Second, the pot shell boiler
There are two types of pot shell boiler: one is a vertical pot shell boiler (longitudinal axis of the pot shell perpendicular to the ground boiler); the second is a horizontal pot shell boiler (longitudinal axis of the pot shell parallel to the ground boiler). The former mainly has four kinds of vertical horizontal water tube boilers, vertical straight water tube boilers, vertical curved water tube boilers and vertical horizontal water tube boilers. The latter mainly horizontal internal combustion boilers and horizontal external combustion boilers.
1. Vertical shell boiler
(1) Vertical horizontal water tube boiler structure This boiler looks like a vertical cylinder from the outside, its structure is shown in Figure 2-2, mainly by the pot shell, head, gallbladder, gallbladder top, horizontal water tubes and cupola and other pressurized parts. There are two types of combustion: a single fixed grate and a double fixed grate. The evaporation capacity of the boiler is generally less than 0.5 tons / hour (t / h), and the rated working pressure is less than 0.4 megapascals (MPa). The flue gas flow of the vertical cross water tube boiler is that the high temperature flue gas produced by burning coal on the grate, rises along the furnace gallbladder, flushes the cross water tube, the furnace gallbladder and the cupola tube, transfers the heat to the pot water, and then discharges from the chimney.
Vertical cross-tube boiler water cycle route is, the pot near the furnace gallbladder, the top of the furnace gallbladder, the cross-tube and the cupola pipe of the water is heated, more vapor content, the specific gravity of the small and upward flow; close to the pot shell of the water is not heated, the vapor content of the small, the specific gravity of the big and downward flow. This will form a water cycle.
Vertical cross-tube boiler is easy to damage the following parts: ① cupola tube of the vapor separation is easy to corrode. ② grate surface above the part of the furnace liner steel plate, in the internal accumulation of scale is prone to overheating and deformation. ③ The steel plate of the lower part of the pot shell is easy to be corroded by moisture. ④ cross water pipe, such as scale, easy to produce overheating bulging. ⑤ Head and cupola connection is easy to burn out.
Prevention of cupola vapor separation corrosion: can be installed in the cupola tube with a pig iron casing prevention. Pig iron casing into the cupola length should be stretched to the minimum water level below the line; pig iron casing outer diameter should be at least 25 millimeters (mm) smaller than the inner diameter of the cupola, in order to facilitate the installation and pumping.
The cross water pipe has three roles: one is to increase the heating surface of the boiler; the second is to facilitate the water circulation in the pot; the third is to improve the pressure-bearing strength of the furnace chamber.
The advantages of vertical cross-tube boilers are: simple structure, easy to operate and maintain; no brick wall, small footprint, easy to carry and install; small water capacity, quick fire, stop the furnace. Disadvantages are: less heating surface, evaporation is small; exhaust temperature is high, low thermal efficiency; water-cooled furnace, only suitable for burning high-quality coal.
(2) Vertical straight water tube boiler structure (Figure 2-3) This boiler has a top and bottom two sections of the drum, straight water tube and the top and bottom of the drum tube plate connected to form a convection tube bundle, the center is equipped with a large-diameter downward tube, convection tube bundle of the outside of the circle has a fire-resistant wall, directly behind the door of the furnace is equipped with a smoke box. Its structure is shown in Figure 2-4, mainly composed of upper and lower boiler, upper and lower tube plate, furnace chamber, throat, straight water pipe and falling pipe and other pressurized parts. Boiler evaporation is generally less than 0.7 tons / hour (t / h), the rated working pressure is less than 0.7 megapascals (MPa). Vertical straight water tube boiler flue gas flow: coal burns on the grate in the furnace gallbladder, and the high temperature flue gas enters the convection tube bundle through the throat at the top of the furnace gallbladder for transverse scouring exothermic and rotates around the overflow tube bundle for one week, then enters the rear flue gas box, and then discharges from the chimney.
Vertical straight water tube boiler water cycle route: the water around the furnace gallbladder and throat is heated up, all the straight water tube water is also heated up, only the middle of the drop tube is less heated, the water flow down. This will form a water cycle.
