Introduction

The present invention relates to a by-product energy conversion system comprising a fluidised bed unit and a heat exchanger, the fluidised bed unit having an air introducer with an air intake and the heat exchanger being connected to an exhaust outlet.

In many processes, a by-product is created that has little or no resale value. One example of such a process is a poultry rearing process, wherein the poultry create a significant amount of litter which is typically quite moist. Another example of such a process is a mushroom production process, resulting in a spent mushroom compost byproduct. It is important to dispose of these by-products in as cost effective and efficient a manner as possible. One way in which these by-products may be disposed of is to thermally treat the by-product, and fluidised bed technology has been suggested as a possible means of carry out this thermal treatment. However, thermal treatment of byproducts is often restricted by law due to the problems of ensuring that satisfactory treatment of pathogens in the by-products has taken place.

When dealing with animal by-products in particular, it can be difficult to ensure that certain potential by-products of combustion of the animal by-product are not emitted in the exhaust materials of the fluidised bed unit.

Throughout the specification, the term animal by-products will be understood to refer to by-products such as poultry litter, meat and bone meal, spent mushroom compost, animal manures and other materials whose combustion may result in harmful substances.

It is an object therefore of the present invention to provide a by-product energy conversion system that overcomes at least some of the above-mentioned issues and provides improved performance. Statements of Invention

According to the invention there is provided a by-product energy conversion system comprising a fluidised bed unit and a heat exchanger, the fluidised bed unit having an air introducer with an air intake and the heat exchanger being connected to an exhaust outlet, wherein the fluidised bed unit receives by-product fuel from a fuel delivery assembly for combustion, generating heated exhaust gases; the by-product energy conversion system further comprising an internal draught system having a forced draught fan and an induction fan; wherein the internal draught system is operable to induce a negative pressure so as to produce a pressure differential within the by-product energy conversion system.

In this way, pressure differential produced by the negative pressure induced by the internal draught system ensures that the flue gases and other exhaust material resulting from the thermal treatment of the by-product in the fluidising bed unit are drawn away from the fluidising bed, through the heat exchanger and onwards. In this way, the recovery of the heat energy generated by the combustion of the animal by-products is facilitated.

In an embodiment of the invention there is provided a by-product energy conversion system in which the internal draught system is configured to induce a negative pressure of between -1.0 mbar and -0.1 mbar. This is a particularly efficient negative pressure value, providing for efficient transport of the fuel and flue gases through the furnace and heat exchanger.

In one embodiment of the invention there is provided a by-product energy conversion system in which internal draught system is configured to induce a negative pressure of between -0.6 mbar and -0.4 mbar. This is a particularly efficient pressure range to ensure that animal by-products travels through the furnace at a suitable rate to ensure that it burns at 850 ⁰ C for at least 2 seconds. Combustion at 850 ⁰ C for at least 2 seconds ensures that the majority of harmful by-products, such as pathogens and dioxins, from the animal by-products are fully combusted and will therefore not be released into the atmosphere. Furthermore, a negative pressure of between -0.6 mbar and -0.4 mbar ensures that the flue gases and other exhaust materials pass through the heat exchanger at a rate to ensure highly efficient heat transfer and to reduce unwanted ash deposition in the by-product energy conversion system. Preferably, the negative pressure is maintained at -0.5 mbar.

In a further embodiment of the invention there is provided a by-product energy conversion system in which the by-product energy conversion system comprises a freeboard area above the fluidising bed unit and a freeboard sensor located within the freeboard area. In this way, the pressure in the fluidising bed unit and the pressure in the freeboard area may be accurately measured. As this is the hottest area of the fluidising bed unit, a measurement of the negative pressure at this point provides useful information on the rate at which the exhaust gases are moving through the by-product energy conversion system. Therefore, by monitoring the negative pressure at this point, the system is effectively monitoring the residence time of the exhaust gases in the hottest part of the by-product energy conversion system. This in turn allows confirmation that the exhaust gases have spent sufficient time at the required temperature to ensure the elimination of hazardous substances.

