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Federal State Budgetary Educational Institution of Higher Professional Education
"Saratov State Technical University named after Yu.A. Gagarin"
Vocational Pedagogical College.
Abstract on the topic: "Ecological problems associated with the use of heat engines"
Work completed
student of group ZChS-912
Petrova Olesya
Introduction
5. Environmental protection from thermal emissions
Conclusion
release thermal atmosphere fuel
Introduction
There is an inextricable relationship and interdependence of the conditions for ensuring heat and power consumption and environmental pollution. The interaction of these two factors of human life and the development of production forces attracts gradual attention to the problem of interaction between heat power engineering and the environment.
At an early stage in the development of thermal power engineering, the main manifestation of this attention was the search in the environment for resources necessary to ensure heat and power consumption and stable heat and power supply to enterprises and residential buildings. In the future, the boundaries of the problem covered the possibility of a more complete use of natural resources by finding and rationalizing processes and technologies, extracting and enriching, processing and burning fuel, as well as improving thermal power plants.
With the growth of unit capacities of units, thermal power plants and thermal power systems, specific and total levels of heat and power consumption, the task arose of limiting polluting emissions into the air basin, as well as more fully using their natural dissipative capacity.
At the present stage, the problem of interaction between thermal power engineering and the environment has acquired new features, spreading its influence over the vast volumes of the Earth's atmosphere.
Even more significant scales of development of heat and power consumption in the foreseeable future predetermine further intensive growth of various impacts on the atmosphere.
Fundamentally new aspects of the problem of interaction between thermal power engineering and the environment have arisen in connection with the development of nuclear thermal power engineering.
The most important aspect of the problem of interaction between thermal power engineering and the environment in the new conditions is the ever-increasing reverse influence, the determining role of environmental conditions in solving practical problems of thermal power engineering (selection of the type of thermal power plants, location of enterprises, choice of unit capacities of power equipment, and much more).
1. General characteristics of thermal power engineering and its emissions
Thermal power engineering is one of the main components of the energy industry and includes the process of generating thermal energy, transportation, considers the main conditions for energy production and the side effects of the industry on the environment, the human body and animals.
As Yu.V. Novikov, in terms of total emissions of harmful substances into the atmosphere, thermal power engineering ranks first among industries.
If a steam boiler is the “heart” of a power plant, then water and steam are its “blood”. They circulate inside the plants, turning the turbine blades. So this “blood” was made supercritical by increasing its temperature and pressure several times. Thanks to this, the efficiency of power plants has increased significantly. In such extreme conditions, ordinary metals could not survive. It was necessary to create fundamentally new, so-called structural materials for supercritical temperatures.
The lion's share of electricity is generated in the world at thermal and nuclear power plants, where water vapor serves as the working fluid. The transition to its supercritical parameters (temperature and pressure) made it possible to increase the efficiency from 25 to 40%, which gave a huge savings in primary energy resources - oil, coal, gas - and in a short time greatly increased the power supply of our country. This became real largely due to the fundamental research of A.E. Sheindlin thermophysical properties of water vapor in supercritical states. In parallel with it, many scientists of the world were developing in this direction, but the domestic energy industry managed to find a solution. He developed methods and experimental setups that had no analogues in the world. The results of calculations by A.E. Sheindlin became the basis for the construction of power plants in many countries. In 1961, Sheindlin created the Institute for High Temperatures, which became one of the leading scientific centers of the Russian Academy of Sciences.
The International Committee for the Global Energy Prize has selected three laureates. The 2004 bonus fund of $900,000 was divided between them. The prize "For the development of physical and technical foundations and the creation of fast neutron power reactors" was awarded to Academician of the Russian Academy of Sciences Fedor Nitenkov and Professor Leonard J. Koch (USA). Academician of the Russian Academy of Sciences Alexander Sheindlin was awarded the prize "For fundamental research of the thermophysical properties of substances at extremely high temperatures for power engineering".
2. Impact on the atmosphere when using solid fuel
Coal industry enterprises have a significant negative impact on water and land resources. The main sources of emissions of harmful substances into the atmosphere are industrial, ventilation and aspiration systems of mines and processing plants, etc.
Air pollution in the process of open and underground coal mining, transportation and enrichment of hard coal is caused by drilling and blasting, the operation of internal combustion engines and boiler houses, dusting of coal storages and rock dumps and other sources.
In 2002, the volume of emissions of harmful substances into the atmosphere from the enterprises of the industry increased by 30 percent compared to 1995, mainly due to newly taken into account methane emissions from ventilation and degassing installations in mines.
In terms of emissions of harmful substances, the coal industry ranks sixth in the industry of the Russian Federation (contribution at the level of 5%). The degree of capture and neutralization of pollutants is extremely low (9.1%), while hydrocarbons and VOCs are not captured.
In 2002, emissions of hydrocarbons (by 45.5 thousand tons), methane (by 40.6 thousand tons), soot (by 1.7 thousand tons), and a number of other substances increased; there was a decrease in emissions of VOCs (by 5.2 thousand tons), sulfur dioxide (by 2.8 thousand tons), solid substances (by 2.2 thousand tons).
The zoning of coal supplied from individual suppliers to thermal power plants exceeds 79% (in the UK it is 22% in accordance with the law, in the USA it is 9%). And the increase in the release of fly ash into the atmosphere continues. Meanwhile, only one Semibratov plant produces electrostatic precipitators for ash collection, satisfying the annual demand for them by no more than 5%.
Solid fuel thermal power plants intensively emit into the atmosphere products of coal and shale, containing up to 50% of non-combustible mass and harmful impurities. The share of thermal power plants in the country's electricity balance is 79%. They consume up to 25% of the produced solid fuel and discharge more than 15 million tons of ash, slag and gaseous substances into the human environment.
In the US, coal continues to be the main fuel for power plants. By the end of the century, all power plants there must become environmentally friendly, and efficiency must be increased to 50% or more (now 35%). To accelerate the adoption of coal cleaning technologies, a number of coal, energy and engineering companies, with support from the federal government, have developed a program that will require $3.2 billion to implement. Within 20 years, in the USA alone, new technologies will be introduced at existing power plants with a total capacity of 140,000 MW and at new converted power plants with a total capacity of 170,000 kW.
Environmentaltechnologyincinerationfuel. The traditional diffusion method of burning even high-quality hydrocarbon fuels leads to pollution of the surrounding atmosphere, mainly by nitrogen oxides and carcinogens. In this regard, environmentally friendly technologies for burning these types of fuel are needed: with a high quality of atomization and mixing with air up to the combustion zone and intensive combustion of a lean, pre-mixed fuel-air mixture, an optimal combustion chamber (CC) from a thermochemical point of view should provide preliminary evaporation of the fuel, complete and uniform mixing of its vapors with air and stable combustion of the lean combustible mixture with a minimum time of its stay in the combustion zone.
In this regard, the traditional diffuse hybrid combustion method is much more efficient, which is a combination of a diffuse zone with a channel for pre-evaporation and mixing of fuel with air.
Technologies have been developed for burning coal in boilers with a circulating fluidized bed, where the effect of binding environmentally hazardous sulfur impurities is achieved. This technology was introduced during the reconstruction of Shaturskaya, Cherepetskaya and Intinskaya GRES. A thermal power plant with modern boilers is being built in Ulan-Ude. The Teploelektroproekt Institute has developed a technology for coal gasification: it is not the coal itself that is burned, but the gas released from it. This is an environmentally friendly process, but so far, like any new technology, it is expensive. In the future, even petroleum coke gasification technologies will be introduced.
When coal is burned in a fluidized bed, the emission of sulfur compounds into the atmosphere is reduced by 95%, and nitrogen oxides - by 70%.
Flue gas cleaning. To clean flue gases, a lime-catalytic two-stage method is used to obtain gypsum, based on the absorption of sulfur dioxide by a limestone suspension in two stages of contact. This technology, as evidenced by world experience, is most common at thermal power plants that burn liquid and solid fuels with different sulfur content in it, and provides a degree of gas purification from sulfur oxides of at least 90-95%. A large number of domestic power plants operate on fuel with an average and high sulfur content in it, so this method should be widely used in the domestic energy sector. In our country, there was practically no experience in cleaning flue gases from sulfur dioxide by the wet limestone method.
