Abstract:
A dust removal method using baghouse filter to process raw syngas from fluidized bed coal gasifier, wherein temperature in the baghouse ( 300 ) is maintained at 180° C.˜250° C., pressure difference between the gas inlet ( 130 ) of the baghouse ( 300 ) and the gas outlet ( 110 ) of the baghouse ( 300 ) is controlled at 1000-5000Pa, the raw syngas from the fluidized bed coal gasifier enters the gas inlet under the pressure of 0.2-3.0Mpa. The present method effectively solves the technical problems of condensation and baghouse block due to high steam and ash content in the raw syngas from the fluidized bed coal gasifier and the present method is also applicable to remove dusts from the raw syngas produced by the fluidized bed coal gasifier under the conditions of high water-gas ratio (the water-gas ratio is up to 37%), high dust content(15-100g/Nm3 dusts) and 0.2-3.0Mpa pressure. The present invention also discloses a baghouse dust collector and a dense phase pneumatic conveying apparatus for the method.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a dust removal method using baghouse filter, in particular, relates to a dust removal method using baghouse filter to process raw syngas from fluidized bed coal gasifier, a baghouse dust collector and a dense phase pneumatic conveying apparatus. 
     BACKGROUND OF THE INVENTION 
     The raw syngas (raw gas) from the fluidized bed coal gasifier must go through cooling and dust removal processes before desulfurizing and decarburizing processes in the next stage in order to obtain qualified syngas (clean gas). Wet dust removal method is commonly used in the prior art, but will seriously result in secondary pollution and water treatment problems. For example, after the deposition of primary black water generated by water-washing method, secondary black water needs further biochemical treatment. Equipments and processes for the biochemical treatment of the black water from wash water are quite costly. Plate heat exchanger used in the water-washing method is also very easily blocked by wet mud, which will result in shutdown during the production, so the plate heat exchange has to be frequently disassembled and washed by chemical agents. Meanwhile, the carbon mud will contain high content of water after the deposition of the black water, and the wet carbon mud cannot be recycled in the industry and treated as three wastes. Accordingly, there is an urgent need to provide an innovative and improved dust removal technology to process the raw syngas from the fluidized bed coal gasifier. 
     A dust removal system using baghouse filter for blast furnace gas is disclosed in a Chinese utility model patent with Publication No. CN2828056 to remove dusts from blast furnace gas. A big dry-type dust remover using baghouse filter for blast furnace gas is also disclosed in a Chinese utility model with Publication No. CN201008774 to remove dusts from blast furnace gas. The blast furnace gas is different from the raw syngas produced by the fluidized bed coal gasifier, for example, the blast furnace gas contains no steam and far less dusts (the blast furnace gas contains about 20 g/m 3  dusts, one fifth of the dust content in the raw syngas from the fluidized coal gasifier), while the raw syngas from the fluidized coal gasifier has high steam content (water-gas ratio is up to 37%, volume concentration, the same hereinafter), so the dust removal method using baghouse filter in the prior art cannot effectively remove dusts from the syngas produced by the fluidized coal gasifier. Due to the condensation of steam and high dust content in the raw syngas from the fluidized bed, the baghouse filter will be blocked during the dust removal process so as to reduce the dust removal efficiency. 
     In addition, dust recycle after the dust removal is another common technical problem for the raw syngas from the fluidized bed coal gasifier in the prior art. An embedded scraper mechanical transport method is commonly used to recycle the dusts, but this technology works under normal pressure while the dusts are removed from the raw syngas produced by the fluidized bed gasifier under certain pressure. Therefore, the embedded scraper mechanical transport method is not applicable in this case. It is also difficult to use the water spraying dust removal method to solve the above problem because the coal ashes collected from the raw syngas produced by the fluidized bed gasifier have high carbon content and hydrophobicity. 
     Currently, pneumatic conveying apparatus is also widely used in the transportation of dry powder (such as flour, sugar powder). However, the fine coal ashes (10 microns) collected from the raw syngas produced by the fluidized bed gasifier after the dust removal have high steam content and tend to be mushy, so those skilled in the art usually consider the pneumatic conveying apparatus not applicable to deliver the coal ashes collected from the raw syngas produced by the fluidized bed gasifier after the dust removal. 
