A system and method for coupling biomass gasification with cement kiln

Abstract

The present invention discloses a system and method for coupling biomass gasification with a cement kiln. The system includes a decomposition furnace, a bypass ventilation system, and a biomass gasification system. The method comprises the following steps: the biomass gasification system utilizes biomass and hot flue gas from the bypass ventilation system to generate biomass fuel gas, which is then fed into the reduction zone of the decomposition furnace; the hot flue gas within the decomposition furnace is drawn out by the bypass ventilation system, subjected to rapid cooling, dust removal, and flue gas reheating, and then fed into the biomass gasification system. The present invention utilizes the heat of the high-temperature flue gas in the smoke chamber while improving the biomass gasification efficiency and the calorific value of the fuel gas. Furthermore, the reducing gases in the biomass fuel gas can reduce the nitrogen oxide content in the cement kiln system, ultimately increasing the proportion of cement kilns utilizing biomass as an alternative fuel.

Description

Technical Field

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

[0002] Existing cement kiln technologies for utilizing biomass as an alternative fuel mostly rely on direct combustion, where the biomass is fed directly into the precalciner. However, the drawbacks include low biomass calorific value, resulting in a low replacement rate and low cement kiln combustion stability. Due to biomass composition (high levels of K, Na, and Cl), direct combustion of large quantities of biomass inevitably leads to problems such as system crusting and blockage, biomass deflagration, and localized high temperatures in the precalciner, all of which affect the normal operation of the cement kiln. To address the accumulation of harmful elements and crusting and blockage, a bypass ventilation system is generally required to discharge the kiln tail flue gas out of the kiln.

[0003] Conventional bypass ventilation systems cool and dust the flue gas before discharging it, which in turn causes losses in system heat and material consumption, increasing production and operation costs. Furthermore, the bypass ventilation system originates from the kiln tail flue chamber, which has a high NOx content, and direct emission carries the risk of pollutant exceeding standards. To utilize the waste heat from the bypass ventilation, a common practice is to separate the flue gas released from the cement kiln tail flue chamber through a bypass, then feed it into the kiln tail heat boiler for power generation. However, this method has the disadvantage that the flue gas after sedimentation contains a large amount of dust. Due to the large amount of dust in the flue gas during the boiler heat exchange process, it will affect the operation of the kiln tail heat boiler, ultimately affecting the stable operation of the cement production system.

[0004] Patent CN209848654U discloses a NOx removal system for a cement kiln using a biomass pyrolysis furnace, which includes a decomposition furnace smoke chamber and a biomass pyrolysis furnace. The patent draws part of the hot air from the decomposition furnace smoke chamber, cools it down and removes dust before entering the biomass pyrolysis furnace, where it reacts with organic matter such as water vapor, coal powder, and biomass powder to generate CO, H2, CH i Reducing gas is used to reduce the remaining NOx in the reduction zone of the decomposition furnace. However, in this patent, the flue gas from the smoke chamber of the decomposition furnace is drawn out by a fan. However, the temperature of the smoke chamber is high (≥1000℃) and the oxygen content is extremely low (<3.0%), which requires extremely high high-temperature resistance of the fan. The flue gas is directly cooled by water in the cooling and dust removal bin, resulting in part of the heat being carried away by the water and cannot be used. In addition, the flue gas has a high dust content and the water is changed frequently. Not only is the smoke dust wasted, but most of the heat of the flue gas is also absorbed by the water, and the evaporated water vapor enters the biomass pyrolysis furnace and finally enters the decomposition furnace. In addition, the temperature of the flue gas entering the biomass pyrolysis furnace is also uncontrollable, and the low oxygen content of the flue gas will also affect the pyrolysis effect of the biomass pyrolysis furnace. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a system for coupling biomass gasification with cement kilns that can significantly increase the proportion of biomass used as an alternative fuel in cement kilns;

[0006] The second object of the present invention is to provide a method for coupling biomass gasification with a cement kiln using the above system.

