WO2015082891A1

WO2015082891A1 - Containerised waste digester

Info

Publication number: WO2015082891A1
Application number: PCT/GB2014/053561
Authority: WO
Inventors: Rex Michau
Original assignee: Rex Michau
Priority date: 2013-12-05
Filing date: 2014-12-01
Publication date: 2015-06-11
Also published as: GB201413379D0; AP2016009321A0; DE202014010661U1; GB2521023A; GB2521023B; GB201321461D0; EP3077496A1

Abstract

A system for anaerobic digestion of organic waste comprising a plurality of containers sealingly connected end-on-end and/or stacked on top of each other to form a tunnel to receive the waste, the tunnel configured to be sealingly closed for given period for digestion of the waste contained therein.

Description

The present invention relates to a system for the digestion of high volumes of organic waste to produce methane gas. The present invention also relates to a method of maintaining the digestion process within a sealed digestion environment.

To date landfills have been one of the mere traditional means of disposal for (mainly) non-hazardous municipal waste, A large proportion of the tola? waste is of organic origin largely deriving from domestic and restaurant food residues. These organic materials are degraded by bacteria and othe natural processes the byproducts of which include gases and liquids, which may be hazardous.. These emissions are potentially very harmful to humans and the wider environment, so in recent years the operation of landfill has become highly regulated in developed economies.

The main hazards include the uncontrolled emissions of gases, methane (highly flammable), hydrogen sulphide (lethal to humans i high concentrations) and carbon dioxide arid liquids (Ieachate) which can contaminate ground water and act as a breeding ground for parasites, mosquitos, insects etc.,

.Post of the biodegradation that takes place on landfill sites occurs under anaerobic conditions (i.e. in th absence of oxygen). This particular environment causes anaerobic bacteria to colonise and thrive. One of their main waste byproducts is methane gas and the liquid phase (Ieachate),

As a result, regulations have been imposed. To prevent contamination of groundwater, landfill sites have to be lined with impermeable: materials so that ieachate circulation and recovery systems can be installed. A network of pipes and pumps are required for gas capture, and capping of deactivated sites is necessary to prevent fire hazard from on-going methane fugitive emissions, which can continue for up to 25 years. These preventative measures are very costly and require constant monitoring and maintenance to prevent leakage and environmental contamination. Also, landfills have a finite life. It is therefore common knowledge to practitioners within the waste industry that anaerobic digestion produces: methane gas as a by-product of organic materials breaking down., it is also known to the waste industry that anaerobic digestion in large volumes is a successful means of driving electricity-producing generators from the methane gas produced in a disused mine or canyon lined and areas filled as a landfill site. Traditionally, the landfill site then naturally becomes what is known as a land bio-reactor and the gas can be taken through a pipework system installed within the landfill. It is also known to use digesters or bio-reactors that operate on a smaller scale in the vertical, horizontal or other orientation. Such digesters operate on a batch basis, or plug basis for, e.g., feedstock, often made up of agricultural waste.

A transportable digester system is known from DE 202010000437 in which modules are combined to create a tunnel through which waste is conveyed in a continuous process.

Continuous processes must always be monitored by a biologist who controls speed, input etc. based on monitored parameters. The amount of gas generated with such continuous systems is highly variable and their scalability for particular situations is limited,

Existing systems are more for low capacity production and not for large municipal operations that could serve a city. Also, conventional digestion systems, primarily designed for farming applications have losses by the nature of their loading operation and unloading openings. These losses dangerously allow the gas into the atmosphere.

The present invention aims to capitalise on these natural processes and virtually eliminate all the associated hazards, by providing a tunnel, containment and material handling system and method that can recover substantially all of the gas created by the anaerobic digestion during the chosen -degradation period in an efficient and effective batch process. According to a firs! aspect, the present invention: provides system for anaerobic digestion of organic waste comprising: a plurality of bins each containing waste to be digested; a plurality of containers sealingiy connected en -on-end and/or stacked on fo of each other to form a tunnel to receive the waste; rails on which said plurality of bins containing the organic waste are loaded into the ^'tunnei; and rails on which the plurality of bins containing the digested organic waste are unloaded from the tunnel; the tunnel configured to received said plurality of bins and then to be seaiingly closed and contain the bins for a given period for digestio of the waste contained therein; the system comprising a cluster of such tunnels arranged side-by-side, each tunnel comprising a pluralit of containers sealingiy connected end-on-end and/or stacked one on to of another, the number and/or size of the containers defining a tunnel selected to define a daily volume of waste to be processed, and the number of slde-by-sitie tunnels selected based on the number of days of the given period of digestion.

