WO2009108079A2

WO2009108079A2 - Method and plant for generating mechanical or electrical power from waste heat and apparatus for a power plant

Info

Publication number: WO2009108079A2
Application number: PCT/RU2008/000101
Authority: WO
Inventors: Norbert Huber; Viacheslav Vsevolodovich Schuchkin
Original assignee: Siemens Aktiengesellschaft
Priority date: 2008-02-22
Filing date: 2008-02-22
Publication date: 2009-09-03
Also published as: WO2009108079A3

Abstract

A method for generating electrical energy with at least one expansion turbine and a thermokinetic compressor, whereby the expansion turbine (20) from which mechanical work is gained is installed downstream the thermokinetic compressor (30) instead upstream. In a power plant for this method with at least one waste heat unit (10), at least one expansion turbine and a thermokinetic compressor (30) with a diffuser (35) the length of the diffuser (35) can be reduced.

Description

METHOD AND PLANT FOR GENERATING MECHANICAL OR ELECTRICAL POWER FROM WASTE HEAT AND APPARATUS FOR A

POWER PLANT

Description The invention is related to a method for generating mechanical or electrical power from waste heat. Beyond the invention is also related to a plant for generating such mechanical or electrical power from waste heat with an improved apparatus. Finally the invention is related to such an apparatus itself.

In US 6 935 096 B 2 a device called thermokinetic compressor (TC) is suggested. This device converts waste heat from airflow at low pressure to airflow at higher pressure. The energy conversion is enabled by adding water spray. The resulting device is a machine without any rotating parts.

The examples of that patent document contains an expansion turbine, which is installed upstream the device called thermokinetic compressor. This feature results in a pressure below atmospheric pressure at the inlet of this thermokinetic compressor (see Figure 1 below).

In the known technique there are some problems. These are: The use of a thermokinetic compressor results in a large axial length of the whole device, i.e. several meters, caused by necessity of static pressure recovery at the outlet. Further there is the necessity of a bypass channel for start up of thermokinetic compressor, installed downstream the expansion turbine.

At least the power density of the device is limited by the following factors: 1. The hot gas density at the inlet of the thermokinetic compressor is due to a pressure level below ambient pressure. 2. A low inlet gas temperature and fixed hot gas mass flow rate limit the amount of evaporated water and pressure recovery value.

Up to now no other and better devices of this kind are known. The mentioned problems were tolerated.

Therefore it is the main object of the invention to create a better arrangement with said thermokinetic compressor and a method to integrate it in a power plant. It is a special aim of the invention to solve above described problems.

In respect to the method the invention is defined in claim 1 , whereby a plant with such an apparatus is defined in claim 7. Special features of the invention are given in the dependent claims. Especially claim 13 defines a basic condition for a better geometry of a thermokinetic compressor for all uses.

The invention can be realized in all kinds of waste heat generating procedures, e.g. in gas turbines, boilers, heat generating processes and combustion machines.

Objective of the invention is that the expansion turbine from which mechanical work is gained is installed downstream the thermokinetic compressor instead upstream.

In an advantageous modification of the invention the Thermokinetic Compressor (TC) with an expansion turbine installed downstream can be combined into a single unit which allows avoiding an extended diffuser part by connecting the expansion turbine directly at the outlet of the thermokinetic compressor. Therefore the length of the device can be reduced drastically.

In a further advantageous modification of the invention both devices can be combined into a single one through combination of the thermokinetic compressor

(TC) with an expansion turbine downstream of it, removing the diffuser part of thermokinetic compressor or at least reduce its length drastically. In this case both parts define together one single apparatus.

There are following advantages realized by the invention: 1. The power output increases: since the thermokinetic compressor is placed upstream the expansion turbine and not downstream like in state of art and evaporated water increases turbine mass flow rate G w GO + Gw of about 10-20%. This allows to increase the power L2 of the machine with a factor I of about 10-20% of L2.

2. The power output increase: because of higher inlet temperature and a resulting higher water evaporation rate can potentially provide a higher energy conversion rate which gives a higher pressure ratio in the thermokinetic compressor. An additionally reduced friction results in a better efficiency with a factor II of about 40-70% of L2.

