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Recovering Materials from Fertiliser Production Waste Water
Dr Stefan Neumann Head, Application Laboratory BU ION LANXESS Deutschland GmbH Loss of ammonia and ammonium nitrate along with waste water during fertiliser production means a loss of 1.5 to 4 per cent of total production yield. Curbing these losses can result in significant increase in yields. The article discusses use of ion exchange resins to recover valuable materials from waste streams of fertiliser production.

As the world population has grown the demand for food has increased dramatically. This gave rise to higher usage of fertiliser products that help to improve soil quality and thereby increase the yield in agricultural production. Since the growth of world population is continuing the demand for fertiliser products will also keep on rising throughout the next decades. Currently the world production rate of nitrogen based fertilisers amounts 100 mio. t/a [1]. In the year 2002 the contribution by larger companies in key countries is China: 23.6 mio. t/a; India 10,6 t/a, USA: 9.4 mio. t/a; Russian Federation: 6.0 mio. t/a; Canada 3.8 mio. t/a, Ukraine: 2.3 mio t/a, Pakistan 2,2 mio. t/a, France: 1,0 mio. t/a; Germany: 1.0 mio. t/a; Egypt, Saudi- Arabia, Poland, Bangladesh, Netherlands, together: 6.2 mio. t/a. The missing amounts of the world production rate are accounted for by smaller production units.

Due to the increased demand for fertilisers the selling prices for nitrogen based products has increased. Table 1 indicates Recovering Materials from Fertiliser Production Waste Water Loss of ammonia and ammonium nitrate along with waste water during fertiliser production means a loss of 1.5 to 4 per cent of total production yield. Curbing these losses can result in significant increase in yields. The article discusses use of ion exchange resins to recover valuable materials from waste streams of fertiliser production. the development for prices of ammonia, Ammonium nitrate and ammoniasulfate from 1990 to 2010 [2]:

Ammonium nitrate in Industry & Environment Ammonium nitrate as a source for nitrogen is a well-known and accepted fertiliser. The first step of production is the neutralisation reaction of gaseous ammonia (100 per cent NH3) and nitric acid (54-60 per cent HNO3) according to the following equation:

NH3 + HNO3 ⇒ NH4NO3

From the resulting 76 per cent ammonium nitrate solution a solid product with a purity level of 99.6 per cent is recovered by evaporation of water in multiple step vacuum-evaporisers, followed by prilling. The evaporated water is condensed and discharged with a temperature of 800C to 900C. Valuable materials are found in this condensed process stream as there are concentrations of 0.3 to 5 g/L ammonia (NH3) and 3 to 10 g/L Ammonium nitrate (NH4NO3).

The loss of ammonia and Ammonium nitrate along with this waste water means a loss of 1.5 per cent to 4 per cent of the total production yield. Depending on the plant design and efficiency of the operation, the loss in yield can even be higher. The loss of thermal energy along with the condensate is another deficit. Both these effects reduce the profitability of the operation. Depending on the plant size this can amount several million Euro per year that "go down the drain" in a proverbial sense of meaning.

The discharge of N-NH4 and N-NO3 into the environment is harmful since the fertilisers enhance growth of algae and bacteria in natural water bodies. Input of nutrients into the water above a natural balanced level causes so called "eutrophication" of the water body and can result in fish kill and a loss of biodiversity.

There have been several attempts already to clean this type of waste water eg, by means of biological treatment methods. But it was found that this method is very costly since with conventional nitrification/denitrification huge amounts of organic material have to be dosed to the waste water to feed the microorganisms with a carbon source. In addition to that nitrogen feed concentrations are relatively high. As a result it is very difficult to accomplish emission limits of 1.5 mg/L N-NH3 to 10 mg/L N-NO3: This would equal a removal rate of 95 per cent and more, which would mean at least a multi-stage plant and most likely a polishing step.

Hence to rely on biological treatment would mean high costs and resource consumption, and neither ammonia nor nitrate would be recovered.

