JPH0774689B2 - Method for slag conversion of hydrous sludge - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for melting and treating sludge containing water such as sewage sludge and night soil sludge to form slag, and particularly sludge having a high water content is converted into high sludge. It is intended to provide a method that can be handled at a rate.

[Conventional technology]

Conventionally, sewage sludge and human waste sludge generated in a sewage treatment plant and human waste treatment plant are usually incinerated in an incinerator after dehydration. However, incineration ash after such treatment is difficult to handle,
It can only be used for landfills.

Against this background, studies have been conducted in recent years to facilitate handling and effective use of slag by melting sludge in a melting furnace to form slag, and some of the sludge has already been put to practical use.

This sludge is melted in the melting furnace by using the combustible content of sludge and auxiliary fuel as a heat source and burning air as an oxidant to melt the ash in the sludge to form slag. As a furnace capable of performing a compact structure with relatively high combustion efficiency, for example, Japanese Patent Laid-Open Nos. 61-71314 and 59-59
A swirl type sludge melting furnace as shown in No. 205508 is used.

[Problems to be Solved by the Invention]

However, the conventional smelting treatment using the swirling sludge melting furnace has the following problems.

In order to raise the temperature in the furnace to the temperature required to dissolve the slag, a two or more stage drying process that reduces the water content of the sludge from about 80% to about 7% is required, which reduces the cost of the drying process. Very high.

Since the temperature in the furnace reaches only 1450 ° C at the maximum, the temperature of the molten slag at the molten slag tap is insufficient, the viscosity of the molten slag increases, and further slag solidification occurs,
The slag tap may be blocked. Therefore, it is necessary to separately heat the slag tap.

Since the melting temperature of slag is low, the recovered molten slag can be used only for low value-added applications such as civil engineering materials, and sludge melting treatment has little merit.

The slag easily rides on the air flow in the furnace, and the residence time cannot be taken sufficiently. Therefore, the collection efficiency of slag is low, and a sufficient slag conversion rate cannot be obtained.

The slag coating on the inner wall of the furnace is likely to be non-uniform, so that the wall material of the furnace is easily consumed.

The present invention, in view of such conventional problems, can be melt-processed with a high slag-forming efficiency even in a high water content sludge,
It is an object of the present invention to provide a method capable of obtaining slag having a high added value in terms of quality without causing problems such as blockage of a slag tap hole and early consumption of furnace wall material.

[Means and Actions for Solving the Problems]

Therefore, the present invention uses an oxygen-enriched air as combustion air in a method for slag-forming water-containing sludge in a swirl-type melting furnace, and uses the oxygen-enriched air in an upright and multiple swirl flow in a vertical furnace. Is blown so as to form.

According to the present invention as described above, the following operational effects can be obtained by the process of generating a strong upward swirling flow in the vertical furnace.

First, the centrifugal action of the powerful swirling flow as described above greatly improves the slag collection rate. That is, the sludge blown into the furnace together with the combustion air is effectively transferred to the furnace wall side by the centrifugal action of the multiple swirling flow, and is mainly melted in the furnace wall (to be precise, the slag coating surface) to be slag. . Further, since the swirl flow is upward and strong, scattering of sludge and slag floating in the furnace to the outside of the furnace due to blow-by can be effectively suppressed. And by these, the slag collection efficiency is improved and the slag conversion rate is greatly improved.

In addition, the formation of the multiple swirl flow ensures a sufficient particle retention time of sludge and slag. That is, the multiple swirling flows formed in the furnace generate downward circulating flows,
The particle retention time is secured by the action of this circulation flow, and the particle retention time is 1.2 to 1.5 times longer than the conventional case where a single swirling flow is formed, and locally about 2 to 3 times longer. Become.

Further, since the circulation flow is formed in the furnace as described above, the flame is effectively held and the combustion is stabilized. Moreover, the evaporation time and the melting time can be shortened and the furnace load can be increased by the sludge mixing promoting action by the multiple swirling flow and the circulation flow.

Thus, the process of generating a strong upward swirling flow in the vertical furnace, a significant working efficiency can be obtained, but since the subject of the method of the present invention is hydrous sludge, among the above working effects In particular, it is important to secure a time for water evaporation of sludge.

However, as compared with the dry burned material, in order to melt the water-containing sludge, it is necessary to take a long particle retention time for evaporation of the water contained in the sludge in the furnace, which results in multiple swirling flow. The particle residence time alone due to formation is still insufficient. For example, as is clear from the graph in the case of using the atmosphere (oxygen concentration 21 vol%) in FIG. 1 which will be described in detail later, it is clearly shown that sludge is not easily melted only by forming multiple swirling flows. Has been done.

