A combined fluidized combustion method for petroleum coke and POX slag

Abstract

The present invention provides a combined fluidized combustion method for petroleum coke POX slag, which is mainly composed of a fast bed and a double-layer fluidized bed connected. Aiming at the difficulties of extremely low volatile matter in petroleum coke POX slag, difficult ignition, slow combustion speed, fast / slow combustion stages, high content of fine slag, etc.; and after carbon reduction of POX slag, heavy metal recovery and harmless treatment are also required. Based on the above difficulties of POX slag, a combined fluidized POX slag carbon reduction process is proposed. The advantages of the process are as follows: The fluidized combustion method can improve the mass transfer and heat transfer rates; the use of a fast bed and staged combustion effectively avoids the backmixing of solid-phase particles; the combustion-supporting air and the material are in reverse heat exchange operation, effectively utilizing the heat energy. The fast bed is respectively connected to the dilute phase / dense phase of the upper-layer fluidized bed. The double-layer fluidized bed is separated by a distributor plate, and the upper / lower layers are connected by an overflow pipe. The material enters from the bottom of the fast bed and is mixed with the return material of the upper-layer fluidized bed for combustion. The product enters the upper bed to complete the cycle. The combustion-supporting air enters from the bottom of the fast bed and the bottom / middle part of the double-layer bed respectively.

Description

Technical Field

[0001] The present invention belongs to the fields of petrochemical industry and environmental protection, and is specifically applied to the carbon reduction treatment of petroleum coke gasification waste residue (petroleum coke POX residue), and provides a combined fluidized combustion method for petroleum coke POX residue. Background Art

[0002] At present, with the tightening of environmental protection policies, high-sulfur petroleum coke cannot be shipped out of the factory without treatment. POX hydrogen production plants in refineries have to use more petroleum coke with high sulfur and heavy metal contents as gasification raw materials. The ash residue generated after hydrogen production by the petroleum coke through the POX device still contains some residual carbon. On the one hand, carbon reduction treatment is required, and on the other hand, it has the value of waste heat recovery. However, the POX residue from petroleum coke is different from conventional coal and solid fuels such as petroleum coke. The carbon content of the POX ash residue of petroleum coke is low (generally between 20% and 30%), the volatile matter is extremely low, and the calorific value is low. These characteristics lead to the fact that the burner design has to overcome the disadvantages of difficult ignition, unstable combustion, and long combustion time, etc. At the same time, the subsequent recovery and harmless treatment requirements of heavy metals in the residual ash have to be considered, and vitreous ash residue that is difficult to treat cannot be generated.

[0003] CN 1959207 A discloses a combustion treatment device for petroleum coke / petroleum coke gasification residue. The main structure of this device is an upper and a lower reactor. The materials in the lower section can enter the upper section through the inner riser for further reaction, and the materials in the upper section enter the lower section through the inner and outer overflow pipes, so as to realize the long-term cyclic residence of the materials in the reactor. Among them, a guide cylinder is provided on the distribution plate of the lower burner, dividing the lower burner into two combustion zones. The gas velocity inside the guide cylinder is 0.15 m / s, the gas velocity outside the guide cylinder is 0.6 - 1.8 m / s, and the gas velocity in the inner riser is 6 - 12 m / s. The combustion auxiliary air enters the burner from the upper / lower distribution pipes / plates. Further, the flue gas in the lower section enters the upper burner together with the materials through the inner riser, and then is discharged from the top of the upper burner through a cyclone. The upper / lower sections are respectively provided with feed inlets, and the particle size of the materials is 0 - 1000 um.

[0004] CN 101666489 A discloses a petroleum coke slurry combustion device. It includes a heat storage cavity in the furnace, and a fuel / oil gas duty nozzle arranged on the furnace wall and communicated with the heat storage cavity. Outside the fuel / oil gas duty nozzle, a petroleum coke slurry atomizing nozzle, an inner layer combustion-supporting air nozzle, and an outer layer combustion-supporting air nozzle communicated with the heat storage cavity are sequentially sleeved from the inside to the outside. An inner layer combustion-supporting air swirl generator and an outer layer combustion-supporting air swirl generator are respectively arranged in the inner layer combustion-supporting air nozzle and the outer layer combustion-supporting air nozzle.

