IE20140295A1 - Advanced production techniques in energy and fuels from waste - Google Patents

Abstract

Custom designed air blowers (2) and air heaters (1) are coupled to the bio dryer (3) to reduce the moisture content of the output (6) to produce high calorific synthetic material (9) and high quality biomass (7) for use in energy and fuel production. Dried biomass (7) is converted into biogas (13) using advanced thermal treatment (12) to operate a gas engine (14) for the production of renewable energy (15) and fuel (16). In another example, the high quality biomass (7) and high calorific synthetics (9) are used in a steam generator (10) to produce energy (11). In a further example, the materials (7) and (9) are transported to other thermal treatment systems, where they are used to produce energy and fuel. In another example, the said dried materials (7) and (9) are blended with other forms of biomass and fossil fuels to produce energy and fuel. <Figure 5a>

Description

This invention relates to advanced production techniques in energy and fuels from waste, which are primarily more robust and efficient than previous methods. Such production techniques can be utilised with various materials across a range of sectors, including commercial, industrial, agricultural and horticultural products, as well as a variety of sludges and effluents.

Our society is facing both national and global structural changes. Environmental issues are gaining higher priority as we seek sustainable ecological solutions that will save our resources and innovative technology will play a key role.

Around 50% of the average Municipal Solid Waste (MSW) is biodegradable (food, paper, cardboard, garden waste, etc), which when landfilled causes harmful gases and toxic leachate. Globat legislation is on the increase in an attempt to divert waste from landfill. In addition, island communities have little or no remaining landfill and incineration is not a palatable option.

Waste treatment is one of the world’s ever-increasing concerns. The methods used today, mainly landfill and incineration, are not sustainable and give rise to both environmental and economic problems. Few of the methods employed for large-scale waste treatment work in harmony with the eco—cycie; instead they often create new problems. The latest innovations are therefore focusing on large—scale, reactor-based biological systems with reliable quality control. Such progression makes it possible to utilise the carbon rich fractions in waste as feedstock for renewable energy and fuels.

The recent financial crisis has somewhat curbed the rise in fossil-energy use, but its iong—term upward path will resume soon on current policies.

Tackling climate change and enhancing energy and fuel security will require a massive decarbonisation of future systems.

'Description of the prior art Regulators the world over are continuing to regulate against Iandfilling of waste, particularly biodegradable waste, as such practice is well known to cause severe irreparable damage to our environment.

MSW and other wastes are incinerated as a way of disposal. Combustion of waste by incineration is a growing public concern, which includes issues such as undesirable toxic emissions and hazardous ash. At the same time, operating standards are becoming more stringent the world over, thus incinerators are becoming increasingly more costly to build and operate.

More recent methods see MSW and other waste shredded and recyclables partially separated, prior to the residuals, commonly known as Refuse Derived Fuel (RDF), or Solid Recovered Fuel (SRF), being gasified to produce syngas, which is then used to power a gas driven electricity generator. The variable physical and chemical nature of such materials makes gasification extremely challenging. in particular, differing bulk densities, melt temperatures, moisture levels and calorific values of such materials cause major processing issues.

Typically, waste to energy facilities will receive mixed MSW, which is shredded and screened using say a 90mm trommel screen to provide certain quantities of ‘overs’ and ‘unders’, as seen in Fig 1.

The ‘overs’ (>90mm) will contain mainly dry non—biodegradable material, such as plastics, textiles, paper, metals, etc, which will normally passed through an air classifier to separate out the dry ‘fines’ from the wet ‘heavies‘, with the dry ‘overs’ and ‘fines’ used as RDFISRF in energy production — Fig 1.

The ‘unders’ (<90mm) will contain mainly wet biodegradables, such as foodstuffs, garden waste, etc. Due to the very high moisture content (circa 50%) these wet ‘unders’ are hugely energy intensive to dry and will normally be sent with the wet ‘heavies’ for disposal to landfill — Fig 1 .

In summary, the variable nature and high moisture content of waste materials make them largely inefficient energy sources. Such methods are proving to be commercially, technically and environmentally demanding and prone to failure.

An object of this invention is to provide advanced methods for processing waste materials more efficiently and cost effectively into energy and/or fuel.

