CN204301025U - Many back-stroke heat-exchange types biomass boiler - Google Patents

Abstract

The utility model discloses a multi-return heat-exchanging biomass boiler. The device includes a boiler body and a blast and air induction system. The water tube furnace, the exhaust pipe, the double furnace mechanism, the water tank outside the furnace, the insulation layer arranged outside the water tank; the entrance of the double furnace mechanism is connected with the feeder and the blower, and the outlet of the double furnace mechanism is connected with the furnace The inlet of the furnace is connected; the outlet of the furnace is connected with the smoke exhaust pipe and the induced draft fan. The technical problem solved by the utility model is to provide a multi-return heat exchange biomass boiler with high thermal efficiency, safety and reliability, convenient installation and small footprint.

Description

Multi-pass heat exchange biomass boiler

technical field

The invention belongs to the field of boilers, in particular to a multi-pass heat exchange biomass boiler.

Background technique

The use of existing biomass boilers can generally be divided into: feeding system, blast and induced air system, boiler combustion system and dust removal system due to the characteristics of uniform thickness of biomass fuel, easy to catch fire, fast combustion time, and light dust after combustion. Due to the clear division of labor of various systems and the relative independence of each system equipment, the existing biomass boilers inevitably have the disadvantages of large equipment footprint, troublesome installation, long paths for heat energy circulation, and waste of heat energy utilization.

Moreover, most of the existing boiler flues are vertically arranged. The small boilers that people use now are generally vertical water tube or fire tube boilers. Factors such as furnace space and flue resistance restrict the arrangement of the tubes, so the thermal efficiency of small boilers has always been Much lower than large boilers and horizontal boilers. The catering industry and small family workshops need small boilers, but they require small size, fast SAIC, and high thermal efficiency. It is difficult for the current small biomass boilers to meet their requirements. The reason for the low density of the water pipes installed in the existing boiler furnace is that if the smoke and dust fall on the top of the water pipes if it is dense, it is easy to block the boiler, and the thermal efficiency of the low-density water pipes is low in practical applications.

Contents of the invention

The purpose of the present invention is to provide a multi-return heat exchange biomass boiler with high thermal efficiency, safety and reliability, convenient installation and small footprint.

In order to achieve the above purpose, the technical solution adopted by the present invention is: a multi-return heat exchange biomass boiler, which includes a boiler body and a blast and air induction system. The boiler body includes a feeder, a double furnace mechanism, a set There are multi-pass water tube furnaces, smoke exhaust pipes, double furnace mechanisms, water tanks outside the furnace, and insulation layers outside the water tanks; the entrance of the double furnace mechanism is connected to the feeder and blower, and the double furnace mechanism The outlet of the furnace is connected with the inlet of the furnace; the outlet of the furnace is connected with the smoke exhaust pipe and the induced draft fan.

The feeder includes a feed hopper, an auger propeller, a shaft coupling, and a discharge port; an auger propeller is arranged below the feed hopper, and one end of the auger propeller is connected with the coupling, and the auger propeller The other end of the propeller is connected to the discharge port; the auger propeller includes a spiral piece and a straight shaft; the spiral piece is installed on the straight shaft above the discharge port, and the starting point of the spiral piece is below the feed hopper , the end point of the spiral piece is the position of the discharge port.

The double furnace mechanism includes a furnace bridge, a common chamber for feeding and burning, a flame compression zone, and a flame spraying zone; the furnace bridge is arranged below the common chamber for charging and burning; the common chamber for charging and burning is connected to the flame compression zone, The flame compression area is connected with the flame spraying area; the common chamber for feeding combustion and the flame spraying area are provided with an observation port furnace door.

The furnace bridge includes a water inlet, a bulk material plate, a furnace bridge pipeline, a bellows, and a water outlet; the furnace bridge pipeline is bent and laid on the bellows, and the furnace bridge pipelines are connected in one direction; the furnace bridge pipeline A bulk plate is installed on the upper bending section; the inlet end of the furnace bridge pipeline is connected to the water inlet, and the outlet end of the furnace bridge pipeline is connected to the water outlet.

