EP1599431A1

EP1599431A1 - Method of obtaining a fertilizer

Info

Publication number: EP1599431A1
Application number: EP04707611A
Authority: EP
Inventors: Michael Macdonald; Niall O'keeffe
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-03
Filing date: 2004-02-03
Publication date: 2005-11-30
Also published as: IE86533B1; IE20040068A1; WO2004069770A1

Abstract

The present invention relates to a process for the production of a fertiliser from a dry mix comprising fly ash and organic waste having a solids content of greater than 35 % by weight. The fertiliser is produced by mixing the fly ash and the organic waste to form the dry mix in an enclosed stablilisation chamber. The organic waste comprises between 30 % to 70 % by weight of the dry mix. The dry mix is allowed to exothermically react to transform to fertiliser and the fertiliser is cooled. The invention further relates to a fertiliser produced by that process.

Description

METHOD OF OBTAINING A FERTILIZER

Introduction

The present invention relates to a process for the production of a fertiliser from a dry mix comprising fly ash and organic waste having a solids content of greater than 35% by weight.

The annual production of organic waste exceeds over 5 million tonnes per annum in Ireland. In the specification the term "organic waste" refers to waste which can be broken down to carbon, hydrogen, oxygen and nitrogen and includes meat and bone meal (MBM), sludge, animal waste such as pig or poultry litter and cattle manure, spent mushroom compost and mushroom waste and vegetable matter.

The annual production of MBM, exceeds over 100,000 tonnes per annum in Ireland. MBM is derived from the carcasses or the bones of the carcasses of animals or a mixture of both. Over 80% of this MBM is free from disease and thus it is free from any possibility of causing incidents of Transmissible Spongiform Encephalopathies (TSEs) such as Bovine Spongiform Encephalopathy (BSE) or Creutzfeldt Jakob Disease (CJD). Because of various EU and Irish regulations however, none of this MBM is allowed to be used in animal feeds or as a fertiliser, because of the fear of transmitting disease and re-entering the food chain . Thus in spite of being certified as safe material this safe MBM cannot be used and thus has to be incinerated with the other non-certified as safe MBM which definitely requires incineration, the latter bone and carcass meal being that MBM that has been derived from questionably healthy animals. However, this legal restriction on using safe MBM in fertiliser is likely to be lifted in the near future.

This is a major problem and is becoming an even greater problem. The effectively uncontaminated MBM has to be stored and subsequently disposed of in a safe manner, such as incineration at relatively high temperatures or has to be exported. Both of these are expensive while at the same time, it is a fact that a very valuable fertiliser... being wasted. A major problem with the disposal of organic waste and especially MBM by incineration is the production of nitrogen oxides which are major pollutants in the atmosphere. The nitrogen oxides (NQx) are precursors to acid rain, photochemical smog and ground level ozone. The oxides are mainly Nitric Oxide (NO) and Nitrogen Dioxide (NO₂) both of which are corrosive and hazardous to health. A further problem with the incineration of MBM is that even if it is used as a source of energy, if s value as a source of energy is considerably less, by many factors, than it's value as a fertiliser.

PCT Publication No. WO 01/30453 discloses a method of disposal of meat and bone meal using alkaline substances such as lime (CaO) and hydrated lime Ca(OH)2 generally referred to as burnt lime and slaked lime respectively. This invention requires the addition of water to convert the lime to hydrated lime so that the resultant product is a solid cement like structure containing immobilised MBM which can be disposed of easily. The disadvantage of this is that the resultant product still has to be disposed of and the only benefit that this product has, is that it has immobilised and denatured MBM. Furthermore, the solid cement-like structure produced has no further use.

Municipal sludge which is derived from treated and dried faecal waste and allied products is produced in Ireland. The current methods of disposal of dried sludge are high temperature drying, land spread, incineration and landfill. There are obvious strict environmental regulations which must be adhered to and thus the cost of sludge disposal and nutrient management is extremely high.

The present methods of destroying and treating animal waste such as pig and poultry litter include direct spreading onto land which has associated disadvantages. Typical methods of disposing of mushroom waste also includes direct landspreading. The main disadvantage of this is that mushroom waste generally has a low nutrient value. Furthermore, it is a variable product in terms of its water content which can sometimes necessitate the need for drying before landspread which is both time consuming and costly. Additionally, mushroom waste can only be landspread at restricted times of the year and so is very difficult and expensive to store and transport.

