Schemes of flue gas heat recovery installation. Method for recovering heat from flue gases
I propose for consideration activities for the disposal of flue gases. Flue gases are available in abundance in any town or city. The main part of 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 smoke from gas boiler houses (industrial or private houses); this is the cleanest type of flue gas, which contains the minimum amount of harmful impurities. You can also use smoke from 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 flue gas are nitrogen, carbon dioxide and water vapor. 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.
Nitrogen gas is used in fire fighting, for the transportation and storage of flammable and explosive media, as a protective gas to protect easily oxidized substances and materials from oxidation, to prevent corrosion of tanks, for purging pipelines and containers, to create inert environments in grain silos. Nitrogen protection prevents the growth of bacteria and 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. Nitrogen gas is widely used to produce liquid nitrogen from it.
To obtain nitrogen, it is enough 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 applications is even greater and its price is much higher.
I suggest getting more complete information about him. Typically, carbon dioxide is stored in 40-liter cylinders painted black with the word “carbon dioxide” written in yellow. More correct name CO2, “carbon dioxide”, but everyone has already become accustomed to the name “carbon dioxide”, it is 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 naturally formed in the human body. The air exhaled by a person usually contains 4.5%. The main use of carbon dioxide is in the carbonation and sale of bottling drinks, it is used as a shielding gas when carrying out welding work 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 water is saturated with carbon dioxide) for the production of microalgae during their artificial cultivation, for preserving and improving the quality of feed and products, for the production of dry ice and its use in cryoblasting installations (cleaning surfaces from contaminants) and for obtaining low temperatures during storage and transportation of food products, 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 easy for people involved in technology to make such an installation themselves. If the technological process standards are observed, 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 special combustion of fuel in the installation itself.
Now the economic side of the matter. The installation 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 CO2 from combustion of 1 cubic meter. m of gas;
hard coal, different deposits – 2.1-2.7 kg CO2 from burning 1 kg of fuel;
propane, butane, diesel fuel, fuel oil - 3.0 kg of CO2 from burning 1 kg of fuel.
It will not be possible to completely extract all the carbon dioxide released, but 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 calculate it yourself specific consumption fuel to obtain one cylinder of carbon dioxide.
It is not that big, for example, in the case of obtaining carbon dioxide from combustion natural gas It is enough to burn 15 m3 of gas.
At the highest rate (Moscow) it is 60 rubles. for 40 liters. 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 fuel costs are reduced and the profit from the installation increases. The installation can operate around the clock, in automatic mode, with minimal human involvement in the process of producing 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). Monthly revenue from the sale of carbon dioxide in this case reaches: 500 rubles/ball. x 25 points/day. x 30 days. = 375,000 rub. The heat released during combustion can be used simultaneously for space heating, and in this case there will be no wasteful use of fuel. It should be borne in mind that the environmental situation at the site where carbon dioxide is extracted 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 combustion also works well. wood waste(waste from logging and wood processing, carpentry shops, etc.). In this case, the same carbon dioxide installation is supplemented with a wood gas generator (factory-made or self-made) to produce wood gas. Wood waste (logs, wood chips, shavings, sawdust, etc.) is poured into the gas generator hopper 1-2 times a day; otherwise, the installation operates in the same mode as in the above.
The yield of carbon dioxide from 1 ton of wood waste is 66 cylinders. Revenue from one ton of waste is (at a carbon dioxide cylinder price of 500 rubles): 500 rubles/ball. x 66 points = 33,000 rub.
With the average amount of wood waste from one wood processing shop being 0.5 tons of waste per day, revenue from the sale of carbon dioxide can reach 500 thousand rubles. per month, and in the case of importing waste from other wood processing and carpentry shops, the revenue becomes even greater.
It is possible to obtain carbon dioxide from combustion car tires, which is also only beneficial for our environment.
In the case of producing carbon dioxide in quantities greater than the local 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 simple technology into environmentally friendly carbon-containing fertilizers, baking powder and etc.) up to the production of motor gasoline from carbon dioxide.
Flue gas condensation system for the company's boilers “ AprotechEngineeringAB” (Sweden)The flue gas condensation system makes it possible to obtain and recover large amounts of thermal energy contained in the wet boiler flue gas, which is usually discharged through chimney in atmosphere.
The heat recovery/flue gas condensation system makes it possible to increase heat supply to consumers by 6–35% (depending on the type of fuel burned and installation parameters) or reduce natural gas consumption by 6–35%
Main advantages:
- Fuel economy (natural gas) - the same or increased heat load of the boiler with less fuel combustion
- Reduction of emissions - CO2, NOx and SOx (when burning coal or liquid fuels)
- Obtaining condensate for the boiler make-up system
Principle of operation:
The heat recovery/flue gas condensation system can operate in two stages: with or without the use of an air humidification system supplied to the boiler burners. If necessary, a scrubber is installed before the condensation system.
