A system and method for coupling alternative fuel drying with cement kiln

Abstract

The present invention discloses a system and method for coupling alternative fuel drying with a cement kiln. The system includes a grate cooler waste heat recovery system, a kiln shell waste heat recovery system, an alternative fuel drying system, a drying gas condensation processing system, and a chimney. The grate cooler waste heat recovery system introduces the kiln head waste heat flue gas of the cement kiln into the alternative fuel drying system to dry the alternative fuel. The kiln shell waste heat recovery system exchanges the collected waste heat with the kiln head waste heat flue gas that has heated the alternative fuel. The kiln head waste heat flue gas after heat exchange dries the alternative fuel again and is then sent to the drying gas condensation processing system or the chimney. The heat medium after heat exchange returns to the kiln shell waste heat recovery system for cyclic heating. The present invention introduces the kiln head waste heat of the cement kiln and the heat dissipation of the rotary kiln shell into the alternative fuel drying system, and while utilizing the waste heat of the cement kiln, dries the alternative fuel by precipitation, thereby improving the calorific value of the alternative fuel and ultimately improving the fuel substitution rate of the cement kiln.

Description

Technical Field

[0001] The present invention relates to a system and method for utilizing alternative fuels in a cement kiln, and in particular to a system and method for coupling alternative fuel drying with a cement kiln. Background Art

[0002] The cement industry has large carbon emissions, and the use of alternative fuels is the most promising means of rapidly and scalably reducing them. Currently available alternative fuels include biofuels and refuse-derived fuels (RDF), as well as solid waste recycled fuels (SRF), dried sludge, waste oil, and solvents. However, most alternative fuels cannot be used directly and need to be pre-processed in special pretreatment plants according to the requirements of the cement process. Most alternative fuels, such as domestic waste and municipal sludge, do not have a high calorific value and a high moisture content, which can affect the stability of the cement firing system when disposed of in large quantities. Reducing the moisture content of alternative fuels and increasing their calorific value are key to improving the co-processing capacity and heat replacement rate of cement kilns. The main approach that can be taken is the drying process.

[0003] Drying odorous alternative fuels, such as household waste and sludge, inevitably produces odors. Direct emission of these odors inevitably pollutes the environment, while adding deodorization facilities for secondary treatment increases investment and operating costs. Some alternative fuels, such as biomass, are cyclical and cannot be guaranteed year-round, leading to idle alternative fuel equipment. Therefore, cement plants require a diverse supply of alternative fuels to ensure continuous operation of related equipment. This requires that the alternative fuel processes employed are also adaptable to multiple alternative fuels.

[0004] Patent CN212581744U discloses a cement kiln sludge co-processing system with a pretreatment device, comprising a sludge pretreatment system and a cement kiln co-processing system. This system fully utilizes the waste heat from the cement kiln to pre-treat the sludge, achieving cascaded utilization of the cement kiln's waste heat while minimizing the impact of co-processing sludge on the kiln process and cement quality.

[0005] However, this patent uses waste heat from exhaust gas to directly heat and dry the sludge, and the dried exhaust gas is then fed into a grate cooler for reuse. This process has two problems. First, the hot flue gas discharged after drying has a high moisture content. A large amount of water vapor in the undehumidified hot flue gas enters the firing system after being heated by the grate cooler. This water vapor has no positive effect in the firing system and, on the contrary, is discharged through the kiln tail, resulting in a certain amount of heat loss from the exhaust gas. Second, because the sludge is being dried, the hot flue gas discharged after drying contains a large amount of malodorous gases. H2S and NH3 are the main sources of malodor pollution, and other trace organic components such as mercaptans, organic sulfides, and amines are secondary sources of malodor pollution. Since the clinker temperature in the rear section of the grate cooler is generally 150°C to 250°C, this temperature cannot remove malodorous gases such as H2S and NH3. After being discharged through the chimney at the kiln tail, it poses an environmental pollution problem. Summary of the Invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a system for coupling alternative fuel drying with a cement kiln, which can increase the calorific value of alternative fuels, thereby increasing the fuel substitution rate of cement kilns, while avoiding environmental pollution;

[0007] The second object of the present invention is to provide a method for coupling alternative fuel drying with a cement kiln using the above system.

