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Engine

Noxtech®’s System, is used to remove NOx, HC (VOCs), carbon based particulate and CO from the exhausts of stationary internal combustion engines (diesel and natural gas) for both retrofit and new engine units. This product can be installed with a reasonable effort on new or existing engines. The Noxtech System reactor is constructed from 304 stainless steel and is expected to be very durable and stable. The control system software was developed by and is proprietary to Noxtech® .

The Noxtech® system chemically treats exhaust gases using urea a low-cost nonhazardous liquid chemical. The Noxtech® system does not use a catalyst. Supplemental fuel is added to maintain a reaction temperature of 1400-1500 F and to create an optimum reaction environment for removal of emissions. Fuel consumption is minimized by recovering heat released for temperature control and reaction optimization. This heat recovery is incorporated into the design of a Noxtech® reactor for internal combustion engines. In its normal operating temperature range (1400-1500oC), the gas-phase NOx reduction is completed in only 150-200 milliseconds, and for exhaust gases with NOx levels as high as 1,000 ppm are reduced below 10 ppm with less than 5 ppm NH3 slip. High NOx levels are reduced in nearly stoichiometric proportion to the urea injection. This non-catalytic treatment selectively removes 90-98% NOx with substantial removal of particulate matter and gaseous organics.

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The Noxtech System can provide the end user for treatment of stationary IC Engines with the following benefits:

Bullet  Greater than 95% NOx reduction for diesel and landfill, digestor and natural gas engines
Bullet  Substantial concurrent depletion of NOx, VOCs, CO & NH3
Bullet  No generation of hazardous by-products
Bullet  No solid catalyst to replace or used catalyst requiring disposal
Bullet  Lower urea cost since the Noxtech System can use agriculture grade urea
Bullet  Simple system has low maintenance costs
Bullet  The Noxtech System’s performance is not affected by the impurities (siloxanes) and poisons contained in biogases
Bullet  Noxtech System operates at relatively low back pressure
Bullet  System is durable and reliable. It has no catalysts and utilizes simple construction from durable materials

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Noxtech, Inc.has commercialized an emissions control system for diesel and digestor, landfill and natural gas fueled engines. Emissions of hydrocarbons, CO, soot, and NOx are removed in a single, one-step process unique patented combustion process. Noxtech uniquely controls emissions autocatalytically by gas-phase reactions. The gas-phase autocatalysis is self-sustained by autothermal combustion, so Noxtech is not affected by contaminants which poison, foul, and plug catalysts.


Autocatalytic Mechanism


Autothermal combustion self-sustains gas-phase autocatalysis in exhaust gases with O2 concentrations above about 2.0% by volume (Figure 1). Emissions of NOx are reduced concurrently by injecting urea or NH3. Controlling a final temperature of 1,400-1,500°F maintains selective NOx reduction with less than 5 ppm NH3 slip and 30 ppm CO, and 3-5 ppm VOCs.

The autocatalytic mechanism uniquely distinguishes Noxtech. Free radical intermediates in autothermal combustion are the catalysts which self-sustain depletion of all criteria pollutants, including soot. The fuel Injection regenerates autocatalysis continuously, so performance is self-sustained and does not depend on solid catalytic surfaces which plug, foul, and poison.

Third party source tests have verified compliance with SCAQMD Rule 1110.2 as amended and in effect February 1, 2008 for criteria emissions. These tests confirmed compliance for diesel and biofueled stationary IC Engines.

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Figure 1

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Process Equipment

Heat recovery minimizes the fuel injection requirement to self-sustain autocatalysis. The Noxtech reactor and heat exchanger (R/Hx) preheat engine exhaust so autothermal.., fuel consumption is about 5-7% of the engine fuel, depending primarily on the reactor heat exchanger efficiency. Commercial designs are expected to require approximately 5" water column of pressure drop.

Figure 2 illustrates this configuration of a Noxtech R/Hx. Engine exhaust is preheated in annular heat exchange tubes. Injected fuel autoignites in the preheated exhaust and self-sustains autocatalysis, while injection of urea or NH3 reduces NOx. Reactants are depleted within 0.150-0.200 seconds before the gas leaves the open reaction chamber and enters the heat exchanger shell.

Autothermal heating in the reaction chamber maintains a thermal gradient for preheating the engine exhaust. After heat recovery, the exhaust is discharged to the stack. The stack temperature is hotter than engine exhaust by the amount of autothermal heating in the reaction chamber (150-250°F).

The Noxtech R/Hx includes a startup burner to warm up cold equipment. This burner starts automatically with the engine and shuts down as soon as the unit reaches normal operating temperatures. Then, fuel injection for the autothermal heating is controlled to maintain reactor exit temperature. This feedback temperature control maintains autocatalysis at all engine loads.


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Figure 2


 

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Figure 3

Figure 3 shows the symmetrical, cylindrical design of the R/Hx.  Annular heat exchange tubes surround the central reactor, and the shell-side of the heat exchanger is baffled to ensure efficient counter current heat transfer.  This design reduces or eliminates thermal cycling.  The equipment is entirely 304 SS and is proven to maintain performance after hundreds of heating and cooling cycles.

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Control System

The Noxtech control system is failsafe. An engine run signal initiates startup, and the subsequent signals required for startup and operation are monitored and confirmed step-by-step by a ladder-logic-controller. Temperature is controlled as long as the engine is loaded, and Noxtech shuts down when the engine is idled. All functions are failsafe, so Noxtech cannot stop the engine. Any failure can only result in excess emissions above compliance limits.

Feedback from a NOx analyzer (an integrated component of the Noxtech System) is used to very accurately control NOx to the desired levels based on NOx levels from the treated exhaust exiting the Noxtech reactor. This feedback control maintains NOx compliance with minimum consumption of chemical. With a NOx analyzer, the Noxtech system may control NOx below compliance limits to generate credits for sale in NOx trading markets or to offset other emissions sources.

Commercial Experience

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In 2004, a Noxtech System was installed on a landfill gas powered 500 kW diesel electric generator at the Tulare County at Woodville Landfill. The Noxtech System has been operating for over 3 years. Third party source tests have verified compliance with SCAQMD Rule 1110.2 as amended and in effect February 1, 2008 for criteria emissions.

The automatic controls have cycled hundreds of times without failure during its operation. These controls include an automatic startup sequence for the burner and reactor exit temperature. Urea is injected using a PLC feedback control system using signals from Noxtech's NOx and oxygen analyzer measuring NOx and O2 from the exhaust gas exiting the Noxtech reactor. During normal load variations for the Woodville Engine-generator, 15-minute averages of NOx measurements do not fluctuate more than about 1-3 ppm.

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