Use: energy, waste heat recovery. The essence of the invention: the gas flow is moistened by passing it through a condensate film formed on a dihedral perforated sheet 4, where the gases are saturated with water vapor. In chamber 2 above sheet 4, volumetric condensation of water vapor occurs on dust particles and tiny droplets of the vapor-gas flow. The prepared vapor-gas mixture is cooled to the dew point temperature by transferring the heat of the flow of the heated medium through the wall of the heat exchange elements 8. Condensate from the flow falls onto inclined partitions 5 with gutters 10 and then enters sheet 4 through the drain pipe 9. 1 il.

The present invention relates to the field of boiler technology, and more specifically to the field of waste gas heat recovery. There is a known method for recycling the heat of exhaust gases (USSR Aut.St. N 1359556, MKI F 22 V 33/18, 1986), which is the closest analogue, in which the combustion products are sequentially forcibly moistened, compressed in a compressor, cooled to a temperature below the dew point temperature together with condensation of water vapor at a pressure above atmospheric pressure, they are separated in a separator, expanded with a simultaneous decrease in temperature in a turboexpander and removed into the atmosphere. There is a known method for recycling the heat of exhaust gases (GDR, Pat. N 156197, MKI F 28 D 3/00, 1982) achieved by countercurrent movement in a heat exchanger of exhaust gases and an intermediate liquid medium, heated to a temperature greater than the dew point temperature of the exhaust gases, which are cooled to a temperature below the dew point. There is a known method of low-temperature heating using the higher calorific value of fuel (Germany, application N OS 3151418, MKI F 23 J 11/00, 1983), which consists in the fact that fuel is burned in a heating device with the formation of hot gases that enter the heating device forward and to the side. In part of the flow path, fuel gases are directed downward to form condensate. The fuel gases at the outlet have a temperature of 40–45 o C. The known method allows cooling of the exhaust gases below the dew point temperature, which slightly increases the thermal efficiency of the installation. However, in this case, condensate is sprayed through the nozzles, which leads to additional energy consumption for its own needs and increases the content of water vapor in the combustion products. The inclusion of a compressor and a turboexpander in the circuit, which, respectively, compress and expand the combustion products, does not increase efficiency, and, in addition, leads to additional energy consumption associated with losses in the compressor and turboexpander. The objective of the invention is to intensify heat exchange with deep utilization of heat from exhaust gases. The problem is solved due to the fact that the gas flow is humidified by passing it through a film of condensate with saturation of the flow with water vapor, followed by condensation of the latter, as well as the condensate falling onto the said film and draining the unevaporated part. The proposed method can be implemented in the device shown in the drawing, where: 1 condensate collector, 2 chamber, 3 housing, 4 dihedral unequal inclined perforated sheet, 5 inclined partitions, 6 tapering two-dimensional diffuser, 7 expanding diffuser, 8 heat exchange surface, 9 drain pipe, 10 gutter, 11 mating surface, 12 - separator, 13 overheating heat exchanger, 14 smoke exhauster, 15 chimney, 16 water seal, 17 horizontal axis. The operation of the device according to the proposed method of utilizing the heat of combustion products is similar to an atmospheric heat pipe. Its evaporative part is located in the lower part of chamber 2, from which the prepared vapor-gas mixture rises, and the condensation part on the heat exchange surfaces 3, from which condensate flows along inclined partitions 5 with gutters 10 through drain pipes 9 onto a dihedral unequal-sided perforated sheet 4, and the excess into condensate collector 1. Combustion products coming from the superheat heat exchanger 13 bubble a film of condensate on a dihedral unequally inclined perforated sheet 4. The condensate is sprayed, heated and evaporated, and its excess flows into the condensate collector 1. Flue gases are saturated with water vapor at a pressure approximately equal to atmospheric. It depends on the mode of joint operation of the fan and smoke exhauster 14. In chamber 2, water vapor is in a supersaturated state, since the vapor pressure in the gas mixture is greater than the saturated vapor pressure. The smallest droplets, dust particles of combustion products become condensation centers, on which the process of volumetric condensation of water vapor occurs in chamber 2 without heat exchange with the environment. The prepared vapor-gas mixture condenses on the heat exchange surfaces 8. At the surface temperature of these heat exchange elements 8 significantly below the dew point temperature, the moisture content of the combustion products after the heat recovery device is lower than the initial one. The final phase of this continuous process is the precipitation of condensate on the inclined partitions 5 with complaints 10 and its entry onto the perforated sheet 4 through the drain pipe 9. The achievement of the task is confirmed by the following: 1. The value of the heat transfer coefficient increased to 180-250 W/m 2 o C, which sharply reduces the heat transfer surface area and, accordingly, reduces the weight and size indicators. 2. A 2.5 to 3 times reduction in the initial moisture content of water vapor in the flue gases reduces the intensity of corrosion processes in the gas path and chimney. 3. Fluctuations in the steam generator load do not reduce the efficiency of the boiler plant.

Claim

A method of utilizing the heat of exhaust gases, which consists in the fact that the gas flow is humidified and cooled to the dew point temperature by transferring the heat of the flow to the heated medium through the wall, characterized in that the gas flow is humidified by passing it through a condensate film with saturation of the flow with water vapor, followed by condensation of the latter, as well as the precipitation of condensate on the mentioned film and the drainage of its unevaporated part.

Use of flue gas heat in gas-fired industrial boiler houses

Use of flue gas heat in gas-fired industrial boiler houses

Candidate of Technical Sciences Sizov V.P., Doctor of Technical Sciences Yuzhakov A.A., Candidate of Technical Sciences Kapger I.V.,
Permavtomatika LLC, sizovperm@ mail .ru

Abstract: the price of natural gas varies significantly around the world. This depends on the country’s membership in the WTO, whether the country exports or imports its gas, gas production costs, the state of industry, political decisions, etc. The price of gas in the Russian Federation in connection with our country’s accession to the WTO will only increase and the government plans to equalize prices for natural gas both within the country and abroad. Let's roughly compare gas prices in Europe and Russia.

Russia – 3 rubles/m3.

Germany - 25 rubles/m3.

Denmark - 42 rubles/m3.

Ukraine, Belarus – 10 rubles/m3.

The prices are quite reasonable. In European countries, condensing-type boilers are widely used, their total share in the heat generation process reaches 90%. In Russia, these boilers are mainly not used due to the high cost of boilers, the low cost of gas and high-temperature centralized networks. And also by maintaining the system for limiting gas combustion in boiler houses.

