Development of an Acid Scrubber for Reducing Ammonia Emissions from Animal Rearing Facilities


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Recent research has shown that over half of nitrogen excreted by chickens is lost into the atmosphere via ammonia volatilization before the litter is removed from poultry houses. Large quantities of particulate matter and volatile organic compounds (VOCs) are also emitted from animal rearing facilities. During the past decade we have developed and patented an acid scrubber for capturing ammonia, VOCs and dust from air exhausted from poultry and swine barns. The objectives of this project were; (1) to re-design the scrubber to improve the ammonia removal efficacy, (2) conduct full-scale testing of the scrubber under controlled conditions at various ventilation rates, (3) evaluate the cost, practicality and efficacy of various acids for scrubbing ammonia, and (4) install scrubbers on exhaust fans of poultry houses located in Virginia and Arkansas and measure the efficiency of ammonia removal from the exhaust air. The efficiency of ammonia removal by the scrubber varied from 55-95%, depending on the type of acid used, air flow rate, and the internal scrubber configuration. This technology could potentially result in the capture of a large fraction of the N lost from AFOs, while simultaneously reducing emissions of bacteria, dust, and odors, which would improve the social, economic, and environmental sustainability of poultry and swine production.

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Development of an Acid Scrubber for Reducing Ammonia Emissions from Animal Rearing Facilities

  1. 1. Development of an Acid Scrubber forReducing Ammonia Emissionsfrom Animal Rearing FacilitiesPhilip Moore, USDA/ARSRory Maguire, Virginia TechMark Reiter, Virginia TechJactone Ogejo, Virginia TechRobert Burns, Univ. of TennesseeHong Li, Univ. of DelawareDana Miles, USDA/ARSMichael Buser, Oklahoma State Univ.
  2. 2. • According to the EPA the biggest source of atmosphericNH3 in the U.S. is animal manure, with poultry reportedlycontributing 27% of the total (Battye et al., 1994).• Atmospheric ammonia contamination can lead toenvironmental problems, such as particulate matter lessthan 10 microns, excessive nitrogen loading into theaquatic environment and soil acidification.• The ammonia emission factor for 50 day old broilers isaround 45.5 g NH3/bird (Moore et al., 2011).• Over half of the N excreted by broilers is lost to theatmosphere via ammonia before the litter is removed fromthe barns.Problems caused by ammonia volatilization
  3. 3. 45.5 g NH3/bird total loss or 37.4 g N/birdTypical ammonia losses from broilersIn Arkansas, where 1.1 billion broilers aregrown each year, this would result in annualemissions of 50 million kg of NH3 which has afertilizer value close to $100 million dollars.We need to convert this waste to worth.
  4. 4. 33.5 lbs NH3/day-houseAverage daily ammonia losses during the flock
  5. 5. Fertilizing pastures with N from scrubbers• In some watersheds, growers cannot apply litter becauseof soil test P thresholds and must purchase commercialfertilizer to meet the N needs of their pasture.• If we could develop a scrubber that would trap anaverage of 5 lbs N per day, then the grower wouldrecover 1825 lbs N/unit/year.• Assuming the grower has 2 units on each chicken houseand a total of four houses, then he/she could recover14,600 lbs N/year. This would be almost enough N tosupply 150 lbs N/acre to 100 acres of pasture.• Air and water quality would also greatly benefit.
  6. 6. Wet scrubber for controlling ammonia and dust• Our unit has been conducting research on ammoniascrubbers on and off for about a decade. Currently wehave one patent on these scrubbers (Moore, 2007) and twomore in the pipeline. These scrubbers would work best onhouses that use 2-4 minimum ventilation fans during thecooler months of the year.
  7. 7. • Cheap – The first scrubber we built cost less than $1,000.• Small – The original scrubber had a 5’ x 5’ footprint.• Simple – There was one pump; no heaters or cool cells.Pros of our original scrubber
  8. 8. • Acid use was high. Dust from poultry houses containsmanure, which has a high alkalinity. More than half ofthe acid was wasted neutralizing the dust.• There were large losses of acid and nitrogen via mist.• In extremely cold weather the contents of the reservoirwould freeze.Cons of our original scrubber
  9. 9. Although it had problems, the originalscrubber did make the NRCS webpage!
