GB1589567A

GB1589567A - Fluidised bed apparatus

Info

Publication number: GB1589567A
Application number: GB3992076A
Authority: GB
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1977-09-15
Filing date: 1977-09-15
Publication date: 1981-05-13

Description

(54) FLUIDISED BED APPARATUS (71) We, NORTHERN ENGINEERING IN DUSTRIES LIMITED, a British Company of NEI House, Regent Centre, Newcastleupon-Tyne NE3 3SB, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to fluidised bed apparatus.

Fluidised bed apparatus according to the invention comprises a chamber in which there is an apertured support for supporting a bed of particles, a fan blower operable to cause a flow of gases through the support, ducting connected to the chamber, a first part of said ducting being connected to the fan or blower and to the chamber beneath the support, and valve means in said ducting which are selectively operable to reverse the direction of said flow of gases.

In one form of the apparatus, said valve means are selectively operable to place said first part in communication with the input side or the output side of the fan or blower.

In another form of the apparatus, said valve means are selectively operable to p]ace said first part in communication with atmosphere or the output side of the fan or blower.

In a third form of the apparatus, said valve means are selectively operable to cause gas from the output side of the fan or blower either to induce gas to flow downwardly through the support and away from the chamber or to flow into the chamber beneath the support.

Three forms of apparatus will now be described to illustrate the invention by way of example with reference to the drawings accompanying the provisional specification in which Figures 1, 2 and 3 are diagrammatic and schematic sections through first second and third forms of apparatus respectively.

The apparatus shown in Figure 1 comprises a chamber 10 containing an apertured support plate 12 supporting a bed of insert particles 14 for example of sand or alumina.

A fan or blower 30 is operable to cause a flow of gases through the support. Ducting is connected to the chamber and contains valve means selectively operable to reverse the direction of said flow of gases as is described more fully below.

The part of the chamber 10 below the support plate 12 is connected, by a first part of said ducting, to the output of a fan or blower 30. Said first part of said ducting is formed by a duct 26 and a duct 29, the duct 26 being connected to the chamber 10 and to a control valve 28 of said valve means and the duct 29 being connected to the valve 28 and the output of the fan or blower 30.

The upper end 15 of the chamber 10 is connected by a second part of said ducting to an exhaust stack 20. The second part of said ducting is formed by a duct 16 containing a control valve 18 and another duct 22, containing a further control valve 24, which leads to the atmosphere, the duct 22 being connected to the duct 16 between the valve 18 and the chamber ]0.

A duct 32 containing a control valve 34 connects the duct 29 to the duct 16 after the valve 18 so that it is in direct communication with the stack 20.

The input side of the fan or blower 30 is connected to a duct 40 containing a control valve 42 and leading to atmosphere. A duct 36, containing a control valve 38, connects the duct 26 to the duct 40 between the valve 42 and the fan or blower 30.

The chamber 10 represents the combustion chamber of a boiler such as a shell boiler. Alternatively, the chamber 10 may represent another type of boiler; or it may represent the furnace of a gasifier apparatus in which coal is heated to produce gases which are used to fuel a boiler (not shown), or are used for other purposes.

In the case of boilers, the chamber 10 has a sufficient freeboard space 15 above the bed to ensure adequate combustion of carbon monoxide and any other combustible gases evolved from the bed and in general the upper level of the bed of particles 14 which is shown slumped and not fluidised will be at or below the mid-level of the chamber 10 when fluidised.

In the case of a boiler, water tubes 44 may, if desired, pass through the bed of particles 14. In one form of the boiler, the tubes 44 may be connected to the interior of a shell 46 which contains a body of water heated by heat transfer through the furnace wall 10. Alternatively the tubes 44 may be connected to an external circuit system. The boiler may be used for producing steam or for heating water. The tubes 44 or similar tubes may be used for controlling the temperature of the bed of particles 14 by control of the flow of water through the tubes independently of the conditions appertaining in the shell 46.

