Method and system for preparing granular fuel by coupling sludge drying with slime moisture adjustment

Abstract

The present application provides a kind of sludge drying coupling slime moisture preparation granular fuel method, comprising the following steps: drying: wet sludge and low pressure steam are carried out intermittent heat exchange, and the water content of the dried sludge is 20%~25%; Mixed granulation: the dried sludge is mixed with wet slime and granulated, and the water content of the cylindrical particle is 25%~35%, 3~7mm; Moisture adjustment: in low temperature flue gas, the water content of the cylindrical particle is adjusted to 12%~15%, and the granular fuel is obtained. The method uses wet sludge and low pressure steam to carry out intermittent heat exchange, effectively dries the sludge, then mixes the obtained dry sludge with wet slime and granulates, improves the efficient use of slime, fully utilizes the characteristics of sludge and slime, and obtains granular fuel by combining low temperature drying and moisture adjustment. Low temperature drying and moisture adjustment granular fuel, small dust emission, and friendly to the external environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sludge and coal slime drying, in particular to a method and system for preparing granular fuel by coupling sludge drying with coal slime moisture adjustment. BACKGROUND

[0002] A large amount of sludge is often generated in sewage treatment plants, petrochemical, printing and dyeing industries, etc. The sludge is in the form of black or black-brown flocculation body in fluid, semi-fluid or mud cake. The sewage in sewage plants can obtain sludge with a water content of 65%-85% after centrifugation or pressure filtration. The organic matter in the sludge has a certain calorific value, and can be used for power generation after drying to a water content of 20%-25%. However, the traditional natural ventilation drying or heating drying can only surface dry, and cannot dehydrate and dry the inside, which is high in cost and time-consuming.

[0003] Coal slime is a byproduct generated in the washing and selection process of coal, which has the characteristics of high water content (water content of 25%-40%), high viscosity, high water retention and low calorific value, and is therefore difficult to realize industrial application. At present, the recycling of coal slime is mostly by the method of blending combustion, i.e. mixing and burning coal slime and coal powder. In order to avoid the introduction of too much water by coal slime, the coal slime needs to be dried first. After drying treatment, the water content of the coal slime can be reduced to about 12%, but the coal slime drying process needs pre-crushing, scattering and anti-wall sticking, which is relatively cumbersome. In addition, the coal slime drying process is prone to produce a large amount of fine powder, causing pollution.

[0004] Therefore, if the sludge can be effectively dried and the efficient utilization of coal slime can be improved, it will have great practical significance. SUMMARY

[0005] Therefore, the present application provides a method for preparing granular fuel by coupling sludge drying with coal slime moisture adjustment. The method uses intermittent heat exchange between wet sludge and low-pressure steam to effectively dry the sludge, and then mixes and granulates the obtained dry sludge with wet coal slime to improve the efficient utilization of coal slime, fully utilize the characteristics of the two materials of sludge and coal slime, and obtain granular fuel by low-temperature drying and moisture adjustment. The low-temperature drying and moisture adjustment granular fuel has small dust emission and is environmentally friendly.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A method for preparing granular fuel by coupling sludge drying with coal slime moisture adjustment, comprising the following steps:

[0008] Drying: intermittent heat exchange between wet sludge and low-pressure steam to obtain dry sludge with a water content of 20%-25%;

[0009] Mixing granulation: the dry sludge is mixed and granulated with the wet coal slime, to obtain columnar particles with water content of 25%-35% and 3-7mm;

[0010] Moisture adjustment: in low-temperature flue gas, the water content of the columnar particles is adjusted to 12%-15%, to obtain the granular fuel.

[0011] In an alternative embodiment, the pressure of the low-pressure steam is 0.3-1.0MPa.

[0012] In an alternative embodiment, the mass ratio of the dry sludge to the wet coal slime is 1:1-2:1.

[0013] In an alternative embodiment, the temperature of the low-temperature flue gas is 120-150℃.

[0014] In an alternative embodiment, the water content of the wet sludge is 65%-85%, and the water content of the wet coal slime is 25%-40%.

[0015] In an alternative embodiment, the tail gas in the drying step and / or the moisture adjustment step is transported to a tail gas treatment center.

[0016] The application also provides a system for preparing granular fuel by coupling sludge drying and coal slime moisture adjustment, comprising a first dryer, a mixer, a granulator and a second dryer which are sequentially connected;

[0017] The first dryer is selected from any one of paddle type, disc type and film type.

[0018] The second dryer is selected from moisture adjustment roller type.

[0019] In an alternative embodiment, the dryer of the moisture adjustment roller type is internally provided with a spiral belt flow channel, which can control and prolong the drying and moisture adjustment time of the material in the moisture adjustment roller type dryer, and reduce the broken particles.

[0020] In an alternative embodiment, the first dryer and / or the second dryer is connected with a tail gas treatment center through an induced draft fan.

