DRYER AND COMBUSTOR FOR TOILET AND OPERATION THEREOF

Abstract

In the treatment of human faeces having a starting moisture content, the faeces are pressed between opposing pressing surfaces of rollers in a dryer, to press out at least some moisture from the faeces. The pressing surfaces are moved to leave an exposed layer of pressed faeces on at least one of the pressing surfaces which is then scraped. This produces partially-treated human faeces having a moisture content of not more than 20 wt %. The partially-dried human faeces may then be combusted. This fuel is fed substantially continuously into a combustor at a rate of 0.4-15 g/min combusted continuously over a time of at least 1 hour. In the combustor, there is a reaction chamber with a drying zone and a first combustion zone. The reaction chamber is orientable to permit gravity-assisted transit of the fuel from the drying zone to the first combustion zone. The drying zone has a drying zone grate configured to hold some of the fuel while combustion of other of the fuel occurs at the first combustion zone. A toilet may incorporate such a dryer and/or combustor.

Claims

1-18. (canceled)

19. A process for the treatment of human faeces, including the steps: providing a fuel comprising partially-treated human faeces, with a moisture content of not more than 20 wt % based on the weight of the partially-treated human faeces; introducing the fuel substantially continuously into a combustor at a rate of 0.4-15 g/min; and combusting the fuel continuously over a time of at least 1 hour.

20. The process according to claim 19 wherein the drying zone grate is moved to deposit the fuel from the drying zone grate into the first combustion zone.

21. The process according to claim 19 wherein the combustor has a first combustion zone grate, the grate holding fuel being combusted in the first combustion zone.

22. The process according to claim 21 wherein the first combustion zone grate is moved to deposit the fuel from the grate into a second combustion zone, disposed beneath the first combustion zone.

23. The process according to claim 22 wherein the combustor has a second combustion zone grate holding fuel being combusted in the second combustion zone.

24. The process according to claim 23 wherein the combustor further includes an ash collection zone disposed in operation beneath the second combustion zone, and wherein the second combustion zone grate is moved to deposit the ash from the second combustion zone grate into the ash collection zone.

25. The process according to claim 24 wherein the movement of the grates is controlled so that when the first combustion zone grate is open, the drying zone grate is closed, and/or so that when the second combustion zone grate is open, the first combustion zone grate is closed.

26. A combustor for the treatment of human faeces, the combustor being adapted to receive a fuel comprising partially-treated human faeces, with a moisture content of not more than 20 wt % based on the weight of the partially-treated human faeces and adapted to receive the fuel substantially continuously at a rate of 0.4-15 g/min, the combustor having a reaction chamber with a drying zone and a first combustion zone, wherein the reaction chamber is orientable to permit gravity-assisted transit of the fuel from the drying zone to the first combustion zone, wherein the drying zone has a drying zone grate configured to hold some of the fuel while combustion of other of the fuel occurs at the first combustion zone.

27. The combustor according to claim 26 wherein the drying zone grate is configured to be moveable to deposit the fuel from the drying zone grate into the first combustion zone.

28. The combustor according to claim 26 or claim 27 having a first combustion zone grate for holding fuel being combusted in the first combustion zone.

29. The combustor according to claim 28 wherein the first combustion zone grate is configured to be moveable to deposit the fuel from the grate into a second combustion zone, disposable in operation beneath the first combustion zone.

30. The combustor according to claim 29 wherein the combustor has a second combustion zone grate for holding fuel being combusted in the second combustion zone.

31. The combustor according to claim 30 having an ash collection zone disposed in operation beneath the second combustion zone, and wherein the second combustion zone grate is configured to be moveable to deposit the ash from the second combustion zone grate into the ash collection zone.

32. A toilet having: a settling tank for receiving human waste and allowing at least partial separation of faeces from urine; a conveyer for moving faeces from the settling tank; a dryer for at least partially drying the faeces to produce partially-treated human faeces; and a combustor, the combustor being adapted to receive a fuel comprising said partially treated human faeces, with a moisture content of not more than 20 wt % based on the weight of the partially-treated human faeces and adapted to receive the fuel substantially continuously at a rate of 0.4-15 g/min, the combustor comprising a reaction chamber with a drying zone and a first combustion zone, wherein the reaction chamber is orientable to permit gravity-assisted transit of the fuel from the drying zone to the first combustion zone, wherein the drying zone has a drying zone grate configured to hold some of the fuel while combustion of other of the fuel occurs at the first combustion zone.

33-38. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0062] FIG. 1 shows a schematic perspective view of a toilet according to an embodiment of the present invention.

[0063] FIG. 2 shows a side view of the dryer and combustor arranged with respect to each other.

[0064] FIG. 3 shows a perspective view of the arrangement of FIG. 2.

[0065] FIG. 4 shows an alternative perspective view of the arrangement of FIG. 2.

