Method for recycling oxygen-rich waste gas and flue gas

Abstract

The invention relates to the field of continuous hot galvanizing production, in particular to a method for recycling oxygen-rich waste gas and flue gas, which comprises the following steps: step 1, step 2, step 3, step 4, step 5, step 6 and step 7. According to the device, oxygen-rich byproduct gas can be subjected to recycling, mixing and pressure equalizing treatment, the oxygen content of the recycled oxygen-rich byproduct gas is accurately detected, the total combustion improver flow value is calculated and determined through the flow value, the flue gas circulation flow value and the component detection value of the flue gas circulation flow value, automatic adjustment of the electric proportional valve is achieved, and the combustion efficiency is improved. According to the method, the oxygen-rich byproduct gas is applied to the continuous hot galvanizing annealing furnace, oxygen-rich combustion, energy conservation and efficient waste gas recycling are achieved, and the method has the advantages that the oxygen-rich byproduct gas is applied to the continuous hot galvanizing annealing furnace, so that oxygen-rich combustion is achieved, energy is saved, and waste gas is recycled and reused efficiently; meanwhile, low-temperature preheating of natural gas can be achieved, the fuel utilization rate is increased, the production cost is reduced, and energy saving can be achieved.

Description

Technical Field

[0001] The invention relates to the field of continuous hot-dip galvanizing production, and in particular to a method for recycling oxygen-rich waste gas and flue gas. Background Art

[0002] There are many methods for hot-dip galvanizing in annealing furnaces, among which the Sendzimir process and the US Steel process are more common in-line annealing methods. The Sendzimir process combines the annealing process with the hot-dip galvanizing process. The oil of the strip is first burned off during continuous annealing, and a thin layer of oxide film is formed on the surface of the strip. The strip then passes through the reduction section of the annealing furnace to reduce the surface oxide film to pure iron, so that the coating and the iron base can be firmly combined when entering the zinc pot. The US Steel process is a variant of the Sendzimir process, which uses an alkaline electrolytic degreasing tank to replace the degreasing function of the oxidation furnace.

[0003] At present, waste gas from hot-dip galvanizing production is mostly discharged directly, which is a waste of resources and energy. Some companies mechanically recover oxygen-rich byproduct gas and apply it to the annealing furnace, but this leads to local air-fuel ratio control disorders in the annealing furnace, local high temperatures, and sometimes overoxidation defects in steel strip quality or energy waste.

[0004] In the hot-dip galvanizing production process, the continuous annealing furnace is one of the key equipment in this process. Its main function is to heat the steel strip to a suitable annealing temperature and ensure that the surface quality of the steel strip meets the requirements of direct galvanizing. There are some problems in the actual operation on site, such as:

[0005] Waste of resources: In the process of nitrogen production, our goal is to produce qualified nitrogen. In enterprises that only have pickling, cold rolling and galvanizing production processes, pressure swing adsorption is often used for preparation. Compressed air is used to produce nitrogen through molecular sieve pressure swing adsorption. During the alternating desorption process between desorption tower A and desorption tower B, oxygen-rich waste gas is discharged into the atmosphere, resulting in a waste of oxygen-rich waste gas resources and also a waste of energy.

[0006] Composition fluctuation: During the desorption process, the oxygen content in the exhaust gas from desorption tower A or desorption tower B is high in the early stage. As the desorption proceeds, the oxygen content decreases and cannot be directly applied to the combustion aid, which will cause the air-fuel ratio to be difficult to adjust.

[0007] High pressure: Nitrogen is prepared by pressure swing adsorption, and the pressure used is relatively high. During the desorption process, the waste gas pressure generated is relatively high, generally (0.1-0.15) MPa, and cannot be used directly for production.

[0008] Theoretical combustion temperature of natural gas is high: independent continuous hot-dip galvanizing enterprises mostly use natural gas as fuel, which has high calorific value and is a clean energy. It is used in the NOF section and is directly burned. Because the steel strip is relatively thin, usually (0.7-3.5) mm, sometimes the temperature is too high or the strip is broken.

[0009] Therefore, in order to solve the problems of resource waste, composition fluctuation, high pressure and high theoretical combustion temperature of natural gas in the above-mentioned hot-dip galvanizing production process, a method for recycling and reusing oxygen-rich waste gas and flue gas can be designed. Summary of the invention

[0010] In order to overcome the problems of resource waste, composition fluctuation, high pressure and high theoretical combustion temperature of natural gas in the hot-dip galvanizing production process.