In the condenser, the exhaust flue gases are cooled using return water from the heating network. When the temperature of the flue gases decreases, a large amount of water vapor contained in the flue gas condenses. Thermal energy Vapor condensation is used to heat the return heating network.
Further cooling of the gas and condensation of water vapor occurs in the humidifier. The cooling medium in the humidifier is the blast air supplied to the boiler burners. Since the blast air is heated in the humidifier, and warm condensate is injected into the air flow in front of the burners, an additional evaporation process occurs in the exhaust flue gas of the boiler.
The blown air supplied to the boiler burners contains an increased amount of thermal energy due to increased temperature and humidity.
This leads to an increase in the amount of energy in the exhaust flue gas entering the condenser, which in turn leads to more effective use heat from a centralized heating system.
The flue gas condensation unit also produces condensate, which, depending on the composition of the flue gases, will be further purified before being fed into the boiler system.
Economic effect.
Comparison of thermal power under the following conditions:
- No condensation
- Flue gas condensation
- Condensation together with humidification of the air supplied for combustion
The flue gas condensation system allows the existing boiler house to:
- Increase heat production by 6.8% or
- Reduce gas consumption by 6.8%, as well as increase revenue from the sale of CO,NO quotas
- Investment size is about 1 million euros (for a boiler house with a capacity of 20 MW)
- Payback period is 1-2 years.
Savings depending on the coolant temperature in the return pipe:
V. V. Getman, N. V. Lezhneva METHODS FOR RECYCLING HEAT OF EXHAUST GASES FROM POWER INSTALLATIONS
Keywords: gas turbine plants, combined cycle gas plants
The work considers various methods recycling the heat of exhaust gases from power plants in order to increase their efficiency, save organic fuel and increase energy capacity.
Keywords: gas-turbine installations, steam-gas installations
In work various methods of utilization of warmth of leaving gases from power installations for the purpose of increasing of their efficiency, economy of organic fuel and accumulation of power capacities are considered.
With the beginning of economic and political reforms in Russia, it is first necessary to make a number of fundamental changes in the country's electric power industry. The new energy policy must solve a number of problems, including the development of modern highly efficient technologies for the production of electrical and thermal energy.
One of these tasks is to increase the efficiency of power plants in order to save fossil fuels and increase energy capacity. Most
Promising in this regard are gas turbine units, the flue gases of which emit up to 20% of the heat.
There are several ways to increase the efficiency of gas turbine engines, including:
Increasing the gas temperature in front of the turbine for a gas turbine unit of a simple thermodynamic cycle,
Application of heat recovery,
Use of flue gas heat in binary cycles,
Creation of a gas turbine unit using a complex thermodynamic scheme, etc.
The most promising direction is considered to be the joint use of gas turbine and steam turbine units (GTU and STU) in order to improve their economic and environmental characteristics.
Gas turbines and combined installations created using them, with currently technically achievable parameters, provide a significant increase in the efficiency of heat and electricity production.
Widespread use of binary PSUs, as well as various combined schemes for technical re-equipment The thermal power plant will allow saving up to 20% of fuel compared to traditional steam turbine units.
According to experts, the efficiency of the combined steam-gas cycle increases with an increase in the initial temperature of the gases in front of the gas turbine plant and an increase in the share of gas turbine power. Of no small importance
There is also the fact that in addition to the gain in efficiency, such systems require significantly lower capital costs, their specific cost is 1.5 - 2 times less than the cost of gas-fuel oil steam turbine units and CCGT units with minimal gas turbine power.
Based on the data, three main areas for the use of gas turbine units and combined cycle gas turbine units in the energy sector can be identified.
The first, widely used in industrial developed countries, - the use of CCGT units at large condensing thermal power plants operating on gas. In this case, it is most effective to use a recovery-type CCGT unit with a large share of gas turbine power (Fig. 1).
The use of CCGT makes it possible to increase the efficiency of fuel combustion at thermal power plants by ~ 11-15% (CCP with gas discharge into the boiler), by ~ 25-30% (binary CCGT).
