Refinery evaluation of optical imaging to locate fugitive emissions

Fugitive emissions account for approximately 50% of total hydrocarbon emissions from process plants. Federal and state regulations aiming at controlling these emissions require refineries and petrochemical plants in the United States to implement a Leak Detection and Repair Program (LDAR). The current regulatory work practice, U.S. Environment Protection Agency Method 21, requires designated components to be monitored individually at regular intervals. The annual costs of these LDAR programs in a typical refinery can exceed US$1,000,000. Previous studies have shown that a majority of controllable fugitive emissions come from a very small fraction of components. The Smart LDAR program aims to find cost-effective methods to monitor and reduce emissions from these large leakers. Optical gas imaging has been identified as one such technology that can help achieve this objective. This paper discusses a refinery evaluation of an instrument based on backscatter absorption gas imaging technology. This portable camera allows an operator to scan components more quickly and image gas leaks in real time. During the evaluation, the instrument was able to identify leaking components that were the source of 97% of the total mass emissions from leaks detected. More than 27,000 components were monitored. This was achieved in far less time than it would have taken using Method 21. In addition, the instrument was able to find leaks from components that are not required to be monitored by the current LDAR regulations. The technology principles and the parameters that affect instrument performance are also discussed in the paper.     

Seasonal variations of hydrophobic organic contaminant concentrations in the water-column of the Seine Estuary and their transfer to a planktonic species Eurytemora affinis (Calanoïda, copepoda). Part 1: PCBs and PAHs

Hydrophobic organic contaminants (HOC) (i.e. PAHs and PCBs) were measured in the water column and in Eurytemora affinis samples from the Seine Estuary collected from November 2002 to February 2005. Results showed seasonal variations of both total PCB and PAH levels in the suspended particulate matter (SPM) and in the copepods with maximum levels during winter times. PAH and PCB concentrations in the SPM ranged from 499 to 5819ngg(-1) and from 58 to 463ngg(-1), respectively. Phenanthrene, pyrene and benzo[b+j+k]fluoranthene (B[b+j+k]F) were the predominant PAH compounds in the water column, while CB 101, 118, 153 and 138 were the most abundant PCB congeners. PCBs and PAHs bioaccumulated by E. affinis (EA) varied between 383 and 1785ngg(-1) and 165-3866ngg(-1). CB101, 153, 138 and B[b+j+k] were, respectively, the major compounds of PCB and PAH fingerprints in EA. Thereby, the copepods could reach high accumulation factor (ACF) (91000 for PCBs and 17000 for PAHs). The principal component analyses of contaminant concentrations and environmental parameter datasets distinguished two groups of copepods. The winter time cluster, with high percentage of adult copepods, which bioaccumulated the highest PCB and PAH body-burdens, and the second cluster with juveniles showing the lowest HOC concentrations. Thus, PAH and PCB concentrations in EA exhibited significant correlations with the percentage of adults making up the samples.     

Study of using microfiltration and reverse osmosis membrane technologies for reclaiming cooling water in the power industry.

A study of using dual membrane technologies, microfiltration (MF) and reverse osmosis (RO), for reclaiming blowdown of the cooling tower was conducted at ZJK power plant, Hebei province, China. The study shows that the combined MF-RO system can effectively reduce water consumption in the power industry. The results indicate that MF process is capable of producing a filtrate suitable for RO treatment and achieving a silt density index (SDI) less than 2, turbidity of 0.2 NTU. The water quality of RO effluent is very good with an average conductivity of about 40 micros/cm and rejection of 98%. The product water is suitable for injection into the cooling tower to counteract with cooling water intrusion. After adopting this system, water-saving effectiveness as expressed in terms of cycles of concentration could be increased from 2.5-2.8 times to 5 times.     

