EP3957909A1 - Asymmetric fluidized-bed furnace for combustion of materials - Google Patents

Abstract

The invention relates to a stationary-type fluidized-bed furnace comprising:a fluidized-bed reactor (A) which is set up to form a fluidized fluidized bed, comprising:a first zone for heat recovery (B1) comprising a fluidized fluidized-bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1 ) with fluidiser elements (6), anda second zone for primary combustion (B2) comprising a fluidized bed area without immersion heating surfaces and a fluidising gas distributor (C2) with fluidiser elements (6');wherein the first zone for heat recovery (B1) and the second zone for Primary combustion (B2) form a common fluidized bed, and wherein the fluidization of the fluidized bed area of the second zone (B2) has a higher speed than that of the first zone (B1), so that a fluidized bed-internal material circulation (F) between the first and second zone along the Sets immersion heating surfaces, andwherein the cross-section fl area of the first zone (B1) from 0.4 to 0.75 of the entire cross section of the fluidized bed reactor;a bed material discharge funnel (D) which is connected in the area below the fluidizing gas distributors (C1, C2); anda free space above the fluidized bed reactor (A), in which burnout air nozzles (3) are arranged within burnout air levels.The fluidized bed furnace and the method for operating the fluidized bed furnace are suitable, in particular, for burning materials with a high calorific value and a high proportion of volatile components . The technical effect is achieved through an asymmetric operation of the fluidized bed.

Description

The invention relates to a fluidized-bed furnace and a method for operating the fluidized-bed furnace for the combustion of substances, in particular materials with high calorific values, problematic composition and/or a high proportion of volatile components, comprising a stationary-type fluidized-bed reactor and a free space above the fluidized-bed reactor for post-combustion .

Background of the Invention

Fluidized bed technology has been used successfully for the combustion of coal and sewage sludge for decades. In the last twenty years or so, the range of fuels has been steadily expanded with, for example, biomass, biogenic residues, waste, production waste through to alternative fuels and other input materials processed from waste, such as paper sludge, RDF ( Refuse Derived Fuel ), SRF ( Solid Recovered Fuel ). At the same time, the requirements for the operation and design of fluidized bed systems have changed and expanded.

The fluidized bed itself consists primarily of bed material, consisting of sand and fuel ash, with a small proportion by mass of the fuel also being in the bed. The fluidized bed is fluidized using the so-called primary air, which is introduced as evenly as possible over the reactor cross-section by a gas distributor in order to achieve safe and uniform fluidization. As a result, the solids are moved three-dimensionally and thus mixed in the horizontal and vertical directions. This results in an even distribution of fuel and thus temperature within the bed. The uniform temperature distribution and the comparatively low fluidized bed temperature are the main advantages of fluidized bed combustion compared to grate and dust firing. The fluidized bed mass acts as a mobile heat accumulator and compensates for fluctuations in fuel quality with regard to calorific value, pollutant content and water content.

EP 0 431 163 A1 refers to a fluidized bed for incineration of various types of waste, characterized by the formation of internal circulation of the bed material. The internal circulation is caused by different fluidization velocities in different zones of the fluidized bed.

EP 2 933 557 A1 discloses a fluidized bed furnace composed of a furnace body, a movable bed plate, a first fluidized bed plate, a second fluidized bed plate, a fan and a turbo fan. The floor of the fluidized bed furnace has openings that are only permeable for the fluidizing gas. The bed material is transported to the extraction openings specially designed for this purpose and drawn off there. An internal bed circulation is set up, which ensures that the bed material is transported away. For this purpose, the fluidizing medium is introduced into the fluidized bed via diffuser plates inclined towards the outlet. In one embodiment, the fluidizing medium exits at two different exit velocities using two diffuser plates, creating a circulating vortex flow.

EP 0 740 109 A2 describes a stationary fluidized bed for the combustion of various materials, such as waste and coal. The design of the fluidized bed furnace described takes particular account of the removal of non-combustible components of the feedstock, such as ash, impurities or agglomerates.

EP 3 124 862 B2 describes in figure 1 discloses a fluidized bed furnace having incombustible matter outlet openings located in the bottom of a fluidized bed furnace. The fluidized bed furnace also includes different fluidized bed areas that have different fluidization speeds. Immersion heating surfaces are arranged in the fluidized bed area with a lower fluidization speed.

As already mentioned, the range of fuels has expanded significantly in recent years. There is a wide variety of fuels and waste fractions, some of which have high calorific values, a problematic ash composition, certain proportions of impurities and a high content of volatile components. Despite the advantages of the fluidized bed reactor, classic grate furnaces are often used for implementation in small to medium-sized thermal plants Although fluidized bed reactors of the circulating type offer procedural advantages, they can only be operated economically for large plants.

The principle of the stationary or bubble-forming fluidized bed is available as a variant of the process. In the case of fuels with a very high calorific value, particular attention must be paid to the fluidized bed temperature in order to prevent agglomerations in the fluidized bed in connection with other difficult fuel properties such as the composition of the ash and its softening behavior under temperature, as well as the presence of accompanying and disruptive substances.

A calorific value of around 18 MJ/kg is often given as the upper limit for the fuel for the stationary fluidized bed. The main reason is the setting of the bed temperature, which should typically be around 850°C, depending on the ash softening behavior, but not higher than the usual 900°C. If the fuel properties cannot be changed, other measures must be taken to ensure safe plant operation.

If too much energy is released in the fluidized bed as a result of the combustion of substances with a high calorific value, such as coal, which is characterized by a high calorific value but a low volatile content, it is necessary to extract heat from the fluidized bed. On the one hand, this can take place via the heat transfer to the reactor walls of the fluidized bed furnace, which are designed, for example, for evaporation in the water/steam cycle. On the other hand, heat dissipation is also possible via immersion heating surfaces additionally arranged within the fluidized bed.

When adjusting the temperature of the fluidized bed, other parameters such as the volatile content must also be taken into account. While in the case of coal (low volatile content) the predominant conversion of the fuel takes place in the bed itself, in the case of fuels with a higher volatile content the conversion is shifted to the free space above the fluidized bed itself The other part is only released on the surface of the fluidized bed, are also increasingly converted above the fluidized bed in the free space in the burnout zone. This reduces the fuel turnover within the bed and thus also the bed temperature.

