Patent Description:
<NUM> NaCl + CaCO<NUM> → Na<NUM>CO<NUM> + CaCl<NUM>.

In practice this direct way is not possible and it needs the participation of other substances and various different process steps to get the final product, soda ash. First reactions occur in salt solution (brine). First of all, ammonia is absorbed (<NUM>) and then, the ammoniated brine is reacted with carbon dioxide to form successive intermediate compounds: ammonium carbonate (<NUM>) then ammonium bicarbonate (<NUM>). By continuing carbon dioxide injection and cooling the solution, precipitation of sodium bicarbonate is achieved and ammonium chloride is formed (<NUM>). Chemical reactions relative to different steps of the process are written below:.

NaCl + H<NUM>O + NH<NUM> ↔ NaCl + NH<NUM>OH     (<NUM>).

<NUM> NH<NUM>OH + CO<NUM> ↔ (NH<NUM>)<NUM>CO<NUM> + H<NUM>O     (<NUM>).

(NH<NUM>)<NUM>CO<NUM> + CO<NUM> + H<NUM>O ↔ <NUM> NH<NUM>HCO<NUM>     (<NUM>).

<NUM> NH<NUM>HCO<NUM> + <NUM> NaCl ↔ <NUM> NaHCO<NUM> ↓ + <NUM> NH<NUM>Cl     (<NUM>).

Sodium bicarbonate crystals are separated from the mother liquor by filtration, then sodium bicarbonate is decomposed thermally into sodium carbonate, water and carbon dioxide (<NUM>).

CO<NUM> is recovered in the carbonation step (see equations <NUM> and <NUM> above). Mother liquor is treated to recover ammonia. The ammonium chloride filtrate (<NUM>) is reacted with alkali, generally milk of lime (<NUM>), followed by steam stripping to recover free gaseous ammonia:
<CHM>.

NH3 is recycled to the absorption step (see equation <NUM> above). Carbon dioxide and calcium hydroxide originate from limestone calcination (<NUM>) followed by calcium oxide hydration (<NUM>).

Brine (NaCl) has to be treated before the input in the process to remove impurities: calcium and magnesium. If not removed they would react with alkali and carbon dioxide to produce insoluble salts contributing to scale formation inside equipment. Brine purification reactions are described in the following equations:.

Ca<NUM>+ + CO<NUM> <NUM>- → CaCO<NUM> ↓     (<NUM>).

Mg<NUM>+ + <NUM> OH- → Mg(OH)<NUM>↓     (<NUM>).

Sodium carbonate formed (equation <NUM>) is called "light soda ash" because its bulk density is approximately <NUM> t/m3. A subsequent operation called densification enables this value to be doubled by crystallisation into sodium monohydrate, by adding water (equation <NUM>) then followed by drying (equation <NUM>). Final product is "dense soda".

Na<NUM>CO<NUM> + H<NUM>O -------- > Na<NUM>CO<NUM>. H<NUM>O     (<NUM>).

One of the major achievements of the Solvay process is the high efficiency of the ammonia recycle loop. The purpose of this important process "distillation" is to recover ammonia from the ammonium chloride containing mother liquors recovered from the bicarbonate filters/centrifuges. The liquid phase coming out from the distillation unit contains: unreacted sodium chloride (reaction (<NUM>) above is not complete due to thermodynamic and kinetic limitations), calcium chloride resulting from reaction with NH<NUM>Cl, solid matter that is derived primarily from the original limestone and finally, small quantity in excess of lime that can ensure a total decomposition of NH<NUM>Cl. This liquid called "DS-liquid" or "Distiller Blow Off DBO" is usually treated in different ways depending on the particular site and processes used.

It is an object of the present invention to further process the distiller waste for a reasonable purpose.

<CIT> describes a process for removing waste obtained from the production of soda ash for producing lime fertilizers. The process disclosed in <CIT> comprises mechanically processing residual components from the Solvay process and mixing them with additional components such as gypsum.

<CIT> describes a process for the production of granulated lime containing fertilizers form waste products.

<CIT> discloses the nitrogen fertilizer on the basis of lime nitrogen.

<CIT> discloses a process for further using waste products from the Solvay process for producing a lime fertilizer.

<CIT> discloses a process for conditioning a lime containing slurry, which comprises drying the slurry in a fluidized bed apparatus.

<CIT> discloses the use of a lime slurry from soda ash production for preparing a composition comprising micro-nutrients.

