WO2018234481A1

WO2018234481A1 - Process fluid injection into shaft furnace with injector status test

Info

Publication number: WO2018234481A1
Application number: PCT/EP2018/066630
Authority: WO
Inventors: Frank Rheker
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude; Air Liquide Deutschland Gmbh
Priority date: 2017-06-22
Filing date: 2018-06-21
Publication date: 2018-12-27
Also published as: EP3642370A1; EP3642370B1; CN111328349B; CN111328349A; RU2020101703A; RU2020101703A3

Abstract

Injection of a process fluid into a shaft furnace by means of n injectors, whereby the status of said n injectors is tested by supplying a test fluid to each injector at a predetermined pressure, measuring a corresponding test fluid flow rate through the injector and comparing the measured test fluid flow rate with a predetermined safe flow-rate range or supplying the test fluid to each injector at a predetermined flow rate, measuring the pressure drop over the injector or a nozzle part thereof and comparing the measured pressure drop with a predetermined safe pressure-drop range.

Description

Process fluid injection into shaft furnace with injector status test

The present invention relates to the operation of shaft furnaces.

The term shaft furnace refers to vertical shaft- or column-shaped furnaces in which combustion takes place. Examples of shaft furnaces are cupolas and blast furnaces. Examples of such processes in which shaft furnaces are used include, but are not limited to the burning of solid waste, the reduction of iron ore to produce pig iron, the melting of metals and mineral wool, etc.

It is known in the art to inject fluids, such as, for example an oxygen-rich gas in a shaft furnace. In order to ensure a relatively high degree of penetration of the fluid into the shaft furnace, it is more specifically known to inject fluids into a shaft furnace at sonic or supersonic velocity.

The injection is effected by means of a set of lances, also referred to as injectors or tuyeres which are distributed around the circumference of the furnace.

These injectors have to operate under particularly harsh conditions and can easily be damaged. In particular, the high temperatures inside the shaft furnace may cause the injector to suffer thermal damage, such as cracking, partial melting or softening and deforming and deposits may be formed on and/or around the injector which deposits may partially or even totally block the injection opening of the injector or modify the direction in which the fluid is injected into the shaft furnace.

It will be appreciated that any damage to the injectors which affects the injection of the fluid into the shaft furnace can have a major detrimental impact on the furnace and on the process taking place therein. For example, a change in the orientation of the injection direction of the fluid may cause damage to the refractory walls of the furnace and reduce the efficiency of the process taking place in the furnace and/or the quality of the product obtained. Any damage to an injector nozzle, in particular a sonic or supersonic nozzle, may lower the injection velocity of the fluid and thus lower the penetration depth of the fluid in the shaft furnace. When the fluid injected by the injector includes a fuel, damage to the injector may also cause potentially catastrophic flashback.

It is therefore necessary to replace any injectors of which it is apparent that they have suffered damage.

As many shaft furnaces operate continuously for extended periods of time, it is generally not possible to check the condition of the injectors from the inside of the furnace.

It is common practice, by way of preventative measure, to replace all injectors of a shaft furnace after a predetermined period of operation, the so-called maximum lifetime. This maximum lifetime is selected, based on tests and/or previous experiences with injectors of the same type, so as to be short enough so that most injectors are replaced before the injectors have suffered any damage which leads to a noticeable deterioration of the furnace structure or of the process taking place in the furnace. A number of injectors will thus be replaced even though they are not yet damaged.

Shaft furnaces can have a significant number of injectors. Depending on the size and type of furnace and the process taking place therein, up to 14 or 16 injectors or even up to 24 or 26 or even more injectors for a same fluid to be injected into the shaft furnace is not uncommon.

Consequently, the replacement of said injectors entails substantial costs for the furnace operator, both as regards the material to be replaced and the labour required.

It would therefore be desirable to be able to use the injectors for a longer period of operation without increasing the safety risks, the risks of damage to the furnace structure or the risk of deterioration of the process taking place therein.

US-A-3346249 discloses a method for supplying blast air and gaseous fuel and to a blast furnace, respectively via a large number (30 to 40 is mentioned) continuously operating tuyeres and corresponding continuously operating fuel injection pipes, whereby a fuel controller stops the fuel flow to a fuel injection pipe when plugging or partial clogging of the fuel injection pipe or the corresponding tuyere is detected. Differential pressure gauges are positioned across an orifice in the gas supply line connecting individual fuel injection pipes to a gaseous fuel ring manifold. When an obstruction in an individual fuel injection pipe causes an unequal fuel distribution with the other individual fuel injection pipes, the differential pressure gauge detects a change in pressure across the orifice of the supply line to the individual fuel injection pipe and generates an alarm signal. Each tuyere is further equipped with thermal sensing means and a pitot tube. An alarm signal is generated and the fuel flow to the corresponding fuel injection pipe is stopped when the thermal sensing means detects an increase in temperature indicative of fuel combustion inside the individual tuyere as well as when the pitot tube detects that the tuyere is plugged or partially blocked.

