CO2-rich Environment Research Articles

Cracking mechanism in API 5L X65 steel in a CO2-saturated environment

Hydrogen charging in low alloy steels poses a significant problem in the oil and gas industry. Detrimental hydrogen effects are not commonly expected in CO2 aqueous environments. However, the acid nature of these environments and the high corrosion rates expected justify the assessment of cracking susceptibility of carbon steel in a CO2-saturated environment as presented in this work. The focus of this investigation is to understand how different surface films/corrosion products influence the hydrogen permeation and cracking mechanism of an API 5L X65 carbon steel in a saturated CO2 environment. The experiments were carried out to assess hydrogen permeation at open circuit potential on steel samples which were either wet-ground, or pre-filmed with iron carbide (Fe3C) rich or iron carbonate (FeCO3) layers. Tafel measurements were also performed to determine the effect of the surface composition on the cathodic reactions. Slow strain rate tests (SSRT) were conducted in order to evaluate the effects of hydrogen on the cracking mechanisms of the steel in this sweet environment. Results indicated that at open circuit conditions, Fe3C was able to increase the steady state hydrogen permeation current due to accentuation of the cathodic hydrogen-evolution reaction. Although FeCO3 suppressed the cathodic reaction at the steel surface, the development of the protective and densely packed crystalline layer increased hydrogen uptake marginally from that of the ground steel reduced. SSRT indicated a very moderate loss of ductility in wet-ground and FeCO3 steel surface conditions. However, a more significant reduction in area was observed in the tests carried out on Fe3C rich samples. These results imply that a corroded API 5L X65 steel surface in a CO2 rich environment can enhance the hydrogen embrittlement (HE) susceptibility and as such, hydrogen permeation susceptibility needs to be considered in material selection.

Fabrication and characterization of a novel carbonated 0-3 piezoelectric γ-C2S composite

0-3 cement-based piezoelectric composites have been proposed as sensors and actuators in civil engineering for structural heath monitoring. Previous studies are focused exclusively on hydraulic binders such as ordinary Portland cement and sulfoaluminate cement. In this paper, a novel 0–3 piezoelectric composite is presented which consists of non-hydraulic gamma dicalcium silicate (γ-C2S) as the matrix and lead zirconate titanate (PZT) as the piezoelectric phase, utilizing carbonation reaction for the attainment of high mechanical strength. The effect of PZT content on the piezoelectric, dielectric and mechanical properties is investigated. When exposed to a CO2-rich environment for 2 h, the composite with 60 vol% PZT develops rapid strength to be 38.5 MPa and possesses a piezoelectric coefficient (d33) of 24.6 pC/N, a dielectric constant of 67.5 and tanδ of 0.11, which are comparable to what has been reported in other studies.

Modeling CO2–Water–Mineral Wettability and Mineralization for Carbon Geosequestration

