JPH0212324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for economically burning sludge. That is, the cake-like sludge obtained by dehydration and separation using a filter is pulverized after a pre-drying window, and then pulverized using so-called oxygen-enriched air, which has a higher oxygen concentration than air using an appropriate method. The present invention relates to a method for treating sludge that is incinerated.

Due to the recent rise in energy prices, there are economic constraints on the conventional method of forced incineration using large amounts of auxiliary fuel such as heavy oil, problems with the soil quality of waste landfill sites, and sludge dumping. Due to sanitary constraints, such as the generation of odors caused by pollutants, and constraints on securing land, it is becoming difficult to dump sludge discharged from water and sewage systems, as well as from treated human waste, for raw dumping or landfill.

Reflecting the social situation mentioned above, the recent trend is to actively recycle sludge and dispose of it. In other words, by effectively utilizing the calorific value of the organic components of sludge, self-combustion of the sludge is planned to reduce the amount of auxiliary fuel, and non-combustible components are ashed to reduce their weight, and if possible, they can be remelted or otherwise remelted. Consideration is being given to turning it into aggregate and recycling it.

The present invention takes into account the above social circumstances, skillfully utilizes the heat generated by combustion of sludge, and allows sludge to self-combust without using auxiliary fuel such as heavy oil.
This project proposes a sludge treatment method that extracts the ash in a molten state and turns it into aggregate all at once.

Specifically, sludge is dried and pulverized in advance, and the pulverized sludge is instantly and completely combusted in a high-speed flame using oxygen-enriched air. The ashes melt at
It flows down and is discharged, and can be directly turned into aggregate without going through processes such as solidification and re-melting outside the furnace.

The purpose of the sludge incineration method according to the present invention is to cause self-combustion without using auxiliary fuel as described above, and to melt and discharge the ash, so it is necessary to extremely increase the atmosphere in the furnace, which is rich in oxygen. One method is to use oxidized air, but it is also necessary to supply the sludge to be combusted in a state that generates as much combustion heat as possible.

The means to achieve this are (i) to reduce the water content in the supplied sludge powder as much as possible;

(ii) Minimize non-combustible inorganic components as much as possible.

(iii) To eliminate unburned residue and achieve complete combustion,
It is desirable to make the sludge particle size as small as possible and supply it in a form that improves contact with O ₂ , specifically in the form of fine powder.

Regarding the method of reducing water content in (i), it is desirable to reduce the dehydration rate using an over-dehydrator.

In general, the moisture content of the cake obtained from current dewatering filters differs depending on the model, but with current filtering technology, the moisture content is about 80 to 65%. ~4 parts by weight is included.

This moisture is dried before it is supplied into the combustion furnace, but from the economical point of view of the combustion system, this pre-drying heat source does not require separate auxiliary fuel such as heavy oil, and if possible, it is possible to dry it inside the furnace. We would like to effectively utilize the heat generated from sludge combustion as a heat source for drying to become self-sufficient.

Although there are slight differences depending on furnace efficiency, supply O ₂ concentration, dryer efficiency, and content of inorganic components, according to the inventors' thermal calculations, the moisture content in the dehydrator is approximately
Once it is below 75%, the moisture in the raw material cake can be easily reduced to below 10%, preferably below 5%, and dried using only the sensible heat of the exhaust gas from the furnace, without using auxiliary fuel such as heavy oil. . As a filtration technique to reduce the water content in the dehydrated raw material cake to 75% or less, a high-pressure type filter press filtration machine is desirable.

The next method to increase self-combustibility would be to reduce the amount of nonflammable inorganic components in sludge. Generally, 50 to 70% of the main components of sludge are flammable organic components, with the remainder being
50-30% is inorganic components.

In addition to the inorganic components originally contained in this sludge, if an inorganic auxiliary agent such as calcium salt or iron salt is used, the inorganic component will be approximately 20 to 30% of the total amount of cake (dry basis). The amount of combustible organic components and non-combustible inorganic components becomes approximately the same. If sludge is to be treated by self-combustion, it is desirable to avoid adding new inorganic components as much as possible, even if the inorganic components originally contained in the sludge are unavoidable. This is a high-pressure filter press dehydrator that can be expected to achieve a high dehydration rate, and does not use inorganic super-aids.
A cake using a polymer flocculant as an auxiliary agent can also be said to be a preferable cake for use in the sludge disposal method according to the present invention.