Any process which can produce a more stable commercially valuable product from the above organic waste is therefore to be favoured. A further problem, in countries which bum combinations of fuels is the need for disposal of the ash. This is a particular problem with peat burning power stations and is undoubtedly a problem for those countries who use peat as a source of power. The problem, for example, in Ireland is that over 100,000 tonnes of fly ash, namely, the residual ash of the burning of peat, has to be disposed of. Peat contains a high proportion of calcium carbonate (CaCO-3) which when burned produces as its main product calcium oxide (CaO). While fly ash has limited nutrient value, it comprises at the same time, many useful ingredients such as calcium oxide, calcium hydroxide, phosphate, and the remainder being silicates and trace elements. Calcium oxide is a calcium caustic dry hygroscopic dust product in its pure form. When calcium oxide (CaO) comes into contact with water it produces calcium hydroxide (Ca(OH)₂) i.e. slaked lime, therefore leading to a disposal problem with fly ash.

It is further well known to use fly ash and products obtained therefrom such as CaO and Ca(OH)₂ to provide fertiliser. US Patent Publication No. 2002/0035858 discloses a process for transforming wet sludge and other wastes from vertebrates into fertiliser comprising adding calcium oxide and at least 10% magnesium oxide. The magnesium oxide is required to increase the temperature of the mixture containing the sludge to above 70°C. The disadvantage of magnesium oxide is that it is an expensive component, however would appear to be required in this process due to the high water content of the sludge. Furthermore, the percentage solids waste in the sludge is about 10% to 20%, therefore this process would be unsuitable for wastes with a high solids content.

The present invention is directed towards overcoming the aforesaid problems and improving national recycling obligations.

Statements of Invention

According to the invention, there is provided a process for the production of a fertiliser from a dry mix comprising fly ash and organic waste having a solids content of greater than 35% by weight, the process comprising: mixing the fly ash and the organic waste to form the dry mix in an enclosed stabilisation chamber, the organic waste comprising between 30% to 70% by weight of the dry mix;

allowing the temperature of the dry mix to increase to greater than 50°C ;

maintaining the dry mix at a ^"temperature of greater than 50°C for at least 30 minutes to transform the dry mix to fertiliser; and

cooling the fertiliser to a temperature of less than 25°C.

The advantage of the organic waste having a solids content of greater than 35% is that it allows a more efficient reaction to take place. As a large portion of water has been expelled it is possible to denature more organic waste in a single batch using less alkali. The final fertiliser is more dense and easier and less expensive to manage and apply to cropland.

The advantage of carrying out the process in an enclosed stabilisation chamber is that any of the gaseous compounds produced during the process such as ammonia are retained in the chamber where they will recombine to produce valuable nutrients in the fertiliser.

The advantage of allowing the temperature to increase to a temperature of greater than 50°C is that the rate of denaturation of the organic waste increases at this temperature and further sanitising occurs.

In one embodiment of the invention the fly ash comprises at least 60% calcium oxide by weight of the fly ash. The advantage of the fly ash comprising at least 60% by weight calcium oxide is that calcium oxide is the active ingredient in the fly ash which denatures the organic waste.

In another embodiment of the invention a sufficient amount of calcium oxide is addecT xTthe dry mix to provide a dry mix comprising between 15% and 50% calcium oxide by weight of the dry mix. Preferably the calcium oxide is added to the dry mix while the dry mix is being maintained at a temperature of greater than 50°C. Less calcium oxide is required when the dry mix is at this temperature than if the calcium oxide is added to a cold mix.

The advantage of adding calcium oxide to the stabilisation chamber while maintaining the dry mix at a temperature of greater than 50°C is that a synergistic effect arises in that much of the available energy, which would normally be used for converting CaO by chemical interaction to heat up the mix, is saved and diverted directly to dramatically sanitise the organic waste further and combine with elements made more receptive to chemical exchange as a result of being active in an already warm medium. Therefore the CaO added at that stage is not required to heat up the mix but rather to maintain the mix at a temperature of 50° C or greater and to denature the organic waste.

Therefore the addition of CaO at this stage as opposed to cold mixing with organic waste allows the CaO to interact more chemically efficiently and effectively. The extra potency of the CaO at this stage allows increased denaturation of the organic waste and other residues which are dangerous to the food chain cycle and which may possibly not be denatured by simple composting. Examples of such residues are pharmaceutical residues and in particular animal hormones and antibiotics which pass through into animal faeces and indeed human faeces where they can be recycled back to the food chain via the animal waste if applied to human food or animal fodder production without proper sanitisation.

