Smoke low-nitrogen combustion process system and process method for expanded cut tobacco incinerator

Abstract

The process system comprises a high-temperature heat exchanger, a hot side inlet of the high-temperature heat exchanger is connected with an outlet of the incinerator, a hot side outlet of the high-temperature heat exchanger is connected with a hot side inlet of a medium-temperature heat exchanger, and a hot side outlet of the medium-temperature heat exchanger is connected with a hot side inlet of a low-temperature heat exchanger; a hot side outlet of the low-temperature heat exchanger is connected with a chimney inlet, a cold side inlet of the high-temperature heat exchanger is connected with a process fan outlet, a cold side outlet of the high-temperature heat exchanger is connected with a cut tobacco expansion device inlet, and a cut tobacco expansion device outlet is connected with a process fan inlet. An outlet of the waste gas fan is connected with a cold-side inlet of the medium-temperature heat exchanger, a cold-side outlet of the medium-temperature heat exchanger is connected with a combustion-supporting gas inlet of the incinerator, a cold-side inlet of the low-temperature heat exchanger is connected with the combustion-supporting gas inlet, a cold-side outlet of the low-temperature heat exchanger is connected with an inlet of the waste gas fan, and the chimney is provided with a flue gas leading-out port used for leading circulating flue gas into the incinerator. According to the invention, the generation amount of nitrogen oxides can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of tobacco processing, and in particular relates to a low-nitrogen combustion process system and process method for flue gas from an expanded tobacco incinerator. Background Art

[0002] The incinerator at the hot end of expanded tobacco in a cigarette factory is the core equipment of the hot end of the dry ice expanded tobacco line. It is a hot air furnace that uses natural gas combustion to heat the process gas for expanding tobacco, and a waste gas incinerator that incinerates the process waste gas after the tobacco expansion is completed. It is an industrial furnace with dual functions. The process gas heated by the incinerator enters the tobacco expansion device to heat and dehydrate the tobacco therein to complete the expansion of the tobacco, and the process gas becomes process waste gas after the tobacco expansion is completed.

[0003] Since the above-mentioned incinerator needs to burn the process waste gas after the tobacco is expanded, and the process waste gas contains nitrogen-containing organic matter volatilized after the tobacco is expanded, the concentration of nitrogen oxides in the combustion flue gas generated by the incinerator is much higher than that of the general natural gas hot air furnace. The converted concentration of nitrogen oxides in the combustion flue gas generated by the incinerator reaches 200mg / Nm under normal operation. 3 Above, the untreated emission values ​​do not meet national or local standards. Summary of the invention

[0004] In view of the above-mentioned defects of the prior art, the present invention provides a low-nitrogen combustion process system and process method for the flue gas of an expanded tobacco incinerator, which introduces part of the flue gas in the chimney into the incinerator as circulating flue gas to reduce the oxygen content of the mixed gas formed by the mixing of the combustion-supporting gas, the process waste gas and the circulating flue gas, thereby reducing the peak combustion temperature, making the combustion temperature more uniform, and reducing the generation of nitrogen oxides, while reducing energy consumption.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A low-nitrogen combustion process system for flue gas from an expanded tobacco incinerator, comprising a high-temperature heat exchanger, wherein the hot side inlet of the high-temperature heat exchanger is connected to the outlet of the incinerator and the hot side outlet is connected to the hot side inlet of a medium-temperature heat exchanger, the hot side outlet of the medium-temperature heat exchanger is connected to the hot side inlet of a low-temperature heat exchanger, the hot side outlet of the low-temperature heat exchanger is connected to the inlet of a chimney, the cold side inlet of the high-temperature heat exchanger is connected to the outlet of a process fan and the cold side outlet is connected to the inlet of a tobacco expansion device, the outlet of the tobacco expansion device is connected to the inlet of the process fan, the outlet of the process fan is also connected to the inlet of an exhaust gas fan, the outlet of the exhaust gas fan is connected to the cold side inlet of the medium-temperature heat exchanger, the cold side outlet of the medium-temperature heat exchanger is connected to the combustion-supporting gas inlet of the incinerator, the cold side inlet of the low-temperature heat exchanger is connected to the combustion-supporting gas inlet and the cold side outlet is connected to the inlet of the exhaust gas fan, and the chimney is provided with a flue gas outlet for introducing circulating flue gas into the incinerator.

