GB2520578A

GB2520578A - A method and apparatus for supplying blast to a blast furnace

Info

Publication number: GB2520578A
Application number: GB1402098.6A
Authority: GB
Inventors: Alex Michael Smith
Original assignee: Siemens VAI Metals Technologies GmbH Austria
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2013-11-21
Filing date: 2014-02-07
Publication date: 2015-05-27
Also published as: GB201402098D0; GB201320536D0

Abstract

Apparatus for supplying blast to a blast furnace 1 comprises a plurality of hot blast stoves 4-6 each of which comprises a cold blast inlet 28, a fuel inlet 17, a combustion air supply 24, a hot blast outlet 7 and a waste gas outlet 34. The apparatus further comprises a heat recovery unit 26 connected between a fuel supply and/or combustion air supply source and the cold blast 12 & 23, whereby heat from the cold blast 12 is transferred to the fuel and/or air fed from their supplies, thus reducing the temperature of the cold blast 23 at the cold blast inlets 28 whilst increasing the temperature of the fuel and/or combustion air. Top gas from the blast furnace 1 is used as fuel for the blast stoves 4-6 after being heated and cleaned.

Description

A METHOD AND APPARATUS FOR SUPPLYING BLAST TO A BLAST

FURNACE

This invention relates to a method and apparatus for supplying blast to a blast furnace.

Typically, blast is heated in stoves before supplying the blast at the desired temperature to the blast furnace. The cold blast temperature at the inlet to the hot blast stove can have a significant effect on the required overall size of the stove. One option to reduce the temperature is to use a cooler unit to chill the cold blast, but this needs to be powered, so increases the running costs.

In accordance with a first aspect of the present invention, apparatus for supplying blast to a blast fbrnace comprises a plurality of hot blast stoves, each stove comprising a cold blast inlet, a fuel inlet, an air supply, a hot blast outlet, and a waste gas outlet; and a heat recovery unit connected between a fuel and/or air supply source and the cold blast inlets; whereby heat from the cold blast is transferred to the fuel and/or air supply reducing the temperature of the cold blast at the cold blast inlets, whilst increasing the temperature of the fuel and/or air at the stove burner inlets.

Preferably, the apparatus further comprises a blast furnace and a connection between the blast furnace and the heat recovery unit whereby recycled top gas is supplied to the heat recovery unit.

In accordance with a second aspect of the present invention, a method of supplying blast to a blast furnace comprises extracting heat in a heat recovery unit from a source of cold blast; heating combustion air or gas in the heat recovery unit with the extracted heat; supplying the cooled cold blast to a hot blast stove; heating the cold blast in the hot blast stove and supplying the heated cold blast as hot blast to the furnace.

Preferably, the method further comprises supplying heated cleaned top gas to the stove as combustion air and/or gas.

An example of a method and apparatus for supplying blast to a blast furnace will now be described with reference to the accompanying drawings in which: Figure 1 illustrates the effect of cold blast inlet temperature on required heating surface area for a typical hot blast stove; Figure 2 illustrates a blast furnace system including hot blast stoves for heating cold blast; and, Figure 3 shows an example of a blast furnace system including apparatus for supplying blast in accordance with the present invention.

As mentioned above, the cold blast temperature at the inlet to the hot blast stove can have a significant effect on the required overall size of the stove. If the cold blast entering the stove is relatively hot, then a larger heating surface area is required for the stove to achieve the required hot blast temperature than if the cold blast entering is relatively cool, The effect of cold blast inlet temperature on required heating surface area for a typical hot blast stove is illustrated in Fig, L An embodiment of a blast furnace system including hot blast stoves for heating cold blast is illustrated in Fig.2 described below, Figure 2 illustrates operation of a conventional blast thrnace plant including a blast furnace 1, a supply mechanism 2, 3, 9 to supply material to the blast furnace and a series of hot blast stoves 4, 5, 6 to supply hot blast for the blast furnace. The hot blast stoves may be internal or external combustion chamber stoves, At any time, one stove, in this example stove 4 is on blast and typically at least one of the other stoves 5, 6 is on gas, When the first stove finishes being on blast, then the controller switches to the next stove ready to go on blast, but for simplicity, not all the lines and connections are shown in this figure. Fuel is supplied 17 to the stoves 5, 6 which are on gas along with air 16 from a fan 18.

The required materials, including iron ore and coke, are supplied from hoppers 2 in controlled amounts and in order, through weighing devices 3 in a stockhouse (not shown) to a charging mechanism 8 at the top of the thrnace, for example via a conveyor belt 9. When a charge of material is released into the furnace 1 it falls downwards and undergoes various chemical reactions before reaching the bottom of the furnace. The coke when it meets hot blast air 7 supplied from a position near to the bottom of the furnace generates heat, Iron and slag result from the various chemical reactions and are removed from the furnace by tapping the furnace and flowing the iron 20 and slag 21 over a dam (not shown) to separate the heavier molten iron from the molten slag and remove them separately for further processing away from the casthouse.

