Overview of the technical performance of GEF high-efficiency industrial boilers

Thread Content

Overview of the Technical Performance of GEF High-Efficiency Industrial Boilers Wang Dunen, Deputy Director of the GEF China High-Efficiency Industrial Boilers Project Office, Senior Engineer 0 Introduction Industrial boilers are important thermal power equipment that are widely used in areas such as factory power generation, building heating, domestic use, and cogeneration; there is a high demand for them. By the end of 1998, the total number of industrial boilers in use across the country was 501,200 units, equivalent to 1.2569 million steam tons. The annual production capacity of industrial boilers by around 700 boiler manufacturing plants remained at roughly 30,000 to 40,000 units, or about 80,000 to 100,000 steam tons. Industrial boilers in China mainly use coal as fuel. Due to the large number of scattered manufacturers, the technical level of their products is low, resulting in poor operational efficiency and high levels of pollutant emissions. Currently, the dust (TSP) emitted by industrial boilers accounts for about 37% of the total national emissions, SO2 accounts for 37% of the total national emissions, and CO2 accounts for around 28% of the total national emissions. These emissions have a direct impact on the global greenhouse effect, drawing attention worldwide. To improve this situation, the Global Environment Facility (GEF) funded China’s GEF Efficient Industrial Boilers project with $32.81 million through a World Bank grant, to support the development of innovative and improved designs for efficient and clean coal-fired industrial boilers. The entire project is divided into nine sub-projects. Sub-projects 1 to 6 involve the improvement of existing boilers by introducing advanced foreign technologies, including: quick-installation water-tube boilers, improved fire-and-water-tube boilers, assembled water-tube boilers, boilers for high-sulfur coal, quick and assembled water-tube hot water boilers, and fire-and-water-tube boilers with a pre-mounted furnace. Sub-projects 7 to 9 are projects for developing new coal-fired industrial boilers using advanced foreign technologies, including: cogeneration stoker boilers, large-capacity hot water boilers, and circulating fluidized bed boilers. This article will provide a brief overview of the technical characteristics of these nine types of industrial boilers. 1 Double-drum vertical chain-grate steam boiler 1.1 Boiler overview This product is an efficient, energy-saving, and low-pollution device that was developed based on the original SZL model produced by Tianshan Boiler Factory, by incorporating advanced technology from the German company Babcock. The boiler features a D-type arrangement, operates under negative pressure, uses balanced ventilation, is ready for quick installation at the factory, and is installed indoors. The boiler is designed to use Shandong Liangzhuang Class II bituminous coal as fuel, and it can also handle various other types of coal; its combustion equipment consists of a scale-type chain grate. This boiler can be widely used in various industrial production processes as well as in some steam-based heating applications. 1.2 Specifications and Basic Data of the Demonstration Boiler
Boiler rated evaporation capacity: 6 T/H
Boiler rated steam pressure: 1.25 Mpa
Steam temperature at the boiler outlet: 139.4 ℃
Boiler feedwater temperature: 20 ℃
Cold air temperature: 20 ℃
Design thermal efficiency of the boiler: 79.4 %
Design coal type: Shandong Liangzhuang Class II bituminous coal
Elemental analysis of the design coal: Car=46.55%, Har=3.06%, Oar=6.11%, Nar=0.86%, Sar=1.94%, Aar=32.48%, War=9.0%, Vdaf=38.5%, Qnet,v,ar =17693 kJ/kg
Fuel consumption: 1170 kg/h
Boiler flue gas temperature: 162.5 ℃
Boiler blowdown rate: 5 %
Radiant heating area of the boiler: 16.74 m2
Convective heating area of the boiler: 124.98 m2
Heating area of the economizer: 33.12 m2
Effective area of the furnace grate: 8.48 m2
Heat load per unit area of the furnace grate: 737 KW/m2
External dimensions of the boiler (length × width × height): 10.6×5.3×4.5 m
Maximum transport dimensions (length × width × height): 8.4×3.4×3.5 m
Maximum weight of the unit during transportation: 40 T

1.3 Brief Introduction to the Boiler Structure
(1) Boiler body: This is a vertically arranged boiler with two drum assemblies, in a D-shaped configuration. The furnace and combustion chamber are located on the right side, while on the left side there are two passes of convective tube banks. The upper drum has a diameter of Ф900×12, while the lower drum has a diameter of Ф800×12; the drums are equipped with surface blowdown devices as well as secondary steam-water separation systems. The furnace chamber is composed of water-cooled walls on both sides and front and rear arch tubes; it is supplied with water by 4 Ф159 downcomers, which facilitates the natural circulation of water within the water-cooled wall tubes. The burnout chamber is located above the rear arch tube, and together with the arc-shaped rear shielding tube it forms a cyclone burnout chamber. The high-temperature flue gas rotates within this chamber, thereby increasing the time that the gas stays there; this allows the combustible substances in the gas to burn completely a second time. Additionally, centrifugal force is used to separate the ash particles from the gas, thus achieving dust removal inside the furnace. The flue gas exiting the swirl nozzles strikes the convective tube bank vertically; the tube bank is made of Ф51 tubes, with a staggered arrangement in the first pass and an in-line arrangement in the second