In one embodiment of the invention when the organic waste is MBM, the fertiliser has a nitrogen content in excess of 4% by dry weight of the fertiliser. The advantage of the fertiliser having a high nitrogen content is that nitrogen is an important nutrient in fertiliser. Nitrogen is continually used and lost in the soil due to the nitrogen cycle where it is oxidised by soil bacteria. It is therefore important that nitrogen is reintroduced into the soil by another source.

Preferably the nitrogen is in the form of one or more of ammonium nitrate, calcium ammonium nitrate and. ammonium sulphate. The advantage of the nitrogen being in the form of nitrates (NOs sQcl- as ammonium nitrate and calcium ammoηium-nitrate^s- that nitrogen in this form is readily available to plants. Preferably the organic waste comprises 50% by weight of the dry mix.

Ideally the organic waste has a solids content of greater than 50% by weight. The advantage of having a high solids content is that less calcium oxide is required to denature and sanitise the waste.

Ideally the fertiliser has a solids content of greater than 70% by weight. The advantage of the fertiliser having a solids content of greater than 70% is that as it contains less water than other fertiliser it is less expensive to handle and transport. As the nutrients are not contained in an over bulky matrix of water and loose solids the fertiliser is more stable at a higher solids content. When MBM is used as the source of organic waste the solids content of the organic waste is generally greater than 80% by weight and results in a fertiliser having a very high solids content.

Ideally the pH of the fly ash is greater than 10. The advantage of the fly ash having a pH of greater than 10 is that it prevents infestation of pests such as insects or rodents and further sanitises the dry mix. Preferably a sufficient amount of fly ash and/or calcium oxide is added to provide a fertiliser having a pH in the range of between 6.5 and 8.0. The advantage of the fertiliser having a pH in this range is that the spreading of fertiliser of this type on the soil will not adversely affect the pH of the soil.

In a further embodiment of the invention, the process further comprises adding microorganisms to the stabilisation chamber. The advantage of adding microorganisms is that they can speed up the reaction kinetics in the stabilisation chamber. One advantage of this invention however is that the addition of microorganisms is not a necessary requirement for the reaction to take place, for the organic waste to be denatured and for a nutrient rich fertiliser to be produced. The advantage of being able to achieve these results by chemical means only if necessary is that microorganisms may produce waste. products some of which are undesirable- Gases such as hydrogen sulphide and rηercapt§r) _. which may be produced require treatment for odour. Furthermore as this process is not dependent on the addition of microorganisms, this obviates the need to maintain the process conditions within strict parameters in particular the parameters pertaining to pH and temperature. Therefore it is possible to carry out the process at temperatures in excess of 50°C, and to introduce an alkali at a pH in excess of 10, where these temperatures and pHs would destroy most microorganisms.

Ideally the process further comprises pelleting or prilling the fertiliser. The advantage of pelleting or prilling the fertiliser is that it allows for easier and more uniform spreading of the fertiliser and reduces dust emissions.

According to the invention, there is further provided a process for the production of a fertiliser from a dry mix comprising fly ash and organic waste having a solids content of greater than 35% by weight, the process comprising:

mixing the fly ash and the organic waste to form the dry mix, the organic waste comprising between 30% to 70% by weight of the dry mix;

allowing the temperature of the dry mix to increase to greater than 50°C ;

maintaining the dry mix at a temperature of greater than 50°C for at least 30 minutes to transform the dry mix to fertiliser; and

cooling the fertiliser to a temperature of less than 25°C.

Detailed Description of the invention

The invention will be more clearly understood from the following description thereof with reference to the accompanying drawings wherein:

Fig. 1 is a process for producing fertiliser according to the present i fehtioή. Referring to Fig. 1, there is provided a process for producing fertiliser indicated generally by the reference numeral 1 comprising a plurality of in-feed hoppers for organic waste 2 and flyash 3, identified by the numerals 4 and 5 respectively. The hoppers 4 and 5 feed a mixing station 6 which thoroughly mixes the organic waste 2 and flyash 3. A discharge outlet 7 feeds the organic waste and flyash mix 8 into an enclosed stabilisation chamber 9. Oxygen in the form of air enters the enclosed stabilisation chamber by an air inlet 10. An auger 11 carries the mix 8 through the chamber 9 allowing the exothermic reaction to take place and formation of fertiliser 12 to occur. A cooler 13 is provided undemeath the chamber 9 which cools the fertiliser 12. The fertiliser 12 is fed through a discharge chute 14 where an endless belt chain scraper 15 is provided to further feed the fertiliser 12 into a storage hopper 16.

