38 JUNE 2019 ENGINEERINGCOMBINED HEAT & POWER
more fluids than anybody else because
we we use about ten different fluids,”
he confirms.
Those fluids, Bini adds, fall into three
distinct categories. The first is those that
are silicone-based and are particularly
appropriate for high-temperature
operations where, for instance, the
operating temperature of the turbine
may be in the range 250-320degC – a
working fluid of this type is used in the
ORC system in use at ORI Martin.
The second is hydrocarbons which can
operate over a range of 100-300degC.
A third comprises refrigerants which
operate over a range of 100-250degC.
As he concedes there is obviously a fair
degree of overlap in the temperature
ranges involved and so other factors
are likely to come into play when the
choice of working fluid is made. One
he mentions is safety – an example is
that a refrigerant was chosen for an
urban application in Austria in close
proximity to domestic accommodation,
he says, because it is non-flammable
An important implication of this is
that the company can supply machines
that work with particular efficiency
when the initial heat source may only
be at a quite low temperature – say the
150degC typical of geothermal energy.
Nevertheless it is still the case that
even ten working fluids is a relatively
small proportion of the total number
of possible options. Around a hundred
different formulations have been
identified as possible ORC workingfluids, says Bini, though he indicates
that the formal literature on the
subject is not very extensive. As such
the company works closely with the
University of Brescia to investigate the
properties of possible fluids not least
their thermal stability.
Meanwhile another distinction the
company can claim, says Bini, is simply
the fact that it has more installations
worldwide than any other supplier of
ORC machines that use biomass as
the initial fuel source. Over 260 of the
300-plus installations the company has
are fuelled in this way. Interestingly
he adds that a current area of
development for the company is to find
a way to increase the usual operating
temperature of biomass-fuelled
installations from around 300degC to
400degC. That will, he adds, involve
the development of more advancedhydrocarbon working fluids.
In fact, though, as Bini confirms, a
400degC operating temperature is the
ultimate target of a product concept
the company has rencently introduced
called Steam and Power. Its distinctive
feature, he indicates, is that it can
generate steam in a greater proportion
than other types of cogeneration
equipment. This machine is, he
continues, rather unusual in that in
its initial version it is intended for
use with natural gas as a fuel – a
material not normally used in an ORC
context – with the biomass-fuelled
version scheduled for introduction in- The already available machine
operates at around 360degC and
so in that respect does get right to
the upper limit of what is currently
achievable. The working fluid in this
case, he says, is an existing ‘thermal
oil’ that Turboden has adopted for use
in this application. “It was not specially
developed,” he states.
As with the ORI Martin installation the
first application of this technology has
also taken place in Brescia.
Meanwhile the use of Turboden’s
ORC technology to generate combined
heat and power from the waste heat
of steel manufacture pioneered on
its home ground has now started to
spread further afield not just in Italy or
even Europe but globally.
http://www.turboden.com