Deep utilization of flue gas heat. Utilization of waste gas heat in industrial gas-fired boiler houses
Currently, the temperature of the exhaust flue gases behind the boiler is taken not lower than 120-130 ° C for two reasons: to exclude condensation of water vapor on hogs, gas ducts and chimneys and to increase the natural draft, which reduces the head of the smoke exhauster. In this case, the heat of the flue gases and the latent heat of vaporization of water vapor can be advantageously used. The use of the heat of the exhaust flue gases and the latent heat of vaporization of water vapor is called the method of deep utilization of the heat of flue gases. Currently there are various technologies implementations of this method tested in Russian Federation and found widespread use abroad. The method of deep utilization of the heat of flue gases makes it possible to increase the efficiency of the fuel-consuming installation by 2-3%, which corresponds to a decrease in fuel consumption by 4-5 kg of fuel equivalent. per 1 Gcal of generated heat. When introducing this method, there are technical difficulties and limitations associated mainly with the complexity of calculating the heat and mass transfer process with deep utilization of heat from exhaust flue gases and the need to automate the process, however, these difficulties can be solved with the modern level of technology.
For the widespread introduction of this method, it is necessary to develop guidelines for the calculation and installation of systems for deep utilization of flue gas heat and the adoption of legal acts prohibiting the commissioning of fuel-using natural gas installations without the use of deep utilization of flue gas heat.
1. Formulation of the problem according to the considered method (technology) of increasing energy efficiency; forecast of excessive consumption of energy resources, or a description of other possible consequences on a national scale, while maintaining the current situation
Currently, the temperature of the exhaust flue gases behind the boiler is taken not lower than 120-130 ° C for two reasons: to exclude condensation of water vapor on hogs, gas ducts and chimneys and to increase the natural draft, which reduces the head of the smoke exhauster. In this case, the temperature of the flue gases directly affects the value of q2 - heat loss with flue gases, one of the main components of the heat balance of the boiler. For example, a decrease in the temperature of flue gases by 40 ° C when the boiler is fired with natural gas and an excess air ratio of 1.2 increases the gross boiler efficiency by 1.9%. This does not take into account the latent heat of vaporization of combustion products. To date, the vast majority of hot water and steam boiler units in our country that burn natural gas are not equipped with installations that use the latent heat of vaporization of water vapor. This heat is lost along with the flue gases.
2. Availability of methods, methods, technologies, etc. to solve the indicated problem
Currently, methods of deep utilization of waste gas heat (VER) are used by using recuperative, mixing, combined devices operating at different techniques utilization of the heat contained in the flue gases. At the same time, these technologies are used in the majority of boilers commissioned abroad, burning natural gas and biomass.
3. Short description the proposed method, its novelty and awareness of it, the availability of development programs; result in case of mass implementation on a national scale
The most commonly used method for deep utilization of flue gas heat is that the combustion products of natural gas after the boiler (or after a water economizer) with a temperature of 130-150 ° C are divided into two streams. Approximately 70-80% of the gases are directed through the main flue and enter the surface-type condensation heat exchanger, the rest of the gases are directed to the bypass flue. In the heat exchanger, the combustion products are cooled to 40-50 ° C, while part of the water vapor condenses, which makes it possible to usefully use both the physical heat of flue gases and the latent heat of condensation of part of the water vapor contained in them. The cooled combustion products after the droplet separator are mixed with non-cooled combustion products passing through the bypass flue and at a temperature of 65-70 ° C are discharged by the smoke exhauster through the chimney into the atmosphere. Initial water for the needs of chemical water treatment or air that is then supplied for combustion can be used as a heated medium in a heat exchanger. To intensify the heat exchange in the heat exchanger, it is possible to supply a vapor atmospheric deaerator into the main gas duct. It should also be noted the possibility of using condensed demineralized water vapor as source water. The result of the introduction of this method is an increase in the boiler gross efficiency by 2-3%, taking into account the use of the latent heat of vaporization of water vapor.
4. Forecast of the effectiveness of the method in the long term, taking into account:
- growth of prices for energy resources;
- growth in the well-being of the population;
- the introduction of new environmental requirements;
- other factors.
This method increases the efficiency of natural gas combustion and reduces emissions of nitrogen oxides into the atmosphere due to their dissolution in condensing water vapor.
5. List of subscriber groups and objects where it is possible to use this technology with maximum efficiency; the need for additional research to expand the list
This method may be used in steam and hot water boilers using natural and liquefied gas, biofuel as fuel. To expand the list of objects where this method can be used, it is necessary to study the processes of heat and mass transfer of combustion products of fuel oil, light diesel fuel and various grades of coal.
6. Outline the reasons why the proposed energy efficient technologies are not applied on a mass scale; outline an action plan to remove existing barriers
This method is not widely used in the Russian Federation, as a rule, for three reasons:
- Lack of awareness of the method;
- The presence of technical limitations and difficulties in the implementation of the method;
- Lack of funding.
7. The presence of technical and other restrictions on the application of the method at various objects; in the absence of information on possible limitations, they must be determined by testing
The technical limitations and difficulties in implementing the method include:
- The complexity of calculating the process of utilization of wet gases, since the process of heat transfer is accompanied by processes of mass transfer;
- The need to maintain the set values of temperature and humidity of the exhaust flue gases, in order to avoid condensation of vapors in the gas ducts and the chimney;
- The need to avoid freezing of heat exchange surfaces when heating cold gases;
- At the same time, it is necessary to carry out tests of gas ducts and chimneys treated with modern anti-corrosion coatings for the possibility of reducing the restrictions on the temperature and humidity of the flue gases leaving after the heat recovery unit.
