A circulating flue gas based bale alternative fuel pre-combustion system

Abstract

This invention discloses a pre-combustion system for bundled alternative fuels based on circulating flue gas, comprising a semi-combustion furnace. The semi-combustion furnace has an alternative fuel inlet, a circulating flue gas inlet, and a semi-combustible material outlet. The circulating flue gas inlet is connected to the flue gas channel of the decomposition furnace, and the semi-combustible material outlet is connected to the smoke chamber channel. Below the semi-combustion furnace outlet, there are multiple stepped sections that gradually rise towards the semi-combustible material outlet, with pulse jet devices installed on each step. The hot flue gas generated by the decomposition furnace enters the semi-combustion furnace through the circulating flue gas inlet, pre-treating the alternative fuel in the furnace at high temperature. This ensures that the alternative fuel undergoes incomplete combustion in a low-oxygen environment, producing coke, ash, volatile matter, and reducing gases. The coke, ash, and reducing gases ultimately enter the decomposition furnace for complete combustion. This invention solves the problem of low utilization efficiency of alternative fuels and combustion-supporting gases when directly feeding alternative fuels into the decomposition furnace in existing technologies, and avoids incomplete combustion within the decomposition furnace.

Description

Technical Field

[0001] This invention relates to fuel processing technology, and in particular to a pre-combustion system for bundled alternative fuels based on recirculated flue gas. Background Technology

[0002] Currently, using alternative fuels is an important method for reducing carbon emissions. Rotary kilns and preheater furnaces operate under alkaline environments and high-temperature, negative-pressure conditions, making them ideal sites for waste reduction, resource recovery, and harmless treatment. There are many types of alternative fuels, including sawdust, rice husks, meat and bone meal, tires, sludge, and plastic waste, most of which have a certain calorific value. Using these alternative fuels for cement calcination not only achieves the harmless treatment of waste but also replaces some fossil fuels, reducing fossil fuel consumption and thus achieving the goal of carbon emission reduction.

[0003] Currently, my country's alternative fuel application technologies are still in a rudimentary stage with low efficiency and low heat substitution rates. Alternative fuels are generally used by directly feeding them into a decomposition furnace or an external online incinerator after appropriate pretreatment, ensuring basic normal cement clinker production while consuming waste. However, when alternative fuels are directly fed into the decomposition furnace, their low calorific value, high moisture content, and large, uneven particle size make them prone to incomplete combustion, producing large amounts of CO. To address this, the high-temperature fan is increased during decomposition furnace commissioning, increasing power consumption and raising both the system's air volume and preheater outlet temperature. This results in significantly higher system heat consumption compared to fossil fuel production, reducing the utilization efficiency of alternative fuels. External online incinerators can accommodate more types of alternative fuels and adjust the residence time within the system according to the fuel's combustion difficulty; however, they also suffer from problems such as high system air volume, which can easily lead to localized high temperatures causing uneven erosion of refractory materials, hindering the stable long-term operation of the decomposition furnace and rotary kiln, and increasing the complexity of installation and operation.

[0004] Furthermore, the current packaging and transportation of alternative fuels primarily utilizes rope bundling, while end-of-life processing typically involves the conveying, transfer, metering, and feeding of bulk materials. Although rope bundling equipment is quite mature, the unpacking process still largely relies on manual operation. During this process, it is difficult to avoid the loss of wires or ropes, as well as long-fiber fuels exceeding controlled dimensions, which may lead to process and environmental problems such as entanglement, blockage, dust generation, and lint. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a pre-combustion system for bundled alternative fuels based on circulating flue gas, which improves the utilization efficiency of alternative fuels and facilitates the stable and long-term operation of the decomposition furnace and rotary kiln.