Due to the need to be able to thermally utilize a wide variety of fuels and waste fractions, the object of the present invention is to expand the range of use of stationary or bubble-forming fluidized bed reactors with regard to the calorific value of the fuels. Particular attention is paid to fuels, some of which have high calorific values, whose ash has a complex composition and/or shows variable softening behavior that is strongly dependent on the temperature (tendency to agglomerate), and a non-negligible proportion of accompanying substances, impurities and volatile components feature.

• eine erste Zone zur Wärmerückgewinnung (B1) umfassend einen fluidisierten Wirbelbettbereich mit Tauchheizflächen (E) und einen Fluidisiergas-Verteiler (C1) mit Fluidiserelementen (6), und
• eine zweite Zone zur Primärverbrennung (B2) umfassend einen fluidisierten Wirbelbettbereich ohne Tauchheizflächen und einen Fluidisiergas-Verteiler (C2) mit Fluidiserelementen (6');
• wobei die erste Zone zur Wärmerückgewinnung (B1) und die zweite Zone zur Primärverbrennung (B2) ein gemeinsames fluidisiertes Wirbelbett ausbilden, und wobei die Fluidisierung des Wirbelbettbereiches der zweiten Zone (B2) eine höhere Geschwindigkeit aufweist als die der ersten Zone (B1), sodass sich eine Wirbelbett-interne Materialzirkulation (F) zwischen der ersten und zweiten Zone entlang der Tauchheizflächen einstellt, und
• wobei die Querschnittfläche der ersten Zone (B1) von 0,4 bis 0,75 des gesamten Wirbelschichtreaktor-Querschnitts umfasst; einen Bettmaterial-Abzugstrichter (D), der sich im Bereich unterhalb der Fluidisiergas-Verteiler (C1, C2) anschließt;
• und einen Freiraum oberhalb des Wirbelschichtreaktors (A), in dem Ausbrandluftdüsen (3) innerhalb von Ausbrandluft-Ebenen angeordnet sind.

This technical problem is solved by a stationary-type fluidized-bed furnace comprising a fluidized-bed reactor (A) which is set up to form a fluidized fluidized bed, comprising:

• a first heat recovery zone (B1) comprising a fluidized bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1) with fluidizing elements (6), and
• a second zone for primary combustion (B2) comprising a fluidized bed area without immersion heating surfaces and a fluidizing gas distributor (C2) with fluidizing elements (6');
• wherein the first zone for heat recovery (B1) and the second zone for primary combustion (B2) form a common fluidized bed, and wherein the fluidization of the fluidized bed region of the second zone (B2) has a higher speed than that of the first zone (B1), so that a material circulation (F) within the fluidized bed between the first and second zone along the immersion heating surfaces occurs, and
• wherein the cross-sectional area of the first zone (B1) comprises from 0.4 to 0.75 of the total fluidized bed reactor cross-section; a bed material discharge funnel (D) which follows in the area below the fluidizing gas distributors (C1, C2);
• and a free space above the fluidized bed reactor (A) in which burnout air nozzles (3) are arranged within burnout air planes.

In preferred embodiments, the cross-sectional area of the first zone (B1) comprises from 0.55 to 0.75 and more preferably from 0.60 to 0.75 of the total fluidized bed reactor cross-section.

According to the present invention, the object is achieved by a stationary type fluidized bed furnace by means of an asymmetric operation. Through combination Various features control the temperature within the fluidized bed furnace, so that in particular substances with a high calorific value that have a high volatile content can be burned with the apparatus according to the invention.

This is done through the local introduction of immersion heating surfaces, different fluidization speeds in different zones of the fluidized bed and control of the oxygen supply in two different zones of the fluidized bed, so that asymmetric operation and thus circulation of the bed material along the immersion heating surfaces are achieved. The oxygen supply is controlled by the separate setting of different fluidization speeds and by the separate control of the oxygen concentration in the fluidizing gas depending on the zone of the fluidized bed. The locally increased fluidization speed advantageously leads to the accumulation of agglomerates in the fluidized bed being reduced or completely prevented and at least slowed down. A partially higher fluidization speed in the fluidized bed zone, in which no immersion heating surfaces are attached, also ensures bed-internal circulation of the fluidized bed material.

The apparatus according to the invention makes it possible at the same time to ensure the removal of agglomerates and impurities and to ensure the post-combustion of the volatile components entering the free space from the fluidized bed. The structure also realizes a staged combustion of the volatiles within the fluidized bed furnace in order to avoid local temperature peaks in the free space.

Brief character description

• figure 1 shows a preferred variant of the fluidized bed reactor (A) for converting feedstocks with a high calorific value.
• figure 2 shows the influence on the bed temperature by varying the fluidized bed height in a variant of the fluidized bed reactor (A).
• Figures 3 and 4 show various possibilities for the geometric design of the cross-sectional area of the fluidized-bed reactor (A) and the arrangement of the immersion heating surfaces within the cross-sectional area of the fluidized-bed reactor (A).
• figure 5 , 6 and 7 show different configurations of the lower area of the fluidized bed reactor (A).
• figure 8 shows a possible embodiment of the fluidized bed reactor (A), in which a guide body (I) is used as an additional heat transfer surface.
• figure 9 shows a possible arrangement of the burnout air nozzles (3, 3') in the case of a circular cross section of the fluidized bed reactor (A).
• figure 10 shows a possible arrangement of the burnout air nozzles (3, 3') in the case of a rectangular cross section of the fluidized bed reactor (A).

Detailed description of the invention

As explained above, the present invention relates to a fluidized bed furnace of the stationary type comprising a fluidized bed reactor (A) which is set up to form a fluidized fluidized bed, comprising a first zone for heat recovery (B1) comprising a fluidized fluidized bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1) with fluidiser elements (6), a second zone for primary combustion (B2) comprising a fluidized fluidized bed area without immersion heating surfaces and a fluidising gas distributor (C2) with fluidiser elements (6'); wherein the fluidization of the fluidized bed area of the second zone (B2) has a higher speed than that of the first zone (B1), so that material circulation (F) within the fluidized bed occurs between the first and second zone.

