Do-it-yourself flue gas heat exchanger. Flue gas heat recovery

Description:

Bryansk heating network together with the design institute VKTIstroydormash-Proekt LLC, we developed, manufactured and implemented installations for the utilization of flue gas heat (UUTG) from hot water boilers in two boiler houses in the city of Bryansk

Flue gas heat recovery plant

N. F. Sviridov, R. N. Sviridov, Bryansk heating networks,

I. N. Ivukov, B. L. Turk, VKTIstroydormash-Proekt LLC

Bryansk Heat Networks, together with the design institute OOO VKTIstroydormash-Proekt, developed, manufactured and implemented in two boiler houses in the city of Bryansk a flue gas heat recovery unit (UUTG) from hot water boilers.

As a result of this implementation, the following was obtained:

Additional capital investments for 1 Gcal/h of heat received, it is more than 2 times lower in comparison if a new boiler house was being built, and they pay off in approximately 0.6 years;

Due to the fact that the equipment used is extremely easy to maintain and free coolant is used, i.e. flue gas (FG), previously released into the atmosphere, the cost of 1 Gcal of heat is 8–10 times lower than the cost of heat generated by boiler houses;

Boiler efficiency increased by 10%.

Thus, all the costs in March 2002 prices for the introduction of the first UUTG with a capacity of 1 Gcal of heat per hour amounted to 830 thousand rubles, and the expected savings per year will be 1.5 million rubles.

Such high technical economic indicators explainable.

There is an opinion that the efficiency of the best domestic boilers with a thermal power of 0.5 MW and above reaches 93%. In fact, it does not exceed 83%, and here's why.

Distinguish between lower and higher calorific value of fuel. The lower calorific value is less than the higher one by the amount of heat that is spent on the evaporation of water formed during the combustion of the fuel, as well as the moisture contained in it. An example for the cheapest fuel is natural gas: DGs formed during its combustion contain water vapor, which occupies up to 19% in their volume; the highest calorific value of its combustion exceeds the lowest by approximately 10%.

To increase the efficiency of the chimneys through which the DGs are emitted into the atmosphere, it is necessary that the water vapor in the DGs does not begin to condense in the chimneys at the most low temperatures environment.

The UUTG projects revived and improved long-forgotten technical solutions aimed at utilizing heat from DGs.

UUTG contains contact and plate heat exchanger and with two independent circuits of circulating and waste water.

The device and operation of the UUTG are clear from the diagram shown in the figure and the description of its positions.

In a contact heat exchanger, DG and atomized circulating water move in vertical countercurrent, i.e. DG and water are in direct contact with each other. To maintain a uniform spray of recycled water, nozzles and a special ceramic nozzle are used.

Heated circulating water, pumped in its own water circuit by an independent pump, gives off the heat acquired in the contact heat exchanger to the waste water in the plate heat exchanger.

For the required cooling of the circulating water, only cold tap water, which, after heating in the UUTG, is brought to the standard temperature in the boilers of existing boiler houses and is further used for hot water supply to housing.

In the contact heat exchanger, the cooled DGs additionally pass through the drop eliminator and, having eventually lost more than 70% of moisture in the form of water vapor condensate, they are connected to a part of the hot DGs (10–20% of the DG volume leaving the boiler), directed immediately from the boiler to the chimney, thus forming a mixture of DG with low moisture content and with a temperature sufficient to pass the chimney without condensing the rest of the water vapor.

The volume of circulating water is continuously increasing due to the condensate of water vapor in the DG. The resulting surplus is automatically drained through a valve with an electromechanical drive and can be used with preparation as additional water in heating system boiler room. The specific consumption of drained water per 1 Gcal of recovered heat is about 1.2 tons. The condensate drain is controlled by level gauges B and H.

The described method and equipment for heat recovery of diesel generators are capable of working with dust-free fuel combustion products that have an unlimited maximum temperature. At the same time, the higher the temperature of the flue gas, the higher the temperature will be heated to the consumption water. Moreover, in this case it is possible to partially use the recycled water for heating heating water. Considering that the contact heat exchanger simultaneously works as a wet dust trap, it is possible to practically utilize the heat of dusty DGs by purifying circulating water from dust by known methods before supplying it to the plate heat exchanger. It is possible to neutralize recycled water contaminated with chemical compounds. Therefore, the described UUTG can be used to work with DGs involved in technological processes during smelting (for example, open-hearth furnaces, glass melting furnaces), during calcination (for example, brick, ceramics), during heating (ingots before rolling), etc.

