Transformation method for adding heat exchange unit of cement kiln tail preheating system

Abstract

The invention discloses a transformation method for adding a heat exchange unit of a cement kiln tail preheating system, which comprises the following steps: a preheating system and a corresponding basic tower are newly arranged on the ground near an original kiln tail tower, the newly arranged preheating system comprises multiple stages of heat exchange units, and each heat exchange unit comprises a cyclone, a connecting heat exchange pipeline and a material pipe; the connecting pipeline is mainly used for realizing gas-solid heat exchange and gas conveying among the heat exchange units, the cyclone cylinder is used for realizing gas-solid separation on a gas-solid mixture subjected to heat exchange, and the material pipe is used for realizing material conveying among the heat exchange units. In addition, gas and material conveying between the newly-built kiln tail preheating system and the original preheating system is achieved by transforming a connecting pipeline, a material pipe and the like between the original kiln tail preheating system and the newly-built kiln tail preheating system. According to the method, a five-stage preheater is transformed into a seven-stage preheater, the flue gas heat loss of an outlet of the preheater is greatly reduced, the decomposition rate of hot raw materials entering the kiln and the burn-off rate of pulverized coal are increased at the same time, and the method is high in feasibility of transformation implementation, low in civil engineering transformation cost, controllable in transformation construction period and short in kiln stopping time.

Description

Technical Field

[0001] The invention relates to a modification method for adding a heat exchange unit to a cement kiln tail preheating system, in particular to a cement kiln tail preheating system with an added heat exchange unit, belonging to the technical field of cement production. Background Art

[0002] The kiln tail preheating system of the cement clinker burning system exchanges heat between the raw material and the high-temperature flue gas through a multi-stage series connection, thereby achieving the preheating of the raw material and the decomposition of part of the calcium carbonate. The kiln tail preheating system generally includes multiple stages of heat exchange units to improve the heat exchange efficiency. The existing conventional kiln tail preheating system mostly adopts a five-stage preheater setting, but with the increase in the national standard "cement unit product energy consumption limit" for the burning heat consumption requirements and the rise in fuel prices, cement companies are more and more eager to reduce heat consumption, and adding heat exchange units to the kiln tail preheating system is an important means to reduce the heat consumption of cement clinker. The outlet temperature of the existing five-stage kiln tail preheating system is generally 320-330℃, and the heat loss of flue gas and fly ash brought out by the preheater system is about 150-170kcal / kg.cl. In the distribution of cement clinker heat consumption, the heat consumed is second only to the heat of cement clinker formation. Therefore, it is an effective means to reduce heat consumption by adding heat exchange units and transforming the existing five-stage preheating system into a six-stage or seven-stage preheating system.

[0003] The existing conventional five-stage kiln tail preheating system is transformed by adding a heat exchange unit. The method of transforming the kiln tail preheating system is to add a layer upward to the original kiln tail frame, arrange the C01 cyclone and C1-C01 connecting air duct on the new layer, connect the C01 cyclone to the original five-stage preheater system through the C1-C01 connecting air duct and the C01 material pipe, and at the same time transform the raw material feeding system, replace or transform the original C1 cyclone, and finally transform it into a six-stage preheater system. This method of adding a layer upward to the existing kiln tail frame, arranging a new C1 cyclone on the new layer, connecting the air duct, etc., is relatively simple to transform, but the kiln tail frame has a large number of new loads, the cost of reinforcing the structural frame is high, and it is limited by the structural strength of the original frame. The feasibility of the transformation is low and it is difficult to implement and promote on a large scale. In addition, it is generally impossible to transform it into a seven-stage preheater. Therefore, it is necessary to develop a more effective kiln tail preheating system. Summary of the invention

[0004] Purpose of the invention: The purpose of the invention is to provide a method for modifying a cement kiln tail preheating system by adding a heat exchange unit.