[0021] In an alternative embodiment, the mixer is selected from a double-shaft mixer, and the granulator is selected from an extrusion granulator.

[0022] In an alternative embodiment, one end of the first dryer is provided with a wet sludge inlet, the other end is provided with a low-pressure steam inlet, the top is provided with a tail gas outlet, the bottom is provided with a discharge valve, and the end opposite to the low-pressure steam inlet is provided with a steam condensate outlet.

[0023] In an alternative embodiment, the mixing machine is provided with a dry sludge inlet and a wet coal sludge inlet respectively, the discharge valve of the first drying machine is communicated with the dry sludge inlet; the bottom of the mixing machine is provided with a material outlet. Preferably, the dry sludge inlet is located on the side of the wet coal sludge inlet away from the material outlet, and the distance between the dry sludge inlet and the wet coal sludge inlet in the horizontal direction is 200-500 mm.

[0024] In an alternative embodiment, the material outlet of the mixing machine is communicated with the top inlet of the granulator, the bottom outlet of the granulator is communicated with the material inlet of the second drying machine; the bottom of the other end of the second drying machine opposite to the material inlet is provided with a discharge valve.

[0025] In an alternative embodiment, the air blower is communicated with one end of the material inlet of the second drying machine through an air heater, the air heater is provided with a steam inlet and a steam condensate outlet.

[0026] The application also provides a method for preparing granular fuel by using the above system, which specifically comprises the following steps:

[0027] Drying: low-pressure steam enters the first drying machine through the low-pressure steam inlet, wet sludge enters the first drying machine through the wet sludge inlet, and the low-pressure steam and the wet sludge perform intermittent heat exchange in the first drying machine to realize drying of the wet sludge, so as to obtain dry sludge with a water content of 20%-25%; the dry sludge is discharged from the discharge valve at the bottom of the first drying machine, and the tail gas after drying is extracted by the induced draft fan to a tail gas treatment center;

[0028] Mixing and granulation: the dry sludge enters the double-shaft mixing machine through the dry sludge inlet, the wet coal sludge enters the double-shaft mixing machine through the wet coal sludge inlet located on the double-shaft mixing machine, the dry sludge and the wet coal sludge are mixed in the double-shaft mixing machine according to a mass ratio of 1:1-2:1, and then the mixed material is discharged from the material outlet at the bottom of the double-shaft mixing machine into the extrusion granulator to perform granulation, so as to obtain columnar particles with a water content of 25%-35% and a size of 3-7 mm;

[0029] Moisture adjustment: the columnar particles enter the screw-belt type drum dryer (i.e. a moisture adjustment drum dryer provided with a screw belt flow channel inside), flue gas is pressurized to 4-8 kPaG by the air blower, heated to 120-150℃ by the heater, and then enters the screw-belt type drum dryer, the columnar particles move in plug flow in the screw-belt type drum dryer along the screw belt inside the drum dryer to adjust the moisture of the columnar particles; by controlling the residence time of the particles, the water content of the particles is controlled to be about 12%-15% for solidification, the particles after moisture adjustment and drying are discharged from the discharge valve at the bottom, and the tail gas is extracted by the induced draft fan to a tail gas treatment center.

[0030] The percentages above are mass percentages.

[0031] Advantages

[0032] 1. The prior art generally uses low-temperature preheating to obtain dried sludge with a moisture content of 20-30%, and then adds coal slime and pretreated straw powder into the dried sludge, and granulates the mixture by a granulator to obtain granular fuel. However, this method has the following problems: (1) the ratio of coal slime, straw powder and dried sludge is difficult to control, and the granular fuel obtained is too dry and easy to be loose, the power of the granulator is large, and the surface is easy to weather and dust, and the granular fuel is too wet and easy to deform; (2) the process of treating coal slime, pretreated straw powder and dried sludge is complex, lime needs to be added in the sludge dewatering process, and straw needs to be added in the granulation process, the application range is narrow, and the method cannot be applied in a large scale; (3) a large amount of low-volatility substances with heat value in the coal slime are wasted due to volatilization.

[0033] In view of the existing sludge drying problem and coal slime recycling problem, the present application provides a method for preparing granular fuel by coupling sludge drying and coal slime moisture adjustment. First, intermittent heat exchange between low-pressure steam and wet sludge is adopted to realize drying of the wet sludge. The dried sludge has a moisture content of 20-25% and has crossed the sticking zone. The dried sludge is relatively loose and has a high heat value. The wet coal slime has a certain stickiness and contains a large amount of low-volatility substances with heat value. The low-temperature drying of the wet coal slime has a large stickiness and a poor drying effect. Therefore, the present application fully combines the characteristics of the wet sludge and the wet coal slime, mixes and granulates the two, and then adjusts the moisture content of the granular fuel by low-temperature drying (adjusting the moisture content by using 120-150℃ low-temperature flue gas to obtain 70-85℃ granular fuel). The method has a mild condition, is not easy to cause dust emission, has a good solidification effect, the low-volatility components in the coal slime are not easy to be discharged, the low-volatility components in the coal slime can be retained, the heat value of the granular fuel can be adjusted, solid waste can be reasonably disposed, and waste can be turned into treasure. Moreover, the low-temperature drying and moisture adjustment of the granular fuel have a small amount of dust emission, are friendly to the external environment, and are energy-saving and environmentally friendly.

