CN215570418U - Flue gas heating system - Google Patents
Flue gas heating system Download PDFInfo
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- CN215570418U CN215570418U CN202121839487.4U CN202121839487U CN215570418U CN 215570418 U CN215570418 U CN 215570418U CN 202121839487 U CN202121839487 U CN 202121839487U CN 215570418 U CN215570418 U CN 215570418U
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Abstract
The utility model relates to the technical field of chemical industry, in particular to a flue gas heating system which comprises a combustion furnace, wherein the combustion furnace is connected with one end of a heat exchanger in a fluidized bed reactor, the other end of the heat exchanger is connected with a circulating fan, and the circulating fan is communicated with the combustion furnace. Compared with the method of simply using the combusted gas for heating, the method has the advantages that the temperature of the mixed flue gas is low, and the material requirements of pipelines and heat exchangers are reduced.
Description
Technical Field
The utility model relates to the technical field of chemical industry, in particular to a flue gas heat supply system.
Background
In the heat exchanger, a cold material flow and a hot material flow respectively pass through two sides of the heat exchanger, and the heat of the hot material flow is transferred to the cold material flow in a non-contact manner.
The endothermic reaction of the materials in the reaction unit can be smoothly carried out only by providing external heat. Since the reaction rate is always increased with increasing temperature, even though the reaction unit is exothermic, heat is sometimes actively supplied to increase the reaction rate in order to increase the efficiency. For reaction units that require heat to be supplied, a fluidized bed reactor with a heat exchanger is an excellent choice. The particles (catalyst particles or material particles) in the fluidized bed are continuously overturned and updated, the heat and mass transfer is uniform, no dead angle exists, and the heat transfer coefficient is large. For example, in the reaction of urea to melamine, the temperature of the reaction mass needs to be maintained at about 400 ℃, and a medium above 400 ℃ is needed as a heat source to provide the reaction heat.
The heat medium introduced into the heat exchanger can be heat conducting oil, molten salt, flue gas and the like. Compared with liquid media such as heat conduction oil or molten salt, the flue gas is gas, and has the advantages of low density, small heat capacity and low heat transfer coefficient. Because the temperature of the smoke outlet (after heat exchange) of the heat exchanger cannot be lower than the temperature of the material, the specific heat of the smoke is small, and the temperature of the smoke inlet is very high, enough heat can be carried, and the heat exchange requirement is met.
The flue gas is obtained by burning fuel in a combustion furnace. The temperature of the hearth can reach over 1000 ℃, and the flue gas with high enough temperature can be generated. The inner wall of the combustion furnace is paved with refractory bricks, and the furnace body has no problem of high temperature resistance. However, the pipeline from the combustion furnace to the reactor and the heat exchanger in the reactor are generally made of steel such as carbon steel, stainless steel and the like, and the temperature resistance is only about 400-550 ℃. This is in contradiction to the aforementioned requirement for high reactor heat exchanger inlet temperatures. Traditionally, high temperature resistant special steel is forced to be used, and the manufacturing cost is sharply increased. Which in turn causes the flue gas to be greatly restricted as a direct heating medium.
SUMMERY OF THE UTILITY MODEL
The utility model aims to provide a flue gas heating system, which solves the technical problem that common stainless steel cannot meet the heating requirement in the prior art.
The utility model discloses a flue gas heating system which comprises a combustion furnace, wherein the combustion furnace is connected with one end of a heat exchanger in a fluidized bed reactor, the other end of the heat exchanger is connected with a circulating fan, and the circulating fan is communicated with the combustion furnace.
The working principle is as follows: the fuel and fresh air enter the combustion furnace and are combusted into high-temperature combusted gas. The low-temperature flue gas also enters the combustion furnace and is mixed with the combusted gas to form mixed flue gas with moderate temperature. The flow rate of the mixed flue gas is obviously larger than that of the burnt gas, so that the heating capacity of the mixed flue gas is not lower than that of the burnt gas although the temperature of the mixed flue gas is lower than that of the burnt gas. The mixed flue gas enters a heat exchanger of the fluidized bed reactor, and is cooled to become low-temperature flue gas after releasing heat. The temperature of the low temperature flue gas is still higher than the temperature of the heated medium in the fluidized bed reactor, and although the low temperature flue gas is named as low temperature flue gas, the temperature is obviously higher than the ambient temperature. And a small part of low-temperature flue gas is discharged outside, and a large part of low-temperature flue gas returns to the combustion furnace under the action of the circulating fan. Compared with the method of simply using the combusted gas for heating, the method has the advantages that the temperature of the mixed flue gas is low, and the material requirements of pipelines and heat exchangers are reduced.
