WO2004054688A1 - A system and apparatus for removal of unwanted substances in a gas flow - Google Patents

A system and apparatus for removal of unwanted substances in a gas flow Download PDF

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Publication number
WO2004054688A1
WO2004054688A1 PCT/DK2003/000899 DK0300899W WO2004054688A1 WO 2004054688 A1 WO2004054688 A1 WO 2004054688A1 DK 0300899 W DK0300899 W DK 0300899W WO 2004054688 A1 WO2004054688 A1 WO 2004054688A1
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WO
WIPO (PCT)
Prior art keywords
solvent fluid
gas flow
hydrophobic membrane
biogas
acid
Prior art date
Application number
PCT/DK2003/000899
Other languages
French (fr)
Inventor
Ismael Touri
Original Assignee
Bioscent
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bioscent filed Critical Bioscent
Priority to CA002558116A priority Critical patent/CA2558116A1/en
Priority to EP03779756A priority patent/EP1572323A1/en
Priority to AU2003287916A priority patent/AU2003287916A1/en
Publication of WO2004054688A1 publication Critical patent/WO2004054688A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/229—Integrated processes (Diffusion and at least one other process, e.g. adsorption, absorption)
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01K—ANIMAL HUSBANDRY; CARE OF BIRDS, FISHES, INSECTS; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K1/00—Housing animals; Equipment therefor
    • A01K1/0047—Air-conditioning, e.g. ventilation, of animal housings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1406—Multiple stage absorption
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P60/00—Technologies relating to agriculture, livestock or agroalimentary industries
    • Y02P60/20—Reduction of greenhouse gas [GHG] emissions in agriculture, e.g. CO2
    • Y02P60/22—Methane [CH4], e.g. from rice paddies

Definitions

  • Scope of the invention relates to a system for removal of unwanted substances in a gas flow, where said system comprises a number of purification modules, each comprising a hydrophobic membrane, a mixing container and a solvent fluid, and where the substances in said gas flow are diffused through a hydrophobic membrane and are absorbed in the solvent fluid, and where the purified gas flow is led to either a further purification module or out into the surrounding environment.
  • a purification module each comprising a hydrophobic membrane, a mixing container and a solvent fluid
  • the present invention furthermore relates to an apparatus for use in the aforementioned system.
  • the present invention furthermore relates to methods for applying the system and apparatus.
  • the amount of one or more specific substances can be too much for the present micro environment to absorb and can thus for example cause lethal levels of ammonium (NH 3 ) in rivers, lakes and/or the groundwater.
  • NH 3 ammonium
  • the solutions for cleaning/purifying emissions are mostly known from factories and can include one ore more of the following; a scrubber, a filter, a micro membrane filter or the like.
  • these systems are meant for a certain amount of emission and only clean the emission of one or two specific substances, which causes the system to be inflexible and very expensive in case the emission is to be purified of all unwanted substances.
  • the user of the system is left with a mass of separated, useless substances, which the user somehow has to dispose of. This adds to the cost of cleaning the emission and is, in some cases, very uneconomical, whereby the incentive to clean the emission is lessened substantially.
  • the solvent fluid either is an alkaline solvent fluid or an acid solvent fluid, where said solvent fluid circulates between a hydrophobic membrane and a rrj ⁇ ring container, and where either concentrated acid or alkaline fluids are added to the solvent fluid in a mixing container in order to maintain a substantially constant pH value in said solvent fluid, and
  • an apparatus comprising a gas inlet, a pre-filter, a water separator, a number of purification modules, a number of blowers, a pipe system, valves, fittings and an air outlet, where each purification module comprises a hydrophobic membrane, a fluid container, a pump, a solvent fluid and a mixing container with a number of outlets and inlets.
  • undesired substances are to be understood as undesired substances contained in the emission, such as volatile fatty acid, aromatic substances and chemical substances like ammonium (NH 3 ), hydrogen sulphide (H 2 S) and carbon dioxide (CO 2 ).
  • NH 3 ammonium
  • H 2 S hydrogen sulphide
  • CO 2 carbon dioxide
  • purification modules which each comprise a hydrophobic membrane, a mixing container and a solvent fluid, and where the substances in the gas flow are diffused through a hydrophobic membrane and are absorbed in the solvent fluid.
  • the solvent fluid has a specific pH value
  • the absorption of unwanted substances in the solvent fluid is greatly increased and it is possible to remove different type of substances at different pH values.
  • the hydrophobic membrane is able to use concentrated unrecycled acid/alkaline fluid. This demands a large amount of acid/alkaline fluid for removal of all unwanted substances from a gas flow and is consequently very expensive.
  • the residual product consists of solvent fluid diluted with merely a small amount of unwanted substances, which are useless and expensive to deposit.
  • the residual product contains a certain amount of useful, separated substances, which can be extracted in a subsequent process.
  • the solvent fluid is circulated between the hydrophobic membrane and the mixing container until it reaches a predetermined degree of saturation, after which the solvent fluid is replaced and reutilized with the absorbed substances.
  • the solvent fluid with a predetermined degree of saturation is separated into different reusable salts, e.g. by drying.
  • These reusable salts can be used as components in fertilizer products or as fertilizers, as components in an industrial process, and/or as components in an industrial product.
  • One way of separating the solvent fluid with a predetermined degree of saturation into different reusable salts is by. drying, where the water and volatile part of the solvent fluid evaporate and the reusable salts remain.
  • An alternative method of separating the saturated solvent fluid into different reusable salts is freeze drying.
  • a system is constructed with at least two purification modules where at least one of said purification modules comprises a hydrophobic membrane, a mixing container and an alkaline solvent fluid for purification of a natural gas or biogas flow.
  • One purification module comprising a hydrophobic membrane, a mixing container and an alkaline solvent fluid for purification of a natural gas or biogas flow is either added to a system with the normal number of purification modules for removing unwanted volatile fatty acid, aromatic substances and chemical substances, or acts as a stand alone purification module, where carbon dioxide (CO 2 ) and hydrogen sulphide (H 2 S) are removed.
  • CO 2 carbon dioxide
  • H 2 S hydrogen sulphide
  • natural gas consists of the following components:
  • biogas consists of the following components:
  • acid alkaline fluids As mentioned is it possible to remove different kinds of substances with an acid solvent fluid or an alkaline solvent fluid.
  • Concentrated acid like for example sulphuric acid (H 2 SO 4 ), hydrochloric acid (HC1), acetic acid (HC 2 H 3 O 2 ), phosphoric acid (H 3 PO 4 ), nitric acid (HNO 3 ), oxalic acid (H 2 C 2 O 4 ), citric acid (C 6 H 8 O 7 ), and the like is either added to the solvent fluid, or concentrated alkaline like for example ammonium hydroxide (NH 4 OH), barium hydroxide Ba(OH) 2 , calcium hydroxide Ca(OH) 2 , potassium hydroxide (KOH), sodium hydroxide (NaOH), and the like is added to the solvent fluid.
  • NH 4 OH ammonium hydroxide
  • Ba(OH) 2 barium hydroxide Ba(OH) 2
  • potassium hydroxide (KOH) sodium
  • H 2 S + 2 NaOH > Na ⁇ + 2 H 2 O where sodium sulphide can be used in the dye industry.
  • 2 CO 2 + 4 KOH 2 K 2 CO 3 + 2 H 2 O where potassium carbonate can be used in the soap and glass industries.
  • ammonium phosphate can be used as a component in fertilizers.
  • R-COOH + NH 3 » R-COONH 4
  • R is a different chemical functional group, i.e. a number of CH groups.
  • the apparatus comprises a gas inlet, a pre-f ⁇ lter, a water separator, a number of purification modules, a number blowers, a pipe system, valves, fittings and an air outlet, where each purification module comprises a hydrophobic membrane, a fluid container, a pump, a solvent fluid and a mixing container with a number of outlets and inlets.
  • the apparatus consists of two purification modules, wherein one purification module is circulation acid solvent fluid for the purpose of removing a certain part of the unwanted substances and wherein the second purification module is circulation alkaline solvent fluid for the purpose of removing the rest of the unwanted substances.
  • each purification module removes a specific substance and thereby delivers a specific useful saturated solvent fluid.
  • the apparatus has both an air-inlet and an air- outlet with couplings, which make it possible to connect the apparatus to an exhaust line, for purifying of the gas flow and for the purpose of connecting the apparatus to for example a chimney.
  • the apparatus is an independent unit, which is placed in the vicinity of the source of odour. The apparatus will then draw in air from the surroundings, treat the air in the hydrophobic membrane and thereafter blow the air out into the surroundings again.
  • the apparatus comprises a pre-filter for filtering larger particles from the gas flow.
  • a pre-filter for filtering larger particles from the gas flow.
  • large particles can be dust, straw, or other kinds of bedding.
  • This pre-filter ensures that the hydrophobic membrane of the purification module does not clog during operation of the purification module.
  • the apparatus comprises a water separator, which functions to separate and collect any moisture or damp in the gas flow. The water is then led back to the mixing container.