In the examples to be described later, the filter cake obtained by the above method is given as an example, but of course cakes from a high dehydration type belt press, cakes from a belt press-filter press combination model, and cakes from a vacuum filter machine are also used. A cake obtained by secondarily re-dehydrating a high-moisture cake to reduce the moisture content, a cake obtained by dehydrating using pulverized coal as a supernatant, etc. can also be treated by the method of the present invention.

In addition, if there is a slight amount of moisture in the cake and the entire process including the drying process is insufficient in terms of calorific value, auxiliary fuel such as heavy oil or kerosene may be used in the combustion furnace or as part of the heat source for the drying process. The combined use of these does not impede the implementation of the present invention.

Prior to the present invention, methods were known in which sludge is pulverized and combusted with air in a swirling flame stream.

In comparison, the present invention is fundamentally different in that it uses oxygen-enriched air, whereas the conventional method uses air.

Figures 6 and 7 show normal air (oxygen concentration 21%).
Examples of calculations of the exhaust gas volume ratio and theoretical flame temperature are shown below when using enriched air with different oxygen concentration levels and when using enriched air with different oxygen concentration levels.

However, the following formula, various numerical values, and some assumptions were used in the calculation.

T・fheo=H _e /G _p・C _pn H _e : Lower cake (assumed moisture content 5%) calorific value 3035 kcal/KgDS G _p : Combustion gas amount Nm ³ /KgDS C _pn : Combustion gas at T・fheo average constant pressure specific heat of
0.36 kcal/Nm ³ ℃ m: Supply oxygen amount/theoretical required oxygen amount ratio Sludge composition: C30%, H5%, O20%, S and P0.5% Figure 6 shows the combustion using air (oxygen concentration 21%). The amount of exhaust gas when used is assumed to be 1.0, and the ratio with the amount of exhaust gas under other conditions is shown. As is clear from this figure, if the oxygen concentration were set to 45%, the amount of exhaust gas would be approximately 1/2 of that when using normal air.

FIG. 7 shows the theoretical flame temperature at each oxygen concentration level. However, the heat loss from the furnace wall and the heat loss carried away by the fly ash after complete combustion was assumed to be zero.

As is clear from this figure, it is clear that when the oxygen concentration increases slightly, the flame temperature increases significantly.

Expressing the above in terms of phenomena in sludge combustion equipment, (1) The flame temperature is high, so it is easy to melt the ash. In particular, since radiant heat is proportional to the fourth power of temperature, it is particularly advantageous when the purpose is to melt and discharge ash.

(2) The combustion speed is fast due to the high oxygen concentration and high flame temperature.

(3) Since the amount of nitrogen unnecessary for combustion is small and the amount of exhaust gas is also small, the combustion furnace and subsequent auxiliary equipment, piping, etc. can be small.

(4) Since there is little nitrogen, the amount of NOX produced is small even though the temperature inside the furnace is high.

(5) When considering the use of sensible heat in exhaust gas, even if the amount of heat is the same, (high temperature - small amount of gas) is better than (low temperature - small amount of gas).
It is more advantageous in terms of heat recovery efficiency than other gases (large amounts of gas).

(6) Since the oxygen concentration is high, the excess rate relative to the theoretical oxygen requirement can be kept low.

(7) It becomes possible to burn low-calorie sludge.

There are many advantages such as:

Among the above, the ability to self-combust low-calorie sludge is one of the major advantages over conventional air combustion systems, and we would like to expand on this in particular.

The calorific value of sludge is approximately 5000kcal/Kg (dry basis) even in the case of raw sludge treated with human waste, which has a very high organic content.In the case of this type of sludge, if it is sufficiently dried, it can be heated using normal air. It is also relatively possible to burn it. However, in the case of digested sludge, it is about 3,200, and in the case of raw sludge discharged from a sewage treatment plant, it is about 3,500.
The calorific value is approximately 4,000 kcal/Kg, which is essentially low, and if there is even a small amount of residual moisture, it becomes difficult to maintain the furnace temperature of 1,200°C or higher, which is necessary for melting and discharging the ash. In such cases, in the case of the conventional air method, it seems that the operation is done in a compromising manner by adding a small amount of pulverized coal or mixing in high-calorie waste to compensate for the calorific value. be.

In some cases, ash may be taken out in the form of unmelted powder, and in this case there is a risk of heavy metals leaching from the dumped ash, and of course it is impossible to make it into aggregate without a remelting process. In contrast, when oxygen-enriched air is used in the present invention, the amount of inert nitrogen is relatively small compared to the air combustion method, and even in the digested sludge with the lowest calorie, the ash remains in a molten state. It is something that can be taken out. According to the inventor's experiments, in a comparative experiment using the combustion furnace shown in Figure 1, the temperature inside the furnace was approximately 400℃ between the conventional method using air and the case using enriched air containing 45% oxygen. A difference in temperature was observed.

