NL2009295C2

NL2009295C2 - Method for manufacturing granules from a liquid.

Info

Publication number: NL2009295C2
Application number: NL2009295A
Authority: NL
Inventors: Wei Wang; Mengguang Wang
Original assignee: Green Granulation Technology Ltd
Priority date: 2012-08-08
Filing date: 2012-08-08
Publication date: 2014-02-11
Also published as: CN103664240A; CN103664240B

Abstract

The invention relates to a method for producing a such as urea or method of ammonium nitrate particle, reducing submicron powder to the water. Method of the invention comprises the preparation scrubbers, gas supply is used as out from the granulator to the first wash, wherein a on the first gas desulfuration material flow, wherein supplied to the third wash, wherein the working temperature of the wash the the first wash. A preferably of the solution, the method comprising each of cycles the material.

Description

NL 17745-Hs/an

METHOD FOR MANUFACTURING GRANULES FROM A LIQUID

The present invention pertains to a method for manufacturing granules from a liquid through a granulation process. Granulation processes are known in the art, and are often applied for the manufacture of, e.g., fertilizers. A S. problem in the manufacture of granules from a liquid of a source material, in particular a fertilizer, is that all fertilizer granulations produce an amount of dust in the granulator and in the coolers. The dust is entrained by the air that the exhaust fan is sucking through the granulator 10 and coolers. That entrained dust has to be removed from the air before the air can be vented back into the atmosphere.

The recovered dust will be recycled back into the process.

Many types of scrubbers have been developed for removing 15 entrained dust from the air, depending on the particle size of the generated dust and on the requested efficiency of the dust removal. There are basically two types of scrubbers, namely dry scrubbers and wet scrubbers. Dry scrubbers include dust removers like cyclones or filters. They work well for 20 coarse dust particles and have the advantage that they recover the dust as a solid product that can be recycled at low energy cost. Their disadvantages are sensitivity to plugging up (especially when humid air has to be scrubbed) and the low efficiency in removing fine dust particles 25 (unless extreme pressure drops over the dust removers and consequently high power consumptions are used). Wet scrubbers dissolve or suspend the dust in water and recover the dust as a low concentration solution or suspension in water. The wet scrubbers come in different types, they are mostly very reliable and are able to remove fine dust particles without increasing tremendously the pressure drop over the scrubber. An issue with wet scrubbers is that most of the water or even 5 all of the water must be removed from the solution or suspension before the recovered dust can be recycled again into the process. The water is mostly removed in a vacuum concentrator; this process consumes at least the same amount of steam as the amount of water that is removed. For this 10 reason it is important that the water content of the recovered solution or suspension is as low as possible.

The dust generated in a granulator is a mixture of coarse particles (0.1 min or even more produced by the 15 crushers) and fine particles (in the 10-50 micron range produced by the sprayers). In some cases like urea or ammonium nitrate granulation, the granulators can also produce an amount of sub-micron dust, i.e. dust with a particle size below 1 micron, more specifically below 0.5 20 micron. Such extremely fine dust is not generated by mechanical items like crushers or sprayers but is produced by reactions between gases present in the air.

For example, in the case of granulation of ammonium nitrate, the ammonium nitrate melt contains an amount of dissolved 25 free ammonia and free nitric acid. When the hot melt comes in contact with air ammonia and acid evaporate from the melt and are entrained by the air, they will recombine later into extremely fine particles when the air stream is cooled.

For urea, extremely fine particles may be formed as follows: 30 at high temperature, e.g., in the range of 120-140°C, urea 3 will partially convert into ammonium cyanate (equilibrium concentration, depending on the temperature in the range of 0-1 wt. %) . At the stated temperature, ammonium cyanate may split into ammonium and cyanuric acid, which may evaporate.

5 Upon a decrease in temperature, the ammonium and cyanuric acid will combine to form very fine particles of ammonium cyanate, which will in turn be converted to urea.

The sub-micron particles are visible in the exhaust air stream as turbidity (after dissipation of the water vapor in 10 case of a wet scrubber). They are too fine to be caught on any mechanical filter or droplet catcher. Some are so fine that they even escape the standard dust sampling methods because those methods do not consider that particle size as "particulate matter" any more. Nevertheless, submicron dust 15 is a pollutant and a loss of product for the process. There is therefore need for a granulation process wherein submicron dust is removed at least in part. Such process should be flexible and energy-efficient.

20 The present invention provides a method for manufacturing granules from a liquid solution of a source material which solves these problems. The process according to the invention enables the manufacture of granules in an effective, energy-efficient, and flexible way, while reducing 25 the amount of submicron dust that is evicted to the atmosphere.

The present invention pertains to a method for manufacturing granules, comprising the steps of 4 • providing a liquid comprising source material to a granulator, • withdrawing solid granules from the granulator and providing them to a granulate cooler, ,§: · withdrawing cooled granules from the granulate cooler, • withdrawing a first dust-containing gas from the granulator, and providing it to a first scrubber, and in the first scrubber contacting the dust-containing gas with an aqueous liquid, resulting in the formation of a first 10 purified gas stream and a first aqueous liquid containing source material, and withdrawing the first purified gas stream from the first scrubber, and withdrawing the first aqueous liquid containing source material from the first scrubber, 15 · withdrawing a second dust-containing gas from the granulate cooler, and providing it to a second scrubber, and in the second scrubber contacting the dust-containing gas with an aqueous liquid, resulting in the formation of a second purified gas stream and a second aqueous liquid 2 0 containing source material, and withdrawing the second purified gas stream from the second scrubber, and withdrawing the second aqueous liquid containing source material from the second scrubber, • providing the first purified gas stream from the first 25 scrubber to a third scrubber, and in the third scrubber contacting the first purified gas stream with an aqueous liquid, resulting in the formation of a third purified gas stream and a third aqueous liquid containing source material, and withdrawing the third purified gas stream from the third 5 scrubber, and withdrawing the third aqueous liquid containing source material from the third scrubber, wherein the operating temperature of the third scrubber is below the operating temperature of the first scrubber.