Summary of the invention According to the invention there is provided advanced methods for producing energy and fuel from waste, such as MSW and Commercial & Industrial (C&l) wastes, which comprises a mixture of bio and non-biodegradable materials.

The invention can be best described by using an example of the design and operation of such a waste to energy and fuel plant.

An average waste to energy facility will process about 1700 tonnes of mixed waste per day, which, for example, will have a particular composition — Fig 2 Due to the high percentage of biodegradables in the ‘unders’ (>52%), plus the air classifier ‘heavies’ fraction (circa 36%), the average moisture content of the total 1,048 tonnes will be circa 50% — Fig 3.

Consequently, a typical waste to energy and fuel plant will consume huge amounts of energy in driving off this moisture.

This invention provides for robust production methods, which are more efficient in reducing the moisture content from circa 50% down to around 20%.

The invention also provides for methods to classify and homogenize such waste materials, whilst driving off the moisture.

Such methods enhance the overall productivity of the downstream equipment, as well as vastly improving the thermal efficiencies of the energy recovery. in one embodiment, a bio-dryer is used to simultaneously dry and size-reduce the wet biodegradable fraction through a combination of biogenic and auto- thermic heating, variably controlled airflow and temperature, as well as the continuous tumbling of the material within the bio-dryer.

The waste material is presented to the loading hoppers of the bio-dryer, from where it is transported to the ram feeders at the loading end of the bio-dryers.

The ram feeders are controlled to deliver the correct amount of material daily to each of the bio-dryers. The rate of delivery is determined by the required moisture content and the maximum particle size in the final biomass.

Tonnages, flow rates, moisture and energy contents are dependent upon the nature of the wastes delivered, therefore subject to variation from day to day.

Depending on local climatic conditions, to achieve moisture contents of around -30% requires increased airflow rates and heating of the air.

In one embodiment of the process the incoming waste is shredded, with the output passed over a 90mm trommel screen to separate the paper, card and plastic for the production of SRF and onward thermal energy, or fuel recovery.

The remaining sub—90mm fraction is mixed with the ‘heavies‘ fraction from the air separator and passed to the bio-dryer for drying and sizing, in order to prepare it for further screening and manufacture into biomass.

The test bio-dryer measured 185ft (56m) long x 12ft (3.5m) diameter, however, bio—dryers can be 230ft (70m) by 20ft (6m)for iarger waste systems.

Air is supplied through the discharge end of the bio-dryer and directed to the front, or loading end, of the bio-dryer.

The air is provided by means of positive displacement blowers, for example, a Roots URAI-615 blower, driven through a gearbox by a 15kW electric motor.

The output of the blower is coupled to the rotary bio-dryer via a 100mm diameter rigid pipe, plus 1m length of 100mm diameter flexible pipe, which is coupled to a 100mm diameter swivel joint, co-axially mounted through the centre of the discharge end plate of the bio-dryer.

The swivel joint also accommodates a 25mm diameter compressed air pipe that supplies the pneumatic cylinders to operate the bio-dryer discharge doors.

The airflow is provided to the fully laden bio-dryer at 321ACFM (9.1m‘°’/min), with a back pressure of 3.5 PSI (0.24 bar).

In typical waste facilities, most of the cardboard and paper will be separated for SRF production by trommel screens. The resultant moisture content of material entering the bio-dryer was determined to be 49.9% and the bulk density of the feedstock was estimated at 475kg/m3.

As the material in the bio-dryer graduaily breaks down, the particle size is reduced and its packing density is increased, whilst its moisture content and therefore bulk density decreases.

Control system monitors the feeding rate to ensure the maximum load within the bio-dryer does not exceed the Safe Working Load (SWL), typically 66% Loading the bio-dryer to a fill ratio of only 60% would result in circa 175 tonnes of unders being loaded, which is well within the maximum SWL capacity.

The number of bio-dryers required to dry the daily delivery of wet material will be a function of the desired moisture content. Therefore, the bio-dryer capacity should provide sufficient redundancy in the event of any bio-dryer outage.

The amount of moisture that can be removed from each bio-dryer per day is a function of (1) the ambient air conditions, (2) the temperature of the air within the bio-dryer and (3) the output air conditions.

To maximise the drying potential, two Roots URAl—615 blowers are used per bio-dryer, coupled through a manifold to the air delivery pipe at the discharge end of the bio-dryer.

