Significance This work reports direct measurements of methane emissions at 190 onshore natural gas sites in the United States. The measurements indicate that well completion emissions are lower than previously estimated; the data also show emissions from pneumatic controllers and equipment leaks are higher than Environmental Protection Agency (EPA) national emission projections. Estimates of total emissions are similar to the most recent EPA national inventory of methane emissions from natural gas production. These measurements will help inform policymakers, researchers, and industry, providing information about some of the sources of methane emissions from the production of natural gas, and will better inform and advance national and international scientific and policy discussions with respect to natural gas development and use.

A series of full-scale industrial flare tests were conducted at low flow and low BTU content of flared gases at an industrial test facility. Both a 24” diameter air-assisted flare with a flow capacity of 144,000 lb/h and a 36” steam-assisted flare with a flow capacity of 937,000 lb/h were employed in the testing. Flared gases were mixtures of natural gas, propylene, and nitrogen or natural gas, propane, and nitrogen. Natural gas to propane or propylene ratio was 1:4 by volume for all experiments. Nitrogen was used as a diluent to achieve the desired lower heating values (LHV) for the vent gas. The range of flared gas flow rates was 0.1% to 0.65% of the flare’s design capacity. Flare operation was characterized by measurements of flow rates to the flare, extractive measurements made of the vent gases fed to the flare, extractive measurements made at the end of the flare plume, and remote sensing measurements of the flare plume made by a variety of spectroscopic instruments. Destruction/removal efficiencies (DRE, fraction of vent gas reacted) of flared species were calculated based on the observed composition of the species in the plume. The tests demonstrated that destruction efficiencies for steam-assisted flares drop dramatically when combustion zone heating values fall below 250 BTU/scf. Air-assisted flares showed a linear drop in DRE as a function of air flow. While the primary focus of the measurements was on DRE, products of incomplete combustion were also measured. Dominant products of incomplete combustion were CO, ethylene, formaldehyde, acetylene, and acetaldehyde. CO represented approximately 24% to 80% (carbon basis) of the total products of incomplete combustion for DRE > 90%. While DREs of 98–99% were observed in some experiments, many operating conditions produced DREs of substantially less than 99%. Since prescribed methods for estimating emissions would have predicted 98–99% DRE for all the tests, some test conditions resulted in the production of flare emissions multiple times the value that would be calculated using the prescribed estimation methods. In practice, total emissions from flares will depend on both operating conditions and the duration of operation at the various operating conditions.

Full-scale tests of steam- and air-assisted industrial flares were conducted using low BTU content (lower heating value) vent gases at low flow rates. A 36″ diameter steam-assisted flare with a flow capacity of 937,000 lb/h and a 24″ diameter air-assisted flare with a flow capacity of 144,000 pounds per hour were operated with mixtures of natural gas, propylene, and nitrogen or natural gas, propane, and nitrogen at flow rates less than 1% of maximum flow. Combustion efficiency (percentage of the flared gases converted to carbon dioxide and water) ranged from less than 50% to more than 99%. For the steam-assisted flare, combustion efficiency (CE) at low steam-to-vent gas flow ratios (0.5–1.0) was typically in excess of 95%. CE would gradually decrease as steam-to-vent gas ratio increased, to a point, after which CE would decrease dramatically. The steam-to-vent gas ratio at which CE would decrease dramatically depended on the heating value of the vent gas and the position of the steam injection. Higher heating values of the vent gas (600 vs 350 BTU/scf) and the minimization of steam coinjected with the vent gas, rather than injected at the flare tip, promoted higher CE. For the air-assisted flare, CE at low air assist rates (<30–50 times the vent gas flow rate) was typically above 90%. The CE decreased linearly with increasing air assist to vent gas ratio and did not exhibit the rapid decrease exhibited by the steam-assisted flare. Combustion efficiencies for vent gases with higher heating values (∼600 BTU/scf versus ∼350 BTU/scf) decreased more slowly in the air assisted flare. For both the steam- and air-assisted flares, the composition of the vent gas (propane vs propylene) had a much smaller effect on combustion characteristics than steam or air injection and vent gas heating value. Products of incomplete combustion were dominated by CO; other significant species included acetylene, ethylene, formaldehyde, acetaldehyde, and acrolein. The effect of wind speed on CE was estimated to be less than 2.5% of the CE, over the range of wind speeds 0–16 mph.

