BE1024583B1 - Method for nutrient recovery via multifunctional use of residual products after thermal decomposition of magnesium ammonium phosphate - Google Patents

Abstract

The invention consists of a double reactor embodiment, wherein in the first reactor under pH controlled conditions MgNH4 PO4.6H2 O due to heating and pressure build-up on the basis of steam injection or steam production in the reactor vessel itself, the crystals have a pressure build-up internally.

Description

DESCRIPTION

This invention relates to the thermal decomposition of magnesium ammonium phosphate (MgNH4PO4.6H2O) or known as the mineral struvite. At present, the formation of struvite is mainly limited to the recovery of phosphate from wastewater or liquid sludge streams.

It is known from the literature (Türker & Celen, 2007. Removal of ammonia as struvite of magnesium and phosphate. Bioresource. Technol. 98: 1529-1534; Sugiyama et al., 2005. Removal of aqueous ammonium with magnesium phopsphates obtained form the ammonium-elimination of magnesium ammonium phosphate. J. Colloid Interface Sei. 292: 133-138; Stefanowicz et al., 1992a. Ammonium removal from waste solutions by precipitation of MgNH4PO4. I. Ammonium removal with use of commercial reagents. Resour. Conserv Recycl. 6: 329-337; Stefanowicz et al., 1992b Ammonium removal from waste solutions by precipitation of MgNH4PO4. II ammonium removal and recovery with recycling of regenerate. Resour. Conserv. Recycl. 6: 339-345) that struvite is not stable at higher temperatures (above 50 ° C). When the temperature rises, the crystalline water will be released and disappear from the crystal grid. If the temperature rises even further, the crystal also loses nitrogen in the form of the volatile ammonia.

Depending on the final temperature, dry or wet heating and the pH, a variety of residual magnesium / phosphate compounds is obtained. These can also be supplemented with the other ions from eg the pH adjustment during the heating process. In addition to this variable magnesium / phosphate residue, the other residual water vapor is enriched with the volatile ammonia.

Several studies indicate that by thermal decomposition of struvite, the residual magnesium / phosphate compounds can be utilized as reagents to reform struvite. In this way it is possible to recover extra nitrogen.

The described methodologies are currently only limited to research on a laboratory scale. An exception to this is the CAFR process (STO WA (1995). Treatment of nitrogen-rich return flows on sewage treatment plants. Practical research on the MAP / CAFR process at WWTP Utrecht, (in Dutch). STO WA report 95-013.). This process is characterized by the use of external stripped air and operation under atmospheric conditions.

The following patents refer to already existing applications in which the residual magnesium / phosphate compounds are reused to remove more nitrogen from waste water on liquid sludge streams. DE102005034138A1, US20090127094, W02008061975A2 and EP2287118 Al.

ADVANTAGES AND DISADVANTAGES OF EXISTING SOLUTIONS

The existing techniques all have the common advantage that through the thermal decomposition they have the possibility to remove the excess nitrogen present in most waste waters or liquid sludge flows further than what would be possible based on struvite production only based on the original quantity phosphate.

Most techniques described hitherto require pulverization of the primary shaped struvite to achieve good dissolution of the struvite. The existing techniques usually also involve a combination of pulverization and pH adjustment of the heated mixture.

The existing techniques do not yet yet combine an automated throughput of the residual magnesium / phosphate compounds to the primary struvite formation.

The existing techniques are currently limited to using only the residual magnesium / phosphate compounds for additional nitrogen removal.

The existing techniques are only based on the higher temperature, whether or not in combination with an adjustment of the pH.

ADVANTAGES PROPOSED INVENTION

The heating of struvite, whether or not in a pH-adjusted environment, is maintained at $ ^{E2017 / 0024} . The existing invention differs essentially in 2 areas from the existing techniques.

Essential difference number 1 is that not only the temperature and adjusted pH are used, but also a process under pressure in combination with a sudden pressure drop, resulting in an additional mechanical destruction of the struvite crystals.

The crystalline bonded water and ammonium-N are released in vapor form internally in the crystal lattice by rapid heating. Due to the volume increase of this crystal lattice internal vapor as a result of the temperature increase, there is an extra stress on the mechanical strength of the crystal. Rapid heating of struvite crystals under atmospheric conditions gives rise to exploding crystals due to the internal pressure build-up.

