Paper Mill Energy Recovery Systems

The paper production process is energy-intensive, with energy costs accounting for a significant portion of the overall cost of production. Implementing energy recovery systems can help paper mills reduce their energy consumption and lower operating costs. This article will explore the different types of energy recovery systems used in paper mills, their benefits, and some challenges and considerations for implementing these systems.

Types of energy recovery systems

Several types of energy recovery systems are commonly used in paper mills.

Waste heat recovery systems

Waste heat recovery systems are typically used to recover the heat generated by the paper production process and generated steam or hot water. The recovered heat can be used for various purposes, such as heating buildings, providing process heat, or generating electricity.

There are several types of waste heat recovery systems that are commonly used in paper mills, including:

• Conventional Heat Recovery (CHR): air-to-air heat recovery for drying and/or building heating.
• Aquatic Heat Recovery (AHR): air-to-water heat recovery for process water and/or glycol network for building heating.
• Scrubber: air-to-water, usually for process water which may include some impurities. An option to replace AHR heat exchangers. This system has significantly better heat recovery but also removes dirt.

Conventional Heat Recovery (CHR)

Air-to-air heat recovery in paper mills is a process in which the waste heat generated by the mill’s industrial processes is recovered and used to preheat incoming air. This can be done in a number of ways, but the most common method involves the use of a heat exchanger.

The heat exchanger is a device that allows heat to be transferred from one fluid to another without the two fluids coming into direct contact. In the case of a paper mill, the heat exchanger is used to transfer heat from the waste air generated by the mill’s processes to the incoming air that is used to heat the mill’s buildings and dry the paper.

To execute this process, the waste air is first drawn into the heat exchanger by a fan or other mechanical means. The heat exchanger is designed to maximize the surface area between the waste air and the incoming air, allowing for efficient heat transfer. As the waste air passes through the heat exchanger, it gives up its heat to the incoming air, which is then used to heat the mill’s buildings and dry the paper.

This process has a number of benefits for paper mills. It reduces the amount of fuel that the mill needs to burn to heat its buildings and dry the paper, saving energy and money. It also reduces the amount of greenhouse gases and other pollutants that are released into the atmosphere, making it a more environmentally friendly way to operate the mill.

Aquatic Heat Recovery (AHR):

In this system, aheat exchanger is used to transfer heat from the waste air generated by the mill’s industrial processes to water. The waste air is drawn into the heat exchanger by a fan or other mechanical means, and as it passes through the heat exchanger, it gives up its heat to the water. The heated water can then be used for a variety of purposes, such as heating the mill’s buildings, drying the paper, and generating steam for power generation.

To implement this process, the paper mill will need to install the necessary equipment, including the heat exchanger and any associated fans or pumps. The mill may also need to make changes to its industrial processes in order to generate sufficient waste air to feed into the heat exchanger. Once the system is in place, it can be easily integrated into the mill’s existing operations, allowing it to recover a portion of the energy that would otherwise be wasted.

Waste heat recovery systems can be highly effective at improving the energy efficiency of paper mills, with some systems able to recover up to 80% of the energy that would otherwise be lost to the environment. However, these systems can also be expensive to install and require regular maintenance and repair to continue functioning effectively.

Heat exchanger-based energy recovery

Heat exchanger-based energy recovery systems use heat exchangers to transfer the heat from one fluid to another, allowing the recovered heat to be used for a variety of purposes, such as heating buildings or providing process heat. These systems can recover up to 95% of the energy that would otherwise be lost.

Read all about our takes on Predictive Maintenance on Heat Exchangers and more

Benefits of energy recovery systems in paper mills

There are several benefits to implementing energy recovery systems in paper mills.

• Improved energy efficiency can lead to significant cost savings. A study by the National Renewable Energy Laboratory found that a paper mill that implemented a waste heat recovery system saw energy cost savings of up to $500,000 per year.
• However, A medium sized paper machine with a standard heat recovery system could expect to be able to recover about 15MW of energy on average. Which leads to roughly 2.4m€ on annual basis
• Energy recovery systems can also help reduce greenhouse gas emissions by decreasing the amount of energy consumed in the paper production process. For example, a study by the Environmental Defense Fund found that a paper mill that implemented a steam turbine-based energy recovery system reduced its greenhouse gas emissions by 10,000 metric tons per year.
• In addition, these systems can help paper mills to meet environmental regulations and reduce their environmental impact.

Challenges and considerations for implementing energy recovery systems

However, implementing energy recovery systems can also come with some challenges and considerations.

• One of the main challenges is the initial investment cost, which can be significant. For example, installing a waste heat recovery system can cost upwards of $1 million per MW.
• Energy recovery systems require regular maintenance and repair to continue functioning effectively, which can add to the overall cost of ownership. It is important for paper mills to carefully consider the long-term maintenance and repair costs when evaluating the potential return on investment for an energy recovery system.
• Finally, it is essential to carefully consider how energy recovery systems will be integrated with existing paper production processes to ensure that they are effective and efficient. This may require changes to the process flow or the installation of new equipment. Retrofitting a heat recovery system or increasing the capacity of the current system is often limited by the amount of available space.

Case studies of successful implementation of energy recovery systems in paper mills

Several examples in the HeatHamster network have successfully implemented energy recovery systems.

• For example, one mill optimized a waste heat recovery system that captures the heat generated during the paper production process and uses it to generate steam for use in the mill. This system has helped the mill to reduce its energy consumption by 20%, resulting in significant cost savings of up to $500,000 per year.
• Another example is a paper mill, which installed a steam turbine-based energy recovery system that generates electricity from the steam generated during the paper production process. This system has helped the company to reduce its energy consumption by 15% and lower its operating costs.

Conclusion

In conclusion, energy recovery systems are an important tool for improving the energy efficiency of the paper production process. These systems can provide significant benefits such as cost savings, reduced greenhouse gas emissions, and improved environmental performance. However, it is crucial to consider the challenges and considerations associated with implementing these systems, including initial investment costs, maintenance requirements, and integration with existing processes. By considering these factors, paper mills can successfully implement energy recovery systems and improve their energy efficiency.

It is worth noting that the potential benefits of energy recovery systems can vary depending on the specific circumstances of a paper mill. For example, a paper mill with a high level of steam generation may see more significant benefits from a steam turbine-based energy recovery system than a mill with a lower level of steam generation. Similarly, a paper mill with a large heating load may see more significant benefits from a waste heat recovery system than a mill with a smaller heating load. It is important for paper mills to carefully evaluate the specific energy recovery options that are available to determine the most cost-effective and efficient solution for their needs.

Overall, energy recovery systems can play a significant role in improving the paper production process’s energy efficiency and reducing paper mills’ environmental impact. By carefully considering the various options and challenges associated with these systems, paper mills can successfully implement energy recovery systems and realize their benefits.