1、Item No. 24226 NACE International Publication 34105 This Technical Committee Report has been prepared by NACE International Task Group 274* on Refinery Corrosion and FoulingEffect of Nondesaltable Halogens: Report Effect of Nonextractable Chlorides on Refinery Corrosion and Fouling August 2005, NACE
2、 International This NACE International technical committee report represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, proces
3、ses, or procedures not included in this report. Nothing contained in this NACE report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting a
4、nyone against liability for infringement of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpredictable circumstances may n
5、egate the usefulness of this report in specific instances. NACE assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE report are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining the
6、ir applicability in relation to this report prior to its use. This NACE report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this report. Users of this NA
7、CE report are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this report. CAUTIO
8、NARY NOTICE: The user is cautioned to obtain the latest edition of this report. NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old. Purchasers of NACE reports may receive cu
9、rrent information on all NACE International publications by contacting the NACE FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281/228-6200). Foreword Recently, an increasing number of refineries have experienced extreme corrosion and fouling in crude distil
10、lation unit overheads and/or naphtha hydrotreating units. The root causes were traced to severe spikes in the chloride levels. The spikes were unexpected because most of the chlorides in the incoming crude oil are usually removed by the desalter and the remaining chlorides are measurable by commonly
11、 used test methods. During the spikes, the chlorides passed through the desalter and were difficult to detect. Therefore, the industry coined the term “phantom chlorides” to describe them.1A number of possible sources of phantom chlorides are discussed later in this report. The source affects the ex
12、pected location of problems, the best test methods for detection and concentration measurement, and the possible corrective actions. Other terms often used synonymously with phantom chlorides are “nonextractable chlorides,” “nondesaltable chlorides,” and “rogue halogens.” Henceforth, this report pri
13、marily uses the term nonextractable chlorides when referring to these species.The purpose of this technical committee report is to increase awareness of the problem of nonextractable chlorides on refinery equipment and to document the lessons learned to date. Because information is still being devel
14、oped by the industry, it is not possible to provide detailed descriptions of all “phantom chloride” sources or definitive solutions to prevent all potential problems. This report lists sources determined to date, includes details on test methods to measure the levels of chlorides, and lists solution
15、s various refiners have used for their specific conditions. This report is intended as a technical resource for materials and corrosion specialists at oil refining, oil production, chemical-treatment suppliers, and other companies involved in analyzing and preventing corrosion at refineries. The top
16、ics included in the scope of this report are: Description of extractable vs. nonextractable chlorides, Known sources of nonextractable chlorides, _ * Chair Cathleen A. Shargay, Fluor Corporation, Aliso Viejo, California. NACE International 2 Test methods, Case histories of problems in crude distilla
17、tion units (CDUs) and naphtha hydrotreaters (NHTs), and Possible solutions used to date. Not included in the scope are: A complete description of mechanism, or Complete solutions for predicting or solving problems. This technical committee report was developed by Task Group (TG) 274 on Refinery Corr
18、osion and FoulingEffect of Nondesaltable Halogens: Report. This TG is administered by Specific Technology Group (STG) 34 on Petroleum Refining and Gas Processing. This report is issued by NACE under the auspices of STG 34. NACE technical committee reports are intended to convey technical information
19、 or state-of-the-art knowledge regarding corrosion. In many cases, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to convey this information are factual and are provided to the reader as input and guidance for consideratio