Thermal power plants account for about 70% of nitrogen oxide emissions into the atmosphere. In the USA and Japan, methods for cleaning flue gases from nitrogen oxides are widely used, in these countries there are more than 100 installations that use the method of selective catalytic reduction of nitrogen oxides with ammonia on a platinum-vanadium catalyst, however, the cost of these installations is very high, and the service life catalyst is negligible.
In recent years, in the United States, Genesis Research of Arizona has developed a technology for producing the so-called self-cleaning coal. Such coal burns better, and when it is used, 80% less sulfur dioxide is found in flue gases, while additional costs are only a fraction of the costs of installing scrubbers. The technology for producing self-cleaning coal includes two stages. Initially, impurities are separated from the coal by flotation, then the coal is ground into powder and added to the sludge, while the coal floats and the impurities sink. At the first stage, almost all inorganic sulfur is removed, while organic sulfur remains. In the second stage, the powdered charcoal is combined with chemicals whose names are trade secrets and then compacted into grape-sized lumps. When burned, these chemicals react with organic sulfur, and the sulfur is securely sealed to prevent it from escaping into the atmosphere. Lumps of such modified coal can be transported, stored and used like regular coal.
Steam and gas systems. An effective integrated system that not only captures harmful impurities from the flue gases of thermal power plants, but also simultaneously reduces the specific fuel consumption for electricity generation by about 20%, was developed at the Power Engineering Institute by G.N. Krzhizhanovsky. Its essence is that before burning in the furnace of TPP steam boilers, coal is gasified, cleaned of solid (containing harmful substances) impurities and sent to gas turbines, where combustion products with a temperature of 400-500 degrees Celsius are discharged into conventional steam boilers. Similar combined-cycle systems are widely used by power engineers in a number of countries to reduce emissions into the atmosphere.
Deep complex processing of coal. Abroad, intensive work is underway to develop technologies and equipment for coal gasification to fully supply the industry with combustible gases, synthesis gas and hydrogen. A demonstration coal oxy-gasification plant for a 250 MW power unit has been commissioned in the Netherlands. It is planned to commission four such units from 175 to 330 MW in Europe, ten units from 100 to 500 MW in the USA and one unit with a capacity of 400 MW in Japan. Gasification processes at high temperatures and pressures make it possible to process a wide range of coals. There are known studies on high-speed pyrolysis and catalytic gasification, the implementation of which promises huge benefits.
The need to deepen the processing of coal is dictated by the previous course of development of the heat and power industry: the best results are achieved with the combined processing of coal into electricity and heat. A qualitative leap in the use of coal is associated with its complex processing within the framework of flexible technologies. The solution of this complex problem will require new technological installations for power and chemical complexes, which will ensure an increase in the efficiency of thermal power plants, a reduction in capital unit costs and a fundamental solution to environmental issues.
3. Impact on the atmosphere when using liquid fuel
At one time, oil supplanted coal and came out on top in the global energy balance. However, this is fraught with certain environmental problems.
Thus, in 2002, Russian industry enterprises emitted 621,000 tons of pollutants (solids, sulfur dioxide, carbon monoxide, nitrogen oxides, etc.) into the atmosphere. Wastewater in the amount of up to 1302.6 million m3 is discharged into surface water bodies and onto the relief.
When liquid fuels (fuel oil) are burned with flue gases, sulfur dioxide and sulfuric anhydrides, nitrogen oxides, gaseous and solid products of incomplete combustion of fuel, vanadium compounds, sodium salts, as well as substances removed from the surface of boilers during cleaning enter the atmospheric air. From an ecological point of view, liquid fuel has more “hygienic” properties: there is no problem of ash dumps, which occupy large areas, exclude their beneficial use and are a source of constant pollution of the atmosphere and the station area due to ash carried away with winds. There is no fly ash in the combustion products of liquid fuels. The use of dual-fuel hybrid combustion chambers instead of traditional single-zone diffusion combustion chambers using partial replacement of a part of hydrocarbon fuel with hydrogen (6% of the mass of hydrocarbon fuel) reduces the consumption of petroleum fuel by 17-20%, the emission levels of soot particles - by an order of magnitude, benzopyrene - by 10-15 times, nitrogen oxides - 5 times).
In most countries, the combustion of petroleum fuels with a sulfur content above 0.5% is prohibited, while in Russia half of the diesel fuel does not fit into this standard, and the sulfur content of boiler fuel reaches 3%.
Burn oil, in the words of D.I. Mendeleev, it's the same as heating the stove with banknotes. Therefore, the share of the use of liquid fuel in the energy sector has been significantly reduced in recent years. The emerging trend will further intensify due to a significant expansion of the use of liquid fuels in other areas of the national economy: in transport, in the chemical industry, including the production of plastics, lubricants, household chemicals, etc. Unfortunately, oil is not used in the best way. In 1984, with the world production of petroleum products of 2750 million tons of gasoline, 600 million tons of kerosene and jet fuel - 210, diesel fuel - 600, fuel oil - 600 million tons were obtained. Japan showed a good example of resource conservation, which seeks to minimize the country's dependence on imports oil. Giant efforts have been made over the past 20 years to solve this important economic problem. Priority attention was given to energy-saving technology. And as a result of the work done, for the production of the same volume of the gross national product of Japan today, half as much oil is required as in 1974. Undoubtedly, innovations have had a positive impact on improving the environmental situation.
4. Impact on the atmosphere when using natural gas
According to environmental criteria, natural gas is the most optimal fuel. The combustion products do not contain ash, soot and carcinogens such as benzopyrene.
When gas is burned, nitrogen oxides remain the only significant air pollutant. However, the emission of nitrogen oxides when natural gas is burned at thermal power plants is on average 20 percent lower than when coal is burned. This is due not to the properties of the fuel itself, but to the peculiarities of the processes of their combustion. The excess air ratio for coal combustion is lower than for natural gas combustion. Thus, natural gas is the most environmentally friendly type of energy fuel in terms of the release of nitrogen oxides during combustion.
Changes in the environment during gas transportation. A modern main pipeline is a complex engineering equipment, which, in addition to the linear part (the pipeline itself), includes installations for preparing oil or gas for pumping, pumping and compressor stations, tank farms, communication lines, an electrochemical protection system, roads running along the route, and entrances to them, as well as temporary residential settlements of operators.
For example, the total length of gas pipelines in Russia is approximately 140,000 km. For example, on the territory of the Udmurt Republic there are 13 main pipelines, the share of emissions of which is more than 30% of the corresponding volume in the republic. Emissions, mainly of methane, are distributed along the length of gas pipelines, mostly outside of populated areas.
Atmospheric air is exposed to significant pollution due to losses from large and small “breaths” of reservoirs, gas leaks, etc.
Atmospheric pollution as a result of an accidental release of gas or the combustion of oil and oil products, which are different on the surface during an accident, is characterized by a much shorter period of exposure, and it can be classified as short-term.
Atmospheric air is also polluted as a result of gas leakage through leaky pipeline connections, leakage and evaporation during storage and loading and unloading operations, losses in oil and gas and oil product pipelines, etc. As a result, vegetation growth can be suppressed and airborne exposure limits can be raised.
5. Protection of the atmosphere from thermal emissions
Solving the problem of protecting the environment from the harmful effects of thermal power plants requires an integrated approach.
Location of TPP. A number of restrictions and technical requirements when choosing a site for construction are dictated by environmental considerations.
Firstly, the so-called pollution background, which arises in connection with the work in this zone of a number of industrial enterprises, and sometimes already existing power plants. If the magnitude of pollution at the site of the proposed construction has already reached or close to the limit values, the location of, for example, a thermal plant should not be allowed.
Secondly, in the presence of a certain, but not high enough pollution background, detailed assessments should be carried out to compare the values of possible emissions from the planned thermal plant with those already existing in the area. In this case, it is necessary to take into account factors of various nature and content: the direction, strength and frequency of winds in this area, the probability of precipitation, the absolute emissions of the station when operating on the intended type of fuel, the instructions for the combustion devices, the indicators of emission purification and trapping systems, etc. After comparing the obtained total (taking into account the impact from the projected thermal power plant) emissions with the maximum allowable, a final conclusion should be made on the feasibility of building a thermal power plant.
During the construction of power plants, primarily thermal power plants, in cities or suburbs, it is planned to create forest belts between the station and residential areas. They reduce the impact of noise on nearby areas, contribute to the retention of dust during winds in the direction of residential areas.
