Stack energy control in combined cycle power plant using heating surface bypasses

A combined cycle power plant comprising:

• a gas turbine that is configured to generate power output and produce exhaust gas;
• a heat recovery steam generator comprising a plurality of heating surfaces located downstream of the gas turbine that is configured to receive the exhaust gas from the gas turbine and produce steam by extracting energy from the exhaust gas;
• an exhaust stack that is configured to dump the exhaust gas after passing through the plurality of the heating surfaces;
• a steam turbine that is configured to receive the steam produced in the heat recovery steam generator to generate power output, and
• a condenser located at an exit of the steam turbine that is configured to feed water to the plurality of the heating surfaces,
• wherein the plurality of the heating surfaces are configured to be partially bypassed by the water during startup of the power plant,
• wherein the exhaust stack is configured to dump the exhaust gas during the startup of the power plant,
• wherein the heat recovery steam generator comprises a high pressure steam system comprising a high pressure economizer,
• wherein the high pressure economizer comprises an upstream high pressure economizer and a downstream high pressure economizer,
• wherein the upstream high pressure economizer comprises an upstream high pressure economizer bypass line connecting an upstream side of the upstream high pressure economizer to a downstream side of the upstream high pressure economizer,
• wherein the upstream high pressure economizer comprises an upstream high pressure economizer bypass valve located at the upstream high pressure economizer bypass line,
• wherein the downstream high pressure economizer comprises a downstream high pressure economizer bypass line connecting an upstream side of the downstream high pressure economizer to a downstream side of the downstream high pressure economizer,
• wherein the downstream high pressure economizer comprises a downstream high pressure economizer bypass valve located at the downstream high pressure economizer bypass line,
• wherein the upstream high pressure economizer bypass valve is configured to control the water to partially bypass the upstream high pressure economizer via the upstream high pressure economizer bypass line,
• wherein the downstream high pressure economizer bypass valve is configured to control the water to partially bypass the downstream high pressure economizer via the downstream high pressure economizer bypass line, and
• wherein a power plant controller is configured to control the upstream high pressure economizer bypass valve and the downstream high pressure economizer bypass valve such that the upstream high pressure economizer bypass line is configured to bypass a higher bypass flow than the downstream high pressure economizer bypass line during the startup of the power plant.