TECHNICAL FIELD

The present application relates to a method for extraction of phosphorous according to claim 1 and to a system for extraction of phosphorous according to claim 14.

BACKGROUND ART

Phosphorus is an important element in all kinds of vegetation and is a necessity for all kinds of life. Phosphorus therefore present in sewage sludge and a large amount of phosphorus from the sewage sludge is not recycled but instead washed out from agriculture lands and from waste-water treatment plants which is very harmful to the aquatic environment. Today’s technologies for recovery of phosphorous from sewage sludge are suffering from that the percentage of phosphorous in the sludge is relatively low and in that the sludge also comprises poisonous substances.

SUMMARY OF THE INVENTION

There is thus, a need for an improved method for extraction of phosphorus from sewage sludge and from other types of phosphorus containing material.

An object of the present disclosure is to provide a method for extraction of phosphorus where some of the problems with prior art technologies are mitigated or at least alleviated.

According to a first aspect there is provided a method for extraction of phosphorous, which comprises the steps of: providing a feedstock comprising a phosphorus containing material, gasification of the feedstock by plasma gasification in an oxygen poor environment, thereby forming gaseous elements comprising phosphorus and/or phosphorus oxides. The method further comprises cooling of the gaseous elements, providing a predetermined amount of water to the gaseous elements in order to form a solution in which phosphorus oxides are dissolved into phosphorus acid and/or phosphoric acidity. The method further comprises separating phosphorus from the phosphorus acid and phosphoric acidity and collecting the separated phosphorus in a first vessel, and separating the remaining phosphorous and phosphorus compounds from the solution and collecting the remaining phosphorus and phosphorus compounds in a second vessel.

The method has a number of advantages.

The method provides for an environmentally friendly method for recycling of phosphorus of which it is a shortage of on Earth. The recycled phosphorus may be used for the production of e.g. fertilizers.

The method provides for that phosphorus containing material, such as sewage sludge, can be recycled, instead of ending up as landfill, or even worse end up in lakes or the sea. The method provides for an environmentally friendly way of extraction of phosphorus since poisonous compounds, such as cadmium, lead and drug residues are taken care of or rendered harmless by the proposed method.

The method also provides for extraction of phosphorus without the need for sorting and separation of the phosphorus containing material and/or possible other types of material of the feedstock prior to performing the method.

The method further provides for a cost efficient way of extraction of phosphorus from phosphorus containing material, such as sewage sludge and other types of organic materials containing phosphorus.

The step of separating phosphorus from the phosphorus acid and phosphoric acidity and collecting the separated phosphorus in a first vessel may comprise providing an alkaline substance to the solution, wherein the phosphorus acid and/or phosphoric acidity react with the alkaline substance and form at least one phosphorus containing salt, and collecting the at least one phosphorus containing salt in a first vessel.

The advantage is that phosphorus from the phosphorus acid and/or phosphorus acidity can be extracted from the solution.

The phosphorus containing material may comprise sewage sludge, abattoir waste and/or plant waste.

The advantage is that different types of phosphorus containing material, as well as a combination of different phosphorus containing materials, can be processed by the method.

If the gaseous elements further comprises sulphur and/or calcium, the method may further comprise a step of separating sulphur and/or calcium from the gaseous elements. The advantage is that, in addition to phosphorus and phosphorus compounds, also calcium and/or sulphur from the phosphorus containing material can be recovered by the same method. The method may further comprise a step of cleaning the remaining gaseous elements and extracting syngas from the remaining gaseous elements.

The advantage is that, in addition to phosphorus, also syngas can be extracted by the method. Thus, by extraction of both phosphorus and syngas, the method becomes very cost efficient. By cleaning the syngas, syngas having a high purity is formed by the method.

The method may further comprise a step of allowing CO from the syngas to react with H2O according to the following formula: CO + H2O => H2 + CO2.

By the proposed method, a high yield of hydrogen gas (H2) is formed in a very efficient way.

