Boiler consists of "pot" and "furnace".
(1) The basic component of a boiler is called the boiler body, which consists of a boiler, a furnace and safety accessories.
1, boiler:
Comprises a steam drum, a tube bundle, a water wall, a header and a downcomer. In the steam-water system in the boiler, the high-temperature combustion product flue gas transfers heat to the lower-temperature water in the boiler through the heating surface, and the water is heated, boiled and vaporized to generate steam.
2, the stove:
(Layer combustion furnace) includes coal hopper, grate, furnace, slag discharge plate, air supply device, etc. The combustion equipment in the boiler body converts the chemical energy of fuel into heat energy through combustion.
3, safety accessories:
Water level gauge, pressure gauge, safety valve, etc. And boiler metal steel frame and platform stairs.
(2) "Boiler" consists of economizer, drum, downcomer, water wall header, water wall, superheater and reheater.
1, economizer:
The vertical flue located at the tail of the boiler heats the boiler feed water by using the waste heat of flue gas, which reduces the exhaust temperature, improves the boiler efficiency and saves fuel.
2, steam drum:
Located at the top of the boiler, it is a cylindrical pressure-bearing container with water below and steam above. It receives water from the economizer and forms a water circulation loop with the downcomer, header and water wall. The steam-water mixture generated by water absorbing heat in the water wall is collected in the drum, and the saturated steam is transported to the superheater after steam-water separation.
3, downcomer:
It is the water supply pipe of water wall, and its function is to introduce the water in the steam drum into the lower header and then distribute it to the water wall pipes. There are two kinds of downcomers: small diameter dispersed downcomers and large diameter centralized downcomers. The small diameter downcomer is not conducive to water circulation.
4, water wall header:
The main function of the header is to collect quality or redistribute the working medium to other pipelines through the header. The header under the water wall is a thick pipe with two closed ends, which is used to connect the downcomer with the water wall so as to collect, mix and redistribute the working fluid.
5, water wall:
Located around the furnace, its main task is to absorb radiant heat in the furnace and make water evaporate. It is the main heating surface of modern boiler and can also protect the furnace wall.
6. Superheater:
Its function is to heat the saturated steam from the drum into superheated steam with a certain temperature.
7. Reheater:
Its function is to reheat the steam that has done some work in the turbine, and then send it to the turbine to continue to do work.
(3) The "furnace" is a combustion system, and its task is to make the fuel burn fully in the furnace and release heat. It consists of a furnace, a burner, an ignition device, an air preheater, a flue, a furnace wall and a frame.
1, furnace:
It is converted into fuel combustion by furnace wall and water cooling wall, and the fuel is suspended and burned in this space, releasing a lot of heat.
2. Burner:
Located at the four corners or walls of the furnace, its function is to inject fuel and air into the furnace at a certain speed, so that they can be well mixed in the furnace to ensure that the fuel can catch fire in time and burn completely quickly. There are two basic types: DC burner and swirl burner.
3. Air preheater:
It is a heat exchanger for exchanging heat between flue gas and air, belonging to combustion system. The air preheater is usually arranged in the flue at the tail of the boiler, and uses the waste heat of flue gas to heat the air at room temperature, so that the air is heated to the temperature required for fuel combustion and then sent to the furnace.
Function:
(1), reduce the exhaust temperature and exhaust heat loss Q2;
(2) The overall effect is to improve the thermal efficiency of the boiler by ensuring the timely ignition of the fuel, stabilizing and improving the combustion and improving the combustion efficiency.
4, smoke duct:
It is a pipe composed of furnace wall, partial heating surface pipes and wall-wrapped pipes, which is used to guide the flow of flue gas and exchange heat through various heating surfaces, and is divided into horizontal flue and tail flue. Auxiliary equipment Auxiliary equipment includes ventilation equipment (induced draft fan and induced draft fan), fuel conveying equipment, pulverizing system, dust removal equipment and desulfurization equipment.
Second, other components:
1, drum:
Its function is to collect, store, purify steam and supplement water supply. In water-tube boilers, there are usually one or two drums, the upper drum is called steam drum, and the lower drum is called water drum or mud drum. The upper drum is internally provided with a water distribution tank with uniform water supply, a steam-water separation device and a continuous blowdown device. There are assembled pipes and baffles in the drum of hot water boiler. Connecting pipes such as main steam valve, auxiliary steam valve, safety valve, air valve, water level gauge, sewage pipe and pressure gauge are installed outside the upper drum. Manhole door at one end or top of the upper drum.
One end of the lower drum is provided with a manhole, and the bottom is provided with a regular blowdown device. The upper and lower drums are connected by many ascending pipes and descending pipes (bundles), and the whole drum is elastic.
The diameter of the upper drum is slightly larger than that of the lower drum, and a convection tube bundle is connected between the two drums. The convection tube bundle consists of seamless steel tubes with an outer diameter of 5 1 mm, which are arranged in series in the convection flue. The convection flue is divided into two halves by the refractory wall in the longitudinal direction, and the flue gas flows in a U shape along the convection flue. Boiler heating surface: absorbs heat from exothermic medium and transfers it to the solid surface of heated medium. According to the characteristics of heat transfer process, it is divided into radiation heating surface, convection heating surface and boiling layer buried tube heating surface.
