RU2553160C2 - Energy extraction from gases in blast-furnace unit - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention relates to gases cleaning in the blast-furnace unit. Method is suggested for thermal power generation from compressed cold air blow of the blast-furnace used with system of waste-heat turbine of blast-furnace gas in form of the turbine expander (20), containing at least one compressor (12) of compressed cold air blow connected with at least one air blow pre-heater (14), at that flow of the compressed blast-furnace gas exhausted by the blast-furnace (10) passes through the blast-furnace gas cleaning device (24) and is supplied in the turbine expander (20) connected with power consumer (34). From the cold air blow heat is extracted, it at least partially is transferred to the cleaned blast-furnace gas upstream the turbine expander (20). Besides, installation for thermal power extraction from the compressed cold air blow of the blast furnace is suggested, it contains device for heat extraction from the compressed cold air blow and its at least partial transfer to the cleaned blast-furnace gas upstream the turbine expander.

EFFECT: improved extraction of the thermal power from the compressed cold air blow of the blast furnace.

13 cl, 2 dwg

Description

This invention relates to the purification of gases in the installation of a blast furnace and, more specifically, to the extraction of energy from the blast furnace gas of the blast furnace in a turboexpander.

As is well known, gases play a fundamental role in the operation of a blast furnace. The first significant gas stream is the air stream (or “blown air”), which is blown in at the transition between the regions of the shoulders and the blast furnace and which reacts with the charge material (iron ore, coke, flux, etc.). Before blowing air is supplied to the tuyeres of the blast furnace, it is heated by passing through regenerative air heaters (also known as coolers), which are usually heated by burning the blast furnace off-gas. Atmospheric air admitted upstream of the Cowper forms a “cold blast”, while preheated blowing air downstream of the Cowper is called “hot blast”.

The other main gas stream in the blast furnace is the gas leaving the blast furnace at the top, known as “blast furnace gas” or “blast furnace gas”, which is a by-product of the blast furnace and is produced when iron ore is reduced by coke and / or other fuels in refined iron. Typically, blast furnace top gas is used as fuel in steel mills or in a cooler, but it can also be burned in boilers and power plants. It can also be combined with natural gas or coke oven gas before it is burned, or with an auxiliary gas burner with a higher calorific value, or oil is provided to maintain combustion.

It is also well known that blast furnaces have been operating for decades with internal overpressure, which, together with the proper dimensions of the furnace, allows a significant increase in the conversion of materials and energy and, thus, the output of pig iron.

Of course, working with internal overpressure also entails significant additional costs associated with equipment and operation. More specifically, it requires the generation of compressed air with a suitable supply pressure level in a cold blast compressor (or blower) to form a cold blast. It is also typical for operation at overpressure that the gas leaving the top gas is at a pressure well above atmospheric pressure. However, blast furnace gas still contains combustible components, mainly carbon monoxide and, to a lesser extent, hydrogen, and can be used as flue gas with low calorific value for the production of thermal or mechanical and electrical energy.

The blast furnace gas leaving the blast furnace also carries a significant amount of solid, mainly in dust form. Prior to the subsequent use of blast furnace gas, this solid material must be removed. This is usually achieved in a gas cleaning auxiliary installation of a blast furnace, which usually contains equipment for the first dry separation with a gravity separator (dust collector) and / or with an axial cyclone and a device for subsequent deep cleaning (wet separation separator). Due to wet cleaning, the temperature of the top gas drops by about 100 ° C, is saturated with water vapor and includes additionally flowing water droplets.

After purification, in addition to using the thermal energy of the top gas, it has long been known to extract the pneumatic energy of the compressed top gas of a blast furnace in a turboexpander. In the turbine, the top gas expands, approaching atmospheric pressure, while simultaneously performing mechanical work. The turbine rotor can be coupled, for example, with an electric generator, with a cold blast compressor, or with any other load.

