IL103736A - Combined waste management process and system - Google Patents

Description

COMBINED WASTE MANAGEMENT PROCESS AND SYSTEM nDK>N 7K> 7i tvn 7in'j7 rmym V7nn nnya π υπ7 man IT7T RADION ENGINEERING CO. LTD. and nMyi 171 v TOTEC LTD. -C: 15697 Inventor: Yehuda Artsiely 15697WAS.TE 1-1234 8.11.92 FIELD OF THE INVENTION The present invention relates to waste management.

BACKGROUND OF THE INVENTION It is generally recognized as being desirable to dispose of solid domestic, commercial and industrial nonhazardous waste in a manner that causes least harm to the environment and, where possible, in a manner that is beneficial both to the environment and to society. It is thus known to recycle materials, particularly glass, metals and plastics, and to incinerate inherently combustible materials so as to generate energy. Organic waste may also be treated so as to produce fertilizer .

Recycling some waste materials and producing energy from others have the effect of reducing the net volume of non-useful waste, typically used as landfill, and of reducing damage therefrom to the environment, particularly when such waste contains chemically and biologically dangerous substances. Further advantages accruing from waste treatment and recycling are the preservation of mineral resources, the provision of a cheap energy source and the production of fertilizer.

Although it is known to separate some specific items for recycling, conventional waste management practice is to concentrate on a particular method or type of treatment, and to process the waste in a largely non-discriminating, bulk fashion.

A well-known method of waste disposal, as mentioned above, is that of incineration. A typical incineration plant includes an incinerator, a feeding and loading system, a steam generating waste heat boiler, a steam turbine generator, a gas cleaning system, and an ash treatment system. The steam turbine generator is operated by the steam produced by the waste heat boiler, to generate electricity.

It is conventional practice to regard waste for incineration as a homogeneous bulk, without regard to the presence therein of materials with a high water content.

•In a publication entitled "Characteristics of Municipal Solid Wastes in the United States i 60 - 2000 - Final Report", published by Franklin Associates, Ltd., 1986 , it is predicted that in the year 2000 approximately 3.2% of municipal solid wastes in the United States will be recyclable, 30.0% will be treatable by incineration, and ¼6 % will be treatable by anaerobic digestion. The remaining 14 % will be disposed of in other ways.

Among disadvantages resulting from the practice of bulk incineration are a relatively low energy production level per unit-volume. Income from energy production is used to offset plant running costs. Accordingly, the relatively low level of income from energy produced by incineration of waste as a bulk leaves the unit disposal cost of waste disposal at a relatively high level. A further disadvantage is that materials that could be reprocessed so as to provide other useful products are destroyed .

As the major portion of typical waste is composed of fermentable materials with a high water content, a further approach is to remove all non- fermentable materials from the waste, and to turn the remaining material into compost for fertilizer. Compost, per se, is a very common fertilizer, and thus has a very low selling price. Furthermore, as a long curing time is required, large areas of land are used. Additionally, as the process takes place in open air, it is a source of air pollution .

SUMMARY OF THE INVENTION The present invention seeks to provide an environment-friendly, relatively inexpensive, waste management process which reprocesses solid domestic, commercial and industrial nonhazardous waste in a way that increases the volume and number of useful byproducts thereof.

There is provided, therefore, in accordance with a preferred embodiment of the invention, a novel process for management of waste containing, inter alia, combustible materials, which process includes the steps of: selecting combustible materials from waste in accordance with predetermined criteria; and incinerating the selected materials.

Additionally in accordance with a preferred embodiment, the waste includes fermentable materials and the process also includes the following additional steps: removing fermentable materials from the waste; and biologically treating the removed fermentable materials so as to produce a plurality of useful byproducts.

Additionally in accordance with a preferred embodiment, the step of incinerating the selected combustible materials also includes producing an energy source, and the step of biologically treating includes the step of anaerobic digestion, thereby to produce one or more of growing substrates, fertilizer, and biogas.