<CIT> also discloses the production of a fertilizer from waste lime sludge.

The inventors of this application found that a lime fertilizer with advantageous properties can be prepared by desalting the distiller waste from soda ash production, and then mixing the desalted composition with lime pieces and lime powder obtained from soda ash production.

The present invention therefore relates to.

Furthermore, the present invention relates to the use of the dry granule obtained by the process according to the invention as lime fertilizer, wherein said dry granule comprises at least <NUM> wt. % of the lime expressed as Ca(OH)<NUM>, and ha a moisture content of from <NUM> to <NUM> wt. % and has a particle size distribution characterized by a d<NUM> value of from <NUM> to <NUM>.

The present invention is directed at a process for the production of a lime fertilizer from by-products obtained during the Solvay process for the production of soda ash. The process of the present invention comprises the uses of three components, lime slurry, lime powder and lime pieces. The process of the invention comprises the following steps:.

wherein the lime slurry provided in step (a) comprises distiller waste resulting from the ammonia regeneration step in a process for producing soda ash according to the Solvay process, and the lime slurry provided in step (a) is made of solid matter suspended in aqueous solution. The solid matter comprises:.

and so that the sum of above solid components is <NUM> wt.

More preferably, the solids comprise at least <NUM>, or at least <NUM>, or at least <NUM>, at least <NUM> wt. %, at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. % of Ca(OH)<NUM>. It is further preferred that the solids comprise at most <NUM>, or at most <NUM>, or at most <NUM> wt. % of Ca(OH)<NUM>. In other embodiments, the solids comprise from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM> wt. % of Ca(OH)<NUM>.

In further preferred embodiments, the solids comprise at least <NUM>, or at least <NUM>, or at least <NUM> wt. % of CaCO<NUM>. In another embodiment, the solids comprise at most <NUM>, or at most <NUM>, or at most <NUM> wt. % of CaCO<NUM>. In other embodiments, the solids comprise from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM> wt. % of CaCO<NUM>.

Preferably, the amount of CaSO<NUM> in the solids is at least <NUM>, or at least <NUM>, or at least <NUM> wt. In another embodiment, the amount of CaSO<NUM> in the solids is at most <NUM>, or at most <NUM> wt. In other embodiments, the amount of CaSO<NUM> in the solids ranges from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM> wt. % expressed as weight of CaSO<NUM> reported to the total weight of the solid. The CaSO<NUM> mineral present in the solid is generally either anhydrous calcium sulfate (CaSO<NUM>), or hydrated calcium sulfate species such as: calcium sulfate hemihydrate (CaSO<NUM>. <NUM><NUM>O), or calcium sulfate dihydrate (CaSO<NUM>. <NUM><NUM>O).

Preferably, the solid matter comprises at least <NUM> wt. % of CaCl<NUM> and at most <NUM> wt. %, preferably at most <NUM> wt. %, more preferably at most <NUM> wt. %, even more preferably at most <NUM> wt. % of CaCl<NUM>.

The amount of calcium chloride in the solids is typically in the range from about <NUM> wt. % to about <NUM> wt.

The solids typically comprise other minerals, such as silica, clays, iron silicate, aluminum silicate, ettringite and combinations thereof.

The amount of these other minerals comprising silica is at most <NUM> wt. %, preferably at most <NUM> wt. %, most preferably at most <NUM> wt.

The solid matter suspended in the aqueous solution preferably has a particles size distribution characterized by a d<NUM> value of at most <NUM>. More preferably, the d<NUM> value is at most <NUM>, most preferably, the d<NUM> value is at most <NUM>.

The d<NUM> value can be determined as known in the art, for example according to the standard techniques defined in ISO <NUM>:<NUM>.

