Waste heat utilisation and use of renewable energy sources in a metal-working enterprise
As the only Austrian manufacturer of oil tempered spring steel wire, the Joh. Pengg AG in Thörl/Styria, has specialised its product line for applications in the automotive, electrical and machinery industries. Manufacturing oil tempered spring steel wire is an energy intensive process with several heating and cooling process steps. The project has three specific goals: To analyse the current energy flow (Sankey diagram), to assess the possibilities to increase the energy conversion efficiency and to investigate the possibilities to increase the use of renewable energy sources.
The energy analysis showed a total consumption of 45,35 MWh/a with 26% electricity and 74% natural gas. The energy cost fraction of the turnover is 6,8% which is above the average of the metal working industry. 58% of the electricity are used for mechanical energy to operate the manufacturing lines, 32% are used for process heat, 6% are used for lighting and 4% for pressurized air. 60% of the natural gas are used for direct process heat in the tempering processes, 29% for the production of hot water process heat and to heat production buildings, 5% to operate the gas radiators, 3% for heating offices and hot water production and 3% for auxiliary power and the exomat.
The analysis of the energy conversion processes identified measures leading to a reduction of 5,70% Mio kWh/a of natural gas and 1,13 Mio KWh/a of electricity. The energy cost fraction of the turnover could be reduced from 6,8% to 6,0%. The biggest potential is seen in the use of waste heat of the gas burners heating the wire at the beginning of the tempering process for supplying heat to the subsequent process steps in an energy cascade.
To increase the use of renewable energy it was suggested to replace the natural gas boiler by a biomass fired boiler for the production of the hot water process heat thus reducing the use of natural gas by additional 9,9 MWh/a. In addition production waste may be incinerated in the boiler. The increased use of hydro electricity is not recommended for economic reasons.
To arrive at reliable estimates the energy and related cost saving potential was analysed with the hep of consulting and manufacturing companies experienced in the supply of process engineering components. While the results of the project may be utilized directly for improving the situation at the plant of the Joh. Pengg AG, they may also be used as a basis for drawing conclusions for other manufacturing companies with a similar high energy demand for production processes for both metal and non-metal products.
Some of the proposed measures have already been implemented, for others a detailed analysis in subsequent projects has been initiated. It could be shown that the overall goal to improve the processes in the direction of a more sustainable production aimed at by the "Factory of Tomorrow Program" may be achieved.
Dipl.-Ing. Henrike Bayer
JOANNEUM RESEARCH, Institut für Energieforschung
Joh. Pengg AG
Dipl.-Ing. Henrike Bayer
Institut für Energieforschung
A 8010 Graz
Tel.: +43 316 876-1422
Fax: +43 316 876-1320