CN103723899B - Sludge comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization - Google Patents

Abstract

The invention relates to the technical field of treatment methods for municipal sludge and industrial sludge, and discloses a comprehensive sludge treatment method based on anaerobic digestion and hydrothermal carbonization, which includes the following steps: 1) pumping liquid sludge into the heat exchange Heated by an anaerobic digester, and then transported to an anaerobic digestion tank for anaerobic digestion treatment to obtain digested sludge and biogas; 2) After mechanical dehydration, the digested sludge is transported to a sludge preheating tank for preheating treatment; 3) Then Inject digested sludge into the hydrothermal carbonization tank, and obtain material 1 after hydrothermal carbonization treatment; 4) Transport material 1 to the decompression flash tank for depressurization flash treatment to obtain material 2; 5) Material 2 is mechanically dehydrated Obtain semi-dry state hydrothermal charcoal. The invention integrates two technologies of anaerobic digestion and hydrothermal carbonization to treat sludge, and optimizes the process from the perspective of material and energy balance, realizes sludge reduction and generates biogas energy at the same time, reduces the operating cost of the process, adopts The hydrothermal carbonization process digests the sludge, eliminates the germs in the sludge and converts it into a hydrothermal charcoal product, and the hydrothermal charcoal produced can be returned to the field for use, which is clean and environmentally friendly.

Description

Comprehensive sludge treatment method based on anaerobic digestion and hydrothermal carbonization

technical field

The invention relates to the technical field of treatment methods for municipal sludge and industrial sludge, in particular to a comprehensive sludge treatment method based on anaerobic digestion and hydrothermal carbonization.

Background technique

A large amount of sludge will be generated during sewage or wastewater treatment. Taking urban sewage treatment plants as an example, every 10,000 ^m3 of sewage will produce 5 to 10 tons of dewatered sludge (based on a moisture content of 80%). According to the requirements of my country's "Twelfth Five-Year Plan" National Urban Sewage Treatment and Reuse Facilities Construction Plan, by 2015, the scale of urban sewage treatment in my country will reach 208.05 million cubic meters per day. Based on this estimate, only urban sewage treatment plants in my country will 37.97-75.94 million tons of dewatered sludge will be produced every year; in addition to urban sewage treatment plants, papermaking, food processing, petrochemical, printing and dyeing industries all produce a large amount of industrial sludge.

Not only is the amount produced huge, sludge usually also contains a wide variety of pollutants with complex components, including biological pollutants such as pathogenic bacteria and parasites (eggs), inorganic toxic substances such as copper, zinc, chromium, mercury, and polychlorinated Persistent organic toxic substances such as benzene and dioxin; on the other hand, sludge is usually rich in a large amount of organic matter (and therefore contains a large amount of chemical energy) and nutrients required for crop growth such as N and P. Therefore, if the sludge is randomly piled up or improperly disposed of, it will cause serious pollution to the environment and endanger people's lives and health. At the same time, it will also cause the loss of additional resources and energy in the sludge.

At present, the treatment and disposal of sludge in my country mainly rely on traditional technologies such as landfill, returning to the field for utilization, and incineration. Landfill is the most unsustainable way of sludge disposal. It not only occupies limited land resources, but it is also difficult to avoid the discharge of pollutants into the air, surface water, groundwater and soil environment. Many countries or regions are very cautious or even prohibit the use of this method. Sludge disposal technology. Sludge returning to the field can partially recover N, P and other nutrient resources in the sludge, but it is also accompanied by the input of pollutants (such as heavy metals, persistent organic pollutants, etc.) In view of the fact that the amount of sludge produced is huge and increasing day by day, this method will be subject to stricter control. Incineration has the advantages of complete sludge reduction and partial recovery of energy in sludge. However, since the sludge incineration process will produce harmful gases, and the effective removal and purification of these gases requires a large amount of facility investment, this technology is facing two challenges: "high operating costs and poor public acceptability".

