CN114752423A - Activated sludge biomass fuel and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of environmental protection, and discloses an activated sludge biomass fuel and a preparation method thereof, wherein in step 1, dried activated sludge is carbonized at the temperature of 900-1100 ℃ in an oxygen-free atmosphere; and 2, crushing the activated sludge carbonized in the step 1, mixing the crushed activated sludge with crushed biomass waste, and performing extrusion forming to obtain the activated sludge biomass fuel. According to the invention, the carbonization temperature of the activated sludge is controlled in an oxygen-free atmosphere, so that the generation of short-chain chlorinated hydrocarbons is reduced, and the generation of dioxin precursors is reduced from the source; the carbonized activated sludge is mixed with biomass waste to prepare the formed biomass fuel with high heat value, and the toxicity equivalent of dioxin generated by the fuel is lower than 0.01ng TEQ/Nm³Is far lower than the national standard, and the whole preparation process is simple and convenient and is suitable for industrialization.

Description

A kind of activated sludge biomass fuel and preparation method thereof

technical field

The invention relates to the technical field of environmental protection, in particular to an activated sludge biomass fuel and a preparation method thereof.

Background technique

Activated sludge is a type of solid waste discharged from sewage treatment plants. Activated sludge is composed of microorganisms (mainly bacteria) and organic and inorganic substances adsorbed and glued together, generally carrying pathogenic bacteria, heavy metals, parasite eggs and refractory organic substances. Because the urban sewage treatment plant mainly receives and treats domestic sewage, the activated sludge discharged contains relatively few heavy metals and refractory organic matter. The disposal methods of activated sludge include landfill, incineration, agricultural utilization, forestry utilization, building materials utilization, etc., as well as some uncommon technical routes, such as the preparation of adsorbents and the preparation of combustible gas by pyrolysis.

Activated sludge landfill disposal, agricultural utilization and forestry utilization bring the risk of secondary pollution, especially groundwater pollution. There is a problem of the emission of dioxin-like gaseous pollutants in incineration disposal, and some dioxins are highly toxic gaseous pollutants. These disposal methods have the above shortcomings, which prompts people to research and develop activated sludge carbonization technology. For example, in the 1990s, about 80% of activated sludge was disposed of by combustion. In order to reduce the emission of dioxin-like gas pollutants, expensive technological processes had to be added to suppress and remove dioxins, as disclosed in CN 102689898 A A method for continuously producing activated carbon from activated sludge has high equipment requirements and complicated technological process.

Recycling is the general direction of activated sludge disposal. The dry basis calorific value of activated sludge is 800-1100kCal/kg, and the calorific value is low when used directly as a fuel. When activated sludge is mixed with agricultural and forestry biomass wastes (such as straw, sawdust, bamboo and wood waste), it not only co-processes agricultural and forestry biomass wastes, but also produces biomass fuels with high calorific value. At the same time as the energy in the mud, the energy of the agricultural and forestry biomass waste is recovered. Therefore, the preparation of biomass fuel from activated sludge mixed with agricultural and forestry biomass waste is a better way to recycle activated sludge.

For example, CN102942978A discloses a method for producing sludge biomass fuel, which is mixed with organic water-containing sludge and biomass raw materials, and subjected to fermentation and dehydration to produce a new sludge biomass fuel. However, the process is complicated, requires multiple fermentations, and takes a long time to ferment, and because the activated sludge contains a certain amount of chlorinated organic compounds, these chlorinated organic compounds will synthesize dioxins in the fuel process, thus avoiding or reducing activated pollution. The production of dioxins from mud biomass fuel is the key technical problem to be solved.

SUMMARY OF THE INVENTION

In order to solve the problems of difficult disposal of activated sludge, recycling of resources, and easy generation of harmful substances such as dioxins, the present invention provides a preparation method of activated sludge biomass fuel. The dioxin emission during use is low, the preparation process is simple and the cost is low.

For achieving the above object, the technical scheme adopted in the present invention is:

A preparation method of activated sludge biomass fuel, comprising the steps:

Step 1, in an oxygen-free atmosphere, carbonize the dried activated sludge at 900-1100°C;

In step 2, the activated sludge carbonized in step 1 is pulverized, mixed with the pulverized biomass waste, and extruded to obtain the activated sludge biomass fuel.