According to a second aspect, the invention provides a method of anaerobic digestion of organic waste comprising seaiingly connecting a plurality of containers end-on-end^' and/or one on top of another to form a tunnel to receive the waste; providing the waste to the tunnel in a plurality of bins, via rails, into the tunnel, sealing the funnel closed, containing the bins for a given digestion period; and unloading the bins via rails after the digestion period; wherein the tunnels are provided in a cluster comprising one tu^'n el for each day of the digestion period, and wherein the number of tunnels is such that as one tunnel Is loaded, another tunnel, in which waste has been contained for the complete digestion period, can be unloaded.

By separating substantially ail the organic material from the waste and containing it in a totally closed system, in a batch process, substantially all the methane gas generated by the biological activity can be captured, and used to generate electricity. Leachate is fully contained and the remaining organic content is reduced to a level where it can be safely discharged to a sewer without further treatment.

Additionally, in preferred embodiments, the containerised waste digester uses doors and loading racks at each end to control the in and out loading of waste if? parcels, e.g. in bins, containers etc.. These doors are closed, once a batc of waste Is loaded; to ensur a full face or airtight sea! and ensure gas is maintained in the tunnel.. The parcels roll or rail or siide or run info the tunnel. The tunnel is thus loaded, end-to-end with bins of organic waste.. After the digestion period, the batch is removed from the other end of the tunnel. The embodiment is not limited to doors , and could have other means for closing the ends of the- tunnel to seat in the. waste,, e.g., hatches, screens, and other structures or closures made of parts, so that the tunnel is sealed at its ends.

The preferred containerised waste digester is designed to ensure that ail the contents are contained with two barriers of spilt containment. A mechanism or air lance or similar means may be- used to break the surface of formed scum so gas may release. in the preferred embodiment, the waste digester is fed with organic waste in cartridges of smaller parcels or bins, containers or skips or buckets and when the tunnel is full the doors at the ends of the funnel are closed, and residual air evacuated (purged) such that high quality methane production can start, a soon as possible.

In the preferred embodiment, .other loading, door operation and purging may be used to operate the system, not to affect the containerised tunnel gas

containment system's primary act of producing methane gas,

The present inventio is preferably configured to be constructed from containers, e.g. shipping containers, stacked end on end and sealed to form a funnel that will gather the gases off the process and transfer to a gas pipeline. A containerised tunnel with doors at each end to create, an enclosed chamber would meet the required throughput of a municipality or waste collection process. As such, the containerised waste digester can meet high demand and consequently produce large volumes of methane gas. The system is useful for municipalities, but is not limited to such use and can also be used, e.g., for industrial or domestic applications. The invention may use containers that are, e.g., vertically, stacked, horizontal circular rectangular, square, long or short, and in some preferred embodiments, uses shipping containers as known to the cargo world. The -containerised waste digester system is preferably configured as described herein. Various embodiments of the present invention will now be described, by way of example only, and with reference to the drawings, in which:

Figure 1 shows a Containerised Waste Digestion System m plan (birds-eye) view and In elevated (side) views.

Figure 2 shows -a containerised waste digestion system pietoriatly as an array or stack of single digestion tunnels as shown in Fig 1 _f

Fig. 3 is a simple diagram showing how the array should be configured.:

Fig. 4 shows an example high level process flow diagram of how the present Invention could be used.

Fig. 5 shows an example of a system for macerating the organic waste prior to digestion.

Fig. 6 is a schematic view showing the piping for an embodiment of the invention. A preferred embodiment of the invention. In broad outline, will now be described with reference to Figure -1. This invention preferably uses a tunnel assembled from one or more containers or tubular structures as a means of containing/capturing degrading organic waste (1). The tunnels may include two or more rows of containers or tubular structures (i.e. made of steei) stacked one on lop of another (2) depending on desired capacity and available ground space.