[0007] Technical solution: The biomass gasification and cement kiln coupling system of the present invention includes a decomposition furnace, a bypass ventilation system, and a biomass gasification system connected to the decomposition furnace; the bypass ventilation system includes a quenching system, a cyclone, a flue gas reheater, a dust collector and an exhaust fan connected in sequence; the flue gas reheater is connected to the biomass gasification system to allow the flue gas after cooling and dust removal to enter the biomass gasification system after heating.

[0008] The outlet of the exhaust fan is divided into two paths, one of which is connected to the flue gas reheater, so as to exchange heat between the flue gas discharged by the exhaust fan and the flue gas after dust removal by the cyclone in the flue gas reheater.

[0009] Wherein, the quenching system is provided with a cold air inlet, and the cold air inlet is connected to the quenching fan.

[0010] Wherein, the air outlet of the quenching fan is provided with a second air volume regulating valve for adjusting the amount of cold air supplied.

[0011] Wherein, a cyclone is provided between the quenching device and the flue gas reheater, and a dust collector is provided between the flue gas reheater and the exhaust fan.

[0012] The biomass gasification system includes a silo, a feeder, a biomass gasification furnace and a blower, and an air inlet of the blower is connected to a flue gas reheater.

[0013] Among them, another air inlet of the blower can also be used to introduce air or oxygen-rich gas, and a first air volume regulating valve is provided on the pipeline.

[0014] The fuel gas generated by the biomass gasification system is connected to the reduction zone of the decomposition furnace through a pipeline.

[0015] The method for coupling biomass gasification with a cement kiln in the above system comprises the following steps:

[0016] (S1) The biomass gasification system uses biomass and hot flue gas from the bypass exhaust system to generate biomass fuel gas and feeds it into the reduction zone of the decomposition furnace;

[0017] (S2) The bypass ventilation system draws out the hot flue gas in the smoke chamber of the decomposition furnace, cools it through the rapid cooling system, and the cooled flue gas is sent to the exhaust fan after dust removal through the cyclone, cooling in the flue gas reheater, and dust removal by the dust collector; the flue gas discharged from the exhaust fan enters the flue gas reheater and is sent to the biomass gasification system after being heated.

[0018] Among them, the flue gas passes through the cyclone and dust collector to remove dust, while also reducing the content of harmful elements inside the cement kiln system.

[0019] Among them, in step (1), when the content of harmful elements in the biomass and cement raw materials used in the cement kiln is low, and the decomposition furnace bypass air volume is small or no air volume is required, the present invention can open the air or oxygen-enriched gas pipeline of the biomass gasification system blower, and adjust the air supply volume through the first air volume regulating valve to ensure the normal operation of the biomass gasification system.

[0020] Among them, in step (2), the quenching system cools the smoke in the smoke chamber by adding cold air. The cold air is sent in through the quenching fan on the quenching system, and the cooling temperature is adjusted by the second air volume regulating valve at the outlet of the quenching fan, and the gasification dosage of the biomass gasification system is also adjusted.

[0021] In addition, in step (2), the outlet of the exhaust fan is divided into two routes, one route is connected to the flue gas reheater and connected to the blower of the biomass gasification system after heating, and the other route is connected to the chimney or the flue gas treatment system. An air volume regulating valve is provided on each of the two flue pipes to adjust the amount of flue gas on the two flue pipes; the present invention gives priority to meeting the air volume fed into the biomass gasification system, and the remaining air volume is fed into the chimney or the flue gas treatment system.

[0022] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0023] (1) The air introduced by the bypass ventilation system serves as a biomass gasification agent, providing a stable gas source for biomass gasification. This invention not only utilizes the heat of the high-temperature flue gas in the smoke chamber, but also the higher biomass air supply temperature improves the gasification efficiency and calorific value of the biomass gasification system. Furthermore, the provision of the bypass ventilation system also reduces the content of harmful elements in the cement kiln. This invention can significantly increase the proportion of biomass used as an alternative fuel in cement kilns, with the kiln tail fuel replacement rate theoretically reaching 100%.

[0024] (2) Using biomass gasification technology to convert CH4, C n H m , H2, CO and other strong reducing gases and biomass fuel gas containing carbon fly ash are sent into the reduction zone of the decomposition furnace to reduce the NO x The effect of concentration.

