Method and system for preparing granular fuel by coupling sludge drying and coal slime humidifying

Abstract

The invention provides a method for preparing granular fuel by coupling sludge drying and coal slime humidifying, which comprises the following steps: drying: carrying out intermittent heat exchange on wet sludge and low-pressure steam to obtain dried sludge with the water content of 20-25%; mixing and granulating: mixing and granulating the dried sludge and wet coal slime to obtain columnar particles of which the water content is 25-35% and the size is 3-7 mm; and humidity adjustment: in low-temperature flue gas, adjusting the water content of the columnar particles to 12%-15% to obtain the granular fuel. According to the method, wet sludge and low-pressure steam are adopted for intermittent heat exchange, sludge is effectively dried, then the obtained dry sludge and wet coal slime are mixed and granulated, the efficient utilization of the coal slime is improved, meanwhile, the characteristics of the sludge and the coal slime are fully played, and the pellet fuel is obtained by combining a low-temperature drying and humidifying method; the low-temperature dry humidifying granular fuel is small in dust discharge amount and friendly to the external environment.

Description

Technical Field

[0001] The invention relates to the field of sludge and coal sludge drying, and in particular to a method and system for preparing granular fuel by coupling sludge drying with coal sludge moisture control. Background Art

[0002] Sewage treatment plants, petrochemicals, printing and dyeing industries often produce a lot of sludge, which is black or dark brown in the form of fluid, semi-fluid, or mud cake flocs. At present, after centrifugation or filter pressing, the sewage from the sewage plant can obtain sludge with a water content of 65% to 85%. The organic matter in it has a certain calorific value. After drying to a water content of 20%-25%, it can be used for combustion and power generation. However, traditional natural ventilation drying or heating drying can only dry the surface, and cannot dehydrate the interior, which is costly and time-consuming.

[0003] Coal slime is a byproduct produced during the coal washing process. It has the characteristics of high moisture (water content reaches 25%-40%), high viscosity, high water holding capacity and low calorific value, so it is difficult to achieve industrial application. At present, the reuse of coal slime is mostly achieved by the method of mixed combustion, that is, the coal slime and coal powder are mixed and burned. In order to avoid the coal slime from bringing in too much water, the coal slime needs to be dried first. After drying, the moisture content of the coal slime can be reduced to about 12%, but the drying process of the coal slime requires pre-crushing, breaking up, and anti-sticking to the wall, and the operation is relatively cumbersome; in addition, the drying process of the coal slime 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 at the same time, it will have great practical significance. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing pelletized fuel by coupling sludge drying with coal sludge moisture control. The method uses wet sludge and low-pressure steam for intermittent heat exchange to effectively dry the sludge, and then mixes the obtained dry sludge with wet coal sludge for granulation. While improving the efficient utilization of coal sludge, the characteristics of both sludge and coal sludge are fully utilized, and pelletized fuel is obtained by combining the method of low-temperature drying and moisture control. The low-temperature drying and moisture control pelletized fuel has low dust emission and is friendly to the external environment.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing pellet fuel by coupling sludge drying with coal sludge moisture control comprises the following steps:

[0008] Drying: The wet sludge is intermittently heat exchanged with low-pressure steam to obtain dried sludge with a water content of 20% to 25%;

[0009] Mixing and granulating: the dried sludge and wet coal sludge are mixed and granulated to obtain columnar particles with a water content of 25% to 35% and a diameter of 3 to 7 mm;

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

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

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

[0013] In an optional embodiment, the temperature of the low-temperature flue gas is 120-150°C.

[0014] In an optional embodiment, the water content of the wet sludge is 65% to 85%; the water content of the wet coal slime is 25% to 40%.

[0015] In an optional embodiment, the exhaust gas in the drying step and / or the humidity adjustment step is transported to an exhaust gas treatment center.

[0016] The present invention also provides a system for preparing granular fuel by coupling sludge drying with coal sludge moisture control, comprising a first dryer, a mixer, a granulator and a second dryer connected in sequence;

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

[0018] The second dryer is selected from a humidity-conditioning drum type.

[0019] In an optional embodiment, a spiral belt flow channel is provided inside the humidity-conditioning drum dryer. By providing the spiral belt flow channel, the drying and humidity-conditioning time of the material in the humidity-conditioning drum dryer can be controlled and prolonged, thereby reducing the breakage of particles.