Hydrothermal Carbonization (Hydrothermal Carbonization) is a biomass value-added treatment method that has developed rapidly in recent years. It uses water as the reaction medium to convert biomass into multifunctional carbon-based carbon with high added value at a certain temperature and pressure. Material (the current international popular professional name is hydrothermal charcoal); recent international studies have shown that hydrochar (Hydrochar) has similar properties to biochar (Biochar) produced by biomass pyrolysis (so hydrochar Sometimes referred to as biochar), it can be used in many fields such as soil improvement, _CO2 fixation, pollutant adsorption and so on. However, there is still a lot of room for improvement in terms of process performance (such as treatment efficiency, hydrothermal charcoal yield, hydrothermal charcoal performance, waste heat utilization, etc.) of this technology.

Contents of the invention

Aiming at the technical problems existing in the prior art, the present invention provides a clean and environment-friendly sludge comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization with high product added value, fast and efficient.

In order to solve the above technical problems, the present invention is solved through the following technical solutions:

A comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization, including the following steps:

Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 50-85°C, and then transport it to the anaerobic digestion tank, where the liquid sludge undergoes anaerobic digestion After digestion, the digested sludge is obtained and biogas is generated at the same time, and the biogas is passed to the desulfurization device, and then transported to the biogas boiler;

Step 2: Pump the digested sludge obtained through anaerobic digestion in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The preheating treatment is carried out in the mud preheating tank, the preheating temperature is 40-70°C, and the preheating treatment time is 1-3 hours; the dehydration liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged;

Step 3: Inject the digested sludge pre-heated in step 2 into the hydrothermal carbonization tank. The injection amount of the digested sludge is 3/5-4/5 of the volume of the hydrothermal carbonization tank. The reaction temperature in the thermal carbonization tank is 180-350°C, the reaction time is 0.5-6 hours, and the digested sludge is hydrothermally carbonized to obtain material 1;

Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank;

Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment. After removing part of the water, obtain semi-dry hydrothermal charcoal with a moisture content of 40-60%. The dehydration liquid produced by mechanical dehydration is purified Discharge after treatment by the treatment device.

The present invention adds a sludge anaerobic digestion treatment process before the hydrothermal carbonization treatment process, which can convert nearly half of the organic matter in the sludge into biogas to achieve sludge reduction, thereby significantly reducing subsequent water consumption. Material handling capacity, energy consumption and operating costs of thermal carbonization, mechanical dehydration, thermal drying and other operating processes. Hydrothermal carbonization is used to convert the sludge left after anaerobic digestion treatment, i.e. digested sludge, into hydrothermal charcoal with properties similar to biochar, and the technology is optimized. The obtained hydrothermal charcoal product It not only better retains the nutrients needed for the growth of crops such as N and P in the sludge, but also better enriches the energy in the sludge, so it has a high added value and can be used as a fertilizer for returning to the field ( Or as the aggregate of compound fertilizer), it can also be used as high-quality solid biofuel. At the same time, the pathogenic microorganisms in the sludge are completely exterminated, most of the heavy metal pollutants in the sludge are dissolved, and the organic and toxic substances in the sludge are effectively decomposed and detoxified, which can ensure the utilization of hydrothermal charcoal in the field. Environmental safety can also ensure the cleanliness of its use as fuel.

Preferably, the semi-dry hydrothermal charcoal obtained in step 5 is transported to a drying machine for drying treatment to obtain dry hydrothermal charcoal.

Preferably, in step 3, the reaction temperature of the digested sludge in the hydrothermal carbonization tank is 200-260° C., and the reaction time is 1-3 hours.

As a preference, citric acid or acetic acid is added in step three to adjust the pH value of material one in the hydrothermal carbonization tank to 5.0-6.2. It can increase the dissolution of heavy metals in sludge and increase the production of hydrothermal carbon.

