JP2006088020A - Stabilizing treatment method for carbonized product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stabilizing treatment method for a carbonized product obtained from sewage sludge where a low-cost inorganic chemical is added in an ultramicro addition amount, and a carbonized product can be securely stabilized. <P>SOLUTION: At the time when dewatered sludge in concentrated sludge generated after sewerage waste water treatment is subjected to hot air drying by a dryer 206, and the dried sludge is subjected to dry distillation treatment by a carbonizing furnace 222, so as to produce a carbonized product, the dewatered sludge before the charge to the dryer 206 or the dried sludge before the charge to the carbonizing furnace 222 is mixed with an inorganic chemical for stabilizing harmful substance, thus the elution of harmful substance from the carbonized product is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for stabilizing a carbonized product obtained by dewatering concentrated sludge generated after sewer drainage treatment, and further drying and carbonizing.

Sewage sludge, after being dewatered, has been landfilled as industrial waste, but it is also being used effectively. It is also used as compost as compost, as a substitute for cement as ash, or as molten ash. It has been practiced to use the generated molten slag as a substitute for natural aggregate.
However, there are limits to their use, and further expansion of their use is required in the future.

  As part of this, in recent years, sewage sludge has been heated in an oxygen-free or low-oxygen atmosphere with an internal or external heating device, and a portion of the water and hydrocarbons are volatilized by pyrolysis or combustion, resulting in a carbon-rich. Carbonized products are produced by carbonization operations that change them into ingredients, and commercialization is starting to be used as soil conditioners and horticultural materials.

In this carbonization treatment, the sludge contains about 45% by weight of carbon in the substrate. Therefore, the carbon content in the sludge is not consumed as in the incineration and melting treatment, but the sludge is oxygen-free or low. By pyrolysis (carbonization) in an oxygen state, the carbon content remains, and is produced as a carbide (carbonized product) having a new composition.
This carbonization operation eliminates the odor that becomes a problem in composting, greatly reduces the amount of CO ₂ generated compared to incineration, and consumes a large amount of energy as in the case of incineration or melting treatment of sludge, increasing the processing cost. Such a problem can be solved.

FIG. 3 shows an example of an apparatus for that purpose.
In the figure, reference numeral 200 denotes a receiving hopper (dehydrated sludge storage tank), and the dehydrated sludge dehydrated to a moisture content of about 75 to 85% is first received by the receiving hopper 200.
The dewatered sludge received here is sent to the dryer 206 through the intermediate storage tank 202 by the quantitative supply device 204 and the transfer device 205, where a predetermined moisture amount, specifically, a moisture amount of about 25 to 45%. Until dry.

The dryer 206 has a stirring shaft 210 inside a rotary drum 208 as shown in FIG.
Here, the stirring shaft 210 is provided at a position eccentric from the center of the rotary drum 208.
A plurality of stirring blades 212 extend radially from the stirring shaft 210.

On the other hand, a plurality of plate-like lifters 214 are provided on the inner peripheral surface of the rotating drum 208 at a predetermined interval in the circumferential direction so as to rotate integrally with the rotating drum 208.
As a result, the sludge (dehydrated sludge) inside the rotary drum 208 is lifted upward from the bottom by the lifter 214 as the rotary drum 208 rotates, and falls by its own weight near the top.
The sludge that has fallen is finely pulverized by the high-speed rotation of the stirring blades 212 positioned below the sludge and falls to the bottom side of the rotary drum 208.

The sludge inside the rotary drum 208 is subjected to such a stirring action and is subjected to a drying process by being exposed to the hot air for drying introduced into the rotary drum 208, so that moisture gradually decreases.
In this dryer 206, sludge is gradually sent in the axial direction inside the rotary drum 208 by the gradient of the rotary drum 208, and further by pulverization by the stirring blade 212 and the scattering action at that time.