8. The need for R&D and additional testing; themes and goals of work
The need for R&D and additional testing is given in clauses 5 and 7.
9. Existing measures of encouragement, coercion, incentives for the implementation of the proposed method and the need to improve them
There are no existing measures to encourage and coerce the introduction of this method. The interest in reducing fuel consumption and nitrogen oxide emissions into the atmosphere can stimulate the introduction of this method.
10. The need to develop new or change existing laws and regulations
It is necessary to develop guidelines for the calculation and installation of systems for deep utilization of heat from flue gases. Perhaps, it is necessary to adopt legal acts prohibiting the commissioning of fuel-using plants using natural gas without the use of deep utilization of flue gas heat.
11. Availability of decrees, rules, instructions, standards, requirements, prohibitive measures and other documents regulating the use of this method and mandatory for execution; the need to amend them or the need to change the very principles of forming these documents; the presence of pre-existing normative documents, regulations and the need for their restoration
There are no questions about the application of this method in the existing regulatory framework.
12. Availability of implemented pilot projects, analysis of their real effectiveness, identified shortcomings and proposals for improving the technology, taking into account the accumulated experience
There is no data on the large-scale implementation of this method in the Russian Federation, there is experience of implementation at RAO UES CHPPs and, as mentioned above, a lot of experience has been accumulated in the deep utilization of flue gases abroad. The All-Russian Thermal Engineering Institute has carried out design studies of installations for deep utilization of heat of combustion products for hot-water boilers PTVM (KVGM). The disadvantages of this method and suggestions for improvement are given in clause 7.
13. Possibility of influencing other processes during the massive introduction of this technology (changes in the environmental situation, possible impact on human health, increasing the reliability of power supply, changing daily or seasonal schedules of power equipment loading, changing economic indicators of energy generation and transmission, etc.)
Mass introduction of this method will reduce fuel consumption by 4-5 kg of fuel equivalent. per one Gcal of generated heat and will affect the environmental situation by reducing emissions of nitrogen oxides.
14. Availability and sufficiency of production facilities in Russia and other countries for the mass implementation of the method
The specialized production facilities in the Russian Federation are able to ensure the implementation of this method, but not in a monoblock version; when using foreign technologies, a monoblock version is possible.
15. The need for special training of qualified personnel for the operation of the introduced technology and the development of production
To implement this method, the existing specialized training of specialists is required. It is possible to organize specialized seminars on the implementation of this method.
16. Prospective ways of implementation:
1) commercial financing (with recoupment of costs);
2) a competition for the implementation of investment projects developed as a result of performance of work on energy planning for the development of a region, city, settlement;
3) budget financing for efficient energy saving projects with long payback periods;
4) the introduction of prohibitions and mandatory requirements for the application, supervision over their observance;
5) other suggestions.
The proposed implementation methods are:
- budget financing;
- attraction of investments (payback period 5-7 years);
- introduction of requirements for the commissioning of new fuel-consuming plants.
To add a description of the energy-saving technology to the Catalog, fill out the questionnaire and send it to marked "to the Catalog".
I propose for consideration the activities for the disposal of flue gases. Flue gases are abundant in any village and city. Most 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 to use the smoke of gas boiler houses (industrial or private houses) is the cleanest type of flue gas, which contains the minimum amount of harmful impurities. You can also use the smoke of boiler houses 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 the flue gas are nitrogen, carbon dioxide and water vapor. The 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 extinguishing, for the transportation and storage of flammable and explosive media, as a protective gas to prevent oxidation of easily oxidized substances and materials, to prevent corrosion of tanks, purge pipelines and tanks, to create inert media in silos. Nitrogen protection prevents the growth of bacteria, is used to clean environments from insects and microbes. IN Food Industry nitrogen atmospheres are often used as a means of increasing the shelf life of perishable foods. 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 use is even greater and its price is much higher.
I propose to get more complete information about him. Usually carbon dioxide is stored in 40-liter cylinders painted black with a yellow label “carbon dioxide”. A more correct name for СО2, "carbon dioxide", but everyone is already accustomed to the name "carbon dioxide", it stuck for СО2 and therefore the inscription "carbon dioxide" on the cylinders is still preserved. There is carbon dioxide in cylinders in liquid form. Carbon dioxide is odorless, non-toxic, non-flammable and non-explosive. It is a substance naturally formed in the human body. In the air exhaled by a person, it usually contains 4.5%. The main application of carbon dioxide is in carbonation and sale in bottling beverages, it is used as a shielding gas during welding with the use of welding semiautomatic devices, 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 water carbon dioxide) the production of microalgae during their artificial cultivation, to maintain and improve the quality of feed and products, to produce dry ice and use it in cryoblasting installations (cleaning surfaces from contamination) and to obtain low temperatures during storage and transportation of food products, etc.
Carbon dioxide is a popular commodity everywhere and the demand 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 produced 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 means of special fuel combustion in the installation itself.
Now the economic side of the matter. The unit can operate on any type of fuel. When fuel is burned (specifically for the production of carbon dioxide), the following amount of CO2 is released:
natural gas (methane) - 1.9 kg of CO2 from combustion of 1 cubic meter m of gas;
bituminous coal, different deposits - 2.1-2.7 kg of СО2 from combustion of 1 kg of fuel;
propane, butane, diesel fuel, fuel oil - 3.0 kg of CO2 from combustion of 1 kg of fuel.