[0005] CN 105441131 A discloses a method for oxidizing and decarbonizing coal gasification ash residue to produce ash and co-generate steam, including an oxidation and decarbonization process, an energy utilization process, and a flue gas purification process. Using coal gasification ash residue as raw material, a combined fast bed and dense bed circulating reactor is adopted to carry out an oxidation and decarbonization reaction with an oxidant to produce ash and co-generate steam; the energy utilization process mainly includes heat removal in the combined bed circulating reactor to co-generate medium-pressure steam, a waste heat boiler to recover the waste heat of high-temperature flue gas to co-generate low-pressure steam, and heat exchange between high-temperature ash and fluidizing gas to cool the ash residue and preheat the fluidizing gas simultaneously.

[0006] CN 201983260 U discloses a utility model related to a petroleum coke powder cyclone combustion device, including a petroleum coke powder burner, a control system, and a high-temperature pulse ignition cap arranged on the nozzle and communicating with the combustion chamber. A pulse action channel communicating with the inside of the petroleum coke powder burner is arranged on the high-temperature pulse ignition cap, and a pulse generating system communicating with the inside of the high-temperature pulse ignition cap is arranged in the pulse action channel. The pulse action channel is also connected to ignition liquefied gas. The atomizing gas system, the primary powder injection channel, the pulse generating system, and the ignition liquefied gas are all connected to the control system. The pre-mixing, semi-pre-mixing technology of petroleum coke powder and combustion-supporting air and the swirl combustion control technology are adopted. By setting a flame ejection hole on the high-temperature pulse ignition cap, it can adapt to different specifications of petroleum coke powder grinding particles.

[0007] CN 202709086 U discloses a novel coal slag powder combustion device for a power station boiler, including a power station boiler furnace and a cyclone combustion cylinder connected to the boiler furnace. The cyclone combustion cylinder is installed at the front and rear of the boiler furnace. Above the cyclone combustion cylinder, there is a spray gun for spraying coal slag powder into the combustion chamber of the cyclone combustion cylinder at high speed. At the top of the cyclone combustion cylinder, there is a primary rotary air supply port for sending the air required for the ignition of coal slag powder; at the upper part of the cyclone combustion cylinder, there is a secondary tangential air supply port for sending the air required for the full combustion of coal slag powder.

[0008] CN 206377652 U discloses a petroleum coke granule combustion device with a dust filtering function, including an outer furnace wall and an inner furnace wall. A closed cavity is formed between the outer furnace wall and the inner furnace wall, and the closed cavity is filled with cooling water. Inside the inner furnace wall, there is a combustion chamber. At the bottom of the combustion chamber, there is a furnace grate. Vertically connected to the lower side of the furnace grate is a furnace air inlet pipe, and the other end of the furnace air inlet pipe is connected to a draft fan. The top of the outer furnace wall is connected to an end cover, and there is a smoke exhaust channel on the end cover. The top surface of the end cover is connected to an elliptical head. Inside the elliptical head, there is a filter box. One end of the smoke exhaust channel penetrates the end cover and communicates with the combustion chamber, and the other end of the smoke exhaust channel is connected to the filter box. The outlet end of the filter box penetrates the elliptical head. The filter box is provided with a filter screen. Along the inner wall circumference of the filter box below the filter screen, a plurality of water atomizing nozzles are fixedly arranged. The bottom of the filter box is connected to a sewage discharge channel.

