2017年11月28日星期二

Residual Heat Utilization of Refractory Gas Burning Kiln

Refractory
Refractory
With the gradual implementation of the national environmental protection policy, the original domestic coal-fired kiln in the refractory industry is about to end its historical mission and replace it with clean natural gas, liquefied gas, light diesel oil, city gas and producer gas as the main New energy kiln. However, China is a large coal producing country, and refractory material are also large energy-hungry households. Some medium-to-low-grade refractories and large-volume refractories are still controlled by the furnace hot gas to ensure fuel supply and production cost control . As a result, the refractory industry has also developed a hot gas tunnel kiln, hot gas intermittent plutonium kiln group, hot gas intermittent shuttle kiln group.
Due to the different kiln body structure and thermal engineering process, intermittent kiln produces 5 times more flue gas than continuous kiln production. In general, the higher the gas temperature, the greater the proportion of heat loss. If the gas temperature is 1093 ℃, the heat loss reaches 55%; when the gas temperature is 1427 ℃, the heat loss reaches 70%. For the firing of refractory hot gas intermittent inverted kiln, according to the relevant experimental data show that: flue gas away from the kiln away from the heat about the furnace total heat expenditure of 35% to 40% in the absence of any heat recovery In the case of the measure, the heat balance calculation results, the thermal efficiency is only 10% ~ 15%. This is a big heat loss. Therefore, the use of flue gas heat is a very important energy recovery.
Set the heat exchanger in the flue is an important means of waste heat recovery. The hot air obtained after the heat exchange can be directly sent to the burner for combustion air, or the hot air can be diluted to the drying medium of the product embryo drying kiln or used to make the thermal efficiency of the kiln reach 30% or higher.
When the firing system uses a heat exchanger to preheat the air and use this hot air to make the combustion-supporting combustion air, the thermal efficiency of the kiln can be improved, the fuel consumption can be reduced, and the energy-saving effect can be achieved. And in the organization of high temperature combustion flame temperature can increase, increase heating efficiency, shorten the heating time (firing cycle). And because the hot air volume expansion, resulting in the burner orifice flow rate increases, accelerating the kiln gas circulation, contribute to the kiln temperature uniformity. The data show that: when the preheated air temperature reaches 220 ~ 250 ℃, can reduce fuel consumption by 6% to 8%. At the same time different combustion temperature, the impact on the flame temperature is very large. Even when the gas is not preheated, the combustion temperature of the gas increases significantly as the preheating temperature of the combustion air increases. This not only can solve the problem of low firing temperature, but also plays an important role in saving energy and reducing consumption.
In intermittent kiln production, because the fuel is changed with the heating stage, the amount of flue gas generated by the fuel also changes. In the event of a large fire, since the amount of fuel per unit time increases, the flue gas and temperature also inevitably increase. Preheat air combustion just to meet the requirements of combustion. Metal pipe heat exchangers are commonly used in production. Due to the limitations of high temperature oxidation and mechanical properties, the maximum service temperature is generally limited to below 500 ° C because of their low life (about 0.5 years). Metal pipe aluminum treatment, its service life is only about a year. The use of heat-resistant stainless steel or heat-resistant cast iron, the maximum temperature is generally limited to below 900 ℃. However, due to its high price, the use of units unbearable.  1. Because the fuel is the producer gas, the chimney bricks will not block. Life can be more than 10 years. Designed to ensure that the heat transfer efficiency, heat transfer area as large as possible (such as a group of 4 × 200m3 Square inverted hearth heat exchange area of ??about 230m2), although the volume is large, but the site conditions permit a one-time investment in the province, the flue System resistance is generally about 147 ~ 196Pa, chimney can be selected according to the height (usually about 50m).

The use of heat exchanger temperature is a very important factor in heat recovery. If the flue gas temperature is 1315 ℃, the use of thermal efficiency of 60% ceramic heat exchanger can save about 48% of fuel, if the use of thermal efficiency of 60% metal heat exchanger, you must first add cold air flue gas temperature dropped to 815 ℃ below, so that only 24% of fuel savings. Table 1 shows the effect of blending cold air on fuel economy.