The furnace bridge pipeline includes the bottom of the bent section, the middle part of the bent section, and the upper part of the bent section; the inclination angle between the upper part of the bent section of the furnace bridge pipeline and the horizontal plane is 45°-60°, and the inclination angle between the middle part of the bent section and the horizontal plane is 30°-45°, the inclination angle between the bottom of the bending section and the horizontal plane is 0°-10°; the inclination angle between the bulk material plate and the horizontal plane is 50°-60°, and the inclination angle between the bulk material plate and the horizontal plane is greater than that of the bent section The inclination angle of the upper part of the segment to the horizontal plane.

The cross-section of the furnace bridge pipe is trapezoidal, the wide side of the trapezoid faces upward, and the narrow side of the trapezoid faces downward.

The furnace includes a first heat exchange area, a second heat exchange area, a third heat exchange area, a fourth heat exchange area, and a smoke exhaust pipe; the first heat exchange area, the second heat exchange area, and the third heat exchange area Water pipes are arranged in the heat exchange area and the fourth heat exchange area; the flue gas inlet of the first heat exchange area is connected to the boiler furnace; the flue gas outlet of the first heat exchange area is connected to the flue gas of the second heat exchange area The inlet is connected; the flue gas outlet of the second heat exchange area is connected to the flue gas inlet of the third heat exchange area; the flue gas outlet of the third heat exchange area is connected to the flue gas inlet of the fourth heat exchange area; the The flue gas outlet of the fourth heat exchange area is connected to the exhaust pipe; the first heat exchange area, the second heat exchange area, the third heat exchange area, and the fourth heat exchange area are all equipped with a The pulling plate device; the pulling plate device is composed of a pull rod and a soot cleaning plate; a slag receiving box is arranged below the flue gas inlet of the first heat exchange area, and the flue gas outlet of the second heat exchange area is connected to the third A slag receiving box is arranged at the connection of the flue gas inlet of the heat exchange area; a smoke removal water tank is arranged between the flue gas outlet of the fourth heat exchange area and the smoke exhaust pipe.

The water pipe arrangement is a spatially staggered arrangement, and the spatially staggered arrangement is such that the vertical axes of adjacent water pipes do not overlap.

The density of water pipes in the first heat exchange zone, the second heat exchange zone, the third heat exchange zone, and the fourth heat exchange zone increases sequentially; the first heat exchange zone, the second heat exchange zone, the The diameters of the water pipes in the third heat exchange zone and the fourth heat exchange zone decrease sequentially.

The double furnace mechanism is provided with an observation port furnace door; the water tank is provided with a cold water inlet pipe and a hot water outlet pipe.

The beneficial effects of the present invention are: (1) The present invention is compact in structure, easy to install, and occupies a small area. The present invention combines the combustion chamber and the feeding area to form a common room for feeding and combustion, and the feeding machine is longitudinally arranged in the common room. Above, the boiler structure is simplified while reducing the footprint of the entire boiler.

(2) The auger propeller of the feeding machine of the present invention replaces the original biomass material with shaft extrusion and rotation to feed to the feed port, avoiding the situation that the long shaft extrusion feeding is easy to jam the material, or even the shaft is broken. The feeding mechanism is an ultra-short light-load energy-saving feeding device. After the fuel enters the fuel cylinder, the dragon advances to the position of the discharge port. Since the main shaft above the discharge port does not have a spiral piece, the biomass raw material is pushed to the discharge port naturally and evenly. drop.

(3) The furnace of the present invention includes a double furnace structure, furnace, water tank and insulation layer. The double furnace structure increases the flame channel, which can realize the full combustion of biomass, and the furnace has a multi-pass structure, adding a water tank The contact area with the double furnace structure and the furnace improves the heat recovery efficiency, and there are multiple water pipes in the furnace. The high-temperature flame zigzags from bottom to top and from top to bottom through multiple return journeys to reach the lowest point. When passing through the furnace, the solid dust in the high-temperature flame gas is blocked on the dense water pipe, which can not only effectively recover the dust in the flue gas, achieve the effect of dust removal at one time, but also effectively absorb the heat generated by the combustion of the flue gas, and the insulation layer It is very good to ensure that the heat will not be lost, thereby improving the thermal efficiency of the furnace and reducing heat loss.

