Initial situation:

In the iron and steel industry as well as other energy-intensive industries, a variety of different thermal process plants are used for the production and heat treatment of products and semi-finished products. On many systems heat recovery systems are used to reduce exhaust gas heat losses and fuel requirements. Nevertheless, waste heat streams with temperatures of more than 300 ° C are also still present at these plants, which are released to the environment without being used. One way of using this waste heat sensibly is the power generation. Various processes such as steam turbines, steam engines or the Organic Rankine Cycle (ORC) are suitable for this purpose. The aim of this collaborative project was to demonstrate the use of a process for generating electricity from the waste heat of four forging furnaces using the example of an SME smithy.

Working topics:

• Operating measurements for recording the actual state at the forging furnaces of Grimm.
• Creation of a furnace balancing program.
• Selection, commissioning and operation of the waste heat transfer process,
• Technical and economic evaluation.

Results:

• Based on the determined technical boundary conditions, the choice was made for an ORC system with an electrical output of 300 kW when operating four turbines. For the installation of the ORC system on the Grimm factory site, various rebuilding measures had to be taken.
• After the commissioning of the ORC plant considerable disruption occurred, which prevented a continuous operation of the ORC plant over a longer period until the end of 2013. As a result, continuous operation of the plant could not be achieved by the end of 2013. After the disturbances at the end of 2013 / beginning of 2014 could be largely eliminated, the beginning of 2014 saw a largely continuous operation. Overall, the utilization of the ORC plant over a period of approx. 14% in 2012 up to approx. 50% increase in 2014. The total net electricity production up to and including July 2014 amounts to approx. 200,000 kWh with a resulting CO2 savings of approx. 120,000 kg. The expected amortization time of the ORC system is between 7.5 and 19.5 years depending on the electricity price. Over the entire lifetime of the ORC system of 20 years to be adopted, a CO2 savings of approx. 11,400 t can be achieved. The profitability analysis has shown that, in the case of intermittent operation, the amortization time for the ORC process is the lowest in comparison with the steam turbine, steam engine and TEG. Overall, however, only in rare cases in the case of a waste heat flow is a currently required customary amortization time of less than 4 years to be expected. Over the entire life span of a power generation system, however, the economy is usually given.
• The project was included in the KlimaExpo.NRW initiative.