基于CPA状态方程的高压含硫天然气压缩因子计算方法研究

对于压力高于70 MPa的含H_2S天然气,其分子之间间距缩小,极性H_2S分子之间缔合作用增强,传统SRK、PR状态方程计算高压含硫天然气的压缩因子准确性有待进一步改进。基于压力3.72～97.58 MPa、H_2S体积分数0%～70.03%的154组压缩因子修正CPA(Cubic-Plus-Association)状态方程中H_2S与CH_4、CO_2分子间二元交互作用系数,综合评价SRK、PR、CPA状态方程对压缩因子的计算精度。结果表明,对于中低压含硫天然气(p35 MPa),采用PR方程精度最高,平均相对偏差为1.12%;对于高压及超高压含硫天然气(p35 MPa),CPA方程精度最高,平均相对偏差为-1.46%。进一步采用法国ST抗硫高压PVT仪测试了4种含硫天然气在70～131 MPa条件下的138组压缩因子实测值,验证了采用CPA状态方程对于高压含硫天然气压缩因子的计算精度。

Study on compressibility factor calculation method for ultra-high pressure and sulfur-containing gas by use of the CPA EoS

For H₂S-containing natural gas with pressures higher than 70 MPa, closer the distance between natural gas molecules is, stronger the association between H₂S molecules becomes. At such conditions, the traditional SRK, PR equations of state are difficult to accurately calculate the gas compressibility factors. In this paper, a total of 154 experimental compressibility factor data with pressure from 3.72 MPa to 97.58 MPa and H₂S contents from 0%-70.03% are used to improve the binary interaction parameters between H₂S and CH₄,CO₂ molecules for CPA(Cubic-Plus-Association)EoS and to evaluate the compressibility factor calculation accuracy of SRK, PR and CPA EoSs. Results show that the PR EoS has the highest accuracy and the average relative deviation is 1.12% for medium and low pressure natural gas (p<35 MPa). The CPA equation has the highest accuracy with average relative of -1.46% for the high pressure and ultra-high pressure natural gas (p>35 MPa). Furthermore, the ST PVT cell is applied to measure a total of 138 compressibility factors for four H₂S-containing gas samples with pressures from 70 MPa to 131 MPa. The experimental results are used to verify the SRK, PR and CPA EoSs. Results demonstrate that CPA EoS has the highest accuracy for calculation of compressibility factors of ultra-high pressure and H₂S-containing gas.