[0008] Technical solution: The system for coupling alternative fuel drying with a cement kiln described in the present invention includes a grate cooler waste heat recovery system, a kiln shell waste heat recovery system, an alternative fuel drying system, a drying gas condensation treatment system and a chimney; the grate cooler waste heat recovery system introduces the kiln head waste heat flue gas of the cement kiln into the alternative fuel drying system to dry the alternative fuel; the kiln shell waste heat recovery system exchanges the collected waste heat with the kiln head waste heat flue gas after heating the alternative fuel; the kiln head waste heat flue gas after heat exchange dries the alternative fuel again and is then sent to the drying gas condensation treatment system or the chimney; the waste heat after heat exchange returns to the kiln shell waste heat recovery system for circulating heating.

[0009] Among them, the drying gas condensation treatment system cools down and condenses the hot and humid gas discharged from the alternative fuel drying system, and the condensed water is discharged from the system. The dehumidified gas is connected to the middle and rear low-temperature section air inlet of the grate cooler or is connected to the middle and rear low-temperature section air inlet and the front high-temperature section fan air inlet at the same time.

[0010] Among them, the drying gas condensation treatment system includes a condenser connected to the exhaust fan outlet of the alternative fuel drying system, the water outlet of the condenser is connected to the water inlet of the cooling tower, and a circulating cooling water pump is arranged between the water outlet of the cooling tower and the water inlet of the condenser to circulate the cooling water between the condenser and the cooling tower; the gas phase outlet of the cooling tower is connected to the air inlet of the grate cooler.

[0011] Among them, the alternative fuel drying system includes a front section and a rear section. The kiln head waste heat flue gas is introduced into the front section to dry the alternative fuel. After the kiln head waste heat flue gas after heating the alternative fuel is exchanged with the collected waste heat, the alternative fuel in the rear section is dried.

[0012] Among them, the alternative fuel drying system includes a belt dryer, a circulating fan, an exhaust fan and connecting pipes; the waste heat flue gas from the kiln head enters through the front section of the belt dryer to dry the alternative fuel, is extracted by the circulating fan and sent to the rear section of the belt dryer, and is dried after heat exchange with the collected waste heat and heated, and is discharged from the lower part of the rear section through the exhaust fan and sent into the chimney.

[0013] Among them, the kiln shell waste heat recovery system includes a circulating medium heat collection device arranged on the rotary kiln, a circulating pump, a heat exchanger arranged in the alternative fuel drying system and connecting pipes; the circulating pump sends the cooling medium into the circulating medium heat collection device, which is heated by the surface of the rotary kiln shell and becomes a heat medium. The heat medium enters the heat exchanger, cools the kiln head waste heat flue gas after heating the alternative fuel, and then returns to the circulating pump.

[0014] Among them, the grate cooler waste heat recovery system includes a grate cooler, a waste heat power generation system, a dust collector, a kiln head induced draft fan, a chimney and connecting pipes; after the exhaust air in the middle of the grate cooler is exhausted through the waste heat power generation system, it passes through the dust collector together with the exhaust air at the tail of the grate cooler, is drawn out through the kiln head induced draft fan and then sent to the alternative fuel drying system, and the excess exhaust air is discharged into the chimney after being regulated by a valve.

[0015] Among them, the outlet of the kiln head draft fan is divided into two routes, one is connected to the alternative fuel drying system, and the other is discharged to the chimney. An air volume regulating valve is provided on each of the two air ducts to adjust the flue gas volume on the two air ducts.

