STEAM PLANT AND METHOD OF OPERATING THE SAME
The invention relates to a steam plant, a method of operating the same, and a method
of upgrading an existing steam plant.
5
In an lndustrlal and heatlng process utlllslng steam, steam Is generated In a boller and
is transferred through pipework at high temperature and pressure to various industrial
processes where the energy in the steam is utilised.
10 It is important to control the quality of the raw water fed to the boiler in order to prevent
undesirable effects from occurring within the steam plant. These undesirable effects
include corrosion of the metal components of the plant, such as pipework and valves,
and the reduction of heat transfer rates which can lead to overheating and the loss of
mechanical strength of components.
15
Water is referred to as being either "hard" or "soft"'. Hard water contains scale-forming
impurities while soft water contains little or none. Hardness is caused by the presence
of the mineral salts of calcium and magnesium and it is these minerals that encourage
the formation of scale. If hard water is supplied to the boiler then scaling of the heat
20 transfer surfaces will occur and this will reduce the heat transfer and efficiency of the
boiler. Further, if the water supplied to the boiler contains dissolved gases, particularly
oxygen, the corrosion of the boiler surfaces, pipework and other surfaces is likely to
occur. IT the pH value of the water Is too low, the acldlc solutlon wlll attack metal
surfaces, and if the pH value is too high and the water is alkaline, other problems such
25 as foaming may occur.
It is also desirable to prevent boiler water from being carried over from the boiler to the
steam system as this can result in the contamination of control valves and heat transfer
surfaces, and the restriction of steam trap orifices. Carryover is typically caused by
either "priming" or "foaming". Priming is the ejection of boiler water into the steam takeoff
and is generally due to either operating the boiler with too high a water level,
operating the boiler below its design pressure, or excessive steam demand. Foaming
is the formation of foam in the space between the water surface and the steam take-off
and is primarily due to a high-level of impurities in the boiler water.
As the boiler generates steam, any impurities which are in the boiler water and which
do not boil off with the steam will concentrate in the boiler water. As the amount of total
dissolved solids (TDS) become more and more concentrated, the steam bubbles tend
to become more stable, failing to burst as they reach the water surface of the boiler.
5 Eventually, a substantial part of the steam space in the boiler becomes filled with
bubbles and foam Is carrled over Into the maln part of the steam plant. It Is therefore
desirable to carefully control the amount of total dissolved solids (TDS) in the boiler
water. The TDS value of the boiler water is monitored using a sensor and water known
as blowdown water is discharged from the boiler to a blowdown vessel in order to
10 maintain the TDS value within acceptable limits. Conventional boilers may be operated
with the TDS in the range of 2000-3500 ppm. The blowdown water is mixed with
colder water in the blowdown vessel and is then discharged to a drain.
Table 1 below shows the technical and commonly used names of some typical
15 impurities in water, their chemical symbols, and their effects.
/ Name 1 Symbol I Common name I Effect
I I I
I 1 Calcium carbonate ( CaCOJ / Chalk, limestone / Soft scale
I
I I I
Table I
Gypsum, plaster of parie
Calcium bicarbonate
Calcium sulphate
Calcium chloride
Magnesium carbonate I MgC03
Magnesium sulphate
Magnesium bicarbonate
Sodium chloride
Sodium carbonate
Sodium bicarbonate
Sodium hydroxide
Sodium sulphate
Silicon dioxide
20 It is known to treat raw water by removing various impurities before providing it to the
i
Soft scale + GO2
Hard scale
Corrosion
Ca(HC03)2
CaS04
CaC12
/ Soft scale
boiler as feedwater so as to minimise the undesirable effects described above. For
MgSOd
Mg(HC0a)l
NaCl
Na2C03
NaHC03
NaOH
NazSOz
SiOz
example, if the water is too hard then soale forms in the boiler, and if the TDS value is
Magnesite
Epsom salts
Common salt
Washing soda or soda
Baking soda
Caustic soda
Glauber salts
Silica
Corrosion
Scale, corrosion
Electrolysis
Alkalinity
Priming, foaming
Alkalinity, embrittlement
Alkalinity
Hard scale
too high then the blowdown rate of the boiler must be increased in order to prevent the
TDS value in the boiler from becoming too high and leading to carryover.