5 A feature of the process according to the invention is that by applying the specified scrubber regimen, the concentration of source material in the final gas stream will be very low. This is because the process according to the 10 invention is equipped to address all dust fractions, including the submicron dust which often passes through conventional processes. Other advantages of the process according to the invention will become clear from the further specification.

15

The present invention is suitable for processing any source material which is converted into particles in a granulating process which is accompanied by dust formation, in particular by the formation of dust which contains a 20 fraction with a particle size in the submicron range.

Examples of suitable source materials are fertilizers, in particular urea and ammonium nitrate.

In the first step of the present invention a liquid 25 comprising of source material is provided to a granulator where granules are formed. Granulators are known in the art, and require no further elucidation. The liquid provided to the granulator generally is as highly concentrated as possible, i.e., it contains as much source material as 30 possible, and as little other material as possible. It may 6 sometimes also be indicated as a melt. For example, for urea, the liquid may comprises 85-97 wt. % of urea, and water, in particular 93-97 wt. %. For another example, for ammonium nitrate, the liquid may comprises 90-99 wt. % of ammonium 5 nitrate, and water, in particular 94-99 wt. %.

The liquid may optionally contain particles of solid material, as long as they do not interfere with the processing conditions. It is within the scope of the skilled person to determine an optimum concentration.

10

The solid granules formed in the granulator are withdrawn from the granulator and provided to a granulate cooler, where they are contacted with a cooling air stream. The cooled granules are removed from the granulator and processed as 15 required. These steps are known in the art and require no further elucidation.

Ά dust-containing gas is withdrawn from the granulator, and provided to a first scrubber. This air stream is coming 20 from the section of the granulator where the liquid comprising source material is sprayed to form granules. The gas stream generally has a temperature of at least 90°C. As a maximum, a value of 140°C may be mentioned.

For urea it is preferred for the gas stream to have a 25 temperature in the range of 90-120°C. For ammonium nitrate it is preferred for the gas stream to have a temperature in the range of 100-140°C, more in particular 125-130°C.

The gas stream withdrawn from the granulator contains a 30 substantial amount of dust, with varying particle sizes. The 7 gas stream contains coarse dust particles generated, e.g., by the crushers, and fine dust particles, generated by, e.g., the sprayers. The invention is particularly suitable for granulation processes where the hot gas stream also contains 5 components that will upon cooling generate submicron dust.

For urea granulation, the amount of submicron dust may, e.g., be in the range of 0.05-1 wt. % of the total urea processed, more in particular in the range of 0.2-0.8 wt. %.

10 Within the context of the present specification, coarse dust consists of particles with an average particle size of at least 0.05 mm, in particular at least 0.1 mm. The average particle size of coarse dust the average particle size generally is below 1 mm, more in particular below 0.8 mm.

15 Fine dust within the context of the present specification is dust with an average particle size in the range of 10-50 micron.

Submicron dust within the context of the present specification is dust with an average particle size below 1 20 micron. In general, the submicron dust has an average particle size in the range of 100 nm to 1 micron, in particular below 0.5 micron. In one embodiment all submicron dust passes through a 0.4 micron dust filter, implying a maximum particle diameter below 0.4 micron.

25 Not wishing to be bound by theory it is believed that the coarse dust is generated for the most part as granulate or in the crushers, while the fine dust is generated for the most part in the sprayers, and the submicron dust is generated by reaction as described above.

30 δ

In the first scrubber the dust-containing gas obtained from the granulator is contacted with an aqueous liquid, resulting in the formation of a first purified gas stream and a first aqueous liquid containing source material. The first purified gas stream and the first aqueous liquid are withdrawn from, the first scrubber.

The first aqueous liquid may be processed as desired. In one embodiment it is recycled in its entirety or in part to the granulation step. Depending on the concentration of the first 10 aqueous liquid, it may be subjected to a concentration step. The concentration of the aqueous solution is determined by the amount of dust, by the amount of liquid contacted with the dust-containing gas stream, and by the concentration of source material in the aqueous liquid provided to the 15 scrubber. It is within the scope of the skilled person to regulate the process condition in the first scrubber.

It is preferred for the first aqueous liquid to have a concentration of source material of at least 35 wt. %. For urea, the concentration is, e.g., in the range of 40-60 wt.%, 20 preferably 45-55 wt, % . For ammonium nitrate the concentration is, e.g. in the range of 40-70 wt.%, in particular 50-70 wt.%.

In one embodiment of the invention it is preferred for the first scrubber to use a relatively large amount of liquid 25 per kg of air, e.g., in the range of at least 0.8 kg liquid per kg air, more in particular at least 1 kg liquid per kg air. This is relatively high as compared to conventional scrubbers, which use an amount of liquid of about 0.3 kg liquid per kg air. The reason behind the preference for a 30 scrubber using a large amount of water per kg air is that it 9 will lead to a relatively high amount of water in the resulting first purified gas stream, and this improves the operating efficiency of the third scrubber, which is used to purify the gas stream from the first scrubber. The maximum I amount of liquid is not critical to this embodiment of the present invention. For reasons of operating efficiency a value of at most 4 kg liquid per kg air may be applied.

In one embodiment, the dust loaded air enters the scrubber from the top, with sprayers being installed in the incoming 10 air duct that spray the scrubber liquid into the air. It is preferred for the sprayers to be installed in such a way that all the incoming air will be properly wetted. Preferably, the sprayers are pointing downwards in order to recover part of the pump energy and save energy in the exhaust fan. During 15 the spraying process water will evaporate from the scrubber liquid to the point that the water content of the air stream will be close to the saturation point of air stream at that respective temperature, in equilibrium with the partial water vapor pressure of the scrubber liquid that has been sprayed. 20 Air and scrubber liquid will be at the same temperature after the sprayers .

