Concentration In Flue Gas Research Articles

Thermodynamic analysis of combined cycle gas turbine power plant with post-combustion CO2 capture and exhaust gas recirculation

Natural gas is expected to make up a significant proportion of the future global energy mix. Therefore, reducing greenhouse gas emissions from gas-fired processes is very essential for most countries, before emission reduction targets can be met. This article aims to carry out thermodynamic analysis of combined cycle gas turbine power plant with post-combustion CO2 capture through modelling and simulation. The combined cycle gas turbine power plant and the CO2 capture plant were simulated in Aspen Plus®. The combined cycle gas turbine power plant model was validated with simulation data from GateCycle® and the CO2 capture plant model was validated with experimental data from the pilot plant at the University of Texas at Austin. The CO2 capture plant was scaled up from pilot plant to commercial scale to process flue gas from a 250 MWe combined cycle gas turbine power plant. The integrated model for combined cycle gas turbine and CO2 capture plant was further used for performance study. Exhaust gas recirculation has been proposed to increase CO2 concentration in flue gas and reduce the flue gas flow rate. Its effect on combined cycle gas turbine power plant performance and capture plant sizing has been investigated. The analysis indicated that exhaust gas recirculation can reduce penalty on thermal efficiency without any major modification to the original power plant.

An experimental investigation of a direct burning of crude Jatropha oil (CJO) and pitch in a commercial boiler system

We conducted a test of a direct burning of crude Jatropha oil (CJO) and pitch in a commercial boiler system. The fuel, crude Jatropha oil is not biodiesel which comes from transesterification process of bio oil, but it is pure plant oil like cooking oil. The higher heating value (HHV) of the CJO is 39.3 MJ/kg (9380 kcal/kg) and is lower than that of commercial heating oil, 44.0 MJ/kg. The kinematic viscosity of CJO is 36.2 mm2/s at 40 °C and 8.0 mm2/s at 100 °C. The burner used in the test is a commercial burner for a commercial heating oil and its capacity is 140 kW (120,000 kcal/h).We did a preliminary test whether the combustion is stable or not. The preliminary test was a kind of open air combustion test using the commercial burner with crude Jatropha oil. We found that the combustion can be stable if the crude Jatropha oil temperature is higher than 90 °C. We measured the flue gas concentration by using a gas analyzer. The NOx concentration of crude Jatropha oil is 80 ∼ 100 ppm and CO concentration is nearly 0 ppm at flue gas O2 concentration of 2.5 and 4.5%. We also tested a pitch combustion and the result shows that the NOx concentration of pitch is about 90 ∼ 110 ppm and CO concentration is below 30 ppm at flue gas O2 concentration of 2.5 and 4.5%. As a reference data, combustion of heating oil was conducted. The NOx concentration of heating oil is about 80 ppm which is the lowest value of tested fuels.

NOx Emission from a Circulating Fluidized Bed Boiler Cofiring Coal and Corn Stalk Pellets

The NOx emission from a circulating fluidized bed (CFB) boiler with 50 MW rated thermal output (50 MWth) during the cofiring of anthracite coal and pelletized corn stalk biomass was investigated. Cofiring could improve combustion efficiency and, thus, the thermal efficiency of the boiler. However, contrary to most results found in bubbling fluidized bed (BFB) combustors and the one found in a CFB boiler burning rice husk, NOx concentration in flue gas and fuel nitrogen conversion ratio increased with the biomass mass fraction. Several causes for such a contradiction were discussed and the configuration in combination with feedstock location of biomass was regarded as the most important one. In a CFB boiler, fuel is mostly burnt above the dense bed, opposite to that in a BFB boiler, and, thus, the average oxygen concentration above the dense bed, where biomass was fed, was higher. High bed temperature and high primary air ratio used for burning the anthracite coal increased NOx emission and enhanced the variation trend. In addition, the catalyst-contained ash also could promote NOx formation. The results indicated that biomass is not necessarily an effective cofiring fuel to reduce NOx emission in a CFB boiler and in order to reduce NOx emission, low primary air ratio, and locating the feedstock ports of biomass below the secondary air should be considered.

