Abstract:
A process for the production of a range of improved biomass material products suitable for use as a fuel and which have been derived from municipal solid waste (MSW). The process comprises the steps of delivering a stream of mixed, MSW derived biomass material into a separator which operates under negative pressure enabling the biomass material to fall down the separator while inducing a sole air stream through the falling material to create a vortex of spinning material within the turbo chamber to separate out by centrifugal action selected denser components of the biomass material enabling such to continue falling to an outlet for collection while redirecting by entrainment in the air stream the remaining biomass material to a second outlet for subsequent processing or for collection.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a process for the production of a range of improved biomass material products, and in particular to the improvement of a biomass material which has been formed as a bi-product from the treatment of municipal solid waste (MSW). The invention further relates to an apparatus for the production of such range of improved biomass material products and the range of biomass materials produced thereby. The biomass material products produced are particularly suitable for use as a fuel for power generation, gasification, hospitals, industrial heating and domestic heating. The biomass materials products produced are suitable as an alternative fuel to fossil fuels, or standard biomass fuels formed from for example shredded dried wood and/or grass. 
     Incineration is a previously known method for the disposal of MSW. MSW generally comprises a combination of waste materials such as paper, vegetation, food, rubbers, textiles, wood, leather, plastics, glass and metals, or could contain waste from commercial outlets for example fast-food restaurants having a substantial mix of food, plastics and paper. Combustion of the MSW produces a heat energy which, for example, can be used to produce electricity. However, burning produces ash and noxious fumes which must be contained and further processed to enable their safe disposal. 
     Many governments now place restrictions on the burning of fuels in order to strictly limit the amount of noxious substances released into the environment. It is therefore desirable to process the MSW in a manner which enables the separation and recovery of inorganic and organic material therefrom. The separated organic material after further processing can then be used as a fuel which can be burnt in an environmentally more friendly manner. 
     Traditionally it is known to separate the organic and inorganic matters by saturating the MSW with water and/or steam, whilst heating and rotating the MSW to cause pulping of the organic material therein. The treated organic matter is then separated from the inorganic components of the waste by allowing it to fall through a screen. Examples of such processes are described in U.S. Pat. Nos. 5,190,226 and 5,556,445. However, these known processes provide a pulped organic matter with a water content of between 35% to 70%, which is extremely wet and therefore further processing is required to reduce the water content to render the pulp suitable for use as a compost or fuel. Also, the pulped material will still contain some non-combustible material such as metals, rubble, glass etc, and combustible toxic materials such as plastics and rubbers which are of a size which has enabled their passage through the perforations of the screen with the thus recovered organic matter. The presence of such non-combustible material and toxic materials reduces the value of the biomass fuel produced from the recovered organic material, since burning of such fuel still results in the production of some noxious gas and ash, lowering its potential energy density. 
     International Patent Application No. WO 03/092922 describes an improved method for the treatment of MSW which provides an organic pulped material having a moisture content of up to 15% which is highly suitable for further processing to produce a fuel or compost. However, the improved organic pulped material is still separated from the non-organic components of the waste by its passage through a trommel screen, and thus still contains some non-organic and toxic components. 
     Air separators are known which use two flows of air to separate out material based on its density. One such system is known from EP 0982082 (Beloit Technologies Inc). In this prior system air is drawn through a vertical separation chamber which is open to the atmosphere. Material to be separated is introduced into the rising stream of air and material having a lower density rises with the uprising air, whilst heavier material falls through the open bottom of the separator. The dispersion of the material is accomplished with a jet of high pressure air which breaks up and disperses the material within the rising air stream. This system is particularly adapted to separate wood chips, with the more dense knotted chips falling through the uprising current of air and, with the lighter chips being drawn up the separation chamber. However, this system is unsuitable for separating MSW. This is because MSW contains items such as glass shards, which although possessing a relatively high density also have a relatively large cross-sectional area which would enable them to be captured by the high pressure jet and forced up the separation chamber, rather than falling down to the outlet for collection. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of processing organic pulped material separated from the MSW during its treatment which produces at least one high quality biomass material containing less non-organic and toxic contaminants and which has when burnt improved noxious emissions, a much reduced ash content, whilst maintaining a good calorific value. 