It has been found that the use of a large amount of liquid per kg air leads to advantages. In one embodiment of the invention a recycle step is operated over the granulator 25 scrubber, wherein liquid containing source material is withdrawn from the bottom of the scrubber and recycled back into the air stream of the scrubber. In this process the granulator scrubber can operate at a much higher concentration of the recovered solution than conventional wet 30 scrubbers, where less liquid per kg air is used. The amount 10 of recycled solution that is sprayed in the incoming air duct is so large, that the evaporation of water from this solution during the spraying will only slightly increase the concentration of the solution/suspension (less than 1% 5 increase, typically 0,5%). In conventional granulator scrubbers the surge in concentration during similar spraying in the air inlet of the scrubber can locally be as much as 10 to 15 times higher, so these scrubbers must operate at lower (safer) source material concentrations in the recovered 10 solution/suspension. For this reason, in this embodiment of the invention operation of this scrubber remains reliable at concentrations very close to salting out concentration of the recovered source material solution/suspension.

15 The first scrubber preferably has the high liquid stream described above. The second scrubber, which scrubs the air from the granulator cooler, and the third scrubber, which scrubs the purified gas stream from the granulator scrubber, may or may not have the above configuration.

20

If so desired, droplet catchers can be installed in the scrubbers at the location where the purified gas is removed from the scrubber. This is of particular relevance in the third scrubber and the second scrubber, where the air that is 25 withdrawn may be vented to the atmosphere. It may also be attractive to install a droplet catcher in the first scrubber, to prevent needless transport of source material from the first scrubber to the third scrubber.

11

It is a feature of the present invention that the third scrubber, which processes the gaseous effluent from the first scrubber is operated at a lower temperature than the first scrubber. In this way, water present in the gas stream 5 entering the third scrubber will condense in the third scrubber. The particles of submicron dust will act as condensation cores, resulting in an increase in particle size, allowing catching of the submicron dust.

The process of catching the submicron dust can be improved, 10 by increasing the condensation of water in the third scrubber. This can be done in various ways.

A first way is to ensure that the water concentration in the gas stream provided to the scrubber is as high as possible. This can be done, e.g., by using a scrubber with a high 15 liquid to air ratio, as described above.

A further way is to increase the difference between the operating temperature of the first scrubber (i.e. the gas temperature from the first scrubber) and the operating temperature from the third scrubber. The larger this 20 temperature difference, the more water will condensate onto the submicron dust particles. In one embodiment, the difference between the operating temperature of the first scrubber and that of the third scrubber is at least 5°C, in particular at least 8°C, more in particular between 8 and 25 10°C.

A further way to increase the condensation of water in the third scrubber is the provision of stream to the gas stream before it enters the third scrubber to increase the degree of saturation with water of the gas stream. The steam will 12 condense on the particles of submicron dust present in the system, resulting in the formation of droplets.

In the third scrubber water will thus condense on the submicron dust particles. The submicron dust particles S dissolve in the condensate. This will further cool the droplet and the solution will pick up more moisture until a concentration is obtained that is in equilibrium with the humidity of the air at this temperature. This process will increase the size of the particles/droplets and makes them 10 easier to catch. In one embodiment a suitable demister pad is installed to catch these droplets. The demister pad may be applied in the air stream after the liquid sprayers.

The efficacy of the process according to the invention 15 can be increased by the application of various recycle streams .

In one embodiment, the aqueous liquid provided to the first scrubber and/or the aqueous liquid provided to the 20 second scrubber and/or the aqueous liquid provided to the third scrubber comprises source material. More specifically, in one embodiment the aqueous liquid provided to the first scrubber consists at least in part of aqueous liquid containing source material withdrawn from the second 25 scrubber. Additionally or alternatively it is preferred for the aqueous liquid provided to the third scrubber to consist at least in part of aqueous liquid containing source material withdrawn from the second scrubber. Additionally or alternatively, at least part of the aqueous liquid withdrawn 30 from the third scrubber is provided to the second scrubber.

13

In one embodiment, the process is carried out in such a manner that fresh water is added to the second scrubber, that the liquid provided to the first scrubber and the third scrubber consists for at least 50 vol. % of aqueous liquids 5 which are recycle streams, in particular for at least 70%, more in particular for at least 90%. In one embodiment, the liquid provided to the first scrubber and the third scrubber consists essentially of recycle streams, with all the water that evaporates from the system or is otherwise removed from 10 the system being compensated by adding fresh clean makeup water to the second (cooler) scrubber.

In one embodiment, the first scrubber and/or the second scrubber and/or the third scrubber are equipped with recycle 15 loops wherein liquid effluent is withdrawn from the bottom of the scrubber and provided to the top of the scrubber. As indicated above, and as will also be discussed in more detail below, liquid may also be provided to the other scrubbers.

The provision of a recycle stream over the scrubber is 20 particularly advantageous where a high liquid to air ratio in the scrubbers is desired, in particular in the first scrubber, as discussed above. In one embodiment the recycle stream in the first scrubber is so high that the ratio of the volume of the recycle stream to the volume of liquid added to 25 the first scrubber is at least 5:1, in particular at least 7:1.

In one embodiment, effluent withdrawn from the first scrubber is recycled to the granulation step, if necessary with an intermediate evaporation step. In general, an evaporation 30 section will be applied wherein most of the water will be 14 evaporated. This evaporation will consume steam so it is important to find a good balance between low steam consumption and reliable operation (no crystallization of the recovered scrubber solution/suspension).

