Study of Heat Recovery Systems for Heating and Moisturing Combustion Air of Boiler Units

Introduction. One of the ways to save natural gas and to improve the environmental conditions in the municipal heat-power engineering is to use progressive technologies for recovering the heat of flue gases from boiler plants, in which the condensation mode of operation of heat-recovery equipment is implemented. To increase the ecological effect in some heat-recovery systems, a humidification process of the combustion air occur. This lowers the combustion temperature of the fuel and reduces the concentration of nitrogen oxides in the combustion products.
Problem Statement. At humidifying combustion air, the boiler exhaust-gases are characterized by high moisture content. In the known calculation methods, there are no data on heat transfer under these conditions. This is a problem for conducting thermal calculations of such installations.
Purpose. Establishing patterns of heat transfer at an increased moisture content of exhaust-gases in heatrecovery equipment, consisting of bundles of transverse-finned pipes, and determining the main parameters of the proposed complex installation.
Materials and Methods. Experimental studies of heat transfer were carried out on a specially created stand. For the thermal and hydraulic calculation of a heat-recovery installation, known calculation methods were used, taking into account the experimental data obtained.
Results. The laws of heat transfer during deep cooling of exhaust-gases with moisture content X = 0.15-0.30 kg/kg d.g. are established. The thermal, hydraulic and operating characteristics of the proposed complex heat-recovery installation with heating and humidification of the combustion air in different modes of operation of the boiler are determined. This installation has been introduced; its tests have been carried out, which have confirmed high thermal and environmental efficiency.
Conclusions. The application of the proposed complex heat-recovery unit allows increasing the coefficient of the use heat of fuel of boiler depending on its operating mode by 13-20%.

1. Jaber, H., Khaled, M., Lemenand, T., & Ramadan, M. (2016, July). Short review on heat recovery from exhaust gas. In AIP Conference Proceedings (Vol. 1758, No. 1, p. 030045). Beirut, Lebanon, AIP Publishing. 
https://doi.org/10.1063/1.4959441
2. Efimov, A. V., Goncharenko, A. L., Goncharenko, L. V., & Esipenko, T. A. (2017). Modern technologies of deep cooling of fuel combustion products in boiler plants, their problems and solutions. Kharkov: NTU «KhPI». [in Russian]. 
URL: http://repository.kpi.kharkov.ua/handle/KhPI-Press/32826 
(Last accessed: 24.07.2019).
3. Dolinskiy, A. A., Fialko, N. M., Navrodskaya, R. A., & Gnedash, G. A. (2014). Basic principles of heat recovery technologies for boilers of the low thermal power. Industrial Heat Engineering, 36(4), 27-35 [in Russian].
4. Edward Levy, Harun Bilirgen, Kwangkook Jeong, Michael Kessen, Christopher Samuelson, & Christopher Whitcombe. Recovery of Water from Boiler Flue Gas.
https://doi.org/10.2172/952467
5. Fialko, N. M., Navrodskaya, R. A., Gnedash, G. A., Presich, G. A., & Stepanova, A. I. (2014). Increasing the efficiency of boiler plants of communal heat energy by combining the heat of the exhaust-gases. International Scientific Journal «Alternative Energy and Ecology», 15, 126-129 [in Russian].
6. Wei, M., Zhao, X., Fu, L., & Zhang, S. (2017). Performance study and application of new coal-fired boiler flue gas heat recovery system. Applied energy, 188, 121-129.
https://doi.org/10.1016/j.apenergy.2016.11.132
7. Navrodskaya, R., Fialko, N., Gnedash, G., & Sbrodova, G. (2017). Energy-efficient heat recovery system for heating the backward heating system water and blast air of municipal boilers. Thermophysics and Thermal Power Engineering, 39(4), 69-75 [in Ukrainian].
https://doi.org/10.31472/ihe.4.2017.10
8. Fialko, N. M., Presich, G. A., Navrodskaya, R. A., & Gnedash, G. A. (2011). Improvement of the complex heat-recovery system of exhaust-gases of boilers for heating and humidifying blown air. Industrial Heat Engineering, 33(5), 88-95 [in Ukrainian].
9. Fialko, N. M., Presich, G. A., Gnedash, G. A., Shevchuk, S. I., & Dashkovska, I. L. (2018). Increase the efficiency of complex heat-recovery systems for heating and humidifying of blown air of gas-fired boilers. Industrial Heat Engineering, 40(3), 38-45[in Ukrainian].
https://doi.org/10.31472/ihe.3.2018.06
10. Navrodska, R., Fialko, N., Presich, G., Gnedash, G., Alioshko, S., & Shevcuk, S. (2019). Reducing nitrogen oxide emissions in boilers at moistening of blowing air in heat recovery systems. In E3S Web of Conferences April 8-10, 2019, Polanica-Zdrój. EDP Sciences. V. 100, p. 00055.
https://doi.org/10.1051/e3sconf/201910000055
11. Patent of Ukraine N 56591. Presich H. O., Fialko N. M., Navrodska R. O. Heat utilizer. [in Ukrainian]. 
URL: http://uapatents.com/3-56591-teploutilizator.html (Last accessed: 30.07.2019).
12. Fialko, N. M., Navrodska, R. O., Shevchuk, S. I., Presich, G. A., & Gnedash, G. A. (2017). Heat Methods of the Gas-Escape Channels of Boiler Installations by Heat-Utillization Technologies Applicatoin. Scientific Bulletin of UNFU, 27(6), 125-130 [in Ukrainian]. 
https://doi.org/10.15421/40270625
13. Kuznetsov N. V., Mitor V. V., Dubovsky I. E. (2011). Thermal calculation of boiler units. Normative method. Moscow, Ekolit.
14. Navrodska, R., Stepanova, A., Shevchuk, S., Gnedash, G., Presich, G. (2018). Experimental investigation of heat-transfer at deep cooling of combustion materials of gas-fired boilers. Scientific Bulletin of UNFU, 28(6), 103-108. 
https://doi.org/10.15421/40280620
15. Guidance Technical Material 108.030.140-87 (1987). Calculation and recommendations for the design of transverse-finned convective heating surfaces of stationary boilers. Leningrad, Ministry of Power Engineering. 33 p. [in Russian].
16. Fialko, N., Presich, G., Navrodska, R., & Gnedash, G. (2013). Ecological efficiency of combined heat recovery systems waste of exhaust gases for boiler plant. Bulletin of Lviv Polytechnic National University. The theory and practice of construction, 755, 429-434 [in Ukrainian]. 
URL: http://ena.lp.edu.ua:8080/handle/ntb/22345 (Last accessed: 30.07.2019).