WO2013082690A1

WO2013082690A1 - Method for disposition of bio-organic waste

Info

Publication number: WO2013082690A1
Application number: PCT/CA2012/000728
Authority: WO
Inventors: Robert Sampson
Original assignee: N-Viro Systems Canada Lp
Priority date: 2011-12-08
Filing date: 2012-08-03
Publication date: 2013-06-13
Also published as: CA2761397A1

Abstract

An improved method for drying an organic material using a dryer is disclosed. The method is of the type wherein a relatively dry material is mixed with the organic material to produce a mixture and the mixture is subjected to a drying process in the dryer to produce a granular product, the organic material being of the type which, if subjected itself to the drying process, would agglomerate. The improvement comprises use of the organic material, said organic material having been previously dried, as the relatively dry material.

Description

METHOD FOR DISPOSITION OF

BIO-ORGANIC WASTE

FIELD OF THE INVENTION

The invention relates to the field of bio-organic waste diversion. BACKGROUND OF THE INVENTION

The disposal of sewage sludge and other bio-organic wastes is a matter of significant concern to many municipalities.

Commonplace methodologies for the disposal of sewage sludge include:

• reduce the volume of the sludge through digestion and apply it to land

• mechanically dewater the sludge; dry the dewatered sludge by mixing with dry alkaline material, such as ash; dry the mixture; and apply the mixture to land or burn it with the use of supplemental fuel

• dry mechanically dewatered sludge in a relatively expensive drying operation [cost being a

function of capital and/or operating cost] and thereafter burn it

SUMMARY OF THE INVENTION

An improved method for drying an organic material using a dryer is disclosed and forms one aspect of the invention. The method is of the type wherein a relatively dry material is mixed with the organic material to produce a mixture and the mixture is subjected to a drying process in the dryer to produce a granular product. The organic material is of the type which, if subjected itself to the drying process, would agglomerate. The improvement comprises: use of the organic material, said organic material having been previously dried, as the relatively dry material.

According to another aspect, the mixture can have less than 60% water by weight. According to another aspect, the relatively dry material can have less than 40% water by weight.

According to another aspect, the granular product can have less than 20% water by weight.

According to another aspect, the granular product can have less than 10% water by weight.

According to another aspect, the granular product can have more than 30% solids by weight and less than 70% solids by weight.

According to another aspect, the granular product can be used as the relatively dry material.

According to another aspect of the invention, the method can be used for drying sewage sludge.

According to other aspects of the invention, the sewage sludge can be raw sewage sludge.

The product made by the use of the method can form yet another aspect of the invention and can be used, according to another aspect of the invention, as a fuel for a combustion power plant to produce electricity and ash.

An improved method for producing a fertilizer from an organic material forms another aspect of the invention. This method is of the type wherein an alkaline material is blended with the organic material to produce a blend and the blend is subjected to a drying process to produce a granular fertilizer product. The improvement comprises use of the ash as the alkaline material.

The product made by the use of this method forms yet another aspect of the invention.

Other advantages, features and characteristics of the present invention will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter being briefly described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a closed-loop waste-to-energy conversion process according to an exemplary embodiment of the invention; and

FIG. 2 is a photograph of the product indicated by reference numeral 26 in FIG. 1.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Reference is now made to FIG. 1 and the exemplary embodiment 20 illustrated therein in schematic form, which will seen to include:

• a drying operation 22, associated with the acceptance of a portion 24A of an incoming bio- organic waste stream 24 from a settling pond 23 and the production of a granular fuel product 26;

• an energy-production operation 28, associated with the combustion of the granular fuel product 26 and the production of ash 30 and electricity 32; and

• a fertilizer production operation 34, associated with the acceptance of the remainder 24B of the incoming bio-organic waste stream and the ash 30 and the production of a fertilizer product 36

Turning first to the exemplary drying operation 22, same will be seen to involve a pug mixer 38 feeding a mixture 40 [52% water by weight] to a rotary dryer 42 and to be characterized in that: a portion 44 of the relatively dry granular fuel product material exiting the dryer [10% water by weight] is mixed as a recycle stream with the portion 24A of the incoming bio-organic waste stream [80% water by weight] so as to produce the 52% water mixture delivered to the pug mixer 38; and the use of waste heat 39 from the energy-production operation 28. Surprisingly, it has been found that this arrangement allows for:

• relatively economical drying of (i) mechanically dewatered raw sewage sludge; (ii) source- separated household organic waste, and

• a relatively fine-grained particulate material. By way of background, it is well known to dry this type of bio-organic waste, but a common arrangement is to pre-dry the waste with a drying agent, typically alkaline waste prior to drying, so as to avoid balling, agglomeration and caking that would normally otherwise occur in the dryer and result, inter alia, in odor. [It is known to avoid balling, agglomeration and caking in the prior art, but this hereto is associated with either (i) specialized and relatively expensive equipment and relatively low operating costs; or (ii) commonplace, relatively inexpensive equipment ran at very low throughputs, with associated relatively high operating costs.]

The drying operation illustrated schematically does not suffer from balling, agglomeration and caking and thus operates relatively economically, i.e. excess cleaning-associated downtime is not a problem. The fuel product 26 itself has a consistency as shown in FIG.2 and will be seen to have the appearance of pebbles or pea gravel, and to be of a size distribution that is relatively easily handled through conventional materials handling equipment.

An advantageous drying cycle involves: the pasteurization of the material at above 70°C for at least 30 minutes, to destroy pathogens, thereby to minimize the need for special handling procedures. With reference now to the exemplary energy production operation 28, same will be seen to involve the combustion of the granular fuel product 26 to produce electricity 32 and ash 30, and, surprisingly, to be characterized by the absence of a supplemental fuel. In this regard, it is commonplace for stabilized sewage sludge to be incinerated, but typically only with another combustible material. Without intending to be bound by theory, it is believed that bio-organic-derived fuels of the prior art typically require supplemental fuel as a result of (i) insufficient granularity; or (ii) the inert materials introduced as part of the drying process, both impacting negatively on combustion characteristics, whereas the fuel product of the present invention has been demonstrated to be capable of self-sustained combustion with negligible hydrocarbon emissions [combustion efficiency estimated at 99.3% based on char carbon content of the ashes and CO and methane concentrations in the flue gas] in a vibrating grate style stoker and combustor at an above bed combustion temperature of 1730 F. The specific characteristics of the fuel product 26 combusted above are as follows:

Proximate analysis

Component As received Dry basis

Total Moisture 9.41 wt.%

Ash 30.60 wt.% 33.78 wt. %

Total Sulfur 0.87 wt. % 0.96 wt. %

Calorific value Btu/lb 5297 BTU/lb 5848 BTU/lt

Ultimate Analysis

Component As received Dry Basis

Total moisture 9.41 wt.%

Ash 30.60 wt.% 33.78 wt.%

Total Sulfur 0.87 wt.% 0.96 wt.%

Carbon 33.79 wt.% 37.30 wt.%

Hydrogen 5.34 wt.% 4.73 wt.%

Nitrogen 2.17 wt.% 2.40 wt.%

Oxygen by Difference 27.23 wt.% 20.83 wt.%

Turning lastly to the exemplary fertilizer production operation 34, this will be understood to involve, inter alia, the blending of a portion 24B of the bio-organic material with an alkaline material in a manner similar to that described in detail in Canadian Patent 2,410,814, incorporated herein by reference, but to be characterized by the use of the ash 30 from the combustion process as the alkaline material, generating a true closed-loop process. The blend 43 is dried in another rotary dryer 42, again fired using waste heat 41 from the energy-production operation 28.

Whereas but a single embodiment is herein described, it will be evident that variations are possible. For example, although a dewatered raw sewage sludge is specifically mentioned, the invention is suitable for use with other bio-organic wastes such as pulp and paper waste, shredded paper and cardboard, fermentation waste, food waste and other commercial/industrial organic waste. Raw as compared to digested sewage sludge is contemplated to be advantageous, as raw sewage sludge has higher available heat of combustion and thus burns more easily. As well, digestion of raw sewage sludge has associated costs. However, digested and dewatered sewage sludge cake can be used.