[0011] The technical solution of the present invention is: a method for recycling oxygen-rich waste gas and flue gas, the steps of which are as follows:

[0012] Step 1: The oxygen-rich waste gas generated in the process of producing nitrogen is recycled alternately into the nitrogen generator adsorption tower A and the nitrogen generator adsorption tower B;

[0013] Step 2: The exhaust gas is input into the pressure gas storage tank through the input pipeline for mixing and pressure equalization. A butterfly valve and a first check valve are installed on the input pipeline, and a third pressure gauge is installed on the upper end of the pressure gas storage tank;

[0014] Step 3: After the exhaust gas is mixed and pressure-equalized, it is decompressed and output through the oxygen-rich exhaust gas delivery pipeline, wherein a part of the exhaust gas is directly delivered to the air heat exchanger through the air hot air pipeline, the air heat exchanger is arranged inside the direct-firing section of the annealing furnace, a thermocouple is arranged in the direct-firing section of the annealing furnace, and a first electric butterfly valve, a pressure reducing valve, a first electric proportional valve, an oxygen content meter, and a first flow meter are installed on the oxygen-rich exhaust gas delivery pipeline;

[0015] Step 4: A portion of the flue gas in the chimney is input into the natural gas exchanger through the circulating flue gas pipeline, and the natural gas is input into the natural gas exchanger through the natural gas pipeline network for low-temperature preheating. The natural gas pipeline network is provided with a ball valve, and the circulating flue gas pipeline is installed with a circulating flue gas detector, a second check valve, a second electric butterfly valve, a second electric proportional valve, a second flow meter, an oxygen detection meter, a first pressure gauge, a third flow meter, and a third electric proportional valve;

[0016] Step 5: The flue gas cooled in the natural gas heat exchanger is input into the air heat exchanger and then exhausted by the blower;

[0017] Step 6: The preheated natural gas is output through a natural gas pipeline and then mixed with another part of the exhaust gas and another part of the flue gas. A natural gas flow meter, a fourth electric proportional valve, and a second pressure gauge are provided on the natural gas pipeline;

[0018] Step 7: The mixed gas is burned in an oxygen-enriched burner, and three oxygen-enriched burners are provided.

[0019] Preferably, the oxygen content in the oxygen-rich waste gas in step 1 is 33%-38%.

[0020] Preferably, the oxygen-rich byproduct gas in the pressure gas storage tank in step 2 has an hourly production of about 100m3 and a pressure of generally 0.1MPa.

[0021] Preferably, in step three, the exhaust gas is reduced in pressure through the first electric butterfly valve and the pressure reducing valve to a working pressure of about 7 kPa of the annealing furnace combustion aid, and its flow rate can reach 1400 m3 / h.

[0022] Preferably, in step three, the temperature is detected by the thermocouple and interlocked with the second electric butterfly valve and the second electric proportional valve of the circulating flue gas to automatically control the opening of the valve.

[0023] Preferably, in step 4, a partial flue gas circulation technology is adopted, and the partial flue gas accounts for 10%-35% of the total flue gas.

[0024] Preferably, in step 4, the natural gas is preheated to 80-120° C. to reduce the flue gas emission temperature.

[0025] Preferably, the pressure gas storage tank is connected to the direct-firing section of the annealing furnace by a metal pipe.

[0026] Preferably, the circulating flue gas duct is connected to the hot air duct.

[0027] The beneficial effects of the present invention are as follows: the method for recycling and reusing oxygen-rich waste gas and flue gas can recycle, mix and pressure-equalize oxygen-rich byproduct gas, accurately detect the oxygen content of the recycled oxygen-rich byproduct gas, calculate through flow value, flue gas circulation flow value and its component detection value, determine the overall combustion-supporting agent flow value, realize automatic adjustment of the electric proportional valve, and thus adapt to the changes in natural gas flow and calorific value, and solve the problem of local high temperature of the flame caused by oxygen-rich combustion and natural gas preheating by adopting partial flue gas circulation. Compared with the traditional method, the method applies oxygen-rich byproduct gas to a continuous hot-dip galvanizing annealing furnace to realize oxygen-rich combustion, save energy, and recycle and efficiently utilize waste gas. At the same time, it can realize low-temperature preheating of natural gas, improve fuel utilization, improve production efficiency, reduce production costs, and achieve energy saving. The application technology of recycling and reusing byproduct gas of the nitrogen generator belongs to the concept of sustainable development, recycles resources, recycles part of the flue gas, and realizes natural gas preheating combustion by adding a high calorific value natural gas exchanger, so as to achieve the purpose of energy saving and carbon reduction, greatly improve resource utilization, reduce environmental pollution, and thus achieve energy saving and low carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a process flow chart for comprehensive utilization of oxygen-rich waste gas and flue gas according to the present invention.

