CO2 Recirculation Research Articles

CO2 Capture and Enhanced Hydrogen Production Enabled by Low-Temperature Separation of PSA Tail Gas: A Detailed Exergy Analysis

Hydrogen from natural gas reforming can be produced efficiently with a high CO2 capture rate. This can be achieved through oxygen-blown autothermal reforming as the core technology, combined with pressure-swing adsorption for hydrogen purification and refrigeration-based tail gas separation for CO2 capture and recirculation of residual hydrogen, carbon monoxide, and methane. The low-temperature tail gas separation section is presented in detail. The main objective of the paper is to study and quantify the exergy efficiency of this separation process in detail. To achieve this, a detailed exergy analysis is conducted. The irreversibilities in 42 different process components are quantified. In order to provide transparent verification of the consistency of exergy calculations, the total irreversibility rate is calculated by two independent approaches: Through the bottom-up approach, all individual irreversibilities are added to obtain the total irreversibility rate. Through the top-down approach, the total irreversibility rate is calculated solely by the exergy flows crossing the control volume boundaries. The consistency is verified as the comparison of results obtained by the two methods shows a relative deviation of 4·10−7. The exergy efficiency of the CO2 capture process is calculated, based on two different definitions. Both methods give a baseline exergy efficiency of 58.38%, which indicates a high degree of exergy utilisation in the process.

Elucidating key mechanistic processes during acidic CO2 electroreduction on gas diffusion electrodes towards stable production of formic acid

The electrochemical reduction of CO2 using renewable electricity could be a sustainable alternative to produce formic acid. Although using bulk acidic electrolyte offers system and downstream processing benefits, neutral to alkaline electrolyte systems prevail due to challenge suppressing hydrogen evolution in acidic environment. In recent years, it has been shown that HER could be mitigated by confining the OH- being generated and constraining the movement of H3O+ towards reaction surface, thereby producing an alkaline reaction environment within the electrode. Herein, we have demonstrated how a porous and highly hydrophobic Bi-based gas diffusion electrode enables remarkably efficient bulk acidic electrolysis. Importantly, the local alkaline reaction environment has been proven via electrochemical impedance spectroscopy and pH visualization. Furthermore, optical monitoring of electrolyte conditions through a transparent cell sheds light on the CO2 recovery process in the acidic system, promoting a better technical practice in handling with electrochemical cells and CO2 recirculation. Finally, HCOOH accumulation as the key degradation reason is unveiled through investigation into the impact of operating modes on the stability at high current density, where earlier studies failed to adequately address. It is believed that this valuable insight could facilitate stable and efficient formic acid production in future work.

Polycyclic aromatic hydrocarbons (PAHs) and soot formations under different gasifying agents: Detailed chemical kinetic analysis of a two-stage entrained flow coal gasifier

The injection of CO2 with coal into coal gasifier is a promising approach to achieve CO2 recirculation. Predicting the formation and evolution of polycyclic aromatic hydrocarbons (PAHs) and soot during coal gasification is particularly important as their presence poses challenges to the gasifier operation and environment. However, the effect of CO2 injection on their formation must be elucidated in more detail to optimize the gasifier design. This work investigates PAHs and soot formations in gas-phase reactions under different gasifying agents (Air, O2/CO2, O2/H2O) in a two-stage entrained flow coal gasifier using a detailed chemical kinetic model (DCKM). Under the O2/CO2– and O2/H2O-blown conditions, aromatics reforming was progressed whereas the yields of tar and soot were effectively suppressed. The benzene was observed as the most abundant PAHs species, followed by naphthalene and acenaphthalene. Regarding the relative oxygen concentration, the conversion behavior of aromatics was significantly influenced in the O2/CO2-blown condition, while the somewhat effect was found in the O2/H2O-blown condition. Tar yield peaked at 50% relative oxygen concentration in the O2/CO2-blown condition. The present finding may have practical significance in the O2/CO2-blown gasifier to facilitate CO2 recirculation for the oxy-fuel IGCC system.

