CA2794735A1 - Boiler energy recovery system - Google Patents

Abstract

The present document describes a system for installation on a boiler for providing energy to a deaerator comprising: a heat exchanger for positioning at an exhaust of the boiler and for connecting to the deaerator for decreasing combustion gases temperature from a temperature T1 to a temperature T2 before evacuation of the combustion gases to atmosphere for providing energy to the feedwater and the deaerator.

Description

, CA 02794735 2012-11-06 File No. P1830CA00 BOILER ENERGY RECOVERY SYSTEM
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of US provisional patent application 61/558,629 filed on November 11,2011.
BACKGROUND
(a) Field [0002] The subject matter disclosed generally relates to an energy recovery system and a boiler system. More particularly, the subject matter disclosed generally relates to an energy recovery system designed to integrate a boiler system including an economizer, and a deaerator.
(b) Related Prior Art [0003] Fossil fuels represent a significant energy source for the production of electrical energy in many countries, such as Canada, United States and the like. It is available throughout much of the countries. Moreover, the plants which convert fossil fuels energy into electrical energy are efficient and, in comparison to hydroelectric projects and other plants, they are easy and inexpensive to construct.

[0004] The actual industry provides steam power plants including a boiler equipped with one or a plurality of deaerators to remove oxygen and other gases from the boiler feedwater prior to admission in boilers. On the other hand, the condensate tank is often used as a thermal deaerator in some small plants.
These gases, such as oxygen, carbon dioxide and other gases, being in effervescence at high temperature, the deaerator is generally maintained at pressures and temperatures slightly above the boiling point of water, which is around 5 PSIG and 227 F.

[0005] The means commonly used to maintain these pressures and temperatures are to inject steam to control the pressure in the deaerator.
Usually, , , CA 02794735 2012-11-06 File No. P1830CA00 the steam comes from the boilers via a control valve to reduce pressure and adjust the flow. However, this mean do not provide with an efficient energy recovery system or plant. In these configurations, the net energetic yield of the boiler may decrease.

[0006] As noted, the feedwater requires deaeration with a deaerator to remove dissolved gases from the feedwater to prevent corrosion and erosion of the system. Deaerators represent mechanical devices that remove dissolved gases from boiler feedwater. A deaerator protects the steam system from the effects of corrosive and erosive gases. It accomplishes this by reducing the concentration of dissolved oxygen and carbon dioxide to a level where corrosion is minimized. A dissolved oxygen level of about 7 parts per billion or lower is needed to prevent corrosion in most boilers. While oxygen concentration of up to 43 parts per billion may be tolerated in low-pressure boilers, equipment life is extended at little or no cost by limiting the oxygen concentration to 7 parts per billion. Dissolved carbon dioxide is essentially completely removed by the deaerator.

[0007] The design of an effective deaeration system depends upon the amount of gases to be removed and the final oxygen gas concentration desired.
This, in turn, depends upon the ratio of boiler makeup to condensates returns and the operating pressure of the boiler. Deaerators use steam to heat the water to the full saturation temperature corresponding to the pressure in the deaerator and to scrub out and carry away dissolved gases. Steam flow may be parallel, cross, or counter to the water flow. The deaerator consists of a deaeration section, a storage tank, and a vent. In the deaeration section, steam bubbles through the water, both heating and agitating it. Steam is cooled by incoming water and condensed at the vent condenser, if there is one (none in 99% of cases). Non-condensable gases and some steam are released through the vent.
Steam fed to the deaerator provides physical stripping action and heats the mixture of condensates returns and condenses makeup to saturation File No. P1830CA00 temperature. Most of the steam condensates, but a small fraction (usually 1%
to 5%) must be vented to accommodate the stripping requirements.

[0008] Normal design practice is to calculate the steam required for heating and then make sure that the flow is sufficient for stripping as well.
If the condensates returns rate is high (higher than about 80%) and the condensates' pressure is high in comparison to the deaerator's pressure, then very little steam is needed for heating and provisions may be made for condensing the surplus flashed steam.

[0009] It is well known that the deaerator steam consumption is equal to the steam required to heat incoming water to its saturation temperature, plus the amount vented with the non-condensable gases, less any flashed steam from hot condensates or steam losses through failed traps. The heat balance calculation is made with incoming water at its lowest expected temperature. The vent rate is a function of deaerator type, size (rated feedwater capacity), and the amount of makeup water. The operating vent rate is at its maximum with the introduction of cold, oxygen-rich makeup water.

