EA034502B1 - Method of producing granulated biofuel and synthesis gas with low gum content from biowaste - Google Patents

Abstract

The invention relates to the field of communal services, agriculture and egergy, in particular, to a method of producing granulated biofuel and synthesis gas with low gum content from biomass, including biowaste such as solid domestic waste, manure, dropping, wood waste, sunflower, millet, rice, etc. husks.

Description

Technical field

This invention relates to the field of public utilities, agricultural production and energy, in particular to a method for producing from biomass, including such types of biowaste as municipal solid waste, manure, litter, wood waste, husk of sunflower, millet, rice, etc., granular biofuels and low tar synthesis gas.

State of the art

Bio waste is subjected to thermochemical treatment, which consists in preliminary drying and low-temperature pyrolysis of biomass, i.e. in heating biomass to a temperature of 150-300 ° C in a reactor in a gaseous environment with a low oxygen content.

With low-temperature pyrolysis of biomass, non-combustible components are removed from it: moisture and, to a large extent, oxygen. The loss of hydrogen in this case is negligible, due to which the heat of combustion of the heat-treated biomass increases.

During low-temperature pyrolysis, resins begin to precipitate from the biomass, which fill the pores in the biomass, and when it cools, they solidify, giving the biomass hydrophobic properties.

In addition, pathogenic bacteria die in the biomass, and the hydrophobic properties of biomass prevent the adsorption of atmospheric moisture and the reproduction of bacteria.

The biomass is pressed in granulator presses, in which the biomass is pushed with the help of scooters through dies of a certain diameter and length, providing its necessary compression.

The processes of drying, pressing, low-temperature pyrolysis require large expenditures of thermal and electric energy. For example, only for biomass pressing, about 200 kW of electric energy per 1 ton of produced granules is required.

On the other hand, in the process of drying and low-temperature pyrolysis of biomass secondary sources of thermal energy are formed, the use of which can significantly increase the energy efficiency of the process.

Also in the process of low-temperature pyrolysis, not only a solid product is formed that does not contain pathogenic microflora, has a higher calorific value and hydrophobicity, but also liquid and gaseous products that contain a certain amount of combustible substances and which can be suitably processed into synthesis gas.

Synthesis gas, in turn, can be used as raw material for the production of synthetic fuel, electric and thermal energy.

However, the synthesis gas thus obtained must be cleaned of solid particles and resins, the concentration of which must be reduced to 100 mg / m ³ . Purification of synthesis gas from solid products and, mainly, from resins is necessary because the resins begin to condense at temperatures below 200 ° C, which leads to the rapid growth of solid deposits on all unheated surfaces of the equipment, which greatly complicates the operation of equipment for production biofuels and synthesis gas, as well as equipment for the storage and transportation of synthesis gas and equipment for its further processing.

It is also obvious that synthesis gas containing a significant amount of solid particles and resins cannot be burned in internal combustion engines due to the rapid wear of the cylinders and piston group of these engines.

Patent RU 2516533 C10J3 / 66, C10J3 / 48, C01B3 / 02 discloses a method and apparatus for producing synthesis gas with a low resin content.

The method provides for sequential thermochemical treatment of biomass in fluidized bed reactors installed one after the other along the gases released during thermochemical treatment.

In this case, an allometric pyrolysis process takes place in the first reactor in a water vapor medium at a temperature of 600-700 ° C, and additional thermal energy is supplied to the reactor using electric heaters.

In the second reactor, a pyrolysis process occurs at a temperature of 800-1000 ° C (preferably 850-950 ° C), the layer consisting of coke particles removed from the first reactor, which are maintained in a fluidized state by the gaseous pyrolysis products obtained in the first reactor, and heat fed into the layer with the help of electric heaters.

The disadvantages of the method and device are the low degree of conversion of resins and gaseous products into synthesis gas in a second reactor in which the pyrolysis process occurs at a temperature of 800-1000 ° C (preferably 850-950 ° C), because it is well known that the operation of chemical fluidized bed reactors is characterized by a breakthrough of the gas phase through the reactor until complete conversion is completed;

low energy efficiency, expressed in the necessity of introducing thermal energy into the second along the gases released during thermochemical processing of biomass, a pyrolysis reactor;

low energy efficiency, expressed in the need for thermal energy to decompose water vapor entering the second reactor for pyrolysis together with gaseous products

- 1,034,502 pyrolysis obtained in the first reactor;

low reliability of the second downstream gas reactor for pyrolysis, as maintaining the bed of coke particles in a fluidized state depends on the flow rate of the gaseous pyrolysis products obtained in the first reactor, while this amount may change during the transition from processing one type of biomass to another.

An object of the invention is to increase the efficiency of processing gaseous pyrolysis products into synthesis gas; increasing the energy efficiency of the process;

improving the reliability of the installation that implements the proposed process.