[0066] FIG. 5 shows a rear view of the arrangement of FIG. 2.

[0067] FIG. 6 shows a schematic cross sectional view through the dryer.

[0068] FIG. 7 shows a schematic view of a fuel feeding arrangement for use with a combustor.

[0069] FIG. 8 shows a schematic cross sectional view of a combustor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] FIG. 1 shows a toilet 100 according to an embodiment of the present invention. As can be seen the drawing, the toilet is freestanding and has a compact design. It can be used without the need for an external electrical power supply, or an external source of water.

[0071] Toilet 100 has a seat 102 and lid 104. Human waste is deposited in the toilet and is transferred into setline tank 106. Urine is separated from the faeces and treated separately by filtration, which is not described here in detail, but the water filtered from the urine is stored in reservoir 108. Faeces is conveyed from the setting tank via screw 110 and transferred into dryer 200 at dryer inlet 202. The combustor is not visible in the view shown in FIG. 1. Water vapour condenser 112 is associated with the urine filtration system and has an exhaust 114.

[0072] FIG. 2 shows a side view of the dryer 200 and combustor 300 arranged with respect to each other. FIG. 3 shows a perspective view of the arrangement of FIG. 2. FIG. 4 shows an alternative perspective view of the arrangement of FIG. 2. FIG. 5 shows a rear view of the arrangement of FIG. 2. These drawings are described together, with the same reference numbers used for similar features where appropriate.

[0073] Dryer 200 and combustor 300 are arranged side by side. Hot exhaust gas from the combustor is directed from the combustor along exhaust duct 302 to manifold 304. The hot gas is used in the dryer to heat the rollers (described later) and to provide a hot atmosphere in the dryer.

[0074] The faeces dried in the dryer collects at the base of screw conveyer 250. The faeces is therefore conveyed upwardly by screw conveyer 250 where is it additionally dried and chopped by the screw conveyer. It is then transferred under gravity in to the combustor 300. The view shown in the drawings is partially cutaway in order to show the heat insulation 310 and also to show the components held inside the heat insulation 310.

[0075] FIG. 6 shows a schematic cross sectional view through the dryer 200. It is intended that the dryer is capable of producing pressed faeces substantially continuously at a rate of 0.4-15 g/min, or 1-15 g/min. The pressed faeces may also be referred to herein as partially-treated faeces.

[0076] The opposing pressing surfaces of the dryer are provided by two opposed rollers 204, 206 that counter-rotate relative to each other, as shown by the thick arrows superimposed on the rollers. The rollers are heatable internally by ducting hot gas from the combustor into the interior of the rollers via manifold 304. As shown, the rollers are cylindrical and have axes of rotation that are parallel to each other and are horizontally oriented and disposed at substantially the same vertical position, so that the rollers 204, 206 rotate side-by-side.

[0077] Roller gap 208, i.e. the non-zero distance between the roller surfaces at their closest point of approach, is about 2 mm. It has been found that such a gap is suitable to provide adequate pressing of the faeces and yet still allows suitable throughput of faeces and provides a barrier and regulator for faeces flow. Pressing of the faeces in the roller gap presses at least some moisture out of the faeces.

[0078] The faeces are fed via inlet 210 to the rollers, from above. The rollers rotate in a direction so that, from above, the faeces is drawn into the roller gap both by gravity and by the relative movement of the rollers.

[0079] In use, it is found that the faeces are pressed at the roller gap. Beyond the roller gap, the opposing surfaces of the rollers move apart from each other, due to the rotation of the rollers. This is found to produce a tearing effect on the faeces, to leave a layer of faeces on each roller surface. This is found to provide particularly suitable conditions for further drying of the faeces.

[0080] In operation, the rollers rotate relatively slowly. For example, the rollers may rotate at about 1 rotation per hour.

[0081] The dryer includes a dryer chamber 212, housing the rollers. In operation, hot air is ducted into the dryer chamber via manifold 304. This is in addition to hot air that is provided internally to the rollers to heat the rollers. The hot air assists the layer of faeces on the rollers to further dry by evaporation. The evaporated moisture is ducted out of the dryer chamber to an exhaust.

[0082] Each roller has an associated scraper 214, 216. The purpose of the scraper is to scrape the layer of pressed faeces from the surface of the roller. The scrapers are urged via spring loading against the surfaces of the rollers. This helps to accommodate wear. The position of the scraper on a roller is such that the layer of faeces travels a suitable distance with the roller, to allow adequate drying. In this embodiment, this distance is the equivalent of more that a half turn from the roller gap, in the direction of rotation of the roller.

