Flue Gas Volume Research Articles

Reduction of energy consumption and pollution emissions for industrial furnace using hydrogen-rich tail gas

Using the recovered tail gas (FG) that consists of 60 mol% (50–70 mol%) of hydrogen gas to replace heavy fuel oil (FO) as furnace fuel was studied. With higher FG/FO ratios, the hydrogen content in the fuel increases so that the volume of flue gas reduces to reduce the furnace internal pressure that leads to slower uprising velocity of the thermal flow in the furnace and hence more efficient thermal transmission in the furnace. The results reveal that complete replacement of fuel oil with the recovered tail gas will reduce about 45.8% of the resulting flue gas, lower the furnace radiation zone temperature by 45 °C, raise the furnace convection zone temperature by 18 °C. Additionally, the annual savings of heavy fuel oil can be 2.3 × 104 m3 heavy fuel oil with the reduction of 53.4 tons SOx emission, 21.9 tons of NOx emission and 4.9 × 104 tons of CO2 emission. Therefore, reusing the recovered tail gas to completely replace heavy fuel oil (FO) as the furnace fuel along with operational adjustments of fresh air flow rate and flue baffle angles will alleviate the discharge of greenhouse gas.

Hybrid Membrane-absorption CO2 Capture Process

The development of CO2 capture systems has largely focused on single separation technologies (absorption, adsorption, membranes, cryogenics, etc.). Few studies have examined the merits of combining multiple separation technologies into a hybrid capture system. Membrane Technology & Research, Inc. (MTR) and the University of Texas at Austin (UT Austin) are collaborating to investigate two variations of a hybrid membrane- absorption capture system which combine MTR's air-swept Polaris™ membrane contactor with UT Austin's 5 m piperazine advanced flash stripper (AFS; 5 m PZ-AFS) capture technology with cold and warm-rich bypass. In one embodiment, the systems are arranged in series and in another, in parallel. In the series configuration, the absorber removes approximately half of the CO2 in the flue gas, followed by additional separation by the membrane contactor to achieve 90% total removal of CO2 by the hybrid capture system. In this arrangement, the absorber operates at a higher lean-loading state and also benefits from the ability of the downstream membrane to mitigate fugitive amine emissions. In the parallel configuration, the flue gas leaving the power plant is split and treated by each system in a parallel arrangement. The principal advantage is that the absorber can be roughly half the size it would normally be. In both configurations, the 5 m PZ-AFS system will treat a more concentrated CO2 stream which is a preferred condition. The project team found that the minimum O2 content in the combustion air stream (18% for retrofit, 17% for Greenfield) acted to limit the potential of the hybrid-series configuration. In the best case design of the hybrid-parallel arrangement, the 5 m PZ-AFS system treats 53% of the total flue gas volume with a CO2 concentration in the flue gas greater than 23%.

Cost and energy sensitivity analysis of absorber design in CO2 capture with MEA

Amine-based CO2 capture processes appear to be the near-term technology for post-combustion CO2 removal from fossil fuel power plants. However, there is no experience with large-scale application of CO2 capture on power plants. A good absorber design is necessary to handle the large volumes of dilute flue gas with high performance, low cost and energy requirement of the plant. In the present work, multi-scale simulations of the absorber were investigated using Aspen RateSep, and a cost estimation model was developed based on mass and energy balances produced by the Aspen Plus simulations, and data from Turton et al. (2012) were applied for cost estimation. Investment costs (CAPEX) and energy requirements of the lean amine circulation pump and absorber blower for variations in the absorber design were compared for two cases: CO2 absorption from a coal-fired power plant, and CO2 absorption from a gas-fired power plant both with a net power output of 400MWe. The flue gas flow rate in the gas-fired power plant case is higher than for the coal-fired power plant, over the same net power output. In the gas-fired power plant case the absorber needs to be designed to process high volumes of flue gas and the pressure drop will often be higher than for a coal-fired power plant due to higher gas velocity. This results in higher capital and operatingcosts. Possible re-design of the absorber is studied and the results show that large electrical energy savings in the feed gas blower can be obtained when a design is chosen giving reduced absorber pressure drop. This can be achieved if the column cross sectional area is increased. This is offset by extra capital cost by a need for slightly more volume of packing. The operational design flexibility in a CO2 capture plant for a gas-fired power plant is higher than for a coal-fired power plant.

