Computer simulation of energy use, greenhouse gas emissions, and process economics of the fluid milk process

Abstract

Energy-savings measures have been implemented in fluid milk plants to lower energy costs and the energy-related carbon dioxide (CO2) emissions. Although these measures have resulted in reductions in steam, electricity, compressed air, and refrigeration use of up to 30%, a benchmarking framework is necessary to examine the implementation of process-specific measures that would lower energy use, costs, and CO2 emissions even further. In this study, using information provided by the dairy industry and equipment vendors, a customizable model of the fluid milk process was developed for use in process design software to benchmark the electrical and fuel energy consumption and CO2 emissions of current processes. It may also be used 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 (40.0 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 grams of CO2 equivalents (CO2e) per kilogram of packaged milk, to within 5% of the value of 96 g of CO 2e/kg of packaged milk obtained in an industry-conducted life cycle assessment and also showed, in agreement with the same study, that plant size had no effect on the carbon footprint of milk but that larger plants were more cost effective in producing milk. Analysis of the pasteurization step showed that increasing the percentage regeneration of the pasteurizer from 90 to 96% would lower its thermal energy use by almost 60% and that implementation of partial homogenization would lower electrical energy use and CO2e emissions of homogenization by 82 and 5.4%, respectively. 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 CO2e 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.

Computer simulation of energy use, greenhouse gas emissions, and costs for alternative methods of processing fluid milk

“…The flow sheet diagram of the fluid milk process from Tomasula et al (2013) is shown in Figure 1. It is used as the template for the inclusion and development of models for UHT processing of milk, crossflow MF with or without HTST pasteurization, crossflow MF with partial homogenization followed by HTST pasteurization, and PEF processing.…”

“…The fluid milk process model (FMPM; Tomasula et al, 2013) incorporates HTST pasteurization of milk with equipment specifications and cost data, using the commercial software package SuperPro Designer (http://www.intelligen.com, Version 9.0 Build 8; Intelligem Inc., Scotch Plains, NJ). The flow sheet diagram of the fluid milk process from Tomasula et al (2013) is shown in Figure 1.…”

“…The values in parentheses are the percentage energy use associated with the operations on a cold-storage-free basis determined by computer simulation (Tomasula et al, 2013). However, cold storage of milk can contribute an estimated 5 to 60% of GHG emissions depending on whether cold storage is considered only as a part of the processing plant or considered to extend to a distribution center and retail outlets.…”

“…Pulsed electric field processing is a nonthermal technology that has the potential to pasteurize milk by exposure to short, high-voltage electric pulses. These processes may demonstrate savings in energy, GHG emissions, and water use compared with HTST pasteurization (Tomasula and Nutter, 2011;Tomasula et al, 2013) but it would be difficult to investigate the processes in a laboratory or pilot-plant setting.…”

“…In a previous study (Tomasula et al, 2013), we developed a model of the fluid milk process for use in process design software as a tool for improving the energy efficiency of processing plants and to lower GHG emissions, or the carbon footprint, of milk processing plants. The model links modules that represent the unit operations composing the fluid milk process, allowing calculation of the mass and energy balances at each unit operation and the economics of the process from literature and industry information.…”