CO2 Concentration In Gas Research Articles

Improvement of SiO2 surface morphology during the selective Si3N4 etching in the multi-layered 3D NAND Si3N4/SiO2 stack structures by the generation of CO2 gas through the control of redox reaction

Selective removal of silicon nitride (Si3N4) layers from multilayer Si3N4/silicon dioxide (SiO2) stack structures is essential for fabricating 3-dimensional (3D) NAND flash memory devices. Although phosphoric acid (H3PO4) selectively etches Si3N4 layers to a certain degree, the tip thicknesses of the SiO2 layers increase owing to oxide regrowth, and the SiO2-layered trenches become clogged. In particular, the oxide regrowth phenomenon worsens as it progresses to the bottom of the structure. In this study, carbon dioxide (CO2) gas was generated by adding acidic reducing agents to H3PO4 to suppress the oxide regrowth in the stack structure. CO2 gas creates a turbulent flow in the slits and SiO2/Si3N4/SiO2 trenches, promoting the diffusion of Si3N4 etch byproducts from the cul-de-sac of the SiO2/Si3N4/SiO2 trench structures to the outside of the stack structure. The addition of oxalic acid to H3PO4 generated a high concentration of CO2 gas and selectively etched Si3N4 layers without oxide regrowth in the stack structure. Finally, the selective etching of Si3N4 layers, which is faster and more uniform than that in pure 85 wt.% H3PO4, was performed without oxide regrowth in the entire 128-layer Si3N4/SiO2 multi-stack structure.

Key technologies for CO2 capture and recycling after combustion: CO2 enrichment in oxygen enriched combustion of converter gas

With the progress of industrial development, global total CO2 emissions have increased exponentially. For example, although iron and steel industries have played an important role in the process of economic development, their CO2 emission intensities have reached 2.0 tCO2/t steel. Therefore, accomplishing CO2 emission reduction in iron and steel industries will have a great impact on the overall CO2 emission reduction. Devising a method for capturing CO2, with low energy consumption and high efficiency, will be of great significance to the large-scale capture of CO2 by iron and steel enterprises. In this study, numerical simulation and experimental research are used to analyze the influence of the parameters of oxygen-enriched combustion and conditions of converter gas on the concentration of CO2 in flue gas and the generation of NOx. The variation laws for the temperature field of oxygen-enriched combustion and flue gas composition of converter gas are explored. A front-stage combustion scheme suitable for CO2 capture after combustion is then defined. Herein, the CO2 content of flue gas was 74.32%, whereas the generation of NOx was 113.3 ppm, which fulfilled the NOx emission standard for new gas-fired boilers in China. The influence of the CO2 content of flue gas on the capture efficiency and energy consumption was further studied. The capture time and power consumption were reduced by 37.6% and 38.8%, respectively. The results of this study can provide a new idea and theoretical data reference for large-scale CO2 capture and utilization in iron and steel industries.

Method for demodulating the overlapping absorption spectra of CO and CH4.

When measuring the concentrations of individual gases in gas mixtures via laser absorption spectroscopy, the widening of adjacent absorption spectral lines can cause them to overlap, which hinders the calculation of the gas concentrations. In this study, the causes of this hindrance are analyzed. By using the Partial Least Squares (PLS) algorithm, the relative error in the measured CO concentration for a mixture of CO and CH4 gases was less than 10% even when the volume ratio VCH4/CO (The ratio of CH4 gas concentration to CO gas concentration) reached 100. These results show that the PLS algorithm is able to determine accurate concentrations even with significant broadening and interference of spectral lines in mixed gases.

Evaluation of carbonation coefficient of reinforced concrete structures

ABSTRACT With the advancement of modern construction technology, reinforced concrete (RC) has become the most widely used composite construction material. Corrosion of embedded reinforcement bars in RC structures, which is essentially the result of carbonation and chloride attack, is regarded as one of the weaknesses. Hence, many research studies have been conducted to evaluate the effect of corrosion on the service life of RC structures. However, so far no proper equation has been derived to predict the extent of carbonation-induced corrosion. Identifying this research gap, the present study intends to derive an equation for the coefficient of carbonation (K), which is the governing measure of the rate of carbonation. This paper identifies concrete grade, exposed CO2 gas concentration, and exposed Relative Humidity (RH) level as the major parameters affecting the carbonation process. The behaviour of each factor along with K was identified by conducting a modified accelerated carbonation test (ACT). These experimentally derived K values were statistically analysed under the principle of multiple linear regression, to derive an equation for predicting K values for RC structures. Based on the results, this paper proposes two user-friendly mathematical models covering the entire environmental RH range to predict the K values of RC structures.

