A combustion system and process for ultra-low calorific value oil shale and oil shale dry distillation semi-coke

Abstract

This invention relates to a combustion system and process for ultra-low calorific value oil shale and semi-coke from oil shale dry distillation, belonging to the field of oil shale resource utilization technology. It includes a fluidized bed boiler, with a cyclone separator installed at the boiler outlet. A return material device is connected to the bottom of the cyclone separator, and the return material device is connected to the fluidized bed boiler via a return material inclined pipe. The top of the cyclone separator is connected to a flue gas duct. A coal feed hopper is connected to the fluidized bed boiler via a first coal conveying pipeline and to the return material inclined pipe via a second coal conveying pipeline. A superheater and evaporative heating surface are installed at the top of the flue gas duct, and an air preheater and economizer are arranged at the bottom of the flue gas duct. A primary air box is installed at the bottom of the fluidized bed boiler, and secondary air boxes are installed on the front and rear walls and / or side walls of the water-cooled walls of the fluidized bed boiler. The flue gas duct is connected to the primary and secondary air boxes. This invention improves the boiler's combustion efficiency while ensuring the ignition, stable combustion, and complete combustion of ultra-low calorific value fuel.

Description

Technical Field

[0001] This invention belongs to the field of oil shale resource utilization technology, and particularly relates to an ultra-low calorific value oil shale and an oil shale dry distillation semi-coke combustion system and method. Background Technology

[0002] Currently, the heating methods used in industrial oil shale retorting furnaces worldwide involve direct contact between a gaseous or solid heat carrier and the oil shale for retorting. These furnaces are categorized into massive shale retorting furnaces and granular shale retorting furnaces. Massive shale retorting typically uses hot combustion gas or hot retorting gas as the gaseous heat carrier, while granular shale retorting typically uses heated shale ash as the solid heat carrier.

[0003] The main problems encountered in the refining process of oil shale using gas heat carrier dry distillation technology are as follows:

[0004] Gas-fired heat transfer retorts can only use lumpy oil shale for refining, specifically lumpy oil shale with a particle size range of 15-75 mm. Small shale particles smaller than 15 mm (accounting for 20-25% of the total) cannot be fed into the retort and must be discarded, resulting in a significant waste of energy. Furthermore, small-particle oil shale cannot be directly used in building materials without combustion treatment, thus leading to low utilization of oil shale resources.

[0005] The solid waste produced after dry distillation of block shale using a gas heat carrier is called oil shale dry distillation semi-coke (or dry distillation residue, referred to as oil shale dry distillation semi-coke throughout this text). The average calorific value of oil shale dry distillation semi-coke is approximately 50% of that of crude oil shale. Furthermore, to ensure the dry distillation furnace is sealed and prevent air from entering, gas heat carrier dry distillation furnaces typically use a wet method to discharge the semi-coke. Therefore, the discharged semi-coke has a high moisture content, which severely affects its calorific value, making it difficult to burn. On the other hand, the semi-coke also contains various trace metal elements, semi-volatile substances, polycyclic aromatic hydrocarbons, oil, phenolic compounds, sulfides, and other substances, causing serious environmental pollution during accumulation, especially to groundwater. Currently, there is no effective treatment method for this solid waste; it can only be dumped in mountains, which is a waste of energy.

[0006] The semi-coke from oil shale refining is black in color, similar to coal, and contains about 1% residual oil and 4-6% residual carbon. This semi-coke may spontaneously combust when stored in air, and without treatment, it is difficult to use directly in building materials. Currently, the only solution is to discard it in piles, which is a waste of resources.

[0007] During open-pit oil shale mining, there is also ultra-low-grade oil shale with an oil content of less than 3%, which is not valuable for dry distillation and refining and is referred to as mining tailings. This portion of oil shale, along with topsoil, is discharged and piled up, unable to be utilized as a resource and classified as general industrial solid waste. It also cannot be directly used to manufacture building materials.

[0008] For oil shale refineries, during normal production, the proportions of semi-coke (12% moisture content) from oil shale retorting, small shale particles with a diameter less than 15mm under the screen, and mining tailings are approximately 70%, 24%, and 6%, respectively. Therefore, the amount of solid waste generated during the oil shale retorting process is enormous.

[0009] Therefore, the basic technical approach to improving the efficiency of oil shale energy resource utilization should adhere to the integrated technology of comprehensive development and utilization of oil shale, that is, converting oil shale as an energy source into shale oil and electricity, and as a resource into building materials and other materials, to achieve comprehensive utilization with zero solid waste emissions—"making the most of every resource"—to maximize and most effectively utilize oil shale energy resources, thereby achieving efficient and comprehensive development and utilization of oil shale.

