ES2956933A1 - ABSORPTION TOWER AND PROCESS TO RECOVER NITROGENATED NUTRIENTS FROM WASTE FROM AGRIBUSINESS (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

The present invention refers to a piece of equipment, system and process that finds industrial application in the use of agro-industrial waste or equivalent and that is especially indicated for the treatment of digestate from anaerobic digestions or similar with a high content of solid fraction. The equipment of the invention is an absorption tower configured to work with concentrations of solids in the liquid phase of up to 10% by weight, where said tower comprises: an inlet for the gas stream, a base with a vibrating system, a central body , an outlet configured to receive the gas phase through the lid. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

ABSORPTION TOWER AND PROCESS TO RECOVER NITROGENATED NUTRIENTS FROM WASTE FROM AGRIBUSINESS

OBJECT OF THE INVENTION

The present invention refers to equipment and a method that finds industrial application in the use of agroindustrial waste to improve the quality of the environment and, more particularly, in the revaluation and decontamination of agroindustrial waste, agroindustries being understood as those that encompass the production, transformation and marketing of agricultural, livestock, forestry, fishing, forestry and natural biological resources products.

BACKGROUND OF THE INVENTION

The use of agroindustrial waste or equivalent and treatment of digestate from anaerobic or similar digestion is characterized by:

- Liquids with high corrosive power;

- Products with solids concentrations at the system inlet of between 3 and 10%

- High concentrations of nitrogenous compounds, such as NH4 compounds

Normally the treatment of waste with these characteristics involves applications to the field through the use of cisterns. The problems associated with this practice are:

- Needs to occupy large areas of agricultural land.

- Complications of logistics management

- Nitrogen load, which is limited to 210 kg/ha.

Currently, there are very few facilities that treat liquid digestate waste from agroindustrial waste with the aim of recovering nutrients (nitrogen compounds and water). The facilities that carry out a process similar to that proposed in this patent application are industrial processes for treating slurry from the livestock industry. The production process is based on anaerobic digestion processes and/or dehydration of the liquid phase based on cogeneration plants.

On the other hand, cogeneration is the joint production of electrical energy and useful heat energy from primary energy which, in most cases, is natural gas.

The process involves:

- Gas engines or turbines that generate electricity using natural gas (NG) and/or biogas as fuel.

- Use of the heat generated for an atmospheric or vacuum evaporation process.

Cogeneration associated with fuels such as NG for waste treatment have been facilities prioritized by public administrations. Currently, these types of facilities are no longer authorized.

The trend in this sector is to treat agroindustrial waste, including livestock waste and other organic waste, in biomethanation plants to obtain biogas and with a subsequent transformation into biomethane injectable into the network, with CO2 recovery.

However, in biomethanization plants with grid injection, residual thermal energy is not available as in the case of cogeneration plants and it is no longer possible to evaporate the resulting liquid fraction at a reasonable cost. In these plants, a new solution must be found for the industrialized treatment of digestate.

A common technology for the recovery of nitrogenous compounds is “Stripping”. The conventional system of this technology requires that the liquid be practically free of solids (total solids concentrations less than 120 ppm). The liquid waste to be treated has high concentrations of solids and to achieve the appropriate solids values, energy-intensive prior treatments are required. Carrying out a conventional Stripping process with solids concentrations higher than those indicated, generates incrustations and blockages in the absorption tower (Stripper) in a few hours or days, leaving it out of service.

Therefore, the present invention seeks to reduce the drawbacks of the previous state of the art associated with the recovery industry of nitrogenous compounds, particularly, ammonium sulfate and others for use as fertilizers, and the recovery of liquid waste for agricultural irrigation, counteracting the current drawbacks and providing new advantages.

EXPLANATION OF THE INVENTION

The present invention refers to equipment and a method that finds industrial application in the use of agroindustrial waste to improve the quality of the environment and, more particularly, in the revaluation and decontamination of agroindustrial waste, agroindustries being understood as those that encompass the production, transformation and marketing of agricultural, livestock, forestry, fishing, forestry and natural biological resources products.

Waste from agribusiness includes, among others, livestock waste, digestate from biogas plants, leachate from landfills, wastewater from agri-food industries, meat industries, which can be used in the present invention to obtain recovered nutrients of high value, as well as a liquid waste that is easier to manage.

The Stripping absorption equipment (degassing), the system and method of the present invention solves the problem of treating digestate and other similar waste, waste with high loads of solids and nitrogenous compounds, using a system that gives movement to the filling of the absorption tower avoiding fouling, blockages and the establishment of preferential channels in the tower. With this system, energy consumption is reduced, reducing waste treatment costs compared to the treatments used in a conventional stripping system and the previous treatments that these systems require.

The first aspect of the invention is an absorption tower (1) to remove at least one compound from a liquid stream, configured to work with concentrations of solids in the liquid phase of up to 10% by weight, where said tower comprises:

a) an inlet for the gas stream (7),

b) a base with a vibrating system (4)

c) a central body (2) that comprises:

Yo. a central tube (7c), preferably made of metal, rigidly attached to the vibrating system (4), where the central tube (7c) has at least one gas flow inlet (7a) at the bottom,

ii. a lower tray (8b) and upper cover (8c) attached to the central tube (7c), Ni. at least one perforated plate (6) attached along the central tube (7c), preferably between 3-5 perforated plates (6),

iv. an inlet system for the liquid phase (5) located in the upper part of the central tube (7c),

v. perimeter closures (8d) that join the lower tray (8b) and the central tube (7c) and the upper cover (8c) and the central tube (7c),

d) an outlet (3) configured to receive the gas phase through the cover (8c).

