ISO/TS 21152:2024

Guidance on water conservation techniques of circulating cooling water in thermal power plants

This document provides technical and management guidance for water conservation of indirect open recirculating cooling water systems in thermal power plants. It is applicable to circulating cooling systems that use surface water, underground water, reclaimed water, and treated domestic sewage from thermal power plant as the make-up water and use physicochemical treatment methods to increase cycles of concentration, thus realizing water conservation and increasing water use efficiency. This document is applicable to recirculating cooling in thermal power plants fuelled by coal, oil, natural gas, and biomass.

Lignes directrices pour les techniques de conservation de l'eau consistant à faire circuler l'eau de refroidissement dans les centrales électriques thermiques

General Information

• Status: Published
• Publication Date: 09-Dec-2024
• ICS: 13.060.25 - Water for industrial use
• ICS: 27.100 - Power stations in general
• Technical Committee: ISO/TC 282/SC 4 - Industrial water reuse
• Drafting Committee: ISO/TC 282/SC 4 - Industrial water reuse
• Current Stage: 6060 - International Standard published
• Start Date: 10-Dec-2024
• Due Date: 19-Jun-2025
• Completion Date: 10-Dec-2024

Overview

ISO/TS 21152:2024 - "Guidance on water conservation techniques of circulating cooling water in thermal power plants" provides technical and management guidance for reducing freshwater use in indirect open recirculating cooling systems. Applicable to coal, oil, natural gas and biomass‑fired thermal power plants, the Technical Specification covers systems that use surface water, groundwater, reclaimed water or treated domestic sewage as make‑up water and that apply physicochemical water treatment to increase cycles of concentration and improve water use efficiency.

Key topics and technical requirements

• Water quality recommendations: guidance on acceptable make‑up water and circulating cooling water parameters (example ranges include pH 7.5–8.8; TSS ≤100 mg/L; TDS ≤5 000 mg/L; conductivity ≤8 500 μS/cm; NH3‑N ≤10 mg/L, ≤5 mg/L for copper condensers).
• Cycles of concentration: definition, calculation methods and limits for selecting appropriate cycles to balance water savings with scaling/corrosion risk.
• Treatment technologies: physicochemical options to increase cycles of concentration, including lime softening, weak acid cation resin treatment, membrane treatment, scale and corrosion inhibition, microbial control, and side‑stream filtration.
• Cooling tower guidance: operational guidance for reducing bleed/blowdown and minimizing evaporative and drift losses while ensuring system safety and heat‑exchange efficiency.
• Monitoring and instrumentation: recommendations for detection, measurement and control systems to manage water quality and dosing strategies.
• Management practices: water utilities management, selection of low‑toxicity/biodegradable chemicals, regulatory awareness and risk‑based operation.
• Supporting annexes: informative annexes include dynamic simulation tests for scale/corrosion inhibitors, laboratory evaluation tests, cycles‑of‑concentration calculations, side‑stream filtration sizing, and intermittent dosing models.

Practical applications

• Optimize make‑up water selection and pre‑treatment to enable higher cycles of concentration and lower freshwater withdrawals.
• Design or upgrade water treatment trains (membranes, softening, inhibitors, filtration) for cooling towers and condensers.
• Improve operational controls, dosing and monitoring to reduce blowdown, scaling and corrosion while maintaining plant reliability.
• Support compliance with environmental regulations and corporate water‑conservation targets.

Who should use this standard

• Plant owners and operators, water treatment and process engineers
• Cooling system designers and EPC contractors
• Environmental and water‑resources managers, regulatory bodies
• Technical consultants, chemical suppliers and instrumentation vendors

Related standards

• ISO/TC 282 (Water reuse) guidance context; cycles of concentration definition cites ISO 16784‑2:2006.