The fluidised bed apparatus is started up from cold as follows: particulate coal, coke or other solid fuel is fed to the bed so as to be spread as a layer on top of the bed of particles 14. A readily ignited material, such as oily, waste rags, is placed on top of the layer of coal and ignited. The fan or blower 30 is started, with the valve 28 closed and with the valves 24, 38 and 34 open. The valves 42 and 18 may be closed or may be slightly open to allow intake of cold air or recirculation of some gas. The hot gases resulting from the combustion of the oily, waste material are drawn downwardly through the bed of particles 14 and through the fuel layer and pass through the fan or blower 30.The boiler is designed so that the valves can be adjusted to give a sufficient pressure drop through the bed to draw an adequate quantity of hot products of combustion from the ignited fuel to heat the bed in a relatively short time. The arrows show the gas flow paths.

When the bed is sufficiently hot, the valves 24, 38 and 34 are closed to stop downward air flow through the bed. The heat capacity of the bed is sufficient to maintain the bed temperature while the valves 18, 28 and 42 are opened and the fan or blower 30 is operated so as gradually to increase the upward flow of air through the bed until it fluidises.

Fuel is then fed to the bed to continue combustion and eventually burning fuel is distributed throughout the bed.

In those instances where the fluidised bed apparatus has tubes 44, at start-up the tubes 44 contain cold water and a particular advantage of apparatus according to the invention, is that the bed is progressively heated from the top by the downward flow of hot gases. When using such a flow of hot gases, the bed is in a packed condition and consequently heat transfer to the tubes 44 is very limited, the majority of the sensible heat in the gases transferring to the particles of the bed. This avoids the drawback inherent in known methods of ignition using an upward flow of hot gases in which, owing to the bed being fluidised, a large proportion of heat is transferred to the cold water in the tubes 44 instead of to fuel in the bed.In many forms of apparatus, in which tubes in the bed contain cold water at start-up, it is impossible to achieve a practicable mode of ignition using upward flow.

Instead of the ignition of waste material, an auxiliary gas or oil burner may be provided to direct a flame on to the top of the bed to ignite fuel during start-up.

Fuel may be mixed with particles throughout the bed before the start-up procedure is begun, in another alternative.

The plate 12 is not subjected to very hot gases during start-up and its temperature can be maintained at all times below, say 2000C.

In another modification, the bed initially may only partially cover the tubes 44, or leave them exposed, the bed depth being increased progressively after initial ignition by the addition of fuel mixed with inert bed particles after the bed has been fluidised upon reaching operating temperature.

Figure 2 shows a second form of the ap Apparatus in which the fan or blower has its output connected via said ducting and valve means to both the chamber below the support 12 and the upper end 15 of the chamber above the support 12, so that the fan or blower can force air downwardly through the bed during start-up and can force air upwardly through the bed for fluidisation during normal running of the boiler.

In Figure 2 parts similar to those shown in Figure 1 are given the same reference number. A first part of said ducting connects the chamber 10 beneath the plate 12 to the output of the fan or blower 30. The first part of said ducting is formed by ducts 50 and 53, the duct 50 being connected to a valve 52 and the chamber 10 and the duct 53 being connected to the valve 52 and to the output of the fan or blower 30.

The duct 53 is connected by,a duct 54 containing a control valve 56 to another duct 58. The duct 58 contains a control valve 60 and connects the upper end of the chamber 10 to the stack 20.

The duct 50 is connected to a duct 62 containing a control valve 64 and leading to the stack 20, being connected to the duct 58 between the valve 60 and the stack 20.

The input of the fan or blower 30 has an inlet duct 70.

During start-up, oily waste is used to ignite a layer of fuel on top of the bed 14, or fuel distributed throughout the bed and air is forced downwardly through the bed by the fan or blower 30. The valve 52 is closed and valves 56 and 64 are open. The valve 60 is either closed or is open slightly to allow some re-circulation of gas if desired.

The arrows show the gas flow paths.

