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 bypass line of the gas duct. 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 bottom of the contact heat exchanger is pumped by a pump to 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 such a 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, the 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 flue gas heat 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, 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, which 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 smoke exhauster 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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The invention relates to the field of power engineering and can be used in heating and air conditioning systems. The invention lies in the fact that the connection of heat-exchange finned tubes in a row and rows to each other is made sequentially by one tube in the course in one branch, and adjacent heat-exchange tubes in a row are connected to each other in series by inter-pipe transitions in the form of bent bends and are equipped with easily removable repair and protective plugs , the number of tubes connected in series in a row and the total number of passes in all rows is selected depending on the actual parameters of the existing heating network and is determined by the hydraulic characteristic of the water heater.

An electrical heat sink that uses computing processors as a heat source. This heatsink for domestic and industrial premises, using computing processors as heat sources, contains a heated package that performs heat transfer between the heat source and the surrounding air, a number Q of processors distributed on a number P of printed circuit boards, forming a heatsink heat source, and a powerful means for performing calculations through external information systems, a human-machine interface that allows you to control the computing and thermal power issued by the radiator, a stabilized power supply for various electronic components, a network interface that allows you to connect the radiator to external networks.

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The invention provides a system and method for steam-gas reforming. The method of combined-cycle cogeneration based on gasification and methanation of biomass includes: 1) gasification of biomass by mixing oxygen and water vapor obtained from an air separation plant with biomass, transporting the resulting mixture through a nozzle to a gasifier, gasifying biomass at a temperature of 1500-1800 ° C and a pressure of 1-3 MPa to obtain a raw gasified gas and transportation of superheated steam having a pressure of 5-6 MPa, obtained as a result of expedient heat recovery, to a steam turbine; 2) conversion and purification: according to the requirements of the methanation reaction, adjusting the hydrogen/carbon ratio of the raw gasified gas formed in step 1) to 3:1 using the shift reaction, and recovering the raw gasified gas at low temperature using methanol for desulfurization and decarbonization , resulting in purified syngas; 3) carrying out methanation: introducing the purified syngas of step 2) into a methanation section consisting of a primary methanation section and a secondary methanation section, the primary methanation section comprising a first primary methanation reactor and a second primary methanation reactor connected in series; allowing part of the process gas from the second primary methanation reactor to return to the inlet of the first primary methanation reactor for mixing with fresh feed gas and then to enter the first primary methanation reactor so that the concentration of reactants at the inlet of the first primary methanation reactor decreases and the temperature of the catalyst bed is controlled by the process gas; introducing syngas after primary methanation into a secondary methanation section comprising a first secondary methanation reactor and a second secondary methanation reactor connected in series, where a small amount of unreacted CO and a large amount of CO2 are converted to CH4, and transporting the superheated intermediate pressure steam generated in the methanation section to steam turbine; and 4) methane concentration: concentration of methane of synthetic natural gas containing trace amounts of nitrogen and water vapor obtained in step 3) by pressure swing adsorption, so that the molar concentration of methane reaches 96% and the calorific value of synthetic natural gas reaches 8256 kcal. /Nm3.

The invention relates to thermal power engineering. The method for deep utilization of flue gas heat includes pre-cooling of flue gases in a gas-gas surface plate heat exchanger, heating dried flue gases in counterflow to create a temperature margin that prevents condensation of residual water vapor in the chimney. Further cooling of flue gases to a temperature close to the dew point of water vapor is carried out in a contact gas-water water heater, which heats the water. The cooled moist flue gases are fed into a gas-air surface plate heat exchanger - a condenser, where the water vapor contained in the flue gases is condensed, heating the air. The dried flue gases are supplied by an additional smoke exhauster to the gas-gas surface plate heat exchanger, where they are heated to prevent possible condensation of water vapor in the gas ducts and the chimney and are sent to the chimney. EFFECT: increased efficiency of flue gas heat utilization due to the use of latent heat of water vapor condensation and elevated temperature of the flue gases themselves. 1 ill., 1 tab.

I propose to consider activities for the disposal of flue gases. Flue gases are abundant in any village and city. The main part of the smoke producers are steam and hot water boilers and internal combustion engines. I will not consider the flue gases of engines in this idea (although they are also suitable in composition), but I will dwell on the flue gases of boiler houses in more detail.

The easiest way is to use the smoke of gas boilers (industrial or private houses), this is the cleanest type of flue gas, which contains the minimum amount of harmful impurities. You can also use the smoke of boilers burning coal or liquid fuel, but in this case, you will have to clean the flue gases from impurities (this is not so difficult, but still additional costs).

The main components of flue gas are nitrogen, carbon dioxide and water vapour. Water vapor is of no value and can be easily removed from the flue gas by contacting the gas with a cool surface. The remaining components already have a price.