Standards Content (Sample)

Technical
Specification
ISO/TS 21152
First edition
Guidance on water conservation
2024-12
techniques of circulating cooling
water in thermal power plants
Lignes directrices pour les techniques de conservation de l'eau
consistant à faire circuler l'eau de refroidissement dans les
centrales électriques thermiques
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions .1
3.2 Abbreviated terms .1
4 General . 2
5 Circulating cooling water quality recommendations . 2
5.1 Water quality recommendations of make-up water .2
5.2 Water quality recommendations of circulating cooling water system .2
6 Technical guidance for water conservation of circulating cooling tower . 4
6.1 Basic guidance .4
6.2 Guidance for treatment of circulating cooling with water quality stabilizer.4
6.2.1 General .4
6.2.2 Scale and corrosion inhibition technology .4
6.2.3 Microbial control technology .5
6.3 Technical guidance for increasing cycles of concentration .6
6.3.1 General .6
6.3.2 Lime treatment .6
6.3.3 Weak acid cation resin treatment .7
6.3.4 Membrane treatment .7
6.4 Technical guidance for reducing water loss .8
7 Guidance for managing water conservation of circulating cooling water . 8
7.1 Guidance for detection and measurement instrumentation .8
7.2 Water utilities management .9
Annex A (informative) Dynamic simulation test of scale and corrosion inhibitor .10
Annex B (informative) Make-up water quality recommendations of circulating cooling water .13
Annex C (informative) Scale and corrosion inhibition test of water treatment agents (laboratory
evaluation test) .15
Annex D (informative) Calculation of cycles of concentration .18
Annex E (informative) Carbonate hardness limit selection test and cycles of concentration limit
test . 19
Annex F (informative) Calculation of side-stream filtration volume and side-stream softening
desalination volume .20
Annex G (informative) Calculation of concentration change with time in intermittent dosing .22
Bibliography .23

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 4,
Industrial water reuse.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Water plays an important role in transferring energy, cooling and cleaning in the process of thermal power
generation. According to the statistics of the International Energy Agency (IEA) and China Water Resources
Bulletin, fossil fuel power generation used approximately 189,6 billion cubic metres of freshwater in
2021, accounting for almost 50 % of global energy system freshwater withdrawals and 5 % of total global
freshwater withdrawals. In China, water withdrawal for thermal power generation in 2021 accounted for
approximately 17,7 % of the industrial water withdrawal, of which cooling water in thermal power plants
accounted for approximately 50 %. To save water resources, improve circulating cooling water use efficiency
and help thermal power plants to enhance water conservation, work efficiently and orderly, and thus
improve the economic and social benefits of thermal power plants, it is important to formulate guidance for
the conservation of water used as circulating cooling water in thermal power plants.
The quantity of circulating cooling water used in thermal power plants ranges from tens to hundreds of
thousands of cubic metres based on their operating capacity. The reduction of circulating cooling water
use should consider the water quality, pipe materials, water treatment, chemicals and other factors.
Meanwhile, to achieve water conservation purposes, the use of residual heat of high temperature circulating
water to reduce the temperature of circulating water in the cooling tower should be considered. Cycles of
concentration is an important index for evaluating water conservation of circulating cooling water, while the
amount of make-up water is closely related to the cycles of concentration of circulating cooling water. The
higher the concentration, the better water conservation efficiency. However, with higher concentrations, the
cost and difficulty of water treatment also increase exponentially.
Circulating cooling water quality control index and water conservation processes differ based on the
quality of make-up water. Researchers and engineers should standardize the water conservation process
of circulating cooling water in thermal power plants by fully considering the cycles of concentration and
other relevant influencing factors, to provide standardized technical guidance for the targeted stake holders
(policy makers, managers, technical consultants, designers, operators of water treatment systems, etc.).
Through analysis and research on the circulating cooling water conservation technology in thermal power
plants, this document sets up a scientific and objective technical control index, management guidance and
implementation methods that are helpful to improve the efficiency of circulating cooling water conservation
and the standardization of technical transformation of thermal power plants.
Starting from the perspective of water conservation management and technology, this document provides
acceptable operation control specifications for common processes of circulating cooling water conservation
for most stakeholders, to improve the operation efficiency and management level of circulating cooling
water conservation, which is conducive to guiding the development of specialization, normalization and
standardization of circulating cooling water conservation.
This document establishes the technical guidance and recommendations for circulating cooling water
conservation technology, provides research direction of circulating cooling water conservation technology,
improves the water conservation efficiency, and promotes the transformation of circulating cooling water
conservation technology to higher efficiency, lower energy consumption, environment friendly and resource
saving, in the end realizing sustainable development.