Carbon dioxide (CO2) capture and storage (CCS) is an important climate change mitigation option along with improved energy efficiency, renewable energy, and nuclear energy. CO2 geosequestration, that is, to store CO2 under the subsurface of Earth, is feasible because the world's sedimentary basins have high capacity and are often located in the same region of the world as emission sources. How CO2 interacts with the connate water and minerals is the focus of this Account. There are four trapping mechanisms that keep CO2 in the pores of subsurface rocks: (1) structural trapping, (2) residual trapping, (3) dissolution trapping, and (4) mineral trapping. The first two are dominated by capillary action, where wettability controls CO2 and water two-phase flow in porous media. We review state-of-the-art studies on CO2/water/mineral wettability, which was found to depend on pressure and temperature conditions, salt concentration in aqueous solutions, mineral surface chemistry, and geometry. We then review some recent advances in mineral trapping. First, we show that it is possible to reproduce the CO2/water/mineral wettability at a wide range of pressures using molecular dynamics (MD) simulations. As the pressure increases, CO2 gas transforms into a supercritical fluid or liquid at ∼7.4 MPa depending on the environmental temperature. This transition leads to a substantial decrease of the interfacial tension between CO2 and reservoir brine (or pure water). However, the wettability of CO2/water/rock systems depends on the type of rock surface. Recently, we investigated the contact angle of CO2/water/silica systems with two different silica surfaces using MD simulations. We found that contact angle increased with pressure for the hydrophobic (siloxane) surface while it was almost constant for the hydrophilic (silanol) surface, in excellent agreement with experimental observations. Furthermore, we found that the CO2 thin films at the CO2-hydrophilic silica and CO2-H2O interfaces displayed a linear correlation, which can in turn explain the constant contact angle on the hydrophilic silica surface. In view of the literature and our study results, a few recommendations seem necessary to construct a molecular system suitable to study wettability with MD simulations. Future work should be conducted to determine the influence of brine salinity on the wettability of minerals with high cation exchange capacity. Mineral trapping is believed to be an extremely slow process, likely taking thousands of years. However, a recent pilot study demonstrated that CO2 mineralization occurs within 2 years in highly reactive basalt reservoirs. A first-principles MD study has also shown that carbonation reactions occur rapidly at the surface oxygen sites of a reactive mineral. We observed carbonate ions on both a newly cleaved quartz surface (without hydrolysis), and a basalt andesine surface after hydrolysis in a CO2-rich environment. Future work should consider the influence of water, gas impurities, and mineral cation type on carbonation.

Stability of MgO-modified geopolymeric gel structure exposed to a CO2-rich environment

The present study investigated the microstructural and compositional formations of the gel phase in MgO-incorporated geopolymer exposed to a high CO2 concentration. Samples were synthesized by the alkali-activation of fly ash with different dosages of MgO. The results showed that a higher level of MgO incorporation into a geopolymer exposed to a CO2-rich environment decreases the porosity, corresponding to an increase in the compressive strength. Furthermore, the microstructural densification of geopolymer caused by the formation of Mg-bearing hydrate was observed, and this may have important implications for use in high-CO2 conditions by reducing the diffusivity of CO2 through the pore structure.

Impact factors on reservoir quality of clastic Huangliu formation in overpressure diapir zone, Yinggehai Basin, China

A reservoir in the upper Miocene Huangliu formation from the Dongfang (DF) area of Yinggehai Basin is characterized by overpressure and hydrothermal fluids with CO2 accumulations. The shallow-marine gravity-flow deposits of the Huangliu formation provide an opportunity to study the impact factors on reservoir quality under overpressure and a CO2-rich environment. The current study examined the impact of sandbody types, diagenetic alteration, high-overpressure and CO2 accumulations on reservoir quality by comparing between the DF-A (CO2-rich) and DF-B (CO2-poor) areas. The channel sandbody, sheet sandbody and neritic sandbar are recognized from the Huangliu formation in the study area. The sandbody type is the most important factor for controlling reservoir quality. The bottom current reworked channel (BCRC) and reworked sheet sandstones of gas layer #I in the DF-B area have the best reservoir properties. This is due to winnowing away the original (very) fine component (such as mud) by bottom current, resulting in a slight increase of grain size and marked increase of pore-throat radius and permeability. Mechanical compaction and cementation are the main diagenetic factors for reducing primary porosity. High-overpressure can protect the primary porosity to some extent by resisting the compaction effect. The intrusion of late CO2-rich hydrothermal fluids affects mesodiagenesis in two ways. On the one hand, it can cause intense dissolution of detrital minerals and early calcite cements, resulting in a higher proportion of secondary porosity in the CO2-rich DF-A area than in the CO2-poor DF-B area. On the other hand, it can result in precipitation of cements, such as siderite and ankerite, through CO2-water-rock reactions. Overall, CO2 accumulations has an insignificant contribution on the increase of porosity. Intense dissolution by CO2 accumulations can increase the connectivity of pores and permeability, whereas precipitation of minerals leads to decreased permeability.

