Method and system for clean gasification of biomass

Abstract

The invention discloses a biomass clean gasification method and system, and belongs to the technical field of substance thermochemical conversion. Biomass raw materials are dried, the dried steam and oxygen are mixed and then completely participate in gasification reaction, external source water vapor is replaced with evaporated water of the raw materials, the temperature control and fluidization effects are achieved, and the raw materials participate in the gasification reaction; the utilization of raw water and evaporation heat of raw materials is realized, the gas water vapor content is reduced, and the downstream condensate water treatment difficulty and cost are reduced. Biomass raw material drying, biomass gasification and tar high-temperature cracking are completed in a grading mode, gas sensible heat is used for raw material drying, fly ash energy is used for tar high-temperature cracking, the gasification heat efficiency is effectively improved, raw material raw water is used for fluidization and gasification reactions, external source water vapor is replaced, and the gas quality and the gasification heat efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermochemical conversion of substances, and in particular to a method and system for clean biomass gasification. Background Art

[0002] Biomass is an abundant renewable energy source that is the only one that can be stored and transported. In the face of global climate change, bio-liquid fuel will become an important means of reducing emissions in the transportation sector. Biomass gasification is the reaction of biomass with oxygen and / or water vapor under high temperature conditions to convert it into combustible gases such as hydrogen and carbon monoxide. It can be used to synthesize green methanol or green jet fuel, and has broad application prospects. In order to reduce the difficulty and cost of downstream gas purification and synthesis, pure oxygen or oxygen / water vapor is usually used as a gasifier to produce clean, high-quality synthesis gas with a high proportion of effective components.

[0003] Typical gasification technologies include fixed bed, fluidized bed and entrained bed. Fixed bed gasification mainly includes updraft and downdraft, which are mature in technology, simple to operate and require low investment. The disadvantages are small processing capacity and easy slagging of the grate. The updraft fixed bed has high thermal efficiency, but the tar content in the produced gas is high, and the subsequent gas purification and water treatment system are complex and costly; the downdraft fixed bed has low tar content in the gas, but has high requirements for grate material and low gasification efficiency. The fluidized bed has strong adaptability to raw materials and is easy to scale up. It usually requires water vapor to assist fluidization. The impurity content of the gas is high and the tar condensate is difficult to handle; the central jet temperature of the ash melting fluidized bed can reach above 1200℃, which reduces the tar content of the gas, but the volatile matter of the biomass raw material is much higher than that of coal, and it is difficult to complete cracking in the high temperature zone of the jet, and the problem of high tar content in the produced gas still exists. The fluidized-bed gasification technology has a high reaction temperature and produces gas without tar, but the biomass needs to be crushed to less than 300 μm and the pretreatment cost is extremely high. There are also problems such as the difficulty of high-concentration biomass powder transportation technology and low cooling efficiency.

[0004] In addition, biomass has a high moisture content, and the moisture content of fresh branches and straw can reach more than 40%. Biomass needs to be dried before gasification, which has high capital and energy costs; or the raw material's own heat is consumed in the gasification process to complete the drying in the furnace. Due to the short residence time in the furnace, only a small part of this drying steam can participate in the gasification reaction, which reduces the efficiency of cold gas and also causes an increase in downstream condensed wastewater.

[0005] In view of this, this application is filed. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method and system for clean biomass gasification, which can effectively improve the quality of fuel gas and the thermal efficiency of gasification.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for clean biomass gasification comprises the following steps:

[0009] (1) The biomass raw materials enter the drying furnace, and the high-temperature fuel gas sensible heat at the outlet of the tar cracking furnace is used for indirect heat exchange to dry the biomass raw materials, thereby obtaining dry biomass and water vapor;

[0010] The water vapor is divided into two parts. The first part of the water vapor is mixed with oxygen and then enters the central injection pipe of the gasifier. The other part of the water vapor is mixed with oxygen and then enters the reaction zone of the gasifier from the air distribution plate. The dry biomass enters the gasifier and undergoes a gasification reaction with the oxygen and water vapor in the gasifier to generate ash and fuel gas.

[0011] (2) The fuel gas flows through the first cyclone separator for gas-solid separation, and the material removed from the first cyclone separator is returned to the gasifier for gasification reaction. The fuel gas from the outlet of the first cyclone separator flows through the second cyclone separator for gas-solid separation. The temperature of the fuel gas at the outlet of the second cyclone separator is increased, and the tar in the fuel gas is cracked. The fuel gas after the tar cracking is sent to the drying furnace to dry the biomass raw materials by indirect heat exchange. The high-quality fuel gas at the outlet of the drying furnace is sent to the downstream for utilization.

