EA039214B1 - Method for wet torrefication (carbonization) of biomass - Google Patents

Abstract

The invention relates to the field of public utilities, agricultural production and energy, in particular, to a method of wet torrefaction (carbonization) of biomass for obtaining hydrocoke, comprising (a) biomass drying; (b) biomass grinding; (c) treatment of dried and ground biomass with superheated steam at excess pressure in a fluidized bed reactor to obtain heat-treated biomass particles and waste water steam, wherein heat-treated biomass particles are continuously removed from the reactor along with the waste steam stream; (d) separation of heat-treated particles of biomass and waste steam, wherein the biomass is loaded into the reactor continuously; biomass processing is carried out at a temperature not higher than 300 C; biomass drying is carried out using the heat of the waste water steam obtained at step (d); biomass grinding is carried out to produce particles of such a size that their movement rate after loss of 40-50% of the mass is 2-3 times higher than the minimum fluidization rate of biomass particles; superheated steam is fed into the reactor at such a rate that the steam velocity in the reactor referred to the cross section of the empty reactor is no more than 1.5 times higher than the minimum fluidization rate of the biomass particles.

Description

Technical field

The invention relates to the field of public utilities, agricultural production and energy, in particular to a method of wet torrefaction (carbonization) of biomass to produce hydrocoke.

State of the art

Biomass is widely used as a food product or as a renewable raw material for energy production, as well as a raw material for the production of various chemicals and activated carbons. In recent years, hydrothermal carbonization, a biomass treatment method, has attracted the attention of researchers due to the possibility of obtaining a solid product, which is called hydrocoke [Z. Liu, F.S. Zhang, Removal of lead from water using biochars prepared from hydrothermal liquefaction of biomass, J. Hazard. mater. 167 (2009) 933-939, Z. Liu, F.S. Zhang, J. Wu, Characterization and application of chars produced from pinewood pyrolysis and hydrothermal treatment, Fuel 89 (2010) 510-514].

The latter can be further used for the synthesis of activated carbon [M. Sevilla, A. Fuertes, R. Mokaya, High density hydrogen storage in superactivated carbons from hydrothermally carbonized renewable organic materials, Energy Environ. sci. 4 (2011) 1400-1410, M. Sevilla, AB Fuertes, Sustainable porous carbons with a superior performance for CO ₂ capture, Energy Environ. sci. 4 (2011) 1765-1771. 802 A. Jain et al./Chemical Engineering Journal 283 (2016) 789-805, Sevilla, JA Macia-Agull0, AB Fuertes, Hydrothermal carbonization of biomass as a route for the sequestration of CO ₂ : chemical and structural properties of the carbonized products, Biomass Bioenergy 35 (2011) 3152-3159].

It is noted that hydrothermal carbonization of biomass makes it possible to obtain hydrocoke with a higher concentration of oxygen functional groups and a low degree of aromatization, which makes the resulting hydrocoke more suitable for further chemical activation [M. Sevilla, A. Fuertes, R. Mokaya, High density hydrogen storage in superactivated carbons from hydrothermally carbonized renewable organic materials, Energy Environ. sci. 4 (2011) 1400-1410, M. Sevilla, A. Fuertes, The production of carbon materials by hydrothermal carbonization of cellulose, Carbon 47 (2009) 2281-2289].

Hydrocoke is also recommended for use as a clean solid fuel [Zhao P., Shen Y., Ge S., Chen Z., Yoshikawa K. Clean solid biofuel production from high moisture content waste biomass employing hydrothermal treatment. Apple Energy 2014; 131:345-67, Bach Q.-V., Skreiberg 0. Upgrading biomass fuels via wet torrefaction: a review and comparison with dry torrefaction. Renew Sustain Energy Rev 2016; 54:665-577, Nizamuddin S., Baloch H.A., Griffin G.J., Mubarak N.M., Bhutto A.W., Abro R., et al. An overview of the effect of process parameters on hydrothermal carbonization of biomass. Renew Sustain Energy Rev 2017; 73: 1289-1299, Volpe M., Fiori L. From olive waste to solid biofuel through hydrothermal carbonization: the role of temperature and solid load on secondary char formation and hydrochar energy properties. J Anal Appl Pyrolysis 2017; 124:63-72], due to a decrease in the moisture content of the obtained biofuel, a decrease in the content of chlorine and nitrogen compounds in it, which reduces harmful emissions during combustion [Zhao P., Shen Y., Ge S., Chen Z., Yoshikawa K. Clean solid biofuel production from high moisture content waste biomass employing hydrothermal treatment. Apple Energy 2014; 131:345-367].

