GB1559800A

GB1559800A - Fluidised bed combustion apparatus

Info

Publication number: GB1559800A
Application number: GB4808175A
Authority: GB
Original assignee: ENERGY EQUIP; Energy Equipment Co Ltd
Current assignee: ENERGY EQUIP; Energy Equipment Co Ltd
Priority date: 1976-11-08
Filing date: 1976-11-08
Publication date: 1980-01-30

Description

(54) FLUIDISED BED COMBUSTION APPARATUS (71) We THE ENERGY EQUIPMENT COMPANY LIMITED, a British Company, of Energy House, Hockliffe Street, Leighton Buzzard, Beds. LU7 8HE. 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 present invention relates to fluidised bed combustion apparatus, e.g. gasifiers, incinerators and boilers.

The provision of heating apparatus including fluidised beds is known. In such apparatus the fluidised bed itself provides zones for the distribution of heat supplied to it, or generated within it.

When using a fluidised bed heating apparatus (such as, for example, that described in our co-pending patent application No. 10188/75 Ser. No. 1 540 378), the heat is generated in the apparatus within the fluidised bed by the combustion of fuel which is supplied to and supported by the bed.

The temperature of a fluidised bed in such apparatus requires precise control to ensure that the bed maintains an optimum temperature to support combustion of the fuel supplied to it. When using a low grade fuel for example, brown coal, it is necessary to supply a significant amount of energy to the bed to maintain combus tion in the apparatus. Using some sorts of fuel it is necessary to supply energy to the bed equivalent to as much as 10% of the total energy produced by the apparatus. In addition, control of the temperature of the bed is difficult when using low grade fuel and the problems associated with controlling the temperature of the bed increase rapidly if the apparatus is to cope with varying loadings, for example variations in temperature or volume of the gas output (if the apparatus is a gasi fier) or of a varying supply in quantity of combustible material supplied to the apparatus.

An object of the invention is to reduce the energy required to support operation of a fluidised bed heating apparatus; other objects include the simplification of control of bed temperature and of the outlet gas temperature.

According to the invention there is provided a fluidised bed combustion apparatus comprising a primary fluidised bed combustion means, one or more main fluidised beds, primary air supply means for supplying air at a relatively higher pressure to the primary fluidised bed combustions means, conduit means for conducting hot gas from the primary fluidised bed combustion means to the or each main fluidised bed to supply heat to the latter, flow control means in said conduit means, and secondary air supply means arranged to supply air at a lower pressure to the conduit means downstream of the flow control means, whereby the primary fluidised bed combustion means may be operated at a constant rate and heat supplied therefrom to the main fluidised bed(s) at a rate controlled by the flow control means.

The mixture of gas and fluidising air may be passed to the or each main bed by a gas injector comprising means for supplying gas to a distributor having a plurality of spaced elements located within the material forming the or each fluidised bed and extending generally transversely thereof, each comprising a hollow tube formed with a plurality of apertures through which gas may pass to the material forming the bed. Such a distributor is described in our co-pending patent application No. 10188/75 (Serial No.

1 540 378).

A pilot burner may be provided to initiate operation of the primary combus tion means. As soon as the primary combustion means has reached its operating temperature the pilot burner may be turned cff.

A stem generator is preferably provided in the primary combustion means, conduit means being provided to carry steam produced by the generator into the main fluidised bed so as to control the temperature of the main iiuidised beds. Steam produced by the steam generator in excess of that needed to control the temperature of the main fluidised beds may be used to control the temperature of the fluidised bed in the primary combustion means.

Chimney means may be provided to collect gas generated in the main fluidised beds.

Gas generated in the primary combution means in excess of that required in the main fluidised beds may be passed via flue means to the said chimney means.

Duct means may be provided to pass air to the chimney means whereby the temperature of the gas collected therein may be controlled.

The proportion of air passed to the chimney means is preferably controllable by operation of further control valves.

Other aspects of the invention provide gasifiers, incinerators and boilers incorporating heating apparatus as aforesaid.

When used as a gasifier the gas produced bv the main fluidised beds may be used directly, for example it may be ducted away from the main beds to dry material.

When used as a boiler it is possible for the main fluidised beds to form part of a shell holler, water tube boiler or other water heating apparatus.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing which shows in schematic form a compound fluidised bed gasifier embodying the invention.