Gaseous nitrogen is used in fire fighting, for the transportation and storage of flammable and explosive media, as a shielding gas to protect easily oxidized substances and materials from oxidation, to prevent corrosion of tanks, to purge pipelines and containers, to create inert media in grain silos. Nitrogen protection prevents the growth of bacteria, is used to clean environments from insects and microbes. In the food industry, a nitrogen atmosphere is often used as a means of increasing the shelf life of perishable products. Gaseous nitrogen is widely used to obtain liquid nitrogen from it.

To obtain nitrogen, it is sufficient to separate water vapor and carbon dioxide from the flue gas. As for the next component of smoke - carbon dioxide (CO2, carbon dioxide, carbon dioxide), the range of its application is even greater and its price is much higher.

I suggest getting more information about it. Typically, carbon dioxide is stored in 40-liter cylinders painted black with a yellow inscription "carbon dioxide". A more correct name for CO2 is “carbon dioxide”, but everyone is already used to the name “carbon dioxide”, it has been assigned to CO2 and therefore the inscription “carbon dioxide” on the cylinders is still preserved. Carbon dioxide is found in cylinders in liquid form. Carbon dioxide is odorless, non-toxic, non-flammable and non-explosive. It is a substance that occurs naturally in the human body. In the air exhaled by a person, it usually contains 4.5%. Carbon dioxide is mainly used in carbonation and sale in bottling drinks, it is used as a protective gas during welding using semi-automatic welding machines, it is used to increase the yield (2 times) of agricultural crops in greenhouses by increasing the concentration of CO2 in the air and increasing ( 4-6 times when saturated with carbon dioxide water) for the production of microalgae during their artificial cultivation, for the preservation and improvement of the quality of feed and products, for the production of dry ice and its use in cryoblasting plants (cleaning surfaces from contamination) and for obtaining low temperatures during storage and food transportation, etc.

Carbon dioxide is a commodity in demand everywhere and the need for it is constantly increasing. In home and small businesses, carbon dioxide can be obtained by extracting it from flue gas in low-capacity carbon dioxide plants. It is not difficult for persons related to technology to make such an installation on their own. Subject to the norms of the technological process, the quality of the resulting carbon dioxide meets all the requirements of GOST 8050-85.
Carbon dioxide can be obtained both from the flue gases of boiler houses (or heating boilers of private households) and by the method of special combustion of fuel in the installation itself.

Now the economic side of things. The unit can operate on any type of fuel. When fuel is burned (especially to produce carbon dioxide), the following amount of CO2 is released:
natural gas (methane) - 1.9 kg of CO2 from the combustion of 1 cu. m of gas;
hard coal, different deposits - 2.1-2.7 kg of CO2 from the combustion of 1 kg of fuel;
propane, butane, diesel fuel, fuel oil - 3.0 kg CO2 from burning 1 kg of fuel.

It will not be possible to fully extract all the carbon dioxide released, and up to 90% (95% extraction can be achieved) is quite possible. The standard filling of a 40-liter cylinder is 24-25 kg, so you can independently calculate the specific fuel consumption to obtain one carbon dioxide cylinder.

It is not so big, for example, in the case of obtaining carbon dioxide from the combustion of natural gas, it is enough to burn 15 m3 of gas.

According to the highest tariff (Moscow) it is 60 rubles. per 40 liter. carbon dioxide bottle. In the case of CO2 extraction from boiler flue gases, the cost of carbon dioxide production is reduced, as fuel costs are reduced and the profit from the installation is increased. The unit can operate around the clock, in automatic mode with minimal involvement of a person in the process of obtaining carbon dioxide. The productivity of the plant depends on the amount of CO2 contained in the flue gas, the design of the plant, and can reach 25 carbon dioxide cylinders per day or more.

The price of 1 cylinder of carbon dioxide in most regions of Russia exceeds 500 rubles (December 2008). Monthly revenue from the sale of carbon dioxide in this case reaches: 500 rubles per ball. x 25 points/day x 30 days = 375,000 rubles. The heat released during combustion can be used simultaneously for space heating, and in this case there will be no irrational use of fuel. At the same time, it should be borne in mind that the environmental situation at the place of extraction of carbon dioxide from flue gases is only improving, as CO2 emissions into the atmosphere are decreasing.

The method of extracting carbon dioxide from flue gases obtained from the combustion of wood waste (waste from logging and wood processing, carpentry shops, etc.) also recommends itself well. In this case, the same CO2 plant is supplemented with a wood gas generator (manufactured or self-manufactured) to produce wood gas. Wood waste (chocks, chips, shavings, sawdust, etc.) is poured into the gas generator hopper 1-2 times a day, otherwise the plant operates in the same mode as in the above.
The output of carbon dioxide from 1 ton of wood waste is 66 cylinders. The revenue from one ton of waste is (at the price of a cylinder of carbon dioxide 500 rubles): 500 rubles per ball. x 66 ball. = 33,000 rubles.