3. There are reduced material consumption and lower space requirements: The thermokinetic compressor diffuser is not required in the scheme in Figure 2 since the high pressure flow expands in the expansion turbine producing power from static and dynamic pressure the device length is almost half smaller in this case. 4. It needs less parts: Using the suggested scheme with high-pressure thermokinetic compressor - as shown in Figure 2 below - a bypass channel is not required for start up since the thermokinetic compressor (TC) is placed upstream the turbine and not downstream like in the scheme of Figure 1 , so obviously a bypass valve is not required in this case.

In the scope of the invention such thermokinetic compressors could be used with a special geometry: Usually such compressors have a zone of geometric acceleration with a cross sectional area of Al in a first waist and a zone of thermal acceleration with a cross sectional area of A2 in a second waist of the 'Laval nozzle'- formed channel. It is advantageous to have a large ratio of Al to A2 in the range:

O,8 < A1 / A2 < 1.

The ratio A1/A2 could be preferably in the range between 0,92 and 0,96.

It was recognized that with geometries having A1/A2 smaller than 0.8 - as in the state of art - according to check-up numerical analysis with ANSYS CFX, potential risk of incident shocks in the supersonic part of the channel can lead to total pressure losses. Therefore only a limited efficiency would result in that case. Potential risk of essential pressure and temperature gradients in the incident shocks may lead to problems with water evaporation and flow instability in the thermokinetic compressor. The first nozzle of thermokinetic compressor of the invention has the function of a Laval nozzle. This means in the apparatus an acceleration of flow from subsonic speed to sonic speed and beyond. In the invention implemented only a weak Laval nozzle with a cross sectional area ratio A1/A2 larger than 0.8. An upper limit of A1/A2 would be 0.99. For sonic incoming flow A1/A2 can also be one (1,0). Especially the placement of obstacles, which are required for water spray injection, in the section of the Laval nozzle requires an adaptation of the outer wall contour.

The device power can potentially be doubled that, however, requires an adequate increase of the water injection rate.

A very preferable situation can be described by having A1/A2 in the range of 0.92 to 0.96 and having a water spray mass flow in the range 15-25% of the hot gas mass flow. This allows increasing device performance improving supersonic flow regime and neglecting risk of incident shocks. A Power Plant with the new arrangement of the thermokinetic compressor and an apparatus with such thermokinetic compressor have following advantages:

1. Over expansion of the first nozzle allows increasing thermokinetic compressor pressure ratio and device power potentially by 100%, according to preliminary analytical and numerical analysis with ANSYS CFX.

2. Low flow acceleration in the first nozzle of prospective channel in Figure2 (A1/A2 = 0.94) allows minimizing total pressure losses neglecting risk of incident shocks providing smooth transaction to supersonic flow regime, as it is seen from comparison with modelling results according to ANSYS CFX. Latter embodiment of a thermokinetic compressor is especially preferable in connection with the inventive method for combining a waste heat producing unit and an expansion turbine downstream to the thermokinetic compressor as claimed in claim 1 and 2. Preferable examples for the waste heat unit are claimed in claims 3 to 6.

But also in other power plants with a conventional combination of the main turbine and the expansion turbine downstream to the thermokinetic compressor it is favourable to use a thermokinetic compressor with such geometric dimensions and ratio of the cross areas Al and A2.

More features, details and advantages of the invention are shown in the detailed description of examples in combination with the figures of the drawing. There are shown:

Figure 1 the state of art with a schematic of an implementation of a thermokinetic compressor in an arrangement of power conversion, Figure 2 a schematic with an arrangement of the invention, Figure 3 a combined device of a thermokinetic compressor without diffuser and an expansion turbine,

Figure 4 the geometry of a known thermokinetic compressor, Figure 5 a prospective thermokinetic channel, and Figure 6 a new contour of the wall.

In the single figures same elements or parts have identical numerals or signs. The figures are described partially together.

Figure 1 and figure 2 show schematics of a waste heat unit with at least one expansion turbine and a thermokinetic compressor in a power plant. Figure 1 presents the schematic of a thermokinetic compressor implementation into the turbines in respect to the state of art: There is usually an unit 10, which produces waste heat, and a turbine 20, which has the function as an expansion turbine. The additional turbine 20 is installed downstream the waste heat unit 10. The waste heat unit 10 can be 3 a gas turbine. The waste heat can also be taken from a boiler or from a chemical or metallurgical process. At least the waste heat unit can also be a combustion machine.