The wet torrefaction process is considered to be similar to the hydrothermal carbonization process.

The wet torrefaction process takes place in an aqueous medium at a temperature of 180-260°C [Yan W., Acharjee T.C., Coronella C.J., Vasquez V.R.. Thermal pretreatment of lignocellulosic biomass. Environ Progress Sustain Energy 2009; 28:435-440, Chen W.-H., Ye S.-C., Sheen H.-K. Hydrothermal carbonization of sugarcane bagasse via wet torrefaction in association with microwave heating. Bioresour Technol 2012; 118:195-203, Yan W., Hastings J.T., Acharjee T.C., Coronella C.J., Vasquez V.R. Mass and energy balances of wet torrefaction of lignocellulosic biomass. Energy Fuels 2010; 24:4738-4742, Runge T., Wipperfurth P., Zhang C. Improving biomass combustion quality using a liquid hot water treatment. Biofuels 2013; 4:73-83, Bach Q.-V., Tran K.-Q., Khalil R.A., Skreiberg 0, Seisenbaeva G. Comparative assessment of wet torrefaction. Energy Fuels 2013; 27:6743-6753, Yang W., Shimanouchi T., Iwamura M., Takahashi Y., Mano R., Takashima K., et al. Elevating the fuel properties of Humulus lupulus, Plumeria alba and Calophyllum inophyllum L. through wet torrefaction. fuel 2015; 146:88-94, Bach Q.-V., Tran K.-Q., Khalil R.A., Skreiberg 0. Wet torrefaction of forest residues. Energy Procedia 2014; 61:1196-1199].

The wet torrefaction process is implemented in batch reactors and includes the following stages [Chen W.-H., Ye S.-C., Sheen H.-K. Hydrothermal carbonization of sugarcane bagasse via wet torrefaction in association with microwave heating. Bioresour Technol 2012; 118:195-203, Bach Q.-V., Tran K.Q., Khalil R.A., Skreiberg 0, Seisenbaeva G. Comparative assessment of wet torrefaction. Energy Fuels 2013; 27:6743-6753]:

loading water and biomass into the reactor in the required ratio, heating the reactor to the required temperature with a rise in pressure inside the reactor to prevent water boiling, the process of wet torrefaction of biomass within a specified time, rapid cooling of the reactor,

- 1 039214 release of pressure and unloading of hydrocoke with subsequent drying.

From the foregoing, the disadvantages of wet torrefaction technology are obvious when it is implemented in a known way:

the frequency of the process, the need to use high-pressure reactors, a large volume of contaminated water that requires further processing.

A known method of carbonization of biomass, according to which in a reactor containing biomass, water saturated steam is supplied under an overpressure of 2.3-2.5 MPa and a temperature of up to 225°C, and the biomass is exposed to steam for several hours, after which the pressure is reduced to atmospheric, and steam is used to heat a fresh portion of biomass, after which the exhaust steam is discharged into an expansion tank, where it is cooled to condensation [Peter Quicker, Kathrin Weber Biokohle Herstellung, Eigenschaften und Verwendung von Biomassekarbonisaten Springer Vieweg, 2016, pp. 128-131].

The disadvantages of the process are:

the frequency of the carbonization process, the need to use reactors operating under high pressure, which increases the cost of equipment and complicates its operation, the long duration of the carbonization process (several hours).

The technical objective of the invention is to ensure the continuity of the carbonization process with an increase in the energy efficiency of the process, an increase in the degree of homogeneity of the carbonization of biomass and an increase in the reliability of the process, as well as a reduction in the duration of the carbonization process.