On the other hand, when normal air is used as blown air,
Since the amount of oxygen required for combustion is constant, the amount of air blown in cannot be changed, which means that the particle residence time will not increase unless the furnace is made large, but increasing the size of the device is a design and cost Unfavorable.

Therefore, in the present invention, in order to further secure the particle retention time and further increase the evaporation time of water, the apparatus configuration remains the same as in the conventional apparatus, and in addition to the formation of multiple swirling flows, oxygen-enriched air is used as combustion air. I decided to use it.

That is, when oxygen-enriched air is used, since the oxygen concentration is higher than that in the atmosphere, the amount of blown air can be reduced, and thus the residence time can be sufficiently secured without increasing the size of the furnace. It is easy to burn and melt even high-moisture content sludge that is rate-determining. Of course, as a result of securing sufficient particle retention time, unburned content is reduced and
The slag collection rate is also improved, which contributes to the achievement of a high slag rate.

Also, by supplying oxygen-enriched air into the furnace, a high furnace temperature can be obtained, and as a result, the fluidity of the slag is improved, so that the slag tap can be prevented from being blocked and the slag can be heated to a high melting temperature. Since it can be dissolved, a high quality slag that has been made into crushed beads and made into fibers can be obtained.

FIG. 1 shows the relationship between the sewage sludge water content and the in-reactor temperature when the sewage sludge is melted (when no auxiliary fuel is used) with the oxygen concentration in the combustion air as a parameter. In general, 13 is required to dissolve sludge in the form of slag.
A furnace temperature of about 50 ° C is required, but as shown in Fig. 1, in the case of the atmosphere (oxygen concentration 21 vol%), in order to obtain a furnace temperature of about 1350 ° C, the water content of sludge is 7%. It is necessary to dry to below.

On the other hand, if oxygen-enriched air with an oxygen concentration of 25 vol% is used, a furnace temperature of 1350 ° C can be secured even with sludge having a water content of 20%. Since sludge can be treated with a water content of 20% in this way, the power and fuel consumed by the dryer can be reduced by about 30%.

FIG. 2 shows the relationship between the melting temperature and the viscosity of sewage sludge molten slag. To secure the fluidity of the sewage sludge molten slag, its viscosity must be 250 poise or less. If the viscosity exceeds 250 poise, there is a risk of clogging of the slag tap due to insufficient viscosity of the slag. Then, as shown in FIG. 2, in order to make the viscosity of the slag 250 poise or less, it is necessary to secure the slag melting temperature at 1390 ° C. or higher.

FIG. 1 shows that by using oxygen-enriched air as the combustion air, the temperature inside the furnace, and by extension, the slag melting temperature, can be greatly increased as compared with the case of using the atmosphere. Taking the example shown in the figure as an example, the water content is 10
% When treating the sewage sludge, the temperature in the furnace is about 1330 ℃ when using the atmosphere, while it is 1470 ℃ with oxygen-enriched air with an oxygen concentration of 25 vol% and 1 with oxygen-enriched air with an oxygen concentration of 30 vol%.
A furnace temperature of about 600 ° C is obtained, and even in the case of sewage sludge with a water content of 15%, the furnace temperature is about 1300 ° C in the atmosphere, whereas it is 1410 ° C in oxygen-enriched air with an oxygen concentration of 25 vol%. With an oxygen-enriched air with an oxygen concentration of 30 vol%, a furnace temperature of about 1550 ° C can be obtained. Even in the case of sewage sludge with a water content of 20%,
When the oxygen concentration is about 28% or more, the furnace temperature of about 1450 ° C can be secured.

Therefore, the melting temperature of slag is 50 to 100
Since it will be about ℃ lower, by using oxygen-enriched air with a desired oxygen concentration as the combustion air, the viscosity of the slag can be set to 250 poise or less, its fluidity can be secured, and the slag tap hole can be blocked. It can be surely prevented.

According to the method of the present invention as described above, sludge having a high water content of about 10% to 20% is used as combustion air with oxygen-enriched air having an oxygen concentration of about 25 vol% to 30 vol%, and is optionally assisted. By using the fuel, it is possible to carry out the melting process with the furnace temperature kept at 1500 ° C. or higher.

Needless to say, molten slag, which is a product with high added value, has a greater advantage as sludge treatment. There are methods such as air crushing beading and fiberizing to make molten slag with high added value, but the melting temperature of slag required to obtain these slags is, for example, in the case of sewage sludge, as shown in FIG. 1500 ° C and 1550 ° C as noted in
The furnace temperature required to obtain such melting temperature is about 16
It is around 00 ℃. And, as described above, by using the oxygen-enriched air, such an in-furnace temperature can be easily achieved, and thereby, a slag such as air-crushed beads, fiberization, etc. can be easily obtained.

Furthermore, in the present invention, since a strong swirl flow can be formed in the vertical furnace up to the vicinity of the combustion gas discharge port by multiple swirl flows,
The slag uniformly adheres to the inner wall of the furnace, and the slag coating layer on the inner wall of the furnace is uniformly and surely formed.

The method of the present invention will be described below with reference to the example shown in the drawings.

FIGS. 3 to 7 show one embodiment of the present invention. 1 is a melting furnace body, 2 is a secondary combustion chamber, 3 is a sludge burner device, 4 is an auxiliary combustion burner device, and 5 is an oxygen enriched film. An oxygen concentrating device comprising a device or a pressure swing type separating device and the like, and 6 is a slag treatment device.

The melting furnace main unit 1 is configured in a vertical cylindrical shape, and a slag tap 11 is formed at the center of a cone-shaped bottom 10 and a combustion gas discharge port 12 having a diameter smaller than the furnace body inner diameter D is formed at the upper end.

A sludge burner device 3 and an auxiliary combustion burner device 4 are provided below the melting furnace body 1, and the auxiliary combustion burner device 4 is located below the sludge burner device 3, that is, near the slag tap 11.

Both burner devices 3 and 4 have a plurality of nozzles in the circumferential direction of the furnace body at substantially the same level.

First, the sludge burner device 3 has nozzles 30a,
Has 30b. The injection directions of these nozzles 30a and 30b are deflected from the center of the furnace so as to form a swirling flow. This sludge burner device 3 has a swirling flow X ₁ having a larger diameter closer to the furnace wall than the swirling flow formed by the auxiliary combustion burner described below, so that the injection direction of the nozzles 30a, 30b is changed to the auxiliary combustion burner device. Is closer to the furnace wall than the injection direction of each nozzle.

In this embodiment, two nozzles 30b facing each other out of the four burners are nozzles exclusively for air injection, and the remaining nozzles 30a are for sludge injection (sludge + conveyance air).

The auxiliary burner device 4 also has nozzles 40a, 40b at four locations in the circumferential direction. In order to form a swirl flow, these nozzles are also arranged so that the injection direction thereof is deflected from the center of the furnace, and a swirl flow X ₂ having a relatively small diameter is formed inside the swirl flow X ₁ .

In this embodiment, the two nozzles 40b facing each other are also dedicated to air blowing, and the remaining nozzles 4b
0a is for auxiliary fuel injection (auxiliary fuel + conveying air).

As described above, some of the plurality of nozzles of the burner units 3 and 4 may be dedicated nozzles for air blowing, or all of the nozzles may be sludge (sludge + air), auxiliary fuel (auxiliary fuel + It may be for air). Generally speaking, the former is suitable for small-diameter furnaces, and the latter for large-diameter furnaces.

Further, in this furnace, the slag outlet 11 is heated by the radiation of flame from the burner. In this embodiment, in order to bring the flame as close to the slag outlet 11 as possible, the nozzles 30a, 30b constituting the sludge burner device 3 are formed. Is inclined downward by an angle θ. For the same purpose, the injection directions of the nozzles 40a, 40b of the auxiliary burner device 4 can also be inclined downward.

Further, the throttle ratio of the combustion gas discharge port 12, that is, the ratio d / D of the inner diameter d to the furnace inner diameter D is preferably 0.3 to 0.7.

In terms of maintaining the swirl flow in the furnace, it is generally appropriate that d / D is small, but with multiple swirl flow as in this method, swirl flow can be maintained up to about 0.7. Also, considering the increase in pressure loss due to the restriction, the lower limit of d / D is practically about 0.3.

A secondary combustion chamber 15 is directly connected to the combustion gas discharge port 12 of the melting furnace body 1. The secondary combustion chamber 15 is also formed in a vertical cylindrical shape, and is provided with a plurality of air blowing ports 16 for forming a swirling flow along the wall surface at a plurality of positions on the inlet side in the circumferential direction. The air blowing port 16 can be provided in a plurality of stages in the vertical direction.

A refractory material having a high thermal conductivity is used for the furnace wall 17 of the melting furnace main body 1, and an appropriate water cooling or air cooling means is usually provided outside the refractory material.