[0029] Explanation of the reference numerals: 1. nitrogen generator adsorption tower A; 2. nitrogen generator adsorption tower B; 3. butterfly valve; 4. first check valve; 5. pressure storage tank; 6. first electric butterfly valve; 7. pressure reducing valve; 8. first electric proportional valve; 9. oxygen content meter; 10. first flow meter; 11. second electric butterfly valve; 12. second electric proportional valve; 13. second flow meter; 14. oxygen detection meter; 15. air heat exchanger; 16. first pressure gauge; 17. third flow meter; 18. third electric proportional valve valve; 19. natural gas flow meter; 20. fourth electric proportional valve; 21. hot air duct; 22. natural gas pipeline; 23. oxygen-enriched burner; 24. second pressure gauge; 25. blower; 26. direct-firing section of annealing furnace; 27. natural gas pipeline network; 28. ball valve; 29. ​​thermocouple; 30. natural gas exchanger; 31. circulating flue gas detector; 32. second check valve; 33. circulating flue gas pipeline; 34. oxygen-enriched exhaust gas delivery pipeline; 35. chimney; 36. third pressure gauge. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0031] See also Figure 1 The present invention provides an embodiment: a method for recycling oxygen-rich waste gas and flue gas, the steps of which are as follows:

[0032] Step 1: The oxygen-rich waste gas with an oxygen content of 33%-38% generated during the nitrogen production process is recycled into the nitrogen generator adsorption tower A 1 and the nitrogen generator adsorption tower B 2 alternately;

[0033] Step 2: The waste gas is input into the pressure gas storage tank 5 through the input pipeline for mixing and pressure equalization. The input pipeline is equipped with a butterfly valve 3 and a first check valve 4. The upper end of the pressure gas storage tank 5 is equipped with a third pressure gauge 36. The waste gas passes through the butterfly valve 3 and the first check valve 4 to the pressure gas storage tank 5. At this time, the hourly output of the oxygen-rich byproduct gas is about 100m3, and the pressure is generally 0.1MPa.

[0034] Step 3: After the exhaust gas is mixed and pressure-equalized, it is decompressed and output through the oxygen-rich exhaust gas delivery pipeline 34. A part of the exhaust gas is directly delivered to the air heat exchanger 15 through the air hot air pipeline 21. The air heat exchanger 15 is arranged inside the direct-firing section 26 of the annealing furnace. A thermocouple 29 is arranged in the direct-firing section 26 of the annealing furnace. Due to the use of oxygen-enriched combustion technology, the theoretical combustion temperature is increased. However, the heating steel belt (0.7-3.5mm) is relatively thin, which is easy to cause heating defects. By detecting the temperature according to the thermocouple 29, the second electric butterfly valve 11 and the second electric proportional valve 12 of the circulating flue gas are realized. Interlock, automatically control the opening of the valve, and then adjust the local high temperature problem of the oxygen-rich burner 23. The oxygen-rich waste gas delivery pipeline 34 is installed with the first electric butterfly valve 6, the pressure reducing valve 7, the first electric proportional valve 8, the oxygen content meter 9, and the first flow meter 10. The output waste gas is reduced to about 7kPa of the annealing furnace combustion agent working pressure through the first electric butterfly valve 6 and the pressure reducing valve 7. The flow rate can reach 1400m3 / h. The oxygen content of the oxygen-rich waste gas is monitored online through the oxygen content meter 9, and the flow rate is controlled by the first electric proportional valve 8, so as to achieve accurate proportioning with air;

