High Temperature Sensible Heat Recovery System

Abstract

Heat is reclaimed from a high temperature gasifier exhaust gas of between 250° C. and 20000C. A first duct receives the exhaust gas, and outputs it at a reduced temperature. A second duct receives a heat transfer fluid and outputs it at an elevated temperature. A heat transfer arrangement conducts heat extracted from the product gas to the heat transfer fluid (steam), thereby elevating the temperature of the heat transfer fluid. A heat pipe formed of sodium, potassium, rubidium, or lithium, has a first end for communicating with the high temperature exhaust gas and a second end for communicating with the heat transfer fluid. The heat pipe has an envelope formed of a selectable combination of stainless steel, Inconel, nickel, molybdenum, tungsten, niobium, carbon, carbon composite, and Hastelloy X, and a safety valve that ensures safe operation. An adiabatic zone is interposed between the first and second ducts.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to power generation systems, and more particularly, to a system for reclaiming high temperature sensible heat from the gaseous exhaust of a conventional or plasma gasifier arrangement.

2. Description of the Related Art

In the current energy environment there is increasing desire to use renewable, or carbon neutral, energy sources. In the process of using these energy sources gasification processes are commonly used to produce syngas. Sometimes plasma is used for the gasification heat source, resulting in syngas exit temperatures that routinely reach 1250° C. Occasionally, higher exit temperatures are achieved depending upon the characteristics of the feedstock being consumed and other process variables. It has been a challenge to reclaim this high temperature sensible heat energy without resorting to complex systems of the type presently used in the nuclear power industry.

It is, therefore, an object of this invention to provide a simple, low cost, highly efficient system of reclaiming high temperature sensible heat energy.

SUMMARY OF THE INVENTION

The foregoing and other objects are achieved by this invention which provides a system for reclaiming heat, the system comprising a heat transfer arrangement for transferring heat from a high temperature exhaust gas of a gasifier to a working fluid, and thereby reclaiming high temperature sensible heat from the high temperature exhaust gas of the gasifier.

The invention provides a method and system for converting high temperature heat energy into a useful product for processes such as electricity production, while minimizing the process carbon footprint.

In an advantageous embodiment of the invention, the high temperature exhaust gas is characterized by a temperature of approximately between 250° C. and 2000° C.

In one embodiment of the invention, the heat transfer arrangement is provided with a first duct having an inlet for receiving the high temperature exhaust gas, and an outlet for exhausting the high temperature exhaust gas at a reduced temperature. Additionally, a second duct has an inlet for receiving a heat transfer fluid and an outlet for exhausting the heat transfer fluid at an elevated temperature. A heat transfer arrangement conducts heat extracted from the product gas in the first duct to the heat transfer fluid in the second duct, thereby elevating the temperature of the heat transfer fluid. In a highly advantageous embodiment of the invention, the heat transfer fluid is steam.

In a further advantageous embodiment of the invention, the heat transfer arrangement includes a heat pipe formed of a selectable combination of sodium, potassium, rubidium, and lithium. The heat pipe has a first end for communicating with the high temperature exhaust gas in the first duct, and a second end for communicating with the heat transfer fluid in the second duct. In respective embodiments, the heat pipe has an envelope formed of a selectable combination of stainless steel, Inconel, nickel, molybdenum, tungsten, niobium, carbon, carbon composite, and Hastelloy X.

A safety valve ensures safe operation in some embodiments. In one embodiment, there is provided a heat transfer fin in the first duct for enhancing the transfer of heat from the high temperature exhaust gas to the heat pipe. Also, in other embodiments, an adiabatic zone is interposed between the first and second ducts.

BRIEF DESCRIPTION OF THE DRAWING

Comprehension of the invention is facilitated by reading the following detailed description, in conjunction with the annexed drawing, in which:

FIG. 1 is a simplified schematic representation of a system for recovering sensible heat in accordance with the principles of the invention; and

FIGS. 2 a and 2b are simplified schematic plan and side representations of a high temperature heat reclamation arrangement constructed in accordance with the principles of the invention.

DETAILED DESCRIPTION

FIG. 1 is a simplified schematic representation of a heat reclamation system 100 that is useful for recovering sensible heat in accordance with the principles of the invention. Heat reclamation arrangement 100, in some embodiments of this invention, is provided with a first duct having an inlet 125 for receiving a product gas from a conventional or plasma gasifier 110. An outlet 125a exhausts the product gas at a reduced temperature.

A second duct has a working fluid inlet 170 that receives spent steam or heat transferring fluid, and a heat energy outlet 150 that exhausts heated steam or heat transferring fluid. There is provided a heat transfer arrangement 135 that conducts heat extracted from the product gas in the first duct to the spent steam in the second duct, to form the heated steam. A specific illustrative embodiment of the invention of transfer arrangement 135 will be described in detail below in relation to FIGS. 2a and 2b.

In one embodiment of the invention, heat transfer arrangement 135 includes at least one sodium, potassium, rubidium, or lithium heat pipe or pipe that has a first end for communicating with the product gas in the first duct, and a second end for communicating with the spent steam in the second duct. The sodium, potassium, rubidium, lithium heat pipe or pipe has, in a specific illustrative embodiment of the invention, an envelope formed of stainless steel, Inconel, molybdenum, nickel, tungsten, niobium, a selectable combination of carbon and carbon composite; or Hastelloy X. A safety valve ensures safe operation.

