WO2019059888A1

WO2019059888A1 - Apparatus and process for converting an aero gas turbine engine into an industrial gas turbine engine for electric power production

Info

Publication number: WO2019059888A1
Application number: PCT/US2017/052225
Authority: WO
Inventors: Joseph D. BROSTMEYER; Russell B. JONES
Original assignee: Florida Turbine Technologies, Inc.
Priority date: 2017-09-19
Filing date: 2017-09-19
Publication date: 2019-03-28

Abstract

An apparatus and a process for converting a twin spool aero gas turbine engine to an industrial gas turbine engine, where the fan of the aero engine is removed and replaced with an electric generator, a power turbine is added that drives a low pressure compressor that is removed from the aero engine, variable guide vanes are positioned between the high pressure turbine and the power turbine, and a low pressure compressed air line is connected between the outlet of the low pressure compressor and an inlet to the high pressure compressor, where a hot gas flow produced in the combustor first flows through the high pressure turbine, then through the low pressure turbine, and then through the power turbine.

Description

APPARATUS AND PROCESS FOR CONVERTING AN AERO GAS TURBINE ENGINE INTO AN INDUSTRIAL GAS TURBINE ENGINE FOR ELECTRIC POWER PRODUCTION GOVERNMENT LICENSE RIGHTS

None.

TECHNICAL FIELD

The present invention relates generally to a gas turbine engine, and more specifically to an apparatus and a process for converting an aero gas turbine engine with a fan into an industrial gas turbine engine for electrical power production.

BACKGROUND

FIG. 1 shows an aero gas turbine engine 10 with a fan that is used in an aircraft. One such engine is the CFM56 series of aero gas turbine engines. The CFM International CFM56 series is a family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of 18,000 to 34,000 pounds-force (80 to 150 kilonewtons). The CFM56 first ran in 1974 and, despite initial export restrictions, is now one of the most common turbofan aircraft engines in the world, with more than 20,000 having been built in four major variants. It is most widely used on the Boeing 737 airliner and, under military designation F108, replaced the Pratt & Whitney JT3D engines on many KC-135 Stratotankers in the 1980s, creating the KC-135R variant of this aircraft. It is also the only engine (CFM56-5C) used to power the Airbus A340-200 and 300 series. The engine (CFM56-5A and 5B) is also fitted to Airbus A320 series aircraft. In the aero engine of FIG. 1, a high pressure spool rotates around a low pressure spool. The high pressure spool includes a high pressure compressor (HPC) 11 connected to a high pressure turbine (HPT) 13 through an outer spool or shaft 17, and a combustor 12 that takes in compressed air from the HPC 11 and produces a hot gas flow from burning a fuel, and the hot gas flow is then passed through the HPT 13. A low pressure turbine (LPT) 15 is located immediately downstream from the HPT 13 and is connected to drive a low pressure compressor (LPC) 14 and a fan 16 through an inner shaft 18. The LPC 14 compresses air that is passed into the HPC 11.

In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine - and therefore the engine - can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.

In an industrial gas turbine engine used for electrical power production, during periods of low electrical demand the engine is reduced in power. During periods of low electrical power demand, prior art power plants have a low power mode of 40% to 50% of peak load. At these low power modes, the engine efficiency is very low and thus the cost of electricity is higher than when the engine operates at full speed with the higher efficiency. Industrial and marine gas turbine engines used today suffer from several major issues that include low component (compressor and turbine) performance for high cycle pressure ratios or low part load component efficiencies or high CO (carbon monoxide) emissions at part load when equipped with low NOx combustors which limit the low power limit at which they are allowed to operate (referred to as the turndown ratio).

One prior art IGT engine uses a single shaft IGT engine with a compressor connected to a turbine with a direct drive electric generator on the compressor end. Another prior art IGT engine is a dual shaft IGT engine with a high spool shaft and a separate power turbine that directly drives an electric generator. Still another IGT engine is a dual shaft aero derivative gas turbine engine with concentric spools in which a high pressure spool rotates around the low pressure spool, and where a separate low pressure shaft that directly drives an electric generator. Another prior art IGT engine uses a three-shaft IGT engine with a low pressure spool rotating within a high pressure spool, and a separate power turbine that directly drives an electric generator.