The method according to US-A-3346249 is only suitable for detecting plugging or clogging injection pipes and tuyeres which operate continuously and at substantially constant flow rates. It is not adapted for detecting plugging or clogging of injectors during pulsed or alternating injection of the fluid. In addition, as the detection is carried out while all of the fuel injection pipes are fluidly connected to the gas ring manifold and while all of the tuyeres are fluidly connected to bustle pipe, the pressure at which gas is supplied to the individual tuyeres and injection pipes and the flow rate with which gas is supplied to the individual tuyeres and injection pipes is not only determined by the gas pressure and flow rate in the bustle pipe respectively gas ring manifold, but also by the condition of the other tuyeres, respectively injection pipes connected to the bustle pipe respectively gas ring manifold. Due to this interference between the different tuyeres, respectively injection pipes, certain instances of plugging or partial clogging may go undetected.The present invention proposes a method of injecting a process fluid into a vertical shaft furnace in which a combustion process takes place and whereby the injectors used for injecting said process fluid into the shaft furnace are subjected to a status check without interrupting the operation of the shaft furnace. The present invention further proposes such a method suitable for discontinuous, in particular pulsed or alternating injection of a process fluid into the shaft furnace.The present invention thus relates to a method of injecting process fluid into a vertical shaft furnace in which a combustion process takes place.

Said shaft furnace presents n injectors, with n at least equal to 3, which a re distributed around the circumference of the shaft furnace. The shaft furnace also presents a fluid distributor which is fluidly connected, on the one hand, to a source of the process fluid to be injected and, on the other hand, to the n injectors.

The shaft furnace further is part of an installation which includes a control unit programmed (a) to control a total amount of the process fluid injected into the shaft furnace through the n injectors by means of a first valve unit between the source of the process fluid and the fluid distributor and (b) to control flows of the process fluid from the fluid distributor to each of the n injectors by means of n individual valve units between the fluid distributor and the n injectors.

In accordance with the present invention, the control unit is also programmed to initiate and execute a status test for each one of the n injectors individually without interrupting the operation of the shaft furnace.

During a status test of one of the n injectors, a test fluid is supplied at a predetermined pressure or at a predetermined flow rate to said injector, said test fluid being therefore also injected into the shaft furnace through said injector.

When the test fluid is supplied to the injector at the predetermined pressure, a flow rate of the fluid through the injector is measured. When the test fluid is supplied to the injector at the predetermined flow rate, a pressure drop or back pressure over the injector or over at least a nozzle part of the injector is measured.

When the test fluid is supplied to the injector at the predetermined pressure and the flow rate of the fluid through the injector is therefore measured, the control unit verifies whether the measured flow rate falls inside a predetermined flow-rate range for the predetermined pressure, referred to as the "safe" flow-rate range for said pressure. When the test fluid is supplied to the injector at the predetermined flow rate and the pressure drop is measured, the control unit verifies whether the measured pressure drop falls inside a predetermined pressure-drop range for the predetermined flow rate, referred to as the "safe" pressure-drop range for said flow rate.

When the measured flow rate does not fall inside the predetermined safe flow-rate range or when the measured pressure drop does not fall inside the predetermined safe pressure-drop range, the control unit emits an output signal signaling that said injector, i.e. the injector of which the status has been tested, must be replaced.

Indeed, when the measured flow rate does not fall inside the predetermined safe flow-rate range or when the measured pressure drop does not fall inside the predetermined safe pressure-drop range, this is a clear indication that the injector has been damaged in such a way that the flow properties of the injector have been affected to the extent that the injector must be replaced.

The present invention thus provides the furnace operator with a fair indication of the status of the n injectors during the combustion process.

The method according to the invention may include the step of determining the pressure, referred to as "predetermined pressure", respectively the flow rate, referred to as "predetermined flow rate" at or with which the test fluid is (to be) supplied to the injector to be tested during the status test.

The predetermined pressure, respectively the predetermined flow rate, typically correspond to a fluid pressure, respectively a fluid flow rate for which the injector was designed or commercialized.

