WO1997010416A1

WO1997010416A1 - Power-generation method using combined gas and steam turbines

Info

Publication number: WO1997010416A1
Application number: PCT/EP1995/003649
Authority: WO
Inventors: Ci Liu; Karsten Radtke; Heinz-Jochen Keller
Original assignee: Krupp Uhde Gmbh
Priority date: 1995-09-16
Filing date: 1995-09-16
Publication date: 1997-03-20
Also published as: AU3568395A

Abstract

The invention concerns a method of power generation using a so-called COGAS (combined gas and steam) turbine installation, the aim being to improve the method with regard to the initial costs and energy consumption so that power can be generated as cheaply as possible. This is achieved by virtue of the fact that air (5) taken from the surrounding atmosphere is split into an essentially oxigen-containing stream (7) and an essentially nitrogen-containing stream (6) and the two streams fed further at approximately atmospheric pressure. The essentially nitrogen-containing stream (6) is mixed with an air stream (10) to form a mixed nitrogen/air stream (11) and the mixed-gas stream thus produced is brought to combustion-chamber pressure in the compressor (107) of the gas turbine (105), the combustion of the combustion gases in the combustion chamber (164) of the gas turbine being carried out with the greater part of this compressed mixed-gas stream.

Description

'Power generation process using a combined gas / steam turbine process'

The invention relates to a power generation process using a so-called combination process, i.e. of a combined gas and steam turbine process, in which the fuel gas used in the gas turbine is generated by partial oxidation of carbon-containing fuels and is fed to a gas turbine as hot compressed gas, and at least the energy of the turbine exhaust gases for generating the steam turbine steam is used.

The methods for power generation must have a high thermodynamic efficiency, correspond to the valid requirements with regard to air pollution control and cause tolerable costs. Among other things, these requirements are met. the combined gas and steam turbine process with integrated fuel gas generation.

In this process, the fuel used is converted into fuel gas by means of partial oxidation. Air, oxygen-enriched gas or oxygen serve as the oxidizing agent. In the present invention, the fuel gas generation takes place in a gasification process in which the fuels are partially oxidized by means of oxygen or by means of oxygen-enriched gas. The carbon-containing fuels used are, for example, coal, wood, peat, bituminous distillation residues from petroleum processing, aqueous emulsions of petroleum or hydrocarbons or fractions from petroleum processing, such as heavy oils or petrol.

The fuel is partially oxidized under pressure and thus gasified, creating a raw fuel gas as a product. Gasification pressures in the range from 25 to 85 bar are used, but the present invention is not restricted to this range.

The gasification of the fuels may be in the temperature range of 800 C to 1,600 ^β * C are made, the in the carburetor ein¬ detected temperature depends on the desired composition of the produced Zu¬ raw fuel gas and the fuel used. At high gasification temperatures above 1,300 ° C, carbon conversion is close to 100% and a high gas purity is achieved, ie very little higher hydrocarbons are formed.

The raw fuel gas is cooled in a raw gas cooler and then freed of dust if necessary. The sulfur compounds separated in the subsequent gas scrubbing are converted to elemental sulfur, which is used as a by-product. can be bought. The pure fuel gas generated in gas cleaning is released to the gas turbine system at a pressure of, for example, approximately 20 bar.

The cleaned fuel gas is burned and expanded in a gas turbine system with a combustion chamber pressure of 16 bar, for example. In a waste heat boiler downstream of the gas turbine plant, high pressure steam is generated with the hot gas turbine exhaust gas, which, like the steam produced in the raw gas cooler after the gasification, is fed to a steam turbine. Over half of the total electrical energy generated comes from the gas turbine.

The main advantages of this combined gas and steam turbine process with integrated fuel gas generation are obvious:

As a result of the thermodynamic advantages due to the higher pressure or temperature level of the energy conversion in the gas turbine and through the combination of the gas and steam turbine processes, a considerably higher degree of efficiency is achieved than in the conventional process in which the fuel used is used in the comparatively low atmosphere ¬ pressure is burned. The cleaning of the raw fuel gas under increased pressure enables an extremely effective and economical separation of the pollutants.

The oxidizing agent consumed in the partial oxidation, that is to say the oxygen or the gas enriched with oxygen, is generated in an air separation plant. The air to be separated is taken from the atmosphere and compressed. By utilizing the Joule-Thomson effect during expansion and by guiding the heat exchange in countercurrent, the air is liquefied and separated by distillation into an oxygen-carrying and a nitrogen-carrying partial flow. The partial streams are released in gaseous form by the air separation and slightly above atmospheric pressure. The oxygen-carrying partial stream is compressed to the gasification pressure and fed into the gasifier. However, it is also possible with other methods of air separation to generate a nitrogen-carrying partial stream at slightly above atmospheric pressure.

