Carbon Dioxide Based Metal Working Fluids.

Metalworking fluids (MWFs) are necessary for most machining operations to ensure proper cooling and lubrication. Conventional mixtures of water, emulsified oils and additives can lead to significant environmental impacts and worker health risks. Delivery of MWFs in minimum quantities using compressed air reduces many of these impacts but the cooling capacity of these sprays is lower than aqueous MWFs. In this research, a novel class of MWFs delivered in carbon dioxide was developed that is environmentally preferable and capable of providing cooling on par with conventional fluids. Above its critical point, CO2 dissolves many common MWF lubricants and can produce a spray of frozen lubricant and dry ice when delivered through a nozzle. The goal of this research was to evaluate the feasibility of supercritical CO2 (scCO2)-based MWFs for manufacturing applications. A prototype for delivery of scCO2-based MWF was developed and proved capable of reducing friction significantly relative to conventional MWFs. Research on the delivery of scCO2–based MWFs indicated that the lubricating potential is easily “tunable” to meet the needs of different machining operations. To test the cooling capacity of scCO2-based MWFs, heat-induced diffusive tool wear was evaluated in high-speed cutting of hard metals. The results yielded compelling reductions in tool flank wear provided by scCO2-based sprays when delivered directly to the flank surface. The results also illustrated the importance of nozzle geometry, proximity of tool and workpiece, and gas pressure for effective heat dissipation. To evaluate the environmental impacts associated with switching to scCO2-based MWFs, a life cycle analysis (LCA) was performed to compare them with water- and air-based systems. It was found that dramatic reductions are possible in aquatic toxicity, water use, and solid waste when switching from water to scCO2-based MWFs. The switch results in increased greenhouse gas emissions but the magnitude of the increase is small compared to other factory operations and can vary depending on allocation strategies. Taken together, the research reveals that scCO2-based MWFs have great potential to improve manufacturing process performance, while reducing tooling costs and the most prominent worker health risks and environmental impacts associated with MWFs today.Ph.D.Environmental Engineering and Natural Resources and EnviroUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58368/1/aclarens_1.pd

Physicochemical factors impacting CO2 sequestration in depleted shale formations: The case of the Utica shale

AbstractFractured shale formations could serve as an attractive target formation for geologic carbon sequestration once they have been depleted of hydrocarbons. The low intrinsic permeability of the shale matrix could reduce the CO2 leakage potential, the kerogen in the shale would provide a matrix within which the CO2 can be permanently sorbed, and the infrastructure in place at gas production sites could all be leveraged to minimize costs. Here, a modeling framework previously developed by the authors to estimate the sequestration capacity of shale formations is extended to better capture the physicochemical realities associated with injecting CO2 into fractured shale formations. The model uses CH4 production data to fit key parameters about the formation and applies those to a unipore diffusion model to characterize the controlling gas transport processes. A number of parameters, including the gas diffusion coefficient, the ratio of adsorbed gas to free phase gas, water saturation and gas adsorption isotherms are considered and their effect on modeling estimates is explored. The model is found to be most sensitive to the ratio of adsorbed gas to the total gas which includes both adsorbed and free phase gas. The equilibrium adsorption parameters of CH4 and CO2 also have significant influence largely because published estimates for these parameters vary considerably. The effect of pore collapse following production was explored in terms of its effect on characteristic diffusion length. The results indicate that increasing this characteristics length by an order of five would triple the time it takes to complete the injection of CO2 into the formation. Similarly, an increase in water content in the formation or in the ratio of free CH4 to sorbed CH4 would decrease the sequestration potential of the formation. Based on this improved constitutive understanding of the modeling inputs and the estimates, the CO2 sequestration capacity of the Utica Shale was calculated and the results were compared with those from Marcellus Shale. The differences could be understood in terms of the distinct petrophysical properties of those two shale formations. This analysis provides recommendations about experimental directions that could be very useful for improving the accuracy of sequestration capacity models

Feasibility of Metalworking Fluids Delivered in Supercritical Carbon Dioxide (TECHNICAL NOTE SUBMITTED TO JOURNAL OF MANUFACTURING PROCESSES)

Abstract This paper presents a new method to lubricate, cool, and evacuate chips in metalworking operations using supercritical carbon dioxide (scCO

Quantification of mineral reactivity using machine learning interpretation of micro-XRF data