(4) The furnace of the present invention includes four heat exchange areas, the volume of the four heat exchange areas is in the form of gradually decreasing, because the heat is also in the form of gradually decreasing, so the small volume can gradually compress the flue gas, improve its The heat per unit area, and the density of the water pipes in the heat exchange area is also gradually increased, increasing the contact area between the water pipes and the flue gas, thereby greatly improving the heat recovery efficiency of the flue gas.

(5) The furnace of the present invention is equipped with a special dust-cleaning pull plate device. One end of the device is equipped with a pull rod extending out of the boiler. As long as the pulling device is used, the smoke and dust at each corner of the inner tank and the dust attached to the water pipe can be removed. It is as clean as new, so the purpose of dust removal is achieved, and the thermal efficiency of the biomass boiler is improved at the same time, and the environmental protection effect is achieved.

(6) The present invention is equipped with a multi-stage dust removal device. The multi-return structure of the furnace and the water pipe arrangement of this device can perform dust removal on the flue gas once, and a slag receiving box is set under each return end of the furnace, and the slag receiving box It is a sink filled with water, and the water absorbs the remaining smoke and dust for secondary dust removal, which can achieve a good dust removal effect, and a smoke removal water tank is installed at the entrance of the smoke exhaust pipe, which can effectively carry out the third dust removal of the furnace smoke and dust , so as to reduce the impact of exhaust gas on the environment.

(7) The furnace bridge of the present invention adopts a backrest structure, that is, the furnace bridge adopts a slope design, and the upper part of the front end is provided with a bulk material plate, which is beneficial to the distribution and bulk material of biomass fuel; due to the relatively uniform distribution of fuel, So it is conducive to the full combustion of fuel.

(8) The furnace bridge of the present invention adopts interconnected furnace bridge pipes, and the furnace bridge pipes are connected to the boiler circulating water, which effectively absorbs the heat energy on the furnace bridge pipes, so that the furnace bridge is not easy to burn out, and at the same time it is beneficial to the furnace bridge. The effective use of heat on the pipeline prolongs the service life of the furnace bridge, and can make full use of heat energy, improve energy utilization rate, save energy and protect the environment.

(9) The trapezoidal design of the furnace bridge pipeline of the present invention has a trapezoidal wide side facing upward and a trapezoidal narrow side downward, which is conducive to air convection and improves the combustion rate.

(10) Since the water in the furnace bridge pipeline of the present invention has taken away a large amount of heat, the water temperature on the surface of the furnace bridge pipeline will not exceed 80°C, and since the steel can withstand temperatures above 800°C, there is no phenomenon of burning out the furnace bridge .

(11) The present invention is equipped with a plurality of ash-taking boxes and observation port furnace doors, which can effectively clean up the soot and maintain the combustion quality of the boiler. It can also observe the furnace through the observation port at any time, so as to know the combustion situation of the boiler in time and ensure Boiler operation safety and operating efficiency.

Description of drawings

Fig. 1 is a main sectional schematic diagram of the structure of the present invention.

Fig. 2 is a front view of the present invention.

Fig. 3 is a schematic diagram of the present invention equipped with a dust-cleaning and pulling plate device.

Fig. 4 is a schematic diagram of the spatial staggered arrangement of water pipes.

Figure 5 is a schematic structural view of the feeder.

Fig. 6 is a structural schematic diagram of the furnace bridge.

Fig. 7 is a front view of the furnace bridge.

Fig. 8 is a structural sectional view of the furnace bridge pipeline.

The numbers mentioned in the accompanying drawings of the specification are indicated as: 1. Feeding machine; 2. Furnace bridge; 3. Common room for feeding and burning; 4. Flame compression area; 5. Flame spraying area; 6. Smoke removal water tank; 7. Slag receiving box; 8. Induced fan; 9. Smoke exhaust pipe; 10. First heat exchange area; 11. Furnace gall; 12. Second heat exchange area; 13. Third heat exchange area; 14. Insulation layer ;15, water pipe; 16, water tank; 17, the fourth heat exchange area; 18, pull plate device; 19, observation port furnace door; 20, blower; 21, cold water inlet pipe; 22, hot water outlet pipe; Hopper; 102, auger propeller; 104, discharge port; 103, coupling; 1021, rotating shaft; 1022, spiral sheet; 201, water inlet; 202, bulk plate; 203, furnace bridge pipe; 204 , bellows; 205, water outlet.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings. The description in this part is only exemplary and explanatory, and should not have any limiting effect on the protection scope of the present invention. .