According to the invention, the cross-sectional area of the first zone (B1) of the fluidized bed comprises from 0.4 to 0.75, preferably from 0.55 to 0.75 and more preferably from 0.60 to 0.75 of the total fluidized bed reactor cross-section.

The fluidized bed furnace also has a bed material discharge funnel (D), which connects in the area below the fluidizing gas distributors (C1, C2), and a free space above the fluidized bed reactor (A), in which burnout air nozzles (3) within burnout air levels are arranged.

In preferred embodiments, the fluidized bed reactor is a bubbling fluidized bed reactor.

"Fuels" within the meaning of this invention are basically substances that contain a certain proportion of combustible material, which in turn converts the stored energy into usable energy through oxidation, mostly in the form of combustion. The use of solid, liquid, sludge-like, pasty or gaseous materials are fundamentally possible. Such combustible materials may include various coals, tailings sludge, oil coal or oil coke, as well as wastes of all kinds and the like. A great advantage of the fluidized bed furnace according to the invention for the combustion of fuels is the thermal utilization or elimination of problematic substances. For example, petroleum coke (a lot of sulphur), chicken manure (low density), landfill gas (low calorific value) and much more can be converted. Other examples include mixed household waste, bulky waste, construction and demolition waste, waste wood, waste paint/varnish, waste oil, hazardous waste, production or industry-specific waste and other types of waste. In particular, residues with a high calorific value that can be used energetically can be used for this purpose, such as animal meal, shredder light fraction, etc. The different fuels can be used both individually (mono-combustion) and in a combination of different fuels.

As already explained above, the cross-sectional area of the first zone (B1) according to the invention comprises from 0.4 to 0.75 of the total fluidized bed reactor cross-section, preferably from 0.55 to 0.75, and more preferably from 0.60 to 0 ,75. The zones of the fluidized bed reactor are subdivided in a way that enables the person skilled in the art to carry out the invention described and bring about the technical effect according to the invention. One way of delimiting the two zones (B1) and (B2) from one another and defining these zones for the purposes of area calculation, i.e. for subdividing the reactor space or the fluidized bed, is as described below: the entire cross section of the fluidized bed is represented by the horizontal Cross-section at the top of the fluidized bed and is divided into two zones (B1, B2) by an imaginary line. The imaginary line runs in the middle between the fluidizing gas distributor of the first zone (C1) and the fluidizing gas distributor of the second zone (C2), so that the imaginary line is at the same distance from the fluidizing gas nozzles of both fluidizing gas distributors (C1, C2). is.

The basic ratio of the area ratio of the first zone of the fluidized bed (B1) to the total cross-sectional area is 40% or higher. In the case of fuels with higher calorific values, it is preferable to choose a fluidized bed furnace in which the proportion of the first zone (B1) is higher, so that the proportion of the second zone (B2) is correspondingly smaller compared to the total cross-sectional area. In those embodiments in which the proportion of the first zone (B1) is more than 50% based on the reactor cross section, the imaginary line separating the two zones from one another separates, shifted towards the second zone (B2) so that an asymmetric arrangement of the faces (B1, B2) along the axis formed by the imaginary line is obtained. The area percentage of the first zone (B1) is preferably 55% or higher, particularly preferably 60% or higher, of the total reactor cross section.

According to the invention, the zones of the fluidized bed have different fluidization rates. A first zone has a fluidization velocity that is less than the fluidization velocity of the second zone. This creates a bed-internal material circulation (F). As a result of the higher material circulation, the entire bed material and thus also the fuel particles distributed throughout the bed material are captured. Due to the higher fluidization in the second zone (B2), the oxygen supply also increases in this zone. This can intensify the combustion there. Due to the internal circulation, the burning particles reach all areas of the fluidized bed. Therefore, the combustion of the fuel takes place preferentially, locally more or less intensively, in the entire fluidized bed.

In general, the formation of agglomerates takes place during fluidized bed operation. The fluidized bed furnace according to the invention is able to at least partially prevent the formation of the agglomerates, alternatively to destroy them, or else to remove them via the discharge funnel. The higher fluidization speed within the second zone causes higher impulses, e.g. between bed material and agglomerates, resulting in more intensive bed material movement and thus promoting the dissolution of agglomerates.

The bed material, ie the solid that is fluidized to form a fluidized bed in the fluidized bed reactor, is a substance or a mixture of substances that does not itself take part in the combustion. The bed material is most often formed from ash, the solid residue from the combustion of organic matter, and, for example, gravel (sand), with approximately one to three percent by weight of the fuel used being added. Over time, the bed material leads to erosion, ie mechanical wear and tear of refractory building materials, eg the immersion heating surfaces arranged within the fluidized bed. In addition to positive side effects, eg the cleaning of the combustion chamber, erosion is to be rated negatively and leads to high material wear. This effect increases proportionally to the fluidization speed.

In preferred embodiments of the present invention, the slower fluidization is provided in the cooled zone of the fluidized bed (B1) to minimize erosion on the immersion heating surfaces arranged there. In the adjacent zone of the fluidized bed (B2), on the other hand, fluidization takes place more quickly in order to drive the circulation of the solids and to break up any agglomerates that may have formed.

The stationary type fluidized bed furnace according to the invention is operated asymmetrically at least with regard to the fluidizing gas quantity distribution within the fluidized bed material. The specific amount of fluidizing gas supplied in the first zone of the fluidized bed (B1) is correspondingly smaller than the specific amount of fluidizing gas in the second zone of the fluidized bed (B2), the specific amount of fluidizing gas corresponding to the amount of fluidizing gas in kg per m ² of the fluidized bed area. The fluidized bed furnace is preferably arranged in such a way that the specific amount of fluidizing gas based on the fluidized bed area of the second zone (B2) is at least 150% of the specific amount of fluidizing gas based on the fluidized bed area of the first zone (B1).

An even more preferred embodiment comprises a fluidized bed furnace constructed in such a way that the specific amount of fluidizing gas based on the fluidized bed area of the second zone (B2) is at least 200% of the specific amount of fluidizing gas based on the fluidized bed area of the first zone (B1).