Unfortunately, in Russia there are no incentives to engage in energy conservation.

B. V. Getman, N. V. Lezhneva

Keywords: gas turbine plants, combined cycle plants

The paper considers various methods waste heat recovery from power plants in order to increase their efficiency, save fossil fuels and increase energy capacities.

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 increase of their efficiency, economy of organic fuel and accumulations of power capacities are considered.

With the beginning of economic and political reforms in Russia, first of all, it is necessary to make a number of fundamental changes in the country's electric power industry. The new energy policy should solve a number of tasks, 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 power capacities. Most

promising in this regard are gas turbine plants, with the exhaust gases of which up to 20% of heat is emitted.

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

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

Heat recovery application,

The use of exhaust gas heat in binary cycles,

Creation of gas turbines according to a complex thermodynamic scheme, etc.

The most promising direction is the joint use of gas turbine and steam turbine units (GTP and STP) in order to improve their economic and environmental performance.

Gas turbines and combined plants created with their use, with parameters that are technically achievable at present, provide a significant increase in the efficiency of heat and electricity production.

The widespread use of binary CCGTs, as well as various combined schemes in the technical re-equipment of thermal power plants, will save 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 gas temperature in front of the gas turbine and an increase in the share of gas turbine power. Important

also has the fact that, in addition to gaining efficiency, such systems require significantly lower capital costs, their unit cost 1.5 - 2 times less than the cost of gas-oil steam turbine units and CCGT with a minimum gas turbine power .

According to the data, three main directions for the use of gas turbines and combined cycle plants in the energy sector can be distinguished.

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

The use of CCGT allows to increase the efficiency of fuel combustion at TPPs by ~ 11-15% (CCGT with gas discharge into the boiler), by ~ 25-30% (binary CCGT).

Until recently, extensive work on the introduction of CCGT in Russia has not been carried out. Nevertheless, single samples of such units have been successfully used for a long time, for example, a CCGT with a high-pressure steam generator (HPG) of the HSG-50 type at the head power unit CCGT-120 and 3 modernized power units with HSPG-120 at the CHPP-2 branch of JSC " TGC-1"; PGU-200 (150) with VPG-450 at the Nevinnomysskaya GRES branch. Three combined-cycle power units with a capacity of 450 MW each have been installed at Krasnodarskaya GRES. The power unit includes two gas turbines with a capacity of 150 MW each, 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 a utilization-type CCGT is possible by improving

gas turbine plant and complicating the scheme of the steam process.

Rice. 1 - Scheme of CCGT with waste heat boiler

Combined-cycle plant with a boiler -

utilizer (Fig. 1) includes: 1-

compressor; 2 - combustion chamber; 3 - gas

turbine; 4 - electric generator; 5 - boiler-

utilizer; 6 - steam turbine; 7 - capacitor; eight

Pump and 9 - deaerator. In the waste heat boiler, the fuel is not reburned, and the generated superheated steam is used in the steam turbine plant.

The second direction is the use of gas turbines to create a CCGT-CHP and GTU-CHP. Per last years many options have been proposed technological schemes CCGT-CHP. At gas-fired CHPPs, it is advisable to use combined heat and power plants

recycling type. A typical example

a large CCGT-CHP of this type is Severo-Zapadnaya CHPP in St. Petersburg. One CCGT unit at this CHPP includes: two gas turbines with a capacity of 150 MW each, two waste heat boilers, a steam turbine. The main indicators of the unit are: electric power - 450 MW, thermal power - 407 MW, specific fuel consumption for electricity supply - 154.5 g of c.u. tons / (kWh), specific consumption of reference fuel for heat supply - 40.6 kg c.u. ton/GJ, efficiency of CHPP for the supply of electric energy - 79.6%, thermal energy - 84.1%.

The third direction is the use of gas turbines for the creation of CCGT-CHP and GTU-CHP of small and medium capacity on the basis of boiler houses. CCGT - CHP and GTU - CHP the best options, created on the basis of boiler houses, provide efficiency for the supply of electric energy in the heating mode at the level of 76 - 79%.