CO2 Thermal Conductivity Detection in Gas Mixture for Concentration Measurement Using Bridge Configuration of Thermopiles

In this research, improvisation was carried out by modifying the market IR thermopile which functions as a thermal conductivity detector to measure the concentration of CO2 gas in the gas mixture. Four thermopiles are configured with a Wheatstone bridge with the aim of increasing the accuracy of the measurement system in detecting changes in CO2 concentration in the gas mixture (N2 and CO2). Using the bridge configuration of these four thermopiles, this measurement system can measure changes in CO2 concentration in small orders. The sensor developed is easy to manufacture, low cost, and has high linearity as evidenced by a correlation coefficient of 0.9943. From the experiments carried out, the sensor works quite accurately in detecting CO2 concentrations with the sensor’s sensitivity of -88.19 Volt/%, the detection range is 0% to 100%, and the RMS error value is 2.25.

ENVIRONMENTAL HEALTH RISK ANALYSIS OF CARBON MONOXIDE GAS EXPOSURE AMONG TRADERS OF GIWANGAN TERMINAL, YOGYAKARTA

Introduction: The characteristics of CO gas are that it has no color, odor, and taste resulting from incomplete combustion, which accounts for 70% of motorized vehicle-related air pollution. Terminal traders are among those who are vulnerable to pollution caused by motorized vehicles. The study's goal was to determine the environmental health risk analysis of CO gas exposure to traders at Yogyakarta's Giwangan Terminal. Methods: This study was quantitative using a cross-sectional design study with the Environmental Health Risk Analysis (EHRA) approach. This study used purposive sampling technique. The population was traders, with a sample of 51 respondents. The research instrument is a questionnaire. The Chi-square test was used to measure the bivariate analysis data. Results and Discussion: The average concentration of CO gas was 0.9523 mg/m³, exposure duration was 12.1 hours/day, exposure frequency was 339.94 days/year, exposure duration was 11.96 years, and inhalation rate was 4.1 m³/o'clock. The highest abnormal blood pressure was 40 respondents. Real-time intake min. 0.0184 mg/kg/day, max. 3.0919 mg/kg/day (arrival), real-time intake min. 0.0190 mg/kg/day, max. 3.2021 mg/kg/day (departure). A total of 43 traders had a risk quotient (RQ) > 1. Conclusion: There was a relationship between the intake and the RQ of CO gas exposure but no relationship between blood pressure and the RQ due to CO gas exposure to traders at the Giwangan Terminal, Yogyakarta.

Solution combustion synthesis derived Li4SiO4 for post-combustion carbon capture

ABSTRACT Lithium-based sorbents are considered as promising candidates for post-combustion carbon capture because of their superior stability compared to CaO. In the present study, Li4SiO4 powders were synthesized by Solution Combustion Synthesis (SCS) technique using LiNO3 as lithium source, TEOS as silicon source and citric acid as the fuel. CO2 sorption tests were carried out for the synthesized samples and, powder prepared at 650°C during 4 h, which has 17 µm of particle size, 5.2 m2 g−1 of specific surface area, 85.2% Li4SiO4 phase purity with 97 nm of crystallite size showed a sorption performance as 29.5 wt% CO2 uptake value, in thermobalance test under 92 vol% CO2 (N2 balance) gas concentration at 600°C. The sample had a CO2 uptake value of 21.4 wt% under 20 vol% CO2 concentration which was chosen to simulate industrial off-gas conditions. Also, the same sample showed a good cyclic durability during the sorption/desorption tests. The sample maintained its cyclic CO2 uptake capability range between 21 and 24 wt% for 15 cycles.

