With the depletion of fossil energy, the supply of energy to support the rapid development of the world economy has become increasingly tense, and the environmental problems caused by the irrational use of energy have become more serious. The energy crisis and environmental pollution have become the triggers for the development of the global economy and haunting human life. . China is a big country for energy production and energy consumption. Economic development depends on energy. In the new situation where the energy issue is becoming increasingly severe, saving resources and environmental protection have imposed higher requirements on the efficient use of energy. Therefore, it is of great significance for China's economic development and environmental protection to change the traditional use of energy technologies and improve energy efficiency.
Low energy efficiency has become one of the important reasons for the shortage of energy supply and demand in China. The output efficiency per tonne of standard coal in China is only equivalent to 10.3% in Japan and 28.6% in the United States. In industrial energy use, nearly 60 to 65% of energy is converted into waste heat resources. If it is used rationally, energy efficiency can be greatly improved. At present, the United States is the country with the most waste heat utilization, with a utilization rate of 60%, Europe's utilization rate is 50%, and China only has 30%. Therefore, China still has a lot of room for development in the field of waste heat and residual energy utilization. China's residual heat and residual energy utilization is mainly based on the steam turbine power generation system consisting of a waste heat boiler matching steam turbine. Although this technology has been applied in industries such as iron and steel, metallurgy and other industries that contain medium and high-temperature waste heat steam, it is not widely used in the field of medium-low temperature waste heat exhaust gas resources. The waste heat exhaust gas utilization system based on two key equipments of reciprocating internal combustion engine and screw expander is gradually recognized by the market for its wide application scope, high flexibility, and high cost performance. It has become an important way for the waste heat utilization of low temperature waste heat.
1. Reciprocating internal combustion engine exhaust gas utilization technology
In industrial waste gas, the quality of gas source, available scale, equipment cost and other factors constrain CBM (coalbed methane produced by surface drilling, gas drainage from coal mines), coke oven gas, and smelting tail gas (iron and steel blast furnace gas). (Steel-making converter gas), low-concentration gas, recovery and utilization of associated gas in oil fields, recovery of power generated by blast furnace and converter gas, low-temperature waste heat power generation, and other heat residual energy power generation technologies. It can be seen that the vigorous development of waste heat and residual energy power generation technology during the 12th Five-Year Plan will greatly help solve the increasingly severe energy-saving and emission reduction targets. Therefore, it is necessary to carry out research on low-temperature waste heat exhaust gas utilization technology, extensively investigate and apply cases, and accumulate rich practical experience to lay a solid foundation for further improving equipment reliability, technical stability, and popularization and application.
Key words: Small-scale power generation equipment Waste heat Waste gas utilization technology Analysis Combustible exhaust gas such as biogas, straw gas, carbon black gas, refining tail gas, oil-base shale gas, and oil companion gas that cannot be exported is not suitable for use in gas turbines and steam turbines, but the reciprocating internal combustion engine The power generation system of the group can be fully utilized to turn waste into treasure.
1.1 Technical Principles
The reciprocating internal combustion engine set power generation system mainly utilizes a reciprocating internal combustion engine to drive a generator to generate electricity, matching a waste heat boiler to form a gas power station, and realizing heating and cooling exhaust gas utilization technology. In general, it can be divided into gas-fired power station heating exhaust gas utilization system and gas-fired power station cooling exhaust gas utilization system.
(1) Gas exhaust gas heating system
The flammable exhaust gas is passed into a reciprocating internal combustion engine (gas engine), and the combustion is performed to drive the generator to generate electricity. The generated flue gas (about 600°C) enters the waste heat boiler and the cooling water (about 90°C) flowing through the gas engine body passes through the heat exchange. The heat is transferred to the waste heat pipe. The water passes through the heat exchanger and then enters the waste heat boiler for heating, producing high-temperature hot water or steam. Steam can be used for industrial production, and hot water can be used for heating and domestic hot water. This technology realizes cogeneration, which can generate electricity and heat. (see picture 1)
Figure 1 Working principle of a typical gas-fired power plant heating system
(2) Gas-fired power station cooling exhaust gas utilization system
Combustible exhaust gas into the gas engine, combustion work to drive the generator to generate electricity, the resulting flue gas (about 600 °C) into the waste heat boiler. The water enters the residual lithium bromide refrigeration unit through the engine body heat exchanger, generating low temperature water and higher warm water. Low temperature water can be used for air conditioning and refrigeration, and higher temperature water can be used as hot water for domestic use. This kind of technology realizes co-generation of heat, electricity, and cooling, which can both generate electricity, heat and cool. (See Figure 2)
Figure 2 The working principle of a typical gas-fired power station refrigeration system
1.2 Technical Features
The conventional power generation efficiency of a single gas turbine is generally about 35%. The commonly used method to increase the efficiency is to recover heat energy from the waste heat boiler and convert it to steam, drive the steam turbine to generate electricity again, and form a gas turbine steam turbine combined cycle power generation, thereby improving efficiency. . However, this combined cycle system has high requirements for water resources, the system is relatively complex, the construction investment is relatively large, and the relocation is relatively difficult.