Thermal Degradation of Aminosilicone Carbamates

The major thermal degradation pathway seen with 1,5-bis(3-aminopropyl)-1,1,3,3,5,5-hexamethyltrisiloxane/triethylene glycol (GAP-1/TEG) is the formation of a urea-containing compound. Degradation is increased at higher temperatures, longer reaction times, higher CO2 concentrations (in the form of carbamate loading), and low water levels. A judicious choice of operating conditions can significantly decrease urea byproduct formation. Reducing the desorption temperature from 140 to 100 °C and adding 5 wt % water to the 60:40 mixture of GAP-1/TEG resulted in a 500-fold reduction in amine loss after 4 days in a CO2-rich environment. After 56 days of continuous heating under the same conditions, ∼87% original GAP-1 was retained at 100 °C compared to only ∼20% at 140 °C. The urea byproduct appears to be the only major degradation pathway under these conditions, with 100% of the mass balance accounted for by the urea and amine components.

Expansion of three reaction zones during underground coal gasification with free and percolation channels

During underground coal gasification (UCG), the expansion of the three reaction zones (oxidation zone, reduction zone, and dry distillation zone) is closely related to the stability of the gasification process and to the calorific value of the producer gas. The gasification channel structure also greatly affects the expansion process. In this article, the temperature field map and changes in producer gas components were monitored and analyzed in real time in an experimental model of UCG. A free channel and percolation channel were used and compared. The three reaction zones were found to expand during stable gasification, including the area ratios of the three zones and their forward and lateral expansion rates. The differences in the expansion of the three zones between free channel and percolation channel are here explained from the viewpoint of mass transfer. The results showed that, during the gasification of Ulanqab lignite in an oxygen- and CO2-rich environment, the average area ratios of the oxidation zone, reduction zone, and dry distillation zone in free and percolation channels were 1:1.20:1.43 and 1:1.73:2.18, respectively, the corresponding forward expansion rates were 0.077m/h and 0.019m/h, and lateral expansion rates were 0.007m/h and 0.0065m/h, respectively. Unlike in the free channel, the porous media structure of percolation channel increased the convective mass transfer rate between gasification agent and coal seam, and the stability of the gasification process and the calorific value of the producer gas. This is why the reaction zone expanded further in the percolation channel than in the free channel.

Geopolymer as well cement and its mechanical integrity under deep down-hole stress conditions: application for carbon capture and storage wells

With regard to the safety, environmental impact and sustainability of carbon capture and storage (CCS) projects, the integrity of injection and production wells plays a major role. In a CCS project, mechanical integrity of well cement should be maintained to sustain the required mechanical strength throughout the life of an oil/gas and CO2 sequestration well. One of the major issues with existing Portland cement based oil well cement is cement degradation in CO2-rich environment. On the other hand, geopolymer cement possesses excellent acid resistant characteristics, shows higher mechanical strength and durability and demonstrates lower permeability. Therefore, this research work focused on studying the mechanical integrity of geopolymers under two different down-hole conditions: (1) effect of CO2 on mechanical behaviour of geopolymers and (2) hydraulic fracturing of geopolymers to study the mechanical integrity under down-hole stress conditions. To study the mechanical integrity under CO2 rich environment, geopolymers were tested in CO2 chamber at a pressure of 3 MPa for up to 6 months and compressive strength and microstructural testings were conducted. It was noted that strength values of geopolymers did not change significantly in CO2 environment for 6 months. There were only about 2 % variations in compressive strength values in CO2 compared to the initial strength value. Scanning electron microscopy (SEM) test results revealed that there is no significance variation in the microstructure of geopolymer after 6 months in CO2. For hydraulic fracturing experiment, four different tests were conducted with various injection pressure (Pin), axial stress (σ1), confining pressure (σ3) and tube length (30 and 40 mm). Geopolymers could not be fractured in any of the four tests, in which maximum values of Pin of 23 MPa and σ1 of 59 MPa were used. There was no fracture development in geopolymers despite maximum ratios of Pin/σ3 of 3.8 and σ1/σ3 of 13.3 was tested. Tests could not be repeated with higher ratios of Pin/σ3 and σ1/σ3 due to the limitation with the triaxial set-up used. Since there is no fracture development in geopolymers at higher ratios of Pin/σ3 and σ1/σ3, it is concluded that required mechanical integrity can be observed when geopolymers are used as well cement.