Techno-economic analyses of Sulfinol-based absorber-stripper configurations for improving the energy consumption of natural gas sweetening process

This work presents a two-step method to reduce the energy consumption (in terms of the reboiler duty) of a natural gas sweetening process via a physical-chemical solvent mixture (Step 1) followed by a techno-economic analysis of 15 different absorber-stripper configurations (Step 2). Initially, an amine-based sweetening process using a H2S-free sour gas was simulated on Aspen HYSYS and the simulation results were validated against real plant data. In Step 1, different ratios of Sulfinol-M and Sulfinol-D based sweetening process were simulated and the superior physical-chemical solvent mixture that provides the lowest reboiler duty while meeting the sweet gas CO2 product concentration specification (i.e., less than 2 mol.%) is the Sulfinol-M solvent that contains 38 wt.% methyl diethanolamine (MDEA), 40 wt.% Sulfolane, and 22 wt.% water. This Sulfinol-M based model is then optimized via a parametric analysis to further improve its performance in terms of the reboiler duty prior to Step 2. The optimized Sulfinol-M based model achieved 65% saving in the reboiler duty while fulfilling the CO2 concentration specification in product gas relative to the base case. In Step 2, four main absorber-stripper configurations, namely absorber intercooling (AI), lean amine stream split flow (LASSF), rich amine stream split flow (RASSF), and mechanical vapor recompression (MVR) along with their 11 possible combinations were simulated in an attempt to decrease the energy consumption of the process and hence, ranked based on their total cost of production (TCOP). The results revealed that the integration of LASSF + RASSF provides the best option as it achieved the lowest TCOP of $4.60 M while fulfilling the CO2 concentration in product gas and contributed to 6.39% savings in the reboiler duty compared to the optimized conventional Sulfinol-M based model.

Oxygen distribution and gaseous products change of coal fire based upon the semi-enclosed experimental system

Coal spontaneous combustion (CSC) is the combustion of the outcrop or shallow part of a coal seam due to long-term oxidation or artificial factors. Because of the continuous development of surface cracks, oxygen is constantly transported to the high-temperature zone, promoting diffusion to the deep coal seam. This study independently established a semi-closed experimental system. Coal samples from Lu'an, Shanxi Province, China were selected as the research objects, and 15 points were established in the coal seam to probe the law of temperature change to determine the high-temperature zone. It further revealed the distribution law of oxygen and gaseous products in the high temperature region during CSC. Finally, various index systems were determined. The results show that CO, CO2, CH4, and C2H4 gas concentrations increased during the heating stage and decreased during the cooling stage. Furthermore, there are “mutation” processes and “delay” in the points between the same layers of various gases. The determination indices in the heating stage were φ(CO)/φ (CO2), Graham number, and Grignard fire coefficients R2 and R3. In contrast, the cooling stages were φ(C2H4)/φ (CH4), Graham number, and Grignard fire coefficients R1 and R2.

IMPLEMENTING BREATH-BY-BREATH VOLUMETRIC CAPNOGRAPHY DEAD-SPACE COMPONENT CALCULATION DURING INCREMENTAL CYCLE EXERCISE

IMPLEMENTING BREATH-BY-BREATH VOLUMETRIC CAPNOGRAPHY DEAD-SPACE COMPONENT CALCULATION DURING INCREMENTAL CYCLE EXERCISE

Dispersion of Carbon Monoxide Pollutant and The Effect of Health (Case Study on Frontage Road Surabaya by Gaussian Line Source Equation Model)

Air pollution was being a very important problem and danger for human life. This was related to diseases that arise due to motor vehicle emissions, especially carbon monoxide. Simulation of air dispersion models is the one way to study about air quality that is needed in this regard. This study aims to determine the distribution of carbon monoxide pollutants in Ahmad Yani's frontage and to anticipate the dangers of these pollutants to the health of the people living around the research location. This research discussed about the mathematical model of the dispersion of CO that emitted from cars that passed through the frontage road on the Ahmad Yani Street, Surabaya. The method used is direct observation in the field and numerical simulation using a mathematical model, Gaussian Line Source Equation Model (GLSEM). GLSEM had prepared based on the mechanism of transport of pollutants in dispersion, diffusion and advection. With GLSEM we calculated CO gas concentration values for certain heights downwind. We validated the model by comparing numerical results and measurements of CO concentration. We used the R2 test and we got an R2 close to one. We simulated GLSEM by used Fortran programming language and visualized it with Surfer. The results of the visualization in June showed that the pattern of CO gas dispersion was influenced by the direction and speed of the wind. The results obtained are that the distribution of CO pollutants in the Ahmad Yani frontage is horizontal/downwind. CO concentrations at night are higher than during the daytime. From the CO dispersion pattern, we had known that there were dangerous of air around the frontage for people health. We conclude that around the frontage road of the Ahmad Yani highway there is sufficient open air space so that the danger of CO pollutants being emitted can be minimized so that the health of the community, namely pedestrians, motorcycle drivers and the community around the location can be protected.