At least a portion of the nitrogen-carrying partial flow produced by the air separation is compressed separately to the combustion chamber pressure and fed into the combustion chamber of the gas turbine. The injection of nitrogen into the combustion chamber of the gas turbine is done with the intention of preventing the formation of nitrogen oxides when the fuel gas is converted into the gas turbine combustion chamber to a minimum.

In the publication by R. Müller and U. Schiffers, "Coal pressure gasification for the combination process; status, efficiency and development goals", published in VGB KRAFTWERKSTECHNIK 68, Issue 10, October 1988, pages 1022 to 1030, combined gas and steam turbine processes with integrated fuel gas generation are shown, the fuel gas generation from coal being the focus of the discussions. In this publication, a process flow diagram for the above-described combined gas and steam turbine process (CCGT process) is given in Figure 4 and Figure 5, respectively. Unfortunately, the captions are reversed. Figure 4 correctly shows the "CCGT power plant with Texaco carburettor" and Figure 5 the "CCGT power plant with PRENFLO carburetor".

In both of the methods shown, the compression work required in air separation to compress the air used is performed by the compressor of the gas turbine system. However, this circuit has a disadvantage which comes into play when the entire power plant is started up. The mutually dependent parts of the system must be started one after the other in the order of their arrangement. In this case, the air Disassembly, then the gasification and then the gas turbine system to produce in a functionally appropriate manner, since the gasification cannot work without the supply of the oxygen-carrying partial gas and, likewise, the supply of the fuel gas generated in the gasification only allows the gas turbine to be started .

In the process flow diagrams shown in Fig. 4 and Fig. 5, however, the function of the air separation depends on the compression work of the gas turbine, i.e. the chain of dependencies is closed and the combined cycle power plant can only be started by means of additional auxiliary devices (not shown). In addition, the dependencies make it more difficult to adapt the combined cycle power plant to changes in load.

WO 92/17775 specifies a method for a combined cycle power plant in which an inert gas is admixed with the fuel gas supplied to the gas turbine system under pressure in order to limit the generation of No _x . Water vapor, nitrogen or CO2 are mentioned as admixtures. There is no indication of adding inert gas to the air drawn in by the compressor of the gas turbine system. However, with the methods of the type described above, it is still not possible to achieve a completely satisfactory use of energy by the fuel used.

The object of the present invention is to achieve an improvement in the known process control with regard to the energy expenditure and the installation costs and to make it as economical as possible.

With a method of the type described in the introduction, this object is achieved according to the invention in that

that the air is taken from the environment and separated into an essentially oxygen-containing sub-stream and an essentially nitrogen-containing sub-stream in an air separation and the sub-streams are continued approximately under ambient pressure,

that the essentially nitrogen-containing partial stream is mixed with an air stream to form mixed air,

- That the resulting mixed air is brought to combustion chamber pressure in the compressor of the gas turbine, and

- That the combustion of the combustion gases in the combustion chamber of the gas turbine system is carried out with the majority of this compressed mixed air. In an embodiment, the invention provides a method in which

a) fuel in a fuel gas production is gasified by partial oxidation under pressure and then cleaned of harmful substances and a purified fuel gas is formed;

b) water vapor is mixed with the cleaned fuel gas and it is burned under pressure in the combustion chamber of a gas turbine system, as a result of which hot compressed gas is produced;

c) the hot compressed gas in the gas turbine of a gas turbine plant is expanded into flue gas and mechanical work is thereby obtained;

d) part of the mechanical work in the generator of the gas turbine plant is converted into electrical current and the remaining mechanical work drives the compressor of the gas turbine plant;

e) air is taken from the environment and it is separated into an essentially oxygen-containing partial flow and an essentially nitrogen-containing partial flow in an air separation and the partial flows are emitted approximately under ambient pressure; f) the oxygen-containing partial stream is brought to the gasification pressure by means of an oxygen compressor and is fed into the pressure gasifier of the fuel gas generation in order to bring about the partial oxidation of the fuel therein;

g) the flue gas obtained in the aforementioned section c) is conducted in a waste heat boiler in indirect heat exchange to water fed into the waste heat boiler, whereby steam is generated in the waste heat boiler, and the thermal energy transferred to the steam by means of a steam turbine and generator is at least partially in electrical Electricity is converted;

h) the flue gas cooled in the waste heat boiler is discharged into the environment;

i) the substantially nitrogen-containing partial stream generated in the aforementioned section e) is at least partially mixed with a further air stream and mixed air is formed;

j) the resulting mixed air in the compressor of the gas turbine system is brought to combustion chamber pressure and, with the essential part of the compressed mixed air, the combustion of the combustion gases in the combustion chamber of the gas turbine system.