Further, in this melting furnace, the sludge burner device 3 or the auxiliary combustion burner device 4 or both of them are provided in a plurality of stages in the vertical direction, and multiple swirl flows can be formed in the furnace, whereby sludge retention in the furnace is increased. Can be further improved.

In this case, the injection direction of the burner is set so that the swirling flow formed by the upper and lower burner devices has a larger diameter on the upper stage side.

Oxygen-enriched air 7, which is combustion air, is introduced into the melting furnace from the sludge burner device 3 and the auxiliary combustion burner device 4 together with the sludge and the auxiliary fuel. This oxygen-enriched air 7
Is a high-concentration oxygen-enriched air obtained in the oxygen concentrator 5 is diluted with the atmosphere 8 to adjust the oxygen concentration. A swirl flow is formed from each burner together with sludge and auxiliary fuel. Is introduced into the furnace. The combustion air (sludge and auxiliary fuel) thus introduced into the furnace flows in the furnace as an upward swirling flow (swirl flow swirling in the same direction) having different diameters. That is, in the furnace, multiple swirl flows are formed by the sludge burner on the outer side (furnace wall side) and the auxiliary combustion burner on the inner side.

The sludge is pushed to the furnace wall side by the centrifugal force of the swirling flow, and is mainly melted on the furnace wall surface (correctly, the slag coating layer surface) to form slag. This slag flows down the wall surface and is discharged from the slag tap 11 It This slag 9 is sent to the slag processing device 6 for forming air-crushed beads, fiberization, etc. in the molten state and undergoes the processing to be processed into a high value-added product. On the other hand, the combustion gas is discharged from the combustion gas discharge port 12 in the upper part of the furnace.

8 to 10 show the gas flow and flow velocity in the furnace. Fig. 8 shows the axial flow velocity (the chain line in the figure shows the flow direction), and Figs. 9 and 10 show Fig. 8 respectively. The swirling flow velocity of the middle BB cross section and the AA cross section are shown. Upward swirling flows X ₁ and X ₂ are generated in the furnace by the sludge burner and the auxiliary combustion burner, and such multiple swirling flows can form a strong swirling flow to the combustion gas discharge port on the downstream side of the furnace. Since the swirling flow containing sludge is formed on the outer side, that is, on the side close to the furnace wall, the sludge easily moves to the furnace wall side in combination with the action of the large centrifugal force due to the strong swirling flow as described above, and The powerful swirl flow also effectively prevents blowout of slag outside the furnace, resulting in a high slag collection rate. On the other hand, since these multiple swirling flows generate downward circulating flows Y ₁ and Y ₂ , respectively, the retention time of sludge in the furnace is sufficiently secured, which also improves the slag collection rate and realizes a high slag conversion rate. To be done. In addition, since the residence time in the furnace is secured, the evaporation time of water in the sludge is sufficiently secured, and sludge with high water content is efficiently slagged.

Also, in this melting furnace, the furnace body is a vertical type, and since multiple swirling flows can form a strong swirling flow to the vicinity of the combustion gas discharge port, the slag adheres evenly to the inner wall of the furnace and the slag coating layer on the inner wall of the furnace is formed. Are formed uniformly and reliably.

FIG. 11 shows an example of the slag coating state and furnace wall temperature distribution in the present melting furnace.The coating layer consists of a fluidized slag layer 19 facing the inside of the furnace and a solidified slag layer 20 facing the refractory side. There is. Since sludge slag has a high heat insulation property, a large temperature gradient occurs in the slag layer.
On the other hand, the refractory is made of a material having high thermal conductivity and the outer surface is cooled, so that the innermost surface 21 of the furnace wall can be maintained at the heat resistant temperature of the material (usually 1200 ° C.) or lower.

〔Example〕

Using a melting furnace as shown in FIGS. 3 to 7 and a conventional type melting furnace (single swirl flow type), the sewage sludge is melted, and the furnace temperature, slag fluidity and The slag formation rate etc. were investigated. The results are shown in Table 1 together with the processing conditions.

In Table 1, Comparative Examples No. 1 to No. 4 are examples using a conventional melting furnace, and No. 5 and subsequent figures are melting furnaces shown in FIGS. 3 to 7. Here is an example.

As is clear from this, in Comparative Examples No. 1 to No. 4 in which only a single swirl flow was formed in the furnace, only a slagging rate of about 98% was obtained at the maximum. Further, in Comparative Examples No. 1 and No. 3 to No. 6 in which the atmosphere is used as combustion air, good slag fluidity is obtained when the water content of sludge is about 7%, but the water content is high. In that case, a sufficient temperature inside the furnace cannot be obtained, and the slag fluidity is extremely lowered despite the use of the auxiliary fuel.