Experimental investigation of carbon dioxide injection effects on methane-propane-carbon dioxide mixture hydrates

In this research, first, hydrate with high saturation in porous media (sand sediments) was formed in fully filled high pressure cell by using a mixture of the following gases at 4 °C: methane (CH4), propane (C3H8) and carbon dioxide (CO2). The feed mole percent of the gases used was selected as follows: CH4 (95%), C3H8 (3%), CO2 (2%). This selection was made in order to form natural gas hydrate of thermogenic origin (sII type hydrate). Thereafter, CO2 injection into the high saturation hydrate media was performed in order to elucidate possible CH4 recovery. However, it was observed that injected CO2 was not able to flow through sediments, because of the impermeable barrier created by hydrate, and because of the fact that no free space was left in the cell as it was completely filled with porous media resulting in mass transfer limitations. Therefore, it was proposed that methane recovery occurred only near the hydrate interface. Taking into consideration obtained results, in the next step we decreased the volume of the sand, to create a space for the free gas evolution above the high saturation hydrate, and further completely replaced free gas composition by CO2. We observed that this time not only CH4, but C3H8 was recovered from hydrate phase implying further reconsideration of the injection of CO2 into sII hydrate. The results of this study imply that it is possible to recover hydrocarbon gases from hydrates more stable than CO2 hydrate by creating a CO2 rich environment.

Application of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes in an oxy-fuel combustion reactor

Oxygen separation from air through ceramic ion transport membranes is anticipated to be one of the technologies that can make fossil fuel power plants to operate without carbon dioxide (CO2) emission. Consequently, the level of carbon emission in the atmosphere, which causes global warming, could be contained. The most promising material for such ion transport membranes is the Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), which has been reported to have the highest oxygen permeation flux. However, lack of chemical stability of these membranes in CO2 rich environment is recognized as a major problem. In this study, the performance and stability of BSCF membranes in an oxy-fuel combustor have been evaluated using methane gas. The flow rate of the methane (CH4) gas has been optimized to the value of 0.65 ml/min at 920 °C. Under this flow rate, the BSCF stability has also been evaluated. The study has shown that the BSCF stability depends on the amount of excess-oxygen in the reactor. If all oxygen, generated by the membrane, is consumed during the combustion reaction then BSCF starts to deteriorate and its permeability decreases with time. On the other hand, when the combustion reaction does not consume all oxygen, and a minimum excess-oxygen is retained, the BSCF remains stable with constant oxygen flux. This fact has been established using two BSCF membranes with different thicknesses and same exposed area of 113 mm2. The first membrane has 1.4 mm thickness and its initial oxygen permeability under combustion reaction is 0.83 µmol cm-2 s−1 with an excess of 7.5% oxygen. After 190 h of combustion, the oxygen permeability has dropped to 0.76 µmol cm−2 s−1 (7.9% reduction). The second BSCF membrane has a thickness of 1.0 mm produces 0.91 µmol cm−2 s−1 with a 15% excess oxygen during the combustion reaction. This membrane has shown excellent stability for more than 200 h of complete methane combustion. This is a remarkable result which shows that a carefully controlled fuel volume introduced in a BSCF membrane-reactor provides high oxygen output and excellent stability for a long period of time.

An NMR Spectroscopic Investigation of Aluminosilicate Gel in Alkali-Activated Fly Ash in a CO₂-Rich Environment.

