Italian manufacturer Turboden has developed large heat pumps that use isobutane (R600a) and isopentane (R601a) in combination with a mechanical steam compressor to reach high temperatures suitable for the energy-intensive pulp and paper industry. 

“We have a project with a thermal output of 12MW [3412.1TR] located in Northern Europe that is capable of delivering superheated steam at 3.5bar [50.8psi] that reaches temperatures of up to 170°C [338°F],” said Emanuele Pingaro, Turboden’s Sales and Business Development Manager. 

Pingaro shared the details of Turboden’s work in the pulp and paper industry, which struggles to decarbonize due to the high temperatures required for production, in a presentation at the European Heat Pump Summit, held in Nuremberg, Germany, from October 24–25. He presented a case study that exemplified the integration of large-scale heat pumps and a mechanical vapor recompression (MVR) steam compressor. 

Based in Brescia, Italy, Turboden, a division of Japanese manufacturer Mitsubishi Heavy Industries Group, is a manufacturer of Organic Rankin Cycle (ORC) systems as well as gas expanders and heat pumps. 

“Delving into technicalities, Turboden’s heat pumps were tailored to meet stringent conditions,” said Pingaro. “Using working fluids like isobutane and isopentane, and an advanced heat exchanger design, we managed to efficiently use low-grade heat sources and wastewater from the paper mill,” he said. 

Pingaro added that those heat sources had temperatures as low as 8°C (46.4°F). 

“With our technology, we managed to achieve a temperature lift of approximately 160°C (320°F),” said Pingaro. 

To deliver heat steam to 170°C (338°F), Turboden paired large heat pumps with an MVR steam compressor.  

“In this case, the large heat pumps initially raise the water temperature to an intermediate level, 114°C (237.2°F) at 1.5bar [21.7psi] of absolute pressure,” said Pingaro. “The steam compressor further escalates the steam to our target of 170°C (338°F) at 3.5bar absolute pressure.”  

The heat source for the large heat pumps is humid air and wastewater from a paper mill, which is integrated into a single chiller water circuit that usually ranges from 7°C (44.6°F) to 12°C (53.6°F) 

Pingaro highlighted that Turboden’s  experience with hydrocarbons in ORC systems spans over 45 units across 20 countries, prevents leakage and complies with ATEX and EN378. 

Refrigerant selection a key factor 

During his talk, Pingaro touched on the numerous considerations that go into choosing a refrigerant. 

“It depends on several factors, including the minimum evaporation temperature at atmospheric pressure and maximum condensation temperature,” said Pingaro. “This selection ensures that the refrigerant is efficient in terms of thermal properties, safe and compliant with environmental standards.” 

Pingaro further elaborated on why isobutane was chosen for this application — and why an MVR steam compressor was also needed.“Isobutane can evaporate around 0°C (32°F), making it suitable for the paper and pulp industry,” said Pingaro. “But isobutane has a critical point 132°C (269.6°F), making it unable to deliver our target temperature of 170°C (338°F). That is why integrating large isobutane heat pumps with steam compressors was necessary.” 

Pingaro shared that the steam compressors came from the Mitsubishi Group and stressed that Turboden is developing these compressors now.

“We have a project with a thermal output of 12MW [3412.1TR] located in Northern Europe that is capable of delivering superheated steam at 3.5bar [50.8psi] that reaches temperatures of up to 170°C [338°F].”

Emanuele Pingaro, Turboden Sales and Business Development Manager

Author Saroj Thapa