     Further, star-shaped feeding valve is requisite in the dilute phase pneumatic conveying apparatus. This kind of star-shaped feeding valve cannot endure high pressure, which will easily result in gas leakage or ash ejection. 
     SUMMARY OF THE INVENTION 
     Aiming at the problem of baghouse filter block due to the high content of steam and ashes in the raw syngas from the fluidized bed coal gasifier, the first technical problem to be solved by the present invention is to provide a dust removal method using baghouse filter to process raw syngas from fluidized bed coal gasifier, which is used for cleaning and removing dust in the raw syngas from the fluidized bed coal gasifier. 
     The second technical problem to be solved by the present invention is to provide a baghouse dust collector for the above method. 
     In a dust removal method using baghouse filter to process raw syngas from the fluidized bed coal gasifier according to one aspect of the present invention, the raw syngas with high water-gas ratio of 37% (volume concentration, the same hereinafter) from the fluidized bed coal gasifier enters a baghouse from a gas inlet of a baghouse dust collector, flows through fibre spaces of the baghouse, and enters a clean gas pipe from a gas outlet of the baghouse dust collector; ashes are blocked and absorbed by outer surface of the baghouse and released from an ash outlet on the lower portion of the baghouse dust collector. 
     In the above-mentioned method, temperature in the baghouse is maintained at 180° C. ˜250° C. Pressure difference between the gas inlet of the baghouse and the gas outlet of the baghouse is controlled at 1000-5000 Pa. 
     In the above-mentioned method, the raw syngas from the fluidized bed coal gasifier enters the gas inlet under the pressure of 0.2-3.0 Mpa. 
     The present invention effectively solves the technical problems of condensation and baghouse block due to high steam and ash content in the raw syngas from the fluidized bed coal gasifier by controlling the temperature in the baghouse at 180 ° C.-250 ° C. and the pressure difference between the gas inlet of the baghouse and the gas outlet of the baghouse at 1000-5000 Pa; and the dust removal method using baghouse filter of the present invention is also applicable to remove dusts from the raw syngas produced by the fluidized bed coal gasifier under the conditions of high water-gas ratio (the water-gas ratio is up to 37%), high dust content (15-100 g/Nm 3  dusts) and 0.2-3.0 Mpa pressure. 
     The dry coal ashes produced by the method of the present invention can be directly used in the cement manufacturing and other industries, which has value in use. The present invention can reduce secondary pollution caused by black water generated by wet method and produce clean syngas (with dust content of 10 mg/Nm 3 ) with high dust recovery rate of 99.5%. 
     The present invention starts a new era in the coal gasification and coal liquefaction industries. The present invention not only achieves safe and consecutive manufacture in the industry, but also saves energy of 50% compared to the wet method. 
     A baghouse dust collector according to another aspect of the present invention comprises: 
     a baghouse dust collector case body; 
     a baghouse in the case body; 
     a gas outlet on the upper potion of the baghouse dust collector case body and in communication with the baghouse, a gas outlet valve is arranged on the gas outlet; 
     a gas inlet on the lower potion of the baghouse dust collector case body and in communication with the bagouse dust collector case body and the outer surface of the baghouse, a gas inlet valve is arranged on the gas inlet; 
     a back flush inlet on the upper portion of the baghouse dust collector case body and in communication with the bagouse dust collector case body and the outer surface of the baghouse, a back flush gas source is connected with the back flush inlet, a back flush valve is arranged on the back flush inlet; by opening the back flush valve, back flush gas, e.g. nitrogen, with certain pressure and quantity is blown to the baghouse dust collector case body to wash the absorption layer on the outer surface of the baghouse rapidly and blow the ashes on the absorption layer into an ash hopper; 
     an ash outlet at the bottom of the baghouse dust collector and in communication with the baghouse dust collector case body and the outer surface of the baghouse; 
     an ash hopper in communication with the ash outlet; 
     the raw syngas from the fluidized bed coal gasifier is introduced into the gas inlet, the gas outlet is connected with a clean gas pipe; an insulating layer is arranged on the outer wall of the baghouse dust collector case body to keep the temperature in the baghouse at 180° C.-250° C. 