Experimental Study on Regularities of Carbonation for CO<sub>2</sub> Capture Using Ammonia Solution

The regularities of carbonation in the process of CO2 capture were investigated using ammonia solution by laboratory-scale and bench-scale device. The research showed that the lower volatility of NH3 and higher rate of carbonization in solution could be achieved with ammonia concentration ranging from 10 to 16 wt%. The emission of ammonia accelerated with the increasing of flow of flue gas, and the bubbling function of air was apparent in a lower CO2 volume fraction, which has an adverse effect on carbonation of solution. Benefits of environment and economic could be achieved in CO2 capture using ammonia solution so long as appropriate ammonia concentration, the flue gas flow and volume fraction of CO2 were determined.

Flue Gas Recirculation and Enhanced Performance of Waste Incinerators under Waste Uncertainty

Variations in waste quantities and composition affect incinerator operating conditions and performance. Fluegas volumes consititute a dominant environmental and financial consideration for efficient waste incinerator (WI) operation, since they affect the temperature, throughput, air pollution control system (APCS) residence time, and pollutant emissions, when the charging rate or composition of any waste is varying. Fluegas recirculation (FGR) in WI is an effective technique for reducing WI atmospheric pollution, mainly NOx emissions, albeit affecting WI throughput, temperature and destruction/removal efficiency. FGR refers to mass recirculation of a possibly cooled fraction of fluegases and differs substantially from fluegas heat recovery. The present work shows that, besides emission control, suitable manipulation of FGR enhances WI performance under waste uncertainty, enabling higher throughput, at the desired temperature and within the allowed APCS residence time range. A dimensionless parameter related to the uncertain wastes' net enthalpy contribution is isolated, which encompasses heat of reaction and enthalpy outflows from fluegas and solids and which reveals whether throughput is decreasing or increasing with temperature and FGR ratio. Normalized throughput and total fluegas volume isotherms manifest the interdependence and enable manipulation for enhanced environmental and economic performance.

Amine Modeling for CO2 Capture: Internals Selection

Traditionally, trays have been the mass-transfer device of choice in amine absorption units. However, the need to process large volumes of flue gas to capture CO2 and the resultant high costs of multiple trains of large trayed columns have prompted process licensors and vendors to investigate alternative mass-transfer devices. These alternatives include third-generation random packings and structured packings. Nevertheless, clear-cut guidelines for selection of packings for amine units are lacking. This paper provides well-defined guidelines and a consistent framework for the choice of mass-transfer devices for amine absorbers and regenerators. This work emphasizes the role played by the flow parameter, a measure of column liquid loading and pressure, in the type of packing selected. In addition, this paper demonstrates the significant economic advantage of packings over trays in terms of capital costs (CAPEX) and operating costs (OPEX).

Oxygen-Enriched Combustion Technology Application and Economical Forecast in Cement Industry Kiln

Using combustion theory to research on the technical theoretical features of oxygen-enriched combustion technology application to the cement industry kiln. On the basis of this, engineering projects of that, a certain enterprise 3000 t/d cement clinker production line applied oxygen-enriched combustion technology, and its economic evaluation were calculated. The results showed that: applying Oxygen-enriched combustion technology to the existing cement clinker calcined equipments, the coal powder consumption, the volume of flue gas and CO2 concentration in the flue gas of unit cement clinker occurred regular changes, When the O2 concentration increased from 21% to 30%, the coal powder consumption decreased by 17.78%, the flue gas volume was reduced by 12.73% and the CO2 concentration in the flue gas increased to 76.57%. If the enterprise used the oxygen-enriched atmosphere of O2 concentration for 30% to form the coal combustion, it can save coal about 71.87 t/d, equipment production capacity increase by 41.75% and capture CO2 products about 2662 t. Every year, this resulted in the profit increasing 103 million yuan.