It will not be possible to extract completely all of the emitted carbon dioxide, and up to 90% (it is possible to achieve 95% extraction) 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 cylinder of carbon dioxide.
It is not that 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.
At the highest tariff (Moscow) it is 60 rubles. 40-liter. carbon dioxide cylinder. In the case of extracting CO2 from the flue gases of boiler houses, the cost of producing carbon dioxide is reduced, since the cost of fuel decreases and the profit from the installation increases. The installation can work around the clock, in automatic mode with minimal human involvement in the process of obtaining carbon dioxide. The productivity of the installation depends on the amount of CO2 contained in the flue gas, the design of the installation 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). The monthly proceeds from the sale of carbon dioxide in this case reaches: 500 rubles / ball. x 25 points / day x 30 days = 375,000 rubles. The heat released during combustion can be used simultaneously for space heating, and there will be no waste of fuel in this case. It should be borne in mind that the environmental situation at the place of extraction of carbon dioxide from flue gases is only improving, since CO2 emissions into the atmosphere are decreasing.
The method of extracting carbon dioxide from flue gases obtained from burning wood waste (waste from logging and wood processing, carpentry shops, etc.) also recommends itself quite well. In this case, the same carbon dioxide plant is supplemented with a wood gas generator (factory or self-made) to obtain wood gas. Wood waste (wood chips, wood chips, shavings, sawdust, etc.) are poured into the bunker of the gas generator 1-2 times a day, otherwise the unit operates in the same mode as in the above.
The output of carbon dioxide from 1 ton of wood waste is 66 cylinders. The proceeds from one ton of waste is (at the price of a carbon dioxide cylinder of 500 rubles): 500 rubles / ball. x 66 points. = 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 delivery of waste from other woodworking and carpentry workshops, the revenue becomes even greater.
The option of obtaining carbon dioxide from combustion is also possible car tires, which also only benefits our ecology.
In the case of production of carbon dioxide in an amount greater than the local sales market can consume, 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, baking powder, etc. etc.) up to the production of gasoline from carbon dioxide.
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UDC 622.73.002.5
Gorfin O.S. Gorfin O.S.
Gorfin Oleg Semenovich, Ph.D., prof. Department of Peat Machines and Equipment, Tver State Technical University (TvSTU). Tver, Academic, 12. [email protected] Gorfin Oleg S., PhD, Professor of the Chair of Peat Machinery and Equipment of the Tver State Technical University. Tver, Academicheskaya, 12
Zyuzin B.F. Zyuzin B.F.
Zyuzin Boris Fedorovich, doctor of technical sciences, prof., Head. Department of Peat Machines and Equipment, TvSTU [email protected] Zyuzin Boris F., Dr. Sc., Professor, Head of the Chair of Peat Machinery and Equipment of the Tver State Technical University
Mikhailov A.V. Mikhailov A.V.
Mikhailov Alexander Viktorovich, Doctor of Technical Sciences, Professor of the Department of Mechanical Engineering, National Mineral Resources University "Mining", St. Petersburg, Leninsky Prospect, 55, bldg. 1, apt. 635. [email protected] Mikhailov Alexander V., Dr. Sc., Professor of the Chair of Machine Building of the National Mining University, St. Petersburg, Leninsky pr., 55, building 1, Apt. 635
THE DEVICE FOR DEEP
FOR DEEP UTILIZATION OF HEAT
HEAT RECOVERY OF COMBUSTION GASES
SMOKE GAS SURFACE TYPE OF SUPERFICIAL TYPE
Annotation. The article discusses the design of a heat exchanger, in which the method of transferring the recovered heat energy from the heat carrier to the medium receiving heat is changed, which makes it possible to utilize the heat of vaporization of fuel moisture during deep cooling of flue gases and fully use it for heating the cooling water, directed without additional processing for the needs of the steam turbine cycle. The design allows in the process of heat recovery to purify flue gases from sulfuric and sulfurous acids, and the purified condensate can be used as hot water... Abstract. The article describes the design of heat exchanger, in which new method is used for transmitting of recycled heat from the heat carrier to the heat receiver. The construction allows to utilize the heat of the vaporization of fuel moisture while the deep cooling of flue gases and to fully use it for heating the cooling water allocated without further processing to the needs of steam turbine cycle. The design allows purifying of waste flue gases from sulfur and sulphurous acid and using the purified condensate as hot water.
Key words: CHP; boiler installations; heat exchanger of surface type; deep cooling of flue gases; utilization of the heat of vaporization of fuel moisture. Key words: Combined heat and power plant; boiler installations; heat utilizer of superficial type; deep cooling of combustion gases; utilization of warmth of steam formation of fuel moisture.
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In boiler houses of thermal power plants, the energy of vaporization of moisture and fuel, together with flue gases, is emitted into the atmosphere.
In gasified boiler houses, heat losses with flue gases can reach 25%. In boiler houses operating on solid fuels, heat losses are even higher.
For the technological needs of TBZ, milled peat with a moisture content of up to 50% is burned in boiler houses. This means that half of the mass of the fuel is water, which, when burned, turns into steam and the loss of energy for vaporization of moisture in the fuel reaches 50%.
Reducing heat losses is not only a matter of saving fuel, but also reducing harmful emissions into the atmosphere.
Reduction of heat energy losses is possible when using heat exchangers of various designs.
Condensing heat exchangers, in which the flue gases are cooled below the dew point, make it possible to utilize the latent heat of condensation of water vapor of fuel moisture.
