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IV. Release and Transport Model

IV. Release and Transport Model

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S. G. SOMMER ET AL.



276



concentration of gaseous NH3 (NH3,G) in equilibrium with liquid NH3

(NH3,L) in the surface liquid layer:

NH3;G

KN

m KH



ẵNHỵ



,

ẵNH

3;L ỵ ẵH

4

ẵNH3;L ẳ



4ị



ẵTAN

1 ỵ ẵHỵ =KN



NH3;G ẳ KH



5ị



ẵTAN

:

1 ỵ ẵHỵ =KN



6ị



Included in the equations is the TAN in the manure surface layers or

soiled areas, the equilibrium between NH3,G in equilibrium with NH3,L is

aVected by Henry’s constant (KH), the equilibrium constant (KN) between



[NHỵ

4 ] and [NH3,L] and livestock slurry surface proton concentration [H ,



pH ẳ log(H )].

The NH3 in solution (NH3,L) is the product of the dissociation of NHỵ

4,

which produces 1 mol of Hỵ for each mole of NH3 [see Eq. (4)]. The

concentration of NH3,L is therefore related to both the concentrations of

[TAN] and [Hỵ] in the solution. Further the concentrations of NH3,G and

NH3,L are aVected by temperature as the equilibrium constants KN and KH

are exponential functions of the temperature of the solution (see Table III).

Therefore, increasing temperature will increase the release of NH3 from the

manure.



A. SOURCES

In livestock housing based on slurry, the sources of NH3 are the soiled

area of the solid floor, slats, side of the slurry store, and the surface of the

slurry stored below the slatted floor (Figs. 2 and 4). The physics and

chemistry of these sources of NH3 may diVer; therefore, we have to split

the housing compartment into NH3 emission elements typical for each

emitting surface (subscript: s ¼ 1 À n). Having characterized the important

elements, these may then be combined as appropriate to calculate NH3

emissions from diVerent housing types. The calculations should take into

account that the period for which a surface may be a source can vary from a

few hours for urine patches to continuous of below slat stored slurry. From

the slurry surface below the slatted floor the resistances may encompass:



Constant

Henry’s constant

Henry’s law constant

KH for ammonia

Henry’s law constant

KH for ammonia

Acid base equilibrium

constant K0 N for

ammoniacal N



Equation

1477:7

T

8621:06

25:6767 InTị ỵ 0:035388 T

InKH ị ẳ 160:559

T



logKH ẳ 1:69 ỵ



logKH ẳ 1:384 103 1:053273Tị

logKN ẳ 0:09018



2729:92

T



Units

No units



Hales and Drewes (1979)

1



Atm. mol liter



Beutier and Renon (1978)



No units



Hashimoto and

Ludington (1971)

Hales and Drewes (1979)



No units



NH3 EMISSION LIVESTOCK HOUSES & MANURE STORES



Table III

The most Used Equilibrium Constants for the Processes of NH3 Transfer from Manure to the Atmosphere in Immediate Contact with Manure



277



278



S. G. SOMMER ET AL.



Figure 4 Conceptual model of NH3 transport processes in animal houses. The emission of

NH3 from the house is given by the sum of emissions from each source in the animal house: (1)

slurry surface, (2) soiled walls of the slurry channel, (3) slats above the slurry channel or store,

and (4) soiled floor.



(i) transport from the surface to slats, (ii) through slats, (iii) from slats to

opening of the house (including ventilation), and (iv) transport through

the openings. Emission from the floor will include transport from the floor

to the opening of the house (including ventilation) and through the openings. Ammonia emission from each source has to be summed to obtain the

emission from the entire house. Emission models for housing with natural

ventilation (e.g., most cattle housing) may be more complex, since the air

exchange rate is dependent on both the thermal buoyancy forces and the

wind pressures on the openings of the building. Although a temperature

diVerence provides a buoyant force that induces ventilation in livestock

buildings, the wind eVects will contribute more to the air exchange as the

wind speed increases. Furthermore, a ventilation opening may act as an inlet

during one period and as an outlet during another period due to variations

in the wind direction.