[0010] A deaerator provides the water storage capacity and the net positive suction head necessary at the boiler feed pumps' inlet. Condensates returns are mixed with makeup water within the deaerator. Operating temperature range from 215 F to more than 350 F, which reduces the thermal shock on downstream preheating equipment and the boilers.

[0011] It is well known that to reduce the energy consumption needed for a deaerator, the deaerator section and storage tank and all piping conveying hot water or steam should be adequately insulated to prevent the condensation of steam and loss of heat as well as personal safety.

[0012] Additionally, to reduce the energy consumption, it is well known that deaerator steam requirements should be reexamined following the retrofit of a File No. P1830CA00 steam distribution system, condensates returns system, or heat recovery energy conservation measures.

[0013] On the other hand, many plants include an economizer in their design to provide an efficient steam system. More particularly, economizers are mechanical devices intended to reduce energy consumption. In simple terms, an economizer is a heat exchanger.

[0014] In boilers, economizers are usually heat exchanger devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid at boiler pressure. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the water used to feed it.

[0015] There is therefore a need in an energy recovery system having a boiler system with an economizer, to integrate a deaerator.
SUMMARY

[0016] According to an embodiment, there is provided a system for installation on a boiler for providing energy to a deaerator comprising a heat exchanger for positioning at an exhaust of the boiler and for connecting to the deaerator for decreasing combustion gases temperature from a temperature T1 to a temperature T2 before evacuation of the combustion gases to atmosphere for providing energy to the feedwater and the deaerator.

[0017] According to another embodiment, the deaerator is for operating at a temperature Tdeaerator.

[0018] According to another embodiment, the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature Tdeaerator by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

File No. P1830CA00 [0019] According to another embodiment, the energy provided by the heat exchanger heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator.

[0020] According to another embodiment, the energy provided by the heat exchanger heats a deaerator condensate returns from a returned temperature to the temperature Tdeaerator and heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator and by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

[0021] According to another embodiment, the deaerator fluid inlet is a make-up water inlet.

[0022] According to another embodiment, the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns.

[0023] According to another embodiment, the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns and the returned temperature of the condensates returns is lower than the temperature Tdeaerator.

[0024] According to another embodiment, the make-up water inlet further comprises oxygen.

[0025] According to another embodiment, the heat exchanger is an economizer.

[0026] According to another embodiment, the economizer is an indirect contact economizer.

File No. P1830CA00 [0027] According to another embodiment, decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere increases combustion efficiency of the boiler.

[0028] According to an embodiment, there is provided a boiler loop system for providing energy to a deaerator comprising: a boiler having an exhaust for evacuation of combustion gases; a heat exchanger positioned at the exhaust of the boiler and connected to the deaerator for decreasing combustion gases temperature from a temperature T1 to a temperature T2 before evacuation of the combustion gases to atmosphere providing energy to the feedwater and the deaerator.

[0029] According to another embodiment, the deaerator is for operating at a temperature Tdeaerator.

[0030] According to another embodiment, the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature Tdeaerator by connecting the heat exchanger to the deaerator's condensates returns of the deaerator.

[0031] According to another embodiment, the energy provided by the heat exchanger heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator.

[0032] According to another embodiment, the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature Tdeaerator and heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator and by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

[0033] According to another embodiment, the deaerator fluid inlet is a make-up water inlet.

, CA 02794735 2012-11-06 File No. P1830CA00 [0034] According to another embodiment, the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns.

[0035] According to another embodiment, the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns and the returned temperature of the condensates returns is lower than the temperature Tdeaerator.

[0036] According to another embodiment, the make-up water inlet further comprises oxygen.

[0037] According to another embodiment, the heat exchanger is an economizer.

[0038] According to another embodiment, the economizer is an indirect contact economizer.

[0039] According to another embodiment, decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere increase combustion efficiency of the boiler.

[0040] According to another embodiment, the temperature Tdeaerator is in a range from about 200 F to about 300 F.

[0041] According to another embodiment, the temperature Tdeaerator is about 227 F.

[0042] According to another embodiment, the combusted gases are carbon dioxide, nitrogen, water vapor, oxygen or a combination thereof.

[0043] According to another embodiment, the temperature T1 is about 450 F.

[0044] According to another embodiment, the temperature T2 is about 350 F.

File No. P1830CA00 [0045] According to another embodiment, the returned temperature of the deaerator condensates returns is from about 150 F to about 200 F.

[0046] According to another embodiment, the lower temperature of the deaerator make-up water is about 50 F.

[0047] According to an embodiment, there is provided a heat recovery process comprising the system as described above.

[0048] The following terms are defined below.

[0049] The term "economizer" is intended to mean any mechanical device intended to reduce energy consumption, or to perform another useful function like preheating a fluid. The economizer may be an indirect contact economizer (ICE) or any other types of economizers.

[0050] The term "deaerator" is intended to mean a mechanical device that removes dissolved gases from boiler feedwater and thereby protects the steam system from the effects of corrosive and erosive gases.

[0051] Features and advantages of the subject matter hereof will become more apparent in light of the following detailed description of selected embodiments, as illustrated in the accompanying figures. As will be realized, the subject matter disclosed and claimed is capable of modifications in various respects, all without departing from the scope of the claims. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not as restrictive and the full scope of the subject matter is set forth in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0053] Fig. 1 is a common arrangement of a heat recovery boiler system as commonly seen in the prior art;

File No. P1830CA00 [0054] Fig. 2 is a flowsheet of a heat recovery boiler system according to one embodiment; and [0055] Fig. 3 is a flowsheet of a heat recovery boiler system according to another embodiment.

[0056] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Referring now to the drawings, and more particularly to Figs. 2 and 3, there is shown a boiler loop system 10. The system 13 is for installation on a boiler 12 for providing energy to a deaerator 14. The system 13 comprises a heat exchanger 16 positioned at an exhaust 20 of the boiler 12 for decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere for providing energy to the deaerator 14. In the system 13, the heat exchanger 16 is for connecting to the deaerator 14.

[0058] Moreover, in the system 13 as described above, the deaerator 14 is for operating at a temperature Tdeaerator. In the embodiments presented in Figs. 2 and 3, the temperature Tdeaerator of the deaerator 14 is about 227 F at a pressure of 5 PSIG. In the system 13, the energy provided by the heat exchanger (0 =
ritCp(T2 ¨ T1)) heats a feedwater 36 from a temperature Tdeaerator to a temperature Tdeaerator + T. Also the energy provided by the heat exchanger 16 may heat a deaerator fluid inlet 18 from a lower temperature to the temperature Tdeaerator +AT.
In the other hand, the energy provided by the heat exchanger 16 heats deaerator condensates returns 30 from a returned temperature to the temperature Tdeaerator +AT. In the system 13 as described above, the deaerator fluid inlet 18 may be a make-up water inlet, but any other fluid, such as a glycol loop, and the like.

[0059] In the system 13, the temperature of the make-up water inlet 18 is lower than the returned temperature of the condensates returns 30.
Additionally, File No. P1830CA00 the returned temperature of the condensates returns 30 is lower than the temperature Tdeaerator=

[0060] Moreover, the make-up water inlet 18 of the system 13 may further comprise oxygen and other gases such as carbon dioxide. It is important to note that in embodiments presented by Figs. 2 and 3, the heat exchanger 16 of the system 13 is an economizer, and more particularly, an indirect contact economizer, or ICE. However, it is important to note, that the heat exchanger may be any type of well known heat exchanger in the industry.

[0061] Also, in the system 13, decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere increases the combustion efficiency of the boiler 12.

[0062] Still referring to Figs. 2 and 3, there is shown an economizer 16 in a boiler loop system for providing energy to the feedwater 36. The economizer 16 transfers heat from a first fluid to a second fluid, in which the first hot fluid is the exhaust gas 22 and the second cold fluid is the feedwater 36. Indeed, the temperature of the exhaust gas 22 decreases from about 450 F to about 350 F, while the temperature of the feedwater 36 increases from about 227 F to about 252 F. The boiler loop system comprises a boiler 12 having an exhaust 20 for evacuation of combustion gases and a heat exchanger 16 positioned at the exhaust 20 of the boiler 12 for decreasing from a temperature T1 to a temperature T2 combustion gases before their evacuation to atmosphere and then providing energy to the feedwater 36. In the boiler loop, the heat exchanger 16 is connected to the deaerator 14.

[0063] As noted before, the deaerator of the boiler loop system is for operating at a temperature Tdeaerator= The energy provided by the heat exchanger 16 of the boiler loop system heats deaerator condensates returns 30 from a returned temperature to the temperature Tdeaerator ,t,T. The energy provided by the File No. P18300A00 heat exchanger 16 may also heat a make-up water inlet 18 from a lower temperature to the temperature Tdeaerator [0064] In the boiler loop system as described above, the temperature Tdeaerator may be in a range from about 200 F to about 300 F. More particularly, in the embodiments presented in Figs. 2 and 3, the temperature Tdeaerator is about 227 F. In the boiler loop and in the boiler system 13, the combustion gases may be carbon dioxide, nitrogen, water vapor, oxygen or a combination thereof.