pass. (2) Combustion equipment: The combustion equipment of this boiler is a scale-type chain grate designed by Tianshan Boiler Factory, based on Babcock Company’s proven expertise. The grate is driven by a rear shaft; the distance between the front and rear shafts is 5900 mm, while the width of the grate is 1590 mm. The adjustable range for the coal layer thickness is 0∽160 mm, and the adjustable range for the grate speed is 2∽20 m/h. The grate consists of main components such as the machine head, front shaft, rear shaft, grate bars, grate pins, clamping plates, air chambers, and air ducts. The grate features single-sided air supply; there are 6 air chambers in total, each of which is supplied with air independently and adjusted via its own control damper. For coal leakage within the air chambers, a pull-out ash discharge device is used, with ash being discharged at the front of the furnace and slag at the back. (3) Other components: 29. This boiler is equipped with a cast-iron economizer; the flue gas flows in two circuits, first downward and then upward, with the feed water entering from below and exiting from above. In accordance with the requirements of the \"Safety Technical Inspection Regulations for Steam Boilers,\" this boiler is equipped with instruments and valves such as spring safety valves, water level gauges, pressure gauges, thermometers, and blowdown valves. To improve the combustion efficiency of the boiler and ensure timely ignition of the fuel, the boiler is equipped with secondary air nozzles at the end of the rear arch. The boiler furnace wall is of a lightweight design; the arches at the front and back of the furnace wall are cast using TDK high-temperature adhesive and refractory concrete. To accommodate the combustion of a wider range of coal types and to meet the requirements for ignition, it is possible to adjust the length of the rear arch casting in order to modify its coverage. The boiler is shipped fully assembled, with its outer wall covered in corrugated panels. Platform escalators are installed behind and on top of the furnace to facilitate maintenance work by the furnace operators as well as the operation of valves and instruments. 1.4 Main evaluation results of thermal and environmental protection tests: The demonstration boiler was operated in the testing boiler room of Tianshan Boiler Factory, and tests for thermal performance and environmental protection showed that the boiler achieved its rated output and specified parameters. l Steam humidity ∠ evaluation index (3%): qualified. The thermal efficiency of the boiler at both the rated load and 60% load exceeds the evaluation criteria (78% and 76%, respectively). The excess air coefficient at the exhaust point and the exhaust temperature are both below the specified evaluation criteria (1.5% and 160°C). The emissions of pollutants from the boiler smoke are all below the assessment criteria (100 mg/m³). The coal used for boiler testing is AⅢ; compared to the designed coal type, it has a lower ash content. The ash contains a high level of carbon. l The fan noise is relatively high. 2 New Type Water-Tube and Fire-Tube Shell Boiler 2.1 Overview of the Boiler This boiler was jointly developed by Yingkou Boiler Factory and South African company JTA. It is designed for use with Class II bituminous coal, and employs a chain grate as the combustion device, which was imported from JTA in South Africa. The boiler features electromagnetic variable speed control, as well as a long, optimized furnace arch; as a result, it has strong adaptability to different types of fuel. This quick-install boiler features a compact design and strong earthquake resistance, and it is widely used in various industrial production processes as well as in some applications that require steam for heating. 2.2 Specifications and Basic Data of the Demonstration Boiler
Rated heat output: 6 T/h
Rated outlet water pressure: 1.2 Mpa
Steam temperature at the boiler outlet: 193.4 ℃
Cold air temperature: 20 ℃
Boiler feedwater temperature: 60 ℃
Design thermal efficiency: 80.62%
Design coal type: Class II bituminous coal
Boiler exhaust gas temperature: 160.36 ℃
Fuel consumption of the boiler: 990 Kg/h
Radiant heating surface area: 14.66 m2
Conductive heating surface area: 92.21 m2
Sparge heater heating surface area: 62.4 m2
Effective area of the grate: 7.43 m2
Grate heat load: 696.7 Kw/m2
Total weight of metals: 24.5 T
Total weight of the boiler: 43.5 T
External dimensions of the boiler: 6.686x3.068x4.274 m (length×width×height)
2.3 Brief Introduction to the Boiler Structure
The most notable feature of this boiler is the use of a coal pre-treatment device in front of the furnace. The fuel is delivered from the coal storage area to the grate through a pre-firing machine and a coal hopper; once it enters the furnace to burn, the flames and smoke pass over the upper part of the rear arch before entering the V-shaped flue channels on both sides. From there, they proceed to the front smoke box, then through the spiral flue tubes, the economizer, and the dust collector, before being exhausted into the chimney by the exhaust fan. The boiler feed water enters the economizer through a stop valve and a check valve, then proceeds to the boiler drum. The hot water circulates naturally within the threaded smoke tubes, the zigzag-shaped flue convective tube banks, as well as various heat-exchanging surfaces such as the water-cooled walls in the furnace; it is heated continuously and evaporates into saturated steam, which gathers at the top of the boiler drum and is then discharged after passing through the steam equalization device inside the boiler. This boiler is of the