Currently, the issue of more complete use of coolant energy is becoming increasingly relevant. The release of heat into the atmosphere not only creates additional pressure on the environment, but also increases the costs of boiler house owners. At the same time, modern technologies make it possible to more fully utilize the heat of flue gases and increase the efficiency of the boiler, calculated based on the lower calorific value, up to a value of 111%. Heat loss with flue gases occupies the main place among the heat losses of the boiler and amounts to 5 ¸ 12% of generated heat. In addition, the heat of condensation of water vapor that is formed during fuel combustion can be used. The amount of heat released during condensation of water vapor depends on the type of fuel and ranges from 3.8% for liquid fuels and up to 11.2% for gaseous fuels (for methane) and is defined as the difference between the higher and lower heat of combustion of the fuel (Table 1 ).

Table 1 - Values ​​of higher and lower heating values ​​for various types of fuel

Fuel type	PCS (Kcal)	PCI ( Kcal )	Difference (%)
Heating oil

It turns out that the exhaust gases contain both sensible and latent heat. Moreover, the latter can reach a value that in some cases exceeds sensible heat. Sensible heat is heat in which a change in the amount of heat supplied to a body causes a change in its temperature. Latent heat is the heat of vaporization (condensation), which does not change the temperature of the body, but serves to change the state of aggregation of the body. This statement is illustrated by a graph (Fig. 1, on which enthalpy (the amount of heat supplied) is plotted along the abscissa axis, and temperature is plotted along the ordinate axis).

Rice. 1 – Dependence of enthalpy change for water

In the section of graph A-B, water is heated from a temperature of 0 °C to a temperature of 100 °C. In this case, all the heat supplied to the water is used to increase its temperature. Then the change in enthalpy is determined by formula (1)

(1)

where c is the heat capacity of water, m is the mass of the heated water, Dt – temperature difference.

Section of the B-C graph demonstrates the process of water boiling. In this case, all the heat supplied to the water is spent on converting it into steam, while the temperature remains constant - 100 ° C. Section C-D of the graph shows that all the water has turned into steam (boiled away), after which heat is spent to increase the temperature of the steam. Then the change in enthalpy for section A-C is characterized by formula (2)

Where r = 2500 kJ/kg – latent heat of vaporization of water at atmospheric pressure.

The biggest difference between the highest and lowest calorific values, as can be seen from table. 1, methane, so natural gas (up to 99% methane) gives the highest profitability. From here, all further calculations and conclusions will be given for methane-based gas. Consider the combustion reaction of methane (3)

From the equation of this reaction it follows that for the oxidation of one methane molecule, two oxygen molecules are needed, i.e. For complete combustion of 1 m 3 of methane, 2 m 3 of oxygen is required. Atmospheric air, which is a mixture of gases, is used as an oxidizer when burning fuel in boiler units. For technical calculations, the conditional composition of air is usually taken as consisting of two components: oxygen (21 vol. %) and nitrogen (79 vol. %). Taking into account the composition of the air, to carry out the combustion reaction, complete combustion of the gas will require a volume of air 100/21 = 4.76 times more than oxygen. Thus, to burn 1 m 3 of methane it will take 2 ×4.76=9.52 air. As you can see from the oxidation reaction equation, the result is carbon dioxide, water vapor (flue gases) and heat. The heat that is released during fuel combustion according to (3) is called the net calorific value of the fuel (PCI).

If you cool water vapor, then under certain conditions they will begin to condense (transition from a gaseous state to a liquid) and at the same time an additional amount of heat will be released (latent heat of vaporization/condensation) Fig. 2.

Rice. 2 – Heat release during condensation of water vapor

It should be borne in mind that water vapor in flue gases has slightly different properties than pure water vapor. They are in a mixture with other gases and their parameters correspond to the parameters of the mixture. Therefore, the temperature at which condensation begins differs from 100 °C. The value of this temperature depends on the composition of the flue gases, which, in turn, is a consequence of the type and composition of the fuel, as well as the excess air coefficient.
The temperature of the flue gases at which condensation of water vapor in the products of fuel combustion begins is called the dew point and looks like Fig. 3.

Rice. 3 – Dew point for methane

Consequently, for flue gases, which are a mixture of gases and water vapor, the enthalpy changes according to a slightly different law (Fig. 4).

Figure 4 – Heat release from the steam-air mixture

From the graph in Fig. 4, two important conclusions can be drawn. First, the dew point temperature is equal to the temperature to which the flue gases were cooled. Secondly, it is not necessary to go through it as in Fig. 2, the entire condensation zone, which is not only practically impossible but also unnecessary. This, in turn, provides various possibilities for implementing thermal balance. In other words, almost any small volume of coolant can be used to cool flue gases.

From the above, we can conclude that when calculating the boiler efficiency based on the lower calorific value with subsequent utilization of the heat of flue gases and water vapor, the efficiency can be significantly increased (more than 100%). At first glance, this contradicts the laws of physics, but in fact there is no contradiction here. The efficiency of such systems must be calculated based on the higher calorific value, and the determination of the efficiency based on the lower calorific value must be carried out only if it is necessary to compare its efficiency with the efficiency of a conventional boiler. Only in this context does efficiency > 100% make sense. We believe that for such installations it is more correct to give two efficiencies. The problem statement can be formulated as follows. To more fully utilize the heat of combustion of flue gases, they must be cooled to a temperature below the dew point. In this case, the water vapor generated during gas combustion will condense and transfer the latent heat of vaporization to the coolant. In this case, cooling of the flue gases must be carried out in heat exchangers of a special design, depending mainly on the temperature of the flue gases and the temperature of the cooling water. The use of water as an intermediate coolant is the most attractive, because in this case it is possible to use water with the lowest possible temperature. As a result, it is possible to obtain a water temperature at the outlet of the heat exchanger, for example, 54°C, and then use it. If the return line is used as a coolant, its temperature should be as low as possible, and this is often only possible if there are low-temperature heating systems as consumers.

Flue gases from high-power boiler units are usually discharged into a reinforced concrete or brick pipe. If special measures are not taken for the subsequent heating of partially dried flue gases, the pipe will turn into a condensation heat exchanger with all the ensuing consequences. There are two ways to solve this issue. The first way is to use a bypass, in which part of the gases, for example 80%, is passed through the heat exchanger, and the other part, in the amount of 20%, is passed through the bypass and then mixed with the partially dried gases. Thus, by heating the gases, we shift the dew point to the required temperature at which the pipe is guaranteed to operate in dry mode. The second method is to use a plate recuperator. In this case, the exhaust gases pass through the recuperator several times, thereby heating themselves.

Let's consider an example of calculating a 150 m typical pipe (Fig. 5-7), which has a three-layer structure. Calculations were performed in the software package Ansys -CFX . It is clear from the figures that the movement of gas in the pipe has a pronounced turbulent character and, as a result, the minimum temperature on the lining may not be in the area of ​​the tip, as follows from the simplified empirical methodology.

