Bubbling Fluidized Bed Combustion Device and Method for Monitoring the Fluidized Bed in Such a Combustion Device

Abstract

A bubbling fluidized bed combustion device (1) comprising a fluidization vessel (2), a fluidized sand bed (3) arranged in the fluidization vessel and an arrangement for monitoring the fluidized sand bed. The arrangement comprises at least one radar level gauge (4) arranged to repeatedly measure a distance (D) in the fluidization vessel from a reference point (5) to at least one portion (6) of the top surface of (7) the fluidized sand bed, and to provide a measurement signal (S) representative of the distance. The invention also relates to a method for monitoring a fluidized bed in a bubbling fluidized bed combustion device.

Claims

1. A bubbling fluidized bed combustion device comprising a fluidization vessel; a fluidized sand bed arranged in said fluidization vessel; and an arrangement for monitoring said fluidized sand bed, said arrangement comprising at least one radar level gauge arranged to repeatedly measure a distance in said fluidization vessel from a reference point to at least one portion of the top surface of the fluidized sand bed, and to provide a measurement signal representative of said distance.

2. The bubbling fluidized bed combustion device according to claim 1, wherein said arrangement further comprises evaluation means configured to repeatedly determine a bed state parameter based on said signal, said state parameter being one of said distance, a level of said fluidized sand bed or a height of said fluidized sand bed.

3. The bubbling fluidized bed combustion device according to claim 2, wherein said evaluation means is configured to repeatedly determine a variation of said bed state parameter including determining an amplitude and/or a frequency of said variation based on current and previously determined bed state parameter values.

4. The bubbling fluidized bed combustion device according to claim 3, wherein said evaluation means is configured to repeatedly store data in a memory, said data including at least one of the determined bed state parameter, the determined amplitude and the determined frequency.

5. The bubbling fluidized bed combustion device according to claim 4, wherein said evaluation means is configured to apply a diagnostic algorithm to at least a sub set of said stored data to determine if said fluidized sand bed comprises agglomerated or sintered sand particles, wherein said diagnostic algorithm includes determining if said determined frequency is changing over time, and if so indicate that said fluidized sand bed comprises agglomerated or sintered sand particles.

6. The bubbling fluidized bed combustion device according to claim 3, further comprising: gas supply means arranged to supply gas to fluidize said sand bed; fuel supply means arranged to supply fuel to said sand bed; and feedback control means arranged to control said gas supply means and/or said fuel supply means based on at least one of the determined bed state parameter, the determined frequency and the determined amplitude in order to control combustion in said sand bed.

7. The bubbling fluidized bed combustion device according to claim 1, wherein the combustion device is configured to operate at a temperature between 750-900 C.

8. The bubbling fluidized bed combustion device according to claim 1, wherein said radar level gauge is configured to operate within a frequency range of 35-100 GHz.

9. A method for monitoring a fluidized bed in a bubbling fluidized bed combustion device comprising a fluidization vessel and a fluidized sand bed arranged in said fluidization vessel, said method comprising providing at least one radar level gauge in or at said fluidization vessel; and repeatedly measuring a distance in said fluidization vessel from a reference point to at least one portion of the top surface of the fluidized sand bed using said radar level gauge.

10. The method according to claim 9, further comprising repeatedly determining a bed state parameter based on a measurement signal from said radar level gauge being representative of said distance, said state parameter being one of said distance, a level of said fluidized sand bed or a height of said fluidized sand bed.

11. The method according to claim 10, further comprising repeatedly determining a variation of said bed state parameter including determining an amplitude and/or a frequency of said variation based on current and previously determined bed state parameter values.

12. The method according to claim 11, further comprising repeatedly storing data in a memory, said data including at least one of the determined bed state parameter, the determined amplitude and the determined frequency.

13. The method according to claim 12, further comprising applying a diagnostic algorithm to at least a sub set of said stored data to determine if said fluidized sand bed comprises agglomerated or sintered sand particles, said diagnostic algorithm including determining if said determined frequency is changing over time, and if so indicating that said fluidized sand bed comprises agglomerated or sintered sand particles.

14. The method according to claim 9, wherein said bubbling fluidized bed combustion device further comprises gas supply means arranged to supply gas to fluidize said sand bed and fuel supply means arranged to supply fuel to said sand bed, said method further comprising controlling combustion in said fluidized sand bed by controlling said gas supply means and/or said fuel supply means based on at least one of the determined bed state parameter, the determined frequency and the determined amplitude.

15. The method according to claim 9, further comprising operating the combustion device at a temperature between 750-900 C.