Ammonia emission from beef feedlots and hardstanding will have one

source element, which is the area enclosed by fences, buildings, or walls

(Fig. 5). The transport taken into account is from the surface to the open

air. For liquid or slurry manure stores the approach will be similar, but

the calculations may in addition have to account for transport through

surface covers and crusts floating on the slurry or through a roof construction. For solid manure stores one may have to account for transport of

air through the manure heap as well as surface process while estimating

NH3 emission.



NH3 EMISSION LIVESTOCK HOUSES & MANURE STORES



279



Figure 5 Transport processes of NH3 emission from (left) stored liquid manure with a

porous surface layer floating on the stored slurry and a roof and (right) a fenced feedlots

(hardstanding).



B. TRANSPORT OF NH3 IN ANIMAL HOUSES

Transport of released NH3 is determined by indoor and outdoor

NH3 concentrations, building ventilation, and NH3 abatement practices.

The approach to transport presented here is based on the following assumptions: (i) the total emitted mass from the sources is transported

into building airspace without any chemical or biological action during

the transport; (ii) the mass diVusion and transfer at the boundary between two layers is in one direction; and (iii) the transport process may be

divided into multilayer subprocesses. Generally, NH3 mass flux per unit

area from surface of a source to building airspace may be described as in

Eq. (1).

Based on the assumptions stated above, the process is divided into n

layers, that is, the atmospheric concentration of ammonia NH3,A is equal

to NH3,n and the ammonia concentration immediately above a contaminant

surface NH3,s is equal to NH3,G in Eq. (1), so we have

FNH3 ẳ K1 NH3;G NH3;1 ị ẳ K2 NH3;1 NH3;2 ị

ẳ ẳ Kn NH3;n1 NH3;n Þ:



ð7Þ



Notice that (i.e., nomenclature used in the transport model is presented in

the abbreviations list)

NH3;G NH3;n ị ẳ NH3;G NH3;1 ị ỵ NH3;1 NH3;2 ị

ỵ ỵNH3;n1 NH3;n ị:



8ị



S. G. SOMMER ET AL.



280



Applying the analogy of the Ohm’s law, combining Eqs. (7) and (8), we

have

1

1

1

1





ỵỵ

ẳ r1 ỵ r2 ỵ ỵ rn

Kt K1 K2

Kn



ð9Þ



and the overall NH3 mass transfer coeYcient given in Eq. (3).

Kt ẳ



1

:

r1 ỵ r2 ỵ ỵ rn



ð10Þ



Transport from the sources in the animal building to the outdoor atmosphere may be simplified as presented in Fig. 4. The four major sources for

NH3 emission considered in the model for a livestock building are: (i)

manure surface, (ii) sidewalls in slurry channels, (iii) surface of the slatted

floor, and (iv) surface of the solid floor. The air volumes in the room space

and in the headspace of a slurry channel are assumed to be fully mixed,

except in the boundary layers near the source surfaces. The locations of

animals in the building are not considered in the model.

An essential issue to consider when characterizing convection transfer is

to determine whether the air motion in the boundary layer is laminar or

turbulent. Surface friction and the convection transfer rates depend strongly

on which of those conditions exists (Incropera and DeWitt, 1990). In a

laminar boundary layer, air motion is highly ordered and it is possible to

identify airflow dynamics. In contrast, air motion in a turbulent boundary

layer is highly irregular and is characterized by velocity fluctuations. These

fluctuations enhance the transfer momentum, energy, and surface friction as

well as mass convection transfer rate.

In a slurry channel, the NH3 emission flux from manure surface may be

described as

Fsl;s ẳ DShsl;s NH3;G NH3;sl;a ị=lsl;s ¼ Ksl;s ðNH3;G À NH3;sl;a Þ

1

ðNH3;G À NH3;sl;a Þ;

¼

rsl;s



ð11Þ



where rsl;s ¼ lsl;s DÀ1 ShÀ1

sl;s is the resistance in the boundary layer over the

emission surface (m sÀ1); D, is the NH3 diVusion coeYcient in air (m2 sÀ1);

NH3,sl,s and NH3,sl,a are NH3 concentrations at the slurry surface and in the

headspace of the slurry channel, respectively. The diVusion coeYcient of

NH3 in air may be calculated by an empirical relation developed by Fuller

et al. (1966),



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