循环储释条件下先进绝热CAES硐库稳定性评价与优化

Stability evaluation and optimization of advanced adiabatic CAES caverns under cyclic storage and release conditions

  • 摘要:
    目的 先进绝热压缩空气储能系统(Compressed Air Energy Storage, CAES)采用换热器回收热量,其在长期服役中涉及高频次高低压的储释循环,这将导致地下硐库围岩的累积损伤,从而降低储库的围岩稳定性。不合理的地下硐库布局与运营压力会进一步加快围岩累计损伤。因此,考虑岩石损伤特征的先进绝热CAES地下硐库围岩稳定性评价研究对保障储能库长期安全服役具有重要意义。
    方法 引入损伤应力水平λ表征损伤驱动强度,开展围压为10 MPa、λ为0.5~1.0的三轴加卸载试验,分析了花岗岩损伤演化特征。进一步通过非线性拟合形成抗压强度-循环次数方程,完善花岗岩循环加卸载下的损伤模型。将该方程应用于某废弃矿洞改建先进绝热CAES地下硐库工程中,基于正交实验法,引入莫尔-库伦强度单元安全系数Fs,评价储释循环31 000次后硐室形状、硐室埋深以及硐室截面积的重要性与最优组合。以最小Fs=2.0作为稳定性安全阈值,结合能量密度优化运营压力区间。
    结果 当λ<0.6时,损伤缓慢增加;0.6≤λ≤1.1时,损伤快速增大;λ>1.1时,损伤再次缓慢增大,且与λ呈幂指数函数关系。最小单元安全系数-循环次数曲线概括为“快速下降-缓慢下降-平稳”3个阶段,具有较高λ呈现极速损伤、较低λ呈现平缓损伤的特征。硐室形状、硐室截面积、硐室埋深对于围岩稳定性的重要性依次降低。硐室稳定的最佳组合为硐室埋深300 m、圆形硐室截面积400 m2。结合该工程实际,4~12 MPa压力区间工况的能量密度最高,为29.56~42.74 MJ/m3。
    结论 该研究未考虑换热器的效率,岩石本构模型为莫尔-库伦模型,材料参数折减仅关联λ和抗压强度的映射,这在合理误差内减小了岩石的损伤程度,提高了最小单元安全系数,优化了硐室的运营范围。未来研究应考虑增加温度因素,结合黏弹塑性本构模型开展温度-应力耦合下花岗岩损伤机制与模型改进研究。

     

    Abstract:
    Objective In advanced adiabatic compressed air energy storage (CAES) systems, heat exchangers recover thermal energy. Prolonged high-frequency cyclic storage and release at varying pressures can cause cumulative damage to the surrounding rocks of underground caverns, compromising their stability. Improper cavern layout and operating pressures will accelerate this damage. Therefore, evaluating the stability of surrounding rocks in advanced adiabatic CAES power plants, considering rock damage characteristics, is crucial for ensuring the long-term safe operation of energy storage caverns.
    Methods The damage stress level λ was introduced to characterize the damage-driven strength. Triaxial loading-unloading tests were conducted on granite under a confining pressure of 10 MPa with λ values ranging from 0.5 to 1.0 to analyze damage evolution characteristics. A compressive strength–cycle number equation was derived through nonlinear fitting to enhance the granite damage model under cyclic loading and unloading. This equation was applied to a project converting an abandoned mine into an underground cavern for an advanced adiabatic CAES power plant. Using the orthogonal experiment method, the Mohr-Coulomb strength element safety factor (Fs) was introduced to evaluate the significance and optimal combination of cavern shape, burial depth, and cross-sectional area after 31, 000 storage-release cycles. With a minimum Fs of 2.0 set as the stability safety threshold, the operating pressure range was optimized by energy density.
    Results Results indicated that when λ < 0.6, damage increased slowly; between 0.6 and 1.1, damage accelerated rapidly; and above 1.1, damage growth slowed again, following a power-exponential relationship with λ. The element safety factor–cycle number curve exhibited three stages: rapid decline, slow decline, and stabilization. Specimens with higher λ experienced rapid damage, while those with lower λ showed gradual damage. The influence of cavern shape, cross-sectional area, and burial depth on surrounding rock stability decreased in that order. The optimal configuration for stability was a burial depth of 300 m and a circular cross-sectional area of 400 m. Considering project conditions, the highest energy density (29.56–42.74 MJ/m3) was achieved within a pressure range of 4–12 MPa.
    Conclusion This study did not consider heat exchanger efficiency. The Mohr-Coulomb model was employed as the rock constitutive model, with material parameter reduction linked solely to the mapping between λ and compressive strength. Within an acceptable error range, this approach reduced rock damage, increased the minimum element safety factor, and optimized the cavern’s operating range. Future research should incorporate temperature effects and investigate granite’s damage mechanisms and model improvements under temperature-stress coupling using visco-elastoplastic constitutive models.

     

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