The second aspect of the invention is therefore related to a system for the recovery of nitrogenous nutrients from agroindustry waste, such as those from food industries, leachates from landfills, digestate from biogas plants and livestock waste, among others. which includes:

- Feeding media (9) for waste from the agri-food industry.

- Means for preheating phase 1 waste (15).

- Means for heating the waste phase 2(10).

- Means for dosing the basic medium (11).

- Absorption tower (1) according to the first aspect of the invention.

- Desorption tower (12).

- Means for dosing the acid medium (13).

- Outlet (14) of the desorption tower adapted for liquids, where said liquids include nitrogenous compounds,

- Suitable media for coagulation and flocculation (16).

- Centrifuge suitable for the separation of solids (17), said centrifuge being located after the coagulation and flocculation means (16).

- Outlet (18) of the centrifuge (17) adapted for the liquid fraction treated in the process.

- Outlet (19) of the centrifuge (17) adapted for the solid fraction treated in the process.

A third aspect of the invention is related to a process for obtaining nitrogenous nutrients, preferably ammonium sulfate and treated water from agroindustry waste using the system of the second aspect of the invention, which comprises the steps:

Yo. provide waste from the agri-food industry,

Yo. subjecting said waste to a heating process to provide a waste at a temperature of 60-75°C.

neither. treating the residue obtained in the previous phase with an alkaline solution to provide a residue with a pH between 7.5 and 10,

iv. extract the nitrogenous compounds from the liquid waste of the previous stage by using an air stream with a flow between 1,500 m3 of gas/m3 of liquid waste to be treated up to 4,000 m3 of gas/m3, preferably between 1,500 and 2,500 m3 of gas /m3 of liquid waste to be treated, in an absorption tower according to the first aspect of the invention, to provide a gas phase rich in nitrogen compounds and a liquid phase with a reduction in its NH3-N content of 65-80 % with respect to the liquid residue.

v. Subjecting said gaseous phase rich in nitrogen compounds obtained in the previous stage to a desorption step through the use of a liquid acid stream, to obtain an acidic liquid phase containing ammonium salts.

saw. Optionally, the liquid phase obtained in step (iv) to a solids elimination step through a coagulation, flocculation and centrifugation step to obtain a solid residue and a liquid, where the solid residue comprises a % by weight of solids between 15-25% and a liquid waste containing at least 95% water, preferably 98% water.

BRIEF DESCRIPTION OF THE DRAWINGS

Both the main object of the invention and the advantages achieved can be seen in the following description of embodiment examples, with references to the diagrams shown in the attached figures, in which:

FIG. 1: shows an isometric view of the stripper system (1) according to a preferred embodiment of the present invention.

FIG. 2: shows an elevation view of the stripper (1) in fig. 1, composed of a central body (2), the vibrating system (4) and the gas outlet (3). The vibrating block is tied to the floor with elastomers (4b) and the vibrating system is moved by the motor vibrators (4a).

FIG. 3: shows an elevation view, in cross section, of the stripper (1) according to figure 2 where the detail of:

- Main air inlet 7.

- Detail of the air inlet through the vertical tube, details 7a and 7b.

- Central support tube 7c.

- Tower closures 8, which incorporates the lower tray 8a, the liquid phase outlet 8b (tangential to the lower tray), the upper cover 8c and the tower closure 8d

- Inlet of the liquid to be treated 5, with the details of the inlet channel 5a and distributor of the liquid to be treated 5b

- Drop separator 3a

- Details of exit 3, with exit cone 3b.

- Detail of the perforated plate, filling support 6.

FIG. 4: shows a plan view of section BB of Fig. 4. This view shows the detail of the plate with the detail of the arrangement of the staggered holes 6a and perforations of the plate 6b.

FIG. 5: shows a plan view of the CC section of Fig. 4. This view shows the detail of the liquid phase inlet (5) with the details of the inlet conduction 5a and distribution ring 5b. At the same time, the closure of the tube 7c by means of the closure 8e is observed.

FIG. 6 shows a plan view of section BB of Fig. 4. This view shows the detail of the plate.

FIG. 7: shows an elevation view, in cross section, of the plate with the filling (6c).

FIG. 8: shows a schematic plan of equipment and a process to recover nitrogenous nutrients from food industry waste.

In all figures, the same references correspond to the same or equivalent elements.

PREFERRED EMBODIMENTS OF THE INVENTION

All embodiments of the invention are described in detail below. However, it should be understood that the invention is not limited in its application to the details of construction and configuration of components set forth in the following description, or illustrated in the drawings. Likewise, it should be understood that the terminology used in the present invention has a descriptive purpose and should not be considered limiting.

A first aspect of the invention is related to an absorption tower (Stripper) (1), adapted to work with high concentrations of solids in the liquid phase, preferably up to 10% solids. In general, absorption towers or strippers are equipment used to remove at least one compound from a liquid stream. This process is achieved through the exchange of cross flows of a liquid and a gas phase. The liquid phase is poured from the top and goes down the tower, generally due to the effect of gravity. As it falls, it encounters the ascending gas phase, which has been introduced under pressure generally from the bottom, achieving intimate contact through a filling with a large contact surface.