The mixing station 6 and the stabilisation chamber 9 may comprise a paddle mixer, a revolving drum mixer or an auger. The fertiliser 12 may then be used directly or may be stored in bunkers or wind rows 17 not shown for further cooling or if desired it may be further processed at a prilling station 18 not illustrated.

In accordance with the invention, when peat is burned at a generating station, the fly ash is collected and mixed with between 30% to 70% organic waste by weight of the dry mix. This process is an exothermic process in that heat is generated from the reaction between organic waste and fly ash which increases the temperature in the stabilisation chamber to greater than 50°C and consequently increases the rate of denaturation.

Calcium oxide (CaO) and Calcium Hydroxide (Ca(OH)₂) which are the main constituents of fly ash, are both alkalis. When calcium oxide comes into contact with water it forms calcium hydroxide by the following reaction mechanism which is an exothermic reaction:

CaO+H₂O →Ca(OH)₂

The protein in the organic waste is denatured as it interacts with these alkalis during this process. During denatoratiδn; the protein's molecular structure is changed and volatile nitrogen in the form of ammonia (NH₃) is released. Ammonia is a gaseous alkaline compound and is lighter than air. As the process takes place in an enclosed stabilisation chamber the loss of volatile nutrients such as ammonia is prevented. The ammonia gas is not lost to the atmosphere but rather is reintroduced into the dry mix where it undergoes a multiplicity of organic interactions. It is further oxidised by incoming air to provide stable nitrates (NO3^") using the following reaction mechanism.

NH₃ + 20 →NO₃ ^" + 2H⁺ +H₂0

The organic waste comprises among other constituents, carbon, hydrogen, oxygen, nitrogen, calcium and phosphate and trace elements which combine with the components of fly ash to produce stable by-products, such as nitrogen usually in the form of nitrates such as ammonium nitrate and calcium ammonium nitrate, phosphate, potash, silica, calcium carbonate, calcium sulphate, (CaSO4), calcium sulphate dihydrate CaSO .2H₂O commonly referred to as gypsum and calcium sulphate hemihydrate CaSO ¹ H₂θ. Calcium sulphate is a calcium salt and the dihydrate and hemihydrate are hydrated forms of this salt.

If ammonium ions (NH₄ ⁺) are present in the mix they can react with water in the stabilisation chamber to provide ammonia using the following reaction mechanism and thus nitrates as illustrated above:

NH₄ ⁺ + H₂O → NH₃ + H₃O⁺

It is also possible to increase the rate of the reaction in the stabilisation chamber by the addition of suitable microorganisms. It is further possible to add additional calcium oxide to the dry mix if analysis shows the composition of calcium oxide in the fly ash is below the preferable levels. As fly ash is a residual product of the burning of peat, its compositional analysis can vary depending on the source. Table 1 shows the elemental and compositional analysis of fly ash from two different sources. Table 1: Fly Ash Elemental & Compositional Analysis

If calcium oxide is added at the same time as the fly ash it has been found that a fertiliser results which has a similar composition to a fertiliser produced from fly ash having a higher percentage of calcium oxide equivalent to the amount of calcium oxide added.

If however the calcium oxide is added during or after the organic exothermic reaction has taken place in the stabilisation chamber, i.e. if the calcium oxide is added to the dry mix having a temperature of greater than 50°C a synergistic effect arises from the fact that much of the available energy which would normally be used for converting CaO by chemical interaction to heat up the medium is saved and diverted directly to dramatically sanitize the organic waste further and combine with elements made more receptive to chemical exchange as a result of being active in an already warm medium.

For this reason the use of the CaO is applied at this stage as opposed to cold mixing with organic waste, it can achieve its objective more chemically efficiently and effectively when introduced to the partially composted material after the basic composting process; has peaked. Therefore less calcium oxide is required when added to a warm mix, than if mixed with a cold dry mix. This is illustrated in further detail in the following table which indicates the effect of heat on the requirement of calcium oxide.