The destruction and removal efficiency (DRE) computation of target hydrocarbon species in the flaring process is derived using carbon balance methodologies. This analysis approach is applied to data acquired during the Texas Commission on Environmental Quality 2010 Flare Study. Example DRE calculations are described and discussed. Carbon balance is achieved to within 2% for the analysis of flare vent gases. Overall method uncertainty is evaluated and examined together with apparent variability in flare combustion performance. Using fast response direct sampling measurements to characterize flare combustion parameters is sufficiently accurate to produce performance curves on a large-scale industrial flare operating at low vent gas flow rates.

Full scale flare tests have been conducted to test the impacts of flare operating conditions on the fraction of flared gases that are converted to carbon dioxide and water (combustion efficiency, CE) for flares combusting low heating value gases (∼350−600 BTU/scf) at low flow rates (∼0.1−0.25% of maximum flow). Flares produce lower flame temperatures when operating with low heating value gases at low combustion efficiencies than when operating with high heating value gases at high combustion efficiencies. This leads to reduced formation of nitrogen oxides (NOx) in the flame. For a series of tests conducted under low flow conditions, with low heating value gases, NOx emission factors ranged between 10 and 120% of the NOx emission factor reported in AP-42. Emissions of NOx were highest for air assisted flares operating at high CE and lowest for steam assisted flares operating at low CE. In general, emissions were lower in steam assisted flare tests than in air assisted flare tests conducted under similar conditions. Photochemical modeling simulations indicated that these reductions in NOx emissions had relatively small impacts on the ozone formation potential of flares operating at low CE.

The simultaneous use of nonequilibrium reaction processing and complex macromolecular architecture is an exciting way to achieve nanostructures that are not easily accessible via standard static block polymer self-assembly. Previous work has shown that the polymerization of styrene in the presence of a poly(styrene)-block-poly(butadiene) (PS-PBD) diblock copolymer induces a nanostructural transition from a lamellar (LAM) to a hexagonally packed cylinder (HEX) morphology. The transition was found to be driven by in situ PS grafting from the PBD block, which transforms the PS-PBD coil−coil diblock copolymer to a poly(styrene)-block-[poly(butadiene)-graf t-poly(styrene)] (PS-b-PBD-g-PS) coil−comb block polymer. In situ small-angle X-ray scattering and oscillatory shear dynamic mechanical spectroscopy measurements show that the order−order transition is not a simple epitaxial transition seen in prototypical block polymers, but undergoes a complex phase path in which the starting LAM phase at room temperature before polymerization initially disorders at elevated temperatures, evolves from a disordered phase to what is presumed to be a hexagonally perforated lamellae phase during the polymerization, and then transitions to a HEX phase on cooling to room temperature. The high-temperature phase persists for extended periods of time during the polymerization process, which allows for both the trapping and the characterization of the structure at room temperature. By utilizing nonequilibrium reactive processing to convert linear block copolymers to comb−coil type polymers, the creation of polymers with complex molecular topologies can be synthetically simplified while simultaneously allowing for the development of new processing modalities.

A magnetic, metallic inverse opal fabricated by infiltration into a silica nanosphere template assembled from spheres with diameters less than 100 nm is an archetypal example of a "metalattice". In traditional quantum confined structures such as dots, wires, and thin films, the physical dynamics in the free dimensions is typically largely decoupled from the behavior in the confining directions. In a metalattice, the confined and extended degrees of freedom cannot be separated. Modeling predicts that magnetic metalattices should exhibit multiple topologically distinct magnetic phases separated by sharp transitions in their hysteresis curves as their spatial dimensions become comparable to and smaller than the magnetic exchange length, potentially enabling an interesting class of "spin-engineered" magnetic materials. The challenge to synthesizing magnetic inverse opal metalattices from templates assembled from sub-100 nm spheres is in infiltrating the nanoscale, tortuous voids between the nanospheres void-free with a suitable magnetic material. Chemical fluid deposition from supercritical carbon dioxide could be a viable approach to void-free infiltration of magnetic metals in view of the ability of supercritical fluids to penetrate small void spaces. However, we find that conventional chemical fluid deposition of the magnetic late transition metal nickel into sub-100 nm silica sphere templates in conventional macroscale reactors produces a film on top of the template that appears to largely block infiltration. Other deposition approaches also face difficulties in void-free infiltration into such small nanoscale templates or require conducting substrates that may interfere with properties measurements. Here we report that introduction of "spatial confinement" into the chemical fluid reactor allows for fabrication of nearly void-free nickel metalattices by infiltration into templates with sphere sizes from 14 to 100 nm. Magnetic measurements suggest that these nickel metalattices behave as interconnected systems rather than as isolated superparamagnetic systems coupled solely by dipolar interactions.

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