The absorption tower for removing at least one compound from a liquid stream, configured to work with concentrations of solids in the liquid phase of up to 10% by weight, where said tower comprises:

a) an inlet for the gas stream (7),

b) a base with a vibrating system (4)

c) a central body (2) that comprises:

Yo. a central tube (7c), preferably made of metal, rigidly attached to the vibrating system (4), where the central tube (7c) has at least one gas flow inlet (7a) at the bottom,

ii. a lower tray (8b) and upper cover (8c) attached to the central tube (7c), nor. at least one perforated plate (6) attached along the central tube (7c), preferably between 3-5 perforated plates (6),

iv. an inlet system for the liquid phase (5) located in the upper part of the central tube (7c),

v. perimeter closures (8d) that join the lower tray (8b) and the central tube (7c) and the upper cover (8c) and the central tube (7c),

d) an outlet (3) configured to receive the gas phase through the cover (8c).

The base with a vibrating system (4). provides movement to the absorption tower assembly (stripper). This system includes at least two motor vibrators. In a preferred embodiment of the first aspect of the invention, the vibrating system is a vibrating cube, that is, it comprises two motor vibrators tied to a metal cube, in turn tied with elastic supports to the ground (4a). The motorvibrators (4b) are located on two of the faces of the cube facing each other, forming an angle with the horizontal of 20-35°, with a preferred value of 25o. The position of the motor vibrators and their vibrating power can be adjusted to give the vibrating tower the movement required by each product to be treated, preferably transferring vertical and rotational movement to the tower simultaneously. The metal cube is hollow and has a pipe for the entry of the gas phase (7), preferably air, on one of the free sides. This pipe, preferably metal, is elastically joined to the pipeline to which it is connected. The hub is connected to the central body (2), through the central tube (7c). Thus, the inlet air arrives through the inlet (7), passes through the interior of the tube and reaches through it to the central tube in its lower part.

The central body (2) is formed by a central tube (7c), made of preferably metallic material, rigidly attached to the vibrating system (4). A lower tray (8b) and a lid (8c) are attached to this tube at the bottom. Perforated plates (6) are fitted along the tube.

The perforated plates have a semitoroidal geometry so that they can be stacked along the central tube (7c). The plates that support the filling have perforations, the perforated part being 20-50% of the surface of the plate depending on the waste to be treated. The diameter of the perforations is also variable depending on the waste to be treated; this diameter can vary from 6 to 12 mm.

Preferably each perforated plate (6) contains a filling (6c) formed from rings or cylinders of plastic or metal materials, for example, stainless steel, polyethylene (PE), rubber or styrene-butadiene rubber (SBR), with a large surface per cubic meter, a ratio of the order of 100-350 m2/m3, preferably 250 m2/m3.

In the upper part, next to the outlet cover, the liquid phase inlet system (5) is placed. Joining the lower tray and the lid, the perimeter closure (8d) is placed. This central body is a cylindrical figure with a diameter (D), height (A), (A/D) ratio of 4-5, preferably 4. The relationship between the diameter of the tube (D1) versus the diameter (D) ( D/D1) is between 2.5-3.5, preferably the D/D1 ratio is 3. The materials required are of high mechanical and chemical resistance, for example, stainless steels, polyethylene (PE), polypropylene (PP), polytetrafluoroethylene ( PTFE) or materials with equivalent characteristics, which must withstand the vibrating movement and corrosion generated by the liquids to be treated. In the case of the perimeter closure (8d), it must be adjusted to the side of each of the perforated plates, preventing the gas phase from finding preferential channels, thus losing part of the performance of the system. This problem can be solved by making a closure with an elastomer, for example, styrene-butadiene rubber (SBR) or butyl.

The entry of the liquid phase to be treated is carried out through the inlet (5) by means of pumping, which, in its connection with the vibrating equipment, has an elastic connection that absorbs the vibration. Preferably, the liquid reaches a distribution ring (5b) with a toroidal geometry and which is located in the upper part hugging the central tube. This ring or toroid at the bottom has perforations with a diameter of 10-15 mm, depending on the product to be treated. Through these perforations, with the geometry and position of the ring, it is achieved that the liquid to be treated reaches the upper plate to the central area where the filling is located (6c).

The gas phase enters the central body, passing from the vibrating system (4) to the central tube (7c) in its lower part. The central tube in its upper part is covered and in the lower part it has some holes (7a) through which the gas phase, air, for example, comes out. At its exit, the air meets the perforated plates (6) with filling (6c) and its only exit is to ascend through them. The tube exit holes are arranged in a distributed manner so as not to reduce the rigidity of the central tube (7c), and not to generate an excessive pressure loss that generates greater energy consumption. These exit holes have a cap (7b) in a slightly upper section of the tube, which prevents the liquid phase from entering them and directs the gas flow to the lower part of the lower perforated plate.

The liquid phase, loaded with the substance to be removed (nitrogen compounds, for example), reaches the upper plate, the liquid tends to go down from plate to plate due to the effect of gravity. The vibrating movement of the tower transmits a movement to the falling liquid that opposes its fall, generating retention. In turn, a movement of the filling (6c) is generated with respect to each perforated plate (6). The filling jumps and rotates with random movements. At the bottom of the tower, through the outlets (7 a), the gas phase (air, for example) exits and rises through the perforated plates (6) and the filling (6c). The effect of the vibrating movement of plates and filling with the effect of the fall of the liquid due to gravity, generates an intimate contact between the liquid and gas phases, favoring the absorption of the compound to be removed from the liquid phase to the gas phase. .

The vibrating movement of the tower, in addition to improving the contact between phases, increasing the performance per m3 of filling with respect to a static system, has another additional advantage; which allows treating liquids with high concentrations of solids compared to a conventional static filling system. In a conventional static filling system, when the liquid contains more than 100-200 ppm of solids, the system generates scale, some channels are closed and others are established as preferential, causing the system to collapse in a short time. With the system object of the invention, the vibrating movement prevents the incrustations from progressing in the perforated plates and the relative movement of the filler with respect to the perforated plates keeps the perforation holes open at all times. In turn, the filling jumps and rotates, hitting each other and the surface that contains it, in this way the encrustations do not progress. In this way, the main advantage of the system is achieved, which is the treatment of liquids with solids concentrations much higher than those treated by a conventional absorption system.