Closed hyperthermic intraperitoneal chemotherapy with CO2 recirculation system compared with the open Coliseum technique in peritoneal malignity treatment

BackgroundCytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal carcinomatosis can be performed in two ways: first, the standard open abdominal technique (Open HIPEC); or second, the closed technique. In recent years, a new technique has been introduced to perform closed HIPEC; the Peritoneal Recirculation System (PRS-1.0 Combat) with CO2 recirculation technology (PRS Closed HIPEC). The objective of this study is to present our experience with the PRS Closed HIPEC by comparing the intraoperative, postoperative and oncological results with the standard Open HIPEC technique (the Coliseum technique). MethodsData on patients undergoing CRS and HIPEC at the Sanchinarro University Hospital, Madrid from October 2012 to June 2021 were collected in a prospective database. The inclusion criteria were patients with primary or recurrent peritoneal metastases in gastrointestinal malignancies or ovarian cancer. The presence of an unresectable peritoneal carcinomatosis, the coexistence of another oncological disease, unresectable and distant metastases were the exclusion criteria. ResultsFrom October 2014 to June 2021, 84 patients underwent CRS and HIPEC at the Sanchinarro University Hospital, Madrid with curative intent. Since the introduction of the PRS Closed HIPEC technique in 2016, 65 patients have been treated. Before the introduction of PRS Closed HIPEC, 19 cases were performed using the Coliseum technique (the Open HIPEC group). The intraoperative results were similar in the two groups. Complete cytoreduction was achieved in all cases in the Open HIPEC group and in 98% in the PRS Closed HIPEC group. The rate of major complications was similar between the groups. Median Overall Survival (OS) resulted better in the Closed HIPEC group (67 months) with respecto to the Open group (43 months) (p < 0,001). Median Disease-Free Survival (DFS) was 15 months in the Open HIPEC group and 40 months in the PRS Closed HIPEC group (p < 0.001). ConclusionThe Peritoneal Recirculation System with CO2 recirculation technology (PRS Closed HIPEC) is a reproducible and safe technique and may represent a valid alternative for the administration of HIPEC.

Mixotrophic chain elongation with syngas and lactate as electron donors.

Feeding microbial communities with both organic and inorganic substrates can improve sustainability and feasibility of chain elongation processes. Sustainably produced H2 , CO2 , and CO can be co-fed to microorganisms as a source for acetyl-CoA, while a small amount of an ATP-generating organic substrate helps overcome the kinetic hindrances associated with autotrophic carboxylate production. Here, we operated two semi-continuous bioreactor systems with continuous recirculation of H2 , CO2 , and CO while co-feeding an organic model feedstock (lactate and acetate) to understand how a mixotrophic community is shaped during carboxylate production. Contrary to the assumption that H2 , CO2 , and CO support chain elongation via ethanol production in open cultures, significant correlations (p < 0.01) indicated that relatives of Clostridium luticellarii and Eubacterium aggregans produced carboxylates (acetate to n-caproate) while consuming H2 , CO2 , CO, and lactate themselves. After 100 days, the enriched community was dominated by these two bacteria coexisting in cyclic dynamics shaped by the CO partial pressure. Homoacetogenesis was strongest when the acetate concentration was low (3.2g L-1 ), while heterotrophs had the following roles: Pseudoramibacter, Oscillibacter, and Colidextribacter contributed to n-caproate production and Clostridium tyrobutyricum and Acidipropionibacterium spp. grew opportunistically producing n-butyrate and propionate, respectively. The mixotrophic chain elongation community was more efficient in carboxylate production compared with the heterotrophic one and maintained average carbon fixation rates between 0.088 and 1.4g CO2 equivalents L-1 days-1 . The extra H2 and CO consumed routed 82% more electrons to carboxylates and 50% more electrons to carboxylates longer than acetate. This study shows for the first time long-term, stable production of short- and medium-chain carboxylates with a mixotrophic community.

Hyperthermic Intraperitoneal Chemotherapy and Recirculation with CO2: A Safe Technique.

