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By Rex K Isaacs on May 2, 2013

Burner retrofits with combustion air control and fuel gas control in process furnaces are an economical solution to achieving lower NOx emissions levels and less operating costs with existing fired equipment. The optimal excess air level for achieving low NOx emissions and less operating cost is around 8% excess combustion air through the burner. This paper will explore how the GLSF Free Jet Burner design can be used with a combustion air control system to achieve less than 50 mg/Nm3 NOx emissions with 316 C combustion air preheat and 0.68% fuel savings compared to operation at 20% excess air.

Since carbon monoxide (CO) formation normally begins at 5%, excess air is provided through the burner in perfectly sealed furnaces without leakage. The burner operates with flue gas temperatures above 760° C, with excess oxygen (O2) and CO monitoring, and can be operated at 8% excess air. Should slight CO formation occurs, the excess air level should be raised accordingly. Note, if significant CO formation occurs, and then the fuel gas pressure should slowly be reduced to ensure that an explosive reaction does not occur. For safety, the combustion air control system is set important to operate at 8% excess air. If CO formation occurs at 8% air, then the control system will increase the excess oxygen level until CO formation is stabilized at an acceptable level. In such cases, CO formation occurs at approximately 5% excess air, and the furnace should be checked for tramp air leakage.

One of the other primary concerns for the end user operating company is the overall cost of ownership for next generation ultra-low NOx burners. They can have higher maintenance costs versus conventional emission burners. Zeeco provides the lowest maintenance design on the market for similar NOx emissions results. Zeeco has developed a patented next generation ultra-low NOx free-jet burner technology with a compact mechanical footprint. The GLSF Free-Jet Burner produces a flame profile with very limited flame-to-flame interaction for multiple burner installations, while also achieving shorter flame lengths. In order to control the fuel gas to the process burners, combustion air control system is installed to properly and safely operation of the burners and fit within small space requirements.

Zeeco will discuss the use of the Free-Jet burner technology, in conjunction with a burner control system in retrofit applications and the performance gains in both NOx emissions and excess combustion air.

 

Application

The purpose of the retrofit application was to replace the burners to achieve ultra-low NOx emissions. The following is a description of an application using the principles of reduced emissions and excess air control. A Coker Furnace was retrofitted with sixty four (64) Zeeco GLSF Free Jet burners each operating with a maximum heat release of 2.93 MW. The total maximum heat release of the Coker Furnace was 187.5 MW. The burners were designed to operate in the forced draft mode with 316 C combustion air preheat at 8% excess air. In addition, the furnace was designed to operate with a furnace flue gas temperature of 820 C of the gases exiting the radiant section.

 

Results

After the sixty-four (64) burners were installed in the Coker Furnace, a third party measured the resulting emissions recorded at the below listed conditions:

Operating Conditions:
Number of Burners: Sixty-four (64)
Burner Heat Release: 2.9 MW per burner
Furnace Heat Release: 185.6 MW per furnace
Excess Air: 8%
NOx Emissions: 49 mg/Nm3
CO Emissions: 5 mg/Nm3
Calculated fuel savings: 0.68% fuel savings compared to operation at 20% excess air

 

Conclusions

The use of an automated excess air control with Next Generation Burners can not only reduce emissions, but also reduce fuel costs. Therefore, lower emissions can be achieved with lower operating costs. Burner retrofits with combustion air control and fuel gas control in process furnaces are an economical solution to achieving lower NOx emissions levels and less operating costs with existing fired equipment. The optimal excess air level for achieving low NOx emissions and less operating cost is around 8% excess combustion air through the burner. This paper provided an example how the GLSF Free Jet Burner design can be used with a combustion air control system to achieve less than 50 mg/Nm3 NOx emissions with 316 C combustion air preheat and 0.68% fuel savings compared to operation at 20% excess air.

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