;i

As indicated above, it is a key feature of the present invention that the operating temperature of the third scrubber is below that of the first scrubber, to allow catching of submicron dust. It has been found that this can 10 be ensured relatively easily by using liquid derived from the second scrubber as feed for the third scrubber. The second scrubber, which scrubs the gas from the cooler section, generally has an operating temperature which is below that of the third scrubber. This means that the liquid derived from 15 the second scrubber can be used in the third scrubber to cool the gas stream to the third scrubber to ensure condensation therein. Another attractive feature is to feed liquid derived from the third scrubber to the second scrubber, where it is cooled again. By applying this combined recycle of cooler 20 liquid from the second scrubber to the third scrubber, and hotter liquid from the third scrubber to the second scrubber, an energy efficient recycle loop is set up.

In one embodiment, the first scrubber, which scrubs the 25 gas from the granulator, has an operating temperature in the range of 40-50°C, while the second scrubber, which scrubs the gas from the granulate cooler, has an operating temperature in the range of 25-40°C, in particular 30-35°C, with the third scrubber, which scrubs the gas from the first scrubber 30 is operated at a temperature between that of the first 15 scrubber and the second scrubber, e.g., in the range of 35-45°C, in particular 35-40°C.

The operating temperature of a scrubber is a balance 5 between the temperature and amount of the ingoing gas, the temperature and amount of the ingoing liquid, and the temperature and amount of the recycle liquid. It is within the scope of the skilled person to regulate the various amounts and temperatures to ensure that the desired operating 10 temperature is obtained. If so desired, intermediate heating or cooling of gas or liquid streams may be applied if desired.

In one embodiment, of the present invention, the source 15 material is urea. In this embodiment the dust-containing gas provided to the first scrubber preferably has a temperature in the range of 100-120°C, and comprises coarse urea dust with an average particle size of at least 0.05 mm, in particular at least 0.1 mm, and fine urea dust with an 20 average particle size below 50 micron. The aqueous liquid provided to the first scrubber has a temperature in the range of 40-50°C, and the temperature of the first aqueous liquid containing urea and the purified air is in the range of 40-50°C .

25 It is preferred for the aqueous liquid containing urea produced in the first scrubber to have an urea concentration in the range of 35-55 wt. %.

In one embodiment the dust-containing gas provided to the second scrubber has a temperature in the range of 60-90°C, 30 and the aqueous liquid provided to the second scrubber has a 16 temperature in the range of 25-40°C, and the temperature of the second aqueous liquid containing urea and the purified air is in the range of 25-40°C. It is preferred for the aqueous liquid containing urea produced in the second S scrubber to have an urea concentration in the range of 1-20 wt.%. Preferably, the effluent gas stream from the first scrubber with a temperature of 40-50°C is provided to the third scrubber to be combined with an aqueous liquid with a temperature in the range of 20-45°C, in particular 25-40°C.

10

In another embodiment, the source material is ammonium nitrate. In this case the dust-containing gas provided to the first scrubber preferably has a temperature in the range of 100-140°C, and comprises coarse ammonium nitrate dust with an 15 average particle size of at least 0.05 mm, in particular at least 0.1 mm, and fine ammonium nitrate dust with an average particle size below 50 micron. The aqueous liquid provided to the first scrubber preferably has a temperature in the range of 40-50°C, and the temperature of the first aqueous liquid 20 containing ammonium nitrate and the purified air is in the range of 40-50°C. In one embodiment, the aqueous liquid containing ammonium nitrate produced in the first scrubber has an ammonium nitrate concentration in the range of 40-70 wt.%. In one embodiment the dust-containing gas provided to 25 the second scrubber has a temperature in the range of 60- 90°C, and the aqueous liquid provided to the second scrubber has a temperature in the range of 25-40°C, and the temperature of the second aqueous liquid containing ammonium nitrate and the purified air is in the range of 25-40°C. It 30 is preferred for the aqueous liquid containing ammonium 17 nitrate produced in the second scrubber has an ammonium nitrate concentration in the range 1-20 wt. %. It is preferred for the effluent gas stream from the first scrubber with a temperature of 40-50°C to be provided to the third scrubber S to be combined with an aqueous liquid with a temperature in the range of 20-45°C, in particular 25-40°C.

In one embodiment, a part of the liquid resulting from the second scrubber which scrubs the gas from the granulate 10 cooler, is provided to the first, granular scrubber. The liquid derived from the second scrubber generally has a relatively low concentration, e.g., less than 10 wt. %, and a relatively low temperature, e.g., in the range of 25-35°C. This lean recovered solution/suspension will be added to the 15 first (granulator) scrubber to dilute and control the concentration of the recovered solution/suspension of that scrubber. Compared to the second (cooler) scrubber, this first granulator scrubber operates at much higher concentration in the recovered solution/suspension (typically 20 at least 45 wt. % depending on the kind of source material). Also the temperature of the air and the recovered solution/suspension is higher after saturation (typically 40 to 50 deg C) The reason for the higher temperature is that the air enters the first scrubber at higher temperature and 25 contains more water than the air entering the second cooler scrubber, as the air provided to the first scrubber contains water that is evaporated from the melt sprayed in the granulator spraying section. In order to guarantee smooth operation of the first (granulator) scrubber, the 30 concentration of the recovered solution/suspension must 18 remain safely below the salting out point of this solution/suspension at this scrubber temperature, and the provision of liquid from the second (cooler) scrubber helps to ensure that this is the case. ψ

The present invention will be elucidated with reference to the drawing without being limited thereto or thereby.

In the drawing the references have the following 10 meaning: L = liquid, used as prefix for liquid stream; S = solid, used as prefix for solid material such as granules, D = dust, used as prefix for dust-containing gas streams.