Preferably, the biogas is stored for selectable running of a combustion engine for peak electricity production.

As a further byproduct CO2 gas is also produced. This gas may be usefully fed into growing enclosures.

It will also be appreciated that the byproducts produced by anaerobic digestion process of fermentable waste materials may be improved by the addition thereto of sewage sludge .

According to a preferred embodiment of the invention, the process further includes the step of producing a liquid fertilizer from the fermentable waste material. Ash which is produced as a byproduct from the incineration step may be mixed with the liquid fertilizer so as to cause enrichment thereof.

Preferably, where available, animals wastes are also added to the fermentable materials.

According to yet a further preferred embodiment of the invention, there is provided a system for management of waste containing inter alia, combustible materials which include fermentable materials. The system includes a waste incinerator for incinerating combustible materials selected from the waste in accordance with predetermined criteria so as not to include selected fermentable materials, and apparatus for biologically treating the selected fermentable materials thereby to produce a plurality of useful byproducts.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a generalized block diagram representation of the waste management process of the present invention; Fig. 2 is a detailed block diagram illustration of a waste management plant constructed in accordance with the present invention ; Fig. 3 is a detailed block diagram illustration of the process of the present invention; and Fig. 4 is a block diagram illustrating sub-processes of the process of the present invention, byproducts thereof, and applications of the byproducts.

DETAILED DESCRIPTION OF THE INVENTION The present invention seeks to provide a highly efficient waste management process which is capable of handling more different types of waste than is possible with conventional waste treatment plants, is friendly to the environment, and is significantly more efficient than conventional processes, both in terms of running costs and in terms of saleable byproducts produced during treatment of the waste.

Referring now to Fig. 1, the process may include as an initial step, unless this has been done at source, the removal from raw waste of materials that are suitable for recycling. This step is indicated at block 10. Recyclable materials typically include glass, plastics and metals. Removal of the recyclable materials is typically manual.

The remainder of the waste, after removal therefrom of recyclable materials, consists mainly of combustible materials, including organic or fermentable materials with a high water content. Some non-recyclable noncombus tible materials are also present .

The remainder of the waste is sorted into one of two groups, namely, combustible materials selected according to predetermined criteria, and other combustible, fermentable, organic materials having a high water content. The selected combustible materials are sent for incineration, as indicated at block 12, and the fermentable materials are sent for biological treatment, preferably anaerobic digestion, as indicated at block 14.

Non-recyclable noncombustible materials may be removed at the sorting stage of the process. Alternatively, or additionally, some non- recyclable noncombus tibles may be sent for incineration together with the selected combustible materials and 103,736/2 removed as residue thereafter.

Some combustible materials are selected for incineration, as mentioned above, in accordance with predetermined criteria. These criteria include the water content or relative dryness of the materials, anaerobic digestion process considerations related to a desired chemical composition of the organic waste, net cost considerations affected by the relative saleable value of incineration and digestion byproducts, respectively, and the handling capacity of the incineration equipment.

Reference is now made to Fig. 2 which is a schematic block diagram illustration of a combined waste management plant (CWMP) , referenced generally 20, constructed in accordance with a preferred embodiment of the present invention. CWMP 20 includes a sorting station 21, incineration sub-process plant 22 and biological treatment sub-process plant 2 h .

Reference is also made to Figs. 3 and k , which are schematic flow diagrams illustrating the process of the present invention.

The selected combustible waste is supplied from sorting location to a waste incinerator 26, via suitable feeding and loading apparatus 27· Waste incinerator 26 has connected thereto a waste heat boiler 28. to which is connected a steam turbine 30. Waste incinerator 26 may be of any suitable type known in the art, such as a rotary kiln or a fluidized bed incinerator. Waste heat boiler 28 may be such as manufactured by any of SULZER BROTHERS LTD. of CH-8^10, Winterthur, Switzerland; ABB PRODUCTS AND TRADE FINANCING LTD. of Baden, CH-5^01, Switzerland, and AALBORG CISERV INTERNATIONAL AS. of P.O.B. 66l , Gasvaerksvej Z , DK-9IOO, Denmark. Steam turbine 30 may be as manufactured by GENERAL ELECTRIC INDUSTRIES LTD. , USA and MITSUBISHI, Japan, for example.

