Introduction

This invention relates to a fluidised bed unit and in particular to a fluidised bed unit for use in thermally treating a by-product such as poultry litter, mushroom compost, meat and bone meal and the like. The fluidised bed unit forms part of an energy conversion system that is suitable for installation on a farm or small scale processing plant that handles the by-product.

Fluidised bed units are commonly used in large scale incineration plants and are typically very large, bulky machines. The known fluidised bed units are operated to thermally treat refuse or other like material in the incineration plant. A problem with the known fluidised bed units is that they are very large, expensive machines that are only suitable for large scale incineration plants with a plentiful supply of refuse. Another problem with the fluidised bed units is that they require constant surveillance and frequent maintenance by skilled personnel to ensure optimal operation. The known fluidised bed units are therefore time consuming and costly to operate as well as being unsuitable for small scale installations such as farms or processing plants. The present invention is not concerned with large scale power generation plants but rather is concerned with relatively small energy conversion systems capable of handling less than 0.5 MegaWatt (MW) electric (500KWe) and 3MW thermal (3000KWth).

It is an object of the present invention to provide a fluidised bed unit that overcomes at least some of these problems, that is compact, relatively simple to maintain and commercially viable so that it may be installed on a farm or in a processing plant to process a by-product.

Statements of Invention

According to the invention there is provided a fluidised bed unit for thermally treating a by-product comprising:

a furnace having a fuel charging inlet; a furnace sump for storing fluidised bed media;

a clinker extraction unit mounted in the sump adjacent the base of the sump for removing clinkers from the fluidised bed media through a sump discharge aperture;

a burner unit; and

an air introducer assembly comprising a forced draught fan, a single air box coupled to the forced draught fan and a plurality of nozzles fed by the air box.

Such a fluidised bed unit is relatively simple in construction and therefore inexpensive to manufacture. Furthermore, the configuration of fluidised bed unit is compact, lightweight and requires relatively little maintenance or surveillance due to the simplicity of its design. The clinker extraction unit will remove clinkers in a straightforward manner that will reduce the amount of maintenance required and improve performance of the fluidized bed unit. Accordingly, the compact fluidised bed unit may be installed on a farm or processing plant where by-product is created and used to thermally treat that by- product. This is most advantageous for two reasons, first of all, it will no longer be necessary for the producer to pay for the transport and disposal of the by-product as he can do this on site and secondly, the heat generated from thermally treating the byproduct may be used to reduce the operating costs of the producer. By having such a unit, it is possible to remove clinkers from a small combustion zone and remove ash without air ingress. It is further possible to control all parameters and maintain clean, safe combustion so that the by-product is subjected to temperatures of the order of 850 ⁰ C for at least 2 seconds. Finally, by providing such a configuration of fluidized bed unit, the minimum amount of steel is required to allow combustion at these temperatures.

In one embodiment of the invention, each of the nozzles is mounted on an upstanding sparge pipe.

In one embodiment of the invention, the nozzles are evenly spaced about the fluidised bed. In one embodiment of the invention, there are provided a pair of air boxes, each having a plurality of nozzles supplied by their respective air box.

In one embodiment of the invention, the air box is mounted in the furnace sump.

In one embodiment of the invention, the air box is spaced apart from the base of the furnace sump.

In one embodiment of the invention, the fluidised bed unit is provided with a pressure sensor.

In one embodiment of the invention, the pressure sensor is located below the plurality of nozzles. This is seen as particularly advantageous location as it provides a very accurate reading of the level of ash in the bed.

In one embodiment of the invention, the clinker extraction unit operates for a predetermined period of time in response to the pressure measured by the pressure sensor being below a predetermined level.

In one embodiment of the invention, there is provided a fluidised bed media dosing system in communication with the charging inlet, the dosing system operates for a predetermined period of time in response to the pressure measured by the pressure sensor being below a predetermined level.

In one embodiment of the invention, the clinker extraction unit comprises a furnace ash removal auger.

In one embodiment of the invention, the furnace sump tapers inwardly towards the bottom of the sump.

In one embodiment of the invention, the furnace sump is wedge shaped. - A -

In one embodiment of the invention, the fluidised bed unit is provided with a plurality of temperature sensors arranged at different heights inside the fluidised bed unit, at least one of which is located in the fluidised bed media, at least one of which is located just above the fluidised bed media in a lower freeboard of the fluidised bed and at least one of which is located adjacent the top of the fluidised bed unit in an upper freeboard of the fluidised bed unit.

In one embodiment of the invention, there are provided four temperature sensors in the fluidised bed media.

In one embodiment of the invention, the fluidised bed is divided into four quadrants and there is one temperature sensor in each quadrant of the fluidised bed.