Advantages of vertical straight water tube boiler: compact structure, water circulation is better; upper and lower tube plate is not easy to overheat and burn; straight water tube maintenance is convenient to remove the scale, the thermal efficiency is higher than the vertical horizontal water tube boiler. Disadvantages: the gallbladder of the water-cooled, not suitable for burning poor-quality coal; the lower tube plate is easy to accumulate ash, such as not clear in time, both affecting heat transfer and corrosion of the steel plate.
(3) the structure of the vertical bend water tube boiler mainly consists of a pot shell, header, furnace gall bladder, the top of the furnace gall bladder, inner and outer bend water tube, pipe and other pressurized parts (Figure 2-5). The evaporation capacity and working pressure of the boiler are the same as those of vertical straight water tube boiler. Vertical watertube boiler flue gas flow: coal combustion grate in the furnace gallbladder, resulting in high-temperature flue gas to the inner watertube exothermic, from the pipe into the back of the smoke box, left, right and two ways around the pot inside and outside of the watertube shell each rotating half a week, lateral scouring of the outer watertube, and then converge in the front smoke box through the chimney discharge.
Vertical bending water pipe boiler water cycle route: near the furnace gallbladder and the inner and outer bending water pipe in the pot of water heated, specific gravity is small and upward flow; near the pot shell of the pot of water heated, weaker than the major and downward flow. This will form a water cycle.
Advantages of vertical curved water tube boiler: boiler with curved water tube, flexible structure; furnace gallbladder to increase the radiation heating surface, can increase the evaporation; water circulation is better, faster pressure. Disadvantages: the furnace water-cooled, unsuitable for burning poor quality coal; inside and outside the bent water pipe is easy to be clogged with scale burnt; outside the bent water pipe is easy to accumulate ash between; smoke box activities, more iron doors, easy to leak the impact of combustion.
(4) vertical cross-fire tube boiler structure mainly consists of pot shell, head, furnace chamber, front and rear tube plate, throat and cross-fire tube and other pressurized parts (Figure 2-6). Boiler steam equivalent is generally less than 1 ton / hour (t / h), the working pressure is less than 0.8 megapascals (MPa). Vertical cross-fire tube boiler water cycle route: near the furnace chamber and cross water tube pot water is heated by strong, small specific gravity and upward flow; near the pot shell of the pot water is heated by the weak, specific gravity and downward flow. This will form a water cycle.
Vertical cross-fire tube boiler flue gas flow: coal burned on the grate in the furnace gallbladder, high-temperature flue gas from the upper part of the furnace gallbladder pipe into the rear flue box, and then through the cross-fire tube to the front flue box, the chimney discharged.
Advantages of vertical cross-fire tube boiler: compact structure, more heating surface; better water circulation, faster pressure rise. Disadvantages: large degree of water cooling in the furnace, not conducive to combustion; easy to accumulate ash in the cross-fire tube; easy to leak the front and rear smoke box door.
Vertical cross-fire tube boiler cross-fire tube role: cross-fire tube on the front and back of the tube plate has the role of supporting the reinforcement, can improve the compressive strength of the tube plate.
Vertical pot shell boiler furnace guts: the lower part of the furnace guts can be set up fixed grate, the upper space can be used as a combustion chamber, is the boiler's radiation heating surface.
Advantages of vertical pot shell boiler with u-shaped foot ring: easy to boiler, furnace gallbladder welding docking, weld quality; structure is rich in elasticity, the boiler has high compressive strength.
2. Horizontal shell boiler
(1) the structure of the horizontal combustion boiler This boiler has a large-diameter shell, in which the set of the furnace gallbladder, grate resting on the gallbladder constitutes the internal combustion chamber, the gallbladder at both ends, respectively, with the front and rear tube plate is connected to the pipe, the flue gas pipe is arranged in the front and rear of the plate, the boiler does not need to lay a brick wall on the outside. Its structure is shown in Figure 2-7, mainly by the pot shell, furnace chamber, before and after the tube plate, smoke pipe and other pressurized parts. Boiler evaporation is generally less than 4 tons / hour (t / h), the working pressure is less than 1.3 megapascals (MPa). Horizontal internal combustion boiler flue gas flow: coal combustion in the furnace gallbladder produces high temperature flue gas, from the front of the furnace gallbladder backward flow, in the back of the boiler turns into the furnace gallbladder on both sides of the flue pipe; from the back of the front to the front of the smoke box, and then upward turn into the upper part of the furnace gallbladder flue pipe, from the front to the back of the flow to the chimney discharge.
