Analysis on real effect of supercritical carbon dioxide dry gas seal at high speed

doi:10.11949/j.issn.0438-1157.20190183

Abstract

Abstract:

The special properties of the supercritical carbon dioxide medium make the various practical effects in the high-speed supercritical carbon dioxide dry gas seal prominent, and ignoring these actual effects may bring large errors to the dry gas seal steady state performance solution. Taking spiral groove dry gas seal as the research object, the governing equation of film pressure considering inertia term and real flow state was derived. The film pressure distribution was obtained using finite difference method. The film stiffness and leakage rate of high-speed supercritical CO₂ dry gas seal based on the real modified model and classical simplified model were compared and analyzed. The effects of real gas effect, inertia effect and turbulent effect on film stiffness and leakage rate under different pressure and velocity conditions were analyzed. The independent and interactive effects of three effects on steady-state performance were revealed. Under the given conditions, the results show that the leakage rate calculated by the classical simplified model is smaller at low speed, and both film stiffness and leakage rate calculated by the classical simplified model are smaller at high speed. Under super-high speed condition, real gas effect significantly increases film stiffness and leakage rate of the gas film, while turbulent effect increases the stiffness of the gas film and reduces the leakage rate. Inertia effect slightly influences film stiffness and leakage rate. There is a strong interaction between real gas effect and turbulent effect on steady performance.

Key words: supercritical carbon dioxide, dry gas seal, real effect, interaction, turbulent effect

摘要：

超临界二氧化碳介质物性的特殊性使得高速超临界二氧化碳干气密封中的多种实际效应突显，忽略这些实际效应可能会给干气密封稳态性能求解带来较大误差。以螺旋槽干气密封为研究对象，推导了考虑惯性项和实际流态的膜压控制方程，采用有限差分法求得膜压分布，对比分析了基于实际修正模型与经典简化模型的高速超临界二氧化碳干气密封气膜刚度和泄漏率，分析了不同介质压力和速度条件下实际气体效应、惯性效应和湍流效应对气膜刚度和泄漏率的影响规律，揭示了三种效应对稳态性能的单独影响及交互影响机理。结果表明：在本文给定条件下，经典简化模型在速度较小时求得的泄漏率偏小，而在超高速时求得的气膜刚度和泄漏率都偏小；在超高速条件下，实际气体效应使气膜刚度和泄漏率都显著增大，湍流效应使气膜刚度增大，而使泄漏率减小，惯性效应对气膜刚度和泄漏率影响很弱；实际气体效应与湍流效应对稳态性能影响之间具有很强的交互影响关系。

关键词: 超临界二氧化碳, 干气密封, 实际效应, 交互影响, 湍流效应

CLC Number:

TH 117.2

Wei SHEN, Xudong PENG, Jinbo JIANG, Jiyun LI. Analysis on real effect of supercritical carbon dioxide dry gas seal at high speed[J]. CIESC Journal, 2019, 70(7): 2645-2659.

沈伟, 彭旭东, 江锦波, 李纪云. 高速超临界二氧化碳干气密封实际效应影响分析[J]. 化工学报, 2019, 70(7): 2645-2659.

Figures/Tables 18

Fig.1 Schematic drawing of spiral groove dry gas seal

Fig.2 Comparison between typical simplified model and real modified model

Fig.3 Program flow chart of numerical calculation

Table 1 Geometric parameter and operating condition parameter

参数	数值	参数	数值
内径 r_i/mm	58.42	螺旋角β/(°)	15
外径 r_o/mm	77.78	槽深 h_g/μm	5
内径压力 p_i/MPa	0.1	槽长比 α	0.5
外径压力 p_o/MPa	8/14	槽宽比 δ	0.5
介质温度 T/K	350	槽数 N_g	12
非槽区膜厚 h₀/μm	3

Fig.4 Verification of calculated program with consideration of turbulent and inertia

Table 2 Examples of supercritical CO2 dry gas seal application conditions

生产单位和应用场地	介质压力 p_o/MPa	密封环线速度 v/(m·s^-1)	介质温度 T/K
Man Turbo, Beula, ND	11.03	146.93	449.97
Production Pump, Texas	13.79	19.41	377.69
Flowserve, NA	15.17	17.76	324.87
MHI, Japan	21.50	65.25	477.77
American Pump, Dallas	17.24	23.59	310.97

Fig.5 Change rule of density and viscosity with pressure and temperature for S-CO2

Fig.6 Pressure differential distribution of supercritical CO2 dry gas seal for real gas compared with ideal gas at different combination of pressure and temperature

Fig.7 Variation of film stiffness and leakage rate of S-CO2 dry gas seal with linear velocity (po=8 MPa)

Fig.8 Variation of film stiffness and leakage rate of S-CO2 dry gas seal with linear velocity (po=14 MPa)

Fig.9 Average radial pressure distribution of supercritical CO2 dry gas seal obtained by different models (po=14 MPa)

Fig.10 Velocity field of supercritical CO2 dry gas seal obtained by four different models

Fig.11 Effect of various effects on increment ratio of film stiffness and leakage rate of S-CO2 dry gas seal

Table 3 Interactive increment ratio of film stiffness of supercritical CO2 dry gas seal of three effects at

压力 p_o/MPa	线速度 v/(m·s^-1)	交互性能增量比/%
压力 p_o/MPa	线速度 v/(m·s^-1)	湍流对实际气体的影响	惯性对实际气体的影响	实际气体对湍流的影响	惯性对湍流的影响	实际气体对惯性的影响	湍流对惯性的影响
8	25	0.52	0.36	0.54	0.34	0.37	0.33
8	150	10.29	-0.07	14.12	0.86	-0.06	0.58
14	25	4.15	0.17	4.38	0.25	0.16	0.24
14	150	31.31	-1.55	43.60	1.87	-1.32	1.06

Table 4 Interactive increment ratio of leakage rate of supercritical CO2 dry gas seal of three effects at

压力 p_o/MPa	线速度 v/(m·s^-1)	交互性能增量比/%
压力 p_o/MPa	线速度 v/(m·s^-1)	湍流对实际气体的影响	惯性对实际气体的影响	实际气体对湍流的影响	惯性对湍流的影响	实际气体对惯性的影响	湍流对惯性的影响
8	25	-0.21	-0.39	-0.17	0.32	-0.32	0.32
8	150	-5.98	-0.89	-4.35	-1.32	-0.70	-1.44
14	25	-2.36	-0.47	-1.55	0.71	-0.31	0.72
14	150	-24.37	-2.14	-12.83	-0.37	-1.46	-0.50

Fig.12 Coupling relationship among real gas effect, turbulent effect and inertia effect

Fig.13 Density distribution of CO2 at different pressure and mathematical models

Fig.14 Local Reynolds number of supercritical CO2 dry gas seal at different linear velocity (po=14 MPa)

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