Studies on magnesium-based wet flue gas desulfurization process with oxidation inhibition of the byproduct

This paper presents a novel magnesium-based wet flue gas desulfurization (FGD) process in which sodium thiosulfate is used to inhibit the oxidation of desulfurization byproduct. Effects of different operating variables in FGD process were experimentally researched in a spray scrubber. The results showed that the magnesium-based wet FGD process was more suitable for low SO2 concentration flue gas and indicated that the adding of Na2S2O3 could slightly enhance the desulfurization process and the MgSO3 content in the byproduct could be maintained above 95% when the thiosulfate-sulfite ratio was controlled above 1:6. A desulfurization process model was established by the double-film theory of mass transfer. The calculated mass transfer coefficients were in reasonable agreement with the experimental values and the absorption process was found to be controlled by gas-film diffusion.

Experimental study of homogeneous mercury oxidation under O2/CO2 atmosphere

Recently oxy-fuel combustion has been investigated as a potential multi-pollutant control technology for coal-fired power plants. However, mercury in flue gas must be removed before CO2 recovery as it can cause liquid metal embrittlement and material failure of aluminum heat exchangers during CO2 purification and compression. Comparing to air combustion, the flue gas constituents and time–temperature profiles changed in oxy-fuel combustion with flue gas recirculation. This may result in different elemental mercury (Hg0(g)) transformation behaviors. Experimental tests on homogeneous Hg0(g) oxidation by Cl2, HCl, NO and SO2 were conducted under simulated O2/CO2 and O2/N2 atmosphere at the temperature of 473–1273K. Results showed that under both O2/CO2 and O2/N2 atmosphere, Cl2 can significantly promote Hg0(g) oxidation while much more HCl and higher temperature (>873K) were needed to obtain comparable Hg0(g) oxidation. Hg0(g) oxidation by Cl2 and HCl in CO2 atmosphere was lower than that in N2 cases, while O2 exhibited significant promotion effect on Hg0(g) oxidation, especially under CO2 atmosphere at 1073K. O2/N2 and O2/CO2 atmosphere showed little difference on Hg0(g) oxidation by NO and SO2, respectively. Hg0(g) oxidation by NO was about 5–30%, depending on NO concentration in flue gas, decreased as the temperature increasing. SO2 exhibited limited Hg0(g) oxidation.

ANN - SQP Approach For NOx Emission Reduction In Coal Fired Boilers

Abstract In this research paper, predictive modelling of NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature and nozzle tilt were studied. The data collected from parametric field experiments were used to build a feed-forward back-propagation artificial neural net (ANN). The coal combustion parameters were used as inputs and NOx emission as outputs of the model. The ANN model was developed for full load condition and its predicted values were verified with the actual values. The algebraic equation containing weights and biases of the trained net was used as fitness function in sequential quadratic programming (SQP) to find the optimum level of input operating conditions for low NOx emission. The results proved that the proposed approach could be used for generating feasible operating conditions.

Measurements of mercury speciation and fine particle size distribution on combustion of China coal seams

The percentage of mercury that is removed in currently used air pollution control devices (APCDs) depends on the speciation in the flue gas exhausting from the coal combustor. Bench-scale measurements were carried out in the flue gas from combustion of different types of coal in a drop-tube furnace set-up to better understand the formation process of three mercury species, i.e. Hg0, Hg2+ and Hgp, in gaseous phase and fine particles. It was observed that due to chemical reaction kinetics limitations, higher mercury concentrations in flue gas lead to lower Hg2+ proportions. The concentration of chlorine has the opposite effect, not as significantly as that of mercury though. With the chlorine concentration increasing, the proportion of Hg2+ increases. Combusting finer sized coal powders results in the formation of more Hg2+. Mineral composition of coal and feed coal particle size has a great impact on fine particle formation. Increased Al in coal results in more finer particle formation, while Fe in coal increases concentration of larger particles. The coexistence of Al and Si can enhance the particle coagulation process. This process is also enhanced at higher coal feed rates, and when feed coal particle sizes are smaller. Results from oxy-coal and conventional air combustion were compared.