Introduction: Hyperthermic IntraPEritoneal Chemotherapy (HIPEC) has evolved as a treatment for peritoneal carcinomatosis in various tumors after a careful and complete cytoreductive surgery, and it demonstrated much better and longer survival than more traditional therapeutic schemas. Our objective has been to examine the safety, efficacy and survival achieved with closed technique with CO2-agitation system Combat PRS® (Peritoneal Recirculation System: PRS). To achieve this, we compared the appearance of adverse events, mortality and survival with the described using classic techniques (open, closed without CO2-agitation) for the treatment of selected patients with peritoneal carcinomatosis; Materials and methods: We studied overall survival, disease-free survival and safety (morbidity and mortality) of the administration of HIPEC through a closed method technique with CO2 recirculation (Combat PRS®) in 482 patients from 11 Spanish hospitals; Results: The mortality of our technique (1.66%) was similar to other published techniques (open, closed). Morbidity exhibited a 9.96% rate of Clavien-Dindo (CD) III/IV complications in 482 patients, which was lower than in other series. Survival (overall survival (OS) and disease-free survival (DFS)) was similar to previously published results: 86% 1y-OS, 54% 3y-OS, 77% 1y-DFS and 31% 3y-DFS; Conclusion: The procedure with closed PRS with CO2 agitation is as safe as standard open and closed procedures for the administration of HIPEC after complete cytoreductive surgery, with similar and very low mortality (1.66%) and lower morbidity (9.96% CD III and IV in our series vs range of 20–40% in the majority of different series); only Kusamura had similar results, with 12% in 205 patients, using the closed technique without CO2 agitation).

Phosphogypsum conversion under conditions of SC-CO2

This article looks into process of supercritical-CO2 phosphogypsum (PG) conversion, which is production residue after making mineral fertilizers by "Kasphosphate" LLC. Nowadays, over 30 million tons of PG have been accumulated in Kazakhstan; its background radiation is low enough to recycle it into valuables such as construction materials, rare earth elements and strontium salts. Complete factorial experiment method was used to describe conversion process; conversion of PG into CaCO3 was optimized using simplex method. Conversion optimization outcomes show possibility of using fewer reagents and shortening conversion process compared to existing technologies. Conversion degree is 87% after 10 min at 33 °С. Conversion was carried out at semi-industrial supercritical equipment with maximum CO2 flow rate up to 5000 g/min and integrated CO2 recirculation system. Characteristics of initial PG samples and conversion products/semi-products were done using X-ray phase analysis, scanning electron microscopy, atomic absorption spectroscopy, ICP-MS, and gravimetric procedure. In order to obtain purer CaCO3 PG was cleared of water-soluble impurities beforehand. As conversion result, finely dispersed CaCO3 and Ca(HCO3)2 as well as Na2SO4 solution were obtained.

Comparative Analysis of Gasification and Adiabatic Digestion of Corn for Practical Implementation in Conventional Gas Turbines

Clean, more responsible energy production in gas turbine power plants is a challenge. Interestingly, various alternative sources could be found in agricultural locations with great potential of being transformed from agricultural waste to energy. Corn cob gasification gas could be successfully implemented in gas turbines through co-firing with natural gas. Concurrently, agricultural biogas could also be employed for such a purpose. The technology could be implemented in locations such as Vojvodina, Serbia, which is an agricultural region with great potential for producing biogas from agricultural waste. Therefore, this paper approaches the practical implementation of gas produced by adiabatic corn digestion with CO2 recirculation. Five different cases were assessed. The results are compared to previous analyses that used co-firing of the corn cob gasification gas in representative gas turbine systems. Impacts of the fuel composition on the characteristics of combustion were analyzed using CHEMKIN PRO with GRI–Mech 3.0. Impacts of fuel quality on the power plant performance were analyzed through calculations with a numerical model based on a Brayton cycle of 3.9 MW power output. The application shows acceptable values during co-firing with natural gas without modification of the overall system, with better outlet parameters compared to pure corn gasification gas.

