How to use municipal sludge as energy

Abstract

To provide a method for using energy of urban sludge.SOLUTION: A method comprises: a sludge preprocessing step (1) of modifying urban sludge with a chemical, press-feeding the sludge into a plate / frame type filter press, and dehydrating the sludge step-by-step by consecutively performing steps of hot pressing, vacuum negative pressuring and purging until the sludge is dehydrated to reach a moisture content of 30-40%; a sludge granulation step (2) of crushing the sludge from the plate / frame type filter press to obtain sludge granules and, after performing dehumidifying and air cooling to the sludge granules, reducing the moisture content to 25% or less; and a sludge gasification step (3) of subjecting the sludge granules to gasification processing, removing dust from crude gas generated by the gasification, and removing tar to obtain clean gas, and rendering a residual carbon ratio of gasified slag less than 4%. The invention attains efficient detoxication, volume reduction, and energy use of urban sludge by a technique of step-by-step dehydration / drying and gasification to sludge.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of sludge energy utilization, and more particularly to a method for utilizing municipal sludge as energy. [Background technology]

[0002] With the rapid development of the economy, the annual generation of urban sludge in China has already reached 60 million tons in 2020. Sludge has attributes of both resources and pollution sources, as it contains a large amount of organic matter, bacteria, heavy metals, etc. Therefore, conventional sludge treatment methods such as dehydration incineration, composting, landfilling, and building material utilization not only do not fundamentally solve the problem, but also cause secondary pollution of soil, water, and air to a greater or lesser extent. Summary of the Invention [Problem to be solved by the invention]

[0003] In order to solve the problems existing in the prior art, the present invention provides a method for utilizing municipal sludge as energy, which efficiently renders municipal sludge harmless, reduces its volume, and utilizes it as energy by using a technology for stepwise dehydration, drying, and gasification of the sludge. [Means for solving the problem]

[0004] The present invention relates to (1) sludge pretreatment step, in which municipal sludge is modified with chemicals, then pumped into a plate and frame filter press, where it is subjected to a step-by-step drying process, such as hot pressing and vacuum dehumidification, until the sludge has a moisture content of 30% to 40%, and then dried; (2) a sludge granulation step in which the sludge from the plate and frame filter press is crushed to obtain sludge granules, which are then dehumidified and cooled in air to reduce the moisture content to 25% or less; and (3) a sludge gasification step in which the sludge granules are subjected to a suction-type gasification treatment, and the crude gas produced by the gasification is dedusted and detarred to obtain a clean gas, while the residual carbon rate of the gasified slag is reduced to less than 4%.

[0005] In the present invention, the sludge is converted into clean gas that replaces conventional fossil energy by stepwise dehydration, drying, and gasification technology, thereby making the sludge harmless, reducing its volume, and converting it into energy. This technology has great technical advantages over conventional methods of thermal drying and incineration of sludge. That is, by performing stepwise dehydration and drying on the sludge, the efficiency is high, the energy consumption is only 60% of that of conventional thermal drying, and the dehydration and drying process is completely sealed and in a negative pressure state, so there is no dust or odor pollution. The dried sludge is gasified with a small amount of air and at a low temperature, which effectively controls the dust content and the migration amount of heavy metals and suppresses the synthesis of dioxins. Compared to direct incineration, the concentration of pollutants in the flue gas can be reduced by 40 to 60%. The residual carbon rate of the gasified slag (white) produced by gasifying sludge granules is less than 3%, which maximizes the gasification of organic components in the sludge and improves the efficiency of converting sludge into energy. Gasification slag can be used as a raw material to produce eco-friendly building materials without any special processing.

[0006] The basic theoretical basis of the present invention is as follows. By utilizing the principle that the boiling point of water decreases under negative pressure, the sludge is dried stepwise, and then combined with sludge gasification technology, that is, a chemical reaction is carried out under low temperature and low oxygen conditions, so that the gasification reaction can effectively reduce the content of free oxygen, inhibit the oxidation of nitrogen, sulfides and benzene, and suppress the generation of SOx, NOx and dioxins. In addition, the low temperature can effectively suppress the volatilization of heavy metals in the sludge, and reduce the content of heavy metals in the gas fly ash. In the sludge gasification process, the gas flow rate is small, so the amount of fly ash carried by the gas flow can be greatly reduced, and the dust removal load of the gas can be reduced.

