Patent Publication Number: US-2023134219-A1

Title: Biomass pyrolysis device and method with optimized matching of thermal energy and microwave energy

Description:
TECHNICAL FIELD 
     The present invention relates to a pyrolysis device and a pyrolysis method, and in particular to a biomass pyrolysis device and a biomass pyrolysis method for optimal matching of thermal energy and microwave energy. 
     BACKGROUND 
     Biomass energy is not only renewable energy with wide distribution and large resource quantity but also environment-friendly low-carbon energy, and biomass energy plays an important role in the whole energy system, so that the development of biomass energy is of great significance for improving energy structure and developing green low-carbon economy. Biomass is mainly composed of woody raw materials, herbaceous raw materials, livestock manure, domestic waste, domestic sewage and the like. 
     At present, thermochemical conversion of biomass resources is achieved mainly by methods such as combustion, pyrolysis and gasification, wherein the pyrolysis is to cut off chemical bonds of macromolecular compounds in biomass by using thermal energy under anaerobic or anoxic conditions, and crack the macromolecular compounds into volatile substances with smaller molecules; meanwhile, the product distribution of pyrolysis products can be regulated by controlling operation parameters, so that biomass energy can be converted into energy products such as biochar, bio-oil and pyrolysis gas. 
     Traditional heating mode for biomass pyrolysis is characterized in that pyrolysis heat is transmitted from the surface of a biomass feedstock to the inside of the biomass feedstock in a heat conduction or convection mode, while microwave heating converts microwave energy into thermal energy in a dissipation mode. As a unique heating method, microwave heating has obvious advantages in the pyrolysis of solid organic waste, it has fast heating rate, performs uniform heating on the whole raw material, and provides some pyrolysis conditions different from traditional pyrolysis, so that different pyrolysis characteristics are formed, the control for temperature regulation, pyrolysis process and desired final products is easy, and the obtained biochar and bio-oil have high quality and great potential for subsequent utilization. However, the microwave absorption capability of the biomass feedstock is weak, and it is difficult to increase the heating rate merely by the microwave absorption factors (moisture and trace elements such as Na +  and K + ,) in biomass; therefore, it is necessary to bake and carbonize the biomass feedstock in the traditional heating mode in advance to increase its absorption constant and improve the utilization of microwave energy. 
     SUMMARY 
     Objective: The present invention aims to provide a biomass pyrolysis device and a biomass pyrolysis method for optimal matching of thermal energy and microwave energy, which reasonably utilize energy, and are green and environment-friendly. 
     Technical scheme: The biomass pyrolysis device for optimal matching of thermal energy and microwave energy of the present invention comprises a feeding device and a condensing unit, and further comprises a power generation system, a drying device and a microwave pyrolysis device; wherein the drying device is a cylinder nested with a flue gas layer and a material layer, a material inlet of the drying device is connected with a feeding device, and a volatile outlet is connected with a condensing unit; the microwave pyrolysis device is connected with a material outlet of the drying device, and a pyrolysis gas outlet of the microwave pyrolysis device is connected with the condensing unit; the condensing unit is connected with the power generation system, and waste gas generated by the power generation system is introduced into the flue gas layer of the drying device. 
     The biomass pyrolysis method for optimal matching of thermal energy and microwave energy of the present invention based on the pyrolysis device described above comprises:
         (1) feeding a material into the drying device through the feeding device for drying, and providing a drying heat source by waste gas generated after the combustion of pyrolysis gas;   (2) performing pyrolysis on the dried material, and condensing the generated pyrolysis gas;   (3) feeding the residual non-condensed gas after purification into an internal combustion engine for combustion, wherein the waste gas generated by combustion is the drying heat source in the step (1), the temperature is 400-600 ° C., the internal combustion engine is connected with a generator, and the generated electrical energy supplies energy for the pyrolysis process in the step (2); and   (4) treating the waste gas after heat exchange by the drying device and then discharging the waste gas.       

