Description:

This invention relates to incinerators, and in particular, but without limitation, to field incinerators, and in particular, but without limitation, to mobile waste to energy conversion systems.

In certain types of humanitarian or military applications, for example in refugee camps, or in forward -operating military positions, it is necessary to provide incineration facilities for the disposal of waste. Incineration offers a convenient, hygienic and cost-effective means of disposing of waste, compared with other solutions, such as landfill. As such, incinerators are often used alongside ad hoc accommodation facilities, such as those found in military forward-operating positions or in refugee camps, field hospitals and the like as they enable the 1 to 5 kg of waste produced per person, per day, to be disposed of conveniently and effectively.

It is known to use incinerators for the disposal of waste and incinerators typically comprises a combustion chamber into which the waste products are placed, which combustion chamber is closed and the waste then burnt. The combustion is typically initiated using a fuel- (e.g. a gas- or diesel-) fired ignitor, but once combustion is underway, due to the configuration of the incinerator and the retention of heat within the combustion chamber, the combustion process can often be self-sustaining subject, of course, to the availability of sufficient fuel and oxygen.

A typical incinerator generally comprises a flue, through which the waste products of combustion, i.e. the flue gases, vented to atmosphere. In many cases, the flue comprises a secondary combustion chamber, which re-heats the flue gases to a temperature at which potentially harmful contaminants in the flue gases are burnt, thereby rendering the flue gases at the outlet of the flue relatively, or completely, harmless. Burning waste products produces heat, which can be captured to provide heating and/or hot water on site, which is a useful by-product of the process, especially in temperate or cold climates. Capturing of energy from the combustion process can be accomplished by providing a heat exchanger in the flue of the incinerator, which captures waste heat and which rejects it into a heat sink, for example a water supply or into a forced hot air supply. A heat exchanger is necessary to avoid contaminating the air and/or water to be heated by the combustion products themselves - in other words, the heating of the air/water is indirect for reasons that will be readily apparent to the skilled reader.

The temperature within the flue of a typical incinerator is very high, often exceeding 1000 to 1500°C. In order to prevent damage to the heat exchanger, it is necessary, therefore, to continuously supply a cooling fluid, for example air or water, to the heat exchanger to prevent it from overheating. In the case of a water heat exchanger, if the flow of water through it stops, the water within the heat exchanger can rapidly boil, which can lead to the heat exchanger exploding under the pressure of the steam so created. Therefore, in order to operate a heat recovery system on incinerator, it is necessary to have a continuous supply of water to the heat exchanger in order to maintain heat exchanger within acceptable operating temperature parameters.

However, in many ad hoc situations, a continuous supply of cooling water is simply not available. Further, it is not always necessary or desirable to engage the heat recovery system all the time, for example in hot climates where heating and/or hot water may not be necessary continuously. This, therefore, places practical restrictions on the usability of a field incinerator because in known filed incinerators, it is generally necessary to have a continuous supply of cooling water or air at all times the incinerator is in use.

The solution to this problem is to deploy a number of incinerators: some of which having a heat recovery system fitted, and others without. With this arrangement, it is possible to choose which of the incinerators to use at different times in order to obtain hot water only when necessary, i.e. using a heat recovery incinerator at those times; but when heat recovery is not required, using a conventional incinerator (without heat recovery equipment).

That said, this solution is contraindicated in many cases due to the cost of transporting multiple incinerators to forward -operating positions or ad hoc locations and, of course, because of the inefficiencies associated with firing-up and turning-off different incinerators at different times of day.

In particular, an incinerator typically needs to be pre-heated before it can be used, during which pre-heating cycle, it is consuming fuel (a valuable resource) but not actually working as an incinerator. Further, on turning the incinerator off, there is a relatively long lead-time associated with the cool-down procedure, during which time the incinerator is also inoperable.

A further and more practical problem also exists in relation to cyclically turning an incinerator on and off, and that is thermal cycling, which can significantly reduce the duty cycle of an incinerator. In particular, the if refractory materials used inside the incinerator are subjected to cyclical thermal expansion and contraction during the firing-up and switching-off procedures, this can significantly reduce the lifespan of an incinerator.

