阅读说明：本技术 利用污水污泥和添加剂的固体燃料制造方法 (Method for producing solid fuel by using sewage sludge and additive ) 是由 刘炳瑞 吴和洙 金燦荣 朴元绪 于 2019-06-21 设计创作，主要内容包括：本发明公开一种在污水污泥添加能够提高污水污泥的透气性和成型性的农副产品,从而能够代替煤炭等化石燃料的固体燃料的制造方法。所述利用污水污泥和添加剂的固体燃料制造方法包括：混合污水污泥储藏槽中供应的污水污泥和发酵微生物使其发酵,从而去除污水污泥的恶臭的一次前处理步骤；在所述一次前处理步骤中发酵的污水污泥中作为添加剂混合锯末、农副产品以及返送污泥的二次前处理步骤；搅拌混合有所述农副产品和返送污泥的污水污泥,使污水污泥的有机物发酵的发酵步骤；将经发酵的污水污泥用太阳热进行加热并干燥的步骤；以及将经太阳热干燥的污水污泥投入到预定形状的成型机中压缩成型,制成球团的步骤。(The invention discloses a method for manufacturing solid fuel, which can add agricultural and sideline products capable of improving the air permeability and the formability of sewage sludge into the sewage sludge so as to replace fossil fuel such as coal and the like. The method for manufacturing the solid fuel by using the sewage sludge and the additive comprises the following steps: a primary pretreatment step of mixing the sewage sludge supplied from the sewage sludge storage tank with a fermenting microorganism to ferment the sewage sludge, thereby removing the offensive odor of the sewage sludge; a secondary pretreatment step of mixing sawdust, agricultural and sideline products and returned sludge as an additive in the sewage sludge fermented in the primary pretreatment step; a fermentation step of stirring the sewage sludge mixed with the agricultural and sideline products and the returned sludge to ferment organic matters of the sewage sludge; heating and drying the fermented sewage sludge by using solar heat; and putting the sewage sludge dried by solar heat into a forming machine with a preset shape for compression forming to prepare pellets.)

1. A method for manufacturing a solid fuel using sewage sludge and an additive, comprising:

a primary pretreatment step of mixing sewage sludge supplied from a sewage sludge storage tank with a fermentation microorganism to ferment the same, thereby removing offensive odor of the sewage sludge;

a secondary pretreatment step of mixing sawdust, agricultural and sideline products and returned sludge as an additive in the sewage sludge fermented in the primary pretreatment step;

a fermentation step of stirring the sewage sludge in which the agricultural and sideline products and the returned sludge are mixed, and fermenting organic matter of the sewage sludge;

heating and drying the fermented sewage sludge by using solar heat; and

a step of putting the sewage sludge dried by solar heat into a forming machine with a preset shape to be compressed and formed into pellets,

the size of the sawdust is 1-5 mm, the agricultural and sideline products are selected from the group consisting of fruit branches, straws, chaff and bean seedlings, the diameter of the agricultural and sideline products is less than 5mm, the length of the agricultural and sideline products is 4-8 mm, the returned sludge is the sludge returning part of the sewage sludge fermented in the fermentation step,

in the sewage sludge mixture subjected to the secondary pretreatment step, the content of the sawdust is 10 to 20 wt%, the content of the agricultural and sideline products is 3 to 15 wt%, the content of the return sludge is 20 to 30 wt%, and the remaining component is sewage sludge supplied from the sewage sludge storage tank.

2. The method for producing a solid fuel using sewage sludge and an additive according to claim 1, wherein the agricultural and sideline products are fruit tree branches or straw.

3. The method for manufacturing a solid fuel using sewage sludge and an additive according to claim 1, wherein the size of the sawdust is 2 to 4mm, and the length of the agricultural byproduct is 5 to 8 mm.

4. The method for producing a solid fuel using sewage sludge and an additive according to claim 1, wherein a water content of the sewage sludge supplied from the sewage sludge storage tank is 75 to 85 wt% or more, a water content of the fermented sewage sludge subjected to the primary pretreatment step is 75 to 85 wt%, a water content of the fermented sewage sludge mixture subjected to the secondary pretreatment step is 60 to 65 wt%, a water content of the sewage sludge subjected to the fermentation step is 40 to 55 wt%, a water content of the sewage sludge subjected to the drying in the primary drying step is 10 to 20 wt%, and a water content of the sewage sludge subjected to the pelletizing step is 10 wt% or less.

