JP2009126982A - Biological desulfurizer for digestion gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for effectively eliminating sulfur compounds which is contained in the digestion gas produced by the methane fermentation of an organic waste, inexpensively in a simple method. <P>SOLUTION: The problem is solved by the biological desulfurizer for sewage gas produced by the methane fermentation of an organic waste which is characterized by comprising a quantitative feeder feeding make-up water to a spray water supply pipe or directly to the biological desulfurizer tower, in a desulfurizer equipped with a biological desulfurizer tower filled with a filler in which sulfur oxidizing bacteria live and equipped with the spray water supply pipe and a sprayed water waste pipe connected to the filler, an oxygen containing gas feeding port, sewage gas inlet and outlet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for removing sulfur compounds contained in methane gas obtained by methane fermentation of organic waste.

  Currently, methane fermentation treatment is frequently used for the treatment of waste from agricultural products processing plants, waste from marine products processing plants, organic wastes with relatively high water content such as dredging and sewage sludge. In this methane fermentation treatment, a water slurry containing organic waste is supplied to a reaction vessel called a digester, heated to an appropriate temperature (30 to 60 ° C.) and held for a predetermined time to generate gas from the organic waste. To be collected. At that time, components in the generated gas are 60 to 70% by volume of methane gas and 30 to 40% by volume of carbon dioxide. Further, 100 to 3000 ppm of hydrogen sulfide gas is usually contained as an impurity.

  By the way, this gas is usually called “digestion gas” and used as fuel gas. For example, it is a fuel such as a boiler for producing hot water or steam, such as a gas engine for power generation, a gas turbine, or a fuel cell. And if hydrogen sulfide is mixed in, sulfur oxides are generated by combustion. Therefore, in any application, problems such as corroding mechanical parts such as engines or increasing the concentration of sulfur oxides in exhaust gas occur. . Therefore, it is necessary to use after reducing hydrogen sulfide.

  In order to reduce this hydrogen sulfide, conventionally, a dry desulfurization apparatus that adsorbs and removes using an adsorbent such as iron oxide and a wet desulfurization apparatus that uses a scrubber treatment using an alkali have been used. The dry-type desulfurization equipment does not require daily operations and is characterized by high desulfurization performance. However, it requires replacement of the desulfurization agent, which increases the cost of replacement work. Although it must be disposed of as waste, there are few disposal destinations and high disposal costs.

In the scrubber treatment (wet type) desulfurization device by neutralization reaction with sodium hydroxide, water is circulated in order to reduce the amount of water used, but the reaction of the following formulas 1 and 2 occurs with carbon dioxide in the digestion gas. Therefore, the scale of sodium bicarbonate or sodium carbonate is deposited and adheres to the nozzle of the absorbing liquid or the wall of the tower, and the cleaning thereof is complicated.
NaOH + CO ₂ → NaHCO ₃ ↓ ・ ・ ・ ・ ・ Formula 1
_{2NaOH + CO 2 → Na 2 CO} 3 ↓ + H 2 O ····· Formula 2

Therefore, a method for desulfurization using sulfur bacteria has been developed. For example, Patent Documents 1 and 2 disclose a desulfurization apparatus using a biological desulfurization tower having a filler layer to which microorganisms that oxidize and decompose hydrogen sulfide are attached.
The reaction in this biological desulfurization tower is shown in Formula 3.
H ₂ S + 2O ₂ → H ₂ SO ₄ ... Formula 3

  The maintenance cost of this biological desulfurization tower is only the power of the circulating water pump, the power of the fan that injects a small amount of air into the digestion gas, and the supplementary water of the circulating water, and the maintenance cost is very low. .