In some embodiments of the invention, a heat transfer fin is disposed in the first duct for enhancing the transfer of heat from the product gas to the heat pipe. Additionally, an adiabatic zone is in some embodiments of the invention interposed between the first and second ducts.

In the practice of an illustrative embodiment of the invention, product gas 125 exits gasifier 100, or a plasma reactor (not shown) in some embodiments, at approximately 1250° C. Approximately 27% of the total energy that is present in product gas 125 from gasifier 110 is primarily in the form of sensible heat. Due to the extreme temperature and composition of product gas 125, most of the heat energy has heretofore been wasted. In accordance with the invention, the heat contained in product gas 125 is recovered in high temperature heat reclamation system 135.

FIGS. 2 a and 2b are simplified schematic representations of an illustrative high temperature heat reclamation system 135a constructed in accordance with the principles of the invention. Elements of structure that have previously been discussed are similarly designated. Referring for the moment to FIG. 2a, which is a side representation of high temperature heat reclamation system 135, product gas 125 is shown to flow along outlet duct 130.

In this embodiment, there is provided high temperature heat reclamation system 135a that uses heat pipes, such as sodium, potassium, rubidium, or lithium heat pipes 140, 142, 144, and 146. The heat pipes are designed to transfer and capture the energy in product gas 125. Basic heat pipes are known in the prior art, and are described in U.S. Pat. No. 2,350,348 that issued to R. S. Gaugler on Jun. 6, 1944, and assigned to General Motors.

At approximately 1250° C., product gas 125 impinges upon the heat pipes. These very efficient heat transfer devices have no moving parts and are optimized to operate at different temperatures depending upon the characteristics of the working (phase change) material and the envelope material that are employed in a practicable embodiment. For example, in embodiments of the invention that employ sodium (not shown) as the working material, and one of a number of possible envelope materials (not specifically designated), such as stainless steel, Inconel, molybdenum, tungsten, niobium, carbon - carbon composite, or Hastelloy X, heat is transferred in the pressure range necessary for super heated or super critical steam (i.e., 3,200 PSI) which is designated as heated/super critical steam 150 in FIGS. 1 and 2a. Heated/super critical steam 150 constitutes, in this embodiment, an energy elevation of return steam 170.

Referring once again to FIG. 2a, an adiabatic zone 152 is interposed between each of the heat pipes 140, 142, 144, and 146. There is additionally provided a finned heat transfer zone 155 to enhance heat transfer to the steam. A plurality of rupture discs 157 are associated with respective ones of the heat pipes and are provided to enable fail safe operation of the heat pipes. FIG. 2b is a top view representation of high temperature heat reclamation system 135 showing the arrangement of heat pipes 140, 142, 144, and 146, as well as additional heat pipes that are not specifically designated.

Although the invention has been described in terms of specific embodiments and applications, persons skilled in the art may, in light of this teaching, generate additional embodiments without exceeding the scope or departing from the spirit of the invention described herein. Accordingly, it is to be understood that the drawing and description in this disclosure are proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof.

Claims

1. A system for reclaiming heat, the system comprising a heat transfer arrangement for transferring heat from a high temperature exhaust gas of a gasifier to a working fluid, and thereby reclaiming high temperature sensible heat from the high temperature exhaust has of the gasifier.

2. The system of claim 1, wherein the gasifier is a plasma gassifier.

3. The system of claim 1, wherein the high temperature exhaust gas is characterized by a temperature of approximately between 250 C and 2000 C.

4. The system of claim 1, wherein said heat transfer arrangement comprises: a first duct having an inlet for receiving the high temperature exhaust gas, and an outlet for exhausting the high temperature exhaust gas at a reduced temperature;a second duct having an inlet for receiving a heat transfer fluid and an outlet for exhausting the heat transfer fluid at an elevated temperature; anda heat transfer arrangement for conducting heat extracted from the product gas in said first duct to the heat transfer fluid in said second duct, to elevate the temperature of the heat transfer fluid.

5. The system of claim 4, wherein the heat transfer fluid is steam.

6. The system of claim 4, wherein said heat transfer arrangement comprises a heat pipe formed of a selectable combination of sodium, potassium, rubidium, and lithium, said heat pipe having a first end for communicating with the high temperature exhaust gas in said first duct, and a second end for communicating with the heat transfer fluid in said second duct.

7. The system of claim 6, wherein said heat pipe further comprises an envelope formed of stainless steel.

8. The system of claim 6, wherein said heat pipe further comprises an envelope formed of Inconel.

9. The system of claim 6, wherein said heat pipe further comprises an envelope formed of nickel.

10. The system of claim 6, wherein said heat pipe further comprises an envelope formed of molybdenum.

11. The system of claim 6, wherein said heat pipe further comprises an envelope formed of tungsten.

12. The system of claim 6, wherein said heat pipe further comprises an envelope formed of niobium.

13. The system of claim 6, wherein said heat pipe further comprises an envelope formed of a selectable combination of carbon and carbon composite.

14. The system of claim 6, wherein said heat pipe further comprises an envelope formed of Hastelloy X.

15. The system of claim 6, wherein there is further provided a safety valve associated with said heat pipe for ensuring safe operation.

16. The system of claim 6, wherein there is further provided a heat transfer fin in said first duct for enhancing the transfer of heat from the high temperature exhaust gas to said heat pipe.

17. The system of claim 6, wherein there is further provided an adiabatic zone interposed between said first and second ducts.