1
Assess your entire process from
obtaining feedstock to exporting
digestate. The first step of any
optimisation process is to understand
what you are (or will be) doing.
Analyse each step to see where
wastage may occur and how it could
be improved.
For example, could you pre-warm
feedstock before it enters the
digester or, if you are already doing
so, could you re-use heat already
generated elsewhere? Does the
proportion of heat to electricity
generated match your requirements?
If you are still planning,
would another unit suit your needs
better? If you are already operating
your plant, could you re-use any heat
which may be wasted? Also look at
your digestate - could you add value
to it, perhaps through pasteurisation
or concentration?
4
Aim for continuous processing.
Having to stop and start parts of your
plant can be inefficient, even if the
process is automated.
Using multi-tank pasteurisation or
digestate concentration systems
means that while one tank is being
heat treated, the other/s can be filling
or emptying, ensuring that the rest of
the AD process is not interrupted.
On top of this, HRS multi-tank
systems use four level temperature
probes in each tank, three in the
bottom of each tank and one in the
top – so that the tanks can be filled to
half capacities should the demand or
flow drop off, allowing for continuous
and flexible production of digestate.
2
Maximise the efficiency of all
processes, from energy generation
to heat exchange. Check the
efficiencies of all processes,
whether in terms of thermal
transfer, electrical output or gas
generation. Keeping equipment,
particularly
heat
exchange
surfaces, clean and maintained will
help it to operate at its maximum
efficiency.
When specifying or researching
equipment, remember that over
the operational life of a plant, the
effects of even a small difference
in overall efficiency could be
considerable. For example, a 0.25%
increase in the electrical efficiency
of a 500 kW CHP unit could be
worth more than £7,000 over the
life of a plant at current wholesale
prices.
Likewise, reducing the volume of
digestate produced by the plant
may create other efficiencies, such
as reducing the amount of storage
required (reducing capital costs) or
transport requirements (lowering
operating costs).
3
Re-use heat which would otherwise
be wasted. It may not seem obvious
at first, but any large quantity of heat
has a use, including the heat given off
by radiators (such as the cooling loop
of a CHP engine), heat exchangers or
other parts of the process.
If you don’t already pre-heat your
feedstock, doing so may increase
the thermal efficiency of the digester, while if you do already pre-heat,
using heat from elsewhere in the
process will be cheaper (and greener) than creating heat just for this
purpose. Likewise, pasteurising the
digestate using recycled heat circumvents the need to install an additional
heat source such as a biomass boiler,
which could add hundreds of thousands of pounds to a project.
Many pasteurisation systems on the
market simply dump the heat used.
HRS systems recycle the heat, making
them up-to 70% more efficient than a
typical ‘heat jacket’ type pasteuriser
and allowing this heat to be reused,
either elsewhere in the process (for
digestate concentration for example)
or exported to other processes.
Carolyn Wheeler, Sales &
Marketing Coordinator
HRS House, 10-12 Caxton Way,
Watford Business Park, Watford,
Herts, WD18 8JY
Tel: 01923 232 335
Direct Email:
[email protected]
Email for publications:
[email protected]
Without these probes, the system
would be put on a ‘go slow’ in order to
wait for the tanks to fill, which would
require more heat as well as incurring
the expense of slowing production
or shutting the system down and
restarting.
www.hrs-heatexchangers.com