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露天煤矿低位发热量的可解释机器学习预测模型

An interpretable machine learning prediction model for lower calorific value of coal in open-pit coal mines

  • 摘要: 煤炭低位发热量(Low Calorific Value, LCV)是露天煤矿配煤定价、采剥规划与贸易结算的核心参数,但传统克里金估值依赖平稳性假设,难以刻画煤质条件的非线性空间变异。现有机器学习方法虽提升了拟合精度,却因“黑箱”特性无法解释指标间的耦合机理,制约了随采配煤的工程应用。为兼顾精度与可解释性,构建低位发热量可解释预测模型,定量揭示各因素对低位发热量的贡献规律,以新疆大南湖二号露天煤矿21层煤、1 992条勘探与生产煤质数据为研究对象,按照样本量构建分层特征集(主力煤层14维全特征/小样本煤层10维精简特征),采用极端梯度提升模型(eXtreme Gradient Boosting, XGBoost)建立回归模型,以贝叶斯优化结合5折交叉检验对9组超参数寻优,并引入保形预测给出95%置信区间。设计精度对比、可解释性与消融3组试验,采用夏普立加解释(SHapley Additive exPlanations, SHAP)和累积局部效应(Accumulated Local Effects, ALE)解析特征作用机制。结果表明:XGBoost在9种回归模型对比中精度最佳,模型在空间块交叉检验模式下均方根误差ERMS为0.760 3 MJ/kg、决定系数R2为0.894 5,较普通克里金ERMS=2.367 3的指标精度提升3.1倍;消融试验证实工业分析指标(灰分、挥发分、水分)为绝对核心特征,缺失后ERMS恶化至151%,并得出结论对于此次试验场景的估计问题仅用该3项指标即可达到工程可用精度。SHAP归因显示,灰分为首要驱动因子,贡献占比约65.5%;ALE所得灰分效应斜率(−0.27 MJ/(kg·%))与煤化学经验公式规律基本一致,并揭示高灰(>25%)、高挥发分(>46%)区域低位发热量存在强负交互作用。据此得到大南湖二矿低位发热量分布特征,全矿预测值为22.21~25.66 MJ/kg,最优“热值柱”出现在中部埋深在150~280 m的区段,垂向呈浅部衰减—中深部富集—深部分化的3段式分异。贝叶斯优化与学习曲线双重诊断表明,该精度已逼近现有信息条件的合理上限,并确定灰分主控、高灰高挥发分强负交互为低位发热量空间富集的主控机理。据此提出异空间规律为依据的采场粗配-煤仓精配的2级配采策略以及不确定性驱动的指示性勘查的机制,并将预测低位发热量结果转化为可执行配比(月度示例混配热为19.65 MJ/kg、劣质煤混配为29.6%),形成了从预测到配采的煤质管控闭环,直接指导采剥时序优化、分采分储管控与动态配煤决策,为露天煤矿从事后化验调整向事前空间预判的精细化煤质管理转型提供了可解释、不确定可控的技术方案。

     

    Abstract: The low calorific value (LCV) of coal is a key parameter for pricing, mining and stripping planning, and trade settlement in open-pit coal mines. However, traditional kriging estimation relies on assumptions of stationarity, making it difficult to capture the nonlinear spatial variation of coal quality. Although existing machine learning methods have improved prediction accuracy, their “black-box” nature limits the understanding of underlying coupling mechanisms among indicators, thereby restricting engineering applications in real-time blending during extraction. To balance accuracy and interpretability, this study constructs an explainable LCV prediction model that quantifies the contribution patterns of various factors to low calorific value. Using 1 992 exploration and production coal quality data from 21 coal seams at the Dainanhua No. 2 Open-pit Mine in Xinjiang, we build stratified feature sets based on sample size—14-dimensional full features for major seams and 10-dimensional simplified features for low-sample seams. An extreme gradient boosting (XGBoost) regression model is established, optimized via Bayesian optimization combined with fivefold cross-validation across nine hyperparameter configurations, and enhanced with conformal prediction to provide 95% confidence intervals. Three experimental groups are designed: accuracy comparison, interpretability analysis, and ablation studies. Feature importance mechanisms are analyzed using SHapley Additive exPlanations (SHAP) and accumulated local effects (ALE). Results show that XGBoost achieves the highest accuracy among nine regression models, with a root mean square error (RMSE) of 0.760 3 MJ/kg and a coefficient of determination R2 of 0.894 5 under spatial block cross-validation, representing a 3.1-fold improvement over conventional kriging (RMSE = 2.367 3). Ablation experiments confirm industrial analysis indicators—ash content, volatile matter, and moisture—as absolute core features; their removal increases RMSE by 151%, indicating that these three parameters alone can achieve engineering-grade accuracy for this scenario. SHAP attribution reveals ash as the primary driver, contributing approximately 65.5%. The ALE-derived ash effect slope (−0.27 MJ/(kg·%)) aligns closely with empirical coal chemistry formulas and highlights strong negative interaction between high-ash (> 25%) and high-volatile (> 46%) zones. The LCV distribution characteristics of Dainanhua No. 2 Mine show predicted values ranging from 22.21 to 25.66 MJ/kg, with the optimal “calorific column” located in the central section at depths of 150–280 m, exhibiting a three-stage vertical differentiation pattern: shallow depletion, mid-depth enrichment, and deep differentiation. Dual diagnostics using Bayesian optimization and learning curves indicate that current accuracy approaches the theoretical upper limit given available data, confirming ash dominance and strong negative interaction between high-ash and high-volatile regions as the main controls on spatial LCV enrichment. Based on these findings, a two-stage blending strategy is proposed: coarse blending at the working face guided by spatial patterns, followed by fine adjustment in stockpiles. Additionally, an uncertainty-driven indicator-based exploration mechanism is introduced. Predicted LCV values are translated into executable blending ratios (e.g., monthly blended low calorific value of 19.55 MJ/kg with 29.6% low-quality coal), forming a closed-loop coal quality management system from prediction to blending. This approach directly supports optimization of mining sequences, segregated extraction and storage control, and dynamic blending decisions, enabling open-pit mines to transition from post-hoc laboratory adjustments to proactive spatial forecasting, providing an interpretable and uncertainty-controllable technical solution for refined coal quality management.

     

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