A further possible solution is to provide an incinerator with a heat recovery system that can be physically switched into, or out of, the flue for example, using a baffle/deflector to divert flue gasses into the heat recovery heat exchanger, or to bypass it, respectively. Such systems have been tested, but have been found to be impractical due to frequent failures of the baffle/deflector (which must be able to withstand the high flue temperatures), and the incidence of leakage around the baffle/deflector as it becomes contaminated over time by the combustion products. This known solution is a high-maintenance system, a requirement that is contraindicated where the availability of trained technicians and spare parts is scarce.

Therefore, there are various well-known drawbacks associated with using existing field incinerators and a need therefore exists for an alternative and/or a solution to one or more of the above problems. This invention aims to provide a solution to one or more the above problems, and/or to provide an alternative incineration apparatus.

Various aspects of the invention are set forth in the appended claims.

According to one aspect of the invention, there is provided an incinerator comprising a combustion chamber and a flue in fluid communication with the combustion chamber; a primary gas-to-gas heat exchanger associated with the flue; a secondary gas-to-liquid heat exchanger; means for forcing a supply of air through the primary and secondary heat exchangers; and a heat sink adapted, in use, to capture heat from the secondary heat exchanger.

The invention differs from known field incinerators fitted with heat recovery systems inasmuch as it comprises two heat exchanger, rather than just a (primary) heat exchanger. The provision of the means for forcing a supply of airthrough the primary and secondary heat exchangers advantageously enables the primary heat exchanger to be continually cooled by an abundant cooling fluid (ambient air), rather than requiring a continuous supply of water.

Suitably, the primary gas-to-gas heat exchanger associated with the flue; a secondary gas-to-liquid heat exchanger; means for forcing a supply of air through the primary and secondary heat exchangers; and a heat sink adapted, in use, to capture heat from the secondary heat exchanger.

Suitably, the primary heat exchanger comprises a hot side through which flue gasses are configured, in use, to pass, and a cold side through which the supply or air is forced.

Suitably, the secondary heat exchanger comprises a hot side though which, in use, the supply of air is forced and a cold side through which, in use, a heat transfer liquid is arranged to pass.

Suitably, the means for forcing the supply of air through the primary and secondary heat exchangers comprises an air blower. Suitably, the air blower is configured to force ambient air into the primary heat exchanger, for example, into an inlet of the cold side thereof. Suitably, the means for forcing the supply of air comprises duct means providing a conduit between the primary and secondary heat exchangers. Suitably, the duct means provides a conduit for the forced air between an outlet of the cold side of the primary heat exchanger and inlet of the hot side of the secondary heat exchanger.

The duct means, where provided, may comprise a diverter valve/baffle/deflector etc. for selectively diverting the supply of forced air towards, or away from, the secondary heat exchanger.

This configuration usefully enables the heat recovery system to be switched on or off at will, that is to say: "on" when the forced air is diverted to the secondary heat exchanger or "off" otherwise. Partial heat recovery may also be possible, for example, by diverting only a selected proportion of the forced air to the secondary heat exchanger.

As the supply of ambient air into the air blower (in one embodiment) is virtually infinite, it is possible to operate the incinerator continuously without the heat recovery system in-use because the supply of forced air can be continuous, thus providing the requisite continuous cooling of the primary heat exchanger, and thereby avoiding the aforementioned problems of heat exchanger overheating. In certain embodiments of the invention, the air blower can be switched off when the heat recovery system is not in use. This is possible because there is no liquid in the primary gas-to-gas heat exchanger, and so the aforementioned problem (associated with the prior art) of the heat exchanger exploding due to boiling of water therein, is obviated.

Suitably, the cold side of the secondary heat exchanger is operatively connected in-series with a closed-loop circuit containing the heat transfer liquid. In certain embodiments of the invention, the heat sink comprises a hot water cylinder through which part of the closed-loop circuit passes, thereby enabling heat from the combustion process (within the combustion chamber) to ultimately be captured in a supply of water to be heated. The hot water cylinder suitably comprises control means for enabling the heated water to be decanted, as desired. Additionally or alternatively, the heat sink comprises a closed-loop central heating system into which the heat from the combustion process (within the combustion chamber) is ultimately captured by the central heating system.

Additionally or alternatively, the heat sink comprises ambient air, whereby the forced air that has been heated by the combustion chamber is simply exhausted to atmosphere. Additionally or alternatively, the heat sink comprises ambient air, although with suitable ducting etc. the heated air (heated by the combustion process) can be fed into a ducted hot air heating supply. Additionally or alternatively, the duct mans may comprise an exhaust port through which the forced air can be exhausted to atmosphere. In certain embodiments, the exhaust port may be selectively connectable, in use, to a ducted hot air heating system.

The heat transfer liquid suitably comprises water, or a water-based solution (e.g. water plus any one or more of the group comprising: an antifreeze, a corrosion inhibitor and a heat capacity altering additive). The use of a water-based heat transfer liquid is often indicated for health and safety reasons, as well as for ease of maintenance and repair.

Various embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic side view of a first embodiment of the invention operating in a first mode;

Figure 2 is a schematic side view of the embodiment of Figure 1 operating in a second mode;

Figure 3 is an embodiment of the invention of Figure 1 operating a third mode;

Figure 4 is a schematic side view of a second embodiment of the invention;

Figure 5 is a schematic side view of a third embodiment of the invention.

Referring to Figures 1 , 2 and 3 of the drawings, a field incinerator 10 comprises a combustion chamber 12 into which waste to be disposed of (not shown) is placed. The waste (not shown) is ignited by an ignitor 14, which is fuelled by a fuel (e.g. gas or diesel) supply 16 via a suitable regulator/control valve 18. Typically, the combustion chamber 12 is pre-heated using the ignitor to get it up to a temperature at which waste products (not shown) will burn easily. During the combustion process, flue gases are exhausted to the atmosphere 20 via a flue pipe 22 which provides a conduit between the interior of the combustion chamber 12 and the atmosphere 20. Waste (not shown) can therefore be placed inside the combustion chamber 12 and burnt, with combustion products being vented to atmosphere 20 via the flue 22.

A secondary combustion chamber (not shown) may be provided to re-heat the combustion products inside the flue to neutralise potentially harmful waste gasses or combustion by-products.

The field incinerator 10 comprises a primary gas-to-gas heat exchanger 24 which comprises a series of fins 26 that are welded to the exterior of the flue 22. The primary heat exchanger 24 is located within a duct 28 having an inlet 30 and an exhaust port 32 located on opposite sides of the primary heat exchanger 24. Air from the atmosphere 20 is forced through the duct 28 by an air blower 34, which is powered by an electrical power source (not shown), for example. Air is thus drawn into the duct 28 via the inlet and is blown over the fins 26 of the primary heat exchanger 24 thereby recovering at least some of the heat from the flue 22. Because the primary heat exchanger 24 is a gas-to-gas heat exchanger, it is possible to extract heat from the flue 22 without the air inside the duct 28 mixing with the combustion products within the flue 22.

A secondary heat exchanger 36 is also located inside the duct 28 downstream of the primary heat exchanger 24. The secondary heat exchanger also comprises a series of fins 38, which are heated by the now-heated air 52 within the duct 28 blown by the blower 34. The secondary heat exchanger 36 is cooled by a closed-loop water cooling circuit 40, which recovers heat from the secondary heat exchanger 36 and which rejects it via a set of coils 42 located inside a hot water tank 44 containing a quantity of water 46 to be heated.

The hot water tank 44 can be filled by an inlet pipe (not shown) and heated by the coil 42 of the cooling circuit 40. Heated water 46 can be decanted from the water tank 44 via an outlet 48, as required. It will be appreciated from the foregoing description that the heat from the combustion products within the flue 22 that would otherwise be rejected to atmosphere 20 can be at least partially recovered by the primary heat exchanger 24 and used, by the secondary heat exchanger 36 to heat a quantity of water 46 for subsequent use.

It will be appreciated that, over time, a desired water temperature 46 within the water tank 44 may be reached, in which case the secondary heat exchanger 36 may be required to be switched-out. To accomplish this, an optional baffle 50 can be located within the duct 28 upstream of the secondary heat exchanger 36, which baffle 50 can be moved between a first position, as shown in Figure 1 and a second position as shown in Figure 2.

Referring now to Figure 2 of the drawings, the air flow 52 is now diverted 54 by the baffle 50 into an outlet limb 56 of the duct 28. The outlet limb 56 comprises a secondary exhaust port 58, through which the diverted air flow 54 is exhausted to atmosphere 20. It will be appreciated that with the baffle 50 in the second position, that the flow of forced air 52 is now diverted away from the secondary heat exchanger 36. Now, therefore, the primary heat exchanger 24 recovers at least some of the heat from the combustion products within the flue 22 (which may be useful, in certain situations, to cool the flue 22) and exhaust the heat via the secondary exhaust port 58 to atmosphere 20, rather than via the main exhaust port 32 after having interacted with the secondary heat exchanger. This configuration usefully enables the secondary heat exchanger 36 to be switched out of the system, for example when the desired water temperature 46 within the water tank 44 has been reached.

