RU2845202C1 - Solid fuel flow gasifier - Google Patents

Abstract

FIELD: heat engineering; chemistry.

SUBSTANCE: invention relates to heat power engineering, particularly to equipment for producing synthesis gas from solid fuel with wide granulometric composition and high humidity. Flow gasifier with controlled residence time of solid fuel, containing a fuel bunker, an auger feeder, a forced-draft fan, a reagent gas heater, a flow divider, a gasification chamber, a cyclone-separator, wherein the vertical gasification chamber consists of a cylindrical portion and a conical portion located thereunder, the solid fuel supply device is located in the conical part of the vertical gasification chamber, flow gasifier further comprises a gas distribution chamber located under the conical section of the vertical gasification chamber, a bladed swirler with an adjustable blade inclination angle, oxidizer gas supply unit is located in the middle of the gas distribution chamber, the blade device is located in the upper part of the gas distribution chamber, blades of the blade device are made with possibility of rotation around the horizontal axis.

EFFECT: improving efficiency and productivity of gasification process, as well as increasing fuel use coefficient due to possibility of operating with fuel of wide fractional composition and different moisture content.

8 cl, 5 dwg

Description

Field of technology

The invention relates to thermal power engineering, in particular to equipment for producing synthesis gas from solid fuel with a wide fractional composition and high humidity.

State of the art

A device for gasifying granulated solid fuel is known and is intended for use in the power engineering, gas and chemical industries for producing synthesis gas and raw gas [RU Patent No. 2486228, published on 27.06.2013]. The gasifier includes a closed reaction vessel containing a fluidized bed formed by fuel, a feed sluice installed in the upper part for continuous fuel loading, an upper gate installed under a funnel-shaped narrowing of the bottom for unloading the resulting ash into an ash removal sluice, a rotating grate built in above the funnel-shaped narrowing of the bottom, with the possibility of introducing a gasifying agent through it from below into the fluidized bed and unloading the resulting ash through it by means of a funnel-shaped narrowing and a tubular section adjacent to it into an ash removal sluice. A slide gate is built into the tubular section. The invention allows for continuous unloading of ash without interrupting the process and negatively affecting the pressure and temperature of the process, and also allows for continuous operation of the rotating grate.

The disadvantages of this solution are the impossibility of processing the fine (dust) fraction, which complicates fuel preparation (granulation) and narrows the fuel base; the use of oxygen as a gasifying agent, which requires an expensive air separation unit; the presence of a rotating grate (a complex device for unloading ash); as well as relatively high temperatures in the lower part of the unit (up to 1500°C), which can lead to slagging.

A device is known for processing solid fuels to produce combustible gas, including synthesis gas, and can be used to process organic fuels with poor gas permeability, prone to unstable combustion with the formation of channels [RU Patent No. 2730063, published on 17.08.2020]. The technical result is to stabilize the position of the combustion zone in the reactor vertically and achieve a uniform distribution of the process over the reactor cross-section. A method for gasifying solid fuel is proposed, including loading solid fuel into the upper part of a vertical shaft reactor, feeding oxygen-containing gas to the lower part of the reactor in a deficit relative to the fuel, pyrolysis and combustion of the solid fuel in a countercurrent gas flow, removing gaseous combustion and pyrolysis products from the upper part of the reactor, measuring the temperature on the reactor walls and unloading the solid combustion residue from the lower part of the reactor. In this case, the maximum temperature of the process is maintained in the middle part of the reactor, a portion of the gaseous products of combustion and pyrolysis is collected from the upper part of the reactor and this portion of the gaseous products of combustion and pyrolysis is forcibly fed into the middle part of the reactor. The feeding of a portion of the gaseous products of combustion and pyrolysis into the middle part of the reactor is carried out through a series of tuyeres uniformly distributed around the circumference in the middle part of the reactor. A device for implementing the said method is also proposed.

The disadvantages of this solution are the use of fuel with a narrow fractional composition and the impossibility of using pulverized fuel; the presence of a rotating grate - a movable device with a complex design in operation; the use of a fan for recirculation of synthesis gas reduces the reliability of the entire system due to the risk of deposits of soot and resins in it; the need for continuous temperature monitoring to determine the location of the supply of combustible gas using adjustable dampers, relatively increasing the supply from the side of the reactor where the temperature is higher and, conversely, decreasing it where the temperature is lower.