[0005] Technical solution: The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to the present invention comprises a five-stage kiln tail preheating system, and comprises the following steps:

[0006] A new preheater tower is set on the ground adjacent to the kiln tail tower of the five-stage kiln tail preheating system. A new preheating system is set on the new preheater tower. The new preheating system contains one or more heat exchange units. Each heat exchange unit includes a cyclone, corresponding connecting heat exchange pipes and material pipes. The function of the connecting pipes is to realize gas-solid heat exchange and gas transportation between heat exchange units. The function of the cyclone is to realize gas-solid separation of the gas-solid mixture that has completed heat exchange. The function of the material pipe is to realize material transportation between heat exchange units.

[0007] Furthermore, the new preheating system is a two-stage heat exchange unit, comprising the following steps:

[0008] (1) The first-stage heat exchange unit of the new preheating system includes a C01 cyclone, and the second-stage heat exchange unit includes a C02 cyclone. The C01 cyclone and the C02 cyclone are respectively located on the upper and lower layers of the preheater tower. The outlet of the C02 cyclone is connected to the inlet of the C01 cyclone through a C02-C01 connecting pipe; the hot raw material collected by the C01 cyclone is sent to the C1-C02 connecting pipe through the C01 cyclone discharge pipe, and is sent to the C02 cyclone with the gas after sufficient heat exchange; the hot raw material collected by the C02 cyclone is sent to the C2-C1 connecting pipe through the C02 cyclone discharge pipe, and is sent to the C1 cyclone of the five-stage kiln tail preheating system with the gas after sufficient heat exchange, thereby completing the material transportation between the newly built preheating system and the original preheating system;

[0009] (2) Partially dismantle the C1 cyclone outlet duct and transform it into a C1-C02 connecting pipe, connect the C1 cyclone outlet with the C02 cyclone inlet of the newly added second-stage heat exchange unit, and complete the gas transportation between the newly built preheating system and the original preheating system;

[0010] (3) The connecting duct between the C1 cyclone and the C2 cyclone of the original five-stage kiln tail preheating system is removed, and the connecting pipe between the C1 cyclone and the C2 cyclone is arranged on the side of the kiln tail tower, and led downward to the bottom of the C02 cyclone of the newly added second-stage heat exchange unit, and then U-turned upward to return to the inlet of the C1 cyclone;

[0011] (4) The raw material feeding system of the original five-stage kiln tail preheating system is dismantled, and a new raw material feeding system is arranged on the side of the preheater tower established in step (1), and the raw material is fed into the C02-C01 connecting pipe on the upper part of the C02 cyclone of the newly added second-stage heat exchange unit, and is sent into the C01 cyclone after heat exchange;

[0012] (5) A tertiary air bypass duct is provided on the tertiary air duct of the original five-stage kiln tail preheating system, and the tertiary air bypass duct is introduced to the bottom of the U-shaped tube at the lower part of the C2-C1 connecting pipeline modified in step (3), so as to introduce a part of the tertiary air to prevent material accumulation at the bottom of the U-shaped tube during operation;

[0013] Furthermore, the tertiary air bypass duct is connected to the tertiary air duct of the five-stage kiln tail preheating system through the tertiary air bypass high-temperature valve, the C01 cyclone outlet duct is connected to the high-temperature fan, and the exhaust gas is transported to the kiln tail exhaust gas treatment system through the C01 outlet duct and discharged into the atmosphere after purification.

[0014] Furthermore, the newly installed preheater tower is arranged on the ground on the side of the original kiln tail tower close to the high-temperature fan.

[0015] Furthermore, the cyclone of the newly added heat exchange unit adopts a 315° large-angle, low-resistance, and high-efficiency cyclone, and the inclination angle between the material pipe of the newly added heat exchange unit and the ground is greater than 60°.

[0016] Furthermore, the flow rate of the bypass tertiary air is controlled, and the flow rate of the bypass tertiary air accounts for 5-10% of the total tertiary air.

[0017] Furthermore, the wind speed in the C2-C1 connecting pipe between the modified C1 cyclone and the C2 cyclone is controlled at 12-15 m / s. At the same time, a constriction is provided, and the wind speed at the constriction is controlled at 16-18 m / s.