[0035] Step 4: A portion of the flue gas in the chimney 35 is input into the natural gas exchanger 30 through the circulating flue gas pipeline 33, and the natural gas is input into the natural gas exchanger 30 through the natural gas pipeline network 27 for low-temperature preheating. The natural gas pipeline network 27 is provided with a ball valve 28, and the circulating flue gas pipeline 33 is installed with a circulating flue gas detector 31, a second check valve 32, a second electric butterfly valve 11, a second electric proportional valve 12, a second flow meter 13, an oxygen detection meter 14, a first pressure gauge 16, a third flow meter 17, and a third electric proportional valve 18. By adopting a part (10%-35% of the total flue gas) of the flue gas circulation technology, the problem of local high temperature caused by oxygen-enriched combustion and the natural gas exchanger 30 of natural gas is solved to achieve the set process heating temperature, and because of the advantages of the flue gas circulation interlock, the natural gas is preheated before combustion, so that the natural gas can be preheated to 80-120°C. The flue gas emission temperature is lowered in one step, and the flue gas waste heat is recovered to the maximum extent to achieve energy saving of 1-2.5%. The oxygen detection meter 14 and the third flow meter 17 detect values, and transmit signals to the third electric proportional valve 18 to achieve precise control of the air-fuel ratio. In order to prevent oxidation of the steel strip, a lower air-fuel ratio is generally used to achieve oxygen-poor combustion, so that the oxygen content in the flue gas is below 0.15%. The on-site circulating flue gas detector 31 will detect and continuously control the oxygen content in the flue gas, and ignore the oxygen carried by the circulating flue gas when calculating the oxygen-rich combustion. The circulating flue gas duct 33 is connected to the air hot air duct 21, and a regulating valve, a detection meter, etc. are added to the connecting pipe and equipped with a sensor to realize remote analysis and control functions, thereby accurately controlling the flue gas circulation. In addition, the circulating flue gas flow is strictly adjusted and controlled according to the temperature detection of the thermocouple 29 in the annealing furnace to ensure that the temperature in the furnace cannot be too high.

[0036] Step 5: The flue gas cooled in the natural gas heat exchanger 30 is input into the air heat exchanger 15 and then extracted and discharged by the blower 25;

[0037] Step 6: The preheated natural gas is output through the natural gas pipeline 22, and then mixed with another part of the exhaust gas and another part of the flue gas. The natural gas pipeline 22 is provided with a natural gas flow meter 19, a fourth electric proportional valve 20, and a second pressure gauge 24. The oxygen content of the gas after the oxygen-rich byproduct gas, the circulating flue gas and the combustion-supporting air are measured, combined with the effective air-fuel ratio setting, converted into an actual control ratio, and intelligently transmitted to the third electric proportional valve 18 and the fourth electric proportional valve 20 to adjust the oxygen-rich combustion-supporting agent and the natural gas flow for precise control;

[0038] Step seven: The mixed gas is subjected to oxygen-enriched combustion by the oxygen-enriched burner 23. Three oxygen-enriched burners 23 are provided. The oxygen-enriched burner 23 is used for oxygen-enriched combustion of the oxygen-enriched exhaust gas. Combined with production practice, the problem of exhaust gas waste can be effectively solved.

[0039] During operation, by recycling the oxygen-rich waste gas (oxygen content 33-38%) generated in the process of preparing nitrogen, according to theoretical calculation, the combustion aid can be enriched with oxygen to 22.0-24.0%, which will achieve an overall energy saving of 1.5-4%, and the waste gas is collected alternately by nitrogen generator adsorption tower A 1 and nitrogen generator adsorption tower B 2, and then passed through butterfly valve 3 and first check valve 4 to pressure gas storage tank 5. By adding pressure gas storage tank 5, the recycled oxygen-rich byproduct gas can be mixed, pressure-equalized, and temporarily stored, and detection meters, pressure gauges, etc. can be installed and equipped with sensors to realize remote analysis and control functions, which is applied to annealing furnaces. The burning stage prepares for increasing the oxygen content of the combustion aid. The hourly output of this oxygen-rich byproduct gas is about 100m3, and the pressure is generally 0.1MPa. Then it is reduced by the first electric butterfly valve 6 and the pressure reducing valve 7 to the working pressure of the annealing furnace combustion aid of about 7kPa. Its flow rate can reach 1400m3 / h for production. After the oxygen content of the oxygen-rich waste gas is monitored online, the flow rate is controlled by a proportional valve to achieve precise proportioning with air. The oxygen detection meter 14 and the third flow meter 17 detect the value, and the signal is transmitted to the electric proportional valve to achieve precise control of the air-fuel ratio, and finally it is sent to the oxygen-rich burner 23 for oxygen-enriched combustion of the oxygen-rich waste gas.