The water treatment system of a steam plant typically comprises a filter unit, a softener
5 unit and a reverse osmosis unit and raw water is passed through these units
sequentially.
The filter unit is typically a carbon filter and acts to remove suspended solids from the
raw water. The filter must be periodically flushed in order to clean the filter and flush
10 away debris that has built up in the filter.
The softener unit acts to reduce the hardness of the filtered water and typically
comprises two softener vessels and a brine tank, Each softener vessel is provided with
a resin to which sodium ions are bonded. As the filtered water is passed over the
15 resin, the sodium ions bonded to the resin are displaced and exchanged for the
calcium and magnesium ions in the water, thus reducing the hardness of the water.
After a period of time, all of the sodium ions will have been displaced from the resin
and replaced with calcium and magnesium ions. Therefore, the softener vessel is
regenerated by flushing the resin with a strong solution of sodium chloride from the
20 brine tank. This causes the calcium and magnesium ions bonded to the resin to be
replaced with sodium ions. The softener vessel is then flushed with water so as to
remove the un-bonded calcium and magnesium ions from the softener vessel.
Typlcally, whllst one sortener vessel Is belng used, the other Is belng regenerated so
that water can be softened without interruption.
25
The reverse osmosis unit acts to reduce the TDS value of the softened water. The
reverse osmosis unit comprises a semi-permeable membrane provided between two
chambers. The softened water having a high TDS value is supplied to one of the
chambers and pressure is applied. The applied pressure causes pure water, having a
30 low TDS and known as permeate, to pass through the semi-permeable membrane to
the other chamber. Concentrate containing a high concentration of impurities, and
consequently having a high TDS value, is retained on the pressurized side of the semipermeable
membrane. The permeate is supplied to the boiler as feedwater via a
feedtank, and the concentrate is discharged to a drain. The softened water supplied to
35 the reverse osmosis unit may have a TDS value of 220 ppm and the permeate used as
feedwater may have a TDS value of 23 ppm.
As should be appreciated from the above, a steam plant requires substantial volumes
of water in order to operate. Specifically, raw water that is ultimately used to generate
steam, cold water that can be mixed with the hot blowdown water, water for the brine
5 tank of the softener unit, and flushing water for both the filter and the softener unit.
Water Is flnanclally an expenslve resource and contributes to a large proportlon of the
running costs of a steam plant. Further, a large proportion of this water is ultimately
discharged to a drain and water authorities typically levy a charge for this. Water is a
finite resource and demand on water supplies is increasing.
I0
Therefore, from both a financial and an environmental point of view it is desirable to
reduce the water consumption of a steam plant.
According to an aspect of the invention, there is provided a steam plant, comprising: a
15 boiler arranged to generate steam; a reverse osmosis unit having a RO inlet arranged
to receive inflow water and a permeate outlet in fluid communication with the boiler
through a permeate line, wherein in use the reverse osmosis unit receives inflow water
and generates permeate which is provided to the boiler through the permeate line; a
blowdown vessel in fluid communication with the boiler so as to receive hot blowdown
20 water from the boiler, and a blowdown vessel outlet which is in fluid communication
with the RO inlet through a blowdown return line, wherein in use the blowdown vessel
generates cooled blowdown water; and a flow controller having a temperature sensor
(or thermostat) arranged to monltor the temperature of the cooled blowdown water,
wherein in use, if the temperature of the cooled blowdown water is below a threshold
25 then the flow controller operates to direct the cooled blowdown water to the RO inlet.
By using coaled blowdown water from the blowdown vessel in the reverse osmosis
unit, less blowdown water is discharged from the steam plant to drain. Therefore, the
cost of disposing of the blowdown water from the steam plant may be reduced, thereby
30 reducing the operating costs of the steam plant and reducing the environmental impact
of the steam plant.
Further, the flow rate through the reverse osmosis unit and the temperature of the flow
through the reverse osmosis unit may be increased, thereby increasing the efficiency of
35 the reverse osmosis unit. This may allow the size of the reverse osmosis unit to be
reduced.
The threshold may be 42' C. The threshold may be between 30" C and 50' C, or
between 35 C and 45 C, or between 37' C and 42 " C.
The steam plant may further comprlse a softener unlt dlsposed In the blowdown return
5 line between the blowdown vessel and the reverse osmosis unit. This softener unit
acts to soften the cooled blowdown water from the blowdown vessel, before it is
provided to the RO inlet of the reverse osmosis unit.
The steam plant may further comprise a storage tank arranged to receive and
10 temporarily store cooled blowdown water, which may be received from the softener
unit.
In use, if the temperature of the cooled blowdown water is above a threshold then the
flow controller may operate to direct the cooled blowdown water to a drain. This
15 ensures that if the temperature of the cooled blowdown water is determined to be of a
temperature that would damage the semi-permeable membrane of the reverse osmosis
unit, the cooled blowdown water is provided to a drain instead, rather than being
provided to the RO inlet.
20 The steam plant may further comprise a heat exchanger, wherein in use, if the cooled
blowdown water Is above the threshold then the flow controller may operate to direct
the cooled blowdown water to the heat exchanger. The heat exchanger may be
arranged to pre-heat feedwater for the boiler. The heat exchanger allows the
temperature of the cooled blowdwn water to be further reduced to ensure that it is
25 below a threshold, for example 43' C, which is the maximum temperature at which it
can be discharged to drain. Also, useful heat from the cooled blowdown water may be
extracted by the heat exchanger, thereby improving the efficiency of the steam plant.
According to another aspect of the invention, there is provided a method of operating a
30 steam plant comprising: providing hot blowdown water from the boiler to a blowdown
vessel where it is mixed with colder water to generate cooled blowdown water:
determining the temperature of cooled blowdown water; and providing the cooled
blowdown water to the RO inlet of w reverse osmosis unit if the temperature of the
cooled blowdown water is below a threshold.
The method may further comprise passing the cooled blowdown water through a
softener unit before providing it to the reverse osmosis unit.
The method according may further comprise temporarily storing cooled blowdown
5 water from the softener unit in a storage tank before it is provided to the reverse
osmosls unlt.
The method may further comprise sending the cooled blowdown water to a drain if the
temperature of the cooled blowdown water is above a threshold.
10
The method may further comprise passing the cooled blowdown water through a heat
exchanger if the cooled blowdown water is above a threshold.
According to another aspect of the invention, there is provided a method of modifying
15 an existing steam plant comprising a boiler arranged to generate steam; a blowdown
vessel in fluid communication with the boiler so as to receive blowdown water from the
boiler and arranged to output cooled blowdown water from a blowdown vessel outlet;
and a reverse osmosis unit having a permeate outlet in fluid communication with the
boiler, the method comprising: fluidically connecting the blowdown vessel outlet with a
20 RO inlet of the reverse osmosis unit such that during use of the steam plant, cooled
blowdown water can be provided to the RO inlet.
The lnventlon may comprise any comblnatlon of the features and/or llmltatlons referred
to herein, except combinations of such features as are mutually exclusive.
25
Embodiments of the present invention will now be described, by way of example, with
reference to the accompanying Figure 1 which schematically shows part of a steam
plant.
30 Figure I schematically shows part of a steam plant 10 comprising a processing unit
12, a reverse osmosis unit 14, a feedtan k (hotwell) 16, a boiler 18, and a blowdown
vessel 20. In use, the processing unit 12 and reverse osmosis I 4 treat raw water
which is supplied to the boiler 18 via the feedtank 16 to generate steam. The steam
generated by the boiler 18 is transferred through pipework at high temperature and
35 pressure to various industrial processes where the energy in the steam is utilised (not
shown). At periodic intervals, blowdown water is discharged from the boiler 18 to the
blowdown vessel 20 where it is cooled and discharged. Although not shown in the
schematic of Figure 1, various pumps, valves and sensors may be provided to control
the flow of water and steam around the system.