2, water wall heating surface:
The water wall is a radiant heating surface arranged around the furnace. In industrial boilers, it is generally made of corroded φ 5 1× 3 ~ φ 63.5× 3.5 mm boiler steel pipe, which is the main heating surface of water-tube boilers. The radiant heating surface absorbs the radiant heat of the flame and shields the furnace wall, thus protecting the furnace wall; At the same time, because of absorbing more heat, the furnace temperature can be reduced and coking of burning coal seam can be prevented.
The upper part of the water wall is directly connected with the upper boiler or connected with the upper boiler drum through the upper header first. Boiler water from the upper drum is pumped into the lower drum and the lower header through the downcomer, absorbed by the water wall to form a steam-water mixture, and rises to the upper drum to form a closed natural circulation.
In the past, fins (also called fins) were welded on both sides of the water wall tubes of some fast-loading boilers. Its purpose is to receive more radiant heat from the furnace and increase the shielding area of the furnace wall. Because of its difficult processing and poor thermal conductivity, it is easy to crack and tear the water wall tube in serious cases, so it has been seldom used and gradually replaced by special-shaped steel tube.
3. Title:
It is the main part of the arrangement and connection of collector tubes, and has the functions of distributing water and leading out. According to its position, it can be divided into upper header and lower header or inlet header and outlet header.
The upper header is located at the upper part of the furnace tube, which collects the water vapor mixture of the ascending tube bundle and leads it to the steam drum through the conduit. Some upper headers are installed outside the furnace wall, and there are rows of hand holes in the position opposite to the furnace tube to clean the inside of the furnace tube.
The lower header is located at the lower part of the furnace tube and connected with the lower drum to supply water and distribute it to the ascending furnace tube. Located on both sides of the grate.
The lower header on the side can prevent the furnace walls on both sides of the grate from burning out or hanging coke, which is called anti-coke box. There is a drain pipe and a hand hole at the end of the lower header for checking and cleaning the inside of the header.
In addition to the header of the boiler body, there are also corresponding headers on the economizer, superheater and other components.
The header is generally welded by seamless steel pipe with large diameter and two end covers. In recent years, some manufacturers have spun the pipe end instead of welding the end cover, which makes the structure more reasonable.
4, convection tube bundle heating surface:
Convection tube bundle, also known as convection tube bundle, is located between the upper and lower drums and generally consists of φ5 1×3mm boiler steel tubes, which are the main heating surfaces of water-tube boilers. In order to fully absorb heat, a trap wall is usually used in the middle of the convection tube bundle to form a back-and-forth or turning flue, increase the flue gas flow, and laterally scour the tube bundle at high smoke velocity. Usually, the tube bundle washed with flue gas first becomes an ascending tube because of the high flue gas temperature, more heat transfer and low density of steam-water mixture in the tube, while the flue gas temperature is low and less heat transfer becomes a descending tube.
Flue gas washing tube bundle generally adopts transverse washing. Because of transverse scouring, the thermal effect is better than that of longitudinal scouring. The heat transfer effect of staggered tubes is better than that of straight tubes, but with the improvement of heat transfer effect, the flow resistance of flue gas increases accordingly.
5. Heating surface of pyrotechnic tube:
Flue pipe is the main heating surface of flue pipe boiler and water-fire pipe combined boiler. Its function is to continuously heat the boiler water outside the furnace when the high-temperature flue gas generated by furnace combustion flows through the tube, so that it gradually becomes steam (or hot water). The flue pipe is generally installed in the boiler shell and fixed on the tube plates at both ends by welding or expansion joints. Because its installation quantity is limited by the boiler shell, the pipeline is easily blocked by dust and scale, which is not suitable for larger boilers. But in recent years, large-scale water-fire tube boilers are also under study, and some progress has been made.
In recent years, a new type of flue pipe, namely threaded flue pipe, has been popularized and applied. It presses a threaded groove with a depth of about 2mm on the flue pipe, which improves the heat dissipation of flue gas to the pipe wall, and the effect is remarkable. Compared with ordinary smoke pipes, the heat transfer effect of this threaded smoke pipe can be improved by nearly two times.
6. Superheater:
Economizer and air preheater. All belong to convection heating surface. Superheaters include convection superheaters and radiation superheaters, and the remaining economizer and preheater are equipped with boiler tail flue. Their main function is to further reduce the exhaust gas temperature and improve the thermal efficiency of the boiler.
The furnace is located in front of the boiler body, where the fuel is burned. It includes combustion equipment and a stove. Because of different fuels, the combustion modes are different, mainly including layer combustion furnace, chamber combustion furnace, cyclone furnace, boiling furnace and so on. Water wall pipes are installed around their stoves. In order to enhance fuel combustion, the layer furnace also has a front arch and a rear arch. Different furnaces have different structures, but they all have room for organizing fuel combustion and corresponding combustion equipment.
The boiler and the furnace are connected through the heat transfer process, and the heating surface is the interface between the boiler and the furnace. Whenever there is an exothermic medium (flame, smoke) on one side, there is a heated medium (water, steam, air) on the other side for heat transfer, and the heat exchange between them depends on the heated surface.
The boiler body consists of drum, heating surface, connecting pipe and flue, combustion equipment and slag tapping equipment, furnace wall and frame (including platform and escalator).