[0016] The method for coupling alternative fuel drying with a cement kiln using the above system comprises the following steps:

[0017] (S1) The grate cooler waste heat recovery system sends the waste heat flue gas from the kiln head into the alternative fuel drying system. The excess exhaust gas is regulated by a valve and discharged into the chimney. The air volume entering the alternative fuel drying system is controlled according to the scale of the alternative fuel drying.

[0018] The cold medium is sent to the circulating medium heat collection device installed on the rotary kiln through the circulating pump. After being heated on the surface of the rotary kiln cylinder, it becomes hot medium. The hot medium flows into the heat exchanger through the pipeline, is cooled by the drying air, and returns to the circulating pump.

[0019] (S2) The waste heat flue gas at the kiln head enters from the upper or lower part of the front section of the alternative fuel drying system, dries the alternative fuel, is extracted by the circulating fan and sent to the upper part of the rear section, and is heated by the heat exchanger to dry the alternative fuel again. The dried waste gas is discharged from the lower part of the rear section of the dryer through the exhaust fan and sent to the drying gas condensation treatment system or chimney;

[0020] When sent into the drying gas condensation treatment system: the hot and humid gas is cooled and condensed by the condenser, the condensed water is discharged, and the dehumidified gas is connected to the air inlet of the grate cooler's blower.

[0021] In step (S2), the dehumidified gas is connected to the air inlet of the medium and low temperature section blower at the middle and rear part of the grate cooler; after heat exchange with the medium and low temperature clinker, it is extracted from the middle and rear parts of the grate cooler by the induced draft fan; the gas in the middle part is cooled by the waste heat power generation system and mixed with the tail gas to enter the dust collector; after passing through the induced draft fan, it enters the alternative fuel dryer to continue drying the alternative fuel;

[0022] Alternatively, the dehumidified gas is simultaneously connected to the air inlet of the middle and rear low-temperature section blower and the air inlet of the front high-temperature section blower of the grate cooler; when connected to the front high-temperature section blower inlet: after heat exchange with the high-temperature clinker, it becomes secondary air entering the kiln or tertiary air entering the furnace.

[0023] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0024] (1) The waste heat from the kiln head of the cement kiln and the heat dissipation of the rotary kiln cylinder are introduced into the alternative fuel drying system, which not only utilizes the waste heat of the cement kiln, but also dries the alternative fuel by precipitation, thereby increasing the calorific value of the alternative fuel and ultimately increasing the fuel substitution rate of the cement kiln. The present invention utilizes the waste heat of the cement kiln without affecting the normal operation of the cement kiln. The final moisture content of the alternative fuel can reach 10% to 15%, or even lower.

[0025] (2) A mixed ventilation belt dryer is used. The front section uses the hot flue gas from the kiln head to dry the alternative fuel, and the rear section uses the waste heat from the cement kiln cylinder to heat the cooled hot flue gas. It has the characteristics of large drying capacity, small drying air volume and low system energy consumption.

[0026] (3) The belt dryer adopts a mixed ventilation method. For different materials, the front section of the dryer can adopt the upper air inlet and lower air outlet method or the lower air inlet and upper air outlet method according to the material head. The rear section adopts the upper air inlet and lower air outlet method. By utilizing the isolation and dust reduction effect of the alternative fuel material layer and the belt, the dust content of the exhaust is very low. According to the on-site operation results, the dust content meets environmental protection requirements and does not require the installation of a dust removal device. The present invention has the advantage of flexibility and adjustability.

[0027] (4) A variety of alternative fuels can be dried. When drying alternative fuels that do not produce odor, the process is simple and the system energy consumption is low. For drying alternative fuels that produce odor, the present invention does not require a deodorization system, resulting in low operating costs. A pipeline leading to the high-temperature section of the grate cooler is also provided to remove non-condensable gases from the circulating gas, ensuring safe operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the system of the present invention;

[0029] Figure 2 Schematic diagram of another structure of the system of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be described in further detail below with reference to the accompanying drawings.

[0031] like Figure 1 and Figure 2 As shown, the present invention provides a system for coupling alternative fuel drying with a cement kiln, including a grate cooler waste heat recovery system, a kiln shell waste heat recovery system, an alternative fuel drying system, and a drying gas condensation disposal system.

