Abstract

Condensing gas boilers are widely employed for their high heat efficiency, which attributes to their ability to use the recoverable sensible heat and latent heat in flue gas. In this paper, the optimal excess air rate of a novel condensing gas boiler is investigated experimentally. With the change of excess air rate, the pre-mixed and post-mixed systems were used to study the performance, the thermal efficiency and emissions of the boiler. The CO emission reduces firstly then increases regardless of which premixed system, when the excess air rate is from 1.15 to 1.4. The NO_x emission decrease from 64 ppm to 10 ppm and the efficiency decreases from 64 ppm to 19 ppm as the excess air rate increases from 1.15 to 1.4. The efficiency decreases from 102.05% to 98.7% and the efficiency decreases from 100.9% to 97.6% as the excess air rate increases from 1.15 to 1.35. Considering both NOx emission and thermal efficiency, the optimum excess air rate is 1.23. With the change of heat load, the emission, the fan speed and the thermal efficiency of the two system were compared. The concentration of CO increases from 7.5 ppm to 65.5 ppm when the pre-mixed system heat load changes from 8 kW to 24 kW. The efficiency of post-mixed system decreases from 106.5% to 97.5% and the efficiency of pre-mixed system decreases from 106.9% to 96.8% as the heat load increases from 9 to 26 kW. The variation of thermal efficiency and condensate volume with various heat load in the post-mixed system with different return water temperature are also studied. The efficiency decreases from 107% to 98.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 30 °C. And the vapor condensation ratio ω decreases from 105% to 97.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 40 °C. In summary, post-mixed system is more suitable for the development of small condensing boilers. The lower the return water temperature and heat load, the higher the thermal efficiency of boiler.

中文翻译：

---

铸造铝硅合金（CASA）冷凝燃气锅炉的预混和后混燃烧系统的性能和排放

摘要

冷凝式燃气锅炉因其高热效率而被广泛采用，这归因于其利用烟气中可回收的显热和潜热的能力。本文通过实验研究了新型冷凝式燃气锅炉的最佳过量空气率。随着过量空气速率的变化，使用了预混合和后混合系统来研究锅炉的性能，热效率和排放。当过量空气速率为1.15至1.4时，无论采用哪种预混系统，CO排放量都会先减少然后增加。该NO _X随着过量空气速率从1.15增加到1.4，排放量从64 ppm降低到10 ppm，效率从64 ppm降低到19 ppm。随着过量空气速率从1.15增加到1.35，效率从102.05％降低到98.7％，效率从100.9％降低到97.6％。同时考虑NO x排放和热效率，最佳过量空气速率为1.23。随着热负荷的变化，比较了两个系统的排放，风扇转速和热效率。当预混合系统的热负荷从8 kW变为24 kW时，CO的浓度从7.5 ppm增加到65.5 ppm。当热负荷从9 kW增加到26 kW时，后混合系统的效率从106.5％降低到97.5％，预混合系统的效率从106.9％降低到96.8％。研究了回水温度不同后混合系统中热效率和冷凝水体积随热负荷的变化。当回水入口温度为30°C时，热负荷从9 kW增加到24 kW，效率从107％下降到98.5％。蒸气凝结比ω当回水入口温度为40°C时，热负荷从9 kW增加到24 kW，则从105％降低到97.5％。综上所述，后混合系统更适合小型冷凝锅炉的开发。回水温度和热负荷越低，锅炉的热效率越高。