Now it is also known that the performance of such a turboexpander (also called Top pressure recovery turbine - TRT (gas recovery non-compressor turbine - GUBT)) can be increased by heating the purified and, thus, cooled top gas directly before it enters the turbine. To this end, it is proposed to pre-heat the purified blast furnace gas upstream of the turbine by burning the expanded blast furnace gas. Alternatively, JP 62074009 proposes the removal of heat from slag granulation and the transfer of this heat to the cold purified gas upstream of the HUBT using a heat exchanger.

FR 2663685 describes a method for extracting energy from a blast furnace gas. Blast furnace gas passes through fine and / or coarse dust filtration, then through a turbine (pressure recovery) connected to a power generator, and then to the gas pipeline for subsequent use. The proportion of gas (3-15%, preferably about 5%) is bypassed before the turboexpander (12), if necessary, through a compressor, and burned in the combustion chamber, possibly enriched with high-calorific fuel, for example natural gas or coke oven gas. Then the gaseous products of combustion expand in the gas turbine. A gas turbine can be coupled to its own generator or to a turboexpander generator via a coupling. Preferably, the temperature of the portion of the cleaned blast furnace gas that is not passed through the bypass rises before it enters the recovery turbine due to heat exchange with the gaseous products of combustion in the gas turbine. Part of the cold blast stream may be burned in a gas turbine.

The aim of this invention is the creation of another, improved method of extracting energy from blast furnace gas in the installation of a blast furnace using HUBT.

This goal is achieved through the method and installation, as claimed in the independent claims.

The present invention provides an optimized method for controlling gas flows in a blast furnace installation, which allows the operation of high-pressure gas turbine with increased productivity, namely, a method for extracting energy from blast furnace gas in a blast furnace installation with a top gas utilization turbine system (turboexpander) containing at least one compressed cold air blast compressor (cold / air blast) connected to at least one air blast heater, including the direction of flow of compressed blast furnace gas emitted by the blast furnace into the blast furnace gas purification device and supply to a turboexpander coupled to an energy consumption device (load). According to the proposed method, heat is extracted from the compressed cold blast stream upstream from the cold blast heaters (i.e., cooler or the like), and then this heat is transferred (at least partially) to the cold stream of purified blast furnace gas upstream of the turbine expander . Extraction of heat from a cold blast is preferable since it circulates in the cold blast pipeline towards the heaters without consuming such cold blast to heat the cleaned top gas.

Thus, the temperature of the cold blast can be lowered in front of the regenerative air heaters and, at the same time, the temperature of the cold cleaned top gas can be increased, which improves the performance of both the cooler and the HUBT. Indeed, it is known that increasing the temperature of blast furnace gas to HLBT improves its productivity and helps to avoid icing risks, while lowering the temperature of the cold blast to the cooler improves the productivity of this preheating stage. More specifically, a lower cold blast temperature increases the heating capacity of the cooler.

It should be understood that while in blast furnace installations according to the prior art, the energy necessary for preheating the cleaned top gas was obtained by burning or extracting from the external environment, for example, slag granulation, and the extracted heat from cold blast wasted, the advantage of this invention is in that the introduction of cold blast and purified blast furnace gas into the heat exchange relationship will be applicable for improved performance of both the cooler and the turbine.

A particularly significant aspect of the present invention is that a kind of “self-regulating” heat exchange is obtained between cold blast and a cooled, purified blast furnace gas. Indeed, the conditions of the flow of cold blast upstream from the blast furnace affect the conditions of the flow of blast furnace gas downstream of the blast furnace (and vice versa), and it follows that the introduction of these two flows into the heat exchange relations automatically compensates for changes on one side or another.

It should be noted that this process is simpler than the process described in FR 2663685, since the gas flow of cold blast is not affected in this process, with the exception of a decrease in heating and, first of all, is not partially selected for burning with top gas in a gas turbine.

Essentially, this method offers a simpler and more efficient way of preheating the purified blast furnace gas to HUBT, which is economically beneficial for the entire installation.

