JP4514529B2 - Sewage sludge melting treatment method - Google Patents

Description

  The present invention relates to a sewage sludge melting treatment method, and relates to a technique that suppresses volatilization into phosphorus exhaust gas by melting treatment of sewage sludge, immobilizes it in slag, and facilitates exhaust gas treatment.

  Conventionally, as shown in FIG. 4, in the sewage sludge melting treatment method, after adding the flocculant (polyiron) 2 to the concentrated sludge 1 and dehydrating with the dehydrator 3, the dehydrated sludge 4 is once stored in the storage pit 5. It dries with the dryer 6, and once the dry sludge 7 is stored in the hopper 8, it melt | dissolves with the melting furnace 9, and it is made the slag 10.

  The exhaust gas 11 discharged from the melting furnace 9 is processed through a waste heat boiler 12, a dry electrostatic precipitator 13, a flue gas processing tower 14, and a wet electrostatic precipitator 15, and the return water 16 is processed by a water treatment facility (not shown).

  Further, as described in Patent Document 1, as a technique for fixing phosphorus in slag in a melting furnace that operates in a reducing atmosphere in the main combustion chamber, when sludge containing phosphorus is treated at a high temperature in the melting furnace, it is converted into slag. As a pre-process, there is a dehydrator in which polyferric sulfate is mixed with raw sludge and dehydrated, the dehydrated cake is dried in a sludge dryer, and the dried cake is put into a melting furnace.

  Moreover, as described in Patent Document 2, as a technique for fixing in slag without volatilizing phosphorus at the time of melting, an acidic oxide generating element P that generates an acidic oxide at a melting processing temperature with respect to an object to be melted. The acid-base ratio defined by the comparison between the concentrations of Si and Si and the concentrations of the basic oxide generating elements Ca, Fe, and Al that generate a basic oxide corresponding to the acidic oxide is equal to or higher than a preset lower limit value. As described above, there is a method in which a component adjusting agent containing one or more basic oxide generating elements is added, and the component-adjusted melting object is introduced into a melting furnace to be melted into slag.

In addition, as described in Patent Document 3, as a technique for fixing phosphorus in a slag without volatilizing phosphorus when melted in a strong reducing atmosphere, the pretreated molten object is melted into slag in a strong reducing atmosphere in a melting furnace. When fixing phosphorus contained in the object to be melted in slag or in a metal that is reduced and generated at the time of melting, in the pretreatment, the concentration of the metal element that fixes phosphorus volatilized at the melting temperature as a phosphide In some cases, the ratio of the acidic oxide-forming element that generates the acidic oxide is defined as an adjustment index ratio R, and the component of the melt target is adjusted so that the adjustment index ratio R is equal to or greater than a predetermined lower limit value.
JP 2000-140895 A JP-A-11-342378 JP 2001-29998 A

  However, in Patent Document 1, there is a corrosion problem because of a strong acidic chemical, and a large amount of alkaline chemical is required for neutralizing exhaust gas. Moreover, in patent document 2, Ca and Al were not able to exhibit a phosphorus fixed effect | action in strong reducing atmosphere. There is a correlation between the reducing atmosphere and Fe / P. However, since the P content fluctuates and the Si analysis takes time, feedforward control is difficult. In Patent Document 3, the dust collection rate is as low as 85% at a high cost, and in order to make the dust collection rate about 100%, the SS load in the return water to the water treatment system becomes large.

  The present invention solves the above-mentioned problems, eliminates stickiness of dust, can perform the shortest feedback control, can suppress phosphorus volatilization, has a dust collection rate of about 100%, and has a small load of returned water SS. It aims at providing the sewage sludge melting processing method.

  In order to solve the above-mentioned problem, the sewage sludge melting treatment method of the present invention described in claim 1 is characterized in that the sewage sludge is dehydrated and dried, and then melted in a melting furnace before the Fe in the sewage sludge. As a rule of thumb, the appropriate value of the Fe / P ratio is determined in the correlation between the / P ratio and the VTS, and the sewage sludge to be melted is analyzed to obtain the Fe / P ratio and VTS. Iron powder is added to the sewage sludge before it is put into the melting furnace so that it is larger than the appropriate value of the rule of thumb.

In the sewage sludge melting treatment method of the present invention described in claim 2, when the sewage sludge is dehydrated and dried and then melted in a melting furnace, the flue of the exhaust gas discharge system is monitored, and the flue is When the phosphoric acid compound volatilized from the melting furnace adheres , iron powder is added with a quantitative feeder to a hopper for introducing sewage sludge into the melting furnace .

  As described above, according to the present invention, phosphorus fixation suppresses phosphorus volatilization and eliminates stickiness of dust, and by using iron powder, the reactivity is fast and the efficiency of feedback control is increased, and feedforward control is also possible. A dust collection rate of about 100% can be achieved, and the return water SS load can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the concentrated sludge 31 is added with a coagulant (polyiron) 32 in a necessary amount for dehydration, dehydrated by a dehydrator 33, temporarily dewatered sludge 34 in a storage pit 35, and then dried by a dryer 36. The dried sludge 37 is once stored in the hopper 38 and then melted in the melting furnace 39 to form the slag 40.

  The exhaust gas 41 discharged from the melting furnace 39 is processed through a waste heat boiler 42, a gas cooling tower 43, a bag filter 44, and a flue gas processing tower 45, and the return water 46 is processed in a water treatment facility (not shown).

