Combustion fuel modification

Tables 5.29 and 5.30 show an example of the effects of hydrotreated diesel fuels on a diesel passenger car already having a low level of pollution owing to technical modifications such as sophisticated injection and optimized combustion. In the standard European driving cycle (ECE + EUDC), between...

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

The WP L cyclone boiler will bum I DE continuously with coal, as about 5% of its fuel mix, with htfle or no modification. By contrast, pulverized-coal boilers, which account for about 80% of the coal-fired capacity in the United States, probably caimot bum tire chips without significant modifications. In these boilers, which bum very fine coal particles in suspension, the heavy chips will fall from the area where best combustion occurs. 

These ideas form the basis of most approaches to NO control with N-containing fuels. In principal, they are readily appHcable to the modification of certain combustors in which the desired divisions in the combustion process exist for other reasons. Although such improvements have been demonstrated, it is difficult in practice to make the required revisions in the air and fuel distribution without adverse effects on other emissions or on performance. It has also been shown that when steam is used to reduce thermal NO production, the formation of NO from fuel N is enhanced, or the reduction is less than otherwise expected. 

TTte most cost-effective methods of reducing emissions of NO are the use of low-NO burners and the use of low nitrogen fuels such as natural gas. Natural gas has the added advantage of emitting almost no particulate matter or sulfur dioxide when used as fuel. Other cost-effective approaches to emissions control include combustion modifications. These can reduce NO emissions by up to 50% at reasonable cost. Flue gas treatment systems can achieve greater emissions reductions, but at a much higher cost. 

Plants (B) with modification of the fuel in combustion-turbine (CRGT) cycles... 

These cycles involve modification of the combustion process, and employ thermo-chemical recuperation (TCR) to produce a fuel of higher hydrogen content. Three simple CRGTs are ... 

Six cycles with oxidant modification are listed as D1 the simple PO open CBT cycle—involving staged combustion of the fuel ... 

We consider next the cycles B of Table 8.IB and the associated Figs. 8.9-8.12 these cycles involve modification of the fuel used in the combustion process by TCR. There are two basic types of chemically recuperated gas turbine (CRGT) cycle ... 

A second type of CRGT plant involving modification of the fuel before combustion (Cycle B3) is shown in Fig. 8.14. Now some part of the exhaust from the turbine (which contains water vapour) is recirculated to the reformer where the fuel is modified. Thus this FG/TCR cycle has an element of the semi-closed cycle plus modification of the combustion process. The chemical process involved in this cycle has been described in Section 8.5.4, but there is now no simple comparison that can be made between the FG/ TCR cycle and the basic STIG cycle, as de.scribed in Section 8.6.2.1. 

In particular, the cycles involving fuel or oxidant modification do not look sufficiently attractive for their development to be undertaken, with the possible exception of the multiple PO combustion plant proposed by Harvey et al. [14]. The Matiant plant has the advantage of relatively simple CO2 removal and high efficiency and may prove to be attractive, but it again looks complex and expensive. 

Because NO, formation is a function of the temperature, fuel-air mixture, and fluid dynamics in the furnace, the goal of a combustion modification is to mix fuel and air more gradually to reduce the flame temperature (lower thermal NO, production), and to stage combustion, initially using a richer fuel-air mixture, thus reducing oxidation of the nitrogen in the fuel. LNBs sewe the role of staged combustion. 

The basic approach taken in the analytical studies of composite-propellant combustion represents a modification of the studies of double-base propellants. For composite propellants, it has been assumed that the solid fuel and solid oxidizer decompose at the solid surface to yield gaseous fuel and oxidizing species. These gaseous species then intermix and react in the gas phase to yield the final products of combustion and to establish the flame temperature. Part of the gas-phase heat release is then transferred back to the solid phase to sustain the decomposition processes. The temperature profile is assumed to be similar to the situation associated with double-base combustion, and, in this sense, combustion is identical in the two different types of propellants. 

On June 19, 1998, U.S. EPA finalized the first phase of the MACT rule. This final rule includes the comparable fuels exclusion and amendments to the permit modification procedures for combustion facilities. 

Basic box models cannot portray effects of nonuniform source patterns. If, for particular chemical species or particular source classes, the dependence of emissions on population density or other identifiable parameters is apparent and significant, we have used modifications to the box modeling approach. As an example, it might be assumed in modeling products of combustion of the lighter fuel oil distillates that source distribution patterns are proportional to population density patterns, because most of such fuel is burned in residential furnaces in cold weather cities. 

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