Referring to Fig. 1, Fig. 2, Fig. 3 and Fig. 4, a multi-return heat exchange biomass boiler, this device includes a boiler body and a blast and air induction system, and the boiler body includes a feeder 1, a double furnace mechanism, There are multi-return dense water pipe furnace 11, smoke exhaust pipe 9, double furnace mechanism, water tank 16 outside the furnace, and insulation layer 14 outside the water tank. The inlet of the double furnace mechanism is connected with the feeder 1 and the blower 20, the outlet of the double furnace mechanism is connected with the inlet of the furnace 11, and the outlet of the furnace 11 is connected with the exhaust pipe 9 and the induced draft fan 8.

Referring to Fig. 5, in a preferred implementation situation, the feeder includes a feed hopper 101, an auger propeller 102, a shaft coupling 103, and a discharge port 104, and the auger propeller 102 is arranged below the feed hopper 101, and the auger propeller 102 is arranged below the feed hopper 101, and the auger propeller 102 is arranged below the feed hopper. One end of the dragon propeller 102 is connected with the coupling 103, and the other end of the auger propeller 102 is connected with the discharge port 104. The auger propeller 102 includes a spiral piece 1021 and a straight shaft 1022, and the spiral piece 1021 is installed at the discharge port On the straight axis 1022 above 104 , the starting point of the spiral piece 1021 is below the feed hopper 101 , and the end point of the spiral piece 1021 is the position of the discharge port 104 .

Referring to Fig. 6, Fig. 7 and Fig. 8, in a preferred implementation situation, the double furnace mechanism includes a furnace bridge 2, a common chamber for charging and burning 3, a flame compression zone 4, and a flame spraying zone 5. Furnace bridge 2 is set under the feed combustion common room 3, the feed combustion common room 3 is connected with the flame compression zone 4, the flame compression zone 4 is connected with the flame spraying zone 5, and the feed material combustion common room 3 and the flame spraying zone 5 are set Observation port furnace door 19 is arranged.

In a preferred implementation situation, the furnace bridge 2 includes a water inlet 201 , a bulk plate 202 , a furnace bridge pipe 203 , an air box 204 , and a water outlet 205 . The furnace bridge pipeline 203 is bent and laid on the bellows 204. The furnace bridge pipelines 203 are connected in one direction. The upper bending section of the furnace bridge pipeline 203 is equipped with a bulk material plate 202. The inlet end of the furnace bridge pipeline 203 is connected to the water inlet. 205 , the outlet end of the furnace bridge pipe 203 is connected to the water outlet 205 .

The furnace bridge pipe 203 includes the bottom of the bent section, the middle part of the bent section, and the upper part of the bent section. °-45°, the inclination angle between the bottom of the bending section and the horizontal plane is 0°-10°, the inclination angle between the bulk material plate 202 and the horizontal plane is 50°-60°, and the inclination angle between the bulk material plate 202 and the horizontal plane is greater than that between the upper part of the bending section and the horizontal plane The inclination of the horizontal plane. The cross section of the furnace bridge pipe 203 is trapezoidal, the wide side of the trapezoid faces upward, and the narrow side of the trapezoid faces downward.

In a preferred implementation, the furnace chamber 11 includes a first heat exchange area 10, a second heat exchange area 12, a third heat exchange area 13, a fourth heat exchange area 17, a smoke exhaust pipe 9, and the first heat exchange area 10 , the second heat exchange area 12, the third heat exchange area 13, and the fourth heat exchange area 17 are provided with water pipes, the flue gas inlet of the first heat exchange area 10 is connected with the boiler furnace, and the flue gas in the first heat exchange area 10 The outlet is connected to the flue gas inlet of the second heat exchange area 12, the flue gas outlet of the second heat exchange area 12 is connected to the flue gas inlet of the third heat exchange area 13, and the flue gas outlet of the third heat exchange area 13 is connected to the fourth The flue gas inlet of the heat exchange area 17 is connected, the flue gas outlet of the fourth heat exchange area 17 is connected with the exhaust pipe 9, the first heat exchange area 10, the second heat exchange area 12, the third heat exchange area 13, the fourth heat exchange area The heat exchange area 17 is equipped with a pull plate device 18 for removing soot on the water pipe, and the pull plate device 18 is composed of a pull rod and a soot cleaning plate.

