JPS5930480B2 - Odeino Mushiyuunetsushiyorihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat treatment method for efficiently dewatering sludge generated from sewage treatment plants and industrial wastewater treatment plants without generating foul-smelling gases.

In order to remove the odor components dissolved in the sludge, we use a method of lowering the pressure to vaporize it and the principle of stripping.
There is a method of distilling it out along with the vapor that evaporates.

However, the degree of vacuum that can be achieved industrially at a relatively low cost is about 20 to 40 mwHg in terms of supply pressure, but at room temperature, odor components cannot be completely removed at this level of pressure.
Vacuum and stripping must be used together.

On the other hand, if the temperature is 100°C or higher, odorous substances can be released along with steam as long as the pressure is released appropriately, but there is a drawback that the sludge decomposes due to the high temperature and can become odor again after releasing odorous substances. .

Oxidation using oxygen (air) is a method for chemically deodorizing sludge at high temperatures.

According to the research results of the present inventors, COD was reduced by 1.5% when sludge was air oxidized at 150°C for 60 minutes (5), and when sludge was treated at 200°C for 60 minutes without introducing air. A comparison of the contents of odor components in CB) is shown in Table 1, and it can be seen that the odor reduction effect due to oxidation is remarkable.

Table 1 B H2S ppm 9.6 6190CH3SRp
pm 5.5 1290(CH3)2S ppm
18.2 710CH3SSCH3ppm 21
．． 4 127A B N(CH3)3 ppm 234
315ONH3ppm 1.
6 61.1ph-CH=CH2ppm
0.11 48, ICHCHOppm
O, 0130, 01 et seq. Conventionally, as sludge heat treatment, a partial oxidation method using moist air and a so-called portias method, in which treatment is performed only by heating without blowing air, are known.

In both cases, sludge is sent to the reactor, and the temperature is 130~20・-0°.
After boiling for 30 minutes or more while maintaining the temperature at C, the heat is recovered by a heat exchanger and discharged.

The former mixes air containing the necessary oxygen into the sludge to oxidize the odorous substances in the sludge, reducing the odor of the treated sludge, and also promoting the separation of bound water in the sludge, significantly improving the dewaterability of the sludge. On the other hand, free air (
Since free oxygen (free oxygen) is always present, the heat exchanger is severely corroded, shortening the service life of the equipment and increasing the cost of working equipment.Furthermore, because a large amount of high-pressure air is supplied for sludge oxidation, This has the disadvantage that processing costs are high due to additional costs.

On the other hand, in the so-called Portias method, which heats sludge without incorporating air, the inside of the heat treatment equipment (heat exchanger, reactor) is in a reducing state, so there is almost no corrosion and the life of the equipment is long, and equipment costs and operating costs are reduced. However, since the sludge is treated at high temperatures, proteins are thermally decomposed in a reducing atmosphere and malodorous components are produced, which tends to cause pollution problems.

The present inventor has conducted various studies in order to combine the advantages of both of the above methods, use a low-cost Portias device, and reliably deal with the odor problem. While maintaining the temperature at 130-180°C for 15 minutes or more, compressed air (the amount of air containing 1-3% of the amount of oxygen required to oxidize COD is sufficient)
Even if 3% or more is used, the effect of odor removal will hardly increase) is brought into contact with the sludge and reacted, and the reaction venting phase (the remainder of the blown air after oxidation, odor components, and water vapor, water vapor is 10 to 10% of the remaining air) is reacted with the sludge. The sludge liquid level in the reactor is kept almost constant by purging the sludge (20 times the volume), and only the liquid phase is taken out from the reactor and cooled to 35-70℃ by exchanging heat with the untreated sludge. During this time, a part of the sludge components reacts with the weakly acidic water constituting the sludge and is hydrolyzed to generate a secondary malodorous gas, giving the sludge a slight odor.

(The malodorous components in sludge are mainly protein decomposition products, but it is difficult to completely oxidize and decompose the core of protein polymer aggregates even if the sludge remains in the reactor for a long time.

