Soot combustion

Organic compounds are a major constituent of the FPM at all sites. The major sources of OC are combustion and atmospheric reactions involving gaseous VOCs. As is the case with VOCs, there are hundreds of different OC compounds in the atmosphere. A minor but ubiquitous aerosol constituent is elemental carbon. EC is the nonorganic, black constituent of soot. Combustion and pyrolysis are the only processes that produce EC, and diesel engines and wood burning are the most significant sources. 

The main combustion pollutants are nitrogen oxides, sulfur oxides, carbon monoxide, unbumed hydrocarbons, and soot. Combustion pollutants can be reduced by three main methods depending on the location of thek appHcation before, after, or during the combustion. Techniques employed before and after combustion deal with the fuel or the burned gases. A thkd alternative is to modify the combustion process in order to minimise the emissions. 

Electrochemical Promotion of Particulate Matter (Soot) Combustion Using a Ceria-Gadolinia Solid Electrolyte and a Dispersed Perovskite Catalyst... 

Figure 12.12. Near full scale monolithic Dinex reactor for electrochemically promoted soot combustion.18 20 Reprinted with permission from the Society of Automotive Engineers.

Heat flux is an important variable in fire growth and its determination is necessary for many problems. In general, it depends on scale (laminar or turbulent, beam length ), material (soot, combustion products) and flow features (geometric, natural or forced). We... 

Similarly, the emission of soot from many practical devices, as well as from flames, is determined by the rate of oxidation of these carbonaceous particles as they pass through a flame zone and into the post-combustion gases. As mentioned in the previous chapter, the soot that penetrates the reaction zone of a co-annular diffusion flame normally bums if the temperatures remain above 1300K. This soot combustion process takes place by surface oxidation. 

The simultaneous removal of NOx and soot on Pt-Ba/Al203 NSRC was investigated by Castoldi et al. (2006). They concluded that the presence of soot does not affect the NOx reduction activity of the NSRC, while the soot combustion is enhanced by the presence of N02. This principle has been already utilized by Toyota in the integrated DPNR (diesel particulate and NOx reduction) system (Nakatani et al., 2002). 

Many different filter designs have been the subject of experimental studies on diesel soot combustion. In the early investigations, structured honeycomb filters made from cordierite, such as those applied for the three-way catalyst for the reduction of spark ignition engine gas emissions, were the focus of the experimental studies [29-39]. The experimental results with these filters were not promising, because the cordierite honeycomb filter did not withstand the thermal stress. Temperature peaks of almost 1200 °C were measured, after which the ceramic structure was partly melted or totally destroyed [29, 40],... 

Many working groups have modeled the performance of diesel particulate traps during the past few decades. Concentrated parameter models (CSTR assumption) have been applied for the evaluation of formal kinetic models and model parameters. The formal kinetic parameters lump the heat and mass transfer effects with the reaction kinetics of the complicated reaction network of diesel soot combustion. Those models and model parameters were used for the characterization of the performance of different filter geometries and filter materials, as well as of the performance of a variety of catalytically active coatings and fuel additives [58],... 

The regeneration curves are often derived from CO2 generation data in closed-loop laboratory systems. It is assumed that the formal kinetics of soot combustion may be described by the oxidation of carbon with oxygen. A typical formal kinetic model comprises two parallel reactions of n-th order ... 

DFG MAK 1.5mg/m3 DOT CLASSIFICATION 4.2 Label Spontaneously Combustible SAFETY PROFILE Moderately toxic by intravenous route. Experimental reproductive effects. It can cause a dust irritation, particularly to the eyes and mucous membranes. See also CARBON BLACK, SOOT. Combustible when exposed to heat. Dust is explosive when exposed to heat or flame or oxides, peroxides, oxosalts, halogens, interhalogens, O2, (NH4NO3 + heat), (NH4CIO4 240°), bromates, Ca(OCl)2, chlorates, (CI2 + Cr(OCl)2), CIO, iodates, IO5, Pb(N03)2, HgNOs, HNO3, (oils + air), (K + air), Na2S, Zn(N03)2. Incompatible with air, metals, oxidants, unsaturated oils. 