Table 2: Effect of temperature on the requirement of calcium oxide

The initial process of cooling the fertiliser will take place in a cooling tower or conveyor system which will reduce the temperature of the material from the exothermic stage to less than 25°C. Preferably the cooler is a contact cooler, however it is possible to also use an air cooler as long as the air is not directly blown through the fertiliser as valuable nutrients may be lost. The fertiliser can be cooled further when stored in bulk bunkers or wind rows. There is an optional stage of pelleting or prilling the fertiliser prior to land application.

It will be noted that the nitrogen is chemically stabilised in the resultant final mixture. When MBM is the source of organic waste the fertiliser produced would be considered to have a high percentage of nitrogen at 4 to 8% by weight of the fertiliser. As nitrogen of this form is of high monetary value, the resultant fertilizer value is also high.

Depending on the type of organic waste used as a starting product, mixing fly ash and that waste on a 50:50 basis, would usually yield a final product comprising 2 to 10% by weight nitrogen, 1 to 5% by weight phosphate, 1 to 2% by weight potash, 4 to 12% by weight silica and 4 to 12% by weight calcium in any of the forms of calcium carbonate, calcium sulphate CaSO , dihydrate CaSO .2H2θ, hemihydrate CaSO H₂O and moisture. Analysis has shown that the organic , waste has been generally denatured. Example 1 : MBM as organic waste source

MBM and fly ash were mixed together in a ratio of 50:50 in an enclosed stabilisation chamber to form a dry mix. The temperature of the dry mix in the stabilisation chamber increased to 55°C before the resulting fertiliser was cooled to less than 25°C.

The components of the resultant fertiliser are tabulated in Table 1.

Table 3: Components of fertiliser from MBM and fly ash, expressed as elemental components.

Example 2: Municipal Sludge as organic waste source

Municipal sludge and fly ash were mixed together in a ratio of 50:50 in an enclosed stabilisation chamber to form a dry mix. The temperature of the mix in the stabilisation chamber increased to 70°C from the exothermic reaction and was maintained at that temperature for 40 minutes. The pH of the dry mix was 13 and this pH was maintained for 3 hours. The resulting fertiliser was found to have a dry matter nitrogen content of 9% and was deemed usable as a fertiliser on tillage land.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa. The invention is not limited to the embodiment hereinbefore described, but may be varied in both construction and detail.

Claims

1. A process for the production of a fertiliser from a dry mix comprising fly ash and organic waste having a solids content of greater than 35% by weight, the process comprising:

mixing the fly ash and the organic waste to form the dry mix in an enclosed stabilisation chamber, the organic waste comprising between 30% to 70% by weight of the dry mix;

allowing the temperature of the dry mix to increase to greater than 50°C ;

cooling the fertiliser to a temperature of less than 25°C.

2. A process for the production of a fertiliser as claimed in claim 1 wherein the fly ash comprises at least 60% calcium oxide by weight of the fly ash.

3. A process for the production of a fertiliser as claimed in claim 1 , further comprising adding a sufficient amount of calcium oxide to the dry mix to provide a dry mix comprising between 15% and 50% calcium oxide by weight of the dry mix

4. A process for the production of a fertiliser as claimed in any preceding claim, wherein when the organic waste is MBM, the fertiliser has a nitrogen content in excess of 4% by dry weight of the fertiliser.

5. A process for the production of a fertiliser as claimed in claim 4 wherein the nitrogen is in the form of one^of more of ammonium nitrate, calcium ammonium nitrate and ammonium sulphate.

6. A process for the production of a fertiliser as claimed in any preceding claim wherein the organic waste comprises 50% by weight of the dry mix.

7. A process for the production of a fertiliser as claimed in any preceding claim wherein the organic waste has a solids content of greater than 50% by weight.

8. A process for the production of a fertiliser as claimed in any preceding claim wherein the fertiliser has a solids content of greater than 70% by weight.

9. A process for the production of a fertiliser as claimed in any preceding claim wherein the pH of the fly ash is greater than 10.

10. A process for the production of a fertiliser as claimed in any preceding claim, wherein a sufficient amount of fly ash and/or calcium oxide is added to provide a fertiliser having a pH in the range of between 6.5 and 8.0.

11. A process for the production of a fertiliser as claimed in any preceding claim further comprising adding microorganisms to the stabilisation chamber.

12. A process for the production of a fertiliser as claimed in any preceding claim further comprising pelleting or prilling the fertiliser.

13. A fertiliser produced by the process as claimed in any of claims 1 to 12.