Engineering Magazine – June 2019

ENGINEERING JUNE 2019 37

COMBINED HEAT & POWER

Organic Rankine Cycle involves a closed system in which a ‘working fluid’

that need not be water absorbs thermal energy though a heat exchange

system before driving a turbine to generate power. Mike Farish reports

Italian job

F

or the last couple of years the

city of Brescia in northern Italy

has benefitted from more than

just the employment provided by

one of its major industrial enterprises

steelmaker ORI Martin. During

the winter months some 2,000

households in the city which nestles

close to the foot of the snow-capped

Alps are kept warm by a district

heating system powered powered by

steam piped recovered from flue gas

generated by an electric arc furnace

used in its manufacturing processes.

But then during the summer when

the southern European sunshine

makes that requirement superfluous

the heat is used instead to generate

electricity on-site that can serve the

needs of around 7,000 families. In

the first case some 11MW of thermal

power is involved and in the second

around 2.2MW of electric power.

Furthermore the whole system

prevents approximately 10,000 tonnes

of CO 2 emissions each year.

The system was set up as part of

a European project called Pitagoras

intended to exploit the potential for

industrial waste heat recovery. But in this

instance, the first of its kind anywhere

when it was initiated, the essential core

technology that generates electricity

during the summer is also of local origin

• a turbine system using the Organic
  Rankine Cycle (ORC) principle from
  technology supplier Turboden based in
  the same city. The essential point about
  ORC is that it involves a closed system
  in which a ‘working fluid’ that need not
  be water absorbs thermal energy though
  a heat exchange system before driving a
  turbine to generate power.

The company was set up in 1980

by Mario Gaia, at the time a professor

at the Politecnico di Milano who still

holds the post of honorary chairman.

Nearly two decades of research and

development passed until the company

installed its first working unit – a

300kW device fuelled by biomass in

Switzerland. Since then its installed

base has increased to over 360 units

with power ratings as high as 17MW.

It has also gone through two changes

of ownership – first in 2009 when the

majority holding was acquired by the

US United Technologies Corporation,

the second in 2013 when it was taken

over by the Japanese conglomerate

Mitsubishi Heavy Industries.

Nevertheless the new owners have

made a policy of allowing an Italian

management team to remain in place.

One of them is managing director

Roberto Bini. Straight away Bini makes

the point that though ORC is not

unique to Turboden that the company

does offer what he regards as a

distinctive degree of flexibility in the use

of the technology to its customers. One

of them is the range of working fluids

its machines can use. “We can say use