In one embodiment of the invention, in operation, the temperature of the fluidised bed is in the region of 610 ⁰ C to 750 ⁰ C, the temperature just above the fluidised bed media is in the region of 850 ⁰ C and the temperature in the upper freeboard is in the region of 1000°C to 1200°C.

In one embodiment of the invention, a fuel conveyor is responsive to the temperature sensor in the fluidised bed and delivers fuel into the fluidised bed unit through the charging inlet on the temperature in the fluidised bed falling below a first predetermined fluidised bed temperature.

In one embodiment of the invention, the burner unit is responsive to the temperature in the fluidised bed unit falling below a second predetermined fluidised bed temperature.

In one embodiment of the invention, the furnace has a depth of the order of 450mm and a width of the order of 450mm.

In one embodiment of the invention, the fluidised bed media comprises quartz silica sand.

In one embodiment of the invention, the fluidised bed media has a particle diameter of the order of between 0.5mm to 1 mm, preferably 0.8mm. In one embodiment of the invention, there is provided a clinker recycling unit coupled to the clinker extraction unit, the clinker recycling unit comprising a sieve to separate clinkers from reusable fluidised bed media.

In one embodiment of the invention, the clinker recycling unit further comprises a crusher to crush clinkers to a predetermined size.

In one embodiment of the invention, the clinker recycling unit comprises an elevator to deliver the recycled fluidised bed media to a fluidised bed media dosing system in communication with the charging inlet.

In one embodiment of the invention, each nozzle is provided with an end cap to prevent ingress of fluidised bed media into the nozzle.

In one embodiment of the invention, the fuel charging inlet comprises an air tight seal to prevent ingress of air into the fluidised bed unit.

In one embodiment of the invention, the forced draught fan has an air intake connected to one end of an air supply conduit, the other end of the air supply conduit being mounted adjacent the top of the fluidised bed unit.

In one embodiment of the invention, the forced draught fan forms part of a negative pressure system to maintain a flow of exhaust gases from the fluidised bed unit.

Detailed Description of the Invention

The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which:-

Figure 1 is a diagrammatic representation of an energy conversion system that incorporates the fluidised bed unit according to the present invention; Figure 2 is a front perspective view of a fluidised bed;

Figure 3 is a perspective view of the fluidised bed shown from below;

Figure 4 is another front perspective view of the fluidised bed;

Figure 5 is a front view of the fluidised bed;

Figure 6 is a top plan view of the fluidised bed;

Figure 7 is a top plan view of an alternative embodiment of fluidised bed;

Figure 8 is a front view of the fluidised bed shown in Figure 7;

Figure 9 is a front view of another embodiment of fluidised bed;

Figure 10 is a rear view of the fluidised bed shown in Figure 9;

Figure 11 is a side view of the fluidised bed shown in Figure 9;

Figure 12 is a plan view of the fluidised bed shown in Figure 9;

Figure 13 is a front perspective view of the fluidised bed unit furnace;

Figure 14 is a rear perspective view of the fluidised bed unit furnace;

Figure 15 is a front perspective view of part of the fluidised bed unit furnace;

Figure 16 is a front perspective view of another part of the fluidised bed unit furnace;

Figure 17 is a front perspective view of another still part of the fluidised bed unit furnace; Figure 18 is a front view of a sparge pipe with nozzle;

Figure 19 is a cross-sectional view along the lines A-A of Figure 18;

Figure 20 is a cross-sectional view of a nozzle cap; and

Figure 21 is a front view of the sparge pipe with a nozzle cap in position, the nozzle cap shown in cross-section.

Referring to the drawings and initially to Figure 1 thereof, there is shown an energy conversion system, indicated generally by the reference numeral 1 , comprising a fluidised bed unit 3 according to the present invention. The energy conversion system further comprises a by-product fuel feed system 5 feeding the fluidised bed, a heat exchanger 7 operatively coupled to the fluidised bed unit 3, an exhaust filter 9 operatively coupled to the heat exchanger 7 and a negative pressure system. The negative pressure system comprises a forced draught fan 11 and an induction draught fan 13 which are operable to maintain a flow of exhaust gases in the direction from the fluidised bed unit 3 through the heat exchanger 7.

The fluidised bed unit 3 further comprises a charging inlet 15 for fuel delivered by the byproduct fuel feed system 5, a diesel burner unit (not shown) connected to a burner unit inlet 17 and a furnace sump 19 containing fluidised bed media. The furnace sump 19 tapers inwardly towards the bottom of the furnace sump where there is a clinker extraction unit, in this case a furnace ash removal auger 21 located at the bottom of the furnace sump 19. The fluidised bed unit further comprises an air introducer assembly most of which is mounted substantially in the furnace sump for delivering air up through the fluidised bed media in the sump. The air introducer further comprises the forced draught fan 11 from the negative pressure system. Above the furnace sump 19 is the furnace freeboard 23.

