How the FLGR Process Works

The FLGR process injects natural gas above the main combustion zone of the furnace to reduce much of the NOx to harmless nitrogen. No physical change is required to the main combustion system, so the type of primary fuel used by the generating unit is inconsequential.

What sets FLGR apart from conventional gas reburning systems is the injection of gas in a manner that optimizes the furnace's stoichiometry on a very localized basis. By doing this, the process avoids creating a fuel-rich zone and maintains overall fuel-lean conditions.

Natural gas injection is carried out at a low furnace temperature, between 2000 and 3000 deg F. This is done using multiple, high-velocity turbulent gas jets that penetrate into the upper furnace to the areas with the highest NOx concentration. FLGR can also maintain acceptable emissions of carbon moNOxide (CO) without overfire air, which must be added in conventional gas reburning systems to ensure that all the reburn fuel and other combustibles burn out completely. This makes the FLGR technology less expensive than conventional reburning.

The Cost Advantages of FLGR

Fuel Lean Gas Reburning is a cost-effective option for utilities faced with the need for NOx emission reduction at a low capital cost.

FLGR equipment typically can be installed at less than $ 8/kW. The process has been shown to reduce NOx by as much as 30-45%, with consumption of natural gas between 5-7% of the total boiler heat input.

This low capital cost--coupled with operating costs based on gas-coal price differentials and gas use of 5-7%--makes FLGR a cost-competitive option for utilities requiring moderate NOx reductions. FLGR can be particularly attractive to plants facing moderate compliance requirements during the summer ozone season, when gas is plentiful and lower in cost. It can also generate SO2 allowance credits in direct proportion to the amount of natural gas that displaces coal, partially offsetting the added costs of reburning.

For boilers limited in generating capacity by either fans or mills, FLGR offers a potential increase of up to 7% in generating capacity. This can be especially beneficial during the high-demand summer months.

FLGR is Compatible with Existing NOx Reduction Equipment

FLGR has been installed on units with no NOx controls, low NOx burners (with and without overfire air) and selective non-catalytic reduction (SNCR) equipment. NOx reductions with FLGR are in addition to reductions achieved with other NOx controls. Fuel Lean Gas Reburning complements other NOx controls, so previous investments in NOx control equipment aren't lost because the existing controls can still be used effectively when FLGR is installed.

Successful Installations

Successful test programs of the FLGR process have been conducted at a number of coal-fired generating units. These units encompass a variety of boiler designs and generating sizes.

Each Situation Is Unique

We approach assignments with a "real world" understanding of the environmental and economical pressures utilities are facing today. We analyze dozens of variables and consider things such as: furnace design, existing NOx controls, operational impacts, coal quality and process conditions to achieve operational and emission guarantees in designing FLGR systems.

A key to Steag Energy Services's (formerly ESA) success is Computational Furnace Modeling (CFM), an advanced form of computational fluid dynamics technology. By producing a working CFM simulation, we can "look inside" the furnace to see distributions of properties such as temperature or stoichiometry and gain insights that can't be achieved with conventional boiler testing. CFM employs Phoenics software to automatically solve finite difference equations for the conservation of mass, momentum and energy at each grid point. To this, our CFM program adds models for furnace-specific conditions such as radiative heat transfer, combustion and NOx kinetics.

Models are constructed and validated to the specific characteristics of each individual boiler. A parametric study of design options is then carried out to identify the best FLGR design.

All of our findings are put into a final study proposal which includes our analysis, the design we recommend and the cost of the project.

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