A solution for this situation is offered by the so called Fertarex® water treatment process which has been developed by the Swiss company Arionex Wasseraufbereitung3. Six plants of this type have been built in Europe and Asia. The first unit was installed in 1975, and over the last 35 years the economics and reliability of the process has been demonstrated4,5

The most recently built Fertarex® unit was commissioned at the end of 2010 in Turkey at the Gemlik Gübre Sanayi A.S fertiliser plant, and since then has been running smoothly. This text will later on give a detailed case study of this unit.

Benefits of Process:
• Almost all the Ammonium nitrate and ammonia is recovered from the waste water, resulting in a much improved production yield.
• Reliably staying within discharge limits protects the environment and prevents penalties.
The waste water is transformed into a demineralised water with rest-conductivities of 0.06-0.1 øS/cm, which can be beneficially reused on site and partially offset the requirement for pure water production.
• The produced demineralised water can be used for the onsite production of nitric acid or as boiler feed water Elegant safety philosophy.
• Zero or significantly less discharge of water into the environment.

Basics of the Process
• Almost all the Ammonium nitrate and ammonia is recovered from the waste water, resulting in a much improved production yield.
• Reliablyst aying within discharge limits protects the environment and prevents penalties.
• The waste water is transformed into a demineralised water with rest-conductivities of 0.06-0.1 øS/cm, which can be beneficially reused on site and partially offset the requirement for pure water production.
• The produced demineralised water can be used for the onsite production of nitric acid or as boiler feed water Elegant safety philosophy.
• Zero or significantly less discharge of water into the environment.

Basics of the Process
At a first glance a Fertarex® plant very much looks like a conventional demineralisation plant with cation - and anion exchanger followed by a mixed bed polisher. But there are several details that make it special. In the following the principle of operation is explained. As shown in figure 1 in a very simplified way the strong acidic cation exchanger (RCat-H) removes ammonia (NH3) along with ammonium (NH4+) ions from the waste water. The reaction scheme is as follows:

Exchange reaction taking place at the strong acidic cation exchanger (RCat-H): NH3 + NH4NO3 + 2 RCat-H ⇔ 2 RCat-NH4 + HNO3

In the following step a middle basic anion exchanger (RAn-OH) removes the nitric acid (HNO3), which is leaving the cation exchanger:

Exchange reaction taking place at the medium base anion exchanger (RAn-OH): HNO3 + RAn-OH ⇔ RNO3 + H2O

As can be seen from reaction schemes (I) and (II) entirely all nitrogen compound entering into the system are bound by the ion exchangers and at the same time water is formed.

After passing through the two filtration steps the water is fairly desalinated and exhibits a rest conductivity of 12-25 øS/ cm. Only traces of salt are left (5 to 15 mg/l NH4NO3). To remove the remaining traces the water is pumped through a mixed bed absorber, which is filled with a mixture of strong acidic cation - and strongly basic anion exchangers. This mixed bed adsorber will remove rest traces of salt down to a rest conductivity of 0.06-0.1øS/cm. This demineralised water is suitable for high purity applications, such as for boiler feed. Once exhausted, the ion exchange filters need to be regenerated and returned to their active form. They are then ready to be returned to service for the next loading cycle. The relevant exchange reactions are:

Exchange reaction at cation exchanger in regeneration:
RCat-NH4 + HNO3 ? RCat-H + NH4NO3

One core element of the Fertarex® process thereby is the use of pre-cooled concentrated nitric acid (55 per cent HNO3). The acid strips the ammonium from the cation exchanger and at the same time converts the functional group back into the so called H-form, which is then ready to be loaded in the next cycle.

The spent regenerant solution draining from the resin will contain 80 g/L (8 per cent) NH4NO3, along with a certain excess of HNO3 in the richest fraction. In parallel the anion exchanger is regenerated, for which a solution of 15 per cent ammonia is used. The regeneration of the exhausted anion exchanger works according to the following equation:

Exchange reaction at anion exchanger in regeneration:
RAn-NO3 + NH4OH ? RAn-OH + NH4NO3

Thereby the ammonia solution strips the nitrate from the resin and transforms it into the OH-form (RAn-OH), which is then ready to be used in the next cycle. Also the spent regenerant of the anion exchanger contains 80 to 100 g/L (8-10 per cent) ammonium nitrate and in addition a large excess of ammonia (NH3).