[0020] In an optional embodiment, the first dryer and / or the second dryer is connected to the exhaust gas treatment center via an induced draft fan.

[0021] In an optional embodiment, the mixer is selected from a twin-shaft mixer; and the granulator is selected from an extrusion granulator.

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

[0023] In an optional embodiment, the upper part of the mixer is provided with a dried sludge inlet and a wet coal sludge inlet, respectively, and the discharge valve of the first dryer is connected to the dried sludge inlet; the bottom of the mixer is provided with a material outlet. Preferably, the dried sludge inlet is located on the side of the wet coal sludge inlet away from the material outlet, and the horizontal distance between the dried sludge inlet and the wet coal sludge inlet is 200 to 500 mm.

[0024] In an optional embodiment, the material outlet of the mixer is connected to the top inlet of the granulator, and the bottom outlet of the granulator is connected to the material inlet of the second dryer; a discharge valve is provided at the bottom of the other end of the second dryer opposite to the material inlet.

[0025] In an optional embodiment, the blower is connected to one end of the material inlet on the second dryer through an air heater, and the air heater is provided with a steam inlet and a steam condensate outlet.

[0026] The present invention also provides a method for preparing particle fuel using the above system, which specifically comprises the following steps:

[0027] Drying: Low-pressure steam enters the first dryer through the low-pressure steam inlet, and wet sludge enters the first dryer through the wet sludge inlet. The low-pressure steam and wet sludge are intermittently heat exchanged in the first dryer to dry the wet sludge and obtain dried sludge with a water content of 20% to 25%. The dried sludge is discharged through the discharge valve at the bottom of the first dryer, and the dried tail gas is extracted to the tail gas treatment center through the induced draft fan;

[0028] Mixing granulation: the dried sludge enters the double-shaft mixer through the dried sludge inlet, and the wet coal slime enters the double-shaft mixer through the wet coal slime inlet located on the double-shaft mixer. The dried sludge and the coal slime are mixed in the double-shaft mixer at a mass ratio of 1:1 to 2:1, and then the mixed material is discharged through the material outlet at the bottom of the double-shaft mixer and enters the extrusion granulator for granulation to obtain columnar particles with a water content of 25% to 35% and a diameter of 3 to 7 mm;

[0029] Humidity control: the columnar particles enter a spiral belt drum dryer (i.e., a humidity control drum dryer with a spiral belt flow channel arranged inside), and the flue gas is pressurized to 4-8 kPaG by a blower and heated to 120-150°C by a heater before entering the spiral belt drum dryer. The columnar particles move along the spiral belt in the spiral belt drum dryer in a plug flow manner to adjust the humidity 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% to solidify. The particles after humidity control and drying are discharged through a bottom discharge valve, and the exhaust gas is extracted by an induced draft fan to an exhaust gas treatment center.

[0030] The above percentages are all by mass.

[0031] Beneficial Effects

[0032] 1. The existing technology generally adopts low-temperature preheating to obtain dried sludge with a moisture content of 20% to 30%, and then adds coal sludge and pretreated straw to it, and granulates it through a pelletizer to obtain granular fuel. However, this method has the following problems: (1) The ratio of coal sludge, straw and dried sludge is difficult to control, and the granular fuel obtained is easy to loosen if it is too dry, the pelletizer has high power and the surface is easy to weather and raise dust, and it is easy to deform if it is too wet; (2) The treatment process of coal sludge, pretreated straw and dried sludge is complicated, quicklime needs to be added in the sludge dehydration process, and straw needs to be added in the granulation process, which has a narrow scope of application and cannot be applied on a large scale in the whole region; (3) A large amount of low-volatile substances with calorific value in coal sludge are wasted due to volatilization.