Ambient air temperature of 181°C and 100% relative humidity (RH) is assumed.

Modelling of the pipework between the blower and bitydryer at a flow—rate of 1550 ACFM (43.9 ma/min) shows that it could be expected to generate an additional 1.5 PSI (0.10 bar) back pressure.

Therefore, to accommodate the airfiow from two blowers at full speed (87.8 m3/min) requires an increased pipe and swivel joint diameter to prevent the total backpressure on the blowers exceeding the rated 7PSl (048 bar). Swivel joints are available up to 250mm diameter as standard.

Assuming that a total backpressure of 7 PSl (0.48 bar) is maintained on the blowers by the bio-dryer and associated pipework at the higher flow rate, the temperature of the air blown into the bio-dryer would be circa 80°F (26.6°C) higher than the ambient resulting in a drying temperature of 180F (82.2°C) From published data, ambient air at 100°F (37.7°C) and 100% RH (worst case) would contain 0.04kg of moisture per kilogram of air. Whereas, air at 82.2°C and 100% humidity would contain 0.7kg of moisture per 1kg of air.

Therefore, ignoring the change in air density and temperature within the system, which will tend to cancel each other, the moisture carried away from the bio- dryer will be of the order of O.7kg/kg (circa O.7kg/m3) of air, dependent on altitude and atmospheric pressure.

The maximum drying potential of each bio-dryer at the higher airflow of 3100 ACFM (87.8m3/min) will be approximately 61kg/min, or 88.5 tonnes per day.

In the test case, 175 tonnes per day (tpd) of wet material was introduced to the bio-dryer at 49.9% moisture, resulting in 122.3 tpd of dried material unloaded (@ <30% moisture), giving 52.4tpd of water evaporated.

The air extraction system at the loading end of the bio-dryer needs to be designed such that the increased volume of 3100 ACF M (87.8 m3/min) can be extracted without increasing the backpressure of the combined bio-dryer and pipework above the 7 PSI (0.48 bar) blower limit.

To increase the air temperature entering the bio-dryer, a custom designed heater is installed in front of the air blowers, for example, a cylindrical type Flow Torch 800, or similarty modified ‘inline heater‘.

For ambient air conditions of say 18.1°C (64.6F) and 100% RH, the moisture content would be 0.02kg/kg. Therefore, the Flow Torch 800 heater will supply 43.9m3/min of warm air to each of the two Roots 615-URAI blowers at 378°C, resulting in 87.8m3/min drying air entering the bio-dryer at 82.2°C.

This combination is sufficient to dry the material from circa 50% to circa 20% moisture content under normal operating conditions — Fig 4.

Once sufficiently dried and sized, the contents are discharged from the bio-dryer and transported to the Material Recycling Facility (MRF). Here it is screened to remove non—biodegradable material, prior to pelletizing for further processing, or shipment off-site.

The biodegradable fraction of the ‘unders‘ and air separator 'heavies’ have been dried and sized in the bio-dryers. This material may still contain some plastics, glass, stones and metals, which can be readily removed by additional screening.

Ferrous and non—ferrous metals are removed from both the non-biodegradable material using magnetic and eddy-current separators.

The biodegradable material is passed through a density separator to remove the light and heavy fractions, which leaves a relatively clean dried biomass to be transferred to a storage bunker, or shipped off-site.