Rice. 7 – temperature field on the surface of the lining

It should be noted that when installing a heat exchanger in a gas path, its aerodynamic resistance will increase, but the volume and temperature of the exhaust gases will decrease. This leads to a decrease in the current of the smoke exhauster. The formation of condensate imposes special requirements on the elements of the gas path in terms of the use of corrosion-resistant materials. The amount of condensate is approximately 1000-600 kg/hour per 1 Gcal of useful heat exchanger power. The pH value of the condensate of combustion products when burning natural gas is 4.5-4.7, which corresponds to an acidic environment. In case of a small amount of condensate, it is possible to use replaceable blocks to neutralize the condensate. However, for large boiler houses it is necessary to use caustic soda dosing technology. As practice shows, small volumes of condensate can be used as make-up without any neutralization.

It should be emphasized that the main problem in the design of the systems noted above is the too large difference in enthalpy per unit volume of substances, and the resulting technical problem is the development of the heat exchange surface on the gas side. The industry of the Russian Federation mass-produces similar heat exchangers such as KSK, VNV, etc. Let's consider how developed the heat exchange surface on the gas side is on the existing structure (Fig. 8). An ordinary tube in which water (liquid) flows inside, and air (exhaust gases) flows from the outside along the fins of the radiator. The calculated heater ratio will be expressed by a certain

Rice. 8 – drawing of the heater tube.

coefficient

K =S nar /S vn, (4),

Where S nar – outer area of ​​the heat exchanger mm 2, and S vn – internal area of ​​the tube.

In geometric calculations of the structure we obtain K =15. This means that the outer area of ​​the tube is 15 times larger than the inner area. This is explained by the fact that the enthalpy of air per unit volume is many times less than the enthalpy of water per unit volume. Let's calculate how many times the enthalpy of a liter of air is less than the enthalpy of a liter of water. From

enthalpy of water: E in = 4.183 KJ/l*K.

air enthalpy: E air = 0.7864 J/l*K. (at a temperature of 130 0 C).

Hence the enthalpy of water is 5319 times greater than the enthalpy of air, and therefore K =S nar /S vn . Ideally, in such a heat exchanger, the coefficient K should be 5319, but since the outer surface in relation to the inner surface is developed 15 times, the difference in enthalpy essentially between air and water is reduced to the value K = (5319/15) = 354. Technically develop the ratio of the areas of the internal and external surfaces to obtain the ratio K =5319 very difficult or almost impossible. To solve this problem, we will try to artificially increase the enthalpy of air (exhaust gases). To do this, spray water (condensate of the same gas) from the nozzle into the exhaust gas. Let's spray it in such an amount relative to the gas that all the sprayed water will completely evaporate in the gas and the relative humidity of the gas will become 100%. The relative humidity of the gas can be calculated based on Table 2.

Table 2. Values ​​of absolute gas humidity with a relative humidity of 100% for water at various temperatures and atmospheric pressure.

T,°C	A,g/m3	T,°C	A,g/m3	T,°C	A,g/m3
	86,74

From Fig. 3 it is clear that with a very high-quality burner, it is possible to achieve a dew point temperature in the exhaust gases T dew = 60 0 C. In this case, the temperature of these gases is 130 0 C. The absolute moisture content in the gas (according to Table 2) at T dew = 60 0 C will be 129,70 g/m 3 . If water is sprayed into this gas, its temperature will drop sharply, its density will increase, and its enthalpy will rise sharply. It should be noted that it makes no sense to spray water above 100% relative humidity, because... When the relative humidity threshold exceeds 100%, the sprayed water will stop evaporating into gas. Let us carry out a small calculation of the required amount of sprayed water for the following conditions: Tg – initial gas temperature equal to 120 0 C, T rise - gas dew point 60 0 C (129.70 g/m 3), required IT: Tgk - the final temperature of the gas and Mv - the mass of water sprayed in the gas (kg.)

Solution. All calculations are carried out relative to 1 m 3 of gas. The complexity of the calculations is determined by the fact that as a result of atomization, both the density of the gas and its heat capacity, volume, etc. change. In addition, it is assumed that evaporation occurs in an absolutely dry gas, and the energy for heating water is not taken into account.

Let's calculate the amount of energy given by gas to water during water evaporation

where: c – heat capacity of gas (1 KJ/kg.K), m – gas mass (1 kg/m 3)

Let's calculate the amount of energy given up by water during evaporation into gas

Where: r – latent energy of vaporization (2500 KJ/kg), m – mass of evaporated water

As a result of substitution we get the function

(5)

It should be taken into account that it is impossible to spray more water than indicated in Table 2, and the gas already contains evaporated water. Through selection and calculations we obtained the value m = 22 g, Tgk = 65 0 C. Let's calculate the actual enthalpy of the resulting gas, taking into account that its relative humidity is 100% and when it is cooled, both latent and sensible energy will be released. Then according to we obtain the sum of two enthalpies. Enthalpy of gas and enthalpy of condensed water.

E voz = Eg + Evod

Eg we find from reference literature 1.1 (KJ/m 3 *K)

EvodWe calculate relative to the table. 2. Our gas, cooling from 65 0 C to 64 0 C, releases 6.58 grams of water. The enthalpy of condensation is Evod=2500 J/g or in our case Evod=16.45 KJ/m 3

Let's sum up the enthalpy of condensed water and the enthalpy of gas.

E voz =17.55 (J/l*K)

As we can see by spraying water, we were able to increase the enthalpy of the gas by 22.3 times. If before spraying water the gas enthalpy was E air = 0.7864 J/l*K. (at a temperature of 130 0 C). Then after sputtering the enthalpy is Evoz = 17.55 (J/l*K). This means that to obtain the same thermal energy on the same standard heat exchanger type KSK, VNV, the heat exchanger area can be reduced by 22.3 times. The recalculated coefficient K (the value was equal to 5319) becomes equal to 16. And with this coefficient, the heat exchanger acquires quite feasible dimensions.

Another important issue when creating such systems is the analysis of the spraying process, i.e. what diameter of a drop is needed when water evaporates in gas. If the droplet is small enough (for example, 5 μM), then the lifetime of this droplet in the gas before complete evaporation is quite short. And if the droplet has a size of, for example, 600 µM, then naturally it remains in the gas much longer before complete evaporation. The solution to this physical problem is quite complicated by the fact that the evaporation process occurs with constantly changing characteristics: temperature, humidity, droplet diameter, etc. For this process, the solution is presented in, and the formula for calculating the time of complete evaporation ( ) drops look like

(6)

Where: ρ and - liquid density (1 kg/dm 3), r – energy of vaporization (2500 kJ/kg), λ g – thermal conductivity of gas (0.026 J/m 2 K), d 2 – drop diameter (m), Δ t – average temperature difference between gas and water (K).

