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10:00   Parallel Session: Operational Experience I
Chair: Piero Colonna
20 mins
Roberto Bini, Fabio Viscuso
Abstract: A new development of ORC technology recently introduced to the market is presented. This class of high efficiency organic Rankine cycle has been introduced to produce electric energy from medium temperature biomass or heat recovery application in the 1 MW el power range. To obtain an electrical efficiency of about 25 % (net of ORC auxiliaries) the cooling of the condenser is kept as low as reasonably possible using air coolers to cool down water circulating in a closed loop. Hence these units have been conceived for ‘power only’ production, i.e. where cogeneration is not required. A further development of the system has been patented by Turboden to allow for a partial utilization in ‘cogeneration mode’. With this implementation it is possible to obtain a fraction of the overall discharged thermal power at a temperature suitable for cogeneration applications (80-90 C), extracting the heat from the ORC unit regenerator. The paper will describe also this solution and the advantages achievable.
20 mins
Jos van Buijtenen
Abstract: Starting from 2002, a novel ORC power unit has been developed by Tri-O-Gen B.V. of The Netherlands, based on technology originally defined in Finland (Lappeenranta University of Technology). The development in The Netherlands was strongly supported by the Dutch government (AgentschapNL), involving among others Delft University of Technology and the Dutch National Aerospace Laboratory NLR. The ORC system is based on a thermally stable hydro-carbon as a working fluid, hence suitable for direct use of intermediate temperature heat sources from 350 C and above. The core of the unit consists of a combined turbine – generator – pump: the High Speed Turbo-Generator (HTG). Thanks to the use of a high speed generator (26 – 27 krpm), the turbine and pump could be laid out at their optimum specific speed, leading to high internal efficiencies. Moreover, this concept allowed for a seal-less design: no shaft seals are necessary, and the only interaction between the internals and the outside world are flanged connections for the working fluid to enter and exit the HTG and the well-sealed electric cables. Lubrication of bearings and cooling of the generator is taken care of by the working fluid itself, so there is no need for lub-oil and related system. The unit can therefore be considered completely hermetic. After successful testing of the prototype, the first commercial package was designed (called the WB1), consisting of four modules for turn-key delivery: • The standard process module, made up of HTG, recuperator, condenser, hot well, pre feed pump, main valve and bypass valve, including connecting piping and instrumentation • The heat supply module: an evaporator tuned at the conditions of the available heat, to be connected directly to the heat source • The heat rejection module: the cooling system for the cooling water which cools the condenser, tuned to the need for extra low temperature heat usage or to the local ambient conditions. • The standard power preparation module, which connects the high speed generator directly to the grid to supply the power at 400 V, 3 phase, 50 or 60 Hz. Fourteen units are now in commercial operation in different applications, while there are more than 10 units on order. Heat sources vary from exhaust gasses of gas- and diesel engines to landfill gas combustion and wood firing as well as industrial waste heat. This presentation will describe the unique features of the design, such as the hermetically closed turbo generator, the cycle design and the balance of plant. Units are being built as a standard packages for 60 to 165 kWe, being adapted to the heat source by sizing the evaporator. Moreover, current operating experience (more than 50.000 accumulated hours) will be reported on.
20 mins
Hartmut Kiehne
Abstract: Small capacity combined heat and power (CHP) plants are suitable for efficient energy conversion. CHP is arguably the only way to use fuel or thermal energy optimally, and the only way to optimally use fuel or thermal energy and the only way to operate ORC plants efficiently. ORC plants for cogeneration are less electrically efficient than plants designed for electricity generation only, as the higher condensation temperature penalizes the thermodynamic cycle. As a result, investors for electricity-only projects demand ORC plants with higher electrical efficiencies, and manufacturers attempt to fulfill this demand with so-called low-condensing temperature ORC plants. Selecting a suitable ORC fluid can help reducing the condensation temperature and thus increasing the electrical efficiency. However, this rules out cogeneration due to the low condensation temperature. Notably, the assumed improved economy deriving from higher electricity production is often offset by the increased electrical power demand for the condenser cooling. In low-temperature ORC plants for generating electricity only, the condenser is generally cooled by means of air-water coolers. The lower the temperature difference between the condenser cooling water and the ambient temperature, the more electricity is required for cooling, i.e. the assumed advantage of increased electrical efficiency is compensated by the higher system electricity demand. The use of so-called low-condensation temperature ORC plants is not advantageous in projects with no heat requirements, as the system electricity requirement can be reduced significantly via higher condensation temperatures, thus achieving higher net electrical efficiency. As ORC plants are often implemented in areas with higher ambient temperatures, a larger temperature difference between the condenser cooling water and the ambient temperature is beneficial.