The essence of the invention

To solve this problem, a method for wet torrefaction (carbonization) of biomass is proposed, according to which the following is carried out:

(a) drying the biomass;

(b) biomass grinding;

(c) treating the dried and ground biomass with superheated pressurized steam in a fluidized bed reactor to produce heat-treated biomass particles and waste steam, wherein the heat-treated biomass particles are continuously removed from the reactor along with the waste steam stream;

(d) separating the heat-treated biomass particles and waste steam; moreover, the biomass is loaded into the reactor continuously;

processing of biomass is carried out at a temperature not exceeding 300°C;

drying of the biomass is carried out using the heat of the waste water vapor obtained in step (d);

biomass grinding is carried out to particles of such a size that their speed of soaring after the loss of 40-50% of the mass by particles is 2-3 times higher than the minimum fluidization rate of the initial biomass particles;

superheated water vapor is fed into the reactor at such a rate that the steam velocity in the reactor, referred to the cross section of the empty reactor, is not more than 1.5 times higher than the minimum fluidization rate of the initial biomass particles.

Brief description of the drawings

In FIG. 1 shows a diagram of a plant for wet torrefaction (carbonization) of biomass that implements the proposed method.

In FIG. 2 is a diagram of a suspended bed reactor.

In FIG. 3 illustrates the appearance of the original biomass (a mixture of chicken manure and straw in an example of the implementation of the proposed method of carbonization (torrefaction) of biomass.

In FIG. 4 illustrates the change in the concentration of CO, CO ₂ , H ₂ and CH ₄ in gaseous non-condensing products of torrefaction of a mixture of manure and sawdust in an environment of superheated water vapor.

Description of the invention

In FIG. 1 shows a diagram of one of the options for the installation for carrying out torrefaction (carbonization) of biomass according to the present invention, which consists of a dryer of the initial biomass 1, a biomass crusher 2, a steam boiler 3, a superheater 4, a reactor for wet torrefaction (carbonization) of biomass in suspended (boiling) layer 5, cyclone 6 for separating heat-treated biomass particles from the gas-vapor stream.

The installation works as follows.

The initial biomass is subjected to drying in the dryer 1 and grinding in the crusher 2.

Almost any biomass of plant or animal origin that is used for fuel generation can be used as the initial biomass. The most preferred type of biomass according to the invention is biowaste with a high initial moisture: bird droppings or a mixture of bird droppings and sawdust or straw, sewage treatment plant sludge, etc. Also

- 2 039214 it is possible to use various wood waste, plant materials, such as millet husks, sunflower, rice.

As the dryer 1 can be used, for example, a vacuum dryer, in the jacket of which the superheated steam exhausted in this process is supplied. Said steam is condensed, whereby the original biomass is dried to a moisture content of less than 20%. Thus, the moisture content of the dried biomass according to the invention can be from 0 to 20%, preferably from 10 to 20%. According to the invention, the moisture content of the biomass after drying does not exceed 20%, since at higher humidity, as experiments show, there are problems with the grinding of the biomass and its fluidization in the reactor.

The dried biomass is fed from the dryer 1 to the crusher 2, where it is crushed.

As crusher 2, you can use a crusher of any known design, such as a hammer mill.

In the steam boiler 3, due to the combustion of fossil fuels or due to electricity, steam is generated with an overpressure of not more than 0.1 MPa, for example, with an overpressure of 0.05 to 0.1 MPa, which is then sent to the superheater 4. Steam production with higher excess pressure, as a rule, does not make sense, since it significantly complicates the design of the installation and, consequently, the cost of manufacturing and operating the steam boiler.

In the superheater 4, which may have a design in the form of a tube coil, for example, by using the heat of the exhaust flue gases of the boiler or by electricity, water vapor is superheated to a temperature of 275 to 300°C.

Superheated water vapor is fed into the fluidized bed reactor 5. The diagram of the reactor 5 is shown in detail in FIG. 2. As shown in FIG. 2, the reactor 5 has a housing 1 in which a fluidized bed 2 of biomass particles is placed. This layer rests on a grate 3, under which a steam receiver 4 is located. The reactor is equipped with an outlet 5 for exhaust steam and heat-treated biomass particles, that is, hydrocoke, as well as a hopper 6 for loading biomass particles into the reactor. The reactor vessel 5 may also be provided with a heating device to maintain the required temperature. In General, the reactor maintain a temperature not higher than 300°C.

According to the process, the biomass subjected to crushing in the crusher 2 is fed into the reactor 5.

