Location: Dairy and Functional Foods ResearchTitle: Computer simulation of energy use, greenhouse gas emissions and process economics of the fluid milk process Author
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2013
Publication Date: 5/1/2013
Publication URL: http://handle.nal.usda.gov/10113/60320
Citation: Tomasula, P.M., Yee, W.C., Mcaloon, A.J., Nutter, D.W., Bonnaillie, L. 2013. Computer simulation of energy use, greenhouse gas emissions and process economics of the fluid milk process. Journal of Dairy Science. 96:3350-3368. Available: http://dx.doi.org/10.3168/jds.2012-6215 Interpretive Summary: Greenhouse gas (GHG) emissions from fluid milk production may have significant environmental impact, with the majority of GHGs produced by methane emissions by cows and manure. Off-farm activities, such as milk processing, packaging and refrigeration, contribute to the remaining GHG emissions in the form of energy-related carbon dioxide (CO2) emissions. Significant reductions in energy use would lower CO2 emissions and the costs associated with off-farm processes. However, processors need to know where the energy hotspots in their plants are located and if costly upgrades will significantly lower CO2 emissions. In this study, a computer model for the fluid milk process was created with input from the dairy industry. The model allows milk processors a way to test various changes in their plants to lower GHG emissions, as well as to instantly calculate the energy cost savings and their equipment costs to implement the changes. The ARS computer model will help the dairy industry realize its goal of reducing CO2 emissions by 25% per gallon of milk by the year 2020.
Technical Abstract: On-farm activities associated with fluid milk production contribute approximately 70% of total greenhouse gas (GHG) emissions while off-farm activities arising from milk processing, packaging, and refrigeration, contribute the remainder in the form of energy-related carbon dioxide (CO2) emissions. While several energy-savings measures have been implemented in fluid milk plants, process-specific measures are needed to lower energy use and CO2 emissions. In this study, using information provided by the dairy industry and equipment vendors, a customizable model of the fluid milk process was developed based on the SuperPro Designer software to benchmark the electrical and fuel energy consumption, CO2 emissions, and costs of current processes and, to test the feasibility of new processing concepts to lower energy and CO2 emissions with calculation of new capital and operating costs. The accuracy of the model in predicting total energy usage of the entire fluid milk process and the pasteurization step was validated using available literature and industry energy data. Computer simulation of small (47.6 million L/yr), medium (113.6 million L/yr) and large (227.1 million L/yr) processing plants predicted the carbon footprint of milk, defined as g CO2 equivalents/kg packaged milk, within 6% of the value (96 g CO2 equivalents/kg packaged milk) obtained in an industry conducted life cycle assessment and also showed, in agreement with the same study, that plant size had no impact on the carbon footprint of milk but that larger plants were more cost effective in producing milk. Sensitivity analysis performed on the pasteurization step showed that increasing the % regeneration of the pasteurizer would lower its energy usage by over 50% and that implementation of partial homogenization would lower energy usage of the process by 4%. It was also demonstrated that implementation of steps to lower non-process related electrical energy in the plant would be more effective in lowering energy use and CO2 emissions than fuel- related energy reductions. The model also predicts process-related water usage but this portion of the model was not validated due to a lack of data. The simulator model can serve as a benchmarking framework for current plant operations and a tool to test cost effective process upgrades or evaluate new technologies that improve the energy efficiency and lower the carbon footprint of milk processing plants.