JPH0156831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method and apparatus for repairing refractory blocks and other substrates used, for example, in blast furnaces, kilns or heating furnaces.

Refractory linings, such as brickwork or coatings in carbonization ovens, especially coke ovens or metal processing ovens, ladles, kilns, soaking pits and combustion chambers, corrode or crack due to the wear, loads and stresses imposed at very high temperatures. It has been known for many years that it is desirable to repair such furnaces in situ. It is often important that the furnace not be allowed to cool much below its operating temperature. Otherwise, severe damage will occur, often resulting in complete loss of the furnace. To solve this problem, a technique known as thermal spraying was established, which involves spraying particles of molten or sintered refractory material from a lance onto the wall area in need of repair in a furnace.
It consists of accumulating said particles at their repair points. The first version of this technology in the UK is believed to have consisted of transporting silica powder in oxygen and supplying acetylene as fuel at the tip of a lance. It will be appreciated that this approach is extremely slow to repair, takes a long time to accumulate significant amounts of refractory material, and poses considerable hazards. These hazards are discussed in more detail below.

Although many proposals have been made in the patent literature, none have reached industrial or even operational status.
Even if there is, it is only a few of them. GB 1151423 describes a prior art proposal consisting of entraining a refractory powder in the fuel gas stream and then sending this fuel gas to a burner for combustion with an oxidizing gas. And instead of using compressed gas to transport the refractory powder, GB 1151423 transports the powder in a liquid fuel, preferably a light fuel oil. Although primarily related to the device, other proposals include UK patent no.
No. 991,046, this patent proposes transporting a refractory powder material in oxygen and supplying it with propane as a fuel gas.

A slightly different approach among the proposals in the prior art is to use an easily oxidized metallic element to provide all or part of the heat required to melt the refractory powder. US Pat. No. 2,741,922 describes the formation of shaped bodies of refractory material by oxidizing mixtures of elements such as magnesium, aluminum or silicon and inert refractory fillers such as MgO, Al ₂ O ₃ or SiO ₂ It is related to. Conveniently, the oxidation reaction products of such elements are themselves refractory oxides. More recently, British Patents Nos. 1330894 and 1330895 describe a thermal spraying apparatus and method using an easily oxidized element of very small average particle size (less than 50 μm) and at least one other substance. It is related to. The powder mixture is preferably conveyed in oxygen-enriched air, more preferably in oxygen, to the lance and, after being injected from the lance, the powder mixture is ignited. It is said that after numerous experimental studies it has been found that the oxidizing element must have an average particle size of less than 30 μm, preferably less than 10 μm. Such a small particle size, and therefore a concomitant large specific surface area, facilitates rapid oxidation and release of heat for melting of the other material or melting of the surface area. It is said that there is a risk of accidental accidents with this method and apparatus, and therefore it is preferred to use an automatic safety device to establish a safe condition if there is a risk of backfire. Now it turns out that this kind of danger is very real. Since the flame propagation velocity of such mixtures in oxygen is considerably greater than the velocity of ordinary gases, flashback is an ever-present danger. Furthermore, the very small particle size of the oxidizing element increases the risk of flashback due to the very large specific surface area, as well as the fact that the particle is ejected from the tip of the lance. This results in very early ignition. This premature ignition leads to the formation of refractory material on or within the tip of the lance, blocking gas flow. Although this method and apparatus allow for industrial use, repair operations are often hampered by the creation of flashback conditions and by the use of a specialist and experienced team of operators. It turned out to be interrupted due to occlusion.

The present invention provides a method and apparatus that overcomes the above-mentioned drawbacks. Accordingly, the present invention provides a method for partially preparing a mixture of a finely divided refractory oxide and one or more finely divided metal or metalloid elements that readily combusts to form a refractory oxide with a relatively inert gas. or metering said mixture into said carrier gas stream by maintaining said mixture in a reservoir in a fully fluidized state and entraining said mixture in said jet stream of relatively inert carrier gas, said mixture being dispersed in said carrier gas in a lance; The present invention provides a process for thermal spraying refractory materials comprising supplying a lance with sufficient oxygen near the outlet of the mixture to combust the elements in the mixture.

The invention also provides a storage tank for refractory material, a means for bringing said material into a partially or fully fluidized state in said storage tank, and a means for bringing said material into a partially or fully fluidized state in said storage tank by entraining said material in a jet stream of a relatively inert carrier gas. an apparatus for thermal spraying of refractory materials, comprising means for metering said material from a carrier gas, means for conveying a mixture to a lance, and means for supplying oxygen to said lance near the outlet of said material in a carrier gas. It also provides.

