Effective NOx Reduction Research Articles

Emission Characteristics of NOx and Unburned Carbon in Fly Ash of Sub-bituminous Coal Combustion.

Sub-bituminous coal is considered to be one substitute fuel for bituminous coal. Since sub-bituminous coal contains more than 20% moisture, there are some problems with its utilization, such as a decrease in combustibility, high NOx emission and so on. This report describes the emission characteristics of NOx and unburned carbon in fly ash of sub-bituminous coal combustion through the use of a pulverized coal combustion test furnace. On the sub-bituminous coal combustion, ignition at the burner exit worsened and the combustion flame became diffused. Then, both NOx emission and the unburned carbon concentration in fly ash became high. In order to keep stable combustion and to form an effective NOx reduction flame, the swirl vane angle of secondary air was reduced and the Air/Coal ratio was lowered. As a result, the combustion flame became moderate, and both NOx emission and unburned carbon concentration in fly ash could be reduced.

Selective non-catalytic reduction of NO x under diesel engine conditions

NOx reduction experiments were conducted by direct injection of urea or NH3 into a diesel-fueled, combustion-driven flow reactor which simulated a single engine cylinder (966 cm3). NOx reduction tests were carried out over a wide range of air/fuel ratios (20–40) using an initial NOx level of 530 ppm and for normalized stoichiometric ratios (NSRs) of reductant to NOx of 1.5–4.0. The results show that effective NOx reduction with urea occurred over an injection temperature range of 1100 to 1350 K. NOx reduction increased with increasing NSR values, and about a 40%–60% reduction of NOx was achieved with NSR=1.5–4.0. Most of the NOx reduction occurred within the cylinder and head section (residence time

99/03841 Cost effective NO x reduction for tangentially fired boilers : Hager, M. et al. FACT (Am. Soc. Mech. Eng., 1998, 22, (1), 103–113

99/03841 Cost effective NO x reduction for tangentially fired boilers : Hager, M. et al. FACT (Am. Soc. Mech. Eng., 1998, 22, (1), 103–113

A highly durable catalytic NOx reduction in the presence of SOx using periodic two steps, an operation in oxidizing conditions and a relatively short operation in reducing conditions

Catalytic NOx reduction system in the presence of excess oxygen using periodic two steps, an operation in oxidizing conditions and a relatively short operation in reducing conditions was investigated over various catalysts, comparing with HC-SCR in full lean conditions. Based on findings and studying the correlation between transient reaction profile from rich to lean excursions and reaction behaviors in both the NOx reductions, a highly effective and durable NOx reduction system in the presence of excess oxygen and sulfur oxides using the periodic two steps was designed. This system consisted of a short operation in oxidizing conditions and a far shorter operation in reducing conditions, and it effectively reduced NOx over Rh supported on alumina with no deterioration in the short-term durability test in the presence of 40 ppm SO 2.

98/03207 The N 2O formation mechanism during devolatilization and char combustion

At an experimental facility of the Stuttgart University, the process of fuel splitting and staging is investigated with a view to lower NOx emissions. Raw coal is introduced into either an electrically heated, entrained flow reactor or a fluidized bed reactor where it is split into pyrolysis gas and residual char. In a following staged combustion, the remaining char or raw coal is used as primary fuel and the pyrolysis gas as reburn fuel. The test facility allows a systematic study to evaluate the effect of different parameters on NOx reduction independently of each other. Pyrolysis experiments, combustion studies, and calculations have been performed to explain the effective NOx reduction with coal pyrolysis gas.To compare the results and show the advantage of this process, investigations with fuel staging were carried out. With gaseous reburn fuels and residence times higher than 1.5 s, minimum NOx emissions below 200 mg/m3 at 6% O2 could be achieved independently of the coal type (200 mg/m3 is approximately equivalent to 100 ppmv). Reburning with coal pyrolysis gas increases the optimum air/fuel ratio from 0.75 to 0.9, yielding the same or even lower NOx emissions. The main parameters are stoichiometry and residence time in the fuel-rich secondary zone. The results also show an increase of the reduction efficiency with increasing reburning temperatures in the reburn zone. The tar components in the reburn fuel and the fuel-N content are very important parameters in achieving excellent results when using coal pyrolysis gas. These appear to have a positive effect on the reduction of NOx emissions. To explain this effect, the model of the perfectly stirred reactor (PSR) was employed. The modeling results agree well with the experimental investigations.