The configuration of single shaft IGT engine with a compressor connected to a turbine with a direct drive electric generator is the most common for electric power generation and is limited by non-optimal shaft speeds for achieving high component efficiencies at high pressure ratios. The mass flow inlet and exit capacities are limited structurally by AN² (last stage blade stress) and tip speeds that limit inlet and exit diameters due to high tip speed induced Mach number losses in the flow. Therefore, for a given rotor speed, there is a maximum inlet diameter and corresponding flow capacity for the compressor and exit diameter and flow capacity for the turbine before the compressor and turbine component efficiencies start to drop off due to high Mach number losses.

Since there is a fixed maximum inlet flow at high pressure ratios on a single shaft, the rotor blades start to get very small in the high pressure region of the compressor flow path. The small blade height at a relatively high radius gives high losses due to clearance and leakage effects. High pressure ratio aircraft engines overcome this limitation by introduction of separate high pressure and low pressure shafts. The high pressure shaft (outer spool or shaft) turns at a faster speed allowing for smaller radius while still accomplishing a reasonable work per stage. An example for this is dual shaft aero derivative gas turbine engine with concentric spools, which is typical of an aero-derivative gas turbine engine used for electrical power production. The speed of the high pressure spool is still limited by having a low speed shaft inside the inner diameter (ID) of the high pressure shaft. This drives the high pressure shaft flow path to a higher radius relative to what might otherwise be feasible, which thereby reduces the speed of the high pressure rotor, creating smaller radius blades which reduce the efficiency of the high pressure spool. The dual-shaft IGT engine with a high spool shaft and a separate power turbine that directly drives an electric generator arrangement is similarly limited in achieving high component efficiencies at high pressure ratios as the single shaft IGT engine with a compressor connected to a turbine with a direct drive electric generator on the compressor end since the entire compressor is on one shaft.

Turn down ratio is the ratio of the lowest power load at which a gas turbine engine can operate (and still achieve CO emissions below the pollution limit) divided by the full 100% load power. Today's gas turbines have a turn down ratio of around 40%. Some may be able to achieve 30%. Low part load operation requires a combination of low combustor exit temperatures and low inlet mass flows. Low CO emissions require a high enough combustor temperature to complete the combustion process. Since combustion temperature must be maintained to control CO emissions, the best way to reduce power is to reduce the inlet mass flow. Typical single-shaft gas turbine engines use multiple stages of compressor with variable guide vanes to reduced inlet mass flow. The limit for the compressor flow reduction is around 50% for single shaft constant rotor speed compressors. The dual-shaft aero derivative gas turbine engine arrangement is similarly limited as the single shaft IGT engine arrangement in flow inlet mass flow reduction since the low pressure compressor runs the constant speed of the generator.

Another prior art IGT engine is a three-shaft IGT engine with a low pressure spool rotating within a high pressure spool, and a separate power turbine that directly drives an electric generator, which is the most efficient option of the current configurations for IGT engines, but is not optimal because the low spool shaft rotates within the high spool shaft, and thus a further reduction in the high spool radius cannot be achieved. In addition, if the speed of the low spool shaft is reduced to reduce inlet mass flow, there is a mismatch of angle entering the LPT (low pressure turbine) from the HPT (high pressure turbine) and mismatch of the flow angle exiting the LPT and entering the PT (power turbine) leading to inefficient turbine performance at part load.

SUMMARY

The present invention advantageously provides a method and system for an apparatus and a process for converting a twin-spool aero engine with a fan into an industrial gas turbine engine that drives an electric generator, where the fan is removed from the aero engine, the low pressure compressor is removed from the aero engine, an electric generator is connected to the low pressure turbine of the aero engine, a power turbine is located downstream from the low pressure turbine, and the low pressure compressor is connected to the power turbine so that a hot gas flow produced in the combustor will pass through the high pressure turbine, then the low pressure turbine to drive the electric generator, and then through the power turbine to drive the low pressure compressor, where the low pressure compressed air is channeled from the low pressure compressor and discharged into an inlet of the high pressure compressor. Inlet guide vanes are located between the low pressure turbine and the power turbine to regulate a speed of the low pressure compressor while maintaining the speed of the electric generator at a constant rotational speed.

In one embodiment, the low pressure compressor of the aero engine can be reused in the industrial engine which will be driven by the power turbine. Variable inlet guide vanes can be used at the inlet to the low pressure compressor in order to regulate flow and thus speed of the engine.