JP-A-2-26615 JP 2003-305328 A

However, the following problems are pointed out in this biological desulfurization tower.
Oxidation of hydrogen sulfide is a biological reaction treatment of sulfur-oxidizing bacteria, so if the acclimatization time and load fluctuation of the bacteria at the initial start-up are extremely large, or if the temperature or pH of the circulating water deviates from the optimum range, The reaction cannot catch up with the load, and the processing performance decreases, and the hydrogen sulfide concentration in the digestion gas at the exit of the biological desulfurization tower remains above the design value.
As a measure against the above (1), there are many cases where a dry desulfurization tower is installed downstream of the biological desulfurization tower, and in this case, there is a problem that the amount of capital investment becomes excessive. Even when hydrogen sulfide is sufficiently removed by the biological desulfurization tower, the digestion gas is always passed through the downstream dry desulfurization tower. The desulfurization agent swells when it is moistened by the water taken into the digestion gas from the water, and the ventilation resistance becomes large. After about one year, the desulfurization agent must be replaced, and the maintenance cost is not reduced. There's a problem.
As a countermeasure for the above (2), a case where a wet desulfurization tower is installed on the downstream side of the biological desulfurization tower can be considered. In a wet desulfurization tower that removes hydrogen sulfide by a neutralization reaction with an alkali, sodium hydrosulfide is produced by the reaction of the following formula 4. When the wastewater is mixed with the sulfuric acid wastewater from the biological desulfurization tower, hydrogen sulfide is immediately generated by the reaction of Formula 5, and it is very dangerous if a person enters the vicinity. Moreover, since hydrogen sulfide is opened to the atmosphere, it causes bad odor pollution in the vicinity.
NaOH + H ₂ S → NaHS + H ₂ O Formula 4
2NaHS + H ₂ SO ₄ → 2H ₂ S ↑ + Na ₂ SO ₄ ... Formula 5
In biodesulfurization, the air that is injected to oxidize hydrogen sulfide reduces the amount of oxygen in the combustible gas that is the processing gas as much as possible. Therefore, only the amount of oxygen necessary for the oxidation of hydrogen sulfide and the amount that slightly increases it are injected. To control. For this reason, oxidation of hydrogen sulfide is likely to be incomplete. In this case, as shown in Equation 6, solid sulfur accumulates in the biological desulfurization tower, accumulates at the bottom of the tower, and adheres to the packing. Since the pressure loss of the aeration gas becomes large, it is necessary to remove it periodically.
H ₂ S + O ₂ → S + H ₂ O... Formula 6
The method for removing solid sulfur accumulated in the biological desulfurization tower is described in detail in Patent Document 2, but for this purpose, the biological desulfurization tower must be stopped, and an absorbent containing solid sulfur is removed. There is a need for industrial disposal, and since the liquid is almost moisture, the disposal amount becomes excessive, and the industrial disposal cost is very high. In addition, sulfur is a hazardous substance, and its disposal destinations are limited. If the transportation destination is a long distance, the transportation cost increases and the disposal cost is high. Is being depleted.
Therefore, it is necessary to prevent solid sulfur from remaining in the biological desulfurization tower.

Regarding the problem (1), in order to maintain the desulfurization performance at a high level, it is necessary to always maintain the pH of the circulating water in the optimum zone. It has been empirically found that this optimum band has a pH range of 1-2. This is probably because the activity of sulfur-oxidizing bacteria is most active at pH 2 or lower.
If the pH is higher than 2, the concentration of hydrogen sulfide in the digestion gas at the outlet of the biological desulfurization tower may exceed 10 ppm. Therefore, it is necessary to operate a dry or wet desulfurization tower installed in the subsequent stage, and maintenance costs are low. Bulky.

In Patent Document 2, a pH meter is installed in the circulating water line, and the pH is adjusted to 1 to 6 by replenishing with fresh water. However, when the pH is 2 or more, the desulfurization performance is inferior. is there. In order to set the pH setting value within a narrow range of 1 to 2, Patent Document 2 only describes that “a part of circulating water is appropriately replaced by replenishing fresh water in order to prevent an extreme drop in pH”. The specific control method of new water is not described in detail.
On the other hand, the pH meter installed at the site for continuous measurement is not operating normally due to the influence of solid sulfur and other scales generated in the reaction of the above-mentioned formula 6 and the cause of the calibration failure of the pH meter itself. There is a case. In addition, in order to replenish makeup water in a batch system, the pH setting level is too narrow and the amount of water retained in the biological desulfurization tower is not so large, so it is easy to over-inject. In this case, the pH value is set. It becomes larger than the value and desulfurization performance falls.

