System and method for warmkeeping sub-critical steam generator

A system for warm keeping components of a plurality of water fill circuits of a sub-critical steam generator including an economizer, furnace waterwall tubes, a boiler drum, and at least one boiler drum downcomer that provides water from the boiler drum to an inlet header to the furnace waterwall tubes, while the sub-critical steam generator is in an unfired stand-by mode of operation, the system comprising:

• water extraction piping to extract water from the at least one boiler drum downcomer that provides water from the boiler drum to the inlet header to the furnace waterwall tubes, the water extraction piping branching from the at least one boiler drum downcomer;
• a deaerator heating system to provide heated deaerated feedwater to the plurality of water fill circuits from an inventory tank, wherein the deaerator heating system is configured to receive the extracted water from the water extraction piping;
• a forwarding pump operatively coupled to the water extraction piping and the deaerator heating system to forward the extracted water to the inventory tank for mixing with the water in the inventory tank, wherein the deaerator heating system heats the mix of water in the inventory tank to a predetermined temperature level to generate the heated deaerated feedwater;
• feedwater piping that supplies the heated deaerated feedwater at the predetermined temperature level from the deaerator heating system towards the sub-critical steam generator;
• a feedwater pump operatively coupled to the feedwater piping and the deaerator heating system to forward the heated deaerated feedwater to the sub-critical steam generator, the heated deaerated feedwater filling the water fill circuits associated with the economizer, the furnace waterwall tubes, the boiler drum, and the at least one boiler drum downcomer;
• and
• a controller configured to control the water extraction piping, the forwarding pump, the deaerator heating system, the feedwater piping and the feedwater pump to operate cooperatively to warm keep the plurality of water fill circuits in accordance with the predetermined temperature level by recirculating the extracted water and the heated deaerated feedwater through the plurality of water fill circuits while the sub-critical steam generator is in the unfired stand-by mode of operation.

A method for warmkeeping a plurality of water fill circuits of a steam generator including an economizer, furnace waterwall tubes, a boiler drum, and at least one boiler drum downcomer that provides water from the boiler drum to an inlet header to the furnace waterwall tubes, at an elevated temperature while the generator is in an unfired stand-by mode of operation, the method comprising:

• extracting water from a component of one of the plurality of water fill circuits with water extraction piping, the component including the at least one boiler drum downcomer that provides water from the boiler drum to the inlet header to the furnace waterwall tubes, the water extraction piping branching from the at least one boiler drum downcomer;
• forwarding the extracted water from the component to a deaerator heating system having an inventory tank of water;
• mixing the extracted water from the component with the water in the inventory tank;
• heating the mix of water in the inventory tank to a predetermined temperature level to form heated deaerated feedwater;
• supplying the heated deaerated feedwater at the predetermined temperature level to the plurality of water fill circuits of the steam generator;
• and
• warmkeeping the plurality of water fill circuits in accordance with the predetermined temperature level while the steam generator is in the unfired stand-by mode of operation by continuously recirculating the heated deaerated feedwater and the extracted water to and from the steam generator until the steam generator returns to service in a firing mode of operation.