The by-product fuel feed system 5 comprises a hopper 25, a variable speed auger 27 and a fuel conveyor 29 to deliver fuel from the hopper to the charging inlet 15 of the fluidised bed unit. The variable speed auger 27 is operated to deliver a desired amount of fuel from the hopper 25 onto the fuel conveyor 29. The heat exchanger 7 comprises a pair of heat exchanger units, an upper heat exchanger unit 31 and a lower heat exchanger unit 33. The lower heat exchanger unit 33 is provided with a cold water flow pipe 35 and the upper heat exchanger unit 31 is provided with a hot water return pipe 37. The upper heat exchanger unit 31 further comprises a heat exchanger soot blower 32 mounted across the heat exchanger and extending between a plurality of tubes (not shown) of the upper heat exchanger unit. The heat exchanger soot blower 32 is rotatably mounted on the upper heat exchanger unit 31. Below the lower heat exchanger unit 33 is a heat exchanger sump 39 which is provided with a heat exchanger ash removal auger 41 to remove ash from the heat exchanger sump. The heat exchanger 7 is operatively coupled to the fluidised bed unit by way of a freeboard interconnector 34. The freeboard interconnector 34 is provided with a plurality of pulsed blower nozzles 36 arranged substantially in line with the floor of the freeboard interconnector 34. Pressurised air is periodically passed through the pulsed blower nozzles 36 to dislodge any settled ash from the floor of the freeboard interconnector 34. A heat exchanger exhaust conduit 43 operatively couples the heat exchanger 7 to the exhaust filter 9.

The exhaust filter 9 is a bag filter having a plurality of bags to catch the fly ash from the exhaust gases. The exhaust filter 9 comprises an ash extractor auger 45 located at the bottom of the exhaust filter 9. The induction draught fan 13 is coupled to the exhaust filter 9 and draws exhaust gases through the energy conversion system from the fluidised bed unit 3, through the heat exchanger 7 and through the exhaust filter 9.

In use, a by-product fuel is delivered from the hopper 25 along the fuel conveyor 29 and is delivered into the fluidised bed unit 3 where it is thermally treated at a temperature of at least 850 ^° C for at least two seconds. The temperature of the fluidised bed is between 610 ^° C and 750 ^° C, preferably approximately 670 ^° C. Just above the fluidised bed, in the lower furnace freeboard, the temperature is approximately 850 ^° C and at the top of the upper furnace freeboard adjacent the freeboard interconnector 34, the temperature is in the region of between 850 ^° C and 1200 ^° C. The height of the furnace freeboard and the negative pressure is such that the fuel remains in the region at or above 850 ^° C for a minimum of 2 seconds and this ensures that all pathogens are killed. A plurality of temperature sensors are arranged in the fluidised bed unit furnace. There are four temperature sensors in the fluidised bed itself, one temperature sensor in the lower furnace freeboard just above the fluidised bed and another temperature sensor in the upper furnace freeboard. These temperature sensors closely monitor the temperature of the fluidised bed unit and if the temperature should deviate from the desired values or ranges, corrective action may be taken. If the temperature of the fluidised bed lowers, the variable speed augers are operated to increase the amount of fuel that is delivered to the fluidised bed unit 3. If the fuel has a relatively high moisture content, the fuel may not immediately cause the temperature to rise in the fluidised bed and other action must be taken. In such an instance, further fuel may be added or alternatively, the diesel burner is started and provides a boost to the fluidised bed.

Referring to Figures 2 to 6, there is shown a plurality of views of a first embodiment of fluidised bed air introducer assembly according to the present invention, indicated generally by the reference numeral 50, where like parts have been given the same reference numerals as before. The air introducer assembly 50 comprises an air box 51 having a plurality of upstanding sparge pipes 53 protruding upwardly and outwardly therefrom. The sparge pipes 53 each have a venting nozzle at their end distal from the air box. An end cap 55 is placed over the free end of each of the sparge pipes to prevent ingress of fluidising bed media into the sparge pipes 53 and yet allow discharge of air from the nozzle into the fluidising bed media (not shown). The nozzles are spread evenly about the fluidised bed to provide uniform discharge of air into the fluidised bed. The furnace sump 19 is wedge shaped so that clinkers that form in the fluidised bed media will travel towards the bottom of the furnace sump to the furnace ash removal auger (not shown) housed in the aperture 57. In this way, clinkers can be effectively removed from the bottom of the fluidised bed so that they do not hinder performance of the fluidised bed.

