Description

The present invention generally relates to a fluidized bed reactor and in particular to a fluidized apparatus comprising a fluidized bed reactor as well as to a method for operating such a fluidized bed reactor. Hereinafter terms like “upper”, “lower”, “horizontal”, “vertical”, “inner” etc. always refer to a regular used position of the fluidized bed reactor. A fluidized bed apparatus typically comprises a fluidized bed reactor, which walls can be made of tubes, through which water runs, wherein said tubes are either welded directly to each other to provide a wall structure or with fins/ribs between parallel running tube sections. The wall of the fluidized bed reactor may also be made of bricks or bricks in combination with tubes.

The fluidized bed reactor comprises a reaction chamber for particulate and/or liquid matter, wherein the reaction chamber has at least one particulate matter inlet for the particulate matter and at least one primary particulate matter outlet for the particulate matter. The fluidized bed reactor may further comprise a fluidizing grate as part of a fluidizing bottom at the bottom of the reaction chamber, wherein the fluidizing grate has multiple openings for an operating fluid to fluidize particulate matter above the fluidizing grate within the reaction chamber. The multiple openings may be embodied by multiple nozzles, wherein each nozzle may have multiple openings.

Typically, the reaction chamber of such a fluidized bed reactor has at least one operating fluid outlet at its upper end, wherein said operating fluid outlet allows a mixture of gases and solid particles (hereinafter called particulate matter) exhausted from the reaction chamber to flow into at least one separator.

The separator serves to disengage the gases and particulate matter. Thereafter the separated reaction gases and the particulate matter are treated separately. The particulate matter may be directly returned into the reaction chamber.

The general design of a circulating fluidized bed apparatus and its components is disclosed in EP 0 495 296 A2.

The general process engineering of this type of a fluidized bed apparatus is more or less defined and includes: providing the particulate matter via an inlet opening into the reaction chamber, fluidizing the particulate matter by a (operating) gas, introduced under pressure via a fluidizing bottom, which may comprise respective nozzles and/or a grate in the grate area of the reaction chamber, eventually transferring the energy (heat) produced in the fluidized bed via heat transfer elements (in particular tubes through which a heat transfer fluid like water or steam flows), arranged in or adj acent to the reaction chamber or transferring the energy from the reaction gases having left the reaction chamber. Depending on the velocity of the provided operating fluid the fluidized bed can be embodied as stationary, bubbling or circulating fluidized bed.

More specifically, the present invention relates to a method for combusting carbonaceous fuel in a fluidized bed reactor, wherein at least one carbonaceous fuel is provided to the reaction chamber of the fluidized bed reactor.

Accordingly, a respective fluidized bed apparatus comprises a fluidized bed reactor, which has a reaction chamber, a fluidizing bottom at the bottom of the reaction chamber and at least one carbonaceous fuel supply above the fluidizing bottom. Furthermore, the fluidized bed apparatus comprises at least one source for a carbonaceous fuel being connected to the carbonaceous fuel supply and at least one fluidizing agent source being connected to the fluidizing bottom, wherein at least one fluidizing agent source is configured to supply a gas comprising gaseous oxygen.

In particular, the carbonaceous fuel may be a solid fuel, which is provided as the above described particulate matter to the reaction chamber. For example, the carbonaceous solid fuel may be coal or biomass. Additionally, a liquid carbonaceous fuel may be provided to the reaction chamber. For example, oil may be provided as liquid carbonaceous fuel to the reaction chamber.

In order that a combustion reaction of the carbonaceous fuel can occur, a fluidizing agent (also referred to as operating gas) comprising gaseous oxygen is provided at the bottom of the fluidized bed chamber, so that the carbonaceous fuel and in particular the solid carbonaceous fuel is fluidized by the provided fluidizing agent. In order that the combustion reaction starts, an ignition device may be arranged within the reaction chamber. The oxygen comprising gas is in particular air, which is supplied as primary air into the reaction chamber at the bottom of the reaction chamber through the fluidizing bottom. In this case, the fluidizing agent source may be the surrounding atmosphere.