In order to play the respective advantages of ceramic and metal heat exchangers, the two are used in tandem, known as a hybrid heat exchanger. First high-temperature flue gas into the ceramic heat exchanger, flue gas temperature dropped to below 815 ℃, and then into the metal heat exchanger. The flow of cold air is first into the metal heat exchanger, the heated air and then into the ceramic heat exchanger for further heating, the final preheated air temperature up to 1093 ℃.

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Application of Dry Sludge in Refractory for Blast Furnace

blast furnace refractory
blast furnace refractory
Blast furnace refractories are often used stemming, commonly used is a water cannabis mud, but when the steel production is high, this iron mouth stem mud is more susceptible to mechanical scouring and chemical erosion of slag iron, resulting in blast furnace slag Not a net, not only affect the smooth and high yield blast furnace, but also prone to iron in the refractory brick process of iron off, leading to runway accidents caused by heavy run. At the same time as Tietou tide, prone to playing Tietou "rocket" burns and other accidents.
The main production of anhydrous stemming ingredients ratio (%): Brown Iron Jade 15-24, 6-15 silicon carbide, coke 20, lime 12-16, tar 18-20. The gun mud compressive strength of 20Mpa, open the mouth opening in the blast furnace refractory openings easy, and anti-erosion performance is better.
The key component of lime mud is too large, will cause mud shrinkage is too large, resulting in cracks, too small, affect the mud plasticity, in the amount of stemming on the basis of 12%, and gradually found in the burn line changes Is +0.3%, the best performance, high plasticity at the moment, when there is good micro-expansion at high temperature tapping, no cracks, effective from the no swelling, cracks caused by channeling iron, , The risk of burned stave in severe cases.
Key components of low, medium temperature sintering agent added in a large amount, will have an impact on the stability of the iron, sintering agent added to the stemming at low temperature to generate low-melt, so anti-erosion ability of stemming deteriorated, splashing spatter . Found that when the ratio of 2.5%, when dealing with the iron mouth, than the water cannons save 25min time, and does not affect the trenches processing, tapping, the iron flow stability.
The above anhydrous mud in the domestic water heaters No. 1 and No. 2 blast furnace used, compared with the same period of water mud, blast furnace technical indicators are as follows: Tiekou pass rate increased by 2%, the punctuality rate rose 6.6%, iron content Poor pass rate rose 8%, iron mouth tapping wind rate decreased 96%, increase once a day tapping, blast furnace operation safety factor has also been improved. The development and application of this anhydrous stem mud has been extremely successful, contributing to the steady and high yield of refractories for blast furnaces.

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How to Choose Refractory Bricks Used for Different Parts of Blast Furnace
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2017年11月23日星期四

Analysis of the reasons of damaged blast furnace lining fire brick

blast furnace refractory lining material
blast furnace refractory lining material
1.Temperature.

The damaged performance of high temperature to fire brick:
(1)Erosion. When the edge air develops excessively, but the factory uses poor quality refractory material which has lower refractoriness under load, if the high temperature is over than allowable temperature, the fire lining brick will be eroded.
(2)Heat stress.
(3)Thermal shock. Thermal shock is a phenomenon when the fire brick meet the unsteady thermal stress and then become damaged.Cracks will occur in the refractory bricks and eventually broken.

2.Mechanical erosion and abrasion

3.Chemical attack

4.One of the important factors of firebrick refractory sale lining damage is unreasonable design, construct and furnace structure. Poor quality refractory and furance construction create the condition for the first kind of destructive factors.

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Factors affecting service life of converter

converter refractory
converter refractory
Factors that affect converter life:

1. Composition of slag. For every 1% increase in iron oxide, the service life of the lining is reduced by 18-20 times; the higher the MgO content in the slag, the lower the erosion of the lining. At present, the iron oxide content of slag is 18-24%.

2. Tapping temperature. The higher the tapping temperature, the shorter the service life. Therefore, the tapping temperature refractory material properties of the converter should be properly controlled.