I granulator 15 2 granulate cooler L3 liquid solution 54 solid granules (hot) 55 solid granules (cooled) 6 ambient air 20 7 ambient air D8 dust-containing gas 9 first scrubber, for scrubbing air from granulator DIO first purified gas from first scrubber II third scrubber, for scrubbing gas derived from the first 25 scrubber D12 purified gas D13 dust-containing gas 14 second scrubber D15 purified gas 30 D16 purified gas to atmosphere 19 L17 water L18 liquid containing source material L19 liquid containing source material L20 liquid containing source material 5 L21 liquid containing source material L22 liquid containing source material L23 liquid containing source material L24 liquid containing source material 10 The liquid material to be granulated (L3) is provided to granulator (1), together with ambient air (6). The liquid material to be granulated is hot. The hot granules (S4) are provided to granulate cooler (2), where they are contained with ambient air ¢7), to result in a cooled material (S5), 15 which is withdrawn from the system.

A dust-containing gas stream (D8) is withdrawn from the granulator. The temperature of the dust-containing gas stream (D8) depends on the granulation conditions. It generally 20 varies between 90°C and 140°C, more in particular between 100°C and 130°C. The dust-containing gas stream is provided to a first scrubber (9), where it is contacted with an aqueous liquid. The aqueous liquid is for the main part recycle liquid from the scrubber itself recycled through 25 lines (L22) and (L23). Liquid effluent from the second scrubber (14), which is a solution containing source material, e.g. urea or ammonium nitrate is provided in a make up stream through line (L21), to compensate for evaporation and removal through (L24). In one embodiment the stream from 20 the second scrubber (L21) makes up 2-10 vol.% of the recycle stream (L23).

The concentration of the source material in stream L21 the solution may vary in wide ranges. In one embodiment it is in 5 the range of 1-20 wt. %, more in particular in the range of Ι-ΙΟ wt.%, still more in particular in the range of 1-5 wt. %.

The temperature in the first scrubber (9) may vary in wide ranges. It is dependent on the gas temperature and on the 10 temperature of the liquid provided to the scrubber. As a general range, a range of 40 to 50°C may be mentioned both for urea and for ammonium nitrate.

From the first scrubber (9} a liquid stream (L22) is withdrawn, which contains source material. The liquid stream 15 generally contains source material in a relatively high concentration, e.g. in a concentration of at least 35 wt.%, more in particular at least 45 wt.%. For urea the liquid stream (L22) contains urea in a concentration of, e.g., 35 to 55 wt.%, in particular of 45 to 55 wt.%. For ammonium 20 nitrate, the concentration in the liquid stream ranges, e.g., from 35 to 70 wt.%, in particular from 40 to 70 wt.%, more in particular from 50 to 70 wt.%.

Part of the liquid stream (L22) may be recycled to the first scrubber (9} through recycle loop (L23). The remaining stream 25 (L24), may be processed as desired. In one embodiment it is recycled in whole or in part to the granulator (1) through combination with stream (L3), whether or not after it has been subjected to one or more concentration steps or further purification steps. In one embodiment the volume of the 21 remaining stream (L24) is quite small, e.g., between 2 and 10 vol. % of recycle stream (L23) .

From the first scrubber (9), a purified gas stream (DIO) 5 is withdrawn, which is provided to a third scrubber (11).

The gas stream derived from the first scrubbed still comprises source material, in particular submicron dust which is formed by reaction of gaseous components in the first scrubber. The reaction conditions applied in the first 10 scrubber are not adequate to remove the submicron dust.

The third scrubber (11) is operated at a temperature below that of the first scrubber (14), so that water present in purified gas stream (DIO) can condensate on the submicron particles present in that stream to increase their particle 15 size and improve the catching thereof. .

The dust-containing gas stream (DIO) generally has the same temperature as the operating temperature of the first scrubber (9), which is 40-S0oC.

20 In the third scrubber (11), the dust-containing gas stream (DIO) is contacted with an aqueous liquid. In the figure, the aqueous liquid is a liquid containing source material (L19), derived from the second scrubber (14). Properties of this liquid will be discussed below. From third 25 scrubber (11), a purified gas stream (D12) is withdrawn, which is which is sufficiently clean to be evacuated to the atmosphere through outlet (16). If so desired intermediate purification equipment, such as an additional demister may be provided in the air stream between the third scrubber (11) 22 and the outlet to the atmosphere (D16), to compensate for faulting apparatus, is present.

From the third scrubber (11) an aqueous liquid 5 containing source material (L20) is withdrawn, which, in the embodiment illustrated in the figure, is provided to second scrubber (14) to act as scrubbing liquid. The aqueous liquid containing source material (L20) has a temperature between that of purified gas stream (DIO) and the liquid (L18) 10 derived from the second scrubber. In one embodiment, the temperature of liquid stream (L20) is in the range of 35-43°C. The concentration of source material present in the liquid (L20) may very between wide ranges, e.g. in the range of 1-20 wt.%, in particular 1-10 wt.%, more in particular 1-5 15 wt.%.

It is interesting to note that the embodiment illustrated in the figure, there is a stream of liquid containing source material (L18, L19) leading from the second scrubber (14) to the third scrubber (11), and a stream of liquid containing 20 source material leading (L20) leading from the third scrubber (11) to the second scrubber (14). The main difference between these streams is that the temperature of the stream (L20) is higher than the temperature of stream (L18, L19). The concentration of source material in the liquid will be in the 25 same range .

From granulate cooler (2), a dust-containing gas (D13) is withdrawn. The dust-containing gas stream (D13) has a temperature which is lower than that of the dust-containing 30 gas (D8) withdrawn from granulator (1). The temperature of 23 dust-containing gas stream D13 generally is in the range of 60 to 90°C, in particular in the range of 70-85°C.

