Waste heat recovery boiler mostly adopts membrane wall structure, composed of steam drum, membrane wall, convection tube bundle, economizer. The deaerated water increases the pressure via feed water pump, absorbs the heat via economizer and enters the steam drum. The steam drum, membrane wall and convection tube bundle are connected by riser and downcomer to form a natural circulation loop. Low flue gas velocity in membrane wall cooling chamber is beneficial to the separation and sedimentation of dust. Therefore, such waste heat recovery boiler is suitable for flue gas with large amount of dust.

Our company carries out energy-saving transformation of the PSA section of Methanol To Hydrogen in a chemical plant. The waste gas enters the incinerator and starts full combustion with mixed hot air. High-temperature flue gas passes through threaded smoke tube evaporator and spiral finned tube economizer, heating water into saturated steam. Compared with traditional membrane wall structure, such waste heat boiler features compact structure, small floor space, less steel consumption, low investment, low exhaust gas temperature, and high heat recovery efficiency.

1. Waste heat recovery boiler designed parameter

2. Waste heat recovery boiler structure design

It contains inlet flue duct, steam drum, evaporation section, intermediate flue duct and economizer. The steam drum, evaporator, riser and downcomer form a natural circulation system. After raising the pressure by feed water pump, the deaerated water enters the economizer inlet header. It absorbs heat with the flue gas through spiral fin tube, and then enters the steam drum. The water enters the evaporation section through downcomers to absorb heat and form a steam-water mixture. Then it enters the steam drum through riser, and after steam-water separation, generating saturated steam.

Through heat balance calculation, the waste heat boiler evaporation capacity is 13.2t/h. The evaporation section adopts fire tube shell structure. The fire tube is threaded tube of φ51x4mm with a thread pitch of 34 mm and a thread depth of 2 mm. The evaporation section has 560pcs threaded fire pipes, heating area is 428m2, and shell length is 6.1 m. The threaded tube on the tube sheet is in triangle, center distance is 75mm, and shell diameter is DN2200.

The economizer adopts spiral finned tube channel structure. The parent tube is φ38mmx4mm, fin height is 19mm, fin spacing is 6.5mm, and fin thickness is 1.1mm. The cross section of flue gas flow is 1.9*1.85m. The transverse pitch of spiral finned tube is 110mm, and longitudinal pitch is 100mm. The heating area is 500m2, and economizer overall dimensions is 2.1*2.7*1.9m.