The method according to the invention may include the step of determining the flow-rate range, referred to as "predetermined safe flow-rate range" for injector at the predetermined pressure of the test fluid, respectively the pressure-drop range, referred to as "predetermined safe pressure-drop range", over the injector at the predetermined flow rate pressure of test fluid through the injector. The "predetermined safe flow-rate range", respectively the "predetermined safe pressure-drop range" may be provided by the manufacturer or supplier of the injectors or may be based on earlier experience with injectors of the same type.

The predetermined safe flow-rate range for the predetermined pressure and the predetermined safe pressure-drop range for the predetermined flow rate typically correspond to a range around the flow rate which is observed when the test fluid is supplied to a new, unused injector of the same type at the predetermined pressure, respectively to a range around the pressure drop which is observed when the test fluid is supplied to such a new, unused injector at the predetermined flow rate. The control unit is advantageously programmed to repeat the status check for each one of the n injectors at predetermined intervals, thus informing the furnace operator of the evolution of the status of the n injectors during the combustion process.

Alternatively, or in combination therewith, the method may enable the initiation of a status check for each one of the n injectors by the control unit by instructing the control unit to do so, for example by means of a touch screen or a remote control device of the control unit. The furnace operator may in particular wish to initiate a status check of the injectors following or before an incident related to the shaft furnace, for example, after an injector has been replaced or before a change to the process takes place in the shaft furnace.

Due to the status check(s) performed by the control unit, the furnace operator no longer needs to rely solely on the experimentally determined maximum lifetime of the injectors and may decide to continue to use an injector beyond said maximum lifetime, provided the status check has shown that the injector continues to operate in the safe range.

The output signal generated by the control unit may be or may include a visual output signal on a screen of the control unit, optionally accompanied by a sound signal. The output signal may also be or include a signal which is transmitted to a remote, typically hand-held or mobile device.

The process fluid may, in particular, be an oxidizing gas consumed by the combustion process in the shaft furnace. The oxidizing gas preferably has an oxygen content greater than 21%vol and up to 100%vol, preferably of at least 90%vol and more preferably of at least 95%vol.

The source of oxidizing gas may be an installation for enriching air with oxygen, typically when the oxygen content of the oxidizing gas is relatively low, for example more than 21%vol and not more than 90%vol. The source of oxidizing gas may also be an air separation unit, a reservoir of liquefied oxygen or a pipeline transporting liquefied oxygen, for example when the oxygen content of the oxidizing gas is between 90%vol and 100%vol, preferably at least 95%vol.

The process fluid may also be or comprise a fuel which is injected into the shaft furnace.

The process fluid may also serve other purposes in the shaft furnace. For example, in the case of a shaft furnace for the reduction of iron ore, the process fluid may be a reducing agent which is injected into the shaft furnace to promote the reduction of the iron ore.

The shaft furnace typically has a substantially circular circumference, but may also have a different shape, such as for example a rectangular circumference. The n injectors are preferably substantially evenly or uniformly distributed around the circumference of the shaft furnace, though other configurations are possible, depending on the furnace structure and the process requirements.

The number n of said injectors is generally greater than 3. A number of up to 14 or 16 injectors may be useful. However, the number n of injectors may also be significantly higher, for example up to 24 or even up to 36 or more.

The fluid distributor is advantageously a fluid distribution ring which surrounds the shaft furnace. According to a first embodiment of the method of the invention, the process fluid is used as test fluid. In that case, in order to ensure that the test fluid is effectively supplied to the injector of which the status is to be tested at the predetermined pressure or at the predetermined flow rate, the control unit closes the n-1 individual valves between the fluid distributor and the n-1 other injectors. As a consequence, during the supply of the test fluid to the injector of which the status is to be tested, all of the process fluid which is supplied to the fluid distributor flows only to the injector of which the status is to be tested and this at the predetermined pressure or at the predetermined flow rate. No process fluid flows from the fluid distributor to the n-1 other injectors during this period so that said n-1 other injectors do not cause interference with the ongoing status test. In order to ensure that the test fluid is effectively supplied to the injector of which the status is to be tested at the predetermined pressure or at the predetermined flow rate, the control unit my also adjust the first valve unit between the source of the process fluid to the fluid distributor to adjust the flow-rate and/or the pressure of the process fluid (used as test fluid) flowing into the fluid distributor. The control unit may be programmed to control flows of the process fluid from the fluid distributor to each of the n injectors so that said injectors continuously inject the process fluid into the furnace in between status tests. Alternatively, the control unit may be programmed to control flows of the process fluid from the fluid distributor to each of the n injectors so that said injectors inject the process fluid into the furnace in a pulsed or alternating manner in between status tests.