vertical type with a single drum. Light tubes and membrane water walls are installed on both sides of the furnace chamber; at the lower end of the water walls, anti-scorch boxes are provided. These, together with the four downcomers with a diameter of 159 millimeters located at each end, form a natural circulation circuit within the furnace. The V-shaped flues arranged on both sides of the boiler drum allow the high-temperature flue gases to cool down to below 800 degrees Celsius after passing through, thereby preventing cracks from forming on the front tube sheet of the drum. The front tube sheet of this boiler uses a low-stress arch-shaped design. The threaded flue tubes inside the drum have been optimized to improve various aspects such as heat transfer, flow resistance, ash accumulation, wear, stiffness, and strength, resulting in a more rational design. The economizer at the rear of the boiler is a high-efficiency, ash-resistant streamlined cast-iron type economizer. The lightweight chain grate furnace was designed and manufactured on the basis of adopting the advanced technologies for sealing, air adjustment, and air distribution developed by South Africa’s JTA company. The air supply system uses a unified chamber with air supply in front of the furnace ； Blind plates are used at the preheating area at the front of the grate, while two movable baffles and three fixed baffles are employed along the length of the grate to regulate air flow. Three fixed guide vanes are installed at the air inlet of the grate to ensure even distribution of air across its width; a special side seal minimizes slag formation and prevents damage. The small-sized grate bars further enhance the uniformity of air distribution. The grate features electromagnetic stepless speed control, facilitating remote and automatic control of combustion. 2.4 Main evaluation of thermal and environmental protection tests The demonstration boiler was tested in the boiler house owned by Yingkou Boiler Factory, and the results of the thermal and environmental protection tests showed that the boiler achieved its rated output and specified parameters. l Steam humidity ∠ evaluation index (3%): qualified. The thermal efficiency of the boiler at both the rated load and 60% load exceeds the evaluation criteria (78% and 76%, respectively). The carbon content in the slag is lower than the expected value (8%). Due to high air leakage in the economizer, the flue gas temperature is low, resulting in a high excess air coefficient at the flue gas outlet (the evaluated values are 160°C and 31 1.5). The emissions of pollutants from the boiler smoke are all below the assessment criteria (100 mg/m³). l The fan noise is relatively high and needs to be reduced. 3 Single-horizontal drum chain grate natural circulation water tube boiler 3.1 Boiler overview This product is an angle-tube boiler that was designed and manufactured using technology from the Danish company VOLUND, introduced by Shanghai Sifang Boiler Factory. The designed coal type is Class II bituminous coal; the furnace and convective heating surfaces feature a self-supporting structure, and the boiler room is arranged in two layers. The boiler is of modular design, with its main body being assembled in sections before leaving the factory. Boilers are highly efficient and energy-saving, and can be widely used in the production processes of various industries as well as in some heating applications. 3.2 Specifications and Basic Data of the Demonstration Boiler
Boiler’s rated evaporation capacity: 10 T/H
Boiler’s rated steam pressure: 1.25 Mpa
Steam temperature at the boiler’s outlet: 193.4 ℃
Rated feedwater temperature: 105 ℃
Cold air temperature: 30 ℃
Design thermal efficiency: 84.09 %
Design coal type: Class II bituminous coal
Elemental analysis of the design coal: Cy=50.37%, Hy=3.06%, Oy=6.15%, Ny=0.75%, Sy=0.2%, Ay=32%, Wy=7.47%; Vr>25%; Qdw y =20.1 MJ/kg
Fuel consumption: 1384.5 Kg/h
Boiler exhaust gas temperature: 165.1 ℃
Radiative heating area: 77.4 m2
Convective heating area: 213 m2
Heating area of the economizer: 234 m2
Effective area of the furnace grate: 12 m2
Heat load per unit area of the furnace grate: 767.86 Kw/m2
Total weight of metal components: 88 T
External dimensions of the boiler: (length × width × height) 11.4×6.35×8.6 m

3.3 Brief Introduction to the Boiler Structure
(1) Boiler drum and internal components: This boiler features a single, unheated boiler drum arranged horizontally in front of the furnace. The heated steam-water mixture is introduced into the boiler drum from the center of the normal water level at the rear of the drum. A partition separates the front and rear sections of the drum, forcing the steam-water mixture to flow toward both ends of the drum. At the top of the front section of the drum, an air distribution plate is installed as a secondary separation device for steam and water, thereby ensuring the quality of the steam. (2) Furnace and convective flue: The surrounding area of this boiler, as well as the partition walls in the middle, feature a fully sealed structure with modular water wall panels. This boiler features an open furnace structure without a rear arch; a refractory concrete front arch is built at the lower part of the front wall of the furnace to serve as the ignition arch, while flame-retardant zones are installed at the lower parts of the side walls of the furnace. The high-temperature flue gas generated after combustion passes through the slag condensation pipes and turns 180° from the top of the furnace toward the convective flue; two sets of flag-type convective heating surfaces are installed within this flue. Downcomers are installed at