RU2796717C1 - Heating boiler heat recovery plant - Google Patents

Abstract

FIELD: thermal power engineering.

SUBSTANCE: energy-saving methods for extracting heat from flue gases from a heating boiler and heating gas supplied to the burner of this boiler. The heating boiler heat recovery plant includes a boiler with a chimney, a combustion chamber and a burner with a fuel and air supply system equipped with a fan, a main heat exchanger installed in the chimney, and an additional heat exchanger located after the primary air fan and connected via a pipeline to the main heat exchanger, thus forming an intermediate coolant circulation system in the form of a closed circuit equipped with a circulation pump. The main heat exchanger is made to maintain the temperature in the chimney not lower than the “dew point” when the boiler is running and is equipped with a temperature sensor at the chimney outlet. The circulation pump is used adjustable and additionally equipped with a control unit that reads the temperature sensor to adjust the pump performance to prevent the temperature of the intermediate heat carrier from rising above its boiling point and reducing the temperature in the chimney below the “dew point”.

EFFECT: protection against rapid failure of the chimney under the action of carbonic acid when temperatures drop below the “dew point” and prevents the destruction of the recovery unit under the action of high pressure inside when the coolant temperature rises above the boiling point.

1 cl, 1 dwg, 1 tbl

Description

SUBSTANCE: invention relates to thermal power engineering, namely to energy-saving technologies for extracting heat from flue gases from a heating boiler and heating gas supplied to the burner of this boiler.

A boiler plant is known (patent RU No. 2392037, IPC F22B 33/18, publ. 02.27.2010, Bull. No. 6), containing a boiler with a furnace in which burners are located connected by an air path to an air heater and a fuel path - to a fuel preparation unit , the outlet gas duct with a contact heat exchanger placed in it, a fuel heater and a heat exchanger of external consumers, moreover, the contact heat exchanger is connected to the air heater, the fuel heater and the heat exchanger of external consumers by the outlet path of heated water, the outlet paths of which are connected through the chilled water by a common outlet line with the inlet to the contact heat exchanger and with a fuel preparation unit.

The disadvantage of this installation is the complexity of manufacturing the burner, since it is necessary to equip the air path and the fuel path with heat exchangers (heaters) at the same time, while narrowing the scope, since it is impossible to use high-temperature coolants (with a temperature of more than 150–200 ° C) due to the possibility of initiation ignition in the heater itself, while there is no control over the temperature of the intermediate heat carrier at the outlet of the heat exchanger located in the flue gas extraction system from the boiler, which can lead to a decrease in temperature in this system below the “dew point” (formation of condensate and, as a result, chemical aggressive carbonic acid) and/or an increase in the temperature of the intermediate heat carrier above the “boiling point”, which is likely to disable the entire heat recovery plant.

The closest in technical essence is the heat boiler recovery system (patent for PM RU No. 115449, IPC F24D 19/00, publ. 27.04.2012, Bull. No. 12), consisting of a combustion chamber with a burner and a heat exchanger, a chimney with a heat exchanger and a fan primary air, moreover, the recovery system is equipped with an additional heat exchanger, which is located in front of the primary air fan and is connected via a pipeline to the smoke exhaust heat exchanger, thus forming a heat carrier circulation system in the form of a closed circuit and equipped with a circulation pump.

The disadvantage of this system is the lack of control over the temperature of the intermediate heat carrier at the outlet of the heat exchanger located in the chimney, which can lead to a decrease in the temperature in this system below the “dew point” (the formation of condensate and, as a result, chemically aggressive carbonic acid that destroys the chimney) and /or an increase in the temperature of the intermediate heat carrier above the “boiling point”, which is likely to disable the entire heat recovery installation.

The technical objective of the proposed invention is to protect against rapid failure of the chimney under the action of carbonic acid when temperatures drop below the "dew point" and the destruction of the recovery unit under the action of high pressure inside when the temperature of the coolant rises above the "boiling point" by controlling the temperature of the intermediate coolant at exit from the heat exchanger located in the chimney, and control the performance of the circulation pump.

