Multi-stage gravity-type sludge drying apparatus and method for drying sludge using same

Abstract

Disclosed are a multi-stage gravity-type sludge drying apparatus and a sludge drying method using the same. The drying apparatus includes: a dryer, a preheater, a steam generator, a filter, a steam or water separation buffer tank, a steam compressor, a cooling water pump, a sealed discharge device, pipes and valves. The dryer includes several indirect dryer modules. The transportation of sludge in the dryer is achieved by gravity. The inner cavity of respective indirect dryers is filled with high-temperature steam to dry the sludge by indirect heating. The condensate water in the cavity is recycled and fed into the preheater to perform preheating and impurity removal on the wet sludge. The secondary steam generated in the dryer is filtered, compressed and overheated to become a new heat source for indirect heating in the cavity and convection drying at a bottom of the dryer.

Claims

1. A multi-stage gravity-type sludge drying apparatus, comprising: a preheater, a sludge dryer, a steam recovery system comprising a filter, a first steam or water separation buffer tank, a steam compressor, a second steam or water separation buffer tank and a heater which are sequentially connected, and a steam generator; wherein a bottom of the preheater is communicated with a sludge inlet of the sludge dryer through a sludge conveyor; the sludge dryer comprises a drying chamber and multiple stages of indirect dryers provided therein; respective indirect dryers comprise a pair of first rollers; a surface of a cylinder of respective first rollers is provided with a plurality of annular grooves; the cylinder of respective first rollers is axially provided with a first joint connecting with a steam pipe and a condensation water pipe; a bottom of the drying chamber is provided with a sludge outlet and a convection steam inlet; a top of the drying chamber is provided with a steam outlet; and the steam outlet is communicated with the steam recovery system through a pipeline.

2. The apparatus of claim 1, wherein the preheater comprises a sludge chamber and a drying module; the sludge chamber is provided on a top of the drying module; the drying module comprises a pair of second rollers, and respective second rollers are axially provided with a second joint connecting with the condensation water pipe; and a bottom of the drying module is connected with the sludge conveyor.

3. The apparatus of claim 1, wherein the annular grooves are evenly distributed on the surface of the cylinder of respective first rollers; a width of respective annular grooves is greater than a distance between two adjacent annular grooves; and a wall surface of respective annular grooves is provided with a draft angle and a fillet.

4. The apparatus of claim 1, wherein there are 5 stages of indirect dryers vertically arranged; surfaces of cylinders of first rollers of the third and fourth stages of indirect dryers from top to bottom are sprayed with an anti-adhesion material; and the anti-adhesion material is Teflon.

5. The apparatus of claim 1, wherein the sludge outlet is connected with a two-stage sealed discharge structure; and the two-stage sealed discharge structure comprises a rotary valve.

6. The apparatus of claim 1, wherein the first steam or water separation buffer tank is provided with a pipe connecting with the condensation water pipe and a cooling pipe connecting with the steam compressor; and the cooling pipe is provided with a cooling water pump.

7. The apparatus of claim 1, wherein a steam outlet of the heater and a steam outlet of the steam generator are converged and then connected with a separate cylinder; steam outlets of the separate cylinder are respectively connected with the steam pipe and the convection steam inlet; and the condensation water pipe is provided with a steam trap.

8. A method of drying sludge using the apparatus of claim 1, comprising: (1) preheating wet sludge in the preheater, and passing the preheated sludge to the sludge conveyor; (2) transporting the preheated sludge to the sludge dryer through the sludge inlet and drying the sludge by the multiple stages of indirect dryers fed with steam; (3) passing secondary steam in the steam outlet provided on a top of the drying chamber sequentially through the filter, the first steam or water separation buffer tank, the steam compressor, the second steam-water separation buffer tank and the heater to recover the secondary steam; merging the recovered secondary steam with steam generated from the steam generator; passing one part of the merged steam into an inner cavity of respective indirect dryers through the steam pipe connecting with respective stages by a separate cylinder to release condensation heat to perform indirect heat-conduction drying and passing the other part of the merged steam into the sludge dryer through the convection steam inlet to convectively dry the sludge from bottom to top; and (4) discharging the dried sludge sequentially through the sludge outlet and a two-stage sealed discharge structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be further described below with reference to the embodiments and drawings to make the technical solutions clearer. Obviously, the embodiments provided below are merely illustrative of the invention and are not intended to limit the invention. Various embodiments made by those skilled in the art without sparing any creative effort should fall within the scope of the invention.

(2) FIG. 1 is a schematic diagram of a multi-stage gravity-type sludge drying apparatus of the invention.

(3) FIG. 2 is a schematic diagram of a sludge dryer of the sludge drying apparatus of the invention.

(4) FIG. 3 is a perspective view of a combination of 5 stages of indirect dryer modules.

(5) FIG. 4A shows the shrinkage of the sludge before heating.

(6) FIG. 4B shows the shrinkage of the sludge after heating.