     In accordance with a first aspect of the present invention there is provided a process for the treatment of municipal solid waste (MSW) derived biomass material to reduce the level of contaminants therein comprising the steps of: 
     delivering a stream of mixed, MSW derived biomass material to a first inlet of a vacuum turbo separator operating under negative pressure; 
     enabling said delivered biomass material to fall as a curtain of material from said first inlet through a turbo chamber to a first outlet of the separator; 
     inducing a sole air stream to flow from a second inlet of the separator through the turbo chamber to a second outlet of the separator; 
     directing said air stream through said falling material in the turbo chamber to entrain said material therein and to induce a vortex of spinning biomass material within the turbo chamber to separate out by centrifugal action denser components of the biomass material; 
     continuing said falling of said separated denser biomass material to said first outlet for collection in a receiving bay; and 
     redirecting said remaining entrained biomass material to said second outlet in said air stream. 
     The step of inducing said air stream may include the step of inducing at a low velocity. The step of redirecting the remaining entrained biomass material in said air stream may include the step of accelerating the air stream in said turbo chamber. 
     The process may comprise the step of air washing said separated denser biomass material with said air stream down stream of said vortex to separate out lighter components of the biomass material therein, and redirecting said separated out lighter components to said second outlet via the air stream. 
     The step of inducing an air stream may include drawing air though the separator and said step of directing includes directing the air stream in substantially the opposite direction to the falling curtain of material. 
     The curtain of falling biomass material and/or the flow of induced air may be adjusted to select the density of components separated from the biomass material. 
     In accordance with a second aspect of the present invention there is provided a process for the treatment of municipal solid waste (MSW) derived biomass material to reduce the level of contaminants therein comprising the steps of: 
     delivering a stream of mixed, MSW derived biomass material into a positive pressure density separator, directing an air stream through the biomass material in the density separator to entrain selected lighter components therein and to move such lighter components a first outlet of the density separator, and collecting the remaining biomass material and sending it to a second outlet of the density separator for collection in a receiving bay. 
     The air stream may be directed obliquely at said redirected biomass material. In a further embodiment the step of conveying is by a positive pressure air conveying steam. 
     The process may further comprise the step of distributing and separating components of the biomass material within the conveying air stream. 
     The separated lighter components may be plastics and may be further separated into various component parts by adjusting the temperature and/or airflow in the density separator. 
     The process may include the step of separating dust from the separated lighter components in a cyclone separator. 
     The process may include the step of directing said separated dust to a dust filter. 
     The process may comprise the step of directing said lighter components from the cyclone to a receiving bay and/or to the or a positive pressure density separator. 
     The mixed MSW derived biomass material may be sieved to remove components therein having a dimension greater than 50 mm, more preferably 10 mm, most preferably 3 mm before the step of delivering. 
     In accordance with a third aspect of the present invention there is provided an apparatus for the treatment of municipal solid waste (MSW) derived biomass material to reduce the level of contaminants therein, comprising a vacuum turbo separator having at least one inlet and two outlets, said inlet being adapted to admit a stream of mixed, MSW derived biomass material, at least one material duct enabling said biomass mass material to fall as a curtain of material from said inlet to a first of the outlets for collection in a receiving bay, a turbo chamber in said material duct, means to supply a sole current of air and to direct it through the falling curtain of biomass material in the turbo chamber for redirecting selected lighter components of the biomass material in the air stream to the second of said outlets, and means to maintain said material duct under negative pressure. 
     The air supply means may direct air at least partially through said material duct downstream of said turbo chamber. 
     The means to maintain said material duct under negative pressure may include at least one air lock at said inlet and/or first outlet. 
     The means to maintain said material duct under negative pressure may include induction means to draw said air stream though the turbo separator. 
     The apparatus may comprise means to adjust the geometry of at least one of the material duct, the turbo chamber, and an exit from the turbo chamber for said redirected lighter components to the second outlet. 
