GB2059284A

GB2059284A - Fluidising medium distribution arrangement

Info

Publication number: GB2059284A
Application number: GB7932779A
Authority: GB
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1979-09-21
Filing date: 1979-09-21
Publication date: 1981-04-23
Also published as: GB2059284B

Abstract

A fluidising air distributor consists of a sparge pipe 1 to which are fitted a plurality of stub pipes 6 having discharge orifices 8 formed therein for the egress of air. The orifices 8 are remote from the wall 2 of the pipe 1 so as to isolate the relatively cooler jet of air issuing therethrough from the relatively hot wall, thereby reducing thermal stressing in that wall. <IMAGE>

Description

SPECIFICATION Fluidising medium distribution arrangement This invention concerns improvements in and relating to the introduction of a fluidising medium into a fluidised bed.

There are many different types of equipment designed for the purpose of introducing a fluidising gas into a bed of particulate material to fluidise the bed, and in recent years there have been increasing efforts to utilise the advantageous heat transfer capabilities of a fluidised combustion bed in which a fuel is burnt. In particular development work has been directed at the conversion of conventional boilers, for example shell boilers, to accept a fluidised combustion bed to replace the usual oil or gas burner. One of the important objectives is to maximise heat transfer to the working fluid through the wall of the combustion chamber or furnace tube.In order to achieve this the maximum contact between the hot fluidised bed and the bounding wall is paramount, and one method attaining this desirable goal is to employ sparge pipes at least some of which are arrayed in close adjacency to the wall in order to ensure fluidisation of the bed material in this region.

In this latter respect, and indeed generally, when sparge pipes are used in a fluidised bed the perforations in the pipes are directed downwardly or towards the bounding walls discharging fluid in high velocity jets to effect the requisite degree of flu idisa- tion and to prevent ingress of bed material.

Sparge pipes are conventionally of considerable length extending through the bed for substantially the whole of the containing furnace tube. It will be appreciated from the foregoing that when the pipes are disposed in the hot environment of a fluidised combustion bed with relatively cooler air issuing as high velocity jets through the perforations, different parts of the pipe are at different temperatures. In this respect the pipe wall in the vicinity of the perforations is cooler than the sides of the pipe which are in intimate contact with the hot and vigorously fluidised combustion bed, whereas the top of the pipe, remote from the perforations, attains an intermediate temperature since a static layer of bed material on the top of the pipe tends to form and effectively insulates that part of the pipe from the hot fluidised material.In view of the temperature variation around the pipe, which can be quite marked, thermal stressing becomes a problem, and it has been found in practice that serious bending of the pipes occurs, thus necessitating replacement.

Various proposals have been made for solving the problem of bending in sparge pipes, and one is embodied in our co-pending Patent Application No.

48633/78 which disclosed the provision of a plate along the top of the sparge pipe with the object of surrounding the whole pipe with air. It is thought however that the cooling of the bottom of the pipe is due to the high convective heat transfer coefficients of high velocity jets rather than mere external contact with air.

An object of the present invention is therefore to provide a fluidising medium distribution arrangement for a fluidised bed which serves to reduce or obviate the problem attendant upon the use of conventional arrangements.

According to one aspect of the invention there is provided a fluidising medium distribution arrangement including at least one pipe having an inlet and a plurality of discharge elements on the wall of the pipe, each element having at least one outlet disposed at a location remote from the wall of the pipe.

Preferably the disposition of the, or each, outlet is such that in practice the egress of the fluidising medium there through has no, or substantially no, cooling effect upon the pipe wall.

The or each element is conveniently in the form of a pipe stub joined at its root to the pipe wall which is provided with complementary apertures to provide a flow path between the interior of the pipe and the pipe stubs which may extend radially from the pipe wall. Each pipe stub has the outlet, of which there may be more than one, in its wall and may advan tageously have a closed end remote from the pipe.

The outlet may be an orifice of any suitable shape, or may be a slot of suitable dimension and form.

