There are various issues that can affect the efficiency of hot
water and steam boiler systems, as Mark Bosley, business
support divisional manager at Purite, explains

Boilers can be expensive to run,
especially when the levels of
impurities in the feedwater are not
taken into consideration or equipment not
specified correctly to control them in the
original design. Operating and maintenance
costs can be significantly reduced by pretreating
boiler feed water using some form
of water treatment or chemical dosing, but
to make the right specifications for your
system you need to understand the different
issues that can affect boiler efficiency
whether they be for steam or hot water
generation.

Low pressure boilers are generally used
for supplying hot water typically for heating
and it is these systems which are generally
supported by ion-exchange softeners or
chemical dosing systems.

All sources of water
contain impurities which
are harmful to boilers.

Common failures are due
to the effects of scaling,
corrosion and the build
up of deposits or sludge.

Essentially, a low
pressure boiler system is
similar to a domestic
kettle, mains water is
heated in tubes that pass
through the shell of the
boiler furnace. Any
hardness in the water –
the result of rainwater
coming into contact
with chalk – will cause
scaling of these boiler
tubes, which coud lead to
catastrophic boiler failure and,
ultimately, costly maintenance
or replacement. To remove hardness, water
softening is applied, typically involving the
use of an ion-exchange water softener to
exchange the hardness-forming calcium and
magnesium compounds with soluble
sodium equivalents.

The effects of corrosion can take longer to
manifest themselves. For corrosion to occur,
dissolved oxygen must be present, eliminating
this by dosing an oxygen scavenger is a cost
effective measure.

For boilers that run at high pressures and
are used to generate steam for power
generation, for example, a far greater water
purity above that of softened water is
required. Water must be ‘ultra-pure’ in terms
of certain critical impurities in order not to
form deposits on the blades of the perfectly
balanced turbines. In particular, the level of
silica is a major concern in applications such
as these and its presence may need to be
limited to as little as 10 or 20ppb. Despite
these tough challenges, high pressure
systems can be supported by reverse osmosis
water purification technology forming the
core of the treatment process.

Reverse osmosis water purification
systems are increasingly being used across
many industries to provide exceptionally
high levels of water purity. In a reverse
osmosis system, pressurised feed water is
passed through specialised semi-permeable
membranes to remove inorganic ions and
dissolved organic contaminants. The latest
membrane elements used in reverse osmosis
systems provide high levels of flow at lower
operating pressures and their performance
not only results in close on 100% purity but
cuts the cost of purification since pump
speeds, and thus energy demand, can be
significantly lowered. Variable speed drives
for purification units can cut costs yet again,
as they enable the speed of each unit to be
matched exactly to the output demands of
the water treatment system.

To maximise the performance and
longevity of the reverse osmosis system, it is
necessary to consider pre-treatment; in fact,
larger or high volume reverse osmosis
systems often include a pre-treatment
package designed to meet the characteristics
of the feed-water. In essence, the
pre-treatment stage is designed
to maximise the operating life
of the reverse osmosis
membranes by removing
contaminants that might
otherwise foul, degrade or scale
the membranes.

The effectiveness of a reverse
osmosis membrane can be
severely compromised by the
accumulation of scale, organic
contamination or biofilm and
to fully optimise equipment,
minimise running costs and
extend operating life, the
reverse osmosis system needs
to be regularly cleaned. The period between
cleans will depend on factors, such as
incoming feed-water quality and the pretreatment
used. However, with routine
cleaning and maintenance, a reverse osmosis
system will deliver consistent levels of
performance, efficiency and reliability,
preventing unexpected downtime and
component failures.