The method may further comprise a step of separating H2 and CO2 into two streams of hydrogen gas and carbon dioxide gas respectively, and collecting the carbon dioxide gas and the hydrogen gas in sealed containers.

The advantage is that carbon dioxide gas (CO2) formed can be collected in a sealed container thereby preventing emission of carbon dioxide gas (CO2) to the atmosphere.

The temperature upon gasification of the feedstock may be in the range of 600-1200 °C, preferably in the range of 725-1125 °C, most preferably in the range of 850-1050 °C in a pyrolysis zone of a gasification unit, and in the range of 2000-3500 °C, preferably in the range of 2250- 3250 °C, most preferably in the range of 2500-3000 °C in a plasma zone of the gasification unit.

The advantage is that, at the proposed temperatures, the gasification becomes efficient in order for extraction of phosphorus and phosphorus compounds from the phosphorus containing material.

The gaseous elements may be cooled to a temperature of below 100 °C, preferably to a temperature in the range of 90 to 20 °C.

By the cooling is the main portion of H2O of the gaseous elements is condensed and thereby separated from the syngas.

The phosphorus containing material may be exposed to a temperature such that the remaining phosphorus and phosphorous compounds comprises red phosphorus, P4, preferably said temperature is comprised in a temperature range with a lowest end point of 300 °C. The advantage is that the phosphorus from the phosphorus containing material may be recovered as red phosphorus, P4, which may be used for production of e.g. fertilizers.

The step of providing a predetermined amount of water to the gaseous elements in order to form a solution in which phosphorus oxides are dissolved and may take place according to the following formulas:

P ₄ O ₆ + 6H ₂ O => 4H ₃ PO ₃

P4O10 + 6H ₂ O => 4H3PO4

The advantage is that the phosphorus oxides from the phosphorus containing material may be recovered as phosphorus acid and/or phosphorus acidity, which may be used for production of e.g. fertilizers.

The feedstock may further comprise a material having a higher energy content as compared to the phosphorus containing material, such as auto shredder residue, ASR and/or plastics.

The advantage is the energy content of the feedstock is increased, thereby the method, and especially the plasma gasification step, becomes more efficient. In addition, extraction of phosphorus from phosphorus containing material can be combined with recovery of other types of materials, from for example auto shredder residue, ASR, and/or plastics.

The method may further comprise a step of transferring heat generated by the method to a heat consumer, such as district heating.

The advantage is that heat generated in the cooling unit may be recovered for heating purposes. Alternatively, the heat may be used for production of electricity by means of a turbine generator.

According to a second aspect there is provided a system for extraction of phosphorus comprising a gasification unit, a cooling unit and a filtering unit, wherein said system is arranged for extraction of phosphorus according to the method above.

The system is able to extract phosphorus according to the proposed method. Thus, the system provides for extraction of phosphorus and has all the above-mentioned advantages of the method. Since the system is modular, comprising a number of different units, it may be tailored to each customer’s specific needs. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically illustrates an example of a system for extraction of phosphorous according to the method of the present disclosure.

Fig. 2 schematically illustrates the method according to the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to a method for extraction of phosphorous.

Fig. 1 schematically illustrates an example of a system 100 for extraction of phosphorus according to the method of the present disclosure.

The system 100 may be modular and comprises a number of different units which will be described more in detail below. The modularity of the system 100 may facilitate design and redesign of the system 100. The system 100 may be tailor-made for example depending on type and size of a feedstock being fed into the system. In one example, the system may be arranged near or at a sewage treatment plant. Standard conduits for liquids and gases may be used for connecting the different units of the system 100 to each other.

As illustrated in Fig. 1 , the system 100 comprises a gasification unit 2, a cooling unit 4 and a filtering unit 9.

The system 100 may further comprise a chopper/shredder unit 1 , a cleaning unit 6, a water-gas-shift unit 7 and/or a pressure swing adsorption (PSA) unit 8. The system may further comprise a container for slug collection 3, an oxygen generator 12, a pump 15, a fan 14, a vessel 5 for collecting phosphoric acid and phosphoric acidity, a vessel for collecting remaining phosphorous and phosphorus compounds 13, a container for collecting H2 10 and/or a container for collecting CO2. By “remaining phosphorous and phosphorus compounds” is meant phosphorus and phosphorus compounds not being dissolved into phosphorus acid and/or phosphoric acidity.

