GB2513185A

GB2513185A - Blast furnace plant

Info

Publication number: GB2513185A
Application number: GB1307117.0A
Authority: GB
Inventors: Alex Michael Smith; Jason Kenneth Rigg
Original assignee: Siemens VAI Metals Technologies GmbH Austria
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2013-04-19
Filing date: 2013-04-19
Publication date: 2014-10-22
Also published as: WO2014170086A1; GB201307117D0

Abstract

A blast furnace hot blast generator which comprises a pressurised combustion chamber 15 in which is located a burner 19, a compressor 18 for compressing blast furnace gas, an inlet 23 for supplying compressed blast furnace gas to the combustion chamber 15, an inlet 24 for supplying pressurised air or oxygen to the combustion chamber 15, a hot blast outlet 16 from the combustion chamber 15 which directs the combusted gases into a blast furnace 1 and means to control heat and gas supply to the combustion chamber 15. The combustion chamber 15 also comprises an inlet 26 for an enrichment gas such as coke oven gas or natural gas and an oxygen inlet 13 is coupled to the hot blast outlet 16. Blast furnace gas is fed from the blast furnace 1, through a gas cleaning unit 2 and a gas store 3 into the hot blast generator.

Description

BLAST FURNACE PLANT

This invention relates to apparatus and method for a blast furnace plant, including generation of hot blast for a blast furnace.

S A conventional blast furnace plant comprises a blast furnace, a gas cleaning stage for cleaning blast furnace gases generated in the blast furnace and stoves for heating cold blast to the required temperature, using the cleaned blast furnace gas as a fuel supply in the stoves. Typically, the cleaned gases are stored in a gas holder and drawn on as required. Hot blast stoves comprise a combustion chamber and a chequer chamber, so that in one cycle of operation heat is generated by combustion in the combustion chamber and stored in the brickwork of the chequer chamber and in another cycle, the stored heat in the chequer chamber is extracted to heat the blast. Hot blast stoves are a significant contributor to the overall emissions of a blast furnace plant. The burning of blast furnace gas (BFG), or coke oven gas (COG), in the stoves during the combustion cycle generates a large volume of C02 in the flue gas, which is vented to atmosphere via a chimney stack.

The emissions levels ofhot blast stoves have been controlled by improving combustion efficiency to reduce the quantity of CO generated. However, by default the volume of C02 increases. The only developments currently in place to reduce C02 emissions from blast furnace sources are carbon capture and storage, whereby the C02 is chemically removed from the gas stream and stored.

In accordance with the present invention a blast furnace hot blast generator, the generator comprising a pressurised combustion chamber; a heat source for the combustion chamber; a compressor to compress blast furnace gas; a blast furnace gas inlet to the combustion chamber for supplying compressed blast furnace gas from the compressor to the chamber; an air or oxygen inlet to the combustion chamber for pressurised air or oxygen; a hot blast outlet from the chamber; and a controller to control heat and gas supply to the chamber.

The present invention addresses the problem of high volumes of C02 being generated in hot blast stoves by means of a system using direct injection of combusted blast furnace gas into the blast furnace in a stoveless system, without venting C02 to atmosphere.

Preferably, the combustion chamber further comprises at least one enrichment gas inlet.

Preferably, the enrichment gas inlet is coupled to a source of high calorific value gas, such as coke oven gas, or natural gas.

S

Preferably, the hot blast generator flirt her comprises an oxygen inlet coupled to the hot blast outlet.

In accordance with a second aspect of the present invention, a blast furnace plant comprises a blast furnace; a gas cleaning unit; and a hot blast generator according to the first aspect.

Preferably, the blast furnace plant further comprises a blast furnace gas store for storing cleaned blast flirnacc gas.

In accordance with a third aspect of the present invention, a method of generating hot blast for a blast furnace in a blast furnace plant comprising a blast furnace, a gas cleaning unit, a compressor and a hot blast generator comprises extracting blast furnace flue gas from the blast furnace; cleaning the blast furnace flue gas in the gas cleaning unit; supplying the cleaned blast furnace flue gas to the compressor; compressing the gas; supplying the compressed cleaned blast furnace flue gas to the hot blast generator; supplying pressurised air or oxygen to the hot blast generator; generating hot blast in the generator; and supplying the hot blast to the blast furnace.

Preferably, the method further comprises controlling addition in the generator of at least one of the blast furnace gas and an enrichment gas to the compressed cleaned blast furnace flue gas to achicvc a prcdctcrmincd hot blast tcmpcraturc.

Preferably, the enrichment gas comprises high calorific value gas, such as coke oven gas, or natural gas.

Preferably, the method further comprises controlling supply of post-combustion oxygen to achieve a predetermined oxygen content in the hot blast supplied to the blast furnace.