During operation of incinerator '26, waste heat boiler 28 is operative to generate steam by circulation of water in heat exchanging contact with flue gases from incinerator 26. This is substantially as known in the art, and may be as employed, for example, in the Waste to Energy Recovery Plant of Technochem Environmental Systems Inc., of 700 Plaza Drive, Secaucus N.J.

An intake 31 (Fig. 4) of turbine 30 is connected to a steam outlet (not shown) of waste heat boiler 28 so as to operate turbine 30, thereby to generate electricity. The electricity generated is fed to an electrical utility.

According to one embodiment of the invention, illustrated in Fig. 2, the turbine exhaust steam is condensed by means of a condenser 32. The resulting condensed water is pumped back to the waste heat boiler via a suitable pump (not shown).

According to an alternative embodiment of the invention, however, as illustrated in Fig. 4, the turbine exhaust steam may be piped away for use with an absorption cooling system 33.

As known in the art, the incinerator flue gases, after leaving the waste heat boiler 28, enter a gas cleaning plant 34 where they are cleaned so as to remove therefrom materials detrimental to the environment. The remaining "clean" gases are then released to the atmosphere via a chimney 35 (Fig. 2). A suitable cleaning plant is such as employed, for example, by Technochem Environmental Systems Inc. of 700 Plaza Drive, Secaucus N.J. 07094.

Preferably, during the gas cleaning operation, C02 is also removed from the flue gases and is delivered, as by a suitable piping arrangement, to growing enclosures 37 (Figs. 2 and 4), for reasons discussed hereinbelow.

Ash that accumulates in the incinerator 26, including both bottom ash and fly ash, is conveyed to a blender 38. Blender 38 may be any suitable type of blending apparatus such as used in fine chemical industries for mixing powders and liquids together. One example of a suitable type of blender is a rotating propeller blender. At blender 38 the ash is mixed with a liquid fertilizer produced by the anaerobic digestion process depicted in Figs. 3 and 4 and as described hereinbelow. The two materials are blended together so as to produce an enriched liquid fertilizer, indicated at block 39 in Figs. 3 and 4 .

The remainder of the noncombus tible residues accumulating in incinerator 26 is sent via any suitable type of conveyor 36 (Fig. 2 ) , to containers (not shown) for tipping as landfill.

The biological treatment sub-process plant 24 includes a pre- treatment plant 40 (Fig. 2 ) , whereat the organic waste selected for anaerobic digestion undergoes various preparatory treatments prior, to being fed to an anaerobic digester 42 . The pre- treatments are well known in the art, and may include the following treatments indicated in Fig. 3 : maceration (block 41), shredding (block 43 ) . enriching (block 45 ) . consistency control (block 47 ) . and homogenizing (block 49 ) .

According to one option, the enrichment pre- treatment may consist of adding sewage sludge to the selected fermentable or organic wastes, via a suitable supply pipe 44 (Fig. 2 ) . This is not only beneficial for the digestion process, but it also provides a useful way of treating the sludge.

The anaerobic digester 42 comprises closed containers in which anaerobic digestion occurs. After pre- treatment , the organic waste material is piped directly for treatment (block 51 . Fig. 3 ) to the anaerobic digester 42 (Figs. 2 and 4 ) .

The anaerobic digestion sub-process requires certain conditions that can be controlled either manually or via a computerized controller 70 (Figs. 2 and 3 ) · Among process conditions required are the following: A. Maintenance of an optimal temperature for a given period typically this is in the range 35 " 55°C - so as to enable both the known dual-stage mesophilic and thermophilic processes to occur. According to a preferred embodiment of the present invention, the mesophilic process requires a temperature of 35 °C and the thermophilic process requires a temperature of 55 °C . Process temperatures may be controlled by exchanging heat with stack gases and via a thermostatic system.

