Liquid-cooled drives: turning a new page for pulp and paper

Paper machine at a Stora Enso mill. Photo: ABB

Jarkko L. Mattila, and Roger Ekstrom, Global Product Managers, ABB System Drives explain why liquid-cooled drives are the ideal solution for challenging pulp and paper environments.

The pulp and paper industry has long used variable speed drives (VSDs) to achieve greater energy efficiency and precise motor control. However, some places within a mill present challenges for air-cooled VSDs.

In some cases, especially in older mills, dust regularly clogs the air intakes, or corrosive gas damages them. In others, the heat given off by the drive during operation is undesirable.  Meanwhile, the larger footprint of an air-cooled VSD may be an issue for facilities with limited floorspace.

Additionally, many old paper machines are refurbished or converted in order to produce board, while also upgrading the production capacity. These improvements must be implemented within the existing footprint of the drive line-up, without requiring significant changes or expansion to the physical space occupied by the machinery.

In these use cases, liquid-cooled drives present a solution. They have already been adopted successfully in many other sectors, such as maritime and oil and gas, where corrosive, dirty and hot environments are unavoidable. Due to their multiple benefits, liquid-cooled drives are increasingly common in the pulp and paper sector, especially in Europe, enabling facilities to maximize uptime and production while lowering their operational costs.

How does liquid cooling work?

All industrial machinery, including drives, generates heat as it operates. This heat needs to be removed – such as by circulating air using a fan and cooling it using an air conditioning system – or it could damage the equipment. Overheating can result in potentially expensive downtime.

Liquid cooling is a more effective way to keep equipment cool. Air has a relatively low heat capacity and is worse at transferring heat when compared with liquids. ABB’s liquid-cooled drives use a commercial coolant called Antifrogen® L. The solution recommended by ABB has a thermal conductivity 18 times greater than air, enabling liquid-cooled drives to continue functioning in ambient temperatures as high as 55°C.

A typical liquid-cooled drive uses two cooling circuits. The first carries heat away from the hot components and passes it to the primary heat exchanger. Within the heat exchanger, the heat is transferred to the secondary cooling circuit. This circuit then takes the heat to be exhausted through an external heat exchanger.

Alternatively, this heat can be captured and put to work in process heating, warming fluid for pulping, or even district heating. Reusing this heat reduces the facility’s total energy consumption.

This process is more energy efficient than air cooling, resulting in lower emissions and operating expenditure (OpEx). It is also highly effective: liquid cooling can dissipate up to 98 percent of a drive’s heat losses. This also results in lower capital expenditure (CapEx) and additional energy savings, as air conditioning and cooling are no longer necessary.

Smaller, more cost effective, and dust-proof

Liquid-cooled drives have a range of advantages that make them ideal for use in demanding pulp and paper applications.

Firstly, they have a significantly smaller footprint than air-cooled drives. This is very beneficial in retrofits where the power need of the paper, board, or tissue machine increases – such as to deal with wider material – and more powerful drives need to be installed in same e-room.

In addition to their smaller footprint, liquid-cooled drives also perform better than air-cooled drives. They can support motors operating at heavier loads, enabling mills to increase throughput.

Air-cooled drives require more maintenance in applications where dust is present – including paper and tissue dust. To prevent the filters from becoming blocked, they must be changed frequently. Failure to do so can result in the drive overheating.

ABB’s ACS880 liquid-cooled drives, in comparison, function without issue even in highly dusty environments. Liquid-cooled drives are also unaffected by humidity and other air quality issues. ABB’s ACS880LC liquid-cooled drives are installed  into  totally enclosed  cabinets and come with IP42 ingress protection (IP) as standard, with an optional upgrade to IP54.  

Maintenance and diagnostics benefits

Liquid-cooled drives use a variety of sensors to continually monitor their condition and adjust their performance. In addition to maintaining a consistent temperature, this enables the system to automatically identify hot spots that may indicate a malfunction and alert an operator.

Modern designs benefit from advanced diagnostics and a thermal model for faster-acting IGBT protection. As a result, system failure and downtime are made less likely, while operator safety increases.

Liquid-cooled drives are also designed for ease of maintenance. The coolant pipes can remain connected for many maintenance processes, saving time and reducing the risk of coolant contamination. The system also uses quick connectors for motor connections, eliminating the need to disconnect cabling.

Further, the same modules can serve all four typical functions (including as an IGBT supply unit (ISU), inverter unit (INU), dynamic brake unit (DBU) and DC/DC-converter (DDC). This means that a spare module can serve any required function, enabling operators to optimize their spare parts inventory.

A cool future for paper and pulp

Liquid-cooled drives offer significant CapEx savings because the e-room can be smaller and there is no need for air conditioning equipment. At the same time, their energy efficiency results in ongoing OpEx savings. They also significantly reduce the need for air conditioning overall, resulting in additional OpEx savings due to reduced energy consumption and CO2 emissions fees.

These advantages of liquid-cooled drives – including more processing power within a given footprint, the ability to reuse waste heat, greater energy efficiency, and being dust-proof – mean that they are ideally suited for the most demanding applications in the pulp and paper industry.

Learn more about liquid-cooled drives: