Development of dynamic computational model for an integrated farming system

Integrated Farming Systems;Dynamic System Model;Swine Production;Anaerobic Digestion;Energy Requirement;Nitrogen Requirement

Yang, Shang-Jen ; Wang ; Xinlei

关键词: Integrated Farming Systems;    Dynamic System Model;    Swine Production;    Anaerobic Digestion;    Energy Requirement;    Nitrogen Requirement;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/73008/Shang-Jen_Yang.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The use of fossil fuels on farming systems is now widely recognized as unsustainable because of diminishing supplies and the contribution of these fuels to the increasing carbon dioxide concentration in the environment. Moreover, farming systems with higher nutrient usage efficiency are important to meet increasing human food demand. Integrated Farming Systems (IFS) that utilize wastes from one subsystem as sources for another subsystem represent a promising way for producing renewable energy and for recycling nutrients. The benefits of IFS are recognized; however, the dynamic properties of the system are not well understood. Previous models have taken static approaches which do not address the dynamic energy/nutrient relationships between subsystems. The current study, instead, focuses on a new approach that proposes the development of a dynamic model for IFS and applies that model to several computer simulations based on different scenarios.This dynamic system model for IFS integrates swine production, swine barn energy requirements, anaerobic digestion (AD) processes, anaerobic digester heat requirements, combined heat and power (CHP) production, and nitrogen requirements for crop production. In this system, swine manure is collected during swine production and is taken as feedstock to the AD system to produce bio-methane. Bio-methane is then fed into the CHP unit for heat and power production. Nutrients from the AD system effluent can subsequently be fed to the cropping system to recycle nutrients for crop growth. Heat/power production by the CHP unit provides energy to maintain operations for swine facilities and digesters. A series of virtual simulations for different scenarios were applied to the proposed model to show different energy usage portfolios.iiiPig growth performance is affected by operation strategies that include the use and non-use of cooling systems during the summer as well as weather conditions specific to various locations. Therefore, the current study employed simulations to compare gilt production in two locations - Springfield, IL and Oklahoma City, OK - under 2010 weather conditions. The results demonstrated that in summer in Springfield higher temperatures without cooling pads increased the feed-to-gain ratio significantly to 3.19 from 2.93 compared to the ratio with cooling pads. The current study also found that in summer in Oklahoma City due to higher heat stress conditions even with cooling pads, gilts had a higher feed-to-gain ratio (3.34) compared to conditions of lower heat stress in Springfield, IL (2.93). On the other hand, in winter in both Oklahoma City and Springfield due to the maintenance of comfortable indoor temperatures for pig growth, swine had similar feed-to-gain ratios.The anaerobic digestion simulation under 2010 weather conditions showed that in winter in Springfield the digester had higher heat requirements compared to the digester in winter in Oklahoma City; however, in summer in both locations the heat requirements for the digester were similar. With all digesters being maintained in mesophilic condition at 35°C, the biogas production portfolios for the digesters in both cities were similar.Simulations were also conducted of the total energy/nutrient production and consumption portfolios between operation strategies in summer and winter in both locations. As the swine facility in Springfield was found to need more heat in winter, this study proposes the use of only one CHP unit to provide sufficient power and to utilize extra biogas as fuel for heaters to support the swine facility heat requirements. On the other hand, because the heat requirements for the swine facility in Oklahoma City in winter were found to be lower, this study proposes two CHP units to produce more power and to generate sufficient heat to support swine production in that location.ivThe simulations, based on different scenarios as applied to the proposed dynamic IFS model, demonstrate how engineering design and operation strategies affect dynamic system properties. The simulations further show the feasibility for future research in the use of the proposed dynamic IFS model to examine new technologies and operation strategies.