There are two main mechanisms by which dioxins are produced. (1) High temperature homogeneous reaction mechanism: Under the high temperature condition of 500-800 °C, the organic solid waste incineration process will produce products of incomplete combustion (PIC). When the chlorides in the organic solid waste are completely burned, Cl ₂ and Cl · radicals are generated. Cl ₂ and Cl · radicals react with PIC again, that is, the chlorination process of PIC. The chlorination and oxidation of PIC are competitive. When the temperature is low, the chlorination reaction is dominant to generate chlorinated PIC, including chlorobenzene, phenoxy and other precursors, and then through the condensation reaction to generate dioxin, the reaction pathway As shown in Figure 1. (2) Low-temperature heterogeneous catalytic reaction mechanism, including (a) de novo synthesis reaction: in the range of 200-400 °C, the incompletely burned carbonaceous substrate undergoes elementary reaction under the action of elements such as oxygen and chlorine to generate dioxins ; (b) Precursor generation reaction: When the temperature in the later stage of combustion drops to the range of 200-450 °C, under the catalysis of fly ash and metal ions, chlorinated organic precursors generate dioxins.

Therefore, in the present invention, for activated sludge, carbonization is carried out at a high temperature of 900-1100 ° C, avoiding the temperature region of dioxin production, and greatly reducing the amount of activated sludge incineration or mixing other biomass incineration processes to synthesize dioxins. It is carried out under anaerobic conditions, in which organic matter is carbonized, which preserves the calorific value of activated sludge and improves its recycling rate. After carbonization, activated sludge and agricultural and forestry biomass waste go through the processes of pulverization, uniform mixing, extrusion molding and cutting to obtain molded biomass fuel. The fuel has high calorific value and significantly reduces dioxin emissions during subsequent combustion and use. quantity, and at the same time convenient for storage and transportation.

Preferably, the carbonization time in step 1 is 30min-2h. Too short carbonization time is not conducive to reducing dioxin emissions when the finished product is burned.

Preferably, the mass ratio of activated sludge to biomass waste in step 2 is 1-1.5:2-4.

The carbonized activated sludge is pulverized to a particle size of 0.1-3mm; the particle size of the pulverized biomass waste is 0.1-3mm.

The biomass waste includes at least one of sawdust, bamboo and wood waste, straw, garden pruning and the like.

The activated sludge biomass fuel is cylindrical with a diameter of 1-10 cm and a length of 5-100 cm.

^The present invention also provides ^{biomass fuel} prepared according to the preparation method. ; The comprehensive combustion performance index is 2.61-5.22×10 ^-7 % ² ·min ² ·K ³ .

The toxic equivalent of dioxins produced by the combustion of the biomass fuel is lower than 0.01ng TEQ/Nm ³ , which is far lower than China's "Standard for Pollution Control of Domestic Waste Incineration (GB18485-2014)" and the EU's "Directive 2000/76/EC of theEuropean" Parliament and of the Council of 4December 2000 on the Incineration of Waste Directive set a limit of 0.1ng TEQ/Nm ³ for dioxin emissions.

Further preferably, in the actual production and application of the present invention, the toxic equivalent of dioxins produced by the combustion of the biomass fuel can be controlled at 0.001-0.004ng TEQ/Nm ³ , which shows the effect of the method of the present invention on reducing dioxin emissions. Significantly.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Compared with the method of controlling the emission of dioxins through process suppression and terminal treatment in the fuel combustion process in the prior art, the present invention only controls the temperature of activated sludge carbonization by carbonization under anaerobic conditions and atmosphere, avoid the temperature range of low-temperature heterogeneous catalysis to generate dioxins, reduce the generation of short-chain chlorinated hydrocarbons, and reduce the generation of dioxin precursors from the source; the carbonized activated sludge is mixed with biomass waste to prepare a High calorific value, shaped biomass fuel.

(2) The molding method of biomass fuel in the present invention is extrusion molding, because the tar substances produced in the carbonization process have a good bonding effect, no external binder is required, and the cost and process complexity are reduced.

