Heat Integration and Renewable Energy in Meat Processing Plants

This thesis aims to optimise energy efficiency at meat processing plants and minimise their carbon footprint, as a way of reducing operating costs and minimising the potential negative impacts of a carbon price on the red meat industry. In the context of the export meat industry, there is continual competition with the live export trade. Therefore, there is a risk that a carbon price could increase the live export trade over domestic processing of meat, thereby exporting emissions rather than lowering global carbon emissions. This thesis aims to provide one possible pathway forward to a lower carbon economy for the meat processing sector which will not lead to the export of carbon emissions to other countries.   
   The detailed investigations of this thesis relate to: optimising energy savings available from heat integration and heat use through investigating the use of 60 °C water for knife sterilisation (rather than 82 °C water); optimising biogas production, through using excess heat below the pinch for maintaining anaerobic pond temperatures; and using renewable fuels for energy supply.   
   Before considering the implications of these results, the limitations should be clearly stated. This analysis is based on theoretical calculations, and so does not make any allowance for system losses, other than those that were inherently included in the calculations (such as the hot water ring main reheat). As such, the results should not be applied without taking into account the operational details of a particular site.   
   If biogas from wastewater is used to provide site electrical needs using cogeneration, it will provide a significant portion of the total site electricity requirement. Biomass has been proposed to supply the residual thermal energy requirements.  
   In the 82 °C sterilisation water case, most of the site heating requirements (other than cooker requirements) can be met by heat recovery from the rendering vapours, with 73 kW of heat addition at just below 40 °C. In reality, substantially more than this is used at plants in Australia, due to the operational requirements that require that the target temperature of 82 °C is met at all times. Additionally, this thesis does not include any losses, which would exist in a real plant situation. Heat integration provided a 47 % saving in heating requirements and a 100% saving in cooling requirements.   
   This thesis confirms that using 60 °C water instead of 82 °C water leads to an 11 % saving in energy (compared to the 82 °C case) utilising waste heat below the pinch. The only heating requirement is to satisfy the cooker requirements. Instead of using a cooling medium, the excess waste heat below the pinch was transferred to the anaerobic pond, to assist with maintaining pond temperatures in the 30-40 °C target range for mesophilic bacteria. This effectively used all the waste heat and created a threshold problem. Heat integration provides a 46 % saving in hot utility.   
   In investigating the potential biogas generation rates at the thesis study site, it was found that they vary considerably, depending on what assumptions are made about factors such as wastewater volumes, water quality and conversion rates in the anaerobic pond. The analysis  assumed that the cogeneration plant only operated during the peak production periods when both electricity and heat are required, not all the time. A cogeneration system using a GE Jenbacher JMS 208 GS-BL biogas cogeneration system was modeled, with 330 kW electrical  output at 39 % electrical conversion efficiency and 190 kW exhaust gas heat recovery (from 500 °C to 180 °C). Biogas from wastewater could provide the entire fuel requirement for cogeneration during the peak and morning shoulder electricity tariff periods even using the most conservative data (70 % biogas capture and National Greenhouse and Energy Reporting data). Heat integration achieved a 67 % saving for the 60 °C case, with cogeneration providing a 33 % saving between both integrated cases.  
   The amount of greenhouse gas saved depends on a range of factors, such as the amount of biogas generated, the amount of biogas captured, the operating hours of heat integration, the operating hours of the cogeneration unit and steriliser water temperature. The greenhouse saving from biogas capture, use and offset grid electricity emission for the thesis host site ranged from 5,110 – 17,400 tCO_2-e/year (or 0.30 -1.04 tCO_2-e/tHSCW). This work indicated that 60 °C steriliser water, biogas cogeneration with heat integration and residual thermal energy from coal would save 49 % of current boiler fuel greenhouse emissions when compared to the 82 °C un-integrated case, or 1,409 tCO_2-e/year (which equates to 0.08 tCO_2-e/tHSCW).  
   The amount of biomass and land required for biomass coppicing for the total site energy requirements (electricity and thermal needs) was estimated by applying a savings “discount” to MLA published benchmarks and thesis calculations. This indicated that 405 - 1,352 hectares (ha) would be required, or 0.027 – 0.08 hectares per tonne of hot standard carcass weight (ha/tHSCW). The amount of biomass and land required for biomass coppicing for the residual thermal needs was estimated using the same method and was estimated to be 127 - 421 ha would be required, or 0.008 – 0.025 ha/tHSCW. For the 60 °C steriliser water, biogas cogeneration with heat integration and residual thermal energy from biomass, 64 - 82 % of greenhouse emissions could be saved, which equates to 0.49 – 0.63 tCO_2-e/tHSCW.