  A quantitative feeder 51 for supplying iron powder is connected to the hopper 38, and the quantitative feeder 51 adds the iron powder to the dry sludge 37 while adjusting the addition amount by changing the set value. The addition of the iron powder may be performed in the middle of a conveyor or the like that is transferred from the hopper 38 to the melting furnace 39, or may be directly added to the melting furnace 39.

  FIG. 2 (a) is a graph showing the relationship between the phosphorus immobilization rate% and the Fe / P ratio when iron powder is added together with the addition of the flocculant (polyiron) according to the present invention. b) is a graph showing the relationship between the phosphorus immobilization rate% and the Fe / P ratio when only a conventional flocculant (polyiron) is added. According to FIG. 2, even when the Fe / P ratio is the same, the phosphorous immobilization rate% is low in the case of only the conventional flocculant (polyiron), and with the addition of the flocculant (polyiron) as in the present invention. When iron powder is added, the phosphorus immobilization rate% increases. This is largely due to the addition of 100% iron in the form of iron powder.

  The iron powder is added by the following method. The correlation between the dry cake VTS (ignition loss)% as shown in FIG. 3 and the dry cake Fe / P ratio is obtained by preliminary operation or laboratory experiment. In FIG. 3, A shows a stable state in which a phosphoric acid compound does not adhere to a flue portion at a specific site when only polyiron is added as a conventional flocculant, and B shows polyiron as a conventional flocculant. In the case where only the addition of polyiron as a conventional flocculant is shown, C shows an unstable state in which a phosphoric acid compound is somewhat adhered to the flue part at a specific part. Shows a blockage state in which a large amount of phosphate compound adheres, and D shows that phosphoric acid is added to the flue portion at a specific site when polyiron is added as a flocculant and a predetermined amount of iron powder is added to dry sludge in the present invention. It shows a stable state where no compound adheres.

In this correlation, a dust adhesion boundary line L that separates a region where a stable state where a phosphate compound does not adhere to a flue portion at a specific site and a region where another phosphate compound adheres is separated.
Next, during operation, the dried sludge 37 is analyzed to obtain the ratio of Fe / P and VTS, and the dried sludge before being introduced into the melting furnace 39 so that the analytical value Fe / P is larger than the appropriate value of the rule of thumb. Add iron powder to 37. This operation enables feedforward control.

  As shown in Table 1, the operation by addition of the iron powder can increase the phosphorus immobilization rate, which is 65% in the conventional method, to 90% and eliminate stickiness of dust. Further, the iron powder is added to the hopper 38 by operating the quantitative feeder 51 by using the presence or absence of the phosphate compound in a specific part monitored by the waste heat boiler 42 as an index, and the dried sludge 37 containing this iron powder is melted in the melting furnace 39. The time required for feedback is shortened by supplying to the time, and the time required for feedback, which is 48 hours in the past, can be shortened to about 6 hours, and phosphorous emission can be suppressed by the shortest feedback control. Moreover, by adding in the state of iron powder, the reactivity can be accelerated and the efficiency of feedback control can be increased. Further, the SS of the return water 46 that is 0.35 in the past can be reduced to 0.024.

  Normally, iron powder is added by the above-described method, but it can also be performed by the following method as a backup. The waste heat boiler 42 is provided with an ITV (industrial television camera) for monitoring a specific portion, for example, a flue portion connecting the radiating portion and the water pipe portion of the waste heat boiler 42.

  A specific part is constantly monitored by this ITV, and when it is recognized that a phosphoric acid compound volatilized from the melting furnace 39 adheres to the specific part, a quantitative feeder is provided to the dried sludge 37 before being put into the melting furnace 39 by the controller 52. A predetermined amount of iron powder is added through 51 to immobilize phosphorus to suppress volatilization and prevent the phosphate compound from adhering.

The flow sheet figure of the sewage sludge melting processing method which shows embodiment of this invention (a) is a graph showing the relationship between the phosphorus immobilization rate% and the Fe ratio of the present invention, and (b) is a graph showing the relationship between the conventional phosphorus immobilization rate% and the Fe ratio. Graph showing the relationship between dry cake VTS% and dry cake Fe / P ratio Flow sheet of conventional sewage sludge melting treatment method

Explanation of symbols

31 Concentrated sludge 32 Coagulant (poly iron)
33 Dehydrator 34 Dehydrated sludge 35 Storage pit 36 Dryer 37 Dry sludge 38 Hopper 39 Melting furnace 40 Slag 41 Exhaust gas 42 Waste heat boiler 43 Gas cooling tower 44 Bag filter 45 Smoke treatment tower 46 Return water 51 Quantitative feeder 52 Controller

Claims (2)

When the sewage sludge is dehydrated and dried and then melted in a melting furnace, an appropriate value of the Fe / P ratio is determined in advance as a rule of thumb in the correlation between the Fe / P ratio in the sewage sludge and the VTS, Analyzing the sewage sludge from the melt to obtain the Fe / P ratio and VTS, and adding iron powder to the sewage sludge before being introduced into the melting furnace so that the analytical value Fe / P is larger than the appropriate value of the rule of thumb. A sewage sludge melting method characterized by adding. When the sewage sludge is dehydrated and dried, and then melted in the melting furnace, the flue of the exhaust gas discharge system is monitored, and when the phosphoric acid compound volatilized from the melting furnace adheres to the flue , the sewage sludge A method for melting sewage sludge , wherein iron powder is added with a quantitative feeder to a hopper that is charged into a melting furnace .

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