Absolute values of the specific fluidizing gas quantities are to be selected depending on various parameters such as bed particle size distribution, bed temperature, composition of the fluidizing gas.

In order to achieve the different fluidization speeds, the zones of the fluidized bed are individually supplied with primary air via fluidizing gas distributors (C1, C2). The primary air corresponds to the fluidizing gas, which consists either of air alone or of a mixture of air and recirculated flue gas. The recirculated flue gas usually corresponds to only part of the gas mixture which is produced during the combustion process of substances in the fluidized bed furnace, is collected and returned to the fluidized bed furnace for the combustion of further substances. The recirculated flue gas can be removed at various points, so that it is uncooled, cooled (e.g. after a steam generator and/or after an air preheater), after gas cleaning, or collected at another point after firing and returned to the fluidized bed furnace for the combustion of other substances. In preferred embodiments, an individual amount of the recirculated flue gas is mixed into the primary air (= fluidization air) in each zone. This makes it possible to set different oxygen concentrations, which are asymmetrical in relation to the cross section of the fluidized bed reactor (A), while at the same time fluidizing is faster.

In preferred embodiments, the fluidized bed furnace is constructed such that the fluidizing gas fed via the fluidizing gas distributors to the first zone (B1) and the second zone (B2) of the fluidized bed is independently composed of air and/or recirculated flue gas.

The faster fluidized zone (B2) of the fluidized bed is preferably designed without internals. This has the advantage that higher gas velocities, i.e. due to greater fluidization, mean that a higher proportion of solids flows upwards. Since the fluidically connected first zone (B1) of the fluidized bed has a slower fluidization of the bed material compared to the second zone (B2), the bed material is sucked into the faster zone (B2), so that internal material circulation and thus good mixing take place. The cooling of the bed material in the first zone (B1) using immersion heating surfaces (E) also ensures that the temperature in the second zone (B2) is also lowered by the internal material circulation.

The proportion of recirculated flue gas in the primary air is advantageously adjusted as required and used to regulate the temperature. The proportion of recirculated flue gas should preferably be selected in such a way that a temperature of 950° C. is not exceeded in the faster zone of the fluidized bed (B2).

In preferred embodiments, the primary air is selected so that the proportion of oxygen is present in stages. The total oxygen Λ _Ges supplied to the fluidized bed furnace is made up of the oxygen Λ _B that is introduced into both zones of the fluidized bed B1 and B2 and of the oxygen that is introduced into the free space. Unless otherwise noted, the oxygen proportions are in each case based on the stoichiometric oxygen requirement for combustion of the total fuel O _min introduced. In particularly preferred embodiments, Λ _Ges has a value from 1.05 to 1.4 and Λ _B has a value from 0.35 to 0.9, preferably from 0.4 to 0.8. Via the air in the free space of the fluidized bed furnace, i.e. the burnout air of all levels, the remaining amount of required oxygen Λ _ABL is added. The Λ _ABL consists of the difference between Λ _Ges and Λ _B , so that Λ _ABL = Λ _Ges - Λ _B .

It is further preferred that the fluidized bed furnace is arranged in such a way that the oxygen content Λ _B , which is added directly to the fluidized bed, from the oxygen Λ B1 introduced into the fluidized bed region of the first zone (B1), from the oxygen Λ _B1 introduced into the fluidized bed region of the second zone (B2) oxygen Λ _B2 introduced and the oxygen introduced into the free space, in each case based on the stoichiometric oxygen demand O _min for combustion of the total fuel introduced, with Λ _B1 being greater than Λ _B2 . Preferably, Λ _B1 is 10% to 30% greater than Λ _B2 . In this way, the operation of the fluidized bed furnace can be asymmetrical with respect to the oxygen conditions within the fluidized bed furnace.

In advantageous embodiments, the fluidizing elements of a fluidizing gas distributor are arranged within a plane below the fluidized bed, with a distance between the individual fluidizing elements so that all fluidizing gas distributors are permeable to agglomerates, bed material and/or impurities that have formed. In this embodiment, the fluidizing gas distributor is designed in such a way that only agglomerates that are no larger than the distance between the fluidizing elements can pass. This advantageous arrangement (hereinafter also referred to as an open fluidizing gas distributor or an open nozzle base) allows impurities and/or agglomerates to be continuously removed, since they would otherwise cause a fluidization disruption. Consequently, there is a distance between the individual fluidizing elements, through which agglomerates, bed material and/or impurities between the nozzle elements are drawn down with the bed and thus transported away from the system.

The fluidizing elements of the fluidizing gas distributor (C1) of the first zone (B1) preferably form a plane that slopes down at an angle of 1° to 75° in the direction of the zone (B2), the plane of the fluidizing elements of the fluidizing gas distributor (C2 ) of the second zone (B2) is preferably aligned horizontally.

The fluidizing elements are preferably individual nozzles that are each supplied with a fluidizing gas. It is particularly preferred that the fluidizing elements are nozzles that sit on a nozzle bar that is filled with fluidizing gas for the number supplied by the nozzles located on the beam. The nozzle bar is preferably straight, curved or ring-shaped. It is advantageous that the fluidized bed furnace is constructed in such a way that, starting from the slowly fluidized zone of the fluidized bed (B1), the fluidizing elements are arranged downwards towards the fast fluidized zone of the fluidized bed (B2) (see also figure 6 ). In this way, the internal fluidized bed circulation is additionally supported.

In the prior art, a closed nozzle base, which is formed from diffuser plates, for example, is often used. A closed nozzle bottom, e.g. the sum of the diffuser plates, has no passage between the fluidizing elements, e.g. nozzles, so that in this case the bed material is transported away along the closed nozzle bottom by means of a central or lateral opening. This has the disadvantage that, in particular, fuels that contain higher amounts of impurities, e.g. non-combustible materials or agglomerates, cannot be converted.

Advantageous embodiments of the fluidized bed furnace according to the invention also contain at least one side wall of the fluidized bed reactor (A), preferably in the region of the fluidized bed of the first zone (B1), which is arranged widened upwards by an opening angle α with respect to the vertical. The opening angle α is 0° or more, preferably 5° or more, more preferably 15° or more. The asymmetrical arrangement of the side walls of the fluidized bed reactor generally favors the flow of solids through the fluidized bed, but in particular the downward-flowing movement of the coarse particles at the edge of the first zone of the fluidized bed.

