Vapor Degreasing Research Articles

Application of fuzzy set theory to industrial pollution prevention: production system modeling and life cycle assessment

This research describes a framework and case study application that merges fuzzy set methods, pollution prevention, and sustainable production concepts. There is a direct linkage between industrial pollution prevention, sustainability, and the solution of large-scale environmental problems. This linkage stems from the inherent desire for economic production, while at the same time protecting the environment from further degradation. The methodology combines systems analysis under imprecise conditions with a life cycle assessment method that is able to accept imprecise data. Analysis of systems under imprecise conditions is accomplished through analysis of process flow diagrams using fuzzy set techniques. Introduction of imprecision into life cycle assessment is accomplished by integration of fuzzy set approaches into a decision support system utilizing multiple criteria decision making. The framework is described and a case study application of an industrial parts cleaning system using an open top vapor degreaser is presented. Results of applying the method show that: (1) It is well suited for analysis of complex systems in which input data is sparse and expensive to collect. (2) The proposed framework includes a decision support system that is able to consider life cycle assessment concepts, and is able to reconcile differing opinions on available options for modification of production systems, thereby leading to more sustainable solutions.

Chlorinated Decreasing Solvents: Physical‐Chemical Properties Affecting Aquifer Contamination and Remediation

AbstractChlorinated degreasing solvents are multicomponent liquids containing not only the chlorinated hydrocarbons with which their name is associated (e.g., trichloroethylene or |TCE]. perchloroethylene or [PCE], 1,1,1‐trichlorocihane [TCA]) but also a number of organic additives included as corrosion inhibitors and antioxidants. The additives, such as 1,4‐dioxane, are likely to be of significant public‐health importance as ground water contaminants due to their toxicity, solubility, and mobility. Following their use in vapor degreasing systems by industry, chlorinated degreasing solvents will also contain about 25% solubilized oil and grease.A number of physical‐chemical properties become especially important in the light of the multicomponent nature of these solvents. First, the higher aqueous solubility and lower sorption of the additives makes it is reasonable to expect that faster moving plumes of these solvent additives will precede plumes of the chlorinated hydrocarbons. Second, due to high losses of chlorinated hydrocarbons by volatilization from vapor degreasers during years in the middle of the century, it is probable that background concentrations of these hydrocarbons are present in ground water flow systems due to their downwind washout. Finally, the solubilized oil and grease may cause profound changes to the wettability of aquifer materials contacted by the solvents during their subsurface migration. It is argued, therefore, that the wettability of aquifer materials contaminated by chlorinated degreasing solvents needs to be experimentally determined before remediation of DNAPL at each site, rather than being simply assumed as water wet.

Characterisation of surface preparation of 2024 aluminium alloy for conversion coating

X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and electrochemical potentiodynamic experiments have been used to study the pretreatment of 2024–T3 aluminium alloy before conversion coating. The pretreatment process included vapour degreasing, alkaline cleaning and Cr based acidic deoxidising steps. This type of pretreatment is appropriate for conversion coatings which meet aerospace standards for corrosion resistance and paint adhesion. During alkaline cleaning an oxide containing Mg, Zn, Si, and Fe developed on the surface of the alloy. During deoxidation there was dissolution and etching of both the intermetallics and the basic oxide scale left after the alkaline cleaning. Characterisation by XPS indicated that the surface was coated with a thin Cr containing coating after deoxidation which provided a degree of passivation to the surface as determined by electrochemical measurements.MST/3372

Characterisation of surface preparation of 2024 aluminium alloy for conversion coating

Abstract X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and electrochemical potentiodynamic experiments have been used to study the pretreatment of 2024–T3 aluminium alloy before conversion coating. The pretreatment process included vapour degreasing, alkaline cleaning and Cr based acidic deoxidising steps. This type of pretreatment is appropriate for conversion coatings which meet aerospace standards for corrosion resistance and paint adhesion. During alkaline cleaning an oxide containing Mg, Zn, Si, and Fe developed on the surface of the alloy. During deoxidation there was dissolution and etching of both the intermetallics and the basic oxide scale left after the alkaline cleaning. Characterisation by XPS indicated that the surface was coated with a thin Cr containing coating after deoxidation which provided a degree of passivation to the surface as determined by electrochemical measurements.MST/3372

