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Design and operation of paper - making sludge circulating fluidized bed boiler

Words:[Big][Medium][Small] Mobile Page Two-Dimensional Code 2018-06-12     

Abstract: in view of the problems existing in mixing and burning papermaking sludge in circulating fluidized bed boiler, the countermeasures adopted in designing circulating fluidized bed boiler were put forward.This paper introduces the main technical parameters of 75t/h mixed sludge circulating fluidized bed boiler for papermaking, and discusses the problems that should be paid attention to in operation.

Key words: paper sludge;Circulating fluidized bed boiler;Design;run

The Design and Operation of Paper Sludge Co - fired CFB Boiler

YIN chong-qing, YIN qing-yong, LI yan-ru

The Abstract:Aimed at the problems existing in CO - firing paper sludge in CFB boiler.The counter measures seems in the design of CFB boiler are put forward. The main technical parameters of 75 t/h paper sludge co - fired CFB boiler are introduced.And the problems to which attention should be paid in operation are discussed.

Key words: co - firing paper sludge;Circulating fluidized bed (CFB) boiler;The design;The operation

Papermaking sludge is a high-moisture discharge substance in papermaking process, which is featured by high moisture content and low calorific value of about 3.4mj /kg[1].It is difficult to treat and utilize papermaking sludge.With the tightening of the national land policy, the increase of transportation costs and the enhancement of energy conservation and environmental protection requirements, how to make rational use of papermaking sludge has become the focus of common concern of papermaking enterprises and energy experts.The key to the utilization of papermaking sludge is technology economy, safety, environmental protection and energy saving.Circulating fluidized bed boiler has the advantages of wide fuel adaptability, high combustion efficiency, high efficiency desulfurization and denitrification, simple fuel treatment system and easy utilization of ash residue, etc.This paper discusses the design and operation of a circulating fluidized bed boiler mixed with paper sludge.

Problems and countermeasures of paper - making sludge mixing

1.1 there are problems with mixing paper sludge

Papermaking sludge moisture is high, easy to cause low temperature corrosion, especially on the final air preheater, and difficult to maintain the temperature of the bed, not conducive to fuel ignition and burnout.Papermaking sludge is not liquid, difficult to load and unload and transport, and easy to cause secondary pollution.The particle size of paper sludge is small, so the amount of fly ash collected by cyclone separator is larger and the particle size is finer.

1.2 countermeasures

(1) reasonable smoke exhaust temperature and corrosion resistant materials

Papermaking sludge moisture is high, up to 50%.In order to prevent low temperature corrosion, the smoke exhaust temperature is designed to be 155℃.The final air preheater is made of corrosion resistant cowden steel (10CrNiCuP).

(2) reliable paper sludge transport system

MNS type plunger pump is equipped with the sludge pipeline conveying system for papermaking, which is simple in structure, long in service life and reliable in performance. It can not only effectively prevent solid precipitation, precipitation, agglomerating, arching and air perforation, but also the outlet pressure of the conveying system can reach 24MPa, the flow rate can reach 60m3/h and the conveying distance can reach 1000m.The transportation system can realize stepless regulation and remote control, and the pipeline layout is flexible, which will not cause pollution to the environment.

Efficient cyclone cyclone separator

Conventional tangential inlet cyclone separator is not suitable for separating paper sludge particles with small particle size below 0.5mm.This is because the inlet channel is unfavorable to the acceleration of material particles and the flow field is not uniform, which easily leads to the low separation efficiency and too few recycled materials.The improved volute cyclone separator USES the same passage section, and the flue gas and its entrained materials can get a more uniform flow field before entering the cyclone separator, which greatly improves the separation performance of the cyclone separator, and the collected fly ash has finer particle size, lower carbon content and more circulating materials.Therefore, it can greatly reduce the wear and rear reburning of the heating surface.In order to prevent the backfeed leg of the separator from blocking, which leads to the poor circulation of materials, an efficient spiral cyclone separator with water-cooled backfeed leg is adopted.In the return feeder, special loose air of high pressure head and low air volume of return feed and feed air of high air volume of low pressure head are provided from the primary fan to ensure the patency of return feed and feed.

(4) use high feed, high wei burning belt

Due to the high water content of papermaking sludge, the use of special sludge spray gun high feed, so that papermaking sludge in the process of falling water evaporation, volatile components constantly precipitation, particles constantly deflective splitting, so that it meets the requirements of normal combustion particle size.In the concentrated phase area of the furnace, the coal with certain particle size is fed to the coal machine as the base material, so that there is enough material concentration in the concentrated phase area to ensure the normal and complete combustion of papermaking sludge.In order to maintain the temperature of the fluidized bed and reduce the wear of the base material to the water cooling wall, the inner wall of the boiler is equipped with the heating belt of anti-wear and temperature proof castable.

2. Main technical parameters

Take the paper - mixed sludge circulating fluidized bed boiler with evaporation rate of 75t/h as an example.Rated steam pressure is 5.3MPa, rated steam temperature is 485℃, thermal efficiency is 87.1%, smoke exhaust temperature is 155℃.Designed low calorific value of fuel is 11.7mj /kg, fuel consumption is 10623kg/h.Particle size of bed material ≤13mm, desulfurization efficiency ≥90%, calcium-sulfur ratio 2, limestone particle size ≤2mm.

3. Matters needing attention in operation

Under the condition of constant air volume, the higher the wind chamber pressure is, the thicker the material layer is. Under the condition that the normal air volume remains unchanged during operation, the wind chamber pressure should be maintained at 6.0 ~ 7.2kpa as far as possible.In the operation, try to keep the thickness of the material layer, so as not to cause the decline of fluidization quality and affect the stable operation of the boiler.This requires boiler operators in the coal, to be gradual, a small number of times to add.To adjust the bed temperature by adjusting the amount of coal into the furnace, do not use paper sludge to adjust the amount of feed.In addition, operational personnel are required to strengthen monitoring and enhance their sense of responsibility. Once the bed temperature rises high, the feed quantity of papermaking sludge should be rapidly reduced to avoid the coking of the furnace bed caused by not timely adjustment, which will lead to coking of the reclaimant.

4 conclusion

The use of mixed combustion papermaking sludge circulating fluidized bed boiler not only reduces the waste of resources and environmental pollution, but also solves the problem of occupying a large number of land, which has a high popularization value.

References:

An wen, wang tao, tian chengwen. Feasibility analysis of mixed burning papermaking sludge in circulating fluidized bed boiler [J]. Energy conservation, 2006, (6) : 42-44.



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