Preferably, the high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the heat exchanger in step 1 and the hydrothermal carbonization tank in step 3 respectively. The biogas generated by anaerobic digestion treatment is fully applied as energy to energy-consuming processes such as sludge anaerobic digestion, hydrothermal carbonization, etc., which improves the utilization efficiency of biogas and rarely or even does not need to supplement external sources of fuel, thus further reducing operating costs of the process system.

Preferably, the high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the dryer. The biogas produced by anaerobic digestion is fully applied to the thermal drying energy-consuming process as an energy source, which improves the utilization efficiency of biogas, and rarely or even does not need to supplement external sources of fuel, thus further reducing the operating cost of the process system.

Due to the adoption of the above technical solutions, the present invention has significant technical effects: the present invention is based on the comprehensive pollution treatment method of anaerobic digestion and hydrothermal carbonization, and adds a sludge anaerobic digestion treatment process before the hydrothermal carbonization treatment process, which can About half of the organic matter in the sludge is converted into biogas to achieve sludge reduction, which can significantly reduce the material handling capacity, energy consumption and operation of subsequent hydrothermal carbonization, mechanical dehydration, thermal drying and other operating processes cost; on the other hand, the present invention fully applies the biogas produced by anaerobic digestion as an energy source to energy-consuming processes such as sludge anaerobic digestion, hydrothermal carbonization, and thermal drying, which improves the utilization efficiency of biogas and rarely requires even There is no need to supplement external sources of fuel, thereby further reducing the operating costs of the process system. The present invention adopts hydrothermal carbonization technology to convert the remaining sludge after anaerobic digestion treatment, that is, digested sludge, into hydrothermal charcoal with properties similar to biochar, and optimizes the process of the technology. The obtained water The thermal charcoal product not only better retains the nutrients needed for the growth of crops such as N and P in the sludge, but also better enriches the energy in the sludge (the hydrothermal charcoal product has a higher calorific value than the sludge ), thus having high added value, it can be used as fertilizer returning to the field (or as aggregate of compound fertilizer), and can also be used as high-quality solid biofuel. After hydrothermal carbonization treatment of digested sludge, the pathogenic microorganisms in the sludge are completely exterminated, most of the heavy metal pollutants in the sludge are dissolved, and the organic toxic substances in the sludge are effectively decomposed and detoxified, which can ensure The environmental safety of hydrothermal charcoal returning to the field can also ensure the cleanliness of its use as fuel; on the other hand, the generated hydrothermal charcoal also contains relatively rich organic carbon, which exists in a stable form. Returning to the field as a fertilizer can increase the content of stable organic carbon in the soil, thereby increasing the potential of soil carbon sinks and mitigating the greenhouse effect.

Description of drawings

Fig. 1 is a schematic flow chart of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

A comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization, including the following steps:

Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 50°C, and then transport it to the anaerobic digestion tank, where the liquid sludge undergoes anaerobic digestion treatment After the digested sludge is obtained, biogas is produced at the same time, and the biogas is passed to the desulfurization device, and then transported to the biogas boiler;

Step 2: Pump the digested sludge obtained through anaerobic digestion in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The preheating treatment is carried out in the mud preheating tank, the preheating temperature is 40°C, and the preheating treatment time is 3 hours; the dehydration liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged;

Step 3: Inject the digested sludge preheated in step 2 into the hydrothermal carbonization tank, the injection amount of the digested sludge is 3/5 of the volume of the hydrothermal carbonization tank, and the digested sludge is in the hydrothermal carbonization tank The reaction temperature is 180°C, and the reaction time is 6 hours. The digested sludge is hydrothermally carbonized to obtain material 1, and citric acid is added to adjust the pH value of material 1 to 5.0;

Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank;

Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment. After removing part of the water, obtain semi-dry hydrothermal charcoal with a moisture content of 40-60%. The dehydration liquid produced by mechanical dehydration is purified After treatment by the treatment device, it is discharged, and the obtained semi-dry hydrothermal charcoal is transported to a dryer for drying treatment to obtain dry hydrothermal charcoal.