     The insulating layer is an electricity-heated insulating layer or a steam-heated insulating layer. The electricity-heated insulating layer comprises an electric heating tube wound around the outer wall of the baghouse dust collector case body, and the electric heating tube is in electric connection with an electric controller. The steam-heated insulating layer comprises a steam tube wound around the outer wall of the baghouse dust collector case body, and the steam tube is connected with a general steam valve. 
     The electric heating tube or the steam tube is spirally wound around the outer wall of the baghouse dust collector case body in circumference direction or arranged along the outer wall of the baghouse dust collector case body in axial direction. 
     Overheated steam at 200° C.˜300° C. is introduced into the steam tube. 
     The back flush valve is a controllable pulse valve. The back flush valve can wash the dust filtration side to remove the dusts from the surface of the baghouse and recover the dust removal ability of the baghouse dust collector when needed or filtration resistance caused by the dust deposition on the dust filtration side (indicated by the pressure difference between the gas inlet and the gas outlet of the baghouse dust collector) increases to 1000˜5000 Pa after the baghouse filter works for a period of time. 
     A temperature sensor is arranged in the baghouse dust collector case body, and the temperature sensor is in signal connection with a controller. 
     The present invention also comprises a dense phase pneumatic conveying apparatus connected with the ash hopper to deliver the collected ashes after dust removal by a dense phase pneumatic conveying method. 
     The dense phase pneumatic conveying apparatus according to the present invention delivers the ashes safely and consecutively out of the system under certain pressure (0.2-3.0 Mpa). The dense phase pneumatic conveying apparatus can reduce the number of used valves and need no star-shaped feeding valve, which can improve gas tightness of the whole dense phase pneumatic conveying apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments according to the present invention will be further described in conjunction with accompanying figures as follows. 
         FIG. 1  shows the structure of the baghouse dust collector according to the present invention; 
         FIG. 2  shows the controlling system principle of the baghouse dust collector according to the present invention; 
         FIG. 3  shows one arrangement of the steam tube in the baghouse dust collector according to the present invention; 
         FIG. 4  shows another arrangement of the steam tube in the baghouse dust collector according to the present invention; 
         FIG. 5  shows the structure of the dense phase pneumatic conveying apparatus according to the present invention; 
         FIG. 6  shows the electronics principle of the dense phase pneumatic conveying apparatus according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment according to the present invention is provided in conjunction with accompanying figures. 
     As shown in  FIG. 1 , a baghouse dust collector according to the present invention comprises a baghouse dust collector case body  100  and a baghouse  300  in the baghouse dust collector case body  100 . The baghouse  300  is installed in the baghouse dust collector case body  100  through a baghouse frame and a lattice board to remove dusts from the raw syngas produced by the fluidized bed coal gasifier. The baghouse  300  uses FMS 9806 filter bag with unit weight of 800 g/m 2 . 
     A gas outlet  110  and a back flush inlet  120  are arranged on the upper portion of the baghouse dust collector case body  100 , a gas inlet  130  is arranged on the lower portion of the baghouse dust collector case body  100 , an ash outlet  140  is arranged at the bottom of the baghouse dust collector case body  100 , and an explosion relief valve  150  is arranged on the top of the baghouse dust collector case body  100  to release pressure automatically when the pressure exceeds a predetermined pressure. 
     The gas outlet  110  is in communication with the baghouse  300  and a gas outlet valve  111  is arranged on the gas outlet  110 . The back flush inlet  120 , the gas inlet  130  and the ash outlet  140  are in communication with the baghouse dust collector case body  100  and the outer surface of the baghouse  300 , and a gas inlet valve  131  is arranged on the gas inlet  130 . 