Description of the invention

This goal is achieved by the fact that the method of producing granular biofuel and synthesis gas with low tar content from biowaste consists in thermochemical processing of biomass by low-temperature pyrolysis in a fluidized bed reactor converted to a fluidized state by water vapor followed by thermochemical processing of the obtained gaseous products, where is to increase the efficiency of processing gaseous products of low-temperature pyrolysis into synthesis gas, to increase the energy efficiency The process and reliability of the installation that implements the process, after processing by the low-temperature pyrolysis method, the resulting solid product is separated from the gas-vapor stream in a known manner, for example, in a cyclone or filter and sent to granulation, the gas-vapor stream purified from the bulk of the solid particles is cooled and condensed, the condensate containing organic particles is sent to the meta-tank for anaerobic digestion in order to obtain methane, the methane obtained, dried and refined by known methods, it is burned as fuel in an internal combustion engine of an electric generating set, which fully or partially supplies electric power to a set of equipment, exhaust gases from an internal combustion engine of an electric generating set together with non-condensable gaseous products of low-temperature pyrolysis with a temperature of at least 250-300 ° C are fed to the pyrolysis reactor from above into a dense layer of biochar granules obtained by pyrolysis of part of a granular solid product at low temperature of pyrolysis temperature in the bed is maintained biochar not less than 800 and not higher than 1000 ° C.

In FIG. 1 shows a diagram of a complex of equipment that implements a method for producing granular biofuels and synthesis gas with a low tar content from biowaste.

The complex consists of a boiler for the production of water vapor 1, a superheater 2, a reactor for low-temperature pyrolysis of biomass 3, a cyclone 4 for separating biomass subjected to low-temperature pyrolysis from a gas-vapor stream, a device for cooling superheated water vapor 5, metaten 6, equipment for granulating biomass 7, electricity generating installation 8 with an internal combustion engine, a reactor for biomass pyrolysis and conversion of gaseous products of low-temperature pyrolysis into synthesis gas 9.

The proposed method is implemented on the described complex of equipment as follows.

In boiler 1, water vapor is generated by burning the original biomass or other type of fuel, which overheats in the superheater 2 to a temperature of 250-300 ° C.

The superheater 2 has a traditional design, for example, made in the form of a coil heat exchanger installed in the furnace of the boiler 1.

After the superheater 2, superheated steam with a temperature of 300 ° C enters the reactor 3 for low-temperature pyrolysis of biomass.

The reactor 3 (Fig. 2) is an apparatus 1 with a fluidized bed of inert material 2, for example silica sand, supported by a grate 3 for distributing superheated water vapor introduced into the fluidized bed. The reactor is equipped with a unit for introducing superheated steam 4 under the grate 3, a unit for outputting 5 gas-vapor mixture, located in the upper part of the apparatus 1, a unit 6 for supplying the initial biomass for processing, having a known design, for example, in the form of a screw.

In the reactor 3, the process of drying and low-temperature pyrolysis of biomass, i.e., pyrolysis at a temperature of 250-300 ° C, occurs, as a result of which, as shown by experiments with this type of biowaste, such as chicken litter with litter, the carbon content can be increased 1.16 times , and the oxygen content is reduced by 2.8 times. In this case, the net calorific value of the resulting fuel can be increased 1.13 times to 18.8 MJ / kg.

Also, as the experimental results show, during low-temperature pyrolysis, biomass is completely disinfected and the biogranules acquire hydrophobic properties, which prevents re-infection of the biomass.

In addition to the solid product, gaseous products are formed during low-temperature pyrolysis, which are divided into condensable and non-condensable.

- 2 034502

Condensable products include water vapor released from biomass, resins, some organic acids and other organic products that condense at temperatures below

200 ° C. Non-condensable gases include carbon dioxide, carbon monoxide, hydrogen, methane and other gases.

As a result of drying and low-temperature pyrolysis in reactor 3 (Fig. 1), the initial biomass loses, as shown by experiments with litters with litter, up to 50% of the initial weight.

Therefore, the heat-treated biomass particles are carried away from the reactor 3 (Fig. 1) together with the gas-vapor stream to cyclone 4 (Fig. 1), where solid particles (heat-treated biomass) are separated from the gas-steam stream.

Next, the gas-vapor stream is subjected to cooling to the temperature of condensation of water vapor in the cooling device 5 (Fig. 1), which is a traditional design, for example, an air condenser, a shell-and-tube steam-water heat exchanger.

The obtained condensate contains, as shown by experiments, about 3-4% of organic substances (biomass particles, resins), the presence of which, as follows from the literature, allows biogas (methane) to be obtained by anaerobic digestion. For these purposes, the condensate is sent to meta-tank 6 (Fig. 1), where the process of methane production by anaerobic digestion takes place.