[0034] 2. The method for preparing granular fuel by coupling sludge drying and coal slime moisture adjustment provided by the present application can change the heat value of the granular fuel by further adjusting the ratio of dried sludge and wet coal slime, and further expand the application prospect. Moreover, the method can be widely applied in the fields of coupling sludge and lignite or other biomass (for example, biogas residue, animal manure and fermented straw residue) drying to prepare granular fuel, and has a wide application prospect.

[0035] 3、The sludge drying coupling coal slime moisture adjusting method for preparing granular fuel provided by the application relates to common solid wastes, such as coal slime and sludge, and has large output and large continuous processing capacity. Low-temperature drying and moisture adjusting retain low volatile components in the coal slime, and high-calorific-value fuel is obtained, and tail gas can be safely discharged by water washing or cooling. The granules in the moisture adjusting and drying process have controllable time, small particle breakage, small dust amount and small odor, and the operation environment is friendly, and the finally prepared granular fuel has wide application.

[0036] 4、The sludge drying coupling coal slime moisture adjusting system for preparing granular fuel provided by the application uses existing devices, and by combining a first dryer, a mixer, a granulator and a moisture adjusting drum dryer, sludge and wet slime can be effectively combined to form granular fuel, and waste is turned into treasure. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0038] Figure 1 The application provides a sludge drying coupling coal slime moisture adjusting system for preparing granular fuel.

[0039] 1-paddle dryer, 2-paddle dryer discharge valve, 3-sludge drying induced draft fan, 4-double-shaft mixer, 5-extrusion granulator, 6-blower, 7-air heater, 8-moisture adjusting drum dryer, 9-moisture adjusting discharge valve, and 10-moisture adjusting induced draft fan. DETAILED DESCRIPTION

[0040] The application will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application, and those skilled in the art can make some non-essential improvements and adjustments to the application according to the above content of the application.

[0041] If the specific experimental steps or conditions are not specified in the examples, the operations or conditions can be performed according to the conventional experimental steps described in the literature in the art. If the reagents or instruments are not specified by the manufacturer, they are all conventional reagent products that can be obtained by market purchase.

[0042] Example 1

[0043] The example provides a sludge drying coupling coal slime moisture adjusting system for preparing granular fuel, which comprises a first dryer, a mixer, a granulator and a second dryer that are sequentially connected.

[0044] The first dryer can be selected from any one of paddle type, disc type and film type.

[0045] The second dryer is selected from a humidity-adjusting roller type.

[0046] In an embodiment, the humidity-adjusting roller type dryer is internally provided with a spiral belt flow channel, which can prolong the drying and humidity-adjusting time and reduce the broken particles.

[0047] In an embodiment, the first dryer and / or the second dryer is communicated with the tail gas treatment center through an air blower.

[0048] In an embodiment, the mixing machine is selected from a double-shaft mixing machine, and the granulator is selected from an extrusion granulator.

[0049] In an embodiment, the first dryer is provided with a wet sludge inlet at one end, a low-pressure steam inlet at the other end, a tail gas outlet at the top, a discharge valve at the bottom, and a steam condensate outlet at the end opposite to the low-pressure steam inlet.

[0050] In an embodiment, the mixing machine is provided with a dried sludge inlet and a wet coal sludge inlet at the upper part, respectively, the discharge valve of the first dryer is communicated with the dried sludge inlet, and the bottom of the mixing machine is provided with a material outlet. Specifically, the dried sludge inlet is located at the side away from the material outlet of the wet coal sludge inlet, and the distance between the dried sludge inlet and the wet coal sludge inlet in the horizontal direction is 200-500 mm.

[0051] In an embodiment, the material outlet of the mixing machine is communicated with the top inlet of the granulator, the bottom outlet of the granulator is communicated with the material inlet of the second dryer, and the bottom of the other end of the second dryer opposite to the material inlet is provided with a discharge valve.

[0052] In an embodiment, the air blower is communicated with one end of the material inlet of the second dryer through an air heater, and the air heater is provided with a steam inlet and a steam condensate outlet.