     A back flush valve  121  is arranged on the back flush inlet  120 . The back flush valve  121  is a submerged pulse valve to back flush by low pressure pulse, and the back flush pressure is 0.35-0.4 MPa. Back flush gas, e.g. nitrogen, is introduced into the back flush valve  121 . The back flush valve  121  can wash the dust filtration side to remove the dusts from the surface of the baghouse  300  and recover the dust removal ability of the baghouse dust collector when needed or especially when filtration resistance caused by the dust deposition on the dust filtration side (indicated by the pressure difference between the gas inlet and the gas outlet of the baghouse dust collector) increases to 1000˜5000 Pa after the baghouse filter works for a period of time. 
     The gas outlet valve  111  is a blind plate valve and the gas inlet valve  131  is a pneumatic butterfly valve for remote operation. Closing the gas outlet valve  111  and gas inlet valve  131  at the same time and separating the baghouse dust collector case body  100  from the system to ensure the safety of repairmen when the baghouse dust collector case body  100  is repaired. 
     The baghouse dust collector according to the present invention can be used separately or with other baghouse dust collectors in parallel. If the baghouse dust collector is used separately, the gas inlet valve  131  is connected with a general raw gas pipe (not shown in the figures) via a manual ball valve (not shown in the figures) and the gas outlet valve  111  is connected with a general clean gas pipe (not shown in the figures) via a manual ball valve (not shown in the figures). If the baghouse dust collector is used with other baghouse dust collectors in parallel, the gas inlet valve  131  is connected with a branch raw gas pipe (not shown in the figures) via a manual ball valve, the branch raw gas pipe (not shown in the figures) is connected with a general raw gas pipe; the gas outlet valve  111  is connected with a branch clean gas pipe (not shown in the figures) via a manual ball valve, the branch clean gas pipe (not shown in the figures) is connected with a general clean gas pipe; the ends of the general raw gas pipe and the general clean gas pipe are connected with a manual ball valve (not shown in the figures) and a discharge pipe to release gas timely when the apparatus is repaired and gas is changed. 
     An insulating layer is arranged on the outer wall of the baghouse dust collector case body  100  to keep the temperature in the baghouse  300  at 180° C.˜250° C. In this embodiment, the insulating layer is a steam-heated insulating layer  400 . Also, an electricity-heated insulating layer can be used instead. The steam-heated insulating layer  400  comprises a steam tube  410  wound around the outer wall of the baghouse dust collector case body  100  in two ways: one way is shown in  FIG. 3 , wherein the steam tube is spirally wound around the outer wall of the baghouse dust collector case body  100  in circumference direction; the other way is shown in  FIG. 4 , wherein the steam tube is arranged along the outer wall of the baghouse dust collector case body  100  in axial direction. If the electricity-heated insulating layer is used instead, the electricity-heated insulating layer comprises an electric heating tube wound around the outer wall of the baghouse dust collector case body  100  and the electric heating tube is in electric connection with an electric controller. The electric heating tube is wound around the outer wall of the baghouse dust collector case body  100  in the same ways as the steam tube  410 . 
     The steam tube  410  is connected with a general steam valve  420  and overheated steam at 200° C.˜400° C. is introduced into the general steam valve  420  to keep the temperature in the baghouse  300  at 180° C.˜250° C. In order to control the temperature in the baghouse  300  at 180° C. ˜250° C., a temperature sensor  500  is arranged in the baghouse dust collector case body  100  according to this embodiment, and the temperature sensor  500  is a thermocouple to convert the detected temperature value into electric signal. A controller  600  is used to control open degree of the general steam valve  420  so as to control the temperature in the baghouse  300 . The controller  600  is a Siemens S7-800 programmable logic controller. 
     In addition, a temperature detection point  510  is set on the outer wall of the baghouse dust collector case body  100  (as shown in  FIG. 2 ) and a temperature detection point  520  is set on the general clean gas pipe. The temperature detection points  510 ,  520  are in signal connection with the controller  600 . 
