Design and operation of a 300 kWth indirectly heated carbonate looping pilot plant

- Successful demonstration of an indirectly heated CaL process in 300 kWth scale.
- Feasibility of indirect heating utilizing heat pipes demonstrated.
- >400 h operation of first indirectly heated CaL pilot plant worldwide.
- >90% CO2 capture in the carbonator was achieved.

Carbonate looping or calcium looping (CaL) is an efficient post-combustion CO2-capture technology particularly suited for retrofitting existing power plants. Limestone, an inexpensive and highly available natural product, is utilized for the CaL process. A new concept with an indirectly heated calciner is presented, where the heat for calcination is transferred by means of heat pipes from an external combustor. This process modification offers higher plant efficiencies and lower CO2 avoidance costs than an oxy-fired CaL process. The worldwide first indirectly heated CaL pilot plant with a nominal power of 300 kWth has been erected at Technische Universität Darmstadt. This paper presents the layout of the pilot plant and first operational results using a natural limestone as sorbent and propane as fuel for the external combustor. The calciner was fluidized with air to support self-fluidization of the sorbent during calcination and to lower the partial CO2 pressure and therewith the calcination temperature. Proof of concept was demonstrated within more than 400 h continuous testing. The reactor system showed good hydrodynamic stability, and the heat pipe heat exchanger an excellent performance. CO2 capture rates up to 90% in the carbonator were reached.