SE535315C2

SE535315C2 - Process for making fertilizer products from residues

Info

Publication number: SE535315C2
Application number: SE1051144A
Authority: SE
Inventors: Gunnar Thelin
Original assignee: Ekobalans Fenix Ab
Priority date: 2010-11-01
Filing date: 2010-11-01
Publication date: 2012-06-26
Also published as: EP2635542A1; SE1051144A1; WO2012060768A1; EP2635542A4

Abstract

The present invention describes a process for the production of a fertilizer product from a residual product, said process comprising the steps of dewatering of the residual product and separation of the dry phase and the wet phase, collecting of the dry phase as a product no 1, precipitation of the wet phase to form at least phosphorous (P) in some solid form as a product no 2, stripping of the remaining wet phase to produce ammonia ((NH3), (g)) which subsequently is reacted with an acid or a mixture of two or several acids and/or salt solutions to produce nitrogen (N) in some solid form as a product no 3 and agglomeration of at least one of the products no 2 and/or no 3 for the production of a fertilizer product.

Description

METHOD FOR THE PRODUCTION OF FERTILIZER PRODUCTS FROMRESIDUES Field of invention The present invention relates to a process for the production of afertilizer product from a residual product.Technical Background Different treatments of residual products, such as e.g. sludge ordigestion residues, are known. lt is e.g. known to dewater and separate asludge and subsequently precipitate different substances for use as fertilizeradditives. Different such processes have been disclosed. For e.g. inUS4098006 there is disclosed a process tor (trying organic waste, such assettrage sturige, hy cchtactiitg the organic vtfaste trrith hot vaoors. Partiaidewaterirtg ot the organic waste is achieved hy adrnixttire with a reoycieciportion of cirieci soiicis foiioxweo hy extrtisioit ot the rnixttire. The restiitaritextruoate is then cirieo, ana the tinrecyoieiri portion is extruoeo ih a separateoperation to form coinpacteo granuies saio to have gooo fiow characteristicssho oeirig stritaote for apoticatiorw hy contrnertoiai fertiiizer soreaoers. More»over, in Uâšâtßeaâ there is described a method said to improve the cieirvata-ring and ooor reduction charaoteristics of a iiotiitt nrastetrrater sitioge, setti~ment, or soiis to uítimateiy forrn a oewatered soiid resictiiai that ihcitittesnutrition enhancement of a resuitaitt materiai that is suitahie for distributionand rnarketihg, anti for ihoorooratiort in a 'iertiiizer hieho. The rnethoo inoitiiïiesthe addition ot seieetive aeicis, such as stiiphuric aoici, phosphorie aoio ornitric acici, artrit isases, rnagrtesitirn oxide, oaioiurn oxicte, potassitirti oxicie,arrrmonia or caicitim itydroxioe, to the iiotiid sitioge witioit forms insoitiiotepreoipitates, anci ehrrieshes the soiios in the siuoge to torrn a graniitar”protttict, Although there exist several known processes today, none of theseprovide an optimal solution for producing fertilizer products from residualproducts. One aim of the present invention is to provide a process involvingthe optimal set of steps. Moreover, another purpose of the present inventionis to provide improvements within different single steps of the process, such 2as in relation to e.g. the first treatment of the residual product and also in relation to the end treatment when providing a fertilizer product.Summary of invention The first purpose above is achieved by a process for the production ofa fertilizer product from a residual product, said process comprising the stepsof: - dewatering of the residual product and separation of the dry phase and thewet phase; - collecting of the dry phase as a product no 1; - precipitation of the wet phase to form at least phosphorous (P) in some solidform as a product no 2; -further processing of the remaining wet phase by adding at least one ionexchanger to form an ammonium (NH4+) enriched solution; - stripping of the ammonium (NHJ) enriched solution to produce ammonia((NH3), (g)) which subsequently is reacted with an acid or a mixture of two orseveral acids and/or salt solutions to produce nitrogen (N) in some solid formas a product no 3; - agglomeration of at least one of the products no 2 and/or no 3 for theproduction of a fertilizer product.

The residual product used for the present invention may e.g. be sludge(wastewater sludge), digestate(s), manure residues, such as liquid manurenot being fermented, or the like.

The step of dewatering of the residual product and the separation ofthe dry phase and the wet phase is normally made simultaneously. Generallyin this context, it is important to understand that different kind of processequipment types may be used to perform the process according to the pre-sent invention, such as continuous processing but also batch or semi-batchoperations. Some steps are naturally performed batch-wise, however othersteps may also be performed continuously.