A jet stream of carrier gas is discharged between axially aligned inlet and outlet piping provided in the material storage tank, these pipes preferably being mounted above the bottom of the storage tank and preferably extending substantially above the bottom of the storage tank. Located in the center. It is particularly advantageous if the gap between the inlet pipe and the discharge pipe can be adjusted in order to vary the entrainment of material into the carrier gas according to the requirements of the operator of the device. However, other arrangements for supplying the jet stream may be used, including, inter alia, a ventilary device supplying the refractory material at one or more points perpendicular to the jet stream. Such a bench lily device is attached to the exterior of the reservoir.

The material carried in a relatively inert carrier gas may be fed directly to the lance, but before feeding it to the lance the material/gas mixture is mixed with a second feed gas of relatively inert gas. It is preferable to do so.

Preferably, the mixture of refractory oxide and metal or metalloid element has a chemical composition after oxidation that is substantially the same as that of the object to be repaired, such as bricks, furnace linings, refractory blocks, etc. It has been found that, depending on the application of the refractory material, a considerable range of refractory oxides are used, varying from acidic bricks, blocks or coatings to basic bricks, blocks or coatings. Commonly used refractory materials consist primarily of silica, alumina or magnesite, with respective minor amounts of other refractory oxides such as ZrSiO ₄ and ZrO ₂ or complex oxides such as spinel. Analyzing the material properties of the material being repaired and establishing by simple trial and error the proportions of oxidizing elements necessary to produce a satisfactory sprayed material to yield the same final composition is a comparative It's a simple matter. The mixture may optionally contain small amounts of other components for particular purposes, for example particles providing a material with high resistance to abrasion and/or a material with better thermal conductivity. good. However, on the other hand, the repaired part is of the same chemical composition as the brick etc. to which it is bonded, but has different physical properties than the parent refractory material, and is usually more wear resistant than the parent refractory material. It has been found to be generally durable.

A convenient source of refractory oxide is crushed brick or a refractory material of the same composition as the refractory material to be repaired. For example, so-called semi-silica or silica bricks are used in carbonization furnaces. Such materials are generally available at the location or factory where repair is desired. Powdered silicon, aluminum and magnesium are commercially available in a variety of nominal particle sizes.
In general, there is no strict limit on the particle size of the mixture, but it is 152 μm, not only because it is cheaper but also because it is believed that releasing heat more slowly from large particles will help avoid the problem of clogging the lance tip. It is preferred to use oxidizing elements with a particle size range of up to . A suitable particle size when using powdered silicon and aluminum is -100BS mesh, and the refractory oxide has a particle size larger than the above elemental particle size, e.g. -0.8
mm is convenient. However, larger particle sizes may also be used, particularly if the larger particle size better matches the crack dimensions or the physical properties of the refractory material to be repaired.

According to the inventors' experimental results, the mixture of refractory material and oxidizing elements does not burn in air, but the use of a more inert gas according to the invention to transport the material makes it even more combustible. It has been found that great safety and reliability can be obtained. Suitable relatively inert gases include nitrogen, helium, carbon dioxide,
Oxygen-depleted air and mixtures of them with air are included. If such a relatively inert gas is used for partial or complete fluidization of the material in the storage tank, the dust explosion type hazard is virtually eliminated despite the reactivity of the metal or metalloid particles. Complete flow is not necessary to achieve the benefits of improved dispensing and metering of material as long as sufficient gas is passed through the material to facilitate material movement.

This is accomplished by using a first supply of relatively inert gas to meter the material and a second supply of relatively inert gas to further disperse the material and transport it to the lance. The method of the invention provides greater control and flexibility in operation. In particular, this facilitates igniting the flame at the lance using a low flow rate of material, which flow rate can then be increased to a flow rate suitable for repairing the substrate. It also facilitates the transport of relatively large particles.

The amount of the mixture carried in the relatively inert gas is typically on the order of 0.1 Kg in gas 50 at operating pressure, with a typical flow rate of about 0.1 Kg per minute.
This is a convenient value for repairing carbonization furnaces, for example, but
Higher flow rates can be used, but have a detrimental effect on operator control of the mixture charge.

The gas used can be supplied from cylinders or tanks, or via piping. For example, compressed air piping may be used if the air is sufficiently dry to avoid problems with material caking in the material storage tank or elsewhere in the equipment.

The amount of oxygen supplied to the above-mentioned preferred amount mixture in the gas depends on the temperature of the repair area, but is about 2:1.
Oxygen: the amount in the volume of the total carrier gas. There is no need to use pure oxygen if sufficient oxygen is provided to support continuous combustion of the elements.

The oxygen supply tube is connected to a tubular manifold mounted around the first supply tube so that the material dispersed in the first gas supply stream is coated with a "skin" of oxygen as it exits the lance. preferable. However, other gas flow configurations can be used and advantageously induce swirling flow patterns.