Further, a flue gas regulating valve is arranged between the heat exchanger and the circulating fan.
Through setting up flue gas governing valve, can avoid burning the too big of burning furnace internal pressure with unnecessary low temperature flue gas discharge system.
Further, the combustion furnace is also connected with an air fan.
Air can be introduced into the combustion furnace by arranging the air fan, and other fans are not needed for exhausting air.
Furthermore, a protective gas inlet is arranged between the circulating fan and the combustion furnace.
If the initial fire is not ignited, a certain amount of mixed gas of fuel and air is already present in the furnace and may be within the explosive limits, and if the fire is suddenly struck in such a situation, danger may be caused. And nitrogen or carbon dioxide is fed through the protective gas inlet to replace the fuel-air mixed gas of the internal system, then fuel and air for combustion are fed again, and ignition is carried out again, so that safety can be ensured.
Further, an external discharge regulating valve is arranged between the circulating fan and the combustion furnace.
Through setting up outer governing valve of arranging, can avoid burning the too big of burning furnace internal pressure with unnecessary low temperature flue gas discharge system.
Further, the outer discharge regulating valve is connected with an outer discharge fan.
By arranging the outer exhaust fan, combustion air can be automatically sucked into the combustion furnace without other fans.
Furthermore, the flue gas pipeline used in the system is made of stainless steel 304 or stainless steel 310.
Cost savings can be achieved by using ordinary piping.
Compared with the prior art, the utility model has the beneficial effects that:
1. the circulation low temperature flue gas that this patent provided mixes with the high temperature flue gas that the burning produced, has reduced the high-end temperature of high temperature flue gas, greatly reduced the material requirement of high temperature flue gas pipeline. The flow rate of high-temperature flue gas is also increased by multiple times, the flow velocity in the heat exchanger is obviously increased, and the heat transfer coefficient is increased;
2. the internal circulation system of this patent can operate under the negative pressure. In this case, the combustion air can be automatically sucked into the combustion unit without a fan. The discharged flue gas of the low-temperature flue gas needs a fan to provide power, so that the low-temperature flue gas is discharged into the atmosphere or other devices;
3. the internal circulation system of the present patent can operate under positive pressure. At the moment, normal-pressure combustion air needs a fan to be introduced into the combustion unit, but discharged low-temperature flue gas usually does not need the fan, and can be discharged to the atmosphere or flow to other devices by means of self pressure;
4. this patent sets up the protection gas interface. If the initial fire is not ignited, a certain amount of mixed gas of fuel and air is already present in the furnace and may be within the explosive limits, and if the fire is suddenly struck in such a situation, danger may be caused. And nitrogen or carbon dioxide is fed through the protective gas inlet to replace the fuel-air mixed gas of the internal system, then fuel and air for combustion are fed again, and ignition is carried out again, so that safety can be ensured.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a schematic view of a heating system according to the present invention.
Fig. 2 is a schematic view of another state of the heating system of the present invention.
FIG. 3 is a schematic diagram of a comparative example system.
FIG. 4 is a schematic diagram of another comparative example system.
In the above drawings, each symbol has the following meaning: 1-combustion furnace, 2-fluidized bed reactor, 3-circulating fan, 4-flue gas regulating valve, 5-air fan, 6-protective gas inlet, 7-external discharge regulating valve, 8-external discharge fan and 9-heat exchanger.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention.
Example 1
The technical scheme adopted in the embodiment is as follows:
as shown in fig. 1 or fig. 2, a flue gas heating system includes a combustion furnace 1, the combustion furnace 1 is connected with one end of a heat exchanger 9 in a fluidized bed reactor 2, the other end of the heat exchanger 9 is connected with a circulating fan 3, and the circulating fan 3 is communicated with the combustion furnace 1.