The high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the heat exchanger in step 1 and the hydrothermal carbonization tank in step 3, and finally the drying process in the plane.

Example 2

A comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization, including the following steps:

Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 85°C, and then transport it to the anaerobic digestion tank. The liquid sludge is anaerobically digested in the anaerobic digestion tank Digested sludge is obtained and biogas is produced at the same time, and the biogas is passed to the desulfurization device, and then sent to the biogas boiler;

Step 2: Pump the digested sludge obtained through anaerobic digestion in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The preheating treatment is carried out in the mud preheating tank, the preheating temperature is 50°C, and the preheating treatment time is 2.5h; the dehydration liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged;

Step 3: Inject the digested sludge preheated in step 2 into the hydrothermal carbonization tank, the injection amount of the digested sludge is 4/5 of the volume of the hydrothermal carbonization tank, and the digested sludge is in the hydrothermal carbonization tank The reaction temperature is 350°C, the reaction time is 0.5h, the digested sludge is hydrothermally carbonized to obtain material 1, and acetic acid is added to adjust the pH value of material 1 to 5.0;

Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank;

Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment. After removing part of the water, obtain semi-dry hydrothermal charcoal with a moisture content of 40-60%. The dehydration liquid produced by mechanical dehydration is purified After treatment by the treatment device, it is discharged, and the obtained semi-dry hydrothermal charcoal is transported to a dryer for drying treatment to obtain dry hydrothermal charcoal.

The high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the heat exchanger in step 1 and the hydrothermal carbonization tank in step 3, and finally the drying process in the plane.

Example 3

A comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization, including the following steps:

Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 70°C, and then transport it to the anaerobic digestion tank, where the liquid sludge undergoes anaerobic digestion treatment After the digested sludge is obtained, biogas is produced at the same time, and the biogas is passed to the desulfurization device, and then transported to the biogas boiler;

Step 2: Pump the digested sludge obtained through anaerobic digestion in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The preheating treatment is carried out in the mud preheating tank, the preheating temperature is 60°C, and the preheating treatment time is 2 hours; the dehydration liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged;

Step 3: Inject the digested sludge preheated in step 2 into the hydrothermal carbonization tank, the injection amount of the digested sludge is 3/5 of the volume of the hydrothermal carbonization tank, and the digested sludge is in the hydrothermal carbonization tank The reaction temperature is 200°C, the reaction time is 5 hours, the digested sludge is hydrothermally carbonized to obtain material 1, and citric acid is added to adjust the pH value of material 1 to 6.2;

Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank;

Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment. After removing part of the water, obtain semi-dry hydrothermal charcoal with a moisture content of 40-60%. The dehydration liquid produced by mechanical dehydration is purified After treatment by the treatment device, it is discharged, and the obtained semi-dry hydrothermal charcoal is transported to a dryer for drying treatment to obtain dry hydrothermal charcoal.

The high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the heat exchanger in step 1 and the hydrothermal carbonization tank in step 3, and finally the drying process in the plane.

Example 4

A comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization, including the following steps:

Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 80°C, and then transport it to the anaerobic digestion tank, where the liquid sludge undergoes anaerobic digestion treatment After the digested sludge is obtained, biogas is produced at the same time, and the biogas is passed to the desulfurization device, and then transported to the biogas boiler;

Step 2: Pump the digested sludge obtained through anaerobic digestion in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The preheating treatment is carried out in the mud preheating tank, the preheating temperature is 70°C, and the preheating treatment time is 1h; the dehydrated liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged;

Step 3: Inject the digested sludge preheated in step 2 into the hydrothermal carbonization tank, the injection amount of the digested sludge is 4/5 of the volume of the hydrothermal carbonization tank, and the digested sludge is in the hydrothermal carbonization tank The reaction temperature is 260°C, and the reaction time is 3 hours. The digested sludge is hydrothermally carbonized to obtain material 1, and acetic acid is added to adjust the pH value of material 1 to 6.2;

Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank;

Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment. After removing part of the water, obtain semi-dry hydrothermal charcoal with a moisture content of 40-60%. The dehydration liquid produced by mechanical dehydration is purified After treatment by the treatment device, it is discharged, and the obtained semi-dry hydrothermal charcoal is transported to a dryer for drying treatment to obtain dry hydrothermal charcoal.