[0065] Moreover, in the boiler loop system as described above, the temperature T1 may be about 450 F and the temperature T2 is about 350 F.
Also, the temperature of the deaerator's condensates returns 30 is about 160 F

and the lower temperature of the make-up water 18 is about 50 F.

[0066] Moreover, still referring to Figs. 2 and 3, there is shown a flowsheet of a boiler loop system 10 according to different embodiments. More particularly, there is provided a boiler loop system 10 for heating and deaerating make-up water 18 of a boiler 12 having an exhaust 20 for evacuation of combustion gases.
The boiler loop system 10 comprises the step of transferring an amount of energy from the combustion gases provided by the exhaust 20 of the boiler 12 to the economizer (or heat exchanger) 16 having a convection surface area, the economizer 16 (or heat exchanger) being positioned at the exhaust 20 of the boiler 12.

[0067] Additionally, the boiler loop system 10 also includes the step of directing combustion gases which energy is transferred by the economizer 16 to feedwater 36. Furthermore, the boiler loop system 10 includes the step of directing the make-up water inlet 18 into a deaerator 14 to remove gases, such as oxygen and/or carbon dioxide, from the make-up water inlet 18 directed to the boiler 12; and where the convection surface area of the economizer 16 provides an heat transfer from the combustion gases evacuated by the exhaust 20 to the File No. P1830CA00 feedwater 36, thereby providing a heat recovery from the combustion gases of the boiler 12 to the deaerator 14.

[0068] The steam admitted to the deaerator 14 heats the condensates returns 30 from its returned temperature to the deaerator temperature Tdeaerator.
More particularly, the steam admitted to the deaerator 14 may heat the condensates returns from its returned temperature, about 150 F, to the deaerator temperature Tdeaerator, about 227 F. Also, the steam admitted to the deaerator may heat the make-up water inlet 18 from a lower temperature to the temperature of the deaerator Tdeaerator. More particularly, the steam admitted to the deaerator may heat the make-up water inlet 18 from a lower temperature, about 50 F, to the temperature of the deaerator Tdeaerator, about 227 F.
Additionally, the steam admitted to the deaerator 14 leads the non-condensable gases that need to be eliminated outside the deaerator 14 via a vent 26.
Generally, from about 1% to 2% of the water or fluid mass flow comes out from the vent 26 of the deaerator 14. The addition of these needs in steam is not negligible. It may present 12% of the steam production of the boiler 12. The steam needs are provided by the economizer 16 installed on the boiler 12. More particularly, the economizer 16 is an indirect contact economizer.

[0069] The boiler loop system 10 replaces a part or the totality of the steam provided by the boiler 12 by the steam provided by the economizer 16.
The economizer 16 may be an indirect contact economizer (ICE) or any other type of economizer. The economizer 16 may be installed on the exhaust 20, where the gases are expelled from the boiler 12. The installation of the economizer 16 decreases the temperature of the combustion gases before their evacuation to the atmosphere. The combustion efficiency of the boiler system is than increased.

[0070] The present invention will be more readily understood by referring to the following examples which are given to illustrate the invention rather than to limit its scope.

File No. P1830CA00 Heat recovery system with a 600HP boiler [0071] In a first example, the boiler loop system 10 includes a 600 HP
boiler (20,000, 000 BTU/hr). The operating pressure of the boiler 12 is up to PSIG at 350 F. The deaerator 14 connected to the boiler 12 operates at a temperature of 227 F and at a pressure of 5 PSIG. When the indirect contact economizer (ICE) 16 is not installed at the exhaust 20 of the boiler 12, the temperature of the combusted gases is about 450 F. The combustion efficiency of the boiler without the indirect contact economizer (ICE) 16 is about 80.6%.
On the other hand, when the indirect contact economizer (ICE) 16 is installed at the exhaust 20 of the boiler 12, the temperature of the combustible gases is about 350 F. The combustion efficiency of the boiler 12 with the indirect contact economizer (ICE) 16 is about 84.2%.

[0072] In this example, 25 000 #/hr of combusted gases are cooled from about 450 F to about 350 F via the indirect contact economizer (ICE) 16. This energy heats 20 000 #/hr of the feedwater 36 from about 227 F to about 252 F.
This feedwater 36 at 252 F is admitted in the deaerator 14, as shown in Fig.
3.
Also, this feedwater 36 at 252 F may be admitted to a reservoir 34 for flashing, as shown in Fig. 2.