The working principle is as follows: the fuel and fresh air enter the combustion furnace 1 and are combusted into high-temperature combusted gas. The low-temperature flue gas also enters the combustion furnace 1 and is mixed with the combusted gas to form mixed flue gas with moderate temperature. The flow rate of the mixed flue gas is obviously larger than that of the burnt gas, so that the heating capacity of the mixed flue gas is not lower than that of the burnt gas although the temperature of the mixed flue gas is lower than that of the burnt gas. The mixed flue gas enters a heat exchanger 9 of the fluidized bed reactor 2, and is cooled to become low-temperature flue gas after releasing heat. The temperature of the low temperature flue gas is still higher than the temperature of the heated medium in the fluidized bed reactor 2, although named low temperature flue gas, the temperature is significantly higher than the ambient temperature. A small part of low-temperature flue gas is discharged outside, and a large part of low-temperature flue gas returns to the combustion furnace 1 under the action of the circulating fan 3. Compared with the method of simply using the combusted gas for heating, the temperature of the mixed flue gas is low, and the material requirements of the pipeline and the heat exchanger 9 are reduced.
Example 2
In this embodiment, as a preferred embodiment of the present invention, a specific structure is shown in fig. 1, which discloses the following improvement on the basis of embodiment 1, a flue gas regulating valve 4 is arranged between a heat exchanger 9 and a circulating fan 3, the combustion furnace 1 is further connected with an air fan 5, a shielding gas inlet 6 is arranged between the circulating fan 3 and the combustion furnace 1, and flue gas pipelines used in the system are all made of stainless steel 310.
Through setting up flue gas governing valve 4, can be with unnecessary low temperature flue gas discharge system, avoid firing burning furnace 1 internal pressure too big.
Air can be introduced into the combustion furnace 1 by providing the air blower 5 without requiring other blowers for exhausting air.
By providing the shielding gas inlet 6, if the initial ignition is not initiated, a certain amount of mixed gas of fuel and air may be present in the combustion furnace 1, which may be within the explosion limit, and if the ignition is done in a trade, a danger may be caused. Nitrogen or carbon dioxide is fed through the protective gas inlet 6 to replace fuel-air mixed gas of an internal system, then fuel and air for combustion are fed again, and ignition is carried out again, so that safety can be ensured.
When in use, urea is used as a reaction raw material, a mixed gas of ammonia and carbon dioxide is used as a carrier gas, and the mixed gas is subjected to a cracking reaction in a fluidized bed reaction to generate reaction outlet gas comprising cyanamide, ammonia, carbon dioxide and other components. A flue gas coil pipe is arranged in the reactor to supply heat for the reaction and maintain the temperature of the materials in the fluidized bed layer to be 400 ℃.
16kg/h of natural gas from a pipeline network, 25 ℃, 15kPa (G) are fed into a combustion furnace 1, and the air for combustion is 303kg/h, 25 ℃. The operating pressure in the furnace 1 is 12kPa (G). After burning, the mixture is changed into carbon dioxide, water vapor, nitrogen and oxygen. 4912kg/h, 450 deg.C low temperature flue gas enters the combustion furnace 1, and is mixed with the mixed gas after combustion to form 5231kg/h, 550 deg.C high temperature flue gas.
The high-temperature flue gas enters a heat exchanger 9 for heat exchange, and when leaving the reactor, the high-temperature flue gas is changed into 5231kg/h, the low-temperature flue gas at 450 ℃ has the heat transfer capacity of 179422W.
The low-temperature flue gas is divided into 4912kg/h and returned to the combustion furnace 1 through a circulating fan 3. The pressure value at the pressure gauge was set to 5kpa (g). The opening degree of the flue gas regulating valve 4 is controlled by a pressure gauge signal, and 319kg/h low-temperature flue gas is automatically discharged by pressure through the regulating valve.
The volume flow of the high-temperature flue gas entering the heat exchanger 9 is 12310m3The volume flow of the low-temperature flue gas out of the heat exchanger is 10814m3H, mean volume flow 11562m3/h。
The highest temperature of the whole flue gas pipeline is 550 ℃, and the flue gas pipeline and the flue gas coil pipe can be made of stainless steel 310
Example 3
In this embodiment, as a preferred embodiment of the present invention, a specific structure is shown in fig. 2, which discloses the following improvement on the basis of embodiment 1, an external discharge regulating valve 7 is arranged between the circulating fan 3 and the combustion furnace 1, the external discharge regulating valve 7 is connected with an external discharge fan 8, and flue gas pipelines used in the system are all made of stainless steel 304.
Through setting up outer row governing valve 7, can be with unnecessary low temperature flue gas discharge system, avoid firing burning furnace 1 internal pressure too big.
Cost savings can be achieved by using ordinary piping.