Until recently, extensive work on the implementation of CCGT systems in Russia was not carried out. However, single samples of such installations have been in use for quite a long time and have been successfully used, for example, CCGT units with a high-pressure steam generator (HSG) type VPG-50 of the main power unit PGU-120 and 3 modernized power units with HPG-120 at the TPP-2 branch of OJSC TGK-1"; PGU-200 (150) with VPG-450 at the Nevinnomyssk State District Power Plant branch. Three combined cycle power units with a capacity of 450 MW each are installed at the Krasnodar State District Power Plant. The power unit includes two gas turbines with a capacity of 150 MW, two waste heat boilers and a steam turbine with a capacity of 170 MW, the efficiency of such an installation is 52.5%. Further
increasing the efficiency of utilization-type CCGT units is possible by improving
gas turbine installation and complication of the steam process circuit.
Rice. 1 - Scheme of a CCGT unit with a waste heat boiler
Combined-cycle plant with boiler -
recycler (Fig. 1) includes: 1-
compressor; 2 - combustion chamber; 3 - gas
turbine; 4 - electric generator; 5 - boiler-
recycler; 6 - steam turbine; 7 - capacitor; 8
Pump and 9 - deaerator. The fuel is not burned in the waste heat boiler, and the superheated steam produced is used in a steam turbine unit.
The second direction is the use of gas turbines to create CCGT-CHP and GTU-CHP. Behind last years Many options for technological schemes of CCGT-CHP have been proposed. At CHPPs operating on gas, it is advisable to use cogeneration CCGT units
recycling type. A typical example
A large CCGT-CHP of this type is the North-West CHPP in St. Petersburg. One CCGT unit at this thermal power plant includes: two gas turbines with a capacity of 150 MW each, two waste heat boilers, and a steam turbine. The main indicators of the unit: electrical power - 450 MW, thermal power - 407 MW, specific consumption of standard fuel for electricity supply - 154.5 g. t./(kW.h), specific consumption of equivalent fuel for heat supply - 40.6 kg. t./GJ, efficiency of thermal power plant by supply electrical energy- 79.6%, thermal energy - 84.1%.
The third direction is the use of gas turbines to create CCGT-CHP and GTU-CHP of low and medium power based on boiler houses. CCGT - CHPP and GTU - CHPP of the best options, created on the basis of boiler houses, provide efficiency for the supply of electrical energy in cogeneration mode at the level of 76 - 79%.
A typical combined cycle plant consists of two gas turbine units, each with its own waste heat boiler, which supplies the generated steam to one common steam turbine.
An installation of this type was developed for the Shchekinskaya State District Power Plant. PGU-490 was designed to generate electrical energy in the basic and partial operating modes of the power plant with the supply of heat to third-party consumers up to 90 MW during winter temperature chart. The schematic diagram of the PGU-490 unit was forced to focus on the lack of space when placing the waste heat boiler and
steam turbine installation in the power plant buildings, which created certain difficulties in achieving optimal conditions for the combined production of heat and electricity.
In the absence of restrictions on the placement of the installation, as well as when using an improved gas turbine unit, the efficiency of the unit can be significantly increased. As such an improved CCGT, a single-shaft CCGT-320 with a capacity of 300 MW is proposed. The complete gas turbine unit for CCGT-320 is the single-shaft GTE-200, the creation of which is expected to be carried out by transition to
double-support rotor, modernization of the cooling system and other components of the gas turbine plant in order to increase the initial gas temperature. In addition to the GTE-200, the PGU-320 monoblock contains a K-120-13 steam turbine with a three-cylinder turbine, a condensate pump, a seal steam condenser, a heater fed by heating steam supplied from the extraction before the last stage of the steam turbine, as well as a two-pressure waste heat boiler containing eight heat exchange areas, including an intermediate steam superheater.
To assess the efficiency of the installation, a thermodynamic calculation was carried out, as a result of which it was concluded that when operating in the condensing mode of the PGU-490 ShchGRES, its electrical efficiency can be increased by 2.5% and brought to 50.1%.
District heating research
combined-cycle plants have shown that the economic indicators of combined cycle gas plants significantly depend on the structure of their thermal circuit, the choice of which is made in favor of an installation that ensures the minimum temperature of the flue gases. This is explained by the fact that flue gases are the main source of energy loss, and to increase the efficiency of the circuit, their temperature must be reduced.
The model of a single-circuit heating CCGT unit, shown in Fig. 2, includes waste heat boiler drum type with natural circulation of the medium in the evaporation circuit. Along the flow of gases in the boiler, heating surfaces are located sequentially from bottom to top:
superheater PP, evaporator I, economizer E and gas superheater for network water GSP.