Once the fuel in the bed is sufficiently ignited and the bed sufficiently hot the valves 56 and 64 are closed. The valves 52 and 60 are opened and the fan or blower 30 is operated so as progressively to fluidise the bed 14.

A third form of the apparatus is shown in Figure 3. In Figure 3, parts similar to those shown in Figures 1 and 2 are given the same reference numerals. In this embodiment, the first part of the ducting connecting the chamber 10 beneath the support plate 12 to the fan or blower 30 includes an ejector pump.

The output of the fan or blower 30 is connected to a duct 72 leading to a nozzle 74. The nozzle 74 discharges into a venturi throat 76 formed in a duct 78 (here shown enlarged). The discharge end of duct 78 is controlled by valve means in the form of a damper valve 80. Duct 50 connects the venturi throat 76 with the chamber beneath the bed, as shown in Figure 2 but with valve 52 omitted. A duct 82 connects the chamber above the bed with stack 20.

During start-up, ignition is effected as described previously and with fan or blower 30 running and the damper valve 80 open. Air discharging from nozzle 74 causes a reduction in pressure in the venturi throat 76 which results in the products of combustion from the ignited fuel being drawn down through the bed, into the venturi throat and discharged through the duct 78 to atmosphere. When the bed is suitably hot, which can be detected by a temperature sensor placed on or near plate 12, damper valve 80 is closed, thus reversing the gas flow along duct 50. The ignited bed becomes fluidised and operates normally; air passing from the fan or blower along the duct 72, through nozzle 74 and along duct 50. This apparatus has a reduced number of valves as compared with the previous two apparatuses.

The nozzle 74 and the venturi pressurereducing throat 76 can be replaced by any other form of ejector pump. For example, the duct 72 can instead lead into an annular duct (not shown) surrounding the mouth of the venturi throat 76, the annular duct having an annular gap through which the air is discharged on to the surface of the venturi throat 76, the air following the contour of the throat 76 (this being known as the Coanda effect). The air flow along the surface of the venturi throat 76 causes air to be entrained and so causes combustion gases to flow along duct 50 into duct 78 when the damper valve 80 is open.

In a modification (shown in chain-dot lines) of the construction of Figure 3, the stack 20, instead of being separate, can form an extension of duct 78, the duct 82 extending in the stack 20 above the damper valve 80 in the duct 78. In this instance, during start-up, since the air flowing into the chamber above the bed is derived from the stack 20 it will contain a proportion of exhaust gases which are entering the stack 20 from the duct 78. The air for supporting combustion will be provided from the fan or blower 30 which is also discharging into the stack from the duct 78. Owing to the mixing of exhaust gases and combustion air, the ambient temperature of the combustion air will tend to rise and so lead to a faster more efficient start-up.

Material which was originally a part of this specification has been made the subject of a divisional Application No.

36152/79 (Serial No. 1589568). That application describes and claims a method of starting up a fluidisable bed in which fuel is to be burned, which method comprises igniting solid fuel at the top of a bed of particles, causing hot gases from the ignited fuel to flow downwardly through the bed to heat the bed and reversing the flow of gases through the bed to fluidise the bed once the bed has reached operating temperature.

WHAT WE CLAIM IS:- 1. Fluidised bed apparatus comprising a chamber in which there is an apertured support for supporting a bed of particles, a fan or blower operable to cause a flow of gases through the support, ducting connected to the chamber, a first part of said ducting being connected to the fan or blower and to the chamber beneath the support, and valve means in said ducting which are selectively operable to reverse the direction of said flow of gases.

2. Apparatus according to claim 1, in which said valve means are selectively operable to place said first part in communication with the input side or the output side of the fan or blower.