Stacking the containers means that the gas generated by the digestion process, which rises naturally, can be discharged at th top of the tunnei and Interconnecting pipes etc. are needed. The tunnei extends from (3) to (4), being the length of the tunnei. The pre-processed mainly organic waste is conveyed into the tunnel e.g. in parcels or bins (5), The parcels or bins of mainly organic waste move into the tunnei (8) by mechanical, gravity or other means. The parcels or bins (7) of mainly organic waste are ready to be. removed .{7} as they have left the tunnei after being in the tunnei for the degradation or digestion period. The paresis or bins- (6) and (7) of mainly organic waste roll, slide, are wedged, are mixed, stopped and travel into and out of the tunnei as required by the design and operatives* choice of operation. Door or opening (9) and door or opening (10) allow for the mainly organic waste to be locked in and an airtight seal be formed, In a batch process, thus containing the gas produced. The end -containers or frameworks (1 ) allow for unloading and (12) for loading. If several containers are used to form the tunnels, the containers or tubular structures a e mechanically fixed (e.g. welded) or tied together and sealed to form an air tight seal (13). A double seal may be used. The containers or structures may rest and tie onto foundations structurally (14), The rising methane gas Is drawn off at a high level from each tunnel section (each container) at the highest point through a pipework system (15).

A- preferred embodiment of the invention will now be described with reference to Figure 2, Figure 2 shows a cluster of tunnels (such as shown in Fig. 1 ) as high and long as required by the process volumes -and degradation period.

Organic waste is fed in, retained and, once digested, fed out. This invention preferably uses shipping containers stacked on top of each other and joined end- on-end. Preferably, the height and length of each -tunnei corresponds to the daily volume- of waste to be processed and the cluste comprises one tunnei per day of the digestion period. This enables a continuous batch processing over the digestio period. Each day, for example, a tunnei is loaded with parcels or bins of mainly organic waste. The next day (or whatever selected period), a next tunnei is loaded, and so on.. The number of tunnels is selected such that each day (or other selected period) a new tunnel is filled and then at the end of the number of days of the digestion period the first tunnei (which was loaded that number of days ago) can be emptied, as the waste is now digested. This tunnel can then be loaded with new waste. The next day, the next tunnel i ready to unload and be refilled, and so on.

The novel,_, rotational batch processing concept can be explained with reference to the simple diagram of Fig, .3. The length and height of the tunnels are selected such that each tunnel has: a volume corresponding to a desired production batch volume ~-i,e. how much waste is loaded in one production hatch. This is preferably a daily volume but could be,, e.g.., half daily, two days, or other volumes depending on the requirements and capabilities of the site. Each tu el is, therefore, filled with a production batch, closed, and left to digest. The .tunnels are arranged side by side with the number of tunnels (no. tunnels wide) determined by the length of the digestion period such that by the time the last tunnel is loaded, the first tunnel has been loaded for the entire digestion period and can be unloaded.

The tunnels may be locked together at ail corner casting positions 5 as demonstrated^'. The cluster lands and toads to foundation piles or plinths or strips 17, 18. The cluster is, in this example, loaded by machine from a level hard standing 17, and unloaded from a bard standing 18 at the opposite end of the funnel. Of course, other methods of loading may be used.

An example of the waste management process is now described with reference to Fig. 4. In ste 20,· waste, is- collected. This can, of course, be collected from any source and in any manner, and brought to the digester site. The Invention is particularly useful for dealing with municipal waste on a relatively large scale but could be used for any waste that contains organic material.

In one particular application, it is proposed that a truck/trailer/container will load say 80m³ of waste and transfer the refuse out of the city, preferably during the night and at off-peak times to minimise an congestion on the roadways.

Operationally, upstream operatives wlii deliver their .loads in e.g.. truck, skip or compactor to one of several -stations^' (step 2 ). The incoming loads can be weighed, recorded and the load visually inspected for illegal items such as medical waste for example.

The transfer of waste from the transfer stations around a city, in a preferred embodiment, is unified by using standard, e.g. 40 ft., waste containers of maximum capacity 70 m³ each locked onto their own skeletal trailers.

During the day the containers may he filled and parked a the transfer stations, ready for later dispatch. To minimise odours, the best practice for the transfer s to happen within 24 or 48 hrs. i.^'his should apply to ail waste received as the transfer stations will preferably receive 24/7.

The containers are preferably transferred at night to capitalise on the light traffic.

