On the study of pulsed metal heating

The pursuit of hidden reserves of energy-saving measures and their utilization represents a crucial factor in enhancing the competitiveness of products. Among finished products, rolling production ranks second in terms of energy consumption, following blast furnace ironmaking. Notably, gas and electricity constitute 95 % of the costs, with 60 % allocated to the heating of ingots for the rolling process [1].

When calculating energy costs in the technological process of metal heating, several approaches are considered:

– manufacturing furnaces with minimal heat release into the environment and the impact of these losses on the metal heating process;

– achieving optimum metal processing temperatures within a shorter duration;

– enhancing the automatic process control system [2 – 4].

The method employed for heating metal ingots, adhe­ring to specified requirements, must achieve optimal temperature conditions within a brief period while exerting localized effects yet transferring adequate heat for processing ingots have a localized effect, but at the same time transfer enough heat to process ingots. Pulse modes of metal heating are considered a technology that fulfills these criteria.

High-speed jet burners operating on natural gas constitute the primary class of burner devices utilized in pulsed heating systems [5]. Pulsed heating relies on either an automatic interrupt-based positioning system or an interruption system with adjustable pulse frequency and ratio, where the “on-off” period ranges from 0.5 to 2.5 min. The convection coefficient a_conv can reach 300 W/(m²·K) or higher [6].

Determining the operating mode of the burners is typically achieved through experimentation during the setup of thermal generating units, a process that is time-consuming due to the high thermal inertia of furnaces. Hence, it is advisable to preliminarily determine the operating parameters of pulsed heating using a mathematical model.

A program has been developed to simulate the outcomes of the following process: an ingot in the form of a plate or cylinder, possessing a homogeneous temperature field, is placed within a through-pass heating furnace. In this setup, the zones are defined with specific temperatures and a_conv values corresponding to the “on” and “off” states of burners. The “on – off” modes switch once the set heating time t or the set temperature diffe­rence ∆T across the ingot’s thickness is reached.

The provided figure illustrates the furnace temperature conditions and the metal heating interval, considering the following parameters:

– temperature in the methodical zone without burners: 800 °C, a_conv: 100 W/(m²·K);

– temperature and a_conv in the welding zone for the “on” and “off” modes: 1700 °C and 300 W/(m²·K), 1100 °C and 100 W/(m²·K), respectively;

– temperature and a_conv in the soaking zone for the “on” and “off” modes: 1300 °C and 200 W/(m²·K), 1100 °C and 100 W/(m²·K), respectively;

– burners’ operation and shutdown time: 1 min.

Conclusions

The software product has been developed to optimize the operating parameters for pulsed heating of metal in through-pass heating furnaces.

Successful implementation of the research prog­ram will enable the formulation of recommendations aimed at improving furnace productivity and enhancing the energy efficiency of the ingot heating process.