As illustrated in Fig. 1 , the system 100 may comprise a chopper/shredder unit 1 to which a feedstock, i.e. a raw material, is provided. In one example, the chopper/shredder unit 1 is arranged for chopping/shredding the feedstock into a desired size. The chopper/shredder unit 1 may be used for mixing different types of materials, such as a phosphorus containing material and a material with a higher energy content. The system 100 may comprise a plurality of chopper/shredder units 1 . The size and type of the chopper/shredder unit 1 may depend on the size and type of feedstock the system is arranged to process. In a further example, the feedstock is provided in a desired size and/or shape prior to entering the system 100 and a chopper/shredder unit 1 is not needed. In such case, the feedstock may be directly fed into a gasification unit 2, which will be described in detail below.

The feedstock comprises a phosphorus containing material. The phosphorus containing material may comprise sewage sludge, abattoir waste and/or plant waste. By sewage sludge is meant a residual, semi-solid material that is produced as a byproduct during sewage treatment of industrial or municipal wastewater wherein at least a part of the water has been removed from the wastewater. Sewage sludge can be dried, forming a dry substance of about 70-80 %. Dried sewage sludge typically comprises about 3-4 % phosphorus of the dry substance. By “dry substance” is meant the percentage of solids in a mixture of substances. The phosphorus from sewage sludge may originate from urine, faeces and detergent residues from the wastewater. In addition to phosphorus, sewage sludge typically comprises nitrogen, calcium, sulphur, and small amounts of metals, such as Fe, Pb, Cd, Co, Cu, Cr, Hg, Mn, Ni, Ag and Zn.

In addition, the feedstock may further comprise a material having a higher energy content as compared to phosphorous containing material, such as auto shredder residue, ASR, and/or plastics. The reason for mixing the phosphorus containing material with a material having a higher energy content compared to phosphorous containing material is to provide an efficient gasification of the phosphorus containing material.

As mentioned above, the system comprises a gasification unit 2. The system 100 may further comprise a feeding unit (not shown) for feeding the feedstock into a gasification unit 2. The feeding unit may for example be a screw arrangement.

The gasification unit 2 may comprise a pyrolysis zone (not shown) and a plasma zone (not shown). The pyrolysis zone may be arranged for gasification of the feedstock in presence of a predetermined amount of oxygen. The oxygen may be provided from an oxygen generator 12. The amount of oxygen provided may be controlled manually or automatically by means of a valve (not shown). The amount of oxygen provided and the temperature upon gasification may depend on the desired degree of gasification of the feedstock. The provision of oxygen is based on the temperature in the gasification unit 2. For example, if the temperature is too low in order to obtain a desired degree of gasification, a higher amount of oxygen is provided in order to maintain a desired temperature in the pyrolysis zone.

The temperature upon gasification of the feedstock, i.e. in the pyrolysis zone, may be in the range of about 600 to 1200 °C, preferably in the range of 725-1125 °C, most preferably in the range of 850-1050 °C. The gasified feedstock, i.e. ash, may then be provided to the plasma zone of the gasification unit 2. The plasma zone of the gasification unit 2 may be heated to a temperature in the range of 2000-3500 °C, preferably in the range of 2250-3250 °C, most preferably in the range of 2500-3000 °C. The plasma zone may comprise a light arc in which the formation into plasma of the gasified feedstock takes place. The light arc itself may have a temperature of about 8000 °C. Due to the very high temperature, the chemical bonds of the compounds of the gasified feedstock are broken and the compounds may be decomposed into a plasma. Oxygen may be provided by the oxygen generator to the plasma zone in order to form carbon monoxide, CO, of carbon being released upon the formation of plasma. The plasma formed in the gasification unit 2 comprises gaseous elements. The gaseous elements comprise phosphorus and phosphorus compounds. In addition, the gaseous elements may comprise syngas, also known as synthesis gas.