[0083] The dryer chamber has a faeces collection zone 220, located at a base portion of the dryer chamber 212. The dryer chamber has guide walls 222, 224 which slope from side walls 226, 228 towards the faeces collection zone 220. The purpose of the guide walls is to allow faeces that are scraped from the roller surface to be guided towards the faeces collection zone 220. The screw conveyor 250 picks up the dried faeces directly from the faeces collection zone 220.

[0084] The dryer chamber is thermally insulated via layers of thermal insulation (not shown).

[0085] Disposed below the roller gap 208 within the dryer chamber is a liquids tray 230. This is disposed in order to catch liquid drops pressed from the faeces. The liquids tray may take the form of a gutter. The gutter slopes from the dryer chamber, to allow the liquid to be conducted out of the dryer. The liquid may be conducted to the settling tank. It is possible in some embodiments to provide means for conveying the contents of the tray (or other receptacle for catching liquids and possibly also some solids from the rollers). For example, a screw conveyor may be disposed to draw off liquids and any solids that fall into the tray. The screw may be at least partially in the same plane as the rollers and may be driven by a belt or gear from the rollers themselves.

[0086] FIG. 7 shows a schematic view of a fuel feeding arrangement for use with a combustor. This is found to be of use in particular in developing the preferred combustor configuration. However, in the preferred embodiment in which the dryer and the combustor are combined, this fuel feed arrangement may be substituted by the screw conveyer described above.

[0087] In FIG. 7, a fuel hopper 310 contains the partially-treated faeces. Below fuel hopper 310 is a lock/metering hopper 312 with a slide valve 314 interposed between them. At the base of the lock/metering hopper 312 is a rotary valve 316 which is rotatable to conduct the fuel into a metering hopper 318. Metering hopper 318 has a further rotary valve 320 to permit metering of the fuel into the combustor. The intention of this arrangement is to reduce the tendency of the fuel to bridge across the fuel inlet system, or to cake within it.

[0088] Further below, we discuss the specific structure and operation of the combustor. However, it is first useful to discuss some further background to aid understanding of the context of the present disclosure.

[0089] The development of alternative sources of energy and the need to protect the environment is changing our perspectives on the way natural resources are utilized and waste is managed. Materials such as municipal solid waste, agricultural residues and sewage sludge that were traditionally considered as waste, and either burnt or discarded into landfills, may now be regarded as feedstocks for bioenergy (Huang and Rein, 2016; Milani et al., 2014; Nussbaumer, 2003; Werle et al., 2016). Human faeces are one of such biomass resources with potential to be used as fuel and converted to heat and/or electricity (T. Onabanjo et al., 2016a).

[0090] The Reinvent the Toilet Challenge funded by the Bill & Melinda Gates Foundation was launched to improve access to affordable, safe and sustainable sanitation while simultaneously utilising the chemical energy contained in the human faeces. The challenge aims to develop innovative household-scale toilets that treat human excreta and recover useful resources at affordable price without producing hazardous products (Bill & Melinda Gates Foundation, 2016a, 2016b; McConville et al., 2014; Parker, 2014).

[0091] The present inventors have approached this challenge by aspiring towards self-sustained operation of a toilet by valorising the faeces without the need for external energy supply. The thermodynamic analysis conducted by the inventors' research group (Hanak et al., 2016) shows the possibility of self-sustained operation and also indicates the need for the efficient management of the energy recovered from the human faeces.

[0092] Onabanjo et al. (T. Onabanjo et al., 2016a) and Muspratt et al. (Muspratt et al., 2014) showed that human faeces have a comparable and, in some instances, higher heat value than wood biomass (both on the dry basis). This chemical energy can be recovered via thermochemical conversion technologies including smouldering (Wall et al., 2015; Yerman et al., 2015), combustion (Monhol and Martins, 2015; T. Onabanjo et al., 2016a), hydrothermal carbonization (Afolabi et al., 2015; Danso-Boateng et al., 2013), and pyrolysis (Ward et al., 2014).

[0093] Combustion presents a significant opportunity for energy recovery in the context of a toilet because of the heat released during the process at temperatures ranging from as low as 250 C. (smouldering) to >1000 C. (combustion), depending on air excess, ignition modes (standard vs. booster), fuel composition, etc. The released heat can be used for removing moisture from fresh human faeces in the dryer, described above, before it is fed into micro-combustor (T. Onabanjo et al., 2016b). Contrary to other thermochemical processes such as pyrolysis and hydrothermal treatment, combustion is mature and widely applied process; thereby, increasing its potential application for sanitary solutions where affordability is a priority, particularly for developing countries. For a domestic-scale toilet, a continuous mode of operation of the micro-combustor would be desirable to limit energy requirement for ignition and to ensure that the bed material is sufficiently hot for incoming partly-moist faecal material.