Flood water hydrogeochemistry characteristics in Pindul Cave, Gunungsewu Karst Area, Indonesia

Pindul cave located in Gunungkidul Regency, Gunungsewu Karst Area, Indonesia has a unique characteristic which is dominated by surface rivers (allogenic recharge) and groundwater (autogenic recharge). The main purpose of this study is to analyze temporal variation of flood water hydrogeochemistry in Pindul Cave. Water sampling for flood hydrogeochemistry analysis is taken in the wet season for three selected flood events. Parameters of hydrogeochemistry analysis consist of major dissolved element (Ca2+ and HCO3 −); conductivity; total dissolved solid; SI calcite; log PCO2; and pH. The result shows that there was correlation between flood discharge and hydrogeochemistry parameters. The hydrogeochemistry of flood events in Pindul Cave typified by a low value of calcium and bicarbonate and high CO2 gas content in water that indicated the dillution by precipitation processes. Pindul Cave also show the negative value of calcite during flood event which mean that groundwater is unsaturated, so it becomes aggressive towards calcite. According to the flood water hydrogeochemistry characteristics, Pindul Cave is dominated by conduit flow from the large-fracture that already developed.

Effects of Low-Concentration Carbon Dioxide Exposure at Bedtime on Sleep in Adults With Insomnia Symptoms

Objectives: Carbon dioxide (CO2) accumulation in an enclosed space might cause drowsiness. This study aimed to assess the effect of bedtime exposure to low concentrations of CO2 gas on the sleep quality of adults with insomnia.Methods: In this double-blind, randomized, sham-controlled cross-over study, we consecutively recruited 24 adults (9 men; age, 55.4±6.3 y) complaining of sleep disturbances (Pittsburgh Sleep Quality Index ≥5). The following two interventions were used in the study: exposure to 2% low-concentration edible CO2 gas (experimental intervention) and exposure to room air (sham-controlled intervention). A sleep air device (Gosleep®, NYX), which atomizes CO2 gas, was used in both experimental and sham-controlled interventions. For the sham session, room air was generated for 18 min, and then, gradually reduced by degrees in the next 5 min with the device finally being turned off.Results: The group exposed to CO2 gas had longer time in bed (361.3±55.2 min vs. 347.2±35.7 min, p=0.034) and total sleep time (311.0±74.3 min vs. 287.2±69.4 min, p=0.010) than the group exposed to room air. Meanwhile, the total arousal (19.7±9.5/h vs. 24.0±13.7/h, p=0.011) and non-REM arousal (20.9±11.3/h vs. 25.1±14.9/h, p=0.008) indices were lower in the group exposed to CO2 gas than in the group exposed to room air. However, perceived total sleep time or sleep latency and Karolinska Sleepiness Scale scores were not significantly different between the two groups.Conclusion: Exposure to low concentrations of CO2 improved the total sleep time and arousal index in adults with insomnia. Unexpectedly, CO2 administration was found to be effective for sleep maintenance.

Environmental impacts of 222Rn, Hg and CO2 emissions from the fault zones in the western margin of the Ordos block, China.

Investigating the emissions of soil gas including radon, mercury and carbon dioxide (222Rn, Hg and CO2) from the solid earth to the atmosphere through active fault zones is of great significance for accession of atmospheric environment. In this study, the concentrations and fluxes of 222Rn, Hg and CO2 were measured at the main active fault zones at the western margin of the Ordos block, China. The concentrations of 222Rn, Hg and CO2 were in the range of 0-60.1kBq m-3, 3-81ng m-3 and 0.04-9.23%, respectively, while the fluxes of 222Rn, Hg and CO2 are in the range of 1.99-306.99mBq m-2s-1, 0-15.12ng m-2h-1 and 0-37.91g m-2d-1, respectively. Most of the major fault zones at the study area are CO2 risk-free regions (CO2 concentration in soil gas < 5%). However, the extend of 222Rn pollution at the fault zones of F1, F4, F5 and F9 (the fault number) and that of Hg pollution at the fault zones of F2, F4, F5 and F7 were higher than the pollution level of 1. The annual emission of Hg and CO2 from the western margin of the Ordos block was estimated to be 2.03kg and 0.70 Mt, respectively. Comprehensive analyses indicated that the higher emission rates of soil gases from the active fault zones were related to the seismic activities. The results suggest that the earthquake activity is a dominant factor enhancing the emission of 222Rn, Hg and CO2 from the solid earth through active fault zones and, furthermore, resulting great impact on the atmospheric environment.