The most widespread are contact and surface heat exchangers. Contact heat exchangers are widely used in industry and power engineering due to their simple design, low metal consumption and high heat exchange rate (scrubbers, cooling towers). But they have a significant drawback: cooling water becomes polluted due to its contact with combustion products - flue gases.
In this respect, surface heat exchangers are more attractive, which do not have direct contact between the combustion products and the coolant, the disadvantage of which is the relatively low temperature of its heating, equal to the temperature of the wet thermometer (50 ... 60 ° C).
The advantages and disadvantages of existing heat recovery units are widely covered in special literature.
The efficiency of surface heat exchangers can be significantly increased by changing the method of heat exchange between the medium that gives off heat and receives it, as is done in the proposed design of the heat exchanger.
The scheme of a heat exchanger for deep utilization of flue gas heat is shown
on the picture. The heat exchanger body 1 rests on the base 2. In the middle part of the body there is an insulated reservoir 3 in the form of a prism, filled with pre-purified running water. Water enters from above through the nozzle 4 and is removed at the bottom of the housing 1 by pump 5 through gate 6.
On the two end sides of the reservoir 3 are located insulated from the middle part of the jacket 7 and 8, the cavities of which through the volume of the reservoir 3 are interconnected by rows of horizontal parallel pipes forming bundles of pipes 9 in which the gases move in one direction. The shirt 7 is divided into sections: lower and upper single 10 (height h) and the remaining 11 - double (height 2h); the jacket 8 has only double sections 11. The lower single section 10 of the jacket 7 is connected by a bundle of pipes 9 to the lower part of the double section 11 of the jacket 8. Further, the upper part of this double section 11 of the jacket 8 is connected by a bundle of pipes 9 to the lower part of the next double section 11 of the jacket 7 and etc. In succession, the upper part of the section of one jacket is connected to the lower part of the section of the second jacket, and the upper part of this section is connected by a bundle of pipes 9 to the lower part of the next section of the first jacket, thus forming a coil of variable cross-section: bundles of pipes 9 are periodically alternated by the volumes of the jacket sections. In the lower part of the coil there is a branch pipe 12 for supplying flue gases, in the upper part there is a branch pipe 13 for exhausting gases. The branch pipes 12 and 13 are interconnected by a bypass gas duct 4, in which a gate 15 is installed, designed to redistribute part of the hot flue gases bypassing the heat exchanger into the chimney (not shown in the figure).
The flue gases enter the heat exchanger and are divided into two streams: the main part (about 80%) of the combustion products enters the lower single section 10 (height h) of the jacket 7 and is directed through the pipes of the bundle 9 to the heat exchanger coil. The rest (about 20%) enters bypass flue 14. Gas redistribution is performed to increase the temperature of cooled flue gases downstream of the heat exchanger to 60-70 ° C in order to prevent possible condensation of fuel moisture vapor residues in the tail sections of the system.
Flue gases are supplied to the heat exchanger from below through the branch pipe 12, and are removed in
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Drawing. Heat exchanger diagram (view A - connection of pipes with jackets) Figure. The scheme of the heatutilizer (a look A - connection of pipes with shirts)
in the upper part of the unit - branch pipe 13. Pre-prepared cold water fills the tank from above through branch pipe 4, and is removed by pump 5 and gate 6 located in the lower part of housing 1. Counterflow of water and flue gases increases the efficiency of heat exchange.
The movement of flue gases through the heat exchanger is carried out by the technological smoke exhauster of the boiler room. To overcome the additional resistance created by the heat exchanger, it is possible to install a more powerful exhaust fan. It should be borne in mind that the additional hydraulic resistance is partially overcome by reducing the volume of combustion products due to the condensation of water vapor of the flue gases.
The design of the heat exchanger provides not only efficient utilization of the heat of vaporization of fuel moisture, but also the removal of the resulting condensate from the flue gas stream.
The volume of the jacket sections 7 and 8 is greater than the volume of the pipes connecting them, therefore the gas velocity in them decreases.
Flue gases entering the heat exchanger have a temperature of 150-160 ° C. Sulfuric and sulphurous acids condense at a temperature of 130-140 ° C, therefore, the condensation of acids occurs in the initial part of the coil. With a decrease in the gas flow rate in the expanding parts of the coil - jacket sections and an increase in the density of condensate of sulfuric and sulfurous acids in the liquid state compared to the density in the gaseous state, multiple changes in the direction of the flue gas flow (inertial separation), the acid condensate precipitates and is washed out from gases part of the condensate of water vapor into the condensate collector of acids 16, from where, when the shutter 17 is triggered, it is removed into the industrial sewage system.
Most of the condensate - water vapor condensate is released with a further decrease in the gas temperature to 60-70 ° С in the upper part of the coil and enters the condensate moisture collector 18, from where it can be used as hot water without additional processing.
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Coil pipes must be made of anti-corrosion material or with an internal anti-corrosion coating. To prevent corrosion, all surfaces of the heat exchanger and connecting pipelines should be gummed.
In this design of the heat exchanger, flue gases containing fuel moisture vapor move through the pipes of the coil. In this case, the heat transfer coefficient is no more than 10,000 W / (m2 ° C), due to which the efficiency of heat transfer is sharply increased. The pipes of the coil are located directly in the volume of the coolant, therefore the heat exchange takes place in a constant contact way. This allows deep cooling of flue gases to a temperature of 40-45 ° C, and all the recovered heat of vaporization of fuel moisture is transferred to the cooling water. The cooling water does not come into contact with flue gases, therefore, it can be used without additional treatment in the steam-turbine cycle and by hot water consumers (in the hot water supply system, heating the return network water, technological needs of enterprises, in greenhouses and greenhouse farms, etc.). This is the main advantage of the proposed design of the heat exchanger.