The pipe may further be provided in the wall thereof with a valve for a purpose to be described hereinafter.

According to a further aspect of the invention there is provided a fluidised bed apparatus including a body for containing a bed of particulate material and a number of fluidising medium distribution arrangements according to the first aspect of the invention located within the body and adapted in use to introduce fluidising medium into the bed of material.

Preferably the body is in the form of a cylindrical shell with its longitudinal axis disposed horizontally, and the pipes of the fluid medium distribution arrangements are arrayed parallel, or substantially parallel to, the said axis.

The discharge elements of the pipes extend towards the wall of the shell such that the ends of the elements are in close adjacency or in contact with the wall, the outlets of the elements thus being closely located next to the wall to provide, in use, for fluidisation of the bed right up to the wall. The outlets are however preferably orientated such that the fluidising medium issues laterally from the elements, and does not impinge directly on to the shell wall thereby avoiding or reducing erosion, and allowing the requisite degree of fluidisation to be attained with lower jet velocities or plenum pressures.

A plurality ofthe pipes is provided in the shell, and the length of the discharge elements on all the pipes may be the same. Alternatively the length of the discharge elements on some ofthe pipes may be different from those on the other pipes such that a staggered effect is achieved, the pipes being at different levels within the shell.

The pipes may in part be supported within the shell by the discharge elements, but may in addition or alternatively be supported by suitable mounting arrangements.

The fluidised bed apparatus is preferably in the form of a combustorfor a boiler.

By way of example only several embodiments of fluidising medium distribution arrangement and fluidised bed apparatus according to the invention are described below with reference to the accompanying drawings in which: Figure 1 is a longitudinal cross-section through a fluidising medium distribution arrangement show- ing various forms of discharge element; Figure 2 is a diagrammatic perspective view of part of a fluidised bed apparatus with an arrangement such as is exemplified in figure 1; and Figure 3 is a diagrammatic part-end view of a further form of fluidised bed apparatus.

Referring to Figure 1 there is shown a fluidising medium distribution arrangement comprising a sparge pipe 1 which has formed in its wall 2 a plurality of holes 4 with each of which registers a discharge element in the form of a pipe stub 6. The pipe stubs 6 may be welded to the pipes 1 or integral therewith and each has at least one outlet. The pipe stub 6 at position (a) has in the wall 10 thereof an outlet in the form of a circular hole 8 located close to the end of the pipe stub, the end 12 being closed and in close adjacency to a shell wall 14. At position (b) more than one hole 8 is provided, one near to the end 12 of the stub 6 and the other intermediate the pipe 1 and the end 12. The pipe stub 6 at position (c) is provided with a number of slots 16 near the end of the stub 6 and the pipe stub 6 at position (d) has at least one tapered slot 18 near to the end thereof.It will be noted that all the outlets 8, 16, 18 are remote from the walls of pipe 1 thereby in use ensuring that the issuing jets of the fluidising medium, generally air, have substantially no direct cooling effect upon the pipe 1 itself. Furthermore the orientation of the outlets in the pipe stubs 6 is lateral with regard to the axes, and therefore the issuing jets, in use, do not impinge directly upon the shell wall 14 but follow a path parallel thereto. The air or gas momentum and hence pressure losses at the shell wall would be reduced and thus wall erosion minimised.

It will be appreciated that in practice one sparge pipe would generally have only one type of outlet in the pipe stubs and the selection of outlet geometry would depend upon the required performance. The degree of fluidisation of material at the shell wall 14 can thereby be related to the air input. Control ofthe heat transfer coefficient at the surface of the shell wall will give a control over the performance of the boiler.

