JPS595540B2 - Limestone firing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the firing of limestone, particularly to a method of firing limestone using a Merz kiln.

A vertical furnace method called a Merz method is used as a means for firing limestone, dolomite, etc. (hereinafter referred to as limestones).

As shown in Figures 1 and 2, this Merz-type kiln is generally divided into a pre-heating zone A, a firing zone opening, and a cooling zone C from the top, and there is a channel at the lower end of the firing zone (upper end of the cooling zone). It consists of a plurality of shafts 1 and 2 connected to each other by shafts 3. During operation, rough stones are charged from the top of each shaft, combustion is performed in shaft 1 or 2 on one side, and shaft 2 is used for unpacking. Alternatively, the combustion of step 1 is stopped to store heat, and this is repeated alternately or sequentially at regular intervals, and a fixed amount of raw ore is charged each time one combustion is completed, thereby causing the ore to descend within the shaft. However, the process of preheating, firing, and cooling is performed in the zone, and the finished product is discharged from the lower part of the shaft.

In such a Meltz-type kiln, gas/liquid fuel is blown downward on the combustion side, and this is completely combusted by the combustion air that flows from top to bottom in parallel with the rough stone, causing the rough stone to be thermally decomposed. On the other hand, on the heat storage side, a mixture of cooling air and combustion gas blown from the lower part of the furnace flows from bottom to top, heating the raw stone and cooling the exhaust gas.

Therefore, according to this method, the heat balance shown in Figure 3 (heat output in parentheses) and the exhaust gas temperature change state shown in Figure 4 can be achieved by repeating the cycle of combustion and heat storage in multiple shafts with good timing. This method has the advantage that thermal efficiency is extremely good compared to other firing methods.

In Figure 3, E is raw ore, combustion air, F is fuel, and G is cold air, and the heat input from them is E = 4%, F = 95%,
G-1%.

In addition, H is decarboxylation reaction heat, ■ is exhaust gas, J is product, K is heat radiation, loss, and these heat outputs are H-85% and 1-10%.
, J-1%.

K=4%.

However, in the conventional Merz-type firing furnace, heavy oil or gas is used exclusively as the firing fuel, and these are used at the upper end of the firing zone (lower end of the preheating zone) of the firing shaft as shown in Figures 1a and 2a.
Blowing can be carried out from lance burners 4a installed in large numbers in a packed bed of rough stones, as shown in FIG.
As a result, the proportion of combustion costs in the production cost of burnt lime has increased with the depletion of petroleum resources and rising prices, resulting in an increase in production costs.

Furthermore, in the above method, the firing fuel is supplied by scattering it over the rough stone layer, which is in a highly consolidated state, so the fuel distribution is inevitably uniform (hard to bend, and as a result, the combustion is uniform across the flat cross section of the furnace). In addition, there was a problem that the heat flow pattern was uneven even on the vertical surface, causing uneven baking of the product.

This is noticeable in the case of swing-type fuel injection, which is mechanically advantageous; in other words, as shown by the diagonal lines in Figure 2, the amount of sprayed fuel tends to decrease in the center and corner areas. Even if the number of lances to be installed is limited, as shown in Figure 2a, corners become dead zones, resulting in considerable uneven burning. It was not possible to fully meet the increasingly strict demands for quality improvement.

One possible method for improving the above-mentioned problems is to use solid fuel as the firing fuel.

One method is to mix raw ore A' and solid fuel B' into a single shaft furnace 30 from above, as shown in Figure 5, and let the mixture fall in the furnace while colliding with the air rising from below. The solid fuel B' is combusted by flowing, and the heat causes a decarboxylation reaction in the limestone, and the fired product is cooled by air from below and discharged out of the furnace.

This method is a well-known type of coke kettle, but the inside of the furnace is not clearly differentiated into preheating, calcination, and cooling zones, and the fuel tends to burn especially near the top entrance.
There is a problem in that the exhaust gas is at a high temperature and the thermal efficiency is significantly lower than that of the previous Meltz type, and the pressure drop is high and drifting tends to occur, making it difficult to prevent uneven baking of products and making it impossible to increase the furnace cross-sectional area. Productivity is also low, and therefore overall effectiveness is poor.