  The dried sludge after being dried in the dryer 206 in this way is then conveyed to the carbonization furnace 222 through the dried sludge storage tank 218 by the conveying devices 216 and 220, where the sludge is carbonized by the dry distillation treatment. Is called.

  As shown in FIG. 5, the carbonization furnace 222 is provided with a cylindrical retort 226 as a dry distillation vessel inside the furnace body 224, and the dried sludge that has been dried by the preceding dryer 206 is illustrated. Is inserted into the retort 226 by a screw feeder that omits.

The supplied dried sludge is first heated by the atmospheric heating inside the external heat chamber 230 by the auxiliary combustion burner (external heat chamber burner) 228 disposed inside the furnace body 224.
Then, the combustible gas contained in the dried sludge escapes into the atmosphere of the external heat chamber 230 through the ejection pipe 232 provided in the retort 226, and the combustible gas is ignited. Thereafter, the combustible gas is burned. The sludge inside the retort 226 is heated.
At this stage, combustion of the auxiliary burner 228 is stopped.

As shown in FIG. 5, an exhaust gas treatment chamber 234 separated from the external heat chamber 230 is provided inside the furnace body 224, and the exhaust gas from the external heat chamber 230 is guided here.
The exhaust gas treatment chamber 234 is provided with an exhaust gas treatment chamber burner 236, and the unburned gas in the exhaust gas introduced into the exhaust gas treatment chamber 234 is secondarily burned in the exhaust gas treatment chamber burner 236. .
The sludge in the retort 226 gradually moves from the left end in the figure to the right in the figure as the retort 226 rotates (the retort 226 has a slight gradient), and finally the carbonization residue (carbonized product) is removed. The retort 226 is discharged from the right end outlet 238 in the drawing, that is, from the carbonization furnace 222.

In FIG. 3, reference numeral 240 denotes a hot air generating furnace, and the hot air generated here is supplied to the dryer 206.
The hot air supplied to the dryer 206 passes through this, passes through the dust collector 242, and further circulates in the circulation fan 244 to the hot air generator 240 through the carbonization furnace exhaust gas heat exchanger 246 and the hot air furnace exhaust gas heat exchanger 248. Be made.

In this circulation system, leak air enters the hot air circulating in the dryer 206.
On the other hand, a constant amount of combustion air is supplied to the hot air generating furnace 240, and therefore, a part of the hot air is extracted here through the branch passage 250 extending from the hot air generating furnace 240 and passes through the hot air furnace exhaust gas heat exchanger 248. It is discharged from the chimney 254 to the outside by the furnace exhaust gas fan 252.
On the other hand, an exhaust path 256 extends from the carbonization furnace 222, and exhaust gas from the carbonization furnace 222 is discharged from the chimney 254 to the outside through the carbonization furnace exhaust gas heat exchanger 246 by the carbonization furnace exhaust gas fan 258 through the exhaust path 256. .
This type of carbonization apparatus is disclosed in, for example, Patent Document 1 and Patent Document 2 below.

By the way, when using the carbonized product thus manufactured, it is naturally necessary to ensure safety so that the pollutant does not flow out into the environment.
In terms of safety assurance, elution of As, Se, and F is particularly problematic from sewage sludge.

The safety assessment methods and standards for carbonized products are not yet clearly defined.
First, regarding the dissolution, when carbonized products are used as a soil conditioner, it is considered safe to adopt the soil environment standard by the test method according to Notification No. 46 of the Environment Agency in 1991 for the dissolution value.
When sewage sludge is used as fertilizer without thermal decomposition, the elution value by the Fertilizer Control Law satisfies the landfill standard value according to the test method by the Environmental Agency Notification No.13. The value seems to be loose.

  In addition, regarding the content of harmful substances, there are doubts about whether or not carbonized products are used for horticulture, but the fertilizer control law is stricter than the soil pollution control law, so It is safe to adopt fertilizer control law standards.

