Rankine Engine

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MICRO CHP
MICRO CHP
the big picture
By Jeremy Harrison
Photo book

 

Stirling Engine | Rankine Engine

The Rankine cycle, like the Stirling cycle is an external combustion cycle; the combustion process is external to the cylinder containing the working gas.  The Rankine cycle is characterised by the working gas undergoing a phase change (from liquid to gas) which can be utilised to achieve high power densities.  The most familiar Rankine engine is the steam engine in which water is boiled by an external heat source, expands and exerts pressure on a piston or turbine rotor and hence does useful work. 

A number of the products below make use of this concept.  However, one of them (the Energetix Genlec) is an organic Rankine engine which uses an organic fluid (a refrigerant) and operates at temperatures and pressures much closer to conventional heating and refrigeration appliances.  This has the significant advantage of allowing the use of conventional, mass produced components and eliminates many of the technical challenges of steam engines. However, the relatively low temperature differential between hot and cold stages of the cycle, limit the Carnot (theoretical) efficiency; in practice efficiencies in single digits are commonplace. 

For further discussion of the relative merits of these engine types see section on papers.

 GENLEC  CLIMATE ENERGY  OTAG  ENGINION  COGEN MICRO

The Energetix Genlec unit, is currently the only truly wall-mounted micro CHP anywhere in the world.

In effect, it is a refrigeration unit working in reverse, using the expanding working gas to power a scroll expander (compressor).

In theory, the ORC (Organic Rankine Cycle) design can be constructed using off the shelf components for the majority of the appliance, leading to low production costs.  However, this product now makes use of bespoke components intended to optimise the performance.

It's relatively low electrical efficiency means that it produces less electricity for a given heat load than some other units, although this should be compensated for by the expected low cost. 

In 2012, Energetix established an energy supply company, Flow Energy, which offers a package including gas and electricity supply as well as the micro CHP unit. 

In July 2013, having gained 40,000 customers, the energy supply company ceased customer acquisition activities to focus on product commercialisation.

The Climate Energy unit also uses a scroll expander, with benefits of simplicity and potentially low manufacturing cost.

However, the use of steam as a working gas raises technical challenges regarding reliability and safety. Against this, the developers claim that the thermodynamic properties of steam permit high heat transfer rates (resulting in compact heat exchangers), tolerate leakage and have no inherent material risks.  It is also non-toxic and thermally stable which, combined with the zero cost make this a competitive technology.

Climate Energy LLC have also launched the Honda ICE based unit in the USA and it is uncertain as to whether they intend to continue development of their external combustion unit.

Illustration shows the Honda Ecowill unit.

Otag have developed a steam powered unit, utilising a single cylinder with two opposing pistons.  An integral linear generator converts the reciprocating motion directly into electrical energy with variable output 3 phase output.

Further details including an excellent animation of the cycle are shown on the Otag website.

Although originally intended to be wood-pellet fired, the unit is currently available in Germany as a gas-fired product only.

The company website provides an illustration of the economic benefits, including tax rebates, which deliver a net benefit of around 1000 annually.

The product has been branded the "Lion Powerblock".

The Enginion Steamcell unit was initially developed as a small commercial unit with a power output of around 50kWe.  It then evolved into  a unit more appropriate for small apartments and hotels; the target power output of ~5kWe made it unsuitable for domestic installations.

Enginion was placed in receivership during late 2005.

The Cogen Micro unit, developed by an engineering consultancy (Applidyne) in Australia is unusual in that it uses reciprocating (single piston) technology.

Historically the very low efficiencies achievable at reasonable temperatures and pressures have not been attractive.

However, novel injector design has enhanced the performance of prototype units which may lead to an ultimately viable product.

In 2011 Cogen Micro appear to have abandoned this novel design in favour of an Organic Rankine Cycle design similar to that from Energetix, the principle difference being that a reciprocating rather than scroll expander is used.

Electrical output

1kWe

Electrical output

3kWe

Electrical output

0.3-2.0kWe

Electrical output

5kWe

Electrical output

2.5kWe

Thermal output

10kWt (modulating)

Thermal output

30kWt

Thermal output

3.5-16kWt

Thermal output

Thermal output

12kWt

Application

Individual family homes

Application

Homes & small commercial

Application

Homes & small commercial

Application

Small commercial

Application

Homes & small commercial

Availability

Laboratory trials 2011

Product sales 2014?

Availability

?

Availability

2006

Availability

Availability

 

Page updated 7th February 2014
 

MICRO CHP
MICRO CHP
the big picture
By Jeremy Harrison
Photo book

 

 

Contact : info@microchap.info

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This site was (partially) last updated on 12th August 2017 Jeremy Harrison