[0018] Furthermore, the wind speed in the lower U-shaped pipe of the connecting pipe between the modified C1 cyclone and the C2 cyclone (C2-C1 connecting pipe) is controlled to be greater than 20m / s.

[0019] Furthermore, the wind speed in the C02-C1 connecting pipe between the air outlet of the C1 cyclone and the C02 cyclone of the second-stage heat exchange unit is controlled at 12 to 15 m / s.

[0020] Furthermore, the wind speed at the inlet of the C01 cyclone of the first-stage heat exchange unit is controlled at 16-18 m / s, and the wind speed at the inlet of the C02 cyclone of the second-stage heat exchange unit is controlled at 14-16 m / s.

[0021] Furthermore, the inlet wind speed of the C01 cyclone of the newly added first-stage heat exchange unit is controlled at 16-18 m / s.

[0022] Furthermore, the wind speed of the connecting pipe of the newly added heat exchange unit is controlled at 12-15 m / s.

[0023] Furthermore, the angle of the spreading plate of the spreading box of the newly added heat exchange unit material pipe is less than 15°.

[0024] The present invention arranges a multi-stage preheating system and a raw material feeding system on the ground outside the existing kiln tail frame, and connects it with the existing kiln tail preheating system by modifying the connecting pipeline, and then removes the original C1 cyclone and replaces it with a new C1 cyclone as a whole. Since the newly added preheater tower is arranged on the ground, the reinforcement cost of the existing kiln tail tower is saved, and the investment cost is effectively reduced.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) The heat consumption of the firing system is greatly reduced. The heat carried away by the exhaust gas at the outlet of the preheater of the present invention accounts for about 15% to 22% of the heat required for clinker firing, which is the biggest factor affecting the firing heat consumption (the heat generated by clinker is not much different and is difficult to reduce). The preheater is equipped with one or more heat exchange units, and the five-stage preheater is transformed into a six-stage or more (especially a seven-stage or eight-stage) preheater. The flue gas temperature at the outlet of the preheater will be greatly reduced, and the heat loss of the exhaust gas will be greatly reduced, thereby reducing the heat consumption of the firing system.

[0027] (2) When the present invention is provided with a 6-stage preheater, the heat consumption can be reduced by about 38 kcal / kg.cl. When it is provided with a 7-stage preheater, the heat consumption can be reduced by about 51 kcal / kg.cl. The heat consumption is significantly reduced.

[0028] (3) Since the newly added preheater tower is arranged on the ground, compared with the existing tower that adds a layer of heat exchange unit, the reinforcement cost of the existing kiln tail tower is greatly saved, effectively reducing the investment cost. At the same time, since the new load of the existing frame is small, the feasibility of the transformation implementation is higher.

[0029] (4) The renovation period is controllable and the kiln downtime is short: the newly added preheater tower of the present invention can be constructed without stopping the kiln, thus reducing the kiln downtime of the renovation.

[0030] (5) The decomposition rate of the hot raw materials entering the kiln and the burnout rate of the coal powder in the decomposition furnace are improved: the preheater of the present invention adds two-stage heat exchange units. After the five-stage preheater is transformed into a seven-stage preheater, the temperature of the hot raw materials entering the furnace is increased, which not only saves heat consumption but also improves the thermal stability of the decomposition furnace. The decomposition rate of the hot raw materials entering the kiln and the burnout rate of the coal powder are both improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0033] Example 1

[0034] like Figure 1 As shown, the modification method of adding a heat exchange unit to a cement kiln tail preheating system of the present invention comprises a five-stage kiln tail preheating system, and the modification method comprises the following steps:

[0035] A new preheater tower is set on the ground adjacent to the kiln tail tower of the five-stage kiln tail preheating system. A new preheating system is set on the new preheater tower. The new preheating system contains one or more heat exchange units. Each heat exchange unit includes a cyclone, corresponding connecting heat exchange pipes and material pipes. The function of the connecting pipes is to realize gas-solid heat exchange and gas transportation between heat exchange units. The function of the cyclone is to realize gas-solid separation of the gas-solid mixture that has completed heat exchange. The function of the material pipe is to realize material transportation between heat exchange units.