As can be seen the gasifier comprises a primary fluidised bed combustor or gasifier 10 which is operable to provide hot gases via ducting 11 for mixing with fluidising air supplied from blowers 12 via ducting 13 to larger main fluidised beds 14. The pronortion of the gas produced by the gasifier 10 which is mixed with fluidising air supplied to the main fluidised beds my be varied by manual or automatic operation of valves 15 and 16 in the ducting 11 and 13.

The gasifler 10 is provided with a fluidised bed 17 through which a number of tubula rair distribution elements 18 extend as shown. The elements 18 are provided along their length with a plurality of holes 19 through which air supplied to each element 18 from a plenum chamber 20, located on one wall of the gasifier 10, is passed into the fluidised bed 17.

Gas is supplied to the plenum chamber 20 from a blower 21 via a pilot burner 22 included in a trim heating arrangement 23 substantially in accordance with the system described in our co-pending application No. 20549/75 filed on the 15th May 1975.

The mixture of gas produced by the gasifier 10 and the fluidising air from the blower 12 in the ducting 13 is carried to plenum chambers 24 from which it is distributed via tubular air distribution elements 25 to the main fluidised beds 14.

The gas generated in the main fluidised beds 14 is collected in a chamber 27 thereabove.

A chimney 28 is formed in the top cover of the chamber 27 to carry gas produced in the apparatus away from the apparatus to where it is used.

A certain proportion of the gas produced by the gasifier 10 may be mixed with the gas produced by the main fluidised beds, this gas being conducted to chamber 27 via a duct or flue 29.

Operation of the combustion apparatus is as follows. To start operation of the apparatus, blower 21 is energized to supply gas to the primary combustor 10 and the pilot burner 22 is activated, with high grade fuel, to bring the fluidised bed 17 up to its optimum operating temperature at which the normal, lower grade, operating fuel for the apparatus may be supplied to it.

As soon as the primary combustor 10 has reached its operating temperature and is being maintained at that temperature by the fuel supplied to it, the pilot burner 22 is turned off and the combustor 10 operates in an autothermic manner main taining its temperature stable.

The valves 15 and 16 are operated to provide a gaslair mixture in the ducting 13 sufficient to support combustion in the main fluidised beds 14. The main operating fuel is then supplied to the beds 14.

Gas generated in the fluidized beds 14 is collected in the chamber 27 and passes to the chimney 28.

Gas produced by the pilot producer 10 in excess of that required to maintain the temperature of the main fluidised beds 14 passes via the flue 29 and by-pass valve 30 to the chamber 27 for mixture with the gases produced in the main beds 14. The temperature of the beds 14 is controlled by means of a steam generator situated in the combustor 10 and generating steam which is injected into the beds via conduits leading to the plenum chambers 24 and air distribution elements 25. Steam from the generator may also, though not shown in the present drawing, be fed to the bed 17 of the pilot producer 10.

It has been found that the gas in the chamber 27 may be at a temperature of as much as 1,600"C which is far too hot for many uses and may also be environmentally objectionable and it is therefore necessary to provide for control of the temperature of the gas issuing from chim ney 28. In order to effect this the present invention provides that dilution air may be provided to the chamber 27 from blowers 31 via ducts 32. The amount of dilution air supplied to the chamber 27 may be controlled by means of valves 33.

When operating any fluidised bed combustion apparatus it is essential that the fluidised bed temperature is maintained at that required for optimum combustion of any material passed to it and it will be seen that the apparatus of the present invention provides two different ways in which the temperature of the fluidised beds may be maintained. Firstly by means of varying the proportion of gas produced by the primary combustor 10 which is mixed with the fluidising air flow in the ducting 13 and secondly, by means of the steam generator situated in the combustor 10.

The temperature of the final mixed gas will be controlled independently of that of the gas supplied by the gasifier and this is catered for, as can be seen in the present invention, by the use of the dilution air-producing means 31 and 32.

Additionally, it is important that the primary combustor as a gasifier is sufficient to provide enough heat to support combustion in the main fluidised beds. To this end, the combustor 10 is operated at higher pressure than the main beds, for example the blower 21 is preferably designed to be able to provide 2,000 c.f.m.

of air to the fluidised bed 17 at a working pressure of 80 W.G.

The gas pressure in the combustor 10 above the fluidised bed is approximately 50" W.G.