[0012] The present application dries the biomass raw material, and the dried steam is mixed with oxygen and all participates in the gasification reaction, which can effectively improve the cold gas efficiency and reduce downstream condensed wastewater. The present invention completes the drying of the biomass raw material, biomass gasification and tar high-temperature cracking in a graded manner, uses the sensible heat of the fuel gas to dry the raw material, uses the fly ash energy to crack the tar, and uses the original moisture of the raw material for fluidization and gasification reactions, replacing exogenous water vapor, thereby improving the fuel gas quality and gasification thermal efficiency.

[0013] As a preferred embodiment of the present invention, the first portion of water vapor accounts for 20-40% of the total mass of water vapor.

[0014] As a preferred embodiment of the present invention, the mass ratio of the first part of water vapor to oxygen is 1:(1-2).

[0015] As a preferred embodiment of the present invention, the mass ratio of the additional portion of water vapor to oxygen is 1:(0.02-0.06).

[0016] As a preferred embodiment of the present invention, the temperature of the gasification reaction is 1000-1200°C.

[0017] As a preferred embodiment of the present invention, the ash is discharged from a slag discharge pipe outside the central injection pipe.

[0018] As a preferred embodiment of the present invention, the material removed by the second cyclone separator enters the tar cracking furnace for combustion after being purged with oxygen, thereby raising the temperature of the fuel gas at the outlet of the second cyclone separator to 1000-1200°C.

[0019] As a preferred embodiment of the present invention, the mass ratio of the material removed by the second cyclone separator to oxygen is 1:(0.5-2).

[0020] The present invention also provides a system for clean biomass gasification, which is used to implement the above-mentioned method for clean biomass gasification, comprising a drying furnace, a gasification furnace, a first cyclone separator, a second cyclone separator, and a tar cracking furnace connected in sequence; the drying furnace is also connected to the gasification furnace through a first mixer and a second mixer, and a tubular reactor is provided on the connecting pipeline between the second cyclone separator and the tar cracking furnace.

[0021] As a preferred embodiment of the present invention, the drying furnace is an indirect heat exchanger, and the raw materials are not in contact with the fuel gas.

[0022] The beneficial effects of the present invention are as follows: (1) The present invention dries the biomass raw material, and the dried steam is mixed with oxygen and all participates in the gasification reaction, so that the evaporated water of the raw material replaces the exogenous water vapor to achieve the temperature control and fluidization effect and participates in the gasification reaction, thereby realizing the utilization of the original water content of the raw material and its evaporation heat, reducing the water vapor content of the fuel gas, and reducing the difficulty and cost of downstream condensed water treatment.

[0023] (2) The present application completes the drying of biomass raw materials, biomass gasification and high-temperature cracking of tar by graded methods, uses the sensible heat of the fuel gas for drying the raw materials, uses the energy of fly ash for high-temperature cracking of tar, effectively improves the thermal efficiency of gasification, and uses the original moisture of the raw materials for fluidization and gasification reactions, replacing exogenous water vapor, thereby improving the quality of the fuel gas and the thermal efficiency of gasification. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the biomass clean gasification system described in this application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0026] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0028] In the present application, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0029] Unless otherwise specified, the components, raw materials or instruments used in the embodiments and comparative examples of the present invention are all commercially available raw materials or instruments, and the components and raw materials used in each parallel experiment are all of the same kind.

[0030] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0031] The present application provides a method for clean biomass gasification, comprising the following steps:

[0032] (1) The biomass raw materials enter the drying furnace, and the high-temperature fuel gas sensible heat at the outlet of the tar cracking furnace is used for indirect heat exchange to dry the biomass raw materials, thereby obtaining dry biomass and water vapor;

[0033] The water vapor is divided into two parts. The first part of the water vapor is mixed with oxygen and then enters the central injection pipe of the gasifier. The other part of the water vapor is mixed with oxygen and then enters the reaction zone of the gasifier from the air distribution plate. The dry biomass enters the gasifier and undergoes a gasification reaction with the oxygen and water vapor in the gasifier to generate ash and fuel gas.

[0034] (2) The fuel gas flows through the first cyclone separator for gas-solid separation, and the material removed from the first cyclone separator is returned to the gasifier for gasification reaction. The fuel gas from the outlet of the first cyclone separator flows through the second cyclone separator for gas-solid separation. The temperature of the fuel gas at the outlet of the second cyclone separator is increased, and the tar in the fuel gas is cracked. The fuel gas after the tar cracking is sent to the drying furnace to dry the biomass raw materials by indirect heat exchange. The high-quality fuel gas at the outlet of the drying furnace is sent to the downstream for utilization.

[0035] In the present application, biomass raw materials are dried, and the dried steam is mixed with oxygen to participate in the gasification reaction. The evaporated water of the raw materials replaces the exogenous water vapor to achieve the temperature control and fluidization effect and participate in the gasification reaction, thereby realizing the utilization of the original water content of the raw materials and the heat of evaporation, reducing the water vapor content of the fuel gas, and reducing the difficulty and cost of downstream condensed water treatment.