     In accordance with a fourth aspect of the present invention there is provided an apparatus for the treatment of municipal solid waste (MSW) derived biomass material to reduce the level of contaminants therein comprising a positive pressure density separator having at least one inlet and two outlets, the inlet being adapted to admit a stream of mixed, MSW derived biomass material, at least one duct to direct the biomass material through a first of the outlets, and means to supply a current of air and direct it through the stream of biomass material to separate out selected lighter components therein and to direct such to a second of the outlets. 
     The apparatus may comprise a positive pressure air conveying system to direct the biomass material through the density separator and the separator may comprise at least one adjustable channel to respectively change the direction of flow of the biomass material stream. The separator may comprise means for directing the airflow at the stream of mixed, MSW derived biomass material as it changes direction. 
     The apparatus may comprise a second inlet for admitting said current of air, and at least one air duct for directing the current of air obliquely at the stream of mixed, MSW derived biomass material. 
     The density separator may comprise a distribution chamber upstream of the adjustable channel and may comprise means to direct the air flow through the remaining stream of biomass material downstream of said adjustable channel. The density separator may be provided downstream of said second outlet of said turbo separator. 
     At least one fan may be provided for providing a positive pressure conveying system for transferring mixed MSW biomass material though the positive pressure density separator. At least one cyclone may be provided having an air inlet connected to the second outlet of the vacuum separator or density separator and at least two cyclone outlets, a first of which cyclone outlets being connection to at least one of the positive pressure density separator and/or collection bay for collection of the improved biomass material. 
     In accordance with the fifth aspect of the present invention there is provided an improved biomass material product as an end product of the process for reducing contaminants in the municipal solid waste (MSW) derived biomass material. The improved biomass material product may find particular application as a fuel and may have a gross calorific value of 13 to 16 kj/kg and/or may have a total moisture content of less than 17%, and/or ash content of less than 16% and/or a chlorine content of less than 0.3%. The process additionally yields a number of bi-products such as glass, rubble, plastics, and non-combustible material each of which can be recycled and/or further processed to form a number of further products, or blended to provide a lower grade fuel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       By way of example only specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of an apparatus for the production of an improved biomass material constructed in accordance with a first embodiment of the present invention; 
         FIG. 2   a  is a sectional view of the vacuum turbo separator of  FIG. 1 ; 
         FIG. 2   b  is an enlarged view of the turbo chamber of  FIG. 2   a ; and: 
         FIG. 3  is a sectional view of the positive pressure density separator of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The starting point for the present process, in accordance with a first embodiment is the provision of a coarse mixed biomass waste material  2  produced as an end product of the treatment of municipal solid waste (MSW) and which comprises pulped organic material, and non-organic and toxic components having no dimension greater than 50 mm. A suitable biomass material of such high quality is produced as an end product by the method of treatment described in International Patent Application No. WO 03/092922. 
     Referring to  FIG. 1  mixed biomass material  2  is fed into a storage hopper  4  for use in the process. From the hopper  4  the biomass material  2  is fed at a controlled rate and then transported via conveyors  6  into a feed hopper  8 . From the feed hopper  8 , via a rotary valve  10  at its outlet, the biomass material  2  is scavenge fed at a controlled rate into a vacuum turbo separator  12  (to be described in more detail further herein under). At this stage of the process the combustible material is separated from the heavier non-combustible material. The heavy non-combustible material thus separated from the mixed biomass material is discharged into a receiving bay  14  via a rotary valve  16 . Induced air which is required for this process is provided by air fan  18 . 
     The remaining mixed biomass material  2  is then conveyed by the air flow out of vacuum turbo separator  12  into a transfer cyclone  20 . The vortex created therein separates dust from the mixed biomass material  2  and discharges it through outlet  22  from where it is conveyed to dust filter  24 . The remaining mixed biomass material is discharged through outlet rotary valve  26  through a diverter valve  28  where it can be selectively sent to either receiving bay  30  or into entry junction  32  of a positive pressure conveying system, with propelling air being provided by conveying fan  34 . The mixed biomass material is either collected or conveyed via the positive pressure conveying system into a positive pressure density separator  36  (to be described in more detail further herein under). The positive pressure density separator  36  is specifically designed to take out the larger pieces of plastics from the biomass combustible material allowing the remaining mixed biomass material, the resultant high quality biomass fuel product, to discharge through rotary valve  38  into a receiving bay  40 . Secondary air required for this process is provided by fan  42 . The removal of these heavy plastics reduces the chlorine content and other noxious emissions and thereby provides an environmentally friendly, high quality biomass fuel product. 