The advantage of this embodiment is that no additional equipment is required for the status test. A disadvantage of this embodiment is that the flow of process fluid to the n-1 other injectors is temporarily interrupted. This is not a problem if this interruption, which must be repeated for the status test of each injector, is sufficiently short and if the process taking place in the shaft furnace is not very susceptible to such interruptions.

In other cases, the following embodiment whereby a fluid other than the process fluid is used as the test fluid may be more useful, even though this requires some additional equipment. According to said further embodiment, during the supply of test fluid to the injector to be tested, the control unit: (a) closes the individual valve connecting the injector of which the status is to be tested to the fluid distributor so that no process fluid flows from the fluid distributor to said injector and

(b) opens a test-fluid valve between a source of test fluid and said injector so that the test fluid is supplied to said injector at the predetermined pressure or at the predetermined flow rate.

The flow of process fluid to the n-1 other injectors may thus continue under the control of the control unit during the status test and disturbance to the process in the shaft furnace is minimal.

In that case, the control unit may be programmed to control the flows of the process fluid from the fluid distributor to each of the n injectors so that said injectors continuously inject the process fluid into the furnace when they are not being subjected to a status test in accordance with the invention. Alternatively, the control unit may be programmed to control flows of the process fluid from the fluid distributor to each of the n injectors so that said injectors inject the process fluid into the furnace in a pulsed or alternating manner when they are not subjected to a status test.

Even though, in this case, the test fluid may have the same or a similar composition to the process fluid, it may be preferable to select a test fluid which does not react with other chemical components present in the shaft furnace so as to limit the impact of the status tests on the process in the shaft furnace even further.

The test fluid may, for example be air, N₂, C0₂ or recycled flue gas.

According to a convenient embodiment, the test fluid distributor is a test-fluid distribution ring which surrounding the shaft furnace, thereby facilitating the supply of test fluid to the n individual injectors during their respective status tests.

When it is considered that some, insubstantial damage to the injectors is allowable and does not require the replacement of such injectors, the predetermined safe flow-rate range or the predetermined safe pressure-drop range may have been selected so as to include the flow characteristics of injectors with such insubstantial damage. In that case, it may nevertheless be useful for the furnace operator to be able to distinguish between substantially intact and only insubstantially damaged injectors. Thereto, distinction may be made between standard ranges, which correspond to substantially intact injectors and warning ranges, which correspond to only insubstantially damaged injectors.

In that case, when the test fluid is supplied to the injector at the predetermined pressure, the predetermined safe flow-rate range consists of a predetermined standard flow-rate range and a predetermined warning flow-rate range on both sides of the standard flow-rate range. The control unit verifies whether the measured flow rate falls outside the standard flow-rate range but inside the warning flow-rate range. When the measured flow rate does indeed fall within the warning flow-rate range the control unit emits an output signal signaling that the injector of which the status has been tested no longer operates within its standard operation conditions

Similarly, when the test fluid is supplied to the injector at the predetermined flow rate, the predetermined safe pressure-drop range consists of a predetermined standard pressure-drop range and a predetermined warning pressure-drop range on both sides of the standard pressure-drop range. The control unit verifies whether the measured pressure drop falls outside the standard pressure-drop range but inside the warning pressure-drop range. When the measured pressure drop falls within the warning pressure-drop range, the control unit emits an output signal signaling that the injector of which the status has been tested no longer operates within its standard operation conditions.

The predetermined standard flow-rate range for the predetermined pressure and the predetermined standard pressure-drop range for the predetermined flow rate typically correspond to a range around the flow rate which is observed when the test fluid is supplied to a new, unused injector of the same type at the predetermined pressure, respectively to a range around the pressure drop which is observed when the test fluid is supplied to such a new, unused injector at the predetermined flow rate. The predetermined standard flow-rate range is however narrower than the predetermined safe flow-rate range and the predetermined standard pressure-drop range is narrower than the predetermined safe pressure-drop range.

The method according to the invention may include the step of determining the flow-rate range referred to as "predetermined standard flow-rate range", respectively the pressure-drop range, referred to as "predetermined standard pressure-drop range". The "predetermined standard flow-rate range", respectively the "predetermined standard pressure-drop range" may be provided by the manufacturer or supplier of the injectors or may be based on earlier experience with injectors of the same type.

For additional security, the method according to the present invention may also be combined with the earlier mentioned maximum lifetime approach. However, due to the information on the actual status of the injector made available through the method of the present invention, a longer maximum lifetime or maximum operation period may safely be selected.

