EnPot enables opening of the operating window for the pots, allowing heat loss from the pot shell to be regulated and controlled from the sidewall of the cell. This allows stable ledge profile to be maintained under varying load conditions. The amperage can be increased and decreased beyond design limits for extended periods of time (months), allowing smelters to dynamically control operations based on market conditions.
The EnPot technology is based on the precise and controlled flow of air to remove heat from the side of the pot.
To achieve this we use a system of fans and ducting to draw air through the intricately designed heat exchangers (up to 60 per pot). The hot air is then ducted away from the pot into a larger ducting system, where it is removed from potroom and vented externally.
Air based, heat exchanger units are custom designed to fit any cell.
Design is optimised to achieve maximum heat removal from the critical zones when amperage is increased and maximum insulating capability when amperage is decreased.
The process of installation includes.
- Air based, heat exchanger units are custom designed to be retrofitted to any existing pot design including pots with fins, without interrupting production
- Each exchanger design is site specific and custom designed requiring full assessment of pot design, operations and performance as part of the design process
- Can be integrated into new pot designs
- Sidewall coverage is maximised. The more coverage the greater the control over the pots heat balance
- Control of the air flow through the exchangers, controls the heat transfer coefficient (HTC) at the shell wall.
- All EnPot systems are designed to ensure there is no impact on any existing operational practices.
- Use of air as the heat transfer medium ensures ease of installation and operation, whilst eliminating any explosion risks that liquid mediums may pose.
Dr Mark Dorreen, Vice President - Technical, forEnergia Potior Ltd, explains how the EnPot system is installed in smelters.
"After the smelter specific design work has been completed and the heat exchangers are custom manufactured, the physical installation process is relatively straight forward", he says.
"To install the system we build the ducting first, and install the fans. Once this system is operative and the fans are running, we can then install the exchanges, connecting them up to the ducting system immediately. It took as little as 3 hours for 3 men to install all 44 exchangers on a pot at the TRIMET Essen smelter, with each one being operative almost from the moment they are mounted.
"What this means is that not only is there little risk during the installation process, the potline can also remain fully operative during the installation process, Dr. Dorreen says.
Which smelters can be EnPot Converted?
The EnPot system can be retrospectively installed on most existing smelters in the world, including both those with basement and pitside layout, as well as those side by side and end to end potlines.
All that is required is for Energia Potior to make a simple assessment for how the ducting could be arrnaged.
The EnPot system is a non-invasive technology that carries low risk to the smelters. With limited moving parts the system is very robust.
Once the design has been optimised, installed and tested the only likely issues that can arise are blockage to the air flow or non operation of the fans. The primary risk smelter operators would be concerned about is fan failure, i.e what happens if one of the fans removing air away from the pot failed.
Firstly, we build the system in manageable modules (from 3-47 pots) and always build redundancy into the ducting system, with spare/redundant fans that can be easily activated in the case of a primary fan shutting down. This means it would require multiple fans failures to stress the system and this would be contained to a single module.
Secondly, the exchangers themselves would automatically be in insulation mode if the fans fail, and this allows the smelter to turn the amperage down until the system is restored. In a worst case scenario, the specially designed spring loaded mounting systems mean that the heat exchangers themselves could be removed from the pot in a matter of minutes if required.
Blockage to the air flow can only occur through physical obstructions by foreign objects in the air stream. For the location of exchangers in the potroom environment the main concern is dust (alumina or cover material) accumulating at the inlet of the exchanger units. This risk is mitigated by designing the system to ensure the air access area is covered sufficiently to stop dust accumulation.
For previous installations this has simply been achieved through a shield above the exchanger to ensure any falling dust falls away from the area of concern. This simple solution has been implemented at the TRIMET Essen smelter and after more than 15 months of operation there has been no accumulation or blocking problems. The rest of the installation is all enclosed so there is no risk of foreign material blocking the airflow. Blockages can also easily be picked up by monitoring of temperatures and flow rates.
potential to recover heat
The air temperatures exiting the EnPot units range from 120 to 180oC. There is the potential of recovering and re-using this waste heat. A range of options exist for use of the heat recovered from the sidewalls. The end use however of the recovered heat will be based on a number of factors including:
- the nature of the energy consumer
- the tolerance of the energy consumer to contaminants and
- the optimum temperature of the hot gases supplying the energy consumer
Options for use of the collected energy include at least:
- Binary cycle power generation, either via ORC (Organic Rankine Cycle) or the Kalina cycle
- Water desalination
- Alumina or anode pre-heating
- Pre-heating green anodes in the carbon baking furnace (CBF)
- Teleheating (District heating)