Specifically, the research team designed, built, and evaluated a proof-of-concept unit that incorporates a biofilter and a heat exchanger to reduce ammonia emissions from livestock barns, while also tempering – or heating up – the fresh air that is pumped into the barns.
The pollution removal component utilizes a biofiltration mechanism, in which polluted air is passed through an organic medium, such as compost or wood chips, that contains bacteria. Those bacteria interact with the pollutants and break them down into harmless or less harmful constituents. Biofiltration also allows recycling of nitrogen because when the “spent” medium is applied on cropland, the nitrogen becomes available to the crops. However, biofiltration also introduces additional costs for animal agriculture operations. The researchers hope to defray those costs by reducing an operation’s energy consumption.
Here’s how their prototype works: warm, polluted air from the livestock facility enters the biofilter, and some of the heat is transferred to the heat exchanger. When fresh air from outside is pumped into the building, it passes over the heat exchanger, warming it up.
The prototype not only helps recover heat from the facility, it also produces its own heat. This heat is generated within the biofilter when heat-producing biochemical reactions occur – for example, when the ammonia is converted into nitrate by bacteria. The heat from the biofilter is also routed to the heat exchanger.
Maintaining the appropriately high temperature is important for chicken and swine operations, because it is essential for rearing chicks and piglets to maturity.
“The technology is best suited for use when an operation wants to vent a facility that has high ammonia concentrations, and pump in cleaner air in preparation for a fresh batch of chicks or piglets – particularly in cold weather. It is also suitable for use when supplemental heat is required for raising the young animals,” says Dr. Sanjay Shah, an associate professor of biological and agricultural engineering at NC State and lead author of a paper describing the research. For this to be feasible, it would be necessary to replace a couple of the conventional cold weather ventilation fans with higher-pressure fans. Shah explains that the technology is not compatible with summer ventilation using tunnel-fans, because of the high cost and choking effect on the fans.
Shah says the researchers focused on ammonia removal because: it is released from chicken and swine houses in large quantities; it contributes to nutrient loading problems such as hypoxia; it is an indirect contributor to greenhouse gases (GHGs) because it can break down in to the potent GHG nitrous oxide in the ground; and because it is a precursor to very fine particulate matter, which contributes to haze and public health problems, such as asthma.
Researchers showed that their design is effective under real-world conditions, operating their prototype in a 5,000-bird chicken house. The prototype removed up to 79 percent of ammonia and reduced the energy needed to maintain the necessary temperature in the facility – recovering as much as 8.3 kilowatts of heat.
“We plan to continue working to improve the system design in order to make it even more efficient,” Shah says.
The paper, “Coupled Biofilter – Heat Exchanger Prototype for a Broiler House,” is published in the December issue of Applied Engineering in Agriculture. The paper was co-authored by David Workman, Jarred Yates, Tom Basden, and Chestina Merriner of West Virginia University, and Dr. June DeGraft-Hanson of the University of Maryland. The research was funded by the Energy Efficiency Program of the West Virginia Development Office.
NC State’s Department of Biological and Agricultural Engineering is a joint department under the university’s College of Engineering and College of Agriculture and Life Sciences.
Note to Editors: The study abstract follows.
“Coupled Biofilter – Heat Exchanger Prototype for a Broiler House”
Authors: S. B. Shah, North Carolina State University; D. J. Workman, J. Yates, T. J. Basden, C. T. Merriner, J. deGraft-Hanson, West Virginia University
Published: December, 2011, Applied Engineering in Agriculture
Abstract: Biofiltration is effective in reducing air emissions from livestock barns but it increases the production cost. Coupling a biofilter with a heat exchanger may allow waste heat recovery to temper the fresh air going back into the livestock barn when supplemental heating is required. A proof-of-concept coupled biofilter – heat exchanger was evaluated for its ability to reduce ammonia emissions and recover heat in a 5,000-bird broiler house in Wardensville, WV. The heat exchanger plenum was stacked on top of the biofilter with a corrugated aluminum sheet serving as the heat transfer surface. The biofilter was effective in treating very high inlet ammonia concentrations (>96 ppm) with removal efficiencies >79% for empty bed residence times ranging from 4.3 to 29.1 s. Accumulation of sulfur in the medium showed that the biofilter may have been effective in trapping some sulfurous gases emitted from the broiler house. Based on 13.5 h of monitoring, the heat exchanger had heat recoveries of 2.3 to 8.3 kW and overall heat transfer coefficients of 7.37 to 35.30 W m-2 K-1. The heat exchanger’s performance was comparable to two commercially-available heat exchangers evaluated in published studies in livestock barns. The biofilter – heat exchanger system can improve air quality and reduce energy use in livestock production where supplemental heating is required but additional design improvements and testing are required for commercial application.