RENEWABLE COMBINED CYCLE LOW TURBINE BOOST

Abstract

A method and system for cost effectively converting a feedstock using thermal plasma, or other styles of gassifiers, into a feedwater energy transfer system. The feedstock can be any organic material, or fossil fuel. The energy transferred in the feedwater is converted into steam which is then injected into the low turbine of a combined cycle power plant. Heat is extracted from gas product issued by a gassifier and delivered to a power plant via its feedwater system. The gassifier is a plasma gassifier and the gas product is syngas. In a further embodiment, prior to performing the step of extracting heat energy, there is is provided the further step of combusting the syngas in an afterburner. An air flow, and/or EGR flow is provided to the afterburner at a rate that is varied in response to an operating characteristic of the afterburner. The air flow to the afterburner is heated.

Claims

1. A method of extracting heat energy from a gassifier and delivering the heat energy to a combined cycle power plant low turbine, the method comprising the steps of: extracting heat energy from a gas product issued by the gassifier; and delivering the extracted heat energy to a feedwater system of a combined cycle power plant.

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

3. The method of claim 1, wherein the gassifier is inductively heated.

4. The method of claim 1, wherein the gassifier is inductively heated and plasma assisted.

5. The method of claim 1, wherein the gas product is syngas.

6. The method of claim 5, wherein prior to performing said step of extracting heat energy there is provided the further step of combusting the syngas in an afterburner.

7. The method of claim 6, wherein there is provided the further step of injecting recirculated exhaust gas into the afterburner.

8. The method of claim 7, wherein there is provided the further step of varying the flow rate of the recirculated exhaust gas in response to an afterburner temperature characteristic.

9. The method of claim 6, wherein there is further provided the step of supplying an air flow to the afterburner.

10. The method of claim 9, wherein said step of supplying an air flow to the afterburner is performed in excess of stoichiometric to cool the outlet charge of the afterburner.

11. The method of claim 9, wherein said step of supplying air flow to the afterburner is performed at an approximately stoichiometric level.

12. The method of claim 9, wherein said step of supplying an air flow to the afterburner is performed at a variable flow rate.

13. The method of claim 12, wherein there is provided the further step of varying the flow rate of the air flow in response to an air/fuel ratio.

14. The method of claim 12, wherein there is provided the further step of varying the flow rate of the air flow in response to an afterburner temperature characteristic.

15. The method of claim 9, wherein there is further provided the step of preheating the air flow to the afterburner to reclaim energy from the system.

16. The method of claim 1, wherein the gassifier is a plasma gassifier, and there is further provided the step of cooling a plasma torch by using an incoming feedwater from the power plant.

17. The method of claim 1, wherein there is provided the further step of supplementing the extracted heat energy with a selectable one of a liquid and a gaseous fuel, and an oxidant.

18. The method of claim 1, wherein there is provided the further step of reducing emissions by subjecting the gas product to a ceramic media filter.

19. A method of providing heat energy from a plasma gasifier to a power plant, the method comprising the steps of: issuing a gas product from the plasma gassifier delivering the gas product to a heat exchanger arrangement; delivering feedwater from the power plant to the heat exchanger arrangement; extracting heat energy from the gas product in the heat exchanger arrangement; delivering the extracted heat energy to the feedwater from the power plant in the heat exchanger arrangement; and returning the feedwater with the extracted heat energy in the form of steam to a low steam turbine of a combined cycle power plant.

20. The method of claim 19, wherein the plasma gassifier is provided with a plasma torch, and there is provided the further step of cooling the plasma torch with the feedwater of the power plant.

21.-28. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0035] Comprehension of the invention is facilitated by reading the following detailed description, in conjunction with the annexed drawing, in which:

[0036] FIG. 1 is a simplified schematic representation of a process and system for generating energy from a renewable energy source constructed in accordance with the principles of the invention; and

[0037] FIG. 2 is a simplified block representation of a modified combined cycle generator.

DETAILED DESCRIPTION

[0038] FIG. 1 is a simplified schematic representation of a process and system for generating energy from a renewable energy source constructed in accordance with the principles of the invention. As shown in this figure, municipal solid waste or other feedstock, designated as MSW 1, is delivered in this specific illustrative embodiment of the invention to system 100 by a crane 20. The feedstock can be any organic material, inorganic mix, or fossil fuel. Crane 20 transfers MSW 1 to a shredder 2. The shredded feedstock (not shown) is then delivered to a plasma chamber 6. It is to be understood that any other form of gassifier can be employed in the practice of the invention.

[0039] The feed system, which includes shredder 2, compresses the incoming feedstock MSW 1 so as to minimize the introduction of air. An in-line high density flow meter 23 monitors feedstock velocity to provide instantaneous feedstock flow rate data (not specifically designated) . Plasma chamber 6, or other conventional gassifier is, in this specific illustrative embodiment of the invention, advantageously operated in a pyrolysis mode, or in air and/or oxygen combustion boosted modes of operation. Additives such as lime 4 are added, in this embodiment, to the gassifier to control emissions and improve the quality of an output slag 7.

[0040] Methods of chemically boosting heat such as with the use of natural gas at natural gas injection port 3 can be used in the practice of the invention. Additionally, propane injection (not shown), or any other fuel oxidation (not shown) can be used to supplement the heat input by plasma torch 5.