From the above, it is clear that it would be advantageous if solid fuel could be used in the Merz type kiln, but there are also problems when using this method.

In other words, even if solid fuel is used, if it is injected into the fuel injection section as in the past, and if the fuel is completely combusted in the combustion side shaft as before, the solid fuel will be atomized. will have to use it.

This method has disadvantages in that it involves an uneconomical pretreatment of pulverization, that a blowing device must be separately devised, and that sufficient safety measures must be taken to avoid coal dust explosion during the pretreatment.

Moreover, in the method of burning pulverized fuel, the firing zone has approximately 14
Since a high temperature area of 00° C. or higher is generated, the ash may melt and adhere to the surface of the fired product, which may deteriorate the quality.

Next, if we adopt a method in which solid fuel is charged in chunks from the conventional gas/liquid fuel injection position, a new special fuel device must be developed, which reduces costs such as modification costs. The disadvantage is also great.

The remaining method is to charge solid fuel from the top of the furnace, but this method also has problems due to the process unique to Melt type kilns.

In other words, in a Merz-type firing furnace, as mentioned earlier, multiple shafts are switched and combustion and heat storage are repeated alternately, one shaft at a time. The amount of residual oxygen in the exhaust gas is 8 to 11%, which is significantly higher than that of normal combustion exhaust gas.

For this reason, if we use the same operating method as before and simply charge solid fuel from the top of the furnace, the solid fuel will burn due to the residual oxygen in the exhaust gas during heat storage, and the heat will not contribute to the decomposition of limestone. It is directly discharged from the top of the furnace to the outside of the system.

Moreover, not only does this lead to a significant decrease in thermal efficiency, but also the backfire of high heat at the top of the furnace damages installed input switching equipment, flues, pollution control equipment, etc. in a short period of time, making stable operation impossible. .

For this reason, solid fuel cannot be used in the past.
It was not possible to reduce fuel consumption or improve product quality.

The present invention was devised through repeated research and experiments in view of the above circumstances, and its purpose is to effectively use solid fuel while taking advantage of the advantages of the Merz firing method, and to achieve superior results over firing using fluid fuel. The object of the present invention is to provide limestone calcinability that allows high-quality calcined products to be produced extremely economically.

Another object of the present invention is to provide a method that allows limestone calcination using solid fuel to be easily carried out using an existing furnace without requiring the development of new equipment or facilities. It is in.

Furthermore, another object of the present invention is to reduce the fuel cost significantly, reduce the blower power consumption rate, thereby substantially improve productivity, and further improve thermal efficiency than conventional methods. The purpose is to provide a firing method.

In order to achieve the above object, the present invention uses lump solid fuel and gas/liquid fuel in combination as firing fuel, co-fires them in a shaft to thermally decompose raw ore, and also uses both of the fuels. The combustion process is not completely combusted in the combustion side shaft as in conventional Melz furnaces, but the combustion process progresses in a unique manner in both the combustion side and heat storage side shafts. This makes it possible to use solid fuel. This successfully solves the problem of the amount of oxygen remaining in the combustion exhaust gas, which has been a bottleneck in the past.

That is, the present invention has a gas/liquid fuel blowing section in the combustion zone, which is connected to another shaft at the lower end of the firing zone by a channel, and which injects combustion air from the top of the shaft on the firing side and cooling air from the bottom of both shafts. In a Merz-type limestone kiln, the raw ore charged from the top of the furnace is preheated and fired, cooled, and sequentially discharged from the bottom of the shaft. A lump solid fuel in an amount responsible for a predetermined proportion of the total amount of heat required for firing is mixed and charged from the top of the shaft furnace on the heat storage side, and the remainder of the total amount of heat is supplied as gas or liquid fuel from the blowing section. The combustion air is controlled so that the fuel is supplied in a reducing atmosphere in the combustion side shaft and in an oxidizing atmosphere in the other shafts.

The present invention will be specifically explained below based on the accompanying drawings.