Experimental study on removals of SO2 and NOX using adsorption of activated carbon/microwave desorption

Experimental studies on desulfurization and denitrification were carried out using activated carbon irradiated by microwave. The influences of the concentrations of nitric oxide (NO) and sulfur dioxide (SO2), the flue gas coexisting compositions, on adsorption properties of activated carbon and efficiencies of desulfurization and denitrification were investigated. The results show that adsorption capacity and removal efficiency of NO decrease with the increasing of SO2 concentrations in flue gas; adsorption capacity of NO increases slightly first and drops to 12.79 mg/g, and desulfurization efficiency descends with the increasing SO2 concentrations. Adsorption capacity of SO2 declines with the increasing of O2 content in flue gas, but adsorption capacity of NO increases, and removal efficiencies of NO and SO2 could be larger than 99%. Adsorption capacity of NO declines with the increase of moisture in the flue gas, but adsorption capacity of SO2 increases and removal efficiencies of NO and SO2 would be relatively stable. Adsorption capacities of both NO and SO2 decrease with the increasing of CO2 content; efficiencies of desulfurization and denitrification augment at the beginning stage, then start to fall when CO2 content exceeds 12.4%. The mechanisms of this process are also discussed. Implications: The prominent SO2 and NOx treatment techniques in power plants are wet flue gas desulfurization (FGD) and the catalytic decomposition method like selective catalytic reduction (SCR) or nonselective catalytic reduction (NSCR). However, these processes would have some difficulties in commercial application due to their high investment, requirement of expensive catalysts and large-scale equipment, and so on. A simple SO2 and NOx reduction utilizing decomposition by microwave energy method can be used. The pollutants control of flue gas in the power plants by the method of microwave-induced decomposition using adsorption of activated carbon/microwave desorption can meet the requirements of environmental protection, which will be stricter in the future.

ANN–GA approach for predictive modeling and optimization of NOx emission in a tangentially fired boiler

An artificial neural network (ANN) and genetic algorithm (GA) approach to predict NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas, is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature, and nozzle tilt were studied. The data collected from parametric field experiments was used to build a feed-forward back-propagation neural net. The coal combustion parameters were used as inputs and NOx emission as outputs of the model. The ANN model was developed for full load conditions and its predicted values were verified with the actual values. The algebraic equation containing weights and biases of the trained net was used as fitness function in GA. The genetic search was used to find the optimum level of input operating conditions corresponding to low NOx emission. The results proved that the proposed approach could be used for generating feasible operating conditions.

Predictive modelling and optimization of nitrogen oxides emission in coal power plant using Artificial Neural Network and Simulated Annealing

In this research paper, predictive modelling of NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature and nozzle tilt are studied. The data collected from parametric field experiments are used to build a feed-forward back-propagation artificial neural net (ANN). The coal combustion parameters are used as inputs and NOx emission as outputs of the model. The ANN model is developed for full load condition and its predicted values are verified with the actual values. The algebraic equation containing weights and biases of the trained net is used as fitness function in simulated annealing (SA) to find the optimum level of input operating conditions for low NOx emission. The result proves that the proposed approach could be used for generating feasible operating conditions. DOI: http://dx.doi.org/10.11591/ij-ai.v1i1.286 Full Text: PDF

Integrated methods to improve efficiency of furnace burning recovered tail gas

Replacing nature gas (NG) by recovered hydrogen-rich tail gas to fuel a full-scale furnace has been proved to improve furnace efficiency and reduce NOx formation. Adjusting residual O2 concentration in flue gases, air preheat temperature and furnace damper angle will further improve the efficiency of the furnace burning the recovered hydrogen-rich tail gas. Prolonging the residence time of the hot gas flow increases the heat release time and reduces the time for the fuel to reach burning temperature so that the furnace efficiency can be improved. On-site test results using a full-scale furnace show that reducing the residual O2 concentration in flue gases from 4.0 to 3.0 vol.% raises the furnace efficiency by 0.6%. Raising the pre-heated incoming air temperature from 200 °C to 240 °C and reducing furnace damper opening angle from 45° to 39° save 2.4 × 106 and 1.9 × 106 m3 of natural gas, respectively. Integrating the adjustment of flue gas residual O2 concentration, temperature of incoming air temperature, and furnace damper opening angle will assist industries in achieving higher overall furnace efficiency and reducing carbon dioxide emission.