The lime slurry used in the process of the invention is typically washed at least once with water in order to at least partially remove salts from the lime slurry. This can be done by using a decanter, known to one of ordinary skill. Alternatively, the washing and desalting can be carried out in a mixer or reactor, by adding water, mixing, and removing the liquid or supernatant. If this is repeated several times an effective depletion of salts is achieved. The washing step can be carried out at least once, or at least twice, or at least three times, or at least four times, or at least five times. The washing step may be carried out <NUM> to <NUM> times, or <NUM> to <NUM> times, or <NUM> to <NUM> times, or <NUM> to <NUM> times, e.g. <NUM>, <NUM> or <NUM>-times. Typically, the washing step is carried out until the concentration of chlorides (mainly in calcium chloride and sodium chloride species) in the solids of the lime slurry is less than <NUM>%, or less than <NUM>%, or less than <NUM>%, or less than <NUM>%, or less than <NUM>%, or less than <NUM>%. Preferably, the washing step is carried out until the concentration of chlorides in the solids of the lime slurry is less than <NUM> wt. %, more preferably less than <NUM> wt. %, even more preferably less than <NUM> wt. Indeed, for agriculture fertilizer to be polyvalent to main crop species, the above limited amounts chlorides (as for instance sodium chloride or calcium chloride species) are particularly preferred.

The solid content of the lime slurry after the desalting step is typically from <NUM> to <NUM> wt.

In one embodiment of the invention, the lime powder is added to the salt-depleted lime slurry in the next step. The lime powder is usually obtained from the de-dusting during lime grinding in the Solvay process. The lime powder has a particle size distribution characterized by the d<NUM> value ranging from about <NUM> to <NUM>. The lime powder preferably has a residual moisture of less than <NUM> wt. %, more preferably of less than <NUM> wt. %, most preferably of less than <NUM> wt.

In an alternative embodiment, lime pieces are added to the salt-depleted lime slurry. The lime pieces are usually obtained from the lime grinding, which takes place before production of milk of lime in the Solvay process. The lime pieces have a particle size distribution characterized by a d<NUM> value ranging from about <NUM> to <NUM>.

In a preferred embodiment, both lime powder and lime pieces are added to the salt-depleted lime slurry. The lime powder and the lime pieces can be added to the salt depleted lime slurry simultaneously or sequentially. The order of the addition is not particularly limited. Though, when no lime pieces is added (ie only lime powder is added to lime slurry) the granulation stage is quite more longer and more-over size distribution of the granules is quite more spread than when lime pieces are also added.

Preferably, the weight ratio of the lime pieces to the lime powder added at step (c) to obtain the wet mass is at least <NUM>:<NUM> and at mot <NUM>:<NUM>, more preferably at least <NUM>:<NUM> and at most <NUM>:<NUM>.

Furthermore, it is preferred that the weight ratio of aqueous lime slurry to the sum of lime pieces and lime powder is at least <NUM>:<NUM> and at most <NUM>:<NUM>.

In a preferred embodiment at steps (c) or (d) the weight ranges.

After addition of the lime powder and the lime pieces, the composition is usually mixed to obtain a wet mass. The mixing can be carried out in a mixer or reactor device, e.g. a reactor of the company Lödige. In a particular embodiment, water is added before, during, or after the mixing. The wet granule obtained after the mixing usually has a water content of at least <NUM> wt. %, or at least <NUM> wt. Water is added if this is necessary in order to achieve the minimum water content of the resulting wet granule.

In other embodiments, the wet granule obtained in step (d) has a water content of at most <NUM> wt. %, or at most <NUM> wt. %, or at most <NUM> wt. In other embodiments, the wet granule obtained in step (d) has a water content ranging from <NUM> wt. % to <NUM> wt. %, or from <NUM> wt. % to <NUM> wt. %, or from <NUM> wt. % to <NUM> wt.

The wet granule is then subjected to a drying step in order to obtain a dry granule. The drying can be carried out by exposing the wet granule to air. It is also possible to accelerate the drying by applying heat to the wet granule. Preferably, the drying is carried out in a fluidized bed device. Such devices are known to the skilled person.

The dry granule has a water content ranging from about <NUM> to about <NUM> wt. Preferably, the water content of the dry granule is from <NUM> to <NUM> wt. %, or from <NUM> to <NUM> wt.

The dry granule has a particle size distribution characterized by a d<NUM> value from about <NUM> to about <NUM>.

The lime fertilizer obtainable by a process described herein comprises at least <NUM> wt. % of lime expressed as calcium hydroxide. Preferably, the lime fertilizer comprises at least <NUM> wt. %, or at least <NUM> wt. %, or at least <NUM> wt. % of lime expressed as calcium hydroxide.

A further aspect of the invention is the use of the dry granule obtained in the process of the invention as lime fertilizer, wherein said dry granule comprises at least <NUM> wt. % of the lime expressed as Ca(OH)<NUM>, and has a moisture content of from <NUM> to <NUM> wt. % and has a particle size distribution characterized by a d<NUM> value of from <NUM> to <NUM>.