Compared with traditional gas turbine power generation systems with large investment, long construction period, and large floor space, reciprocating internal combustion engine sets are used as power plants for gas-fired power stations. The power generation efficiency of the units is usually between 30% and 40%. The more common models are Generally it can reach 35%. Its most prominent advantages are high power generation efficiency, followed by high equipment integration, quick installation, low requirement for dust in gas, basic water, and low unit kilowatt cost. The supporting waste heat utilization equipment required for the construction of gas-fired power stations is also relatively flexible, and small-sized waste heat equipment can be well matched for use. In general, a gas-fired power station based on a reciprocating internal combustion engine set has all the thermoelectric functions of the gas turbine combined cycle power plant in the waste heat utilization technology field, and has the advantages of low gas supply quality requirements, quick production, low investment, and wide range of use. At present, reciprocating internal-combustion engine sets produced by domestic companies can achieve a power generation efficiency of at least 30% at least for power plants. With a waste heat boiler or a refrigeration unit, a heat absorption rate of about 30% can be achieved, and about 20% can be absorbed by a heat exchanger. Heat, thus achieving a comprehensive energy efficiency of the power station of more than 75%. Although China’s reciprocating internal combustion engine technology is relatively mature, the construction of gas-fired power plants using it as the basic equipment still faces problems such as lack of engineering design experience, small scale, incompatibility of power station equipment, and poor intelligence and information management. Its large-scale development and application still face challenges.
With the gradual implementation of relevant national policies and regulations, measures such as the establishment of a waste heat power generation gas power plant demonstration project, the development of a unified development plan and standard system, and the enhancement of technical cooperation and technical exchanges of supporting companies will help promote the use of waste heat recovery tools such as reciprocating internal combustion engines. The integration of resources and optimized allocation of equipment will effectively alleviate the problem of uncoordinated and unsynchronized construction and development of gas-fired power plants, and ultimately achieve simultaneous development of power generation projects and waste heat utilization projects.
2, screw expansion unit waste heat energy utilization technology
2.1 Technical Principles
The screw expansion unit power generation system mainly recovers the waste heat residual energy utilizing technology of the waste heat steam, hot water, hydrothermal fluid, and flue gas residual heat of the generator through the screw expander. According to whether the low calorific value heat source directly drives the screw expander to work, the screw expansion unit power generation system can be divided into a conventional circulation system and an organic Rankine cycle system.
(1) Conventional circulatory system
The conventional circulatory system, also known as the single-cycle system, is to directly introduce the hot fluid into the screw expander unit, which promotes the expansion of the main engine to perform work. This type of system is relatively simple and suitable for energy recovery of high temperature and high pressure fluids. Due to the limitation of the expansion capacity, the heat source of the direct-drive screw expansion power machine is in the range of 0.15 to 3.0 MPa steam at a temperature less than 300°C or hot water at a pressure of 0.8 MPa or higher and higher than 170°C.
(2) Organic Rankine Cycle System
The organic Rankine cycle system, also known as the double-cycle system, is to introduce the gaseous working medium into the screw expander machine after the heat exchange between the working medium and the hot fluid, and promote the expansion of the host machine to do work. For less than 0.1 MPa of steam or hot water with a pressure of 0.8 MPa or higher and higher than 85°C, the secondary circulation organic working screw expander system can be used for waste heat recovery. For the flue gas above 200°C, the screw expansion unit with waste heat boiler can be used for waste heat recovery.