20、n when applying this technology in the future. However, these statements are not intended to be recommendations for general application of this technology, and must not be construed as such. Section 1: Introduction Most chloride salts in the crude oil coming into a refinery are inorganic (sodium, ma
21、gnesium, or calcium chloride) and are effectively removed by the desalter. The nonextractable chlorides are not removed in the desalter, but can break down from downstream heating and processing to form hydrochloric acid (HCl). They sometimes cause corrosion and fouling problems. The forms of these
22、chlorides are still being determined, but probably include organic chlorides (either natural or added via treatment chemicals or by the disposal of slops into the crudes); inorganic chlorides encapsulated in high-melting-point waxes or asphaltenes; or chlorinated solvents used in upstream operations
23、. The primary locations of problems to date have been in CDUs and NHTs. Within this report, the term CDU includes atmospheric and/or vacuum distillation units. Some types of nonextractable chlorides break down (by hydrolysis and pyrolysis), primarily in the CDU atmospheric and/or vacuum heaters, cau
24、sing corrosion problems in the tower overheads. With other types, only a very small percentage break down in the CDU and most of the chlorides go downstream to the NHT. There are also reports of nonextractable chlorides found in gas oils going into the applicable downstream units. Even with as littl
25、e as 1% of the nonextractable chlorides breaking down in the CDU, a major increase in the atmospheric tower overhead HCl and chloride levels can occur and cause severe corrosion and fouling problems. One refinery had new overhead condenser tubes fail in less than 14 hours with a corrosion rate of ab
26、out 1,000 mm/y (40,000 mpy). All incoming chlorides are converted to HCl by the hydrotreating reaction in NHT units. One refinery with nonextractable chloride corrosion in the NHT experienced 5 to 30 mm/y (200 to 1,200 mpy) rates on the tubes and shell of the feed/effluent exchangers, reducing the s
27、ervice life of the exchangers to 33 days. Section 2: Extractable vs. Nonextractable Chlorides Chlorides in crude oils fall into two major categories: those that can be removed by extraction into an aqueous phase and those that cannot be extracted by water. Extractable Chlorides Crude oils are usuall
28、y contaminated with inorganic salts. These salts are dissolved in the produced water, which is appropriately referred to as brine. The predominant cations are sodium, calcium, and magnesium. There are many different anions, but the acidic condition resulting from the hydrolysis of chloride salts is
29、the primary cause of corrosion. The calcium and magnesium chloride salts (CaCl2and MgCl2) hydrolyze during the crude distillation process to form hydrogen chloride gas, while sodium chloride (NaCl) goes into the reduced crude or residuum streams. The hydrogen chloride gas passes up the distillation
30、towers to the point at which water starts to condense. There it readily dissolves in the water and forms HCl that is extremely corrosive to many metallurgies. Various corrosion mechanisms can occur and an array of control methods are used to minimize these overhead corrosion concerns.2At various ste
31、ps in the crude production and handling process, some of the brine solution is normally removed in the oil field in order to meet limits set by contract. This separation and removal is often facilitated by the use of chemical, thermal, electrical, and mechanical means before the crude reaches the re
32、finery. However, there is typically enough emulsified brine to cause serious corrosion problems. Refiners usually address this problem by washing the crude with cleaner water and applying electric fields and/or chemicals such as surfactants and emulsion breakers. This is typically done to heated cru
33、de in the CDU in a vessel called a desalter. The function of the desalter is to extract the water-soluble inorganic salts into the water layer. This water layer is usually discarded to the refinerys effluent system. This water-washing process typically removes more than 90% of the inorganic salts as
34、sociated with the crude oil. Because NACE International 3 this removal efficiency has an impact on the integrity of the CDU, plant operators and chemical vendors usually measure the extractable chloride levels of the incoming crude and desalted crude. Some units use two desalters in series (double d
35、esalting) to achieve higher removal efficiencies. Historically, the discussion of chloride-related corrosion, as well as the testing and analysis, was based on the assumption that all the chloride found in the CDU was derived from inorganic, and therefore water-extractable, salts. Nonextractable Chl
