CN115265182A - Belt type roasting machine production line for classified cooling of pellets - Google Patents

Abstract

The invention discloses a production line of a belt type roasting machine for classified cooling of pellets, which comprises the following steps: the system comprises a belt type roasting machine, a first cold air pipe, a second cold air pipe and a heat regeneration mechanism; the straight grate comprises: a blast drying section, an air draft drying section, a preheating section, a roasting section, a cooling section and a cooling section are sequentially arranged along the processing movement direction of the pellets; the outlet of the air-blast drying section is connected with the inlet of a cold air pipe, and the outlet of the cold air pipe is connected with the cooling section; the outlet of the cooling section being connected to the roasting sectionThe outlet of the air draft drying section, the outlet of the preheating section and the outlet of the roasting section are used for being connected with the inlet of the waste gas discharge system; the inlet of the secondary cooling air pipe is used for being connected with the outlet of the cooling fan, and the outlet of the secondary cooling air pipe is connected to the cooling section. The scheme can effectively reduce the exhaust emission, thereby effectively reducing the dust and SO of the pellet production process ₂ And NO _X And the total amount of pollutants discharged is equal, so that the effects of energy conservation and emission reduction are achieved.

Description

A belt-type roasting machine production line with graded cooling of pellets

technical field

The invention relates to the technical field of iron and steel metallurgy, in particular to a belt roaster production line for pellet cooling by stages.

Background technique

The belt roaster process is currently a major process for pellet production in iron and steel metallurgical enterprises, and the waste gas emitted from its production is mainly composed of the main exhaust system and the furnace hood exhaust system. Among them, the fume exhaust system of the furnace hood mainly deals with the hot air after the raw pellets are dried. The exhaust gas mainly comes from the cooling air duct, after the cooling pellets become hot air at about 300°C, and then enter the dry section of the dry bulb through the blower to dry the wet bulb, and after the moisture in the wet bulb is brought out, the temperature drops to about 100°C. After being dedusted by the furnace hood dust collector, it reaches the emission standard and is discharged.

According to the relevant provisions of GB 21256-2013 "Crude Steel Production Main Process Unit Product Energy Consumption Limits": The new construction and expansion of crude steel production main process unit product energy consumption pellet process access value must be ≤ 24kgce/t. And "we should strive to make the pelletizing process reach the advanced value of ≤ 15kgce/t through energy-saving technological transformation and strengthening energy-saving management." Through the joint efforts of experts and scholars in the industry and the promotion of advanced equipment, the energy consumption of the pelletizing process in iron and steel plants has reached ≤20kgce/t, but it is still far away from the advanced value index of ≤15kgce/t.

Therefore, how to optimize the existing process to realize energy saving and emission reduction has become an important technical problem to be solved urgently by those skilled in the art.

Contents of the invention

In view of this, the present invention provides a pellet grading cooling belt roaster production line, which can effectively reduce exhaust gas emissions, thereby effectively reducing the discharge of dust, SO ₂ and NO _X and other pollutants in the pellet production process Total amount, to achieve the effect of energy saving and emission reduction.

To achieve the above object, the present invention provides the following technical solutions:

A belt roasting machine production line for graded cooling of pellets, including: a belt roasting machine, a first cold air pipe, a second cold air pipe and a heat recovery mechanism;

The belt roaster includes: a blast drying section, a draft drying section, a preheating section, a roasting section, a cooling section and a cooling section 2 arranged in sequence along the pellet processing movement direction;

The outlet of the blast drying section is connected to the inlet of the cold air pipe, and the outlet of the cold air pipe is connected to the cooling section;

The outlet of the cooling section is connected to the inlet of the roasting section, the outlet of the roasting section is connected to the inlet of the air drying section through the heat recovery mechanism, the air drying section, the preheating section and the The outlet of the roasting section is used to connect the inlet of the waste gas exhaust system;

The inlet of the two cooling air pipes is used to connect to the outlet of the cooling fan, and the outlet of the two cooling air pipes is connected to the second cooling section.

Preferably, it also includes: the exhaust gas exhaust system.

Preferably, the waste gas exhaust system includes: a main electrostatic precipitator and a main exhaust fan connected in sequence.

