or in the case of vapour recompression systems electrical energy drives a heat pump which could deliver up to 60 kj of heat by consuming 1 kj of electricity alternatively the dryer 140 may be a contact dryer such as for example vacuum tray vertical agitated double cone horizontal pan plate vacuum band horizontal paddle or indirect rotary dryers the dryer 140 may also be a dispersion convective dryer other than a fluidized bed dryer such as spouted bed direct rotary and pneumatic conveying dryers or layer convective dryers such as convective tray through circulation turbo tray tunnel moving bed paddle or a rotary louvre dryer in addition to the calcium carbonate crystal aggregates in stream 132 stream 105 of make up calcium carbonate is introduced into drying unit 140 to account for losses of calcium compounds throughout the process the source of make up calcium carbonate could be limestone stream 142 of dry calcium carbonate crystal aggregates and make up calcium carbonate are now ready for the final processing step the calcium carbonate crystal aggregates are then reacted to reform the calcium oxide which was used in the first step in the process and release a gas stream containing co 2 via reaction 3 above.