Hood Efficiencies of Vapor Degreasers Under Operating Conditions

The objective of this research was to measure capture efficiency of local exhaust hoods used to control vapor degreasing tanks during normal operations and to compare the observed capture efficiencies to the American Conference of Governmental Industrial Hygienists (ACGIH) design criteria. Solvent emission rates and local exhaust hood capture efficiencies were measured at 15 vapor degreasers. The degreasers were located in 12 private industrial settings and studied under normal operating conditions. Where possible, hourly concentration data were collected during two 8-h shifts for each degreaser. Site-average fugitive emissions to the workspace (mean = 0.173 g/m{sup 2}/s, range = 0.001 {minus} 1.08 g/m{sup 2}/s) were in excellent agreement with previously reported tests for vapor degreasers under operating conditions. The ACGIH recommended flow of 0.25 m{sup 3}/s/m{sup 2} (50 cu ft/min/sq ft) of tank surface appears to be adequate for some conditions but inadequate for other conditions. An increase in flow, above design recommendations, did not necessarily improve hood performance. Hood capture efficiency was slightly correlated with hood face velocity, although there is significant variability in the data. Emissions of solvent to the workspace were only slightly correlated with duct emissions. This suggests that fugitive emissions are as strongly related to workmore » practices as they are to control device design.« less

Receptor modeling of VOCS — II. Development of VOC control functions for ambient ozone

In this study we developed an exploratory method to investigate the potential effect of VOC reduction from specific source categories on maximum ozone. The method is based on measurement of speciated organic compounds in air and application of chemical mass balance receptor modeling (CMB) to allocate ambient concentrations to specific source categories. This evaluation results in a sample-specific emission inventory, an estimate of the VOC emissions by source in an air mass which includes variations in source discharge not reflected in the conventional emission inventory. In addition, the CMB model in conjunction with the chemical profiles for each source, provides a basis for allocating very reactive organic components not measured in the atmosphere but contributing to O3 formation. The carbon bond reaction kinetics model (CBM-IV) is used with observed meterological conditions and the specific source contributions to predict precursor conversion to ozone. Predictions of maximum O3 using the technique for 9 days in Chicago in the summer of 1987 compared favorably with measured ground-level concentrations determined to be downwind by trajectory analysis. Source categories modeled included vehicle tailpipe exhaust, gasoline vapor, petroleum refinery emissions, architectural coatings, graphicarts, vapor degreasing, dry cleaning, and waste water treatment. The end-product is a family of control response curves which show the relationship between changes in VOC precursor emissions from each source and potential maximum ozone. The control functions for vehicle exhaust indicated that control of VOC from automobiles will be effective on some high O3 days but not on others. The method complements grid-based photochemical models in that it will allow many more control options to be investigated than would be possible due to computational constraints.

Trichloroethylene exposure in vapour degreasing and the urinary excretion of N-acetyl-beta-D-glucosaminidase.

In order to elucidate the potential nephrotoxicity of low level occupational exposure to trichloroethylene (TRI), urine analysis of the tubular enzyme N-acetyl-beta-D-glucosaminidase (U-NAG) was included in a cross-sectional study of metal degreasers in central Sweden. Eighty-six percent of 8-h TRI in air measurements were well below 50 mg/m3. Normal levels of NAG were found in morning urine samples from 29 workers compared to a historical reference group. A weak positive correlation (r = 0.48; P < 0.01) was observed between U-NAG activity and the concentration of the TRI metabolite trichloroacetic acid in urine but not with other estimates of recent or long-term exposure. In conclusion, TRI does not seem to be nephrotoxic at low exposure levels.

Assessment of Intermittent Trichloroethylene Exposure in Vapor Degreasing

Assessment of Intermittent Trichloroethylene Exposure in Vapor Degreasing

Assessment of intermittent trichloroethylene exposure in vapor degreasing.

To validate various sampling strategies in assessment of trichloroethylene (TCE) exposure, urine and air samples were obtained from 29 metal workers involved in vapor degreasing. Urinary trichloroacetic acid and trichloroethanol were useful metabolites to estimate TCE exposure on a group basis, but the predictive value of a single urine sample was low when related to the air concentration. With intermittent TCE exposure, the best information is obtained by analyzing both metabolites.