3. Apparatus according to claim 2, in which said valve means and said ducting comprise a first control valve connected to a first duct, a second duct connected to the first valve and to the output side of the fan or blower, the first and second ducts being said first part of said ducting, a third duct, containing a second control valve, connected to the second duct and leading to atmosphere, a fourth duct, containing a third control valve, connected to the input side of the fan or blower and open to atmosphere,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. During start-up, oily waste is used to ignite a layer of fuel on top of the bed 14, or fuel distributed throughout the bed and air is forced downwardly through the bed by the fan or blower 30. The valve 52 is closed and valves 56 and 64 are open. The valve 60 is either closed or is open slightly to allow some re-circulation of gas if desired. The arrows show the gas flow paths. Once the fuel in the bed is sufficiently ignited and the bed sufficiently hot the valves 56 and 64 are closed. The valves 52 and 60 are opened and the fan or blower 30 is operated so as progressively to fluidise the bed 14. A third form of the apparatus is shown in Figure 3. In Figure 3, parts similar to those shown in Figures 1 and 2 are given the same reference numerals. In this embodiment, the first part of the ducting connecting the chamber 10 beneath the support plate 12 to the fan or blower 30 includes an ejector pump. The output of the fan or blower 30 is connected to a duct 72 leading to a nozzle 74. The nozzle 74 discharges into a venturi throat 76 formed in a duct 78 (here shown enlarged). The discharge end of duct 78 is controlled by valve means in the form of a damper valve 80. Duct 50 connects the venturi throat 76 with the chamber beneath the bed, as shown in Figure 2 but with valve 52 omitted. A duct 82 connects the chamber above the bed with stack 20. During start-up, ignition is effected as described previously and with fan or blower 30 running and the damper valve 80 open. Air discharging from nozzle 74 causes a reduction in pressure in the venturi throat 76 which results in the products of combustion from the ignited fuel being drawn down through the bed, into the venturi throat and discharged through the duct 78 to atmosphere. When the bed is suitably hot, which can be detected by a temperature sensor placed on or near plate 12, damper valve 80 is closed, thus reversing the gas flow along duct 50. The ignited bed becomes fluidised and operates normally; air passing from the fan or blower along the duct 72, through nozzle 74 and along duct 50. This apparatus has a reduced number of valves as compared with the previous two apparatuses. The nozzle 74 and the venturi pressurereducing throat 76 can be replaced by any other form of ejector pump. For example, the duct 72 can instead lead into an annular duct (not shown) surrounding the mouth of the venturi throat 76, the annular duct having an annular gap through which the air is discharged on to the surface of the venturi throat 76, the air following the contour of the throat 76 (this being known as the Coanda effect). The air flow along the surface of the venturi throat 76 causes air to be entrained and so causes combustion gases to flow along duct 50 into duct 78 when the damper valve 80 is open. In a modification (shown in chain-dot lines) of the construction of Figure 3, the stack 20, instead of being separate, can form an extension of duct 78, the duct 82 extending in the stack 20 above the damper valve 80 in the duct 78. In this instance, during start-up, since the air flowing into the chamber above the bed is derived from the stack 20 it will contain a proportion of exhaust gases which are entering the stack 20 from the duct 78. The air for supporting combustion will be provided from the fan or blower 30 which is also discharging into the stack from the duct 78. Owing to the mixing of exhaust gases and combustion air, the ambient temperature of the combustion air will tend to rise and so lead to a faster more efficient start-up. Material which was originally a part of this specification has been made the subject of a divisional Application No. 36152/79 (Serial No. 1589568). That application describes and claims a method of starting up a fluidisable bed in which fuel is to be burned, which method comprises igniting solid fuel at the top of a bed of particles, causing hot gases from the ignited fuel to flow downwardly through the bed to heat the bed and reversing the flow of gases through the bed to fluidise the bed once the bed has reached operating temperature. WHAT WE CLAIM IS:-

1. Fluidised bed apparatus comprising a chamber in which there is an apertured support for supporting a bed of particles, a fan or blower operable to cause a flow of gases through the support, ducting connected to the chamber, a first part of said ducting being connected to the fan or blower and to the chamber beneath the support, and valve means in said ducting which are selectively operable to reverse the direction of said flow of gases.

and a fifth duct, containing a fourth control valve, connected to the first duct and to the fourth duct between said third valve and the fan or blower.