For safety reasons when handling oxygen, it is preferable to use arsenic-free copper, stainless steel, or brass, rather than mild steel, for all-metal fittings that come into contact with oxygen or oxygen-enriched gases.

suitable mixture composition and carrier gas flow rate;
The jet or spray stream discharged from the lance is readily ignited by contact with the hot walls of the furnace or by contact with the flame provided the oxygen flow rate is achieved. The jet stream or spray stream immediately atomizes the refractory material, and when the flame spray contacts an abrasive or cracked area in the furnace, it melts the refractory material that impinges on that area, dislodging the molten or sintered particles into the area. A very strong bond is created between the furnace wall and the refractory coating build-up. It is preferred to move the flame spray gradually across the repair area to avoid flaking off of the coating due to excessively localized coverage of the refractory material.

It has been found that combustion of the mixture does not occur for some distance from the tip of the lance, which is the distance at which sufficient mixing of the oxygen and mixture is achieved. This prevents the tip of the lance from being significantly blocked by build-up of refractory material and allows for easier continuous operation.

It will be appreciated that if the lance is used for extended periods of time in a high temperature environment, such as at depth in a carbonization furnace, it is advantageous to cool the lance. This can be accomplished by circulating water through tubes or coils in thermal contact with the supply tubes, or by forced air or forced gas cooling.

The invention will be explained below with reference to the figures which show, by way of example, a device according to the invention.

A charging material for welding powder 1 is held in a material storage tank 2. This reservoir 2 can be easily opened for recharging with welding powder charge material. A compressed nitrogen inlet pipe 3 and a compressed nitrogen discharge pipe 4 are provided close to the bottom of the storage tank but away from the bottom, and these pipes have their axes aligned with each other and have a gap 5 between their ends. compartmentalize. The gap 5 can be adjusted in length by a simple mechanical arrangement mounted on the outside of the reservoir to allow the operator to adjust the feed rate of the welding powder suspended (dispersed) in the gas in the discharge piping. can. cylinders of compressed nitrogen 6 and cylinders of compressed oxygen 7, which are conveniently placed on transportable supports, which may or may not be used for the retention of said materials in refractory material storage tanks; Nitrogen and oxygen are supplied through a valve 8, a flow rate indicator such as a rotameter 9, a nitrogen pipe 10 and an oxygen pipe 11 (which may be omitted). Both lines are controlled by valves 12 and 13 near the lance, generally indicated at 14, to give the lance operator virtually complete control over the gas supply flow rate. The oxygen line supplies oxygen directly into the handheld mixing chamber 15 (which is part of the lance). A portion of the nitrogen is fed into the chamber 16 below the reservoir 2 and partially fluidizes the welding powder 1 (charge 1) through a number of holes provided in the bottom. The nitrogen jet stream takes in a controlled amount of welding powder and exits the exhaust line 4.
through which it is conveyed in a dispersed state to the mixing chamber 15. A lance 17 is removably fitted into the mixing chamber, which is connected to the furnace,
It can be selected depending on the ability to reach the area to be repaired, such as a kiln or ladle, and the required ability.

Practical tests repairing both high and low temperature (approximately 600°C) substrates have shown that operators can perform repairs effectively with just a few minutes of training. After the pressure reducing valve 8 is brought into conduction, the valve 12 in the nitrogen piping is opened.
is adjusted to change the welding powder transport speed to the mixing chamber 15. By then adjusting the opening of the valve 13 in the oxygen line, the operator can optimize the combustion of the welding powder during the flame atomization operation. Rotameters 9 serve to direct the nitrogen and oxygen flow rates so that the operator can monitor the spray operation. The rotameter is of course chosen to clearly indicate in the central area the nitrogen and oxygen flow rates which have generally been found to be suitable, but it is clear that the nitrogen and oxygen flow rates need not be the same.

An important requirement related to the function and location of these valves is the ability of the operator to momentarily stop the thermal spray operation in the event of an emergency or anticipated emergency.

A typical repair material composition for cracked or worn semi-silica refractory walls is 9% by weight aluminum, 31% by weight silicon, and 60% by weight crushed semi-silica refractory brick. Metal elements are 10% crushed to -100BBS,
The above bricks are crushed to 0.8mm or less. The reactivity of the welding powder can be varied by varying the proportion of semi-silica in the mixture. Other suitable welding powders are 12% silicon, 4% aluminum and silica.
Consisting of 84%.