When designing and building thermal power plants, it is necessary to plan their equipping with highly efficient means of cleaning and recycling waste, discharges and emissions of pollutants, and the use of environmentally friendly fuels.
Air basin protection. Protection of the atmosphere from the main source of TPP pollution - sulfur dioxide - occurs primarily through its dispersion in the higher layers of the air basin. To do this, chimneys are built 180, 250 and even 420 m high. A more radical means of reducing sulfur dioxide emissions is the separation of sulfur from the fuel before it is burned at thermal power plants.
The most effective way to reduce sulfur dioxide emissions is the construction of limestone sulfur trapping units at thermal power plants and the introduction of installations for the extraction of pyrite sulfur from coal at concentrating plants.
One of the important documents in the protection of the atmosphere from thermal emissions on the territory of the Republic of Belarus is the Law of the Republic of Belarus "On the Protection of Atmospheric Air". The Law emphasizes that atmospheric air is one of the main vital elements of the environment, the favorable state of which is the natural basis for sustainable socio-economic development of the republic. The law is aimed at preserving and improving the quality of atmospheric air, its restoration to ensure the environmental safety of human life, as well as preventing harmful effects on the environment. The law establishes the legal and organizational framework for the norms of economic and other activities in the field of the use and protection of atmospheric air.
Conclusion
The main danger of thermal power engineering for the atmosphere is that the combustion of carbon-containing fuels leads to the appearance of carbon dioxide CO2, which is released into the atmosphere and contributes to the greenhouse effect.
The presence of sulfur additives in the burning coal leads to the appearance of sulfur oxides, they enter the atmosphere and, after reacting with water vapor in the clouds, create sulfuric acid, which falls to the ground with precipitation. This is how acid precipitation with sulfuric acid occurs.
Another source of acid precipitation is nitrogen oxides, which occur in the furnaces of thermal power plants at high temperatures (at ordinary temperatures, nitrogen does not interact with atmospheric oxygen). Further, these oxides enter the atmosphere, react with water vapor in the clouds and create nitric acid, which, together with precipitation, falls to the ground. This is how acid precipitation with nitric acid occurs.
A coal-fired thermal power plant that generates electricity with a capacity of 1 GW = 10 "W consumes 3 million coal annually, emitting 7 million tons of CO2, 120 thousand tons of sulfur dioxide, 20 thousand tons of nitrogen oxides NO2, and 750 thousand tons of nitrogen oxides into the environment. tons of ash.
Coal and fly ash contain significant amounts of radioactive impurities. An annual release into the atmosphere in the area of a 1 GW thermal power plant leads to the accumulation of radioactivity on the soil, which is 10-20 times higher than the radioactivity of annual emissions from a nuclear power plant of the same power.
Thus, the protection of the atmosphere from thermal emissions should be aimed at reducing the volume of gas emissions and their purification and include the following measures:
Monitoring the state of the environment;
Application of methods, methods and means that limit the volume of gas emissions and its supply to the field gas collection network;
Use in emergency cases of flare devices that ensure complete combustion of the discharged gas;
Ensuring compliance with environmental standards by the designed facilities and structures;
Application of a system of automatic blocking of technological flows in oil refining, which allows sealing hazardous areas in emergency situations and discharging this link into the flare system;
The maximum possible change in the fuel modes of thermal power plants in favor of environmentally friendly types of fuel and modes of its reduction;
Achievement of the main volume of reducing gas emissions in oil refining through the construction of installations for the treatment of associated and petroleum gas and gas pipeline systems that ensure utilization.
Reducing the volume of harmful emissions and oil refining is achieved in the process of reconstruction and modernization of the oil refining industry, accompanied by the construction of environmental facilities.
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Among other social dangers, one of the first places is occupied by those associated with the use of heat engines.
What are heat engines for us
Every day we deal with the engines that drive cars, ships, industrial machinery, railway locomotives and aircraft. It was the emergence and widespread use of heat engines that rapidly advanced the industry.
The environmental problem of using heat engines is that thermal energy emissions inevitably lead to heating of surrounding objects, including the atmosphere. Scientists have long been struggling with the problem of the rise in the level of the World Ocean, considering the main factor influencing human activity. Changes in nature will lead to a change in the conditions of our life, but despite this, energy consumption is increasing every year.
Where are heat engines used?
Millions of vehicles powered by internal combustion engines are engaged in the transport of passengers and goods. Powerful diesel locomotives go along the railways, motor ships go along the water trajectories. Airplanes and helicopters are equipped with piston, turbojet and turboprop engines. Rocket engines "push" stations, ships and Earth satellites into outer space. Internal combustion engines in agriculture are installed on combines, pumping stations, tractors and other objects.
Ecological problem of using heat engines
Machines used by man, heat engines, automobile production, the use of gas turbine propulsion systems, aviation and rocket carriers, pollution of the aquatic environment by ships - all this has a catastrophically destructive effect on the environment.
Firstly, when coal and oil are burned, nitrogen and sulfur compounds are released into the atmosphere, which are harmful to humans. Secondly, the processes use atmospheric oxygen, the content of which in the air drops because of this.
Air emissions are not the only factor in the impact of heat engines on nature. The production of mechanical and electrical energy cannot be carried out without significant amounts of heat being removed to the environment, which cannot but lead to an increase in the average temperature on the planet.
It is aggravated by the fact that the burned substances increase the concentration of carbon dioxide in the atmosphere. This, in turn, leads to the emergence of the "greenhouse effect". Global warming is becoming a real danger.
The environmental problem of using heat engines is that the combustion of fuel cannot be complete, and this leads to the release of ash and soot flakes into the air we breathe. According to statistics, worldwide power plants annually release into the air more than 200 million tons of ash and more than 60 million tons of sulfur oxide.
All civilized countries are trying to solve the environmental problems associated with the use of heat engines. The latest energy-saving technologies are being introduced to improve thermal engines. As a result, energy consumption for the production of the same product is significantly reduced, reducing the harmful effect on the environment.
Thermal power plants, internal combustion engines of automobiles and other machines are discharged into the atmosphere in large quantities, and then into the soil, waste harmful to all living things, for example, chlorine, sulfur compounds (during the combustion of coal), carbon monoxide CO, nitrogen oxides, etc. Car engines release about three tons of lead into the atmosphere every year.
At nuclear power plants, another environmental problem in the use of thermal engines is the safety and disposal of radioactive waste.
Due to the incredibly high energy consumption, some regions have lost the ability to self-purify their own airspace. The operation of nuclear power plants has helped to significantly reduce harmful emissions, but operation requires huge amounts of water and large space under the ponds to cool the exhaust steam.
Solutions
Unfortunately, humanity is unable to abandon the use of heat engines. Where is the exit? In order to consume an order of magnitude less fuel, that is, to reduce energy consumption, it is necessary to increase the efficiency of the engine to carry out the same work. The fight against the negative consequences of the use of heat engines is only to increase the efficiency of energy use and switch to energy-saving technologies.
In general, it would be wrong to say that the global environmental problem of using heat engines is not being solved. An increasing number of electric locomotives are replacing conventional trains; battery cars are becoming popular; energy-saving technologies are introduced into the industry. There is hope that environmentally friendly aircraft and rocket engines will appear. The governments of many countries are implementing international programs to protect the environment against pollution of the Earth.
21. Environmental problems of energy and ways to solve them.
At present, energy needs are met mainly by three types of energy resources: organic fuel, water, and the atomic nucleus. Water energy and atomic energy are used by man after turning it into electrical energy. At the same time, a significant amount of energy contained in organic fuel is used in the form of heat, and only part of it is converted into electricity. However, in both cases, the release of energy from organic fuel is associated with its combustion, and, consequently, with the release of combustion products into the environment.
Environmental problems of thermal power engineering
The impact of thermal power plants on the environment largely depends on the type of fuel burned.
solid fuel. When solid fuels are burned, fly ash with particles of unburned fuel, sulfurous and sulfuric anhydrides, nitrogen oxides, a certain amount of fluorine compounds, as well as gaseous products of incomplete combustion of fuel, enter the atmosphere. Fly ash in some cases contains, in addition to non-toxic components, more harmful impurities. So, in the ash of Donetsk anthracites, arsenic is contained in small quantities, and in the ash of Ekibastuz and some other deposits - free silicon dioxide, in the ash of shale and coals of the Kansk-Achinsk basin - free calcium oxide. Solid fuels include coal and peat.