Lime slurry with calcium chloride from the soda ash production was washed four times to reduce the concentration of CaCl<NUM> to less than <NUM> wt. Thereafter the suspension has been dewatered in a centrifuge to a lime slurry (mud) with about <NUM>% dry matter.

The washed and dewatered lime slurry, lime pieces and lime powder, all obtained as by-products from a plant for the production of soda ash according to the Solvay process, were used to prepare lime granules. The lime slurry was introduced into a laboratory ploughshare mixer LM <NUM> and washed four times with water. Lime pieces and lime powder were added to the salt-depleted slurry, mixed and granulated. The obtained granules had an average particle size ranging from <NUM> to <NUM>.

After this lab-scale production had been successfully completed, an upscaled format was carried out using industrial equipment, as described in Example <NUM>.

It should be shown in this experiment that <NUM> tons of granulate can be produced by the method of the invention. Accordingly, it should be demonstrated that this process can be carried out at an industrial scale.

The following by-products from soda ash production were used:.

The lime pieces were obtained from Solvay Chemicals at the plant in Bernburg, Germany. They were sieved with a sieving machine (mesh size <NUM>). The moisture content of the sieved granules was <NUM> wt. The particle size distribution after sieving was characterized by d<NUM> values in the range from <NUM> to <NUM>.

The lime powder was also obtained from Solvay Chemicals in Bernburg and was provided in flexible intermediate bulk containers, referred to as "BigBags" hereinafter. The moisture content of the lime powder was in the range from <NUM> to <NUM> wt. The particles size distribution was characterized by d<NUM> value in the range from <NUM> to <NUM>.

The lime slurry was first subjected to a washing step and a concentration step. The washing was carried out in order to remove the salt in the lime slurry, particularly the calcium chloride. To do so, the plough share mixer FKM <NUM> D of the company Lödige Maschinenbau GmbH was used. The lime slurry was transferred into the mixer, water was added and the liquid phase was then removed using the decanter CA <NUM>-<NUM>-<NUM> obtained from GEA Westfalia Separator Group in the Technikum Oelde. The lime slurry has been pumped from the mixer to the decanter with a defined quantity. This decanter was equipped with a standard screw and a regulating disk <NUM>. The feeding tube had a length of <NUM>. The decanter was operated with a drum speed of <NUM>,<NUM>-<NUM> and a screw speed of <NUM> to <NUM>-<NUM>. An acceptable result was obtained at a throughput of about <NUM> liter/h. The clear phase at this throughput rate had a solid content of <NUM>/liter. The clear phase was discarded and the slurry was packaged into barrels, in order to carry out the granulation experiments. The drying loss of the washed and concentrated slurry (average value from <NUM> samples) was as follows.

As mentioned above, slurry from the deposition pond ("Haldenschlamm" or "Kalkteich") was used as an alternative source for the lime slurry. This slurry was also provided by Solvay Chemicals Bernburg. It was taken from the upper layers of the deposits after a natural dewatering. The residual moisture was <NUM> wt. %, corresponding to a solid content of <NUM> wt.

The mixing and granulation of the above mentioned components was carried out batch-wise in the Lödige ploughshare mixer FKM <NUM>. For each batch the following amounts were put into the mixer:.

The components were mixed at a speed of <NUM>-<NUM>. The blades were operated at a speed of <NUM>,<NUM>-<NUM>. After the mixing, the produced granulate was taken from the mixer and air-dried on the floor of a hall.

In a particular experiment, only two components were used, namely lime slurry and lime powder.

The total amounts of the components and produced granulates were as follows:.

Up to <NUM> batches per day were produced. Assuming an average moisture content of <NUM> %, the theoretical dry mass of the produced granulates would be <NUM>,<NUM>.

The produced granulates were air dried and then filled into BigBags. The total mass of the BigBags measured after filling was <NUM>,<NUM>.

The residual moisture of the wet granulates obtained from the mixture was about <NUM> to <NUM> wt. The average moisture content of the air-dried granulates was about <NUM> wt. %, the individual batches ranged from about <NUM> to about <NUM> wt.

The particle size distribution of the granulates yielded a d<NUM> value of about <NUM>. The sphericity SPHT3 of the dried granulates was at least <NUM>, i.e. the form of the particles was close to sphericity. When commercially producing the granulate, the drying in a fluidized bed would appear more suitable. This would allow further reducing the residual moisture of the dried granulates close to <NUM> % water.