According to the proposed method, the grinding of biomass is carried out to particles of such a size that their speed of soaring after the loss of 40-50% of the mass by particles is 2-3 times higher than the minimum fluidization rate of biomass particles.

The minimum fluidization speed, also referred to as the fluidization start speed, is understood to be that gas velocity, ie, in the case of the present invention, the superheated water vapor velocity at which the bed of biomass particles is completely fluidized.

The soaring speed, also called entrainment speed, is understood to mean that gas speed, that is, in the case of the present invention, the speed of superheated water vapor, at which particles are carried out of the suspended bed with the gas flow.

The minimum fluidization rate and soaring rate for a particular type of biomass particle can be determined by one skilled in the art by any suitable method known in the art. Suitable methods are very diverse and are widely described in the specialized literature, for example in [Baskakov A.P. High-speed non-oxidizing heating and heat treatment in a fluidized bed. Moscow: Metallurgy, 1968, p. 16, 18],

According to one embodiment, the grinding of biomass is carried out to particles with a size of 0.4 -1.1 mm.

Superheated water vapor passes through the grate from the reactor 5 and brings the layer of biomass particles into suspension. Due to the high rates of heat and mass transfer in the suspended layer, intensive thermal treatment of biomass particles in the reactor 5 occurs. fluidization of the initial biomass particles.

Here, the steam velocity is understood precisely as the water vapor velocity referred to the cross section of the empty reactor, since if we measure the steam velocity in a reactor filled with a layer of particles, then the steam velocity will be the steam velocity in the gaps between the particles and at the same steam flow rate through the reactor, it will vary with particle size.

Thus, during heat treatment in the reactor 5, the biomass loses up to 40-50% of its own mass, the speed of the biomass particles is two to three times higher than the minimum fluidization rate of the initial particles, and superheated water vapor is fed into the reactor at such a rate that its speed, referred to the cross section of the empty reactor, was not more than one and a half times higher than the minimum fluidization rate of the initial biomass particles. Accordingly, the lighter heat-treated biomass particles (hydrocoke particles) are carried out with the flow of exhaust steam and gases released during the torrefaction process. This flow of exhaust steam, gas and hydrocoke particles is sent to cyclone 6, in which the heat-treated biomass particles are separated from the steam and gas flow and sent to the consumer (they can be used as biofuel, soil improver or organic fertilizer; hydrocoke particles can also be processed into a sorbent by activation, for example, by a chemical method).

Increasing the rate of water vapor supplied to the reactor for carbonization, referred to the cross section of the empty reactor, to values of more than one and a half times compared to the minimum rate of fluidization of biomass particles is not advisable, since it leads to an increase in steam consumption and additional energy consumption for the carbonization process.

Due to the fact that the speed of the biomass particles hovering after the completion of the carbonization process and the loss of 40-50% of biomass particles is two to three times higher than the minimum fluidization rate of the initial biomass particles, then at an operating steam speed that exceeds the minimum fluidization rate by one and a half times, there is a guaranteed removal from fluidized bed of biomass particles, the carbonization of which is completed.

Thus, continuous input of biomass particles into the carbonization reactor, energy efficient thermal treatment and removal of thermally treated biomass particles (hydrocoke particles) from the torrefaction reactor are ensured.

As experiments on wet torrefaction of, for example, bird droppings show, the duration of the carbonization process according to the proposed technology does not exceed 10 minutes, and the characteristics of the obtained hydrocoke largely correspond to the characteristics of hydrocoke obtained by hydrothermal carbonization by known methods.

The exhaust steam is sent to the dryer for the original biomass 1.

Calculations show that drying the initial biomass in an amount of 1 ton from an initial moisture content of 40% to a moisture content of 20% requires approximately the same amount of thermal energy as can be obtained by condensing the spent superheated water vapor required for torrefaction of the dried biomass.

To confirm the effectiveness of the proposed technology, experiments were carried out on wet carbonization (torrefaction) of a mixture of chicken manure and straw. The experiments were carried out on a facility that included a steam electric boiler, an electric superheater, and a reactor for studying the process of torrefaction of biomass particles in a fluidized bed. The gaseous products of torrefaction, together with the exhausted water vapor, entered the refrigerator. Non-condensable gases entered the gas holder, behind which a VarioPlus SinGaz gas analyzer was installed for continuous analysis of the chemical composition of non-condensable gaseous torrefaction products.