Source Activity Modeling of Freon® Emissions from Open-Top Vapor Degreasers

Abstract Freon® emissions from vapor degreasing operations at an electronics manufacturing firm were studied. Freon concentrations were measured at nine locations around two open-top vapor degreasers (OTVDs) while simultaneous activity observations were made. Concentration measurements were obtained using both charcoal tube/gas chromatographic and Tedlar bag/infrared absorption methods. Advective air flow was found to influence the concentration pattern in the sampling area surrounding the degreasers. Because of this, the box model and an advective-diffusion model were used to translate area concentration measurements into emission rates. Regression analysis between emission rates and activity factors was used to develop emission factors for the degreasing operation. The two models gave very similar estimates of the total emissions from the two degreasers. The average emission predicted by the box model for the 6 hours with bag and charcoal-tube data was 74 g/hour, very close to the 95 g/hour predicted by the advection—diffusion model for the same hours. The correlation coefficient between the two models for these 6 hours was 0.91. Emissions were found to be a function of solvent dragout. Dragout is best represented as total surface area of parts cleaned, surface area of cupped parts, and the observation of Freon dripping from loaded baskets. Randomly loaded cupped parts were found to carry over three times more dragout than uncupped parts on a per surface area basis. The emission factor based on total surface area cleaned is 37 g/m2. When the model is adjusted for type of parts cleaned, emission factors are 21 g/m2 for uncupped parts, 75 g/m2 for cupped parts, and 7 g/load with visible solvent dripping. An addition 20 g/hour not associated with solvent dragout was identified.

A survey of vacuum material cleaning procedures: A subcommittee report of the American Vacuum Society Recommended Practices Committee

A subcommittee of the American Vacuum Society (AVS) Recommended Practices Committee has conducted a survey of the cleaning procedures practiced by the ultrahigh vacuum industry and government laboratories. Although no two organizations practiced identical procedure, there was sufficient commonality among those canvassed to suggest that there is a sound basic procedure around which many variations have evolved. In the case of chemical cleaning of stainless steel, it is vapor degreasing, alkaline detergent washing and/or acid cleaning, water rinsing, and then heat drying. Various methods of mechanical, chemical, and thermal cleaning of metals and nonmetals practiced by sample organizations are presented with commentary. The Subcommittee recognizes that different situations call for different cleaning procedures. For this reason it aims to disseminate information so that one may formulate his own procedure best suited to his situation, rather than to recommend a single procedure as the best universally.

A Process-Based Method for Substitution of Hazardous Chemicals and its Application to Metal Degreasing

To reduce risk due to dangerous chemicals a process–based method has been developed. The method includes: listing chemical products; obtaining information on composition; developing data sheets; describing the processes; assessing the risk; and providing possibilities for substitution. In a substitution, the chemicals in the final situation should be potentially less dangerous than in the initial situation. A substitution may consist of the introduction of new chemicals, new process design or even a new processs. It is especially important to avoid chemicals with long–term effects. The method has been applied to metal degreasing, manually and by vapor degreasing, dipping, lye–boiling, high pressure hosing and electrodegreasing. The main strategy is to substitute from the use of organic solvents to aqueous alkaline solutions. Another substitution is from cyanide to phosphate solutions in electrodegreasing. Degreasing solutions can be recirculated, e.g. through an ultrafiltration unit, reducing environmental problems.

Emission Factors for Trichloroethylene Vapor Degreasers

Emission factors were developed for two production trichloroethylene (TCE) vapor degreasers: an open-top (0.76 m x 1.16 m x 1.8 m) and a conveyor-fed enclosed design. Both were fitted with functioning local exhaust hoods. Emissions were determined from field data by using a Fick's law diffusion approach and the observed variation in time of the TCE concentration gradient within 4 m of each device. The average emission factor for the open-top degreaser was 2.6 g TCE/min [2.9 g TCE/(m2.min)] which corresponds to 9.5% of the total degreaser emissions escaping into the workplace. The average emission factor for the enclosed degreaser was 0.67 g TCE/min, a release of 3% of the total emissions into the work area. These values are considered to be representative of the average lower limit of emissions during production from TCE degreasers of like designs with similar local exhaust controls (which were typical but did not meet American Conference of Governmental Industrial Hygienists' [ACGIH] airflow rate criteria).

Source Fingerprints for Receptor Modeling of Volatile Organics

The development of receptor models for the determination of the sources of an ambient air pollutant requires that the composition of the pollutant at the point of emission be known. For this study, composition information for 10 sources of volatile organic compounds (VOC) were evaluated and source fingerprints developed. The source categories include motor vehicles, gasoline vapor, petroleum refineries, architectural coatings, graphic arts, waste-water treatment, vapor degreasing, drycleaning, automobile assembly (including body painting), and polyethylene production. The fingerprints are presented for a group of 23 compounds. These compounds were selected for a variety of reasons including ease of measurement in the ambient environment, compound toxicity, reactivity, and usefulness in previous receptor modeling applications. In general, the data for sources of VOC are remarkably consistent from study to study. Because the profiles for many of the sources of VOC are controlled by physical and chemical processes (e.g. combustion) and not raw material composition, the fingerprints have general applicability.