In the above-mentioned soil environment standard, 6 items of Cd, Pb, hexavalent Cr, As, total Hg, and Se are required to satisfy the standard value.
Because this standard value is a strict standard, carbonization products that are currently produced due to fluctuations in the quality and operating conditions of sewage sludge, such as molten slag, that is not melted at high temperatures and contained in the glass structure In fact, it cannot be said that all of these satisfy the elution standard values for As, Se, and F.

  The present invention relates to a stabilization technique that suppresses elution of As or the like below a reference value by adding an inorganic chemical to sewage sludge and then heat-treats it to less than a reference value, thereby increasing the safety of carbonized products.

  In addition, since the content of the harmful substance in the carbonized product is significantly lower than the standard value of the Fertilizer Control Law, there is no problem even if the harmful substance is fixed to the carbonized product by chemical treatment.

Although there is no published publicly known technique for stabilizing carbonized products, the following methods are possible.
One of them is a method of stabilizing by adding a chelating agent having a piperazine group, a dithiocarbamic acid group or a piperazine bisdithiocarbamic acid group used for stabilization of incineration fly ash or molten fly ash, that is, an organic agent to a carbonized product. It is.
However, since chelating agents are organic agents, there are concerns about stability, such as the possibility of decomposition in the environment in which they are used in an environment exposed to sunlight or acid rain, and there is a risk of generating harmful gases due to decomposition. There is also a problem that the use of carbonized products is hindered due to odor.
In addition, As and Se do not exist in the cation but exist in the form of an anion, so there is a problem that it cannot be stabilized by a general chelating agent.

Another possible method is to add an inorganic agent to the carbonized product.
In this method, the inorganic chemical is added when the carbonized product discharged from the vicinity of the carbonization furnace or discharged from the carbonization furnace is cooled or cooled.
However, in the method of adding in the vicinity of the outlet of the carbonization furnace, the contact time between the carbonized product and the chemical is too short and the reaction efficiency is poor, so the amount of chemical added increases or unreacted chemical flows out to the waste water from the carbonized product cooling water tank. Therefore, it is necessary to newly install a wastewater treatment device, which increases the cost of medicine and equipment, and securing installation space becomes a problem.
Further, in the addition in the water tank, it is necessary to add the chemical to the entire water in the washing tank and the pipe, not to the carbonized product itself, and the amount of the chemical used is increased and the cost is increased.

In the above two methods, since the chemical is added after the carbonization step, part of As and Se is volatilized in the carbonization step, and there is a problem that harmful substances are accompanied in the exhaust gas.
Release of harmful substances into the atmosphere will cause environmental pollution, so it will be necessary to collect exhaust gas through a dust collector after cooling, and it will also be necessary to stabilize the collected soot, making the structure of the carbonizer complex. become.

JP-A-11-37644 Japanese Patent Laid-Open No. 11-33599

The problem to be solved by the present invention is to prevent destabilization as in the case of an organic drug even in the use environment even after the chemical treatment, and to prevent subsequent use of the carbonized product.
Next, by taking sufficient reaction time between sludge and chemicals and adding heat to increase the degree of stabilization of the reactants, the amount of chemicals added, i.e., processing costs, is reduced, and carbonization costs and carbonized product prices increase. Is to suppress and promote its use.

In addition, chemicals are added before carbonization to fix harmful substances in sludge to prevent volatilization and save additional equipment and chemical costs.
Furthermore, the problem with the use of inorganic chemicals is that corrosion does not occur in the dryer and carbonization furnace, and that no large additional equipment is required.

  The method according to claim 1 of the present application, which has been devised to solve such a problem, dehydrates the concentrated sludge generated after sewage drainage treatment to form dehydrated sludge having a moisture content of 75 to 85%, and the dehydrated sludge is dried. The dried sludge is dried into hot sludge in a carbonization furnace and heated in an oxygen-free or low-oxygen condition in a carbonization furnace to produce a carbonized product by dry distillation treatment. On the other hand, it is characterized in that elution of the harmful substance from the carbonized product is suppressed by mixing an inorganic agent that stabilizes the harmful substance.