     The separated pieces of plastics are conveyed out of the density separator  36  into a high efficiency cyclone  44  in which the plastics are separated from the conveying air and are discharged via rotary valve  46  into a receiving bay  48 . The removed air is then directed into the dust filter  24  which contains a fabric filter. The filtered air is emitted via exhaust fan  50 , whilst the dust collected by the dust filter  24  is discharged via rotary valve  52  into a storage hopper (not illustrated) to feed to a tanker or for blending back into the fuel products. 
     In the vacuum turbo separator  12 , as best illustrated in  FIG. 2  the mixed biomass material  2  is fed at a controlled rate via a rotary airlock  10  onto an adjustable spreader plate  72 . This converts a single stream of waste into a uniform wide band of material  1  that will fall as a continuous curtain of waste at junction  74  into a turbo/vortex chamber  75  and then into an air wash column  76 . 
     The vacuum turbo separator  12  is operated under vacuum. A controlled amount of air  78  is drawn via fan  18  into the separator  12  though a series of adjustable air inlets  80 , which may contain a filter, and are designed to allow a variable velocity profile to be created. The air  78  passes down into the inside of the separator  12  to junction  82 , whereat it turns though 180° and then flows at a low velocity, in this embodiment at a velocity of between 5 to 15 m/s, upwards though the air wash column  76  in the opposite direction to the flow of material  1  into the turbo chamber  75 . The geometry of the turbo chamber  75 , the flow of air current into the turbo chamber and the falling of the material is designed to create a vortex of material  3  to spin in the turbo chamber  75 . This centrifuges out the denser material and agglomerated product  5  and to accelerates the air allowing the lighter separated materials  7  to pass out with the air stream through an acceleration chamber  84 , at a speed of approximately 20 m/s, and then via a bend into transfer duct  86 . Meanwhile the denser material and agglomerated product  5  falls under gravity into the air wash column  76  which is held under vacuum and causes the remaining lighter product  9  to decelerate, turn through 180° to be washed out of the product steam and entrained into the air stream  78  and then carried back up the air wash column  76  and out through acceleration chamber  84 . The denser components of the waste  5  continue to fall down the air wash column  76  and from there are discharged through rotary valve  16  into receiving bay  14 . The rotary valves  16  and  10  enable the separator to operate under vacuum. 
     The degree of separation is controlled by adjusting the geometry of the air wash column  76  to increase or decrease the width and angles within by means of adjuster  87 ,  89  and/or adjusting the velocity of the airflow  78 ,  78   1  and/or the geometry of the turbo chamber  75 . 
     In the positive density separator  36 , as best illustrated in  FIG. 3 , the mixed biomass material entering from the transfer cyclone  20  travels from transfer duct  86  at a predetermined velocity into a vertical duct  88  and then passes into an adjustable distribution chamber  90 . The distribution chamber  90  is designed to distribute and separate the products of the mixed biomass material within the conveying air stream. The separating biomass material then passes through an adjustable annulus  92 , where an initial separation takes place, in that the lighter components of the biomass material turn through 180° and carry on up through a second annulus  94  and out through spigot  96 . The lighter components of the biomass waste are thus conveyed upwards by secondary air  102  blown up the separator  36 . The heavier components slide down cone  98  and fall into a second separation chamber  100 . As the heavier components fall down through the second separation chamber  100 , the secondary air  102  is blown in the opposite direction up the chamber  100  in order to separate out any lighter components which could not turn through 180° at the adjustable annulus  92 . The thus separated lighter components join the previously separated lighter components and exit at spigot  96 . The remaining heavier components carry on down the chamber  100  and are evacuated via a rotary valve from the base  104  of the conical hopper  99 . 
     The secondary air  102  is provided via fan  42  and is fed into the system at  106  and is then fed through a series of chambers  108 ,  110  to arrive at the base of the second separation chamber  100  at point  112  and at a predetermined velocity. 
     The size of the annulus  92  is adjusted by lifting or lowering the distribution chamber  90  by use of a screw  114 . The geometry of the annulus  94  can be adjusted by replacing distribution chamber  90  by a larger or smaller unit  118  (shown in dotted lines). The size of the chamber  100  can be adjusted by replacing inner sleeve  116  with a smaller or larger unit. 
     In separator  36  the lighter, plastics leaving the spigot  96  are conveyed into the cyclone separator  44 . 
     A chemical burn analysis of the final high quality biomass fuel product, this being a mixture of end fuel products obtained from the process of embodiments 1 and 2 described above, when compared to the mixed biomass product at the start of the process is shown in table 1. From which it is apparent that contaminants and potentially noxious components have been considerably reduced, whilst yielding a product with a good calorific value. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Biomass 
                   
