A comparison between pollutants and greenhouse gas emissions from operation of different dryers based on energy consumption of power plants

Production and emission of greenhouse gases are an indispensable part of every agricultural practice. This gains more significance for the energy-intensive process of drying. SO2, CO2 and NOX emissions were analyzed during drying of dog-rose using hot-air, infrared, hybrid hot air-infrared, microwave, hot air-microwave, vacuum, and hybrid photovoltaic-thermal solar dryers. The energy demand of these dryers was supplied from different steam, gas turbine, and combined cycle power plants that use natural gas, heavy oil and gas oil as fuels. Experimental results showed that greenhouse gas emissions increased when increasing temperature and airflow velocity during hot-air drying. For infrared and hybrid hot air-infrared dryers, greenhouse gas emissions followed a falling trend when increasing the radiation level and temperature and decreasing the airflow velocity. Results from exploiting solar power in the hybrid photovoltaic-thermal solar dryer showed that the greenhouse gas level was lower when solar power had a larger share in supplying the required drying heat. Generally, the highest CO2 emission of vacuum dryer was 33,141.06 g recorded at 40 °C and vacuum pressure of 750 mbar in the gas turbine plant operating on gas oil. Additionally, the lowest CO2 emission (38.55 g) was recorded for the microwave dryer while using 500 W power in the steam power plant using natural gas. The highest and lowest NOX levels were 183.09 g (vacuum dryer) and 1.54 g (microwave dryer), respectively.