The air provided by the blowers 16 is preferably at 8,000 c.f.m. and 40" W.G.

After mixing in the ducting 13 the pressure in the plenum chambers 24 is preferably of the order of 24" W.G. and the final gas pressure in the chamber 27 of the order of 3" W.G.

The primary combustor heat output capacity is approximately 10% of the capacity of the main, low pressure beds and combustion within the bed 17 of the combustor 10 is maintained by the trim heater 23 with the pilot burner 22 accepting high grade support fuel.

The capacity of the trim heater 23 is approximately 10% of the capacity of the pilot producer so that the maximum sup port fuel consumption during the temperature raising periods does not exceed 1% of the full rated capacity of the apparatus as a whole.

The combustor 10 is able to operate continuously at full load so that it can be established as a stable autothermic unit.

In this case the trim heater although always at stand-by will not be firing, and hence the amount of support fuel used for combustion for continuous operation of the apparatus as a whole is negligible.

The hot gas from the combustor 10 surplus to control requirements for the main fluidised beds is by-passed and mixed with the gas outlet of the total plant and in this way it is possible to maintain a steady load with autothermic operating conditions in the combustor 10 hence obviating the requirement for supporl by supplementary high grade fuel.

The fuel supplied to the fluidised beds is introduced thereto by conventional means such as ram feed spreaders in the case of coal or other solid hydrocarbons or by submerged injectors in the case of oil or other liquid fuels.

The pressure compounded fluid bed burning apparatus described herein can be applied to gasifiers, as described in the embodiment, and to combustor gasifiers associated with water tube boilers and shell boilers.

It can be seen that a main advantage of the present invention is that once established the combustor 10 operates on the same fuel as the main beds removing the necessity, except for stand-by purposes, of a support fuel. The main beds are able to operate over a wide range of qualities of fuel supplied thereto, and required gas loads, which is permitted by the temperature control provided by the constant load autothermic combustor.

It is envisaged that in addition to being used as a combustor apparatus the present invention is applicable for use as a drier, that is to say that the main fluid beds may be used as drying beds, articles to be dried being passed through the beds.

WHAT WE CLAIM IS: 1. A fluidised bed combustion apparatus comprising a primary fluidised bed combustion means, one or more main fluidised beds, primary air supply means for supplying air at a relatively higher pressure to the primary fluidised bed combustion means, conduit means for conducting hot gas from the primary fluidised bed combustion means to the or each main fluidised bed to supply heat to the latter, flow control means in said conduit means, and secondary air supply means arranged to supply air at a lower pressure to the conduit means downstream of the flow control means, whereby the primary