The present study investigated aluminosilicate gel in alkali-activated fly ash exposed to a CO2-rich environment by means of NMR spectroscopy. The alkali-activated fly ash was exposed to an atmospheric CO2 concentration of 10% after curing at 80 °C initially for 24 h. Under high concentrations of CO2, highly reactive components Na and Al, which completely reacted within the first few hours, were unaffected by carbonation, while Si, with relatively slower reactivity, behaved differently. Despite a lower degree of the reaction in the carbonated sample, the monomeric silicates rapidly became of higher polymerization, meaning that exposure to high concentrations of CO2 caused Si to form a binding gel phase. Consequently, the carbonated sample possessed a higher amount of binding gel. The obtained results may be useful to understand the fundamental chemistry and behavior of aluminosilicate gel under high concentrations of CO2.

Ab initio thermodynamics of magnesium carbonates and hydrates in water-saturated supercritical CO2 and CO2-rich regions

ab initio Thermodynamics is used to determine how free energies of magnesium carbonates and hydrates in a CO2-rich environment change with water concentration across a range temperature and pressure relevant to geochemistry and carbon sequestration (275K to 375K and pCO2 of 1 to 210bar). The methodology is based on first principles density-functional theory (DFT) calculations of the total energies and vibrational entropy of periclase, magnesite, brucite, nesquehonite, and hydromagnesite coupled to the experimental chemical potentials of CO2 and H2O. The impact of water in supercritical CO2 (scCO2), even though less than 1% at saturation, is found to have a significant impact on the stability of hydrated carbonate minerals. Hydromagnesite and nesquehonite are found to be more thermodynamically stable than periclase and brucite in water-saturated scCO2 and hence may be expected to result kinetically from carbonation of these minerals during CO2 sequestration. Under dehydrating conditions nesquehonite destabilizes rapidly, whereas hydromagnesite is much more likely to persist in a CO2-rich environment, consistent with the observations that hydromagnesite is widespread in nature and nesquehonite is relatively rare.

Hydrophobin purification based on the theory of CO2-nanobubbles

ABSTRACTPurification is a critical step to obtain hydrophobin HFBII for use in positive applications. In this study, hydrophobin HFBII was produced by Trichoderma reesei via submerged fermentation. Using the CO2-foam fractionation method yielded a fourfold increase in protein concentration. The foamate (αL-HFBII) was dried using a nano spray-dryer under optimal temperature. The gushing activity of the dried foamate (αS-HFBII) decreased. Addition of Tween 80 to the foamate before the drying process partially prevented the deactivation of hydrophobin HFBII. The purity of the powder was enhanced based on the theory of CO2-nanobubbles in a CO2-rich environment. The collected CO2-nanobubbles were added to an apolar–polar system and the interface of these two phases was collected. After evaporation of the apolar phase, the purity of the hydrophobins assembled on the surface of the liquid was significantly improved.

A review on cement degradation under CO2-rich environment of sequestration projects

Global warming arising from the release of greenhouse gasses into the atmosphere is one of the biggest issues attracting a lot of attention. One of the conventional problems in sequestration projects is the degradation of Portland cement due to its exposure to supercritical CO2. This paper gives a review on the laboratory work performed to understand changes in the mechanical and transport properties of cement when it is in a CO2 rich environment. The results obtained indicated that pozzolanic material could be useful in enhancing the cement resistance against CO2, although more studies are still required to confirm this conclusion.

Effect of CO<sub>2</sub> Exposure on Mechanical Resistivity of Cement Pastes with Incorporated Ceramic Waste Powder

Carbonation is chemical process associated with CO2 penetration into the material porous structure causing subsequent chemical changes in the structure of cement pastes. In this work, carbonation of several pastes containing varying amount of cement replacement by three waste ceramic powders is studied. Chemical composition of particular tested materials is accessed using XRF analysis. Matrix density, bulk density, total open porosity, compressive and bending strength are measured for all developed pastes with incorporated ceramic materials. Simultaneously, the effect of carbonation on these material properties is researched. The obtained results show significant improvement of materials mechanical strength due to the carbonation. Here, the measured compressive strength is typically about ~ 60% higher for materials exposed to CO2 rich environment compared to the materials cured in laboratory conditions.

