Alkali-thermal hydrolysis process for sludge

Abstract

The invention relates to the technical field of sludge treatment, in particular to a sludge alkali-thermal hydrolysis process, which can be used for treating sludge to obtain a high-protein liquid fertilizer which can meet the fertilizer application requirements of crops, has higher economic value and realizes waste reutilization, and comprises the following steps: (1) mixing water into sludge for dilution, preheating the diluted sludge, and adding the preheated sludge into the sludge for hydrolysis; lime milk is prepared; (2) mixing the preheated sludge, lime milk and saturated steam, and carrying out pyrohydrolysis treatment; (3) carrying out flash evaporation treatment on the sludge subjected to thermal hydrolysis, recovering heat and reducing the temperature of the sludge; (4) carrying out solid-liquid separation on the sludge subjected to flash evaporation, collecting filtrate and dry residues, and composting the dry residues to be used as garden covering soil; (5) treating the collected filtrate, and adding nitric acid to adjust the pH value of the filtrate; and (6) evaporating and concentrating the adjusted filtrate, and then outputting the filtrate to a liquid fertilizer production device to generate a high-protein liquid fertilizer meeting actual requirements, thereby realizing the recycling of sludge nutrients.

Description

Technical Field

[0001] The invention relates to the technical field of sludge treatment, in particular to a sludge alkaline-thermal hydrolysis process. Background Art

[0002] Sludge is a by-product of sewage treatment. It contains toxic and harmful substances and will have a great impact on the environment. It cannot be discharged directly, so it needs to be treated. The existing treatment methods cannot effectively utilize the organic matter in the sludge, resulting in waste of resources. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a sludge alkaline-thermal hydrolysis process, which can obtain high-protein liquid fertilizer after sludge treatment, can meet the fertilization needs of crops, has high economic value, and realizes waste recycling.

[0004] The technical scheme is as follows: a sludge alkaline-thermal hydrolysis process, characterized in that it comprises the following steps: (1) Mixing water into the sludge to dilute it, preheating the diluted sludge, and preparing lime milk; (2) Mixing the preheated sludge, lime milk and saturated steam and subjecting them to thermal hydrolysis treatment; (3) Flash evaporation is performed on the sludge after thermal hydrolysis to recover heat and reduce the sludge temperature; (4) The sludge after flash evaporation is separated into solid and liquid, and the filtrate and dry residue are collected. The dry residue is used for composting and then as garden covering soil; (5) Treating the collected filtrate and adding nitric acid to adjust the pH of the filtrate; (6) The adjusted filtrate is evaporated and concentrated, and then output to the liquid fertilizer production device to produce high-protein liquid fertilizer that meets actual needs, thereby realizing the recovery and utilization of sludge nutrients.

[0005] The method is further characterized in that, in step (1), the sludge having a moisture content of 80% to 82% is diluted to 83% to 84%, preheated to 60° C. to 80° C., and stirred; In step (1), the mass ratio of lime to water is 0.15:1 to 0.17:1; In step (2), the ratio of sludge and lime milk sprayed is 2.5:1, the thermal hydrolysis time is 60-90 minutes, and the thermal hydrolysis temperature is 120-150°C; In step (3), a two-stage flash evaporation device is used, and the temperature of the sludge is reduced to 90-100°C after flash evaporation; In step (5), the pH value of the filtrate is adjusted to 6-7; In step (6), the filtrate is concentrated 16 to 20 times to make the density of the filtrate reach 1.2 to 1.3 g / cm 3 .

[0006] After the present invention is adopted, the sludge is directly mixed and contacted with the hydrolysis agent and steam, and the thermal hydrolysis method is used to make the sludge evenly heated, thereby improving the effect of the alkali thermal hydrolysis of the sludge, so that the organic matter and protein contents of the filtrate after solid-liquid separation reach 2.3% and 2.2% respectively, and the ammonia nitrogen content reaches 1600 mg / L, so that high-protein liquid fertilizer can be produced, the fertilization demand of crops can be met, the economic value is high, and waste recycling is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The organic matter and protein contents of the filtrate produced under different working conditions (the same holding time is controlled, and the reaction temperature is set to 120° C., 130° C., and 150° C.; the same reaction temperature is controlled, and the reaction time is set to 90 minutes, 70 minutes, and 60 minutes) of the present invention; Figure 2 The COD and ammonia nitrogen contents of the filtrate produced under different working conditions (the same holding time is controlled, the reaction temperature is set to 120°C, 130°C, and 150°C; the same reaction temperature is controlled, and the reaction time is set to 90 minutes, 70 minutes, and 60 minutes) of the present invention; Figure 3 It is the moisture content of the mud cake formed by the hydrolyzate produced under different working conditions of the present invention (controlling the same insulation time, the reaction temperature is set to 120°C, 130°C, 150°C; controlling the same reaction temperature, the reaction time is set to 90 minutes, 70 minutes, 60 minutes) under the pilot filter press plate frame (pressing pressure 1.2MPa) and the laboratory small filter press equipment (pressing pressure 0.6MPa); Figure 4 The properties of the protein concentrate produced by the solid-liquid separation system when the filtrate is evaporated and concentrated 16 to 18 times under the conditions of 6.5% sludge hydrolysis agent dosage (based on 80% water content), 120°C thermal hydrolysis temperature, and 90 minutes of holding time are shown in the present invention. DETAILED DESCRIPTION