Rice. 2 - Thermal diagram of a single-circuit CCGT
Calculations of the system showed that when the parameters of fresh steam change, the power generated by the CCGT unit is redistributed between thermal and electrical loads. As steam parameters increase, the generation of electrical energy increases and the generation of thermal energy decreases. This is explained by the fact that as the parameters of fresh steam increase, its production decreases. At the same time, due to a decrease in steam consumption with a small change in its parameters in the extractions, the thermal load of the network water heater is reduced.
A double-circuit CCGT, just like a single-circuit one, consists of two gas turbines, two waste heat boilers and one steam turbine (Fig. 3). Heating of network water is carried out in two ASG heaters and (if necessary) in a peak network heater.
Along the flow of gases in the waste heat boiler
the following are located sequentially
heating surfaces: high-pressure superheater PPHP, high-pressure evaporator IVD, high-pressure economizer EHP, steam superheater low pressure PPND,
low pressure evaporator IND, low pressure gas heater GPND, gas heater for network water GSP.
Rice. 3 - Principal thermal diagram
double-circuit CCGT
Rice. 4 - Scheme of heat recovery from gas turbine exhaust gases
In addition to the waste heat boiler, the thermal circuit includes a steam turbine with three cylinders, two network water heaters PSG1 and PSG2, a deaerator D and feed pumps PEN. The exhaust steam from the turbine was sent to PSG1. Steam from the turbine exhaust is supplied to the PSG2 heater. All network water passes through PSG1, then part of the water is sent to PSG2, and the other part after the first heating stage is sent to the GSP, located at the end of the gas path of the waste heat boiler. The condensate of the heating steam PSG2 is drained into PSG1, and then enters the HPPG and then into the deaerator. The feed water after the deaerator partially flows into the economizer of the high-pressure circuit, and partially into drum B of the low-pressure circuit. Steam from the low pressure circuit superheater is mixed with the main steam flow after the high pressure cylinder (HPC) of the turbine.
As a comparative analysis has shown, when using gas as the main fuel, the use of utilization schemes is advisable if the ratio of thermal and electrical energy is 0.5 - 1.0, with ratios of 1.5 or more, preference is given to CCGT units using a “discharge” scheme.
In addition to adjusting the steam turbine cycle to the gas turbine cycle, recycling the heat of exhaust gases
GTU can be implemented by supplying steam generated by a waste heat boiler to the combustion chamber of the GTU, as well as by implementing a regenerative cycle.
The implementation of the regenerative cycle (Fig. 4) provides a significant increase in the efficiency of the installation, by 1.33 times, if, when creating a gas turbine unit, the degree of pressure increase is selected in accordance with the intended degree of regeneration. This circuit includes a K-compressor; R - regenerator; KS - combustion chamber; ТК - compressor turbine; ST - power turbine; CC - centrifugal compressor. If a gas turbine unit is designed without regeneration, and the degree of pressure increase l is close to the optimal value, then equipping such a gas turbine unit with a regenerator does not lead to an increase in its efficiency.
The efficiency of the installation that supplies steam to the combustion chamber is increased by 1.18 times compared to a gas turbine unit, which makes it possible to reduce the consumption of fuel gas consumed by the gas turbine unit.
A comparative analysis showed that the greatest fuel savings are possible when implementing the regenerative cycle of a gas turbine unit with high degree regeneration, a relatively low pressure increase ratio in the compressor l = 3 and with small losses of combustion products. However, in most domestic TKAs, aviation and marine gas turbine engines with a high degree of pressure increase are used as a drive, and in this case, heat recovery from exhaust gases is more efficient in a steam turbine unit. Installation with steam supply to the combustion chamber is structurally the simplest, but less effective.
One of the ways to achieve gas savings and solutions environmental problems is the use of combined cycle gas plants at compressor stations. IN research developments Two alternative options for using steam obtained by recycling the heat of gas turbine exhaust gases are being considered: a combined cycle gas turbine driven by a steam turbine of a natural gas supercharger and by a steam turbine of an electric generator. The fundamental difference between these options is that in the case of a CCGT with a supercharger, not only the heat of the exhaust gases of the GPU is recovered, but also one GPU is replaced by a steam turbine pumping unit, and in the case of a CCGT with an electric generator, the number of GPUs is maintained, and due to the recovered heat, electricity is generated by a special steam turbine unit. The analysis showed that CCGT units with a natural gas supercharger drive provided the best technical and economic indicators.
In the case of creating a combined cycle gas plant with a waste heat boiler on the basis of a compressor station, the gas turbine unit is used to drive the supercharger, and the steam power plant (SPU) is used to generate electricity, while the temperature of the exhaust gases behind the waste heat boiler is 1400C.
