Volume 26, number 3, December 2012

ArcelorMittal Montréal — New reheat furnace for Longueuil rolling mill

ArcelorMittal Montréal’s mission is to produce safe, sustainable steel, minimizing impacts for future generations. The company has 1,800 employees, who work in Contrecœur, Longueuil, Montréal, and La Prairie in Québec, as well as in Hamilton and Ottawa in Ontario. It produces more than two million tonnes of steel annually.

The reheat furnace for billets from the rolling mill in Longueuil was erected in situ in 1973. Since then, several major modifications have been made with the aim of increasing production capacity from 54 t/h to 90 t/h, so as to increase the volume of annual production from 185,000 t to about 308,000 t.

Over the years, the furnace required more and more maintenance to ensure its operational reliability. Also, the furnace was not fitted with a heat recovery system. The plant thus examined the need to make a major investment to upgrade the reheat furnace and control the increase in operating costs.

A specialized civil engineering firm studied the structural condition of the reheat furnace with the objective of evaluating the feasibility of making repairs. Its report confirmed that the concrete walls and the columns supporting the furnace had exceeded their useful life, thus requiring their replacement in the short term in order to maintain the same rate of production and eliminate the risk of accidents.

Report findings

The report showed that in addition to its age, the design of the furnace made it uncompetitive compared with modern furnaces, which could be detrimental to the viability of the plant in the medium term.

The furnace did not have the capacity to meet operational needs during the rolling of large products. Also, it was hardly able to meet customer requirements for leaf springs in terms of decarburization.

The annual natural gasconsumption by the old furnace was around 1.85 GJ per tonne of rolled products. As regards environmental aspects, average GHG emissions were about 95 kg of CO2 per tonneof finished products.

The following findings were also reported:

  1. The work environment was difficult for maintenance employees due to the high level of CO2 and the high temperature under the furnace.
  2. The hydraulic cylinders used for adjusting the four mobile cylinders were not synchronized, which led to frequent delays since the billetts could be badly aligned on leaving the furnace.
  3. The static pressure inside the furnace was controlled by a set of flaps on the natural draw of the chimney stack. When the furnace’s capacity was increased from 54 t/h to 90 t/h, the chimney’s drawing capacity had to be increasedin order to maintain static pressure and reduce heat loss from the envelope.
  4. The distance between the descaler and the first cage was too short. The maximum speed of the descaler was controlled by Cage 1, which was too slow to reduce heat loss to a minimum as the bars passed and to prevent black spots from occasionally forming on the billets.
  5. The tempering zone was too narrow at the furnace exit, preventing the uniform heating of the billetts.The temperature differential rose to about 150°C vertically and to 200°C from one extremity to the other. This complicated operations and required close monitoring in order to control the dimension of the bars.
  6. There was no heat recovery system.
  7. The refractory plankswere too thin (380 mm versus 600 in modern furnaces), thus increasing thermal losses.

ArcelorMittal Montréalconfronted a dilemma: renovate the existing furnace or acquire a new one.

Decision and result

After analyzing the pros and cons, the conclusion seemed obvious: the existing furnace was in a very bad state. In fact, it could not be counted on to meet the capacity standards and quality of production required. It was impossible to change the distance between the various parts, thus compromising future improvements.

A new furnace would permit adding two new cages to standardize the size of the billetts, thus simplifying the rolling process. The estimate of the cost for improving the existing furnace was around $14 million, while the cost of a new furnace was estimated at $21 million.

The scope of the project entailed installing a new natural gas furnace with a production capacity of 120 t/h (compared with 90 t/h), fitted with a heat recovery system and a new programmable logic control system.

Considerable savings were able to be achieved since the plant continued to use natural gas and the existing electrical power input was sufficient for the new furnace and related equipment.

This major decision allowed ArcelorMittal Montréal to continue to operate the plant and keep jobs in Québec thanks to its competitive position in the marketplace, the reduction in operating costs, the choice of natural gas as energy source, and its increased production capacity froman efficient installation.

View of the chimney stack, heat recuperators and ventilators of the new furnace.

View of the new furnace.

André Gévry
Manager
ArcelorMittal Contrecœur-Ouest Inc.

Richard Meunier, Eng.
Advisor, Energy Efficiency Technologies
DATECH Group, Gaz Métro