The advantage of the proposed device is also the fact that the heat exchanger regulates the time of heat transfer from the hot flue gas environment of the coolant, and therefore its temperature, by changing the flow rate of the liquid using a gate.
To check the results of using the heat exchanger, heat and technical calculations were made for the boiler plant with a boiler steam output of 30 t of steam / h (temperature 425 ° C, pressure 3.8 MPa). The furnace burns 17.2 t / h of milled peat with a moisture content of 50%.
Peat with a moisture content of 50% contains 8.6 t / h of moisture, which, when peat is burned, turns into flue gases.
Dry air (flue gas) consumption
Gfl. g = a x L x G, ^^ = 1.365 x 3.25 x 17 200 = 76 300 kg d. / h,
where L = 3.25 kg dry. g / kg of peat is the theoretically required amount of air for combustion; a = 1.365 - the average coefficient of air leakage.
1. Heat of utilization of flue gases Enthalpy of flue gases
J = ccm x t + 2.5 d, ^ w / kG. dry gas,
where ccm is the heat capacity of the flue gases (heat capacity of the mixture), w / kg ° K, t is the temperature of the gases, ° K, d is the moisture content of the flue gases, G. moisture / kg. d. g.
Specific heat of the mixture
ssM = sr + 0.001dcn,
where cr, cn - heat capacity of dry gas (flue gases) and steam, respectively.
1.1. Flue gases at the inlet to the heat exchanger with a temperature of 150 - 160 ° C, we take Ts.y. = 150 ° C; cn = 1.93 - heat capacity of steam; cg = 1.017 is the heat capacity of dry flue gases at a temperature of 150 ° C; d150, G / kg. dry d - moisture content at 150 ° C.
d150 = GM./Gfl. g. = 8600/76 300 x 103 =
112.7 g / kg. dry G,
where Gvl. = 8600 kg / h - the mass of moisture in the fuel. ccm = 1.017 + 0.001 x 112.7 x 1.93 = 1.2345 ^ w / kg.
Flue gas enthalpy J150 = 1.2345 x 150 + 2.5 x 112.7 = 466.9 ^ l / kg.
1.2. Flue gases at the outlet of the heat exchanger with a temperature of 40 ° С
ccm = 1.017 + 0.001 x 50 x 1.93 = 1.103 ^ w / kG ° C.
d40 = 50 g / kg dry g.
J40 = 1.103 x 40 + 2.5 x 50 = 167.6 ^ w / kg.
1.3. In the heat exchanger, 20% of the gases pass through the bypass gas duct, and 80% - through the coil.
The mass of gases passing through the coil and participating in heat exchange
GzM = 0.8Gfl. g. = 0.8 x 76 300 = 61 040 kg / h.
1.4. Heat recovery
Ex = (J150 - J40) x ^ m = (466.9 - 167.68) x
61 040 = 18.26 x 106, ^ l / h.
This heat is spent on heating the cooling water.
Qx ™ = W x sv x (t2 - t4),
where W is the water consumption, kg / h; sv = 4.19 ^ w / kg ° C - heat capacity of water; t 2, t4 - water temperature
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respectively at the outlet and inlet to the heat exchanger; we take tx = 8 ° С.
2. Consumption of cooling water, kg / s
W = Qyra / (sv x (t2 - 8) = (18.26 / 4.19) x 106 / (t2 - 8) / 3600 = 4.36 x 106 / (t2 -8) x 3600.
Using the obtained dependence, it is possible to determine the flow rate of cooling water of the required temperature, for example:
^, ° С 25 50 75
W, kg / s 71.1 28.8 18.0
3. Condensate consumption G ^^ is:
^ ond = GBM (d150 - d40) = 61.0 x (112.7 - 50) =
4. Checking the possibility of condensation of residual moisture vaporization of the fuel in the tail elements of the system.
Average moisture content of flue gases at the outlet of the heat exchanger
^ p = (d150 x 0.2 Gd. + d40 x 0.8 Gd. y.) / GA r1 =
112.7 x 0.2 + 50 x 0.8 = 62.5 g / kg dry. G.
On the J-d diagram, this moisture content corresponds to a dew point temperature tp. R. = 56 ° C.
The actual temperature of flue gases at the outlet of the heat exchanger is
tcjmKT = ti50 x 0.2 + t40 x 0.8 = 150 x 0.2 + 40 x 0.8 = 64 ° C.
Since the actual temperature of the flue gases behind the heat recovery unit is higher than the dew point, condensation of moisture vapor in the fuel in the tail elements of the system will not occur.
5. Coefficient of efficiency
5.1. Efficiency of utilization of the heat of vaporization of moisture in the fuel.
The amount of heat supplied to the heat exchanger
Q ^ h = J150 x Gft r = 466.9 x 76 300 =
35.6 x 106, M Dzh / h.
KPDutl. Q = (18.26 / 35.6) x 100 = 51.3%,
where 18.26 x 106, MJ / h is the heat of utilization of vaporization of fuel moisture.
5.2. Fuel moisture recovery efficiency
KPDutl. W = ^ cond / W) x 100 = (3825/8600) x 100 = 44.5%.
Thus, the proposed heat exchanger and its method of operation provide deep cooling of flue gases. Due to the condensation of moisture vapor in the fuel, the efficiency of heat exchange between the flue gases and the coolant is sharply increased. In this case, all the recovered latent heat of vaporization is transferred to heat the coolant, which can be used in the steam turbine cycle without additional processing.