Preferably, the exhaust gas evacuation system further includes: a main flue gas main pipe, a denitrification and desulfurization system, and a chimney.

Preferably, the heat recovery mechanism includes: a heat recovery main air duct and a heat recovery fan.

Preferably, it also includes: a blow dryer;

The outlet of the second cooling section is connected to the inlet of the blast drying section through the blast drying fan.

Preferably, it also includes: a furnace hood row cooling air fan;

The outlet of the blast drying section is connected to the inlet of the first cold air pipe through the hood exhaust air cooler.

Preferably, it also includes: a regulating valve; the first cold air pipe communicates with the second cold air pipe through the regulating valve;

Alternatively, the first cold air pipe and the two cold air pipes are connected as a whole to form a main cooling air pipe.

Preferably, it also includes: the cooling fan.

Preferably, the controllers of the cooling fan, the main exhaust fan of the exhaust gas exhaust system, the heat recovery fan of the heat recovery mechanism, the blower fan and the hood cooling air fan are all frequency conversion controllers.

It can be seen from the above-mentioned technical scheme that the belt-type roaster production line of pellet graded cooling provided by the present invention optimizes the existing belt-type roaster production process, reduces waste gas emissions by about 35%, and makes The sensible heat of this part of the exhaust gas remains in the system, which reduces the investment and operation and maintenance costs of the furnace hood dust collector, furnace hood chimney and other equipment, and also reduces the capacity of the cooling fan, which can greatly reduce the energy consumption of the process , to make a small contribution to reducing carbon emissions.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the structural schematic diagram of the band roaster of pellet graded cooling provided by the embodiment of the present invention;

Fig. 2 is the schematic structural view of the 4 million tons belt roaster pellet production line provided by the embodiment of the present invention;

Fig. 3 is a schematic structural view of a 2,000,000-ton belt roaster pellet production line provided by the embodiment of the present invention;

Fig. 4 is a schematic structural diagram of another 2 million tons belt roaster pellet production line provided by the embodiment of the present invention.

Wherein, 10 is a belt roaster, 11 is a blast drying section, 12 is an air drying section, 13 is a roasting section, 14 is a cooling section, and 15 is a cooling section two;

21 is a cold air duct, and 22 is a second cold air duct;

31 is a drying blower, and 32 is a furnace hood row cooling air blower;

40 is the main exhaust pipe, 41 is the electrostatic precipitator, 42 is the exhaust fan, 43 is the denitrification and desulfurization system, and 44 is the chimney;

51 is the heat recovery main air duct, and 52 is the heat recovery blower.

Detailed ways

First, explain the technical terms involved in this program as follows:

Belt roaster: a process equipment for pellet production;

Furnace hood dust collector: Furnace hood exhaust gas emission treatment and purification equipment.

Cooling fan: provide cooling air to reduce the pellet temperature to low temperature.

Drying fan: Make the hot air that has partially cooled the pellets dry the wet pellets.

Main exhaust system: the waste gas exhaust system produced by the roasting machine (including the main electrostatic precipitator, main exhaust fan, desulfurization and denitration equipment, etc.).

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

After a number of actual measurements, the exhaust gas from the furnace hood has a temperature of about 100°C, an oxygen content of about 21%, and a small amount of SO ₂ and NO _X (both within the emission range stipulated by the state). The exhaust gas is actually air, and the output ratio of the waste heat recovery device is not high, and the waste of direct emission of energy is serious. Therefore, the high-temperature pellet grading cooling technology is used as the cooling air for cooling the high-temperature pellets; when the pellets are cooled below 600°C, normal-temperature air is used for cooling to ensure that the cooling effect is consistent with the traditional process.