[0036] The present application completes the drying of biomass raw materials, biomass gasification and high-temperature cracking of tar by classification, uses the sensible heat of the fuel gas for drying the raw materials, uses the energy of fly ash for high-temperature cracking of tar, effectively improves the thermal efficiency of gasification, uses the original moisture of the raw materials for fluidization and gasification reactions, replaces exogenous water vapor, and improves the fuel gas quality and the thermal efficiency of gasification.

[0037] In one embodiment, the first portion of water vapor is 20-40% of the total mass of water vapor.

[0038] The present application can effectively maintain fluidization above the air distribution plate and effectively prevent slagging of the air distribution plate by controlling the contents of the two parts of water vapor.

[0039] In one embodiment, the mass ratio of the first portion of water vapor to oxygen is 1:(1-2).

[0040] In one embodiment, the mass ratio of the additional portion of water vapor to oxygen is 1:(0.02-0.06).

[0041] In one embodiment, the temperature of the gasification reaction is 1000-1200°C.

[0042] In one embodiment, the ash is discharged from a slag discharge pipe outside the central injection pipe.

[0043] In one embodiment, the material removed by the second cyclone separator is purged with oxygen and then enters the tar cracking furnace for combustion, thereby raising the temperature of the fuel gas at the outlet of the second cyclone separator to 1000-1200°C.

[0044] In one embodiment, the mass ratio of the material removed by the second cyclone separator to oxygen is 1:(0.5-2).

[0045] like Figure 1 As shown, one embodiment of the present application provides a system for clean gasification of biomass, which is used to implement the above-mentioned method for clean gasification of biomass, including a drying furnace, a gasification furnace, a first cyclone separator, a second cyclone separator, and a tar cracking furnace connected in sequence; the drying furnace is also connected to the gasification furnace through a first mixer and a second mixer, and a tubular reactor is provided on the connecting pipeline of the second cyclone separator and the tar cracking furnace.

[0046] In one embodiment, the drying furnace is an indirect heat exchanger, and the raw materials are not in contact with the fuel gas.

[0047] In one embodiment, the gasifier uses water vapor obtained by drying raw materials and injects it together with oxygen to react with biomass to form a high-temperature jet zone. The water vapor obtained by drying raw materials participates in fluidization and controls the reaction temperature of the central jet zone.

[0048] The following examples are provided to facilitate understanding of the present invention. These examples are not provided to limit the scope of the claims.

[0049] Example 1

[0050] A system for clean biomass gasification includes a drying furnace 30, a gasification furnace 14, a first cyclone separator 11, a second cyclone separator 9, and a tar cracking furnace 3 connected in sequence; the drying furnace is also connected to the gasification furnace through a first mixer 17 and a second mixer 25, and a tubular reactor 6 is provided on the connecting pipeline between the second cyclone separator and the tar cracking furnace.

[0051] The working principle of the system described in the present application is as follows: the biomass raw material 1 enters the drying furnace 30, and is dried by indirect heat exchange using the sensible heat of the high-temperature fuel gas 2 at the outlet of the tar cracking furnace 3, to obtain dry biomass 28 and water vapor 32. The dry biomass raw material 28 enters the gasifier 14 for gasification; the water vapor 32 is divided into two parts: water vapor 13 and water vapor 31; the water vapor 13 is mixed with oxygen 16 in the first mixer 17, the water vapor and oxygen mixture 18 enters the central injection pipe 20 of the gasifier from the inlet 19, the water vapor 31 is mixed with oxygen 26 in the second mixer 25, and the water vapor and oxygen mixture 24 enters the reaction zone from the inlet 23 through the air distribution plate 15.

[0052] The dry biomass 28 from the drying furnace 30 outlet enters the fluidized bed gasifier 14, and reacts with the oxygen and water vapor introduced into the fluidized bed gasifier 14 to generate ash 22 and fuel gas 12. The ash 22 melted in the high temperature area of ​​the central jet is discharged from the slag discharge pipe 21 outside the central injection pipe 20; the fuel gas 12 flows through the primary cyclone 11 and the secondary cyclone 9 in sequence for gas-solid separation, and the material 27 removed from the primary cyclone 11 is sent back to the gasifier 14 to continue gasification.

[0053] The raw fuel gas 10 from the outlet of the first-stage cyclone 11 enters the second-stage cyclone 9 for further gas-solid separation. The charcoal ash 8 and oxygen 7 removed from the second-stage cyclone 9 are mixed in the pipeline 6, and the mixture 5 of charcoal ash and oxygen is sprayed into the tar cracking furnace 3 for combustion; the temperature of the fuel gas 4 from the outlet of the second-stage cyclone 9 is increased to 1000-1200°C, and the tar in the fuel gas is cracked at high temperature; the high-temperature fuel gas 2 after the tar cracking is sent to the drying furnace 30 to dry the biomass raw material 1 by indirect heat exchange, and the fuel gas 29 at the outlet of the drying furnace is sent to the downstream for utilization.