16. The method according to claim 9, wherein said radar level gauge operates within a frequency range of 35-100 GHz.

17. The method according to claim 16, wherein said radar level gauge operates within a frequency range of 50-80 GHz.

18. The bubbling fluidized bed combustion device according to claim 8, wherein said radar level gauge is configured to operate within a frequency range of 50-80 GHz.

19. A method for monitoring a fluidized bed in a bubbling fluidized bed combustion device comprising a fluidization vessel, a fluidized sand bed arranged in said fluidization vessel, gas supply means arranged to supply gas to fluidize said sand bed, and fuel supply means arranged to supply fuel to said sand bed, said method comprising providing at least one radar level gauge in or at said fluidization vessel, said radar level gauge operating within a frequency range of 35-100 GHz; repeatedly measuring a distance in said fluidization vessel from a reference point to at least one portion of the top surface of the fluidized sand bed using said radar level gauge; repeatedly determining a bed state parameter based on a measurement signal from said radar level gauge being representative of said distance, said state parameter being one of said distance, a level of said fluidized sand bed, or a height of said fluidized sand bed; repeatedly determining a variation of said bed state parameter including determining an amplitude and a frequency of said variation based on current and previously determined bed state parameter values; repeatedly storing data in a memory, said data including at least one of the determined bed state parameter, the determined amplitude, and the determined frequency; applying a diagnostic algorithm to at least a subset of said stored date to determine if said fluidized sand bed comprises agglomerated or sintered sand particles, said diagnostic algorithm including determining if said determined frequency is changing over time, and if so indicating that said fluidized sand bed comprises agglomerated or sintered sand particles; controlling combustion in said fluidized sand bed by controlling said gas supply means and/or said fuel supply means based on at least one of the determined bed state parameter, the determined frequency and the determined amplitude; and operating the combustion device at a temperature between 750-900 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and other aspects of the present invention will now be described in more detail with reference to the appended drawings, which show presently preferred embodiments of the invention, wherein:

[0025] FIG. 1 shows a schematic illustration of an embodiment of a bubbling fluidized bed combustion device according to the first aspect of the invention, and

[0026] FIG. 2 shows a flow chart of an embodiment of a method according to the second aspect of the invention.

DETAILED DESCRIPTION

[0027] FIG. 1 shows a schematic illustration of an embodiment of a bubbling fluidized bed combustion device 1 according the first aspect of the invention. The bubbling fluidized bed combustion device 1 comprises a fluidization vessel 2, a fluidized sand bed 3 arranged in the fluidization vessel, and an arrangement for monitoring the fluidized sand bed. The arrangement comprises a radar level gauge 4 and evaluation means 8.

[0028] The fluidization vessel 2 is a cylindrical container and is provided with a gas inlet or gas supply means 10 configured to communicate gas from below to the bed 3 at a sufficient velocity (for example within the range 0.6 m/s to 1.5 m/s) such that the bed is fluidized. The bed 3 comprises solid particles or sand, which may be silicate sand. In the figure, the gas supply means is connected to the interior of the fluidization vessel through a bottom end or surface thereof, but may in other embodiments have different physical shapes and positions, as long as the desired effect is achieved, i.e. to fluidize the bed 3. The gas comprises oxygen for the combustion of the fuel to take place in the fluidized bed.

[0029] The fluidization vessel is also provided with an exhaust gas outlet 11 arranged to evacuate exhaust gas from the fluidization vessel generated from combustion in the bed 3. In the figure, the exhaust gas outlet is connected to the interior of the fluidization vessel 2 through an upper end or surface 2a thereof, but may in other embodiments have different physical shapes and positions, as long as the desired effect is achieved, i.e. to evacuate generated exhaust gas.

[0030] The fluidization vessel is furthermore provided with fuel supply means 9 configured to communicate fuel to the fluidized bed 3. The fuel supply means 9 is arranged above the upper surface 7 of the bed, such that fuel is added to the bed from above. In the figure, the fuel supply means is connected to the interior of the fluidization vessel through a side surface thereof, but may in other embodiments have different physical shapes and positions, as long as the desired effect is achieved, i.e. to provide fuel to the fluidized bed. The fuel is combusted in the fluidized bed at a temperature between 750-900 C.

[0031] A water heating conduit 12 is provided in the fluidization vessel 2 above the bed 3, and is provided with an inlet 12a for water and an outlet 12b for heated water or water steam. The water heating conduit 12 functions as a heat exchanger wherein water entering the conduit is heated or evaporated by heat from hot exhaust gas (originating from combustion in the bed 3) which rises upwards towards the exhaust gas outlet 11. The bubbling fluidized bed combustion device in FIG. 1 may thus be referred to as a bubbling fluidized bed boiler.