A typical combined cycle plant consists of two gas turbines, 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 Shchekinskaya GRES. CCGT-490 was designed to generate electricity in the base and partial operating modes of the power plant with heat supply to an external consumer up to 90 MW during winter temperature graph. circuit diagram unit CCGT-490 was forced to focus on the lack of space when placing the waste heat boiler and

steam turbine plant in the power plant buildings, which created certain difficulties in achieving optimal modes of combined heat and power generation.

In the absence of restrictions on the location of the installation, as well as when using an improved gas turbine unit, it is possible to significantly increase the efficiency of the unit. A single-shaft CCGT-320 with a capacity of 300 MW is proposed as such an improved CCGT. The complete gas turbine unit for CCGT-320 is the single-shaft GTE-200, the creation of which is supposed to be carried out by switching to

double-support rotor, modernization of the cooling system and other units of the gas turbine in order to increase the initial gas temperature. In addition to the GTE-200, the CCGT-320 monoblock contains a K-120-13 STP 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 heat exchanger, and a two-pressure waste heat boiler containing eight heat exchange areas, including an intermediate steam superheater.

To evaluate the efficiency of the unit, a thermodynamic calculation was carried out, as a result of which it was concluded that when operating in the condensing mode of the CCGT-490 ShchGRES, its electrical efficiency can be increased by 2.5% and brought up to 50.1%.

Heating research

combined-cycle plants have shown that the economic indicators of CCGTs significantly depend on the structure of their thermal scheme, the choice of which is carried out in favor of the plant that provides the minimum temperature of the flue gases. This is explained by the fact that exhaust gases are the main source of energy losses, and in order to increase the efficiency of the circuit, their temperature must be reduced.

The model of a single-loop cogeneration CCGT, shown in fig. 2 includes a drum-type waste heat boiler with natural circulation of the medium in the evaporator circuit. In the course of gases in the boiler from bottom to top, heating surfaces are sequentially located:

superheater PP, evaporator I, economizer E and gas heating water heater GSP.

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

The calculations of the system showed that when the live steam parameters change, the power generated by the CCGT is redistributed between the thermal and electrical loads. With the growth of steam parameters, the generation of electrical energy increases and the generation of thermal energy decreases. This is explained by the fact that with an increase in the parameters of live steam, 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 decreases.

A double-circuit CCGT, as well as a single-circuit one, consists of two gas turbines, two waste heat boilers and one steam turbine (Fig. 3). Network water is heated in two PGS heaters and (if necessary) in a peak network heater.

In the course of gases in the waste heat boiler

the following are in sequence

heating surfaces: superheater high pressure HDPE, HPH high pressure evaporator, HDPE high pressure economizer, HDPE low pressure superheater,

low-pressure evaporator IND, low-pressure gas heater GPND, gas supply water heater GSP.

Rice. 3 - Thermal circuit diagram

double-circuit CCGT

Rice. 4 - Scheme of utilization of the heat of the gas turbine exhaust gases

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

As a comparative analysis showed, when gas is used as the main fuel, the use of utilization schemes is advisable if the ratio of heat and electric energy is 0.5 - 1.0, with ratios of 1.5 or more, preference is given to CCGT according to the "discharge" scheme.

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

The gas turbine can be carried out by supplying steam generated by the waste heat boiler to the combustion chamber of the gas turbine, 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 a factor of 1.33, if the degree of pressure increase is chosen during the creation of the gas turbine in accordance with the planned degree of regeneration. Such a scheme includes a K-compressor; R - regenerator; KS - combustion chamber; TC - compressor turbine; ST - power turbine; CC - centrifugal compressor. If the gas turbine is made without regeneration, and the degree of pressure increase l is close to the optimal value, then equipping such a gas turbine with a regenerator does not lead to an increase in its efficiency.

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

Comparative analysis showed that the greatest fuel economy is possible in the implementation of the regenerative cycle of the GTU with a high degree regeneration, a relatively low value of the degree of pressure increase 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, exhaust gas heat recovery is more efficient in the steam turbine unit. Installation with steam supply to the combustion chamber is structurally the most simple, but less efficient.