In one embodiment of the invention there is provided a by-product energy conversion system further comprising a bed pressure sensor located in the fluidising bed unit. In this way, a measurement of the pressure in the fluidising bed can be obtained. The pressure in the bed is an indicator of the ash build-up therein, and when the pressure increases, it is necessary to remove some of the bed ash. Typically, the pressure in the fluidising bed will be approximately 20 mbar.

In another embodiment of the invention there is provided a by-product energy conversion in which the bed pressure sensor is located below the fluidising medium of the fluidising bed unit. This is a particularly effective location for the bed pressure sensor.

In one embodiment of the invention there is provided a by-product energy conversion system in which the air introducer comprise a plurality of nozzles and the bed pressure sensor is located adjacent and below the nozzles. In this way, a very accurate measurement of the pressure in the fluidising bed can be obtained - A -

In a further embodiment of the invention there is provided a by-product energy conversion system further comprising a control system operable to receive pressure data from the pressure sensors and control the operation of the forced draught fan and induction fan. In this way, the operation of the fans may be controlled so as to ensure a suitable pressure is maintained within the by-product energy conversion system. The control system can react to any unwanted variations in the detected pressure and instruction the internal draught system to compensate such that a desired pressure reading is obtained.

In another embodiment of the invention there is provided a by-product energy conversion system in which the forced draught fan is connected to the air intake. In this way, the forced draught fan will provide air to the fluidised bed media thus ensuring the bed is sufficiently fluidised to ensure thorough combustion of the animal by-product.

In an alternative embodiment of the invention there is provided a by-product energy conversion system in which the induction fan is connected to the exhaust outlet. In this way, the negative pressure induced by the internal draught system guides the exhaust materials completely through the by-product energy conversion system to the point where they are released to the atmosphere.

Detailed Description of the Invention

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

Fig. 1 is a diagrammatic representation of a first embodiment of a by-product energy conversion system according to the present invention;

Fig. 2 is a representation of the furnace sump of the invention;

Fig. 3 is a representation of the forced draught fan of the invention; and Fig. 4 is a diagrammatic representation of the by-product energy conversion system.

Referring to the drawings and initially to Fig. 1 thereof, there is shown a by-product energy conversion system, indicated generally by the reference numeral 1 , comprising a fluidised bed unit 3, a by-product fuel feed system 5 feeding the fluidised bed unit 3, a heat exchanger 7 operatively coupled to the fluidised bed unit 3, an exhaust filter 9 operatively coupled to the heat exchanger 7 and an internal draught system. The internal draught system comprises a forced draught fan 11 and an induction draught fan 13, which are operable to induce a negative pressure within the by-product energy conversion system 1 so as 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 (not shown) connected to a burner 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 comprising a furnace ash removal auger and a furnace ash removal auger 21 outlet, located at the bottom of the furnace sump 19. The fluidised bed unit 3 further comprises an air introducer assembly most of which is mounted substantially in the furnace sump 19 for delivering air up through the fluidised bed media in the furnace sump 19. The air introducer further comprises the forced draught fan 11 from the internal draught system. The forced draught fan 11 is connected to an air intake 22 which is in turn connected to an air inlet (not shown) located in the furnace sump 19 above the furnace ash removal auger outlet 21. Above the furnace sump 19 is the freeboard area 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 burner. 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 3 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 between the exhaust filter 9 and an exhaust outlet 47, and draws exhaust gases through the by-product energy conversion system 1 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 burnt 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 freeboard area, the temperature is approximately 850 ^° C and at the top of the freeboard area adjacent the freeboard interconnector 34, the temperature is in the region of between 900 ^° C and 1200 ^° C. The height of the freeboard area and the negative pressure induced by the internal draught system 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 eliminated. A plurality of temperature sensors are arranged in the fluidised bed burner furnace. There are four temperature sensors in the fluidised bed itself, one temperature sensor in the lower freeboard area just above the fluidised bed and another temperature sensor in the upper freeboard area. These temperature sensors closely monitor the temperature of the fluidised bed unit 3 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 unit 3.