Further, whereas specific moisture contents, mix ratios and compositions are indicated herein, it will be appreciated that these are by way of example, only:

• The quantity of the recycle stream 44 will vary, inter alia, with the moisture content of the granular fuel product 26 exiting the dryer and the moisture content of the incoming bio-organic waste stream 24, but as a general rule, it has been found that if the mix produced by the mixer 38 in the drying operation 22 has no more than about 60% water by weight, the drying operation will work effectively and permit drying of the blend to 10% water content or less in conventional dryers

· in the exemplary embodiment, the granular product is dried to 10% water content or less, but this is not necessary; drying to 40% water content or less allows for the product to be stored for later use as a recycle stream, to seed the process; drying to 20% water content or less requires less energy than drying to 10% water content or less while providing a product that is capable of self-sustained combustion at least in combustors such as fluidized bed combustors ; drying to 10% water content or less relatively reliably provides a product that is capable of self-sustained combustion in at least some common combustors, such as stokers; drying to 30-50% solids produces a product that is easily stored and suitable for land application via conventional methods

Further, whereas the exemplary drying process uses waste heat from the energy-production process, this is not necessary; any form of inexpensive heat can advantageously be used. The same applies to the heat used by the rotary dryer 42 in the fertilizer process 34. As well, whereas rotary dryers are specified, this is not necessary. Other types of dryers can be utilized; the dryer can be a direct dryer or an indirect dryer; and can further include direct concurrent flow dryers, horizontal single, double and triple pass indirect dryers, and vertical counter flow dryers.

Additionally, whereas pug mixers are described, other mixers can be utilized. Further, whereas specific moisture contents are indicated above, these are not essential and will indeed be varied, to suit the characteristics of the available feedstocks and equipment. Suitable organic wastes will typically range between 15 and 30% solids: this can originate with, for example, only:

• source-separated household organic waste, which typically contains about 15% solids

• mechanically dewatered sewage wastes (dewatered via filter presses, centrifuges, etc.) which typically contain 15-30% solids)

Persons of ordinary skill readily appreciate process optimization and accordingly, further detail in this regard is neither required nor provided.

Accordingly, the invention should be understood as limited only by the accompanying claims, purposively construed.

Claims

1. An improved method for drying an organic material using a dryer, the method being of the type wherein a relatively dry material is mixed with the organic material to produce a mixture and the mixture is subjected to a drying process in the dryer to produce a granular product, the organic material being of the type which, if subjected itself to the drying process, would agglomerate, the improvement comprising: use of the organic material, said organic material having been previously dried, as the relatively dry material.

2. The method according to claim 1, wherein the mixture has less than 60% water by weight.

3. The method according to claim 1 or claim 2, wherein the relatively dry material has less than 40% water by weight.

4. The method according to any one of claims 1 to 3, wherein the granular product has less than 20% water by weight.

5. The method according to any one of claims 1 to 3, wherein the granular product has less than 10% water by weight.

6. The method according to claim 1, wherein the granular product has more than 30% solids by weight and less than 50% solids by weight.

7. The method according to any one of claims 1 to 6, wherein the granular product is used as the relatively dry material.

8. Use of the method of claim 1 for drying sewage sludge.

9. Use of the method of claim 7 for drying sewage sludge.

10. The product made by the use of the method of claim 1 for drying sewage sludge.

11. The product made by the use of the method of claim 7 for drying sewage sludge.

12. The product made by the use of the method of claim 1 for drying raw sewage sludge.

13. The product made by the use of the method of claim 5 for drying raw sewage sludge.

14. The product made by the use of the method of claim 7 for drying raw sewage sludge.

15. Use of the product of claim 12 as a fuel for a combustion power plant to produce electricity and ash.

16. Use of the product of claim 13 as a fuel for a combustion power plant to produce electricity and ash.

17. An improved method for producing a fertilizer from an organic material, the method being of the type wherein an alkaline material is blended with the organic material to produce a blend and the blend is subjected to a drying process to produce a granular fertilizer product, the improvement comprising: use of the ash produced by the use of claim 15 as the alkaline material.

18. An improved method for producing a fertilizer from an organic material, the method being of the type wherein an alkaline material is blended with the organic material to produce a blend and the blend is subjected to a drying process to produce a granular fertilizer product, the improvement comprising: use of the ash produced by the use of claim 16 as the alkaline material.

19. The product made by the use of the method of claim 17.

20. The product made by the use of the method of claim 18.