The concentration of hydrogen sulfide in digestion gas produced by methane fermentation treatment of organic waste is derived from the properties of the organic waste that is the raw material, and if the properties of the organic waste do not change significantly There is little fluctuation in the hydrogen sulfide concentration. In view of this, we have devised a method for continuously injecting a fixed amount of water in proportion to the sulfuric acid load generated in the biological desulfurization tower by taking advantage of the small fluctuation of the hydrogen sulfide concentration. Specifically, the sulfuric acid load is obtained from the digestion gas amount and the hydrogen sulfide concentration, the sulfuric acid concentration that gives an optimum pH in the biological tower is calculated, and the injection amount of makeup water is calculated so that the sulfuric acid concentration is obtained. This setting is only necessary at first because the amount of digestion gas and hydrogen sulfide concentration are generally small. As the equipment, a metering injection pump is required. Preferably, by installing a water meter capable of integrating and measuring the injection amount, the injection amount of fresh water can be accurately grasped.
In this case, control with circulating water pH meter becomes unnecessary. By continuously injecting fresh water, the sulfuric acid continuously produced in the biological desulfurization tower is always diluted at a constant rate, so that the pH is always kept in an optimum state within the optimum value.

  Therefore, in the invention according to claim 1 of the present application, a filler in which sulfur-oxidizing bacteria inhabit is filled, a spray water supply pipe and a spray water drain pipe for supplying water to the filler are connected, and oxygen A desulfurization apparatus having a biodesulfurization tower having a supply port for contained gas and a digestion gas introduction port and an exhaust port, provided with a fixed-quantity supply device for supplying makeup water directly to the spray water supply pipe or to the biodesulfurization tower The present invention provides a desulfurization apparatus for digestion gas obtained by methane fermentation of organic waste.

  Next, in the above (1), in order to maintain the desulfurization performance at a high level, it is necessary to always maintain the temperature of the circulating water in the optimum zone. Patent Document 2 states that it is desirable to maintain the temperature of the circulating water at 15 to 40 ° C. However, it is empirically found that the desulfurization performance is lowered when the temperature is 25 ° C or lower. Therefore, in the winter season, the operation of heating the circulating water is indispensable. However, since the pH of the circulating water is very low for directly heating the circulating water, the heater and the heat exchanger are easily corroded. In addition, the heat exchanger must be made of corrosion-resistant material such as expensive titanium, but it is expensive.

  Therefore, in the present invention, it has been devised that the circulating water is heated by installing an electric heater in the new water line of the continuously injected makeup water to be installed and heating the makeup water. In this case, since fresh water is not a corrosive liquid, an expensive material is not necessary and the cost is low. As control, when the temperature of the circulating water is 25 ° C. or lower, the heater is turned on, and when it is 27 ° C. or higher, the heater is turned off.

Therefore, the invention according to claim 2 of the present application is characterized in that a heating device is provided in the water supply pipe.
By adding the above-mentioned improvements in pH and water temperature, the concentration of hydrogen sulfide in the digestion gas at the outlet of the biological desulfurization tower is always 10 ppm or less, and no subsequent desulfurization operation is required. When cleaning the solid sulfur in the desulfurization tower or when the fluctuation of the hydrogen sulfide load of the digestion gas becomes excessive, hydrogen sulfide remains in the digestion gas at the exit of the biodesulfurization tower. is required.

As described in (2) above, using a dry desulfurization tower as a subsequent desulfurization apparatus is simple in operation, but is not advantageous from the viewpoint of capital investment and maintenance costs. Therefore, the latter-stage desulfurization apparatus is preferably a one-pass scrubber treatment that neutralizes with sodium hydroxide. However, as shown in (3), the sulfuric acid waste water from the biological desulfurization tower and the latter-stage wet sodium hydroxide When mixed, there is a problem that hydrogen sulfide is generated as shown in Formula 5. As an object, we devised to oxidize sodium hydrosulfide by injecting an oxidizing agent such as sodium hypochlorite into the drainage of the wet desulfurization tower. This reaction formula is shown in Formula 7.
NaHS + NaClO → S ↓ + NaCl + NaOH Formula 7

  Therefore, in the invention according to claim 3 of the present application, a wet desulfurization tower is connected to the digestion gas discharge port, and a hypochlorous acid or salt supply pipe is connected to the alkaline aqueous solution discharge side of the wet desulfurization tower. It is characterized by being.

In said (4), solid sulfur tends to accumulate in the biological desulfurization tower, and it is necessary to stop the biological desulfurization tower for periodic cleaning. Moreover, the absorbent containing solid sulfur must be industrially disposed of, which increases the disposal cost.
The specific gravity of solid sulfur is relatively heavy at about 2 and tends to accumulate at the bottom of the biological desulfurization tower. However, it was found that the property of sulfur produced by biodesulfurization maintaining the pH at 1 to 2 is less sticky, free flowing, and has little adhesion to the filler.

