Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to: the utility model provides a pyrolysis gasification process and system for municipal solid waste, which mainly solve the problems of low heat value, secondary pollution risk and high cost of the current pyrolysis gasification fuel gas for municipal solid waste.
In order to solve the technical problems, the invention adopts the following technical scheme:
a material pyrolysis gasification process comprises preheating, drying, pyrolysis, gasification and heat recovery in sequence, wherein a heat source required by the preheating is provided by dried medium-temperature flue gas with the temperature of more than 250 ℃; the heat source required by drying and pyrolysis is provided by gasified medium-temperature flue gas with the temperature of more than 750 ℃ in an external heat supply mode; the heat source required by gasification is provided by high-temperature flue gas with the temperature of more than 1000 ℃ formed by combustion of combustible gas generated by gasification; after the gasified medium-temperature flue gas with the temperature of more than 750 ℃ is subjected to heat recovery, low-temperature flue gas with the temperature of more than 100 ℃ is produced, after the low-temperature flue gas is subjected to gas-solid separation, the gas part is purified into combustible gas, and the solid part is mixed and granulated to produce the organic compound fertilizer; the gasification medium required by gasification comprises water vapor produced in the drying and pyrolysis process, pyrolysis produced gas produced in the pyrolysis process and medium-temperature steam produced in the heat recovery process.
In addition, according to the process, the superheated steam discharged before pyrolysis is used for gasification of the pyrolysis semicoke powder, and after the semicoke after pyrolysis is cooled, the semicoke powder is prepared by screening and crushing; the superheated steam generated in the preparation process of the semi-coke powder is used as a conveying medium to convey the semi-coke powder for gasification; the particle size of the semi-coke powder is 50-100 meshes; the retention time of the semi-coke powder in the gasification process is between 0.5 and 2.0 s; the mass ratio of the water vapor to the material pyrolysis semicoke is 0.2-1.0.
In addition, the invention also provides a pyrolysis and gasification system for the municipal domestic waste, which comprises a preheating unit, a drying unit, a pyrolysis unit, a gasification unit and a heat recovery unit, wherein the pyrolysis unit comprises a pyrolysis furnace, and the gasification unit comprises a gasification furnace; the heat source required by the preheating unit is provided by middle-temperature flue gas with the temperature of more than 250 ℃ generated by the drying unit; the heat sources required by the drying unit and the pyrolysis furnace are provided by the form of external heat supply of the medium-temperature flue gas with the temperature of more than 750 ℃ after gasification of the gasification furnace; the heat source required by the gasification furnace is provided by high-temperature flue gas with the temperature of more than 1000 ℃ formed by combustion of combustible gas generated by gasification; the method comprises the following steps that (1) low-temperature flue gas at the temperature of more than 100 ℃ is produced after heat recovery is carried out on medium-temperature flue gas at the temperature of more than 750 ℃ produced by a gasification furnace, gas part of the low-temperature flue gas is purified into combustible gas after gas-solid separation, and solid part of the low-temperature flue gas is mixed and granulated to produce organic compound fertilizer; the gasification medium required by gasification of the gasification furnace comprises water vapor produced by the drying unit and the pyrolysis furnace, pyrolysis produced gas produced by the pyrolysis furnace and medium-temperature steam produced during heat recovery.
As an optimized mode of the pyrolysis furnace, the pyrolysis furnace comprises a furnace body shell and an inner cylinder, wherein the inner cylinder is used for containing materials, the top of the furnace body shell is simultaneously provided with a flue gas inlet and outlet and a pyrolysis gas outlet, and the flue gas inlet and outlet are provided with a conversion valve for changing an inlet heat source so as to respectively meet the heat required by drying and pyrolysis; the top of the pyrolysis furnace is connected with a pyrolysis gas conveying pipeline for conveying out pyrolysis gas, and heating flue gas is introduced into a jacket of the pyrolysis furnace for drying and pyrolyzing materials.
More preferably, the pyrolysis furnace adopts the form of flue gas external heating, and the inner tube is sent into the pyrolysis furnace after expecting, lets in the flue gas of different temperatures respectively and is used for drying, the pyrolysis of material, and the moisture in the material is heated by the flue gas and is evaporated during the drying, and after the drying is accomplished, switches to the flue gas of higher temperature and is used for the material pyrolysis.
