Adapting the Thermal Cycle of A Waste-to-Energy (WtE) Plant to a Higher Performance

Abstract

The objective of the project is to evaluate the best way of adapting the thermal cycle of a Waste-to-Energy (WtE) plant to a higher performance. Current situation The current thermal cycle, the furnace/boiler allows a thermal load of 46,511 MWt from the combustion of the waste, generating steam at 61 bar (abs) and 380 ºC, which is sent to a steam turbine. The steam at the outlet of the turbine goes to the aero condenser, from there to the feed tank, and is finally returned to the furnace/boiler. The impulsion of the feed water is done by an electric pump, although a turbo-pump is available to move the above-mentioned water flow. A small fraction of steam is withdrawn from the steam drum so as to heat the air used for combustion in the furnace. Expected situation Due to different improvements in the furnace system, the admissible thermal load can be increased in 10%, reaching a total of 51,162 MWt. Moreover, a modification in the boiler economizer provides that the temperature of the exit gases (140.000 Nm3/h) can be reduced to 35ºC, which allows to generate even more steam in the boiler. To deal with this excess of steam, and considering a global modification of the plant, the possibilities are the following: To use 2.0 tons/h of live steam for a nitrogen oxide reduction facility, this steam is previously expanded up to 34 bar (abs) and returned hot and condensed to the feed tank. To use 2.4 tons/h of live steam in an external drying process, this steam is previously expanded up to 28 bar (abs) and returned hot and condensed to the feed tank. To permanently use the turbo- pump instead of the electric pump, and to send its exit steam to the degasser. This steam replaces, either partially or completely, the steam withdrawn from the main turbine so as to heat the feed tank.