The closest solution selected as a prototype is a jet-vortex gasification unit for low-reactivity solid fuels (patent RU 165512, published 20.10.2016), which contains a vertical gasification chamber, a coal feeding device consisting of a dust feeding bin and a screw feeder, an oxidizer feeding system consisting of a blower fan and an air heater, a device for removing generator gas, and the unit also contains a device for feeding nanomaterials located in front of the coal feeding device, a water injection device located in front of the entrance to the vertical gasification chamber, a blade apparatus located inside the vertical gasification chamber, a dosing chamber with a regulating valve located inside the vertical gasification chamber.

The disadvantages of this solution are strict requirements for preliminary preparation (granulometric composition) of the initial fuel (coal dust), the use of nanomaterials, which increases costs at any degree of use of nanomaterials, and the presence of a device for unloading ash from the bottom of the device. The limited functionality of the prototype object is the inability to operate on solid fuel with a wide granulometric composition and high humidity. This is due to the use of a blade device without the ability to regulate the degree of flow swirl, as well as the cylindrical profile of the unit above the blade device. The lack of flow swirl adjustment does not allow controlling the residence time of the fuel in the unit, which greatly limits the possible granulometric composition and humidity of the fuel used. The cylindrical profile of the unit above the blade device ensures the same flow velocity along the entire path of the fuel, which prevents gravitational separation of fuel with a wide granulometric composition. The agglomeration (ash) removal hole in the prototype is located under the fuel feed point, which complicates the removal of agglomerations from the gas-dispersed flow and leads to premature removal of large fuel particles from the installation.

Disclosure of the essence of the invention

The proposed invention is aimed at solving the problem of increasing the efficiency of the gasification process, as well as increasing the degree of conversion of solid fuel of a wide fractional composition and different humidity due to the possibility of regulating the residence time of solid fuel in the installation.

The problem is solved by changing the shape of the gasification chamber, which in the proposed solution includes cylindrical and conical parts, and by supplementing the gasifier with a blade tilt unit (blade apparatus) and a flow splitter between the gasification chamber and the gas distribution chamber, which ensures the ability to regulate the intensity of particle circulation when changing the humidity and size of the fuel. When operating on fuel with high humidity, the air swirl angle of the blade apparatus increases to intensify the particle circulation. When operating on fuel with low humidity, the air swirl angle of the blade apparatus decreases to reduce the particle circulation. It is known that the problem of conical-cylindrical devices is the occurrence of fuel slopes (stagnant zones) on the slopes of the conical part. The proposed design solves the problem of slopes by redirecting the reagent gas (air, oxygen, steam and their mixtures) to the walls of the conical part of the unit, due to which the slopes are destroyed and the conversion process of the entire mass of fuel is intensified. With the blades of the blade apparatus in a straight position (zero degree of swirl), the flow of the reagent gas is redirected to the walls of the unit due to the flow splitter installed in the central part of the blade apparatus. The opening in the center of the splitter serves as a place for the removal of the formed agglomerations of fuel particles. The agglomerations from the gasification chamber enter the gas distribution chamber and then leave the unit. A relatively small air flow through the central opening of the splitter from the gas distribution chamber to the gasification chamber prevents the removal of small fuel particles together with the agglomerations. The recirculation zone that occurs in the center of the unit increases the residence time of the fuel particles, their degree of conversion and the efficiency of the gasifier.

The proposed gasifier comprises a vertical gasification chamber, a gas distribution chamber, a solid fuel supply device, an oxidizer supply unit, a device for removing synthesis gas, a blade apparatus located between the gasification chamber and the gas distribution chamber. The gasification chamber consists of an upper cylindrical section and a lower conical section. The conical and cylindrical sections of the gasification chamber have a height of 0.5-1 m, and the diameter of the cylindrical part is 0.5-1 m. The diameter of the gas distribution chamber is 0.05-0.1 m. The solid fuel supply device is located in the conical part of the gasifier. The gasifier additionally comprises a blade angle adjustment unit for the blade apparatus and a splitter mounted on the blade apparatus axis, in the center of which there is an opening for removing agglomerations. The blade angle adjustment unit for the blade apparatus is equipped with a blade rotation mechanism, in which the movement is carried out using a lever transmission.

The technical result of the invention consists in increasing the efficiency of the gasification process, as well as increasing the degree of conversion of solid fuel of a wide fractional composition and different humidity due to the possibility of regulating the residence time of solid fuel in the installation.