[0032] The grate cooler waste heat recovery system includes a grate cooler 4, a waste heat power generation system 5, a dust collector 6, a kiln head induced draft fan 7, a chimney 10 and connecting pipes; in the grate cooler waste heat recovery system, the air extracted from the middle of the grate cooler 4 is heat exchanged through the waste heat power generation system 5, and then passes through the dust collector together with the exhaust gas at the tail end of the grate cooler 4, is drawn out through the kiln head induced draft fan 7, and is sent to the alternative fuel drying system through the first air volume regulating valve 8. The excess exhaust gas is regulated by the second air volume regulating valve 9 and can be discharged into the chimney 10.

[0033] The outlet of the kiln head induced draft fan 7 is divided into two routes, one is connected to the belt dryer 11, and a first air volume regulating valve 8 is provided on the connecting pipeline; the other is discharged to the chimney 10, and a second air volume regulating valve 9 is provided on the connecting pipeline.

[0034] The kiln shell waste heat recovery system includes a circulating medium heat collection device 2, a circulating pump 1, a rotary kiln 3, a heat exchanger 13, and connecting pipes. In this embodiment, the circulating medium heat collection device 2 is a circulating water heat collection hood, and the circulating pump 1 is a circulating water pump. Cooling water is delivered to the circulating water heat collection hood by the circulating pump 1. After being heated by the surface of the rotary kiln 3, the hot water flows through pipes into the heat exchanger 13, is cooled by drying air, and then returns to the circulating pump 1.

[0035] The alternative fuel drying system of the present invention comprises a belt dryer 11, a circulating fan 12, an exhaust fan 14, a third air volume regulating valve 15, a fourth air volume regulating valve 16 and connecting pipes. The hot flue gas from the kiln head enters the dryer through the lower part of the front section of the belt dryer 11, or enters the dryer through the upper part of the front section, respectively. Figure 1 、 Figure 2 As shown, the alternative fuel on the belt is dried, extracted by the circulating fan 12 and sent to the rear section of the belt dryer 11. After heat exchange and temperature increase in the heat exchanger 13, the alternative fuel is dried again and discharged from the lower part of the rear section of the belt dryer 11 through the exhaust fan 14. It is sent to the drying gas condensation disposal system through the third air volume regulating valve 15 or enters the chimney 10 through the fourth air volume regulating valve 16.

[0036] The drying gas condensation disposal system of the present invention includes a condenser 17, a cooling tower 18, a circulating cooling water pump 19, a fifth air volume regulating valve 20, a sixth air volume regulating valve 21, and connecting pipes. The hot and humid gas exhausted by the exhaust fan 14 in the alternative fuel drying system is cooled and condensed by the condenser 17. The condensed water in the hot and humid gas then exits the condenser 17. The dehumidified gas is then fed through the sixth air volume regulating valve 21 to the front high-temperature section fan inlet of the grate cooler and then through the fifth air volume regulating valve 20 to the mid-to-low temperature section inlet at the rear of the grate cooler.

[0037] According to the actual situation of the application site, the cooling tower 18 can be open or closed.

[0038] Different methods are used to dry different alternative fuels using the above system, as follows:

[0039] Method 1: When disposing of alternative fuels that do not produce odor in the drying process, such as biomass fuels such as sawdust, bark, roots, straw, etc., the following steps are included:

[0040] (S1) Extraction of waste heat from the kiln head: In the waste heat recovery system of the grate cooler, the air extracted from the middle of the grate cooler 4 is subjected to heat exchange in the waste heat power generation system 5, and then passes through the dust collector 6 together with the exhaust gas from the tail of the grate cooler 4. After being extracted through the kiln head induced draft fan 7, it enters the belt dryer 11 through the first air volume regulating valve 8, and the excess exhaust gas is regulated by the second air volume regulating valve 9 and discharged into the chimney 10; the amount of flue gas on the two air ducts can be adjusted by adjusting the opening of the first air volume regulating valve 8 and the second air volume regulating valve 9; when the alternative fuel drying system is not in operation, the exhaust air from the kiln head induced draft fan 7 is all connected to the chimney 10 for discharge.