all four corners of the furnace and flue, forming a frame together with the upper and lower header tanks; all of the boiler’s upper header tanks as well as those on both sides are made of steel pipes. The heating surface in this section is delivered in five components: the left wall, right wall, front wall, rear wall of the furnace chamber, and rear wall of the flue. (3) Economizer: The flue gas that has passed through the horizontally scrubbed flag-type heating surfaces flows upward from the bottom of the flue duct through the economizer. There are two sets of economizers in total: one set is a steel-tube economizer, and the other set is an iron-cast economizer. The tube-type economizer located in the high-temperature section is composed of spiral finned tubes arranged in a staggered pattern; the flue gas flows from top to bottom, while the water inside the tubes flows from bottom to top, resulting in counterflow. In the cast-iron economizer tubes located in the low-temperature section, the feedwater flows from top to bottom, resulting in a co-current arrangement; the feedwater first passes through the cast-iron economizer and then through the steel-tube economizer before being sent to the boiler tubes. (4) Boiler support: This boiler has a frame structure; the boiler body is supported by four support points welded to the lower header sections on the left and right side walls. The front right support point serves as a fixed point, while the other support points can expand independently, allowing the entire boiler to expand upward. The coal burner section of the province is supported by a separate tail steel frame. (5) Furnace wall insulation: This boiler features a membrane-type water wall structure; the outer surface temperature of the water-cooling tubes is low, so lightweight insulation materials applied outside the wall are sufficient to meet the boiler’s insulation requirements. The light insulation material is welded to the round steel and wire mesh located on the fins of the membrane wall; these are fixed on the outside of the membrane wall. Corrugated sheets are wrapped around the insulation material, giving the boiler an attractive and neat appearance. (6) Chain grate: The chain grate installed in the boiler is of the L-type scale-type design, imported from Volund Company in Denmark. Coal is fed into the furnace through layered coal hoppers, with larger particles at the bottom and smaller particles at the top, so as to burn on the grate surface. The ash resulting from combustion passes through an ash trap and enters the ash hopper. The primary air required for combustion enters the furnace chamber from the large air ducts beneath the grate, through several sets of small air valves located between these ducts and the grate surface. There are four sets of air regulation mechanisms arranged along the length of the grate; each set controls 18 small air valves, thereby meeting the varying air volume requirements of the coal during combustion. Front shaft drive for the grate. To improve the burnout of the combustible materials in the coal within the furnace, eight secondary air nozzles were installed on the front and rear walls of the furnace chamber respectively. The volume of secondary air indeed accounts for 9-10% of the total air volume. 3.4 Main evaluation of thermal and environmental protection tests: The demonstration boiler was tested in the boiler room of the Urumqi Railway Bureau’s locomotive depot in Xinjiang. Thermal and environmental protection tests showed that the boiler achieved its rated output and specified parameters. Steam humidity ∠ evaluation index (3%), qualified. The boiler’s thermal efficiency at both the rated load and 60% load exceeds the evaluation criteria (80% and 78%), respectively. The exhaust excess air coefficient and exhaust temperature of 33 l are both below the evaluation criteria (1.5, 160°C). The original exhaust gas concentration is below the evaluation threshold (2000 mg/m³). The smoke darkness, SO2 emissions, and noise levels are all below the specified evaluation criteria (<1, 1000 mg/m3). The user has not used the dust collector specified in the design, resulting in excessive smoke and dust emission concentrations from the boiler; this needs to be improved. The carbon content in the slag is higher than the expected value (8%), and improvement is needed. 4 Two-Stage Fluidized Bed Boilers 4.1 Overview of the Boiler This boiler was designed and manufactured by Jiangxi Boiler Factory of Jianglian Company, utilizing patented technology from German company Bay. The different fluidization speeds of the upper and lower beds create an internal circulation of the material within the bed, which not only preserves the advantages of high combustion efficiency, as well as good desulfurization and other pollution control performance that are characteristic of circulating fluidized bed boilers, but also results in a structure that is simpler and more reliable compared to external-circulation fluidized bed boilers. This boiler is designed to use Class II bituminous coal as its fuel, offering a wide range of applicable fuels. It has broad application prospects in small and medium-sized boilers, especially among users that burn high-sulfur coal. The furnace of this boiler features a full membrane wall, a single drum, a fully suspended structure, and a back-to-back layout. The superheater uses a membrane wall wrapped around the curved flue ducts; lightweight protective plates are installed outside the tail shaft, with these plates being suspended from the lower header beneath the wall-cladding tubes. The economizer is composed of spiral finned tubes, which are supported by beams mounted on the protective plates. This boiler is suitable for indoor double-layer installation, with the steel structure designed to withstand an earthquake intensity of degree 7. 