Horizontal internal combustion boiler water cycle route: near the furnace chamber and smoke tube of the water is heated more strongly, the specific gravity of the small and rising, near the pot shell of the water is heated more weakly, the specific gravity of the big and down, so the formation of water circulation in the pot.
Advantages of horizontal internal combustion boilers: the boiler as a whole factory, fast and easy to install; the furnace does not need to build a brick wall, covering a small area; short time to raise the fire, produce steam quickly. Disadvantages: large water-cooled furnace, not suitable for burning poor-quality coal; easy to accumulate ash in the flue pipe, need to be frequently cleaned; pot between the flue pipe scale, not easy to remove; flue pipe tube end of the expansion port is easy to leak.
Horizontal internal combustion boiler is easy to damage the part: the boiler's furnace chamber before the first two sections of the high temperature, such as the accumulation of scale in the pot or a serious lack of water, the furnace chamber is prone to overheating deformation and collapse; uneven heating or accumulation of scale in the flue gas pipe, the front and back of the tube plate is easy to bulge out of the deformation or the flue gas pipe end of the expansion port leakage, serious cases of cracks between the tube holes will be produced.
(2) Horizontal external combustion boiler This boiler shell within the furnace gallbladder into a number of flue tubes, the grate is moved to the bottom of the shell, constituting the external combustion chamber, the boiler outside the light brick wall. Its structure is shown in Figure 2-8, mainly by the pot shell, before and after the tube plate, flue gas pipe, water-cooled wall pipe, down tube and set of boxes and other pressurized parts. The evaporation capacity of the boiler is less than 6 tons / hour (t / h), the working pressure is less than 1.3 megapascals (MPa).
Horizontal external combustion boiler flue gas flow: external combustion of high-temperature flue gas in the furnace chamber, scouring the bottom of the pot shell and the two sides of the water-cooled wall tubes, from the rear of the boiler into the first part of the flue pipe, from the back to the forward flow, arriving in front of the smoke box and then turn 180 ° turn into the second part of the flue pipe, and from the front to the back of the flow, and finally discharged into the atmosphere through the induced draft fan and the chimney.
Horizontal external combustion boiler water cycle route is divided into two parts: one part is the water in the pot shell through the downward tube into the collection box, allocated to the water-cooled wall pipe; water-cooled wall pipe is heated, the water flows upward to return to the pot shell, the formation of water circulation. The other part is the first part of the smoke pipe inside the pot shell is heated strongly, the surrounding water flows upward; the second part of the smoke pipe is heated weakly, the surrounding water flows downward, forming a water cycle.
Advantages of the horizontal external combustion boiler: the boiler as a whole factory, easy to transport and install; short time to raise the fire, produce steam quickly; furnace space is larger, conducive to combustion, high thermal efficiency. Disadvantages: easy to accumulate ash in the flue tube, need to be cleaned frequently; water-cooled wall tubes in the hearth are easy to overheat and burn out, such as serious scaling in the pot, the bottom of the pot shell is easy to overheat and bulging; after the tube plate of the flue pipe expansion is easy to leak or between the pipe holes are easy to produce cracks.
Third, water-tube boiler
Evaporative heating surface is composed of all the water tubes, and the boiler is not arranged in the pot tube evaporative heating surface, called water-tube boiler. Common forms of double longitudinal pot tube water tube boiler, double horizontal pot tube water tube boiler and single longitudinal pot tube water tube boiler.