After reaching the recycling plant the full containers are offloaded to the site stack and the empty containers are loaded to the trailers. The full containers are stacked. The recycling plant Is then charged overnight and ready to commence the morning shift of recycling.

Tipping rigs may enable longitudinal elevation of the containers and therefore rear door discharge through specifically designed machines.

Prior to the daylight shift, recycling plant in-feed hoppers are filled. The hopper size will preferably be a minimum of 150% of a container capacity.

During the recycling shifts there will preferably be no deliveries from the transfer stations. The fork! if t is dedicated to its operation in support of the tipping rigs feeding the in-feed hoppers. The container's storage area is minimal in area to minimise fork to tipping rig transfer times.

The waste is sorted to extract e.g., .recyclable waste etc. First, medical waste is removed as described above. This can be performed with magnets and highly trained staff.

The rest of the waste may be sorted e.g. by being received onto the main sorting lines after, preferably, passing through a machine hall that will mechanically slit open any film or low-density plastic (LDP) hags to optimise the pickers visibility of the waste. This is for safety and efficiency.

The waste then travels down the math conveyors which can be of any desired size. Each picker has been trained to identify a specific waste stream (e.g. clear film or bottles etc). Each picker has a transparent clear Perspex tube- between themselves_, and the conveyor. These tubes have mechanical type flaps at floor level jus! above the transverse conveyors- which are filled by the operatives, in adoption, line Inspectors will review what is being picked by the operatives prior to random Inspections. This allows the inspectors to correct any irregularities before reaching the transfer conveyors that run under the main lines. The effect is stop/go quality control thai will prove effective If the fine inspectors are welt, trained.

The pickers select the recyelables from the main conveyor and place the picked waste tiirough their Perspex tubes which feed down onto the transverse conveyors, whic then feed furthe into bins. These, bins are then stacked away from f the recycling lines and processed as required by different, recycling material and the purchaser of these recyelables (step 27).

Automated sorting o the waste is also possible to remove all but the organic waste to be fed to the digester.

Whilst such sorting is preferable, the invention could also operate without this step, but such operation is not ideal.

The main conveyors. In this embodiment, will be set at a constant speed in- order to process the waste.

The organic waste will remain on the conveyor to preferably be macerated and placed into bins that will ultimately he loaded into the digester.

Of course, the organic waste can be separated out, for digestion, in any other suitable manner.

In this preferred method, the system of waste transportation moves the waste through the transfer stations in the city quickly, moves the waste In enclosed bins, stacks the waste in closed bins until it is ready to be sorted, can sort in the cool of the night time to minimise sweating and odour, the high volume sorting lines sort quickly so eac container is open and the organic (more odoyrised waste) enclosed into the bio-reactor within, say, one hour of being open to the local atmosphere, the bio-reactor seals all waste odours in. Once .the organic waste has been separated from other waste, it is

conveyed to the digester. Preferably, the organic material 60 is macerated in a machine as shown in Fig. 5. This unifies the material and makes the degradation process more efficient. It is an important factor in achieving a reliable known digestion period, but is not essential for operation of the invention.

The (often odorous) organic material is loaded into; bins or the like within as short. as- ossible time of collection and sorting. These bins (which may be similar to gold mining bins) are loaded; into the tunnel selected for that day's operation. The funnels are filled from end-to-end with organic - waste- filled bins and the doors closed. The preferably gas seafab!e doors stay closed for the digestion period, e.g. 45 clays. The odours or gas can onl escape via the draw off pipe. The next day the next tunnel is loaded. The day after, the next tunnel is loaded. This continues day in day out Preferably the number of tunnels equals the number of days of the digestion period so that when all tunnels are filled the first Is simply discharged of its nutrients (digestaie or compost) (step 23) and refilled with new gas-producing organic material. The nutrients then are processed, pasteurised {if required) and put back safely into the land. in embodiments where the tunnels are loaded with bins of waste, there is a gas tight and double spill containment effect, provided by the sealed bins inside the sealed tunnels, which provides an advantage over landfill sites.

Another advantage of the use of bins inside containers Is that any contamination will be reduced to/contained within the bin containing the

contaminant, and will not spread to cross contaminate the whole of the collected waste as could happen, e.g., in a landfill site.

