click icon to print  

   ORC technology to use waste heat in MUs  evaluated  
The waste energy produced by under-floor traction equipment in MU stock may be used for comfort functions. While the use of waste heat by means of heat exchangers is limited to heating, advanced technology based on the Organic Rankine Cycle (ORC) allows for the production of electric power from waste heat and thus for the use of waste energy for cooling or lighting purposes.
Technology field: Optimisation of comfort functions
close main section General information
  close sub-section Description
   

Principle

The waste energy produced by under-floor traction equipment in MU stock may be used for comfort functions. While the use of waste heat by means of heat exchangers is limited to heating, advanced technology based on the Organic Rankine Cycle (ORC) allows for the production of electric power from waste heat and thus for the use of waste energy for cooling or lighting purposes.

The Rankine Cycle

In the Rankine cycle superheated steam produced by a boiler is expanded in a steam turbine which drives a generator converting the work into electricity. The remaining steam is condensed and fed back to the boiler. This thermodynamic cycle is used to generate electricity in many power stations.

The Organic Rankine Cycle (ORC)

In the Rankine cycle overheating of the steam water mixture is required. The efficiency of the cycle can be improved by using organic substances instead, that can be used below 400°C and do not need overheating. This is called an Organic Rankine Cycle (ORC). By means of the ORC, waste heat can be exploited to produce electricity at low temperatures where a steam cycle would be inefficient. Organic compounds eligible for the use in ORC include CFCs, freon, iso-pentane and ammonia. The substance used should match the temperature of the available waste heat (waste heat temperatures can be as low as 70-80°C). ORC reach an efficiency 10 to 20% depending on temperature levels.

Fields of application

Possible applications of ORC technology range from low temperature waste heat recovery in industry and efficiency improvement in power stations to the recovery of geothermal and solar heat.

close main section General criteria
  close sub-section Status of development: research & experiments
    In 1996, a feasibility study on the potential for power generation from waste heat in EMUs was commissioned by DB AG.
  Time horizon for broad application: 5 - 10 years
    (no details available)
  Expected technological development: highly dynamic
    (no details available)
    Motivation:
    Energy saving
  Benefits (other than environmental): none
    (no details available)
  Barriers: high
   

Energy recovery potential in EMUs

Whereas the potential is high in DMUs due to high temperatures occurring in diesel engines, the potential is somewhat lower in EMUs since waste heat is available only at temperatures between 80 and 120°C.

Costs

Based on present prices, the payback of an application in EMU stock would be 20 years and more and is therefore not yet profitable. The situation is more favourable for DMUs.

Complexity

The implementation of an ORC cycle for the under-floor equipment would considerably increase the complexity of MU stock.

Technological maturity

Although ORCs are already in use in stationary applications in industry, there is no experience with ORC technology for railway vehicles. In the initial phase, downtimes and maintenance costs could therefore be high.

    Success factors:
    (no details available)
  Applicability for railway segments: high
    Type of traction:  electric - DC, electric - AC, diesel
    Type of transportation:  passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines
    The use of ORCs to generate electricity from waste heat is only feasible for MU stock.
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): highly uncertain
    At present, the use of ORCs meets high barriers in both DMUs and EMUs. The future potential could be high but is highly uncertain.
    Example:
    (no details available)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: 2 - 5%
  Energy efficiency potential throughout fleet: 1 - 2%
    Theoretically, the amount of waste energy produced is sufficient to cover the entire operation of comfort functions (in a EMU in regional operation waste energy is over 30 % of the energy needed for traction). However, in practice only a part of this energy can be exploited. ORCs reach efficiencies of 10 to 20%. Given this and the fact that comfort functions account for about 20% of total energy demand for passenger train operation, the saving potential will be below 5 %.
  Other environmental impacts: ambivalent
    Negative impacts on the climate from the organic compounds used have to be assessed but are estimated to be small.
close main section Economic criteria
  close sub-section Vehicle - fix costs: high
    (no details available)
  Vehicle - running costs: significant reduction
    (no details available)
  Infrastructure - fix costs: none
    (no details available)
  Infrastructure - running costs: unchanged
    (no details available)
  Scale effects: high
    (no details available)
  Amortisation: > 5 years
    Based on present energy prices and initial investment for ORC technology, the payback of an application in EMU stock would be 20 years and more. The situation is somewhat more favourable for DMUs.
close main section Application outside railway sector
  close sub-section Status of development outside railway sector: in use
    Small scale ORCs have reached the commercial stage in the 1980s and 1990s.
  Time horizon for broad application outside railway sector: in 5 - 10 years
    (no details available)
  Expected technological development outside railway sector: highly dynamic
    (no details available)
  Market potential outside railway sector: medium
    (no details available)
close main section Overall rating
  close sub-section Overall potential: interesting
  Time horizon: long-term
    The use of the Organic Rankine Cycle is an interesting approach to the recovery of waste energy in MUs. In contrast to heat exchangers, ORC technology allows for a generation of power and thus for the use of waste energy for all comfort functions instead of heating only. Implementation in DMUs may become economically feasible in mid-term. In contrast, applications in EMUs are still far from being profitable. Nevertheless, given the energy efficiency potential, further progress in ORC technology should be followed closely.
References / Links:  europa.eu.int
Attachments:
Related projects:
Contact persons:
 date created: 2002-10-09
 
© UIC - International Union of Railways 2003