[0007] Preferably, the chemical in step (1) is a PAM solution, the sludge has a water content of 80%, and the mass ratio of the sludge to the chemical is 4: 1. The chemical modification mainly serves to enable the aggregation and precipitation of sludge granules, and to improve the dewatering efficiency of the sludge.

[0008] More preferably, the solute content of the PAM solution is 0.2 wt %.

[0009] Preferably, the hot pressing conditions in step (1) are a pressure of 0.8 to 1.6 MPa and a temperature of 60°C to 80°C.

[0010] Preferably, the negative pressure condition in step (1) is −0.08 to −0.09 MPa.

[0011] Preferably, the gasification conditions in step (3) are that air is used as a gasification medium, the equivalence ratio is 0.23 to 0.35, the gasification temperature is 700° C. to 850° C., and an intermittent supply-continuous gasification method is adopted as the gasification method.

[0012] Preferably, the gasification slag produced by gasification in step (3) is discharged by a dry slag discharge method. The dry slag discharge method means that when the gasification slag is discharged, the gasification slag is maintained at a high temperature, and a combustion reaction with air can occur, and the heat from the combustion reaction is returned to the combustion chamber by hot air, so as to greatly reduce the carbon content in the gasification slag and improve the energy utilization efficiency of the sludge granule fuel.

[0013] More preferably, in the dry slag discharge method, specifically, the discharge temperature of the gasification slag is 600°C to 800°C. Effect of the Invention

[0014] Compared with the prior art, the present invention has the following advantages: 1. Saving traditional energy: Using urban sludge to produce sludge granule fuel, improving the energy density and transportation efficiency of sludge, and more efficient gasification technology can realize high-efficiency and clean energy utilization of sludge, thus saving fossil energy. The energy utilization of 1 ton of dried sludge can save 0.18-0.25 tons of standard coal and reduce carbon dioxide emissions by 0.48-0.67 tons. In other words, the use of sludge as energy is fully in line with China's "carbon peak-out and carbon neutral" strategy. 2. Reduction of environmental pollution: Compared with sludge incineration technology, sludge gasification reduces SO x , NO x It is also possible to significantly reduce the generation of dioxins, thereby mitigating the impact of toxic and harmful substances on the environment. 3. Gasification slag can be directly recycled: Compared to conventional pyrolysis gasification technology, the sludge gasification slag produced by this technology has a very low residual carbon rate (less than 4%) and can be directly used to manufacture various eco-friendly building materials. The residual carbon in the gasification slag obtained by conventional pyrolysis gasification technology is generally more than 10%, and the high residual carbon rate prevents the gasification slag from being recycled, so it must be incinerated and decarbonized for subsequent use. [Brief description of the drawings]

[0015] [Figure 1] 1 is a process flow chart of a method for utilizing municipal sludge as energy according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following examples are intended to further illustrate the present invention but are not intended to be limiting thereof.

[0017] Unless otherwise defined, all technical terms used below have the same meaning as those commonly understood by those skilled in the art. The technical terms used herein are only for describing specific examples and are not intended to limit the scope of the present invention. Unless otherwise specified, all experimental materials and reagents described herein are common commercial products in the art.

[0018] The method for utilizing urban sludge as energy according to this embodiment includes the following steps.