As an optimization mode of the gasification furnace, the gasification furnace internally comprises a plurality of small-diameter steel pipes, an entrained flow bed structure is adopted, high-temperature flue gas is externally heated, pyrolysis generated gas from the pyrolysis furnace carries semi-coke powder to be fed, water vapor is used as a gasification agent, gasification gas generated by gasification is subjected to gas-solid separation after heat exchange, the gas is purified for later use, and the solid is collected and granulated to be used for preparing other additional products; the heat required by the gasification of the semi-coke powder in the gasification furnace comes from high-temperature flue gas generated by the combustion of combustible gas generated by the gasification; the particle size of the semi-coke powder is 50-100 meshes; the retention time of the semi-coke powder in the gasification furnace is between 0.5 and 2.0 s; the mass ratio of the water vapor to the material pyrolysis semicoke is 0.2-1.0.
Optionally, the pyrolytic semicoke and the coal coke of the material are co-gasified during the pyrolysis of the semicoke, the reaction temperature is 750-.
More preferably, the gasification furnace comprises a gasification section and a methanation section, wherein the gasification furnace comprises an entrained flow bed structure, gas generated by pyrolysis is used as a carrier to send the semi-coke powder into the gasification section for gasification reaction, the gasified gas after reaction enters the methanation section for methanation reaction under the action of a catalyst, and heat released by methanation is recycled to be used for preparing a gasification agent required by the gasification reaction.
Furthermore, in the gasification furnace, the catalyst added in the gasification reaction comprises calcium carbonate or calcium oxide, the addition amount of CaO/C is 0.5, and the reaction temperature is 750-800 ℃.
The process or the system of the invention is particularly used for the pyrolysis and gasification of municipal domestic waste, domestic sludge or straws.
Compared with the prior art, the invention has the following technical effects:
the pyrolysis gasification process for the municipal solid waste provided by the invention can realize self-sufficiency of energy in the pyrolysis gasification process of the waste, generate fuel gas with higher comprehensive heat value and organic products with higher added values, can be coupled with a gas boiler/gas turbine, fully recover energy, meet the consumption of water vapor in the pyrolysis gasification process, and has the remarkable advantages of high gasification efficiency, high comprehensive heat value of the fuel gas, high energy utilization efficiency and the like, particularly:
1. the invention combines the fixed bed drying-pyrolysis and entrained flow bed gasification technologies, realizes the optimal conversion from the domestic garbage to the gas fuel, and improves the heat value of the output gas;
2. the process can efficiently utilize the domestic garbage, convert the domestic garbage into combustible gas and ash containing organic carbon, and can adjust the component proportion of the produced gas by adding a proper catalyst in the methanation section of the gasification furnace according to the requirement on the combustible gas components;
3. the drying and pyrolysis of the process are carried out in the same reactor, the raw materials do not need a pretreatment process, and the water vapor generated in the process can be used as carrier gas for conveying the semi-coke powder to a gasification furnace and can also be used as a gasification agent for gasification reaction of the semi-coke powder;
4. the process of the invention adopts the steam as the gasifying agent to greatly improve the gas production rate, increase the content of combustible gas components and increase the gas production heat value by pulverizing the pyrolysis semicoke and conveying the steam into the gasifying furnace for gasification reaction.
Example 1:
according to the above technical solution, as shown in fig. 1 to 3, the present embodiment provides a pyrolysis gasification system, taking municipal solid waste as an example, the whole process mainly includes feeding, drying, pyrolysis, gasification, and energy recovery and reuse, and specifically includes the following steps:
firstly, pretreating sludge, straws and household garbage by magnetic separation and the like, mixing and preheating, and loading the preheated mixed material into an inner cylinder of a pyrolysis furnace; the inner tube that will fill with the material is arranged in the pyrolysis oven, the furnace roof is equipped with flue gas import and export and pyrolysis gas outlet pipeline simultaneously, flue gas import and export department is equipped with the conversion valve, be used for changing the entry heat source and satisfy the drying respectively, the required heat of pyrolysis, gas flowmeter and pressure regulating valve are installed to pyrolysis gas export, be used for detecting pyrolysis gas flow and adjusting the interior pressure of stove, be equipped with two temperature detection points in the pyrolysis oven, be located wall and pyrolysis oven top export respectively, be used for detecting the temperature variation condition of material in the pyrolysis oven, the required heat source of dry pyrolysis is provided through the form of outside heat supply by the middle temperature flue gas after: at the initial stage of the drying stage, firstly, air in the pyrolysis furnace is pumped away, the material is ensured to be in an anoxic or anaerobic environment, the pyrolysis gas pipeline is closed, the material containing inner cylinder is in a sealed state, water in the material is heated and gradually heated and evaporated to generate water vapor in the heating process, the pressure in the furnace is continuously increased, the heat transfer rate among gas, solid and