5 The processing unit 12 has an inlet 22 for receiving raw water, and an outlet 24 for
dlscharglng treated water. The processlng unlt 12 comprises a fllter 26, In the form of a
carbon filter, and a softener unit 28 that are fluidically connected in series. The filter 26
is arranged to remove suspended solids from the raw water and the softener unit 28 is
arranged to reduce the hardness of the water. The filter 26 is also provided with a
10 flushing water line 36 and a drain line 38. The softener unit 28 includes first and
second softener vessels 30, 32, each containing a resin to which sodium ions are
bonded, and a brine tank 34 for regenerating the softener vessels 30, 32. The softener
unit 28 is also provided with control valves that allow filtered water to flow through one
softener vessel 30, 32 whilst the other softener vessel 30, 32 is being regenerated.
15 This allows the softener unit 28 to be continuously used. The softener unit 28 is also
provided with a brine tank fill line 40, a flushing water line 42, and drain lines 44.
Although it has been described that there is a filter 26 and a softener unit, in other
embodiments only one may be present. For example, if the raw water is soft water, on
20 only a filter may be provided. Further, additional water treatment devices or units may
be incorporated into the processing unit 12 as necessary.
The outlet 24 of the processlng unlt 12 Is fluldlcally connected to the RO Inlet 46 of the
reverse osmosis unit 14 with an inflow water line 48. This allows raw water treated by
25 the processing unit 12 to be supplied to the reverse osmosis unit 14. The reverse
osmosis unit 14 is arranged to reduce the total dissolved solids (TDS) value of treated
inflow water provided from the processing unit 12. As schematically shown in Figure 1,
the reverse osmosis unit 14 comprises an inflow chamber 50 and a permeate chamber
52 separated by a semi-permeable membrane 54. The RO inlet 46 opens into the
30 inflow chamber 50 which is further provided with a concentrate outlet 56 from which
concentrate, having a high TDS value, can be discharged. The permeate chamber 52
is provided with a permeate outlet 58 from which permeate, having a low TDS value,
can be discharged. In use, the inflow chamber 50 is maintained under pressure and
inflow water is provided to this chamber through the RO inlet 46. Pure water, known as
35 permeate and low in impurities, passes through the membrane 54 where it can be
discharged from the permeate outlet 58, whilst concentrate, high in impurities, can be
drawn from the concentrate outlet 56.
The permeate outlet 58 of the reverse osmosis unit 14 is connected to a permeate line
5 00 which is configured to supply the permeate generated by the reverse osmosis unit
14 to the feedtank 16. In turn, the feedtank 16 Is fluldlcally connected to the boller 18
by a feedwater supply line 62 so that feedwater in the feedtank 16 can be supplied to
the boiler 18. The boiler 62 is configured to generate steam from the feedwater and is
provided with a steam supply line 64 for delivering and transferring the steam to
10 various processes (not shown) within the steam plant.
The boiler 18 is also provided with a blowdown outlet 66 towards the bottom of the
boiler to which a blowdown line 68 is attached. The blowdown line 68 connects the
boiler 18 to the blowdown vessel 20 such that hot blowdown water can be discharged
15 from the boiler 18 to the blowdown vessel 20. The blowdown vessel 20 is further
provided with a blowdown line 70 which allows cooled blowdown water to be provided
from the blowdown vessel 20 through a blowdawn vessel outlet 84.