Then, according to (6), the lifetime of a droplet with a diameter of 100 μM. (1*10 -4 m) is τ = 2*10 -3 hours or 1.8 seconds, and the lifetime of a drop with a diameter of 50 µM. (5*10 -5 m) is equal to τ = 5*10 -4 hours or 0.072 seconds. Accordingly, knowing the lifetime of a drop, its flight speed in space, the speed of gas flow and the geometric dimensions of the gas duct, one can easily calculate the irrigation system for the gas duct.

Below we will consider the implementation of the system design, taking into account the relations obtained above. It is believed that the exhaust gas heat exchanger must operate depending on the street temperature, otherwise the house pipe will be destroyed when condensation forms in it. However, it is possible to manufacture a heat exchanger that operates regardless of the street temperature and has a better heat removal from exhaust gases, even to subzero temperatures, despite the fact that the temperature of the exhaust gases will be, for example, +10 0 C (the dew point of these gases will be 0 0 C). This is ensured by the fact that during heat exchange the controller calculates the dew point, heat exchange energy and other parameters. Let's consider the technological diagram of the proposed system (Fig. 9).

According to the technological diagram, the following are installed in the heat exchanger: adjustable dampers a-b-c-d; heat exchangers d-e-zh; temperature sensors 1-2-3-4-5-6; o Sprinkler (pump H, and a group of nozzles); control controller.

Let us consider the functioning of the proposed system. Let the exhaust gases escape from the boiler. for example, a temperature of 120 0 C and a dew point of 60 0 C (indicated in the diagram as 120/60). The temperature sensor (1) measures the temperature of the boiler exhaust gases. The dew point is calculated by the controller relative to the stoichiometry of gas combustion. A gate (a) appears in the path of the gas. This is an emergency shutter. which closes in the event of equipment repair, malfunction, overhaul, maintenance, etc. Thus, the damper (a) is fully open and directly passes the boiler exhaust gases into the smoke exhauster. With this scheme, heat recovery is zero; in fact, the flue gas removal scheme is restored as it was before the installation of the heat exchanger. In operating condition, the gate (a) is completely closed and 100% of the gases enter the heat exchanger.

In the heat exchanger, the gases enter the recuperator (e) where they are cooled, but in any case not below the dew point (60 0 C). For example, they cooled down to 90 0 C. No moisture was released in them. The gas temperature is measured by temperature sensor 2. The temperature of the gases after the recuperator can be adjusted with a gate (b). Regulation is necessary to increase the efficiency of the heat exchanger. Since during condensation of moisture, the mass present in gases decreases depending on how much the gases have been cooled, it is possible to remove from them up to 2/11 of the total mass of gases in the form of water. Where did this figure come from? Let's consider the chemical formula of the methane oxidation reaction (3).

To oxidize 1m 3 of methane, 2m 3 of oxygen is required. But since the air contains only 20% oxygen, 10 m 3 of air will be required to oxidize 1 m 3 of methane. After burning this mixture, we get: 1 m 3 of carbon dioxide, 2 m 3 of water vapor and 8 m 3 of nitrogen and other gases. We can remove from the exhaust gases by condensation just under 2/11 of all exhaust gases in the form of water. To do this, the exhaust gas must be cooled to outside temperature. With the release of the appropriate proportion of water. The air taken from the street for combustion also contains minor moisture.

The released water is removed at the bottom of the heat exchanger. Accordingly, if the entire composition of gases (11/11 parts) passes along the path of the boiler-recuperator (e)-heat recovery unit (e), then only 9/11 parts of the exhaust gas can pass along the other side of the recuperator (e). The rest - up to 2/11 parts of the gas in the form of moisture - can fall out in the heat exchanger. And to minimize the aerodynamic resistance of the heat exchanger, the gate (b) can be opened slightly. In this case, the exhaust gases will be separated. Part will pass through the recuperator (e), and part through the gate (b). When the gate (b) is fully opened, the gases will pass through without cooling and the readings of temperature sensors 1 and 2 will coincide.

An irrigation system with a pump H and a group of nozzles is installed along the path of the gases. Gases are irrigated with water released during condensation. Injectors that spray moisture into the gas sharply increase its dew point, cool it and compress it adiabatically. In the example under consideration, the gas temperature drops sharply to 62/62, and since the water sprayed in the gas completely evaporates in the gas, the dew point and the gas temperature coincide. Having reached the heat exchanger (e), latent thermal energy is released on it. In addition, the density of the gas flow increases abruptly and its speed decreases abruptly. All these changes significantly change the heat transfer efficiency for the better. The amount of water sprayed is determined by the controller and is related to the temperature and gas flow. The gas temperature in front of the heat exchanger is monitored by temperature sensor 6.

Next, the gases enter the heat exchanger (e). In the heat exchanger, the gases cool down, for example, to a temperature of 35 0 C. Accordingly, the dew point for these gases will also be 35 0 C. The next heat exchanger on the path of the exhaust gases is the heat exchanger (g). It serves to heat combustion air. The air supply temperature to such a heat exchanger can reach -35 0 C. This temperature depends on the minimum outside air temperature in a given region. Since some of the water vapor is removed from the exhaust gas, the mass flow of exhaust gases almost coincides with the mass flow of combustion air. Let the heat exchanger, for example, be filled with antifreeze. A gate (c) is installed between the heat exchangers. This gate also operates in discrete mode. When it warms up outside, there is no point in extracting heat from the heat exchanger (g). It stops its operation and the gate (c) opens completely, allowing exhaust gases to pass through, bypassing the heat exchanger (g).

The temperature of the cooled gases is determined by the temperature sensor (3). These gases are then sent to the recuperator (e). Having passed through it, they are heated to a certain temperature proportional to the cooling of the gases on the other side of the recuperator. The gate (d) is needed to regulate the heat exchange in the recuperator, and the degree of its opening depends on the outside temperature (from sensor 5). Accordingly, if it is very cold outside, then the gate (d) is completely closed and the gases are heated in the recuperator to avoid the dew point in the pipe. If it is hot outside, then gate (d) is open, as is gate (b).

CONCLUSIONS:

An increase in heat exchange in a liquid/gas heat exchanger occurs due to a sharp jump in gas enthalpy. But the proposed water spraying should occur in strictly measured doses. In addition, dosing of water into the exhaust gases takes into account the outside temperature.

The resulting calculation method allows one to avoid moisture condensation in the chimney and significantly increase the efficiency of the boiler unit. A similar technique can be applied to gas turbines and other condenser devices.

With the proposed method, the design of the boiler does not change, but is only modified. The cost of modification is about 10% of the cost of the boiler. The payback period at current gas prices is about 4 months.