Pursuing the Oxy-fuel Light-/heavy Oil Retrofit Route in Oil Refineries - A Small Scale Retrofit Study

Two commercial, one light- and one heavy oil burner for a CEN 250kW boiler was modified by simple means to allow for operation at controlled dry oxy-fuel conditions. The variables measured for both air- and oxy-firing were the flue gas components; CO2, CO, O2 and NOx, the flue gas exit temperature and boiler water temperatures (in/out). Both burners were run on air based base cases for comparison. The light- and the heavy oil burners were fired at 90kW and 130kW, respectively. For the light oil burner an experimental matrix consisting of five runs on air with varying excess air, λ = 1.1-1.25, ratio was performed. For each of the air-fired runs five additional cases were run, with a mixture of O2/CO2 replacing the air as oxidizer, with constant XO2 and increasing XCO2. However, for the heavy oil burner only two base cases where run at =1.15 and 1.25 and compared to oxy-fuel conditions with fixed XO2 and varying CO2 dilution. The main reason for the low number of runs with heavy oil was the large amounts of soot formed, which made heat flux measurements rather difficult.The results for the light oil burner show that on the average, the flue gas volume when shifting to oxy-firing is about 0.7 times the volume when firing with air. A mass based comparison show that shifting from air- to oxy-firing, on the average results in a reduction in NO formation, an increase in CO, CO2 and O2 in the flue gas of about 19, 2.4,4.1 and 4.3 times, respectively. For light fuel oil the flame temperature for air- vs. oxy-firing coincides at around 35-37% O2 through the burner. Although radiation measurements with light fuel oil was only measured in a single point, it was noticed that the measured radiation flux tends to increase linearly with increasing O2 concentration, on the average about ×1.5 higher than with air-firing.For heavy fuel oil firing it has been shown that close to air-firing conditions can be reached at oxy-fuel operation at around 30/70. However, peaks of around 1.4 × air firing were observed at certain positions. As with light fuel oil oxy- fuel experiments, heavy fuel oil seemed to be just as adaptable to oxy-firing. Also here no operational problems were observed and it is possible to achieve stable oxy-fuel conditions similar to that of air-firing.The main conclusion so far, based on the current experience with simple oxidant switching burning light- to heavy oil on an existing burner/boiler geometry, indicates that operation similar to air-fired burner/boiler behavior is easily achievable. Besides the large amount of soot formed during heavy oil combustion no operating or technical difficulties were experienced with any of the retrofitted burners and combustion conditions comparable with air firing in terms of ignition, flame stability and flame shape was achieved in the oxy-firing mode.

Generating Electricity from Fluegas Produced By Boilers through a Thermodynamic ORC (Organic Rankine Cycle) Driven by R245fa

In recent years, an increase in fossil fuel prices and imposing strict laws and regulations by environmental organizations have resulted in an increasing interest on the parts of researchers in oil industry to implement various projects to eliminate pollutants emitted by fluegas in order to achieved the desired standards. Today, different processes including heaters, furnaces, and boilers are used by different industries resulting in the production of a large volume of fluegas. The energy and heat wasted by these gases can be recovered even in low temperatures in order to be used in various processes such as preheating refinery fluid flows or generating electricity. ORC (Organic Rankine Cycle) is a thermodynamic cycles used for generating electricity in the majority of plants and also in this article; furthermore, its function is similar to Karno cycle. In ORC thermodynamic cycle, superhot vapor of fluegas is first produced by a boiler and then it is sent to an evaporator then sent to a turbo-expander to produce electricity. Finally, the remaining vapor is condensed by an air cooler and it is sent back to the ORC thermodynamic cycle. ORC thermodynamic cycles are usually based on vapor working fluid fluids such as NOVEC7000, R123, R134a, and R245fa (1,1,1,3,3-pentafluoropropane), (employed in the present article) as the working fluid of ORC thermodynamic cycle.