Liquid fuel. When burning liquid fuel (fuel oil) with flue gases, sulfur dioxide and sulfuric anhydrides, nitrogen oxides, vanadium compounds, sodium salts, as well as substances removed from the surface of boilers during cleaning, enter the atmospheric air. From an environmental point of view, liquid fuel is more “hygienic”. At the same time, the problem of ash dumps completely disappears, which occupy large areas, exclude their useful use and are a source of constant atmospheric pollution in the station area due to the removal of part of the ash with the winds. There is no fly ash in the combustion products of liquid fuels. Liquid fuels include natural gas (???).
Thermal power plants use coal, oil and oil products, natural gas and, less commonly, wood and peat as fuel. The main components of combustible materials are carbon, hydrogen and oxygen, sulfur and nitrogen are contained in smaller amounts, traces of metals and their compounds (most often oxides and sulfides) are also present.
In the thermal power industry, the source of massive atmospheric emissions and large-tonnage solid waste are thermal power plants, enterprises and installations of steam power facilities, i.e. any enterprises whose work is associated with fuel combustion.
Along with gaseous emissions, thermal power engineering produces huge masses of solid waste; these include ash and slag.
Waste from coal preparation plants contains 55-60% SiO2, 22-26% Al2O3, 5-12% Fe2O3, 0.5-1% CaO, 4-4.5% K2O and Na2O, and up to 5% C. They enter the dumps, which produce dust, smoke and drastically worsen the state of the atmosphere and adjacent territories.
A coal-fired power plant requires 3.6 million tons of coal, 150 m3 of water and about 30 billion m3 of air annually. These figures do not take into account environmental disturbances associated with the extraction and transportation of coal.
Considering that such a power plant has been actively operating for several decades, then its impact can be compared with that of a volcano. But if the latter usually throws out the products of volcanism in large quantities at a time, then the power plant does this all the time.
Pollution and waste of energy facilities in the form of gas, liquid and solid phases are distributed into two streams: one causes global changes, and the other - regional and local. The same is true in other sectors of the economy, but still energy and fossil fuel combustion remain a source of major global pollutants. They enter the atmosphere, and due to their accumulation, the concentration of small gas components of the atmosphere, including greenhouse gases, changes. In the atmosphere, gases appeared that were practically absent in it before - chlorofluorocarbons. These are global pollutants that have a high greenhouse effect and at the same time participate in the destruction of the stratospheric ozone screen.
Thus, it should be noted that at the present stage, thermal power plants emit about 20% of the total amount of all hazardous industrial waste into the atmosphere. They significantly affect the environment of the area of their location and the state of the biosphere as a whole. The most harmful are condensing power plants operating on low-grade fuels.
Waste water from thermal power plants and storm water from their territories, contaminated with waste from technological cycles of power plants and containing vanadium, nickel, fluorine, phenols and oil products, when discharged into water bodies, can affect water quality and aquatic organisms. A change in the chemical composition of certain substances leads to a violation of the habitat conditions established in the reservoir and affects the species composition and abundance of aquatic organisms and bacteria, and ultimately can lead to violations of the processes of self-purification of water bodies from pollution and to a deterioration in their sanitary condition.
The so-called thermal pollution of water bodies with diverse violations of their condition is also dangerous. Thermal power plants produce energy using turbines driven by heated steam. During the operation of the turbines, it is necessary to cool the exhaust steam with water, therefore, a stream of water continuously departs from the power plant, usually heated by 8-12 ° C and discharged into the reservoir. Large thermal power plants need large volumes of water. They discharge 80-90 m3/s of water in a heated state. This means that a powerful stream of warm water is continuously flowing into the reservoir, approximately on the scale of the Moscow River.
The heating zone, formed at the confluence of a warm "river", is a kind of section of the reservoir, in which the temperature is maximum at the spillway point and decreases with distance from it. The heating zones of large thermal power plants occupy an area of several tens of square kilometers. In winter, polynyas form in the heated zone (in the northern and middle latitudes). During the summer months, the temperatures in the heated zones depend on the natural temperature of the intake water. If the water temperature in the reservoir is 20 °C, then in the heating zone it can reach 28-32 °C.
As a result of an increase in temperatures in a reservoir and a violation of their natural hydrothermal regime, the processes of “blooming” of water are intensified, the ability of gases to dissolve in water decreases, the physical properties of water change, all chemical and biological processes occurring in it are accelerated, etc. In the heating zone the transparency of water decreases, pH increases, the rate of decomposition of easily oxidized substances increases. The rate of photosynthesis in such water is markedly reduced.
Environmental problems of hydropower
Despite the relative cheapness of energy obtained from hydro resources, their share in the energy balance is gradually decreasing. This is due both to the depletion of the cheapest resources and to the large territorial capacity of lowland reservoirs. It is believed that in the future, the world production of hydroelectric energy will not exceed 5% of the total.
One of the most important reasons for the decrease in the share of energy received at HPPs is the powerful impact of all stages of construction and operation of hydroelectric facilities on the environment.
According to various studies, one of the most important impacts of hydropower on the environment is the alienation of large areas of fertile (floodplain) land for reservoirs. In Russia, where no more than 20% of electricity is produced through the use of hydro resources, at least 6 million hectares of land were flooded during the construction of hydroelectric power stations. Natural ecosystems have been destroyed in their place.
Significant areas of land near reservoirs are experiencing flooding as a result of rising groundwater levels. These lands, as a rule, go into the category of wetlands. In flat conditions, flooded lands can be 10% or more of the flooded. The destruction of lands and their ecosystems also occurs as a result of their destruction by water (abrasion) during the formation of the coastline. Abrasion processes usually last for decades, resulting in the processing of large masses of soil, water pollution, and siltation of reservoirs. Thus, the construction of reservoirs is associated with a sharp violation of the hydrological regime of rivers, their ecosystems, and the species composition of hydrobionts.
In reservoirs, the warming of waters sharply increases, which intensifies the loss of oxygen and other processes caused by thermal pollution. The latter, together with the accumulation of biogenic substances, creates conditions for the overgrowth of water bodies and the intensive development of algae, including poisonous blue-green ones. For these reasons, as well as due to the slow renewal of waters, their ability to self-purify is sharply reduced.
The deterioration of water quality leads to the death of many of its inhabitants. The incidence of fish stocks is increasing, especially the susceptibility to helminths. The taste qualities of the inhabitants of the aquatic environment are reduced.
Fish migration routes are being disrupted, forage grounds, spawning grounds, etc. are being destroyed. The Volga has largely lost its significance as a spawning ground for Caspian sturgeon after the construction of a hydroelectric power station cascade on it.
Ultimately, the river systems blocked by reservoirs turn from transit systems into transit-accumulation ones. In addition to biogenic substances, heavy metals, radioactive elements and many pesticides with a long life span are accumulated here. Accumulation products make it problematic to use the territories occupied by reservoirs after their liquidation.
Reservoirs have a significant impact on atmospheric processes. For example, in arid (arid) regions, evaporation from the surface of reservoirs exceeds evaporation from an equal land surface by tens of times.
A decrease in air temperature and an increase in foggy phenomena are associated with increased evaporation. The difference between the thermal balances of reservoirs and the adjacent land determines the formation of local winds such as breezes. These, as well as other phenomena, result in a change in ecosystems (not always positive), a change in the weather. In some cases, in the area of reservoirs, it is necessary to change the direction of agriculture. For example, in the southern regions of our country, some heat-loving crops (melons) do not have time to ripen, the incidence of plants increases, and the quality of products deteriorates.
The costs of hydraulic construction for the environment are noticeably lower in mountainous regions, where reservoirs are usually small in area. However, in seismic mountainous areas, reservoirs can provoke earthquakes. The likelihood of landslides and the likelihood of disasters as a result of the possible destruction of dams is increasing.
Due to the specifics of the technology of using water energy, hydropower facilities transform natural processes for very long periods. For example, a hydroelectric power station reservoir (or a system of reservoirs in the case of a hydroelectric power station cascade) can exist for tens and hundreds of years, while in place of a natural watercourse a man-made object arises with artificial regulation of natural processes - a natural-technical system (NTS).
