Classifications

• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/58—Ammonia
• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/346—Controlling the process
• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/77—Liquid phase processes
  • B01D53/78—Liquid phase processes with gas-liquid contact
• • 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
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/77—Liquid phase processes
  • B01D53/79—Injecting reactants
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C1/00—Ammonia; Compounds thereof
  • C01C1/24—Sulfates of ammonium
  • C01C1/242—Preparation from ammonia and sulfuric acid or sulfur trioxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/206—Ammonium compounds
  • B01D2251/2067—Urea
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/50—Inorganic acids
  • B01D2251/504—Nitric acid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/50—Inorganic acids
  • B01D2251/506—Sulfuric acid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/406—Ammonia
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/02—Other waste gases
  • B01D2258/0266—Other waste gases from animal farms

Definitions

• ammonia is absorbed in an aqueous solution where the pH of the aqueous solution is typically controlled to a value of 3-7 by the addition of sulfuric acid (H2SO4) or nitric acid (HNO3). Due to the absorption of ammonia from the gas phase, the pH increases, which must be compensated by adding sulfuric acid or nitric acid. In combination with ammonia, this forms a solution of ammonium sulfate ((NEU ⁇ SC ) or ammonium nitrate (NH4NO3).
• H2SO4 sulfuric acid
• HNO3 nitric acid
• the Relative Humidity (RH) of the air in stables is typically not saturated with water.
• the RH can range between 50% and 80%.
• the recommended relative humidity (RH) range in pig stables is between 60% and 70%. This range has been shown to be the best for fighting respiratory infections. Too low humidity can cause respiratory problems in pigs, as it can dry out their nasal passages and make them more susceptible to infection. Too high humidity can also cause respiratory problems in pigs, as it can create a breeding ground for bacteria and viruses. Additionally, high humidity can lead to condensation, which can cause mold and mildew growth.
• the ideal RH range for pig stables can vary depending on the climate, the type of ventilation system, and the number of pigs in the stable. However, in general, the RH should be kept between 60% and 70% to promote pig health and welfare ⁇ Simple ventilation tips as warm weather approaches” Ken Lamm and Casey Zangaro, Michigan State University Extension - March 10, 2020).
• the RH inside the stable and inside the air scrubber can differ due to changes in temperature, the RH of the air is often still unsaturated and this, in combination with the low salt concentration in the scrubbing liquid, causes water to evaporate, and leads to the consumption of large amounts of water.
• Present invention solves such problems in the art for acid based ammonia scrubbing of air which is unsaturated with water (RH ⁇ 90% when entering the scrubber) by keeping the Relative humidity (RH) of the treated ammonia containing air higher than the Deliquescent Relative Humidity (DRH) of the salt or combination of salts dissolved in the aqueous washing liquid (the scrubbing solution).
• RH Relative humidity
• DRH Deliquescent Relative Humidity
• the required water is withdrawn from the treated air.
• the invention also includes measures to ensure the RH of the treated air remains above the DRH of the washing liquid, by chemical addition (e.g. urea) and/or by pre-humidification.
• the produced ammonium sulfate or ammonium nitrate and optionally urea solution has a high salt concentration of 25-75 wt%.
• the present invention solves the problems of the related art by ensuring the Deliquescence Relative Humidity of the dissolved salt or salts is lower than the relative humidity of the treated air, which allows a higher salt concentration in the product to be obtained while avoiding salt crystallization.
• This higher salt concentration is advantageous since it enables the system to match the equilibrium relative humidity of the product with the relative humidity of the treated air.
• the RH of the air needs to be sufficiently lower than the DRH to have a sufficient driving force for salt nucleation to occur and the lower limit for the RH of the air can be set somewhat lower than the DRH.
• the lower limit for the RH of the scrubber can therefore be set between 10% above and 20% below the DRH, depending on the implemented safety margin.
• the DRH of the salt solution is lowered by the addition of chemicals (e.g. urea) to the aqueous scrubbing solution.