36、orides By contrast, nonextractable chlorides are not dissolved in emulsified water, removed by desalters, or reflected in extractable chloride measurements. Some solvents may be able to extract these chlorides, but for the purposes of this report, the term nonextractable applies to nonextractable in
37、 water. Nonextractable Chlorides Known to Date One form of nonextractable chlorides is organic solvents that have at least one carbon-to-chlorine (or other halogen) bond. This bond is not easily broken, but the conditions in a CDU can cause substantial hydrolysis or possibly some thermal breakdown t
38、hat can result in considerable amounts of HCl in the overhead system. The remaining nonhydrolyzed chlorides from these sources typically go into the naphtha. These solvents are extremely oleophilic and cannot be removed or extracted by water. One common source is chlorinated solvents. Nonextractable
39、 ChloridesUnconfirmed Structures and Types In the early 1990s, several deposits high in chlorides were found in CDUs, hydrocrackers, and hydrotreaters that processed gas oils. Nonextractable chlorides were found in residuum. This was a major change from the previous chloride “behavior”the chlorinate
40、d solvents and hydrolyzed chlorides went into the overhead, while the sodium chloride salts stayed in the reduced crude/residuum. The presence of nonextractable chlorides in gas oils and residuum appears to be a recently reported phenomenon. There is no definitive evidence identifying the cause of c
41、hlorides in gas oils and residuum. At a refinery in which the atmospheric residuum is sent to a residuum desulfurizer (RDS), the following chloride levels have been measured: Sample Point Extractable Chlorides (ppmw) Nonextractable Chlorides (ppmw) 1. Crude Oil Feed 4 to 10 1 to 8 2. Desalted Crude
42、Oil 0.4 to 1.7 2 to 5 3. Atmospheric Residuum 0.4 to 1.4 1 to 2 This unit injects caustic upstream from the crude heater and has 80 to 200 ppmw chlorides in the atmospheric tower overhead water. Various chloride corrosion problems are occurring in both the CDU and RDS. The source of the nonextractab
43、le chlorides has not yet been determined. In general, there have been several chemicals or conditions proposed to explain this phenomenon (see also Section 4). These are listed in Table 1. NACE International 4 Table 1: Potential Sources of Nonextractable Chlorides and Other Halogens Chemical(A)Possi
44、ble Source Desaltable? Oil-wetted inorganic salt crystals Natural Yes Filming amine hydrochlorides Production and refinery corrosion inhibitor Unknown; unlikely Neutralizing amine hydrochlorides Production and refinery corrosion inhibitor Yes Alcohol amine hydrochlorides Production and refinery wast
45、e Yes Asphaltene hydrochlorides Natural Unknown Amine chloride polymer (cationic polymer) Refinery flotation and emulsion breakers Unknown Treatment chemicals (cold-flow improvers) Production Unknown; unlikely Quaternary amine chloride compounds (production treatment chemicals) Production Unknown Wa
46、ste-chlorinated oils (polychlorinated biphenyls PCBs) Illegal dumping No HF acid-soluble oil (ASO) HF alkylation units Unknown Alumina treater spent alumina Refinery No Fire-retardant polybrominated biphenyl (PBB) Waste dumping/disposal No Catalytic reformer hydrogen from modified alumina-based chlo
47、ride traps with alumina that is at end of run Refinery (export hydrogen is used in hydrotreating units) No (A)Some of these chemicals can be desaltable, but in some units are added downstream from the desalter. Section 3: Sources of Nonextractable Chlorides Chlorinated Solvents Used in Upstream Oper
48、ations The occurrence of organic chlorides in crude oil has often been the result of chemical cleaning solvents used in the oil production field. Solvents such as carbon tetrachloride, 1,1,1 trichloroethylene, various chlorofluorocarbon (CFC)-based solvents, and perchloroethylene (PERC) have been us
49、ed in the past to dissolve deposits in production facilities. Typical uses were to clean industrial equipment or remove paraffin, wax, or tar deposits from crude gathering lines, tanks, pipelines, or similar equipment. These practices have been banned by most oil-producing countries. However, localized cases of “dumping” have been reported. Other sources of organic chlorides are typically the result of biocide application downhole or in pipelines. Halogenated biocides, such as 2,2-dibromo-3-nitrilopropionamide (DBNPA) and chlorinated cyanurate
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