Due to the nature of the heat treatment, consisting of either direct steam injection or boiling of the struvite / water mixture, in a closed pressure resistant pressure vessel, internal pressure build-up will initially be weakened by the higher ambient back pressure.

If the pressure drops after the pressure build-up in the reactor vessel, this will lead to rapid increases in the differential pressure. This will result in an intense mechanical destruction of the crystals. This further intensifies the thermal decomposition.

The pressure drop will also discharge the ammonia-enriched water vapor. This discharged vapor phase continues to the second reactor section where the separated ammonia will be washed in an acidic solution.

Essential difference number 2 is that not only residual magnesium / phosphate compounds recovered in this way can be reused for extra nitrogen recovery.

The residual magnesium / phosphate compounds can, in addition to being used as reagents for secondary struvite formation, also serve for the formation of other types of struvite, in particular potassium struvite. In this potassium struvite, the initial ammonium is replaced by potassium.

In addition to the end product, the separated nitrogen can also be used again for the secondary struvite formation. This application is possible on waste waters or liquid sludge streams that naturally contain a shortage of or no nitrogen at all, but are otherwise loaded with phosphate.

The third application possibility is that the residual magnesium / phosphate compounds can be split into separate Mg ²⁺ and PO4-P ³ 'reagents via classical ion exchange techniques. This makes it possible to finally end via internal struvite formation with internal recirculation of only the Mg ²⁺ stream and discharge of a separate phosphate and nitrogen concentrate.

DESCRIPTION OF THE FIGURE

Figure 1 gives an overview of the combined reactor vessels, the interconnections as well as the supply and discharge of the various material flows according to the invention.

DETAIL OPERATION OF THE INVENTION

For explanation of the operation and specifications of the invention, reference is made to Figure 1 without any limitation in character of the embodiment.

Figure 1 gives an overview of the combined reactor vessels, the interconnections as well as the supply and discharge of the various material flows.

The treatment of the primary struvite goes through 3 different phases.

Phase 1 consists of the transfer in the empty reactor vessel 1 of a mixture of primary struvite and water. The lines between reactor vessels 1 and 2 are closed at this time. After the desired pressure in the reactor vessel has been reached, the valve opens between the two reactors on line 5. Due to the pressure drop explode struvite crystals, and there is a transfer from the ammonia-enriched ^ ^2017/0024 water vapor / steam to the reactor vessel through distribution frame 7. This will continue until pressure equalization across the reactors cycle back.

In Phase 2, the reactor vessel is maintained at temperature and the ammonia-enriched headspace will pass through reactor vessel 2 via the forced ventilation via compressor 6. If desired, an additional strip effect can be started up in reactor vessel 1 via the bypass line 19 on line 4 by means of compressor 20 and distribution frame 21.

Phase 3 involves stopping heating and compressors. After sufficient cooling, the various residue streams of matter can be removed and, depending on the process details, either reused on-site or disposed of.

The primary struvite produced in reactor 4 is moved via line 3 to reactor vessel 1. This first reactor vessel 1 is the decomposition reactor where the nitrogen from the struvite will be dissolved. In addition, there is reactor vessel 2 where the separated nitrogen will be captured in an acid solution under ammonia form.

Both reactor vessels 1 and 2 are connected by 2 different pipes that are responsible for the transport of the ammonia-enriched water vapor from reactor vessel 1 to reactor vessel 2, via line number 5. The discharge of the ammonia-enriched water vapor will proceed in phase 1, depressing the pressure build-up reactor vessel 1. After pressure equalization, the vapor phase from the headspace reactor vessel 1 can be continuously brought to reactor vessel via an adjustable line via line 5 and with forced ventilation for an adjustable time. The necessary return flow between reactor vessel 2 to reactor vessel 1 is currently possible via line number 4.

The forced ventilation is via a compressor number 6 which ensures sufficient pressure and flow to get the ammonia-enriched water vapor through the washing solution.

Line number 4 is also provided with a separately activated bypass, which in turn allows the headspace vapor phase of reactor 2 to be blown through the contents of reactor vessel 1. This can be done via bypass line 19 and compressor 20. The injection in reactor vessel 1 is via distribution frame 21.

