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Waste Heat Recovery in Industrial Drying Processes

Periodic Reporting for period 3 - DryFiciency (Waste Heat Recovery in Industrial Drying Processes)

Reporting period: 2019-11-01 to 2021-08-31

The industrial sector accounts for 25% of the total final energy consumption in EU-27, of which 12% to 25 % is attributable to industrial drying. Drying and dehydration processes are currently primarily fossil-fired, generating large volumes of low grade waste heat that are not or only minimally utilized. Hence, industrial drying offers large potential for improved energy efficiency, reduction of fossil carbon emissions, and increased competitiveness by introducing advanced energy efficiency technologies.

The overall objective of the DryFiciency project was to lead the European energy intensive industry to high energy efficiency and a reduction of fossil carbon emissions by means of waste heat recovery and its valorisation by making use of high temperature heat pump technologies. The consortium elaborated techno-economic solutions for upgrading idle waste heat streams into process heat supply at temperature levels up to 160 °C. The key elements were three advanced high temperature vapor compression heat pumps: two closed loop heat pumps for air drying processes, and an open loop heat pump for steam driven drying processes.

The DryFiciency demonstrations have shown for the first-time in industrial settings at TRL7 that high temperature heat pumps reliably work up to 160°C. Further pilot installations in other sectors/applications are required to establish additional trust through reliable operation and scientific monitoring. In a next step, the technologies need to be scaled up to larger working installations. Capacities for large-scale production and integration need to be set-up to cater for the demand on industrial heat pumps projected.
Parameters of drying processes were determined, schematic integration schemes were developed, and boundary conditions/capacities for integration were defined. 5 KPIs allowing the demonstrators’ evaluation were elaborated. In parallel, key components were developed. For the closed loop, a novel lubrication oil, working well with refrigerant selected at temperature up to 160°C, was developed. More than 20 samples had to be analysed. A screw compressor was adapted for HT application. 40 parts were replaced, omitted, or left in place. A piston compressor was tested with different lubrication oils. 8 piston and 4 screw compressors were built/tested. For the open loop, an electric, oil-free steam turbo compressor designed to allow temperature lifts of up to 50K in a two-stage vapor compression cycle was developed. 2 prototypes were built, tested, and integrated in the open loop HP. Designs of main components of HP cycles were simulated for most efficient/reliable operations. For the closed loop, 4 cycle configurations were analyzed in-depth. Two HP prototypes were built. In case of the open loop, the HP system was designed, constructed, and installed at a test rig to be tested extensively using different turbo compressor models. Simulated compressor maps were produced successfully before sending the system for installation. Final demonstrator layouts were worked out in accordance with quality/safety standards. Space and infrastructural requirements were evaluated. Operational schedules and control strategies were elaborated and implemented. Components, services, and infrastructural facilities for HP integration were sourced and installed. For the open loop, adapted batch dryers were designed, built, and integrated. Start-up and trial operations were conducted according predefined operating conditions to test HP functionalities. Closed loop HPs passed commissioning. For the open loop, only dryers were fully commissioned. 2 HTHPs were fully operated first-time in industrial setting at TRL7 and analysed in terms of performance/improvement potential. Data acquisition systems were set-up including reporting with interactive data visualization. Maintenance/adjustment work was conducted. Measures to improve on efficiency were worked implemented. Measured data was validated in terms of KPIs defined at project start.

Core results include three advanced HTHP solutions for upgrading idle waste heat streams to process streams of up to 160°C (closed) resp. 155°C (open loop) in industrial drying processes. Each of the closed loop demonstrators used for air drying was operated for more than 4,000 hours. Both showed end-energy and carbon emission savings of up to 80%. Open loop dryer has shown improved efficiency and capacity of more than 75%. Additional operational hours will be used to further optimize and validate the systems.

Follow-up research and innovation projects geared at decreasing ROI, further improving performance, and implementing HTHPs in other applications and sectors including a.o. food, chemical or wood processing have started already respectively will be further pursued including DryFiciency partners but also new ones. In order to increase competence on industrial HP technologies and overcome obstacles for broad application 4 DryF online seminars, a DryF final conference, and DryF online training program (+100 trainees) were developed and implemented. Event recordings, presentations, and videos on three demonstrators were made accessible on YouTube and the projects’ website. Besides, the project and selected results were presented at more than 25 conferences/WS and in 10 conference publications with more results to be published post-project.
The DryFiciency heat pump demonstrators are first-of-their-kind operated in industrial settings for waste heat upgrade of up to 160°C (closed loop) resp. 155°C (open loop). Several innovations were achieved on component and system level.

Closed loop heat pump technologies
• Fine-tuned, synthetic lubricant for high temperature applications working stable with novel, non-flammable, non-toxic refrigerant with a minimum global warming potential.
• Adapted screw/piston compressor technologies, working well with lubricant-refrigerant mixture selected at temperature levels up to 160°C.
• Novel system concepts/configurations successfully validated up to 160°C for closed loop heat pump installations (> 4.000 operation hours each; max. heat output of 375kW; COP of 2-5 at varying source temperatures).
• Training program tested with more than 100 trainees.

Open loop heat pump system
• Advanced, low-cost, oil-free turbo compressor prototype based on newly developed and patented step-up technology.
• Novel, highly efficient MVR dryer technology with a 75% increase in efficiency, while reducing energy consumption by 70%.
• System concept and configuration of an open loop heat pump system successfully tested under lab conditions up to discharge temperatures of 155°C; at a temperature lift up to 45K, in a two-stage compression with a COP of >4.
The solutions developed have the potential to cover the full range of industrial drying processes. With heat supply temperatures of up to 160°C, they are replicable in many sectors, such as chemicals, food, minerals, or the paper industry.

Socio-economic impact and wider societal implications
Besides being a competitive advantage, the use of refrigerants with no respectively low global warming potential, limits the risk of environmental harm and health problems induced by them. The project positively impacted on the set of skills, knowledge, understanding and ultimately the employability of a number of stakeholders, and created large awareness on industrial heat pump technologies, their potential, and benefits.
DryF Logo
DryF open loop MVR system
DryF demonstrator at Wienerberger
DryF WBG demo-event
DryF demonstrator at Agrana