[0036] This embodiment takes a newly added two-stage heat exchange unit system as an example, and the specific steps are as follows:

[0037] (1) The first-stage heat exchange unit of the new preheating system includes a C01 cyclone 1, and the second-stage heat exchange unit includes a C02 cyclone 2. The C01 cyclone 1 and the C02 cyclone 2 are respectively located on the upper and lower layers of the preheater tower. The outlet of the C02 cyclone 2 is connected to the inlet of the C01 cyclone 1 through the C02-C01 connecting pipe 7. The hot raw material collected by the C01 cyclone 1 is sent to the C1-C02 connecting pipe 6 through the C01 cyclone discharge pipe 3, and is sent to the C02 cyclone 2 with the gas after sufficient heat exchange. The hot raw material collected by the C02 cyclone 2 is sent to the C2-C1 connecting pipe 5 through the C02 cyclone discharge pipe 4, and is sent to the C1 cyclone 11 of the five-stage kiln tail preheating system with the gas after sufficient heat exchange, completing the material transportation between the new preheating system and the original preheating system;

[0038] (2) The outlet air duct of C1 cyclone 11 is partially dismantled and transformed into C1-C02 connecting heat exchange pipe 6, and the outlet of C1 cyclone 11 is connected to the inlet of C02 cyclone of the newly added second-stage heat exchange unit; thus completing the gas transportation between the new preheating system and the original preheating system.

[0039] (3) The connecting duct between the C1 cyclone 11 and the C2 cyclone of the original five-stage kiln tail preheating system is removed, and the connecting pipe between the C1 cyclone 11 and the C2 cyclone is arranged on the side of the kiln tail tower, and is led downward to the bottom of the C02 cyclone of the newly added second-stage heat exchange unit, and then makes a U-turn upward and returns to the inlet of the C1 cyclone 11;

[0040] (4) The raw material feeding system of the original five-stage kiln tail preheating system is dismantled, and a new raw material feeding system is arranged on the side of the preheater tower established in step (1), and the raw material is fed into the C02-C01 connecting pipe 7 on the upper part of the C02 cyclone 2 of the newly added second-stage heat exchange unit, and is sent into the C01 cyclone 1 after heat exchange;

[0041] (5) A tertiary air bypass duct 9 is provided on the tertiary air duct of the original five-stage kiln tail preheating system. The tertiary air bypass duct 9 is introduced to the bottom of the lower U-shaped tube of the C2-C1 connecting pipe 5 modified in step (3) to introduce a part of the tertiary air to prevent material accumulation at the bottom of the U-shaped tube during operation.

[0042] In addition, the newly installed preheater tower is arranged on the ground on the side of the original kiln tail tower near the high-temperature fan. The original C1 cyclone was dismantled and replaced with a low-resistance and high-efficiency C1 cyclone 11. The cyclone of the newly added heat exchange unit adopts a 315° large-angle low-resistance and high-efficiency cyclone, and the inclination angle of the material pipe of the newly added heat exchange unit to the ground is greater than 60°. The tertiary air bypass duct is connected to the tertiary air duct of the five-stage kiln tail preheating system through the tertiary air bypass high-temperature valve 10, and the C01 cyclone 1 outlet duct is connected to the high-temperature fan. The exhaust gas is transported to the kiln tail exhaust gas treatment system through the C01 outlet duct and discharged into the atmosphere after purification.