The belt roaster production line for pellet graded cooling provided in the embodiment of the present invention includes: a belt roaster 10, a cold air pipe 21, a second cold air pipe 22 and a heat recovery mechanism, the structure of which can be shown in FIG. 1 ;

Wherein, the belt roaster 10 includes: a blast drying section 11, a draft drying section 12, a preheating section, a roasting section 13, a cooling section 14 and a cooling section 15 arranged in sequence along the pellet processing movement direction;

The outlet of the blast drying section 11 is connected to the inlet of a cold air pipe 21, and the outlet of a cold air pipe 21 is connected to the cooling section 15;

The outlet of the cooling section 13 is connected to the inlet of the roasting section 13, and the outlet of the roasting section 13 is connected to the inlet of the draft drying section 12 through the heat recovery mechanism, and part of the high-temperature waste gas of the roasting section 13 is sent into the draft drying section 12 through the heat recovery mechanism, and the exhaust air The outlet of the drying section 12 is used to connect the inlet of the waste gas exhaust system; it should be noted that the flue gas in the roasting section is divided into two parts, one part is reheated and dried by the reheating mechanism, and the other part of the flue gas is directly discharged outside; it needs to be discharged The flue gas will be combined with the exhaust gas from the exhaust drying section and the preheating section, and then discharged together;

The inlet of the second cold air pipe 22 is used to connect the outlet of the cooling fan 20 , and the outlet of the second cold air pipe 22 is connected to the second section of cooling 15 .

Working process: After the raw balls enter the belt roaster and get the finished balls, they pass through the blast drying section 11, the exhaust drying section 12, the preheating section, the roasting section 13, the soaking section cooling section 14 and the cooling section 15, and become Qualified pellets exit the roaster and enter the blast furnace. This patent divides the cooling air duct into a cold air duct 21 and two cold air ducts 22 . The cooling air from the cooling fan 20 enters the secondary cooling air duct 22 and acts on the second cooling section 15. After cooling the pellets, the cooling air entering the second cooling section 15 becomes hot air at about 300°C and enters the blast drying section 11 to dry the green pellets. moisture. The dried waste gas enters into a cold air pipe 21 and acts on the cooling section 14 to cool down the high-temperature pellets at about 1000°C. The high-temperature flue gas after cooling the pellets is used as the secondary air for roasting the pellets, and is mixed with the gas to heat the pellets. After passing through the heat recovery mechanism, it enters the exhaust air drying section for 12 cycles of drying and cooling. After cooling down, the temperature drops to about 150°C. Exhaust into the atmosphere after treatment by the exhaust system. Under the premise of not affecting the emission requirements of the main exhaust air and the quality of the pellet products, the low-temperature exhaust gas emission will be reduced by about 35%, and the corresponding total emission of dust, SO ₂ and NO _X will be reduced, and the effect of energy saving and emission reduction will be great. It goes without saying.

It can be seen from the above-mentioned technical solutions that in the belt roaster production line for pellet graded cooling provided by the embodiment of the present invention, the original furnace cover waste gas that needs to be discharged outside does not need to be discharged outside, and it is returned to the roaster for recycling. , reducing the amount of exhaust gas emissions, so that the exhaust gas has been fully utilized; thereby improving the heat utilization of the existing roasting machine and reducing energy consumption.

Specifically, a cold air pipe 21 can be connected with 1-20 air boxes, and the size of the air boxes can be freely adjusted according to the process conditions.

The belt roaster production line for pellet graded cooling provided in the embodiment of the present invention also includes: an exhaust gas exhaust system, which is used to treat the exhaust gas produced by the roaster and reduce the emission of dust, SO ₂ and NO _x .

Preferably, the waste gas exhaust system includes: a main electrostatic precipitator 41 and a main exhaust fan 42 connected in sequence, and the original furnace hood dust collector is cancelled. Its structure can refer to that shown in FIG. 1 , the outlet of the main electrostatic precipitator 41 is connected to the inlet of the main exhaust fan 42 . Specifically, the main electrostatic precipitator 41 may be an electrostatic precipitator.

Further, the exhaust gas exhaust system also includes: a main flue gas main pipe 40 , a denitrification and desulfurization system 43 and a chimney 44 . Wherein, the outlet of the exhausting drying section 12 is connected to the inlet of the main flue gas main pipe 40, the outlet of the main flue gas pipe 40 is connected to the inlet of the main electrostatic precipitator 41, and the outlet of the main exhaust fan 42 is connected to the inlet of the denitrification and desulfurization system 43, The outlet of the denitrification and desulfurization system 43 is connected to the inlet of the chimney 44, and the outlet of the chimney 44 is released into the atmosphere.

