DOI: 10.52150/2522-9117-2025-39-10

L. P. Gres¹, D. Sc. (Tech.), Professor, ORCID 0000-0002-5343-3438
O. V. Gupalo^1,*, Ph. D. (Tech.), Associate Professor, ORCID 0000-0003-3145-9220
Ye. O. Karakash¹, Ph. D. (Tech.), Associate Professor, ORCID 0000-0003-3833-2396
O. O. Yeromin¹, D. Sc. (Tech.), Professor, ORCID 0000-0001-8306-578X
Ye. V. Peretiatko¹, Master’s degree, ORCID 0009-0009-2026-2239

¹Ukrainian State University of Science and Technologies, Lazariana St., 2, Dnipro, 49010, Ukraine

^*Corresponding author: o.v.gupalo@ust.edu.ua

FEATURES OF HEAT RECOVERY OF LOW-TEMPERATURE FLUE GAS FROM DLAST FURNACE STOVES

Abstract. The aim of achieving the air-blast temperature exceeding 1080 °С for heating hot-blast stoves typically involves the use of blast furnace gas (BFG) enriched with natural gas. This practice leads to significant natural gas consumption. An effective alternative to using natural gas is to preheat the combustion components (BFG and atmospheric air) by utilising the heat of the waste flue gases of the hot-blast stoves. The implementation of such a flue gas heat recovery system at PJSC “Zaporizhstal” in 2004 enabled savings of approximately 30 million m³/year of natural gas and allowed the air-blast temperature to reach 1180-1230°. However, despite the low temperature of the flue gases at the heat exchanger inlet (260-280°C), their service life proved to be short (2.3-3.5 years for the air heat exchanger and 8.2-8.5 years for the gas heat exchanger). The primary cause of the low durability of the heat exchangers was determined to be low-temperature sulphuric acid corrosion of the steel tubes. The aim of this research is to determine the impact of changes in the initial parameters of the BFG and the preheating temperature of the combustion components on the performance indicators of the hot-blast stoves, and to improve the existing waste heat recovery system of PJSC “Zaporizhstal”. The study investigated the effect of changes in the initial BFG temperature on its humidity, calorific value, and calorimetric temperature. It was determined that raising the gas temperature from 30 °C to 60°C leads to a significant increase in its humidity (from 32 to 176 g/m³ and from 34 to 189 g/m3 at total gas pressures of 111.132 and 102.973 kPa, respectively). This, in turn, causes a reduction in the BFG’s calorific value by 13% and the calorimetric temperature by 9 %. To achieve a temperature under the hot-blast stove dome of 1350°C with the BFG preheated to 180°C, the required combustion air temperature is 120-190°C in winter and 150-310°C in summer. Upon combustion of the BFG, sulphur oxides are formed, which react with water vapour to create sulphuric acid vapours contained within the combustion products. It was established that, under the conditions of hot-blast stoves, the sulphuric acid dew point temperature ranges between 118-130°C. It was found that the short service life of the heat exchangers in the existing waste heat recovery system is due to the sulphur content in the steel of the tubes and the acidic nature of the condensate. Furthermore, the existing heat recovery system was identified as having a number of drawbacks, the most critical of which is the lack of measures to prevent corrosion of the metal tubes. An improved heat recovery system is proposed, which involves the use of three sections in each heat exchanger, vertical tube placement, and a triple regulation system to ensure the minimum allowable flue gas temperature remains above the sulphuric acid vapour dew point. Structural solutions have been developed to enable the cleaning of the heat exchanger tubes and the replacement of the sections most susceptible to corrosion. The proposed system is projected to increase the heat exchangers’ inter-repair service life by 2-3 times, raise the average air-blast temperature by 50-60°C, and ultimately ensure a reduction in the cost of iron production.

Key words: heat recovery, heat exchangers, blast furnace stoves, sulfuric acid corrosion of metal.

For citation: Gres, L. P., Gupalo, O. V., Karakash, Ye. O., Yeromin, O. O., & Peretiatko, Ye. V. (2025). Features of heat recovery of low-temperature flue gas from blast furnace stoves. Fundamental and applied problems of ferrous metallurgy, 39, 175-194. https://doi.org/10.52150/2522-9117-2025-39-10

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Received 11.07.2025
Accepted 21.10.2025
Published online 01.12.2025