Design Optimization of Convective Heat Transfer Surface of Pressurized Oxy-Fuel Coal-Fired Boiler

Based on the thermal calculation, the paper makes a contrastive analysis on the parameters of flue gas, and convection heat properties of the coal-fired boiler under atmospheric air combustion, atmospheric oxy-fuel combustion and pressurized (6MPa) oxy-fuel combustion conditions. It takes a 300MW pressurized(6MPa) oxy-fuel combustion boiler as research object, the result indicates that: compared to the coal-fired boiler atmospheric air combustion, the flue gas volume flow in the pressurized oxy-fuel combustion has a decrease of 98.79%; convective heat output has a decrease of 24.69% with the same difference in temperature. In the pressurized oxy-fuel combustion, both the flue gas convective heat transfer coefficient and the pressure drop are greater than the atmospheric oxy-fuel combustion, flue cross-sectional area is smaller than conventional boiler, and heating surface area is less than atmospheric oxy-fuel combustion. With a method named dynamic minimization of costs the best flue gas velocity in this paper is 1.07m/s

The Thermodynamic Characteristic of Diesel with 21-30% Oxygen-Enhanced Combustion

The study was carried out on the burning test-bed which was controlled by Programmable Logic Controller (PLC) model and diesel was used as the fuel. The thermodynamic characteristic of oxygen-enhanced combustion, including fuel consumption, flue gas volume, flue gas components’ volume concentration, theoretical flame temperature, flame emissivity, energy efficiency and thermal efficiency, etc, were analyzed. The results showed that: with oxygen concentration was increased from 21% to 30%, fuel consumption was decreased by 40.6% and flue gas volume was decreased by 57.5%. Additionally, higher oxygen concentration leaded to higher theoretical temperature and stronger flame blackness because of the decreasing of N2 volume in supporting air. What’s more, the decreasing of energy brought away by flue gas and the thermal efficiency were both increased with the increasing of oxygen concentration.

Advances in high permeability polymeric membrane materials for CO2separations

Global CO2 emissions have increased steadily in tandem with the use of fossil fuels. A paradigm shift is needed in developing new ways by which energy is supplied and utilized, together with the mitigation of climate change through CO2 reduction technologies. There is an almost universal acceptance of the link between rising anthropogenic CO2 levels due to fossil fuel combustion and global warming accompanied by unpredictable climate change. Therefore, renewable energy, non-fossil fuels and CO2 capture and storage (CCS) must be deployed on a massive scale. CCS technologies provide a means for reducing greenhouse gas emissions, in addition to the current strategies of improving energy efficiency. Coal-fired power plants are among the main large-scale CO2 emitters, and capture of the CO2 emissions can be achieved with conventional technologies such as amine absorption. However, this energy-consuming process, calculated at approximately 30% of the power plant capacity, would result in unacceptable increases in power generation costs. Membrane processes offer a potentially viable energy-saving alternative for CO2 capture because they do not involve any phase transformation. However, typical gas separation membranes that are currently available have insufficiently high permeability to be able to process the massive volumes of flue gas, which would result in a high CO2 capture. Polymer membranes highly permeable to CO2 and having good selectivity should be developed for the membrane process to be viable. This perspective review summarizes recent noteworthy advances in polymeric materials having very high CO2 permeability and good CO2/N2 selectivity that largely surpass the separation performance of conventional polymer materials. Five important classes of polymer membrane materials are highlighted: polyimides, thermally rearranged polymers (TRs), substituted polyacetylenes, polymers with intrinsic microporosity (PIM) and polyethers, which provide insights into polymer designs suitable for CO2 separation from, for example, the post-combustion flue gases in coal-fired power plants.

DEVELOPMENT OF TECHNOLOGY AND DESIGN MODEL OF HEAT AND MASS TRANSFER IN A PLASMA SHAFT FURNACE FOR WASTE PROCESSING

A new plasma shaft furnace for thermal plasma processing and vitrification of solid toxic waste is developed and investigated. Complex theoretical studies on its operation conditions are carried out. Numerical analysis and calculations have shown that waste plasma processing in the shaft furnace proposed is characterized by the acceptable energy consumption, significantly smaller length of the operating zone, and a low volume of flue gases compared to fuel furnaces, and good possibility for aerosols absorption by the bulk waste charged in the furnace shaft, compared to batch or rotary processes.

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.