Miniaturized CO2 Gas Sensor Using 20% ScAlN-Based Pyroelectric Detector.

NDIR CO2 gas sensors using a 10-cm-long gas channel and CMOS-compatible 12% doped ScAlN pyroelectric detector have previously demonstrated detection limits down to 25 ppm and fast response time of ∼2 s. Here, we increase the doping concentration of Sc to 20% in our ScAlN-based pyroelectric detector and miniaturize the gas channel by ∼65× volume with length reduction from 10 to 4 cm and diameter reduction from 5 to 1 mm. The CMOS-compatible 20% ScAlN-based pyroelectric detectors are fabricated over 8-in. wafers, allowing cost reduction leveraging on semiconductor manufacturing. Cross-sectional TEM images show the presence of abnormally oriented grains in the 20% ScAlN sensing layer in the pyroelectric detector stack. Optically, the absorption spectrum of the pyroelectric detector stack across the mid-infrared wavelength region shows ∼50% absorption at the CO2 absorption wavelength of 4.26 μm. The pyroelectric coefficient of these 20% ScAlN with abnormally oriented grains shows, in general, a higher value compared to that for 12% ScAlN. While keeping the temperature variation constant at 2 °C, we note that the pyroelectric coefficient seems to increase with background temperature. CO2 gas responses are measured for 20% ScAlN-based pyroelectric detectors in both 10-cm-long and 4-cm-long gas channels, respectively. The results show that for the miniaturized CO2 gas sensor, we are able to measure the gas response from 5000 ppm down to 100 ppm of CO2 gas concentration with CO2 gas response time of ∼5 s, sufficient for practical applications as the average outdoor CO2 level is ∼400 ppm. The selectivity of this miniaturized CO2 gas sensor is also tested by mixing CO2 with nitrogen and 49% sulfur hexafluoride, respectively. The results show high selectivity to CO2 with nitrogen and 49% sulfur hexafluoride each causing a minimum ∼0.39% and ∼0.36% signal voltage change, respectively. These results bring promise to compact and miniature low cost CO2 gas sensors based on pyroelectric detectors, which could possibly be integrated with consumer electronics for real-time air quality monitoring.

Poly(ionic liquid) boosts overall performance of electrocatalytic reduction of low concentration of CO gas

Electrocatalytic reduction of CO (CORR) provides a feasible way for not only CO2 conversion via tandem CO2-to-CO-to-C2+ process but also CO utilization from industrial exhaust gases. In this work, poly(ionic liquid) modified Cu catalyst (Cu@PIL) was employed as the electrocatalyst to convert low concentration CO gas to high-value C2+ products. An over 90 % faradaic efficiency of C2+ products (FEC2+) was obtained at a constant current density of 125.0 mA cm−2 within a broad range of feedstock concentrations from 100.0 to 40.0 vol%. Remarkably, excellent comprehensive performance was achieved with feeding CO gas as less as 5.0 vol%, delivering a high FEC2+ of 71.1 % with high CO conversion (67.4 %) and high energetic efficiency (29.1 %). Mechanistic studies suggest the local enrichment of CO via adsorption and accelerated mass transfer by porous PIL layer as well as the suppression of hydrogen evolution reaction enables the CO-to-C2+ transformation with diluted CO gas.

Electronic properties of the GaN nanowires surface activated by Cs/Li/NF3/Cs/Li alternate method in a high-concentration residual gas environment

The characteristics of models that adsorb different concentrations of H2O and CO2 residual gases on the surface of GaN nanowires activated alternately by Cs/Li/NF3/Cs/Li investigated systematically using first-principles, including adsorption energy, atomic structure, and work function, electron affinity and dipole moment. For the Cs/Li/NF3/Cs/Li alternately activated surface, H2O molecules are more likely to remain on the surface than CO2 molecules. In a high-concentration residual gas atmosphere, Cs/Li/NF3/Cs/Li alternately activated surface can be more stable than pure p-type surfaces. However, high concentrations of H2O and CO2 gas have a destructive effect on the activation layer, and it can even make the activated surface lose its negative electron affinity. The newly generated dipole moment from Cs and Li atoms to residual gas molecules greatly affects the normal operation of the cathode activation layer. From the analysis of characteristic data such as charge distribution and work function, the alternately activated cathode needs to work in a high vacuum state as much as possible to avoid generating a high-concentration residual gas environment.

