Abstract
A gas fired tangentially boiler was modeled under full load conditions. Furnace was simulated by CFD and then was joint with two mathematical models to calculate heat transfer in the convective section, and metal temperature of waterwall tubes. Effects of changing the combustion excess air (0 to 20%) and burners tilt angle (-30° to +30°) were studied. Results showed that the boiler efficiency is optimum if excess air= 10% and the burners have a negative angle. However, these optimum settings cannot produce a superheated and reheated steam of 538 °C which is desirable. Indeed, a zero or positive tilt angle with 10% excess air, or a negative burner angle with 15% excess air lead to highest efficiency by considering the potential of generating superheated steam of 538 °C. In addition, CO emission in low excess air values growths by increasing the burner tilt angle. NOx emission in low and high excess air ratios is lower at positive burner angles while a moderate excess air (10%) needs a zero tilt angle to minimize NOx emission. Furthermore, a critical fouling thickness was computed, considering boiler's circulation ratio, in which the metal temperature of the waterwall exceeds the short overheating threshold. With a certain thickness of scale layers inside the tubes, a burner tilting equal to 0° or 30° postpones tube rupture. These results could be utilized by operating engineers to keep their utility boilers in the most efficient state and avoiding overheating and tube rupture.
Highlights
Boilers are one of the most important components in steam power plants from design and operation viewpoints
The results showed that no tilt situation has the minimum NOx while the negative tilting angle leads to highest NOx discharge
It is important to know how does excess air and burner angle affect the amount of generated steam (Figure 3)
Summary
Boilers are one of the most important components in steam power plants from design and operation viewpoints They are at the heart of steam stations and many other industries such as petroleum processing. This importance was the main source of a lot of attempts for modeling the utility boilers during past decades. Computational fluid dynamics gains a great attention in the boiler simulation during past decades after rising the computational abilities. They were used mostly for determining the distribution of flow and heat inside a furnace, predicting pollutant emissions, detecting malfunctions in a boiler and proposing modifications to prevent them
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