Saving energy with heat pipe exchangers in ceramics

Materials World magazine
,
25 Mar 2019

Heat pipe technology is proven to fuel new low-emission, low-energy, kilns and save money in ceramics. Shardell Joseph reports.

A £5m project in a working factory in Pavullo, Italy, has proven successful as an energy and cost-saving measure by installing heat pipe exchangers.

The Design for Resource and Energy efficiency in cerAMic kilns (the H2020 DREAM project) reported that results showed huge-scale savings on energy, costs and emissions within a six-month observation period – cutting emissions by 20.5t a year and saving £28,000 a year.

The tests in the factory show the heat pipe heat exchanger (HPHE) recycles waste heat 25% more efficiently than conventional heat exchangers. The H2020 DREAM project researchers reported results demonstrating that the companies using this technology should make their money back in savings within two years of installation.

‘We refer to it as return on investment, so any system that we install needs to get the money invested back in less than two years,’ says Brunel University Professor of Thermal Engineering and leader of the H2020 Dream project, Hussam Jouhara. ‘Our return on investment target for this project was two years and it was successful.’

Europe has a huge ceramics industry – making a quarter of global ceramics, £30bln a year, and employing 240,000 people. The energy savings research programme in Europe has grown in importance in recent years, and the European Commission set a target to reduce greenhouse emissions by 80-95% by 2050.

The new heat pipe exchanger is an incentive to demonstrate architecture for ceramic industrial furnaces – characterised by optimised fuel energy consumption, reduced emissions, and lower operating costs.

The heat pipes

The main energy-consuming process is the firing stage, taking up more than 50% of all of the power required for the process, which is then released during cooling. To improve the amount of heat recovered throughout this stage, a development of a radiative heat pipe ceiling has since been explored.

A heat pipe is a structure with very high thermal conductivity enabling the transportation of heat while maintaining almost uniform temperature along its heated and cooled sections. Generally, heat pipes act as passive thermal transfer devices with the capacity to transport large amounts of heat over relatively long distances, using phase-change processes and vapour diffusion.

The main structure of a heat pipe consists of a hermetically sealed tube filled with a small mass of saturated working fluid that exists in liquid and vapour form, occupying the whole of the internal volume of the tube. They are commonly employed as heat recovery devices to reclaim the wasted heat energy from exhaust outlets so it may be further reused or stored.

Nowadays, heat pipe technology is commonly used for cooling electronic equipment, from smartphones to central processing units. However, NASA initially developed them as effective heat sinks – a solution to complex thermal control problems associated with spacecraft, cooling down small-scale electronic equipment in space. They used the technology to transport heat from the hot side to the cold side of the capsule to evenly distribute it and cool the aircraft.

The technology used by NASA was very expensive, requiring a lot of manufacturing skills and complex designs. However, heat pipes were recognised as one of the most efficient passive heat transfer technologies available, popular for their high efficiency.

Since the energy crisis in the 1980s regarding the global instability of the oil market, energy-saving technologies have been created with the incentive to decrease energy consumption and greenhouse gas emissions of major industrial sectors including metals, ceramics and concrete.

But factors such as cost, technology development and areas of application have hindered commercial application of heat pipe technology. Compared with conventional heat transfer methods, such as aluminum extrusions and cast heat sinks, heat pipes can have a higher initial cost – the main reason why heat pipes have not been used where cooling can be performed by simple conductive heat sinks.

The HPHE combats the cost and energy limitations of current heat pipes, while adapting further technological development. Due to the success of the HPHE and the H2020 DREAM project, the team plans on expanding the use of technology across countries and different industries.

‘It's a good example for European countries so we are planning to install it in Spain and other countries after the project is concluded,’ says Jouhara. ‘Now the steel industry is interested, we are installing a [heat exchanger for steel] system next year – as well as another system for a different section of the ceramic industry, which is the spray dryer section.’