Considering the impact of HPPs on the environment, one should still note the life-saving function of HPPs. Thus, the generation of each billion kWh of electricity at HPPs instead of TPPs leads to a decrease in mortality by 100-226 people per year.
Problems of nuclear power
Nuclear power can currently be considered as the most promising. This is due both to the relatively large stocks of nuclear fuel and to the gentle impact on the environment. The advantages also include the possibility of building a nuclear power plant without being tied to resource deposits, since their transportation does not require significant costs due to small volumes. Suffice it to say that 0.5 kg of nuclear fuel allows you to get as much energy as burning 1000 tons of coal.
Many years of experience in the operation of nuclear power plants in all countries shows that they do not have a significant impact on the environment. By 1998, the average NPP operation time was 20 years. The reliability, safety and economic efficiency of nuclear power plants is based not only on the strict regulation of the operation of nuclear power plants, but also on reducing the impact of nuclear power plants on the environment to an absolute minimum.
During normal operation of nuclear power plants, releases of radioactive elements into the environment are extremely insignificant. On average, they are 2-4 times less than from thermal power plants of the same capacity.
Before the Chernobyl disaster in our country, no industry had a lower level of industrial injuries than nuclear power plants. 30 years before the tragedy, accidents, and even then not for radiation reasons, killed 17 people. After 1986, the main environmental hazard of nuclear power plants began to be associated with the possibility of an accident. Although their probability at modern nuclear power plants is low, it is not excluded.
Until recently, the main environmental problems of NPPs were associated with the disposal of spent fuel, as well as with the liquidation of NPPs themselves after the end of their permissible operating life. There is evidence that the cost of such liquidation works is from 1/6 to 1/3 of the cost of the NPPs themselves. In general, the following impacts of NPPs on the environment can be mentioned: 1 - destruction of ecosystems and their elements (soils, soils, water-bearing structures, etc.) in ore mining sites (especially with an open method); 2 - withdrawal of land for the construction of nuclear power plants themselves; 3 - withdrawal of significant volumes of water from various sources and discharge of heated water; 4 - radioactive contamination of the atmosphere, waters and soils during the extraction and transportation of raw materials, as well as during the operation of nuclear power plants, storage and processing of waste, and their disposal is not ruled out.
Undoubtedly, in the near future, thermal energy will remain dominant in the energy balance of the world and individual countries. There is a high probability of an increase in the share of coal and other types of less clean fuel in energy production. Some ways and methods of their use can significantly reduce the negative impact on the environment. These methods are based mainly on the improvement of fuel preparation technologies and hazardous waste capture. Among them:
1. Use and improvement of cleaning devices.
2. Reducing the entry of sulfur compounds into the atmosphere through preliminary desulfurization (desulfurization) of coal and other fuels (oil, gas, oil shale) by chemical or physical methods.
3. Great and real opportunities for reducing or stabilizing the flow of pollution into the environment are associated with energy savings.
4. No less significant are the possibilities for saving energy in everyday life and at work by improving the insulating properties of buildings. It is extremely wasteful to use electrical energy to produce heat. Therefore, direct combustion of fuel to produce heat, especially gas, is much more efficient than turning it into electricity and then back into heat.
5. The efficiency of the fuel is also noticeably increased when it is used instead of a thermal power plant at a thermal power plant. + Use of alternative energy
6. Use of alternative energy sources whenever possible.
INTERNAL COMBUSTION ENGINES AND ECOLOGY.
1.3. Alternative fuels
1.5. Neutralization
Bibliography
INTERNAL COMBUSTION ENGINES AND ECOLOGY
1.1. Harmful emissions in the composition of exhaust gases and their impact on wildlife
With the complete combustion of hydrocarbons, the final products are carbon dioxide and water. However, complete combustion in reciprocating internal combustion engines is technically impossible to achieve. Today, about 60% of the total amount of harmful substances emitted into the atmosphere of large cities is accounted for by road transport.
The composition of the exhaust gases of internal combustion engines includes more than 200 different chemicals. Among them:
- products of incomplete combustion in the form of carbon monoxide, aldehydes, ketones, hydrocarbons, hydrogen, peroxide compounds, soot;
- products of thermal reactions of nitrogen with oxygen - nitrogen oxides;
- compounds of inorganic substances that are part of the fuel - lead and other heavy metals, sulfur dioxide, etc.;
- excess oxygen.
The amount and composition of exhaust gases are determined by the design features of the engines, their operating mode, technical condition, quality of road surfaces, weather conditions. On fig. 1.1 shows the dependences of the content of basic substances in the composition of exhaust gases.
In table. 1.1 shows the characteristics of the urban rhythm of the car and the average values of emissions as a percentage of their total value for a full cycle of conditional urban traffic.
Carbon monoxide (CO) is formed in engines during the combustion of enriched air-fuel mixtures, as well as due to the dissociation of carbon dioxide, at high temperatures. Under normal conditions, CO is a colorless, odorless gas. The toxic effect of CO lies in its ability to convert part of the hemoglobin in the blood into carbo-xyhemoglobin, which causes a violation of tissue respiration. Along with this, CO has a direct effect on tissue biochemical processes, resulting in a violation of fat and carbohydrate metabolism, vitamin balance, etc. The toxic effect of CO is also associated with its direct effect on the cells of the central nervous system. When exposed to a person, CO causes headache, dizziness, fatigue, irritability, drowsiness, and pain in the region of the heart. Acute poisoning is observed when air is inhaled with a CO concentration of more than 2.5 mg/l for 1 hour.
Table 1.1
Characteristics of the urban rhythm of the car
Nitrogen oxides in exhaust gases are formed as a result of the reversible oxidation of nitrogen with atmospheric oxygen under the influence of high temperatures and pressure. As the exhaust gases cool and dilute them with atmospheric oxygen, nitrogen oxide turns into dioxide. Nitric oxide (NO) is a colorless gas, nitrogen dioxide (NO 2) is a red-brown gas with a characteristic odor. Nitrogen oxides, when ingested, combine with water. At the same time, they form compounds of nitric and nitrous acid in the respiratory tract. Nitrogen oxides irritate the mucous membranes of the eyes, nose, and mouth. Exposure to NO 2 contributes to the development of lung diseases. Symptoms of poisoning appear only after 6 hours in the form of coughing, suffocation, and increasing pulmonary edema is possible. NOX is also involved in the formation of acid rain.
Nitrogen oxides and hydrocarbons are heavier than air and can accumulate near roads and streets. In them, under the influence of sunlight, various chemical reactions take place. The decomposition of nitrogen oxides leads to the formation of ozone (O 3). Under normal conditions, ozone is unstable and quickly decomposes, but in the presence of hydrocarbons, the process of its decomposition slows down. It actively reacts with moisture particles and other compounds, forming smog. In addition, ozone corrodes the eyes and lungs.
Individual hydrocarbons CH (benzapyrene) are the strongest carcinogens, the carriers of which can be soot particles.
When the engine is running on leaded gasoline, particles of solid lead oxide are formed due to the decomposition of tetraethyl lead. In the exhaust gases, they are contained in the form of tiny particles with a size of 1–5 microns, which remain in the atmosphere for a long time. The presence of lead in the air causes serious damage to the digestive organs, central and peripheral nervous system. The effect of lead on the blood is manifested in a decrease in the amount of hemoglobin and the destruction of red blood cells.
The composition of the exhaust gases of diesel engines differs from gasoline engines (Table 10.2). In a diesel engine, fuel combustion is more complete. This produces less carbon monoxide and unburned hydrocarbons. But, at the same time, due to the excess air in the diesel engine, a greater amount of nitrogen oxides is formed.
In addition, the operation of diesel engines in certain modes is characterized by smoke. Black smoke is a product of incomplete combustion and consists of carbon particles (soot) 0.1–0.3 µm in size. White smoke, mainly generated when the engine is idling, consists mainly of aldehydes, which have an irritating effect, particles of evaporated fuel and water droplets. Blue smoke is formed when exhaust gases are cooled in air. It consists of droplets of liquid hydrocarbons.
A feature of the exhaust gases of diesel engines is the content of carcinogenic polycyclic aromatic hydrocarbons, among which dioxin (cyclic ether) and benzapyrene are the most harmful. The latter, like lead, belongs to the first hazard class of pollutants. Dioxins and related compounds are many times more toxic than poisons such as curare and potassium cyanide.