The basic principle of the process is - in addition to later elaborations - to combine these two spent regenerant solutions into one and to balance the excess of ammonia by further addition of nitric acid. Thereby an 18 to 25 per cent ammonia nitrate solution is obtained that can be fed back into the fertiliser production.

The process principle described above is simplified. In practice the effluents from the ion exchangers produced during their regeneration are separated into fractions and used in a specific way. The purpose of these additional steps is to produce an ammonia nitrate solution with the highest possible concentration and to avoid secondary waste water.

A. The first and fourth fraction derived from the regenerant is fed back into the waste water storage tank. It contains only small amounts of ammonia nitrate.
B. The second fraction that contains 90-95 per cent of eluted NH4NO3 and around 50 to 60 per cent of excess chemicals (HNO3 or NH3) is neutralised, concentrated (eg, by evaporation) and sent back into the fertiliser production.
C. The third fraction that contains 40 to 45 per cent of the excess of the regenerant chemicals (HNO3 or NH3) is used to completely exhaust the anion exchanger or - after saturation with NH3 - is used to prepare a new batch of regenerant solution for the regeneration of the anion exchanger.

Well-thought-out Safety Concept
To contact ion exchange resins with concentrated nitric acid can be dangerous because this acid is a strong oxidant and improper handling can result in an exothermic reaction. The other hazard connected to this process is through the potential for impurities to enter into the final product. Organic impurities would give rise to the formation of the instable ammoniumnitrite (NH4NO2) that can initiate an explosion of the product. Therefore it is very essential that the ion exchange resins used for the process are clean and do not leak organic material.

The well-thought-out safety concept of the process meets these concerns by the implementation of the following elements:
• Avoidance of dead volumes in columns and pipelines
• Cooling of cation exchanger and nitric acid before application
• Short contact time of acid and ion exchanger
• Relatively small specific volume of nitric acid applied (0.3 BV)
• Sophisticated measure and controlconcept with emergency switch off
• Use of special ion exchange resins with high stability and purity (Slow oxidation of resin and low level release of organics)

As mentioned as the last element of the safety concept the process makes use of special ion exchange resins with high oxidative stability and low leakage level of organics.

Stability against oxidative agents is provided by a high degree of cross-linkage of the polymer backbone of the resin. The required purity is provided by the use of high quality chemicals, proper rinse processes and quality control. All Fertarex® plants that have been started up to now have been filled with Lanxess premium ion exchange resins.

The resins applied here were originally developed for highly demanding applications in the catalysis of organic chemicals, in food processing industry and in semiconductor and electronic industry. These resins have demonstrated their suitability over the last decades of use in this application. Specifically the strong acidic cation exchanger Lewatit® K 2629 und the medium base anion exchanger Lewatit® S 4428 as well as mixed bed resins such as Lewatit® S 150 and Lewatit® M 800.

Case Study of the Youngest Fertarex® plant at Gemlik Gübre in Turkey The company Gemlik Gübre Sanayi belongs to the Yildirim Holding Turkey, and has produced fertiliser products for many decades in their facilities at Gemlik. This is close to the city of Bursa, population of 2 million, at the border of the Sea of Marmara in the north west of Turkey. The yearly production rate of calcium Ammonium nitrate (CAN) is at ca. 600.000 t/y. In October of 2010 a fully automated Fertarex® ion exchange system was installed to treat 40 m??/h process condensate from the AN-production and was successfully taken into operation. This Fertarex® unit comprises two lines of demineralisation filters each consisting of cation-, anion- and mixed bed polishers.

Additionally there is a cooling station, several tanks to store and to mix liquids and chemicals, as well as a vacuum evaporation plant for the production of a 75 per cent Ammonium nitrate solution from the spent regenerants of the ion exchangers. The investment cost amounts to roughly 6 million Euro.

The principle flow scheme is shown in figure 2: Basic and detailed-engineering was carried out by the Swiss company Arionex (Process Inventor). The construction work was all done by local engineers and workshops of Gemlik Gübre. The full automated control system was invented and constructed by the German company HP-Consulting. Logistic, technical and commercial support was given by Ökotek Cevre Teknolojisi ve Kimy San Ltd ??ti from Istanbul, Turkey. Eight cubic meters anionand 13 cubic metres cation-exchanger as well as 8 cubic metres of mixed bed resin were delivered from Germany by Lanxess Deutschland GmbH.