In a preferred embodiment, solid carbonaceous fuel is provided to the reaction chamber, whereas liquid carbonaceous fuel may be added as auxiliary carbonaceous fuel. The combustion of carbonaceous fuel within a reaction chamber of a fluidized bed reactor is generally known, for example from EP 0 495 296 A2.

It is also known to add gaseous ammonia to the flue gases of the combustion reaction in order to reduce the nitrogen oxide emission. This method is known as selective non-catalytic reduction (SNCR). In order that a selective non- catalytic reduction occurs, ammonia (or urea) is inj ected at locations, where the temperature of the flue gases is between 760 °C and 1090 °C. If ammonia would be inj ected to the flue gases at higher temperatures, additional nitrogen oxide would be produced.

EP 0 280 016 A2 discloses a device for introducing a gaseous medium into a reaction chamber of a fluidized bed reactor. The disclosed device for introducing a gaseous medium can be arranged at multiple locations within the reaction chamber. It is disclosed, that the device is arranged at the bottom of the reaction chamber or above the bottom of the reaction chamber, so that the outlets of the device would be arranged within or above the fluidized bed during operation. Accordingly, the device disclosed in EP 0 280 016 can be used as fluidizing bottom or as a device for introducing gaseous medium within or above the fluidized bed. EP 0 280 016 A2 also discloses that ammonia can be supplied with the device. But it is not disclosed, at which location ammonia is supplied by the device. In light of the general technical knowledge it has to be assumed that the device is used to add ammonia to the flue gases, so that a selective non-catalytic reaction occurs.

Against this background, it is an obj ect of the present invention to provide a fluidized bed apparatus and a method for combusting carbonaceous fuel in a fluidized bed reactor, with which the CO2 emission can be reduced.

A solution for this obj ect is provided with a fluidized bed reactor and a method for combusting carbonaceous fuel in a fluidized bed reactor according to the features of the respective independent claim. Further solutions and preferred embodiments of the fluidized bed reactor and the method are subj ect matter of the dependent claims and the above and below description, wherein single features of the preferred embodiments can be combined with each other in a technically meaningful manner. Features disclosed with regard to the method can be applied to the fluidized bed reactor and vice versa.

In particular, it is suggested that ammonia (NH3) is combusted to provide thermal energy to the reaction chamber. Accordingly, the fluidized bed apparatus comprises at least one ammonia source, which is connected to a bottom of the reaction chamber.

With other words: The present invention suggests providing thermal energy to the reaction chamber, in which carbonaceous fuel is combusted, by combusting ammonia, wherein the thermal energy of the combustion of the carbonaceous fuel and the thermal energy of the combustion of ammonia can be withdrawn by the heat transfer elements of the fluidized bed reactor. The combustion of ammonia does not produce additional CO2. Furthermore, the invention can be implemented in existing fluidized bed apparatuses with only little effort. The thermal energy can either be produced directly in the reaction chamber by combusting ammonia within the reaction chamber or by combusting ammonia in order to heat up a medium which is supplied into the reaction chamber.

In a preferred embodiment ammonia is provided at the bottom of the reaction chamber. Accordingly, the at least one ammonia source is connected to the fluidizing bottom. With other words: Ammonia is added to the fluidizing bed, in which the combustion reaction of the carbonaceous fuel with the gaseous oxygen occurs, so that ammonia itself can react with the gaseous oxygen in a combustion reaction in an exothermic manner. This way, ammonia provided from the bottom of the reaction chamber can be combusted in a fluidized bed reactor together with the carbonaceous fuel. In this regard, it is believed that the ignition temperature for the combustion of ammonia within the fluidized bed is provided by the combustion process of the carbonaceous fuel.

By combusting ammonia, preferably within the fluidized bed of the reaction chamber, the emission of CO2 can be reduced without reducing the thermal energy generated, as ammonia may partly replace the carbonaceous fuel. Ammonia may be produced in times of a surplus of electrical energy of renewable energy sources. On the other hand, ammonia can be combusted on demand with the inventive method and apparatus. This way, a surplus of electrical energy may be chemically stored in the ammonia and used by the method of the present invention.

