Qichao Yang

Dynamic characteristics of suction valves for reciprocating compressor with stepless capacity control system

The dynamic characteristics of suction valves for reciprocating compressor with a stepless capacity control system are studied in this article. The self-acting valve model that is applicable for stepless capacity control condition is derived. For the suction valve movement controlled by actuator, a simulation of the hydraulic and mechanical system is conducted. An experimental platform is setup, which is used to test the valve dynamic when it is controlled by actuator. The results from the mathematical model show that the valve impact speeds are influenced by the valve lift, Mach number of the flow in the valve clearance and the initial crank rotation angle of the valve closing process. The simulation results agree well with experimental results. The simulated maximum speed is about 0.53 m/s, and the maximum speed tested by experiment is about 0.58 m/s, both of which are much lower than the speed of the automatic valve (3 m/s). In addition, simulation results show that the maximum speed is at constant when the hydraulic piston stroke increases, which is much different from the automatic valve. It becomes apparent from the aforementioned results that with stepless capacity control system the dynamic characteristics of the suction valve are changed. The valve can be limited at a low speed, and the valve impact speeds to seat and stopper decrease significantly, which would be helpful for extending the life of the valve plate.

Experimental investigation of the water–injected process-gas screw compressor

The test rig for water-injected process-gas screw compressor is designed and established. The dry gas seal technology was adopted for the shaft seal of screw compressor and the test rig has the function of regulating and controlling the mass flow of injected water. The performance characteristics of process-gas screw compressor under different working conditions are investigated by experimental research. The effect of rotational speed, the injected water mass flow, and the discharge pressure on the performance of screw compressor including discharge temperature and power consumption were obtained. The experimental results show that the water injection could reduce the discharge temperature of compressor significantly and increase the capacity of screw compressor at the same time. There exists an optimum mass flow of injected water that could effectively reduce the discharge temperature and seal the clearance between the female and male rotor simultaneously. For the tested screw compressor prototype, the proper injected water-to-air mass ratio is about 2–3 L/m3. The additional power consumption caused by the injected water is small compared with the total shaft power. The established compressor test rig and the experimental results are helpful for the development and improvement on the performance of water-injected process-gas screw compressor.

Analysis of performance of two-stage screw compressor under various operating conditions:

The screw compressor has a promising application in the process industry due to its appropriate pressure and flow rate. In this paper, a mathematical model of a two-stage oil-free screw compressor is developed to simulate the working process under various operating conditions. The results show that the interstage pressure of the two-stage oil-free screw compressor is built automatically depending on the equal mass flow rate of each stage. It increases with the suction pressure, discharge pressure, and clearance, but decreases with rotating speed. Although the power consumption of the 2nd stage decreases with the suction pressure, the power consumption of the whole compressor always increases with the suction pressure, discharge pressure, rotating speed, and clearance. The volumetric efficiency increases with the suction pressure and rotating speed, but decreases with the discharge pressure and clearance for each stage. The indicated efficiency increases with the rotating speed but decreases with the clearance. A maximum indicated efficiency is found. The volumetric and indicated efficiency of the 2nd stage is more sensitive to the operating condition than that of the 1st stage.

Numerical analysis of aerodynamic damping for a centrifugal impeller

ABSTRACT In order to realize the numerical analysis of aerodynamic damping for the centrifugal impellers, a numerical code integrating the flow-structure data transfer, grid deformation and flow simulation under the moving grid system is first developed. To decrease the huge consumptions of CPU time and memory space, the compactly supported radial basis function is adopted to carry out the data transfer and grid deformation, and the alternating digital tree technique is utilized to calculate the wall distances. By the test cases of an oscillating cascade and a centrifugal impeller, the correctness of the code for the flow simulations with moving boundaries and the flow fields in centrifugal impellers is validated. Then taking a centrifugal impeller as the research object, the calculations of aerodynamic damping characteristics were carried out. The results show that, the modal aerodynamic damping ratio has no relationship with the vibrating amplitude under small vibrations. For the disk-dominant vibration mode, the modal aerodynamic damping ratio decreases as the operating point shifts toward the stall point. The aerodynamic damping caused by the backward traveling wave vibration is larger than that by the forward traveling wave vibration.

Experimental research on stability enhancement for centrifugal compressors using active control casing treatment system

Centrifugal compressors are widely used in many fields, where they become unstable when operated at the edge of the surge line. This paper presents a method, which is based on the active control casing treatment to enhance the operating stability of the centrifugal compressor. To investigate the effect of the active control casing treatment system on the performance of a centrifugal compressor, a test rig with rotating speed of 15,000 r/min was built up. The experimental results show that the active control casing treatment system can significantly decrease the surge flow rate and extend the envelope of stable operation via injecting gas (so-called the control gas) into the casing of the centrifugal compressor. The tested maximal enhancement ability is 30.55% at the condition of 10,586 r/min when the flow rate of the control gas is 2.5 m3/min. It was found that the enhancement ability increases with the decrease of the rotating speed of the centrifugal compressor. The increment of the control gas flow rate results in a smaller surge flow rate of the centrifugal compressors.

A Stability Enhancement Method for Centrifugal Compressors using Active Control Casing Treatment System

The centrifugal compressors are widely used in many fields. When the centrifugal compressors operate at the edge of the surge line, the compressor will be unstable. In addition, if the centrifugal compressor runs at this situation long time, the damage will be occurred on compressor. There are some kinds of method to improve and enlarge the range of the centrifugal compressors, such as inlet guide vane, and casing treatment. For casing treatment method, some structures have been researched, such as holed recirculation, basic slot casing treatment and groove casing treatment. All these researches are the passive methods. This paper present a new stability enhancement method based Active Control Casing Treatment (ACCT). All parts of this new method are introduced in detail. The control strategy of the system is mentioned in the paper. As a research sample, a centrifugal compressor having this system is researched using CFD method. The study focuses on the effect of the active control system on the impeller flow. The vortex in impeller is changed by the active control system. And this leads to the suppression of the extension of vortex blockage in impeller and to contribute to the enhancement of the compressor operating range.

Simulation on actuator response time of capacity adjustment system in reciprocating compressor

Large scale reciprocating compressor in petrochemical process is usually operated under partial load based on the system condition, and adjusted its capacity by controlling suction valve is an efficient method for energy saving. In this paper, a mathematical model coupled suction valve and actuator is built to describe the dynamic response process of suction valve and actuator and the response time influenced by some parameters are analyzed. The simulation results show that the power consumption has a variation of approximately direct proportion with the mass flow rate. The response time of actuator increases with the diameter of hydraulic cylinder either in opening or closing process. The high pressure oil supply and low pressure oil discharge lead to the faster motion of actuator. The larger opening time and smaller closing time can be obtained by increasing the thickness of reset spring. Optimizing the parameters of actuator is helpful to improve the system performance.