Syngas is a gas mixture comprising primarily of H2 and CO. Depending on the process in which the syngas is formed, such as the material of the feedstock and temperatures in the pyrolysis zone and the plasma zones of the gasification unit 2, the syngas may also comprise small amounts of other gases, such as H2O, CO2, N2 and CH4. As an example, cooled syngas may comprise about 2 % Isl and about 10-15% CO2. Before being cooled, as will be described more in detail below, the syngas may also comprise up to 25 % of H2O. When the syngas is cooled to temperature of below 100 °C, preferably to a temperature in the range of 90 to 20 °C, the main portion of H2O is condensed and thereby separated from the syngas.

By providing pure oxygen instead of air, it is avoided that the resulting syngas comprises unnecessarily high amounts nitrogen or nitrogen compounds.

Upon formation of the syngas, there may also be some residual materials formed in the gasification unit 2, such as inorganic materials, which is condensed before the gas is leaving the plasma zone or is not fully decomposed into plasma. These materials may be collected in a slag collection unit 3. The materials collected in the slag collection unit 3 are typically materials having a relatively high boiling point. Examples of such materials are metals, such as Cu and Si, and metallic compounds. The materials collected in the slag collection unit 3 may be recycled and for example be reused in manufacturing industry. Poisonous metallic materials such as cadmium, may be collected into one or more slag collection units (not shown) being arranged for collecting materials having relatively low boiling points and being connected to e.g. the cooling unit 4 or filtering unit 9. Drug residues, which typically mainly comprises organic compounds, are gasified in the gasification unit 2, thereby contributing to the formation of syngas.

The system 100 may comprise more than one gasification unit 2 in order to ensure a high utilization of the material of the feedstock.

The system 100 may further comprise a cooling unit 4. The cooling unit 4 is arranged to cool the gaseous elements being formed in the gasification unit 2. The cooling unit 4 may comprise a radiation or convection cooler (not shown) and a water spray unit (not shown). Preferably, the gaseous elements are cooled to a temperature of below 100 °C, preferably to a temperature in the range of 90 to 20 °C. During cooling is the main portion of H2O of the gaseous elements is condensed and water-soluble elements of the gaseous elements are solved in the condensed water and thereby separated from the syngas.

In one example, as shown in Fig. 1 , a closed system 17 may be arranged to circulate a working fluid, such as water, by means of a pump 15 from the cooling unit 4 to a water-gas-shift unit 7 and back to the cooling unit 4. The working fluid may be circulated to different parts of the system, thereby heating and/or cooling different units of the system 100. Typically, heat is generated in the cooling unit 4 and/or in the water-gas-shift unit 7.

The heat generated in the cooling unit 4 and/or in the water-gas-shift unit 7 may be used for heating other arrangements, for example arrangements within the building in which the system 100 is arranged. In yet an example, heat generated by the system may be transferred from the system to a heat consumer, such as via district heating. In yet an example, the system 100 may comprise a turbine generator 16, preferably being arranged in connection to the closed system 17 in which a working fluid is arranged to circulate. Electricity generated by the turbine generator may be used for operation of the electricity of the system 100, and optionally also for operation of other arrangements of the building within which the system 100 is arranged.

A predetermined amount of water is provided to the cooling unit 4 from a water container 19. By a predetermined amount of water is meant an amount of water being sufficient for dissolving phosphorus oxides formed in the gasification unit 2 into phosphorus acid a phosphoric acidity. In one example, the water provided is the same water that is used for the cooling of the gaseous elements in the cooling unit 4.

The system 100 may further comprise a first vessel 5 in which the phosphorus acid and phosphoric acidity are collected. The phosphoric acid and phosphoric acidity may be used for production of fertilizers and/or in industrial processes.

