Fault detection of catalyst loss in FCC disengager based on autoencoder and multi-scale symbolic transfer entropy

doi:10.11949/0438-1157.20250169

Abstract

Abstract:

Fluid catalytic cracking (FCC) disengager catalyst loss faults are complex, with multiple variables deviating from normal when occurring. These faults must be detected and mitigated promptly to ensure the long-term stable operation of the FCC unit. This study proposes an unsupervised run-off fault detection method (AEM) that integrates autoencoder (AE) and multi-scale symbol transfer entropy (MSTE), which fully considers the complex time dependency in time series data and the non-stationarity of the time series after the fault. The dual attention (DA) mechanism is incorporated into a long short-term memory (LSTM) network with an encoder-decoder structure. By applying the feature attention (FA) mechanism to assign weights to input feature variables, key features are dynamically emphasized, enabling the identification of the main fault variables. The temporal attention (TA) mechanism further enhances fault detection by assigning weights to capture dependency information at each time step along the time dimension. Additionally, a causal diagram is constructed for the nonstationary process using the MSTE method to reveal time delays between variables and eliminate indirect causal relationships. The effectiveness of AEM is verified by analyzing the perforation process of the fast-separating head of the settler, and the interpretability of the decision-making process is improved.

Key words: process control, safety, unsupervised learning, neural networks, causality discovery

摘要：

催化裂化（fluid catalytic cracking，FCC）沉降器跑剂故障复杂，故障发生时多个参数会偏离正常状态，需迅速检测和缓解，以保障FCC装置长周期稳定运行。提出了一种集成自编码器（autoencoder，AE）和多尺度符号转移熵（multi-scale symbol transfer entropy，MSTE）的无监督跑剂故障检测方法（AEM），充分考虑了时间序列数据中复杂的时间依赖关系及故障后时间序列的非平稳性。将双重注意力（dual attention，DA）机制融入长短期记忆单元（long short-term memory，LSTM）的编码器-解码器结构中，其中特征注意力（feature attention，FA）机制通过为输入特征变量分配权重，动态强调关键特征并识别主要故障变量；时间注意力（temporal attention，TA）机制则通过为时间维度内的每个时间步分配权重，捕获其依赖信息，从而进一步提升检测效果。此外，利用MSTE方法构建了非平稳过程的因果关系图，揭示了变量之间的时间延迟并排除了间接因果关系。通过分析沉降器快分头封头穿孔过程，验证了AEM的有效性，且提升了决策过程的可解释性。

关键词: 过程控制, 安全, 无监督学习, 神经网络, 因果关系发现

CLC Number:

TQ 021

Chunmeng ZHU, Zeng LI, Nan LIU, Yunpeng ZHAO, Xiaogang SHI, Xingying LAN. Fault detection of catalyst loss in FCC disengager based on autoencoder and multi-scale symbolic transfer entropy[J]. CIESC Journal, 2025, 76(9): 4512-4523.

朱春梦, 李增, 柳楠, 赵云鹏, 石孝刚, 蓝兴英. 基于自编码器和多尺度符号转移熵的FCC沉降器跑剂故障检测[J]. 化工学报, 2025, 76(9): 4512-4523.

Figures/Tables 13

Fig.1 Encoder architecture with integrated AM and LSTM

Fig.2 Decoder architecture with integrated AM and LSTM

Fig.3 Fault detection flowchart with integrated CFD, AE and MSTE

Fig.4 Structure and variable distribution of FCC disengager system

Table 1 Process variables in the FCC disengager system

工业变量	变量描述	单位
F1	顶旋入口催化剂流量	kg·s^-1
F2	催化剂跑损量	kg·s^-1
P1	下部稀相空间压力	kPa
P2	上部稀相空间压力	kPa
P3	快分出口压力	kPa
P4	顶旋压降	kPa
D1	快分出口催化剂浓度(固含率)	—
D2	隔离罩槽口催化剂浓度(固含率)	—
D3	顶旋入口催化剂浓度(固含率)	—
U1	快分出口线速	m·s^-1
U2	顶旋入口线速	m·s^-1
T1	下部稀相空间温度	K
T2	沉降器顶部温度	K
T3	快分出口温度	K
T4	顶旋入口温度	K

Fig.5 Fault detection results for high-fidelity datasets

Fig.6 Forms of data presentation

Fig.7 Fault detection results with data noise added

Fig.8 Fault contribution diagram based on the FA mechanism

Fig.9 The causality generated by MSTE

Fig.10 Causal diagram with time delay of vortex quick-separation perforation fault generated by MSTE

Fig.11 MSTE changes with τ in FCC disengager system for variables P3 and P1 or for variables P4 and P1

Fig.12 The causality generated by MTE, STE and MSTE

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