One way to achieve gas savings and solutions environmental issues is the use of steam-gas plants at the CS. In research developments, two alternative options for using steam obtained by utilizing the heat of exhaust gases from gas turbines are considered: a combined-cycle plant driven by a steam turbine of a natural gas blower and from a steam turbine of an electric generator. Fundamental difference of these options lies in the fact that in the case of a CCGT with a supercharger, not only the heat of the exhaust gases of the GPU is utilized, but one GPU is replaced by a steam turbine pumping unit, and with a CCGT with an electric generator, the number of GPUs is preserved, and due to the utilized heat, electricity is generated by a special steam turbine unit. The performed analysis showed that CCGT with a natural gas blower drive provided the best technical and economic indicators.

In the case of creating a steam-gas plant with a waste heat boiler on the basis of the CS, the GTU 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 the use of organic fuel in decentralized heat supply systems, it is possible to reconstruct heating boiler houses with the placement of gas turbine units (GTP) of small capacity 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 the thermal or electrical load curves, as well as on economic factors.

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

maximum load of the consumption area.

Comparative analysis of a gas turbine unit with a CHP generating steam in the amount of 0.144 kg/kg s. , condensing specifications and gas turbines without CHP and with dry heat exchange specifications showed the following: useful

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

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

are used for pre-heating of network water before hot water boilers, heat exchange is carried out with the condensation of water vapor contained in the exhaust gases, and the water is heated in the boiler itself already in the “dry” heat exchange mode.

According to the data, along with fuel economy, 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 through the boiler, it is necessary to transfer part of the return water from the heating network in an amount equal to the recirculation flow from the return pipe to the supply pipe.

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

generators, there are several options for utilizing the heat of exhaust gases, for example, using a utilizing

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

steam turbine generator to increase power generation. An analysis of the plant operation, taking into account heat recovery with the help of UTO, showed a significant increase in the heat utilization factor, in some cases by 2 times or more, and experimental studies of the EM-25/11 power unit with an NK-37 engine made it possible to draw the following conclusion. Depending on the specific conditions, the annual supply of utilized heat can vary from 210 to 480 thousand GJ, and the real savings in gas amounted to 7 to 17 thousand m3.

Literature

1. V.M. Maslennikov, Thermal Power Engineering, 3, 39-41 (2000).

2. V.I. Romanov, V.A. Krivutsa, Thermal Power Engineering, 4, 27-30 (1996).

3. L.V. Arseniev, V.G. Tyryshkin, Combined installations with gas turbines. L.: Mashinostroenie, 1982, 407 p.

4. V.I. Dlugoselsky, A.S. Zemtsov, Thermal Power Engineering, 12, 3-7 (2000).

5. B.M. Troyanovsky, A.D. Trukhniy, V.G. Gribin, Thermal Power Engineering, 8, 9-13 (1998).

6. A. D. Tsoi, Industrial Energy, 4, 50-52 (2000).

7. A.D. Tsoi, A.V. Klevtsov, A.V. Koryagin, Industrial Energy, 12, 25-32 (1997).

8. V.I. Eveno, Thermal Power Engineering, 12, 48-50 (1998).

9. N.I. Serebryannikov, E.I. Tapelev, A.K. Makhankov, Energy saving and water treatment, 2, 3-11 (1998).

10. G.D. Barinberg, V.I. Dlugoselsky, Thermal Power Engineering, 1, 16-20 (1998)

11. A.P. Bersenev, Thermal Power Engineering, 5, 51-53 (1998).

12. E.N. Bukharkin, Industrial Energy, 7, 34-37 (1998).

13. V.I. Dobrokhotov, Thermal Power Engineering, 1, 2-8 (2000).

14. A.S. Popov, E.E. Novgorodsky, B.A. Permyakov, Industrial Energy, 1, 34-35 (1997).

15. I.V. Belousenko, Industrial Energy, 5, 53-55 (2000).

16. V.V. Getman, N.V. Lezhnev, Vestnik Kazan. technol. Univ., 18, 174-179 (2011).

17. N.V. Lezhnev, V.I. Elizarov, V.V. Hetman, Vestnik Kazan. technol. Univ., 17, 162-167 (2012).

© V.V. Getman - Cand. tech. Sciences, Assoc. cafe automation of technological processes and production FGBOU VPO "KNRTU", 1ega [email protected] yaMech; N. V. Lezhneva - Ph.D. tech. Sciences, Assoc. cafe automation of technological processes and production FGBOU VPO "KNRTU", [email protected]

Waste flue gas heat recovery

Flue gases leaving the working space of furnaces are very high temperature and therefore carry away with them a significant amount of heat. In open-hearth furnaces, for example, about 80% of all 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 with them the more heat, the higher their temperature and the lower the heat utilization factor in the furnace. In this regard, it is advisable to ensure the recovery of the heat of flue gases, which can be carried out in principle by two methods: 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 the 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 the combustion temperature and save fuel. With the second method of utilization, the heat of flue gases is used in thermal power boilers and turbine plants, which achieves significant savings fuel.