Specifically, the heat recovery mechanism includes: a heat recovery main air duct 51 and a heat recovery fan 52 . Its structure can be shown in FIG. 1 with reference to, the outlet of the roasting section 13 is connected to the inlet of the reheating main air duct 51 , and the outlet of the regenerating main air duct 51 is connected to the inlet of the draft drying section 12 .

The pellet grading cooling belt roasting machine production line provided by the embodiment of the present invention also includes: a blower dryer 31, the structure of which can be shown in FIG. 1 ;

Wherein, the outlet of the second cooling section 15 is connected to the inlet of the blast drying section 11 through a blower blower 31 . After the cooling pellets in the cooling second section 15 of the cooling air pipeline become hot air at about 300°C, they pass through the drying blower 31 and enter the dry section blasting air 11 to dry the wet pellets.

The pellet grading-cooled belt roaster production line provided by the embodiment of the present invention also includes: a furnace hood row cooling air blower 32, the structure of which can be shown in FIG. 1 ;

Wherein, the outlet of the blast drying section 11 is connected to the inlet of a cold air pipe 21 through a hood row cooling air blower 32 . The dried exhaust gas enters a cold air pipe 21 through the furnace hood cooling air fan 32, and enters the cooling section 14 to cool the high-temperature pellets at about 1000°C.

The pellet grading cooling belt roaster production line provided by the embodiment of the present invention also includes: a regulating valve 23, the structure of which can be shown in FIG. 1 ;

Wherein, the first cold air pipe 21 and the second cold air pipe 22 communicate through a regulating valve 23 . Arranged in this way, the middle of the first cold air pipe 21 and the second cold air pipe 22 is communicated with the regulating valve 23, and the air volume and air temperature of the cooling stage 14 and the cooling stage 15 can be adjusted according to production needs. Alternatively, the first cold air pipe 21 and the second cold air pipe 22 may not be connected with the regulating valve 23, and the cooling air main pipe may be integrally formed, as shown in Fig. 3 and Fig. 4 .

The pellet grading cooling belt roaster production line provided by the embodiment of the present invention further includes: a cooling fan 20 . The cooling air from the cooling fan 20 enters the second cooling air pipe 22 and acts on the second cooling section 15. After the cooling air entering the second cooling section 15 cools the pellets, it becomes hot air at about 300°C.

Preferably, the controllers of the cooling fan 20, the main exhaust fan 42 of the exhaust gas exhaust system, the heat recovery fan 52 of the heat recovery mechanism, the drying blower 31 and the furnace hood cooling air fan 32 are all frequency conversion controllers. In order to ensure production safety, the capacity of the cooling fan may not be reduced. Frequency conversion control is adopted. During normal production, the load of the cooling fan is about 20%, and it runs at full load in an accident state to prevent the temperature of the finished pellets from being too high.

Below in conjunction with specific embodiment this scheme is further introduced:

Embodiment 1, as shown in Figure 2, take the 4 million tons belt roaster pellet production line as an example:

After the 504t/h raw pellets enter the belt roaster, they pass through the blast drying section, the draft drying section, the preheating section, the roasting section, the soaking section, the cooling section 1, and the cooling section 2, and then they become qualified pellets and exit the roasting machine and enter the blast furnace. . This patent divides the cooling air pipe into a cold air pipe and a second cold air pipe, and the middle is connected with a regulating valve. The cooling fan (shown as the second cooling fan) is adjusted from the original 4000Kw, 1.5 million m ³ /h to 2240Kw, 960,000 m ³ /h. The cooling air enters the second cooling air pipe, and after being distributed by the bellows, a small part enters the first cooling stage, and a large part enters the second cooling stage. The fan is 2240Kw, 960,000 m ³ /h, and enters the blast drying section to dry the moisture in the green pellets. The dried exhaust gas passes through the furnace hood row cooling fan, whose wind pressure is adjusted from 5Kp to 8Kp, and then enters a cold air pipe. After being distributed by the bellows, all the exhaust gas enters the cooling section to cool the high-temperature pellets at about 1000°C. The high-temperature flue gas after cooling the pellets is used as the secondary air for roasting the pellets, and is mixed with the gas to heat the pellets. Part of it passes through the reheating fan and enters the exhaust drying section for circulation and drying. After cooling down, the temperature drops to about 150°C, 1.5 million m ³ /h exhaust gas is discharged into the atmosphere after entering the desulfurization and denitrification system through the main electrostatic precipitator and the main exhaust fan. The first cold air pipe and the second cold air pipe are connected by a regulating valve, and the air volume and air temperature of the first cooling section and the second cooling section can be adjusted according to production needs. The exhaust gas from the original 960,000 m ³ /h furnace cover of this scheme does not need to be discharged outside, and the sensible heat of about 100°C brought by the exhaust gas returns to the roaster system to participate in the roasting of pellets, without affecting the main exhaust air discharge requirements, and does not affect the pellets Under the premise of product quality, the emission of low-temperature exhaust gas is reduced by about 40%, and the corresponding total emission of dust, SO ₂ and NO _X will be reduced, and the effect of energy saving and emission reduction is self-evident.