B. Keeping the treated material homogenized during the entire sub-process. This may be done, for example, by entrainment of biogas into a lower portion of the digestion chamber. As the biogas bubbles upward towards the top of the chamber, mixing of the material is provided.

As will be appreciated by persons skilled in the art, it is also desirable to maintain constant predetermined chemical ratios, including, for example the carbon : ni trogen ratio.

Two materials are produced as a result of retention in the digester 42, namely, processed slurry and biogas.

The processed slurry is removed from digester 42 and sent for further processing (block 59 . F - 3 ) a a washing and sieving station 60 . Washing and sieving station 60 employs a water supply in conjunction with a suitable type of sieve, for example, a vibrating sieve. At the sieving station, the slurry is placed on the sieve and water or steam is sprayed over the slurry so as to wash through the sieve liquid material suitable for use as organic fertilizer. The liquid fertilizer is piped to blending station 39 for mixing with incinerator ash, as described above. The mixing together of the liquid material and the ash produces an enriched liquid fertilizer. The fertilizer produced, is a very high quality liquid, pure organic fertilizer suitable for piped delivery to growing enclosures 37 (Fig- 4 ) , agricultural plantations and the like. A further use of the liquid fertilizer 1,0 is as feed for aquiculture organisms, such as fish, in aquiculture ponds, indicated at block 64. in Fig. 4.

A further product produced from the processed slurry is a high quality . growing substrate material of a grade similar to or better than highest grade pit moss. This material is constituted by the solid fraction of the processed slurry that remains on the sieve after the remainder of the slurry has been washed through. The solid material is accumulated under or adjacent the sieve so as to await packaging at a packing station 62 (Fig. 2) . If desired, the quality of the growing substrate material may be further improved by open-air composting.

The biogas , which consists typically of about 40% CO2 and about 60# methane, typically has a high calorific value of 5400 - 627Ο kcal.Nm"3.

As shown in Figs. 2 and 4, the biogas produced during the anaerobic digestion step 5 (Fig- 3) is compressed via a compressor 46 into a storage tank 48. According to a preferred mode of operation of the plant of the present invention, the biogas is selectably fed from the storage tank 48 to a combustion engine 50 by means of valve 53 a peak hours. An electricity generator 52 is connected to the combustion engine 50 so as to generate electricity.

According to an alternative embodiment of the invention, the biogas may be fed directly as fuel to a combustion engine for on-line electricity production.

Exhaust gases from the combustion engine, having a high C02 content, estimated to be up to approximately 8θ# , may be directed (cool or hot, as required) into growing enclosures 37· This has well known beneficial effects of increasing produce, blooms, and foliage. Hot or warm CO2 may also be usefully fed to growing enclosures at night thereby to provide heating thereof and as to prevent cold damage to plants therein.

According to a preferred embodiment of the invention, heated cooling water and, optionally, exhaust gases from engine 50 may be used for cogeneration . Cogeneration may be defined as the sequential utilization of energy to produce electric power and a lower form of thermal energy, such as process heat (Benz, 1986 ) . Accordingly, the cooling water and exhausts gases may be directed to absorption cooling system 33 « Cooling system 33 may be connected to any suitable facility so as to provide cooling, for example, for an airconditioning facility 56 . a refrigeration system 58 , an ice production plant, and the like.

The combustion engine 50 may be of any suitable type. Engine 50 may thus be an internal combustion engine, such as a diesel engine, or an external combustion engine, such as a Stirling engine.

It has been found by the applicants that combustible wastes of a typical municipal waste sample selected for incineration in accordance with criteria described hereinabove has a calorific value of as much as approximately 80% higher than the calorific value that the overall combustible waste has when incinerated as a single, homogeneous bulk. In terms of energy per unit weight, mass incineration of combustible waste has been found to provide approximately 17 ^ 8 . kcal, whereas incineration of combustible waste selected according to criteria as discussed above, so as to exclude specific high water content fermentable wastes, has been found to provide approximately 3227 - 3 kcal.