According to the invention, there are advanced methods for producing energy and fuel from waste, including: using a specially designed ram feeding system to convey un—shredded or shredded mixture of waste materials into a custom designed hydraulically, or mechanically, driven rotating bio-dryer that is best described as a mechanical biological treatment rotary bio-dryer system; breaking down the biodegradable fraction of the mixed waste in around 2 days by both microbial and mechanical activity; regulating the environment within the rotating bio-dryer using air and water to create the optimum biological activity; using increased air flow at eievated temperatures towards the backend of the rotating bio-dryer to dry the contents prior to discharge; following the 2 day residence time in the rotary bio-dryer, the biodegradable fraction of the waste is less than say 25 mm in size, so it is readily separated from the non-biodegradable fraction that remains mostly whole; discharging the dry homogenised waste material from the rotary bio-dryer and conveying it to a primary screen that readiiy separates the biodegradable material, or high quality biomass, from the non-biodegradable materials‘, whereas the biomass passes through the screen and the non-biodegradable material passes over the screen; passing the non-biodegradable material through ferrous metal and aluminium separators to recover the recyclables, leaving a largely inert high calorific residual, or synthetics, which is converted to energy and fuel; 8 screening to produce a biomass typically more than 90% biomass and as much as 95% biomass, with a moisture content in the range of 20% to 30%; collecting and storing the biomass for renewable energy and/or fuel production; producing high quality gas from the biomass, utilising any exhaust heat from the process to further reduce the moisture content after which advanced thermal treatment (gasification, or pyrolysis) is used to extract a high quality biogas; driving a gas turbine to produce renewable energy from the biogas directly combusting the biomass to create steam and using it to drive a steam turbine that produces renewable energy liquefying the biogas to produce marketable fuels providing the biomass as a feedstock blend material for power producers converting the biomass and the synthetics to a fuel by utilising various chemical reactors, including the well-known Fischer Tropsch type method in this invention, all forms of thermal treatment equipment are utilised to convert the biomass and synthetics into bio-gas or steam, for the production of the energy and fuel, including. boilers, gasifiers, pyrolysers, plasma, microwave, or any such form of thermal treatment.

In one embodiment of the invention the process includes heating the dry homogeneous biomass in an oxygen depleted atmosphere to extract biogas from the biomass.

In another embodiment the process includes using the biogas to generate energy in a gas engine, or a gas turbine.

In a further embodiment the process includes iiquefying the biogas to produce a fuel, utilising the Fischer Tropsch method or other type methodology.

In another embodiment the process includes delivering the biomass to a boiler, or steam generator, or oxygen rich atmosphere, for generating steam. in a further embodiment the process includes delivering the steam to a steam turbine for generating electrical power. in another embodiment the process includes cleaning the biogas prior to using it in a gas engine, or gas turbine.

In another embodiment the process includes collecting condensate during biogas production and delivering it through a water treatment plant.

In a further embodiment the process includes passing the biomass through a classifier, to remove any inert materials, such as stones or aggregate materials.

In another embodiment the process includes further screening of the biomass to extract any particles sized greater than 5 mm.

In another embodiment the process includes extracting valuable recyclable metals and non—metals from the material. in another embodiment the process includes feeding the synthetics, which comprises mainly of plastics and textiles, through various forms of thermal treatment systems for a range of ievels of energy and fuel recovery.

In a further embodiment the biomass is blended with other forms of biomass materials and used for energy and fuel production, or sold on the open market.

Brief description of the drawinqs The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 5a and 5b are schematic illustrations of a process for extracting dried homogenised high quality biomass from MSW and other waste materials, using a rotary bio-dryer, along with an energy or fuel generating plant used in the process according to the invention; Referring to the drawings, in Fig 5a: Using loading equipment, such as ram feeder #4a, to deliver MSW #4, or other waste, to the bio-dryer #3 The rotary bio-dryer #3 is essentially a long cylindrical steel, or stainless steel, drum that is rotated hydraulically, or mechanically, on 2 tyres #33, generally horizontal, with a small downward incline with a gradient of about 1 degree.

Providing inner wall protection of the bio-dryer #3 with a series of longitudinal bars #3b spaced apart around an entire inside circumference, which also act as a biodegradable medium for the naturally occurring microbes.

Utilising stainless steel baffles #3c within the bio-dryer #3 to help regulate the flow of material through the bio-dryer #3.

Utilising portholes #3d to monitor and optimise the processing conditions within the bio-dryer #3 before discharging the waste material through doors #3e Utilising in-line blowers #2 coupled to the bio-dryer #3 in order to increase the air flow rate within the bio-dryer #3 for the purpose of drying the contents Utilising in-line heaters #1 in front of the in-line blowers #2 coupled to the bio- dryer #3 in order to increase the air temperature within the bio-dryer #3 The bio—dryer #3 simultaneously dries and size-reduces the wet biodegradable fraction through a combination of naturally occurring biogenic and auto—thermic heating, which is substantially enhanced by variably controlling the airflow and air temperature within the bio-dryer #3. continuous tumbling of the material within the bio-dryer #3 also results in the biodegradable fraction being broken down.