[0025] (3) The flue gas extracted by the bypass vent mainly comes from the kiln gas of the rotary kiln, and its NO x The present invention not only utilizes the waste heat of the bypass flue gas, but also utilizes the reducing atmosphere generated by biomass gasification to reduce the NO in the bypass flue gas. x content to avoid emission problems.

[0026] (4) The present invention uses biomass gasification to deliver biomass gas to the decomposition furnace, achieving uniform combustion of biomass gasification products within the decomposition furnace and realizing fuel substitution. Compared with the direct combustion method, the way of connecting gas to the decomposition furnace is more flexible and diverse. By optimizing the jet velocity and delivery position for cement production lines of different sizes, a better decomposition furnace combustion environment and adjustment space are achieved, with less impact on the cement burning system.

[0027] (5) The present invention utilizes the air introduced by the bypass ventilation system as a biomass gasification agent. By adjusting the air volume of the cooling fan, the blast volume and blast temperature of the biomass gasification system can be adjusted. In addition, the blower of the biomass gasification system is also provided with a passage for introducing air or oxygen-rich gas, so that the gasification effect of the biomass gasification system for different biomass types and feed amounts becomes controllable.

[0028] (6) The present invention is provided with a flue gas reheater, which can further increase the temperature of the hot flue gas in the biomass gasification system, improve the gasification efficiency, and also reduce the amount of cold air added. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the system structure of the present invention;

[0030] Figure 2 The numerical simulation results of the temperature at different parts of the decomposition furnace connected to the biomass gas of the present invention are as follows;

[0031] Figure 3 These are the numerical simulation results of NO molar concentrations at different locations of the biomass gas decomposition furnace according to the present invention. DETAILED DESCRIPTION

[0032] The present invention is described in further detail below.

[0033] like Figure 1As shown, the present invention provides a system for coupling biomass gasification and cement kiln, comprising a biomass gasification system 100, a decomposition furnace 2, and a bypass ventilation system 300; the fuel gas generated by the biomass gasification system 100 is connected to the reduction zone of the decomposition furnace; the bypass ventilation system comprises a quenching system 5, a cyclone 6, an ash discharge valve 7, a flue gas reheater 8, a dust collector 9 and an exhaust fan 10; the bypass ventilation system 300 extracts a set proportion of high-temperature flue gas from the tail smoke chamber of the decomposition furnace 2, which is mixed with cold air through the quenching system 5 and cooled before being connected to the cyclone 6; the separated large particles of ash are sent to the decomposition furnace 2 through the ash discharge valve 7; the remaining flue gas is extracted by the exhaust fan 10 after heat exchange in the flue gas reheater 8 and dust removal in the dust collector 9, and is heated in the flue gas reheater 8 and sent to the biomass gasification system 100, and the excess flue gas is sent to the chimney or flue gas treatment system of the cement kiln production line.

[0034] The biomass gasification system 100 includes a silo 101, a feeder 102, a biomass gasifier 103, and a blower 104. The biomass enters the biomass gasifier 103 through the silo 101 and the feeder 102. The blower 104 sends the hot flue gas into the biomass gasifier 103. The biomass gas generated by the biomass gasifier 103 is connected to the reduction zone of the decomposition furnace 2 through a pipeline. The power for gas transmission is generated by the negative pressure of the decomposition furnace 2. Figure 2 、 3 The numerical simulation analysis shows that compared with other parts connected to the decomposition furnace 2, the biomass gas enters the reduction zone below the tertiary air duct interface of the decomposition furnace 2, the decomposition furnace 2 can obtain a better combustion temperature distribution, and entering from the reduction zone avoids local high temperature, and also plays a role in reducing NOx in the decomposition furnace; Among them, Figure 2 、 Figure 3 In (a), the gas enters the furnace together with the tertiary air, (b) the gas enters the furnace above the tertiary air, and (c) the gas enters the furnace from the center of the cone of the decomposition furnace, that is, from the reduction zone. The blower 104 has two air inlets: one for the high-temperature flue gas discharged from the bypass venting system 300, and one for air or oxygen-enriched gas. A first air volume regulating valve 105 is provided on the pipeline. When the content of harmful elements such as K, Na, and Cl in the biomass and cement raw materials being processed is low, and the bypass venting volume of the decomposition furnace 2 is low or unnecessary, the present invention can open the air or oxygen-enriched gas pipeline to ensure the normal operation of the biomass gasification system, and adjust the air supply volume through the first air volume regulating valve 105.

