1、 NACE/EFC Joint Publication Monitoring and Adjustment of Cooling Water Treatment Operating Parameters This NACE International (NACE) and European Federation of Corrosion (EFC) special publication represents a consensus of those individual members who have reviewed this document, its scope, and provi
2、sions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, processes, or procedures not included in this publication. This publication should in no way be interpreted as a restriction on the use of better procedures or materials not di
3、scussed herein. Neither is this publication intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this report in specific instances. EFC and NACE assume no responsibility for the interpretation or use of this publication by other parties. Us
4、ers of this publication are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this publication prior to its use. This publication may not necessarily address all potential health and safety problems or
5、 environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this report. Users of this publication are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate r
6、egulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this publication. Approved 2009-07-30 ISBN: 1-57590-228-1 European Federation of Corrosion NACE International 1 Carlton House Terrace 1440 South Creek Dr. London SW1Y 5D
7、B Houston,Texas 77084-4906 United Kingdom +1 281-228-6200 +44 20 7451 7336 2009, NACE and EFC Item No. 24238 NACE/EFC Joint Publication 1 Monitoring and Adjustment of Cooling Water Treatment Operating Parameters Contents FOREWORD 1 INTRODUCTION . 2 PRINCIPAL PROBLEMS ARISING FROM THE USE OF WATER IN
8、 COOLING SYSTEMS . 2 TYPES OF COOLING WATER SYSTEMS 5 TYPES OF COOLING TOWERS . 9 MONITORING COOLING WATER SYSTEM OPERATION 10 USING ANALYTICAL DATA TO MONITOR PERFORMANCE . 22 SELECTION OF CONTROL METHODOLOGY . 23 MICROBIOLOGICAL MONITORING AND CONTROL 24 PROCESS CONTAMINATION MONITORING AND CONTRO
9、L . 28 MONITORING CORROSION CONTROL 29 MONITORING SCALE, DEPOSIT, AND BIOFILM 36 DERIVING CONTROL ACTIONS FROM MONITORING DATA 41 SPECIAL CONDITIONS 44 REFERENCES 45 BIBLIOGRAPHY 46 APPENDIX A: Cooling Water Treatment Selection Guides . 48 Figure 1: Once-Through Cooling Water System 5 Figure 2: Clos
10、ed Recirculating Cooling Water System 6 Figure 3: Open Recirculating Cooling Water System . 9 Figure 4: Schematic of Typical pH Control System . 17 Table 1: Common Types of Inhibitors for Closed Cooling Water Systems . 7 Table 2: Common Formulations for Closed Cooling Water Systems . 8 Table 3: Comp
11、onents of Cooling Water Inhibitor Packages . 17 Table 4: Commonly Used Oxidizing Biocides and Monitoring Methods . 25 Table 5: Nonoxidizing Microbiocide Monitoring and Control 27 Table 6: Comparison of In-Situ Corrosion Measurement Methods 34 Table 7: Cooling Water Microorganism Enumeration Methods
12、39 Table 8: Cooling Water System Biofilm Monitoring Techniques 40 Table 9: Possible Malfunctions 43 Table 10: Possible Remedial Actions 44 Table A1: Selection Guide for Cooling Water Treatment . 49 Table A2: Principal Formulations Available 53 Table A3: Selection Guide for Corrosion (C) and Scaling
13、(S) Inhibitors . 54 Table A4: Selection Guide for Biocides and Biodispersants 57 FOREWORD The efficient and safe operation of a cooling water system(1) typically involves a substantial amount of routine monitoring of chemical, physical, and microbiological factors. This technical publication is inte
14、nded for personnel directly responsible for daily operation and control of cooling water systems, facility engineering and maintenance personnel, and cooling water treatment vendor sales and technical staff personnel. The purpose of this publication is to provide a concise compilation of what are co
15、nsidered common practices in this area. Monitoring and control of cooling water systems generally occur in three phases: (1)In this publication, cooling water “system” is synonymous with cooling water “circuit.” NACE/EFC Joint Publication 2 Initial cooling water system surveys, conducted after assum
16、ing responsibility for the management or operation of a new or unfamiliar system; Monitoring and adjustment of cooling water system operating parameters during a campaign of operation; and Inspections and measurements of the condition of a cooling water system during offline periods such as outages
17、or turnarounds. This publication is specifically concerned with the second topicmonitoring and adjustment of cooling water systems during routine operation. This publication was prepared by NACE/EFC Joint Task Group (TG) 361, “Cooling Water Systems: Monitoring and Control.” TG 361 is administered by
18、 Specific Technology Group (STG) 11, “Water Treatment,” and sponsored by NACE STG 34, “Petroleum Refining and Gas Processing;” STG 36, “Process Industry: Materials Performance in Chemicals;” STG 38, “Process Industry: Pulp and Paper;” STG 41, “Electric Utility Generation, Transmission, and Distribut