In one embodiment of the invention, the gap between the inlet and outlet piping is set to 6.4 mm (1/4 inch), and the supply control valve is configured to supply nitrogen at an inlet gauge pressure of 1.035 bar ⁽ 15 Psi). The flow rate is adjusted to be approximately 50/min. The oxygen supply is then set to deliver 100/ ^min at a gauge pressure of 1.104 bar (16 Psi), ie slightly more pressurized than the nitrogen pressure. Under these conditions, the powder transport rate is on the order of 100-120 g/min, which gives an actual welding (spraying) operation time of 1 hour, assuming a hopper capacity of 5 kg. The powder spray emitted from the lance is ignited by contact with the heated (800°C) carbonization furnace wall and becomes a flame spray, which, when directed towards the repaired area, deposits a glass-like solid there and burns the surface. chemically bond to.

The device of this invention is relatively simple and reliable;
It does not require a skilled operator or skilled routine maintenance and is believed to be particularly safe to operate. A highly portable device can be produced at low cost, thus making it possible to equip each site with equipment to repair defects before they become further damaged. This is a significant difference from most conventional industrial thermal spray processes, which require a team of skilled operators. This known method required great care and many safety precautions since the welding powder (spray powder) was transported in oxygen. Additionally, in the prior art, due to cost considerations, it was common practice to accumulate many individual defects before making necessary repairs.

Compared to known devices, the device of the present invention provides a mechanically simple device for reliable particle feeding to the lance without separate sedimentation or size separation of the feed particles. Additionally, a single operator can control all the parameters necessary to perform repair operations with successful results. This means that one operator can easily control all the parameters necessary for safe operation and does not have to rely on communication with other operators. Repairs can also be made using the method and apparatus of the present invention on cold substrates, for example, by igniting a spray of refractory material with a separate flame.

[Brief explanation of drawings]

The figure is a schematic explanatory diagram of an apparatus according to the present invention. In the diagram: 1... Welding powder, 2... Material storage tank (storage tank), 3... Compressed nitrogen introduction pipe, 4... Compressed nitrogen discharge pipe, 5... Gap, 6... Compressed nitrogen cylinder,
7... Compressed oxygen cylinder, 8... Valve, 9... Rotameter, 10... Nitrogen piping, 11... Oxygen piping,
12... Valve (for nitrogen), 13... Valve (for oxygen), 1
4... Lance, 15... Mixing room, 16... Room.

Claims (1)

[Scope of Claims] 1. A method of thermally spraying a refractory material by burning a finely divided metallic element or metalloid element mixed with a finely divided refractory oxide, the mixture being placed in a refractory material storage tank. metering the entrained mixture into a relatively inert carrier gas by keeping it in a fully or partially fluidized state with a relatively inert gas and entraining the mixture into a jet stream of the relatively inert carrier gas; A method for thermal spraying a refractory material, characterized in that the elements are supplied to a lance near the exit of the mixture from the lance, and sufficient oxygen is supplied to the lance near the exit of the mixture from the lance to combust the said element. 2. The method according to claim 1, wherein a jet stream of carrier gas is discharged between an inlet pipe and an outlet pipe whose axes are aligned and are provided in a refractory material storage tank. 3. A method according to claim 2, in which the amount of the mixture taken into the carrier gas stream is adjusted by adjusting the gap between the inlet pipe and the discharge pipe. 4. A method according to claim 1 or 2 or 3, wherein the amount of the mixture entrained in the carrier gas is approximately 0.1 kg per 50 kg of carrier gas. 5. The method according to any one of claims 1 to 4, wherein the flow rate of the mixture is about 0.1 Kg/min. 6. A method according to any one of claims 1 to 5, wherein the carrier gas is selected from nitrogen, helium, carbon dioxide, oxygen-depleted air, and mixtures thereof with air. 7. The method of claim 6, wherein the carrier gas is air and provides oxygen for combustion support at a volume ratio of about 2:1 oxygen:air. 8. An apparatus for spraying refractory material through a lance, the apparatus comprising a refractory material reservoir, means for fully or partially fluidizing the refractory material in the reservoir;
means for metering the refractory material from the reservoir by entraining the refractory material in a jet stream of relatively inert gas, means for transporting the entrained refractory material to the lance, and proximate the outlet of the lance; A refractory material thermal spraying apparatus, characterized in that it is provided with means for supplying oxygen to the apparatus. 9. The apparatus of claim 8, wherein the jet stream of carrier gas is arranged to be discharged between the carrier gas inlet and outlet piping which are aligned in the material storage tank. 10. The apparatus of claim 9, wherein the gap between the inlet pipe and the discharge pipe can be adjusted to vary the amount of refractory material taken into the carrier gas. 11. According to any one of claims 8 to 10, wherein the amount of gas supplied to flow the refractory material and the amount of gas supplied to entrain the refractory material into the carrier gas can be controlled separately. equipment.