The technical problem is solved by an installation for heat recovery of a heating boiler, including a boiler with a chimney, a combustion chamber and a burner with a fuel and air supply system equipped with a fan, a main heat exchanger installed in the chimney, and an additional heat exchanger located after the primary air fan and connected by means of a pipeline to the main heat exchanger, thus forming an intermediate heat carrier circulation system in the form of a closed circuit equipped with a circulation pump.

What is new is that the main heat exchanger is made to maintain the temperature in the chimney not below the “dew point” when the boiler is running and is equipped with a temperature sensor at the outlet of the chimney, and the circulation pump is used adjustable and additionally equipped with a control unit that reads the intermediate heat carrier temperature sensor for adjusting the pump performance to prevent an increase in the temperature of the intermediate heat carrier above its boiling point and a decrease in the temperature in the chimney below the “dew point”, and the pump is turned on when the temperature of the intermediate heat carrier reaches the “dew point”.

The drawing shows a diagram of the installation.

The installation for heat recovery of the heating boiler 1 includes a boiler 1 with a chimney 2, a combustion chamber (not shown) and a burner 3 with a fuel supply system 4 and air 5 equipped with a fan 6, a main heat exchanger 7 installed in the chimney 2, and an additional heat exchanger 8, located in front of the primary air fan 6 and connected via a pipeline 9 to the main heat exchanger 7, thus forming an intermediate heat carrier circulation system in the form of a closed circuit, equipped with a circulation pump 10. The main heat exchanger 7 is made from the condition of maintaining the temperature in the chimney 2 not below the "dew point" when the boiler 1 is running and is equipped with a temperature sensor 11 at the outlet of the chimney 2. The circulation pump 10 is used adjustable and is additionally equipped with a control unit 12 that reads the readings from the temperature sensor 11 to adjust the performance of the pump 10 to prevent an increase in the temperature of the intermediate heat carrier above its boiling point. The pipeline 9 is equipped with an expansion tank 13 to level the expansion or reduction of the intermediate coolant due to temperature differences in the pipeline 9 and / or the evaporation of the coolant itself (the authors do not claim this, since this is known from open sources for a closed circuit).

As an intermediate heat carrier, you can use, for example:

water (density ρ≈1000 kg/m ³ , specific heat c _p =4.2 kJ/(kg•°K), freezing point t _c =0°C, boiling point t _k =100°C);

antifreeze, for example, G11 (density ρ≈1071 kg / m ³ , specific heat with _p = 3.6 kJ / (kg • ° K), freezing point (crystallization) t _c = -35 ° C, boiling point t _k = 130°C);

high-temperature coolant, for example, Therminol-59 (density ρ≈878 kg / m ³ , specific heat capacity with _p \u003d 2.1 kJ / (kg • ° K), freezing point t _c \u003d -50 ° C, boiling point t _k \u003d 320°C).

As you can see, for closed heat-insulated rooms, it is possible to use prepared (softened) fresh water as an intermediate coolant (service life before replacement is no more than 2 years), for a temperate climate zone - antifreeze (service life - 5 years), and for industrial (production) powerful installations operating in the regions of the Far North and under conditions of large temperature differences - high-temperature coolant (service life - 10 years or more).

Any liquid known heat carriers can be used as an intermediate heat carrier.

To calculate the main heat exchanger, use the formula:

where Q is the size of the heat flux, W;

F - the area of the working surface of the heat exchanger, m ² ;

k - heat transfer coefficient of the heat exchanger material - heat transfer coefficient (taken from reference literature), W / (m ² • °K);

Δt - temperature difference, that is, the modulus of the difference between the temperatures of the carrier (flue gases) at the outlet (t ₂ ) to the apparatus and at the inlet (t ₁ ) from it, °K or °C.

