JPS598435B2 - Treatment method for reduced chamber wastewater at a garbage incinerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method by effectively utilizing contaminated wastewater (also referred to as smoke washing wastewater) discharged from a reduced chamber for combustion exhaust gas in a waste incinerator.

Normally, at urban incineration plants, high-temperature exhaust gas of 800 to 900 degrees Celsius, which is generated when burning garbage, is passed through a temperature-reducing chamber to reduce its temperature to 30 degrees Celsius in order to prevent damage to dust collectors and chimneys.
It is necessary to reduce the temperature to around 0°C.

Generally, to reduce the temperature, a method is used that utilizes the latent heat of vaporization of water, and this is done by spraying water.

In recent large-scale garbage incinerators, 20kgf/c
Many companies use a non-drainage method in which water is injected at a high pressure of rA or higher, almost eliminating water discharged from the reduced temperature chamber, and a small amount of discharged water is absorbed into the incinerated ash.
In existing facilities and small and medium-sized facilities, approximately 80 to 90% of the spray water used for temperature reduction generally becomes water vapor.
The gas is exhausted together with the cooled gas, but the remaining 10 to 20% that has not been completely evaporated is discharged as surplus water with a water temperature of 50 to 70°C.

The amount of water discharged varies considerably depending on the type of waste, the amount of waste processed, the incineration temperature, the structure of the incinerator, etc., but in actual measurements it is 30 to 100 tons per wax of waste, and although the amount of water is not that large, the following As mentioned above, this is wastewater with a high concentration of contamination.

In other words, the exhaust gas from garbage incineration contains a large amount of dust derived from incineration ash, and the dust contains Cd, Pb, and C.
It is known to contain various heavy metals such as
The exhaust gas contains hydrogen chloride gas generated by the combustion of plastics such as vinyl chloride.

The wastewater discharged from the reduced temperature chamber absorbs hydrogen chloride gas and becomes strongly acidic, and is characterized by a high concentration of dissolved substances that dissolve heavy metals and other substances in the dust. The water quality is around pH 2, COD around 100 ppm, suspended solids (SS:) 200-1300 ppl, chlorine ions 1000-6000 ppl [[l1 evaporation residue 200 ppm].
0 to 10,000 solution (including 60 to 70% ignition residual) and chromaticity of 50 to 600, and among various heavy metals, Zn,
Pb and Cu have relatively high concentrations.

Furthermore, the wastewater has a tar odor and is brown in color, and this colored substance is thought to be mainly tar-based organic matter.The color can be removed by activated carbon treatment, but it is difficult to remove by neutralization or chemical coagulation treatment of the wastewater. It is.

Conventionally, wastewater from reduced temperature chambers is often diluted and discharged after adjusting the pH due to the small amount of water, but as mentioned above, this wastewater contains heavy metals, although at a low concentration, making it difficult to discharge. In some places where the amount of water in rivers is low, it accumulates in the soil without being diluted and dissipated, causing a social problem.

In addition, through the neutralization treatment, heavy metals also become hydroxide flocs and are removed to some extent, but not completely.

As described above, many waste incinerators are forced to use non-drainage systems due to the fact that the amount of water discharged from reduced temperature chambers is relatively small, it contains heavy metals, and it is difficult to remove the organic matter it contains. The current situation is that

A non-drainage system uses a method that circulates wastewater and does not release it to the outside, but when recycling high-concentration wastewater, certain measures are taken to ensure that there is no risk of scale formation or corrosion in the pipe material. It is a condition.

An object of the present invention is to provide a drainage-free system that eliminates problems caused by scale formation and corrosion of auxiliary equipment and piping, makes effective use of water resources, and renders the system harmless by not discharging wastewater.

The present invention stores wastewater generated in a reduced temperature chamber for reducing the temperature of high-temperature combustion exhaust gas discharged from a garbage incinerator,
An alkaline agent and an organic polymer flocculant are added to the wastewater of the reduced temperature chamber to adjust the pH of the wastewater to a range of 6.0 to 8.0, and the resulting precipitated flocs are separated by sedimentation, and this separated water is transferred to the reduced temperature chamber. This is a method for treating wastewater from a reduced-temperature chamber at a waste incinerator, which is characterized by circulating and re-evaporating the wastewater.

To explain one embodiment of the present invention with reference to the drawings, the temperature of the waste combustion exhaust gas f is reduced while passing through the attenuation chamber 7 where spray water d is injected from the incinerator 8, but it flows out from the attenuation chamber 7. The wastewater a reaches a drainage pit 1, from which it is quantitatively transferred by a pump 2 to a neutralization mixing tank 3, where an alkaline agent b such as caustic soda is added to adjust the pH to 6.0 to 8.
Adjust to 0 range.