In addition to the components described above, the steam plant 10 further comprises a
20 flow controller 86 that is operable to either direct cooled blowdown water to a drain, or
to the RO inlet 46 of the reverse osmosis unit 14. The flow controller 86 comprises an
inlet 88, a temperature sensor 90, a three-ay valve 92, a return outlet 94 and a drain
outlet 96. The Inlet 88 of the flow controller 86 Is connected to the blowdown llne 70 so
that cooled blowdown water can be provided to the flow controller 86. The temperature
25 sensor 90 is configured to monitor the temperature of the cooled blowdown water and
the valve 92 is configured to direct the cooled blowdown water to either the return
outlet 94 or the drain outlet 96 depending on the temperature.
The return outlet 94 of the flow controller 86 is fluidically connected to the RO inlet 46
30 by a blowdown return line 98 and a softener unit 100 and storage tank 102 are
connected in series in the blowdown return line 98 between the flow controller 86 and
the RO inlet 46. This allows cooled blowdown water to be provided to the reverse
osmosis unit 14.
35 The softener unit 100 is similar to the softener unit 28 of the processing unit 12 and
comprises two softener vessels 104 and 106 and a brine tank (not shown). The
softener unit 100 operates in substantially the same way as softener unit 28 of the
processing unit 12 to reduce the hardness of cooled blowdown water passing through
it. It can also be regenerated from the brine tank (not shown) in the same manner.
The storage tank 102 can temporarily store (softened) cooled blowdown water before it
5 is provided to the reverse osmosis unit 14.
The drain outlet 96 of the flow controller 86 is connected to a drain line 108 and a heat
exchanger 1 10 is disposed in the drain line 108. The heat exchanger 1 I 0 is arranged
to extract useful heat form the cooled blowdown water. The heat exchanger 110 may
10 be used to pre-heat boiler feedwater, for example, and as such may be disposed in the
permeate line 40 such that it can pre-heat the permeate from the reverse osmosis unit
14 before it is passed to the feedtank 16.
In use, raw water is provided to the inlet 22 of the processing vessel 12 and is passed
15 through the carbon filter 26 to remove any suspended particulate in the water. The
filtered water is then passed through the softener unit 28 to reduce the hardness of the
water. The softener unit 28 comprises two softener vessels 30, 32 and the filtered
water is passed through one of these vessels 30, 32 whilst the other vessel is being
regenerated (as will be explained below). As the filtered water is passed over the resin
20 in the softener vessel 30, 32, the magnesium or calcium ions in the water displace and
replace the sodium ions bonded to the resin. This therefore reduces the hardness of
the water by replacing the magnesium and calcium ions with sodium ions. The filtered
and softened water Is then fed to the RO Inlet 46 of the reverse osmosls unlt 14 as
treated inflow water through the inflow water line 48. The treated inflow water enters
25 the inflow chamber 50 of the reverse osmosis unit 14 and is subjected to a high
pressure. Permeate that is low in impurities, and which consequently has a low TDS
value, passes through the membrane 54 to the permeate chamber 52, whilst
concentrate high in impurities, and which consequently has a high TDS value, is
retained in the inflow chamber 50. The concentrate is drawn through the concentrate
30 outlet 56 of the reverse osmosis unit 14 at a known rate. The permeate, which is
relatively soft and which has a relatively low TDS value, is fed to the feedtank 16
through the permeate line 60. Various chemicals are supplied to the feedwater in the
feedtank 16. Boiler feedwater is fed to the boiler 18 through the feedwater supply line
62 where it is heated to generate steam. The steam is transferred to various industrial
35 processes in the steam plant 10 through the steam supply line 64.
The impurities in the boiler water within the boiler 18 concentrate as they do not boil off
and the TDS value of the boiler water therefore increases. As previously discussed, if
the TDS value is too high then foam forms within the boiler which may be carried over
into the remainder of the steam system. Therefore, at periodic intervals, blowdown
5 water having a high TDS value is discharged from the boiler 18 through the blowdown
outlet 66 to the blowdown vessel 20 via the blowdown water line 68. The temperature
of the blowdown water is too high for it to be immediately discharged to a drain.
