Waste heat recovery for power generation using organic rankine cycle in a pulp and paper mill

In achieving a sustainable greener future, more awareness on potential energy recovery in industrial processes is important as their energy demand continues to grow. This paper discusses how unused thermal energy can be effectively recovered in pulp and paper mills, hence improving mill's energy efficiency and increase clean energy generation. Pulp and paper mills usually feature medium grade heat in the recovery boiler stack of black liquor due to limited boiler efficiency and safety reasons. The unused heat is to be recovered and used to generate power using an Organic Rankine Cycle (ORC). The waste heat from the ORC is also recovered and used for water heating. This technology promises a reasonable payback time with no or little supervision of operation. Analyzing the characteristics of the available waste heat, a waste heat recovery heat pipe (thermal oil) loop is integrated at the back end of the boiler recovery to harness the heat which is delivered to the ORC. Heat from the condensing unit of the ORC is used to preheat water for process use. A modeled ORC power plant is used to determine power generated from a pulp and paper mill. The simulation study shows that using an ORC-based power generation greatly improve the mill energy efficiency reduce fossil fuel electricity consumption and decrease CO2 emission.