Typical case of carbon capture and utilization in Chinese iron and steel enterprises: CO2 emission analysis

The CO2 emission intensity of the iron and steel industry has reached 2.0 tCO2/t steel, whereas the CO2 emission of the global iron and steel industry has exceeded 3.6 billion tons. Reduction of the CO2 emissions of the iron and steel industry is therefore the focus of this study. Based on the first set of tail gas captured from the CO2 converter smelting process of a lime kiln in China, this study compares the CO2 emissions of CO2-capture converter smelting processes after converter gas combustion, devises two system boundaries, and formulates four CO2 capture process paths. Through detailed calculation and analysis, the CO2 emission of chemical absorption is determined to be greater than that of pressure swing adsorption. Furthermore, the participation of CO2 in converter smelting is demonstrated to be able to reduce CO2 emission. An increase in CO2 concentration in the feed gas is conducive to reducing the CO2 emission of the CO2-capture converter smelting process. When the CO2 mixing ratio is 9.68%, a CO2 emission reduction of 25.32 kg CO2/t steel can be achieved. In 2020, China's long industrial processes will produce 954 million tons of crude steel; if the flue gas (80% CO2) is subjected to pressure swing adsorption after converter gas combustion, an annual CO2 emission reduction of 242 million tons can be reached.

Modification of a 240 kWth grate incineration system for oxyfuel combustion of wood chips

The objective of this work is the application of the oxyfuel combustion technology for grate incineration systems to increase the CO2 concentration in the flue gas for higher efficiency when processing the gas for storage or utilization. Therefore, an experimental 240 kWth moving grate combustion facility has been modified to allow the investigation of the combustion behavior under various oxyfuel conditions. Subsequent to the modification, combustion experiments with dried wood chips under air and several oxyfuel atmospheres have been performed. During oxyfuel operation, the oxygen concentration in the gas supply streams towards the furnace has been set to 30 vol.-% dry with recycled flue gas being the rest of the gas composition. The oxygen distribution between primary and secondary zone has been varied (30%/70%, 40%/60%). Additionally, one case with increased oxygen concentration in the primary zone (40 vol.-% dry) has been investigated. The results show that oxyfuel grate incineration of the given fuel in this setup is feasible. However, the combustion behavior differs significantly between air and oxyfuel conditions in the investigated cases. The CO2 concentration in the dry flue gas could be increased to around 73 vol.-% with 5.7 vol.-% excess O2. Compared to the reference air cases the emission rates of CO were also increased during oxyfuel operation. However, it seems manageable given enough excess oxygen (∼7 vol.-% dry). Although the temperature at the end of the furnace is comparable among the cases, oxyfuel combustion leads to lower maximum temperatures along the combustion chamber. Differences between 150 °C and 200 °C have been measured among corresponding air and oxyfuel cases. Also, the temperatures of the grate and inside the fuel bed are reduced during oxyfuel operation even in the case with increased O2 concentration leading to the impression that the thermal strain on the grate is lower compared to air operation with the same fuel throughput.

Gas absorption in a hydraulic air compressor. Part II: Experimental verification

Experimental verification of a one-dimensional steady-state bubbly flow model is presented. For initialisation of the liquid-phase concentrations of gas species, a formulation for modelling the time-evolution of the concentration of dissolved gas species in the circulating liquid of a hydraulic air compressor (HAC) was developed and integrated with the steady-state bubbly flow model. Observations from experiments conducted on a pilot scale HAC are presented employing CO2 as a tracer gas. The composition of the input gas inducted by the pilot HAC was deliberately varied by mixing different controlled amounts of CO2 gas while continuously monitoring the gas and liquid phase concentrations of CO2 at key points in the HAC process. Predictions of the concentration of CO2 in the compressed gas produced by the pilot HAC and the circulating liquid at system equilibrium were in good agreement with measured values. Concentrations of CO2 measured in the gas above the tailrace water level were elevated above background levels and responded in accordance with the input CO2 gas mass flow and liquid CO2 concentrations indicating exsolution of gas from the liquid as predicted. Observations of the pH of the circulating liquid identified the bicarbonate equilibrium as the likely mechanism for CO2(aq) production not captured by the model which caused the model to under predict CO2(aq) concentrations for experiment set points with CO2(aq) concentrations above 140 ppm.