[0008] Example 1 A sludge alkaline-thermal hydrolysis process comprises the following steps: (1) In the working preheating mud tank, add water to dilute the municipal dewatered sludge with a water content of 80% to 82%, and stir it evenly to make it have good fluidity. Add 850 kg of lime and 5 tons of water in the reagent mixing tank, mix and stir to make lime milk; (2) The homogenized sludge slurry, the prepared lime milk and the purchased saturated steam are mixed at the feed port of the continuous thermal hydrolysis unit through a screw pump and then subjected to thermal hydrolysis reaction. The thermal hydrolysis time is controlled to be 90 minutes by adjusting the flow rate of the sludge, the injection ratio of the sludge to the lime milk is controlled to be 2.5:1 by adjusting the flow rate of the hydrolysis agent, and the thermal hydrolysis temperature is controlled to be 120°C by adjusting the steam flow rate; (3) The hydrolyzed liquid formed after the thermal hydrolysis reaction is transported to a two-stage flash evaporation device to reduce the sludge temperature to 90°C, and the flash steam is directly introduced into the front-end working preheating mud tank; (4) The hydrolyzate after flash evaporation is pumped into a plate and frame filter press for solid-liquid separation. The feed pressure is set to 1.0 MPa, the feed time is set to 90 minutes, the pressing pressure is set to 1.2 MPa, and the pressing time is set to 90 minutes. After the filtrate passes through the filtration device, the water insoluble matter in the filtrate is removed, and the filtrate and dry residue are collected. The dry residue is composted and used as garden mulch.

[0009] (5) Treat the collected filtrate and add nitric acid to adjust the pH of the filtrate.

[0010] (6) The adjusted filtrate is evaporated and concentrated, and then output to the liquid fertilizer production device to produce high-protein liquid fertilizer that meets actual needs, thereby realizing the recovery and utilization of sludge nutrients.

[0011] Example 2 A sludge alkaline-thermal hydrolysis process comprises the following steps: (1) In the working preheating mud tank, add water to dilute the municipal dewatered sludge with a water content of 81% to 83%, and stir it evenly to make it have good fluidity. Add 800 kg of lime and 5 tons of water in the reagent mixing tank, mix and stir to make lime milk; (2) The homogenized sludge slurry, the prepared lime milk and the purchased saturated steam were mixed at the feed port of the continuous thermal hydrolysis unit through a screw pump and then subjected to thermal hydrolysis reaction. The thermal hydrolysis time was controlled to be 70 minutes by adjusting the flow rate of the sludge, the injection ratio of the sludge to the lime milk was controlled to be 2.5:1 by adjusting the flow rate of the hydrolysis agent, and the thermal hydrolysis temperature was controlled to be 130°C by adjusting the steam flow rate; (3) The hydrolyzed liquid formed after the thermal hydrolysis reaction is transported to a two-stage flash evaporation device to reduce the sludge temperature to 90°C, and the flash steam is directly introduced into the front-end working preheating mud tank; (4) The hydrolyzate after flash evaporation is pumped into a plate and frame filter press for solid-liquid separation. The feed pressure is set to 1.0 MPa, the feed time is set to 90 minutes, the pressing pressure is set to 1.2 MPa, and the pressing time is set to 90 minutes. After the filtrate passes through the filtration device, the water insoluble matter in the filtrate is removed, and the filtrate and dry residue are collected. The dry residue is used for composting and then used as garden mulch soil.

[0012] (5) Treat the collected filtrate and add nitric acid to adjust the pH of the filtrate.

[0013] (6) The adjusted filtrate is evaporated and concentrated, and then output to the liquid fertilizer production device to produce high-protein liquid fertilizer that meets actual needs, thereby realizing the recovery and utilization of sludge nutrients.

