The promotion of "coal-to-clean-energy conversion" is an inevitable trend. In the trend of replacing coal....
The promotion of "coal-to-clean-energy conversion" is an inevitable trend. In the trend of replacing coal boilers with gas boilers, the low-nitrogen emission renovation of gas boilers has become a new pain point in the current times. This article briefly introduces the efforts and achievements made by our company in the low-nitrogen and ultra-low-nitrogen emission renovation of gas boilers in response to the new market situation and in pursuit of innovation and change.
I. The theoretical basis for reducing nitrogen oxide emissions in gas boilers
Natural gas is mainly composed of alkanes, with methane accounting for the vast majority. When the combustion temperature reaches above 1000℃, nitrogen in the air is oxidized by oxygen, generating a large amount of thermal-type nitrogen oxides. Therefore, to reduce the generation of nitrogen oxides, controlling the oxygen content and combustion temperature has become a crucial link.
II. Technical solutions for reducing nitrogen oxide emissions in gas boilers
1. As an external force, selecting high-quality low-nitrogen burners has a significant impact on the low-nitrogen emission of gas boilers. Currently, our company differentiates and configures burners with different emission grades such as 150mg/m3, 80mg/m3, and 30mg/m3 according to different regional emission requirements, fully meeting the market demands at different levels.
2. While improving the external force, the cultivation of internal strength is even more important. Our company draws on the experience of coal powder boiler FGR combustion technology and designs, tests, and optimizes the scheme for gas boilers. After repeated attempts, the FGR technology has been successfully applied to gas boilers.
FGR combustion technology, also known as smoke gas recirculation technology, refers to introducing the tail-end smoke gas of the boiler into the burner's air inlet, mixing with the combustion air, and then sent into the combustion nozzle to mix with the gas and be burned again. The principle is to extract a portion of the burned low-temperature and low-oxygen smoke gas, mix it with the air from the inlet, reduce the combustion temperature and oxygen content, and thereby achieve the effect of reducing the concentration of nitrogen oxide emissions. The smoke gas circulation rate is usually 5-20% of the total tail gas volume. FGR is divided into external smoke gas circulation and internal smoke gas circulation, and different FGR technologies are adopted according to different evaporation volumes and furnace types.
Emission and efficiency are a pair of contradictions for boilers. To meet national emission standards without reducing the boiler's thermal efficiency, our company optimizes the design of the boiler's heating surface and combustion space in the furnace, sets up energy-saving devices and condensers at the tail end to reduce the exhaust gas temperature, and takes various measures such as lowering the exhaust gas temperature. Currently, the efficiency of our company's gas boilers is generally above 93%, and the application of the condensing heat exchanger can even increase the thermal efficiency to >100%.
III. Our company's gas boiler series
1. Large fuel oil and gas boilers (15-240t/h), through furnace optimization design and recirculation of circulating smoke gas, combined with ultra-low-nitrogen burners, the initial nitrogen oxide emission is controlled below 80/30mg/Nm3.
Technical features:
According to different fuel requirements, adopt double-tube longitudinal D-type horizontal layout or single-tube transverse vertical layout;
Full membrane water-cooled wall sealing structure, micro-positive pressure combustion, eliminating air leakage;
Smoke gas recirculation design, meeting the requirements of low-nitrogen emission;
Fully automatic intelligent control, simple and reliable operation.
2. WNS series, from 0.5 to 15t/h, all designed as condensing type, with an exhaust temperature of ≤80℃, thermal efficiency ≥98%. And meet the structural requirements of NOx initial emission ≤80mg/Nm3;
Technical features:
Horizontal smoke gas three-loop integrated low-resistance design, compact and beautiful shape, easy installation;
Wave-shaped furnace shell combustion chamber and threaded smoke tubes heat transfer surface integrated design, with the same volume of traditional furnace types, increasing the heat absorption area;
External independent energy saver and condenser, effectively improving thermal efficiency, convenient for maintenance and replacement;
Fully automatic intelligent control, simple and reliable operation.
IV. Product expansion
In addition to conventional gas-fired and liquefied gas boilers, our company, in accordance with the needs of users in different industries, has expanded the fuel sources to include light oil, heavy oil, residue oil, methanol, blast furnace gas, coke oven gas, syngas, biogas, and carbon black tail gas, etc. This has significantly enriched the product range and met the growing market demands.