[0043] In this embodiment, a new preheater tower is built on the side of the original kiln tail tower of the five-stage kiln tail preheating system. The new preheater tower has two layers. The C02 cyclone 2 is located on the first layer of the new preheater tower, and the C01 cyclone 1 is located on the second layer. The original C1 outlet air duct is partially dismantled and transformed into a C1-C02 connecting air duct 6. The C1 cyclone outlet is connected to the C02 cyclone inlet through the C1-C02 connecting air duct 6. The C01 cyclone discharge pipe 3 sends the hot raw materials collected by the C01 cyclone 1 into the C02 cyclone 2 through the C1-C02 connecting air duct 6 after heat exchange. The connecting duct between the C1 cyclone 11 and the C2 cyclone of the original five-stage kiln tail preheating system was removed and transformed into a C2-C1 connecting duct 5, which was arranged on the side of the kiln tail tower and led downward to the bottom of the C02 cyclone 2 and then returned to the C1 cyclone 11. The C02 cyclone discharge pipe 4 sent the hot raw material collected by the C02 cyclone 2 to the C1 cyclone 11 through the rising section of the C2-C1 connecting duct 5 after heat exchange, completing the material transportation between the new preheater system and the original preheater system. The outlet air of the C01 cyclone is connected to the high-temperature fan through the C01 outlet pipe 8, and the exhaust gas is transported to the kiln tail exhaust gas treatment system through the C01 outlet pipe 8, and discharged to the atmosphere after purification. The original raw material feeding system was removed, and a new raw material feeding system was arranged on the side of the new preheater tower, feeding the raw material into the C02-C01 connecting duct 7, and then sent to the C01 cyclone 1 after heat exchange. A tertiary air bypass duct 9 is set on the existing tertiary air duct, and the tertiary air bypass duct 9 is introduced to the bottom of the U-shaped tube at the bottom of the C2-C1 connecting air duct 5 to introduce a part of the tertiary air to prevent material accumulation at the bottom of the U-shaped tube during operation. After the above transformation, the C01 cyclone 1, C02 cyclone 2, C02-C01 connecting air duct 7 and other equipment form a two-stage new heat exchange unit on the new tower, and are connected with the original five-stage preheater system to form a 7-stage kiln tail preheating system.

[0044] After the above transformation, the wind speed in the C2-C1 connecting air duct 5, C1-C02 connecting air duct 6 and C02-C01 connecting air duct 7 is controlled at 12-15m / s, and the wind speed in the lower U-shaped tube of the C2-C1 connecting air duct 5 is controlled to be greater than 20m / s; the lower part of the spreading box of the C01 cyclone 1 and the C02 cyclone 2 is provided with a constriction, and the wind speed at the constriction is controlled at 16-18m / s. The spreading plate angle of the spreading box of the newly added heat exchange unit material pipe is less than 15°. The inlet wind speed of the C02 cyclone 2 is controlled at 14-16m / s; the inlet wind speed of the C01 cyclone 1 is controlled at 16-18m / s. Control the flow rate of the bypass tertiary air, and the flow rate of the bypass tertiary air accounts for 5-10% of the total tertiary air.

[0045] Example 2

[0046] The transformation process is the same as in Example 1, except that the two-stage heat exchange unit on the newly installed preheater tower is changed to a one-stage heat exchange unit. Other connection methods are the same.

[0047] Example 3

[0048] The temperature distribution table of the preheater is calculated by the heat exchange model between the modified kiln tail preheating system of Example 1 and Example 2 and the original five-stage kiln tail preheating system.

[0049] The heat carried away by the exhaust gas at the outlet of the preheater accounts for about 15% to 22% of the heat required for clinker burning (the conventional heat consumption of the five-stage preheating system is 720 to 750 kcal / kg.cl), which is the factor that has the greatest impact on the heat consumption of burning (the heat of clinker formation is not much different and is difficult to reduce). After the above-mentioned embodiments 1 and 2 are used for modification, the preheater is increased by one stage (embodiment 2) or two stages (embodiment 1) of heat exchange units, and the five-stage preheater is modified into a six-stage or seven-stage preheater. The flue gas temperature at the outlet of the preheater will be greatly reduced, and the heat loss of the exhaust gas will be greatly reduced, thereby reducing the heat consumption of the burning system.