Research and Development of the Oxy-Fuel Combustion Power Cycles with CO2 Recirculation

The transition to oxy-fuel combustion power cycles is a prospective way to decrease carbon dioxide emissions into the atmosphere from the energy sector. To identify which technology has the highest efficiency and the lowest emission level, a thermodynamic analysis of the semiclosed oxy-fuel combustion combined cycle (SCOC-CC), the E-MATIANT cycle, and the Allam cycle was carried out. The modeling methodology has been described in detail, including the approaches to defining the working fluid properties, the mathematical models of the air separation unit, and the cooled gas turbine cycles’ calculation algorithms. The gas turbine inlet parameters were optimized using the developed modeling methodology for the three oxy-fuel combustion power cycles with CO2 recirculation in the inlet temperature at a range of 1000 to 1700 °C. The effect of the coolant flow precooling was evaluated. It was found that a decrease in the coolant temperature could lead to an increase of the net efficiency up to 3.2% for the SCOC-CC cycle and up to 0.8% for the E-MATIANT cycle. The final comparison showed that the Allam cycle’s net efficiency is 5.6% higher compared to the SCOC-CC cycle, and 11.5% higher compared with the E-MATIANT cycle.

Cytoreductive surgery and mitomycin C hyperthermic intraperitoneal chemotherapy with CO2 recirculation (HIPEC-CO2) for colorectal cancer peritoneal metastases: analysis of short-term outcomes.

Peritoneal dissemination from colorectal cancer (CRC) has long been associated with unfavorable prognosis. However, in the last decades, the combination of cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) was able to obtain up to 30% 5-year survival rate in selected centers. Despite the wide diffusion of CRS and HIPEC, until now, there are no clear recommendations on the drug of choice for HIPEC nor its technique, and safety and efficacy data of HIPEC regimens and techniques are lacking. We performed a retrospective analysis of a prospectively maintained database of 26 CRS and mitomycin C HIPEC with CO2 recirculation (HIPEC-CO2) for CRC peritoneal metastasis (PM) performed at our center. The main endpoints were morbidity, mortality, the temperature of perfusate during HIPEC and metabolic changes throughout the procedure. Morbidity was assessed by analysis of postoperative adverse events according to the Common Terminology Criteria for Adverse Events (CTCAE version 4.0). Continuous variables of Arterial Blood Gas (ABG) analysis at three time-points were compared by the Student t test. There were no postoperative deaths. The overall grade 3-4 CTCAE complications rate at 30days was 38.4%, with ten severe adverse events occurring to six (23.0%) patients. The temperature within HIPEC perfusion maintained between 41 and 42°C in all cases and we experienced no HIPEC-related intraoperative complications. We observed a significant difference between all baseline and pre-HIPEC ABG parameters evaluated but no statistically significant differences between pre- and post-HIPEC ABG outcomes. This study shows that mitomycin C HIPEC-CO2 is feasible and has a safety profile comparable to that of other HIPEC techniques reported in the literature. Further research is needed to validate prospectively the safety and efficacy of this technique.

Design and evaluation of a novel system for the flue gas compression and purification from the oxy-fuel combustion process

The process of flue gas compression and purification is essential for oxy-fuel combustion, because of its significance in determining the quality of the CO2 product. Based on the difference of dew points between CO2 and acid contaminants, a novel system, which integrated the partial CO2 recirculation with the flue gas purification, was proposed and evaluated in this study. The simulation results confirmed that a CO2 stream with a purity of 99.9% could be achieved, and the distillate after treatment in SO2 and NO absorbers could be directly recycled back to the boiler. The performance of CO2 recovery was enhanced by elevating the condensing pressure to 3.0–4.0 MPa. Besides, there was a critical ratio between the recycled CO2 liquid and the raw flue gas for the abatement of contaminants, which was 11.0 L/m3. Furthermore, the performances of SO2 and NO removal were investigated. The efficiencies of SO2 and NO abatement could be more than 99% when the reaction pressures were 0.5 MPa and 1.5 MPa separately. Besides, a critical molar ratio of SO2 to NO in the raw feeding flue gas was determined, and the removal of SO2 was restrained when the SO2/NO molar ratio increased over the critical point. As for the NO abatement, the continuous re-oxidation of NO released from the dissociation of HNO2 was dominant in the NO absorber, and the performance of NO removal was dramatically enhanced with the presence of NO pre-oxidation at low reaction pressures.