In that case, the control unit preferably also tracks the operation time of each of the n injectors. When the actual operation time of one of the n injectors reaches a predetermined maximum operation time, the control unit generates an output signal identifying said injector as having reached its maximum operation time, whereupon said injector will typically be replaced by the furnace operator. According to one embodiment, the control unit is programmed to initiate and execute the status test for each one of the n injectors in succession without interruption between two successive status tests of different injectors. Alternatively, the control unit can be programmed to initiate and execute the status test for each one of the n injectors with an interval free of status tests between two successive status tests of different injectors. This latter embodiment may be useful when extending the status checks over a longer period could have a negative impact on the process taking place in the shaft furnace.

The shaft furnace may be a waste combustion furnace. However, the invention is particularly useful when the furnace is a furnace in which a charge material, other than the fuel which is combusted with the oxidizing agent, is transformed. The invention is thus particularly useful when the shaft furnace is a glass- melting furnace, a mineral-wool-melting furnace or a metal-melting furnace.

The shaft furnace may be a cupola. The shaft furnace may also be an ironmelting blast furnace.

The present invention and its advantages are illustrated in the following examples, reference being made to figures 1 to 3, whereby:

• figure 1 is a schematic representation of a first embodiment of an installation for melting cast iron and suitable for use in the method of the invention, including a cross-section representation of the cupola-type shaft furnace of the installation,

• Figure 2 is a schematic representation of a second embodiment of such an installation, and

• Figure 3 is a partial schematic representation of a screenshot of a user interface suitable for use in the context of the present invention.

The shaft furnace 10 of figures 1 and 2 has a substantially circular cross section. A charge 20 of metal (cast iron) to be melted and coke is introduced at the top end 11 of the shaft furnace 10. Flux materials are generally also introduced in this manner. The charge 20 is typically introduced 10 so as to form successive horizontal layers inside the shaft furnace 10, for example a layer of metal, followed by a layer of coke, followed by a layer of flux material, followed by a layer or metal, etc. The coke is combusted with combustion oxidant in a combustion zone 12 located further down in the shaft furnace 10. Thereto, the combustion oxidant is injected into the shaft furnace 10 by means of oxidant injectors or tuyeres 30 which are positioned around the combustion zone 12.

The heat of combustion causes the metal in the charge immediately above the combustion zone 12 to melt and the molten metal trickles through the combustion zone 12 to the bottom area 13 of the furnace. The combustion gases generated in combustion zone 12 travel further upwards through the layered charge, thereby preheating the charge, until they are removed from the shaft furnace via a flue gas outlet 16. The molten metal is removed from the bottom area 13 of the shaft furnace 10 via tapping spout 14. The slag which is formed during the melting process is removed from the shaft furnace 10 via slag spout 15 located at a level above the level of tapping spout 14.

A control unit 40 controls the operation of the shaft furnace 10.

In the illustrated embodiment, six (6) oxidant tuyeres 30 are evenly distributed around the combustion zone 12 of the shaft furnace 10. Each oxidant tuyere 30 is individually connected to an oxidant distributor in the form of an oxidant ring 31 which surrounds the shaft furnace 10. Combustion oxidant is supplied to the oxidant ring 31 from an oxidant source, such as an air separation unit or an oxygen reservoir (not shown). Valve 32 is used to control the flow of oxidant from the oxidant source to the oxidant distributor 31. Valves 33 are used to control the flow of oxidant from oxidant distributor 31 to the individual oxidant tuyeres 30, one valve 33 per oxidant tuyere 30. The functioning of the individual valves 32, 33 is controlled by or through control unit 40.

In the embodiments illustrated in figures 1 and 2, oxidant tuyeres 30 are tuyeres for the injection of oxygen with a degree of purity of between 90%vol and 100%vol, preferably of at least 95%vol. In order to enable the sonic or supersonic injection of oxygen into the shaft furnace 10, each tuyere 30 is equipped with a laval nozzle 34.

According to a preferred embodiment, when the total rate of oxidant injection into furnace 10 is lower than the rate at which said oxidant would be injected into furnace 10 when all of the oxidant tuyeres 30 inject said oxidant at sonic or supersonic velocity into the furnace 10, central control unit 40 preferably causes valves 33 to open and close in such a way as to achieve pulsed injection of said oxidant as described for example in DE-A-10249235, whereby the tuyeres 30 alternate between an active phase during which the tuyere 30 injects oxidant at sonic or supersonic velocity and a passive phase during which said tuyere 30 injects no oxidant into furnace 30 or injects oxidant at sub-sonic velocity and at a fraction of the rate at which oxidant is injected during an active phase of said tuyere 30.