[0009] Petroleum coke POX slag contains a certain amount of carbon, generally between 20% and 40%. From existing patents, there are coal gangue treatment devices mentioned using circulating fluidized beds for treatment. However, the combustion rates at different stages of petroleum coke POX slag are different, and simply increasing the residence time for treatment cannot be done, as this reduces the volumetric efficiency of the reactor. There are also some patents mentioning composite fluidized combustion devices for treating gasified coal slag and biomass fuels. But there is currently no combustion process and device that specifically addresses the characteristics of petroleum coke POX slag, such as poor reactivity, a particularly distinct staged reaction process, a wide particle size distribution, and the requirements for the ash morphology in subsequent heavy metal recovery. Summary of the Invention

[0010] The object of the present invention is to provide a combined fluidized POX waste slag combustion method, which mainly consists of a fast bed and a double-layer fluidized bed connected to form a reaction unit. The basic principle of this design is in response to the obvious difficulties in the combustion process of petroleum coke POX slag, including: difficult ignition due to low volatile matter in POX slag, difficult stable combustion due to low carbon content, fast reaction at the beginning and slow reaction later, and requirements for the morphology of the post-combustion ash. Firstly, the fluidized combustion method is selected to improve the mass transfer, heat transfer, and combustion rate of the overall reaction. Secondly, the use of a fast bed and staged combustion can effectively match the combustion speeds at different stages of POX slag, and avoid backmixing of solid-phase particles during the reaction process, improving the processing efficiency of the reactor. Finally, staged combustion can effectively carry out the heat exchange combination distribution of the combustion air and materials, facilitating the smooth and stable operation of the reaction. Among them, the fast bed operates in a gas-solid co-current upward flow mode. The outlet of the fast bed is connected to the upper part of the double-layer fluidized bed through a cyclone. In addition to the feed inlet, the bottom of the fast bed is also connected to the return material port of the upper fluidized bed for returning materials. The double-layer fluidized bed is designed in a combination manner of two fluidized beds separated by a distributor plate. The upper fluidized bed and the bottom of the lower fluidized bed are connected through internal and external overflow pipes. The unburned bed material in the upper fluidized bed is further burned in the lower fluidized bed and finally discharged. The combustion air enters from the bottom (middle) of the fast bed, the bottom / middle of the double-layer fluidized bed respectively, and the flue gas is uniformly discharged from the upper part of the double-layer fluidized bed. Water-cooled heat extraction devices are provided on the walls of both the fast bed and the double-layer bed to maintain the reaction temperature of the burner while recovering heat energy.

[0011] To achieve the above object, first, the processed petroleum coke POX slag with a particle size range of 0 - 1 mm enters the bottom of the fast bed reactor from the silo, and is rapidly heated to above 600°C, and is mixed with the combustion-supporting air entering from the bottom of the fast bed for combustion reaction. At the top of the fast bed, it enters the upper expansion section cyclone of the double fluidized bed through a connecting pipeline. After separation, the gas is discharged into the subsequent heat exchange and purification system, and the material enters the upper layer of the double fluidized bed to continue combustion. Part of the upper layer material circulates into the fast bed through the return inclined pipe connected to the fast bed, and the mass ratio of the return material to the feed is controlled between 2:1 and 6:1. The combustion temperature in the upper layer of the double fluidized bed is controlled at 600°C - 1000°C. The upper fluidized bed controls the bed material to enter the lower fluidized bed through the inner / outer overflow pipe device to continue the reaction. The reaction temperature of the lower fluidized bed is controlled at 600°C - 1000°C, and is discharged from the lower fluidized bed when the carbon conversion rate reaches the 95% standard. The double fluidized bed is divided into two layers by an intermediate distribution plate. The combustion-supporting air is fed into the reactor from three air inlet points, namely the lower air distribution plate, under the upper air distribution plate, and the bottom of the fast bed. The air intake at the upper and lower air inlet points of the multi-layer fluidized bed is adjusted between 0:1 and 3:1. The feed distribution of the fluidized bed and the fast bed is adjusted between 0:1 and 1:1 during continuous operation.

[0012] Furthermore, the double fluidized bed can have the same diameter for the upper and lower bed layers, and an expansion section is connected above the upper fluidized bed, and the ratio of the expansion section to the combustion section is between 1:1 and 3:1. The upper and lower sections of the combustion reactor can have different diameters, specifically, the diameter ratio of the upper section to the lower section is between 2:1 and 1:1.