In order to increase the efficiency of using organic fuel in decentralized heat supply systems, it is possible to reconstruct heating boiler houses with the placement of small-capacity gas turbine units (GTUs) and utilization of combustion products in the furnaces of existing boilers. At the same time, the electrical power of the gas turbine depends on the operating modes according to thermal or electrical load schedules, as well as on economic factors.
The effectiveness of boiler house reconstruction can be assessed by comparing two options: 1 - original (existing boiler house), 2 - alternative, using a gas turbine unit. The greatest effect was obtained with an electric power of the gas turbine equal to
maximum load of the consumption area.
Comparative analysis of a gas turbine unit with a HRSG producing steam in the amount of 0.144 kg/kg s. g., condensing TU and GTU without HRSG and with TU of dry heat exchange showed the following: useful
electric power - 1.29, natural gas consumption - 1.27, heat supply - 1.29 (12650 and 9780 kJ/m3 of natural gas, respectively). Thus, the relative increase in gas turbine power when introducing steam from the HRSG was 29%, and the consumption of additional natural gas was 27%.
According to operational test data, the temperature of flue gases in hot water boilers is 180 - 2300C, which creates favorable conditions for recycling the heat of gases using condensing heat exchangers (HU). In TU, which
are used to preheat network water before hot water boilers, heat exchange takes place with the condensation of water vapor contained in the flue gases, and the heating of the water in the boiler itself occurs in the “dry” heat exchange mode.
According to the data, along with fuel savings, the use of technical specifications also provides energy savings. This is explained by the fact that when an additional flow of circulating water is introduced into the boiler, in order to maintain the calculated flow rate through the boiler, part return water transfer the heating network in an amount equal to the recirculation flow rate from the return pipe to the supply pipe.
When completing power plants from separate power units with a gas turbine drive
electric generators, there are several options for recycling the heat of exhaust gases, for example, using a recovery
heat exchanger (HTE) for heating water, or using a waste heat boiler and
steam turbine generator to increase electricity generation. An analysis of the station's operation taking into account heat recovery using heat treatment showed a significant increase in the heat utilization coefficient, in some cases by 2 times or more, and experimental studies of the EM-25/11 power unit with the NK-37 engine allowed us to draw the following conclusion. Depending on specific conditions, the annual supply of recovered heat can range from 210 to 480 thousand GJ, and real gas savings ranged from 7 to 17 thousand m3.
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© V.V. Getman - Ph.D. tech. Sciences, Associate Professor department automation of technological processes and production FSBEI HPE "KNRTU", 1ega151@uaMech; N.V. Lezhneva - Ph.D. tech. Sciences, Associate Professor department automation of technological processes and production of FSBEI HPE "KNRTU", [email protected].
Use: energy, waste heat recovery. The essence of the invention: the gas flow is moistened by passing it through a condensate film formed on a dihedral perforated sheet 4, where the gases are saturated with water vapor. In chamber 2 above sheet 4, volumetric condensation of water vapor occurs on dust particles and tiny droplets of vapor-gas flow. The prepared vapor-gas mixture is cooled to the dew point temperature by transferring the heat of the flow of the heated medium through the wall of the heat exchange elements 8. Condensate from the flow falls onto inclined partitions 5 with gutters 10 and then enters sheet 4 through the drain pipe 9. 1 silt.