  • the purification module comprises a number of pumps:
  • One pump doses concentrated acid/alkaline fluid to the mixing container. This pump is controlled by the pH value of the solvent fluid, so that a measurement of the pH value in the mixing container indicates if it is necessary to add more concentrated acid/alkaline fluid.
  • Another pump is used for circulating the solvent fluid between the mixing container and the hydrophobic membrane. This pump is controlled so that the flow of the solvent fluid is adjusted to the gas flow in such a way that the unwanted substances can be absorbed in the solvent fluid.
  • the concentrated acid/alkaline fluid is deposited in a fluid container, whose size can differ according to the amount of gas flow needed to be purified. If the purification module comprises a large fluid container the apparatus can operate for a long time without needing for additional concentrated acid/alkaline fluid.
  • the problem is that a fluid container of a larger dimension occupies more space inside the purification module.
  • a small fluid container is easy to incorporate in the purification module, but the user has to fill the fluid container more often.
  • the hydrophobic membrane is an ordinary micro hydrophobic membrane and comprises, for example a large number of capillary tubes.
  • the gas flow is introduced into the micro hydrophobic membrane and flows past the capillary tubes.
  • a solvent fluid with certain chemical characteristics is pumped into the capillary tubes.
  • the solvent fluid reacts with a certain substance in the gas flow and absorbs this substance into the solvent fluid.
  • the blower is arranged in the pipe system, which connects the gas-inlet with the hydrophobic membrane and the gas out-let, in such a way that the gas flow is kept at a stable level and complies with the flow of solvent fluid.
  • the apparatus is provided with a control system, where said control system is capable of controlling the blowers and the pumps.
  • This control system must at least be able to be programmed to dose a certain amount concentrated acid/alkaline fluids in situ to the mixing container over a determined period of time and to set the speed of both the pump for circulating the solvent fluid and the blower in such a way that the period of time, during which the gas flow is in near contact with the solvent fluid inside the hydrophobic membrane, is of a sufficient length in order to allow the unwanted substances to be totally or partly absorbed in the solvent fluid.
  • the apparatus is furthermore provided with means for registration of the pH values of the solvent fluid in the mixing container and/or the degree of saturation of substances in the solvent fluid and/or the content of substances remaining in the purified gas flow.
  • the blowers and pumps are controlled by a control system according to the different kinds of registrations obtained.
  • the registration of the pH value of the solvent fluid in the mixing container reduces the need to program the control systems manually in order to dispense concentrated acid/alkaline fluid each time a parameter changes.
  • a parameter could for example be the temperature of the gas/solvent fluid, the type of unwanted substances and the content of substances in the gas flow.
  • the degree of saturation of substances in the solvent fluid is a useful registration and controlling parameter. With continuous registration of the. degree of saturation of substances in the solvent fluid it will be possible to determine the appropriate time for changing the solvent fluid instead of adding more concentrated acid/alkaline fluid. This ensures that the absorption of unwanted substances in the solvent fluid is as good as possible and allows the user to know the exact content of useful residual product in the discharged solvent fluid.
  • the apparatus is provided with a by-pass or re-circulation, it is possible to either process the gas flow an extra time or to release clean gas to the environment without further treatment.
  • To be able to determine when the gas flow is clean enough to release it is necessary to register the content of substances remaining in the purified gas flow. Furthermore, this registration can act as documentation/evidence that the user complies with the laws and regulations regarding level of emission of unwanted substances into the surrounding environment.
  • a by-pass or re-circulation option furthermore enables the user to obtain a solvent fluid with a specific degree of saturation, which enhances the value of the residual product for reutilization purposes.
  • control system and/or means for registration are connected to a computer, allowing the control system and/or means for registration to be remote controlled and the registration data to be saved.
  • the user can centrally from a position in a control-room operate and check several apparatuses at the same time without having to be physically next to the apparatus every time a change is required.
  • the computer could furthermore comprise data storage, so that it later would be possible to access previous operating data and analyse the different registrations, for example in comparison with the amount of useful residual product, thus making it is possible to further optimize the operation of the apparatus.
  • the system according to the present invention can be used in different ways.
  • the system furthermore comprises at least one feeding source, a number of exchange columns arranged for fransferring substances from said feeding source to a gas flow, and a number of blowers for circulating.
  • the feeding source can be bio-degradable waste from a waste treatment facility or sludge from a wastewater treatment facility that can produce biogas by degrading.
  • the exchange columns are arranged in such a way that it is possible to lead liquid and/or degradable waste in the exchange columns and then in counter flow circulate air through the liquid and/or degradable waste.
  • the counter flow arrangement is an advantage because it ensures efficient transportation of unwanted substances from the liquid and or degradable waste.
  • This air flow can be treated in a purification module with a hydrophobic membrane according to the present invention where it is necessary to use an acid solvent to absorb the ammonium.
  • a method for removal of ammonium from a feeding source to a biogas process is described as: said feeding source is led though said exchange columns, where a gas flow is circulated by said blowers for reducing/absorbing said ammonium in said feeding source,
  • said feeding source is led to said biogas reactor
  • a biogas flow is added to a gas flow, which is circulated by a blower between said exchange columns and said purification module with said hydrophobic membrane, where said ammonium in said gas and biogas flow mixture is diffused through said hydrophobic membrane and is absorbed in an acid solvent fluid.
  • a system according to the present invention comprising a number of filters, a number of sterilisation chambers and a number of blowers can advantageously be used in offices, hospitals, laboratories, kitchens, trucks, cars, airplanes and/or transport containers, or other places where specific requirements to air quality apply, for example with regard to odour or sterilisation.
  • the type of filter is determined by the environment in which the system is used. For example in kitchens, the filter could be a filter made of felt adapted to capture grease particles.
  • the system comprises a sterilisation chamber where the air flow is radiated with UN light from a UN unit.
  • the blower is used to transport the air flow through the whole system including filter, purification modules, and sterilisation chamber.
  • the air contains various kinds of substances it is necessary to supply the system with a purification module with acid solvent fluid for absorbing, e.g. ⁇ H 3 , R- OH and the like,' and with a purification module with alkaline solvent fluid for absorbing, e.g. H 2 S, CO, CO 2 , R-COOH and the like.
  • a purification module with acid solvent fluid for absorbing e.g. ⁇ H 3 , R- OH and the like
  • alkaline solvent fluid for absorbing, e.g. H 2 S, CO, CO 2 , R-COOH and the like.
  • the reduction or removal of nutrients such as ammonium or sulphate from the manure is an advantage. It would be preferable to use a system according to the present invention where the system furthermore comprises a number of heat exchangers, a number of heating units, a number of heat treatment units, and a number of biogas reactors.
  • the heat exchangers are air to air heat exchangers where the air from the stable flows on one side, and heated air from the heat treatment units/purification modules flows on the other side.
  • the temperature of the air from the stable is typically app. 20°C, and the heated air from the heat treatment units/ purification modules has a temperature of app. 70°C.
  • the first step of heating the air from the stable is by using the air from heat treatment units/purification modules.
  • the second step of heating the air from the stable is obtained by the heating units which can be solar panels, electric heaters, gas burners or the like.
  • Manure from the stable is transported to the heat treatment units where the heated air from the stable is circulated, thereby drying the manure which is either led to storage, distributed on the fields, or led to a bio reactor for producing biogas.
  • the biogas from the biogas reactor can be used in the heating units to heat the air from the stable.
  • the treated/clean air is led though the heat exchangers, and the temperature difference causes the water content of the air to condensate.
  • the output from the heat exchanger is clean air and condensated water which can be led to the environment without causing any harm.
  • system and apparatus can be used in farming where the apparatus for example is connected to an air-outlet from a stable, or the system and apparatus can be used in places where it is necessary to clean emissions of volatile fatty acids, aromatic substances, and/or chemical substances such as ammonium (NH 3 ), hydrogen sulphide (H 2 S), and carbon dioxide (CO 2 ). Examples of such places are:
  • factories e.g. production areas, production machine and/or from a vat. - on farms, e.g. a covered farmyard manure containers. on drilling platforms, e.g. when purifying natural gas of hydrogen sulphide (H 2 S) and/or carbon dioxide (CO 2 ).
  • H 2 S hydrogen sulphide
  • CO 2 carbon dioxide
  • Fig. 1 is a diagram illustrating the system according to the invention
  • Fig. 2 is a diagram illustrating the system according to the invention with an extra purification module for cleaning natural gas or biogas,
  • Fig. 3 is a diagram illustrating the influence of the pH value when purifying a gas
  • flow Fig. 4 is a diagram illustrating the system according to the invention for removal of ammonium from a feeding source to a biogas process
  • Fig. 5 is a diagram illustrating an alternative system according to the invention for removal of ammonium from a feeding source to a biogas process
  • Fig. 6 is a diagram illustrating the system according to the invention for cleaning an air flow
  • Fig. 7 is a drawing of the system in Fig. 6 in a transportable embodiment
  • Fig. 8 is a diagram illustrating the system according to the invention for drying waste, preferably manure, and cleaning a gas flow, preferably an air flow from a stable.