Hereinafter, embodiments of the present invention will be explained by way of examples.

Example 1 1.0 part by weight of a polymer flocculant (Ishifloc C-90) was added to 100 parts of solids in digested sludge wastewater (containing about 4% solids (by weight)) discharged from the M city sewage treatment plant. The floc obtained by adding
A cake (moisture content: 68%) obtained by squeezing at 20 kg/cm ² using a 4-chamber) was used as a sample.

A combustion experiment apparatus is shown in FIG. 1, and an example of a combustion system according to the method of the present invention is shown in FIG.

In Figure 1, combustion furnace 1 has an inner diameter of 30 cm and a height of 50 cm.
The structure is such that powdered sludge and oxygen-enriched air are blown into the upper part of the space from two nozzles 2 and 2' provided in the direction of the cutting line shown in FIG.

After raising the atmospheric temperature inside the furnace 1 to 800° to 1000°C using an auxiliary starting kerosene burner 3 temporarily installed at the upper end of the combustion furnace chamber 1, oxygen-enriched air carrying sludge powder is delivered to the nozzles 2 and 2'. When it is squirted out, it ignites spontaneously,
A swirling flame flow F is formed along the peripheral wall, and even if the auxiliary burner 3 is then stopped, combustion can be continued smoothly due to self-heat generation due to sludge combustion.

The temperature inside the furnace gradually rises from 1200°, and after starting 30
It stabilizes at around 1400°C to 1500°C after 60 minutes to 60 minutes.

The enriched air used is a pressure swing type device (oxygen generator manufactured by S company) that uses zeolite as an adsorbent (O ₂ 80%), and this is divided into 1 part (volume) of air to 1 part (volume). Mixed and used in proportion.

O ₂ in (enriched air + air + odor-containing air) compared to the theoretical amount of oxygen required for complete combustion of organic matter in sludge.
is equivalent to 1.2 times (m).

The ash in the sludge has fluidity under the high-temperature atmosphere inside the furnace, and the centrifugal force of the swirling flow F and the nozzle 2,
Coupled with the spraying effect of 2', most of it melts to the furnace peripheral wall, flows down, falls into the water seal tank 7 from the shelf 9 in the lower part of the furnace, and solidifies as a lump.

The high-temperature exhaust gas is discharged from the undershelf chamber 5 in the lower part of the furnace through the air passage 6, and a small amount of scattered dust is collected by the cyclone 111 shown in FIG.
2. Flue 129 through the hot cuttlell 130
is discharged from.

In the waste heat boiler 112, approximately 50% of the sensible heat of the gases exhausted from the furnace is recovered in the form of steam, which can be used for power generation, space heating, and other heat sources; used this as a heat source for drying a wet cake.

The dryer 113 is a paddle type steam dryer (N
Steam is passed through the shaft, and the rotary blades attached to the shaft heat the wet sludge, crushing the plate cake (initial moisture content 68%) from the filter and drying it. urge The moisture content could be reduced to 4%.

The dried sludge cake is coarsely crushed to about 5 to 10 degrees of wear and then processed using a fine crusher 122 (manufactured by N Machinery Co., Ltd.; M-4).
mold). The particle size of the powder was 100 to 300 mesh.

This fine sludge powder is once stored in the storage tank 121, and then air-fed into the furnace with enriched air, air, or a nitrogen stream as required, and is subjected to combustion. Crusher 1
22 was replaced with a nitrogen stream 125' from a nitrogen reservoir 125 as necessary to prevent unexpected explosions and fires. Nitrogen by-produced from the oxygen generator 123 is conveniently used for this purpose.

The rough cake mass and the exhaust gas from the dryer contain a strong odor and moisture, so it is undesirable to release this directly to the outside from the viewpoint of maintaining the surrounding environment and the workplace environment, so it is necessary to generate it with a small amount of air. The contents of the cake hopper 144 and dryer 113 are lightly suctioned to prevent moisture and odor from leaking outside, and then guided into the cooler 115 to condense the moisture. Since the condensed water 124 also contains odor components, it is returned to the large amount of water in the biological treatment tank 117 for reprocessing. Uncondensed gas 124' (odorous air) is fed into the sludge combustion furnace as primary or secondary air. Odor components are completely decomposed in a high temperature atmosphere, so the source of odor from the sludge drying process can be completely suppressed.