This invention also relates to a plant for extracting energy from blast furnace top gas, comprising:

at least one cold blast compressor,

- at least one air blast heater for heating the compressed cold blast obtained in at least one cold blast compressor and supplying it after heating to a blast furnace,

- a device for cleaning blast furnace gas discharged from a blast furnace,

- a turboexpander having an output shaft coupled to the energy consumption device and located downstream of the top gas purification device,

- a heating device for cleaned top gas located between the device for cleaning up top gas and a turboexpander,

characterized in that it comprises means for extracting heat from the compressed cold air blast and at least partially transferring it to the cleaned top gas in a heating device.

Preferred embodiments of this method and installation of a blast furnace are set forth in the respective dependent claims.

It should be noted that any suitable technology can be used to extract heat from the compressed cold blast and at least partially transfer it to the purified blast furnace gas. In this regard, any suitable type of heat exchanger can be used in conjunction with the heat transfer circuit. A possible type of heat transfer system is the so-called “heat pipe” (direct or ring type), where the evaporation section is located on the cold blast side and the condensation section is on the side of the cleaned blast furnace gas.

The invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a first embodiment of a blast furnace installation with a gas energy extraction system,

FIG. 2 is a schematic diagram of an alternative embodiment of a blast furnace installation with a gas energy extraction system.

A first embodiment of the inventive blast furnace installation is shown schematically in FIG. 1 (only equipment for cleaning / air conditioning is provided). Reference numeral 10 denotes a blast furnace to which a hot blast stream is supplied from an air blast system comprising a blower 12 (or a compressor) and a preheater device comprising a set of three regenerative air heaters 14, as is common in the art. The blower 12 compresses the air and forms a cold blast stream that flows through the cold blast pipe 16 to the regenerative air heaters 14. The cold blast stream is heated in regenerative air heaters to temperatures in the order of 900 ° C to 1300 ° C and flows through the hot blast pipe 18 to the tuyeres (not shown), where a stream of hot blast is injected into the blast furnace 10.

The blast furnace gas exiting the blast furnace 10 is sent, at least in part, to a blast furnace gas turbine expander (recovery turbine) 20 to extract pneumatic energy from it. Reference numeral 22 denotes a flue gas pipeline that discharges the top gas to the top gas treatment device (auxiliary installation) 24. The blast furnace gas purification device 24 may include a pneumatic separator 26 connected in series with the wet separation separator 28. The device 24 may implement any type of cleaning technology.

The cleaned blast furnace gas stream is fed through the pipe 30 to the turbo expander 20 by means of a heating device 32 to heat the blast furnace gas stream, which is cooled due to the cleaning process in the device 24. In the turbo expander 20, the cleaned blast furnace gas expands with decreasing pressure and temperature and transfers mechanical work to the load 34 (here depicted as a generator) connected to the output shaft of a turbo expander. Extended blast furnace gas downstream of the turboexpander 20 through the exhaust pipe 31 can be returned to the cleaned gas network or transported to user / consumer enterprises, such as, for example, a power plant.

It becomes clear that this blast furnace installation comprises means for extracting heat from the compressed cold blast and transferring it, at least partially, to the cleaned top gas in the heating device 32. Preferably, this is achieved by means of a cold blast installed on the pipe 16 of the heat exchanger 35 (heat exchanger cold blast) transporting compressed cold air to regenerative air heaters 14. In the heat exchanger 35, the cold blast is led into the heat exchange (but without mixing) with the coolant and h from the heat exchange circuit, indicated by 36. Preferably, the heat exchange circuit includes a pump system (not shown) that directs the heat transfer medium from the heat exchanger 35 to the heating device 32, where the extracted heat is at least partially transferred to the cleaned top gas.

Extraction of heat from the cold blast for its transfer to the cleaned top gas provides a very preferred way of heating the purified gas before expanding it in the HUBT system. This also increases the performance of both the regenerative air heaters 14 and the turboexpander 20. Compared with the known methods in which the heat of cold blast wasted and heating the cleaned top gas required the use of burners or the like, they obtained a “self-regulating effect”. Indeed, the modes of flow of top gas upstream and downstream from the blast furnace are connected, and the following example shows the essence of their work.

