Sour water strippers design

For most sour water stripper design work, a computer is used to perform the calculations. Several of the proposed sour-water modules were incorporated into a tower program and a series of designs on a typical sour-water stripper have been undertaken. 

N. P. Lieberman, "Sour Water Strippers Design and Operation," Petroleum Technical Quarterly (PTQ), Q2,2013. 

Figure 47.1 Conventional sour water stripper design used in newer units.

The van Krevelen et al. (1949) study is considered to be a pioneering effort in Ibe correlation of vapor-liquid equilibrium data for systems of tbis type. It has saved as the basis for several sour water stripper design procedures, including the widely used approach described by Beychok (1967) and Wild s calculator program for sour water stiippa design (1979). 

Table 4-10 Sour Water Stripper Design Calculation Input Data and Results ...

As an introduction to the technical aspects of the conference, the results of some studies conducted by the writer on two relevant subjects are presented below. The first commentary is concerned with the design of sour-water strippers and the effects of thermodynamic data on these designs the second commentary is concerned with the calculation of enthalpies of steam-containing mixtures, essential to the design of coal processing and related plants. 

Miles, D. H. and Wilson, G. M. "Vapor-Liquid Equilibrium Data for Design of Sour Water Strippers", Annual Report to the American Petroleum Institute for 1974, October 1975 (Data in this report are also summarized in reference 2). 

Sour water strippers are designed primarily for the removal of sulfides and can be expected to achieve 85-99% removal. If acid is not required to enhance sulfide stripping, ammonia will also be stripped, the percentage varying widely with stripping pH and temperature. Depending on pH, temperature, and contaminant partial pressure, phenols and cyanides can also be stripped with removal as high as 30%. 

Normal vertical knockout drums are designed for a K value of about 0.20 to 0.25. If we are installing a KO drum ahead of a reciprocating compressor—and they really hate liquids in their feed—a K value of 0.14 might be selected. If we really do not care very much about entrainment, a K value of 0.4 might be selected. An example of this would be venting waste gas to the flare from a sour-water stripper reflux drum. 

Until recently the ability to predict the vapor-liquid equilibrium of electrolyte systems was limited and only empirical or approximate methods using experimental data, such as that by Van Krevelen (7) for the ammonia-hydrogen sulfide-water system, were used to design sour water strippers. Recently several advances in the prediction and correlation of thermodynamic properties of electrolyte systems have been published by Pitzer (5), Meissner (4), and Bromley ). Edwards, Newman, and Prausnitz (2) established a similar framework for weak electrolyte systems. 

Watkins, R.N. Sizing Separators and Accumulators. Hydrocarbon Processing, November 1967, p. 253. Walker, G.J. Design Sour Water Strippers Quickly. Hydrocarbon Processing, June 1969, p. 121. 

Solvent or stripped liquid concentration > design boilup rate or steam stripping rate too low/feed concentration > expected/feed contamination for sour water stripper acid in feed may be chemically bonded with NH3 and prevent adequate stripping of NH3/[foaming] /leak in preheater exchanger/[column malfunction]. ... 

But is this really true For example, I discussed the design of an existing sour water stripper with BP engineers and operators. As this was a water stripper, the relief valve had not been connected to the flare. 

There are three ways to design refinery sour water strippers ... 

The two sour water strippers that 1 was troubleshooting in India both conformed to the bad method of process design. 

The design shown in Fig. 47.2 was common in my youth (i.e., the 1960s). However, it also suffers from the same heat balance drawbacks and needless complications that I discussed for Fig 47.1. That is, a lot of equipment is added to generate reflux. This is very wasteful, as there is no fractionation required between the stripper feed and the overhead product. All we are trying to do is strip out the NH and HjS. That s why it s called a sour water STRIPPER ... 

In 1969, while working for the Amoco International Oil Company in the United Kingdom, I designed a sour water stripper that eliminated the unnecessary features of the unit shown in Fig. 47.2, which worked just fine. 

Of course, no one could take into account such factors. They are unknown. But what is known is the performance of existing sour water strippers in pretty much identical services. There are decades worth of operating data available for sour water strippers. I helped design a sour water stripper in 1965 (with dumped ceramic packing, which did not work) for American Oil. It s far safer to design a new sour water stripper based on a prototype than on a purely theoretical basis. 

Special techniques have to be used for processing gas streams containing appreciable amounts of ammonia such as effluents from refinery sour water strippers. The ammonia must be destroyed in the reaction furnace to avoid deposition of ammonium salts on the cataly.st beds. Two methods are available to successfully accomplish this. The first method involves a split-flow reaction furnace design the second requires a high-intensity reaction furnace burner. It is essential that the ammonia be almost completely destroyed because ammonia concentrations as low as SOO to 1,000 ppmv can cause plugging problems (Anon., 1973). 

In most similar activities in petroleum refineries, the vapors from stripping "sour water" are processed in a Claus plant. With care in design and operation of the stripper, the vapors typically consist of equal volumes of H2S, NH3 and H2O. Such a mixture can support high-temperature reducing flame in which NH3 is destroyed. 

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