[0007] Furthermore, the flue gas outlet is connected to one end of a flue gas external circulation pipeline, and the other end of the flue gas external circulation pipeline is connected to a pipeline between the combustion-supporting gas inlet and the cold side inlet of the low-temperature heat exchanger.

[0008] Furthermore, the smoke inlet is connected to one end of a smoke external circulation pipe, and the other end of the smoke external circulation pipe is connected to a pipe between a cold side outlet of the low-temperature heat exchanger and an inlet of an exhaust gas fan.

[0009] Furthermore, the smoke inlet is connected to one end of a smoke external circulation pipe, and the other end of the smoke external circulation pipe is connected to a pipe between a process fan outlet and an exhaust gas fan inlet.

[0010] Furthermore, the flue gas outlet is connected to one end of a flue gas external circulation pipe, and the other end of the flue gas external circulation pipe is connected to a pipe between the cold side outlet of the medium temperature heat exchanger and the combustion-supporting gas inlet of the incinerator.

[0011] Furthermore, a smoke regulating valve is provided on the smoke external circulation pipeline for regulating the amount of circulating smoke entering the smoke external circulation pipeline.

[0012] Furthermore, a variable frequency flue gas circulation fan is provided on the flue gas external circulation duct to adjust the amount of circulating flue gas entering the flue gas external circulation duct.

[0013] Furthermore, the process fan outlet is connected to the cold side inlet of the high-temperature heat exchanger by a first pipe, and the process fan outlet is connected to the inlet of the tobacco expansion device by a second pipe. The first pipe is provided with a first regulating valve for regulating the amount of gas entering the first pipe through the process fan, and the second pipe is provided with a second regulating valve for regulating the amount of gas entering the second pipe through the process fan. The first regulating valve and the second regulating valve cooperate to regulate the temperature of the gas entering the tobacco expansion device; the process fan outlet is connected to the exhaust gas fan inlet by a third pipe, and the third pipe is provided with a third regulating valve for regulating the amount of gas entering the third pipe through the process fan.

[0014] A low-nitrogen combustion process method for flue gas in an expanded tobacco incinerator, specifically: the process gas extracted by the process fan enters the high-temperature heat exchanger and is heated, the heated process gas enters the tobacco expansion device to heat the tobacco and complete the expansion of the tobacco, and the process gas becomes process waste gas after the tobacco expansion is completed, one part of the process waste gas discharged from the tobacco expansion device passes through the process fan and the high-temperature heat exchanger in turn and enters the tobacco expansion device again, the other part of the process waste gas passes through the process fan and is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger, and then enters the medium-temperature heat exchanger through the waste gas fan and is heated, and then enters the incinerator and is mixed with natural gas to burn the natural gas, and the flue gas generated after combustion passes through the high-temperature heat exchanger, the medium-temperature heat exchanger and the low-temperature heat exchanger in turn and is discharged to the outside through a chimney, wherein part of the flue gas in the chimney passes through the flue gas outlet and is introduced into the incinerator as circulating flue gas.

[0015] Further, part of the flue gas is introduced into the incinerator as circulating flue gas through the flue gas outlet, specifically including the following methods:

[0016] 1) The pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the cold side inlet of the low-temperature heat exchanger is used to form a driving force, so that part of the flue gas in the chimney passes through the flue gas outlet and the flue gas external circulation pipeline in turn and is mixed with the combustion-supporting gas, then enters the low-temperature heat exchanger and is heated, and then is mixed with the process exhaust gas passing through the process fan, enters the medium-temperature heat exchanger through the exhaust gas fan and is heated, and then enters the incinerator;

[0017] 2) The pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the cold side outlet of the low-temperature heat exchanger is used to form a driving force, so that part of the flue gas in the chimney passes through the flue gas outlet and the flue gas external circulation pipeline in turn and is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger, and then is mixed with the process exhaust gas passing through the process fan at the inlet of the exhaust gas fan, and then enters the medium-temperature heat exchanger through the exhaust gas fan and is heated, and then enters the incinerator;

[0018] 3) Using the pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the exhaust gas fan inlet to form power, part of the flue gas in the chimney passes through the flue gas outlet and the flue gas external circulation pipeline in turn and is mixed with the process exhaust gas passing through the process fan, and then is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger at the inlet of the exhaust gas fan, and then enters the medium-temperature heat exchanger through the exhaust gas fan and is heated, and then enters the incinerator;