     A controllable ash outlet valve  141  is arranged on the ash outlet  140 , the ash outlet valve  141  is connected with an ash hopper  700 , and the ash outlet valve  141  is a pneumatic ball valve in connection with the controller  600 . 
     The present invention can further comprise dust density detectors  530  and  540  respectively arranged on the general clean gas pipe and the branch clean gas pipe. The dust density detectors  530  and  540  are in signal connection with the controller  600  to detect the density of the clean gas. 
     The controller  600  is further in signal connection with the gas inlet valve  131 , the gas outlet valve  111 , the back flush valve  121  and the general steam valve  420  to control gas inlet valve  131 , the gas outlet valve  111 , the back flush valve  121  and the general steam valve  420 . 
     The complete course of the dust removal by the baghouse dust collector will be described as follows: the raw syngas produced by the fluidized bed coal gasifier directly enters the baghouse dust collector case body  100  via the general raw gas pipe or the branch raw gas pipe, the manual ball valve  132 , the gas inlet valve  131  and the gas inlet  230 . Then, the raw syngas flows through fibre spaces of the baghouse  300  and enters the general clean gas pipe or the branch clean gas pipe via the gas outlet  110 , the gas outlet valve  111  and the manual ball valve  112 . The ashes are blocked by the baghouse  300  and absorbed on the outer surface of the baghouse  300 , and some ashes fall into the ash outlet  140  at the bottom of the baghouse dust collector case body  100  after colliding with each other. In prior art, block of the baghouse  300  will be caused by resistance due to increasing thickness of absorption layer on the outer surface of the baghouse  300  as time goes by, as well as condensation of steam in high content, and high ash content in the raw syngas from the fluidized bed coal gasifier. According to present invention, the insulating layer is arranged outside the baghouse dust collector case body  100  to control the temperature in the baghouse  300  at 180° C.˜250° C., which will not result in block of the baghouse  300 . 
     When filtration efficiency falls below a predetermined value, the outer surface of the baghouse  300  is washed rapidly to blow the ashes on the absorption layer into the ash outlet  140  at the bottom of the baghouse dust collector case body  100  by turning off the gas inlet valve  131  and opening the back flush valve  121  to blow back flush gas, e.g. nitrogen, with certain pressure and quantity to the baghouse  300  via back flush inlet  120  so as to recover gas permeability, dust removal ability of the baghouse  300  and penetrability of the raw gas. Then, stopping cleaning dusts by turning off the back flush valve  121  and starting filtering gas for the next round. Some of the dust removal units are used for filtering gas, while the others are used for stopping filtering gas and reversely blowing the dust. Besides timing operation method, the dust cleaning process can be started according to resistance drop of the absorption layers inside and outside the baghouse  300 . During the dust cleaning process, the resistance drop inside and outside the baghouse  300  increases with the rising amount of the dusts absorbed on the surface of the baghouse  300 . When the resistance drop reaches a predetermined value, starting the dust cleaning process. The dust cleaning process can be performed by online and offline method. 
     The ashes can fall into the ash hopper  700  by opening the ash outlet valve  141 . When the ashes in the ash hopper  700  reach a certain height, the ashes are discharged in the way of dense phase pneumatic transmission by a dense phase pneumatic conveying apparatus connected with the ash hopper  700 . 
     As shown in  FIG. 4  and  FIG. 5 , the dense phase pneumatic conveying apparatus according to the present invention comprises an ash conveying vessel  800 , an ash conveying pipe  900 , pressure-equalizing pipes  910 ,  910 ′, a first small hole exhaust valve  920 , a pressure decrease timer F, a first solid exhaust valve  930 , an over pressure release timer E, a second solid exhaust valve  950 , a second small hole exhaust valve  960 , an conveying vessel shutoff valve  730 , an over load timer C, an inlet shutoff delay timer D, a conveying vessel inlet valve  830 , a balance timer B, a conveying vessel level meter  850 , a gas nozzle electromagnetic valve  940 , a pressure release overtime timer H, a pressure increase timer I, an over conveying timer J, a pressure sensor  860 , a pressure low timer K, an air nozzle electromagnetic valve  970 , an aeration timer A, a conveying vessel outlet valve  840  and a valve positioning timer G. 