The liquid, after passing through the perforated plates of the tower, ends up falling into the lower tray (8a). This tray has an outlet pipe (8b), which is joined to the rest of the system installations by means of an elastic union. This conduit is located tangentially at the bottom of the lower tray. The vibrating movement of the tray causes the liquid to rotate and its exit is facilitated due to the centrifugal force it experiences.

The gas phase, after passing through the perforated plates of the tower, reaches the upper part of the tower, to the part called the lid (8c). In this part there is also a cover (8e), which covers the central tube (7c) and facilitates the passage of gas to the outlet (3). This cover (8c) is rigidly attached to the outlet (3).

The outlet (3) receives the gas phase (for example, air loaded with nitrogenous compounds) through the cover (8c). This outlet has a cylindrical part where a drop separator (3a) is housed and a conical part (3b) that reduces the section smoothly to avoid overpressures, also reducing drag and pressure losses.

The cylindrical part is intended to house the drop separator. The diameter of the drop separator (D2) has a relationship with the diameter of the tower D, D/D2 of 0.4-0.6, with a preferred value of 0.5. The conical part joins the drop separator with the flexible outlet that connects the equipment to the rest of the installation. The cone has a ratio between the largest diameter D2 and the smallest diameter D3, (D2/D3) of 0.3-0.6, with a preferred value of 0.5. The cone ratio between D2 and height A2 (D2/A2) is 1-1.5, with a preferred value of 1.2. The incorporation of the drop separator prevents the entrainment of small water droplets that can be dragged by the gas stream due to the significant agitation that the liquid phase undergoes due to the vibrating movement.

The gas phase obtained in the equipment after the treatment of the liquid phase, is conducted for subsequent treatment in a system that regenerates the gas phase, recovering the absorbed element (for example, nitrogen compounds).

A second aspect of the invention is related to a system intended for the revaluation of agro-industrial waste to improve the quality of the environment, which is suitable for the recovery of nitrogenous compounds, particularly useful as nutrients. The system of the present invention is characterized by being versatile, since it adapts to the treatment of various types of waste, such as livestock waste, biogas plant digestates, landfill leachates, wastewater from agri-food industries, meat industries or mixtures of the same, all with a minimum energy cost. With the system of the present invention, it is possible to recover nitrogenous compounds that are high-value nutrients.

The system of the present invention to recover nitrogenous compounds useful as nutrients from agroindustry waste, such as those from food industries, leachates from landfills, digestates from biogas plants, livestock waste, among others, comprises:

- Feeding media (9) for waste from the agri-food industry,

- Suitable means for preheating the waste (15),

- Suitable means for heating the waste (10),

- Means for dosing basic medium (11),

- Absorption tower (1) according to the first aspect of the invention,

- Desorption tower (12),

- Means for dosing acid medium (13),

- Outlet (14) of the desorption tower (12) adapted for liquids, where said liquids include nitrogenous compounds,

- Suitable media for coagulation and flocculation (16).

- Centrifuge suitable for separating solids, said centrifuge (17) being located after the coagulation and flocculation means (16),

- Outlet (18) of the centrifuge adapted for the liquid fraction treated in the process,

- Outlet (19) of the centrifuge (17) adapted for the solid fraction treated in the process.

The residue to be treated in the liquid phase (9) arrives at the process to be heated from room temperature, 20°C, to 50-80°C, preferably 60-75°C, more preferably 70°C. This heating is carried out in the heat exchange equipment (15) and (10). The first phase of heating, preheating (15), is carried out in a heat recovery, prepared for two fluids with high concentrations of solids, a spiral type exchanger. In this equipment, part of the energy possessed by the treated waste at the exit of the absorption tower (1) is recovered. With this preheating it is possible to provide between 30-40% of the energy required for the process, preferably 35%. This means energy savings and optimization of the process. The preheated waste passes to a water tube shell exchanger (10), where the heating process is completed until the desired temperature is reached depending on the waste to be treated and the required performance of the process. These values can be between 50 and 80oC, the preferred value being between 60-75°C, more preferred 70°C. This phase of heating the waste is carried out by providing hot water or steam generated by external equipment to the heating equipment (10).

Between the heater and the absorption tower (1) there are means for dosing a basic agent (11) that are intended to reduce the consumption of the basic agent in subsequent stages, raising the pH of the liquid waste stream that has been been previously heated with the aim of improving the performance of the recovery of nitrogenous compounds. An advantage of this work system in a basic environment compared to an acidic one is that it facilitates protection against deterioration of the mechanical equipment that follows the process, making them more robust and reliable.

The absorption tower (1) connected upstream of the basic PH adjustment system (11), is configured for washing in basic medium the condensed phase coming from the heater (10). Said absorption tower (1) has perforated plates with a filling. The tower assembly has a vibrating movement that favors the absorption process of the liquid phase with the gas phase (preferably air) and prevents deposits from forming in the system, allowing work with a liquid phase with high concentrations of solids.

In turn, the absorption tower (1) is connected to a desorption tower (12), which is configured to wash the gas phase rich in nitrogen compounds from the absorption tower or Stripper (1), using a acid stream.

The outlet (14), adapted for liquids, is configured for the outlet of a liquid phase rich in ammonium salts, coming from the desorption tower (12). Said liquid phase, rich in ammonium salts, is useful as a nutrient and particularly comprises ammonium sulfate.