Hydrogen Chloride Bonding with Calcium Hydroxide in Combustion and Two-Stage Combustion of Fuels from Waste

The present study deals with the problem of limiting HCl mobility in processes of combustion of two solid recovered fuels (SRF1 and SRF2) having significant but different contents of chlorine. Large-scale experiments were carried out at a temperature of 1050 °C with the use of a stoker-fired flat grate boiler with the heat output of 1 MW, and with a two-stage combustion system for medical waste incineration (MWI) with the same heat output in which first the process of gasification in the temperature of 650 °C occurs, and subsequently the previously obtained syngas is fired in the temperature of 1000 °C in the reburning chamber of the gas generator. In such a way, two different technologies of combustion have been compared, with regard to HCl capture efficiency using widely available calcium hydroxide sorbent Ca(OH)2. In order to simulate the increased concentration of chlorine in SRF1, the fuel was being supplemented with three various additions of poly(vinyl chloride) (PVC) recyclate. Before combustion, SRF1 and SR2 were also blended with Ca(OH)2 whose weight amount was being changed: from 0 to 3 wt % with a step equal to 0.5 wt % (combustion) and from 0 to 1.5 wt % with a step equal to 0.5 wt % (two-stage combustion). For both of the methods of SRFs combustion, series of experimental findings have been presented, showing trends in the changes of HCl concentration in flue gas, depending on (i) the amount of PVC recyclate added to SRF1 and amount of Ca(OH)2 added to both fuels; and (ii) the molar ratio Ca/Cl2. Finally, the ratio of HCl concentrations in flue gas after combustion and two-stage combustion, depending on the amount of added PVC and Ca(OH)2 to the fuels was analyzed. The achieved results indicate that in a two-stage process (gasification and recombustion), HCl can be much more effectively bonded than during combustion in stoker-fired boiler.

Effect of SO2 on mercury binding on carbonaceous surfaces

Density functional theory calculations were performed to investigate the effect of SO2 on mercury adsorption on a carbonaceous surface. The carbonaceous surface is represented by a six-fused benzene ring model in which the edge atoms on the upper side are unsaturated to simulate the active sites. All of the possible approaches in which SO2 was adsorbed on the edge sites of the carbonaceous surface were considered to examine their effects on Hg adsorption. The results indicated that SO2 adsorptions on the carbonaceous surface with OO approach and OS approach are thermally favorable. The effects of SO2 on Hg adsorption are complicated, which depends on the SO2 concentration in flue gas. The adsorption of SO2 increases the adsorption capacity of the carbonaceous surface for Hg0 by increasing the activity of its neighbor sites. However, higher concentrations of SO2 decrease the Hg adsorption capacity since SO2 competes for the activate sites on the carbonaceous surface.

Distribution of Polybrominated Diphenyl Ethers (PBDEs) in a Fly Ash Treatment Plant

PBDES are used as the flame retardants and have adverse effects on human health. Electric arc furnaces (EAF) are one of major emission source of PBDEs. The PBDE contents in the fly ashes of an EAF (29.3 ng/g) examined in this study were one to three orders higher than those in environmental soils. EAF fly ash treatment plants are established to resolve the disposal of this material, and also to recover the remaining iron or zinc from it. However, very little is known about the fate of PBDEs in EAF fly ash treatment plants. The EAF fly ash treatment plant investigated in this work can be divided into three sub-systems, including a pelletizer, reducing furnace and submerged arc furnace (SAF). The fly ash generated from the pelletizer process exhibited the highest PBDE content (7.69 ng/g), and contributed about 91% of the total PBDE inputs (4.40 g/day). The total PBDE concentrations in the stack flue gases of the pelletizer, reducing furnace and SAF were 24.5, 2.88 and 4.71 ng/Nm3, respectively. The high PBDE concentrations of the pelletizer resulted from not only the thermal desorption of lighter brominated congeners, but also fugitive particles of EAF fly ashes. Together, the three stacks accounted for 40.8% of the total PBDE outputs, revealing that the air pollution control devices deployed in the current study were not very effective with regard to removing PBDEs from the flue gas. The PBDE output/input ratio of the EAF fly ash treatment plant was 0.0378, and thus most PBDEs introduced into the system were decomposed. The EAF fly ash treatment plant examined in this work is thus a reliable facility with regard to the disposal of this material.