The method according to the invention has a number of advantages:

The essentially nitrogen-carrying partial flow that is compulsory in the air separation is mixed with the air intended for the combustion of gas in the combustion chamber. The compressor of the gas turbine system conveys a constant delivery quantity which is dependent on the respective pressure ratio. The admixed nitrogen-carrying partial flow replaces a corresponding part of the air in the delivery volume. The delivery rate thus consists of mixed air, in which the oxygen content is reduced compared to that of the air taken from the environment. This possibility of influencing the oxygen content of the mixed air supplied to the combustion chamber can surprisingly be used to reduce nitrogen oxide formation in the combustion chamber.

Another significant advantage arises from the fact that a separate compressor, which has to bring the partial nitrogen-carrying partial flow to the combustion chamber pressure, is no longer required. This significantly reduces investment and operating costs. The operating cost savings is given by the fact that the proportion of the air in the delivery volume replaced by the nitrogen can no longer be compressed.

Another major advantage is that more electricity can be delivered to the grid at the plant boundary. This increases the efficiency of the energy conversion. This is an environmentally friendly effect because more electricity is generated per fuel unit used or, conversely, less carbon dioxide, which acts as a greenhouse gas, is emitted per kilowatt hour generated.

Further advantages, details and features of the invention result from the following description and from the drawing. In the single figure, this shows a process closure diagram in a simplified representation.

In the figure, the part of the plant in the foreground, namely the gas turbine plant, is generally designated by 100, the upstream air separation plant by 200 and the downstream steam turbine plant, which is less important here, by 300.

In the example shown, the fuel is fed from left to right according to arrow 1 into a fuel gas generator 101, where the path of the fuel gas is represented by a line that is stronger than the other lines. The following parts of the system are the fuel gas purification 102, fuel gas humidification 103 which may be provided, the combustion chamber 104, the gas turbine 105 and the waste heat boiler 106 acted upon by the exhaust gases.

The route of the fuel gases after the fuel gas generation 101 is denoted by 2, that of the exhaust gases by 3; the exhaust gases after the waste heat boiler are symbolized by an arrow 4.

Air is also fed into the system, specifically for the first time in the air separation 200, where the air inlet is designated by 5. By air separation, a predominantly nitrogen-containing gas stream 6 is discharged from the air separation and a stream 7 predominantly containing oxygen. The oxygen 7 is compressed by a compressor 201 and supplied in compressed form to the fuel gas generation 101. The oxygen flow compressed to the prevailing gasifier pressure bears the reference number 8. Water vapor or water is optionally fed to the fuel gas humidification 103, the corresponding arrow is designated by 9 in the figure. Of importance for the invention is a second air supply into the system, namely to act on the compressor 107 of the gas turbine system 100, which is driven by the gas turbine 105, the latter also driving the gas turbine generator 108 to generate electricity. This second air supply is designated 10, it is evidently acted upon by the nitrogen flow 6, the two flows mixed into one another being fed to the compressor 107 according to arrow 11 and being fed into the combustion chamber 104 as a compressed base flow or mixed air flow 16. The figure also shows a decrease in excess air according to arrow 13.

The process steam extraction 14 from the waste heat boiler 106 to act on the steam turbine 109, which drives the generator 110, is merely indicated in the figure.

In addition to the fuel, oxygen and steam are fed into the fuel gas generator 101 as a gasifying agent and the gasification is carried out at an increased pressure, for example above 30 bar. The resulting raw gas is cooled, whereby steam can be generated, which can be used in the water / steam cycle process, for example by means of the steam turbine 109, to generate electricity. During the fuel gas cleaning 102, the fuel gas accompanying substances NH3, H2S, COS and dust are extracted from the raw fuel gas, whereby different cleaning depending on the fuel supplied can be provided. The cleaned fuel gas is, as already briefly stated above, saturated or moistened with water vapor in the fuel gas humidification 103, the amount of fuel gas being, for example, 18.1 kg / s. The fuel gas is fed to the gas turbine system 100 at a pressure of, for example, 22 bar and a temperature of, for example, 240 ° C. One of the possible compositions is shown in the table at the end of the description.

