NOx Reduction

Pollutant-emission laws governing combustion equipment are increasing every year. One of the environmental regulations now affecting the Chemical Process Industries (CPI) are the laws covering Nitrogen Oxides (NOx) emissions. FIS has been helping users and owners by providing design and engineering services to reduce their NOx emissions, improve the efficiency and capacity of their fired heaters, boilers, and waste heat recovery units. Finding the means for limiting NOx from fired heaters has become a major thrust of many sectors in the CPI.

FIS have completed over 300 engineering studies and projects. We currently have a team of 45 skilled engineers on board with offices in Sugar Land, TX and in New Delhi, India. We have experience in design and revamp all types of refinery fired heaters.

NOx Emissions

Pollutant-emission laws governing combustion equipment are increasing every year. One of the environmental regulations now affecting the Chemical Process Industries (CPI) are the laws covering Nitrogen Oxides (NOx) emissions.

Finding the means for limiting NOx from fired heaters has become a major thrust of many sectors in the CPI.

Reducing NOx Emissions in Fired Heaters

The following options are used in the Chemical and Petrochemical companies to reduce NOx emissions. Flue gas recirculation (FGR) extracts a portion of the flue gas from the stack and returns it to the furnace along with combustion air. This lowers the peak flame temperature, and cuts thermal-NOx formation. The addition of flue gas also reduces the Oxygen available to react with the Nitrogen.

Selective Catalytic Reduction (SCR) involves injecting ammonia into the flue gas upstream of a catalyst bed. The chemical reaction involved is:

O2 + 4NO + 4NH3 = 4N2 + 6H2O

NOx and NH3 combine on the catalyst’s surface, forming an ammonium salt intermediate that subsequently decomposes to produce elemental Nitrogen and Water. The catalyst lowers the activation energy of the NOx decomposition reaction, thereby enabling use of this technology at lower flue gas temperatures. The optimum temp. range for SCR is 600° to 700°F.

Ultra Low NOx Burners, Several designs are available today that combine two NOx reduction steps into one burner without any external equipment. These burners typically incorporate staged air with internal FGR or staged fuel with internal FGR.

Choosing the Best Option for You

FIS has executed several projects regarding low NOx emission. We have the experience and the knowledge to customize the best option for you.

Case Study

An USA company approach FIS looking for a practical solution to reduce the NOx in their Crude Heater. This crude heater is the biggest heater within the clients system, with a heat duty of 750 MMBtu/hr. The scope was to install a selective catalytic reduction unit, to reduce NOx emissions to less than 0.01lb/MMBtu. The convection section was split to get the correct flue gas temperature window for the SCR. A novel scheme was implemented by FIS that saved 5 million dollars to the client. FIS option didn’t require installing new ID fans or duct work. The ID/FD fans were upgraded. FIS performed the CFD analysis to ensure there is proper mixing of Ammonia with the flue gases in the SCR unit and there is uniform distribution of flue gases over the catalyst bed. FIS reduced the flue gas temperature leaving stack from 420 deg F to 300 deg F, thus improving the efficiency by 3.5%. The annual fuel savings are approximately 1.5 million dollars. As you can see, this picture shows the conventional scheme versus FIS scheme. The alternative is to route the cold and hot flue gas ducting into convection section instead of the stack. The convection section is split into two parts by installing a blanking plate. This eliminates the need to install new ID fans and stack and saves on duct work.