Press Release

Systems with ORC (Organic Rankine Cycle) generate electric energy. Today the systems for residual and waste heat utilization are considered technically mature and become more and more popular. The underlying thermodynamic process allows cost-effective conversion of small thermal energy sources into electricity. The waste heat of CHP units, for example, is used to heat a low-boiling working fluid in an evaporator. This way pressure is generated, which is then released by means of an ORC turbine and converted into electric energy via a generator. "The ORC process allows generating electricity from residual heat that would be wasted otherwise", says Ralph Sawallisch, key account manager for feed-in technology at SIEB & MEYER. "The efficiency of the process is about 10 percent. If the waste heat is used, the overall efficiency of a CHP unit can be increased considerably. These results are very interesting for unit operators with respect to amortization and they provide a persuasive argument for manufacturers of ORC systems." The process is also suited to the utilization of industrial process heat. Since the process heat arises during production anyway, it can be used to generate electricity without additional primary energy demand.

Application-oriented Development

SIEB & MEYER has developed a feed-in converter for operation with high speed compressors especially used in CHP units with higher performance ranges and downstream ORC systems. The device is based on the frequency converter SD2S for synchronous and asynchronous high speed motors. The converter is designed for speeds of 100.000 rpm, for example, and higher. In combination with other components the  generated current is converted into grid-compatible current. Depending on the ORC unit the Lueneburg based company provides various forms of feed-in converters customized for the individual application.

This technology is comparatively new and requires solid know-how in regard to control systems for high speed compressors and the specific design of the feed-in converter. "This field of application also requires a clever control method with high dynamics. Devices based on solar power inverters can't provide the proper technique for passive rectification of the generator voltage to the level requested", Sawallisch points out. If the compressor runs without control, a failure would occur. For this reason the controller must react quickly to changing operating states; in case of a pressure increase, for example, the control must readjust promptly. Otherwise the overspeed threshold would be exceeded quickly causing the compressor to operate in a range where its functionality is not ensured anymore.