The equipment also includes at least one desorption tower (12) - which includes means for dosing acid medium (13), said desorption tower (12) is suitable for washing gases in acid medium.

Additionally, the equipment includes a tank (13) adapted to store liquid solids and means to provide acidic pH.

The treated water outlet from the absorption tower (1), prior to its conduction to the solids separation system (17), reaches the heat exchange equipment (15). In this equipment, part of the heat is transferred to the liquid waste to be treated (9). After recovering part of the heat from the treated liquid waste, it is taken to the coagulation and flocculation means (16).

The coagulation and flocculation media (16) are suitable for improving the performance of solids separation with the centrifuge (17), reaching yields in the separation of (SST) with this process greater than 80% of total suspended solids. (TSS) of the residue stream, preferably 75%.

Said centrifuge (17) is located after the coagulation and flocculation means (16), that is, upstream of them.

A third aspect of the invention is related to a process for obtaining nitrogenous nutrients, preferably ammonium sulfate from agroindustry waste, through the system of the second aspect of the invention that comprises the steps:

Yo. provide waste from agribusiness,

ii. subjecting the waste from the previous stage to a two-phase heating process, to provide a waste at a temperature,

ii. treating the residue obtained in the previous stage with an alkaline solution to provide a liquid residue with a pH between 7.5 and 10,

iv. extract the nitrogenous compounds from the liquid waste of the previous stage, by using an air stream with a flow between 1500 m3 of air/m3 of liquid waste to be treated up to 4000 m3 of air/m3 of liquid waste to be treated, preferably between 1500-2500 m3 of air/m3 of liquid waste to be treated, in an absorption tower (1), to provide a gas phase rich in nitrogen compound and a liquid phase with an NH3-N content between 60-10 mg/ l, and,

v. subjecting said gaseous phase rich in nitrogen compounds obtained in the previous step to a desorption step through the use of a liquid stream of acid, to obtain an acidic liquid phase containing ammonium salts, preferably ammonium sulfate,

saw. Optionally, subject the liquid phase obtained in phase (iv) to a solids elimination step through a coagulation, flocculation step and subsequently centrifugation to obtain a solid and a liquid fraction with reduced content of suspended solids.

The heating of stage (ii) occurs in two stages, a preheating carried out with the residual heat of the treated product in a spiral exchanger (15), where between 30-35% of the required energy is added to the input liquid waste. . In the second phase, a second heating of the waste is carried out in a shell-tube exchanger or similar, with energy in the form of hot water at 70-90°C heated in equipment external to the process. In this stage, the temperature of the waste is raised, adjusting it depending on the composition of the waste and the performance of the required process, preferably between 50 and 800C, more preferably at 60-750C. even more preferably at 700C.

In stage (v), the waste, after giving up part of the thermal energy, is subjected to a solids elimination process through a physical-chemical process composed of flocculation and coagulation (16) and separation in a centrifuge (17). The overall performance of this process in separating solids is 60-80%, preferably 75-80%.

The liquid waste treated in stage (vii) at its exit retains heat that is recovered to preheat the input waste to be treated (9). A spiral type heat exchanger (15) is used for this process, which allows good performance in the heat transfer of two fluids with high concentrations of solids.

The liquid waste containing nitrogenous compounds obtained in step (ii) adjusts its pH to a range between 7.5-10 by adding an alkaline solution, preferably sodium hydroxide, in an absorption tower (1). In said absorption tower (1), the alkaline solution is brought into contact with a gas stream, preferably in an air stream for the absorption of nitrogen compounds, so that a liquid phase with a low content of nitrogen compounds is obtained. nitrogen and a gas phase rich in nitrogen compounds, for example ammonia; Then said gas phase, rich in nitrogen compounds, is subjected to a desorption process in a desorption tower (12), by adding a liquid stream of acid for the formation of an acidic liquid phase rich in ammonium salts and a gas stream, which essentially contains air, which is recirculated in a loop towards the interior of the absorption tower (1), where stage iv) of extraction of the nitrogen compounds in an air stream takes place, with the consequent conservation of heat energy, which favors the absorption process of nitrogen compounds from the liquid phase of the waste.

The concentration of the ammonium salts that leave the desorption tower (12) in solution is controlled by measuring the conductivity of the salt produced.

During stage v) of desorption of gaseous nitrogen compounds, the gas phase from the extraction stage of nitrogen compounds (iv) carried out in an absorption tower (1) is brought into contact with a liquid phase acidic, preferably comprising sulfuric acid in a desorption tower (12), in this way a liquid phase rich in ammonium salts and a gas phase poor in nitrogen compounds is obtained that is recirculated to the extraction stage (iv) in the absorption tower (1). In this stage the following reaction is carried out when the acid phase contains sulfuric acid:

2NH3 H2S04-> (NH4) SO4, with a purity of more than 40%.

The process for obtaining nitrogenous nutrients of the present invention is especially adapted for the treatment of waste obtained from anaerobic digestion processes, preferably liquids in the form of sludge, wastewater from agri-food industries, livestock waste, landfill leachates or mixtures of the same, preferably in a percentage by weight of solids up to 10% by weight, preferably the percentage of solids is between 1 and 8%, even more preferably the percentage of solids is between 12 and 16%.

Additionally, the waste from step (i) comprises nitrogenous compounds, preferably comprising NH3-N in a concentration by weight in the residue between 0.1-5 kg/m3.

In the centrifugation step (vi), preferably, the resulting liquid residue obtained has a solids concentration of less than 1.5%.