With an average amount of wood waste from one wood processing shop of 0.5 tons of waste per day, the proceeds from the sale of carbon dioxide can reach 500 thousand rubles. per month, and in the case of the import of waste from other woodworking and carpentry shops, the revenue becomes even greater.

It is also possible to obtain carbon dioxide from the burning of car tires, which is also only for the benefit of our ecology.

In the case of the production of carbon dioxide in an amount greater than it can be consumed by the local market, the produced carbon dioxide can be independently used for other activities, as well as processed into other chemicals and reagents (for example, using a simple technology into environmentally friendly carbon-containing fertilizers, dough baking powder and etc.) up to the production of motor gasoline from carbon dioxide.

Evaluation of Efficiency of Deep Recuperation of Power Plant Boilers’ Combustion Productions

E.G. Shadek, Candidate of Engineering, independent expert

keywords: combustion products, heat recovery, boiler plant equipment, energy efficiency

One of the methods to solve the problem of fuel economy and improvement of energy efficiency of boiler plants is development of technologies for deep heat recuperation of boiler exhaust gases. We offer a process scheme of a power plant with steam-turbine units (STU) that allows for deep recuperation of heat from boiler combustion products from STU condenser using cooler-condensate with minimum costs without the use of heat pump units.

Description:

One of the ways to solve the problem of fuel economy and improve the energy efficiency of boiler plants is the development of technologies for deep utilization of the heat of waste gases from boilers. boiler of combustion products due to the presence of a cooler - condensate from the PTU condenser.

E. G. Shadek, cand. tech. Sciences, independent expert

One of the ways to solve the problem of fuel economy and increase the energy efficiency of boiler plants is the development of technologies for deep utilization of the heat of flue gases from boilers. We offer a technological scheme of a power plant with steam turbine units (STP), which allows, at minimal cost, without the use of heat pump units, to carry out deep utilization of the heat of combustion products leaving the boiler due to the presence of a cooler - condensate from the STP condenser.

Deep utilization of the heat of combustion products (FP) is ensured when they are cooled below the dew point temperature equal to 50–55 0 С for natural gas PS. The following phenomena occur:

• condensation of water vapor (up to 19-20% of the volume or 12-13% of the weight of the combustion products),
• utilization of physical heat of the substation (40–45% of the total heat content),
• utilization of the latent heat of vaporization (60–55%, respectively).

It was previously established that fuel savings with deep utilization in comparison with a boiler with a passport (maximum) efficiency of 92% is 10–13%. The ratio of the amount of utilized heat to the heat output of the boiler is about 0.10–0.12, and the efficiency of the boiler in condensing mode is 105% in terms of the net calorific value of the gas.

In addition, with deep utilization in the presence of water vapor in the PS, the emission of harmful emissions is reduced by 20–40% or more, which makes the process environmentally friendly.

Another effect of deep utilization is the improvement of the conditions and service life of the gas path, since condensation is localized in the chamber where the utilization heat exchanger is installed, regardless of the outdoor temperature.

Deep disposal for heating systems

In advanced Western countries, deep utilization for heating systems is carried out using condensing-type hot water boilers equipped with a condensing economizer.

The low, as a rule, return water temperature (30–40 0 С) with a typical temperature graph, for example, 70/40 0 С, in the heating systems of these countries allows for deep heat recovery in a condensing economizer equipped with a condensate collection, removal and treatment unit ( with its subsequent use for feeding the boiler). Such a scheme provides the condensing mode of operation of the boiler without an artificial coolant, i.e. without the use of a heat pump unit.

The effectiveness and cost-effectiveness of deep disposal for heating boilers do not need to be proven. Condensing boilers are widely used in the West: up to 90% of all manufactured boilers are condensing. Such boilers are also operated in our country, although we do not have their production.

In Russia, unlike countries with a warm climate, the temperature in the return line of heating networks is usually higher than the dew point, and deep utilization is possible only in four-pipe systems (very rare) or when using heat pumps. The main reason for Russia's lagging behind in the development and implementation of deep utilization is the low price of natural gas, high capital costs due to the inclusion of heat pumps in the scheme, and long payback periods.

Deep disposal for power plant boilers

The efficiency of deep utilization for boilers of power plants (Fig. 1) is much higher than for heating ones, due to a stable load (KIM = 0.8–0.9) and large unit capacities (tens of megawatts).

Let us estimate the heat resource of the combustion products of station boilers, taking into account their high efficiency (90–94%). This resource is determined by the amount of waste heat (Gcal/h or kW), which is uniquely dependent on the heat output of the boiler Q K , and temperature behind gas boilers T 1UX, which in Russia is accepted not lower than 110–130 0 С for two reasons:

• to increase the natural draft and reduce the pressure (energy consumption) of the smoke exhauster;
• to prevent condensation of water vapor in flues, gas ducts and chimneys.