The system 100 further comprises a filtering unit 9. The filtering unit may comprise at least one filter, preferably the filtering unit 9 comprises a plurality of filters. In yet an example, the filtering unit 9 further comprises a centrifugal separator (not shown). The at least one filter may be arranged to collect remaining phosphorus and phosphorus compounds. By phosphorus and phosphorus compounds is meant solid phosphorus and phosphorus compounds, such as particles, which have not been dissolved into phosphorus acid and/or phosphoric acidity. In one example, the remaining phosphorus and phosphorus compounds comprises P4. The at least one filter may be a mechanical filter, such as a baghouse filter. The at least one filter may be cleaned by pressurized recirculated syngas at a predetermined time interval, or when needed due to a large amount of phosphorus and phosphorus compounds being collected by the at least one filter. As will be described below, the phosphorus and phosphorus compounds being collected by the at least one filter may be collected in a vessel 13. In yet an example, the filtering unit 9 may be arranged for separating other compounds, such as calcium and/or sulphur, in addition to the remaining phosphorus and phosphorus compounds, from the gaseous elements.

The system 100 may further comprise a second vessel 13 in which remaining phosphorus and phosphorus compounds from the solution is collected. Typically, the remaining phosphorus and phosphorus compounds are in solid form. In one example, red phosphorus, P4, is formed.

The phosphorus and phosphorus compounds may be used for production of fertilizers.

The system 100 may further comprise a cleaning unit 6. The cleaning unit 6 is arranged for cleaning and purifying of the remaining gaseous elements. In one example, the remaining gaseous elements may be led from the cooling unit 4 to the cleaning unit 6 by means of a fan device 14.

The cleaning unit 6 may comprise filters and/or a cleaning liquid which is circulated in the cleaning unit 6 by means of a pump system. In one example, the gaseous elements is firstly led through one or more filters in order to purify the gaseous elements from undesired compounds. Secondly, the gaseous elements are “showered” by the cleaning liquid. The cleaning liquid may typically be water. The cleaning liquid being used in the cleaning unit 6 may be recirculated to the cooling unit 4 and be reused in the water spray unit for spraying water to the gaseous elements in the cooling unit 4. In this step, water (H2O) and water-soluble compounds may be separated from the gaseous elements. The extracted syngas may be repeatedly circulated within the cleaning unit 6 until the syngas has reached a desired purity.

The system 100 may comprise a plurality of cleaning units 6 arranged after one another. In one example, the plurality of cleaning units 6 may comprise different types of filters and/or cleaning liquids. The syngas resulting from the cleaning unit 6 typically comprises hydrogen gas (H2) and carbon monoxide (CO) in the ratio of 1 :1 . In addition, the syngas may comprise small amounts of carbon dioxide gas (CO2), nitrogen gas (N2) and traces of methane gas (CH4).

The syngas resulting from the cleaning unit 6 may, but need not, be compressed by a compressor (not shown).

The system 100 may further comprise a water-gas-shift unit 7, to which CO and H2 (syngas) is fed. In the water-gas-shift unit 7, water steam is provided, wherein CO from the syngas reacts with water, thereby forming CO2 and H2 according to the following formula:

CO + H ₂ O => H ₂ + CO ₂

The water-gas-shift unit 7 may be a commercially available water-gas-shift unit. As discussed above, the water-gas-shift unit 7 may generate heat which may be arranged to heat the working fluid in the closed system 17.

The system 100 may further comprise a pressure swing adsorption, PSA, unit 8. Pressure swing adsorption is a well-known technique used to separate some gas species from a mixture of gases. In the system 100, the pressure swing adsorption unit 8 is arranged for separating CO2 and H2. The resulting H2 being separated by the swing adsorption unit 8 has a high purity, typically in the range of 99.99 %.

The CO2 being separated in the PSA unit 8 may preferably be liquefied and be stored in a sealed container 11 . The separated CO2 may be subject to carbon capture and utilization, CCU. CCU is a process where carbon dioxide is captured and is recycled for further usage. The aim of CCU is to convert the captured carbon dioxide into e.g. plastics, concrete or biofuel in a controlled way, thereby preventing the CO2 from reaching the atmosphere. Alternatively, the CO2 may be subject to carbon capture and storage, CCS, wherein the CO2 may be permanently stored in an underground geological formation, thereby preventing the CO2 from reaching the atmosphere.