It is also preferred to make the immersion depth of the immersion heating surfaces (E) and thus their possible heat absorption variable. The height of the fluidized bed is preferably chosen so that the immersion heating surfaces (E) in the fluidized bed of the first zone (B1) are either completely surrounded by the bed material or partially protrude into the free space of the fluidized bed furnace. When the entire immersion heating surfaces are surrounded by the bed material, the highest amount of heat can be absorbed. As the proportion of the uncovered immersion heating surface increases, the proportion of the absorbed heat quantity also decreases, so that the cooling effect of the immersion heating surfaces on the temperature of the fluidized bed decreases accordingly. In this way, the temperature in the fluidized bed can be regulated depending on the combustion properties of the substances to be burned.

In some preferred embodiments, at least one substantially vertically arranged guide body (I) is immersed in the fluidized bed between the fluidized bed of the first zone (B1) and the fluidized bed of the second zone (B2), so that there is a distance to the nozzle bottom and to the fluidized bed surface, wherein the geometric base area of the guide body (I) is flat or three-dimensional. The guide body (I) preferably serves as an additional heat transfer surface. Furthermore, the guide body (I) is preferably shaped with tapering inflow sides at the bottom and rounded outflow side at the top. If the fluidized-bed furnace has a guide body (I), this leads to an increase in circulation throughout the fluidized bed.

The technical effect of the guide body (I) only comes into its own if the immersion heating surfaces are arranged perpendicularly to the side surface of the guide body, as is shown in figure 8 is shown. By designing the immersion heating surfaces as in Figure 3 and Figure 4 as the right figure reveals, the immersion heating surfaces themselves preferably fulfill the function of the guide body (I).

The fluidized bed furnace has a discharge hopper for the discharge of bed material, ash and impurities. In preferred embodiments, the opening of the bed material discharge hopper (D) may be located below the first zone (B1), below the second zone (B2) or centered below the fluidized bed reactor (A). The walls of the bed material discharge hopper (D) are preferably designed as additional heat transfer surfaces. Likewise, in preferred embodiments, the walls of the fluidized bed reactor (A) are configured entirely or partially as heat transfer surfaces, preferably as evaporators.

In particularly preferred embodiments, the bed material discharge funnel (D) comprises additional gas supply nozzles. As a result, local loosening and/or fluidization of the bed material is achieved on the one hand, so that the removal of the solids, for example the disruptive matter, the ash and/or the bed material, is ensured. The additional gas feed into the discharge funnel (D) also leads to further cooling of the solid to be discharged. This also promotes the ejection of the solids without influencing the amount of heat inside the reactor, because the gas flowing in through the hopper (D) cools the solids to be removed and then rises warmed up in the fluidized bed.

According to the invention, the fluidized bed furnace has a free space above the fluidized bed reactor (A), in which combustion air nozzles (3) are arranged within combustion air levels. These burnout air nozzles (3) are preferably aligned within a burnout air plane tangentially to an imaginary tangential circle (G) lying in the free space of the reactor cross section.

The free space of the fluidized bed reactor (A) comprises at least a second burnout air level, the burnout air nozzles (3') of which are tangentially aligned to an imaginary tangential circle (H) lying in the free space of the reactor cross section, the tangential circle (G) of the first burnout air level having a different diameter than the Tangential circle (H) of the second burnout air level. In particularly preferred embodiments, the combustion air nozzles (3') of the second combustion air level are arranged at the same level as or above the combustion air nozzles (3) of the first combustion air level.

The free space comprising the burnout air levels or the burnout air level forms a so-called burnout zone in the free space of the fluidized bed furnace above the fluidized bed. The post-combustion gas is also referred to as burnout air and can consist of either air, air mixed with recirculated flue gas, or air mixed with other gases such as vapors and exhaust air. The burnout air is flown into the burnout zone with a high impulse and tangentially aligned in order to obtain a twisted flow, i.e. gas flows twisted into one another, and thus a good mixing of the gases in the free space.

The number of burnout air levels is selected as required. The requirement results from the content of volatile components in the fuel used. The higher the volatile content and thus also the proportion of the required burnout air above the fluidized bed, the more levels with burnout air should preferably be provided. The design of several burnout air levels has the advantage that the afterburning of the volatile components is staged in such a way that the temperatures within the fluidized bed furnace do not exceed a certain upper limit, which depends on the fuel itself.

Safe plant operation with fuels with problematic fuel properties can also be guaranteed by various other measures to reduce the tendency to agglomerate. Aside from the use of lower bed temperatures, appropriate fluidized bed material is appropriate selected for the fuel used, so that the tendency to agglomerate is prevented or at least reduced.

A regular or at least partially continuous replacement of the fluidized bed material with fresh material is also conceivable. Additional additives, e.g. mineral substances, can be added to the fluidized bed in order to reduce or prevent the formation of liquid or sticky phases within the fluidized bed reactor.

An increased fluidization speed can also contribute to preventing or at least slowing down the accumulation of agglomerates, since agglomerates that have already formed can be broken up again by the stronger bed movement and the larger impulses. At the same time, the stronger fluidization can support the equalization of the temperature.

The invention also relates to a method for operating the fluidized bed furnace described. In particular, the invention relates to a method for incinerating substances in a stationary-type fluidized-bed furnace, the substances being introduced into a fluidized-bed reactor (A) and being combusted, the fluidized-bed reactor (A) forming a fluidized fluidized bed comprising a first zone for Heat recovery (B1) comprising a fluidized bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1) with fluidizing elements (6), and a second primary combustion zone (B2) comprising a fluidized bed area without immersion heating surfaces and a fluidizing gas distributor (C2) with fluidizing elements (6'), wherein the fluidizing of the fluidized bed area of the second zone (B2) has a higher speed than that of the first zone (B1), so that a fluidized bed-internal material circulation (F) between the first and second zone along the Immersion heating surfaces sets, and wherein the cross-sectional area of the first en zone (B1) from 0.4 to 0.75, of the total cross section of the fluidized bed reactor; and wherein impurities, agglomerates and/or the bed material are drawn off via a bed material discharge hopper (D) which is connected in the area below the fluidizing gas distributor (C1, C2); and post-combustion being carried out in a free space above the fluidized bed reactor (A) in which burnout air nozzles (3) are arranged within burnout air levels.

