L

Ammonia ring pipe

1 Engine/turbine, single or multiple units

2 Muffler/sound attenuation unit

3 Ammonia injection systems

Absorption vessel

Ammonia ring pipe

Ammonia Storage Tank

Vaporizer

1 Engine/turbine, single or multiple units

2 Muffler/sound attenuation unit

3 Ammonia injection systems

4 CER-NOX reactor

5 Central, CEM system

6 Ammonia storage tank functional diagram of a cogeneration plant with two prime movers (gas turbines or reciprocating engines) featuring an SCR system. Shown are muffler/sound attenuation units, ammonia injection systems (controlled by residual NOX measurement), the reactors with SCR (which may also include oxidation catalysts downstream), the central CEM and operating control system, and the ammonia storage tank. This system utilizes zeolite composite extruded honeycomb modules.

Figure 17-37 is a cutaway diagram of the reactor/converter. The system operates as follows:

• NH3 is injected into the waste gas stream in front of the reactor when the exhaust gases are in the proper temperature range. Below 572°F (300°C), NH3 may form ammonia-disulfate with sulfur bearing fuel. Above 950°F (510°C), NH3 thermally oxidizes excessively, yielding more NOX. At 970°F (521°C), about 15% excess NH3 is consumed.

• The rate of NH3 injection is based on feedback signals from continuous NOX measurements (CEM system). The system draws off a small quantity of waste gas downstream of the reactor. The sample is filtered and dried and sent to NOX, CO, and O2 analyzers. These data are relayed to the process controller. The controller activates a motor-driven valve on the NH3 injection panel.

• Aqueous ammonia, 25.0 to 29.4% ammonia in water, or 33 to 40% urea, which is the reducing agent, is supplied by a metering pump through a feeder line from a non-pressurized stainless steel tank. A small sulfuric acid scrubber is used to eliminate ammonia vapors created during thermal venting of the tank.

• Both NOX and NH3 are absorbed into the micropores of the catalyst. An exothermic reaction in the zeolite micropore structure increases pressure from which the reaction products (N2 and H20 vapor) are forcefully expelled from the micropores, causing a self-cleaning action of the catalyst surface.

Figure 17-38 is a diagram of a ceramic molecular sieve catalyst (SCR) NOx abatement system installed with a

Fig. 17-36 Functionality Diagram of Cogeneration Plant with Two

Prime Movers Featuring an SCR System.

Source: Environmental Emissions Systems, Inc./Steuler

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