[0019] Before energy conversion, urban sludge has dispersed sludge granules and is prone to clogging the filter net, so it requires pretreatment to aggregate the sludge granules to increase the dewatering efficiency of the sludge. The concentrated sludge (water content is about 95%) at the urban sewage treatment plant is modified with chemicals and then pumped to a plate and frame filter press, where it is subjected to the processes of hot pressing (pressure 0.8-1.6Mpa, temperature 60℃-80℃), vacuum negative pressure dehumidification (-0.08--0.09Mpa), and purging in sequence, and the sludge is dehydrated and dried until the water content is 30%-40%. After crushing the sludge from the plate and frame filter press, it is placed in a dry sludge storage tank, which is equipped with a screw conveyor and an upper dehumidification fan to further remove the water in the sludge. The sludge in the dry sludge storage tank is fed to a granulator by a screw conveyor and compacted, and the sludge and the water contained in it are heated (about 80°C) during the compaction and friction process, generating a large amount of water vapor, and after the sludge granules are dehumidified and air-cooled, the water content of the municipal sludge can be reduced to 25% or less. The sludge granules have a high energy density, are easy to transport, and have a calorific value of 7000-10000kJ / kg.

[0020] The sludge granules processed by the above-mentioned stepwise dehydration and drying are treated by gasification technology under gasification conditions of air as the gasification medium, equivalence ratio of 0.23-0.35, and gasification temperature of 700℃-850℃. The gasification process adopts the intermittent supply-continuous gasification method, and the sludge granule fuel is sequentially subjected to the processes of drying, pyrolysis, reduction, and oxidation until the entire gasification is completed, thereby realizing the conversion of the organic components in the sludge into gases such as H2, CO, CH4, and CO2, small molecular hydrocarbon substances, and benzene-based substances (tar). After the crude gas produced by gasification is cleaned and tar is removed, clean gas is obtained, which can be widely applied in fields such as thermal power generation, fuel synthesis, and urban gas supply. The residual carbon rate of the gasification slag is less than 4%, so it can be directly applied to the production of various environmentally friendly building materials. Example 1

[0021] As shown in FIG. 1, the method for utilizing municipal sludge as energy according to the present embodiment includes the following steps. 1. Sludge pretreatment: First, the municipal sludge slurry was modified by adding PAM solution, where the sludge was based on a water content of 80%, the mass ratio of the sludge to the PAM solution was 4:1, and the solute content of the PAM solution was 0.2 wt%. The modified sludge was coagulated and precipitated, and then pumped into a plate and frame filter press, where it was subjected to a hot pressurization process under hot pressurization conditions of pressure: 1.0 MPa and temperature: 70°C, and a vacuum negative pressure dehumidification process under vacuum negative pressure conditions of -0.085 MPa, and the municipal sludge was dried at high temperature to obtain a dried sludge with a water content of less than 40%. Finally, the dried sludge was molded and granulated by a sludge granulator. The dried sludge was crushed uniformly and then sent to the sludge granulator. After the sludge was treated by extrusion molding, vacuum dehumidification and air cooling technology, the sludge granules were sieved by a vibrating sieve to obtain sludge granule fuel (moisture content less than 25%) that meets the actual gasification requirements. 2. Gasification of sludge granule fuel: A suction-type fixed-bed gasification system was used to gasify the sludge granule fuel. Specifically, the sludge granule fuel was intermittently sent to a fixed-bed gasifier, and continuous gasification was performed at a temperature of 800°C using air as the gasification medium (equivalent ratio 0.23-0.26), to obtain a gasified raw gas. Next, the gasified raw gas was purified, including dust removal (removal of solid granules in the fuel gas) and tar removal (liquid tar was ejected into the gasifier through the reflux pipe and gasification was repeated), to obtain a clean gas mainly composed of H2, CO, CH4, CO2, N2, etc. The gasified slag was quantitatively discharged by dry slag discharge (the discharge temperature of the gasified slag was 700°C), and the residual carbon rate of the gasified slag was less than 4%, which can be directly applied to the production of various environmentally friendly building materials. Comparative Example 1

[0022] The sludge was treated in the same manner as in Example 1, except that the concentrated municipal sludge was dried at high temperature after the hot pressurization step under hot pressurization conditions of a pressure of 1.0 MPa and a temperature of 60°C and the purging step. The moisture content of the obtained dried sludge exceeded 40%. Comparative Example 2