[0006] Technical Solution: To achieve the above objectives, the present invention provides a pre-combustion system for bundled alternative fuels based on circulating flue gas. This system is located on one side of the flue chamber at the tail of a rotary kiln. A decomposition furnace is arranged above the flue chamber, and both the system and the rotary kiln are connected to the decomposition furnace via the flue chamber. The system includes a semi-combustion furnace, which has an alternative fuel inlet, a circulating flue gas inlet, and a semi-combustible material outlet. The circulating flue gas inlet is connected to the flue gas passage of the decomposition furnace, and the semi-combustible material outlet is connected to one side of the flue chamber. Below the outlet of the semi-combustion furnace, there are multiple steps that gradually rise towards the semi-combustible material outlet, and each step is equipped with a pulse jet device. Circulating flue gas from the decomposition furnace enters the semi-combustion furnace through the circulating flue gas inlet, pre-treating the alternative fuel in the furnace at high temperature. This allows the alternative fuel to undergo only incomplete combustion in a low-oxygen environment, and the resulting semi-combustible material enters the decomposition furnace through the flue chamber for complete combustion.

[0007] The semi-combustible material includes coke dust and ash, as well as volatile matter and reducing gases; wherein the coke dust and ash rise along the steps under the action of circulating flue gas and pulse jet device, thereby entering the flue gas chamber channel and being connected to the decomposition furnace for complete combustion, and the volatile matter and reducing gases are connected to the decomposition furnace for complete combustion by the hot flue gas in the rotary kiln through the upper part of the flue gas chamber channel.

[0008] The staircase is designed with shallow sections, each section has a relatively gentle slope, and the height difference between adjacent sections is small, forming a long slope.

[0009] The pulse jet device is a nozzle arranged on the vertical wall of the stepped structure. The nozzle is connected to air and sprays air onto the horizontal stepped surface.

[0010] The alternative fuel is encapsulated in a thin film to form a capsule structure.

[0011] The alternative fuel inlet is equipped with a rotary airlock feeding device. The rotary airlock feeding device has concave storage tanks evenly distributed around its rotating drum. Each storage tank can hold one capsule-shaped alternative fuel. The amount of alternative fuel fed can be adjusted by adjusting the rotation speed of the rotary airlock feeding device.

[0012] The alternative fuel inlet is equipped with a double-helix extrusion device for opening and breaking up the capsule-structured alternative fuel. The shaft end of the double-helix extrusion device is supported by a bearing seat on the outside of the semi-combustion furnace body. A water jacket is installed outside the bearing seat, and circulating water is introduced into the water jacket to cool the bearing seat.

[0013] The circulating flue gas inlet is connected to the flue gas outlet of the decomposition furnace via a circulating flue gas pipeline; the connection between the circulating flue gas pipeline and the circulating flue gas inlet and the flue gas outlet of the decomposition furnace, as well as the connection between the semi-combustible outlet and one side of the smoke chamber, are all made using high-temperature resistant expansion joints.

[0014] The circulating flue gas duct is equipped with a high-temperature valve for adjusting the intake air volume, a high-temperature fan for balancing the system pressure, and a cyclone dust collector.

[0015] The cross-section of the semi-combustion furnace gradually decreases from the bottom to the outlet direction, and an electric or pneumatic push rod is installed at the bottom of the semi-combustion furnace, with a load sensor installed at the bottom support position.

[0016] Beneficial effects: The present invention has the following advantages: 1. The system uses the high-temperature circulating flue gas in the decomposition furnace to heat the alternative fuel, so that it undergoes thermal decomposition and incomplete combustion. The volatiles, coke dust, carbon monoxide and other reducing gases generated in this process are used as the final fuel of the decomposition furnace, which solves the problem that alternative fuels are prone to incomplete combustion in the decomposition furnace in the prior art, producing a large amount of CO, resulting in low utilization rate of alternative fuels.

[0017] 2. This system uses an extrusion device to unpack and break up the alternative fuel, avoiding the problem of increased energy consumption in the decomposition furnace caused by increasing the air volume of the high-temperature blower to ensure complete combustion when directly fed into the decomposition furnace, which is not conducive to the stable long-term operation of the decomposition furnace.

[0018] 3. The reducing gas generated by this system forms a strong reducing atmosphere flow field in the high-temperature region above the smoke chamber and below the tertiary air inlet, which inhibits the generation of nitrogen oxides and makes the entire combustion process more environmentally friendly.

