Plant design contact process

EPAR ATION and purification processes account for a large portion of the design, equipment, and operating costs of a chemical plant. Further, whether or not a mixture forms an azeotrope or two liquid phases may determine the process flowsheet for the separations section of a chemical plant. Most separation processes are contact operations such as distillation, gas absorption, gas stripping, and the like, the design of which requires the use of accurate vapor-liquid equilibrium data and correlating models or, in the absence of experimental data, of accurate predictive methods. Phase behavior, especially vapor-Uquid equilibria, is important in the design, development, and operation of chemical processes. 

Two basically different types of maintenance can be incorporated in the plant design. Direct maintenance involves personal contact service on the equipment in place and requires thorough decontamination, usually a very slow procedure, before entry into the process area. Where possible,... 

The single contact process is generally used with an SO2 content of inlet gases of 6-10% in new plants, the conversion efficiency is about 98.5% as a daily average and can be upgraded to 99.1% by good design and use of specially adapted doped Cs catalyst. 

The gases exiting from the converter passes contain SO3 and SO2—their relative quantities being dependent on the conversion of SO2 that has taken place so far. In the case of a four-pass converter of a sulfuric acid contact process plant, the typical extent of conversion of SO2 are 60-65% in the first pass, 80-85% in second pass, 90-95% in the third pass, and up to 98-99.8% in the last pass, depending on the plant design, catalyst loading, operating conditions, etc. 

Data from the bench scale studies clearly indicated sufficient incentive for further study. Consequently in 1968, Kellogg designed and constructed a pilot plant reactor system which could be used for cracking a variety of feedstock types in the optimum contact time range established by the bench scale work. In this design, the process variables were incorporated in a manner that assured that the data obtained would be comparable with eventual full scale yields and process conditions. The pilot plant will be described in detail in the present paper. 

The main difficulty facing powder process engineers and powder plant designers is the need for information on two powder phenomena firstly, the resistance to product flow generated by particles within the product and secondly, how easily a powdered product can flow over the metal, plastic or ceramic contact area or internal surfaces of plant equipment. 

Sulfuric acid is the strong acid most widely used by the chemical industry, due to its low cost of synthesis. It is manufactured by the contact process, which is covered in detail earlier in this Book. Here we will concentrate only on one stage — which illustrates some of the principles important in plant design — the combination of sulfur dioxide with oxygen to give sulfur trioxide in the presence of a catalyst (usually V2O5) ... 

The most recent UK Royal Ordnance Factory (ROF) continuous process for the manuf of TNT is described by Thomas (Ref 90b). It uses a novel method of achieving continuous counter-current contacting between heavy and light phases in the trinitration section and some of the washing stages . The plant is also designed to operate based on the use of 96—100% sulfuric acid in the trinitration stage instead of the oleum used at Radford TNT Purification. 

All DAFs are similar to each other in terms of theory, principles, design, operation, and secondary flotation performance. The authors select the circular DAF process equipment manufactured by KEC for the purpose of feasibility studies. The users should contact more than one major DAF and DAFF manufacturers for appropriate pilot plant demonstrations and cost comparisons. Rectangular DAF and DAFF clarifiers are as good as circular DAF and DAFF clarifiers. 

In the design of an industrial scale reactor for a new process, or an old one that employs a new catalyst, it is common practice to carry out both bench and pilot plant studies before finalizing the design of the commercial scale reactor. The bench scale studies yield the best information about the intrinsic chemical kinetics and the associated rate expression. However, when taken alone, they force the chemical engineer to rely on standard empirical correlations and prediction methods in order to determine the possible influence of heat and mass transfer processes on the rates that will be observed in industrial scale equipment. The pilot scale studies can provide a test of the applicability of the correlations and an indication of potential limitations that physical processes may place on conversion rates. These pilot plant studies can provide extremely useful information on the temperature distribution in the reactor and on contacting patterns when... 

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