3. Smelting time. Long smelting time, will speed the erosion of the lining up.

4. Lining structure. As the various parts of the converter are in different damage conditions, so it should adopt the integrated masonry method.

5. Furnace maintenance. For back and forth, regularly repair with hot self-flow repair materials.

6. Influence of converter blowing. Nitrogen gas, carbon dioxide, argon or oxygen are blown into the furnace through the purging plug placed at the bottom of the converter to enhance the mixing of the molten pool, thus shortening the steel making time, improving the quality of molten steel and reducing the cost of steel making. But the blown also speed the erosion of refractory materials up, resulting in increased consumption of refractory materials.

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2017年11月2日星期四

How to extend the life of refractory materials

refractory materials
refractory materials
How to extend the life of refractory materials. Generally divided into kiln kiln is divided into four bands, namely, decomposition zone, transition zone, firing zone and cooling zone. Four belt, firing with kiln lining the most critical, at home and abroad in the pre-decomposition kiln burning with the main use of alkaline refractory brick.
Thermal, mechanical and chemical factors contribute to the stress in the kiln lining and cause damage. With the kiln, operation and kiln lining in the kiln position of the different factors of the damage is also different. Which decisive role is the flame, kiln and kiln body deformation, they make the kiln bearing a variety of different stress.
For alkaline tiles, there are eight kinds of destructive factors, namely clinker melt infiltration, agglomeration of volatile components, reduction or reduction - oxidation, overheating, thermal shock, thermal fatigue, extrusion and grinding. However, these eight factors have different effects on the damage of different refractory brick lining in kiln, and the mechanism of damage to alkaline brick is described in this paper.
1, clinker melt infiltration:
Clinker melt mainly from the kiln and fuel, infiltration phase is mainly C2S, C4AF. The infiltration of C2S and C4AF in the metamorphic layer strongly dissolves magnesia and chrome ore in magnesia carbon bricks, precipitates secondary silicates such as CMS and magnesium rose pyroxene (C3MS2), and sometimes even precipitates potassium Stone; and the melt will be filled with brick lining pores, so that part of the brick layer of dense and embrittlement; combined with thermal stress and mechanical stress dual role, resulting in easy cracking refractory brick peeling. Due to C2S, C4AF above 550 ℃ began to form, and pre-decomposition kiln into the kiln material temperature has reached 800 ℃ ~ 860 ℃, so clinker melt penetration throughout the pre-decomposition kiln, the clinker melt on the pre-decomposition Kiln lining with a certain infiltration into the erosion effect.
2, the condensation of volatile components:
Pre-decomposition kiln, alkaline sulphate and chloride and other components volatile agglomeration, repeated circulation, resulting in the accumulation of these components in raw materials. By the production practice, the R2O, SO3 and CI- contents of the raw material in the warmest preheater of the kiln are often increased to 5 times, 3 to 5 times and 80 to 100 times respectively higher than that of the raw material. When the hot material enters the third part of the kiln cylinder (800 ° C to 1200 ° C), the volatile components in the material will aggregate in all the brick and brick layers, And the erosion of the adjacent components other than magnesite, resulting in brick thermal penetration stability of the infiltration layer is significantly reduced, the formation of expansion of potassium nepheline, garnet, the refractory brick lime damage, and thermal - mechanical stress Under the combined action of peeling off. The more the depth of the kiln lining is affected by the alkali salt, Selection.
3, reduction or reduction - oxidation reaction:
When the thermal system in the kiln is unstable, it is easy to produce the reduction flame or the incomplete combustion, so that the Fe3 + reduction or Fe2 + in the magnesia-chrome brick shrinks, and the migration and diffusion of Fe2 + in the magnesite crystal is stronger than Fe3 + More, which further exacerbated the volume shrinkage effect, so that the brick hole, the structure weakened, the intensity decreased. At the same time, the reduction of the kiln gas and the alternating atmosphere of the oxidation of the shrinkage and expansion of the volume effect occurs repeatedly, the brick will produce chemical fatigue. This process mainly occurs in the absence of kiln protection of magnesium chrome brick.
4, overheating:
When the kiln heat load is too high, so that the brick surface for a long time to lose the protection of the kiln, the hot surface layer of the matrix at high temperature melting and moving to the cold layer direction, leaving the brick lining layer of dense, hot surface layer is loose Porous (generally easy to occur in the firing area of ​​the firing zone), which is not resistant to abrasion, shock, vibration and thermal fatigue, easy to damage.
5, thermal shock:
When the kiln is not working properly or kiln leather is unstable, the alkaline tiles are susceptible to thermal shock. Kiln of the sudden collapse of the brick surface temperature caused by a sudden surge (or even up to thousands of degrees), leaving the brick to produce a lot of thermal stress. In addition, the frequent opening and closing of the kiln to produce alternating alternating heat within the brick. When the thermal stress, once beyond the structural strength of the brick lining, the brick suddenly cracks, and along the structure of the weakening of the Department continue to deepen the deepening, and finally the brick fragmentation. When the kiln skin falls, the broken brick in the hot surface layer is taken to keep the brick from damage. The thermal shock phenomenon can easily occur in the transition zone near the kiln.
6, thermal fatigue:
In the kiln operation, when the brick lining is not in the material layer, the surface temperature is lowered, and when the brick lining is exposed to the flame, the surface temperature is increased. Kiln each turn a week, brick lining surface temperature rise and fall range of up to 150 ℃ ~ 230 ℃, the impact of depth 15mm ~ 20mm. Such as pre-decomposition kiln speed of 3r / min, this periodic temperature rise and fall of up to 130,000 times per month. This repeated temperature rise and fall causes the thermal fatigue of the surface layer of the alkaline brick to accelerate the peeling of the brick.
7, squeeze:
Rotary kiln operation, the kiln refractory lining material by the pressure, tension, torque and shear mechanical stress, such as the combined effect. Among them, the rotation of the kiln, the oval of the kiln and the kiln fall, the bricks are subjected to the dynamic load; the weight of the refractory brick and the kiln and the thermal expansion of the brick itself make the brick bear the static load. In addition, between the lining brick and the kiln body, the relative movement between the brick lining and the brick lining, and the welds on the retaining ring and the kiln body, will cause the brick lining to withstand various mechanical stresses. When all these stresses exceed the structural strength of the brick, the brick is cracked. This phenomenon occurs in the kiln lining of the precalciner kiln.
8, wear:
Pre-decomposition kiln kiln discharge area without kiln leather protection, and clinker and large kiln leather and hard, will be on the part of the brick lining, resulting in more serious impact and abrasion damage.
In short, the impact of kiln lining consumption of more factors, but also more complex, and only continue to explore, the use of new technologies, new materials, improve the operation and management level, in order to achieve both reduce consumption, but also the kiln system balanced and stable operation.
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Principle of Selection of Refractories for Cement Kiln