The temperature of the flue gases at the outlet of boiler 1 is taken as the input temperature for, for example, for heating boiler 1 - furnace PTB-5-40E No. 4 at UPVSN-1 "Andreevka" NGDU "Nurlatneft" it was t ₁ \u003d 350 ° С ( ≈623°K), and for the outlet temperature - the temperature is above the "dew point", for example, for the same furnace it should be above 52°C (≈325°K), to ensure these parameters are guaranteed even in winter with a normally operating (within the passport data) boiler 1 took t ₂ =120°C (≈493°K), i.e. Δt=230°C. Taking into account the heat transfer coefficient of stainless steel with a thickness of 10 mm k = 56.7 W / (m ² • ° K) and the average thermal power of the flue gases Q = 490 kW (≈9% of the average furnace power) of the PTB-5-40E furnace No. 4 .

Formula (2) was obtained from formula (1):

From which the working surface area of the main heat exchanger 7 was determined:

F \u003d 490000 / (56.7‧230) \u003d 37.6 m ³

Based on the data obtained, according to the manufacturer's passport data, the main heat exchanger 7 was selected.

To select the required circulation pump 10, we used the equation for the heat balance of the heat exchanger:

where Q is the size of the heat flux, W;

G ₁ - mass consumption of the heating medium (flue gases), kg/h;

G ₂ - mass consumption of the heated medium (intermediate coolant), kg/h;

c _p1 - specific heat capacity of flue gases, kJ/kg•°С;

c _p2 - specific heat capacity of the intermediate heat carrier, kJ/kg•°С;

t ₁ ⁱⁿ - flue gas temperature at the inlet to the main heat exchanger, °C;

t ₁ ^out - flue gas temperature at the inlet from the main heat exchanger, °C;

t ₂ ^out - the temperature of the intermediate coolant at the outlet of the main heat exchanger, °C;

t ₂ ⁱⁿ - temperature of the intermediate heat carrier at the inlet to the main heat exchanger, °C.

Knowing the size of the heat flow, from formula (3) we obtained formula (4) for the mass flow rate of the intermediate coolant:

t ₂ ^out \u003d 90 ° С - for water the temperature was taken 10% lower than the boiling point, and t ₂ ⁱⁿ \u003d 20 ° С - room temperature was taken.

That is:

G ₂ \u003d 490000 / (4200 (90-20)) \u003d 1.6 kg / h

To obtain the volumetric performance of the circulation pump 10, we use the formula (5):

where G _2v - volumetric performance of the circulation pump 10, m ³ / h;

G ₂ - mass consumption of the heated carrier (intermediate coolant), kg / h;

ρ is the density of the intermediate coolant, kg/m ³ .

For water as an intermediate heat carrier G _2v =1.6•10 ^-3 m ³ /h.

For other types of coolants, calculations are carried out in a similar way.

Knowing the performance of the circulation pump 10, the parameters (working surface area) of the additional heat exchanger 8 are determined by inverse calculations using formulas (5) (4) and (2), which, according to the passport data, is selected for the air supply system 5 to the burner 3. The optimal temperature for maintaining combustion is 60-70°C (determined empirically), on the basis of which a fan 6 is selected for the air supply system 5.

The heating boiler heat recovery unit operates as follows.