[0010] my country's oil shale resources are characterized by low calorific value, low oil content, and high ash content. Taking the Beipiao oil shale in Liaoning Province as an example, the net calorific value (NDV) of small-particle oil shale (less than 15mm in diameter) on an as-received basis is 500–560 kcal / kg, while the NDC of semi-coke from oil shale retorting is 240–370 kcal / kg on a dry basis. In contrast, the NDC of tailings from mining (with an oil content of approximately 1.1–2.9%) on an as-received basis is only 310–460 kcal / kg. The treatment of such ultra-low calorific value waste is a major challenge and pain point for the industry. Summary of the Invention

[0011] The purpose of this invention is to provide a combustion system and method for ultra-low calorific value oil shale and oil shale dry distillation semi-coke, in order to solve the three major problems of ignition, stable combustion, and burnout faced in the fluidized combustion of ultra-low calorific value oil shale, oil shale dry distillation semi-coke, mining tailings, and mixtures of two or three of them in different proportions. This invention provides a combustion method and technical solution for ultra-low calorific value fuels. New fluidized bed and circulating fluidized bed boilers developed according to this method and technical solution can effectively solve the problems of ignition, stable combustion, and burnout of the aforementioned ultra-low calorific value fuels.

[0012] To achieve the above objectives, the specific technical solution of the present invention regarding a combustion system and method for ultra-low calorific value oil shale and oil shale dry distillation semi-coke is as follows:

[0013] Fluidized bed and circulating fluidized bed combustion technologies are the most suitable combustion technologies for oil shale, oil shale dry distillation semi-coke, mining tailings, and fuels of two or three of these in different proportions. However, for such waste with extremely low calorific value, there are currently no dedicated fluidized bed and circulating fluidized bed combustion technologies or boilers in the world.

[0014] The purpose of this invention is to overcome the shortcomings of existing technologies and to make substantial innovations in them, proposing a high-preheated air fluidized combustion technology that is rationally designed, widely applicable, and simple to operate, capable of processing ultra-low calorific value oil shale, oil shale dry distillation semi-coke, mining tailings, and two or three of these mixed fuels in different proportions. This method is also applicable to high-preheated air fluidized combustion of ultra-low calorific value coal gangue, coal, organic waste, and biomass.

[0015] A combustion system for ultra-low calorific value oil shale and semi-coke from oil shale dry distillation includes a coal feed silo, a fluidized bed boiler, a cyclone separator, and flue gas ducts. A cyclone separator is installed at the outlet of the fluidized bed boiler. The bottom of the cyclone separator is connected to a return feed device via a riser. The function of the return feed device is to return the high-temperature fly ash collected by the cyclone separator back to the fluidized bed boiler for recirculation and combustion via a return feed inclined pipe between the return feed device and the boiler furnace. The return feed device is connected to the fluidized bed boiler via the return feed inclined pipe. For a circulating fluidized bed boiler, a portion of the ultra-low calorific value fuel is fed to the return feed inclined pipe via a coal feeder. In the return feed inclined pipe, the ultra-low calorific value fuel and high-temperature circulating ash are mixed before being fed into the furnace, increasing the temperature of this portion of ultra-low calorific value fuel upon entering the furnace and effectively enhancing the ignition and stable combustion of the ultra-low calorific value fuel. The proportion of fuel passing through the return feed inclined pipe accounts for 30-50% of the total boiler fuel, depending on the boiler structure and fuel characteristics. The top of the cyclone separator is connected to the flue gas duct; the coal feed silo is connected to the fluidized bed boiler through the first coal conveying pipeline and to the return inclined pipe through the second coal conveying pipeline; a superheater and an evaporative heating surface are installed at the top of the flue gas duct, and an air preheater and an economizer are arranged at the bottom of the flue gas duct along the flue gas flow direction.

[0016] The furnace of a fluidized bed boiler is divided into a dense phase zone and a dilute phase zone. The static bed material in the dense phase zone is higher than that in conventional coal-fired fluidized bed and circulating fluidized bed boilers, i.e., the static bed material height in the dense phase zone is 800-1300mm. This increases both the bed material storage capacity and the heat storage capacity in the dense phase zone. While ensuring that the impact of newly entered fuel on the bed temperature is reduced, it ensures rapid ignition, stable combustion, and complete combustion of oil shale, oil shale dry distillation semi-coke, mining tailings, and two or three of these mixed fuels in different proportions. The furnace of the ultra-low calorific value new fluidized bed and circulating fluidized bed boiler adopts an adiabatic combustion method, with at least the furnace wall in the dense phase zone being an adiabatic furnace wall, reducing heat loss from the furnace wall in the dense phase zone and ensuring that the temperature in the dense phase zone is within the temperature range of 800℃-950℃. The insulation height of the furnace in the dilute phase zone is determined by the fuel characteristics. The insulation height of the furnace in the dilute phase zone is adjusted by laying refractory materials on the heating surface of the water-cooled wall in the dilute phase zone. The limit is that the entire dilute phase zone uses insulated furnace walls to ensure that the temperature of the dilute phase zone is close to or higher than that of the dense phase zone.