During the operation of the heat exchanger, the flue gases are cleaned from sulfuric and sulfurous acids, and therefore the vapor condensate can be used for hot heat supply.
Calculations show that the efficiency is:
When utilizing the heat of vaporization
fuel moisture - 51.3%
Fuel moisture - 44.5%.
Bibliography
1. Aronov, I.Z. Contact heating of water by natural gas combustion products. - L .: Nedra, 1990 .-- 280 p.
2. Kudinov, A.A. Energy saving in heat power engineering and heat technologies. - M .: Mashinostroenie, 2011 .-- 373 p.
3. Pat. 2555919 (RU). (51) IPC F22B 1 | 18 (20006.01). Heat exchanger for deep recovery of heat from flue gases of surface type and method of its operation /
O.S. Gorfin, B.F. Zyuzin // Discovery. Inventions. - 2015. - No. 19.
4. Gorfin, O.S., Mikhailov, A.V. Peat processing machinery and equipment. Part 1. Production of peat briquettes. - Tver: TvGTU 2013 .-- 250 p.
In. V. Getman, N. V. Lezhneva METHODS OF RECOVERY OF HEAT OF OUTLET GASES FROM POWER PLANTS
Key words: gas turbine plants, combined cycle plants
The paper discusses various methods for utilizing the heat of exhaust gases from power plants with the aim of increasing their efficiency, saving fossil fuels and increasing 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 accumulation 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 problems, including the development of modern highly efficient technologies for the production of electrical and thermal energy.
One of these tasks is to improve the efficiency of power plants in order to save fossil fuels and increase energy capacity. Most
promising in this respect are gas turbine plants, with exhaust gases of which up to 20% of the heat is emitted.
There are several ways to improve the efficiency of gas turbine engines, including:
Gas temperature rise in front of the turbine for a gas turbine with a simple thermodynamic cycle,
Heat recovery application,
Heat utilization of flue gases in binary cycles,
Creation of a gas turbine plant according to a complex thermodynamic scheme, etc.
The most promising direction is the joint use of gas turbine and steam turbine units (GTU and STU) in order to improve their economic and environmental characteristics.
Gas turbine and combined plants created with their use, with technically achievable parameters at present, provide a significant increase in the efficiency of heat and electricity production.
The widespread use of binary CCGT units, as well as various combined schemes for the technical re-equipment of TPPs, 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 unit and an increase in the share of gas turbine capacity. Important value
It also has the fact that, in addition to gaining in efficiency, such systems require significantly lower capital costs, their unit cost is 1.5 - 2 times less than the cost of gas-fuel oil steam turbine units and CCGT units with a minimum gas turbine capacity.
According to the data, three main directions of using GTU and CCGT in power engineering can be distinguished.
The first, widely used in industrialized countries, is the use of CCGT at large condensing thermal power plants operating on gas. In this case, it is most effective to use a utilization-type CCGT with a large share of gas turbine capacity (Fig. 1).
The use of a CCGT unit makes it possible to increase the efficiency of fuel combustion at TPPs by ~ 11-15% (CCGT unit with gas discharge into the boiler), by ~ 25-30% (binary CCGT units).
Until recently, extensive work on the introduction of CCGT in Russia was not carried out. Nevertheless, single samples of such installations have been used for a long time and have been successfully used, for example, a CCGT unit with a high-pressure steam generator (HPG) of the VPG-50 type of the head power unit CCGT-120 and 3 modernized power units with VPG-120 at the CHPP-2 branch of JSC TGK-1 "; CCGT-200 (150) with VPG-450 at the Nevinnomysskaya SDPP branch. Three combined-cycle power units with a capacity of 450 MW are 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
an increase in the efficiency of a utilization-type CCGT unit is possible by improving
gas turbine plant and the complication of the steam process scheme.
Rice. 1 - Scheme of a CCGT unit with a waste-heat boiler
Combined-cycle plant with 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 afterburned, and the generated superheated steam is used in the steam turbine unit.
The second direction is the use of gas turbines for the creation of CCGT - CHP and GTU - CHP. In recent years, many options for the CCGT-CHPP technological schemes have been proposed. It is advisable to use combined heat and power plants at CHPPs operating on gas.
utilization type. A typical example
a large CCGT - CHPP of this type is the North-Western 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, and a steam turbine. The main indicators of the unit: electric power - 450 MW, thermal power- 407 MW, specific consumption of equivalent fuel for electricity supply - 154.5 g. tons / (kWh), specific consumption of equivalent fuel for heat supply - 40.6 kg of c.u. t / GJ, efficiency of the CHPP for electricity supply - 79.6%, heat energy - 84.1%.
The third direction is the use of gas turbines for the creation of CCGT - CHPP and GTU - CHPP of small and medium capacity on the basis of boiler houses. CCGT - CHP and GTU - CHP best options, created on the basis of boiler houses, provide an efficiency of electricity supply in the heating mode at the level of 76 - 79%.
A typical combined cycle plant consists of two GTUs, each with its own waste-heat boiler supplying the generated steam to one common steam turbine.
An installation of this type was developed for the Shchekinskaya GRES. CCGT-490 was designed to generate electrical energy in basic and partial operating modes of the power plant with heat supply to a third-party consumer up to 90 MW during winter temperature chart. Schematic diagram the CCGT-490 unit was forced to focus on the lack of space when placing the waste heat boiler and
steam turbine plant in the buildings of the power plant, which created certain difficulties for achieving optimal modes of combined heat and power generation.