Embodiment 2, as shown in Figure 3, take the 2 million tons belt roaster pellet production line as an example:

After the 280t/h raw pellets enter the belt roaster, they pass through the blast drying section, the draft drying section, the preheating section, the roasting section, the soaking section, the cooling section 1, and the cooling section 2, and then the qualified pellets exit the roasting machine and enter the blast furnace. . This patent has only one cooling air main pipe, and after the wind of the hood row cooling fan and the cold wind of the second cooling fan merge, they enter the cooling air main pipe together to cool the pellets. The air volume of the cooling fan (shown as the second cooling fan in the figure) is adjusted from 810,000 m ³ /h to 600,000 m ³ /h. The exhaust gas from the cooling air and the exhaust air cooler of the hood row is combined and then enters the cooling air main pipe. After the pellets are cooled by the cooling air in the blasting drying section, it turns into hot air at about 300°C, which passes through a blast drying fan of 600,000 m ³ /h and enters the blasting drying section to dry the moisture in the green pellets. After the dried exhaust gas is adjusted from the original 5Kp to 8Kp by the wind pressure of the exhaust air cooler of the furnace hood, it passes through the check valve to prevent mixing with the cooling air and then enters the cooling air main pipe, and after being distributed by the bellows, part of it enters the cooling section, and part of it enters the Cooling stage two. After entering the cooling section to cool the high-temperature pellets at about 1000°C, the high-temperature flue gas, used as the secondary air for roasting the pellets, is mixed with the gas to heat the pellets, and part of them enters the exhausting drying section through the reheating fan and then the temperature drops after being circulated and dried. At about 150°C, 990,000 m ³ /h of exhaust gas is discharged into the atmosphere after being treated by the main electrostatic precipitator and main exhaust fan into the desulfurization and denitrification system. The original 520,000 m ³ /h furnace cover exhaust gas in this scheme does not need to be discharged outside, and the sensible heat of about 100 °C brought by the exhaust gas returns to the roaster system to participate in the pellet roasting, without affecting the main exhaust air discharge requirements, and does not affect the pellets Under the premise of product quality, the emission of low-temperature exhaust gas is reduced by about 40%, and the corresponding total emission of dust, SO ₂ and NO _X will be reduced, and the effect of energy saving and emission reduction is self-evident.

Embodiment 3, as shown in Figure 4, take the 2 million tons belt roaster pellet production line as an example:

