System and method for top platform assembly of heat recovery steam generator (HRSG)

A method of constructing a heat recovery steam generator (HRSG), comprising:

• forming a first top platform auxiliary module having a first frame, a steam manifold or a high pressure (HP) drum disposed in the first frame, a first terminal fluid connection corresponding to the HP drum or the steam manifold, and a first mounting feature spaced from the first terminal fluid connection a first predetermined distance;
• forming a second top platform auxiliary module having a second frame, an intermediate pressure (IP) drum disposed in the second frame, a second terminal fluid connection corresponding to the IP drum, and a second mounting feature spaced from the second terminal fluid connection a second predetermined distance;
• forming a third top platform auxiliary module having a third frame, a low pressure (LP) drum disposed in the third frame, a third terminal fluid connection corresponding to the LP drum, and a third mounting feature spaced from the third terminal fluid connection a third predetermined distance;
• forming a base of the HRSG including a first ridge configured to support the first top platform auxiliary module by engaging the first mounting feature, and including a first base fluid connection spaced from the first ridge a fourth distance corresponding to the first predetermined distance such that the first terminal fluid connection is configured to align with the first base fluid connection when the first ridge engages the first mounting feature;
• forming the base of the HRSG including a second ridge configured to support the second top platform auxiliary module by engaging the second mounting feature, and including a second base fluid connection spaced from the second ridge a fifth distance corresponding to the second predetermined distance such that the second terminal fluid connection is configured to align with the second base fluid connection when the second ridge engages the second mounting feature;
• forming the base of the HRSG including a third ridge configured to support the third top platform auxiliary module by engaging the third mounting feature, and including a third base fluid connection spaced from the third ridge a sixth distance corresponding to the third predetermined distance such that the third terminal fluid connection is configured to align with the third base fluid connection when the third ridge engages the third mounting feature;
• lifting the first top platform auxiliary module to elevation, and disposing the first top platform auxiliary module on the base of the HRSG such that the first mounting feature engages the first ridge and the first base fluid connection is aligned with the first terminal fluid connection;
• lifting the second top platform auxiliary module to elevation, and disposing the second top platform auxiliary module on the base of the HRSG such that the second mounting feature engages the second ridge and the second base fluid connection is aligned with the second terminal fluid connection;
• and
• lifting the third top platform auxiliary module to elevation, and disposing the third top platform auxiliary module on the base of the HRSG such that the third mounting feature engages the third ridge and the third base fluid connection is aligned with the third terminal fluid connection.