In figure 1 the waste heat unit 10 is followed by the expansion turbine 10 with a generator 25, which produces electrical power L2, and the thermokinetic compressor 30. It is possible to use the mechanical power of the turbine directly, for example in pump. There is a bypass from the waste hear unit 10 to the thermokinetic compressor

30 with a valve 15.

The inlet pressure for turbine 20 is equal to P* = 1 atm. The pressure difference for turbine 20 is achieved by a low pressure exhaustion, for example P* = 0.7 atm, provided by a thermokinetic compressor 30, which subsequently recovers a total pressure value back to P* = latm at the atmospheric outlet. The thermokinetic compressor 30 has usually a diffuser 35 for pressure regain of the waste gas.

Figure 2 presents the new principle scheme of thermokinetic compressor implementation with a different arrangement of components. This scheme allows further increase of power output and essentially reduces the length of the device. The thermokinetic compressor 30 is placed upstream to the expansion turbine 20. The temperature T at the inlet of the thermokinetic compressor 30 is higher in this case and the pressure ratio can potentially be increased through an increase of evaporated water mass flow rate Gw up to 20% from total mass flow rate GO of the power plant. A total flow G with increased mass flow rate

G = GO + Gw and an increased total pressure p enters the turbine 20 raising its power, potentially by 100%, compared with the case of the state of the art presented in the Figure 1. In figure 2 it is shown that the diffuser 35, which is part of the thermokinetic compressor 30, can be omitted in special cases, what is described below. Normally there is a diffuser 35 for pressure regain, which length is dependant of the geometry, open angle, etc. This can be a long part, for example in the range of meters.

Now the length L of the diffuser 35 can be varied in a wide range, for example shortened or even cancelled. If the diffuser 35 has a length L and an inner diameter D3 at the beginning, the length of the diffuser 35 could be shortened in dependence to the diameter D3 in respect to the relation

0 < L/D3 < 20

There are a big advantage and a remarkable gain in efficiency.

Figure 3 presents the arrangement of a combined device including the thermokinetic compressor 30 and an expansion turbine 20 with a row of blades 21, which operates as a diffuser consuming kinetic energy generated in thermokinetic compressor 30 and transferred into mechanical work, reducing thereby total pressure till atmospheric level at the outlet. The expansion turbine 20 is physically integrated in the thermokinetic compressor 30 and define together one single apparatus.

Figure 4 presents the geometry of the thermokinetic compressor 30 channel as used in the state of art. The cross sectional area in the first waist is Al and the cross sectional area in the following channel is A2. In the entrance part there is the cross sectional area A3. The cross sectional areas correspond to a special inner diameter of the channel, e.g. Dj with i = 1, 2 or 3. Numeral 50 represents the line ofdisturbant shock waves in the channel Main characteristic of the geometry in Figure 4 is the first nozzle expansion ratio Al/A2=0.58 < 0.8, which determines pressure ratio P*_Out/P*in of thermokinetic compressor and the power of the device. The flow in the first nozzle of the channel in Figure 4, where A1/A2 = 0.58 < 0.8, accelerates to Mach number M = 2.0. This essential flow acceleration leads to the potential risk of significant total pressure losses as a result of incident shock initiation and propagation 40 downstream the channel, as it is seen from the results of numerical analysis with ANSYS CFX (= commercial Software program).

As presented in the Figure 5 the ratio of cross sectional areas is increased for example to A1/A2 = 0.94 for the prospective channel. It would be in the range 0.8 < A1/A2 < 0.99.

The Mach number M = 1.2 is noticeably less then M = 2.0 in the original case. Low flow acceleration allows minimizing the total pressure losses neglecting the risk of incident shocks initiation and propagation downstream the channel, as it is seen in this figure.

To keep supersonic flow regime in the middle part of the channel water mass flow rate should be increased for the case with over expanded nozzle with the geometrical parameter

A1/A2 = 0.94, e.g. 0.8 < A1/A2 < 0.99 - in any case < 1 -, from Gw « 10% up to Gw « 20% according to the results of numerical analysis. This is reasonable since small acceleration in the first nozzle should be compensated by thermal acceleration through water evaporation and supersonic flow cooling. Thermal acceleration of the flow in the evaporation zone does not lead to shock wave initiation since channel geometry is constant and supersonic flow does not change its direction during the acceleration process.