  • Fig. 1 shows a gas flow 1 containing unwanted substances which is led through a pre- filter 2 where dust and larger particles are separated from the gas flow and at the same time water is separated from the gas flow, for example through steam.
  • the gas flow 1 is then sucked through the hydrophobic membrane 3 via a blower 5, where the unwanted substances pass through the hydrophobic membrane 3.
  • a water separator 4 containing a water seal is arranged, and the condensed water steam is led to the mixing container 8.
  • concentrated acid fluid is dosed by means of a dosing pump 7 to the mixing container 8, where the level of the pH value of the solvent fluid is maintained at a substantially constant level.
  • the solvent fluid is re-circulated between the mixing container 8 and the hydrophobic membrane 3 by a circulation pump 9.
  • the unwanted substances which diffuse through the hydrophobic membrane 3 are absorbed in the solvent fluid.
  • the solvent fluid is led out at 10 for reutilization such as drying or separation into different reusable salts.
  • the purified gas flow 11 is led through another hydrophobic membrane unit 12 by means of a blower 13, where the alkali solvent unwanted, substances diffuse through the hydrophobic membrane 12 and the purified gas flow 19 is led out to the surroundings or back into the apparatus for recycling purposes.
  • a concentrated alkali fluid is dosed by means of a dosing pump 15 to the mixing container 16, where the level of the pH value of the solvent fluid is maintained at a substantially constant level.
  • the solvent fluid is re-circulated between the mixing container 18 and the hydrophobic membrane 12 by means of a circulation pump 17.
  • the unwanted substances, which diffuse through the hydrophobic membrane 12, are absorbed in the solvent fluid.
  • the solvent fluid After the solvent fluid has reached a predetermined degree of saturation in the mixing container 18, the solvent fluid is led out at 18 for reutilization such as drying or separation into different reusable salts.
  • Fig. 2 shows how the gas flow 19 is treated in another purification module 31, where the gas flow 19 is led though a hydrophobic membrane 20 by either blower 30 or blower 21.
  • the gas flow 19 is re-circulated and treated again in the hydrophobic membrane 20.
  • the pipe system is provided with valves 28 and 29 which completely or partly lead the gas flow 19 back into the pipe system or through the blower 30 and lead the gas flow 27 to the surroundings.
  • Purification of the gas flow in the hydrophobic membrane 20 is obtained as mentioned regarding the hydrophobic membrane 3 and 12, where a solvent fluid is circulated between the mixing container 26 and the hydrophobic membrane 20 by a pump 25, and where a concentrated acid/alkali fluid is dosed from the fluid container 22 to the mixing container 24 by a pump 23.
  • This purification module is advantageously used to purify a natural gas or biogas flow.
  • Fig. 3 shows a diagram with a graph showing how the level of the pH value affects the purification of a gas flow of hydrogen sulphide (H 2 S).
  • H 2 S hydrogen sulphide
  • the graph shows that the pH value of the solvent fluid has to be higher than 11-12 in order to obtain an effective purification of the hydrogen sulphide (H 2 S).
  • Fig. 4 shows a system 30 for removal of ammonium from a feeding source 31 in a biogas process.
  • the feeding source 31 is preheated and led to a filled and insulated exchanger column 32 where an air flow 33 in a counter flow is passed though the feeding source 31.
  • thermophilic process the temperature of the feeding source 31 is app. 30-55°C, and for a mesopilic process the temperature of the feeding source 31 is app. 25-37°C.
  • the air flow 33 is circulated between exchanger column 32 and the hydrophobic membrane 35 of the purification module 34 by blower 38, and an acid solvent fluid 39 is circulated between the hydrophobic membrane 35 and the mixing container 36 by the circulation pump 37.
  • the ammonium in air flow 33 diffuses through the hydrophobic membrane 35 and is absorbed in the acid solvent fluid 39. After the acid solvent fluid 39 has reached a predetermined degree of saturation in the mixing container 36, the acid solvent fluid 39 is led out at 41 for reutilization such as drying or separation into different reusable salts.
  • the almost ammonium free feeding source 31 is led from the exchange column 32 to the bio reactor 40, where biogas is produced and led out at 42 to a storage tank (not shown) for later use, e.g. for burning in a heating process.
  • Fig. 5 shows a system 50 for removal of ammonium from a feeding source 31 in a biogas process.
  • the feeding source 31 is led to a bio reactor 40 where a part of the feeding source 31a is circulated between bio reactor 40 and exchanger column 32 wherein an air flow 53 in a counter flow is passed though the feeding source 31a.
  • the air flow 53 which consists of re-circulated air and biogas 51 from the biogas reactor 40, is circulated between exchanger column 32 and the hydrophobic membrane 35 of the purification module 34 by blower 38, and an acid solvent fluid 39 is circulated between the hydrophobic membrane 35 and the mixing container 36 by the circulation pump 37.
  • ammonium-saturated air flow 53 is led through the hydrophobic membrane 35 where ammomum is diffused and absorbed in the acid solvent fluid 39.
  • the acid solvent fluid 39 After the acid solvent fluid 39 has reached a predetermined degree of saturation in the mixing container 36, the acid solvent fluid 39 is led out at 41 for reutilization such as drying or separation into different reusable salts.
  • Biogas from the bio reactor is led out at 52 to a storage tank (not shown) for later use.
  • Fig. 6 shows a system 60 for cleaning an air flow 61.
  • the contaminated air flow 61 is passed through a filter 62 for filtering particles and is then led though a first hydrophobic membrane 63a where substances absorbable in an alkaline solvent fluid 64 are circulated between hydrophobic membrane 63a and container 65a by circulation pump 66a.
  • the air flow 61 is led though a second hydrophobic membrane 63b, where substances absorbable in an acid solvent fluid 67 is circulated between hydrophobic membrane 63b and container 65b by circulation pump 66b.
  • the air flow 61 is then led though a sterilisation chamber 68 where the air flow 61 is radiated with UN light.
  • the air flow 61 is passed though the whole system 60 by blower 69.
  • Fig. 7 shows a transportable air-cleaning apparatus 70 with a system 60 as shown in
  • FIG. 6 where the air inlet 71 is connected to a ventilation system (not shown) or just to the open, where an air flow is passed though the whole system 60 by blower 69.
  • the air cleaning apparatus 70 is provided with a panel 73 with three different indication lamps 74, 75, 76 where for example a red lamp 74 indicates when the container 65b with acid solvent fluid must be changed,
  • Fig. 8 shows a system 80 for drying, waste, preferably manure, and cleaning a gas flow, preferably an air flow from a stable 81. From the stable 81, air 2 containing ammonium is led through an air to air heat exchanger 83 to heating unit 85. When the desired temperature has been achieved, the air is led to drying and heat treatment unit 86.
  • the heating unit 85 consists of a liquid/air heat exchanger where the energy supply is from solar panels 99.
  • the energy supply is supplemented by burning of biogas 96 in a burner 97.
  • oil or some other source of energy 99 can be used for the heating unit 95.
  • a portion of the dry manure 90 is led to reactor 95 together with manure 84 in which it is used as a feeding source for anaerobe fermentation by which biogas 96 is produced.
  • the heat treatment unit 86 consists of an adjustable belt conveyor on which manure 84 having a low content of dry matter is led from stable 81 to drying and heat treatment unit 86.
  • the dry manure 90 is conveyed out of heat treatment unit 86.
  • the heated air is saturated with water in drying and heat treatment unit 86 and is subsequently led to the hydrophobic membrane 87.
  • the solution is recirculated at the other side of the hydrophobic membrane 87 by means of a circulation pump 88 where the ammonium diffuses through the hydrophobic membrane 87 and is absorbed in the solution.
  • the solution 94 is either led back to the drying and heat treatment unit S6 for being mixed with the degassed manure from the reactor, or alternatively, the solution 94 can be deposited as separate fertilizer.
  • Sulphuric acid (H 2 SO 4 ) in the solvent fluid is used for removing ammonium (NH 3 ) from the biogas contained in exhaust air coming from a stable.
  • NH 3 ammonium
  • the test was run again over a period of 8 hours, with a larger membrane area, and a slower biogas flow.
  • the result showed almost total purification of hydrogen sulphide and a lager purification of carbon dioxide (CO 2 ).
  • the result was the following:
  • Air flow 150 1/min.
  • Bags with 100 litres of air were collected directly from the odour source and compared to bags with 100 litres of air collected after the air flow had been through the system.
  • a smell panel evaluated the odours from the different bags, and it was concluded that the result was a significant improvement, and that the system was very efficient in cleaning an air flow.