A synchronized amphibian metamorphosis assay as an improved tool to detect thyroid hormone disturbance by endocrine disruptors and apolar sediment extracts

Amphibian metamorphosis assays are used to evaluate potential effects of endocrine disrupting compounds on the thyroid hormone axis. In this study, Xenopus laevis tadpoles are kept in a solution of 0.2% thiourea (TU) to arrest and synchronise them in their development. The advantage of this synchronized amphibian metamorphosis assays is that synchronised tadpoles are available at any time to start metamorphosis experiments, and experimental groups are much more homogenous at the start of experimental exposure compared with groups selected from an untreated pool of animals. The water volume per animal was kept constant throughout the experimental period to overcome the influence of declining numbers of animals per aquarium due to metamorphosis and mortality on the density dependent development of the remaining tadpoles. Clophen A50 (a technical PCB mixture), the single congener 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and apolar sediment extracts that were previously tested positive in the T-Screen, an in vitro proliferation assay for thyroid hormone disruption, were tested in the Synchronized Amphibian Metamorphosis Assay. Endpoints studied were mortality, malformations, body weight, and percentage of metamorphosed froglets at the end of the 60-day experimental period, percentage of tadpoles in different developmental stages, and developmental stage-dependent awarded penalty points. Dietary exposure to Clophen A50 (0.2-50mg/kg food) resulted in a significant increased percentage of tadpoles that did not pass metamorphosis at concentrations higher than 2mg/kg food. Time until metamorphosis in those animals that were able to metamorphose after the 60-days experimental period was significantly decreased. Dietary exposure to PCB 77, a congener that can be readily metabolised, did not result in significant effects in any exposure group (2-500 microg/kg food). Apolar sediment extracts from two of the three sites that are contaminated with a wide variety of chemicals significantly decreased the percentage of metamorphosed animals and significantly increased the number of tadpoles that remained in early and late metamorphic stages. These effects already occurred when the extracts where diluted more than 1000 times (on an organic carbon base) compared to environmental concentrations. The rank of potency was comparable to results obtained with the T-screen. This suggests the presence of thyroid hormone disrupting compounds in the aquatic environment and possible effects of such compounds on animal development in the wild.     

Exemplifying whole-plant ozone uptake in adult forest trees of contrasting species and site conditions

Whole-tree O3 uptake was exemplified for Picea abies, Fagus sylvatica and Larix decidua in stands at high and low altitude and contrasting water availability through sap flow measurement in tree trunks, intrinsically accounting for drought and boundary layer effects on O3 flux. O3 uptake of evergreen spruce per unit foliage area was enhanced by 100% at high relative to low elevation, whereas deciduous beech and larch showed similar uptake regardless of altitude. The responsiveness of the canopy conductance to water vapor and, as a consequence, O3 uptake to soil moisture and air humidity did not differ between species. Unifying findings at the whole-tree level will promote cause-effect based O3 risk assessment and modeling.     

On the presence of enriched amounts of 235U in hot particles from the terrestrial area affected by the Palomares accident (Spain)

The characterisation by ICP-MS of an isolated Pu-U hot particle originating from the nuclear weapons accident in Palomares (Spain) shows, for the first time, that its uranium content is highly enriched in (235)U. The enrichment has been confirmed by independent analyses of two surface soil samples collected in a heavily contaminated area close to the impact point of one of the bombs. This finding clarifies better the composition of the weapons involved in the accident and is of importance when the inventory of U and Pu in the contaminated area are to be calculated.     

Risk assessment of trace elements in the stomach contents of Indo-Pacific Humpback Dolphins and Finless Porpoises in Hong Kong waters