Figure 6 shows that with an extended wall contour any ratio of inlet cross sectional area to cross sectional area at the waist point of the Laval nozzle A1/A2 (e.g. A2 is the cross sectional area at the end of Laval nozzle, Al the cross sectional area of

Laval Nozzle) can be realized even if obstacles like the spray nozzle need a significant portion of the cross section.

Overall the invention described in respect to the figures propose a method for generating electrical energy with at least one expansion turbine and a thermokinetic compressor, whereby the expansion turbine from which mechanical work is gained will be installed downstream the thermokinetic compressor instead upstream. In a power plant for this method with at least one waste heat unit, at least one expansion turbine and a thermokinetic compressor with a diffuser the length of the diffuser 35 can be drastically reduced.

List of Numbers

Figure 1 State of Art of power generation (schematic) 10 Gas Turbine Unit or boiler or any other unit with waste heat 15 Valve 20 Expansion turbine

25 Generator

30 Thermokinetic Compressor 35 Diffuser

G, GO, Gw Gas mass flow rates L2 Elektrical or mechanical Power

H₂O Water Injection

Figure 2 schematic of invention

Figure 3 alternative apparatus of invention

20' expansion turbine part 21 Rows of blades

Figure 4 State of Art for Thermokinetic Compressor-Geometry

31 Wall Contour of Thermokinetic Compressor 50 line of shock waves

Al Cross section area in the first waist A2 Cross section area in the compressor channel

A3 Cross section area in the second waist

D3 Diameter in the second waist

L Diffuser length

Figure 5 modified Thermokinetic Compressor (TC) 32 Contour of modified TC

M Mach-Number

GA Geometric acceleration zone

Th.A Thermal acceleration zone

GD Geometric deceleration tone Figure 6 modified thermokinetic compressor

33 Modified wall contour to allow larger obstacles outside

40 obstacles water spray field H2O-inlet

Claims

1. A method for generating electrical or mechanical power from waste heat with at least one expansion turbine and a thermokinetic compressor, whereby the expansion turbine (20) from which mechanical work is gained is installed downstream the thermokinetic compressor (30) instead upstream. (FIG 2)

2. The method of claim 1, whereby the thermokinetic compressor (30) and the expansion turbine (20) installed downstream are combined into a single unit.(FIG 3)

3. The method of claim 1 or claim 2, whereby the waste heat is taken from a gas turbine.

4. The method of claim 1 or claim 2, whereby the waste heat is taken from a boiler.

5. The method of claim 1 or claim 2, whereby the waste heat is taken from a chemical or metallurgical process.

6. The method of claim 1 or claim 2, whereby the waste heat is taken from combustion machine.

7. A plant for the method of one of foregoing claims, with at least one heat exhaust unit (10), at least one expansion turbine (20) and a thermokinetic compressor (30) with a diffuser (35) with a special length (L) and diameter (D3), whereby the length (L) of the diffuser (35) is reduced.

8. The plant of claim 7, whereby the length (L) of the diffuser (35) is shortened in dependence to the diameter (D3) of the diffuser (35) in respect to the relation 0 < L/D3 < 20

9. The plant of claim 3, whereby the diffuser (35) of the thermokinetic compressor (35) is replaced by the expansion turbine (20).

10. The plant of claim 9, whereby the expansion turbine (20) is physically integrated in the thermokinetic compressor (30) and define together one single apparatus.

11. The plant of one of claims 7 to 10 with a thermokinetic compressor (30), which has a defined cross area (Al) in a first part, especially in the zone of geometric acceleration, and a defined cross area (A2) in a second part, especially in the zone of thermal acceleration, whereby the ratio of Al to A2 is: O.8 ≤ A1/A2 < 1.

12. The plant of claim 11, whereby the ratio of Al to A2 is in the range of 0.92 to 0.96.

13. An apparatus for use in a plant for generating electrical or mechanical power from waste heat, with the combination of at least one expansion turbine (20) and a thermokinetic compressor (30), whereby the thermokinetic compressor (30 ) has an inlet part with a defined area (Al) and a channel of a defined area (A2), which is greater than the area (Al) in the inlet part, characterized in that the ratio of the area (Al) in the inlet part to the area (A2) of the channel is related to A1/A2 > 0.8.

14. The apparatus of claim 12, whereby the ratio A1/A2 is in the range: O.8 ≤ A1/A2 < 1.

15. The plant of claim 13, whereby the ratio of Al to A2 is in the range of 0.92 to 0.96.