  According to the method of claim 2, the concentrated sludge generated after sewer drainage treatment is dehydrated to dehydrated sludge. The dehydrated sludge is dried with hot air in a dryer to obtain a dried sludge having a moisture content of 25 to 45%. When producing a carbonized product by heating in oxygen-free or low-oxygen conditions in a carbonization furnace, by mixing an inorganic chemical that stabilizes harmful substances with respect to the dried sludge before being charged into the carbonization furnace, It is characterized by suppressing elution of the harmful substance from the carbonized product.

  The method of claim 3 is characterized in that, in claim 2, the inorganic agent is added after pulverizing the dried sludge to 10 mm or less.

  The method of claim 4 is the method according to any one of claims 1 to 3, wherein the addition rate of the simple or combined total of the inorganic chemicals is 0 in terms of the pure content of the inorganic chemicals with respect to 100 parts of the solid content mass of the sludge. .2 copies or more.

  The method according to claim 5 is the method according to any one of claims 1 to 4, wherein at least one of ferrous chloride, ferric chloride, and ferrous sulfate and / or a calcium agent is used as the inorganic agent in a solid state or It is added in liquid form.

As described above, in the present invention, the carbonized product is stabilized as follows.
That is, by using an inorganic chemical having a stable performance as a chemical and further applying a heating operation, the fear of deterioration of the stabilizing effect in the use environment is eliminated.

The carbonized product is manufactured through a process as shown in FIG.
The addition place of the inorganic chemicals of the present invention is the place where the sludge enters the dryer or carbonization furnace after becoming dehydrated sludge, and the place where the internal pressure of the apparatus is about atmospheric pressure. It is.
The sludge temperature to be reacted with the chemical is in the range from normal temperature to a maximum of about 1050 ° C. in the carbonization furnace.

The dewatered sludge in FIG. 1 usually has about 80% of moisture, and the internal pressure is high because the conveyance is performed by a screw conveyor, a Mono pump or the like.
Therefore, it is preferable that the chemical addition is performed when the atmospheric pressure at the stage of moving from the transfer device to the storage tank is reached.
At this stage, the dehydrated sludge is cake-like and has a slightly large lump, so mixing with the drug is not good at the time of addition. However, since the conveyance time is long, sufficient mixing and reaction time can be taken.

  The dryer in FIG. 1 usually has a stirring shaft and stirring blades inside, and uses a system in which dehydrated sludge is crushed and dried with hot air to a moisture of about 40%, and the dried sludge usually has a granularity of several tens of mm or less. Therefore, mixing with chemicals is better than dewatered sludge.

Further, if a pulverizer such as a paddle type not shown in FIG. 1 is provided before being put into the carbonization furnace and the dried sludge is made finer, the reaction efficiency of the chemical increases, the carbonization reaction is promoted, and the processing capacity increases.
A screw conveyor, a flight conveyor, a paddle conveyor, or the like is used as a dry sludge conveying device. Here, since the sludge filling level is low, the internal pressure is almost atmospheric pressure, so that the chemical can be added at any point.

The carbonization furnace in FIG. 1 is a furnace that dehydrates and pyrolyzes dry sludge in an oxygen-free or low-oxygen atmosphere, and burns combustible gas generated by pyrolysis as a heat source.
When the combustion place is in the retort, it is called an internal heat type, and when it is outside the retort, it is called an external heat type.
By this carbonization operation, the dried sludge is converted into a carbonized product having pores of about 50% of carbon and the remaining components of which are inorganic, and can be used effectively.

  The direct water cooling and discharging apparatus in FIG. 1 is generally composed of a water tank filled with water and a conveyor for discharging carbonized products, and also serves as a carbonization furnace and an atmospheric seal. Increases and costs increase.