This approach can significantly reduce the metal consumption of the structure and, accordingly, its cost. In addition, the aerodynamic resistance of the heat exchanger drops significantly, and the load on the smoke exhauster is reduced.

LITERATURE:

1.Aronov I.Z. Use of heat from flue gases of gasified boiler houses. – M.: “Energy”, 1967. – 192 p.

2.Thaddeus Hobler. Heat transfer and heat exchangers. – Leningrad: State scientific publication of chemical literature, 1961. – 626 p.

Flue gas condensation system for the company's boilers “ AprotechEngineeringAB” (Sweden)

The flue gas condensation system allows the capture and recovery of large amounts of thermal energy contained in the wet boiler flue gas, which is usually discharged through the chimney into the atmosphere.

The heat recovery/flue gas condensation system makes it possible to increase heat supply to consumers by 6–35% (depending on the type of fuel burned and installation parameters) or reduce natural gas consumption by 6–35%

Main advantages:

• Fuel economy (natural gas) - the same or increased boiler heat load with less fuel combustion
• Reduction of emissions - CO2, NOx and SOx (when burning coal or liquid fuels)
• Obtaining condensate for the boiler make-up system

Principle of operation:

The heat recovery/flue gas condensation system can operate in two stages: with or without the use of an air humidification system supplied to the boiler burners. If necessary, a scrubber is installed before the condensation system.

In the condenser, the exhaust flue gases are cooled using return water from the heating network. When the temperature of the flue gases decreases, a large amount of water vapor contained in the flue gas condenses. The thermal energy of vapor condensation is used to heat the return heating network.

Further cooling of the gas and condensation of water vapor occurs in the humidifier. The cooling medium in the humidifier is the blast air supplied to the boiler burners. Since the blast air is heated in the humidifier, and warm condensate is injected into the air flow in front of the burners, an additional evaporation process occurs in the exhaust flue gas of the boiler.

The blown air supplied to the boiler burners contains an increased amount of thermal energy due to increased temperature and humidity.

This leads to an increase in the amount of energy in the exhaust flue gas entering the condenser, which in turn leads to more efficient use of heat by the district heating system.

In the flue gas condensation unit, condensate is also produced, which, depending on the composition of the flue gases, will be further purified before being fed into the boiler system.

Economic effect.

Comparison of thermal power under the following conditions:

1. No condensation
2. Flue gas condensation
3. Condensation together with humidification of the air supplied for combustion

The flue gas condensation system allows the existing boiler house to:

• Increase heat production by 6.8% or
• Reduce gas consumption by 6.8%, as well as increase revenue from the sale of CO,NO quotas
• Investment size is about 1 million euros (for a boiler house with a capacity of 20 MW)
• Payback period is 1-2 years.

Savings depending on the coolant temperature in the return pipe:

Heat recovery methods. The flue gases leaving the working space of the furnaces have a very high temperature and therefore carry away a significant amount of heat. In open-hearth furnaces, for example, about 80% of the total heat supplied to the working space is carried away from the working space with flue gases, in heating furnaces about 60%. From the working space of furnaces, flue gases carry away more heat with them, the higher their temperature and the lower the heat utilization coefficient in the furnace. In this regard, it is advisable to ensure the recovery of heat from exhaust flue gases, which can be done in two ways: with the return of part of the heat taken from the flue gases back to the furnace and without returning this heat to the furnace. To implement the first method, it is necessary to transfer the heat taken from the smoke to gas and air (or only air) going into the furnace. To achieve this goal, heat exchangers of recuperative and regenerative types are widely used, the use of which makes it possible to increase the efficiency of the furnace unit, increase combustion temperature and save fuel. With the second method of utilization, the heat of exhaust flue gases is used in thermal power boiler houses and turbine plants, which achieves significant fuel savings.

In some cases, both described methods of heat recovery from flue gases are used simultaneously. This is done when the temperature of the flue gases after regenerative or recuperative heat exchangers remains sufficiently high and further heat recovery in thermal power plants is advisable. For example, in open-hearth furnaces, the temperature of the flue gases after the regenerators is 750-800 °C, so they are reused in waste heat boilers.

Let us consider in more detail the issue of recycling the heat of exhaust flue gases with the return of part of their heat to the furnace.

It should first of all be noted that a unit of heat taken from the smoke and introduced into the furnace by air or gas (a unit of physical heat) turns out to be much more valuable than units of heat obtained in the furnace as a result of combustion of fuel (a unit of chemical heat), since the heat of heated air ( gas) does not entail heat loss with flue gases. The value of a unit of sensible heat is greater, the lower the fuel utilization factor and the higher the temperature of the exhaust flue gases.

For normal operation of the furnace, the required amount of heat must be supplied to the working space every hour. This amount of heat includes not only the heat of the fuel Q x, but also the heat of heated air or gas Q F, i.e. Q Σ = Q x + Q f

It is clear that for Q Σ = const an increase in Q f will allow you to decrease Q x. In other words, utilization of heat from flue gases makes it possible to achieve fuel savings, which depends on the degree of heat utilization from flue gases

R = N in / N d

where N in and N d are, respectively, the enthalpy of heated air and flue gases escaping from the working space, kW or

kJ/period.

The degree of heat recovery can also be called the heat recovery coefficient of the recuperator (regenerator), %

efficiency p = (N in / N d) 100%.

Knowing the degree of heat recovery, you can determine fuel economy using the following expression:

where N " d and N d are, respectively, the enthalpy of the flue gases at the combustion temperature and those leaving the furnace.

Reducing fuel consumption as a result of using the heat of exhaust flue gases usually provides a significant economic effect and is one of the ways to reduce the cost of heating metal in industrial furnaces.

In addition to saving fuel, the use of air (gas) heating is accompanied by an increase in the calorimetric combustion temperature T k, which may be the main purpose of recovery when heating furnaces with fuel with a low calorific value.

Increase in Q F at leads to an increase in combustion temperature. If it is necessary to provide a certain amount T k, then an increase in the temperature of heating the air (gas) leads to a decrease in the value , i.e., to reduce the share of gas with a high calorific value in the fuel mixture.

Since heat recovery allows for significant fuel savings, it is advisable to strive for the highest possible, economically justified degree of utilization. However, it must immediately be noted that recycling cannot be complete, i.e. always R< 1. Это объясняется тем, что увеличение поверхности нагрева рационально только до определенных пределов, после которых оно уже приводит кочень незначительному выигрышу в экономии тепла.

Characteristics of heat exchange devices. As already indicated, the recovery of heat from exhaust flue gases and their return to the furnace can be carried out in heat exchange devices of regenerative and recuperative types. Regenerative heat exchangers operate in a non-stationary thermal state, while recuperative heat exchangers operate in a stationary thermal state.

