*3.6. Application of the Coating*

In engineering application, the ceramic coating was applied to the heating surfaces of boiler water-wall tubes of tower 2 at JINJU INDUSTRY power plant in Chungcheongbuk-do province of Korea (Figure 11). The effect of ceramic coating on fouling resistance and energy efficiency was evaluated after 3 months of operation of the boiler. As seen in Figures 11 and 12, a significant difference in the coated and uncoated areas of the boiler surfaces was observed. The coated surfaces were relatively clean with only small amount of unwanted matters attached on a small part of boiler surface. However, it should be noted that, these matters are bonded weakly with boiler surface and they can be easily removed by a low-pressure air gun. Meanwhile, fouling and slagging severely deposited on the uncoated surfaces and it is quite hard to remove them even with a high-pressure air gun.

**Figure 11.** Application of the ceramic coating in real boiler systems: (**a**) slurry spraying process and (**b**) anti-fouling ceramic coating after 3 months operation.

**Figure 12.** Photography of the uncoated areas of the boiler surfaces.

The thermal efficiency of boilers was calculated before and after applying the composite ceramic coating. To do this, it is useful to check the amount of incinerated waste (input amount or burn fuel) and the amount of produced steam (production amount). For simplicity, thermal efficiency (η) before and after using the coating is defined as the rate of total steam production over the fuel consumption. Figure 13 collected the thermal efficiency without and with using the ceramic coating in the same period, respectively. As can be seen in Figure 13, the thermal efficiency increased about 62.34% after applying the ceramic coating. Of course, there are some other operating conditions can affect the result, but it is worth concluding that the developed ceramic coating has great potential to be applied in real boiler systems to improve their overall thermal efficiency.

**Figure 13.** The thermal efficiency before and after applying the ceramic coating in boiler systems at JINJU INDUSTRY power plant in Chungcheongbuk-do (Korea).

#### **4. Conclusions**

The purpose of this study was to develop a ceramic coating to prevent the fouling deposition of fly ash. The results can be summarized as follows.


**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-6412/8/10/353/s1. Table S1: Input and output production amount of tower 2 in period of 2017.04–2017.06 (JINJU INDUSTRY's data); Table S2: Input and output production amount of tower 2 in period of 2018.04–2018.06 (JINJU INDUSTRY's data).

**Author Contributions:** Conceptualization, M.D.N. and W.T.K.; Methodology, M.D.N. and J.W.B.; Software, M.D.N. and A.S.B.; Validation, M.D.N., K.H.H. and V.-H.P.; Formal Analysis, M.D.N. and A.S.B.; Investigation, M.D.N., Y.H.K. and K.H.H.; Resources, M.D.N. and J.W.B.; Data Curation, V.-H.P., Y.H.K. and K.H.H.; Writing-Original Draft Preparation, M.D.N.; Writing-Review & Editing, M.D.N. and W.T.K.; Visualization M.D.N. and J.W.B.; Supervision, W.T.K. and Y.H.K.; Project Administration, W.T.K.; Funding Acquisition, W.T.K.

**Funding:** This research were supported by the National Strategic Project-Carbon Upcycling of the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT), the Ministry of Environment (ME), and the Ministry of Trade, Industry and Energy (MOTIE) (Grant No. 2017M3D8A2086035); the Korea Institute for Advancement of Technology (KIAT) (Grant No. P012700050).

**Acknowledgments:** The authors would like to thank Jeong Min Bak, Korea for SEM technical advice.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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