After installing the selected main 7 and additional 8 heat exchangers in the chimney 2 and the air supply system 5 after the fan 6, respectively, the heat exchangers 7 and 8 are connected by a pipeline 9 equipped with the selected adjustable circulation pump 10 (for example, with a frequency-controlled drive - not shown) and obtaining closed loop. The pipeline 9 at the outlet of the main heat exchanger 7 outside the chimney 2 is equipped with an intermediate heat carrier temperature sensor 11, which is technologically connected to the control unit 12 of the circulation pump 10. Through the expansion tank 13, the pipeline 9, the circulation pump 10 and the heat exchangers 7 and 8 of the closed circuit are filled with an intermediate heat carrier, freeing it from air pockets. After that, fuel (diesel oil, fuel oil, gas, or the like) is supplied to the burner 3 to form a combustible mixture through the fuel supply system 4 and air through the air supply system 5 with a fan 6. After initiating the ignition of the combustible mixture in burner 3, electric, piezoelectric, open or the like. fuse (not shown), the combustible mixture burns in the combustion chamber of the boiler 1, heating water, oil, fuel, or the like, while the combustion products in the form of flue gases are removed from the boiler 1 through the chimney 2, passing through the main heat exchanger 7, heating the intermediate coolant in it, which is recorded by the temperature sensor 11. Since the circulation pump 10 does not work at the heating stage of the boiler 1, heat is not removed from the chimney 2, without interfering with the natural convection of the flue gases from the boiler 1. After an increase in the temperature of the intermediate heat carrier, recorded by the sensor 11, above the “dew point” temperature, the control unit 12 sends a signal to start the circulation pump 10, which supplies the heated intermediate coolant to the additional heat exchanger 8 to heat the air blown by the fan 6 into the burner 3, increasing the combustion efficiency of the fuel supplied through the fuel supply system 4, and , as a result, increasing the temperature in the combustion chamber of the boiler 1. The intermediate coolant cooled in the additional heat exchanger 8 through the pipeline 9 again enters the inlet of the main coolant 7 for heating in the chimney 2. Then the cycle repeats. As a result, the temperature of the flue gases in the chimney 2, the intermediate heat carrier in the main heat exchanger 7 and the additional heat exchanger 8, increases, increasing the temperature of the air blown by the fan 6 through its supply system 5, leading to the optimal mode (with the highest possible efficiency - efficiency) of the boiler 1.

In the event (for example, when the boiler 1 fails, the fuel supply to the burner 3 decreases, the quality of the fuel deteriorates, etc.) the temperature of the intermediate heat carrier, recorded by the sensor 11, decreases, the control unit 12 reduces the performance of the circulation pump 10, and in case of approaching this temperature to the "dew point" - turn off the operation of the circulation pump 10. As a result, heat removal from the main heat exchanger 7 and, as a result, from the chimney 2 is reduced or completely prevented, increasing the temperature in it and eliminating the condensate from the flue gases, which forms in the presence condensate (water) with carbon dioxide aggressive carbonic acid. After increasing and/or restoring the temperature of the intermediate heat carrier, the control unit 12 resumes and/or restores the operation of the circulation pump 10.