It will be appreciated that the illustrated embodiment is only one of many possible embodiments.

For example, the charge 20 may be introduced into the shaft furnace 10 via a shaft door in the mantle 17 of the furnace 10 at top end 11, rather than through the roof of the furnace 10. The combustion gases may be evacuated from furnace 10 via a gas outlet in the roof of the furnace 10 rather than via a flue gas outlet 16 in the mantle 17.

The number of oxidant tuyeres 30 may be greater or smaller than in the illustrated embodiment.

Additional fuel, such as coal, fuel oil or gaseous fuel, may also be introduced into the combustion zone 12. The additional fuel may be introduced into the furnace 10 via burners, via fuel tuyeres, which may be separate from the oxidant tuyeres or which may form a tuyere ensemble with (some of) the oxidant tuyeres 30, or, in particular in the case of solid particulate additional fuel, directly through the oxidant tuyeres 30. The furnace 10 may also comprise multiple sets of tuyeres for combustion oxidant. For exemple, a set of air tuyeres for the injection of air, which may or may not be enriched with oxygen, may be connected to a wind ring around the shaft furnace and a set of oxygen tuyeres may be connected to a separate oxygen ring around the shaft furnace.

When, in the embodiment illustrated in figure 1, control unit 40 initiates a status test of one of the oxidant injectors or tuyeres 30, valve 33 corresponding to the oxidant tuyere 30 to be tested is opened or remains open and valves 33 corresponding to the other tuyeres 30 are closed so as to fluidly disconnect said other oxidant tuyeres 30 from oxidant ring 31. In this manner, the pressure with which or the flow rate at which oxidant from oxidant ring 31 is supplied to the oxidant tuyere 30 to be tested can be regulated to correspond to a predetermined test level without interference from the other tuyeres 30.

In accordance with the present invention, when during the status test, oxidant from oxidant ring 31 is supplied to the injector 30 to be tested at said predetermined pressure, sensor 35 determines the flow rate at which said oxidant flows through said injector 30 under the status test conditions. Similarly, when during the status test, oxidant from oxidant ring 31 is supplied to the injector 30 to be tested at the predetermined flow rate, sensor 35 determines the pressure drop or back pressure over said injector 30 or over at least the laval nozzle part 34 of said injector 30.

The flow rate, respectively pressure, determined by sensor 35 is transmitted to control unit 40, where the determined value is compared with a predetermined safe parameter range of the flow rate, respectively pressure at status test conditions for the tuyere 30 being tested. When the determined value lies outside the predetermined safe parameter range, an alarm signal is sent to the furnace operator, for example via a user interface such as a monitoring screen and/or a mobile device, such as a smart phone, so that the furnace operator may take the necessary action for replacing the faulty tuyere 30.

In addition to comparing the determined value with a predetermined safe parameter range, the determined value may also be compared with a predetermined warning parameter range which lies within the safe parameter range but outside a standard range for said parameter. When the determined value lies within the predetermined safe parameter range, but also within the predetermined warning range for said parameter, the furnace operator receives a warning signal, thus allowing the operator to anticipate or plan the replacement of the corresponding tuyere 30 and, if necessary, to order new replacement tuyeres. Whereas in the case of an alarm signal, immediate action is normally required, this is not the case for a warning signal as described in this paragraph. After the status test of tuyere 30 is completed, control unit 40 may revert the injection of oxidant by means of the six tuyeres 30 back to the normal operation for melting iron in shaft furnace 10 and initiate the status test of one of the other tuyeres 30 at a later, typically preprogrammed, moment in time. Alternatively, control unit 40 may initiate a status test of each oxidant tuyere 30 in succession, i.e. one after the other, and revert the injection of oxidant by means of the six tuyeres 30 back to the normal operation for melting iron in shaft furnace 10 only after the status of all six tuyeres 30 has been tested.