[0040] Combined with production practice, the recovered oxygen-rich by-product gas is mixed and pressure-equalized, and applied to the direct-firing section of the annealing furnace to increase the oxygen content of the combustion aid to achieve oxygen-enriched combustion technology. The oxygen content of the combustion aid starts from 21% to 24%. Every 1% increase can increase the theoretical combustion temperature: 12-18°C, while reducing the amount of smoke generated: 3-5%, and achieving energy saving: 1.5-4%.

[0041] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for recycling oxygen-rich waste gas and flue gas, characterized in that: The steps are as follows: Step 1: The oxygen-rich waste gas generated in the process of producing nitrogen is recycled into nitrogen generator adsorption tower A (1) and nitrogen generator adsorption tower B (2) alternately; Step 2: the exhaust gas is input into the pressure gas storage tank (5) through an input pipeline for mixing and pressure equalization, a butterfly valve (3) and a first check valve (4) are installed on the input pipeline, and a third pressure gauge (36) is installed at the upper end of the pressure gas storage tank (5); Step 3: After the exhaust gas is mixed and pressure-equalized, it is decompressed and output through the oxygen-rich exhaust gas delivery pipeline (34), wherein a portion of the exhaust gas is directly delivered to the air heat exchanger (15) through the air hot air pipeline (21), the air heat exchanger (15) is arranged inside the direct-firing section (26) of the annealing furnace, a thermocouple (29) is arranged inside the direct-firing section (26) of the annealing furnace, and a first electric butterfly valve (6), a pressure reducing valve (7), a first electric proportional valve (8), an oxygen content meter (9), and a first flow meter (10) are installed on the oxygen-rich exhaust gas delivery pipeline (34); Step 4: a portion of the flue gas in the chimney (35) is introduced into the natural gas exchanger (30) through the circulating flue gas pipeline (33), and the natural gas is introduced into the natural gas exchanger (30) through the natural gas pipeline network (27) for low-temperature preheating. The natural gas pipeline network (27) is provided with a ball valve (28), and the circulating flue gas pipeline (33) is equipped with a circulating flue gas detector (31), a second check valve (32), a second electric butterfly valve (11), a second electric proportional valve (12), a second flow meter (13), an oxygen detection meter (14), a first pressure gauge (16), a third flow meter (17), and a third electric proportional valve (18); Step 5: The flue gas cooled in the natural gas heat exchanger (30) is input into the air heat exchanger (15), and then extracted and discharged by the blower (25); Step 6: The preheated natural gas is output through a natural gas pipeline (22) and then mixed with another part of the exhaust gas and another part of the flue gas. The natural gas pipeline (22) is provided with a natural gas flow meter (19), a fourth electric proportional valve (20), and a second pressure gauge (24); Step 7: The mixed gas is passed through an oxygen-enriched burner (23) for oxygen-enriched combustion. Three oxygen-enriched burners (23) are provided.

2. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: The oxygen content in the oxygen-rich exhaust gas in step 1 is 33%-38%.

3. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: The oxygen-rich byproduct gas in the pressure gas storage tank (5) in step 2 has an hourly production of about 100m3 and a pressure of generally 0.1MPa.

4. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: In step 3, the exhaust gas is decompressed to a working pressure of about 7 kPa of the annealing furnace combustion aid through the first electric butterfly valve (6) and the pressure reducing valve (7), and its flow rate can reach 1400 m3 / h.

5. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: In step 3, the temperature is detected by the thermocouple (29), and the second electric butterfly valve (11) and the second electric proportional valve (12) of the circulating flue gas are interlocked to automatically control the opening of the valves.

6. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: In step 4, a partial flue gas circulation technology is adopted, and the partial flue gas accounts for 10%-35% of the total flue gas.

7. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: In step 4, the natural gas is preheated to 80-120°C to reduce the flue gas emission temperature.

8. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: The pressure gas storage tank (5) is connected to the direct-firing section (26) of the annealing furnace by a metal pipeline.

9. The method for recycling oxygen-rich waste gas and flue gas according to claim 1, characterized in that: The circulating flue gas duct (33) is connected to the hot air duct (21).

Images