[0017] A primary air box is installed at the bottom of the fluidized bed boiler, and secondary air boxes are installed on the front and rear walls and / or side walls of the water-cooled boiler. To enhance the stable combustion and burnout of ultra-low calorific value fuels, multiple layers of secondary air boxes are arranged, i.e., 2-5 layers of secondary air are arranged. The secondary air boxes are connected to the fluidized bed boiler through multiple secondary air ducts. The number of secondary air ducts is determined according to the width of the front and rear walls and the side walls. For specific arrangements, see [link to specific details]. Figure 5 View A. Additionally, depending on the fuel type, secondary air can be arranged only on the front and rear walls or both side walls. This arrangement is beneficial for creating localized strong mixing zones, which, based on enhanced combustion, increases the residence time of ultra-low calorific value fuels in the furnace, strengthens the combustion and burnout of ultra-low calorific value fuels, and has a significant effect on improving in-furnace combustion and reducing CO and NOx emissions; the flue gas duct is connected to the primary air box through a high preheated air duct and a primary air duct, and to the secondary air box through a high preheated air duct and a secondary air duct. The high preheated air duct is also connected to both the primary and secondary air ducts.

[0018] The air in the flue gas duct is preheated by the air preheater and economizer. The preheated air is then divided into two streams through the high-temperature preheated air duct: one is the boiler primary air, and the other is the boiler secondary air. The boiler primary air enters the primary air box along the primary air duct and is then sent to the fluidized bed boiler. The boiler secondary air enters the secondary air box along the secondary air duct and is then sent to the fluidized bed boiler. Specifically, the boiler primary air is sent from the bottom of the fluidized bed boiler through the air caps on the air distribution plate into the dense phase zone of the fluidized bed boiler, and its proportion varies from 50% to 100% of the total boiler air volume. The boiler secondary air is sent from the front and rear walls and the side walls of the boiler water-cooled wall, and its proportion varies from 0% to 50% of the total boiler air volume.

[0019] Furthermore, both the primary and secondary air of the boiler originate from the primary air fan. A low-temperature air preheater, a low-temperature economizer, a high-temperature economizer, and a high-temperature air preheater are sequentially installed along the flue gas flow direction in the flue gas duct. To ensure that ultra-low calorific value fuels ignite immediately upon entering the dense phase region and maintain stable combustion within this region, high-temperature preheated air is used for both the primary and secondary air in the boiler. This preheated air temperature ranges from 350-600℃, depending on the fuel characteristics. The high-temperature preheated air originates from the boiler's high-temperature air preheater and does not require an external heating source.

[0020] Furthermore, the primary air of the boiler comes from the primary air fan, and the secondary air of the boiler comes from the secondary air fan. The primary air low-temperature air preheater, the secondary air low-temperature air preheater, the low-temperature economizer, the high-temperature economizer, the primary air high-temperature air preheater, and the secondary air high-temperature air preheater are installed sequentially along the flue gas flow direction in the flue gas duct.

[0021] The height settings for primary air high-temperature air preheaters and secondary air high-temperature air preheaters;

[0022] The height of the primary air low-temperature air preheater and the secondary air low-temperature air preheater are set.

[0023] Furthermore, both the primary and secondary air of the boiler come from the primary air fan, and a low-temperature air preheater, a low-temperature economizer, a medium-temperature air preheater, a high-temperature economizer, and a high-temperature air preheater are sequentially installed in the flue gas duct along the flue gas flow direction.

[0024] Furthermore, the primary air of the boiler comes from the primary air fan, and the secondary air of the boiler comes from the secondary air fan. The primary air low-temperature air preheater, the secondary air low-temperature air preheater, the low-temperature economizer, the primary air medium-temperature air preheater, the secondary air medium-temperature air preheater, the high-temperature economizer, the primary air high-temperature air preheater, and the secondary air high-temperature air preheater are installed in sequence along the flue gas flow direction.