refractory material
refractory material
Preheat zone and decomposition zone
The temperature of these two places is relatively low,  refractory material requiring brick lining of the thermal conductivity is small, good wear resistance, in this area from raw materials, fuel sulfuric acid base and chlorinated alkali began to evaporate, in the kiln condensation and enrichment, and infiltration brick internal. Ordinary clay brick and alkali reaction to form kaolinite and garnet, so that the brick surface crisp, brick body expansion caused by cracking peeling. And containing Al2O3 25% ~ 28% and SiO2 65% ~ 70% of the alkali-resistant or alkali-resistant insulation brick at a certain temperature and alkali reaction, the brick surface immediately formed a layer of high viscosity glaze layer, to prevent the Peeling, but this brick can not resist the use of more than 1200 ℃ temperature. So the preheating zone is generally combined with high alumina refractory bricks, anti-peeling high alumina bricks or resistant to alkali brick.
Decomposition with the general use of anti-peeling good high alumina brick, silicon brick in the performance is better than the anti-peeling good high alumina brick, life than peeling off the high alumina brick about twice as high, but the price is higher, kiln The tail feed should be made of anti-crusted silicon carbide castable.
Transition zone and firing zone
Transition zone kiln leather is unstable, require kiln lining resistance to climate change ability, good thermal shock resistance, thermal conductivity is small, wear. Foreign recommended magnesium aluminum spinel brick, but the thermal conductivity of the brick, the cylinder temperature is high, the relative heat consumption is large, is not conducive to reducing energy consumption. Domestic silicon Mo brick thermal conductivity is small, wear, its performance to a certain extent, comparable with imported materials.
Burning zone with high temperature, intense chemical reaction, requiring brick lining anti-clinker erosion, anti-SO3, CO2 capacity. Foreign generally use magnesium aluminum spinel brick, but the brick hanging kiln skin is more difficult, and dolomite brick thermal shock resistance is not good, easy to hydrate; foreign magnesium iron spinel brick in the hanging kiln skin effect is better , But the cost is too high. The use of new low-chromium perovskite composite spinel brick use is better.
Cooling belt and kiln mouth
Cooling zone and kiln temperature as high as 1400 ℃ or so, the temperature fluctuations, clinker grinding and air erosion are very serious. Requirements of brick lining of the thermal conductivity is small, wear resistance, thermal shock resistance; good thermal shock resistance of alkaline bricks, such as spinel brick or high alumina brick for cooling zone. Foreign generally recommended the use of spinel brick, but the spinel brick thermal conductivity, and wear resistance is not good. Most of the domestic use in recent years, silicon-resistant brick and anti-peeling good wear-resistant brick.
Kiln parts of the use of good resistance to thermal shock castable. Such as: wear-resistant heat-resistant high-alumina brick or steel fiber toughened castables and low-cement high-alumina refractory castable, but the kiln temperature is very high in the large kiln is the use of ordinary, or steel fiber toughening Of the corundum castable.
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2017年10月30日星期一