The gas is piped off (step 25) at extremely low and therefore safe pressures to interface with a generator for producing electricity, e.g. a Clarke Energies jenbacher gas powered mdprooatin^'g generator (by GE), a caterpillar generator, or other generator, to generate electricity.

The system uses "rotational batch processing" and can reach high volumes per day at a fraction of the cost of landfill bio-reactor systems. The bins will remain closed in their tunnels for the digestion period., in one example 45 days (but can, of course, be a longer or shorter period), where the bins' organic content will break down and gas will be taken off.

The organic material in the bins may be static for the digestion period, Alternatively, the bins could have interconnecting pipework or a means of pumping teachate, gas or even mixing a pre-biended accelerator through, up through of into the mass of organic material, for example, with rod or pipe risers to allow the individual bins to have percolation or their contents to have some movement if performance enhancement is required. This ma require pumping from outside to inside the tunnels.

Further, the tunnels may be heated, cooled; or temperature controlled as desired by the operator.

Rates of digestion are well known and well documented. Rate of digestion ca vary due to the effects of temperature, the waste content and waste quality. This in turn will produce different levels of gas volumes and quality. It is well known thai food waste provides good quality gas.

The digester of the invention provides a unified array or cluster of tunnels for this digestion to take place In the most preferred, embodiment, the cluster comprises a plurality of tunnels connected side-by-side. The tunnels each comprise a plurality of containers connected end-on-end and, in some

embodiments, stacked one on top of another, corresponding to t e dally volume of waste. Th number of tunnels connected side-by-side in the cluster corresponds to the number of days of the chosen digestion period. As an example, wher the digestion period is, say, 45 days, the bio-reactor preferably has 45 sets of funnels. If, as a example, these have a set capacity per tunnel , the operators will therefore replenish on tunnel each day with up to capacity with organic matter.

The present system therefore provides a high mass, static cluster of waste digesters where high volumes of waste are constantly undergoing digestion without any action or supervision from scientists or the like. The only movement in the process is the unloading and loading of the bins into .the containers.

Also, this big volume or mass of digesting waste, being essentially static {as compared to e.g. moving through the tunnels In a dynamic manner) provides a largely constant volume of gas being piped off and supplied to the generator. The resulting generated energy is thus fairly constant and reliable.

After the digestion period, the chosen tunnel^" for that day's replenishment may be isolated from the other tunnels by closing valves on the main gas take off manifold. The tunnel may then be opened by opening the doors on each end, Stacked bins may then be lifted out of the digester as new bins are loaded to the other end pushing the rolling stock through the tunnel,

With the bins stacked at the unloading end of the bio-reactor. A second fDfkiat with a rotator on it works to tip the contents of the digested waste into the pit area provided.

The system of the invention provides an extremely environmentally friendly system with limited spill and noxious or toxic gas emission.

Any residual liquid may be drained off and pumped to a water treatment plant for purification to EU standards before being released to the local waterways.

The solids (nutrients) left in the digested waste are then loaded by a front end loader to waste containers and may be trucked to farmland area defined for thi "composts^'' receipt.

This operation shall preferably happen during the day so trucks, trailers and waste containers are best utilised. At night these trailers are transferring waste from the transfer stations.

The digester and generation plant is preferably interconnected by a pipework system, shown in Fig. 6. In one example, using a blower, the gas is sucked from the digester, A well-designed gas collection system flexibly captures the gas from various spots and handles high temperature leaehate, condensates and air content - thus ensuring a cost-efficient collection as well as stable gas quality.

As the doors open, for loading, the valve via whic the gas Is drawn off will be closed (manually or automatically). The doors then close when ^'the tunnel has been loaded and a valve is opened to create a partial vacuum (i.e. to create anaerobic conditions). The valve for the pipe to draw off the generated gas is then opened. In more detail, with reference to Fig. 8, Fig. 6 shows an array of tunnels 31 slacked three high, just as an example. In practice, one or more tiers of tunnels can be used. Gas generated by digestion of the waste flow upwards through connections between the stacked tunnels.