FIG. 6 shows an embodiment of the limestone firing method according to the present invention. Reference numerals 1 and 2 are shafts, which are divided from the top into a preheating zone A, a firing zone opening, and a cooling zone C. They are interconnected by channel 3 at the lower end.

A diverting device 5 for distributing the charge to each shaft is provided above the shaft 1.2, a chimney 6, a charging gate 7 and a weighing mechanism 8 are provided above it, and a common hopper is provided at the bottom of the shaft. 9 and a discharge mechanism 10 are provided.

Furthermore, gas/liquid fuel blowing sections 4, 4 are provided at the upper end of the firing zone.
is arranged, and a blower 11 is provided at the upper end of the shafts 1 and 2.
A combustion air line 12 is led from the shaft 1.2, and a cooling air line 14 from the blower 13 is led to the lower end of the shaft 1.2.

In the present invention, when calcining limestone using the Merz kiln having such a configuration, solid fuel is first used as raw stone firing fuel.

Specifically, coke, coal, pulverized charcoal, etc. are used as the solid fuel, but commercially available lumps with a sieve size in the range of 10 to 80 mr/L without pretreatment such as pulverization are sufficient.

Solid fuel is mixed with raw ore, but the issue is the amount used.

That is, it is also possible to mix solid fuel so as to cover the entire amount of heat consumption required for firing the raw ore, resulting in a so-called dedicated firing method.

However, in the Melz furnace, the solid fuel charged at the top of the furnace passes through the preheating zone and firing zone, and from the cooling zone to the product cutting, the solid fuel is kept at a constant temperature of 20 to 20 minutes until the product is cut out.
Since it takes about 24 hours, if the amount of solid fuel is 100% of the heat consumption required for firing the raw ore and is injected from the top of the furnace, problems will arise that make it difficult to adjust the furnace conditions in a short time.

Therefore, the present invention uses solid fuel and air/gas as a fuel for burning raw ore.
It is recommended to use liquid fuel in combination.Specifically, using the total heat consumption required for firing the raw stone as an index, adjust it so that it is in the range of solid fuel heat / total heat consumption -0.3 to 0.8, and then use the remaining amount. The aim is to make use of gas and liquid fuels.

The reason why the upper limit of the solid fuel ratio is set at 0.8 is that if it is higher than 0.8, it is not possible to expect the effect of fine adjustment of calorific value by combining gas and liquid fuel, large degree of freedom in terms of required time, etc. The reason why is set at 0.3 is that below this value, the benefits of using solid fuel cannot be fully demonstrated.

The combination of the solid fuel and the raw ore is fed into the shaft of the heat storage cycle, but in order to do this, for example, the sixth
As shown in the diagram, each storage tank 15.16 for raw ore A and solid fuel B
A mixing weighing machine 17 is provided for the weighing machine 17. In this case, the weighing machine 11 mixes the ore A and the solid fuel B, and sends the mixed charge C to the weighing mechanism 8 and the charging gate 7 via the existing transport machine 18. The turning device 5 may be used to charge the material from the top of the furnace in exactly the same manner as in the conventional method.

In this way, the raw ore A (1!) mixed and charged solid fuel B descends in this order to the preheating zone A and the opening of the firing zone, and at this time, a fuel injection device (lance type burner or swing type burner) is used at the upper end of the firing zone. Inject gas/liquid fuel into the mixed material in an amount corresponding to the solid fuel mixture ratio.

For example, as shown in FIG. 6, the method is to connect the gas/liquid fuel supply system, the solid fuel supply system, and the temperature measurement system by a control circuit equipped with a control device 19 including a computer, and in a steady state, a predetermined The opening degree of the throttle valve 20 is set according to the amount of solid fuel used according to the program.
The control device 19 may be used to adjust the throttle valves to adjust the amount of gas/liquid fuel injected into the furnace depending on the furnace condition.

In addition, the ignition temperature at the start of operation is raised using a conventional heating burner (
Any method is fine.