The transfer from reactor vessel 1 to reactor vessel 2, both in phase 1 and phase 2, takes place via the distribution frame number 7. In this way a maximum transfer of the ammonia to the acid wash solution is possible.

Overpressure build-up over the combined reactor vessels 1 and 2 can be removed via a pressure lock number 8 to the outside air via outlet number

9.

The supply of steam and / or external heat for heating the contents of reactor vessel 1 can be via direct steam injection number 10 or via heat exchange in reactor vessel 1, also via an adapted pipe number 10.

After phase 3, the residual magnesium / phosphate compounds produced can be used again via secondary number 11 for secondary struvite formation in a classic struvite installation number 18.

After phase 3, the residual magnesium / phosphate compounds produced can be re-used for secondary struvite formation via outlet No. 12 with the addition of any potassium salt to produce potassium struvite.

After phase 3, the residual magnesium / phosphate compounds produced can undergo further treatment either via outlet number 13, whereby this stream can be divided into a Mg concentrate stream number 14 and phosphate concentrate stream number 15.

After phase 3, the separated nitrogen concentrate stream can be used for discharge via number 17 for further external processing.

After phase 3, the separated nitrogen concentrate stream can serve for secondary struvite formation via drain number 17 to classic struvite installation number 18.

General legend Figure 1:

1. Reactor vessel 1 = reactor decomposition

2. Reactor vessel 2 = reactor reactor

3. Supply of primary struvite

4. Primary struvite reactor

5. Drain pipe from reactor vessel 1 to reactor vessel 2

6. Compressor reactor vessel 1 to reactor vessel 2

7. Distribution window vapor phase reactor vessel 2

8. Pressure vessel reactor vessel 2

9. Exhaust

10. Steam injection or heat medium heat exchanger io 11. Drain résidu reactor vessel 1 to classical secondary struvite formation

12. Drain résidu reactor vessel 1 to potassium struvite formation

13. Drain résidu reactor vessel 1 to ion exchanger

14. Drain Mg concentrate flow

15. Discharge of phosphate concentrate flow is 16. Discharge of nitrogen concentrate flow

17. Drain nitrogen concentrate flow to classic secondary struvite formation

18. Struvite reactors

19. Bypass pipe from reactor vessel 2 to reactor vessel 1

20. Compressor bypass pipe reactor vessel 2 to reactor vessel 1

21. Distribution window vapor phase reactor vessel 1

Claims (8)

CONCLUSIONS BE2017 / 0024 1. The invention consists of a double reactor embodiment, in which MgNH4PO4.6H2O is heated in the first reactor under pH-controlled conditions by heating and pressure build-up on the basis of steam injection or steam production. 5 the reactor vessel itself, the crystals internally have a pressure build-up. 2. After the desired final temperature and corresponding pressure have been reached in reactor vessel 1, obtained in the manner described in claim 1, the ammonia will be washed out in reactor vessel 2 by a controlled release of the built-up pressure. io 3. After pressure equalization, obtained according to claim 2, forced ventilation will continue the ammonia washing process in a closed circuit, by selective transfer of the headspace from one reactor vessel to the sub-distribution window of the other reactor. 4. The process as described in claims 1, 2 and 3 can be adjusted by adjusting the 15 correct regulation whether batchwise, semi-batch or continuous work. The residue obtained in reactor vessel 1, resulting from the operations described in claims 1, 2, and 3, can be directly reused for the production of ammonium struvite or can be reused for the production of potassium struvite. 20 The residue obtained in reactor vessel 1, resulting from the operations described in claims 1, 2, and 3, can serve as a substrate to be further split into an Mg concentrate and a phosphate concentrate stream. The nitrogen concentrate stream obtained in reactor vessel 2, the result of the operations described in claims 1, 2 and 3 can serve for the 25 production of secondary struvite. The nitrogen concentrate stream obtained in reactor vessel 2, result of the operations described in claims 1, 2, and 3, can be removed for reuse as raw material. Method for nutrient recovery via multi-functional use of residual products after thermal decomposition of magnesium ammonium phosphate The invention consists of a double reactor, in which MgNH4PO4.6H2O in the first reactor under pH-controlled conditions 5 heating and pressure build-up based on steam injection or steam production in the reactor vessel itself, the crystals have an internal pressure build-up.