During combustion, a fluidized bed temperature and a free space temperature are set that differ significantly from one another. Depending on the fuel in question and its fuel properties as well as the type and amount of volatile substances, the fluidized bed can be operated, for example, at temperatures below 800°C, above 850°C or between 800°C and 950°C. When selecting the temperatures, legal requirements and regulations must also be taken into account. In addition, the temperatures can be freely selected. The fugitives are mostly burned in the open air.

Fluidized bed furnaces are preferably used in the process according to the invention, the cross-sectional area of the first zone (B1) of the fluidized bed being from 0.55 to 0.75 and more preferably from 0.60 to 0.75 of the total fluidized bed reactor cross section.

The process preferably has an oxygen content Λ _B which is added directly via the fluidized bed. This is made up of the oxygen Λ _B1 introduced into the fluidized bed area of the first zone (B1), the oxygen Λ _B2 introduced into the fluidized bed area of the second zone (B2) and the oxygen introduced into the free space, each based on the stoichiometric oxygen demand O _min for burning all the fuel introduced, where Λ _B1 is greater than Λ _B2 . In preferred embodiments of the method, Λ _B1 is 10% to 30% greater than Λ _B1 .

In some embodiments, at least 150% of the specific amount of fluidizing gas in the first zone (B1) flows into the second zone (B2). In particularly preferred embodiments, at least 200% of the specific amount of fluidizing gas in the first zone (B1) flows into the second zone (B2).

The fluidizing elements of a fluidizing gas distributor are preferably arranged within a plane below the fluidized bed. A distance between the individual fluidizing elements is advantageous, so that formed agglomerates, bed material and/or impurities are passed through between the individual fluidizing elements of the fluidizing gas distributor.

Contaminants, agglomerates and/or the bed material are preferably drawn off continuously via the bed material discharge funnel (D).

In preferred embodiments, the method comprises the tangential inflow of a gas for post-combustion onto an imaginary circle (G) lying in the free space of the reactor cross section.

According to the invention, the fuel should preferably be fed in in such a way that distribution in or on the fluidized bed is as uniform as possible. In this case, the entire volume of the fluidized bed is preferably used for the fuel conversion. The internal circulation is preferably designed to be even and the fuel distributed homogeneously. Different types of fuel are added to the combustion either individually or one after the other (mono-combustion) or simultaneously in combination.

The fluidized bed furnace according to the invention and the method for burning substances in this fluidized bed furnace can in principle be used for all combustible substances. Normally, the combustion of fuels with such high calorific values in classic stationary type fluidized bed furnaces leads to problems such as uncontrollable local temperature peaks and increased agglomeration formation. The fluidized bed furnace is advantageously used for fuels with an average calorific value of more than 15 MJ/kg in the state when they are introduced into the fluidized bed. Advantageously, the fluidized bed furnace can be used for the combustion of fuels with a calorific value of more than 20 MJ/kg as they are placed in the fluidized bed.

The fluidized bed furnace according to the invention and the method for burning substances in this fluidized bed furnace can also be used advantageously when fuels are used with a content of volatile components of more than 50% by weight, based on the water- and ash-free fuel substance in the state when it is introduced the fluidized bed. The invention is even more advantageous for fuels with a volatile content of more than 70% by weight, based on the water- and ash-free fuel substance in the state when it is introduced into the fluidized bed.

Preferred aspects of the fluidized bed furnace according to the present invention are described in more detail in the following figures:
figure 1 shows a preferred variant of the fluidized bed reactor (A) according to the invention for the conversion of feedstocks with a high calorific value. Different Quantities of fluidizing gas (6 and 6') consisting of combustion air (1, 1') or a mixture of combustion air and recirculated flue gas (2, 2') are used, so that a fluidized bed area with slow fluidization (B1) and a Forms fluidized bed area with rapid fluidization (B2). In the area of slow fluidization (B1), immersion heating surfaces (E) are also used to remove reaction heat from the bed and thus adjust the bed temperature to the desired value.

In the area of fast fluidization (B2), the outflow speed of the fluidizing gas (6') is set higher, preferably much higher, than the outflow speed of the fluidizing gas (6) of the slower area (B1). As a result, significantly higher impulses are exerted on the particles in this area (B2), so that the cross-mixing between the slow bed (B1) and the fast bed (B2) is intensified. The arrows (F) represent the main circulation in the fluidized bed. While the upward movement of the bed material is forced in the area of fast fluidization (B2), the bed material preferably sinks again in the slowly fluidized part (B1).

Through the open gas distributor (C1, C2), coarse particles, agglomerates or even impurities can get into the bed material discharge hopper (D) and be continuously or discontinuously discharged from there together with the bed material (4). In order to complete the combustion and to be able to convert the volatile components discharged from the bed and optionally coke particles, combustion air is added as so-called burnout air (3) in the free space above the fluidized bed.

In figure 2 shows the influence on the bed temperature by varying the fluidized bed height. In order to influence the heat extracted by means of the immersion heating surfaces (E), in addition to influencing the fuel conversion in the bed by adjusting the available oxygen content, the method of lowering the fluidized bed is also available. In the case shown, the fluidized bed height is lowered, resulting in less immersion heating surface in the bed, where the high heat transfer coefficients prevail, and thus the heat absorption is reduced. Analogously shows figure 1 a completely immersed heating surface, which can thus absorb the maximum possible amount of heat. The basic operation corresponds to the description figure 1 .

Figure 3 and 4 show the geometric design of the fluidized bed cross-sectional area. This can be round, square or rectangular. In figure 3 different variants according to the invention of the arrangement of the immersion heating surfaces (E) are shown in a round reactor cross section.

In figure 4 different variants according to the invention of the arrangement of the immersion heating surfaces (E) are shown in a rectangular reactor cross section.