As described above, a further energy, source is constituted by the production and selective use of biogas to generate electricity. As the biogas is stored, it is possible to generate the electricity produced thereby during peak hours, when the price that may be obtained for the electricity may be as much as 450# of the off-peak price. This factor renders the electricity produced from biogas more profitable than the electricity produced as a byproduct of the incineration sub- process, and substantially increases the overall energy production capacity per unit volume of treated waste.

It will further be appreciated that, while the incineration sub-process is significantly improved by removal of organic wastes having a high water content from the remainder of the combustible material, the high water content wastes are themselves treated biologically so as to produce useful byproducts which serve to further increase income streams of the overall process.

An inherent advantage of the anaerobic digestion process is that it occurs in the absence of oxygen and accordingly, as described above, takes place in closed containers or tanks. This provides a number of advantages over the conventional aerobic decomposition process, among which are the following : A. the anaerobic digester plant does not require large areas of land, B. the anaerobic sub-process does not cause air pollution, C. the retention time of waste in the digester 2 is relatively short, being about 7 ~ 10 times less than the retention time in the conventional aerobic process, and D. the anaerobic sub-process may be closely controlled by computer, and enables the production of high quality byproducts, as described herein.

A further advantage of the process of the present invention is in the ability to add thereto organic wastes originating in sources that conventionally are required to provide separate solutions to their waste disposal needs.

One example of this is the addition of sewage sludge to the high water content organic waste material, as described above. Addition of the sewage sludge enriches the organic material being treated and so significantly increases the amount of biogas that can be produced by the present sub-process. This provides a good solution to the problem of disposal of sewage slurry. By use of the process of the present invention, sewage sludge need no longer merely be made "safe", before being returned to the environment but, the use of sewage sludge for increasing the production of biogas actually helps to preserve fossil fuels as well as to increase income generated by waste management .

Similarly, animal wastes collected, for example, from zoos, animal farming facilities, and public streets may also be added to the digestion sub-process as part of the enriching step 45 (Fig. 3)· This increases the amount and quality of the various byproducts and reduces the retention time of the waste in the digesters. This has an additional effect of reducing the initial cost of the anaerobic digestion equipment by reducing the required holding capacity.

It will appreciated, therefore, by persons skilled in the art, that the combined waste management process of the present invention provides a way of breaking down municipal wastes of many types into four basic classes and processing each class in the most efficient and beneficial manner for that class. The present process, furthermore, incorporates various byproducts which may themselves require disposal - into another sub-process, thereby enhancing the byproducts thereof and thus inherently obviating the need to dispose of that byproduct by other means.

Among advantages of the process of the present invention, and of the CWMP 20 (Fig. 2) are the following: 1. The setting -up of a CWMP requires an initial investment that is significantly smaller than that of a conventional incineration plant capable of handling comparable volumes of waste. This is due to the fact that, for a given amount of waste, the size and cost of incineration equipment are reduced by approximately half.

Although installation of the anaerobic digestion equipment constitutes an additional cost, this is much lower than the cost of an incinerator with a similar waste handling capacity. It is estimated by the Applicants that the overall cost of setting up a CWMP as described hereinabove may be up to approximately less than the cost of setting up an incineration plant capable of processing the same amount of waste. 2. The combined process of the invention generates additional income, in the form of the above-described energy, growing substrates, and fertilizer byproducts, that render the net running costs of a CWMP significantly lower than net running costs of conventional waste disposal plants. 3. The CWMP is, as described above at length, much more friendly to the environment than conventional waste management plants. ' 4. The combined process reduces to a minimum the volumes of waste that cannot be either treated or recycled. 5. The combined process produces, inter alia, a storable energy source that can be used to provide significantly higher income for a CWMP than is attainable with conventional waste disposal plants .