Brief description of graphic materials

The essence of the claimed invention is explained by graphic materials, where Fig. 1 shows a diagram of a solid fuel gasifier device.

1 - fuel bunker, 2 - screw feeder, 3 - blast fan, 4 - reagent gas heater, 5 - gas distribution chamber, 6 - blade swirler with adjustable blade angle, 7 - flow divider, 8 - gasification chamber, 9 - cyclone separator.

Fig. 2 shows a prototype model: a) geometry b) computational grid.

Fig. 3 shows the results of modeling the gasification process in a prototype with particles of 100 μm diameter, axial and tangential velocity of 0.18 m/s and a swirl angle of 45°: a) particle velocity, m/s; b) particle residence time, s; c) gas velocity modulus, m/s; d) tangential gas velocity, m/s; d) axial gas velocity, m/s.

Fig. 4 shows the model geometry of a solid fuel flow gasifier: a) geometry b) computational grid.

Fig. 5 shows the results of modeling the gasification process in the proposed solution with particles of 100 μm diameter, axial and tangential velocity of 5 m/s and a swirl angle of 45°: a) particle velocity, m/s; b) particle residence time, s; c) gas velocity modulus, m/s; d) tangential gas velocity, m/s; d) axial gas velocity, m/s.

Implementation of the invention

The gasifier contains a fuel bin 1, a screw feeder 2, a blast fan 3, a reagent gas heater 4, a gas distribution chamber 5, a blade swirler with an adjustable blade angle 6, a flow divider 7, a gasification chamber 8, and a cyclone separator 9.

Solid fuel (biomass, coal, MSW, etc.) enters fuel bin 1 from where it is fed by screw feeder 2 to the middle part of conical section of gasification chamber 8. Reagent gas (air, oxygen, steam and their mixtures) is fed to gasifier by means of blast fan 3, heated in heater 4 and enters gas distribution chamber 5 from where it enters gasification chamber 8 through vane swirler. Vane swirler blades are fixed on axles which are driven by lever transmission. The axles are fixed on outer and inner cylinders of vane apparatus. Small fuel particles are carried away from conical section by ascending gas flow and are gasified in cylindrical section. Large fuel particles descend along walls of conical section to air supply nozzle where they are picked up by ascending stream and rise upward. As the particles rise due to the expansion of the cross-section of the gasifier, the gas velocity decreases, and the gas velocity on the reactor axis remains lower than in the center. When the gas velocity decreases to a critical value, the particles begin to descend. As a result, the particles circulate and are separated by size. In the lower part of the conical section, an increased content of large particles is achieved, and in the upper part of the conical section, small particles. As the particle mass decreases due to the processes of drying, pyrolysis and gasification of the coke residue, the particles rise higher along the cone. Thus, in the conical section, drying, pyrolysis and coke gasification zones are formed sequentially (from bottom to top). Synthesis gas and fly ash exit from the top through an opening in the gasifier cover and enter a cyclone separator, in which the fly ash is separated from the synthesis gas flow. Synthesis gas can be used in power engineering or the chemical industry. If the carbon content in the fly ash is high, it can be mixed with fresh fuel. The agglomerations leave the unit through an opening in the flow divider 7, which is installed in the central part of the blade apparatus. The flow divider is rigidly mounted in the gas distribution chamber by four steel rods connected to the wall of the gas distribution chamber.

The geometric dimensions (height and diameter) of the gasification chamber and the fuel consumption are related in such a way that the average porosity of the circulating material in the conical section is 0.95-0.98. Such a high porosity in the conical section ensures a flow mode of operation in the cylindrical part of the unit. The ratio of fuel and air (oxidizer consumption coefficient) is selected in such a way that the temperature at the outlet of the unit is 900-1000°C. Such a temperature is, on the one hand, low enough to avoid slagging, and on the other hand, high enough for endothermic reactions of solid fuel gasification to occur.

Due to the specific length of the cylindrical section and the specific ratio between the diameter of the cylindrical section and the fuel consumption, a specific speed is achieved in the cylindrical section, at which the carried away small particles of fuel and coke residue are completely gasified during the time of ascent along the cylindrical section. Large particles of fuel circulate and are partially gasified in the conical section until their size becomes sufficient for complete gasification in the cylindrical section. Wet particles of fuel, due to their greater mass, circulate in the lower part of the cone until they dry. Due to the circulation of particles, the temperature is equalized along the height of the conical section and stable ignition of particles and pyrolysis gases is achieved.

