A Waste Heat Assessment of a Manufacturing Facility with Consideration for Demand Matching through Thermal Energy Storage

A waste heat assessment of a manufacturing facility was conducted. A physical survey identified potential waste heat sources. For these sources, the temporal fluctuations in temperature and flow rate, and the frequency of occurrence of the waste heat, were determined from measurements, calculations, and company records. The energy and exergy of the waste heat were calculated. The total annual waste heat is 36.5 TJ of energy which represents 0.84 TJ of exergy. The boiler, plant vacuums, and chiller comprise 96% of the energy rejected and are the major contributors to the rejected exergy. Using the waste heat for space heating is evaluated. Based on fuel consumption in the boiler, the annual energy for space heating is estimated 8.5 TJ. Theoretically, waste heat from the boiler flue, polypropylene dryers, and plant vacuums could meet up to 39% of this energy without storage. Simply allowing the vacuum exhausts to cool in the building could theoretically meet up to 27%. Models are developed to investigate using waste heat recovery and thermal energy storage (TES) to provide space heating for a prototype warehouse building, and estimates for the initial costs of the recovery system are developed. Modeling indicates that TES is highly beneficial for matching short-term demand fluctuations and for smoothing the temporal oscillations in the waste heat. A nine-month heating season is simulated to determine the fraction of the load met by the recovery system. A small amount of thermal storage, e.g. 12.5 - 25% of daily waste heat, improved the fraction of demand that could be met. Larger sizes had diminishing returns and significantly increased the initial cost and payback period. To reduce initial cost, a refined recovery system design which uses a TES as an intermediate and for storage is proposed. The study highlights the need to consider fluctuations in the waste heat supply and sink demand, for thermal storage, and to identify relatively simple modifications to recover waste heat.