The hot exhaust gases rise up through the by-product energy conversion system 1 through the lower and upper freeboard area, through the interconnecting freeboard 34 and down through the heat exchanger 7. The heat exchanger 7 comprises a plurality of tubes (not shown) filled with water and the water in the tubes is heated by the hot exhaust gases passing over the tubes. The hot exhaust gases are then passed out of the heat exchanger to the exhaust filter 9 where fly ash is removed from the exhaust gases and the filtered exhaust gases are released into the atmosphere. The exhaust gases released into the atmosphere are still at approximately 150 ^° C to 200 ^° C. An exhaust filter has an ash extractor auger 45 which removes ash out from the filter. The ash taken from the filter typically has a phosphate content of 18% by weight of the ash and 8% potash by weight of the ash and may be sold on as a useful by-product for fertilizers and the like.

The heat exchanger 7 may also be coupled to a heating system (not shown) which comprises a radiator bank and at least one fan for circulating hot air surrounding the fan. In order to couple the heat exchanger to the heating system, the hot water return pipe 37 is connected to the radiator bank and the cold water flow pipe 35 is connected to a water source such as a water buffer tank or a return from the radiator bank. If a water buffer tank is used the water filling the water buffer tank may come from the radiator bank. The heating system is preferably for an animal housing such as a poultry housing however the present invention could be used as a heating system with other types of animals, agricultural processes such as mushroom growing or domestic heating systems.

Referring now to Fig. 2, in which like parts have been given the same reference numerals as before, there is shown the furnace sump 19 comprising a cylindrical air bank 50 which forms part of the air introducer assembly and is connected to an air inlet 52 and is mounted within a sump casing 54. The sump casing comprises a substantially rectangular upper section and a wedged shaped lower section that tapers inwardly to the base. The air bank 50 supplies air to a plurality of sparge pipes 56 that project upwardly therefrom. Each sparge pipe comprises a nozzle and end cap assembly 58 at the upper end thereof. The furnace sump 19 further comprises a furnace ash removal auger (not shown) in the base of thereof which is connected to a furnace ash removal auger outlet 29 located below the air inlet 52 of the air bank 50.

Referring now to Fig. 3, in which like parts have been given the same reference numerals as before, there is shown the vertically mounted forced draught fan 11 connected to the air intake 22 in the furnace sump 19 of the fluidised bed unit 3.

Referring now to Fig. 4, in which like parts have been given the same reference numerals as before, there is shown the by-product energy conversion system 1 with having a base pressure sensor 60, a bed pressure sensor 62 and a freeboard pressure sensor 64. The base pressure sensor 60 is located within the sump 19, below the fluidising bed media (not shown). The bed pressure sensor is located in the fluidised bed unit 3 just below the nozzles 58 of the air introducer assembly. The freeboard pressure sensor 64 is located in the upper freeboard area of the fluidised bed unit 3. Fig. 3 also comprises a plurality of arrows indicating the flow of exhaust gases through the byproduct energy conversion system 1 , as will be described below. Each of the pressure sensors are equipped with communication means so as to supply transmit pressure date to a control system (not shown).

In use, the internal draught system comprising the forced draught fan 11 and the induction draught fan 13 is operated to induce a negative pressure so as to produce a pressure differential within the by-product energy conversion system 1. The forced draught fan 1 1 forces air through the fluidised bed media in the furnace sump 19 so as to form a fluidised bed for the combustion of the by-product fuel. The fluidised bed will in general operate at a differential pressure of 20mbar, measured between the base pressure sensor 60 and the bed pressure sensor 62. The exhaust materials, including heated gases, soot and ash are then drawn through the freeboard area 23 and heat exchanger 7 to the exhaust filter 9 by the negative pressure induced by the induction draught fan 13 and forced draught fan 11 of the internal draught system. The path of the gas flow in the by-product energy conversion system 1 is described below. In the first stage, the gases travel up through the lower freeboard area and upper freeboard area of the fluidised bed unit 3. In the second stage, the exhaust gases and other materials travel from the upper freeboard area through the freeboard interconnector 34 and into the heat exchanger freeboard. In the third stage, the gases travel through the heat exchanger 7 so as to transfer the heat energy to water in tubes within the heat exchanger 7. In the fourth stage, the exhaust gases travel through the exhaust filter 9. In the fifth stage, the cooled and filtered exhaust gases are emitted to the atmosphere through the exhaust outlet 47.