Moreover, according to the present invention there may be a negativepressure applied from the dewatering to the stripping and subsequentreaction between ammonia ((NH3), (g)) and an acid or a mixture of two or several acids and/or salt solutions. This implies that a negative pressure 3(underpressure) is applied from the dewatering step and forward to drive any produced gaseous (volatilized) ammonia towards and into the containerintended to collect this gas component, i.e. the container where ammonia isreacted with an acid or a mixture of two or several acids and/or salt solutionsto produce nitrogen (N) in some solid form as a product no 3. Such ammoniamay e.g. be produced in minor amounts already at the dewatering step or forinstance in the precipitation.

As may be noted from above, the process according to the presentinvention comprises dewatering/separation, precipitation, ammonia genera-tion, acid treatment and provision of end product, the latter being made byagglomeration, such as e.g. granulation, pelletization and compaction.Detailed description The present invention provides a method for treatment of residualproducts which focuses on optimization of total yield of nutrients and henceprovides economic advantages in comparison to today known processes. lnview of the purpose disclosed above and dependent on the residual product,it may be of interest to pretreat the influx before the dewatering and separa-tion. Such known pretreatments today only have the purpose of providing amixture which is easier to dewater. According to the present invention, how-ever, the optional pretreatment is provided to optimize the total yield ofnutrients as well as providing a mixture which is easy to dewater and separa-te. According to one specific embodiment of the present invention, the pre-treatment is any one ofﬂocculation, fiber addition, pH adjustment, addition ofa divalent ion solution, magnetic field provision or a combination thereof.

Generally, flocculation is a process where colloids come out ofsuspension in the form of floc or ﬂakes. ln this case, ﬂocculation is performed by adding a substance, e.g. a polymer, which improves the dewatering ability of the residual product by binding organic material into larger aggregates.Added fiber improves the dewatering ability as suspended organicmaterial (SOM) is bound to the added fibers. The fibers can act as “filtermaterial” in the filtering process. When a sludge including fibers is filtered,fibers will be deposited on the filter and this will greatly enhance the specific surface area available for binding of SOM. This effect can also be used by 4first filtering a small amount of sludge with fiber added and then sludge without fiber. Alternatively, the sludge can be filtered through a fiber material.Fiber addition may be a better alternative than polymer addition, since theintended types of fiber is much cheaper than polymers, and the added fibercan be used as energy in the dry phase. The risk of both flocculation and fiberaddition is that too large nutrient fractions are allocated to the dry phase. lncreasing the pH value using e.g. sodium hydroxide before dewateringwill lead to the release of positively charged nutrient ions into the wet phaseand will decrease the need for pH increase later in the precipitation step.However, the dewatering ability will probably decrease, since the addition ofmonovalent cations will disperge the organic material. When negativelycharged ends of the organic material are occupied by monovalent cations thedifferent pieces of organic material will repel each other.

The addition of a divalent ion solution, e.g. calcium or magnesiumhydroxide, will release positively charged nutrient ions and lower the need forpH increase later in the precipitation step, as in the above case. However,addition ofdivalent cations will not disperge the organic material, but insteadbind it together. A divalent calcium ion can bind to two different pieces oforganic material and thus probably improve the dewatering ability.lf a residual product is pumped through a container or a pipe where a strongmagnetic field is applied across the container or pipe cell membranes willrupture and nutrients contained within cells will enter into the solution andincrease the share of nutrients that end up in the wet phase after dewatering.This will probably reduce the dewatering ability of the residual product. There-fore, the technique will probably be used in combination with anyone offlocculation, fiber addition or addition of a divalent ion solution. UV-light orultrasound are alternatives to a magnetic field, and also possible to useaccording to the present invention. Moreover, pretreatments such as treat-ment with ozone are also possible according to the present invention.

There are also other advantages with the process disclosed accordingto the present invention. One such is the removing of ecologically harmfulsubstances in the process. Therefore, according to one specific embodiment of the present invention, the step of dewatering of the residual product and 5separation of the dry phase and the wet phase also involves removing of heavy metal compounds which are collected in the dry phase. Heavy metalsin the residual product are to a very high degree strongly bound to the organicmaterial. Thus a dewatering step removing organic material from the solutionwill simultaneously remove the bulk of the heavy metals from the solution.This effect can be increased by the addition of substances with a high capa-city of binding heavy metals.

As may be understood from above, the heavy metals follow the dryphase. However, the heavy metals shall eventually also be separated fromthe dry phase and be deposited. Such separation from the dry phase may beperformed both before, such as by use of a substance with a high capacity ofbinding heavy metals as disclosed above, and also after the combustion ofthe dry phase. ln the case of separation after the combustion of the dry phase(or product no 1), this may be performed either by first removal of phosphor-rous and other nutrients from the ash so that the heavy metals aftervvards willbe found in a residue, or by first removal of the heavy metals from the ash sothat the nutrients will be found in a residue. Therefore, according to one spe-cific embodiment of the process according to the present invention, the heavymetal compounds are separated either from the dry phase (product no 1)before combustion, or from the ash after combustion of the dry phase(product no 1).