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the bed 17 of the pilot producer 10. It has been found that the gas in the chamber 27 may be at a temperature of as much as 1,600"C which is far too hot for many uses and may also be environmentally objectionable and it is therefore necessary to provide for control of the temperature of the gas issuing from chim ney 28. In order to effect this the present invention provides that dilution air may be provided to the chamber 27 from blowers 31 via ducts 32. The amount of dilution air supplied to the chamber 27 may be controlled by means of valves 33. When operating any fluidised bed combustion apparatus it is essential that the fluidised bed temperature is maintained at that required for optimum combustion of any material passed to it and it will be seen that the apparatus of the present invention provides two different ways in which the temperature of the fluidised beds may be maintained. Firstly by means of varying the proportion of gas produced by the primary combustor 10 which is mixed with the fluidising air flow in the ducting 13 and secondly, by means of the steam generator situated in the combustor 10. The temperature of the final mixed gas will be controlled independently of that of the gas supplied by the gasifier and this is catered for, as can be seen in the present invention, by the use of the dilution air-producing means 31 and 32. Additionally, it is important that the primary combustor as a gasifier is sufficient to provide enough heat to support combustion in the main fluidised beds. To this end, the combustor 10 is operated at higher pressure than the main beds, for example the blower 21 is preferably designed to be able to provide 2,000 c.f.m. of air to the fluidised bed 17 at a working pressure of 80 W.G. The gas pressure in the combustor 10 above the fluidised bed is approximately 50" W.G. The air provided by the blowers 16 is preferably at 8,000 c.f.m. and 40" W.G. After mixing in the ducting 13 the pressure in the plenum chambers 24 is preferably of the order of 24" W.G. and the final gas pressure in the chamber 27 of the order of 3" W.G. The primary combustor heat output capacity is approximately 10% of the capacity of the main, low pressure beds and combustion within the bed 17 of the combustor 10 is maintained by the trim heater 23 with the pilot burner 22 accepting high grade support fuel. The capacity of the trim heater 23 is approximately 10% of the capacity of the pilot producer so that the maximum sup port fuel consumption during the temperature raising periods does not exceed 1% of the full rated capacity of the apparatus as a whole. The combustor 10 is able to operate continuously at full load so that it can be established as a stable autothermic unit. In this case the trim heater although always at stand-by will not be firing, and hence the amount of support fuel used for combustion for continuous operation of the apparatus as a whole is negligible. The hot gas from the combustor 10 surplus to control requirements for the main fluidised beds is by-passed and mixed with the gas outlet of the total plant and in this way it is possible to maintain a steady load with autothermic operating conditions in the combustor 10 hence obviating the requirement for supporl by supplementary high grade fuel. The fuel supplied to the fluidised beds is introduced thereto by conventional means such as ram feed spreaders in the case of coal or other solid hydrocarbons or by submerged injectors in the case of oil or other liquid fuels. The pressure compounded fluid bed burning apparatus described herein can be applied to gasifiers, as described in the embodiment, and to combustor gasifiers associated with water tube boilers and shell boilers. It can be seen that a main advantage of the present invention is that once established the combustor 10 operates on the same fuel as the main beds removing the necessity, except for stand-by purposes, of a support fuel. The main beds are able to operate over a wide range of qualities of fuel supplied thereto, and required gas loads, which is permitted by the temperature control provided by the constant load autothermic combustor. It is envisaged that in addition to being used as a combustor apparatus the present invention is applicable for use as a drier, that is to say that the main fluid beds may be used as drying beds, articles to be dried being passed through the beds. WHAT WE CLAIM IS:

1. A fluidised bed combustion apparatus comprising a primary fluidised bed combustion means, one or more main fluidised beds, primary air supply means for supplying air at a relatively higher pressure to the primary fluidised bed combustion means, conduit means for conducting hot gas from the primary fluidised bed combustion means to the or each main fluidised bed to supply heat to the latter, flow control means in said conduit means, and secondary air supply means arranged to supply air at a lower pressure to the conduit means downstream of the flow control means, whereby the primary

fluidised bed combustion means may be operated at a constant rate and heat supplied therefrom to the main fluidised bed(s) at a rate controlled by the flow control means.

2. Apparatus as claimed in claim 1, wherein the primary fluidised bed combustion means comprises a single fluidised bed combustor gasifier.

3. Apparatus as claimed in Claim 1 or claim 2, wherein said mixture of gas and secondary air is passed to the or each main bed by a gas injector including a distributor having a plurality of spaced elements located within the material forming the or each fluidised bed and extending generally transversely thereof, each said element comprising a hollow tube formed with a plurality of apertures through which gas may pass to a material forming the bed.

4. Apparatus as claimed in any preceding Claim, further comprising a pilot burner to initiate operation of the primary combustion means.

5. Apparatus as claimed in any preceding Claim, wherein a steam gas generator is provided in the primary combustion means, and conduit means are provided to carry steam produced in the generator into the main fluidised beds such that the temperature of the main fluidised beds may be controlled.

6. Apparatus as claimed in Claim 5, wherein the steam provided by said steam generator is used to control the temperature of the fluidised bed in the primary combustion means.

7. Apparatus as claimed in any preceding Claim, comprising chimney means for collecting gas generated in the main fluidised beds.

8. Apparatus as claimed in Claim 9, further comprising flue means to enable gas generated in the primary combustion means in excess of that required in the main fluidised beds to be passed to the said chimney means.

9. Apparatus as claimed in Claim 7 or Claim 8, wherein duct means are provided to pass air to the chimney means whereby the temperature of the gas collected therein may be controlled.

10. Apparatus as claimed in Claim 9, wherein the proportion of air passed to the chimney means is adapted to be controlled by operation of further control valves.

11. A fluidised bed combustion apparatus substantially as hereinbefore described with reference to the accompanying drawings.

12. A gasifier comprising apparatus as claimed in any one of Claims 1 to 11.

13. A drier comprising apparatus as claimed in any one of Claims 1 to 11.

14. A boiler comprising apparatus as claimed in any one of Claims 1 to 11.