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radiant section
ABSTRACT High temperature alloys tubes are used in the hottest section in the radiant box of petrochemical furnaces commonly known as ethylene furnaces or fired heaters. Many metallurgical improvements to these alloys are intended so the material can withstand the elevated temperature and aggressive environment to obtain a longer operation time. This paper explains the most common damage mechanisms of these alloys in radiant section such as creep/carburization, thermal fatigue/carburization, and thermal shock. State of the art analytical techniques such as macro-etching of carburization depth, optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) were utilized in analyzing these failures. Preventive solutions were recommended to overcome such failures in the future and ultimately increase the operation time and most importantly increase the production rate. INTRODUCTION The secret of the use of high temperature alloys in the aggressive environment of furnaces is the addition of the alloying elements. These alloying elements diffuse interstitially and substitutionally into the structure. Pure metals tend to be very soft because the crystal structure is not distorted and the atoms can move relatively easily. So the addition of the alloying elements will create different phases and that will enhance the thermos-mechanical and thermo-chemical properties. Numerous factors are considered during the design and material selection of the furnace. This paper discusses only the metallurgical aspects of furnace tubes. The focus during the design of the furnace tubes is always to improve the resistance to high temperature attack. Some metals, such as aluminum and chromium are so reactive that they react with oxygen at room temperature to form an oxide layer which is so stable that it becomes an impenetrable oxide barrier preventing the diffusing of hydrocarbon into the parent tube metal at high temperature service. This is the reason of having the chromium as a basic component of most high temperature alloys. Nickel and silicon are also important because they are major contributors to improve the resistant to oxidation. Other elements such as molybdenum, titanium and nitrogen are added to modify the metallurgical and mechanical properties. The furnace in general consists of two sections as shown in Figure 1. The two sections are radiant where the tubes are exposed to extremely high temperature and the second section is the convection section where the heat is less than radiant section. The tubes in the radiant section are heated by a direct radiant heat by the burners. The excessive heat from the radiant section move to the convection section to heat the tubes. The gas feed enter the convection section and then is heated up gradually till reaches the radiant section. The material selection of the tubes are varied based on the exposed temperature from carbon steel at the beginning of the feed to high grade austenitic alloy in the radiant section.
- Materials > Metals & Mining (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Oil & Gas > Downstream (0.85)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations (1.00)
- Well Drilling (0.75)
Abstract Some oilfield operators have experienced a marked increase in steam generator catastrophic tube failures due to changes in water quality reaching the steam generators and aging of the steam generators. One operator in the South Belridge Field has been replacing one-third to one-half of the radiant tubes in each steam generator every year for several years. In addition, some operators have been limited trying to increase steam generator throughput by both the steam generator's design and other interrelated facilities. Minor piping and control system changes allow the conversion of a typical 50MMBtu/hr steam generator's radiant heat recovery section from a design of one (1) single water/steam pass to a design of two (2) parallel water/steam passes. The result is that the water/steam mixture has half the distance to traverse in the radiant section and does so at half the velocity. The water quality problem or steam generator aging problem seems to benefit from the reduced velocity since no tube wall loss has been detected in six (6) months on steam generators receiving this change. In addition, since pressure loss depends on length and velocity to the second and third powers, lower pressure drop in the radiant section has allowed significant increases in steam generator throughput thus lowering unit steam costs. Here a simple mechanical change in the steam generator provided a solution that was uneconomical to address chemically or with other facilities. Introduction In the South Belridge Field, one operator began experiencing an abnormal number of steam generator tube failures in 1991. This followed by 18 to 24 months a change in the method used to soften steam generator feedwater from one of strong acid (sodium chloride brine) cation exchange to one using caustic precipitation followed by weak acid (hydrochloric acid) cation exchange. Inspection of failed parts showed both severe erosion and scale deposition next to the erosion. Analysis of the scale showed it to be calcium and silica scale. At first the tube failures occurred in the 180 degree tube returns in the steam generator radiant section. Later, tube failures occurred in the straight length of the radiant tubes, although the 180 degree tube returns remained the preferred location. The problem continued to grow. Ultrasonic tube wall thickness measurements were begun to warn of impending tube failures so replacements could be made before failures occurred. During one year in the early 1990's radiant tubes and tube