APC+™: A universal pot control system that addresses the major challenges of an aluminium smelter

Background

Though the industrial production of aluminium in a reduction cell was started in the 1850s, the computer control of reduction cells did not start until the 1960s. There are several systems used today, of which most are supplied as a package by the technology provider. There are, therefore, very few independent pot control providers, including smelter in-house developed systems. There are essentially no systems for pot technologies operating with less than 200 kA.

 Nevertheless, there are challenges that all primary aluminium smelters face that can be attenuated with an effective pot control system. The APC+™ system by MetSol is an effective solution.

The Process Control System

The ADVANCE PROCESS CONTROL PLUS (APC+™) system was developed by MetSol as a solution to three major issues facing the primary aluminium industry today, namely:

1. Power Consumption

Let us keep in mind that primary aluminium production is an energy-intensive process. Large smelters such as Alba have a power load that is about 1/5 of the summer electricity capacity of such States as Massachusetts in the United States. On the other hand, and in general, the energy cost for smelters should be no more than 30 to 35% of the total cost of production. However, with recent increases in the cost of energy, many smelters found themselves above that range, which has forced many of them out of business, particularly in the US and Europe. Hence, the need to reduce power consumption is crucial. With APC+, a lower specific power consumption is achieved.

2. Sustainability and environmental footprint

With perfluorocarbon (PFC) emissions emitted during anode effects, the primary aluminium industry is considered a source of potent Greenhouse gases. Furthermore, with the introduction of the carbon tax or tax on pollution and the introduction of green aluminium, smelters are forced to find ways to manage CO₂ equivalent emissions emanating from their process, not only to remain compliant with environmental regulations but also to remain competitive in a carbon-taxed economy. APC+™ is effective at suppressing anode effects as well as terminating them should they occur. APC+™ efficiently reduces the anode effect overvoltage or duration, resulting in lower PFC or CO₂-equivalent emissions.

3. Productivity

Metal produced by aluminium smelters is sold as a commodity, the price of which has been stagnant for years. One way to overcome this challenge is to increase productivity. With APC+™, one achieves higher current efficiency, thereby increasing metal output.

Fundamental concept

The pot controller by MetSol (APC+™) is a PLC-based system developed to control and optimize voltage,

alumina feed and aluminium fluoride addition into an electrolytic aluminium reduction cell, commonly referred to as a pot. The system uses a proprietary algorithm that processes signals from various sensors and other readings to optimize alumina feeding and pot voltage. The system is also equipped with an HMI touch panel through which the user interacts with the system and uses a dedicated server to process data for the SCADA.

APC+™ operates on a strategy to keep alumina feed holes full of the ore and closed. As a result, alumina is preheated, and volatiles are driven off. This, in turn, allows for the rapid dissolution of alumina when it enters the bath and from the rate of dissolution, the system determines the starting concentration and makes decisions about the next feed event based on the slope of dissolution. Again, this done to make sure there is always sufficient alumina to prevent anode effects while keeping the bottom of the pot clean.

 The APC+™ system uses a standard 847x636x300mm cabinet as shown in Figure 1 below. The cabinet can be mounted on the wall or column near the pot being controlled and is made of polyester material for complete electrical isolation.

APC+™ Pot Controller System – A product of MetSol

The APC+™ pot controller is universal and can be used for any smelter technology:

• Soderberg

• Horizontal Stud
• Vertical Stud

• Prebake:

• Point Feed (PBPF)
• Side Worked (PBSW)
• Centre Worked (PBCW)

In addition to development work conducted at KAP in Montenegro, the APC+™ was tested at several smelters. The development work at KAP was conducted on both PBPF and PBSW. The system is now being implemented on a larger scale at 2 smelters. Below are the results of development work and trials:

Performance

• Development Work Results: KAP PFPB – Old pot technology

• PBSW – Old technology smelter

• PBPF – New technology smelter

Implementation/Deployment

MetSol’s philosophy is to customize the APC+™ system to fit smelter conditions with minimal changes, if any.

This makes the system indeed universal and adaptable. The process of implementing the APC+™ system is described in Figure 2 below:

MetSol Steps to Implementing APC+ as a Customized Solutions

Hence the Deployment of the system is done in 2 phases:

Phase I – Development and Testing

• Conduct trials

• Evaluate the system in terms of:

• Current Efficiency
• Power Consumption
• Anode Effects / PFC emissions

• Finetune system to achieve best performance

Phase II – Large Scale Deployment

• Commissioning APC+ beyond 20 units

• Provide a SCADA system

• Train Personnel

Participating in a trial

MetSol is ready to arrange for a trial at your smelter regardless of age and technology of your potline.