Stack gases, available energy

The available energy flou through five major sections of sulphuric acid plant is given in figure 2. The major inputs to this system are sulphur and pouer, with demineralised (DM) water uet air, process water and cooling water from environment. The useful outputs from the system are sulphuric acid and steam. Losses to environment include heat losses from various equipments blowdown water steam from deaerator vent warm water and stack gas. 

Adaptability. In the future the market for low sulfur fuel oil may become less attractive for several reasons. Among these are increasing use of nuclear energy, installation of stack gas-desulfurization processes, and increased availability of low sulfur fuels. Should this occur it would be desirable to put to alternative use any facility installed today to desulfurize fuel oil. At such a time, the market could revert to the traditional U.S. pattern in which high sulfur residual oil is a low value material, and there would be a consequent economic incentive to convert it to lighter products. 

Prepare a graph in which the vertical axis shows the fraction of the gross energy input from the fuel in a combustion process that is available for transfer to the process as a fraction of the stack gas temperature in F on the horizontal axis. Use as a third parameter lines of percent excess air that are used in the combustion. The graph you prepare can be used to answer such questions as ... 

Using formulas presented in (6), the total available energy in the stack gases may be calculated as the sum of three contributions, which for convenience (but without attaching strict physical significance) can be called thermal, pressure, and chemical. The available energy contributions in the stack gas can be determined as follows ... 

U ecently, interest in sulfur utilization in asphalt paving materials has been rekindled. One of the foremost reasons for this is the potential availability of surplus sulfur recovered from secondary sources in connection with meeting environmental pollution standards (I). These sources include sulfur recovered from sour gas, from refining of petroleum, and from smelter and powerplant stack gases. Another potential saving of energy and petroleum is possible by replacing part of the asphalt binder with sulfur (2). 

In the absence of complicating factors such as capillary condensation and competitive adsorption, the process of physical adsorption has no activation energy that is, it is diffusion-controlled and occurs essentially as rapidly as vapor molecules can arrive at the surface. The process will be reversible and equilibrium will be attained rapidly. Because the forces involved are the same as those involved in condensation, physical adsorption will generally be a multilayer process—that is, the amount of vapor that can be adsorbed onto a surface will not be limited simply by the available solid surface area, but molecules can stack up to a thickness of several molecules in a pseudoliquid assembly (Fig. 9.3). If the vapor pressure of the gas reaches saturation level, in fact, the condensation and adsorption processes overlap and become indistinguishable. The fact that physical adsorption can be a multilayer process is very important to the mathematical modeling and analysis of the process, as will be seen below. 

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