The thermal efficiency of the boiler is one of the most important indicators of the boiler, the main factors affecting the efficiency of low-NOx boilers are: heat loss from exhaust temperature, heat loss, incomplete combustion of fuel and boiler scaling. As the burner is modified after the heat loss and boiler scaling compared with the pre-modification has not changed, so the thermal efficiency of the boiler has no effect, the burner modification before and after the burner modification to change the two main factors, namely, the heat loss of the exhaust temperature and the degree of incomplete combustion of fuels, so this paper focuses on the impact of these two factors on the efficiency of the boiler.

The heat loss of exhaust temperature is the most important one in the heat loss of gas boiler, which mainly depends on the exhaust temperature and excess air coefficient λ. (Excess air coefficient is the ratio of air mass actually supplied by burning 1kg of fuel to the theoretical mass of air needed for complete combustion of 1kg of fuel, and it is a common index for the study of the composition of combustible mixtures in our country and in Russia, and is often expressed by the symbol λ.) λ and the heat loss of exhaust smoke q1 relationship: according to the empirical formula: q1 = (0.5 + 3.5λ) (T exhaust smoke - T ambient temperature).

In operation, to reduce q1 to improve the combustion efficiency of the boiler as far as possible under the condition of ensuring complete combustion, the boiler exhaust temperature is high will lead to a reduction in the thermal efficiency of the boiler. Exhaust heat loss increases with the increase in exhaust temperature and air coefficient. Gas boiler exhaust contains steam, and superheated steam is the main carrier of heat in the flue gas. Therefore, in addition to sensible heat, there is a large amount of latent heat in the flue gas discharged from the gas boiler, and most of this heat loss (about 70%) can be recovered through contact heat exchange equipment. Low-NOx boiler retrofit can be divided into the following two ways according to whether the furnace size is up to standard:

1、Replacement of low-NOx burners (full premix, flue gas external circulation, flue gas internal circulation)

2、Replacement of boilers (condensing boilers, three-way gas boilers + low-NOx combustion head) Because the condensing furnace is more environmentally friendly and low-NOx, the choice to replace the condensing boiler in the low-NOx retrofit has become an inevitable trend:

(1), ultra-high efficiency: condensing low-nitrogen boilers than ordinary boiler efficiency 20% -30%, condensing low-nitrogen boiler thermal efficiency up to 108.9%.

(2), condensing low-nitrogen boiler exhaust temperature is low: exhaust temperature as low as 35 ℃.

(3), the water supply temperature adjustable range: condensing low-nitrogen boiler with the world's most advanced, best quality water temperature control system and unique structure and combustion methods.

(4), more environmentally friendly: condensing low-nitrogen boiler nitrogen oxides (NOx) emissions of only 30 ppm, lower than the European standard 5 level of 56 ppm. carbon monoxide emissions are much lower than the general boiler emission standards. Due to high combustion efficiency, the carbon dioxide generated is much lower than ordinary gas boilers. The operation noise is less than 40dB.