Therefore, the bottom is mortared so that sulfur does not accumulate in the biological desulfurization tower. Further, a pump for stirring the tank bottom is provided separately from the circulation pump, and the liquid sucked from the tank bottom is constantly pressurized by the stirring pump and discharged toward the tank bottom to stir the inside of the tank. At this time, the pipe diameter of the discharge port is reduced to increase the flow rate, and the solid sulfur deposited on the bottom of the tank is constantly lifted and floated by the discharge flow having a high flow rate. In addition, by providing a line that transfers the discharge destination of this agitation pump to the neutralization tank by switching the valve separately from the agitation in the tank, when the water level of the biological desulfurization tower exceeds the specified value due to make-up water, it is drained. And solid sulfur can be discharged out of the system.
With such a device, solid sulfur is not accumulated in the biological desulfurization tower, periodic cleaning is unnecessary, and disposal of solid sulfur is unnecessary.

  In view of this, the invention according to claim 4 of the present application is characterized in that a stirring pump for stirring the liquid in the bottom of the biological desulfurization tower is provided.

  According to the present invention, sulfur compounds contained in digestion gas obtained by subjecting organic waste to methane fermentation can be efficiently and inexpensively removed by a simple method.

  The biological desulfurization tower of the desulfurization apparatus of the present invention is provided with a digestion gas inlet and outlet, an oxygen-containing gas supply port, a spray water supply port and a spray water discharge port, and a filler for inhabiting sulfur-oxidizing bacteria inside Is contained.

  The shape of the tower body is usually a cylindrical shape, but may be a box shape or the like. A filler is accommodated in the central portion, and spaces are provided above and below. The bottom may be a flat bottom but is preferably mortar-shaped.

  The filler may be any material that can be inhabited by sulfur-oxidizing bacteria, and is usually a gas-liquid contact filler. The shape may be a particle shape, a tubular shape, a sheet shape, or the like. Preferable examples include synthetic resin particles having a specific gravity of 0.9 to 1.05 and a void ratio of 80 to 95%. A preferable example of the synthetic resin is polypropylene.

  Bacteria to be planted in the filler are those that oxidize hydrogen sulfide to produce sulfuric acid, and are so-called sulfur-oxidizing bacteria. Sulfur-oxidizing bacteria are present in the liquid in the aeration tank that performs the activated sludge treatment in the sewage treatment plant, and a small amount of the liquid in the aeration tank may be introduced into the biological desulfurization tower.

The digestion gas may be moved in the biological desulfurization tower by either a downward flow or an upward flow, and one of the introduction port and the discharge port is provided at the upper part and the other is provided at the lower part accordingly.
The oxygen-containing gas is used for the oxidation of hydrogen sulfide. Usually, air is used and supplied to the biological desulfurization tower together with the digestion gas. In this case, the digestion gas inlet serves as the oxygen-containing gas supply port. This oxygen-containing gas supply port may be provided independently.

The water supply to the biological desulfurization tower is for growing sulfur bacteria to perform desulfurization, and is usually performed by sprinkling water from above the filler layer. Therefore, normally, the spray water supply port is provided in the upper part of the tower and the spray water drain port is provided in the lower part. Further, a spray water circulation line is provided between the spray water supply port and the spray water discharge port so that the spray water is circulated in the tower.
Further, the makeup water supply port may be joined to the spray water circulation line or may be provided independently in the biological desulfurization tower.

  A fixed amount supply device is provided in the makeup water pipe connected to the spray water circulation line. In this fixed quantity supply device, a fixed quantity supply pump having a flow rate adjusting mechanism can be used, but in addition, if the supplied water has water pressure, a nozzle or a valve can be used. In the present invention, the pH of water in the biological desulfurization tower is kept at 1 to 2 by quantitatively supplying water with this quantitative supply device.

  The replenishing water pipe is further provided with a heating device for water to be replenished. This heating device is for keeping the water in the biological desulfurization tower at 25 ° C. or more and activating desulfurization by bacteria. The type of the heating device is not particularly limited, and various known heating devices can be used such as providing a heat exchanger to supply steam or other heat medium, using an electric heater, or the like.