In figure 5 only the lower part of the fluidized bed is shown. In the embodiment shown, the bed material outlet (4) is located geometrically below the fast fluidized bed (B2). This embodiment is to be favored if, for example, coarse impurities are expected in the input material. Due to the increased fluidization speed, it is also possible to ensure that coarse impurities are discharged through the open nozzle floor in the direction of bed material discharge.

By adding additional gas (7, 7') to the bed material discharge funnel (4), the discharge, i.e. the outflow of the bed material through local loosening due to the gas addition, can be achieved. At the same time, the bed material to be drawn off is cooled by the addition of gas (7, 7'). The additional gas, also called hopper gas (7, 7'), can consist of air (1, 1'), of recirculated flue gas (2, 2') or of any mixture thereof.

The amount of hopper gas added can also vary locally in the hopper (4). The decisive factor here is the extent to which cooling is necessary and the extent to which an addition is necessary to ensure mechanical transport along the sloping funnel. For example, in the representation of figure 5 the addition of the hopper gas (7') can be dispensed with for transport reasons, since the hopper slope is very steep here, which ensures that the material is transported away and "slips". On the side of the addition (7), however, it is advantageous to add the funnel gas in order to support the material transport in the direction of the outlet (4) through local loosening. On both sides, however, the addition of hopper air (7, 7') may still be desirable in order to cool the material before it is discharged.

In figure 6 only the lower part of the fluidized bed is shown. In the variant shown, the arrangement of the gas distributor (C) is selected such that, starting from the slowly fluidized bed (B1), the gas distributor elements are arranged sloping in the direction of the rapidly fluidized part of the bed (B2). As a result, the circulation of the fluidized bed material, represented by the arrows (F), can be significantly supported.

figure 7 shows a modified embodiment of the fluidized bed according to FIG figure 6 . While the simplest form according to the present invention is a vertical configuration of the side walls in the bed area with either a round cross-section, or with a rectangular, or with a square cross-section, it is advantageous if the side walls are configured differently. The structure in shows an advantageous option for an alternative design figure 7 , in which in particular the wall of the fluidized bed reactor (A) associated with the first zone of the fluidized bed area (B1) widens slightly upwards (shown here by the opening angle α with respect to the vertical). This widening favors the flow of solids through the fluidized bed and in particular the coarse particles flowing downwards in the edge zones, ie on the wall of the fluidized bed reactor.

figure 8 shows an alternative embodiment of the fluidized bed reactor (A) with built-in guide body (I). A guide body (I) can advantageously be used to support the solids circulation that occurs within the fluidized bed. This is inserted vertically between the slow fluidized bed (B1) and the fast fluidized bed (B2) so that it is immersed inside the bed. There is a distance to the nozzle floor at the bottom and to the fluidized bed surface at the top, so that the bed material can follow the preferential circulation (F), but is supported in the direction of circulation by the guide body (I).

The guide body (I) can also be designed as a heat transfer surface, like the immersion heating surfaces (E), but can also be designed simply as a body without a heat absorption function.

The guide body can, as in figure 8 be schematically indicated fluidically advantageous shaped. For example, with tapered inflow sides at the bottom and rounded outflow side at the solids overflow at the top.

In the Figures 9 and 10 exemplary arrangements of the burnout air nozzles are shown in a reactor cross section. The fuels to be used are characterized by a high calorific value with often difficult ash properties at the same time, which tend to agglomerate and which can also contain impurities. These properties, such as those that occur in a wide variety of waste, residues or processed waste fractions, are often accompanied by a high content of volatile components.

This means that the conversion of the volatiles that are released during the combustion process and only partially oxidize in the fluidized bed must also be taken into account. For this reason, the design of the combustion air addition in the free space of the fluidized bed furnace according to the invention provides for an injection method above the fluidized bed to produce a sufficiently large amount of mixing.

figure 9 shows the exemplary arrangement of the burnout air nozzles in the case of a circular reactor cross section. The outflow direction of a part of the nozzles (3) is aligned tangentially to a larger virtual tangential circle (G) lying centrally in the cross section. Another part of the nozzles (3') is aligned tangentially to a smaller virtual tangential circle (H) lying centrally in the cross section.

As with the circular free space cross-section, the same method of adding burnout air can also be used in the case of square or rectangular cross-sections, as in figure 10 shown as an example.

The combustion air (3, 3') can consist of air or a mixture of air and recirculated flue gas (recigarette gas). Recigas can be added to the burnout air in a targeted manner, on the one hand to increase the discharge impulses of the nozzles, which improves the mixing in the flue gas flow (5) and/or to lower the temperature in the post-combustion zone due to the presence of Recigas.

A further improvement in the post-combustion zone, which can be achieved, for example, by improving the mixing and/or by grading the addition of burnout air, thus enlarging the reaction zone, which in turn helps to avoid temperature peaks, can be achieved by increasing the level of the burnout air addition ( 3) and (3') is chosen differently. The means that the injection of the combustion air is carried out in that the injection directed at the "small" tangential circle (H) takes place above or below the injection directed at the "larger" tangential circle (G).

reference list

A

= fluidized bed reactor

B1

= first zone of the fluidized bed (slowly fluidized)

B2

= second zone of the fluidized bed (rapidly fluidized)

C1

= fluidizing gas distributor of the first zone B1

C2

= fluidizing gas distributor of the second zone B2

D

= bed material discharge funnel

E

= immersion heating surface

f

= dominant direction of main fluidized bed material movement

G

= larger tangent circle

H

= smaller tangent circle

I

= guide body

S

= cutting line

1

= combustion air

1'

= combustion air

2

= recirculated flue gas

2'

= recirculated flue gas

3

= combustion air, burnout air

3'

= combustion air, burnout air

4

= bed material

5

= flue gas

6

= fluidizing gas

6'

= fluidizing gas

7

= funnel gas

7'

= funnel gas

a

= angle

Claims (17)