     The ash hopper  700  has a first ash inlet  710  on the top and a first ash outlet  720  at the bottom, and the first ash inlet  710  is in communication with the ash outlet valve  141  at the bottom of the baghouse dust collector case body  100 . 
     The ash conveying vessel  800  has a second ash inlet  810  on the top and a second ash outlet  820  at the bottom, the first ash outlet  720  at the bottom of the ash hopper  700  is in communication with the second ash inlet  810  on the top of the ash conveying vessel  800  via the conveying vessel shutoff valve  730  and the conveying vessel inlet valve  830 , the second ash outlet  820  at the bottom of the ash conveying vessel  800  is in communication with the ash conveying pipe  900  via the conveying vessel outlet valve  840 . The ash conveying pipe  900  is in communication with the ash hopper  700  and the ash conveying vessel  800  via the pressure-equalizing pipes  910 ,  910 ′. The conveying vessel inlet valve  830  is connected with the balance timer B, the conveying vessel shutoff valve  730  is connected with the over load timer C and the inlet shutoff delay timer D, the conveying vessel outlet valve  840  is connected with the valve positioning timer G. 
     The first small hole exhaust valve  920  and the first solid exhaust valve  930  are arranged on the pressure-equalizing pipe  910  between the ash conveying pipe  900  and the ash conveying vessel  800 , the first solid exhaust valve  930  is connected with the over pressure release timer E, and the first small hole exhaust valve  920  is connected with the pressure decrease timer F. 
     The second solid exhaust valve  950  and the second small hole exhaust valve  960  are arranged on the pressure-equalizing pipe  910 ′ between the ash conveying vessel  800  and the ash hopper  700 . 
     In addition, the gas nozzle electromagnetic valve  940  is arranged on the upper portion of the ash conveying vessel  800 , and the air nozzle electromagnetic valve  970  is arranged on the lower potion of the ash conveying vessel  800 . The gas nozzle electromagnetic valve  940  is connected with the pressure release overtime timer H, the pressure increase timer I and the over conveying timer J. The conveying vessel level meter  850  and the pressure sensor  860  are arranged in the ash conveying vessel  800 , the conveying vessel level meter  850  is connected with the balance timer B, and the pressure sensor  860  is connected with the pressure low timer K. 
     As shown in  FIG. 6 , a controller  1000  is connected with the first small hole exhaust valve  920 , the pressure decrease timer F, the first solid exhaust valve  930 , the over pressure release timer E, the second solid exhaust valve  950 , the second small hole exhaust valve  960 , the conveying vessel shutoff valve  730 , the over load timer C, the inlet shutoff delay timer D, the conveying vessel inlet valve  830 , the balance timer B, the conveying vessel level meter  850 , the gas nozzle electromagnetic valve  940 , the pressure release overtime timer H, the pressure increase timer I, the over conveying timer J, the pressure sensor  860 , the pressure low timer K, the air nozzle electromagnetic valve  970 , the aeration timer A, the conveying vessel outlet valve  840  and the valve positioning timer G. 
     The dense phase pneumatic conveying apparatus according to the present invention can load and deliver ashes in the ash hopper  700  to corresponding stations by the ash conveying vessel  800  and the ash conveying pipe  900  continuously. The steps are described as follows: 
     First, closing the first solid exhaust valve  930  and the first small hole exhaust valve  920  between the ash conveying pipe  900 . The air nozzle electromagnetic valve  970  of the ash conveying vessel  800  carries out pulse operation according to “aeration-on” and “aeration-off” time of the aeration timer A; when the pressure in the ash conveying vessel  800  is higher than or equal to the pressure in the baghouse dust collector case body  100  minus the offset pressure (OP) in the ash hopper  700 , switching off the air nozzle electromagnetic valve  970  and opening the conveying vessel inlet valve  830  between the conveying vessel  800  and the ash hopper  700 . When the conveying vessel inlet valve  830  is opened, the balance timer B starts counting time (5 seconds) and the conveying vessel  800  balances and offsets the pressure in the ash hopper  700  by the closed second small hole exhaust valve  960  according to a controlled rate. When the balance timer B is due, the conveying vessel inlet valve  830  and the second small hole exhaust valve  960  are opened. After the conveying vessel inlet valve  830  is opened, the conveying vessel shutoff valve  730  is opened and the over load timer C starts working (2 times of normal material discharging time). When the conveying vessel inlet valve  830  is opened, the ash hopper  700  uses “aeration-on” and “aeration-off” time of the aeration timer A to make the air nozzle electromagnetic valve  970  work. The materials fall into the ash conveying vessel  800  from the ash hopper  700  under gravity. 