4. Apparatus according to claim 2 or 3, in which said valve means and said ducting comprise a second part of said ducting which contains a control valve and which is connected to the chamber above the support and to a stack.

5. Apparatus according to claim 4, in which said second part of said ducting comprises two ducts one of which contains the control valve and the other being connected to said one duct between the valve and the chamber, said other duct containing a further control valve and leading to atmosphere.

6. Apparatus according to claim 4 or 5 as dependent on claim 3, in which said third duct leads to atmosphere through the stack.

7. Apparatus according to claim 1, in which said valve means are selectively operable to place said first part in communication with atmosphere or the output side of the fan or blower.

8. Apparatus according to 'claim 7, in which said valve means and said ducting comprise a first control valve connected to a first duct, a second duct connected to the first valve and to the output side of the fan or blower, the input side of the fan or blower being open to atmosphere, the first and second ducts being said first part of said duct, a third duct, containing a second con trol valve, connected to the second duct, a fourth duct, containing a third control valve, connected to the first duct and leading to atmosphere, and a fifth duct, containing a fourth control valve, connected to the chamber above the support and leading to atmo sphere, the third duct being connected to said fifth duct between the chamber and said fourth valve.

9. Apparatus according to claim 8, in which the fifth duct is connected to a stack.

10. Apparatus according to claim 9, in which the fourth duct leads to atmosphere through the stack.

11. Apparatus according to claim 9 or 10, in which the fourth duct is connected to the fifth duct between said fourth valve and the stack.

12. Apparatus according to claim 1, in which said valve means are selectively oper able to cause gas from the output side of the fan or blower either to induce gas to flow downwardly through the support and away from the chamber or to flow into the chamber beneath the support.

13. Apparatus according to claim 12, in which said first part of said ducting in cludes an ejector pump, a first duct being connected to the ejector pump at a position which is at low pressure when said ejector pump is in an induction mode and to the chamber and a second duct connecting the output side of the fan or blower to the ejector pump, the input side of the fan or blower being open to atmosphere, said valve means being selectively operable to switch said pump between the induction mode of operation in which said flow is downwardly through the support and a mode of operation in which air from the fan or blower flows through the first duct into the chamber.

14. Apparatus according to claim 13, in which said ejector pump comprises a nozzle positioned centrally of a venturi pressurereducing throat and a third duct extending away from the throat, the second duct terminating in said nozzle, said valve means comprising a damper valve located in said third duct.

15. Apparatus according to claim 13, in which said ejector pump comprises a venturi pressure-reducing throat, a third duct extending away from the throat and an annular duct surrounding the mouth of the throat, the annular duct having an annular gap through which air is discharged, during use of the apparatus, on to the surface of the throat, the second duct being connected to the annular duct, said valve means comprising a damper valve located in said third duct.

16. Apparatus according to any one of claims 12 to 15, in which a second part of said ducting is connected to the chamber above the support and is connected to a stack.

17. Apparatus according to claim 16 as dependent on claim 13, in which the exhaust from the ejector pump is connected to the stack.

18. Apparatus according to any one of the preceding claims, in which the chamber is the combustion chamber of the boiler.

19. Apparatus according to claim 18, in which the boiler is a shell boiler.

20. Apparatus according to claim 18 or 19, in which water tubes are positioned above the support in the chamber whereby, in use, the tubes are at least partially submerged in the bed of particles.

21. Apparatus according to any one of claims 1 to 17, in which the chamber is the furnace of a gasifying apparatus.

22. Apparatus according to any one of the preceding claims, in which an auxilliary burner is positioned such that, in use, a flame therefrom is directed on to the bed.

23. Fluidised bed apparatus according to claim 1 substantially as described herein with reference to any one of the drawings accompanying the provisional specification.