The proposed arrangement of the blade apparatus for feeding the reagent gas facilitates the formation of a recirculation zone in the center of the unit and the separation of the pyrolysis and gasification zones. The decomposition and partial oxidation of the resins released from the fuel in the pyrolysis zone occurs at a high rate on the surface of the coke particles that circulate in the gasification zone. The minimum resin content in the synthesis gas is achieved due to the high temperature and low particle concentration.

In addition, the proposed solution ensures stable ignition of particles and pyrolysis gases when burning biomass of a wide fractional composition and different humidity. This result is achieved due to a certain length of the cylindrical part and a certain ratio between the diameter of the cylindrical part and the fuel consumption, which ensures a certain speed in the unit, at which the carried away small particles of fuel and coke residue are completely gasified during the circulation time. Large particles of fuel are recirculated until their size is sufficient to be carried out of the unit. Wet particles of fuel, due to their greater mass, are recirculated in the lower part of the cone until they dry out.

When using this solution, cluster formation is minimized, and the yield of resins and soot is reduced by 90%. This result is achieved due to the primary turbulence of the flow, which leads to improved conditions for mass transfer and mass exchange with the gaseous oxidizer of the pyrolysis products. This leads to a decrease in the yield of resins and soot, an increase in the chemical efficiency of gasification and the quality of the produced synthesis gas.

Below are the results of comparative CFD modeling of gasification processes in the prototype and the proposed solution. Pine sawdust was used as fuel for the gasifier calculations. The sawdust characteristics are given in Table 1.

Table 1 - Sawdust composition (% of working mass)

W A S C H N O 12.8 0.3 0,1 42.9 5.5 0.2 38.2

The initial data for modeling the proposed gasifier and prototype are given in Table 2. They were selected based on a literature search and represent one of the most popular and effective modes for air flow gasification of biomass.

Table 2 - Initial data of the modeling experiment of the proposed installation

Parameter Meaning Mass fuel consumption, kg/h 20 Mass flow rate of gas at the inlet, kg/h 18 Gas temperature at the inlet, K 423 Wall temperature, K 1273 Excess air coefficient 0.2 Particle size, µm 100-1000 Particle density, kg/ ^m3 300

According to the prototype, fuel enters the dust feed bin, nanomaterials are simultaneously fed there by the nanomaterial feeder, the mixture of coal dust and nanomaterials is fed by a screw feeder into the dosing chamber. Then the mixture of fuel and nanomaterials from the dosing chamber is fed into the vertical gasification chamber through a control valve. In the vertical gasification chamber, the process of mixing coal dust with an oxidizer occurs and the gasification process takes place.

Fig. 2 shows the geometry (2a) and computational grid (2b) for computer modeling of the gasification process in the prototype. The computational grid (Fig. 2b) consists of 122 thousand tetrahedrons and prisms with five layers of smaller computational elements at the walls of the installation.

The results of computer modeling for the prototype of the particle trajectory and velocity field with a diameter of 100 μm, axial and tangential velocity of 0.18 m/s, which corresponds to a twist angle of 45°, are shown in Fig. 3. It is evident that all particles move uniformly from bottom to top without the occurrence of any additional vortex structures. From Fig. 3d, it can be concluded that zones with negative axial velocity do not occur, which indicates the absence of gas and particle recirculation. Recirculation is suppressed by the presence of a fuel feed pipe on the axis of the installation, which leads to a decrease in the residence time, the degree of fuel conversion and the efficiency of the installation.

Fig. 4 shows the geometry (4a) and the computational grid (4b) for computer modeling of the gasification process in the proposed solution. Fig. 5 shows the results of computer modeling for the proposed solution of particle trajectories and velocity fields with a diameter of 100 μm, axial and tangential velocity of 5 m/s, which corresponds to a twist angle of 45°.