[0019] 4) Using the suction force generated by the variable frequency flue gas circulation fan, part of the flue gas in the chimney passes through the flue gas outlet and the flue gas external circulation pipeline in turn and is mixed with the combustion-supporting gas carrying process waste gas heated by the medium temperature heat exchanger before entering the incinerator.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] The low-nitrogen combustion process system of the flue gas of the expanded tobacco incinerator of the present invention comprises the following steps: the process gas extracted by the process fan enters the high-temperature heat exchanger and is heated; the heated process gas enters the tobacco expansion device to heat the tobacco and complete the expansion of the tobacco; the process gas becomes process waste gas after the tobacco expansion is completed; a part of the process waste gas discharged from the tobacco expansion device passes through the process fan and the high-temperature heat exchanger in turn and enters the tobacco expansion device again; the other part of the process waste gas passes through the process fan and is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger; the mixture enters the medium-temperature heat exchanger through the waste gas fan and is heated; the mixture then enters the incinerator and is mixed with natural gas to burn the natural gas; the flue gas generated after the combustion passes through the high-temperature heat exchanger, the medium-temperature heat exchanger and the low-temperature heat exchanger in turn and is discharged to the outside through the chimney; part of the flue gas in the chimney passes through the chimney The gas is drawn out of the chimney and introduced into the incinerator as circulating flue gas; in this way, part of the flue gas in the chimney is introduced into the incinerator as circulating flue gas to reduce the oxygen content of the mixed gas formed by the mixture of the combustion-supporting gas, process waste gas and circulating flue gas entering the incinerator, thereby reducing the peak combustion temperature in the incinerator, making the combustion temperature in the incinerator more uniform, reducing the amount of nitrogen oxides generated from the source, and thus making the nitrogen oxide concentration in the emitted flue gas meet the emission requirements, avoiding the problem of large investment caused by the end-of-pipe treatment method. In addition, since the temperature of the circulating flue gas drawn out from the chimney is relatively high, the furnace temperature of the incinerator will be increased after entering the incinerator, and thus too much natural gas is not needed for combustion, thereby relatively saving the amount of natural gas. Therefore, the low-nitrogen combustion process system of the expanded tobacco incinerator flue gas of the present invention is both environmentally friendly and energy-saving and carbon-reducing.

[0022] In the present invention, the process fan outlet is connected to the cold side inlet of the high-temperature heat exchanger by a first pipe, the process fan outlet is connected to the inlet of the tobacco expansion device by a second pipe, a first regulating valve is provided on the first pipe, a second regulating valve is provided on the second pipe, and the process fan outlet is connected to the exhaust gas fan inlet by a third pipe, and a third regulating valve is provided on the third pipe; in this way, the amount of gas entering the first pipe through the process fan can be adjusted by the first regulating valve, and then the amount of gas entering the tobacco expansion device after being heated by the high-temperature heat exchanger can be adjusted, the amount of gas entering the second pipe through the process fan can be adjusted by the second regulating valve, and then the amount of gas directly entering the tobacco expansion device through the process fan can be adjusted, so the first regulating valve and the second regulating valve can cooperate to adjust the temperature of the gas entering the tobacco expansion device, so as to heat the tobacco more accurately and complete the expansion of the tobacco, and the amount of gas entering the third pipe through the process fan can be adjusted by the third regulating valve, and then the amount of process waste gas entering the incinerator after being heated by the medium-temperature heat exchanger can be adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a gas circulation flow chart of the low-nitrogen combustion process system of flue gas from an expanded tobacco incinerator in Example 1 of the present invention;

[0024] Figure 2 It is a gas circulation flow chart of the low-nitrogen combustion process system of flue gas from an expanded tobacco incinerator in Example 2 of the present invention;

[0025] Figure 3 It is a gas circulation flow chart of the low-nitrogen combustion process system of flue gas from an expanded tobacco incinerator in Example 3 of the present invention;

[0026] Figure 4 This is a gas circulation flow chart of the low-nitrogen combustion process system of the flue gas from the expanded tobacco incinerator in Example 4 of the present invention.

