Cycles RA3

Cycles' objective is to improve cycles for converting heat-surplus to power, heat pumping cycles and energy storage. Vapour compression and expansion cycles, refrigeration and drying with energy recovery are main focuses alongside intelligent energy storage on a system level. Intelligent energy storage will enable large improvements within energy efficiency.

Cycles targets high capacity applications to maximise its impact on the energy consumption in Norwegian industry.

Potential innovations:

  • Competitive low and medium temperature power cycle concepts with cross-sectorial applicability
  • High-efficient HTHP cycle concepts for upgrading surplus heat to steam, displacing fossil fuel use
  • Integrated refrigeration units able to provide simultaneous heating/cooling/freezing/AC
  • Lightweight bottoming cycle & heat exchanger technology improving offshore/marine energy efficiency
  • New, enhanced technology concepts for large scale energy storage, crucial in future energy grids

Cycles consists of the following Work Packages (WP)

RA3 Cycles Trond Andresen SINTEF Energy Research
WP3.1 Energy-to-power conversion Trond Andresen SINTEF Energy Research
WP3.2 HTHP, cooling, and drying Michael Bantle SINTEF Energy Research
WP3.3 Energy storage Hanne Kauko SINTEF Energy Research

2019 Results

Energy-to-power conversion

The energy recovery system at a silicon smelting plant has been analysed using a new dynamic model developed in HighEFF. Furnace off-gas energy recovery systems are subject to rapid changes in thermal load which is challenging with respect to both equipment safety and energy efficiency. The new model was applied to identify a new control strategy that can simultaneously boost electricity generation and improve thermal stability in the off-gas system. The model was developed and validated using data and measurements from the actual system.

Energy recovery concepts for practical energy recovery from metal casting have been evaluated. The thermal energy contained in the liquid metal in ferroalloy production makes it an interesting heat source for energy recovery. The starting temperature is typically in the range of 1500 °C which gives great potential for heat-to-power conversion. This heat is released during casting as the metal solidifies, but not utilized today. There are also some safety and environmental concerns related to common processes for Ferroalloy casting today. An initial new-concept evaluation that included a heat capture structure, thermal storage and power conversion was completed with promising results. A successful technical solution will not only improve the plant's energy efficiency, but also enable significant reductions in dust emissions and improved safety.

High temperature heat pumps, cooling and drying

Upgrading industrial waste heat with high temperature heat pumps (HTHP) is a popular alternative for many industries. However, there are limits in both supply temperature and availability. For now, the industry standards can deliver supply temperatures of around 90 °C, while ongoing research projects and a few smaller heat pump companies can deliver supply temperatures up to 160 °C

Last year, two promising concepts for higher supply temperatures were analysed in depth. The investigated concepts were a 3-stage turbo compressors system using water as refrigerant, and a reversed Brayton cycle using CO2 as refrigerant. The systems were found technically and economically feasible solutions for process heat supply of up to 280 °C. These solutions are using large-scale equipment from oil and gas industries for applications in energy-intensive industries.

A pair of newly developed oil-free turbo compressors being tested at SINTEF Energy Lab.

The suggested systems benefitted from the economy of scale and access to low electricity prices. The concepts outperformed a biogas-based solution, and they were competitive with biomass or natural gas systems with respect to economic performance. It was concluded that an electricity-based heat supply is possible for a wide range of industrial applications and accordingly represents an important contribution to fulfilling the objectives of lower climate impact of energy supply in industry. The results were published in the journal "Energy Conversion and Management."

In addition, an international conference on high temperature heat pumps in Copenhagen was organized by SINTEF and approximately 100 delegates from 13 different countries were present to discuss the most recent developments.

Shanghai Jiao Tong University experimentally investigated the performance of a 280 kW high temperature heat pump with water as refrigerant using a single stage screw compressor prototype.

Water is an excellent refrigerant for high temperature heat pumps because of the high critical temperature which theoretically enables condensation up to 373 °C. However, water requires a high evaporating temperature, around 70°C or more, because of the low steam density at low temperatures. The heat pump from Shanghai Jiao Tong University demonstrated a saturated temperature increase of 65 °C, and a maximum heat supply of 150 °C. The results were published in the prestigious journal "Energy".