[0053] Specifically, as shown in FIG. 1, the system for preparing granular fuel by coupling sludge drying and coal sludge humidity adjustment comprises a paddle type dryer 1, a double-shaft mixing machine 4, an extrusion granulator 5 and a humidity-adjusting roller dryer 8 internally provided with a spiral belt flow channel, which are communicated in sequence. Figure 1

[0054] One end of the paddle type dryer 1 is provided with a wet sludge inlet, the other end is provided with a low-pressure steam inlet, the top is provided with a tail gas outlet (which is communicated with a tail gas treatment center through a sludge drying air blower 3), the bottom is provided with a paddle type dryer discharge valve 2, and the end opposite to the low-pressure steam inlet is provided with a steam condensate outlet.

[0055] ​The double-shaft mixer 4 is provided with a dry sludge inlet and a wet coal slurry inlet, the discharge valve of the paddle dryer 1 is communicated with the dry sludge inlet, and the material outlet at the bottom of the double-shaft mixer 4 is communicated with the top inlet of the extrusion granulator 5. The dry sludge inlet is located at the side away from the wet coal slurry inlet to the material outlet, and the distance between the dry sludge inlet and the wet coal slurry inlet in the horizontal direction is 200-500 mm;

[0056] The bottom outlet of the extrusion granulator 5 is communicated with the material inlet of the humidifying drum dryer 8; the bottom of the other end of the humidifying drum dryer 8 opposite to the material inlet is provided with a humidifying discharge valve 9, and the humidifying drum dryer 8 is communicated with the tail gas treatment center through a humidifying induced draft fan 10. The air heater 7 is communicated with one end of the material inlet of the humidifying drum dryer 8 through the air blower 6, and the air heater 7 is provided with a steam inlet and a steam condensate outlet.

[0057] Example 2

[0058] The embodiment provides a method for preparing granular fuel by using the above system, which comprises the following steps by using the system as shown in the figure: Figure 1 The method comprises the following steps:

[0059] Drying: low-pressure steam with a pressure of 0.3-1.0 MPa enters through a low-pressure steam inlet located at one end of the paddle dryer, wet sludge with a water content of 65%-85% enters through a wet sludge inlet located at the other end of the paddle dryer, then the low-pressure steam and the wet sludge perform intermittent heat exchange in the paddle dryer to realize drying of the wet sludge, and dry sludge with a water content of 20%-25% is obtained; the dry sludge is discharged through a discharge valve at the bottom of the paddle dryer, and the tail gas after drying is extracted to a tail gas treatment center through an induced draft fan;

[0060] Mixing and granulation: the dry sludge enters the double-shaft mixer through the dry sludge inlet, wet coal slurry with a water content of 25%-40% enters the double-shaft mixer through a wet coal slurry inlet located on the double-shaft mixer, the dry sludge and the wet coal slurry are mixed in the double-shaft mixer according to a mass ratio of 1:1-2:1, then the mixed material is discharged through a material outlet at the bottom of the double-shaft mixer and enters the extrusion granulator to perform granulation, and columnar granules with a water content of 25%-35% and a size of 3-7 mm are obtained;

[0061] Humidifying: the columnar granules enter the humidifying drum dryer, flue gas is pressurized to 4-8 kPaG through the air blower, heated to 120-150 DEG C through the air heater, and then enters the humidifying drum dryer to humidify the columnar granules to about 12%-15% solidification, and the columnar granules (i.e. granular fuel) after humidifying are discharged through a bottom discharge valve, and the tail gas is extracted to the tail gas treatment center through an induced draft fan.

[0062] The low-ash coal slime ash content of the granular fuel is 20%~32%, the mixed heat value is 9~17.5 MJ / kg, and the ash content is 30%~45%; the medium-ash coal slime ash content is 30%~50%, the mixed heat value is 6~10 MJ / kg, and the ash content is 38%~60%; the heat value of the biogas residue is 9~15.7 MJ / kg, and the mixed heat value is 5.5~12.5 MJ / kg.

Claims

1. A method for preparing granular fuel by coupling sludge drying with slime moisture adjustment, characterized in that, The method comprises the following steps: drying: the wet sludge is intermittently exchanged with low-pressure steam to obtain dried sludge with water content of 20%-25%; mixing and granulating: the dried sludge is mixed and granulated with wet coal sludge to obtain columnar particles with water content of 25%-35% and particle size of 3-7mm; moistening: the water content of the columnar particles is adjusted to 12%-15% in low-temperature flue gas, thereby obtaining granular fuel with temperature of 70-85℃; the pressure of the low-pressure steam is 0.3-1.0MPa; the mass ratio of the dried sludge to the wet coal sludge is 1:1-2:1; the temperature of the low-temperature flue gas is 120-150℃.

2. The method of claim 1, wherein, the water content of the wet sludge is 65%-85%, and the water content of the wet coal sludge is 25%-40%.

3. The method of claim 1 or 2, wherein, the tail gas in the drying step and / or the moistening step is transported to a tail gas treatment center.

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