| OCR Text |
Show heat. At this point the heat from the oxy-fuel burner mixes with the furnace atmosphere increasing the temperature of exhaust gases going to the pollution control system and attacking furnace components and electrodes. The result is that the oxy-fuel burner must be shut down at a point in the process when much of the scrap is relatively cold. PYRETRON COMBUSTION APPROACH Beginning in mid-1984 American Combustion conducted extensive research and development efforts aimed at overcoming limitations related to oxygen utilization in high temperature heating and melting applications. A systems engineering approach was used involving current knowledge of combustion chemistry and of heat transfer phenomena to develop a new set of design criteria. These criteria are based upon optimizing oxygen utilization to provide higher combustion and heating efficiency by: -boosting flame luminosity and velocity -better control over the chemistry of combustion products -more active control of radiative and convective components of heat fluxes generated by the flame -reduced NOx emissions at higher flame temperatures -the use of oxygen with preheated combustion air with no practical limit on the temperatures of preheating. As a result, the PYRETRON combustion system has been developed to be capable of more intelligently responding to the dynamics of the heating process than traditional combustion systems. This new type system can sigIlificantly reduce energy costs by increasing the level of oxygen participation in applications where only a few percent of oxygen is currently used; in reducing the oxygen waste traditionally experienced in oxy-fuel burners by increasing the heat transfer capability of oxygen rich flames; and by improving the utilization of combustion air. In addition, the PYRETRON provides a higher level of management of the dynamics of oxygen and fuel mixing by independently controlling the introduction into the combustion process of two distinct oxygen and air based oxidizers having. significant differences in oxygen content. PARALLEL STAGED COMBUSTION - The c ombustion of gaseous fuels consists of a series of sophisticated aerodynamic, energy and chemical mass transfer 174 phenomena occurring together in the diffusion and kinetic stages of combustion. The result is the formation of distinguishable flame patterns capable of delivering different levels of heat flux to the load. Because the diffusion of the gases involved in the flame pattern formation is by far the slowest part of the combustion process, an improvement in mixing controllability is the most practical way to affect the flame structure. Staged combustion is successfully used to increase the mixing controllability of large flame patterns by sequencing the introduction of an oxidizing gas in time and rate so as to create an oxygen deficiency in part of the flame structure causing partial pyrolysis of the fuel stream. This can be used to improve flame luminosity and to increase flame length. The pyrolitic process consists of the thermal and oxidizing pyrolysis of natural gas, both of which are endothermic and may therefore, be controlled by designing the mixing of the involved components to shape the kinetics of the involved reactions so as to control the introduction of heat into the reaction zone. The main difficulty in accomplishing the pyrolysis of natural gas when using air is the absorbtion of heat from the combustion zone by the nitrogen molecules in the combustion air. This significantly reduces the flame core temperature and therefore the diffusion and kinetic activity in the pyrolitic zone. The result of these lower temperatures is a reduction in the rate of carbon microparticles formation, and therefore flame emissivity, as illustrated in Figure 4. To boost flame pattern luminosity and the temperature of carbon microparticles in the pyrolytic zone, the PYRETRON method reduces (or completely eliminates) nitrogen participation in pyrolysis and, by the use of a parallel staged combustion t echnique as illustrated in Figure 5, delivers additional heat to the pyrolytic zone. This additional heat is released simultaneously with the pyrolysis reaction t~rough the complete oxidation of a port~ on of the fuel outside of the pyrolytic zone. This increased temperature accelerates the rate of the pyrolytic reaction as shown in Figure 6 and makes the entire combustion cycle controllable in the PYRETRON flame envelope. In addition, the higher temperatures in the pyrolytic zone cause formation of a larger number of smal microparticles of carbon which have a greater total surface area for a given volume of carbon resulting in a gain in radiative heat flux. |