Technical Field

The present invention relates to a method for producing a solid (solid) fuel using sewage sludge and an additive, and more particularly, to a method for producing a solid fuel by adding an additive capable of improving the air permeability and moldability of sewage sludge to sewage sludge and substituting for fossil fuels such as coal.

Background

Sewage sludge is sludge of suspended matter (solid matter) of treated water such as corpses on which microorganisms have precipitated in a sewage treatment process, and is composed of solid matter and water, and usually contains much water in an amount of 90 wt% or more (96 to 98 wt% in the case of the initially precipitated sludge and 99 to 99.5 wt% in the case of the activated sludge). The case in korea is: 625 public sewage treatment facilities (500 m) all over the country³Over one day), 93 plants operated with sewage sludge treatment facilities and produced 384 million tons (2015 standard) of sewage sludge per year. According to the statistics of the environmental part in 2015, the daily average current use of sewage and sludge is as follows: at the whole 480,593m³In one day, the daily life of the product is 236,222m³Day (49.1%) and power generation 79,814m³Per day (16.6%), sale at 117,941m³Per day (24.5%), others account for 46,615m³Day (9.7%), etc. The sewage sludge contains about 80 wt% of water even after the dehydration process for removing water, and 45 to 60 wt% of the remaining solid portion is organic matter; therefore, there are problems that it is difficult to treat the water and organic substances, and much cost is required for the treatment of the water and organic substances. In addition, sewage sludge has a problem that the odor is serious in the treatment process, the selected treatment method is strict, and the utilization degree of by-products after treatment is low.

Sewage sludge is composed of inorganic substances and organic substances in addition to water, and organic substances are useful resources having a calorific value similar to that of coal, and therefore, are used as energy sources as a preferred form of treatment for sewage sludge. Therefore, sewage sludge has been treated by methods such as discharging to the ocean, incineration, and solidification, and recently, it has been used as a fuel for a power plant after being dried. On the other hand, the depletion of fossil fuels and the problem of climate change have attracted global attention under the framework convention of climate change in united nations and the kyoto treatise, which has led to an increasing demand for the recycling and energy conservation of organic wastes. In addition, since the water quality regulation of sewage treatment water in korea is also being strengthened, the amount of sludge production is increasing every year. Therefore, international efforts to cope with climate change can be complied with by using sewage sludge as a solid fuel; also, for korea whose energy self-sufficiency is low, this can not only contribute to stable possession of energy resources, but also facilitate utilization of energy having a potentially high value as national natural renewable energy.

Organic sludge such as sewage sludge contains about 50 to 60 wt% of organic matter, and therefore has a very high utility value as fuel, but in order to be used as fuel, it is necessary to reduce the water content from about 80 wt% to 10 wt%. Various technologies have been developed to use organic sludge such as sewage sludge as fuel. A method for uniformly mixing sewage sludge and thermal medium oil to manufacture fuel is disclosed in granted patent No. 10-1433141; the methods of mixing sludge and additives such as waste oil, sawdust, ethylene, slaked lime, anthracite and the like, drying, molding and the like to prepare fuel are disclosed in the issued patent No. 10-1592937, the issued patent No. 10-2012-0023276, the issued patent No. 10-2013-0052846, the issued patent No. 10-1039378 and the issued patent No. 10-0997522; a method for producing fuel coal, in which a mixing step of sewage sludge and an additive, a hot air drying step and a pulverization step are simultaneously performed, is disclosed in laid-open patent publication No. 10-2015-0106561; a method of manufacturing fuel by electro-drying using the sun is disclosed in issued patent No. 10-1095819.

As described above, in the drying of ordinary sewage sludge, a mechanical drying method such as a multistage method or a rotary method (rotation) method is used. However, since fossil fuel is used in the mechanical drying, a lot of drying costs are required, and in the drying process, pollutants are discharged due to generation of offensive odor, condensed water, and the like, resulting in a problem of secondary environmental pollution. In addition, the conventional method for producing a solid fuel using sewage sludge has disadvantages that the fermentation efficiency of sewage sludge is low due to insufficient air permeability of sewage sludge, and that it is difficult to produce a solid fuel in a desired form due to insufficient moldability of sewage sludge.