Subjected to drying and low-temperature pyrolysis, the disinfected biomass is sent to the complex for granulating biomass 7 (Fig. 1). This is a complex of traditional design, consisting of a biomass crusher, a storage hopper of crushed biomass, a press granulator of biomass, a device for cooling the crushed biomass.

Obtained as a result of anaerobic digestion of condensate containing organic particles, methane, after processing by known methods (drying, removal of mechanical impurities) is used as fuel for an internal combustion engine of an electric generating unit 8 (Fig. 1). The electricity produced by the installation 8 is used to fully or partially supply electricity to the entire complex of equipment used to implement the method.

Installation 8 (Fig. 1) also produces thermal energy contained in the exhaust gases of the internal combustion engine of installation 8 (Fig. 1).

The obtained granular heat-treated biomass with a higher calorific value, which has hydrophobic properties and does not contain pathogenic microflora, is divided into two streams: most of this biomass is sent to the consumer as biofuel, and a smaller part is sent to reactor 9 (Fig. 1) for pyrolysis of biomass and the conversion of gaseous non-condensable products of low temperature pyrolysis into synthesis gas containing a minimum amount of resins.

The reactor 9 (Fig. 3) is a pyrolysis apparatus 1 of a known design with a dense layer of granules 2 moving on top of the granule 2, supported by a grate 3. The reactor is equipped with a unit 4 for loading a granular solid product of low-temperature pyrolysis located in the upper part of the apparatus 1, and a unit unloading ash 5, located in the lower part of the apparatus 1, as well as the input unit 6 of the exhaust gas mixture of the internal combustion engine of installation 8 (Fig. 1) and non-condensable gaseous products of low-temperature pyrolysis m in the upper part of the apparatus 1, and node 7 for outputting the resulting synthesis gas located in the lower part of the apparatus 1.

The following processes occur in reactor 9.

As you know, the main components of biomass are cellulose, hemicellulose and lignin. When biomass is heated, the destruction of these components occurs: at a temperature of 180-300 ° C, destruction of hemicellulose is observed, in the temperature range 270-370 ° C - destruction of cellulose, in the temperature range 200-540 ° C, destruction of lignin is observed. Moreover, the destruction of hemicellulose and lignin is an exothermic process, while the process of destruction of cellulose to 450 ° C is an endothermic process, and at a higher temperature it is an exothermic process. In this case, the free heat of exothermic reactions reaches 1000-1150 kJ / kg. As follows from the literature, this thermal effect is sufficient for a dry biomass heated to a temperature of 240-250 ° C, in the absence of heat loss, to self-heat up to 800 ° C and higher.

Experiments show that self-heating of biomass is observed in a dense layer of almost dry (humidity less than 8%) granular solid product of low-temperature pyrolysis, heated to a temperature of 240-250 ° C.

Such heating occurs when a mixture of exhaust gases of an internal combustion engine having a temperature of 550-650 ° C and non-condensable gaseous products of low temperature pyrolysis having a temperature of 250-300 ° C is supplied to the upper part of the layer of granular solid product of low temperature pyrolysis 2 (Fig. 3).

Then, as the gas stream moves from top to bottom, self-heating of the entire layer of granular solid product of low-temperature pyrolysis in reactor 9 takes place to a temperature of 800-1000 ° C and above.

In this temperature range, the process of pyrolysis of a granular solid product of low-temperature pyrolysis in reactor 9 occurs, as a result of which this product turns into bio-char.

- 3 034 502

When interacting with hot biochar non-condensing gaseous products of low-temperature pyrolysis of biomass, the following reactions occur:

CO ₂ + C 2 CO (1)

H ₂ O + C CO + H ₂ (2)

С ₄ Н ₄ О ₂ 2 СО + 2 Н ₂ (3) СН ₂ О ₂ + С 2 СО + Н ₂ (4) СзНбОз 3 СО + 3 Н ₂ (5) СЗН ₆ О СО + 3 Н ₂ + 2 С (6) С ₅ Н ₄ О ₂ ^ 2 СО + 2 Н ₂ + 3 С (7)

The degree of heterogeneous decomposition of gaseous products depends both on the temperature in the zone of their contact with biochar and on the residence time of volatiles in this zone.

It was experimentally proved that at a temperature in the biochar layer of 1000 ° C and a contact time of biochar with gaseous products of the order of 4 s, almost complete conversion of gaseous products to synthesis gas occurs.

The reactivity of biochar at such a temperature is so high that almost the entire volume of CO _{2 has} been converted to CO.

At a lower temperature, an increase in the conversion coefficient can be achieved by increasing the thickness of the biochar layer and increasing the residence time of gaseous products in the biochar layer.

In the table. Figure 1 shows the composition and the calorific value of synthesis gas obtained from two types of biomass (wood and peat), which underwent low-temperature pyrolysis and heat treatment in a layer of hot biochar.