Extended analysis of a large array 1 of experimental data of balance, commissioning tests conducted by specialized organizations, regime maps, reporting statistics of stations, etc. and the results of calculating the values ​​of heat loss with outgoing combustion products q 2 , the amount of heat recovered 2 Q UT and indicators derived from them in a wide range of loads of station boilers are given in Table. thirteen . The goal is to determine q 2 and the ratios of the quantities Q K , q 2 and Q UT under typical operating conditions of boilers (Table 2). In our case, it does not matter which boiler: steam or hot water, industrial or heating.

Table indicators. 1, highlighted in blue, were calculated according to the algorithm (see reference). Calculation of the deep utilization process (definition Q UT, etc.) were carried out according to the engineering method given in and described in. The heat transfer coefficient "combustion products - condensate" in the condensate heat exchanger was determined according to the empirical method of the heat exchanger manufacturer (OAO Calorific Plant, Kostroma).

The results testify to the high economic efficiency of the deep utilization technology for station boilers and the profitability of the proposed project. The payback period of systems is from 2 years for a boiler of minimum power (Table 2, boiler No. 1) to 3–4 months. The resulting ratios β, φ, σ, as well as savings articles (Table 1, lines 8–10, 13–18) allow you to immediately assess the capabilities and specific indicators of a given process, boiler.

Heat recovery in a gas heater

The usual technological scheme of the power plant provides for the heating of condensate in a gas heater (part of the tail surfaces of the boiler, economizer) on flue gases leaving the boiler.

After the condenser, pumps (sometimes through a block desalination plant - hereinafter BOU) condensate is sent to the gas heater, after which it enters the deaerator. With the standard quality of the condensate, the BOU is bypassed. To prevent condensation of water vapor from the flue gases on the last pipes of the gas heater, the temperature of the condensate in front of it is maintained at least 60 0 С by recirculating heated condensate to the inlet to it.

To further reduce the temperature of the flue gases, a water-to-water heat exchanger is often included in the condensate recirculation line, cooled by the make-up water of the heating system. Heating of network water is carried out by condensate from a gas heater. With additional cooling of gases by 10 0 С in each boiler, it is possible to obtain about 3.5 Gcal/h of heating load.

To prevent the condensate from boiling in the gas heater, control feed valves are installed behind it. Their main purpose is to distribute the condensate flow between the boilers in accordance with the heat load of the PTU.

Deep recovery system with condensing heat exchanger

As can be seen from the process diagram (Fig. 1), the steam condensate from the condensate collector is pumped by pump 14 to the collection tank 21, and from there to the distribution manifold 22. Here, the condensate is divided into two streams using the automatic control system of the station (see below): one is supplied to the deep utilization unit 4, to the condensing heat exchanger 7, and the second to the low-pressure heater (LPH) 18, and then to the deaerator 15. The temperature of the steam condensate from the turbine condenser (about 20–35 heat exchanger 7 to the required 40 0 ​​C, i.e. to ensure deep utilization.

The heated steam condensate from the condensing heat exchanger 7 is fed through the LPH 18 (or bypassing 18) to the deaerator 15. The condensate of the combustion products obtained in the condensing heat exchanger 7 is drained into the sump and tank 10. From there it is fed into the contaminated condensate tank 23 and pumped by the drain pump 24 into the tank condensate reserve 25, from which the condensate pump 26 through the flow regulator is supplied to the area for cleaning the condensate of the combustion products (not shown in Fig. 1), where it is processed according to known technology. Purified condensate of combustion products is fed into HDPE 18 and then into deaerator 15 (or directly into 15). From the deaerator 15, the flow of pure condensate is fed by the feed pump 16 to the high-pressure heater 17, and from it to the boiler 1.

Thus, the heat of combustion products utilized in the condensing heat exchanger saves the fuel consumed in the technological scheme of the power plant for heating the station condensate in front of the deaerator and in the deaerator itself.

The condensation heat exchanger is installed in chamber 35 at the junction of boiler 27 with the flue (Fig. 2c). The heat load of the condensing heat exchanger is regulated by bypassing, i.e., the removal of part of the hot gases in addition to the condensing heat exchanger through the bypass channel 37 with a throttle valve (gate) 36.

The simplest would be the traditional scheme: a condensing economizer, more precisely, the tail sections of the boiler economizer, such as a gas heater, but operating in a condensing mode, i.e. with cooling of the combustion products below the dew point temperature. But at the same time, difficulties arise in the constructive and operational plan (maintenance, etc.), requiring special solutions.