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly described hereinabove. The scope of the present invention is limited, rather, solely by the claims, which follow.

Claims (25)

1. A novel process for management of waste containing inter alia, combustible materials, the process comprising the following steps: selecting combustible materials from waste in accordance with predetermined criteria; and incinerating the selected materials.

2. A process according to claim 1, and wherein said step of incinerating the selected combustible materials also comprises the step of producing an energy source.

3. · A process according to either of claims 1 or 2, and wherein the combustible materials in the waste also include fermentable materials, and said process also includes the following additional steps: removing from the waste fermentable materials not selected in said step of selecting combustible materials; and biologically treating the removed fermentable materials so as to produce a plurality of useful byproducts.

4. A process according to claim 3. and wherein said step of biologically treating comprises the step of anaerobic digestion .

5. · A process according to claim 4, and wherein said step of anaerobic digestion comprises the additional step of producing biogas .

6. A process according to claim 5. an also including the additional step of using the biogas to produce electricity.

7. A process according to claim 6, and wherein said step of using the biogas to produce electricity comprises the step of running a combustion engine on the biogas.

8. A process according to claim 7. and wherein said step of running a combustion engine on the biogas comprises the additional step of producing C02 as an exhaust gas.

9. A process according to claim 8, and also including the additional step of feeding the C02 into a growing enclosure.

10. A process according to claim 3. and also including the additional step of enriching the fermentable materials by adding sewage sludge thereto.

11. A process according to claim 3» and wherein said step of. biologically treating comprises the step of producing at least one of the group which consists of: growing substrates, fertilizer, and biogas .

12. ' A process according to claim 3. and wherein step of biologically treating comprises the step of producing liquid fertilizer, said step of incinerating the selected combustible materials causes the accumulation of ash, and wherein said process also includes the additional step of mixing the ash with the liquid fertilizer so as to cause enrichment thereof.

13. · A process according to claim 3. and also including the additional step of adding animal wastes to waste to be treated.

14. A process according to claim 3. and wherein the waste also includes recyclable materials and wherein said process also includes the following additional steps: removing recyclable materials from the waste, and sending the recyclable materials for recycling.

15. · A system for management of waste containing inter alia, combustible materials including fermentable materials, and comprising : a waste incinerator for incinerating combustible materials selected from the waste in accordance with predetermined criteria so as not to include selected fermentable materials; and means for biologically treating the selected fermentable materials thereby to produce a plurality of useful byproducts .

16. . A system according to claim 15 , and wherein said incinerator also comprises an energy source.

17. . A system according to claim 15 » and wherein said means for biologically treating comprises anaerobic digestion means.

18. . A system according to claim 17 , and wherein said anaerobic digestion means includes means for producing biogas.

19. 1 . A system according to claim 18 , and also including: a combustion engine adapted to run on biogas; an electricity generator operatively associated with said combustion engine; and means for selectably feeding biogas from said anaerobic digestion means to said electricity generator.

20. A system according to claim 15. and wherein said means for biologically treating comprises at least one of the group which consists of: means for producing growing substrates, means for producing fertilizer, and means for producing biogas.

21. A system according to claim 15. and wherein said means for biologically treating comprises means for producing liquid fertilizer, and said system also comprises means for blending incinerator ash with the liquid fertilizer so as to cause enrichment thereof.

22. A process according to any of claims 1 - 14 and substantially as illustrated and described hereinabove in conjunction with any of Figs. 1 - 4.

23. A process according to any of claims 1 - 14 and substantially as illustrated in any of Figs. 1 - 4.

24. A system according to any of claims 15 - 21 and substantially as illustrated and described hereinabove in conjunction with any of Figs. 1 - 4.

25. A system according to any of claims 1 - 21 and substantially as illustrated in any of Figs. 1 - 4. For the AppljLpants , Sanford T. Colb & Co C:15697 I-1234