Process equipment fundamentals

I couldn t help but notice that the blue fish was permanently dead. Most sadly, it was floating on its side. The cause of death was clear. The water circulation through the aquarium filter had slowed to a thin trickle. Both the red and silvery striped fish also appeared ill. I cleaned the filter, but the water flow failed to increase. 

As you can see from Fig. 1.1, the filter is elevated above the water level in the fish tank. Water is lifted up, out of the tank, and into the elevated filter. Water flowing up through the riser tube is filtered, and then the clean water flows back into the aquarium. 

I tried increasing the air flow just a bit to the riser tube. The water began to gurgle and gush happily through the filter. Encouraged, 1 increased the air flow a little more, and the gush diminished back to a sad trickle. 

It was too bad about the blue fish. It was too bad that I didn t understand about the air, or the filter, or the water flow. It was really bad because I have a master s degree in chemical engineering. It was bad because I was the technical manager of the process division of the Good Hope Refinery in Louisiana. Mostly, it was bad because I had been designing process equipment for 16 years, and didn t understand how water circulated through my son s aquarium. 

But then I realized that I had seen all this before. Six years before, in 1974, 1 had been the operating superintendent of a sulfuric acid regeneration plant in Texas City. Acid was lifted out of our mix tank by injecting nitrogen into the bottom of a 2-inch riser pipe. The shift operators called it an air lift pump.  

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Incidentally, if a bird builds its nest on top of one our roof toilet vents, we find the toilet will no longer flush properly. The experienced plumber states that the toilet won t flush because it is suffering from vapor lock and this is true. A working knowledge of process equipment fundamentals often comes in quite handy around the home. 

The next part of the procedure involves risk assessment. This includes a deterrnination of the accident probabiUty and the consequence of the accident and is done for each of the scenarios identified in the previous step. The probabiUty is deterrnined using a number of statistical models generally used to represent failures. The consequence is deterrnined using mostiy fundamentally based models, called source models, to describe how material is ejected from process equipment. These source models are coupled with a suitable dispersion model and/or an explosion model to estimate the area affected and predict the damage. The consequence is thus determined. 

Table 3 lists typical failure rate data for a variety of types of process equipment. Large variations between these numbers and specific equipment can be expected. However, this table demonstrates a very fundamental principle the more compHcated the device, the higher the failure rate. Thus switches and thermocouples have low failure rates gas—Hquid chromatographs have high failure rates. 

The Separation Stage. A fundamental quantity, a, exists in all stochastic separation processes, and is an index of the steady-state separation that can be attained in an element of the process equipment. The numerical value of a is developed for each process under consideration in the subsequent sections. The separation stage, which in a continuous separation process is called the transfer unit or equivalent theoretical plate, may be considered as a device separating a feed stream, or streams, into two product streams, often called heads and tails, or product and waste, such that the concentrations of the components in the two effluent streams are related by the quantity, d. For the case of the separation of a binary mixture this relationship is... 

The mechanisms of comminution are complex involving breakage along particle cracks and fissures etc., and depend on the hardness and structure of the feed particle. The Institution of Chemical Engineers (London) produced a major report on comminution (IChem, 1975), which was followed by reviews by Bemrose and Bridgwater (1987), Prior etal. (1990) and Jones (1997). These reviews included sections on both the fundamental and practical aspects of comminution and attrition in process equipment, test methods and an extensive list of references. 

The electrostatic precipitator in Example 2.2 is typical of industrial processes the operation of most process equipment is so complicated that application of fundamental physical laws may not produce a suitable model. For example, thermodynamic or chemical kinetics data may be required in such a model but may not be available. On the other hand, although the development of black box models may require less effort and the resulting models may be simpler in form, empirical models are usually only relevant for restricted ranges of operation and scale-up. Thus, a model such as ESP model 1 might need to be completely reformulated for a different size range of particulate matter or for a different type of coal. You might have to use a series of black box models to achieve suitable accuracy for different operating conditions. 

There are numerous materials, both metallic and ceramic, that are produced via CVD processes, including some exciting new applications such as CVD diamond, but they all involve deposition on some substrate, making them fundamentally composite materials. There are equally numerous modifications to the basic CVD processes, leading to such exotic-sounding processes as vapor-phase epitaxy (VPE), atomic-layer epitaxy (ALE), chemical-beam epitaxy (CBE), plasma-enhanced CVD (PECVD), laser-assisted CVD (LACVD), and metal-organic compound CVD (MOCVD). We will discuss the specifics of CVD processing equipment and more CVD materials in Chapter 7. 

Chemical process equipment is basically the same now, as it was in the 1930 s, or at least the 1950 s. The trays, K.O. drums, compressors, heaters, steam systems have not - and probably will not change. The fundamental nature of process equipment operation has been well established for a very long time. Modern methods of computer control, and process design have not, and cannot, change the basic performance of the bulk of process equipment. These tools just seem to have made learning about the working of the equipment more difficult. 

Other than saving procurement time for long-lead-time items, it is not often cost-effective to purchase used equipment. The fundamental reason is that the major part of the cost of a project is the installation cost. Also, one is never sure about the actual condition of used process equipment. 

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