liquid phases is also gradually increased, when free water on the surface of the material and compound water in the material are completely evaporated, the material is continuously heated, the temperature in the furnace is continuously increased, the water vapor is in an overheat state and becomes superheated steam, the pressure in the pyrolysis furnace is controlled by adjusting a pressure adjusting valve of a pyrolysis gas outlet pipeline, the exhausted water vapor can be used for gasifying pyrolysis semi-coke powder, and after the drying process is finished (the water content is about 10%), a heating heat source is switched and the pyrolysis stage is started; the dried material starts to be heated and pyrolyzed in the environment of superheated steam, the generated pyrolysis gas is led out through a pyrolysis gas pipeline at the top of the furnace, the pressure is controlled by a pressure regulating valve, and the pyrolyzed semicoke is cooled for later use; screening the pyrolysis semicoke by a screening machine, crushing by a crusher, and preparing semicoke powder for storage and standby; the method comprises the following steps that superheated steam generated in the process is used as a conveying medium to convey semi-coke powder into a gasification furnace, the gasification furnace and pyrolysis gas led out from the top of the pyrolysis furnace are subjected to gasification reaction, a heat source required by gasification comes from high-temperature flue gas formed by combustion of fuel gas generated by gasification, and the steam is selected as the gasification medium and is provided by the steam in the pyrolysis gas and medium-temperature steam generated in the heat energy recovery process; a plurality of small-diameter steel pipes are uniformly arranged in the gasification furnace, the semi-coke powder and the gasification agent are simultaneously fed into the steel pipes, high-temperature flue gas enters the gasification furnace through the bottom and carries out countercurrent indirect heat exchange with materials in the steel pipes, the materials are heated by the high-temperature flue gas to be rapidly heated, and the gasification temperature is controlled between 800 ℃ and 900 ℃ to be favorable for the gasification of pyrolysis semi-coke;
preferably, in order to increase the output of combustible gas and improve the gasification efficiency, a proper amount of catalyst can be added into the gasification furnace, calcium oxide is preferably selected, the content of the combustible gas in the gasified gas can be improved, the cracking of tar in the pyrolysis process can be promoted, the addition amount of CaO/C is 0.5, and the reaction temperature is 750-;
in order to increase the heating area of the semicoke and improve the gasification rate, the grain diameter of the semicoke powder is 50-100 meshes;
in order to ensure the gasification effect of the semicoke, the residence time of the particles in the gasification furnace is controlled to be between 1.5 and 2.0 s;
the mass ratio of the water vapor to the garbage pyrolysis semicoke is 0.2-1.0;
in order to increase the content of methane in the gasified gas and improve the heat value of the combustible gas, the gasification furnace can be designed into a two-section entrained flow bed structure, the upper section is a gasification section, the lower section is a methanation section, the gasified gas coming out of the gasification section immediately enters the methanation section to carry out secondary reaction under the action of a catalyst, and the content of methane in the combustible gas is improved;
preferably, the content of methane gas in the combustible gas can be adjusted by controlling the gasification temperature, and the gasification temperature is 700-950 ℃, which is beneficial to the generation of methane;
the heat required in the whole process is provided by the combustion of combustible gas generated by gasification, high-temperature flue gas (>1100 ℃) generated after the combustion of the combustible gas firstly enters a gasification furnace to provide the heat required by the gasification, the temperature of the flue gas discharged from the gasification furnace is-750 ℃, the flue gas is divided into two parts, one part enters a steam generator to generate medium-temperature steam, the other part enters a garbage pyrolysis unit to provide the heat required by the garbage pyrolysis, the temperature of the flue gas discharged from a pyrolysis section is-500 ℃, the flue gas is used for drying the garbage, the temperature of outlet flue gas after the drying is-250 ℃, is used for assisting to generate middle-temperature steam, the low-temperature flue gas after the heat is recovered by the steam generation can be further used for air preheating, as the drying and the pyrolysis of the garbage are carried out in the same reactor, in actual working conditions, a plurality of pyrolysis furnaces are required to be connected in series, and the flue gas with different tastes is reasonably distributed and utilized;
the gasification unit selects steam as a gasification agent, and the source of the steam comprises two parts: a large amount of water vapor generated in the drying and pyrolysis process enters a gasification furnace together with pyrolysis gas and is used as a gasification agent to participate in the gasification reaction of the semi-coke powder; the produced gas from the gasification furnace needs to be subjected to heat recovery through a steam generator before entering a gas-solid separator, and the produced medium-temperature steam can be used as a gasification agent to supplement the requirements of a gasification process;
in order to increase the energy density of the garbage pyrolytic semicoke and improve the heat value of gasified gas, the pyrolytic semicoke and the coal coke of the garbage can be co-gasified at the reaction temperature of 750 ℃ and 950 ℃ and the mixing ratio of the pyrolytic semicoke and the coal coke is 1: 1.