Various types of heat exchangers are applicable: shell-and-tube, straight-tube, with knurled fins, lamellar or efficient design with a new shape of the heat exchange surface with a small bend radius (RG-10 regenerator, Anod Research and Production Center). In this scheme, as a condensing heat exchanger, heat exchange block-sections based on a bimetallic air heater of the VNV123-412-50ATZ brand (OAO Calorific Plant, Kostroma) are taken.

The choice of the layout of sections and connections for water and gases allows you to vary and ensure the speed of water and gases within the recommended limits (1-4 m / s) . The flue, chamber, gas path are made of corrosion-resistant materials, coatings, in particular stainless steels, plastics - this is a common practice.

* There are no heat losses due to chemical combustion incompleteness.

Features of deep utilization with condensing heat exchanger

The high efficiency of the technology makes it possible to regulate the thermal power of the system in a wide range, while maintaining its profitability: the degree of bypass, the temperature of the combustion products behind the condensing heat exchanger, etc. The heat load of the condensing heat exchanger QUT and, accordingly, the amount of condensate supplied to it from collector 22 ), is determined as optimal (and not necessarily maximum) according to technical and economic calculations and design considerations, taking into account the operating parameters, capabilities and conditions of the boiler and plant process flow diagram as a whole.

After contact with the combustion products of natural gas, the condensate retains its high quality and needs simple and inexpensive treatment - decarbonization (and even then not always) and degassing. After treatment at the chemical water treatment site (not shown), the condensate is pumped through the flow regulator to the condensate line of the station - to the deaerator, and after it to the boiler. If the condensate is not used, it is drained into the sewer.

In the condensate collection and treatment unit (Fig. 1, pos. 8, 10, Fig. 2, pos. 23–26), well-known standard equipment of deep disposal systems is used (see, for example,).

The plant produces a large amount of excess water (water vapor condensate from the combustion of hydrocarbons and blast air), so the system does not need to be recharged.

The temperature of the combustion products at the outlet of the condensing heat exchanger T 2УХ is determined by the condition of water vapor condensation in the outgoing combustion products (in the range of 40–45 0 С).

In order to prevent condensation in the gas path and especially in the chimney, bypassing is provided, i.e. bypassing part of the combustion products through the bypass channel in addition to the deep utilization unit so that the temperature of the gas mixture behind it is in the range of 70–90 0 C. Bypassing worsens all process parameters. The optimal mode is operation with bypass during the cold season, and in summer, when there is no danger of condensation and icing, without it.

The flue gas temperature of the boilers (usually 110–130 0 С) makes it possible to heat the condensate in the condensing heat exchanger before the deaerator to the required 90–100 0 С. Thus, the technology requirements for temperatures are met: both condensate heating (about 90 0 С) and product cooling combustion (up to 40 0 ​​С) before condensation.

Comparison of combustion product heat recovery technologies

When deciding on the utilization of heat from the combustion products of the boiler, one should compare the effectiveness of the proposed deep utilization system and the traditional scheme with a gas heater as the closest analogue and competitor.

For our example (see reference 1), we obtained the amount of heat recovered from deep utilization Q UT equal to 976 kW.

We assume that the temperature of the condensate at the inlet to the gas condensate heater is 60 0 C (see above), while the temperature of the combustion products at its outlet is at least 80 0 C. Then the heat of the combustion products utilized in the gas heater, i.e. heat savings, will be equal to 289 kW, which is 3.4 times less than in the deep utilization system. Thus, the “issue price” in our example is 687 kW, or, on an annualized basis, 594,490 m 3 of gas (with KIM = 0.85) worth about 3 million rubles. The gain will grow with the power of the boiler.

Advantages of deep recycling technology

In conclusion, we can conclude that, in addition to energy saving, the following results are achieved with deep utilization of the combustion products of a power plant boiler:

• reduction of emissions of toxic oxides CO and NOx, ensuring the environmental cleanliness of the process;
• obtaining additional, excess water and thereby eliminating the need for boiler make-up water;
• condensation of water vapor of combustion products is localized in one place - in the condensing heat exchanger. Apart from a slight mist entrainment after the droplet eliminator, condensation is excluded in the subsequent gas path and the associated destruction of gas ducts from the corrosive effects of moisture, the formation of ice in the path and especially in the chimney;
• in some cases, the use of a water-to-water heat exchanger becomes optional; there is no need for recirculation: mixing part of hot gases with cooled ones (or heated condensate with cold ones) in order to increase the temperature of the outgoing combustion products to prevent condensation in the gas path and chimney (saving energy, money).