19、ion;” and STG 60, “Corrosion Mechanisms;” and EFC Working Party (WP) 15, “Corrosion in Refineries,” and WP 1, “Corrosion and Scale Inhibition (including Water Treatment).” It is issued by NACE International under the auspices of STG 11 and by the European Federation of Corrosion. INTRODUCTION In coo
20、ling water systems, corrosion and fouling problems are not new, but continuing trends in environmental legislation are leading to ever-greater degrees of evaporation and consequently to very high residual concentrations of various species. Thus, even if the make-up waters used are initially clean an
21、d noncorrosive, because of this concentration effect, they become corrosive and their tendency to induce fouling increases. Faced with this situation, those responsible for cooling water treatment tend to respond on a case-by-case basis, leading to a wide variety of treatments. However, the cooling
22、water system operator, who pays for these treatments, must be able to assess their validity. This publication endeavors to describe in clearly understandable terms what happens in the cooling water as it becomes more concentrated, and what occurs during the different treatments to which the cooling
23、water is subjected. It is then possible to consider the interaction between a particular cooling water and the materials with which it is in contact. It is emphasized that the design, construction materials, and the mode of operation of a plant can often be much more important than the composition o
24、f the make-up water to its cooling water system. This publication provides the theoretical and practical background necessary to understand what goes on within cooling water systems, and how to evaluate corrosion and fouling. Readers will then be in a position to discuss problems and solutions with
25、their cooling water treatment vendors, and the aim of this publication will have been achieved. Appendix A incorporates four tables listing important criteria for selecting and applying water treatment chemicals and controls for open recirculating cooling water systems based on available technology
26、at the time of publication. PRINCIPAL PROBLEMS ARISING FROM THE USE OF WATER IN COOLING SYSTEMS Problems in cooling water systems are of two major types: Corrosion Fouling In practice, these problems are often strongly interrelated, and corrective actions taken to treat one of them frequently have r
27、epercussions on the other. NACE/EFC Joint Publication 3 Corrosion Corrosion reduces the economic life of water handling equipment such as heat exchangers in cooling water service. Aqueous corrosion of a metal (M) is electrochemical in nature and involves two independent reactions, corresponding to o
28、xidation of the metal and reduction of some species in the corrosive medium. The metal oxidation reaction is anodic and releases positively charged metal ions (M+n) into the solution and electrons (e) into the metal, as shown in Equation (1): (M)metal (M+n)solution+ ne (1) The electrons liberated in
29、 the metal reduce an oxidant (Ox) in the corrosive solution to a reduced species (Red) in the cathodic reaction, as shown in Equation (2): (Ox+q)solution+ (ne)metal (Redqn)solution(2)The most common electron receptor is the hydrogen ion (H+), as shown in Equation (3): 2H+ 2e 2H H2(3) In natural wate
30、r, the H+concentration is related principally to the amount of dissolved carbon dioxide (CO2), via the first carbonic acid (H2CO3) dissociation reaction, as shown in Equation (4): H2CO3 HCO3+ H+(4)The most common oxidant is dissolved oxygen in the water, as shown in Equation (5): O2+ 2H2O + 4e 4OH(5
31、) The oxygen concentration of water depends both on its origin and the type of system concerned. Oxygen has two effects, acting both as an electrochemical oxidant in the corrosion reaction and as a chemical oxidant in the conversion of the primary corrosion products (e.g., oxidation of multivalent m
32、etal ions such as Fe+2to Fe+3), as shown in Equation (6): M+m+ ne Mmn(6)The water itself can serve as an oxidant, as shown in Equation (7): 2H2O + 2e H2+ 2 OH(7) On a macroscopic scale, the overall corrosion may be uniform, with no apparent net current, or may be heterogeneous, with currents flowing
33、 between local anodes and cathodes. In certain cases, the corrosion may be completely confined to local regions (e.g., pitting and crevice corrosion). A corrosion inhibitor is a substance that reduces the rate of either the anodic or the cathodic reaction, the most effective ones acting on both (“mi
34、xed” inhibitors). So-called “anodic” inhibitors have a greater effect on the anodic reaction. Although they can be extremely efficient, a risk exists that a local loss of inhibition may lead to catastrophic pitting attack. Fouling Fouling is any deposit that forms on a heat exchange surface that red