(3) The toxic equivalent of dioxin produced by the combustion of biomass fuel prepared by the present invention is lower than 0.01ng TEQ/Nm ³ , which is far lower than the emission limit of dioxin in the national standard, and the whole preparation process is simple and convenient, suitable for Industrialized and industrial production has been achieved, with good results.

Description of drawings

Figure 1 shows a possible pathway for the formation of dioxins in the high temperature gas phase.

FIG. 2 is a schematic diagram of the preparation process flow of activated sludge biomass fuel.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. Those skilled in the art can make modifications or equivalent replacements on the basis of understanding the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, and all should be included within the protection scope of the present invention.

In the following specific embodiments, the activated sludge comes from the sludge workshop of the Chengdong Sewage Treatment Plant in Jiande City, Zhejiang Province, and the biomass fuel includes sawdust, bamboo and wood waste, straw, garden pruning and the like.

Example 1

The schematic diagram of the preparation process of biomass fuel is shown in Figure 2. Under anaerobic conditions, the dried activated sludge is fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature is 900 °C, and the carbonization time 2h, carbonized activated sludge was obtained. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel is normally burned in the boiler, and the measured dioxin toxicity equivalent in the flue gas is 0.001ng TEQ/Nm ³ .

Comparative Example 1

Under aerobic conditions, the dried activated sludge is fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature is 900°C and the carbonization time is 2h to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The formed biomass fuel was normally burned in the boiler, and the TEQ of dioxin was measured to be 0.43ng TEQ/Nm ³ . It can be seen that the amount of dioxin released by biomass fuel prepared from activated sludge under aerobic conditions is still not low.

Example 2

Under anaerobic conditions, the dried activated sludge is fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature is 1000°C and the carbonization time is 2h to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel was normally burned in the boiler, and the TEQ of dioxin was measured to be 0.002ng TEQ/Nm ³ .

Comparative Example 2

Under anaerobic conditions, the dried activated sludge was fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature was 400°C and the carbonization time was 2h to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel was normally burned in the boiler, and the TEQ of dioxin was measured to be 0.013ng TEQ/Nm ³ .

Example 3

Under anaerobic conditions, the dried activated sludge is fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature is 900°C and the carbonization time is 1h to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel was normally burned in the boiler, and the TEQ of dioxin was measured to be 0.003ng TEQ/Nm ³ .

Comparative Example 3

Under anaerobic conditions, the dried activated sludge was fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature was 900°C and the carbonization time was 10min to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry biomass waste powder are respectively transferred to the mixing bin according to the mass ratio of 3:5, and are uniformly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel was normally burned in the boiler, and the TEQ of dioxin was measured to be 0.26ng TEQ/Nm ³ . It can be seen that the carbonization time is too short, and the amount of dioxin released when the biomass fuel prepared by activated sludge is burned is still not low.

Example 4

Under anaerobic conditions, the dried activated sludge is fed into the belt carbonizer from the feed bin located at the front end of the carbonizer. The carbonization temperature is 900°C and the carbonization time is 2h to obtain carbonized activated sludge. The carbonized activated sludge is pulverized to a particle size of 0.1-3.0 mm. Pulverize agricultural and forestry wastes to a particle size of 0.1-3.0 mm. The carbonized activated sludge powder and the agricultural and forestry waste powder are respectively transferred to the mixing bin according to the proportion of 60%, 40% and 20%, and are evenly mixed to obtain the mixture. The mixed material is conveyed to the screw molding machine, and the mixed material is extruded by controlling the advancing speed of the screw. The mixed material is output from the screw heating molding machine and enters the cutting machine to obtain molding biomass fuel. The shaped biomass fuel was normally burned in the boiler, and the test results are shown in Table 1.