[0013] Furthermore, the reaction device can operate jointly, or the double fluidized bed can operate independently of the fast bed, or the fast bed can operate jointly with the upper fluidized bed. The double fluidized bed can be extended to a multi-layer fluidized bed. When extended to a multi-layer fluidized bed, the outlet of the fast bed is connected to the top of the multi-layer fluidized bed, and any layer of the multi-layer fluidized bed can be connected to the bottom of the fast fluidized bed for return of the material.

[0014] Furthermore, the feed inlet of the reaction system can be at the bottom of the fast bed, the upper or lower layer of the double fluidized bed, etc., for simultaneous feeding, or two of these points can be selected for feeding, such as the bottom of the fast bed / one of the two layers of the double fluidized bed. The materials fed include but are not limited to petroleum coke POX waste residue, and can also be other carbon-containing solid fuels such as coal / petroleum coke / biomass. Their ash residues or inert materials can also be used as heat carriers to be added to the system for circulation.

[0015] Furthermore, the fast bed reactor is a co-current entrainment conveying bed reactor, and the operating gas velocity in it is not less than 2 m / s, and the operating gas velocity in the double fluidized bed reactor is between 0.2 - 1.8 m / s.

[0016] Further, the combustion reaction combination system can use air as the combustion-supporting air, or can use oxygen-enriched air or pure oxygen as the combustion-supporting air for operation. Each air inlet point can use air, oxygen-enriched air or pure oxygen for the reaction. The air inlet device includes, but is not limited to, forms such as a distribution plate and a distribution pipe.

[0017] Advantages that can be obtained by the present invention:

[0018] The method provided by the present invention overcomes the disadvantages that petroleum coke POX slag is difficult to ignite, difficult to stably burn, burns slowly and in stages. Through the optimized combination of reactors, the low reactor efficiency caused by using a single fluidized bed or a circulating fluidized bed device in the POX slag combustion process is reduced, and at the same time, the processing flexibility of the reaction system is further improved, and the operation mode of the combined reactor is adapted to the carbon content of the POX slag.

[0019] The method provided by the present invention effectively distributes the heat of the system through a combined operation mode. For example, the circulation of the upper bed material in the fluidized bed can quickly heat up the cold material in the fast bed and stably burn. For example, the excess air in the lower part of the double-layer bed can be preheated by the lower fluidized bed, thereby accelerating or stabilizing the combustion effect of the upper fluidized bed.

[0020] The method provided by the present invention can control the metal oxidation state in the POX ash by controlling combustion in different stages, thereby achieving the purpose of helping heavy metal recovery. Description of the Drawings

[0021] Attached Figure 1 is a flow chart of a petroleum coke POX waste residue combustion device.

[0022] The descriptions of the numbers in the drawings are as follows:

[0023] 1. Silo; 2. Fast burner; 3. Coke conveying top pipe; 4. Gas-solid separator; 5. Flue gas outlet; 6. Upper section of the multi-layer reactor; 7. Lower section of the multi-layer reactor; 8. Outer overflow pipe; 9. Inner overflow pipe; 10. Coke conveying bottom pipe; 11. Heat extraction from the fast bed; 12. Heat extraction from the double-layer fluidized bed; 13. Enlarged section of the multi-layer reactor. Detailed Embodiments

[0024] The present invention provides a composite fluidized reaction method for POX waste residue combustion, which will be further described below with reference to the drawings.

[0025] In the silo (1), the POX waste residue with a particle size of 0 - 1 mm enters the rapid combustor (2) from the feeder and is mixed with high-temperature coke at 600 - 900 °C entering through the bottom coke conveying pipe. The petroleum coke POX slag rapidly heats up and burns. At the same time, the solid-phase particles are rapidly entrained upward with the gas flow, and the operating gas velocity is controlled at 3 - 10 m / s. Then it enters the top of the multi-layer fluidized reactor through the top coke conveying pipe. After being separated by the cyclone separator (4) in the upper section of the multi-layer bed, the solid phase enters the upper section (6) of the multi-layer reactor for combustion reaction, and the reaction temperature in the upper section is between 600 - 1000 °C. The flue gas leaves the combustor through the gas-solid separator (4) at the top of the reactor and is discharged to the downstream purification and separation unit. Part of the bed material in the upper section (6) of the multi-stage reactor enters the lower section (7) of the combustor through the external overflow pipe (8) or the internal overflow pipe (9) to continue combustion. The internal overflow pipe controls the overflow amount through the pressure difference, and the slide valve on the external overflow pipeline controls the overflow amount. When the carbon conversion rate reaches the standard of 95%, the residue is discharged from the lower section combustor (7). The double-layer reactor is connected to the rapid reactor through an inclined pipe, and part of the ash slag is recycled to the bottom of the rapid reactor to be mixed with the newly introduced cold POX slag, playing a role in rapidly heating up and igniting. The combustion-supporting air enters the reactor for combustion support respectively from the bottom of the rapid combustor, the lower part of the multi-stage combustor, and below the distributor in the upper section of the multi-stage combustor. The system controls the combustion temperature through the heat exchanger on the reactor wall.