[0041] (S2) Kiln shell waste heat recovery: Cooling water is sent to the circulating water heat collecting cover 2 installed on the rotary kiln 3 through the circulating water pump 1. After being heated by the surface of the rotary kiln 3, it becomes hot water. The hot water flows into the heat exchanger 13 through the pipeline, is cooled by the drying air, and then returns to the circulating water pump 1.

[0042] (S3) Alternative Fuel Drying: Hot flue gas from the kiln head enters the alternative fuel drying system from the front section of the belt dryer 11, drying the alternative fuel on the belt. It is then drawn out by the circulating fan 12 and sent to the upper part of the rear section of the dryer 11. After heat exchange and heating in the heat exchanger 13, the alternative fuel is dried again. The dried exhaust gas is discharged from the lower part of the rear section of the dryer via the exhaust fan 14. There are two options for how the hot flue gas enters the alternative fuel drying system from the front section of the belt dryer 11:

[0043] Option 1: Enter from the lower part of the front section, such as Figure 1 This solution is suitable for alternative fuels that are not easy to generate dust and have a low dust content. The front section of the dryer 11 has air intake, and the rear section has air intake. The alternative fuel is dried with hot air from both sides, and has the advantages of a large drying contact surface, uniform drying, and good drying effect.

[0044] Option 2: Enter from the upper part of the front section, such as Figure 2 As shown; this solution is suitable for alternative fuels that are easy to generate dust and light. The front and rear sections of the dryer 11 both use upper air intake, and the alternative fuel is pressed on the dryer belt by the wind. It is not easy to generate dust inside the dryer, the drying environment is better, and it is not easy to explode; if it is used for drying wood chips and straw, it is suitable to adopt solution 2.

[0045] (S3) Exhaust Gas Discharge: The dried exhaust gas is discharged through the exhaust fan 14 and then discharged into the chimney 10 through the fourth air volume regulating valve 16. At this time, the fourth air volume regulating valve 15 is closed. This solution has a simple process and low system energy consumption.

[0046] Method 2: When disposing of alternative fuels that generate odor in drying projects, such as domestic waste, sludge, etc., the following steps are included:

[0047] (S1) Extraction of waste heat from the kiln head: In the waste heat recovery system of the grate cooler, the air extracted from the middle of the grate cooler 4 is exchanged with the waste heat power generation system 5, and then passes through the dust collector 6 together with the exhaust gas at the tail end of the grate cooler 4. After being extracted through the kiln head induced draft fan 7, the first air volume regulating valve 8 is opened and the second air volume regulating valve 9 is closed, and all the hot air from the kiln head enters the belt dryer 11 to prevent odor leakage and environmental pollution; when the alternative fuel drying system is not running, the first air volume regulating valve 8 is closed and the second air volume regulating valve 9 is opened, and the air outlet of the kiln head induced draft fan 7 is all connected to the chimney 10 for discharge.

[0048] (S2) Kiln shell waste heat recovery: same as the above method 1.

[0049] (S3) Alternative fuel drying: same as the above method 1.

[0050] (S4) Drying gas condensation: The third air volume regulating valve 15 is opened, and the fourth air volume regulating valve 16 is closed. The hot and humid gas discharged by the exhaust fan 14 in the belt dryer 11 enters the condenser 17. The gas is cooled by the circulating cooling water sent by the circulating cooling water pump 19 inside the condenser 17. After the temperature drops to the dew point, the condensed water is precipitated and discharged from the condenser 17. The cooling water absorbs heat and rises in temperature. The cooling water enters the cooling tower 18 to dissipate heat and cool down. After cooling, the cooling water is pumped out by the circulating cooling water pump 19 and sent to the condenser 17, completing the cycle.