                   
               
               
                   
                   
                 Material 
                 Biomass Fuel 
               
               
                   
                   
                 Before 
                 Product After 
               
               
                   
                 Units 
                 Processing 
                 Processing 
                 Comments 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Total Moisture 
                 % 
                 15-20 
                 12-17 
                 Reduced 
               
               
                 Ash 
                 % 
                 15-20 
                 10-16 
                 Reduced 
               
               
                 Volatile Matter 
                 % 
                 — 
                 60-65 
                 — 
               
               
                 Sulphur 
                 % 
                 1.0-0.6 
                 0.4-0.8 
                 Reduced 
               
               
                 Chlorine 
                 % 
                 0.4-0.6 
                 0.1-0.3 
                 Reduced 
               
               
                 Gross Calorific 
                 Kj/Kg 
                 13-18 
                 13-16 
                 Decreased* 
               
               
                 Value 
               
               
                 Net Calorific 
                 Kj/Kg 
                 12-16 
                 12-14 
                 Decreased* 
               
               
                 Value 
               
               
                 Energy Density 
                 Gj/M 3   
                 — 
                 3-4 
                 — 
               
               
                 Arsenic 
                 Mg/Kg 
                  3-10 
                 3-5 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Antimony 
                 Mg/Kg 
                  3-10 
                  3-10 
                 — 
               
               
                   
                 Dry 
               
               
                 Cadmium 
                 Mg/Kg 
                 0.4-1   
                 0.2-0.5 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Chromium 
                 Mg/Kg 
                 15-30 
                 10-20 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Copper 
                 Mg/Kg 
                 25-65 
                 25-35 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Lead 
                 Mg/Kg 
                  50-150 
                  50-100 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Mercury 
                 Mg/Kg 
                 &lt;1 
                 0.05-0.2  
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Nickel 
                 Mg/Kg 
                 12-25 
                 10-15 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Vanadium 
                 Mg/Kg 
                 25-50 
                 20-30 
                 Reduced 
               
               
                   
                 Dry 
               
               
                 Zinc 
                   
                  50-120 
                  50-120 
                 — 
               
               
                   
               
             
          
         
       
     
     The calorific value is slightly reduced due to the removal of plastics, plastics having a high calorific value. The reduction in plastics contaminants leads to a significant reduction in environmental pollutants such as for example chlorine. 
     The resultant high quality biomass fuel product is additionally environmentally friendly when compared with a fossil fuel such as coal and compares with the environmental agency limits set for power stations to obtain government renewable obligations certificates (ROCS) for burning biomass fuels. The results of the test conducted are shown in table 2. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Environmental 
                 Biomass Fuel 
                   