v
Technical Specification ISO/TS 21152:2024(en)
Guidance on water conservation techniques of circulating
cooling water in thermal power plants
1 Scope
This document provides technical and management guidance for water conservation of indirect open
recirculating cooling water systems in thermal power plants. It is applicable to circulating cooling systems
that use surface water, underground water, reclaimed water, and treated domestic sewage from thermal
power plant as the make-up water and use physicochemical treatment methods to increase cycles of
concentration, thus realizing water conservation and increasing water use efficiency.
This document is applicable to recirculating cooling in thermal power plants fuelled by coal, oil, natural gas,
and biomass.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
water conservation of circulating cooling water
process to increase cycles of concentration (3.1.2) thus increasing water use efficiency
3.1.2
cycles of concentration
ratio of the concentration of specific ions in the circulating cooling water to the concentration of the same
ions in the make-up water
[SOURCE: ISO 16784-2:2006, 3.6]
3.2 Abbreviated terms
BOD biochemical oxygen demand at five days
CFU colony forming unit
COD chemical oxygen demand
DO dissolved oxygen
NH -N ammonia-nitrogen
NTU nephelometric turbidity unit
TDS total dissolved solids
TSS total suspended solids
4 General
The following principles should be followed for water conservation of circulating cooling water in thermal
power plants:
— Users should develop efficient circulating cooling water treatment technology, improve the cycles of
concentration under the premise of ensuring system safety and energy saving.
— Users should be aware of the requirements of local environment protection regulation.
— Water treatment chemicals with high efficiency, low toxicity and good chemical stability should be used;
biodegradable water treatment chemicals should be given priority; toxic and harmful water treatment
chemicals should be strictly restricted.
5 Circulating cooling water quality recommendations
5.1 Water quality recommendations of make-up water
When surface water, underground water, seawater, reclaimed water, and treated domestic sewage from
thermal power plants are used as make-up water for circulating cooling water system in power plants,
the quality of the source water and of the circulating cooling water and the working conditions should
be analysed, and technical and economic comparison should be made to select the appropriate cycles
of concentration. Table B.1 in Annex B contains water quality recommendations when surface water,
underground water is used as make-up water for circulating cooling water system after pre-treatment.
Table B.2 in Annex B contains water quality recommendations when reclaimed water is used as make-
up water for circulating cooling water system after pre-treatment. When treated domestic sewage from
thermal power plant is used as make-up water for circulating cooling water system, the water quality after
treatment should not be lower than the recommendations in Table B.2 in Annex B. Table B.3 in Annex B
contains water quality recommendations when seawater is used as make-up water of circulating cooling
water system.
5.2 Water quality recommendations of circulating cooling water system
The water quality of circulating cooling water systems using surface water, underground water, reclaimed
water, and domestic sewage from thermal power plants as make-up water should meet the recommendations
of Table 1.
Table 1 — Water quality recommendations of circulating cooling water systems using surface
water, underground water, reclaimed water, and domestic sewage from thermal power plants as
make-up water
Parameters Units Recommended values
pH (25 °C) — 7,5 to 8,8
TSS mg/l ≤ 100
2- - a
(CO ) + (HCO ) mg/l 400 to 500
3 3
SiO mg/l 150 to 200
2+ a
(Mg ) ∙ (SiO ) mg/l ≤ 60 000
2+ 2- a 6
(Ca ) ∙ (SO ) mg/l ≤ 2,5 × 10
2+ 2+ 2- a 6 6
(Ca + Mg ) ∙ (CO ) mg/l 2 × 10 to 4 × 10
-
Cl mg/l According to the material of heat exchange
COD mg/l ≤ 100
Cr
NH -N mg/l ≤ 10 (≤ 5 for copper tube condenser)
b
TDS mg/l ≤ 5 000
b
Conductivity μS/cm ≤ 8 500
a 2+ 2+ - 2-
Ca , Mg , HCO and CO are calculated by CaCO (mg/l).
3 3 3
b
Conductivity and TDS are non-binding parameters, only for reference. Common parameters having great effect on corrosion
and scaling in water have been listed in this table. Although other dissolved ions contribute to the conductivity and TDS, they
generally have little effect on corrosion and scaling, so these two parameters are only given as reference indicators for water
quality.
The water quality of circulating cooling water systems using seawater as make-up water should be
determined through the dynamic simulation test of scale and corrosion inhibitor (Annex A), or it should be
controlled according to the recommendations of Table 2.
Table 2 — Water quality recommendations of circulating cooling water systems using seawater as
make-up water
Parameters Units Recommended values
TSS mg/l ≤ 30
Turbidity NTU ≤ 20
pH (25 °C) — 8,0 to 9,0
M alkalinity
mg/l ≤ 350
(calculated by CaCO )
2+
Ca mg/l ≤ 1 000
2+
Mg mg/l ≤ 3 200
Total Fe mg/l ˂ 1,0
-
Cl mg/l ≤ 45 000
2-
SO mg/l ≤ 6 000
2+ a
(Cu ) mg/l ≤ 0,1
Oils mg/l ˂ 5
b
Residual chlorine mg/l 0,1 to 1,0 (or lower, meet environmental requirements)
c
TDS mg/l 100 000
c
Conductivity mS/cm ≤ 150
a
The copper ion concentration in seawater circulating cooling water systems containing copper materials should be
monitored.
b
The concentration of free residual chlorine should be controlled when adding oxidizing biocides.
c
Conductivity and TDS are non-binding parameter, only for reference. Common parameters having great effect on corrosion
and scaling in water have been listed in this table. Although other dissolved ions contribute to TDS, they generally have little
effect on corrosion and scaling, so these two parameters are only given as reference indicators for water quality.