(7) FIG. 5 is a partial enlarged view of the heating surface of the indirect dryer during the rapid heating stage.

(8) In the drawings: 1: sludge dryer; 1-1: sludge inlet; 1-2: secondary steam outlet; 1-3: steam pipeline inlet; 1-4: convection steam inlet; 1-5: sludge outlet; 1-6: condensation water pipe inlet; 1-7: condensation water pipe outlet; 2: preheater; 3: sludge injection pump; 4: filter; 5 first steam or water separation buffer tank; 6: steam compressor; 7: second steam or water separation buffer tank; 8: cooling water pump; 9: heater; 10: steam generator; 11: separate cylinder; 12: sealed discharge structure; 13: steam trap; 14: annular groove; 15: rotary joint; a, b, c, d: valves; A: indirect dryer free of Teflon coating; B: indirect dryer sprayed with Teflon coating; B-1: dryer cylinder; B-2: Teflon coating; B-3: steam film; B-4: sludge near the heating surface; B-5: sludge; and C: surface of the indirect dryer cylinder.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The technical solutions in the embodiments of the invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the invention, and are not intended to limit the invention. Other embodiments obtained by those skilled in the art without sparing any creative efforts shall fall within the scope of the invention.

(10) An object of the invention is to provide a multi-stage gravity-type sludge drying apparatus and a drying method using the same to solve the problems in the prior art such as high energy consumption, complicated apparatus, difficult maintenance, wall sticking and slow drying rate.

(11) In order to make the objects, features and advantages of the invention more obvious and understood, the invention will be further described with reference to the drawings and embodiments.

(12) The sludge drying apparatus of the present invention is shown in the figures. FIG. 1 is a schematic diagram of a multi-stage gravity-type sludge drying apparatus of the invention; FIG. 2 is a schematic diagram of the sludge dryer, where the dryer is modularly designed through the combination of 5 stages of indirect drying modules; FIG. 3 is a perspective view of the combination of 5 stages of indirect dryer modules, where cylinders of the third and forth stages of dryers are sprayed with an anti-adhesion material; FIG. 4A schematically shows the shrinkage of the sludge before heating and FIG. 4B schematically shows the shrinkage of the sludge after heating; and FIG. 5 is a partial enlarged view showing the heating surface of the indirect dryer during the rapid heating stage.

(13) As shown in FIGS. 1 and 3, respective stages of indirect dryer modules are combined, and then installed in a closed housing to form a sludge dryer. A top of the sludge dryer is provided with a sludge inlet 1-1 connected with a sludge injection pump 3, and a secondary steam outlet 1-2, where the secondary steam outlet 1-2 is connected successively with a filter 4, a first steam or water separation buffer tank 5, a steam compressor 6, a second steam or water separation buffer tank 7 and a heater 9. A bottom of the sludge dryer is provided with a sludge discharge outlet 1-5 and a convection steam inlet 1-4, where the sludge outlet 1-5 is connected with a two-stage sealed discharge structure 12, and the convection steam inlet 1-4 is connected with a steam outlet of the separate cylinder 11. Individual indirect dryers include a pair of rollers, and a surface of a cylinder of each roller is provided with a plurality of annular grooves 14. The individual indirect dryers are axially provided with a rotary joint 15 to connect with a steam pipe inlet 1-3 and a condensation water pipe inlet 1-6, and the steam pipe inlet 1-3 is further connected with a steam outlet of the separate cylinder 11.

(14) A steam outlet of a steam generator 10 and a steam outlet of the heater 9 are converged and then connected with a steam inlet of the separate cylinder 11.

(15) A lower part of the preheater 2 is provided with a large drying module, which is axially provided with a rotary joint to connect with the condensation water pipe outlet 1-7. Further, a condensation water pipe is arranged between the condensation water pipe inlet 1-6 and the condensation water pipe outlet 1-7, where a steam trap 13 is arranged at the condensation water pipe.

(16) The condensate water outlets of the first steam or water separation buffer tank 5 and the second steam or water separation buffer tank 6 are connected with the condensation water pipe, where the condensate water outlet of the first steam or water separation buffer tank 5 is connected with a cooling water pump 8 and then connected with a cooling water sprinkler of the steam compressor 6.

(17) The embodiment also provides a sludge drying method using the above apparatus, which is specifically described as follows.

(18) After fed through the feed inlet 1-1, the sludge moves downwards under the action of gravity and the rotation of the rollers. At this time, one parts of the steam in the separate cylinder 11 enters the inner cavity of respective indirect dryers from the steam pipe inlet 1-3 to indirectly dry the sludge, and the other part of steam enters the drying chamber from the convection steam inlet 1-4 to convectively dry the sludge. Due to the rapid heat transfer of the indirect dryer A, a sludge thin layer is quickly dried in the sludge dryer 1 to show volume shrinkage and a steam film is generated between the surface of the indirect dryer cylinder C and the sludge. FIG. 4 shows the volume changes of the sludge before and after the heating in the indirect dryers.

