Lingjuan Wang

Modeling Ammonia Emissions from Broiler Litter at Laboratory Scale

The objectives of this study were to develop a mechanistic emission model to estimate ammonia flux from broiler litter and to evaluate the model at laboratory scale. In the proposed model, the ammonia flux is essentially a function of the litters total ammoniacal nitrogen (TAN) content, moisture content, pH, and temperature, as well as the Freundlich partition coefficient (Kf), mass transfer coefficient (KG), ventilation rate (Q), and emission surface area (A). The Freundlich partition coefficient (Kf) was used as a fitting parameter in the model. A dynamic flow-through chamber system and a wind tunnel were designed to measure ammonia fluxes from broiler litter. The dynamic flow-through chamber experiments evaluated the proposed model with various litter samples under a constant temperature and wind profile. The wind tunnel experiments evaluated the proposed model under various temperatures and wind profiles. Model parameters such as Kf and KG were estimated. The results from the two experiments were consistent with each other. The estimated KG ranged from 1.11 to 27.64 m h-1, and the estimated Kf ranged from 0.56 to 4.48 L kg-1. A regression sub-model was developed to estimate Kf as function of litter pH and temperature, which indicated that Kf increased with increasing litter pH and decreased with increasing temperature. The proposed model was used to estimate the equilibrium gas phase ammonia concentration (Cg,0) in litter, and the model-predicted values were compared with the observed values. The normalized mean error (NME), the normalized mean square error (NMSE), and fractional bias (FB) were calculated to be 25%, 12%, and -0.3%, respectively, for all 94 measurements, and the model was able to reproduce 80% of the variability of the data. Sensitivity analysis of the model showed that ammonia flux is very sensitive to litter pH and to a lesser extent temperature. The relative sensitivity of pH or temperature increases as the pH or temperature increases.

A THEORETICAL APPROACH FOR PREDICTING NUMBER OF TURNS AND CYCLONE PRESSURE DROP

A new theoretical method for computing travel distance, number of turns, and cyclone pressure drop has been developed and is presented in this article. The flow pattern and cyclone dimensions determine the travel distance in a cyclone. The effective number of turns was calculated based on the travel distance. Cyclone pressure drop is composed of five pressure loss components. The frictional pressure loss is the primary pressure loss in a cyclone. This new theoretical analysis of cyclone pressure drop for 1D2D, 2D2D, and 1D3D cyclones was tested against measured data at different inlet velocities and gave excellent agreement. The results show that cyclone pressure drop varies with the inlet velocity, but not with cyclone diameter.

A Review of Emission Models of Ammonia Released from Broiler Houses

Over the last ten years, animal feeding operations (AFOs) have expanded greatly. As a component of animal waste, immeasurable ammonia is released. In both Europe and the United States, the largest source of ammonia emissions is animal production. With increasingly stringent federal and state air pollution regulations and the emerging pressure to regulate agricultural enterprises, ammonia emissions from animal production have become an increasing concern to regulators, producers, and environmental groups in the United States. However, efforts to regulate these emissions have been confounded by a lack of information. One of the technical challenges is the need for modeling the process of ammonia emissions from animal feeding operations. Broiler houses are one aspect of agriculture that is of particular interest to regulators and environmental groups. In recent publications, various models have been proposed to estimate ammonia emissions from broiler houses. These models are diversified in their structures and applications. It appears that a comprehensive review of theses available models would be of benefit to research in this field. This paper summarizes the scientific basis of ammonia emissions from broiler litter and the major factors that may influence ammonia emissions. The theoretical principles and the structures of the models are generalized. These models improved understanding of the physical and chemical processes of ammonia release, and can be useful to improve the accuracy and simplicity in estimating ammonia emissions from broiler houses. The current technical challenges and future direction of developments are discussed.

