EP4209710A1

EP4209710A1 - Fluidised bed unit

Info

Publication number: EP4209710A1
Application number: EP22020003.4A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Icmea Leader Of Temporary Association Of Cos Icmea Srl Tecnomec Engineering Srl Cnr Irsa Srl
Current assignee: Icmea Leader Of Temporary Association Of Cos Icmea Srl Tecnomec Engineering Srl Cnr Irsa Srl
Priority date: 2022-01-10
Filing date: 2022-01-10
Publication date: 2023-07-12

Abstract

This invention relates to a fluidised bed unit for use in thermally treating biomass, waste, dried sewage sludge or by-products in general. The application is to be intended not limited to thermal treatments but has to be intended extended to any application involving a fluidised bed reactor.

The unit forms part of a larger system including a forced draft fan and an induced draft fan suitable to maintain the reactor operating temperature and pressure. The system is suitable for installation on a small or medium scale installation in the range 500kWth - 3Mth for thermal treatment application or in general in the range 10kg/h to 1000kg/h of feedstock. The unit comprises three cylinders arranged in an inverted "U" shape hereafter described.

The first cylinder is vertical and comprises a feedstock inlet, a fluidisation agent inlet, a nozzle inlet box, a plurality of nozzles for injecting the fluidisation agent in the bed, a plurality of temperature and pressure sensors. The flow in the first cylinder is upward.

The second cylinder is horizontal and comprises a flue gas temperature control device and an explosion protection device. The flow in the second cylinder is horizontal moving from the first cylinder toward the third cylinder.

The third cylinder is vertical and comprises a temperature control device, a catalytic filter, an auger for feeding new catalyst and extracting exhausted catalyst, and trapped particles, a plurality of temperature and pressure sensors. The flow in the third cylinder is downward.

The fluidised bed unit is compact, relatively simple to maintain and commercially viable so that it may be skid mounted in the factory and transported to the installation site.

The fluidised bed unit can also be part of an energy conversion system that is suitable for installation on small and medium scale processing plants.

Description

Technical Field to which invention relates

This invention relates to an improved small and medium scale fluidised bed reactor that can be equipped with an internal catalytic filter suitable for factory skid mounting and for site treatment of small and medium quantity of feedstock.