Therefore, the hot blowdown water supplied to the blowdown vessel 20 is mixed with
cooler water within the blowdown vessel 20 before it is output from the blowdown
10 vessel 20 through blowdown vessel outlet 84.
In this embodiment, the cooled blowdown water is output through the blowdown vessel
outlet 84 and is supplied to the flow controller 86. The temperature sensor 90 of the
flow controller 86 monitors the temperature of the cooled blowdown water and the flow
15 controller 86 determines if it is above or below a threshold, which in this embodiment is
If the temperature of the cooled blowdown water is below the threshold, the flow
controller 86 operates the valve 92 so as to direct the cooled blowdown water to the
RO inlet 46 through the blowdown return line 98. Before reaching the reverse osmosis
unit 14, the cooled blowdown water passes through one of the softener vessels 104,
I06 of the softener unit 100. The softened cooled blowdown water is then passed to
the storage tank 102, where It Is temporarlly stored, before It Is provlded to the RO Inlet
46.
The threshold temperature of the flow controller 86 is set such that if the cooled
blowdown water is directed to the RO inlet 46, by the time it reaches the reverse
osmosis unit 14, it is below a temperature that would damage the membrane 54 of the
reverse osmosis unit 1 4. For example, the membrane 54 may be able to withstand
temperatures of up to 37'C. If this is the case, the threshold of the flow controller 86
must be set such that by the time the cooled blowdown water reaches the reverse
osmosis unit 14, it has a temperature of 37'C or less. If the thermal loss of the water
between the flow controller 86 and the reverse osmosis unit 14 is expected to be 5'C,
then the threshold of the flow controller 86 can be set at 42' C. However, if the return
35 line 98 is well insulated, the threshold may have to be reduced.
The cooled blowdown water provided to the RO inlet 46 will be of a higher temperature
than the inflow water provided through the inflow water line 48 from the processing unit
12. The cooled blowdown water will therefore act to increase the temperature of the
water in the reverse osmosis unit 14. This increase in temperature causes the reverse
5 osmosis unit 14 to function more efficiently and may enable a smaller reverse osmosis
unlt to be used. Further, by supplying the cooled blowdown water to the RO Inlet 46,
the flow rate of the water through the reverse osmosis unit 14 will be increased. This
also increases the efficiency of the reverse osmosis unit 14. Therefore, the use of
cooled blowdown water in the reverse osmosis unit 14 provides improvements in the
10 efficiency of the operation of the reverse osmosis unit and ensures that less blowdown
water is discharged to drain, thereby at least reducing the cost of disposing of the
blowdown water.
If the temperature of the cooled blowdown water is above the threshold, the flow
15 controller 86 operates the valve 92 so as to direct the cooled blowdown water to the
heat exchanger 1 I0 and then to drain through the drain line 108. The heat exchanger
I 1 0 acts to further reduce the temperature of the cooled blowdown water and extracts
useful energy that may used to pre-heat the feedwater. The heat exchanger 110 may
act to futther cool the blowdown water so that before it is discharged to drain, it is
20 below a legal limit (e.g. 43' C). If the heat exchanger 110 is used to pre-heat
feedwater, this may increase the efficiency of the boiler 18.
Although it has been described that the threshold is 4232, it should be appreciated that
any suitable threshold temperature may be set.
25
Although not shown in Figure I , an additional flow controller may be provided in the
blowdown return line 98 before RO inlet 46. This additional flow controller may monitor
the temperature of the cooled blowdown water in the btowdown return line 98 and if the
temperature is above 37' C, the water may be discharged to a drain, in order to protect
30 the semi-permeable membrane of the reverse osmosis unit 14.
Although it has been described that the flow controller 86 comprises a temperature
sensor 90, it should be appreciated that the temperature sensor may be a thermostat
or a bi-metallic valve or any other suitable component for monitoring the temperature of
35 the cooled blowdown water and controlling the opening or closing of a valve.