[0019] 4. The alternative fuels in this system are prepared into capsule-shaped "fuel bombs" or "fuel eggs". During transportation, storage and use, the alternative fuels can be better managed in terms of moisture prevention, dust-free and zero odor, which improves the utilization efficiency of alternative fuels. At the same time, it is also convenient to realize standardized three-dimensional warehousing and low-intervention logistics automation control management, thereby improving the utilization efficiency of the site and the management level of the project. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system framework.

[0021] Figure 2 This is a schematic diagram of the system principle;

[0022] Figure 3 This is a schematic diagram of the pulse jet blowing device in this system;

[0023] Figure 4 A schematic diagram of the instantaneous circulating flue gas flow trajectory during pulse jet cleaning;

[0024] In the diagram: 1. Semi-combustion furnace, 1.1 Alternative fuel inlet, 1.2 Circulating flue gas inlet, 1.3 Semi-combustion outlet, 1.4 Step, 1.5 Pulse jet cleaning device, 2. Twin-screw extrusion device, 3. Rotary airlock feeding device, 4. High-temperature valve, 5. High-temperature fan, 6. Cyclone dust collector, 7. Expansion joint, 8. Circulating flue gas pipeline. Detailed Implementation

[0025] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0026] like Figure 1 and 2 As shown, the present invention discloses a pre-combustion system for bundled alternative fuels based on circulating flue gas, comprising a semi-combustion furnace 1, wherein the semi-combustion furnace 1 is provided with an alternative fuel inlet 1.1, a circulating flue gas inlet 1.2, and a semi-combustible material outlet 1.3; the circulating flue gas inlet 1.2 is connected to the flue gas channel outlet of the decomposition furnace through a flue gas pipe 8, and the semi-combustible material outlet 1.3 is connected to the flue gas channel inlet of the decomposition furnace through the upper part of the flue gas chamber channel.

[0027] The smoke chamber is located at the tail of the rotary kiln, the semi-combustion furnace 1 is located on one side of the smoke chamber, and the decomposition furnace is located above the smoke chamber. Both the rotary kiln and the semi-combustion furnace 1 are connected to the decomposition furnace through the smoke chamber. The hot flue gas in the rotary kiln enters the decomposition furnace through the smoke chamber, and the pre-decomposed material in the decomposition furnace enters the rotary kiln through the smoke chamber. The volatile matter, carbon monoxide, and other reducing gases produced by the alternative fuel in the semi-combustion furnace 1 enter the decomposition furnace through the smoke chamber along with the hot flue gas in the rotary kiln.

[0028] The connection points between flue gas duct 8 and the circulating flue gas inlet 1.2 and the outlet of the decomposition furnace flue gas passage, as well as the connection points between the semi-combustion outlet 1.3 and the flue gas passage, are all made using high-temperature resistant expansion joints. Flue gas duct 8 is equipped with a high-temperature valve 4 for adjusting the intake air volume, a cyclone dust collector 6 for removing dust from the flue gas entering the semi-combustion furnace, and a high-temperature fan 5 for balancing system pressure.

[0029] The alternative fuels are encapsulated in a thin film, forming capsule-like "fuel bombs" or "fuel eggs".

[0030] A rotary airlock feeding device 3 is provided at the alternative fuel inlet 1.1. The device has concave storage tanks evenly distributed around the rotating drum, and each storage tank can hold one alternative fuel capsule. The amount of alternative fuel fed can be adjusted by adjusting the rotation speed of the rotary airlock feeding device 3.

[0031] The alternative fuel inlet 1.1 is equipped with a double helix extrusion device 2 to open and break up the fuel capsules; the shaft end of the double helix extrusion device 2 is supported by a bearing seat on the outside of the semi-combustion furnace body, and a water jacket is set outside the bearing seat, through which circulating water is circulated to cool the bearing seat.

[0032] like Figure 3As shown, the cross-section of the semi-combustion furnace 1 gradually decreases from the bottom towards the semi-combustion outlet 1.3, and below the semi-combustion outlet 1.3, there are multiple steps 1.4 that gradually approach the semi-combustion outlet 1.3. The steps 1.4 are arranged in a shallow, long, and gradually ascending manner, and each step is equipped with a pulse jet device 1.5. Figure 3 As shown, the pulse jet device 1.5 is a nozzle arranged on the vertical wall of the step 1.4, and the nozzle is connected to air to spray the horizontal step surface.