1. double longitudinal cylinder water tube boiler according to its structural characteristics can be divided into two types of D-shaped and and KB-shaped. D-shaped structure is characterized by the arrangement of the furnace in the double longitudinal side of the cylinder, the other side of the convection flue. And KB-shaped structure is characterized by the layout of the furnace in the center of the double longitudinal cylinder, because the lower pot is shorter than the upper pot, the empty space just arranged for the furnace, the rear of the convection flue.
(1) double longitudinal cylinder (D-shaped) water tube boiler structure mainly consists of the upper and lower longitudinal cylinder, convection tube bundle, water-cooled wall tubes, descending tubes and collector box and other pressurized components (Figure 2-9). In the upper and lower longitudinal cylinder is arranged between a number of bent water pipe (convection tube bundle) constitutes the convection flue; furnace is arranged in the convection flue side, the furnace is arranged around the water-cooled wall tubes and collector box. The whole furnace shape is similar to D shape. The combustion equipment adopts chain grate or reciprocating grate, and there is a coal economizer in the tail flue. Boiler evaporation is generally less than 6 tons / hour (t / h), the working pressure is less than 1.3 megapascals (MPa). Double longitudinal drum (D-shaped) water tube boiler flue gas flow route: coal combustion in the furnace produces high-temperature flue gas, flue gas outlet from the rear side of the furnace into the convection flue, first through the first convection bundles from the back to the front flow, to reach the front end of the flue 180 ° turn into the second convection bundles, and then from the front to the back of the flow, and finally through the economizer, by the induced draft fan and chimney discharge.
Double longitudinal cylinder (D-shaped) water tube boiler water cycle is divided into two parts: one part is the upper cylinder of the water by the weaker heat of the second convection tube bundle down to the lower cylinder, and then from the stronger heat of the first convection tube bundle up to return to the upper cylinder and the formation of the cycle; the other part of the water-cooled wall tubes around the hearth water heating to rise to the upper cylinder, from the upper and lower cylinders were led out of the downward tube connected to the collection box The other part is that the water in the water-cooled wall tube around the furnace is heated and rises to the upper cylinder.
Double longitudinal cylinder (D-shaped) water tube boiler advantages: the upper and lower longitudinal cylinder water capacity, good adaptability to load changes; convection tube bundles are curved tubes, the structure of the elasticity; long and narrow hearth, suitable for the use of mechanized grate, high thermal efficiency. Disadvantages: convective tube bundles are easy to accumulate ash, such as not timely removal, will make the thermal efficiency decline; the quality of the feed water requirements are strict, otherwise the scale is not easy to remove.
(2) double longitudinal cylinder water tube boiler structure mainly consists of upper and lower longitudinal cylinder, convection tube bundle, water-cooled wall tubes, collector box and downward tube and other pressurized components. Its structure is shown in Figure 2-10, the length of the lower cylinder is about half shorter than that of the upper cylinder, the empty space is set up for the furnace, between the two cylinders are arranged in a curved water pipe, the furnace is arranged around the water-cooled wall pipe. The combustion equipment adopts coal thrower or coal thrower with inverted chain grate, and there is a coal economizer in the tail flue. Boiler evaporation is generally less than 20 tons / hour (t / h), the working pressure is less than 2.5 megapascals (MPa).
The flue gas flow of double longitudinal pot-bellied (KB-shaped) water tube boiler: high temperature flue gas from the right side of the furnace exit into the rear convection flue, along the two smoke walls in an S-shape flow, transverse scouring of the convection tube bundles, and then from the left side of the furnace wall flow through the coal economizer, by the induced draft fan and chimney discharge.
Double longitudinal cylinder (and KB-shaped) water tube boiler water cycle is divided into two parts: one part is the upper cylinder of the water from the rear of the weaker heat convection tube bundle down to the lower cylinder, and then by the lower part of the lower cylinder in front of the convection tube bundle of the stronger heat to rise, and return to the upper cylinder and the formation of the cycle; the other part of the water-cooled wall tubes around the hearth water heating to rise to the upper cylinder, from the lower cylinder led to the lower tube through the various collector to the water-cooled wall tube water supply, forming a water cycle. The other part is the water around the furnace water-cooled wall pipe is heated up to the upper cylinder, the lower cylinder leads to the descending tube through the collection box to the water-cooled wall pipe water supply, the formation of water circulation.