The total number of heterotrophic bacteria in circulating cooling water should not be more than 1 × 10 CFU/
ml, and the amount of biological slime should not be more than 3 ml/m .
6 Technical guidance for water conservation of circulating cooling tower
6.1 Basic guidance
6.1.1 The selection of cycles of concentration in circulating cooling water system should comprehensively
consider the water source conditions, water quantity and water quality balance, environmental protection
requirements, circulating cooling water system material and other factors. Scale and corrosion inhibition
test (Annex C) should be performed, and technical and economic comparisons should be made; dynamic
simulation test of scale and corrosion inhibitor should be used when necessary. Within the safe range of
scale and corrosion inhibition, the cycles of concentration should be increased as much as possible. The
calculation of cycles of concentration should refer to Annex D.
6.1.2 A side-stream treatment system should be set up if key indexes such as TSS, NH -N and salt content
significantly exceed the water quality recommendations of the circulating cooling water system after
increasing cycles of concentration, leading to potential risks of system corrosion, blockage and scaling.
6.1.3 The side-stream treatment of circulating cooling water includes side-stream filtration, softening
or desalination process. The selection of a side-stream treatment process should be determined by a
comprehensive comparison of the circulating cooling water quality, the type and volume of pollutants to be
removed and other factors. The calculation of side-stream treatment volume should refer to Annex F.
6.1.4 Side-stream filtration treatment should be set up after technical and economic comparison when
there are more than 5 cycles of concentration of circulating cooling water system, or if there is severe
seasonal sandstorm.
6.1.5 When reclaimed water is used as make-up water for circulating cooling water, if the water quality
does not meet the recommendations of Table B.2 in Annex B, then the treatment process and operation
control scheme of circulating cooling water should be determined by scale and corrosion inhibition test and
dynamic simulation test of scale and corrosion inhibitor.
6.1.6 When a clarification tank is used to treat circulating cooling water blowdown, the influence of
temperature fluctuation on the treatment effect should be taken into account. Automatic temperature
regulation device and air separation device should be installed. The influent temperature variations of the
clarification tank should not be more than 2 °C/h.
6.2 Guidance for treatment of circulating cooling with water quality stabilizer
6.2.1 General
Water quality stabilization treatment is essential to circulating cooling water treatment, whether it is to
adopt natural balance of pH treatment or other treatments such as softening, adding acid, desalting or
partial desalting. Water quality stabilization treatments includes scale and corrosion inhibition, microbial
control and other technologies.
6.2.2 Scale and corrosion inhibition technology
6.2.2.1 The performance and evaluation of scale and corrosion inhibitor for circulating cooling water
should be determined according to the volume of make-up water and the material of circulating cooling