[0035] The bypass ventilation system 300 consists of a quenching system 5, a second air volume regulating valve 4, a quenching fan 3, a cyclone 6, an ash discharge valve 7, a flue gas reheater 8, a dust collector 9, an exhaust fan 10, a third air volume regulating valve 11 and a fourth air volume regulating valve 12; the decomposition furnace 2 is connected to the quenching system 5 in the bypass ventilation system 300 through a flue gas duct arranged on the smoke chamber; the quenching system 5 is cooled by adding cold air, and the cold air serves as a gasifying agent for the biomass gasification system; the cold air is fed in through the quenching fan 3 on the quenching system 5, and the outlet of the quenching system 5 is connected to the air inlet of the cyclone 6; the air outlet of the quenching fan 3 is provided with a second air volume regulating valve 4 for adjusting the amount of cold air fed into the quenching system; the quenching fan 3 can also use a frequency conversion device to adjust the air supply volume.

[0036] The cyclone 6 separates the large particles of ash in the flue gas after rapid cooling and sends them to the decomposition furnace 2. The remaining flue gas is connected to the flue gas reheater 8; the flue gas reheater 8 is connected to the dust collector 9 and the exhaust fan 10, and the flue gas sent into the cyclone 6 is cooled and sent to the dust collector 9. After the dust is removed by the dust collector 9, it enters the exhaust fan 10; at the same time, the flue gas discharged by the exhaust fan 10 is heated and sent to the biomass gasification system 100, and the two flue gases undergo indirect heat exchange in the flue gas reheater.

[0037] When the dust collector 9 adopts a conventional bag dust collector, the heat resistance temperature is generally ≤200°C. At this time, the temperature entering the dust collector 9 can be controlled within this temperature range by adjusting the air volume of the quenching fan 3. Under the condition that the air volume required by the biomass gasification system is met, the dust collector 9 can also adopt a high-temperature dust collector, and its operating temperature can reach 300-400°C. The use of a high-temperature dust collector can further increase the temperature of the bypass hot flue gas, thereby improving the gasification efficiency of the biomass gasification system and reducing the exhaust loss of the entire system.

[0038] The exhaust fan 10 has two outlets: one connected to the flue gas reheater 8, and the other discharged to the cement kiln chimney or other treatment pathways, such as the flue gas treatment system. A third air volume regulating valve 11 and a fourth air volume regulating valve 12 are respectively provided on each of these flue pipes to regulate the flue gas volume. When the volume of the hot flue gas from the bypass, after rapid cooling, exceeds the volume required by the biomass gasification system, the fourth air volume regulating valve 12 is opened. The present invention prioritizes the volume of air supplied to the biomass gasification system, with the remaining volume supplied to the chimney or flue gas treatment system.

[0039] The method for coupling biomass gasification with a cement kiln using the above system comprises the following steps:

[0040] (S1) The biomass gasification system uses biomass and hot flue gas from the bypass exhaust system to generate biomass fuel gas and feeds it into the reduction zone of the decomposition furnace. If the hot flue gas is insufficient, the blower in the biomass gasification system can also introduce air or oxygen-enriched gas from another channel, and the input amount is adjusted by the air volume control valve;

[0041] (S2) When a large amount of biomass is disposed of, causing harmful components to accumulate inside the decomposition furnace, the bypass ventilation system is opened to draw the hot flue gas from the smoke chamber of the decomposition furnace, cool it through the quenching system, separate the large particles of ash from the cyclone, and return it to the decomposition furnace. The cooled flue gas is then cooled through the flue gas reheater and dusted by the dust collector before being sent to the exhaust fan;

[0042] (S3) The quenching system cools the flue gas in the smoke chamber by adding cold air. The cold air serves as a gasifying agent for the biomass gasification system. The cold air is fed into the smoke chamber through a quenching fan on the quenching system. A second air volume regulating valve at the air outlet of the quenching fan is used to regulate the amount of cold air fed into the quenching system. The added air serves as a gasifying agent for the biomass gasification system. The second air volume regulating valve not only regulates the cooling temperature but also regulates the amount of gasifying agent for the biomass gasification system.

