DRIPax™ – MIDREX® Plant Process Optimization System: Status Report of the New Generation Technology

EDITOR’S NOTE:
This article details an integrated process optimization system for MIDREX® Direct Reduction Plants designed by Primetals Technologies (formerly Siemens VAI) and Midrex Technologies, Inc. to aid in plant state evaluation as well as prediction of product carbon content and metallization. The enhanced system is marketed under the name of DRIpax™ to new and existing MIDREX Plants.

INTRODUCTION

The goal of DRI plant process optimization is to provide smooth and stable operation plus high performance. One of the challenges is to cope with the delay of several hours between a process change and the resulting actual product analysis available from the laboratory.

DRIpax™ is not just a new name for the DRI modeling system, it is a new and improved method for direct reduction plant process optimization. It offers product quality prediction models based on first principle calculations, while incorporating the lessons learned from the neural networks based predecessor SIMPAX.

The development of DRIpax was a joint effort between Midrex and Primetals Technologies. The capabilities of both partners were brought to bear, including MIDREX® Direct Reduction Technology, operational know-how, automation competence, information technology, and physical / mathematical models.

DRIPAX™ ARCHITECTURE

DRIpax™ is structured into three modular system layers: the Process Information & Data Management System, the DRI Plant Process Models, and the DRI Plant Expert System, as shown in Figure 1. The Carbon and Metallization Prediction Models are the key to the benefits of DRIpax. The ability to predict the metallization and carbon levels enables better control of DRI consistency. This is achieved through the ability of DRIpax to take into account the MIDREX® Superdata results and inputs from the lab to predict what the met and carbon will be based on the current operation of the plant. DRIpax’s predictive ability can help plant operators avoid off-spec DRI by enabling them to diagnose problems earlier. This helps produce a more consistent DRI quality.

MIDREX® SUPERDATA MODEL

The MIDREX® Superdata model has been painstakingly developed through the processing of data from various MIDREX® Plants over decades of operation in a variety of situations and locations. It runs cyclically and performs mass and energy calculations using online measurements, feed materials and product analyses. Calculations are carried out to provide further useful information to the operators, especially data concerning the quality of the different gas streams and operation of the MIDREX® Shaft Furnace and MIDREX® Reformer. It can be used to monitor and assess reduction furnace utilization, bustle gas quality and flows, DRI production rate, reformer performance, combustion air requirements, flue gas flows and analyses, and heat recovery performance.

The Superdata Model is fully integrated into DRIpax, enabling DRIpax to provide:

• Scheduling of the model calculations
• Collection and preparation of the model input data
• Display of model result data integrated in the HMI 
• Report viewer to open the model reports 
• Display of calculation log data

In contrast to a standalone installation of the MIDREX® Superdata Model, the benefits of this full integration include time savings to operating personnel and avoidance of common errors, since no manual input is required to execute the calculations.

METALLIZATION AND CARBON PREDICTION MODELS

The system uses a modular design to predict DRI metallization and carbon content. This benefits the plant by reducing the amount of off-spec product that could be made from the time a process change is made to the time feedback on the DRI is measured by the lab. Having this model installed will provide a benefit across operators, by providing a consistent measure that can help smooth out operations.

Within the MIDREX® Shaft Furnace, the retention time in the Reduction Zone depends on the production rate and material bulk density. The DRI then passes through the Transition Zone and the Cooling Zone (CDRI) or hot lower cone (HBI/HDRI) before it leaves the shaft furnace and a product analysis can be taken. After the sample is taken, it is sent to the laboratory to be analyzed. As a consequence of the time lags created by these events, the operator is informed of the DRI analysis several hours after it was discharged (and even longer since it was actually made at the bustle or transition zone of the furnace).

Oxide reduction and carbon addition are essentially completed when the DRI leaves the Reduction Zone. DRIpax utilizes plant data, previously sampled product analyses, user inputs, and trend analysis to calculate a predicted product quality as oxide enters the process. The result is a predictable and consistent quality DRI product. In addition, the plant operator will typically not change process set points based on only one sample result. Often there are requests for additional laboratory samples to provide more data to eliminate or reduce the possibility of laboratory error. This can further delay any corrective action that an operator may wish to take to alleviate any product quality deviations.

DRIpax Metallization and Carbon Prediction Models bridge this delay by calculating the metallization and carbon content based on process measurements and raw material quality parameters. The operators can then adjust process parameters based on metallization/carbon forecasts to achieve a more consistent DRI quality. The product quality prediction is based on model calculations from current information and tracked trends, and has been proven in use at Qatar Steel Module II, a 1.5 million ton per year MIDREX® Plant. The plant target metallization and carbon levels were 94.5% and 2.3% respectively. Figure 2 shows the tight tolerances obtained using DRIpax. The standard deviation of carbon content was reduced 31% and metallization 27%.

MATERIAL TRACKING

Iron oxide and the produced DRI can be tracked through the reduction furnace by using feed material and product properties, feed and discharge rates, technological knowledge about the changes in the material properties during the reduction process, and other data.