Turning now to Figure 3 of the drawings, it can be seen that the baffle 50 is now in an intermediate position between the first position shown in Figure 1 of the drawings, and the second position shown in Figure 2 of the drawings. In this situation, the forced airflow 52 is split into a first portion 54 that is exhausted by the secondary exhaust port 58 to atmosphere 20; and a second portion 60 passes through the secondary heat exchanger 36 and is vented to atmosphere 22 via the main exhaust port 32 of the duct 28. In this situation, heat recovered from the flue 22 is partially diverted away from, and partially diverted towards, the secondary heat exchanger 36, thereby enabling a reduced heating rate of the water 46 within the water tank 44 to be obtained.

It will be noted from Figures 1 , 2 and 3 of the drawings that the field incinerator system 10 is containerised that is to say being housed within a bulk transport container (for example, an ISO container) 62, which is supported off the ground 64 on feet 66. The primary advantage of containerising the field incinerator 10 is that it can be readily transported to site, for example by road, rail or sea, with relative ease and it provides a robust enclosure for the components of the field incinerator 10 previously described. Conveniently, the flue 22 is formed from a number of nested sections, which enable the part 68 of the flue 22 extending above the roofline of the container 62 to be removed for transportation and storage purposes. However, when the container 62 has been moved to a desired location, the flue stack 22 can be reassembled with an upper part 68 protruding above the roofline of the container 62.

Other embodiments of the invention are shown in Figures 4 and 5 of the drawings, which share many of the features of the embodiment shown in Figures 1 , 2 and 3 referred to previously. To avoid repetition, identical features have been identified by identical reference signs in Figures 4 and 5.

The main difference between the embodiment of the field incinerator 100 shown in Figure 4 of the drawings and that shown in Figures 1 , 2 and 3 of the drawings, is the location of the baffle 500, which now is now located downstream of the secondary heat exchanger 36. This configuration enables the forced air 52 within the duct 28 to be exhausted continuously to the main exhaust port 32 of the duct 28. In other words, forced air flow 52 passes through the primary heat exchanger 24 and a secondary heat exchanger 36 at all times thereby providing continuous heating of the water 46 within the tank 44 at all times the blower 34 is in operation. In this embodiment of the invention, the amount of heat recovery is controlled by the speed of the blower 34: higher flow rates 52 leading to greater heat recovery rates from the flue 22, and vice-versa, as will be readily appreciated by the skilled reader. In the embodiment shown in Figure 4 of the drawings, the baffle 500 can be moved between first, second and intermediate positions (similar to those shown in Figures 1 , 2 and 3 of the drawings, to deflect selected proportions of the forced air 54 into a ducted hot air heating system (not shown) in accommodation units, tenting, buildings 502, etc. and this may enable the field incinerator 100 to be used to heat such accommodation units 502, as required.

Referring now to Figure 5 of the drawings, which shows a third embodiment of a field incinerator 200 in accordance with the invention, a configuration very similar to that shown in relation to Figures 1 , 2 and 3 above further comprises a tertiary, water-to-water heat exchanger 202, which can be connected in- series, or in parallel, with the closed loop cooling circuit 40 described previously. In this particular configuration, heat recovered from the flue 22 by the primary heat exchanger 24 can be used to heat a supply of hot water 46, or water in a central heating circuit 204 comprising one or more radiators 206. The flow of water in the primary circuit 40 can be controlled using valves (not shown for simplicity) to enable the ratio of water 46 heating and radiator 206 heating to be controlled at will.

It will be appreciated that the embodiments of the invention shown in the drawings are merely exemplary and that other combinations and/or permutations of the features described could be used to suit different applications. For example, may be desirable to provide a wet central heating system 204, 206 rather than a hot water system 40, 44, in which case the secondary heat exchanger 36 will be connected directly to the central heating circuit 204 and not to a hot water heating circuit 40 as described herein. Furthermore, it may be possible to position the baffle 50 shown in Figure 5 of the drawings and the secondary limb 56 of the duct 28 downstream of the exhaust port 32 in a manner similar to that shown in Figure 4 of the drawings. Other combinations and permutations will be readily apparent to the skilled reader.