Deep dehydration method of sludge pyrohydrolysate

Abstract

The invention discloses a deep dehydration method of sludge pyrohydrolysate, which comprises the following steps: firstly, taking the sludge pyrohydrolysate, measuring the water content of the sludge pyrohydrolysate, then adding an iron salt conditioner according to 1-4% of the dry weight of sludge, stirring and then heating; and then conveying the heated sludge into filter pressing dehydration equipment for deep dehydration to form a sludge cake. In order to solve the problem of dehydration of the pyrohydrolysate obtained by carrying out pyrohydrolysis conditioning on the residual sludge of the sewage plant, an iron salt conditioner is added into the pyrohydrolysate for conditioning again, the temperature is kept at 60 DEG C or above for reaction, and then the mixture is conveyed to filter-pressing dehydration equipment for deep dehydration, so that the dehydration performance of the sludge can be remarkably improved, and the dehydration efficiency is improved. Compared with a common sludge thermal hydrolysate direct dehydration method, the sludge deep dehydration efficiency and effect can be obviously improved, stable operation can be achieved, and the comprehensive treatment cost of sludge is reduced.

Description

Technical Field

[0001] The invention relates to a sludge dehydration method, in particular to a deep dehydration method of sludge thermal hydrolysis liquid. Background Art

[0002] Sludge is a mixture of microorganisms, inorganic matter, organic matter and other components. Organic matter is an important component of sludge, mainly from the difficult-to-degrade substances in the raw sewage and the degradation products of microorganisms, algae, humus and the like. With the development of the economy and the improvement of infrastructure, the COD of the sewage plant influent continues to increase, and the residual sludge gradually turns into sludge with high organic content. If the high organic sludge is not properly handled, it will not only pollute the surrounding environment, but also eventually produce a greenhouse effect and aggravate climate change. Sludge deep dehydration technology is one of the main technologies to achieve sludge reduction. After conventional chemical conditioning + mechanical dehydration, the sludge moisture content can be reduced from 98% to about 80%. It is very difficult to further dehydrate, mainly because of the high compressibility and colloidal stability of the sludge. The extracellular polymers (EPS) present in the sludge have a strong water-locking ability. EPS wraps water and microbial communities to form sludge flocs, and the surface of the sludge flocs is negatively charged and has a double-layer structure. The flocs cannot agglomerate due to the repulsion of the surface charges and are stable. In addition, when the sludge flocs are compressed by external mechanical force, due to the high hydrophilicity and compressibility of the EPS polymer network structure, a large amount of water in the sludge flocs is still firmly "locked" in the flocs.

[0003] Currently, the commonly used methods for deep sludge dehydration include: (1) deep dehydration after conditioning the sludge with FeCl3+lime, but this method can generally only reduce the sludge moisture content to about 60%, and 80% of the sludge needs to be diluted to 95% with water before conditioning, and the dehydrated filtrate also needs further disposal; (2) anaerobic digestion or deep dehydration after thermal hydrolysis of the sludge, but the dehydration properties of the sludge thermal hydrolysis liquid are unstable and are greatly affected by temperature, season and mud properties.

[0004] Patent CN202010903121.2 discloses a sludge thermal hydrolysis process, which belongs to the sludge pretreatment process. After the sludge is thermally decomposed, although the extracellular polymers can be destroyed to a certain extent and the cellular water can be released, the dehydration capacity of the sludge pyrolyzate is affected by the properties of the sludge and seasonal temperature changes, and it cannot operate stably; Patent CN117342776 B and Patent CN 114804570 B are both aimed at sewage plant sludge. The deep dehydration process of sludge without thermal hydrolysis can generally only reduce the sludge moisture content to about 50% to 60%, and it is very difficult to further dehydrate. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a deep dehydration method of sludge thermal hydrolyzate which can greatly improve the sludge dehydration efficiency and dehydration effect.

[0006] Technical solution: The deep dehydration method of sludge thermal hydrolysis liquid of the present invention comprises the following steps:

[0007] (1) Take the sludge thermal hydrolysis solution and measure its water content;

[0008] (2) adding an iron salt conditioning agent to the sludge thermal hydrolysis solution at a rate of 1 to 4% of the dry weight of the sludge, and then allowing the solution to react after being stirred and kept warm;

[0009] (3) The sludge after heating treatment is transported to the filter press dehydration equipment for deep dehydration to form a mud cake.