The H2 being separated in the PSA unit may be collected in a sealed container 10 and be used in for example industrial processes. The system can for example be arranged at, and connected to, an industrial plant requiring hydrogen in their processes and thereby transport of the hydrogen can be eliminated.

Fig. 2 schematically illustrates the method according to the present disclosure.

The method for extraction of phosphorous comprises a step of providing a feedstock 201 comprising a phosphorus containing material. The phosphorus containing material may comprise sewage sludge, abattoir waste and/or plant waste. As mentioned above, the feedstock may further comprise a material having a higher energy content compared to phosphorous containing material, such as auto shredder residue, ASR and/or plastics. ASR comprises for example glass, fiber rubber, automobile liquid and/or plastics. The reason that the feedstock further may comprise a material having a higher energy content compared to phosphorous containing material is to obtain an efficient gasification process. The phosphorus containing material, such as sewage sludge, and the material having a higher energy content compared to phosphorous containing material may, but need not, be mixed in order to form a homogenous mixture, for example in a chopper/shredder unit before gasification of the feedstock.

The method further comprises a step of gasification of the feedstock 202 by plasma gasification in an oxygen poor environment, thereby forming gaseous elements comprising phosphorus and/or phosphorus oxides. As noted above, due to the very high temperature upon the gasification, the chemical bonds of the compounds of the gasified feedstock are broken and the compounds may be decomposed into a plasma. The gaseous elements may further comprise syngas. Syngas, also known as synthesis gas, is a gas mixture comprising primarily of H2 and CO. Depending on the process in which the syngas is formed, such as the material of the feedstock and temperatures in the pyrolysis zone and the plasma zones of the gasification unit 2. The syngas may also comprise small amounts of other gases, such as H2O, CO2, N2 and CH4. As an example, cooled syngas may comprise about 5 % N2 and about 5 % CO2. Before being cooled, the syngas may also comprise up to 25 % of H2O.

By oxygen poor environment is meant an environment with a deficit of oxygen. In the oxygen poor environment, phosphorous oxides such as P4O6 and P2O3 are typically formed. If there is an excess of oxygen, other phosphorus oxides are typically formed, such as P2O5. As oxygen poor environment is at hand, the yield of hydrogen formed upon gasification is also maximized.

The amounts and types of phosphorous oxides formed in the oxygen poor environment may thus be dependent on the amount of oxygen supplied to the gasification unit during the gasification step.

The amount of oxygen being supplied depends on the type of feedstock, i.e. on the energy content of the feedstock. In one example, the amount of oxygen provided in the method may be in the range of 0.1 -0.5 kg oxygen per kg feedstock when the feedstock has an energy content of about 17-26 M J/kg. The lower energy content of the feedstock, the more oxygen needs to be supplied in order to obtain an efficient gasification. In one example, the feedstock may comprise 1/3 phosphorus containing material, such as sewage sludge, and 2/3 comprising a material having a higher energy content compared to phosphorous containing material, such as auto shredder residue, ASR, and/or carbon fibre reinforced plastics.

As discussed with reference to the system above, the temperature upon gasification of the feedstock may be in the range of 600-1200 °C, preferably in the range of 725-1 125 °C, most preferably in the range of 850-1050 °C in the pyrolysis zone of the gasification unit, and in the range of 2000-3500 °C, preferably in the range of 2250-3250 °C, most preferably in the range of 2500-3000 °C in the plasma zone of the gasification unit.

The phosphorus containing material is exposed to a temperature such that the phosphorus formed may comprise red phosphorus, P4, preferably said temperature is comprised in a temperature range with a lowest end point of 300 °C.

The method further comprises a step cooling of the gaseous elements 203. The step of cooling the gaseous elements are discussed with reference to the system above.