Energy and exergy analysis of biogas fired regenerative gas turbine cycle with CO2 recirculation for oxy-fuel combustion power generation

In this paper, thermodynamic performance of oxy-biogas regenerative gas turbine cycle with CO2 recirculation is evaluated. The CO2 stream is split into the primary and dilution zones. In the primary zone, chemical-equilibrium-model is applied for exergy analysis. Influences of relevant parameters—CO2-to-O2 molar ratio (CtO) in the primary zone and primary diluent ratio (PDR)—on the temperature of combustion chamber (CC) and turbine, net produced power, thermal efficiency, specific fuel consumption (SFC) and CO2 capturing mass flow rate are studied. Decreasing CtO and raising PDR result in high net produced power. Thermal efficiency has a maximum value in the range of CtO (1.5<CtO<4.0) and PDR (0.2<PDR<0.6) and by enhancing CtO, exergy destruction diminishes in both zones. With increasing the CtO in the range of 1.5–2.98, thermal efficiency is increased by 9.92% while variation of CtO in the range of 2.98–4 results in reduction of thermal efficiency by 1.3%. In the range of PDR, the minimum value of SFC is 388 g/kWh and in the range of CtO, the lowest achievable SFC is 387.4 g/kWh. Additionally, dilution zone exergy destruction and CC exergy efficiency increases with PDR and CtO. The two-zone model provided an appropriate control on the turbine inlet temperature.

Improving the Carbon Capture Efficiency for Gas Power Plants through Amine-Based Absorbents

Environmental concern for our planet has changed significantly over time due to climate change, caused by an increasing population and the subsequent demand for electricity, and thus increased power generation. Considering that natural gas is regarded as a promising fuel for such a purpose, the need to integrate carbon capture technologies in such plants is becoming a necessity, if gas power plants are to be aligned with the reduction of CO2 in the atmosphere, through understanding the capturing efficacy of different absorbents under different operating conditions. Therefore, this study provided for the first time the comparison of available absorbents in relation to amine solvents (MEA, DEA, and DEA) CO2 removal efficiency, cost, and recirculation rate to achieve Climate change action through caron capture without causing absorbent disintegration. The study analyzed Flue under different amine-based solvent solutions (monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA)), in order to compare their potential for CO2 reduction under different operating conditions and costs. This was simulated using ProMax 5.0 software modeled as a simple absorber tower to absorb CO2 from flue gas. Furthermore, MEA, DEA, and MDEA adsorbents were used with a temperature of 38 °C and their concentration varied from 10 to 15%. Circulation rates of 200–300 m3/h were used for each concentration and solvent. The findings deduced that MEA is a promising solvent compared to DEA and MDEA in terms of the highest CO2 captured; however, it is limited at the top outlet for clean flue gas, which contained 3.6295% of CO2 and less than half a percent of DEA and MDEA, but this can be addressed either by increasing the concentration to 15% or increasing the MEA circulation rate to 300 m3/h.

Prospective randomized controlled trial on comparison of standard CO2 pressure pneumoperitoneum insufflator versus AirSeal\xae

BackgroundAirSeal® is a valve-free insufflation system that enables a stable pneumoperitoneum with continuous smoke evacuation and CO2 recirculation during laparoscopic surgery. Comparative evidence on the use of AirSeal® and standard CO2 insufflator in laparoscopic general surgery procedures is scarce. The aim of this study was to compare surgical outcomes between AirSeal® and standard CO2 insufflators in patients undergoing the most frequently performed laparoscopic procedures.MethodsOne hundred and ninety-eight patients undergoing elective laparoscopic cholecystectomy, colorectal surgery and hernia repair were randomized to either AirSeal® (group A) or standard pressure CO2 insufflator (group S). The primary endpoints were operative time and level of postoperative shoulder tip pain (Visual Analog Scale). Secondary outcomes included Clavien–Dindo grade complications, surgical side effect and length of hospital stay.ResultsPatients were randomized to either group A (n = 101) or group S (n = 97) and were analyzed by intention-to-treat. There was no significant difference in mean operative time between the groups (median [IQR]; 71 min [56–94] in group A vs. 69 min [52–93] in group S; p = 0.434). Shoulder tip pain levels were significantly lower in group S (VAS 0 [0–3] in group S vs. 2 [0–4] in group A; p = 0.001). There was no significant difference in complications, surgical side effects (subcutaneous emphysema was not observed in any group) and length of hospital stay.ConclusionThis randomized controlled trial showed that using the AirSeal® system did not reduce operative time and was associated with a higher postoperative shoulder tip pain compared to standard CO2 insufflator for short elective surgeries.ClinicalTrials.gov (NCT01740011).