Refractory materials for coke ovens

Refractory materials
Refractory materials
Coke oven is the technical equipment of coking plant, is a complex and continuous production of thermal equipment, mainly by the combustion chamber, carbonization room, regenerative, roof, chute, small flue and other components. Its purpose is in the isolated air conditions, the coal heated to 950 ~ 1100 ℃, after dry distillation to obtain coke and other by-products.
At present, the life of a coke oven is generally 25 to 30 years, the use of refractories mainly silica brick, clay brick, high alumina refractory bricks. The environmental conditions of the various parts of the coke oven and the requirements for refractory materials are as follows:
Carbonization chamber and partition wall of combustion chamber
The partition wall acts to heat the heat and isolate the furnace gas and support the load. Coke coking temperature is generally 950 ~ 1050 ℃, in order to ensure coking, coke oven wall carbonization chamber side of the surface temperature should be heated to 1100 ~ 1450 ℃; carbonization chamber side of the wall to be thrusting wear; due to coal dry distillation, coking The process in the isolated air conditions, the requirements of the wall air tightness, high temperature airtight, does not occur shrinkage deformation, product shape regular, accurate size to ensure that the small cracks and not cause cracks in the cracks; carbonization chamber in the coking process There is water discharge, the combustion of indoor combustion products contain a small amount of water, and because of coal salt chemical erosion and gas decomposition and carbon deposition, may damage the walls of the organization and performance, strength decreased.
Based on the above characteristics, carbonization chamber and combustion chamber with refractory materials, the world's coke oven almost all use silicon brick. Silica brick compared with other refractories, in the range of 700 ~ 1450 ℃ within the product changes and thermal conductivity of the small changes in its high temperature strength is high, the load softening temperature and its similarity (1620 ~ 1660 ℃), wear resistance, It is not easy to hydrate. With the large-scale coke oven and strengthen the production needs, can also be used thermal conductivity, volume stability, high temperature strength are high silicon carbide refractories. But the price is expensive, in the oxidative atmosphere easily oxidized damage, so the curtain wall is rarely used. And the incorporation of metal oxide high-density high thermal conductivity of silicon brick, wall thickness can be reduced, the intensity of heat transfer, improve the productivity of coke oven, but also improve the furnace life.

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Residual Heat Utilization of Refractory Gas Burning Kiln

Refractory With the gradual implementation of the national environmental protection policy, the original domestic coal-fired kiln in the...