NOx reduction by hydrazine in a pilot-scale reactor

Abstract The effects of the hydrazine molar ratio, reaction temperature and addition of CO on the NOx reduction in flue gas containing 12% oxygen were determined in a pilot-scale flow reactor. The optimum reaction temperature and molar ratio for maximum NOx reduction were found to be about 873 K and 4.0, respectively. With CO, hydrazine provides a wider temperature window for effective NOx reduction. The proposed model predicts the reduction of NO reasonably well at high oxygen content.

Energy efficient plasma processing of gaseous emission using a short pulse discharge

This letter reports efficient treatment of NO emission with a transient, nonequilibrium plasma created by pulsed corona discharge. The transient plasma (≈50 ns) is found to reduce NO emission by 50% in a flow of 2–25 l/s with energy cost ≈10–20 eV/molecule, corresponding to a fraction of source power of ≈5%. The efficiency of NOx reduction is a complex function of parameters that include pulse width, pulse polarity, current density, repetition rate, and reactor design. It was found that the best efficiencies are correlated with a low current density (0.2 A/cm2)and high repetition rate (1 kHz) under high flow rate. Careful optimization of all these parameters is required to reach cost effective NOx reduction.

Impact of temperature and fuel-nitrogen content on fuel-staged combustion with coal pyrolysis gas

At an experimental facility of the Stuttgart University, the process of fuel splitting and staging is investigated with a view to lower NOx emissions. Raw coal is introduced into either an electrically heated, entrained flow reactor or a fluidized bed reactor where it is split into pyrolysis gas and residual char. In a following staged combustion, the remaining char or raw coal is used as primary fuel and the pyrolysis gas as reburn fuel. The test facility allows a systematic study to evaluate the effect of different parameters on NOx reduction independently of each other. Pyrolysis experiments, combustion studies, and calculations have been performed to explain the effective NOx reduction with coal pyrolysis gas. To compare the results and show the advantage of this process, investigations with fuel staging were carried out. With gaseous reburn fuels and residence times higher than 1.5 s, minimum NOx emissions below 200 mg/m3 at 6% O2 could be achieved independently of the coal type (200 mg/m3 is approximately equivalent to 100 ppmv). Reburning with coal pyrolysis gas increases the optimum air/fuel ratio from 0.75 to 0.9, yielding the same or even lower NOx emissions. The main parameters are stoichiometry and residence time in the fuel-rich secondary zone. The results also show an increase of the reduction efficiency with increasing reburning temperatures in the reburn zone. The tar components in the reburn fuel and the fuel-N content are very important parameters in achieving excellent results when using coal pyrolysis gas. These appear to have a positive effect on the reduction of NOx emissions. To explain this effect, the model of the perfectly stirred reactor (PSR) was employed. The modeling results agree well with the experimental investigations.

Combustion control of direct injection methanol engine using a combination of charge heating and exhaust gas recirculation

The feasibility of a highly efficient, low-NOx spark-assisted direct injection methanol engine has been investigated using a combination of charge heating and EGR under light load conditions. The results show that, as the charge temperature is increased, rapid premixed combustion initiated by spark ignition occurs and self-ignition of subsequent fuel spray is induced. Thus the combustion progresses rapidly in a stable state, improving the brake thermal efficiency. It was found that the oxygen concentration in the charge can be reduced by conducting EGR at high rate under high charge temperature, so that effective NOx reduction is possible.

Flue Gas NOX Reduction Using Ammonia Radical Injection

A novel technique has been developed for flue gas NOX reduction through the injection of plasma-treated ammonia and its decomposition products. Numerical investigation of the chemical kinetics shows nearly complete NO removal when ammonia radicals are injected into the flue gas. The feasibility of this new technique was experimentally explored on a small-scale laboratory combustor at Carnegie Mellon University and concurrently on a larger-scale combustor at the DOE Pittsburgh Energy Technology Center. Preliminary experimental results have shown that ammonia plasma-injection is more effective than simple ammonia-injection at low flue gas temperatures. NOX reduction of 85 to 90 percent was achieved at a low plasma power input. This technique is expected to provide additional opportunities for inexpensive and effective NOX reduction in stationary sources.