On the other hand, in the example of the present invention in which oxygen-enriched air was used as combustion air to form a multi-swirl flow in the furnace, a high slag conversion rate of 97% was obtained and a high water content of 20%. Even in the case of sludge, a high furnace temperature was obtained and good slag fluidity was obtained. Further, in No. 9 and No. 11, a high slag temperature is obtained that enables slag to be beads and fiberized.

[Effects of the Invention] According to the present invention described above, the following effects can be obtained.

A strong upward swirl flow is generated in the vertical furnace, and due to the centrifugal action of such a strong swirl flow, the sludge is effectively transferred to the furnace wall side to form slag, and sludge floating in the furnace, The scattering of slag to the outside of the furnace due to blow-by is effectively suppressed, and as a result, the slag collection efficiency is increased and the slag conversion rate is greatly improved.

The downward circulation flow generated by the multiple swirl flow effectively holds the flame in the furnace to stabilize the combustion, and the multiple swirl flow and the circulation flow promote the sludge mixing to promote the evaporation time. The melting time can be shortened and the furnace load can be increased.

Due to the formation of multiple swirl flow, the particle residence time of slag is 1.2 to 1.5 times longer than that of the conventional single swirl flow and locally about 2 to 3 times longer. By using the modified air, it is possible to sufficiently secure the particle retention time required to slag sludge moisture without increasing the size of the apparatus. That is, when oxygen-enriched air is used, the amount of air blown in can be reduced because the oxygen concentration is high, and the particle retention time can be further increased. However, it is easy to burn and melt. Of course, since the particle retention time can be sufficiently secured, the unburned content is reduced and the slag collection rate is improved, which contributes to the achievement of a high slag rate.

By using oxygen-enriched air as combustion air, and by forming multiple swirling flows of this combustion air, it is possible to efficiently perform melting treatment not only for water-containing sludge with a water content of 10% or more but also for high water content of around 20%. Therefore, the power and fuel required for the water-containing sludge can be significantly reduced. For example, when treating sewage sludge with a water content of 20% using oxygen-enriched air with an oxygen concentration of 25 vol%, the same sewage sludge has a water content of 7%.
% Of the power and fuel consumed in the drying process compared to the case where the atmosphere is treated as combustion air after being dried up to 30%
Can also save.

By using the oxygen-enriched air, the combustibility is improved and the temperature inside the furnace can be increased, so that good slag fluidity can be obtained and the clogging of the slag tap can be appropriately prevented.

Since the slag can be melted at a high melting temperature, it is possible to obtain slag of high added value that has been made into crushed beads and made into fibers, and the merit of melting sludge can be greatly enhanced.

[Brief description of drawings]

FIG. 1 shows the relationship between the water content of sewage sludge and the temperature in the furnace in the melting of sewage sludge with the oxygen concentration in the combustion air as a parameter. FIG. 2 shows the relationship between the melting temperature and the viscosity of sewage sludge molten slag. 3 to 7 show one embodiment of the present invention. FIG. 3 is an overall explanatory view, FIG. 4 is a vertical sectional view of a melting furnace, and FIG. 5 is a VV line in FIG. 6 is a sectional view taken along line VI-VI, and FIG. 7 is a sectional view taken along line VII-VII.
It is sectional drawing which follows the line. 8 to 9 show the flow and flow velocity of gas in the melting furnace of FIG. 4, FIG. 8 is an explanatory view showing the flow and flow velocity in the axial direction, and FIG. 9 is B- in FIG. FIG. 10 is an explanatory diagram showing the gas flow velocity in the B section, and FIG. 10 is an explanatory diagram showing the gas flow velocity in the AA section similarly.
FIG. 11 is an explanatory view showing an example of the slag coating state and furnace wall temperature distribution in the melting furnace of FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuro Inokawa, 1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Minoru Suzuki 1-2-2, Marunouchi, Chiyoda-ku, Tokyo Inside the Steel Pipe Co., Ltd. (72) Inventor Nei Hoshino 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Inside the Nippon Steel Pipe Co., Ltd. (56) Reference JP-A-2-150611 (JP, A) JP-A-60- 126512 (JP, A) JP 59-205508 (JP, A)

Claims (1)

[Claims] 1. A method for slagging water-containing sludge in a swirl-type melting furnace, wherein oxygen-enriched air is used as combustion air, and the oxygen-enriched air is directed upward in a vertical furnace to form multiple swirl flows. Method for slagging hydrous sludge characterized by blowing so as to form