A neutralization tank is installed in the middle of the drain pipe. This is because the water discharged from the biological desulfurization tower has a pH of 1-2, so that the water is adjusted to near neutrality.
The bottom of the biological desulfurization tower is preferably formed in a mortar shape so that sulfur does not accumulate. When the bottom is flat, the bottom side wall is mortared with concrete or the like to form a mortar. Further, a pump for agitating the tank bottom is installed separately from the circulation pump, and the circulating fluid sucked from the tank bottom is constantly pressurized by the agitation pump and discharged toward the tank bottom to stir the inside of the tank. At this time, the pipe diameter of the discharge port is reduced to increase the flow rate, and the solid sulfur deposited on the bottom of the tank is constantly lifted and floated by the discharge flow having a high flow rate. In this case, the following conditions are desirable. The gradient of the mortar portion is preferably 30 to 60 degrees where sulfur slurry is difficult to deposit. The diameter of the flat surface at the center of the bottom is desirably 0.3 to 1.0 m within a range where the stirring discharge flow can reach. Incidentally, the tower diameter is about 1 to 3 m. The discharge speed of the stirring flow is desirably 3 m / sec to 10 m / sec, which can wind up the sulfur slurry at the bottom. As for the diameter of the bottom plane, the stirring outlet is preferably 10 mm to 50 mm.

A method for maintaining the pH of the circulating water in the biological desulfurization tower in the optimum region using the desulfurization apparatus of the present invention will be described.
When the digestion gas amount is 100 Nm ³ / H and the hydrogen sulfide concentration is 1,000 ppm, the makeup water amount when the pH value is 2 or less is calculated as follows.

Processed air volume Q _G : 100Nm ³ / H
Hydrogen sulfide concentration C: 1,000 ppm
Hydrogen sulfide load q _H2S :
q _H2S = 100 Nm ³ / H × 24H × 1000 ppm × 10 ⁻⁶ ÷ 22.4 = 0.107 kmol / day Oxidative degradation reaction by organism:
H ₂ S + 2O ₂ → H ₂ SO ₄
Sulfuric acid load q _H2SO4 : 0.107 kmol / day (because hydrogen sulfide and sulfuric acid are equivalent reactions)
Maximum pH of circulating water: 2
Relationship between hydrogen ion concentration and pH: pH = −log [H ⁺ ] → [H ⁺ ] = 10 ^−pH
Upper limit [H ⁺ ] concentration (g ion / L): 0.01
Lower limit sulfuric acid concentration C _H2SO4 (mol / L): 0.005 (value of sulfuric acid: 2, ionization degree: 1)
Upper limit water supply amount Qw = q _H2SO4 ÷ C _H2SO4 = 21.4 (kL / day)
Percentage ratio of upper limit to digestion gas for make-up water:
л = Qw ÷ (Q _G × 24H) × 100 = 0.89%
As described above, when the hydrogen sulfide concentration is 1000 ppm, it is sufficient to quantitatively inject makeup water of about 0.89% or less with respect to the digestion gas amount.
From the above, the upper limit value of the ratio of the makeup water amount to the digestion gas amount л may be made proportional to the hydrogen sulfide concentration C in the digestion gas.
л (%) <0.89% × C (ppm) ÷ 1000 (ppm)
If the hydrogen sulfide concentration in the digestion gas changes seasonally, this л can be calculated by the above calculation and the discharge rate of the metering pump can be adjusted. For this amount of discharge, it is common to use a diaphragm pump as a metering pump, and this type of pump discharge amount can be adjusted simply by adjusting the discharge stroke with a dial gauge. The operation is also easy.

  However, the above-mentioned ratio л is the case where the reaction of Formula 3 occurs 100%. Actually, it remains in the intermediate elemental sulfur, and there is a ratio in which some elemental sulfur is carried out of the system. Therefore, it is only necessary to inject makeup water at a rate slightly lower than the rate actually calculated in this calculation.

Next, a method for maintaining the temperature of the circulating water in the biological desulfurization tower in the optimum range will be described.
It is empirically known that the desulfurization performance is lowered when the circulating water temperature of biological desulfurization is 20 ° C. or lower. The optimum zone is 25 ° C. or higher, and it is necessary to heat in the winter when the outside air temperature decreases.
Factors that lower the temperature of the circulating water include (1) a decrease in the temperature of digestion gas, (2) a decrease in the temperature of makeup water, and (3) a decrease in the temperature of outside air. As a measure of (3), it can be prevented by covering the outside of the biological desulfurization tower in contact with the outside air with a heat insulating material. In a certain example, the ratio (1) :( 2) :( 3) of the heat dissipated after coating was about 45%: 40%: 15%.