Generally, in the context of the present invention it is important torealize that the dry phase may be seen as or called the organic phase.According to the process of the present invention, organic material is intendedto be collected in the dry phase. Fact is that the maximum level of organicmaterial in the wet phase is intended to be set at 5%. ln other words, theseparation of a dry and wet phase may also be seen as a separation oforganic material so that the level of such organic material is depressed in thewet phase.

Besides the none-active process step of collecting of the dry phase,precipitation of the wet phase to form at least phosphorous (P) in some solidform is performed after the separation step. According to the present invent- tion, different solid P forms are possible. Examples thereof are struvite 6(ammonium magnesium phosphate, formula ((NH4)lVlgPO4-6H2O)), apatites, other calcium phosphates or combinations thereof. Apatite is a group ofphosphate minerals, usually referring to hydroxyapatite, ﬂuorapatite, chlor-apatite and bromapatite. The formulas of the admixtures of the four mostcommon are written as Ca10(PO4)6(OH, F, Cl, Br)2. lt is important to under-stand that many other solid forms are possible according to the presentinvention, such as e.g. calcium phosphate (Ca3(PO4)2).

The precipitate, in this example struvite, may be produced by e.g.adding magnesium dichloride (MgClg) and sodium hydroxide (NaOH), eitherin one container e.g. simultaneously or in different containers sequentially.Either of them may be added first in the process. The precipitate may also beproduced by increasing the pH value of the wet phase by stripping C02 (g)from the mixture. At pH value about 8-9, struvite begins to precipitate. Afterachieving a struvite solution, as particles and struvite from a magnesiumchloride treatment container, as struvite solution from a sodium hydroxidetreatment container, or in fact as both from a combined treatment container,this solution is fed to a filter, where the precipitate struvite is separated andthereafter obtained by dewatering. Filtration is one suitable technique for thisstep, however also other separation techniques are possible to use. lrrespective of actual pretreatment and type of produced precipitation,it is according to present invention possible to precipitate at least 95% of thephosphorous in the wet phase. lt is important to understand that when describing precipitations, bothcrystalline and amorphous precipitations, as well as combinations thereof, arecontemplated in relation to the present invention. One advantage of producingstruvite is the fact that it crystallizes very clearly. Moreover, seed chargingmay be used during the precipitation to increase the efficiency of the processstep. Furthermore, e.g. struvite may in fact be produced in minor amounts tofunction as a seed promoting the precipitation of other amorphous and/orcrystalline precipitates. ln other words, in this case struvite only functions as aprecipitation promoter and is not intended as the main precipitationcomponent to be produced. 7As mentioned above, MgClg and NaOH may be used as precipitation promoting substances for precipitation of P solids. Other known suchsubstances are magnesium sulphate (MgSO4), calcium chloride (CaClg),calcium hydroxide (Ca(OH)2), calcium sulphate (gypsum, CaSO4* %H2O) andin fact also sea water or bittern, a residual product after the evaporation andcrystallization of sodium chloride from brines and sea water. Bittern contains,in concentrated form, the calcium and magnesium chlorides and sulfates,bromides, iodides, and other chemicals originally present in the brine. Thesesubstances are known for usage in precipitation steps as according to above.However, the present invention also provides one new substance not knownfor such usage. Therefore, according to one specific embodiment of thepresent invention, green Iiquor s|udge is used as the precipitation promotingsubstance. Green Iiquor s|udge is a residual product from pulping processesand it contains inter a|ia metal salts, mainly sulphides including magnesiumsulphide.

There are other nutrients which may be recovered by the processaccording to the present invention. According to one specific embodiment ofthe present invention, also potassium (K) and/or nitrogen (N) in some solidform is precipitated in the step of precipitation of the wet phase. The amountof potassium in the residual product used varies a lot. The purpose of theinvention, is of course to obtain as much potassium as possible from the startresidual product. lf potassium is present, it is present in the wet phase afterseparation according to the invention. According to the present invention it ispossible to precipitate at least 50%, such as at least 70%, e.g. in the range of70-95%, of the potassium present in the wet phase. Nitrogen may be produ-ced in different solid forms. According to one specific embodiment of thepresent invention, nitrogen (N) is precipitated in some solid nitrate form.