[0025] The primary air low-temperature air preheater and the secondary air low-temperature air preheater are arranged at the same height.

[0026] This invention also provides a process for the combustion system of ultra-low calorific value oil shale and oil shale dry distillation semi-coke, comprising the following steps:

[0027] Considering the characteristics of low calorific value, low volatile matter, low fixed carbon, and high ash content, the ultra-low calorific value fuels, including oil shale, oil shale dry distillation semi-coke, mining tailings, and blends of two or three of them in different proportions, are fuels that are designed for ignition, combustion, and burnout. The particle size of these ultra-low calorific value fuels is controlled within the range of 0-6 mm.

[0028] Therefore, the ultra-low calorific value fuel with a particle size of 0-6mm in the coal feed bin is controlled. Part of it is sent to the fluidized bed boiler through the first coal conveying pipeline, accounting for 50-70% of the total boiler fuel. The other part of the ultra-low calorific value fuel is sent to the return feed inclined pipe through the second coal conveying pipeline and mixed with circulating ash before being sent to the fluidized bed boiler together. This part accounts for 30-50% of the total boiler fuel. The two parts of fuel are fluidized and combusted together in the fluidized bed boiler, and the combustion temperature is controlled within the range of 800-950℃.

[0029] The primary and secondary air of the boiler are preheated by an air preheater. The preheated hot air is divided into two streams: one is the primary air of the boiler, and the other is the secondary air of the boiler. The primary air is fed into the boiler from the bottom of the fluidized bed boiler, and the other is fed into the fluidized bed boiler from the front and rear walls and / or the side walls of the water-cooled wall. The proportion of primary air in the boiler is 50%-100% of the total boiler air volume, and the proportion of secondary air in the boiler is 0%-50% of the total boiler air volume.

[0030] The return material device sends the high-temperature fly ash collected by the cyclone separator back to the fluidized bed boiler for recycling and combustion through the return material inclined tube.

[0031] The combustion system and method for ultra-low calorific value oil shale and oil shale dry distillation semi-coke of the present invention have the following advantages:

[0032] 1. By adopting fluidized bed or circulating fluidized bed combustion methods, the combustion efficiency of the boiler can be improved while ensuring the ignition, stable combustion and burnout of ultra-low calorific value fuels;

[0033] 2. The design of the dense phase zone and dilute phase zone of the boiler has been optimized, which has increased the heat storage capacity of the bed material in the dense phase zone and effectively solved the ignition and stable combustion problems of ultra-low calorific value fuels during fluidized combustion.

[0034] 3. The use of adiabatic combustion effectively reduces boiler heat loss, effectively controls the combustion temperature inside the furnace, and effectively solves the problems of stable combustion and burnout during fluidized combustion of ultra-low calorific value fuels;

[0035] 4. High-preheated air is used as the primary and secondary air of the boiler, which supplements the heat of low-calorific-value fuels entering the furnace and effectively solves the problems of ignition, stable combustion and burnout of ultra-low-calorific-value fuels during fluidized combustion.

[0036] 5. Controlling the size of fuel particles can effectively ensure ignition and burnout during fluidized combustion of ultra-low calorific value fuels, thereby improving the combustion efficiency of the boiler. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of an ultra-low calorific value oil shale and oil shale dry distillation semi-coke combustion system according to Embodiment 1 of the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of an ultra-low calorific value oil shale and oil shale dry distillation semi-coke combustion system according to Embodiment 2 of the present invention.

[0039] Figure 3 This is a schematic diagram of the structure of an ultra-low calorific value oil shale and oil shale dry distillation semi-coke combustion system according to Embodiment 3 of the present invention.

[0040] Figure 4 This is a schematic diagram of the structure of an ultra-low calorific value oil shale and oil shale dry distillation semi-coke combustion system according to Embodiment 4 of the present invention.

[0041] Figure 5 for Figure 4 A cross-sectional view of a medium fluidized bed boiler along the AA direction.

[0042] Explanation of markings in the diagram: 1. Coal feed silo; 101. First coal conveying pipeline; 102. Second coal conveying pipeline; 105. Return material inclined pipe; 106. High-temperature preheating air duct; 107. Secondary air duct; 108. Primary air duct; 110. Air duct; 2. Primary air box; 3. Air cap; 4. Fluidized bed boiler; 5. Cyclone separator; 6. Return material device; 7. Secondary air box; 8. Superheater; 9. Evaporator heating surface; 10. High-temperature air preheating... Heaters; 10a, Primary air high-temperature air preheater; 10b, Secondary air high-temperature air preheater; 11, High-temperature economizer; 12, Low-temperature economizer; 13, Low-temperature air preheater; 13a, Primary air low-temperature air preheater; 13b, Secondary air low-temperature air preheater; 14, Medium-temperature air preheater; 14a, Primary air medium-temperature air preheater; 14b, Secondary air medium-temperature air preheater; 15, Flue gas duct; 16, Secondary air duct. Detailed Implementation

[0043] To better understand the purpose, structure, and function of this invention, the following detailed description, in conjunction with the accompanying drawings, provides an explanation of an ultra-low calorific value oil shale and an oil shale dry distillation semi-coke combustion system and method.