Wintertime source-reconciliation of ambient organics

The application of a Chemical Mass Balance air pollution model to ambient measurements of volatile organic compounds (VOC) is presented. Twenty-six air samples were collected at three sites in the Chicago metropolitan area (suburban, inner-city and industrial) and analyzed for the concentration of 23 compounds including alkanes, aromatics and chlorinated organics. The average daily temperatures on sampling days varied between −15.0 and 4.4°C. Consequently, the potential for significant photochemical reaction was not present. Each ambient sample was evaluated for the contribution from eight sources of VOC (vehicles, gasoline vapor, petroleum refineries, architectural coatings, graphic arts, vapor degreasing, dry cleaning and wastewater treatment). The contribution from sources not included in the model was also evaluated. Average contributions from vehicles ranged from 43 μg m −3 at the suburban location to 70 μg m −3 at the inner-city location. Contributions from petroleum refineries appeared to reflect the distances from the sources to the monitoring sites with average contributions ranging from 28 to 33 μg m −3 near the sources (inner-city and industrial receptors, respectively) to 10 μg m −3 away from the sources (suburban receptor). Contributions from architectural coatings, graphic arts, vapor degreasing, wastewater treatment and dry cleaning also suggested this effect of source-receptor geometry. Evaluation of the results shows that the site-averaged coefficients for vehicles, gasoline vapor and all other unmodeled sources are in close agreement with the State's emission inventory.

Comparison of chemical cleaning methods of aluminum alloy vacuum chambers for electron storage rings

Three chemical precleaning methods suitable for aluminum alloy vacuum chambers for electron storage rings have been compared. The methods ranged from vapor degreasing with no chemical attack to light alkaline etching and strong alkaline etching in NaOH. The techniques used to evaluate and compare the three treatments included Auger analysis, thermal outgassing, electron and x-ray induced neutral gas desorption, argon glow discharge cleaning, and scanning electron microscope examination of the surface. In general, the NaOH treatment was best followed closely by the light alkaline etch and then the vapor degreasing. A variant of the light alkaline etch method was used to clean the 2000 Al vacuum chambers of the CERN large electron positron storage ring project. Two chambers cleaned by this method were exposed to synchrotron radiation in a dedicated beam line of a synchrotron radiation source. Compared to a reference chamber cleaned by NaOH these two chambers were initially worse, but after 1 A h of machine operation the difference practically vanished.

A study of the mechanism of cathodic debonding of adhesively bonded neoprene rubber from steel

The feasibility of applying surface analysis techniques to study adhesion has been well established. Some of these techniques were utilized in this study of cathodic debonding of neoprene to steel bonds to examine the interfacial failure surfaces. Auger electron spectroscopy (AES) showed the poor cleaning capabilities of vapor degreasing and the modest effect of alkali on the oxide layer. The neat phenol-formaldehyde-based primer exhibited a significant amount of degradation characterized by changes in the chemical composition as shown by X-ray photoelectron spectroscopy (XPS). The analysis of the cathodically debonded surfaces showed cohesive failure in the primer close to the interface.

Evaluation of passive monitors for assessing vapor degreaser emissions

A two-phase study was conducted to assess the suitability of passive monitoring for the collection of airborne vapor degreasing solvents under laboratory and field conditions. The laboratory stage of the investigation involved the determination of collection efficiencies for methyl chloroform (MC) and trichloroethylene (TCE). A 6920 L static chamber was used to establish standard atmospheres of these solvents at various concentrations, which were then sampled using passive monitors; samples were subsequently analyzed by gas-liquid chromatography. In the second part of the investigation, several MC and TCE vapor degreaser operations were monitored at US Army industrial plants. The purpose of the field study was to develop worker exposure prof iles and to obtain a side-by-side comparison of the passive monitor with the traditional charcoal tube sampler. Presented are statistically reduced data and the performance characteristics of both collection techniques.

Effect of surface exposure time on bonds to aluminum

Lap joints with AF-126 adhesive were prepared from surfaces of 2024-T3, 2024-T3 alclad, and 6061-T4 aluminum alloys treated by either FPL etch, sandblasting, or vapor degreasing. The strength data were described by a two-parameter Weibull distribution. Allowing between 1 hr and 30 days to elapse between surface preparation and actual bonding had no appreciable effect on bond strength. This was true for all three alloys surface treated in each of the three ways as well as for bonds either tested at ambient conditions or aged for 30 days at 120°F and 95% R.H. 2024-T3 aluminum, both bare and alclad, formed bonds that showed better strength than 6061-T4 aluminum.

アルミニウム洗浄時におけるパークロルエチレンとトリクロルエチレンの安定度の比較について

アルミニウム洗浄時におけるパークロルエチレンとトリクロルエチレンの安定度の比較について