In a preferred implementation situation, a slag receiving box 7 is provided below the flue gas inlet of the first heat exchange zone 10, and a A smoke removal water tank 6 is arranged between the slag receiving box 7 , the flue gas outlet of the fourth heat exchange zone 17 and the smoke exhaust pipe 9 .

In a preferred implementation situation, the water pipes 15 are arranged in a spatially staggered manner, and the spatially staggered arrangement is such that the vertical directions of the axes of adjacent water pipes do not overlap.

In a preferred implementation, the density of water pipes in the first heat exchange area 10, the second heat exchange area 12, the third heat exchange area 13, and the fourth heat exchange area 17 increases sequentially, and the first heat exchange area 10, the second heat exchange area The diameters of the water pipes 15 in the second heat exchange area 12 , the third heat exchange area 13 , and the fourth heat exchange area 17 decrease in order.

In a preferred implementation situation, the double furnace mechanism is provided with an observation port furnace door 19, and the water tank is provided with a cold water inlet pipe 21 and a hot water outlet pipe 22.

In the specific operation, the biomass is stirred and pushed from the feed hopper 101 by the spiral piece 1021 to the discharge port 104, and enters the common feeding and combustion chamber 3 for combustion. The common feeding and combustion chamber 3 is designed in an arc shape, and the flame outlet is located Below, the flame compression zone 4 is formed. Due to the arc design, the flame compresses downward and returns to semi-gasification combustion, and then enters the flame spraying zone 5; the smoke generated by combustion enters the furnace 11 for heat exchange and dust removal, and the smoke passes through the first The heat exchange area 10, the second heat exchange area 12, the third heat exchange area 13, and the fourth heat exchange area 17, because the inner wall surface of the furnace 11 is concave-convex, and the furnace 11 is a snake-shaped multi-return structure and its There are multiple water pipes 15 inside, thereby increasing the contact area between the furnace 11, the water tank 16 and the water in the water pipe 15, improving the heat exchange efficiency, and also increasing the collision area between the flue gas and the furnace, so as to achieve the effect of dust removal once. Dust and ash in the flue gas fall into the slag receiving box 7 below the furnace; when the flue gas reaches the smoke exhaust pipe 9 through the multi-return furnace tube, it is removed through the smoke removal water tank 6 for dust removal.

After the boiler burns for a period of time, the pull plate device 18 is used to clean the water pipes 15 in the furnace 11 to ensure that the boiler burns and heats normally.

It should be noted that, in this document, the term "comprising", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements, It also includes other elements not expressly listed, or elements inherent in the process, method, article, or apparatus.

In this paper, specific examples are used to illustrate the principle and implementation of the present invention. The description of the above examples is only used to help understand the method and core idea of the present invention. The above is only a preferred embodiment of the present invention. It should be pointed out that due to the limitation of literal expression, there are objectively unlimited specific structures. Under these circumstances, several improvements, modifications or changes can also be made, and the above-mentioned technical features can also be combined in an appropriate manner; these improvements, modifications, or combinations, or the idea and technical solution of the invention can be directly applied to other occasions without improvement should be regarded as the protection scope of the present invention.

Claims (7)

1. the biomass boiler of back-stroke heat-exchange type more than, is characterized in that this device comprises boiler body and forced draft induced draft system; Described boiler body comprise charger, twin furnace mechanism, be provided with many backhauls gather water pipe internal furnace, smoke exhaust pipe, be arranged on twin furnace mechanism, flue outside water tank, be arranged on the heat-insulation layer of water tank outside; The entrance of described twin furnace mechanism is connected with charger, air blast, and the outlet of twin furnace mechanism is connected with the entrance of flue; The outlet of described flue is connected with smoke exhaust pipe, air-introduced machine.

2. one many back-stroke heat-exchange types biomass boiler according to claim 1, it is characterized in that, described charger comprises feed hopper, packing auger propeller, shaft coupling, discharging opening; Be provided with packing auger propeller below described feed hopper, one end of packing auger propeller is connected with shaft coupling, and the other end of packing auger propeller is connected with discharging opening; Described packing auger propeller comprises flight, d-axis; Described flight is arranged on the d-axis above discharging opening, and described flight starting point is below feed hopper, and described flight terminal is discharging opening position.

