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Show multi-venturi gas/air mixers, flame stabilizers, and a refractory-lined firetube to enhance flame stability at high excess air operation and ensure completeness of combustion before quenching of the combustion products by the air to be heated. The measured NOx level from a test CXA burner was 1 to 1.6 vppm. The CO was only detectable at low firing conditions and fluctuated considerably over the 6 to 40 vppm range at the highest excess air ratio.10 By using two parallel venturi sections, each of which has a turndown not exceeding 4.5: 1, a two-stage configured burner can achieve an overall turndown ratio of 9: 1. The CXA burner is commercialized and widely used in Europe and Australia. Comparisons of NOx and CO emissions between the CXA burner and the present cyclonic combustor operating at different firing loads are presented in Figures 11 and 12. NOx emissions from the test CXA burner were decreased from 1 to 0.6 vppm with the load increasing from 12% to 95%, as shown in Figure 11. However, the test cyclonic combustor can operate at 40: 1 turndown with NOx emissions from 0.3 to 1 vppm. The CO emissions comparison, as shown in Figure 12, has demonstrated that the CXA burner can only operate at a very small range in order to control CO emissions of less than 4 vppm. At very low (below 25% of full load) and high loads (above 90% of full load), CO emissions from the test CXA burner increases dramatically. In contrast, CO emissions from the test cyclonic combustor can be controlled below 4 vppm with 40: 1 turndown operation. Also, it should be noted that in order to achieve 9:1 turndown, the CXA burner must be composed of a two-stage combustor, resulting in the reduction of combustion intenSity to onehalf. Therefore, the test cyclonic combustor has demonstrated better performance compared to the CXA burner, particularly in a much larger operating range with steady ultra-low emissions. The levels of all emissions produced by this combustor is lower than the requirement for direct-fired air heaters, according to EPA, CFR, ANS, and GRI. A comparison of combustion performance from various direct gas-fired air heaters shows that the present cyclonic combustor demonstrated the lowest combustion emissions (NOx' N02, and CO) and the highest turndown ratio. The Alzeta prototype space heater equipped with a Pyrocore, radiant burner outperforms other infrared and blue-flame burners with respect to most emission products and compares favorably with the Japanese fan heater. However, the IGT/Maxon test cyclonic combustor has demonstrated much lower amounts of combustion emissions than all burners listed in Table 1.3 Moreover, these low combustion emissions were obtained over 40:1 turndown operation (8:1 for a single-stage operation alone), which is up to ten times greater than that for the other burners. It must be noted that, because a chemiluminescent analyzer is used currently to measure NO and NOx directly, N02 values are determined by difference. Consequently, some workers in this field question the absolute values of the N02 data reported in the vast majority of studies.13 This suggests that there is a need to develop and validate a scientifically based standardized N02 measurement protocol. However, this suggested uncertainty does not cast doubt on the ultra-low-emission performance achieved in the test combustor because the maximum N02 emissions in all tests were below 0.5 vppm, which is lower than the target for good indoor air quality. 13 |