Farm-Scale Evaluation of Ozonation for Mitigating Ammonia Concentrations in Broiler Houses

Abstract This study evaluated the effectiveness of in-house ozonation within the public health standard limit (0.1 parts per million [ppm]) for mitigating ammonia (NH3) concentrations inside commercial broiler houses. The project was conducted in four identical tunnel-ventilated houses. Two houses served as treatment and the other two served as control units. The experiment was replicated in five consecutive flocks. Except for ozonation treatment, all other operational parameters including feed, broiler strain, age and number of broilers, and ventilation system were the same among four houses. NH3 and carbon dioxide (CO2) concentrations in the treatment and control houses were measured for a minimum of 48 hr/week throughout the five flocks of 8 or 9 weeks each. The gas measurements were conducted using portable multigas units (PMUs). House temperatures were recorded with data loggers in each flock. Comparison of temperatures and CO2 concentrations among houses indicated no significant differences in ventilation rates among treatment and control houses in any of the five flocks. As a result, comparisons of NH3 concentrations inside houses were used to evaluate the effectiveness of house ozonation for NH3 emission mitigation. Statistical test of mean NH3 concentrations for each flock separated by house indicated that the house-to-house variation was significantly smaller than the flock-to-flock variation. There was a substantial variation in NH3 concentrations across different flocks, but no house had consistently higher or lower mean NH3 concentrations than any other. Evaluations for differences in mean NH3 from week to week, between treatment groups, and differences in week-to-week variations between treatment groups suggested that ozone effect was not uniform for each week and the effect was not statistically significant for any week. Tests of overall ozone treatment effect and treatment-week interaction indicated there was no difference in mean NH3 between the control and ozone treatment groups (P = 0.25), nor was the week effect different for control and treatment groups (P = 0.46). The results of this field evaluation indicate that there was no statistical evidence to suggest that the ozone treatment has any effect on average NH3 concentrations in these chicken houses.

EFFECT OF AIR DENSITY ON CYCLONE PERFORMANCE AND SYSTEM DESIGN

1D3D and 2D2D cyclones were tested at Amarillo, Texas, to evaluate the effect of air density on cyclone performance. Both airflow rate and cyclone inlet velocity change with the change in air density. Two sets of inlet design velocities determined by the different air densities were used for the tests: one set based on the actual airflow, and the other set based on standard airflow. Experimental results indicate that optimal cyclone design velocities, which are 16 m/s (3200 ft/min) of standard air for 1D3D cyclones and 15 m/s (3000 ft/min) of standard air for 2D2D cyclones, should be determined based on standard air density. It is important to consider the air density effect on cyclone performance in the design of cyclone abatement systems. The proposed design velocities should be the basis for sizing cyclones and determining the cyclone pressure drop. The recommended sizes for 1D3D, 2D2D, and 1D2D cyclones are reported in this article.

CORRECTING PM10 OVER-SAMPLING PROBLEMS FOR AGRICULTURAL PARTICULATE MATTER EMISSIONS: PRELIMINARY STUDY

The Federal Reference Method (FRM) ambient PM10 sampler does not always measure the true PM10 concentration. There are inherent sampling errors associated with the PM10 samplers due to the interaction of particle size distribution (PSD) and sampler performance characteristics. These sampling errors, which are the relative differences between theoretical estimation of the sampler concentration and the true concentration, should be corrected for equal regulation between industries. An alternative method to determine true PM10 concentration is to use the total suspended particulate (TSP) concentration and PM10 fraction of the PSD in question. This article reports a new theoretical method to correct PM10 sampling errors for a true PM10/TSP ratio. The new method uses co-located PM10/TSP samplers’ measurements to derive the mass median diameter (MMD) of PSD and true PM10/TSP ratio. Correction equations and charts have been developed for the PMs with GSDs of 1.2, 1.3, ..., 2.1, respectively, and the PM10 sampler with a cutpoint of 10 .m and slope of 1.5. These equations and charts can be used to obtain a corrected PM10/TSP ratio for the given GSD and sampler characteristics. The corrected PM10/TSP ratio will be treated as the true PM10/TSP ratio for PM10 concentration calculations. This theoretical process to obtain a corrected PM10/TSP ratio will minimize the inherent PM10 sampler errors and will provide more accurate PM10 measurement for the given conditions.

PERFORMANCE CHARACTERISTICS OF A LOW-VOLUME PM10 SAMPLER

Four identical PM10 pre-separators, along with four identical low-volume (1 m3 h-1) total suspended particulate (TSP) samplers were tested side-by-side in a controlled laboratory particulate matter (PM) chamber. The four PM10 and four TSP samplers were also tested in an oil pipe cleaning field to evaluate the PM10 samplers’ performance characteristics. The PMs used in the chamber tests had mass median diameters (MMDs) larger than 10 .m, whereas the PM emitted from the oil pipe cleaning system for the field tests had MMD smaller than 10 .m. The co-located TSP and PM10 sampler testing results indicate that PM10 samplers over-sample when exposed to ambient PM having MMD larger than 10 .m aerodynamic equivalent diameter (AED) and under-sample when exposed to ambient PM with MMD smaller than 10 .m. The over-sampling and under-sampling rates varied with the change of MMD and the PM loading (TSP concentration). The cutpoints and slopes of the PM10 pre-separator changed with the change of MMD of inlet PM.