Hydrogeochemical tracing of mineral water in Jingyu County, Northeast China.

The east Jilin Province in China, Jingyu County has been explored as a potential for enriching mineral water. In order to assess the water quality and quantity, it is of crucial importance to investigate the origin of the mineral water and its flow paths. In this study, eighteen mineral springs were sampled in May and September of 2012, May and September of 2013, and May 2014 and the environment, evolvement, and reaction mechanism of mineral water formation were analysed by hydrochemical data analysis, geochemical modelling and multivariate statistical analysis. The results showed that the investigated mineral water was rich in calcium, magnesium, potassium, sodium, bicarbonate, chloride, sulphate, fluoride, nitrate, total iron, silicate, and strontium, and mineral water ages ranged from 11.0 to more than 61.0years. The U-shape contours of the mineral ages indicate a local and discrete recharge. The mineral compositions of the rocks were olivine, potassium feldspar, pyroxene, albite, and anorthite and were under-saturated in the mineral water. The origin of mineral water was from the hydrolysis of basalt minerals under a neutral to slightly alkaline and CO2-rich environment.

Point Defect Equilibria and Diffusion in Siderite (FeCO3) Passive Film Studied Using Density Functional Theory

In a CO2-rich anoxic aqueous environment as in some oil fields, a layer of siderite (FeCO3) grows on carbon steel as a byproduct of steel corrosion. This layer acts as a resistive barrier that kinetically slows down further corrosion of steel. Understanding and predicting the rates of progression of both general and pitting corrosion requires a fundamental understanding of defect equilibria and diffusion in the passive film [1]. In this work we address this need by modelling point defect equilibria and mobility using a combination of density functional theory (DFT) and thermodynamic analysis. The defects of interest in this study are the native cation and anion vacancies and extrinsic chlorine defects whose concentrations vary depending on temperature and the chemical potential gradient from the steel/siderite interface (iron rich) to the siderite/water interface (carbonate rich). Defect formation energies were calculated using the DFT+U approach and defect mobility’s were computed the nudged elastic band method. Preliminary results indicate that iron vacancies are predominantly fully ionized (2- charge state), whereas oxygen vacancies are mainly neutral and carbon vacancies are never fully ionized (charge state less than 4-) as shown in Figure 1. In addition we identified hole polarons localized on iron cations to be a predominant electronic defect that participate in the equilibria of charged defects in this material. The predictions of point defects thermodynamics and kinetics in FeCO3 is major step toward an atomistics-informed corrosion model of carbon steel in oil fields. [1] D. D. Macdonald, Pure Appl. Chem., 71, 951, (1999). Figure 1

The effect of carbon dioxide rich environment on carbonic anhydrase activity, growth and metabolite production in indigenous freshwater microalgae

Indigenous freshwater microalgae from natural habitats may have potential for bio-mitigation of atmospheric CO2. The present study evaluates the response of three indigenous microalgal isolates viz., Desmodesmus sp., Kirchneriella sp. and Acutodesmus sp., to CO2 rich environment (10, 20 and 30%) in a closed photobioreactor. In a time course study, levels of CO2 in culture medium were observed to modulate the activity of carbonic anhydrase (CA), a key enzyme of carbon concentrating mechanism (CCM) of microalgae. The CA activity decreased on availability of free CO2 and increased on depletion of free CO2 in the culture medium. Maintenance of algal cultures in CO2 rich environment for a period of 16days enhanced the biomass concentration, specific growth rate, chlorophyll and carbon dioxide biofixation rate by 2–4 fold. Overall productivity, carbon, carotenoid and lipid contents also increased. Palmitic and oleic acids were the major fatty acids of the algal lipids. CO2 rich environment affected the fatty acid profile in Desmodesmus sp. with an increase in unsaturated fatty acids.

