Gas seal apparatus and method for use in cogeneration applications

A method of providing combustion oxygen to a heat recovery steam generator comprising a part of a cogeneration application, comprising:

• providing a transition piece between a gas turbine exhaust outlet of a gas turbine generator to a combustion oxygen input for the heat recovery steam generator;
• providing a stack that is pneumatically coupled to the transition piece;
• forming a column of ambient air in the stack, which ambient air has a greater density, at least on average, than exhaust from the gas turbine generator;
• providing at least one induction fan at an output of the heat recovery steam generator to at least relieve high back pressure on the gas turbine generator such that combustion oxygen is substantially pulled through the heat recovery steam generator rather than substantially pushed there through;
• when the gas turbine generator is providing gas turbine exhaust, using a gas seal comprised of the ambient air to prevent substantial portions of the gas turbine exhaust from exiting through the stack;
• and
• when the gas turbine generator is not providing the gas turbine exhaust, providing at least some combustion oxygen through the stack to the heat recovery steam generator.

Apparatus for use in a cogeneration application having a gas turbine generator, which gas turbine generator provides both power and gas turbine exhaust, and a heat recovery steam generator that generates steam using, at least in part, the gas turbine exhaust, the apparatus comprising:

• transition piece means disposed between an exhaust output of the gas turbine generator and an input to the heat recovery steam generator for feeding gas turbine exhaust from the gas turbine generator to the heat recovery steam generator, wherein the transition piece means has substantially no mechanical dampers disposed therein;
• induction means disposed at an output of the heat recovery steam generator for at least relieving high back pressure on the gas turbine generator;
• stack means pneumatically coupled to the transition piece means for forming a column of ambient air therein, which ambient air has an average density that is greater than the gas turbine exhaust, and for:
• in a first mode of operation, when the gas turbine generator is providing gas turbine exhaust, providing a gas seal that substantially prevents any gas turbine exhaust from exiting through the stack means;
• and
• in a second mode of operation, when the gas turbine generator is not providing gas turbine exhaust, providing ambient air through the stack means to the input of the heat recovery steam generator;
• such that the heat recovery steam generator continues to generate steam without substantial interruption regardless of whether the gas turbine generator is operating.