The present invention relates to the field of boiler technology, and more specifically to the field of waste gas heat recovery. There is a known method for recycling the heat of exhaust gases (USSR Aut.St. N 1359556, MKI F 22 V 33/18, 1986), which is the closest analogue, in which the combustion products are sequentially forcibly moistened, compressed in a compressor, cooled to a temperature below the dew point temperature together with condensation of water vapor at a pressure above atmospheric pressure, they are separated in a separator, expanded with a simultaneous decrease in temperature in a turboexpander and removed into the atmosphere. There is a known method for recycling the heat of exhaust gases (GDR, Pat. N 156197, MKI F 28 D 3/00, 1982) achieved by countercurrent movement in a heat exchanger of exhaust gases and an intermediate liquid medium, heated to a temperature greater than the dew point temperature of the exhaust gases, which are cooled to a temperature below the dew point. There is a known method of low-temperature heating using the higher calorific value of fuel (Germany, application N OS 3151418, MKI F 23 J 11/00, 1983), which consists in the fact that fuel is burned in a heating device with the formation of hot gases that enter the heating device forward and to the side. In part of the flow path, fuel gases are directed downward to form condensate. The fuel gases at the outlet have a temperature of 40-45 o C. The known method allows cooling of the exhaust gases below the dew point temperature, which somewhat increases the thermal efficiency of the installation. However, in this case, condensate is sprayed through the nozzles, which leads to additional energy consumption for its own needs and increases the content of water vapor in the combustion products. The inclusion of a compressor and a turboexpander in the circuit, which, respectively, compress and expand the combustion products, does not increase efficiency, and, in addition, leads to additional energy consumption associated with losses in the compressor and turboexpander. The objective of the invention is to intensify heat exchange with deep utilization of heat from exhaust gases. The problem is solved due to the fact that the gas flow is humidified by passing it through a film of condensate with saturation of the flow with water vapor, followed by condensation of the latter, as well as the condensate falling onto the said film and draining the unevaporated part. The proposed method can be implemented in the device shown in the drawing, where: 1 condensate collector, 2 chamber, 3 housing, 4 dihedral unequal inclined perforated sheet, 5 inclined partitions, 6 tapering two-dimensional diffuser, 7 expanding diffuser, 8 heat exchange surface, 9 drain pipe, 10 gutter, 11 mating surface, 12 - separator, 13 overheating heat exchanger, 14 smoke exhauster, 15 chimney, 16 water seal, 17 horizontal axis. The operation of the device according to the proposed method of utilizing the heat of combustion products is similar to an atmospheric heat pipe. Its evaporative part is located in the lower part of chamber 2, from which the prepared vapor-gas mixture rises, and the condensation part on the heat exchange surfaces 3, from which condensate flows along inclined partitions 5 with gutters 10 through drain pipes 9 onto a dihedral unequal-sided perforated sheet 4, and the excess into condensate collector 1. Combustion products coming from the superheat heat exchanger 13 bubble a film of condensate on a dihedral unequally inclined perforated sheet 4. The condensate is sprayed, heated and evaporated, and its excess flows into the condensate collector 1. Flue gases are saturated with water vapor at a pressure approximately equal to atmospheric. It depends on the mode of joint operation of the fan and smoke exhauster 14. In chamber 2, water vapor is in a supersaturated state, since the vapor pressure in the gas mixture is greater than the saturated vapor pressure. The smallest droplets, dust particles of combustion products become condensation centers, on which in chamber 2 without heat exchange with environment the process is underway volumetric condensation of water vapor. The prepared vapor-gas mixture condenses on the heat exchange surfaces 8. At the surface temperature of these heat exchange elements 8 significantly below the dew point temperature, the moisture content of the combustion products after the heat recovery device is lower than the initial one. The final phase of this continuous process is the precipitation of condensate on the inclined partitions 5 with complaints 10 and its entry onto the perforated sheet 4 through the drain pipe 9. The achievement of the task is confirmed by the following: 1. The value of the heat transfer coefficient increased to 180-250 W/m 2 o C, which sharply reduces the heat transfer surface area and, accordingly, reduces the weight and size indicators. 2. A 2.5 to 3 times reduction in the initial moisture content of water vapor in the flue gases reduces the intensity of corrosion processes in the gas path and chimney. 3. Fluctuations in the steam generator load do not reduce the efficiency of the boiler plant.
Claim
A method of utilizing the heat of exhaust gases, which consists in the fact that the gas flow is humidified and cooled to the dew point temperature by transferring the heat of the flow to the heated medium through the wall, characterized in that the gas flow is humidified by passing it through a condensate film with saturation of the flow with water vapor, followed by condensation of the latter, as well as the precipitation of condensate on the mentioned film and the drainage of its unevaporated part.
Proceedings of Instorf 11 (64)
UDC 622.73.002.5
Gorfin O.S. Gorfin O.S.
Gorfin Oleg Semenovich, Ph.D., prof. Department of Peat Machines and Equipment of Tver State Technical University (TvSTU). Tver, Akademicheskaya, 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 RECYCLING OF COMBUSTION GASES
FLUE GASES OF SUPERFICIAL TYPE
Annotation. The article discusses the design of a heat exchanger, in which the method of transferring recovered thermal energy from the coolant to a heat-receiving environment has been changed, making it possible to utilize the heat of vaporization of fuel moisture during deep cooling of flue gases and completely use it to heat cooling water, directed without additional processing to 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 use the purified condensate 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; surface heat exchanger; deep cooling of flue gases; recovery of the heat of vaporization of fuel moisture. Key words: Combined heat and power plant; boiler installations; heatr of superficial type; deep cooling of combustion gases; utilization of warmth of steam formation of fuel moisture.
Proceedings of Instorf 11 (64)
In boiler houses of thermal power plants, the energy of vaporization of moisture and fuel along with flue gases is released into the atmosphere.