Table

No. p / p Name Designation Unit. Receive method Load Without heat exchanger With heat exchanger Fuel natural gas Qn ^p \u003d 8762 kcal / Nm ³ 1 Fuel temperature t °С rev. 35 35 2 Inlet gas pressure Rg ^To kgf / cm ² rev. 3.0 3.0 3 Manifold fuel pressure Rg ^To kPa rev. 29.1 29.1 4 Fuel pressure on burners #1/#2 R _G ^G Pa rev. 320/180±50 320/180±50 5 Estimated gas consumption Vg nm ³ / h. calc. 153.9 154.0 Oil 1 Heating capacity of the installation according to the reverse balance Qn ^o6p Gcal/h calc. 1.021 1.053 2 Heat output of the installation according to direct balance Qn ^np Gcal/h calc. 1.030 1.054 3 Oil emulsion consumption Gh m ³ / h rev. 245 280 4 The pressure of the oil emulsion at the inlet to the installation Rne’ kgf / cm ² rev. 5.8 6.4 5 The pressure of the oil emulsion at the outlet of the installation Rne" MPa rev. 0.39 0.4 6 The temperature of the oil emulsion at the inlet to the installation t' °С rev. 58.5 57.5 7 The temperature of the oil emulsion at the outlet of the installation t" °С rev. 69.0 66.9 8 Temperature difference of the installation Δt °С calc. 10.5 9.4 Air 1 Manifold air pressure R _V ^To Pa rev. 250±50 250±50 2 Combustion air temperature t _{WHO .} °C rev. 38 57 3 VFD output frequency fb Hz rev. 16.1 16.0 Flue gas content downstream of the furnace (averaged) 1 triatomic gases CO2 % anal. 5.96 6.00 2 Carbon monoxide SO ppm anal. 39 31 3 Oxygen O2 % calc. 10.4 10.4 5 Nitrogen N ₂ % 83.6 83.6 6 Excess air factor A _wow - calc. 1.88 1.87 7 Flue gas temperature tyx °C anal. 155.1 146.8 Thermal balance of the furnace 1 Loss of heat from uh. gas. q2 % calc. 8.84 7.03 2 Heat loss due to chemical underburning q3 % calc. Absent 3 Heat loss in the environment Wednesday q5 % calc. 15.42 14.96 4 The amount of heat loss ∑q % calc. 24.26 21.99 5 Gross plant efficiency in terms of reverse balance ηbr ^about % calc. 75.74 78.01 6 Gross plant efficiency in direct balance ηbr ^P % calc. 76.41 78.12 Specific fuel consumption 1 Specific reference fuel consumption Wus kg.ce/ Gcal calc. 188.61 183.14 2 Specific consumption of natural fuel Vn nm ³ / Gcal calc. 150.69 146.31

In the event (for example, when boiler 1 fails due to a failure of the automation that increases the fuel supply to the burner 3, fuel quality improvement, or the like) an increase in the temperature of the intermediate heat carrier recorded by the sensor 11, the control unit 12 increases the performance of the circulation pump 10. As a result, heat removal from the main heat exchanger 7 and, as a result, from the chimney 2 increases, reducing the temperature in it and eliminating the boiling of the intermediate heat carrier. After the temperature of the intermediate heat carrier is restored, the control unit 12 restores the operation of the circulation pump 10 in the previous mode.

The tests were successfully passed on the heating boiler 1 - furnace PTB-5-40E No. 4 at UPVSN-1 "Andreevka" NGDU "Nurlatneft", the data of this test were summarized in a table. For two years of operation, there was not a single case of condensate in the chimney and boiling of the intermediate heat carrier in a closed circuit (especially in the main heat exchanger 7), which made it possible to increase the overhaul period by 1.5 times and completely eliminate emergency situations. At the same time, the installation does not require changes in the design of boiler 1 and its components, which reduces the cost of implementation, and the efficiency of boiler 1 increased by about 1% compared to the closest analogue, but the authors do not claim this, since this is within the measurement error.

The proposed installation for heat recovery of a heating boiler is equipped with protection against a quick failure of the chimney under the action of carbonic acid when temperatures drop below the "dew point" and the destruction of the recovery installation under the influence of high pressure inside when the temperature of the heat carrier rises above the "boiling point" due to temperature control intermediate coolant at the outlet of the heat exchanger, and control the performance of the circulation pump.

Claims (1)

Installation for heat recovery of a heating boiler, including a boiler with a chimney, a combustion chamber and a burner with a fuel and air supply system equipped with a fan, a main heat exchanger installed in the chimney, and an additional heat exchanger located after the primary air fan and connected via a pipeline to the main heat exchanger, at the same time forming an intermediate heat carrier circulation system in the form of a closed circuit equipped with a circulation pump, characterized in that the main heat exchanger is made to maintain the temperature in the chimney not lower than the "dew point" when the boiler is running and is equipped with a temperature sensor at the outlet of the chimney, and the circulation pump an adjustable and additionally equipped with a control unit that reads the readings of the intermediate heat carrier temperature sensor to adjust the pump performance to prevent the temperature of the intermediate heat carrier from rising above its boiling point and reducing the temperature in the chimney below the "dew point", and the pump is turned on when the "dew point" temperature is reached intermediate coolant.

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