In the second scrubber (14) the dust-containing gas (D13) is contacted with an aqueous liquid. The aqueous liquid can be 5 derived from various sources. In one embodiment, not shown in the figure, liquid withdrawn from the second scrubber is recycled back to the second scrubber. This could, e.g., be a splitoff from line (L19). In one embodiment, the liquid withdrawn from the second scrubber is divided into two 10 fractions, e.g. with a volume ratio in the range of 20:80 to 80:20, more specifically 40:60 to 60:40 wherein one fraction is provided to the third scrubber (11) and the other fraction is provided to the second scrubber (14). In the figure, makeup water is provided to the scrubber through stream 15 (L17), but it may also be provided to the stream (L18). In one embodiment the fresh water feed (L17) makes up between 5 and 10 wt.% of the total liquid provided to the second scrubber (14). In the illustrated embodiment, the amount of fresh water added through L17 is the same as the amount of 20 liquid removed through L24 plus any evaporation from the system. It will be evident to the skilled person that makeup water can also be added at other locations in the system. Liquid to the second scrubber (14) may also be provided from the third scrubber (11). This stream (L20) has a 25 concentration of source material in the same range as stream (LI9) to the first scrubber, but a higher temperature.

The temperature in the second scrubber (14) is determined by the temperature of the dust-containing gas stream, and the temperature of the various liquid streams. The second 30 scrubber (14) is generally operated at a temperature in the 24 range of 25 to 40°C, in particular 30-35°C, both for urea and ammonium nitrate. The second scrubber (14) generates a purified gas stream (D15), which is sufficiently clean to be evacuated to the atmosphere through outlet (16).

5

The liquid (L18) withdrawn from the second scrubber (14) contains source material. In general, this solution is relatively dilute, containing source material in a concentration of, e.g., less than 10 wt.%, e.g. in the range 10 of 1-5 wt.%. The liquid containing source material (L18) generally has a temperature in the range of 25-40°C, in particular 30-35°C.

The liquid containing source material (L18) can be processed in various manners. In one embodiment, not shown on the 15 figure, the liquid is recycled in part to second scrubber (14), as discussed above. Further, as also discussed above the liquid may be provided in part to the first scrubber (9) as liquid containing source material (L21). The liquid may, again as discussed above be provided in part to the third 20 scrubber (11) as liquid containing source material (L19). In one embodiment, of the total of the liquid containing source material (L18), 5 to 10 vol.% is provided to the first scrubber (9) as liquid containing source material (L21), while 40 to 60 vol.% is provided to the third scrubber (11) 25 as liquid containing source material (L19), and 40 to 60 vol.% is recycled back to scrubber (14).

Claims

1. Werkwijze voor het vervaardigen van granules, omvattende de stappen van • toevoeren van een vloeistof die uitgangsmateriaal omvat aan een granulator, 5. verwijderen van vaste granules uit de granulator en toevoeren daarvan aan een granulaatkoeler, • verwijderen van gekoelde granules uit de granulaatkoeler, • verwijderen van een eerste stof-bevattend gas uit de granulator en toevoeren daarvan aan een eerste wasser, en in 10 de eerste wasser in contact brengen van het stof-bevattende gas met een waterige vloeistof, resulterend in de vorming van een eerste gezuiverde gasstroom en een eerste waterige vloeistof omvattende uitgangsmateriaal, en verwijderen van de eerste gezuiverde gasstroom uit de eerste wasser en 15 verwijderen van de eerste waterige vloeistof omvattende uitgangsmateriaal uit de eerste wasser, • verwijderen van een tweede stof-bevattend gas uit de granulaatkoeler en toevoeren daarvan aan een tweede wasser, en in de tweede wasser in contact brengen van het stof- 20 bevattende gas met een waterige vloeistof, resulterend in de vorming van een tweede gezuiverde gasstroom en een tweede waterige vloeistof omvattende uitgangsmateriaal, en verwijderen van de tweede gezuiverde gasstroom uit de tweede wasser, 25. verschaffen van de eerste gezuiverde gasstroom uit de eerste wasser aan een derde wasser, en in de derde wasser in contact brengen van de eerste gezuiverde gasstroom met een waterige vloeistof, resulterend in de vorming van een derde gezuiverde gasstroom en een derde waterige vloeistof omvattende uitgangsmateriaal,, waarbij de werktemperatuur van het derde wasser beneden de werktemperatuur van de eerste .Ir wasser is.A method for manufacturing granules, comprising the steps of • supplying a liquid comprising starting material to a granulator, 5. removing solid granules from the granulator and supplying them to a granulate cooler, • removing cooled granules from the granulate cooler, Removing a first dust-containing gas from the granulator and feeding it to a first washer, and bringing the dust-containing gas into contact with an aqueous liquid in the first washer, resulting in the formation of a first purified gas stream and a first aqueous liquid comprising starting material, and removing the first purified gas stream from the first washer and removing the first aqueous liquid comprising starting material from the first washer, removing a second dust-containing gas from the granulate cooler and supplying it to a second washer, and bringing dust into contact in the second washer 2 O containing gas with an aqueous liquid, resulting in the formation of a second purified gas stream and a second aqueous liquid comprising starting material, and removal of the second purified gas stream from the second washer, 25. providing the first purified gas stream from the first washer to a third scrubber, and bringing the first purified gas stream into contact with an aqueous liquid in the third scrubber, resulting in the formation of a third purified gas stream and starting material comprising a third aqueous liquid, wherein the working temperature of the third scrubber is below the working temperature of the first .Ir washer.