• Present invention concerns a method or system of purifying air comprising ammonia with a Relative Humidity (RH) ⁇ 90%, by scrubbing the air with an acid containing aqueous washing liquid consequently to contain a salt or combination of salts, characterised in that the formation of salt crystals is prevented by ensuring the RH of the treated air is always kept above a predetermined threshold, which is set between 10 % above the Deliquescent Relative Humidity (DRH) and 20 % below the DRH. Under normal operation (> 70% of the operation time on annual basis) the relative humidity of the treated air is above the DRH of the salt or combination of the aqueous solution.
• a predetermined threshold which is set between 10 % above the Deliquescent Relative Humidity (DRH) and 20 % below the DRH.
• Present invention also concerns a method or system of taking up and purifying ammonia from an incoming air with Relative Humidity (RH) ⁇ 90%, by scrubbing the air by an acid containing aqueous washing liquid and containing a salt or combination of salts, whereby the formation of salt crystals is prevented by ensuring the RH of the treated air to be above the predetermined threshold which has a maximum acceptable value of 10 % above the Deliquescent Relative Humidity (DRH) of the salt or combination of salts and a minimum acceptable value of 20 % below the DRH of the salt or combination of salts and possibly urea with the exact threshold value chosen based on the safety margin which is chosen to be implemented, the method comprising increasing the RH of the incoming air and/or decreasing the DRH of the salt or combination of salts and possibly urea in the scrubbing liquid when the RH of the treated air falls outside of the threshold range.
• the incoming air has a Relative Humidity (RH) of
• the RH of the air to be treated is increased by pre-humidification.
• the pre-humidification is done by spraying water in the treated air, injecting steam into the gas stream or by bringing the air in contact with water in a gas-liquid contactor and the DRH of the dissolved salt can be decreased by altering the composition of the scrubbing solution through addition of chemical compounds in the aqueous washing liquid and the acid can be nitric acid, sulphuric acid or a combination thereof. In some aspect or a combination of nitric acid and/or sulphuric acid and/or urea.
• the present invention provides that the RH of the incoming air or air to be treated is sensed or monitored and whereby the DRH of the salts in the aqueous washing liquid is sensed and whereby if the relative humidity of the incoming air approaches the DRH of the salts in the aqueous washing liquid, the relative humidity of the air to be treated is increased through pre-humidification and/or the DRH in the aqueous washing liquid is decreased by chemical addition.
• the present invention provides that the RH of the incoming air or air to be treated is sensed or monitored and whereby the DRH of the salts in the aqueous washing liquid is sensed and whereby if the relative humidity of the incoming air approaches the predetermined threshold (between 10% above and 20% below the DRH of the salts in the aqueous washing liquid), the relative humidity of the air to be treated is increased through pre-humidifi cation and/or the DRH in the aqueous washing liquid is decreased by adding a salt with high deliquescence relative humidity (above 70% at 20°C) and/or urea.
• Intensive livestock farming is a major source of airborne ammonia, but industrial emission sources can also have a significant contribution.
• wet scrubbers have been implemented as an end-of-pipe treatment technique.
• absorbed ammonia NH3 is digested by bacteria into nitrite (NO 2 ) and then into nitrate (NO3 ).
• Some biological scrubbers are equipped with an additional denitrification tank, which converts the nitrates into anaerobic conditions in nitrogen gas (N2).
• N2 nitrogen gas
• the aqueous solution has a neutral pH to maintain the bacterial culture responsible for the process.
• the pH of the aqueous solution is typically controlled to a value of 3- 7 by the addition of sulfuric acid (H2SO4) or nitric acid (HNO3). Due to the absorption of ammonia from the gas phase, the pH increases, which must be compensated by adding sulfuric acid or nitric acid. In combination with ammonia, this forms a solution of ammonium sulfate ((NH ⁇ SC ) or ammonium nitrate (NH4NO3).
• H2SO4 sulfuric acid
• HNO3 nitric acid
• the acid scrubbers have a superior ammonia removal rate (typically > 95 %), while biological scrubbers achieve typically only 70 %.
• the invention which will be described below is an improvement compared to current state of the art acid ammonia scrubbers in three ways: (1) the problem of salt formation in the packed bed is resolved, (2) the final product is more concentrated and (3) the amount of water lost due to evaporation is reduced significantly, or even eliminated.