Preferably, a combustion chamber of the hot blast generator is maintained at a substantially constant pressure Apparatus and a method for the generation of hot blast for a blast furnace will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a conventional blast furnace plant arrangement; Figure 2 illustrates operation of a hot blast stove in the plant of Fig. 1 in more detail; Figurc 3 shows a blast thrnacc plant arrangement according to thc prcscnt S invention; and, Figure 4 is a flow diagram of a method of operation according to the present invcnt ion.

In operation of a conventional blast furnace plant, as illustrated in Fig.1, gas from the top of a blast furnace I is taken off and supplied 20 to a gas cleaning plant 2.

The extracted gas passes through the gas cleaning plant 2 in order to remove dust from thc gas. Cleaned gas is thcn supplied 21 to a gas holder 3 whcrc it is storcd until required and then supplied 9 to hot blast stoves 4 to be burned to provide heat for heating the cold blast for the blast furnace.

Operation of one of the stoves is illustrated in more detail in Fig.2. In the hot blast stovc, thc blast furnace gas supply 9 is burncd in a combustion chambcr 6 along with coke oven gas 10 to increase the flame temperature and a combustion air supply 11. The products of this combustion pass up through the combustion chamber 6 and into a chequer chambcr 5, whcrc a large mass of rcfractory bricks absorb and storc thc heat from the combustion. The products of combustion then exit the stove as a waste gas stream 12 in a waste gas system and are vented to atmosphere. This waste gas strcam 12 is a significant sourcc of emissions for thc blast furnace plant, with large volumes of CO2 generated during combustion, along with other pollutants including CO and NOx.

Once the hot blast stove is up to temperature the coke oven gas 10, blast furnace gas 9 and air 11 supplies are stopped. At this point the stove is then pressurised using a small volume of cold blast 7. Once the stove has reached the required blast pressure the thll cold blast supply 7 is opened. This cold blast supply, enriched with oxygen 13 then enters the stove 4 and travels up through the chequer chambers, absorbing the heat previously storcd in thc refractory bricks, bcforc heading down through the combustion chamber 6 and out through a hot blast exit 8. Due to the nature of the hot blast stove, and the method of heating and cooling, as the cold blast absorbs heat from the refractory bricks, the final hot blast temperature at the hot blast outlet reduces over time. In order to supply a constant hot blast temperature to the blast furnace then the hot blast stove outlet temperature is higher than required at the blast furnace and a cold blast bypass 14 is used in order to cool the hot blast 8 to a constant temperature.

Once the temperature at the outlet of the stove 4 has dropped to a set target S minimum temperature, the next stove in the system is brought on blast and the current stove then vents its pressure back down to atmospheric pressure and recommences the combustion phase, in order to regain the heat energy lost during the blast phase.

In the present invention, as illustrated in Fig.3, the entire hot blast stove system 4 is replaced by one or more a hot blast generators 15 comprising at least one high pressure burner 19 in a high pressure combustion chamber in order to directly inject oxygen enriched flue gas, from combustion of the blast furnace gas 9, into the furnace I as hot blast 17. High prcssure in this context is blast furnace pressure, typically a gauge pressure of the order of 3 bar to 5 bar. The blast furnace gas 9 is compressed in compressor 18 to boost the gas pressure to blast furnace pressure, then the blast furnace gas 9 passes through inlet 22 and is mixed in a high pressure combustion chamber with high pressure combustion air or oxygen 11 supplied through inlet 23, which has also been compressed 22 to blast furnace pressure and optionally also with an enrichment gas 10, such as coke oven gas. All inputs to the system either into the burner, or into the hot blast main afterwards are at blast furnace pressure or higher. This mixture is burned and supplied directly to the blast fumace 1. The basic fuel gas for combustion is the blast furnace gas 9, which is mixed with the air or oxygen 11. In order to increase the maximum temperature, a second combustion gas may be added through enrichment inlet 26 which is an enrichment gas supply, typically a high calorific value gas, such as cokc oven gas, or natural gas or any othcr high calorific value gas.

Further oxygen 13 may then be added to the high temperature, high pressure flue gas 1 6 from this combustion to create a gas with the same oxygen content as traditional hot blast. The gas is then used as blast 17 for the furnace. The blast temperature may be increased and controlled by the addition of the enrichment gas 10, such as coke oven gas, or natural gas to the combustion, or by adjusting the volume of air or oxygen 11 supplied for combustion. Varying the volume of gas enrichment 10 in the combustion varies the blast temperature, as the final blast temperature is directly related to the flame temperature in the high pressure combustion chamber of the generator 15. This replaces the cold blast bypass which was used to control the blast temperature in the hot blast stoves. Typically, the desired temperature of the hot blast for the blast furnace is in the range of 1000°C to 1250°C.

Use of blast furnace flue gas as the source of hot blast, rather than using air has the effect that nitrogen, a large component of air, is no longer being added as blast. The main inert gas in flue gas from blast furnace gas combustion is C02. The furnace is started up with flue gas from combustion, although this initial gas may be supplied from a separate supply until the plant is up and running and the blast furnace gas has cycled through the system and become available.