Example

The higher the blast furnace gas pressure (TGP), the higher the hot blast pressure (HBP): HBP = TGP + dP, where dP is the pressure loss in the blast line, blast furnace and blast furnace gas cleaning device 24 in front of the turboexpander 20 (dP is greater or a lesser degree of constant value, depending on the specifics of the blast furnace, and is in the range from 1.0 to 2.5 bar). Thus, the higher the TGP, the greater the drop in top gas temperature (TGT) during expansion in a turboexpander (HUBT) 20.

Heated purified blast furnace gas to the turboexpander 20 is of interest. If the cleaned top gas is not heated, then the temperature of the top gas after the turbo-expander 20 will be lower, which will lead to the risk of icing of the turbo-expander and a decrease in the production of electric energy in the generator 34. However, if the temperature of the top gas after the turbo-expander 20 is too high, problems such as overheating of the turbo-expander 20 or combustion of seals in a clean gas network downstream of the turboexpander.

However, by heating the blast furnace gas to the turboexpander using heat extracted from the cold blast, a preferred heating circuit is obtained that provides automatic proper heating. If the pressure of the top gas in the blast furnace 10 is increased, the blower 12 is forced to compensate for this increase in pressure, and the pressure of the cold blast increases with a corresponding increase in the temperature of the cold blast.

At the same time, the pressure drop in the turboexpander 20 increases. But the risks of icing and the like are prevented, since increasing the pressure downstream of the blast furnace implies an increase in pressure and temperature of the cold blast upstream from the blast furnace 10 and, therefore, more heat to be transferred from cold blast into the cleaned blast furnace gas through the heat exchange circuit 36.

Similarly, as the top gas pressure decreases (for example, to stop the blast furnace), the temperature of the top gas in front of the turboexpander 20 decreases, since the pressure of the hot blast also drops with the temperature of the hot air and less heat is required to heat the top gas in front of the expander. This is convenient because less heat is available from the cold blast, the pressure of which has also decreased.

For purposes of illustration, in FIG. 1, temperature and pressure values were recorded at different places in the gas purification circuit of the blast furnace 10. These values were calculated. As you can see, the blower directs compressed air into the cold blast pipe 16 at a temperature of 215 ° C and a pressure of 5.1 bar g. (overpressure). After passing through the heat-supplying side of the heat exchanger 35, the temperature of the cold blast is 105 ° C and a pressure of 5 bar.

After cleaning, the temperature of the top gas drops to 45 ° C at a pressure of 2.3 bar. Then it flows through the heat-supply circuit of the heating device (heater) 32, where the temperature rises to 103 ° C at a pressure of 2.2 bar. Then, the heated hot gas stream enters and leaves turbo expander 20 at a temperature of 25 ° C and network pressure.

Heat is transferred from the cold blast to the top gas by means of a heat exchange circuit 36, which is in hydraulic connection with the heat sink side of the heat exchanger 35 and the heat supply side of the heating device 32. It should be noted that in this example the temperature of the heat exchanger 35 leaving the heat exchanger 35 is 170 ° C. After the heating device 32, the coolant gives off a substantial part of the heat to the top gas and has a temperature of 75 ° C.

As can be seen from this example, this operation scheme is sufficient to heat blast furnace gas to the CBHT by increasing its productivity and at a level that avoids the risks of icing and overheating. In other words, the self-regulating effect not only allows heating of blast furnace gas in front of the HUBT, but also ensures reliable and appropriate operation of the HOBT system inside the blast furnace installation, as well as for users downstream of the HUBT.

However, as shown in FIG. 1, the heat removed from the cold blast may be sufficient under normal operating conditions, but you may want to supply additional heat to the cleaned blast furnace gas upstream of the turboexpander 20. In FIG. 2 depicts two alternative or additional ways of ensuring this, where the same reference numbers indicate the same components of a blast furnace installation.

Firstly, additional heat can be provided using a burner or similar device, indicated by the reference numeral 40, installed in the heat exchange circuit on the heat transfer stream from the heat exchanger 35 to the heating device 32. In addition, the heater 42 can be installed on the cleaned gas pipe 30 between the heating device and turboexpander 20. For additional heaters 40 and 42, any type of technology can be used, such as, for example, connected to burner heat exchangers.