Ammonia may be added together with the gas comprising gaseous oxygen at the bottom of the reaction chamber, so that ammonia is part of the fluidizing agent. For example, the fluidizing agent source may be connected to a duct leading to the fluidizing bottom, wherein an inj ection apparatus is arranged within the duct and wherein the inj ection apparatus is connected to the ammonia source, so that ammonia is inj ected in the oxygen comprising gas supplied from the first fluidizing agent source through the duct. In this case, ammonia is part of the fluidizing agent provided through the fluidizing bottom into the reaction chamber.

In a specific embodiment, the inj ection apparatus may comprise at least one inj ector and at least one static mixer, wherein the at least one static mixer is arranged within the duct downstream of the at least one inj ector. In this configuration, ammonia inj ected through the inj ector into the duct is blended with the oxygen comprising gas, so that an evenly distributed mixture of the oxygen comprising gas and ammonia is supplied into the reaction chamber via the fluidizing bottom.

In a further specific embodiment, the inj ection apparatus comprises at least one pipe arranged within the duct, wherein at least one pipe has multiple inj ection openings through which ammonia is inj ected into the duct. By using such an array-like arrangement with multiple (at least two, preferably at least five or at least ten) pipes arranged over the cross section of the duct, ammonia can be inj ected at multiple locations (at least 20 or at least 50) over the cross section of the duct. Also in this configuration, an evenly distributed mixture of the oxygen comprising gas and the gaseous ammonia is provided to the reaction chamber via the fluidizing bottom.

Alternatively, ammonia may be introduced at the bottom of the reaction chamber in close vicinity of the location, at which the fluidizing agent is introduced into the reaction chamber at the bottom of the reaction chamber. For example, the fluidizing bottom may comprise multiple first openings and multiple second openings, wherein the multiple first openings are connected to the at least one first fluidizing agent source and wherein the multiple second openings are connected to the ammonia source.

The multiple openings of the fluidizing bottom may be embodied by multiple nozzles, which each may comprise at least one or more openings. Alternatively, the openings of the fluidizing bottom may be embodied in pipes, so that the fluidizing agent and ammonia are provided through a pipe (system) to the bottom of the reaction chamber. It may also be possible that the multiple openings of the fluidizing bottom are embodied as a perforated plate. In each case a group of first multiple openings may be connected to the first fluidizing agent source and another group of multiple openings may be connected to the ammonia source, in case ammonia is not mixed with the oxygen comprising gas beforehand.

In an alternative embodiment ammonia is combusted outside the reaction chamber, wherein the thermal energy produced by the combustion of ammonia is supplied into the reaction chamber. In particular, the combustion gases of the ammonia combustion are used to heat up a medium, in particular the fluidizing agent, which is supplied into the reaction chamber. For example, the fluidizing agent source may be connected to the duct leading to the fluidizing bottom, wherein a burner is arranged within the duct, wherein the burner is connected to the ammonia source so that combusted ammonia is added to the oxygen comprising gas supplied form the fluidizing agent source through the duct.

The ammonia is preferably stored at a pressure in a respective vessel, at which at least part of the ammonia may be in the liquid phase. In this case, it is preferable that gaseous ammonia is withdrawn from the ammonia source and provided to the reaction chamber.

Alternatively, ammonia in the liquid phase may be withdrawn from the ammonia source, in which case ammonia evaporates, when it is inj ected into the reaction chamber or into the duct leading to the reaction chamber.

In a preferred embodiment and independent if the gaseous ammonia is provided in a mixture with the oxygen comprising gas as fluidizing agent or if ammonia is provided separately from the fluidizing agent at the bottom of the reaction chamber, ammonia makes 2 % by volume to 30 % by volume of the whole volume of the gases provided at the bottom. Preferably, 5 % by volume to 25 % by volume and most preferably 10 % by volume to 20 % by volume of the gases provided at the bottom of the fluidized bed chamber is ammonia.

In an embodiment, the mass ratio of ammonia to carbonaceous fuel is between 0,05 and 0,5. Preferably, the mass ratio of ammonia to carbonaceous fuel is between 0, 1 and 0,25 and most preferably between 0,2 and 0, 1. Accordingly, 5 % to 50 % by mass of the carbonaceous fuel may be replaced by ammonia to receive a similar heat output. Even if the carbonaceous fuel is not replaced by ammonia but ammonia is added to the combustion process at a constant mass supply of the carbonaceous fuel, the mass of the supplied ammonia may be between 5 % to 50 % of the mass of the supplied carbonaceous fuel.