In the example of the present invention, the cost of the drug is reduced by using an inorganic drug such as iron sulfate, iron chloride, or lime that is distributed in the market and inexpensive.
Iron sulfate is easy to use as a solid ferrous sulfate or a liquid obtained by dissolving ferrous sulfate in water, but it can also be used in powder form.
As for iron chloride, aqueous solutions of ferrous chloride and ferric chloride are on the market, and it is easy to add them, but they can also be used in powder form.
The calcium agent is suitably added in the form of powder or slurry of slaked lime, quick lime, calcium carbonate, calcium bicarbonate.

In the present invention, a phenomenon is used in which As and Se complex ions existing in the form of negative ions are co-precipitated when iron sulfate or iron chloride is precipitated as iron hydroxide.
Moreover, F utilizes Ca and precipitates as CaF ₂ having a low solubility.
It also takes advantage of the fact that these products turn into more stable materials upon heating.

  Since the present invention is thus a method with excellent stabilization performance, the addition rate can be lowered even with a simple inorganic acid, and since a calcium agent is used together for safety reasons, existing equipment is not corroded.

  Further, in the present invention, the chemical addition is performed at room temperature, and the existing line of the conventional carbonization device can be used. New devices include a chemical reservoir, a chemical quantitative supply device, a pipe, a dry sludge crushing device and a conveying device, etc. There is an advantage that a simple device can be used.

  Furthermore, by utilizing the fact that sludge and chemicals are vigorously stirred in a dryer or carbonization furnace, the reaction can proceed efficiently and the chemical consumption can be reduced. In addition, no new stirring device is required, saving equipment costs and space. it can.

  It should be noted that the addition of the drug is preferably performed under almost atmospheric pressure (-50 Pa to +50 Pa), and in this case, the monitoring of the addition status of the drug and the maintenance can be easily performed during the operation.

Effects and effects of the invention

The safety evaluation of carbonized products currently uses the test method of Notification No. 46 of the Environment Agency of 1991.
In this method, the concentration of carbonized product: distilled water is shaken in a container at 1:10, the supernatant is filtered through a 0.45 μm membrane, and a solution extracted by solvent extraction or strong acid is used to measure the As concentration and the like.
Therefore, the elution value of As, etc. of carbonized products shows how much colloidal substances including compound ions, such as As dissolved by shaking, and fine As particles separated from carbonized products by shaking, pass through the 0.45 μm membrane. It can be said that it is decided by.
As described above, the elution values of As, Se, and F become a problem in most cases of carbonized products derived from sewers.
Therefore, the stability of carbonized products can be ensured by stabilizing As and the like present in both ionic form and fine particle (colloid) state.

In the case of adding iron sulfate or iron chloride used as an example of the present invention, if the pH is neutral to alkaline, iron hydroxide is generated and precipitated. At that time, complex ions of As and Se are also co-precipitated. Se stabilization effect.
In addition, F cannot be stabilized by adding iron sulfate or iron chloride, but when calcium agent such as lime is added, it precipitates as CaF ₂ and can stabilize F.

Further, in another example of the present invention, the method of sharing calcium agent and iron chloride or the like further increases the effect because both ionic and colloidal forms of As and Se are coagulated and precipitated.
In this case, when iron sulfate or iron chloride is precipitated as iron hydroxide, As and Se are co-precipitated, the calcium agent assists it and performs pH adjustment function, and iron sulfate or iron chloride is added excessively It is desirable to add to the sludge upstream of the iron sulfate and iron chloride.
The ferrous chloride may be either ferrous chloride or ferric chloride, but ferrous chloride having a slightly higher pH than ferric chloride is easier to use.
The same applies to iron sulfate.

This invention is useful as a means for stabilizing a carbonized product that is inexpensive and has an excellent stabilizing effect because the carbonized product can be reliably stabilized by using an inorganic agent with a low unit price at a very small addition rate.
In addition, the use of chemicals worried about the effect on product quality, but since it was added in a small amount, it did not pose a problem for effective use.
Therefore, it promotes the use of carbonized products, and helps to preserve the environment by extending the life of landfills and reducing CO ₂ emissions.

