A Numerical Model for Ash Deposition Based on Actual Operating Conditions of a 700 MW Coal-Fired Power Plant: Validation Feedback Loop via Structural Similarity Indexes (SSIMs)

Abstract

The combustion of coals will result in significant ash-related issues, which will ultimately lead to the efficiency loss of coal-fired utility boilers. While there have been numerous attempts to predict ash deposition dynamics using numerical approaches, the majority of these models were constructed using experimental data from pilot-scale furnaces and without integration with combustion models. Therefore, the current study collects meaningful power plant data from ash sampling activities at one of Malaysia's 700 MW sub-critical coal-fired power plants, enabling the ash deposition behavior in a real coal-fired utility boiler to be adequately captured and converted into a reliable ash deposition numerical model. The validation feedback loop of the ash deposition model was run using in-situ measurement data (ash sampling picture) and the actual power plant operating conditions during the ash sampling activities. The image processing algorithm was used to determine the degree of similarity between the actual ash sampling image and the predicted ash deposition image from the numerical model. Prior to the validation feedback loop, the overall numerical model (solver, combustion, turbulence, radiation) was successfully validated with the FEGT from the actual power plant, revealing a difference of less than 5 %. The current study found that the baseline ash deposition model (created from experimental data) underestimates the quantity of ash deposition gathered. The validation feedback loop of the baseline ash deposition model successfully established a new set of impaction efficiency constants, which increased the similarity of the images between the actual and predicted ash depositions. The current study's drawback, however, is mostly in the validation basis, which is largely qualitative in nature. Although the Structural Similarity Index (SSIM) value is useful for comparing the similarity of images between actual and predicted ash depositions, a more quantitative measurement that can provide extra meaningful data points and higher accuracy on the deposited ash is preferable. However, based on this modified version of the ash deposition model, the agreement is found to be satisfactory in terms of gaining a rudimentary insight of the ash deposition behavior in a coal-fired boiler.

Oil Palm Wastes Co-firing in an Opposed Firing 500 MW Utility Boiler: A Numerical Analysis

“…The detailed chemical reaction modelling schemes of solid fuel combustion used in this research work are similar to those demonstrated in our previous research [35][36]. The chemical kinetics and combustion models used in this study account for the three main stages of solid fuel combustion: devolatilisation, char conversion/reaction, and volatiles reactions.…”

“…The three-dimensional (3D) configuration of a coal-fired boiler as shown in Figure 1 was created using as-built dimensions from the actual coal-fired power plant under consideration. The boiler has a wall-firing design with 36 coal burners that are also the primary air (PA) inlets, with 36 secondary air (SA) inlets circumferentially positioned at each burner-PA inlet to enable better mixing of the incoming coal and air, as well as to provide a dry low NOx region closer to the burner area where the incoming SA creates a recirculation zone for the incoming coal and air [35][36]. Each side of a boiler (front and rear walls) has each 18 burner-PA inlets and 18 SA inlets located at three different heights at a burner zone due to the wall-firing layout.…”

“…Each side of a boiler (front and rear walls) has each 18 burner-PA inlets and 18 SA inlets located at three different heights at a burner zone due to the wall-firing layout. To reduce computational costs, the tube bundles of superheaters and reheaters were simplified to a few thin walls [35][36]. The accuracy of computational works considered, heat transfer models' implementation to thin walls to replicate the heat transport process between the flue gas and the steam within the heat exchanger bundles.…”

“…Mills 1-6, as shown in Figure 1, supply coal and PA for each burner-PA inlet elevation (A to F). In a common utility coal-fired boiler framework, the coal-fired boiler integrates the piping structure and the furnace as one system, with all mills connected to discharge pipes that deliver coal particles and PA into the boiler [35][36]. However, in order to save computational costs, the piping structure is not part of the computational domain for this study.…”

“…To assure that the spatial convergence accuracy is sufficient, the grid independent test is performed. Meshes (elements) are built with orthogonal quality and skewness in mind to reflect mesh attributes that influence the level of spatial discretisation errors [35][36]. To ensure that acceptable mesh qualities could be constructed, the orthogonal and skewness features of all generated meshes in the grid independent test were controlled.…”