[0010] Wherein, in step (1), the preparation process of the sludge thermal hydrolysis liquid is: heating the sludge to 160-200°C for thermal hydrolysis or performing alkaline thermal hydrolysis reaction between the sludge and an alkaline agent at 100-120°C to obtain the sludge thermal hydrolysis liquid; after flash evaporation and heat release, the temperature of the hydrolyzed sludge is 80-100°C; and the water content of the sludge thermal hydrolysis liquid is 80%-85%.

[0011] Wherein, in step (1), the sludge thermal hydrolysis liquid is depressurized and cooled and then transported to the filter press dehydration equipment for dehydration at a temperature of 70 to 80°C.

[0012] Wherein, in step (2), the iron salt conditioning agent is FeCl3 and / or polyferric sulfate.

[0013] Wherein, in step (2), the iron salt conditioning agent is added in a proportion of 1 to 4% by mass ratio: Fe / sludge dry weight*100%.

[0014] Wherein, in step (2), the temperature of the sludge thermal hydrolysis liquid is 80-100°C.

[0015] Wherein, in step (2), after adding the iron salt conditioning agent, the reaction temperature of the sludge thermal hydrolysis liquid is 60-80°C.

[0016] Wherein, in step (2), the insulation temperature is 65-90° C., the stirring time is 20-30 min, the static reaction temperature is 65-90° C., and the static reaction time is 10-20 min.

[0017] Wherein, in step (2), the iron salt conditioning agent is dissolved and then added to the sludge hydrolyzate for thorough mixing and stirring to promote its reaction.

[0018] Wherein, in step (3), the feed pressure in the filter pressing and dehydration process is ≥0.6MPa, and the pressing pressure is ≥1.0MPa, so that the moisture content of the sludge after the filter pressing is reduced to below 45%; preferably, the feed pressure is 0.6-0.8MPa, and the pressing pressure is 1.0-2.0MPa.

[0019] Among them, in step (3), the sludge feeding and conveying can adopt pressure conveying equipment such as air pressure pipeline, plunger pump, screw pump, diaphragm pump, etc.; the sludge dehydration and pressing can adopt diaphragm plate and frame filter press.

[0020] Among them, the filtrate obtained in step (3) is rich in crude protein and has a high COD content, and can be used as a carbon source for sewage treatment plants, greening liquid fertilizer or concentrated protein liquid for resource utilization; the dehydrated water cake can be used as a raw material for biomass fuel, compost and other resources for resource utilization.

[0021] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0022] (1) The present invention aims at the dehydration problem of the hot hydrolyzed liquid obtained by thermal hydrolysis of the residual sludge in the sewage treatment plant. By adding an iron salt conditioning agent to the hot hydrolyzed liquid for reconditioning, and maintaining the temperature at or above 60°C for reaction, and then transporting the hot hydrolyzed liquid to a filter press dehydration device for deep dehydration, the dehydration performance of the sludge can be significantly improved. Compared with the direct dehydration method of the conventional sludge hot hydrolyzed liquid, the present invention can significantly improve the efficiency and effect of the deep dehydration of the sludge, can operate stably and reduce the comprehensive treatment cost of the sludge. (2) The deep dehydration method of sludge provided by the present invention can stably reduce the moisture content of the sludge to below 45%, meeting the moisture content requirement of the sludge self-sustaining incineration required by general thermal power plants. (3) The sludge conditioning and deep dehydration method provided by the present invention is less affected by the season and can operate stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a process flow chart of the deep dehydration method of sludge thermal hydrolysis liquid. DETAILED DESCRIPTION

[0024] The present invention is described in further detail below.

[0025] Example 1

[0026] like Figure 1 As shown, a method for conditioning and deep dehydration of sludge thermal hydrolyzate comprises the following steps:

[0027] (1) Preparation of sludge alkaline hot water pyrolysis liquid: The residual sludge from the municipal sewage treatment plant was conditioned with PAM and then centrifuged to dehydrate to a moisture content of about 80%. Then, 30% of the dry weight of CaO and 2000% of water were added to the sludge, and the temperature was raised to 120°C and kept for 2 h to perform alkaline hot water hydrolysis on the sludge. The alkaline hot water hydrolysis liquid was cooled to 80°C by flash evaporation, and the pH value was 12.6.