[0033] The furnace lining of the semi-combustion furnace 1 is made of high-temperature and wear-resistant castable. An electric or pneumatic pusher is installed at the bottom, which can mechanically turn the fuel piled up at the bottom of the furnace, so that it can fully contact the high-temperature flue gas to coke and improve the efficiency of incomplete combustion of alternative fuels.

[0034] A load sensor is installed at the bottom support position of the semi-combustion furnace 1 to monitor the burning loss of the dispersed alternative fuel inside the furnace. Observation ports and high-temperature cameras are installed on the side wall of the semi-combustion furnace to observe and record the fuel condition inside the furnace.

[0035] The system operates as follows: Circulating flue gas from the decomposition furnace enters the semi-combustion furnace 1 through circulating flue gas inlet 1.1, where it undergoes high-temperature pretreatment of the alternative fuel. This pretreatment ensures that the alternative fuel undergoes incomplete combustion in a low-oxygen environment, producing coke, ash, volatiles, and a large amount of reducing gases such as carbon monoxide. The volatiles and reducing gases are introduced into the decomposition furnace through the smoke chamber, flowing with the hot flue gas from the rotary kiln. A strong reducing atmosphere is formed in the high-temperature region above the smoke chamber and below the tertiary air inlet, suppressing the formation of nitrogen oxides. The tertiary air refers to the tertiary air at the kiln tail, which is introduced into the decomposition furnace through the tertiary air duct, ensuring complete combustion of the combustible components produced by the alternative fuel.

[0036] Simultaneously, the non-volatile solid phase and ash, after high-temperature dry distillation, mix and, under the action of circulating flue gas and pulse jet cleaning device 1.5, are ejected and tumbled, climbing step by step along each stage, and repeatedly pounded against the windward wall of each stage. Finally, at the semi-combustible outlet 1.3, they are carried by the hot flue gas from the rotary kiln into the decomposition furnace for complete combustion. Figure 4 The image shows the flow trajectory of circulating flue gas during pulse jet injection. Simultaneously, the air volume of high-temperature fresh air in the decomposition furnace is appropriately increased, i.e., the tertiary air at the kiln tail, to fully utilize the enthalpy of the alternative fuel.

[0037] The circulating flue gas in this system has a high temperature and low oxygen content, making it suitable as a heat transfer medium for alternative fuels. In order to ensure that the alternative fuels can undergo incomplete combustion smoothly, the air volume of the decomposition furnace should be kept as low as possible. At the same time, an appropriate amount of combustion aid can be added during the preparation of alternative fuels, so that the fixed carbon in the alternative fuels can be incompletely burned to generate carbon monoxide.

[0038] In addition, based on weight data obtained from load sensors, combustion images obtained from high-temperature cameras, and chemical and industrial data of the burning alternative fuels, a composite algorithm can be used to simulate the burning and distribution of coke and ash in the furnace, so as to adjust the circulating flue gas volume, the feed amount of alternative fuels, and the blowing frequency of air cannons at each stage.

[0039] For heavy, difficult-to-burn alternative fuels, some tertiary air from the kiln tail can be introduced to appropriately increase the oxygen content of the flue gas. At the same time, the material pile can be turned over at the bottom of the furnace by electric or pneumatic pushers to ensure that it fully contacts the high-temperature flue gas to form coke. For alternative fuels containing difficult-to-burn or non-combustible impurities, a grate system can be added to the bottom of the furnace.

[0040] Compared to existing technologies, this system creates a high-temperature reducing environment by introducing circulating flue gas from the semi-combustion furnace 1. This allows for high-temperature pretreatment of the alternative fuel, ensuring deterministic, orderly, and controllable incomplete combustion. Furthermore, within the semi-combustion furnace 1, the alternative fuel undergoes significant qualitative changes that enhance diffusion and combustion. When it enters the decomposition furnace for combustion, it achieves effects similar to pulverized coal, enabling it to replace pulverized coal and reduce dependence on traditional fossil fuels, thus mitigating environmental pollution.

