18 May 2017

O.3.9.4 Research on Utilization of Waste Heat and Waste Resource in a Soy Protein Powder Plant

Soy bean is one of the main cereal crops in the world, the protein content of which accounts for nearly 40%. As nourishing
food, soy protein has been widely applied in food industry. Alkali extraction and acid precipitation is the main manufacturing
technique of soy protein. The energy consumption of this manufacture process is considerable. In the traditional manufacture
process, exhaust air from the cyclone and the soy whey water are discharged to the environment directly. However, the
temperature and the humidity of the exhaust air is much higher than those of the environment, thus, there is great potential to
recover heat from the exhaust air. The soy whey water is the wastewater from the manufacturing process. More than 60 tons
of wastewater will be discharged to the environment to produce 1 ton of soy protein according to the survey data. It contains
nearly 2% of protein and other substances in the wastewater, and it will not only pollute the environment but also causes
resource waste by discharging directly. Condensing the wastewater could solve the problem, as the condensing product could
be used as feed for animals, which could recover resource and prevent pollution at the same time.
A water loop with a heat pump is established as the waste heat recovery system from the exhaust air. The whole year
operating performance is analyzed according to the meteorological parameters. Compared with the traditional manufacture
process, the total energy saving amount could reach 3100 tce per year, and the energy saving rate is 21%.
A mechanical vapor recompression system is established as the waste resource recovery system from the soy whey water.
Operating performance under different evaporating temperature is analyzed of the system. When the evaporating temperature
is 60 oC, the energy consumption of the compressor is 31 kWh to evaporate per ton of water. Both of the evaporation rate and
the energy consumption increase as the increase of the evaporating temperature. And there is a trade-off between the
evaporation rate and the energy consumption.