Regenerative type heat exchangers have the following main disadvantages:

1) cannot provide a constant temperature for heating air or gas, which drops as the bricks of the nozzle cool, which limits the possibility of using automatic control of the furnace;

2) cessation of heat supply to the furnace when the valves are switched;

3) when heating the fuel, gas is carried out through the chimney, the value of which reaches 5-6 % full flow rate;

4) very large volume and mass of regenerators;

5) inconveniently located - ceramic regenerators are always located under the furnaces. The only exceptions are cowpers placed near blast furnaces.

However, despite very serious disadvantages, regenerative heat exchangers are sometimes still used in high-temperature furnaces (open hearth and blast furnaces, in heating wells). This is explained by the fact that regenerators can operate at very high flue gas temperatures (1500-1600 °C). At this temperature, recuperators cannot yet operate stably.

The recuperative principle of heat recovery from exhaust flue gases is more progressive and perfect. Recuperators provide a constant temperature for heating air or gas and do not require any changeover devices - this ensures smoother operation of the furnace and greater opportunity for automation and control of its thermal operation. Recuperators do not carry gas into the chimney; they are smaller in volume and weight. However, recuperators also have some disadvantages, the main ones being low fire resistance (metal recuperators) and low gas density (ceramic recuperators).

General characteristics of heat exchange in recuperators. Let us consider the general characteristics of heat exchange in the recuperator. The recuperator is a heat exchanger operating under stationary thermal conditions, when heat is constantly transferred from cooling flue gases to heated air (gas) through the dividing wall.

The total amount of heat transferred in the recuperator is determined by the equation

Q = KΔ t av F ,

Where TO- total heat transfer coefficient from smoke to air (gas), characterizing the overall level of heat transfer in the recuperator, W/(m 2 -K);

Δ t avg- average (over the entire heating surface) temperature difference between flue gases and air (gas), K;

F- heating surface through which heat is transferred from flue gases to air (gas), m2.

Heat transfer in recuperators includes three main stages of heat transfer: a) from flue gases to the walls of recuperative elements; b) through the dividing wall; c) from the wall to the heated air or gas.

On the smoke side of the recuperator, heat from the flue gases to the wall is transferred not only by convection, but also by radiation. Therefore, the local heat transfer coefficient on the smoke side is equal to

where is the heat transfer coefficient from the flue gases to the wall

convection, W/(m 2 °C);

Heat transfer coefficient from flue gases to the wall

by radiation, W/(m 2 °C).

Heat transfer through the dividing wall depends on the thermal resistance of the wall and the condition of its surface.

On the air side of the recuperator, when heating the air, heat is transferred from the wall to the air only by convection, and when heating the gas - by convection and radiation. Thus, when air is heated, heat transfer is determined by the local convection heat transfer coefficient; if the gas is heated, then the heat transfer coefficient

All noted local heat transfer coefficients are combined into the total heat transfer coefficient

, W/(m 2 °C).

In tubular recuperators, the total heat transfer coefficient should be determined for a cylindrical wall (linear heat transfer coefficient)

, W/(m °C)

Coefficient TO called the heat transfer coefficient of the pipe. If it is necessary to attribute the amount of heat to the area of ​​the internal or external surface of the pipe, then the total heat transfer coefficients can be determined as follows:

,

Where a 1 - heat transfer coefficient on the inside

pipes, W/(m 2 °C);

a 2 - the same, on the outside of the pipe, W/(m 2 °C);

r 1 and r 2 - respectively, the radii of the inner and outer

pipe surfaces, m. In metal recuperators, the value of the thermal resistance of the wall can be neglected , and then the total heat transfer coefficient can be written in the following form:

W/(m 2 °C)

All local heat transfer coefficients necessary to determine the value TO, can be obtained based on the laws of heat transfer by convection and radiation.

Since there is always a pressure difference between the air and smoke sides of the recuperator, the presence of leaks in the recuperative nozzle leads to air leakage, sometimes reaching 40-50%. Leaks sharply reduce the efficiency of recuperative installations; the more air sucked in, the lower the proportion of heat usefully used in the ceramic recuperator (see below):

Leakage, % 0 25 60

Final flue gas temperature,

°C 660 615 570

Air heating temperature, °C 895 820 770

Recuperator efficiency (without taking into account

losses), % 100 84 73.5

Air leakage affects the value of local heat transfer coefficients, and air trapped in the flue gases not only

Rice. 4. Schemes of movement of gaseous media in recuperative heat exchangers

reduces their temperature, but also reduces the percentage of CO 2 and H 2 0, as a result of which the emissivity of gases deteriorates.

Both with an absolutely gas-tight recuperator and with a leak, the local heat transfer coefficients change along the heating surface, therefore, when calculating recuperators, the values ​​of the local heat transfer coefficients for the top and bottom are determined separately and then the total heat transfer coefficient is found using the average value.

LITERATURE

1. B.A.Arutyunov, V.I. Mitkalinny, S.B. Stark. Metallurgical heat engineering, vol. 1, M, Metallurgy, 1974, p. 672
2. V.A. Krivandin and others. Metallurgical heat engineering, M, Metallurgy, 1986, p. 591
3. V.A. Krivandin, B.L. Markov. Metallurgical furnaces, M, Metallurgy, 1977, p.463
4. V.A. Krivandin, A.V. Egorov. Thermal work and designs of ferrous metallurgy furnaces, M, Metallurgy, 1989, p.463

V. V. Getman, N. V. Lezhneva METHODS FOR RECYCLING HEAT OF EXHAUST GASES FROM POWER INSTALLATIONS

Key words: gas turbine plants, combined cycle gas plants

The work examines various methods for recycling the heat of flue gases from power plants in order to increase their efficiency, save fossil fuels and increase energy capacity.

Keywords: gas-turbine installations, steam-gas installations

In work various methods of utilization of warmth of leaving gases from power installations for the purpose of increasing of their efficiency, economy of organic fuel and accumulation of power capacities are considered.

With the beginning of economic and political reforms in Russia, it is first necessary to make a number of fundamental changes in the country's electric power industry. The new energy policy must solve a number of problems, including the development of modern highly efficient technologies for the production of electrical and thermal energy.

One of these tasks is to increase the efficiency of power plants in order to save fossil fuels and increase energy capacity. Most

Promising in this regard are gas turbine units, the flue gases of which emit up to 20% of the heat.

There are several ways to increase the efficiency of gas turbine engines, including:

Increasing the gas temperature in front of the turbine for a gas turbine unit of a simple thermodynamic cycle,

Application of heat recovery,

Use of flue gas heat in binary cycles,

Creation of a gas turbine unit using a complex thermodynamic scheme, etc.