• a nitric acid based scrubber which produces an ammonium nitrate solution, is already characterized by a lower DRH than the sulfuric acid based scrubber, which produces an ammonium sulfate solution.
• the DRH of a nitric acid based scrubber and a sulphuric acid based scrubber can both be lowered by addition of Urea.
• Figure 5 Equilibrium relative humidity as a function of ammonium nitrate concentration for different temperatures for an aqueous solution of Ammonium nitrate/urea with a weight ratio of 1/0.8
• a state of the art acid ammonia scrubber comprises a packed bed (A) in which the ammonia containing air (C) is brought into contact with the aqueous solution.
• the treated air (D) is vented or sent to other downstream processing steps.
• the aqueous solution is sent to a buffer tank (B) from which it is recirculated to the packed bed (A).
• the pH of the aqueous solution is measured with a pH sensor (E) and controlled by adding acid (K).
• the salt concentration is measured with a conductivity sensor (F) and the conductivity is set to a fixed maximum, typically set in such a way that the salt concentration does not exceed 1/5 to 1/3 of its solubility limit. If the maximum is exceeded, part of the aqueous solution is drained (M). Water (L) is added to compensate for the drained product (M) and for evaporation taking place in the packed bed (A).
• Table 1 process control method for state of the art ammonia scrubbing with acids, compared to the method of the present invention, with two different embodiments of the present invention.
• the pH of the washing liquid is monitored to remain below a predetermined value (typically between 3 and 6).
• a predetermined value typically between 3 and 6
• concentrated acid nitric acid or sulfuric acid
• the relative humidity of the incoming air is measured with a humidity sensor (J).
• J the relative humidity of the incoming air
• the RH of the incoming air is higher than a predetermined limit (between 10 % above and 20 % below the DRH).
• a predetermined limit between 10 % above and 20 % below the DRH.
• the DRH of the washing liquid can be determined by a combination of a temperature measurement with a temperature sensor (H), a pH measurement with a pH sensor (E) and/or a conductivity measurement with a conductivity sensor (F) and/or a density measurement with a density sensor (G) and/or by monitoring the acid addition (K) and/or by monitoring the salt addition (O).
• a temperature sensor (H) is sufficient to determine the DRH, as the DRH is equal to the DRH of the ammonium salt corresponding to the used acid (NH4NO3 for nitric acid, (NH4)2SO4 for sulfuric acid, a combination of NH4NO3 and urea when using a mixture of urea and HN03 as acid, or a combination of (NH4)2SO4 and urea when using a mixture of urea and H2SO4 as acid).
• the equilibrium relative humidity of the solution will automatically evolve to match the relative humidity of the treated air.
• the concentration automatically increases due to continuous ammonia absorption, acid addition to compensate for the ammonia absorption, and due to water evaporation. If the equilibrium relative humidity is lower than the RH of the treated air, it is increased automatically without taking action due to water absorption.
• FIG. l is a graphic showing the solubility of ammonium sulfate in water as a function of temperature
• FIG. 2 is a graphic showing the solubility of ammonium nitrate in water as a function of temperature
• FIG. 3 is a graphic showing the deliquescence Relative Humidity (DRH) of Ammonium Nitrate, Ammonium Sulfate and combinations of Ammonium nitrate, ammonium sulfate and urea with given weight ratio’s for a temperature range of 0-30 °C.
• FIG. 4 is a graphic showing the equilibrium relative humidity as a function of ammonium nitrate concentration for different temperatures for an aqueous solution of ammonium nitrate
• FIG. 5 is a graphic showing the equilibrium relative humidity as a function of ammonium nitrate concentration for different temperatures for an aqueous solution of
• FIG. 6 is a schematic overview of the acid ammonia scrubber

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• Engineering & Computer Science (AREA)
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• Treating Waste Gases (AREA)
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• 2023
  • 2023-08-30 KR KR1020257009797A patent/KR20250057840A/ko active Pending
  • 2023-08-30 WO PCT/EP2023/073819 patent/WO2024047118A1/en not_active Ceased
  • 2023-08-30 CN CN202380073411.0A patent/CN120152778A/zh active Pending
  • 2023-08-30 EP EP23762497.8A patent/EP4580784A1/de active Pending

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