After the 280t/h raw pellets enter the belt roaster, they pass through the blast drying section, the draft drying section, the preheating section, the roasting section, the soaking section, the cooling section 1, and the cooling section 2, and then the qualified pellets exit the roasting machine and enter the blast furnace. . The air volume of the patented cooling fan is 810,000 m ³ /h. The difference from Example 2 is that the fan outlet of the furnace hood row cooling fan is connected to the cold air inlet of the cooling fan, and after mixing, it enters the cooling air main pipe to cool the pellets; after the cooling air enters the cooling air main pipe, part of the roasting chamber enters the cooling stage. Part of it enters the second section of the roasting chamber for cooling. After the pellets are cooled by the cooling air entering the second section, it turns into hot air at about 300°C. It passes through a blower dryer of 600,000 m ³ /h and enters the blast drying section to dry the moisture in the raw pellets. . After the dried exhaust gas passes through the hood row cooling fan, the wind pressure is adjusted from the original 5Kp to 8Kp, and after mixing with the air, it enters the cooling fan together and starts the hot air circulation. Finally, after distribution through the bellows, part of it enters the first stage of cooling, and part of it enters the second stage of cooling. After entering the cooling section to cool the high-temperature pellets at about 1000°C, the high-temperature flue gas, used as the secondary air for roasting the pellets, is mixed with the gas to heat the pellets, and part of them enters the exhausting drying section through the reheating fan and then the temperature drops after being circulated and dried. At about 150°C, 990,000 m3/h of exhaust gas is discharged into the atmosphere after being treated by the desulfurization and denitrification system through the main electrostatic precipitator and main exhaust fan. The exhaust gas from the original 520,000 m3/h furnace cover of this scheme does not need to be discharged outside, and the sensible heat of about 100°C brought by the exhaust gas returns to the roaster system to participate in the roasting of pellets, without affecting the exhaust requirements of the main exhaust, and does not affect the pellet products Under the premise of quality, the emission of low-temperature exhaust gas is reduced by about 40%, and the corresponding total emission of dust, SO ₂ and NO _X will be reduced, and the effect of energy saving and emission reduction is self-evident.

Each embodiment in this specification is described in a progressive manner, each embodiment focuses on the difference from other embodiments, and the same and similar parts of each embodiment can be referred to each other.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. The utility model provides a belt roasting machine production line of pellet grading cooling which characterized in that includes: the system comprises a belt type roasting machine (10), a cold air pipe (21), a secondary cold air pipe (22) and a heat return mechanism;

the straight grate roasting machine (10) comprises: a blast drying section (11), an air draft drying section (12), a preheating section, a roasting section (13), a cooling section (14) and a cooling section (15) which are arranged in sequence along the pellet processing movement direction;

the outlet of the forced air drying section (11) is connected with the inlet of the cold air pipe (21), and the outlet of the cold air pipe (21) is connected with the cooling section (15);

the outlet of the cooling section (14) is connected with the inlet of the roasting section (13), the outlet of the roasting section (13) is connected with the inlet of the air draft drying section (12) through the heat return mechanism, and the outlets of the air draft drying section (12), the preheating section and the roasting section (13) are used for being connected with the inlet of a waste gas discharge system;

the inlet of the secondary cooling air pipe (22) is used for being connected with the outlet of the cooling fan (20), and the outlet of the secondary cooling air pipe (22) is connected with the cooling two sections (15).

2. The belt roaster for pellet classification cooling as claimed in claim 1, wherein the one cold air duct (21) is connected with 1-20 wind boxes.

3. The pellet sized belt roaster of claim 1, further comprising: the waste gas discharge system;

the exhaust gas outward discharge system comprises: a main electric dust collector (41) and a main air exhauster (42) which are connected in sequence.

4. The pellet sized belt roaster of claim 3, wherein the exhaust gas discharge system further comprises: a main smoke exhaust main pipe (40), a denitration and desulfurization system (43) and a chimney (44).

5. The pellet sized belt roaster of claim 1, wherein the heat recovery mechanism comprises: a main regenerative air pipe (51) and a regenerative fan (52).

6. The pellet sized belt roaster of claim 1, further comprising: a blower (31);

the outlet of the cooling section (15) is connected to the inlet of the forced air drying section (11) through the forced air drier (31).

7. The pellet sized belt roaster of claim 1, further comprising: a furnace hood cold air exhausting machine (32);

the outlet of the air blowing and drying section (11) is connected with the inlet of the cold air pipe (21) through the furnace cover cold air exhausting air machine (32).

8. The pellet sized belt roaster of claim 1, further comprising: a regulating valve (23); the first cold air pipe (21) is communicated with the second cold air pipe (22) through the regulating valve (23);

or the first cold air pipe (21) and the second cold air pipe (22) are connected into a whole to form a cooling air main pipe.

9. The pellet sized belt roaster of claim 1, further comprising: the cooling fan (20).

10. The belt roasting machine for pellet graded cooling according to claim 9, wherein the controllers of the cooling fan (20), the main exhaust fan (42) of the exhaust gas discharge system, the regenerative fan (52) of the regenerative mechanism, the drying fan (31) and the hood cooling fan (32) are all frequency-variable controllers.

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