Table 1.2
The amount of toxic components (in g),
formed during the combustion of 1 kg of fuel
Acreolin was also found in the exhaust gases (especially when diesel engines are running). It has the smell of burnt fats and, at levels above 0.004 mg/l, causes irritation of the upper respiratory tract, as well as inflammation of the mucous membrane of the eyes.
Substances contained in car exhaust gases can cause progressive damage to the central nervous system, liver, kidneys, brain, genital organs, lethargy, Parkinson's syndrome, pneumonia, endemic ataxia, gout, bronchial cancer, dermatitis, intoxication, allergies, respiratory and other diseases. . The probability of occurrence of diseases increases as the time of exposure to harmful substances and their concentration increases.
1.2. Legislative restrictions on emissions of harmful substances
The first steps to limit the amount of harmful substances in exhaust gases were made in the United States, where the problem of gas pollution in large cities became the most urgent after World War II. In the late 60s, when the megacities of America and Japan began to suffocate from smog, the government commissions of these countries took the initiative. Legislative acts on the mandatory reduction of toxic emissions from new cars have forced manufacturers to improve engines and develop neutralization systems.
In 1970, a law was passed in the United States, according to which the level of toxic components in the exhaust gases of 1975 model year cars was to be less than that of 1960 cars: CH - by 87%, CO - by 82% and NOx - by 24%. Similar requirements have been legalized in Japan and in Europe.
The development of pan-European rules, regulations and standards in the field of the ecology of automotive technology is carried out by the Inland Transport Committee within the framework of the United Nations Economic Commission for Europe (UNECE). The documents issued by it are called the UNECE Rules and are obligatory for the countries-participants of the 1958 Geneva Agreement, to which Russia has also joined.
According to these rules, permissible emissions of harmful substances since 1993 have been limited: for carbon monoxide from 15 g/km in 1991 to 2.2 g/km in 1996, and for the sum of hydrocarbons and nitrogen oxides from 5.1 g/km in 1991 to 0.5 g/km in 1996. In 2000, even more stringent standards were introduced (Fig. 1.2). A sharp tightening of the standards is also provided for diesel trucks (Fig. 1.3).
Rice. 1.2. Emission limits dynamics
for vehicles weighing up to 3.5 tons (gasoline)
The standards introduced for cars in 1993 were called EBPO-I, in 1996 - EURO-II, in 2000 - EURO-III. The introduction of such norms brought European regulations to the level of US standards.
Along with the quantitative tightening of the norms, their qualitative change is also taking place. Instead of restrictions on smoke, rationing of solid particles has been introduced, on the surface of which aromatic hydrocarbons dangerous to human health, in particular benzapyrene, are adsorbed.
Particulate emission regulation limits the amount of particulate matter to a much greater extent than smoke limiting, which allows only such amount of particulate matter to be estimated that makes the exhaust gases visible.
Rice. 1.3. Dynamics of harmful emission limits for diesel trucks with a gross weight of more than 3.5 tons established by the EEC
In order to limit the emission of toxic hydrocarbons, standards are being introduced for the content of the methane-free group of hydrocarbons in the exhaust gases. It is planned to introduce restrictions on the release of formaldehyde. Limitation of fuel evaporation from the power supply system of cars with gasoline engines is provided.
Both in the USA and in the UNECE Regulations, the mileage of cars (80 thousand and 160 thousand km) is regulated, during which they must comply with the established toxicity standards.
In Russia, standards that limit the emission of harmful substances by motor vehicles began to be introduced in the 70s: GOST 21393-75 “Cars with diesel engines. Exhaust smoke. Norms and methods of measurements. Safety requirements” and GOST 17.2.1.02-76 “Nature protection. Atmosphere. Emissions from engines of cars, tractors, self-propelled agricultural and road-building machines. Terms and Definitions".
In the eighties, GOST 17.2.2.03-87 “Nature Protection. Atmosphere. Norms and methods for measuring the content of carbon monoxide and hydrocarbons in the exhaust gases of vehicles with gasoline engines. Safety requirements” and GOST 17.2.2.01-84 “Nature protection. Atmosphere. Diesel automobiles. Exhaust smoke. Norms and methods of measurements”.
The norms, in accordance with the growth of the fleet and the orientation towards similar UNECE Regulations, were gradually tightened. However, already from the beginning of the 90s, Russian standards in terms of rigidity began to be significantly inferior to the standards introduced by the UNECE.
The reasons for the backlog are the unpreparedness of the infrastructure for the operation of automotive and tractor equipment. For the prevention, repair and maintenance of vehicles equipped with electronics and neutralization systems, a developed network of service stations with qualified personnel, modern repair equipment and measuring equipment, including in the field, is required.
GOST 2084-77 is in force, providing for the production in Russia of gasolines containing lead tetraethylene. Transportation and storage of fuel do not guarantee that leaded residues will not get into unleaded gasoline. There are no conditions under which owners of cars with neutralization systems would be guaranteed against refueling with gasoline with lead additives.
Nevertheless, work is underway to tighten environmental requirements. The Decree of the State Standard of the Russian Federation dated April 1, 1998 No. 19 approved the “Rules for carrying out work in the system of certification of motor vehicles and trailers”, which determine the temporary procedure for the application in Russia of UNECE Rules No. 834 and No. 495.
On January 1, 1999, GOST R 51105.97 “Fuels for internal combustion engines. Unleaded gasoline. Specifications”. In May 1999, Gosstandart adopted a resolution on the enactment of state standards that limit the emission of pollutants by cars. The standards contain authentic text with UNECE Regulations No. 49 and No. 83 and come into force on July 1, 2000. In the same year, the standard GOST R 51832-2001 “Gasoline-powered positive-ignition internal combustion engines and motor vehicles” was adopted. with a gross weight of more than 3.5 tons, equipped with these engines. Emissions of harmful substances. Technical requirements and test methods”. On January 1, 2004, GOST R 52033-2003 “Vehicles with gasoline engines. Emissions of pollutants with exhaust gases. Norms and methods of control in assessing the technical condition”.
In order to comply with increasingly stringent standards for the emission of pollutants, manufacturers of automotive equipment are improving power and ignition systems, using alternative fuels, neutralizing exhaust gases, and developing combined power plants.
1.3. Alternative fuels
All over the world, much attention is paid to replacing liquid petroleum fuels with liquefied hydrocarbon gas (propane-butane mixture) and compressed natural gas (methane), as well as alcohol-containing mixtures. In table. 1.3 shows comparative indicators of emissions of harmful substances during the operation of internal combustion engines on various fuels.
Table 1.3
The advantages of gas fuel are a high octane number and the possibility of using converters. However, when using them, the engine power decreases, and the large mass and dimensions of the fuel equipment reduce the performance of the vehicle. The disadvantages of gaseous fuels also include high sensitivity to fuel equipment adjustments. With unsatisfactory manufacturing quality of fuel equipment and with a low operating culture, the toxicity of exhaust gases from an engine running on gas fuel may exceed the values of the gasoline version.
In countries with a hot climate, cars with engines running on alcohol fuels (methanol and ethanol) have become widespread. The use of alcohols reduces the emission of harmful substances by 20-25%. The disadvantages of alcohol fuels include a significant deterioration in the starting qualities of the engine and the high corrosiveness and toxicity of methanol itself. In Russia, alcohol fuels for cars are not currently used.
Increasing attention, both in our country and abroad, is being paid to the idea of using hydrogen. The prospects of this fuel are determined by its environmental friendliness (for cars running on this fuel, the emission of carbon monoxide is reduced by 30–50 times, nitrogen oxides by 3–5 times, and hydrocarbons by 2–2.5 times), unlimitedness and renewability of raw materials. However, the introduction of hydrogen fuel is constrained by the creation of energy-intensive hydrogen storage systems on board the car. Currently used metal hydride batteries, methanol decomposition reactors and other systems are very complex and expensive. Considering also the difficulties associated with the requirements of compact and safe generation and storage of hydrogen on board a car, cars with a hydrogen engine do not yet have any noticeable practical application.