In the absence of restrictions on the location of the unit, as well as using an improved gas turbine unit, the unit's efficiency can be significantly increased. A single-shaft CCGT-320 with a capacity of 300 MW is proposed as such an improved CCGT unit. A complete GTU for CCGT-320 is a single-shaft GTE-200, the creation of which is supposed to be carried out by switching to
two-bearing rotor, modernization of the cooling system and other units of the gas turbine unit in order to increase the initial gas temperature. In addition to the GTE-200, the CCGT-320 monoblock contains a K-120-13 STU with a three-cylinder turbine, a condensate pump, a condenser for steam seals, a heater fed with heating steam supplied from the extraction before the last stage of the PT, as well as a waste-heat boiler of two pressures, containing eight heat exchange areas, including an intermediate steam superheater.
To assess the efficiency of the installation, a thermodynamic calculation was carried out, as a result of which it was concluded that when operating in the condensation mode of CCGT-490 ShchGRES, its electrical efficiency can be increased by 2.5% and brought to 50.1%.
Research of heating
combined cycle plants have shown that the economic indicators of CCGTs significantly depend on the structure of their thermal circuit, the choice of which is carried out in favor of a plant that provides minimum temperature flue gases. This is due to the fact that the 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-circuit cogeneration CCGT unit shown in Fig. 2, includes a drum-type waste heat boiler with natural circulation of the medium in the evaporation circuit. In the course of gases in the boiler from bottom to top, heating surfaces are sequentially located:
steam superheater PP, evaporator I, economizer E and gas superheater of network water GSP.
Rice. 2 - Thermal diagram of a single-circuit CCGT
The calculations of the system showed that when the parameters of live steam change, the power generated by the CCGT unit is redistributed between the thermal and electrical loads. With an increase in steam parameters, the production of electric power increases and the production of thermal energy decreases. This is due to 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 extraction, the heat load of the heating system water heater decreases.
A two-circuit CCGT unit, as well as a single-circuit one, consists of two gas turbines, two waste heat boilers and one steam turbine (Fig. 3). Heating of the network water is carried out in two PGS heaters and (if necessary) in a peak network heater.
In the course of gases in the waste heat boiler
the following
heating surfaces: superheater high pressure PPVD, high-pressure evaporator IVD, high-pressure economizer EVD, low-pressure steam superheater PPND,
low pressure evaporator IND, gas heater of low pressure GPND, gas heater of network water GSP.
Rice. 3 - Basic thermal diagram
double-circuit CCGT
Rice. 4 - Scheme of utilization of heat of exhaust gases of GTU
In addition to the waste heat boiler, the heat circuit includes a steam turbine with three cylinders, two heaters for heating water PSG1 and PSG2, a deaerator D and feed pumps PEN. The exhaust steam of the turbine was sent to PSG1. Steam from the turbine take-off is supplied to the PSG2 heater. All network water passes through PSG1, then part of the water is directed to PSG2, and the other part, after the first stage of heating, goes to the GSP located at the end of the gas path of the waste heat boiler. The condensate of the heating steam PSG2 is drained into the PSG1, and then enters the LPHG and further into the deaerator. The feed water after the deaerator partly enters the economizer of the high-pressure circuit, and partly into the drum B of the low-pressure circuit. Steam from the low pressure superheater is mixed with the main steam flow after the high pressure cylinder (HPC) of the turbine.
As shown by a comparative analysis, when using gas as the main fuel, the use of utilization schemes is advisable if the ratio of thermal and electric energy is 0.5 - 1.0, with ratios of 1.5 or more, preference is given to CCGT according to the “waste” scheme.
In addition to adjusting the steam turbine cycle to the GTU cycle, waste heat recovery
The GTU can be carried out by supplying steam generated by the waste heat boiler to the combustion chamber of the GTU, as well as by implementing a regenerative cycle.
The implementation of the regenerative cycle (Fig. 4) provides a significant increase in the efficiency of the installation, by a factor of 1.33, if, when creating a gas turbine unit, the degree of pressure increase is selected in accordance with the planned degree of regeneration. This circuit includes a K-compressor; Р - regenerator; КС - combustion chamber; ТК - compressor turbine; ST - power turbine; CC - centrifugal compressor. If a gas turbine plant is performed without regeneration, and the degree of pressure increase l is close to the optimal value, then equipping such a gas turbine unit with a regenerator does not lead to an increase in its efficiency.
The efficiency of the unit supplying steam to the combustion chamber is 1.18 times higher than that of the gas turbine unit, which makes it possible to reduce the consumption of fuel gas consumed by the gas turbine unit.
Comparative analysis showed that the greatest fuel economy is possible when the regenerative cycle of a GTU with a high degree of 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 the majority of domestic TKA, aircraft and marine gas turbine engines with a high degree of pressure increase are used as a drive, and in this case, the utilization of the heat of exhaust gases is more efficient in the steam turbine unit. Installation with steam supply to the combustion chamber is structurally the most simple, but less effective.
One of the ways to achieve gas savings and solve environmental problems is the use of combined cycle plants at the compressor station. Research developments address two alternative options the use of steam obtained during the utilization of the heat of exhaust gases from a gas turbine unit: a CCGT unit driven by a steam turbine of a natural gas blower and from a steam turbine of an electric generator. The fundamental difference between these options lies in the fact that in the case of a CCGT unit with a supercharger, not only the heat of the exhaust gases of the GPU is utilized, but also one GPU is replaced by a steam-turbine pumping unit, and with a CCGT unit with an electric generator, the number of GPU unit. The performed analysis showed that CCGT units with a natural gas blower drive provided the best technical and economic indicators.