[0044] A combustion system for ultra-low calorific value oil shale and oil shale dry distillation semi-coke includes a coal feed silo 1, a fluidized bed boiler 4, a cyclone separator 5, and a flue gas duct 15. The cyclone separator 5 is installed at the outlet of the fluidized bed boiler 4. The bottom of the cyclone separator 5 is connected to a return material device 6 via a riser. The return material device 6 is connected to the fluidized bed boiler 4 via a return material inclined pipe 105. The top of the cyclone separator 5 is connected to the flue gas duct 15. The coal feed silo 1 is connected to the fluidized bed boiler 4 via a first coal conveying pipeline 101 and to the return material inclined pipe 105 via a second coal conveying pipeline 102. A superheater 8 and an evaporative heating surface 9 are installed at the top of the flue gas duct 15. An air preheater and an economizer are arranged at the bottom of the flue gas duct 15 along the flue gas flow direction.

[0045] The furnace of the fluidized bed boiler 4 is divided into a dense phase zone and a dilute phase zone. The static bed material height in the dense phase zone is 800-1300mm, and the furnace wall in the dense phase zone is an insulated furnace wall.

[0046] A primary air box 2 is installed at the bottom of the fluidized bed boiler 4. Secondary air boxes 7 are installed on the front and rear walls and / or side walls of the water-cooled wall of the fluidized bed boiler 4. The secondary air boxes 7 are arranged in multiple layers. The secondary air boxes 7 are connected to the fluidized bed boiler 4 through multiple secondary air ducts 16. The flue gas duct 15 is connected to the primary air box 2 through the high preheated air duct 106 and the primary air duct 108, and is connected to the secondary air box 7 through the high preheated air duct 106 and the secondary air duct 107.

[0047] Example 1:

[0048] The primary and secondary air of the boiler both come from the primary air fan. The low-temperature air preheater 13, the low-temperature economizer 12, the high-temperature economizer 11 and the high-temperature air preheater 10 are arranged sequentially along the flue gas flow direction in the flue gas duct 15.

[0049] Both primary and secondary air for the boiler originate from the primary air fan. Air from the primary air fan passes through duct 110, first through the low-temperature air preheater 13, and then through the high-temperature air preheater 10. High-temperature preheated air from the high-temperature air preheater 10 first enters the high-temperature preheated air duct 106, and is then divided into two streams: one is the boiler primary air, and the other is the boiler secondary air. The boiler primary air enters the primary air box 2 along the primary air duct 108 and is then fed into the boiler through the air caps 3 on the air distribution plate. The boiler secondary air is fed into the secondary air box along the secondary air duct 107 and, as secondary air, is fed into the boiler through the front and rear walls and side walls of the boiler water-cooled wall. This arrangement is described in [reference needed]. Figure 1 As shown.

[0050] Example 2:

[0051] The boiler's primary air comes from a primary air fan, and the boiler's secondary air comes from a secondary air fan. In the flue gas duct 15, a primary air low-temperature air preheater 13a, a secondary air low-temperature air preheater 13b, a low-temperature economizer 12, a high-temperature economizer 11, a primary air high-temperature air preheater 10a, and a secondary air high-temperature air preheater 10b are arranged sequentially along the flue gas flow direction.

[0052] The height settings of the primary air high-temperature air preheater 10a and the secondary air high-temperature air preheater 10b are as follows;

[0053] The primary air low-temperature air preheater 13a and the secondary air low-temperature air preheater 13b are set at the same height.

[0054] Separate primary and secondary air fans are installed. Air from the primary air fan passes through primary air duct 108, first through a primary low-temperature air preheater 13, then through a primary high-temperature air preheater 10a, and then through primary air duct 108 into the primary air box 2, before being sent into the boiler's dense phase zone via air caps 3 on the air distribution plate. Air from the secondary air fan passes through secondary air duct 107, first through a secondary low-temperature air preheater 13b, then through a secondary high-temperature air preheater 10b. Air from the secondary high-temperature air preheater 10b is then sent through secondary air duct 107 into the secondary air box and, as secondary air, is sent into the boiler through the front and rear walls and side walls of the boiler's water-cooled walls. This arrangement is described in [reference needed]. Figure 2 As shown.

