Boilers come in two types: those holding water to produce steam and those generating heat through combustion. To efficiently transfer combustion heat to water, a sufficient heat transfer area is crucial. Tube boilers are developed to expand this area, enhancing heat transfer.

 

Within these bundles, water must circulate continuously, absorbing heat energy and separating steam to the upper part of the tube. The water then flows into the lower part of the tube, distributing to each bundle to absorb heat in the furnace. These upper and lower assembly boxes, referred to as boiler headers, play a crucial role.

 

 

The manifold header is not an independent component but a part of the water wall, economizer, superheater, and other elements. Types include water wall headers, economizer headers, and superheater headers. Its function is to collect or distribute steam and water working fluid, reducing the pipeline for working substance transportation and connections. The lower header near the grate on both sides of the furnace wall prevents coking, earning the name "coke-proof box."

 

Constructed as a thick-diameter tube with welded flat heads at both ends, the header is made of seamless steel pipe. It connects to many heating surface pipes, and holes in the box allow for welding or expanding pipes. The economizer and superheater tubes connect to the header, with the lower end of the water wall also connected. The upper end can be linked to the header, and a few pipes can be drawn from the head to the drum, or the upper end of the water wall tube can be directly connected to the drum.

 

 

To enhance boiler efficiency, boilers transition into tubular designs, increasing the heat transfer area. The pot water flows from the pot barrel to the lower box through the downward tube, distributing to each tube bundle by the box body. Water in these bundles continuously absorbs heat energy, collecting into the upper box body and then flowing back into the pot barrel. These upper and lower box body headers are vital components, with headers divided into upper and lower categories.

 

 

The main function of headers is to collect, mix, and distribute working fluids, ensuring even distribution and heating. The lower header, also known as the coke-proof box, cools coking slag without bonding with the side wall. Types include upper and lower headers, inlet and outlet headers, and various headers for water walls, superheaters, and economizers.

Headers are pipe fittings for mixing working substances in boilers, ensuring uniform heating. Industrial boilers furnace walls, composed of rows of tubes (water-cooled walls), lack uniform heat absorption due to size differences. Headers address this by converging working substances in each tube and distributing them to the next level, reducing thermal deviation and optimizing heat absorption, fluid flow, and cooling efficiency. Headers connect different sections to ensure a smooth flow of working substances.

 

 

Structure and Material

 

Header structures, consistent across boiler types, mainly include barrel, end cap, large and small pipe joints, tees, elbows, and accessories. Diameter ranges from 89mm to 914mm, wall thickness from 7mm to 150mm, and maximum length at 23000mm. Materials include carbon steel, low alloy heat-resistant steel, medium alloy heat-resistant steel, and ultra-supercritical boiler materials. Manufacturing equipment includes groove machines, drilling machines, boring machines, automatic submerged arc welding machines, CO2 gas shield welding machines, pipe benders, hydraulic presses, heat treatment furnaces, and plunger hydraulic pumps.

 

 

1. Barrel Blanking

 

Large diameter seamless steel tubes are used, cut by a magnetic wheel gas cutting machine. Pre-drilling a hole of 7mm is necessary for thick-walled tubes, with additional preheating measures for specific materials.

 

2. Pressure of Elbows

 

Most elbows are thick-walled with a large diameter, using a pressing process. Two methods involve either multiple compression and extrusion for seamless steel tubes or using steel plates for thin-walled elbows.

 

3. Manufacture of Large Caliber Tees

 

Forging tees, widely used for small flow resistance, are made from large diameter seamless tubes. Welded tees are used in economizer systems with minimal flow resistance, while punching and welding tees are used in reheater systems with thinner wall thickness.

 

4. Barrel Borehole

 

Pipe holes are machined by rocker drilling machines or CNC multi-axis drilling machines, ensuring high production efficiency and precise pitch size.

 

5. Installation and Welding of Pipe Joints

 

Large and small pipe joints on the header cylinder are installed and welded. Large pipe joints use saddle-shaped welding, while small pipe joints, critical due to connection with tube panels, are positioned carefully during installation and welding.

 

6. Header Heat Treatment

 

Headers undergo integral heat treatment in large-scale furnaces to meet heat treatment requirements.

 

 

Hydraulic pressure tests ensure structural integrity, with specific temperature recommendations for carbon steel and alloy steel. After the test, water is drained, the outer surface is dried, and the inner part is blown by compressed air to remove any accumulated water.

 

 

Strict control of cleanliness is crucial to prevent accidents during power plant operation. Cleaning procedures involve removing debris after drilling holes, avoiding dropping debris during filling and welding, covering tube joints during filling and chamfering after hydraulic pressure, inspecting each pipe joint with a wire rope before leaving the factory, using compressed air to remove debris inside the cylinder body, and utilizing an endoscope for internal inspections.

 

In conclusion, the manifold header assembly is a critical component in boiler systems, ensuring efficient heat transfer, fluid circulation, and overall safety.