Particle Size Distribution of Particulate Matter Emitted from a Layer Operation in Southeast U.S.

This paper reports a field study on characterizing particle size distribution (PSD) of particulate matter (PM) emitted from a commercial layer operation in Southeast U.S. across three seasons from October of 2008 to April of 2009. Six low-volume (1m3/hr) total suspended particulate (TSP) samplers were used to collect PM samples in two high-rise layer houses. Laser diffraction particle size analyzer (LS13 320) was applied to measure PSD of PM samples collected by the TSP samplers. Results of the study indicate that TSP concentrations across the three seasons ranged from 888 to 5333 µg/m3. TSP concentration was affected by season, animal activity, floor and equivalent air flow rate factor. It was observed that TSP concentration in winter was higher than that in spring; concentration on the second floor was higher than that on the first floor; the more active the animals were, the higher the TSP concentration; the more the fans on, the lower the concentration. Compared with PM concentration, PSD (characterized by the mass medium diameter, MMD, & geometric standard deviation, GSD) was much less affected by season, animal activity, floor and equivalent flow rate factor. The MMD was affected by floor and equivalent flow rate factor, but the degree of affection was within the range of one standard deviation. Overall MMDs of PM samples collected in fall, winter and spring were 15.80±1.05µm, 17.13±0.81µm and 18.44±1.44µm, respectively. The difference of MMD among three seasons was within the range of one standard deviation. GSD was relatively constant and not affected by those factors. The overall GSD was 2.65±0.08.

Analysis of Cyclone Collection Efficiency

Particle motion in the cyclone outer vortex was analyzed in this paper to establish the force balance differential equation. The Barth’s “static particle” theory combined with the force balance equation was applied in the theoretical analyses for the models of cyclone cut-point and collection probability distribution in the cyclone outer vortex. Cyclone cut-points for different dusts were traced from measured cyclone overall collection efficiencies and the theoretical model for calculating cyclone overall efficiency. The traced cutpoints indicate that Barth’s d50 model needs to be corrected for particle size distribution (PSD). The cut-point correction factors (K) for 1D3D and 2D2D cyclones were developed through regression fit from traced cutpoints The regression results also indicate that cut-points are more sensitive to mass median diameter (MMD) of PSD than to geometric standard deviation (GSD) of PSD. The theoretical overall efficiency model developed in this research can be used for cyclone total efficiency calculation with the corrected d50 and PSD.

Effect of ozonation on particulate matter in broiler houses.

The effects of ozonation on particulate matter were studied on a commercial broiler farm. The farm consisted of 4 identical tunnel-ventilated houses (12.8×152.4 m): 2 houses were treated with O3 (maximum concentration 0.1 ppm) and the other 2 served as control units. The particle size distributions of total suspended particulate (TSP) samples from both control and treated houses were found to have very similar profiles with no statistical difference. The TSP concentrations were significantly higher in treated houses as compared with those in control houses, and the mean of the differences was 5.50 mg/m3. In both treated and control houses, there were substantial vertical TSP concentration gradients and the concentrations decreased with height. At broiler chicken height (0.28 m), TSP concentrations were 13±3 mg/m3 in control houses and 17±2 mg/m3 in treated houses. At human breathing height (1.55 m), TSP concentrations were 8±4 mg/m3 in control houses and 7±2 mg/m3 in treated houses. Particle phase NH4+ concentrations were higher in treated houses (ranging from 0.59 to 42.01 mg/m3 with mean=17.49 mg/m3) than in control houses (ranging from 0.34 to 13.55 mg/m3 with mean=4.42 mg/m3). The TSP samples from locations in the vicinity of the farm showed higher concentrations downwind than that upwind, but there were no significant differences observed among different ambient locations for TSP NH4+ concentrations. The results from this study did not show that direct application of ozonation technique has beneficial effects for particulate matter control in broiler houses.