     When the conveying vessel level meter  850  detects that the materials in the conveying vessel  800  reaches high level, the conveying vessel shutoff valve  730  is closed, and the inlet shutoff delay timer D (5 seconds) starts working. When the inlet shutoff delay timer D is due, the conveying vessel inlet valve  830  and the second solid exhaust valve  950  between the ash conveying vessel  800  and the ash hopper  700  are closed. When the conveying vessel inlet valve  830  and the second solid exhaust valve  950  between the ash conveying vessel  800  and the ash hopper  700  are closed, the first solid exhaust valve  930  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  is opened, and the over pressure release timer E starts counting time (2 times of normal pressure releasing time). The ash conveying vessel  800  releases gas by closed ash conveying vessel  800  and the pressure-equalizing pipe  910  according to a controlled rate. 
     When the over pressure release timer E is due, the pressure in the ash conveying vessel  800  falls to OP; the first small hole exhaust valve  920  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  is opened, and the pressure decrease timer F starts counting time (5 seconds). When the pressure decrease timer F is due, the pressure in the ash conveying vessel  800  is released and the load of the materials is completed. 
     The first solid exhaust valve  930  and the first small hole exhaust valve  920  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  are closed. When the first solid exhaust valve  930  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  are closed, the valve positioning timer G starts (2 seconds). The shutoff signals of the conveying vessel inlet valve  830 , the second solid exhaust valve  950  between the ash conveying vessel  800  and the ash hopper  700 , and the first solid exhaust valve  930  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  must appear within the time of the valve positioning timer G. 
     When the valve positioning timer G is due and the conveying vessel outlet valve  840  is opened, the GCM gas nozzle electromagnetic valve  940  is activated, the pressure increase timer I starts counting time and the over conveying timer J starts counting time (2 times of normal time). If the pressure in the ash conveying vessel  800  is lower than or equal to the conveying pressure minus the offset pressure (OP) in the ash conveying vessel  800 , the air nozzle electromagnetic valve  970  of the ash conveying vessel  800  carries out pulse operation according to “aeration-on” and “aeration-off” time of the aeration timer A. 
     When the ash conveying vessel  800  and the ash conveying pipe  900  are cleaned by air, the pressure in the ash conveying vessel  800  falls quickly. When the pressure falls below PS 2 , the GCM gas nozzle electromagnetic valve  940  is powered off, the pressure release overtime timer H starts working (2 times of normal pressure releasing time), and the pressure in the ash conveying vessel  800  is released by the ash conveying pipe  900 . When the pressure in the ash conveying pipe  900  falls to OP, the pressure low timer K starts (5 seconds). When the pressure low timer K and the over pressure release timer E are due, an alarm for over pressure in the ash conveying vessel  800  will be generated (not emergent). The pressure in the ash conveying vessel  800  continues to be released. When the pressure low timer K is due, the first solid exhaust valve  930  and the first small hole exhaust valve  920  between the ash conveying vessel  800  and the pressure-equalizing pipe  910  are opened, and the conveying vessel outlet valve  840  is closed. The ash conveying vessel  800  completes the transportation circle. 
     Insulating layers  701 ,  801  and  901  are respectively arranged on the ash hopper  700 , the ash conveying vessel  800  and the ash conveying pipe  900  to recycle the fine ashes (10-30 μm) from the baghouse dust collector effectively and hermetically.