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Hot Metal Desulphurization’s aim is relative to the evaluation of cost consequences of the lime – magnesium co – injection as well as the expectations on the plant process capability.

Operational results
The model calculations are used for both pure lime or lime and Mg co-injection. The obtained data is collected and processed. The predicted end S contents are based on recalculation made at the end  of injection process when the real lime and Mg consumptions are known and also the actual approximate injection time is also known. Metal volume is based on operators estimation, as weighting system of hot metal in each torpedo is missing. It is important to note the following:

  • Injection time is measured usually on the tendency curves screen, its accuracy being around 1 minute.  
  • Estimated weight is based on observed level and its accuracy is within 5 %. Collected data showed a positive weight estimation (for an average tonnage of 118 t, the estimated tonnage was 124 t) while the relation between estimated and real tonnage as presented below.

                                      Figure #1. Comparison between estimated and real torpedo tonage.

Taking into account previous observations as well as model calculations it may be concluded that:

  • Best option to diminish desulphurization cost ($/t) is to work with torpedoes filled to their maximum capacity (>140 t ).
  • Highest productivity is achieved when Mg is used in co-injection process. Mg share can vary from 7-25 % but each extra percentage of Mg increases the reagent cost significantly. An acceptable compromise can be reached under actual conditions when  Mg content in the co-injected mix is kept at about 10 %.
  • Highest productivity however is achieved when the desulphurization cost ( due to reagent cost) is increased with about 0,6 $/ t. under optimum desulphurization conditions and diminished dikishing  ( it is including estimated manpower, overhead cost, maintenance, energy cost and reagent cost ) but can easily reach 1,5 $/t if operating far away from optimum.
  • Further increase of hot metal S content will negatively affect operating performances of DS unit including cost/t and processing capacity.




Objectives of the Assistance
The objectives of the Assistance are to:

  • Increase the Pellet Plant output equivalent to the design capacity up to the 4.5 million Tonnes per annum
  • Prepare the Plant to achieve an Annual Availability of 90.4%.  (The Annual Availability is defined as the Actual Operating Days divided by 365.)
  • Define the requirements and provide a capital cost estimate to attain an annual pellet production of 4.5 million Tonnes at an Annual Availability of 90.4%
  • Maximize green pellet quality and screening
  • Optimum DR grade pellet quality
  • Utilization of the pellet plant reserve capacity
  • Assist Pellet Plant management, operations, process and maintenance to attain and maintain the new capacity

A Team of five (5) experienced grate-kiln Pellet Plant Specialists provided on-site Assistance over a period of 30 (thirty) weeks:

  • One (1) Team leader, on site for a total of eight (8) weeks.  The Team Leader is present during the critical stages of the project.  The number and duration of his/her visits are determined by necessity and mutual consultation between TOA and the client, but are not exceed four (4);
  • Two (2) Operations / Process Specialists, on site for twenty-six (26) weeks each;
  • Two (2) Maintenance Specialists, on site for twenty-six (26) weeks each.

Phase 1 Preparation

  • Phase 1 will have a duration of four (4) weeks;
  • TOA mobilises its five (5) Specialist Team;
  • The client designates its Project Team, who reports to the client Project Manager with sufficient authority within the organisation to implement recommendations made by TOA during the project.

Phase 2 Core Team Formation and Prioritizing

  • Phase 2 is a duration of four (4) weeks.
  • TOA’s Specialists and the client’s Project Team form the Core Team. The Core Team reports to the above-mentioned client Project Manager.
  • TOA’s Team Leader will be the main interface with the Project Manager on all matters pertaining to the project.  One member of TOA’s Specialist Team acts as an Interim Team Leader during his absence;
  • The Core Team develops project priorities, an Action Plan and a time table for execution;
  • The emphasis in the Action Plan is on improving operational and maintenance practices and procedures, so as to avoid investment in plant and equipment;
  • The requirements and availability of spares and replacement parts required to perform outstanding “catch-up” maintenance is identified;
  • Practical improvements with a high rate of return and suitable for immediate implementation is executed during Phase 2;
  • At the end of Phase 2, TOA’s Specialists submits a Progress Report, containing the outline of an Action Plan. This is used as a basis for the Action Plan that is presented by the Core Team to the client before the start of the next project phase.

Phase 3 Execution of the Action Plan

  • Phase 3 has a duration of twenty-two (22) weeks;
  • The Core Team executes the Action Plan.  Monthly reviews are made to measure progress and make adjustments to the Action Plan, as required;
  • TOA’s specialists present regular progress reports at the end of each four- or five-week period. This Progress Report outlines project progress and necessary adjustments to the Action Plan. The Progress Report at the end of Phase 3 highlights outstanding issues, to be resolved during Phase 4;
  • TOA’s Specialist Team performs a study into the requirements to attain 4.5 million Tonnes of pellets per year. The resulting list of requirements include the necessary equipment upgrades and a budgetary cost estimate.  The results are presented to Management at the end of Phase 3 in the form of a Preliminary Report. Feedback by the client’s Management is included in a Final Report concerning this issue, to be issued in Phase 4.

Phase 4 Finalization

  • Phase 4 has duration of four (4) weeks.
  • TOA’s specialists submit the final report in the first week of Phase 4.  The final report summarise the requirements and a cost estimate to achieve an annual 4.5 million Tonnes of pellet production.
  • The Core Team compare the actual achievements to the project objectives as stated in  this Proposal;
  •  TOA’s Specialists make a final presentation and deliver a Project Summary at the end of the last Assistance week. The Project Summary highlights the achievements of the past months, and action required for further improvement.

Project Organization
The Project Organization is outlined in Table 1 below:

                                                 Table 1:  Project Manning and Man-weeks on-site


On-site Weeks per Specialist

On Site

One (1) Team Leader



Two (2) Operations/Process Specialists



Two (2) Maintenance Specialists



Total on-site Assistance provided





Productivity tripled in total MTPY in seven (7) years as shown in Figure #2.

                                              Figure #2. Production during seven consecutive year.

Plants that TOA have been involved in have gone to world class levels and daily production has increased significantly. Straight grate Pellet Plant abrasion has reached 4.5% as shown in Figure #3.



                                                             Figure #3. Pellet Physical Quality.