[0043] (S4) The exhaust fan outlet is divided into two routes, one route is connected to the flue gas reheater and connected to the blower of the biomass gasification system after heating, and the other route is connected to the chimney or the flue gas treatment system; an air volume regulating valve is provided on each of the two flue pipes to adjust the flue gas volume on the two flue pipes; the present invention gives priority to meeting the air volume fed into the biomass gasification system, and the remaining air volume is fed into the chimney or the flue gas treatment system.

[0044] The relevant calculations of the present invention are as follows:

[0045] (1) Composition of hot flue gas after rapid cooling in the bypass ventilation system

[0046] Assuming that the temperature of the cold air blown into the quenching system is 25℃ and the kiln gas temperature in the kiln tail smoke chamber is 1050℃, the composition of the hot flue gas after quenching in the bypass ventilation system is shown in Table 1.

[0047] Table 1 Composition of hot flue gas after rapid cooling in bypass ventilation system

[0048]

Claims

1. A system for coupling biomass gasification and cement kiln, comprising a decomposition furnace and a bypass ventilation system, characterized in that: It also includes a biomass gasification system connected to the decomposition furnace; the bypass ventilation system includes a quenching system, a cyclone, a flue gas reheater, a dust collector and an exhaust fan connected in sequence; the flue gas reheater is connected to the biomass gasification system to heat the flue gas after cooling and dust removal before entering the biomass gasification system; The exhaust fan outlet is divided into two paths, one of which is connected to the flue gas reheater, for allowing the flue gas discharged by the exhaust fan to exchange heat with the flue gas from the cyclone in the flue gas reheater; The quenching system is provided with a cold air inlet, which is connected to the quenching fan; the quenching fan outlet is provided with a second air volume regulating valve for regulating the amount of cold air supplied; The biomass gasification system includes a silo, a feeder, a biomass gasification furnace and a blower, and an air inlet of the blower is connected to a flue gas reheater.

2. The biomass gasification and cement kiln coupling system according to claim 1, characterized in that: A cyclone is provided between the quenching system and the flue gas reheater, and a dust collector is provided between the flue gas reheater and the exhaust fan.

3. The biomass gasification and cement kiln coupling system according to claim 1, characterized in that: Another air inlet of the blower can also be used to introduce air or oxygen-rich gas, and a first air volume regulating valve is provided on the pipeline.

4. The biomass gasification and cement kiln coupling system according to claim 1, characterized in that: The fuel gas generated by the biomass gasification system is communicated with the reduction zone of the decomposition furnace through a pipeline.

5. A method for coupling biomass gasification with a cement kiln using the system of claim 1, characterized in that: The following steps are involved: (S1) The biomass gasification system uses biomass and hot flue gas from the bypass ventilation system to generate biomass fuel gas and feeds it into the reduction zone of the decomposition furnace; (S2) The bypass ventilation system draws out the hot flue gas from the smoke chamber of the decomposition furnace, cools it through the quenching system, and the cooled flue gas is sent to the exhaust fan after dust removal by the cyclone, cooled by the flue gas reheater, and dust removed by the dust collector; the flue gas discharged from the exhaust fan enters the flue gas reheater and is sent to the biomass gasification system after being heated.

6. The method for coupling biomass gasification with a cement kiln according to claim 5, characterized in that: In step (2), the quenching system cools the smoke in the smoke chamber by adding cold air. The cold air is fed into the quenching fan on the quenching system, and the cooling temperature is adjusted by the second air volume regulating valve at the quenching fan outlet. The gasification dosage of the biomass gasification system is also adjusted.

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