Thus, since the ratio of the temperature drop of the makeup water in (2) accounts for a relatively large proportion of the temperature drop of the circulating water, it is not necessary to heat the circulating water, but to warm the makeup water without corrosion problems. It is advantageous if the circulating water temperature can be maintained.
Therefore, a heating heater is attached to the line for continuously injecting makeup water performed in [0032], and the heater is turned on at 25 ° C. so that the temperature of the circulating water is about 25 ° C. to 27 ° C. Turn off the heater.

  Electric heaters are cheaper and easier to install. When the equipment capacity is large and cheap hot water can be supplied by waste heat recovery, the hot water may be heated directly, or a small amount of hot water may be injected as part of the makeup water.

The neutralization method of the waste water of wet desulfurization and biological desulfurization waste water of the latter stage is demonstrated.
A wet desulfurization tower is installed in the latter stage assuming that the hydrogen sulfide concentration in the digestion gas at the biological desulfurization tower outlet exceeds the specified value. The reaction of the wet desulfurization tower is as follows, and a sodium hydroxide aqueous solution equivalent to or slightly in excess of the residual amount of hydrogen sulfide is supplied.
NaOH + H ₂ S → NaHS + H ₂ O... Formula 4
However, the digestion gas contains a large amount of carbon dioxide, and in the circulation type, the reaction of the following formulas 1 and 2 occurs with the carbon dioxide in the digestion gas. It adheres to the nozzles and tower walls and is complicated to clean. For this reason, it is desirable to use a spray tower which is not a circulation type but has one pass (one-time type) and is difficult to scale.
NaOH + CO ₂ → NaHCO ₃ ↓ ・ ・ ・ ・ ・ Formula 1
_{2NaOH + CO 2 → Na 2 CO} 3 ↓ + H 2 O ····· Formula 2

Digestion gas always passes through the wet column in the latter stage regardless of whether hydrogen sulfide remains, and when the hydrogen sulfide residue exceeds the allowable value, it is equivalent to the residual hydrogen sulfide concentration or a little excess sodium hydroxide. Inject. For hydrogen sulfide, a continuous measuring device may be installed, but a simple measuring device such as a detector tube may be used.
In order to reduce the pH of the aqueous sodium hydroxide solution, it is important to dilute it with water to make it 0.001 to 0.01%, preferably about 0.004%. It is to be.

When the drainage of sodium hydrosulfide produced by the neutralization reaction of Formula 4 is mixed with the sulfuric acid drainage of the biological desulfurization tower, hydrogen sulfide is generated immediately by the reaction of Formula 5, and a person enters the vicinity. Is very dangerous. Moreover, since hydrogen sulfide is opened to the atmosphere, it causes bad odor pollution in the vicinity.
2NaHS + H ₂ SO ₄ → 2H ₂ S ↑ + Na ₂ SO ₄ ... Formula 5
As a countermeasure, an oxidizing agent such as sodium hypochlorite is injected into the waste water of the wet desulfurization tower to oxidize sodium hydrosulfide. This reaction formula is shown in Formula 7.
NaHS + NaClO → S ↓ + NaCl + NaOH Formula 7

The injection amount may be the same as sodium hydroxide injected into the wet desulfurization tower, and about 12% of commercially available sodium hypochlorite may be injected into the bottom of the spray tower or the drain pipe with a metering pump.
If this waste water is placed in the neutralization tank of the biological desulfurization tower, it contains sodium hydroxide, which helps to neutralize the sulfuric acid waste water of the biological desulfurization tower, and is economical.

  The necessity of neutralization of biological desulfurization wastewater is as follows. That is, since the liquid in the biological desulfurization tower increases due to continuous injection, the liquid is discharged out of the system by a pump when the specified water level is exceeded. Since this waste water exceeds pH 5.8 to 8.6 on the basis of discharge to sewer at pH 1 to 2, neutralization is necessary. The neutralization treatment procedure is as follows. Sulfuric acid wastewater is once put in a neutralization tank, and sodium hydroxide is gradually injected with a pH meter installed in the neutralization tank, and sulfuric acid and sodium hydroxide are mixed with a stirrer. If it enters the range of the reference pH, the injection of sodium hydroxide is stopped, and this is drained into the sewer. Since the pH value of the biological desulfurization tower is obtained as the pH value at the time when the wastewater in the biological tower flows in with a pH meter and a recording chart installed in the neutralization tank, the biological value described in Patent Document 2 A pH meter installed in the desulfurization tower or in the circulating water is unnecessary.