In engineering applications, the organic Rankine cycle screw expansion power station system pressurizes the low-pressure liquid organic working substance through a working fluid pump. The evaporator absorbs the heat of the working substance and converts it into high-temperature and high-pressure steam. The high-temperature and high-pressure steam then pushes the screw expander to work. Produce energy output, the low-pressure steam of the outlet of the expander enters the condenser, releases heat to the low-temperature heat source and condenses into a liquid state, so reciprocatingly circulates.
Fig. 3 Schematic diagram of organic Rankine cycle screw expansion power station system
2.2 Technical Features
As the main equipment of the screw expansion unit power generation system, the screw expander has fewer main parts and the operation and maintenance costs are very low. It is not necessary to run and warm the engine during operation, and it can not fly, and it can be directly driven and started. The operation is simple and can be realized. Unmanned, it is suitable for industrial and mining enterprises. In addition, the screw expander is also suitable for high-alkali strong alkali fluids, the body itself can remove dirt and self-cleaning, so the quality of residual heat fluid is not high, further expanding the scope of application.
Compared to steam turbines, which can only be applied to heat sources such as superheated steam and clean steam with relatively stable steam flow and parameters, the screw expansion unit power generation system is suitable for superheated steam, saturated steam, vapor-liquid two-phase mixture, flue gas, polluted hot water, Different types of industrial waste heat such as hot liquid, when the heat source heat source parameters (pressure, flow, etc.) change significantly, the unit efficiency can still remain relatively stable. In practical applications, the screw expansion unit power generation system is generally used for heat sources below 300°C, where there is a small amount of residual heat. When the heat source temperature is around 200°C, the heat power conversion efficiency (the ratio of the external output mechanical energy to the heat energy contained in the low-temperature heat source) can reach 15%. If the quality is lower, the heat work efficiency can reach 8%~13. %.
At present, the screw expander power generation system has a certain market space by virtue of its technical advantages of being not picky eaters, uncomplicated, occupying less land, small construction volume, and high cost performance. It is widely used in petroleum, chemical, metallurgy, steel, cement, paper, printing and dyeing. And other fields. Although the use of screw expansion units to recover waste heat power has a vast market space, the actual development is not optimistic. The main reason for this is limited by the capacity of expansion. The power of stand-alone machines is generally not high, and users cannot comprehensively measure the effect of energy conservation. In addition, the entry threshold for industry access technology is not high, and competition among industrial enterprises is fierce. The lack of unified development plans and standards also has a certain impact on its development.
In order to realize the long-term national energy-saving and emission reduction plan, the screw expander residual heat and residual energy utilization technology can become a gas-fired power generation system and a reciprocating internal combustion engine power generation system by identifying market positioning, establishing a standardized industry order, and formulating unified standards and other measures. After that, there is another important way to use residual heat energy.
3ã€Conclusion
In summary, the full utilization of waste heat and energy can provide a new development idea for us to solve the energy crisis. However, the development of waste heat and residual energy industry still faces many problems such as unsound market mechanism, low equipment reliability, and lack of industry standards. To solve these problems, the use of residual heat and energy will remain on the stage of paper discussion, and even restrict the smooth implementation of the national energy-saving emission reduction targets. In the long-term perspective, taking the overall planning of the country, the serious supervision of the relevant functional agencies, and the company's serious efforts in technological research, innovation and cooperation, and the formulation of uniform technical standards, will help promote technological progress in the field of waste heat and energy utilization, and protect the industry. Good and fast development will make greater contribution to China's energy-saving and emission reduction business.
Litehome LED Linear Light adopts linear design and classic pure black or white color. It can add modern art to your space. In addition, it can achieve seamless splicing, forming a long strip, making your space more malleable. Splicing does not require any tools, which can greatly reduce installation time and labor costs. Lens design, a variety of beam angles for you to choose (eg: 30°/60°/90°/polar 20°). Anti-glare, better care of your eyes. Not only that, this Lens Linear Light has the characteristics of high luminous efficiency, low energy consumption, long life, easy to install, etc., which is very suitable for Office Lighting, Supermarket Lighting, Home Lighting and School lighting.
Modern Linear Light Fixture,Suspended Linear Light Fixture,Black Linear Light Fixture,Kitchen Island Lighting Modern
SHENZHEN LITEHOME OPTOELECTRONIC TECHNOLOGY CO., LTD. , https://www.litehomelight.com