In one embodiment, a process of converting a twin-spool aero gas turbine engine having an outer spool and an inner spool with a fan into an industrial gas turbine engine that drives an electric generator includes the steps of: removing the fan from the aero engine; removing a low pressure compressor from the inner spool of the aero engine; connecting the inner spool to the electric generator; placing a power turbine downstream from a low pressure turbine of the aero engine such that an exhaust from the low pressure turbine drives the power turbine; connecting a low pressure compressor to the power turbine such that the power turbine drives the low pressure compressor to produce low pressure compressed air; and passing the low pressure compressed air from the low pressure compressor into a high pressure compressor of the outer spool.

In one aspect of the embodiment, the process of converting a spool aero gas turbine engine into an industrial gas turbine engine further includes the step of: placing a row of variable inlet guide vanes at an inlet to the power turbine.

In one aspect of the embodiment, the process of converting a twin spool aero gas turbine engine into an industrial gas turbine engine further includes the step of: reusing the low pressure compressor of the aero engine as the low pressure compressor driven by the power turbine in the industrial engine.

In one aspect of the embodiment, the process of converting a twin spool aero gas turbine engine into an industrial gas turbine engine further includes the step of: placing a row of variable inlet guide vanes at an inlet to the low pressure compressor.

In one embodiment, an industrial gas turbine engine converted from a twin spool aero gas turbine engine with a fan and a low pressure compressor includes: a low spool shaft with a low pressure turbine directly connected at one end and an electric generator connected at an opposite end and the low pressure compressor removed from the low spool shaft; a high spool shaft rotatable over the low spool shaft, the high spool shaft having a high pressure compressor connected to a high pressure turbine; a combustor connected between the high pressure compressor and the high pressure turbine; a power turbine located downstream from the low pressure turbine such that hot gas exhaust from the low pressure turbine drives the power turbine; a low pressure compressor driven by the power turbine; the power turbine 21 being located between the low pressure turbine and the low pressure compressor; a compressed air line connecting an outlet of the low pressure compressor to an inlet of the high pressure compressor; and a row of variable guide vanes located between the low pressure turbine and the power turbine.

In one aspect of the embodiment, the compressors and the turbines are all axial flow devices.

In one aspect of the embodiment, a hot gas flow produced in the combustor passes through the high pressure turbine first, then through the low pressure turbine, and then through the power turbine.

In one aspect of the embodiment, the low pressure compressor of the industrial gas turbine engine is a low pressure compressor of an aero engine, and the industrial gas turbine engine further includes a row of variable inlet guide vanes at an inlet to the low pressure compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 shows a schematic representation of an aero gas turbine engine with a fan of the prior art; and

FIG. 2 shows a schematic representation of the aero engine from FIG. 1 converted into an industrial gas turbine engine for electrical power production according to the present invention. DETAILED DESCRIPTION

The present invention is an apparatus and a process for converting an aero gas turbine engine with a fan such as the aero engine in FIG. 1 into an industrial gas turbine engine that is used to drive an electric generator and produce electrical power. The aero gas turbine engine 10 may be converted into an industrial gas turbine (IGT) engine 20, shown in FIG. 2. The converted IGT engine 20 includes the high speed spool with the high pressure compressor 11 connected to the high pressure turbine 13 and the combustor 12 located between them.

In the FIG. 2 converted industrial gas turbine (IGT) engine 20, the low pressure compressor (LPC) 14 and the fan 16 of the FIG. 1 engine is removed and replaced with an electric generator 26 that is driven directly by the inner spool or shaft 18 connected to the low pressure turbine (LPT) 15. In the FIG. 2 converted IGT engine 20, the LPT 15 now becomes an intermediate or middle pressure turbine (MPT) 15 (and is therefore referred to as the LPT/MPT 15), and a low pressure turbine (LPT) 21 (which is also referred to herein as a power turbine 21) is added in a downstream flow path from the LPT/MPT 15 and air exhaust of the LPT/MPT 15 drives the LPT/power turbine 21. The low pressure compressor 14 of the aero gas turbine engine 10 can be reused or repurposed as the low pressure compressor 22 of the converted IGT engine 20 that is driven by the LPT/power turbine 21. The LPT/power turbine 21 is connected by a spool or shaft 25 to a low pressure compressor (LPC) 22 that supplies compressed air to an inlet volute 24 of the HPC 11 through a compressed air line 23. Turbine exhaust from the LPT/power turbine 21 flows out from the converted IGT engine 20 as seen by the arrow in FIG. 2 (flowing out from the LPT/power turbine 21), while ambient air is drawn into the LPC 22 through a duct as seen by the arrow in FIG. 2 (flowing into the LPC 22). The HPC 11 can also include multiple variable stator vanes (VSV). Variable inlet guide vanes 28 can be used in the converted IGT engine 20 at the inlet to the low pressure compressor 22 in order to regulate the flow and thus control the speed of the converted IGT engine 20. Variable inlet guide vanes 27 are also used at an inlet to the LPT/power turbine 21.