water system. The test for selecting and performance evaluation of scale and corrosion inhibitors for
circulating cooling water should include the following:
a) The carbonate hardness limit selection test, cycles of concentration limit selection test (Annex E) and
scale and corrosion inhibitor concentration selection test (Annex C).
b) The effect of bactericide and its effect on the performance of scale and corrosion inhibitor.
c) Corrosion inhibition performance test (when the material is stainless steel, electrochemical corrosion
performance test should be conducted).
d) Analysis items of operation control (chloride ion, hardness, alkalinity, conductivity, pH, etc.) and its
control recommendations.
6.2.2.2 The formula of scale and corrosion inhibitor for circulating cooling water should be determined by
the dynamic simulation test of scale and corrosion inhibitor and by technical and economic comparison. The
following factors should be considered in dynamic simulation test:
a) make-up water quality;
b) thermal resistance value of fouling;
c) corrosion rate;
d) cycles of concentration;
e) material of heat exchange equipment;
f) condenser approach temperature of heat exchange equipment;
g) inlet and outlet water temperature of heat exchanger;
h) water flow rate in heat exchange equipment;
i) the stability of chemicals and their influence on the environment.
6.2.3 Microbial control technology
6.2.3.1 The selection of biocide or other control technology should be based on the type of microorganism,
such as heterotrophic bacteria, iron bacteria, sulfate reducing bacteria, nitrifying bacteria etc.
6.2.3.2 The selection of bactericide for circulating cooling water should consider cooling water quantity,
water quality conditions, biological species, heat exchange equipment material and other factors.
6.2.3.3 If the proposed microbiological control program is suspected to have a possible positive or
negative influence on the effectiveness of the inhibitor program being tested, then the dosing of chemicals
for microbiological control should be undertaken in accordance with the manufacturer's instructions or
appropriate standards for microbiological growth inhibition.
6.2.3.4 Sodium hypochlorite, liquid chlorine, chlorine ingot, chlorine dioxide and monochloramine should
be used as oxidizing bactericides for circulating cooling water. The dosing mode and dosage should meet the
following principles:
a) Sodium hypochlorite, solid chlorine tablet, monochloramine or liquid chlorine should be added
continuously or by impactor via sequential treatment. For continuous dosing, the residual chlorine in
cooling water blow down should be controlled between 0,1 mg/l and 0,5 mg/l; for impact dosing, it
should be added one to three times a day, and the residual chlorine in water should be controlled between
0,5 mg/l and 1,0 mg/l and maintained for two to three hours; for solid chlorine tablet, the chemicals can
be put into a solid woven bag and hoisted around the cooling pool. The dosage is controlled once every
week of every two weeks, and the dosage concentration is 10 mg/l;

b) Chlorine dioxide should be added continuously. When the bacterial concentration is 10 CFU/ml to
10 CFU/ ml, the amount of chlorine dioxide in circulating cooling water blow down should be controlled
at 0,5 mg/l;
c) Monochloramine can be used in sequential treatment in order to reduce the quantities of bactericide
used and the chemical discharges while maintaining treatment efficiency.
6.2.3.5 The non-oxidizing biocide should have the properties of high efficiency, low toxicity, broad
spectrum, wide ran
...