4.2 Specifications and Dimensions of the Demonstration Boiler: The boiler’s rated evaporation capacity is 15 T/H; its rated steam pressure is 2.4 Mpa, and its rated steam temperature is 240 ℃. The boiler’s feedwater temperature is 105 ℃, while the temperature of the cold air is 30 ℃. The boiler’s slag discharge rate is 2 %. The fuel designated for use in this boiler is Class II bituminous coal. (1) Drum and its internal components: The drum is suspended from the ceiling by 4 suspension rods. The drum is equipped with 8 cyclone separators for secondary steam-water separation; a wire mesh separator is used for this purpose. A grid is installed at the inlet end of the large-diameter downcomer, and the boiler is fitted with systems for continuous blowdown and chemical dosing. (2) Water cooling system: The water cooling system consists of four main components: downcomers, membrane-type water walls, steam and water outlet pipes, and buried pipes. The lower part of the membrane-type water walls is bent into the bed surface of a high-low bed air distribution system, on which air nozzles with different opening rates are installed. The furnace is composed of four membrane-type water walls. The front membrane-type wall consists of a main circulation circuit and an auxiliary circuit; the secondary circuit is further divided into two separate circulation circuits on the left and right sides. Both the left and right side water walls are each divided into three circulation circuits, while the rear membrane-type wall forms one independent circulation circuit. (3) Superheater 34: The saturated steam is led from the boiler drum to the header on the rear wall tubes via two steam guide pipes. After flowing through the membrane walls of the rear wall tubes, it enters the lower header at the rear wall. The steam then passes through right-angled elbows on both sides to reach the lower header of the side wall tubes, and after flowing through the membrane walls of those side wall tubes, it is directly fed into the surface-type desuperheater. The steam at the rated temperature after temperature reduction enters the steam collection header and is then sent out. (4) Economizer: The economizer is composed of steel spiral finned tubes and 180° elbows, with a total of three sets installed. The economizer tubes are supported on transverse beams by tube clamps; these beams are mounted on the frame guards on both sides, while the frame guards are suspended from the lower header of the envelope tube superheater and expand downward along with the boiler as a whole. (5) Feeding system: Three positive-pressure screw feeders are installed in front of the furnace; coal is supplied from the left and right sides, while limestone is supplied from the middle. The outlets of all three feeders are fixed to the membrane wall and expand downward together with it. The speed of the three feeders is adjusted continuously by variable-frequency drive motors. The feeders on the left and right rotate in opposite directions to counteract the torque exerted by the rotating components. (6) Air distribution system: This boiler employs a staged combustion technique, and is divided along its depth into three beds equipped with air distribution plates. These are, in order, a bed with low wind speed but high height (referred to as the front low-speed bed), a bed with high wind speed but low height (referred to as the high-speed bed), and another bed with low wind speed but high height (referred to as the rear low-speed bed). Coal and limestone are fed into the high-speed bed. Each bed air distribution plate is equipped with different cylindrical heat-resistant steel air nozzles, and the width of the bed surface is the same. During normal operation, the air volume supplied to the high-speed beds accounts for about 50% of the total air volume; the air volume supplied to the low-speed beds at the front and back makes up around 45% of the total air volume, while the secondary air accounts for approximately 5% of the total air volume. The boiler is ignited using hot air; a fuel ignition system is installed beneath the bed. The high-temperature flue gas generated during startup mixes with high-pressure air to reach a temperature of around 800°C. It enters the distribution plate from the high-speed bed air chamber to heat the material layer. 4.4 Main evaluation of thermal and environmental protection tests The demonstration boiler was tested in the boiler room of Kenneford Company in Dongguan, Guangdong; thermal and environmental protection tests confirmed that: 1 The boiler achieves its rated output and specified parameters. The quality of the superheated steam meets the standard requirements. The thermal efficiency of the boiler at both the rated load and 60% load exceeds the evaluation criteria (82% and 80%, respectively). The flue gas temperature and excess air coefficient are both below the evaluation criteria (160°C and 1.4). The dust emission concentration, darkness, SO2 levels, and boiler noise from the boiler are all below the specified evaluation values (<1, 1000 mg/m3). The carbon content in the slag has reached the expected value (2%). After adding limestone to the boiler, the original dust emission concentration exceeded the specified criteria, and further research is needed. 5 Angular tube hot water boiler 5.1 Boiler overview This boiler was designed and manufactured by Changzhou Boiler Factory by utilizing advanced Danish technology. The boiler is of the corner-tube type, with its main body being a self-supporting structure; the boiler room can be arranged in a single layer. The hot water circulation is a forced circulation driven by a water pump, while the combustion equipment is an Eco-type chain grate furnace with stepless speed control. The boiler is designed to use Class II bituminous coal; by adjusting the water-cooled adjustable furnace arch, it can also be used with other types of coal, giving it a very wide range of applicable coal types. This boiler component is shipped out of the factory; after being installed by the user, it is widely used in hot water heating systems. 5.2 Specifications and Basic Data of the Demonstration Boiler
