Thermodynamic and economic analysis of industrial biscuit oven and waste heat recovery

Biscuit baking ovens are produced as tunnel type to reduce the cost of final product and increase the production capacity. Tunnel type ovens are designed in the form of conveyor and wire mesh or steel belt is preferred as a carrier element according to the biscuit type. In tunnel type biscuit ovens, the product that enters as dough from one end of the tunnel comes out as a cooked product from the other end of the tunnel. Thermodynamic analysis of each nodal point of biscuit oven is done according to biscuit oven flow chart. As a result of the analysis, it is determined that energy efficiency of the biscuit oven is 3.90% and 49.35% of the energy consumption is released as a waste heat from chimney to the atmosphere. Organic rankine cycle (ORC) is designed according to the parameter of waste flue gasses. In this study, producing electricity energy is aimed by passing waste flue gasses through organic cycle. Organic rankine cycle is designed by using net present value method (NPV). As a result of design which is done for 20 years of service life of equipment, 58.62 kW of electrical energy is produced in the organic rankine cycle by using R113 as a working fluid and net present value (NPV) is evaluated as 1.979 million US dollars. It has been observed that the energy efficiency of the biscuit oven increased from 3.90% to 11.04% and the exergy efficiency of the biscuit oven increased from 0.5% to 6.22% by generating electricity energy with organic rankine cycle (ORC) investment. Alternatively, waste flue gasses passed through a heat exchanger to heat baking air of another oven to 200 ℃. Biscuit and cake baking is aimed by generating heat from heat exchanger. As a result of waste heat recovery with heat exchanger 331.58 kW of energy is gained and 29.6 𝑚3/ℎ𝑜𝑢𝑟 natural gas saved. In other word, 38.2% fuel consumption is reduced, energy efficiency of the often increased from 3.90% to 44.29% and exergy efficiency of the oven is increased from 0.5% to 32.87%.