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

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

First of all, it should 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 a unit of heat obtained in the furnace as a result of fuel combustion (a unit of chemical heat), since the heat of the heated air (gas) does not entail heat loss with flue gases. The value of a unit of physical heat is the greater, the lower the fuel utilization factor and the higher the temperature of the flue gases.

For normal operation of the furnace, the required amount of heat should be supplied to the working space every hour. This amount of heat includes not only the heat of the fuel, but also the heat of the heated air or gas, i.e.

It is clear that with = const the increase will allow to decrease . In other words, waste heat recovery from flue gases allows to achieve fuel savings, which depends on the degree of heat recovery from flue gases.

where - respectively, the enthalpy of heated air and flue gases leaving the working space, kW, or kJ / period.

The degree of heat recovery can also be called efficiency. recuperator (regenerator), %

Knowing the degree of heat recovery, it is possible to determine the fuel economy by the following expression:

where I "d, Id - respectively, the enthalpy of flue gases at the combustion temperature and leaving the furnace.

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

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

An increase in at leads to an increase in the combustion temperature. If it is necessary to provide a certain value, then an increase in the air (gas) heating temperature leads to a decrease in the value, i.e., to a decrease in the proportion of gas with a high calorific value in the fuel mixture.

Since heat recovery can significantly save fuel, it is advisable to strive for the highest possible, economically justified degree of utilization. However, it should be immediately noted that recycling cannot be complete, that is, always. This is explained by the fact that an increase in the heating surface is rational only up to certain limits, after which it already leads to a very insignificant gain in heat savings.

The heat of the flue gases leaving the furnaces, in addition to heating the air and gaseous fuel, can be used in waste heat boilers to generate steam. While the heated gas and air are used in the furnace unit itself, the steam is sent to external consumers (for production and energy needs).

In all cases, one should strive for the greatest heat recovery, i.e., to return it to the working space of the furnace in the form of heat from the heated combustion components (gaseous fuel and air). Indeed, an increase in heat recovery leads to a reduction in fuel consumption and to an intensification and improvement of the technological process. However, the presence of recuperators or regenerators does not always exclude the possibility of installing waste heat boilers. First of all, waste heat boilers have found application in large furnaces with a relatively high temperature of flue gases: in open-hearth steel-smelting furnaces, in copper-smelting reverberatory furnaces, in rotary kilns for roasting cement clinker, in the dry method of cement production, etc.

Rice. 5.

1 - superheater; 2 - pipe surface; 3 - smoke exhauster.

The heat of flue gases from the regenerators of open-hearth furnaces with a temperature of 500 - 650 ° C is used in gas-tube waste heat boilers with natural circulation of the working fluid. The heating surface of gas-tube boilers consists of fire tubes, inside which flue gases pass at a speed of approximately 20 m/s. Heat from the gases to the heating surface is transferred by convection, and therefore an increase in speed increases heat transfer. Gas-tube boilers are easy to operate, do not require lining and frames during installation, and have a high gas density.

On fig. 5 shows a gas-tube boiler of the Taganrog plant with an average productivity D cf = 5.2 t/h with the expectation of passing flue gases up to 40,000 m 3 /h. The steam pressure generated by the boiler is 0.8 MN/m 2 ; temperature 250 °C. The temperature of the gases before the boiler is 600 °C, behind the boiler 200 - 250 °C.

In boilers with forced circulation, the heating surface is made up of coils, the location of which is not limited by the conditions of natural circulation, and therefore such boilers are compact. Coil surfaces are made of pipes of small diameter, for example d = 32×3 mm, which lightens the weight of the boiler. With multiple circulation, when the circulation ratio is 5 - 18, the water velocity in the tubes is significant, at least 1 m / s, as a result of which the precipitation of dissolved salts from the water in the coils decreases, and the crystalline scale is washed off. However, the boilers must be fed with water chemically purified by cationic filters and other water treatment methods that meet the feed water standards for conventional steam boilers.

Rice. 6.