The lime granulates obtained from different batches were analyzed after drying, and the following results were obtained:.

The experiments carried out demonstrate that the waste components obtained during the Solvay process for the production of soda ash can be used for producing granulates with properties which make them easy to store and handle. In particular, the particle size and the moistures obtained ensure good flowability and transportability when residual moisture is between <NUM> and <NUM> wt. When moisture is above <NUM> wt. % the granules are sticky. As this behavior is sensitively improved with a residual moisture of at most <NUM> wt. %, and preferably when at most <NUM> wt. % it is recommended to dry the product to less than <NUM> , preferably less than <NUM> wt. % residual moisture (water).

Though a too intensive-drying (below <NUM> wt% residual moisture) of the granules, leads to a strong dusting behavior when granules are handled, transported and spread. Therefore advantageously said residual moisture (ie water content) should be in the range from <NUM> to <NUM> wt. %, preferably from <NUM> to <NUM> wt. %, and more preferably from <NUM> to <NUM> wt. %, or from <NUM> to <NUM> wt.

Chemical analysis showed that the granule contains valuable micro-nutrients (see tables <NUM> to <NUM>). As a consequence, the granule can be used as a lime fertilizer. After initial experiments had shown the general feasibility of this approach, it was further shown that also the production of <NUM> tons of granules can be performed.

The granule obtained in example <NUM> was distributed on soil. The area was categorized into five different sections, which were applied with <NUM>, <NUM>, <NUM>, <NUM> and <NUM> tons of lime fertilizer per hectar, respectively. The application of the lime fertilizer did not adversely affect the pH value of the soil. Further, the use of the lime fertilizer did not negatively affect the growth of the corn.

It was therefore concluded that the granule is useful as a lime fertilizer in agricultural applications.

The production of the lime fertilizer was based on the by-products lime slurry, cyclone dust (lime powder) and lime pieces (unburned limestone grid). A ratio of <NUM>/<NUM>/<NUM> mass% was chosen for the large scale test.

In order to produce a homogeneous blend the individual components were stacked layer by layer with an excavator or wheel loader. After that the material of this storage was dug off with a crusher bucket for excavator or loader. The lime components were mixed and crushed during the transport through the bucket (see <FIG>). Particles/granules of undefined size were obtained which can be passed through a sieve with the desired grain size. A temporary storage is possible or the screening can be done directly after the treatment with the crusher bucket. During the large scale test a double screen-deck was used with a screen cut of <NUM>.

The lime fertilizer was analyzed in a laboratory and had the following composition:.

Claim 1:
A process for the production of a lime fertilizer, comprising
(a) providing an aqueous lime slurry comprising calcium chloride,
(b) depleting salts in said lime slurry comprising calcium chloride so as to obtain a salt-depleted lime slurry,
(c) adding lime powder and lime pieces to the salt-depleted lime slurry to obtain a wet mass and optionally adding water, wherein the lime powder has a particle size distribution characterized by a d<NUM> value of from <NUM> to <NUM>, and the lime pieces have a particle size distribution characterized by a d<NUM> value of from <NUM> to <NUM>,
(d) mixing and granulating the wet mass to obtain a wet granule, and
(e) drying the wet granule to obtain a dry granule with a moisture content of from <NUM> to <NUM> wt.-% and with a particle size distribution characterized by a d<NUM> value of from <NUM> to <NUM>,
and wherein said lime slurry provided in step (a) comprises distiller waste resulting from the ammonia regeneration step in a process for producing soda ash according to the Solvay process, and the lime slurry is made of solid matter suspended in an aqueous solution, and said solid matter comprises:
- at least <NUM> and at most <NUM> wt.% lime expressed as Ca(OH)<NUM>,
- at least <NUM> and at most <NUM> wt.% calcium carbonate expressed as CaCO<NUM>,
- at least <NUM> and at most <NUM> wt.% calcium sulfate expressed as CaSO<NUM>,
- at most <NUM> wt.% magnesium hydroxide expressed as Mg(OH)<NUM>,
- at most <NUM> wt.%, preferably at most <NUM> wt.% or at most <NUM> wt.% of other minerals comprising silica, such as: silica, clays, iron silicate, aluminum silicate, or ettringite, and mixtures thereof,
and so that the sum of above solids components is <NUM> wt.%.