) In order to decompose the malodorous components from the sludge that has become slightly malodorous again, it is supplied to a vacuum evaporator and heated to a vacuum degree of 74.
The sludge is flushed to a temperature of 0 to 720 mrnHg (25-35°C), and the generated steam strips off the malodorous components to make the sludge odorless. This is the best condition that does not cause odor pollution.

An ejector is used to maintain a vacuum in the vacuum evaporator, and the exhaust gas (steam + foul-smelling gas) from the ejector is sent to a boiler or other combustion chamber where it is burned.

A heat recovery deodorization technology using vacuum evaporation uses the principle of multi-stage flash evaporation to recover heat around the reactor (
(Japanese Patent Application Laid-Open No. 49-38476), this method uses steam generated by flashing the high-temperature, high-pressure sludge in multiple stages after the reaction to preheat the untreated sludge entering the reactor. .

Since flushing always generates saturated steam, condensed water (mostly pure water) is always produced by the amount of heat given to the untreated sludge.

It is self-evident that this condensed water redissolves malodorous components, and in this method, essentially only the deodorizing effect of the vacuum works, and the stripping effect is eliminated.

Now, the sludge from which malodorous components have been removed by depressurization and stripping in the vacuum evaporator is discharged into the heat-treated sludge thickening tank. This allows it to operate with less corrosion.

Hereinafter, the present invention will be described in detail with reference to embodiment figures. Sludge drawn from the lower part of a raw sludge storage tank 1 is delivered by a high-pressure sludge pump 2 and fed into an inner pipe of a heat exchanger 3.

At that time, the compressed air from the air compressor (compressor: 4) is used to oxidize 1 to 3 of the amount of oxygen required to oxidize all the COD in the sludge.
% of air is blown into the sludge, and the sludge mixed with air is heated in the outer tube 6 of the A2 heat exchanger 5 and sent to the outside of the Al heat exchanger 3. It is preheated through a pipe 7, mixed with steam 10 sent from a steam boiler 9 in a special mixer 8, and then fed into a reactor 11.

Then, the sludge is vigorously stirred by the compressed air contained in the reaction chamber 11a, and an oxidation reaction takes place, and the odor gas that is easily released is oxidized (the oxidation time varies depending on the properties of the sludge, but it takes approximately 15 to 60 minutes) ) and accumulates in the storage chamber 11b together with water vapor (approximately 10 times the volume of air) and the remaining air, and these gaseous substances pass through the exhaust gas pipe 12 and the valve 13,
It is guided to the furnace of steam boiler 9 and heated to 0 at a temperature of 650℃ or higher.
．． After staying for 3 seconds, the sludge becomes an odorless gas and is released into the atmosphere.The sludge is separated from the oxidizing gas, water vapor, and unreacted gas, and is removed through a funnel-shaped inlet with an inlet slightly below the liquid level. The sludge is taken out of the reactor 11 through the pipe 11c, so that when taking out the sludge that has completed the reaction in the reactor 11, free oxidizing gas and excess air are prevented from entering the sludge. (If free surplus air is included and the sludge temperature is high, it will generate foul-smelling gas and corrode the heat exchanger). The sludge discharged from the reactor 11 passes through the inner pipe of the 52 heat exchanger 5, and then through the inner pipe 14 of the sludge cooler (the outer pipe is cooled by passing water through it) and is cooled to a sludge temperature of 35°C to 70°C. After that, the slurry is sent to the gas separation chamber/gas storage chamber 16a of the vacuum evaporator 16 via the automatic sludge valve 16.

Therefore, the degree of vacuum inside the vacuum evaporator 16 is set to 740 to 7201.
It consists of a gas separation chamber/gas reservoir chamber 16a that maintains ftrIL/Hg and separates moisture in the sludge and residual malodorous gas from the sludge, and a reservoir chamber 16b for the separated sludge. The upper part is equipped with a steam ejector 18 via an exhaust gas pipe 17, and the steam ejector always maintains the gas separation chamber and gas reservoir chamber at a vacuum level of 740 to 720 mrrt.
/Hg.