Disclosure of Invention

The invention aims to provide a method for producing solid fuel by using sewage sludge and additives, which can improve the air permeability and the formability of the sewage sludge in the process of producing the solid fuel by fermenting the sewage sludge.

Another object of the present invention is to provide a method for producing a solid fuel using sewage sludge and an additive, which can greatly reduce energy consumed for fermentation and drying of sewage sludge by enhancing air permeability of sewage sludge to promote fermentation.

Another object of the present invention is to provide a method for producing a solid fuel using sewage sludge and an additive, which can improve the molding strength of sewage sludge and can facilitate molding of a solid fuel.

In order to achieve the above object, the present invention provides a method for manufacturing a solid fuel using sewage sludge and an additive, comprising: a primary pretreatment step of mixing the sewage sludge supplied from the sewage sludge storage tank with a fermenting microorganism to ferment the sewage sludge, thereby removing the offensive odor of the sewage sludge; a secondary pretreatment step of mixing sawdust, agricultural and sideline products and returned sludge as an additive in the sewage sludge fermented in the primary pretreatment step; a fermentation step of stirring the sewage sludge mixed with the agricultural and sideline products and the returned sludge to ferment organic matters of the sewage sludge; heating and drying the fermented sewage sludge by using solar heat; and a step of putting sewage sludge dried by solar heat into a forming machine of a predetermined shape to be compressed and formed into pellets, wherein the size of the sawdust is 1 to 5mm, the agricultural and sideline products are selected from the group consisting of fruit tree branches, rice straws, chaff and bean seedlings, the diameter of the agricultural and sideline products is 5mm or less, the length of the agricultural and sideline products is 4 to 8mm, the return sludge is sludge returning a part of the sewage sludge fermented in the fermentation step, the content of the sawdust in a sewage sludge mixture subjected to the secondary pretreatment step is 10 to 20 wt%, the content of the agricultural and sideline products is 3 to 15 wt%, the content of the return sludge is 20 to 30 wt%, and the remaining components are sewage sludge supplied from a sewage sludge storage tank.

According to the method for manufacturing the solid fuel by using the sewage sludge and the additive, in the process of manufacturing the solid fuel by fermenting the sewage sludge, the fermentation is promoted by improving the air permeability of the sewage sludge, so that the energy consumed in the fermentation and drying of the sewage sludge can be greatly reduced, the forming strength of the sewage sludge can be improved, and the solid fuel can be easily formed.

Drawings

Fig. 1 is a schematic view for explaining a process of mixing, drying and solidifying sewage sludge and additives according to the present invention to manufacture solid fuel.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a flow chart for explaining a method of manufacturing a solid fuel (solid fuel) using sewage sludge and an additive according to the present invention.

As shown in FIG. 1, in order to produce a solid fuel from the sewage sludge according to the present invention, first, the sewage sludge and the fermenting microorganisms are mixed and fermented, thereby performing a primary pretreatment step S10 of removing the offensive odor of the sewage sludge.

The sewage sludge as a raw material of the present invention is used in the primary pretreatment process after the sewage sludge concentrated and dewatered in a sewage treatment plant is transported and stored in a sewage sludge storage tank. The sewage sludge contains water and solids of organic and inorganic substances, the water content of the sewage sludge supplied to the sewage sludge storage tank is about 80 wt%, for example, 75 to 85 wt%, and the organic substance content of the solids of the sewage sludge is 40 wt% or more, preferably 45 to 60 wt%. The sewage sludge contains a large amount of water and organic substances due to a water content of about 80 wt%, even if the sewage sludge is subjected to a dehydration process in a sewage treatment plant, and thus is easily rotten and smells. As the fermentation microorganism used for fermentation and deodorization of sewage sludge, useful fermentation microorganisms capable of reducing harmful bacteria contained in the sewage sludge may be used, and there is no particular limitation; for example, EM active liquid (korean, EM life science research institute product) may be used. The EM active liquid is a combination of one or more Microorganisms that are advantageous to humans and the environment, such as Effective Microorganisms (Effective Microorganisms) of 10 to 100 kinds of Microorganisms, which are combined and cultured among Microorganisms existing in the natural world, including photosynthetic bacteria (absorbing carbon dioxide and hydrogen to generate oxygen), lactic acid bacteria (converting sugars into lactic acid bacteria to inhibit the propagation of harmful bacteria by sterilization), yeast (contributing to fermentation to produce wine and bread, producing Microorganisms and physiologically active substances), and the like.

