“ ORGANIC RANKINE CYCLE ( ORC ) IN BIOMASS PLANTS : AN OVERVIEW ON DIFFERENT APPLICATIONS “

The ORC technology in cogenerative systems has by now reached a level of full maturity in biomass applications. In Europe, there are over 120 plants in operation with sizes between 0.2 and 2.5 MW electric. ORC systems are very flexible and can be used in different applications like district heating systems, pellet production factories, sawmills and tri-generation systems with absorption chillers. In this article we summarize the possible application of ORC units in biomass field, focusing the attention on the possibility to use the ORC modules in processes that are not directly tie to electricity production like sawmills, pellet factories, district heating systems, etc. optimizing the global efficiency of the plant using the waste biomass coming from these existing production processes to produce, thanks to the ORC technology, hot water for internal use (belt driers, district heating, etc) and electricity. With this target we have collected the results of different studies, presented in various exhibitions, in order to make an overview on the different biomass solutions with ORC modules. 1 ORC SYSTEM DESCRIPTION Over the last 15 years the ORC turbogenerators has demonstrated to be a well proven industrial technology for application in small decentralized biomass CHP plants (0,2 – 2,5 MWel). Typical systems are based on the following main items: • biomass fuel is burned in a combustor made according to the well established techniques also in use for hot water boilers. These combustors with their set of accessories (filters, controls, automatic ash disposal and biomass feed mechanism etc.) are nowadays safe, reliable, clean and efficient; • hot thermal oil is used as heat transfer medium, providing a number of advantages, including low pressure in boiler, large inertia and simple adaptability to load changes, automatic and safe control and operation. Moreover, the adopted temperature (about 310°C) for the hot side ensures a very long oil life. The utilization of a thermal oil boiler also allows operation without requiring the presence of licensed operators as for steam systems in many European countries; • an Organic Rankine Cycle turbogenerator is used to convert the available heat to electricity. Thanks to the ORC, that is thanks to the use of a properly formulated working fluid and to the optimization of the machine design, both high efficiency and high reliability are obtained. The condensation heat of the turbogenerator is used to produce hot water at typically 80 – 120°C, a temperature level