The most promising direction is considered to be the joint use of gas turbine and steam turbine units (GTU and STU) in order to improve their economic and environmental characteristics.

Gas turbines and combined installations created using them, with currently technically achievable parameters, provide a significant increase in the efficiency of heat and electricity production.

The widespread use of binary CCGT units, as well as various combined schemes during the technical re-equipment of thermal power plants, will allow saving up to 20% of fuel compared to traditional steam turbine units.

According to experts, the efficiency of the combined steam-gas cycle increases with an increase in the initial temperature of the gases in front of the gas turbine plant and an increase in the share of gas turbine power. Of no small importance

There is also the fact that in addition to the gain in efficiency, such systems require significantly lower capital costs, their specific cost is 1.5 - 2 times less than the cost of gas-fuel oil steam turbine units and CCGT units with minimal gas turbine power.

Based on the data, three main areas for the use of gas turbine units and combined cycle gas turbine units in the energy sector can be identified.

The first, widely used in industrialized countries, is the use of CCGT units at large condensing thermal power plants operating on gas. In this case, it is most effective to use a recovery-type CCGT unit with a large share of gas turbine power (Fig. 1).

The use of CCGT makes it possible to increase the efficiency of fuel combustion at thermal power plants by ~ 11-15% (CCP with gas discharge into the boiler), by ~ 25-30% (binary CCGT).

Until recently, extensive work on the implementation of CCGT systems in Russia was not carried out. However, single samples of such installations have been in use for quite a long time and have been successfully used, for example, CCGT units with a high-pressure steam generator (HSG) type VPG-50 of the main power unit PGU-120 and 3 modernized power units with HPG-120 at the TPP-2 branch of OJSC TGK-1"; PGU-200 (150) with VPG-450 at the Nevinnomyssk State District Power Plant branch. Three combined-cycle power units with a capacity of 450 MW each are installed at the Krasnodar State District Power Plant. The power unit includes two gas turbines with a capacity of 150 MW, two waste heat boilers and a steam turbine with a capacity of 170 MW, the efficiency of such an installation is 52.5%. Further

increasing the efficiency of utilization-type CCGT units is possible by improving

gas turbine installation and complication of the steam process circuit.

Rice. 1 - Scheme of a CCGT unit with a waste heat boiler

Combined-cycle plant with boiler -

recycler (Fig. 1) includes: 1-

compressor; 2 - combustion chamber; 3 - gas

turbine; 4 - electric generator; 5 - boiler-

recycler; 6 - steam turbine; 7 - capacitor; 8

Pump and 9 - deaerator. In the waste heat boiler, the fuel is not burned, and the superheated steam produced is used in a steam turbine unit.

The second direction is the use of gas turbines to create CCGT-CHP and GTU-CHP. In recent years, many options for technological schemes of CCGT-CHP have been proposed. At CHPPs operating on gas, it is advisable to use cogeneration CCGT units

recycling type. A typical example

A large CCGT-CHP of this type is the North-West CHPP in St. Petersburg. One CCGT unit at this thermal power plant includes: two gas turbines with a capacity of 150 MW each, two waste heat boilers, and a steam turbine. The main indicators of the unit: electric power - 450 MW, thermal power - 407 MW, specific consumption of standard fuel for electricity supply - 154.5 g. t./(kW.h), specific consumption of equivalent fuel for heat supply - 40.6 kg. t./GJ, efficiency of the thermal power plant for the supply of electrical energy - 79.6%, thermal energy - 84.1%.

The third direction is the use of gas turbines to create CCGT-CHP and GTU-CHP of low and medium power based on boiler houses. CCGT - CHPP and GTU - CHPP of the best options, created on the basis of boiler houses, provide efficiency for the supply of electrical energy in cogeneration mode at the level of 76 - 79%.

A typical combined cycle plant consists of two gas turbine units, each with its own waste heat boiler, which supplies the generated steam to one common steam turbine.

An installation of this type was developed for the Shchekinskaya State District Power Plant. PGU-490 was designed to generate electrical energy in the basic and partial operating modes of the power plant with the supply of heat to third-party consumers up to 90 MW under a winter temperature schedule. The schematic diagram of the PGU-490 unit was forced to focus on the lack of space when placing the waste heat boiler and

steam turbine installation in the power plant buildings, which created certain difficulties in achieving optimal conditions for the combined production of heat and electricity.

In the absence of restrictions on the placement of the installation, as well as when using an improved gas turbine unit, the efficiency of the unit can be significantly increased. As such an improved CCGT, a single-shaft CCGT-320 with a capacity of 300 MW is proposed. The complete gas turbine unit for CCGT-320 is the single-shaft GTE-200, the creation of which is expected to be carried out by transition to

double-support rotor, modernization of the cooling system and other components of the gas turbine plant in order to increase the initial gas temperature. In addition to the GTE-200, the PGU-320 monoblock contains a K-120-13 steam turbine with a three-cylinder turbine, a condensate pump, a seal steam condenser, a heater fed by heating steam supplied from the extraction before the last stage of the steam turbine, as well as a two-pressure waste heat boiler containing eight heat exchange areas, including an intermediate steam superheater.

To assess the efficiency of the installation, a thermodynamic calculation was carried out, as a result of which it was concluded that when PGU-490 ShchGRES operates in condensation mode, its electrical efficiency can be increased by 2.5% and brought up to 50.1%.

District heating research

combined cycle plants have shown that the economic indicators of combined cycle gas plants significantly depend on the structure of their thermal circuit, the choice of which is made in favor of an installation that ensures the minimum temperature of the flue gases. This is explained by the fact that flue gases are the main source of energy loss, and to increase the efficiency of the circuit, their temperature must be reduced.

The model of a single-circuit heating CCGT unit, shown in Fig. 2, includes a drum-type waste heat boiler with natural circulation of the medium in the evaporation circuit. Along the flow of gases in the boiler, heating surfaces are located sequentially from bottom to top:

superheater PP, evaporator I, economizer E and gas superheater for network water GSP.

Rice. 2 - Thermal diagram of a single-circuit CCGT

Calculations of the system showed that when the parameters of fresh steam change, the power generated by the CCGT unit is redistributed between thermal and electrical loads. As steam parameters increase, the generation of electrical energy increases and the generation of thermal energy decreases. This is explained by the fact that as the parameters of fresh steam increase, its production decreases. At the same time, due to a decrease in steam consumption with a small change in its parameters in the extractions, the thermal load of the network water heater is reduced.

A double-circuit CCGT, just like a single-circuit one, consists of two gas turbines, two waste heat boilers and one steam turbine (Fig. 3). Heating of network water is carried out in two ASG heaters and (if necessary) in a peak network heater.