Moisture can sometimes be observed on a metal spoon held over a flame, but water will not be the only material observed on the spoon. There will also be soot. Combustion is usually not the clean, simple reaction outlined above. Combustion is usually a complicated conglomerate of many reactions in which fragments of hydrocarbons, or soot, are produced. Some of the most interesting behaviors of combustion reactions are a result of incomplete combustion and more complicated reactions. 

Morrison E.D. and Federer W.D., Sol-gel derived diesel soot combustion catalysts on Nextel ceramic fiber filters. Presented at the 5th A.l.Ch.E. Meeting, Miami, FL (1992). 

Neither the fuel additive nor the catalytic soot combustion coating have the ability to substantially reduce the emission of carbon monoxide or aldehydes. To achieve this, a different, precious metal based, catalytic coating can be applied to the filter, or a precious metal based catalyst can be added in line with the filter system. To date, filtering systems have not reached widespread application, mainly because of the high costs associated with their complexity. 

The gas-solid reaction involved in non-catalytic soot combustion is a relatively slow process.76,84 Catalytic assistance (gas-solid-solid process) provides an increase in the rate of soot oxidation, although the process efficiency is mainly determined by the type of contact (tight or loose) established between the soot and the catalyst.76,78,84,85 As mentioned... 

The NOx that is present in diesel exhaust gas, can be an advantage in the oxidation of soot. Several studies report an important increase of catalytic soot combustion by addition of NO to the gas phase [2, 7], Probably an oxidation cycle with NO as an intermediate for oxygen transfer plays an important role. This cycle can be catalysed at one or more stages. The oxidation of NO to NO2 can be catalysed, but also the subsequent oxidation of soot by NO2 can be catalysed. This observation is confirmed by very recent experiments with bi-metallic fuel additives [8]. 

The new broad signal (AH-1670 G) detected at 673 K could arise fi om the agglomeration of isolated copper species in form of aggregates during the soot combustion. Once this combustion is finished (773 K), the broad signal intensity decreases, whereas, an increase of the monomer intensity is observed. It seems that a rearrangement of Cu species in the catalyst occurs during and after the soot combustion. 

Figure 5. Evolution of the EPR spectrum of a soot-lCulCel073 mixture during the soot combustion as a function of temperature.

The presence of sulphur in diesel exhaust gases or particles has to be considered as a poisoning agent for the catalysts used in soot combustion reactions. Copper oxide has been reported to be sensitive towards sulphur dioxide (7) which implies a deactivation of the solid and then eventual modifications of its sinface properties. In this way, lCulCel073 sample was treated in a microflow reactor under SO2 flow (2L.h ) at room temperature for 30 minutes. 

In this work, it is shown that the copper-cerium oxide catalysts are active in the diesel soot combustion reaction. The isolated Cu ions seem to be the most active sites in such catalysts. The activity depends on the copper concentration and the pre-treatment of solids. Among all the tested catalysts, the lCulCe673 oxide, calcined at a relatively low temperature and containing the highest copper concentration, is the most active. 

Diesel particulates are a health hazard and legislation has been established (in the U.S.A.) to reduce diesel particulate emissions. Particulate traps have been developed which can filter (up to 90%) of these particulates [Ref. 1], but require some external means to burn the collected particulates. One way to ignite these particulates effectively at low temperatures is to use traps which initiate soot combustion catalytically. 

In addition to the description of the two-stage method, the activity of selected base metal and noble metal catalysts are compared. The mechanism for soot combustion is also discussed in light of the combustion rates found. 

No catalyst was involved in this study. Hillenbrand and Trayser [Ref. 8] took soot collected from an engine, mixed it with metal salts (Cu, Na, Co, and Mn), and burned it in a laboratory reactor. A substantial lowering of the combustion temperature was observed with the use of such salts. McCabe and Sinkevitch [Ref. 9] also looked at mixing base metal additives either with the soot or the fuel and then determined the effect on soot combustion temperature. Finally, Goldenberg, et al. [Ref. 10] looked at soot oxidation either alone or on a catalytic material. 

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