Abstract

The present invention relates to a system and an apparatus for removal of unwanted substances in a gas flow (1) comprising a number of purification modules, each module comprising a hydrophobic membrane (3), a mixing container (10), and a solvent fluid, where the substances in the gas flow (1) are diffused through the hydrophobic membrane (3) and are absorbed in the solvent fluid, and where the purified gas flow (11) is led to either a further purification module or to the surrounding environment, wherein the solvent fluid either is an alkaline solvent fluid or an acid solvent fluid, where said solvent fluids circulate between said hydrophobic membrane (3) and said mixing container (10), and where either concentrated acid or alkaline fluids are added to said solvent fluid in the mixing container (10) in order to maintain a substantially constant pH value in the solvent fluid. The invention furthermore relates to methods for removing ammonium from a biogas process, for cleaning an air flow, and for drying waste.

Description

A system and apparatus for removal of unwanted substances in a gas flow
Scope of the invention The present invention relates to a system for removal of unwanted substances in a gas flow, where said system comprises a number of purification modules, each comprising a hydrophobic membrane, a mixing container and a solvent fluid, and where the substances in said gas flow are diffused through a hydrophobic membrane and are absorbed in the solvent fluid, and where the purified gas flow is led to either a further purification module or out into the surrounding environment.
The present invention furthermore relates to an apparatus for use in the aforementioned system.
The present invention furthermore relates to methods for applying the system and apparatus.
Background of the invention Some industries, such as farms and factories, can be very difficult to situate near or in the vicinity of an urban area because of the various emissions that these industries emit to the surrounding environment. These emissions are the source of great dissatisfaction among people living in nearby residential areas, either because of the strong unpleasant odour or because of the unwanted chemical content of the emissions.
To protect the environment and reduce the health risk of people living in nearby residential areas, a number of countries have passed several laws and regulations concerning the level of emissions allowed and the allowed content of the emission. This has forced the farmers/industry to invent several various systems for the purpose of cleaning the emitted gas in order to comply with the laws and regulations while at the same time enlarging and optimizing their production. The need desire to enlarge and optimize the production will, in some cases, collide with the sustainability of the surrounding environment. For example: - if a farmer wants to increase his production of pigs, the farmer needs a new and larger stable. Obtaining a.permit to build a larger stable is difficult when the farm is situated near or in the vicinity of an urban area. even if the content of the emission complies with national laws and regulations, the amount of one or more specific substances can be too much for the present micro environment to absorb and can thus for example cause lethal levels of ammonium (NH3) in rivers, lakes and/or the groundwater.
The solutions for cleaning/purifying emissions are mostly known from factories and can include one ore more of the following; a scrubber, a filter, a micro membrane filter or the like. Typically, these systems are meant for a certain amount of emission and only clean the emission of one or two specific substances, which causes the system to be inflexible and very expensive in case the emission is to be purified of all unwanted substances. Furthermore, the user of the system is left with a mass of separated, useless substances, which the user somehow has to dispose of. This adds to the cost of cleaning the emission and is, in some cases, very uneconomical, whereby the incentive to clean the emission is lessened substantially.
Object of the invention
It is therefore the object of the present invention to provide a system and an apparatus which has a reasonable size, is easy to operate and can remove all unwanted substances' from a gas flow and where the separated, unwanted substances can be reused.
This is obtained with: - a system according to claim 1 wherein the solvent fluid either is an alkaline solvent fluid or an acid solvent fluid, where said solvent fluid circulates between a hydrophobic membrane and a rrj±ring container, and where either concentrated acid or alkaline fluids are added to the solvent fluid in a mixing container in order to maintain a substantially constant pH value in said solvent fluid, and
an apparatus comprising a gas inlet, a pre-filter, a water separator, a number of purification modules, a number of blowers, a pipe system, valves, fittings and an air outlet, where each purification module comprises a hydrophobic membrane, a fluid container, a pump, a solvent fluid and a mixing container with a number of outlets and inlets.
Description of the invention
In the following "unwanted substances" are to be understood as undesired substances contained in the emission, such as volatile fatty acid, aromatic substances and chemical substances like ammonium (NH3), hydrogen sulphide (H2S) and carbon dioxide (CO2).
It is proven that it is possible to remove unwanted substances from a gas flow with purification modules, which each comprise a hydrophobic membrane, a mixing container and a solvent fluid, and where the substances in the gas flow are diffused through a hydrophobic membrane and are absorbed in the solvent fluid.
If the solvent fluid has a specific pH value, the absorption of unwanted substances in the solvent fluid is greatly increased and it is possible to remove different type of substances at different pH values. Thus it is important to determine the appropriate level of pH value for each type of unwanted substance.
Furthermore, tests have shown that it is equally important to maintain a substantially constant pH value in the solvent fluid. A fluctuation of the pH value of the solvent fluid makes it very difficult to predict the amount of concentrated acid/alkaline fluid necessary to obtain maximal absorption of the unwanted substances in the solvent fluid, which may led to unnecessary consumption of concentrated acid/alkaline.
To avoid these problems caused by fluctuation of the pH value, the hydrophobic membrane is able to use concentrated unrecycled acid/alkaline fluid. This demands a large amount of acid/alkaline fluid for removal of all unwanted substances from a gas flow and is consequently very expensive.
Furthermore, the residual product consists of solvent fluid diluted with merely a small amount of unwanted substances, which are useless and expensive to deposit.
When the solvent fluid circulates between the hydrophobic membrane and the mixing container, the evaporation of fluid and absorption of substances will slowly change the pH value of the circulated solvent fluid and the degree of absorption will decrease.
Therefore small amounts of concentrated acid/alkaline fluid are added to the solvent fluid in the mixing container during the gas cleaning/purifying process.
Instead of leaving the user with a mass of separated substances in a useless, residual product, which the user somehow has to dispose of, it would be an advantage if the residual product from the cleaning process could be reutilized.
In order to obtain any kind of economical gain by reutilising the residual product, it is necessary that the residual product contains a certain amount of useful, separated substances, which can be extracted in a subsequent process.
Therefore the solvent fluid is circulated between the hydrophobic membrane and the mixing container until it reaches a predetermined degree of saturation, after which the solvent fluid is replaced and reutilized with the absorbed substances.
The solvent fluid with a predetermined degree of saturation is separated into different reusable salts, e.g. by drying. These reusable salts can be used as components in fertilizer products or as fertilizers, as components in an industrial process, and/or as components in an industrial product.
One way of separating the solvent fluid with a predetermined degree of saturation into different reusable salts is by. drying, where the water and volatile part of the solvent fluid evaporate and the reusable salts remain. An alternative method of separating the saturated solvent fluid into different reusable salts is freeze drying.
For small scale users it could be too much of an economical investment, if the solvent fluid with a predetermined degree of saturation has to be processed into different reusable salts in another appurtenant apparatus.
Instead, it would be advantageous for the user to contact a company that specializes in collecting residual products and converting them into useful products. This solution demands that the user has sufficient storage space to store the amount of residual product between two visits/collections from the specialized company.
To purify a gas flow, such as natural gas or biogas, from all unwanted substances, a system is constructed with at least two purification modules where at least one of said purification modules comprises a hydrophobic membrane, a mixing container and an alkaline solvent fluid for purification of a natural gas or biogas flow.
One purification module comprising a hydrophobic membrane, a mixing container and an alkaline solvent fluid for purification of a natural gas or biogas flow is either added to a system with the normal number of purification modules for removing unwanted volatile fatty acid, aromatic substances and chemical substances, or acts as a stand alone purification module, where carbon dioxide (CO2) and hydrogen sulphide (H2S) are removed.
When cleaning natural gas or biogas it is important to remove as much as possible of the sulphide components in the gas; by burning natural gas or biogas sulphuric acid is produced, which in turn leads to acid rain and thereby damages the environment. Therefore the natural gas or biogas flow is re-circulated though the hydrophobic membrane until it reaches a predetermined degree of purity, after which the purified natural gas or biogas flow is led to either a gas burner or to a receptacle. The purified natural gas or biogas constitutes a cheap addition to/complementation of the heating source of the farm/factory.
The difference between natural gas and biogas is that natural gas consists of the following components:
Methane (CH4) 88.1%
Ethane (C2H6) 6.4%
Propane (C3H8) 2.8%
Iso-butane (C4H10) 0.4% n-butane (C4H10) 0.6%
Iso-pentane (C5Hι2) 0.1% n-pentane (C5H12) 0.08%
Hexane (C6H14) 0.06%
Nitrogen (N2) 0.3% Carbon dioxide (CO2) 1.2%
and biogas consists of the following components:
Methane (CH4) 65-70%
Carbon dioxide (CO2) 30-35%
Hydrogen sulphide (H2S) 1 %
As mentioned is it possible to remove different kinds of substances with an acid solvent fluid or an alkaline solvent fluid. The choice of acid alkaline fluids depends on which substances the user wants to remove from the gas flow. Concentrated acid like for example sulphuric acid (H2SO4), hydrochloric acid (HC1), acetic acid (HC2H3O2), phosphoric acid (H3PO4), nitric acid (HNO3), oxalic acid (H2C2O4), citric acid (C6H8O7), and the like is either added to the solvent fluid, or concentrated alkaline like for example ammonium hydroxide (NH4OH), barium hydroxide Ba(OH)2, calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), sodium hydroxide (NaOH), and the like is added to the solvent fluid.