Along the flow of gases in the waste heat boiler

the following are located sequentially

heating surfaces: high-pressure superheater PPHP, high-pressure evaporator IVD, high-pressure economizer EHP, low-pressure superheater PPND,

low pressure evaporator IND, low pressure gas heater GPND, gas heater for network water GSP.

Rice. 3 - Principal thermal diagram

double-circuit CCGT

Rice. 4 - Scheme of heat recovery from gas turbine exhaust gases

In addition to the waste heat boiler, the thermal circuit includes a steam turbine with three cylinders, two network water heaters PSG1 and PSG2, a deaerator D and feed pumps PEN. The exhaust steam from the turbine was sent to PSG1. Steam from the turbine exhaust is supplied to the PSG2 heater. All network water passes through PSG1, then part of the water is sent to PSG2, and the other part after the first heating stage is sent to the GSP, located at the end of the gas path of the waste heat boiler. The condensate of the heating steam PSG2 is drained into PSG1, and then enters the GPND and then into the deaerator. The feed water after the deaerator partially flows into the economizer of the high-pressure circuit, and partially into drum B of the low-pressure circuit. Steam from the low pressure circuit superheater is mixed with the main steam flow after the high pressure cylinder (HPC) of the turbine.

As a comparative analysis has shown, when using gas as the main fuel, the use of utilization schemes is advisable if the ratio of thermal and electrical energy is 0.5 - 1.0, with ratios of 1.5 or more, preference is given to CCGT units using a “discharge” scheme.

In addition to adjusting the steam turbine cycle to the gas turbine cycle, recycling the heat of exhaust gases

GTU can be implemented by supplying steam generated by a waste heat boiler to the combustion chamber of the GTU, as well as by implementing a regenerative cycle.

The implementation of the regenerative cycle (Fig. 4) provides a significant increase in the efficiency of the installation, by 1.33 times, if, when creating a gas turbine unit, the degree of pressure increase is selected in accordance with the intended degree of regeneration. This circuit includes a K-compressor; R - regenerator; KS - combustion chamber; ТК - compressor turbine; ST - power turbine; CC - centrifugal compressor. If a gas turbine unit is designed without regeneration, and the degree of pressure increase l is close to the optimal value, then equipping such a gas turbine unit with a regenerator does not lead to an increase in its efficiency.

The efficiency of the installation that supplies steam to the combustion chamber is increased by 1.18 times compared to a gas turbine unit, which makes it possible to reduce the consumption of fuel gas consumed by the gas turbine unit.

A comparative analysis showed that the greatest fuel savings are possible when implementing the regenerative cycle of a gas turbine unit with a high degree of regeneration, a relatively low pressure ratio in the compressor l = 3 and with small losses of combustion products. However, in most domestic TKAs, aviation and marine gas turbine engines with a high degree of pressure increase are used as a drive, and in this case, heat recovery from exhaust gases is more efficient in a steam turbine unit. Installation with steam supply to the combustion chamber is structurally the simplest, but less effective.

One of the ways to achieve gas savings and solve environmental problems is to use combined cycle gas plants at compressor stations. Research developments consider two alternative options for using steam obtained from the recovery of heat from gas turbine exhaust gases: a combined cycle gas turbine driven by a steam turbine of a natural gas supercharger and by a steam turbine of an electric generator. The fundamental difference between these options is that in the case of a CCGT with a supercharger, not only the heat of the exhaust gases of the GPU is recovered, but also one GPU is replaced by a steam turbine pumping unit, and in the case of a CCGT with an electric generator, the number of GPUs is maintained, and due to the recovered heat, electricity is generated by a special steam turbine unit. The analysis showed that CCGT units with a natural gas supercharger drive provided the best technical and economic indicators.

In the case of creating a combined cycle gas plant with a waste heat boiler on the basis of a compressor station, the gas turbine unit is used to drive the supercharger, and the steam power plant (SPU) is used to generate electricity, while the temperature of the exhaust gases behind the waste heat boiler is 1400C.

In order to increase the efficiency of using organic fuel in decentralized heat supply systems, it is possible to reconstruct heating boiler houses with the placement of small-capacity gas turbine units (GTUs) in them and the utilization of combustion products in the furnaces of existing boilers. At the same time, the electrical power of the gas turbine depends on the operating modes according to thermal or electrical load schedules, as well as on economic factors.

The effectiveness of boiler house reconstruction can be assessed by comparing two options: 1 - original (existing boiler house), 2 - alternative, using a gas turbine unit. The greatest effect was obtained with an electric power of the gas turbine equal to

maximum load of the consumption area.

Comparative analysis of a gas turbine unit with a HRSG producing steam in the amount of 0.144 kg/kg s. g., condensing TU and GTU without HRSG and with TU of dry heat exchange showed the following: useful

electric power - 1.29, natural gas consumption - 1.27, heat supply - 1.29 (12650 and 9780 kJ/m3 of natural gas, respectively). Thus, the relative increase in gas turbine power when introducing steam from the HRSG was 29%, and the consumption of additional natural gas was 27%.

According to operational test data, the temperature of flue gases in hot water boilers is 180 - 2300C, which creates favorable conditions for recycling the heat of gases using condensing heat exchangers (HU). In TU, which

are used for preheating network water in front of hot water boilers, heat exchange is carried out with the condensation of water vapor contained in the flue gases, and the heating of the water in the boiler itself occurs in the “dry” heat exchange mode.

According to the data, along with fuel savings, the use of technical specifications also provides energy savings. This is explained by the fact that when an additional flow of circulating water is introduced into the boiler, in order to maintain the calculated flow rate through the boiler, it is necessary to transfer part of the return water of the heating network in an amount equal to the recirculation flow rate from the return pipe to the supply pipe.

When completing power plants from separate power units with a gas turbine drive

electric generators, there are several options for recycling the heat of exhaust gases, for example, using a recovery

heat exchanger (HTE) for heating water, or using a waste heat boiler and

steam turbine generator to increase electricity generation. Analysis of the station's operation, taking into account heat recovery using heat treatment, showed a significant increase in the heat utilization coefficient, in some cases by 2 times or more, and experimental studies of the EM-25/11 power unit with the NK-37 engine allowed us to draw the following conclusion. Depending on specific conditions, the annual supply of recovered heat can range from 210 to 480 thousand GJ, and real gas savings ranged from 7 to 17 thousand m3.

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© V.V. Getman - Ph.D. tech. Sciences, Associate Professor department automation of technological processes and production FSBEI HPE "KNRTU", 1ega151@uaMech; N.V. Lezhneva - Ph.D. tech. Sciences, Associate Professor department automation of technological processes and production of FSBEI HPE "KNRTU", [email protected].