ORC modul maxxtec

ORC Modules for electricity power generation with Organic Rankine Cycle (ORC)

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 3 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 of the overall concept for optimized primary energy efficiency, the advanced partial stream principle was developed.

ORC systems with partial stream principle allow a much better utilization of the exhaust heat in biomass fired combustion systems. Therefore partial stream principle is now a standard for such applications where the electrical power generation has priority compared to heat supply.



The vapour phase organic fluid allows the use of low temperatures to generate electrical power from a few kW to 3 MW module.


This results in following advantages:

  • High efficiency
  • Extreme high efficiency of the turbine
  • 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.
  • Automatic start-up and shut-down operation
  • 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
  • Low noise emission

The availability of synthetic heat transfer media and the long time experiences with high temperature thermal oil applications has enabled Maxxtec to increase the overall efficiency. 



ORC modules for electricity power generation with organic rankine cycle (ORC)


ORC modules up to an electrical output of 800 kW can be 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.






Meanwhile, the whole world is aware of the fact that fossil fuel supply is limited and further exploration will become unbearable expensive. In addition, emission of fossil fuels generates billions of tons of CO2, which is the main cause of global warming and environmental changes. The long term impact of these negative developments can still not be predicted in details. Many international operating associations like Greenpeace as well as prominent scientist have highlighted these problems since decades and meanwhile there are bonus systems in place to counteract and to persuade the industry to invest in “renewable energy”.


Besides additional income by trading carbon credits, many countries have granted high prices for feeding the national grid with power generated by renewable energies.


In this interrelation, also biomass combustion with the generation of electrical power is one of these renewable energies. Due to national and international development programs the use of biomass as renewable energy wins more and more of importance.


The cycle of usage and production of biomass as renewable energy is balanced. Biomass can be produced almost everywhere and has several environmental advantages over fossil fuels. The main advantage is that biomass is a renewable resource, offering a sustainable, dependable supply. Other advantages include the fact that the amount of carbon dioxide (CO2) emitted during the combustion process is typically 90% less than when burning fossil fuel. Biomass fuel contains minimal amounts of sulphur and heavy metals. It is not a threat to acid rain pollution, and particulate emissions are controllable.


With few exceptions, biomass is not subject of international trading, nor is war fought over the exploitation of biomass resources. During the Second World War when many parts of Europe were destroyed, wood was one of the major fuel sources to generate heat and energy for vehicles (wood gasification). Nowadays, advanced technologies and processes have changed the perception of biomass. Biomass is CO2 neutral, easy to produce in large quantities, often a waste product of other processes and still available for usually significantly less costs than competing fossil fuels.


The production of electrical energy from biomass has a higher importance than producing heat from biomass. Electricity can be supplied far distances with very little loss and can be sold on the spot, where it is required.


In general there are 2 ways to produce electrical power from biomass in the range up to 2 MW; biomass combustion and biomass gasification.


The biomass gasification process is the process of heating biomass in an oxygen-starved environment until volatile pyrolysis gases (carbon monoxide and hydrogen) are released from the biomass. The gases can be mixed with air or pure oxygen for complete combustion and the heat produced can be transferred to a boiler for energy distribution. Otherwise, the gases can be cooled, filtered, and purified to remove tars (a major concern for any wood gasification process) and particulates and used as fuel for internal combustion engines (Stirling motor), micro turbines, and gas turbines. Stirling motors have been used successfully but are limited in their available capacity ranges.

Biomass vary a lot in particle size, moisture content, ash content, calorific value and density depending on the source (wood, rice husk, palm oil fibres, etc.). The production and use of biomass gas is only economic if the fuel composition is consistent and the gasifier is monitored and serviced on a regular basis.

The second process of power generation with biomass is the combustion of it in a furnace attached to a boiler. The combustion takes place on a static or moving grate under high temperature and staged combustion air supply. Modern biomass combustion systems are PLC controlled, high efficient and do not pollute the environment. These modern combustion systems are often used with steam boilers for generating process steam or for CHP systems to operate a steam turbine with generator. The disadvantage of steam power plants below 1 MW is the fact that these systems are expensive in design and operation due to the complicated control systems, water treatment issue and high steam pressures required. The normal operation, start-up and shut down of such systems need highly qualified operators. In addition, steam systems require a super heater which is one of the most critical parts in such combustion system. In cold countries one faces an additional problem with the freezing point of water. If the plant has been shut down for a longer period, one needs to drain the complete system. That's one of the reasons why ORC turbo generators has been developed and became so popular in such a short time. The ability to generate electrical power in small power plants (< 1 MW) with biomass combustion and thermal oil systems makes these systems so attractive.


ORC Module - The process

1. Biomass is combusted in a furnace and generates hot gases of ~ 950

    deg. C, which are heating up a thermal oil circuit. The thermal oil

    is heated up to 300-330 deg. C.


2. The thermal oil heats up a secondary circuit, which contains the organic

    fluid for the ORC module. The organic fluid is evaporated and drives the

    turbine to generate electricity in the generator.


3. The water cooled condenser will condense the vapour and the heated

    cooling water can be used for various heating application such as heating

    dryers or hot water heating systems in buildings.




Biomass is utilized in modern highly efficient combustion systems, which are successfully operated in large numbers. These systems with their sophisticated fuel feeding, grate system, staged combustion air supply, de-ashing system, filter, control and safety instrumentation are reliable and perform flawless.


The heat transfer media of the primary circuit is thermal oil. Thermal oil offers advantages like low system pressure, almost no freezing problems, save control and operation and long life time.


The generated heat from the biomass combustion is converted into electrical power by the ORC turbo generator. The ORC process is highly efficient, reliable and easy to control. The turbine rotor runs will low r.p.m. and is directly connected with the generator. All ORC components are shop-assembled and tested. This reduces installation and testing time at site. Compared to steam, organic fluids do not cause any corrosion problems, no erosion in system components like valves, turbine blades and piping. This benefits the long life time and reliability of the power plant.


The design of the turbo generator follows criteria, which allow:

  • Quick start-up within minutes
  • Remote controlled monitoring and load control
  • Operation without permanent operator at site
  • Remote data management for monitoring and trouble shooting





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