FIG. 1 shows the configuration of a desulfurization apparatus which is an embodiment of the present invention.
This apparatus comprises a biological desulfurization tower, a wet desulfurization tower, and a neutralization tank.
The biological desulfurization tower has a cylindrical shape with a diameter of 2 m and a height of 5.5 m, and a heat insulating material is mounted on the outer surface. Inside, a gas-liquid contact filler made of polypropylene is accommodated as a filler. A digestion gas supply pipe is connected to the top, and an air supply pipe as an oxygen-containing gas is connected to the top. A flow meter is attached to both the digestion gas supply pipe and the air supply pipe. A water supply pipe is connected to the upper part of the tower, and a watering nozzle is arranged in the tower so that water can be sprayed over the entire surface. The lower part of the tower is shaped like a mortar with a haunch, and a spray water drain pipe is connected to it. The spray water drain pipe is connected to the spray water supply pipe via a pump to form a circulation line.

A makeup water tank for supplying water is connected to a pipe in the middle of this circulation line, and this pipe also constitutes a water supply pipe. A metering pump, a flow meter, a heater, and a valve are attached in the middle of the piping.
Digestion gas outlets are provided in the lower part of the tower and are connected to a wet desulfurization tower by piping. An H ₂ S meter is attached in the middle of the piping.

  A drain pipe is also connected to the lower part of the tower, and the other end of the drain pipe is connected to a neutralization tank through a drain valve. In addition, a circulation line is formed which branches from the middle of the drain pipe and returns to the lower part of the tower via a pump. The liquid in the lower part of the tower is stirred by this circulation line. This pattern is shown in FIG.

  The wet desulfurization tower has a digestion gas inlet at the bottom and an outlet at the top. Further, a pipe is connected to the upper part through a pump from a caustic soda tank, and a pipe from a makeup water tank for diluting the caustic soda is connected in the middle. In the upper part of the tower, a nozzle is arranged so that this caustic soda solution can be sprayed over the entire surface.

At the lower part of the wet desulfurization tower, a discharge port for a sodium hydrosulfide solution that has absorbed H ₂ S is provided, and is connected to a neutralization tank through a pump from there. In the middle of this pipe, a pipe from a tank of sodium hypochlorite aqueous solution is connected via a pump.

In the neutralization tank, in addition to the drainage pipe of the biological desulfurization tower and the drainage pipe from the wet desulfurization tower,
A supply pipe from a caustic soda tank is also connected via a pump, and this pump is operated by a command from a pH meter provided in the neutralization tank.

  Since the desulfurization apparatus of the present invention can efficiently remove sulfur compounds contained in digestion gas obtained by subjecting organic waste to methane fermentation at low cost, it can be widely used in this methane fermentation apparatus. Is.

It is a figure which shows the structure of the desulfurization apparatus which is one Example of this invention. It is a figure which shows typically the stirring condition of the biodesulfurization tower bottom part.

Claims (4)

  Filling material inhabiting sulfur-oxidizing bacteria is filled, a spray water supply pipe and a spray water drain pipe for supplying water to the filler are connected, and an enzyme-containing gas supply port and a digestion gas introduction port And a desulfurization apparatus having a biological desulfurization tower having a discharge port, characterized in that a fixed-quantity supply device for supplying makeup water to the spray water supply pipe or directly to the biological desulfurization tower is provided. Desulfurization equipment for digestion gas obtained by methane fermentation of waste   The desulfurization apparatus according to claim 1, wherein a heating device is provided in the makeup water pipe.   An organic waste is characterized in that a wet desulfurization tower is connected to the digestion gas outlet, and a supply pipe for hypochlorous acid or a salt thereof is connected to the discharge side of the alkaline aqueous solution of the wet desulfurization tower. Desulfurization equipment for digestion gas obtained by methane fermentation   A desulfurization apparatus for digestion gas obtained by methane fermentation of organic waste, characterized in that a bottom of the biological desulfurization tower is formed into a mortar shape and a stirring pump for stirring the liquid there is provided.

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