[0014] Example 3 A sludge alkaline-thermal hydrolysis process comprises the following steps: (1) In the working preheating mud tank, add water to dilute the municipal dewatered sludge with a water content of 82% to 84%, and stir it evenly to make it have good fluidity. Add 750 kg of lime and 5 tons of water in the reagent mixing tank, mix and stir to make lime milk; (2) The homogenized sludge slurry, the prepared lime milk and the purchased saturated steam are mixed at the feed port of the continuous thermal hydrolysis unit through a screw pump and then subjected to thermal hydrolysis reaction. The thermal hydrolysis time is controlled to be 60 minutes by adjusting the flow rate of the sludge, the injection ratio of the sludge and the lime milk is controlled to be 2.5:1 by adjusting the flow rate of the hydrolysis agent, and the thermal hydrolysis temperature is controlled to be 150°C by adjusting the steam flow rate; (3) The hydrolyzed liquid formed after the thermal hydrolysis reaction is transported to a two-stage flash evaporation device to reduce the sludge temperature to 100°C, and the flash steam is directly introduced into the front-end working preheating mud tank; (4) The hydrolyzate after flash evaporation is pumped into a plate and frame filter press for solid-liquid separation. The feed pressure is set to 1.0 MPa, the feed time is set to 90 minutes, the pressing pressure is set to 1.2 MPa, and the pressing time is set to 90 minutes. After the filtrate passes through the filtration device, the water insoluble matter in the filtrate is removed, and the filtrate and dry residue are collected. The dry residue is used for composting and then used as garden mulch soil.

[0015] (5) Treat the collected filtrate and add nitric acid to adjust the pH of the filtrate.

[0016] (6) The adjusted filtrate is evaporated and concentrated, and then output to the liquid fertilizer production device to produce high-protein liquid fertilizer that meets actual needs, thereby realizing the recovery and utilization of sludge nutrients.

[0017] The experimental data are as follows: Under different thermal hydrolysis temperatures and holding times, the properties of the filtrate after sludge hydrolysis and the moisture content of the dry residue are as shown in the attached figure. Figures 1 to 3 The properties of the protein concentrate are shown in the attached Figure 4As shown. When the lime addition amount is 6.5% of the wet sludge, the thermal hydrolysis temperature is 150°C, and the insulation time is 60 minutes, the organic matter content of the filtrate produced by the solid-liquid separation system reaches 2.43%, the protein content reaches 2.32%, the ammonia nitrogen content reaches 2166 mg / L, and the moisture content of the dry residue reaches 37.72%. After the filtrate is acidified and concentrated 17 times, the density reaches 1.29 g / cm3, the organic matter content reaches 26.44%, and the free amino acid content is greater than 30 g / L. Applying it to the soil can increase soil organic matter, improve the quality of cultivated land, improve the root environment of crops, and promote the absorption and utilization of nutrients by crops. Therefore, the present invention solves the technical problems of incomplete hydrolysis of municipal sludge and poor solid-liquid separation effect, achieves the improvement of the fertilizer efficiency of liquid fertilizer and the reduction of the moisture content of dry residue, and realizes the efficient resource utilization of sludge.

Claims

1. A sludge alkaline-thermal hydrolysis process, characterized in that: It includes the following steps: (1) Mixing water into the sludge to dilute it, preheating the diluted sludge, and preparing lime milk; (2) Mixing the preheated sludge, lime milk and saturated steam and subjecting them to thermal hydrolysis treatment; (3) Flash evaporation is performed on the sludge after thermal hydrolysis to recover heat and reduce the sludge temperature; (4) The sludge after flash evaporation is separated into solid and liquid, and the filtrate and dry residue are collected. The dry residue is used for composting and then as garden covering soil; (5) Treating the collected filtrate and adding nitric acid to adjust the pH of the filtrate; (6) The adjusted filtrate is evaporated and concentrated, and then output to the liquid fertilizer production device to produce high-protein liquid fertilizer that meets actual needs, thereby realizing the recovery and utilization of sludge nutrients.

2. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1), the sludge with a moisture content of 80% to 82% is diluted to 83% to 84%, preheated to 60° C. to 80° C., and stirred.

3. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1), in step (1), the mass ratio of lime to water is 0.15:1 to 0.17:

1.

4. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1) and step (2), the ratio of sludge and lime milk sprayed is 2.5:1, the thermal hydrolysis time is 60-90 minutes, and the thermal hydrolysis temperature is 120-150°C.

5. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1) and step (3), a two-stage flash evaporation device is used, and the temperature of the sludge drops to 90-100°C after flash evaporation.

6. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1) and step (5), the pH value of the filtrate is adjusted to 6-7.

7. A sludge alkaline-thermal hydrolysis process according to claim 1, characterized in that: In step (1) and step (6), the filtrate is concentrated 16 to 20 times to a density of 1.2 to 1.3 g / cm 3 .

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