As already indicated, this process is specially designed for the treatment of digestate from anaerobic or similar digestion and is characterized by having:

- High flow rates from 3 m3/h.

- Liquids with high corrosive power.

- Solids concentrations in the product input of 2-6%.

- High concentrations of nitrogenous compounds, for example, NH4 derivatives.

This indicates that the method and equipment of the present invention (absorption tower (1)) is configured to be able to operate with liquid waste with very high concentrations for this type of equipment.

The process of the present invention allows the following advantages to be obtained:

- This is a recuperative and non-eliminative process.

- Allows the recovery of a very high percentage of nitrogenous waste (70-85%) as fertilizer in the form of ammonium sulfate, without prior treatment to eliminate solids.

- Low consumption of electrical and thermal energy in the entire process. With respect to thermal energy, no phase changes are required. Part of the energy (>30%) is recovered from the waste heating process. With respect to electrical energy, the main consumption is pumps and vibrators, of low power, not comparable with alternative systems such as reverse osmosis or nitrificationdenitrification (NDN) processes for the elimination of NH4.

- Operational improvements associated with the use of a basic pH in the extraction stage.

- Obtaining ammonium sulfate with up to 40% purity.

- High performance in obtaining ammonium sulfate per tons/kilograms of treated waste.

Particular and preferred modalities of the absorption tower (stripper) (1), of the nitrogen nutrient recovery system and of the process to recover them have been previously described, without prejudice to the fact that changes in materials, shapes, sizes, geometry, arrangement and order can be made. without departing from the scope of the present invention defined in the claims that follow.

EXAMPLES

Example 1:

Figure 1 shows an absorption tower (Stripper) (1) according to the first aspect of the present invention, which can be used as an absorption tower in recovery processes, with a treatment capacity at least equivalent to conventional ones.

The base is formed by the vibrating cube (4), which incorporates the inlet of the gas phase (7) and the motor vibrators that give movement to the tower (4b). This vibrating hub is rigidly joined to the central body (2), through the central tube (7c) that transmits the vibrating movement to the tower assembly.

The central body (2) is made up of the central tube (7c), which structures the assembly, with a diameter (D1) of 400 mm and a height of 5,000 mm. At the bottom, the lower tray (8), the upper cover (8c) with the lid (8e) and the entry and distribution system for the waste to be treated (5) are attached to this central tube. That is, this central tube supports the main elements of the tower. The perimeter closure of the central body is a styrene butadiene rubber (SBR) elastomer. This closure joins the lower tray (8) and the upper cover (8c), resting on the sides of the perforated plates (6). At the bottom of the tube are the outlets for the gas phase (air). The air enters through the vibrating cube, which is hollow, and passes into the tube (7c). This central tube is closed at the top, so the air that enters can only exit through the outlets located at the bottom (7a). These outlets are arranged in at least 4 points and in order to reduce losses. of load, the equivalent surface is twice that of the entrance section. To prevent the liquid phase from reaching the air inlets, a cap (7b) is placed at the top to protect the outlet holes.

The lower tray (8), embraces the tube (7c), has an external diameter D, 1200 mm. The treated liquid waste is collected in this tray and leaves the tower driven by the vibrating movement through the tangential channel designed for this purpose (8b).

The perforated plates (6) have staggered holes with a diameter of 8 mm, the free surface for the passage of the gas phase and liquid residue being 50%. The plates are filled up to the upper edge with a plastic filler. , which, with the vibrating movement, jump and rotate on the plate (6).

The entry of the liquid waste is carried out through the upper part of the tower, through the entry system (5). This system consists of a pipeline (5 a) and a distribution ring (5b) placed on the tube (7c). In this way, the liquid waste to be treated is distributed uniformly on the perforated plate (6) located at the top of the tower and descends along all the plates that make up the tower.

The gas phase (air) that has entered through the bottom, rises through the plates of the tower and exchanges the NH4 on its way up to the outlet cover (8e). In this upper cover (8c), the gas phase loaded with nitrogenous compounds is conducted to the drop separator (3a) of 600 mm in diameter. The droplet separator has the function of eliminating small droplets that the gas phase (air) can drag in its rise and contact with the liquid waste. The gas, after passing through the drop separator (3 a), is led to the outlet of the equipment through the cone that leads to the outlet tube (3b).

Example 2.

System for nutrient recovery.

Figure 7 illustrates a suitable system to recover nitrogenous nutrients from agribusiness waste, particularly from the agri-food industry; leachate from landfills, digestate from biogas plants and livestock waste or mixtures thereof. The equipment includes: waste feeding means (9), in fluid communication with means for heating the liquid waste in two phases, a first preheating phase (15) and a final heating in exchange equipment (10). The residue then passes through a dosing means (11) of an aqueous NaOH solution that is located downstream of the absorption tower (1). The absorption tower (1) is configured to put said liquid phase rich in Nitrogen compounds from the exchanger (10) whose pH has been adjusted to a value between 8-9, into contact with a gaseous phase consisting mainly of air, and in this way extract from the absorption tower (1) a gas phase rich in nitrogenous compounds, which comprise N and NH3 and a residual liquid phase poor in nitrogenous compounds, after 70-90% of the compounds have been removed from the liquid stream. nitrogen from waste.

For its part, the Scrubber-type desorption tower (12) is configured to put said gas phase rich in nitrogenous compounds that comprises N and NH3 in contact with an acidic liquid phase and in this way desorb the N compounds from the gas phase. and NH3 such as ammonium salts dissolved in the acidic liquid phase. For this reason, the desorption tower (12) is equipped with an acid aqueous solution dosing system (13).