In the alternative embodiment illustrated in figure 2, a test fluid distributor or ring 50 also surrounds the mantel 17 of furnace 10 near the oxidant tuyeres 30. Individual connections 51 are provided between test fluid ring 50 and each of the oxidant tuyeres 30, each connection 51 being equipped with an on/off valve 52 for fluidly connecting or disconnecting the corresponding oxidant tuyere 30 with the test fluid ring 50. During normal operation of shaft furnace 10, all on/off valves 52 are closed so that none of the oxidant tuyeres 30 are in fluid connection with test fluid ring 50. When control unit 40 initiates a status test of one of the oxidant injectors or tuyeres 30, valve 33 corresponding to the oxidant tuyere 30 to be tested is closed entirely and valve 51 corresponding to said oxidant tuyere 30 is opened, while the remaining valves 51 corresponding to the other oxidant tuyeres 30 remain closed. During the status test, test fluid from test fluid ring 50 is supplied to the oxidant tuyere 30 to be tested (only) at a predetermined pressure, respectively at a predetermined pressure and sensor 35 corresponding to the tuyere 30 being tested determines the flow rate of test fluid through said tuyere 30, respectively the pressure drop or back pressure over said tuyere 30 or at least over the nozzle 34 of said tuyere 30. In this manner a status test of tuyere 30 can be conducted while sufficient oxidant from oxidant ring 31 for iron melting continues to be injected into the shaft furnace 10 by means of the other oxidant tuyeres 30. At the end of the status test of tuyere 30, on/off valve 52 corresponding to said tuyere 30 is closed and control unit 40 may reconnect said tuyere 30 to oxidant ring 31 at an appropriate moment in time (for example immediately or, in the case of pulsed oxidant injection as described above, at the start of its next active phase) by opening valve 32 which corresponds to said tuyere.

Figure 3 illustrates one of the manners in which the invention makes it possible to inform the furnace operator of the status of the different injectors, such as the oxidant injectors or tuyeres 30 of the embodiments illustrated in figures 1 and 2.

Figure 3 shows a touchscreen with a schematic representation of a cross section of shaft furnace 10 at the level of oxidant tuyeres 30. Oxidant ring 31 and valves 32 are equally shown. Information on the status or operating conditions of the different elements shown in the representation can be obtained by "clicking" on the element concerned. Three examples of such operator feedback are shown in figure 3.

A predetermined maximum operation time has been stored in control unit 40. For each oxidant injector 30, the date of installation of the injector 30 has been stored in the control unit 40 and the control unit 40 calculates the anticipated date of replacement of said tuyere 30 on the basis of the maximum operation time starting from the date of installation.

When a status test has been performed on a given oxidant tuyere, the value determined by sensor 35 is supplied to control unit 40 where it is compared with a predetermined safe range and a predetermined warning range within said safe range for the given parameter and tuyere.

When the determined parameter lies within the safe range and outside the warning range, as is the case for tuyere nr. 3, the screen shows the tuyere to be safe and indicates the anticipated date of replacement for the tuyere based on the maximum operation time.

When the determined parameter lies within the warning range, as is the case for tuyere nr. 5, the screen indicates that the tuyere is safe but affected in its functioning, while again indicating the anticipated date of replacement for the tuyere based on the maximum operation time.

Finally, when the determined parameter lies outside the safe range, as is the case for tuyere nr. 4, the screen indicates that the tuyere is damaged and needs to be replaced as soon as possible.

A color code, such as green-orange-red, may advantageously also be used to indicate the status of the individual tuyeres 30 as respectively safe, safe-affected and damaged.

Claims

Method of injecting a process fluid into a vertical shaft furnace (10) in which a combustion process takes place, whereby:

• the shaft furnace (10) presents n injectors (30) substantially uniformly distributed around the circumference of the shaft furnace (10) , with n > 3, and a fluid distributor (31) which is fluidly connected, on the one hand, to a source of the process fluid to be injected and, on the other hand, to the n injectors (30),

• the shaft furnace (10) is part of an installation which includes a control unit (40) programmed to control (a) a total amount of the process fluid injected into the shaft furnace (10) through the n injectors (30) by means of a first valve unit (32) between the source of the process fluid to the fluid distributor (31) and (b) to control flows of the process fluid from the fluid distributor (31) to each of the n injectors (30) by means of n individual valve units (33) between the fluid distributor (31) and the n injectors (30),

characterized in that:

• the control unit (40) is also programmed to initiate and execute a status test for each one of the n injectors (30) individually while the combustion process takes place in the shaft furnace (10), status test during which:

o a test fluid is supplied at a predetermined pressure or at a predetermined flow rate to the injector (30) of which the status is tested,

o when the test fluid is supplied to the injector (30) at the predetermined pressure, a flow rate of the fluid through the injector (30) is measured and when the test fluid is supplied to the injector (30) at the predetermined flow rate, a pressure drop over the injector (30) or over at least a nozzle part of the injector (30) is measured; o when the test fluid is supplied to the injector (30) at the predetermined pressure and the flow rate of the fluid through the injector (30) is measured, the control unit (40) verifies whether the measured flow rate falls inside a predetermined safe flow-rate range for the predetermined pressure and when the test fluid is supplied to the injector at the predetermined flow rate and the pressure drop is measured, the control unit (40) verifies whether the measured pressure drop falls inside a predetermined safe pressure-drop range for the predetermined flow rate, o when the measured flow rate does not fall inside the predetermined safe flow-rate range or when the measured pressure drop does not fall inside the predetermined safe pressure-drop range, the control unit (40) emits an output signal signaling that the injector (30) of which the status has been tested must be replaced.