The converted IGT engine 20 of FIG. 2 uses the LPT/MPT 15 to directly drive the electric generator 26 through the inner spool or shaft 18 and thus will operate at a constant rotational speed such as 3,600 rpm for a US generator (60 Hz) or 3,000 rpm for a European generator (50 Hz). The high spool (outer spool or shaft 17) with the HPC 11 and the HPT 13 can operate at variable speeds with respect to the low spool (inner spool or shaft 18) because the two spools or shafts are not connected mechanically. Additionally, the shaft 25 with the LPT/power turbine 21 and the LPC 22 is not connected mechanically to the high spool (outer spool or shaft 17) or the low spool (inner spool or shaft 18) and can thus be operated as a separate unit from the high spool by using the variable inlet guide vanes 27 so that compressed air delivered to the HPC 11 can be controlled based on the engine load (full power or partial power). In one embodiment, the compressors (for example, the HPC 11 and the LPC 22) and the turbines (for example, the HPT 13, the LPT/MPT 15, and the LPT/power turbine 21) are all axial flow devices.

Variable inlet guide vanes can be used in the converted IGT engine 20 of the present invention in three different embodiments. Variable inlet guide vanes can be used at the inlet to the LPT/power turbine 21 (variable inlet guide vanes 27), or at the inlet to the low pressure compressor 22 (variable inlet guide vanes 28), or at the inlets of both the LPT/power turbine 21 and the low pressure compressor 22 (variable inlet guide vanes 27 and 28, respectively).

In one embodiment, a process of converting a twin-spool aero gas turbine engine 10 having an outer spool 17 and an inner spool 18 with a fan 16 into an industrial gas turbine engine 20 that drives an electric generator 26 includes the steps of: removing the fan 16 from the aero gas turbine engine 10; removing a low pressure compressor 14 from the inner spool 18 of the aero gas turbine engine 10; connecting the inner spool 18 to the electric generator 26; placing a power turbine 21 downstream from a low pressure turbine 15 of the aero gas turbine engine 10 such that an exhaust from the low pressure turbine 15 drives the power turbine 21; connecting a low pressure compressor 22 to the power turbine 21 such that the power turbine 21 drives the low pressure compressor 22 to produce low pressure compressed air; and passing the low pressure compressed air from the low pressure compressor 22 into a high pressure compressor 11 of the outer spool 17.

In one aspect of the embodiment, the process of converting a spool aero gas turbine engine 10 into an industrial gas turbine engine 20 further includes the step of: placing a row of variable inlet guide vanes 27 at an inlet to the power turbine 21.

In one aspect of the embodiment, the process of converting a twin spool aero gas turbine engine 10 into an industrial gas turbine engine 20 further includes the step of: reusing the low pressure compressor 14 of the aero engine 10 as the low pressure compressor 22 driven by the power turbine 21 in the industrial gas turbine engine 20.

In one aspect of the embodiment, the process of converting a twin spool aero gas turbine engine 10 into an industrial gas turbine engine 20 further includes the step of: placing a row of variable inlet guide vanes 28 at an inlet to the low pressure compressor 22.

In one embodiment, an industrial gas turbine engine 20 converted from a twin spool aero gas turbine engine 10 with a fan 16 and a low pressure compressor 14 includes: a low spool shaft 18 with a low pressure turbine 15 directly connected at one end and an electric generator 26 connected at an opposite end and the low pressure compressor 14 removed from the low spool shaft 18; a high spool shaft 17 rotatable over the low spool shaft 18, the high spool shaft 17 having a high pressure compressor 11 connected to a high pressure turbine 13; a combustor 12 connected between the high pressure compressor 11 and the high pressure turbine 13; a power turbine 21 located downstream from the low pressure turbine 15 such that hot gas exhaust from the low pressure turbine 15 drives the power turbine 21; a low pressure compressor 22 driven by the power turbine 21; the power turbine 21 being located between the low pressure turbine 15 and the low pressure compressor 22; a compressed air line 23 connecting an outlet of the low pressure compressor 22 to an inlet of the high pressure compressor 11 ; and a row of variable inlet guide vanes 27 located between the low pressure turbine 15 and the power turbine 21.

