Demonstration TAP pilot

On March 7 the project team presented the results and a full functional pilot of the TAP (Thermo Acoustic Power) to the public. The TAP is build and installed at the premises of Smurfit Kappa Solid Board located in the north of the Netherlands. For a selected group of about 25 representatives from industry, economic affairs (SBIR) and press, the operation of the TAP generating electricity from the waste heat in the flue gas of the STEG was successfully demonstrated.

Project results

The aim of this pilot was to prove the scalability of thermoacoustics from lab to industrial temperature and power levels, and to prove the economic feasibility of the TAP. The first goal, the scalability of the thermoacoustic process, converting heat into acoustic (= mechanic) power, up to industrial levels was proven successful, showing an exegetic efficiency of 38% (see previous post). The economic target however is still behind, consequently delaying the intended market introduction for this year. For the conversion of acoustic power (generated from the waste heat) into electricity, linear alternators were deployed. The costs of these alternators was, and is still, found too high. Current cost of the alternators only, already exceeds the target cost of the complete TAP installed (3000 € / kW_e ).

One of the conclusions from the pilot is that, based on cost reduction figures for the alternators and the other components, the power level of the TAP should be scaled up to  least 50-100 kW electric output power to become economic viable. More details can be found in the final report (in Dutch)

Eindrapportage TAP (SBIR09313)

The pilot has made clear that the conversion from waste heat into acoustic power is efficient and scalable. In the pilot set-up however the limited capacity of the linear alternators prevented utilizing the full acoustic output generated by the engine. Therefore, the further development and cost reduction on the TAP, and thermoacoustic waste heat recovery in general, will be continued on two tracks;

1. Development of a scalable and cost effective  alternative for the conversion of acoustic power into electricity for the TAP. Beside improvements on the linear alternators, a serious cost reduction could be obtained by converting the acoustic output power into mechanical rotation allowing for the use of standard generators. Recent experiments with a small scale bi-directional impulse turbine were encouraging. A full scale turbine with generator is under construction for testing in the current pilot set-up.
   
2. Utilizing the concept as a heat transformer, eliminating the need for alternators or other mechanical moving parts completely.  A heat transformer is a (multi-stage) themoacoustic engine acoustically coupled with a  thermoacoustic heat pump by sharing the same traveling wave acoustic resonance or feedback circuit.

For use as a heat transformer, the waste heat from an industrial process is split in two flows. One flow is supplied to the engine stages. The other flow is supplied to the heat pump to raise its temperature above the pinch.  In other words, a part of the useless waste heat of a too low temperature is converted into heat with a higher temperature so it can be reused in the industrial process. This way, primary energy is saved and CO₂ emission reduced.  Advantages of a thermoacoustic heat transformer over existing heat pumps are the lack of exotic cooling refrigerants, the flexibility and the extreme large operating temperature range. For example, the output of the same device could be cold as well by simply commute the heat pump high and low temperature heat exchangers connections.