The sparge pipe 1 is provided with at least one valve 30 which is the bimetallic type which is designed to be open when cold, or of the ball and cope type which is closed when the internal pressure acting thereon is greater than a predetermined value or zero. A diagrammatic illustration of both types is shown in figure 2. The function of the valves 30 is in their relief mode during the time a fluidised combustion bed is being started from cold or when only a small portion of the bed is to be fluidised. It is generally more difficult to fluidise a bed of particles when cold than when at an elevated temperature since the resistance to the passage of air is greater.There is therefore a possibility that the outlets in the pipe stubs 6 could become blocked thereby creating a back pressure of air which is relieved through the valves 30, the air flowing into the bed area above the pipes 1 to fluidise the bed above the pipes. Once the bed has reached a higher temperature or more air is introduced i nto the pipe the valves will close and the air will issue from the outlets.

Referring now to Figure 2 a pipe 1 is shown diagrammatically with its pipe stubs 6 arranged radially and disposed downwardly towards the shell wall 14, suitable support mountings (not shown) being provided. In practice, a plurality of pipes 1 is provided in the furnace tube or shell of a boiler (not shown) and have in one embodiment (not shown) pipe stubs of the same length.

In an alternative embodiment, shown in Figure 3, a plurality of pipes 1 is provided and arranged within a furnace tube or shell 40 and various pipes 1 have pipe stubs 6 of different lengths from those of adjacent pipes effectively giving a staggered array of pipes in different echelons. The object of providing this assembly is to allow the use of larger diameter pipes, and to avoid the possibility of the fluidised bed 50 slugging or the bridging by bubbles which sometimes occurs between pipes arranged at the same level. This bridging is believed to be caused by the air issuing from beneath the pipes travelling up at an increased speed between the pipes creating a system of stationary bubbles, or preferential channelling between two pipes. Slugging is believed to be largely responsible for entraining solids into the freeboard above the bed and subsequent loss of bed material.

The present invention thus provides a new and improved fluidising medium distribution arrange ment which enables sparge pipes to be employed in the absence of the usually attendant problems of bending by removing the air outlets from the wall of the pipe to a position remote therefrom. This design results in an even temperature distribution around the pipe and therefore reduces thermal stressing which results in bending. Furthermore the provision of the pipe stubs on the sparge pipes enables fluidisation of bed material right up to the shell wall without the high erosive effect sometimes experienced when employing conventional sparge pipes.

Moreover the use of valves or pipe stub openings which relate the level at which air is released into the bed, to the quantity of air passed, offers the possibility of controlling the extent of fluidisation, and hence combustion, from slumberto maximum output.

Claims

1. A fluidising medium distribution arrangement including at least one pipe having an inlet and a plurality of discharge elements on the wall of the pipe, each element having at least one outlet dis posed at at a location remote from the wall of the pipe.

2. An arrangement according to claim 1 in which the or each discharge element is in the form of a pipe stub joined at its root to the wall of the pipe which is provided with complementary apertures to provide a flow path between the interior of the pipe and the pipe stubs.

3. An arrangement according to claim 2 in which the pipe stubs extend radially of the pipe.

4. An arrangement according to claim 2 or 3 in which the or each pipe stub has the outlet disposed near to the end thereof remote from the pipe wall.

5. An arrangement according to any one of claims 2 to 4 in which the end of the pipe stubs remote from the pipe wall is closed.

6. An arrangement as claimed in any one of the preceding claims in which the or each outlet in the or each discharge element is an orifice.

7. An arrangement as claimed in any one of claims 1 to 5 in which the or each outlet in the or each discharge element is a slot.

8. An arrangement as claimed in claim 7 in which the slot is tapered.

9. An arrangement as claimed in any one of the preceding claims in which the or each pipe has located in the wall thereof a valve adapted to be open at a relatively low temperature and closed at a relatively higher temperature.

10. Fluidised bed apparatus including a body for containing a bed of particulate material and a number of fluidising medium distribution arrangements according to any one of the preceding claims, the arrangements being located within the body and adapted in use to introduce fluidising medium into the bed of material.

11. Apparatus according to claim 10 in which the body is in the form of a cylindrical shell with the longitudinal axis thereof disposed horizontally and the pipes of the distribution arrangements are arrayed parallel or substantially parallel to the axis.