As an alternative to internal combustion engines, electric power plants using electrochemical energy sources, batteries and electrochemical generators are of great interest. Electric vehicles are distinguished by good adaptability to variable modes of urban traffic, ease of maintenance and environmental friendliness. However, their practical application remains problematic. First, there are no reliable, light and sufficiently energy-intensive electrochemical current sources. Secondly, the transition of the car fleet to power electrochemical batteries will lead to the expenditure of a huge amount of energy on their recharging. Most of this energy is generated in thermal power plants. At the same time, due to the multiple conversion of energy (chemical - thermal - electrical - chemical - electrical - mechanical), the overall efficiency of the system is very low and the environmental pollution of the areas around the power plants will many times exceed the current values.
1.4. Improving power and ignition systems
One of the disadvantages of carburetor power systems is the uneven distribution of fuel over the engine cylinders. This causes uneven operation of the internal combustion engine and the impossibility of depleting the carburetor adjustments due to the over-depletion of the mixture and the cessation of combustion in individual cylinders (an increase in CH) with an enriched mixture in the rest (a high content of CO in the exhaust gases). To eliminate this shortcoming, the order of operation of the cylinders was changed from 1–2–4–3 to 1–3–4–2 and the shape of the intake pipelines was optimized, for example, the use of receivers in the intake manifold. In addition, various dividers were installed under the carburetors, directing the flow, and the intake pipeline is heated. In the USSR, an autonomous idle system (XX) was developed and introduced into mass production. These measures made it possible to meet the requirements for the XX regimes.
As mentioned above, during the urban cycle up to 40% of the time, the car operates in forced idle mode (PHX) - engine braking. At the same time, under the throttle valve, the vacuum is much higher than in the XX mode, which causes the re-enrichment of the air-fuel mixture and the cessation of its combustion in the engine cylinders, and the amount of harmful emissions increases. To reduce emissions in the PHH modes, throttle damping systems (openers) and EPHH forced idle economizers were developed. The first systems, by slightly opening the throttle, reduce the vacuum under it, thereby preventing the over-enrichment of the mixture. The latter block the flow of fuel into the engine cylinders in the PXC modes. PECH systems can reduce the amount of harmful emissions by up to 20% and increase fuel efficiency by up to 5% in urban operation.
Emissions of nitrogen oxides NOx were fought by lowering the combustion temperature of the combustible mixture. For this, the power systems of both gasoline and diesel engines were equipped with exhaust gas recirculation devices. The system, at certain engine operating modes, passed part of the exhaust gases from the exhaust to the intake pipeline.
The inertia of fuel dosing systems does not allow creating a carburetor design that fully meets all the requirements for dosing accuracy for all engine operating modes, especially transient ones. To overcome the shortcomings of the carburetor, so-called "injection" power systems were developed.
At first, these were mechanical systems with a constant supply of fuel to the intake valve area. These systems made it possible to meet the initial environmental requirements. Currently, these are electronic-mechanical systems with phrased injection and feedback.
In the 1970s, the main way to reduce harmful emissions was to use increasingly leaner air-fuel mixtures. For their uninterrupted ignition, it was necessary to improve the ignition systems in order to increase the power of the spark. The restraining fakir in this was the mechanical break of the primary circuit and the mechanical distribution of high-voltage energy. To overcome this shortcoming, contact-transistor and non-contact systems have been developed.
Today, non-contact ignition systems with static distribution of high-voltage energy under the control of an electronic unit, which simultaneously optimizes fuel supply and ignition timing, are becoming more common.
In diesel engines, the main direction of improving the power system was to increase the injection pressure. Today, the norm is the injection pressure of about 120 MPa, for promising engines up to 250 MPa. This allows more complete combustion of fuel, reducing the content of CH and particulate matter in the exhaust gases. As well as for gasoline, for diesel power systems, electronic engine control systems have been developed that do not allow engines to enter smoke modes.
Various exhaust gas aftertreatment systems are being developed. For example, a system has been developed with a filter in the exhaust tract, which retains particulate matter. After a certain operating time, the electronic unit gives a command to increase the fuel supply. This leads to an increase in the temperature of the exhaust gases, which, in turn, leads to soot burning and filter regeneration.
1.5. Neutralization
In the same 70s, it became clear that it was impossible to achieve a significant improvement in the situation with toxicity without the use of additional devices, since a decrease in one parameter entails an increase in others. Therefore, they actively engaged in the improvement of exhaust gas aftertreatment systems.
Neutralization systems have been used in the past for automotive and tractor equipment operating in special conditions, such as tunneling and mine development.
There are two basic principles for constructing converters - thermal and catalytic.
Thermal converter is a combustion chamber, which is located in the exhaust tract of the engine for afterburning the products of incomplete combustion of fuel - CH and CO. It can be installed in place of the exhaust pipeline and perform its functions. The oxidation reactions of CO and CH proceed quite quickly at temperatures above 830 °C and in the presence of unbound oxygen in the reaction zone. Thermal converters are used on engines with positive ignition, in which the temperature necessary for the effective flow of thermal oxidation reactions is provided without the supply of additional fuel. The already high exhaust gas temperature of these engines rises in the reaction zone as a result of the burning out of part of CH and CO, the concentration of which is much higher than that of diesel engines.
The thermal neutralizer (Fig. 1.4) consists of a housing with inlet (outlet) pipes and one or two flame tube inserts made of heat-resistant sheet steel. Good mixing of the additional air required for the oxidation of CH and CO with the exhaust gases is achieved by intense vortex formation and turbulence of gases as they flow through the holes in the pipes and as a result of changing the direction of their movement by a baffle system. For effective afterburning of CO and CH, a sufficiently long time is required, so the speed of the gases in the converter is set low, as a result of which its volume is relatively large.
Rice. 1.4. Thermal converter
To prevent a drop in the temperature of the exhaust gases as a result of heat transfer to the walls, the exhaust pipeline and the converter are covered with thermal insulation, heat shields are installed in the exhaust channels, and the converter is placed as close as possible to the engine. Despite this, it takes a significant amount of time to warm up the thermal converter after starting the engine. To reduce this time, the temperature of the exhaust gases is increased, which is achieved by enriching the combustible mixture and reducing the ignition timing, although both of these increase fuel consumption. Such measures are resorted to to maintain a stable flame during transient engine operation. The flame insert also contributes to a decrease in the time until the effective oxidation of CH and CO begins.
catalytic converters– devices containing substances that accelerate reactions, – catalysts . Catalytic converters can be "single-way", "two-way" and "three-way".
One-component and two-component oxidizing-type neutralizers afterburn (re-oxidize) CO (one-component) and CH (two-component).
2CO + O 2 \u003d 2CO 2(at 250–300°С).
C m H n + (m + n/4) O 2 \u003d mCO 2 + n / 2H 2 O(over 400°С).
The catalytic converter is a stainless steel housing included in the exhaust system. The carrier block of the active element is located in the housing. The first neutralizers were filled with metal balls coated with a thin layer of catalyst (see Fig. 1.5).
Rice. 1.5. Catalytic converter device
As active substances were used: aluminum, copper, chromium, nickel. The main disadvantages of the first generation neutralizers were low efficiency and short service life. Catalytic converters based on noble metals - platinum and palladium - proved to be the most resistant to the "poisonous" effects of sulfur, organosilicon and other compounds formed as a result of the combustion of fuel and oil contained in the engine cylinder.
The carrier of the active substance in such neutralizers is special ceramics - a monolith with many longitudinal honeycombs. A special rough substrate is applied to the surface of the honeycombs. This makes it possible to increase the effective contact area of the coating with exhaust gases up to ~20 thousand m 2 . The amount of noble metals deposited on the substrate in this area is 2–3 grams, which makes it possible to organize the mass production of relatively inexpensive products.
Ceramics can withstand temperatures up to 800–850 °C. Malfunctions of the power supply system (difficult start) and prolonged operation on a re-enriched working mixture lead to the fact that excess fuel will burn in the converter. This leads to the melting of the honeycombs and the failure of the converter. Today, metal honeycombs are used as carriers of the catalytic layer. This makes it possible to increase the area of the working surface, obtain less back pressure, accelerate the heating of the converter to the operating temperature, and expand the temperature range to 1000–1050 °C.
Reducing media catalytic converters, or three-way neutralizers, are used in exhaust systems, both to reduce CO and CH emissions, and to reduce emissions of nitrogen oxides. The catalytic layer of the converter contains, in addition to platinum and palladium, the rare earth element rhodium. As a result of chemical reactions on the surface of a catalyst heated to 600-800 ° C, CO, CH, NOx contained in the exhaust gases are converted into H 2 O, CO 2, N 2:
2NO + 2CO \u003d N 2 + 2CO 2.