[0023] The sludge was treated in the same manner as in Example 1, except that the concentrated municipal sludge was dried at high temperature after a vacuum dehumidification process under a vacuum negative pressure condition of -0.085 MPa and a purging process. The moisture content of the obtained dried sludge exceeded 40%. Comparative Example 3

[0024] Regarding the gasification slag, the sludge was treated in the same manner as in Example 1, except that the slag was discharged using the slag discharge method in conventional pyrolysis gasification technology, i.e., wet slag discharge (wet slag discharge: during slag discharge, the gasification slag is brought into contact with water to rapidly lower the temperature). The residual carbon rate of the gasification slag generally exceeded 10%. Example 2

[0025] The sludge was treated in the same manner as in Example 1, except that the hot pressurization conditions were a pressure of 0.8 MPa and a temperature of 80°C, the vacuum negative pressure conditions were -0.08 MPa, and the gasification conditions were an equivalence ratio of 0.26 to 0.30 and a gasification temperature of 750°C. The residual carbon rate of the gasification slag is less than 3.5%, and it can be directly applied to the production of various environmentally friendly building materials. Example 3

[0026] The sludge was treated in the same manner as in Example 1, except that the hot pressurization conditions were a pressure of 1.6 MPa and a temperature of 60°C, the vacuum negative pressure conditions were -0.09 MPa, and the gasification conditions were an equivalence ratio of 0.30 to 0.32 and a gasification temperature of 850°C. The residual carbon rate of the gasification slag is less than 3%, and it can be directly applied to the production of various environmentally friendly building materials. Example 4

[0027] The sludge was treated in the same manner as in Example 1, except that the hot pressurization conditions were a pressure of 1.2 MPa and a temperature of 75° C., the vacuum negative pressure conditions were -0.09 MPa, and the gasification conditions were an equivalence ratio of 0.32 to 0.35 and a gasification temperature of 700° C. The residual carbon rate of the gasification slag is less than 2.5%, and it can be directly applied to the production of various environmentally friendly building materials.

[0028] The description of the above embodiments is only intended to facilitate understanding of the technical solutions and core ideas of the present invention. Those skilled in the art may make some improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications shall also fall within the patentable scope of the claims of the present invention.

Claims

1. A method for utilizing urban sludge as energy, comprising the steps of: A sludge pretreatment step (1) in which municipal sludge is modified with chemicals to flocculate and settle, then pumped into a plate and frame filter press, where it is gradually dried through successive processes of hot pressing and vacuum dehumidification, until the sludge has a moisture content of 30% to 40%, and then dried; (2) a sludge granulation step, in which the sludge from the plate and frame filter press is crushed to obtain sludge granules, which are then dehumidified and cooled in air, and the moisture content is reduced to 25% or less; (3) a sludge gasification step, in which the sludge granules are gasified, and the crude gas produced by the gasification is dedusted and detarred to obtain a clean gas; The gasification conditions in the step (3) are as follows: air is used as a gasification medium, the equivalence ratio is 0.23 to 0.35, the gasification temperature is 700°C to 850°C, and an intermittent supply-continuous gasification method is adopted as the gasification method; A method for utilizing urban sludge as energy, characterized in that in step (3), the gasification slag produced by the gasification is discharged by a dry slag discharge method, and the dry slag discharge method is a method in which slag is discharged while the slag discharge temperature of the gasification slag is maintained at 600°C to 800°C during the discharge of the gasification slag.

2. 2. The method according to claim 1, wherein the chemical in step (1) is a PAM solution, the sludge is based on a moisture content of 80%, and the mass ratio of the sludge to the chemical is 4:

1.

3. 3. The method of claim 2, wherein the solute content of the PAM solution is 0.2 wt %.

4. 2. The method according to claim 1, wherein the hot pressing conditions in step (1) are a pressure of 0.8-1.6 MPa and a temperature of 60°C-80°C.

5. 2. The method according to claim 1, wherein the negative pressure condition in step (1) is −0.08 to −0.09 MPa.

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