Volumetric expander, process of starting the volumetric expander, closed-cycle plant, and process for converting thermal energy into electric energy using said plant

A method of operating a volumetric expander wherein the volumetric expander comprises:

• at least one casing having at least one general inlet configured for enabling introduction of a working fluid inside the casing and at least one general outlet configured enabling expulsion of the working fluid from said casing,
• a piston inside the casing defining a variable volume expansion chamber,
• a main shaft cinematically connected to the piston,
• at least one valve configured for selectively opening and closing an inlet and outlet of said expansion chamber enabling at least:
• an introduction condition, in which the working fluid is introduced into the expansion chamber,
• an expansion condition, in which the working fluid expands in the expansion chamber, and
• a discharge condition, in which the working fluid is discharged from said expansion chamber,
• wherein the casing internally defines a discharge chamber in fluid communication with the general outlet, the discharge chamber being further configured for being put in fluid communication with the outlet of the expansion chamber during the discharge condition,
• wherein the casing comprises at least one auxiliary inlet in communication with the discharge chamber and, via this latter, with the general outlet,
• said method comprising:
• introducing a working fluid into the discharge chamber of the casing through the auxiliary inlet and heating at least one of the casing and the valve,
• introducing the working fluid through the general inlet and starting operation of the volumetric expander.

A method of operating a closed circuit plant comprising:

• a volumetric expander which comprises:
• at least one casing having at least one general inlet configured for enabling introduction of a working fluid inside the casing and at least one general outlet configured enabling expulsion of the working fluid from said casing,
• a piston inside the casing defining a variable volume expansion chamber,
• a main shaft cinematically connected to the piston,
• at least one valve configured for selectively opening and closing an inlet and outlet of said expansion chamber enabling at least:
• an introduction condition, in which the working fluid is introduced into the expansion chamber,
• an expansion condition, in which the working fluid expands in the expansion chamber, and
• a discharge condition, in which the working fluid is discharged from said expansion chamber,
• wherein the casing internally defines a discharge chamber in fluid communication with the general outlet, the discharge chamber being further configured for being put in fluid communication with the outlet of the expansion chamber during the discharge condition,
• wherein the casing comprises at least one auxiliary inlet in communication with the discharge chamber and, via this latter, with the general outlet;
• and at least one electric energy generator connected to the main shaft of the volumetric expander and configured for generating electric energy upon rotation of the main shaft;
• said method comprising:
• introducing a working fluid into the discharge chamber of the casing through the auxiliary inlet for pre-heating at least one of the casing and the valve,
• then introducing the working fluid through the general inlet and starting operation of the volumetric expander.