By altering the speed of the forced draught fan 11 and induction draught fan 13 of the internal draught system of the invention, it is possible to control the temperature and pressure within the by-product energy conversion system 1. For ideal operation, the temperature in the fluidised bed during combustion should be in the range 610 ⁰ C to 750 ⁰ C, and ideally between 650°C and 670 ⁰ C. In this way, the temperature in the lower freeboard area will be maintained at 850 ⁰ C or above. It is necessary for the substances within the by-product energy conversion system 1 to be thermally treated at 850°C for a minimum of 2 seconds. The duration is controlled by the speed at which the gases and other substances move through the by-product energy conversion system 1 , which is in turn controlled by the internal draught system. By maintaining a negative pressure of between -1.0 mbar and -0.1 mbar in the by-product energy conversion system 1 , and ideally a negative pressure of -0.5 mbar, it can be ensured that all substances within the fluidised bed unit 3 are thermally treated at a temperature of 850°C for a minimum of 2 seconds. This provides for safe exhaust emissions from the by-product energy conversion system 1.

The control system receives pressure data from the pressure sensors and is operatively linked to the forced draught fan 11 and induction draught fan 13 so as to vary their speed of operation as required. The control system calculates a bed differential pressure from the readings from the base pressure sensor 64 and the bed pressure sensor 62. A bed differential pressure of approximately 20mb is desirable within the fluidising bed itself so ensure optimal operation. The pressure data from the freeboard pressure sensor 64 is used by the control system to control the operation of the internal draught system so as to ensure the pressure within the by-product energy conversion system 1 remains around -0.5 mbar.

If the pressure at the freeboard pressure sensor 64 drops too much below -0.5 mbar, for example to -1.1 mbar, the exhaust gases may move too quickly through the by-product energy conversion system 1. This would lead to insufficient thermal treatment of the byproduct fuel, due to insufficient residence time for the exhaust materials. The exhaust materials may spend less than 2 seconds within the area of the by-product energy conversion system that it at 850 ⁰ C or greater. Additionally, a negative pressure too much below -0.5 mbar may lead to inefficient heat transfer in the heat exchanger 7 as the exhaust materials would move too quickly past the heat exchanger units and would not allow time for the water therein to be heated.

If the pressure at the freeboard pressure sensor 64 goes too much above -0.5 mbar, for example 0.1 mbar, the exhaust gases may move too slowly through the by-product energy conversion system 1. This may lead to excessive unwanted deposition of particulates such as soot and ash from the exhaust materials within the by-product energy conversion system 1 , which can lead to reductions in efficiency. Additionally, the slow movement of exhaust materials would reduce the efficiency of the heat exchanger 7.

Some embodiments of the by-product energy conversion system 1 may comprise a soot and ash fouling prevention system which in turn comprises freeboard soot blowers and heat exchanger soot blowers. The operation of the soot fouling prevention system will affect the pressure within the by-product energy conversion system 1 , however the control system will adjust the forced draught fan 11 and induction draught fan 13 as necessary to ensure that the desired negative pressure is maintained. It will be understood by the person skilled in the art that, ideally, the by-product energy system should be air-tight to maintain the negative pressure induced therein. Therefore it will be clear that all connections made between components should be as airtight as possible. This airtight seal may be accomplished in a known manner, however, it the most part the inter-component connections are made by welding any joints together.

It will be further understood that references to "thermally treating" the by-product fuel, or any grammatical variations thereof, should be interpreted as incinerating, burning, combusting, cremating, igniting and/or creating an oxidising reaction with the by-product fuel.

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.

In the specification the terms 'comprise', 'comprises', 'comprised' and 'comprising' or any variation thereof and the terms 'include', 'includes', 'included' or 'including' or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation.

The invention is not limited to the embodiment herein described, but may be varied in both construction and detail within the terms of the claims.