Flue gas concentration

Note that the ground-level concentrations do not depend on the flue gas concentrations but rather on the amount of pollutant emitted. It is therefore not worth diluting the flue gases with fresh air (other than to raise the efflux velocity). 

However, the main problem with excess air is that it introduces oxygen into the flue gas. Typical flue gas concentrations for natural gas and coal combustion in power production are given in Table 6.3. 

Nitrogen oxides, NO, NOi, and N,0, are formed in the combustion of fossil fuels. Typical flue gas concentrations range from 400 to 1500 ppm. Activated carbon can be used as a reducing agent, as a catalyst, or as an adsorbent for the removal of these compounds [50]. 

The mass-transfer coeflBcients measured with low sulfur coal for both limestone and sodium hydroxide were essentially the same. In a packed tower, limestone will absorb and react with SO2 to the same extent as a strong alkali for flue gas concentrations less than 1000 ppm. 

Figure 5. Predicted CO2 concentrations as a result of step changes in the CO2 flue gas concentration (2).

Due to practical difficulties, no sonic speed measurement was available and a model based on only density, conductivity, and refractive index was used. During this experiment, the CO2 concentration in the feed gas was varied in step of 2 vol% from 12% to 0%, which is well covered by the model predictions. The flue gas concentration changes resulted in temperature variations between 32 and 42 °C, introducing some additional inaccuracies in the model predictions. The small drops in predicted CO2 concentration that are regularly occurring were not expected, but were concluded to be caused by the level control of the set-up that was used. It shows that the real-time predictions are capable of identifying operational issues that are occurring on rather small time scales. 

The mercury removal performance of pilot-scale ICDAC and of Norit s FGD carbon were determined in a 0.236 m% (0.25 MWe) pilot plant operated by CONSOL, Inc., Library, PA. The pilot plant can simulate flue gas conditions downstream of the air preheater in a coal fired utility power plant. The flue gas mercury concentration studied (10-15 pg/m ) is typical of utility flue gas concentration. Mercury removals were evaluated in the flue gas duct, which provided a gas residence time of approximately 2 seconds, and in the baghouse, where the solids retention times can be as long as 30 min. Common test conditions were flue gas flow, 0.165 m /s flue gas wet bulb temperature, 50-53°C flue gas composition, 1000 ppmv dry SO2, 10 vol% dry O2, and 10 vol% dry CO2. All tests were conducted with a fly ash obtained from a coal-fired utility boiler firing an eastern bituminous coal. The fly ash feed rate was 4.5 kg/hr (solids loading of 90.6-104.7 gm/dcm ). Mercury removal was determined from the mercury feed rate, the solids (carbon and fly ash) feed rate, and mercury analysis of the feed and recovered solids (by combustion followed by cold vapor atomic absorption spectroscopy). Except where noted, all mercury removal results discussed in this paper include mercury removal by the carbon sorbent and the fly ash. A more detailed description of the pilot test unit is given elsewhere (27]. 

Recovered catalyst and blowdown gas (- 3% of the flue gas) exit from the bottom of the separator to an electrostatic precipitator or to a small, fourth-stage cyclone for further concentration of catalyst fines. The flue gas, with 70—90% of the catalyst particles removed, passes from the separator into the power expander. 

Limestone is pulverized to 80 to 90 percent through 200 mesh. Shiny concentrations of 5 to 40% have been checked in pilot plants. Liquid to gas ratios are 0.2 to 0.3 gaLMSCF. Flue gas enters at 149°C (300°F) at a velocity of 2.44 m/s (8 ft/s). Utilization of 80 percent of the solid reagent may be approached. Flow is in parallel downward. Residence times are 10 to 12 s. At the outlet the particles are made just diy enough to keep from sticking to the wall, and the gas is within 11 to 28°C (20 to 50°F) of saturation. The fine powder is recovered with fabric filters. 

Flue gas recirculation (FGR) is the rerouting of some of the flue gases back to the furnace. By using the flue gas from the economizer outlet, both the furnace air temperature and the furnace oxygen concentration can be reduced. However, in retrofits FGR can be very expensive. Flue gas recirculation is typically applied to oil- and gas-fired boilers and reduces NO, emissions by 20 to 50%. Modifications to the boiler in the form of ducting and an energy efficiency loss due to the power requirements of the recirculation fans can make the cost of this option higher. 

By this method it is possible to determine the total concentration of reduced-sulfur compounds or the concentration of TRS compounds, as in a paper pulp plant. The oxidation temperature of the furnace is about 800 °C. The flue gas must contain a minimum of 1% oxygen to ensure that all TRS compounds are fully oxidized to sulfur dioxide. 

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

By recirculating a part of the flue gas to the furnace, the combustion zone turbulence is increased, the temperature is lowered and the oxygen concentration is reduced. All of these factors lead to a reduction of NO, fonnation. 

The distance above the catalyst bed at which the flue gas velocity has stabilized is referred to as the transport disengaging height (TDH). At this height, the catalyst concentration in the flue gas stays constant none will fall back into the bed. The centerline of the first-stage cyclone inlets should be at TDH or higher otherwise, excessive catalyst entrain ment will cause extreme catalyst losses. 

Electrostatic precipitators (ESP) and wet gas scrubbers (WGS) are widely used to remove particulates from the FCC flue gas. Both can recover over 80% of filtrable solids. An ESP (Figure 10-6) is typically installed downstream of the flue gas heat recovery (prior to atmospheric discharge) to minimize particulate concentration. If both low particulate and low SO requirements are to be met, a wet gas scrubber such as Belco s (Figure 10-7) should be considered. If SO removal... 

NOj, levels in the FCC flue gas typically range from 50-500 ppm. Nitrogen content of the feed, excess oxygen, regenerator residence time, dense phase temperature, and CO promoter all influence the concentration of NO. ... 

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