JPS5844929B2 - How to burn digestive gas - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for burning digester gas.

An important problem is how to burn the digestive scum generated from human waste in an odorless manner and without generating nitrogen oxides (NOx), but there is currently no satisfactory method.

In view of this point, the present invention provides a combustion method that is odorless and reduces NOx.

The present invention will be explained in detail below with reference to illustrative drawings.

Now, the composition of digestive gas is ammonia (NH3), methane gas (CH4), carbon dioxide gas (CO2), and water vapor (H20).
The content ratios are as shown in Table 1, for example.

In the present invention, focusing on the above components, 90% of the total digestive gas
% is directly burned at high temperature in the X combustion furnace, but the remaining 1
0% is CH4, CO2 that does not dissolve in water and N that dissolves in water.
For example, using a scrubber for H3 and H20, the former (
CH4, CO2) is combusted at a high temperature at the same time as 90% of the former, and an ammonia aqueous solution of the latter (NH3°H20) is sprayed into the CH4, CO2 combustion gas, so that the temperature of the waste residue after thermal decomposition is such that NOx is generated. Difficult 700-9000C
The ammonia aqueous solution reduces the NOx generated by the high-temperature combustion.

As mentioned above, NH3, which is a source of odor, is burned at a high temperature to make it as odorless as possible.

In the above description, the amount of digestion gas to be burned at high temperature in the X combustion furnace is exemplified as 90% of the total amount, but the amount is not limited to this and is preferably 90% or less.

This is shown in FIG.

In other words, in Figure 1, the digestive gas 1 is 90% 1' as it is 5
CH4 that does not dissolve in the water that has passed through scrubber 2, which will be described later.
It is guided to the combustion furnace 5 together with CO2 gas and burned at high temperature.

On the other hand, the remaining 10% 1'' of the digestion gas 1 is led to the scrubber 2.

In this process, NH3 in this digestion gas is dissolved together with H20 to form aqueous ammonia 3.

CH4 and CO2 in the digestion gas are not dissolved in water and are led to the combustion furnace 5 as gas 4 along with 90% of the total digestion gas 1', where they are completely combusted at a high temperature, for example, 1000°C.

6 is an auxiliary combustion burner that contains 90% of the digestion gas and scrubber 2.
The gases 4 of CH4 and CO2 (CO2 is not combusted) that have passed through the combustion chamber 4 self-combust after being assisted by the auxiliary burner 6.

The ammonia water 3 in which NH3 is dissolved in the water is led to the combustion furnace 5, where 90% of the digestion gas and the gases 4 of CH4 and CO2 that have passed through the scrubber 2 are burned.
Spray pyrolysis is carried out so that the temperature of the exhaust gas after pyrolysis is within the range of 700 to 900°C (preferably 800°C), a temperature at which nitrogen oxides are difficult to generate.

As mentioned above, one of the two halves of the digestion gas is burned as is, but naturally NH3 is oxidized and NOx is generated.

By bringing the other part of the digestion gas into contact with water, NH3 is dissolved in the water, and by spraying this water into the combustion gas, the previously generated NOx is reduced according to the following principle (this principle is well known). ).

NO+NH40H-+N2+H20 More than 90% of the NOx generated during combustion is NO.

The above reduces the generation of NOx due to combustion.

As mentioned above, 90% of the digestion gas is burned at a high temperature suitable for deodorization, but the remaining 10% is forced into contact with water, and the CH4 and CO2 that do not dissolve in water remain as gases and become the 90% of the digestion gas. Complete combustion at high temperature with ammonia water and N
minutes is the ambient temperature at which it is difficult to oxidize (the temperature of the exhaust gas after thermal decomposition 7
00 to 900°C).

If the entire amount is burned without being dissolved in water for 2 minutes, NH3 in the gas will be oxidized and a large amount of NOx will be generated.

Also, if the entire amount is brought into contact with water for less than 2 minutes, NH3 in the digestion gas
By dissolving these substances, the amount of wastewater to be treated increases.

According to the present invention as described above, NH, which is the source of the raw odor of digestive gas,
No. 3 is burned at a high temperature as much as possible, which has the advantage that the volume of the thermal furnace 5 required for thermal decomposition of NH3 is small, that is, it is economical, and it is odorless and NOx can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the method of burning digestion gas according to the present invention. 1.1', 1"... Digestion gas, 2...
Scrubber, 3...Ammonia water, 4...
...Methane gas and carbon dioxide gas, 5... Combustion furnace,
6...Auxiliary combustion burner, 7...Exhaust combustion gas.

Claims (1)

[Claims] 1. The entire digestive gas is divided into two parts, and one part is burned as is in an X-combustion furnace, while the other part contains CH4, which is not soluble in water.
It is divided into CO2 and NH3 and H20 that dissolve in water, and the former is burned in a combustion furnace together with the first one, and the latter NH
3. The ammonia aqueous solution in which H20 is dissolved is fed into a combustion furnace that burns OH4, which is separated from the first one and the remaining one of the digestion gases, and the exhaust gas temperature after pyrolysis reaches 700.
A method for burning digestion gas, characterized by thermally decomposing it at a temperature in the range of ~900'C. 2. The method for burning digester gas according to claim 1, wherein the whole digester gas is divided into two parts and combusted as they are in an X-combustion furnace, with one half accounting for 90% or less of the whole.