1 - economizer surface; 2 - evaporation surface; 3 - superheater; 4 - drum-collector; 5 - circulation pump; 6 - sludge trap; 7 - smoke exhauster.

On fig. 6 shows the layout of coil heating surfaces in vertical chimneys. The movement of the steam-water mixture is carried out circulation pump. The designs of boilers of this type were developed by Tsentroenergochermet and Gipromez and are manufactured for flue gas flow rates up to 50 - 125 thousand m 3 / h with an average steam production from 5 to 18 t / h.

The cost of steam is 0.4 - 0.5 RUR/t instead of 1.2 - 2 RUR/t for steam taken from steam turbines of CHPPs and 2 - 3 RUR/t for steam from industrial boilers. The cost of steam is made up of energy costs for driving smoke exhausters, costs for water preparation, depreciation, repairs and maintenance. The speed of gases in the boiler is from 5 to 10 m/s, which ensures good heat transfer. The aerodynamic resistance of the gas path is 0.5 - 1.5 kN / m 2, so the unit must have artificial draft from the smoke exhauster. The increase in draft that accompanies the installation of waste heat boilers, as a rule, improves the operation of open-hearth furnaces. Such boilers have become widespread in factories, but their good operation requires protection of the heating surfaces from being carried in by dust and slag particles and systematic cleaning of the heating surfaces from entrainment by blowing with superheated steam, washing with water (when the boiler stops), by vibration, etc.

Rice. 7.

To use the heat of flue gases from copper-smelting reverberatory furnaces, water-tube boilers with natural circulation are installed (Fig. 7). Flue gases in this case have a very high temperature (1100 - 1250 ° C) and are polluted with dust in an amount of up to 100 - 200 g / m 3, and part of the dust has high abrasive (abrasive) properties, the other part is in a softened state and can slag boiler heating surface. It is the high dustiness of the gases that makes it necessary for the time being to abandon heat recovery in these furnaces and to limit the use of flue gases in waste heat boilers.

The transfer of heat from gases to the screen evaporation surfaces proceeds very intensively, which ensures intensive vaporization of slag particles, cooling, granulating and falling into the slag funnel, which eliminates slagging of the convective heating surface of the boiler. The installation of such boilers for the use of gases with a relatively low temperature (500 - 700 ° C) is impractical due to the weak heat transfer by radiation.

In the case of equipping high-temperature furnaces with metal recuperators, it is advisable to install waste heat boilers directly behind the working chambers of the furnaces. In this case, the flue gas temperature in the boiler drops to 1000 - 1100 °C. With this temperature, they can already be directed to the heat-resistant section of the heat exchanger. If the gases carry a lot of dust, then the waste heat boiler is arranged in the form of a screen slag granulator boiler, which ensures the separation of entrainment from gases and facilitates the work of the heat exchanger.

The owners of the patent RU 2606296:

The invention relates to thermal power engineering and can be used in any enterprise operating hydrocarbon fuel boilers.

KSK-type heaters (Kudinov A.A. Energy saving in heat-generating installations. - Ulyanovsk: UlGTU, 2000. - 139, p. 33), which are mass-produced by the Kostroma heater plant, are known, consisting of a gas-water surface heat exchanger, the heat exchange surface of which is made of finned bimetallic tubes, strainer, distribution valve, droplet eliminator and hydropneumatic blower.

KSK type heaters work as follows. Flue gases enter the distribution valve, which divides them into two streams, the main gas stream is sent through a strainer to the heat exchanger, the second one - along the gas duct bypass line. In the heat exchanger, the water vapor contained in the flue gases condenses on the finned tubes, heating the water flowing in them. The resulting condensate is collected in a sump and pumped to the heating network feed circuit. The water heated in the heat exchanger is supplied to the consumer. At the outlet of the heat exchanger, the dried flue gases are mixed with the initial flue gases from the bypass line of the flue and are directed through the smoke exhauster to the chimney.

To operate the heat exchanger in the mode of condensation of its entire convective part, it is required that the water heating temperature in the convective package does not exceed 50°C. To use such water in heating systems, it must be additionally heated.

To prevent the condensation of residual water vapor of flue gases in the gas ducts and the chimney, part of the source gases are mixed through the bypass channel with the dried flue gases, increasing their temperature. With such an admixture, the content of water vapor in the exhaust flue gases also increases, reducing the efficiency of heat recovery.