  10. 10. Our second version consisted of two scrubbers; the first was a water scrubberwhich captured most (>99%) of the total dust. The second was an acid scrubber.However, acid and N losses were still occurring even there were no “leaks”.It was ugly…but it worked!acid scrubber dust scrubber
  11. 11. • Data from this scrubber showed N levels in the reservoirwould build up to a certain point, then decline, eventhough the pH was still low.• When an acid containing sulfate was used in the acidscrubber the concentration of sulfate would slowlydecline throughout the growout, indicating a leak wasoccurring.• However, we could not find a conventional leak. So weconcluded that the losses were occurring as a fine mist.Apparent leaks in the scrubber
  12. 12. • A fine mist may only equal one drop per second.• 1 drop per second = 3 ml/minute• 180 ml/hr• 4,320 ml/day• 224.6 L/growout for 50 day birds• Reservoir volume = 360 L• At that rate 62% of the acid and N is lost.Mist collection is essential
  13. 13. • Exhaust air from broiler houses is warm, however,depending on the growth cycle of the birds any one fanmay not run very often.• Acids and acid/salt mixtures tend to have a lowerfreezing point than water, however they will still freeze.• To avoid this problem heaters were installed in both thedust and acid scrubber.Internal heater is also essential
  14. 14. Objectives:• Re-design the scrubber to improve efficiency.• Conduct full-scale testing at various ventilation ratesunder controlled conditions.• Evaluate the cost, practicality and efficacy of variousacids for scrubbing ammonia.• Build and install scrubbers on poultry farms in AR, DE,PA and VA and measure ammonia, dust and VOCemission reductions.This research was funded by USDA/ARS and by grants from USDA/NRCS andthe National Fish and Wildlife Foundation.
  15. 15. The current version hastwo scrubbers; one fordust and the second forammonia.The shells are made outof fiberglass. Each hasa 360 L reservoir.These scrubbers aremade for minimum ventfans in order to get themost N per dollar spent(Melse et al.,2006).DustscrubberAmmoniascrubber
  16. 16. The dust scrubber can holdup to 8 rows of woodenslats at 45 degree angles.Our design goal was tokeep static pressure below0.3”.If this is exceeded, thenrows of slats can beremoved, as needed.Wood is much cheaper thanplastic or fiberglass.
  17. 17. A simple float switch is used to control the water level.An inexpensive submersible pump is used to recirculate the water.To avoid freezing, a heating element was included in the current design.
  18. 18. The ½ HP pump used in the dustscrubber delivers 22 gal/min.120 volts, 6 amps.Little Giant 6EN-CIA-SFS.
  19. 19. • Acid scrubbers used in Holland and Germany usenozzles to scrub ammonia.• However, if the solution used for scrubbing is beingrecycled, these nozzles will inevitably clog, due to thelarge amount of particulate matter in the exhaust frompoultry houses.• Using nozzles also results in fine droplets, which willenhance the loss of nitrogen as mist.Dutch and German scrubbers use nozzles
  20. 20. To avoid these problemswe chose a simpledelivery system of largeorifices (0.040”) whichresults in a watercurtain.The distances betweenthese holes are 2” nearthe pump, 1.5” in themiddle third and 1” aparton the far side of thepump.
  21. 21. This system can be run for several flocks without clogs. However, if they dooccur, they can be unclogged in less than a minute with a long-handled brush.
  22. 22. The dust scrubber has a screen above the reservoir to catch feathers andvery large particulate matter (including rats, cats, etc.).feathertrap
  23. 23. Acid tolerant heaters are made by Vulcan Industries. They turn on at 38degrees and have 120 degree limit switch.If all of the heaters and pumps are working simultaneously the maximumelectrical use will be 24 amps.