The ignition temperature reflects the difficulty of the fuel ignition and the initial combustion reaction. The lower the ignition temperature, the easier the fuel is to ignite and the better the ignition performance. It can be seen from Table 1 that the ignition temperature of activated sludge is 246 °C, the ignition temperature of wood chips is 298 °C, and the ignition temperature of molded biomass fuel (283-298 °C) gradually increases as the proportion of activated sludge decreases. The ignition temperature of molded biomass fuel is closely related to the type of volatiles it contains. The volatiles in activated sludge are mainly fats, proteins and sugars, and CO in activated sludge can convert refractory volatiles into It is easy to decompose volatile matter, which reduces the ignition temperature of activated sludge. The volatile components in wood chips are mainly cellulose, hemicellulose and lignin which are difficult to decompose. Therefore, the ignition temperature of wood chips is relatively high. With the increase of the proportion of activated sludge, the ignition temperature of the briquette fuel is getting lower and lower, because the volatile matter of the activated sludge can be precipitated and burned at a lower temperature, which improves the ignition performance of the briquette fuel.

The burnout temperature is an important parameter to reflect the burnout characteristics of the fuel. The lower the burnout temperature, the easier the fuel burns out. It can be seen from Table 1 that the burnout temperature of the molded biomass fuel increases with the increase of the proportion of activated sludge, indicating that wood chips are more easily burnt out than activated sludge, because the activated sludge contains difficult-to-burn organic matter and Inorganic salts.

Although the ignition temperature can directly reflect the ignition characteristics of the fuel combustion process, it is not enough to reflect the reaction ability of the fuel in the early stage of combustion. Therefore, the concept of the flammability index C is introduced, and the definition C=(dw/dt) _max /T _i ² . The higher the flammability index, the better the ignition stability of the fuel. The flammability index showed that with the increase of activated sludge proportion, the ignition stability of shaped biomass fuel became worse.

In order to comprehensively evaluate the combustion of the formed biomass fuel, the comprehensive combustion performance index Sw is used to evaluate the combustion performance of the fuel, and the definition Sw=(dw/dt) _max ·(dw/dt) _mean /(T _i ² ·T _h ) . The comprehensive combustion performance index reflects the combustion situation of the sludge from ignition to burnout. The larger the comprehensive combustion performance index, the better the combustion performance of the fuel. With the increase of wood chip content, the comprehensive combustion characteristics index of the fuel increased gradually, indicating that the addition of wood chips improved the overall combustion performance of the briquette fuel.

Although the TEQ of dioxin gradually increased with the proportion of activated sludge, the value was still lower than the 0.01ng TEQ/Nm ³ required by the national standard.

Combustion performance of biomass fuel prepared in Example 4 of Table 1

Claims (9)

1. The preparation method of the activated sludge biomass fuel is characterized by comprising the following steps:

Step 1, carbonizing dried activated sludge at the temperature of 900-1100 ℃ in an oxygen-free atmosphere;

and 2, crushing the activated sludge carbonized in the step 1, mixing the crushed activated sludge with crushed biomass waste, and performing extrusion forming to obtain the activated sludge biomass fuel.

2. The method for preparing the activated sludge biomass fuel according to claim 1, wherein the carbonization time in step 1 is 30min-2 h.

3. The method for preparing the activated sludge biomass fuel according to claim 1, wherein the mass ratio of the activated sludge to the biomass waste in the step 2 is 1-1.5: 2-4.

4. The method for preparing the activated sludge biomass fuel according to claim 1, wherein the carbonized activated sludge is pulverized to have a particle size of 0.1 to 3 mm; the particle size of the crushed biomass waste is 0.1-3 mm.

5. The preparation method of the activated sludge biomass fuel according to claim 1, wherein the biomass waste comprises at least one of sawdust, bamboo wood waste, straw and garden pruning.

6. The method for preparing the activated sludge biomass fuel according to claim 1, wherein the activated sludge biomass fuel is in a columnar shape with the diameter of 1-10 cm and the length of 5-100 cm.

7. The biomass fuel produced by the production method according to any one of claims 1 to 6.

8. The biomass fuel as claimed in claim 7, wherein the biomass fuel has a heat value of 10487-16722 kJ-kg^-1Flammability index of 6.88-12.92X 10^-5％·min·K²(ii) a The comprehensive combustion performance index is 2.61-5.22 x 10^-7％²·min²·K³。

9. The biomass fuel according to claim 7, wherein the toxic equivalent of dioxin in flue gas generated by combustion of the biomass fuel is less than 0.01ng TEQ/Nm³。

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