Design of a Moderate Speed-High Capacity Centrifugal Compressor With Application to PSA and VPSA Air Separation Processes

Author(s):  
Ahmed Abdelwahab

The performance of the PSA (Pressure Swing Adsorption) or VPSA (Vacuum Pressure Swing Adsorption) cycle in an oxygen air separation process is significantly dependent upon the working capacity and working selectivity afforded by the adsorbent. These parameters in turn are dependent on the adsorption pressures employed in the VPSA cycle. Despite the increasing demand for increased capacity and pressure in VPSA air separation plants, they have conventionally used rotary-type positive displacement blowers as the process machinery. These blowers, while most adapted to the oscillating nature of the pressure swing cycles, have increasing high cost per capacity at higher capacities and become very inefficient as the cycle pressures are increased. A new low cost and more efficient process machinery solution is introduced through the use of a moderate speed direct coupled integrated feed and vacuum centrifugal compressor with inlet guide vanes to achieve high efficiencies during the varying operating conditions of the VPSA cycle. In this paper the fundamentals of a VPSA cycle as it applies to a centrifugal compressor operation is presented. A model of the design and predicted performance of a feed and vacuum VPSA centrifugal compressor is presented. A discussion of the proposed design in comparison to a conventional blower is presented. The model and predictions indeed show the superiority of the new design concept to the conventional process machinery equipment in terms of power savings and capacity increase. This new design however requires a feedback control system for the inlet guide vanes.

Author(s):  
Ronald P. Porter

A high efficiency, low cost gas compressor is under development. Design has been completed and fabrication is in process. The manufacturer’s background in centrifugal compressor design and current methodology is discussed along with product definition. Assembly and test of the first unit is planned for summer 1996. The design features a single-stage overhung centrifugal compressor, variable inlet guide vanes, and dry gas seals.


Author(s):  
Yubao Tian ◽  
Yonghong Tang ◽  
Zhiheng Wang ◽  
Guang Xi

A shrouded centrifugal compressor model stage used for 120,000 m3/h oxygen production air separation unit was designed and tested at several IGV stagger angles from −15° to +60° and machine Mach number from 0.97 to 0.5. Present research works aimed to assess the influence of the adjustable IGVs and the IGV modeling on the shrouded centrifugal compressor performance characteristics and inlet flow field and to explore the effect factors of the CFD prediction accuracy and compressor stability at different IGV stagger angles. The measured results show that the model stage with 0° IGV stagger angle yields almost the same stagnation pressure ratio performance as the stage-only model but at a lower peak isentropic efficiency. With an appropriate IGV stagger angle setting ranging from −15° to +30°, the compressor stability could be efficiently enhanced. Numerical studies indicate that a large IGV hub gap may lead to a significant lag effect on the flow angle generated by the inlet guide vanes when increasing the IGV stagger angle.


Author(s):  
Hiroshi Uchida ◽  
Mutsuo Shiraki ◽  
Akinobu Bessho ◽  
Yoichi Yagi

In Japan, a program of research and development of a 100 kW automotive ceramic gas turbine (CGT) has been carried out in the Petroleum Energy Center with active cooperation of petroleum, automobile and ceramics industries as well as other related industries. As a part of this research and development program, we have studied and developed a centrifugal compressor with variable inlet guide vanes for CGT engines. There has been a strong demand for a compressor with a high efficiency and a wide flow range. The compressor performance goals are an adiabatic efficiency of 81% and a surge margin of 8% under maximum power operating conditions. This paper describes the methods for designing impellers, diffusers and variable inlet guide vanes, and presents the results of compressor performance tests. The test results reveal that the surge margin and compressor efficiency at partial load are improved by using inlet guide vanes.


Author(s):  
Armin Zemp ◽  
Reza S. Abhari ◽  
Beat Ribi

Forming the first part of a two-part paper, the quantification of the resonant response levels and the damping quantities for a centrifugal compressor impeller with variable inlet guide vanes under engine representative operating conditions is detailed in this work. The motivation for the investigation is the lack of experimental data that are needed to improve and validate computational tools used during the design phase. Measurements were performed during resonant blade vibrations with the inlet pressure, the inlet guide vane angle and the operating point as the varying parameters. The flow non-uniformity introduced into the inlet flow field was measured with an aerodynamic probe. These measurements showed an increase in flow distortion for increased guide vane angles. The response amplitudes were acquired with dynamic strain gauges. A curve-fit method was applied to estimate the critical damping ratios. The results showed a linear correlation of the aerodynamic damping with the inlet pressure. The mode dependent material damping was therefore derived using a linear extrapolation to vacuum conditions of the inlet pressure dependent overall damping. The resonant blade dynamics could be captured with a single degree of freedom model. The aerodynamic damping and the maximum strain response were found to significantly depend on the inlet guide vane angle setting and on the throttle setting of the compressor.