  24. 24. A 1/3 HP magnetically drivenpump is used in the acidscrubber. It’s expensive ($500),but can withstand extremelyacidic conditions, such asconcentrated sulfuric acid.When the pump is not running,the acid drains back into thereservoir, reducing the risk offrozen pipes during winter.It will deliver 14 gal/min and uses3.4 amps.IWAKI MD-100RCT
  25. 25. Plastic cool cell material waswas enclosed in a stainlesssteel frame on the exhaust end.Although this material is aneffective medium for acidscrubbing it also helps with mistcollection.It is on hinges, allowing for easyaccess into the scrubber.Made by GEA(Polypropylene Humipacking)
  26. 26. We have tested variousconfigurations, includingdual cool cells. This setupcan remove >95% of theNH3 at airflows of 5,000 cfmwith 25 ppm NH3. However,we think cleaning and othermaintenance would be verydifficult with this design, sowe are only using one layerof cool cell material.
  27. 27. • The main criteria for ammonia scrubbers set forth byNRCS is the pressure drop should be less than 0.3”.• Initial research was conducted to determine how slat angleaffects static pressure (SP) and air flow.• The goal was to determine the angle that would maximizeparticle collisions with a wet surface while minimizingpressure drop.• We also evaluated how the number and arrangement ofslats, water curtains and cool cells would affect pressuredrop and air flow.Preliminary design studies
  28. 28. FANSunitvariable speedpoultry housefanplenumdustscrubberacidscrubberPreliminary testing of the new scrubber was conducted by attaching a variablespeed fan to the scrubber via a plenum. This fan was capable of airflows up to20,000 cfm. Air flow was measured with a FANS unit. Static pressure wasmeasured with a Setra 2601MS1 differential pressure sensor.
  29. 29. 0 10 20 30 40 50 60 70 80 9000. Angle (degrees)StaticPressure(incheswater)one row of slats in dust scrubber60 Hz40 Hz
  30. 30. 0 10 20 30 40 50 60 70 80 900200040006000800010000120001400016000180002000022000Angle of slat (degrees)Airflow(cfm)60 Hz40 Hzone row of slats in dust scrubber
  31. 31. 0 2 4 6 8 10 12 14 1600. of slats in dust and acid scrubberStaticPressure(incheswater)no cool cell, no water curtainone cool cell, no water curtainone cool cell, one water curtainone cool cell, two water curtainsone cool cell, three water curtainstwo cool cells, three water curtainsfan setting = 40 Hzcurrent configuration
  32. 32. • We evaluated the effects of water, a neutral salt (calciumchloride), five acid salts (alum, aluminum chloride, ferricchloride, ferric sulfate, and sodium bisulfate) and fourstrong acids (sulfuric, hydrochloric, nitric andphosphoric) on ammonia reduction.• Rates of each acid were equivalent to 2 liters ofconcentrated sulfuric acid (up to 19 lbs material for somesalts).• Each acid was tested for three runs that were two hourseach at two fan speeds; (1) 40 Hz – which resulted inairflows of about 5,000 cfm, and (2) 60 Hz – 8,000 cfm.Acid Testing
  33. 33. Anhydrous ammonia was metered intoa distribution system located in front ofthe fan. The amount entering thesystem was varied, as needed, toachieve 25 ppm in the plenum.All personnel involved in this researchwore respirators equipped withammonia cartridges.
  34. 34. During each run airflowwas measured using aFANS Unit.Ammonia was introducedvia a distribution systemdirectly in front of the fan.Ammonia concentrationsentering and leaving thescrubber were measuredevery five minutes duringthe two hour trials usingan Innova 1412.
  35. 35. At 5,000 cfm, air residence time in scrubber = 3 seconds1.5 seconds in the acid scrubber.
  36. 36. Stainless steel starsamplers were usedto sample intake andexhaust air.
  37. 37. Five whatmanFive whatman36 filters were36 filters wereplaced on aplaced on aframe duringframe duringthe initial testingthe initial testingto evaluateto evaluateacid/N loss viaacid/N loss viamist. Mistmist. Mistlosses werelosses weresmall.small.
