Peter Kai

CFD Investigation of a Partly Pit Ventilation System as Method to Reduce Ammonia Emission from Pig Production Units

The objective of this work was to investigate the efficiency of a partly pit ventilation system with cleaning of the air exhausted from the pit. The analysis, including Computational Fluid Dynamics (CFD) methods, showed that evacuating and cleaning of 10% of the total ventilation capacity from a pit may reduce the ammonia emission of the system by 73%, and the ammonia concentration in the room was significantly reduced. In a similar production system without pit ventilation cleaning of 10% of the ventilation capacity reduced the ammonia emission by 41% compared to no cleaning. A drawback of the pit ventilation system is that it increases the ammonia release from the slurry surface by 26% and, consequently, may increase the operating cost of a cleaning system in order to remove this extra ammonia.

Modeling Ammonia Mass Transfer Process from a Model Pig House Based on Ventilation Characteristics

Airflow characteristics above the emission surface inside animal houses play an important role in gaseous and odor emissions. The influence of airflow characteristics, i.e., air velocities and turbulence intensities, on ammonia mass transfer processes were investigated in a model of a finishing pig house. The 1:6 scale model was 1750 × 1000 × 605 mm (L × W × H) and had two sidewall inlets and an exhaust opening in the middle of the ceiling. Different airflow characteristics were generated by using three ventilation control strategies: constant inlet opening area, constant inlet velocity, and constant inlet momentum. Due to the symmetrical nature of the airflow pattern in the scale model, the investigation was conducted in left half of the model. Nonlinear modeling simulated the ammonia mass transfer coefficient (AMTC) as a function of airflow characteristics and jet momentum number. Changes in ventilation control strategies, given the variation of floor air characteristics, changed the ammonia emissions and AMTC. The mean floor air velocities and the root mean square of the floor air velocity fluctuations were correlated to the jet momentum number to the power of 0.56 and 0.54, respectively. AMTC increased proportionally to floor air velocity and turbulence intensity. The AMTC values determined in this experiment were compared to a published study using a 1:12.5 scale model. The correlation of AMTC and jet momentum number for the two models was similar. The relationships obtained in this study could be helpful in understanding the airflow characteristics in the floor region and simulating emission rates from pig houses, while the dependence of AMTC on jet momentum number was confirmed for two different scale models. There is a need to validate it in full-scale houses since the presence of pigs, slatted floors, and porous partitions could alter the relationship of jet momentum number with AMTC.

Reducing Odor Emission from Pig Production Buildings by Ventilation Control

Odor emissions from pig buildings have been the topic for many research projects. However, the fact that the odor emission is dependent on air as transportation medium is far less investigated. Therefore, more comprehensive investigations on the effects of odor release of airflow patterns and ventilation airflow rates are needed. The objective of this project was to study the feasibility of reducing ammonia and odor emission by choosing ventilation control strategies. At present, the ventilation capacity of a pig production building is based on an absolute maximum ventilation rate, which is determined according to the largest body weight of the animals during the production cycle. However, in modern batch production systems, the maximum ventilation rate is only required when the animals reach end weight and the outdoor temperature exceeds a certain level. In this study, a ventilation control strategy using a restricted maximum ventilation rate according to the pigs’ actual weight in the building was investigated. According to computer simulations, limiting the maximum ventilation rate to the actual body weight is feasible in practical application to reduce odor emission. That is in agreement with a primary investigation performed in field measurements by Danish Pig Production. In addition, the studies on the correlation between emission and airflow characteristics have shown that by choosing a proper ventilation control strategy, emission can be also reduced. The investigations were performed in scale model experiments and CFD (Computational Fluid Dynamics) simulations. Strategies such as constant inlet opening, constant inlet velocity, and constant inlet momentum were studied. The proposed control strategy suggests that the ventilation rates in a pig production building should be controlled to maintain a low inlet air momentum to reduce emission.