The EM active solution (product of EM life science research institute, korea) is used by diluting a stock solution with 5 to 10 times (weight ratio) of water (1: 5 to 10). For fermenting sewage sludge, 0.1 to 0.6 parts by weight, preferably 0.4 to 0.5 parts by weight of diluted EM active liquid is charged per 100 parts by weight of sewage sludge. The time for the primary pretreatment of the sewage sludge, i.e., the microbial fermentation, is usually 1 to 3 days, preferably 2 days. Wherein, if the usage amount of the EM active liquid is too small, or the fermentation time is too short, a large malodor may be emitted in the sewage sludge; if the EM active liquid is used in an excessive amount, there are disadvantages in that time and cost required for fermenting sewage sludge are excessive/high due to an increase in moisture content. In the primary pretreatment step S10, the storage amount of sewage sludge in the storage tank for supplying sewage sludge may be different depending on the purpose of use. For example, the storage is performed for 1 to 3 days, and the amount that can be handled within 2 days is preferable. The water content (moisture content) of the fermented sewage sludge subjected to the primary pretreatment step S10 is preferably 75 to 85 wt%. If the water content is too low, it indicates that the sewage sludge is excessively fermented, and if the water content is too high, it indicates that the sewage sludge is insufficiently fermented.

Then, the sewage sludge fermented in the primary pretreatment step is subjected to a secondary pretreatment step S20, and in the secondary pretreatment step S20, sawdust, agricultural and sideline products, and returned sludge are mixed as additives. Sawdust added as a first additive in the sewage sludge is a wood byproduct, and has the effect of improving the air permeability of the sewage sludge; the sawdust has a size (length) of 1 to 5mm, preferably 2 to 4mm, and a water content of 30 wt% or less. Agricultural and sideline products added as a second additive in the sewage sludge have the effect of improving the air permeability and the forming strength of the sewage sludge, and agricultural residues such as crushed fruit tree stems, straws, chaff, bean seedlings and the like can be used, and the fruit tree stems or the straws are preferred. The diameter of the pulverized agricultural residues, i.e., agricultural byproducts is 5mm or less, for example, preferably 1 to 5 mm; a length of 4 to 8mm, preferably 5 to 8mm, more preferably 5 to 6 mm; the water content is 30 wt% or less.

The first and second additives not only increase the air permeability of the sewage sludge to promote fermentation and increase the calorific value of the solid fuel to improve the value of the solid fuel, but also increase the molding strength of the fermented sewage sludge to enable the solid fuel to be easily molded into a desired shape in the next aerobic fermentation step. That is, in the present invention, considering the high viscosity property of sewage sludge, korean agricultural and sideline products rich in natural resources are added as not only the first additive but also the second additive, thereby more smoothly supplying air to sewage sludge to promote fermentation and improving the moldability of fermented sewage sludge and the calorific value as fuel. For example, generally, the lower heating value of sewage sludge is 2500 to 3000kcal/kg, whereas when the second additive is added, the lower heating value is increased to about 4500kcal/kg, thus contributing to an increase in calorific value. The returned sludge added to the sewage sludge is a component that returns a part of the sewage sludge fermented in the next fermentation step and then is introduced in the secondary pretreatment step to promote fermentation of the sewage sludge, and the water content of the returned fermented returned sludge is 45 to 55 wt%.