[0051] (S5) Waste gas treatment: The dehumidified gas enters the middle and rear low-temperature section air inlet of the grate cooler 4 through the fifth air volume regulating valve 20. After heat exchange with the medium- and low-temperature clinker in the grate cooler 4, it is extracted from the middle and rear of the grate cooler 4 by the kiln head induced draft fan 7. The gas in the middle is cooled by the waste heat power generation system 5 and mixed with the tail gas to enter the dust collector 6. After passing through the kiln head induced draft fan 7, it enters the alternative fuel dryer to continue drying the alternative fuel.

[0052] The dehumidified gas can also be connected to the air inlet of the high-temperature section blower at the front of the grate cooler 4 through the sixth air volume regulating valve 21. After heat exchange with the high-temperature clinker in the grate cooler 4, it becomes secondary air entering the kiln or tertiary air entering the furnace. These non-condensable gases containing odors are completely burned and removed after high-temperature calcination.

[0053] The fifth air volume regulating valve 20 is in a normally open state, and the sixth air volume regulating valve 21 is in an intermittently open state. Since the drying of alternative fuels that are prone to produce odor, toxic and harmful gases requires the drying exhaust gas to continuously undergo a cycle of heating in the grate cooler 4 → heat release in the belt dryer 11 → condensation and water separation in the condenser 17 → heating in the grate cooler 4, the non-condensable gases such as H2S and NH3 produced by the alternative fuel will be enriched, posing leakage and safety risks. Therefore, when the drying exhaust gas contains a high content of non-condensable gases, the sixth air volume regulating valve 21 is opened to extract a certain amount of drying exhaust gas and transport it to the high-temperature section of the grate cooler 4. After heat exchange with the high-temperature clinker, it becomes secondary air entering the kiln or tertiary air entering the furnace. This solution adopts a closed system, and the drying gas is not discharged, which will not cause gas pollution to the surrounding environment.

Claims

1. A system for coupling alternative fuel drying with a cement kiln, characterized in that: It includes a grate cooler waste heat recovery system, a kiln shell waste heat recovery system, an alternative fuel drying system, a drying gas condensation processing system, and a chimney. The grate cooler waste heat recovery system introduces the kiln head waste heat flue gas into the alternative fuel drying system to dry the alternative fuel. The kiln shell waste heat recovery system exchanges the collected waste heat with the kiln head waste heat flue gas that has heated the alternative fuel. The kiln head waste heat flue gas after heat exchange dries the alternative fuel again and is then sent to the drying gas condensation processing system or chimney. The waste heat after heat exchange is returned to the kiln shell waste heat recovery system for circulated heating. The drying gas condensation treatment system includes a condenser (17) connected to the air outlet of the alternative fuel drying system, the water outlet of the condenser (17) is connected to the water inlet of the cooling tower (18), and a circulating cooling water pump (19) is provided between the water outlet of the cooling tower (18) and the water inlet of the condenser (17) so that the cooling water circulates between the condenser (17) and the cooling tower (18); the gas phase outlet of the cooling tower (18) is connected to the air inlet of the grate cooler; The alternative fuel drying system includes a belt dryer (11), a circulating fan (12), an exhaust fan (14) and connecting pipes; waste heat flue gas from the kiln head enters through the front section of the belt dryer (11) to dry the alternative fuel, is extracted by the circulating fan (12), and is sent to the rear section of the belt dryer (11), where it is dried after heat exchange with the collected waste heat and heated, and is discharged from the lower part of the rear section through the exhaust fan (14) and sent to the drying gas condensation treatment system or chimney; The kiln shell waste heat recovery system comprises a circulating medium heat collecting device (2) provided on the rotary kiln (3), a circulating pump (1), a heat exchanger (13) provided in the alternative fuel drying system, and connecting pipes; the circulating pump (1) sends the cooling medium into the circulating medium heat collecting device (2), which is heated by the surface of the rotary kiln (3) shell to become a heat medium, which enters the heat exchanger (13), cools the kiln head waste heat flue gas after heating the alternative fuel, and then returns to the circulating pump (1); The grate cooler waste heat recovery system comprises a grate cooler (4), a waste heat power generation system (5), a dust collector (6), a kiln head induced draft fan (7), a chimney and connecting pipes; after the exhaust gas from the middle of the grate cooler is heat-exchanged by the waste heat power generation system (5), it passes through the dust collector (6) together with the exhaust gas from the tail of the grate cooler, is drawn out through the kiln head induced draft fan (7), and is then sent to the alternative fuel drying system, and the excess exhaust gas is discharged into the chimney through valve regulation; The outlet of the kiln head induced draft fan (7) is divided into two routes, one route is connected to the alternative fuel drying system, and the other route is discharged to the chimney. An air volume regulating valve is provided on each of the two air ducts to regulate the amount of smoke on the two air ducts.