[0027] Explanation of the reference numerals in the figure: 1. high-temperature heat exchanger, 2. incinerator, 3. medium-temperature heat exchanger, 4. low-temperature heat exchanger, 5. chimney, 6. process fan, 7. tobacco expansion device, 8. exhaust gas fan, 9. first pipeline, 10. second pipeline, 11. first regulating valve, 12. second regulating valve, 13. third pipeline, 14. third regulating valve, 15. combustion-supporting gas inlet, 16. combustion-supporting air regulating valve, 17. flue gas external circulation pipeline, 18. flue gas regulating valve, 19. variable frequency flue gas circulation fan, 20. natural gas inlet, 21. environmental process exhaust gas inlet. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. These embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0029] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] like Figure 1-4 As shown, a low-nitrogen combustion process system for flue gas of an expanded tobacco incinerator 2 comprises a high-temperature heat exchanger 1, wherein the hot side inlet of the high-temperature heat exchanger 1 is connected to the outlet of the incinerator 2 and the hot side outlet is connected to the hot side inlet of a medium-temperature heat exchanger 3, the hot side outlet of the medium-temperature heat exchanger 3 is connected to the hot side inlet of a low-temperature heat exchanger 4, the hot side outlet of the low-temperature heat exchanger 4 is connected to the inlet of a chimney 5, the cold side inlet of the high-temperature heat exchanger 1 is connected to the outlet of a process fan 6 and the cold side outlet is connected to the inlet of a tobacco expansion device 7, the outlet of the tobacco expansion device 7 is connected to the inlet of the process fan 6, the outlet of the process fan 6 is also connected to the inlet of an exhaust gas fan 8, the outlet of the exhaust gas fan 8 is connected to the cold side inlet of the medium-temperature heat exchanger 3, the cold side outlet of the medium-temperature heat exchanger 3 is connected to the combustion-supporting gas inlet of the incinerator 2, the cold side inlet of the low-temperature heat exchanger 4 is connected to the combustion-supporting gas inlet 15 and the cold side outlet is connected to the inlet of the exhaust gas fan 8, and the chimney 5 is provided with a flue gas outlet for introducing circulating flue gas into the incinerator 2.

[0032] In this way, the process gas extracted by the process fan 6 enters the high-temperature heat exchanger 1 and is heated. The heated process gas enters the tobacco expansion device 7 to heat the tobacco and complete the expansion of the tobacco. The process gas becomes process waste gas after the tobacco expansion is completed. Part of the process waste gas discharged from the tobacco expansion device 7 passes through the process fan 6 and the high-temperature heat exchanger 1 in turn and enters the tobacco expansion device 7 again. The other part of the process waste gas passes through the process fan 6 and is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger 4, and then enters the medium-temperature heat exchanger 3 through the waste gas fan 8 and is heated. Thereafter, it enters the incinerator 2 and is mixed with natural gas to burn the natural gas. The flue gas generated after combustion passes through the high-temperature heat exchanger 1, the medium-temperature heat exchanger 3 and the low-temperature heat exchanger 4 in turn and is discharged to the outside through the chimney 5, wherein part of the flue gas in the chimney 5 passes through the flue gas outlet and is introduced into the incinerator 2 as circulating flue gas.

[0033] Specifically, natural gas is burned in the incinerator 2 to generate hot flue gas, wherein the natural gas is transported to the incinerator 2 through the natural gas inlet 20, the hot flue gas enters the high-temperature heat exchanger 1 from the hot side inlet of the high-temperature heat exchanger 1 to increase the temperature of the high-temperature heat exchanger 1, and is discharged from the hot side outlet of the high-temperature heat exchanger 1 and enters the medium-temperature heat exchanger 3 from the hot side inlet of the medium-temperature heat exchanger 3 to increase the temperature of the medium-temperature heat exchanger 3, and is discharged from the hot side outlet of the medium-temperature heat exchanger 3 and enters the low-temperature heat exchanger 4 from the hot side inlet of the low-temperature heat exchanger 4 to increase the temperature of the low-temperature heat exchanger 4, and then is discharged to the outside through the chimney 5, wherein the process gas entering the high-temperature heat exchanger 1 from the cold side inlet of the high-temperature heat exchanger 1 is mixed with the process gas from the cold side inlet of the high-temperature heat exchanger 1. The hot flue gas entering the high-temperature heat exchanger 1 from the hot side inlet of the high-temperature heat exchanger 1 undergoes heat exchange, and is heated to the required temperature and enters the tobacco expansion device 7 to heat the tobacco, wherein the gas entering the medium-temperature heat exchanger 3 from the cold side inlet of the medium-temperature heat exchanger 3 undergoes heat exchange with the hot flue gas entering the medium-temperature heat exchanger 3 from the hot side inlet of the medium-temperature heat exchanger 3, and enters the incinerator 2 after being heated, wherein the gas entering the low-temperature heat exchanger 4 from the cold side inlet of the low-temperature heat exchanger 4 undergoes heat exchange with the hot flue gas entering the low-temperature heat exchanger 4 from the hot side inlet of the low-temperature heat exchanger 4, and enters the medium-temperature heat exchanger 3 from the cold side inlet of the medium-temperature heat exchanger 3 through the exhaust gas fan 8 after being heated.