[0033] In view of the existing sludge drying problem and coal sludge recycling problem, the present invention provides a method for preparing pellet fuel by coupling sludge drying and coal sludge moisture adjustment. First, low-pressure steam is used for intermittent heat exchange with wet sludge to achieve the drying of wet sludge. When the sludge is dried to 20%-25%, it has crossed the viscosity zone. The dried sludge is relatively loose and has a high calorific value. However, wet coal sludge has a certain viscosity and contains a large amount of low-volatile substances with calorific value. Low-temperature drying has a large viscosity and poor drying effect. Therefore, the present invention fully combines the characteristics of the two, uses the two to mix and granulate, and then uses low-temperature drying to adjust humidity (using 120-150℃ low-temperature flue gas for humidity adjustment to obtain 70-85℃ pellet fuel). Not only is the condition mild, it is not easy to raise dust, and the curing effect is good, but also the low-volatile components in the coal sludge are not easy to be discharged, and the low-volatile components in the coal sludge can be retained, the calorific value of the pellet fuel can be adjusted, and solid waste can be reasonably disposed of to turn waste into treasure. Moreover, the low-temperature drying and moisture adjustment pellet fuel has small dust emission, is friendly to the external environment, and is energy-saving and environmentally friendly.

[0034] 2. The method for preparing pellet fuel by coupling sludge drying and coal sludge moisture adjustment provided by the present invention can change the calorific value of pellet fuel by further adjusting the ratio of dry sludge to wet coal sludge, thereby expanding more application prospects. Moreover, it can be widely promoted and applied to the fields of preparing pellet fuel by coupling drying of sludge and lignite or other biomass (for example, biogas residue, animal feces, and fermented straw residue), and has broad application prospects.

[0035] 3. The method for preparing pelletized fuel by coupling sludge drying and coal sludge moisture adjustment provided by the present invention involves coal sludge and sludge, both of which are common solid wastes, and have large output and continuous processing capacity. Low-temperature drying and moisture adjustment retains the low volatile matter in the coal sludge to obtain a fuel with a higher calorific value, and the tail gas can be safely discharged only by washing or cooling. The time of the pelletized particles in the moisture adjustment and drying process is controllable, the particles are less breakable, the amount of dust is small, the odor is small, the operation environment is friendly, and the pelletized fuel finally obtained is widely used.

[0036] 4. The system for preparing granular fuel by coupling sludge drying and coal sludge moisture adjustment provided by the present invention adopts existing devices. By combining the first dryer, the mixer, the granulator and the moisture-adjusting drum dryer, the sludge and the wet mud can be effectively combined to form granular fuel, turning waste into treasure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 The present invention provides a system for preparing granular fuel by coupling sludge drying with coal sludge moisture adjustment.

[0039] Among them, 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-humidity-controlled drum dryer; 9-humidity-controlled discharge valve; 10-humidity-controlled induced draft fan. DETAILED DESCRIPTION

[0040] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0041] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0042] Example 1

[0043] This embodiment provides a system for preparing pelletized fuel by coupling sludge drying with coal sludge moisture control, comprising a first dryer, a mixer, a granulator, and a second dryer connected in sequence;

[0044] Wherein, 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-conditioning drum type.

[0046] In one embodiment, a spiral belt flow channel is provided inside the humidity-conditioning drum dryer. By providing the spiral belt flow channel, the drying and humidity-conditioning time can be prolonged and the breakage of particles can be reduced.

[0047] In one embodiment, the first dryer and / or the second dryer is connected to the exhaust gas treatment center via an induced draft fan.

[0048] In one embodiment, the mixer is selected from a twin-shaft mixer; and the granulator is selected from an extrusion granulator.

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

[0050] In one embodiment, a dried sludge inlet and a wet coal sludge inlet are respectively provided at the upper part of the mixer, and the discharge valve of the first dryer is connected to the dried sludge inlet; a material outlet is provided at the bottom of the mixer. Specifically, the dried sludge inlet is located on the side of the wet coal sludge inlet away from the material outlet, and the horizontal distance between the dried sludge inlet and the wet coal sludge inlet is 200 to 500 mm.

[0051] In one embodiment, the material outlet of the mixer is connected to the top inlet of the granulator, and the bottom outlet of the granulator is connected to the material inlet of the second dryer; a discharge valve is provided at the bottom of the other end of the second dryer opposite to the material inlet.

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

[0053] Specifically, Figure 1 As shown, the system for preparing pellet fuel by coupling sludge drying with coal sludge moisture control comprises: a paddle dryer 1, a double-shaft mixer 4, an extrusion granulator 5 and a moisture control drum dryer 8 with a spiral belt flow channel arranged therein, which are connected in sequence;

[0054] A wet sludge inlet is provided at one end of the paddle dryer 1, a low-pressure steam inlet is provided at the other end, a tail gas outlet is provided at the top (the tail gas outlet is connected to the tail gas treatment center through the sludge drying induced draft fan 3), a paddle dryer discharge valve 2 is provided at the bottom; and a steam condensate outlet is provided at the end opposite to the low-pressure steam inlet.