The torrefaction reactor is made of stainless steel and has a diameter of 80 mm and a height of 800 mm. The reactor walls are thermally insulated. The amount of manure loaded into the reactor was 20–23 g. During torrefaction, the content of carbon dioxide, carbon monoxide, CH4, and hydrogen in the gases behind the refrigerator was continuously measured using the VarioPlus SynGaz gas analyzer. The experiment was terminated when the gas analyzer ceased to record the release of these gases. After the completion of the experiment, the reactor was purged with cold nitrogen for 2 h, after which hydrocoke was unloaded from it.

The original biomass had a moisture content of 18%. Other characteristics of the original biomass, as well as hydrocoke are given in table. one.

Table 1

0.232 mm. The minimum rate of fluidization of such particles by steam at a temperature of 300°C was 0.6 m/s. The speed of soaring of such particles under the same conditions and after the loss of 40% of their mass was 1.8 m/s, i.e. three times the minimum fluidization rate of the original biomass particles. The duration of the torrefaction process in the fluidized bed was approximately 600 s.

- 4 039214

In table. Table 2 shows the data on the chemical composition of the initial mixture of manure and hydrocoke obtained by classical hydrothermal carbonization at a temperature of 300°C for 480 min [Bashir M. Ghanim, Daya Shankar Pandey, Witold Kwapinski, James J. Leahy Hydrothermal carbonization of poultry litter: Effects of treatmenttemperature and residence time on yields and chemical propertiesof hydrochars//Bioresource Technology, 216, (2016), 373-380].

table 2

Characteristics of the litter mixture before and after hydrothermal carbonization

Material Component content FROM, % N,% N, % S, % about ₂ , % Ash, % Lower calorific value combustion MJ/kg Initial biomass 42.22 5.59 - 30.96 16.37 17.18 Hydrocoke after hydrothermal carbonization at 480 °C for 300 minutes 49.83 4.45 3.22 37.69 22.46

Comparison of the data presented in table. 1 and 2, allows us to state that the proposed method of processing biomass in a fluidized bed in an environment of superheated water vapor will make it possible to obtain hydrocoke of approximately the same quality as in thermal treatment by the method of hydrothermal carbonization, while speeding up the process by 30 times compared to the known embodiment of hydrothermal carbonization. carbonization to ensure the continuity of the carbonization process and increase energy efficiency through the use of exhaust steam.

Claims (5)

1. The method of wet torrefaction (carbonization) of biomass, including (a) drying the biomass; (b) biomass grinding; (c) treating the dried and ground biomass with superheated pressurized steam in a fluidized bed reactor to produce heat-treated biomass particles and waste steam, wherein the heat-treated biomass particles are continuously removed from the reactor along with the waste steam stream; (d) separating the heat-treated biomass particles and waste steam; moreover, the biomass is loaded into the reactor continuously; processing of biomass is carried out at a temperature not exceeding 300°C; drying of the biomass is carried out due to the heat of the waste water vapor separated in stage (d); grinding of biomass is carried out to particles of such a size that their speed of soaring after the loss of 40-50% of the mass of particles was 2-3 times the minimum speed of fluidization of biomass particles; superheated water vapor is fed into the reactor at such a rate that the steam velocity in the reactor, referred to the cross section of the empty reactor, is not more than 1.5 times higher than the minimum fluidization rate of biomass particles. 2. The method according to claim 1, characterized in that water vapor with an excess pressure of 0.05 to 0.1 MPa is superheated to a temperature of 275 to 300°C before being fed into the reactor. 3. The method according to claim 1, characterized in that the biomass is dried to a moisture content of not more than 20%, the drying of the biomass is carried out in a vacuum dryer and the grinding of the biomass is carried out to particles with a size of 0.4-1.1 mm. 4. The method according to claim 1, characterized in that the initial biomass is selected from the group including bird - 5 039214 litter, a mixture of bird droppings and sawdust, a mixture of bird droppings and straw, sewage treatment plant sludge, wood waste, millet husks, sunflower, rice. 5. The method according to claim 1, characterized in that the duration of the biomass treatment in step (c) does not exceed 10 minutes.