Rated thermal power: 7.0 MW
Rated outlet water pressure: 1.0 Mpa
Rated outlet water temperature: 95 ℃
Rated inlet water temperature: 70 ℃
Design thermal efficiency: 87.24%
Fuel consumption: 1576 Kg/h
Design coal type: Class II bituminous coal
Elemental analysis of design coal: Cy=46.75%, Hy=3.2%, Oy=8.45%, Ny=0.65%, Sy=0.73%, Ay=34.62%, Wy=5.6%, Vr=22%, Qdw y =18145 kJ/kg
Radiative heating surface area: 82.8 m2
Conductive heating surface area: 147 m2
Economizer heating surface area: 179 m2
Effective area of the grate: 13.2 m2
Grate heat load: 601.8 Kw/m2
Total weight of metals: 68.5 T
Weight of the grate assembly: 21 T
Total volume of water in the boiler: ∽ 8.5 m3
External dimensions of the boiler: (length × width × height) 11.4×6.35×8.6 m
Transport dimensions of the grate: (length × width × height) 6.8×3.3×2 m
5.3 Brief Introduction to the Boiler Structure
(1) Boiler heating surfaces: The boiler’s heating surfaces consist of radiant heating surfaces in the furnace, two sets of flag-type conductive heating surfaces, and two sets of serpentine-tube economizers. Four downcomers are arranged at the four corners of the boiler; they also serve as supports for the boiler body. The connection between the four supports and the foundation is fixed at one point with three points being movable, to allow for the expansion of the boiler. The furnace chamber consists of a front wall, a middle partition wall, and two symmetrically arranged water-cooled walls, all of which are membrane walls. Front wall water-cooled wall, with the lower part bent into a front arch at a 40° horizontal inclination. The lower part of the water wall in the intermediate partition wall is bent into a rear arch with a horizontal inclination of 20°. The water wall of the intermediate partition wall, together with the water wall of the rear wall and the rear parts of the water walls on both sides, form the vertical flue of the convective tube bank. The weight of the economizer is transferred to the four columns through two hollow beams; the connection between the legs of these hollow beams and the columns is fixed at one point while being movable at three points, which facilitates expansion. (2) Combustion system: The coal hopper is located in front of the furnace, and the opening degree of the coal gate is adjusted via a worm gear mechanism in order to control the thickness of the coal layer. The chain grate 36 features an Eco-grate system based on imported technology; the front shaft is a driven shaft while the rear shaft is a driving shaft, and the tension of the chain can be adjusted by moving the front shaft. The grate and coal hopper are shipped out as a complete set. Coal-leakage-free grate bars are used, arranged in a fish-scale pattern. The ventilation cross-section ratio of the grate is about 6%. The grate and the heating surface of the main body adopt a contact-type sealing structure. The grate is equipped with a planetary gear reducer, which enables stepless speed control to adjust the coal feeding rate of the boiler. Six air chambers are arranged longitudinally beneath the grate; primary air enters these chambers from the air boxes on both sides of the grate. Ash removal devices are installed in these chambers to periodically remove coal that leaks through the grate. Secondary air nozzles are installed on the front wall of the boiler. In addition to the front and rear arches, a water-cooled adjustable arch is also installed in the middle of the furnace; by adjusting the angle of this adjustable arch, it is possible to adapt to the combustion of different types of coal. The cooling water for the adjustable arch is circulated using a separate circulation pump. 5.4 Main evaluations of thermal and environmental protection tests: Conducted operational tests at this plant, and the thermal and environmental protection tests have shown that the boiler achieves its rated output and specified parameters. The boiler’s thermal efficiency at both the rated load and 60% load exceeds the evaluation criteria (80% and 78%), respectively. The flue gas excess air coefficient and flue gas temperature are both below the evaluation criteria (1.5, 160°C). The original smoke emission concentration and the boiler dust emissions are both below the evaluation criteria (2000 mg/Nm3, 100 mg/Nm3). The smoke darkness, SO2 emissions, and noise levels are all below the specified evaluation criteria (<1, 1000 mg/m³). The carbon content in the slag is higher than the expected value (8%), and improvement is needed. 6 Front-fired water-tube and fire-tube steam boilers 6.1 Overview of the boiler This boiler was jointly designed by Zhengzhou Boiler Factory and the German company BAY. It features a front furnace chamber and a vertical single drum. The combustion unit adopts the scale-type chain grate technology from German company B&W as an integrated system, with automatic control of the combustion process. The designed fuel is Class II bituminous coal; the furnace is located at the front, with water-cooled wall tubes arranged around it. The furnace outlet is connected to the boiler drum, and inside there are three-pass heating surfaces composed of a furnace liner and flue tubes. At the rear is an iron-cast economizer. The boiler is assembled into three main parts – upper, lower, and rear – before being shipped out; the boiler room can be arranged on a single floor. The boiler is suitable for seismic zones of intensity 7, and can be widely used in various industrial production processes as well as in applications that require steam for heating purposes. 6.2 Specifications and Basic Data of the Demonstration Boiler