It should be noted that the above description is made for illustrative purposes. The term "heat exchanger" here includes any suitable type of device in which gas / air can be introduced into a heat exchange relationship with another gas or fluid, but without mixing with each other. Any technology compatible with the use of a blast furnace can be used. First of all, heat pipes can be used to transfer heat from the cold blast to the top gas, and the condensation section would be located in the heating device 32, and the evaporation section would be on the cold blast side. Also, for a turboexpander 20, an additional blast furnace gas purification device 24, regenerative air heaters 14, or coolant circuit 36, a detailed description is not required, since the type of equipment and its use are known to those skilled in the art.

Claims (13)

1. A method of extracting thermal energy from compressed cold air blast of a blast furnace used with a top gas utilization turbine system in the form of a turboexpander (20) containing at least one compressor (12) of compressed cold air blast connected to at least one regenerative air heater (14) air blasting, including the direction of flow of compressed blast furnace gas (10) into the device (24) for cleaning blast furnace gas and feeding sweat articulated to the expander (20) thermal energy generation (34), characterized in that heat is extracted from the compressed cold air blast, which is at least partially transferred to the cleaned top gas upstream of the turboexpander (20). 2. The method according to claim 1, characterized in that a heating device (32) is installed between the top gas purification device (24) and the turbo expander (20), comprising a heat exchanger having a heat sink side intersected by the cleaned top gas and a heat sink side fed by the heat carrier to which heat is extracted from compressed cold air blast. 3. The method according to claim 2, characterized in that between the at least one compressor (12) of the compressed cold air blast and the at least one air heater (14) of the air blast, a cold blast heat exchanger (35) is used having a heat supply side intersected by the compressed cold blast, and the heat sink side through which the coolant circulates. 4. The method according to claim 2, characterized in that heat is added to the heat carrier flowing to the heating device upstream of the turboexpander. 5. The method according to claim 3, characterized in that heat is added to the heat carrier flowing to the heating device upstream of the turboexpander. 6. The method according to one of claims 1 to 5, characterized in that the heat is also added to the cleaned top gas upstream of the turboexpander. 7. Installation for extracting thermal energy from compressed cold air blast furnace, containing:
at least one compressor (12) of compressed cold air blast (cold blast),
at least one regenerative air heater (14) of air blast for heating the compressed cold blast obtained in at least one compressor (12) of compressed cold air blast and supplying it after heating to the blast furnace (10),
a blast furnace gas top purification device (24) (10),
a turboexpander (20) having an output shaft coupled to a thermal energy consumption device (34) and located downstream of the device (24) for purification of blast furnace gas,
a heated blast furnace gas preheater (32) located between the blast furnace gas treatment device (24) and a turboexpander (20),
characterized in that it contains means for extracting heat from compressed cold air blast and at least partially transferring it to the cleaned top gas in a heating device (32). 8. Installation according to claim 7, characterized in that the heating device (32) comprises a heat exchanger (35) having a heat sink side, in which the cleaned top gas is supplied towards the turbine expander, and a heat supply side made to receive heat from the cold blast. 9. Installation according to claim 8, characterized in that the heat exchanger (35) is installed upstream of at least one regenerative air heater (14) of the air blast and has a heat supply side fed by cold blast and a heat sink side connected to the coolant circuit, and a coolant circuit (36) connected to the heat-supplying side of the heat exchanger in the heating device (32). 10. Installation according to claim 7, characterized in that heat pipes are used as heat exchangers located in the heating device (32), and their evaporation section is on the side of the cold blast. 11. Installation according to any one of paragraphs.7-10, characterized in that in the stream of purified blast furnace gas between the heating device (32) and the turboexpander (20) there is an additional heating device (42). 12. Installation according to claim 9, characterized in that a heating device (40) is located in the coolant circuit (36) to supply additional heat to the heating device (32). 13. Installation according to claim 11, characterized in that a heating device (40) is located in the coolant circuit (36) to supply additional heat to the heating device (32).

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