Literature

1. Shadek E., Marshak B., Anokhin A., Gorshkov V. Deep utilization of waste heat from heat generators // Industrial and heating boilers and mini-CHPs. 2014. No. 2 (23).
2. Shadek E. Trigeneration as a technology for saving energy resources // Energy Saving. 2015. No. 2.
3. Shadek E., Marshak B., Krykin I., Gorshkov V. Condensation heat exchanger - modernization of boiler plants // Industrial and heating boilers and mini-CHPs. 2014. No. 3 (24).
4. Kudinov A. Energy saving in heat generating installations. M. : Mashinostroenie, 2012.
5. Ravich M. Simplified method of heat engineering calculations. M. : Publishing House of the Academy of Sciences of the USSR, 1958.
6. Berezinets P., Olkhovsky G. Promising technologies and power plants for the production of thermal and electrical energy. Section six. 6.2 gas turbine and combined cycle plants. 6.2.2. Steam and gas installations. OAO VTI. "Modern environmental technologies in the energy sector". Information collection, ed. V. Ya. Putilova. M. : MPEI Publishing House, 2007.

1 Primary source of data: surveys of hot water boilers (11 units in three boiler houses of heating networks), collection and processing of materials.

2 Method of calculation, in particular Q UT, given in.

The use of exhaust gas heat in industrial gas-fired boilers

The use of exhaust gas heat in industrial gas-fired boilers

Ph.D. Sizov V.P., Ph.D. Yuzhakov A.A., Ph.D. Kapger I.V.,
LLC "Permavtomatika" [email protected]mail .en

Abstract: the price of natural gas around the world varies significantly. It depends on the country's membership in the WTO, whether the country exports or imports its gas, the cost of gas production, the state of the industry, political decisions, etc. The price of gas in the Russian Federation due to our country's accession to the WTO will only grow 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 / m 3.

Germany - 25 rubles / m 3.

Denmark - 42 rubles / m 3.

Ukraine, Belarus - 10 rubles / m 3.

Prices are quite relative. In European countries, condensing-type boilers are widely used, their total share in the process of heat generation reaches 90%. In Russia, these boilers are generally not used due to the high cost of boilers, low gas prices and high-temperature centralized networks. As well as maintaining the system for limiting gas combustion at boiler houses.

At present, the question of a more complete use of the energy of heat carriers is becoming more and more 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 use the heat of flue gases and increase the efficiency of the boiler, calculated according to the lower calorific value, up to a value of 111%. The loss of heat with flue gases occupies the main place among the heat losses of the boiler and is 5 ¸ 12% of generated heat. Additionally, the heat of condensation of water vapor, which is formed during the combustion of fuel, can be used. The amount of heat released during the condensation of water vapor depends on the type of fuel and ranges from 3.8% for liquid fuels to 11.2% for gaseous fuels (for methane) and is determined as the difference between the highest and lowest calorific values ​​of the fuel (Table 1). ).

Table 1 - Values ​​​​of higher and lower calorific value for various types of fuel

It turns out that the exhaust gases contain both sensible heat and latent heat. Moreover, the latter can reach a value that in some cases exceeds the apparent heat. Sensible heat is the heat at 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, where the abscissa shows the enthalpy (amount of supplied heat), and the ordinate shows the temperature).

Rice. 1 - Dependence of enthalpy change for water

On the section of the 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 enthalpy change is determined by the formula (1)

(1)

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

Plot B-C shows the process of boiling water. In this case, all the heat supplied to the water is spent on converting it into steam, while the temperature remains constant - 100 ° C. Plot C-D 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 the section A-C is characterized by the formula (2)

where r = 2500 kJ/kg is the latent heat of vaporization of water at atmospheric pressure.

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

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

If water vapor is cooled, then under certain conditions they will begin to condense (pass from a gaseous state to a liquid state) and an additional amount of heat will be released at the same time (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 mixed with other gases and their parameters correspond to the parameters of the mixture. Therefore, the temperature at which condensation begins is different 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 coefficient of excess air.
The flue gas temperature at which water vapor begins to condense in the fuel combustion products is called the dew point and looks like Fig.3.

Rice. 3 - Methane dew point

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

Figure 4 - The release of heat from the vapor-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 are cooled. The second - it is not necessary to pass, as in Fig. 2, the entire condensation zone, which is not only practically impossible, but also unnecessary. This, in turn, provides various possibilities for realizing the heat balance. In other words, almost any small amount of coolant can be used to cool the flue gases.

From the foregoing, we can conclude that when calculating the efficiency of the boiler according to the lower calorific value with the subsequent utilization of the heat of flue gases and water vapor, it is possible to significantly increase the efficiency (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 from the gross calorific value, and the determination of the efficiency from the lower calorific value should be carried out only if it is necessary to compare its efficiency with that of a conventional boiler. Only in this context does an 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. For a more complete use of the heat of combustion of the exhaust gases, they must be cooled to a temperature below the dew point. In this case, the water vapor formed during the combustion of gas will condense and transfer the latent heat of vaporization to the coolant. In this case, the cooling of the flue gases should 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 heat carrier 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. In the case of using a return line as a heat carrier, 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-capacity boiler units, as a rule, are 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 condensing heat exchanger with all the ensuing consequences. There are two ways to resolve 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 partially dried gases. Thus, by heating gases, we shift the dew point to the required temperature at which the pipe is guaranteed to operate in dry mode. The second way is to use a plate heat exchanger. At the same time, the exhaust gases pass through the heat exchanger several times, thereby heating themselves.