If a combined cycle plant with a waste heat boiler is created on the basis of a compressor station, the gas turbine unit is used to drive the blower, and the steam power plant (PSU) 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 fossil fuel use in decentralized heat supply systems, it is possible to reconstruct heating boiler houses with the placement of gas turbine units (GTU) of small capacity in them and utilization of combustion products in the furnaces of existing boilers. At the same time, the electrical power of a gas turbine unit depends on the operating modes for 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 - the original (existing boiler house), 2 - alternative, using a gas turbine. The greatest effect was obtained when the electric power of the gas turbine was equal to
maximum load of the consumption area.
Comparative analysis of a gas turbine unit with a boiler unit producing steam in an amount of 0.144 kg / kg s. g., condensing TU and GTU without KU and with TU dry heat exchange 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 the capacity of the gas turbine unit with steam injection from the WHB was 29%, and the consumption of additional natural gas - 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 utilizing the heat of gases using condensing heat recovery units (TU). In TU, which
are used to preheat the heating water before hot water boilers, heat exchange is carried out with condensation of water vapor contained in the flue gases, and the heating of water in the boiler itself occurs already in the “dry” heat exchange mode.
According to the data, along with fuel economy, the use of TC 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 estimated flow through the boiler, a part return water bypass 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
electric generators, there are several options for utilizing the heat of exhaust gases, for example, using a utilization
heat exchanger (UTO) for heating water, or using a waste heat boiler and
a steam turbine generator to increase power generation. The analysis of the station operation taking into account the heat utilization with the help of UHT 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 the NK-37 engine made it possible to draw the following conclusion. Depending on the specific conditions, the annual supply of recovered heat can vary from 210 to 480 thousand GJ, and the real gas savings amounted to 7 to 17 thousand m3.
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© V.V. Getman - Cand. tech. Sciences, Assoc. department automation of technological processes and production FGBOU VPO "KNITU", 1ga [email protected] yaMech; N.V. Lezhneva - Cand. tech. Sciences, Assoc. department automation of technological processes and production of FGBOU VPO "KNITU", [email protected]
The heat of flue gases leaving the furnaces, in addition to heating 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 found application in large furnaces with a relatively high temperature of exhaust flue gases: in open-hearth steel-making furnaces, in copper-smelting reverberatory furnaces, in rotary kilns for burning cement clinker, with a dry method of cement production, etc.
Rice. five.
1 - superheater; 2 - tubular surface; 3 - smoke exhauster.
The heat of flue gases leaving 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 smoke tubes, inside which flue gases pass at a speed of about 20 m / s. Heat is transferred from gases to the heating surface 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.
In fig. 5 shows a gas-tube boiler of the Taganrog plant of average productivity D avg = 5.2 t / h with the calculation for the passage of 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 gas temperature before the boiler is 600 ° С, behind the boiler 200 - 250 ° С.
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 small diameter pipes, for example d = 32 × 3 mm, which makes the weight of the boiler lighter. With multiple circulation, when the circulation rate is 5 - 18, the water velocity in the tubes is significant, not less than 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 powered by water chemically treated with cation exchange filters and other water treatment methods that meet the feed water standards for conventional steam boilers.
Rice. 6.
1 - economizer surface; 2 - evaporating surface; 3 - superheater; 4 - drum-collector; 5 - circulation pump; 6 - sludge trap; 7 - smoke exhauster.
In fig. 6 shows the layout of the coil heating surfaces in vertical chimneys. The movement of the steam-water mixture is carried out by a 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 capacity of 5 to 18 t / h.
The cost of steam is 0.4 - 0.5 rubles / ton instead of 1.2 - 2 rubles / ton for steam taken from the steam turbines of the CHPP and 2 - 3 rubles / ton for steam from industrial boiler houses. The cost of steam is made up of energy costs for driving the smoke exhausters, costs for water preparation, depreciation, repairs and maintenance. The gas velocity in the boiler is 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 an artificial draft from the exhauster. Strengthening the thrust that accompanies the installation of waste heat boilers, as a rule, improves the operation of open-hearth furnaces. Such boilers are widespread in factories, but for their good operation, protection of heating surfaces from drift by dust and slag particles and systematic cleaning of heating surfaces from entrainment by blowing with superheated steam, rinsing with water (when the boiler stops), vibration, etc. are required.
Rice. 7.
To use the heat of flue gases coming from the copper-smelting reverberatory furnaces, water-tube boilers with natural circulation are installed (Fig. 7). The flue gases in this case are very high temperature(1100 - 1250 ° C) and are contaminated 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 the boiler heating surface. It is the high dust content of the gases that forces us to abandon heat recovery in these furnaces for the time being and restrict ourselves to the use of flue gases in waste heat boilers.
The transfer of heat from gases to the screen evaporating surfaces is very intensive, due to which intensive vaporization of slag particles is ensured, cooling, granulating and falling into a slag funnel, which excludes slagging of the convective heating surface of the boiler. Installation of such boilers for the use of gases with a relatively low temperature (500 - 700 ° C) is impractical due to poor heat transfer by radiation.
In the case of equipment high temperature furnaces It is advisable to install waste heat boilers with metal recuperators directly behind the working chambers of the furnaces. In this case, the flue gas temperature in the boiler drops to 1000 - 1100 ° C. At this temperature, they can already be directed to the heat-resistant section of the recuperator. If the gases carry a lot of dust, then the waste heat boiler is arranged in the form of a screen boiler-slag granulator, which ensures the separation of entrainment from the gases and facilitates the work of the recuperator.