CCS と微生物機能の融合技術 (Bio-CCS) リスク評価の試み

Among in-situ microbes within depleted oil-gas reservoir, the species dominant in CO2 rich environment produce methane much faster than those dominant in CO2 poor environment. CO2 acts as a catalyst in the reaction. If we maintain preferable conditions for methanogenic microbes during geological CCS, we will be able to abate greenhouse gas emission and produce natural gas as one of natural energy resources at the same time. We named the technological concept as‘ Microbial Associated Geological CCS (Bio-CCS)'. In Bio-CCS, CO2 will be injected from a well for two purposes: to abate greenhouse gas emission and to cultivate methanogenic geomicrobes. CH4 gas will be produced later using other wells. The procedure is similar to the Enhanced Oil/Gas Recovery (EOR/EGR) operation, but in Bio-CCS, the target is production of methane gas out of residual oil in depleted oil/gas reservoir CO2 abatement. To evaluate the basic feasibility of the new conceptual technology, we conducted preliminary risk assessment of Bio-CCS conceptual process. First of all, based on result of numerical calculations using geological model of Bio-CCS process, we assumed a procedure of Bio-CCS site: 1 million CO2 will be injected into depleted oil reservoir in 10 years; the reservoir will be kept still for 90 years and 0.5 million t CH4 will be produced; after 100 years from the first CO2 injection, CH4 production will be started. We developed hazard scenarios by way of literature survey and statistical analysis of accident statistics. Then we applied the hazard scenarios to the assumed Bio-CCS procedure. As the result, the preliminary risk assessment assures that the Bio-CCS process will be safe. Even it happens any leaking accidents, most impacts on peripheral area of Bio-CCS site will be negligible.

Computational modelling of co-firing of biomass with coal under oxy-fuel condition in a small scale furnace

Utilization of biomass as a co fired fuel has proved to be a significant option for the mitigation of Green House gas emissions. In this study, a computational fluid dynamics modelling of the co-combustion of pulverised Russian coal with highly volatile biomass called Shea meal having different blending ratio has been considered in a 0.5 MWth combustion test facility (CTF) for air and CO2-rich environment by using a commercial CFD tool called AVL Fire version 2009.2 coupled with the user defined subroutines for the aerodynamics of irregular shaped biomass particle, devolatilisation and char Combustion modelling. Results are validated comparing against the experimental data to examine the effects of co-firing under different operating conditions and a reasonably good agreement was observed with the differences in range of 5–10% with the experimental data. Operating conditions were varied with the recycled ratios (RR) (68%, 72% and 75%) and the biomass sharing (20% and 40%). Results are presented in terms of temperature distributions, CO2 concentrations, and the effects of co-firing ratio under different oxy-fuel combustion. With the increase of biomass sharing from 20% to 40%, the volume of the flame increases, but the flame stability and the peak temperature decreases due to higher volatile content in the biomass. The relationship of the peak and mean flame temperature and furnace exit temperature with the normalized total flow (NTF) and normalized O2 (NO) are presented. The heat transfer is significantly manipulated by the biomass sharing with different recycled ratio. The working range for the co-firing of 20% biomass sharing suggested that optimum recycled ratio (RR) for flame temperature and radiative heat transfer to be closely matched with air-firing found at 71%, but for 40% sharing, a value of RR70% may be needed. Finally, unburned carbon in ash (CIA) is predicted and improved burnout is observed in oxy-fuel cases with higher biomass sharing. This study highlights the possible effects of varying the fuel on ignition environment and heat transfer characteristics of a small scale furnace, emphasizing the minor reform that may be needed when transforming to higher biomass sharing co-firing.