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

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

[0057] Example 2

[0058] This embodiment provides a method for preparing particle fuel using the above system, using Figure 1 The system shown specifically includes the following steps:

[0059] Drying: 0.3-1.0MPa low-pressure steam enters through the low-pressure steam inlet at one end of the paddle dryer, and wet sludge with a water content of 65%-85% enters through the wet sludge inlet at the other end of the paddle dryer. Then the low-pressure steam and the wet sludge are intermittently heat exchanged in the paddle dryer to achieve drying of the wet sludge, and dried sludge with a water content of 20%-25% is obtained; the dried sludge is discharged through the discharge valve at the bottom of the paddle dryer, and the dried tail gas is extracted to the tail gas treatment center through the induced draft fan;

[0060] Mixing granulation: dried sludge enters the twin-shaft mixer through the dried sludge inlet, and wet coal sludge with a water content of 25% to 40% enters the twin-shaft mixer through the wet coal sludge inlet located on the twin-shaft mixer. The dried sludge and wet coal sludge are mixed in the twin-shaft mixer at a mass ratio of 1:1 to 2:1, and then the mixed material is discharged through the material outlet at the bottom of the twin-shaft mixer and enters the extrusion granulator for granulation to obtain columnar particles with a water content of 25% to 35% and a diameter of 3 to 7 mm;

[0061] Humidity control: The columnar particles enter the humidity control drum dryer. The flue gas is pressurized to 4-8 kPaG by the blower and heated to 120-150°C by the heater before entering the humidity control drum dryer. The particles are humidified to about 12%-15% and solidified. The humidified columnar particles (i.e., particle fuel) are discharged through the bottom discharge valve, and the exhaust gas is drawn out by the induced draft fan to the exhaust gas treatment center.

[0062] After testing, the low-ash coal sludge of the pellet fuel has an ash content of 20% to 32%, a calorific value of 9 to 17.5 MJ / kg after mixing, and an ash content of 30% to 45%; the medium-ash coal sludge has an ash content of 30% to 50%, a calorific value of 6 to 10 MJ / kg after mixing, and an ash content of 38% to 60%; the calorific value of the biogas slag is 9 to 15.7 MJ / kg, and a calorific value of 5.5 to 12.5 MJ / kg after mixing.

Claims

1. A method for preparing pellet fuel by coupling sludge drying with coal sludge moisture control, characterized in that: The steps include: Drying: The wet sludge is intermittently heat exchanged with low-pressure steam to obtain dried sludge with a water content of 20% to 25%; Mixing and granulating: the dried sludge and wet coal sludge are mixed and granulated to obtain columnar particles with a water content of 25% to 35% and a diameter of 3 to 7 mm; Humidity adjustment: In low-temperature flue gas, the water content of the columnar particles is adjusted to 12% to 15% to obtain pellet fuel.

2. The method according to claim 1, characterized in that The pressure of the low-pressure steam is 0.3-1.0 MPa.

3. The method according to claim 1 or 2, characterized in that The mass ratio of the dried sludge to the wet coal slime is 1:1 to 2:

1.

4. The method according to claim 1 or 2, characterized in that: The temperature of the low-temperature flue gas is 120-150°C.

5. The method according to claim 1 or 2, characterized in that: The water content of the wet sludge is 65% to 85%; the water content of the wet coal slime is 25% to 40%.

6. The method according to claim 1 or 2, characterized in that: The tail gas in the drying step and / or the humidity adjustment step is transported to a tail gas treatment center.

7. A system for preparing pellet fuel by coupling sludge drying with coal sludge moisture control, characterized in that: It includes a first dryer, a mixer, a granulator and a second dryer which are connected in sequence; The first dryer is selected from any one of a paddle type, a disc type and a film type; The second dryer is selected from a humidity-conditioning drum type.

8. The system according to claim 7, characterized in that A spiral belt flow channel is arranged inside the humidity-controlled drum dryer.

9. The system according to claim 7 or 8, characterized in that The first dryer and / or the second dryer are connected to the tail gas treatment center via an induced draft fan.

10. The system according to claim 7 or 8, characterized in that The mixer is selected from a double-shaft mixer; the granulator is selected from an extrusion granulator.

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