[0034] The present invention introduces part of the flue gas in the chimney 5 into the incinerator 2 as circulating flue gas to reduce the oxygen content of the mixed gas formed by mixing the combustion-supporting gas, process waste gas and circulating flue gas entering the incinerator 2, thereby reducing the peak combustion temperature in the incinerator 2, making the combustion temperature in the incinerator 2 more uniform, reducing the amount of nitrogen oxides generated from the source, and thus making the nitrogen oxide concentration in the emitted flue gas meet the emission requirements, avoiding the problem of large investment caused by the end-of-pipe treatment method. In addition, since the temperature of the circulating flue gas introduced from the chimney 5 is relatively high, the furnace temperature of the incinerator 2 will be increased after entering the incinerator 2, and thus too much natural gas is not required for combustion, thereby relatively saving the amount of natural gas. Therefore, the low-nitrogen combustion process system of the flue gas of the expanded tobacco incinerator 2 of the present invention is both environmentally friendly and energy-saving and carbon-reducing.

[0035] Preferably, the outlet of the process fan 6 is connected to the cold side inlet of the high-temperature heat exchanger 1 by a first pipe 9, and the outlet of the process fan 6 is connected to the inlet of the tobacco expansion device 7 by a second pipe 10. The first pipe 9 is provided with a first regulating valve 11 for regulating the amount of gas entering the first pipe 9 through the process fan 6, and the second pipe 10 is provided with a second regulating valve 12 for regulating the amount of gas entering the second pipe 10 through the process fan 6. The first regulating valve 11 and the second regulating valve 12 cooperate to regulate the temperature of the gas entering the tobacco expansion device 7; the outlet of the process fan 6 is connected to the inlet of the exhaust gas fan 8 by a third pipe 13, and the third pipe 13 is provided with a third regulating valve 14 for regulating the amount of gas entering the third pipe 13 through the process fan 6.

[0036] In this way, the first regulating valve 11 can be used to adjust the amount of gas entering the first pipeline 9 through the process fan 6, and then the amount of gas entering the tobacco expansion device 7 after being heated by the high-temperature heat exchanger 1 can be adjusted. The second regulating valve 12 can be used to adjust the amount of gas entering the second pipeline 10 through the process fan 6, and then the amount of gas directly entering the tobacco expansion device 7 through the process fan 6 can be adjusted. Therefore, the first regulating valve 11 and the second regulating valve 12 can cooperate to adjust the temperature of the gas entering the tobacco expansion device 7 so as to heat the tobacco more accurately and complete the expansion of the tobacco. The third regulating valve 14 can be used to adjust the amount of gas entering the third pipeline 13 through the process fan 6, and then the amount of process waste gas entering the incinerator 2 after being heated by the medium-temperature heat exchanger 3 can be adjusted.

[0037] Preferably, the combustion-supporting gas is combustion-supporting air, and a combustion-supporting air regulating valve 16 is provided on the pipeline between the combustion-supporting gas inlet 15 and the cold side inlet of the low-temperature heat exchanger 4, which is used to adjust the amount of combustion-supporting air entering the cold side inlet of the low-temperature heat exchanger 4. Preferably, the ambient process exhaust gas is mixed with the combustion-supporting air and then drawn to the cold side inlet of the low-temperature heat exchanger 4, wherein the inlet of the ambient process exhaust gas is called the ambient process exhaust gas inlet 21.