Claims

1. A pre-combustion system for baleable alternative fuels based on circulating flue gas, wherein the system is arranged on one side of the flue chamber at the tail of a rotary kiln, a decomposition furnace is arranged on the upper side of the flue chamber, and both the system and the rotary kiln are connected to the decomposition furnace through the flue chamber, characterized in that: The system includes a semi-combustion furnace (1), which is provided with a substitute fuel inlet (1.1), a circulating flue gas inlet (1.2), and a semi-combustion outlet (1.3). The circulating flue gas inlet (1.2) is connected to the flue gas passage of the decomposition furnace, and the semi-combustion outlet (1.3) is connected to one side of the smoke chamber. Below the outlet of the semi-combustion furnace (1) are multiple steps (1.4) that gradually rise towards the semi-combustion outlet (1.3), and each step (1.4) is provided with a pulse jet device (1.5). The circulating flue gas in the decomposition furnace enters the semi-combustion furnace (1) through the circulating flue gas inlet (1.2) to pre-treat the alternative fuel in the furnace at high temperature, so that the alternative fuel only undergoes incomplete combustion in a low-oxygen environment, and the resulting semi-combustion enters the decomposition furnace through the smoke chamber for complete combustion.

2. The pre-combustion system for bundled alternative fuels based on recirculated flue gas according to claim 1, characterized in that: The semi-combustible material includes coke dust and ash, as well as volatile matter and reducing gases; wherein the coke dust and ash rise along the steps (1.4) under the action of circulating flue gas and pulse jet device (1.5), thereby entering the flue gas chamber channel and being connected to the decomposition furnace for complete combustion, and the volatile matter and reducing gases are connected to the decomposition furnace for complete combustion by the hot flue gas in the rotary kiln through the upper part of the flue gas chamber channel.

3. The circulating flue gas based bale replacement fuel pre-combustion system according to claim 1, characterized in that: The pulse jet device (1.5) is a nozzle arranged on the vertical wall of the step (1.4), and the nozzle is connected to air to spray the horizontal step surface.

4. The circulating flue gas based bale replacement fuel pre-combustion system according to claim 1, characterized in that: The alternative fuel is encapsulated in a thin film to form a capsule structure.

5. A circulating flue gas based bale replacement fuel pre-combustion system according to claim 4, characterised in that: The alternative fuel inlet (1.1) is equipped with a rotary airlock feeding device (3). The rotary airlock feeding device (3) rotates around a drum and evenly distributes concave storage tanks. Each storage tank can hold one capsule-shaped alternative fuel. The amount of alternative fuel fed can be adjusted by adjusting the rotation speed of the rotary airlock feeding device (3).

6. The circulating flue gas based bale replacement fuel pre-combustion system according to claim 4, characterized in that: The alternative fuel inlet (1.1) is equipped with a double helix extrusion device (2) for opening and breaking up the capsule-structured alternative fuel; the shaft end of the double helix extrusion device (2) is supported by a bearing seat on the outside of the semi-combustion furnace (1), and a water jacket is provided outside the bearing seat, through which circulating water is introduced to cool the bearing seat.

7. The pre-combustion system for bundled alternative fuels based on recirculated flue gas according to claim 1, characterized in that: The circulating flue gas inlet (1.2) is connected to the flue gas passage outlet of the decomposition furnace through a circulating flue gas pipe (8); the connection between the circulating flue gas pipe (8) and the circulating flue gas inlet (1.2) and the flue gas passage outlet of the decomposition furnace, and the connection between the semi-combustion outlet (1.3) and one side of the smoke chamber, are all connected by high-temperature resistant expansion joints (7).

8. The pre-combustion system for bundled alternative fuels based on recirculated flue gas according to claim 7, characterized in that: The circulating flue gas duct (8) is equipped with a high-temperature valve (4) for adjusting the intake air volume, a high-temperature fan (5) for balancing system pressure, and a cyclone dust collector (6).

9. The pre-combustion system for bundled alternative fuels based on recirculated flue gas according to claim 1, characterized in that: The cross-section of the semi-combustion furnace (1) gradually decreases from the bottom to the outlet direction, and an electric or pneumatic push rod is provided at the bottom of the semi-combustion furnace (1), and a load sensor is provided at the bottom support position.

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