The polyester plant of FEPV is the first among FENC production sites to install chain grate boilers. In terms of investment or operational performance, chain grate boilers are best suited for heating the heat conduction oil based on the scale of production for this plant. However, we faced a few major challenges during the process. Depending on the type of coal used, boiler slagging may occur, which affects production. The desulfurization system also needs improvement. Therefore, the polyester plant of FEPV established an interdepartmental team to tackle system improvement. After a year of hard work, the team has greatly improved the reliability and stability of the chain grate boilers. The clogging issue at the desulfurization tower has also been solved, thus improving its efficiency, reducing SOx by 60% and lower the costs for fly ash treatment by NT$ 2.13 million. Furthermore, the plant has also accumulated valuable experience in operating and repairing coal boilers, and will be able to share the knowledge with other production units.