Examples of chemical reactions:
H2S + 2 NaOH => Na^ + 2 H2O where sodium sulphide can be used in the dye industry. 2 CO2 + 4 KOH = 2 K2CO3 + 2 H2O where potassium carbonate can be used in the soap and glass industries.
CO2 + Ca(OH)2 => CaCO3 + H2O where calcium carbonate can be used in the building industry.
CO2 + NaOH = Na2CO3 + H2O where sodium carbonate can be used in detergents.
2 NH3 + H2SO4 => (NH4)2SO4 where ammonium sulphate can be used as a component in fertilizers.
2 NH3 + H3PO4 => (NH4)2HPO4 where ammonium phosphate can be used as a component in fertilizers.
The general chemical reaction for removing ammonium (NH3) is:
R-COOH + NH3 =» R-COONH4 where R is a different chemical functional group, i.e. a number of CH groups.
In order to clean the gas flow of all unwanted substances the apparatus comprises a gas inlet, a pre-fϊlter, a water separator, a number of purification modules, a number blowers, a pipe system, valves, fittings and an air outlet, where each purification module comprises a hydrophobic membrane, a fluid container, a pump, a solvent fluid and a mixing container with a number of outlets and inlets.
Typically the apparatus consists of two purification modules, wherein one purification module is circulation acid solvent fluid for the purpose of removing a certain part of the unwanted substances and wherein the second purification module is circulation alkaline solvent fluid for the purpose of removing the rest of the unwanted substances.
However, any numbers of purification modules for cleaning of a gas flow containing a large number of different unwanted substances are possible within the scope of the invention, where each purification module removes a specific substance and thereby delivers a specific useful saturated solvent fluid.
In one embodiment of the invention the apparatus has both an air-inlet and an air- outlet with couplings, which make it possible to connect the apparatus to an exhaust line, for purifying of the gas flow and for the purpose of connecting the apparatus to for example a chimney.
In another embodiment of the invention the apparatus is an independent unit, which is placed in the vicinity of the source of odour. The apparatus will then draw in air from the surroundings, treat the air in the hydrophobic membrane and thereafter blow the air out into the surroundings again.
The apparatus comprises a pre-filter for filtering larger particles from the gas flow. Such large particles can be dust, straw, or other kinds of bedding. This pre-filter ensures that the hydrophobic membrane of the purification module does not clog during operation of the purification module.
If the gas flow contains any moisture or damp, the apparatus comprises a water separator, which functions to separate and collect any moisture or damp in the gas flow. The water is then led back to the mixing container.
To circulate the solvent fluid and to dose concentrated acid/alkaline solvent fluid the purification module comprises a number of pumps:
One pump doses concentrated acid/alkaline fluid to the mixing container. This pump is controlled by the pH value of the solvent fluid, so that a measurement of the pH value in the mixing container indicates if it is necessary to add more concentrated acid/alkaline fluid.
- Another pump is used for circulating the solvent fluid between the mixing container and the hydrophobic membrane. This pump is controlled so that the flow of the solvent fluid is adjusted to the gas flow in such a way that the unwanted substances can be absorbed in the solvent fluid.
The concentrated acid/alkaline fluid is deposited in a fluid container, whose size can differ according to the amount of gas flow needed to be purified. If the purification module comprises a large fluid container the apparatus can operate for a long time without needing for additional concentrated acid/alkaline fluid.
The problem is that a fluid container of a larger dimension occupies more space inside the purification module. On the other hand a small fluid container is easy to incorporate in the purification module, but the user has to fill the fluid container more often.
When using an apparatus with a fluid container, is it necessary to protect the apparatus against accidental bumping/collision causing leakage of the fluid container and spillage of the content onto humans and or animals or pollution of the ground.
The hydrophobic membrane is an ordinary micro hydrophobic membrane and comprises, for example a large number of capillary tubes. The gas flow is introduced into the micro hydrophobic membrane and flows past the capillary tubes.
A solvent fluid with certain chemical characteristics is pumped into the capillary tubes. When the gas flow gets into contact with the surface of capillary tubes the solvent fluid reacts with a certain substance in the gas flow and absorbs this substance into the solvent fluid. The blower is arranged in the pipe system, which connects the gas-inlet with the hydrophobic membrane and the gas out-let, in such a way that the gas flow is kept at a stable level and complies with the flow of solvent fluid.
To be able to dose the right amount of concentrated acid/alkaline fluids to the mixing container and to match the flow of gas to the flow of solvent fluid in order to optimize the absorbance level of unwanted substances, the apparatus is provided with a control system, where said control system is capable of controlling the blowers and the pumps.
This control system must at least be able to be programmed to dose a certain amount concentrated acid/alkaline fluids in situ to the mixing container over a determined period of time and to set the speed of both the pump for circulating the solvent fluid and the blower in such a way that the period of time, during which the gas flow is in near contact with the solvent fluid inside the hydrophobic membrane, is of a sufficient length in order to allow the unwanted substances to be totally or partly absorbed in the solvent fluid.
To optimize the cleaning of the gas flow the apparatus is furthermore provided with means for registration of the pH values of the solvent fluid in the mixing container and/or the degree of saturation of substances in the solvent fluid and/or the content of substances remaining in the purified gas flow.
The blowers and pumps are controlled by a control system according to the different kinds of registrations obtained. For example the registration of the pH value of the solvent fluid in the mixing container reduces the need to program the control systems manually in order to dispense concentrated acid/alkaline fluid each time a parameter changes. A parameter could for example be the temperature of the gas/solvent fluid, the type of unwanted substances and the content of substances in the gas flow.
To optimize the consumption of acid/alkaline fluids and to obtain a useful residual product the degree of saturation of substances in the solvent fluid is a useful registration and controlling parameter. With continuous registration of the. degree of saturation of substances in the solvent fluid it will be possible to determine the appropriate time for changing the solvent fluid instead of adding more concentrated acid/alkaline fluid. This ensures that the absorption of unwanted substances in the solvent fluid is as good as possible and allows the user to know the exact content of useful residual product in the discharged solvent fluid.
If the apparatus is provided with a by-pass or re-circulation, it is possible to either process the gas flow an extra time or to release clean gas to the environment without further treatment. To be able to determine when the gas flow is clean enough to release, it is necessary to register the content of substances remaining in the purified gas flow. Furthermore, this registration can act as documentation/evidence that the user complies with the laws and regulations regarding level of emission of unwanted substances into the surrounding environment.
A by-pass or re-circulation option furthermore enables the user to obtain a solvent fluid with a specific degree of saturation, which enhances the value of the residual product for reutilization purposes.
If one or more apparatuses are installed as a part of a large ventilation system, it would be an advantage that the control system and/or means for registration are connected to a computer, allowing the control system and/or means for registration to be remote controlled and the registration data to be saved.
In this way, the user can centrally from a position in a control-room operate and check several apparatuses at the same time without having to be physically next to the apparatus every time a change is required.
The computer could furthermore comprise data storage, so that it later would be possible to access previous operating data and analyse the different registrations, for example in comparison with the amount of useful residual product, thus making it is possible to further optimize the operation of the apparatus. The system according to the present invention can be used in different ways.
For example in a biogas process would it be an advantage if it is possible to reduce the amount of ammonium in the feeding source to the biogas reactor, because it is an unusable part of the biogas which consists mainly of methane and carbon dioxide, and ammonium will be emitted to the environment during the biogas process or burning of the biogas.
To reduce or remove the amount of ammonium in the feeding source to a biogas reactor, the system furthermore comprises at least one feeding source, a number of exchange columns arranged for fransferring substances from said feeding source to a gas flow, and a number of blowers for circulating.
The feeding source can be bio-degradable waste from a waste treatment facility or sludge from a wastewater treatment facility that can produce biogas by degrading.
The exchange columns are arranged in such a way that it is possible to lead liquid and/or degradable waste in the exchange columns and then in counter flow circulate air through the liquid and/or degradable waste. Hereby it is possible to transport unwanted substances and odours to the air flow. The counter flow arrangement is an advantage because it ensures efficient transportation of unwanted substances from the liquid and or degradable waste.
This air flow can be treated in a purification module with a hydrophobic membrane according to the present invention where it is necessary to use an acid solvent to absorb the ammonium.
In one embodiment of the invention a method for removal of ammonium from a feeding source to a biogas process is described as: said feeding source is led though said exchange columns, where a gas flow is circulated by said blowers for reducing/absorbing said ammonium in said feeding source,
- said gas flow is saturated with said ammonium and led to said purification modules and through said hydrophobic membrane, where said ammonium in said gas flow is diffused through said hydrophobic membrane and is absorbed in an acid solvent fluid, and
- said ammonium-reduced feeding source is led from said exchange column to said biogas reactor.