[0073] While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure.
Such modifications are considered as possible variants comprised in the scope of the disclosure.

Claims (32)

1. A system for installation on a boiler for providing energy to a deaerator comprising:
- a heat exchanger for positioning at an exhaust of the boiler and for connecting to the deaerator for decreasing combustion gases temperature from a temperature T1 to a temperature T2 before evacuation of the combustion gases to atmosphere for providing energy to the feedwater and the deaerator.

2. The system of claim 1, wherein the deaerator is for operating at a temperature T deaerator.

3. The system of claim 2, wherein the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature Tdeaerator by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

4. The system of claim 2, wherein the energy provided by the heat exchanger heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator.

5. The system of claim 2, wherein the energy provided by the heat exchanger heats a deaerator condensate returns from a returned temperature to the temperature Tdeaerator and heats a deaerator fluid inlet from a lower temperature to the temperature Tdeaerator by connecting the heat exchanger to the fluid inlet of the deaerator and by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

6. The system of anyone of claim 4 or 5, wherein the deaerator fluid inlet is a make-up water inlet.

7. The system of anyone of claim 5 or 6, wherein the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns.

8. The system of claim 7, wherein the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns and the returned temperature of the condensates returns is lower than the temperature T deaerator.

9. The system of claim 6, wherein the make-up water inlet further comprises oxygen.

10. The system of claim 1, wherein the heat exchanger is an economizer.

11. The system of claim 10, wherein the economizer is an indirect contact economizer.

12. The system of claim 1, wherein decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere increases combustion efficiency of the boiler.

13. A boiler loop system for providing energy to a deaerator comprising:
- a boiler having an exhaust for evacuation of combustion gases;
- a heat exchanger positioned at the exhaust of the boiler and connected to the deaerator for decreasing combustion gases temperature from a temperature T1 to a temperature T2 before evacuation of the combustion gases to atmosphere providing energy to the feedwater and the deaerator.

14. The boiler loop system of claim 13, wherein the deaerator is for operating at a temperature T deaerator.

15. The boiler loop system of claim 14, wherein the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature T deaerator by connecting the heat exchanger to the deaerator's condensates returns of the deaerator.

16. The boiler loop system of claim 14, wherein the energy provided by the heat exchanger heats a deaerator fluid inlet from a lower temperature to the temperature T deaerator by connecting the heat exchanger to the fluid inlet of the deaerator.

17. The boiler loop system of claim 14, wherein the energy provided by the heat exchanger heats a deaerator condensates returns from a returned temperature to the temperature T deaerator and heats a deaerator fluid inlet from a lower temperature to the temperature T deaerator by connecting the heat exchanger to the fluid inlet of the deaerator and by connecting the heat exchanger to the deaerator condensates returns of the deaerator.

18. The boiler loop system of anyone of claim 16 or 17, wherein the deaerator fluid inlet is a make-up water inlet.

19. The boiler loop system of anyone of claim 17 or 18, wherein the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns.

20. The boiler loop system of claim 19, wherein the lower temperature of the deaerator fluid inlet is lower than the returned temperature of the condensates returns and the returned temperature of the condensates returns is lower than the temperature T deaerator.

21. The boiler loop system of claim 18, wherein the make-up water inlet further comprises oxygen.

22. The boiler loop system of claim 13, wherein the heat exchanger is an economizer.

23. The boiler loop system of claim 22, wherein the economizer is an indirect contact economizer.

24. The boiler loop system of claim 13, wherein decreasing from a temperature T1 to a temperature T2 the combustion gases before their evacuation to atmosphere increase combustion efficiency of the boiler.

25. The boiler loop system of claim 13, wherein the temperature T deaerator is in a range from about 200°F to about 300°F.

26. The boiler loop system of claim 25, wherein the temperature T deaerator is about 227 F.

27. The boiler loop system of claim 13, wherein the combusted gases are carbon dioxide, nitrogen, water vapor, oxygen or a combination thereof.

28. The boiler system of claim 13, wherein the temperature T1 is about 450 F.

29. The boiler system of claim 13, wherein the temperature T2 is about 350°F.

30. The boiler system of anyone of claims 15-17, wherein the returned temperature of the deaerator condensates returns is from about 150°F to about 200°F.

31. The boiler system of anyone of claims 15-17, wherein the lower temperature of the deaerator make-up water is about 50°F.

32. A heat recovery process comprising:
- the system of claim 1.