The invention and the technical background will now be described with regard to the figures. The figures show schematically

Figure 1 : a fluidized bed apparatus with a duct leading to a fluidizing bottom,

Figure 2: an embodiment of an inj ection apparatus arranged in the duct and

Figure 3 : a further embodiment of an inj ection apparatus arranged in the duct.

The fluidized bed apparatus shown in Figure 1 comprises a fluidized bed reactor 1 , which has a reaction chamber 2, at which bottom a fluidizing bottom 3 is arranged. A duct 8 is connected to the fluidizing bottom 3, through which duct 8 an oxygen comprising gas from a fluidizing agent source 6 is supplied to the fluidizing bottom 3.

An inj ection apparatus 9 is arranged within the duct 8. The injection apparatus 9 is connected to an ammonia source 7, so that ammonia can be inj ected into the duct 8 and into the oxygen comprising gas flowing towards the fluidizing bottom 3.

The fluidized bed apparatus comprises two carbonaceous fuel sources 5, which are connected to respective carbonaceous fuel supplies 4 arranged above the fluidizing bottom. For example, solid fuel such as coal or biomass may be provided from the carbonaceous fuel source 5 into the reaction chamber 2 via the upper carbonaceous fuel supply. Furthermore, oil as liquid carbonaceous fuel may be supplied from the carbonaceous fuel source 5 through the lower carbonaceous fuel supply 4.

The fluidized bed apparatus further comprises a secondary air supply 15, with which secondary air may be supplied into the reaction chamber 2. Additionally, the fluidized bed apparatus comprises an ignition device 14, which is arranged within the reaction chamber 2.

A separator 16 is arranged adj acent to the reaction chamber 2, wherein the separator 16 is connected via a return duct 17 to the reaction chamber 2 above the fluidizing bed 3.

During operation, carbonaceous fuel is supplied from the carbonaceous fuel supply 4 into the reaction chamber 2, in which the carbonaceous fuel is fluidized by a gas mixture provided from duct 8 through the fluidizing bottom 3. The fluidizing agent provided through the duct 8 comprises an oxygen comprising gas from the fluidizing agent source 6 and ammonia from the ammonia source 7. In order to start a combustion process, the ignition device 14 is actuated.

When the combustion process is started, the carbonaceous fuel reacts with the oxygen and ammonia reacts with the oxygen in combustion processes. Accordingly, the thermal energy generated in the reaction chamber 2 is based on a combustion of the carbonaceous fuel and of ammonia. Secondary air may be added to the combustion process through the secondary air supply 15. As the combustion process is not solely based on the combustion of carbonaceous fuel, less carbon dioxide is exhausted.

Solid particles leaving the reaction chamber 2 at the upper end are separated from the combustion gases 9in separator 16, whereas the separated solid particles are returned to the reaction chamber 2 via the return duct 17.

The inj ection apparatus 9, with which ammonia is inj ected into the duct 8 may comprise multiple injectors 10, as depicted in Figure 2. Each inj ector 10 has a single opening, through which ammonia is inj ected into the duct 8. A static mixer for each inj ector 10 is arranged downstream to the inj ector 10 within the duct 8. Thereby, ammonia is evenly mixed with the oxygen comprising gas.

In the embodiment according to Figure 3, multiple pipes 12 are arranged beside each other within the duct 8, wherein each pipe 12 comprises multiple openings 13 through which ammonia is inj ected into the duct 8. Accordingly, ammonia is evenly distributed inj ected into the duct 8 already at the plane of inj ection. Reference signs

Fluidized bed reactor Reaction chamber Fluidizing bottom Carbonaceous fuel supply

Carbonaceous fuel source

Fluidizing agent source Ammonia source

Duct

Inj ection apparatus

Inj ector

Static mixer

Pipe

Inj ection opening

Ignition device

Secondary air supply

Separator

Return duct