flow-through chamber system Zifei Liu, Lingjuan Wang, David B. - PowerPoint PPT Presentation

Modeling ammonia emissions from broiler litter with a dynamic flow-through chamber system Zifei Liu, Lingjuan Wang, David B. Beasley Department of Biological and Agricultural Engineering

Ammonia emissions from broiler houses Ammonia emissions: the primary concern for Ammonia in broiler house: regulatory reporting affect bird performance under CERCLA NH 3 NH 3 Broiler litter

Estimation of emission rates • Seasonal conditions • Regional conditions • House design • Management practices • Litter properties … Wide variations have been found!

Scientific basis of ammonia emissions from broiler litter Free air stream C g, ∞ Convection mass transfer NH 3 (g) C g, 0 Partitioning between aqueous and gaseous phase ammonia, K d Chemistry of ammonia + NH 3 (aq) + H + NH 4 in aqueous solution Biomass Ammonia generation Partitioning between solid and aqueous phase + (adsorbed) NH 4 ammonia Moisture Litter solid layer

Factors that may influence ammonia emissions from broiler litter • Air and litter temperature • Ventilation rate • Air velocity • Litter pH • Litter nitrogen content • Litter moisture content • …

Emission models 1. To calculate site-specific emissions, using the local design and operating parameters; 2. To quantify and evaluate the effectiveness of the various control strategies; 3. To simulate seasonal and geographic variations in ammonia emission factors.

Research objective • To develop a mathematical emission model so that ammonia emissions can be predicted under given conditions; • To evaluate the effects of various influencing factors on ammonia emissions from broiler litter.

The dynamic flow-through chamber system Motor Vent Ambient air Flow controller Impeller Pump NH 3 free air Carbon filter TEI NH 3 Flux Chamber NH 3 analyzer Litter Data logger Data logger ECH2O moisture sensor

Operating conditions • The ventilation rates of the chamber: 10.0 to 74.0L/min • Residence time : 40 to 300 seconds • Air velocity at the litter surface: 0.10 to 0.99 m/s • Room temperature: 22 o C

Litter samples and ammonia measurements • Litter samples at various ages were taken from three commercial broiler farms in North Carolina. • For each test, 3000 gram litter samples with a depth of about 5 cm. • The ammonia analyzer + HOBO data logger record ammonia concentrations at one-minute intervals. • The ammonia concentration in chamber at steady-state once the variation in concentration < 0.5 ppm in ten minutes.

Properties of the tested litter samples Variable N Mean Min. Max. TKN (μg/g) 73 41109 30844 67298 TAN (μg/g) 73 3553 636 11172 pH 73 8.11 6.20 9.08 Moisture content (w/w %) 73 32.94 13.39 101.41 Total carbon content (%) 73 37.44 27.95 46.20 Total nitrogen content (%) 73 4.04 2.56 6.85

Model structure General mass transfer flux equation Mass balance equation J = K m (C g, 0 - C g, chamber ) J = (Q/A) C g, chamber J = ((Q/A) -1 + K m -1 ) -1 C g, 0 J = K e * C g, 0

Model structure J = ((Q/A) -1 + K m -1 ) -1 C g, 0 • K m : Determination of K m is largely empirical. It was usually calculated as a function of air velocity and temperature. • C g, 0 : Dependent on the equilibrium between gas phase ammonia and the NH 3 -N content in litter.

Estimate the mass transfer coefficient K m • The general mass transfer flux equation J = K m (C g, 0 - C g, chamber ) C g, chamber = C g, 0 - (1/K m ) J • Linear regression of C g, chamber vs. J -1/K m

Estimate the mass transfer coefficient K m • Three series of tests were conducted on three litter samples. • The K m was estimated to have an average value of 8.59 m/h. • K m : 0.36m/h to 8.28m/h - finishing pig house (Ni, 1999) • K m : 15.5m/h to 42.1m/h - soil following manure spreading (Svensson and Ferm, 1993)

Ammonia fluxes from litter vs. NH 3 -N content in litter 1200 Ammonia emission fluxes (mgN m -2 h -1 ) 1000 800 600 400 200 0 0 200 400 600 800 1000 NH 3 -N content in litter (μg/g)

The equilibrium concentration of gas phase ammonia at litter surface C g,o • C g, 0 : estimated from the measured C g, chamber , Q and the estimated K m . • The following nonlinear model was established. C g, 0 = 7.674 + 0.323* [NH 3 -N] - 0.0002 * [NH 3 -N] 2 C g, 0 has unit of mgN/m 3 . [NH 3 - N] has unit of (μg/g) on a dry basis. • The R-square of the model : 0.9272 (N=32).

The partitioning ratios of C g,o over NH 3 -N content in litter • In the range of 0.14 to 0.69 (mgN m -3 ) / (μg g -1 ). 0.8 0.7 Ratio of C g, 0 /[NH 3 -N] 0.6 -1 ) -3 / μg g 0.5 0.4 (mgN m 0.3 0.2 0.1 0.0 0 200 400 600 800 1000 NH 3 -N content in litter (μg/g)

The NH 3 -N contents in litter • Taking pH, moisture content, carbon content and TKN content as independent variables, and the TAN content as dependent variable. • [TAN] = 9133.8 - 1405.0*pH - 3.5683*10 7 *[MC] 0.5 / [TKN] + 2822.7*[MC] 0.5 - 104.05*[MC] - 1.1133*[C] 2 • [NH 3 -N]/[TAN] = K d / (10 -pH +K d ) • Log K d = - 0.0918 - 2729.92/T (Kamin et al., 1979); At 22 o C, K d = 10 -9.3.

Summary of Model J = K e * C g, 0 C g, 0 ~ Function of [NH 3 -N] K e = ((Q/A) -1 + K m -1 ) -1 [NH 3 -N] ~ Function of [TKN], pH, [MC], [C] and K d

Sensitivity Analysis • Relative sensitivity is defined as: S r = (∆J/J) / (∆x/x) In which, – S r is relative sensitivity, %; – ∆J is change of ammonia emission flux, mgN h -1 m -2 ; – J is mean ammonia emission flux, mgN h -1 m -2 ; – ∆x is change of the input variable over the range being considered; – x is mean value of the input variable.

Sensitivity Analysis TKN content pH Moisture content Range (μg/g) S r Range S r Range (%) S r 34000-36000 1.45 7.2-7.4 8.85 15-20 0.69 40000-42000 0.96 7.8-8.0 11.34 30-35 0.42 46000-48000 0.71 8.4-8.6 8.79 45-50 0.28 Total carbon content K m Q Range Range (%) S r Range (m/h) S r S r (L/min) 30-32 -0.36 4-6 0.99 10-20 0.08 36-38 -0.58 8-10 0.97 30-40 0.03 42-44 -0.91 12-14 0.96 50-60 0.02

Relative magnitude of Q/A and K m J = ((Q/A) -1 + K m -1 ) -1 C g, 0 Controlling Example Emissions factor condition C g, chamber ≈ 0 When Q/A >> K m K e ≈ K m Open field J ≈ K m *C g, 0 C g, chamber ≈ C g, 0 When Q/A << K m K e ≈ Q/A Closed chamber J ≈ Q/A*C g, 0

Conclusions • A statistical model was developed to estimate ammonia emission flux from broiler litter based on experimental results from a dynamic flow-through chamber system. • The model inputs: the litter TKN content, litter pH value, litter moisture content, litter carbon content, the mass transfer coefficient K m and ventilation rate Q.

Conclusions • Under the designed operating condition, the mass transfer coefficient Km: an average value of 8.59 m/h. • The model results: ammonia emission flux increased with litter increasing TKN content, pH, litter moisture content, mass transfer coefficient and ventilation rate, and decreased with increasing litter carbon content. • The model was most sensitive to litter pH value than to other input variables.