In this example, the combustion of the fuel gas 2 in the combustion chamber 104 of the gas turbine system 100 produces hot compressed gases 3 of 199.8 kg / s, which are fed to the gas turbine 105. The hot compressed gas 3 enters the gas turbine 105 from the combustion chamber 104 at a temperature of 1190 ° C. and a pressure of 18 bar.

A shaft power of 154 MW is generated by the gas turbine 105, of which 81 MW are delivered to the compressor 107 in the example described here, and 71 MW of electrical power are generated from the rest. The flue gas 15 passed on from the gas turbine 105 to the waste heat boiler 106 has the consequence of the previous expansion Ambient pressure still a temperature of 573 ^β C, which is used for the generation of steam acting on the steam turbine 109 (arrow 14).

To supply the combustion chamber 104, 148.1 kg / s air from the environment are combined with 38.9 kg / s nitrogen 6 from the air separation 200 and combined to form a mixed air quantity of 187.0 kg / s.

This mixed air 11 is brought in the compressor 107 to the fuel pressure of 18 bar, an excess air quantity 13 of up to 5.3 kg / s being able to be taken from the compressed mixed air flow for control purposes. The mixed air 12 enters the combustion chamber at 420 ° C. The composition of the mixed air 11 is also given in the table below.

Due to the fact that such a mixed air flow is generated according to the invention, 13 MW of compressor work can be saved in the example presented here, which enable a corresponding additional production of electric current.

Table 1:

Table 1

Claims

claims

1.Power generation process using a so-called combination process, i.e. a combined gas and steam turbine process, in which the fuel gas used in the gas turbine is generated by partial oxidation of carbon-containing fuels and is fed to a gas turbine as hot compressed gas, and wherein at least the energy of the turbine exhaust gases is used to generate the steam turbine steam is used, characterized in that

that air is taken from the environment and separated into an essentially oxygen-containing partial flow and an essentially nitrogen-containing partial flow in an air separation and the partial flows are carried on approximately under ambient pressure,

- That the resulting mixed air in the compressor of the gas turbine is brought to combustion chamber pressure and

- That the combustion of the combustion gases in the combustion chamber of the gas turbine system is carried out with the majority of this compressed mixed air.

2. Power generation method according to claim 1, characterized in that a) that the fuel is gasified in a fuel gas generation by means of partial oxidation under pressure and then cleaned of pollutants and a purified fuel gas is formed;

b) that the cleaned fuel gas is admixed with water vapor and it is burned under pressure in the combustion chamber of a gas turbine system, thereby producing hot compressed gas;

c) that the hot compressed gas is expanded into flue gas in the gas turbine of a gas turbine system and mechanical work is thereby obtained;

d) that part of the mechanical work in the generator of the gas turbine system is converted into electrical current and the remaining mechanical work drives the compressor of the gas turbine system;

e) that air is taken from the environment and separated into an essentially oxygen-containing partial stream and an essentially nitrogen-containing partial stream in an air separation and the partial streams are released at approximately ambient pressure; f) that the oxygen-containing partial stream is brought to the gasification pressure by means of an oxygen compressor and fed into the pressure gasifier of the fuel gas generation in order to bring about the partial oxidation of the fuel therein;

g) that the flue gas obtained in the aforementioned section c) is conducted in a waste heat boiler in indirect heat exchange to the water fed into the waste heat boiler, whereby steam is generated in the waste heat boiler and the thermal energy transferred to the steam by means of a steam turbine and generator is at least partially in electrical ¬ tric current is converted;

h) that the flue gas cooled in the waste heat boiler is discharged into the environment,

i) that the essentially nitrogen-containing partial stream generated in the aforementioned section e) is at least partially admixed with a further air stream and mixed air is formed;

j) that the resulting mixed air in the compressor of the gas turbine system is brought to combustion chamber pressure and that the essential part of the compressed mixed air combustion of the fuel gas is effected in the combustion chamber of the gas turbine system.

3. Power generation method according to claim 1 or 2, characterized in that the nitrogen-containing gas stream (6) is admixed with CO2 or the nitrogen is replaced by CO2.

4. Power generation process according to one of the preceding claims, characterized in that the nitrogen-containing gas stream (6) is mixed with inert gases with combustible admixtures (weak gases) or that N2 is replaced by these gases.

5. Power generation method according to a preceding Ansprü¬ che, characterized in that the gas turbine (105) for driving work machines, e.g. a compressor for an NH2 or CH3θH system, is used.