In another embodiment of the invention, a method for removal of ammonium from a feeding source to a biogas process is described as follows:
said feeding source is led to said biogas reactor,
from said biogas reactor a part of said feeding source is circulated though said exchange columns,
- from said biogas reactor a biogas flow is added to a gas flow, which is circulated by a blower between said exchange columns and said purification module with said hydrophobic membrane, where said ammonium in said gas and biogas flow mixture is diffused through said hydrophobic membrane and is absorbed in an acid solvent fluid.
By following one of the aforementioned methods it is possible to extract biogas from the biogas reactor and a solvent fluid saturated with ammonium from the mixing container of the purification module.
A system according to the present invention comprising a number of filters, a number of sterilisation chambers and a number of blowers can advantageously be used in offices, hospitals, laboratories, kitchens, trucks, cars, airplanes and/or transport containers, or other places where specific requirements to air quality apply, for example with regard to odour or sterilisation.
The air flow enters a filter for removing large particles. The type of filter is determined by the environment in which the system is used. For example in kitchens, the filter could be a filter made of felt adapted to capture grease particles.
To eliminate any risk of contamination from airborne sources, it is necessary to ensure that bacteria/viruses are killed before the air is reintroduced into the room.
Therefore the system comprises a sterilisation chamber where the air flow is radiated with UN light from a UN unit.
The blower is used to transport the air flow through the whole system including filter, purification modules, and sterilisation chamber.
Because the air contains various kinds of substances it is necessary to supply the system with a purification module with acid solvent fluid for absorbing, e.g. ΝH3, R- OH and the like,' and with a purification module with alkaline solvent fluid for absorbing, e.g. H2S, CO, CO2, R-COOH and the like.
The space available for the system in offices, hospitals, laboratories, kitchens, trucks, car, airplanes and/or transport containers, may be limited. Therefore it is necessary to build a compact and simple system which can be arranged in a box or similar construction so that it can be mounted in the room on the wall, under a table, in a closet or the like.
In one embodiment of the invention a method for cleaning an air flow is described according to which said airflow is led
- through said filter, for removal of particles, - through a first purification module with said hydrophobic membrane, where a number of impurities in said air flow is diffused through said hydrophobic membrane and are absorbed in an alkaline solvent fluid,
- through a second purification module with said hydrophobic membrane where a number of impurities in said air flow is diffused through said hydrophobic membrane and are absorbed in an acid solvent fluid, and
- through a sterilisation chamber for sterilisation.
In agriculture, the large amounts of manure produced by ariimals pose a problem because the manure has to be spread onto the fields or disposed of in another way.
For example, in Denmark there are limits to the amount of manure that may be spread per hectare of land because of the risk of nutrients reaching the ground water or washing into streams, lakes or the sea, thereby destroying drink water reserves or killing animal life.
Thus the reduction or removal of nutrients such as ammonium or sulphate from the manure is an advantage. It would be preferable to use a system according to the present invention where the system furthermore comprises a number of heat exchangers, a number of heating units, a number of heat treatment units, and a number of biogas reactors.
The heat exchangers are air to air heat exchangers where the air from the stable flows on one side, and heated air from the heat treatment units/purification modules flows on the other side.
The temperature of the air from the stable is typically app. 20°C, and the heated air from the heat treatment units/ purification modules has a temperature of app. 70°C. The first step of heating the air from the stable is by using the air from heat treatment units/purification modules.
The second step of heating the air from the stable is obtained by the heating units which can be solar panels, electric heaters, gas burners or the like.
It is important to reach temperatures of app. 70°C of the air from the stable to ensure an efficient heat treatment/drying of the manure in the heat treatment units.
Manure from the stable is transported to the heat treatment units where the heated air from the stable is circulated, thereby drying the manure which is either led to storage, distributed on the fields, or led to a bio reactor for producing biogas.
The biogas from the biogas reactor can be used in the heating units to heat the air from the stable.
Before the heated air from the heat treatment unit is circulated back to the heat exchangers, it is led though a purification module where unwanted substances such as ammonium are removed in a hydrophobic membrane and absorbed in an acid solvent fluid.
The treated/clean air is led though the heat exchangers, and the temperature difference causes the water content of the air to condensate. The output from the heat exchanger is clean air and condensated water which can be led to the environment without causing any harm.
The method for drying waste, preferably manure and cleaning a gas flow, preferably an air flow from a stable, is described in the following way:
- said gas flow is preheated.in said heat exchangers and by said heating units, - said waste is dried and heated by said preheated gas flow in said heat treatment units,
- said gas flow is then circulated through said purification modules and back to said heat exchangers, and
- said dried and heated waste is led to said biogas reactors.
Furthermore the system and apparatus can be used in farming where the apparatus for example is connected to an air-outlet from a stable, or the system and apparatus can be used in places where it is necessary to clean emissions of volatile fatty acids, aromatic substances, and/or chemical substances such as ammonium (NH3), hydrogen sulphide (H2S), and carbon dioxide (CO2). Examples of such places are:
- in factories, e.g. production areas, production machine and/or from a vat. - on farms, e.g. a covered farmyard manure containers. on drilling platforms, e.g. when purifying natural gas of hydrogen sulphide (H2S) and/or carbon dioxide (CO2).
Short description of the drawing
The invention is explained in more detail below with reference to the drawing, where
Fig. 1 is a diagram illustrating the system according to the invention,
Fig. 2 is a diagram illustrating the system according to the invention with an extra purification module for cleaning natural gas or biogas,
Fig. 3 is a diagram illustrating the influence of the pH value when purifying a gas , flow, Fig. 4 is a diagram illustrating the system according to the invention for removal of ammonium from a feeding source to a biogas process,
Fig. 5 is a diagram illustrating an alternative system according to the invention for removal of ammonium from a feeding source to a biogas process,
Fig. 6 is a diagram illustrating the system according to the invention for cleaning an air flow,
Fig. 7 is a drawing of the system in Fig. 6 in a transportable embodiment,
Fig. 8 is a diagram illustrating the system according to the invention for drying waste, preferably manure, and cleaning a gas flow, preferably an air flow from a stable.
Detailed description of the invention
Fig. 1 shows a gas flow 1 containing unwanted substances which is led through a pre- filter 2 where dust and larger particles are separated from the gas flow and at the same time water is separated from the gas flow, for example through steam. The gas flow 1 is then sucked through the hydrophobic membrane 3 via a blower 5, where the unwanted substances pass through the hydrophobic membrane 3.
At the exit of the hydrophobic membrane 3 a water separator 4 containing a water seal is arranged, and the condensed water steam is led to the mixing container 8. From the fluid container 6 concentrated acid fluid is dosed by means of a dosing pump 7 to the mixing container 8, where the level of the pH value of the solvent fluid is maintained at a substantially constant level.
The solvent fluid is re-circulated between the mixing container 8 and the hydrophobic membrane 3 by a circulation pump 9. The unwanted substances which diffuse through the hydrophobic membrane 3 are absorbed in the solvent fluid. After the solvent fluid has reached a predetermined degree of saturation in the mixing container 8, the solvent fluid is led out at 10 for reutilization such as drying or separation into different reusable salts.
Next, the purified gas flow 11 is led through another hydrophobic membrane unit 12 by means of a blower 13, where the alkali solvent unwanted, substances diffuse through the hydrophobic membrane 12 and the purified gas flow 19 is led out to the surroundings or back into the apparatus for recycling purposes..
From the fluid container 14 a concentrated alkali fluid is dosed by means of a dosing pump 15 to the mixing container 16, where the level of the pH value of the solvent fluid is maintained at a substantially constant level.
The solvent fluid is re-circulated between the mixing container 18 and the hydrophobic membrane 12 by means of a circulation pump 17. The unwanted substances, which diffuse through the hydrophobic membrane 12, are absorbed in the solvent fluid.
After the solvent fluid has reached a predetermined degree of saturation in the mixing container 18, the solvent fluid is led out at 18 for reutilization such as drying or separation into different reusable salts.
Fig. 2 shows how the gas flow 19 is treated in another purification module 31, where the gas flow 19 is led though a hydrophobic membrane 20 by either blower 30 or blower 21. Using the blower 21, the gas flow 19 is re-circulated and treated again in the hydrophobic membrane 20. To control the re-circulation, the pipe system is provided with valves 28 and 29 which completely or partly lead the gas flow 19 back into the pipe system or through the blower 30 and lead the gas flow 27 to the surroundings. Purification of the gas flow in the hydrophobic membrane 20 is obtained as mentioned regarding the hydrophobic membrane 3 and 12, where a solvent fluid is circulated between the mixing container 26 and the hydrophobic membrane 20 by a pump 25, and where a concentrated acid/alkali fluid is dosed from the fluid container 22 to the mixing container 24 by a pump 23.
This purification module is advantageously used to purify a natural gas or biogas flow.
Fig. 3 shows a diagram with a graph showing how the level of the pH value affects the purification of a gas flow of hydrogen sulphide (H2S). Along the X axis is shown the pH value of the solvent fluids and along the Y-axis is shown the amount of hydrogen sulphide (H2S) (ppm) in a gas flow after treatment in the hydrophobic membrane. The graph shows that the pH value of the solvent fluid has to be higher than 11-12 in order to obtain an effective purification of the hydrogen sulphide (H2S).