  38. 38. 0 2 4 6 805101520253035Time (hours)Ammoniaconcentration(ppm)sodium bisulfate (PLT) in acid scrubberIntakeExhaust60 Hz 40 Hz 60 Hz 40 Hz
  39. 39. 0 2 4 6 805101520253035Time (hours)Ammoniaconcentration(ppm)IntakeExhaustWater in acid scrubber40 Hz 60 Hz 40 Hz 60 Hz
  40. 40. • Water is cheap! It can scrub ammonia from air as long asthe pH is below about 8.• If a corn grower was irrigating with acid well water, then itwould be easy to devise a system where fresh water wasconstantly trickled into the dust and “acid” scrubber beforebeing discharged into a pond or reservoir.• If the residence time in the scrubber was equal to an hourof fan time, then the N concentration would increase to 50-100 mg N/L, which would help meet N needs of the crop.• Disadvantage of water alone – amount used would requirea pond, which may require a permit (Reg 5 in AR).Could water scrubbers be the most sustainable?
  41. 41. 0 2 4 6 805001000150020002500Time (hours)Ammoniaconcentrationinacidreservoir(mgN/L)WaterPLTy = 14x + 43R = 0.74y = 278x + 97R = 0.9722
  42. 42. 0 2 4 6 80246810Time (hours)pHWaterPLTNH3 + H+ NH4+
  43. 43. 0 1 2 3 4 5 6 7-505101520Run numberAmountNcapturedbytapwaterindustscrubber(g)
  44. 44. 6 7 8 9 10 11-505101520Initial water pHAmountNcaptured(g)y = -3.8x + 43R = 0.402
  45. 45. water calcium sodium aluminum aluminum ferric ferric020406080100Ammoniareductioninexhaust(%)40 Hz (~5,000 cfm)60 Hz (~8,000 cfm)CAABABCABCDDa abbcdecdeffchloride bisulfate chloride sulfate choridesulfate
  46. 46. water sulfuric hydrochloric nitric phosphoric sodium020406080100Ammoniareductioninexhaust(%)40 Hz (~5,000 cfm)60 Hz (~8,000 cfm)cdede deedefABC ABCCCCDacid acid acid acid bisulfate
  47. 47. -20020406080100120140160NitrogenCaptured(gN/hr)40 Hz (~5,000 cfm)60 Hz (~8,000 cfm)waterffcdabcaabcabEECDABABC ABCAcalcium sodium aluminum aluminum ferric ferricchloride bisulfate chloride sulfate choridesulfate
  48. 48. -20020406080100120140NitrogenCaptured(gN/hr)water40 Hz (~5,000 cfm)60 Hz (~8,000 cfm)ABCDDCDBCDCDEcdedebcdcdfsulfuric hydrochloric nitric phosphoric sodiumacid acid acid acid bisulfate
  49. 49. Scott Becton, one of mytechnicians, has playeda key role in designingand assembling thescrubbers.So far we have built 6of the new scrubbers (4in VA and 2 in AR).This year we will build 5more, which go to farmsin AR, DE, and PA.Carpenter, electrician, mechanic, plumber, and ventilation
  50. 50. Conclusions• The re-designed scrubber does a good job of removingammonia from air, even at high flow rates. The goal ofkeeping pressure drop at less than 0.3” was met.• Acid salts of Al and Fe worked better per mole of H+thanstrong acids or sodium bisulfate (PLT). However, webelieve Al and Fe hydroxides will clog the cool cell.• Due to the inherit danger of strong acids, we have decidedto use PLT in our future research. It is sold as a litteramendment to poultry growers, so it is readily available.It is also relatively easy to dissolve.• Water may be the most sustainable scrubbing solution.However, the volumes needed will require a pond and
  51. 51. Future Plans• Four ammonia scrubbers will be attached to the sidewallfans of a broiler house in Madison County, AR.• We will evaluate the efficacy for reducing ammonia,particulate matter and VOCs.• We will also measure how much PLT, water andelectricity is used by the scrubbers, as well as how muchN is captured. A cost-benefit analysis will be performed.• Data on the efficacy to scrub ammonia will also becollected on farms in DE, PA, and VA.• We will also evaluate water as a scrubbing solution, but itmay only be cost-effective on farms irrigating crops.