Boiler’s rated evaporation capacity: 10 T/H
Boiler’s rated steam pressure: 1.25 Mpa
Boiler’s rated steam temperature: 194 ℃
Boiler feedwater temperature: 30 ℃
Cold air temperature: 20 ℃
Boiler’s designed thermal efficiency: 82.94 %
Boiler exhaust gas temperature: 157 ℃
Steam humidity: ≤3 %
Design coal type: Hebei Fengfeng Class II bituminous coal
Elemental composition of the design coal: 37 Car = 46.18%, Har = 2.76%, Oar = 4.85%, Nar = 0.75%, Sar = 0.2%, Aar = 39.19%, War = 6.07%, Vaf = 25.63%, Qnet.v.ar = 18862 KJ/kg; T1 = 1350℃, t2 = 1380℃, t3 = 1460℃
Boiler’s fuel consumption: 1697 kg/h
Area for radiation heating: 64.7 m2
Area for convection heating: 220 m2
Area for economizer heating: 91.6 m2
Effective area of the furnace grate: 11.86 m2
Furnace volume: 39.5 m3
Total weight of the boiler’s metal components: ~80 T
Maximum weight of a single transport unit: ~28 T
External dimensions of the boiler when installed: (length × width × height) 12.7×5.5×9.5 m
Dimensions of the largest transport unit: (length × width × height) 6.15×3.17×3.32 m
6.3 Brief Introduction to the Boiler Structure
(1) Front furnace: The water walls on both sides of the front furnace are membrane-type water walls; behind them, double-sided water walls extend into the furnace. The lower parts of the front and rear water walls form the front and rear arches of the furnace, which facilitate the ignition and complete combustion of the fuel. (2) Boiler drum: A total of three return paths are arranged inside the boiler drum. The first pass is the corrugated furnace chamber, while the second and third passes are the flue tubes; water-cooled turning flue chambers are arranged at the outlet of the corrugated furnace chamber and at the inlet of the second pass. The boiler drum is supported on crossbeams, with the front support being fixed while the rear support is movable. The boiler drum is equipped with a steam-water separator and continuous surface blowdown pipes to ensure steam quality. (3) Economizer: A cast-iron economizer is used, with flue gas flowing from bottom to top. (4) Combustion system: A scale-type chain grate is used, with air intake on one side; the grate is divided into 5 separate air chambers along its length. The grate drive mechanism is an L-100 B type reduction gearbox, and the grate speed ranges from 2 to 20 m/s. There are 6 secondary air inlets at the rear arch end of the furnace, supplied with air by separate secondary air fans. (5) Automatic control: The boiler is equipped with a fully automatic fuel ignition system, as well as alarms for high and low water levels and steam overpressure, along with interlock protection devices. An electric three-way valve is used to control the boiler’s feed water and the amount of water returning to its circulation circuit. It features a fully automatic surface blowdown system equipped with an electric periodic blowdown valve and automatic detection of the conductivity of water and electricity in the furnace. The boiler uses an advanced single-loop regulator to achieve automatic control of the combustion system. 6.4 Main evaluation of thermal and environmental protection tests The demonstration boiler was tested in the boiler house owned by Zhengzhou Boiler Factory, and the thermal and environmental protection tests showed that the 38 l boiler achieved its rated output and parameters. l Steam humidity ∠ evaluation index (3%): qualified. The thermal efficiency of the boiler at both the rated load and 60% load exceeds the evaluation criteria (78% and 76%, respectively). The excess air coefficient at the smoke exhaust point and the smoke exhaust temperature are both below the specified evaluation criteria (1.5 and 160°C). l The carbon content in the slag is lower than the expected value (8%). l The emissions of pollutants from the boiler’s flue gas are all below the specified limits (100 mg/m3). l The fan is noisy; noise reduction is needed. 7 Coal thrower reverse chain grate boiler 7.1 Overview of the boiler This boiler is a water-tube boiler with an open furnace, horizontal double drum arrangement, and natural circulation; it was developed through cooperation between Jinan Boiler Factory and South African company JTA, which provided the design and manufacturing technology. A combustion method using a coal feeder and an inverted grate is adopted, allowing the use of bituminous coal, subbituminous coal, and lignite. The furnace features a membrane-type water wall structure. The superheater is divided into high and low sections, with a temperature reducer located in between; a economizer and an air preheater are installed at the rear end. The boiler is shipped in bulk, designed with a double-layer layout indoors, and the operating level is at 6 meters. The boiler frame is of metal construction, with a seismic resistance rating of 6 degrees. This boiler can be widely used by users in cogeneration, regional power plants, and industrial steam applications. 