[0028] (2) taking the 80° C. sludge alkaline-thermal hydrolysis solution obtained in step (1), and measuring the water content thereof to be 82%;

[0029] (3) adding liquid polyferric sulfate to the sludge alkaline-thermal hydrolyzed solution of step (2) at 3% of the dry weight of the sludge based on the Fe in the liquid polyferric sulfate, i.e., Fe(m) / dry weight of the sludge*100%=3%, stirring for 20 minutes, and maintaining the sludge temperature at 70°C for further reaction for 10 minutes;

[0030] (4) The conditioned sludge was transported to a small diaphragm plate-frame filter press using a diaphragm pump, with a feed pressure of 0.7 MPa, a feed time of 30 min, a pressing pressure of 1.0 MPa, and a pressing time of 30 min. The small plate-frame filter press was turned on, and the mud cake thickness was measured to be 27 mm, and the mud cake moisture content was 42%. The mud cake was transported for disposal, and the filtrate was evaporated and concentrated to form concentrated protein liquid for sale.

[0031] The parameters of this embodiment are shown in Table 1 below.

[0032] Table 1

[0033]

[0034]

[0035] Example 2

[0036] A method for conditioning and deep dehydration of sludge thermal hydrolyzate, comprising the following steps:

[0037] (1) Preparation of sludge alkaline hot water pyrolysis liquid: The residual sludge from the municipal sewage treatment plant was conditioned with PAM and then centrifuged to dehydrate to a moisture content of 80%. Then, 200% of the dry weight of the sludge was added to the sludge with a moisture content of 80%. The temperature was raised to 180°C and kept for 1 hour to perform thermal hydrolysis on the sludge. The thermal hydrolysis liquid was cooled to 90°C by flash evaporation, and the pH value was 6.8.

[0038] (2) taking the above 90°C sludge alkaline-thermal hydrolyzate and measuring the water content to be 83.3%;

[0039] (3) adding liquid polyferric sulfate (in terms of Fe) at 4% of the dry weight of the sludge, stirring for 20 minutes, and maintaining the sludge temperature at 80°C for further reaction for 10 minutes;

[0040] (4) The conditioned sludge was transported to a small diaphragm plate-frame filter press using a diaphragm pump, with a feed pressure of 0.7 MPa, a feed time of 30 min, a pressing pressure of 1.0 MPa, and a pressing time of 30 min. The small plate-frame filter press was opened, and the thickness of the mud cake was measured to be 25 mm, with a moisture content of 43%. The mud cake was transported for disposal, and the filtrate was concentrated by evaporation to form a concentrated protein liquid for sale.

[0041] The parameters of this embodiment are shown in Table 2 below:

[0042] Table 2

[0043]

[0044]

[0045] Example 3

[0046] On the basis of Example 1, the difference from Example 1 is that the iron salt dosage is adjusted to 1%. The dewatered mud cake thickness is 25 mm, and the mud cake moisture content is 45%. The specific parameters are shown in Table 3 below.

[0047] Table 3

[0048]

[0049] Example 4

[0050] On the basis of Example 1, the difference from Example 1 is that the iron salt dosage is adjusted to 4%. The dewatered mud cake thickness is 28 mm, and the mud cake moisture content is 40%. The parameters are shown in Table 4 below.

[0051] Table 4

[0052]

[0053] Comparative Example 1

[0054] Based on Example 1, the difference from Example 1 is that no iron salt conditioning agent is added. The obtained mud cake has a thickness of 18 mm and a moisture content of 61%. The specific parameters are shown in Table 5 below.

[0055] Table 5

[0056]

[0057]

[0058] Comparative Example 2

[0059] Based on Example 2, the difference from Example 2 is that no iron salt conditioning agent is added. The obtained mud cake has a thickness of 17 mm and a moisture content of 63%. The specific parameters are shown in Table 6 below.

[0060]

[0061] Table 6

[0062] Comparative Example 3

[0063] On the basis of Example 2, the difference from Example 2 is that the hydrolyzed sludge after the alkaline-thermal hydrolysis reaction is cooled to 40°C and then 3% iron salt is added for conditioning. The obtained mud cake has a thickness of 21 mm and a moisture content of 55%. The specific parameters are shown in Table 7 below.