Embodiment 2 FIG. 4 shows the structure of a main part of a combustion furnace in which opposing nozzles 2 and 2' are used to blow out oxygen-enriched air containing sludge powder in opposite directions and cause flame streams to collide with each other.

In the case of opposing flame flows, the collision of the gas flows causes a strong stirring and mixing effect, accelerating the combustion rate.
The flame flow is shortened, a large exothermic reaction proceeds in a relatively small combustion space, and since the flame center does not contact the wall, there is less heat loss and higher temperatures can be generated. In addition, the fine molten ash particles collide with each other, and the particles become large, which has the advantage of making it easier to separate the flying ash. This flame flow impingement combustion method is particularly suitable for large-scale sludge incineration plants in large cities that require large-scale capacity. A three-nozzle structure or a four-nozzle structure arranged at 90° intervals can also be adopted.

The operating method, exhaust gas treatment method, heat recovery method, etc. using these apparatuses employing the flame flow impingement combustion method are the same as those for the swirl flow type combustion apparatus shown in the main text of the specification and in Example 1.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional side view of a combustion furnace used in the sludge treatment method according to the present invention, and FIG.
3 is a flow diagram of the sludge treatment system according to the present invention, FIG. 4 is a vertical sectional side view of another embodiment of the combustion furnace, and FIG.
FIG. 3 is a sectional view taken along line BB' in the figure. Figure 6 is a graph showing the relationship between exhaust gas volume ratio and oxygen concentration.
FIG. 7 is a graph showing the relationship between theoretical flame temperature and oxygen concentration. Explanation of symbols, 1... Combustion furnace, 2, 2'... Nozzle,
3... Auxiliary burner, 5... Undershelf room, 6... Exhaust gas air path, 7... Water seal tank, 9... Shelf, 101... Sewage, 102
...Polymer flocculant, 111...Cyclone, 112...
Waste heat boiler, 113... Dryer, 114... Cake hopper, 115... Cooler, 116... Condensed water storage tank, 117... Biological treatment tank, 118... Coagulation tank, 11
9... Dehydrator, 121... Sludge powder storage tank, 122... Pulverizer, 123... Oxygen enriched air generator, 124...
Uncondensed gas, 125...Nitrogen tank, 126...Oxygen-enriched air tank, 128...Steam line, 12
9... Flue, F... swirling flow, T ₁ , T ₂ ... thermometer.

Claims (1)

[Scope of Claims] 1. After raising the atmospheric temperature in the furnace with a starting burner installed in the combustion furnace, powdered sludge is blown into the furnace with an oxygen-enriched air flow, and this sludge is self-combusted by self-combustion ignition. A method for incinerating sludge containing organic matter, characterized in that the ash is discharged from the furnace in a molten state, and is cooled and solidified. 2. A method for incinerating organic-containing sludge, characterized in that the oxygen concentration in the enriched air used in the method according to claim 1 is in the range of 25% to 80%. 3. A method for incinerating organic-containing sludge, characterized in that the water content of the sludge powder supplied in the method according to claim 1 is 10% by weight or less. 4. A method for incinerating organic matter-containing sludge according to claim 1, characterized in that the sludge powder and the oxygen-enriched air flow are blown into a combustion furnace in the tangential direction along the peripheral wall and burned in a swirling flow. . 5 By the method described in claim 1 above,
A method for incinerating organic-containing sludge, characterized in that, when sludge powder is burned, oxygen-enriched airflow containing sludge powder is ejected from nozzles arranged opposite each other, and combustion is performed in a state where flame flows collide with each other. . 6 In the method recited in claim 1 above,
A method for incinerating organic-containing sludge, which comprises jetting sludge powder and oxygen-enriched air flow toward the center of the furnace from multiple nozzles provided on the furnace wall, causing flame flows to collide near the center and causing combustion. . 7. A method for incinerating organic matter-containing sludge according to claim 1, which comprises discharging the ash in a molten state from the furnace chamber and letting it flow into a water tank provided at the bottom of the lower chamber to be cooled and solidified. 8. Incineration of organic-containing sludge in the method set forth in claim 1, characterized in that the ash is discharged from the furnace chamber in a molten state, and is slowly cooled and crystallized in a cooling chamber provided at the bottom of the lower chamber. Method. 9 In the method set forth in claim 1 above, the starting auxiliary burner is used to raise the atmospheric temperature in the furnace to 800 to 800.
A method for incinerating organic-containing sludge, which comprises raising the temperature to 1000°C and then blowing the powdered sludge into a furnace using an oxygen-enriched air stream.