7.2 Specifications and basic data of the demonstration boiler: Rated evaporation capacity: 75 t/h; Rated steam pressure: 3.82 Mpa; Rated steam temperature: 450 ℃; Feedwater temperature: 105 ℃; Air preheating temperature: 130 ℃; Flue gas temperature: 152 ℃; Design fuel: Qnet,ar = 18862 kJ/kg (bituminous coal); Design thermal efficiency of the boiler: 84%; Fuel consumption: 13554 kg/h; Axial distance between the front and rear of the grate: 7650 mm; Grate width: 6825 mm; External dimensions of the boiler: Length – 21870 mm, Width – 13300 mm, Height – 26800 mm. 7.3 Brief introduction to the boiler structure: (1) Boiler drum and its interior fittings: The boiler is equipped with a double boiler drum, and both are joined to the convective tube bank by expansion joints. The upper drum is equipped with 28 cyclone separators, and wave plates are installed at the top of these separators; the humidity level of the steam after secondary separation is less than 1%. The upper drum is equipped with a feed water pipe, a recirculation pipe, a chemical dosing pipe, and a continuous blowdown pipe; the boiler’s blowdown rate is 2%. The upper drum is supported on the lower drum by a convection tube bundle, allowing it to expand and contract freely axially as well as upward, while the lower drum is supported on the boiler frame by three supports. (2) Water cooling system: Membrane water wall is used for the furnace chamber. The front wall water wall consists of the front lower header, the middle header on the front wall, up to the upper drum ； The rear wall water wall extends from the rear lower header to the lower drum ； The two side water walls are connected to the front and rear upper header tanks respectively by front and rear assemblies located at the lower sides, and they lead to the upper drum through steam guide tubes. The downcomer runs from the lower drum to the lower header beneath the rear wall as well as to the lower headers on both sides; the front, rear, left, and right lower headers are interconnected with each other. The ratio of the total cross-sectional area of the downcomer to that of the upcomer is 26.8%. Each circulation loop exhibits reliable water circulation performance under low-load conditions. At 60% load, the minimum circulation ratio in the circulation loop is 40.9. Between the upper and lower drum tubes, a series of counterflow tube bundles (3) made of φ51 steel tubes are arranged, which include superheater tubes and economizers. The superheaters are arranged in two stages: low-temperature and high-temperature. The low-temperature superheater operates in counterflow, while the high-temperature superheater operates in co-flow. Two sets of **temperature reducers** are installed between the high-temperature and low-temperature superheaters. To smooth the curve of the superheated steam temperature at the outlet of the convective superheater as it varies with load, no slag tubes are installed at the furnace outlet. Two acoustic soot blowers are installed between the high-temperature and low-temperature superheaters. The superheater header is fixed to the steel frame beams on the top of the furnace, and the superheater tubes are suspended from the header, allowing them to expand freely downward. The regulation range for the superheated steam temperature is 2.6%, the hydraulic unevenness coefficient of the superheater is 0.9, while the thermal unevenness coefficient is set at 1.3. The wall temperature calculations show that the selected materials are safe and reliable. The economizer adopts a coiled tube structure made of spiral finned tubes; the feed water flows upward along these coiled tubes in counterflow to the flue gas. The economizer tube bundle expands from bottom to top, and the crossbeams supporting the economizer are cooled by air. A multiple-tube separator inside the furnace is installed between the convection tube bank and the economizer; the fly ash captured by the separator is sent back to the furnace for re-ignition. (4). Combustion system: The boiler is equipped with inverted chain grates, with two grates arranged side by side, and features a chain plate structure tensioned by a catenary cable, assembled on-site. The ventilation cross-sectional area of the grate is 3%, and the grate bars are made of heat-resistant materials. Reduction gears for left and right side transmission; the grate speed can be adjusted within the range of 0.165 to 0.0165 M/min. The drive shaft is the front shaft, and the grate expands as a whole toward the front of the furnace. In front of the furnace, air-driven coal feeders are arranged at equal intervals along the width direction, and the amount of coal fed is adjusted by a coal feeder driven by a speed-regulating motor. The primary air for the grate is supplied through air distribution chambers in the large air chamber. The grate ensures even air distribution in the width direction. Air distribution chambers are equipped with air control valves to ensure that the air distribution along the length of the grate meets the requirements for coal combustion. The secondary air for the boiler enters in two layers along the height of the furnace, on both the front and rear walls of the furnace; the proportion of secondary air to the total air volume is around 30%. 7.4 Main evaluation of thermal and environmental protection tests The demonstration boiler was tested in the Baohua Heat Power Plant in Heilongjiang, and the results of the thermal and environmental protection tests showed that: the boiler achieved its rated output and specified parameters. The thermal efficiency of the boiler at both the rated load and 60% load exceeds the evaluation criteria (>80%). The exhaust temperature and excess air coefficient at 40 L are both below the evaluation criteria (160°C and