Consider an example of calculating a 150 m typical pipe (Fig. 5-7), which has a three-layer structure. Calculations were made in the software package Ansys -CFX . It can be seen from the figures that the gas movement in the pipe has a pronounced turbulent character and, as a result, the minimum temperature on the lining may not be in the head area, as follows from the simplified empirical technique.

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

It should be noted that when the heat exchanger is installed in the 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 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 equal to 1000-600 kg / h per 1 Gcal of the useful capacity of the heat exchanger. The pH value of the condensate of combustion products during the combustion of natural gas is 4.5-4.7, which corresponds to an acidic environment. In the 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 apply the 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 too large a difference in enthalpy per unit volume of substances, and the resulting technical problem is the development of a heat exchange surface on the gas side. The industry of the Russian Federation commercially produces similar heat exchangers such as KSK, VNV, etc.. Let us consider how developed the heat exchange surface from the gas side is on the operating structure (Fig. 8). An ordinary tube, inside which water (liquid) flows, and from the outside, air (exhaust gases) flows around the radiator fins. The calculated ratio of the heater will be expressed by a certain

Rice. 8 - drawing of the heater tube.

coefficient

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

where S bunk - the outer area of ​​\u200b\u200bthe heat exchanger mm 2, and S ext is the inner area of ​​the tube.

In the geometric calculations of the structure, we obtain K =15. This means that the outer area of ​​the tube is 15 times the inner area. This is because the enthalpy of air per unit volume is many times less than the enthalpy of water per unit volume. 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 \u003d 4.183 KJ / l * K.

enthalpy of air: E voz \u003d 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 bunk /S ext . Ideally, in such a heat exchanger, the coefficient K should be 5319, but since the outer surface is 15 times developed in relation to the inner, the difference in enthalpy between air and water decreases to the value K \u003d (5319/15) \u003d 354. Technically develop the ratio of the areas of the inner and outer surfaces until a ratio is obtained 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 from the nozzle into the exhaust gas (condensate of the same gas). We spray it in such an amount in relation 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 the absolute humidity of gas with a relative humidity of 100% for water at various temperatures and atmospheric pressure.

It can be seen from Fig. 3 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, then its temperature will drop sharply, the density will increase, and the enthalpy will rise sharply. It should be noted that spraying water above a relative humidity of 100% does not make sense, because. when the relative humidity threshold exceeds 100%, the sprayed water will stop evaporating into gas. Let's carry out a small calculation of the required amount of sprayed water for the following conditions: T gn - initial gas temperature equal to 120 0 С, T dew - gas dew point 60 0 C (129.70 g / m 3), required n ait: T gk - the final temperature of the gas and M in - the mass of water dispersed in the gas (kg.)

Decision. All calculations are carried out with respect to 1 m 3 of gas. The complexity of the calculations is determined by the fact that as a result of spraying, 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.

Calculate the amount of energy given by the gas to water during the evaporation of water

where: s is the heat capacity of the gas (1 kJ/kg.K), m - mass of gas (1 kg / m 3)

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 the substitution, we get the function

(5)

In this case, 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. By selection and calculations, we obtained the value m = 22 gr, Т gk = 65 0 С. Let us calculate the actual enthalpy of the obtained 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 get the sum of two enthalpies. The enthalpy of the gas and the enthalpy of the condensed water.

E woz \u003d Eg + Evod

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

Evodwe calculate with respect to the table. 2. We have gas cooling down from 65 0 C to 64 0 C, it releases 6.58 grams of water. The enthalpy of condensation is Evod=2500 J/g or in our case Evod \u003d 16.45 KJ / m 3

We sum up the enthalpy of the condensed water and the enthalpy of the gas.

E woz \u003d 17.55 (J / l * K)

As we can see by spraying water, we managed to increase the enthalpy of the gas by 22.3 times. If, before the spraying of water, the enthalpy of the gas was E woz \u003d 0.7864 J / l * K. (at a temperature of 130 0 C). Then after spraying, the enthalpy is E woz \u003d 17.55 (J / l * K). And this means that in order to obtain the same thermal energy on the same standard heat exchanger of the KSK, VNV type, 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 realizable dimensions.