Fig.4 illustrates an example of a method of generating hot blast in a stoveless blast furnace plant once the blast furnace is up and running. Blast furnace flue gas is extracted 30 from the blast furnace and cleaned 31 in the gas cleaning unit 2. If necessary, the cleaned gas is stored 32 in the gasholder 3 for later use. When needed, the cleaned gas is compressed 33 and supplied 34 to the hot blast generator 15.

Combustion gas or enrichment gas, or both, are mixed 35 with the blast furnace gas and then heated 36 by the burner in the combustion chamber. Ifrequired, post-combustion oxygen 17 is added and the hot blast is then supplied to the blast furnace.

The main advantages of the present invention as compared with traditional blast furnace plants using hot blast stoves are significant reductions in emissions and cost.

The waste gas stream 12 from the hot blast stoves 4 is effectively eliminated. By direct injection of flue gas from high pressure blast furnace gas combustion into the blast furnace, all flue gas from combustion is sent to the furnace, so there are no stack emissions as per a hot blast stove. There is a significant reduction of the overall emissions of the blast furnace plant, particularly if the resulting gas from the top of the blast furnace is also fully utilised. A further feature is that by replacing the entire hot blast stove system with a much smaller system, both space requirements and costs are reduced.

Another problem with the operational process for hot blast stoves is that they eventually suffer pressure fatigue due to the continuous cycle of pressurising and depressurising according to whether they are on gas, on blast or being maintained.

Using the arrangement of the present invention, once brought into operation, the burner is kept at a constant pressure, typically blast furnace pressure (which may have a gauge pressure in the range of 3 bar to 5 bar), so the burner 15 does not suffer from the stresses associated with constant pressurising and depressurising that stoves 4 do.

Within the blast furnace 1, nitrogen traditionally contained within the blast furnace gas is replaced with CO2. The effect of this change on the blast furnace chemistry needs to be taken into account when considering the carbon and oxygen balances within the blast furnace and more specifically the CO: CO2 balance due to the S effects of the Boudouard reaction, whereby CO2 reacts with carbon to form carbon monoxide at high temperatures. This reaction is highly endothermic and therefore the required heat input to the furnace needs to be carefully controlled. The balance of CO / C02 supplied to the furnace may be controlled by reducing or increasing the efficiency of combustion, i.e. if the combustion in the hot blast generator is less efficient, the CO level in the gas supplied to the furnace is higher.

Claims

CLAIMS1. A blast furnace hot blast generator, the generator comprising a pressurised combustion chamber; a heat source for the combustion chamber; a compressor to compress blast furnace gas; a blast furnace gas inlet to the combustion chamber for supplying compressed blast furnace gas from the compressor to the chamber; an air or oxygen inlet to the combustion chamber for pressurised air or oxygen; a hot blast outlet from the chamber; and a controller to control heat and gas supply to the chamber.
2. A hot blast generator according to claim 1, wherein the combustion chamber further comprises at least one enrichment gas inlet.
3. A hot blast generator according to claim 2, wherein the enrichment gas inlet is coupled to a source of high calorifIc value gas, such as coke oven gas, or natural gas.
4. A hot blast generator according to any preceding claim, further comprising an oxygen inlet coupled to the hot blast outlet.
5. A blast furnace plant comprising a blast furnace; a gas cleaning unit; and a hot blast generator according to any preceding claim.
6. A blast fUrnace plant according to claim 5, further comprising a blast furnace gas store for storing cleaned blast furnace gas.
7. A method of generating hot blast for a blast furnace in a blast furnace plant comprising a blast furnace, a gas cleaning unit, a compressor and a hot blast generator; the method comprising extracting blast furnace flue gas from the blast furnace; cleaning the blast furnace flue gas in the gas cleaning unit; supplying the cleaned blast furnace flue gas to the compressor; compressing the gas; supplying the compressed cleaned blast furnace flue gas to the hot blast generator; supplying prcssuriscd air or oxygen to the hot blast generator; generating hot blast in the generator; and supplying the hot blast to the blast furnace.
8. A method according to claim 7, further comprising controlling addition in the generator of at least one of the blast thrnace gas and an enrichment gas to the compressed cleaned blast furnace flue gas to achieve a predetermined hot blast tcmpcraturc.S
9. A method according to claim 8, wherein the enrichment gas comprises high calorific valuc gas, such as cokc ovcn gas, or natural gas.
10. A method according to any of claims 8 or claim 9, further comprising controlling supply of post-combustion oxygen to achieve a predetermined oxygen content in the hot blast supplied to the blast furnace.
11. A method according to any of claims 8 to 10, wherein a combustion chamber of the hot blast generator is maintained at a substantially constant pressure.