Claims

1. Combustion method of petroleum coke POX slag, characterized in that: (1) Rapid combustion stage: The treated petroleum coke POX slag with a particle size range of 0 - 1 mm enters the fast bed from the silo, mixes with the returned material from the upper layer of the double-fluidized bed, rapidly heats up to above 600 °C, and combustion air is fed into the bottom of the fast bed for combustion reaction. The ratio of the returned material quantity to the feed quantity is controlled between 2:1 and 6:

1. (2) Slow fluidized combustion stage: It enters the upper-layer cyclone separator of the double-fluidized bed through a connecting pipe at the top of the fast bed. After separation, the gas is discharged into the subsequent heat exchange and purification system. The material in the dipleg of the cyclone separator enters the double-fluidized bed to continue combustion. Part of the upper-layer material circulates into the fast bed through the return chute connected to the fast bed. The combustion temperature in the upper layer of the double-fluidized bed is controlled between 600 °C and 1000 °C. (3) Residual carbon combustion stage: The double-fluidized bed is divided into two layers by an intermediate distributor plate. The upper-layer fluidized bed enters the lower-layer fluidized bed through internal and external overflow pipes to continue the reaction. The reaction temperature in the lower-layer fluidized bed is controlled between 600 °C and 1000 °C. After reaching the standard of 95% carbon conversion rate, it is discharged from the lower-layer fluidized bed. (4) Combustion air distribution method: Combustion air is fed into the double-fluidized bed and the fast bed from three air inlet points, namely the lower air distributor plate, the upper air distributor plate, and the bottom of the fast bed. The air inlet quantity at the two air inlet points in the upper and lower parts of the double-fluidized bed varies between 0:1 and 3:

1. When the double-fluidized bed and the fast bed are operating continuously, the feed distribution is adjusted between 0:1 and 1:

1. (5) Heat extraction method: Water-cooled walls are provided on the walls of the fast bed and the double-fluidized bed, which can recover the excess heat beyond maintaining the reaction temperature and control the reaction temperature simultaneously without forming vitreous ash.

2. The method according to claim 1, wherein: The fast bed and the double-fluidized bed operate jointly, or the double-fluidized bed operates independently of the fast bed.

3. The method according to claim 1, wherein: The upper and lower bed layers of the double-fluidized bed have the same diameter, and an enlarged section is connected above the upper-section fluidized bed. The ratio of the diameter of the enlarged section to that of the combustion section is between 1:1 and 3:1; or the upper and lower sections of the double-fluidized bed have different diameters, and the ratio of the diameter of the upper section to that of the lower section is between 2:1 and 1:

1. The fast bed is a co-current entrainment conveying bed, and the operating gas velocity in the fast bed is not less than 2 m / s, and the operating gas velocity in the double-fluidized bed is between 0.2 and 1.8 m / s.

4. The method according to claim 1, characterized in that: Feed is carried out simultaneously at the bottom of the fast bed, the upper part or the lower part of the double-fluidized bed; or two of these points are selected for feeding.

5. The method according to claim 1, wherein: Air, oxygen-enriched air or pure oxygen is used as combustion air for operation, or air, oxygen-enriched air, and pure oxygen are respectively selected as combustion air for each air inlet point of the fast bed and the double-fluidized bed.

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