The furnace I is provided with a furnace top valve 10 to close the furnace off from the charging mechanism and various offlakes II to direct the top gases resulting from the reactions in the furnace to a downcomer 19. Bleeder valves 13 are provided to allow top gases to vent from the blast furnace to protect the furnace top from sudden gas pressure changes. Top gases pass through the downcomer 19, a dustcatcher, or cyclone 14 and a venturi scrubber 15 to dean them of particulate matter. The cleaned blast furnace top gas, which may contain nitrogen, carbon dioxide, carbon monoxide and hydrogen, is used in the stove combustion process, with the combustion air 16 in the stove. The cleaned top gas is returned 22, 17 to the hot blast stoves 5, 6 for combustion in order to heat the stoves. A refractory lining of each stove on gas is heated by the combustion of the cleaned gas. The stove on blast receives air from a blower 25 via a cold blast main 12 and this air takes up the heat from the refractory lining to produce hot blast 7, which is fed into the blast furnace I, near to the bottom.

In the process of heating the stoves, during the on gas phase, waste gases are generated.

These waste gases are then vented through a chimney stack 34.

In order to reduce the size of each stove required for heating the cold blast, the required heating surface area needs to be reduced, In the present invention this reduction in heating surface area is achieved by reducing the temperature of the cold blast at the inlet to the stoves by means of a heat exchanger which uses combustion air and/or gas as a coolant for the cold blast. This is illustrated in the example of Fig.3. The operation is as in Fig.2, unless otherwise described, Air in the cold blast main 12 from the blower 25 does not connect directly to the stove inlet 38, but passes through a heat exchanger 26. The combustion air 16 from fan 18 also passes through the heat exchanger before being supplied 24 to the stove which is on gas. The combustion air from fan 18 is cold and the cold blast air 12 from the blower is initially hot, but by passing through the heat exchanger, the combustion air is warmed up and the warmed air 24 supplied to the stove on gas. Similarly, the cold blast air 23 input to the stove 4 is cooled down by passing through the heat exchanger. Thus, the invention has the advantage that the cold blast temperature is reduced, whilst the combustion air/gas temperature is also consequentially increased and this increase in combustion air/gas temperature has benefits of its own, including an increase in sensible heat canled into the stove and an increase in the achievable flame temperature through combustion. The running costs are reduced when the invention is retrofitted to existing stoves and for a new build stove, there is also the advantage that smaller stoves may be used, The relatively cold combustion gas or air (typically at a temperature in the range 20°C to 40°C, for example around 30°C) provides the cooling medium for cooling the cold blast from a typical temperature at the inlet in the range of 150°C to 250°C, more tvpically200°C to temperatures in a range of 100°C to 200°C, according to the original temperature. Although, it would be possible to achieve cooling of the cold blast by means of a cooler unit between the blower 25 and the cold blast inlet 28, this would be a stand-alone that uses power and the additional benefit of increasing the supply temperature of combustion gas and/or air is not provided by a stand-alone cooler.

Using an example stove operating under three stove cyclic mode, producing a blast volume of 250,000Nm3/h at a temperature of 1200°C, a cold blast temperature of 160°C would result in a required heating surface area of 41,500 m2, If the cold blast temperature were to be reduced to 100°C, the required heating surface area drops to 37,450m2, a reduction of almost 10%.

Given a starting combustion air temperature of 20°C, and assuming a linear relationship between temperature rise and fall across a heat exchanger, (although the actual relationship depends upon such things a relative flow rates, or heat capacities), this drop in cold blast temperature results in a rise in combustion air temperature to 80°C, which provides benefits on the combustion side of the stove due to the increased sensible heat carried in to the stove by the hotter air supply, combined with the previously stated beneficial effects of lower cold blast temperature.

In addition, a C02 regenerator, as described in more detail in our co-pending patent application no. PCT/EP2O 13/076109 may be incorporated into the system of Fig.3 to regenerate C02 from the blast before it enters the blast ifimace. The carbon dioxide stream provides a replacement for conventional hot blast from ambient air. A regenerator may be provided between the stoves 4, 5, 6 and the furnace ito process hot blast that has been generated from stoves waste gas. This hot blast contains carbon dioxide, C02 is extracted from the hot blast, then a pressurized, heated carbon dioxide stream is combusted with a carbonaceous fuel, such as coal, in a pressurised vessel with oxygen to regenerate carbon monoxide, by burning the C02 down to CO, resulting in a CO reductant gas stream prior to transport to the blast thrnace bustle pipe, the hearth tuyere inlet. The reductant gas stream goes into the furnace directly, rather than being made in the furnace. As a result, it is possible to save on the amount of raw carbon required in the furnace reactions,

Claims

CLAIMS1. Apparatus for supplying blast to a blast fhrnace comprising a plurality of hot blast stoves, each stove comprising a cold blast inlet, a fuel inlet, an air supply, a hot blast outlet, and a waste gas outlet; the apparatus further comprising a heat recovery unit connected between a friel and/or air supply source and the cold blast inlets; whereby heat from the cold blast is transferred to the thel and/or air supply reducing the temperature of the cold blast at the cold blast inlets, whilst increasing the temperature of the iftel and/or air at the stove burner inlets.
2. Apparatus according to claim 1, further comprising a blast furnace and a connection between the blast furnace and the heat recovery unit whereby recycled top gas is supplied to the heat recovery unit.
3. A method of supplying blast to a blast fUrnace comprising extracting heat in a heat recovery unit from a source of cold blast; heating combustion air or gas in the heat recovery unit with the extracted heat; supplying the cooled cold blast to a hot blast stove; heating the cold blast in the hot blast stove and supplying the heated cold blast as hot blast to the fUrnace.
4. A method according to claim 3, fUrther comprising supplying heated cleaned top gas to the stove as combustion air and/or gas.