Stationary type fluidized bed furnace comprising: a fluidized bed reactor (A), which is set up to form a fluidized bed, comprising: a first heat recovery zone (B1) comprising a fluidized bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1) with fluidizing elements (6), and a second zone for primary combustion (B2) comprising a fluidized bed area without immersion heating surfaces and a fluidizing gas distributor (C2) with fluidizing elements (6'); wherein the first zone for heat recovery (B1) and the second zone for primary combustion (B2) form a common fluidized bed, and wherein the fluidization of the fluidized bed region of the second zone (B2) has a higher speed than that of the first zone (B1), so that a material circulation (F) within the fluidized bed between the first and second zone along the immersion heating surfaces occurs, and
wherein the cross-sectional area of the first zone (B1) comprises from 0.4 to 0.75 of the total fluidized bed reactor cross-section; a bed material discharge funnel (D) which follows in the area below the fluidizing gas distributors (C1, C2); and a free space above the fluidized bed reactor (A), in which burnout air nozzles (3) are arranged within burnout air levels. The fluidized bed furnace according to claim 1, wherein the proportion of oxygen Λ _B that is added directly to the fluidized bed is derived from the oxygen Λ _B1 introduced into the fluidized bed area of the first zone (B1), from the oxygen introduced into the fluidized bed area of the second zone (B2). Λ _B2 and the oxygen introduced into the free space, in each case based on the stoichiometric oxygen requirement O _min for combustion of the total fuel introduced, where Λ _B1 is greater than Λ _B2 , preferably Λ _B1 is 10% to 30% greater than Λ _B2 . The fluidized bed furnace according to claim 1 or 2, wherein the fluidizing elements of a fluidizing gas distributor are arranged within a plane below the fluidized bed and wherein there is a distance between the individual fluidizing elements, so that all fluidizing gas distributors are permeable to agglomerates, bed material and/or impurities formed. The fluidized-bed furnace according to claim 3, wherein the fluidizing elements of the fluidizing gas distributor (C1) of the first zone (B1) form a plane inclined at an angle of 1° to 75° in the direction of the zone (B2) and wherein the plane of the fluidizing elements of the Fluidizing gas distributor (C2) of the second zone (B2) is preferably aligned horizontally. The fluidized bed furnace of any one of claims 1 to 4, wherein the fluidizing gas fed via the fluidizing gas distributors to the first zone (B1) and the second zone (B2) of the fluidized bed is independently composed of air and/or recirculated flue gas. The fluidized bed furnace according to any one of claims 1 to 5, wherein the combustion takes place throughout the fluidized bed. The fluidized bed furnace according to one of claims 1 to 6, wherein the specific amount of fluidizing gas based on the fluidized bed area of the second zone (B2) is at least 150%, preferably 200% of the specific amount of fluidizing gas based on the fluidized bed area of the first zone (B1). The fluidized bed furnace according to one of Claims 1 to 7, wherein at least one essentially vertically arranged guide body (I) is immersed in the fluidized bed between the fluidized bed of the first zone (B1) and the fluidized bed of the second zone (B2), so that the nozzle bottom and there is a distance to the surface of the fluidized bed, the geometric base area of the guide body (I) being present in a planar or three-dimensional form. The fluidized bed furnace according to any one of claims 1 to 8, wherein the bed material discharge hopper (D) has additional gas supply nozzles. The fluidized bed furnace according to one of claims 1 to 9, wherein the burnout air nozzles (3) within a burnout air plane tangentially to an open space are aligned with the imaginary tangential circle (G) lying in the reactor cross-section. The fluidized bed furnace according to claim 10, wherein the free space of the fluidized bed reactor (A) contains at least a second level of burnout air, the burnout air nozzles (3') of which are aligned tangentially to an imaginary tangential circle (H) lying in the free space of the reactor cross section, the tangential circle (G) of the first Burnout air level has a different diameter than the tangential circle (H) of the second burnout air level. A method of burning materials in a stationary type fluidized bed furnace, wherein the materials are placed in a fluidized bed reactor (A) and burned,
wherein the fluidized bed reactor (A) forms a fluidized bed, comprising a first zone for heat recovery (B1) comprising a fluidized fluidized bed area with immersion heating surfaces (E) and a fluidizing gas distributor (C1) with fluidizing elements (6), and a second zone for primary combustion ( B2) comprising a fluidized fluidized bed area without immersion heating surfaces and a fluidizing gas distributor (C2) with fluidizing elements (6'), the fluidization of the fluidized bed area of the second zone (B2) having a higher speed than that of the first zone (B1), so that establishing a fluidized-bed internal material circulation (F) between the first and second zones along the immersion heating surfaces, and wherein the cross-sectional area of the first zone (B1) comprises from 0.4 to 0.75 of the total fluidized-bed reactor cross-section; and
whereby impurities, agglomerates and/or the bed material are drawn off via a bed material discharge hopper (D), which is connected in the area below the fluidizing gas distributor (C1, C2); and
post-combustion being carried out in a free space above the fluidized bed reactor (A) in which burnout air nozzles (3) are arranged within burnout air levels. Process according to Claim 12, in which impurities, agglomerates and/or the bed material are continuously drawn off via the bed material discharge hopper (D). Process according to Claim 12 or 13, in which, for afterburning, a gas is flowed in tangentially in an orientation towards an imaginary circle (G) lying in the free space of the reactor cross section. Process according to one of Claims 12 to 14, in which the proportion of oxygen Λ _B , which is added directly via the fluidized bed, is derived from the oxygen Λ B1 introduced into the fluidized bed region of the first zone (B1), from the oxygen Λ _B1 introduced into the fluidized bed region of the second zone ( B2) introduced oxygen Λ _B2 and the oxygen introduced into the free space, in each case based on the stoichiometric oxygen demand O _min for combustion of the total fuel introduced, where Λ _B1 is greater than Λ _B2 , preferably Λ _B1 is 10% to 30% greater as Λ _B1 . Method according to one of claims 12 to 15, wherein at least 150%, preferably at least 200%, of the specific amount of fluidizing gas in the first zone (B1) flows into the second zone (B2). The method according to any one of claims 12 to 16, wherein the fluidizing elements of a fluidizing gas distributor are arranged within a plane below the fluidized bed and wherein there is a distance between the individual fluidizing elements so that agglomerates, bed material and/or impurities formed between the individual fluidizing elements of the fluidizing gas distributor are carried out.

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