2. Werkwijze volgens conclusie 1, waarbij de waterige vloeistof die toegevoerd wordt aan de eerste wasser en/of de waterige vloeistof die toegevoerd wordt aan de tweede wasser 10 en/of de waterige vloeistof die toegevoerd wordt aan de derde wasser uitgangsmateriaal omvat.2. A method according to claim 1, wherein the aqueous fluid supplied to the first washer and / or the aqueous fluid supplied to the second washer 10 and / or the aqueous fluid supplied to the third washer comprises starting material.

3. Werkwij ze volgens conclusie 1 of 2, waarbij de werktemperatuur van het derde wasser hoger is dan die van de 15 tweede wasser.3. Method according to claim 1 or 2, wherein the operating temperature of the third washer is higher than that of the second washer.

4. Werkwijze volgens een der voorgaande conclusies, waarbij de waterige vloeistof die toegevoerd wordt aan de derde wasser ten minste gedeeltelij k bestaan uit waterige vloeistof 20 die uitgangsmateriaal omvat afkomstig uit de tweede wasser.4. Method as claimed in any of the foregoing claims, wherein the aqueous liquid that is supplied to the third washer consists at least in part of aqueous liquid comprising starting material from the second washer.

5. Werkwijze volgens een der voorgaande conclusies, waarbij ten minste een deel van de waterige vloeistof verwijderd uit de derde wasser toegevoerd wordt aan de tweede wasser, en 25 tenminste een deel van de waterige vloeistof verwijderd uit de tweede wasser toegevoerd wordt aan de derde wasser, waarbij de vloeistof die uit de tweede wasser aan de derde wasser wordt toegevoerd een lagere temperatuur heeft dan de vloeistof die uit het derde wasser naar het tweede wasser 30 wordt toegevoerd.5. Method as claimed in any of the foregoing claims, wherein at least a part of the aqueous liquid removed from the third washer is supplied to the second washer, and at least a part of the aqueous liquid removed from the second washer is supplied to the third washer wherein the liquid supplied from the second washer to the third washer has a lower temperature than the liquid supplied from the third washer to the second washer.

6. Werkwijze volgens een der voorgaande conclusies, waarbij vers water wordt toegevoerd aan de tweede wasser, en waarbij de waterige vloeistofstromen die aan de eerste en de derde wasser worden toegevoerd voor ten minste 50 vol.% bestaan uit j waterige vloeistof-recirculatiestromen, in het bijzonder voor ten minste 70%, meer in het bijzonder voor ten minste 90%.6. A method according to any one of the preceding claims, wherein fresh water is supplied to the second washer, and wherein the aqueous liquid streams supplied to the first and the third washer consist of at least 50% by volume of aqueous liquid recycle streams, in in particular for at least 70%, more in particular for at least 90%.

7. Werkwijze volgens een der voorgaande conclusies, waarbij de eerste wasser en/of de tweede wasser en/of derde wasser, 10 met name de eerste wasser, voorzien zijn van recirculeringslussen waarbij vloeibaar effluent uit de bodem van de wasser wordt ontrokken en naar de bovenzijde van de wasser wordt toegevoerd.7. Method as claimed in any of the foregoing claims, wherein the first washer and / or the second washer and / or third washer, in particular the first washer, are provided with recirculation loops wherein liquid effluent is withdrawn from the bottom of the washer and sent to the top of the washer is supplied.

8. Werkwijze volgens een der voorgaande conclusies, waarbij effluent uit de eerste wasser wordt teruggevoerd naar de granulatiestap, zo nodig met een tussenliggende Indampstap.A method according to any one of the preceding claims, wherein effluent is recycled from the first washer to the granulation step, if necessary with an intermediate evaporation step.

9. Werkwijze volgens een der voorgaande conclusies, waarbij 20 de waterige vloeistof toegevoerd aan de eerste wasser wordt toegevoerd in een hoeveelheid van ten minste 0,8 kg vloeistof/kg gas toegevoerd aan de eerste wasser.9. A method according to any one of the preceding claims, wherein the aqueous liquid supplied to the first washer is supplied in an amount of at least 0.8 kg of liquid / kg of gas supplied to the first washer.

10. Werkwijze volgens een der voorgaande conclusies, waarbij 25 het uitgangsmateriaal ureum is, en het stof-bevattende gas dat toegevoerd wordt aan de eerste wasser een temperatuur heeft in het bereik van 100-120 °C, en grof ureumstof omvat met een gemiddelde deeltjesgrootte van ten minste 0,05 mm, in het bijzonder ten minste 0,1 mm en fijn ureumstof met een gemiddelde deeltjesgrootte van minder dan 50 micron, en de waterige vloeistof die aan de eerste wasser wordt toegevoerd een temperatuur heeft in het bereik van 40-50°C en de temperatuur van de eerste waterige vloeistof die ureum omvat 5 en de eerste gezuiverde gasstroom in het bereik is van 40-50 °C.10. Method as claimed in any of the foregoing claims, wherein the starting material is urea, and the dust-containing gas supplied to the first washer has a temperature in the range of 100-120 ° C, and comprises coarse urea dust with an average particle size of at least 0.05 mm, in particular at least 0.1 mm, and fine urea dust with an average particle size of less than 50 microns, and the aqueous liquid supplied to the first washer has a temperature in the range of 40- 50 ° C and the temperature of the first aqueous liquid comprising urea and the first purified gas stream is in the range of 40-50 ° C.

11. Werkwijze volgens conclusie 10, waarbij de waterige vloeistof die ureum bevat in de eerste wasser een 10 ureumgehalte heeft in het bereik van 35-55 gew.%.The method of claim 10, wherein the aqueous fluid containing urea in the first washer has a urea content in the range of 35-55% by weight.