From the desorption tower (12), a liquid phase rich in ammonium salts is extracted through the outlet (14) where said salts will be used as fertilizer, while the spent gas phase that leaves the desorption tower (12) is recirculated to the absorption tower (1) for a new alkaline washing cycle

The Stripper-type absorption tower (1) is also connected (the liquid phase) with a spiral exchanger (15), in order to recover the heat of the waste at its exit for preheating the input waste. This system reduces waste heating costs by 30-35%. After the elimination and recovery of the nitrogenous waste and the thermal recovery, it is led to a system for the elimination of solids.

For the solids removal process, there is a system (16) intended to coagulate and flocculate the suspended solids of the treated waste and to promote their elimination in the subsequent centrifugation stage, a centrifuge (17) in fluid communication located current above said coagulation and flocculating means (16), where said centrifuge (17) is configured to separate solids by decantation and obtain a residual liquid phase (18).

Example 3.

Description of the recovery process of nitrogenous nutrients, such as ammonium sulfate:

Starting, preferably from a lung tank, the residual liquid to be treated is introduced in a two-phase heating process corresponding to stage (II) in order to improve performance in nutrient recovery in subsequent stages. The two phases of heating the waste are carried out in the exchange equipment (15) and (10) respectively. The first phase consists of preheating with the residual heat of the treated liquid at the outlet of the absorption tower (1) and the second in a shell-tube exchanger, with hot water at 850C heated by external equipment. The energy recovered represents 35% of the total energy needed to heat the waste.

The next step iii) an alkaline solution, for example, NaOH, is dosed to adjust the pH of the liquid residue from the heating stage, up to a value of 8.5.

The liquid waste goes to absorption stage (iv) where the nitrogenous compounds are recovered in the absorption tower (1) in the form of a gas phase. In the absorption tower (1), a rising air current is brought into contact to extract a gas phase rich in nitrogenous compounds and an aqueous phase from which 80% of the nitrogenous compounds (total N) have been removed.

The gas phase rich in nitrogen compounds is taken to a desorption tower (12) for its regeneration and for the recovery of the nitrogen compounds. To do this, the gas phase rich in nitrogenous compounds is brought into contact with a liquid phase containing sulfuric acid, to form ammonium salts, according to the following equation:

2NH3 H2S 04 ^ (NH4)2S 04,

This compound is concentrated at the base of the desorption tower (12) until it reaches a concentration of 40%. Said liquid phase rich in ammonium sulfate is purged continuously through the outlet (14), thus obtaining a high-value fertilizer.

The desorption tower (12) comprises a storage and dosing facility for the 40% by weight sulfuric acid solution (13).

Example 4

Description of another embodiment of the recovery process of nitrogenous nutrients such as ammonium sulfate.

We consider a liquid waste from the digestate of a small or medium-sized biogas plant of an agri-food industry with:

- 40,000 m3/year.

- Density approx. 1 kg/l.

- Solids percentage 4%

- Hours per year of process 8,500 hours.

- Input NH3-N concentration 4.5 kg/ m3

The process begins with the heating stage of the liquid waste to improve performance in later stages. In the next step, the waste is conditioned by adjusting its pH to a value of approximately 8.5 by adding an alkaline aqueous solution in order to improve the performance in the absorption tower. In this stage the temperatures and pH of the liquid waste are:

- Temperature of 70°C.

- PH 8

The liquid waste that comes out of the previous stage is taken to the absorption tower (stripper). The waste, after entering the absorption tower, leaves it having transferred the nitrogenous compounds to the gas phase (air), obtaining at the end of this stage a liquid waste with 80% less nitrogenous compounds. In this stage, a gaseous stream is generated, rich in nitrogenous compounds, which is taken to the desorption tower where the nitrogenous compounds are desorbed from the gaseous stream. For this purpose, a liquid stream of diluted H2SO4 acid is used to obtain a high-value fertilizer that includes ammonium sulfate. At the output of this set of processes we obtain:

- Output NH3-N concentration 0.9 kg/ m3

- Ammonium Sulfate at 40% purity by weight

The liquid phase obtained from the absorption tower (1) is a liquid waste with a high solids load and 20% of the original nitrogen compounds coming from the liquid waste. This waste is taken to the next stage where most of the solids and a part of the nitrogenous compounds are eliminated from the liquid phase.

Next, a coagulation and flocculation stage is carried out, so that the waste is conditioned to improve the separation of solids. In the next step, the conditioned waste is taken to the centrifugal decanter, obtaining a solids separation performance of more than 80%. After this set of processes, the treated waste has the following characteristics:

- Solid fraction removed with a flow rate of 6,400 Tn/year and a humidity of 80%.

- Liquid fraction to manage 33,600 m3/year.

- NH3-N concentration of the outlet liquid fraction of 0.58 kg/m3

Claims (1)