Along with the above-mentioned supply of raw ore and fuel, combustion and heat storage are alternately repeated at fixed time intervals (10 to 15 minutes) in the shaft 1.2 as before, and the shaft on the combustion side is equipped with seven wires. Combustion air is blown from the opening 21 or 22 at the top end of the furnace through the combustion air pipe 11 and the combustion air pipe 12, and cooling air is blown from the lower part of the shaft on both the combustion side and the heat storage side through the blower 13 and the combustion air pipe 14.

At this time, conventionally, the combustion air enters the firing zone after receiving heat from the rough ores previously heated in the heat storage cycle in the preheating zone, and the fuel starts combustion with the combustion air and is completely combusted in the combustion side shaft. (The raw stone is heated, e.g.
Thermal decomposition of CaCO3-CaO+CO2 is carried out at 00℃.
O2 is released, becomes CaO, enters the cooling zone, is cooled by the cooling air from the lower end of the cooling zone, and is discharged outside the furnace as a product.

The cooling air then exchanges heat with the product, is heated, flows upward, mixes with the combustion exhaust gas from the combustion side, passes through channel 3, passes through the heat storage shaft to the firing zone, and then to the preheating zone. However, in this method, the combustion exhaust gas entering the preheating zone contains 8 to 11% of residual oxygen and has a temperature of 600 to 700'C.u.

In addition, the descending speed of one charge of raw ore (with or without solid fuel mixed in) in the furnace in one cycle is 10-4 m/Se.
c, and the superficial velocity of the hot gas in the furnace is on average 4.7B
, /see.

Therefore, when solid fuel is used, the combustion of the solid fuel spreads quickly, and as mentioned earlier, there arises the problem that it burns in the furnace region during heat storage.

Therefore, the present invention does not simply perform combustion by using solid fuel in combination with gaseous or liquid fuels, but also sets and implements special operating conditions so as to limit the ignition area of these fuels to the firing zone. Instead of the operating system in which fuel is completely combusted in the combustion-side shaft, an operating system is adopted in which the fuel is reduced and combusted in the combustion-side shaft, and complete combustion is performed in the heat-storage-side shaft.

To explain this specifically, blowing combustion air into the combustion side shaft and blowing cooling air into both shafts is the same as before, but at this time, regarding the combustion air and cooling air, there is no absolute The required amount of cooling air is secured, and the amount of combustion air charged from the top of the furnace is significantly reduced so that the sum of combustion air and cooling air is the stoichiometric air amount required for combustion under these conditions. It is operated by adjusting.

By doing this, the amount of residual oxygen in the combustion exhaust gas at the inlet of the preheating zone (upper end of the firing zone) of the shaft on the heat storage side is controlled to a significantly low value of about 2% or less, and the problem of using solid fuel is solved.

Moreover, this method can be used even if the solid fuel particle size is small or the combustion rate is unexpectedly slow due to other physical properties. The advantage is that there is no left over.

In addition, according to this method, the temperature distribution in the furnace has two peaks due to the repetition of partial combustion in the upper part of the firing zone by combustion air from above and complete combustion by oxygen lynch exhaust gas from below in the next cycle. There are several places.

That is, the peak temperature in the furnace occurs at the top of the firing zone during partial combustion, and at the bottom of the firing zone during complete combustion.

As described above, since the second peak of temperature appears at the lower side of the shaft on the heat storage side, in the case of the present invention, there is no problem with the influence of high temperatures shown in the channel arch person-resistant structure.

As mentioned above, the amount of combustion air charged at the top of the furnace can be easily adjusted by adjusting the opening of the throttle valves 23 of the combustion air piping 12 or by controlling the drive of the blower 11. In order to automatically control them, for example, as shown in FIG.
The combustion air amount can be adjusted based on the signal from the furnace top exhaust gas detection end, etc., and the amount of combustion air supplied can be adjusted.

Next, specific examples of the present invention will be shown.

(I) Using the present invention, limestone was fired in a Merz type kiln.

Coke varnish was used as the solid fuel for firing, and heavy oil was used as the gas/liquid fuel.

The fuel components are shown in Table 1 below.

(n) When using the above lump solid fuel, it was decided that the amount used would be 70% of the total amount of heat required for limestone firing, and the remaining 30% would be covered by gas/liquid fuel.