Indication of background art

Fluidised bed units are commonly used in large scale incineration plants and are typically very large, bulky machines with typical height higher than 6m and horizontal dimensions larger than three meters. The known fluidised bed units are operated to thermally treat coal, waste or other like material in incineration plants. A problem with the known fluidised bed units is that they are very large, expensive machines that are only suitable for large scale combustion or incineration plants with a plentiful supply of feedstock. Another problem with the fluidised bed units is that they require constant surveillance and frequent maintenance by skilled personnel to ensure optimal operation.
The known fluidised bed units are therefore time consuming and costly to operate as well as being unsuitable for small scale installations such as processing plants. The present invention is concerned with relatively small installations capable of handling up to 3MW thermal and up to 1000kg/h of feedstock.
A fluidised bed reactor easily permits process scale, has a great processing capacity and good control of the process temperature. It also allows the addition of catalyst in the bed to improve process performance.
In general, fluidised bed reactors require a specific granulometry, homogeneity and specific preparation of the feedstocks. Sintering and agglomeration of the bed can result because of the thermo mechanical properties of the material and the melting temperature of the ashes.
In general, fluidised bed reactors can be bubbling or circulating.
A bubbling fluidised bed reactor consists of a silica sand or similar material bed, fluidised by a gaseous stream coming from the bottom of the bed. The bubbling regime is characterised by formation and coalescence of bubbles causing solid mixing. The minimum velocity at which bubbles form is known as minimum fluidisation velocity. Use of bubbling fluidised bed reactors are well known for heat treating, of biomass, waste, coal, or other by-products with the objective, for example, of drying, thermal decomposition or combustion. The speed of thermal reactions depends on the operating conditions and fluidisation level across the entire bed. The air flow rate is normally of the order of 1 m/s. The solid matter concentration is low in the gas flow above a clearly limited bubbling fluidised bed. Temperature reactor space above the fluidised bed in a bubbling bed reactor can be raised by additional air supply or reduced by injecting cooling water into the gas flow. To increase carbon conversion, dust particles present in the gas flow can be separated with a distinct cyclone, in which the particles are returned to the bottom of the reactor space. "Winkler gasifiers" of this type are described in documents DE2751911 and DE19548324 .
In circulating fluidised bed reactors solid particles are fluidised and rise together with the air flow blown into the reactor. The air flow rate, which is typically on the order of 5 m / s, is higher and the size of the fluidised particles is smaller than in a bubbling bed reactor.
The fluidised particles are entrained by the product gas in the cyclone, in which the particles and the carbonisation residue derived from the fuel are separated and returned to the bottom of the reactor space. To obtain the retention time required for the gasification reaction, the circulating fluidised bed reactors have been given a height substantially greater than that of the bubbling fluidised bed reactors. Other typical properties of circulating fluidised beds comprise uniform temperature and relatively uniform viscosity of the solid matter suspension in the reactor space, without a clearly limited fluidised bed characteristic of bubbling fluidised beds. A typical fuel gasification process based on circulating fluidised bed reactors is disclosed in F162554.
Prior art is disclosed in EP0889943 , a fluidised bed reactor system and a method for operating said system. The reactor system comprising: a fluidised bed reactor chamber, a particle separator connected to the reactor chamber, for separating solid material from exhaust gases. A gas cooler having cooling surfaces is connected to the particle separator. According to the invention, means are provided for branching off a flow of solid bed material from the material separated in the particle separator and for introducing said branched off flow of bed material into the gas cooler. A flow of bed material is branched off from the main flow of solid particles, before or after discharging said first flow of solid particles from the particle separator. The branched off flow of solid particles are introduced into the gas discharged from the separator during, or before cooling of the gas, so that these particles mechanically dislodge deposits from cooling surfaces.
Another patented system is protected in the EP1286113 that describes a combustion method and apparatus in which combustible matter, e.g., waste matter, coal, etc., is gasified to produce a combustible gas containing a sufficiently large amount of combustible component to melt the ash by its own heat. A fluidised-bed furnace has an approximately circular horizontal cross-sectional configuration. A moving bed, in which a fluidised medium settles and diffuses, is formed in the central portion of the furnace, and a fluidised bed, in which the fluidised medium is actively fluidised, is formed in the peripheral portion in the furnace. The fluidised medium is turned over to the upper part of the moving bed from the upper part of the fluidised bed, thus circulating through the two beds. Combustible matter is cast into the upper part of the moving bed and gasified to form a combustible gas while circulating, together with the fluidised medium. The amount of oxygen supplied to the fluidised-bed furnace is set so as to be the same contained in an amount of air not higher than 30% of the theoretical amount of combustion air. The temperature of the fluidised bed is maintained at 450 °C to 650 °C so that the combustible gas produced contains a large amount of combustible component. The combustible gas and fine particles produced in the fluidised-bed furnace are supplied to a melt combustion furnace where they are burned at high temperature, and the resulting ash is melted. Another patent document of the prior art is the invention EP0433547 refers to an apparatus to gasify solid fuels, which consists of a gas producer having a pre-charging silo, a carbonisation or coking and gasification silo and a furnace and is particularly suitable to gasify low cost products such as wood waste and chips, solid biomasses in general, tyres, peat, lignite, coal and other materials, and advantageously solid urban wastes, a direct flame or flames and a downward flame or flames being included in the furnace of the gas producer.
Another document of the prior art is European patent EP1432779 refers to a method and apparatus for gasifying fuel in a fluidised bed reactor containing fluidised solid material particles. The fuel is introduced into the reactor bottom part, and product gas formed in gasification is led from the reactor top to a separator, such as a cyclone, which separates solid particles from the gas for recirculation to the reactor. In accordance with the invention, a bubbling fluidised bed containing coarser particles, and above this, a circulating bed containing finer particles are maintained in the reactor by recirculating the particles separated from the product gas to the reactor, to the top of the bubbling fluidised bed or above this. The reactor may comprise a lower part for the bubbling fluidised bed and an upper part larger in cross-section for the circulating fluidised bed, the speed of the ascending gas flow in the circulating bed being equal to or lower than that of the bubbling bed. The separating limit in the cyclone may be adjusted such that the discharged product gas flow entrains solid particles, which have a binding effect on tacky ash particles. The product gas is cooled in two successive heat exchangers before filtration of the gas. The method is suitable for gasification of biomasses and recycled fuels forming tars and/or containing chlorine, thus providing a solution to the problems of fouled and clogged gas ducts.