The effect of SO 2 on CO 2 capture by CaO-based pellets prepared with a kaolin derived Al(OH) 3 binder

High-temperature CO 2 capture by Ca looping cycles was investigated in the presence of SO 2. The sorbents tested included natural limestone (HV-P), pellets formed from powdered limestone with a binder (HV-AH) and pellets formed from powdered acetified limestone with a binder (HV10-AH). The binder used in pellet preparation was Al(OH) 3 obtained from acid leaching of kaolin. Simulated flue gas with a composition of 15% CO 2, 3% O 2, 0.45% SO 2, and N 2 balance was used during the CO 2 capture step. Two calcination conditions were employed for sorbent regeneration: pure CO 2 at 920 °C and pure N 2 at 850 °C. By five reaction cycles, the well-developed porous texture of HV10-AH acetified by 10 vol.% acetic acid did not offer better CO 2 capture than that for natural limestone at 650 °C for calcination in CO 2; instead it promoted a higher SO 2 retention than that for the limestone. Unfortunately, the CO 2 capture capacity for all sorbents calcined in CO 2 in the presence of SO 2 was effectively eliminated after 2–3 cycles. Calcination in N 2 did not significantly enhance CO 2 sorbent capture capacity; but instead it improved the SO 2 retention ability of HV10-AH, for which the sulphation level was over twice that of the natural limestone. Increasing the carbonation temperature to 700 °C enhanced sulphation rather than carbonation with HV10-AH, but produced the opposite effect with natural limestone. In general, it appears that SO 2 impedes CO 2 capture, leading to a negligible CO 2 capture capacity after only few cycles regardless of how the sorbent morphology is modified, which suggests any method designed to improve sorbent performance for CO 2 capture will not be proof against significant SO 2 concentrations in flue gas. These results suggest that despite the fact that sorbent performance can be influenced to some extent by altering carbonation and calcination conditions; the presence of SO 2 must be avoided if the objective is CO 2 capture from flue gas.

Oxygen Enriched and Oxyfuel Combustion - Promising Trends for Low Carbon Future

The escalation of ambient CO2 concentration due excessive use of coal in power generation has put impetus on the development of technologies for utilization of vast and cheap resources available through out the world. Eco-scrub, Oxygen enriched and oxyfuel combustion are among the promising technologies guaranteeing the low carbon future. In our recent investigations, pulverized coal (Russian) was fired in a 20 kW down fired combustion rig under simulated exhaust gas recirculation. The effect of CO2 at burner inlet on the combustion efficiency, flue gas CO2 and NO emission was studied. The test conditions were essentially achieved by replacing the secondary air with a mixture of O2 and CO2 in different proportion. The test conditions do imitate the four key conditions for eco-scrub project. The basic theme under eco-scrub project is to use limited oxygen addition to reduce the volume of flue gas for processing, increase the efficiency of post combustion scrubbing due to higher CO2 levels and reduced the size and cost of post combustion capture. The exhaust gas CO2 was observed to increase linearly with increasing the CO2 at burner inlet. The flue gas concentration for 35% and 45% flue gas recycle was recorded to be 24% and 30% respectively. The NO emission was most of the time under the base line emission of 818 ppm. A maximum of 66% reduction was observed when the burner inlet CO2 was 45% and 21% O2. How ever an increase of 37% was seen when 80% of the secondary air was replaced with a 50%O2-50%CO2 mixture.

Combustion and inorganic bromine emission of waste printed circuit boards in a high temperature furnace

High temperature combustion experiments of waste printed circuit boards (PCBs) were conducted using a lab-scale system featuring a continuously-fed drop tube furnace. Combustion efficiency and the occurrence of inorganic bromine (HBr and Br2) were systematically studied by monitoring the main combustion products continuously. The influence of furnace temperature (T) was studied from 800 to 1400°C, the excess air factor (EAF) was varied from 1.2 to 1.9 and the residence time in the high temperature zone (RTHT) was set at 0.25, 0.5, or 0.75s.Combustion efficiency depends on temperature, EAF and RTHT; temperature has the most significant effect. Conversion of organic bromine from flame retardants into HBr and Br2 depends on temperature and EAF. Temperature has crucial influence over the ratio of HBr to Br2, whereas oxygen partial pressure plays a minor role. The two forms of inorganic bromine seem substantially to reach thermodynamic equilibrium within 0.25s. High temperature is required to improve the combustion performance: at 1200°C or higher, an EAF of 1.3 or more, and a RTHT exceeding 0.75s, combustion is quite complete, the CO concentration in flue gas and remained carbon in ash are sufficiently low, and organobrominated compounds are successfully decomposed (more than 99.9%).According to these results, incineration of waste PCBs without preliminary separation and without additives would perform very well under certain conditions; the potential precursors for brominated dioxins formation could be destroyed efficiently. Increasing temperature could decrease the volume percentage ratio of Br2/HBr in flue gas greatly.