Assessment of carbon capture thermodynamic limitation on coal-fired power plant efficiency

The most mature CO2 carbon capture process comes with a 12–10% pts efficiency loss when coupled with a coal-fired power plant and for both post and oxy-combustion. Pre-combustion induces less efficiency loss but at the cost of a more complicated overall process. Since the last decade numerous improvements have been made and this work tries to evaluate the thermodynamic minimum impact of CO2 capture processes on such coal power plants. After detailing the calculation hypothesis, the purely thermodynamic impact has been assessed: they are 3.2% pt for post-combustion divided into 40% for separation and 60% for compression, 4.2% for pre-combustion especially due to CO-shift (60%), the rest evenly divided between separation and compression and 2.9% for oxy-combustion divided into one third for O2 production and two thirds for compression and with a small efficiency gain compared to aero-combustion due to the reduction in flue gas volume. In the second part of this work, the realistic minimum energy consumption is assessed with some assumptions about compressor and pump efficiency, temperature pinch and overall process conditions. This study shows a 6.8% pt loss of efficiency for MEA absorption post-combustion process combined with classical compression train, 5.8% pt for a cryogenic post-combustion process, 6.6% pt for a MDEA absorption pre-combustion process with classical compression train, 5.4% pt for the cryogenic ASU oxy-combustion with standard cryogenic CPU.These realistic minimal impacts of CO2 capture on supercritical coal power plants highlight the difficulty in designing a process with less than 5% pt of efficiency loss which is the main technological challenge of the CO2 capture field at the moment. The better performance achievable seems around 6.0% pt loss of efficiency with good integrated low regeneration duty solvent for post-combustion or highly efficient ASU and CPU for oxy-combustion. However, a power plant practical efficiency of more than 40% is readily achievable with a well designed IGCC plant and, in near future, with USCPC power plant.

Impact of oxygen enriched combustion on the performance of a single cylinder diesel engine

In the present experiment, a computerized single cylinder diesel engine with a data acquisition system was used to study the effects of oxygen enriched combustion technology (OECT) on the performance characteristics. The use of different levels of oxygen-enriched air was compared with respect to percentage load. Increasing the oxygen content in the air leads to faster burn rates and increases the combustibility at the same stoichiometry (oxygen-to-fuel ratio). These effects have the potential to increase the thermal efficiency and specific power output of a diesel engine. The power increases considerably with oxygen enrichment. In addition, oxygen enrichment can also be considered as a way to reduce the sudden loss in power output when the engine operates in a high load condition. Assessed high combustion temperature from the oxygen enriched combustion leads to high combustion efficiency. OECT reduces the volume of flue gases and reduces the effects of greenhouse effects. Engine tests were conducted in the above said engine for different loads and the following performance characteristics like brake power (BP), specific fuel consumption (SFC), mean effective pressure, brake thermal efficiency, mechanical efficiency, and exhaust gas temperature were studied. The objective of this paper is to address, in a systematic way, the key technical issues associated with applying OECT to single cylinder diesel engines.

Novel $\hbox{NO}_{\rm x}$ and VOC Treatment Using Concentration and Plasma Decomposition

Stringent NOx and volatile organic compound (VOC) flue gas regulation are set force for various industrial emission sources. The conventional emission control technologies such as selective catalytic reduction for NOx treatment and incineration and catalysts for VOC treatment have limitations in terms of operating conditions, costs, and performance. A novel, economical, and cost-effective device is mandated to meet the regulations. A new approach consists of flue gas adsorption, desorption (concentration and adsorbent regeneration), followed by nonthermal plasma decomposition. This concept was applied for NOx, various VOCs, and other hazardous air pollutant treatment. More than 90% of NOx and VOC reduction was achieved using a series of surface discharge units. The energy efficiencies of 3.35 g( NO2)/kWh for NOx and 34.2 g/kWh for toluene were achieved using concentration technique, followed by surface discharge plasma reactor. These hybrid processes make the flue gas volume order of magnitude small, resulting in the reduction of the energy yield, reactor size, power supply, and total system costs.

Impact of Oxygen Enriched Air Intake on the Exhaust of a Single Cylinder Diesel Engine

Problem statement: The objective of the research is to investigate the effect of using oxygen enriched air on Diesel engine exhaust emission. Approach: In the present experimental work a computerized Single cylinder Diesel engine with data acquisition system was used to study the effects of oxygen enriched air intake on Exhaust emissions. Engine test has been carried out in the above said engine for different loads and Exhaust Emissions like CO, CO2, NOx and HC with respect to different percentage of oxygen enrichment were discussed. Results and Conclusion: Increasing the oxygen content with the air leads to faster burn rates and the ability to control Exhaust Emissions. Added oxygen in the combustion air offers more potential for burning diesel. Oxy-fuel combustion reduces the volume of flue gases and reduces the effects of green house effect also.

