Oxy-fuel combustion

Recent studies have addressed the combustion of natural gas with pure oxygen, highly diluted with exhaust gases (CO2 and H2O) in order to mitigate both NO and CO2 emissions from power plants. The so-called oxy-fuel combustion includes an air separation unit, which delivers O2 to the catalytic stage, where it is mixed with natural gas and the exhaust recycle stream. An example is the Advanced Zero Emission GT, first jointly studied by Norsk Hydro and ABB Alstom Power [28-31]. 

The Advanced Zero Emission Power (AZEP) concept replaces the traditional combustor with a more complex and highly integrated unit, consisting of a combustor, an air preheater, a membrane section and a high-temperature heat exchanger section. 

The concentration of carbon dioxide in flue gas can be increased greatly by using oxygen instead of air for combustion, either in a boiler or a gas turbine -a process known as oxy-fuel combustion . The oxygen would be produced by cryogenic air separation, which is already employed on a large scale, for example in the steel industry. When fuel is burnt in pure oxygen, the flame 

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The C02 stream obtained from oxy-fuel combustion shows high levels of water vapour, sulphur compounds, N 02 and impurities such as mercury in the flue gas. NOx emission is low when compared with air combustion. 

Toftegaard, Maja Bog et al. Oxy-fuel combustion of solid fuels. Progress in Energy and Combustion Science. 2010, 36(5). 581-622. 

Rich catalytic combustion will offer wide opportunities with respect to most of the above issues, including flexible integration in different machines, low-temperature ignition ability, tolerance to fuel concentration and temperature non-uniformities and fuel flexibility. Further, the production of syngas in short contact time catalytic reactors could be exploited in several energy-related applications such as fuel cell and oxy-fuel combustion. 

Technology development and cost reduction of COj capture using oxy-fuel combustion and amine separation ... 

O2 separation Compressed air o2 Oxygen for gasification of fossil fuels (coal, heavy oil, biomass) Oxygen for oxy-fuel combustion Oxygen for combustion of remaining fuel from various process streams... 

Oxy/fuel combustion has been used in many applications in the steel industry including both continuous and batch reheat furnaces, soaking pits, and ladle preheaters. Fuel savings of up to 60% have been reported.27 Typical fuel savings achieved by converting from air/fuel to oxy/fuel combustion are given in Table 1.4.28... 

Ding, M. G. and Du, Z., Energy and environmental benefits of oxy-fuel combustion, in Proceedings of the 1995 International Conference on Energy Environment, Shanghai, China, May 1995, Begell House, New York, 1995, 674. 

Abernathy, R., McElroy, J., and Yap, L. T., The performance of current oxy-fuel combustion technology for secondary aluminum melting, Light Metals 1996, Hale, W., Ed., The Minerals, Metals, and Materials Society, Warrendale, PA, 1996, 1233. 

Oxy/fuel combustion is a recognized method for reducing NOx emissions under carefully controlled conditions.2 The glass industry in particular has rapidly converted from air/fuel to oxy/fuel primarily to reduce NOx emissions from 70 to 95%.3 The next section discusses the theory to explain how OEC reduces NOx. 

FIGURE 2.14 Comparison of particle entrainment in a furnace using air/fuel and oxy/fuel combustion. 

The oil tube/atomizer section was removed from the dual fuel burner and an oxy/fuel burner was inserted in its place. The burner retrofit package including the natural gas and oxygen flow control trains were prefabricated to prevent furnace downtime. The oxy/fuel flow controls and safety switches were interlocked to the conventional air/fuel controls, thus creating a hybrid air-oxy/fuel combustion system. 

A rotary-type copper-alloy-melting furnace, rated for 1.2 ton/h, experimented with oxy/fuel combustion and productivity improvements and energy savings were realized.4 The results of the test are tabulated in Table 6.5. 

Oxy/fuel combustion Conventional reverberatory (Al, Cu), TBRC, rotary (Cu, Al, Pb) No Low Medium 90-100%... 

Smith, C. D. and Saha, D., Advances in oxy/fuel combustion, paper presented at International Wrought Copper Council Conference, Singapore, October 1997. 

The frit segment has the most furnaces converted to oxygen. The pressed and blown, fiberglass, and container industries have converted fewer furnaces but account for the most tonnage of glass produced by oxy/fuel combustion. As of the end of... 

Full oxy/fuel combustion greatly reduces the emissions of NOx and particulates. NOx emissions are reduced by over 80% for an oxy/fuel furnace compared with its air/fuel counterpart. This is due mainly to the fact that there are simply fewer nitrogen molecules around to react and form NOx. 

This is important especially for processes using expensive volatile components such as lead oxide since it can significantly improve the economics in favor of oxy/fuel firing. The impact of conversion will vary with furnace and glass type. However, oxy/fuel combustion nearly eliminates particulates attributable to carryover or entrainment of batch particles. 

Advanced refractory corrosion has been noted in some furnaces with full oxy/fuel combustion.11 This phenomenon is due to the condition discussed in Section 7.3.1.5.2. The problem can be minimized by selecting the appropriate refractory, keeping joint sizes small, and minimizing air infiltration.12... 

Ertl, D. and McMahon, A., Conversion of a fiberglass furnace from 100% electric to oxy/fuel combustion, in Proceedings from 54th Conference on Glass Problems, Oct. The American Ceramic Society, Westerville, OH, 1993, 186-190. 

Valve stand — A free-standing frame including several fluid flow runs that is used to physically control the fluid flow to a combustion process. A typical oxy/fuel combustion equipment valve stand will include an instrument airflow run, an oxygen flow run, and a fuel flow run. The equipment on the valve stand typically includes the on/off valves, pressure regulators, flow control valves, and associated instrumentation necessary to operate a combustion process. 

This guideline applies specifically to the design of equipment used to control the flow of oxygen gas (-20 to 200°F or -30 to 90°C, with pressures below 250 psig) and a fuel (gas or liquid) to a burner and, to safely address the related issues involved in a typical oxy/fuel combustion application. The related issues may include furnace purging, ignition, flame supervision, burner concerns, furnace concerns, and miscellaneous concerns. 

A safety shutdown of the oxy/fuel combustion equipment system by any of the prescribed safety features or devices shall require manual intervention of an operator for reestablishment of normal operation of the system, per NFPA 86 (sect. 5-2.3). 

Typically, an oxy/fuel combustion equipment system is considered to be a Class 1, Division 2, Group D electrical installation per NFPA 70 (articles 500, 501, and 502). Note that the Group is defined as a function of the flammable fuel being handled. See NFPA 497A for help in determining the classification of a particular oxy/fuel combustion application. All components, enclosures, conduits, and wires must be suited for the particular classification of the oxy/fuel equipment system electrical installation. 

An Operating and Maintenance Manual is required for every oxy/fuel combustion equipment system per NFPA 86 (sect. 1-5.6). As a minimum, the manual must include oxygen and fuel safety literature appropriate approved drawings of the... 

If pure oxygen is used, the same procedure can be used to determine the fuel flow rate. For oxy/fuel combustion, no excess oxygen is needed. The fuel flow is 4487.1 mol/h, which is only 51% of the fuel required compared with that when air is used for combustion. 

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