Process evaluation compressors

Part Three includes chapters that provide instruction and examples of the design of heat exchangers, multistage and packed towers, and pumps, compressors, and expanders. In addition, Chapter 16 provides guidelines for selecting processing equipment and equations for estimating the purchase costs of a broad array of equipment items. Furthermore, Section 16.7 shows how to use the Aspen Icarus Process Evaluator (IPE), with the process simulators, to estimate purchase costs and the total permanent investment for a chemical plant. 

For the purpose of illustrating the various steps in the reliability quantification process, a simplified case example has been used in this paper were application of subsea gas compressors are evaluated. This case example has been used throughout this paper to illustrate the process however the example has been modified and simplified to fit the purpose of this high level presentation of the research work which has been conducted when develop this guideline. 

The evaluation showed economic advantages for the compressor process and in consequence design engineering was adjusted accordingly. 

Most other rotor parts in gas turbines are individually forged. This includes compressor wheels, spacers, distance pieces, and stub shafts. All are made from quenched and tempered low-alloy steels (Cr-Mo-V or Ni-Cr-Mo-V) with the material and heat treatment optimized for the specific part. The intent is to achieve the best balance of strength, toughness with ductility, processing and nondestructive evaluation capability, particularly when it is recognized that some... 

A process engineer s task is often to evaluate the performance of a compressor unit based on gas throughputs and terminal pressures. Since compressor stations are complex machines and operations, the analysis required is sophisticated and goes well beyond simple computations on a personal computer, although some preliminary evaluations can certainly be made. In this section we summarize the working expressions for standard compressor operations. Compressor operations can be categorized under three thermodynamic categories ... 

In addition to failure as a result of their utihty supply, items of equipment are subject to individual failure through mechanical malfunction. Such items include pumps, fans, compressors, mixers, instruments and control valves. The process upset resulting from such malfunctions (e.g., loss of a reflux pump) may in turn result in emergency conditions and the potential for overpressure. These contingencies should be examined and evaluated. 

Centrifugal compressors are not items that the process company or its mgineers should attempt to design in great detail. Rather, it is more important that they be in a strong position to (a) specify what is needed for the process, (b) understand the manufacturer s recommendations, and (c) evaluate the recommended design and performance in the process situation. Also see reference 117. 

All operating parameters must be considered to make certain that an acceptable operating compressor and process fit exists. The key parameter must be evaluated as part of an overall operating analysis and considered independently. Peters 2 points out that the API Specification 617, the ASME codes, and other applicable codes may require some modification when applied to side load compressors. 

Davis discusses the evaluation of multistage compressors for conversion to new or different process applications. 

The efficiency factors of gas compressors are based on ideal comparative processes such as the isothermal or isentropic ones, and therefore show considerable differences according to the method used for evaluation. 

The first two effects are calculated directly from the overall process design. The frictional losses are obtained from the compressor power requirements. They amount to a total exergy destruction of 10 MW. Heat exchanger losses due to heat transfer in Units 1-6 (excluding the reformer) can be evaluated from the exergy exchange calculations they amount to 49 MW for a 20K temperature difference. 

We begin with a fairly simple process consisting of a reactor, condenser, separator, compressor, and stripper with a gas recycle stream (Fig. 8.1). This process was developed and published by Downs and Vogel (1993) as an industrial plantwide control test problem. A FORTRAN program is available from them that does the derivative evaluations for the process. The user must write a main program that initializes the simulation, does the controller calculations, performs the numerical integration, and plots the results. 

The process inefficiencies that are responsible for the increased work- expenditure can be identified by evaluating the entropy production of each element of the process, namely, by evaluating the irreversibilities. The largest portions of this entropy production, shown in Figure 1, are the main exchanger, the nitrogen compressors, the nitrogen coolers, and the tower. 

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