[0055] Example 3:

[0056] The primary and secondary air of the boiler both come from the primary air fan. The low-temperature air preheater 13, the low-temperature economizer 12, the medium-temperature air preheater 14, the high-temperature economizer 11 and the high-temperature air preheater 10 are arranged sequentially along the flue gas flow direction in the flue gas duct 15.

[0057] To ensure a high preheated air temperature, it is also possible to... Figure 1 A medium-temperature air preheater 14 is arranged between the high-temperature economizer 11 and the low-temperature economizer 12. That is, air exiting the low-temperature air preheater 13 first enters the medium-temperature air preheater 14 and then enters the high-temperature air preheater 10. All other arrangements remain unchanged. This arrangement is described in [reference needed]. Figure 3 As shown;

[0058] Example 4:

[0059] The boiler's primary air comes from a primary air fan, and the boiler's secondary air comes from a secondary air fan. In the flue gas duct 15, along the flue gas flow direction, a primary air low-temperature air preheater 13a, a secondary air low-temperature air preheater 13b, a low-temperature economizer 12, a primary air medium-temperature air preheater 14a, a secondary air medium-temperature air preheater 14b, a high-temperature economizer 11, a primary air high-temperature air preheater 10a, and a secondary air high-temperature air preheater 10b are arranged sequentially.

[0060] The primary air low-temperature air preheater 13a and the secondary air low-temperature air preheater 13b are arranged at the same height.

[0061] To ensure a high preheated air temperature, it is also possible to... Figure 2 Between the high-temperature economizer 11 and the low-temperature economizer 12, a primary air intermediate temperature air preheater 14a and a secondary air intermediate temperature air preheater 14b are arranged. Specifically, air exiting the primary air low-temperature air preheater 13a first enters the primary air intermediate temperature air preheater 14a, and then enters the primary air high-temperature air preheater 10a; air exiting the secondary air low-temperature air preheater 13b first enters the secondary air intermediate temperature air preheater 14b, and then enters the secondary air high-temperature air preheater 10b. All other arrangements remain unchanged. This arrangement is described in [reference needed]. Figure 4 As shown.

[0062] A combustion system for ultra-low calorific value oil shale and oil shale dry distillation semi-coke includes a coal feed silo 1, a fluidized bed boiler 4, a cyclone separator 5, and a flue gas duct 15. The cyclone separator 5 is installed at the outlet of the fluidized bed boiler 4. The bottom of the cyclone separator 5 is connected to a return material device 6 via a riser. The function of the return material device 6 is to return the high-temperature fly ash collected by the cyclone separator 5 back to the fluidized bed boiler 4 for recirculation combustion via a return material inclined pipe 105 between the return material device 6 and the furnace of the fluidized bed boiler 4. The return material device 6 is connected to the fluidized bed boiler 4 via the return material inclined pipe 105. For the circulating fluidized bed boiler 4, a portion of the ultra-low calorific value fuel is fed to the return material inclined pipe 105 via a coal feeder. In the return material inclined pipe 105, the ultra-low calorific value fuel and the high-temperature circulating ash are mixed and then fed into the furnace together, increasing the temperature of this portion of ultra-low calorific value fuel when it enters the furnace, effectively enhancing the ignition and stable combustion of the ultra-low calorific value fuel. The proportion of fuel through the return feed inclined tube 105 accounts for 30-50% of the total fuel in the boiler, depending on the boiler structure and fuel characteristics. The top of the cyclone separator 5 is connected to the flue gas duct 15; the coal feed hopper 1 is connected to the fluidized bed boiler 4 through the first coal conveying pipeline 101, and to the return feed inclined tube 105 through the second coal conveying pipeline 102; the top of the flue gas duct 15 is equipped with a superheater 8 and an evaporative heating surface 9, and the lower part of the flue gas duct 15 is arranged with an air preheater and an economizer along the flue gas flow direction;