After a successful commissioning-campaign the plant is now operated by Gemlik Gübre staff without any problems. Due to the automation concept the plant only requires one operator per shift to monitor the operation.

The systems treat around 40 m3 per hour of waste water. The average mass related feed rate of Ammonium nitrate and ammonia is around 156 kg/h NH4NO3 (1953 mol-eq/h) and around 28,8 kg/h NH3 (1696 mol-eq/h). The concentrations are around 2 to 4 g/L NH4NO3 and 0,5 to 0,8 g/L NH3.

The unit produces around 38 m3/h fully demineralised water with a rest conductivity of < 0,1 øS/cm. The spent regenerants of the ion exchangers are neutralised with nitric acid resulting in 2868 kg/h of a 22 per cent NH4NO3 solution that subsequently is concentrated by evaporation to obtain a 75 per cent solution with a mass flow rate of 841 kg/h. This flow contains 631 kg/h of ammonia nitrate that is passed directly back into the production lines. An overview of the technical data is given in table 2.

By recovery of product from the waste water alone, more than 6247 t/a of calcium ammonium-nitrate and around 300960 m3/a of demineralised water is recovered, which all together results in savings of 2 to 2.4 million Euro per year. Hence the plants invest cost amortise in around 3 to 3.5 years. Taking into account savings in the area of penalties, biological waste water treatment as well as maintenance and operational costs of a separate demineralisation plant, the investment pays off even earlier. Summary, Outlook

Six units have now been built: at Doljchim (Romania), CCH-Arad (Romania), INA Petrokemija, Kutina (Croatia), Péti Nitrogen (Hungary) and Azomures S.A. (Romania), and now the youngest and most advanced Fertarex® waste water treatment plant for the recovery of Ammonium nitrate, ammonia and ultra-pure demineralised water has been successfully taken into operation at Gemlik Gübre Sanayi in Turkey at the end of 2010. The Fertarex® process works on the well accepted principal of the application of ion exchangers in water demineralisation. The process preferentially makes use of ion exchange resins of the Lewatit® brand offering high quality standards to assure safe operation. Multiple engineering features are integrated into the process to accomplish challenging targets as there are: a) high economic efficiency requirements b) safety constraints.

Simply from the economic view several arguments can be found for the decision to install a Fertarex® unit, such as An increased production yield of 1.5 to 4 per cent (sometimes even more); Simultaneous production of high purity demineralised water that can be utilised in the production of nitric acid and other sophisticated processes; Very low energy costs since ion exchange filters operate with low pressure loss.

Also, the concentration of the regenerant stream by evaporation is connected with low energy costs since the feed stream of the evaporator already has a high concentration and the evaporator is operated with saturated steam or steamrecompression; and Reliable attainment of emission limits thereby avoiding penalties. In addition to that it has to be clearly pointed out that the regenerant chemicals such as nitric acid and ammonia are produced by the fertiliser producer itself and do not get lost with any waste. Since the regenerant chemicals later are fed back into the production process along with the recovered valuable materials, they do not appear in the cost-balance as operating costs. Further, the time for amortisation can be less than three years, depending on the local conditions.

Along with noticeable economic advantages for the producer alone there is the overall benefit of saving valuable raw materials and protecting the environment: Sustainable economic practice is becoming the expected norm for business.

In the expectation that environmental limits as a trend are getting stricter fertiliser producers all around the world will be forced to intensify their activities to protect the environment. This technology offers a cost effective and economically advantageous method for doing so. Additionally, producers of porous Ammonium nitrate for explosives in Russia, Ukraine, India, Pakistan, Eastern-Europe, Australia and China may benefit from this process technology.

Projects can be organized with high flexibility. One option is to use Arionex as the main contractor who, along with subcontractor plans, builds, commissions and eventually even operates the plant. Another option is for the construction and operation of the plant to be undertaken by local companies and the end customers themselves, as was the case for Gemlik Gübre.