2NO + 2H 2 \u003d N 2 + 2H 2 O.
The efficiency of a three-way catalytic converter reaches 90% under real operating conditions, but only on condition that the composition of the combustible mixture differs from the stoichiometric one by no more than 1%.
Due to changes in engine parameters due to its wear, operation in non-stationary modes, drift of power system settings, it is not possible to maintain the stoichiometric composition of the combustible mixture only due to the design of carburetors or injectors. Feedback is needed that would evaluate the composition of the air-fuel mixture entering the engine cylinders.
To date, the most widely used feedback system using the so-called oxygen sensor(lambda probe) based on zirconium ceramics ZrO 2 (Fig. 1.6).
The sensitive element of the lambda probe is a zirconium cap 2 . The inner and outer surfaces of the cap are covered with thin layers of platinum-rhodium alloy, which act as the outer 3 and domestic 4 electrodes. With threaded part 1 the sensor is installed in the exhaust tract. In this case, the outer electrode is washed by the processed gases, and the inner one - by atmospheric air.
Rice. 1.6. The design of the oxygen sensor
Zirconium dioxide at temperatures above 350°C acquires the property of an electrolyte, and the sensor becomes a galvanic cell. The EMF value on the sensor electrodes is determined by the ratio of oxygen partial pressures on the inner and outer sides of the sensing element. In the presence of free oxygen in the exhaust gases, the sensor generates an EMF of the order of 0.1 V. In the absence of free oxygen in the exhaust gases, the EMF increases almost abruptly to 0.9 V.
The composition of the mixture is controlled after the sensor has warmed up to operating temperatures. The composition of the mixture is maintained by changing the amount of fuel supplied to the engine cylinders at the boundary of the probe EMF transition from low to high voltage level. To reduce the time to reach the operating mode, electrically heated sensors are used.
The main disadvantages of systems with feedback and a three-way catalytic converter are: the impossibility of running the engine on leaded fuel, a rather low resource of the converter and the lambda probe (about 80,000 km) and an increase in the resistance of the exhaust system.
Bibliography
- Vyrubov D.N. Internal combustion engines: theory of reciprocating and combined engines / D.N. Vyrubov et al. M.: Mashinostroenie, 1983.
- Automobile and tractor engines. (Theory, power systems, designs and calculation) / Ed. I. M. Lenin. M.: Higher. school, 1969.
- Automotive and tractor engines: In 2 hours Design and calculation of engines / Ed. I. M. Lenin. 2nd ed., add. and reworked. M.: Higher. school, 1976.
- Internal combustion engines: Design and operation of reciprocating and combined engines / Ed. A. S. Orlin, M. G. Kruglov. 3rd ed., revised. and additional M.: Mashinostroenie, 1980.
- Arkhangelsky V. M. Automobile engines / V. M. Arkhangelsky. M.: Mashinostroenie, 1973.
- Kolchin A. I. Calculation of automobile and tractor engines / A. I. Kolchin, V. P. Demidov. M.: Higher. school, 1971.
- Internal combustion engines / Ed. Dr. tech. Sciences prof. V. N. Lukanin. M.: Higher. school, 1985.
- Khachiyan A.S. Internal combustion engines / A.S. Khachiyan et al. M.: Vyssh. school, 1985.
- Ross Tweg. Gasoline injection systems. Device, maintenance, repair: Prakt. allowance / Ross Tweg. M.: Publishing house “Behind the wheel”, 1998.
Fuel combustion products have a decisive influence on the energy and environmental performance of various heat engineering installations. However, in addition to these products, a number of other substances are formed during combustion, which, due to their small amount, are not taken into account in energy calculations, but determine the environmental performance of furnaces, furnaces, heat engines and other devices of modern heat engineering.
First of all, the so-called toxic substances that have negative effects on the human body and the environment should be attributed to the number of environmentally harmful products of combustion. The main toxic substances are nitrogen oxides (NOx), carbon monoxide (CO), various hydrocarbons (CH), soot and compounds containing lead and sulfur.
Nitrogen oxides are formed as a result of the chemical interaction of nitrogen and atmospheric oxygen if the temperature exceeds 1500 K. During the combustion of fuels, mainly nitric oxide NO is formed, which is then oxidized to NO2 in the atmosphere. The formation of NO increases with increasing gas temperature and oxygen concentration. The dependence of NO formation on temperature creates certain difficulties in terms of increasing the thermal efficiency of a heat engine. For example, with an increase in the maximum cycle temperature from 2000 K to 3000 K, the thermal efficiency of the Carnot cycle increases by 1.5 times and reaches a value of 0.66, but the calculated maximum concentration of NO in the combustion products increases by 10 times and reaches 1.1% by volume. .
NO2 in the atmosphere is a reddish-brown gas, which in high concentrations has a suffocating odor that is harmful to the mucous membranes of the eyes.
Carbon monoxide (CO) is formed during combustion in the absence of oxygen. Carbon monoxide is a colorless and odorless gas. When inhaled together with air, it intensively combines with blood hemoglobin, which reduces its ability to supply the body with oxygen. Symptoms of carbon monoxide poisoning include headache, palpitations, shortness of breath and nausea.
Hydrocarbons (CH) consist of original or decayed fuel molecules that did not take part in combustion. Hydrocarbons appear in the exhaust gases (EG) of internal combustion engines due to the extinguishing of the flame near the relatively cold walls of the combustion flame. In diesel engines, hydrocarbons are formed in the over-enriched zones of the mixture, where the pyrolysis of fuel molecules occurs. If, during the expansion process, these zones do not receive enough oxygen, then CH will end up in the composition of the exhaust gas. Hydrocarbons under the action of sunlight can interact with NOx, forming biologically active substances that irritate the respiratory tract and cause the appearance of the so-called smog.
Emissions of benzene, toluene, polycyclic automatic hydrocarbons (PAHs) and, first of all, benzpyrene have a particular impact. PAHs are so-called carcinogenic substances; they are not excreted from the human body, but accumulate in it over time, contributing to the formation of malignant tumors.
Soot is a solid product consisting mainly of carbon. In addition to carbon, soot contains 1–3% (by mass) of hydrogen. Soot is formed at temperatures above 1500 K as a result of thermal decomposition (pyrolysis) with a strong lack of oxygen. The presence of soot in the exhaust gases causes black smoke at the outlet.
Soot is a mechanical pollutant of the nasopharynx and lungs. A great danger is associated with the property of soot to accumulate carcinogenic substances on the surface of its particles and serve as their carrier.
Some toxic substances, after they enter the atmosphere as part of the products of combustion, undergo further transformations. For example, in the presence of hydrocarbons, nitrogen oxides and carbon monoxide in the atmosphere, intense ultraviolet radiation from the sun produces ozone (O3), which is the strongest oxidizing agent and, at an appropriate concentration, causes a deterioration in people's well-being.
With a high content of NO2, Oz and CH in a sedentary and humid atmosphere, a brown fog arises, which is called "smog" (from the English "smoke" - smoke and "fog" - fog). Smog is a mixture of liquid and gaseous components, it irritates the eyes and mucous membranes, impairs visibility on the roads.
The main sources of emission of toxic products of combustion are cars, industry, thermal and power plants. In some cities, the content of toxic products of combustion in the atmosphere exceeds the maximum permissible concentration by several tens of times.
To combat this evil, in most countries of the world, relevant laws have been adopted that limit the content of toxic substances in combustion products emitted into the atmosphere.
The fulfillment of the norms of permitted normal emission prescribed by the relevant laws has become one of the central tasks of heat engineering. In many cases, the operation of industrial heat engineering facilities is controlled in such a way as to provide the required compromise between their energy, economic and environmental performance. In many cases, the level of economic performance achieved in this way exceeds that permitted by modern standards. Therefore, the neutralization and purification of combustion products before their release into the atmosphere has become of great importance. For this purpose, various neutralizers and filters are used. At the same time, the composition of hydrocarbon fuels is improving (reducing the content of the sphere, lead, aromatic hydrocarbons), and the use of gas fuels is expanding. In the future, the use of hydrogen as a fuel will completely exclude the content of CO, CH and other toxic carbon-containing components in the combustion products.