Accurate characterizations of mineral reactivity require mapping of spatial heterogeneity, and quantifications of mineral abundances, elemental content, and mineral accessibility. Reactive transport models require such information at the grain-scale to accurately simulate coupled processes of mineral reactions, aqueous solution speciation, and mass transport. In this work, millimeter-scale mineral maps are generated using a neural network approach for 2D mineral mapping based on synchrotron micro x-ray fluorescence (μXRF) data. The approach is called Synchrotron-based Machine learning Approach for RasTer (SMART) mapping, which reads μXRF scans and provides mineral maps of the same size and resolution. The SMART mineral classifier is trained on coupled μXRF and micro-x-ray diffraction (μXRD) data, which is what distinguishes it from existing mapping tools. Here, the SMART classifier was applied to μXRF scans of various sedimentary rock samples including consolidated shales from the Eagle Ford (EFS1), Green River (GRS1), Haynesville (HS1), and New Albany (NAS1) formations and a syntaxial vein from the Upper Wolfcamp formation. The data were obtained using an x-ray microprobe at beamline 13-ID-E at the Advanced Photon Sources. Individual mineral maps generated by the SMART classifier well-captured distributions of both dominant and minor phases in the shale rocks and revealed EFS1 and GRS1 to be carbonate rich shales, and NAS1 and HS1 to be sulfide rich shales. The EFS1 was further characterized for its trace mineral abundances, grain sizes, trace element composition, and accessibility. Approximately 4.4 wt% of the rock matrix were found to be pyrite, with a median grain size of 3.17 μm in diameter and 62% of the grains predicted to be smaller than 4 μm. Quantifications of trace elements in pyrite revealed zinc concentrations up to 4.2 wt%, along with minor copper and arsenic copresence. Mineral accessibility was examined by contact with other phases and was quantified using a new type of image we are calling an adjacency map. Adjacency analyses revealed that of the total pyrite surface present in the EFS1, 28% is in contact with calcite. The adjacency maps are useful for quantifying the likelihood that a mineral could be exposed to fluids after dissolution of a contacting reactive phase like calcite. Lastly, pooling data from different samples was demonstrated by training a classifier using two sets of coupled μXRF-μXRD data. This classifier yielded an overall accuracy of \u3e96%, demonstrating that data pooling is a promising approach for applications to a wide suite of rock samples of different origin, size, and thickness

Wettability Phenomena at the CO₂–Brine–Mineral Interface: Implications for Geologic Carbon Sequestration

Geologic carbon sequestration (GCS) in deep saline aquifers results in chemical and transport processes that are impacted by the wettability characteristics of formation solid phases in contact with connate brines and injected CO₂. Here, the contact angle (θ) at the CO₂–brine–mineral interface is studied for several representative solids including quartz, microcline, calcite, kaolinite, phlogopite, and illite under a range of GCS conditions. All were found to be water wetting (θ < 30°) with subtle but important differences in contact angles observed between the surfaces. Temperature and pressure conditions affected the results but did not produce discernible trends common to all surfaces. Brine composition, in terms of pH and ionic strength, was a better predictor of interfacial behavior. For the nonclays, the wettability is impacted by the pH at the point of zero charge of the solid. For the clays, the response was more complex. Under nonequilibrium conditions, hysteretic effects were observed when CO₂ was dissolving into the bulk fluid and this effect varied between minerals. Contact angle was found to decrease during the CO₂ phase transition from supercritical or liquid phase to gas phase. These results are useful for developing a more complete understanding of leakage through caprocks and capillary trapping in GCS

Environmental Life Cycle Analysis of Water and CO₂‑Based Fracturing Fluids Used in Unconventional Gas Production

Many of the environmental impacts associated with hydraulic fracturing of unconventional gas wells are tied to the large volumes of water that such operations require. Efforts to develop nonaqueous alternatives have focused on carbon dioxide as a tunable working fluid even though the full environmental and production impacts of a switch away from water have yet to be quantified. Here we report on a life cycle analysis of using either water or CO₂ for gas production in the Marcellus shale. The results show that CO₂-based fluids, as currently conceived, could reduce greenhouse gas emissions by 400% (with sequestration credit) and water consumption by 80% when compared to conventional water-based fluids. These benefits are offset by a 44% increase in net energy use when compared to slickwater fracturing as well as logistical barriers resulting from the need to move and store large volumes of CO₂. Scenario analyses explore the outlook for CO₂, which under best-case conditions could eventually reduce life cycle energy, water, and greenhouse gas (GHG) burdens associated with fracturing. To achieve these benefits, it will be necessary to reduce CO₂ sourcing and transport burdens and to realize opportunities for improved energy recovery, averted water quality impacts, and carbon storage