Before allowing gas to be drawn off via the valves 32, another valve 35 is opened (once the tunnels have been loaded and closed) to remove air and create a vacuum or partial vacuum. This valve 35 is then closed and valves 32 ar opened. Generated gas is draw through pipe 33 to generator 34,

The gas generated from the organic material is contained during the entire digestion process,

The system is relatively low cost in terms of materials, installation, operation and maintenance. The system can be operated continuously and has few

moveable parts. It is structurally strong and robust and makes more: efficient use of land than landfills. The system is moveable, sale-able and re-usable: whereas landfills are forever. The above-ground system can be emptied and relocated as a working system should an area be developed for housing for example. The system has less energy consumption; there are no moving parts apart from roiling stock wheels. This means the system is. unlike normal mechanical systems. Ho heating or mechanical intervention is required, The process simply performs its digestion naturally, The operational cost savings are significant.

There is also scope for more energy gains. The roof of the bio-reactor provides the perfect platform for solar panels if additional energy for heat

generation within the bloreactor is required. The grid structure makes for the most cost effective insulation and a safe clean, environment for the solar panels. Solar energy can, for example, help, to power the plant,

The sides of the container cluster are ideal marketing and advertising mediums. This will help promotion and this space could even be sold.

Unlike landfills, the organic feed stock can be selected, added to (e.g.

teachate) and therefor the gas production optimised. It has been long established that the shipping container Industry has the abilit to build: such volumes with ease, allowing this, solution for ail countries, and all cities worldwide.

With, container ^'factories being able to build hundreds a day, a system can be delivered and installed within a year. That means gas production and therefore electricity generation can be started within year. Other forms of "downstream" waste management can take five plus years to build and have working.

The system satisfies and meets fee requirements of:-

0 Landfill, Gas, Anaerobic Digestion and Chartered Engineering consultants SLR Consultants Ltd, from the UK. (SLR are world renowned experts in the field confirm the gas take off meets the projects expectations.

□ the gas supply meet the gas generators needs in terms of gas quality and volume to enable to be generated.

□ ASME pressure containment codes and standards for Methane Gas at the systems tow working pressure.

0 British structural codes and standards for industrial buildings and facilities. D NFPA regulations for fire.

□ UK BSE requirements for Health and Safety of personal and the working environment,

Π UK code PPG2 and ali standards for the safe static storage and containment of hazardous liquids.

□ British standards for corrosion protection of machines- in contact with highly corrosive substances.

Claims

Claims;

1. A system for anaerobic digestion of organic waste comprising;

a plurality of bins each containing waste to be digested'

a plurality of containers sea li ngly connected end^ri-end. and/or stacked on top of each other to form a tunnel to receive the waste;

rails on which said plurality of bins containing the organic waste are loaded into the tunnel; and

rails on which the plurality of fains containing the digested organic waste are unloaded from the tunnel;

the tunnel configured to received said plurality of bins and then to be sealingly closed and contain the bins for a given period for digestion of the waste contained therein; t e: system comprising a cluster of such tunnels arranged sfde- tay-side, each tunnel comprising a piuraiity of containers sealing!y connected end- on-end and/or stacked one on top of another, the number and/or size of the containers defining a tunnel selected to define a daily volume of waste to be processed, and the number of side-by-side tunnels selected based on the number of days of the given period of digestion.

2. The system of claim Ί , further comprising a gas outlet via whic gas generated in the tunnel during the digestion period can be drawn off.

3. The system of any preceding claim, wherein the containers comprise cargo containers.

4, The system of any of claims 1 to 3, wherei the containers comprise tubes.

5, A method of anaerobic digestion of organic waste comprising, sealing !y connecting a piuraiity of containers end-on-end and/or one on top of another to form a tunnel to receive the waste; providing the waste to the tunnel in a piuraiity of bins, vi rails, into the tunnel, sealing the tunnel closed, containing the bins for a given digestion period; and unloading the bins via rails after the digestion period;

wherein the tunnels are provided in a cluster comprising one tunnel for each day of the digestion period, and wherein the number of tunnels is such that as one tunnel is loaded, another tunnel in which waste has been contained for the complete digestion period, can be unloaded.

0, The method of claim 8 comprising drawing off gas produced from the waste during the digestion period,

7. The method of claim 6, further comprising roviding the gas to drive- a generator for generating electricity,

8, The method of any of claims 5 to ?, further comprising collecting waste from a plurality of sites and providing said waste in bins into said tunnels.

9. The method of claim 8, wherein the bins are loaded into the tunnels on rails.