[0038] Example 1

[0039] like Figure 1 As shown, the flue gas outlet is connected to one end of the flue gas external circulation pipeline 17, and the other end of the flue gas external circulation pipeline 17 is connected to the pipeline between the combustion-supporting gas inlet 15 and the cold side inlet of the low-temperature heat exchanger 4.

[0040] In this way, the pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure at the cold side inlet of the low-temperature heat exchanger 4 is used to form power, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and mixes with the combustion air to enter the low-temperature heat exchanger 4 and be heated, and then mixes with the process exhaust gas passing through the process fan 6 and enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as an auxiliary combustion gas for natural gas.

[0041] Example 2

[0042] like Figure 2 As shown, the flue gas outlet is connected to one end of the flue gas external circulation pipe 17, and the other end of the flue gas external circulation pipe 17 is connected to the pipe between the cold side outlet of the low-temperature heat exchanger 4 and the inlet of the exhaust gas fan 8.

[0043] In this way, the pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the cold side outlet of the low-temperature heat exchanger 4 is used to form power, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and is mixed with the combustion air heated by the low-temperature heat exchanger 4. After that, it is mixed with the process exhaust gas passing through the process fan 6 at the inlet of the exhaust gas fan 8, and then enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as an auxiliary combustion gas for natural gas.

[0044] Example 3

[0045] like Figure 3 As shown, the flue gas outlet is connected to one end of the flue gas external circulation pipeline 17, and the other end of the flue gas external circulation pipeline 17 is connected to the pipeline between the outlet of the process fan 6 and the inlet of the exhaust gas fan 8.

[0046] In this way, the pressure difference generated by the slight positive pressure at the flue gas outlet and the negative pressure at the inlet of the exhaust gas fan 8 is used to generate power, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and is mixed with the process exhaust gas passing through the process fan 6. After that, it is mixed with the combustion-supporting air heated by the low-temperature heat exchanger 4 at the inlet of the exhaust gas fan 8, and then enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as an auxiliary combustion gas for natural gas.

[0047] In embodiments 1, 2 and 3, a flue gas regulating valve 18 is provided on the flue gas external circulation duct 17 for regulating the amount of circulating flue gas entering the flue gas external circulation duct 17 .

[0048] Example 4

[0049] like Figure 4 As shown, the flue gas outlet is connected to one end of the flue gas external circulation pipe 17, and the other end of the flue gas external circulation pipe 17 is connected to the pipe between the cold side outlet of the medium-temperature heat exchanger 3 and the combustion gas inlet of the incinerator 2. The flue gas external circulation pipe 17 is provided with a variable frequency flue gas circulation fan 19 for adjusting the amount of circulating flue gas entering the flue gas external circulation pipe 17.

[0050] In this way, the suction force generated by the variable frequency flue gas circulation fan 19 is utilized to make part of the flue gas in the chimney 5 pass through the flue gas outlet and the flue gas external circulation pipe 17 in turn and mix with the combustion air carrying process exhaust gas heated by the medium temperature heat exchanger 3, and then enter the incinerator 2 and serve as the auxiliary combustion gas of natural gas.

[0051] A low-nitrogen combustion process method for flue gas of an expanded tobacco incinerator 2, specifically: the process gas extracted by the process fan 6 enters the high-temperature heat exchanger 1 and is heated, the heated process gas enters the tobacco expansion device 7 to heat the tobacco and complete the expansion of the tobacco, the process gas becomes process waste gas after the tobacco expansion is completed, most of the process waste gas discharged from the tobacco expansion device 7 passes through the process fan 6 and the high-temperature heat exchanger 1 in turn and enters the tobacco expansion device 7 again, while a small part of the process waste gas passes through the process fan 6 and is mixed with the combustion-supporting air heated by the low-temperature heat exchanger 4, and then enters the medium-temperature heat exchanger 3 through the waste gas fan 8 and is heated, and then enters the incinerator 2 and is mixed with natural gas to burn the natural gas, the flue gas generated after combustion passes through the high-temperature heat exchanger 1, the medium-temperature heat exchanger 3 and the low-temperature heat exchanger 4 in turn and is discharged to the outside through the chimney 5, wherein part of the flue gas in the chimney 5 is introduced into the incinerator 2 as circulating flue gas through the flue gas outlet, specifically including the following methods:

[0052] 1) The pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the cold side inlet of the low-temperature heat exchanger 4 is used to form power, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipeline 17 in turn and is mixed with the combustion air and then enters the low-temperature heat exchanger 4 and is heated, and then is mixed with the process exhaust gas passing through the process fan 6 and enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as the auxiliary combustion gas of natural gas;