[0064] Table 7

[0065]

[0066] Comparative Example 4

[0067] On the basis of Example 1, the difference from Example 1 is that after adding the iron salt conditioning agent and stirring for 20 minutes, the reaction was not continued under heating conditions. The obtained mud cake had a thickness of 24 mm and a moisture content of 51%. The parameters are shown in Table 8 below.

[0068] Table 8

[0069]

[0070]

[0071] Comparative Example 5

[0072] On the basis of Example 1, the difference from Example 1 is that when the iron salt conditioning agent is added, stirring is not performed, and the reaction is directly carried out at 70° C. for 10 minutes. The obtained mud cake has a thickness of 21 mm and a moisture content of 58%. The parameters are shown in Table 9 below.

[0073] Table 9

[0074]

[0075]

[0076] Compared with Example 1, when no iron salt conditioning agent was added during the secondary conditioning, the mud cake parameters obtained in Comparative Example 1 were 18 mm in thickness and 61% in moisture content; compared with Example 2, when no iron salt conditioning agent was added during the secondary conditioning, the mud cake parameters obtained were 17 mm in thickness and 63% in moisture content; this indicates that when the sludge is conditioned by thermal hydrolysis without adding iron salt, under the same filter press dehydration parameter conditions, the mud cake thickness is reduced by more than 50%, and the mud cake moisture content is increased by about 20%.

[0077] Compared with Example 2, in Comparative Example 3, the hydrolyzed sludge after the alkaline-thermal hydrolysis reaction was cooled to 40°C and then 3% iron salt was added for conditioning, and the dehydrated mud cake thickness was 21 mm and the moisture content was 55%. Compared with Comparative Example 1, the mud cake thickness was reduced by 22% and the moisture content was increased by 13%, indicating that the addition of iron salt to the cooled hydrolyzed sludge for secondary conditioning would significantly reduce its dehydration performance.

[0078] It can be seen from Comparative Examples 4 and 5 that, during the secondary conditioning, the stirring reaction is omitted or the reaction is continued, and the sludge dewatering performance is significantly reduced.

[0079] In summary, it can be seen that the present invention adds iron salt to the hot hydrolyzed sludge for secondary conditioning. The test results show that after adding iron salt to the hydrolyzed sludge at 60°C and above for stirring reaction and continued reaction, the dewatering performance of the sludge can be significantly improved, which greatly improves the efficiency and effect of the sludge dewatering treatment.

Claims

1. A method for deep dehydration of sludge thermal hydrolysis liquid, characterized in that: The following steps are involved: (1) Take the sludge thermal hydrolysis solution and measure its water content; (2) adding an iron salt conditioning agent to the sludge thermal hydrolysis solution at a rate of 1 to 4% of the dry weight of the sludge, and then allowing the solution to react after being stirred and kept warm; (3) The sludge after heating treatment is transported to the filter press dehydration equipment for deep dehydration to form a mud cake.

2. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (2), the iron salt conditioning agent is FeCl3 and / or polyferric sulfate.

3. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (1), the preparation process of the sludge thermal hydrolysis liquid is: heating the sludge to 160-200°C for thermal hydrolysis or performing alkaline thermal hydrolysis reaction between the sludge and an alkaline agent at 100-120°C to obtain hydrolyzed sludge, and after flash evaporation and heat release, the temperature of the hydrolyzed sludge is 80-100°C.

4. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (2), when the iron salt conditioning agent is added, the temperature of the sludge thermal hydrolysis liquid is 60-80°C.

5. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (2), the insulation temperature is 65 to 90° C. and the stirring time is 20 to 30 minutes.

6. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (2), the static reaction temperature is 65 to 90° C., and the static reaction time is 10 to 20 minutes.

7. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (2), the iron salt conditioning agent is dissolved and then added to the sludge thermal hydrolysis solution for thorough mixing and stirring to promote its reaction.

8. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (1), the water content of the sludge thermal hydrolysis liquid is 80% to 85%.

9. The method for deep dehydration of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (1), the sludge thermal hydrolysis liquid is depressurized and cooled and then transported to a filter press dehydration device for dehydration at a temperature of 70 to 80°C.

10. The deep dehydration method of sludge thermal hydrolysis liquid according to claim 1, characterized in that: In step (3), the feed pressure in the filter pressing and dehydration process is ≥0.6MPa, and the pressing pressure is ≥1.0MPa, so that the moisture content of the sludge after the filter pressing is reduced to below 45%.

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