Knowing the position of material in the reduction furnace is essential for the process data in the mass and energy balance equations. For each new product analysis, DRI is backtracked in order to find out when the reduction was essentially finished. The respective predicted values at this time are displayed together with the measured analysis data. Trends of measured and predicted values indicate the accuracy of both – the models as well as the laboratory results. Deviations in the results are compared with process target values set for plant operation and help operators make better operational decisions.

PROCESS INFORMATION MANAGEMENT SYSTEM

DRIpax is a package unit configured to be easily integrated into an existing or new basic automation system of a MIDREX® Plant. The system is configured using state-of-the-art technology with regard to both hardware and software platforms, as well as advanced process modeling technology.

The system consists of a Server-Client Architecture with a link to an arbitrary process control system via the worldwide standardized communication interface. This ability allows the Licensee complete control to provide access to the system in other areas of the plant or remote viewing.

DRIpax provides a communication interface to other platforms such as SAP/MES systems as well as to the laboratory information management system. A link to the laboratory has the benefit that all material analyses are read automatically, checked for plausibility and used immediately in the model calculations. In addition, the received analyses are displayed in a Human Machine Interface (HMI) and can be added into certain reports as well. The HMI covers data visualization and data management functions like trending tools, process data visualization, material and analysis management, log/alarm display, user management etc. Figure 3 shows typical screens.

DRIpax™ uses Vaironment as its operating platform for the process optimization system. Vaironment system is also used by Primetals Technologies for other process optimization systems in the field of iron and steelmaking.

The data is visualized graphically using advanced techniques for user machine interfaces. Microsoft Office Products can be connected to the process optimization system to perform studies, evaluations and presentations of the MIDREX DRI Plant data. The Primetals’s Process Explorer HMI is the backbone of the Human Machine Interface acting as a container for all provided applications of the process optimization system. Reports can be generated cyclically, e.g. every shift, daily, monthly or on de mand using a flexible reporting system based on Microsoft Excel.

The full functionality of Microsoft Excel can be exploited to generate and easily modify reports.

DRIPAX APPLICATION AND DOWNSTREAM BENEFITS

DRIpax can be utilized in new or existing MIDREX Plants and the system’s flexibility enables it to be easily adjusted to various plant configurations.

Meltshops will also benefit from DRIpax. Having a tighter tolerance and more consistent DRI feed, an EAF should expect to see reduced electricity and refractory consumptions, reduced tap-to-tap time and an increase in yield and productivity.

NEXT STEPS

The MIDREX Superdata Model and the Quality Prediction Models evaluate the state of the process and the expected product quality. In case of undesired process conditions or product quality it is the operator’s duty to perform corrective actions.

Primetals Technologies has many years of experience with closed-loop expert systems for blast furnaces and sinter plants. The basic idea of these expert systems is an evaluation of the actual state and the generation of corrective actions to alleviate the undesired conditions. The knowledge base of these expert systems consists of operational rules and knowledge of metallurgical experts.

The next step in the development of DRIpax is the implementation of an Expert System for MIDREX Plants for the shaft furnace and the reformer areas. Midrex is contributing the process and operation know-how and Primetals Technologies is creating the knowledge base for the existing Expert System shell. The DRIpax Expert System will provide closed-loop and semi-automatic operation mode; in semi-automatic mode, suggestions made by the expert system will be executed only after acceptance by the operator. In closed-loop mode, operator acceptance is not required for the execution of corrective actions – however he can still reject corrective actions, keeping the human factor in the plant. Figure 4 shows the system configuration.

The knowledge base of the DRIpax Expert System is principally defined by MIDREX specialists. Nevertheless, special operational rules and control philosophy of the individual customers will also be included in the knowledge base. In this sense, each customer will get a tailored expert system perfectly fitting to his needs.

With the introduction of the DRIpax Expert System a first powerful step will be taken in the direction of fully automated quality control and equipment protection. The application of an expert system helps to foster uniform operator decisions over all shifts and early detection of undesired process conditions resulting in small corrective actions that have a positive impact on the overall plant performance and efficiency.

DRIpax™ Expert will be launched for the first time at the voestalpine Texas MIDREX Plant that will start up in the second half of 2016 in Corpus Christi, Texas, USA.

THE POSSIBILITIES OF DRIPAX™

The future of efficiency in MIDREX Plants is DRIpax. Bringing consistent, controllable product quality to the operation, DRIpax is a tool for operators and managers to improve what they do best, running their MIDREX Plant. The benefits of carbon and metallization prediction bring consistency across operators with different experience levels, across shift changes, and the benefits carry throughout the complex and downstream to the meltshop. Qatar Steel, working with Midrex and Primetals Technologies has enhanced the system and is now enjoying its benefits. Available in new plants and as an upgrade to existing plants, DRIpax is advancing the state-of-the-art in process optimization.