STACK DESIGN OVERVIEW

This chapter explores the design of stacks from the point of view of the downwind observer whose task is to determine the connection between stack design, process emissions, meteorology, and, most important, environmental effects. Stacks must be designed to specifications based on meteorological conditions and environmental air quality standards, which may be quite umelated to process requirements 

The principal factors which must be accounted for when designing a stack for air pollution control purposes are the dispersion and transport of the pollutants and the performance criteria against which the stack will be compared. These factors include (1) air quality standards, (2) meteorological conditions, and (3) topographical peculiarities. 

Source operators must, therefore, be certain that they are familiar with the standards applicable to plant operations, for the performance of the source may ultimately be compared against a variety of standards. The rule of thumb in determining which state or federal standard applies when they appear to conflict is that the more stringent standard prevails. 

The first step in designing a stack for air pollution control purposes is to determine exactly what regulatory constraints and requirements exist at the particular site. These constraints and requirements may be so severe that alternative means of air pollution control may have to be sought. In any case, the regulations specify a performance standard to which the stack must be designed, and against which the design can be evaluated. 

Meteorological conditions, as much as any other consideration, determine how a stack should be designed for air pollution control purposes. Operating transport mechanisms are determined by the micro meteorological conditions, and any attempt to predict ground-level pollutant concentrations is dependent on a reasonable estimate of the convective and dispersive potential of the local air. The following are meteorological conditions which need to be determined  

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In real applications, a cell stack is composed of several single cells as mentioned in Section 9.2. The cell size can be designed to achieve the desired power rate, but in practice other factors also need to be taken into consideration, such as thermal stability, mechanical strength, shunt current, dimension of the components and so forth. Figure 9.25 provides an overview of the construction of a cell stack. Generally, the cell stack is constructed in a parallel-feed design, in which the cells are connected electrically in a series and the electrol5des are pumped into the cells in parallel. 

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