3. one many back-stroke heat-exchange types biomass boiler according to claim 1, is characterized in that, described twin furnace mechanism comprises grate, charge combustion shares room, flame compressional zone, FLAME district; Described grate is arranged on the below that charge combustion shares room; Described charge combustion shares room and is connected with flame compressional zone, and flame compressional zone is connected with FLAME district, and the channel space of flame compressional zone is less than the channel space that charge combustion shares room and FLAME district; Described charge combustion shares room and FLAME district and is provided with observation panel fire door.

4. one many back-stroke heat-exchange types biomass boiler according to claim 3, is characterized in that, described grate comprises water inlet, bulk material plate, grate pipeline, bellows, delivery port; Described grate pipeline is bent, is layed on bellows, unilaterally connected between grate pipeline; Described grate conduit upper bending segment is provided with bulk material plate; The arrival end of described grate pipeline connects water inlet, and the port of export of grate pipeline connects delivery port.

5. one many back-stroke heat-exchange types biomass boiler according to claim 4, is characterized in that described grate pipeline includes bottom bending segment, in the middle part of bending segment, bending segment top; The bending segment top of grate pipeline and the inclination angle of horizontal plane are 45 °-60 °, are 30 °-45 ° with the inclination angle of horizontal plane in the middle part of bending segment, are 0 °-10 ° with the inclination angle of horizontal plane bottom bending segment; Described bulk material plate and the inclination angle of horizontal plane are 50 °-60 °, and the inclination angle of bulk material plate and horizontal plane is greater than the inclination angle of bending segment top and horizontal plane.

6. the one many back-stroke heat-exchange types biomass boiler according to claim 4 or 5, is characterized in that described grate cross-section of pipeline is trapezoidal, and towards being trapezoidal broadside above, court is trapezoidal narrow limit below.

7. one many back-stroke heat-exchange types biomass boiler according to claim 1, is characterized in that, described flue comprises the first heat transfer zone, the second heat transfer zone, the 3rd heat transfer zone, the 4th heat transfer zone, smoke exhaust pipe; Water pipe is provided with in the first described heat transfer zone, the second heat transfer zone, the 3rd heat transfer zone, the 4th heat transfer zone; The smoke inlet of described first heat transfer zone is connected with boiler furnace; The exhanst gas outlet of described first heat transfer zone is connected with the smoke inlet of the second heat transfer zone; The exhanst gas outlet of described second heat transfer zone is connected with the smoke inlet of the 3rd heat transfer zone; The exhanst gas outlet of described 3rd heat transfer zone is connected with the smoke inlet of the 4th heat transfer zone; The exhanst gas outlet of described 4th heat transfer zone is connected with smoke exhaust pipe; The plate pulling device for removing cigarette ash on water pipe is provided with in described first heat transfer zone, the second heat transfer zone, the 3rd heat transfer zone, the 4th heat transfer zone; Described plate pulling device is made up of pull bar and ash-removing plate; Be provided with below the smoke inlet of described first heat transfer zone and connect slag box, the exhanst gas outlet of described second heat transfer zone and the smoke inlet junction of the 3rd heat transfer zone are provided with and connect slag box; A smoke abatement water tank is provided with between the exhanst gas outlet of the 4th described heat transfer zone and smoke exhaust pipe.

8. one many back-stroke heat-exchange types biomass boiler according to claim 7, is characterized in that described water pipe arrangement is spatial intersecting arrangement, and described spatial intersecting arrangement is that the axes normal direction of adjacent water pipe does not overlap.

9. one many back-stroke heat-exchange types biomass boiler according to claim 8, is characterized in that the water pipe density in the first described heat transfer zone, the second heat transfer zone, the 3rd heat transfer zone, the 4th heat transfer zone is rise successively; Water pipe diameter in the first described heat transfer zone, the second heat transfer zone, the 3rd heat transfer zone, the 4th heat transfer zone is in declining successively.

10. one many back-stroke heat-exchange types biomass boiler according to claim 1, is characterized in that, described twin furnace mechanism is provided with observation panel fire door; Described water tank is provided with cold water inlet and hot water outlet pipe.