In the sewage sludge mixture subjected to the secondary pretreatment step, the content of the sawdust is 10 to 20% by weight, preferably 13 to 17% by weight, the content of the agricultural and sideline products is 3 to 15% by weight, preferably 5 to 10% by weight, the total content of the sawdust and the agricultural and sideline products is preferably 30% by weight or less, and the content of the return sludge is 20 to 30% by weight, preferably 23 to 27% by weight. In the sewage-sludge mixture subjected to the secondary pretreatment step, the residual component is sewage sludge supplied from a sewage-sludge storage tank, and the content of the sewage sludge is, for example, 35 to 67 wt%. As described above, when the secondary pretreatment step of mixing sawdust, agricultural and sideline products, and returned sludge as additives in sewage sludge is performed, the water content of the sewage sludge mixture is preferably 60 to 65% by weight. As described above, according to the primary and secondary pretreatment steps S10 and S20, the foul odor of sewage sludge can be reduced, the air permeability can be ensured, and the fermentation in the next process can be promoted.

Then, a fermentation step S30 is performed in which the sewage sludge (sewage sludge mixture subjected to the secondary pretreatment step) in which the agricultural and sideline products and the returned sludge are mixed is stirred and fermented with organic substances of the sewage sludge. The fermentation step S30 is an aerobic fermentation step in which sewage sludge is fermented in the air by aerobic microorganisms, and generally, the fermentation may be performed for 10 to 16 days. In the fermentation step S30, the sewage-sludge mixture is preferably stirred 2 to 4 times a day, wherein air is preferably injected from the bottom of the fermentation tank, and the amount of air injected may be generally 200 to 400 ml/min per 1kg of the sewage-sludge mixture. In the fermentation step S30, the water content of the sewage sludge after completion of the fermentation is usually 40 to 55% by weight, preferably 45 to 55% by weight.

In the fermentation step S30, the stirring of the sewage sludge mixture may be performed by an automatic rotary stirring device equipped with a rotating device. For example, the fermentation step S30 may be performed by installing a rail (rail) at the bottom of the fermentation tank where the fermentation step S30 is performed, and then installing an automatic stirring device on the rail to move back and forth along the rail, thereby stirring the sewage sludge mixture. Preferably, air is injected into the sewage sludge at a lower portion of a fermentation tank for fermenting the sewage sludge mixture, thereby fermenting organic matter in the sewage sludge. An example of the automatic rotary stirring apparatus is disclosed in laid-open patent nos. 10-2018-0025223.

As described above, the fermented sewage sludge is heated by solar heat, thereby completing the primary drying S40. In the drying step S40, the sewage-sludge mixture after fermentation is naturally dried for 1 to 3 days by solar heat without using mechanical drying (hot air or the like) to a water content of 10 to 20% by weight, preferably 13 to 15% by weight. Therefore, fossil fuel is not used at all in the primary drying step S40.

Then, the sewage sludge dried by the primary solar heat is put into a molding machine of a predetermined shape to be compression molded, and pellets are produced S50. If necessary, the pelletized sewage sludge may be further subjected to secondary drying to produce solid fuel S60 having a water content of 10 wt% or less, for example, 7 to 9 wt%. The step S50 of compression molding the sewage sludge and the step S60 of secondary drying may be performed in parallel, i.e., simultaneously, by the drying and molding apparatus. The secondary drying step S60 may be performed by solar heat and/or mechanical drying (hot air), and when the water content of the sewage sludge that is formed into pellets by compression molding is 10 wt% or less, the secondary drying step S60 may be omitted.

According to the method for manufacturing the solid fuel by using the sewage sludge and the additive, in the process of manufacturing the solid fuel by fermenting the sewage sludge, the fermentation is promoted by improving the air permeability of the sewage sludge, so that the energy consumed in the fermentation and drying of the sewage sludge can be greatly reduced, the forming strength of the sewage sludge can be improved, and the solid fuel can be easily formed. In addition, according to the method for manufacturing the solid fuel, the water evaporation is carried out through the microorganisms, the solar heat is used, the use of fossil fuels such as coal and the like can be greatly reduced, the fuel cost is effectively saved, the generation of secondary pollutants such as waste water or air pollutants and the like is greatly reduced, and the method has the advantage of greening the environment. The drying apparatus for pelletizing sewage sludge according to the present invention has been described above with reference to specific examples, however, the present invention is not limited thereto, and various modifications may be made within the scope of the appended claims.