Some of the components of the steam plant 10 described above with reference to
Figure 1 may already be present in an existing steam plant; although configured
entirely differently. Therefore, it may be possible to upgrade or modify an existing
steam plant 10 to use cooled blowdown water from the blowdown vessel 20 in other
5 parts of the plant 10, thereby making the existing steam plant more efficient and
envlronrnentally trlendly.
Where it has been described that a particular component is in fluid communication with
another component by a particular line, it should be appreciated that this may be
10 directly, or indirectly, and other components may be disposed in the fluid path between
the two. For example, in the above described embodiment the reverse osmosis unit 14
is in fluid communication with the boiler 18 through the permeate line 60. However, a
feedtank 16 is disposed in the fluid path between the two, and a further fluid line 62
from the feedtank 16 to the boiler 18 is provided.

13
CLAIMS:
1. A steam plant, comprising:
a boiler arranged to generate steam;
5 a reverse osmosis unit having a RO inlet arranged to receive inflow water and a
permeate outlet In fluid communication with the boiler through a permeate line, wherein
in use the reverse osmosis unit receives inflow water and generates permeate which is
provided to the boiler through the permeate line;
a blowdown vessel in fluid communication with the boiler so as to receive hot
10 blowdown water from the boiler, and a blowdown vessel outlet which is in fluid
communication with the RO inlet through a blowdown return line, wherein in use the
blowdown vessel generates cooled blowdown water; and
a flow controller having a temperature sensor arranged to monitor the
temperature of the cooled blowdown water, wherein in use, if the temperature of the
15 cooled blowdown water is below a threshold then the flow controller operates to direct
the cooled blowdown water to the RO inlet.
2. A steam plant according to claim 1, further comprising a softener unit disposed
in the blowdown roturn line between the blowdown vessel and the reverse osmosis
20 unit.
3. A steam plant according to claim 2, further comprising a storage tank arranged to
receive and temporarily store cooled blowdown water from the softener unit.
25 4. A steam plant according to any preceding claim, wherein in use, if the
temperature of the cooled blowdown water is above a threshold then the flow controller
operates to direct the cooled blowdown water to a drain.
5. A steam plant according to claim 4, further comprising a heat exchanger, wherein
30 in use. If the cooled blowdown water is above the threshold then the flow controller
operates to direct the cooled blowdown water to the heat exchanger.
6. A method of operating a steam plant comprising:
providing hot blowdown vi/ater from a boiler to a blowdown vessel where it is
35 mixed with colder v\^ter to generate cooled blowdown water;
determining the temperature of cooled blowdown water; and
14
providing the cooled blowdown water to the RO inlet of a reverse osmosis unit if
the temperature of the cooled blowdown water is below a threshold.
7. A method according to claim 6, further comprising:
5 passing the cooled blowdown water through a softener unit before providing it to
the reverse osmosis unit.
8. A method according to claim 7, further comprising:
temporarily storing cooled blowdown water from the softener unit in a storage
10 tank before it is provided to the reverse osmosis unit.
9. A method according to any of claims 6-8, further comprising:
sending the cooled blowdown water to a drain if the temperature of the cooled
blowdown water is above a threshold.
15
10. A method according to claim 9, further comprising:
passing the cooled blowdown water through a heat exchanger if the cooled
blowdown water is above a threshold.
20 11. A method of modifying an existing steam plant comprising a boiler arranged to
generate steam; a blowdown vessel in fluid communication with the boiler so as to
receive blowdown water from the boiler and arranged to output cooled blowdown water
from a blowdown vessel outlet; and a reverse osmosis unit having a permeate outlet In
fluid communication with the boiler, the method comprising:
25 fluidically connecting the blowdown vessel outlet with a RO inlet of the reverse
osmosis unit such that during use of the steam plant, cooled blowdown water can be
provided to the RO inlet.
12. A method according to claim 11, wherein, during use of the steam plant, if the
30 temperature of the cooled blowdown water is below a threshold the cooled blowdown
water is provided to the reverse osmosis unit.