Welcome to this lecture on reduction of pollutant emissions. In previous lectures, we discussed the impact of energy industries on the environment, how to assess the impact, and institutional methods of ensuring environmental safety. Moreover, there are technologies that reduce the impact of energy facilities on the environment. This is especially relevant in the case of plants that use fossil fuels. There are two approaches to reducing pollutant emissions into the atmosphere. Emissions can be purified with filters, pollutants can be captured and neutralized or you can change the operation mode of your equipment to reduce toxic emissions. In this lecture, we will consider the second group of air pollution reduction methods. After this lecture, you will be able to list methods of reduction of air pollution emissions, describe how to increase the efficiency of power plants and explain how it affects reduction of pollutant emissions. Methods to reduce air pollution by emissions from stationary fuel burning plants, by changing the operating mode can be classified in this way. Increasing the use of fuels with high environmental characteristics in the fuel burns, reducing fuel consumption by increasing combustion efficiency, and reducing heat losses during transportation and use. Use of energy saving equipment and energy processing of solid fuels. Let's consider the operation of the thermal power plant and the possibility of reducing fuel consumption by using energy saving equipment for deep use of the heat of exhaust gases. The consumption of fossil fuel for each technological process depends on the need for thermal energy, fuel calorific value, and efficiency factor of the heat generating plant. The analysis of the formula shows that it is necessary to use fuel with high calorific value, as well as to use fuel combustion units with higher efficiency factor. The efficiency is reduced due to various heat losses. Heat loss is to these exhaust gases, heat loss is from chemical incompleteness of combustion, heat loss is from mechanical incompleteness of combustion and with heat of waste, heat loss is throughout walls. The highest loss is through this exhaust gases accrue than burning fuel in the industrial furnaces without utilization of combustion products, are the 50 percent. This losses have a significant impact on the efficiency of the boiler, reducing its efficiency. Thus, we understand that the lower the temperature of fuel gas, the higher the boiler efficiency. Optimum temperature of exhaust gases for different fuels and boiler operating parameters is determined on the basis of technical and economic calculations at the earliest stage of its construction. The temperature of exhaust gases is usually in the range from 120-180 degrees Celsius. This values are determined taking into account environmental safety factors. But first of all, based on the requirements to the performance and long life of equipment. Thus, the minimum threshold is set to exclude the risk of condensation in the convective part of the boiler and further along the path. However, to prevent corrosion, it is not necessary to lose heat, which is emitted into the atmosphere instead of doing useful work. Of course, corrosion is an pleasure phenomenon that can affect the safe operation of the power plant and significantly shorten its operating lifetime. The exhaust gases of natural gas boilers mainly consists of the following combustion products. Water vapor, carbon dioxide, carbon monoxide, and unburned hydrocarbons. Since the atmospheric air contains a large amount of nitrogen, the combustion products produce nitrogen oxides, which are harmful to the environment and human health. Nitrogen oxides then combined with the water form corrosive nitric acid. When fuel oil and coal are burnt sulfur oxides appear in combustion products. The negative impact on the environment is also widely researched. Traditionally, the flue gas temperature, as mentioned above, is chosen in such a way as to protect the equipment from acid deposition on the boiler heating surfaces. Of course, there are certain standards that limit the permissible concentrations of nitrogen and sulfur oxides. But this doesn't change the fact of accumulation of these combustion products in the Earth's atmosphere and they fall out as acid rains. Implementation of the set of measures to reduce the temperature of flue gases behind the boiler provides an increase in efficiency of the entire plan, which includes the boiler unit using primarily the boiler itself. The concept of such solutions is, in the section of the gas duct to the stack is mounted to a heated exchanger that takes the heat from the flue gases by cooling flue, for example water. This water, can be as directly final coolant, which must be heated or in the immediate agent that transmits the heat throughout additional heat is changed and equipment to another counter. The principal scheme is shown in the picture. The resulting condensate is collected directly in the volume of the heat exchanger, which is made of corrosion resistant materials. This is due to the fact that due point temperature threshold for moisture contained in the volume of exhaust gases is overcome exactly inside the heat exchanger. The design of the heat exchanger may be either conventional regenerative heat exchanger. The transfer of heat from gas to liquid occurs throughout the dividing wall. Or contact heat exchanger, in which the flue gases directly come into contact with water, which is sprayed by nozzles in the flow. Cooling the boiler exhaust gases using such solutions can be quite deep, up to 30 in 20 degrees Celsius with the initial 120, 130 degrees Celsius. The resultant heat is quite enough to heat the water for the needs of chemical water treatment, hot water, and even heating systems. At the same time, fuel saving can reach from 5-10 percent and the efficiency of the boiler unit can be increased by three percent. Thus, implementation of this described technology, allows solving several tasks at once. These are the most complete and useful use of heat from flue gases, which leads to a reduction in fossil fuel combustion and as a result reduced emissions, including carbon dioxide. Reduction of NOX and SOX emissions into the atmosphere, obtaining additional resource, preheated water, and the elimination of the smoke flame, it becomes slightly visible or disappears completely. After this lecture, you have learned about methods of reduction of air pollution emissions, how to increase the efficiency of power plants, and how it affects the reduction of pollutant emissions.