returns in some 60 steam generators were replaced due to failures or predictive measurements. This operator's inventory consisted of only 44 fifty million Btu per hour (50MMBtu/hr) steam generators. Pressure Limited Throughput At the same time, steam generator throughput was limited by the available supply pressure and the field steam distribution and measurement system. Steam generators operated at 65% to 75% of design capacity. Although this limitation was mostly a result of inadequate system facility design, no doubt the calcium and silica scale served to elevate steam injection pressures to at least some extent. More detailed study showed that major and costly changes would be required to address the problem of pressure limited throughput from a facility standpoint. Solutions Investigated Since the onset of the tube failures followed with some delay the change to precipitation and weak acid softening, and inspection of the failures showed uniform scale deposition next to the failures, it seemed natural to look for a solution in water chemistry. The most widely accepted failure mechanism was that released scale caused the erosion and thus the tube return failures. So if the scale could be prevented, the failures could be prevented. Although calcium hardness was detected at less than 1 part per million (ppm) at the water plant, scale continued to occur. Some suggested adding magnesium hydroxide to the precipitation sludge recirculation to cause more silica to drop out. Without silica as a precipitation site, less calcium should drop out as scale. P. 21^
- Energy > Power Industry (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Treatment (0.41)
Abstract Recovery of the substantial crude oil reserves in central California has been restricted by stringent state regulations limiting the NO emissions from steam generators used to enhance the recovery process. These regulations specify that emissions reductions below a baseline level are required when certain ambient NO triggering levels are exceeded. There have been nocomprehensive test programs aimed at defining baseline emissions from steamgenerators or the effects of design parameters on those emissions. There have, however, been many individual tests of steam generators that have been performed primarily to comply with licensing requirements and these show that NOx emissions from standard 15 MW (50 × 10-6 Btu/hr) generators vary by a factor of five, from 160 to 825 cm3/m3 NOx corrected to 3 percent O2. Clearly, this indicates a need to identify an established baseline to which emissions levels from alternative configurations may be compared. The study described in this paper entailed compilation of all available test results and analysis of these to 1) define the NO emissions baseline, 2)delineate the effects of several design variables on emissions, and 3) address the effectiveness of field tested NO reduction techniques and equipment. From these results, the 15 MW (50 × 10-6 Btu/hr) steam generator with a conventional burner was observed to be the most common configuration. The type of burner and steam generator were found to be relatively unimportant, probably because of similarities in design between manufacturers. The generator capacity was of greater importance. Steam generators with 6 MW (20 × 10-6 Btu/hr) nominal capacity exhibited NOx emissions exceeding the 15 MW (50 × 10 Btu/hrconventional burner levels, as did 15 MW (50 × 10-6 Btu/hr) generators equipped with low excess air burners (designed for high thermal efficiency). Field test results from two NO reduction methods were also analyzed. Ammonia injection into the combustion products showed significant effect on NO emissions; current technology low NO burners were characterized by emissions near conventional burner levels. Introduction Deteriorating air quality in the San Joaquin Valley of central California has prompted the state's Air Resources Board (CARB) to regulate NO emissions from thermal enhanced oil recovery (TEOR) steam generators in Kern County, where the majority of TEOR operations are located. These regulations require that 1) certain new stationary sources (including steam generators) use either the Best Available Control Technology (BACT) or the Lowest Achievable Emission Rate (LAER) to control emissions of any air contaminant or precursor for which there is a national ambient air quality standard (this includes NO), and 2) NOx emissions from all steam generators be reduced to 0.3 lb/10-6 Btu (about 225 cm3/m3) by July 1, 1982 with further reductions to 0.25 and 0.14 lb/10-6Btu (about 190 and 105 cm3/m3) if certain ambient NO levels are exceeded.(Note: all concentrations included in this report are corrected to 3 percent 02. Also, the units cm /m are equivalent to the more familiar ppm by volume.)the CARB emissions reduction levels were based on an inventory of steamgenerator emissions which assumed that the baseline NO emission level from conventional generators was 300 cm /m. The specific objectives of this investigation were to: . Characterize the NO emissions from the TEOR steam generator population; . Determine the effects of various design and operating variables on NO emissions; and . Evaluate the potential for achieving the regulated emission levels using current commercial equipment or technologies under development. All available results from field tests of steam generators were compiled. Data were obtained from several steam generator owner/operators and from the records of CARB and the Kern County Air Pollution Control District (KCAPCD).Most of the data were the results of emissions compliance tests or tests conducted by independent test agencies. P. 263
- Energy > Power Industry (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.49)