Next, embodiments of the present invention will be described in detail below.
Tables 1 and 2 show invention examples and comparative examples for the types and addition rates of the drugs, the conditions at the time of addition, and the dissolution test results.

  The dewatered sludge used was from the basin sewerage treatment facility, the chemical type, the addition rate and the addition location were changed in the actual equipment for carbonized product production, and the others were operated under the same operation, and evaluated using the obtained carbonized product. .

The stabilization evaluation method for carbonized products was based on the aforementioned Environmental Agency Notification No. 46.
In order to clarify the effect, the shaking was carried out by side shaking where the carbonized product was vigorously stirred and was most easily eluted.
The analysis items were mainly pH, As, Se, and F.
In the analysis of the test solution, As and Se were based on hydride generation atomic absorption method, and F was based on direct distillation-absorptiometry.

In Tables 1 and 2, inorganic chemicals 1 and 2 indicate any category when two types of chemicals are used.
The addition rate refers to the outer mass% of the pure chemical with respect to the amount of sludge on the dry basis.
Sludge moisture is inherently contained in the sludge, does not include added water, and moisture = (water content / (water content + dry base sludge content)) × 100%.
The presence or absence of pulverization refers to whether or not the dried sludge is crushed before adding the chemical before carbonization.
The test solution pH refers to the pH at 25 ° C. of the filtered solution after shaking after the shaking operation by the Environmental Agency Notification No. 46, and after standing.

  As is apparent from the results of Tables 1 and 2, it can be seen that the carbonized product can be satisfactorily stabilized by adding the inorganic chemical according to the present invention.

In FIG. 2, an example of a suitable addition timing or addition location of the inorganic drug is indicated by an arrow.
Here, the addition of the inorganic agent may be performed not only in any one of FIG. 2 but also in a plurality of periods or locations.

It is a figure which shows the manufacturing process of carbonization products. It is a figure which shows the example of the suitable addition time of an inorganic chemical | medical agent, and an addition location. It is a figure which shows a carbonization processing apparatus. It is a figure which shows the dryer of FIG. 3 in detail. It is a figure which shows the carbonization furnace of FIG. 3 in detail.

Explanation of symbols

206 Dryer 222 Carbonization furnace

Claims (5)

Concentrated sludge generated after sewage wastewater treatment is dehydrated to a dehydrated sludge with a moisture content of 75 to 85%, the dehydrated sludge is dried with hot air in a drier, and the dried sludge is oxygenated or low in a carbonization furnace. When producing carbonized products by heating in oxygen conditions and dry distillation,
Stabilization of carbonized product characterized by suppressing elution of the harmful substance from the carbonized product by mixing an inorganic agent that stabilizes the harmful substance with respect to the dewatered sludge before being put into the dryer. Processing method. Concentrated sludge generated after sewage drainage treatment is dehydrated to dehydrated sludge. The dehydrated sludge is dried with hot air in a dryer to obtain a dried sludge with a moisture content of 25 to 45%. When producing carbonized products by heating in oxygen conditions and dry distillation,
Stabilization of carbonized product characterized in that elution of the harmful substance from the carbonized product is suppressed by mixing an inorganic chemical that stabilizes the harmful substance with respect to the dried sludge before charging into the carbonization furnace. Processing method.   The method for stabilizing a carbonized product according to claim 2, wherein the inorganic chemical is added after the dried sludge is crushed to 10 mm or less.   In any one of Claims 1-3, the addition rate of the said simple or combination total of the said inorganic chemical | medical agent is 0.2 parts or more in conversion of the pure part of this inorganic chemical | medical agent with respect to 100 mass of solid content mass of the said sludge. A method for stabilizing carbonized products characterized by the above.   In any one of Claims 1-4, 1 or more types and / or a calcium agent in any one of ferrous chloride, ferric chloride, and ferrous sulfate are added as said inorganic chemical | medical agent in solid form or liquid form. A method for stabilizing carbonized products.

Images