In gasified boiler houses, heat losses from exhaust flue gases can reach 25%. In boiler houses operating on solid fuel, heat loss is even higher.
For the technological needs of the TBZ, milled peat with a moisture content of up to 50% is burned in boiler rooms. This means that half the mass of the fuel is water, which during combustion turns into steam and energy losses due to vaporization of fuel moisture reach 50%.
Reducing thermal energy losses is not only a matter of saving fuel, but also reducing harmful emissions into the atmosphere.
Reducing thermal energy losses is possible by using heat exchangers of various designs.
Condensation 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 and fuel moisture.
The most widespread are contact and surface heat exchangers. Contact heat exchangers are widely used in industry and energy due to their simplicity of design, low metal consumption and high heat exchange intensity (scrubbers, cooling towers). But they have a significant drawback: the cooling water becomes contaminated due to its contact with combustion products - flue gases.
In this regard, more attractive are surface heat exchangers that do not have direct contact of combustion products and coolant, the disadvantage of which is the relatively low temperature its heating, equal to the temperature of the wet thermometer (50...60 °C).
The advantages and disadvantages of existing heat exchangers are widely covered in specialized 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 heat exchanger design.
The diagram of a heat exchanger for deep utilization of heat from flue gases is shown
on the image. The body 1 of the heat exchanger rests on the base 2. In the middle part of the body there is an insulated tank 3 in the form of a prism, filled with pre-cleaned running water. Water enters from above through pipe 4 and is removed at the bottom of housing 1 by pump 5 through gate 6.
On the two end sides of the tank 3 there are jackets 7 and 8, isolated from the middle part, the cavities of which through the volume of the tank 3 are connected to each other by rows of horizontal parallel pipes forming bundles of pipes 9 in which gases move in one direction. Shirt 7 is divided into sections: lower and upper single 10 (height h) and the remaining 11 - double (height 2h); shirt 8 has only double sections 11. The lower single section 10 of shirt 7 is connected by a bundle of pipes 9 to the bottom of the double section 11 of shirt 8. Next top part this double section 11 of the jacket 8 is connected by a bundle of pipes 9 to the bottom of the next double section 11 of the jacket 7 and so on. Consistently, 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 bottom of the next section of the first jacket, thus forming a coil of variable cross-section: the bundles of pipes 9 periodically alternate with the volumes of the sections of the jackets. In the lower part of the coil there is a pipe 12 for supplying flue gases, in the upper part there is a pipe 13 for the exit of gases. Branch pipes 12 and 13 are connected to each other by a bypass flue 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 sent through the pipes of the bundle 9 to the heat exchanger coil. The rest (about 20%) enters bypass flue 14. Redistribution of gases is carried out to increase the temperature of the cooled flue gases behind the heat exchanger to 60-70 ° C in order to prevent possible condensation of residual fuel moisture vapor in the tail sections of the system.
Flue gases are supplied to the heat exchanger from below through pipe 12, and removed to
Proceedings of Instorf 11 (64)
Drawing. Diagram of the heat exchanger (type A - connection of pipes with jackets) Figure. The scheme of the heatutilizer (a look A - connection of pipes with shirts)
upper part of the installation - pipe 13. Pre-prepared cold water fills the tank from above through pipe 4, and is removed by pump 5 and gate 6, located in the lower part of housing 1. The 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 a 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 smoke exhauster. 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 in the flue gases.
The design of the heat exchanger ensures not only effective utilization of the heat of vaporization of fuel moisture, but also removal of the resulting condensate from the flue gas flow.
The volume of sections of jackets 7 and 8 is greater than the volume of the pipes connecting them, so the speed of gases in them is reduced.
The flue gases entering the heat exchanger have a temperature of 150-160 °C. Sulfuric and sulfurous acids condense at a temperature of 130-140 °C, so 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 - sections of the jacket and an increase in the density of the condensate of sulfuric and sulfurous acids in liquid state compared to the density in gaseous state, by repeatedly changing the direction of movement of the flue gas flow (inertial separation), the acid condensate precipitates and is washed out of the gases by part of the water vapor condensate into the acid condensate collector 16, from where, when the shutter 17 is activated, it is removed into the industrial sewer.
Most of the condensate - condensate of water vapor - is released with a further decrease in the temperature of the gases to 60-70 ° C in the upper part of the coil and enters the moisture condensate collector 18, from where it can be used as hot water without additional treatment.