12. Werkwijze volgens conclusie 10 of 11, waarbij het stof-bevattende gas dat aan de tweede wasser wordt toegevoerd een temperatuur heeft in het bereik van 60-90°C, en de waterige 15 vloeistof die aan de tweede wasser wordt toegevoerd een temperatuur heeft in het bereik van 25-40 °C, en de temperatuur van de tweede waterige vloeistof die ureum bevat en de tweede gezuiverde gasstroom in het bereik is van 25-40 °C. 2012. A method according to claim 10 or 11, wherein the dust-containing gas supplied to the second washer has a temperature in the range of 60-90 ° C, and the aqueous liquid supplied to the second washer has a temperature in the range of 25-40 ° C, and the temperature of the second aqueous liquid containing urea and the second purified gas stream is in the range of 25-40 ° C. 20

13. Werkwij ze volgens een der conclusies 10-12, waarbij de waterige vloeistof die ureum omvat in de tweede wasser een ureumgehalte heeft in het bereik van 1-20 gew.%.The method of any one of claims 10-12, wherein the aqueous liquid comprising urea in the second washer has a urea content in the range of 1-20% by weight.

14. Werkwijze volgens een der conclusies 10-13, waarbij het effluent gas uit de eerste wasser met een temperatuur van 40 — 50°C wordt toegevoerd aan de derde wasser, waar het gecombineerd wordt met een waterige vloeistof met een temperatuur in het bereik van 20-45°C. 30A method according to any of claims 10-13, wherein the effluent gas is supplied from the first washer at a temperature of 40 - 50 ° C to the third washer, where it is combined with an aqueous liquid with a temperature in the range of 20-45 ° C. 30

15. Werkwijze volgens een der voorgaande conclusies 1-9, waarbij het uitgangsmateriaal ammoniumnitraat is en het stof-bevattende gas dat toegevoerd wordt aan de eerste wasser een temperatuur heeft in het bereik van 100-130°C, en grof Si ammoniumnitraatstof omvat met een gemiddelde deeltjesgrootte van ten minste 0,05 mm, in het bij zonder ten minste 0,1 mm en fijn ammoniumnitraatstof met een gemiddelde deeltjesgrootte van minder dan 50 micron, en de waterige vloeistof die aan de eerste wasser wordt toegevoerd een temperatuur heeft in het 10 bereik van 40-50 °C en de temperatuur van de eerste waterige vloeistof die ammoniumnitraat omvat en de eerste gezuiverde gasstroom in het bereik is van 40-50 °C.A method according to any one of the preceding claims 1-9, wherein the starting material is ammonium nitrate and the dust-containing gas supplied to the first washer has a temperature in the range of 100-130 ° C, and coarse Si comprises ammonium nitrate dust with a average particle size of at least 0.05 mm, in particular at least 0.1 mm and fine ammonium nitrate dust with an average particle size of less than 50 microns, and the aqueous liquid supplied to the first washer has a temperature in the range of 40-50 ° C and the temperature of the first aqueous liquid comprising ammonium nitrate and the first purified gas stream is in the range of 40-50 ° C.

16. Werkwij ze volgens conclusie 15, waarbij de waterige 15 vloeistof die ammoniumnitraat omvat uit de eerste wasser een ammoniumnitraatconcentratie heeft in het bereik van 35-70 gew.%.16. A method according to claim 15, wherein the aqueous liquid comprising ammonium nitrate from the first scrubber has an ammonium nitrate concentration in the range of 35-70% by weight.

17. Werkwijze volgens conclusie 15 of 16, waarbij het stof-20 bevattendde gas toegevoerd aan de tweede wasser een temperatuur heeft in het bereik van 60-90°C, en de waterige vloeistof die aan de tweede wasser wordt toegevoerd een temperatuur heeft in het bereik van 25-40°C, en de temperatuur van de tweede waterige vloeistof die 25 ammoniumnitraat omvat en de tweede gezuiverde gasstroom in het bereik is van 25-40 °C.17. Method as claimed in claim 15 or 16, wherein the dust-containing gas supplied to the second washer has a temperature in the range of 60-90 ° C, and the aqueous liquid supplied to the second washer has a temperature in the range of 25-40 ° C, and the temperature of the second aqueous liquid comprising ammonium nitrate and the second purified gas stream is in the range of 25-40 ° C.

18. Werkwij ze volgens een der conclusies 15-17, waarbij de waterige vloeistof die ammoniumnitraat omvat geproduceerd in de i weed o waasi.i u- η. a nx· n i urw 11 i r a t cn c·,.· π f r a fJ e he·.· f t _:i he* 1. r -"·! k v a n 1-70 j e w, -· .A method according to any one of claims 15-17, wherein the aqueous liquid comprising ammonium nitrate produced in the weed o waasi.i u-η. a nx · n i urw 11 i r a t cn c ·,. · π f r a f y e he ·. · f t _: i he * 1. r - "·! k from a 1-70 y e w, - ·.

10. We r kv; i j ;= vviaer.s een der vvnvlvvies lb-18, wa.ai.bi_i het 5 ef 0 I ueut Jin ·;; t d-r ee: ste wns'ier met een tc-ept; .atu.ir van 41 : 11 *c t *ie ν:·ν·-'αci v.'OL'lt aan derde Wa?;n.<;; or» -3--1-- <n-bi neei 1 te w *, :cier: ne 1 ven wateiioe v 1«. ~j = 1 . i :- e t >:e:i ten pe raruur n hat b e r e i k van ,: 0 - /- 5" C .10. We r kv; one of the examples 1b-18, in which case it is the same as Jin. t d-r ee: ste wns'ier with a tc-ept; .atu.ir from 41: 11 * c t * ie ν: · ν · -'αci v.'OL'lt to third party Wa?; n. <;; or »-3--1-- <n-bi neei 1 te w *,: cier: ne 1 ven wateiioe v 1«. ~ j = 1. i: - e t>: e: i p raruur n hat e, i, - 0 - / - 5 "C.