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To ensure the proper operation of steam generation systems,it is essential that the purity of the boiler feed water is high.

High quality feed water will reduce the use of boiler

chemicals because of less frequent blowdown requirements

(reducing blowdown frequency by as much as a factor of ten).

Lower blowdown frequency lowers fuel costs. Furthermore, scale

build-up is reduced because there are less impurities in the boiler

feed water to foul heat transfer surfaces. The lower concentration

of impurities also reduces corrosion rates in the boiler. When a

boiler is used to run a steam turbine, blade erosion is less likely to

occur because of the high quality of steam generated.

The use of reverse osmosis (RO) in feed water purification

systems can cuts chemical costs by reducing the frequency of ionexchange regeneration. A complete system, which includes RO

and ion exchange, typically produces a more cost effective system

when compared to systems that do not use RO. However,

conventional RO systems require pretreatment units, which

obviously adds to the total cost of the system.

Silicate and colloidal deposits decrease boiler efficiency and

also cause premature failure of turbines. Ultrafiltration (UF) can

remove more than 99% of colloidal silica, as well as precipitatediron and aluminum. The reduction in particulate matter,

suspended solids and total organic carbon (TOC) also enhance

turbine and boiler efficiency. However, the use of conventional

membrane technologies can suffer from substantial membrane

fouling problems.

 VSEP Membrane System

Technological advances in membrane filtration systems have

created an opportunity for industrial boiler and steam power

plants to effectively treat boiler feed water streams. The

Vibratory Shear Enhanced Processing technology or VSEP

®

makes it possible to filter influent water, without the fouling

problems exhibited by conventional membrane systems. The

VSEP membrane system can significantly reduce total dissolved

solids (TDS), total suspended solids (TSS), total organic carbon

(TOC), colour bodies, silica and hardness from influent streams

originating from city water, well water, and river/surface waters,

and therefore minimize treatment cost.

The VSEP treatment system can use UF, nanofiltration

(NF) or RO membrane modules to generate a permeate

stream that meets the quality criteris for boiler feed water,

e.g. concentrations of suspended and dissolved solids, silica

and hardness. After final polishing with ion exchange

resins, the clear permeate can be used as boiler feed water.

In summary, the VSEP treatment system can be used to

treat boiler feed water with only minor final polishing by

ion exchange resins. VSEP will eliminate pretreatment

requirements and can substantially reduce chemical usage

for regeneration, and therefore reduce disposal of spent

regenerant and the associated costs.

Process Conditions

The influent water to a power plant can come from a variety

of sources, including groundwater well (aquifer), surface

water or a municipality, so it has to be treated to meet thequality requirements for boiler feed water.

For boiler feed water treatment, depending on its

requirements, a number of processes can be used,

including chemical treatment/lime softening, dual media

28 June 2003 ISSN 0015-1882/03 © 2003 Elsevier Ltd. All rights reserved

Feed Water Treatment forIndustrial Boilers & Power Plants

In steam generation systems, ensuring the quality of the boiler feed water is essential for successful unit operation. Power plants traditionally 

employ a multi-step process to remove impurities from the influent water.

Belwo, New Logic Research Inc, USA, explains why its VSEP technology,fitted with NF or RO membrane modules, is a commercially viable 

alternative to exisitng boiler feed water treatment processes.

featurearticle

City water

VSEPtreatmentsystem

Chemical injection(opional)

Concentrateto disposal

Ion exchangepolishing units

Boilers

Posttreatment filter

Supply pump

Storage tank withsterile vent filter

Figure 1: A single VSEP membrane system can replacea multi-stage pretreatment for boiler feed water.

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filtration, carbon

adsorption,

conventional RO

membranes and final

ion exchange resin

polishing. However,

significant waste is

generated from these

unit operations,

including spent carbon

and spent regenerating

chemicals from the ion

exchange resins.

To avoid scale in the

boilers, power plants

normally utilize a

multi-step process to

remove the hardness of 

the incoming water, i.e.chemical treatment or

ion exchange, as well as

other less advanced

methods, such as multi-

media filtration. These

multi-step processes can be replaced by a single pass VSEP

system, which will purify the influent in one step.

A process schematic for the treatment of boiler feed water

using a VSEP treatment system is presented in Figure 1. This

system can use either NF or RO membrane filtration system to

replace the entire pretreatment step that would be usually

required, i.e. lime or cation softening, dual media filters, carbonadsorbers, and conventional RO units. City water can be treated

in a single step VSEP treatment system followed by a final ion

exchange polishing unit. The treated boiler feed water can then

be fed to the boiler via a supply pump.

Boiler Feed Water Treatment

Figure 2 is a process block flow diagram, showing the integration

of VSEP systens into a boiler feed water treatment process at an

industrial manufacturing facility. The city water is preheated in

the Stage I heat exchanger, and then further heated with a

steam-heated exchanger to a temperature of 42 °C. The higher

feed temperature improves permeate flux through the VSEP

treatment unit and provides the energy drive for the first

exchanger. The preheated water is introduced into the

equalization tank, where sulfuric acid can be added for pH

adjustment. Other chemicals, such as alum and polymer, can

also be injected at this point to help coagulation. The

equalization tank effluent is then transferred to the feed storage

tank where it is fed to the VSEP units at a rate of 473 litres/min.

Two industrial scale VSEP units process the preheated city water.

VSEP generates a permeate stream of approximately

380 litres/min, which is sent to the heat recovery exchanger and

then stored in the treated water tank prior to final polishing by

ion exchange. A concentrated waste stream is generated at a flowrate of 95 litres/min, which is routed to the holding ponds and

then the sewer.

Two industrial VSEP treatment units are used. The raw city

water has a concentration of 160 to 240 mg/l of hardness,

10 mg/l of silica, and 510 µS of conductivity. The permeate

concentration is reduced to <15 mg/l of hardness, <1 mg/ l of 

silica, and ~10 µS of conductivity, all well below the designed

water quality limits.

Conclusions

Using a NF or RO module in the VSEP system is a

commercially viable option for the treatment of boiler feed

water at industrial boilers and power plants. Nearly 80% of the

influent water is recovered as treated water suitable for final

polishing at a boiler facility, while less than 20% is disposed as

concentrate.

Membrane selection is based on material compatibility, flux

rates (capacity) and concentration requirements (hardness, silica,

TDS, conductivity). In this example, the hardness reduction is

over 90% and TDS and conductivity are also reduced by a

similar amount.

New Logic Research has successfully installed VSEP

separation technology into many industrial processes. The

industrial boilers and power plants, as well as the cogeneration

industries’ effort to meet system performance criteria and

environmental regulations can be helped by combining

membrane filtration with VSEP technology.

The development towards applications for industrial boilers

and power plants, along with the availability of new membrane

materials and VSEP technology, make it possible to treat the

more difficult streams with technically and economically

successful results.

Contact:

New Logic Research Inc,1295 Sixty Seventh Street,

Emeryville, CA 94608, USA.Tel: +1 510 655 7305,Fax: +1 510 655 7307;

E-mail: info@vsep.com;Website: www.vsep.com

Filtration+Separation June 2003 29

City water

Heat exchanger(stage I)

Heat

exchanger(stage II)

Equalizationtank

Concentratetank

Concentrate todisposal

Steam condensateto drain

Treatedwater tank

Treated

water pump

Feedpump

Treated water to final polishing

Steam H2SO

4

Feedtank

Two industrialscale VSEPs

PLC

featurearticle

Figure 2: Schematic showing how VSEP integrates into a boiler feed watertreatment process.