The solid fuel is mixed with raw ore and charged from the top of the furnace using the same method as conventional raw ore input, while the gas and liquid fuel are blown into the existing burner, while the combustion air is greatly reduced and adjusted at the beginning of the operation. The cycle of , combustion, and heat storage was repeated.

For comparison, we also conducted a conventional method that burns gas and liquid fuels.

The operating conditions at this time are shown in Table 2 below.

(Il[) The temperature distribution inside the furnace under the above operating conditions is shown in Figure 7, and the analysis results of the heat storage side shaft furnace top exhaust gas in the method of the present invention at this time are shown in Table 3 below. That's it.

In FIG. 7, the thin line and the dotted line represent the combustion cycle and heat storage cycle of the conventional method, and the thick line and the dashed-dotted line represent the combustion cycle and heat storage cycle of the method of the present invention.

From Table 3 and FIG. 1, it can be seen that according to the present invention, combustion is carried out in a reducing atmosphere in the combustion side shaft, combustion is carried out in an oxidizing atmosphere in the heat storage side shaft, and the combustion exhaust gas is It can be seen that the firing process was conducted under conditions that kept the amount of residual oxygen in the container low.

This residual oxygen amount is the exhaust gas composition in the case of the conventional method, that is, at m=1.32, CO2: 19.7%, 02:
10.7%.

N2: 60.5%, N20: 9.0%, S02: 0.1
%, and it can be seen that the problem that was considered to be a bottleneck in the use of solid fuels has been successfully solved.

(IV) Next, in order to compare the economic efficiency of the method of the present invention and the conventional method, the results of trial calculations of fuel costs and electric power consumption are shown in Tables 4 and 5 below.

Note that in both Tables 4 and 5, the operation was assumed to be 330 days, and η (efficiency) was −85%.

From these Tables 4 and 5, it is clear that in the case of the present invention, the fuel cost can be significantly reduced, and the blower electric power consumption can be greatly reduced due to the reduction in shaft internal resistance due to the reduction in the total amount of air, resulting in extremely economical operation. I know it can be done.

Also, due to the latter feature, the resistance inside the furnace was reduced to the existing value of 2400 mm.
If Aql is set, the production volume equivalent to the air volume at that time is 5
0% or more, making it possible to produce 150 T/D.

Furthermore, the results of calculating the thermal efficiency in the present invention are shown in Table 6 below.

As is clear from a comparison between Table 6 and FIG. 3, the present invention reduces exhaust gas heat loss compared to the conventional method, and it is possible to further increase the thermal efficiency of the furnace.

This is because the amount of exhaust gas can be reduced by reducing the total amount of air as described above, and the method of the present invention is also advantageous in terms of thermal efficiency.

(V) Next, Table 7 shows the results of inspecting the quality of the products obtained by the method of the present invention and the conventional method according to the position of the furnace plane cross section.

The positions in Table 7 are based on FIG. 8, and the activity in the table is the 50 gr 4NHC1310 minute value.

It can be seen from Table 7 that according to the present invention, variations in product quality can be reduced and products with high activity can be obtained.

This is because by mixing the solid fuel with the ore, the fuel can reach corners that could not be covered with conventional fuel, making it possible to burn evenly.

(VD) We investigated the effects of ash, which is inherent in solid fuels, on operations and products, but found that melted ash did not adhere to products or cause blockages in the furnace.

This is considered to be because, in the method of the present invention, the atmosphere in the firing zone is relatively low, around 1200° C., as shown in FIG.

Furthermore, showing the results of analyzing the components by particle size of the product, the 8th
As shown in the table.

From Table 8, it can be seen that in the case of the present invention, S, which is the main component of ash,
102 + F e203 + A 1203 is 1mm
It is concentrated in the following particle sizes, which indicates that the ash was discharged as a solid.

And, the yield rate of the product taken out of the oven is usually 2 to 3% below lit.
The sifter is used for low-grade slaked lime for fertilizers, etc., so economic efficiency will not be affected.