The impact of the AirSeal® valve-less trocar system in robotic colorectal surgery: a single-surgeon retrospective review.

Traditional trocar systems suffer from several innate flaws due to their silicone seal design. The AirSeal® is a valve-less trocar system that overcomes these flaws by utilizing a system of laminar flow and CO2 recirculation. The purpose of this paper is to examine the effect of the AirSeal® versus a traditional trocar system in operative time, EBL and post-operative complications. To the best of our knowledge, this is the first analysis of this system in robotic colorectal surgery. A single surgeon's database was reviewed and all LAR and right hemicolectomy robotic cases from 2014-2015 and 2017-2018 were included for analysis. Patient demographic information was evaluated and primary outcomes examined were operative time, EBL, post-operative complications and hospital LOS. Ninety four patients were identified in the LAR cohort and 56 patients were identified in the right hemicolectomy cohort. Mean operative time for LAR was 293 ± 91.6min in 2014-2015 and 232 ± 74.6min in 2017-2018 (p = 0.001); however, this significant difference was not seen between right hemicolectomies. Mean EBL for LAR was 209 ± 189cc in 2014-2015 and 150 ± 173.9cc in 2017-2018 (p = 0.05); again, this significant difference was not appreciated for right hemicolectomies. There was no statistically significant difference in rates of wound infections, pneumonia, post-operative pneumonia, DVT/PE, intra-abdominal/pelvic abscesses, or unplanned 30-day readmission rate between 2014-2015 and 2017-2018. Length of stay was reduced in both populations between 2014-2015 and 2017-2018; however, it neither reached statistical significance. In patients undergoing low anterior resections, the AirSeal® trocar system demonstrated a statistically significant reduction in mean operative time and EBL compared to the traditional trocar system. There was also a trend towards decreased length of stay and post-operative complications with AirSeal® use in low anterior resections and right hemicolectomies. In patients undergoing distal colorectal procedures, the AirSeal® trocar system should be considered.

Supercritical CO2 Drying of Red Bell Pepper

Supercritical CO2 food drying technique was investigated on red bell pepper with a lab-scale reactor equipped with CO2 recirculation. Box–Behnken design was used as experimental design to analyze the impact of temperature (313–333 K), pressure (10–14 MPa), CO2 flow rate (80–220 kg/h), and treatment time (6 and 16 h) on the final water activity. The results demonstrated that temperature was the most influential variable, reaching the lowest value of water activity (aw = 0.262) at 333 K, 12 MPa, and 100 kg/h. Efficient drying with a similar final water activity could be achieved at the lowest temperature considered (313 K) and longer drying time (16 h) with an appropriate combination of pressure (14 MPa) and flow rate (160 kg/h). Sc-CO2 samples showed similar values of color changes compared with freeze-dried samples with main differences corresponding to the “a” and “b” axes, i.e., in red and yellow. Textural properties of Sc-CO2 dried samples were not statistically different compared with freeze-drying. Sensory evaluation showed promising evidence for the use of supercritical CO2 as an alternative drying method to produce dried bell pepper products.

HIPEC-Closed Technique with CO2 Recirculation (PRS/Biosurgical®) in The Treatment of Peritoneal Carcinomatosis.

Background: Cytoreductive surgery asociated with Hyperthermic Intraperitoneal Chemotherapy (HIPEC) is turning out to be the recommended treatment of peritoneal carcinomatois especially in types of tumors where its efficacy has been demonstrated. Traditionally two types of application of the intaperitoneal chemotherapy are known: the open or so called “Coliseum technique” and the traditional closed technique, each technique with its advantages and inconveniences.