Known heat exchanger (RU 2323384 C1, IPC F22B 1/18 (2006.01), publ. 27.04.2008), containing a contact heat exchanger, a drop catcher, a gas-gas heat exchanger included in a co-current scheme, gas ducts, pipelines, a pump, temperature sensors, valves - regulators. A water-to-water heat exchanger and a water-to-air heat exchanger with a bypass channel along the air flow are arranged in series along the return water course of the contact heat exchanger.

A known method of operation of this heat exchanger. Outgoing gases enter the gas duct through the gas duct to the inlet of the gas-gas heat exchanger, successively passing through its three sections, then to the inlet of the contact heat exchanger, where, passing through the nozzle, washed by the circulating water, they are cooled below the dew point, giving off apparent and latent heat to the circulating water. Further, the cooled and wet gases are released from most of the liquid water carried away by the flow in the droplet eliminator, heated and dried in at least one section of the gas-gas heat exchanger, sent to the pipe by a smoke exhauster and released into the atmosphere. At the same time, the heated circulating water from the tray of the contact heat exchanger is pumped by a pump into the water-to-water heat exchanger, where it heats cold water from the pipeline. The water heated in the heat exchanger is supplied to the needs of technological and domestic hot water supply or to a low-temperature heating circuit.

Further, the circulating water enters the water-to-air heat exchanger, heats at least part of the blast air coming from outside the premises through the air duct, cooling to the lowest possible temperature, and enters the contact heat exchanger through the water distributor, where it removes heat from the gases, simultaneously washing them from suspended particles, and absorbs part of nitrogen and sulfur oxides. The heated air from the heat exchanger is supplied by a blower fan to a regular air heater or directly to the furnace. The circulating water is optionally filtered and treated in known ways.

To implement this method, a control system is required due to the use of recovered heat for hot water supply purposes due to the variability of the daily hot water consumption schedule.

The water heated in the heat exchanger, supplied for the needs of hot water supply or to the low-temperature heating circuit, requires it to be brought to the required temperature, since it cannot be heated in the heat exchanger above the temperature of the water in the circulation circuit, which is determined by the saturation temperature of water vapor in the flue gases. Low air heating in the water-air heat exchanger does not allow using this air for space heating.

Closest to the claimed invention are a device and a method for utilizing the heat of flue gases (RU 2436011 C1, IPC F22B 1/18 (2006.01), publ. 10.12.2011).

The flue gas heat recovery device comprises a gas-gas surface plate heat exchanger made according to the counterflow scheme, a surface gas-air plate condenser, an inertial droplet eliminator, gas ducts, a smoke exhauster, air ducts, fans and a pipeline.

The initial flue gases are cooled in a gas-gas surface plate heat exchanger, heating the dried flue gases. The heating and heated medium move countercurrently. In this case, deep cooling of wet flue gases occurs to a temperature close to the dew point of water vapor. Further, the water vapor contained in the flue gases condenses in a gas-air surface plate heat exchanger - condenser, heating the air. The heated air is used for space heating and meeting the needs of the combustion process. The condensate after additional processing is used to make up for losses in the heating network or steam turbine cycle. To prevent condensation of residual water vapor carried away by the flow from the condenser, a part of the heated, dried flue gases is mixed in front of the additional smoke exhauster. The dried flue gases are supplied by a smoke exhauster to the heater described above, where they are heated to prevent possible condensation of water vapor in the gas ducts and the chimney and are sent to the chimney.

The disadvantages of this method is that mainly the latent heat of condensation of water vapor contained in the flue gases is utilized. If the recuperative heat exchanger cools the initial flue gases to a temperature close to the dew point of water vapor, then the heating of the outgoing dried flue gases will be excessive, which reduces the efficiency of utilization. The disadvantage is the use of only one medium for heating - air.

The objective of the invention is to increase the efficiency of flue gas heat recovery by using the latent heat of water vapor condensation and the increased temperature of the flue gases themselves.

In the proposed method of deep utilization of flue gas heat, as well as in the prototype, flue gases are pre-cooled in a gas-gas surface plate heat exchanger, heating dried flue gases, condense water vapor contained in flue gases in the condenser, heating the air.

According to the invention, between the heat exchanger and the condenser, the flue gases are cooled down to a temperature close to the dew point of water vapor by heating the water.