Energy storage

Different thermal energy storage (TES) concepts suited for storing steam in industrial applications have been evaluated, with focus on four technologies: steam accumulator, latent heat storage, molten salt storage, and concrete storage. Industrial steam demand is enormous, and most of the demand worldwide is still covered by fossil fuels. Utilizing TES in combination with concentrated solar power or power-to-heat technologies (electric boiler or high-temperature heat pumps) opens up the possibility for steam production based on renewables, thus cutting emissions related to steam production. While a steam accumulator is currently the only off-the-shelf technology available for storing steam, it is only suitable for storage on very short time scales, and alternative technologies are required to facilitate the green shift in industrial steam production.

Investigated concept for energy recovery from metal casting.

In addition to such short-term, high-temperature TES systems, a study on the technologies suited for seasonal storage of industrial waste heat has been carried out. Vast amounts of industrial waste heat is dumped into the fjords especially in the summer. Seasonal thermal storage may result in this heat being available for use in the winter. The outlet temperatures available from such storages are however moderate.

At the low-temperature end, PhD candidate Håkon Selvnes (NTNU) has continued his work on developing a novel cold TES technology based on phase change materials (PCM) for applications in the food industry. The construction of a prototype unit in the SINTEF/ NTNU laboratory at Gløshaugen was completed in mid-July, and tests have been carried out since August. This cold TES technology will potentially be implemented at a large poultry processing plant being under construction in Orkanger. The plant has a large and varying cooling demand and integrating cold TES in the refrigeration system may enable load shifting and a reduction in the required cooling system capacity by up to 20%, thus reducing both operational and investment costs.

2018 Results

Energy-to-power conversion

A new methodology for design/off-design semi-steady state analysis of power production over variable heat source and -sink conditions was developed and demonstrated  in a potential study on utilizing available surplus low-pressure steam at Mo Industripark. In addition to optimizing power output, the new methodology evaluated optimal distribution of heat exchanger sizes in the system using a novel "generic heat exchanger model" (GHX). HighEFF partner Alfa Laval contributed  withperformance data from their commercial heat exchangers to allow for a validation of the model; and the resulting comparison of heat transfer areas for the same design specifications matched very well.

Development of thermo-electric generation systems for industrial surplus heat conversion resulted in a preliminary concept design of a redundant 480 W (24 V) TEG system including electrical architecture. Work in 2019 will target source/sink heat exchangers and fouling aspects, as well as evaluating impact potential for a selected industrial application.

High temperature heat pumps, cooling and drying

A heat pump for combined delivery of ice-water (0-4°C) and hot water (100-110 °C) was verified in a 20 kW demo unit in cooperation with HighEFFlab and HeatUp project. The compressor
prototypes were delivered by HighEFF partner Dorin Innovations (through RA2). A concept for a closed loop heat pump system, based on turbo-compressors, was evaluated with focus on more compact de-superheating in order to reduce the system size. This activity will be followed up by experimental investigations in the next years. Additionally, the so-called reversed Brayton Cycle was investigated; which has promising results for heat delivery of up to 500°C.

The advantages of R744 for process chilling was moutlined and compared with state of the art freezing/chilling systems. Such systems show high potential mfor increased productivity due to the mincrease heat removal.

Energy storage

2018 activities were focused on two tasks: 1 evaluation of thermal energy storage (TES) potential for industry clusters to reduce the use of peak heating; and 2 mapping processes within the industries represented in HighEFF that are suitable for, and that could benefit from, the application of high-temperature TES.

The first task was carried out as a case study towards Mo Industry park, and the work will be continued during 2019. The most promising cases from task (2) will be investigated further with in 2019. PhD candidate Håkon Selvnes continued his work on a novel cold thermal energy storage (CTES) related to a mfood processing factory. A pilot CTES unit was delivered  to the VATL laboratory at Gløshaugen by the local supplier Skala at the end of 2018, and the unit will be tested during 2019.

Trond Andresen

Senior Research Scientist
Name
Trond Andresen
Title
Senior Research Scientist
Phone
915 74 380
Department
Gas Technology
Office
Trondheim
Company
SINTEF Energi AS