[0032] The radar level gauge 4 is arranged through the upper end surface 2a of the fluidization vessel, and is arranged to measure a distance D in the fluidization vessel from a reference point 5 to at least one surface portion 6 of the top surface 7 of the fluidized sand bed. The radar level gauge is provided with an antenna, for example of the parabolic type, directed downwards towards the bed. The surface portion 6 is typically only a few square centimeters of size. The radar level gauge has a small angle of dispersion, for example 4 degrees. To provide a better measure of the fluidization of the entire bed, several radar level gauges may be used arranged to measure distance to different surface portions of the top surface of the bed. In other embodiments, the radar level gauge 4 may be arranged through a side wall or surface of the fluidization vessel. In this embodiment, the radar level gauge operates within a frequency range between 50-80 GHz.

[0033] The radar level gauge 4 provides a measurement signal S representative of the distance D. The radar level gauge is electrically connected to the evaluation means 8 to communicate the measurement signal S thereto. When the radar level gauge performs a measurement, frequency modulated continuous microwaves or pulses containing microwaves of electromagnetic radiation or a combination of both are transmitted from the radar level gauge in a direction towards the bed 3 and are reflected on the top surface 7 of the bed back to the antenna. In the figure, the path of the microwave beam or pulses is illustrated by the vertical dotted line shown in the figure, but it is understood that the measurements do not have to be performed vertically. The reference point in this embodiment is the position in the radar level gauge where the microwaves or microwave pulses are emitted (or received).

[0034] As will be discussed below in more detail with reference to FIG. 2, the radar level gauge 4 is configured to measure the distance repeatedly, i.e. at more than one instance, for example measure the distance continuously or with one or more predetermined time intervals, or with a predetermined rate, such as 6 times per minute. The evaluation means 8 is configured to repeatedly, e.g. continuously or with predetermined time interval(s) or with a predetermined rate, which may be between 6 to 60 times per minute, process the signal S and determine a bed state parameter, an amplitude and a frequency of a variation thereof and apply a diagnostic algorithm. This will also be discussed in more detail below with reference to FIG. 2.

[0035] In another embodiment of the device, which comprises all features of the embodiment described above with reference to FIG. 1, the device furthermore comprises feedback control means arranged to control said gas supply means 10 and/or said fuel supply means 9 based on at least one of the determined bed state parameter, the determined frequency and the determined amplitude in order to control combustion in said sand bed. For this purpose, the gas supply means may further include an electrically controllable blower or the like which allows the gas flow to be adjusted, and the fuel supply means may further include an electrically controllable pump or the like which allows the fuel flow to be adjusted. Alternatively, the gas supply means and fuel supply means may be provided with valves or throttles which allow respective incoming flows to be throttled. The feedback control means may be a separate physical unit, for example an electronic control unit (ECU), or may be implemented in the evaluating means or in another existing processing unit in or at the device.

[0036] FIG. 2 shows a flow chart of an embodiment of a method according to the second aspect of the invention. The method is for monitoring a fluidized bed in a bubbling fluidized bed combustion device comprising a fluidization vessel, a fluidized sand bed arranged in the fluidization vessel, for example according to the embodiment shown in FIG. 1.

[0037] The first step 101 of the method comprises providing at least one radar level gauge in or at the fluidization vessel.

[0038] In step 102, a distance in the fluidization vessel from a reference point to at least one portion of the top surface of the fluidized sand bed is measured using the radar level gauge.

[0039] In step 103, a bed state parameter is determined based on a measurement signal from the radar level gauge being representative of the distance. The bed state parameter being determined is one of the distance, a level of the fluidized sand bed or a height of the fluidized sand bed.

[0040] In step 104, a variation of the bed state parameter is determined based on the bed state parameter value determined in step 103 and at least one previously determined bed state parameter value. The at least one previously determined bed state parameter value has, in a previous iteration of the method loop, been stored in a memory in step 105, see below.

[0041] In step 105, data is stored in a memory. The data includes the determined bed state parameter, the determined amplitude and the determined frequency.

[0042] In step 106, a diagnostic algorithm is applied to at least a sub set the data stored in the memory to determine if the fluidized sand bed comprises agglomerated or sintered sand particles. The diagnostic algorithm includes determining if the determined frequency is changing over time (based on stored frequency values).

[0043] After step 106, the method returns to step 102 to once again measure the distance. In this manner, the method steps 102-106 are repeated with predetermined time interval(s) or with a predetermined rate. The memory will thus contain time resolved values of the bed state parameter, the amplitude and the frequency, i.e. values determined at each instant the method steps 102-106 are performed. The predetermined rate may be between 6 times per minute to 60 times per minute.

[0044] The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example the fluidization vessel does not necessarily have to be cylindrical, and the evaluation means may be separate from the actual bubbling fluidized bed combustion device or may be included as software in another processing means. The scope of protection is determined by the appended patent claims.