Fig. 4 shows a system 30 for removal of ammonium from a feeding source 31 in a biogas process.
The feeding source 31 is preheated and led to a filled and insulated exchanger column 32 where an air flow 33 in a counter flow is passed though the feeding source 31.
For a thermophilic process the temperature of the feeding source 31 is app. 30-55°C, and for a mesopilic process the temperature of the feeding source 31 is app. 25-37°C.
The air flow 33 is circulated between exchanger column 32 and the hydrophobic membrane 35 of the purification module 34 by blower 38, and an acid solvent fluid 39 is circulated between the hydrophobic membrane 35 and the mixing container 36 by the circulation pump 37.
The ammonium in air flow 33 diffuses through the hydrophobic membrane 35 and is absorbed in the acid solvent fluid 39. After the acid solvent fluid 39 has reached a predetermined degree of saturation in the mixing container 36, the acid solvent fluid 39 is led out at 41 for reutilization such as drying or separation into different reusable salts.
The almost ammonium free feeding source 31 is led from the exchange column 32 to the bio reactor 40, where biogas is produced and led out at 42 to a storage tank (not shown) for later use, e.g. for burning in a heating process.
Fig. 5 shows a system 50 for removal of ammonium from a feeding source 31 in a biogas process.
The feeding source 31 is led to a bio reactor 40 where a part of the feeding source 31a is circulated between bio reactor 40 and exchanger column 32 wherein an air flow 53 in a counter flow is passed though the feeding source 31a.
The air flow 53, which consists of re-circulated air and biogas 51 from the biogas reactor 40, is circulated between exchanger column 32 and the hydrophobic membrane 35 of the purification module 34 by blower 38, and an acid solvent fluid 39 is circulated between the hydrophobic membrane 35 and the mixing container 36 by the circulation pump 37.
The ammonium-saturated air flow 53 is led through the hydrophobic membrane 35 where ammomum is diffused and absorbed in the acid solvent fluid 39.
After the acid solvent fluid 39 has reached a predetermined degree of saturation in the mixing container 36, the acid solvent fluid 39 is led out at 41 for reutilization such as drying or separation into different reusable salts.
Biogas from the bio reactor is led out at 52 to a storage tank (not shown) for later use.
Fig. 6 shows a system 60 for cleaning an air flow 61. The contaminated air flow 61 is passed through a filter 62 for filtering particles and is then led though a first hydrophobic membrane 63a where substances absorbable in an alkaline solvent fluid 64 are circulated between hydrophobic membrane 63a and container 65a by circulation pump 66a.
The air flow 61 is led though a second hydrophobic membrane 63b, where substances absorbable in an acid solvent fluid 67 is circulated between hydrophobic membrane 63b and container 65b by circulation pump 66b.
The air flow 61 is then led though a sterilisation chamber 68 where the air flow 61 is radiated with UN light.
The air flow 61 is passed though the whole system 60 by blower 69.
Fig. 7 shows a transportable air-cleaning apparatus 70 with a system 60 as shown in
Fig. 6 where the air inlet 71 is connected to a ventilation system (not shown) or just to the open, where an air flow is passed though the whole system 60 by blower 69.
From the air outlet 72, odourless and sterilized air is released to a ventilation system (not shown) or just to the open,
The air cleaning apparatus 70 is provided with a panel 73 with three different indication lamps 74, 75, 76 where for example a red lamp 74 indicates when the container 65b with acid solvent fluid must be changed,
- a blue lamp 75 indicates when the container 65a with alkaline solvent fluid must be changed, and
- a green lamp 76 indicates when the apparatus 70 is running normally.
Fig. 8 shows a system 80 for drying, waste, preferably manure, and cleaning a gas flow, preferably an air flow from a stable 81. From the stable 81, air 2 containing ammonium is led through an air to air heat exchanger 83 to heating unit 85. When the desired temperature has been achieved, the air is led to drying and heat treatment unit 86.
The heating unit 85 consists of a liquid/air heat exchanger where the energy supply is from solar panels 99. The energy supply is supplemented by burning of biogas 96 in a burner 97. Alternatively, oil or some other source of energy 99 can be used for the heating unit 95.
A portion of the dry manure 90 is led to reactor 95 together with manure 84 in which it is used as a feeding source for anaerobe fermentation by which biogas 96 is produced. The heat treatment unit 86 consists of an adjustable belt conveyor on which manure 84 having a low content of dry matter is led from stable 81 to drying and heat treatment unit 86.
After drying and heat treatment, the dry manure 90 is conveyed out of heat treatment unit 86.
The heated air is saturated with water in drying and heat treatment unit 86 and is subsequently led to the hydrophobic membrane 87.
From the mixing container 89, the solution is recirculated at the other side of the hydrophobic membrane 87 by means of a circulation pump 88 where the ammonium diffuses through the hydrophobic membrane 87 and is absorbed in the solution. After saturation of the solution in the mixing container 89, the solution 94 is either led back to the drying and heat treatment unit S6 for being mixed with the degassed manure from the reactor, or alternatively, the solution 94 can be deposited as separate fertilizer.
The dried and saturated air is led through air/air heat exchanger 83 though a siphon 93 in which the clean air 91 and condensated water 92 are separated due to a drop of temperature and pressure change in heat exchanger 83. Test results
During the development of the present invention a test system has been tried which has obtained the following results from an operative test apparatus:
Result 1:
Sulphuric acid (H2SO4) in the solvent fluid is used for removing ammonium (NH3) from the biogas contained in exhaust air coming from a stable. A test run over a period of 45 days has shown that the actual consumption of concentrated sulphuric acid
(H2SO4) per day used for absorbing the ammonium (NH3) equals the pre-calculated consumption of sulphuric acid (H2SO4).
The following chemical reaction occurs: 2 NH3 + H2SO4 => (NH4)2SO4 and the flow of the exhaust air was approximately 165 m3/h during the test period.
Ammonium (NH3) in the exhaust air - measured: 1,171.50 mg/nι3 Ammonium (NH3) in the exhaust air - measured: 28.12 g/day Ammonium (NH3) in the exhaust air - calculated: 28.15 g/day Consumption of sulphuric acid (H2S04) - calculated: 43.26 ml/day
Consumption of sulphuric acid (H2S04) - measured: 43.31 ml/day
This shows that it is possible to calculate the consumption of either the acid or the alkaline solvent fluids very accurately and to control the system in order to remove a pre-determined amount of unwanted substances from the biogas flow.
Result 2:
To show which level of pH value in the solvent fluid is optimal for purifying a biogas flow of hydrogen sulphide (H2S), a test run was made where the biogas flow and biogas temperature were kept constant and the pH value of the solvent fluid was changed. 25
After the treatment in the hydrophobic membrane, the content of hydrogen sulphide (H2S) was measured to:
Figure imgf000027_0001
The conclusion from this test was that the content of hydrogen sulphide (H2S) is best removed from the biogas flow if the solvent fluid has a pH value above 11-12. The graph illustrating this test is shown in Fig. 3.
Result 3: To remove carbon dioxide (CO2) and hydrogen sulphide (H2S) from a flow of biogas, sodium hydroxide (NaOH) is used as the solvent fluid.
The following chemical reaction occurs:
H2S + 2 NaQH : Na,S + 2 H O C02 + NaOH => N-^CO-, + H2O
The biogas flow (2.6 litres per minute) and pH value (approx. 12.3) of the solvent fluid were constant, and the test period was 85 minutes. The test showed the following contents of hydrogen sulphide (H2S) and carbon dioxide (CO2): Start concentration:
Hydrogen sulphide (H2S) 2300 ppm
Carbon dioxide (CO2) 35.0%
Methane (CH4) 65%
End concentration:
Hydrogen sulphide (H2S) 25 ppm
Carbon dioxide (CO2) 20.2%
Methane (CH4) 79.8%
The results show that it is possible to remove 14.8 % of the carbon dioxide (CO,) and approximately 99 % of the hydrogen sulphide (H2S) which results in a biogas which burns well.
The test was run again over a period of 8 hours, with a larger membrane area, and a slower biogas flow. The result showed almost total purification of hydrogen sulphide and a lager purification of carbon dioxide (CO2). The result was the following:
Start concentration: Hydrogen sulphide (H2S) 2300 ppm
Carbon dioxide (CO2) 35.0%
Methane (CH4) '65.0%
End concentration: Hydrogen sulphide (H2S) <10 ppm
Carbon dioxide (CO2) 20.0%
Methane (CH4) 80.0% •
The results show that it is possible to remove almost all the hydrogen sulphide (H2S) and use the system to reduce the content of carbon dioxide (CO2) significantly.