               
               
                   
                   
                 Agency 
                 Product 
               
               
                   
                   
                 Biomass 
                 After 
               
               
                 Parameter 
                 Units 
                 Limits ROCS 
                 Processing 
                 Coal Typical 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Total 
                 % 
                 25 
                 12-17 
                 6-8 
               
               
                 Moisture 
               
               
                 Ash 
                 % 
                 10 
                 10-16 
                  5-12 
               
               
                 Volatile 
                 % 
                 — 
                 60-65 
                 26-37 
               
               
                 Matter 
               
               
                 Sulphur 
                 % 
                 0.4 
                 0.4-0.8 
                 0.8-3   
               
               
                 Chlorine 
                 % 
                 0.4 
                 0.1-0.3 
                 0.1-0.4 
               
               
                 Gross 
                 Kj/Kg 
                 — 
                 13-16 
                 — 
               
               
                 Calorific 
               
               
                 Value 
               
               
                 Net Calorific 
                 Kj/Kg 
                 &gt;14 
                 12-14 
                 23-31 
               
               
                 Value 
               
               
                 Energy 
                 Gj/M 3   
                 — 
                 3-4 
                 24 
               
               
                 Density 
               
               
                 Arsenic 
                 Mg/Kg 
                 5 
                 2-5 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Antimony 
                 Mg/Kg 
                 — 
                  3-10 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Cadmium 
                 Mg/Kg 
                 0.2 
                 0.2-0.5 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Chromium 
                 Mg/Kg 
                 30 
                 10-20 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Copper 
                 Mg/Kg 
                 50 
                 25-35 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Lead 
                 Mg/Kg 
                 20 
                  50-100 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Mercury 
                 Mg/Kg 
                 0.05 
                 0.05-0.2  
                 Not available 
               
               
                   
                 Dry 
               
               
                 Nickel 
                 Mg/Kg 
                 30 
                 10-15 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Vanadium 
                 Mg/Kg 
                 20 
                 20-30 
                 Not available 
               
               
                   
                 Dry 
               
               
                 Zinc 
                 Mg/Kg 
                 80 
                  50-120 
                 Not available 
               
               
                   
                 Dry 
               
               
                   
               
             
          
         
       
     
     As an alternative a lower range of quality fuel products can be produced by adjusting the controls in the density apparatus  36 . Such fuel products collected are suitable for use in gassifiers, cement and paper industries, low grade biomass fuel product for coal fired power stations, local community and industrial heating schemes, and for blending to produce other fuels such as a household fuel. 
     The various stages of separation each result in a different waste product. The glass and rubble, the non-combustible material and plastics collected in a respective receiving bay can each be further separated for recovery and recycling of the various components therein. 
     Although the starting material has been described as having no component part greater than 50 mm, the starting material could have components of different maximum dimensions. The mixed biomass material could be passed over a trommel screen to pre-select the maximum dimension of the components parts. 
     Although the starting point of mixed biomass waste has been described as being produced by the method of treatment of MSW described in WO 03/092922, it is to be understood that the present process could be applied to other types of biomass waste. Furthermore one or more of the various stages could be omitted from the present process to achieve a lower grade biomass fuel. 
     Although the process has been described as separating out plastics into receiving bay  40  using the positive density separator  36 , the process could be adapted to further separate the plastics whereby adjusting the temperature and airflow within the separator recyclable plastics such as P.E.T. could be separated from the less reusable plastics such as P.V.C. At selected temperature the P.E.T. melts into and collates into a more coherent mass which can be blown into a separate receiving bay. Recyclable plastics thus separated provide a reusable bi-product and further reduce the amount of material destined for disposal by landfill 
     While the invention has been described in detail in terms of specific embodiments thereof, it will be apparent that various changes and modifications can be made therein by one skilled in the art without departing from the scope thereof.