(19) In the early period, the sludge is dried in a constant rate drying stage, and has high moisture content and a relatively lower viscosity. At the middle stage, the sludge viscosity reaches the maximum. At this time, the sludge is passing through the indirect dryer B sprayed with Teflon coating.

(20) FIG. 5 is a partial enlarged view showing the heating surface of the indirect dryer B during the rapid heating stage, where the outer surface of the dryer cylinder B-1 is coated with a Teflon coating B-2 with low surface energy, which can reduce the surface energy of the heating surface while ensuring the heat transfer efficiency, reducing the adhering effect between the sludge and the heating surface.

(21) During the middle stage of the drying (i.e., viscosity-reducing indirect drying stage), the normal-temperature sludge is in contact with the indirect heating surface to enter the indirect heating stage. As shown in FIG. 4, the surface drying rate of the sludge B-4 near the heating surface is higher than that of the sludge B-5. The volume of the sludge B-4 near the heating surface is shrunk rapidly after the sharp decrease in moisture content, and a steam film B-3 is formed between the sludge B-4 near the heating surface and the Teflon coating B-2 with low surface energy, which allows the sludge B-5 to be separated transiently from the heating surface, facilitating the separation of sludge from the heating surface. Due to the rapid reduction in the moisture content of the sludge B-4 near the heating surface and the low surface energy of the heating surface, the adhesive substances in the sludge B-5 cannot contact the heating surface well, so that it fails to generate the wall-adhering effect, greatly reducing the wall-adhering effect between the sludge and the heating surface.

(22) Meanwhile, the condensed water generated in the inner cavity of the indirect dryers is discharged from the condensation water pipe inlet 1-6 to the preheater 2 through the steam trap 13 to remove the impurities and preheat the wet sludge in the sludge chamber, which can increase the fluidity of the sludge, avoiding the blockage in the sludge injection pump 3 and the occurrence of condensation during the initial stage of the drying in the sludge dryer 1, improving the drying efficiency. The preheater 2 can also play a role in removing impurities and protecting apparatus.

(23) The secondary steam generated in the sludge dryer 1 is discharged from the secondary steam outlet 1-2 to the filter 4 to remove impurities such as dust in the steam. The filtered secondary steam is passed into the first steam or water separation buffer tank 5 to remove water droplets from the steam. Then the secondary steam is increased in the enthalpy value and temperature through the steam compressor 6 and then passed into the second steam or water separation buffer tank 7 to remove the water droplets after the compression. After properly overheated by the heater 9, the secondary steam is mixed with the primary steam supplemented by the steam generator 10 to be as a new heat source. Through the separate cylinder 11, some of the mixed steam enters into the inner cavity of the indirect dryers from the indirect steam pipe inlet 1-3, and the rest of the mixed steam enters the drying chamber from the convection steam inlet 1-4.

(24) The dust and water droplets in the secondary steam can be removed after passing through the filter 4 and the first steam or water separator buffer tank 5, protecting the steam compressor 6 and extending the service life thereof. At the same time, a high exhaust temperature will occur after the long-term operation of the steam compressor 6, so a part of the condensate water in the first steam or water separation buffer tank 5 is pumped by the cooling water pump 8 to cool the steam compressor 6, and the other condensate water is used to preheat the sludge in the preheater 2.

(25) After indirectly dried by the multiple stages of indirect dryers and convectively dried by the convection steam in the dryer 1, the sludge is discharged from the sludge outlet 1-5 through the two-stage sealed discharge structure 12.

(26) The sludge dryer is mainly composed of several indirect dryer modules. Compared to the paddle dryer and the plate dryer, the energy consumed by the mechanical operation of the sludge dryer provided herein is greatly reduced since the transportation of sludge in the dryer is achieved by gravity. The inner cavity of the indirect dryers is filled with high-temperature steam to indirectly and rapidly dry the sludge, which results in a decrease in the moisture content and volume of the sludge, allowing the sludge to shrink toward the center. At the same time, a steam film is formed between the sludge and the heating surface, reducing the viscosity. The condensed water in the inner cavity is recycled and fed into the preheater 2 to perform preheating and impurity removal on the wet sludge. The secondary steam generated in the sludge dryer is filtered, compressed and overheated to become a new heat source for the indirect heating in the cavity and convection drying at the bottom of the sludge dryer. The Teflon coating with low surface energy sprayed on the heating contact surfaces of the third and fourth stages of the indirect dryers enables the sludge to pass through the indirect dryers smoothly when the viscosity reaches the maximum during the middle stage of the drying, avoiding the wall adhesion.

(27) The apparatus adopts a modular design, which not only facilitates the installation and manufacturing, reduces the energy consumption for mechanical operation and avoids the wall adhesion, but also recycles all the latent and sensible heat of the secondary steam generated during the drying, having significant energy-saving effects.

(28) The above embodiments are merely illustrative of the invention, and are not intended to limit the invention. Various modifications and changes made by those skilled in the art based on the content disclosed herein should fall within the scope of the invention.