Performance analysis of the heat supply system with the waste heat recovery from the sterilization of the mushroom sticks

Shiitake mushroom has been one of the most edible fungus varieties in China. However, a large amount of the waste heat has been discharged during the industrialized production and sterilization of mushroom sticks, as the cultivation scale develops rapidly in recent years. The waste heat has also posed a serious threat to environmental pollution, even disorderly spilling of exhausted steam condensate during the process. In this study, a new type of heat exchanger with a porous channel was designed for a mushroom production factory in Zibo City, Shandong Province, China. A waste heat recovery system was also proposed to apply for the exhaust steam and condensed water of the sterilization, where the engineering data was measured in practice. The results show that the waste heat in the heating season was used for the heating of cultivation sheds, office buildings, and dormitories in the factory. The temperature range of the water supply was 36-48 ℃, and the daily heat supply was between 8-18 GJ. In non-heating seasons, the waste heat was used for the secondary preheating of the water supply to a gas boiler, or the bathing water. The temperature range of the water supply was 65-75 ℃, and the daily heat supply was 8-10 GJ, where the total heat transfer coefficient of the heat exchanger was about 70-105 W/(m2•K). As such, the efficient recovery of the waste heat was achieved for the exhausted steam wastewater from mushroom sterilization over the entire year. It was estimated that the net saved cost was 194 000 Yuan, the initial investment can be recovered in about 3.1a. Reduce carbon dioxide emissions by 135.6 t/a, reduce sulfur dioxide emissions by 10.35 kg/a, reduce nitrogen dioxide emissions by 43.5 kg/a, and reduce smoke and dust emissions by 16.57 kg/a, reflecting better economic and environmental benefits. Small-scale agricultural waste heat recovery projects should try to use waste heat throughout the year to shorten the payback period. The hot water storage tank can be used in the design to realize the contradiction between the time mismatch between the waste heat and the heat supply. During the operation, attention should be paid to the operation mode of the heating system when the waste heat is insufficient and how to maximize the use of waste heat. The research methods and results of this project can provide references for the recovery and utilization of agricultural waste heat, and are of great significance for reducing energy consumption, reducing energy costs of shiitake mushrooms, reducing pollution emissions, and improving the ability of agricultural sustainable development. © 2022, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.