Stripper sizing

For most field gas units it is not necessary to specify a stripper size. Vendors have standard design amine circulation packages for a given amine circulation rate, acid-gas loading, and reboiler. These concepts can be used in a preliminary check of the vendor s design. However, lor detailed design and specification of large units, a process simulation computer model should be used. 

In this condenser, part of the stripper off-gases are condensed (the heat of condensation is used to generate low pressure steam). The carbamate formed and noncondensed NH and CO2 are put into the reactor bottom and conversion of the carbamate into urea takes place. The reactor is sized to allow enough residence time for the reaction to approach equiUbrium. The heat required for the urea reaction and for heating the solution is suppHed by additional condensation of NH and CO2. The reactor which is lined with 316 L stainless steel, contains sieve trays to provide good contact between the gas and Hquid phases and to prevent back-mixing. The stripper tubes are 25-22-2 stainless steel. Some strippers are still in service after almost 30 years of operation. 

Use of HTU and K a Data In estimating the size of a commercial gas absorber or hquid stripper it is desirable to have data on the... 

The reflux accumulator is a separator used to separate the acid gases from the condensed water. The water is accumulated and pumped back (n the top of the stripper as reflux. With the vapor and liquid rates know n. the accumulator can be sized using the procedures in Volume 1 for iwo phase separator.s. 

Catalyst circulation coke is a hydrogen-rich coke from the reactor-stripper. Efficiency of catalyst stripping and catalyst pore size distribution affect the amount of hydrocarbons carried over into the regenerator. 

The gas pressure drop is a function of the gas and liquid flow rates and the size and type of packing. It relates to the overall cost of the air stripper and to its performance. The gas pressure drop through a stripping unit can be determined from the pressure drop curve. 

Perhaps the additional capacity might not be needed. If it is not needed then the size of the reactors, evaporator and stripper can be reduced. Keeping the original process capacity with parallel operation of the reactors would mean a tradeoff between the increased capital cost of two (smaller) reactors versus reduced capital cost of the evaporator and stripper. An economic comparison would be required to judge whether this would be beneficial. 

Occluded coke is a function of the operating conditions of the FCCU stripper, of catalyst pore volume and pore size distribution. This coke that has the higher content of hydrogen is the lowest refractory between the different kinds of coke produced in the FCC process. Althongh in this study it was not directly evalnated, it may be associated with the peak A at the lowest temperature ( 500°C-550°C). So once the... 

Use of HTU and K a Data In estimating the size of a commercial gas absorber or liquid stripper it is desirable to have data on the overall mass-transfer coefficients (or heights of transfer units) for the system of interest, and at the desired conditions of temperature, pressure, solute concentration, and fluid velocities. Such data should best be obtained in an apparatus of pilot-plant or semiworks size to avoid the abnormalities of scale-up. Within the packing category, there are both random and ordered (structured) packing elements. Physical characteristics of these devices will be described later. 

Contactors have a number of advantages compared to simple liquid/gas absorb-er/strippers or liquid/liquid extractors. Perhaps the most important advantage is high surface area per volume. The contact area of membrane contactors compared to traditional contactor columns is shown in Table 13.2. Membrane contactors provide 10-fold higher contactor areas than equivalent-sized towers. This makes membrane... 

In Europe, the TNO [27] and Kvaerner [19] are both developing contactors to remove water and carbon dioxide from natural gas. Glycol or amines are used as the absorbent fluid. The goal is to reduce the size and weight of the unit to allow use on offshore platforms, so oftentimes only the absorber, the largest piece of equipment in a traditional absorber/stripper, is replaced with a membrane contactor. Kvaerner has taken this technology to the demonstration phase and commercial units are expected to be introduced soon. 

The most frequently used component separators are absorbers, strippers, fractona-tors, and extractors. According to Humphrey [74], fractionators are used in 90 to 95% of the separations in the US. The principles of conponent separators are covered extensively in several texts such as Treybal [29], King [30] and Henley and Seader [31, 65]. We will only consider short cut sizing methods. These methods are useful for preliminary design estimates and for first guesses for more exact calculations, requiring iterative calculation procedures. 

Assuming dilute solutions, Table 6.21 lists the equations for sizing absorbers and strippers in terms of a key component and Table 6.22 outlines the calculation procedure. In numbering the relationships in Table 6.21, A, S, P, and T means absorption, stripping, packed columns and tray columns, respectively. Processing dilute solutions implies that heat effects will be small, and therefore, the separation is essentially isothermal. If the column is both isothermal and isobaric, the equilibrium value will be constant. Also, dilute solution means that the gas and liquid flow rates will essentially be constant. In absorption, the gas flow rate is fixed and the liquid flow rate must be estimated, whereas in stripping the liquid flow rate is fixed and the gas flow rate must be estimated. 

The first step in the sizing procedure is to determine the minimiun liquid flow rate for an absorber or the minimum gas flow rate for a stripper. For gas absorption, die entering liquid and gas concentrations are known, which is shown in Figure 6.16. The subscript 1 refers to the top of the separator, and the subscript 2 to the bottom of the separator, as shown in Figure 6.16. The fractional absorption and therefore the exit gas concentration is also known, fixing point 1 - at the top of the column. The exit liquid concentration is not known. Therefore, point 2 - at the bottom of the column - is not fixed. The minimmn liquid flow rate occurs... 

Table 6.21 SUMMARY OF EQUATIONS FOR SIZING ISOTHERMAL ABSORBERS AND STRIPPERS - COLUMN HEIGHT...

TABLE 6.22 Calculation Procedure for Sizing Isothermal Absorbers or Strippers-Column Height ... 

Table 6.23 Summary of Equations for Sizing Absorbers, Strippers, or Fractionators - Column Diameter...

Occasionally separating multicomponent solutions requires designing a sequence of fractionators. Henley and Seader [31] discuss some aspects of this problem. Once the sequence has been established, then estimate the size of each fractionator. Table 6.27 lists the equations for a short cut method for calculating the height and diameter of fractionators and Table 6.28 outlines the calculation procedure. Like rotary drum filtration, absorbers, and strippers, discussed earlier, the final design may require testing to support the calculations. 

Membrane contactors can be applied also to the sparkling water production. In beverage industry, the sparkling water is usually produced in two towers of large size (stripper and absorber) on the contrary, membrane contactors are able to carry out the process in the same unit with a substantial reduction in size. 

The function of the packing material in an air stripper is to provide a large wetted surface area for mass transfer of contaminants to the gas phase, or ambient air. Several shapes and sizes are available, such as rings, saddles, and spheres. The packing material is commonly manufactured from polypropylene, PVC, or ceramic. 

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