1- An absorption tower (1), to remove at least one compound from a liquid stream, configured to work with concentrations of solids in the liquid phase of up to 10% by weight, where said tower comprises to. an inlet for the gas stream (7), b. a base with a vibrating system (4), c. a central body (2) that comprises Yo. a central tube (7 c), preferably made of metal, rigidly attached to the vibrating system (4), where the central tube (7 c) has at least one gas flow inlet (7 a) at the bottom, ii. a lower tray (8b) and an upper cover (8c) attached to the central tube (7 c), iii. at least one perforated plate (6) attached along the central tube (7c), preferably between 3-5 perforated plates (6), iv. an inlet system for the liquid phase (5) located in the upper part of the central tube (7 c), v. perimeter closures (8d) that join the lower tray (8b) and the central tube (7 c) and the upper cover (8c) and the central tube (7 c), d. an outlet (3) for the gas flow through the cover (8c). 2- The absorption tower (1) according to the previous claim, where the vibration of the vibrating system (4) is generated by at least two motor vibrators that generate vertical and rotational movement simultaneously, preferably the vibrating system is configured as a cube vibrant. 3- The absorption tower (1) according to any previous claim, where the vibrating system (4) allows the entry of gas phases through the inlet (7) for conduction and exit through the tube (7c) through of some holes (7a) and a cap (7b). 4- The absorption tower (1) according to any previous claim where the relationship between height (A) and diameter (D) (ratio (A/D)) of the central body (2) is between 4-5. 5- The absorption tower (1), according to any previous claim, where the perforated plates (6) have a relationship between the external diameter (D) and the internal diameter (D1) (ratio (D/D1)) between 2.5-3.5. 6- The absorption tower (1) according to any previous claim, where the perforated surface of the plates is between 20-50% of the total surface of the plate. 7. The absorption tower (1) according to any previous claim, where the perforations of the plates have a diameter between 6 to 12 mm. 8- Absorption tower (1) according to any previous claim, where the perforated plates (6) have a semitoroidal geometry. 9. Absorption tower (1) according to any preceding claim, wherein the perforated plates (6) comprise a filler, preferably a plastic filler. 10- Absorption tower (1) according to any previous claim, where the central body (5) has a distribution system for the liquid phase (5) that is composed of an inlet (5a) and a ring or toroid of distribution with perforations (5b). 11- The absorption tower (1) according to any previous claim, where the upper part of the gas outlet (3) has a cylindrical shape and comprises a drop separator (3a). 12- The absorption tower (1) according to any previous claim, where the lower tray (8b) has an outlet conduit (8a) for the liquid phase. 13- The absorption tower (1) according to any previous claim, where the gas outlet (3) is configured to minimize pressure losses. 14. Use of the absorption tower (1) according to any of the preceding claims to remove at least one compound from a liquid stream. 15- System configured for the recovery of nitrogenous nutrients from waste from the agri-food industry or similar where the equipment includes the following elements: - Feeding media (9) for waste from the agri-food industry, - Means for preheating phase 1 waste (15), - Means for heating phase 2 waste (10), - Means for dosing the basic medium (11), - Absorption tower (1) according to any of claims 1 to 14, - Desorption tower (12), - Means for dosing the acid medium (13), - Outlet (14) of the desorption tower (12) adapted for liquids, where said liquids include nitrogenous compounds, - Suitable media for coagulation and flocculation (16), - Centrifuge suitable for the separation of solids (17), said centrifuge (17) being located after the coagulation and flocculation means (16), - Outlet (18) of the centrifuge (17) adapted for the liquid fraction treated in the process, - Outlet (19) of the centrifuge (17) adapted for the solid fraction treated in the process, 16- The system configured for the recovery of nitrogenous nutrients from waste from the agri-food industry according to the previous claim, where the waste is selected from the list consisting of: waste from food industries, leachate from landfills, plant digestate of biogas and livestock waste or mixtures thereof. 17- The system configured for the recovery of nitrogenous nutrients from waste from the agri-food industry or similar according to previous claims 15-16, where the heating of the liquid phase (9) that enters the system is heated in two phases, preferably the means for preheating the waste (15) is a spiral type exchanger and the means for heating the waste (10) is a tube shell type exchanger. 18- Process for obtaining nitrogenous nutrients, preferably ammonium sulfate, from agroindustry waste or similar, using the system according to any of the previous claims 15-17 that comprises the steps: Yo. provide waste from agribusiness, ii. subjecting the waste from the previous stage to a two-phase heating process, to provide a waste at a temperature of 60-75°C. iii. Treat the liquid residue obtained in the previous phase with an alkaline solution to provide a liquid residue with a pH between 7.5 and 10. iv. extract the nitrogenous compounds from the liquid waste of the previous stage by using a gas stream with a flow between 4,000 m3 of gas /m3 of liquid waste to be treated to 1,500 m3 of gas /m3 of liquid waste to be treated in an absorption tower ( 1) to provide a gas phase rich in nitrogen compounds and a liquid phase with 70-85% less nitrogen compounds compared to the liquid residue, v. subjecting said gas phase rich in nitrogenous compounds obtained in the previous phase to a desorption step through the use of an acidic aqueous stream, to obtain a liquid phase comprising nitrogenous nutrients, preferably ammonium salts, saw. optionally, the liquid phase obtained in step (iv) is subjected to a solids removal step through coagulation, flocculation and centrifugation steps to obtain a solid residue and a liquid, where the solid residue comprises a % by weight of solids between 15-25% and a liquid waste that contains at least 95% water, preferably 98% water. 19- The process for obtaining nitrogenous nutrients according to the previous claim, where the agribusiness waste comes from anaerobic digestion processes, wastewater from agri-food industries, livestock waste and/or landfill leachate. 20- The process for obtaining nitrogenous nutrients according to previous claims 18-19, where the agroindustry waste from stage (i) comprises a percentage by weight of solids between 1 and 10% by weight, preferably comprising a percentage of solids between 2-5% by weight. 21- The process for obtaining nitrogenous nutrients according to previous claims 18-20, where the agroindustry waste from stage (i) comprises NH3-N in a weight concentration in the waste between 0.1-5 kg/ m3. 22- The process for obtaining nitrogenous nutrients according to claims 18-21, wherein the liquid phase obtained in step (v) comprises ammonium sulfate in a concentration between 30% and 45% by weight.