In addition, in the present invention, if the solid fuel in the lower part of the preheating zone is partially thermally decomposed under the influence of high-temperature exhaust gas, and especially if there is water vapor for purging from the existing fuel injection device, Table 9 shows the results based on the reaction equation below. A water gasification reaction occurs.

Note that the formula (IO2) is 1000°C, and the formula (2) is 600-7
Occurs at 00°C.

C+H2O=C0+H2-28400Km...
...(1)C+2H20=C02+2H2-18000
Km... (2) CO+H2O-CO2+H2±
10400K (211!Z...(3) However,
The zone that matches this kind of pyrolysis atmosphere is
Judging from the temperature distribution in FIG. 7, this is a narrow range of about 0.5 m, and the amount of solid fuel in that zone is also small.

From this, if a solid fuel with low volatile content is used, the loss due to the thermal decomposition can be ignored and there is no problem.

In addition, the amount of solid fuel used is set at 35% of the total calorific value, the production volume is 111 T/D, and the amount of raw ore charged is 2.3 T/D.
Cycle, product cutout amount 1.31T/cycle, number of cycles 85 times, cycle time 1016SeC1 setting heat consumption rate 900Kcal/kycaO, 1 cycle AvO
”) Heavy oil amount 921/cycle, ■ cycle coke amount 60 kg/cycle, combustion air amount 310 ONm/h,
The experiment was carried out under operating conditions with a cooling air flow rate of 3000 Nrrl/h, and the same good results as above were shown.

According to the present invention as described above, since limestone is fired using a Merz-type kiln and by rationally utilizing solid fuel, the following excellent effects can be obtained.

(1) It is possible to produce limestone extremely economically by significantly reducing the fuel cost for calcination, reducing the blower power consumption by reducing the total air volume, and improving thermal efficiency by reducing the amount of exhaust gas. can.

(2) Since lump solid fuel can be used effectively, combustion is performed uniformly on the flat surface of the furnace, making it possible to produce products of good quality with little variation. By using fuel in combination, reactor conditions can be handled flexibly.

(3) Solid fuel is used in its lump form, does not require any pretreatment, and does not require any special equipment other than a weighing machine or transport machine.
Since the existing Metzl furnace can be used almost as is, it can be carried out easily and at low cost.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic explanatory diagrams showing the conventional method for calcining limestone. b shows a cross-sectional view of the fuel injection part and the distribution characteristics of the blown fuel in FIGS. 1a and 1b, respectively. Figure 3 is a heat balance diagram for the conventional method, and Figure 4 is the same.
Fig. 5 is a longitudinal sectional side view illustrating a conventional method of burning in an exhaust gas temperature, Fig. 6 is a longitudinal sectional side view illustrating an outline of the limestone calcination method according to the present invention, and Fig. 7 is a longitudinal sectional side view showing a calcination method using a general coke pot. A graph showing the temperature distribution in the furnace of the invention method and the conventional method, and FIG. 8 is an explanatory diagram showing the sampling positions for product quality comparison in the embodiment of the present invention. 1.2... Shaft, 3... Channel, 4... Gas/liquid fuel blowing part, 15.1
6...Storage vessel, 17...Mixing weighing machine,
12... Combustion air piping, 14... Cooling air piping, 20, 23... Throttle valves, A...
...Rough stone, B...Lump solid fuel.

Claims (1)

[Claims] 1 The firing zone has a gas/liquid fuel injection section, which is connected to another shaft at the lower end of the firing zone by a channel, and fuel air is blown from the top of the furnace on the firing side, and cooling air is blown from the bottom of both shafts. In a Merz-type limestone kiln, combustion and heat storage are alternately repeated in the shaft, and while the raw stone charged from the top of the furnace descends (it is preheated, fired, and cooled and discharged sequentially from the bottom of the shaft),
The raw ore is mixed with an amount of lump solid fuel that accounts for a predetermined proportion of the total amount of heat required for firing it, and charged from the top of the shaft furnace on the heat storage side. A method for firing limestone, characterized in that the combustion air is adjusted so that the fuel is combusted in a reducing atmosphere in the combustion side shaft and in an oxidizing atmosphere in the other shafts.