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Organic Rankine Cycle (ORC) type external combustion engine

The Maxxtec ORC engine is an industrial, autonomous, robust biomass cogeneration platform; fuelled from  thermal heat generated from forest slash chips, bark, agro-food waste and/or energy crops.

These electrical generation engines exhibit numerous particularities:

  • 15% electrical generation efficiency
  • an autonomous system requiring only periodic supervision (an atmospheric pressure thermal oil heating fluid)
  • a combined conversion efficiency exceeding 90% for hot water cogénération applications
  • a high modulation efficiency - system low regime operation down to 15% nominal
  • system duty cycle > 8000 hrs/an
  • factory assembled modules from 300 KWe to 2 000 KWe


Thermal heat sources to power the ORC engine are numerous:

  • industrial process thermal heat recovery streams > 400°C (gas or liquid streams)
  • biomass fuelled thermal heat leveraging a Chiptec Wood Energy System  gasifier system; ideally for clean woody biomass fuel
  • MSW, bark and/or  sludge residual waste fuelled thermal heat leveraging the  Waste2Energy gasification platforms


A 1,5MWe cogeneration system, complete with a 8 MWth  65ºC hot water hydronic heating circuit, provides a 17% electrical generation efficiency for a duty cycle of  8000 hrs/year.  (i.e. a combined system efficiency of  90%)

The reduction of harmful emissions in our atmosphere must be one of the priority targets of responsible policy. Environment-friendly energy production practices and careful use of energy will help keep clean the air we breathe and protect it for later generations!

To reach this target Maxxtec-Adoratec develop, produce and supply:

  • ORC (Organic Rankine Cycle) systems for generating electricity from low temperature heat (geothermal energy, industrial waste heat, etc)
  • ORC systems for generating electricity from biomass
  • ORC systems for generating electricity from engine exhaust heat

A range of different plant technologies exist for generating electricity from solid biomass. One of the technologies that has proved its suitability for years in field operations is ORC technology. In excess of 50 ORC power plants with capacities ranging between 200 and 1,500 kW (per module) have already been operating in central Europe since 1998, most of which are used in biomass power plants.

At the moment, ORC plants are operated mainly in Italy, Austria, Switzerland and Germany.

If a biomass power plant is going to be suitable for day-to-day use, is it essential that it has high availability and that the operation and maintenance costs are kept as low as possible. In many cases, the plants are not operated by professional energy producers but by companies wishing to exploit existing fuel material by generating power in addition to their core business. Therefore it is particular important that the power plant requires as little attention as possible. ORC plants offer this possibility, since they can be operated without supervision.

Of course the efficiency is also decisive since this determines the fuel consumption, which, in addition to the aforementioned criteria, is important in terms of achieving economic viability. For outputs less than around 2 MW, ORC plants are more efficient than conventional steam turbines.

Improving the flue gas heat recovery from solid fuel combustion plants, by innovative design of the heat transfer system, enables the efficiency of ORC plants to be considerably increased. Comparable systems, such as steam-powered power plants, come nowhere near to achieving this efficiency within this output range.

This industrial electrical cogeneration solution is powered from forest slash residue, wood chips, energy crops chips and/or MSW & waste material.

The system, delivered in factory-assembled, stand-alone modules from 300 KWe to 2000 KWe, produces both electricity and hot water. The electricity is generated in an autonomous, closed loop process, operating at atmospheric pressure.

The system is operational in cogeneration mode for 8000 hrs/year featuring an electric generation efficiency of 17% for a 1,5MWe module with an 8 MWth water circuit @ 65ºC. (i.e. for a combined cogeneration efficiency @ 90%)

Combined Heat and Power (CHP) with ORC modules

The Organic Rankine Cycle

ORC modules represent an efficient and reliable way to generate electrical power with relatively low temperatures. Since more than a decade such systems operate safely in many places worldwide in a range form a few kW up to 2 MW.

The concept

The Organic Rankine Cycle (ORC) is a thermodynamic process similar to a conventional steam cycle but using a different media to drive the turbine. ORC systems use high molecular organic fluids instead of water.

The organic media is compressed and circulated in a closed loop by a pump. It will be evaporated in a shell and tube heat exchanger by absorbing the thermal heat of the thermal oil primary circuit.

The organic vapour expands in a special designed turbine which drives the electrical generator and will be condensed in another heat exchanger by using a cooling media like water.

The condensate will then be compressed again by the circulation pump, which closes the thermodynamic cycle.

Neither the thermal oil of the primary circuit, nor the cooling water is in direct contact with the organic media.

For high temperature applications it is possible to increase the efficiency by using a regenerator behind the turbine.

In search of further optimization, Maxxtec reviewed the overall concept of primary energy input, the thermal oil system and the heat recovery and came up with the advanced partial stream principle.

This advance ORC system allows a much better utilization of the exhaust heat in biomass fired combustion systems. The partial stream principle is now a standard for such applications where the electrical power generation has priority compared to recovered heat.


The vapour phase organic fluid allows the use of low temperatures to generate electrical power from a few kW to 2.5 MW modules.

This results in following advantages:

  • Extreme high efficiency of the turbine (up to 85%)
  • Low mechanical stress for the turbine due to low speed design
  • The low speed allows the direct coupling of the generator without the use of a gearbox
  • Extraordinary start-up and partial load behaviour due to wide spectrum usage of the organic fluid.
  • Fully automatic operation with low maintenance and operational costs
  • No corrosion problem due to the non-corrosive organic fluid
  • No erosion problems of the turbine blades due to "dry" vapour phase
  • Long lifetime



The availability of synthetic heat transfer media and the long time experiences with high temperature thermal oil applications has enabled Maxxtec to increase the electrical power output significant. This is now achieved by operating Maxxtec/ Adoratec ORC modules on a higher temperature of the primary circuit.


ORC modules up to an electrical output of 500 kW are delivered pre-assembled on a skid. All main equipment parts of the turbo generator e.g. heat exchanger, feed pump, turbine, generator piping, instruments/wiring and other auxiliary equipment are pre installed and allow cost effective transport and installation at site.

Maxxtec AG is one of the leading suppliers of plants for efficient power generation from biomass and industrial waste heat.

The products are used for the generation of electricity and for the decentralised supply of group heating schemes as well as in heat-intensive industrial processes. The products are used for the generation of electricity and heat from solid biomass as well as in heat-intensive industrial companies.

  • More than 100 exhaust heat recovery systems sold for biomass application.
  • Superior technology with high level of innovation: Maxxtec's two-pass exhaust gas heater model and Maxxtec's accessories (i.e Airmaxx and Pumpmaxx) permits longer operation times and a higher efficiency.
  • Perfectly harmonized systems due to in-house engineering and the design of ORC modules and exhaust heat recovery systems.
  • The partial stream design, developed by Maxxtec's, increases the electrical output by 5-7% by utilizing additional thermal energy from exhaust gases.
  • At the end of 2007 approx. 110 ORC-biomass-power-plants have been in operation in Europe, whereas Maxxtec delivered the exhaust gas heat recovery system for 75 plants.