[0054] Example 2

[0055] A method for clean biomass gasification, based on the system for clean biomass gasification of embodiment 1, comprises the following steps:

[0056] After 1kg of biomass raw material enters the drying furnace for drying, 0.30kg of water vapor and 0.70kg of dry biomass raw material are obtained. 0.09kg of water vapor is mixed with 0.14kg of oxygen and enters the central injection pipe of the gasifier, and the other 0.21kg of water vapor is mixed with 0.01kg of oxygen and enters the gasifier from the air distribution plate. The dry biomass reacts with the oxygen and water vapor in the gasifier to generate ash and fuel gas.

[0057] (2) The ash and slag melted in the high-temperature zone of the central jet are discharged from the slag discharge pipe outside the central injection pipe; the fuel gas flows through the first cyclone separator and the second cyclone separator in turn for gas-solid separation, and the material removed from the first cyclone separator is sent back to the gasifier to continue gasification.

[0058] (3) The carbon ash removed from the second cyclone separator is purged with oxygen, mixed with oxygen and then burned in a tar cracking furnace; the gas temperature is increased from 750-850°C to 1000-1200°C, and the tar in the gas is cracked at high temperature; the high-temperature gas after tar cracking is sent to a drying furnace to dry the biomass raw materials, which dries the biomass raw materials by indirect heat exchange, and the high-quality gas at the outlet of the drying furnace is sent to the downstream for use.

[0059] Among them, the carbon ash removed from the second cyclone separator is about 0.05kg, and the amount of purging oxygen is 0.05kg.

[0060] Among them, the volume ratio of H2 and CO in the fuel gas of this embodiment is above 60%, and the gasification thermal efficiency is about 90%.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for clean biomass gasification, characterized in that: The following steps are involved: (1) The biomass raw materials enter the drying furnace, and the high-temperature fuel gas sensible heat at the outlet of the tar cracking furnace is used for indirect heat exchange to dry the biomass raw materials, thereby obtaining dry biomass and water vapor; The water vapor is divided into two parts. The first part of the water vapor is mixed with oxygen and then enters the central injection pipe of the gasifier. The other part of the water vapor is mixed with oxygen and then enters the reaction zone of the gasifier from the air distribution plate. The dry biomass enters the gasifier and undergoes a gasification reaction with the oxygen and water vapor in the gasifier to generate ash and fuel gas. (2) The fuel gas flows through the first cyclone separator for gas-solid separation, and the material removed from the first cyclone separator is returned to the gasifier for gasification reaction. The fuel gas from the outlet of the first cyclone separator flows through the second cyclone separator for gas-solid separation. The temperature of the fuel gas at the outlet of the second cyclone separator is increased to crack the tar in the fuel gas. The fuel gas after the tar cracking is sent to the drying furnace to dry the biomass raw materials by indirect heat exchange. The high-quality fuel gas at the outlet of the drying furnace is sent to the downstream for utilization.

2. The method for clean biomass gasification according to claim 1, characterized in that: The first portion of water vapor accounts for 20-40% of the total mass of the water vapor.

3. The method for clean biomass gasification according to claim 1, characterized in that: The mass ratio of the first part of water vapor to oxygen is 1:(1-2).

4. The method for clean biomass gasification according to claim 1, characterized in that: The mass ratio of the other part of water vapor to oxygen is 1:(0.02-0.06).

5. The method for clean biomass gasification according to claim 1, characterized in that: The temperature of the gasification reaction is 1000-1200°C.

6. The method for clean biomass gasification according to claim 1, characterized in that: The ash is discharged from the slag discharge pipe outside the central injection pipe.

7. The method for clean biomass gasification according to claim 1, characterized in that: The material removed by the second cyclone separator is blown with oxygen and then enters the tar cracking furnace for combustion, thereby raising the temperature of the fuel gas at the outlet of the second cyclone separator to 1000-1200°C.

8. The method for clean biomass gasification according to claim 8, characterized in that: The mass ratio of the material removed by the second cyclone separator to oxygen is 1:(0.5-2).

9. A biomass clean gasification system, characterized in that: A method for realizing clean gasification of biomass as described in any one of claims 1 to 8, comprising a drying furnace, a gasification furnace, a first cyclone separator, a second cyclone separator, and a tar cracking furnace connected in sequence; the drying furnace is also connected to the gasification furnace through a first mixer and a second mixer, and a tubular reactor is provided on the connecting pipeline of the second cyclone separator and the tar cracking furnace.

10. The biomass clean gasification system according to claim 9, characterized in that: The drying furnace is an indirect heat exchanger, and the raw materials and the fuel gas do not come into contact.

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