Steam cycle efficiency improvement with pre-economizer

1. A system for pulp mill steam cycle operation, comprising:

a deaerator tank with a plurality of fluidic connections adapted for receiving a supply of water, said deaerator tank operating at a pressure;

a pre-economizer fluidically connected to said deaerator tank for receiving water therefrom, said pre-economizer being located inside a boiler and being fluidically connected to receive said supply of water from said deaerator tank, said pre-economizer also adapted for heating said supply of water;

a feedwater heater located outside of the boiler and fluidically connected to said pre-economizer for receiving said supply of water from said pre-economizer and for heating said supply of water, the feedwater heater also being fluidically connected to a turbine to receive steam from the turbine for heating said supply of water;

an economizer inside the boiler and directly fluidically connected to said feedwater heater, said economizer being fluidically connected to receive said supply of water directly from said feedwater heater;

wherein the deaerator tank is fluidically connected to receive a supply of makeup feedwater directly from outside the system by a first conduit, to separately receive a supply of feedwater from a feedwater heater by a second conduit, and to separately receive a supply of steam from the turbine by a third conduit;

wherein the deaerator tank is fluidically connected to the pre-economizer by a fourth conduit, wherein the fourth conduit is the only fluidic connection for providing water to the pre-economizer, and wherein the fourth conduit is the only fluidic connection for water leaving the deaerator;

wherein a pressure reducing valve is in the fluidic path between the turbine and the deaerator, and the pressure reducing valve is adapted to lower the pressure of the deaerator tank to a second pressure.

2. The system of claim 1 , wherein said second pressure is at or above atmospheric pressure.

3. The system of claim 1 , further comprising a turbine for lowering the pressure of the deaerator tank to a second pressure.

4. The system of claim 3 , wherein said second pressure is at or above atmospheric pressure.

5. The system of claim 1 , further comprising a heat exchanger communicatively connected to said deaerator tank, said heat exchanger being adapted to add heat to said supply of water.

6. The system of claim 1 , further comprising a heat exchanger fluidically attached to a supply of make-up water, said heat exchanger adapted to add heat to said supply of make-up water.

7. The system of claim 1 ,

wherein a pressure reducing valve is in a separate, direct fluidic path between the turbine and the deaerator, and the pressure reducing valve is adapted to lower the pressure of the deaerator tank to a second pressure.

8. A system for pulp mill steam cycle operation, comprising:

a deaerator tank fluidically connected for receiving a supply of makeup feedwater directly from outside the system by a first conduit, said deaerator tank operating at a pressure;

a pre-economizer fluidically connected to said deaerator tank for receiving water therefrom, said pre-economizer being located inside a boiler and being fluidically connected to receive said supply of water from said deaerator tank, said pre-economizer also adapted for heating said supply of water;

wherein the deaerator tank is directly fluidically connected to the pre-economizer by a pre-economizer conduit, wherein the pre-economizer conduit is the only fluidic connection for providing water to the pre-economizer, and wherein the pre-economizer conduit is the only fluidic connection for water leaving the deaerator;

a feedwater heater outside of the boiler fluidically connected to said pre-economizer for receiving said supply of water from said pre-economizer for heating said supply of water, wherein said feedwater heater is separately fluidically connected to receive steam from a turbine, and wherein the feedwater heater is adapted to use steam from the turbine to heat the supply of water received from the pre-economizer; and

an economizer inside the boiler and fluidically connected to said feedwater heater, said economizer adapted to receive said supply of water from said feedwater heater.

9. A method for improving pulp mill steam cycle efficiency, comprising:

providing the system according to claim 8 ;

wherein the deaerator tank has a first pressure;

lowering the pressure of said deaerator tank to a second pressure;

providing said supply of makeup feedwater to the deaerator tank from outside the system through the first conduit;

delivering said supply of water from the deaerator tank to the pre-economizer through the pre-economizer conduit, said pre-economizer being located inside a boiler arrangement;

heating said supply of water in said pre-economizer;

delivering said supply of water away from said boiler arrangement to at least one feedwater heater, said feedwater heater being fluidically connected to said boiler arrangement;

heating said supply of water by said at least one feedwater heater; and

delivering said supply of water to an economizer located in said boiler.

10. The method of claim 9 , wherein the pressure of the deaerator tank is lowered by employing a pressure-reducing valve.

11. The method of claim 10 , wherein said second pressure is at or above atmospheric pressure.

12. The method of claim 9 , wherein the pressure of the deaerator tank is lowered by extracting from a turbine at a lower pressure than the first pressure.

13. The method of claim 12 , wherein said second pressure is at or above atmospheric pressure.