Wanner Hydra-Cell Pro^® Pumps for NOx Reduction Applications

A common application for Wanner Hydra-Cell Pro^® pumps is power-generation NOx reduction through high-pressure water and reagent injection.

What is NOx?

NOx is a general term mostly related to nitric oxide and nitrogen dioxide — gases formed when fossil fuels (oil, gasoline, natural gas and coal) are burned. When combustion exceeds roughly 2,800°F, the reaction that produces NOx accelerates.

NOx is regulated because of health and environmental effects such as smog and acid rain. California has the strictest limits. Several states, including New York, New Jersey, Oregon and Massachusetts, have adopted standards modeled after California’s. Those limits raise the cost of generation through fees, equipment upgrades or a shift toward solar, wind, nuclear and other non-combustion sources.

The practical approach for a fossil-fuel plant is to raise process efficiency and control peak combustion temperature.

Inlet Fogging = Power Boost and NOx Control

Deionized (DI) water is sprayed at high pressure through fine nozzles. DI or tightly filtered reverse-osmosis water is required because of the nozzle orifices. Mineral-free water is aggressive to iron, steel, brass and even 304 stainless steel. Piping is usually 316 stainless or duplex stainless. Hydra-Cell Pro pumps are available in those alloys.

The droplets evaporate at the compressor inlet. That evaporative cooling densifies the air and increases compressor capacity. The higher air-to-fuel ratio leans the mixture, and the cooler air lowers peak flame temperature. The combination reduces NOx and adds a power boost.

Fine droplets need smooth pumping at high pressure, typically 1,000–3,000 PSIG. The target is a uniform 10–20 micron spray. Larger droplets reduce cooling and can erode compressor blades. Pressure ripple at the nozzle produces coarser spray, so a smooth discharge is essential.

Hydra-Cell Pro pumps deliver that flow. The same trait shows up in spray-dry flue-gas desulfurization and in SCR/SNCR reagent systems.

Water Injection = NOx Control

Injecting water directly into the flame is a more direct temperature control. It is used mainly on peaker plants (grid support during high air-conditioning demand) and on plants burning distillate oil. Base-load and newer combined-cycle plants usually rely on selective catalytic reduction because the water volume for direct injection is impractical.

Water mixed with the fuel lowers peak flame temperature and therefore NOx. Flow is proportional to fuel flow (turbine load), so a positive-displacement pump is required. Hydra-Cell Pro pumps run through a 10:1 turndown and meet API 675 metering standards for repeatability, steady-state accuracy and linearity — the control traits that keep combustion predictable.

Unlike inlet fogging, water mixed with fuel does not need a fine atomizing orifice, so discharge pressure is typically 700–800 PSIG. Smooth, repeatable flow is still required for combustion control.

Proportionality matters most on peaker plants. They ramp continuously, so fuel and water both have to track load. Some plants use both methods: cooler inlet air for compressor efficiency, plus steam or water into the flame for temperature control.

SCR and SNCR NOx Reduction

Selective catalytic and non-catalytic reduction inject aqueous ammonia (SCR) or urea (SNCR) into the flue gas, where it reacts with NOx.

SCR is usually a few gallons per minute at pressures up to 300 PSIG. Aqueous ammonia is corrosive and volatile, so a sealless Hydra-Cell Pro pump is the practical choice.

SNCR needs higher flow and pressure, sometimes to 2,000 PSIG. Urea or ammonia is injected into flue gas at 1,600–2,100°F. There is no catalyst, so atomization and distribution have to be uniform in a short residence time. That is a different duty than SCR, where the reagent sits on the catalyst surface and spray quality is less critical.

Wet Flue Gas Desulfurization (FGD)

Wet FGD is used mainly to cut SO₂ (a driver of acid rain and smog). Hydra-Cell Pro pumps feed 20–25% lime slurry to air-atomized spray nozzles. Compressed air does the atomizing and discharge pressure is modest, so the design advantage is the sealless wet end — no packed or mechanical shaft seal on an abrasive slurry.

Wet FGD will absorb some NO₂ but little NO, so it only polishes total NOx. The process converts SO₂ to calcium sulfate; some NO₂ is absorbed in that reaction.

Related Hydra-Cell Pro Models

• F20 — typical SCR reagent skid
• M03 — compact SCR / low-flow injection
• D15 — inlet-fogging skids
• D35 — water-injection and higher-flow NOx skids
• Hydra-Cell Pro design overview
• Components of a high-pressure pump skid

Additional Resources

• NOx Reduction with Turbine Inlet Fogging (PDF)
• Hydra-Cell Pro pumps for TEG injection
• Pumping difficult-to-handle liquids
• Hydra-Cell Pro pump inquiry form