[0063] The furnace of the fluidized bed boiler 4 is divided into a dense phase zone and a dilute phase zone. The static bed material in the dense phase zone is higher than that in conventional coal-fired fluidized bed and circulating fluidized bed boilers 4, that is, the static bed material height in the dense phase zone is 800-1300mm. This increases both the storage capacity and the heat storage capacity of the dense phase zone bed material. While ensuring that the impact of newly entered fuel on the bed temperature is reduced, it ensures rapid ignition, stable combustion and burnout of oil shale, oil shale dry distillation semi-coke, mining tailings and two or three of them mixed in different proportions. The furnace of the ultra-low calorific value new fluidized bed and circulating fluidized bed boiler 4 adopts an adiabatic combustion method. At least the furnace wall in the dense phase zone is an adiabatic furnace wall to reduce heat loss from the furnace wall in the dense phase zone and ensure that the temperature in the dense phase zone is within the temperature range of 800℃-950℃. The insulation height of the furnace in the dilute phase zone is determined by the fuel characteristics. The insulation height of the furnace in the dilute phase zone is adjusted by laying refractory materials on the heating surface of the water-cooled wall in the dilute phase zone. The limit is that the entire dilute phase zone uses insulated furnace walls to ensure that the temperature of the dilute phase zone is close to or higher than that of the dense phase zone.

[0064] A primary air box 2 is installed at the bottom of the fluidized bed boiler 4. Secondary air boxes 7 are installed on the front and rear walls and / or side walls of the water-cooled walls of the fluidized bed boiler 4. To enhance the stable combustion and burnout of ultra-low calorific value fuels, the secondary air boxes 7 are arranged in multiple layers, i.e., 2-5 layers of secondary air are arranged. The secondary air boxes 7 are connected to the fluidized bed boiler 4 through multiple secondary air ducts 16. The number of secondary air ducts 16 is determined according to the width of the front and rear walls and the side walls. For specific arrangements, see [details omitted]. Figure 5A-direction view. Additionally, depending on the fuel type, secondary air can be arranged only on the front and rear walls or both side walls. This arrangement is beneficial for creating a localized strong mixing zone, which, based on enhanced combustion, increases the residence time of ultra-low calorific value fuel in the furnace, strengthens the combustion and burnout of ultra-low calorific value fuel, and has a considerable effect on improving in-furnace combustion and reducing CO and NOx emissions; the flue gas duct 15 is connected to the primary air box 2 via the high preheated air duct 106 and the primary air duct 108, and is connected to the secondary air box 7 via the high preheated air duct 106 and the secondary air duct 107;

[0065] The air in the flue gas duct 15 is preheated by the air preheater and economizer. The preheated air is divided into two streams by the high preheated air duct 106. One stream is the boiler primary air and the other is the boiler secondary air. The boiler primary air enters the primary air box 2 along the primary air duct 108 and is sent to the fluidized bed boiler 4. The boiler secondary air enters the secondary air box 7 along the secondary air duct 107 and is sent to the fluidized bed boiler 4. Specifically, the boiler primary air is sent from the bottom of the fluidized bed boiler 4 through the air cap 3 on the air distribution plate into the dense phase zone of the fluidized bed boiler 4. Its proportion varies from 50% to 100% of the total boiler air volume. The boiler secondary air is sent from the front and rear walls and the side walls of the boiler water-cooled wall. Its proportion varies from 0% to 50% of the total boiler air volume.