[0053] 2) The pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure of the cold side outlet of the low-temperature heat exchanger 4 is used to form a driving force, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and is mixed with the combustion-supporting air heated by the low-temperature heat exchanger 4, and then is mixed with the process exhaust gas passing through the process fan 6 at the inlet of the exhaust gas fan 8, and then enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as the auxiliary combustion gas of natural gas;

[0054] 3) The pressure difference generated by the slight positive pressure of the flue gas outlet and the negative pressure at the inlet of the exhaust gas fan 8 is used to form a driving force, so that part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and is mixed with the process exhaust gas passing through the process fan 6, and then is mixed with the combustion-supporting air heated by the low-temperature heat exchanger 4 at the inlet of the exhaust gas fan 8, and then enters the medium-temperature heat exchanger 3 through the exhaust gas fan 8 and is heated, and then enters the incinerator 2 and serves as the auxiliary combustion gas of natural gas;

[0055] 4) By utilizing the suction force generated by the variable frequency flue gas circulation fan 19, part of the flue gas in the chimney 5 passes through the flue gas outlet and the flue gas external circulation pipe 17 in turn and is mixed with the combustion air carrying process exhaust gas heated by the medium temperature heat exchanger 3, and then enters the incinerator 2 and serves as the auxiliary combustion gas of the natural gas.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A low-nitrogen combustion process system for flue gas from an expanded tobacco incinerator, characterized in that: The invention comprises a high-temperature heat exchanger (1), wherein the hot side inlet of the high-temperature heat exchanger (1) is connected to the outlet of the incinerator (2), and the hot side outlet is connected to the hot side inlet of the medium-temperature heat exchanger (3), the hot side outlet of the medium-temperature heat exchanger (3) is connected to the hot side inlet of the low-temperature heat exchanger (4), the hot side outlet of the low-temperature heat exchanger (4) is connected to the inlet of the chimney (5), the cold side inlet of the high-temperature heat exchanger (1) is connected to the outlet of the process fan (6), and the cold side outlet is connected to the inlet of the tobacco expansion device (7), and the outlet of the tobacco expansion device (7) is connected to the inlet of the process fan (6). The inlet of the process fan (6) is connected, the outlet of the process fan (6) is also connected to the inlet of the exhaust gas fan (8), the outlet of the exhaust gas fan (8) is connected to the cold side inlet of the medium temperature heat exchanger (3), the cold side outlet of the medium temperature heat exchanger (3) is connected to the combustion-supporting gas inlet of the incinerator (2), the cold side inlet of the low temperature heat exchanger (4) is connected to the combustion-supporting gas inlet (15) and the cold side outlet is connected to the inlet of the exhaust gas fan (8), and the chimney (5) is provided with a flue gas outlet for introducing circulating flue gas into the incinerator (2).

2. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 1, characterized in that: The flue gas outlet is connected to one end of a flue gas external circulation pipeline (17), and the other end of the flue gas external circulation pipeline (17) is connected to a pipeline between the combustion-supporting gas inlet (15) and the cold side inlet of the low-temperature heat exchanger (4).

3. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 1, characterized in that: The smoke outlet is connected to one end of a smoke external circulation pipe (17), and the other end of the smoke external circulation pipe (17) is connected to a pipe between the cold side outlet of the low-temperature heat exchanger (4) and the inlet of the exhaust gas fan (8).

4. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 1, characterized in that: The smoke outlet is connected to one end of a smoke external circulation pipe (17), and the other end of the smoke external circulation pipe (17) is connected to a pipe between the outlet of the process fan (6) and the inlet of the exhaust gas fan (8).

5. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 1, characterized in that: The smoke outlet is connected to one end of a smoke external circulation pipe (17), and the other end of the smoke external circulation pipe (17) is connected to a pipe between the cold side outlet of the medium temperature heat exchanger (3) and the combustion-supporting gas inlet of the incinerator (2).

6. A low-nitrogen combustion process system for flue gas from an expanded tobacco incinerator according to claim 2, 3 or 4, characterized in that: The smoke external circulation pipe (17) is provided with a smoke regulating valve (18) for regulating the amount of circulating smoke entering the smoke external circulation pipe (17).

7. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 5, characterized in that: The smoke external circulation pipeline (17) is provided with a variable frequency smoke circulation fan (19) for adjusting the amount of circulating smoke entering the smoke external circulation pipeline (17).

8. The low-nitrogen combustion process system of expanded tobacco incinerator flue gas according to claim 1, characterized in that: The outlet of the process fan (6) is connected to the cold side inlet of the high-temperature heat exchanger (1) via a first pipe (9), and the outlet of the process fan (6) is connected to the inlet of the tobacco expansion device (7) via a second pipe (10). The first pipe (9) is provided with a first regulating valve (11) for regulating the amount of gas entering the first pipe (9) through the process fan (6). The second pipe (10) is provided with a second regulating valve (12) for regulating the amount of gas entering the second pipe (10) through the process fan (6). The first regulating valve (11) and the second regulating valve (12) cooperate to regulate the temperature of the gas entering the tobacco expansion device (7). The outlet of the process fan (6) is connected to the inlet of the exhaust gas fan (8) via a third pipe (13). The third pipe (13) is provided with a third regulating valve (14) for regulating the amount of gas entering the third pipe (13) through the process fan (6).

9. A method for low-nitrogen combustion of flue gas from an expanded tobacco incinerator, using the low-nitrogen combustion process system for flue gas from an expanded tobacco incinerator as claimed in any one of claims 1, 2, 3, 4, 5, 7 or 8, characterized in that: Specifically, the process gas extracted by the process fan (6) enters the high-temperature heat exchanger (1) and is heated. The heated process gas enters the tobacco expansion device (7) to heat the tobacco and complete the expansion of the tobacco. After the tobacco expansion is completed, the process gas becomes process waste gas. A part of the process waste gas discharged from the tobacco expansion device (7) passes through the process fan (6) and the high-temperature heat exchanger (1) in sequence and enters the tobacco expansion device (7) again. The other part of the process waste gas passes through the process fan (6). (6) and mixed with the combustion-supporting gas heated by the low-temperature heat exchanger (4), and then enter the medium-temperature heat exchanger (3) through the exhaust gas fan (8) and be heated, and then enter the incinerator (2) and mix with the natural gas to burn the natural gas, and the flue gas generated after the combustion passes through the high-temperature heat exchanger (1), the medium-temperature heat exchanger (3) and the low-temperature heat exchanger (4) in sequence and is discharged to the outside through the chimney (5), wherein part of the flue gas in the chimney (5) is introduced into the incinerator (2) through the flue gas outlet as circulating flue gas.

10. The low-nitrogen combustion process of expanded tobacco incinerator flue gas according to claim 9, characterized in that: Part of the flue gas is introduced into the incinerator (2) as circulating flue gas through the flue gas outlet, specifically including the following methods: 1) Part of the flue gas in the chimney (5) passes through the flue gas outlet and the flue gas external circulation pipe (17) in sequence and is mixed with the combustion-supporting gas before entering the low-temperature heat exchanger (4) and being heated. Thereafter, the part of the flue gas is mixed with the process waste gas passing through the process fan (6) and is passed through the waste gas fan (8) before entering the medium-temperature heat exchanger (3) and being heated. Thereafter, the part of the flue gas enters the incinerator (2); 2) a portion of the flue gas in the chimney (5) passes through the flue gas outlet and the flue gas external circulation pipe (17) in sequence and is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger (4), and then is mixed with the process exhaust gas passing through the process fan (6) at the inlet of the exhaust gas fan (8), and then enters the medium-temperature heat exchanger (3) through the exhaust gas fan (8) and is heated, and then enters the incinerator (2); 3) a portion of the flue gas in the chimney (5) passes through the flue gas outlet and the flue gas external circulation pipe (17) in sequence and is mixed with the process waste gas passing through the process fan (6), and then is mixed with the combustion-supporting gas heated by the low-temperature heat exchanger (4) at the inlet of the waste gas fan (8), and then passes through the waste gas fan (8) into the medium-temperature heat exchanger (3) and is heated, and then enters the incinerator (2); 4) Part of the flue gas in the chimney (5) passes through the flue gas outlet and the flue gas external circulation pipe (17) in sequence and is mixed with the combustion-supporting gas carrying the process waste gas after being heated by the medium-temperature heat exchanger (3), and then enters the incinerator (2).

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