Another important issue in creating such systems is the analysis of the sputtering process, i.e. What is the diameter of a drop required for the evaporation of water in a gas? If a sufficiently small droplet (for example, 5 μM), then the lifetime of this droplet in the gas until complete evaporation is rather short. And if a drop has a size of, for example, 600 μM, then naturally it stays in the gas for a much longer time until complete evaporation. The solution of this physical problem is rather 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 total evaporation time ( ) drops has the form

(6)

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

Then, according to (6), the lifetime of a drop 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 microns. (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 gas flow rate and the geometric dimensions of the gas duct, it is easy to calculate the irrigation system for the gas duct.

Below, we consider the implementation of the system design, taking into account the relationships obtained above. It is believed that the flue gas heat exchanger must work depending on the outside temperature, otherwise the house pipe is destroyed when condensate forms in it. However, it is possible to manufacture a heat exchanger that operates regardless of the outdoor temperature and has a better heat removal from exhaust gases, even to negative temperatures, while the temperature of the exhaust gases will be, for example, +10 0 С (the dew point of these gases will be 0 0 С). This is ensured by the fact that during heat exchange, the controller calculates the dew point, heat transfer energy and other parameters. Consider the technological scheme of the proposed system (Fig. 9).

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

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

In the heat exchanger, gases enter the heat exchanger (e) where they cool down, 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 heat exchanger can be adjusted by the gate valve (b). This regulation is necessary to increase the efficiency of the heat exchanger. Since, during the condensation of moisture, its mass in the gases decreases, depending on how much the gases were 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 number come from. Consider the chemical formula of the methane oxidation reaction (3).

For the oxidation of 1m 3 of methane, 2m 3 of oxygen is needed. But since the oxygen in the air contains only 20%, then the air for the oxidation of 1m 3 of methane will require 10m 3. After burning this mixture, we get: 1m 3 carbon dioxide, 2 m 3 water vapor and 8m 3 nitrogen and other gases. We can remove from the waste gases by condensing a little less than 2/11 of all waste gases in the form of water. To do this, the exhaust gas must be cooled to outside temperature. With the allocation of the appropriate proportion of water. The air taken from the street for combustion also contains negligible moisture.

The released water is removed at the bottom of the heat exchanger. Accordingly, if along the way the heat recovery boiler (d) - heat recovery unit (e) passes the entire gas composition of 11/11 parts, then only 9/11 parts of the exhaust gas can pass through the other side of the heat exchanger (e). The rest - up to 2/11 parts of 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 slightly opened. This will separate the exhaust gases. Part will pass through the heat exchanger (d), and part through the gate (b). When the gate (b) is fully opened, the gases will pass without cooling and the readings of temperature sensors 1 and 2 will coincide.

An irrigation plant with a pump H and a group of nozzles is installed on the gas path. Gases are irrigated with water released during condensation. Nozzles that spray moisture into the gas, sharply raise 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 dispersed 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 velocity decreases abruptly. All these changes significantly change the heat transfer efficiency for the better. The amount of water to be sprayed is determined by the controller and is related to temperature and gas flow. The gas temperature in front of the heat exchanger is controlled by temperature sensor 6.

Then 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 the combustion air. The temperature of air supply to such a heat exchanger can reach -35 0 С. This temperature depends on the minimum outdoor air temperature in the given region. Since part 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 antifreeze be poured into the heat exchanger, for example. A damper (c) is installed between the heat exchangers. This gate also works in discrete mode. With warming outside, the meaning of heat extraction in the heat exchanger (g) disappears. It stops its work and the damper (c) opens completely, passing the exhaust gases, bypassing the heat recovery unit (g).

The temperature of the cooled gases is determined by the temperature sensor (3). Further, these gases are sent to the recuperator (d). Having passed it, they heat up to a certain temperature proportional to the cooling of gases on the other side of the heat exchanger. The damper (g) is needed to regulate the operation of heat exchange in the heat exchanger, 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 heat exchanger to avoid dew points in the pipe. If it is hot outside, then the gate (d) is open, as is the gate (b).

FINDINGS:

The increase in heat transfer in the liquid / gas heat exchanger occurs due to a sharp jump in the enthalpy of the gas. But the proposed spraying of water should be strictly dosed. In addition, the dosing of water into the flue gases takes into account the outside temperature.

The obtained calculation method allows 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 condensing devices.

With the proposed method, the design of the boiler does not change, but is only being finalized. The cost of completion 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 decreases significantly, and the load on the smoke exhauster decreases.

LITERATURE:

1.Aronov I.Z. Use of heat from exhaust gases of gasified boiler houses. - M .: "Energy", 1967. - 192 p.

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

Description:

Bryansk heating 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

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 per 1 Gcal / h of heat received are more than 2 times lower in comparison if a new boiler house was being built, and 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 and economic indicators are understandable.

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 lowest ambient temperatures.

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

UUTG contains contact and plate heat exchangers 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 circulating water, only cold tap water should be used, 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 the heating system of the 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.