[0066] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A process for ultra-low heat value oil shale and oil shale retort semi-coke combustion system, characterized in that, The method comprises the following steps: The coal feeding bin (1) is used to feed the ultra-low calorific value fuel with a particle size of 0-6 mm, a part of which is sent into the fluidized bed boiler (4) through the first coal conveying pipeline (101), and the proportion of the part of the ultra-low calorific value fuel accounts for 50-70% of the total fuel amount of the boiler; another part of the ultra-low calorific value fuel is sent to the return material inclined pipe (105) through the second coal conveying pipeline (102) to be mixed with the circulating ash and then sent into the fluidized bed boiler (4), and the proportion of the part of the ultra-low calorific value fuel accounts for 30-50% of the total fuel amount of the boiler; the two parts of the fuel are combusted in the fluidized bed boiler (4) in a fluidized state, and the combustion temperature is controlled in the range of 800-950 ℃; The primary and secondary air of the boiler is preheated by the air preheater, the preheated hot air is divided into two parts, one part is the primary air of the boiler, and the other part is the secondary air of the boiler, the primary air of the boiler is sent into the boiler from the bottom of the fluidized bed boiler (4), and the other part is sent into the fluidized bed boiler (4) from the front and rear walls and / or the two side walls of the water-cooled wall of the fluidized bed boiler (4); the proportion of the primary air of the boiler accounts for 50%-100% of the total air amount of the boiler, and the proportion of the secondary air of the boiler accounts for 0%-50% of the total air amount of the boiler; The return material device (6) sends the high-temperature fly ash collected by the cyclone separator (5) back to the fluidized bed boiler (4) through the return material inclined pipe (105) to be combusted in a circulating manner; The ultra-low calorific value oil shale and oil shale dry distillation semi-coke combustion system comprises a coal feeding bin (1), a fluidized bed boiler (4), a cyclone separator (5) and a flue gas pipeline (15), the outlet of the fluidized bed boiler (4) is provided with the cyclone separator (5), the bottom of the cyclone separator (5) is connected with the return material device (6) through a vertical pipe, the return material device (6) is connected with the fluidized bed boiler (4) through the return material inclined pipe (105), the top of the cyclone separator (5) is communicated with the flue gas pipeline (15), the coal feeding bin (1) is connected with the fluidized bed boiler (4) through the first coal conveying pipeline (101) and connected with the return material inclined pipe (105) through the second coal conveying pipeline (102), and the top of the flue gas pipeline (15) is provided with a superheater (8) and an evaporation heating surface (9), and the air preheater and the economizer are arranged in the lower part of the flue gas pipeline (15) along the flue gas flow direction; The hearth of the fluidized bed boiler (4) is divided into a dense phase zone and a dilute phase zone, the height of the static bed material in the dense phase zone is 800-1300 mm, and the furnace wall of the dense phase zone is an adiabatic furnace wall; The bottom of the fluidized bed boiler (4) is provided with a primary air bellow (2), the front and rear walls and / or the two side walls of the water-cooled wall of the fluidized bed boiler (4) are provided with a secondary air bellow (7), the secondary air bellow (7) is provided with multiple layers, the secondary air bellow (7) is connected with the fluidized bed boiler (4) through multiple secondary air pipes (16), and the flue gas pipeline (15) is connected with the primary air bellow (2) and the secondary air bellow (7) through a high preheated air duct (106), a primary air duct (108) and a secondary air duct (107) respectively. The coal feeder (1) stores the ultra-low calorific value fuel with the calorific value of 240-560 kcal / kg, the coal feeder (1) directly sends a part of the ultra-low calorific value fuel to the fluidized bed boiler (4) through the first coal conveying pipeline (101), and the coal feeder (1) sends 30-50% of the total fuel amount of the boiler to the return material inclined pipe (105) through the second coal conveying pipeline (102), and the ultra-low calorific value fuel is mixed with the high-temperature circulating ash and then sent to the fluidized bed boiler (4); The primary air and the secondary air of the boiler are both from the primary air fan, the low-temperature air preheater (13), the low-temperature economizer (12), the high-temperature economizer (11) and the high-temperature air preheater (10) are arranged in the flue gas pipeline (15) along the flue gas flow direction in sequence, and the primary air and the secondary air of the boiler adopt high preheated air, and the temperature range of the high preheated air is 350-600℃.

2. The process for ultra-low heat value oil shale and oil shale retort semi-coke combustion system according to claim 1, characterized in that, The primary air of the boiler is from the primary air fan, the secondary air of the boiler is from the secondary air fan, the primary air low-temperature air preheater (13a), the secondary air low-temperature air preheater (13b), the low-temperature economizer (12), the high-temperature economizer (11), the primary air high-temperature air preheater (10a) and the secondary air high-temperature air preheater (10b) are arranged in the flue gas pipeline (15) along the flue gas flow direction in sequence; The primary air high-temperature air preheater (10a) and the secondary air high-temperature air preheater (10b) are arranged at the same height. The primary air low-temperature air preheater (13a) and the secondary air low-temperature air preheater (13b) are arranged at the same height.

3. The process for ultra-low heat value oil shale and oil shale retort semi-coke combustion system of claim 1, wherein, The primary air and the secondary air of the boiler are both from the primary air fan, the low-temperature air preheater (13), the low-temperature economizer (12), the medium-temperature air preheater (14), the high-temperature economizer (11) and the high-temperature air preheater (10) are arranged in the flue gas pipeline (15) along the flue gas flow direction in sequence.

4. The process for ultra-low heat value oil shale and oil shale retort semi-coke combustion system of claim 1, wherein, The primary air of the boiler is from the primary air fan, the secondary air of the boiler is from the secondary air fan, the primary air low-temperature air preheater (13a), the secondary air low-temperature air preheater (13b), the low-temperature economizer (12), the primary air medium-temperature air preheater (14a), the secondary air medium-temperature air preheater (14b), the high-temperature economizer (11), the primary air high-temperature air preheater (10a) and the secondary air high-temperature air preheater (10b) are arranged in the flue gas pipeline (15) along the flue gas flow direction in sequence. The primary air low-temperature air preheater (13a) and the secondary air low-temperature air preheater (13b) are arranged at the same height.

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