[0094] Work from the present inventors' research group using a bench-scale reactor (T. Onabanjo et al., 2016b) showed the feasibility of combustion of faeces; however, the need for controlled air supply for self-sustained ignition and flame propagation was emphasised. The paper also highlighted the desirability for removing the ash, and so the present disclosure proposes an embodiment with a regulated ash removal system, that can prevent the build-up of ash in the combustion zone but in sufficient amount to retain heat for continuous thermal treatment. To ensure the safety of the users and minimise heat losses, which increases thermal efficiency, special attention was paid to material selection for the micro-combustor in the preferred embodiment. It is also considered that some scales of reactor may have too high a capacity (e.g. even the range of 1.5-2.3 g/min may be too large for a toilet designed for a single household with ten user capacity) and therefore special attention should be paid to ensuring that the combustor can operate at lower faeces burn rate, e.g. at about 0.4 g/min (T. Onabanjo et al., 2016a). A flexible mode of operation is also desirable to accommodate different toilet user capacities, faeces generation rate, and lifestyle such as vacation from home.

[0095] The justification for designing a new a prototype for combustion of human faeces was based on results from previous experimental studies carried out with a bench scale facility (T. Onabanjo et al., 2016b), designed at RTI International/Colorado State University and tested at Cranfield University. This new design was needed considering to be used by a smaller community (which will affect the scale of the system) and aims to use a continuous combustion process, in opposite to the batch operation performed previously. Thus, the focus of this disclosure is a micro-combustor system that is suitable for the thermochemical conversion of human faeces and for continuous, or substantially continuous, self-sustained operation in the context of a toilet.

[0096] Returning now to a discussion of the preferred embodiments, FIG. 8 shows a longitudinal cross sectional view of a combustor 300.

[0097] The combustor receives a fuel (not shown) comprising partially-treated human faeces from the dryer. The combustor has reaction chamber 350 formed from a machinable ceramic material. A drying zone 352 is formed above drying zone grate 354. First combustion zone 356 is formed above first combustion zone grate 358. In view of the vertical orientation of the reaction chamber 350, gravity-assisted transit of the fuel from the drying zone to the first combustion zone is permitted. When fuel is combusted at first combustion zone 356, fuel held at the drying zone grate is further dried. In the first combustion zone, the fuel may be combusted and/or pyrolysed and/or gasified.

[0098] The drying zone grate 354 is movable by rotation to deposit the fuel from the grate into the first combustion zone 356.

[0099] Similarly, the first combustion zone grate 358 is movable by rotation to deposit the fuel from the grate into second combustion zone 360, which has second combustion zone grate 362. The second combustion zone is disposed beneath the first combustion zone. In the second combustion zone, the fuel is combusted and/or gasified and/or may be subjected to char burn. It is preferred that the fuel is fully combusted by the end of its time in the second combustion zone, in order to leave ash.

[0100] The combustor further includes ash collection zone 364. This is disposed in operation beneath the second combustion zone 360. The second combustion zone grate is capable of moving by rotation to deposit the ash from the grate into the ash collection zone 364. Ash collection zone has ash port 366 to allow emptying of ash from the combustor.

[0101] In operation, the movement of the grates 354, 358, 362 is controlled so that when the first combustion zone grate 354 is open, the drying zone grate is closed. Similarly, it is preferred that when the second combustion zone grate is open, the first combustion zone grate is closed. This avoids unwanted transit of fuel directly from the drying zone to the second combustion zone, and/or unwanted transit of fuel directly from the first combustion zone to the ash collection zone.

[0102] The combustor is of small scale. This is of interest in terms of maintaining a small overall size for the toilet. However, more importantly, it is considered to be of assistance in promoting self-sustaining substantially continuous combustion based on the low feed rate of fuel available. In FIG. 8, distance A is about 45 mm, distance B is about 70 mm and distance C is about 70 mm. The internal diameter of the reaction chamber 350 is about 40 mm.

[0103] Combustion air is fed into the reaction chamber at air inlet 370. Heater 372 is provided to heat the combustion air, particularly during ignition. As can be seen in FIG. 8, the combustion air is fed into the first combustion zone 356, and so the combustor has a downdraft configuration. Secondary air is provided via secondary air inlets 374, 376, to the second combustion zone 360. This assists with char burn-out.

[0104] In this embodiment, the exhaust gas outlet 378 is provided at the upper end of the combustor. This has the advantage that ash entrained in the exhaust gas can fall back into the ash collection zone 364 from the annular exhaust passage 380 surrounding the reaction chamber 350 and communicating between the ash collection zone 364 and the exhaust gas outlet 378.

[0105] The ash collection zone has a sloping guide wall 382 to guide the ash falling from the second combustion zone, and/or from the annular exhaust passage 380, towards an ash outlet. The ash outlet 366 is offset from the centre line of the reaction chamber 350, to assist in preventing ash from clogging the exit of exhaust gas from the reaction chamber.

[0106] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0107] All references referred to above and/or below are hereby incorporated by reference.

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