After the precipitation of the “first” wet phase, the remaining wet phaseis further processed according to the present invention by addition of at leastone ion exchanger to form an ammonium (NH4+) enriched solution. Suchtreatment may e.g. be performed in a zeolite container where also an eluent,such as sodium chloride (NaCl), is added. Zeolite functions as an ion exchanger, but it is important to understand that also other such exchangers 8may be used. After this step “clean” water solution, which may be recirculated back to the dewatering or in fact used as clean process water, andammonium solution is produced. The ammonium solution is fed to a stripper,e.g. holding a pressure of 0.5-0.9 bar, where ammonia ((NH3), (g)) and“clean” water solution is produced, the latter e.g. processed together withclean water solution from the ion exchange treatment. The ammonia is ﬂowedinto an acid tank so that remaining nitrogen (N) is produced in some solidform. Different acids may be used, such as e.g. sulphuric acid (H2SO4),hydrochloric acid (HCI) and nitric acid (HNOg), the latter however not in cleanform as ammonium nitrate (NH4NO3), which is explosive, of course is undesi-rable. Moreover, a mixture of two or several acids and/or salt solutions mayalso be used. For instance if sulphuric acid is used, ammonium sulphate((NH4)2SO4) is produced as the nitrogen solid form after the acid treatment.The nitrogen solid form is obtained after sedimentation. After this treatment,the present process achieves a level of at least 90% of the nitrogen (N) in thewet phase being collected in a solid form.

As mentioned above, the last step according to the present process isthe agglomeration of at least one of the obtained solid products from theprocess for the production of a fertilizer product. Moreover, according to onespecific embodiment of the present invention, substances from ash fromcombusted product no 1, i.e. obtained from the separation, or from othertypes of ash is admixed with at least one of the products no 2, i.e. obtainedfrom the precipitation, and/or 3, i.e. from the acid treatment, for the productionof a fertilizer product.

The agglomeration may according to the present invention be perfor-med in different ways and by different means. According to one specificembodiment of the present invention, the agglomeration is performed bygranulation, pelletization or compaction. Granulation may be preferred insome applications according to the invention. Granulation may e.g. beperformed by drum granulation or by means of a fluidized bed.

Furthermore, the agglomeration step may besides the actual mechani-cal treatment also involve other treatment, such as e.g. adding at least one agglomeration promoting substance. According to one specific embodiment of 9the present invention, the aggiomeration is performed by granulation and the granulation involves adding a binder, said binder in this case being the agglo-meration (granulation) promoting Substance.

Generaiiy, it is important to understand that different steps of theprocess according to the present invention may be performed in different plants, e.g. if this is efficient or necessary for a specific case or application.

Claims

1. Claims 1. Process for the production of a fertilizer product from a residual product,said process comprising the steps of: - dewatering of the residual product and separation of the dry phase and thewet phase; - collecting of the dry phase as a product no 1; - precipitation of the wet phase to form at least phosphorous (P) in some solidform as a product no 2; -further processing of the remaining wet phase by adding at least one ionexchanger to form an ammonium (NH4+) enriched solution; - stripping of the ammonium (NHJ) enriched solution to produce ammonia((NH3), (g)) which subsequently is reacted with an acid or a mixture of two orseveral acids and/or salt solutions to produce nitrogen (N) in some solid formas a product no 3; - agglomeration of at least one of the products no 2 and/or no 3 for theproduction of a fertilizer product.

2. Process according to claim 1, wherein there is a negative pressure appliedfrom the dewatering to the stripping and subsequent reaction betweenammonia ((NH3), (g)) and an acid or a mixture of two or several acids and/or salt solutions.

3. Process according to claim 1 or 2, wherein pretreatment of the residualproduct is performed before the dewatering and which pretreatment is anyone of ﬂocculation, fiber addition, pH adjustment or addition of a divalent ion solution, magnetic field provision or a combination thereof.

4. Process according to anyone of claims 1-3, wherein the step of dewateringof the residual product and separation of the dry phase and the wet phasealso involves removing of heavy metal compounds which are collected in the dry phase. 11

5. Process according to claim 4, wherein the heavy metal compounds are separated either from the dry phase (product no 1) before combustion, orfrom the ash after combustion of the dry phase (product no 1).

6. Process according to anyone of c|aims 1-5, wherein green Iiquor sludge isused as a precipitation promoting substance.

7. Process according to anyone of c|aims 1-6, wherein also potassium (K)and/or nitrogen (N) in some solid form is precipitated in the step ofprecipitation of the wet phase.

8. Process according to claim 7, wherein also nitrogen (N) in some solid nitrate form is precipitated in the step of precipitation of the wet phase.

9. Process according to anyone of the preceding c|aims, wherein substancesfrom ash from combusted product no 1 or from other types of ash is admixedwith at least one of the products no 2 and/or 3 for the production of a fertilizer product.

10. Process according to anyone of the preceding c|aims, wherein the agglomeration is performed by granulation, pelletization or compaction.

11. Process according to claim 10, wherein the agglomeration is performed by granulation.

12. Process according to claim 11, wherein the granulation is performed bydrum granulation or by means of a fluidized bed.

13. Process according to anyone of the preceding c|aims, wherein theagglomeration involves adding at least one agglomeration promotingsubstance. 12

14. Process according to claim 11 or 12, wherein the agglomeration is performed by granulation and the granulation involves adding a binder.