free lime (f-CaO) content plays a crucial
role in determining the quality of cement. However, the existing
methods are mainly based on laboratory analysis and with significant
time delays, which makes the closed-loop control of f-CaO
content impossible. In this paper, a multisource data ensemble
learning-based soft sensor model is developed for online estimation
of clinker f-CaO content. To build such a soft sensor
model, input flame images, process variables, and the corresponding
output f-CaO content data for a rotary cement kiln
were collected from No. 2 rotary kiln at Jiuganghongda Cement
Plant which produces 2000 tonnes of clinker per day. The raw
data were preprocessed to distinguish the flame image regions of
interest (ROI) and remove process variable outliers. Three types
of flame image ROI features, i.e., color, global configuration,
and local configuration features, were then extracted without
segmentation. Further, a kernel partial least square technique
was applied for extracting the compressed score matrix features
from the concatenated flame image features and filtered process
variables to avoid high-dimensional, nonlinear, and correlated
problems. Feed-forward neural networks with random weights
were employed as base learners in our proposed ensemble modeling
framework, which aims to enhance the model’s reliability and
prediction performance. A total of 157 flame images, the associated
process variable data, and the experimentally measured
f-CaO content data were used in our experiments. A comparative
study on the f-CaO content estimator built by various feature
compressed techniques and learner models and robustness analysis
were carried out. The results indicate that the proposed
multisource data ensemble soft sensor model performs favorably
and has good potential in real world applications