OCR Text |
Show EXPERIMENTAL EVALUATION OF A RADIANT TUBE COMBUSTION SYSTEM FIRED WITH OXYGEN ENRICHED COMBUSTION AIR Steven R. Huebner, Christopher A. Hersch Midland-Ross Corporation Michael A. Lukasiewicz Gas Research Institute Surface Combustion Division Chicago, Illinois, USA Toledo, Ohio, USA "Abstract" This paper discusses the results of testing a gas fired radiant tube combustion system fired with oxygen enriched combustion air. The thermal efficiency of a radiant tube combustion system depends on furnace temperature, the geometry of the radiant tube, the firing rate of the burner and the combust ion ai r oxygen concentrat ion. Because of the 1 arge quant i ty of parameters involved, an experimental .approach was selected for determining the effect of oxygen enrichment on radiant tube thermal efficiency. The exper iments were performed wi th a standard radiant tube combustion system as normally used wi th standard air. The range of furnace temperatures tested was 700°C to 1315°C and the combustion air oxygen concentration varied from 21 to 80 percent. Radiant tube diameters tested were 0.102, 0.181 and 0.254 m. Various thermal loading conditions were tested to simulate actual firing practices experienced in the field. The results indicated that increasing the oxygen concentration of the combustion air substantially increases the thermal efficiency of the combustion system. Additionally, the increase in flame temperature due to the increase in combustion air oxygen concentration had little effect on the radiant tube or burner materials. The radiant tube temperature is primarily a function of furnace temperature and firing rate. CONVENTIONAL COMBUSTION SYSTEMS using ambient air are inherently inefficient due to the large quantity of nitrogen, which must be heated to exhaust gas temperature. Oxygen enrichment of 49 combustion air simply reduces the volume of nitrogen per unit volume of oxygen, thus reducing the fl ue gas heat losses. The economics of using oxygen enriched combustion air have not been favorab 1 e in the past due to the high cost ratio of oxygen to natural gas. Recent developments in nitrogen separation equipment have reduced this cost ratio to a value where it has become reasonable to investigate the effects of app lyi ng oxygen enri chment to conventional combustion systems. The purpose of this research was to quantify the effect of oxygen enriched combustion air on the thermal performance of a conventional radiant tube combustion system. A conventional system was selected for the experiments since it would be advantageous to apply oxygen enrichment to existing systems if reasonable improvements could be realized without detrimental effects to components such as the burner and radiant tube. TECHNICAL APPROACH An experimental approach was selected to quantify the effects of oxygen enriched combustion air on the thermal efficiency of radiant tube combustion systems. This approach, as opposed to an analytical approach, gives operating experience with oxygen enriched combustion air under circumstances similar to field conditions. Variables to be studied which effect the thermal efficiency obtained by oxygen enrichment are firing rate, furnace temperature and radiant tube diameter. Additionally, operating experience was desired over the practical range of application of each variable. For these reasons, the range of variables in Table 1 was studied. |