Gas boilers have a high flue gas temperature (130°C for large power boilers, 150°C-170°C for small boilers). To cool flue gases before condensation, two devices are used: a recuperative gas-gas heat exchanger and a waste water heater.

The initial flue gases are pre-cooled in a gas-gas surface plate heat exchanger, heating the dried flue gases by 30-40°C higher than the saturation temperature of the water vapor contained in them, to create a temperature margin with possible cooling of the flue gases in the pipe. This makes it possible to reduce the heat exchange area of ​​the recuperative heat exchanger in comparison with the prototype and it is useful to use the remaining heat of the flue gases.

A significant difference is the use of a contact gas water heater for the final cooling of wet flue gases to a temperature close to the dew point of water vapor. At the inlet to the water heater, flue gases have a sufficiently high temperature (130°С-90°С), which allows heating water up to 50°С-65°С with its partial evaporation. At the outlet of the contact gas water heater, flue gases have a temperature close to the dew point of the water vapor contained in them, which increases the efficiency of using the heat exchange surface in the condenser, eliminates the formation of dry zones of the condenser and increases the heat transfer coefficient.

The method of waste heat recovery is shown in Fig.1.

Table 1 shows the results of the verification calculation of the installation option for a natural gas boiler with a capacity of 11 MW.

The method of deep utilization of the heat of flue gases is carried out as follows. The initial flue gases 1 are pre-cooled in a gas-gas surface plate heat exchanger 2, heating the dried flue gases. Next, the flue gases 3 are finally cooled in a contact gas-water water heater 4 to a temperature close to the dew point of water vapor, spraying water, for which it is advisable to use the condensate obtained in the condenser. At the same time, part of the water evaporates, increasing the moisture content of flue gases, and the rest is heated to the same temperature. The water vapor contained in the flue gases 5 is condensed in a gas-air surface plate heat exchanger - condenser 6 with a drop catcher 7, heating the air. Condensate 8 is supplied for heating to a contact gas-water water heater 4. The heat of condensation is used to heat cold air, which is supplied by fans 9 from the environment through duct 10. Heated air 11 is sent to the production room of the boiler shop for its ventilation and heating. From this room, air is supplied to the boiler to ensure the combustion process. The dried flue gases 12 are supplied by a smoke exhauster 13 to the gas-gas surface plate heat exchanger 2 for heating and sent to the chimney 14.

To prevent condensation of residual water vapor carried away by the flow from the condenser, a part of the heated dried flue gases 15 (up to 10%) is mixed in front of the smoke exhauster 13, the value of which is initially adjusted by the damper 16.

The temperature of the heated air 11 is controlled by changing the flow rate of the dried flue gases 1 or by changing the air flow rate, by adjusting the speed of the exhaust fan 13 or fans 9 depending on the outside temperature.

Heat exchanger 2 and condenser 6 are surface plate heat exchangers made of unified modular packages, which are arranged in such a way that the movement of heat carriers is carried out in countercurrent. Depending on the volume of dried flue gases, the heater and condenser are formed from the calculated number of packages. Water heater 4 is a contact gas-to-water heat exchanger that provides additional cooling of flue gases and heating of water. Heated water 17 after additional processing is used to make up for losses in the heat network or steam turbine cycle. Block 9 is formed from several fans to change the flow of heated air.

Table 1 shows the results of the verification calculation of the installation version for a natural gas boiler with a capacity of 11 MW. Calculations were carried out for the outdoor air temperature -20°С. The calculation shows that the use of a contact gas water heater 4 leads to the disappearance of the dry zone in the condenser 6, intensifies heat transfer and increases the power of the installation. The percentage of recovered heat increases from 14.52 to 15.4%, while the dew point temperature of water vapor in the dried flue gases decreases to 17°C. Approximately 2% of the thermal power is not utilized, but is used for recuperation - heating the dried flue gases to a temperature of 70°C.

The method of deep utilization of flue gas heat, according to which flue gases are pre-cooled in a gas-gas surface plate heat exchanger, by heating dried flue gases, they are additionally cooled in a water heater to a temperature close to the dew point of water vapor, by heating water, water vapor contained in flue gases is condensed in the condenser, heating the air, characterized in that a surface tubular gas-water water heater is installed between the heat exchanger and the condenser for cooling wet flue gases and heating water, while the main heat recovery occurs in the condenser during air heating, and additional - in the water heater.

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