Technical problem to be solved

The prior art systems are aimed at processing large amounts of feedstock and have the disadvantage of complexity.
State of the art systems are very tall to limit the entrained particles and to allow the residence time required to complete the expected reactions. The height of state-of-the-art systems does not allow factory skid mounting because of the limited height and horizontal dimensions permitted for transportation. None of the state-of-the-art systems is equipped with internal devices for effective trapping and possible catalytic post treatment of flue gas and products that are entrained from the bed. The present invention allows the required residence time with a limited height compatible with factory skid mount significantly reducing installation cost. It also permits a precise flue gas temperature control downstream from the bed and effective internal filtering and catalytic processing of the flue gas.

Disclosure of invention

In accordance with the present invention, a fluidised bed reactor that comprises three cylinders arranged in an inverted "U" shape, hereafter described, is disclosed.
The first cylinder is vertical and comprises a feedstock inlet, a fluidisation agent inlet, a nozzles inlet box, a plurality of nozzles for injecting the fluidisation agent in the bed, a plurality of temperature and pressure sensors. The flow in the first cylinder is upward.
The second cylinder is horizontal and comprises a flue gas temperature control device and an explosion protection device. The flow in the second cylinder is horizontal moving from the first cylinder toward the third cylinder.
The third cylinder is vertical and comprises a temperature control device, a catalyst filter, an auger for feeding new catalyst and extracting exhausted catalyst and trapped particles, a plurality of temperature and pressure sensors. The flow in the third cylinder is downward.
The fluidised bed unit is compact, relatively simple to maintain and commercially viable so that it may be skid mounted in the factory and transported to the installation site.
The fluidised bed unit can also be part of an energy conversion system that is suitable for installation on small and medium scale processing plants.
Advantageously, the system is characterised by an inverted 'U' shape in which the flue gas flow is first upward, then horizontal and finally downward. Such arrangement allows to accomplish the necessary residence time to complete the reactions with a lower height than prior art systems, it can also allow temperature control in the freeboard, effective entrained ash and particle removal and a catalytic flue gas post processing with the internal catalytic filter.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

Brief Description of the drawings

Fig. 1 is a perspective view of a fluidised bed reactor in accordance with the preferred embodiment of the present invention.
Fig. 2 is an exploded perspective view of the fluidised bed reactor as shown in Fig. 1.
Fig. 3 is one cross-sectional view of the fluidised bed reactor as shown in Fig. 1.
Fig. 4 is cross-sectional views of the first and the third cylinder at right angles to Fig. 3
Fig. 5 is a perspective view of the particle separator system embedded in a fluidised bed reactor as shown in Fig. 1
Fig. 5 includes a perspective and an exploded view of the particle separator system embedded in a fluidised bed reactor as shown in Fig. 1
Fig. 6 includes is a perspective view and an exploded view of the nozzle inlet box and nozzles embedded in a fluidised bed reactor as shown in Fig. 1.
Fig. 7 includes a perspective view of an example of skid mounting of a complete system including a flue gas clean up section and fans.

Description of at least one way of carrying out the invention

Referring to the drawings and initially to Figs. 1-6, a fluidised bed reactor for thermal treatment of biomasses, waste, by-products in general and for any known application involving fluidised bed reactors, in accordance with the preferred embodiment of the present invention, comprises a nozzle inlet box 1, a plurality of fluidisation agent injection nozzles 2, a bed of olivine or similar material 3, an upward flow cylinder 4, a horizontal cylinder 5 equipped with a temperature control device 6, a downward flow cylinder 7, a catalyst filter comprising a catalytic bed 10, an outer cylinder 16 and an inner cylinder 18, a catalyst and trapped solid particles extraction device 9, an explosion protection device 15, a feedstock inlet 12 and a flue gas outlet 11.
In the preferred embodiment the fluidisation agent enters the system through the inlet flange 14 pressurising the nozzle inlet box 1. The nozzle inlet box 1 acts as a pressure dampener so that the pressure upstream each nozzle 2 is the same and thus the fluidisation agent velocity entering the reactor 4, allowing consistent fluidisation regime across the bed. Reactions start in the bed 3 and continue in the first, second and third cylinder. The horizontal cylinder 5 is equipped with an explosion protection device, such as a hydraulic seal 15 or an equivalent device, a temperature control device 6, allowing water to be sprayed to decrease, or injecting air to increase, flue gas temperature. The third downward flow cylinder 7 is equipped with a temperature control device 13 and with the catalytic filtration system detailed in the Fig. 5. The catalytic filtration system is composed by cylinders 16 and 17. The catalyst bed 10 is positioned in the space between cylinder 7 and cylinder 16 and in the space between cylinder 16 and cylinder 17. The flue gas passes through the catalyst bed 10 in downward direction in the space between the cylinder 7 and the cylinder 16 and in upward direction in the space between cylinder 16 and cylinder 17. Subsequently flue gas passes through the holes 18 and flows in downward direction inside the cylinder 17 and eventually exits the system through the outlet 11. The auger 9 allows removal of exhausted catalyst, ashes and trapped particles collected through the outlet 19 and addition of fresh catalyst via the inlet 20.
Referring to Fig. 7 the preferred embodiment of a skid mount of a complete system including the fluidised bed reactor, a flue gas clean-up section and fans is disclosed.
Although the invention has been explained in relation to its preferred embodiment as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claims will cover such modifications and variations that fall within the true scope of the invention.