230kg/h ethanol and 6482kg/h combustion air were fed to the furnace 1 for combustion. The operation pressure in the combustion furnace 1 is-5 kPa (G), and the air for combustion is automatically sucked into the combustion furnace 1 after being regulated by an external discharge regulating valve 7 and an external discharge fan 8; 30900kg/h of low-temperature flue gas at 300 ℃ also enters the combustion furnace 1 and is mixed with the mixed gas after combustion to form high-temperature flue gas at 400 ℃, 5kPa (G) and 37612 kg/h. The high temperature flue gas in the heat exchanger 9 provides 1158521W heat for the process air, and the temperature of the process air is reduced to 300 ℃ to become low temperature flue gas. The pressure gauge on the low-temperature flue gas header pipe after heat exchange is set to be-8 kPa (G) and is controlled by the flow of discharged flue gas. 6712kg/h low temperature flue gas is changed into positive pressure by an external exhaust fan 8 to be discharged.
The highest temperature of the whole flue gas system is 400 ℃, and the flue gas system is made of cheap stainless steel 304.
Comparative example 1
The conditions of natural gas and combustion air were unchanged compared to example 2. The high-temperature flue gas from the heat exchanger 9 is completely discharged and does not return to the combustion furnace 1. 319kg/h of high-temperature flue gas at the outlet of the combustion furnace 1, the temperature is over 1000 ℃ (the theoretical calculation value reaches 1914 ℃). The temperature of the flue gas leaving the heat exchanger 9 was still 450 ℃ and the heat transfer to the process mass was 179422W in accordance with example 1. The average flow velocity in the coil is 4.7m/s, and the heat transfer coefficient is 12W/m 2-K.
Because the high-temperature flue gas temperature is too high, special materials are required to be selected, and the prices of the flue gas pipeline and the flue gas coil pipe are several times to dozens of times higher than those of common steel.
Comparative example 2
The conditions of natural gas and combustion air were unchanged compared to example 3. The high-temperature flue gas from the heat exchanger 9 is completely discharged and does not return to the combustion furnace 1. The temperature of the high-temperature flue gas entering the heat exchanger 9 is 833 ℃, and the temperature of the low-temperature flue gas leaving the heat exchanger 9 is 300 ℃. The high-temperature flue gas pipeline and the heat exchanger need to be resistant to 833 ℃ and need to be made of special temperature-resistant materials.
The above embodiments are just exemplified in the present embodiment, but the present embodiment is not limited to the above alternative embodiments, and those skilled in the art can obtain other various embodiments by arbitrarily combining with each other according to the above embodiments, and any other various embodiments can be obtained by anyone in light of the present embodiment. The above detailed description should not be construed as limiting the scope of the present embodiments, which should be defined in the claims, and the description should be used for interpreting the claims.
Claims (7)
1. A flue gas heating system comprises a combustion furnace (1), and is characterized in that: the combustion furnace (1) is connected with one end of a heat exchanger (9) in the fluidized bed reactor (2), the other end of the heat exchanger (9) is connected with a circulating fan (3), and the circulating fan (3) is communicated with the combustion furnace (1).
2. A flue gas heating system according to claim 1, wherein: and a flue gas regulating valve (4) is arranged between the heat exchanger (9) and the circulating fan (3).
3. A flue gas heating system according to claim 1, wherein: the combustion furnace (1) is also connected with an air fan (5).
4. A flue gas heating system according to claim 1, wherein: and a protective gas inlet (6) is arranged between the circulating fan (3) and the combustion furnace (1).
5. A flue gas heating system according to claim 1, wherein: an external discharge regulating valve (7) is arranged between the circulating fan (3) and the combustion furnace (1).
6. A flue gas heating system according to claim 5, wherein: the outer discharge regulating valve (7) is connected with an outer discharge fan (8).
7. A flue gas heating system according to claim 1, wherein: the flue gas pipeline used in the system is made of stainless steel 304 or stainless steel 310.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202121839487.4U CN215570418U (en) | 2021-08-06 | 2021-08-06 | Flue gas heating system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202121839487.4U CN215570418U (en) | 2021-08-06 | 2021-08-06 | Flue gas heating system |
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| Publication Number | Publication Date |
|---|---|
| CN215570418U true CN215570418U (en) | 2022-01-18 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202121839487.4U Active CN215570418U (en) | 2021-08-06 | 2021-08-06 | Flue gas heating system |
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| CN (1) | CN215570418U (en) |
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2021
- 2021-08-06 CN CN202121839487.4U patent/CN215570418U/en active Active
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