The method further comprises a step of providing a predetermined amount of water 204 to the gaseous elements in order to form a solution in which phosphorus oxides are dissolved into phosphorus acid and/or phosphoric acidity. The step of providing a predetermined amount of water to the gaseous elements in order to form a solution in which phosphorus oxides are dissolved may take place according to the following formulas:

P4O6 + 6H2O => 4H3PO3 (phosphoric acidity)

P4O10 + 6H2O => 4H3PO4 (phosphorus acid) The amount of phosphorus acid and phosphoric acidity that are formed in relation to the amount of solid phosphorus and phosphorus compounds is determined by the amount of oxygen that is supplied during the gasification of the feedstock. The amount of oxygen supplied during the gasification of the feedstock may be automatically controlled based on the temperature in the gasification unit 2. If the temperature is too low to form the desired amount of phosphorus acid and phosphoric acidity in relation to the amount of solid phosphorus and phosphorus compounds, an increased amount oxygen is supplied to the gasification unit 2 in order to maintain the temperature in the gasification unit 2.

The method further comprises a step of separating phosphorus from the phosphorus acid and phosphoric acidity 205 and collecting the separated phosphorus in a first vessel.

Many alternatives are possible to use as method of separation, for example by adding an alkali substance to the solution and then evaporating, and collecting the salt, for a later acidification as described below. It is also possible to use distillation, all depending on the end user demands for the phosphorus material.

In one example, the step of separating phosphorus from the phosphorus acid and phosphoric acidity (205) and collecting the separated phosphorus in a first vessel comprises providing an alkaline substance to the solution, wherein the phosphorus acid and/or phosphoric acidity react with the alkaline substance and form at least one phosphorus containing salt, and collecting the at least one phosphorus containing salt in a first vessel.

An example of alkaline substance is a chemical compound comprising calcium, such as calcium carbonate, CaCOs, also known as limestone, or calcium hydroxide, Ca(OH)2. The phosphorous containing salt(s) may be for example calcium phosphate. In one example, the at least one phosphorus containing salt(s) is separated from the solution and collected in the first vessel by means of an osmotic membrane.

The method further comprises a step of separating the remaining phosphorus and phosphorus compounds 206 from the solution and collecting the phosphorus in a second vessel. Typically, the phosphorus and phosphorus compounds being separated in this step is in solid phase and not soluble in water. The separation of phosphorus and phosphorus compounds takes place as described with reference to the filtering unit 9 above.

If the gaseous elements comprise sulphur and/or calcium, the method may further comprise a step of separating sulphur and/or calcium 207 from the gaseous elements. The method may further comprise a step of cleaning the remaining gaseous elements and extracting syngas 208 from the remaining gaseous elements.

In this step, water-soluble compounds and solids are removed from the syngas. This may be performed by the cleaning unit 6 as described with regard to the system above.

The method 200 according to any of the preceding claims, further comprising a step of allowing CO from the syngas to react with H2O 209 according to the following formula:

CO + H ₂ O => H ₂ + CO ₂ .

Preferably, the H2O is water steam. This this step the yield of hydrogen is increased. As described above, this step may be performed by the water-gas-shift unit 7. This is followed by a step of of separating H2 and CO2 into two streams 210 of hydrogen gas and carbon dioxide gas respectively, and collecting the carbon dioxide and hydrogen gas in sealed containers. The CO2 being separated in the PSA unit 8 may preferably be liquefied and be stored in the sealed container. The separated CO2 may be subject to carbon capture and utilization, CCU. CCU is a process where carbon dioxide is captured and is recycled for further usage. The aim of CCU is to convert the captured carbon dioxide into e.g. plastics or biofuel in a controlled way, thereby preventing the CO2 from reaching the atmosphere. Alternatively, the CO2 may be subject to carbon capture and storage, CCS, wherein the CO2 may be permanently stored in an underground geological formation, thereby preventing the CO2 from reaching the atmosphere.

The method may further comprise a step of transferring heat generated by the method to a heat consumer 211 , such as district heating.