Small fuel particles are carried away by the ascending gas flow and are gasified in the cylindrical section. Large fuel particles descend along the walls of the conical section to the air supply nozzle, where they are picked up by the ascending stream and rise upward. As the particles rise due to the expansion of the gasifier cross-section, the gas velocity decreases, and the gas velocity on the reactor axis remains lower than in the center. When the gas velocity decreases to a critical value, the particles begin to descend. As a result, the particles circulate and are separated by size. In the lower part of the conical section, an increased content of large particles is achieved, and in the upper part of the conical section, small particles. As the particle mass decreases due to the processes of drying, pyrolysis, and gasification of the coke residue, the particles rise higher along the cone. Thus, in the conical section, drying, pyrolysis, and coke gasification zones are successively formed (from bottom to top). Synthesis gas and fly ash exit from the top, through an opening in the gasifier cover, and agglomerations leave the unit through an opening in the diffuser, which is installed in the central part of the blade apparatus.

When comparing the results obtained during modeling on the prototype and the proposed installation, it can be concluded that the residence time of fuel particles in the proposed installation is significantly longer due to the emergence of a recirculation zone on the installation axis. An increase in the residence time of particles entails an increase in the degree of conversion and efficiency of the installation by approximately 30%. A decrease in the velocity in the upper part of the proposed installation leads to an increase in the residence time of small particles, and large particles are retained in the lower part of the installation under the action of gravity.

By changing the angle of the blades of the blade apparatus, the circulation of particles in the unit is regulated when the fuel humidity changes. When working on fuel with high humidity, the angle of the blades increases to intensify the circulation of particles. When working on fuel with low humidity, the angle of the blades decreases to reduce the tangential velocity of the gas, thereby reducing the trajectory of movement and the residence time of the fuel particles in the unit.

In addition, the proposed solution ensures stable ignition of particles and pyrolysis gases when burning biomass of a wide fractional composition and different humidity. This result is achieved due to a certain length of the cylindrical part and a certain ratio between the diameter of the cylindrical part and the fuel consumption, which ensures a certain speed in the unit, at which the carried away small particles of fuel and coke residue are completely gasified during the circulation time. Large particles of fuel are recirculated until their size is sufficient to be carried out of the unit. Wet particles of fuel, due to their greater mass, are recirculated in the lower part of the cone until they dry out.

When using this solution, cluster formation is minimized, and the yield of resins and soot is reduced by 90%. This result is achieved due to the primary turbulence of the flow, which leads to improved conditions for mass transfer and mass exchange with the gaseous oxidizer of the pyrolysis products. This leads to a decrease in the yield of resins and soot, an increase in the chemical efficiency of gasification and the quality of the produced synthesis gas.

Increasing the swirl from 0 to 45° increases the residence time of particles in the installation and the gasification efficiency by more than 40%.

Claims (24)

1. A flow gasifier with adjustable solid fuel residence time containing: fuel bunker, screw feeder, blower fan, reagent gas heater, flow divider gasification chamber cyclone separator, characterized in that the vertical gasification chamber consists of a cylindrical section and a conical section located underneath it, the solid fuel feed device is located in the conical part of the vertical gasification chamber, The flow gasifier additionally contains a gas distribution chamber located under the conical section of the vertical gasification chamber, vane swirler with adjustable blade angle, the oxidizer gas supply unit is located in the middle of the gas distribution chamber, the blade apparatus is located in the upper part of the gas distribution chamber, The blades of the blade apparatus are designed to rotate around a horizontal axis. 2. A flow gasifier according to item 1, characterized in that the upper cylindrical part is made with a diameter of 0.5–1 m. 3. A flow gasifier according to paragraph 1, characterized in that the height of the conical section of the vertical gasification chamber and the diameter of the cylindrical section of the vertical gasification chamber are equal to 0.5–1 m. 4. A flow gasifier according to item 1, characterized in that the gas distribution chamber is made in the form of a cylinder with a diameter of 0.1–0.2 m and a height of 0.2–0.4 m. 5. A flow gasifier according to paragraph 1, characterized in that the blade apparatus is two rigidly fastened coaxially cylinders, between which blades are located, and the cylindrical wall of the gas distribution chamber is used as the outer cylinder, and the inner cylinder is rigidly fastened to the outer cylinder. 6. A flow gasifier according to item 1, characterized in that the inner cylinder of the blade apparatus is made with a diameter of 0.025–0.05 m. 7. A flow gasifier according to item 1, characterized in that a divider is fixed to the upper part of the inner cylinder of the blade apparatus, made in the form of a truncated cone with a height in the range of 0.1–0.2 m and a taper equal to the taper of the conical part of the conical section of the vertical gasification chamber. 8. A flow gasifier according to paragraph 1, characterized in that the bottom of the gas distribution chamber is made in the form of a cone with an opening for removing ash and slag.