JPS6138618A - Treatment of waste gas - Google Patents

Abstract

PURPOSE:To increase the energy efficiency in a method for removing NOx by bringing the carbonized product of sludge discharged from the microbiological treatment system of waste water into contact with a waste gas. CONSTITUTION:The excess sludge discharged from a microbiological treatment system of waste water is carbonized in a carbonizer. The carbonizing process is continuously performed by charging successively the sludge into the inside of a dry distillation tower from a hopper and taking out successively the carbonized products from the bottom part of the dry distillation tower. The obtained car- bonized products are provided as a packed layer 22 incorporated in a treatment tower 21 and after the waste gas is introduced through a gas introducing passage 23 and NOx contained in the waste gas is removed by being passed through the packed layer, it is discharged from a discharge passage 24.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is directed to the treatment of nitrogen oxides (NOx) such as boiler waste gas.
) The present invention relates to a treatment method for removing nitrogen oxides from waste gas containing nitrogen oxides.

[Conventional technology]

As a method for treating this kind of waste gas, a method of bringing the waste gas into contact with coke has conventionally been provided. When the waste gas is brought into contact with coke, NOx in the waste gas is removed by the coke, that is, C, by being reduced to NHa in the presence of water and to N2 in the presence of water.

[Problem that the invention seeks to solve]

However, in the above conventional method, the treatment temperature is 70
There is a problem in that it requires a high temperature of 0 to 1000°C, which is not desirable from an energy efficiency standpoint.

[Means for solving problems]

The present invention uses carbonized sludge discharged from a wastewater microbiological treatment system in place of conventional coke as a means to solve the above problems.

[Effect]

The operation of the present invention based on the above configuration is as follows.

When the waste gas containing NOx is brought into contact with the carbonized sludge, the carbonized sludge undergoes Nor reduction. A low temperature of about 400 to 600°C is sufficient for the treatment temperature during kernel cutting. The low-temperature reduction mechanism of NOz by the carbide is not clear, but it may be based on the reducibility derived from heavy metals contained in the sludge, or because the carbide has a special carbon structure. It is thought that this is due to the reducing properties derived from organic matter, or due to the overlapping effects of these.

〔Effect of the invention〕

Since the present invention has the above configuration and function, it is possible to remove NOx from waste gas containing NOx by low-temperature treatment.
The energy efficiency has been significantly improved (compared to conventional methods), and if the sludge discharged from conventional wastewater microbiology high treatment systems is landfilled, it will cause secondary pollution due to the heavy metals it contains.
Incinerating sludge requires a huge amount of energy, which has been difficult to dispose of, and this has the effect of eliminating problems in the disposal of such sludge.

〔Example〕

The sludge of the present invention is extracted, for example, from a wastewater microbiological treatment system as shown in FIG. In the figure, wastewater is introduced into the treatment tank (2) through the water supply path (I return), mixed with activated sludge in the treatment tank (2), and aerated by the aeration means (3) to contain it under aerobic conditions. The organic matter is decomposed and removed by microorganisms in the activated sludge (1), and then transferred from the communication path (4) to the sedimentation tank (5).
), the sludge contained in the wastewater is separated in the sedimentation tank (5), and some of the sludge is returned to the treatment tank (2) from the return path (6) as return sludge, and other parts are is discharged from the discharge path (7) as surplus sludge.

In the present invention, surplus sludge discharged from the above-mentioned wastewater microbiological treatment system is generally used as the sludge. To carbonize the sludge, for example, a carbonization device as shown in FIG. 2 is used. In the figure, sludge 00) is charged into the dry distillation tower a from the hopper (11), and is placed in an inert gas atmosphere such as N2 gas or argon gas introduced from the air passage aJ that connects to the bottom of the dry distillation tower Q. Normally 500-700℃
It is heated and carbonized. It is desirable that the sludge be preliminarily dried prior to such carbonization. The pre-drying may be done, for example, by drying in the sun for about 2 to 3 days and then drying for 10 days.
Drying is carried out for several hours at a temperature of around 0°C.

Further, in the carbonization step, it is desirable to mix pebbles with a particle size of about a few cods into the sludge so that the carbonized material of the sludge does not stick. The mixing ratio is usually 3 to 7:3, preferably 5:5, by weight of sludge:pebbles. The carbonization process is carried out continuously by sequentially charging the sludge αω from the hopper αυ into the dry distillation tower α, and successively taking out the carbonized material from the bottom of the dry distillation tower a through the take-out path α. That is, dry distillation of sludge is carried out in a fluidized phase. What is taken out from the bottom of the dry distillation tower a is a mixture of pebbles and sludge char. To separate the carbide from the mixture, separation based on the difference in specific gravity, filtration, sieving, etc. are applied. The carbide may be used for waste gas treatment in a mixed state with pebbles without being separated.

The carbide thus obtained is usually provided as particles with a diameter of several fins, and the general composition is as follows.

Industrial analysis〉 Elemental analysis〉 <Ash composition> To treat waste gas with the carbide of the present invention, for example, as shown in Fig. 3, a packed bed (2
The waste gas is passed through the gas introduction path (c) at the bottom of the treatment tower (2υ) and NOx contained in the waste gas is removed through a packed bed (2) at a temperature of usually 400 to 600°C. ).If boiler waste gas is used as the waste gas, the flow rate is 150 ONm/hr, the volume of the packed bed 4 is 1 go, and the packed particles are 2 to 3 times, the amount of NOx in the waste gas before and after treatment is: The procedure is as follows.The treatment temperature is 500°C.

In this comparative example, coke was used instead of the carbide of the present invention. According to the above results, coke hardly removes NOx at a low temperature of about 500°C. To obtain the same N0yc removal rate as uninvented carbide, the treatment temperature is 90°C.
It is necessary to raise the temperature to around 0°C.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a microbiological treatment device for wastewater, FIG. 2 is a schematic diagram of a carbonization device, and FIG. 3 is a schematic diagram of a waste gas treatment device. In the figure (21)...Treatment tower, (2)...Carbide packed bed Patent applicant Asahi Coke Industry Co., Ltd. Me 1
Senpu 2 Senai 3 Figure--2

Claims (1)

[Claims] A method for treating waste gas, which comprises bringing nitrogen oxide-containing waste gas into contact with carbonized sludge discharged from a wastewater microbiological treatment system.