A pressure sensor is provided in the fluidised bed just below the level of the nozzles. As clinkers and ash form, the heavier clinker and ash materials drop to the bottom of the fluidised bed and the pressure in the fluidised bed increases. The furnace ash removal auger operates for a predetermined period of time in response to the pressure increasing above a predetermined level to remove the clinkers from the fluidised bed. Further fluidising medium is then dosed into the fluidised bed until the pressure decreases to below the predetermined level.

Referring to Figures 7 and 8, there is shown an alternative embodiment of fluidised bed air introducer assembly, indicated generally by the reference numeral 60, mounted in a furnace sump 19, where like parts have been given the same reference numeral as before. The air introducer assembly comprises a pair of air boxes 61 , 63, each having a plurality of upstanding sparge pipes 53 protruding upwardly and outwardly therefrom. The sparge pipes 53 each have a venting nozzle at their end distal from the air box 61 , 63. An end cap 55 is placed over the free end of each of the sparge pipes to prevent ingress of fluidising bed media into the sparge pipes 53 and yet allow discharge of air from the nozzle into the fluidising bed media (not shown). The nozzles are spread evenly about the fluidised bed to provide uniform discharge of air into the fluidised bed.

Referring to Figures 9 to 12, there are shown various detailed views of another embodiment of fluidised bed air introducer assembly, indicated generally by the reference numeral 70, mounted in a furnace sump 19, where like parts have been given the same reference numeral as before. The air introducer assembly is similar to that shown in Figures 2 to 6 with the exception that the nozzles do not protrude above the top 71 of the furnace sump casing 19. This construction is more compact than that shown in Figure 2 to 6 and less prone to damage in transit. Furthermore, this construction allows for ease of removal of the section for repair or replacement.

Referring to Figures 13 to 17, there are shown detailed views of parts of the fluidised bed unit 3. Referring specifically to Figures 13 and 14, there is shown parts of the fluidised bed furnace 80 that sit directly above the furnace sump 19. These comprise a lower furnace casing 81 which comprises the charging inlet 15, the burner inlet 17, a fuel chute 83 leading to the charging inlet 15 and the access hatch 55. Mounted above the lower furnace casing 81 is an intermediate furnace casing 85 which has a plurality of access points 87 for temperature probes and/or air introducer nozzles. The lower furnace casing 81 and the intermediate furnace 85 casing house the lower freeboard of the fluidised bed unit. Referring specifically to Figure 17, there is shown an upper furnace casing 88 that sits on top of the intermediate furnace casing 85. The upper furnace casing 88 houses the upper freeboard of the fluidised bed unit and defines an exhaust gas outlet 89 for through passage of exhaust gases into the heat exchanger (not shown).

Referring to Figures 18 to 21 , there are shown detailed views of the nozzle and nozzle cap of the air introducer assembly, where like parts have been given the same reference numerals as before. The nozzle is at the free end of a sparge pipe 53 and is covered by an end cap 55. The end cap 55 prevents ingress of fluidised bed media into the sparge pipe through the nozzle yet allows air to be delivered through the sparge pipe into the fluidised bed media. The nozzle comprises four apertures 91 in the end of the sparge pipe (Figure 19). A further pair of mounting apertures (not shown) is provided for reception of an end cap mounting pin 93 (Figure 20). The end cap 55 is held in place by having the pin 93 inserted through the mounting apertures 95 of the sparge pipe and through corresponding mounting apertures in the end cap 55.

In the embodiments described, the fluidised bed media is preferably quartz silica sand having a particle diameter of the order of between 0.5mm and 1mm. It is envisaged that the ash and the clinker removed from the fluidised bed could be recycled as fluidising bed media by first of all passing the ash and clinker through a sieve to catch the clinkers above a predetermined size. The ash below that size may be delivered directly back to a fluidising bed media dosing system in communication with the charging inlet and put back into the fluidising bed. The clinker may be crushed in a crusher until it is at an acceptable particle size whereafter the crushed clinker may be delivered directly back to a fluidising bed media dosing system in communication with the charging inlet and put back into the fluidising bed.

By thermal treatment or thermally treating the by-product, what is meant is that the byproduct is burnt or incinerated in the fluidized bed. Reference has been made to the incineration of waste and/or by-products and the terms have been used largely interchangeably throughout the specification. For example, in some jurisdictions, poultry litter or mushroom compost is considered to be a by-product whereas in other jurisdictions it is considered to be a waste. Furthermore, the by-product described in the specification has included poultry litter, spent mushroom compost and meat and bone meal however the use of the fluidised bed unit is not limited to these and by-product could include wet wood chips, miscanthus, sludge, straw, animal manures other biomass fuels.

In this specification the terms "comprise, comprises, comprised and comprising" and the terms "include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation.

The invention is in no way limited to the embodiment hereinbefore described but may be varied in both construction and detail within the scope of the specification.