Near zero emissions oxy-combustion CO2 purification technology

Abstract Oxyfuel combustion CO2 capture technology presents an excellent opportunity for achieving near zero emissions from the coal-fired power plants. In the oxyfuel technology, the volume of flue gas is reduced by a factor of four to five (on a dry basis) due to elimination/reduction of nitrogen from combustion. This reduced volume of CO2-rich flue gas has to be compressed to 25 to 35 bar (a) for purification, thus further reducing the actual volume of flue gas by a factor of 25 to 35. If the equipment for removing trace impurities (SOx, NOx and Hg) is installed downstream of the flue gas compressor, the capital investment could be significantly reduced compared to that for the air-fired operation. Furthermore, by processing the entire volume of flue gas in the CO2 purification unit, it is possible to remove and concentrate the trace impurities in the solid and liquid waste streams and to produce a vent stream with near zero emissions and a high purity CO2 relatively free of trace impurities. Praxair is developing an oxy-combustion flue gas purification technology that will leverage these synergies. This technology will reduce emissions of CO2, SOx and Hg by >99% and NOx emissions by >95% compared to an air-fired pulverized coal power plant. The benefits of the technology include management of air ingress problems, capital and operating cost savings for SOx and NOx removal, reduction in CO2 capture cost and production of high purity CO2 stream for sequestration. These benefits will translate to lower cost of electricity for power plants with CO2 capture. This paper presents the experimental data for the SOx/NOx removal and high CO2 recovery processes and the results of the commercial viability assessment.

Predictions of the impurities in the CO 2 stream of an oxy-coal combustion plant

Whilst all three main carbon capture technologies (post-combustion, pre-combustion and oxy-fuel combustion) can produce a CO 2 dominant stream, other impurities are expected to be present in the CO 2 stream. The impurities in the CO 2 stream can adversely affect other processes of the carbon capture and storage (CCS) chain including the purification, compression, transportation and storage of the CO 2 stream. Both the nature and the concentrations of potential impurities expected to be present in the CO 2 stream of a CCS-integrated power plant depend on not only the type of the power plant but also the carbon capture method used. The present paper focuses on the predictions of impurities expected to be present in the CO 2 stream of an oxy-coal combustion plant. The main gaseous impurities of the CO 2 stream of oxy-coal combustion are N 2/Ar, O 2 and H 2O. Even the air ingress to the boiler and its auxiliaries is small enough to be neglected, the N 2/Ar concentration of the CO 2 stream can vary between ca. 1% and 6%, mainly depending on the O 2 purity of the air separation unit, and the O 2 concentration can vary between ca. 3% and 5%, mainly depending on the combustion stoichiometry of the boiler. The H 2O concentration of the CO 2 stream can vary from ca. 10% to over 40%, mainly depending on the fuel moisture and the partitioning of recycling flue gas (RFG) between wet-RFG and dry-RFG. NO x and SO 2 are the two main polluting impurities of the CO 2 stream of an oxy-coal combustion plant and their concentrations are expected to be well above those found in the flue gas of an air-coal combustion plant. The concentration of NO x in the flue gas of an oxy-coal combustion plant can be up to ca. two times to that of an equivalent air-coal combustion plant. The amount of NO x emitted by the oxy-coal combustion plant, however, is expected to be much smaller than that of the air-coal combustion plant. The reductions of the recirculated NO x within the combustion furnace by the reburning mechanism and the char-NO reactions are the main reason for a smaller amount of NO x emitted by the oxy-coal combustion plant. The concentration of SO 2 in the flue gas of an oxy-coal combustion plant can be up to six times to that of an equivalent air-coal combustion plant if the recycling flue gas is not desulphurized. The flue gas volume flow rate of an oxy-coal combustion plant is much smaller (<20%) than that of an equivalent air-coal combustion plant, which is a significant advantage for the purification of the flue gas.