Referring to the drawings in Fig 5b: The dried and homogenised output material from the bio—dryer #3 is put through a screen #5 to separate the biodegradables #7 from the non—biodegradables #9.

The dried biodegradables, or biomass, #7 is stored in a silo #8 Once metals and non—metals have been recovered, the non-biodegradables, or SRF #9, is stored in a separate silo #10, for use internally, or shipment off—sEte.

The high quality dry biomass #7 is thermally treated #12 to extract the biogas #135 which is used in a gas engine #14 to produce renewable energy #15, or fuel #16.

The SRF #9 is used to produce energy #11a or fuel #11b, for use within the facility, or for export.

The invention is not limited to the embodiments hereinbefore described, which may be varied in both construction and detail within the scope of the appended claims.

Claims (1)

1. CLAIMS A unique production process for simultaneously extracting, drying and homogenising high grade biomass and clean high calorific synthetics from waste materials, such as MSW and other waste, which comprises a mixture of biodegradable and non-biodegradable materials including: manufacturing custom rotary bio-dryers within certain specification tolerances to optimise their performance and increase their working life; delivering sorted and unsorted MSW and other waste material into the purpose built rotary bio-dryer equipment; effectively feeding the mixed MSW and other waste into the rotary bio-dryer using a custom designed ram feeder type equipment; treating the sorted and unsorted MSW and other waste in the rotary biodryer for around 2 days to convert the biodegradable fraction of the waste material into dry biomass mixed with non-biodegradable materials; adding air and water to regulate the bio-dryer environment for the purpose of optimising the biological and mechanical activity within the bio-dryer; increasing the air flow rate through the rotary bio-dryer to decrease the moisture content of the materials within the rotary bio-dryer; increasing the air temperature within the bio-dryer to further reduce the moisture level of the biddryer contents; examining the process performance with the aid of special access portholes along the length of the rotary bio-dryer; using purpose designed ribs and stress bars inside the rotary bio-dryer as a means of providing a biological medium as well as bio-dryer shell protection; 13 ‘IO regulating the flow of the material within the bio-dryer using custom baffles; insulating the rotary bio-dryer to limit internal temperature deviations caused by seasonal climate changes to avoid adverse process performance; discharging the treated mixed materials from the bio—dryer and delivering said treated materials to a screen separator; separating the inert non—biodegradable materials from the biomass in the screen separator and individually discharging the non—biodegradable material and the homogenous high quality biomass from the separator; delivering the homogenous high grade biomass through a de-stoner to improve its quality and its biomass content; subjecting the high grade biomass to advanced thermal treatment and extracting biogas from said high grade biomass; utilising the said biogas to operate a gas engine and generating energy; using the said high grade biomass to generate steam for production of energy; utilising the high grade biomass to produce a fuel. A process as claimed in claim 1 wherein the process includes heating the homogeneous high grade biomass in an oxygen depleted atmosphere and extracting the biogas from the biomass. A process as claimed in claim 1 or claim 2 wherein the process includes re- circulating heat and to assist dry the high grade biomass. A process as claimed in any preceding claim wherein the process includes using the biogas to generate energy in a gas engine. 10. 11. 12. 13. 14. 15. A process as claimed in any of claims 1 to 4 wherein the process includes liquefying the biogas to produce a liquid fuel. A process as claimed in any preceding claim wherein the process includes screening the high grade biomass for extracting any particles sized greater than 15 mm to 25 mm. A process as claimed whereby secondary screening and de—stoning extracts any particles greater than 5 mm to 15 mm. A process as claimed whereby exhaust gas from the electrical generator is passed through a heat exchanger for drying the high grade biomass. A process as claimed for the said biomass is used in a steam boiler for generating steam. A process as claimed in claim 9 wherein the process includes delivering the steam to a steam turbine for generating electrical power. A process as claimed in any preceding claim wherein the process includes cleaning the gas. A process as claimed in any preceding claim wherein the process includes collecting condensate and treating it to remove impurities. A process as claimed in any preceding claim wherein the process includes using a scrubber or biofilter to remove any impurities and odours. A process as claimed in any preceding claim wherein the process includes extracting metal and non—metal materials from the inert non—biodegradable material to leave a clean synthetics material. A process as claimed in any of claims 1 to 14 wherein the process includes shipping the synthetics to an energy or fuel production plant. 15