The gasification furnace of the invention generates output gas with higher heat value (the composition is about phi (H)2)=20%-26%,φ(CO)=28%-42%,φ(CO2)=16%-23%,φ(CH4) 10-20 percent and 10-13MJ/m of calorific value3) (ii) a The gasified semicoke residue and cloth bag ash contain rich organic carbon and can be used for producing organic carbon fertilizer, harmful heavy metals such as lead, cadmium, arsenic and the like can be treated by adopting a ceramic mode, and the formed ceramic material can be used for floor tiles and the like. The heat required by the gasification of the semi-coke powder in the gasification furnace comes from high-temperature flue gas generated by combustion of combustible gas generated by gasification, and the gas generated by the gasification furnace exchanges heat through a heat exchanger to recover heat and produce medium-temperature steam. The process has self-sufficient energy, high gasification efficiency and high heat value of the produced gas, and has obvious advantages
Mainly include pyrolysis oven and gasifier, wherein: the pyrolysis furnace adopts an external heating and inner cylinder feeding mode, a heating flue gas inlet pipeline is arranged at the top of the pyrolysis furnace and is respectively used for drying and pyrolyzing the household garbage to generate pyrolysis gas, and a pyrolysis gas conveying pipeline is used for leading out the pyrolysis gas for later use;
the pyrolysis furnace adopts a mode of externally heating flue gas, the inner cylinder is filled with materials and then is fed into the pyrolysis furnace, flue gas with different temperatures is respectively introduced into the heat exchange tubes for drying and pyrolyzing the household garbage, moisture in the garbage is heated and evaporated by the flue gas in the drying stage, and after the garbage is dried, the flue gas with higher temperature is switched to be used for pyrolyzing the garbage;
the top of the pyrolysis furnace is connected with a pyrolysis gas conveying pipeline for conveying pyrolysis gas out, and the reacted semicoke is cooled, screened and crushed to prepare semicoke powder for later use;
the gasification furnace is internally composed of a plurality of small-diameter steel pipes, an entrained flow bed structure with high-temperature flue gas heated externally is adopted, pyrolysis gas discharged from the pyrolysis furnace carries semi-coke powder to be fed, water vapor is used as a gasification agent, the gasification gas generated by gasification is subjected to gas-solid separation after heat exchange and cooling, the gas is purified for later use, and the solid is collected and used for preparing other additional products;
in the gasification furnace, after the domestic garbage is mixed with the kitchen and the sludge, the domestic garbage contains high-content calcium and potassium elements and metals with catalytic action, such as iron, magnesium, manganese and the like, most of the metals can be converted into metal oxides with certain catalytic action in the pyrolysis and gasification processes,
such as CaO, MgO, etc., the presence of these metal oxides is advantageous for increasing the yield of combustible gas in the gasification process when the gasification temperature is higher than 700 ℃;
the heat source required by gasification of the gasification furnace is high-temperature flue gas generated by combustion of combustible gas generated by gasification, part of the flue gas is used for heat recovery to generate steam after coming out of the gasification furnace, and part of the flue gas is used for pyrolysis and drying of garbage, a preheating unit of air and the like;
as a further optimization of the invention, the gasification furnace can preferably adopt a two-section (gasification section and methanation section) entrained flow bed structure, the gas produced by pyrolysis is used as a carrier to send the semi-coke powder into the gasification furnace for gasification reaction, the gasified gas after reaction enters the methanation section for methanation reaction under the action of a catalyst, the yield of methane in the high-yield gas is increased, and the heat released by methanation can be used for preparing the gasification agent steam required by the gasification reaction after being recovered;
as a further preferred aspect of the present invention, the catalyst added in the gasification reaction in the gasification furnace is preferably calcium carbonate or calcium oxide;
as a further preferred aspect of the present invention, the water vapor required for the gasification reaction in the gasification furnace is derived from pyrolysis gas on the one hand and intermediate-temperature water vapor generated by heat recovery on the other hand;
effect verification:
after drying and pyrolyzing municipal solid waste, the main components of the pyrolysis gas generated by drying and pyrolyzing municipal solid waste are CO and CH4The proportion is basically 1: 1; after drying, pyrolysis and gasification, when the gasification temperature is higher than 850 ℃, the conversion rate of carbon can reach more than 99 percent, and combustible gas (H) in the gas is produced2,CO,CH4) Can reach more than 92 percent, wherein H2The components can reach over 59 percent, and the heat value of the obtained combustible gas can reach 10MJ/Nm3The above.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.