12. Apparatus according to claim 11 in which the discharge elements of the pipes extend towards the wall of the shell such that the ends thereof are in close adjacency to or are in contact with the wall.

13. Apparatus according to claim 12 in which the outlets of the discharge elements are orientated such that, in use, fluidising medium issues laterally from the elements and follows a path along the wall of the shell.

14. Apparatus according to any one of claims 11 to 13 in which a plurality of the pipes of the distribution arrangements are provided in the shell, the length of the discharge elements on all the pipes being the same.

15. Apparatus according to any one of claims 11 to 13 in which a plurality of the pipes of the distribution arrangements are provided in the shell, the length of the discharge elements on some of the pipes being different from the length of the discharge elements on the other pipes such that the pipes are at different levels within the shell.

16. Apparatus according to any one of the claims 10 to 15 in which the apparatus is a combustorfor a boiler.

17. Fluidised bed apparatus substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

17. A boiler incorporating apparatus as claimed in claim 16.

18. Afluidising medium distribution substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

19. Fluidised bed apparatus substantially as hereinbefore described with reference to Figures 1,2 and 3 of the accompanying drawings.

New claims or amendments to claims filed on 27.8.80.

Superseded claims: All (i.e. Claims 1-19).

New or amended claims:

1. Fluidised bed apparatus including a body for containing a bed of particulate material, a number of fluidising medium distribution arrangements located within the body and adapted in use to introduce fluidising medium into the bed of material, the or each arrangement comprising a pipe having an inlet and a plurality of discharge elements on the wall of the pipe, each element having at least one outlet disposed at a location remote from the wall of the pipe.

2. An apparatus according to claim 1 in which the or each discharge element is in the form of a pipe stub joined at its root to the wall of the pipe which is provided with complementary apertures to provide a flow path between the interior of the pipe and the pipe stubs.

3. An apparatus according to claim 2 in which the pipe stubs extend radially ofthe pipe.

4. An apparatus according to claim 2 or 3 in which the or each pipe stub has the outlet disposed near to the end thereof remote from the pipe wall.

5. An apparatus according to any one of claims 2 to 4 in which the end of the pipe stubs remote from the pipe wall is closed.

6. An apparatus as claimed in any one of the preceding claims in which the or each outlet in the or each discharge element is an orifice.

7. An apparatus as claimed in any one of claims 1 to 5 in which the or each outlet in the or each discharge element is a slot.

8. An apparatus as claimed in claim 7 in which the slot is tapered.

9. An apparatus as claimed in any one ofthe preceding claims in which the or each pipe has located in the wall thereof a valve adapted to be open at a relatively low temperature and closed at a relatively higher temperature.

10. Apparatus according to claim 10 in which the body is in the form of a cylindrical shell with the longitudinal axis thereof disposed horizontally and the pipes of the distribution arrangements are arrayed parallel or substantially parallel to the axis.

11. Apparatus according to claim 10 in which the discharge elements of the pipes extend towards the wail of the shell such that the ends thereof are in close adjacency to or are in contact with the wall.

12. Apparatus according to claim 11 in which the outlets of the discharge elements are orientated such that, in use, fluidising medium issues laterally from the elements and follows a path along the wall of the shell.

13. Apparatus according to any one of claims 10 to 12 in which a plurality of the pipes ofthe distribution arrangements are provided in the shell, the length ofthe discharge elements on all the pipes being the same.

14. Apparatus according to any one of claims 10 to 12 in which a plurality ofthe pipes of the distribution arrangements are provided in the shell, the length ofthe discharge elements on some ofthe pipes being different from the length of the discharge elements on the other pipes such that the pipes are at different levels within the shell.

15. Apparatus according to any one of the preceding claims in which the apparatus is a combustor for a boiler.

16. A boiler incorporating apparatus as claimed in claim 16.