relatively high. Although the previous energy-saving effect has been remarkable, the coal consumption per kilowatt-hour of electricity has been reduced to about 390 grams of standard coal, which is still 50 to 80 grams higher than the international advanced level of 320 grams. Compared with the annual power generation, it consumes tens of millions of tons of standard coal, the most important of which is The reason is the existence of a large number of small and medium-sized old units. These small and medium-sized power plants have low boiler parameters and backward technology, and the unit energy consumption of power generation is about 30% higher than the advanced level. They should be eliminated as soon as possible. Large-scale thermal power plants and the use of advanced large-scale boilers are the most important way to save energy in thermal power plants. The gas-steam combined cycle technology that is under development is an advanced power generation technology. It uses gas directly as the first working fluid to make the gas turbine do work. The exhaust gas that still has high temperature enters the waste heat boiler to produce steam and enters as the second working fluid. The steam turbine performs work, and the exhaust steam after the work enters the condenser, thus forming a closed cycle. Because this method makes full use of the high-quality heat of the gas without affecting the production of high-quality steam, the efficiency of converting energy into electrical energy is very high, up to about 50%, which is about 10% higher than that of modern pulverized coal stoves. Thermal power plants are also a way to comprehensively utilize energy and improve energy efficiency. In places where conditions permit, such as the establishment of thermal power plants near industrial areas, the use of combined heat and power can increase the utilization rate of heat energy. This is also proven by many thermal power plants. The boiler equipment in the general power plant or factory implements a single energy production method, that is, the power plant only generates electricity and the industrial boiler only produces steam. Condensing steam turbines for the purpose of simple power generation, high-quality energy steam enters the condenser after expanding and doing work. The cooling water takes away all the potential energy (here, the heat of vaporization of water) in the condenser. This part The heat loss is very large, about 45% of the calorific value of the fuel. If the back pressure steam turbine unit is used to realize the cogeneration mode, this part of the heat after the work is taken out for external heating, its quality is still no less than the steam of a general industrial boiler. In this way, the total utilization rate of thermal energy in thermal power plants is doubled compared to pure power generation. At the same time, because the steam and heat supply of the thermal power plant replaces the boiler group in the heat load center, the environmental pollution is also greatly reduced.

Industrial kilns are also "big users" of heat and have great potential for energy saving. There are many types and numbers of industrial furnaces in China. Smelting, cement, ceramics, glass and other kilns generally suffer from outdated equipment and low thermal efficiency. The average thermal efficiency is only half of the international advanced level. There are even many earth kilns with thermal efficiency only 5%~10%. A large number of kilns need to be modified. And eliminated. For example, in the cement industry, the national cement production capacity reached 1.3 billion tons in 2005, of which about 60% was produced by backward wet-process vertical kilns. The energy consumption per unit product was 60% higher than that of dry-process rotary kilns. It can be seen that the process can reduce energy consumption What a great significance.

The recycling of waste heat is another important aspect of energy saving. We have said that we should cherish high-quality energy and let it turn into low-quality waste heat. However, waste heat does exist after all, and there is no lack of high-quality energy in it. It would be a pity if it is not recycled.

Table: Waste heat resources in major industries

What is waste heat? Broadly speaking, all the heat contained in the flue gas and the material to be cooled with a temperature higher than the environment are waste heat. There are abundant waste heat resources in China's industrial production process, which can be divided into 6 categories: high-temperature flue gas, high-temperature products and slag, cooling medium, combustible exhaust gas, waste hot water, and chemical reaction heat. Among them, high-temperature flue gas waste heat is the most common, accounting for about half of all waste heat resources; cooling media such as cooling water accounts for about 20%; waste hot water and hydrothermal fluid account for more than 10%. In terms of industry, the most waste heat is iron and steel, petroleum, chemicals, building materials, light industry, food, etc. Their waste heat resources account for about 15% of the total industrial energy consumption, that is, 150 million tons of standard coal. If half of the waste heat can be recovered, energy can be saved. It is also very impressive. The so-called "waste heat resource" refers to the part of heat energy that may be recovered but not recovered under current conditions, not waste heat in a broad sense. The utilization of waste heat is not only determined by the quality of the heat energy itself, but also by technical feasibility and economic rationality. There are two types of waste heat utilization: direct utilization and comprehensive utilization. Direct utilization refers to the use of heat exchangers to preheat the air entering the kiln, dry materials, produce steam and hot water to reduce product energy consumption, such as the use of boiler flue gas to pass through the "economizer".

Heat exchanger heating pot such as "heat pipe"
The make-up water of the furnace reduces the energy consumption of steam production. Comprehensive utilization means that the recovered heat energy is used in other technological occasions, so as to "make the best use of everything." There are also various recycling methods used. One of them is called "heat pump technology", which is an advanced technology with a promising future, which is being developed in depth and is worthy of attention. Since thermal energy is similar to electric energy, it is not easy to store. When using the recovered waste heat in other process equipment, it must be well coordinated to avoid mutual inconsistency.

Energy-saving, science and technology can only provide various possibilities, and the implementation of this possibility still requires human effort. People who are accustomed to extensive production and management may find it troublesome to save energy. As for energy saving, they have to invest in development and are even less interested in applying advanced technology. This requires management. The use of legal means, the adoption of energy-saving encouragement policies, and the establishment of management institutions are all effective management measures. From an industrial perspective, eliminating outdated production and enabling enterprises to implement such management measures as cleaner production, whether from a large-scale area or from an enterprise unit, will achieve economic benefits while also receiving energy-saving effects. This is the role of energy-saving management and cannot be replaced.

Eliminating backward production is an inevitable trend to improve the economic efficiency of enterprises, and it is also a key measure for energy conservation. Many old industrial enterprises usually have small production scale, backward process equipment, low production efficiency, high energy consumption, serious environmental pollution and difficult to manage, and their life is also very difficult. For such enterprises, it is necessary to implement an encouraging policy of renewal and transformation, and at the same time implement energy-saving targets. Only when the two are not partial can the enterprise have pressure and enterprising spirit. Many small-scale productions such as small metallurgy, small fertilizers, small papermaking, small electricity, and small cement should be resolutely eliminated. Small-scale production has played a positive role in China's industrialization process, but it should be gradually discarded as the situation develops. Especially for products with high energy consumption intensity, only large-scale production can achieve consumption reduction and gain.

The implementation of cleaner production is an important part of saving resources and energy, reducing waste emissions, and implementing a sustainable development strategy. It has received global attention and has been formally written into the Rio Declaration and Agenda 21. The connotation of cleaner production includes five aspects: improvement of process and product design, choice of clean energy, energy saving and consumption reduction, comprehensive utilization of waste and waste heat, improvement of production and environmental management. There is no doubt that the amount of waste and energy emissions is inseparable from the effect of energy saving, and cleaner production will directly save energy. Since 2003, China has implemented the "Cleaner Production Promotion Law", marking that cleaner production has entered a period of full implementation in accordance with the law, and it is fortunate. With the promotion of relevant government management departments, many enterprises are formulating clean production measures and implementing them into action. Both the economic and energy-saving effects are very significant.