Features of Formation and Suppression of Sulfur Oxide Emissions During Burning Fuels in an Oxygen Medium With CO2 Recirculation

The main mechanisms of formation and suppression of sulfur oxides during combustion of solid fuels in a CFB and the main regime factors affecting the concentration of sulfur oxides during air combustion are considered. Features are demonstrated for mechanisms of formation and suppression of sulfur oxide emissions during combustion with oxygen, which are largely associated with a high partial pressure of carbon dioxide mixed with oxygen. Comparative analysis of the effect of entrapping SOx and regime factors during combustion of oxygen and CO2 in air and the environment is performed. The most preferred mathematical models for calculating SOx emissions are given and the calculated results are compared with experimental data. Directions and approaches for further research are indicated, primarily in the direction of modeling under conditions of combined combustion of coal and biomass. It is shown that it is important to conduct comprehensive studies of processes for formation and suppression of harmful emissions from combined combustion of coal and various types of biomass, especially when burning in an oxygen atmosphere with CO2 recirculation.

Process and sustainability analyses of the integrated biomass pyrolysis, gasification, and methanol synthesis process for methanol production

Technical and sustainability analyses of the methanol production via the integrated biomass pyrolysis, gasification, and methanol synthesis (IBPGM) process using rice straw as feedstock, are performed. The utilization of emitted CO2 by recycling to a gasifier as a gasifying agent is investigated for technical and environmental reasons. The effects of CO2 recirculation on the product distribution and energy consumption of the IBPGM process are examined. The production rate of methanol is improved with the increased CO2 recycle fraction, while that of bio-oil does not change. The IBPGM is a highly exothermic process, with the largest energy-releasing unit being the methanol reactor. The energy consumption at the gasifier exhibits the same trend and thermal self-sufficiency is consequently achieved when the recycle fraction is raised to 0.76. Environmental assessment using a life cycle analysis tool reveals that the energy management of methanol synthesis unit and syngas processor needs to be improved as they highly contribute toward the carbon footprint and potential environmental impact. The technical and environmental factors of the IBPGM process are evaluated by the analysis hierarchy process, calculated by a multi-criteria decision analysis method. The IBPGM process with the CO2 recycle fraction of 0.2 offers the best performance. Under this condition, the methanol and bio-oil production rates of 0.23 and 0.09 kmol h−1, respectively, and the energy efficiency of 60.7% can be achieved, based on the biomass feed rate of 1 kmol h−1.

Spectral Radiation Analysis of Premixed Oxy-Methane Flames

For a hydrocarbon burning with oxygen, the resulting exhaust stream is composed mainly of carbon dioxide and water vapor. This exhaust allows for easier carbon capture and sequestration since the water can be condensed out. Another advantage is the significant reduction of NOx since much of the nitrogen found in air-fired systems is eliminated. Although beneficial, many of the exhaust gas products' radiative heat transfer characteristics are unknown. Motivated by this, this paper focuses on the spectral radiation measurement of premixed oxy-methane combustion flames. This is important for combustion system designers since radiative heat from the flame is significant for oxy-flames. This study is conducted by varying equivalence ratio, firing input, and CO2 recirculation ratio. The spectral radiation of premixed oxy-methane flames is collected from 1.2 μm to 5 μm wavelengths. During the experimental study, it is found that the water vapor emits at 1.4 μm, 1.85 μm, and 2.5 μm wavelengths. A short band of carbon dioxide emission is detected at 1.96 μm. Three other carbon dioxide radiation maxima are observed at the proximity of 2.71 μm, 2.85 μm, and 4.38 μm. The study revealed that the spectral intensity of CO2 and H2O for oxy-methane combustion increases almost five times compared to the air-methane combustion at stochiometric condition. It is also found that the spectral intensity decreases as the equivalence ratio increases. The spectral radiative emission intensity increases as the firing input increases. Another observation includes the fact that spectral intensity increases up to five times when 60% CO2 is recirculated as a diluent in the flame.