In one aspect of the embodiment, the compressors 11, 22 and the turbines 13, 15, 21 are all axial flow devices.

In one aspect of the embodiment, a hot gas flow produced in the combustor 12 passes through the high pressure turbine 13 first, then through the low pressure turbine 15, and then through the power turbine 21.

In one aspect of the embodiment, the low pressure compressor 22 of the industrial gas turbine engine 20 is a low pressure compressor 14 of an aero gas turbine engine 10, and the industrial gas turbine engine 20 further includes a row of variable inlet guide vanes 28 at an inlet to the low pressure compressor 22.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims

What is claimed is:

1. A process of converting a twin- spool aero gas turbine engine (10) having an outer spool (17) and an inner spool (18) with a fan (16) into an industrial gas turbine engine (20) that drives an electric generator (26), the process comprising the steps of:

removing the fan (16) from the twin-spool aero gas turbine engine

(10);

removing a low pressure compressor (14) from the inner spool (18) of the twin-spool aero gas turbine engine (10);

connecting the inner spool (18) to the electric generator (26);

placing a power turbine (21) downstream from a low pressure turbine (15) of the twin-spool aero gas turbine engine (10) such that an exhaust from the low pressure turbine (15) drives the power turbine (21);

connecting a low pressure compressor (22) to the power turbine (21) such that the power turbine (21) drives the low pressure compressor (22) to produce low pressure compressed air; and

passing the low pressure compressed air from the low pressure compressor (22) into a high pressure compressor (11) of the outer spool (17). 2. The process of converting a twin spool aero gas turbine engine (10) into an industrial gas turbine engine (20) of claim 1 , and further comprising the step of:

placing a row of variable inlet guide vanes (27) at an inlet to the power turbine (21).

3. The process of converting a twin spool aero gas turbine engine (10) into an industrial gas turbine engine (20) of claim 1 , and further comprising the step of:

reusing the low pressure compressor (14) of the twin-spool aero gas turbine engine (10) as the low pressure compressor (22) driven by the power turbine (21) in the industrial gas turbine engine (20).

4. The process of converting a twin spool aero gas turbine engine (10) into an industrial gas turbine engine (20) of claim 1, and further comprising the step of:

placing a row of variable inlet guide vanes (28) at an inlet to the low pressure compressor (22). 5. An industrial gas turbine engine (20) converted from a twin spool aero gas turbine engine (10) with a fan (16) and a low pressure compressor (14), the industrial gas turbine engine (20) comprising:

a low spool shaft (18) with a low pressure turbine (15) directly connected at one end and an electric generator (26) connected at an opposite end and the low pressure compressor (14) removed from the low spool shaft (18);

a high spool shaft (17) rotatable over the low spool shaft (18), the high spool shaft (17) having a high pressure compressor (11) connected to a high pressure turbine (13); a combustor (12) connected between the high pressure compressor (11) and the high pressure turbine (13);

a power turbine (21) located downstream from the low pressure turbine (15) such that hot gas exhaust from the low pressure turbine (15) drives the power turbine (21);

a low pressure compressor (22) driven by the power turbine (21); the power turbine (21) being located between the low pressure turbine (15) and the low pressure compressor (22);

a compressed air line (23) connecting an outlet of the low pressure compressor (22) to an inlet of the high pressure compressor (11); and

a row of variable inlet guide vanes (27) located between the low pressure turbine (15) and the power turbine (21).

6. The industrial gas turbine engine (20) of claim 5, wherein:

the compressors (11, 22) and the turbines (13, 15, 21) are all axial flow devices.

7. The industrial gas turbine engine of claim 5, wherein:

a hot gas flow produced in the combustor (12) passes through the high pressure turbine (13) first, then through the low pressure turbine (15), and then through the power turbine (21).

8. The industrial gas turbine engine (20) of claim 5, wherein the low pressure compressor (22) of the industrial gas turbine engine (20) is a low pressure compressor (14) of an aero engine (10), the industrial gas turbine engine (20) further comprising a row of variable inlet guide vanes (28) at an inlet to the low pressure compressor (22).