Result 4: A test to remove ammonium (NH3) from the feeding source of a biogas process was performed on a system as described in Fig. 4 (without a biogas reactor). The following results were found, based on the test parameters given below:
Exchange column: Diameter: 25 cm. Height: 80 cm. Flow of solvent fluid (H2SO4): 1 1/min. Flow of gas flow: 40, 50, 60, 70 and 80 1/min. Area of hydrophobic membrane: 0.4 m2 Temperatures: 52°C and 37°C pH value: 7.5-8.5
Free ammonium in feeding source: 2600 mg/1 Residue from mixing container: (NH4)2SO4
Figure imgf000029_0001
The results show that it is possible to remove up to 80% of the free ammonium in the feeding source, and that the optimum relationship between the flow of solvent fluid and the flow of the gas flow is 1 : 65.
Furthermore it would be possible to optimise the process by optimising the dimension of the exchange column and by increasing the pH value to 7.5-9.5.
Result 5:
A test to clean an air flow was performed on a system as described in Fig. 6 (without a UN unit). The following results were found, based on the test parameters given below:
Air flow: 150 1/min.
Area of hydrophobic membranes: 2 x 0.1 m2 pH value of alkaline solvent fluid: >11 pH value of .acid solvent fluid: 2
To simulate the odour from an operating room in a hospital, different kinds of meat were burned using a soldering iron, and a suction head was placed above the origin of the odour.
Bags with 100 litres of air were collected directly from the odour source and compared to bags with 100 litres of air collected after the air flow had been through the system.
A smell panel evaluated the odours from the different bags, and it was concluded that the result was a significant improvement, and that the system was very efficient in cleaning an air flow.
Similar tests were performed with air from tainted meat, fish waste, tainted vegetables and the like. The results were the same. In each case, the conclusion of the smell panel was that the system was very efficient in cleaning an air flow.

Claims

1. System for removal of unwanted substances in a gas flow comprising a number of purification modules, each module comprising a hydrophobic membrane (3), a mixing container (8) and a solvent fluid, where the substances in the gas flow are diffused through the hydrophobic membrane (3) and are absorbed in the solvent fluid, and where the purified gas flow (11) is led to either a further purification module or to the surrounding environment, where said solvent fluid either is an alkaline solvent fluid or an acid solvent fluid, characterised in that said solvent fluids circulate between said hydrophobic membrane (3) and said mixing container (8), and where either concentrated acid or alkaline fluids are added to said solvent fluid in the mixing container (8) in order to maintain a substantially constant pH value in the solvent fluid.
2. System according to claim 1, characterised in that the solvent fluid is circulated between the hydrophobic membrane (3) and mixing container (8) until it reaches a predetermined degree of saturation, after which the solvent fluid is led away for reutilizing together with the absorbed substances.
3. System according to any of the claims 1-2, characterisedin that the solvent fluid with a predetermined degree of saturation is separated into different reusable salts, e.g. by drying the saturated solvent fluid.
4. System according to any of the claims 1-3, characterised in that said system is constructed with at least two purification modules, and where at least one of said purification modules (31) comprises a hydrophobic membrane (20), a mixing container (26) and an alkaline solvent fluids for purification of a natural gas or biogas flow.
5. System according to claim 4, characterisedin that the natural gas or biogas flow (19) is re-circulated though the hydrophobic membrane (20) until it reaches a predetermined degree of purity after which the purified natural gas or biogas flow (27) is led to either a gas burner or to a receptacle.
6. System according to any of the claims 1-3, characterised in that concentrated acid like for example sulphuric acid (H2SO4), hydrochloric acid (HC1), acetic acid (HC2H3O2), phosphoric acid (H3PO4), nitric acid (HNO3), oxalic acid (H2C2O4), citric acid (C6HsO7), and the like is added to the solvent fluid.
7. System according to any of the claims 1-3, characterised in that concentrated alkaline like for example ammonium hydroxide (NH4OH), barium hydroxide Ba(OH)2, calcium hydroxide Ca(OH)2, potassium hydroxide (KOH), sodium hydroxide (NaOH) and the like is added to the solvent fluid.
8. System according to claim l,characterisedin that it furthermore comprises at least one feeding source, a number of exchange columns arranged for transferring substances from a first gas flow to a second gas flow, a number of blowers for circulating said second gas flow between said exchange columns and purification modules, and a number of biogas reactors.
9. System according to claim l,characterisedin that it furthermore comprises a number of filters, a number of sterilisation chambers, and a number of blowers.
10. System according to claim 1, characterised in that it furthermore comprises a number of heat exchangers, a number of heating units, a number of heat treatment units, and a number of biogas reactors.
11. Apparatus for removal of unwanted substances in a gas flow by said system according to any of the claims 1-7, characterised in that the apparatus comprises a gas inlet, a pre-filter (2), a water separator (4), a number of purification modules, a number of blowers (5), a pipe system, valves, fittings, and an air outlet, where each purification module comprises a hydrophobic membrane (3), a fluid container (6), a number of pumps (7, 9), a solvent fluid, and a mixing container (8) with a number of outlets and inlets.
12. Apparatus according to claim 11, characterisedin that said apparatus is provided with a control system, where said control system is capable of controlling the blowers (5) and the pumps (7, 9).
13. Apparatus according to any of the claims 11-12, characterisedin that said apparatus furthermore is provided with means for registration of the pH value of the solvent fluid in the mixing container (8) and/or the degree of saturation of substances in the solvent fluid and/or the content of substances remaining in the purified gas flow
(11).
14. Apparatus according to any of the claims 12-13, characterised in that the control system and/or means for registration are connected to a computer, allowing said control system and/or said means for registration to be remote controlled and to save registration data.
15. Method for removal of ammonium from a feeding source to a biogas process with a system according to claim 8, characterised in that:
- said feeding source is led though said exchange columns, where a gas flow is circulated by said blowers for reducing/absorbing said ammonium in said feeding source, said gas flow is saturated with said ammonium and led to said purification modules and through said hydrophobic membrane, where said ammonium in said gas flow is diffused through said hydrophobic membrane, and is absorbed in an acid solvent fluid, and - said ammonium-reduced feeding source is led from said exchange column to said biogas reactor.
16. Method for removal of ammonium from a feeding source to a biogas process with a system according to claim 8, characterisedin that: - said feeding source is led to said biogas reactor,
- from said biogas reactor a part of said feeding source is circulated though said exchange columns, - from said biogas reactor a biogas flow is added to a gas flow, which is circulated by a blower between said exchange columns and said purification module with said hydrophobic membrane, where said ammonium in said gas and biogas flow mixture is diffused through said hydrophobic membrane and is absorbed in an acid solvent fluid.
17. Method for cleaning an air flow with a system according to claim 9, c h a r a c t e r i s e d in that said air flow is led:
- through said filter, for removal of particles, - through a first purification module with said hydrophobic membrane, where a number of impurities in said air flow are diffused through said hydrophobic membrane and are absorbed in an alkaline solvent fluid,
- through a second purification module with said hydrophobic membrane where a number of impurities in said air flow are diffused through said hydrophobic membrane and are absorbed in an acid solvent fluid, and through a UN unit for sterilisation.
18. Method for drying waste, preferably manure, and cleaning a gas flow, preferably an air flow from a stable, with a system according to claim 10, c h a r a c t e r i s e d in that: said gas flow is preheated in said heat exchangers and by said heating units, said waste is dried and heated by said preheated gas flow in said heat treatment units,
- said gas flow is then circulated through said purification modules and back to said heat exchangers, and said dried and heated waste is led to said biogas reactors.
PCT/DK2003/000899 2002-12-18 2003-12-18 A system and apparatus for removal of unwanted substances in a gas flow WO2004054688A1 (en)

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EP2433700A1 (en) * 2010-09-23 2012-03-28 Alstom Technology Ltd Trace component removal in CO2 removal processes by means of a semipermeable membrane
WO2013136310A1 (en) * 2012-03-16 2013-09-19 Aker Process Systems As Hydrocarbon gas treatment
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WO2008128776A3 (en) * 2007-04-23 2009-01-15 Heinrich Follmann Method for the purification of biogas, and biogas produced using said method
US9339760B2 (en) 2010-06-11 2016-05-17 Dvo, Inc. Methods and apparatuses for removal of hydrogen sulfide and carbon dioxide from biogas
EP2433700A1 (en) * 2010-09-23 2012-03-28 Alstom Technology Ltd Trace component removal in CO2 removal processes by means of a semipermeable membrane
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WO2014197005A1 (en) * 2013-06-04 2014-12-11 Southern Company Systems and methods for sequestering co2
EP3406319A1 (en) 2017-05-04 2018-11-28 Martin Schönhammer Method for operating a chemical gas scrubber
CN112739445A (en) * 2018-10-15 2021-04-30 摩瑞奇曼公司 Hydrogen sulfide removal process
CN112739445B (en) * 2018-10-15 2023-01-24 摩瑞奇曼公司 Hydrogen sulfide removal process
CN110102153A (en) * 2019-04-25 2019-08-09 成都同创紫气科技有限公司 A kind of membrane type deodoriser and its component, system and deodorizing methods

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