Method according to claim 1, whereby the control unit (40) is programmed to repeat the status check for each one of the n injectors (30) at predetermined intervals.

Method according to claim 1 or 2, whereby the fluid distributor (31) is a fluid distribution ring surrounding the shaft furnace (10).

Method according to any one of the preceding claims, whereby the process fluid is used as test fluid and whereby during the supply of the test fluid to the injector (30) of which the status is to be tested, the control unit (40) closes the n-1 individual valves (33) between the fluid distributor (31) and the n-1 other injectors (30) so that all process fluid supplied to the fluid distributor (31) flows to the injector (30) of which the status is to be tested at the predetermined pressure or at the predetermined flow rate and no process fluid flows from the fluid distributor (31) to the n-1 other injectors (30).

Method according to claim 4, whereby the control unit (40) is programmed to control the flows of the process fluid from the fluid distributor (31) to the n injectors (31) so that said injectors (31) inject the process fluid either continuously or in a pulsed manner into the shaft furnace (10) when no status test is executed by the control unit (40).

Method according to any one of claims 1 to 3, whereby a fluid other than the process fluid is used as the test fluid and whereby, during the supply of test fluid to the injector (30) to be tested, the control unit (40) (a) closes the individual valve (33) connecting the injector (30) of which the status is to be tested to the fluid distributor (31) so that no process fluid flows from the fluid distributor (31) to said injector (30) and (b) opens a test-fluid valve (52) between a source of test fluid (50) and said injector (30) so that the test fluid is supplied to said injector (30) at the predetermined pressure or at the predetermined flow rate.

7. Method according to claim 6, whereby the test fluid does not react with other chemical components present in the shaft furnace (10).

8. Method according to claim 6 or 7, whereby the test fluid distributor (31) is a test-fluid distribution ring surrounding the shaft furnace (10).

9. Method according to any one of claims 6 to 8, whereby the control unit (40) is programmed to control the flows of the process fluid from the fluid distributor (31) to the n injectors (31) so that when an injector (31) is not being subjected to a status test, said injector (31) injects process fluid into the shaft furnace (10) either continuously or in a pulsed manner

10. Method according to any one of the preceding claims, whereby

o whereby the test fluid is supplied to the injector (30) at the predetermined pressure and the predetermined safe flow-rate range consists of a predetermined standard flow-rate range and a predetermined warning flow-rate range on both sides of the standard flow-rate range, and whereby the control unit (40) verifies whether the measured flow rate falls outside the standard flow-rate range but inside the warning flow-rate range, or

o whereby the test fluid is supplied to the injector (30) at the predetermined flow rate and the predetermined safe pressure-drop range consists of a predetermined standard pressure-drop range and a predetermined warning pressure-drop range on both sides of the standard pressure-drop range, and whereby the control unit (40) verifies whether the measured pressure drop falls outside the standard pressure-drop range but inside the warning pressure-drop range,

and whereby:

o when the measured flow rate falls within the warning flow-rate range or when the measured pressure drop falls within the warning pressure-drop range, the control unit (40) emits an output signal signaling that the injector (30) of which the status has been tested no longer operates within its standard operation conditions.

11. Method according to any one of the preceding claims, whereby the control unit (40) further tracks the operation time of the n injectors (30) and whereby when the operation time of one of the n injectors (30) reaches a predetermined maximum operation time, the control unit (40) generates an output signal identifying said injector (30) as having reached its maximum operation time.

12. Method according to any one of the preceding claims, whereby the control unit (40) initiates and executes the status test for each one of the n injectors (30) in succession, without interruption between two successive status tests of different injectors (30).

13. Method according to any one of claims 1 to 11, whereby the control unit (40) initiates and executes the status test for each one of the n injectors (30) with an interval without status tests between two successive status tests of different injectors (30).

14. Method according to any one of the preceding claims, whereby the shaft furnace (10) is a cupola.

15. Method according to any one of the preceding claims, whereby the process fluid is a combustion oxidant presenting an oxygen content higher than 21%vol and at most 100%vol.