The reason why the pH of the wastewater a is adjusted in the range of 6.0 to 8.0 is as follows.

In other words, the waste water a flowing out from the reduced temperature chamber 7 has a large amount of dissolved hard components such as calcium and magnesium, so it is in a state where it is extremely easy to form scales.
{s. On the strong alkaline side of o or more, scale can easily form inside pumps and piping, etc.
The cyclic reuse operation described below becomes impossible, and on the other hand,
This is because the waste water a also contains large amounts of chlorine ions and sulfate ions, so that if it is acidic with a pH of 6.0 or higher, it will result in accelerated corrosion of steel materials.

Next, when the pH of the wastewater a is adjusted to a range of 6.0 to 80, agglomerated flocs are often generated, and in this case,
After injecting polymer b' to improve floc settling properties, the flocs are separated by sedimentation or filtered in a settling tank 4, and the separated water is stored in a spray water tank 5.

Also, the spray water tank 5 is always replenished with new water C in the same amount as the water lost by evaporation, diluted to about 2 to 5 times, and pressurized by the pump 6 and circulated to the reduced temperature chamber 7 to provide spray water. As d, it is injected from an injection nozzle, atomized, and exposed to a high-temperature combustion gas flow to actively re-evaporate and be reused.

The precipitated sludge e that has been sedimented and separated in the sedimentation tank 4 is disposed of separately, but as a disposal method at a garbage incinerator, it is dehydrated using a separator such as a centrifuge or an offshore filter, and then incinerated with the garbage. or how to dispose of the waste along with the incinerated ash, and after dehydration and drying on a solar drying bed,
Possible methods include incinerating it with the garbage, disposing of it together with the incinerated ash of the garbage, and absorbing it into the incinerated ash.

On the other hand, the gas coming out of the reduced temperature chamber 7 passes through a dust collector 9, a gas absorption tower 10, a suction fan 11, etc. as necessary, and is released into the atmosphere from a chimney.

As described above, according to the present invention, a non-drainage method is adopted which can achieve the effective use of water resources by circulating and reusing wastewater from a reduced-temperature chamber and detoxification by not releasing wastewater, and eliminates various heavy metals that cause scale. It easily forms agglomerated flocs of small oxides, and the flocs have good sedimentation properties and can be separated and removed, making it easy to accurately prevent problems such as scale formation and corrosion on attached equipment and piping. It is possible to
Since wastewater is evaporated using the exhaust combustion gas, it can be treated extremely efficiently and economically.In addition to effectively using wastewater, the organic polymer flocculant can also be recycled and the amount of chemical injection can be reduced. It is possible to save money and can be treated economically, is simple and sanitary in terms of operation and management, and can be treated without causing any pollution problems.

Next, examples of the present invention will be shown.

At a waste incineration plant with a municipal waste processing capacity of 60 t/d and a reduced chamber wastewater volume of 8 i/d, the pH of the reduced chamber wastewater is adjusted to 8.0 or higher, and the supernatant water from which the produced flocs are precipitated and separated is circulated as spray water in the reduced chamber. When using the spray water pump, after about one month of operation, scale adhered inside the spray water pump and operation became impossible, but the pH of the wastewater was adjusted to 6.0 to 80. Similarly, as a result of circulating the supernatant water as spray water in the attenuated chamber, no problems related to scale formation or corrosion occurred in the pump or piping, and smooth operation was possible.

[Brief explanation of the drawing]

The drawing is a system explanatory diagram showing one embodiment of the present invention. 1... Drain pit, 2... Pump, 3
... Neutralization mixing tank, 4 ... Sedimentation tank, 5.
...Spray tank, 6...Pump, 7.
...Reduced chamber, a...Drainage, b...
・Alkali agent, b'...Polymer, C...
... Water, d ... Spray water, e ... Precipitated sludge, f ... Combustion exhaust gas.

Claims (1)

[Claims] 1. Storage of wastewater from the reduced temperature chamber generated in a reduced temperature chamber for reducing the temperature of high-temperature combustion exhaust gas discharged from a garbage incinerator, and addition of an alkali agent and an organic polymer flocculant to the reduced temperature chamber wastewater. and adjusting the pH of the wastewater to a range of 6.0 to 8.0, sedimenting and separating the generated precipitated flocs, and circulating and injecting this separated water into the attenuated chamber for re-evaporation. A method for treating wastewater from a reduced-temperature chamber. 2. A method for treating reduced chamber wastewater in a waste incinerator as claimed in claim 1, wherein make-up water is mixed with the separated water and recycled. 3. The method for treating wastewater from a reduced temperature chamber in an incineration plant according to claim 1 or 2, wherein the separated water is pressurized and recycled to the reduced temperature chamber.