The potential health risks due to inorganic substances, mainly metals, was evaluated for the two resident marine mammals in Hong Kong, the Indo-Pacific Humpback Dolphin (Sousa chinensis) and the Finless Porpoise (Neophocaena phocaenoides). The stomachs from the carcasses of twelve stranded dolphins and fifteen stranded porpoises were collected and the contents examined. Concentrations of thirteen trace elements (Ag, As, Cd, Co, Cr, Cs, Cu, Hg, Mn, Ni, Se, V and Zn) were determined by inductively coupled plasma mass spectrometer (ICP-MS). An assessment of risks of adverse effects was undertaken using two toxicity guideline values, namely the Reference Dose (RfD), commonly used in human health risk assessment, and the Toxicity Reference Value (TRV), based on terrestrial mammal data. The levels of trace metals in stomach contents of dolphins and porpoises were found to be similar. Risk quotients (RQ) calculated for the trace elements showed that risks to the dolphins and porpoises were generally low and within safe limits using the values based on the TRV, which are less conservative than those based on the RfD values. Using the RfD-based values the risks associated with arsenic, cadmium, chromium, copper, nickel and mercury were comparatively higher. The highest RQ was associated with arsenic, however, most of the arsenic in marine organisms should be in the non-toxic organic form, and thus the calculated risk is likely to be overestimated.     

A field trial for an ex-situ bioremediation of a drilling mud-polluted site

The remediation of drilling mud-polluted sites in the Southeast of Mexico is a top priority for Mexican oil industry. The objective of this work was to find a technology to remediate these sites. A field trial was performed by composting in biopiles, where four 1ton soil-biopiles were established, one treatment in triplicate and one unamended biopile. Amended biopiles were added with nutrients to get a C/N/P ratio of 100/3/0.5 plus a bulking agent (straw) at a soil/straw ratio of 97/3. Moisture content was maintained around 30-35%. Results showed that, after 180 d, total petroleum hydrocarbon (TPH) concentrations decreased from 99300+/-23000mgTPHkg(-1) soil to 5500+/-770mgTPHkg(-1) for amended biopiles and to 22900+/-7800mgTPHkg(-1) for unamended biopile. An undisturbed soil control showed no change in TPH concentrations. Gas chromatographic analysis showed residual alkyl dibenzothiophene type compounds. Highest bacterial counts were observed during the first 30 d which correlated with highest TPH removal, whereas fungal count increased at the end of the experimentation period. Results suggested an important role of the straw, nutrient addition and water content in stimulating aerobic microbial activity and thus hydrocarbon removal. This finding opens an opportunity to remediate old polluted sites with recalcitrant and high TPH concentration.     

Biological solids reduction using the Cannibal process.

A laboratory study of the Cannibal process was undertaken to determine if the Cannibal system would generate less sludge compared with a conventional activated sludge system. Side-by-side sequencing batch reactors were operated--one using the Cannibal configuration and the other as conventional activated sludge. It was found that the Cannibal process generated 60% less solids than the conventional activated sludge system, without any negative effect on the effluent quality or the settling characteristics of the activated sludge. The oxygen uptake rate for the centrate from the Cannibal bioreactor showed that readily biodegradable organic matter was released from the recycled biomass in the Cannibal bioreactor. It is proposed that the mechanism for reduced solids from the Cannibal system is that, in the Cannibal bioreactor, iron is reduced, releasing iron-bound organic material into solution. When the Cannibal biomass is recirculated back to the aeration basin, the released organic material is rapidly degraded.     

Heterogeneous uptake of octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) onto mineral dust aerosol under variable RH conditions

We have carried out kinetic studies to characterize the heterogeneous decay of octamethylcyclotetrasiloxane (D₄) and decamethylcyclopentasiloxane (D₅) in the presence of representative mineral dust aerosol in order to obtain a better understanding of the atmospheric fate of these siloxanes. The heterogeneous chemistry of D₄ and D₅ with various mineral dusts was studied in an environmental aerosol reaction chamber using FTIR absorption spectroscopy to monitor the reaction. The apparent heterogeneous uptake coefficient, γ_app, for D₄ and D₅ with various mineral dusts was measured under dry conditions and as a function of relative humidity (RH). In addition, the effect of initial D₄ and D₅ concentration on the rate and yield of the reaction was examined. The uptake coefficient, γ_app, for D₄ and D₅ was similar for the most reactive aerosols tested, with kaolinite ≈hematite > silica. Limited uptake onto carbon black and calcite surfaces was observed for either siloxane. Reaction with hematite and kaolinite resulted in multilayer coverages, suggesting extensive polymerization of D₄ and D₅ on the aerosol surface.