The sludge sent to the gas separation chamber and gas storage chamber generates water vapor with an amount of heat equivalent to the liquid temperature depending on the vacuum degree of the vacuum evaporator, and at the same time, as the water vapor partial pressure increases, odor gas is released together with the water vapor. The foul-smelling gas is separated from the entrained sludge, accumulates in the sludge storage chamber 16b from which the foul-smelling gas was separated, passes through the sludge discharge valve 19, enters the sludge heat treatment thickening tank 20, and enters the sludge heat treatment thickening tank 20.
The oxidized concentrated sludge that has settled at the bottom of the sludge is pumped to the filter 22 by the sludge pump 21, filtered, and carried out as a hard cake containing about 50% water and incinerated.

The mixture of foul-smelling gas, residual air and steam extracted by the steam ejector is stored in the external furnace or in the furnace of the steam boiler 9 at 65
After residence at a temperature of 0°C or higher for 0.3 seconds or more, it becomes an odorless gas and is released into the atmosphere.

On the other hand, the high-temperature treated sludge discharged from the reactor 11 is boiled.2 When passing through the inner tube of the heat exchanger 5, the outer tube 6 is passed through a heat exchange liquid to heat and raise the temperature. The untreated sludge supplied to the reactor 11 is preheated by passing it through the outer tube 7 of the boiler 1 heat exchanger 3 through the communication pipe 26.

In addition, during the process of the present invention, the liquid level of the reactor 11 is controlled by opening and closing the automatic mud draining valve 15 using the liquid level gauge 23.
The liquid level in the reactor should always be maintained at an optimal level.

Further, the liquid level of the vacuum evaporator 16 is controlled by opening and closing the automatic sludge draining valve 19 using the liquid level gauge 24 to maintain the liquid level at an optimal constant value at all times.

In addition to high-pressure and high-temperature sludge, high-pressure air is constantly fed into the reactor 11, and a fixed amount of oxidizing gas, water vapor, and excess air are released so that the pressure inside the reactor can be kept constant. is equipped with a safety valve 25 in case of sudden pressure rise.

[Brief explanation of the drawing]

The drawings are process diagrams showing embodiments of the present invention. 1... Raw sludge storage tank, 2... High pressure sludge pump, 3... Al heat exchanger, 4... Air compressor, 5... ... Rei 2 heat exchanger, 6...
・Outer tube of A2 heat exchanger, 7... Outer tube of Al heat exchanger, 8... Special mixer, 9... Steam boiler, 10... ...Steam, 11...Reactor, 11a...Reaction chamber, 11b...
Reservoir chamber, 11c... Take-out pipe, 12...
Exhaust gas pipe, 13...Valve, 14...Inner pipe of cooler, 15...Upper moving sludge valve, 16...
・Vacuum evaporator, 16a... Gas separator/gas reservoir chamber, 16b... Sludge reservoir chamber, 17... Exhaust gas pipe, 18... Steam ejector -119...
... Sludge valve, 20 ... Sludge heat treatment thickening tank, 2
1...Sludge pump, 22...Filter,
23...Liquid level gauge, 24...Curved liquid level gauge, 25...
... Safety valve, 26 ... A1, A2 heat exchanger connection pipe, 2T ... Heat exchange liquid circulation pump.

Claims (1)

[Claims] 1. Compressed air containing 1 to 3% of the amount of oxygen required to oxidize all the COD in the sludge is mixed into the raw sludge, and after being preheated through a heat exchanger, it is sent to the sludge reaction chamber together with steam. By maintaining the temperature at 130 to 180°C for 15 to 60 minutes, the generated reacted gas is stored in the upper part of the sludge reaction chamber and removed through the exhaust gas pipe to be released after deodorization treatment. The reacted sludge is taken out without containing free gas through a funnel-shaped reacted sludge removal pipe with an inlet located slightly below the liquid level, cooled to 35 to 70°C via a heat exchanger, and then transferred to a vacuum evaporation can. The odor gas remaining in the sludge is further extracted by cooling it to 25-35°C,
A method for odorless heat treatment of sludge, which comprises maintaining the extracted gas at a temperature of 650° C. or higher for 0.3 seconds or more and then releasing it into the atmosphere.