Claims

A fluidised bed, for applications known to the art, comprising three interconnected cylinders, two vertical and one horizontal that connects the two vertical cylinders near the top of the vertical cylinders; such that the gas flow passes up the first vertical cylinder, across the horizontal cylinder and down the second vertical cylinder hereinafter referred as "inverted U-shaped fluidised bed unit".
An inverted U-shaped fluidised bed unit as claimed in (1) for thermally treating biomass, waste, dried sludge, and by-products in general comprising a nozzle inlet box, a plurality of nozzles for fluidisation agent injection, a catalyst filter, flue gas temperature control devices, an explosion protection device, an auger for feeding the catalyst and extracting the trapped particles, a feedstock inlet and a flue gas outlet.
A fluidised bed unit as claimed in any preceding claim, in which the horizontal cylinder is equipped with a temperature control device and an explosion protection device.
A fluidised bed unit as claimed in any preceding claim, in which the third cylinder is equipped with a temperature control device, a catalytic filter and an auger to feed and extract the catalyst.
A fluidised bed unit as claimed in any preceding claim in which the catalytic filter is composed by an outer cylinder and an inner cylinder welded on the top to a plate.
A fluidised bed unit as claimed in in any preceding claims in which the outer cylinder of the catalytic filter is shorter than the inner one and the inner cylinder is equipped with suitable openings above the level of the catalyst to allow the flue gas to pass through.
A catalytic filtration system as claimed in (5) and (6) for a fluidised bed unit as claimed in any preceding claims in which the flue gas flows downward in the section outside the outer cylinder, upward in the section between the outer and the inner cylinder and downward inside the inner cylinder.
A fluidised bed unit as claimed in any preceding claim in which the fluidised bed unit is provided with a plurality of temperature sensors arranged at different heights inside the fluidised bed unit, at least one of which is located in the fluidised bed media, at least one of which is located just above the fluidised bed media in a lower freeboard of the fluidised bed and at least one of which is located adjacent the top of the first cylinder, at least one of which is located in the third cylinder above the catalyst filter, at least one of which is located in the third cylinder inside the catalyst filter.
A fluidised bed unit as claimed in any preceding claim in which the fluidised bed unit is provided with a plurality of pressure sensors arranged at different heights inside the fluidised bed unit, at least one of which is located in the nozzle inlet box below the plurality of nozzles, at least one of which is located adjacent the top of the first cylinder, at least one of which is located in the third cylinder above the catalyst filter, at least one of which is located in the third cylinder downstream the catalyst filter.
A fluidised bed unit as claimed in any preceding claim in which in operation, the temperature of the fluidised bed is in the region of 450°C to 1000°C, the temperature just above the fluidised bed media is in the region of 600°C to 1200°C and the temperature in the third cylinder is in the region of 100°C to 800°C and the pressure is in the region -300 mbar to +300 mbar.
A fluidised bed unit as claimed in any preceding claim in which the fluidised bed media comprises, but it is not limited to quartz silica sand, olivine.
A fluidised bed unit as claimed in any preceding claim, in which the pressure of the system is controlled by an induced draft fan, which is in turn automatically controlled with feedback from any of the pressure sensors as claimed in (9) and the bed temperature is automatically controlled by a forced draft fan with feedback from the temperature sensor located inside the bed as claimed in (8).
A fluidised bed unit as claimed in any preceding claim for any known application involving fluidised bed reactors other than thermal treatment of feedstock.
A fluidised bed unit as claimed in any preceding claim where any cylindrical component can be replaced by a square, rectangular or other cross section.
A fluidised bed unit substantially as herein before described with reference to and as illustrated by the accompanying drawings.