Adsorption ◽  
2020 ◽  
Author(s):  
Ester Rossi ◽  
Giuseppe Storti ◽  
Renato Rota

Abstract Among the adsorption-based separation processes for gaseous mixtures, those exploiting pressure variations, so-called Pressure Swing Adsorption (PSA) processes, are the most popular. In this work, we focus on the specific PSA configuration known as Dual Reflux-Pressure Swing Adsorption (DR-PSA) given its ability to achieve sharp separations. In the case of binary mixtures, an analytical approach based on Equilibrium Theory has been proposed to identify the operating conditions for complete separation under the assumption of linear isotherms. This same approach is not available when the separation is not complete. Accordingly, in this work we study the features of non-complete separations by solving numerically a general DR-PSA model with parameter values suitable to approach equilibrium conditions (no mass transport resistances, no axial mixing, isothermal conditions and no pressure drop), thus reproducing the analytical solution when complete separations are examined. Even for non-complete separations, triangularly shaped regions at constant purity can be identified on a plane whose axes correspond to suitable design parameters. Moreover, we found a general indication on how to select the lateral feed injection position to limit the loss in product purities when complete separation is not established, whatever is the composition of the feeding mixture. Finally, a sensitivity analysis with respect to pressure ratio, light reflux ratio and heavy product flowrate is proposed in order to assess how to recover product purities according to the specific degrees of freedom of a DR-PSA apparatus.


2020 ◽  
Vol 12 (11) ◽  
pp. 168781402097490
Author(s):  
Fenghui Han ◽  
Zhe Wang ◽  
Yijun Mao ◽  
Jiajian Tan ◽  
Wenhua Li

Inlet chambers (IC) are the typical upstream component of centrifugal compressors, and inlet guide vanes in the IC have a great impact on its internal flow and aerodynamic loss, which will significantly influence the performance of the downstream compressor stages. In this paper, an experimental study was carried out on the flow characteristics inside a radial IC of an industrial centrifugal compressor, including five testing sections and 968 measuring points for two schemes with and without guide vanes. Detailed distributions of flow parameters on each section were obtained as well as the overall performance of the radial IC, and the causes of the flow loss inside the IC and the non-uniformity of flow parameters at the outlet section were investigated. Besides, numerical simulations were performed to further analyze the flow characteristics inside the radial IC. The experimental and numerical results indicate that, in the scheme without guide vanes, sudden expansions in the spiral channel and flow separations in the annular convergence channel are the major sources of flow loss and distortions generated in the radial IC; while in the scheme with guide vanes, the flow impacts, separations and wakes caused by the inappropriate design of guide vanes are the main reasons for the flow loss of the IC itself and the uneven flow distributions at the IC outlet.


Author(s):  
Seyyed M. Ghoreishi ◽  
Z. Hoseini Dastgerdi ◽  
Ali A Dadkhah

A pressure swing adsorption air separation process in a commercial aircraft using 13X zeolite with a more complex cycle than the classic Skarstrom was simulated via a predictive dynamic model to evaluate and optimize oxygen generation system. The coupled mass, energy, and momentum differential equations were discretized using the implicit central finite-difference technique and the obtained equations were solved by Newton-Raphson method. The validated model in conjunction with an optimization procedure (Successive Quadratic Programming) was utilized to investigate the oxygen separation efficiency as a function of β (ratio between the bed time constant and the particle diffusion time constant), Cfp (purge orifice coefficient), θcycle (cycle time), Cff (feed valve), Cfe (exhaust valve) and pH* (high pressure operation). A set of optimum values (β=150, Cfp=0.7, θcycle=1.5, Cff=31, Cfe=52 and pH*=3.8) was obtained and recommended to achieve maximum recovery (0.26) at 98% purity.


Author(s):  
Levi André B. Vigdal ◽  
Lars E. Bakken

The introduction of variable inlet guide vanes (VIGVs) upfront of a compressor stage affects performance and permits tuning for off-design conditions. This is of great interest for emerging technology related to subsea compression. Unprocessed gas from the wellhead will contain liquid condensate, which affects the operational condition of the compressor. To investigate the effect of guide vanes on volume flow and pressure ratio in a wet gas compressor, VIGVs are implemented upfront of a centrifugal compressor stage to control the inlet flow direction. The guide vane geometry and test rig setup have previous been presented. This paper documents how changing the VIGV setting affects compressor performance under dry and wet operating conditions. The reduced performance effect and operating range at increased liquid content are of specific interest. Also documented is the change in the VIGV effect relative to the setting angle.


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