[0050] Table 1 is the temperature distribution table of the multi-stage cyclone preheater calculated by Mr. Zhu Zupei through the heat exchange model. The number n in the table only refers to the number of stages of the preheater heat exchange unit, and does not include the lowest decomposition stage (which only plays the role of gas-solid separation and has no heat exchange effect). That is to say, when n=4, it refers to the conventional 5-stage preheater, when n=5, it refers to the conventional 6-stage preheater (that is, one stage of heat exchange unit is added above the original five stages), and when n=6, it refers to the conventional 7-stage preheater (that is, two stages of heat exchange units are added above the original five stages). It can be seen that the theoretical outlet temperature of the five-stage preheater is about 310°C, while the theoretical outlet temperature of the six-stage preheater is about 288°C. However, due to the improvement of the cyclone separation efficiency and the pipeline heat exchange efficiency, the actual outlet temperature of the six-stage preheater can be reduced to about 250-260°C. There is no actual operation case of the seven-stage preheater yet, but according to the theoretical outlet temperature and the actual outlet temperature of the six-stage preheater, the actual outlet temperature of the seven-stage preheater can be reduced to about 220-230°C.

[0051] Table 1 Temperature distribution of preheaters with different stages

[0052] t g0 =900℃,t M0 =50℃,Δt GM =10℃, r=0.80

[0053]

[0054] Table 1 is extracted from "Temperature distribution of multi-stage cyclone preheater", Zhu Zupei, Cement Technology, 1990 No. 4

[0055] Table 2 is a comparison of the original five-stage kiln tail preheating system before and after the transformation of Example 1 and Example 2. It can be seen from Table 2 that when the 5-stage preheater is transformed into a 6-stage preheater, the heat consumption can be reduced by about 33kcal / kg.cl, and when the 5-stage preheater is transformed into a 7-stage preheater, the heat consumption can be reduced by about 51kcal / kg.cl.

[0056] Table 2 Heat loss at outlet of preheater with different stages

[0057]

[0058] *Note: The unit of specific heat of gas is kcal / Nm 3 / ℃, solid specific heat unit is kcal / kg / ℃; gas volume unit is Nm 3 / kg.cl, the unit of solid amount is kg / kg.cl.

[0059] The transformation cost is effectively reduced through the transformation of Example 1 or Example 2, and the feasibility of implementation is high. Since the newly added preheater tower is arranged on the ground, compared with the existing transformation method of adding a layer of heat exchange units on the tower, the reinforcement cost of the existing kiln tail tower is greatly saved, and the investment cost is effectively reduced. At the same time, since the newly added load of the existing frame is small, the feasibility of transformation implementation is high. The transformation period is controllable, the kiln stop time is short, and the newly added preheater tower can be constructed without stopping the kiln, which reduces the kiln stop time of the transformation. The decomposition rate of the hot raw material entering the kiln and the burnout rate of the coal powder in the decomposition furnace are improved. After the preheater adds two-stage heat exchange units and is transformed from a five-stage preheater to a seven-stage preheater, the temperature of the hot raw material entering the furnace is increased, which not only saves heat consumption, but also improves the thermal stability of the decomposition furnace. The decomposition rate of the hot raw material entering the kiln and the burnout rate of the coal powder are improved.

[0060] The above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made without departing from the spirit of the present invention and the scope of protection of the claims. These obvious changes or modifications derived from the spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for modifying a cement kiln tail preheating system by adding a heat exchange unit, comprising a five-stage kiln tail preheating system, characterized in that: The following steps are involved: A new preheater tower is set on the ground adjacent to the kiln tail tower of the five-stage kiln tail preheating system. A new preheating system is set on the new preheater tower. The new preheating system contains one or more heat exchange units. Each heat exchange unit includes a cyclone, corresponding connecting heat exchange pipes and material pipes. The function of the connecting pipes is to realize gas-solid heat exchange and gas transportation between heat exchange units. The function of the cyclone is to realize gas-solid separation of the gas-solid mixture that has completed heat exchange. The function of the material pipe is to realize material transportation between heat exchange units.

2. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 1, characterized in that: The new preheating system is a two-stage heat exchange unit, which includes the following steps: (1) The first-stage heat exchange unit of the new preheating system includes a C01 cyclone, and the second-stage heat exchange unit includes a C02 cyclone. The C01 cyclone and the C02 cyclone are respectively located on the upper and lower layers of the preheater tower. The outlet of the C02 cyclone is connected to the inlet of the C01 cyclone through a C02-C01 connecting pipe; the hot raw material collected by the C01 cyclone is sent to the C1-C02 connecting pipe through the C01 cyclone discharge pipe, and is sent to the C02 cyclone with the gas after sufficient heat exchange; the hot raw material collected by the C02 cyclone is sent to the C2-C1 connecting pipe through the C02 cyclone discharge pipe, and is sent to the C1 cyclone of the five-stage kiln tail preheating system with the gas after sufficient heat exchange, thereby completing the material transportation between the newly built preheating system and the original preheating system; (2) Partially dismantle the C1 cyclone outlet duct and transform it into a C1-C02 connecting pipe, connect the C1 cyclone outlet with the C02 cyclone inlet of the newly added second-stage heat exchange unit, and complete the gas transportation between the newly built preheating system and the original preheating system; (3) The connecting duct between the C1 cyclone and the C2 cyclone of the original five-stage kiln tail preheating system is removed, and the connecting pipe between the C1 cyclone and the C2 cyclone is arranged on the side of the kiln tail tower, and led downward to the bottom of the C02 cyclone of the newly added second-stage heat exchange unit, and then U-turned upward to return to the inlet of the C1 cyclone; (4) The raw material feeding system of the original five-stage kiln tail preheating system is dismantled, and a new raw material feeding system is arranged on the side of the preheater tower established in step (1), and the raw material is fed into the C02-C01 connecting pipe on the upper part of the C02 cyclone of the newly added second-stage heat exchange unit, and is sent into the C01 cyclone after heat exchange; (5) A tertiary air bypass duct is provided on the tertiary air duct of the original five-stage kiln tail preheating system, and the tertiary air bypass duct is introduced to the bottom of the U-shaped tube at the lower part of the C2-C1 connecting pipeline modified in step (3), so as to introduce a part of the tertiary air to prevent material accumulation at the bottom of the U-shaped tube during operation.

3. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 1, characterized in that: The tertiary air bypass duct is connected to the tertiary air duct of the five-stage kiln tail preheating system through the tertiary air bypass high-temperature valve. The C01 cyclone outlet duct is connected to the high-temperature fan. The exhaust gas is transported to the kiln tail exhaust gas treatment system through the C01 outlet duct and discharged into the atmosphere after purification.

4. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 3, characterized in that: The newly installed preheater tower is arranged on the ground on the side of the original kiln tail tower close to the high-temperature fan.

5. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 2, characterized in that: The flow rate of bypass tertiary air accounts for 5-10% of the total tertiary air.

6. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 2, characterized in that: The wind speed in the C2-C1 connecting pipe between the modified C1 cyclone and the C2 cyclone is controlled at 12-15 m / s.

7. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 2, characterized in that: The wind speed in the lower U-shaped pipe of the connecting pipe between the modified C1 cyclone and the C2 cyclone (C2-C1 connecting pipe) is controlled to be >20m / s.

8. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 2, characterized in that: The wind speed in the C02-C1 connecting pipe between the C1 cyclone outlet and the C02 cyclone of the second-stage heat exchange unit is controlled at 12 to 15 m / s.

9. The method for modifying a cement kiln tail preheating system by adding a heat exchange unit according to claim 2, characterized in that: The inlet wind speed of the C01 cyclone of the first-stage heat exchange unit is controlled at 16-18 m / s, and the inlet wind speed of the C02 cyclone of the second-stage heat exchange unit is controlled at 14-16 m / s.

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