Removal of Sulfur Dioxide from Sintering Flue Gas with Coking Wastewater

Coking wastewater comprising a lot of ammonia is a good desulfurizer for recycling. Sintering flue gas is characterized by large volume, low sulfur dioxide (SO2) concentration and large variation amplitude and etc. The purpose for treating waste with waste can be carried out by treating sintering flue gas with coking wastewater. This paper uses a spray tower countercurrent device, ensures the contact between coking wastewater and sintering flue gas, and detects SO2 concentration of inlet flue gas and outlet flue gas on line by using an automatic flue gas detection instrument. This paper studies on the change regularity for the SO2 concentration at outlet flue gas during the process of treating sintering flue gas with coking wastewater, the influence of SO2 initial concentration in sintering flue gas to the removal efficiency of SO2, the influence of gas-liquid ratio between the sintering flue gas and the coking wastewater to the removal efficiency of SO2, and the change regularity for the pH value of coking wastewater after desulfurizing. The results show that the sintering flue gas which is treated can live up to the atmospheric pollutant effluent standard of iron and steel industry; the pH value of coking wastewater is reduced after treating, and the conditions for the implementation of subsequent coking wastewater treatment process are provided.

Waste combustion as a source of ambient air polybrominated diphenylethers (PBDEs)

Abstract The first comprehensive set of U.S. data on polybrominated diphenylether (PBDE) concentrations from municipal waste combustion (MWC), with more than 40 PBDE congeners reported, was compared to ambient air levels of PBDEs in the U.S. The PBDE profiles in the raw MWC flue gas reflected the historical production and usage pattern of PBDE-based flame retardants in North America, which favored Penta- and Deca- BDE formulations. The pattern of selected, routinely measured in the environment, PBDEs (TeBDE-47, PeBDE-99, PeBDE-100, HxBDE-153 and DcBDE-209) was similar in the MWC emissions and profiles most commonly reported for the U.S. atmosphere. The mean Σ PBDE concentrations in the clean flue gases collected from the stack were 0.13 and 1.7 ng dscm −1 during the steady state and transients of MWC, respectively (which was 98.6% reduction compare to the levels in the raw flue gases). The major PBDE congeners in the MWC flue gases were those typically found in PBDE technical mixes (TeBDE-47, PeBDE-99, PeBDE-100, HxBDE-153, HpBDE-183, OcBDE-197, NoBDE-206, NoBDE-207, NoBDE-208, DcBDE-209). The profile of the PBDEs in the raw flue gas was dominated by heavier congeners, especially DcBDE-209, while the profile of the stack flue gases profile was dominated by the lighter congeners (TeBDE-47, PeBDE-99, PeBDE-100 accounted for around 80% of total stack emissions). Some of the MWC flue gas samples exhibited enrichment of lower brominated congeners that are minor or not present in the technical mixtures, suggesting that debromination occurs during combustion. Congeners substituted in non- and mono- ortho positions (TeBDE-77, PeBDE-126, HxBDE-156 and -169) were detected mostly during the transients of MWC.

Improving furnace and boiler cost‐effectiveness and CO2 emission by adjusting excess air

AbstractReducing the input excess air or airflow rate to a furnace or boiler will result in decreasing transmission rate of the thermal flow from the radiation zone to the convection heating surface zone in the furnace. Results of the plant‐scale test presented in this article show that if the furnace is operated at 3.6 × 107 kcal/h of combustion capacity, decreasing the residual O2 concentration in the furnace flue gas from 4% to 2.5% will save 9.3 × 103 m3 of natural gas consumption, and 2.1 × 104 tons of CO2 emission annually. For the boiler tested in the study, 1.8 × 105 m3 of natural gas consumption and 3.9 × 105 tons of CO2 emission will be reduced annually if it is operated with 90 ton/h steam yield. Hence, controlling the input excess air (or oxygen) as an important operating alternative to enhance thermal efficiency, and alleviate environmental impact of a heater furnace and boiler has been confirmed in this research. © 2011 American Institute of Chemical Engineers Environ Prog, 2012