35、uces the rate of heat transfer into or out of the cooling water system. A fouling deposit may do one or more of the following: (a) form an insulating layer on NACE/EFC Joint Publication 4 the heat exchange surface; (b) reduce the cross-sectional area of the flow path for the water; and (c) increase
36、the frictional resistance of the water/deposit interface, which in turn reduces the water flow rate. Fouling reduces the efficiency of a cooling water system. Fouling consists of one or more of the following types: inorganic compounds such as scales and corrosion products; microorganisms, which form
37、 biomasses; suspended solids (SS) such as silt and mud; and process leaks such as hydrocarbons. In open recirculating cooling water systems, fouling is generally initiated by the adherence of the sticky polysaccharides of microorganisms to the heat transfer surface forming the sites for other foulan
38、ts such as scale, corrosion products, and SS to adhere. In such systems, fouling is normally a mixture of two or more types of foulants, one of which is normally biomass. Plant heat exchangers are designed to allow a certain amount of fouling. That amount is the design fouling factor (FF) and is spe
39、cified in the heat exchanger process specifications. As long as the actual FF is equal to or less than the design FF and the heat exchanger is otherwise operated in conformance with its design (process flow rate, process temperatures, cooling water flow rate, and cooling water temperatures), the hea
40、t exchanger will perform its designed function. However, once the actual FF exceeds the design FF, the heat exchanger will fail to perform satisfactorily. The FF may be determined via a variety of online monitors that determine the heat transfer coefficient (U) first under clean conditions and then
41、under fouled conditions, as shown in Equation (8): FF = 1/Uf 1/Uc(8) where, FF = fouling factor Uc= heat transfer coefficient under clean conditions Uf= heat transfer coefficient under fouled conditions Scaling Scaling is a type of fouling that occurs when a metallic or nonmetallic surface becomes c
42、overed by an adherent mineral deposit. Scale is a mineral deposit consisting of salts of calcium, magnesium, and/or silica. Scale is distinguished from fouling deposits produced by sedimentation of solid particles from the water by the fact that the scale adheres to the surface. Scale deposits can i
43、ncrease trapping of SS. In a cooling water system, scaling is essentially caused by the formation of minerals such as calcium carbonate, calcium phosphate, and calcium sulfate. The scale may also contain other substances, such as corrosion products, SS, and microorganisms. Nucleation and Growth of D
44、eposits If the water is supersaturated with respect to any mineral such as calcium carbonate, calcium sulfate, or calcium phosphate, growth of nuclei will result in precipitation, either directly on the heat exchanger surfaces or in the bulk water, which is then transported onto the heat exchanger s
45、urfaces to cause scaling. Kinetics of Scaling Kinetics of precipitation is a function of supersaturation with respect to various minerals and the temperature of both the bulk water and heat exchanger surfaces. In practice, various materials are present in the cooling water system. Heat exchangers ar
46、e generally constructed from metals and alloys, whereas cooling towers contain many polymer heat exchange surfaces. The kinetics of deposition can also be a function of the turbulence and the surface condition of the heat exchangers. NACE/EFC Joint Publication 5 TYPES OF COOLING WATER SYSTEMS The pu
47、rpose of cooling systems is to remove heat generated by some industrial process. Water is the cooling fluid most commonly used for this purpose. The nature of the materials used to construct the cooling water system and the equipment to be cooled (condensers, heat exchangers, fluid refrigerators, mo
48、tors, reactors, furnaces, etc.) are extremely varied. Cooling water systems are of three typesonce-through, closed recirculating, and open recirculating. Once-Through Cooling Water System In this system, water is pumped from the natural surroundings and is returned there after a single passage throu
49、gh the cooling water system (Figure 1). The system is characterized by a cooling water flow rate and by the difference in temperature between the inlet and outlet of the equipment to be cooled. Unless there is a process leak, the concentration of impurities in the cooling water remains constant from entry to return to the source. Supply Cooling water Cold process fluid Hot process fluid Heat Exchanger Pump Waste Figure 1: Once-Through Cooling Water System Closed Recirculating Cooling Water System In this system, all the cooling water is confined in a clo
