Assessment of the renewability of black, instant and ice tea production and waste valorization processes

Energy and exergy utilization, carbon dioxide (CO2) emission and exergy destruction were calculated for the "orchard to the retail market" industrial production of the black tea in Turkey and pilot scale production of the instant and ice tea. Energy and exergy utilization was 12,748 and 45,532 MJ/t of black tea produced, being consistent with the results given in the literature. The total amount of the CO2 emission in the entire process was 1,732 kg/t of black tea. In the entire black tea process, 70 per cent of the total energy and 86 per cent of the total exergy utilization was allocated to the processing of the tea, which also accounted for 72 per cent of the total amount of the carbon dioxide emission. The largest amounts of energy and exergy were used in the drying, withering and packaging stages of the processes, respectively. The total exergy utilized in drying process was 22,424 MJ/t, corresponding to 52 per cent of the total exergy utilization. HVAC units employed in withering were causing the largest exergy destruction, 2,542 MJ/t of black tea, followed by 318 MJ/t of black tea of exergy destruction during drying. Energy and exergy utilization from agriculture to packaging were 1,431 MJ/kg and 3,987 MJ/kg of instant tea and 3,571 MJ/kg and 4,464 MJ/kg of ice tea, respectively. The total amount of the CO2 emission in the entire process was 140 kg/ kg of instant tea and 267 kg/ kg of ice tea. Waste from the extraction step was analyzed further for potential conversion into value added products - activated carbon, hydrogen and adsorbent. Energy and exergy requirement for the activated carbon production from tea waste was 59.8 MJ/kg and 249.5 MJ/kg of waste tea and for the adsorbent production 3.7 MJ/kg and 15.2 MJ/kg of waste tea, respectively. Instant tea production was the most and the brewed tea was the least energy and exergy utilizing process among all the cases studied. The cumulative degree of perfection (CDP) and renewability indicator of the products showed that all of these processes were nonrenewable.