[0041] In this embodiment of the invention, plasma torch 5 has its cooling water flowing in series with feedwater inlet 10. The series connection of such feedwater to plasma torch 5 and associated components are not shown in the figure for the sake of clarity. Such routing of the plasma torch cooling water obviates the need for a cooling tower and increases the overall efficiency of the plant.

[0042] A syngas product is supplied via a syngas line 21 to an unlined or refractory lined afterburner 8 to extract the chemical heat from the product gas. In this embodiment of the invention, the afterburner is a conventional thermal oxidizer or a chamber specifically designed to combust the syngas. In other embodiments, the afterburner will further function as a cyclone separator. A large flow of preheated air is injected into the afterburner in a quantity that is typically, but not always, greater than stoichiometric. This lowers the outlet charge temperature of the afterburner, a function that in some embodiments is critical due to the extremely high working temperatures of the plasma chamber exhaust, which becomes the input to the afterburner.

[0043] The high air flow that is injected into afterburner 8 lowers its outlet temperature down to where a conventional heat exchanger, which in this embodiment takes the form of a high temperature boiler 9, extracts the heat energy. In the present embodiment, the heat energy is transferred into a feedwater loop 10 coming from a power plant and is returned to the plant with additional heat added via steam outlet 11. The heat energy extracted from the MSW that is delivered to the feedwater is used in place of fossil fuel heat energy in the power plant, thereby increasing the thermal efficiency of the power plant and reducing its fossil fuel consumption. Any form of heat transfer such as generic steam generation to be used in heating or supplement a simple cycle turbine would qualify for generation of renewable energy.

[0044] The spent syngas continues through an emissions control device 24. In some embodiments of the invention, emissions control device 24 includes a ceramic media filter (not shown). Commercially available sorbents are injected into respective ones of ports 29 and 30 to reduce emissions of SO.sub.2, HCl, Hg, NO.sub.x, etc. A low temperature combustion air heat recovery system 14 is used to preheat the afterburner combustion air, which increases efficiency.

[0045] A blower 17 provides pressurized ambient air to the low temperature combustion air heat recovery system 14. Blower 17 can be variable speed or valved (not shown) to improve performance, and is controlled by a feedback signal (not shown) responsive to the afterburner air/fuel ratio, the afterburner outlet temperature, or other combustion related parameters.

[0046] An induction fan 18 pulls a slight vacuum on the complete system, and in some embodiments of the invention, is designed to utilize a variable speed driver (not shown) to improve system efficiency. A stack 19 is optionally employed in this embodiment as an emergency oxidizer or a simple exhaust stack depending on the redundancy desired in the system design. The stack is useful to consume the fuel in system 100 in emergency situations where the system needs to be shut down quickly.

[0047] FIG. 2 is a simplified schematic representation of a combined cycle generator 200 that produces electrical power. Elements of structure that nave previously been discussed are similarly designated. Many of the Rankine cycle components are not required to be used in the feed-water-to-steam system 100 shown in FIG. 1. Instead, these components are present in combined cycle generator 200 shown in FIG. 2, thereby significantly reducing the capital investment needed for the renewable energy facility.

[0048] As shown in FIG. 2, fuel is received at fuel input line 19. The fuel input line delivers the fuel to a combustion chamber 40 that supplies the resulting combusted gasses to a gas turbine 42. The exhaust of the gas turbine is issued as exhaust gas 44 via an output line 46. The rotational displacement of gas turbine 42 is coupled by a shaft (not specifically designated) to a gas turbine generator 50 that issues electricity 52.

[0049] As a secondary power generation system, there is provided a low steam turbine 60 that operates in the context of a closed loop, as follows: A liquid (not specifically designated) that includes water is present in a condenser 62. The liquid is conducted along a line 64 to a heat recovery steam generator 66 that is disposed in the exhaust path (output line 46) of gas turbine 42. The liquid in line 64 is heated by the exhaust of the gas turbine, and is converted to steam (not specifically designated) in a steam line 68. The steam line supplies the steam to low steam turbine 60, the spent steam output of which is delivered to condenser 62, whereby the spent steam is re-liquified and the cycle is thus repeated continuously.

[0050] In this specific illustrative embodiment of the invention, the steam that is provided by high temperature boiler 9 via steam line 11 in FIG. 1 is injected into the combined cycle low steam turbine 60 at steam input line 11a in FIG. 2. In addition, feedwater (not specifically designated) from condenser 62 is issued at outlet port 10a and is delivered to high temperature boiler 9 in FIG. 1 via feedwater input line 10.

[0051] Modern combined cycle generator design allows for up to a 60% turn down, or stated another way, the facility can be operated with reasonable efficiency at 40% power. Low steam turbine generator 70 supplies over 50% of the total electrical output of the combined cycle generator. This allows the renewable energy facility's steam output to represent approximately 30% of the total combined cycle's power generation without unstable control characteristics. In addition, this design flexibility allows the turbine manufacturer to include in the design additional capacity into low steam turbine 60 that can be utilized for peaking if desired when a full complement of renewable steam is present and the primary gas generator is running at full load. The combined cycle generator can also be operated with no renewable steam input and a reduced electrical generation using fossil fuel exclusively.

[0052] It is to be understood that the invention is not limited in its application to enhancing feedwater for use in a power plant, as any Rankine or other steam process, or any process that requires steam can benefit from the energy transfer system of the present invention.

[0053] Although the invention has been described in terms of specific embodiments and applications, persons skilled in the art can, in light of this teaching, generate additional embodiments without exceeding the scope or departing from the spirit of the invention described and claimed 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.