Table 1

Mode, material The composition of the synthesis gas,% (volume) Calorific value N With CH ₄ MJ / m ³ Bial coal temperature 850 ° C Wood 39 28 10 11.3 Peat 40 27 8 10.6 Biochar temperature 950 ° C Wood 47 41 1 10.6 Peat 43 40 2 10,4 Bio-charcoal temperature 1000 ° C Wood 46 46 0.4 10.9 Peat 49 41 0.1 10.8

As follows from the table. 1, in a dense layer of hot biochar deep processing of gaseous products of low-temperature pyrolysis of biomass takes place and synthesis gas can be obtained, 90% or more consisting of a mixture of carbon monoxide and hydrogen. This synthesis gas can be used to produce synthetic liquid fuel or, for example, it can be used as fuel for boiler 1 (Fig. 1) in the described equipment package.

A dense layer of hot biochar eliminates the breakthrough of gaseous products of low-temperature pyrolysis without heat treatment. In addition, the use of granular biochar particles reduces the solids content in the resulting synthesis gas, which simplifies its further use, because requires less cleaning costs from mechanical impurities.

Experiments show that due to the self-heating of biomass in reactor 9, the cost of thermal energy for the pyrolysis of biomass in this reactor and maintaining the temperature of biochar in reactor 9 (Fig. 1) at a given level are reduced by about 5 times in comparison with the cost of thermal energy, which would take place on these processes without taking into account self-heating.

Maintaining the temperature of biochar in the reactor 9 is due to a continuously passing process of self-heating and pyrolysis of the granular solid product of low-temperature pyrolysis newly entering the reactor 9 (Fig. 1). This solid granular product of low-temperature pyrolysis re-entering the reactor 9 compensates for the loss of biochar in the reactor 9 (Fig. 1), which is triggered as a result of reactions (1) - (7).

Ash from the reactor 9 (Fig. 1) is discharged through an ash discharge unit 5 (Fig. 3).

Thus, the proposed method for producing granulated biofuels or fertilizers with improved characteristics and not containing pathogenic microflora from biomass and a set of equipment that implements this method increase the efficiency of processing gaseous products of low-temperature pyrolysis into synthesis gas by eliminating the leakage of the gaseous product of low-temperature pyrolysis through

- 4,034,502 biochar layer without treatment. The efficiency of the process of processing gaseous products of low temperature pyrolysis into synthesis gas is also determined by the fact that due to the use of superheated water vapor for the low temperature pyrolysis process with its subsequent condensation, the obtained gaseous products of low temperature pyrolysis do not contain ballast in the form of nitrogen or its oxides;

increasing the energy efficiency of the process through the use of thermal energy of the exothermic effect observed during the pyrolysis of biomass, as well as through the generation of biogas from the condensate of superheated water vapor and the use of this biogas as a fuel of the internal combustion engine of an electric generating unit, which fully or partially compensates for the entire complex of equipment’s electricity requirements ;

improving the reliability of the installation that implements the proposed process, since the stable operation of the reactor for the pyrolysis and processing of gaseous non-condensable products of low-temperature pyrolysis into synthesis gas does not depend on the performance of the reactor for low-temperature pyrolysis for non-condensable gaseous products.

Claims (4)

1. A method of producing synthesis gas with a low resin content from biomass, including: a) thermochemical treatment of biomass by low-temperature pyrolysis at a temperature of 250-300 ° C in a fluidized bed reactor, converted to a fluidized state by water vapor, to obtain a solid product and a gas-vapor mixture; b) separation of the solid product from the gas-vapor mixture and its granulation; c) feeding part of the granular solid product to the pyrolysis reactor with pyrolysis and formation of biochar; d) cooling and condensing the separated gas-vapor mixture to obtain a condensed product and a non-condensable gaseous product; e) directing the obtained condensed product containing organic particles to the meta-tank for anaerobic digestion to produce methane; f) burning the obtained methane as fuel in an internal combustion engine of an electric generating installation with the generation of electricity, fully or partially supplying equipment for implementing the method; g) the supply of exhaust gases from the internal combustion engine of the power generating installation together with non-condensable gaseous products at a temperature of 250-300 ° C into the above pyrolysis reactor into the biochar layer obtained in stage c) from above, with the formation of synthesis gas. 2. The method according to claim 1, characterized in that the exhaust gases from the internal combustion engine of the power generating installation together with non-condensable gaseous products of low-temperature pyrolysis are fed to the pyrolysis reactor with a temperature of not lower than 250-300 ° C and not higher than 650 ° C. 3. The method according to claim 1, characterized in that the biochar temperature is maintained not lower than 800 and not higher than 1000 ° C. 4. The method according to claim 1, characterized in that the separation of the solid product from the gas-vapor mixture is carried out using a cyclone or filter.