Proceedings of Instorf 11 (64)
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 heat exchanger design, flue gases containing fuel moisture vapor move through the coil pipes. The heat transfer coefficient in this case is no more than 10,000 W/(m2 °C), due to which the efficiency of heat transfer sharply increases. The coil pipes are located directly in the coolant volume, so heat exchange occurs constantly contact method. This allows for 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 cooling water. 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 of return network water, technological needs of enterprises, in greenhouses and greenhouse farms, etc.). This is the main advantage of the proposed heat exchanger design.
The advantage of the proposed device is also that in the heat exchanger the time of heat transfer from the environment of hot flue gases to the coolant, and therefore its temperature, is regulated by changing the liquid flow rate using a gate.
To check the results of using a heat exchanger, thermal and technical calculations were carried out for a boiler installation with a boiler steam output of 30 tons of steam/h (temperature 425 °C, pressure 3.8 MPa). 17.2 t/h of milled peat with a moisture content of 50% is burned in the firebox.
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.g./h,
where L = 3.25 kg dry. g/kg peat - theoretically required amount combustion air; a =1.365 - average air leakage coefficient.
1. Heat of flue gas recovery Flue gas enthalpy
J = cm x t + 2.5 d, ^zh/kgG. dry gas,
where ccm is the heat capacity of the flue gases (heat capacity of the mixture), ^l/kg °K, t is the temperature of the gases, °K, d is the moisture content of the flue gases, G. moisture/kg. d.g.
Heat capacity of the mixture
ссМ = сг + 0.001dcn,
where sg, cn are the heat capacity of dry gas (flue gases) and steam, respectively.
1.1. Flue gases at the inlet to the heat exchanger are at a temperature of 150 - 160 °C, we take C. g. = 150 °C; cn = 1.93 - heat capacity of steam; сг = 1.017 - 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 - mass of moisture in the fuel. scm = 1.017 + 0.001 x 112.7 x 1.93 = 1.2345 ^f/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 at a temperature of 40 °C
scm = 1.017 + 0.001 x 50 x 1.93 = 1.103 ^f/kg °C.
d40 =50 G/kg dry g.
J40 = 1.103 x 40 + 2.5 x 50 = 167.6 ^f/kg.
1.3. In the heat exchanger, 20% of the gases pass through the bypass flue, 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
exc = (J150 - J40) x ^m = (466.9 - 167.68) x
61,040 = 18.26 x 106, ^f/h.
This heat is spent on heating the cooling water
Qx™= W x w x (t2 - t4),
where W is water consumption, kg/h; sv = 4.19 ^l/kg °C - heat capacity of water; t 2, t4 - water temperature
Proceedings of Instorf 11 (64)
respectively at the outlet and inlet of the heat exchanger; we take tx = 8 °C.
2. Cooling water flow, kg/s
W=Qyra /(st x (t2 - 8) = (18.26 / 4.19) x 106 / (t2 - 8)/3600 = 4.36 x 106/ (t2 -8) x 3600.
Using the obtained dependence, you can determine the flow rate of cooling water at the required temperature, for example:
^, °С 25 50 75
W, kg/s 71.1 28.8 18.0
3. Condensate flow rate G^^ is:
^ond = GBM(d150 - d40) = 61.0 x (112.7 - 50) =
4. Checking the possibility of condensation of residual moisture from fuel vaporization in the tail elements of the system.
Average moisture content of flue gases at the outlet of the heat exchanger
^р = (d150 x 0.2 Gd.g. + d40 x 0.8 Gd.g.) / GA g1 =
112.7 x 0.2 + 50 x 0.8 = 62.5 G/kg dry. G.
According to the J-d diagram, this moisture content corresponds to a dew point temperature equal to tp. R. = 56 °C.
The actual temperature of the 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 exchanger is above the dew point, condensation of fuel moisture vapor in the tail elements of the system will not occur.
5. Coefficient useful action
5.1. Efficiency of utilization of the heat of vaporization of fuel moisture.
The amount of heat supplied to the heat exchanger
Q^h = J150 x Gft g = 466.9 x 76 300 =
35.6 x 106, M Dj/h.
Efficiency Q = (18.26 /35.6) x 100 = 51.3%,
where 18.26 x 106, МJ/h is the heat of utilization of vaporization of fuel moisture.
5.2. Efficiency of fuel moisture utilization
Efficiency 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 fuel moisture vapor, the efficiency of heat exchange between flue gases and coolant increases dramatically. 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 purified 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
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O.S. Gorfin, B.F. Zyuzin // Discoveries. Inventions. - 2015. - No. 19.
4. Gorfin, O.S., Mikhailov, A.V. Machines and equipment for peat processing. Part 1. Production of peat briquettes. - Tver: TvSTU 2013. - 250 p.