Themes

In a lot of thermal processes arising waste heat can’t be recovered for immediate reuse but few moments later, process heat on the same or a lower temperature level could be used. A typical example occurs in the ceramic industry. Heat from the kiln is used for clay drying but many times there is a time gap between these two processes.

A process can need a constant thermal input while the power level of an adapted waste heat stream is fluctuating above and below that level or is even often interrupted.

A typical example where huge high temperature thermal storage is used are Concentrating Solar Power stations (CSP) to get them producing electricity also at night.

By storing coldness it could be avoided to cause short but high power demands to the grid by cooling machines when high cooling loads are applied, for instance by filling a cold store with fresh products.

In HVAC as well as in cold stores, it can also be applied to shift electricity consumption to lower price periods.

During the seminar, you will learn about the status for industrial use by means of research results, outcome of case studies and references brought by some manufacturers. A lab scale demo can be visited and will be explained and demonstrated. It concerns a 150 kWh PCM based storage with melting temperature of 222°C. Also a software tool to design thermal processes including thermal storage will be demonstrated.

This seminar is also meant as a final dissemination activity within the frame of the CORNET-project “Short term heat or cold storage in industry (Shortstore)”

Project partners are:

UGentTEI   research group (coordinator)
 
VITO   Flemish research organization on cleantech and sustainable development
 
DLR   German Aerospace Center
 
IZF   The Brick and Tile Research Institute, Germany
 
GFAI   Society for the Advancement of Applied Computer Science, Germany
 

Research frame: CORNET with project partners in Belgium (Flanders) and Germany, also funded by the Flemish (VLAIO) and German (AiF) governments.

To allow the increase of share of renewable electricity generation, more flexibility on the demand side is required.

One of the possibilities is to convert electricity into heat for direct use or to store during over supply of (renewable) electricity. During shortage, electricity could be generated out of the stored heat again. The round trip efficiency is an important quality parameter.

Together with CORNET partner DLR, UGent is involved in the H2020 project called “CHESTER”, meaning “Compressed Heat Energy Storage for Energy from Renewable sources”, currently running (01/04/2018 to 31/03/2022).

The concept contains two heat storage buffers at different temperatures. The lower one (stratified 40-90°C) can be fed by waste heat, thermal solar panels, geothermal heat (if present) etc… When excess renewable electricity is available, a heat pump will be applied to upgrade heat (80-90°C) to the temperature level of the high temperature storage (130-180°C). When shortage occurs, electricity will be generated out of the high temperature storage by means of an ORC (Organic Rankine Cycle). Because of a lower condenser temperature (~40°C) compared to the heat source temperature of the heat pump, part of the cycle losses could be covered.

During the conference first results will be presented.

By using cogeneration, also called Combined Heat and Power (CHP) installations major part of the waste heat appearing on classical thermal power stations can be recovered and used for heating applications or industrial process heat. By doing so, compared with equal amounts of electricity and heat, generated on the classical way, 20-30% of primary energy savings with corresponding CO2-emission reduction can be obtained.

However, the hard link between electricity and heat generation with a fixed ratio prevents flexible operation. If the heat demand is fluctuating, the CHP only can deliver part of it if it is dimensioned to the average demand or part load operation with reduced efficiency and economic return will occur.

On the other hand, also the value of the generated electricity can be very variable, for instance very low or even negative during periods of high production by renewables and low demand. In many cases CHP-exploiters cannot make use of this situation because the CHP must keep working because of the heat demand.

By integrating Thermal Energy Storage (TES), a CHP will become much more flexible also meet the requirements for optimal operation in the current energy markets. Even existing CHPs could be adapted this way.

For storage temperatures below 100°C water buffer tanks are a proven solution. No technological research is needed for that. But as this solution is often used on the smaller engine based CHPs, a lot of exploiters are still buying electricity against fixed contract prices.

Above 100°C mostly steam producing gas turbine based CHPs are chosen. Here TES is still very rare despite adapted solutions are existing and in use in for example Concentrating Solar Power (CSP) installations to allow them producing electricity at night or during cloudy periods. The two-tank molten salt system is common state of the art for the bigger CSPs, up to 100 MWe and more. For smaller installations, research is ongoing to other technologies such as concrete, Phase Changing Materials (PCMs), rocks etc. as a storage material or even storage via reversible thermo chemical reactions.

Combined electrical-gas fired steam boilers are appearing as well. When electricity prices are low steam is generated with electricity.

If applied, all of the proposed solutions should increase generated revenues for CHP owners but also increase the flexibility of the energy market needed to increase the share of renewable energy generation.

A new CORNET project proposal, named “Increase flexibility of your cogeneration unit by adding thermal storage” is in preparation to formulate an answer on following questions:

  • How can CHP operators better make use of variable electricity prices?
  • Can the latter be optimized by adding thermal storage?
  • What kind of thermal storage systems are well adapted and available for CHPs?

Beneficiaries of the project results are exploiters of both small and bigger CHPs, present in very different industrial branches, CHP manufacturers and installers, engineering offices, grid operators and energy contractors. All of them will be represented in the user groups.

During the conference state of the art will be introduced. Also you will learn about the organization of the electricity market and about some existing references of electricity generation units with integrated thermal storage.