The advantages of double longitudinal cylinder (KB-shaped) water tube boiler: the upper cylinder is longer, the water capacity is large, the operating load is more stable; convection tube bundle are curved tubes, free expansion performance is good. Disadvantages: easy to accumulate ash between the convective tube bundles; strict requirements for the quality of feed water; high concentration of soot, high carbon content of fly ash, the heating surface and induced draft fan easy to wear.
2. The structure of the double cross-bottle water tube boiler mainly consists of upper and lower cross-bottle, convection tube bundle, water-cooled wall pipe, down tube and set of box and other pressurized components (Figure 2-11). The front of the boiler is the furnace, which is surrounded by water-cooled walls; the upper and lower cross-bottom tubes are located at the back of the furnace, and the two tubes are connected by a curved water pipe. The combustion equipment mostly adopts chain grate, some are pulverized coal furnace or boiling furnace, equipped with superheater, coal economizer and air preheater. Boiler evaporation is generally less than 20 tons / hour (t / h), the working pressure is less than 2.5 megapascals (MPa). Flue gas flow of the double transverse boiler water tube boiler: high-temperature flue gas from the furnace chamber after the upper flow through the superheater into the convection flue, first down and then up in an S-shape rise, transverse scouring of the convection tube bundles to reach the upper part of the flue and then folded down into the tail flue, through the economizer, the air preheater, by the induced draft fan, chimney discharge into the atmosphere.
The water circulation of the double cross-bottom water tube boiler is divided into two parts: one is the convection tube bundle between the upper and lower cross-bottom boiler for water circulation; the other part is the water-cooled wall tubes around the furnace for water circulation, in which the vapor-water mixture in the water-cooled wall tubes in the front and back directly into the upper boiler, and the vapor-water mixture in the two water-cooled wall tubes on both sides of the water-cooled wall tubes need to be through the upper collector and the guide tube into the upper boiler. The water in each water-cooled wall tube is supplied by the drop tube leading from the lower cylinder.
Advantages of double cross-bottom water tube boiler: reasonable and reliable structure, good load adaptability, high thermal efficiency, easy operation and maintenance, low labor intensity. Disadvantages: high volume, frame metal consumption; the quality of water supply and the technical level of the furnace requires a high level.
3. The structure of the single longitudinal cylinder water tube boiler is divided into a light wall furnace type and heavy wall bulk furnace type of two kinds of longitudinal cylinder, water-cooled wall tubes, convection tube bundles and the left and right set of boxes are composed of. Its construction features: longitudinal arrangement of the pot in the center of the upper part of the hearth, two groups of convection tube bundle and water-cooled wall tubes were arranged on both sides of the hearth, left and right symmetry, similar to the A-shaped. Figure 2-12 for the lightweight wall of the whole furnace type, combustion equipment using chain grate, boiler evaporation less than 6 tons / hour (t / h), the working pressure is less than 1.3 megapascals (MPa). The flue gas flow of the lightweight furnace wall type: the high temperature flue gas enters the left convection flue from the left outlet at the back of the hearth, passes through the transverse flue at the front end of the drum from back to front, folds into the right convection flue, and then flows to the coal economizer from front to back, and is discharged through the induced draft fan and the chimney.
The water circulation of the light-weight walled complete furnaces: the water in the upper cylinder descends to the lower header through the weaker convection tube bundles on the left and right sides, and then is distributed to the water-cooled wall tubes on the left and right sides and the stronger convection tube bundles by the lower header, and rises back to the upper cylinder.
Advantages of single longitudinal cylinder water tube boiler: the use of a cylinder, saving steel; the furnace body is A-shaped, the roof insulation layer is convenient to lay; convection tube bundles on both sides of the wall is not built, the structure is simple. Disadvantages: a single cylinder water capacity is small, the operation of the vapor pressure, water level fluctuations; the quality of water supply and operation and management level requires a high level.