The high-temperature steam generated by the biogas boiler in step 1 is sent to the steam distributor, and the steam distributor distributes and sends the high-temperature steam to the heat exchanger in step 1 and the hydrothermal carbonization tank in step 3, and finally the drying process in the plane.

In a word, the above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the patent of the present invention.

Claims (6)

1. The sludge comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization, is characterized in that: comprise the following steps: Step 1: Pump the liquid sludge with a moisture content of 90-98% into the heat exchanger and heat it to 50-85°C, and then transport it to the anaerobic digestion tank, where the liquid sludge undergoes anaerobic digestion After digestion, the digested sludge is obtained and biogas is generated at the same time, and the biogas is passed to the desulfurization device, and then transported to the biogas boiler; Step 2: Pump the digested sludge obtained through anaerobic digestion treatment in the anaerobic digestion tank in step 1 into the dehydrator for mechanical dehydration treatment, dehydrate until the moisture content of the digested sludge is 75-85%, and then transport it to the sewage The mud preheating tank is preheated, the preheating temperature is 40-70°C, and the preheating time is 1-3h; the dehydrated liquid obtained by mechanical dehydration is treated by the purification treatment device before being discharged; Step 3: Inject the digested sludge pre-heated in step 2 into the hydrothermal carbonization tank. The injection amount of the digested sludge is 3/5-4/5 of the volume of the hydrothermal carbonization tank. The reaction temperature in the thermal carbonization tank is 180-350°C, the reaction time is 0.5-6 hours, and the digested sludge is hydrothermally carbonized to obtain material 1; Step 4: The material one obtained in the step 3 is transported to the decompression flash tank, and the decompression flash treatment is carried out to obtain the material 2, and the flash steam generated during the reaction in the decompression flash tank is transported to the sewage in the step 2 mud preheating tank; Step 5: Transport the material 2 obtained in step 4 to a mechanical dehydration device for mechanical dehydration treatment, and obtain semi-dry hydrothermal charcoal with a moisture content of 40-60% after removing part of the water. The dehydration liquid produced by mechanical dehydration is purified Discharge after treatment by the treatment device. 2. The sludge comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization according to claim 1, characterized in that: the semi-dry hydrothermal charcoal obtained in step 5 is transported to a drying machine for drying treatment, Obtain dry hydrothermal charcoal. 3. The comprehensive sludge treatment method based on anaerobic digestion and hydrothermal carbonization according to claim 1, characterized in that: in step 3, the reaction temperature of the digested sludge in the hydrothermal carbonization tank is 200-260°C, and the reaction time is For 1 ~ 3h. 4. The comprehensive pollution treatment method based on anaerobic digestion and hydrothermal carbonization according to claim 1, characterized in that: in step 3, citric acid or acetic acid is added to adjust the pH value of material 1 in the hydrothermal carbonization tank to 5.0-6.2 . 5. The pollution comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization according to claim 1, characterized in that: in step 1, the high-temperature steam produced by the biogas boiler is delivered to the steam distributor, and the steam distributor distributes the high-temperature steam They are sent to the heat exchanger in step one and the hydrothermal carbonization tank in step three respectively. 6. The pollution comprehensive treatment method based on anaerobic digestion and hydrothermal carbonization according to claim 2, characterized in that: in step 1, the high-temperature steam produced by the biogas boiler is delivered to the steam distributor, and the steam distributor distributes the high-temperature steam and sent to the drying machine.