2. The system of coupling alternative fuel drying and cement kiln according to claim 1, characterized in that: The drying gas condensation treatment system cools down and condenses the hot and humid gas discharged from the alternative fuel drying system, and the condensed water is discharged from the system. The dehumidified gas is connected to the middle and rear low-temperature section fan inlet of the grate cooler or is connected to the middle and rear low-temperature section fan inlet and the front high-temperature section fan inlet at the same time.

3. The system of coupling alternative fuel drying and cement kiln according to claim 1, characterized in that: The alternative fuel drying system includes a front section and a rear section. The kiln head waste heat flue gas is introduced into the front section to dry the alternative fuel. After the kiln head waste heat flue gas heated by the alternative fuel is exchanged with the collected waste heat, the alternative fuel in the rear section is dried again.

4. A method for coupling alternative fuel drying with a cement kiln using the system of claim 1, characterized in that: The following steps are involved: (S1) The grate cooler waste heat recovery system sends the waste heat flue gas from the kiln head into the alternative fuel drying system. The excess exhaust gas is regulated by a valve and discharged into the chimney. The air volume entering the alternative fuel drying system is controlled according to the scale of the alternative fuel drying. The cold medium is sent to the circulating medium heat collecting device (2) provided on the rotary kiln (3) through the circulating pump (1), and is heated by the surface of the rotary kiln (3) to become the hot medium. The hot medium flows into the heat exchanger (13) through the pipeline, is cooled by the drying air, and then returns to the circulating pump (1); (S2) The waste heat flue gas from the kiln head enters from the upper or lower part of the front section of the alternative fuel drying system, dries the alternative fuel, is extracted by the circulating fan (12), and is sent to the upper part of the rear section. After heat exchange and temperature increase in the heat exchanger (13), the alternative fuel is dried again. The dried waste gas is discharged from the lower part of the rear section of the dryer through the exhaust fan (14) and sent to the drying gas condensation treatment system or chimney; When the dry gas is fed into the condensation treatment system, the hot and humid gas is cooled and condensed by the condenser (17), the condensed water is discharged, and the dehumidified gas is connected to the air inlet of the blower of the grate cooler.

5. The method for coupling alternative fuel drying with a cement kiln according to claim 4, characterized in that: In step (S2), the dehumidified gas is connected to the air inlet of the medium and low temperature section blower at the middle and rear part of the grate cooler. After heat exchange with the medium and low temperature clinker, the gas is extracted from the middle and rear parts of the grate cooler by the induced draft fan. The gas in the middle part is cooled by the waste heat power generation system and then mixed with the tail gas. It enters the dust collector and then passes through the induced draft fan to enter the alternative fuel dryer to continue drying the alternative fuel. Alternatively, the dehumidified gas is simultaneously connected to the air inlet of the middle and rear low-temperature section blower and the air inlet of the front high-temperature section blower of the grate cooler; when connected to the front high-temperature section blower inlet: after heat exchange with the high-temperature clinker, it becomes secondary air entering the kiln or tertiary air entering the furnace.

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