     Beneficial effects: The present invention has the following remarkable advantages compared with the prior art. 
     According to the present invention, a biomass feedstock is baked by adopting thermal energy, the microwave absorption constant of the biomass feedstock is increased, and then the biomass feedstock is fed into the microwave pyrolysis device, so that the pre-carbonized biomass in microwave has higher energy absorption efficiency and the greatly improved energy utilization, so as to achieve the purpose of optical matching of thermal energy and microwave energy; meanwhile, biomass energy can be high-efficiently converted into chemical raw materials or fuels, and these products have very broad prospects for their characteristics, which can not only improve the economic value of biomass but also alleviate environmental pollution and energy problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of the structure of the device disclosed herein; and 
         FIG.  2    is a cross-sectional view of the drying device of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The technical scheme of the present invention is further described below with reference to the drawings. 
     As shown in  FIG.  1   , the present embodiment comprises a feeding device, a condensing unit  19 , a power generation system, and a drying device  7  and a microwave pyrolysis device  13  arranged between the feeding device and the condensing unit  19 . 
     The feeding device comprises a material bin  1 , a screw elevator  2  and two air lockers, the material bin  1  is connected with the screw elevator  2 , an outlet  3  of the screw elevator is connected with the air locker  4 , the air locker  4  is connected with the air locker  5 , and the air locker  5  is connected with a material inlet  6  of the drying device  7 . 
     The drying device  7  is a cylinder nested with a flue gas layer and a material layer. The drying device  7  is provided with a first flue gas layer  71  along a central axis and a second flue gas layer  73  along an outer wall, and an annular space between the first and second flue gas layers is the material layer  72 . An inlet  9  of the flue gas layer is connected with a waste gas outlet of the power generation system and is supplied with heat by the waste gas of the power generation system. The design that the flue gas layer and the material layer are nested can not only fully utilizes the heat of waste gas, but also make the flue gas and the material fully exchange heat, thereby improving drying efficiency. 
     A material outlet  8  of the drying device  7  is connected with the microwave pyrolysis device  13 , and a coke outlet  16  of the microwave pyrolysis device  13  is connected with a carbon storage bin  17 . The microwave pyrolysis device  13  comprises a microwave generator  14  arranged on the surface of the microwave pyrolysis device and a screw conveyor arranged at the central axis of the inside of the microwave pyrolysis device. A pyrolysis gas outlet  15  of the microwave pyrolysis device  13  and a volatile outlet  11  of the drying device  7  are connected with a gas inlet  18  of the condensing unit  19 . Volatile component gas and pyrolysis gas are condensed in the condensing unit. 
     The condensing unit  19  is a spray tower-type device, a spray layer is arranged inside of the condensing unit, one side of the condensing unit  19  is provided with a gas inlet, the other side thereof is provided with a gas outlet, and the inlet and the outlet have height difference, so that the condensable components in the gas are fully condensed. The non-condensed combustible gas is discharged from an outlet  20  of the condensing unit and introduced into the power generation system. 
     The power generation system comprises a gas purification device  21 , an induced draft fan  22 , an internal combustion engine  23  and a generator  24  sequentially arranged behind the condensing unit  19 . The non-condensable gas is purified and fed to the internal combustion engine for combustion, the heat provided by combustion enables the generator  24  to generate power, and the power is used for supplementing electrical energy of the microwave generator in the microwave pyrolysis device  13 , so as to realize the full utilization of resources and energy. The internal combustion engine  23  is also connected with the flue gas layer of the drying device  7 , an outlet  10  of the flue gas layer is connected with a waste gas purification device  26 , and the flue gas after heat exchange is treated and then discharged. Different power generation devices can be selected according to biomass treatment capacity, and the present embodiment takes an internal combustion engine as an example. 
     The specific working principle of the present device is as follows. 
     A biomass feedstock is fed out from the material bin  1  through the material outlet  3  of the screw elevator  2 , and introduced into the drying device  7  through the air locker  4  and the air locker  5  from the material inlet  6  of the drying device  7 , and the biomass feedstock is dried and baked at a temperature of 250-350° C. to remove moisture from the biomass feedstock and partially pre-carbonize it. The generated volatile gas is introduced into the condensing unit  19  from the gas outlet  9 . 
     The dried and upgraded biomass is introduced into a heater from a material inlet  12  of the microwave pyrolysis device  13 , and is subjected to deep pyrolysis under the heating action of the microwave generator. The generated biochar is introduced into the carbon storage bin  17  through the material outlet for storage and collection. The generated pyrolysis gas is introduced into the spray-type condenser  19  through the gas outlet  15  to collect bio-oil. 
     The non-condensed combustible gas in the spray-type condenser  19  is discharged into the internal combustion engine  23  through the gas purification device  21  by the induced draft fan  22  for combustion, which drives the generator  24  to generate power. High-temperature waste gas generated by combustion is introduced into the rolling-type drying-baking device  7  as a heat source, and the exhaust gas generated after heat exchange and drying-baking is introduced into the waste gas purification device  26  and then is discharged. 
     Biomass is introduced into the rolling-type drying-baking device through two air lockers under the action of the elevator. After drying and baking, the moisture in the biomass is removed and the raw material is partially pre-carbonized. Subsequently, the upgraded biomass is introduced into the microwave pyrolysis section through the screw elevator for deep pyrolysis to obtain biochar with higher quality. The generated pyrolysis gas is collected by the spray-type condenser to obtain bio-oil with high quality. Meanwhile, the internal combustion engine enables the power generation system to generate electrical energy, the electrical energy is used for supplementing energy consumption of the microwave pyrolysis device, and the waste gas is used for heating the drying-baking section; the system has high energy efficiency and no exhaust gas emission during operation, and the operation parameters can be adjusted according to the biomass feedstock, so that the system has high operation safety and low cost.